Investigation On Adsorption Properties Of Hydrogen Molecules On Palladium (100) Surface At Microscopic Scale

Hydrogen energy has many advantages, such as non-pollution, high energy efficiency, reproducible and so on. It’s the ideal energy in the future for human. In order to gain high purity hydrogen, metal palladium membranes have been widely used to separate and purify hydrogen gas. During the process, the adsorption of hydrogen molecules on palladium surfaces is the first and significantly important step, which decides directly the separation membrane performances. Therefore, investigation on the adsorption behavior of hydrogen on palladium surface at the microscopic scale is of great theoretical and realistic significance.Firstly, molecular dynamic simulation method has been adopted to study the effect of coverage ratio and foreign gases on the adsorption behavior of hydrogen molecules on palladium(100) surface. The results show that the coverage ratio and foreign gases such as CO, CO2 and H2 O have significant effect on the adsorption properties of hydrogen molecules. Furthermore, density functional theory is utilized to study parallel and vertical adsorption properties of hydrogen molecules on palladium(100) surface at quantum mechanics scale, and it has found that hydrogen molecules parallel approaching palladium(100) surface will dissociate into two hydrogen atoms while those vertically approaching the surface will retain molecular forms. Further changing the initial distance between the hydrogen molecules and palladium surface gains the critical initial distance for hydrogen molecules to dissociate, which equals to 2.5?. Molecules approach palladium surfaces in any way will dissociate as long as the initial distance is less than 2.5?. The differences between physical and chemical adsorption have been compared by analyzing deformation charge density, total density of states, partial density of states and energy evolution path, and revealed the nature origin of the existence of different adsorption behaviors. Compared to physical adsorption, the interaction between hydrogen and palladium atoms is much stronger in chemical adsorption. In addition, energy barrier from physical to chemical adsorption has been attained by taking TS search with LST/QST algorithm.In a word, the research is helpful to understand more profoundly the microscopic mechanism and process of the adsorption of hydrogen molecules on palladium surface, and can provide theoretical guidance for preparing more efficiently new hydrogen separation membranes.