Oscillatory dynamics of the electrochemical oxidation of H₂ in the presence of Cu²⁺: Structure sensitivity and the role of anions

We studied the oscillatory galvanostatic H₂-oxidation on the three low-index Pt surfaces in the presence of Cu²⁺ and different electrolytes: H₂SO₄, H₂SO₄ + Cl^- and H₂SO₄ + Br^-. It was found that both surface orientation of the Pt-electrode as well as the nature of the anions strongly influence the dynamics. Halide ion adsorption plays an essential role for the occurrence of oscillations; their binding strengths on the different single-crystal electrodes correlate with the dynamic behaviour of the respective system. The reaction was further investigated using ring-disk electrodes ( Pt Pt and Pt Au). This allowed the quantitative determination of the change of the copper coverage and the H₂-current during oscillations as well as their phases relative to the electrode potential. From these studies a simple threevariable model (taking into account the coverages of copper and anions as well as the potential) was deduced, based on competitive adsorption of halides and Cu. The model explains the occurrence of oscillations and predicts the correct phase relationships of the oscillating variables.