Reversible hydrogen storage in destabilized LiAlH4-MgH 2-LiBH4 ternary-hydride system doped with TiF3
- Citation data:
Journal of Physical Chemistry C, ISSN: 1932-7447, Vol: 114, Issue: 26, Page: 11643-11649
- Publication Year:
- Chemistry; Materials Science; Energy; Reversible; hydrogen; storage; destabilized; LiAIH4; MgH2; LiBH4; Ternary; Hydride; System; Doped; TiF3; Arts and Humanities; Life Sciences; Medicine and Health Sciences; Social and Behavioral Sciences
This paper reports the hydrogen storage properties of a ternary hydride system, LiAlH-MgH-LiBH (molar ratio 1:1:1), both undoped and doped with TiF addition. It was found that there is a mutual destabilization among the three hydrides. This new ternary system possesses superior hydrogen desorption properties compared with the unary components (LiAlH, MgH, and LiBH) or binary mixtures of those components (LiAlH-MgH, LiAlH -LiBH, and MgH-LiBH). On doping with TiF, the system starts to release hydrogen at 60 °C and completes dehydrogenation below 400 °C. Three major dehydrogenation steps were observed in the undoped and TiF-doped systems, which corresponds to the decomposition of LiAlH, MgH, and LiBH, respectively. X-ray diffraction (XRD) measurements on the as-dehydrogenated samples were executed to identify the dehydrogenation pathway. The third step decomposition enthalpy of the doped system was determined by pressure-composition-temperature (PCT) measurements and the van't Hoff equation to be 54 kJ/mol H, which is smaller than that of LiBH alone (74 kJ/mol H). In addition, the TiF-doped system is partially reversible at moderate temperature and pressure (4 MPa, 400 °C) with good cycling. The enhancement of the hydrogen sorption properties was attributed to the formation of intermediate compounds, including Li-Mg, Mg-Al, and Mg-Al-B alloys, upon dehydrogenation, which change the thermodynamics of the reactions through altering the de/rehydrogenation pathway. The TiF component in the doped system plays a catalytic role through the formation of Ti-containing and F-containing catalytic species, which strengthens this interaction and thus further improves the dehydrogenation and hydrogenation of this system. © 2010 American Chemical Society.