An isothermal model of a laboratory intermediate temperature fuel cell using PBI doped phosphoric acid membranes

A two-dimensional isothermal model is described for an intermediate temperature fuel cell using a phosphoric acid doped polybenzimidazole (PBI) membrane. The model considered the membrane-electrode-assembly and gas flow channels. All the major transport phenomena were taken into account except the cross-over of species through the membrane. The catalyst layers were treated as spherical catalyst agglomerates with porous inter-agglomerate spaces. The inter-agglomerate spaces are filled with a mixture of electrolyte (hot phosphoric acid) and polytetrafluoroethylene (PTFE). The model was validated against experimental data and used to study the influence of the catalyst layer properties on performance. Through the analyses of the effectiveness factor the model showed that utilisation of catalyst particles was very low at high current densities. At these conditions, the reaction occurs mainly on the surface of the agglomerate. An optimum phosphoric acid loading was found from the model simulations. The model was also used to demonstrate the resistance of the intermediate temperature fuel cell to anode poisoning by CO.