This Biofuel Cell Is A Super Stretchy Electronic Skin Powered By Sweat!
Stretchy fuel cells that extract energy from sweat and can power electronics – such as LEDs and Bluetooth radios – have been developed by a team of engineers at the University of California San Diego.
“Sweat is a neglected, unappreciated biofluid,” Amay Bandodkar, a former graduate research scholar at UCSD and first author of the biofuel cell study said. “However, from an energy point of view, it contains certain chemicals that can be exploited to produce usable energy.”
The epidermal biofuel cells are a major breakthrough in the field, which has been struggling with making the devices that are stretchable enough and powerful enough. The biofuel cell that the Engineers from the University of California San Diego in the US developed can stretch and flex, conforming to the human body. The research led by Professor Joseph Wang, who directs the Center for Wearable Sensors at the university, used a combination of clever chemistry, advanced materials, and electronic interfaces.
In a paper, published in the journal Energy & Environmental Science, the researchers described how they connected the biofuel cells to a custom-made circuit board and demonstrated that the device was able
to power an LED while a person wearing it exercised on a stationary bike.To make the biofuel cells flexible and stretchable, the engineers decided to use what they call a “bridge and island” structure developed in Professor Sheng Xu’s research group.
Because the aim of the project was to develop a biofuel cell to power wearable devices, the technology was designed and fabricated in a soft, stretchable format – one that can easily mate with the soft, curvilinear nature of the human skin.
A “bridge-and-island” design gave the device a layout of isolated “islands” interconnected with thin, spring-like structures. The fuel cell’s anodes and cathodes were fabricated on top of the standalone enclaves.
When the island-bridge structure is stretched, most of the strain is accommodated by the serpentine interconnects, while leaving the islands unharmed. The spring-like gold structures, manufactured via lithography, stretch and bend – making the cell flexible without deforming the anode and cathode.
“Since island-bridge architecture permits negligible strain on the islands, we had the freedom to deposit active anode and cathode materials in a dense fashion without the fear of them experiencing mechanical stress and the subsequent degradation when the device stretched during routine use,” said Bandodkar.
As a second step, researchers used screen printing to deposit layers of biofuel materials on top of the anode and cathode dots. The researchers’ biggest challenge was increasing the biofuel cell’s energy density, meaning the amount of energy it can generate per surface area. Increasing energy density is key to increasing performance for the biofuel cells. The more energy the cells can generate, the more powerful they can be.
Carbon nanotube-based cathode and anode arrays, developed through lithography and screenprinting processes, formed an essential piece of the technology. To increase power density, engineers screen-printed a 3D carbon nanotube structure atop the anodes and cathodes. The 3D nature of the carbon-nanotube pellet system allowed higher loadings of the lactate oxidase enzyme – and higher electron transfer. The arrangement led to power density levels higher than previously reported devices: approximately 1mW/cm2 of power from human sweat.
“The very fact that we were able to increase the power density to almost 10 times as compared to previous works, make the device soft and stretchable, and power an energy-hungry device, such as a Bluetooth radio, is most exciting to me,” said Bandodkar, who is currently a Postdoctoral Fellow at Northwestern University.
The team still has several challenges they hope to address, including the stabilization of the lactate oxidase enzyme, which degrades over time, and increase of the system’s power density.
“It would also be great if we can combine the biofuel cell with other forms of wearable energy harvesting systems, such as wearable solar cells and thermoelectrics, so that such an integrated energy harvesting system can produce energy from multiple sources,” said Bandodkar.
