Thermodynamic Properties and Hydrogen Accumulation Ability of Fullerene Hydride C₆₀H₃₆

Abstract

Thermodynamic properties of fullerene hydride C₆₀H₃₆ in the ideal‐gas and crystal states were studied by theoretical methods. Molecular structures and vibration frequencies were calculated for 9 isomers of C₆₀H₃₆ by the density functional theory (DFT) by use of a combination of the B3LYP functional with 6‐31G* basis sets. Ideal‐gas thermodynamic properties were calculated based on those parameters. Enthalpies of formation of C₆₀H₃₆ isomers in the ideal‐gas state were derived from homodesmic reactions involving adamantane, cyclohexane, and C₆₀ fullerene. Using the standard methods of statistical mechanics, heat capacity and derived thermodynamic properties of crystalline C₆₀H₃₆ were calculated at 340–1000 K that extended the range of experimental measurements. With a crystal‐gas heat capacity difference, the experimental value of sublimation enthalpy was extrapolated to room temperature as Δ_sub H _m ^o (298.15 K)=(193±10) kJ · mol⁻¹. Combining this value with the known experimental enthalpy of formation in the crystalline state, the ideal‐gas enthalpy of formation of C₆₀H₃₆ at the synthesized sample isomer composition was obtained: Δ_f H _m ^o (298.15 K)=(1206±28) kJ · mol⁻¹. Equilibrium constants and compositions were calculated for the reactions of hydrogenation of C₆₀ fullerene in different states. It was shown that C₆₀ can act as a hydrogen accumulator.

Keywords:

• Fullerene hydride
• thermodynamic properties
• hydrogen accumulator
• DFT calculation