纳米结构LSCF-SDC复合阴极的制备及其氧还原机理研究

利用浸渍法制备了La_0.6Sr_0.4Co_0.8Fe_0.2O_3-δ(LSCF)/Ce_0.8Sm_0.2O_1.9(SDC)纳米复合阴极, 利用XRD、SEM对阴极的相组成及微观结构进行了分析。LSCF前驱体在800℃煅烧4 h后获得平均颗粒尺寸为50 nm的纯LSCF相。测试了在不同LSCF浸渍量及氧分压条件下阴极的阻抗谱, 研究了O₂在LSCF/SDC复合阴极的还原机制及LSCF的浸渍量对复合阴极性能的影响。研究结果表明, 在浸渍法制备的LSCF/SDC纳米复合阴极中, O₂在阴极的还原反应涉及到O₂在阴极表面的吸附与解离、O^2-在阴极体内的传输及O^2-在电极与电解质的界面之间的传输三个子过程, 其中O^2-在阴极体内的传输为O₂的还原反应的速率控制步骤。改变LSCF在阴极的浸渍量并没有改变O^2-在复合阴极的反应机制, 阴极极化电阻随LSCF浸渍量的增加先减小再增大, 浸渍相的体积分数为16.5%时, 阴极极化电阻最小。

Preparation and Oxygen-reduction Mechanism Investigation of Nanostructure LSCF-SDC Composite Cathodes

The solid oxide fuel cell nanometer composite cathodes were prepared by infiltration of La_0.6Sr_0.4Co_0.8Fe_0.2O_3-δ(LSCF) precursor solution into porous Ce_0.8Sm_0.2O_1.9(SDC) scaffolds followed by being calcined at 800℃for 4 h. The composition and the microstructure of the cathodes were analysed by X-ray diffraction (XRD) and scanning electron microscope (SEM). Average particle size of the LSCF phase is about 50 nm after being calcined at 800℃ for 4 h. The reduction reaction mechanism of O₂ in the LSCF/SDC cathodes and the influence of LSCF loadings on the cathode properties were studied in terms of frequency response, electrode resistance and reaction order at different oxygen partial pressures p(O₂). Three elementary steps are considered to be involved in the cathodes reaction: (1) absorption and dissociation of molecular O₂; (2) oxygen ion conduction in the bulk cathode; (3) oxygen ion transfer at the cathode-electrolyte interface. The oxygen ion conduction in the bulk cathode is found to be the rate-determining steps in the nano-sized LSCF-SDC composite cathode. The reduction reaction mechanism of O₂ in the cathodes is similar to the samples with different LSCF loadings. The polar resistance of the cathode firstly decreases and then increases with increasing the LSCF loadings. The cathode polar resistance reaches the lowest when the volume fraction of LSCF loadings is 16.5vol%.