复合添加剂MgF_2@C对LiBH_4放氢性能的影响

Excellent Effects of Composite Additives MgF_2@C on Hydrogen Release Properties of LiBH_4

LiBH_4作为一种最具潜力的高容量储氢材料,存在着放氢温度高、放氢速率慢和可逆性差等问题。采用高温碳化法得到复合添加剂MgF_2@C,同时对比研究了该添加剂和MgF_2对LiBH_4储氢性能的影响。研究表明,含F添加剂MgF_2能促使LiBH_4热力学失稳,从而大幅改善体系的储氢性能碳骨架的存在保证了储氢基体在高温条件下不团聚且不与添加剂分离,高度分散的MgF_2能够极大增大体系反应活性位点,促进氢在其表面的解离与重组,提高催化效率。结果表明,MgF_2@C可使LiBH_4的初始放氢温度和放氢峰值温度分别降低100℃和86℃,且最终放氢量能够达到6.58wt%。并且,在等温放氢过程中,LiBH_4-MgF_2@C复合储氢材料的放氢速率是LiBH_4-MgF_2复合体系的3倍。

Lithium borohydride （LiBH4 ） has gained extensive attention as potential hydrogen storage media, however, high thermodynamic stability, slow kinetics, and limited reversibility are still major hurdles. In this paper, high-dispersed MgF/@ C was successfully synthesized via carbonization process at high temperature, and a series of work have been taken for the influences of MgF2 and MgF2@ C on LiBH4. Microstructure analyses reveal that the MgF2 could cause F, and accelerate the thermodynamic instability for LiBH4, therefore, improve the hydrogen storage property. This fundamental understanding provides us with that the existence of carbon skeleton could prevent the aggregation of the composite or separation for the additive in the de/hydrogenation process at high temperature, and the high-dispersed MgF2 could provide more reactive sites, which greatly increase the dissociation and restructuring for H2 , thus improve the catalytic efficiency. Temperature programmed desorption （TPD） analyses show that MgF2@ C could reduce the onset temperature and the peak temperature for 100 ℃and 86 ℃, respectively, and the final hydrogen desorption capacity reaches 6. 58 wt% , indicating that the addition of MgF2 @ C does not significantly reduce the hydrogen capacity. In the process of isothermal hydrogen desorption, the rate of LiBH4-MgF2@C composite is three times of LiBH4-MgF2@ C.