A Moisture Wicking Battery

As the number of portable and wearable devices continues to increase, the question becomes not only how to efficiently power them all, but also how to manage the vast amount of electronic waste they produce.  

When considering the power issue, most people today rely on “bricks” or “power banks” to charge up. Meanwhile, wearable devices are reliant on traditional batteries that are rigid, heavy, and show degraded performance over time. Researchers from Binghamton University thought there must be a better way to power future wearable devices and have been focusing on creating a small, disposable power source. Now, they have developed an innovative new paper-based battery that is powered via moisture capture. 

“Our laboratory has been conducting experiments using bacteria, a strain called bacillus subtilis, to generate power,” said Yang “Lexi” Gao, a doctoral student in Seokhaun “Sean” Choi’s Bioelectronics and Microsystems Laboratory at Binghamton. “They have very rich functional groups on their surface which can capture moisture.” 

Those bacteria can break down the water molecules into positive and negative ions, which can then be leveraged to create an electric charge. However, to use moisture as a nutrient source for the biobattery, the researchers needed to find a material that was super-absorbent and compatible to the bacteria, Gao explained. 

“For the battery to work, the material has to be porous enough so the moisture can go in and get to the bacteria. When we looked at different materials, we narrowed down our choices and paper popped out as the best candidate,” she said. 

A paper-based design helps to make the prototype small and easy to dispose of without guilt, but the use of paper did come with some design challenges, Gao added. 

“Paper is really cheap, but it is also stressful to use. We had to design a pattern and figure out the best way to make it align so the moisture can get in,” she said. “We had to try multiple times to get the right design and, to be frank, we wasted a lot of paper to get there.” 

Discover the Benefits of ASME Membership

Since there is no reference of work for these sorts of innovative “papertronics,” the group has had to do a great deal of trial and error to get to the right design, said Anwar Elhadad, an assistant professor who works with Gao and Choi. 

“It’s like you’re alone in the jungle, trying to figure out what works, what doesn’t, and what the actual mechanism is,” he explained. “We’ve had to figure out how to make this work step by step and to make sure it is working as designed, we’ve had to test every step to get to this point.” 

The single cell paper battery the group designed is approximately the size of a nickel. A Janus paper layer, which is hydrophobic on one side and hydrophilic on the other, pulls water in from the air and then keeps it inside the battery device so the bacteria can process it. After the organism breaks down the ions into separate bacterial spores, it is then taken up by the paper’s capillaries. The paper’s gradient pulls more positive ions on top, ultimately creating a small electric charge. 

“The cell can give you voltage of around 0.5 or 0.6 volts depending on the humidity level,” Gao said. Twenty cells connected can muster enough current to power an LED light, while charging an iPhone would likely require chaining “at least 100 times more” cells together, Gao estimated. 

This new battery is a step forward in Choi’s pursuit of wearable devices made entirely out of paper. They would offer a revolutionary approach to electronics that are light, flexible, scalable, and, most importantly, disposable without the risks of traditional electronic waste. As the group advances its designs, Choi hopes such biobatteries can help provide electricity for low-power sensors, wearable drug delivery devices, or even electrical stimulation implants.  

Check This Out: Simple Electric Bandage Heals Chronic Wounds

In the meantime, the team is working to create a more powerful battery that not only takes in moisture from the air but also wicks sweat from the body. The research group is also looking at adding nanoparticles to help the battery absorb moisture more “effectively and efficiently” to help improve performance and power generation.  

“Sweat can be a good moisture source to feed the bacteria,” Gao explained. “We need to find materials that won’t just work with the bacteria, but also the skin. In our ongoing work, we are connecting the microbial fuel cell [MFC] and the material together so the MFC can use sweat from the skin and the material can use moisture from the air. That way, when you are sweating, the MFC can generate power, but if you are not, the material can also generate continuous power from the air, making a perpetual power source.” 

Kayt Sukel is a technology writer and author in Houston.