Molecular oxygen reduction in PEM fuel cell conditions: ToF-SIMS analysis of Co-based electrocatalysts

Lefevre, Marcel;Dodelet, JP.;Bertrand, Patrick
(2005) The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical — Vol. 109, n° 35, p. 16718-16724 (2005)

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Authors
  • Lefevre, MarcelUCLouvain
    Author
  • Dodelet, JP.
    Author
  • Bertrand, PatrickUCLouvain
    Author
Abstract
A series of Co-based electrocatalysts for oxygen reduction in acid media has been prepared using two different Co precursors: cobalt acetate (CoAc) and a cobalt porphyrin (CoTMPP). These catalysts have been analyzed by ToF-SINIS to obtain information on the number and the structure of catalytic active sites in these materials. The results are compared with the results of a similar analysis already performed on a series of Fe-based electrocatalysts (J. Phys. Chem. B 2002, 106, 8705) also prepared with two different Fe precursors: iron acetate (FeAc) and an iron porphyrin (ClFeTMPP). The interpretation of ToF-SIMS data for Fe-based catalysts allowed us to conclude that whatever the Fe precursor was, the same catalytic sites (FeN2/C and FeN4/C, with their respective dominant ToF-SIMS signatures: FeN2C4+ and FeN4C8+ ions) were found. The comparison of the ToF-SIMS data with the activity of those catalysts led to the conclusion that the FeN2/C catalytic site was more active than FeN4/C. When the same procedure is applied to ToF-SIMS data measured for Co-based catalysts, the following conclusions are drawn: (i) as for Fe precursors, both Co precursors also give similar results; (ii) as for Fe-based catalysts, the same four families of MetalN(x)C(y)(+) ions, with 1, 2, 3, and 4 nitrogen atoms, are also found in the spectra of Co-based catalysts, but there is no dominant CoNxCy+ ion signature; (iii) only CoN4/C can be ascertained on the basis of ToF-SIMS measurements. There is no strong support from ToF-SIMS measurements for (or against) the existence of CoN2/C in Co-based catalysts as there is for FeN2/C in Fe-based catalysts; (iv) contrary to Fe-based catalysts, all catalytic sites (if there are any besides CoN4/C are about equally active in Co-based electrocatalysts.
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Lefevre, M., Dodelet, JP., & Bertrand, P. (2005). Molecular oxygen reduction in PEM fuel cell conditions: ToF-SIMS analysis of Co-based electrocatalysts. The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical, 109(35), 16718-16724. https://doi.org/10.1021/jp0529265 (Original work published 2005)