Synergistic effect of two metal porphyrins in a polymer catalyst for oxygen electroreduction

Abstract

This work considers the formation and catalytic properties of films of individual hydroxyphenyl porphyrin complexes with manganese (manganese(III) acetate 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (MnAc(4-OHPh)P)) and iron (iron(III) chloride 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (FeCl(4-OHPh)P)) and their composites. The films of individual metalloporphyrins and bimetallic composites were obtained by superoxide-assisted electrochemical deposition in dimethylsulfoxide solutions. The formation of the bimetallic (Mn + Fe) porphyrin composite was confirmed by spectral methods. An analysis of the atomic-force microscopy results showed that the composite films consisted of larger globules and were rougher than those of individual porphyrins. The electroactive surface areas of the individual porphyrin films and the composite were significantly different from each other. The mechanism and kinetics of the oxygen electroreduction reaction (ORR) on the films of individual porphyrins and bimetallic composite were evaluated using a rotating disk electrode. The kinetic current density of the Tafel slope and the position of the ORR current wave on the surface of the poly-(MnAc(4-OHPh)P + FeCl(4-OHPh)P) composite indicate smaller kinetic limitations and lower overvoltage on this material than on carbositall and films of individual porphyrins. The smaller kinetic limitations and better energy characteristics can be explained by the synergistic effect produced by the combined action of the Mn- and Fe- catalytically active centers during ORR on the composite film.