Preparation And Supercapacitive Properties Of Benzenesulfonic Functionalized Carbon Nanotubes-Based Composites

As an energy storage device, supercapacitor has attracted more attention recently owing to its high power property and long cycle life. Nowadays, in order to obtain higher specific energy density in the case of high current density, a hybrid of carbon nanotubes (CNTs) with good electronic double layer capacitance and electroactive materials with good faradaic pseudocapacitance has been proposed as ideal electrode materials for supercapacitors, because such hybrid system can create synergy in achieving complementary advantages of two types of capacitor materials. Therefore, in this thesis, we focus upon the preparation and characterization of the CNTs-based composites and their application in electrochemical capacitors (ECs), of which details are described below:First, benzenesulfonic functionalization of MWCNTs (f-MWCNTs) was performed by using in-situ aryl diazonium salts reaction. The hydrophilic benzenesulfonic groups enable excellent dispersibility of f-MWCNTs even under vigorous stirring or static placing in aqueous system. Simultaneously, the negatively charged benzenesulfonic groups can also effectively attract and tether reactive precursors, which make them assembled and grow on the f-MWCNTs surfaces preferentially.Second, the RuO₂·xH₂O, in the case of high loadings, was successfully dispersed onto the surface of f-MWCNTs uniformly via the mild hydrothermal method by using f-MWCNTs as substrate. Electrochemical results demonstrated that the synthesized RuO₂/f-MWCNTs composites (15 wt. % loading) could deliver a high specific capacitance (SC) of 1228.7 F g^-1 for the RuO₂·xH₂O matrix, resulting in an electrochemical utilization of 61.7 %. Even though the RuO₂?xH2O loading increases to 45 wt. %, the utilization of RuO₂?xH2O still possesses as high as 844.4 F g^-1, which is still higher than 798 F g^-1 of RuO₂/p-MWCNTs with 32 wt. % RuO₂?xH2O loading, indicating a good energy capacity in the case of heavy loading.Third, uniformly dispersing of NiO and Co(OH)₂ onto the surface of MWCNTs were achieved via chemical precipitation process by using f-MWCNTs as substrate. f-MWCNTs here was bifunctional both for serving as a substrate with high surface area and for tethering Ni²⁺ and Co²⁺ precursors onto its surfaces by supplying surface binding sites and anchoring groups. Electrochemical results demonstrated that the synthesized NiO/f-MWCNTs and Co(OH)₂/f-MWCNTs composites possess higher electrochemical utilization of electrode active materials than that of NiO/p-MWCNTs and Co(OH)₂/p-MWCNTs under the same mass loading. A SC of 306 F g^-1 and 421 F g^-1 could be delivered at 1.0 A g^-1, which exceeded about 50 % and 60 % as much as that of NiO/p-MWCNTs and Co(OH)₂/p-MWCNTs, respectively.Fourth, a facile and efficiency nitrate pyrolysis route was employed to synthesize CoNiO_x/f-MWCNTs composite with core-shell structure by using f-MWCNTs as substrate. Due to the fact that CoNiO_x in contact with an alkaline solution tends to change asβ?phase nickel hydroxide which has high energy density and cobalt hydroxide which has good electron conductivity, the composite could present better energy and power characteristics. The SC of CoNiO_x/f-MWCNTs composite still remains at 633.6 F g^-1 even though the current density increases to 1.0 A g^-1.Finally, in-situ polymerization method was used to synthesize the nanocomposites of conducting polymer/f-MWCNTs. Electrochemical data demonstrated that the composites presented better rate response, energy storage capability and better cycle life. The superior electrochemical performances could be ascribed to the formation of a three dimensional porous conducting network which facilitate the transportation of electrolyte ion and electron into the inner space of electrode as well as an ability of rapid in-situ doping/de-doping process between the benzenesulfonic groups on the surface of f-MWCNTs and conducting polymer.