In a paper published February 13 in the journal Advanced Science, a team of engineers from the University of Glasgow described how they used layers of graphene and polyurethane to create a flexible supercapacitor that can generate power from the sun and store excess energy for later use. They demonstrated the effectiveness of the new material by powering a series of devices, including a string of 84 LEDs and the high-torque motors in a prosthetic hand, allowing it to grasp a series of objects.
Research into energy autonomous e-skin and wearables is the latest development from the university’s Bendable Electronics and Sensing Technologies (BEST) research group, led by Ravinder Dahiya, PhD, a professor of electronics and nanoengineering.
The top touch-sensitive layer is made from graphene, a highly flexible, transparent form of carbon that is just one atom thick. Sunlight, which passes through the layer of graphene, is used to generate power via a layer of flexible photovoltaic cells below. Any surplus power is stored in a newly developed supercapacitor, made from a graphite-polyurethane composite.
The team developed a ratio of graphite to polyurethane that provides a relatively large, electroactive surface area where power-generating chemical reactions can take place, creating an energy-dense flexible supercapacitor that can be charged and discharged quickly. Similar supercapacitors have delivered voltages of one volt or less, making single supercapacitors largely unsuited for powering many electronic devices. The team’s new supercapacitor can deliver 2.5 volts, making it more suited for many common applications.
In laboratory tests, the supercapacitor has been powered, discharged and powered again 15,000 times with no significant loss in its ability to store the power it generates.
“Our previous generation of flexible e-skin needed around 20 nanowatts per square centimeter for its operation, which is so low that we were getting surplus energy even with the lowest-quality photovoltaic cells on the market,” said Dahiya. “We were keen to see what we could do to capture that extra energy and store it for use at a later time, but we weren’t satisfied with current types of energy storages devices such as batteries to do the job, as they are often heavy, non-flexible, prone to getting hot, and slow to charge.
“Our new flexible supercapacitor, which is made from inexpensive materials, takes us some distance towards our ultimate goal of creating entirely self-sufficient flexible, solar-powered devices, which can store the power they generate.
Editor’s note: This story was adapted from materials provided by the University of Glasgow.