Synergistic enhancement of nitrate-to-ammonia conversion and supercapacitor performance by binuclear copper-modified...

The design of electrode materials that combine high efficiency and low cost to effectively reduce environmental pollution and energy consumption represents a core challenge. Herein, a binuclear copper-modified Keggin-type Polyoxometalate (POM) complex based on 1,4-cby ligand (1,4-cby = 1-(4-carboxybenzyl)-4,4'-bipyridine chloride), namely [Cu₂(1,4-cby)₂(1,4-Hcby)₄(H₂O)₂(GeMo₁₂O₄₀)₂]·3H₂O (Cu-GeMo₁₂) is synthesized under hydrothermal conditions by utilizing Keggin POMs, renowned as "electron sponges", and binuclear copper complex with excellent catalytic activity. Notably, Cu-GeMo₁₂ achieves an outstanding NH₃ yield rate of 14.26 mg h^-1 mg_cat^-1 and a high Faradaic efficiency of 94.06%, significantly surpassing its mononuclear analogue [Cu(1,4-Hcby)₄]H₃(GeMo₁₂O₄₀)₂ (NH₃ yield rate of 7.73 mg h^-1 mg_cat^-1 and Faradaic efficiency of 59.83%). Integrated results from in situ Fourier-transform infrared, cyclic voltammetry, and density functional theory calculations reveal that the excellent nitrate-to-ammonia reduction performance of Cu-GeMo₁₂ stems from the continuous electron supply from the POM cluster to the binuclear copper centers, along with the redox-mediating role of the copper sites in promoting the stepwise reduction of nitrogen-containing intermediates. Furthermore, Cu-GeMo₁₂ demonstrates remarkable pseudocapacitive behavior, delivering a high specific capacitance of 1385.09 F·g^-1 and retaining 97.27% of its initial capacitance after 5000 cycles. This work provides a novel design strategy for developing POMs functionalized with binuclear metal centers, offering a promising route toward bifunctional materials for applications in electrocatalysis and energy storage.