Tailoring the Kinetic Behavior of Hydride Forming Materials for Hydrogen Storage

Abstract

Hydride forming materials, i.e., binary, complex hydrides, and their mixtures, have been extensively investigated owing to their potential hydrogen storage properties. They possess high volumetric hydrogen capacity and relative high gravimetric hydrogen capacity. However, one of the main constraints for their practical application is their slow kinetic behavior. For this reason, enormous effort has been devoted to improve the hydrogenation and dehydrogenation rates. Several strategies have been developed for the enhancement of the kinetic behavior of the most relevant hydride forming materials such as MgH

Modeling the kinetic behavior of the Li-RHC system for energy-hydrogen storage: (I) absorption

“…The approach used in the present work is the Separable Variable approach as described by equation (3) [34,35]. In this model, it is possible to obtain the variation of the reacted fraction α as a function of time t by determining three variables, namely, K(T), F(P) and G(α).…”

“…For the complete table, please refer to Supplementary Material Table S1. For a more in-depth discussion of the application of these gas-solid kinetic models, please refer to the work of Puszkiel [34]. This is a preprint version of an article accepted as contribution to the International Journal of Hydrogen Energy.…”

“…In order to do so, the so-called "Sharp and Jones" method (named after the original works of Sharp et al [43] and Jones et al [44] and also known as "Reduced Time Method") has been shown to be the most efficient tool, as it gives more parameters for evaluation that help determining how good is the agreement of the experimental data to each of the reaction models. A general description of the employed method has been given in the work of Puszkiel [34].…”

“…The evaluation of the best-fitting model is based on the values of three parameters; the coefficient of determination R² closest to 1, a Y-axis intercept closest to 0 and a slope closest to 1 [34,43,44]. All results are summarized in Table 2.…”

“…However, already for simple gas-solid hydride forming reactions, a wide variety of pressure dependence relations are used [52,53,62]. This fact is related to the different hydride forming materials, experimental conditions and rate-limiting steps associated to the F(P) [34].In the case of complex hydrides, it is well accepted that in general the relation between the applied pressure P and the equilibrium pressure Peq can describe the driving force term for the formation of a metal hydride. For instance, in the case of NaAlH4, the functionality of the pressure was empirically determined, and the best function was determined as the first order Taylor series' approximation (centered around Peq) of the change of the free energy for the hydrogenation process, i.e., (P -Peq)/Peq [51].…”