Journal of Applied Electrochemistry

, Volume 23, Issue 6, pp 597–605

Temperature dependence of the Tafel slope for oxygen reduction on platinum in concentrated phosphoric acid

  • S. J. Clouser
  • J. C. Huang
  • E. Yeager
Papers
  • 623 Downloads

Abstract

Oxygen reduction on bright platinum in concentrated H3PO4 has been investigated with the rotating disc electrochemical technique at temperatures from 25 to 250° C and oxygen pressures up to 1.77 MPa. Cyclic voltammetry has been employed to study the anodic film formed on platinum in concentrated H3PO4 and the possible electroreduction of H3PO4 on platinum. The apparent transfer coefficient for the oxygen reduction has been found to be approximately proportional to temperature rather than independent of temperature. Such behaviour is difficult to reconcile with accepted theories for the effect of electrode potential on the energy barriers for electrode processes. It is of importance to establish an understanding of this phenomenon. Possible factors which can contribute to the temperature dependence of the transfer coefficient but which would not necessarily result in a direct proportionality to temperature include potential dependent adsorption of solution phase species, restructuring of the solution in the compact layer, proton and electron tunnelling, a shift in rate-determining step, changes in the symmetry of the potential energy barrier, penetration of the electric field into the electrode phase, insufficient correction for ohmic losses, and impurity effects.

Nomenclature

α

transfer coefficient

β

symmetry factor

β′

temperature independent component of β

ν

stoichiometric number

ω

rotation rate (r.p.m.)

a,c

constant and temperature coefficient in Equation 4 (no unit and K−1, respectively)

B

slope of Koutecky-Levich plot (mA cm−2 (r.p.m.)1/2)

b

Tafel slope (V dec.−1)

E

potential (V)

F

Faraday (C mol−1)

i

current density (A cm−2)

iL

diffusion limiting current density (A cm−2)

K

temperature independent component of Tafel slope (V dec−1.)

R

gas constant (J mol−1 K−1)

T

temperature (K)

n

number of electrons

\((^{\ddag } ){\rm O}\)

standard free energy of activation for forward process (J mol−1)

\((^{\ddag } ){\rm O}\)

standard enthalpy of activation for forward process (J mol−1)

\((^{\ddag } ){\rm O}\)

standard entropy of activation for forward process (J mol−1 K−1)

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. [1]
    B. E. Conway and D. J. MacKinnon,J. Electrochem. Soc. 116 (1969) 1665.Google Scholar
  2. [2]
    B. E. Conway, D. J. MacKinnon and B. V. Tilak,Trans. Faraday Soc. 73 (1969) 1203.Google Scholar
  3. [3]
    B. E. Conway, in ‘Modern Aspects of Electrochemistry’, (edited by B. E. Conway, J. O'M. Bockris and R. White), Vol. 16, Plenum, New York (1986), Chapter 2, p. 103Google Scholar
  4. [4]
    J. N. Agar,Disc. Faraday Soc. (1947) 81.Google Scholar
  5. [5]
    W. Roiter and R. Jampolskaja,Acta Physiochim. 7 (1937) 247.Google Scholar
  6. [6]
    B. R. Scharifker, P. Zelenay and J. O'M. Bockris,J. Electrochem. Soc. 134 (1987) 2714.Google Scholar
  7. [7]
    E. Kirowa-Eisner, M. Schwarz and E. Gileadi,Electrochim. Acta 34 (1989) 1103.Google Scholar
  8. [8]
    S. J. Clouser, Ph.D. thesis, Department of Chemistry, Case Western Reserve University, Cleveland, OH, (1982).Google Scholar
  9. [9]
    W. M. Vogel and J. M. Baris,Electrochim. Acta 23 (1968) 463.Google Scholar
  10. [10]
    A. Damjanovic, D. B. Sepa and M. V. Vojnovic,ibid. 24 (1979) 887.Google Scholar
  11. [11]
    E. Custidiano, T. Kessler, W. E. Triaca and A. J. Arvia,ibid. 31 (1986) 1671.Google Scholar
  12. [12]
    J. C. Huang, R. K. Sen and E. Yeager,J. Electrochem. Soc. 126 (1979) 736.Google Scholar
  13. [13]
    J. O'M. Bockris and S. U. M. Khan, ‘Quantum Electrochemistry’, Plenum, New York, (1979).Google Scholar
  14. [14]
    B. E. Conway, D. F. Tessier and D. P. Wilkinson,J. Electroanal. Chem. 199 (1986) 249.Google Scholar
  15. [15]
    R. Parsons,J. Electroanal. Chem. 21 (1969) 35.Google Scholar
  16. [16]
    M. Ghoneim, S. Clouser and E. Yeager,J. Electrochem. Soc. 132 (1985) 1160.Google Scholar

Copyright information

© Chapman & Hall 1993

Authors and Affiliations

  • S. J. Clouser
    • 1
  • J. C. Huang
    • 1
  • E. Yeager
    • 1
  1. 1.Case Center for Electrochemical Sciences and the Department of ChemistryCase Western Reserve UniversityClevelandUSA
  2. 2.Foil DivisionNow at Gould Inc.EastlakeUSA
  3. 3.Now at General Motors Research CenterWarrenUSA

Personalised recommendations