Active Reaction Sites for Oxygen Reduction in La0.9Sr0.1,MnO3/YSZ Electrodes

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Lee, Hee Y.; Cho, Woo S.; Oh, Seung M.; Wiemhofer, H.-D.; Gopel, W.
Issue Date
Electrochemical Society
J. Electrochem. Soc., 142, 2659 (1995)
Active reaction sites for 02 reduction in La0.~Sr01MnO3 electrode have been characterized by addressing the origin of
the cathodic polarization effects on this electrode material. Cathodic polarization (up to - 1.2 V vs. Pt reference electrode}
had several effects on O2 reduction kinetics. First, the O2 reduction rate was favorably increased when the perovskite
electrode was cathodically polarized. Second, in situ x-ray photoelectron spectroscopy results indicated that the Mn ions
are electrochemically reduced and concomitantly the oxygen stoichiometry decreases. Reduction of Mn ions was further
demonstrated in the cyclic voltammogram traced under nitrogen atmosphere. Third, hysteresis in cathodic currents was
observed in the cyclic voltammograms of the perovskite/YSZ/Pt system, and the hysteresis phenomena were more prominent
at higher O~ pressure. We interpreted these findings to mean that the internal and/or external surface oxide vacancies
participate in the O2 reduction reaction. However, it has been explained from the Po2-dependent hysteresis phenomena that,
even though those surface sites are active in the O2 reduction~ their activity is less than that of the three-phase boundary
sites since additional diffusional processes are required for the former sites. Consequently, the three-phase boundary sites
are the major reaction sites at lower O2 pressure, which leads to a small hysteresis. However, at higher 02 pressure, the
surface sites also participate in the reaction, resulting in a larger hysteresis.
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Chemical and Biological Engineering (화학생물공학부)Journal Papers (저널논문_화학생물공학부)
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