Hydrogen oxidation on PtRuPEM anodes -: Mechanism, effective mass transfer, and influence of CO2

The hydrogen oxidation reaction (HOR) on a PtRu anode catalyst has been investigated, and polarization curves for H-2 mixed with N-2, Ar, He, and CO2 have been measured in symmetrical H-2 vertical bar H-2 cells. HOR on the PtRu catalyst follows the Tafel-Volmer mechanism based on the observation of limiting currents that were not due to mass transfer but rather reaction limitations. The mass transfer rate in the gas diffusion layer was found to be very high. Transport through the ionomer in the catalyst layer covering the active catalyst also contributed to the mass transfer resistance, but it was not possible to estimate the relative importance of this compared to the reaction limiting current due to the Tafel step. The influence of CO2 on the performance of the PtRu anode was significant in symmetrical cells. Nitrogen did not have any effect on anode performance other than dilution. Recovery of the symmetrical H-2 vertical bar H-2 cell after exposure to CO2 was slow and not complete. To achieve complete recovery, it was required to electrochemically activate the electrodes by oxidation of adsorbed contaminants. (c) 2006 The Electrochemical Society.