Ar ion bombardment modification of Pd-Au/MWCNTs catalyst surfaces studied by electron spectroscopy

B. Lesiak, L. Stobinski, L. Kövér, J. Tóth, K. J. Kurzydłowski

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Abstract

The Pd-Au multiwall carbon nanotubes (MWCNTs) supported catalyst prepared by polyol method was found to be catalytically active material in direct formic acid fuel cell electrooxidation reaction and during cyclic voltammetry (CV) measurements. The surface of the catalyst after calcination and reduction treatments was investigated previously. The effect of Ar ion bombardment modification on the calcinated catalyst was studied by electron spectroscopy. The chemical and structural changes were deduced from the X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES) spectra. The XPS quantitative and qualitative analysis of different chemical forms of atoms indicated that the sputtering causes an increase of Pd surface content, accompanied by decreasing content of N, O, C sp 2, and Au (due to preferential sputtering of Au) and significant increase of C sp 3 amount. A decrease was also observed in the surface content of (i) carboxyl groups, (ii) water, and (iii) Pd oxide (mainly less stable PdO 2). Analysis of XPS inelastic background shape by QUASES indicates that Pd crystallites phase is covered by PdO x + C amorphous overlayer of decreasing thickness after sputtering. Namely, thickness of PdO x overlayer decreased from 8.2 to 3.5 nm and the thickness of amorphous carbon overlayer located on the top increased from 2.3 to 3.5 nm. Significant increase of C sp 3 content results from carbon nanotube (CNT) π bonds damaging, whereas decrease of PdO 2 content from lower stability of PdO 2. Larger thickness of C amorphous overlayer, in contrary to PdO x, may result from higher preferential sputtering of oxygen than carbon atoms and cracking of the MWCNTs structure by Ar + ions.

Original languageEnglish
Pages (from-to)1791-1795
Number of pages5
JournalPhysica Status Solidi (A) Applications and Materials Science
Volume208
Issue number8
DOIs
Publication statusPublished - Aug 1 2011

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Keywords

  • Ar ion modification
  • Pd-Au/MWCNTs catalyst
  • electron spectroscopy methods

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Electrical and Electronic Engineering
  • Materials Chemistry

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