…we are batteries for the machines.
- Clothing the body electric
Starting with a T-shirt from a local discount store, Li’s team soaked it in a solution of fluoride, dried it and baked it at high temperature. They excluded oxygen in the oven to prevent the material from charring or simply combusting.
The surfaces of the resulting fibers in the fabric were shown by infrared spectroscopy to have been converted from cellulose to activated carbon. Yet the material retained flexibility; it could be folded without breaking.
“We will soon see roll-up cell phones and laptop computers on the market,” Li said. “But a flexible energy storage device is needed to make this possible.”
The once-cotton T-shirt proved to be a repository for electricity. By using small swatches of the fabric as an electrode, the researchers showed that the flexible material, which Li’s team terms activated carbon textile, acts as a capacitor. Capacitors are components of nearly every electronic device on the market, and they have the ability to store electrical charge.
Moreover, Li reports that activated carbon textile acts like double-layer capacitors, which are also called a supercapacitors because they can have particularly high energy storage densities.
But Li and Bao took the material even further than that. They then coated the individual fibers in the activated carbon textile with “nanoflowers” of manganese oxide. Just a nanometer thick, this layer of manganese oxide greatly enhanced the electrode performance of the fabric. “This created a stable, high-performing supercapacitor,” said Li.
This hybrid fabric, in which the activated carbon textile fibers are coated with nanostructured manganese oxide, improved the energy storage capability beyond the activated carbon textile alone. The hybrid supercapacitors were resilient: even after thousands of charge-discharge cycles, performance didn’t diminish more than 5 percent.
“By stacking these supercapacitors up, we should be able to charge portable electronic devices such as cell phones,” Li said.
- How Your Body Heat Could Power Future Devices
The technology is based on a principle discovered nearly 200 years ago by physicist Thomas Johann Seebeck, who found that a combination of materials, when warmer on one side and colder on another, produces electricity.
Current heat wave notwithstanding, the human body’s temperature of around 98.6 degrees Fahrenheit is usually hotter than the air around it. So Perpetua has developed an armband, soon to become a wristband, that produces enough power for small electronics — not smartphones, but items that connect to them, such as Bluetooth devices. Wearing a mock-up wristband connected to a meter, Wiant put out enough body heat for a consistent 3 to 4 volts. Headsets using a technology called Bluetooth Low Energy need only about 2 volts, he said.