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.