The first urine-powered paper battery has been created by physicists
in Singapore. The credit-card sized unit could be a useful power
source for cheap healthcare test kits for diseases like diabetes, and
could even be used in emergency situations to power a cellphone, they
said. Testing urine can reveal the identity of illnesses, and the new
paper battery could allow the sample being tested to also power the
diagnostic device.
The urine-powered battery was able to generate a voltage of about 1.5
volts - with a corresponding power of 1.5 micro-watts - using just 0.2
millilitres of urine, said Lee. And if a second droplet of urine was
added 15 hours after the battery was first activated, the replenished
urine could generate still more electricity.
The battery is made of a layer of filter paper steeped in copper
chloride, sandwiched between strips of magnesium and copper. This
"sandwich" is then laminated in plastic to hold the whole package
together. The resulting battery is just 1 millimeter thick and 60 by
30 mm across - slightly smaller than a credit card.
To activate the battery, a drop of urine is added and soaks through
the sandwiched filter paper. The chemicals dissolve and react to
produce electricity. The magnesium layer acts as the anode, losing its
electrons. And the copper chloride acts as the cathode, mopping up the
electrons. He added that the voltage, current and capacity of the
battery could be improved by different designs or by switching the
electrode or electrolyte materials used.

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