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

The integration of the KHCO3-fed bipolar membrane (BPM) electrolyzer with potassium hydroxide (KOH)-based carbon dioxide (CO2) capture enables directly in situ conversion of captured CO2 into valuable carbonaceous products, eliminating costly CO2 recovery and compression steps. Even this integrated BPM system assembly holds promise; the critical lack of CO2 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 CO2 capture-regeneration-conversion. Within this synergistic process involving Ar-saturated KHCO3 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 CO2 capture and conversion systems, establishing them as critical enablers for advancing efficient and scalable electrochemical CO2 valorization.