论文部分内容阅读
随着燃料电池、燃料电池汽车的快速发展,LiBH4被认为是最具应用前景的储氢材料之一。然而,LiBH4吸放氢温度高以及吸放氢速率相对缓慢限制了其广泛应用。为改善LiBH4吸放氢性能,在LiBH4中添加少量Al,采用基于密度泛函理论的第一原理赝势平面波方法,计算了LiBH4合金化前后体系的氢化物形成热、H原子解离能,体系的晶体与电子结构。氢化物形成热、H原子解离能计算结果发现:Al合金化后体系相结构稳定性变差,体系解氢过程中所吸收的热量减少,H原子解离能减小,体系解氢能力增强。电子态密度(DOS)、电子密度和Mulliken电子占据数的结果表明:LiBH4结构稳定、解氢困难的电子结构原因是B-H之间较强的共价键,Al对LiBH4体系解氢性能增强主要是Al-LiBH4体系Fermi能级附近能隙值发生变化以及Li-BH,B-H间成键作用减弱。理论上揭示Al添加改善LiBH4体系解氢性能的微观机制,为LiBH4实际应用提供理论指导。
With the rapid development of fuel cells and fuel cell vehicles, LiBH4 is considered as one of the most promising hydrogen storage materials. However, the high hydrogen absorption and desorption temperatures and the relatively slow rate of absorption and desorption of LiBH4 have limited their wide application. In order to improve the hydrogen absorption and desorption properties of LiBH4, a small amount of Al was added to LiBH4. The first principle pseudopotential plane wave method based on density functional theory was used to calculate the hydride formation heat and dissociation energy of H system before and after LiBH4 alloying Crystal and electronic structure. Hydride formation heat and H atom dissociation energies were calculated. The results show that the phase structure stability of Al alloy becomes worse, the amount of heat absorbed during the hydrogen desorption process decreases, the dissociation energy of H atom decreases, and the hydrogen desorption capacity of the system increases . The results of electronic density of states (DOS), electron density and Mulliken electron occupancy show that the structure of LiBH4 is stable and the hydrogen dissociation is difficult due to the strong covalent bond between BH and the enhancement of hydrogen desorption property of Al to LiBH4 Al-LiBH4 Fermi energy level near the band gap value changes and Li-BH, BH bond between the weakened. The microscopic mechanism of Al addition to improve the hydrogen evolution performance of LiBH4 system is theoretically revealed, which provides theoretical guidance for the practical application of LiBH4.