UBC Theses and Dissertations
Oxidation-resistant catalyst supports for proton exchange membrane fuel cells (PEMFCs) Chhina, Harmeet
Proton exchange membrane fuel cells (PEMFCs) are electrochemical energy conversion devices that react hydrogen and oxygen to produce electricity. PEMFCs can be used for power generation in the portable, stationary and transportation sectors. Severe performance degradation during extended operation is hindering commercialization of PEMFCs. One of the mechanisms causing performance degradation includes catalyst support corrosion. Tungsten carbide (WC) and indium tin oxide (ITO) were selected as supports of choice. Platinum was dispersed on commercial samples of WC and ITO. Both the thermal and electrochemical stability of the supported catalyst was determined. The stability of the supports was compared with both commercial catalyst (Hispec 4000) and in-house Pt catalyst. The in-house Pt catalyst was supported on commonly used high surface area carbon Vulcan XC-72R catalyst support. The electrochemical testing involved applying oxidation cycles between +0.6 V to +1.8 V and monitoring the loss in activity of the supported catalyst over 100 oxidation cycles. Tungsten carbide was found to be extremely stable. However, direct comparison of its stability to Vulcan XC-72R is currently difficult. The electrochemical stability of 40 wt% Pt dispersed on WC was compared with that of 40 wt% Pt/C. Even though there are large differences in the densities of C and WC some comparisons are possible. An alternative method to more directly compare the stabilities of WC and C involved dispersing a similar amount of Pt on similar powder volumes of WC and C. The solid densities of both carbon and WC were also used to disperse similar volumes of Pt on both supports in order to more directly compare the electrochemical stability. Indium tin oxide lost approximately 50% of its activity after 30 oxidation cycles, whereas Vulcan XC-72R lost almost 100% of its activity after 10 oxidation cycles. Both the electrochemical oxidation and thermal stability tests showed that IT0 is extremely stable compared to Vulcan XC- 72R.
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