Interpretation of negative temperature dependence of hydriding reaction in LaNi5-Mg alloys by modified Chou model

Abstract

A modified Chou model with parameters of temperature (T), initial hydrogen pressure (P0), enthalpy change (ΔH) and entropy change (ΔS) is proposed in consideration of thermodynamic driving force. The meaningful activation energy Ev can be calculated for the negative temperature dependence of hydriding reaction in hydrogen storage materials. This model is verified by the hydriding/dehydriding experimental data of (LaNi5)1−xMgx (x=0, 0.018, 0.041, 0.063). The calculated results indicate that the hydriding kinetics of (LaNi5)1−xMgx alloys are controlled by diffusion of hydrogen atom in hydride. The addition of small amount of magnesium improves the kinetic performance of LaNi5 slightly. Furthermore, the modified Chou model was compared with the previous model that successfully explain the negative temperature depending hydrogenation reaction of Mg-based alloys. The fitting results show that the modified Chou model can describe the hydrogen absorption kinetic mechanism of negative temperature dependent materials more accurately.