Frontline Autocatalysis Mediates the Water Reaction with Single-Layer ZnO

The interaction of H2O with oxides is an important step in many chemical processes. However, questions remain about the critical factor that controls the interaction of H2O with oxides. In this work, we investigate the H2O interaction with a single-layer ZnO film grown on Au(111) by using in situ high-pressure scanning tunneling microscopy (HP-STM). It shows that H2O molecules readily dissociate at the domain boundaries of the ZnO film to form the Zn(OH)x domain and reaction fronts between the unreacted ZnO domain and the newly formed Zn(OH)x domain. The reaction rate along the reaction fronts is about 27 times higher than that along domain edges and 3 orders of magnitude higher than that at the domain interior area. Hydroxyl groups at the reaction front can promote adsorption and dissociation of H2O at the adjacent ZnO sites through a local H-bond network, leading to sustained hydroxylation. This dynamic atomic-level observation illustrates the critical role of frontline autocatalysis in surface reactions with water.