Tuning Active Hydrogen via Spillover Enables the Wide-Potential Electrochemical Reduction of Nitrate to Ammonia

The electrochemical nitrate reduction reaction (NO₃RR) offers a sustainable route for green ammonia synthesis under ambient conditions. However, achieving high NH₃ selectivity across a broad potential window, which is crucial for integration with fluctuating renewable energy sources, remains challenging due to difficulties in precisely controlling the active hydrogen supply. Herein, a hydrogen spillover strategy is presented to address this challenge by optimizing hydrogen activity. This strategy is realized using a Pt nanoparticle decorated nanoporous Co₂P (Pt/np-Co₂P) catalyst. In situ Fourier transform infrared spectroscopy, density functional theory calculations, and a suite of control experiments reveal that Pt nanoparticles generate active hydrogen, which migrates via the spillover pathway to hydrogenate *NO on Co₂P. This process significantly lowers both thermodynamic and kinetic barriers for *NO hydrogenation. As a result, the Pt/np-Co₂P catalyst maintains a Faradaic efficiency (FE) above 90% across a wide 600 mV potential window by ensuring sufficient *H availability at low overpotentials and suppressing the competing hydrogen evolution reaction at high overpotentials. The FE approaches 100% at an industrially relevant current density of ≈1 A cm^-2. Similar performance enhancements observed for other noble metal-decorated np-Co₂P confirm the universality of hydrogen spillover strategy for designing efficient catalysts toward practical ammonia synthesis.