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The group of Dr. Zhong Lin at Georgia Tech has recently been pumping out a range of interesting papers on the use of zinc oxide (ZnO) “nanoribbons” for energy generation. (People may be best aware of ZnO as a sunscreen material — you used to smear the white stuff on your nose.)

The basic principal is that ZnO is a piezoelectric and thus generates small amounts of charge when it is mechanically changed (stress or strain). This is the so-called direct piezoelectric effect. ZnO is also a semiconductor, so that charge from the piezoelectric effect can be used to generate actual electric current.

They published two recent interesting papers. The first, which I saw a few days ago in Nature covers “Microfiber-nanowire hybrid structure for energy scavenging”. In short, they followed up on their basic science with a proof of concept, using the nanoribbons for “energy scavenging” — converting mechanical energy from walking, moving, etc. into electrical energy. From each thread, they found picoamps of current, which is small, but predicted 20-80 mW per square meter of fabric. That won’t light up any lightbulbs, since even one of those new LED flashlights requires about 1 Watt — about 50 times more. But it does show that we could power small sensors or other devices.

Their other paper was more technical, covering the mechanism of charging up the ZnO wires. Previously, they had noticed poor electrical contact between the platinum probe and the ZnO wire. By coating the wires with a conducting polymer, they had a conducting (Ohmic) contact to the wire, but a difference between the ZnO and the polymer. It turns out that the conductivity of the OPV polymer they picked was close to optimum. If the conductivity was too high, it would minimize the piezoelectric effect, but if it were too low, it wouldn’t allow the electrical current to pass.

In short… there are some cool things going on with nano-scale piezoelectric materials. We can use them as potential alternative energy sources. Of course I’m a little biased.