Orchestrated electron transfer in reduced polyoxometalate-based coordination architectures for facilitating...

The electrochemical nitrate reduction to ammonia (ENRA) process is critically hindered by sluggish multistep proton/electron transfer kinetics, limiting its practical viability for sustainable ammonia (NH₃) synthesis. To address this challenge, we designed a bioinspired family of polyoxometalate (POM)-based crystalline electrocatalysts-(HNCP)₂[M(H₂O)₃]₂[MMo₁₂(HPO₄)₄(PO₄)₄O₃₀] (where HNCP = 2-(4-carboxyphenyl)imidazo(4,5-f)(1,10) phenanthroline and M = Ni, Co, or Fe; denoted as M-P₄Mo₆)-by mimicking the cluster geometry and proton-coupled electron transfer (PCET) dynamics of natural nitrate reductase (NR) for the efficient conversion of nitrate (NO₃^-) to NH₃. Among them, Ni-P₄Mo₆ demonstrates highly effective ENRA performance, achieving a Faradaic efficiency (FE) of 91.0 % at -1.2 V vs. reversible hydrogen electrode (RHE) and an NH₃ yield rate of 7.4 mg h^-1 mg^-1_cat. at -1.3 V vs. RHE. In situ Fourier transform infrared spectroscopy (in situ FTIR) captures critical nitrogen valence transitions (N⁵⁺ → N^-3). Density functional theory (DFT) calculations reveal a collaborative mechanism: directional electron delocalization from the POM skeleton to the Ni center synergistically optimizes the d-band electronic structure, reducing the energy barrier of *NO₃ adsorption (*denotes the adsorbed state, Gibbs free energy (ΔG) = 0.13 eV) and effectively suppressing hydrogen evolution. In this work, we establish a universal electronic structure engineering paradigm for designing high-efficiency POM electrocatalysts, opening new avenues for sustainable NH₃ synthesis.