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

Nitrate is a toxic anthropogenic surface and groundwater contaminant that poses human-health and ecological hazards. Electrochemical approaches can use renewable electricity to transform this waste nitrogen to value-added products in a distributer, scalable manner at costs comparable to traditional ion exchange methods. This project aims to understand how competition between the electrochemical nitrate reduction reaction (NO₃RR) and competing hydrogen evolution reaction (HER) is dependent on material electronic structure, as well as the resultant selectivity towards our desired product, ammonium (NH₄⁺). Here we present NO₃RR activity and selectivity of several different transition metal foils (e.g. Cu, Ni, Ni_0.67Cu_0.33, Fe, Ti, and Co), relating) these performance metrics to electronic structure (work function, 𝜙, and d-band center, E_d, relative to E_vac) and the critical role in proton affinity and NO₃RR FE and selectivity to NH₄⁺. These findings provide guidance for new alloy compositions that maximize both FE and selectivity in NO₃RR.