Elucidating the Intrinsic Activity and Selectivity of Cu for Nitrate Electroreduction

Cu-based catalysts have been widely explored for the electrochemical nitrate reduction reaction (NO 3 RR), while the intrinsic activity and selectivity of Cu metal for the NO 3 RR remain ambiguous, preventing a genuine comparison of the NO 3 RR performance. Here we use polycrystalline Cu foils for benchmarking and elucidate the impact of often overlooked factors on the NO 3 RR, including Cu facet exposure, nitrate concentration, and electrode surface area. An electropolished Cu foil exhibits a higher activity and selectivity for the NO 3 RR to NH 3 than a wet-etched Cu foil, benefiting from greater exposure of Cu(100) facets that are more favorable for the NO 3 RR. While the NH 3 selectivity shows no apparent dependence on the nitrate concentration, it increases monotonically with the Cu electrode area, which is attributed to a promoted conversion of intermediately produced NO 2 – to NH 3 on a larger electrode, as validated by a 15 N isotope labeling experiment. Our work provides mechanistic insights toward the rational design of NO 3 RR electrocatalysts.