Researchers invent ultra-thin, self-charging device that generates electricity from moisture in the air

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Imagine being able to generate electricity by harnessing the humidity in the air around you with everyday objects like sea salt and a piece of cloth, or even powering everyday electronics with a battery. non-toxic as thin as paper. A team of researchers from the College of Design and Engineering (CDE) of the National University of Singapore (NUS) have developed a novel moisture-based electricity generation (MEG) device consisting of a thin layer of tissue approximately 0.3 millimeters (mm) in diameter. thickness – sea salt, carbon ink and special water-absorbing gel.

The concept of MEG devices is based on the ability of different materials to generate electricity from the interaction with the humidity in the air. This area is attracting growing interest due to its potential for a wide range of real-world applications, including self-powered devices such as wearable electronics like health monitors, electronic skin sensors, and storage devices. information.

The main challenges of current MEG technologies include water saturation of the device when exposed to ambient humidity and unsatisfactory electrical performance. Thus, the electricity generated by conventional MEG devices is insufficient to power electrical appliances and is also not sustainable.

To overcome these challenges, a research team led by Assistant Professor Tan Swee Ching from the Department of Materials Science and Engineering at CDE designed a new MEG device containing two regions of different properties to perpetually maintain a difference in water content between the regions to generate electricity. and allow electrical production for hundreds of hours.

This technological breakthrough was published in the print version of the scientific journal Advanced materials May 26, 2022.

Long-lasting, self-recharging fabric-based “battery”

The NUS team’s MEG device consists of a thin layer of fabric coated with carbon nanoparticles. In their study, the team used a commercially available fabric made of wood pulp and polyester.

A region of the fabric is coated with a hygroscopic ionic hydrogel, and this region is known as the moist region. Made from 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 because of its non-toxic properties and its potential to provide a sustainable option for desalination plants to remove the sea salt and brine generated,” explained the professor. Asst 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.

After the MEG device is assembled, electricity is generated when sea salt ions are separated as water is absorbed in the wet region. The positively charged free ions (cations) are absorbed by the negatively charged carbon nanoparticles. This causes changes on the surface of the tissue, generating an electric field across it. These surface changes also give the fabric the ability to store electricity for later use.

By using a unique design of wet and 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 maintain 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 humid region demonstrating the effectiveness of the device in maintaining electrical output.

“With this unique asymmetrical structure, the electrical performance of our MEG device is significantly improved over previous MEG technologies, making it possible to power many common electronic devices, such as health monitors and wearable electronics,” explained Professor Asst Tan.

The team’s MEG device also demonstrated great flexibility and was able to withstand twisting, rolling and bending stresses. Interestingly, its exceptional flexibility was demonstrated by the researchers by folding the fabric into an origami crane which did not affect the device’s overall electrical performance.

Portable power and more

The MEG device has immediate applications due to its ease of scalability and commercially available raw materials. One of the most immediate applications is use as a portable power source for mobile power electronics directly from ambient humidity.

“After water absorption, a 1.5 by 2 centimeter piece of energy-generating fabric can provide up to 0.7 volts (V) of electricity for more than 150 hours in a constant environment,” said Dr. Zhang Yaoxin, member of the research team.

The NUS team also successfully demonstrated the scalability of their new device in generating electricity for different applications. The NUS team connected three pieces of the energy-generating fabric together and placed them inside a 3D-printed case the size of a standard AA battery. The voltage of the assembled device has been tested to reach as high as 1.96V – higher than a commercial AA battery by approximately 1.5V – which is sufficient to power small electronic devices such as ‘an alarm clock.

The scalability of the NUS invention, the convenience of obtaining commercially available raw materials as well as the low manufacturing cost of around S$0.15 per square meter make the MEG device suitable for mass production.

“Our device exhibits excellent scalability at low manufacturing cost. Compared to other MEG structures and devices, our invention is simpler and easier for scaling integrations and connections. We believe that it holds great promise for commercialization,” said Professor Asst Tan.

The researchers have filed a patent for the technology and plan to explore potential commercialization strategies for real-world applications.

Video: https://youtu.be/8WOh-trN9cw

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