Theoretical analysis of the effect of isotropy on the effective diffusion coefficient in the porous and agglomerated phase of the electrodes of a PEMFC

Abstract

Abstract In polymer membrane fuel cells (PEMFC), the pore microstructure and the effective diffusion coefficient (\({D}_{eff}\)) of the catalytic layer have a significant impact on the overall performance of the fuel cell. In this wok, numerical methods to simulate PEMFC catalytic layers were used to study the effect of isotropy (\({I}_{xy}\)) on the \({D}_{eff}\). The proposed methodology studies reconstructed systems by Simulated Annealing (SA) imaging with different surface fractions of microstructures composed by two diffusive phases: agglomerates and pores. The \({D}_{Eff}\) is determined numerically by the Finite Volume Method (FVM) solved for Fick's First Law of Diffusion. The results show that the proposed methodology can effectively quantify the effect of isotropy on the \({D}_{eff}\) for both diffusion phases. Two trends were obtained in the magnitude of the \({D}_{eff}\) concerning the change in isotropy: a) when the surface fraction is more significant than 50%, the \({D}_{eff}\) decreases linearly at the beginning and exponentially at the end of the isotropy change, which indicates that small changes in isotropy in the particulate material modify it drastically. b) When the surface fraction is less than 50%, the \({D}_{eff}\) decreases exponentially at the beginning and linearly at the end of the isotropy change, which shows that small isotropy changes in the bar-aligned material drastically alter it. The proposed methodology can be used as a design tool to improve the mass transport in porous PEMFC electrodes.