XPS studies on the gold oxide surface layer formation |
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| Affiliation: | 1. Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University, 3-4-1, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan;2. Environmental Research Laboratory, Kindai University, 3-4-1, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan;1. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, Universidad Nacional de La Plata - CONICET, Sucursal 4 Casilla de Correo 16, 1900 La Plata, Argentina;2. Área de Química Física, Departamento de Química, Facultad de Ciencias, Universidad de La Laguna, Instituto de Materiales y Nanotecnología, Avda. Francisco Sánchez, s/n, 38071 La Laguna, Tenerife, Spain |
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| Abstract: | 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 ∼1.3 to 2.1 V causes increase in intensity of the XPS spectra at an electron binding energy εb=85.9 eV for gold and at εb=530 eV for oxygen. These εb 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 εb 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≈1.3 V. At EB=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 ∼0.15 mC cm−2, since the Au(OH)3 molecule is planar and occupies about four atomic sites on the electrode surface. |
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