Staff directory Pedro Gómez Romero

Pedro Gómez Romero

CSIC Research Professor and Group Leader
pedro.gomez(ELIMINAR)@icn2.cat
Novel Energy-Oriented Materials

ORCID: 0000-0002-6208-5340

Publications

2024

Hybrid Materials: A Metareview
Gomez-Romero, Pedro; Pokhriyal, Anukriti; Rueda-Garcia, Daniel; Bengoa, Leandro N; Gonzalez-Gil, Rosa M Chemistry Of Materials; 36 (1): 8 - 27. 2024. 10.1021/acs.chemmater.3c01878.
In situ Raman analysis of reduced-graphene oxide-based electroactive nanofluids
Parpal, Monica; El Sachat, Alexandros; Torres, Clivia M Sotomayor; Gomez-Romero, Pedro; Rueda-Garcia, Daniel; Chavez-Angel, Emigdio Diamond And Related Materials; 141: 110541. 2024. 10.1016/j.diamond.2023.110541.
Platinum Electrodeposited onto MoS_x for Hydrogen Evolution Reaction: A Kinetic Model under Diffusive-Convective Transport Influence
Bianca Tainá Ferreira; Rosa M. González-Gil; Pedro Gómez‐Romero; Fritz Huguenin Journal Of Physical Chemistry. C./Journal Of Physical Chemistry. c; 2024. 10.1021/acs.jpcc.4c00071.
Understanding the Role of Additives on The Electrochemistry and Performance of Zn Energy Storage Devices
Bengoa, L N; Gonzalez-Gil, R M; Gomez-Romero, P Chemelectrochem; 11 (6) 2024. 10.1002/celc.202300517.

2023

Energy harvesting in the course of acid solution neutralization
Ferreira, BT; Rueda-Garcia, D; Gomez-Romero, P; Huguenin, F Journal Of Electroanalytical Chemistry; 928: 117042. 2023. 10.1016/j.jelechem.2022.117042. IF: 4.500
Interlaboratory study assessing the analysis of supercapacitor electrochemistry data
Gittins, JW; Chen, Y; Arnold, S; Augustyn, V; Balducci, A; Brousse, T; Frackowiak, E; Gómez-Romero, P; Kanwade, A; Köps, L; Jha, PK; Lyu, D; Meo, M; Pandey, D; Pang, L; Presser, V; Rapisarda, M; Rueda-García, D; Saeed, S; Shirage, PM; Slesinski, A; Soavi, F; Thomas, J; Titirici, MM; Wang, HX; Xu, Z; Yu, AP; Zhang, MW; Forse, AC Journal Of Power Sources; 585: 233637. 2023. 10.1016/j.jpowsour.2023.233637. IF: 9.200
Nanostructured Thick Electrode Strategies toward Enhanced Electrode-Electrolyte Interfaces
Pokhriyal, A; Gonzalez-Gil, RMN; Bengoa, LNM; Gomez-Romero, P Materials (Basel); 16 (9): 3439. 2023. 10.3390/ma16093439. IF: 3.400
Polyoxometalate-Stabilized Silver Nanoparticles and Hybrid Electrode Assembly Using Activated Carbon
Goberna-Ferrón, S; Cots, L; Perich, MP; Zhu, JJ; Gómez-Romero, P Nanomaterials; 13 (15): 2241. 2023. 10.3390/nano13152241. IF: 5.300
To flow or not to flow. A perspective on large-scale stationary electrochemical energy storage
Pokhriyal, A; Rueda-García, D; Gómez-Romero, P Sustainable Energy & Fuels; 7 (23): 5473 - 5482. 2023. 10.1039/d3se00955f. IF: 5.600

2022

Coherent Integration of Organic Gel Polymer Electrolyte and Ambipolar Polyoxometalate Hybrid Nanocomposite Electrode in a Compact High-Performance Supercapacitor
Zhu J.-J., Martinez-Soria L., Gomez-Romero P. Nanomaterials; 12 (3, 514) 2022. 10.3390/nano12030514. IF: 5.076

We report a gel polymer electrolyte (GPE) supercapacitor concept with improved pathways for ion transport, thanks to a facile creation of a coherent continuous distribution of the electrolyte throughout the electrode. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was chosen as the polymer framework for organic electrolytes. A permeating distribution of the GPE into the electrodes, acting both as integrated electrolyte and binder, as well as thin separator, promotes ion diffusion and increases the active electrode–electrolyte interface, which leads to improvements both in capacitance and rate capability. An activation process induced during the first charge–discharge cycles was detected, after which, the charge transfer resistance and Warburg impedance decrease. We found that a GPE thickness of 12 μm led to optimal capacitance and rate capability. A novel hybrid nanocomposite material, formed by the tetraethylammonium salt of the 1 nm-sized phosphomolybdate cluster and activated carbon (AC/TEAPMo12), was shown to improve its capacitive performance with this gel electrolyte arrangement. Due to the homogeneous dispersion of PMo12 clusters, its energy storage process is non-diffusion-controlled. In the symmetric capacitors, the hybrid nanocomposite material can perform redox reactions in both the positive and the negative electrodes in an ambipolar mode. The volumetric capacitance of a symmetric supercapacitor made with the hybrid electrodes increased by 40% compared to a cell with parent AC electrodes. Due to the synergy between permeating GPE and the hybrid electrodes, the GPE hybrid symmetric capacitor delivers three times more energy density at higher power densities and equivalent cycle stability compared with conventional AC symmetric capacitors. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

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Controlling the electrochemical hydrogen generation and storage in graphene oxide by in-situ Raman spectroscopy
Pinilla-Sánchez A., Chávez-Angel E., Murcia-López S., Carretero N.M., Palardonio S.M., Xiao P., Rueda-García D., Sotomayor Torres C.M., Gómez-Romero P., Martorell J., Ros C. Carbon; 200: 227 - 235. 2022. 10.1016/j.carbon.2022.08.055.

Hydrogen, generated from water splitting, is postulated as one of the most promising alternatives to fossil fuels. In this context, direct hydrogen generation by electrolysis and fixation to graphene oxide in an aqueous suspension could overcome storage and distribution problems of gaseous hydrogen. This study presents time-resolved determination of the electrochemical hydrogenation of GO by in-situ Raman spectroscopy, simultaneous to original functional groups elimination. Hydrogenation is found favoured by dynamic modulation of the electrochemical environment compared to fixed applied potentials, with a 160% increase of C–H bond formation. Epoxide groups suppression and generated hydroxide groups point at these epoxide groups being one of the key sites where hydrogenation was possible. FTIR revealed characteristic symmetric and asymmetric stretching vibrations of C–H bonds in CH2 and CH3 groups. This shows that hydrogenation is significantly also occurring in defective sites and edges of the graphene basal plane, rather than H-Csp3 groups as graphane. We also determined a −0.05 VRHE reduction starting potential in alkaline electrolytes and a 150 mV cathodic delay in acid electrolytes. The identified key parameters role, together with observed diverse C-Hx groups formation, points at future research directions for large-scale hydrogen storage in graphene. © 2022

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Dramatic Drop in Cell Resistance through Induced Dipoles and Bipolar Electrochemistry
Fuentes-Rodríguez L., Abad L., Pujades E., Gómez-Romero P., Tonti D., Casa-Pastor N. Journal of the Electrochemical Society; 169 (1, 016508) 2022. 10.1149/1945-7111/ac492d. IF: 4.316

The use of slurries of conducting particles has been considered a way to extend the electrode area in some energy storage electrochemical cells. When suspensions of conducting particles are used in electrolytes a decreased impedance is observed, even for concentrations much lower than the theoretical percolation limits. Indeed, it is known that polarization occurs when a conducting material is immersed in an electrolyte in presence of electric fields, and bipolar electrochemistry processes may occur. This work demonstrates the dramatic drop in resistance for electrochemical cells with just a few macroscopic conducting pieces immersed in the electrolyte, in the absence of any electrical contact, through bipolar induction. Furthermore, mediation of soluble redox species between adjacent induced poles of opposite charge results in an additional mechanism for charge transfer, contributing further to the decrease in impedance. Relevant parameters like size, geometry, and spatial occupation of inducible pieces within the electric field, are relevant. Remarkably, the effects observed can explain some empirical observations previously reported for carbon suspensions and slurries. Thus, no electronic percolation requiring particle contact, nor ordering, are needed to explain the good performance associated to lowered impedance These results suggest new engineering designs for electrochemical cells with enhanced currents. © 2022 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

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Energy harvesting in the course of acid solution neutralization
Ferreira, BT; Rueda-Garcia, D; Gomez-Romero, P; Huguenin, F Journal Of Electroanalytical Chemistry; 927 2022. 10.1016/j.jelechem.2022.116957. IF: 4.598
Facile preparation of glycine-based mesoporous graphitic carbons with embedded cobalt nanoparticles
Wang W., Tesio A.Y., Olivares-Marín M., Gómez Romero P., Tonti D. Journal of Materials Science; 57 (28): 13403 - 13413. 2022. 10.1007/s10853-022-07421-3.

A simple route has been developed for the preparation of mesoporous graphitic carbons with embedded cobalt nanoparticles just using glycine as a nitrogen source, cobalt nitrate and distilled water. After heating the mixture to 300 °C under magnetic stirring, a dry solid product was obtained, which was then carbonized at 900 ºC under argon atmosphere. Changing the glycine/Co molar ratio allowed controlling the size of the cobalt particles and their dispersion in the carbon matrix, the porosity of the carbon and its graphitic character. The carbon–metal composites obtained were tested as oxygen cathodes in Li–O2 batteries. Cells assembled exhibited a full discharge capacity up to 2.19 mAh cm−2 at a current of 0.05 mA cm−2 and over 39 cycles at a cutoff capacity of 0.5 mAh cm−2. This work provides a green, feasible and simple way to prepare mesoporous graphitic carbons with embedded cobalt nanoparticles without involving templates. Graphical abstract: [Figure not available: see fulltext.]. © 2022, The Author(s).

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Impact of Battery Energy System Integration in Frequency Control of an Electrical Grid with Wind Power
Pokhriyal, A; Dominguez-Garcia, JL; Gomez-Romero, P Clean Technologies; 4 (4): 972 - 986. 2022. 10.3390/cleantechnol4040060.
Polyoxometalate intercalated MXene with enhanced electrochemical stability
Zhu J.-J., Gomez-Romero P. Nanoscale; 2022. 10.1039/d2nr01410f.

MXene/polyoxometalate (POM) hybrids are useful target materials for a variety of applications. Yet, the goal of preparing simple binary hybrids by intercalation of POMs into MXene has not been achieved. We propose and demonstrate here a method to intercalate POMs (phosphotungstate, PW12) into Ti3C2Tx MXene through the interaction between POM anions and pre-intercalated surfactant cations. A variety of quaternary ammonium cations have been used to expand Ti3C2Tx interlayer spacing. Cetyltrimethylammonium cations (CTA+) lead to an expansion of 2 nm while allowing intercalation of a considerable load (10 wt%) thanks to their tadpole-like shape and size. CTAPW12 has a layered structure compatible with Ti3C2Tx. The CTA+-delaminated Ti3C2Tx keeps the large interlayer spacing after being coupled with PW12. The PW12 clusters are dispersed and kept isolated thanks to CTA surfactant and the confinement into Ti3C2Tx layers. The redox reactions in CTA+-delaminated Ti3C2Tx/PW12 are diffusion-controlled, which proves the well-dispersed PW12 clusters are not adsorbed on the surface of Ti3C2Tx particles but within Ti3C2Tx layers. The CTA+- delaminated Ti3C2Tx/PW12 shows superior electrochemical stability (remaining redox active after 5000 cycles) over the other MXene/POM hybrids prepared in this work (inactive after 500 cycles). We associate this improved stability to the effective intercalation of PW12 within Ti3C2Tx layers helped by the CTA cations, as opposed to the external aggregation of PW12 clusters into micro or nanocrystals taking place for the other cations. The results provide a solid guide to help develop high-performance MXene/POM hybrid materials for a variety of applications. © 2022 The Royal Society of Chemistry.

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Rational design of MXene/activated carbon/polyoxometalate triple hybrid electrodes with enhanced capacitance for organic-electrolyte supercapacitors
Zhu J.-J., Hemesh A., Biendicho J.J., Martinez-Soria L., Rueda-Garcia D., Morante J.R., Ballesteros B., Gomez-Romero P. Journal of Colloid and Interface Science; 623: 947 - 961. 2022. 10.1016/j.jcis.2022.04.170.

We report a triple hybrid electrode (MXene/activated carbon (AC)/polyoxometalates (POMs)) combining the merits of three materials: MXene (high volumetric capacitance), AC (high gravimetric capacitance) and Phosphotungstate (fast redox). Phosphotungstic acid (HPW12) and tetraethylammonium phosphotungstate (TEAPW12) were the two POMs used to prepare MXene/AC/POMs triple hybrids. MXene/AC/TEAPW12 outperformed MXene/AC/HPW12 in 1 M tetraethylammonium tetrafluoroborate (TEABF4)/acetonitrile. Nano-dispersion of POMs facilitates charge storage through surface capacitive processes (91% at 2 mV s−1). MXene/AC/TEAPW12 delivered significantly higher gravimetric capacitance (87F g−1 at 1 mV s−1) than MXene (40F g−1 at 1 mV s−1) in the same organic electrolyte, without sacrificing much volumetric capacitance (less than 10%). The gravimetric capacitance of the triple hybrid was similar to that of MXene/AC, whereas its volumetric capacitance was 1.5 times higher. Replacing TEA cations with 1-ethyl-3-methylimidazolium cations (EMIM+), the capacitance improved by 21%. Coupled with AC positive electrodes in an asymmetric cell, MXene/AC/TEAPW12 delivered 4.6 times higher gravimetric energy density and 3.5 times higher volumetric energy density than a similar MXene asymmetric cell at relatively high-power densities. This study proves that MXene/AC/TEAPW12 combines the merits and compensates for the demerits of each component and is a promising electrode material for organic-electrolyte supercapacitors. © 2022 The Author(s)

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2021

MOF-derived conformal cobalt oxide/C composite material as high-performance electrode in hybrid supercapacitors
Hosseinzadeh B., Nagar B., Benages-Vilau R., Gomez-Romero P., Kazemi S.H. Electrochimica Acta; 389 (138657) 2021. 10.1016/j.electacta.2021.138657. IF: 6.901

By pyrolysis of a simple Cobalt Metal Organic Framework (MOF) we have been able to synthesize a high-performance hybrid composite electrode with fibrous morphology conformal to the MOF, in a single step and at relatively low temperature (700°C). Indeed, the composite material containing cobalt oxide micro-nano-particles in highly graphitized carbon matrix (cobalt oxide/C-700) presents superb capacity of 1372 F/g (381 mAh/g) at a current density of 2.5 A/g. Besides, an asymmetric supercapacitor (ASC) was fabricated by using the CoxOy/C-700 composite as positive electrode and activated carbon (AC) as negative electrode. This ASC system delivered maximum energy density of 51.5 Wh/kg and maximum power density of 1687 W/kg © 2021

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Optimisation of NiO electrodeposition on 3D graphene electrode for electrochemical energy storage using response surface methodology
Agudosi E.S., Abdullah E.C., Numan A., Khalid M., Mubarak N.M., Benages-Vilau R., Gómez-Romero P., Aid S.R., Omar N. Journal of Electroanalytical Chemistry; 882 (114992) 2021. 10.1016/j.jelechem.2021.114992. IF: 4.464

In this study, NiO was electrodeposited on a 3D graphene electrode to produce a nanocomposite with enhanced electrochemical properties. The electrodeposition process parameters such as electrolyte concentration, deposition time, and deposition potential were statistically optimised using response surface methodology. The statistical analysis showed that the optimal electrodeposition conditions to be 0.3 M, 10 min, and -1.2 V for electrolyte concentration, deposition time, and deposition potential, respectively. Furthermore, the predicted model and experimental results for the specific capacity of G-NiO were determined to be 240.91 C/g and 240.58 C/g at 3 mV/s. The results show that the electrochemical deposition technique can be employed as a fast and reliable synthesis route to develop graphene-based metal oxide nanocomposites. The structural and morphological properties were determined by XRD and FESEM studies. The electrochemical measurements revealed the excellent electrochemical performance of 3D graphene NiO composite (G-NiO) for energy storage applications. © 2021 Elsevier B.V.

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Polyoxometalates (POMs): From electroactive clusters to energy materials
Horn M.R., Singh A., Alomari S., Goberna-Ferrón S., Benages-Vilau R., Chodankar N., Motta N., Ostrikov K., Macleod J., Sonar P., Gomez-Romero P., Dubal D. Energy and Environmental Science; 14 (4): 1652 - 1700. 2021. 10.1039/d0ee03407j. IF: 38.532

Polyoxometalates (POMs) represent a class of nanomaterials, which hold enormous promise for a range of energy-related applications. Their promise is owing to their "special"structure that gives POMs a truly unique ability to control redox reactions in energy conversion and storage. One such amazing capability is their large number of redox active sites that arises from the complex three-dimensional cluster of metal-oxide ions linked together by oxygen atoms. Here, a critical review on how POMs emerged from being molecular clusters for fundamental studies, to next-generation materials for energy applications is provided. We highlight how exploiting the versatility and activity of these molecules can lead to improved performance in energy devices such as supercapacitors and batteries, and in energy catalyst applications. The potential of POMs across numerous fields is systematically outlined by investigating structure-property-performance relationships and the determinant factors for energy systems. Finally, the challenges and opportunities for this class of materials with respect to addressing our pressing energy-related concerns are identified. This journal is © The Royal Society of Chemistry.

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Sheet-on-sheet like calcium ferrite and graphene nanoplatelets nanocomposite: A multifunctional nanocomposite for high-performance supercapacitor and visible light driven photocatalysis
Israr M., Iqbal J., Arshad A., Gómez-Romero P. Journal of Solid State Chemistry; 293 (121646) 2021. 10.1016/j.jssc.2020.121646. IF: 3.498

Calcium ferrite-graphene nanoplatelets nanocomposites with sheet-on-sheet like morphology are fabricated and investigated for their physicochemical characteristics, electrochemical energy storage capacity and photocatalysis. Interestingly, the (CF)1-x (GNPs)x nanocomposite-based electrode has shown maximum specific capacitance up to 422 Fg-1 at 0.25 Ag-1 with excellent cycling stability, 2.6 times higher than that of neat CF nanosheets. Furthermore, the synergistic contribution from photocatalytic and photo-Fenton reactions enables (CF)1-x (GNPs)x nanocomposites to offer superior photocatalytic activity (99.4% dye removal in 90 min). The inclusion of GNPs significantly enhances the charge carriers separation and transportation. The excellent electrochemical efficiency of (CF)1-x (GNPs)x could be attributed to the 2D interfacial interactions that provide a better charge transport at electrode/electrolyte interface. These interactions are also responsible for creating effective charge transport pathways and efficient e−/h+ separation leading to rapid dye-degradation, which make the material potential for remediation of water pollution and energy storage systems. © 2020 Elsevier Inc.

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2020

Can polyoxometalates enhance the capacitance and energy density of activated carbon in organic electrolyte supercapacitors?
Zhu J.-J., Benages-Vilau R., Gomez-Romero P. Electrochimica Acta; 362 (137007) 2020. 10.1016/j.electacta.2020.137007. IF: 6.215

Polyoxometalates (POMs) have been shown to work as faradaic additives to activated carbon (AC) in acidic aqueous electrolytes. Yet, their use in organic media allows not only for added capacity but also higher voltage. Here we show that the tetraethylammonium derivative of phosphotungstate [PW12O40]3− (PW12) can be homogeneously distributed throughout the pores of activated carbon (AC) in organic solvents such as N,N’-dimethylformamide (DMF) and demonstrate the use of this hybrid electrode material in an organic electrolyte (1 M TEABF4 in acetonitrile) supercapacitor. Our results show the efficient electroactivity of the PW12 cluster even in the absence of protons, providing a higher voltage than aqueous electrolytes and fast and reversible redox activity. The hybrid material shows a combination of double-layer (AC) and redox (PW12) capacities leading to an increase (36%) in volumetric capacitance with respect to pristine AC in the same organic electrolyte (1 M TEABF4 in acetonitrile). Remarkably, we were able to quantify this increase as coming predominantly from non-diffusion-limited processes thanks to the utterly dispersed nature of POMs. Moreover, the hybrid material delivers a good rate capability and excellent cycle stability (93% retention of the initial capacitance after 10,000 cycles). This study has a profound significance on improving capacitance of carbon-based materials in organic electrolytes. © 2020 Elsevier Ltd

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Dual carbon potassium-ion capacitors: Biomass-derived graphenelike carbon nanosheet cathodes
Dubal D.P., Pham H.D., Mahale K., Hoang T.M.L., Mundree S.G., Gomez-Romero P. ACS Applied Materials and Interfaces; 12 (43): 48518 - 48525. 2020. 10.1021/acsami.0c12379. IF: 8.758

Potassium-ion storage devices are attracting tremendous attention for wide-ranging applications on account of their low cost, fast charge transport in electrolytes, and large working voltage. However, developing cost-effective, high-energy electrodes with excellent structural stability to ensure long-term cycling performance is a major challenge. In this contribution, we have derived two different forms of carbon materials from almond shells using different chemical treatments. For instance, hard carbon (HC) and graphene-like activated carbon (AC) nanosheets are developed by employing simple carbonization and chemical activation routes, respectively. The resultant hard carbon (AS-HC) and activated carbon (AS-AC) exhibit outstanding electrochemical performance as negative and positive electrodes in a potassium-ion battery (KIB), respectively, through their tailor-made surface properties. These promising benefits pave a way to construct a biomass-derived carbon potassium-ion capacitor (KIC) by employing AS-HC as the negative electrode and AS-AC as the positive electrode in a K-based electrolyte. The as-fabricated KIC delivers a reasonable specific energy of 105 Wh/kg and excellent cycling life with negligible capacitance fading over 10 000 cycles. This "waste-to-wealth"approach can promote the development of sustainable KICs at low cost and inspire their use for fastrate K-based energy storage applications. © 2020 American Chemical Society.

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Enhancement of organophosphate degradation by electroactive pyrrole and imidazole copolymers
Hryniewicz B.M., Wolfart F., Gómez-Romero P., Orth E.S., Vidotti M. Electrochimica Acta; 338 (135842) 2020. 10.1016/j.electacta.2020.135842. IF: 6.215

Many chemical warfare agents and agrochemicals are composed by organophosphates, that present high toxicity and difficult spontaneous degradation. Amongst the different catalysts to degrade these compounds, heterogeneous systems stand out since they provide easy recovery of the catalyst. However, the limited diffusion of the substrate decreases the rate of the reactions when compared to homogeneous catalysis. To reach a good efficiency in the dephosphorylation, we created heterogeneous catalysts based on pyrrole and imidazole that can enhance the degradation by different effects; both catalytic activity of imidazole and electroactivity of polypyrrole were evaluated. Spectroelectrochemical studies evidenced that the rate constant changes with the applied potential, indicating different reaction mechanisms with the material in the oxidized and neutral states. In summary, a new perspective allying conducting polymers with chemical catalysts was explored. This cooperative effect should be considered in future works concerning the search for new materials to monitor and eliminate organophosphates. © 2020 Elsevier Ltd

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Fabrication of 3D binder-free graphene NiO electrode for highly stable supercapattery
Agudosi E.S., Abdullah E.C., Numan A., Mubarak N.M., Aid S.R., Benages-Vilau R., Gómez-Romero P., Khalid M., Omar N. Scientific Reports; 10 (1, 11214) 2020. 10.1038/s41598-020-68067-2. IF: 3.998

Electrochemical stability of energy storage devices is one of their major concerns. Polymeric binders are generally used to enhance the stability of the electrode, but the electrochemical performance of the device is compromised due to the poor conductivity of the binders. Herein, 3D binder-free electrode based on nickel oxide deposited on graphene (G-NiO) was fabricated by a simple two-step method. First, graphene was deposited on nickel foam via atmospheric pressure chemical vapour deposition followed by electrodeposition of NiO. The structural and morphological analyses of the fabricated G-NiO electrode were conducted through Raman spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS). XRD and Raman results confirmed the successful growth of high-quality graphene on nickel foam. FESEM images revealed the sheet and urchin-like morphology of the graphene and NiO, respectively. The electrochemical performance of the fabricated electrode was evaluated through cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) in aqueous solution at room temperature. The G-NiO binder-free electrode exhibited a specific capacity of ≈ 243 C g−1 at 3 mV s−1 in a three-electrode cell. A two-electrode configuration of G-NiO//activated charcoal was fabricated to form a hybrid device (supercapattery) that operated in a stable potential window of 1.4 V. The energy density and power density of the asymmetric device measured at a current density of 0.2 A g−1 were estimated to be 47.3 W h kg−1 and 140 W kg−1, respectively. Additionally, the fabricated supercapattery showed high cyclic stability with 98.7% retention of specific capacity after 5,000 cycles. Thus, the proposed fabrication technique is highly suitable for large scale production of highly stable and binder-free electrodes for electrochemical energy storage devices. © 2020, The Author(s).

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Graphene triggered enhancement in visible-light active photocatalysis as well as in energy storage capacity of (CFO)1-x(GNPs)x nanocomposites
Israr M., Iqbal J., Arshad A., Rani M., Gómez‐Romero P., Benages R. Ceramics International; 46 (3): 2630 - 2639. 2020. 10.1016/j.ceramint.2019.09.232. IF: 3.830

Cobalt ferrite-graphene nanoplatelets ((CFO)1-x(GNPs)x) nanocomposites are promising for efficient photocatalysis and high-performance supercapacitors. Multifunctional (CFO)1-x(GNPs)x nanocomposites prepared via facile chemical method have been investigated for their physio-chemical characteristics like crystal structure, morphology, chemical composition, optical properties, infrared vibrational modes, photocatalytic and supercapacitor applications. Interestingly, the photocatalytic activity of CFO nanostructures has been improved significantly from 38.3% to 98.7% with the addition of graphene which can be attributed to control over recombination of charge carriers. It is also found that the specific capacitance of the prepared (CFO)1-x(GNPs)x nanocomposite electrode at 0.5 Ag-1 is three times higher than that of only CFO based electrode which could be due to the conducting nature of graphene nanoplatelets (GNPs). The enhanced photocatalytic and improved electrochemical characteristics suggest the effective use of prepared nanocomposites in water purification and supercapacitor nanodevices. © 2019 Elsevier Ltd and Techna Group S.r.l.

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Highly Loaded Mildly Edge-Oxidized Graphene Nanosheet Dispersions for Large-Scale Inkjet Printing of Electrochemical Sensors
Nagar B., Jović M., Bassetto V.C., Zhu Y., Pick H., Gómez-Romero P., Merkoçi A., Girault H.H., Lesch A. ChemElectroChem; 7 (2): 460 - 468. 2020. 10.1002/celc.201901697. IF: 4.154

Inkjet printing of electrochemical sensors using a highly loaded mildly edge-oxidized graphene nanosheet (EOGN) ink is presented. An ink with 30 mg/mL EOGNs is formulated in a mixture of N-methyl pyrrolidone and propylene glycol with only 30 min of sonication. The absence of additives, such as polymeric stabilizers or surfactants, circumvents reduced electrochemical activity of coated particles and avoids harsh post-printing conditions for additive removal. A single light pulse from a xenon flash lamp dries the printed EGON film within a fraction of a second and creates a compact electrode surface. An accurate coverage with only 30.4 μg of EOGNs per printed layer and cm2 is achieved. The EOGN films adhere well to flexible polyimide substrates in aqueous solution. Electrochemical measurements were performed using cyclic voltammetry and differential pulse voltammetry. An all inkjet-printed three-electrode living bacterial cell detector is prepared with EOGN working and counter electrodes and silver-based quasi-reference electrode. The presence of E. coli in liquid samples is recorded with four electroactive metabolic activity indicators. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Multifunctional MgFe2O4/GNPs nanocomposite: Graphene-promoted visible light driven photocatalytic activity and electrochemical performance of MgFe2O4 nanoparticles
Israr M., Iqbal J., Arshad A., Gómez‐Romero P., Benages R. Solid State Sciences; 110 (106363) 2020. 10.1016/j.solidstatesciences.2020.106363. IF: 2.434

Herein, the electrochemical and photodegradation properties of magnesium ferrite and graphene-nanoplatelets nanocomposites, (MFO)1-x(GNPs)x, (x = 0.25, 0.50, 0.75) are reported. Benefitting from the effective interfacial interaction of the bi-phase nanocomposite and superior electrical conduction of GNPs, a significant enhancement in supercapacitive performance has been demonstrated. Interestingly, the electrochemical properties of nanocomposite electrode were found to depend on the loading ratio of GNPs. Notably the (MFO)0.50(GNPs)0.50 (50 wt % GNPs) shows an outstanding energy storage capacity i.e., 612 Fg–1 at 0.5 Ag–1 with 21.25 Wh kg−1 energy density at power density of 125 W kg−1 and retains ~76.8 % of the first cycle capacitance after continuous 1500 charge/discharge cycles. Furthermore, the (MFO)0.75(GNPs)0.25 (25 wt % GNPs) composite demonstrates admirable photodegradation efficiency (99.3 % in 60 min of visible light illumination) which is 3.2 times than that of neat MFO nanoparticles. The superior electrochemical and photodegradation performance suggests that the prepared nanocomposites can be effectively utilized in high‐performance energy storage devices and low cost, eco-friendly water purification systems. © 2020 Elsevier Masson SAS

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2019

Development of low-melting point molten salts and detection of solid-to-liquid transitions by alternative techniques to DSC
Rodríguez-Laguna M.D.R., Gómez-Romero P., Sotomayor Torres C.M., Lu M.-C., Chávez-Ángel E. Solar Energy Materials and Solar Cells; 202 (110107) 2019. 10.1016/j.solmat.2019.110107. IF: 6.019

The ‘Solar salt’ (60% NaNO3-40% KNO3, wt. %) is the most used heat transfer and storage material in high temperature CSP systems. The main drawback is its high melting temperature of 228 °C, which requires extra-energy to keep it in the liquid state and avoid damage to pipes at low temperatures. Multi-component salts are combinations of different cations and anions. The difference in size of the ions hinders the crystallization of the material and provides lower melting temperatures. Multi-component salts are considered in this study to replace simpler combinations, such as binary and ternary eutectic mixtures. Herein, we report on two novel six-component nitrates with a melting temperature of 60–75 °C and a thermal stability up to ~500 °C under a linear heating program in N2 atmosphere. Properties such as the thermal conductivity in solid and molten state, heat capacity and vibrational spectra were evaluated. The study of the thermal behaviour of these materials using differential scanning calorimetry was insufficient, hence alternative and complementary techniques were used, such as: the three-omega technique, optical transmission and Raman spectroscopy. Multi-component salts were found to solidify as amorphous solids even at slow cooling rates and water was found to behave as a catalyst of crystallization. © 2019 Elsevier B.V.

View abstract
From thermal to electroactive graphene nanofluids
Rueda-García D., Del Rocío Rodríguez-Laguna M., Chávez-Angel E., Dubal D.P., Cabán-Huertas Z., Benages-Vilau R., Gómez-Romero P. Energies; 12 (23, 4545) 2019. 10.3390/en12234545. IF: 2.707

Here, we describe selected work on the development and study of nanofluids based on graphene and reduced graphene oxide both in aqueous and organic electrolytes. A thorough study of thermal properties of graphene in amide organic solvents (N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone) showed a substantial increase of thermal conductivity and specific heat upon graphene integration in those solvents. In addition to these thermal studies, our group has also pioneered a distinct line of work on electroactive nanofluids for energy storage. In this case, reduced graphene oxide (rGO) nanofluids in aqueous electrolytes were studied and characterized by cyclic voltammetry and charge-discharge cycles (i.e., in new flow cells). In addition, hybrid configurations (both hybrid nanofluid materials and hybrid cells combining faradaic and capacitive activities) were studied and are summarized here. © 2019 MDPI AG. All rights reserved.

View abstract
Fully printed one-step biosensing device using graphene/AuNPs composite
Nagar B., Balsells M., de la Escosura-Muñiz A., Gomez-Romero P., Merkoçi A. Biosensors and Bioelectronics; 129: 238 - 244. 2019. 10.1016/j.bios.2018.09.073. IF: 9.518

Driven by the growing need of simple, cost efficient and flexible sensing systems, we have designed here a fully printed Reduced Graphene Oxide (rGO) based impedimetric sensor for one step sensing of DNA. The DNA sensor was fabricated by stamping of layered rGO and rGO/gold nanoparticles/single stranded DNA (rGO/AuNPs/ssDNA) composites over PET substrates using wax-printing technique. rGO works as an excellent working electrode, while the AuNPs create a suitable environment for ssDNA immobilization. Counter and reference electrodes were previously screen-printed on the plastic substrate, making thus a compact and highly integrated sensing platform. The change in electron transfer resistance after hybridization with a target ssDNA specific of Coxsackie B3 virus was monitored using electrochemical impedance spectroscopy (EIS), finding a linear response in the range of concentrations 0.01–20 µM. The novel, simple and straightforward one-step printing process for fabrication of a biosensing device developed keeps in mind the growing need of large scale device manufacturing. The successful proof-of-concept for the detection of DNA hybridization can be extended to other affinity biosensors, taking advantage of the integration of the bioreceptor on the sensor surface. Such ready-to-use biosensor would lead to a one-step electrochemical detection. © 2018 Elsevier B.V.

View abstract
Metal–Organic Framework (MOF) Derived Electrodes with Robust and Fast Lithium Storage for Li-Ion Hybrid Capacitors
Dubal D.P., Jayaramulu K., Sunil J., Kment Š., Gomez-Romero P., Narayana C., Zbořil R., Fischer R.A. Advanced Functional Materials; 29 (19, 1900532) 2019. 10.1002/adfm.201900532. IF: 15.621

Hybrid metal–organic frameworks (MOFs) demonstrate great promise as ideal electrode materials for energy-related applications. Herein, a well-organized interleaved composite of graphene-like nanosheets embedded with MnO 2 nanoparticles (MnO 2 @C-NS) using a manganese-based MOF and employed as a promising anode material for Li-ion hybrid capacitor (LIHC) is engineered. This unique hybrid architecture shows intriguing electrochemical properties including high reversible specific capacity 1054 mAh g −1 (close to the theoretical capacity of MnO 2 , 1232 mAh g −1 ) at 0.1 A g −1 with remarkable rate capability and cyclic stability (90% over 1000 cycles). Such a remarkable performance may be assigned to the hierarchical porous ultrathin carbon nanosheets and tightly attached MnO 2 nanoparticles, which provide structural stability and low contact resistance during repetitive lithiation/delithiation processes. Moreover, a novel LIHC is assembled using a MnO 2 @C-NS anode and MOF derived ultrathin nanoporous carbon nanosheets (derived from other potassium-based MOFs) cathode materials. The LIHC full-cell delivers an ultrahigh specific energy of 166 Wh kg −1 at 550 W kg −1 and maintained to 49.2 Wh kg −1 even at high specific power of 3.5 kW kg −1 as well as long cycling stability (91% over 5000 cycles). This work opens new opportunities for designing advanced MOF derived electrodes for next-generation energy storage devices. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Modification of the raman spectra in graphene-based nanofluids and its correlation with thermal properties
Rodríguez-Laguna M.D.R., Romero P.G., Torres C.M.S., Chavez-Angel E. Nanomaterials; 9 (5, 804) 2019. 10.3390/nano9050804. IF: 4.034

It is well known that by dispersing nanoparticles in a fluid, the thermal conductivity of the resulting nanofluid tends to increase with the concentration of nanoparticles. However, it is not clear what the mechanism behind this phenomenon is. Raman spectroscopy is a characterization technique connecting the molecular and macroscopic world, and therefore, it can unravel the puzzling effect exerted by the nanomaterial on the fluid. In this work, we report on a comparative study on the thermal conductivity, vibrational spectra and viscosity of graphene nanofluids based on three different amides: N, N-dimethylacetamide (DMAc); N, N-dimethylformamide (DMF); and N-methyl-2-pyrrolidinone (NMP). A set of concentrations of highly stable surfactant-free graphene nanofluids developed in-house was prepared and characterized. A correlation between the modification of the vibrational spectra of the fluids and an increase in their thermal conductivity in the presence of graphene was confirmed. Furthermore, an explanation of the non-modification of the thermal conductivity in graphene-NMP nanofluids is given based on its structure and a peculiar arrangement of the fluid. © 2019, MDPI AG. All rights reserved.

View abstract
On the Enhancement of the Thermal Conductivity of Graphene-Based Nanofluids
Rodriguez-Laguna M.R., Torres C.M.S., Gomez-Romero P., Chavez-Angel E. Proceedings of the IEEE Conference on Nanotechnology; 2018-July (8626244) 2019. 10.1109/NANO.2018.8626244. IF: 0.000

Heat transfer fluids have been extensively used in both low-temperature and high temperature applications (e.g. microelectronics cooling and concentrated solar power). However, their low thermal conductivity is still a limit on performance. One way to enhance thermal properties is to disperse nanomaterials, such as graphene flakes in the base fluid. In this work, we have developed highly stable DMAc-graphene nanofluids with enhanced thermal properties. Furthermore, the displacement of several Raman bands as a function of graphene concentration in DMAc suggests that the solvent molecules are able to interact with graphene surfaces strongly. © 2018 IEEE.

View abstract
Polypyrrole Nanopipes as a Promising Cathode Material for Li-ion Batteries and Li-ion Capacitors: Two-in-One Approach
Dubal D., Jagadale A., Chodankar N.R., Kim D.-H., Gomez-Romero P., Holze R. Energy Technology; 7 (2): 193 - 200. 2019. 10.1002/ente.201800551. IF: 3.163

Lithium ion capacitor (LIC) is a promising energy storage system that can simultaneously provide high energy with high rate (high power). Generally, LIC is fabricated using capacitive cathode (activated carbon, AC) and insertion-type anode (graphite) with Li-ion based organic electrolyte. However, the limited specific capacities of both anode and cathode materials limit the performance of LIC, in particular energy density. In this context, we have developed “two in one” synthetic approach to engineer both cathode and anode from single precursor for high performance LIC. Firstly, we have engineered a low cost 1D polypyrrole nanopipes (PPy-NPipes), which was utilized as cathode material and delivered a maximum specific capacity of 126 mAh/g, far higher than that of conventional AC cathodes (35 mAh/g). Later, N doped carbon nanopipes (N-CNPipes) was derived from direct carbonization of PPy-NPipes and successfully applied as anode material in LIC. Thus, a full LIC was fabricated using both pseudo-capacitive cathode (PPy-NPipes) and anode (N-CNPipes) materials, respectively. The cell delivered a remarkable specific energy of 107 Wh/kg with maximum specific power of 10 kW/kg and good capacity retention of 93 % over 2000 cycles. Thus, this work provide a new approach of utilization of nanostructured conducting polymers as a promising pseudocapacitive cathode for high performance energy storage systems. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract

2018

All nanocarbon Li-Ion capacitor with high energy and high power density
Dubal D.P., Gomez-Romero P. Materials Today Energy; 8: 109 - 117. 2018. 10.1016/j.mtener.2018.03.005. IF: 0.000

An energy storage device reaching energy densities of 102 Wh/Kg at power densities of 104 W/Kg would mean the possibility of charging such a device in 36 s. The nanocarbon device presented here is closer to that feat than any previously reported system. N-doped Carbon Nanopipes were used as anode and Partially Reduced Graphene Oxide as cathode, with LiPF6 EC/PC electrolyte. This system yields simultaneously high energy and power densities (262 at 450 W/kg and 78 Wh/kg at 9000 W/kg) which are energy/power combinations considerably higher than those of present Li-ion batteries. Our cell exhibits excellent cycle stability (∼91% capacity retention after 4000 cycles “0.01–4 V”). These breakthrough results are based on the kinetic balancing of the nanocarbon electrodes, which can deliver excellent high energy density at high rates and low costs. © 2018 Elsevier Ltd

View abstract
Battery and supercapacitor materials in flow cells. Electrochemical energy storage in a LiFePO4/reduced graphene oxide aqueous nanofluid
Rueda-Garcia D., Cabán-Huertas Z., Sánchez-Ribot S., Marchante C., Benages R., Dubal D.P., Ayyad O., Gómez-Romero P. Electrochimica Acta; 281: 594 - 600. 2018. 10.1016/j.electacta.2018.05.151. IF: 5.116

Exploring conceptual frontiers between batteries, supercapacitors, redox flow batteries (RFBs) and fuel cells (FCs), we have used a battery material (i.e. LiFePO4) and a supercapacitor material (i.e. graphene) in the form of nanoparticles dispersed in an aqueous electrolyte to characterize the electrochemical activity of the resulting electroactive nanofluids. X-ray diffraction, TEM, Raman, XPS and AFM analyses were carried out to characterize the solid LiFePO4 and RGO components. The corresponding electroactive nanofluids were prepared by dispersion in an aqueous Li2SO4 electrolyte and stabilized with Diaminobenzoic Acid (DABA). Cyclic voltammetry measurements were used to analyze their electrochemical behavior in three-electrode cells. Charge-discharge tests of the LiFePO4/RGO (positive) vs. RGO (negative) nanofluids were also performed. Effective utilization of dispersed electroactive particles (ca. 100 mAh/g(LFP) at 1C) was demonstrated, which turned out to be superior to the same LFP material used as solid electrode. A charge-transfer percolation effect provided by the RGO dispersion is proposed as the mechanism for the good performance of LiFePO4 (not coated with carbon!) and RGO Nanofluids. Our results constitute a first step and proof of concept of the possible application of electroactive nanofluid electrodes in alternative flow batteries. © 2018 Elsevier Ltd

View abstract
Design and Fabrication of Printed Paper-Based Hybrid Micro-Supercapacitor by using Graphene and Redox-Active Electrolyte
Nagar B., Dubal D.P., Pires L., Merkoçi A., Gómez-Romero P. ChemSusChem; 11 (11): 1849 - 1856. 2018. 10.1002/cssc.201800426. IF: 7.411

Inspired by future needs of flexible, simple, and low-cost energy storage devices, smart graphene-based micro-supercapacitors on conventional Xerox paper substrates were developed. The use of redox-active species (iodine redox couple) was explored to further improve the paper device's performance. The device based on printed graphene paper itself already had a remarkable maximum volumetric capacitance of 29.6 mF cm−3 (volume of whole device) at 6.5 mA cm−3. The performance of the hybrid electrode with redox-active potassium iodide at the graphene surface was tested. Remarkably, the hybrid device showed improved volumetric capacitance of 130 mF cm−3. The maximum energy density for a graphene+KI device in H2SO4 electrolyte was estimated to be 0.026 mWh cm−3. Thus, this work offers a new simple, and lightweight micro-supercapacitor based on low-cost printed graphene paper, which will have great applications in portable electronics. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Energy harvesting from neutralization reactions with saline feedback
Lima G., Dubal D.P., Rueda-García D., Gómez-Romero P., Huguenin F. Electrochimica Acta; 275: 145 - 154. 2018. 10.1016/j.electacta.2018.04.075. IF: 5.116

This work proposes an acid-base machine consisting of insertion electrodes for protons and alkaline metal ions placed in electrolytic solutions with different pH values and alkaline ion concentrations to harvest energy from a neutralization reaction. We simulate energy harvesting during acidic wastewater treatment with base (KOH) by using phosphomolybdic acid and nickel hexacyanoferrate as the negative and the positive electrodes, respectively, in aqueous H2SO4 and K2SO4 solutions. In this configuration, the machine harvests energy from a change in the free energy related to changes in the proton and in the potassium ion concentrations after neutralization reactions, with feedback from the saline solution resulting from neutralization. The electrochemical impedance spectroscopy diagrams provide insight into the practical proton and potassium ion electroinsertion reversibility in acidic and neutral media. Based on the charge/discharge curves at pH = 2 and pH = 5.8, the acid-base machine harvests ca. 10 kJ per mol of electro-inserted protons in the first cycles. These results demonstrate that the methodology is viable for sustainable growth—it can harvest energy from wastewater treatment, a practice that can be especially profitable for the industrial sector, which produces great amounts of wastewater. © 2018 Elsevier Ltd

View abstract
Hybrid Graphene-Polyoxometalates Nanofluids as Liquid Electrodes for Dual Energy Storage in Novel Flow Cells
Dubal D.P., Rueda-Garcia D., Marchante C., Benages R., Gomez-Romero P. Chemical Record; 18 (7): 1076 - 1084. 2018. 10.1002/tcr.201700116. IF: 4.891

Solid Hybrid materials abound. But flowing versions of them are new actors in the materials science landscape and in particular for energy applications. This paper presents a new way to deliver nanostructured hybrid materials for energy storage, namely, in the form of nanofluids. We present here the first example of a hybrid electroactive nanofluid (HENFs) combining capacitive and faradaic energy storage mechanisms in a single fluid material. This liquid electrode is composed of reduced graphene oxide and polyoxometalates (rGO-POMs) forming a stable nanocomposite for electrochemical energy storage in novel Nanofluid Flow Cells. Two graphene based hybrid materials (rGO-phosphomolybdate, rGO-PMo12 and rGO-phosphotungstate, rGO-PW12) were synthesized and dispersed with the aid of a surfactant in 1 M H2SO4 aqueous electrolyte to yield highly stable hybrid electroactive nanofluids (HENFs) of low viscosity which were tested in a home-made flow cell under static and continuous flowing conditions. Remarkably, even low concentration rGO-POMs HENFs (0.025 wt%) exhibited high specific capacitances of 273 F/g(rGO-PW12) and 305 F/g(rGO-PMo12) with high specific energy and specific power. Moreover, rGO-POM HENFs show excellent cycling stability (∼95 %) as well as Coulombic efficiency (∼77–79 %) after 2000 cycles. Thus, rGO-POM HENFs effectively behave as real liquid electrodes with excellent properties, demonstrating the possible future application of HENFs for dual energy storage in a new generation of Nanofluid Flow Cells. © 2018 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Mechanisms behind the enhancement of thermal properties of graphene nanofluids
Rodríguez-Laguna M.R., Castro-Alvarez A., Sledzinska M., Maire J., Costanzo F., Ensing B., Pruneda M., Ordejón P., Sotomayor Torres C.M., Gómez-Romero P., Chávez-Ángel E. Nanoscale; 10 (32): 15402 - 15409. 2018. 10.1039/c8nr02762e. IF: 7.233

While the dispersion of nanomaterials is known to be effective in enhancing the thermal conductivity and specific heat capacity of fluids, the mechanisms behind this enhancement remain to be elucidated. Herein, we report on highly stable, surfactant-free graphene nanofluids, based on N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF), with enhanced thermal properties. An increase of up to 48% in thermal conductivity and 18% in specific heat capacity was measured. The blue shift of several Raman bands with increasing graphene concentration in DMF indicates that there is a modification in the vibrational energy of the bonds associated with these modes, affecting all the molecules in the liquid. This result indicates that graphene has the ability to affect solvent molecules at long-range, in terms of vibrational energy. Density functional theory and molecular dynamics simulations were used to gather data on the interaction between graphene and solvent, and to investigate a possible order induced by graphene on the solvent. The simulations showed a parallel orientation of DMF towards graphene, favoring π-π stacking. Furthermore, a local order of DMF molecules around graphene was observed suggesting that both this special kind of interaction and the induced local order may contribute to the enhancement of the fluid's thermal properties. © The Royal Society of Chemistry.

View abstract
Synthesis and Caracterization of Mesoporous FePO4 as Positive Electrode Materials for Lithium Batteries
Salamani A., Merrouche A., Telli L., Gómez-Romero P., Huertas Z.C. Surface Engineering and Applied Electrochemistry; 54 (1): 55 - 63. 2018. 10.3103/S106837551801012X. IF: 0.000

Mesoporous iron phosphates were synthesized using sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) as surfactants. The material synthesized in the presence of SDS was not applied as a positive electrode active material of a lithium battery. The results show that the obtained FePO4 has a mesoporous structure with a specific surface area of 70 m2 g−1 and a dominant pore diameter of 3 nm. Those mesoporous were characterized by different microstructural and electrochemical analyzes. Among the materials studied under different conditions, those calcined at 450°C preserve mesoporous structures and exhibit the best electrochemical performance when used as active materials of the positive electrodes of lithium batteries. Effectively, a relatively high specific capacity of 135 and 122 mAh g−1 was registered at C/20 collected experimentally by the samples synthesized in the presence of SDS and CTAB, respectively. © 2018, Allerton Press, Inc.

View abstract
Synthesis and characterization of porous sulfur/MWCNTs composites with improved performance and safety as cathodes for Li-S batteries
Fedorkova A.S., Kazda T., Gavalierova K., Gomez-Romero P., Shembel E. International Journal of Electrochemical Science; 13 (1): 551 - 562. 2018. 10.20964/2018.01.67. IF: 1.369

Sulfur-carbon (S-C-MWCNTs) composites and sulfur-LiFePO4 (S-LFP-MWCNTs) composites were synthesised with MWCNTs additive by sulfur sublimation and solid state reaction. As prepared materials are characterized with scanning electron microscopy, thermogravimetry, FTIR, elemental analysis, XPS, cyclic voltammetry and galvanostatic charge/discharge tests. The composite S-LFP cathode with MWCNTs additive shows improved discharge capacity and performance. It shows an initial discharge capacity of 1167 mAh/g-sulfur, or 70% of theoretical capacity. The discharge capacity measured after 20 cycles for S-LFP-MWCNTs composite cathode was 80% of the initial capacity and remained stable. After 160 charge/discharge tests, the cathode displays a stable capacity of 561 mAh/g-sulfur at the C-rate of 0.2 C. Combination of sulfur, LiFePO4 and MWCNTs prevents aggregation and volume change of the cathode particles and improves the conductivity and electrochemical stability during the long-term cycling. 3-D FTIR spectroscopy measurements confirmed improved chemical stability and safety of sulfur composites also at higher temperatures. © 2018 The Authors.

View abstract
Towards flexible solid-state supercapacitors for smart and wearable electronics
Dubal D.P., Chodankar N.R., Kim D.-H., Gomez-Romero P. Chemical Society Reviews; 47 (6): 2065 - 2129. 2018. 10.1039/c7cs00505a. IF: 40.182

Flexible solid-state supercapacitors (FSSCs) are frontrunners in energy storage device technology and have attracted extensive attention owing to recent significant breakthroughs in modern wearable electronics. In this study, we review the state-of-the-art advancements in FSSCs to provide new insights on mechanisms, emerging electrode materials, flexible gel electrolytes and novel cell designs. The review begins with a brief introduction on the fundamental understanding of charge storage mechanisms based on the structural properties of electrode materials. The next sections briefly summarise the latest progress in flexible electrodes (i.e., freestanding and substrate-supported, including textile, paper, metal foil/wire and polymer-based substrates) and flexible gel electrolytes (i.e., aqueous, organic, ionic liquids and redox-active gels). Subsequently, a comprehensive summary of FSSC cell designs introduces some emerging electrode materials, including MXenes, metal nitrides, metal-organic frameworks (MOFs), polyoxometalates (POMs) and black phosphorus. Some potential practical applications, such as the development of piezoelectric, photo-, shape-memory, self-healing, electrochromic and integrated sensor-supercapacitors are also discussed. The final section highlights current challenges and future perspectives on research in this thriving field. © 2018 The Royal Society of Chemistry.

View abstract
Ultrathin Hierarchical Porous Carbon Nanosheets for High-Performance Supercapacitors and Redox Electrolyte Energy Storage
Jayaramulu K., Dubal D.P., Nagar B., Ranc V., Tomanec O., Petr M., Datta K.K.R., Zboril R., Gómez-Romero P., Fischer R.A. Advanced Materials; 30 (15, 1705789) 2018. 10.1002/adma.201705789. IF: 21.950

The design of advanced high-energy-density supercapacitors requires the design of unique materials that combine hierarchical nanoporous structures with high surface area to facilitate ion transport and excellent electrolyte permeability. Here, shape-controlled 2D nanoporous carbon sheets (NPSs) with graphitic wall structure through the pyrolysis of metal–organic frameworks (MOFs) are developed. As a proof-of-concept application, the obtained NPSs are used as the electrode material for a supercapacitor. The carbon-sheet-based symmetric cell shows an ultrahigh Brunauer–Emmett–Teller (BET)-area-normalized capacitance of 21.4 µF cm−2 (233 F g−1), exceeding other carbon-based supercapacitors. The addition of potassium iodide as redox-active species in a sulfuric acid (supporting electrolyte) leads to the ground-breaking enhancement in the energy density up to 90 Wh kg−1, which is higher than commercial aqueous rechargeable batteries, maintaining its superior power density. Thus, the new material provides a double profits strategy such as battery-level energy and capacitor-level power density. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Unveiling BiVO4 nanorods as a novel anode material for high performance lithium ion capacitors: Beyond intercalation strategies
Dubal D.P., Jayaramulu K., Zboril R., Fischer R.A., Gomez-Romero P. Journal of Materials Chemistry A; 6 (14): 6096 - 6106. 2018. 10.1039/c8ta00549d. IF: 9.931

Energy storage is increasingly demanded in many new niches of applications from wearables to unmanned autonomous vehicles. However, current energy storage systems are unable to fulfill the power requirements (high energy at high power) needed for these novel applications. Recently, Li-ion capacitors (LICs) have been spotted as hybrid devices with the potential to display high energy and high power. Nevertheless, it is still a great challenge to achieve high performance LICs due to the unmatched kinetic properties and capacity between anode and cathode materials. Herein, we are presenting our first seminal report on the use of BiVO4 nanorods as a new anode material for LICs coupled with a partially reduced graphene oxide (PRGO) cathode. The BiVO4 nanorods show an excellent reversible capacity of 877 mA h g-1 (ultrahigh volumetric capacity of 4560 mA h cm-3) at 1.1 A g-1 with a great capacity retention (in half-cell design), which is the highest value reported so far for metal vanadates. Later on, a LIC was constructed with BiVO4 as the anode and PRGO as the cathode electrode, delivering a high energy density of 152 W h kg-1 and a maximum power density of 9.6 kW kg-1 compared to that for hard carbon and intercalation (such as Li4Ti5O12 and Li3VO4) based anode materials. Additionally, the BiVO4//PRGO LIC exhibits a good cyclability of 81% over 6000 cycles. Thus, this investigation opens up new opportunities to develop different LIC systems. © 2018 The Royal Society of Chemistry.

View abstract

2017

Asymmetric Supercapacitors Based on Reduced Graphene Oxide with Different Polyoxometalates as Positive and Negative Electrodes
Dubal D.P., Chodankar N.R., Vinu A., Kim D.-H., Gomez-Romero P. ChemSusChem; 10 (13): 2742 - 2750. 2017. 10.1002/cssc.201700792. IF: 7.226

Nanofabrication using a “bottom-up” approach of hybrid electrode materials into a well-defined architecture is essential for next-generation miniaturized energy storage devices. This paper describes the design and fabrication of reduced graphene oxide (rGO)/polyoxometalate (POM)-based hybrid electrode materials and their successful exploitation for asymmetric supercapacitors. First, redox active nanoclusters of POMs [phosphomolybdic acid (PMo12) and phosphotungstic acid (PW12)] were uniformly decorated on the surface of rGO nanosheets to take full advantage of both charge-storing mechanisms (faradaic from POMs and electric double layer from rGO). The as-synthesized rGO-PMo12 and rGO-PW12 hybrid electrodes exhibited impressive electrochemical performances with specific capacitances of 299 (269 mF cm−2) and 370 F g−1 (369 mF cm−2) in 1 m H2SO4 as electrolyte at 5 mA cm−2. An asymmetric supercapacitor was then fabricated using rGO-PMo12 as the positive and rGO-PW12 as the negative electrode. This rGO-PMo12∥rGO-PW12 asymmetric cell could be successfully cycled in a wide voltage window up to 1.6 V and hence exhibited an excellent energy density of 39 Wh kg−1 (1.3 mWh cm−3) at a power density of 658 W kg−1 (23 mW cm−3). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
BiVO4 Fern Architectures: A Competitive Anode for Lithium-Ion Batteries
Dubal D.P., Patil D.R., Patil S.S., Munirathnam N.R., Gomez-Romero P. ChemSusChem; 10 (21): 4163 - 4169. 2017. 10.1002/cssc.201701483. IF: 7.226

The development of high-performance anode materials for lithium-ion batteries (LIBs) is currently subject to much interest. In this study, BiVO4 fern architectures are introduced as a new anode material for LIBs. The BiVO4 fern shows an excellent reversible capacity of 769 mAh g−1 (ultrahigh volumetric capacity of 3984 mAh cm−3) at 0.12 A g−1 with large capacity retention. A LIB full cell is then assembled with a BiVO4 fern anode and LiFePO4 (LFP, commercial) as cathode material. The device can achieve a capacity of 140 mAh g−1 at 1C rate, that is, 81 % of the capacity of the cathode and maintained to 104 mAh g−1 at a high rate of 8C, which makes BiVO4 a promising candidate as a high-energy anode material for LIBs. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Capacitive vs Faradaic Energy Storage in a Hybrid Cell with LiFePO4/RGO Positive Electrode and Nanocarbon Negative Electrode
Cabán-Huertas Z., Dubal D.P., Ayyad O., Gómez-Romero P. Journal of the Electrochemical Society; 164 (1): A6140 - A6146. 2017. 10.1149/2.0211701jes. IF: 3.259

We report an advanced device based on a Nitrogen-doped Carbon Nanopipes (N-CNP) negative electrode and a lithium iron phosphate (LiFePO4) positive electrode. We carefully balanced the cell composition (charge balance) and suppressed the initial irreversible capacity of the anode in the round of few cycles.We demonstrated an optimal performance in terms of specific capacity 170 mAh/g of LiFePO4 with energy density of about 203 Wh kg-1 and a stable operation for over 100 charge-discharge cycles. The components of this device (combining capacitive and faradaic electrodes) are low cost and easily scalable. This device has a performance comparable to those offered by the present technology of LIBs with the potential for faster charging; hence, we believe that the results disclosed in this work may open up new opportunities for energy storage devices. © The Author(s) 2016. Published by ECS.

View abstract
Direct electrodeposition of imidazole modified poly(pyrrole) copolymers: synthesis, characterization and supercapacitive properties
Wolfart F., Hryniewicz B.M., Marchesi L.F., Orth E.S., Dubal D.P., Gómez-Romero P., Vidotti M. Electrochimica Acta; 243: 260 - 269. 2017. 10.1016/j.electacta.2017.05.082. IF: 4.798

In this manuscript we report the direct electrosynthesis of a new conducting copolymer based on the incorporation of imidazole molecules within the polypyrrole chain. Different proportions of the monomers were tested during the direct electropolymerization of the copolymer. The resulting materials were characterized by electrochemical and spectroscopic techniques (Raman and XPS) and a mechanism of polymerization is proposed. Our findings showed that imidazole acts as an inhibitor of the polymerization process, decreasing the overall number of actives sites for the polymerization on the electrode surface producing a polymeric morphology very different compared with pure polypyrrole, as observed by Scanning Electron Microscopy images and corroborated by Electrochemical Impedance Spectroscopy. This behavior significantly affects the supercapacitive performance of the resulting p(Py-IMZ) modified electrodes where the specific capacitance of the material increased from 122 to 201 Fg−1 (64%) at 10 mV s−1. Furthermore, a unique pseudo-capacitive behavior described herein emphasizes the role of the imidazole as inductor of the morphology and co-monomer in the unique electrochemical signature of the material. The results suggest that the incorporation of IMZ increases the specific capacitance of PPy electrode by around 64%. © 2017 Elsevier Ltd

View abstract
Functionalization of Polypyrrole Nanopipes with Redox-Active Polyoxometalates for High Energy Density Supercapacitors
Dubal D.P., Ballesteros B., Mohite A.A., Gómez-Romero P. ChemSusChem; 10 (4): 731 - 737. 2017. 10.1002/cssc.201601610. IF: 7.226

Hybrid materials are very attractive for the fabrication of high-performance supercapacitors. Here, we have explored organic–inorganic hybrid materials based on open-end porous 1 D polypyrrole nanopipes (PPy-NPipes) and heteropolyoxometalates (phosphotungstate ([PW12O40]3−, PW12) or phosphomolybdate ([PMo12O40]3−, PMo12)) that display excellent areal capacitances. Two different hybrid materials (PMo12@PPy and PW12@PPy) were effectively synthesized and used for symmetric supercapacitors. The anchoring of the inorganic nanoclusters onto the conducting polymer nanopipes led to electrodes that stood up to our best expectations exhibiting outstanding areal capacitances that are almost 1.5 to 2 fold higher than that of pristine PPy-NPipes. In addition, symmetric cells based on PMo12@PPy and PW12@PPy hybrid electrodes were fabricated and showed significant improvement in cell performance with very high volumetric capacitances in the range of 6.3–6.8 F cm−3(considering the volume of whole device). Indeed, they provide extended potential windows in acidic electrolytes (up to 1.5 V) which led to ultrahigh energy densities of 1.5 and 2.2 mWh cm−3for PMo12@PPy and PW12@PPy cells, respectively. Thus, these unique organic-inorganic hybrid symmetric cells displayed extraordinary electrochemical performances far exceeding those of more complex asymmetric systems. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
Hurdles to organic quinone flow cells. Electrode passivation by quinone reduction in acetonitrile Li electrolytes
Rueda-García D., Dubal D.P., Hugenin F., Gómez-Romero P. Journal of Power Sources; 350: 9 - 17. 2017. 10.1016/j.jpowsour.2017.03.048. IF: 6.395

The uses of quinones in Redox Flow Batteries (RFBs) has been mainly circumscribed to aqueous solutions (of derivatives with polar groups) despite a larger solubility and wider electrochemical window provided by organic media. The redox mechanism of quinones in protic media is simpler and better known than in aprotic media, where radical species are involved. This paper reports the behaviour of methyl-p-benzoquinone (MBQ) under electrochemical reduction conditions in a LiClO4[sbnd]CH3CN electrolyte and various working electrodes. We detected the reversible generation of a bright green coating on the working electrode and the subsequent formation of a polymer (the nature of which depends on the presence or absence of oxygen). These coatings prevent the regular redox process of methyl-p-benzoquinone from taking place on the surface of the electrode and is generated regardless of the electrode material used or the presence of O2 in solution. In addition to MBQ, the green passivating layer was also found for less sterically hindered quinones such as p-benzoquinone or 1,4-naphthoquinone, but not for anthraquinone. We have also shown the central role of Li+ in the formation of this green layer. This work provides important guidelines for the final use of quinones in RFBs with organic electrolytes. © 2017

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Influence of texture in hybrid carbon-phosphomolybdic acid materials on their performance as electrodes in supercapacitors
Palomino P., Suarez-Guevara J., Olivares-Marín M., Ruiz V., Dubal D.P., Gómez-Romero P., Tonti D., Enciso E. Carbon; 111: 74 - 82. 2017. 10.1016/j.carbon.2016.09.054. IF: 6.337

In this paper, phosphomolybdic acid H3PMo12O40 (PMo12) was anchored to four synthetic micro-mesoporous carbons and a commercial one to analyse the relationship between the porous texture of the support, the PMo12 adsorption and the performance of the resulting hybrid materials as electrodes in supercapacitors. The uptake of PMo12 on carbon supports follows a clear correlation with the micropore volume, which implies that PMo12 is mainly adsorbed in microporosity as a consequence of a greater confinement in this kind of pores instead of mesopores. Transmission electron microscopy indicates that the PMo12 adsorbed is homogeneously dispersed in the carbon texture. Finally, the addition of PMo12 to the original carbon electrodes provided capacitances up to 293 F per gram of electrode, substantially larger than the 206–240 F g−1 of the unmodified activated carbon. This result represented an increase of up to 35% in terms of gravimetric energy density and 160% in terms of volumetric energy density, after PMo12 integration into the carbon matrix. © 2016 Elsevier Ltd

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Mimics of microstructures of Ni substituted Mn1−xNixCo2O4 for high energy density asymmetric capacitors
Tamboli M.S., Dubal D.P., Patil S.S., Shaikh A.F., Deonikar V.G., Kulkarni M.V., Maldar N.N., Inamuddin, Asiri A.M., Gomez-Romero P., Kale B.B., Patil D.R. Chemical Engineering Journal; 307: 300 - 310. 2017. 10.1016/j.cej.2016.08.086. IF: 6.216

The preparation of nanostructured hierarchical Mn1−xNixCo2O4 metal oxides as efficient supercapacitors of different structures and configurations especially for the miniaturized electronics is still a challenge. In this context, we report template free facile hydrothermal synthesis of hierarchical nanostructured Mn1−xNixCo2O4 with excellent supercapacitive performance. Significantly, the morphology of pure MnCo2O4 transformed from 3D microcubes to 1D nanowires with incorporation of Ni. The electrochemical study shows highest specific capacitance i.e. 1762 F/g for Mn0.4Ni0.6Co2O4 with high cycling stability of 89.2% which is much higher than pristine MnCo2O4 and NiCo2O4. Later, asymmetric capacitor has been fabricated successfully using Mn0.4Ni0.6Co2O4 nanowires as positive electrode and activated carbon (AC) as negative electrode in a KOH aqueous electrolyte. An asymmetric cell could be cycled reversibly in the high-voltage range of 0–1.5 V and displays intriguing performances with a specific capacitance of 112.8 F/g (6.87 F/cm3) and high energy density of 35.2 Wh/kg (2.1 mWh/cm3). Importantly, this asymmetric capacitor device exhibits an excellent long cycle life along with 83.2% specific capacitance retained after 2000 cycles. © 2016 Elsevier B.V.

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Nanostructured mixed transition metal oxides for high performance asymmetric supercapacitors: Facile synthetic strategy
Tajik S., Dubal D.P., Gomez-Romero P., Yadegari A., Rashidi A., Nasernejad B., Inamuddin, Asiri A.M. International Journal of Hydrogen Energy; 42 (17): 12384 - 12395. 2017. 10.1016/j.ijhydene.2017.03.117. IF: 3.582

Exceptionally simple and cost-effective solid-state method is reported for the synthesis of different mixed transition metal oxides (MTMOs) including FeCo2O4, MnCo2O4 and ZnCo2O4 with unique nanostructures. The morphological analysis show that MTMOs possess distinct nanostructures such as tetragonal, spherical nanoparticles and hexagonal nanosheets. Furthermore, these MTMOs showed excellent supercapacitive properties with specific capacitances of 660–1263 F/g at current density of 2 A/g. Asymmetric capacitor was fabricated with FeCo2O4 as positive and activated carbon as negative electrode which exhibits a specific capacitance of 88 F/g with energy density of 24 Wh/kg (1.1 mWh/cm3) and cycle life (93%) over 5000 cycles. © 2017 Hydrogen Energy Publications LLC

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Ultrahigh energy density supercapacitors through a double hybrid strategy
Dubal D.P., Nagar B., Suarez-Guevara J., Tonti D., Enciso E., Palomino P., Gomez-Romero P. Materials Today Energy; 5: 58 - 65. 2017. 10.1016/j.mtener.2017.05.001. IF: 0.000

Herein, we are presenting all-solid-state symmetric supercapacitors (ASSSCs) with an innovative double hybrid strategy, where a hybrid material based on reduced graphene oxide (rGO) anchored with phoshotungstic acid, rGO-H3PW12O40) is combined with hybrid electrolyte (hydroquinone-doped gel electrolyte). Initially, a hybrid electrode is fabricated by decorating H3PW12O40 nanodots onto the surface rGO (rGO-PW12). Next, a symmetric cell based on rGO-PW12 electrodes was assembled with PVA-H2SO4 polymer gel-electrolyte. Interestingly, rGO-PW12 symmetric cell revealed a substantial enhancement in the cell performance as compared to parent rGO systems. It featured a widened potential range of 1.6 V, thereby providing 1.05 mWh/cm3 energy density. The electrochemical performance of rGO-PW12 cell was further advanced by introducing redox-active (hydroquinone) species in to the PVA-H2SO4 gel-electrolyte. Indeed, the performance of rGO-PW12 cell was surprisingly improved with an ultra-high energy density of 2.38 mWh/cm3 (more than two-fold). © 2017 Elsevier Ltd

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Ultrathin Mesoporous RuCo2O4 Nanoflakes: An Advanced Electrode for High-Performance Asymmetric Supercapacitors
Dubal D.P., Chodankar N.R., Holze R., Kim D.-H., Gomez-Romero P. ChemSusChem; 10 (8): 1771 - 1782. 2017. 10.1002/cssc.201700001. IF: 7.226

A new ruthenium cobalt oxide (RuCo2O4) with a unique marigold-like nanostructure and excellent performance as an advanced electrode material has been successfully prepared by a simple electrodeposition (potentiodynamic mode) method. The RuCo2O4 marigolds consist of numerous clusters of ultrathin mesoporous nanoflakes, leaving a large interspace between them to provide numerous electrochemically active sites. Strikingly, this unique marigold-like nanostructure provided excellent electrochemical performance in terms of high energy-storage capacitance (1469 F g−1 at 6 A g−1) with excellent rate proficiency and long-lasting operating cycling stability (ca. 91.3 % capacitance retention after 3000 cycles), confirming that the mesoporous nanoflakes participate in the ultrafast electrochemical reactions. Furthermore, an asymmetric supercapacitor was assembled using RuCo2O4 (positive electrode) and activated carbon (negative electrode) with aqueous KOH electrolyte. The asymmetric design allowed an upgraded potential range of 1.4 V, which further provided a good energy density of 32.6 Wh kg−1 (1.1 mWh cm−3). More importantly, the cell delivered an energy density of 12.4 Wh kg−1 even at a maximum power density of 3.2 kW kg−1, which is noticeably superior to carbon-based symmetric systems. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

View abstract
V2O5 encapsulated MWCNTs in 2D surface architecture: Complete solid-state bendable highly stabilized energy efficient supercapacitor device
Pandit B., Dubal D.P., Gómez-Romero P., Kale B.B., Sankapal B.R. Scientific Reports; 7 ( 43430) 2017. 10.1038/srep43430. IF: 4.259

A simple and scalable approach has been reported for 2O5 encapsulation over interconnected multi-walled carbon nanotubes (MWCNTs) network using chemical bath deposition method. Chemically synthesized 2O5/MWCNTs electrode exhibited excellent charge-discharge capability with extraordinary cycling retention of 93% over 4000 cycles in liquid-electrolyte. Electrochemical investigations have been performed to evaluate the origin of capacitive behavior from dual contribution of surface-controlled and diffusion-controlled charge components. Furthermore, a complete flexible solid-state, flexible symmetric supercapacitor (FSS-SSC) device was assembled with 2O5/MWCNTs electrodes which yield remarkable values of specific power and energy densities along with enhanced cyclic stability over liquid configuration. As a practical demonstration, the constructed device was used to lit the 'VNIT' acronym assembled using 21 LED's. © The Author(s) 2017.

View abstract

2016

Ag:BiVO4 dendritic hybrid-architecture for high energy density symmetric supercapacitors
Patil S.S., Dubal D.P., Tamboli M.S., Ambekar J.D., Kolekar S.S., Gomez-Romero P., Kale B.B., Patil D.R. Journal of Materials Chemistry A; 4 (20): 7580 - 7584. 2016. 10.1039/c6ta01980c. IF: 8.262

We demonstrate the fabrication of Ag:BiVO4 with a dendritic architecture by a template free hydrothermal method. Then, symmetric cells based on Ag:BiVO4 electrodes were assembled which exhibit an extended voltage window of up to 1.6 V with an excellent energy density of 2.63 mW h cm-3 (38.43 W h kg-1) and a power density of 558 mW cm-3 (8.1 kW kg-1). © 2016 The Royal Society of Chemistry.

View abstract
Aqueous synthesis of LiFePO4 with Fractal Granularity
Cabán-Huertas Z., Ayyad O., Dubal D.P., Gómez-Romero P. Scientific Reports; 6 ( 27024) 2016. 10.1038/srep27024. IF: 5.228

Lithium iron phosphate (LiFePO4) electrodes with fractal granularity are reported. They were made from a starting material prepared in water by a low cost, easy and environmentally friendly hydrothermal method, thus avoiding the use of organic solvents. Our method leads to pure olivine phase, free of the impurities commonly found after other water-based syntheses. The fractal structures consisted of nanoparticles grown into larger micro-sized formations which in turn agglomerate leading to high tap density electrodes, which is beneficial for energy density. These intricate structures could be easily and effectively coated with a thin and uniform carbon layer for increased conductivity, as it is well established for simpler microstructures. Materials and electrodes were studied by means of XRD, SEM, TEM, SAED, XPS, Raman and TGA. Last but not least, lithium transport through fractal LiFePO4 electrodes was investigated based upon fractal theory. These water-made fractal electrodes lead to high-performance lithium cells (even at high rates) tested by CV and galvanostatic charge-discharge, their performance is comparable to state of the art (but less environmentally friendly) electrodes.

View abstract
Electroactive graphene nanofluids for fast energy storage
Dubal D.P., Gomez-Romero P. 2D Materials; 3 (3, 031004) 2016. 10.1088/2053-1583/3/3/031004. IF: 9.611

Graphenes have been extensively studied as electrode materials for energy storage in supercapacitors and batteries, but always as solid electrodes. The conception and development of graphene electroactive nanofluids (ENFs) reported here for the first time provides a novel way to 'form' graphene electrodes and demonstrates proof of concept for the use of these liquid electrodes for energy storage in novel flow cells.Astabilized dispersion of reduced graphene oxide (rGO) in aqueous sulfuric acid solution was shown to have capacitive energy storage capabilities parallel to those of solid electrode supercapacitors (169 F g-1(rGO)) but working up to much faster rates (from 1mV s-1 to the highest scan rate of 10 V s-1) in nanofluids with 0.025, 0.1 and 0.4 wt% rGO, featuring viscosities very close to that of water, thus being perfectly suitable for scalable flow cells. Our results provide proof of concept for this technology and include preliminary flow cell performance of rGO nanofluids under static and continuous flow conditions. Graphene nanofluids effectively behave as true liquid electrodes with very fast capacitive storage mechanism and herald the application not only of graphenes but also other 2D materials like MoS2 in nanofluids for energy storage and beyond. © 2016 IOP Publishing Ltd.

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Electrochemical supercapacitive properties of polypyrrole thin films: influence of the electropolymerization methods
Wolfart F., Dubal D.P., Vidotti M., Holze R., Gómez-Romero P. Journal of Solid State Electrochemistry; 20 (4): 901 - 910. 2016. 10.1007/s10008-015-2960-2. IF: 2.327

A detailed study of the effects of different electropolymerization methods on the supercapacitive properties of polypyrrole (PPy) thin films deposited on carbon cloth is reported. Deposition mechanisms of PPy thin films through cyclic voltammetry (CV), potentiostatic (PS), and galvanostatic (GS) modes have been analyzed. The resulting PPy thin films have been characterized by X-ray photoelectron spectroscopy (XPS), SEM, and TEM. The electrochemical properties of PPy thin films were investigated by cyclic voltammetry and galvanostatic charge/discharge. The results showed that the different electrodeposition modes of synthesis significantly affect the supercapacitive properties of PPy thin films. Among different modes of electrodeposition, PPy synthesized by a potentiostatic mode exhibits maximum specific capacitance of 166 F/g with specific energy of 13 Wh/kg; this is attributed to equivalent proportions of the oxidized and neutral states of PPy. Thus, these results provide a useful orientation for the use of optimized electrodeposition modes for the growth of PPy thin films to be applied as electrode material in supercapacitors. © 2015, Springer-Verlag Berlin Heidelberg.

View abstract
Fern-like rGO/BiVO4 hybrid nanostructures for high-energy symmetric supercapacitor
Patil S.S., Dubal D.P., Deonikar V.G., Tamboli M.S., Ambekar J.D., Gomez-Romero P., Kolekar S.S., Kale B.B., Patil D.R. ACS Applied Materials and Interfaces; 8 (46): 31602 - 31610. 2016. 10.1021/acsami.6b08165. IF: 7.145

Herein, we demonstrate the synthesis of rGO/BiVO4 hybrid nanostructures by facile hydrothermal method. Morphological studies reveal that rGO sheets are embedded in the special dendritic fern-like structures of BiVO4. The rGO/BiVO4 hybrid architecture shows the way to a rational design of supercapacitor, since these structures enable easy access of electrolyte ions by reducing internal resistance. Considering the unique morphological features of rGO/BiVO4 hybrid nanostructures, their supercapacitive properties were investigated. The rGO/BiVO4 electrode exhibits a specific capacitance of 151 F/g at the current density of 0.15 mA/cm2. Furthermore, we have constructed rGO/BiVO4 symmetric cell which exhibits outstanding volumetric energy density of 1.6 mW h/cm3 (33.7 W h/kg) and ensures rapid energy delivery with power density of 391 mW/cm3 (8.0 kW/kg). The superior properties of symmetric supercapacitor can be attributed to the special dendritic fern-like BiVO4 morphology and intriguing physicochemical properties of rGO. © 2016 American Chemical Society.

View abstract
Growth of polypyrrole nanostructures through reactive templates for energy storage applications
Dubal D.P., Caban-Huertas Z., Holze R., Gomez-Romero P. Electrochimica Acta; 191: 346 - 354. 2016. 10.1016/j.electacta.2016.01.078. IF: 4.803

This work presents a facile reactive template route to prepare polypyrrole (PPy) with a given, chosen nanostructure among three different morphologies (i.e., nanotubes, nanofibers and urchins). This approach exploits the variability of MnO2 morphologies and its versatility as sacrificial template. The morphological evolution for this template-assisted growth of PPy nanostructures has been briefly explained. These unique architectures significantly enhance the electroactive surface area of the PPy nanostructures, leading to better interfacial/chemical distribution at the nanoscale, fast ion and electron transfer and good strain accommodation. Thus, when used as supercapacitor electrodes, a maximum specific capacitance of 604 F/g at a current density of 1.81 A/g was reached for PPy nanofibers. Even after more than 1000 cycles at 9 A/g, a capacitance of 259 F/g with 91% retention was achieved. Moreover, the same PPy nanofibers can be used as cathode material for lithium-ion batteries (LIBs), showing a capacity of 70.82 mAh/g at a rate of 0.10 C with good cycling stability and rate capability. Our results provide sound evidences that PPy nanostructures can be properly tuned and make the difference for the practical application of these materials in electrochemical energy storage devices. © 2016 Elsevier Ltd. All rights reserved.

View abstract
Hybrid core-shell nanostructured electrodes made of polypyrrole nanotubes coated with Ni(OH)2 nanoflakes for high energy-density supercapacitors
Wolfart F., Dubal D.P., Vidotti M., Gómez-Romero P. RSC Advances; 6 (18): 15062 - 15070. 2016. 10.1039/c5ra23671a. IF: 3.289

This work describes the design of Ni(OH)2@PPy-NTs core-shell nanostructures with potential application as an electrode material for supercapacitors. Initially, one dimensional (1D) polypyrrole nanotubes (PPy-NTs) were synthesized through a chemical oxidation mediated soft template-directed route using as the anion the azo dye methyl orange (MO). Subsequently, three dimensional (3D) Ni(OH)2 nanoflakes were grown onto PPy-NTs by a simple hydrothermal route. This exclusive Ni(OH)2@PPy-NTs nano-architecture helps to improve the overall electrochemical performance of the electrode, due to the high surface area provided by 3D nanoflakes and excellent electronic/ionic conductivity of 1D nanotubes. The maximum specific capacitance obtained for Ni(OH)2@PPy-NTs was 536 F g-1 with good capacity retention after 1000 charge/discharge cycles. Last but not least, EIS technique showed a low electrochemical series resistance for Ni(OH)2@PPy-NTs confirming their promise as a high-performance energy storage material. © The Royal Society of Chemistry 2016.

View abstract
Synthetic approach from polypyrrole nanotubes to nitrogen doped pyrolyzed carbon nanotubes for asymmetric supercapacitors
Dubal D.P., Chodankar N.R., Caban-Huertas Z., Wolfart F., Vidotti M., Holze R., Lokhande C.D., Gomez-Romero P. Journal of Power Sources; 308: 158 - 165. 2016. 10.1016/j.jpowsour.2016.01.074. IF: 6.333

Pseudocapacitive materials are highly capable to achieve high energy density integrated with high power electrostatic capacitive materials. However, finding a suitable electrostatic capacitive material to integrate with pseudocapacitive material in order to achieve high energy density with good rate capability is still a challenge. Herein, we are providing a novel synthetic approach starting from the synthesis of polypyrrole nanotubes (PPy-NTs) and ending up at the carbonization of PPy-NTs to obtain N-doped carbon nanotubes (N-CNTs). With highly porous nature of PPy-NTs and great graphitic texture with copious heteroatom functionalities, N-CNTs significantly promoted the faradic pseudo-capacitors, demonstrating high single-electrode capacitance over 332 F/g(PPy-NTs) and 228 F/g(N-CNTs) in 1 M H2SO4 aqueous solution. Further, a novel asymmetric supercapacitor with PPy-NTs as positive and N-CNTs as negative electrode has been fabricated. This PPy-NTs//N-CNTs cell effectively provides high operation voltage (1.4 V) and hence high energy density over 28.95 W h/kg (0.41 mW h/cm3) with a high power density of 7.75 kW/kg (113 mW/cm3) and cyclic stability of 89.98% after 2000 cycles. © 2016 Elsevier B.V. All rights reserved.

View abstract

2015

3D hierarchical assembly of ultrathin MnO2 nanoflakes on silicon nanowires for high performance micro-supercapacitors in Li- doped ionic liquid
Dubal D.P., Aradilla D., Bidan G., Gentile P., Schubert T.J.S., Wimberg J., Sadki S., Gomez-Romero P. Scientific Reports; 5 ( 9771) 2015. 10.1038/srep09771. IF: 5.578

Building of hierarchical core-shell hetero-structures is currently the subject of intensive research in the electrochemical field owing to its potential for making improved electrodes for high-performance micro-supercapacitors. Here we report a novel architecture design of hierarchical MnO2 @silicon nanowires (MnO2 @SiNWs) hetero-structures directly supported onto silicon wafer coupled with Li-ion doped 1-Methyl-1-propylpyrrolidinium bis(trifluromethylsulfonyl)imide (PMPyrrBTA) ionic liquids as electrolyte for micro-supercapacitors. A unique 3D mesoporous MnO2 @SiNWs in Li-ion doped IL electrolyte can be cycled reversibly across a voltage of 2.2V and exhibits a high areal capacitance of 13Fcm-2. The high conductivity of the SiNWs arrays combined with the large surface area of ultrathin MnO2 nanoflakes are responsible for the remarkable performance of these MnO2 @SiNWs hetero-structures which exhibit high energy density and excellent cycling stability. This combination of hybrid electrode and hybrid electrolyte opens up a novel avenue to design electrode materials for high-performance micro-supercapacitors.

View abstract
A high voltage solid state symmetric supercapacitor based on graphene-polyoxometalate hybrid electrodes with a hydroquinone doped hybrid gel-electrolyte
Dubal D.P., Suarez-Guevara J., Tonti D., Enciso E., Gomez-Romero P. Journal of Materials Chemistry A; 3 (46): 23483 - 23492. 2015. 10.1039/c5ta05660h. IF: 7.443

In pursuit of high capacitance and high energy density storage devices, hybrid materials have quickly garnered well-deserved attention based on their power to merge complementary components and properties. Here, we report the fabrication of all-solid state symmetric supercapacitors (ASSSC) based on a double hybrid approach combining a hybrid electrode (reduced graphene oxide-phoshomolybdate, rGO-PMo12) and a hybrid electrolyte (hydroquinone doped gel-electrolyte). To begin with, a high-performance hybrid electrode based on H3PMo12O40 nanodots anchored onto rGO was prepared (rGO-PMo12). Later, an all-solid state symmetric cell based on these rGO-PMo12 electrodes, and making use of a polymer gel-electrolyte was assembled. This symmetric cell showed a significant improvement in cell performance. Indeed, it allowed for an extended potential window by 0.3 V that led to an energy density of 1.07 mW h cm-3. Finally, we combined these hybrid electrodes with a hybrid electrolyte incorporating an electroactive species. This is the first proof-of-design where a redox-active solid-state gel-electrolyte is applied to rGO-PMo12 hybrid supercapacitors to accomplish a significant enhancement in the capacitance. Strikingly, a further excellent increase in the device performance (energy density of 1.7 mW h cm-3) was realized with the hybrid electrode-hybrid electrolyte combination cell as compared to that of the conventional electrolyte cell. Thus, this unique symmetric device outclasses the high-voltage asymmetric counterparts under the same power and represents a noteworthy advance towards high energy density supercapacitors. © The Royal Society of Chemistry 2015.

View abstract
An innovative 3-D nanoforest heterostructure made of polypyrrole coated silicon nanotrees for new high performance hybrid micro-supercapacitors
Aradilla D., Gaboriau D., Bidan G., Gentile P., Boniface M., Dubal D., Gómez-Romero P., Wimberg J., Schubert T.J.S., Sadki S. Journal of Materials Chemistry A; 3 (26): 13978 - 13985. 2015. 10.1039/c5ta03435c. IF: 7.443

In this work, an innovative 3-D symmetric micro-supercapacitor based on polypyrrole (PPy) coated silicon nanotree (SiNTr) hybrid electrodes has been fabricated. First, SiNTrs were grown on silicon substrates by chemical vapor deposition (CVD) and then via an electrochemical method, the conducting polymer coating was deposited onto the surface of SiNTr electrodes. This study illustrates the excellent electrochemical performance of a hybrid micro-supercapacitor device using the synergistic combination of both PPy as the electroactive pseudo-capacitive material and branched SiNWs as the electric double layer capacitive material in the presence of an aprotic ionic liquid (N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide; PYR13TFSI) as the electrolyte. The hybrid device exhibited a specific capacitance as high as ∼14 mF cm-2 and an energy density value of ∼15 mJ cm-2 at a wide cell voltage of 1.5 V using a high current density of 1 mA cm-2. Furthermore, a remarkable cycling stability after thousands of galvanostatic charge-discharge cycles with a loss of approximately 30% was obtained. The results reported in this investigation demonstrated that PPy coated SiNTr-based micro-supercapacitors exhibit the best performances among hybrid micro-supercapacitors made of silicon nanowire electrodes grown by CVD in terms of specific capacitance and energy density. © The Royal Society of Chemistry.

View abstract
Asymmetric supercapacitors based on hybrid CuO@reduced graphene oxide@sponge versus reduced graphene oxide@sponge electrodes
Dubal D.P., Chodankar N.R., Gund G.S., Holze R., Lokhande C.D., Gomez-Romero P. Energy Technology; 3 (2): 168 - 176. 2015. 10.1002/ente.201402170.

An asymmetric supercapacitor was fabricated by using CuO@reduced graphene oxide@sponge (CuO@rGO@SP) composites as the positive electrode and rGO@SP as the negative electrode in Na2SO4 aqueous electrolyte. Macroporous and low-costing sponges were explored as skeletons to construct a homogeneous 3D interconnected network of rGO. Initially, rGO was deposited on the sponge by the "dip-and-dry" method. Subsequently, a CuO nanosheet cluster was deposited by using the chemical bath deposition method on the rGO-coated sponge substrate. The CuO@rGO@SP electrodes could be operated even under a high scan rate of 200mVs-1 and exhibited a maximum specific capacitance of 519Fg-1. An asymmetric supercapacitor device based on CuO@rGO@SP//rGO@SP could be cycled in the high voltage range of 1.7V and displayed high specific capacitance of 77.84Fg-1 and a high energy density of 31.24Wh-1kg-1. Impressively, this asymmetric device exhibited an excellent long cycle life and 83% of the specific capacitance was retained after 2000cycles. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

View abstract
Diamond-coated silicon nanowires for enhanced micro-supercapacitor with ionic liquids
Gund G.S., Dubal D.P., Aradilla D., Mueller-Sebert W., Bidan G., Gaboriau D., Gentile P., Schubert T.J.S., Wimberg J., Sadki S., Gomez-Romero P. 2015 International Conference on Industrial Instrumentation and Control, ICIC 2015; ( 7150916): 1125 - 1128. 2015. 10.1109/IIC.2015.7150916. IF: 0.000

Silicon nanowires (SiNWs) and diamond-coated SiNWs (D@SiNWs) on highly n-doped silicon wafer substrates were prepared through standard chemical vapor deposition (CVD) method as electrodes for micro-supercapacitors. The surface of electrodes exhibited uniform distribution of SiNWs on silicon wafer and continuous diamond coating on SiNWs. Electrochemical measurements were carried out in order to test the combined effect of using Ionic Liquid electrolytes and diamond coating on SiNWs on energy storage performance. Optimal values of areal capacitance, energy density and power densities were 317 μF cm-2, 0.13 μWh cm-2 and 150 μW cm-2, respectively. So, the work reported here confirms the suitability and compatibility of D@SiNWs electrode materials and ionic liquid electrolytes for the fabrication of high-performing and robust micro-supercapacitors. © 2015 IEEE.

View abstract
Hybrid energy storage: The merging of battery and supercapacitor chemistries
Dubal D.P., Ayyad O., Ruiz V., Gómez-Romero P. Chemical Society Reviews; 44 (7): 1777 - 1790. 2015. 10.1039/c4cs00266k. IF: 33.383

The hybrid approach allows for a reinforcing combination of properties of dissimilar components in synergic combinations. From hybrid materials to hybrid devices the approach offers opportunities to tackle much needed improvements in the performance of energy storage devices. This paper reviews the different approaches and scales of hybrids, materials, electrodes and devices striving to advance along the diagonal of Ragone plots, providing enhanced energy and power densities by combining battery and supercapacitor materials and storage mechanisms. Furthermore, some theoretical aspects are considered regarding the possible hybrid combinations and tactics for the fabrication of optimized final devices. All of it aiming at enhancing the electrochemical performance of energy storage systems. This journal is © The Royal Society of Chemistry.

View abstract
Influence of Mn incorporation on the supercapacitive properties of hybrid CuO/Cu(OH)2 electrodes
Shinde S.K., Dubal D.P., Ghodake G.S., Gomez-Romero P., Kim S., Fulari V.J. RSC Advances; 5 (39): 30478 - 30484. 2015. 10.1039/c5ra01093d. IF: 3.840

Here, we are presenting the effect of Mn doping on the supercapacitive properties of CuO/Cu(OH)2 hybrid electrodes. Briefly, Mn doped CuO/Cu(OH)2 (Mn:CuO/Cu(OH)2) thin films have been synthesized by a successive ionic layer adsorption and reaction (SILAR) method which are further characterized by different physiochemical techniques. Our results revealed the formation of hybrid CuO/Cu(OH)2 thin films with significant morphological deviation through Mn doping. Moreover, considerable positive effect of Mn doping on the electrochemical properties of hybrid CuO/Cu(OH)2 electrodes have been witnessed. Later, the results suggest that at 3% Mn doping in CuO/Cu(OH)2 electrodes with nanoflower-like nanostructures exhibits the highest specific capacitance. The maximum specific capacitance achieved for a 3% Mn:CuO/Cu(OH)2 hybrid electrode is 600 F g-1 at 5 mV s-1 in 1 M Na2SO4 electrolyte. Additionally, a Ragone plot confirms the potential of the Mn:CuO/Cu(OH)2 hybrid electrode for electrical energy storage applications. © The Royal Society of Chemistry 2015.

View abstract
Low-cost flexible supercapacitors with high-energy density based on nanostructured MnO2 and Fe2O3 thin films directly fabricated onto stainless steel
Gund G.S., Dubal D.P., Chodankar N.R., Cho J.Y., Gomez-Romero P., Park C., Lokhande C.D. Scientific Reports; 5 ( 12454) 2015. 10.1038/srep12454. IF: 5.578

The facile and economical electrochemical and successive ionic layer adsorption and reaction (SILAR) methods have been employed in order to prepare manganese oxide (MnO2) and iron oxide (Fe2O3) thin films, respectively with the fine optimized nanostructures on highly flexible stainless steel sheet. The symmetric and asymmetric flexible-solid-state supercapacitors (FSS-SCs) of nanostructured (nanosheets for MnO2 and nanoparticles for Fe2O3) electrodes with Na2SO4/Carboxymethyl cellulose (CMC) gel as a separator and electrolyte were assembled. MnO2 as positive and negative electrodes were used to fabricate symmetric SC, while the asymmetric SC was assembled by employing MnO2 as positive and Fe2O3 as negative electrode. Furthermore, the electrochemical features of symmetric and asymmetric SCs are systematically investigated. The results verify that the fabricated symmetric and asymmetric FSS-SCs present excellent reversibility (within the voltage window of 0-1 V and 0-2 V, respectively) and good cycling stability (83 and 91%, respectively for 3000 of CV cycles). Additionally, the asymmetric SC shows maximum specific capacitance of 92 Fg-1, about 2-fold of higher energy density (41.8 Wh kg-1) than symmetric SC and excellent mechanical flexibility. Furthermore, the "real-life" demonstration of fabricated SCs to the panel of SUK confirms that asymmetric SC has 2-fold higher energy density compare to symmetric SC. © 2015 Macmillan Publishers Limited.

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Nickel cobaltite as an emerging material for supercapacitors: An overview
Dubal D.P., Gomez-Romero P., Sankapal B.R., Holze R. Nano Energy; 11: 377 - 399. 2015. 10.1016/j.nanoen.2014.11.013. IF: 10.325

Supercapacitor (SCs) with excellent power and reasonably high energy densities are becoming a perfect solution towards the recent demand of various energy storage applications. Present review is focused on the synthetic methods used for spinel NiCo2O4 nanomaterials with different mysterious architectures for supercapacitor application. Synthesis of different nanostructures, hetero-structures, chemical modification and incorporation with high surface area conductive nanoarchitectures are the major strategies in the development of recent high-performance NiCo2O4-based electrodes for supercapacitors. This review runs through the creativity of current science when it comes to these nano-architectured electrodes. It is organized by techniques used for synthesis including chemical methods with and without templates along with their electrochemical supercapacitive properties. Plentiful works reviewed in this review shown enhanced electrochemical performance in the spinel NiCo2O4-based electrode materials. Finally, the future research directions and the remaining challenges toward the fabrication of different nanostructured NiCo2O4-based electrode materials for next-generation SCs are discussed (224 references). © 2014 Elsevier Ltd.

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SiNWs-based electrochemical double layer micro-supercapacitors with wide voltage window (4V) and long cycling stability using a protic ionic liquid electrolyte
Aradilla D., Gentile P., Ruiz V., Gomez-Romero P., Wimberg J., Iliev B., Schubert T.J.S., Sadki S., Bidan G. Advances in Natural Sciences: Nanoscience and Nanotechnology; 6 (1, 15004) 2015. 10.1088/2043-6262/6/1/015004. IF: 0.000

The present work reports the use and application of a novel protic ionic liquid (triethylammonium bis(tri fluoromethylsulfonyl)imide; NEt3H TFSI) as an electrolyte for symmetric planar micro-supercapacitors based on silicon nanowire electrodes. The excellent performance of the device has been successfully demonstrated using cyclic voltammetry, galvanostatic charge-discharge cycles and electrochemical impedance spectroscopy. The electrochemical characterization of this system exhibits a wide operative voltage of 4 V as well as an outstanding long cycling stability after millions of galvanostatic cycles at a high current density of 2 mA cm-2. In addition, the electrochemical double layer micro-supercapacitor was able to deliver a high power density of 4 mWcm-2 in a very short time pulses (a few ms). Our results could be of interest to develop prospective on-chip micro-supercapacitors using protic ionic liquids as electrolytes with high performance in terms of power and energy densities. © 2015 Vietnam Academy of Science & Technology.

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The influence of solvents and salts on the properties of high-voltage cathode materials
Kazda T., Vondrák J., Sedlaříková M., Gómez-Romero P., Musil M., Čudek P., Fedorková Straková A., Kašpárek V. International Journal of Electrochemical Science; 10 (8): 6288 - 6301. 2015. . IF: 1.500

Lithium - ion batteries play an increasingly important role in the battery industry and they have become the dominant source of energy in the recent years, especially for portable electronic devices due to their high gravimetric energy density. This article examines the influence of mixtures of solvents with different combinations of lithium salts on the stability of two types of high-voltage cathode materials: LiNi0.5Mn1.5O4 and LiCr0.1Ni0.4Mn1.5O4 produced by a solid phase reaction. These materials were combined with several different electrolytes, cycled at various loads and higher temperature. Various combinations of solvents ethylene carbonate (EC), dimethyl carbonate (DMC) and Tetrahydrothiophene 1.1-dioxide (Sulfolane) were used for these measurements. Salts LiPF6 , LiNO3 and LiTFSI were used. The influence of solvents and salts on the properties of high-voltage cathode materials was tested by cycling at different current loads and by cycling at high temperature. It was found out, by LSV analysis, that the addition of Sulfolane increases the stability of electrolyte. The addition of chromium to the cathode material LiNi0.5Mn1.5O4 causes increasing of capacity and stability at high temperature. The combination of the cathode material LiCr0.1Ni0.4Mn1.5O4 with the electrolyte 1.5 M LiPF6 EC:DMC:Sulfolane 1:2:1 w/w/w leads to increased stability in comparison with other electrolytes. © 2015 The Authors.

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Three-dimensional arrays of 1D MnO2 nanocrystals for all-solid-state asymmetric supercapacitors
Dubal D.P., Holze R., Gomez-Romero P. ChemPlusChem; 80 (6): 944 - 951. 2015. 10.1002/cplu.201500054. IF: 3.026

Abstract Reported is the synthesis of 3D hierarchical structures based on one-dimensional MnO2 nanobuilding blocks (nanorods, nanowires, and nanoneedles) by means of a facile and scalable coprecipitation method and their use as electrodes for the assembly of all-solid-state supercapacitors. Asymmetric devices were also assembled by using these nanostructured MnO2 materials as the positive electrode and reduced graphene oxide (rGO) as the negative electrode with a polymeric gel electrolyte. The asymmetric cells successfully extend the working voltage windows beyond 1.4 V and allowed for a maximum voltage of 1.8 V. An asymmetric device based on hierarchical nanoneedle-like MnO2 and rGO achieved a maximum specific capacitance of 99 Fg-1 at a scan rate of 10 mVs-1 with a stable operational voltage of 1.8 V. This high value allowed for a large specific energy of 24.12 Whkg-1. New builders on the block: The synthesis of 3D hierarchical structures based on 1D MnO2 nanobuilding blocks by means of a facile and scalable coprecipitation method and their use as electrodes for the assembly of all-solid-state supercapacitors is described. The figure show an example of an asymmetric device based on hierarchical nanoneedle (Nn)-like MnO2 and reduced graphene oxide. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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2014

Development of hybrid materials based on sponge supported reduced graphene oxide and transition metal hydroxides for hybrid energy storage devices
Dubal, D.P.; Holze, R; Gomez-Romero, P. Scientific Reports; 2014. 10.1038/srep07349. IF: 5.078
High performance of symmetric micro-supercapacitors based on silicon nanowires using N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide as electrolyte
Aradilla, D.; Gentile, P.; Bidan, G.; Ruiz, V.; Gómez-Romero, P.; Schubert, T.J.S.; Sahin, H.; Frackowiak, E.; Sadki, S. Nano Energy; 9: 273 - 281. 2014. 10.1016/j.nanoen.2014.07.001. IF: 10.211
Hybrid energy storage: High voltage aqueous supercapacitors based on activated carbon-phosphotungstate hybrid materials
Suárez-Guevara, J.; Ruiz, V.; Gomez-Romero, P. Journal of Materials Chemistry A; 2 (4): 1014 - 1021. 2014. 10.1039/c3ta14455k. IF: 0.000
Novel hybrid micro-supercapacitor based on conducting polymer coated silicon nanowires for electrochemical energy storage
Aradilla, D.; Bidan, G.; Gentile, P.; Weathers, P.; Thissandier, F.; Ruiz, V.; Gómez-Romero, P.; Schubert, T.J.S.; Sahin, H.; Sadki, S. RSC Advances; 4 (50): 26462 - 26467. 2014. 10.1039/c4ra03192j. IF: 3.708
Stable graphene-polyoxometalate nanomaterials for application in hybrid supercapacitors
Suárez-Guevara, J.; Ruiz, V.; Gómez-Romero, P. Physical Chemistry Chemical Physics; 16 (38): 20411 - 20414. 2014. 10.1039/c4cp03321c. IF: 4.198

2013

Fractal porosity in metals synthesized by a simple combustion reaction
Gómez-Romero, P.; Fraile, J.; Ballesteros, B. RSC Advances; 3: 2351 - 2354. 2013. 10.1039/c2ra22441k. IF: 2.562
Incorporation of benzimidazolium ionic liquid in proton exchange membranes ABPBI-H3PO4
Hernández Carrillo, R.; Suarez-Guevara, J.; Torres-González, L.C.; Gómez-Romero, P.; Sánchez, E.M. Journal of Molecular Liquids; 181: 115 - 120. 2013. 10.1016/j.molliq.2013.02.014. IF: 1.684
Organic-Inorganic Hybrid Materials for Supercapacitors
Ruiz, V. ; Suárez-Guevara, J. ; Gomez-Romero, P. ECS transactions; 50 (43): 117 - 123. 2013. 10.1149/05043.0117ecst. IF: 0.000
Rechargeable Batteries: From Hybrid Materials to Devices .
Gomez-Romero, P. ; Ruiz, V. ; Suarez-Guevara, J. ; Ayyad, O. ; Muñoz-Rojas, D. ECS transactions; 50 (24): 29 - 35. 2013. 10.1149/05024.0029ecst. IF: 0.000

2012

Copper@Polypyrrole Nanocables
Suárez-Guevara, J.; Ayyad, O.; Gómez-Romero, P. Nanoscale Research Letters; 2012. .
Hybrid electrodes based on polyoxometalate-carbon materials for electrochemical supercapacitors
Ruiz, V.; Suárez-Guevara, J.; Gomez-Romero, P. Electrochemistry Communications; 24: 35 - 38. 2012. 10.1016/j.elecom.2012.08.003.
Rechargeable Batteries: From Hybrid Materials to Hybrid Electrodes and Devices
Gomez-Romero, P. ; Ruiz, V. ; Suarez-Guevara, J.; Ayyad, O.; Muñoz-Rojas, D. ECS transactions; 50: B4-0652. 2012. .

2011

Direct synthesis of a macroscopic array of naked Ag nanoparticles
Ayyad, O.; Muñoz-Rojas, D.; Gómez-Romero, P. Chemical Communications; 47: 11285 - 11287. 2011. 10.1039/c1cc13353e.
Electrical and mechanical properties of poly(ethylene oxide)/intercalated clay polymer electrolyte
Moreno, M.; Quijada, R.; Santa Ana, M.A.; Benavente, E.; Gomez-Romero, P.; González, G. Electrochimica Acta; 58: 112 - 118. 2011. 10.1016/j.electacta.2011.08.096.
Polydiphenylamine/carbon nanotube composites for applications in rechargeable lithium batteries
Baibarac, M.; Baltog, I.; Lefrant, S.; Gomez-Romero, P. Materials Science & Engineering B: Solid-State Materials for Advanced Technology; 176: 110 - 120. 2011. 10.1016/j.mseb.2010.10.008.
Polymer electrolyte membrane fuel cells | Pilas de combustible de membrana polimérica
Asensio, J.A.; Peña, J.; Pérez-Coll, D.; Ruiz-Morales, J.C.; Marrero-Lopez, D.; Nuñez, P.; Ballesteros, B.; Canales-Vazquez, J.; Borrós, S.; Gómez-Romero, P. Afinidad; 68: 246 - 258. 2011. .
Shaping hybrid nanostructures with polymer matrices: The formation mechanism of silver-polypyrrole core/shell nanostructures
Muñoz-Rojas, D.; Oró-Solé, J.; Ayyad, O.; Gómez-Romero, P. Journal of Materials Chemistry; 21: 2078 - 2086. 2011. 10.1039/c0jm01449d.

2010

From silver nanoparticles to nanostructures through matrix chemistry
Ayyad, O.; Muñoz-Rojas, D.; Oró-Solé, J.; Gómez-Romero, P. Journal of Nanoparticle Research; 12: 337 - 345. 2010. 10.1007/s11051-009-9620-3.
High-concentration compact agar gels from hydrothermal synthesis
Ayyad, O.; Muñoz-Rojas, D.; Agulló, N.; Borrós, S.; Gómez-Romero, P. Soft Matter; 6: 2389 - 2391. 2010. 10.1039/b926713a.
Hybrid organic-inorganic materials: From child's play to energy applications
Gómez-Romero, P.; Ayyad, O.; Suárez-Guevara, J.; Muñoz-Rojas, D. Journal of Solid State Electrochemistry; 14 (11): 1939 - 1945. 2010. 10.1007/s10008-010-1076-y.
Polyfluorinated boron cluster - [B12F11H]2- - based electrolytes for supercapacitors: Overcharge protection
Ionica-Bousquet, C.M.; Casteel Jr., W.J.; Pearlstein, R.M.; GirishKumar, G.; Pez, G.P.; Gómez-Romero, P.; Palacín, M.R.; Muñoz-Rojas, D. Electrochemistry Communications; 12: 636 - 639. 2010. 10.1016/j.elecom.2010.02.018.
Proton-conducting membranes based on benzimidazole polymers for high-temperature PEM fuel cells. A chemical quest
Asensio, J.A.; Sánchez, E.M.; Gómez-Romero, P. Chemical Society Reviews; 39: 3210 - 3239. 2010. 10.1039/b922650h.
Structural and electrochemical studies of PPy/PEG-LiFePO4 cathode material for Li-ion batteries
Fedorková, A.; Nacher-Alejos, A.; Gómez-Romero, P.; Orináková, R.; Kaniansky, D. Electrochimica Acta; 55: 943 - 947. 2010. 10.1016/j.electacta.2009.09.060.
Titanium dioxide/amine hybrid nanotubes. Optical properties and behavior as lithium-ion electrode
Vasquez, J; López, Z; Zuñiga, A; Nacher, A; Lira-Cantú, M; Gómez-Romero, P; Ana, M.A.S; Benavente, E; González, G. Electrochimica Acta; 55 (4): 1373 - 1379. 2010. 10.1016/j.electacta.2009.05.010.

2009

Complementary microstructural and chemical analyses of Sepia officinalis endoskeleton
Florek, M.; Fornal, E; Gómez-Romero, P; Zieba, E; Paszkowicz, W; Lekki, J; Nowak, J; Kuczumow, A. MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS; 29 (4): 1220 - 1226. 2009. 10.1016/j.msec.2008.09.040.
High-Yield preparation of titanium dioxide nanostructures by hydrothermal conditions
Vasquez, J; Lozano, H; Lavayen, V; Lira-Cantu, M; Gomez-Romero, P; Ana, M.A.S; Benavente, E; Gonzalez, G. Journal of Nanoscience and Nanotechnology; 9 (2): 1103 - 1107. 2009. 10.1166/jnn.2009.C097.
Spontaneous self-assembly of Cu2O@PPy nanowires and anisotropic crystals
Muñoz-Rojas, D.; Oró-Solé, J.; Gómez-Romero, P. Chemical Communications; : 5913 - 5915. 2009. 10.1039/b910796g.
Surface enhanced Raman scattering studies on poly(3,4-ethylene dioxythiophene)/single-walled carbon nanotubes composites and their application to rechargeable lithium batteries
Baltog, I; Baibarac, M; Lefrant, S; Gomez-Romero, P. Journal of Nanoscience and Nanotechnology; 9 (10): 6204 - 6209. 2009. 10.1166/jnn.2009.1548.

2008

Conjugated polymers as part of multifunctional organic/inorganic hybrid materials for photovoltaic applications Symposium on Organic-Inorganic Hybrid Materials, Apr 9-13, 2007 San Francisco, USA Source: ORGANIC/INORGANIC HYBRID MATERIALS - 2007 Book Series: MATERIALS RESEARCH SOCIETY SYMPOSIUM PROCEEDINGS
Lira-Cantu, M.; Krebs, F.C.; Gomez-Romero, P.; Yanagida, S. Materials Research Society Symposium - Proceedings; 1007: 249 - 257. 2008. .
Facile one-pot synthesis of self-assembled silver@polypyrrole core/shell nanosnakes
Muñoz-Rojas, D.; Oró-Solé, J.; Ayyad, O.; Gómez-Romero, P. Small; 4: 1301 - 1306. 2008. 10.1002/smll.200701199.
From nanosnakes to nanosheets: A matrix-mediated shape evolution
Muñoz-Rojas, D.; Oró-Solé, J.; Gómez-Romero, P. Journal of Physical Chemistry C; 112: 20312 - 20318. 2008. 10.1021/jp808187w.

2007

Improvement in the Ppy/V2O5 hybrid as a cathode material for Li ion batteries using PSA as an organic additive
Boyano, I.; Bengoechea, M.; de Meatza, I.; Miguel, O.; Cantero, I.; Ochoteco, E.; Rodríguez, J.; Lira-Cantú, M.; Gómez-Romero, P. Journal of Power Sources; 166: 471 - 477. 2007. 10.1016/j.jpowsour.2006.12.106.
Influence of acids in the Ppy/V2O5 hybrid synthesis and performance as a cathode material
Boyano, I.; Bengoechea, M.; de Meatza, I.; Miguel, O.; Cantero, I.; Ochoteco, E.; Grande, H.; Lira-Cantú, M.; Gomez-Romero, P.; Gómez-Romero, P. Journal of Power Sources; 174: 1206 - 1211. 2007. 10.1016/j.jpowsour.2007.06.175.
Spectroscopic evidence for the bulk polymerization of N-vinyl carbazole in the presence of single-walled carbon nanotubes
Baibarac Mihaela*; Baltog Ioan; Lefrant Serge; Gomez-Romero Pedro Polymer; 48 (18): 5279 - 5280. 2007. .

2005

Hybrid materials approach in the design of electrodes and electrolytes for energy storage and conversion
Cuentas-Gallegos, K.; Lira-Cantú, M.; Casañ-Pastor, N.; Asensio, J.A.; Gómez-Romero, P. Materials Research Society Symposium - Proceedings; 847 (Article number EE12.4): 431 - 438. 2005. .
Recent developments on proton conducting Poly(2,5-benzimidazole) (ABPBI) membranes for high temperature polymer electrolyte membrane fuel cells
Asensio, J.A.; Gómez-Romero, P. Fuel Cells; 5 (3): 336 - 343. 2005. 10.1002/fuce.200400081.