Voltammetric Investigation of Hydrogen Sorption/Desorption at/within Oxide-Derived Pd Electrodes in NaOH and H₂SO₄

Oxide-derived Pd electrodes are prepared from PdO-coated titanium electrodes (fabricated by thermal decomposition) after polarization at 0 V (vs. reversible hydrogen electrode, RHE) for 30 min. Hydrogen sorption/desorption at/within these electrodes as well as that at ordinary bulk Pd were compared by cyclic voltammetry. In contrast to the results for a bulk palladium electrode, both hydrogen adsorption and absorption peaks are clearly observed on the negative CV sweeps and hydrogen evolution commences after the hydrogen absorption becomes saturated for the oxide-derived Pd electrodes in NaOH and H₂SO₄ solutions. Different sources of proton supply (H₊/H₃O₊ in acid and H₂O in base), HSO₄, SO₄^2- adsorption, and hydrogen damage of the Pd lattice structure account for the different responses in acidic and basic solutions. Surface morphologies of the bulk Pd and the oxide-derived Pd electrodes (where oxide is reduced in either acidic or basic solutions) were examined by scanning electron microscopy to elucidate the effect of surface roughness.