Researchers discovered an organic semiconductor which can produce hydrogen from water without using an eletric power source.
Source: TechXplore
EPFL researchers have shown that a single organic semiconductor layer can drive either hydrogen or oxygen production, depending only on the molecular layer beneath it. Using this effect, they built the first organic semiconductor-based photocatalyst sheet that splits water using simulated sunlight with no applied bias.
Photocatalyst sheets combine hydrogen- and oxygen-releasing regions side by side on one conductive substrate. This avoids the external wiring of photoelectrochemical cells and the dissolved redox mediators of particle suspensions, which makes the architecture attractive for large-scale solar hydrogen production. Until now, however, these sheets have relied on inorganic semiconductor particles that are difficult to assemble into a working sheet.
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In a study published in Nature Energy, a team led by Dr. Nicolas Diercks and Dr. Jin Su Park of the LIMNO lab at EPFL took a different approach. They deposited a solution-processed semiconducting polymer bulk heterojunction (PBDTTTPD:PNDIHDT) onto FTO substrates modified with self-assembled small molecules whose dipoles point in opposite directions. On a carbazole-based contact (2PACz), the film acts as a photocathode for hydrogen production. On a new naphthalimide-based contact (NI-PA), the same film acts as a photoanode for oxygen production.
The team patterned the two molecules into microdomains by contact printing, then added platinum and iridium-oxide co-catalysts. The resulting sheet split water without bias for more than 2 hours, producing hydrogen and oxygen in the expected 2:1 ratio. The stabilized hydrogen rate of 1.3 µmol h⁻¹ cm⁻² corresponds to a modest solar-to-hydrogen efficiency of about 0.1%.
The study also identifies what limits performance. Shrinking the domains from 1 mm to 100 µm or 10 µm reduced efficiency, because charge extraction is weaker at the boundaries between domains. A simple spray-deposition route for the patterned underlayer shows how the concept could be scaled up. The efficiency is still too low for practical application, but the work sets out a design strategy for organic photocatalyst sheets and points to clear next steps. These include narrower-bandgap acceptors, better charge-selective molecules and more selective co-catalyst deposition.
