Effect of Ti compounds on hydrogen desorption-absorption of LiNH₂

Abstract

Solid hydrogen storage materials have been investigated as hydrogen carriers due to their safety in hydrogen applications. In contrast, they also have some disadvantages, such as a low hydrogen capacity, very high desorption/absorption temperature, low kinetic rate, and low reversibility. Many attempts have been made to identify and improve materials that can be applied for on-board hydrogen storage for fuel cells. In this work, Ti and Ti compounds were used to enhance the kinetics rate and stability of metal hydrides. The results report the effects of Ti and Ti compounds (Ti0₂ and TiCl₃) on hydrogen desorption and absorption cycles of a LiNH₂/LiAlH₄/MgH₂ system and their implications on the system. We demonstrated that the formation of ammonia from the decomposition of LiNH₂ was suppressed by adding LiAlH₄ and MgH₂. In addition, LiNH₂/LiAlH₄/MgH₂ showed a lower onset desorption temperature than that of neat LiNH₂, up to 200°C. Moreover, doping with Ti0₂ or TiCl₃ also lowered the decomposition temperature and accelerated the H₂ desorption of the ternary mixture (LiNH₂/LiAlH₄/MgH₂). In addition, the H₂ reabsorption ability of LiNH₂/LiAlH₄/ MgH₂ was improved by doping it with Ti and Ti compounds, and Ti exhibited the best performance in the reversible H₂ capacity, 0.4 wt%. XRD patterns revealed the small peaks of Mg(AlH₄) 2 and Mg(NH₂)2, which were indicated as the reversible phases of the ternary mixture. Moreover, the addition of carbon nanotube in 2:1:1 LiNH₂/LiAlH₄/MgH₂ also affected the reversibility of the hydrides.