Síntese e caracterização de eletrólitos compósitos à base de céria e sais fundidos

Abstract

Solid electrolyte is the part of the fuel cell has three essential functions: separate reagents, blocking electronic current and have high ionic conductivity of the elements that compose it. Composite electrolytes consisting of a ceria (CeO2) or ceria-gadolinia (Ce0,9Gd0,1O2, CGO) ceramic matrix and eutectic mixtures of Na2CO3/Li2CO3 or LiCl/KCl allow reducing the operating temperature of ceramic fuel cells from 600 - 800°C to 400 – 600 °C. In this paper, composite electrolytes based on ceria and molten salts (eutectic mixtures of carbonates and chlorides) were obtained by the citrate method. The adopted chemical route enabled the simultaneous synthesis of the two phases, with precise control of composition and microstructure, providing substantial chemical interaction between phases. The study evaluated the effects of composition (carbonate or chloride content in the ceria based matrix) and processing (sintering temperature) on microstructure and transport properties of the composites. The structural characterization by X-ray diffraction showed that the carbonates and chlorides exist as amorphous phases. Despite the low relative densities (between 52 and 75%), as a result of reduced sintering temperatures (ceria/carbonate at 690°C and ceria/chloride between 400 and 600°C), it was observed that the fusion of the amorphous phase acts as a seal that can prevent the flow of gases through the samples. The correlation between the composition and the electrical behavior, using the infrared spectroscopy techniques, scanning electron microscopy and impedance spectroscopy, has observed a homogeneous microstructural distribution between phases, indicating the formation of a ceramic skeleton based on ceria, surrounded by a mixture of amorphous salts, obtaining a conductivity of 0.079 S cm-1 and 0,058 cm-1 S for the ceria composite and carbonates at 600 ° C and 0.0016 S cm-1 and 0.0011 S cm-1 for composites ceria and chlorides at 450 ° C.