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Abstract: In the present work, the role of NbF5 addition amount in affecting the comprehensive hydrogen storage properties (dehydrogenation, rehydrogenation, cycling performance, hydrogen capacity) of 2LiBH4–MgH2 system as well as the catalytic mechanism of NbF5 have been systematically studied. It is found that increasing the addition amount of NbF5 to the 2LiBH4–MgH2 system not only results in dehydrogenation temperature reduction and hydriding–dehydriding kinetics enhancement but also leads to the de/rehydrogenation capacity loss. Compared with other samples, 2LiBH4–MgH2 doping with NbF5 in weight ratios of 40:4 exhibits superior comprehensive hydrogen storage properties, which can stably release ∼8.31 wt.% hydrogen within 2.5 h under 4 bar H2 and absorb ∼8.79 wt.% hydrogen within 10 min under 65 bar H2 at 400 °C even up to 20 cycling. As far as we know, this is the first time that excellent reversibility as high as 20 cycles without obvious degradation tendency in both of hydrogen capacity and reaction rate has been achieved in the 2LiBH4–MgH2 system. The further experimental study reveals that the highly catalytic effects of NbF5 on the 2LiBH4–MgH2 system are derived from the reaction between NbF5 and LiBH4, which provides a fundamental insight into the catalytic mechanism of NbF5. [Copyright &y& Elsevier]

The thermodynamically and kinetically stable regions of the temperature–H 2 pressure phase boundaries for the ZrCo H system were established using the Temperature-Concentration-Isobar (TCI) method. Based on this, the enthalpy change and entropy change values of dehydrogenation and disproportionation reactions were successfully obtained. The average enthalpy change (ΔH) and entropy change (ΔS) estimated from the phase boundaries for dehydrogenation of ZrCoH 3 to ZrCo are respectively 103.07 kJ mol −1 H 2 and 148.85 J mol −1 H 2 K −1 , which are well agreement with the data reported in literature. The average ΔH and ΔS were estimated to be −120.91 kJ mol −1 H 2 and -149.32 J mol −1 H 2 K −1 for the disproportionation of ZrCoH 3 , whereas the ΔH and ΔS were calculated to be −84.6 kJ mol −1 H 2 and -92.29 J mol −1 H 2 K −1 for disproportionation of ZrCo. In addition, it was found from the established phase boundaries that the anti-disproportionation property of ZrCo alloy can be enhanced if the phase boundaries of hydrogenation/dehydrogenation are far away from the phase boundaries of disproportionation by adjusting the thermodynamics. Meanwhile, it is possible to keep ZrCo away from disproportionation even at high temperature of 650 °C under hydrogen atmosphere, if the temperature-H 2 pressure trajectory is carefully controlled without crossing the phase boundaries of disproportionation. Therefore, the established phase boundaries can be used as a guide to the eye avoiding disproportionation and improving the anti-disproportionation property of ZrCo alloy. [ABSTRACT FROM AUTHOR]