Mn_xO_y-Co₃O₄/Graphene Composite:Construction And Study Of Dual Electrocatalyst System For Oxygen Reduction Reaction

Here we employed graphene oxide（GO） which synthesized by a modified Hummers method as carbon support for Co3O4. The Co3O4 nanoparticles were successfully loaded on the surface of GO through precipitation. In order to improve the crystallinity of Co3O4 and to complete the nitrogen doping process in GO matrix in the same time, the as-synthesized Co3O4/GO was treated by a hydrothermal in the presence of ammonia and turned into Co3O4/NGO. By controlling the temperature of hydrothermal process and monitoring the changes in phrase structure and morphology of Co3O4 and the N doping and also analyzing their ORR catalytic activity. The Co3O4/NGO with the most excellent electro-activity was synthesized at hydrothermal temperature of 150℃ and with the loading of Co3O4 to be 100wt.% The results show that the electro-activity of these hybrid material is related to the loading of Co3O4 especially related to the C-O-Co bonds.Mn₃O₄ has been proved to a good chemical catalyst towards decomposition of hydrogen peroxide and is more stable. Base on this, a novel ternary composite composed of Co3O4, Mn₃O₄ and N-doped graphene oxide has been developed, XRD result proved these three phase to be pure. The STEM results revealed that Mn₃O₄ nanocrystals had been successfully epitaxially deposited onto the surface of Co3O4 nanoparticles and the formed Mn304-on-Co3O4 nanostructrures were well dispersed on the surface of the graphene oxide. The reason for Mn₃O₄ to preferably epitaxially growing on the surface of Co3O4 is that both two oxides are of spinel structure and the metal atom sizes are close to each other. Compared to Co3O4/NGO, In an alkaline environment, the Mn₃O₄-Co3O4/NGO composite exhibits much better electrocatalytic activity and durbility towards ORR. The electro-activity of those Mn₃O₄-Co3O4/NGO composites differs while the loading of Mn₃O₄ was adjusted. The Mn₃O₄-Co3O4/NGO showed the highest activity towards ORR at a weight ratio of 20%. The tested half-wave potential is 0.785 V（vs RHE）, and its Hydrogen peroxide yield was down to 6.45%. By analysing the XPS and electrochemical test results, the improvement of Mn₃O₄-Co3O4/NGO in ORR catalyzing can be attributed to the synergetic effects between Mn₃O₄ and Co3O4.