| Summary: | In automotive applications, when proton exchange membrane fuel cells (PEMFCs) are subjected to frequent startup-shutdown cycles, a significant drop in performance is observed. One reason for this drop in performance is oxidation of the carbon in the catalyst layer when cathode potential excursions as high as 1.5V are observed. In this work, non-carbon based catalyst support materials were studied. The materials investigated include: tungsten carbide (WC), tungsten oxide (WOx), and niobium (Nb) or tungsten (W) doped titania.
Platinum was dispersed on commercial samples of WC and WOx. Stability tests were performed by stepping the materials between 0.6 to 1.8V. Higher stability of both WC and WOx was observed compared to carbon based commercial catalyst (HiSpec 4000). The performance of Pt supported on WC or WOx was found to be lower than that of Pt/C due to poor dispersion of Pt on these low surface area commercial powders.
High surface area Nb and W doped titania materials synthesized using sol-gel techniques were subjected to several heat treatments and atmospheres, and their resulting physical properties characterized. The materials’ phase changes and their impact on electrical conductivity were evaluated. W doped titania was found to be resistive, and for Nb doped titania, the rutile phase was found to be more conductive than the anatase iii phase. Conventionally, 10-50 wt% Pt is supported on carbon, but as the non-carbon catalyst support materials have different densities, similar mass ratios of catalyst to support will not result in directly comparable performances. It is recommended that the ratio of Pt surface area to the support surface area should be similar when comparing Pt
supported on carbon to Pt supported on a non-carbon support. A normalization approach
was investigated in this work, and the ORR performance of 40wt.%Pt/C was found to be
similar to that of 10wt.%Pt/Nb-TiO2. Fuel cell performance tests showed significantly
higher stability of Pt on Nb doped titania catalyst when compared to conventional Pt on
carbon catalyst. It was found that, of the materials studied, only the rutile phase of Nb doped titania synthesized under reducing conditions is useful as a potential PEMFC
catalyst support.
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