Dioxygen reduction at a graphite electrode modified by mononuclear tetraneopentoxyphthalocyaninatocobalt(II) and related polynuclear species

Abstract

Potentiodynamic data were obtained under argon for the mononuclear species tetraneopentoxyphthalocyaninatocobalt(II) species adsorbed on glassy carbon (GC), ordinary pyrolytic graphite (OPG), and highly oriented pyrolytic graphite (HOPG). Comparative data show that the most convenient material to use is HOPG whereon a limiting monolayer is apparently achieved. Data were also presented for the mononuclear and polynuclear analogues on HOPG under both argon and dioxygen. Comparison is made of the potential data obtained in water and in organic solvent. A pH dependence study shows that the dioxygen reduction potential tracks the Co(II)TNPc/Co(I)TNPc redox couple with a slope of approximately −65 mV/pH for the mononuclear species, in the acid regime, but substantially less than −65 mV/pH for the polynuclear species. There is no pH dependence in the alkaline regime. Possible mechanisms are discussed. Keywords: phthalocyanine, electrochemistry, dioxygen reduction, pH dependence, graphite electrode, cobalt phthalocyanine.