Tunable oxidation state of Co in CoOx@N-doped graphene derived from PANI/Co3O4 and the enhanced oxygen reduction catalysis

Metal@nitrogen-doped carbon core-shell structure, processing both the stability of inner metal species and manipulated electron structure of outer carbons, is regarded as a promising catalysts for oxygen reduction reaction. In the traditional fabrication of such materials, metal ions are reduced into metallic particles, which make it hard to control oxidation state of metals. In this work, we report tunable oxidation state of Co in CoOx@N-doped graphene simply by changing the pyrolysis temperature of Co3O4/polyaniline. Under high temperature, polyaniline decompose and release various organic gases, which can partially reduce Co3O4 and serve as gaseous precursors for the in-situ growth of graphene in the meantime. The balance of these two reactions is crucial to control the oxidation state of Co. Thus, its catalytic activity towards oxygen reduction reaction can be easily tuned by inner CoOx core with different electron structure.