DIOXYGEN REDUCTION ELECTROCATALYSIS IN ACIDIC MEDIA - EFFECT OF PERIPHERAL LIGAND SUBSTITUTION ON COBALT TETRAPHENYLPORPHYRIN

The influence of peripheral electron-accepting or electron-donating substituents was investigated after deposition onto an active charcoal using the rotating disc electrode technique (RDE). The samples were characterized by H-1 NMR and ESR before and after heat treatments. Preliminary electrochemical experiments were carried out in order to determine the influence of the surface rugosity on the I-E curves. Under O-2 within the defined experimental conditions, all samples initially displayed the same activities for both Soreflon and Nafion(R) electrodes in the Tafel activation region and after correction by a pseudo-capacitance factor. After a 100 h polarization period at 500 mV (RHE) (diffusion activation domain), the decrease in activity is more pronounced with the highest electron-accepting ligand. This result emphasizes the effect of the (CoO2)-O-III superoxo species on the electrode stability.