Abstract
A comparative study of the dehydrogenation of pure, ScCl3-, TiCl3-, VCl3-, and MnCl2-doped sodium alanate is reported. The samples wet-doped with transition metal halides exhibit significant lowering of both first and second dehydrogenation temperatures when compared with the pure sodium alanate. The reduction of the dehydrogenation temperature, Delta T-dec, is maximum for the VCl3-doped alanates: 37 and 55 degrees C, respectively, for the decomposition steps yielding Na3AlH6 and NaH. Among the transition metal halides, the order in which the decomposition temperature is lowered is Mn < Sc < Ti < V. The reduction in the dehydrogenation temperature of alanates and the observed order are explained by considering the Pauling's electronegativity of Sc, Ti, V, Mn, and Na. Transition metals inductively diminishes the bond strength of the adjacent Al-H bond and renders its easy cleavage to form molecular hydrogen. The transition metal-induced instability shows a quadratic dependence on the electronegativity, in accordance with the Pauling's electronegativity equation. (C) 2008 Elsevier B.V. All rights reserved.