Hierarchical Model of Reaction Rate Distributions and Effectiveness Factors in Catalyst Layers of Polymer Electrolyte Fuel Cells

The cathode catalyst layer incurs a major proportion of the total voltage loss in a polymer electrolyte fuel cell. Objectives of the present study are to investigate how catalyst layer performance depends on electrostatic interactions between reacting protons and the charged metal phase and how these relations are affected by composition and microstructure of agglomerates as well as transport phenomena at the macro-scale. To this end, we present a hierarchical model to study structure-performance relations of cathode catalyst layers based on a refined description of the porous agglomerated morphology. The model consists of coupled relations for reactant transport, metal charging behavior, and interfacial charge transfer kinetics, considered under steady state conditions. Results of the model are evaluated by comparison with experimental data from different sources. The effectiveness factor calculated for cathode catalyst layers is 1–4% which lies in the range of experimentally found values.