Scientists from the University of Glasgow in Scotland have developed a new type of flexible supercapacitor designed to allow a new generation of wearable devices such as heart rate and health monitors to be powered by human sweat.
Engineers from the Bendable Electronics and Sensing Technologies (BEST) group at the University of Glasgow published their findings in a paper published Monday in the Advanced Materials journal detailing how their new type of flexible supercapacitor replaces the electrolytes found in conventional batteries with sweat.
The new design coats 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 is particularly absorbent and PEDOT:PSS combines flexibility with high conductivity and is environmental friendly to boot.
As the cloth begins to absorb the wearer’s sweat, the positive and negative ions in the sweat begin to interact with the polymer’s surface to create an electrochemical reaction which, in turn, generates energy.
According to the research, the new flexible supercapacitor can be fully charged with as little as 20 microlitres of sweat and is robust enough to survive 4,000 cycles of the types of flexes and bends it might encounter in real-world use.
The researchers had volunteers run outdoors and on a treadmill while wearing a 2cm x 2cm cell version of the new supercapacitor. According to the results, the runner sweated enough to allow the device to generate about 10 milliwatts of power – approximately enough to power a small bank of LEDs – and kept the LEDs running until the runner stopped.
Importantly, part of the inspiration for the research was the need to develop more environmentally friendly batteries which do not rely as much on dangerous and detrimental mining.
“Conventional batteries are cheaper and more plentiful than ever before, but they are often built using unsustainable materials which are harmful to the environment,” said lead researcher Professor Ravinder Dahiya, head of the BEST group, based at the University of Glasgow’s James Watt School, of Engineering.
“That makes them challenging to dispose of safely, and potentially harmful in wearable devices, where a broken battery could spill toxic fluids onto skin.
“What we’ve been able to do for the first time is show that human sweat provides a real opportunity to do away with those toxic materials entirely, with excellent charging and discharging performance.
“As wearable devices like health monitors continue to increase in popularity, it opens up the possibility of a safer, more environmentally-friendly method of generating sustainable power – not just for wearables but possibly also for emerging areas such as e-bikes and electric vehicles, where sweat equivalent solution could replace the human sweat.”
Professor Dahiya and his team have already developed a number of new bendable technologies including solar-powered “electronic skin” which could one day be used in prosthetics and robotics. Unsurprisingly, the team are also planning future research on the possibility of integrating sweat power into these electronic skin devices.
“It’s an exciting development, and we’re keen to continue exploring the possibilities that sweat power provides for the future of wearable electronics,” added BEST group’s Dr Libu Manjakkal, who contributed to the paper.