Structural characterization and effect of dehydration on the Ni-doped titanate nanotubes Dong Hyun Kim a, *, Jum Suk Jang b , Nam Hoon Goo a , Min Serk Kwon c , Jin Woo Lee d , Sun Hee Choi e , Dong Wook Shin a , Sun-Jae Kim f , Kyung Sub Lee a a Division of Materials Science & Engineering, Hanyang University, 133-791 Seoul, Republic of Korea b Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, TX 78712, United States c Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea d Department of Mechanical Engineering, Choongnam University, Yuseong-gu, Daejeon 305-764, Republic of Korea e Pohang Accelerator Laboratory, Beamline Research Division, Pohang 790-784, Republic of Korea f Institute/Faculty of Nanotechnology and Advanced Materials Engineering, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, Republic of Korea 1. Introduction One dimensional titania have been extensively studied for photocatalysis, dye-sensitized solar cell, lithium ion batteries, hydrogen storage, and electrochemical capacitors [1–5] due to its large specific surface area, numerous surface defects and physicochemical potentials [6–9]. Specially, there have been reports to apply titanate nanotubes for hydrogen storage, however, absorbing reaction occurred only at high temperature and/or low temperature (at 196 8C and over 120 8C) [10]. Bavykin et al. reported that the hydrogen could be intercalate between layers in the walls of TiO 2 nanotubes forming host–guest compounds TiO 2 xH 2 , where x  1.5 and decreases at higher temperatures [11]. Also, the TiO 2 nanotubes by Lim et al. showed that about 2 wt% hydrogen could be reproducibly stored at room temperature and 6 MPa [10]. However, in spite of these efforts, much work on the characterizations of structural and hydrogen absorption of titanate nanotubes are required. Also, systematic study on dehydration of nanotubes and interlayer spacing has yet to be done. Most researchers reported that the crystal structures of the titanate nanotubes have A 2 Ti 3 O 7 ,H 2 Ti 4 O 9 H 2 O (A = Na and/or H), and lepidocrocite titanates with monoclinic crystal structure [12–14]. However, the corresponding of XRD patterns was not fully coincided with the crystal structure from JCPDS (Joint Committee on Power Diffraction Standards). In our previous work, Ni-doped titanate nanotubes were synthesized by hydrothermal method using Ni-doped TiO 2 rutile powders and demonstrated exact crystal structure of the nanotubes (Ni-doped H 2 Ti 2 O 5 H 2 O) [15]. However, nanotubes had lots of hydrate in the crystal and on the surface which acted as a brake on hydrogen absorbing. In this work, Ni-doped titanate nanotubes were synthesized by hydrothermal method and simple firing and effect of dehydration on the Ni-doped titanate nanotubes for hydrogen storage was studied. And the crystal structures of synthesized nanotubes have been discussed. Also, the hydrogen absorption of nanotube was investigated by the conventional volumetric pressure–composition (P–C) isothermal method using an automated Sivert’s type apparatus. 2. Experimental The Ni-doped powders (0.8 g) and 15 mL of a 10 M NaOH aqueous solution were mixed with stirring for 1 h and placed in a Ni-lined stainless-steel autoclave at 120 8C for 24 h, and then Catalysis Today 146 (2009) 230–233 ARTICLE INFO Article history: Available online 23 May 2009 Keywords: Titanate nanotubes Hydrothermal method Hydrogen storage XFAS Ni dopant ABSTRACT Titanate nanotubes and Ni-doped titanate nanotubes were synthesized by hydrothermal method and simple firing using rutile powders as starting materials. The hydrogen absorption of the nanotubes was investigated by the conventional volumetric pressure–composition (P–C) isothermal method using an automated Sivert’s type apparatus. The microstructure and morphology of the synthesized nanotubes were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR- TEM). Titanate nanotubes compose of H 2 Ti 2 O 5 H 2 O in accordance with DFT (Density Functional Theory) calculation and has outer and inner diameter of 10 and 6 nm, and the interlayer spacing about 0.65– 0.74 nm. The storage capacity of hydrogen in the Ni-doped nanotubes increased linearly with pressure and revealed reliable evidence of hydrogen sorption at room temperatures. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +82 2 2281 4914; fax: +82 2 2281 4914. E-mail address: dhk@hanyang.ac.kr (D.H. Kim). Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod 0920-5861/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2009.04.007