Photoelectron study of electrochemically oxidized nickel and water adsorption on defined NiO surface layers

Electrochemically oxidized nickel and the water adsorption on NiO prepared in UHV were studied by XPS, TPD and UPS, Potassium ions are intercalated in the electrochemically oxidized nickel surface. No molecular water inserted in the electrochemically formed NiOOH layer was observed after transfer to UHV. Two reduction steps can be distinguished during the reduction of the electrochemically oxidized nickel surface in H-2 atmosphere. The interactio n of water with NiO depends on the surface structure. The TPD signal of the monolayer desorption of H2O on NiO(100) demonstrates two different adsorpt ion states. The water does not dissociate on the smooth NiO(100) surface as well as on the defected NiO(100) surface. In contrast on the polar NiO(111 ) surface approximately 0.5 ML (monolayer) water dissociate to OH and H aft er starling water adsorption. (C) 1999 Elsevier Science Ltd. All rights res erved.