Ions Transport Of Electrolyte Solution In Porous Electrode:a Numerical Simulation

In this work, solute transport model of soil porous media was used to investigate theions transport in electrode porous media. MIM model was used to analyze the influence ofporosity, adsorption constant, mass transfer coefficient, etc. on the ions transport propertiesin electrode porous media. The existing researches generally adopt ADE model to simulatethe process of solute transport. However, the simulation results of ADE model deviate fromthe actual situation, the main deviations contains two aspects as follows:Firstly, the solute density peak value at the sample point achieved by ADE simulationis less than the actual situation, and the time required to reach the peak value is less than theactual situation.Secondly, the density curve of ADE simulation is roughly symmetrical, but the actualdensity evolution shows an obvious trailing behavior.Analysis show that ignoring the effect of adsorption is the main reason causing thesephenomena. Solute would adsorb on the internal pore surface of the porous media, the soluteadsorbed by the internal pore surface may be taken away by solvent or diffuse into thesolution. The adsorption of solute would delay the solute transport, result in the trailingbehavior. So the other model—MIM model was adopted in numerical simulation. MIMmodel couples Darcy law and solute transport equation. Liquid phase is divided into twodomains in MIM model: mobile domain and immobile domain. Diffusion mechanismdominates the solute transport between the mobile and immobile domains and the diffusionrate is in proportion with concentration difference. The simulation results of MIM model aresimilar to the actual situation. Moreover, the effect of the fraction mobile liquid, masstransfer coefficient, and the adsorption coefficient on the properties of solute transport isalso discussed in this paper.Numerical simulation of ions transport of electrolyte solution in porous electrode wasconducted using MIM model. The influence of the porosity and thickness of catalyst layerand diffusion layer on the battery performance was analyzed in detail. The results show thatthe thickness and porosity of catalyst layer have little influence on the battery performance,since catalyst layer is thin and the transport resistance is usually small; the thickness andporosity of diffusion layer have a significant impact on the battery performance, so it isimportant to choose a proper thickness of diffusion layer based on the other factors toachieve a better performance; the current density is in proportion to the porosity of diffusionlayer, big porosity can reduce the transport resistance and promote the battery performance, meanwhile aggravate the solute channeling between the catalyst layer and diffusion layer, soit is necessary to select a proper porosity.