Revisiting the Electrochemical Competition between Nitrogen Reduction and Hydrogen Evolution: The Role of Surface H-mediated Mechanism

The fast performance decay with potentials is an immense obstacle to achieving an efficient electrocatalytic N2 reduction reaction (eNRR), which is attributed to the competition from hydrogen evolution. However, the potential-dependent competitive behavior and reaction mechanism are still under debate. Herein, by means of constant-potential/hybrid-solvent framework, we revisited the potential-dependence of the competitive adsorption between N2 and H on the FeN4 and RuN4 catalysts, and for the first time defined N2 adsorption, H mediation, and H2 evolution as three crucial regions along potentials. We revealed that the surface H-mediated mechanism is responsible for the experimentally detected volcanic performance at low potentials, but introduces a sluggish reaction kinetics, displaying a double-edged sword nature. We proposed an effective strategy to achieve high-performance NH3 synthesis by enlarging the binding strength difference between N2 and H, endowing a wide potential interval for N2-dominated adsorption and direct electroreduction. This work provides essential insights on the computational design of robust electrocatalysts for practical applications in experiments.