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) or 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) catalyses 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 FeII CRPc(-2)/HOPG electrode is much less stable when electrocatalytic oxygen reduction takes place on its surface.