用基于密度泛函理论的第一性原理,对Sc作为催化剂对氢气在Mg(0001)表面解离和扩散性能进行了研究.首先,对Sc原子在Mg(0001)表面的稳定吸附和替代位置进行了研究,结果表明,Sc原子将替代在表面的第二层稳定.接下来有对氢气在Sc替代在第二层的Mg(0001)表面解离和扩散性能进行了研究.结果显示由于Sc的存在,氢气在其表面的解离势垒下降至0.57 eV,氢原子在其表面扩散的势垒降低至0.11 eV,利用分波态密度分析得出Sc原子d轨道上的电子对氢气在Mg表面解离起到了促进的作用;更重要的是,氢原子在Sc原子上方的hcp位向Mg内部扩散的势垒由0.69 eV下降至0.26 eV.大幅度降低氢原子向Mg内部扩散的阻力,也为氢原子向Mg内部扩散提供了更多的通道.Sc有效提高了镁基储氢材料的吸放氢动力学性能,是改善镁基储氢材料的动力学性能很好的催化剂.
First-principles calculations within the density functional theory (DFT) have been carried out to study the hydrogen molecule dissociation and hydrogen atom diffusion on pure and Sc atom doped Mg(0001) surfaces.Firstly,we study the stability of Mg(0001) surface doped with Sc atom.The result show that Sc tend to substituted on of the second layer of Mg surface.Secondly,we study the energy of hydrogen molecule dissociation and hydrogen atom diffusion on pure and Sc atom doped Mg(0001) surfaces.When Mg(0001) surface doped Sc atom,the dissociation barrier has descend to 0.57 eV;the diffusion barrier has descend to 0.11 eV.The d orbit of Sc was beneficial for hydrogen molecule dissociation on the surface.In addition,the path of hydrogen atom diffusion into Mg surface from hcp site to the top of Sc,the barrier energy of diffusion into Mg suface is decreased 0.69 to 0.26 eV,which will provide more dissociation path for diffusion paths for hydrogen atom into Mg surface.The present results are beneficial to clarify the experimentally observed fast hydrogenation kinetics for Sc-capped Mg materials.
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