Scanning electron microscope images of the super-hydrophobic surface. Images courtesy of Nature Communications.
Scanning electron microscope images of the super-hydrophobic surface. Images courtesy of Nature Communications.

Engineers at the University of California (UC) San Diego have developed a super-hydrophobic surface that can produce an electrical voltage. When salt water flows over this specially patterned surface, it can generate at least 50 millivolts.

This proof-of-concept work could lead to the development of new power sources for lab-on-a-chip platforms and other microfluidic devices. According to the engineers, it could someday even be used to harvest energy in water desalination plants.

A team of researchers led by Prab Bandaru, a professor of mechanical and aerospace engineering at the UC San Diego Jacobs School of Engineering, and first author Bei Fan, a graduate student in Bandaru's research group, reported this work in a paper in Nature Communications.

The idea is to create electrical voltage by moving ions over a charged surface. And the faster you can move these ions, the more voltage you can generate, explained Bandaru.

His group created a surface so hydrophobic that it allows water (and any ions it carries) to flow over at high speeds. The surface also holds a negative charge, and so a rapid flow of positive ions in salt water with respect to this negatively charged surface results in an electrical potential difference, creating an electrical voltage.

"The reduced friction from this surface as well as the consequent electrical interactions helps to obtain significantly enhanced electrical voltage," said Bandaru.

The surface was made by etching tiny ridges into a silicon substrate and then filling the ridges with oil (such as the synthetic motor oil used for lubrication). In tests of this surface, the researchers used a syringe pump to pass dilute salt water over it in a microfluidic channel, and then measured the resulting voltage across the ends of the channel.

There have been previous reports on generating a voltage with super-hydrophobic, or so-called ‘lotus leaf’, surfaces designed to speed up fluid flow. However, these surfaces have been patterned with tiny air pockets – and since air does not hold charge, the result is a smaller electric potential difference and thus a smaller voltage. By replacing air with a liquid like synthetic oil – which holds charge and won't mix with salt water – Bandaru and Fan created a surface that produces at least 50% more electrical voltage than previous designs.

According to Bandaru, higher voltages may also be obtained through faster liquid velocities and narrower and longer channels. Moving forward, his team is now working on creating channels with these patterned surfaces that can produce even more electrical power.

This story is adapted from material from University of California San Diego, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.