## 4 Conclusions  
LiAlH\({}_{4}\) and NaAlH\({}_{4}\) nanoparticles were successfully synthesized via a facile solvent evaporation method using various types of surfactants as a stabilizer. Increasing the surfactant concentration to 10 mM resulted in the smallest average particle size between 10 to 200 nm. Following the HSAB principle, it was found that surfactants with matching hard character exhibited the best stabilizing effect and displayed a stronger binding to the particle surface which eventually leads to the formation of smaller particles. This study also revealed that the size of alanates nanoparticles can be controlled through an appropriate choice of surfactants. Surfactants with longer linear carbon chains would favour the growth of smaller nanoparticles due to the strong steric hindrance, whereas surfactants with higher intrinsic steric hindrance would result in larger nanoparticles. Also, surfactants with thiol and amine head groups enable the release of hydrogen at lower temperature due to their thermal reactivity with LiAlH\({}_{4}\). In addition, the reduction in particle size and the interaction with surfactant were found to enhance the hydrogen desorption properties of LiAlH\({}_{4}\). In contrast, no clear trend was obtained when comparing the dehydrogenation temperature of NaAlH\({}_{4}\) as a function of particle size. As such, it can be concluded that the successful stabilization of alanate nanoparticles is not sufficient to enable adequate hydrogen storage properties. Agglomeration of the alanate nanoparticles, likely to occur upon decomposition or melting of surfactants during heating for hydrogen release, should be restrained. In this respect, future work on the nanostructuring of core-shell alanates is still required to further stabilize and restrict the alanate particles to withstand the high temperature during hydrogen cycling. Nevertheless, it is necessary to understand the effect of surfactants on the surface state of the alanate nanoparticles, i.e., binding strength and redox potential, in order to enable a homogenous shell growth. To this aim, the material which can reduce the reduction kinetics of alanates and has an average size of 20-30 nm will be considered for the core-shell synthesis. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12094742/s1](https://www.mdpi.com/article/10.3390/app12094742/s1)]([https://www.mdpi.com/article/10.3390/app12094742/s1](https://www.mdpi.com/article/10.3390/app12094742/s1)). Figure S1: Typical TEM images of pristine LiAlH\({}_{4}\) and NaAlH\({}_{4}\), Figures S2-S16: Typical TEM images of surfactant stabilized LiAlH\({}_{4}\) and NaAlH\({}_{4}\), Figure S17: Elemental mapping of stabilized LiAlH\({}_{4}\) and NaAlH\({}_{4}\), Figures S18-S20: XRD of LiAlH\({}_{4}\) and NaAlH\({}_{4}\) nanostructures, Figures S21-S28: TGA/DSC-MS of as-synthesized LiAlH\({}_{4}\) and NaAlH\({}_{4}\) nanoparticles, Figure S29: Decomposition temperature of LiAlH\({}_{4}\) particles, Figure S30: Decomposition temperature of NaAlH\({}_{4}\) nanoparticles, Table S1: Particle size of all synthesized materials, Table S2: Crystalline size of all synthesized material, Table S3: Decomposition temperature of the investigated surfactants, Table S4: FTIR vibration of the investigated surfactants and Table S5: Gravimetric hydrogen capacities of all synthesized materials. **Author Contributions:** [PERSON] carried out all of the experimental work which was conceived and designed with K.-F.A.-Z. All authors have read and agreed to the published version of the manuscript. **Funding:** This research received no external funding. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Data is contained within the article or supplementary material. **Acknowledgments:** Financial supported by UNSW Internal Research Grant program is gratefully acknowledged. We appreciate the use of instruments in the Mark Wainwright Analytical Centre at UNSW.