Processing of Hierarchical and Anisotropic Porosity LSM‐YSZ Composites

Abstract

Aqueous dispersions of lanthanum strontium manganite (LSM) and yttria‐stabilized zirconia (YSZ) particles were controllably freeze‐cast and then partially sintered resulting in anisotropic, hierarchically porous ceramics for Solid Oxide Fuel Cell (SOFC) cathodes. The resulting microstructures have aligned pores with a characteristic spacing (λ) between pore centers. The effect of freezing rate, slurry viscosity, and solid loading on solidification velocity and resultant microstructures was explored. Varying these parameters resulted in samples with a range of independently controllable and reproducible microstructures. Homogenous dispersion of LSM and YSZ in the freeze‐cast structures was confirmed through elemental mapping. Freezing rate was found to have a significant effect on λ while solid loading affected overall porosity and ceramic wall‐ to‐pore size ratio but had only a small influence on λ. Viscosity was found to have a complex albeit small impact on λ but a significant effect on particle dispersion and colloid stability.

Dispersion, connectivity and tortuosity of hierarchical porosity composite SOFC cathodes prepared by freeze-casting

“…Lastly, the viscosity of the slurry must remain high enough to partially coagulate the suspension, hindering the majority of particle segregation, while at the same time be low enough to still allow the slurry to be easily freeze-cast. 7 The high Fig. 1.…”

“…In the previous few years, freezecasted composite anodes have been produced by several research groups, 4-6 but only recently, the successful processing of freezecast LSM-YSZ cathode materials has been reported. 7 Within the context of freeze-cast processing as a means of microstructure tailoring, studying the influence of processing parameters on the microstructure of the ceramic walls is essential. Indeed, the electrochemical performance of a freeze-cast electrode is highly dependent on the microstructure of its walls, which is controlled by the sintering temperature, freezing conditions and initial slurry characteristics (composition, particle size, dispersion, etc.).…”

Freeze‐cast yttria‐stabilized zirconia pore networks: Effects of alcohol additives

“…20 Other methods of increasing TPB area without significantly increasing tortuosity include incorporating a second sacrificial phase or by partial sintering to achieve submicron porosity, as it is not achievable in freeze-cast structures. 37,43 Alternatively, SOFCs can be improved by modifying the electrode pore surface through infiltration of particles. 44 Studies by Chen, et al, have demonstrated that freeze-tape-casting of nickel-gadolinium-doped ceria can be used to produce hierarchically porous cathodes with low tortuosity that, when infiltrated with SSC (Sm 0.5 Sr 0.5 CoO 3 ) particles, have high cell power output.…”

Ice templating of ZrB2–SiC systems

“…However, when biphasic systems with different particle size ranges are considered, the process should be substantially revised to avoid demixing and particle segregation, as well the rheology should be optimized to ensure unidirectional ice growth [17,18].…”