The Loss of Interfacial\nWater-Adsorbate Hydrogen Bond\nConnectivity Position Surface-Active Hydrogen as a Crucial Intermediate\nto Enhance Nitrate Reduction Reaction

The electrochemical nitrate reduction reaction (NO<sub>3</sub>RR)\noffers a promising solution for remediating nitrate-polluted wastewater\nwhile enabling the sustainable production of ammonia. The control\nstrategy of surface-active hydrogen (*H) is extensively employed to\nenhance the kinetics of the NO<sub>3</sub>RR, but atomic understanding\nlags far behind the experimental observations. Here, we decipher the\ncation-water-adsorbate interactions in regulating the NO<sub>3</sub>RR kinetics at the Cu (111) electrode/electrolyte interface using\nAIMD simulations with a slow-growth approach. We demonstrate that\nthe key oxygen-containing intermediates of the NO<sub>3</sub>RR (e.g.,\n*NO, *NO<sub>2</sub>, and *NO<sub>3</sub>) will stably coordinate\nwith the cations, impeding their integration with the hydrogen bond\nnetwork and further their hydrogenation by interfacial water molecules\ndue to steric hindrance. The *H can migrate across the interface with\na low energy barrier, and its hydrogenation barrier with oxygen-containing\nspecies remains unaffected by cations, offering a potent supplement\nto the hydrogenation process, playing the predominant factor by which\nthe *H facilitates NO<sub>3</sub>RR reaction kinetic. This study provides\nvaluable insights for understanding the reaction mechanism of NO<sub>3</sub>RR by fully considering the cation–water–adsorbate\ninteractions, which can aid in the further development of the electrolyte\nand electrocatalysts for efficient NO<sub>3</sub>RR.