The engineers from the Bendable Electronics and Sensing Technologies (BEST) group at the university developed a new kind of flexible supercapacitor that replaces the electrolytes found in conventional batteries with sweat. The supercapacitor can be fully charged with 20 microlitres of fluid and can survive 4,000 cycles of the types of flexes and bends it might encounter in real-world use. It works by coating polyester cellulose cloth in a thin layer of a polymer known as poly (3,4-ethylenedioxythiophene) polystyrene sulfonate – or PEDOT:PSS.
The polyester cellulose cloth was chosen as it is particularly absorbent, and PEDOT:PSS provides a combination of flexibility, high conductivity and environmental friendliness. PEDOT:PSS acts as the supercapacitor’s electrode.
As the cloth absorbs its wearer’s sweat, the positive and negative ions in the sweat interact with the polymer’s surface, creating an electrochemical reaction which generates energy.
The effectiveness of the new technology was tested by volunteers running outdoors and on a treadmill while wearing a 2cm x 2cm cell version of the device. The runners’ sweat allowed the device to generate about 10 milliwatts of power – enough to power a small bank of LEDs – which kept it going until the runner stopped.
The research was led by Professor Ravinder Dahiya, head of the BEST group, based at the University of Glasgow’s James Watt School, of Engineering.
Prof Dahiya said: “Conventional batteries are often built using unsustainable materials which are harmful to the environment. That makes them challenging to dispose of safely, and potentially harmful in wearable devices, where a broken battery could spill toxic fluids onto skin.
Professor Dahiya and his team have already designed a number of novel bendable technologies, including solar-powered ‘electronic skin’ which could be used in prosthetics and robotics. Future research will look at the possibility of integrating sweat power into these devices.
The team’s paper, titled ‘Wearable Supercapacitor based on Conductive PEDOT: PSS Coated Cloth and Sweat Electrolyte’, is published in Advanced Materials. The research was funded by the Engineering and Physical Sciences Research Council (EPSRC) and the Royal Society.