Synthesis And Modification Of CNTs On Ti Matrix And Their Hydrogen Storage Property

Carbon nanotubes (CNTs) are seamless hollow tubes obtained by rolling graphene with single or multi layers along a given direction and reconnecting the carbon bonds, which are rich in one-dimensional nanopores. Because of their small scale in the radial direction, CNTs have large specific surface area. Composites composed of CNTs and metals, which utilize the special microstructure of CNTs and the hydrogen adsorption behavior of metals, are promising materials for hydrogen storage.In this paper, catalysts on titanium powders were prepared by deposition-precipitation method, and CNTs were synthesized on titanium powders by chemical vapor deposition method. The effects of the kinds of catalysts, the contents of Ni in Ni/Ti catalysts, and the CNTs synthesized temperatures were studied in details. Experiment results reveal that when Ni is selected as catalyst, CNTs can be synthesized on the titanium powder at 550°C. Under this temperature, the CNTs/Ti composite powders were synthesized with different Ni contents in Ni/Ti catalysts. The electrochemical hydrogen storage results show that when the Ni content is 3 wt%, the electrochemical hydrogen storage capacity of CNTs/Ti sample is highest. H2 adsorption test indicates that H2 is adsorbed into CNTs by physical adsorption at 25°C and -196°C, while CNTs/Ti adsorbs H2 by chemical and physical adsorption at 300°C. At the same H2 pressure, the hydrogen storage capacity of CNTs/Ti at 300°C is highest among the three temperatures considered in our research.We also studied the effect of ball milling on the hydrogen storage property of CNTs/Ti samples which are mixed directly with pure Ti powder and CNTs. After ball milling, the lengths of CNTs are shorten and the defects in CNTs is increased. It is found that the electrochemical hydrogen capacity of CNTs can be improved by the ball milling process. The ball-milled CNTs/Ti composite powders can adsorb H2 by physical adsorption at 25°C and -196°C, and absorb H₂ by chemical and physical adsorption at 300°C. Among the three temperatures, the hydrogen storage capacity of the ball-milled CNTs/Ti composite powders at 300°C is highest.The effect of surface modification on improving hydrogen storage capacity of CNTs was also studied. TiO₂ nanoparticles were loaded on the CNTs by sol-gel method. Experiment results reveal that with the mass ratio of TiO₂ and CNTs at a certain range, the electrochemical hydrogen storage capacity of CNTs decorated with TiO₂ nanoparticles can be significantly improved, which may be attributed to the photocatalytic hydrolysis and preferable redox ability of TiO₂ nanoparticles.