SNU–KAIST–KBSI joint research team identifies “hidden reaction sites” of silver nanocatalysts

It has been discovered for the first time that the same silver (Ag) nanocatalyst operates at different reaction sites depending on whether the solid oxide cell is generating electricity or producing hydrogen. This finding introduces a new design principle for improving the performance of next-generation solid oxide cells.

A joint research team led by Professors WooChul Jung and Jeong Woo Han from the Department of Materials Science and Engineering at Seoul National University (SNU), in collaboration with Professor Sang Ouk Kim’s team at KAIST and Dr. Beomgyun Jeong’s team at the Korea Basic Science Institute (KBSI), has elucidated the operating mechanism of silver nanocatalysts that enhance the performance of solid oxide cells. The team confirmed that the sites and mechanisms of oxygen reactions vary depending on the operating mode of the cell.

Solid oxide cells are next-generation energy devices that use the transport of oxygen ions to either generate electricity or split water to produce hydrogen. They are considered a key technology for expanding clean power generation and hydrogen utilization, as they can be applied to a wide range of systems—from distributed combined heat and power systems in buildings and factories that generate electricity while utilizing the high-temperature heat produced during operation to renewable energy–based green hydrogen production.

The findings were published in the globally renowned journal Energy & Environmental Science (Impact Factor: 30.5) and were selected as an Outside Back Cover article, highlighting their significance.

The performance and lifespan of solid oxide cells are largely determined by the rate of oxygen reactions at the air electrode. However, due to the structural complexity of actual electrodes, it has been difficult to identify precisely where and how nanocatalysts contribute to these reactions. While previous studies established that metal nanocatalysts improve cell performance, it remained unclear whether the catalytic activity primarily occurs on the catalyst surface or at the interface between the catalyst and the electrode. It was also unknown whether the catalysts operate in the same way during electricity generation and hydrogen production.

To address these challenges, the research team developed a model electrode system with a precisely controlled structure and composition, rather than using structurally complex real electrodes. They arranged uniformly sized and spaced metal nanoparticles in ordered arrays to precisely analyze their catalytic roles.

First, various metal nanocatalysts—including silver, cobalt, palladium, and platinum—were deposited on a thin-film perovskite oxide electrode, and their ability to promote oxygen reactions was compared. Among them, silver nanocatalysts exhibited the strongest catalytic enhancement.

Next, by systematically varying the size and arrangement of silver nanoparticles on the model platform, the team analyzed the reaction sites. They found that during the oxygen reduction reaction (electricity generation), the reaction rate increased with the length of the interface between the silver nanoparticles and the electrode, indicating that this interface serves as the primary reaction site. In contrast, during the oxygen evolution reaction (hydrogen production), the reaction rate increased with the surface area of the silver nanoparticles, demonstrating that the particle surface itself serves as the key reaction site.

The team further compared the two reactions in detail by controlling the applied voltage and oxygen concentration. They found that silver nanocatalysts facilitate electron transfer to oxygen during oxygen reduction, while during oxygen evolution, they promote the combination of oxygen atoms into oxygen molecules and their subsequent release.

The researchers also conducted synchrotron-based analysis, which enabled them to observe changes on the electrode surface during operation, together with atomic-scale theoretical calculations. These analyses revealed that silver nanocatalysts modify the electronic structure of the electrode surface to promote oxygen reduction and provide a favorable environment for oxygen atom coupling during oxygen evolution.

This study is significant because it demonstrates that nanocatalysts are not merely additives that increase reaction rates, but that their reaction sites and mechanisms can change depending on the operating mode. In particular, it proposes a new design strategy in which the catalyst surface and the catalyst–electrode interface should be optimized separately when designing air electrodes for solid oxide fuel cells and solid oxide electrolysis cells.

If applied to practical devices, this design principle is expected to increase the power generation efficiency of distributed energy systems for buildings and factories and reduce electricity consumption in renewable energy–powered water electrolysis systems for green hydrogen production. Furthermore, it could accelerate the commercialization of reversible solid oxide cells, which can both generate electricity and produce hydrogen in a single system, enabling more efficient energy production and storage in residential and industrial settings.

In addition, the precisely controlled nanoparticle array-based model electrode developed in this study serves as a research platform for distinguishing where and how catalysts operate in real systems. This platform can be applied not only to solid oxide cells but also to hydrogen production devices, various electrochemical energy conversion systems, and oxygen separation technologies.

Professor WooChul Jung, who led the study, stated: “This research is significant because it quantitatively evaluates the performance of nanocatalysts while also identifying their actual reaction sites and operating mechanisms.”

He added: “We plan to further establish this as a new design principle that can be applied to various energy conversion materials and catalytic systems.”

Dr. Jinwook Kim, who led the research, is currently a postdoctoral researcher at Northwestern University and will soon join the University of Seoul as an assistant professor in the Department of Materials Science and Engineering. He plans to continue research on nanocatalysts and solid oxide cells, expanding this work toward the development of high-efficiency energy conversion materials and devices.

This research was supported by the Ministry of Science and ICT and the National Research Foundation of Korea (RS-2024-00452853, RS-2025-00521316). Synchrotron-based AP-XPS research at the KBSI-PAL 8A2 AP-XPS beamline was supported by Pohang Accelerator Laboratory/POSTECH and Korea Basic Science Institute.

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