Fig. 6. Comparison of anodic and cathodic polarization curves for ORR and HPRR at 1600 rpm on a rotating Pd(poly) electrode in: a) 0.1 M HClO4; b) 0.1 M NaOH solution.Figure optionsDownload full-size imageDownload as PowerPoint slide
3.4. Changes of Pd(poly) surface during ORR
3.4.1. CV indication of Pd(poly) surface changes after ORR and HPRR/HPOR
In order to have an insight into a possible Pd(poly) surface changes that Cy5 hydrazide might occur in the course of ORR and HPRR/HPOR reactions, cyclic voltammetry was performed again after these measurements in oxygen as well as hydrogen peroxide free solutions, and presented in Fig. 7. In both acid (Fig. 7a) and alkaline (Fig. 7b) solutions, the first reversible Pd oxide formation/reduction peaks are suppressed, even more than in the case of repeating cycling (see Fig. 1a). We suppose that during the interaction of Pd surface with the excess of O2 or H2O2 in the solution , a significant disturbance of surface structure takes place as a consequence. This causes the disappearance of Pd surface sites suitable for OH adsorption, which is reflected to the suppression of CV peaks.