Storing energy in carbon nanotubes

A history of carbon-based intercalation compounds

carbon-based guest-host solids The development of nanotube energy storage materials is the result of a natural progression from earlier work on other carbon-based guest–host solids. The time line representing the development of these solids, shown in the figure, runs clockwise starting at the upper left.

An early graphite intercalation compound, KC₈, consists of alternating layers of graphene and potassium. Lithium-ion batteries are made from the lithium analogue of this compound (LiC₈ represents the fully charged form). Molecular hydrogen does not intercalate into graphite, but it physisorbs on external surfaces at cryogenic temperatures.

Electrochemically doped polyacetylene, [Na_y(CH)]_x, is an example of a material that showed initial promise for battery applications but was never commercialized.

The interstitial sites in the molecular solid C₆₀ (fullerene) can be filled with alkali metals or molecular hydrogen. K₃C₆₀ and related phases exhibit superconductivity at temperatures exceeded only by the cuprate-based high-T_c superconductors. The alkali metal atoms occupy tetrahedral and octahedral crystallographic sites in the cubic close-packed fullerene lattice. Molecular hydrogen can fill most of the octahedral sites, giving a maximum H/C ratio of 1:120. This low ratio precludes any practical applications, but the material is an excellent example of the effect of lattice confinement on molecular rotations (8).

An idealized SWNT rope (see Figure 2, middle, for a real one) shows atoms or small molecules residing in the channels formed by the close-packed tubes. There is no experimental evidence that such a structure exists.

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	Storing energy in carbon nanotubes
	A history of carbon-based intercalation compounds The development of nanotube energy storage materials is the result of a natural progression from earlier work on other carbon-based guest–host solids. The time line representing the development of these solids, shown in the figure, runs clockwise starting at the upper left. An early graphite intercalation compound, KC₈, consists of alternating layers of graphene and potassium. Lithium-ion batteries are made from the lithium analogue of this compound (LiC₈ represents the fully charged form). Molecular hydrogen does not intercalate into graphite, but it physisorbs on external surfaces at cryogenic temperatures. Electrochemically doped polyacetylene, [Na_y(CH)]_x, is an example of a material that showed initial promise for battery applications but was never commercialized. The interstitial sites in the molecular solid C₆₀ (fullerene) can be filled with alkali metals or molecular hydrogen. K₃C₆₀ and related phases exhibit superconductivity at temperatures exceeded only by the cuprate-based high-T_c superconductors. The alkali metal atoms occupy tetrahedral and octahedral crystallographic sites in the cubic close-packed fullerene lattice. Molecular hydrogen can fill most of the octahedral sites, giving a maximum H/C ratio of 1:120. This low ratio precludes any practical applications, but the material is an excellent example of the effect of lattice confinement on molecular rotations (8). An idealized SWNT rope (see Figure 2, middle, for a real one) shows atoms or small molecules residing in the channels formed by the close-packed tubes. There is no experimental evidence that such a structure exists.
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