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Using Sea Salt to Produce Electricity

Imagine being able to use commonplace objects like sea salt and a piece of cloth to capture moisture in the air to generate electricity or even power everyday gadgets with a non-toxic battery that is as thin as paper.

Using Sea Salt to Produce Electricity.
Asst Prof Tan Swee Ching (center), together with Dr. Zhang Yaoxin (left) and Mr. Qu Hao (right), developed a self-charging fabric that generates electricity from air moisture. Image Credit: National University of Singapore

A novel moisture-driven electricity generation (MEG) device has been created by a team of scientists from the College of Design and Engineering (CDE) at the National University of Singapore (NUS). It is made of a thin fabric layer that is about 0.3 mm thick, sea salt, carbon ink, and a unique water-absorbing gel.

The basis of MEG technology is the capacity of various materials to produce electricity through their interaction with atmospheric moisture.

Due to the potential for a wide range of practical applications, such as self-powered gadgets like wearable electronics like health monitors, electronic skin sensors, and information storage devices, this field has been attracting increasing interest.

However, two major issues with existing MEG technologies are the device becoming saturated with water when exposed to ambient humidity and subpar electrical performance. As a result, traditional MEG devices do not produce enough electricity to sustainably power electrical equipment.

To address these issues, a research group from the Department of Materials Science and Engineering within CDE developed a novel MEG device with two areas with distinct properties that continuously maintain a disparity in water content across the regions to create power and enable electrical output for hundreds of hours. Assistant Professor Tan Swee Ching led the study team.

On May 26th, 2022, the scientific journal Advanced Materials released a print edition of this technological advancement.

Long Lasting, Self-Charging Fabric-Based “Battery”

The carbon nanoparticle-coated thin piece of cloth makes up the NUS team’s MEG gadget. The scientists employed a commercially available fabric comprised of polyester and wood pulp for their study.

The wet zone refers to the area of the cloth that is coated with a hygroscopic ionic hydrogel. The unique water-absorbing gel, which is created from sea salt, can absorb more than six times its initial weight and is used to draw moisture from the atmosphere.

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.

Tan Swee Ching, Assistant Professor, Materials Science and Engineering, National University of Singapore

The other end of the fabric does not contain a hygroscopic ionic hydrogel layer and is classed as the dry region. This is to ensure that water is confined to the wet region and the dry region is kept dry.

After the MEG device has been put together, electricity is produced when the sea salt’s ions are split apart as water is absorbed in the wet area.

The negatively charged carbon nanoparticles absorb free ions with a positive charge (cations). An electric field is created throughout the fabric because of changes to its surface. The cloth can store electricity for later use, thanks to these modifications to the surface.

Scientists from NUS were able to keep a high water content in the wet zone and low water content in the dry region by using a novel design of wet–dry regions. Even when the wet area is completely submerged in water, this will maintain electrical production.

Water was still present in the wet area after 30 days in an exposed, humid environment, proving the device’s capability to sustain 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 MEG gadget created by the team also showed remarkable flexibility and could sustain pressure from twisting, rolling, and bending. The fabric was folded into an origami crane by the researchers to demonstrate the fabric’s remarkable flexibility, which did not compromise the device’s overall electrical performance.

Portable Power Supply and More

The MEG device’s simplicity in scaling and readily accessible raw materials allow for quick applications. One of the most urgent uses is enabling mobile devices to be powered directly by ambient humidity as a portable power source.

After water absorption, one piece of power-generating fabric that is 1.5 by 2 centimeters in size can provide up to 0.7 volts (V) of electricity for over 150 hours under a constant environment,” said research team member Dr. Zhang Yaoxin.

The NUS team has also effectively shown how its novel technology can be scaled up to generate electricity for various uses. The NUS team assembled three sections of the cloth that generates power and put them in a 3D printed box the size of an AA battery.

The completed device’s voltage was tested and found to be as high as 1.96 V, which is greater than the 1.5 V of a typical AA battery and sufficient to power small electrical devices like an alarm clock.

The MEG device is suited for mass manufacturing due to the NUS invention’s scalability, the ease with which commercially accessible raw materials can be obtained, and the low fabrication cost of roughly $0.15 per square meter.

Our device shows excellent scalability at a low fabrication cost. Compared to other MEG structures and devices, our invention is simpler and easier for scaling-up integrations and connections. We believe it holds vast promise for commercialization,” shared Assistant Professor Tan.

The scientists intend to investigate possible commercialization options for practical applications after filing a patent application for the invention.

Journal Reference:

Zhang, Y., et al. (2022) An Asymmetric Hygroscopic Structure for Moisture-Driven Hygro-Ionic Electricity Generation and Storage. Advanced Materials.

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