Long-lasting, self-charging fabric-based ‘battery’
The NUS team’s MEG device consists of a thin layer of fabric which was coated with carbon nanoparticles. In their study, the team used a commercially available fabric made of wood pulp and polyester.
One region of the fabric is coated with a hygroscopic ionic hydrogel, and this region is known as the wet region. Made using sea salt, the special water-absorbing gel can absorb more than six times its original weight, and it is used to harvest moisture from the air.
“Sea salt was chosen as the water-absorbing compound due to its non-toxic properties and its potential to provide a sustainable option for desalination plants to dispose of the generated sea salt and brine,” shared Asst Prof Tan.
The other end of the fabric is the dry region which does not contain a hygroscopic ionic hydrogel layer. This is to ensure that this region is kept dry and water is confined to the wet region.
Once the MEG device is assembled, electricity is generated when the ions of sea salt are separated as water is absorbed in the wet region. Free ions with a positive charge (cations) are absorbed by the carbon nanoparticles which are negatively charged. This causes changes to the surface of the fabric, generating an electric field across it. These changes to the surface also give the fabric the ability to store electricity for use later.
Using a unique design of wet-dry regions, NUS researchers were able to maintain high water content in the wet region and low water content in the dry region. This will sustain electrical output even when the wet region is saturated with water. After being left in an open humid environment for 30 days, water was still maintained in the wet region demonstrating the effectiveness of the device in sustaining electrical output.
“With this unique asymmetric structure, the electric performance of our MEG device is significantly improved in comparison with prior MEG technologies, thus making it possible to power many common electronic devices, such as health monitors and wearable electronics,” explained Asst Prof Tan.
The team’s MEG device also demonstrated high flexibility and was able to withstand stress from twisting, rolling, and bending. Interestingly, its outstanding flexibility was shown by the researchers by folding the fabric into an origami crane which did not affect the overall electrical performance of the device.