EPFL Builds First Organic Photocatalyst Sheet That Splits Water

• EPFL researchers built an organic-semiconductor photocatalyst sheet that split water for over 2 hours with no applied voltage.
• One polymer film makes hydrogen or oxygen depending on the molecular contact printed beneath it.
• Efficiency is about 0.1%, which EPFL says is still too low for practical use.

Researchers at EPFL in Lausanne have built an organic-semiconductor photocatalyst sheet that splits water into hydrogen and oxygen with no applied voltage. It ran under simulated sunlight. The work was published in Nature Energy on Nov. 11, 2026. EPFL calls it the first organic semiconductor-based sheet of its kind.

The design depends on what sits under the light absorber. A single solution-processed polymer blend, PBDTTTPD:PNDIHDT, evolves hydrogen on a carbazole-based contact molecule called 2PACz. On a new naphthalimide-based contact, NI-PA, the same film evolves oxygen. The team printed the two molecules side by side as microdomains on conductive glass, then added platinum and iridium-oxide co-catalysts.

The output is small, and the authors say so. For scale, a University of Tokyo-led team ran a 100-m² array of photocatalyst panels in 2021. Its inorganic strontium titanate photocatalyst reached a maximum of 0.76% solar-to-hydrogen efficiency.

The sheet in numbers

• 1.3 µmol of hydrogen per hour per cm² after 30 minutes of stabilization, with hydrogen and oxygen at the expected 2:1 ratio.
• 0.1% solar-to-hydrogen efficiency, averaged over several independently made devices.
• 26 mg of hydrogen per square meter per hour at the stabilized rate (list.solar calculation).
• 0.72 µmol per hour per cm² after 120 minutes, about 45% below the stabilized rate (list.solar calculation).
• 1,000-µm domains worked best; sheets with 100-µm and 10-µm domains lost more charges at domain boundaries.
• 11.1% is the authors' theoretical efficiency limit for this blend, rising to 16% to 17% with narrower-bandgap polymers.

Photocatalyst sheets place hydrogen- and oxygen-evolving areas on one conductive substrate. That removes the external wiring of photoelectrochemical cells and the dissolved redox mediators that particle suspensions need. Until now such sheets used inorganic particles. The paper cites a sheet of doped strontium titanate and bismuth vanadate on gold at 1.1% efficiency.

A second EPFL lab and UNIST in South Korea took part in the study. In October, a UNIST team reported an all-organic tandem photocathode at 7.9% efficiency. The EPFL group also showed a spray method for patterning the contact molecules, a step toward larger solar fuel devices.

"The efficiency is still too low for practical application," EPFL said in a news release. The lab's next steps are narrower-bandgap acceptors, better charge-selective molecules and more selective co-catalyst deposition. It gave no timeline.