Assessment of the Chemical Compatibility Between Ba7Nb4MoO20 Electrolyte and Some Electrode Materials for Solid Oxide Fuel Cells

Abstract

A solid oxide fuel cell (SOFC) is an electrochemical device that consists of an anode, electrolyte, and cathode and directly converts the chemical energy of fuel–oxygen reaction into electrical energy. However, the high operating temperatures (700–900°C) required for effective ion transport lead to thermal degradation and chemical interactions between the fuel cell components. This issue can potentially be resolved only through the use of electrolytes with high conductivity at 500–600°C. Such materials include perovskite Ba₇Nb₄MoO₂₀. Nevertheless, its chemical compatibility with electrode materials remains poorly studied. In this regard, we examined the chemical compatibility of the Ba₇Nb₄MoO₂₀ electrolyte with CuO, CoO, and Fe₂O₃, as potential components of the Me_xO_y/Ba₇Nb₄MoO₂₀ anode, and with the Ba_0.5Sr_0.5Zn_0.2Fe_0.8O₃ cathode material using XRD analysis after annealing of the mixtures at 600–700°C for 10 h. The results show that Ba₇Nb₄MoO₂₀ exhibits low chemical compatibility with CuO, CoO, and Fe₂O₃, as interaction between the mixture components occurs already at 600–700°C. At 800°C, the Ba₇Nb₄MoO₂₀ phase either completely disappears or remains only in small amounts. Based on the residual content of the Ba₇Nb₄MoO₂₀ phase after annealing at different temperatures, its chemical compatibility with the studied metal oxides decreases in the following order: CoO > Fe₂O₃ > CuO. In the Ba₇Nb₄MoO₂₀– Ba_0.5Sr_0.5Zn_0.2Fe_0.8O₃ mixture, no interaction is observed at 600–700°C. At 800°C, the Ba₇Nb₄MoO₂₀ phase completely dissolves in Ba_0.5Sr_0.5Zn_0.2Fe_0.8O₃. Under typical cathode sintering parameters (950–1050°C, 3 h), chemical interaction between the electrolyte and the cathode also occurs, resulting in the formation of solid solutions based on BaNbO₃, SrMoO₃, and BaNb₂O₆.