Publications
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3D Ordering at the Liquid–Solid Polar Interface of Nanowires
Zamani M., Imbalzano G., Tappy N., Alexander D.T.L., Martí-Sánchez S., Ghisalberti L., Ramasse Q.M., Friedl M., Tütüncüoglu G., Francaviglia L., Bienvenue S., Hébert C., Arbiol J., Ceriotti M., Fontcuberta i Morral A. Advanced Materials; 32 (38, 2001030) 2020. 10.1002/adma.202001030. IF: 27.398
The nature of the liquid–solid interface determines the characteristics of a variety of physical phenomena, including catalysis, electrochemistry, lubrication, and crystal growth. Most of the established models for crystal growth are based on macroscopic thermodynamics, neglecting the atomistic nature of the liquid–solid interface. Here, experimental observations and molecular dynamics simulations are employed to identify the 3D nature of an atomic-scale ordering of liquid Ga in contact with solid GaAs in a nanowire growth configuration. An interplay between the liquid ordering and the formation of a new bilayer is revealed, which, contrary to the established theories, suggests that the preference for a certain polarity and polytypism is influenced by the atomic structure of the interface. The conclusions of this work open new avenues for the understanding of crystal growth, as well as other processes and systems involving a liquid–solid interface. © 2020 The Authors. Published by Wiley-VCH GmbH
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A SnS2 Molecular Precursor for Conformal Nanostructured Coatings
Zuo Y., Li J., Yu X., Du R., Zhang T., Wang X., Arbiol J., Llorca J., Cabot A. Chemistry of Materials; 32 (5): 2097 - 2106. 2020. 10.1021/acs.chemmater.9b05241. IF: 9.567
We present a simple, versatile, and scalable procedure to produce SnS2 nanostructured layers based on an amine/thiol-based molecular ink. The ratios amine/thiol and Sn/S, and the reaction conditions, are systematically investigated to produce phase-pure SnS2 planar and conformal layers with a tremella-like SnS2 morphology. Such nanostructured layers are characterized by excellent photocurrent densities. The same strategy can be used to produce SnS2-graphene composites by simply introducing graphene oxide (GO) into the initial solution. Conveniently, the solvent mixture is able to simultaneously dissolve the Sn and Se powders and reduce the GO. Furthermore, SnS2-xSex ternary coatings and phase-pure SnSe2 can be easily produced by simply incorporating proper amounts of Se into the initial ink formulation. Finally, the potential of this precursor ink to produce gram-scale amounts of unsupported SnS2 is investigated. Copyright © 2020 American Chemical Society.
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A yolk–albumen–shell structure of mixed Ni–Co oxide with an ultrathin carbon shell for high-sensitivity glucose sensors
Xuan Zhang, Yawei Zhang, Wei Guo, Kai Wan, Ting Zhang, Jordi Arbiol, Yong-Qing Zhao, Cai-Ling Xu, Mao-Wen Xu, Jan Fransaer Materials Advances; 1 (4): 908 - 917. 2020. 10.1039/d0ma00230e.
Non-enzymatic glucose sensors based on different Co–Ni–C composite materials were developed by pyrolysis of bimetallic or single metal based metal–organic frameworks (MOFs). The structure and composition of the resulting materials were explored by XRD, nitrogen adsorption/desorption isotherms, SEM, HRTEM and STEM-EELS. The electrochemical performance of the bimetallic MOF derived novel yolk–albumen–shell structure of Ni–Co@C (YASNiCo@C) stands out from these materials. The YASNiCo@C electrode exhibited a sensitivity of 1964 μA cm−2 mM−1 with the detection limit of 0.75 μM, a linear range from 5 μM to 1000 μM and good stability for the detection of glucose. These promising electrochemical performances prove that YASNiCo@C is a promising material for glucose sensors. Moreover, the strategy outlined in this work for the design of MOF based nanomaterials can also be used beyond glucose sensors.
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Bismuth telluride-copper telluride nanocomposites from heterostructured building blocks
Zhang Y., Liu Y., Calcabrini M., Xing C., Han X., Arbiol J., Cadavid D., Ibáñez M., Cabot A. Journal of Materials Chemistry C; 8 (40): 14092 - 14099. 2020. 10.1039/d0tc02182b. IF: 7.059
Appropriately designed nanocomposites allow improving the thermoelectric performance by several mechanisms, including phonon scattering, modulation doping and energy filtering, while additionally promoting better mechanical properties than those of crystalline materials. Here, a strategy for producing Bi2Te3-Cu2-xTe nanocomposites based on the consolidation of heterostructured nanoparticles is described and the thermoelectric properties of the obtained materials are investigated. We first detail a two-step solution-based process to produce Bi2Te3-Cu2-xTe heteronanostructures, based on the growth of Cu2-xTe nanocrystals on the surface of Bi2Te3 nanowires. We characterize the structural and chemical properties of the synthesized nanostructures and of the nanocomposites produced by hot-pressing the particles at moderate temperatures. Besides, the transport properties of the nanocomposites are investigated as a function of the amount of Cu introduced. Overall, the presence of Cu decreases the material thermal conductivity through promotion of phonon scattering, modulates the charge carrier concentration through electron spillover, and increases the Seebeck coefficient through filtering of charge carriers at energy barriers. These effects result in an improvement of over 50% of the thermoelectric figure of merit of Bi2Te3. © The Royal Society of Chemistry.
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Cobalt Hexacyanoferrate as a Selective and High Current Density Formate Oxidation Electrocatalyst
Han L., González-Cobos J., Sánchez-Molina I., Giancola S., Folkman S.J., Tang P., Heggen M., Dunin-Borkowski R.E., Arbiol J., Giménez S., Galan-Mascaros J.R. ACS Applied Energy Materials; 3 (9): 9198 - 9207. 2020. 10.1021/acsaem.0c01548. IF: 4.473
Herein we report the selectivity, stability, and electrochemical characterization of cobalt hexacyanoferrate, the Co-Fe Prussian Blue derivative (CoFePB), as a formate/formic acid oxidation electrocatalyst in aqueous media. CoFePB is able to quantitatively catalyze (100% Faradaic efficiency within less than 8% standard error at pH 5) the electrochemical oxidation of formate to CO2 over a pH range of 1-13. This quantitative formate elecrooxidation is possible due to the exclusive selectivity of the catalyst in a wide potential window (from ca. 1.2 to 1.7 V vs RHE), where no other substrate in aqueous conditions is activated: neither other organic molecules, such as alcohols or acids, nor water itself. CoFePB is one of the first heterogeneous noble-metal-free catalysts reported for the electrooxidation of small hydrocarbon molecules. Importantly, the catalyst showed a very high tolerance against surface poisoning during the reaction, as supported by the cyclic voltammetry and electrochemical impedance spectroscopy data, thereby allowing CoFePB to operate at greater current density than state-of-the-art noble metal catalysts. For example, we observed that CoFePB is able to achieve a formate oxidation current ∼10 mA cm-2 at pH 5, 0.4 M formate at 1.4 V vs RHE, whereas a Pt disk and Pd(5%)/C electrodes had currents of 0.4 and 1.4 mA cm-2, respectively, under identical conditions. The remarkable selectivity, stability, and high current density of CoFePB, in contrast to state-of-the-art catalysts based on platinum-group metals, is an important step in the search for inexpensive earth-abundant materials for oxidation of organic molecules for use in liquid fuel cells or for selective organic molecule sensors. Furthermore, because CoFePB is not poisoned by intermediates and can achieve higher current density than Pt or Pd, improvement of the catalyst onset potential can lead to higher power density formate oxidation fuel cells using earth-abundant metals than with Pt or Pd. Copyright © 2020 American Chemical Society.
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Coherent Epitaxial Semiconductor-Ferromagnetic Insulator InAs/EuS Interfaces: Band Alignment and Magnetic Structure
Liu Y., Luchini A., Martí-Sánchez S., Koch C., Schuwalow S., Khan S.A., Stankevič T., Francoual S., Mardegan J.R.L., Krieger J.A., Strocov V.N., Stahn J., Vaz C.A.F., Ramakrishnan M., Staub U., Lefmann K., Aeppli G., Arbiol J., Krogstrup P. ACS Applied Materials and Interfaces; 12 (7): 8780 - 8787. 2020. 10.1021/acsami.9b15034. IF: 8.758
Hybrid semiconductor-ferromagnetic insulator heterostructures are interesting due to their tunable electronic transport, self-sustained stray field, and local proximitized magnetic exchange. In this work, we present lattice-matched hybrid epitaxy of semiconductor-ferromagnetic insulator InAs/EuS heterostructures and analyze the atomic-scale structure and their electronic and magnetic characteristics. The Fermi level at the InAs/EuS interface is found to be close to the InAs conduction band and in the band gap of EuS, thus preserving the semiconducting properties. Both neutron and X-ray reflectivity measurements show that the overall ferromagnetic component is mainly localized in the EuS thin film with a suppression of the Eu moment in the EuS layer nearest the InAs and magnetic moments outside the detection limits on the pure InAs side. This work presents a step toward realizing defect-free semiconductor-ferromagnetic insulator epitaxial hybrids for spin-lifted quantum and spintronic applications without external magnetic fields. Copyright © 2019 American Chemical Society.
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Engineering grain boundaries at the 2D limit for the hydrogen evolution reaction
He Y., Tang P., Hu Z., He Q., Zhu C., Wang L., Zeng Q., Golani P., Gao G., Fu W., Huang Z., Gao C., Xia J., Wang X., Wang X., Zhu C., Ramasse Q.M., Zhang A., An B., Zhang Y., Martí-Sánchez S., Morante J.R., Wang L., Tay B.K., Yakobson B.I., Trampert A., Zhang H., Wu M., Wang Q.J., Arbiol J., Liu Z. Nature Communications; 11 (1, 57) 2020. 10.1038/s41467-019-13631-2. IF: 12.121
Atom-thin transition metal dichalcogenides (TMDs) have emerged as fascinating materials and key structures for electrocatalysis. So far, their edges, dopant heteroatoms and defects have been intensively explored as active sites for the hydrogen evolution reaction (HER) to split water. However, grain boundaries (GBs), a key type of defects in TMDs, have been overlooked due to their low density and large structural variations. Here, we demonstrate the synthesis of wafer-size atom-thin TMD films with an ultra-high-density of GBs, up to ~1012 cm−2. We propose a climb and drive 0D/2D interaction to explain the underlying growth mechanism. The electrocatalytic activity of the nanograin film is comprehensively examined by micro-electrochemical measurements, showing an excellent hydrogen-evolution performance (onset potential: −25 mV and Tafel slope: 54 mV dec−1), thus indicating an intrinsically high activation of the TMD GBs. © 2020, The Author(s).
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GaAs nanoscale membranes: Prospects for seamless integration of III-Vs on silicon
Raya A.M., Friedl M., Martí-Sánchez S., Dubrovskii V.G., Francaviglia L., Alén B., Morgan N., Tütüncüoglu G., Ramasse Q.M., Fuster D., Llorens J.M., Arbiol J., Fontcuberta I Morral A. Nanoscale; 12 (2): 815 - 824. 2020. 10.1039/c9nr08453c. IF: 6.895
The growth of compound semiconductors on silicon has been widely sought after for decades, but reliable methods for defect-free combination of these materials have remained elusive. Recently, interconnected GaAs nanoscale membranes have been used as templates for the scalable integration of nanowire networks on III-V substrates. Here, we demonstrate how GaAs nanoscale membranes can be seamlessly integrated on silicon by controlling the density of nuclei in the initial stages of growth. We also correlate the absence or presence of defects with the existence of a single or multiple nucleation regime for the single membranes. Certain defects exhibit well-differentiated spectroscopic features that we identify with cathodoluminescence and micro-photoluminescence techniques. Overall, this work presents a new approach for the seamless integration of compound semiconductors on silicon. © 2019 The Royal Society of Chemistry.
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Monodisperse CoSn and NiSn Nanoparticles Supported on Commercial Carbon as Anode for Lithium- And Potassium-Ion Batteries
Li J., Xu X., Yu X., Han X., Zhang T., Zuo Y., Zhang C., Yang D., Wang X., Luo Z., Arbiol J., Llorca J., Liu J., Cabot A. ACS Applied Materials and Interfaces; 12 (4): 4414 - 4422. 2020. 10.1021/acsami.9b16418. IF: 8.758
Monodisperse CoSn and NiSn nanoparticles were prepared in solution and supported on commercial carbon black. The obtained nanocomposites were applied as anodes for Li- and K-ion batteries. CoSn@C delivered stable average capacities of 850, 650, and 500 mAh g-1 at 0.2, 1.0, and 2.0 A g-1, respectively, well above those of commercial graphite anodes. The capacity of NiSn@C retained up to 575 mAh g-1 at a current of 1.0 A g-1 over 200 continuous cycles. Up to 74.5 and 69.7% pseudocapacitance contributions for Li-ion batteries were measured for CoSn@C and NiSn@C, respectively, at 1.0 mV s-1. CoSn@C was further tested in full-cell lithium-ion batteries with a LiFePO4 cathode to yield a stable capacity of 350 mAh g-1 at a rate of 0.2 A g-1. As electrode in K-ion batteries, CoSn@C composites presented a stable capacity of around 200 mAh g-1 at 0.2 A g-1 over 400 continuous cycles, and NiSn@C delivered a lower capacity of around 100 mAh g-1 over 300 cycles. Copyright © 2020 American Chemical Society.
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Phosphorous incorporation in Pd2Sn alloys for electrocatalytic ethanol oxidation
Yu X., Liu J., Li J., Luo Z., Zuo Y., Xing C., Llorca J., Nasiou D., Arbiol J., Pan K., Kleinhanns T., Xie Y., Cabot A. Nano Energy; 77 (105116) 2020. 10.1016/j.nanoen.2020.105116. IF: 16.602
Direct ethanol fuel cells (DEFCs) show a huge potential to power future electric vehicles and portable electronics, but their deployment is currently limited by the unavailability of proper electrocatalysis for the ethanol oxidation reaction (EOR). In this work, we engineer a new electrocatalyst by incorporating phosphorous into a palladium-tin alloy and demonstrate a significant performance improvement toward EOR. We first detail a synthetic method to produce Pd2Sn:P nanocrystals that incorporate 35% of phosphorus. These nanoparticles are supported on carbon black and tested for EOR. Pd2Sn:P/C catalysts exhibit mass current densities up to 5.03 A mgPd−1, well above those of Pd2Sn/C, PdP2/C and Pd/C reference catalysts. Furthermore, a twofold lower Tafel slope and a much longer durability are revealed for the Pd2Sn:P/C catalyst compared with Pd/C. The performance improvement is rationalized with the aid of density functional theory (DFT) calculations considering different phosphorous chemical environments. Depending on its oxidation state, surface phosphorus introduces sites with low energy OH− adsorption and/or strongly influences the electronic structure of palladium and tin to facilitate the oxidation of the acetyl to acetic acid, which is considered the EOR rate limiting step. DFT calculations also points out that the durability improvement of Pd2Sn:P/C catalyst is associated to the promotion of OH adsorption that accelerates the oxidation of intermediate poisoning COads, reactivating the catalyst surface. © 2020
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Rhodium as efficient additive for boosting acetone sensing by TiO2 nanocrystals. Beyond the classical view of noble metal additives
Epifani M., Kaciulis S., Mezzi A., Zhang T., Arbiol J., Siciliano P., Landström A., Concina I., Moumen A., Comini E., Xiangfeng C. Sensors and Actuators, B: Chemical; 319 (128338) 2020. 10.1016/j.snb.2020.128338. IF: 7.100
Anatase TiO2 nanocrystals were prepared by solvothermal synthesis and modified by in- situ generated Rh nanoparticles, with a starting nominal Rh:Ti atomic concentration of 0.01 and 0.05. After heat-treatment at 400 °C the TiO2 host was still in the anatase crystallographic phase, embedding Rh nanoparticles homogeneously distributed and whose surface had been oxidized to Rh2O3, as established by X-ray diffraction, Transmission Electron Microscopy and X-ray Photoelectron spectroscopy. Moreover, Rh seemed also homogeneously distributed in elemental form or as Rh2O3 nanoclusters. The acetone sensing properties of the resulting materials were enhanced by Rh addition, featuring a response increase of one order of magnitude at the best operating temperature of 300 °C. Moreover, Rh addition enlarged the detection range down to 10 ppm whereas pure TiO2 was not able of giving an appreciable response already at a concentration as high as 50 ppm. From the sensing data, the enhancement of the sensor response was attributed to the finely dispersed Rh species and not to the oxidized Rh nanocrystals. © 2020 Elsevier B.V.
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Selective Methanol-to-Formate Electrocatalytic Conversion on Branched Nickel Carbide
Li J., Wei R., Wang X., Zuo Y., Han X., Arbiol J., Llorca J., Yang Y., Cabot A., Cui C. Angewandte Chemie - International Edition; 59 (47): 20826 - 20830. 2020. 10.1002/anie.202004301. IF: 12.959
A methanol economy will be favored by the availability of low-cost catalysts able to selectively oxidize methanol to formate. This selective oxidation would allow extraction of the largest part of the fuel energy while concurrently producing a chemical with even higher commercial value than the fuel itself. Herein, we present a highly active methanol electrooxidation catalyst based on abundant elements and with an optimized structure to simultaneously maximize interaction with the electrolyte and mobility of charge carriers. In situ infrared spectroscopy combined with nuclear magnetic resonance spectroscopy showed that branched nickel carbide particles are the first catalyst determined to have nearly 100 % electrochemical conversion of methanol to formate without generating detectable CO2 as a byproduct. Electrochemical kinetics analysis revealed the optimized reaction conditions and the electrode delivered excellent activities. This work provides a straightforward and cost-efficient way for the conversion of organic small molecules and the first direct evidence of a selective formate reaction pathway. © 2020 Wiley-VCH GmbH
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Semiconductor-Ferromagnetic Insulator-Superconductor Nanowires: Stray Field and Exchange Field
Liu Y., Vaitiekėnas S., Martí-Sánchez S., Koch C., Hart S., Cui Z., Kanne T., Khan S.A., Tanta R., Upadhyay S., Cachaza M.E., Marcus C.M., Arbiol J., Moler K.A., Krogstrup P. Nano Letters; 20 (1): 456 - 462. 2020. 10.1021/acs.nanolett.9b04187. IF: 11.238
Nanowires can serve as flexible substrates for hybrid epitaxial growth on selected facets, allowing for the design of heterostructures with complex material combinations and geometries. In this work we report on hybrid epitaxy of freestanding vapor-liquid-solid grown and in-plane selective area grown semiconductor-ferromagnetic insulator-superconductor (InAs/EuS/Al) nanowire heterostructures. We study the crystal growth and complex epitaxial matching of wurtzite and zinc-blende InAs/rock-salt EuS interfaces as well as rock-salt EuS/face-centered cubic Al interfaces. Because of the magnetic anisotropy originating from the nanowire shape, the magnetic structure of the EuS phase is easily tuned into single magnetic domains. This effect efficiently ejects the stray field lines along the nanowires. With tunnel spectroscopy measurements of the density of states, we show that the material has a hard induced superconducting gap, and magnetic hysteretic evolution which indicates that the magnetic exchange fields are not negligible. These hybrid nanowires fulfill key material requirements for serving as a platform for spin-based quantum applications, such as scalable topological quantum computing. Copyright © 2019 American Chemical Society.
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SnS2/g-C3N4/graphite nanocomposites as durable lithium-ion battery anode with high pseudocapacitance contribution
Zuo Y., Xu X., Zhang C., Li J., Du R., Wang X., Han X., Arbiol J., Llorca J., Liu J., Cabot A. Electrochimica Acta; 349 (136369) 2020. 10.1016/j.electacta.2020.136369. IF: 6.215
Tin disulfide is a promising anode material for Li-ion batteries (LIB) owing to its high theoretical capacity and the abundance of its composing elements. However, bare SnS2 suffers from low electrical conductivity and large volume expansion, which results in poor rate performance and cycling stability. Herein, we present a solution-based strategy to grow SnS2 nanostructures within a matrix of porous g-C3N4 (CN) and high electrical conductivity graphite plates (GPs). We test the resulting nanocomposite as anode in LIBs. First, SnS2 nanostructures with different geometries are tested, to find out that thin SnS2 nanoplates (SnS2-NPLs) provide the highest performances. Such SnS2-NPLs, incorporated into hierarchical SnS2/CN/GP nanocomposites, display excellent rate capabilities (536.5 mA h g−1 at 2.0 A g−1) and an outstanding stability (∼99.7% retention after 400 cycles), which are partially associated with a high pseudocapacitance contribution (88.8% at 1.0 mV s−1). The excellent electrochemical properties of these nanocomposites are ascribed to the synergy created between the three nanocomposite components: i) thin SnS2-NPLs provide a large surface for rapid Li-ion intercalation and a proper geometry to stand volume expansions during lithiation/delithiation cycles; ii) porous CN prevents SnS2-NPLs aggregation, habilitates efficient channels for Li-ion diffusion and buffer stresses associated to SnS2 volume changes; and iii) conductive GPs allow an efficient charge transport. © 2020 Elsevier Ltd
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Stability of Pd3Pb Nanocubes during Electrocatalytic Ethanol Oxidation
Yu X., Luo Z., Zhang T., Tang P., Li J., Wang X., Llorca J., Arbiol J., Liu J., Cabot A. Chemistry of Materials; 32 (5): 2044 - 2052. 2020. 10.1021/acs.chemmater.9b05094. IF: 9.567
Intermetallic Pd3Pb nanocrystals with controlled size and cubic geometry exposing (100) facets are synthesized and tested as electrocatalysts for ethanol oxidation in alkaline media. We observe the ethanol oxidation activity and stability to be size-dependent. The 10 nm Pd3Pb nanocrystals display the highest initial current densities, but after few hundred cycles, the current density of smaller nanocrystals becomes much larger. All of the catalysts exhibit a pronounced current decay during the first 500 s of continuous operation, which is associated with the accumulation of strongly adsorbed reaction intermediates, blocking reaction sites. These adsorbed species can be removed by cycling the catalysts or maintaining them at slightly higher potentials for a short period of time to oxidize and later reduce the Pd surface. Such simple cleaning processes, that can be performed during operation breaks without cell disassembly, is sufficient to effectively remove the poisoning species adsorbed on the surface and recover the electrocatalytic activity. Copyright © 2020 American Chemical Society.
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Synergistic computational-experimental discovery of highly selective ptcu nanocluster catalysts for acetylene semihydrogenation
Ayodele O.B., Cai R., Wang J., Ziouani Y., Liang Z., Spadaro M.C., Kovnir K., Arbiol J., Akola J., Palmer R.E., Kolen'ko Y.V. ACS Catalysis; 10 (1): 451 - 457. 2020. 10.1021/acscatal.9b03539. IF: 12.350
Semihydrogenation of acetylene (SHA) in an ethylene-rich stream is an important process for polymer industries. Presently, Pd-based catalysts have demonstrated good acetylene conversion (XC2H2), however, at the expense of ethylene selectivity (SC2H4). In this study, we have employed a systematic approach using density functional theory (DFT) to identify the best catalyst in a Cu-Pt system. The DFT results showed that with a 55 atom system at∼1.1 Pt/Cu ratio for Pt28Cu27/Al2O3, the d-band center shifted -2.2 eV relative to the Fermi level leading to electron-saturated Pt, which allows only adsorption of ethylene via a π -bond, resulting in theoretical 99.7% SC2H4 at nearly complete XC2H2. Based on the DFT results, Pt-Cu/Al2O3 (PtCu) and Pt/Al2O3 (Pt) nanocatalysts were synthesized via cluster beam deposition (CBD), and their properties and activities were correlated with the computational predictions. For bimetallic PtCu, the electron microscopy results show the formation of alloys. The bimetallic PtCu catalyst closely mimics the DFT predictions in terms of both electronic structure, as confirmed by X-ray photoelectron spectroscopy, and catalytic activity. The alloying of Pt with Cu was responsible for the high C2H4 specific yield resulting from electron transfer between Cu and Pt, thus making PtCu a promising catalyst for SHA. © 2019 American Chemical Society.
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Tin Selenide Molecular Precursor for the Solution Processing of Thermoelectric Materials and Devices
Zhang Y., Liu Y., Xing C., Xing C., Zhang T., Li M., Pacios M., Yu X., Arbiol J., Arbiol J., Llorca J., Cadavid D., Ibáñez M., Cabot A., Cabot A. ACS Applied Materials and Interfaces; 12 (24): 27104 - 27111. 2020. 10.1021/acsami.0c04331. IF: 8.758
In the present work, we report a solution-based strategy to produce crystallographically textured SnSe bulk nanomaterials and printed layers with optimized thermoelectric performance in the direction normal to the substrate. Our strategy is based on the formulation of a molecular precursor that can be continuously decomposed to produce a SnSe powder or printed into predefined patterns. The precursor formulation and decomposition conditions are optimized to produce pure phase 2D SnSe nanoplates. The printed layer and the bulk material obtained after hot press displays a clear preferential orientation of the crystallographic domains, resulting in an ultralow thermal conductivity of 0.55 W m-1 K-1 in the direction normal to the substrate. Such textured nanomaterials present highly anisotropic properties with the best thermoelectric performance in plane, i.e., in the directions parallel to the substrate, which coincide with the crystallographic bc plane of SnSe. This is an unfortunate characteristic because thermoelectric devices are designed to create/harvest temperature gradients in the direction normal to the substrate. We further demonstrate that this limitation can be overcome with the introduction of small amounts of tellurium in the precursor. The presence of tellurium allows one to reduce the band gap and increase both the charge carrier concentration and the mobility, especially the cross plane, with a minimal decrease of the Seebeck coefficient. These effects translate into record out of plane ZT values at 800 K. Copyright © 2020 American Chemical Society.
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Understanding galvanic replacement reactions: the case of Pt and Ag
Merkoçi F., Patarroyo J., Russo L., Piella J., Genç A., Arbiol J., Bastús N.G., Puntes V. Materials Today Advances; 5 (100037) 2020. 10.1016/j.mtadv.2019.100037. IF: 0.000
Synthesis of nanocrystals (NCs), where material science elements are addressed with organic chemistry precision techniques, is especially challenging and difficult to control. This difficulty arises from the increased complexity of the mineralization processes and the generation of a liquid-solid interface. These aspects, along with a strong susceptibility to reaction kinetics, ultimately translate into serious challenges for reproducibility and morphological control. By systematically varying the different parameters used to control the morphology of NCs, including complexing agents, coreducers, and cooxidants, the general reaction landscape can be mapped and the most stable and reproducible recipes can be identified. We apply this concept to the model transmetallation reaction between immiscible Pt and Ag forming hollow Pt NCs by galvanic replacement reactions. In this work, 648 synthetic recipes were performed and characterized per duplicate, from which a subset of 307 recipes leading to the controlled formation of hollow NCs were further analyzed to correlate reaction conditions with the final obtained structure and stability (reproducibility). As a result, we present robust general synthetic protocols leading to the ad hoc production of Pt-based hollow NCs with independent control of shell thickness, void size, surface roughness, and degree of porosity. © 2019 The Authors
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ZnSe/N-doped carbon nanoreactor with multiple adsorption sites for stable lithium-sulfur batteries
Yang D., Zhang C., Biendicho J.J., Han X., Liang Z., Du R., Li M., Li J., Arbiol J., Llorca J., Zhou Y., Morante J.R., Cabot A. ACS Nano; 14 (11): 15492 - 15504. 2020. 10.1021/acsnano.0c06112. IF: 14.588
To commercially realize the enormous potential of lithium-sulfur batteries (LSBs) several challenges remain to be overcome. At the cathode, the lithium polysulfide (LiPS) shuttle effect must be inhibited and the redox reaction kinetics need to be substantially promoted. In this direction, this work proposes a cathode material based on a transition-metal selenide (TMSe) as both adsorber and catalyst and a hollow nanoreactor architecture: ZnSe/N-doped hollow carbon (ZnSe/NHC). It is here demonstrated both experimentally and by means of density functional theory that this composite provides three key benefits to the LSBs cathode: (i) A highly effective trapping of LiPS due to the combination of sulfiphilic sites of ZnSe, lithiophilic sites of NHC, and the confinement effect of the cage-based structure; (ii) a redox kinetic improvement in part associated with the multiple adsorption sites that facilitate the Li+ diffusion; and (iii) an easier accommodation of the volume expansion preventing the cathode damage due to the hollow design. As a result, LSB cathodes based on S@ZnSe/NHC are characterized by high initial capacities, superior rate capability, and an excellent stability. Overall, this work not only demonstrates the large potential of TMSe as cathode materials in LSBs but also probes the nanoreactor design to be a highly suitable architecture to enhance cycle stability. © 2020 American Chemical Society.
