Investigation of sol-derived Co-phenylene diamine/carbon materials as oxygen reduction catalysts in alkaline media

Co-1,2-phenylenediamine (Co-pda) catalysts, dispersed on high surface area Vulcan Carbon (VC) or carbon nanotube (CNT) supports, and then heat-treated at between 500 and 1100°C, demonstrate excellent performance as oxygen reduction (ORR) catalysts in alkaline media. While the ORR activity of carbon, and of pda on carbon, is shown to be quite good, adding Co to pda causes a notable further improvement (ca. 10 times) in the cathode activity. The Koutecky–Levich corrected Tafel data show that the best performance is obtained for the 900°C heat-treated materials and a Co:pda molar ratio of 1:2 (22% Co nominally), similar to the case in acidic solutions. The transfer coefficient (α) is close to 1 for the best catalysts, suggesting that a chemical step following a first electron transfer step is rate determining. Further, the low H2O2 yield indicates that the predominant reaction pathway involves the direct 4-electron reduction of O2 to water. All of these ORR performance characteristics are essentially independent of the type of carbon powder substrate used, consistent with the proposal that the ORR active sites arise from the surface product formed by the thermal decomposition of pda.