Rather than plugging it into the wall, imagine charging a cell phone or other portable device by simply rubbing it with the palm of your hand. The user actually creates the electricity and becomes a discrete, reliable and the ultimate distributed source of power generation. It could transform the electric industry and life as we know it.
Researchers presented these commercial possibilities and a unique vision for green energy at the National Meeting & Exposition of the American Chemical Society (ACS) recently held in Dallas, Texas. ACS is the world’s largest scientific society.
Zhong Lin Wang, Ph.D., and his team presented the work, and have set out to revolutionize the way we look at mechanical energy.
The researchers have developed a device that generates electricity through contact and friction that might one day be used to harvest the energy from human motion to charge portable electronics and more. They designed a compact, lightweight generator consisting of a copper-plated disk that spins and rubs against a static base containing a layer of electrodes and a conducting surface. The device can harvest mechanical energy from a gentle wind, water flow and normal body movements.
Conventional energy sources have relied on century-old science that requires scattered, costly power plants and a grid to distribute electricity far and wide.
“Today, coal, natural gas and nuclear power plants all use turbine-engine driven, electromagnetic-induction generators,” Wang said. “For a hundred years, this has been the only way to convert mechanical energy into electricity.”
But a few years ago, Wang’s team at the Georgia Institute of Technology was working on a miniature generator based on an energy phenomenon called the piezoelectric effect, which is electricity resulting from pressure. But to their surprise, it produced more power than expected. They investigated what caused the spike and discovered that two polymer surfaces in the device had rubbed together, producing what’s called a triboelectric effect, essentially what most of us know as static electricity.
Building on that discovery, Wang then developed the first triboelectric nanogenerator (TENG). He paired two sheets of different materials together. One donates electrons, and the other accepts them. When the sheets touch, electrons flow from one to the other. When the sheets are separated, a voltage develops between them.
Since his lab’s first publication on TENG in 2012, they have since boosted the power output density by a factor of 100,000, with the output power density reaching 300 watts per square meter. Now, with one stomp of his foot, Wang can light up a sheet of one thousand LED bulbs.
His group has incorporated TENG into shoe insoles, whistles, foot pedals, floor mats, backpacks and ocean buoys for a variety of potential applications. These gadgets harness the power of everyday motion from the minutest vibrations, rubbing and stepping, to the largest such as ocean waves. These movements produce mechanical energy that has been around us all along, but scientists didn’t know how to convert it directly to usable power in a sustainable way until now.
“The amount of charge transferred depends on surface properties,” Wang said. “Making patterns of nanomaterials on the polymer films’ surfaces increases the contact area between the sheets and can make a 1,000-fold difference in the power generated.”
With those improvements, Wang said his group is now working on commercializing products to recharge cell phones and other mobile devices using TENG. Down the road, he envisions these nanogenerators can make a far bigger impact on a much larger scale. Researchers could use the technology to tap into the endless energy of ocean waves, rain drops and the wind with tiny generators rather than towering turbines, to help feed the world’s ever-growing energy demand, he said.
If proved economically and technologically practical, the benefits of TENG technology could relieve the mounting pressure on our already aging and over-burdened electrical grid. By potentially removing the energy drain of millions of plug-in devices from the grid, and by creating new nanogenerating capacity, an immediate, cleaner, more sustainable future may be realizable.