Electrochemical Catalytic Reduction of Oxygen by a Self-Doped Polyaniline–Co-Porphyrin Complex-Modified Glassy Carbon Electrode

Abstract

The four-electron reduction of oxygen to water takes place on a glassy carbon electrode by electrocatalysis using the Co-porphyrin–polyaniline complex. The four-electron transfer processes were confirmed by electrochemical measurements such as cyclic voltammetry, rotating disk voltammetry (RDV), and rotating ring-disk voltammetry (RRDV). The number of electrons transferred was determined on the basis of the Koutecky–Levich plot in RDV. Large amounts of H2O2 formation were not detected by RRDV. RRDV revealed that the direct four-electron reduction of oxygen proceeded without the formation of H2O2. The process obeys a mechanism in which the four-electron reduction takes place through a multiple electron injection from the polyaniline to the cobalt complex after electron transfer from Co to oxygen. The four-electron reduction of oxygen also proceeds in a pseudo-neutral medium (pH 6.2). Poly(2,3-dicarboxyaniline) acts as an excellent electron mediator from the electrode to the Co-porphyrin matrix and shows stable redox activity over a wide pH range due to the self-dopable carboxy substituents in the polymer chain.