In a development that could reshape how renewable energy is stored and transported, a team at Osaka University has demonstrated a method that uses sunlight to convert seawater into hydrogen peroxide—a compound that can later be used to generate electricity in fuel cells. The finding, published in a recent study, offers a new twist on solar energy capture, addressing a long-standing challenge: how to keep the lights on after the sun goes down.
The researchers point out that while solar power is abundant during the day, its intermittent nature—due to day-night cycles and weather—limits its reliability. Storing solar energy as chemical fuel, rather than in batteries, is one proposed solution. Previous efforts focused on splitting pure water to harvest hydrogen, but that process is energy-intensive and the resulting gas is difficult to store safely. The Osaka team instead turned to seawater, the planet's most plentiful resource, and produced hydrogen peroxide (H2O2) directly from water and oxygen in the air.
Hydrogen peroxide offers practical advantages over hydrogen gas. It can be stored as an aqueous solution, which is easier and safer to handle, and it holds more energy per unit volume than compressed hydrogen. However, existing methods to produce H2O2 were too energy-hungry to be practical. This is the first time a photocatalytic approach has been efficient enough to make the process viable for fuel cell use.
How the Process Works
The system relies on a new photoelectrochemical cell. When sunlight strikes the photocatalyst, it absorbs photons and triggers chemical reactions that produce H2O2. In a 24-hour test, the concentration of hydrogen peroxide in seawater reached about 48 millimolar (mM), compared to just 2 mM in pure water. The team attributes this boost to the negatively charged chlorine ions in seawater, which enhance the photocatalysis.
While the efficiency still trails other solar power technologies, the researchers see it as a starting point. They plan to refine the materials and reduce costs to make large-scale production feasible. Shunichi Fukuzumi, one of the researchers, stated, “In the future, we plan to work on developing a method for the low-cost, large-scale production of H2O2 from seawater. This may replace the current high-cost production of H2O2 from H2 (from mainly natural gas) and O2.”
The implications extend beyond just another renewable option. If scaled successfully, this method could provide a cleaner way to produce a valuable chemical currently manufactured using fossil fuels. It also offers a potential solution for coastal regions with abundant sunlight, turning an everyday resource into a storable energy source. The study adds to a growing portfolio of alternative energy technologies as the world seeks to cut greenhouse gas emissions.