【作者】 肖红；

【导师】 曹觉先；

【作者基本信息】 湘潭大学 ， 凝聚态物理， 2010， 硕士

【摘要】 氢气是二十一世纪最有希望替代化石能源的一种新型清洁能源燃料。目前,在氢能商业化应用的过程中遇到的最大难题之一就是如何安全、有效、经济的储氢。传统储氢方式中的高压气态储氢,液态和固态储氢都不是理想的储氢方式,难以满足未来氢储存的要求。过渡金属元素储氢在氢吸附强度与储氢能力上都表现出了室温储氢的发展潜力,因此,近年来人们做了大量利用过渡金属元素设计高密度储氢材料的研究。本论文基于密度泛函第一性原理的计算方法详细研究了单个3d过渡金属原子的氢吸附结构、吸附机制、及过渡金属原子Sc、Ti、V与满壳层过渡金属原子Pd分散在基底(8,0)碳纳米管上的氢吸附情况和氢吸附机制。其主要内容包括:首先详细研究了3d过渡金属原子的氢吸附能力、强度、结构和氢吸附机制。研究结果表明:所有3d过渡金属中除Cu与Zn不吸附氢以外,其他的过渡金属元素均能至少吸附8个氢分子,且吸附8个氢分子的稳定结构很相似。这些有趣的氢吸附结构的出现是由于过渡金属元素的氢吸附机制决定的。因为:(i)过渡金属元素的氢吸附结构是由过渡金属元素吸附氢后占据在d轨道的电子排布决定,氢分子分布在金属原子电荷密度分布较少的区域。因此,d轨道的电子排布不仅影响其吸附结构,而且决定了该元素的氢吸附能力。(ii)过渡金属元素的氢吸附能主要由静电吸附决定。该静电吸附是由于过渡金属原子吸附氢后,其4s→3d电荷转移,从而在金属元素周围形成了较大的极化静电场,导致氢分子的极化吸附。同时吸附的氢分子在极化电场作用下形成的超分子结构,使H2-H2之间存在较强的相互作用,进一步降低了金属对氢分子的吸附能。通过过渡金属单原子氢吸附的研究表明,早期过渡金属元素Sc,Ti,V具有非凡的氢吸附能力。而碳纳米管具有独特优越的性质,可作为分散衬底材料。作为示例,我们研究了Sc,Ti,V分散在(8,0)碳纳米管上的氢吸附能力。正如我们预测的一样,由于空间结构的影响,Sc,Ti,V/(8,0)SWCNT可吸附4个氢分子。如果Sc,Ti,V原子均匀分散在(8,0)SWCNT上,其储氢重量比可达8.00 wt.%,且吸附能(约–0.54 eV)在室温储氢范围内。这些计算结果表明:Sc、Ti、V与SWCNT复合体系都是一种非常优越的储氢材料,这为我们设计储氢材料提供了理论依据。此外我们还探讨了满壳层Pd原子分散在SWCNT上的氢吸附。单个Pd原子附着在SWCNT上,最多能吸附2个氢分子。如果Pd均匀分散在SWCNT上,其储氢重量比为2.88 wt.%。该计算结果与实验测量值能很好的相符,有力的佐证了我们计算方法和模型的有效性。更多还原

【Abstract】 Hydrogen has been recognized as an ideal energy carrier to replace fossil fuels in 21st century. Recently, its commercial use as an alternate energy has substantial the most difficult challenge is how to safely, effectively and economically storage hydrogen. Conventional methods of hydrogen storage such as high-pressure gas, liquid or solid-state aren’t ideal storage methods, and cannot fulfill future storage goals. Transition metals (TM) were shown to be very promising for hydrogen storage in terms of hydrogen binding strength and storage capacity at ambient conditions. Recently, intensive research has been done for designed high density hydrogen storage material based on transition metals. In this thesis, we investigate the hydrogen adsorption structure and mechanism on isolated 3d transition metal, and Sc,Ti , V , Pd decorated on (8,0) SWCNT based on first-principle calculations.We first study the hydrogen storage structure, ability and storage mechanism of isolated 3d transition metal. It is found that all of 3d TM can absorb 8 hydrogen moleculars with similar structures except Cu and Zn atom. Those ingesting results are determined by the hydrogen adsorption mechanism. The adsorption binding mechanism is (i) the hydrogen adsorption structure of 3d transition metal is determined by the electron arrange of d orbit, hydrogen adsorbed at the low charge density area. Hydrogen storage structure and their adsorption ability are determined by arrangement of the electron at d orbit of transition metals; (ii) the adsorption energy of hydrogen on 3d TM is determined by the electrostatic Coulomb attraction, which is induced by the electric field due to the charge transfer from metal 4s to 3d. It was found that all those adsorbed hydrogen molecules around the metal atoms form supercell structures, and further lowers the binding energy.The study of 3d TM showed that Sc,Ti and V have great ability of hydrogen storage, while carbon nanotube has light weight and high surface to volume ratios. We investigated the hydrogen adsorption and binding mechanism on transition metals (Sc, Ti, V) decorated (8,0) single walled carbon nanotubes. Our results show that non-filled shell TM (Sc, Ti, V) coated on SWCNTs can uptake over 8 wt.% hydrogen with the binding energy range in room hydrogen storage (about -0.54 eV), promising potential high capacity hydrogen storage material. While full filled shell TM Pd-decorated single-walled carbon nanotubes (SWCNT), the most hydrogen storage capacity is 2.88 wt. % for the uniformly Pd-decorated SWCNT. The result is good agreement with the experimental measurement, which also proved our method and model is valid.更多还原