To reduce the use of platinum in polymer electrolyte fuel cells (PEFCs), it is important to reduce the oxygen transport resistance in the cathode catalyst layer (CL). The oxygen transport resistance in the CL can be divided into diffusion resistance in the vacancies of the CL and transport resistance through ionomers. In this study, we focused on the resistance through ionomers, which is expected to be dominant in the low Pt CLs. CLs with low Pt loadings were fabricated, and the effects of I/C, weight ratio of ionomer to carbon in the CL, on the oxygen transport resistances were investigated. First, similar structures of CL with the same I/C were confirmed regardless of the thickness. Then, the oxygen transport resistance was experimentally evaluated using the low Pt CLs. It was shown that the lower the I/C, the smaller the value of pressure-independent resistance, which mainly corresponds to the oxygen transport resistance in the CL. The electrochemical effective reaction area (ECSA) was also measured for further discussion, and the results showed that the ECSA values tend to decrease as the I/C decreases.
MATSUSHIRO et al. (Wed,) studied this question.