Transition Metal Nitride Catalysts for Electrochemical Reduction of Nitrogen to Ammonia at Ambient Conditions

Abstract

Computational screening for catalysts that are stable, active and selective towards electrochemical reduction of nitrogen to ammonia at room temperature and ambient pressure is presented from a range of transition metal nitride surfaces. Density functional theory (DFT) calculations are used to study the thermochemistry of cathode reaction so as to construct the free energy profile and to predict the required onset potential via the Mars-van Krevelen mechanism. Stability of the surface vacancy as well as the poisoning possibility of these catalysts under operating conditions are also investigated towards catalyst engineering for sustainable ammonia formation. The most promising candidates turned out to be the (100) facets of rocksalt structure of VN, CrN, NbN and ZrN that should be able to form ammonia at -0.51 V, -0.76 V, -0.65 V and -0.76 V vs. SHE, respectively. Another interesting result of the current work is that for the introduced nitride candidates, hydrogen evolution is no longer the competing reaction; thus, high formation yield of ammonia is expected at low onset potentials.

Quantification of Active Sites and Elucidation of the Reaction Mechanism of the Electrochemical Nitrogen Reduction Reaction on Vanadium Nitride

“…To determine the density of surface N sites active in the ENRR on the VNO catalyst, we develop a novel quantitative isotopic exchange strategy. This method is based on the understanding that the ENRR on VNO follows the MvK mechanism, with surface N actively involved in the catalytic turnovers. It follows that all surface N sites involved in the ENRR would be replaced by 15 N when the ENRR proceeds with 15 N 2 as the feed, leading to the formation of 14 NH 3 (Figure A).…”

Vanadium oxynitrides as stable catalysts for electrochemical reduction of nitrogen to ammonia: the role of oxygen

“…It has been observed experimentally that the best yield rate and Faradic efficiencies are obtained for transition metal oxynitrides (TMON) compared to pure nitride catalysts 22,[26][27][28] . Existing theoretical work 21,29,30 has focused on the N 2 RR mechanism on nitride surfaces, and have not studied the atomistic mechanism, thermodynamic limitations on oxynitrides in details. For example, vanadium nitride, which has been investigated theoretically 29 , does not display good long term stability [31][32][33] in the N 2 RR electrochemical environment as nitrogen and vanadium leach into typical electrolyte solutions, thus limiting its application in ammonia electro-synthesis through N 2 RR.…”

Fast Screening Method for Nitrogen Reduction Reaction (NRR) Electrocatalytic Activity with Rotating Ring‐Disc Electrode (RRDE) Analysis in Alkaline Environment

“…A further important application of the RRDE-based analysis technique was referred to the time stability evaluation of nitrogen -containing catalyst in the operative environment (i. e. alkaline environment). N-based materials have been suggested as one of the most promising class of electrocatalysts [32][33][34] for highly selective N 2 reduction at low overpotentials, but they are also looked in distrust because they could be themselves the nitrogen source, invalidating the NRR process analysis. Due to the high sensibility of RRDE setup, we employed the CV fingerprints in Ar-saturated electrolyte at OCP and at the investigated reductive potentials to identify possible false positives.…”