Modeling electrochemical CO2 reduction at silver gas diffusion electrodes using a TFFA approach

A spatially resolved mathematical model for low temperature electrochemical CO2 reduction (eCO(2)R) at silver gas diffusion electrodes is presented and validated using flow cell measurements. The combination of experimental and model results provides novel insights regarding an inhibition of the catalyst performance by the product carbon monoxide. The developed model shows good agreement with experimental results concerning the overpotential and the Faradaic efficiency in dependence of the current density over a range of KHCO3 electrolyte concentrations (0.75-1.25 M) and CO2 fractions in the gas feed (25-100 vol.%). The model results highlight two main problems that have to be overcome to achieve a more efficient eCO(2)R process at high current densities: Firstly, the electrode performance becomes strongly limited by CO2 mass transport at higher current densities. Secondly, only around 50% of the CO2 consumed is converted electrochemically, while the remainder chemically absorbs in the electrolyte in form of carbonate and bicarbonate, resulting in a low carbon efficiency. Addressing these issues will be crucial to make eCO(2)R feasible for industrial application.