Dissolution and adsorption of hydrogen at smooth Pd wires at potentials of the alpha phase. Influence of electrolyte

The dissolution and adsorption of hydrogen atoms was determined as a function of potential in the region of the alpha phase of a smooth Pd wire in 0.5 M H₂SO₄, 0.5 M KOH, and 0.5 M HCl by a pulse technique. Specifically adsorbable chloride ions were found to decrease the hydrogen coverage at constant potential as on platinum. In contrast to platinum hydroxyl ions did not lead to an increase of the hydrogen bond strength. The isotherms of hydrogen adsorption can be approximated by a Temkin type relationship in a range of medium coverage. The logarithm of the bulk concentration of dissolved hydrogen atoms directly below the surface was a linear function of potential between about 0.25 V and 0.1 V, interpretable in terms of the non-ideal behaviour of the atoms in the first layer below the surface.