Turning sunlight into clean hydrogen fuel is one of the most promising ways to produce energy without carbon emissions.
Hydrogen can be used to power vehicles, store renewable energy, or generate electricity, with water as the only byproduct.
However, one major challenge has slowed progress: most materials used to capture sunlight cannot use a large portion of the sun’s energy.
Now, researchers at the Institute of Science Tokyo have developed a new photocatalyst that can absorb long-wavelength visible light, allowing it to use more sunlight than conventional systems.
This breakthrough could significantly improve the efficiency of solar hydrogen production and help bring sustainable hydrogen technologies closer to everyday use.
Photocatalysts are materials that absorb light and use that energy to drive chemical reactions, such as splitting water into hydrogen and oxygen.
Many existing photocatalysts only absorb high-energy visible light, leaving much of the solar spectrum unused. In real outdoor conditions, this limits how much hydrogen can be produced.
To solve this problem, the research team designed a dye-sensitized photocatalyst. In these systems, a dye molecule acts like a tiny solar antenna.
It absorbs light and transfers the energy to the catalyst, which then uses it to generate hydrogen. Most dye-sensitized systems rely on dyes containing the metal ruthenium, which can only absorb visible light up to about 600 nanometers.
The researchers made a key change by replacing ruthenium with osmium at the center of the dye molecule. This allowed the new dye to absorb much longer wavelengths of visible light, extending up to around 800 nanometers.
These longer wavelengths make up a large portion of sunlight, especially under cloudy skies or indirect light.
Because the new dye can capture more of the solar spectrum, it produces more excited electrons. These electrons are essential for driving the chemical reactions that release hydrogen. As a result, the new photocatalyst achieved hydrogen production rates up to twice as high as those of traditional systems under the same conditions.
The improvement is linked to a physical effect associated with heavy metals like osmium.
This effect allows electrons to move into lower-energy states that can be activated by longer-wavelength light. In simple terms, osmium helps the catalyst make better use of gentler, less energetic sunlight that was previously wasted.
This ability is especially important for real-world solar applications, where sunlight is often weak or scattered.
Technologies such as artificial photosynthesis, solar fuel generation, and renewable hydrogen systems could benefit greatly from materials that perform well even under less-than-ideal lighting.
While further research is needed to improve durability, cost, and large-scale manufacturing, the study provides an important step forward. By expanding the range of usable sunlight, the new photocatalyst moves sustainable hydrogen production closer to being practical, efficient, and widely available.
