Scientists built a battery-free device that turns sunlight into fuel

For decades, scientists have been trying to recreate one of nature's most remarkable tricks: the ability of a leaf to use sunlight, water and carbon dioxide to produce energy-rich compounds.

Now, researchers at Osaka Metropolitan University say they have moved a 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 run using sunlight alone. Researchers say the breakthrough could simplify solar fuel production, reduce costs and make the technology more practical for real-world deployment.

How does the artificial leaf turn carbon dioxide into fuel?

Artificial photosynthesis is designed to mimic the way plants convert sunlight into usable energy.

In most engineered systems, photovoltaic panels generate electricity, which is then used by an electrolyser to convert carbon dioxide and water into fuels or other useful chemicals.

The challenge has always been sunlight itself.

Because solar power fluctuates throughout the day, many systems require batteries or sophisticated electronic controls to stabilise performance and maintain fuel production.

The Osaka team took a different approach. Instead of relying on battery-powered controls, researchers redesigned the electrolyser to include a self-regulating chemical component that automatically responds to changing sunlight conditions.

This allows the system to continue operating without conventional battery-based control mechanisms.

Why does the system not 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, which often require batteries.

Rather than storing energy in a battery, the system powers its components directly from solar panels.

According to the research description, the electricity needed for pumps, controllers, valves and the microprocessor comes directly from photovoltaic panels through a buck-boost DC/DC converter.

The system also uses low-power components, including piezoelectric pumps and a low-power microprocessor, helping 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 increasingly attracting attention as both a fuel and an 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 drives electrochemical reactions that combine carbon dioxide and water, creating formic acid while storing solar energy in chemical bonds.

Researchers say the device converts carbon dioxide and pure water into a pure aqueous formic acid solution using a specialised three-compartment electrolyser designed for stand-alone and unmanned operation.

Why are scientists interested in artificial photosynthesis?

The significance of the development extends beyond producing fuel.

Batteries are often among the most expensive and maintenance-intensive parts of renewable energy systems. Removing them could lower deployment costs, simplify operation and improve durability, particularly in remote locations.

The project was developed at the Research Centre for Artificial Photosynthesis at Osaka Metropolitan University and tested in Sugimoto, Osaka, Japan, in May 2024.

Researchers also demonstrated the system's capabilities by generating enough power to operate a display installation at Expo 2025 Osaka, showing that it could function outside tightly controlled laboratory settings.

What does this mean for the future of solar fuels?

The new system arrives as scientists around the world continue searching for ways to store solar energy in chemical form.

Recent advances in artificial photosynthesis have focused on converting carbon dioxide into methane, methanol, hydrogen and other energy-rich compounds using sunlight as the primary energy source.

The Osaka team's work points towards a future where solar technologies do more than generate electricity. Instead, they could directly manufacture transportable fuels, turning sunlight and carbon dioxide into storable energy resources without relying on battery storage systems.

As researchers continue refining these technologies, artificial photosynthesis is moving closer to becoming a practical tool for producing carbon-neutral fuels at scale.

(With TOI inputs)