As the world becomes increasingly dependent on connected devices, wearable sensors, and the Internet of Things (IoT), scientists are searching for energy sources that are not only renewable but also capable of working continuously without batteries or external power.
Now, researchers led by Guo have found an unusual solution hiding on the ground: fallen leaves.
Instead of treating dry leaves as waste, the team developed a leaf-based energy harvester (LEH) that can generate electricity from moisture naturally present in the atmosphere. The technology combines the unique microscopic structure of leaves with a special moisture-absorbing iron hydrogel, turning an ordinary fallen leaf into a small energy-generating device.
The approach could offer a sustainable way to power low-energy electronics while also giving a second life to an abundant natural material.
Why Harvest Energy From Moisture?
Many self-powered devices already exist. One promising technology is the triboelectric nanogenerator (TENG), which produces electricity through repeated contact and separation between materials. Such devices have been explored for wearable electronics, medical patches, electrotherapy and other applications.
However, TENGs generally need mechanical movement. If there is not enough motion, their energy production can be limited.
Atmospheric moisture provides an interesting alternative.
Water vapor is practically everywhere on Earth. Unlike sunlight, it does not disappear at night, and unlike mechanical energy, it does not necessarily require a person or machine to keep moving.
Scientists have therefore been developing materials such as hydrogels, metal-organic frameworks and other moisture-absorbing materials that can capture water from humid air.
The major challenge is turning that captured moisture into useful electricity efficiently, affordably and sustainably.
This is where leaves offer an unexpected advantage.
Nature Has Already Designed the Structure
Leaves are highly sophisticated natural structures.
Their surfaces contain microscopic and nanoscale features that control how water interacts with them. Their veins form interconnected pathways that transport water and nutrients throughout the leaf. At the same time, the internal cellular structure provides mechanical strength while keeping the material lightweight.
These characteristics have already inspired technologies ranging from water-repellent surfaces to artificial photosynthesis and bio-based materials.
Guo and colleagues realized that these same structures could also help create an energy-harvesting device.
Instead of manufacturing a complicated artificial structure from scratch, the researchers used fallen leaves as the natural substrate.
The resulting device is called a leaf-based energy harvester (LEH).
How Does the Leaf Generate Electricity?
The process begins by preparing the fallen leaf.
The researchers first remove lignin from the leaf and then give it a conductive coating using carbon black (CB). After that, a moisture-absorbing iron hydrogel is applied asymmetrically to only one side of the leaf.
This uneven structure is crucial.
When the hydrogel absorbs moisture from the surrounding air, water becomes concentrated on the coated side. The hydrogel's network structure helps retain this water, while the natural veins of the leaf restrict its movement toward the opposite side.
As a result, a water gradient develops across the leaf.
In simple terms, one part of the leaf becomes wetter while the other remains relatively dry.
This difference creates conditions that allow ions to move and electrical charges to separate. An electrical double layer (EDL) forms along the surface, producing a voltage.
The researchers observed a built-in potential difference of approximately 0.5 volts, which could remain for more than 200 hours after moisture absorption.
The energy is effectively stored in these electrical double layers. When an external circuit is connected, the stored charge can flow through it as electrical current.
The Leaf Can Recharge Itself
One of the most interesting features of the system is its ability to regenerate.
After the stored energy is discharged, moisture from the surrounding environment can help rebuild the electrical charge.
According to the researchers, the system can rapidly replenish its energy through moisture absorption and desorption. This creates a self-regeneration process, allowing continuous electrical output rather than relying on a single charge.
This is particularly important for applications such as sensors and wearable electronics, which may require small amounts of electricity continuously over long periods.
Why Are Leaves So Effective?
The natural structure of the leaf does more than simply provide a cheap substrate.
Its tiny grooves and cellular features help the carbon black coating spread relatively uniformly across the surface instead of forming large aggregates.
This produces a highly conductive surface.
The combination of the conductive carbon coating, moisture-absorbing hydrogel and natural leaf structure gives the LEH impressive performance.
The researchers reported a short-circuit current density of approximately 49 μA/cm² and a volumetric power density of about 497 μW/cm³. Under external resistance, the device could produce around 12.43 μW/cm².
The team also assembled multiple leaf-based harvesters into a power panel. The integrated system produced approximately 13 volts and 0.2 mA/cm², demonstrating that individual leaf devices can potentially be combined to produce useful electrical outputs.
An Abundant and Low-Cost Material
Another major advantage is the enormous availability of fallen leaves.
Leaves are produced naturally every year and are often collected and discarded as waste. The researchers noted that the United States alone generated more than 8.8 million tons of fallen leaves in 2018, equivalent to roughly 1.76 billion filled rubbish bags.
Turning even a portion of this waste into energy-harvesting materials could create a new form of resource recovery.
Instead of manufacturing every component from expensive synthetic materials, the approach takes advantage of a structure that nature has already created.
Life-cycle assessment also indicated that the environmental impact of these leaf-based harvesters could be considerably lower than that of several other energy-harvesting approaches.
Important Challenges Remain
Despite the promising results, the technology is not yet ready to replace conventional power sources.
The current manufacturing process involves multiple chemical treatments and requires the hydrogel to be applied precisely to one side of the leaf. These steps increase labor, energy and material requirements.
The small size of individual leaves is another limitation.
A single leaf can only produce a limited amount of power. Producing a large-area energy harvester would therefore require many individual leaves to be connected together. For example, creating approximately 1 m² of active area could require processing around 200 leaves.
The researchers have suggested automated assembly systems as a possible solution, but factors such as hydrogel viscosity and machine parameters still need optimization.
There is also an important question about what happens after the device reaches the end of its useful life.
Although the leaf itself is biodegradable, the added carbon coating, hydrogel and chemical treatments may affect how easily the final device decomposes. Developing completely biodegradable or bioresorbable versions could therefore be an important direction for future research.
Furthermore, the current environmental and cost assessments are simplified. They do not fully account for factors such as labor, equipment, energy consumption and material waste during large-scale manufacturing.
A New Way to Think About Waste
The leaf-based energy harvester demonstrates an important principle: advanced technology does not always require advanced synthetic materials.
Sometimes, nature has already solved part of the engineering problem.
Leaves possess complex channels for water transport, microscopic surface structures and lightweight architectures that can be repurposed for energy harvesting. By combining these natural features with conductive carbon and hygroscopic hydrogel, researchers have created a device capable of converting atmospheric moisture into electricity.
The technology is still at an experimental stage, and significant work is needed to simplify manufacturing, increase scalability, improve biodegradability and reduce environmental impacts.
Nevertheless, the concept opens an intriguing possibility.
The fallen leaves that we sweep away as waste could one day become miniature power sources for the sensors, wearables and connected devices of the future.
Rather than simply throwing nature's leftovers away, scientists are beginning to explore how those materials can be transformed into functional technologies—showing that sometimes, the path toward sustainable energy may literally be lying beneath our feet.
Reference: Guo, S., Zhang, Y., Yu, Z. et al. Leaf-based energy harvesting and storage utilizing hygroscopic iron hydrogel for continuous power generation. Nat Commun 16, 5267 (2025). https://doi.org/10.1038/s41467-025-60341-z
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