Chang-Hwan Choi, a professor in the Department of Mechanical Engineering, has been awarded a three-year grant for $200,000 from the National Science Foundation (NSF) to explore the fundamentals of nanofluidic energy manufacturing systems and develop the basis for a highly efficient nanoscale hydroelectric power source, with real world applications.
Working as a “hydropower plant on a chip”, the new technology will harvest energy from water to create a self-sustainable energy supply system to power small devices, without the use of batteries.
Choi's new approach will produce up to two orders of magnitude more energy than current systems and nearly 100 percent energy conversion efficiency. The project has two aspects: First, establishing the conditions for the nearly 100 percent energy conversion efficiency and the maximized output power of the system. Second, verifying the results with nanofluidic experiments.
“There is great interest in developing alternative energy sources, like wind, and solar energy to serve nanotechnology innovation,” said Choi, who is also director of the Nano and Microfluidics Laboratory at Stevens. “Our idea is to investigate the concept of using hydropower in nanoscale channels to generate energy, using the naturally abundant resource of water.”
Nanofluidic materials are substances that contain nanoscale channels (1-100nm in size) and allow the manipulation of fluids confined to these structures. They are readily available both in nature and manufactured materials, such as soil, clay, sandstone, nanoporous membranes and filters. However, nanofluidic systems have not been widely developed as a source for energy, due to their low energy conversion efficiency, usually less than 10 percent, mainly due to the frictional energy loss.
The key to the new system’s high efficiency are the nanoscale channel structures engineered in Choi’s lab. The walls of the channels have a non-wetting exterior called superhydrophobic surface. These surfaces have nanoscale bumps that can trap air bubbles. As a result, liquid in the nanoscale channels are partly resting on air bubbles, thus minimizing liquid-to-solid contact area. This mechanism reduces friction and frictional energy loss at the channel walls.
“The water on the superhydrophobic surface is moving on a thin layer of air, much like a puck glides on an air-hockey table,” Choi said. “The inspiration for this technology is found in nature,” he said. “Many wing insects, the skin of marine mammals and the leaves of plants exhibit a similar water-repelling characteristic known as the 'Lotus Effect'.”
A diminutive amount (less than a milliliter) of water flowing through the nanoscale channels can generate meaningful electric power to run small devices. The idea is to use ions in the water. A little pressure generated by a difference in ionic concentration, or by a pump, is sufficient to produce the flow of these ions, which act as charge carriers. This is called a streaming current. The released chemical energy can be transformed into electricity and ultimately kept in energy storage devices.
This project will test single channels to see how they can reduce friction and increase output power. The researchers hope to eventually develop thin membranes with arrays of channels to serve larger devices, such as cell phones, wearable electronics, and bridge condition assessment sensors.