Electrocatalytic properties of La0.9Sr0.1MnO3-based electrodes for oxygen reduction
Electrochemical reduction of oxygen at the interface between a La0.9Sr0.1MnO3 (LSM)-based electrode and an electrolyte, either yttria-stabilized-zirconia (YSZ) or La0.8Sr0.2Ga0.9Mg0.1O3 (LSGM), has been investigated using DC polarization, impedance spectroscopy, and potential step methods at temperatures from 1053 to 1173 K. Results show that the mechanism of oxygen reduction at an LSM/electrolyte interface changes with the type of electrolyte. At an LSM/YSZ interface, the apparent cathodic charge transfer coefficient is about 1 at high temperatures, implying that the rate-determining step (r.d.s.) is the diffusion of partially reduced oxygen species, while at an LSM/LSGM interface the cathodic charge transfer coefficient is about 0.5, implying that the r.d.s. is the donation of electrons to atomic oxygen. The relaxation behavior of the LSM/electrolyte interfaces displays an even more dramatic dependence on the type of electrolyte. Under cathodic polarization, the current passing through an LSM/YSZ interface increases with time whereas that through an LSM/LSGM interface decreases with time, further confirming that it is the triple phase boundaries (TPBs), rather than the surface of the LSM or the LSM/gas interface, that dominate the electrode kinetics when LSM is used as an electrode.
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