Structural and electrochemical characterization of binary, ternary, and quaternary platinum alloy catalysts for methanol electro-oxidation

Bogdan Gurau, Rameshkrishnan Viswanathan, Renxuan Liu, Todd J. Lafrenz, Kevin L. Ley, E. S. Smotkin, Erik Reddington, Anthony Sapienza, Benny C. Chan, Thomas E. Mallouk, S. Sarangapani

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Abstract

The bifunctional model for methanol electro-oxidation suggests that competent catalysts should contain at least two types of surface elements: those that bind methanol and activate its C-H bonds and those that adsorb and activate water. Our previous work considered phase equilibria and relative Pt-C and M-O (M = Ru, Os) bond strengths in predicting improved activity among single-phase Pt-Ru- Os ternary alloys. By addition of a correlation with M-C bond strengths (M = Pt, Ir), it is possible to rationalize the recent combinatorial discovery of further improved Pt-Ru-Os-Ir quaternaries. X-ray diffraction experiments show that these quaternary catalysts are composed primarily of a nanocrystalline face-centered cubic (fcc) phase, in combination with an amorphous minor component. For catalysts of relatively high Ru content, the lattice parameter deviates positively from that of the corresponding arc-melted fee alloy, suggesting that the nanocrystalline fee phase is Pt-rich. Anode catalyst polarization curves in direct methanol fuel cells (DMFC's) at 60 °C show that the best Pt-Ru-Os-Ir compositions are markedly superior to Pt-Ru, despite the higher specific surface area of the latter. A remarkable difference between these catalysts is revealed by the methanol concentration dependence of the current density. Although the rate of oxidation is zero order in [CH3OH] at potentials relevant to DMFC operation (250-325 mV vs RHE) at Pt-Ru, it is approximately first order at Pt-Ru-Os-Ir electrodes. This finding implies that the quaternary catalysts will be far superior to Pt-Ru in DMFC's constructed from electrolyte membranes that resist methanol crossover, in which higher concentrations of methanol can be used.

Original languageEnglish (US)
Pages (from-to)9997-10003
Number of pages7
JournalJournal of Physical Chemistry B
Volume102
Issue number49
StatePublished - Dec 3 1998

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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    Gurau, B., Viswanathan, R., Liu, R., Lafrenz, T. J., Ley, K. L., Smotkin, E. S., Reddington, E., Sapienza, A., Chan, B. C., Mallouk, T. E., & Sarangapani, S. (1998). Structural and electrochemical characterization of binary, ternary, and quaternary platinum alloy catalysts for methanol electro-oxidation. Journal of Physical Chemistry B, 102(49), 9997-10003.