The perturbation of the nitrogen cycle via fertilizer amendment and fossil-fuel combustion has resulted in alarmingly increased nitrate concentrations in groundwater and coastal areas, with global human-health threatening consequences. Denitrification of drinking water, municipal cooling tower waste water, and industrial waste streams is a growing area of energy consumption, though still outpaced by the carbon-intensive Haber-Bosch production of ammonia from nitrogen for fertilizer production. Electrocatalytic nitrate reduction offers a competitive, distributable, and cyclic alternative to conventional fertilizer-production approaches, using electrons as a reducing agent without the need for added chemicals or elevated temperatures and pressures. However, nitrate reduction Faradaic efficiency to desired products (e.g. ammonium) is limited by two primary factors: (1) competition with the process of water reduction (i.e. reducing protons to form hydrogen gas); and (2) a complex reduction pathway where nitric oxide (NO) plays a critical role in determining selectivity.

Here we investigate nitrate reduction in neutral pH phosphate buffer over a series of 3d (Cu, Ni, Ni_0.68Cu_0.32, Co, Fe, Ti) and 4d¹⁰ (Ag) transition metals (TMs), identifying properties of bulk resting electronic structure (e.g. work function [Φ] and d-band center energy [E_d]) as descriptors for nitrate reduction Faradaic efficiency and selectivity to ammonium. We frame our discussion of these results within theoretical and empirical literature on hydrogen evolution and nitric oxide adsorption, finding Φ dictates total nitrate reduction Faradaic efficiency while E_d determines selectivity towards ammonium. Nitrate reduction FE trends with work function, in-line with well-established trends between HER activity and work function. Selectivity towards ammonium increases as E_d approaches and overcomes the Fermi level, increasing the adsorption energy of nitrate reduction intermediates (such as NO) by decreasing occupation of anti-bonding states.