Pfsi

Fig.2 2D-Schematic internal structure of the catalyst layers.

outside the agglomerates of AB were covered with the PFSI in the catalyst layer. Furthermore, AB has smaller pore volume on the surface of carbon primary particles.4 Pt particles in those pores are out of contact with the PFSI. The active surface area and the Pt utilization of the cell with AB were higher than that with AB18.

Effect of the preparation method of the catalyst layer on the cell performance. — The polarization curves of the cells in table 1 are shown in Fig. 3. The performance of the cell C was inferior to that of the cell A. Though the carbon support was optimized, the cell with lowered Pt loading did not achieve the sufficient performance. The preparation method was improved with AB in order to increase the reaction area. The performance of the cell D was superior to that of the cell A. The current densities at 850 mV(IR free) of the cell C and D were 9 mA/cm" and 11.5 mA/cm2, respectively. Furthermore, the voltage at 1200 mA/cm2 of the cell D was equal to that of the cell B. In the EPMA line analysis of the cross section of M&E assemblies, the thickness of the catalyst layer of the cell B and D were about 45 and 50 pm. The Pt content of Pt-C with 0.1 mgPt/cm2 was lower than that with 0.5 mgPt/cm" . The reaction area increased and the supply of the reaction gases to the reaction sites were improved even the thickness of the catalyst layer kept unchanged. In the previous method the PFSI colloid coagulated before being adsorbed immediately on Pt-C. While in the improved method the PFSI solution was dropped into the mixture of Pt-C and butyl acetate. The PFSI colloid right after formation was adsorbed on Pt-C before coagulation and dispersed on Pt-C finely. The thickness of the PFSI on Pt particles got thinner due to the high dispersion of the PFSI on Pt-C. Consequently, the high performance of the cell with ultra low Pt loading was achieved.

Table 1 Specification of the cells.

cell

Pt loading mg/cm2

carbon support

preparation method

0 0

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