Tailoring of BaCe0.9Y0.1O3-d Electrolyte Properties by Co-Doping

Abstract

BaCe0.9Y0.1O3–δ has been known as one of the best proton conducting electrolyte, which enables its application in intermediate-temperature solid oxide fuel cells (IT-SOFC) operating between 500 °C and 700 °C. The main disadvantage of this material is its instability in a CO2-rich atmosphere that limits its application with respect to fuel selection. Therefore, many attempts has been made to improve its stability by replacing yttrium with other dopants, or by co-doping. In this study, we compared BaCe0.9Y0.1O3–δ and BaCe0.85Y0.1M0.05O3–δ (M = {In, Zr, Nb}) electrolytes by taking into consideration the dopant properties (primarily the valence, electronegativity and ionic radius) and how they influenced the microstructure, conductivity and chemical stability of doped BaCeO3. The samples were synthesized by the citric-nitric autocombustion method. BaCe0.85Y0.1In0.05O3–δ was sintered at 1400 °C for 5 h in air, while the temperature of 1550 °C was required for the other materials to complete the sintering. This makes the doping with In a preferable method since sintering temperatures above 1500 °C can lead to a certain materials degradation resulting in BaO loss. The total conductivities (σ) measured at 700 °C in wet hydrogen decreased in the following order: BaCe0.9Y0.1O3–δ > BaCe0.85Y0.1Zr0.05O3–δ > BaCe0.85Y0.1Nb0.05O3–δ > BaCe0.85Y0.1In0.05O3–δ. By comparing the stability of the ceramics exposed to a 100% CO2 atmosphere at 700 °C for 5 h and examined by X-ray analysis, it was observed that only BaCe0.85Y0.1In0.05O3–δ could sustain the aggressive environment. The exposed sample contained only traces of secondary phases, while the other compositions were partially or significantly decomposed. By taking into account the values of the Goldschmidt tolerance factor (t) and dopant electronegativity