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

Abstract

Achieving both high activity and selectivity presents a significant challenge for electrochemical N2 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 N2 adsorption, *N2 hydrogenation, and corresponding potential-dependent kinetics is presented. This data reveals that N2 adsorption at EEI is kinetically facile. Upon *N2 adsorption, the subsequent hydrogenation is influenced by electrode potentials. At lower overpotentials, *N2 hydrogenation is more facile than HER. However, at higher overpotentials, eNRR becomes kinetically disadvantaged due to limited N2 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 N2 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.