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Stop at a gas station and you've likely got two things to take care of: putting fuel in the car and relieving yourself in the restroom.

But there may very well come a time when both refueling and bladder relief will come in a single action, once a handful of researchers in Scotland make their urea-powered fuel cell efficient enough.

The idea first came to Professor Shanwen Tao when, as a youngster in China, he noticed that farmers used urea, the compound the body uses to excrete nitrogen, to fertilize their fields. What can fertilize can also fuel. And urea, he realized, was cheap, plentiful, and environmentally sound.

When separated from urine, it's a solid (actually, it's a solid when suspended in the urine as well), so it's easy to transport. In humans, urea comprises between 0.5 and 3.0% of urine, and more in some animals, so the substance is plentiful and not hard to come by.

"I think the average person produces one and a half to two liters of urine a day. That's approximately 10 billion liters of urine sloshing about the place," says Robert Goodfellow, the team's knowledge exchange manager (currently at Heriot-Watt University in Edinburgh, although he and the rest of the team are soon to move to the University of Strathclyde in Glasgow). "There's quite a bit out there."

Urea granules.

Converting it to a powder with the proper particle size proved difficult. Now, an alkaline membrane breaks the urea down into nitrogen, carbon dioxide, water, and a small amount of electricity. The alkaline is significantly more inexpensive than the membranes used to for proton exchange with hydrogen.

Finding the right catalyst was a similar challenge. Again, achieving the right particle size was the biggest hurdle. The nickel or silver catalysts they're using now are 10 to 100 times cheaper than those used with a hydrogen fuel cell.

Since their initial paper came out in January of 2010, the team was awarded £100,000 to produce a large-scale fuel cell. "By large scale, we mean we will have a membrane approximately 100 cm square that can power a small fan or a light using urea, urine, or ammonia as a fuel source," says Goodfellow.

So it may be a while before you pull over at the rest stop, remove the gas cap, let fly, and drive off. But the team is hoping to have a product on the market in two or three years.

"The main application would depend on the fuels that we're using. For urine, you could collect at the source almost, then go directly to the fuel cell for recharging batteries," says Goodfellow. "It would reduce the energy burden at municipal treatment plants. We've had a number of interesting inquiries from people who have toilets in remote areas, and are looking for water treatment applications."

Michael Abrams is an independent writer.

I think the average person produces one and half to two liters of urine a day—that’s approximately 10 billion liters of urine sloshing about the place. Robert Goodfellow, Heriot-Watt University

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