Electrochemical reduction of CO2 provides a promising route for sustainable production of fuels and chemicals such as multi-carbon hydrocarbons and oxygenates. While most efforts are focused on developing catalytic materials for CO2 electroreduction, it is also critical to understand other factors beyond catalytic materials such as the local environment of the catalysts, which can mediate the transport and local concentration of reaction species and influence reaction pathways. Here we present our recent study of catalyst microenvironment for CO2 electroreduction in flow cells with gas-diffusion electrodes (GDEs). For proof-of-concept, we use commercial Cu nanoparticles and homogeneously disperse polytetrafluoroethylene (PTFE) nanoparticles in the catalyst layer, which created a hydrophobic microenvironment of the Cu catalysts. The Cu/C/PTFE electrode showed a significant improvement in the activity, Faradaic efficiency, and C2+ product selectivity for CO2 reduction compared to a regular Cu/C electrode without added PTFE. Moreover, the CO2 reduction activity on the Cu/C/PTFE electrode increased with the CO2 gas flow rate, suggesting a gas-phase transport of CO2 inside the catalyst layer. The improved performance is attributed to the reduced diffusion layer thickness that accelerates CO2 mass transport, increases the local concentration of CO2 near the catalyst, and enhances CO2 adsorption for the reaction. A similar improvement in the catalytic performance was also achieved for CO2 electroreduction to formate on Bi-based catalyst with PTFE added in the GDE. Compared to regular GDEs, the electrode with added PTFE creates a balanced gas/liquid microenvironment and solid-liquid-gas interfaces inside the catalyst layer, which can enhance the mass transport and kinetics of CO2 electrolysis, providing a general approach to improve gas-involving electrocatalysis.

Improving CO2 gas-diffusion electrolysis by controlling local gas/liquid environment in the catalyst layer

ACS Spring 2022

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