Macromolecular Synthesis by Air Oxidative Polymerization through Multi-electron Transfer

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Research of the four-electron reduction of oxygen to water is important in order not only to determine the life mechanism but also to make novel catalysts.As face-to-face Cobalt Dinuclear Porphyrins (CoP2) are known as excellent catalysts to promote the reaction. Polymer complexes of CoP2 with Polyaniline were prepared on the electrode as a catalyst. Electrochemical properties of Polyaniline-CoP2 complex was investigated and proved to catalyze 4-electron reduction by 80%, compared to 50% by CoP2 modified electrode. In order to establish essential factor to promote catalytic efficiency of CoP2, various conducting polymers including self-dope polyaniline, and proton transfer redox polymer were synthesized. It probed that the efficiency of 4-electron reduction is strongly dependent on the redox potential of the polymer-matrix, indicating that redox potential of polymer is an important factor in this catalytic system. As PCAn acts as an efficient electron mediator even in neutral conditions due to its stable redox activity over wide pH range, catalytic reduction of oxygen was carried out using PCAn-CoP2 complex in neutral conditions (pH=6.2). A catalytic efficiency up to 95% toward 4-electron reduction of oxygen was observed by RDV, and RRDV measurements. One-step 4-electron reduction was occurred, not two steps 2-electron transfer by RRDV. It is because PCAn has acidic domain in the polymer matrix, which is thought to keep acidity in the film to some extent, even in neutral conditions, that 4-electron reduction of oxygen occurs in the neutral conditions.