摘 要

La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ钙钛矿型复合氧化物因为具有良好的热稳定性和化学稳定性以及足够高的电化学催化活性，所以很有希望成为新一代的中温固态氧化物燃料电池（IT-SOFC）的阴极材料。本论文采用甘氨酸-硝酸盐法制备得到La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ超细微粉体，选择Ce_0.8Sm_0.2O_1.9作为电解质基体，采用丝网印刷法制备得到La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ多孔电极，研究了La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ多孔电极的电极厚度对电催化活性的影响，研究阴极极化状态下电极的电化学行为，从理论上分析电极厚度对电极材料电化学性能的影响，探索La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ多孔电极合适的电极厚度，进一步提高La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ多孔电极材料的电催化活性。

制备了La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ/ Ce_0.8Sm_0.2O_1.9（SDC）/Pt 三电极结构的半电池，采用电化学阻抗谱和计时电位法研究了La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ多孔电极的氧催化还原反应的主要过程，得到了各个电极过程和总电化学反应过程的极化电阻，以及该电极材料800下过电势与电流密度的关系。研究结果表明，La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ多孔电极的氧交换过程包括电极与电极表面氧物种之间的电子转移过程和电极表面氧分子的吸附-解离过程。其中，氧分子的吸附-解离过程对电极极化的具有更为显著贡献。

通过改变丝网印刷的次数，研究了La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ多孔电极在不同电极厚度下的电化学性能。研究结果表明，在一定范围内，随电极厚度的增大（5-20），多孔电极的电极反应总极化电阻降低，表现出电化学活化的趋势。分析其原因，主要是由于电极厚度会影响电极材料的电子转移过程和电极表面氧分子的吸附解离过程。电极厚度的增大利于La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ多孔电极表面的氧交换过程的发生，因此在一定范围内，增大电极厚度能提高电极的电化学性能。

确定了La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ多孔电极在厚度为20的时候具有理想的显微结构和电化学性能。在800下，厚度为20的La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ多孔电极的极化电阻为0.112，在200的电流密度下的过电势为22.50,在平衡状态下的交换电流密度达到了330。这一优异的电化学性能使它具有成为新一代IT-SOFC阴极材料的潜力。

关键词：La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ，阴极材料，电极厚度，电化学性能

ABSTRACT

The perovskite complex oxides of the La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ system are seemed as a new generation of intermediate temperature solid oxide fuel cell (IT-SOFC) cathode material because of their high ionic and electrical conductivity, good thermal stability and chemical stability, high chemical reaction catalytic activity. In this work, La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ ultrafine powder was prepared by glycine-nitrate method. Ce_0.8Sm_0.2O_1.9 was chosen as the electrolyte matrix. Porous electrode was prepared by screen printing method, the effect of the thickness of La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ electrode on the structure and electrocatalytic activity was studied. Electrochemical behavior of the electrode under cathodic polarization was evaluated and the influence of electrode thickness on the electrochemical properties of electrode materials was analyzed theoretically. In order to develop La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ with high electrocatalytic activity , The suitable electrode thickness of La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ porous electrode was explored.

Three-electrode half cells based on Ce_0.8Sm_0.2O_1.9 electrolyte substrates and using La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ as working electrodes were prepared. Electrochemical impedance spectroscopy and chronopotentiometry were employed to investigate the main electrochemical reaction. The polarization resistance of each electrode process and the total electrochemical reaction was obtained, and the relationship between the overpotential and the current density under different temperature was measured. It was found that overall electrode polarization consists of electron transfer process between the electrodes and atomic oxygen species on the surface of the electrodes. The latter reaction provides more remarkable contribution to the overall electrode polarization of La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ electrodes.

By means of changing the times of screen printing, the electrochemical performance of La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ porous electrode under different electrode thickness was studied. The result indicated that in the specific thickness range, the total polarization resistance of the electrode reaction on the porous electrode would decrease with the increase of the electrode thickness, and it presented the tendency of electrochemical activation. Analyzing the cause, it may generate from the truth that the electrode thickness will influent the oxygen ion transport process at the electrode-electrolyte interface and the oxygen exchange process on the electrode surface. Increasing the electrode thickness will be favorable for the oxygen exchange process on the surface of La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ porous electrode. Therefore, the electrode thickness has a positive effect on the electrochemical performance of the electrode.

When the thickness comes to 20μm, the La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ porous electrode has the ideal microstructure and electrochemical properties, in which the polarization resistance is 0.112, and the overpotential at the current density of 200 is 22.50 mV, The exchange current density in the state reaches 330. The good electrochemical properties endorse their potential for utilization as cathodes for IT-SOFC.

Keywords: La_0.3Ca_0.7Fe_0.7Cr_0.3O_3-δ, Cathode, Electrode thickness, Electrochemical properties