Hydrogen storage properties of Mg[BH 4] 2

• Published in: Journal of alloys and compounds Vol. 459; no. 1; pp. 583 - 588
• Main Authors: Matsunaga, T., Buchter, F., Mauron, P., Bielman, M., Nakamori, Y., Orimo, S., Ohba, N., Miwa, K., Towata, S., Züttel, A.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.01.2008; Elsevier
• Subjects: Alternative fuels. Production and utilization; Applied sciences; Energy; Exact sciences and technology; Fuels; Hydrogen; Hydrogen absorbing materials; Thermal analysis; Thermodynamic properties; Thermodynamic properties; Hydrogen absorbing materials; Thermal analysis; Differential scanning calorimetry; Hydrogen storage; TDS; Absorption; Enthalpy; Desorption; Magnesium Hydroborates; X ray diffraction
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2007.05.054

Among the large variety of possible complex hydrides only few exhibit a large gravimetric hydrogen density and stability around 40 kJ mol −1H 2. Mg[BH 4] 2 is based on theoretical approaches a complex hydride with an equilibrium hydrogen pressure of approximately 1 bar at room temperature and a hydrogen content of 14.9 mass%. The reaction of Li[BH 4] with MgCl 2 at elevated temperatures was investigated as a possible route to synthesize Mg[BH 4] 2. Li[BH 4] reacts with MgCl 2 at a temperature >523 K at a pressure of 10 MPa of hydrogen, where the product contains LiCl and Mg[BH 4] 2. The desorption pc-isotherm of the product obtained at 623 K shows two flat plateaus, which indicates that the decomposition of the product consists of a two-step reaction. The products of the first and the second decomposition reaction were analyzed by means of X-ray diffraction and found to be MgH 2 and Mg, respectively. The enthalpy for the first decomposition reaction was determined to be Δ H = −39.3 kJ mol −1H 2 by the Van’t Hoff plot of the equilibrium measurements between 563 K and 623 K, which is significantly lower than that for pure Li[BH 4] (Δ H = −74.9 kJ mol −1H 2). However, only the second reaction step (MgH 2 → Mg) is reversible at the condition up to 623 K at 10 MPa of hydrogen.