Electrolyte engineering for efficient molten-carbonate electrolysis of CO2

Molten carbonate electrolysis cells (MCEC) are a promising electrochemical CO 2 capture and conversion process. However, the CO 2 absorption and energy efficiencies are limited by the sluggish CO 2 absorption kinetics and high electrode overpotentials. Herein, we propose an electrolyte engineering strategy to improve the CO 2 absorption rate and reduce overpotentials at both the anode and the cathode. When BO 3 3− was added into molten Li 2 CO 3 -Na 2 CO 3 -K 2 CO 3 , the CO 2 adsorption efficiency was improved from 3.3% to 60%, the overpotential was reduced by ∼ 567 mV at the cathode and by ∼ 238 mV at the anode under 200 mA cm −2 . Accordingly, the energy efficiency reached 76.2 % at 650 °C. The improved CO 2 absorption and energy efficiencies are thanks to the BO 3 3− that changes the thermodynamic properties of the molten carbonate, i.e., the BO 3 3− –CO 3 2− complex reduces the energy barrier for the reduction of CO 3 2− at the cathode and for the liberation of O 2− that can be oxidized at a lower potential than CO 3 2− at the anode. Therefore, the electrolyte engineering is an effective strategy for designing high-temperature CO 2 electrolyzers with high CO 2 absorption and energy efficiency.