Solution Combustion Synthesis Of Cobalt Oxides And Their Composites As Supercapacitor Electrode Materials

The rapid development of portable electronic devices and new energyvehicles, has triggered the increasingly stringent requirements for energy storagedevices. Supercapacitors are very suitable for the uasage in short duration, highpower energy storage field, because of their high power densities, long cyclinglives, good temperature characteristic and environmental-friendliness nature.Supercapacitor consist of positive and negative electrodes, separator andelectrolyte. Electrode materials are one of important factors affecting theelectrochemical performance of supercapacitor. Cobalt oxides (Co3O4and CoO)have been identified as promising supercapacitor electrode materials, owing toits ultra-high theoretical specific capacitance and good corrosion resistance.However, cobalt oxides also show obvious disadvantages of poor electricconductivity and toxicity, and thus limiting their electrochemical properties andpractical application. The introduction of conductive materials and cheap oxidesinto cobalt oxides can improve the electric conductivity and reduce cobaltapplication, which is a good strategy.Although there are many approaches to synthesize cobalt oxides, Such asprecipitation, electrodeposition, hydrothermal and solvothermal, and the derivedsamples always show excellent electrochemical performance. But these methodswere time consuming and difficult to meet the large scale and speciallycontinuous preparation of cobalt oxides. Solution combustion synthesis utilizes the self-sustained exothermic reaction between oxidizer (usually nitrates) and fuel to prepare porous nano materials, which is high efficiency and low cost. In this paper, cobalt oxides and its ternary, quaternary nanocomposites were synthesized by solution combustion process, and related electrochemical properties were studied optimized. The main contents are as follows:1. CO3O4and CO3O4/CoO nanoparticles have been synthesized by solution combustion process. The effects of citric acid/Co(NO3)2·6H2O molar ratios on phase composition and morphology of products were investigated by XRD and SEM. With the increase of the fuel dosage, the products transformed from granular aggregates of cubic Co3O4into a mixture of cubic Co3O4and tetragonal CoO with fluffy sheet morphologies. Electrochemical measurements indicated that the products (Co3O4) showed a capacitance up to179.7F·g-1(at0.2A·g-1) when the citric acid/Co(NO3)2·6H2O molar ratio was7/27. Then, the capacitance could be further improved to362.8F·g-1(at0.2A·g-1) after annealing at350℃for3h under nitrogen atmosphere. This annealed sample also demonstrated decent rate performance (285.7F·g-1at4A·g-1) and cycling stability (73.5%retention after1000cycles).2. On the basis of the combustion method, cobalt-nickel oxides/C/Ni ternary nanocomposites have been synthesized by a scalable, one-step solution combustion process at only300℃within30min in air. During the solution combustion process, the carbonization of the citric acid formed the amorphous carbon and reduce Ni2+to Metal Ni particles. Electrochemical tests indicated that the optimized product showed a high specific capacitance of446F·g-1at1A·g-1(or280F·g-1at10A·g-1) with a Co:Ni:C6H8O7molar ratio of4:5:86/9. After1000cycles, the capacity retention was80.5%.3. Cobalt-nickel oxides/C/Ni/CNTs quarternary nanocomposites were prepared by one-step solution combustion process by simply adding acid-treated CNTs into precursor combustion solution. Experimental results indicated that the specific capacitance could be579F·g-1at1A·g-1, or350F·g-1at10A·g-1. The capacity retention was84.1%after1000cycles.