Scientists built a battery-free device that turns sunlight into fuel
Now researchers at Osaka Metropolitan University say they’re one step closer to that goal with a battery-free artificial photosynthesis system that can continuously convert sunlight, water, and carbon dioxide into formic acid, a liquid fuel and energy storage chemical.
Unlike many existing artificial photosynthesis systems that rely on batteries or electronic controllers to maintain stable operation, the newly developed system is designed to operate using only sunlight. The researchers say this breakthrough could simplify solar fuel production, reduce costs and make the technology more practical for real-world deployment.
How does an artificial leaf convert carbon dioxide into fuel?
Artificial photosynthesis is designed to mimic the way plants convert sunlight into usable energy.
In most engineering systems, photovoltaic panels generate electricity, which is then used by an electrolyzer to convert carbon dioxide and water into fuels or other useful chemicals.
The challenge has always been the sunlight itself.
Because solar energy fluctuates throughout the day, many systems require batteries or advanced electronic controls to stabilize performance and maintain fuel production. The Osaka team took a different approach. Rather than relying on battery-powered controls, the researchers redesigned the electrolyzer to include a self-regulating chemical component that automatically responds to changing sunlight conditions.
This allows the system to continue operating without traditional battery-based control mechanisms.
Why doesn’t the system need a battery?
One of the main goals behind the proposed “chemical MPPT system” was to eliminate the cost and redundancy associated with traditional electronic maximum power point tracking systems that often require batteries.
Rather than storing energy in a battery, the system powers its components directly from solar panels.
According to the research statement, the electricity needed for the pumps, controllers, valves and microprocessor comes directly from the photovoltaic panels via a step-down DC/DC converter.
The system also uses low-power components, including piezoelectric pumps and a low-power microprocessor, helping to reduce the amount of energy required for operation.
The result is a simpler architecture that maintains stability while reducing complexity and cost.
What fuel does the artificial leaf produce?
The system produces formic acid, a carbon-based liquid that is gaining increasing attention as both a fuel and energy carrier.
Formic acid can store hydrogen in a stable liquid form and can be produced directly from captured carbon dioxide.
In the Osaka system, solar-generated electricity activates electrochemical reactions that combine carbon dioxide and water, creating formic acid and storing solar energy in chemical bonds.
The researchers say the device converts carbon dioxide and pure water into pure aqueous formic acid solution using a special three-chamber electrolyzer designed for independent and unmanned operation.
Why are scientists interested in artificial photosynthesis?
The importance of development extends beyond producing fuel.
Batteries are often among the most expensive and maintenance-intensive parts of renewable energy systems. Removing them can reduce deployment costs, simplify operation and increase durability, especially in remote locations.
The project was developed at the Artificial Photosynthesis Research Center of Osaka Metropolitan University and tested in May 2024 in Sugimoto, Osaka, Japan.
The researchers also demonstrated the system’s capabilities by generating enough power to power a display installation at Expo 2025 Osaka, demonstrating that it can operate outside of tightly controlled laboratory environments.
What does this mean for the future of solar fuels?
The new system comes as scientists around the world continue to search for ways to store solar energy in chemical form.
Recent advances in artificial photosynthesis have focused on the conversion of carbon dioxide into methane, methanol, hydrogen and other energy-rich compounds using sunlight as the primary energy source.
The Osaka team’s work points to a future where solar technologies do more than generate electricity. Instead, they can directly produce portable fuels by converting sunlight and carbon dioxide into storable energy sources without the need for battery storage systems.
As researchers continue to develop these technologies, artificial photosynthesis is moving closer to becoming a practical means for producing carbon-neutral fuels on a large scale.
(With TOI entries)
