CATHODIC REDUCTION OF OXYGEN AND HYDROGEN-PEROXIDE AT COBALT AND IRON CROWNED PHTHALOCYANINES ADSORBED ON HIGHLY ORIENTED PYROLYTIC-GRAPHITE ELECTRODES

The surface electrochemistry of iron and cobalt crowned phthalocyanine (FeIICRPc(-2) and CoIICRPc(-2)) adsorbed on a highly oriented pyrolytic graphite (HOPG) electrode has been explored under an argon atmosphere. The redox processes of surface bound CoIICRPc(-2)/[CoICRPc(-2)]-, [FeIIICRPc(-2)]+/FeIICRPc(-2), and FeIICRPc(-2)/[FeICRPc(-2)]- couples were identified and their pH dependence reported in the range 1-13. Under an oxygen atmosphere at the CoIICRPc(-2)/HOPG electrode, two reduction processes, oxygen to hydrogen peroxide and hydrogen peroxide to water, were clearly delineated and their pH dependences explored. Surface bound FeIICRPc(-2) catalyzes the four-electron reduction of oxygen in alkaline medium. The CoIICRPc(-2)/HOPG electrode is very stable both in the presence and absence of oxygen, but the FeIICRPc(-2)/HOPG electrode is much less stable when electrocatalytic oxygen reduction takes place on its surface.