Effects of Heat-Treatment and Pyridine Addition on the Catalytic Activity of Carbon-Supported Cobalt-Phthalocyanine for Oxygen Reduction Reaction in Alkaline Electrolyte

Carbon-supported non-precious metal (cobalt) catalysts, namely Py-CoPc/C, where Py is the pyridine and Pc is the phthalocyanine, are synthesized for oxygen reduction reaction (ORR) using combined solvent-impregnation and high-temperature treatment process. The heat-treatment effect on the catalysts' activity toward ORR is examined using catalysts obtained at 600, 700, 800, and 900oC, respectively. The effect of pyridine addition on the ORR activity is also studied. It is found that the formed Py-CoPc/C catalysts all show the higher ORR activities than that of CoPc/C catalyst, and the catalyst obtained at 700oC treatment gives the best activity for the ORR in 0.1M KOH solution, which are tested using both CV and RDE techniques. XRD, TEM as well as XPS are employed to study the crystal structures, morphologies and surface structure changes of the synthesized Py-CoPc/C catalysts. Both XRD and TEM analysis indicate the formation of different amounts of Co-NX-C active site at different heat-treatment temperatures, which is well correlated with the catalysts' ORR activities. XPS results suggest that the pyridinic-N and graphitic-N groups are both responsible for the enhanced ORR activity, and the catalyst formed at 700oC treatment shows the most amount of these two groups, leading to the most active ORR catalyst.