Streams plus nanostrands equals electricity

Since the discovery of carbon nanotubes in 1991, scientists have marveled at the structures’ superlative strength and their promising electronic and optical properties. Now it seems that the tubes might also serve as tiny hydropower plants.

New measurements by scientists in India show that a dense bundle of so-called single-wall nanotubes–atom-thick sheets of carbon rolled into cylinders (SN: 1/4/03, p. 14: Carbon nanotubes beam electrons)–develops a voltage difference along its length when immersed in a slow-flowing liquid. Moreover, that electrical potential, which ranges up to 10 millivolts (mV), increases with flow speed.

This newfound trait may lead to nanotubes’ use as exquisitely sensitive flow sensors, feedback components in microfluidics devices, or power sources for micromachines, says physicist Ajay K. Sood of the Indian Institute of Science (IIS) in Bangalore. He and his colleagues report their findings in the Feb. 14 Science.

In its experiments, the team studied a sesame-seed-size nanotube bundle containing an estimated 50 trillion tubes. The researchers mounted the bundle between metal electrodes inside a glass conduit and then measured the voltage generated as various liquids flowed over the bundle.

The scientists observed that hydrochloric acid, which contains many ions, produced a voltage about five times that produced by water, which contains relatively few ions, and nearly 60 times that of methanol, the least-ionized of the tested liquids. Given the apparent influence of ion concentrations, Sood and his colleagues propose that transient imbalances between positive and negative charges in the passing liquids affect charges in the tubes, causing voltages to develop.

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