Engineering CuOxNanoparticles on Cu Foam for Acidic Nitrate Reduction to Ammonium

The electrochemical conversion of NOx (including NO3– and NO2–) to ammonium using renewable energy is emerging as a green alternative pathway for decarbonization of high emission industry to meet net zero emission targets. The key to efficient NOx electrolysis relies on the understanding of surface chemistry to establish the structure–activity relationships that will govern future scaleup of this process. In this work, we have undertaken a mechanistic investigation, wherein by tuning the surface oxidation state of CuOx nanoparticles on Cu foam (referred as CuOx/CuF), we are able to investigate its impact on conversion of NOx to ammonium (NH4+) under acidic reaction conditions. Supported by in situ Raman measurements, we reveal the importance of tuning the Cu oxidation state to maximize Cu2O formation, which forms beneficial Cu2O/Cu interfaces during reaction, allowing an enhanced NH4+ yield with a production rate of 45 nmol s–1 cm–2 and Faradaic efficiency (FENH4+) of 83% at −0.5 V vs RHE. Further, we reveal the promising stability of such interfaces under acidic conditions during long-term electrolysis for usage of up to 20 h.