La0.175WO3-perovskite: chemical characterization of the single crystal (111)/aqueous solution interface by XPS/UPS
✍ Scribed by H. Kohler; W. Neu; K.-D. Kreuer; D. Schmeißer; W. Göpel
- Book ID
- 103063406
- Publisher
- Elsevier Science
- Year
- 1989
- Tongue
- English
- Weight
- 838 KB
- Volume
- 34
- Category
- Article
- ISSN
- 0013-4686
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✦ Synopsis
The electrochemical reactions at the La 0.L75 WO,(ll l)/aqueous solution interface were studied by X-ray/w-photoelectron (XPS/UPS) surface analytical techniques and emf measurements. The electrochemical experiments were performed in a glove box. A special UHV sample transfer box was used for the sample transfer to the UHV analysis chamber. Using XPS/UPS enabled the nature of the irreversible surface reactions to be revealed: The La3d and W4' core level spectra indicate a decrease of the La surface concentration in acidic solutions and a decrease of the W concentration in high pH solutions due to steady state dissolution processes. The selective dissolution of WO, gives rise to a decreasing degree of oxidation of the surface, le a decreasing mean tungsten surface oxidation state with decreasing electrolyte acidity. The UPS valence band spectra indicate the formation of hydrogen bronzes due to La3+/H+ ion exchange reactions. These irreversible surface processes were considered along with reversible reactions like oxygen adsorption and reactions involving protons and WO:-so as to explain the observed unusual emf dependence on both, the activity of dissolved oxygen and the solution acidity.