ALMACENAMIENTO DE HIDRÓGENO EN MATERIALES NANOESTRUCTURADOS EN BASE Mg CATALIZADOS POR LiBH4

Complex borohydrides are promising materials as solid – hydrogen storage media. In this work hydride systems composed of Mg–Ni and Mg–Fe combined with small amounts of LiBH4 are investigated. These materials are synthesized via short milling times under argon atmosphere and its thermodynamic and kinetic properties analyzed. Experimental results show that reversible hydrogen capacities of 7wt% (LiBH4–Mg–Ni) and 5.5 wt% (LiBH4–Mg–Fe) at 573 K are reached in just 300 seconds. Although the addition of LiBH4 does not modify the thermodynamic behavior of Mg–doped (Ni and Fe) hydrides, it accounts for the microstructural and morphological changes which facilitate the hydrogen diffusion through the formed hydride layer. Further examinations of the LiBH4–Mg–Ni hydride system proved the formation of MgNi3B2 phase under mild hydrogen cycle conditions, i.e. 350 ºC under 2.5 MPa of H2. The detection of this ternary phase evidences irreversible Mg–B interaction during hydrogen cycling and its presence might have effects on the observed kinetic behavior. Therefore, LiBH4 has a catalytic role enhancing the hydrogen storage properties of the materials under research