2630
Synthesizing Core-Shell Heterostructures for SOFCs Using a Solution Precipitation Method

Wednesday, 16 May 2018: 16:40
Room 309 (Washington State Convention Center)
B. Levitas, Y. Zhu, and S. Gopalan (Boston University)
In the last three decades, solid oxide fuel cells (SOFCs) have garnered significant interest for viable distributed power generation systems. In this work, we focus on the cathode in SOFCs, where oxygen reduction occurs in two steps—adsorption and electronation, and surface/bulk diffusion to incorporation sites. Transition metal oxides such as strontium-doped lanthanum manganite (LSM) and strontium-doped cobalt iron oxide (LSCF) have been used as cathode materials, however both individually lack the key characteristics to successfully complete oxygen reduction. Furthermore, the accumulation of chromium (chromium poisoning) on SOFC cathodes is known to significantly hinder the performance of the cells. Incorporating core-shell hetero-structures as the cathode material could alleviate this problem: effectively combining the functionalities of both materials, and providing a nanoscale protection from Cr poisoning with a shell such as Cr-doped LSM (LSCM). However, synthesizing core-shell cathode structures previously has proved difficult requiring multiple steps, resulting in non-uniform core-shell structures. In this work we propose utilizing a molten salt synthesis process to create core-shell structures with precise composition with relative ease. The core is synthesized using high-temperature calcination and ball milled with the precursors of the target shell material. The milled powder mixtures are added to a LiCl-KCl eutectic melt to form core-shell hetero-structures via heterogeneous nucleation. Prior results have shown the successful formation of LSM and LSCF using the molten salt synthesis, along with the formation of core-shell LSCF-LSM hetero-structures. Synthesis temperatures dropped from the conventional 1000 ºC to 500 ºC, with dwell times as low as 10 minutes. Furthermore, SOFC cathodes consisting of LSCM were found to have stable polarization resistances, whereas the polarization resistance in LSM cathodes steadily increased. This result provides a strong motivation to further explore LSCM as a shell for core-shell cathodes to ensure protection from chromium poisoning. In essence, this work demonstrates an inexpensive method to synthesize core-shell cathodes that can simultaneously provide high power densities and low rates of degradation arising from Cr-poisoning.