Phase-field modelling of electro-deoxidation in molten salt

Abstract

A phase-field approach is used to describe electro-deoxidation, i.e. direct electrochemical reduction of solid oxides in molten salts. Based on this description, temporal evolutions of chemical and electric potential fields are simulated numerically in one and two dimensions of a hypothetical system. The results of the simulations illustrate three distinct stages of electro-deoxidation, including a relatively rapid initial stage in which the reduction process propagates at the surface of cathode. This initial stage of ‘surface reduction’, if present, can influence the process kinetics substantially. The existence of the initial stage is shown to depend most significantly on a specific topological property of the modelled cell, namely on the connectivity of the internal boundaries between pairs of model entities, i.e. cathode, current collector and electrolyte. The preliminary results also suggest the overall kinetics of electro-deoxidation, within the examined range of parameters, to be diffusion controlled and thus independent of the initial value of the electric conductivity of oxide.