May 29, 2007
Nanochannels generate electricity from fluid flow
Tiny fluidic channels engineered on a substrate conjure up images of "lab-on-a-chip" style manipulation of liquids, but the nanosized geometry can also be used to generate electricity. Scientists in the Netherlands have demonstrated an energy-conversion efficiency of 3.25% by flowing salt solutions through a 75 nm high, 50 micron wide and 4.5 mm long channel.
Ultimately, the team from Delft University of Technology thinks that an efficiency of 10% should be possible. Researchers believe that the technique could provide onboard power for micro- and nanofluidic devices.
Dubbed electrokinetic power generation, the Delft system relies on a pressure difference across the nanochannel to pump an aqueous solution of potassium chloride or lithium chloride from one end to the other. The liquid's motion induces a streaming current that is fed through an external load resistor to harvest electrical energy from the fluidic system.
"The charge neutrality of the liquid is disturbed close to the channel wall, which makes net-charge transport and power generation possible," Frank H J van der Heyden of Delft's Kavli Institute of Nanoscience told nanotechweb.org. "This mechanism is particularly efficient in nanochannels as they have a high surface-to-volume ratio – in other words a lot of charged walls."
The concept of generating electrical power by forcing liquids through narrow channels is not new, but advances in nanoscale fabrication mean that practical geometries can now be engineered and put to the test.
Van der Heyden and his colleagues fabricated the channels in fused silica using a direct bonding technique. It turns out that the naturally occurring surface charge density of untreated fused silica is close to optimal for their experiments.
"To further improve the efficiency, a material or surface coating should be sought that has a similar surface charge, but less Stern conductance," said van der Heyden. "In our power-generation experiments the Stern conductance acts as a parallel internal conductor through which electrical current can leak away."
The researchers reported their work in Nano Letters.
About the author
James Tyrrell is editor of nanotechweb.org