| Abstrakt: |
The complex of Co(III) with the macrocyclic ligand ph-tim (ph-tim = 2,3,9,10-tetraphenyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) adsorbs irreversibly on roughly polished pyrolitic graphite electrodes. The adsorbed complex exhibits two, reversible, one-electron voltammetric waves corresponding to Co(III)/Co(III) and Co(II)/Co(I) redox couples located at 0.32 V and −0.07 V, respectively. The adsorbed Co(II) complex generated at 0.32 V catalyzes the electroreduction of O2to H2O2in a separate voltammetric step at more negative potentials which vary with pH. Catalytic plateau currents for the reduction of O2at rotating pyrolytic graphite disk electrodes coated with [(ph-tim)Co]ads3+ar elimited by the rate of coordination of O2to the reduced catalyst, [(ph-tim)Co]]ads2+. An upper limit of 150 M−1was placed on the equilibrium constant for the binding of O2to [(ph-tim)Co]ads2+. A catalytic mechanism compatible with the results is proposed and discussed. |
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