Elucidating the Intrinsic Activity and Selectivity of Cu for Nitrate Electroreduction

Cu-based catalysts have been widely explored for the electrochemical nitrate reduction reaction (NO3RR), while the intrinsic activity and selectivity of Cu metal for the NO3RR remain ambiguous, preventing a genuine comparison of the NO3RR performance. Here we use polycrystalline Cu foils for benchmarking and elucidate the impact of often overlooked factors on the NO3RR, including Cu facet exposure, nitrate concentration, and electrode surface area. An electropolished Cu foil exhibits a higher activity and selectivity for the NO3RR to NH3 than a wet-etched Cu foil, benefiting from greater exposure of Cu(100) facets that are more favorable for the NO3RR. While the NH3 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 NO2– to NH3 on a larger electrode, as validated by a 15N isotope labeling experiment. Our work provides mechanistic insights toward the rational design of NO3RR electrocatalysts.