In Situ Construction of Cu¹⁺/Cu⁰ and Cu²⁺/Cu⁰ Pairs of Cu-Based Catalysts for Electrocatalytic Nitrate Reduction

Electrocatalytic nitrate reduction reaction (NO₃RR) as a sustainable nitrogen cycle regulation strategy provides a new pathway to achieve carbon neutrality goals. In this study, CuO, Cu₂P₂O₇ and Cu₃(PO₄)₂ (CuPO) are synthesized as pre-catalysts via a sol-gel process for NO₃RR, in which CuO exhibits excellent NH₃ yields of 8.16 mg h^-1 mg_cat ^-1 (FE = 95.72%, -0.95 V vs. RHE) compared to Cu₂P₂O₇ (7.33 mg h^-1mg_cat ^-1, 94.88%) and Cu₃(PO₄)₂ (6.53 mg h^-1mg_cat ^-1, 92.04%). The combination of in situ Raman and XPS spectra reveal that the pre-catalyst surface is reconfigured to form stable active sites of Cu¹⁺/Cu⁰ (CuO-derived) and Cu²⁺/Cu⁰ pairs (CuPO-derived) during the NO₃RR process. Tracking the evolution of intermediates using online differential electrochemical mass spectrometry (DEMS) spectra and in situ Fourier transform infrared spectroscopy (FT-IR) spectra reveal that Cu¹⁺/Cu⁰ pairs possess rapid catalytic kinetics for the conversion of *NO₃ ^- to *NO₂ ^-. Density functional theory (DFT) calculations confirm that Cu¹⁺/Cu⁰ exhibits a lower potential-determining step, and its exceptional *H generation and enrichment capabilities promote further hydrogenation reactions, thereby achieving excellent activity and selectivity in NH₃ production via NO₃RR. This study reveals the distinct advantages of reconstructed active sites in Cu-based catalysts during NO₃RR, providing guidance for designing other advanced catalysts.