Effects of helical GNF on improving the dehydrogenation behavior of LiMg(AlH4)3 and LiAlH4

The present paper reports the effect of graphitic nanofibres (GNFs) for improving the desorption kinetics of LiMg(AlH4)(3) and LiAlH4 LiMg(AlH4)(3) has been synthesized by mechano-chemical metathesis reaction involving LiAlH4 and MgCl2. The enhancement in dehydrogenation characteristics of LiMg(AlH4)(3) has been shown to be higher when graphitic nanofibres (GNFs) were used as catalyst Out of two different types of nanofibres namely planar graphitic nanofibre (PGNF) and helical graphitic nanofibre (HGNF), the latter has been found to act as better catalyst We observed that helical morphology of fibres improves the desorption kinetics and decreases the desorption temperature of both LiMg(AlH4)(3) and LiAlH4 The desorption temperature for 8 mol% HGNF admixed LiAlH4 gets lowered from 159 degrees C to 128 degrees C with significantly faster kinetics In 8 mol% HGNF admixed LiMg(AlH4)(3) sample, the desorption temperature gets lowered from 105 degrees C to similar to 70 degrees C The activation energy calculated for the first step decomposition of LiAlH4 admixed with 8 mol% HGNF is similar to 68 kJ/mol, where as that for pristine LiAlH4 It IS 107 kJ/mol The activation energy calculated for as synthesized LiMg(AlH4)(3) is similar to 66 kJ/mol Since the first step decomposition of LiMg(AlH4)(3) occurs during GNF admixing, the activation energy for initial step decomposition of GNF admixed LiMg(AlH4)(3) could not be estimated (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd All rights reserved