As global energy demands continue to escalate, scientists are increasingly focusing on sustainable energy generation to ensure grid stability and address the urgent challenges posed by the unfolding climate crisis.

“Humidity is a vast, sustainable reservoir of energy that, unlike solar and wind, is continuously available,” wrote a team of scientists led by Jun Yao, assistant professor of electrical and computer engineering at UMass Amherst’s College of Engineering, in a recent study published in Advanced Materials. “However, previously described technologies for harvesting energy from air humidity are either not continuous or require unique material synthesis or processing, which has stymied scalability and broad deployment.”

Yao and his team have therefore developed a category of devices they termed “Air-gens” that continuously harvest electricity from moisture in the air through a newly elucidated sustainable mechanism that he says can be applied to any material.  

“The Air-gen device is made from a thin film containing many small holes called nanopores, which have a diameter smaller than one thousandth of the diameter of human hair,” Yao said in an email.  “The top of the film interface is exposed to air, whereas the bottom interface of the film is sealed.

“Water molecules [in the air] can pass through these nanopores from the top interface to the bottom interface, but they easily ‘bump’ into the pore surface before they can travel long,” he continued. “This means that the top interface will be bumped into more frequently than the bottom interface. Water molecules [in the air] can carry electricity or charge — this is why we can have lightning during a thunderstorm — and so they donate a portion of the charge to the thin film when they contact its surface.”

As the top of the thin film has more contact with water molecules than the bottom, a charge separation builds up between the two layers, which when connected, results in a flow of electricity.

‘The working principle behind an Air-gen device is similar to that of a cloud building up charge before producing lightning,” added Yao. “Both utilize the movement and charge-carrying in air water molecules to build up a charge separation. That’s why, in a loose sense, we may view the Air-gen device as a small-version ‘man-made cloud’.”

A happy accident

The team have been working on the design since 2018, where the initial effect came about as a serendipitous discovery. Yao and his students were studying the sensing properties of a material made of protein nanowires that had been synthesized from a bacterium called Geobacter.

“Our initial intention was to make an electronic sensor out of the material, but my student at the time, Xiaomeng Liu, accidentally forgot to plug in power and still observed electrical signal in ambient environment,” said Yao.

This happy accident diverged the team’s focus from sensors to energy generation. Yao says the initial discovery also inferred the likelihood of a “generic mechanism”, meaning different types of protein nanowires or materials could give similar results. “From there, we began to think about […] how it could be applied to other materials for broad impact, which has led to our recent paper,” he added.

More is needed before this technology is ready to hit the market, but Yao already has ideas for its use. “Air in itself does not contain high energy density, but excels in terms of abundance and continuity,” he said. “The power volume in Air-gens may be improved with vertical stacking — like accommodating more people in a tall building. This means that they may be engineered into different form factors/sizes for various usages, ranging from small-scale (e.g., portable electronics), medium-scale (e.g., environmental deployment of devices), to large-scale (e.g., household usage) solutions.

“It would be good to not to compete for space but to use waste space for energy harvesting, since air is everywhere,” he added.

While this technology represents a promising advancement toward sustainable energy generation, there are several critical areas that require attention before it can be scaled up effectively. These areas include improving the device’s conversion efficiency, reducing costs, and addressing scalability challenges. “This is where federal funding and industrial investments will play a critical role in determining how fast the pace is,” said Yao.

Reference: Jun Yao, et al., Generic Air-Gen Effect in Nanoporous Materials for Sustainable Energy Harvesting from Air Humidity, Advanced Materials (2023). DOI: 10.1002/adma.202300748