Engineering CuO_xNanoparticles on Cu Foam for Acidic Nitrate Reduction to Ammonium

The electrochemical conversion of NO x (including NO 3 – and NO 2 – ) 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 (NH 4 + ) under acidic reaction conditions. Supported by in situ Raman measurements, we reveal the importance of tuning the Cu oxidation state to maximize Cu 2 O formation, which forms beneficial Cu 2 O/Cu interfaces during reaction, allowing an enhanced NH 4 + yield with a production rate of 45 nmol s –1 cm –2 and Faradaic efficiency ( FE NH 4 + ) 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.