Molten salt CO₂ capture and electrochemical transformation (MSCC-ET process) into carbon and oxygen [1] is a promising way for effectively capturing and utilizing the greenhouse gas. In the process, CO₂ is first absorbed by the molten salt to form carbonate ions and then they are reduced to carbon on the cathode. There are several advantages of the process over others: (1) high current density; (2) high selectivity and current efficiency; (3) lower decomposition potential and overpotential for both anode and cathode reaction; (4) value-added product of functional carbon; (5) simple and cost-affordable electrodes; (6) scalability; (7) environmental friendly and etc. Although electrodeposition of carbon in molten carbonates was first reported in 1960s [2], it is very recent that it becomes a research focus due to the great concern of global warming. There is some new advancement in the field either on the fundamental aspects or practical applications in recent years. Herein, we report the absorption kinetics and thermodynamics of CO₂ by molten salt under different temperature and partial pressure of CO₂ using a home-made CO₂ absorption testing system [3]. The absorption capacity of dissolved Li₂O was 0.835 mol_CO2/mol_Li2O at 723 K in Li₂O containing ternary eutectic carbonate. The mass transfer of carbonates was the dominating factor governing the rate of static absorption. The reduction mechanism of cathode and anode was evaluated by in-situ gas analyzing. There was no CO was detected at 723K over a wide potential range. The reduction kinetics of carbonate was further investigated by cyclic voltammetry and steady-state polarization curve measurements under different temperature and the rate-limiting step was determined. Furthermore, carbon materials with different morphology and composition were obtained under different electrolysis temperature, cell voltage or in different molten salts. It was found that the MSCC-ET process can not only capture CO₂ but also absorb SO₂ in flue gas. Sulfur doped carbon was obtained by using flue gas as raw material and zero SO₂ emission was realized in the process. The obtained carbons show very high specific capacitance and specific capacity as electrode materials for supercapacitor and lithium ion battery, respectively [4].

References:

[1] H.Y. Yin, X.H. Mao, D.Y. Tang, W. Xiao, L.R. Xing, H. Zhu, D.H. Wang, D.R. Sadoway, Energy Environ. Sci., 2013, 6, 1538-1545.

[2] M.D. Ingram, B. Baron, G.J. Janz, Electrochim. Acta, 1966, 11 ,1629-1639.

[3] BW Deng, JJ Tang, XH Mao., YQ Song, H Zhu, W Xiao, and DH Wang, Environ. Sci. Technol., 2016, 50, 10588–10595

[4] JJ Tang, BW Deng, F Xu, W Xiao, DH Wang, Journal of Power Source ，2017，341, 419-426