Subscribe to our free daily newsletters
  Energy News  




Subscribe to our free daily newsletters



ENERGY TECH
A Dash Of Disorder Yields Very Efficient Photocatalyst

A nanoscale look at a photocatalyst that is both durable and very efficient. This high-resolution transmission electron microscope image of a titanium dioxide nanocrystal after hydrogenation reveals engineered disorder on the crystal's surface, a change that enables the photocatalyst to absorb infrared light.
by Staff Writers
Berkeley CA (SPX) Feb 01, 2011
A little disorder goes a long way, especially when it comes to harnessing the sun's energy. Scientists from the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) jumbled the atomic structure of the surface layer of titanium dioxide nanocrystals, creating a catalyst that is both long lasting and more efficient than most materials in using the sun's energy to extract hydrogen from water.

Their photocatalyst, which accelerates light-driven chemical reactions, is the first to combine durability and record-breaking efficiency, making it a contender for use in several clean-energy technologies.

It could offer a pollution-free way to produce hydrogen for use as an energy carrier in fuel cells. Fuel cells have been eyed as an alternative to combustion engines in vehicles. Molecular hydrogen, however, exists naturally on Earth only in very low concentrations. It must be extracted from feedstocks such as natural gas or water, an energy-intensive process that is one of the barriers to the widespread implementation of the technology.

"We are trying to find better ways to generate hydrogen from water using sunshine," says Samuel Mao, a scientist in Berkeley Lab's Environmental Energy Technologies Division who led the research. "In this work, we introduced disorder in titanium dioxide nanocrystals, which greatly improves its light absorption ability and efficiency in producing hydrogen from water."

Mao is the corresponding author of a paper on this research that was published online Jan. 20, 2011 in Science Express with the title "Increasing Solar Absorption for Photocatalysis with Black, Hydrogenated Titanium Dioxide Nanocrystals." Co-authoring the paper with Mao are fellow Berkeley Lab researchers Xiaobo Chen, Lei Liu, and Peter Yu.

Mao and his research group started with nanocrystals of titanium dioxide, which is a semiconductor material that is used as a photocatalyst to accelerate chemical reactions, such as harnessing energy from the sun to supply electrons that split water into oxygen and hydrogen. Although durable, titanium dioxide isn't a very efficient photocatlayst. Scientists have worked to increase its efficiency by adding impurities and making other modifications.

The Berkeley Lab scientists tried a new approach. In addition to adding impurities, they engineered disorder into the ordinarily perfect atom-by-atom lattice structure of the surface layer of titanium dioxide nanocrystals. This disorder was introduced via hydrogenation. The result is the first disorder-engineered nanocrystal. One transformation was obvious: the usually white titanium dioxide nanocrystals turned black, a sign that engineered disorder yielded infrared absorption.

The scientists also surmised disorder boosted the photocatalyst's performance. To find out if their hunch was correct, they immersed disorder-engineered nanocrystals in water and exposed them to simulated sunlight. They found that 24 percent of the sunlight absorbed by the photocatalyst was converted into hydrogen when using a sacrificial reagent, a production rate that is about 100 times greater than the yields of most semiconductor photocatalysts under the same conditions. More work needs to be done in order to reach comparable efficiency without the use of a sacrificial reagent, according to Mao.

In addition, their photocatalyst did not show any signs of degradation during a 22-day testing period, meaning it is potentially durable enough for real-world use.

Its landmark efficiency stems largely from the photocatalyst's ability to absorb infrared light, making it the first titanium dioxide photocatalyst to absorb light in this wavelength. It also absorbs visible and ultraviolet light. In contrast, most titanium dioxide photocatalysts only absorbs ultraviolet light, and those containing defects may absorb visible light. Ultraviolet light accounts for less than ten percent of solar energy.

"The more energy from the sun that can be absorbed by a photocatalyst, the more electrons can be supplied to a chemical reaction, which makes black titanium dioxide a very attractive material," says Mao, who is also an adjunct engineering professor in the University of California at Berkeley.

The team's intriguing experimental findings were further elucidated by theoretical physicists Peter Yu and Lei Liu, who explored how jumbling the latticework of atoms on the nanocrystal's surface via hydrogenation changes its electronic properties. Their calculations revealed that disorder, in the form of lattice defects and hydrogen, makes it possible for incoming photons to excite electrons, which then jump across a gap where no electron states can exist. Once across this gap, the electrons are free to energize the chemical reaction that splits water into hydrogen and oxygen.

"By introducing a specific kind of disorder, mid-gap electronic states are created accompanied by a reduced band gap," says Yu, who is also a professor in the University of California at Berkeley's Physics Department. "This makes it possible for the infrared part of the solar spectrum to be absorbed and contribute to the photocatalysis."

This research was supported by the Department of Energy's Office of Energy Efficiency and Renewable Energy. Transmission electron microscopy imaging used to study the nanocrystals at the atomic scale was performed at the National Center for Electron Microscopy, a national user facility located at Berkeley Lab.



Share This Article With Planet Earth
del.icio.usdel.icio.us DiggDigg RedditReddit
YahooMyWebYahooMyWeb GoogleGoogle FacebookFacebook



Related Links
Lawrence Berkeley National Laboratory (Berkeley Lab)
Powering The World in the 21st Century at Energy-Daily.com



Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News


ENERGY TECH
New Reactor Paves The Way For Efficiently Producing Fuel From Sunlight
Pasadena CA (SPX) Jan 21, 2011
Using a common metal most famously found in self-cleaning ovens, Sossina Haile hopes to change our energy future. The metal is cerium oxide-or ceria-and it is the centerpiece of a promising new technology developed by Haile and her colleagues that concentrates solar energy and uses it to efficiently convert carbon dioxide and water into fuels. Solar energy has long been touted as the solut ... read more







ENERGY TECH
Neiker-Tecnalia Creates Air-Conditioned Greenhouse With Alternative Energies

Mexico supplies electricity to wintry Texas

Endeavor Power Recycles 250,000 Pounds Of Electronic Waste Per Month

China and the U.S. sign energy deals

ENERGY TECH
License row holds up Indonesia's coal

Undersea electricity cable envisioned

Iraqi Kurdistan to resume oil exports 'soon'

US Energy Enters Into Acquisition, Exploration And Development Agreement

ENERGY TECH
Construction Begins On Dempsey Ridge Wind Project

India's Suzlon wins $1.28 bn wind power deal

German wind sector hopes for 2011 comeback

U.S. behind China in wind power energy

ENERGY TECH
Enecsys Solar PV Micro-Inverter Gain UL Certification

Duke Energy And SunEdison Announce Completion Of Solar Farm

Pepco Energy To Implement PV Project For US DoE

GSLO Expects Booming iPhone Sales To Drive Demand For Volt

ENERGY TECH
Animals at nuclear sites trapped, tested

Sweden kicks off large-scale nuclear accident exercise

Russia to help Belarus build nuclear power plant

China to boost nuclear power

ENERGY TECH
Rentech Fuels First Cross-Country Drive On 100 Percent Synthetic Diesel

Malaysian peatswamps obliterated for palm oil: study

Scania Receives Large Order For Biofuel Buses In Sweden

Biofuels Production From Integrated Seawater Agriculture System

ENERGY TECH
Slow progress in U.S.-China space efforts

China Builds Theme Park In Spaceport

Tiangong Space Station Plans Progessing

China-Made Satellite Keeps Remote Areas In Venezuela Connected

ENERGY TECH
China farmers to get $15 bn subsidies amid drought

Man, Volcanoes And The Sun Have Influenced Europe's Climate Over Recent Centuries

Senators vow to strip Obama climate power

Uncovering Links Between Ancient Climate Change And Mass Extinction


The content herein, unless otherwise known to be public domain, are Copyright 1995-2010 - SpaceDaily. AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by SpaceDaily on any Web page published or hosted by SpaceDaily. Privacy Statement