Layered protonated titanate nanotubes, synthesized via a hydrothermal reaction in alkaline solution, were calcined at different temperatures (200-500 °C) in air to achieve the products of various morphologies and crystal-phase compositions. The microstructure of obtained products was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N 2 adsorption. The electrochemical lithium storage of these samples was studied by galvanostatic method and cyclic voltammetry. It is found that the protonated titanate nanotubes maintain layered structure below 300 °C and undergo phase transition to a mixture of anatase and TiO 2 (B) with anatase as the main phase between 300 and 500 °C. In addition, the hollow nanotube morphology still remains below 400 °C, but the tubes convert to solid nanorods during the calcination at 500 °C. It is found the nanotubes calcined at 300 and 400 °C have larger surface areas and exhibit relatively large reversible capacity and good reversibility (remain about 200 mA h/g after 80 cycles). Moreover, the electrochemical lithium storage is controlled by the pseudocapacitive effect, the mixed process of both the pseudocapacitive effect, and diffusion-limited reaction, and the diffusion-limited reaction depends on different microstructures of the resulting samples. The relationship among their phase composition, morphology, porous structure, and electrochemical properties is also discussed.

Boron nitride (BN) nanotubes were synthesized through chemical vapor deposition over a wafer made by a LaNi5/B mixture and nickel powder at 1473 K. Scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were performed to characterize the microstructure and composition of BN nanotubes. It was found that the obtained BN nanotubes were straight with a diameter of 30-50 nm and a length of up to several microns. We first verify that the BN nanotubes can storage hydrogen by means of an electrochemical method, though its capacity is low at present. The hydrogen desorption of nonelectrochemical recombination in cyclic voltammograms, which is considered as the slow reaction at BN nanotubes, suggests the possible existence of strong chemisorption of hydrogen, and it may lead to the lower discharge capacity of BN nanotubes. It is tentatively concluded that the improvement of the electrocatalytic activity by surface modification with metal or alloy would enhance the electrochemical hydrogen storage capacity of BN nanotubes.

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