Water Adsorption on a Co(0001) Surface

We have investigated the adsorption of water on a Co(0001) surface by means of temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and low-energy electron diffraction (LED). At 130 K, the interaction between adsorbed water (H2O(a)) and Co(0001) is quite weak, and water adsorption forms an intact, nonwetting, and three-dimensional layer on Co(0001). The monolayer and multilayer of H2O(a) could be distinguished by XPS, and they desorb molecularly upon heating but only giving a single water desorption peak. An ordered p(2 x 2) LEED pattern was observed at low exposures of water. At room temperature, water adsorbs dissociatively on Co(0001), forming chemisorbed atomic oxygen (O(a)) and atomic hydrogen (H(a)). Upon heating, H(a) recombines into H-2 desorbing from the surface, whereas O(a) remains on the surface. The interaction of water with Co(0001) is greatly influenced by the presence and nature of the oxygen species on Co(0001). Water adsorption on Co(0001) precovered with 0.45 ML O(a) at 130 K forms a mixture layer of OH(a) and H(a) via the reaction of 2H(2)O(a) + O(a) -> 30H(a) + H(a). However, on oxide-like Co(0001) surface, the water decomposition is completely passivated even at room temperature. These results broaden our fundamental understanding of water interaction with metal surfaces and provide insights into the water-involved catalytic reactions catalyzed by cobalt.