In the last few years, we have seen a large increase in the number of companies investing in wearable technology. There are quite a few unique products already on the market because of this surge. However, there has been a common issue with most devices in the wearables market, and that is how to power them.
Supplying power to these devices may seem like a trivial task, but designing a power source that can bend and flex while providing power and retaining functionality has been proven to be very difficult. Our current devices are powered by quite a few different means, ranging from solar to flexible silicon batteries; but the amount of power that these devices are producing and consuming is typically very low.
Various international research teams have made attempts to tackle the problem of harvesting energy from the body’s motion or environment, but have not succeeded in creating a power source that can be fitting in both flexibility and power for future devices.
In a recent article published in the journal Energy and Environmental Science, a team of researchers and engineers from the University of California San Diego have developed a type of biofuel cell that is capable of creating energy from a chemical reaction with sweat.
The device is called an epidermal biofuel cell and it is considered to be a major advancement in the fuel of wearable power supplies.
Stretchable, Sweat-Powered Fuel Cells
The biofuel cell the team developed is capable of conforming to the body as well as stretching and flexing in a multitude of ways.
The team, led by director of the Center for Wearable Sensors at the university made use of electronic interfaces, advanced materials, and some niche chemistry to produce the device.
The biofuel cells work by making use of a biochemical reaction between an enzyme and the lactic acid contained inside of human sweat to produce a small current. After establishing this reaction, the team turned to the design of the biofuel cell.
The cell needed to be flexible and conform to current devices. In order to achieve this, the group used a design called the "bridge and island" structure. The biofuel cell was designed in rows of cathode and anode dots, each connected by a spring like structure to allow the cell to flex and stretch while being able to return to their original structure.
The bridge and island structure. Image courtesy of UC San Diego
The bridge island was fabricated through a standard lithography technique, then layered with the biofuel enzyme. In order to further increase the energy that the cell could produce, the engineers placed carbon nanotube structures that could be filled with enzyme as well as facilitate electron transfer.
Next, the team tested the cell by placing them on several different test subjects on exercise bikes. The cell was found to be capable of producing enough energy to power a LED light for 4 minutes. While the result may not seem entirely impressive, this is the first time we had seen a biofuel cell produce this much energy; in fact, 10 times the amount that any previous biofuel call had.
The engineers will be investing more research into finding a better cathode oxide that will not degrade with light or time, as well as further developing the device to store the energy for later consumption; or gradual discharge.
There are obviously design challenges with such a power source. (For one thing, not everyone sweats at the same rate.) However, this is still a stride towards more flexible power sources, as well as wearable power sources.
Would you design a device with sweat-powered biofuel cells?