Effect of temperature on surface processes at the Pt(111)-liquid interface: Hydrogen adsorption, oxide formation, and CO oxidation
The variation of the adsorption pseudocapacitance with temperature is used to obtain the enthalpy, entropy, and free energies of adsorption of H{sub upd} and OH{sub ad} on Pt(111) as a function of pH and nature of the anion of the supporting electrolyte. It is shown that the heat (enthalpy) of adsorption of hydrogen on Pt(111) at the electrochemical interface is essentially independent of either the pH of the electrolyte or the nature of the supporting anion. The heat of adsorption has a linear decrease with {Theta}{sub Hupd}, from {approximately}42 kJ/mol at {Theta}{sub Hupd} = 0.66 ML. The heat of adsorption of OH{sub ad} is more sensitive to the nature of the anion in the supporting electrolyte. This is presumably due to coadsorption of the anion and OH{sub ad} in electrolytes other than the simple alkali bases. From the isosteric heat of adsorption of OH{sub ad} in alkaline solution (ca. {approximately}200 kJ/mol) and the enthalpy of formation of pH{sup {sm{underscore}bullet}} the authors estimated the Pt(111)-OH{sub ad} bond energy of 136 kJ/mol. This value is much smaller than the Pt-o{sub ad} bond energy at a gas-solid interface ({approximately}350 kJ/mol). In basic solution the electrooxidation of CO proceeds at low overpotentials (<0.2 V) between the adsorbed states of CO{sub ad} and OH{sub ad}, the latter forming at low overpotentials selectively at defect sites. In acid solution, however, these sites are not active because they are blocked by specific adsorption of anions of the supporting electrolyte.
- Research Organization:
- Univ. of California, Berkeley, CA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 20001144
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 103, Issue 40; Other Information: PBD: 7 Oct 1999; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- English
Similar Records
Energetics of the underpotential deposition of hydrogen on platinum electrodes. 1: Absence of coadsorbed species
The effect of specific chloride adsorption on the electrochemicalbehavior of ultrathin Pd films deposited on Pt(111) in acidsolution