Dual-mode in situ monitoring of CO2 conversion via pH indicator and UV-vis spectroscopy

The integration of the KHCO 3 -fed bipolar membrane (BPM) electrolyzer with potassium hydroxide (KOH)-based carbon dioxide (CO 2 ) capture enables directly in situ conversion of captured CO 2 into valuable carbonaceous products, eliminating costly CO 2 recovery and compression steps. Even this integrated BPM system assembly holds promise; the critical lack of CO 2 adsorption intermediate species tracking necessitates the development of a monitoring platform. This work pioneers a novel dual-modal strategy employing simultaneous indicator-based sensing with in situ ultraviolet-visible (UV-vis) spectroscopy, achieving real-time visualization of triphasic dynamics during integrated CO 2 capture-regeneration-conversion. Within this synergistic process involving Ar-saturated KHCO 3 decomposition and electrochemical reduction, an etched indium (In) catalyst achieves 50% formate Faradaic efficiency (FE) at −1.1 V vs. RHE (reversible hydrogen electrode). The synergistic application of these complementary in situ diagnostics unlocks fundamental mechanistic insights into integrated CO 2 capture and conversion systems, establishing them as critical enablers for advancing efficient and scalable electrochemical CO 2 valorization.