Two Colgate researchers have managed to create an electrical generator with little more than a leaf.
Money may not grow on trees, but in the future, batteries might. Assistant Professor of Physics Ramesh Adhikari and his student Neha Viradia ’25 have created a way to harness electricity using little more than leaves collected from around campus, submerged in a bath of water. “It’s basically a battery where water is the fuel,” Adhikari says. “As long as you have access to water, it will continue to run.”
Water has long been used to generate energy from hydroelectric dams, geothermal heat, and turbines driven by waves. But those processes all rely on mechanical or physical properties. “The energy within the molecules themselves is not tapped,” Adhikari says. By contrast, their leaf-based technique creates something called a hydrovoltaic generator, in which electricity is created from the electrical potential of water molecules themselves. While such generators have previously produced low amounts of current, their generator could produce enough electricity to light an LED bulb or power a small device such as a thermometer or other sensor for hours on end. Better yet, it is environmentally friendly. “We create so much waste with electronics,” says Viradia. “Making them out of biodegradable materials can have a huge impact.”
The researchers describe their methods in a new paper published in the journal iScience, “Leaves for High Power Density Hydrovoltaic Generators.” The secret lies in the fact that leaves have built-in channels that circulate water, as well as pores on their undersides called stomata through which they perspire water vapor to keep cool. By treating the top of the leaf with a solution of sodium hydroxide (NaOH), a highly corrosive base, the researchers are able to open pores on that side as well, creating small channels across the thickness of the leaf.
The treatment also “functionalizes” the wall of those channels by making negatively charged hydroxyl ions (OH-) stick on them. This allows only the positively charged hydrogen ions (H+) to move across the channel, making the channels “ion-selective.” Adhikari and Viradia then sandwich the leaf between two electrodes with aluminum on top. As the hydrogen ions react with the aluminum, they generate electrons that can move through a circuit to create electricity.
Adhikari has been experimenting with leaf-based electronics since 2019, embedding them with wires or using their properties to store memory. The generator process comes out of attempts by Viradia to create a leaf-based capacitor to store electricity. “The device was somehow making its own power,” says Viradia, “which is not supposed to happen.” Adhikari realized that because the leaf was wet, it was generating small amounts of electricity from water, making it a bad capacitor but a potentially good hydrovoltaic generator.
The pair continued to experiment to maximize the effect. By itself, a wet leaf only produced about six hours of decent current before it eventually dried out. They were able to increase that time by using a wick to ensure a constant supply of water for the device. By far the biggest increase, however, occurred when they submerged the battery entirely in water, allowing them to produce a substantial voltage and current for 300 hours — more than two weeks — before the leaf deteriorated and the aluminum corroded. They are currently experimenting with techniques to extend that life even more, but already the leaf battery represents a huge improvement over previous hydrovoltaic generators. While past generators have been able to create .5 volts of electricity, theirs can generate 1.5 volts — equivalent to an AA battery. Their ability to generate electrical current is even more impressive, increasing that of current generators by approximately a factor of one hundred.
The most immediate application for the device would be powering environmental sensors, for example, to detect chemicals in water, by submerging them full time in a water source. The device could also be potentially used as rainfall sensors because they only generate electrical current when wet, at the same time extending the usable life of the battery.
In the future, Adhikari envisions being able to take a device hiking or backpacking to create a sustainable battery on the trail to charge a phone or flashlight for days with minimal environmental impact. When that day comes, all that would be needed to generate power would be to “Just add water.”