Reaction of potassium with thin epitaxial NiO(1 0 0) films

Nickel is frequently used as catalyst in alkaline electrochemical systems where the alkaline metal adsorbs on the oxygen electrodes. Therefore the reaction of potassium with thin nickel oxide films deposited on an Ag(1 0 0) surface was study by ultraviolet photoelectron spectroscopy, low-energy electron diffraction and X-ray photoelectron spectroscopy, which allows to investigate the oxidation states of the potassium and the nickel. Due to the deposition of metallic potassium the formed oxides cannot be stoichiometric. The potassium reacted with the nickel oxide film, whereby the nickel was partially reduced and the potassium was oxidized. The reaction started at low temperatures and finished at approx. 300 K.