Estimating the thermal conductivity and diffusion coefficient of the microporous layer of polymer electrolyte membrane fuel cells

Investigation of the role in which the microporous layer (MPL) affects the overall diffusion of gases and conduction of heat in polymer electrolyte membrane (PEM) fuel cells is of great interest. In this study, we used stochastic models to generate a three-dimensional reconstruction of the MPL. This work is a continuation of the methods presented in [10]. A parametric study was carried out to investigate the effects of the MPL structure and MPL porosity on its diffusion coefficient and thermal conductivity. It was found that increasing the volume of the small pores of the MPL while keeping its overall porosity constant results in an increase in the Knudsen diffusion; hence a decrease of the overall diffusion coefficient. This similar trend is observed again once the porosity of the MPL is decreased. An increase in the volume of small pores also resulted in an increase of the thermal conductivity of the MPL. The parametric study was also extended to understand the effect of applying the MPL onto the gas diffusion layer (GDL). In this case, we investigated the effect of MPL thickness, porosity and its penetration into the GDL. The effect of the thickness on the thermal conductivity and diffusion coefficient of an MPL/GDL assembly can be explained using a resistance network. An increase in the penetration depth of the MPL results in an increase of the thermal conductivity and a decrease of the diffusion coefficient.