Effect of metal type and loading on hydrogen storage on NaAlH₄

Abstract

Although hydrogen has a great potential as clean energy, safe practical storage of hydrogen for applications such as fuel cells has been a major challenge. NaAlH₄ is one of the metal hydrides, which are candidates for hydrogen storage in vehicles. However, the rather slow absorption/desorption kinetics is still a significant drawback. To alleviate this problem, purified NaAlH₄ was ground with TiCl₃, ZrCl₄, or HfCl₄. Desorption kinetics and capacities were observed under TPD-like operation. Absorption efficiency was determined by raising the temperature up to 125 8C. Of the three doped metals investigated for the positive effect on facilitating NaAlH₄ decomposition, TiCl₃ assists the best on the first reaction while ZrCl₄ and HfCl₄ do for the second one. Despite the kinetics enhancement directly involves with the ZrCl₄ amount, there is a threshold of ZrCl₄-content which affects. 6% ZrCl₄ is considered as an appropriate amount to improve the hydrogen release because it simultaneously decreases the desorption temperature and gives the outstanding rate. In hydrogen desorption, ZrCl₄ provides the most amount of released hydrogen, but for hydrogen absorption TiCl₃-doped NaAlH₄ possesses the highest capacity. It is believed that the metal size is one of the key factors resulting in such the behavior.

Key Words:

• Hydrogen storage
• NaAlH₄
• Catalytic effect
• ZrCl₄
• TiCl₃
• HfCl₄