12540
J. Phys. Chem. C 2008, 112, 12540–12544
Enhancement Effect of LiAlH4 Addition on Reversible Hydrogen Storage Property for the Face-Centered Cubic Hydride Mg7TiH16 Prepared by a Gigapascal Hydrogen Pressure Method Tomoaki Takasaki,* Takashi Mukai, Naoyuki Kitamura, Shigeo Tanase, and Tetsuo Sakai* Research Institute for Ubiquitous Energy DeVices, National Institute of AdVanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan ReceiVed: January 9, 2008; ReVised Manuscript ReceiVed: June 10, 2008
It was found that the preparation ratio of the fcc Mg7TiH16 phase on the UHP synthesis was greatly enhanced by adding a small amount of LiAlH4. In addition, reversible hydrogen storage capacity of the sample was significantly increased. The Rietveld refinement results for synchrotron X-ray diffraction (XRD) data indicated that the Li ion would substitute the Mg site in the Mg7TiH16 phase. Differential scanning calorimeter measurements indicated that the LiAlH4 added Mg7TiH16 phase exhibited reversible hydrogen releasing and restoring behaviors under 0.1-0.5 MPa of hydrogen pressure. The reversible hydrogen storage capacities were in the range of 3.8-4 wt % on the pressure-composition isotherms. 1. Introduction Hydrogen has been studied as a clean alternative to petroleum oil. In the case of automotive fuel, safe and compact hydrogen storage system has to be developed. Metal hydrides would be a good solution to store gaseous hydrogen at normal pressure and ambient temperature. High hydrogen capacity (>5.5 wt %) with low releasing temperature (
