期刊
PHYSICAL REVIEW B
卷 79, 期 23, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.79.233408
关键词
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资金
- Korea Government MEST
- Korean Government MOEHRD [KRF-2006-341-C000015]
- Hanwha Chemical Co
Using density functional theory electronic structure calculations, we investigate the calcium-hydroxyl group complex for potential applications to the hydrogen storage at near ambient temperature and pressure. The Ca atom is bound to the hydroxyl group with a binding energy comparable to the cohesive energy of bulk Ca, and we find that each Ca atom binds up to seven H-2 molecules in the molecular form. Binding of an unexpectedly large number of H2 molecules is attributed to the fact that d orbitals of Ca positive ions are downshifted and partially occupied, thereby validating the empirical 18-electron rule as in the transition metal atoms. The binding energy turns out to be similar to 0.1 eV/H-2, somewhat smaller than the requirement (>= 0.2 eV/H-2) of the room-temperature application. We also show that an important bonding mechanism of H-2 molecules on Ca is the polarization, namely, the electric dipole moment of H-2 induced by the partially ionized Ca. Based on this result, the possibility of the organic material functionalized with hydroxyl groups for a hydrogen storage medium is discussed.
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