Temperature dependent surface electrochemistry on Pt singlecrystals in alkaline electrolyte: Part 3: The oxygen reductionreaction
The kinetics of the oxygen reduction reaction (ORR) was studied in alkaline electrolyte at 293-333K on Pt(hkl) surfaces by means of the rotating ring-disk electrode technique with solution phase peroxide detected at the ring electrode. The ORR on Pt(hkl) was found to be highly structure sensitive with activities increasing in the sequence (111) > (100) > (110)(1x2). Very similar apparent activation energies (37-45 {+-} 5 kJmol-1, {eta} = 0.35 V) were found on all three surfaces. Furthermore, at elevated temperature, significantly smaller amounts of peroxide are formed in agreement with enhanced peroxide reduction rates by increasing temperature. We found that the Tafel slopes on all three single crystal surfaces decrease with increasing temperature, indicating that the logi-E relationship is not represented by a classical Butler-Volmer expression. Based on the kinetic analysis of the polarization curves and from simulations of logi-E curves, we propose that the rate of the ORR on Pt(hkl) in alkaline solution is mainly determined by the potential/temperature dependent surface coverage by OH{sub ad}. We propose two modes of action of the OH{sub ad}: (i) OH{sub ad} blocks the adsorption of O{sub 2} on active platinum sites; and (ii) OH{sub ad} alters the adsorption energy of intermediates which are formed during the ORR on Pt sites.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Assistant Secretary for Energy Efficiency andRenewable Energy
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 917797
- Report Number(s):
- LBNL-51404; R&D Project: 500901; BnR: EE0502000; TRN: US200817%%870
- Journal Information:
- Physical Chemistry Chemical Physics, Vol. 5, Issue 2; Related Information: Journal Publication Date: 2003; ISSN 1463-9076
- Country of Publication:
- United States
- Language:
- English
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