Synthesis Of Carbon Supported Cobalt Oxide Hybrid Catalyst And The Origin Of Activity Ehancement For Oxygen Reduction Reaction

Oxygen reduction reaction (ORR) electrocatalysts are very important for all kinds of renewable energy applications (such as fuel cell and metal-air battery) and energy-intensive industries (such as chlor-alkali industry). The design and synthesis of ORR electrocatalysts with highly catalytic activity, excelent durability and low cost remains challenging. In this article, four kinds of carbon materials (home-made nitrogen doped carbon nanotubes (NCNTs), commercial carbon nanotubes (CNTs), graphitized carbon black (GCB), ordinary Vulcan XC-72carbon black (CB)) was chosen as carriers to support Co3O4by hydrothermal and high temperature calcination method. The morphology, structure, performance towards ORR and key facters affecting the catalytic activity of the prepared hybrid catalysts was studied. The main work is as follows:1. Based on different carbon carriers, four kinds of hybrid catalyst was prepared by hydrothermal method successfully. Co3O4nanoparticles with size of3-5nm were uniformly deposited on carbon support. Electrochemical performance towards ORR showed that catalytic activity followed the order of Co3O4/CB> Co3O4/NCNTS=Co3O4/CNTs> Co3O4/GCB. The oxygen reduction mechanism of four kinds of materials indicated that the difference of activity mainly come from the doping nitrogen atom in the carbon lattice and the effective nitrogen content. It was hard to dop nitrogen in GCB carrier due to its complete flake graphite layer, which resulting in the poor ORR catalytic activity of CO3O4/GCB. Instead, the unusual catalytic activity of Co3O4/CB arises from more effective nitrogen content.2. Co3O4/GCB hybrid catalysts were prepared by high temperature calcination method. The effects of annealing temperature on the morphology, structure and ORR performance of hybrid catalysts was studied. The results demonstated that carbon carrier can induce the generation of defects of Co3O4through the displaced Co atoms during the calcination process, which can be easily observed in the abnormal peak intensity in XRD diffraction. The higher the degree of graphitization of carbon carrier, the more induced defect was. And there is a relationship between structure defect and catalytic activity. The higher the defects proportions, the more the exposed trivalent cobalt ions and more formed covalent bonds between carbon carrier and Co3O4, resulting the better catalytic activity.