Stabilization of Reactive Hydrogen Species via N-H Bonding on Fe₂N for Efficient Electrochemical Hydrogenation

Electrochemical hydrogenation utilizing reactive hydrogen (H*) derived from water dissociation offers a sustainable route for chemical synthesis and environmental remediation. However, besides the sluggish generation of H*, its utilization efficiency, and consequently the overall electrochemical hydrogenation performance, is limited by competing hydrogen evolution and barrier interfacial H* transfer. Here, using combined theoretical and in situ spectroscopic-electrochemical analyses, we demonstrate that nitrogen vacancy (N_V)-rich Fe₂N surfaces serve as highly efficient catalytic sites for generating and stabilizing H* for subsequent reactions. During water dissociation, the resulting OH species adopt a bridging μ₂-configuration between adjacent Fe atoms and undergo facile desorption, overcoming a known rate-limiting step. Simultaneously, H* is stabilized at nitrogen sites in the form of N-H moieties with high recombination energy barriers, creating an effective H* reservoir. This mechanism guides the application of Fe₂N-N_V as a simple yet highly active catalyst for nitrate reduction, achieving over 94% Faradaic efficiency and NH₃ selectivity. Furthermore, the accumulated H* on Fe₂N-N_V enables tandem hydrogenation with cocatalysts such as cobalt ensembles (Co_n), extending its utility to coupled electrochemical hydrogenation.