21-04-2021 | By Robin Mitchell
Recently, researchers from Japan announced developing a wearable fuel cell powered by human sweat. What challenges do traditional power sources face, what has the team developed, and how could it help with powering future wearable devices?
Wearable electronics is an area of electronics concerned with the development of devices that can be worn on the body. While smartwatches do exist, these devices are bulky and cumbersome making them inconvenient and unnatural.
A true wearable device would be one that can move organically with the human body (such as clothing), and be comfortable to wear. Currently, there have been many great strides in this area with the development of flexible displays and even entire processors, but one area remains; power.
Power sources greatly vary in shape, size, and construction, but most are ridged in nature. Since the amount of power provided by a power source is often related to their size, wearable devices (which need to be light and flexible), often provided minuscule amounts of power.
Furthermore, energy-dense technologies such as lithium-ion contain chemicals that can react violently when exposed to air, sustain damage, and are not suitable for body mounting or wearing. Some more exotic forms of power such as wearable TEGs may appear to be ideal, but in fact generate so little energy that they will not be practical for generations.
When looking for energy sources, many turn to the sun, heat from the human body, or motion from the human body. But recently, a team of researchers from Japan have developed a wearable patch that integrates multiple biofuel cells that directly convert human sweat to electricity.
Specifically, the research team has utilised lactate, a naturally occurring compound in sweat, as the fuel source. An enzyme with two different electrodes creates an electrochemical reaction that generates power. Individually, a single cell generates a minuscule amount of energy. Still, the team has combined many in series and parallel to create a power source that can be worn on the arm like a bandage while providing 3.66V at 4.3mW.
While this amount of power may seem minimal, it is far more than enough to use in an energy storage unit which can then go on to power devices such as microcontrollers and Bluetooth modules. In fact, the team was able to power an activity meter for 1.5 hours using a single drop of artificial sweat.
Interestingly, the fuel cell also operates as a sensor as the output power is proportional to the lactate concentration. From there, the power output can be read by a module, and this can be wirelessly streamed to a device for health monitoring.
One major development the research team have made is the ease of manufacture for the fuel cells. The cells can be screen-printed in layers which makes them far easier to construct. For example, instead of using silver compounds (like other fuel cells), the new cell uses porous carbon ink that is easily printable. Paper layers are used by the design to help transport sweat from the skin to the fuel cells, and the bandage design makes wearing the device far more comfortable than other battery technologies.
Such fuel cells that are powered by human sweat theoretically have an infinite energy supply; so long as the wearer drinks water and moves enough to cause sweat to form. While the energy output of the test device is small, either the team can continue to advance the technology to increase this, or future electronics can consume less energy to make the most of the wearable fuel cell.