New Mechanistic Insights into Electrokinetic Competition Between Nitrogen Reduction and Hydrogen Evolution Reactions

Achieving both high activity and selectivity presents a significant challenge for electrochemical N-2 reduction (eNRR) due to the competing hydrogen evolution reaction (HER). Although density functional theory-based computations can identify eNRR-favored electrocatalysts, there is a significant gap between theoretical predictions and experimental observations. In this work, a comprehensive analysis of the kinetic competition between eNRR and HER at the electrode-electrolyte interface (EEI) from three perspectives: kinetic N-2 adsorption, *N-2 hydrogenation, and corresponding potential-dependent kinetics is presented. This data reveals that N-2 adsorption at EEI is kinetically facile. Upon *N-2 adsorption, the subsequent hydrogenation is influenced by electrode potentials. At lower overpotentials, *N-2 hydrogenation is more facile than HER. However, at higher overpotentials, eNRR becomes kinetically disadvantaged due to limited N-2 availability at the EEI, while HER kinetics accelerate and eventually dominate. Therefore, the electrochemical eNRR potential window for different catalysts is identified. A compelling evidence is presented that enhancing N-2 concentration near the EEI is the key to improving eNRR activity. These findings offer critical fundamental insights for future strategies aimed at making green ammonia synthesis more efficient.