The core factor that determines the performance of solid oxide fuel cells is the cathode at which the reduction reaction of oxygen occurs. Conventionally, oxides with perovskite structure (ABO₃) are used in cathodes. However, despite the high performance of perovskite oxides at initial operation, the performance decreases with time, limiting their long-term use. In particular, the condition of high temperature oxidation state required for cathode operation leads to surface segregation phenomenon, in which second phases such as strontium oxide (SrO_x) accumulate on the surface of oxides, resulting in decrease in electrode performance. The detailed mechanism of this phenomenon and a way to effectively inhibit it has not been suggested.

Using computational chemistry and experimental data, Professor WooChul Jung’s team at the Department of Materials Science and Engineering observed that local compressive states around the Sr atoms in a perovskite electrode lattice weakened the Sr-O bond strength, which in turn promote strontium segregation. The team identified local changes in strain distribution in perovskite oxide as the main cause of segregation on strontium surface.

Based on these findings, the team doped different sizes of metals in oxides to control the extent of lattice strain in cathode material and effectively inhibited strontium segregation.

This technology can be implemented by adding a small amount of metal atoms during material synthesis, without any additional process. I hope this technology will be useful in developing high-durable perovskite oxide electrode in the future.

—Professor Jung

Resources

• Bonjae Koo, Hyunguk Kwon, YeonJu Kim, Han Gil Seo, Jeong Woo Han and WooChul Jung (2018) “Enhanced oxygen exchange of perovskite oxide surfaces through strain-driven chemical stabilization” 11, 71-77 doi: 10.1039/C7EE00770A