Estudo das rotas de síntese, métodos de sinterização e diferentes dopantes na produção de perovskitas BaCe0,2Zr0,7M0,1O3-ẟ (M=Y, Gd,Sm, Yb), para células a combustível

Abstract

Fuel cells are composed of two electrodes separated by an electrolyte and generate electrical energy from renewable sources. Among the various types, Solid Oxide Fuel Cells (SOFCs) operate with a dense solid ceramic electrolyte and present the highest operating temperature. A promising strategy to reduce this temperature is the use of proton-conducting ceramics, such as barium cerate and barium zirconate-based perovskites. However, these materials require high sintering temperatures and long processing times. To enhance their sinterability, approaches such as the addition of sintering aids and the use of non-conventional sintering techniques, like reactive sintering and microwave-assisted sintering can be applied. This work investigates the perovskite phase formation and electrical performance of BaCe0,2Zr0,7M0,1O3-δ (BCZM, M = dopant)-based ceramics, prepared via solid-state reaction (SSR) and solid-state reactive sintering (SSRS), using both conventional and microwave-assisted sintering. The effects of Sm, Gd, Y, and Yb dopants, as well as the sintering additive ZnO (2 mol%), were investigated. In the case of the SSRS route, parameters such as heating rate, mixing time, and sintering dwell time were evaluated. Perovskite formation was influenced by the electronic properties of the dopants, with increasing reactivity following the order: Yb < Y < Gd < Sm. ZnO proved essential for densification in both SSR and SSRS routes, with emphasis on microwave sintering, which enabled high densification (>95%) in only 30 minutes and mitigated barium losses due to volatilization. In the case of reactive sintering, only the Sm-doped samples achieved apparent porosity below 5%. Among the SSRS, the Sm-doped samples sintered via microwave exhibited the highest total conductivity (~1.00 mS/cm), while the SSR sample doped with Gd, without ZnO, achieved the best overall electrical performance (2.20 mS/cm), contradicting expectations based on proton trapping and electronegativity. Moreover, microwave sintering promoted a distinct contribution of grain boundary conductivity, reducing the activation energy for conduction. Overall, the results indicate that the combination of the SSRS route, microwave sintering, and suitable dopants enable the production of dense conductive ceramic electrolytes with significant processing time savings (> 35h), without compromising microstructural and transport properties.