On the First Principles Calculation of Redox Potential in Molten LiCl-KCl Eutectic Based on Adiabatic Substitution

Abstract

A first principles approach based on adiabatic substitution is proposed to evaluate the redox potentials of a series of solute cations Mm + (Cu+, Au+, Tl+, Nd2+, Sc3+, Y3+, Ce3+, Pr3+, Nd3+, Gd3+, Tb3+, U3+, Pu3+, Np3+ and Am3+) in molten LiCl-KCl eutectic solvent at 723 K. A thermodynamic cycle is designed by adiabatic substitution of cation and neutral atom in molten salt with reference cation and reference neutral atom (Ag+ and Ag0 for monovalent cations, Ni2+ and Ni0 for divalent cation, and La3+ and La0 for trivalent cations) and vice versa. The redox potentials of these cations are evaluated relative to theAg+(sol)|AgCl(s)|Ag(s), Ni2 +(sol)|NiCl2(s)|Ni(s) and La3 +(sol)|LaCl3(s)|La(s) reference electrodes, respectively. Good agreements with experimental values are obtained with maximum absolute error of 0.354 V and standard deviation of 0.226 V. In addition, the first principles molecular dynamics (FPMD) is applied to the study of solvation structures of MClm in molten LiCl-KCl eutectic in terms of radial distribution functions and partial static structure factors in satisfactory agreement with X-ray and neutron diffraction characterizations. It is revealed that the solute cation affects significantly the intermediate-range order of Li+–Li+ but slightly of Cl−–Cl− and K+–K+.