Electrolyte engineering for efficient molten-carbonate electrolysis of CO2

Abstract

Molten carbonate electrolysis cells (MCEC) are a promising electrochemical CO2 capture and conversion process. However, the CO2 absorption and energy efficiencies are limited by the sluggish CO2 absorption kinetics and high electrode overpotentials. Herein, we propose an electrolyte engineering strategy to improve the CO2 absorption rate and reduce overpotentials at both the anode and the cathode. When BO33− was added into molten Li2CO3-Na2CO3-K2CO3, the CO2 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 CO2 absorption and energy efficiencies are thanks to the BO33− that changes the thermodynamic properties of the molten carbonate, i.e., the BO33−–CO32− complex reduces the energy barrier for the reduction of CO32− at the cathode and for the liberation of O2− that can be oxidized at a lower potential than CO32− at the anode. Therefore, the electrolyte engineering is an effective strategy for designing high-temperature CO2 electrolyzers with high CO2 absorption and energy efficiency.