We demonstrate a hybrid electrolyzer design for CO₂electrolysis to multicarbon products using a cation exchange membrane and different electrode separations. Reducing the thickness of the catholyte flow field from 5 to 2.4 mm significantly decreases the cell voltage while maintaining longer-term stability.

Electrochemical carbon dioxide reduction (CO2R) is an attractive route to use renewable electricity to convert CO2 emissions to carbon-based chemicals. Continuous-flow electrolyzers with gas diffusion electrodes (GDEs) allow for the CO2R at high reaction rates. In addition to the electrolyzer configuration and operating conditions, the product selectivity strongly depends on the morphology of the electrocatalyst. This study demonstrates electrodeposition of copper (Cu) catalysts as a simple and efficient approach for preparing GDEs with good control over morphology. We study the influence of the activation process of the gas diffusion layer and the electrodeposition conditions on the morphology. Four Cu GDEs with different morphologies showed distinctly different current responses and product distributions. The partial current density for ethanol (jethanol) ranged from −18 mA cm–2 to −29 mA cm–2. Depending on the Cu GDE morphology, jethylene ranged between −25 mA cm–2 and −44 mA cm–2. Although the catalyst layers revealed surface restructuring after CO2 electrolysis, the morphologies remained distinctly different and retained the crystal structure of polycrystalline Cu. Electrodeposited Cu-GDEs maintained their selectivity for 6 h at a cell voltage of 4 V, representing a 5-fold improvement compared to sputtered Cu GDEs. Overall, this study demonstrates a facile approach for preparing GDEs with control over the catalyst morphology to tune CO2R to specific gaseous and liquid products.