A novel three-step method for preparation of a TiB2-promoted LiBH4-MgH2 composite for reversible hydrogen storage

The reversible dehydrogenation properties of the 2LiBH(4)-MgH2 composite can be effectively improved by incorporating heterogeneous nucleation agents, typically transition metal borides. A careful study of the 2LiBH(4)-MgH2 composite with a titanium trifluoride (TiF3) additive finds that using the conventional one-step milling method renders only a partial conversion from TiF3 to titanium boride (TiB2) through an intermediate of titanium hydride (TiH2). Based on a fundamental understanding of the reaction processes of the system, we developed a three-step preparation method, which involves pre-milling the LiBH4-TiF3 mixture, isothermal treatment and milling together with MgH2. A combination of phase/chemical state/microstructural analyses using X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy techniques shows that the newly developed method can effectively promote the formation of TiB2 and meanwhile, ensure a homogeneous dispersion of TiB2 nanoparticles in the composite matrix. As a consequence, the composite sample prepared by the new method exhibits a favorable combination of high hydrogen capacity, fast reaction kinetics and satisfactory cyclic stability.