Energetics of the underpotential deposition of hydrogen on platinum electrodes. 2: Presence of coadsorbed sulfur
Overlayers of chemisorbed sulfur, S{sub chem}, on polycrystalline Pt can be formed spontaneously by Pt immersion in aqueous Na{sub 2}S solution and they entirely suppress the underpotential deposition of hydrogen, UPD H. Auger electron spectroscopy and core-level electron energy loss spectroscopy measurements indicate that S{sub chem} is not present in an oxidized or reduced state; S{sub chem} has a partial negative charge (well below unity) due to charge redistribution between the Pt substrate and the S{sub chem} adsorbate. The layer of S{sub chem} can be gradually removed from the Pt surface through its oxidative desorption under cyclic-voltammetry conditions in clean H{sub 2}SO{sub 4} electrolyte. The oxidative desorption was strongly affected by the temperature-variation. The S{sub chem} desorption under T-control conditions resulted in formation of submonolayers of S{sub chem} whose coverage could be controlled to within 5% of a complete overlayer. The UPD H on Pt free of S{sub chem} follows the Temkin adsorption isotherm, while in the presence of S{sub chem} having {theta}{sub S} = 0.10, the process follows a Frumkin-type adsorption isotherm with the energy of later interactions being T-dependent. The underpotential-deposited H, H{sub UPD}, reveals enhanced surface mobility in the presence of S{sub chem} than in its absence. The S{sub chem} overlayer ({theta}{sub S} = 0.10) significantly decreases the Pt-H{sub UPD} surface bond energy. This behavior can be explained in terms of the electronic blocking effects which arise from direct electrostatic interaction between the adsorbates.
- Research Organization:
- Univ. de Sherbrooke, Quebec (CA)
- Sponsoring Organization:
- Natural Sciences and Engineering Research Council of Canada (NSERC); National Science Foundation (NSF); USDOE
- DOE Contract Number:
- AC02-76ER01198
- OSTI ID:
- 20003950
- Journal Information:
- Journal of the Electrochemical Society, Vol. 146, Issue 11; Other Information: PBD: Nov 1999; ISSN 0013-4651
- Country of Publication:
- United States
- Language:
- English
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