XPS studies on the gold oxide surface layer formation

The initial stage of gold oxide layer formation on the gold electrode surface was investigated in 0.5 M H2SO4. X-ray photoelectron spectroscopy (XPS) spectra of pure gold and the anodically polarized gold electrode surface were compared quantitatively. It was found that gold anodic polarization in the 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 and 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 larger 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) hydroxide surface layer, takes place in the E range of the anodic current wave beginning at E approximate to 1.3 V. At E-B = 1.7 V (the potential of the Burshtein minimum) the stationary surface layer consists of 2.5 to 3 molecular layers of Au(OH)(3). The theoretical amount of charge required for the reduction of one molecular layer of Au(OH)(3) is similar to 0.15 mC cm(-2), since 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 reserved.