Elucidating the Intrinsic Activity and Selectivity of Cu for Nitrate Electroreduction

Cu-based catalysts have been widelyexplored for theelectrochemicalnitrate reduction reaction (NO3RR), while the intrinsicactivity and selectivity of Cu metal for the NO3RR remainambiguous, preventing a genuine comparison of the NO(3)RRperformance. Here we use polycrystalline Cu foils for benchmarkingand elucidate the impact of often overlooked factors on the NO3RR, including Cu facet exposure, nitrate concentration, andelectrode surface area. An electropolished Cu foil exhibits a higheractivity 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 theNH(3) selectivity shows no apparent dependence on the nitrateconcentration, it increases monotonically with the Cu electrode area,which is attributed to a promoted conversion of intermediately producedNO(2) (-) to NH3 on a larger electrode,as validated by a N-15 isotope labeling experiment. Ourwork provides mechanistic insights toward the rational design of NO3RR electrocatalysts.

Automated summary

Cu-based catalysts have been investigated for the electrochemical nitrate reduction reaction (NO3RR), but the activity and selectivity of Cu metal for the NO3RR are still unclear. This study reveals the significance of Cu facet exposure, nitrate concentration, and electrode surface area on the NO3RR. A polished Cu foil with more exposed Cu(100) facets exhibits higher activity and selectivity for the NO3RR to NH3 compared to a wet-etched Cu foil. The NH3 selectivity shows no dependence on nitrate concentration but increases with the Cu electrode area, attributed to the enhanced conversion of intermediately produced NO2(-) to NH3 on a larger electrode, as confirmed by isotope labeling experiments. Mechanistic insights from this work can guide the rational design of NO3RR electrocatalysts.