Electrochemical nitrate reduction uses electricity to convert nitrate (NO₃^-), a common water pollutant, into other nitrogen-containing compounds, including nitrite (NO₂^-) and ammonia (NH₃). This process is attracting interest for water remediation and sustainable chemical production. However, improving the efficiency of these processes requires a better understanding of the mechanisms and factors influencing the reaction.

Researchers from the ICN2 NanoElectrocatalysis and Sustainable Chemistry Group (NanoESC) have published two studies investigating this question using silver electrodes. In the first study, the team made a curious discovery: as the nitrate concentration increased, the electrochemical signal changed from one peak to two distinct peaks. Such signals are often used to identify electrochemical processes, raising an important question: did these peaks correspond to different reactions, or could the same reaction occur under different conditions? To investigate this, the researchers combined electrochemical measurements with scanning electrochemical microscopy (SECM), a technique that enables the detection of reaction products close to the electrode surface. By monitoring nitrite formation and complementing these measurements with product quantification, they demonstrated that all three signals were associated with the same reaction: the conversion of nitrate into nitrite. Further analysis revealed that the different signals reflect distinct proton-transfer regimes involving dihydrogen phosphate (H₂PO₄⁻) and water.

This research, led by Jaxiry Barroso-Martínez and supervised by ICREA Prof. Maria Escudero-Escribano, has been published in ACS Catalysis.

In a complementary study led by Dr Gabriel Floriano Costa, the group used time-resolved surface-enhanced Raman spectroscopy (TR-SERS) to analyse the interaction between nitrate, nitrite and silver electrodes. This technique offers a molecular-level view of the reaction and allows researchers to track changes in the vibrational signals of nitrate and nitrite in real time during both nitrate and nitrite reduction. This approach gave them insight into how these species adsorb onto the electrode surface and how their interactions change during the reaction. This is the first demonstration of TR-SERS being used to track adsorbate dynamics during electrochemical nitrate-to-nitrite conversion on silver.

The study, published in JACS Au, was carried out in collaboration with researchers from CIC energiGUNE (Vitoria-Gasteiz, Spain) and Trinity College Dublin’s School of Chemistry.

Together, the studies highlight the importance of gaining a molecular-level understanding of the processes that occur at the electrode-electrolyte interface. While electrochemical measurements and kinetic analysis show the influence of proton donors, Raman spectroscopy reveals the interactions of nitrate-derived species with the silver surface. These insights can help guide the development of future electrocatalytic systems for more sustainable chemical processes and environmental protection.

Reference articles:

Barroso-Martínez, J. S.; Costa, G. F.; Escudero-Escribano, M. Proton-Donor Identity Shapes Electrochemical Nitrate Reduction on Silver. ACS Catalysis (2026). https://pubs.acs.org/accacs/article/doi/10.1021/acscatal.6c03804/5448417/Proton-Donor-Identity-Shapes-Electrochemical

Costa, G. F.; Barroso-Martínez, J. S.; Fenoll Silvestre, D. A.; Brennan-Pollak, C.; García-Melchor, M.; Escudero-Escribano, M. Time-Resolved Raman Spectroscopy of Nitrate Electroreduction Reveals Dynamic Interfacial Adsorbate Evolution. JACS Au (2026). https://doi.org/10.1021/jacsau.6c01050