Separate but Together

<br>

Photocatalytic splitting of water uses sunlight to split water into hydrogen and oxygen. It is an environmentally friendly way to obtain hydrogen for fuel cells.

In the journal Angewandte Chemie, Japanese researchers have now introduced a new method for the production of more effective photocatalysts. Their method uses tiny hollow spheres coated with different cocatalysts on the inside and the outside.

In a photocatalytic water splitting reaction, the catalyst, usually a semiconductor, captures photons. Electrons get excited and rise from the valence band to the conduction band. The electronic voids left behind in the valence band are regarded as positively charged “holes”. If the electrons and holes manage to migrate to the surface of the catalyst before the opposite charges recombine, they can be transferred to water molecules and used to reduce the water to make hydrogen or oxidize it to make oxygen.

New catalyst systems are constantly being researched and developed, but their efficiency has always been found to be lacking. Theoretically, catalysts based on tantalum nitride (Ta3N5) should be especially well-suited candidates for photocatalysis with visible light. However, two main problems have hindered their successful use in practice: First, on the surface of the catalyst, the resulting products, oxygen and hydrogen, immediately react to produce water. Second, the charge separation of the electrons and holes formed in the reaction doesn’t quite work correctly as they recombine too quickly.

Cocatalysts are meant to improve efficiency by capturing the electrons or holes and transferring them to the water. Precious metals like platinum can improve the individual step of reduction to hydrogen; metal oxides such as iridium and cobalt oxide catalyze the oxidation to oxygen. However, equipping photocatalysts with both types of cocatalyst has not resulted in any resounding successes.

A team led by Kazunari Domen at the University of Tokyo had a clever idea: what if both cocatalysts were not uniformly distributed over the catalyst, but instead were spatially separated? To achieve this, the researchers developed a simple method for the production of core/shell microparticles. In the first step, they coated silicon dioxide microspheres with platinum nanoparticles and then with tantalum oxide, which was converted to tantalum nitride by reaction with ammonia in the next step.

The spheres were then coated with either iridium or cobalt oxide. The silicon dioxide core can be selectively dissolved, leaving behind whisper-thin, porous, hollow spheres made of tantalum nitride, coated on the inside with platinum nanoparticles and on the outside with iridium or cobalt oxide. This special construction prevents the two reaction steps from taking place in close proximity, improving the charge separation and thus the photocatalytic activity.

About the Author
Dr. Kazunari Domen is a Professor at the University of Tokyo, Deparrtment of Chemical System Engineering. He has been investigating photocatalysis for water splitting to produce hydrogen for more than 30 years. He is now the president of Catalysis Society of Japan.
Author: Kazunari Domen, University of Tokyo (Japan),
http://www.domen.t.u-tokyo.ac.jp/english/index_framepage_E.html
Title: Core/Shell Photocatalyst with Spatially Separated Cocatalysts for Efficient Reduction and Oxidation of Water

Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201303693

Media Contact

Kazunari Domen Angewandte Chemie

All latest news from the category: Life Sciences and Chemistry

Articles and reports from the Life Sciences and chemistry area deal with applied and basic research into modern biology, chemistry and human medicine.

Valuable information can be found on a range of life sciences fields including bacteriology, biochemistry, bionics, bioinformatics, biophysics, biotechnology, genetics, geobotany, human biology, marine biology, microbiology, molecular biology, cellular biology, zoology, bioinorganic chemistry, microchemistry and environmental chemistry.

Back to home

Comments (0)

Write a comment

Newest articles

Lighting up the future

New multidisciplinary research from the University of St Andrews could lead to more efficient televisions, computer screens and lighting. Researchers at the Organic Semiconductor Centre in the School of Physics and…

Researchers crack sugarcane’s complex genetic code

Sweet success: Scientists created a highly accurate reference genome for one of the most important modern crops and found a rare example of how genes confer disease resistance in plants….

Evolution of the most powerful ocean current on Earth

The Antarctic Circumpolar Current plays an important part in global overturning circulation, the exchange of heat and CO2 between the ocean and atmosphere, and the stability of Antarctica’s ice sheets….

Partners & Sponsors