Role of additives in LiBH4–MgH2 reactive hydride composites for sorption kinetics

Abstract

The influence of additives on the reaction kinetics and for microstructure refinement in LiBH 4-MgH 2 composites is investigated in detail. Indications on the rate limiting processes during the reactions are obtained by comparison of the measured reaction kinetics to simulations with one specific rate limiting process. The kinetics of the sorption reactions are derived from volumetric measurements as well as from in-situ Xray diffraction (XRD) measurements. During desorption, the hydrogen is released at a constant rate, which possibly is correlated to the one-dimensional growth of MgB 2 platelets. In contrast, the kinetic curves of the absorption reactions exhibit the typical shape of contracting-volume controlled kinetics. The microscopical interpretation of kinetic measurements are supported by transmission electron microscopy (TEM) images confirming the formation of additive-nanostructures in the grain boundaries upon cycling. The present investigations underline the importance of the additives as nucleation substrates and the influence of the microstructure on the reaction kinetics.

Recent Progress in Metal Borohydrides for Hydrogen Storage

“…Since Bogdanovic et al found that the addition of Ti-based compounds significantly promoted the dehydrogenation-rehydrogenation reactions of NaAlH 4 [193], the development of complex hydrides for hydrogen storage has significantly increased. Stimulated by this finding, a large number of additives from oxides, halides, metals, and carbon-based materials to M(BH 4 ) n have been examined [19,20,58,87,101,130,144,150,161,168,170,171,191,[194][195][196][197][198][199][200][201][202][203][204][205][206][207][208][209][210]; the corresponding dehydrogenation and rehydrogenation properties are summarized in Table 5. For instance, the most effective additive for LiBH 4 was found to be the mixture of 0.2 MgCl 2 + 0.1 TiCl 3 , in which approximately 5 mass% of hydrogen was released from 333 K and 4.5 mass% of hydrogen was rehydrogenated at 873 K in 7 MPa H 2 [195].…”

Improved reversible dehydrogenation of 2LiBH4+MgH2 system by introducing Ni nanoparticles

“…Unlike the previous study that the transition metals or transition metal halides are normally introduced just as catalyst. 42,43 In this work, the nano-Ni is introduced not only as a catalyst in catalyzing the decomposition of MgH 2 but also as an additive, which is totally involved into the decomposition of LiBH 4 , resulting the formation of Mg-Ni-B ternary alloy. For example, the presence of nano-Ni in 2LiBH 4 -MgH 2 -0.5Ni sample will firstly catalyze the dehydrogenation of MgH 2 .…”

Characterization of Gas‐Solid Reactions using In Situ Powder X‐ray Diffraction

“…[65] A detailed investigation of the reaction pathway was obtained by in situ SR-PXD measurements, which show interesting differences between the two samples. In LiBH 4 [61,62,66,67] The most significant decrease in hydrogen release temperature is observed in LiBH 4 -MgH 2 -Al (4:1:5), likely owing to absence of Mg-Al intermediates.…”

“…LiBH 4 -YH 3 , [59] LiBH 4 -SrH 2 , [60] and a promising and well-studied composite LiBH 4 -MgH 2 (2:1). [61][62][63] The dehydrogenation mechanism of the latter is investigated with in situ SR-PXD (Figure 4), which reveals a two-step decomposition reaction, i.e. MgH 2 decomposes to form Mg and gaseous H 2 , and finally LiBH 4 and Mg react to form LiH, MgB 2 and H 2 gas.…”

“…A variety of different models can be used to analyse the kinetic data [12] and the Johnson-Mehl-Avrami (JMA) type nucleation and growth rate equation is among the most frequently used: [62] α(t) = exp(-(kt) n )…”