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

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 degrees C, fulfilling the operation temperature of a PEM fuel cell. In the nano-CeO2 doped NaAlH4 system, CeO2 is first reduced to CeH2.51. In the subsequent cycles, the formed CeH2.51 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.