The composition at active sites on RuO2 electrode and the electrode behavior during electrolysis have been investigated by means of XPS, UPS and cyclic voltammetry. The results show that O-deficient sites are the active sites for oxygen evolution reaction on RuO2 electrode. During electrolysis, the O-deficient concentration on the real surface of RuO2 electrode continuously decreases. On the other hand, new O-deficient sites are continuously exposed because of enlarging and penetrating of the reactive region for oxygen evolution on RuO2 electrode. The O-deficient sites of outer surface on RuO2 electrode greatly affect the activation for oxygen evolution. Furthermore, the corrosion and shedding of the coat are also one of the reason for deactivation.

Key words: OXYGEN, ELECTRODE, X-RAY PHOTOELECTRON SPECTROMETRY, ACTIVE CENTER, ELECTROCHEMISTRY, RUTHENIUM OXIDE, SEPARATE