Study on Diffusion Dynamics of O2- in Molten CaCl2 for Molten Salt Electrolysis

Full-atom models of O2-/CaCl2 were constructed and the systems were described by Born-Mayer-Huggins (BMH) potential function to investigate the diffusion dynamic behavior of O2- in CaCl2 molten salt based on molecular simulations. The results show that the calculated diffusion coefficient of O2- at 1073 K is about 2.01×10-5 cm2/s, which is consistent with the reported value of Ferro's literature. At the same time, the diffusion coefficient of O2- is closely related to temperatures. When the temperature increases to 1473 K, the diffusion coefficient of O2- is 5.66×10-5 cm2/s. The activation energy for diffusion of O2- in CaCl2 molten salt is 15.6 kJ/mol by fitting diffusion coefficients at various temperatures. In terms of the microstructure, Ca2+ can form a positive coordination layer to inhibit the diffusion of O2- due to the electrostatic attraction. The energy barrier that O2- needs to escape from the Ca2+ coordination layer is about 1.7 J. This article not only reveals the diffusion dynamic behaviors of O2- in CaCl2, but also provides guide for the research of molten salt compounds by computer simulation. © 2021, Science Press. All right reserved.