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

Abstract

CO₂ dissolved in aqueous solutions CO₂(aq) is important to CO₂ capture, storage, photo-/electroreduction in the fight against global warming and to CO₂ analysis 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 CO₂ molar 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 KHCO₃ electrolytes with CO₂(aq) > ~1 M, CO₂ electroreduction (CO₂RR) to formate reached >98% Faradaic efficiencies on copper (Cu₂O/Cu)-based electrocatalyst. Furthermore, CO₂ dissolution/desolvation kinetics showed large hysteresis and ultraslow reversal of CO₂(aq) supersaturation in aqueous systems, with implications to CO₂ capture, storage, and supersaturation phenomena in natural water bodies.