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1.Introduction: Complex metal hydrides (MH), with high volumetric/gravimetric hydrogen contents should meet the requirements for the energy storage systems needed to overcome the worldwide demand in energy with secured supply and limited impacts on the environment.Research efforts have focused for the last two decades on alanates (e.g.NaAlH4) and more recently on borohydrides.This later class of materials are of general formulae Mn+(BH4-)n, e.g.LiBH4 (18.5 wt.% H)1.However their de/re-hydrogenation properties have to be improved to ensure their practical use.2.The Synthesis: Wet chemistry and mechano-chemical (ball milling) synthesis are usually used.Both are based on exchange-metathesis reactions2 but reactions of MH with aminoboranes or diborane and synthesis with high temperature/pressure from the elements are also applied.Each procedure has is drawback and for industrial applications more systematic studies should be conducted.3.The decomposition reactions: Most of the new synthesized borohydrides are structurally well characterized but their decomposition remain poorly understood.Most of them undergo polymorphic transformationsl and melting prior to decomposition.The end products depend on the decomposition temperatures, below 200oC B2H6 will form2, on the H2 backpressure and on the stability of the corresponding MH.4.De/Re-hydrogenation properties: Destabilization of the borohydrides and/or stabilization of the products are keys to tailor their properties.Their stability correlates with the Pauling electronegativity of the cations and synthesis with the appropriate electronegativities have been successful to destabilize the borohydride.The stabilization of the dehydrogenated products has also been successfully applied using mixed system e.g.LiBH4 + All.The kinetics is enhanced by using catalyst or nano-confinement.Nevertheless, one drawback is the formation of B2H6 compromising the reversibility.[1] Blanchard, JPCC C, 113(2009), 14059-14066.[2] Blanchard, CdBH4, accepted in JAC.