Mesostructure Engineering of Copper Catalyst Layers for Enhanced Ethylene Production in Electrochemical Reduction of Carbon Dioxide

To realize efficient CO ₂ electroreduction, it is important to regulate “beyond catalyst” factors, including the diffusional contribution, which reflects local partial pressures of the CO ₂ reactant and the key intermediate, CO, at the three‐dimensional porous electrode under industrially relevant conditions (e.g., at current density exceeding 200 mA cm ⁻² ). Structural parameters of the catalyst layers, such as porosity, thickness, and pore size, play a decisive role in determining selectivity and CO ₂ conversion rates, as they directly control mass transport within the electrode. This study systematically investigates the impact of the mesostructure of Cu catalyst layers originating from CuO _x precursor nanoparticles with flake‐, leaf‐, and sphere‐like morphologies, as well as their combinatorial assemblies. The maximum CO ₂ conversion rate and CO ₂ electroreduction selectivity varied greatly with catalyst particle morphology and mesoscopic catalyst‐layer properties, including void architectures and pathways for gaseous molecules. Even with Cu alone, variations in electrode mesostructure substantially modulate CO ₂ mass transfer and local CO concentration, highlighting the critical role of mesoscale architecture in determining CO ₂ reduction kinetics and selectivity. Based on these insights, we developed a tandem catalyst layer to improve ethylene productivity.