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Potentional-programmed reduction: a new technique for investigating the thermodynamics and kinetics of chemisorption on catalysts supported on solid electrolytes

Jiang Yi, Gentekakis Ioannis, Vayenas, Costas G

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Περίληψη

A new technique is presented for investigating the kinetics and thermodynamics of chemisorption of oxygen and, potentially, of other adsorbates on conductive catalyst films deposited on solid electrolytes, such as yttria-stabilized zirconia, an O2− conductor. In this technique, termed potential-programmed reduction (PPR), the catalyst surface is first exposed to the chemisorbing gas and then the catalyst potential is swept linearly by, typically −1 V, causing the reduction of chemisorbed oxygen to O2− at distinct and well-resolved catalyst potential values Ep. In this way current peaks centered at Ep are generated. The area of each peak provides direct quantitative information about the coverage of adsorbed oxygen and the corresponding Ep value about its Gibbs free energy. The PPR technique has certain similarities with temperature-programmed reduction but is isothermal and provides direct thermodynamic as well as kinetic information. It is, however, limited to conductive catalyst films which can be supported on solid electrolytes. In the present work the PPR technique is used to investigate oxygen chemisorption on Ag and Pt. In the case of Ag two types of oxygen are resolved at temperatures 300 to 450°C (atomically adsorbed and subsurface), while on Pt there is usually one peak corresponding to atomic oxygen with a second peak developing after prolonged exposure to positive potentials.

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