Energetics of the underpotential deposition of hydrogen on platinum electrodes. 1: Absence of coadsorbed species
- Univ. de Sherbrooke, Quebec (Canada). Dept. de Chimie
Research on the underpotential deposition of hydrogen (UPD H) on Pt electrodes by cyclic voltammetry in 0.05, 0.10, and 0.50 M aqueous H{sub 2}SO{sub 4} solutions at temperatures from 273 to 343 K shows that the adsorption-desorption profiles shift toward less positive values upon temperature (T) increase. Treatment of the experimental results based on a general electrochemical adsorption isotherm allows determination of {Delta}G{sub ads}{sup o} (H(UPD)) as a function of T and the H(UPD) surface coverage, {theta}{sub H(UPD)}; {Delta}G{sub ads}{sup o} (H(UPD)) varies from {minus}11 to {minus}25 kJ/mol. The relation between {Delta}G{sub ads}{sup o} (H(UPD)) and T for {theta}{sub H(UPD)} = const allows determination of {Delta}S{sub ads}{sup o} (H(UPD)), which is from {minus}40 to {minus}90 J/mol K. Subsequently, {Delta}H{sub ads}{sup o} (H(UPD)) is determined and varies from {minus}27 to {minus}46 kJ/mol. An analysis of the values of {Delta}H{sub ads}{sup o} (H(UPD)) and {Delta}S{sub ads}{sup o} (H(UPD)) leads to conclusion that the UPD H on Pt electrodes is an enthalpy-driven process. Knowledge of {Delta}H{sub ads}{sup o} (H(UPD)) permits determination of the bond energy between Pt and H(UPD), E(Pt-H(UPD)), which is from 245 to 265 kJ/mol. The value of E(Pt-H(UPD)) falls close to that of the bond energy between Pt and H(chem), E(Pt-H(chem)), which varies from 243 to 247 kJ/mol. Proximity of E(Pt-H(UPD)) to E(Pt-H(chem)) indicates that H(UPD), and H(chem) have a similar binding mechanism in presence of the electrified solid/liquid interface and under gas-phase conditions; it shows that H(UPD) and H(chem) might occupy the same adsorption sites, thus indicating that H(UPD), like H(chem), is strongly embedded in the surface lattice of the Pt substrate.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 556823
- Journal Information:
- Journal of the Electrochemical Society, Vol. 144, Issue 9; Other Information: PBD: Sep 1997
- Country of Publication:
- United States
- Language:
- English
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