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

The influence of peripheral electron-accepting or electron-donating su bstituents was investigated after deposition onto an active charcoal u sing the rotating disc electrode technique (RDE). The samples were cha racterized by H-1 NMR and ESR before and after heat treatments. Prelim inary electrochemical experiments were carried out in order to determi ne the influence of the surface rugosity on the I-E curves. Under O-2 within the defined experimental conditions, all samples initially disp layed the same activities for both Soreflon and Nafion(R) electrodes i n the Tafel activation region and after correction by a pseudo-capacit ance factor. After a 100 h polarization period at 500 mV (RHE) (diffus ion activation domain), the decrease in activity is more pronounced wi th the highest electron-accepting ligand. This result emphasizes the e ffect of the (CoO2)-O-III superoxo species on the electrode stability.