Hydrogen in Light-Metal Cage Assemblies: Towards a Nanofoam Storage
Isomeric alternatives to usual metal-hydrides as hydrogen-storage materials are considered. Presented are results of ab initio calculations for Be n (n≤18) clusters with up to two endohedral H2 molecules which undergo in-cage dissociation. The systems structures and stabilities are discussed, including energy barriers for hydrogen exit from the cage. The origin of the observed metastability, allowing for a lower-temperature release of H2, is explored. Preservation of the cage integrity and hydrogen confinement is investigated when such core-shell units are merged into larger assemblies structurally resembling fragments of hydrogen-filled metal nanofoams, possible isomeric forms of metal-hydride solid. Different “nanofoam” isomers are composed of pairs or single H atoms suspended electrostatically inside the metal cage units (“nanobubbles”). Interesting features include simultaneous exit of two H atoms, etc. Structural extrapolations suggest potential hydrogen storage capacity up to ∼10 weight-%.
KeywordsHydrogen Storage Capacity Potential Energy Barrier Hydrogen Anion Small Dipole Moment Cluster Cage
The authors thank the RSC and the NSERC of Canada for the financial support of this work via a travel grant to FN. The staff of the HPC facilities of the UOIT Faculty of Science and of the Sharcnet network of Ontario are acknowledged for their invaluable technical support. FN is grateful to the University of Cambridge Department of Chemistry for their hospitality during his sabbatical visit.