The device the researchers developed in this study is a type of energy harvester called a biofuel cell (BFC) powered by lactate, a dissolved compound in sweat. From the outside, it looks like a simple piece of foam connected to a circuit with electrodes, all attached to the pad of a finger. The foam is made out of carbon nanotube material, and the device also contains a hydrogel that helps maximize sweat absorption.
“The size of the device is about 1 centimeter squared. Its material is flexible as well, so you don’t need to worry about it being too rigid or feeling weird. You can comfortably wear it for an extended period of time,” says Yin.
Within the device, a series of electrochemical reactions occur. The cells are equipped with a bio enzyme on the anode that oxidizes, or removes electrons from, the lactate; the cathode is deposited with a small amount of platinum to catalyze a reduction reaction that takes the electron to turn oxygen into water. Once this happens, electrons flow from the lactate through the circuit, creating a current of electricity. This process occurs spontaneously: as long as there is lactate, no additional energy is needed to kickstart the process.
Separate from but complementary to the BFC, piezoelectric generators — which convert mechanical energy into electricity — are also attached to the device to harvest up to 20% additional energy. Relying on the natural pinching motion of fingers or everyday activities like typing, these generators helped produce extra energy from barely any work: a single press of a finger once per hour required only 0.5 mJ of energy but produced over 30 mJ of power, a 6,000% return in investment.
The researchers were able to use the device to power effective vitamin C- and sodium-sensing systems, and they are optimistic about improving the device to have even more extraordinary abilities in the future, which might make it suitable for health and wellness applications such as glucose meters for people with diabetes. “We want to make this device more tightly integrated in wearable forms, like gloves. We’re also exploring the possibility of enabling wireless connection to mobile devices for extended continuous sensing,” Yin says.
The device harvests power from your sweaty fingertips while you sleep
