In contrast to the traditional metal hydrides, in which hydrogen storage involves the reversible hydrogen entering/exiting of the host hydride lattice, LiBH4 releases hydrogen via decomposition that produces segregated LiH and amorphous B phases. This is obviously the reason why lithium borohydride applications in fuel cells so far meet only one requirement - high hydrogen storage capacity. Nevertheless, its thermodynamics and kinetics studies are very active today and efficient ways to meet fuel cell requirements might be done through lowering the temperature for hydrogenation/dehydrogenation and suitable catalyst. Some improvements are expected to enable LiBH4 to be used in on-board hydrogen storage.
The Non-Random Two-Liquid activity coefficient model is applied to describe the kinetics of pure gas adsorption on energetically heterogeneous solid surfaces. The surface energetic heterogeneity has been represented by the Gaussian-like function of the adsorption energy distribution. Two different kinetic isotherms have been presented. One of them, determined by using the statistical rate theory, has been critically discussed. The applicability of the presented approach has been demonstrated by a quantitative analysis of two sets of experimental data previously reported in the literature.
Experimental data of bismuth activity coefficients at 1773 K were obtained by isopiestic method and compared to calculated values. Thermodynamic properties of the Sn-Ni-Bi liquid phase were estimated by means of the general solution model and by the methods of Kohler. Description of the ternary liquid phase (Gibbs excess energy dependence on the temperature and the composition) was achieved by using available thermodynamic data of the constitutive binary systems (Ni-Bi, Sn-Bi, Sn-Ni). A comparison between calculated quantities and experimental data wasconducted. The present assessment with thermodynamically optimized values of the system Sn-Ni-Bi (obtained by the CALPHAD approach) was in good agreement. The suggested appearance of a liquid phase miscibility gap at high temperatures is in agreement with the experimental bismuth activity data and with the assessed thermochemical functions. [...]