The effect of Mn addition on the promotion of oxygen reduction reaction performance for PtCo/C catalysts

Shu Ping Hsu, Chen Wei Liu, Hong Shuo Chen, Tsan Yao Chen, Chien Ming Lai, Chih Hao Lee, Jyh Fu Lee, Ting Shan Chan, Li Duan Tsai, Kuan Wen Wang

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

The effect of Mn addition on the promotion of oxygen reduction reaction (ORR) performance for PtCo/C catalysts is investigated. The structures, surface compositions, chemical compositions, local structural parameters including coordination numbers and bond distances, morphologies and electrochemical properties of prepared catalysts are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-atomic emission spectrometer (ICP-AES), extended X-ray absorption fine structure (EXAFS), high resolution transmission electron microscopy (HRTEM) and rotating disk electrode (RDE) technique, respectively. For PtCo/C catalysts modified with 0.4 and 3.2 wt% of Mn, the Pt/Co atomic ratio is 3.5 and the size is about 3.0 nm with the same face centered cubic (fcc) structure. Moreover, Mn-modified PtCo/C catalysts have the same surface composition, which is about Pt/Co/Mn of 62/32/6, and their ORR activity are both higher than that of PtCo/C and commercial Pt/C catalysts. After accelerated durability test (ADT) of 1700 cycles, Mn-2 with 3.2 wt% Mn addition still presents the best ORR mass activity, which is about 420% of commercial Pt/C. In the Mn-modified PtCo/C system, due to the existence of the neighboring Co and/or Mn oxide, there is OH repulsion between Pt-OH and these non-noble metal hydroxides or oxides, decreasing the OH coverage on Pt and increasing the number of free Pt active sites. Besides, based on the XAS analysis, the unfilled d-orbital values and extent of hybridization of Pt and Co/Mn of the PtCo and Mn-modified samples are very similar. Therefore, the promotional effect on ORR performance of Mn-2 is attributed to the most enhanced Pt-skin structure, highest Pt usage, and comparable electron transfer number during ORR instead of changes in d-orbital vacancy and alloying degree.

Original languageEnglish
Pages (from-to)180-187
Number of pages8
JournalElectrochimica Acta
Volume105
DOIs
StatePublished - 2013

Keywords

  • (EXAFS)
  • Electron transfer number
  • Extended X-ray absorption fine structure
  • Mn
  • Oxygen reduction reaction (ORR)
  • PtCo/C catalysts

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