Cutting batteries out of artificial photosynthesis could make solar fuel systems simpler and cheaper.
Researchers at Osaka Metropolitan University say they have built an artificial photosynthesis system that generates solar fuel more consistently without battery-based control equipment. The team said the advance came from integrating a self-regulating chemical component directly into the electrolyzer.
Artificial photosynthesis uses sunlight to transform water and carbon dioxide into energy-rich compounds. One product is formic acid, a chemical that can serve as a fuel and a way to store energy.
In these systems, an electrolyzer converts electricity from solar cells into chemical energy, which is then stored in fuels such as formic acid. A key problem is keeping the system operating efficiently as sunlight changes during the day.
Many systems deal with that by using Maximum Power Point Tracking, or MPPT, which adjusts voltage and current so solar cells can deliver the highest possible power output. But conventional MPPT setups usually rely on batteries and extra electronic components to smooth energy flow, adding cost and complexity.
To get around that, a team led by Associate Professor Yasuo Matsubara and Professor Yutaka Amao at the Research Center for Artificial Photosynthesis at Osaka Metropolitan University, working with Iida Group Holdings Co., Ltd, redesigned the electrolyzer itself.
The researchers used a specially designed solid electrolyte built directly into the device. They said that lets the electrolyzer perform the MPPT function on its own, without battery-based control systems.
Instead of depending on external electronics, converters or batteries, the electrolyzer changes its electrical characteristics 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 said. “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.
In outdoor testing, the system consistently produced formic acid from water and carbon dioxide even as sunlight levels changed.
“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 findings were published in EES Solar in a paper by Yasuo Matsubara, Hinako Kawakami, Yasuhito Kajita and Yutaka Amao.
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