<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>