Coordination-Asymmetry-Regulated Reconstruction of Electron-Rich Cu Sites for pH-Dependent Nitrate-to-Ammonia...

Electrocatalytic nitrate reduction reaction (e-NO₃RR) offers a promising route to valorize nitrate-contaminated wastewater while enabling sustainable ammonia production; however, how local coordination asymmetry regulates Cu-site evolution and reaction pathways across different pH environments remains insufficiently understood. Herein, three- and four-nitrogen-coordinated Cu single-atom motifs, denoted as Cu─N₃ and Cu─N₄, are constructed as well-defined pre-catalyst models to elucidate how the initial Cu coordination environment directs pH-dependent active-site reconstruction. Operando X-ray absorption spectroscopy and wavelet-transform EXAFS reveal that Cu─N₄ readily undergoes rapid reconstruction under acidic, neutral, and alkaline conditions, generating low-coordinated, electron-enriched Cu species while concomitantly inducing Cu─Cu aggregation and excessive Cu─site reduction. In contrast, Cu─N₃ displays more regulated site evolution, with limited activation under acidic conditions but progressive formation of low-coordinated Cu─N_x active structures under neutral and alkaline conditions. In situ ATR-FTIR further verifies that the dynamically evolved Cu─N₃ sites enhance nitrate adsorption, facilitate N─O bond activation, and promote the formation of hydrogenated nitrogen intermediates. These findings establish coordination-governed site evolution as a design principle for balancing productive Cu─site activation and metal-centered over-reduction, providing molecular-level guidance for the design of pH-adaptive NO₃RR catalysts.