Nano-hybrid Composites Based On Carbon Nanotubes As Supercapacitive Electrode Materials

Carbon nanotubes with high surface area,high conductivity and good stability are suitable electrode materials for electrochemical double layer supercapacitors,but the double-layer capacitance of carbon materials is relatively low and highly depends on the pore accessibility and pre-treatment;the conjugated polymers and oxidations of transition metal have high specific capacitances,but they are were not stable enough comparing with the carbon nanotubes during cycling.The combined advantages from carbon nanotubes and the conjugated polymers and oxidations of transition metal and the cooperative effect could make such hybrid composites excellent choices for supercapacitive electrode materials.In our work,we fabricated successfully the nano-hybrid composites of polyaniline/carbon nanotubes with core-shell structures,the manganese dioxide microcrystallites/carbon nanotubes,and ternary composites of carbon nanotubes/manganese dioxides/polyaniline.As supercapacitive electrode materials,structures and properties of these nano-hybrid composites were studied.Our main results are listed as following:1.Multi-wall carbon nanotubes/polyaniline composites with core-shell structures were fabricated using the commercial multi-wall carbon nanotubes treated in the condensed hydrochloric acid and the aniline monomer.By changing the carbon nanotubes and aniline monomer ratio,we can easily control the thickness of polyaniline layer.The structures and morphologies of the composites were studied by means of SEM,TEM,FTIR,Raman and XRD,and more attentions were paid to their electrochemical properties as supercapacitive electrode materials.The results showed that the supercapacitive behavior for the nano-hybrid composites included the electrochemical double-layer capacitance type and the pseudocapacitive type,and the composites exhibited good stable electrochemical properties during recycling.The highest specific capacitance to 560 F/g was obtained for 33wt%multi-wall carbon nanotubes in the composites.2.A series of nano-hybrid composites were synthesized by the hydrothermal reaction of manganese dioxides microcrystallites and the multi-wall carbon nanotubes, in which potassium permanganate was used as oxidant,manganese acetate and multi-wall carbon nanotubes as reducing agent.The morphologies and microstructures of manganese dioxides microcrystallites could be controlled in order of increasing acid strength.The results showed that among these composites,the needle-like manganese dioxide microcrystallites coated on multi-wall carbon nanotubes exhibited excellent supercapacitive properties,in which the multi-wall carbon nanotubes acted as an effective electron conductor,and the needle-like manganese dioxide microcrystallites have large surface area.Good cycling stability of nano-hybrid composites benefited from the structural stability due to the formation of the core-shell structures,and the specific capacitance was about 550 F/g.3.A novel ternary hybrid materials composed of multi-wall carbon nanotubes, manganese dioxides microcrystallites and polyaniline was prepared by using the needle-like manganese dioxide microcrystallites coated on multi-wall carbon nanotubes as the reactive template and ultrasonic assisted in-situ polymerization of aniline.These ternary hybrid materials are very interesting since materials have large surface area, good conductive channel and flexible processing.Measurements of the electrochemical properties of these materials show that manganese dioxide and the polyaniline played important roles during electrochemical process,and the specific capacitance to 134 F/g was obtained.This kind of hybrid materials was the more potential candidates for high-performance supercapacitive electrode materials.Ternary hybrid system could be further optimized to bring the cooperative effect into full play.