Preparation And Supercapacitor Performance Of Composite Of Cobalt Hydroxide/Oxides And Nitrogen Doped Carbon Nanotubes

Supercapacitor is attracting more and more attention due to its high efficiency and environmental friendliness. For developing supercapacitor, it is of great practical value and theoretical significance to explore electrode materials with high specific capacitance. Nitrogen doped carbon nanotubes（NCNTs） with good water dispersbiliity, high specific surface area and good conductivity, while cobalt hydroxide and oxide can provide high faradaic pseudocapacitance, but their cycling stability is worse. Preparing the composites to combine the advantages of the cobalt compounds and NCNTs has an significance on the supercapacitor with high performance. In this study, the Co（OH）₂/NCNTs composite is produced by using liquid phase precipation, in which NCNTs is used as a raw material. Then the Co₃O₄/NCNTs and CoO/NCNTs are produced by the air thermal oxidation or the heat treatment of nitrogen atmosphere on the Co（OH）₂/NCNTs. The ratio of raw materials, air thermal oxidation temperature and nitrogen atmosphere heat treatment temperature is studied in order to find out their influence on the morphology, structure and the supercapacitor performance of Co（OH）₂/NCNTs, Co₃O₄/NCNTs and CoO/NCNTs.For the Co（OH）₂/NCNTs produced by liquid phase deposition, while the weight ratio of cobalt salt and NCNTs is 1:4, the Co（OH）₂ in the shape of nanometer particles（size for 10 to 15 nm） are uniform deposited and distributed on the surface of NCNTs. The composite material has the feature of high specific surface area and more mesoporoes. As a supercapacitor materials, the specific capacitance of this composites is 99.3 F·g-1 at the charge-discharge current of 0.1A·g-1, and the retention of specific capacitance is 72.2% after 1000 cycles.The Co（OH）₂/NCNTs composite material with appropriate texture, structure and electrochemical properties was used as the precursor for the preparation of Co₃O₄/NCNTs and CoO/NCNTs. Air thermal oxidation makes Co（OH）₂/NCNTs converted into Co₃O₄/NCNTs, it’s the supercapacitor performance of Co₃O₄/NCNTs is not better than the Co（OH）₂/NCNTs. The nitrogen atmosphere heat treatment makes the Co（OH）₂/NCNTs converted into the CoO/NCNTs. The CoO/NCNTs obtained by the heat treatment of 600℃ whose the CoO particles with smaller size are deposited evenly onto the NCNTs. The composite material has the hierarchical pore structure from micropore to macroporoes. The specific capacitance of CoO/NCNTs-600 composites is 102.6 F·g-1 at charge-discharge current of 0.1A·g-1, and the retention of capacitance remains is more than 82% after 1000 cycles.By comparing the cobalt base NCNTs composite materials, it has been demonstrated that that the CoO/NCNTs converted from the Co（OH）₂/NCNTs by heat treatment of inert atmosphere has the best performance for using as the supercapacitor electrode materials.