IDENTIFICATION OF REACTION MECHANISM OF OXYGEN REDUCTION AT LSCF/GDC INTERFACE

摘要

In this paper, the impedance of oxygen reduction at the La_(0.8)Sr_(0.2)Co_(0.2)Fe_(0.8)O_3 (LSCF)/Gd_(0.2)Ce_(0.8)O_(1.9)(GDC) interface under different oxygen partial pressures (from 1 atm to 0.0011 atm) and temperatures was investigated. Results show that there are at least three reaction steps involved in oxygen reduction at the LSCF/GDC interface. The interface conductivity corresponding to the high-frequency (HF) arc shows weak dependence on oxygen partial pressure, which suggests that the HF arc is likely due to oxide-ion diffusion in the LSCF bulk cathode or transfer of oxide ions from LSCF surface into bulk or incorporation of oxide ions from TPB into GDC electrolyte. The interface conducitivity corresponding to the intermediate-frequency (MF) arc shows strong dependence on oxygen partial pressure, which suggests the MF arc could be due to charge transfer of adsorbed oxygen to adsorbed O~- species and/or surface diffusion of oxygen-containing species. The interface conductivity corresponding to the low-frequency (LF) arc was approximately proportional to the oxygen partial pressure, which suggests the LF arc is due to mass transfer of bulk oxygen in porous LSCF cathode.