(Invited) Electrochemical Nitrogen Reduction to Ammonia on Transition Metal Nitrides

Abstract

Renewable production of ammonia, a building block for most fertilizers, via the electrochemical nitrogen reduction reaction (ENRR) is desirable; however, selective electrocatalysts are lacking. Here we show that transition metal nitrides are a family of active, selective, and stable ENRR catalysts. In particular, vanadium nitride nanoparticles have an ENRR rate and a Faradaic efficiency of 3.3 × 10−10 mol s−1 cm−2 and 6.0% at −0.1 V within 1 h, respectively. ENRR with 15N2 as the feed produces both 14NH3 and 15NH3, which indicates that the reaction follows a Mars−van Krevelen mechanism. Ex situ X-ray photoelectron spectroscopy characterization of fresh and spent VN catalysts reveals that multiple vanadium oxide, oxynitride, and nitride species are present on the surface and identified vanadium oxynitride as the active phase in the ENRR, which is supported by operando X-ray absorption spectroscopic results. Quantitative isotopic label studies are conducted to determine the density of the initial and steady-state active surface N sites.