A PLASTIC skin that generates electricity could drive a miniature
airship鈥攁nd power tomorrow鈥檚 laptop computers, lawnmowers or even a small
plane, says its inventor. The skin, patented by aerospace giant Lockheed Martin,
is actually a very extended, hyper-thin fuel cell. Its one drawback is that it
is fuelled by explosive hydrogen gas.
The idea for an energy-generating skin was hatched by Lockheed Martin
engineer Laurence Williams as part of a project to develop lightweight,
remote-controlled reconnaissance airships. 鈥淵ou want something that is low-cost,
lightweight and long range,鈥� he says. But with conventional engines, his tiny
vehicles would only have been able to carry enough fuel for short flights.
Williams decided he could solve the problem by marrying fuel-cell technology
with advanced flexible polymers鈥攎aking a skin for the airship that would
also generate power. The hydrogen inside the balloon reacts with oxygen from the
air outside to produce electricity.
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Today鈥檚 fuel cells are heavy blocks as big as a car engine. Williams鈥檚 idea
is to use a polymer fuel cell as an expanse of flexible skin. In an airship, the
hydrogen would not only serve as fuel, but also provide extra lift.
At the heart of the membrane is an acidic polymer layer that acts as the
electrolyte. The polymer separates the oxygen on the outside from the hydrogen
inside, while allowing hydrogen ions to pass through. Thin layers of platinum
catalyse the reaction, while a fine wire mesh covering each surface acts as the
electrodes.
At the anode, on the inside of the skin, hydrogen gas loses its electrons to
form hydrogen ions (see Diagram),
which travel through the polymer layer. When
they reach the cathode on the outside of the polymer sandwich they react with
oxygen from the air to form water vapour. The energy liberated pulls electrons
into the electrode, driving current round the circuit. The ultimate source of
the power is lithium hydride, a solid that liberates hydrogen when it reacts
with water.
Because it doesn鈥檛 have to carry heavy batteries or aviation fuel, a
4-metre-long airship fitted with cameras, GPS satellite navigation and radio
communications equipment would weigh just 3 kilograms. The airship would have a
power output of 200 watts and a range of around 700 kilometres, says Williams.
It could 鈥渓oiter鈥� over its target area for days or weeks.
鈥淭his is an entertaining idea,鈥� says fuel cell expert David Hart of Imperial
College, London. 鈥淚 don鈥檛 see any reason why it shouldn鈥檛 work.鈥� He says the
main problems are likely to come in making the skin large, flexible and durable
enough. Williams has a suitable material in mind鈥攁 commercially available
鈥減roton exchange鈥� polymer called Nafion, designed for use as the electrolyte
membrane in standard fuel cells.
The airships could help monitor crowds, search for missing people at sea, or
inspect power lines. Williams has also calculated that hydrogen-filled wings
with a fuel-cell skin could power an aeroplane big enough to carry four
people鈥攁nd provide extra lift.
Williams, who has retired since the patent was filed, says that the skin
could even provide a light, portable power source for devices like laptops or
lawnmowers. It would provide power for up to five times as long as batteries,
and could be recharged instantly by replacing the lithium hydride that generates
the hydrogen.