Synthesis Of Cobalt Oxide （Co₃O₄） Rods By Microemulsion Method And Their Catalysis Activity For Orr

Spinel cobalt oxide （Co₃O₄） is an important p-type semiconductorwith variable oxidation state.A variety of methods such as solid statereaction method, precipitation method, chemical vapor deposition andhydrothermal synthesis methods have been used to prepare the cobaltoxides. However, these methods often involved a multi-step procedureor/and demanded the delicate control of preparation parameters, and theparticle sizes and distribution were difficult to controll.In this article, a simple approach was used for the synthesis of Co₃O₄rods via a microemulsion method. The precursors CoC₂O₄·2H₂O werefirst prepared by mixing two microemulsions, which consist of CTAB/n-butanol/cyclohexane/CoCl₂and CTAB/n-butanol/cyclohexane/H₂C₂O₄respectively, and the final Co₃O₄rods were obtained by thermaldecomposition of the CoC₂O₄·2H₂O precursors.Dfferent factors whicheffect the morphology of CoC₂O₄·2H₂O precursor and rod-like Co₃O₄were investigated, such as, the types of precipitant, thetypes of surfactant, the ratio of [H₂O]/[surfactant], the ratio ofcyclohexane/H₂O and CTAB/n-butanol,the calcination temperature andso on. Furthermore, polyethyleneglycol （PEG） was used as dispersingagent, which greatly improved the morphology of the precursors and theobtained rods. Three different aspect ratio Co₃O₄nanorods were obtainedin different types of microemulsion systems,67-150in bicontinuousmicroemulsion,50-125in W/O microemulsion and10-50in O/Wmicroemulsion. The small sized Co₃O₄obtained in O/W microemulsionwas further discussed. The influencing factors were researched asfollows: the ionization of the oxalic acid, the effect of polyethyleneglycol and n-butanol.Pt/Co₃O₄composite was prepared by a simple reduction methodusing glucose as reductant. The morphologies of Pt/Co₃O₄wascharactered by TEM. It was showed that Pt particles was uniformlyloaded on the surface of Co₃O₄rods and the size of Pt was focusing on1.6nm. CV curves measured with Co₃O₄or Pt/Co₃O₄alone, showed that theoxygen reduction potential at-0.50^-0.40V, peak current density at0.5⁰.6mA·mg-1. Indicated they have little oxygen reductionreaction（ORR） activity in alkaline solutions. However, when mixed withcarbon black（Vulcan-72） exhibited surprisingly high performance inORR. The oxygen reduction peak potential was between-0.35^-0.30 V and peak current density was at6¹1mA·mg-1, the improvement ofthe peak potential and peak current density showed a good oxygenreduction activity of Co₃O₄when mixed with carbon black. And rotatingdisk experiments show thatwithout Co₃O₄, O2was through mainly2ereaction with carbon black as catalyst in alkaline solution. But Co₃O₄andPt/Co₃O₄mixed with carbon black were through mainly4e reaction whichshowed a synergistic effect.