Researchers demonstrate cobalt exsolution in solid oxide fuel cell cathodes in oxidizing atmospheres, presenting a new direction for fuel cell research
CHUNGCHEONG PROVINCE, South Korea, Oct. 3, 2025 /PRNewswire/ — Fuel cells are an efficient, clean alternative to traditional fossil-fuel-based energy systems. Solid oxide fuel cells (SOFCs) are especially attractive due to their ability to use multiple fuels, high efficiency and reversibility. Cobalt (Co)-doped rare-earth layered perovskite oxides are attractive cathode materials for low- and medium-temperature SOFCs. They offer excellent electrochemical performance, owing to their high oxygen content and flexible control of oxygen transport.
Yet, electrodes made from these materials demonstrate low long-term stability. Key strategies to address this issue include the substitution of some Co with Iron (Fe) and growing Co nanoparticles on the electrode surface through a process called metal exsolution. However, exsolution has only been demonstrated under high temperature-reducing atmospheres. Under the actual oxidizing operating environment of SOFC cathodes, this process is reversed.
A research team led by Professor Junghyun Kim from the Department of Advanced Materials Engineering at Hanbat National University, Republic of Korea, has now challenged this view. “We have presented the first experimental evidence of Co exsolution occurring in a high-temperature oxidizing atmosphere, challenging the conventional paradigm,” explains Prof. Kim. Their study was made available online on May 21, 2025, and published in Volume 648 of the Journal of Power Sources on August 30, 2025.
The researchers first studied the electrochemical properties and oxygen (O) content of two layered perovskite structures: SmBa0.45Sr0.5(Co1-xFex)1.9O5+d (SBSCF 1.9) and SmBa0.5Sr0.48(Co1-xFex)2.05O5+d (SBSCF 2.05). Two specific samples of these structures: one with 30% Fe substitution in SBSCF 1.9 (SBSCF 1.9-0.3) and one with 50% Fe substitution in SBSCF 2.05 (SBSCF 2.05-0.5) showed the highest electrochemical performance and were chosen for further study. When exposed to oxidizing atmospheres at high temperatures, both samples exhibited Co exsolution above 700 °C. The number of particles increased with increasing temperatures, reaching a maximum at 900° C.
The researchers explained that under oxidising conditions and high temperature environments, the weaker Co-O bonds are broken, while the Fe-O bonds remain stable. These dissociated oxygen atoms diffuse to the surface, forming oxygen vacancies in the material. These vacancies and Co, then segregate together towards the surface, leading to Co-exsolution. As temperatures increase, more Co exsolution particles appear.
Interestingly, SBSCF 1.9-0.3 formed smaller, but more exsolved Co particles than SBSCF 2.05-0.5. This resulted in a lower area specific resistance (ASR) and higher oxygen reduction reaction (ORR) activity. This was linked to its higher surface oxygen vacancy concentration, originating from its lower Fe content. It also had higher Co-content.
“Our results show that formation of finely dispersed exsolved Co particles is crucial for optimizing the electrochemical performance of SOFC cathodes,” says Prof. Kim. “Beyond SOFCs, these findings can also benefit oxygen separation membranes and environmental catalytic systems for clean-air technologies, and upcoming protonic ceramic fuel cells.“
This study presents a new direction for fuel cell research, leading to more efficient and high-performance designs.
Reference
Title of original paper: Metal Co exsolution for catalyst design and electrochemical enhancement of non-stoichiometric solid oxide fuel cell cathodes
Journal: Journal of Power Sources
DOI: 10.1016/j.jpowsour.2025.237402
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SOURCE Hanbat National University
