Improved hydrogen storage performances of LiAlH ₄ + Mg( BH ₄ ) ₂ composite with TiF ₃ addition

Abstract

Summary This paper studies on the preparation of the alanate‐borohydride combined system, LiAlH4 + Mg(BH4)2 with diverse molar ratios (1:1, 1:2, and 2:1) using the ball milling technique. The findings show that there is a mutual destabilization between the hydrides where the newly combined system has superior hydrogen storage performances as opposed to the unary components (LiAlH4 and Mg[BH4]2). Analysis on the initial decomposition temperature and isothermal de/hydrogenation kinetics has proven that the 2LiAlH4 + Mg(BH4)2 system possesses better performance. In an endeavor to ameliorate the performances of the hydrogen storage of 2LiAlH4 + Mg(BH4)2, the destabilized system was doped with TiF3. Three major steps of desorption were detected during the heating process in the 2LiAlH4 + Mg(BH4)2 system with and without the addition of TiF3, which are correlated to the decomposition of Mg(AlH4)2, MgH2 and LiBH4. It is found that 2LiAlH4 + Mg(BH4)2 + 5 wt.% TiF3 has decreased the initial decomposition temperature at about 60°C, which is 55°C lower than the non‐catalyzed 2LiAlH4 + Mg(BH4)2 system. The isothermal absorption/desorption kinetics of the 2LiAlH4 + Mg(BH4)2 system have also been enhanced by the addition of TiF3. The activation energy for Mg(AlH4)2‐, MgH2‐, and LiBH4‐relevant decomposition after doped 2LiAlH4 + Mg(BH4)2 with TiF3 are reduced to 36.5, 23.3, and 17.6 kJ mol−1. Studies on the structural characteristics analysis of the 2LiAlH4 + Mg(BH4)2 + TiF3 sample hint to the fact that the formation of the MgF2, LiF, TiH2 and Ti‐Al species, during desorption, is the main responsible factor for the observed thermodynamics change of the reactions by modifying the dehydrogenation and hydrogenation pathway. The catalytic role played by TiF3 may have encouraged the interaction between Mg(AlH4)2, MgH2, and LiBH4, further ameliorate the de/hydrogenation of the 2LiAlH4 + Mg(BH4)2 + TiF3 destabilized system.

Additive Destabilization of Porous Magnesium Borohydride Framework with Core‐Shell Structure

“…Different strategies have been applied over the past years to decrease the activation energies and reduce the decomposition temperatures of metal hydrides, such as the introduction of complex metal borohydrides, [ 14,15 ] adding catalysts and reducing the particle size of the functional materials. [ 16–18 ] Notably, nanostructured hydride materials can directly reduce the barrier of reaction pathways for both hydrogen diffusion and mass transport, so their kinetic properties could be tuned independently of their bulk counterparts.…”

“…[12] Unfortunately, bulk Mg(BH 4 ) 2 decomposes in several steps, passing through intermediate species like stable MgB 12 H 12 phase where the activation energy is as high as 311 ± 20 kJ mol −1 , leading to an undesirable decomposition temperature of above 350 °C. [13] Different strategies have been applied over the past years to decrease the activation energies and reduce the decomposition temperatures of metal hydrides, such as the introduction of complex metal borohydrides, [14,15] adding catalysts and reducing the particle size of the functional materials. [16][17][18] Notably, nanostructured hydride materials can directly reduce the barrier of reaction pathways for both hydrogen diffusion and mass transport, so their kinetic properties could be tuned independently of their bulk counterparts.…”

Enhanced dehydrogenation performance ofNaAlH4by the addition of sphericalSrTiO3

“…[3][4][5][6] Currently, metal hydrides and light complex hydrides are considered promising ways to store hydrogen in a solidstate form. [7][8][9][10][11][12] Sodium alanate (NaAlH 4 ) is often investigated as a solid-state hydrogen storage material owing to its reasonable cost and high theoretical hydrogen capacity. [13][14][15] Theoretically, NaAlH 4 contains 7.4 wt% of hydrogen and decomposes in three dehydrogenation steps when heated above 400 C. In the first reaction step, hydrogen is released from 185 to 230 C, as Equation (1) shows: Heating the samples to 400 C will cause the decomposition of NaH, as stated in Equation (3):…”