Electronic Structure-Selectivity Trends for Electrocatalytic Nitrate Reduction to Ammonium on 3d Transition Metals

Nitrate is a toxic anthropogenic groundwater contaminant, accumulating in drinking water and posing a human-health hazard. Nitrogen loading and accumulation of aqueous nitrate in groundwater is of a comparable scale and pervasiveness as global CO₂ emissions. In parallel, production of ammonia (NH₃) by the thermal Haber-Bosch process accounted for 1.8% of the global energy consumption and represented the most carbon-intensive commodity of 2020.^[1] This project aims to understand how Faradaic efficiency (FE) and selectivity towards ammonium (NH₄⁺) during the electrochemical nitrate reduction reaction (NO3RR) is dependent on bulk, resting material electronic structure. Here we present NO3RR activity and selectivity of several transition metal foils (e.g. Cu, Ni, Ni_0.67Cu_0.33, Fe, and Ti), relating this information to electronic structure (work function, 𝜙, and d-band center, E_d, relative to E_vac) and how it plays a critical role in proton affinity and NO3RR FE and selectivity to NH₄⁺.