Battery-Free Device Only Needs Water, Sunlight, and CO2 to Make Fuel

Researchers at Osaka Metropolitan University have developed a new artificial photosynthesis system that can generate solar fuel more consistently without relying on battery-based control systems.

The technology could provide a simpler and potentially lower-cost approach to storing clean energy.

The breakthrough was achieved by integrating a self-regulating chemical component directly into the electrolyzer, eliminating the need for one of the expensive components commonly used in similar systems.

Like photosynthesis in plants, artificial photosynthesis uses sunlight to convert water and carbon dioxide into useful fuels. One example is formic acid, a chemical that can store energy for future use.

How the System Produces Fuel

An important part of the process is the electrolyzer, which converts electricity generated by solar cells into chemical energy. This allows fuels such as formic acid to be produced and stored.

A major challenge for artificial photosynthesis systems is maintaining efficiency as sunlight levels change throughout the day. To solve this, many systems use Maximum Power Point Tracking (MPPT), a control method that continuously adjusts voltage and current to keep solar cells operating at peak efficiency.

However, MPPT systems typically require batteries and additional electronic components to stabilize energy flow, increasing both cost and complexity.

Self-Regulating Design

To simplify the process, a research team led by Associate Professor Yasuo Matsubara and Professor Yutaka Amao at the Research Center for Artificial Photosynthesis at Osaka Metropolitan University, in collaboration with Iida Group Holdings Co., Ltd, redesigned the electrolyzer using a special solid electrolyte.

In the new system, the electrolyzer performs the MPPT function on its own, removing the need for batteries and external control hardware.

Instead of using separate electronics, converters, and batteries to optimize performance, the electrolyzer automatically adjusts its electrical characteristics by changing its thermal and impedance properties.

Professor Amao explained:

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. 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.

Successful Outdoor Testing

Researchers tested a prototype equipped with the new technology under real outdoor sunlight. The system successfully and consistently produced formic acid from water and CO2, even as sunlight levels fluctuated.

The research findings were published in the journal EES Solar.