SIMULTANEOUS THERMAL DESORPTION OF HYDROGEN AND DEUTERIUM FROM TIH_XD_2-X

The thermodynamics and kinetics of several metal-hydride systems used for hydrogen such as Pd^[1] and Mg^[2] were investigated in the literature based on isotope effects. Titanium hydride has received considerable attentions for various technological applications due to its high hydrogen storage capacity. Yet, there is no data on the literature regarding the kinetic aspects of its isotopic species. In the current study, temperature programmed desorption mass spectrometry (TPD-MS) was utilized for studying the simultaneous desorption of hydrogen and deuterium from a titanium-hydride-deuteride (TiH_xD_2-x) sample for better understanding the different stages in titanium hydride decomposition kinetics. The composition of the powdered sample, initially synthesized via a gas/solid isotope exchange reaction between a commercial TiH₂ powder (98%, Sigma) and D₂ gas (99.7%) at 400⁰C, leaded to deuterium enriched surface particles. Such inhomogeneity enabled us to resolve some geometric features of the rather complex dehydrogenation mechanism of titanium hydride. The TPD spectra of the desorbed isotopic species (H₂, HD, D₂) comprised two characteristic desorption peaks followed by a high temperature shoulder, from which the following observations were deduced as follows: (1) the low T peak centered at ~500⁰C where T_D2< T_HD< T_H2, counters the isotope effect expected for a diffusion process, i.e. D_H>D_D, thus strongly indicating a core-shell mechanism; (2) a second desorption peak, positioned at ~616⁰C irrespective of the isotopic composition of the desorbed specie.

References

[1]F. Leardini, J.F. Fernandez, J. Bodega, C. Sanchez, "Isotope effects in the kinetics of simultaneous H and D thermal desorption from Pd", Journal of Physics and Chemistry of Solids 69 (2008), 116-124.

[2]F. Leardini, J.R. Ares, J.F. Fernandez, J. Bodega, C. Sanchez, "An investigation effect of the thermodynamics and kinetics of magnesium hydride decomposition based on isotope effects", Int. J. hydrogen energy 36 (2011), 8351-8357.