Researchers in China have demonstrated that an effective design of single-walled carbon nanotubes (SWCNTs) can be used to convert the surface energy of liquids into electricity. The surface-energy generator's mechanism works due to the unique channels among individual SWCNTs, in which a continuous, steady flux of liquid forms and the flow of liquid inside the carbon nanotube channels is driven by surface tension.
Nanorope device

SWCNT 'rope' of approximately 25 mm length and 0.6 mm diameter is made by aligning individual nanotubes. The researchers connected this nanorope to electrodes of aluminum film and suspended this structure on a glass slide. This device was then placed into a beaker partially filled with ethanol, with an angle between the SWNT rope and the ethanol level. When the ethanol level reaches the SWCNT rope, the voltage begins to increase. This increase is almost linear from zero to 200 µV for the first 240 seconds, then the voltage saturates gradually at 219 µV where is remains constant over 6 hours. Researchers found that the voltage can remain constant as long as the ethanol level is contacting the SWCNT rope.

This concept can be used to design self-powered devices at the nanoscale. Its advantages are high power output (up to about 1800 pW per device), low inner resistance (tens to hundreds of Ohm), stability (the polar liquid can be used like fuel), and no moving parts. It is easy to integrate with other low-energy-cost electronic devices and power them. Furthermore, the generators can be connected in serial and parallel to get higher output.