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Solid oxide fuel cells (SOFCs) can convert chemical energy into electricity efficiently and use a range of fuels. Carbon monoxide (CO), including CO in syngas, is attractive because it can be used directly. But under some operating conditions, CO can form solid carbon on the nickel-based anode. Deposited carbon blocks pores and active reaction sites, reducing performance. To design more durable cells, we need to know where this carbon first forms and why.

In our study, we focused on the interface between nickel and yttria-stabilized zirconia (Ni–YSZ) in the anode functional layer. We fabricated two anode-supported thin-film SOFCs with different Ni–YSZ interface densities while keeping the other cell layers comparable. We tested the cells at 500 °C using hydrogen, pure CO, and a 1:1 hydrogen–CO mixture, and paired the experiments with density functional theory calculations to examine CO at the atomic scale.

A higher interface density improved initial performance: under syngas, the high-interface cell reached a maximum power density of 622 mW/cm², compared with 454 mW/cm² for the low-interface cell. The same interface-rich structure, however, was more vulnerable to carbon. After two hours under syngas, the measured carbon atomic percentage increased from 10.91% to 30.63% in the high-interface cell, compared with 11.12% to 16.30% in the low-interface cell. The high-interface cell also showed greater performance loss. This reveals a trade-off: Ni–YSZ interfaces provide useful reaction sites, but also potential starting points for degradation.

The calculations help explain why. At some Ni–YSZ interfacial sites, nickel atoms transfer more electron density to adsorbed CO. This interaction, known as π back-donation, weakens the carbon–oxygen bond and makes CO dissociation and carbon formation more favorable. Once carbon appears, nearby interfacial sites can support further deposition.

These findings show why maximizing interface density alone may not produce the most durable anode. Anode design should balance electrochemical activity with resistance to carbon nucleation. By identifying how carbon begins at Ni–YSZ interfaces, this work provides a mechanistic basis for future interface engineering and fuel-specific operating strategies to improve the durability of CO-fueled SOFCs.

"Only Nothing is Absolute, Everything Else is Relative".

Daniel Gil

Seoul National University / Mechanical Engineering Department / Renewable Energy Conversion Laboratory, Republic of Korea

danielgil123@snu.ac.kr

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