Fabrication Of Carbon Nanotube Film And Its Application In Rechargeable Zn-air Batteries

Carbon nanotube (CNT), have gained considerable attention in various fields including Physics, Chemistry, Materials Science and Engineering, and Biology and been the focus of nanomaterials since been detected by Transmission electron microscopy, due to its unique 1D nanostructure, alone with excellent mechanical, electrical, optical properties. However, the CNTs, after a 20-year period of development, failed to move toward large-scale application mainly result from the difficulty in operating the nanoscale CNTs precisely, thus it is necessary and urgent to assemble CNTs into macroscopic structures such as film to bridge the gap between micro-world and the macro-world. Recently, due to its onn-step and continuous process, Floating catalyst chemical vapor deposition (FCCVD) has already been regarded as the most potential method for achieving the preparation of CNTs in large. In this dissertation, we systemically investigated the influence of a series of parameters in FCCVD system on the growth of CNTs and the continuity of formation of the thin films, and fabricated large-area high-performance CNT films in a controlled way. And on this basis we explored the possibility of application of this CNT film in oxygen electrode and Zn-air batteries. And a novel free-standing and substrate-free catalytic composite materials with excellent flexible had been then developed based on this CNT film, and it could directly be used as a high-performance bifunctional air electrode for ORR and OER without any extra current collector. Furthermore, we developed a new flexible translucent all-solid-state Zn-air battery base on CNT film. The main content are summarized as follow.Preparation and properties of CNT films. The synthesis work was conducted to know the effects of the key parameter such as temperature, catalyst composition, gas proportion and flow rate on the growth of CNTs and continuous collection of thin film. The as-prepared large-scale (～1m2) CNT film is promising to be a candidate for electrode material due to its high tensile strength (>100 MPa), high electrical conductivity (>700 Scm-1) and large specific surface area alone with an interconnected networks structure. On the basis of that, Si-doped CNT films was prepared in large scale for the first time. As the introduction of heteroatom into hexagonal carbon framework dramatically altered the structure of CNTs, some of CNTs collapsed under their own pressure. Due to the larger area contact and stronger interfacial adhesions induced by the collapse, the as-prepared Si-CNT films exhibit superior mechanical properties.CNT composite film based bifunctional air electrode. Based on the excellent mechanical property, high electrical conductivity, large specific surface area and 3D porous networks of CNT film, the application and prospect in the field of oxygen electrode are explored. A new electrochemical oxidation method was developed to generate oxygen-containing functional groups (e.g. carboxylic groups) on CNT surface to improve the electronic conductivity and wettability, meanwhile, expand the networks to offer sufficient space and exposed surface for the deposition of NiCo2O4 Furthermore, numerous defect sites on the surface of CNT result from electrochemical oxidation enhanced the interaction with nitrogen source, thus the total N contents increased gradually and the relative amount of pyridinic N went up at the same time which effectively improved the electrochemical property of composite film. The resultant NiCo2O4@N-OCNT film exhibited excellent catalytic activity for both ORR and OER and stability due to its extremely high electrical conductivity, optimal N-doping, large specific surface area and strongly coupled Core-Shell Structure. This novel film could directly be used as a high-performance bifunctional air electrode for Zn-air battery without any extra current collector and the primary battery exhibited high specific capacity～745 mAh/g (corresponding to an energy density of 835 WhkgZn-1) and stable operation for 120h after mechanical recharging. The bifunctional catalytic activity of the electrode can be reflected by the longtime durability test, even after 200h pulse cycle, the discharge and charge potentials remain virtually unchanged and the residual energy efficiency remain ～60%.CNT composite film based translucent all-solid-state Zn-air battery. Transparent devices have recently attracted substantial attention. Various applications have been demonstrated, including displays,touch screens, and solar cells; however, transparent batteries, a key component in fully integrated transparent devices, have rarely been reported due to the luck of available transparent electrode. We have demonstrated previously that CNT composite film can be developed as a free-standing high-performance bifunctional air electrode, thus in this dissertation a translucent all-solid-state Zn-air battery was fabricated in which a transparent CNT film coated with a layer of Zn was used as anode while a transparent NCNT/Co3O4 film was used as cathode. The resultant Zn-air battery exhibited a excellent flexibility and a good transparency of-40% and superior cyclic stability.