Electrocatalytic Reduction of CO 2 to Ethylene: Catalyst Design and Synchrotron‐Based Characterizations

ABSTRACT Electrochemical reduction of carbon dioxide (CO 2 ) to value‐added chemicals, particularly ethylene, offers a promising approach to mitigating carbon emissions while enabling renewable electricity storage in chemical form. Among various catalysts, Cu‐based materials are uniquely capable of converting CO 2 into multi‐carbon (C 2+ ) products through complex multi‐electron and multi‐proton transfer pathways. However, achieving high selectivity and efficiency remains challenging due to the intricate interplay between catalyst structure, oxidation state, local reaction microenvironment, and intermediate coverage. This review systematically discusses the reaction mechanisms of CO 2 reduction on Cu electrodes, highlighting key active sites, surface reconstructions, and the influence of morphology and oxidation states on C─C coupling pathways. Recent progress in the rational design of Cu‐based catalysts, through morphology control, interfacial engineering, alloying, and microenvironment modulation, is summarized and critically analyzed. Moreover, special emphasis is placed on synchrotron radiation‐based characterization techniques that provide element‐specific, time‐resolved in situ insights into the dynamic evolution of Cu catalysts and intermediates. These advanced methods bridge experimental and theoretical understanding, offering fundamental guidance for developing efficient, durable, and selective CO 2 ‐to‐ethylene electrocatalysts.