Modelling of electroreduction of porous oxides in molten salt

► We model the role of porosity and metallic particles on electroreduction of oxides. ► We use phase field approach to describe metal/oxide interfaces. ► There is an optimum porosity value to achieve high reduction rate. ► Metallic particles distributed in oxide have not considerable effect on reduction rate. A numerical model has been used to investigate the role of porosity, as well as the initial metallic content, in the kinetics of the direct electroreduction process. Equations of electrical charge transfer, interfacial reactions, and diffusion of oxygen in cathode are solved for a model system, with different levels of porosity. The results show that the overall reaction kinetics is an outcome of the interplay between oxygen diffusion and charge transfer. It has been found that increasing the porosity up to certain level accelerates the reduction process, resulting in lower reduction times, while further increase of porosity may lead to imperfect reduction. The numerical results thus imply existence of an optimum porosity level for real systems. Also, analysis of metal/oxide mixtures suggests that addition of metallic particles to the cathode has a positive effect only on the initial reduction rate.