Role of ion-selective membranes in the carbon balance for CO(2) 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 CO(2) reduction in GDE-type flow electrolyzers. By using different ion-selective membranes, we show nearly identical catalytic selectivity for CO(2) 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 dynamic change of electrolyte speciation, we demonstrate the explicit discrepancy in carbon balance paths for the captured CO(2) at the cathode/catholyte interface via reaction with OH(−) when using different ion-selective membranes: (i) the captured CO(2) could be transported through an anion exchange membrane in the form of CO(3)(2−), subsequently releasing CO(2) along with O(2) in the anolyte, and (ii) with a cation exchange membrane, the captured CO(2) would be accumulated in the catholyte in the form of CO(3)(2−), while (iii) with the use of a bipolar membrane, the captured CO(2) could be released at the catholyte/membrane interface in the form of gaseous CO(2). The unique carbon balance path for each type of membrane is linked to ion species transported through the membranes.