Electronic Structure Based Intuitive Design Principle of Single‐Atom Catalysts for Efficient Electrolytic Nitrogen Reduction

Abstract

AbstractAs an alternative to cost‐ and energy intensive Haber‐Bosch process, the implementation of electrolytic ammonia synthesis from dinitrogen molecule has been a long‐sought goal. State‐of‐the‐art electrocatalysts for nitrogen reduction reaction (NRR) face not only activity but also selectivity problem with the competitive hydrogen evolution reaction (HER). Recently, single‐atom catalysts (SACs) have emerged as promising for various reactions as they combine the best of homogenous and heterogenous catalysts. The reason for their high activity compared to their bulk and nanoparticle counterparts are yet to be completely understood. Inspired by the structure of nitrogenase FeMo cofactor, here we studied 13 transition metals anchored on MoS2 monolayer at Mo‐top positions, as possible electrolytic NRR catalysts using first‐principles methods. Employing the implicit solvation model, we calculated free energy barriers for proton abstraction by N2 molecule in end‐on configuration and adsorption free energy of hydrogen on all SACs. Based on these two parameters, Fe, Co, and Ru were found to be the most active and highly selective electrolytic NRR catalysts. Compared with other mechanisms, the limiting potentials (and hence activity) for enzymatic mechanism were found to be higher on these three SACs, with Ru SAC having a very low overpotential of 0.38 V vs SHE. Bader charge transferred from transition metal to N2 molecule and group number of transition metals correlate strongly with the NRR activity and hence emerge as two key descriptors for catalytic activity. These intuitive principles for rational designing of promising alternatives to the currently used bulk Ru(0001) catalyst could accelerate the search for highly efficient and selective SACs for electrolytic NRR.