HYDROGEN PHYSISORPTION BY POTASSIUM-GRAPHITE INTERCALATION COMPOUNDS PREPARED FROM MESOCARBON MICROBEADS

Potassium is intercalated into mesocarbon microbeads (MCMBs) with different heat-treatment temperatures (HTTs) and the hydrogen physisorption of the resulting compounds (KCx; 8 less than or equal to x less than or equal to 36) is investigated. The hydrogen-physisorption behavior depends largely on the HTT of MCMB. Particularly, KCx compounds prepared from MCMB with a H?T of 1500 degrees C (KCx(HTT-1500)) show anomaly in the composition range from KC8 to KC12; the saturated amount of physisorbed hydrogen is remarkably large compared to that observed in the usual KCx 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 KCx(HTT-1500; 8 less than or equal to x less than or equal to 11) compounds have a stage-1 structure. This is in contrast to KCx(HTT-2600; 8 less than or equal to x less than or equal to 11) compounds, which have a mixture of stages 1 and 2 as is the case with KCx prepared from graphite. This means that the density of the potassium layer in KCx(HTT-1500; 8 less than or equal to x less than or equal to 11) is smaller than that of usual stage-1 KC8. 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.