Efficient electroreduction of nitrate via enriched active phases on copper-cobalt oxides

Electrochemical conversion of nitrate (NO3−) to ammonia (NH3) can target two birds with one stone well, in NO3−-containing sewage remediation and sustainable NH3 production. However, single metal-based catalysts are difficult to drive high-efficient NO3− removal due to the multi-electron transfer steps. Herein, we present a tandem catalyst with simple structure, Cu-Co binary metal oxides (Cu-Co-O), by engineering intermediate phases as catalytic active species for NO3− conversion. Electrochemical evaluation, X-ray photoelectron spectroscopy, and in situ Raman spectra together suggest that the newly-generated Cu-based phases was prone to NO3−-to-NO2− conversion, then NO2− was reduced to NH3 on Co-based species. At an applied potential of −1.1 V vs. saturated calomel electrode, the Cu-Co-O catalyst achieved NO3−-N removal of 90% and NH3 faradaic efficiency of 81% for 120 min in 100 mL of 50 mg/L NO3−-N, consuming only 0.69 kWh/mol in a two-electrode system. This study provides a facile and efficient engineering strategy for developing high-performance catalysts for electrocatalytic nitrate conversion.