Engineering CuOx Nanoparticles on Cu Foam for Acidic Nitrate Reduction to Ammonium.

The electrochemical conversion of NO_x (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 NO_x 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 CuO_x nanoparticles on Cu foam (referred as CuO_x/CuF), we are able to investigate its impact on conversion of NO_x 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. [ABSTRACT FROM AUTHOR]