The Adsorption And Dissociation Of Oxygen-contained Gas Molecule On Uranium Surface:a First-principles Study

Nuclear energy is a key to solve the energy crisis. Uranium plays a very important role in the nuclear industry. Due to the extremely chemical activity, uranium is easy to suffer from oxidation when exposure to atmosphere, leading to a degradation. Thereby, finding a effective and safe technique for uranium storage attracts fully attention. The radioactivity and toxicity of uranium creates dangers hard to eliminate for experimental research, so that the theoreti-cal study becomes particularly important for uranium materials. In the present work, the first-principle approach based on density functional theory is employed to study the properties of gas molecules(O2, CO, CO2and H2O) adsorption on the a-U(001) surface, including the favorable adsorption site, the adsorption energy, and the dissociation or migration barrier. O-U surface phase diagram is also established by ab initio atomic thermodynamics.The calculation shows that there is no dissociation barrier when O2adsorbed on the urani-um surface, the O2adsorption energy is much larger than other molecules, and the strong ionic bond forms between oxygen and uranium atoms. O-U surface phase diagram indicates that O2is easy to adsorb on the uranium surface. Oxygen atoms will fully cover the surface and diffuse into interstices even in the ultra-high vacuum. C is the favorable terminal for both CO and CO2adsorption. Based on thermodynamics principle, the dissociation of the adsorbate will stabi-lize the adsorption configuration. C atom can diffuse into the near-surface interstice, forming UC compound, while O atom prefers to adsorb and migrate on the surface. H2O tends to be adsorbed directly on the top of the uranium atom and parallel to the (001) surface. The weak covalent bond between H2O and uranium makes the adsorption energy relatively low. How-ever, adsorbed H2O can dissociate to various partial and completely adsorption configurations spontaneously, and the adsorbates from dissociation can bind with substrate by the ionic bonds, raising the adsorption energy and stabilizing the configuration.