Taking cue from lightning, Tel Aviv University team creates power from humidity
Researchers find that voltage develops between 2 metal surfaces when humidity rises above 60%; could lead to batteries chargeable by water vapor
Sue Surkes is The Times of Israel's environment reporter
Israeli scientists have already learned how to produce water from air. Now they may be poised to create power from humidity.
The research — led by Prof. Colin Price in collaboration with Prof. Hadas Saaroni and doctoral student Judi Lax, all of Tel Aviv University’s Porter School of the Environment and Earth Sciences — is based on the knowledge that electricity is generated by the interaction of water molecules and metal surfaces.
“We sought to capitalize on a naturally occurring phenomenon — electricity from water,” explained Price. “Electricity in thunderstorms is generated only by water in its different phases — water vapor, water droplets, and ice. Twenty minutes of cloud development is how we get from water droplets to huge electric discharges — lightning — some half a mile in length.”
In the nineteenth century, English physicist Michael Faraday discovered that water droplets could charge metal surfaces due to friction between the two. A more recent study showed that certain metals spontaneously build up an electrical charge when exposed to humidity.
Building on the findings of earlier discoveries such as these, the researchers set out to test the possibility of making a tiny low-voltage battery that uses nothing but humidity in the air.
They exposed two different metals to different levels of humidity, while one was grounded.
“We found that there was no voltage between them when the air was dry,” Price said. “But once the relative humidity rose above 60 percent, a voltage began to develop between the two isolated metal surfaces. When we lowered the humidity level to below 60%, the voltage disappeared. When we carried out the experiment outside in natural conditions, we saw the same results.”
He went on, “Water is a very special molecule. During molecular collisions, it can transfer an electrical charge from one molecule to the other. Through friction, it can build up a kind of static electricity.
“We tried to reproduce electricity in the lab and found that different isolated metal surfaces will build up different amounts of charge from water vapor in the atmosphere, but only if the air relative humidity is above 60%. This occurs nearly every day in the summer in Israel and every day in most tropical countries.”
According to Price, this study challenges established ideas about humidity and its potential as an energy source. “People know that dry air results in static electricity and you sometimes get ‘shocks’ when you touch a metal door handle. Water is normally thought of as a good conductor of electricity, not something that can build up charge on a surface. However, it seems that things are different once the relative humidity exceeds a certain threshold,” he said.
The researchers were able to show that humid air may be a source of charging surfaces to voltages of around one volt. “If an AA battery is 1.5V, there may be a practical application in the future: to develop batteries that can be charged from water vapor in the air,” Price said.
“The results may be particularly important as a renewable source of energy in developing countries, where many communities still do not have access to electricity, but the humidity is constantly about 60%.”
The research, released last week by the university, was published in Nature Scientific Reports in May.
