Theoretical insights into the hydrophobicity of low index CeO₂ surfaces

The hydrophobicity of CeO₂ surfaces is examined here. Since wettability measurements are extremely sensitive to experimental conditions, we propose a general approach to obtain contact angles between water and ceria surfaces of specified orientations based on density functional calculations. In particular, we analysed the low index surfaces of this oxide to establish their interactions with water. and we found the CeO₂ (111) surface to be the most hydrophobic, whereas the CeO₂ (110) surface is mildly hydrophilic. Also, we found that the O terminated (100) surface was unstable unless fully covered by molecularly adsorbed water. We identified a strong attractive interaction between the hydrogen atoms in water molecules and surface oxygen, which gives rise to the hydrophilic behaviour of (110) surfaces. The findings here shed light on the origin of the intrinsic wettability of rare earth oxides in general and CeO₂ surfaces in particular and also explain why CeO₂ (100) surface properties are so critically dependant on applied synthesis methods.