水分子和二氧化铈(111)表面相互作用的DFT+U研究

采用引入Hubbard参数U修正的密度泛函理论(DFT+U)方法, 对水分子在二氧化铈(111)表面的吸附作用进行了研究. 计算结果表明: 在氧化的二氧化铈(111)表面, 水分子以单氢键构型吸附在二氧化铈表面, 但是不能自发解离; 在还原的二氧化铈(111)表面, 水分子或化学吸附在衬底上, 或自发解离成表面羟基结构. 与氢气在氧化的二氧化铈(111)表面上物理吸附体系的总能相比, 羟基化表面构型是能量更低的构型, 所以羟基解离形成氢气, 从而使表面被氧化的过程需要有外部条件, 反应不能自发进行. 因此, 水分子在还原的二氧化铈(111)表面有两个可能的状态, 即无氢键结构的化学吸附和表面羟基结构的解离吸附. 在一定的外部条件下, 表面羟基结构进一步解离形成氢气, 并使还原的二氧化铈(111)表面得以氧化.

DFT+U Study on the Interaction of Water Molecule and Ceria(111)Surface

The interaction of water molecule and a ceria (111) surface was investigated using DFT+U (density functional theory with the inclusion of on-site Coulomb interaction by introducing Hubbard U parameter) method. The results show that water molecules adsorb on the oxidized ceria (111) surface through a single H-bond configuration and they do not decompose. On a reduced ceria (111) surface, the water molecules adsorb through a non-H-bond configuration. Furthermore, water molecules prefer to dissociate and form a hydroxyl surface. The hydroxyl surface is much more stable than the physisorption state of H_2 on the oxidized ceria (111) surface. In other words, reoxidation of the reduced ceria (111) surface through the dissociation of the hydroxyl surface and the generation of H_2 molecules is an endothermic process. Therefore, there are mainly two adsorption states for water molecules on the reduced ceria (111) surface: ⅰ)chemisorption through a non-H-bond configuration andⅱ) dissociative adsorption with a hydroxyl surface. The hydroxyl surface may dissociate under certain conditions and reoxidize the reduced ceria (111) surface.