Investigation of Oxygen Reduction Reaction on La_0.1Sr_0.9Co_0.8Fe_0.2O_3-δElectrode by Electrochemical Impedance Spectroscopy

Abstract

The oxygen reduction reaction (ORR) on La0.1Sr0.9Co0.8Fe0.2O3-δ (LSCF1982) electrode is investigated by electrochemical impedance spectroscopy (EIS) in 550–650°C range under different oxygen partial pressures (pO2). The distribution function of relaxation time (DRT) analysis of EIS data enabled us to distinguish 3 individual sub-processes contributing toward the overall electrode polarization during ORR. Based on these results, oxygen chemical diffusivity (Dchem) and surface exchange coefficient (Ksur) values are obtained under open circuit voltage (OCV) conditions by Gerischer impedance model. In 500–650°C range, Ksur values ranges between 10−5−10−8 cm⋅s−1 and Dchem values are in 10−4−10−6 cm2⋅s−1 range which, due to the higher ionic conductivity of LSCF1982, is relatively higher than those for similar mixed-conducting LaxSr1−xCo1−yFeyO3−δ (LSCF). The values of activation overpotential are separated under the fixed current load, which are well-fitted to the Butler-Volmer equation. Under the current load, the variation of exchange current density (i0) with pO2 indicated that at the high temperature the total reaction-rate is determined by charge transfer reaction, but when temperature is decreased the reaction-rate is determined by the gas diffusion reaction.