Featured Research

from universities, journals, and other organizations

Chemists challenge conventional understanding of how photocatalysis works

Date:
May 19, 2014
Source:
University of California - Riverside
Summary:
Photocatalysts are most often semiconductors, with metals (platinum, gold) added to promote their activity. However, these metals (or 'promoters') are expensive; hence the quest for more economical alternatives. Now a team of chemists has come up with a model to explain this promoting effect that could shift the focus in the search for substitutes of the metals, and help identify better promoters for photocatalysis in the near future.

Photocatalysis -- catalysis assisted by light -- is a promising route to convert solar energy into chemical fuels. Particularly appealing is the possibility to use photocatalysis to split water molecules into molecular hydrogen. Although photocatalysis has been around for many years, the search for viable photocatalysts to facilitate the splitting of water molecules continues to date.

Photocatalysts are most often semiconductors, with metals such as platinum or gold added to promote their activity. However, these metals (or "promoters") are expensive. There is a need, therefore, to find more economical alternatives.

Now a team of chemists at the University of California, Riverside has come up with a model to explain this promoting effect that could shift the focus in the search for substitutes of the metals and help identify better promoters for photocatalysis in the near future.

Study results appear online this week in the Proceedings of the National Academy of Sciences.

The conventional understanding is that the production of hydrogen from water is promoted due to a fast transfer of excited electrons from the semiconductor to the metal. The UC Riverside researchers report experimental evidence that challenges this well-established explanation.

They note in their paper that electron transfer from the semiconductor to the metal may not play a significant role in photocatalysis. Instead, their data support a model where the excited electron promotes the reduction of hydrogen atoms on the surface of the semiconductor, not the metal, and where the reduced atomic hydrogen then migrates from the semiconductor to the metal to recombine and yield molecular hydrogen. In effect, the metal acts as a regular catalyst for the recombination of hydrogen atoms.

"The idea that the function of the metal is to act as a chemical rather than an electronic agent, by recombining hydrogen atoms rather than trapping electrons, is somewhat radical, and has not been proposed before -- as far as we know," said Francisco Zaera, a distinguished professor of chemistry, who led the research. "Our results lead us to argue that what is needed is a good atomic hydrogen recombination catalyst."

Hydrogen is arguably the fuel of the future. Like natural gas or oil, it can be burned to generate large amounts of heat and energy. However, its combustion is clean, producing only water. Although handling of hydrogen, a gas, presents some challenges, it could still be a viable cheap fuel for some applications if good photocatalysts were to be developed.

The model proposed by the UCR team paves the way for identifying better alternatives for photocatalysts used in water splitting.

"Currently, many of the photocatalyst promoters considered are expensive precious metals," Zaera said. "Some scientists are searching for cheaper alternatives, but, in our opinion, perhaps with the wrong premise. In our paper we offer an example of how carbon, which could be a choice based on the conventional model, does not work as a photocatalyst, whereas nickel oxide, which should not work if the conventional model is to be believed, does."

Zaera was joined in the study by Yadong Yin, an associate professor of chemistry, and Christopher Bardeen, a professor of chemistry, both at UCR, and by Ji Bong Yoo, a former postdoctoral researcher in Zaera's lab and the first author of the research paper, Robert Dillon, a former graduate student in Zaera's lab, and Ilkeun Lee, an associate specialist.

The research was funded by a grant to Zaera from the Department of Energy.

Details:

The UCR researchers started working on the research project when Yin's lab made novel yolk-shell nanostructures (with gold nanoparticles inside titania shells) that offered great control of the structural parameters of the samples, something not always easy to do. Once the researchers realized that the photophysical behavior of the titania shells was not affected by the presence of the gold nanoparticle inside, they moved on to study more conventional systems.

"We did not set ourselves to challenge the existing model," Zaera said. "It was only when the photophysical measurements yielded unexpected results that we began working on coming up with an alternative mechanism."

Already, the team is working on further understanding the basics of the chemistry involved in photocatalysis, returning to the use of the


Story Source:

The above story is based on materials provided by University of California - Riverside. The original article was written by Iqbal Pittalwala. Note: Materials may be edited for content and length.


Journal Reference:

  1. Ji Bong Joo, Robert Dillon, Ilkeun Lee, Yadong Yin, Christopher J. Bardeen, and Francisco Zaera1. Promotion of atomic hydrogen recombination as an alternative to electron trapping for the role of metals in the photocatalytic production of H2. PNAS, 2014 DOI: 10.1073/pnas.1405365111

Cite This Page:

University of California - Riverside. "Chemists challenge conventional understanding of how photocatalysis works." ScienceDaily. ScienceDaily, 19 May 2014. <www.sciencedaily.com/releases/2014/05/140519160708.htm>.
University of California - Riverside. (2014, May 19). Chemists challenge conventional understanding of how photocatalysis works. ScienceDaily. Retrieved October 22, 2014 from www.sciencedaily.com/releases/2014/05/140519160708.htm
University of California - Riverside. "Chemists challenge conventional understanding of how photocatalysis works." ScienceDaily. www.sciencedaily.com/releases/2014/05/140519160708.htm (accessed October 22, 2014).

Share This



More Matter & Energy News

Wednesday, October 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Chameleon Camouflage to Give Tanks Cloaking Capabilities

Chameleon Camouflage to Give Tanks Cloaking Capabilities

Reuters - Innovations Video Online (Oct. 22, 2014) — Inspired by the way a chameleon changes its colour to disguise itself; scientists in Poland want to replace traditional camouflage paint with thousands of electrochromic plates that will continuously change colour to blend with its surroundings. The first PL-01 concept tank prototype will be tested within a few years, with scientists predicting that a similar technology could even be woven into the fabric of a soldiers' clothing making them virtually invisible to the naked eye. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Jet Sales Lift Boeing Profit 18 Pct.

Jet Sales Lift Boeing Profit 18 Pct.

Reuters - Business Video Online (Oct. 22, 2014) — Strong jet demand has pushed Boeing to raise its profit forecast for the third time, but analysts were disappointed by its small cash flow. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
Internet of Things Aims to Smarten Your Life

Internet of Things Aims to Smarten Your Life

AP (Oct. 22, 2014) — As more and more Bluetooth-enabled devices are reaching consumers, developers are busy connecting them together as part of the Internet of Things. (Oct. 22) Video provided by AP
Powered by NewsLook.com
What Is Magic Leap, And Why Is It Worth $500M?

What Is Magic Leap, And Why Is It Worth $500M?

Newsy (Oct. 22, 2014) — Magic Leap isn't publicizing much more than a description of its product, but it’s been enough for Google and others to invest more than $500M. Video provided by Newsy
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