Controlled Synthesis And Properties Study Of 3D Porous Carbon Nanotube Sponge Composites

Carbon nanotube(CNT) sponges consist of multiwalled carbon nanotubes stacking in a three-dimensional(3D) porous network, with broad applications in energy and environmental areas. In order to facilitate practical applications, it is necessary to further improve the mechanical, electrical and other related properties of CNT sponges,particularly the structural stability and the ability of elastic recovery during deformation.Furthermore, controlled introduction of active materials inside CNT sponges is an effective way to prepare high performance functional devices. This thesis studied the controlled fabrication, mechanical and electrochemical properties of CNT sponge-based composites, and explored the application in the area of energy devices. Porous composites materials with controlled structure have been prepared through uniform deposition of amorphous carbon and polyaniline into CNT sponges, which significantly improved the mechanical and electrochemical properties, respectively.CNT/amorphous carbon composite sponges have been prepared and their mechanical properties have been studied. The amorphous carbon was directly deposited inside the sponges by chemical vapor deposition using acetylene as the carbon source,resulting in unique core-shell structures consisting of a uniform amorphous carbon layer coated on the surface of CNTs. The thickness of the depositing layer can be tailored by factors such as the reaction time, and the overlapping points between CNTs can be effectively welded, thus forming a monolithic, stable 3D framework. Mechanical tests show that the compressive elastic modulus and compressive strength of CNTvsponges have been improved by 40-fold and 60-fold, respectively, after introducing amorphous carbon, with elastic recovery at compressive strains of 10% to 50% and no plastic deformation after 1000 compressive cycles. The underlying mechanisms have been analyzed and it is found that wrapping and welding of CNTs by the amorphous carbon are key factors to ensure the structural stability of sponges under compression, leading to superelastic behavior.CNT/polyaniline composite sponges have been prepared and their electrochemical properties have been studied. Polyaniline was polymerized in CNT sponges by electrodeposition using aniline as raw material, resulting in polyaniline-coated CNT core-shell structures. Also, the thickness of the polyaniline layer can be tuned while the overlapping points between CNTs can be welded. The electrochemical properties of thecomposite sponges were tested in a three-electrodes system and the resulti showed that the specific capacitance was improved from about 30 F/g to 753 F/g after loading polyaniline. The sponges retained more than 70% of original specific capacitances in highly compressed conditions, and the volume-normalized specific capacitance was improved simultaneously. The cycling stability was improved significantly(more than90% retention after 1000 cycles) by introducing an intermediate polypyrrole layer between the CNTs and the polyaniline shell. The 3D conductive CNT network and the uniformly deposited pseudocapacitive materials are two important factors in enhancing the electrochemical properties, with promising applications in the area of high performance supercapacitors.