Toward High-Performance Electrochemical Ammonia Synthesis by Circumventing the Surface H-Mediated N Reduction.

The rapid performance decay with potentials is a significant obstacle to achieving an efficient electrocatalytic N reduction reaction (eNRR), which is typically attributed to competition from hydrogen evolution. However, the potential-dependent competitive behavior and reaction mechanism are still under debate. Herein, we theoretically defined N adsorption, H mediation, and H evolution as three crucial regions along the potentials by revisiting the potential-dependent competitive adsorption between N and H on FeN and RuN catalysts. We revealed that the surface H-mediated mechanism makes eNRR feasible at low potentials but introduces sluggish reaction kinetics, showing a double-edged sword nature. In view of this, we proposed a new possibility to achieve high-performance NH synthesis by circumventing the H-mediated mechanism, where the ideal catalyst should have a wide potential interval with N-dominated adsorption to trigger direct eNRR. Using this mechanistic insight as a new criterion, we proposed a theoretical protocol for eNRR catalyst screening, but almost none of the theoretically reported electrocatalysts passed the assessment. This work not only illustrates the intrinsic mechanism behind the low-performance dilemma of eNRR but also points out a possible direction toward designing promising catalysts with high selectivity and high current density.