Peculiarities of the absorption and desorption of hydrogen by opal matrices

Abstract

The absorption and desorption of hydrogen at high pressure and temperature by opal matrices formed by amorphous silica spheres with a diameter of 0.235 and 1.6 μm have been studied. The Raman spectra of hydrogen-saturated opal matrices measured at a temperature of 80 K and ambient pressure show that hydrogen molecules are adsorbed in two different ways, directly into silica spheres and mesopores between them. The kinetics of hydrogen desorption was studied in-situ from a change in the relative intensity of rotational modes in the Raman spectra under annealing at 163–213 K. The hydrogen content decreases exponentially under isothermal heating, while the exponential decay time constant τ increases with a decreasing temperature showing the activation nature of desorption. The data for various temperatures are well described by the Arrhenius dependence τ(Т) = A × exp(EA/kBT) with the activation energy EA=(162 ± 13) meV and time constant А= (1.8 ± 0.5) × 10−2 s.