Featured Research

from universities, journals, and other organizations

Catalysis: Optimizing water splitting

Date:
September 28, 2012
Source:
The Agency for Science, Technology and Research (A*STAR)
Summary:
Computer simulations of a metal–sulfide alloy unlock the secrets to designing solar-powered catalysts that generate hydrogen fuel from water.

Water. Splitting water molecules to produce hydrogen will become more efficient with newfound knowledge on the key electronic properties needed to turn special alloys into a long-lived photocatalyst.
Credit: photocreo / Fotolia

Computer simulations of a metal-sulfide alloy unlock the secrets to designing solar-powered catalysts that generate hydrogen fuel from water.

Partnerships can pay off when it comes to converting solar into chemical energy. By modeling a cadmium sulfide (CdS)-zinc sulfide (ZnS) alloy with special computational techniques, a Singapore-based research team has identified the key photocatalytic properties that enable this chemical duo to 'split' water molecules into a fuel, hydrogen gas (H2). The theoretical study was published by Jianwei Zheng from the A*STAR Institute of High Performance Computing and his co-workers.

Chemists had already identified CdS and ZnS semiconductors as promising photocatalysts for water splitting. However, both came with a drawback related to the size of their so-called 'band gap' -- the energy difference between occupied and unoccupied electronic states that determine photo-activity. While CdS can readily harvest solar energy because of its small band gap, it needs a metal co-catalyst to produce H2. On the other hand, ZnS requires high-energy ultraviolet light to initiate water splitting owing to its large band gap.

Recently chemists had overcome these problems by alloying CdS and ZnS together into a 'solid solution': a physical state where Zn ions are distributed homogenously inside the crystal lattice of CdS. Altering the proportion of ZnS in these alloys enables production of photocatalysts with tunable responses to visible light and high H2 evolution rates in water. Improving the design of a Cd-ZnS solid solution is difficult, because its underlying mechanism is poorly understood.

As a workaround, Zheng and his co-workers used a technique known as 'special quasi-random structures' (SQS) to mimic a completely random alloy with a series of small, periodic models. After carefully working to correlate experimental random hexagonal crystals with their SQS approximations, they calculated the electronic properties of the Cd-ZnS solid solution using hybrid density functional theory -- a computational method that gives accurate descriptions of band gaps.

When the researchers gradually increased the Zn content of their model alloy, they saw that the band gap deviated from a linear combination of the two components. This effect, known as band 'bowing', arises from volume deformations within the Cd-ZnS solid solution and is an essential parameter for predicting catalytic solar H2 production.

Further calculations revealed that the alloy's high catalytic activity stemmed from obvious elevation of the position of unoccupied electronic states, and a subtle change in the position of occupied electronic states, as the amount of Zn increased. But to retain strong light harvesting capabilities and to avoid premature corrosion, the team proposes an equal ratio of ZnS to CdS for optimal photocatalytic water splitting.


Story Source:

The above story is based on materials provided by The Agency for Science, Technology and Research (A*STAR). Note: Materials may be edited for content and length.


Journal Reference:

  1. Jian-Chun Wu, Jianwei Zheng, Chelsey L. Zacherl, Ping Wu, Zi-Kui Liu, Rong Xu. Hybrid Functionals Study of Band Bowing, Band Edges and Electronic Structures of Cd1–xZnxS Solid Solution. The Journal of Physical Chemistry C, 2011; 115 (40): 19741 DOI: 10.1021/jp204799q

Cite This Page:

The Agency for Science, Technology and Research (A*STAR). "Catalysis: Optimizing water splitting." ScienceDaily. ScienceDaily, 28 September 2012. <www.sciencedaily.com/releases/2012/09/120928093315.htm>.
The Agency for Science, Technology and Research (A*STAR). (2012, September 28). Catalysis: Optimizing water splitting. ScienceDaily. Retrieved October 21, 2014 from www.sciencedaily.com/releases/2012/09/120928093315.htm
The Agency for Science, Technology and Research (A*STAR). "Catalysis: Optimizing water splitting." ScienceDaily. www.sciencedaily.com/releases/2012/09/120928093315.htm (accessed October 21, 2014).

Share This



More Matter & Energy News

Tuesday, October 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Graphene Paint Offers Rust-Free Future

Graphene Paint Offers Rust-Free Future

Reuters - Innovations Video Online (Oct. 21, 2014) British scientists have developed a prototype graphene paint that can make coatings which are resistant to liquids, gases, and chemicals. The team says the paint could have a variety of uses, from stopping ships rusting to keeping food fresher for longer. Jim Drury reports. Video provided by Reuters
Powered by NewsLook.com
Gulfstream G500, G600 Unveiling

Gulfstream G500, G600 Unveiling

Flying (Oct. 20, 2014) Watch Gulfstream's public launch of the G500 and G600 at their headquarters in Savannah, Ga., along with a surprise unveiling of the G500, which taxied up under its own power. Video provided by Flying
Powered by NewsLook.com
Japanese Scientists Unveil Floating 3D Projection

Japanese Scientists Unveil Floating 3D Projection

Reuters - Innovations Video Online (Oct. 20, 2014) Scientists in Tokyo have demonstrated what they say is the world's first 3D projection that floats in mid air. A laser that fires a pulse up to a thousand times a second superheats molecules in the air, creating a spark which can be guided to certain points in the air to shape what the human eye perceives as an image. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-Fuel Impala

Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-Fuel Impala

3BL Media (Oct. 20, 2014) Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-fuel Impala Video provided by 3BL
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins