Probing dissolved CO2(aq) in aqueous solutions for CO2electroreduction and storage

Abstract

CO2dissolved in aqueous solutions CO2(aq) is important to CO2capture, storage, photo-/electroreduction in the fight against global warming and to CO2analysis in drinks. Here, we developed microscale infrared (IR) spectroscopy for in situ dynamic quantitating CO2(aq). The quantized CO2(g) rotational state transitions were observed to quench for CO2(aq), accompanied by increased H2O IR absorption. An accurate CO2molar extinction coefficient ε was derived for in situ CO2(aq) quantification up to 58 atm. We directly measured CO2(aq) concentrations in electrolytes under CO2(g) bubbling and high-pressure conditions with high spectral and time resolutions. In KHCO3electrolytes with CO2(aq) > ~1 M, CO2electroreduction (CO2RR) to formate reached >98% Faradaic efficiencies on copper (Cu2O/Cu)–based electrocatalyst. Furthermore, CO2dissolution/desolvation kinetics showed large hysteresis and ultraslow reversal of CO2(aq) supersaturation in aqueous systems, with implications to CO2capture, storage, and supersaturation phenomena in natural water bodies.