Flexible, ultra-thin device generates electricity from moisture in the air


Researchers have created an ultra-thin, self-charging device that generates electricity from the humidity in the air.

Imagine being able to generate electricity by harnessing the humidity in the air around you with just everyday objects like sea salt and a piece of cloth, or even powering everyday electronics with a non-toxic battery as thin as paper.

The researchers developed the new moisture-generating (MEG) device consisting of a thin layer of fabric about 0.3 millimeters (about 0.0118 inches) thick, sea salt, d carbon ink and a 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 memory 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 Tan Swee Ching, Assistant Professor in the Department of Materials Science and Engineering, College of Design and Engineering (CDE), National University of Singapore, 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 enable electrical production for hundreds of hours.

An article about the work appears in the journal Advanced materials.

The new moisture-powered electricity-generating device capitalizes on the difference in moisture content of the wet and dry regions of the carbon-coated fabric to create an electrical current. Sea salt is used as a moisture absorbent for the humid region.

The researchers’ 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,” says 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 wet-dry region design, the 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,” says Tan. .

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

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 absorbing water, 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,” says Zhang. Yaoxin, member of the research team.

The researchers also successfully demonstrated the scalability of the new device in generating electricity for different applications. The team connected three pieces of the power-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 1.96V, which is more than a commercial AA battery of approximately 1.5V, which is sufficient to power small electronic devices such as an alarm clock.

The scalability of the invention, the convenience of obtaining commercially available raw materials as well as the low manufacturing cost of approximately 0.15 Singapore dollars (0.11 USD) per square meter make the MEG device suitable to mass production.

“Our device has excellent scalability at a low manufacturing cost. Compared to other MEG structures and devices, our invention is simpler and easier for scaling integrations and connections. We think it holds great promise for commercialization,” says Tan.

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

Source: National University of Singapore

Original study DOI: 10.1002/adma.202201228


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