Probing dissolved CO 2 (aq) in aqueous solutions for CO 2 electroreduction and storage.

CO 2 dissolved in aqueous solutions CO 2 (aq) is important to CO 2 capture, storage, photo-/electroreduction in the fight against global warming and to CO 2 analysis in drinks. Here, we developed microscale infrared (IR) spectroscopy for in situ dynamic quantitating CO 2 (aq). The quantized CO 2 (g) rotational state transitions were observed to quench for CO 2 (aq), accompanied by increased H 2 O IR absorption. An accurate CO 2 molar extinction coefficient ε was derived for in situ CO 2 (aq) quantification up to 58 atm. We directly measured CO 2 (aq) concentrations in electrolytes under CO 2 (g) bubbling and high-pressure conditions with high spectral and time resolutions. In KHCO 3 electrolytes with CO 2 (aq) > ~1 M, CO 2 electroreduction (CO 2 RR) to formate reached >98% Faradaic efficiencies on copper (Cu 2 O/Cu)-based electrocatalyst. Furthermore, CO 2 dissolution/desolvation kinetics showed large hysteresis and ultraslow reversal of CO 2 (aq) supersaturation in aqueous systems, with implications to CO 2 capture, storage, and supersaturation phenomena in natural water bodies.