Role of Ion-Selective Membranes in the Carbon Balance for CO2 Electroreduction via Gas Diffusion Electrode Reactor Designs

In this work, the effect of ion-selective membranes on the detailed carbon balance was systematically analyzed for high-rate CO₂ reduction in flow electrolyzers. By using different ion-selective membranes, we show nearly identical catalytic selectivity for CO₂ reduction, which is primarily due to a similar local reaction environment created at the cathode/electrolyte interface via the introduction of a catholyte layer. In addition, based on a systematic exploration of gases released from electrolytes and the dynamical change of electrolyte speciation, we demonstrate the explicit discrepancy in carbon balance paths for the captured CO₂ at the cathode/catholyte interface via reaction with OH^- when using different ion-selective membranes: (i) the captured CO₂ could transport through an anion exchange membrane in the form of CO₃^2-, subsequently releasing CO₂ along with O₂ in the anolyte, (ii) with a cation exchange membrane, the captured CO₂ would be accumulated in the catholyte in the forms of CO₃^2-, (iii) whereas under the operation of a BPM, the captured CO₂ could be released at the catholyte/membrane interface in the form of gaseous CO₂. The unique carbon balance path for each type of membrane is linked to ion species transported through membranes.