In-situ Study Of The Surface Chemistry Of Nano-catalysts And Energy Devices

Physical and chemical properties of materials surface play crucial role in nano-catalysis and energy area. Many researches on nano-catalysis or energy area were using well-ordered materials ?like single crystals? as model system and studied under vacuum condition. These researches have got a lot of fundamental knowledge on many aspects in this two fields. However, these results cannot reveal the real surface properties of catalysts or energy devices under working conditiondue to the existence of "pressure gap" and "material gap". Therefore, in-situ study of the surface chemistry of catalysts or energy devices under working condition is one of the most important direction in the surface science fields. In this thesis, we studied the in situ surface chemistry evolution of a series of oxide thin films, thin film supported metal clusters, two-dimensional catalysts, and Na-O2 battery devices under actual working conditions using various characterization techniques, including ambient pressure X-ray photoelectron spectroscopy ?APXPS? and grazing incident small angel X-ray scattering ?GISAXS?. The main contents are as follows:?1? We in situ studied the electronic structure of Al₂O₃, TiO₂ and ZnO ultrathin films under oxygen atmosphere by APXPS. After introducing oxygen, upward band bending was observed on the surface of all three samples comparing to the UHV condition, which is attributed to the strong chemisorbed oxygen species.The change of electron affinity with and without oxygen was further aquired through simutanous measurement of the band bending and work function change. At room temperature, the electron affinity of Al₂O₃ and ZnO films decreased after oxygen exposure, which can be ascribed to the formation of dipoles between the weak chemisorbed oxygen on the Lewis acid sties of Al₂O₃ and ZnO surfaces. We also studied the influence of temperature on the oxygen adsorption which also proved the existence of weak chemisorbed oxygen.?2? The redox property and aggregation phenomenon of Al₂O₃ and TiO₂ supported silver clusters were in situ studied by APXPS and GISAXS. Electronic structure study of silver clusters and supports at different temperatures and gas atmospheres indicates that the silver clusters are chemically more stable than bulk silver materials owing to the strong interaction btween substrates and silver clusters. The silver clusters on TiO₂ can hardly aggregate even under high temperature compared with other substrates, due to the stronger silver clusters-TiO₂ interaction. The tunneling eletrons transported from the substrates to silver clusterswere also observed, owing to the three monolayer thickness of the oxide films.?3? Stability and phase transition of single layered WS₂ upon heating and aqueous storage were studied by APXPS and Raman spectroscopy. Single layered WS₂ prepared by lithium intercalation is 1T phase, which has better electrocatalytic performance in water electrolysis hydrogen evolution reaction ?HER?. Our results indicate that the unstable IT phase WS₂ changed to 2H phase after being heated to 200 ?. The effect of preservation condition on the chemical properties of WS₂ was also studied, which suggests that the sample preserved in aqueous solution are easy to be oxidized. And the oxidized sample can be reduced during HER process, which also resulted in the IT to 2H phase transition.?4? The varation of surface species during charge and discharge cycles in solid-state sodium oxygen battery was in situ studied in oxygen and carbon dioxide atmospheres by APXPS. With oxygen atmosphere, the discharge product of the battery was only several nanometersthick on the surface.When carbon is abundant on the surface, the favorable discharge product is sodium carbonate since sodium ion and oxygen will react with carbon on the surface.The discharge product will be sodium superoxide in the absence of carbon on the surface. In carbon dioxide atmosphere, carbon deposition was found on the surface after running the battery, which blocked the sodium ion channel and resulted in the decrease of battery capacity.