First-principles Study Of Hydrogen Adsorption, Dissociation And Diffusion On Thin Mg(0001)Films Supported By Mo(110) Substrate

Hydrogen as a energy carrier attract more and more attentions for its abundance in nature, high energy efficiency, renewable and environment friendliness. As one of the most important aspects for its application on automobile,studying of hydrogen storage materials is urgent and also a challenge task. Mg-based hydrogen storage material is one of the ideal candidate for its high capacity and safety for hydrogen storage. Therefore,it is very important to take a theoretical study in order to reduce the dynamic barrier and thermodynamic stability of the material for absorption and release hydrogen as well as the hydrogen absorption processes.Since Mg (0001) and Mo (110) has similar crystal lattice constants and Mo is a very good catalyst for hydrogen adsorption dissociation on Mg film in experiment. In this dissertation, we have carried out the first-principles calculations which based on density functional theory about molecular and atomic hydrogen adsorption, dissociation and diffusion on Mg (0001) films supported by Mo (110) substrate and make a comparison with the result of these processes on freestanding Mg (0001) film. We found that Mo substrate have already no catalytic effect on hydrogen adsorption and diffusion on the Mg (0001) films as it is thicker beyond five layers, and however the Mo substrate may reduce the diffuse barrier of hydrogen penetrating into the underlayer of the five-layer-thickness Mg film. Comparing to the freestanding Mg film, the diffusion barrier decreases about 0.1 eV. We also calculated the diffuse barrier for hydrogen penetrating from the subsurface into the third layer, and obtained an even larger reduced diffuse barrier. Our theoretical studies demonstrated clearly that the Mo substrate still have an obviously effect on hydrogen diffusion from surface of the Mg film into the internal region when the Mg film is as thick as five layer. However, by calculating the dissociation barrier of molecular hydrogen dissociated on the five-layer-thickness Mg(0001)/Mo(110), we found that a similar dissociation barrier was obtained compared with the case on the freestanding Mg film, indicating that Mo substrate can not promote the dissociation of H2 on the five-layer-thickness Mg films.