**3.2 Complex Metal Hydride - LiBH4 + ½MgH2 + Xmol% ZnCl2**

Based on the by-product LiCl appearance in the reaction discussed in Section 3.1 and to enhance the hydrogen storage capacity, the concentration of ZnCl2 was

**Figure 2.**

*Differential Scanning Calorimetric profiles of 2LiBH4 + ZnCl2 mixture with different catalysts (up to 3 mol%), such as TiF3, MgH2, nano-Ni.*

#### *Advanced Applications of Hydrogen and Engineering Systems in the Automotive Industry*

reduced in steps of few mol% on the LiBH4 + ½MgH2 complex metal hydride system. LiBH4 and MgH2 were ball milled (2 hours) together with 1:0.5 ratio and ZnCl2 have been admixed with different mol% concentrations to form complex composite hydride, LiBH + ½MgH2 + Xmol% ZnCl2 (X = 0, 2, 4, 6, 8 and 10). **Figure 4** represents the XRD patterns of the complex metal hydride with different value of X. When X = 0, with no ZnCl2, the structure is more or less the mixture of LiBH4 and MgH2. However, if the value of X increases to 2 mol%, the appearance Zn peak and the reduction of LiBH4 relative intensity are observed. For X = 4, an unknown peak appears around 20.5<sup>o</sup> because of the reaction of

**Figure 3.** *X-ray diffraction patters of 2LiBH4 + ZnCl2 mixture without and with different catalysts (1–4 mol% concentrations).*

**Figure 4.** *XRD profiles of LiBH4 + ½MgH2 + Xmol% ZnCl2 ball milled for 30 min in reactive (H2) atmosphere.*

#### *Light Weight Complex Metal Hydrides for Reversible Hydrogen Storage DOI: http://dx.doi.org/10.5772/intechopen.95808*

LiBH4 and available Zn to form Zn(BH4)2 as per the Eq. (3) and hence the byproduct formation of LiCl was inevitable. For the X value of 10 mol%, the LiBH4 phase and the pure Zn phase drastically reduced, however there was no changes in the MgH2 structural phase. Therefore, the XRD profiles confirm the Eq. (3) with concentration optimization of ZnCl2 which could further control the by-product LiCl formation. The Fourier Transform Infrared (FTIR) Spectroscopic profiles of LiBH4 + ½MgH2 + Xmol% ZnCl2 (X = 0, 2, 4, 6, 8 and 10) shows the presence of B-H stretch, at wavenumbers, 2276 cm−1 and 2213 cm−1 and another peak

**Figure 5.**

*FTIR of LiBH4 + ½MgH2 + Xmol% ZnCl2 (X = 0, 2, 4, 6, 8 and 10) ball milled for 30 min in reactive (H2) atmosphere.*

**Figure 6.**

*Desorption Data Collected on a PCT for LiBH4 + ½MgH2 + 2 mol% ZnCl2 Ball Milled 2 Hours Under H2 Ambient.*

#### **Figure 7.**

*PCT Desorption at 250°C and 350°C for the mixture, LiBH4 + ½MgH2 + 2 mol% ZnCl2 Ball Milled 2 Hours Under H2 Ambient.*

correspond to BH2 deformation band was observed at 1118 cm−1 and 1091 cm−1 due to LiBH4 (see **Figure 5**). These stretches were decreased in transmittance values when X increases from 2 to 10 mol%. No additional impurity peaks were observed.

The hydrogen absorption and desorption characteristics of LiBH4 + ½MgH2 + 2 mol% ZnCl2 was demonstrated using the PCT Sievert's type apparatus. The hydrogen desorption experiments were performed at various temperatures, for example from 1 to 3 cycles at 250°C, 4–6 cycles at 300°C and 8–10 cycles at 350°C. As the temperatures increased from 250–350°C, the hydrogen storage capacity increases five-fold as shown in **Figure 6**. At the end of each desorption run, the sample was hydrogenated at high pressure, up to 40 atmosphere and at temperature of 200°C for several hours. The PCT isotherm of 11th desorption run at 350°C demonstrates the plateau pressure of hydrogen desorption, at around 4–5 bars and the storage capacity of ~3.0 wt.% (see **Figure 7**). Based on the aforementioned characteristics, these complex metal hydrides bearing light weight elements or compounds, for example LiBH4 and MgH2 with catalysts dopants may be considered as potential applications for clean energy or fuel (hydrogen) storage.
