Electrochemical promotion of catalytic CO oxidation on Pt/YSZ catalysts under low pressure conditions

Catalytic CO oxidation has been investigated under low pressure conditions (p approximate to 10(-6) mbar) employing porous Pt films on a solid state electrolyte (yttrium stabilized ZrO2=YSZ) as catalyst. The samples were characterized by impedance spectroscopy and linear sweep voltammetry before rate measurements were conducted in an UHV chamber with a differentially pumped mass spectrometer, a Kelvin probe for integral and a photoelectron emission microscope (PEEM) for spatially resolved measurements of the work function (WF). Different types of samples prepared by different groups were investigated. An electrocatalytic effect was found for all samples but within the experimental uncertainty (up to a factor of two) the effect was Faradaic. Surprisingly, despite nearly identical electrochemical characteristics the electrocatalytic behavior of the catalysts with the porous Pt films varied drastically depending on the preparation. Whereas on the samples provided from a different group the WF of the porous Pt films followed more or less the variation in the electric potential (V-WR), the samples prepared here exhibited no detectable WF change at all upon variation of V-WR. Within the spatial resolution of PEEM (Delta x approximate to 1 mu m) the observed WF changes occurred spatially homogeneous.