The dehydrogenation kinetics and reversibility improvements of Mg(BH_4)_2 doped with Ti nano-particles under mild conditions

摘要

Magnesium borohydride, Mg(BH4)(2), is ball-milled with Ti nano-particles. Such catalyzed Mg(BH4)(2) releases more hydrogen than pristine Mg(BH4)(2) does during isothermal dehy-drogenation at 270, 280, and 290 degrees C. The catalyzed Mg(BH4)(2) also exhibits better dehydro-genation kinetics than the pristine Mg(BH4)(2). Based on kinetics model fitting, the activation energy (Ea) of the catalyzed Mg(BH4)(2) is calculated to be lower than pristine Mg(BH4)(2). During partial dehydrogenation, the catalyzed Mg(BH4)(2) releases 4.23 wt % (wt%) H-2 for the second dehydrogenation at 270 degrees C, comparing to 4.05, and 3.75 wt% H-2 at 280, and 290 degrees C. The reversibility of 4.23 wt% capacity is also one of the highest for Mg(BH4)(2) dehydroge-nation under mild conditions such as 270 degrees C as reported. 4 cycles of Mg(BH4)(2) dehydroge-nation are conducted at 270 degrees C. The capacities degrade during 4 cycles and tend to be stable at about 3.0 wt% for the last two cycles. By analyzing the hydrogen de/absorption products of the catalyzed sample, Mg(BH4)(2) is found to be regenerated after rehydrogenation according to Fourier Transform Infrared (FTIR) spectroscopy. Ti nano-particles can react with Mg(BH4)(2) during ball-milling and de/rehydrogenation. The products include TiH1.924, TiB, and TiB2, which can improve the dehydrogenation properties of Mg(BH4)(2) from a multiple aspect. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.