Study On The Hydrogen Storage Properties Of MgH₂ Enhanced By MXene Supported Rare Earth Fluoride

Hydrogen energy is a green secondary energy.The development of safe,efficient and economic hydrogen storage materials is particularly important for the development and utilization of hydrogen.As a representative of solid hydrogen storage materials,MgH₂has broad application prospects due to its high hydrogen storage capacity（7.6wt%）and good reversibility.However,the high hydrogen desorption temperature and slow hydrogen absorption and desorption kinetics limit its large-scale application.In order to reduce the hydrogen absorption and desorption temperature and improve hydrogen absorption and desorption kinetics of MgH₂,the effect and mechanism of MXene derivatives on the hydrogen storage performance of MgH₂were systematically studied in this paper.Firstly,two-dimensional Ti₃C₂ MXene supported PrF₃nanoparticle（PrF₃/Ti₃C₂）composites were prepared by hydrothermal method with Ti₃C₂with PrCl₃as raw materials.The PrF₃/Ti₃C₂composite catalyst with the best catalytic effect was selected by adjusting the hydrothermal reaction temperature and raw material ratio,and its catalytic performance is superior to that of Ti₃C₂and PrF₃.The initial dehydrogenation temperature of MgH₂-5 wt%PrF₃/Ti₃C₂was reduced to 180°C,which is 107°C lower than that of pure MgH₂（287°C）.7.0 wt%hydrogen was rapidly released within 3 min at 260°C and 6.6 wt%hydrogen was rapidly absorbed within 36 s at 200°C.In addition,MgH₂-5 wt%PrF₃/Ti₃C₂showed a high capacity retention rate of 92.5%after10 cycles.The experimental results show that the stable PrF₃in the process of ball milling,hydrogen absorption and desorption is conducive to improve the catalytic activity of multivalent titanium(Ti⁰,Ti²⁺and Ti³⁺)and promote the electron transfer between Ti³⁺and Ti²⁺.The joint action between Ti species and PrF₃is the key factor to improve the hydrogen storage performance of MgH₂.Secondly,two-dimensional V₂C MXene supported PrF₃nanoparticle（PrF₃/V₂C）composites were prepared by hydrothermal method with V₂C with PrCl₃as raw materials,and their effects on the hydrogen absorption/desorption properties of MgH₂were studied.The results indicate that the catalytic effect of PrF₃/V₂C is obviously better than that of V₂C and PrF₃.The addition of PrF₃/V₂C effectively reduced the initial dehydrogenation temperature and improved the hydrogen absorption and desorption kinetics of MgH₂.The initial dehydrogenation temperature of MgH₂-5 wt%PrF₃/V₂C was reduced to 182°C,which is 105°C lower than that of pure MgH₂,and the hydrogen release reached 7.1 wt%.7 wt%hydrogen was rapidly released within 6 min at 260°C and 5.9 wt%hydrogen was rapidly absorbed within 48 s at 200°C.After 8cycles of cyclic hydrogen release test,the hydrogen release amount is still 6.1 wt%in30 min,showing good cyclic stability.The stable V⁰,V²⁺and Pr⁰in MgH₂-5 wt%PrF₃/V₂C system synergistically catalyze the hydrogen absorption/desorption reaction of MgH₂and effectively improve the hydrogen storage performance of MgH₂.