A fully functional solid-oxide fuel cell membrane wafer (credit Shriram Ramanathan)

First macro-scale thin-film solid-oxide fuel cell demonstrated

Scientists have demonstrated the first fully functional macro-scale SOFC which could be a source for clean energy.

Researchers at the Harvard School of Engineering and Applied Sciences (SEAS) and SiEnergy Systems LLC made the breakthrough which is the first time any research group has overcome the structural challenges of scaling micro-technology SOFCs up to a practical size.

The findings reported Nature Nanotechnology journal demonstrates that the technology is scalable with a proportionally higher power output, indicating the potential of electrochemical fuel cells to be a viable source of clean energy.

"The breakthrough in this work is that we have demonstrated power density comparable to what you can get with tiny membranes, but with membranes that are a factor of a hundred or so larger," said principal investigator Shriram Ramanathan, associate professor of Materials Science at SEAS.

SOFCs create electrical energy via an electrochemical reaction that takes place across an ultra-thin membrane.

This 100-nanometer membrane, comprising the electrolyte and electrodes, has to be thin enough to allow ions to pass through it at a relatively low temperature - in the range of 300 to 500 degrees Celsius for ceramic fuel cells.

This allows for a quick start-up, a more compact design, and less use of rare-earth materials.

Until now thin films have been successfully implemented only in micro-SOFCs, where each chip in the fuel cell wafer is about 100 microns wide.

For practical applications, such as use in compact power sources, SOFCs need to be about 50 times wider.

The electrochemical membranes are so thin that creating one on that scale is roughly equivalent to making a 16-foot-wide sheet of paper.

Lead author Masaru Tsuchiya, co-author Bo-Kuai Lai and Ramanathan fortified the thin film membrane using a metallic grid, which provides the critical structural element for the large membrane while also serving as a current collector.

Ramanathan's team was able to manufacture membrane chips that were 5 mm wide, combining hundreds of these chips into palm-sized SOFC wafers.

While other researchers' earlier attempts at implementing the metallic grid showed structural success, Ramanathan's team is the first to demonstrate a fully functional SOFC on this scale.

Their fuel cell's power density of 155 milliwatts per square centimeter (at 510 degrees Celsius) is comparable to the power density of micro-SOFCs.

When multiplied by the much larger active area of this new fuel cell, that power density translates into an output high enough for relevance to portable power.

Previous work in Ramanathan's lab has developed micro-SOFCs that are all-ceramic or that use methane as the fuel source instead of hydrogen.

The researchers hope that future work on SOFCs will incorporate these technologies into the large-scale fuel cells, improving their affordability.

In the coming months, they will explore the design of novel nanostructured anodes for hydrogen-alternative fuels that are operable at these low temperatures and work to enhance the microstructural stability of the electrodes.

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