**3.1 Complex metal hydride - 2LiBH4 + ZnCl2 without and with different catalysts**

The complex metal hydride mixture, 2LiBH4 + ZnCl2 was prepared by hand mixing in ceramic mortar and via ball milling for different time duration under inert or reactive ambient. The obtained Zn(BH4)2 per the Eq. (3) was further treated with different catalysts doping. All these as-synthesized materials are then subjected to thermogravimetric and differential scanning calorimetric measurements (TGA-DSC or SDT). **Table 1** represents the onset, and peak temperature of hydrogen decomposition from the complex metal hydride with total weight loss. From the **Table 1**, it is discernible that the pristine mixture 2LiBH4 + ZnCl2 milled shows lower hydrogen decomposition temperature by at least 25°C when compared to hand mix counterparts. Additionally, the nano-Ni doping concentration of at least 1–4 mol% on the complex metal hydride mixture shows temperature reduction of at least 15–20°C for the hydrogen release. Overall, the total gravimetric weight loss due to hydrogen decomposition at the peak temperature, ranges from 12 to 15 wt% of hydrogen was obtained for both undoped and doped complex metal hydride mixtures. The hand mix sample show the weight loss of 9.4 wt.% due to partial formation of Zn(BH4)2. The TGA and DSC profiles as shown in **Figures 1** and **2** supports the **Table 1** results.

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


**Table 1.**

*TGA-DSC measurements data of pristine and catalyst doped complex metal hydride mixture, 2LiBH4 + ZnCl2.*

**Figure 1.** *Thermogravimetric profiles of 2LiBH4 + ZnCl2 mixture with different catalysts (up to 4 mol%), such as TiF3, MgH2, nano-Ni.*

A closer look of the TGA profiles (**Figure 1**), one can find a detailed observation as follows. Comparison between the metal hydride mixtures, LiBH4 + ½ ZnCl2 ball milled for 20 minutes shows greater hydrogen release at lower temperatures than the sample, 2LiBH4 + ZnCl2 hand mixed for 10 minutes, which emphasize the need of mechanical milling to complete the reaction stated in Eq. (3). Regarding the different concentrations of TiF3, 2 mol% reveals at least 0.5% more of hydrogen release and at temperatures at least 1°C lesser than the concentration 1 mol% TiF3. For the 2 mol% MgH2 doping, which showed similar performance like TiF3 dopant in terms of both thermal decomposition temperature and weight loss characteristics and are inferior to the pristine LiBH4 + ½ ZnCl2 mixture milled for 20 minutes. Nano-nickel on the other hand, doping with different concentrations, 1–4 mol%, demonstrated

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

superior thermal decomposition behavior with 3 mol% as an optimum concentration as shown in **Figure 1**.

The DSC profiles as exhibited in **Figure 2**; the endothermic peaks are due to thermal hydrogen decomposition where the weight loss was observed in **Figure 1**. As it is mentioned that the partial reaction of the hand mixed compounds as noted earlier is supported well with the DSC studies in which there were two endo- peaks obtained, one may be due to the LiBH4 phase and other may be due to the partial Zn(BH4)2 phase. However, the ball milled samples show only one endo sharp peak, the area under this curve enhanced at lower temperatures, by nano-Ni catalyst doping as shown in **Figure 2**.

The x-ray diffraction patterns of all the samples listed in **Table 1** are carried out with the similar experimental conditions and background parameters and are depicted in **Figure 3**. It is very well confirmed from the XRD profiles that the hand mix metal hydride samples show the existence of unreacted LiBH4 and ZnCl2. Whereas, the ball milled counterparts reveals the appearance of by-product, LiCl, thus the consumption or reaction of 2LiBH4 and ZnCl2 to produce a new Zn(BH4)2 compound, with unknown peak appeared at around 20.5o . For the catalysts, doped 2LiBH4 + ZnCl2, the peaks correspond to TiF3, or nano-Ni are not visible due to the low concentration (<4 mol%), and the XRD patterns were very similar to the pristine complex metal hydride ball milled for 20 minutes. The presence of LiCl phase affects the total hydrogen storage capacity reported in **Table 1**, because of the dead weight contribution from the LiCl. Overall, the XRD profiles of the complex metal hydrides supports the reaction (3) and the thermal characteristics as discussed above.
