Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Catalysis: Optimizing water splitting

01.10.2012
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.

The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing

References:

Wu, J.-C., Zheng, J.-W., Zacherl, C. L., Wu, P., Liu, Z.-K. & Xu R. Hybrid functionals study of band bowing, band edges and electronic structures of Cd1–xZnxS solid solution. Journal of Physical Chemistry C 115, 19741–19748 (2011).

A*STAR Research | Research asia research news
Further information:
http://www.research.a-star.edu.sg/
http://www.researchsea.com

More articles from Life Sciences:

nachricht Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY

nachricht NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Global study of world's beaches shows threat to protected areas

19.07.2018 | Earth Sciences

New creepy, crawly search and rescue robot developed at Ben-Gurion U

19.07.2018 | Power and Electrical Engineering

Metal too 'gummy' to cut? Draw on it with a Sharpie or glue stick, science says

19.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>