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Hydrogel advances wearable electronics

By Tim Sandle     Jul 4, 2017 in Technology
A polyacrylamide hydrogel has been developed. This should lead to super-stretchable and super-compressible supercapacitors for use with the growing trend for wearable electronic devices.
The polyacrylamide hydrogel electrolyte leads to the development of supercapacitors that are very stretchable and compressible. Supercapacitors are high-capacity capacitors which bridge a gap between electrolytic capacitors and rechargeable batteries. These capacitors can store 10 to 100 times more energy per unit volume or mass than electrolytic capacitors and they deliver charge much faster than batteries. In addition, supercapacitors can tolerate many more charge and discharge cycles than rechargeable batteries. This makes them ideal for next generation electronic devices.
Supercapacitors are often used in regenerative braking, as power buffers in wind turbines. They are also seen as key to future electronics like wearables and paper electronics. One limitation is, however, that current supercapacitors do not stretch very well. To overcome this, Chunyi Zhi from the City University of Hong Kong has been working on alternatives.
The stretchable and compressible polyelectrolyte, reports, works in combination with carbon nanotube composite paper electrodes to form the new type of supercapacitor. The capacitor can, remarkably, be stretched to 1,000 percent in length and compressed down to 50 percent in thickness. With both these extremes there is no loss of capacity.
The development is down to the new electrolyte material: a polyelectrolyte that can be stretched without breaking, cracking, or suffering other forms of damage. Much of the strechability is due to a hydrogel that is reinforced with vinyl-functionalized silica nanoparticles . The ability to stretch is due to cross-links between the vinyl-silica nanoparticles. The concavity relates to the polyelectrolyte. This electrolyte can swells with water and hold and transfers ions.
The final design resembles a wavy structure, which is said to look a little like an accordion when magnified. In trials the electrochemical behavior of the supercapacitor was evaluated. Not only were the properties maintained when the supercapacitor was stretched, the electrochemical performance appeared to become enhanced as the material was stretched. These tests suggest the new supercapacitor will prove useful in the design of next generation electronics.
The findings are published in Angewandte Chemie International Edition, in a research paper titled “An Intrinsically Stretchable and Compressible Supercapacitor Containing a Polyacrylamide Hydrogel Electrolyte.”
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