02-Mar-2018 - Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

Nanostructuring increases efficiency of metal-free photocatalysts by factor eleven

Solar–to-hydrogen conversion

Polymeric carbon nitrides exhibit a catalytic effect in sunlight that can be used for the production of hydrogen from solar energy. However, the efficiency of these metal-free catalysts is extremely low. A team at the Tianjin University in China, in collaboration with a group at the Helmholtz-Zentrum Berlin, has increased the catalytic efficiency of these polymeric carbon nitrides by a factor eleven through a simple process resulting in a larger surface area.

One of the major challenges of the energy transition is to supply energy even when the sun is not shining. Hydrogen production by splitting water with the help of sunlight could offer a solution. Hydrogen is a good energy storage medium and can be used in many ways. However, water does not simply split by itself. Catalysts are needed, for instance Platinum, which is rare and expensive. Research teams the world over are looking for more economical alternatives. Now a team headed by Dr. Tristan Petit from the HZB, together with colleagues led by Prof. Bin Zhang from Tianjin University, Tianjin, China, has made important progress using a well-known class of metal-free photocatalysts.

Nanolayers with large pores

Bin Zhang and his team specialise in the synthesis of polymeric carbon nitrides (PCN) that is considered a good candidate as a catalyst for hydrogen production. The PCN molecules form a structure that can be compared to thin layers of filo pastry dough: sheets of this material lie on top of each other tightly packed together. The Chinese chemists have now succeeded by means of a relatively simple two-step heat treatment in separating the individual sheets from each other – the same way that puff pastry separates into individual crispy layers in the oven. The heat treatment produced samples consisting of individual nanolayers with large pores containing different amino groups with specific functionalities.

Amino- and oxygenated groups analysed at BESSY II

Petit and his team investigated a series of these PCN samples at BESSY II. “We were able to determine which amino and oxygenated groups had been deposited in the pores”, PhD-student Jian Ren and co-first author of the publication explains. They could analyse how specific amino groups pull electrons to themselves, a particularly favourable property for splitting water, and how new oxygen-based defects were formed.

Efficiency increased by factor eleven

When combined with nickel as a co-catalyst, those samples of nanostructured PCN actually exhibited record-breaking efficiency, eleven times that of normal PCN under visible light irradiation.

Photocatalytic processes at BESSY II unraveled

“This demonstrates that PCN is an interesting potential catalyst for solar-to-hydrogen production, approaching the efficiency of inorganic catalysts”, explains Petit, who is a Volkswagen Foundation Freigeist Fellow. “Furthermore, this work also shows that soft X-ray spectroscopies are essential tools to unravel possible catalytically active sites on photocatalysts.”

Facts, background information, dossiers
  • polymeric carbon nitrides
  • photocatalysts
  • hydrogen
More about Helmholtz-Zentrum Berlin für Materialien und Energie
More about Tianjin University
  • News

    Lithium-ion batteries that last longer in extreme cold

    When temperatures fall below freezing, cellphones need to be recharged frequently, and electric cars have shorter driving ranges. This is because their lithium-ion batteries’ anodes get sluggish, holding less charge and draining energy quickly. To improve electrical performance in the extre ... more

    Low-cost energy-efficient materials

    An international team of scientists from the National University of Science and Technology "MISIS" (NUST MISIS), Tianjin University (China), as well as from Japan and the United States has developed new energy-efficient iron-based alloys which combine high mechanical and magnetic properties ... more

    Double-layered porous nanotubes with spatially separated photoredox surfaces

    Solar energy conversion of water into H2 through photocatalysis is envisaged to be an attractive approach for H2 production. However, the separation efficiency of charge carriers is the key to improve the efficiency of photocatalytic hydrogen production. A recent study reveals that the doub ... more