Examination of Gadolinium Doped Ceria Mixed with Yttrium Stabilized Zirconia Mixed Ionic Electronic Conducting Solid Electrolytes for Use As Reversible High Temperature Cells

Abstract

Reversible cells can be used as solid oxide fuel cells (SOFC) and solid oxide electrolyzer cells (SOEC). The solid electrolytes used for such cells frequently have pure ionic conduction with insignificant electronic conduction. A previous study (Virkar and Tao, 2015) has shown that cells made of ceria doped yttrium stabilized zirconia (YSZ), a mixed ionic electronic conducting (MIEC) material, can be made to operate at the same efficiency level and with superior stability compared to a pure ionic conductor, like pure YSZ. This work is a continuation of that study, examining the use of gadolinium doped ceria (GDC) mixed with YSZ. The MIEC cell, 8mol%GDC+YSZ, will be further tested and designed to consume fuel or water vapor, generate power or hydrogen, and release heat at the same rate as the pure ionic conducting cell, YSZ, when operating in SOFC or SOEC mode. Future testing will also determine if the GDC MIEC cell can match or exceed the durability of the ceria doped YSZ.The electrolyte layer, made of either pure 8YSZ or 8YSZ doped with 8mol%GDC, was die pressed and sintered at 1400oC (2oC/min) for five hours. On one side of the electrolyte, the anode interlayer is mixed with isopropyl alcohol and painted on the electrolyte's surface. The anode interlayer is composed of 50wt% NiO and 50wt% 8YSZ. The cell was heated to 950oC (2oC/min) for one hour. The anode functional layer, 70wt% NiO and 30wt% 8YSZ, was painted on top of the anode interlayer. The sample was then again heated to 950oC (2oC/min) for one hour to burn off any organic compounds. A cathode interlayer was then painted on the other side of the electrolyte layer. The cathode interlayer was also painted on and consists of 50wt% lanthanum strontium manganite (LSM) and 50wt% YSZ. The cell is heated to 1200oC (2oC/min) for two hours. Finally, a pure LSM layer is painted on top as the cathode current collector material and heated to 1100oC (2oC/min) for one hour to ensure good porosity. The cells were then sealed by compression-loading at the edges using glass-mica seals.Results of tests will be reported for both SOEC and SOFC modes at 800oC. Data to be reported include open-circuit voltage, area-specific resistance, corresponding ionic currents based on an applied voltage, and long-term durability of the two cells in both SOFC and SOEC modes.