Milling and Additive Effects on Hydrogen Desorption Reactions of Li-N-H and Li-Mg-N-H Hydrogen Storage Systems

摘要

Hydrogen desorption reactions of the mixtures of (i) lithium amide and lithium hydride (LiNH{sub}2/LiH), and (ii) magnesium amide and lithium hydride (Mg(NH{sub}2){sub}2/4LiH) were studied. Titanium compounds and nano-particles including fullerene (C{sub}60), were doped to those hydrogen storage mixtures respectively. The hydrogen desorption reactions were monitored by means of temperature programmed desorption (TPD) technique under an Ar atmosphere. The reaction of LiNH{sub}2/LiH was accelerated by adding either 1mol% of Ti species or 0.2mol% of fullerene (C{sub}60), while those additives did not show significant acceleration effects on the reaction of Mg(NH{sub}2){sub}2/4LiH. Kinetic studies revealed the enhanced hydrogen desorption reaction rate constant for TiCl{sub}3 doped LiNH{sub}2/LiH, k=3.1×10{sup}(-4) s{sup}(-1) at 493K, and the prolonged ball-milling further improved reaction rate, k=1.1×10{sup}(-3) s{sup}(-1) at the same temperature. For the dehydrogenation reaction of TiCl{sub}3 doped LiNH{sub}2/LiH, the activation energies estimated by Kissinger plot (95kJ mol{sup}(-1)) and Arrhenius plot (110kJ mol{sup}(-1)) were in reasonable agreement each other. The LiNH{sup}2/LiH mixture without additive exhibited slower hydrogen desorption process and the kinetic traces deviated from single exponential behavior. The results indicated the Ti(III) additives change the hydrogen desorption reaction mechanism of LiNH{sub}2/LiH.