Synergistic defect ensembles in Cu catalysts for CO2 electroreduction: An integrated perspective on synthesis, characterization, and performance

The excessive consumption of fossil fuels globally has led to a sharp increase in atmospheric carbon dioxide (CO 2 ) concentration (exceeding 420 ppm by 2023), resulting in urgent issues related to the greenhouse effect and ecological imbalance. Electrochemical CO 2 reduction (CO 2 RR) technology offers a sustainable pathway toward carbon neutrality by converting CO 2 into value-added carbon-based fuels ( e.g. , ethylene and ethanol) and chemical feedstocks. Copper (Cu)-based catalysts, distinguished by their unique capability to facilitate carbon monoxide intermediate (∗CO) coupling, remain the only metallic materials capable of efficient C 2+ product synthesis. However, their intrinsic activity is constrained by limitations such as high overpotential, low selectivity, and insufficient stability. Defect engineering provides a powerful atomic-scale strategy to address these challenges. Unlike previous reviews that focus on isolated defect categories, this review presents a systematic analysis of the full defect spectrum including vacancies, doping, grain boundaries, and lattice strain, with emphasis on their synergistic interplay. We establish a unified framework demonstrating how diverse defect types converge on modulating the d-band center and ∗CO surface coverage, the two decisive descriptors for C 2+ selectivity. By integrating in situ characterization techniques and theoretical computations, we elucidate the structure-activity relationships between defect sites and the adsorption energies of key intermediates ( e.g. , ∗COOH and ∗CO), and analyze the influence of defect density/distribution on C-C coupling efficiency. Furthermore, we highlight applications of advanced characterization methods ( e.g. , synchrotron radiation and spherical aberration-corrected transmission electron microscopy) in studying the dynamic evolution of defects. We elucidate structure-activity relationships between defect configurations and intermediate adsorption energetics, while bridging atomic-level design with industrial performance requirements. We posit that the synergistic integration of multiple defect types represents the critical frontier for achieving industrial-level C 2+ production from CO 2 electroreduction. This review provides a theoretical foundation and practical roadmap for rational design of next-generation CO 2 RR catalysts.