Electrochemical analysis of BaZr0.8Y0.2O3-8-Gd0.2Ce0.8O2-d composite electrolytes by distribution of relaxation time method

BaZr0.8Y0.2O3-8 (BZY)-Gd0.20Ce0.80O2-delta (GDC) composite electrolytes have been fabricated by mechanical mixing the BZY and GDC powders with different weight ratio (30 wt%, 50 wt % and 70 wt %). The ceramic powders were synthesized by a sol-gel method, and the crystalline structure of the ceramic powders and composite electrolytes was examined by X-ray diffraction (XRD). Good chemical compatibility between BZY and GDC has been shown based on the XRD analysis. The morphology and element distribution of the BZY and composite electrolyte were observed by the scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDX). The conductivity measurement was conducted in both oxidizing and reducing atmospheres by the means of electrochemical impedance spectroscopy (EIS). The equivalent circuit and distribution of relaxation times (DRT) method were employed to analyze the obtained EIS data. For the composite electrolytes, two different types of grain boundaries can be identified in the DRT diagram derived from the impedance data measured in reducing atmosphere at lower temperature (< 450 ?). The influence of the GDC content on the resistance between the two grain boundaries was investigated and the result can be attributed to the different average grain size of the samples. The total conductivity of the composite electrolytes in each atmosphere was also analyzed and discussed, and the composition of 30 wt%BZY-70%GDC (BG37) shows the highest conductivity of 0.0269 Scm(-1) at 700 degrees C in reducing atmosphere. Single cell based on BG37 electrolyte was fabricated and tested, maximum power density of 0.442 Wcm(-2) at 700 degrees C with the OCV of 0.89V were achieved.