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EXAFS studies of carbon supported fuel cells electrocatalysts

EXAFS studies of carbon supported fuel cells electrocatalysts
EXAFS studies of carbon supported fuel cells electrocatalysts

Carbon supported Pt, PtRu and PtMo fuel cells catalysts were investigated by means of advanced synchrotron X-ray adsorption spectroscopies (XAS), in particular extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) EXAFS results at both the Pt LIII and Ru K edges for the PtRu/C electrocatalysts have highlighted the interference of the backscattering from secondary metal element, Ru, with that from Pt when the neighbours were at similar distances. The resulting phase cancellation in the EXAFS at about k ~ 10o A-1 gave rise to a splitting of the main peak of the Fourier transform. The extent of intermixing in the alloy could then be related to the extent to which this peak was split. Shortened first shell Pt-Pt coordination distances and decreased first shell coordination numbers provided evidence of the smaller size of carbon supported small platinum particles when modified with Ru or Mo. While the complementary Ru K edge investigation reflected the metallic nature of the Ru at a reducing potential. XAS results at the Mo K edge indicated the presence of Mo oxyhydroxide species at the surface of the particle related to the presence of the redox couple Mo(IV)/MO(VI), as indicated by changes in the XANES feature as function of potential. The performance of proton exchange membrane fuel cells with PtRu and PtMo catalysts on reformate mixes containing up to 100 ppm CO was enhanced over that of Pt. The enhancement of the catalytic activity for the CO electro-oxidation reaction by PtRu/C electroanalysis is thought to arise from an intrinsic mechanism rather than the presence of oxide on the Ru surface. Whereas the Mo oxyhydroxide species are thought to play a significant role of oxidise CO adsorbed species at lower potentials than Pt. Finally, in situ EXAFS investigation of fuel cell electrocatalysts was shown to be sensitive to the surface composition of the metal particles (CO and O) and therefore, may be used to investigate the chemistry of the fuel cell reactions.

University of Southampton
Maniguet, Stéphanie
cd69841b-03b4-4c98-9ef7-141d56e67228
Maniguet, Stéphanie
cd69841b-03b4-4c98-9ef7-141d56e67228

Maniguet, Stéphanie (2002) EXAFS studies of carbon supported fuel cells electrocatalysts. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Carbon supported Pt, PtRu and PtMo fuel cells catalysts were investigated by means of advanced synchrotron X-ray adsorption spectroscopies (XAS), in particular extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) EXAFS results at both the Pt LIII and Ru K edges for the PtRu/C electrocatalysts have highlighted the interference of the backscattering from secondary metal element, Ru, with that from Pt when the neighbours were at similar distances. The resulting phase cancellation in the EXAFS at about k ~ 10o A-1 gave rise to a splitting of the main peak of the Fourier transform. The extent of intermixing in the alloy could then be related to the extent to which this peak was split. Shortened first shell Pt-Pt coordination distances and decreased first shell coordination numbers provided evidence of the smaller size of carbon supported small platinum particles when modified with Ru or Mo. While the complementary Ru K edge investigation reflected the metallic nature of the Ru at a reducing potential. XAS results at the Mo K edge indicated the presence of Mo oxyhydroxide species at the surface of the particle related to the presence of the redox couple Mo(IV)/MO(VI), as indicated by changes in the XANES feature as function of potential. The performance of proton exchange membrane fuel cells with PtRu and PtMo catalysts on reformate mixes containing up to 100 ppm CO was enhanced over that of Pt. The enhancement of the catalytic activity for the CO electro-oxidation reaction by PtRu/C electroanalysis is thought to arise from an intrinsic mechanism rather than the presence of oxide on the Ru surface. Whereas the Mo oxyhydroxide species are thought to play a significant role of oxidise CO adsorbed species at lower potentials than Pt. Finally, in situ EXAFS investigation of fuel cell electrocatalysts was shown to be sensitive to the surface composition of the metal particles (CO and O) and therefore, may be used to investigate the chemistry of the fuel cell reactions.

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Published date: 2002

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Local EPrints ID: 464786
URI: http://eprints.soton.ac.uk/id/eprint/464786
PURE UUID: 369ea5b8-d96c-47cd-81c5-4b17ed8c7f2a

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Date deposited: 05 Jul 2022 00:01
Last modified: 05 Jul 2022 03:10

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Author: Stéphanie Maniguet

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