Characterization and Stack Testing of Solid Oxide Fuel Cells with Cathodes Prepared by Infiltration

Abstract

Large footprint (144 cm 2 ) cells with infiltrated (La 0.6 Sr 0.4 ) 0.95 FeO 3 /yttria-stabilized zirconia (LSF-YSZ) cathodes were fabricated on a pre-production scale (approximately 90 cells/batch). The excellent electrochemical performance of the cells was confirmed both on single cell as well as on stack level. Changes in electrode properties were mapped out as a function of heat-treatment temperature. The microstructure of the porous zirconia backbone remained unchanged, but the surface area of the ferrite phase decreased gradually, as the electrode was treated to higher temperatures. Changes in surface area were accompanied by corresponding changes in pore size and total pore volume. In contrast to traditional composite electrodes, the in-plane conductivity of infiltrated LSF-YSZ cathodes decreased with increasing sintering temperature, a trend likely explained by microstructure alterations during the sintering of the non-random structure. Recently, the use of infiltration as a method for solid oxide fuel cell (SOFC) electrode preparation has gathered significant scientific interest.1-6 The infiltration (or impregnation) method resembles the wet impregnation and incipient wetness methods employed in heterogeneous catalysis. 7,8 The electrodes are prepared by the introduction of perovskite precursors (e.g. in the form of nanoparticles, aqueous nitrate solutions, or molten salts 9 ) into sintered porous backbone structures, typically made of electrolyte materials such as yttria-stabilized zirconia (YSZ) 1,9-12 or doped ceria. 3,6,13 Such electrodes have several advantages over traditional SOFC electrodes. Infiltration approach allows for the use of a wider range of active materials.1,2,10,12,14 Furthermore, infiltrated electrodes promise improved mechanical properties over traditional electrodes due to the lower thermal expansion mismatch between the electrolyte and cathode layers, 1,10 and enhanced performance due to the high surface area of the active phase. 1,6,12,16 Finally, the possibility of synthesizing the electrode active phase in situ within the electrolyte pores from relatively cheap nitrate precursors may offer significant materials cost advantages over traditional electrodes, where expensive perovskite powders with finely tuned particle size distributions are required for screen-printing. 17The results on infiltrated electrodes reported in the literature have so far been obtained almost exclusively on button cells with electrode active areas on the order of 1 cm 2 or less. A notable exception is the work by C. S. Ni et al., who have recently fabricated and tested 5 × 5 cm 2 cells where both the anode and the cathode was prepared by infiltration. 18 Here, we report the physical characterization and stack testing of 12 × 12 cm 2 planar cells with cathodes prepared by infiltration of a perovskite precursor solution into a stabilized zirconia (SZ) backbone. The results reported here were obtained primarily on infiltrated (La 0.6 Sr 0.4 ) 0.95 FeO 3 (LSF)-SZ electrodes. LSF-SZ is an excellent model sy...

Tailoring SOFC Electrode Microstructures for Improved Performance

“…[189] They did multiple impregnation steps and followed the amount of added material, and then looked at both the microstructure and in-plane electrode resistance, to correlate with cell performance. They used standard cell impregnation methods to improve cathodes.…”

“…Topsoe fuel cells have looked at impregnation on the stack level to help the performance and durability of its stacks. They used standard cell impregnation methods to improve cathodes . They did multiple impregnation steps and followed the amount of added material, and then looked at both the microstructure and in‐plane electrode resistance, to correlate with cell performance.…”

On the Properties and Long-Term Stability of Infiltrated Lanthanum Cobalt Nickelates (LCN) in Solid Oxide Fuel Cell Cathodes

“…Degradation in infiltrated electrodes is commonly attributed to nano-particle coarsening. 18,19,24,34,54,[56][57][58] Numerous independent studies have shown that electrocatalyst particle size (and hence the electrochemically active surface area) plays a major role in determining the performance of infiltrated electrodes. In one such study, the performance of an infiltrated La 0.8 Sr 0.2 FeO 3 electrode, deactivated by heattreatment, could be restored to close to original performance by a single infiltration of fresh La 0.8 Sr 0.2 FeO 3 , and the extent of re-activation could be predicted from the associated electrode BET surface area increase.…”

“…Another advantage of the cathode backbone concept is that of number of sintering steps in manufacturing process of the SOFCs is reduced. 34 Here only one sintering process at high temperatures is necessary; the heat-treatment steps that follow the infiltration process are performed at much lower temperature (≤400 • C) (Figure . 1b).…”

Structure—Properties—Performance: Modelling a Solid Oxide Fuel Cell with Infiltrated Electrodes

“…21,22 Figure 1 shows two representative images of conventional and infiltrated architectures a . While the latter architecture guarantees a large density of reaction sites, thus decreasing the electrode polarization resistance, [23][24][25] the durability over extended operation [26][27][28] and redox cycling 29,30 requires additional optimization, 31,32 especially for infiltrated Ni in the anode.…”