Summertime heat and humidity are cranking up in the Northern Hemisphere, leading many to switch on an electric fan or air conditioner for relief.
But imagine if that electric power could be drawn from the humid air itself.
Engineers at the University of Massachusetts Amherst said they have shown that nearly any material can be turned into a device that continuously harvests electricity from humidity in the air.
The technique relies on the ability to pepper the material with nanopores less than 100 nanometers in diameter. The research appeared in the journal Advanced Materials.
The air contains an enormous amount of electricity, the researers said. For example, each water droplet in a cloud contains a charge. When conditions are right, the cloud can produce a lightning bolt. The researchers created a human-built, small-scale cloud that produces electricity predictably and continuously so that it can be harvested.
The laboratory cloud depends on the “generic Air-gen effect,” and builds on work previously completed in 2020 showing that electricity could be continuously harvested from the air using a specialized material made of protein nanowires grown from the bacterium Geobacter sulfurreducens.
The researchers said that after making the Geobacter discovery they realized that the ability to generate electricity from the air is generic: any kind of material can harvest electricity from air, as long as it has a certain property.
That property is the requirement to have holes smaller than 100 nanometers. This is because of a parameter known as the “mean free path,” the distance a single molecule of a substance–in this case water in the air–travels before it bumps into another single molecule of the same substance. When water molecules are suspended in the air, their mean free path is about 100 nm.
The researchers designed a harvester made from a thin layer of material filled with nanopores smaller than 100 nm that would let water molecules pass from the upper to the lower part of the material. But because each pore is so small, the water molecules would easily bump into the pore’s edge as they pass through the thin layer. They said this means that the upper part of the layer would be bombarded with many more charge-carrying water molecules than the lower part, creating a charge imbalance, like that in a cloud, as the upper part increased its charge relative to the lower part. This would effectually create a battery that runs as long as there is any humidity in the air.
The researchers said that because humidity is ever-present, the harvester would run 24/7, which would solve the intermittency challenge with technologies like solar or wind.
The research was supported by the National Science Foundation, Sony Group, Link Foundation, and the Institute for Applied Life Sciences at UMass Amherst.
