Potassium and oxygen diffusion and segregation in nickel

Nickel is used as catalyst in alkaline electrochemical systems like batteri es, electrolyzers and fuel cells. Adsorption experiments from potassium on a thin NiO(100) epitactic layer on sun Ag(100)-single crystal substrate sho wed that potassium intrudes in that NiO-layer where at a temperature of 350 K a mixed oxide phase was built. At 120 K metallic potassium was adsorbed on the NiO surface. A symmetric K2p-peak showed that potassium is in the ox idized stale compared to the asymmetric peak of metallic potassium. No pota ssium diffused into metallic nickel at a temperature of 450 K. The electroc hemically oxidized surface layer consisted of nickel, oxygen and also potas sium. After heating and ion-etching no more: potassium was detectable by x- ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectrosco py (EDX). But it was visible again after oxidizing and heating of the sampl e to 670 K. Therefore, the potassium must have been in the bulk. It diffuse d to the surface if there was oxygen at sufficiently high temperatures. Fur ther beating reduces the surface and the potassium also disappeared.