Silver Nanocatalysts Change Reaction Sites in Solid Oxide Cells

Scientists have discovered that silver nanocatalysts can switch their primary reaction sites within solid oxide cells, depending on whether the cell is generating electricity or producing hydrogen. This finding could lead to more efficient designs for clean energy technologies. The research was conducted by teams from Seoul National University (SNU), KAIST, and the Korea Basic Science Institute (KBSI).

Solid oxide cells are versatile devices that can both generate electricity and split water to produce hydrogen. Their performance and durability rely on the speed of oxygen reactions at the air electrode. Previous research showed that metal nanocatalysts improve cell performance. However, the exact locations and mechanisms of these catalytic activities remained unclear.

The research team created a model electrode with precisely controlled structures. They compared several metal nanocatalysts, including silver, cobalt, palladium, and platinum. Silver demonstrated the strongest catalytic improvement among the tested metals. The scientists then investigated how silver nanoparticles function under different operating conditions.

During electricity generation, the reaction rate increased with the length of the boundary between the silver nanoparticles and the electrode. This indicates that the interface is the main reaction site for electricity production. Conversely, during hydrogen production, the reaction rate increased with the surface area of the silver nanoparticles. This shows that the surface of the silver particles becomes the primary reaction site for hydrogen production.

Further analysis, including synchrotron-based observations and theoretical calculations, revealed the atomic-level mechanisms. Silver nanocatalysts modify the electronic structure of the electrode surface to favor oxygen reduction during electricity generation. For oxygen evolution, they facilitate the combination of oxygen atoms into molecules. This understanding allows for a new design strategy for solid oxide cells, focusing on optimizing both the catalyst surface and the catalyst-electrode interface separately. This approach could enhance electricity generation efficiency and reduce the energy required for green hydrogen production.