XPS studies on the gold oxide surface layer formation

The initial stage of gold oxide layer formation on the gold electrode surfa ce was investigated in 0.5 M H2SO4. X-ray photoelectron spectroscopy (XPS) spectra of pure gold and the anodically polarized gold electrode surface we re compared quantitatively. It was found that gold anodic polarization in t he E range from similar to 1.3 to 2.1 V causes increase in intensity of the XPS spectra at an electron binding energy epsilon(b) = 85.9 eV for gold an d at epsilon(b) = 530 eV for oxygen. These epsilon(b), values correspond to Au3+ and O2- oxidation states in hydrous or anhydrous gold oxide. The larg er the amount of the anodically formed surface substance the higher is the intensity of the spectrum at the epsilon(b) values mentioned above. It was concluded that gold anodic oxidation, yielding most likely an Au(III) hydro xide surface layer, takes place in the E range of the anodic current wave b eginning at E approximate to 1.3 V. At E-B = 1.7 V (the potential of the Bu rshtein minimum) the stationary surface layer consists of 2.5 to 3 molecula r layers of Au(OH)(3). The theoretical amount of charge required for the re duction of one molecular layer of Au(OH)(3) is similar to 0.15 mC cm(-2), s ince the Au(OH)(3) molecule is planar and occupies about four atomic sites on the electrode surface. (C) 2000 Elsevier Science S.A. All rights reserve d.