Síntese e caracterização de BaCe0,2Zr0,7Y 0,1O3-δ (BCZY) dopado com Ca e Sr para utilização em células a combustível

Abstract

Solid oxide fuel cells (SOFC) are an alternative source of clean energy, with low emissions of greenhouse gases, converting chemical energy into electrical energy, with high efficiency and with components in solid state. The SOFC is composed by electrolyte and two electrodes, the cathode and the anode. The ceramic materials that present applicable electrical properties to produce SOFC have the perovskite (ABO3) structure, and the type of conduction can be protonic or ionic. The objective of this work is to study the synthesis of a perovskite of the type BaCe0,2Zr0,7Y0,1O3- (BCZY) with calcium and strontium additives, for electrolytes usage, these elements will replace A sites ions in the crystalline structure, to improve protonic conductivity and chemical stability. The synthesized compositions are: Ba1-xCaxCe0,2Zr0,7Y0,1O3 and Ba1-xSrxCe0,2Zr0,7Y0,1O3-, where the values of x are 0,05 and 0,025; that equate to 1%mol and 0,5%mol of additive element, respectively. The ceramic with these compositions were based in the BaCe0,2Zr0,7Y0,1O3- perovskite, which have optimal electrical properties and present proton conductivity. The compositions were prepared by solid state reaction. The samples were compressed by uniaxial pressing. The samples were sintered for 1500°C for 2 and 4 hours. The characterization was done by X-ray diffraction, scanning electron microscopy, impedance spectroscopy, porosity and density. The expected compositions were obtained with single phase, with structure type of perovskite. The compositions with Sr additives did not densify, with 30% porosity, what did not make possible to do electric measures. Sintering time had little effect in the properties values. Compositions with 0,5 in %mol of Ca, Ba0,975Ca0,025Ce0,2Zr0,7Y0,1O3, presented density of 5,72 g/cm3, porosity of 0,96% and relative density of 93,8%. Indicating that Ca improves densification. The composition with 0,5 in %mol Ca presented conductivity of 2,98.10-3 S.cm-1 and total activation energy of 0,70eV.