Low-index surface investigation of KAlH4: Theoretical attempt to study the surface effect on the hydrogen storage properties

Different preparations of complex hydrides lead to different hydrogen uptake and release. Besides, Potassium Aluminum hydride is a structure with different re/dehydrogenation properties than the rest of alanates. Given these considerations, we investigated nine stable cleavages on the (100), (010), (001), (111), and (101)KAlH4 surfaces. The results reveal that, while the (010) surface energy is much higher, all the other surfaces are approximately in the same range of energy. Some of these surfaces would be placed on top of the nanocrystallites and the different decomposition pathways may be originated from the different characteristics of these surfaces, which is one of the central issues of the present study. Our results are in accordance with experimental data indicating that long hours milling of alanates just creates fresh surfaces and the structures remain unchanged. Due to the surface effect, huge changes in electronic and geometric characteristics occur. The band gaps are narrowed up to 2eV, which alongside with massive changes in chemical bonds, lead to an improved dehydrogenation relative to the bulk.