Adsorption and melting of hydrogen in potassium-intercalated graphite

Volumetric adsorption and quasielastic neutron scattering are used to study the diffusion and thermodynamics of sorbed H2 in the graphite intercalation compound KC24. A sorption enthalpy of 8.5 kJ/mol at zero coverage is determined from H2 adsorption isotherms. From measurements of total elastic-neutron-scattering intensity as a function of temperature, a melting transition of the H2 adsorbate is observed at 35 K for KC24 H2 1. Quasielastic-neutron-scattering QENS spectra reveal distinct slowand fast-H2-diffusion processes which exist simultaneously at temperatures above the transition point. The temperature dependence of the characteristic diffusion times follows an Arrhenius relation = 0 exp Ea /T , where 0 =1.0 0.1 ps,