Significantly improved hydrogen storage properties of NaAlH4 catalyzed by Ce-based nanoparticles

Abstract

NaAlH₄, a prototypical high energy density complex hydride, possesses a favorable thermodynamics and high hydrogen storage capacity. However, the poor kinetics and degradation of cycling stability retard its practical application. To ease these problems, CeB₆, CeF₃ and CeO₂ nanoparticles with a size of about 10 nm are synthesized by the wet-chemistry method and introduced into NaAlH₄ systems as additives in this work. The results show that all of the nanoparticles are effective in improving the hydriding–dehydriding kinetics of NaAlH₄, and nano-CeB₆ possesses the highest catalytic activity. The rehydrogenation of dehydrogenated NaAlH₄ doped with nano-CeB₆ can be accomplished in less than 20 min with a high capacity of 4.9 wt%, which shows a 20% increase in capacity compared to that of chloride-doped NaAlH₄. Due to the structural stability and good dispersion of nano-CeB₆ and nano-CeF₃, a favorable cycling stability with high capacity retention is achieved for their doped samples. Moreover, hydrogen can be released from the hydrogenated sample doped with nano-CeB₆ at a temperature as low as 75 °C, fulfilling the operation temperature of a PEM fuel cell. In the nano-CeO₂ doped NaAlH₄ system, CeO₂ is first reduced to CeH_2.51. In the subsequent cycles, the formed CeH_2.51 gradually transforms into Ce–Al, and simultaneously the kinetics of the doped system is further enhanced. It is believed that the utilization of Ce-based nanoparticles as catalysts would substantially improve the practical applications of NaAlH₄ for hydrogen storage.