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

Abstract

Catalytic CO oxidation has been investigated under low pressure conditions (p B 10~6 mbar) employing porous Pt Ðlms on a solid state electrolyte (yttrium stabilized as catalyst. The samples were ZrO 2 \ YSZ) characterized by impedance spectroscopy and linear sweep voltammetry before rate measurements were conducted in an UHV chamber with a di †erentially pumped mass spectrometer, a Kelvin probe for integral and a photoelectron emission microscope (PEEM) for spatially resolved measurements of the work function (WF). Di †erent types of samples prepared by di †erent groups were investigated. An electrocatalytic e †ect was found for all samples but within the experimental uncertainty (up to a factor of two) the e †ect was Faradaic. Surprisingly, despite nearly identical electrochemical characteristics the electrocatalytic behavior of the catalysts with the porous Pt Ðlms varied drastically depending on the preparation. Whereas on the samples provided from a di †erent group the WF of the porous Pt Ðlms followed more or less the variation in the electric potential the samples prepared here exhibited no detectable WF change at all upon variation of (V WR), Within the spatial resolution of PEEM (*x B 1 lm) the observed WF changes occurred spatially V WR . homogeneous.

Catalytic Reduction of NO by Methane Using a Pt∕C∕polybenzimidazole∕Pt∕C Fuel Cell

“…In our previous papers 5, 6 we have defined two types of electrochemical promotion, based on the assumption that the catalytic activity was a result of a change in the Fermi level of the catalyst during electrochemical polarization of the catalyst. [12][13][14][15][16][17][18] The Fermi level can be changed simply by charging of the electric double layer at the interface catalyst-support ͑change of the outer, Volta potential͒ without electrochemical reaction. Therefore, this kind of electrochemical promotion was called charge-induced ͑CI͒ EP.…”

Electrochemical Promotion of NO Reduction by Hydrogen on a Platinum/Polybenzimidazole Catalyst

“…The change in the work function was measured using the Kelvin probe technique. However, it has been found later [18][19][20][21][22] that work function changes of catalyst with different morphology, measured using a Kelvin probe, may be only a part of the applied polarization or do not change at all. Summarizing the results of Refs.…”

“…This phenomenon was named NEMCA effect ͑nonfaradaic electrochemical modification of catalytic activity͒ or electrochemical promotion. 4 The NEMCA effect has been demonstrated for more then 50 heterogeneous 2,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] and one homogeneous 1 catalytic reactions. According to Vayenas et al, [5][6][7][8][9][10] the NEMCA effect can be described by the following parameters.…”

Electrochemical Promotion of Oxidative Coupling of Methane on Platinum/Polybenzimidazole Catalyst

“…Taking into account the considerations described and the published data on the electrochemical promotion, [2][3][4][5][6][7][8][9][10][11][12][13][14] we can define three types of electrochemical promotion depending on values of the faradaic current ͑I͒ and 1. The electrochemical promotion effect is the charge-induced ͑electrostatic͒ change of the strength of chemisorptive bonds at the catalyst-reactant interface ͑CI-effect͒.…”

“…2 The term ''electrochemical promotion'' was first proposed by Pritchard 3 in his response to Vayenas's paper. 2 The NEMCA effect has been demonstrated for more than 50 heterogeneous [3][4][5][6][7][8][9][10][11][12][13] and one homogeneous 14 catalytic reactions. Thus, for example, it was shown that CH 4 oxidation to CO 2 on the Pt/yttria-stabilized zirconia ͑YSZ͒ catalyst can be electrochemically promoted up to five times.…”