Investigations On Synergetic Improvement To LiBH₄ Via Nanoconfinement,Catalysis And Composite And The Action Mechanisms

LiBH₄ has the attractive characteristics of high gravimetric and volumetric hydrogen storage density,so it is regarded as the most promising solid state hydrogen storage material.However,on the road to its practical application,it still faces the problems of unfavorable high dehydrogenation temperature,relatively sluggish reaction kinetics and poor reversibility.Based on a detailed overview and in-depth analysis of the current research results of LiBH₄,carbon nanotubes coating with amorphous porous carbon（CNT@PC）with high porosity and specific surface area,and further loaded with nano-V₂O₃ catalyst precursor on its surface,which is used as a scaffold to confine LiBH₄.In addition,it is also proposed to composite LiBH₄ with Y（BH₄）₃ that has a low dehydrogenation temperature to form eutectic solution with a low melting point,which is further confined by CNT@PC.Through the methods mentioned above and their synergistic effect,the de/rehydrogenation temperature of LiBH₄ is effectively reduced,the kinetic performance and reversibility are improved as well.By systematically investigating the correlation between the structure of the system and hydrogen storage performance,and the structural and morphological changes of the system during de/rehydrogenation process,the mechanism of improved hydrogen storage performance of the system is revealed.The research provides a new method and theoretical basis for the composition and structure design of LiBH₄-based hydrogen storage material with high-capacity.CNT@PC with one-dimensional network-like morphology which has high specific surface area and porosity synthesized by the hard template method is used as a LiBH₄ nanoconfinement scaffold.When the loading contents of LiBH₄ is 70 wt%,the onset and the peak dehydrogenation temperature of the system are 205°C and346°C,which is 169°C and 89°C lower than the bulk LiBH₄,respectively.The system can rapidly release 6.4 wt%hydrogen at 350°C within 65 minutes,and shows favorable reversibility under milder conditions.Nano-V₂O₃ is loaded on CNT@PC by hydrothermal method,which is used as a scaffold to confine LiBH₄.Nano-V₂O₃ reacts with LiBH₄ during melt-infiltration and initial dehydrogenation process,forming a variety of catalysts in-situ that can effectively promote the hydriding/dehydriding kinetics of LiBH₄.The results indicate that under the synergistic effect of nanoconfinement and catalyst,the hydrogen storage performance of LiBH₄ has been significantly improved.The system loaded with 60 wt%LiBH₄ starts to dehydrogenate when heated to 195°C with a main dehydrogenation peak at 324°C.6.1 wt%hydrogen can be released within 45 minutes at 350°C.After 5 cycles,the hydrogen storage capacity retention rate is still above80%,confirming the cyclic stability is significantly promoted.By analyzing the relationship between the enthalpy of fusion as well as the dehydrogenation temperature and the LiBH₄/Y（BH₄）₃ addition ratio,an equimolar ratio of LiBH₄/Y（BH₄）₃ dual-cation borohydride eutectic system with low de/rehydrogenation temperature is obtained,which is further confined by CNT@PC.The study shows that,the onset and peak dehydrogenation temperature of the confined system loaded with 70 wt%LiBH₄/Y（BH₄）₃ decrease to 168°C and233°C.The kinetic performance of the confined system is significantly improved,it takes only 20 minutes at 320°C to release 4.7 wt%hydrogen.Beside that,the cyclic stability is also significantly improved compared to LiBH₄/Y（BH₄）₃ system.Y（BH₄）₃preferentially decomposes during dehydrogenation,the decomposition products can further destabilize LiBH₄.The high thermal conductivity of the confined system can be achieved by introducing CNTs,this can effectively accelerate the conduction of heat during dehydrogenation,and thus also improve the hydrogen storage performance.