Electron-sponge polyoxometalate for interfacial electron and hydrogen regulation toward nitrate to ammonia reduction

Electrocatalytic nitrate reduction to ammonia (ENRA) offers a sustainable strategy for simultaneously mitigating nitrate pollution and producing green ammonia under ambient conditions. However, its efficiency is severely limited by sluggish multi-electron transfer kinetics and the competing hydrogen evolution reaction (HER), particularly due to insufficient regulation of interfacial active hydrogen species (*H). Polyoxometalates (POMs) feature abundant oxygen-rich sites capable of reversible protonation, thereby serving as an effective source of *H. Here, we report a POMs-modulated Cu₂O–Cu catalyts that enables synergistic regulation of interfacial electron distribution and *H availability. X-ray photoelectron spectroscopy confirms pronounced electron transfer between POMs and Cu₂O–Cu, while electrochemical analyses reveal that POMs modification significantly enhances the adsorption and storage capacity of *H, thereby promoting nitrate activation and hydrogenation. Density functional theory (DFT) calculations further reveal that POMs-induced interfacial charge redistribution optimizes nitrate intermediate adsorption and lowers the energy barrier of key proton-coupled electron transfer steps, thereby accelerating the ENRA pathway. As a result, the optimized catalyst delivers a high ammonia yield of 36.5 mg h⁻¹ mg_cat.⁻¹ and excellent Faradaic efficiency of 97.4%. This work provides a general strategy for constructing POMs-based electrocatalysts via interfacial electron and hydrogen regulation, offering new insights into the rational design of selective ENRA systems.