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

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.