Thermal desorption study of Oxygen adsorption on Pt, Ag & Au films deposited on YSZ
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The Thermal Desorption or Temperature Programmed Desorption (TPD) technique has been used for the study of oxygen adsorption on Pt, Ag and Au catalyst films deposited on YSZ. The catalyst film was deposited on the one side of the YSZ specimen while on the other side gold counter and reference electrodes were deposited, constructing a three-electrode electrochemical cell similar to those used in Electrochemical Promotion studies. Oxygen adsorption has been carried out either by exposing the samples to gaseous oxygen (gas phase adsorption) or by the application of a constant current between the catalyst/working electrode and the counter electrode (electrochemical adsorption) or by mixed gas phase and electrochemical adsorption. Oxygen adsorption was carried out at temperatures between 200 and 480 °C. After exposure to gaseous oxygen, normal adsorbed atomic oxygen species have been observed on Pt and Ag surfaces while there was no detectable amount of adsorbed oxygen on Au. Electrochemical O2− pumping to Pt, Ag and Au catalyst films creates strongly bonded “backspillover” anionic oxygen, along with the more weakly bonded atomic oxygen. Electrochemical O2− pumping to Pt, Ag and Au catalyst films in presence of preadsorbed oxygen creates strongly bonded “backspillover” anionic oxygen, with a concomitant pronounced lowering of the Tp of the more weakly bound preadsorbed atomic oxygen. The two oxygen species co-exist on the surface. The activation energy for oxygen desorption or, equivalently, the binding strength of adsorbed oxygen was found to decrease linearly with increasing catalyst potential, for all three metal electrodes.
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