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

Apr 04, 2011 By Caroline Perry
First macro-scale thin-film solid-oxide fuel cell demonstrated by scientists
The electrochemical membrane, showing the texture of the metallic grid on its surface. Stabilizing the membrane with this grid has allowed materials scientists at Harvard to successfully scale the technology up to a practical scale, enabling clean-energy applications. Credit: Shriram Ramanathan.

(PhysOrg.com) -- Materials scientists at the Harvard School of Engineering and Applied Sciences (SEAS) and SiEnergy Systems LLC have demonstrated the first macro-scale thin-film solid-oxide fuel cell (SOFC).

While SOFCs have previously worked at the micro-scale, this is the first time any research group has overcome the structural challenges of scaling the technology up to a practical size with a proportionally higher power output.

Reported online April 3 in Nature Nanotechnology, the demonstration of this fully functional SOFC indicates 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, demonstrating that the technology is scalable," says principal investigator Shriram Ramanathan, Associate Professor of Materials Science at SEAS.

SOFCs create electrical energy via an 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 (which, for ceramic fuel cells, lies in the range of 300 to 500 degrees Celsius). These low temperatures allow for a quick start-up, a more compact design, and less use of rare-earth materials.

A fully functional solid-oxide fuel cell membrane wafer. The structured surface of each square chip lends stability to the incredibly thin film that is used for the electrochemical membrane. Credit: Shriram Ramanathan.

So far, however, have been successfully implemented only in micro-SOFCs, where each chip in the 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. Naturally, the structural issues are significant.

"If you make a conventional thin membrane on that scale without a support structure, you can't do anything—it will just break," says co-author Bo-Kuai Lai, a postdoctoral fellow at SEAS. "You make the membrane in the lab, but you can't even take it out. It will just shatter."

With lead author Masaru Tsuchiya (Ph.D. '09), a former member of Ramanathan's lab who is now at SiEnergy, Ramanathan and Lai fortified the thin film membrane using a metallic grid that looks like nanoscale chicken wire.

Scanning electron microscopy reveals the structured surface of the electrochemical membrane. Ramanathan's team found circles and hexagons to provide the most stable structure. Credit: Shriram Ramanathan.

The tiny metal honeycomb provides the critical structural element for the large membrane while also serving as a current collector. Ramanathan's team was able to manufacture 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 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.

Explore further: Thinnest feasible nano-membrane produced

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User comments : 8

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jkbgbr
1 / 5 (2) Apr 04, 2011
"power density translates into an output high enough for relevance to portable power".

How. Much.
Quantum_Conundrum
5 / 5 (1) Apr 04, 2011
Based on the information in the article with the 155milliwatts per square centimeter surface area, the we have:

Assuming two-sided surfaces folded along orthogonal planes, and assuming surfaces are a half centimeter away from one another, I figure you ought to be able to fit enough surface area inside a one decimeter cube (10cm per edge) to theoretically produce 1200 to 1300 watts.

This doesn't count other parts of the system, just the surface area of the catalyst material you could "probably" fold up and cram inside that area, and it's probably a fair estimate.

So basicly, a cubical fuel cell of 20cm per edge, or roughly 8 inches per edge, could theoretically produce around 10,000 watts.

This is definitely not all of the components the system would need, but is smaller than the engine alone on a gasoline generator
fmfbrestel
5 / 5 (2) Apr 04, 2011

How. Much.



5 mm wide

155 milliwatts per square centimeter

combining hundreds of these chips into palm-sized SOFC wafers


it would take 4 chips to get a square centimeter, and with a minumum of 200 chips ("hundreds") you would get 7.75 Watts from the wafer.

Seriously, read the article, know how to do some basic arithmetic, and you will probably be a less frustrated person.
Eikka
1 / 5 (1) Apr 04, 2011
What interests me with fuel cells, and relatedly, metal-air batteries is how are they planning to keep the dust out?

How clean does the air supply have to be to not clog the entire thing in a week?
Eikka
not rated yet Apr 04, 2011
Seriously though. Even one of those wafers is easily enough to run an iPod or a smarphone, though you need a tiny battery or a supercapacitor on the side for making calls and other tasks that require bigger bursts of power.
jkbgbr
3 / 5 (2) Apr 04, 2011
My fault, sorry.
Eikka
5 / 5 (1) Apr 06, 2011
I'm sorry if the question seems inconvinient, but it's a serious concern.

As I see it, SOFCs work by passing oxygen ions through the membrane. This is opposite to PEM cells where the hydrogen ions are drawn through the membrane and combined with oxygen on the other side. The difference is in which way the flow goes.

As that oxygen must come from the outside air, it carries with it dust which is drawn onto the membrane as the air is pumped past it. So how clean must the air be? Do you need ten layers of HEPA filters to make the thing work in the long term?
CHollman82
1 / 5 (1) Apr 06, 2011
Good question Eikka, in for answer...

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