Experts at Tel Aviv University have confirmed that water vapor has the potential to serve as a renewable energy source. The research is based on the discovery that interactions between water molecules and metal surfaces produce electricity.
“We sought to capitalize on a naturally occurring phenomenon: electricity from water,” explained Professor Colin 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 as a result of friction. More recently, researchers demonstrated that certain metals become electrically charged when exposed to humidity.
For the current study, the Tel Aviv team set out to develop a tiny low-voltage battery that requires only humidity from the air to charge. The scientists designed a lab experiment to determine the voltage between two different metals exposed to high relative humidity, while one is grounded.
“We found that there was no voltage between them when the air was dry,” said Professor Price. “But once the relative humidity rose above 60%, 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.”
“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.”
Professor Price noted that the 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.”
The researchers showed that humid air may be a source of charging surfaces to voltages of around one volt.
“If a 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,” said Professor Price.
“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 study is published in the journal Scientific Reports.