Ca-intercalated graphite as a hydrogen storage material: Stability against decomposition into CaH{sub 2} and graphite

Journal Article · Wed Jun 15 00:00:00 EDT 2011 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2011.04.013· OSTI ID:21580089

Skipper, N T; Gillan, M J ^[1]

---

1. Department of Physics and Astronomy, University College London, Gower Street, London WCIE 6BT (United Kingdom)

We have used calculations based on density functional theory to investigate the energetics of hydrogen absorption in calcium-intercalated graphites. We focus particularly on the absorption energy and the stability of the hydrogenated material with respect to decomposition into graphite and calcium hydride, which is essential if this material is to be used for practical H{sub 2} storage. The calculations are performed with two commonly used approximations for the exchange-correlation energies. Our calculations confirm earlier predictions that the absorption energy is approximately -0.2 to -0.4 eV, which is favourable for practical use of Ca-intercalated graphite as a hydrogen storage medium. However, we find that the hydrogenated material is strongly unstable against decomposition. Our results therefore explain recent experiments which show that H{sub 2} does not remain stable in CaC{sub 6} but instead forms a hydride plus graphite. - Graphical abstract: The hydrogenation of Ca-graphite (left) results in its decomposition into pure graphite (middle) and CaH{sub 2} (right). Highlights: > We investigate the stability of hydrogenated Ca-intercalated graphite with DFT. > Dissociated H absorption in CaC{sub 6} is most favourable, with reasonable binding energies. > Molecular H{sub 2} absorption is most favourable in CaC{sub 8} and CaC{sub 14}. > We find all scenarios are unstable against decomposition into CaH{sub 2} and graphite. > The decomposition will be strongly exothermic in agreement with experiments.

• OSTI ID: 21580089
• Journal Information: Journal of Solid State Chemistry, Vol. 184, Issue 6; Other Information: DOI: 10.1016/j.jssc.2011.04.013; PII: S0022-4596(11)00181-2; Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ABSORPTION
APPROXIMATIONS
BINDING ENERGY
CALCIUM
CALCIUM HYDRIDES
DECOMPOSITION
DENSITY FUNCTIONAL METHOD
ELECTRON CORRELATION
GRAPHITE
HYDROGEN
HYDROGEN STORAGE
HYDROGENATION
STABILITY
ALKALINE EARTH METAL COMPOUNDS
ALKALINE EARTH METALS
CALCIUM COMPOUNDS
CALCULATION METHODS
CARBON
CHEMICAL REACTIONS
CORRELATIONS
ELEMENTS
ENERGY
HYDRIDES
HYDROGEN COMPOUNDS
METALS
MINERALS
NONMETALS
SORPTION
STORAGE
VARIATIONAL METHODS