Characterization of the Dehydrogenation Process of LiBH4 Confined in Nanoporous Carbon

Annealing in the transmission electron microscope allows direct comparison of the same nanoporous carbon scaffold particles following dehydrogenation of the confined LiBH4. At a nominal temperature of 200 C, a granular crust of cubic and cuboidal LiH nanocrystals similar to 8-15 nm wide grew on the outer surface of the scaffold. Furthermore, these crystals migrated on the carbon support film away from the scaffold. Ejection of material from the scaffold also occurred upon dehydrogenation in a differential scanning calorimeter. The form of the ejected material was different, being bristles instead of cubes or cuboids. This ejection of LiH and thus preferential segregation of lithium from boron is proposed to explain the observed continual decrease in hydrogen storage capacity with the number of cycles.