The oxygen concentration profiles, which develop at the interfaces between niobium pentoxide and the Al or Pt electrode in a metal-insulator-metal stack, were investigated by means of the X-ray and electron energy loss spectroscopies in a scanning transmission electron microscope with high resolution. The contact between Al and Nb₂O₅ was found to facilitate diffusion of oxygen from Nb₂O₅ to the Al electrode and to support the formation of a thin aluminum oxide layer at the Nb₂O₅/Al interface. In contrast, almost no diffusion of oxygen from Nb₂O₅ was observed at the Nb₂O₅/Pt interface. Different extent of the oxygen diffusion correlates with the observed differences in the resistive switching of the Pt/Nb₂O₅/Al and Pt/Nb₂O₅/Pt stacks.