For a long time, scientists have eyed fuel cells as a promising, clean source—especially for vehicles. But fuel cells have never quite lived up to their potential because they are generally too expensive, inefficient, or both. Researchers from the University of Wisconsin (UW) Madison aimed to solve the problems associated with this technology with a bio-inspired fuel-cell design that uses less expensive materials and an organic compound for moving electrons and protons in the cell.
The energy output of a new fuel cell design developed at the University of Wisconsin-Madison produces about 20 percent of what is possible in hydrogen fuel cells currently on the market. But the system is about 100 times more effective than biofuel cells that use related organic shuttles. (Image source: Matt Wisniewski)
Using an Organic Mediator
According to a UW news release, the team took a unique approach to its fuel-cell design to try to tackle problems associated with the catalyst needed to accelerate the reactions required to make a fuel-cell work, said Colin Anson, one of the lead researchers on the project and a postdoctoral researcher in the lab of UW-Madison professor Shannon Stahl, who oversaw the project.
Researchers paired an organic mediator, quinone, with an off-electrode heterogeneous catalyst, in the design of their fuel cell, Anson explained in the release. “People have worked with mediators in fuel cells before, but no one has used our pairing before,” he said. “We believe that our unique coupling of the organic mediator and heterogeneous catalyst gives us special advantages that aren’t apparent with other systems.”
In traditional fuel-cell designs, the device generates electricity directly from chemicals such as hydrogen and oxygen, producing only water vapor as emissions. The cell works by the transport of hydrogen electrons and protons from one electrode to another, where they combine with oxygen to produce water. As mentioned before, the device uses a catalyst to accelerate the reactions.
Currently, the best catalyst on the market for fuel cells is platinum, which is expensive and thus makes devices that use it more costly to produce. This is one of the reasons that there are only a few thousand roadworthy vehicles in the United States running on hydrogen fuel.
The UW-Madison team worked with a lower-cost metal, cobalt, putting it into a reactor nearby the cell. The team then devised a strategy to shuttle electrons and protons back and forth from this reactor to the fuel cell, researchers said.
In the fuel-cell design, the quinone carries two electrons and protons at a time, shuttling from the fuel cell electrode to the nearby reactor filled with the cobalt catalyst. The quinone then returns to the fuel cell to repeat the process and carry more “passengers” back and forth.
They also found a way around one of the typical problems with working with quinones, which is that they can degrade into a tar-like substance after only a few round trips. To remedy this, the team designed an ultra-stable quinone derivative with modifications that drastically slow down the material’s deterioration, Anson said.
While energy output of the new fuel cell design produces about 20 percent of what is possible in hydrogen fuel cells currently on the market, the system can last up to 5,000 hours—about 100 times more effective than biofuel cells that use related organic shuttles for the protons and electrons, researchers said.
“The potential for greater efficiency comes from the coupling of the heterogeneous catalyst and the hydroquinone mediator,” Anson explained. “They are able to work in a synergistic way to help reduce oxygen. This pathway isn’t available for typical fuel-cell designs, and this coupling will allow us to get to higher cell voltages than even the best platinum-based fuel cells cannot get.”
The team plans to continue its work to take full advantage of the pairing of the quinone and the catalyst, with simulations of their work suggesting that it could be used to create an even more efficient and powerful fuel cell, Anson said.
“We have some simulations that suggest we could obtain voltages of over 1 volt, while traditional fuel cells usually max out at around 0.8 to 0.95 volts,” he said. “Again, this increase is due to the mediator and the catalyst working together, instead of just having a normal catalyst.”
Researchers also aim to discover more active catalysts or ones that can oxidize mediators more quickly, which will allow new fuel cell designs to be as compact and as inexpensive as possible, Anson added.
Researchers published a paper on their work in the journal Joule.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.
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