WANG Zhangwei ^{1, 3}, LUO Linghong^{1, 3}, CHENG Liang ^{2, 3}, WANG Leying ^{1, 3}, XU Xu ^{1, 3},
YU Jianfeng ^{1, 3}, LIU Shaoshuai ^{1, 3}, ZHANG Shuangshuang ^{1, 3}
(1. School of Materials Science and Engineering, Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China; 2. National Engineering Research Center for Domestic & Building Ceramics, Jingdezhen Ceramic University, Jingdezhen 333001, Jiangxi, China; 3. Jiangxi Provincial Key Laboratory of Fuel Cell Materials and Devices, Jingdezhen 333001, Jiangxi, China)

Abstract: The relationship between the thickness and electrochemical performance of La _0.6 Sr0.4 Co_0.2Fe _0.8O_3−δ-Gd_0.1Ce_0.9O_1.95 oxygen electrode was studied by using a symmetrical oxygen electrode cell. Electrochemical impedance spectroscopies of the oxygen electrode with thicknesses of 5–22 μm were measured at various open-circuit voltages. The electrochemical impedance spectra and cyclic voltammetry curves of the fuel supported button cells with oxygen electrodes of different thicknesses were also tested. It is found that the total polarization impedance (Rp) changes with thickness change of the oxygen electrode. The total polarization impedance is derived from oxygen ion transfer, oxygen surface exchange and oxygen diffusion. By analyzing the impedances of different processes, it can be found that the high frequency oxygen ion transport process has a weak dependence on the oxygen electrode thickness. The surface exchange and diffusion of oxygen are strongly dependent on thickness of the oxygen electrode. The electrochemical performance of the oxygen electrode can be improved by optimizing the thickness. The lowest value of resistance is reached at 12 μm, which is 0.034 Ω·cm² at 750 ℃. Accordingly, the maximum power density of the fuel electrode supported button cell (NiO-YSZ||YSZ||20GDC||LSCF-10GDC) is 1098 mW·cm⁻², with 3 vol.% H₂O + 97 vol.% H₂ as fuel and static air as oxidant at 800 ℃. Because the optimal thickness of the oxygen electrode obtained is only about half of the thickness of the currently similar oxygen electrode, the concept of “thin film oxygen electrode” was proposed for possible commercialization.
Key words: SOFC;La_0.6Sr0.4 Co_0.2Fe _0.8O_3−δ-Gd_0.1Ce_0.9O_1.95 ; oxygen electrode thickness; electrochemical properties