Influence of Key Parameters of Pulsed Oxidation Technique on the Mitigation of Carbon Monoxide Poisoning in a Polymer Electrolyte Fuel Cell

Hydrogen generated by reforming various hydrocarbons contains impurities such as Carbon monoxide (CO) in small quantities (10-50 ppm) [1]. CO concentrations of this level rapidly poison the platinum and platinum alloy catalysts used in polymer electrolyte fuel cells (PEFC)s even at elevated temperatures. Hydrogen produced by reforming can be treated to be used as a fuel for stationary and automotive fuel cell applications. However, the cost of obtaining pure hydrogen (99.999% purity) for these applications becomes very high. Several mitigation strategies have been proposed and developed to make this fuel compatible with PEFC applications. This includes bleeding air [2,3] into the fuel stream to oxidize the CO and the use of pulsed oxidation to periodically remove CO from the surface of the catalyst. [4, 5]. Although air bleeding can remove CO, it has some disadvantages. Air bleeding into a fuel cell stack can cause overheating at the anode if the air is not controlled and mixed properly and can result in the formation of hydrogen peroxide which can lead to membrane degradation. In comparison with the study and development of air bleeding, pulsed oxidation studies involve use of pulses of current through an external source to oxidise CO in the feed. Previous studies involved only half cell work or room temperature studies which don’t demonstrate practical applications of this technique. In this work, we present results of a study which investigates the use of pulsed oxidation technique to mitigate the effect of CO on the performance of a PEFC. Experiments were carried out on a 5 cm2 active area single cell fuel cell Measurements were done at 80 ºC using membrane electrode assemblies with a Pt-Ru/C anode catalyst and a Pt/C cathode catalyst. 500 ppm CO mixed with pure hydrogen was fed to the anode and air was fed to the cathode. To conduct the experiments, the cell potential was monitored when the fuel source was switched from pure hydrogen to 500 ppm CO doped hydrogen. Current pulses of varying magnitude were initiated through a potentiostat when the cell voltage had fallen to a predetermined level (threshold voltage) to oxidize CO adsorbed on the Pt active sites. In this paper, results will be presented to demonstrate the effect of pulse width, threshold voltage and pulse current on the overall efficiency of the pulsed oxidation process. It was observed that an optimized pulsed oxidation technique allows us to effectively run a PEFC at steady state conditions at a given current density even in the presence of a high concentration of CO. Acknowledgement: This work is supported by the funding provided by IndianOil R&D and Simon Fraser University under the SFU-IOCL joint PhD program in clean energy. [1] Hydrogen production from liquid hydrocarbon fuels for PEMFC application Y. Chen, H. Xu, Y. Wang, X. Jin and G. Xiong, Fuel Process. Technol. 87, 971 (2006) [2] L. Sung, B. Hwang, K. Hsueh, F. Tsau, J. Power Sources, 195, 1630 (2010) [3] W.A. Adams, J. Blair, K.R. Bullock, C.L. Gardner, J. Power Sources, 145, 55 (2005) [4] L.P.L. Carrette, K.A. Friedrich, M. Huber and U. Stimming, Phys. Chem. Chem. Phys., 3, 320 (2001) [5] C.G. Farrell, C.L. Gardner and M. Ternan, J. Power Sources, 117, 282 (2007)

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