Effect of CO2 Bubbling into Aqueous Solutions Used for Electrochemical Reduction of CO2 for Energy Conversion and Storage

CO2 bubbling into electrolytes is widely used for the electrochemical and photoelectrochemical reduction of CO2 as a carbon source. However, the effects of the CO2 bubbling into the electrolytes have rarely been studied and are not clear. The CO2 bubbling into different electrolytes such as KHCO3, K2CO3, KCl, and KOH was investigated in this research. The concentrations of total dissolved carbon (TC), H2CO3* (sum of dissolved CO2 and H2CO3), HCO3, and CO32 in different solutions before and after bubbling with CO2 until saturation were evaluated. The CO2 bubbling caused the pH of the electrolytes to decrease and affected the existence forms of the dissolved carbonaceous species. After bubbling with CO2, the major form of dissolved CO2 in KHCO3, K2CO3, and KOH was HCO3, while H2CO3* was the dominant species in KCl, HCl, and H2O. The ratio of H2CO3*/TC reduces as the concentration of KHCO3 increases, which is possibly the reason for the decrease of CO2 reduction by the solution of high KHCO3 concentration. Furthermore, CO2 partial pressure increasing caused by the CO2 bubbling strongly enhanced the concentration of CO2 in H2O, which is in accordance with Henrys law.