The Loss of Interfacial Water-Adsorbate Hydrogen Bond Connectivity Position Surface-Active Hydrogen as a Crucial Intermediate to Enhance Nitrate Reduction Reaction

The electrochemical nitrate reduction reaction (NO3RR) offers a promising solution for remediating nitrate-polluted wastewater while enabling the sustainable production of ammonia. The control strategy of surface-active hydrogen (*H) is extensively employed to enhance the kinetics of the NO3RR, but atomic understanding lags far behind the experimental observations. Here, we decipher the cation-water-adsorbate interactions in regulating the NO3RR kinetics at the Cu (111) electrode/electrolyte interface using AIMD simulations with a slow-growth approach. We demonstrate that the key oxygen-containing intermediates of the NO3RR (e.g., *NO, *NO2, and *NO3) will stably coordinate with the cations, impeding their integration with the hydrogen bond network and further their hydrogenation by interfacial water molecules due to steric hindrance. The *H can migrate across the interface with a low energy barrier, and its hydrogenation barrier with oxygen-containing species remains unaffected by cations, offering a potent supplement to the hydrogenation process, playing the predominant factor by which the *H facilitates NO3RR reaction kinetic. This study provides valuable insights for understanding the reaction mechanism of NO3RR by fully considering the cation–water–adsorbate interactions, which can aid in the further development of the electrolyte and electrocatalysts for efficient NO3RR.