Chinese researchers have developed an organic catalyst that keeps solar-generated charges separated for about 1,000 times longer than a conventional version.
The material helped produce hydrogen from water at high rates under both ultraviolet and visible light. The findings point to a way of improving organic photocatalysts used in solar hydrogen production.
The study was carried out by researchers at the Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences, together with scientists from the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences.
Their work focuses on photocatalytic water splitting, a process that uses light to separate water into hydrogen and oxygen. The study was published in Nature Synthesis.
A major problem in this process is the rapid recombination of electrons and holes created when a photocatalyst absorbs light. When they recombine too quickly, less of the captured solar energy is available to drive hydrogen production. The researchers designed a material that slows this loss and keeps the charges apart for longer.
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Rigid Structure Controls Energy
The material belongs to a class called covalent organic frameworks (COFs). These are porous structures made by joining organic molecules with strong chemical bonds, and their structures can be adjusted for different applications. Their tunable properties make COFs useful candidates for photocatalytic reactions.
The team focused on the chemical links that connect the building blocks of a COF. In conventional conjugated COFs, flexible links can rotate out of the main molecular plane, which disrupts the movement of electrons and increases energy loss. The researchers replaced these flexible links with a rigid, flat coumarin structure through a one-pot polycondensation process.
The coumarin linkage helped maintain the material’s π-conjugation, which allows electrons to move across the structure more effectively. It also reduced structural movement that can interfere with charge separation. As a result, the new COF maintained separated charges for roughly 1,000 times longer than its imine-linked counterpart.
Faster Electron Transfer To Platinum
The researchers then added platinum nanoparticles as a cocatalyst to help drive the hydrogen-producing reaction. After absorbing light, electrons moved from the COF to the platinum particles in about 407 picoseconds. This transfer allowed the electrons to take part in proton reduction, a key step in generating hydrogen.
Under 440-nanometre light, the coumarin-linked COF produced hydrogen at a rate of 531 millimoles per gram per hour. Its apparent quantum yield reached 37.95% at 405 nanometres, measuring how efficiently incoming light was converted into the chemical process.
The material also remained active under broader visible light. With light above 420 nanometres, it recorded a hydrogen evolution rate of 166 millimoles per gram per hour. This result shows that the catalyst can operate beyond the shorter-wavelength light used for its highest reported production rate.
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A Route Toward Solar Hydrogen
The researchers said the work demonstrates a way to control charge behaviour in conjugated COFs by changing their chemical linkages.
Professor Zhang Tao of NIMTE, a corresponding author, said the approach provides a simple strategy for tuning charge dynamics in these materials. He added that the findings support the design of organic photocatalysts for solar hydrogen production.
Photocatalytic water splitting remains an area of research because it directly links sunlight with hydrogen generation.
Improving how long useful charges survive inside organic catalysts is one way to reduce energy losses during the process. The new COF design gives researchers another approach for developing photocatalysts that make more effective use of absorbed light.
The reported performance will also provide a basis for further testing under practical solar conditions. Future work will determine how the material performs over longer operating periods and in systems designed for larger-scale hydrogen production.
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