Battery-free artificial photosynthesis stabilises solar-fuel output, Osaka team reports
Osaka Metropolitan University built a battery-free artificial photosynthesis system that turns CO2 and water into formic acid fuel, stable as sunlight shifts.
Photo by Siarhei Nester on Pexels
Researchers in Japan have built an artificial photosynthesis system that makes a liquid solar fuel from carbon dioxide and water and keeps producing it steadily as sunlight rises and falls, without the batteries that such systems normally need. Osaka Metropolitan University set out the design in an announcement on 10 June 2026, drawn from a study published in the journal “EES Solar” on 20 March 2026. The work was led by Associate Professor Yasuo Matsubara and Professor Yutaka Amao at the university’s Research Center for Artificial Photosynthesis, with Iida Group Holdings Co., Ltd.
The fuel is formic acid, made by using sunlight to combine CO2 and water. The change the team made sits inside the electrolyzer — the part that turns the solar cell’s electricity into chemical energy — and lets the device regulate itself, removing a costly piece of hardware from the system.
How the battery-free artificial photosynthesis system works
In an artificial photosynthesis system, a solar cell generates electricity and an electrolyzer uses that electricity to drive the chemistry that stores energy as fuel. Sunlight is not steady, so most systems add Maximum Power Point Tracking (MPPT): a control method that constantly adjusts voltage and current to pull the most power from the solar cell. Conventional MPPT relies on batteries and extra electronics to smooth the energy flow, which raises both the cost and the complexity of the system.
The Osaka group built a special solid electrolyte into the electrolyzer so that the electrolyzer itself performs the MPPT job. Instead of external electronics, the device adjusts its own electrical behaviour 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 stated. That self-regulation, he added, keeps fuel production more stable through the day while cutting the dependence on batteries and costly external parts.
The two approaches differ mainly in what does the controlling, as summarised below.
| Feature | Conventional MPPT system | Chemical MPPT system (this study) |
|---|---|---|
| How peak power is tracked | External electronics adjust voltage and current | Electrolyzer self-adjusts via thermal and impedance properties |
| Batteries and converters | Required | Not required |
| System cost and complexity | Higher | Lower |
| Behaviour under fluctuating sunlight | Needs active control to stay stable | Stays stable automatically |
| Fuel produced | Depends on system | Formic acid from CO2 and water |
Source: Osaka Metropolitan University; Matsubara et al., “EES Solar”, 2026.
Why stable artificial photosynthesis matters
Tying fuel output to the weather is one of the practical problems with solar-driven chemistry, the same intermittency challenge that shapes the rest of the energy transition — a question Winss Solutions examines in its look at whether renewable energy is really unreliable due to intermittency. When the team tested a device built with the new electrolyzer, it produced formic acid from water and CO2 under real sunlight even as the light intensity changed. Because the control is chemical rather than electronic, the system needs fewer parts to hold that output steady.
The approach also turns carbon dioxide into a usable product rather than releasing it, placing the work within wider efforts to manage emissions across major economies, as covered in the status of carbon emissions in China, the USA and Europe. Formic acid is a liquid at room temperature, which makes it easier to store and move than gaseous hydrogen, and it is studied both as a way to carry hydrogen and as a chemical feedstock.
The team has reported a real-world demonstration. “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, noting that the device “successfully generated enough formic acid to power a miniature diorama in the pavilion.” The result is an early proof of concept rather than a commercial product: it was shown on a small device, and the announcement does not report energy-conversion efficiency, output volume, or cost figures for a scaled system. The group has filed a Japan patent application (2024-124743) on the chemical MPPT method, and the research was funded by Iida Group Holdings.
About the Research Center for Artificial Photosynthesis
Artificial photosynthesis copies the core trick of plants — using light to turn CO2 and water into energy-rich molecules — to make fuels and chemicals from sunlight rather than fossil resources. Osaka Metropolitan University was formed in 2022 from the merger of Osaka City University and Osaka Prefecture University and is one of Japan’s largest public universities. Its Research Center for Artificial Photosynthesis works on catalysts, electrolyzers, and full systems that convert CO2 into fuels such as formic acid, and the group has used public exhibitions, including the Osaka Kansai Expo 2025, to test its prototypes. The continuing aim across the field, and the point of this latest design, is to make solar-fuel production simpler and steadier so it can run reliably on sunlight that never holds still — part of the broader shift mapped in the future of green energy.
Sources: EES Solar; EurekAlert! / Osaka Metropolitan University; Asia Research News
Featured image: photo by Siarhei Nester on Pexels (free Pexels license).
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I specialize in sustainability education, curriculum co-creation, and early-stage project strategy. At WINSS, I craft articles on sustainability, transformative AI, and related topics. When I’m not writing, you’ll find me chasing the perfect sushi roll, exploring cities around the globe, or unwinding with my dog Puffy — the world’s most loyal sidekick.
