Metalloporphyrin-modified perovskite-type oxide for the electroreduction of oxygen

Perovskite-type oxide-carbon (Vulcan XC72) mixture (La0.6Sr0.4Mn0.6Fe0.4O3/C) was modified by a metalloporphyrin (cobalt octaethylporphyrin: Co-OEP) having two-electron O2 reduction activity, and its electrochemical reduction activity for O2 (ORR) was investigated in an alkaline solution by rotating ring disk electrode (RRDE) voltammetry. The Co-OEP/La0.6Sr0.4Mn0.6Fe0.4O3/C catalyst showed improved ORR activity, with a positive shift of the onset potential. In addition, a decreased ring current compared to Co-OEP/C suggested that the quasi-four-electron reduction of O2 was also enhanced. Further experiments showed that ORR activity was also enhanced by Co-OEP-modification of other types of carbon (Ketjenblack EC600JD, Denka Black) or perovskite-type oxide (La0.6Ca0.4Mn0.6Fe0.4O3, La0.8Sr0.2Co0.6Fe0.4O3). In the case of the addition of other porphyrin complexes (cobalt tetraphenylporphyrin (Co-TPP), iron octaethylporphyrin (Fe-OEP)) to a La0.6Sr0.4Mn0.6Fe0.4O3/C catalyst, the onset potential did not shift to the positive side due to the lower activity compared to Co-OEP.