Various CO₂-to-CO Electrolyzer Cell and Operation Mode Designs to avoid CO₂-Crossover from Cathode to Anode

Abstract

Abstract The electrochemical CO 2 reduction reaction (CO 2 RR) towards CO allows to turn CO 2 and renewable energy into feedstock for the chemical industry. Previously shown electrolyzers are capable of continuous operation for more than 1000 h at high faradaic efficiencies and industrially relevant current densities. However, the crossover of educt CO 2 into the anode gas has not been investigated in current cell designs: Carbonates (HCO 3 − and CO 3 2− ) are formed at the cathode during CO 2 RR and are subsequently neutralized at the anode. Thus, CO 2 mixes into the anodically evolved O 2 , which is undesired from commercial perspectives. In this work this chemical transport was suppressed by using a carbonate-free electrolyte. However, a second transport mechanism via physically dissolved gases became apparent. A transport model based on chemical and physical absorption of CO 2 and O 2 will be proposed and two solutions were experimentally investigated: the use of an anode GDL (A-GDL) and degassing the anolyte with a membrane contactor (MC). Both solutions further reduce the CO 2 crossover to the anode below 0.1 CO 2 for each cathodically formed CO while still operating at industrially relevant current densities of 200 mA/cm 2 .