Modelling the reactive transport processes in different reconstructed agglomerates of a PEFC catalyst layer

Abstract

The reactive transport processes occurred in catalyst layer of a polymer electrolyte fuel cell (PEFC) are essential to characterize the local transport resistance, which acts as an essential barrier for cost reduction. A multiscale strategy was developed to model the coupled transport behaviors of oxygen and water in different reconstructed agglomerates and the transport phenomenon of reactant species and charges in a 1-D cathode catalyst layer. The local transport resistances sensitive to the electrode structural parameters were well captured and compared with existing experimental studies and analytical expressions. Results show that the agglomerate morphology characterizing the heterogenous carbon particles and ionomer distributions can well reproduce the structure-dependent local transport resistance. The local transport resistance increases linearly with the ionomer content and ω/(1-ω) value, where ω is the platinum mass fraction in catalyzed Pt/C mixtures, and increases exponentially with the uncatalyzed volume fraction of carbon. Contribution of pores to the total electrode resistance and the oxygen transport resistance in gas diffusion layer and gas channel are critical to determine the limiting current density at high platinum loading. The mean size of primary pores increases with the proportion of primary porosity in agglomerates, which is favored to minimize the local transport resistance.