A general descriptor for guiding the electrolysis of CO2 in molten carbonate

Molten carbonate is an excellent electrolyte for the electrochemical reduction of CO2to carbonaceous materials.However,the electrolyteelectrode-reaction relationship has not been well understood.Herein,we propose a general descriptor,the CO2activity,to reveal the electrolyteelec trode-reaction relationship by thermodynamic calculations and experimental studies.Experimental studies agree well with theoretical predictions that both cations(Li+,Ca2+,Sr2+and Ba2+) and anions(BO2-,Ti5O148-,SiO32-) can modulate the CO2 activity to control both cathode and anode reactions in a typical molten carbonate electrolyzer in terms of tuning reaction products and overpotentials.In this regard,the reduction of CO32-can be interpreted as the direct reduction of CO2generated from the dissociated CO32-,and the CO2activity can be used as a general descriptor to predict the electrode reaction in molten carbonate.Overall,the CO2activity descriptor unlocks the electrolyte-electrodereaction relationship,thereby providing fundamental insights into guiding molten carbonate CO2electrolysis.