OSCILLATORY DYNAMICS OF THE ELECTROCHEMICAL OXIDATION OF H-2 IN THE PRESENCE OF CU2- STRUCTURE SENSITIVITY AND THE ROLE OF ANIONS( )

We studied the oscillatory galvanostatic H-2-oxidation on the three lo w-index Pt surfaces in the presence of Cu2+ and different electrolytes : H2SO4, H2SO4 + Cl- and H2SO4 + Br. It was found that both surface or ientation of the Pt-electrode as well as the nature of the anions stro ngly influence the dynamics. Halide ion adsorption plays an essential role for the occurrence of oscillations; their binding strengths on th e different single-crystal electrodes correlate with the dynamic behav iour of the respective system. The reaction was further investigated u sing ring-disk electrodes (Pt/Pt and Pt/Au). This allowed the quantita tive determination of the change of the copper coverage and the H-2-cu rrent during oscillations as well as their phases relative to the elec trode potential. From these studies a simple three-variable model (tak ing into account the coverages of copper and anions as well as the pot ential) was deduced, based on competitive adsorption of halides and Cu . The model explains the occurrence of oscillations and predicts the c orrect phase relationships of the oscillating variables.