For efficient use of Pt catalyst in polymer electrolyte membrane fuel cells, the effects of cathode catalyst layer (CL) structure on the cell performance were evaluated by experiments and model analysis. CLs with various structures were fabricated and oxygen transport resistances of these CLs were measured from the limiting current densities with different total pressures. Using the experimental results and the model analysis, the contributions of resistance components for oxygen transport, in the CL pores, at the interface between gas and ionomer, and at the interface between ionomer and Pt surface, were evaluated individually. The parameters determining dominant resistances of oxygen transport such as the effective diffusion coefficient in the CL pores, the dissolution rate into ionomer, and the transfer rate at Pt surface, were also estimated. Furthermore, we discuss the method of reducing oxygen transport resistance in thin CL with low Pt loading.

To improve the performance of polymer electrolyte fuel cells (PEFC), it is important to reduce the oxygen transport resistance in the cathode catalyst layer (CL). The authors have been conducted detailed analysis of the oxygen transport resistance elements: the diffusion resistances in the CL pores, the dissolution resistance into the ionomer, and the transport resistance at the Pt surface. This study improved the method to determine the limiting current density in the analysis, and the cell performances with two types of ionomer, Nafion and Aquivion, based CLs were compared from the viewpoint of the oxygen transport resistance. It was shown that Aquivion based CLs have the lower limiting current densities than those with Nafion, while the voltage is higher in the middle current density range. The analysis suggested that this is due to the higher oxygen transport resistance at the Pt surface, caused by aggregation of Aquivion near the Pt.

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