Role of oxide support in electrocatalytic nitrate reduction on Cu

The electrochemical nitrate reduction reaction (NO3RR) has the potential for distributed water treatment and renewable chemical synthesis. Cu is an active monometallic electrocatalyst for the NO3RR in acidic and alkaline electrolytes, where activity is limited by reduction of adsorbed nitrate to nitrite. Oxygen-vacancy forming metal-oxide supports provide sites for N-O bond activation in thermal reduction, impacting product distribution as well. Here we compare the electrochemical NO3RR activity of Cu deposited on two metal-oxide supports (cerium dioxide [Cu/CeO2‑δ] and fluorine-doped tin dioxide [Cu/FTO]) to a Cu foil benchmark. Considering activity in phosphate-buffered neutral media, nitrate and adsorbed hydrogen compete for surface sites under NO3RR conditions. The less-cathodic overpotential on Cu/CeO2‑δ compared to Cu/FTO is attributed to stronger nitrate adsorption, similar to thermal nitrate reduction. Utilization of CeO2‑δ as electrocatalyst support slightly shift product distribution towards more oxidized products, either by enhancing nitrate affinity or by a more dynamic process involving formation and healing of oxygen vacancies. These results suggest supporting catalysts on metal-oxides may enhance activity by promoting adsorption of anionic reactants on cathodic electrocatalysts.