Single‐Site Polyoxometalate Complexes with Engineered Electron Channels for Efficient Electrocatalytic Ammonia Synthesis from Nitrate

Electrochemical nitrate reduction to ammonia (ENRA) is a sustainable approach for the electrosynthesis of ammonia (NH₃) and the purification of wastewater. Herein, three polyoxometalate-based (POM-based) mononuclear complexes, namely [M(HNCP)₂(H₂O)][PW₁₂O₄₀]·H₂O (HNCP = 4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)benzoic acid; M = Ni, Co, Zn, referred to as M-PW₁₂), that feature atomically dispersed metal sites are prepared. Among them, Ni-PW₁₂ exhibits outstanding ENRA performance, with a Faradaic efficiency (FE) of 90.3% and an NH₃ yield rate of 11.2 mg h^-1 mg_cat. ^-1 at -1.3 V versus reversible hydrogen electrode (RHE). An in-depth computational study reveals that directional electron transfer from the POM cluster to the metal center diminishes the energy barrier associated with the rate-determining step (^*N → ^*NH) and improves protonation energetics along the NO₃ ^- to NH₃ pathway. This study demonstrates that electron-transfer engineering via POM-metal-hybrid systems delivers a 24.1-39.3% enhancement in NH₃ FE compared to a POM-only catalyst. The core mechanism lies in the electron transfer effect between POM and metal components: this effect optimizes the electronic structure of reaction active sites, suppresses the competitive hydrogen evolution reaction, and thus improves the selectivity of NH₃ generation. This work provides a concrete strategy for high-performance POM-based electrocatalysts and advancessustainable ammonia production.