Behavior of hydrogen absorption by alkali metal-graphite intercalation compounds (AM-GICs) at low temperatures was investigated in order to utilize them as a cryosorption material for hydrogen isotopes. The equilibrium hydrogen pressures at the condition where fractional absorption was 0.5 were determined to be 0.32 and 0.71 Torr for CsC₂₄ and RbC₂₄, respectively, which were considerably low as compared with 32 Torr for KC₂₄ and 83 Torr for molecular sieve 5A (MS 5A) under the same condition. Among AM-GICs, Cs-GIC was found to be the most promising because of low equilibrium pressure. Rb-GIC was also considered to be a good absorber. In contrast with the Langmuir type absorption observed for Cs- and Rb-GICs, K-GICs showed a complicated behavior, i. e. the characteristic sigmoid pressure dependence in its isotherm.
The effect of heat treatment temperature (HTT) of the pristine carbon material on the absorption behavior was also examined. In the case of Cs-GICs, the GIC sample prepared from well graphitized carbon material (with high HTT value) had larger absorption capacity of hydrogen absorption than those prepared from less graphitized one. On the contrary, K-GICs prepared from material with HTT of 1500°C showed maximum capacity of hydrogen absorption in low pressure region (below 1 Torr) among those prepared from materials with HTT of 1000, 1500, 2000 and 2600°C, although it was still inferior to Csand Rb-GICs in absorbing ability of hydrogen gas.