Prediction of Highly Selective Electrocatalytic Nitrogen Reduction at Low Overpotential on a Mo-Doped g-GaN Monolayer
Lesheng Li, John Mark P. Martirez, Emily A. Carter
Abstract
Identifying efficient electrocatalysts with low overpotential and high selectivity for producing ammonia from nitrogen gas is essential for any future electrocatalytic nitrogen reduction reaction (NRR)-based ammonia synthesis. Via density functional theory calculations and the computational hydrogen electrode model, we systematically examine the prospect of using a single-transition-metal (TM)-atom-doped graphene-like GaN (g-GaN) monolayer as an electrocatalyst for artificial nitrogen reduction. Among 15 TMs investigated, the Mo-doped g-GaN (Mo@g-GaN) monolayer is the only electrocatalyst predicted to be feasible for the NRR. The Mo@g-GaN monolayer satisfies all screening criteria considered for activating the inert N≡N triple bond effectively, including stabilization of the adsorbed (*) NRR intermediate *NNH and destabilization of the *NH2 species. This monolayer also possesses sufficient overall stability. A complete analysis of the likely mechanisms involved in the NRR on this catalyst suggests that the Mo@g-GaN monolayer could exhibit promising NRR catalytic activity. It achieves this via one specific (distal) pathway, which has a very low onset potential of −0.33 V vs the reversible hydrogen electrode (RHE), corresponding to a low overpotential of 0.42 V vs the RHE, defined using the measured equilibrium potential for NRR of 0.09 V vs the RHE. The potential-determining step, conversion of *NH2 to *NH3, also exhibits a surmountable barrier of 0.42 eV, suggesting kinetics will be facile. Finally, the Mo@g-GaN monolayer is predicted to exhibit substantial selectivity (∼31%) toward ammonia synthesis over the competing hydrogen evolution reaction. These findings may open a potential route for artificial ammonia synthesis using a single-atom catalyst under ambient conditions.