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 ([P2WVI 17VV 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.