Coordination‐Asymmetry‐Regulated Reconstruction of Electron‐Rich Cu Sites for pH‐Dependent Nitrate‐to‐Ammonia Electrocatalysis

Abstract

ABSTRACT Electrocatalytic nitrate reduction reaction ( e‐ NO 3 RR) 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─N 3 and Cu─N 4 , 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─N 4 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─N 3 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─N 3 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 NO 3 RR catalysts.