Energetics of the Underpotential Deposition of Hydrogen on Platinum Electrodes: I. Absence of Coadsorbed Species

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 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 as a function of T and the surface coverage, θHUPD ; varies from −11 to −25 kJ mol−1. The relation between and T for allows determination of , which is from −40 to −90 J mol−1 K−1. Subsequently, is determined and varies from −27 to −46 kJ mol−1. An analysis of the values of and leads to conclusion that the UPD H on Pt electrodes is an enthalpy‐driven process. Knowledge of permits determination of the bond energy between Pt and , EPt‐HUPD , which is from 245 to 265 kJ mol−1. The value of EPt‐HUPD falls close to that of the bond energy between Pt and , EPt‐Hchem , which varies from 243 to 247 kJ mol−1. Proximity of EPt‐HUPD to EPt‐Hchem indicates that , and have a similar binding mechanism in presence of the electrified solid/liquid interface and under gas‐phase conditions; it shows that and might occupy the same adsorption sites, thus indicating that , like , is strongly embedded in the surface lattice of the Pt substrate.