Besides the Li-N-H and Li-Mg-N-H systems, other (i.e., Li-Ca-N-H) metal amide-metal hydride systems were also investigated. Some researchers focused on the decomposition of metal amides alone to discover new working pairs, and to address the NH\({}_{3}\) emission problem [18; 19; 20; 21; 22; 23; 24; 25; 26], whereas some other authors examined the Li-Ca-N-H system, but the results were not superior compared to Li-N-H and Li-Mg-N-H systems [27; 28]. Apart from the type of the complex hydride system, the preparation procedure also plays a significant role in the hydrogen storage characteristics of the complex hydrides. The favorable effects of mechanical activation (MA) via ball milling, such as reducing the onset temperature of desorption, enhancing the reaction kinetics, and lowering the activation energy, have been known for a while, and these favorable effects are associated with the creation of nanocrystallites, smaller particle sizes, and increased surface area [29; 30; 31]. Regarding the amide systems, MA is especially important in preventing the release of NH\({}_{3}\) by enhancing the homogeneous mixing of the constituents. Since the conversion of amide to amide is an ammonia-mediated process as explained in Equations (2) and (3), a metal hydride compound can effectively capture NH\({}_{3}\) only if the M-amide-M-imide interface could be created at the nanoscale. It was shown that increasing the milling time decreases the grain size monotonically and increases the surface area up to around 5 h milling, as well as enhances the desorption kinetics considerably [30; 32; 33; 34]. [PERSON] et al. further confirmed that reducing the particle size enhances the reaction kinetics, and reduces the NH\({}_{3}\) emission [35]. [PERSON] et al., investigated the low temperature milling, and the results showed that desorption kinetics is faster for the sample milled at \(-\)196 \({}^{\circ}\)C compared to the samples milled at \(-\)40 \({}^{\circ}\)C and 20 \({}^{\circ}\)C [36]. Ammonia emission, even in trace levels, is undesirable in the amide systems because it poisons the fuel cells and causes loss of hydrogen, which in return results in the loss of gravimetric capacity [37]. The effect of NH\({}_{3}\) emission on cyclic behavior and capacity loss is further elaborated, and the results showed that NH\({}_{3}\) emission can be mitigated by ball milling. Ammonia emission is more pronounced for the Li-Mg-N-H system compared to the Li-N-H system since the reaction rate of MgH\({}_{2}\) with NH\({}_{3}\) is slower than the reaction rate between LiH and NH\({}_{3}\)[38; 39; 40; 41]. Another important strategy in improving the performance of the complex hydrides is the utilization of catalysts. The seminal study of [PERSON] on Ti-doped NaAlH\({}_{4}\) paved the way for further investigations of the favorable effects of various catalysts in complex hydrides [42]. The favorable effects of catalysts in enhancing the reactions kinetics, lowering the desorption temperature, and alleviating NH\({}_{3}\) emission in the amide systems have been studied by many researchers [43; 44; 45; 46; 47; 48; 49]. [PERSON] et al. was the first to investigate the effects of TiCl\({}_{3}\), Ni, Co and Fe on NH\({}_{3}\) emission, reaction kinetics, and the desorption temperature of the Li-N-H system, and the results showed that TiCl\({}_{3}\) is superior compared to Ni, Co and Fe [39]. [PERSON] et al. focused on Ti\({}^{\text{nano}}\), Ti\({}^{\text{micro}}\), TiCl\({}_{3}\), TiO\({}_{2}\)\({}^{\text{nano}}\), and TiO\({}_{2}\)\({}^{\text{micro}}\) in the Li-N-H system, and proved the importance of the particle size of the catalysts. The nanocatalysts were superior compared to micro catalysts [44]. [PERSON] et al. investigated Mn, V, MnO\({}_{2}\), and V\({}_{2}\)O\({}_{5}\) in the Li-N-H system, and showed that Mn, V, MnO\({}_{2}\), and V\({}_{2}\)O\({}_{5}\) has no effect in hydrogen desorption, but enhances the ammonia emission [45].