Hydrogen physisorption by potassium-graphite intercalation compounds prepared from mesocarbon microbeads

Abstract

Potassium is intercalated into mesocarbon microbeads (MCMBs) with different heat-treatment temperatures (HTTs) and the hydrogen physisorption of the resulting compounds (KC x ; 8 ≤ x ≤ 36) is investigated. The hydrogen-physisorption behavior depends largely on the HTT of MCMB. Particularly, KC x compounds prepared from MCMB with a HTT of 1500 °C (KC x (HTT-1500)) show anomaly in the composition range from KC 8 to KC 12; the saturated amount of physisorbed hydrogen is remarkably large compared to that observed in the usual KC x compounds prepared from graphite, and the H 2 D 2 separation coefficient is also very large. It is found by X-ray diffraction measurement that KC x (HTT-1500; 8 ≤ x ≤ 11) compounds have a stage-1 structure. This is in contrast to KC x (HTT-2600; 8 ≤ x ≤ 11) compounds, which have a mixture of stages 1 and 2 as is the case with KC x prepared from graphite. This means that the density of the potassium layer in KC x (HTT-1500; 8 < x ≤ 11) is smaller than that of usual stage-1 KC 8. It is considered that nanospaces of this ‘dilute’ stage-1 structure can accommodate large amounts of hydrogen and that it is suitable for the hydrogen-isotope separation.