Catalyst Ink Preparation Matters for Electrocatalytic Carbon Dioxide Reduction

Electrocatalytic CO2 reduction (CO2R) offers a promising pathway for closing the carbon cycle. Metallic Cu-based catalysts are the only materials capable of converting CO2 to C2+ products with significant selectivity and activity. Achieving industrially relevant current densities in CO2R requires the use of gas diffusion electrodes (GDEs), making the structure and properties of the catalyst layer (CL) on GDEs critical to the CO2R performance of Cu catalysts. However, limited research has explored how catalyst ink composition affects CL features and, consequently, CO2R performance under operating conditions. In this study, we investigate the influence of catalyst ink composition on CL structure and morphology, and how these properties affect CO2R performance. We find that the water content in the ink modifies active site density, thickness, and porosity of the CL, as well as the state of the Nafion binder, thereby altering the microenvironment of the active sites during CO2R, including local CO2 concentration and pH. Our results reveal a strong correlation between CO2R performance and the structural characteristics of the CL. Specifically, optimizing the ethanol-to-water ratio in the catalyst ink enhances C2+ product selectivity and current density to 75 % and 450 mA cm(-2), respectively. This approach provides a simple yet effective strategy to improve CO2R activity and selectivity under practical conditions.