Lawrence Berkeley National Laboratory

Bicarbonate electrolyzers are devices designed to convert CO2 captured from point sources or the atmosphere into chemicals and fuels without needing to first isolate pure CO2 gas. We report here an experimentally validated model that quantifies the reaction chemistry and mass transfer processes within the catalyst layer and cation exchange membrane layer of a bicarbonate electrolyzer. Our results demonstrate that two distinct chemical microenvironments are key to forming CO at high rates: an acidic membrane layer that promotes in situ CO2 formation and a basic catalyst layer that suppresses the hydrogen evolution reaction. We show that the rate of CO product formation can be increased by modulating the catalyst and membrane layer properties to increase the rate of in situ CO2 generation and transport to the cathode. These insights serve to inform the design of bicarbonate and BPM-based CO2 electrolyzers while demonstrating the value of modeling for resolving rate-determining processes in electrochemical systems.