Electrochemical characteristics of some cathodes for medium temperature solid oxide fuel cells, synthesized by solid state reaction technique

Abstract

Electrochemical characteristics of various half-cells for solid oxide fuel cells operating at intermediate temperatures, based on samaria and gadolinia doped ceria electrolytes and La0.6Sr0.4CoO3–, Pr0.6Sr0.4CoO3– and Gd0.6Sr0.4CoO3– cathodes as well as so called mixed cathodes 70 wt% La0.6Sr0.4CoO3– + 30 wt% Ce0.8Gd0.2O2–, 70 wt% La0.6Sr0.4Co0.8Fe0.2O3– + 30 wt% Ce0.8Gd0.2O2– and Ag + La0.6Sr0.4CoO3– have been obtained by electrochemical impedance, cyclic voltammetry and chronoamperometry methods. X-ray diffraction, scanning electron microscopy, atomic force microscopy and gas adsorption measurement methods have been used for comparative analysis of physical properties of cathodes and electrolytes under study. The kinetically mixed process (slow mass transport and electron transfer stages) seems to take place for all systems studied. The values of activation energy, decreasing with the increasingly negative cathode potential, and the transfer coefficient c > 0.5 indicate that in addition to the slow electron transfer process (reduction of oxygen) the mass transfer process of electrochemically active species in solid cathode material or at the internal porous cathode surface can probably be the rate - determining steps in agreement with the fitting results of the Nyquist plots. The operation time stability test results show that electrochemical characteristics for half-cells have a good stability during long operation times.