In this work we investigate by in-situ near-ambient pressure photoemission (NAPP) spectroscopy the phenomenon of Electrochemical Promotion of Catalysis (EPOC). We studied the reduction and diffusion kinetics of alkaline ions in a solid electrolyte cell formed by a nickel electrode supported on K+-β-alumina electrolyte. Experiments in ultra-high vacuum and in the presence of steam showed that the amount of potassium atoms supplied to the surface is probably affected by nickel electronic modifications induced by adsorbed OH− groups. It was also deduced that part of the segregated potassium would be adsorbed at inner interfaces where it would be inaccessible to the photoelectron analyzer. A migration mechanism of the promoter is proposed consisting in: (i) the electrochemical reduction of the alkali ions (potassium) at the Ni/solid electrolyte/gas interface; (ii) the spillover of potassium atoms onto the Ni gas-exposed surface; and (iii) the diffusion of potassium atoms to Ni inner grain boundary interfaces.