Molecular Weaving of Mixed‐Addenda Polyoxometalates into MOF Nanochannels as Electron‐Buffering Reservoirs for Enhanced Nitrate‐to‐Ammonia Electrocatalysis

Electrochemical conversion of nitrate pollutants into value-added ammonia (e-NO₃RA) offers a sustainable pathway for nitrogen valorization, yet hinges on the development of efficient electrocatalysts. Herein, we systematically synthesize a series of three V/W mixed-addenda polyoxometalate ([P₂W^VI ₁₇V^V ₁O₆₂]^7-, noted as P₂W₁₇V₁) based metal-organic frameworks [X₉(DPYB)₉(OX)₆(H₂O)₆][P₂W₁₇V₁O₆₂] denoted as XMOF-V₁ (X = Fe; Co; Zn, DPYB = 1,4-Di(pyridin-4-yl)benzene, OX = oxalic acid). The incorporation of P₂W₁₇V₁ not only reinforced structural ruggedness and stability, but also promotes multi-electron transfer, substantially promoting e-NO₃RA activity. Among them FeMOF-V₁ delivers exceptional electrocatlytic nitrat-to-ammonia performance with an achieves over 95% Faradaic efficiency across a wide voltage range of -0.6 to -1.4 V vs RHE. This superiority stems from synergistic interplay: P₂W₁₇V₁ acts as an electron reservoir enhancing proton-coupled charge transfer, while the minimal bandgap of FeMOF-V₁ facilitates directional electron injection. DFT analyses reveal Fe-specific mechanisms including strong 3d-orbital hybridization with NO₃ ^- near Fermi Level (Ef), highly positive Fe sites optimizing adsorption, and transfer weakening N-O bonds, as corroborated by in situ FTIR identification of *NO₃/*NO/*NH₂ intermediates. Together with effectively suppressed HER (ΔG_*H > ΔG_*NO3), these attributes collectively enable highly selective NH₃ synthesis. This study establishes mixed-addenda POMOFs as a versatile and efficient platform for sustainable nitrate-to-ammonia conversion.