THE CATHODIC REDUCTION OF OXYGEN AT COBALT PHTHALOCYANINE - INFLUENCE OF ELECTRODE PREPARATION ON ELECTROCATALYSIS

Oxygen reduction has been investigated in acid and alkaline solutions on electrodes with the same catalyst (cobalt phthalocyanine or cobalt tetrasulfonato-phthalocyanine), but prepared by different methods. It is concluded that the number of active sites can differ widely from the expected number of active sites as derived from the total amount of catalyst present on the electrode surface. In acid solution, where the reduction is irreversible, the half-wave potential shifts with respect to the number of active sites, according to a theoretical description. For the determination of the 'intrinsic catalytic activity' (turnover number), electrodes with an irreversibly absorbed (sub)monolayer are recommended.