Polyoxometalate as Hydrogen–Electron Hub in Metal–Organic Complex for Electrocatalytic Nitrate Reduction to Ammonia
Qiushuang Jiang, Xinming Wang, Shengji Tian, Haijun Pang, Yongbin Song, Huiyuan Ma
Abstract
ABSTRACT Electrocatalytic nitrate reduction to ammonia (ENRA) is a sustainable strategy for decentralized ammonia synthesis and wastewater purification, but its efficiency in neutral media is limited by slow water dissociation and insufficient active hydrogen (*H) supply. Herein, we address this challenge through the rational design of chain‐like polyoxometalate‐based metal–organic complexes that feature dinuclear ([M(H 2 O) 2 C 20 O 2 N 4 H 11 ] 4 [SiW VI 12 O 40 ], M‐SiW 12 ‐1D) and trinuclear ([M 1.5 (H 2 O) 2 C 20 O 3 N 4 H 11 ] 4 [PW VI 7 W V 5 O 40 ], M‐PW 12 ‐1D) architectures (M = Ni, Co, Fe) that create continuous electron channels. Among them, trinuclear Ni‐PW 12 ‐1D exhibits exceptional ENRA performance in neutral electrolytes, delivering a very high Faradaic efficiency of 95.0% and a remarkable ammonia yield rate of 16.9 mg h −1 mg cat. −1 at −1.2 V vs. RHE. In situ Fourier‐transform infrared spectroscopy, differential electrochemical mass spectrometry, and density functional theory calculations are used to elucidate the synergistic mechanism operating in this system: polyoxometalate (POM) moieties promote water dissociation to generate *H that migrates to metal–organic reaction sites. Meanwhile, electron transfer from the POM to the metal cluster enhances the adsorption of the nitrate intermediate and lowers the energy barrier of the rate‐determining step (NO → *NOH). This synergy balances hydrogenation and suppresses the competing hydrogen evolution reaction, providing insights into multinuclear cluster structure–activity relationships for sustainable nitrogen cycling.