From Dopant Periodicity to Asymmetric Sites: Steering C─C Coupling in Single-Atom Alloy Catalysts for Electrochemical CO2 Reduction.

The electrochemical reduction of CO2 into multicarbon (C2⁺) products is a promising strategy for producing sustainable fuels and chemicals, but conventional Cu catalysts suffer from poor selectivity and limited efficiency. Single-atom alloys (SAAs), in which isolated dopants are incorporated into a Cu host, offer an atomic-scale platform to modulate surface chemistry. Here we report a systematic theoretical investigation of 29 Cu-based SAAs, combining grand-canonical density functional theory, surface Pourbaix diagrams, and constant-potential ab initio molecular dynamics with explicit solvation. We uncover a general non-monotonic periodic trend in adsorbate binding strength-strong → weak → strong-arising from dopant-induced perturbations of the Cu electronic structure. This universal trend provides a guiding principle: asymmetric active sites, formed by the coexistence of strong- and weak-binding motifs, enable more favorable *CO-*CO coupling and thereby enhance selectivity toward C2⁺ products. Importantly, we identify net electron transfer from dopant to host as an effective and easily computable descriptor for rapidly screening SAA candidates with low C─C coupling barriers. Guided by this framework, we highlight ScCu, VCu, ZrCu, NbCu, and TaCu as promising SAAs, exhibiting suppressed hydrogen evolution, electrochemical robustness, and efficient C─C bond formation. In particular, NbCu(111) displays a low C─C coupling barrier of 0.87 eV and a thermodynamically viable pathway to ethanol, confirmed under realistic electrolyte conditions. These findings establish atomic-scale asymmetry as a general design paradigm for advancing SAAs catalysts in CO2 electroreduction.