Toward battery-free artificial photosynthesis: Stable fuel production at lower cost

Researchers at Osaka Metropolitan University have developed an artificial photosynthesis system capable of producing solar fuels more stably by integrating a self-regulating chemical component directly into the electrolyzer itself. The new device doesn’t rely on a battery-powered control method, removing an expensive component of such systems.

Similar to its natural version, artificial photosynthesis uses sunlight to convert water and carbon dioxide into useful fuels such as formic acid.

In artificial photosynthesis systems, the electrolyzer plays a central role by converting electricity generated by solar cells into chemical energy that can be stored as fuel in the form of formic acid.

To keep this energy conversion operating efficiently under changeable sunlight conditions, many systems use Maximum Power Point Tracking (MPPT), a control method that continuously adjusts the voltage and current to maximize the power output of the solar cells. However, MPPT systems typically rely on batteries or additional electronics to stabilize energy flow, increasing both the cost and complexity of the overall system.

A research group led by Associate Professor Yasuo Matsubara and Professor Yutaka Amao at the Research Center for Artificial Photosynthesis, Osaka Metropolitan University, in collaboration with Iida Group Holdings Co., Ltd, redesigned the system to incorporate a special solid electrolyte into the electrolyzer. In their new system, the electrolyzer itself performs the MPPT function automatically, eliminating the need for batteries.

Instead of using external electronics, batteries, and converters to keep the solar cell operating efficiently, the electrolyzer autonomously adjusts its own electrical behavior through its thermal and impedance properties.

“As sunlight increases, the electrolyzer naturally heats up. The system is designed so that this warming causes the electrical resistance to drop, allowing electricity to flow more freely,” Professor Amao explained. “This makes the system automatically adjust its electrical behavior.”

“This self-regulating behavior helps keep fuel production more stable throughout the day and automates the system, while reducing dependence on batteries and costly external components,” he added.

When the team tested a device incorporating the technology, it stably produced formic acid from water and CO₂ under real sunlight conditions, even when light intensity fluctuated.

“We were confident that it would be successful, as we previously showcased this research at the ‘Joint Pavilion Iida Group × Osaka Metropolitan University’ exhibition as part of the Osaka Kansai Expo 2025,” Professor Matsubara said. “It successfully generated enough formic acid to power a miniature diorama in the pavilion, showing its potential as an efficient artificial photosynthesis system that could potentially be used to charge applications in our homes.”

The study was published in EES Solar.

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