## 3 Results and Discussion
### Hydrogen Desorption Properties  
LiAlH\({}_{4}\) and NaAlH\({}_{4}\) nanomaterials, i.e., LiAlH\({}_{4}\) stabilized by 10 mM DDA and 1 mM DDA, respectively, were further investigated by TGA/DSC and MS to determine any influence of the surfactants' binding strength on the hydrogen desorption profiles. For pristine LiAlH\({}_{4}\), melting occurs at 182 \({}^{\circ}\)C. In contrast, surfactants stabilized LiAlH\({}_{4}\) melted at lower temperatures between 166 and 169 \({}^{\circ}\)C depending on the surfactant (Figure 9). This indicates an influence of particle size reduction on the melting behavior of LiAlH\({}_{4}\) akin to previous observations with metal nanoparticles [76; 77; 78]. To our surprise, such a reduction in melting point for the surfactants stabilized NaAlH\({}_{4}\) particles followed two separate trends related to the nature of the surfactant (i.e., of hard or soft character). For hard surfactants including DDA, TDA, and TBAB, the melting point decreases as a function of particle size similar to that of LiAlH\({}_{4}\). In contrary, for the soft thiol-stabilized NaAlH\({}_{4}\) particles, the overall melting point was decreased by \(\sim\)8 \({}^{\circ}\)C with no clear correlation to the particle size. Compared to LiAlH\({}_{4}\), the reduction in melting point of NaAlH\({}_{4}\) is less pronounced. A similar phenomenon was reported with nanoconfined NaAlH\({}_{4}\) where only a \(\sim\)13 \({}^{\circ}\)C decrease in the apparent melting temperature was observed when NaAlH\({}_{4}\) was confined within the 35 nm porosity of metal-organic frameworks [79]. This suggests that the melting point of NaAlH\({}_{4}\) only marginally reduces despites a significant reduction in particle size. The desorption profile of the as-synthesized LiAlH\({}_{4}\) nanoparticles still occurs in three steps. However, a correlation between the particle size with the dehydrogenation of LiAlH\({}_{4}\) can be seen from the first major decomposition step of LiAlH\({}_{4}\) into Li\({}_{3}\)AlH\({}_{6}\) (Figure 10). Figure 9: Evolution of the melting point as function of the particle size for: (**a**) LiAlH\({}_{4}\) and (**b**) NaAlH\({}_{4}\) stabilized with the investigated surfactants (the red dotted lines are a guide to the eye). All of the surfactant stabilized LiAlH\({}_{4}\) particles decomposed at lower temperatures as compared to pristine LiAlH\({}_{4}\) (218 \({}^{\circ}\)C). Notably when the particle size was reduced below 10 nm, the temperature required to decompose LiAlH\({}_{4}\) decreased by 21 \({}^{\circ}\)C. Furthermore, the dehydrogenation of LiAlH\({}_{4}\) was found to roughly correlate with its mean particle size. As such, this can be taken as an indication that a change in particle size can eventually leads to the improve hydrogen release properties for LiAlH\({}_{4}\)[80]. Unfortunately, further decomposition of Li\({}_{3}\)AlH\({}_{6}\) and LiH did not show a similar trend, and this is most likely due to the premature decomposition of the surfactants which in turn contribute to the loss of nanosizing effects (Figure S29). Nevertheless, it is not certain that the reduction in particle size may be the sole contributor to the improved dehydrogenation temperatures as the interaction between LiAlH\({}_{4}\) and surfactants may also affect the hydrogen releasing mechanism. Remarkably, all of the amine-stabilized LiAlH\({}_{4}\) started to release hydrogen from 75 \({}^{\circ}\)C (Figure S23). Indeed, many LiAlH\({}_{4}\)-NH\({}_{2}\) systems have been reported to induce hydrogen release at low temperatures [81,82], owing to the H\({}^{5+}\) (amine) and H\({}^{6-}\) (hydride) interaction [83]. For LiAlH\({}_{4}\) stabilized by thiol bases surfactants, a modest amount of hydrogen was observed between 65 to 160 \({}^{\circ}\)C prior to the major decomposition of LiAlH\({}_{4}\) into Li\({}_{3}\)AlH\({}_{6}\) at \(\sim\)200 \({}^{\circ}\)C (Figure 11 and Figure S24). This was attributed to the reaction between the remaining thiol group and LiAlH\({}_{4}\)[70].