Self‐Tandem Catalysis of Unsaturated Cu with Dual Active Sites for Efficient Ammonia Electrosynthesis

ABSTRACT Tuning the adsorption behavior of key reaction intermediates is the crucial pathway for optimizing the performance of Cu‐based catalysts in electrochemical nitrate reduction to ammonia. Constructing tandem catalytic sites by alloying to regulate the adsorption properties of nitrate and protons is regarded as a key approach to enhancing the performance of NH 3 ‐oriented conversion. However, constructing the self‐tandem catalytic sites merely on the Cu surface remains a challenge. Here, we report a Cu‐based catalyst featuring unsaturated defect sites on its surface. This catalyst achieves an NH 3 Faradaic efficiency approaching 92.37% and a production rate of 2.0 mmol cm −2 h −1 at −0.4 V versus the reversible hydrogen electrode. Through electrokinetic analysis, in situ spectroscopic investigation, and theoretical calculations, we reveal that this catalyst realizes efficient self‐tandem catalysis via its dual active sites, in which the Cu(111) facet serves as the active site for selective nitrate adsorption, while the engineered surface unsaturated defect sites promote water activation to supply protons. This synergistic effect not only optimizes the proton‐coupled electron transfer step (identified as the rate‐determining step) but also balances the surface coverage of nitrate and protons. These findings hold significant guiding implications for designing effective Cu‐based self‐tandem catalytic sites in electrochemical nitrate reduction.