Study of the 2LiBH4 + MgH2 reactive hydride composite doped with Fe and F3Fe for hydrogen storage

J. A. PUSZKIEL; F. C. GENNARI; P. ARNEODO LAROCHETTE

Moscú, Rusia

Simposio; International Symposium on Metal-Hydrogen Systems-Fundamentals and Applications; 2010

International Symposium on Metal-Hydrogen Systems

LiBH4 is a promising material to store hydrogen because of its interesting characteristics. It has high hydrogen gravimetric capacity (18.4 wt%) which is far above of the target established by the International Energy Agency (5.0 wt% of hydrogen) and high volumetry capacity (121 kg.m-3 H2) [1–3]. However, the main constraint of LiBH4 is its high thermodynamic stability (ΔHLiBH4= 74 kJ.mol−1 H2) wich consequently results in an elevated dehydrogenation temperature (Tdesorption= 370 ºC at 1 bar) and harsh hydrogenation conditions (600 ºC and 155 bar of hydrogen) [4]. Thus, the physicochemistry of LiBH4 precludes its practical application, for example as a medium to store hydrogen for vehicular purposes. One of the applied concepts to reduce the stability of LiBH4 is the combination with other compounds such as binary hydrides as for example MgH2. This approach leads to the reduction of the enthalpy of the overall reaction (2LiBH4 + MgH2 ↔ MgB2 + 2LiH + 4 H2, ΔH = 40.5 kJ.mol-1 H2) and reversible decomposition of the borohydride via boride compounds formation [5, 6]. Nonetheless, the reacction between LiBH4 and MgH2 may have kinetic restrictions that do not permit to operate at temperatures below 400 ºC as predicted by thermodynamic reaction (T(1 bar) = 225ºC). In order to improve the operative conditions at wich the 2LiBH4 + MgH2 reactive hydride composite uptake/release hydrogen, we add Fe and F3Fe as catalysts. We assess the microestructural and thermal properties before and after hydrogen cycling and the rate of absorption/desorption of hydrogen as well as the hydrogen cycling of 2LiBH4 + MgH2 doped with Fe and F3Fe. Experimental results show that the kinetics of 2LiBH4 + MgH2 is improved by the catalyst addition, reaching reversible capacities of about 10 wt% H, but the operative temperature is above 350 ºC.