Water-splitting Photocatalyst Brought to Light

June 16, 2010 by Kendra Snyder
(a) Structure of pure anatase; (b) N/Ti3+/O vacancy defect complex with O opposite N; (c) "Merging" of two O into central position. In (b) and (c), the Ti3+ ion is obscured from this viewpoint.

(PhysOrg.com) -- To produce "green" fuels, some scientists are looking for a little help from above. Sunlight is the key ingredient in photocatalytic water splitting, a process that breaks down water into oxygen and, most importantly, hydrogen, which could be used in future energy technologies like fuel cells. The problem is that the most effective photocatalysts, like pure titanium dioxide, are only activated by ultraviolet light.

"Of the sunlight that reaches the Earth's surface, only about five percent is ultraviolet light," said NSLS researcher Abdul Rumaiz. "If we can alter to react to visible light, we'd have the power of the entire solar spectrum."

Recently, scientists have found a way to do that by adding, or "doping," a small amount of to titanium dioxide. This slight change makes a big difference in the material's catalytic activity; nitrogen-doped titanium dioxide is highly reactive to .

At the NSLS, Rumaiz and a group of scientists from the National Institute of Standards and Technology and the University of Delaware set out to reveal what’s so special about the doped form of the material.

"There was some controversy surrounding the of nitrogen-doped titanium dioxide," said NIST researcher Joe Woicik. "We wanted to resolve that fundamental issue."

The group analyzed samples made at the University of Delaware with hard x-ray photoelectron spectroscopy (HAXPES) studies at NSLS beamline X24A - the only facility in the United States that performs this advanced technique. HAXPES allows researchers to probe the electronic structure of materials deeper than regular photoemission studies, which are usually limited to surfaces. By combining this data with calculations carried out by the theory group at NIST, the researchers found out how nitrogen affects the overall material.

(a) Theoretical DOS and the experimental valence band for pure anatase TiO2. (b) Theoretical DOS and the experimental valence band for N doped anatase TiO2. The curves have been scaled to equal peak height.

"The addition of nitrogen changed the electronic structure both directly and indirectly," Rumaiz said. "The indirect one has the biggest impact."

By adding nitrogen to the material, a certain amount of oxygen was forced out, he said. The resulting oxygen vacancy, combined with the presence of nitrogen, explains the observed electronic structure

"This research is a really nice example of how closely tied the electronic structure is to the atomic structure of a material," Woicik said.

Other authors include E. Cockayne (NIST) and Hong-Ying Lin, G. Hassnain Jaffari, and S. Ismat Shah (University of Delaware). Their results were published in the December 28, 2009 edition of Applied Physics Letters.

• PhysOrg.com iPhone / iPad Apps
PhysOrg.com Audio Podcasts / iTunes
Join PhysOrg.com on Facebook!
Follow PhysOrg.com on Twitter!

Explore further: Sunlight turns carbon dioxide to methane

More information: A.K. Rumaiz, J.C. Woicik, E. Cockayne, H.Y. Lin, G. H. Jaffari, and S.I. Shah, “Oxygen Vacancies in N Doped Anatase TiO2: Experiment and First-principles Calculations,” Applied Physics Letters, 95, 262111 (2009).

Related Stories

Sunlight turns carbon dioxide to methane

March 5, 2009

Dual catalysts may be the key to efficiently turning carbon dioxide and water vapor into methane and other hydrocarbons using titania nanotubes and solar power, according to Penn State researchers.

Titanium dioxide -- It slices, it dices ...

March 30, 2007

Chemists from the National Institute of Standards and Technology and Arizona State University have proposed an elegantly simple technique for cleaving proteins into convenient pieces for analysis. The prototype sample preparation ...

Carbon Nanotubes Make Fuel Cells Cheaper

February 9, 2009

(PhysOrg.com) -- As fuel cells are becoming more popular due to their potential use in applications such as hydrogen-powered vehicles, auxiliary power systems, and electronic devices, the need for the precious metal platinum ...

Recommended for you

Visualizing single molecules in whole cells with a new spin

December 12, 2017

Cell biologists traditionally use fluorescent dyes to label and visualize cells and the molecules within them under a microscope. With different super-resolution microscopy methods, they can even light up single molecules ...

Two holograms in one surface

December 12, 2017

A team at Caltech has figured out a way to encode more than one holographic image in a single surface without any loss of resolution. The engineering feat overturns a long-held assumption that a single surface could only ...


Adjust slider to filter visible comments by rank

Display comments: newest first

2 / 5 (2) Jun 16, 2010
The "Airy Light" article today says light sent through crystals, light waves bounce inside the crystal, changing their wavelength and color.

These two teams need to get together and discuss how a crystal will work rather than doping.
not rated yet Jun 17, 2010
Nature can give the answers, the plants are doing the same thing, they take H20 and take the H2, and gives us 02,they are doing it from a lots of time and I am sure that they have optimised the proces.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.