Interaction of potassium-graphite intercalation compounds with hydrogen at pressures up to 2000 atm

Abstract

The equilibria in KC4n-H2 (n = 1 or 2) systems were experimentally studied at hydrogen pressures up to 2000 atm in the temperature range 78–700 K. The maximum content of hydrogen in the samples was achieved at 78 K under pressure higher than 500 atm and it was close to the stoichiometry KC8H3.5–4. The rate of hydrogen interaction is very high and there is no hysteresis for the studied reactions even at liquid-nitrogen temperature. The shape of the absorption-desorption isotherms at room temperature and at 361 K may be considered as almost ideal parabolic, corresponding to the linear dependence of hydrogen content in hydride on P1/2. However, a considerable change in isotherm shape and a sharp increase in hydrogen capacity at 78 K occur compared with higher temperature conditions. After a hydrogen pressure decrease the sample always has the composition KC8H0.5 in spite of the previous treatment. X-ray diffraction data obtained under ambient conditions for the samples are close to that known for KC8H0.66–0.8 stage 2 compounds.