A team of engineers at the University of California, San Diego, has developed wearable fuel cells capable of powering electronics, such as LEDs and Bluetooth radios.
They extract energy from sweat.
Yes, you read that right. These epidermal biofuel cells are equipped with an enzyme that oxidizes the lactic acid in sweat to generate current. They are being called a major breakthrough in a field that has been struggling to make devices like these, with challenges including stretchability and power capacity. The new cells generate 10 times more power per surface area than anything else out there right now.
As reported in the journal Energy & Environmental Science, the engineers demonstrated the device’s ability to power an LED while being worn by a person exercising on a stationary bike.
Engineers used what they referred to as a “bridge and island’ structure to make the cell flexible. The cell is essentially made up of rows of dots; half of them represent the cell’s anode, the other half are the cathode. They are connected by stretchable, spring-shaped structures that allow the cell to bend without deformation of its electrode dots.
The overall structure is made of gold and manufactured via lithography. In order to increase power density, a 3D carbon nanotube structure was screen-printed on top of the dots to allow easier electron transfer. Layers of biofuel materials were also added onto the dots.
"We needed to figure out the best combination of materials to use and in what ratio to use them," said Amay Bandodkar, a former Ph.D. student and one of the paper's first authors. Bandodkar worked with the research group of Prof. Joseph Wang, who directs the Center for Wearable Sensors at UC San Diego.
Moving forward, the researchers will need to find a more stable material than silver oxide, which is currently being used as the cathode, as it is light-sensitive and degrades over time. They are also exploring a way to store the energy produced and release it gradually since the concentration of lactic acid in a person’s sweat gets diluted over time.