Role of Ion-Selective Membranes in the Carbon Balance for CO2 Electroreduction via Gas Diffusion Electrode Reactor Designs
<p></p><p></p><p>In this work, the effect of ion-selective membranes on the detailed carbon balance was systematically analyzed for high-rate CO<sub>2</sub> reduction in flow electrolyzers. By using different ion-selective membranes, we show nearly identical catalytic selectivity for CO<sub>2</sub> 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 CO<sub>2</sub> at the cathode/catholyte interface via reaction with OH<sup>-</sup> when using different ion-selective membranes: (i) the captured CO<sub>2</sub> could transport through an anion exchange membrane in the form of CO<sub>3</sub><sup>2-</sup>, subsequently releasing CO<sub>2</sub> along with O<sub>2</sub> in<sub> </sub>the anolyte, (ii) with a cation exchange membrane, the captured CO<sub>2</sub> would be accumulated in the catholyte in the forms of CO<sub>3</sub><sup>2-</sup>, (iii) whereas under the operation of a BPM, the captured CO<sub>2</sub> could be released at the catholyte/membrane interface in the form of gaseous CO<sub>2</sub>. The unique carbon balance path for each type of membrane is linked to ion species transported through membranes.</p><p></p><p></p>