SURFACE ENERGIES OF SOLID ELECTRODES

Theoretical relations are derived for the determination of the surface energy of solid electrodes on quartz oscillators from the bending of the quartz plate or from the associated changes in the oscillator frequency. The dependence of the charges for the reversible adsorption of a certain mass and the corresponding changes in superficial energy measured for the underpotential deposition of lead on polycrystalline gold at zero strain is in good agreement with the thermodynamic prediction using the Lippmann equation. According to the general Lippmann equation, the superficial energy is expected to depend on elastic strain and surface stress. This contribution was dominant for the underpotential deposition of thallium on gold at a strain of ca. 10(-4). The compressive volume stress produced by dissolving hydrogen at constant volume in a heterogeneous mixture of alpha- and beta-palladium was used to estimate a reaction volume for the exchange of hydrogen between the two phases. The electrochemical dissolution rate of hydrogen into palladium increased with tensile stress and decreased with compressive stress.