Energetics of the underpotential deposition of hydrogen on platinum electrodes. 1: Absence of coadsorbed species

Journal Article · Mon Sep 01 04:00:00 EDT 1997 · Journal of the Electrochemical Society

DOI:https://doi.org/10.1149/1.1837955· OSTI ID:556823

Zolfaghari, A; Chayer, M; Jerkiewicz, G ^[1]

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1. 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, Journal Name: Journal of the Electrochemical Society Journal Issue: 9 Vol. 144; ISSN JESOAN; ISSN 0013-4651
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ADSORPTION
BINDING ENERGY
CHEMICAL BONDS
DESORPTION
ELECTRIC POTENTIAL
ELECTRODEPOSITION
HYDRIDATION
HYDROGEN EMBRITTLEMENT
HYDROGEN STORAGE
PLATINUM
THERMODYNAMIC PROPERTIES