Oscillatory dynamics of the electrochemical oxidation of H 2 in the presence of Cu 2+ : Structure sensitivity and the role of anions

We studied the oscillatory galvanostatic H 2 -oxidation on the three low-index Pt surfaces in the presence of Cu 2+ and different electrolytes: H 2 SO 4, H 2 SO 4 + Cl − and H 2 SO 4 + 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 ( PtPt and PtAu ). This allowed the quantitative determination of the change of the copper coverage and the H 2 -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.