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Urine Battery Turns Pee Into Power

John Roach
for National Geographic News
August 18, 2005
 
Before you next flush the toilet, consider this: Scientists in Singapore have developed a battery powered by urine.

Researchers at the Institute of Bioengineering and Nanotechnology created the credit card-size battery as a disposable power source for medical test kits.

Scientists have been scrambling to create smaller, more efficient, and less expensive "biochips" to test for diseases such as diabetes. Until now, however, similarly small batteries to power the devices remained elusive.

Diagnostic test kits commonly analyze the chemical composition of a person's urine to detect a malady. Ki Bang Lee and his colleagues realized that the substance being tested—urine—could also power the test.

"In order to address this problem, we have designed a disposable battery on a chip, which is activated by biofluids such as urine," Lee wrote in an e-mail to National Geographic News.

The research team describes the battery in the current issue of the Journal of Micromechanics and Microengineering.

Daniel Kammen, director of the Renewable and Appropriate Energy Laboratory at the University of California, Berkeley, said the technology is a welcome innovation in a time of rising energy prices.

"All jokes [about] urine aside, what is needed are low-cost batteries. …" he said. "The other neat thing about this is the fact that it's basically a biodegradable battery."

Urine Power

To make the battery, Lee and his colleagues soaked a piece of paper in a solution of copper chloride and sandwiched it between strips of magnesium and copper. This sandwich was then laminated between two sheets of transparent plastic.

When a drop of urine is added to the paper through a slit in the plastic, a chemical reaction takes place that produces electricity, Lee said.

The prototype battery produced about 1.5 volts, the same as a standard AA battery, and runs for about 90 minutes. Researchers said the power, voltage, and lifetime of the battery can be improved by adjusting the geometry and materials used.

Urine contains many ions (electrically charged atoms), which allows the electricity-producing chemical reaction to take place in the urine battery, said UC Berkeley's Kammen. Other bodily fluids, such as tears, blood, and semen, would work easily as well to activate the battery.

"Little bags of urine may generate chuckles," Kammen said. "But really urine is just a nice example [of] a whole variety of compounds that do this stuff." Even children's lunch-box fruit-juice packets are sufficient, he added.

Alternative Energy

While medical devices inspired the urine battery, it can activate any electric device with low power consumption, according to Lee, the battery's co-inventor.

"For example, we can integrate a small cell phone and our battery on a plastic card. This can be activated by body fluids, such as saliva, during an emergency," he said.

According to Kammen the technology could even be applied to laptop computers, mp3 players, televisions, and cars. Body-fluid-powered batteries "can do all kinds of things. The issue is how they scale up" to produce more power, he said.

One approach is to simply build larger batteries. Another method is to link lots of little battery cells side by side, which is how the batteries in laptop computers work, Kammen explained.

Kammen, who advocates government funding for alternative energy research, says the wide number of applications for cheap and efficient biofluid-powered batteries illustrates the value of research. "Investigation leads to innovation," he said.

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