Gd_0.2Ce_0.8O₂ Diffusion Barrier Layer between (La_0.58Sr_0.4)(Co_0.2Fe_0.8)O_3−δ Cathode and Y_0.16Zr_0.84O₂ Electrolyte for Solid Oxide Fuel Cells: Effect of Barrier Layer Sintering Temperature on Microstructure

Abstract

Combining high-performance (La 0.58 Sr 0.4 )(Co 0.2 Fe 0.8 )O 3-δ (LSCF) cathodes with Y-doped ZrO 2 (YDZ) electrolytes in solid oxide fuel cells leads to the formation of SrZrO 3 (SZO) as secondary phase with exceedingly low oxygen ion conductivity and poor catalytic capability. A promising prevention strategy is the insertion of Gd-doped CeO 2 (GDC) as a reaction barrier. In this work, screen-printed GDC layers were sintered on YDZ substrates at temperatures varying from 1100 to 1400 °C. Subsequently, screen-printed LSCF was sintered on top at 1080 °C. The goal of this work was to understand microstructure formation during the two subsequent sintering processes by the analysis of nanometer-scale elemental distributions, crystal structures, and grain sizes of this extended cathode/ electrolyte interface as a function of the GDC sintering temperature. Various representative regions on all samples were analyzed by transmission electron microscopy combined with energy dispersive X-ray spectroscopy with high spatial resolution. For the lowest GDC sintering temperature an almost continuous ion-blocking SZO layer is formed during subsequent LSCF sintering. Although GDC densification does not occur, SZO formation is increasingly suppressed if higher GDC sintering temperatures are applied. This is attributed to a dense interdiffusion layer forming at the GDC/YDZ interface, which increases in thickness with GDC sintering temperature and contains a Zr-depleted region adjacent to the porous GDC layer. The dense and Zr-poor sublayer prevents the reaction of Sr species transported via gas phase during LSCF sintering with the Zr-rich YDZ substrate. The microstructural features have a pronounced influence on the electrical performance. Electrochemical impedance spectroscopy measurements at open circuit voltage conditions reveal differences in the polarization resistance of up to 3 orders of magnitude.

Numerical Simulation of the SrZrO3 Formation in Solid Oxide Fuel Cells

“…1673K. These values are chosen based on the CGO layer microstructure after sintering as presented in [8]. Fig.…”

“…So far, a large number of experimental investigations have been conducted on the SZO formation with different heat-treatment conditions for the CGO layer and several common findings have been reported [6][7][8][9][10][11][12][13][14][15]. When CGO is sintered below 1200 ºC, sintering the LSCF cathode at 1100 ºC for 2 h results in a SZO layer covering the YSZ electrolyte surface entirely.…”

“…However, in the case of CGO sintered at 1300 ºC, with prolonging cathode sintering time up to 16 h, SZO can still cover the YSZ electrolyte surface entirely as presented by Matsuda et al [15]. With regard to cell performance, latest studies [8,13]…”

Computational engineering of the oxygen electrode-electrolyte interface in solid oxide fuel cells

“…In Step 2, a LSCF layer is deposited on the CGO layer, followed by sintering at a slightly lower temperature (950-1150 °C), where the interdiffusion across the YSZ-CGO interface will still continue, but in a much less degree due to much slower diffusion kinetics. Despite of the existence of the CGO barrier layer, formation of the SZO phase at the YSZ-CGO interface is confirmed by a large number of experimental investigations so far 13,15,[22][23][24][25][26][27][28][29][30] . Sr accumulated at the YSZ-CGO interface is believed to diffuse from the LSCF cathode through the CGO barrier layer mainly during the cathode-sintering process.…”

Improved performance of a samarium-doped ceria interlayer of intermediate temperature solid oxide electrolysis cells by doping the transition metal oxide Fe2O3

“…By adding CuO in the GDC interlayer, the sintering temperature of the interlayer is reduced, so as to prevent the solid-state reaction between the interlayer and YSZ electrolyte. [16][17][18][19] In addition, cosintering can reduce the cost of the manufacturing process by reducing the necessary heat-treatment temperature, which is conducive to the commercialization of SOECs. It can be seen that improving the interlayer performance can enhance the performance of the oxygen electrode and the SOEC.…”