Featured Research

from universities, journals, and other organizations

Inexpensive Photochromic Material May Help Next Generation Of Energy-Efficient Windows

Date:
August 26, 1998
Source:
Lawrence Berkeley National Laboratory
Summary:
Scientists at the Department of Energy's Lawrence Berkeley National Laboratory and the University of California, Berkeley have discovered serendipitously an inexpensive material that changes color on exposure to light.

BERKELEY, CA. -- Scientists at the Department of Energy's Lawrence Berkeley National Laboratory and the University of California, Berkeley have discovered serendipitously an inexpensive material that changes color on exposure to light.

The material, which they were studying in an effort to improve the performance of an advanced rechargeable battery, may be useful in developing a next generation of energy-efficient windows that switch from transparent to opaque spontaneously upon exposure to increasing levels of sunlight, or by the application of a small voltage.

Robert Kostecki and Frank McLarnon of Berkeley Lab's Environmental Energy Technologies Division were studying an electrode consisting of thin transparent films of nickel hydroxide [Ni(OH)2] and titanium dioxide [TiO2]. This layered sandwich was formed on glass.

"We were looking for an additive to improve the performance of rechargeable alkaline batteries which use nickel hydroxide electrodes," says chemist Kostecki. "So we added the titanium dioxide film to the nickel hydroxide film in an attempt to inhibit unwanted oxygen gas formation. I wanted to see what would happen when I exposed it to ultraviolet light. When we did this, we saw that the electrode, which had been nearly transparent, darkened. This result indicated that the combination has potential use as either a photochromic device or an electrochromic device, or both."

A photochromic material is one that changes from transparent to a color when it is exposed to light, and reverts to transparency when the light is dimmed or blocked. An electrochromic material changes color when a small electric charge is passed through it. Both photochromic and electrochromic materials have potential applications in many types of devices.

Electrochemical reactions driven by light in the ultraviolet spectrum produce the photochromic behavior. When light strikes the titanium-nickel sandwich, electrons from the Ni(OH)2 layer flow to the TiO2 film. The NiII(OH)2 oxidizes into a form of higher nickel (NiIII and NiIV) oxides. As it does, what was a transparent film gradually darkens into shades of gray and black. When the light is blocked, the reaction reverses itself. Full coloration of the prototype device from transparency to its darkest state requires about 10 minutes.

"They are promising for 'smart' energy-efficient windows and information display panels," says McLarnon. "They can control visible light and solar radiation levels passing through them, so they are able to regulate illumination levels, as well as glare, heat gain and heat loss."

"Smart" windows based on these technologies could remain transparent while the sun is low in the sky, and gradually darken as it rises and begins to heat a building's interior spaces. By keeping the heat out, the building uses less energy for air conditioning, thereby saving money and reducing air pollution associated with burning fossil fuels. Then as the sun sets and exterior light levels decrease, the window will gradually return to transparency. An intriguing advantage of the new material is the ability to "override" its natural response when used as a conventional electrochromic device.

Other possible applications of the material include large-scale photoelectrochromic display panels for computers and other electronic equipment, "smart" windows and rear-view mirrors for cars and trucks, photochromic lenses for sunglasses, and new types of light detectors, optical switches and light intensity meters. Another application is as a low-cost memory device for optical computers. It is the material's ability to store information in a binary form -- transparent or dark, representing zeros and ones -- or to encode data as levels of gray, that makes it a candidate for the display-panel and memory-device applications.

"Several problems have prevented the large-scale fabrication of photochromic and electrochromic devices," says McLarnon. "They include the lack of adequate reversibility (switching back and forth from transparency to a colored state), instability of the material over the long term, and high cost."

Although more research and development is needed, the new material addresses certain problems. "One advantage is that it turns gray on exposure to light," says Kostecki. "Also, you can deposit it on any type of substrate -- glass, plastic or ceramic -- whether it is conductive or not. Current photochromic materials are expensive, whereas electrochromic materials require a conductive substrate. Finally, titanium dioxide and nickel hydroxide are easy to produce and very inexpensive, and are widely used in ceramics, pigments, catalysts and other products."

The research team still must solve some problems and do additional work. "Now, the material darkens mainly in response to the ultraviolet light. We need to modify the film so it will respond efficiently to the solar spectrum," Kostecki explains. "Also, we need to develop technology to produce TiO2 and Ni(OH)2 films which are as uniform and transparent as possible."

Kostecki and McLarnon were assisted by Thomas Richardson (Chemical Sciences Division) in recent stages of this work. A paper by Kostecki, Richardson and McLarnon titled "Photochemical and Photoelectrochemical Behavior of a Novel TiO2/Ni(OH)2 Electrode" has been published in the July issue of the Journal of the Electrochemical Society (Vol. 145, no.7, pp. 2380-2385), and a patent application is pending.

Berkeley Lab is a U.S. Department of Energy National Laboratory located in Berkeley, California. It conducts unclassified research and is managed by the University of California


Story Source:

The above story is based on materials provided by Lawrence Berkeley National Laboratory. Note: Materials may be edited for content and length.


Cite This Page:

Lawrence Berkeley National Laboratory. "Inexpensive Photochromic Material May Help Next Generation Of Energy-Efficient Windows." ScienceDaily. ScienceDaily, 26 August 1998. <www.sciencedaily.com/releases/1998/08/980826083325.htm>.
Lawrence Berkeley National Laboratory. (1998, August 26). Inexpensive Photochromic Material May Help Next Generation Of Energy-Efficient Windows. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/1998/08/980826083325.htm
Lawrence Berkeley National Laboratory. "Inexpensive Photochromic Material May Help Next Generation Of Energy-Efficient Windows." ScienceDaily. www.sciencedaily.com/releases/1998/08/980826083325.htm (accessed July 28, 2014).

Share This




More Matter & Energy News

Monday, July 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Europe's Highest Train Turns 80 in French Pyrenees

Europe's Highest Train Turns 80 in French Pyrenees

AFP (July 25, 2014) Europe's highest train, the little train of Artouste in the French Pyrenees, celebrates its 80th birthday. Duration: 01:05 Video provided by AFP
Powered by NewsLook.com
TSA Administrator on Politics and Flight Bans

TSA Administrator on Politics and Flight Bans

AP (July 24, 2014) TSA administrator, John Pistole's took part in the Aspen Security Forum 2014, where he answered questions on lifting of the ban on flights into Israel's Tel Aviv airport and whether politics played a role in lifting the ban. (July 24) Video provided by AP
Powered by NewsLook.com
Creative Makeovers for Ugly Cellphone Towers

Creative Makeovers for Ugly Cellphone Towers

AP (July 24, 2014) Mobile phone companies and communities across the country are going to new lengths to disguise those unsightly cellphone towers. From a church bell tower to a flagpole, even a pencil, some towers are trying to make a point. (July 24) Video provided by AP
Powered by NewsLook.com
Algonquin Power Goes Activist on Its Target Gas Natural

Algonquin Power Goes Activist on Its Target Gas Natural

TheStreet (July 23, 2014) When The Deal's Amanda Levin exclusively reported that Gas Natural had been talking to potential suitors, the Ohio company responded with a flat denial, claiming its board had not talked to anyone about a possible sale. Lo and behold, Canadian utility Algonquin Power and Utilities not only had approached the company, but it did it three times. Its last offer was for $13 per share as Gas Natural's was trading at a 60-day moving average of about $12.50 per share. Now Algonquin, which has a 4.9% stake in Gas Natural, has taken its case to shareholders, calling on them to back its proposals or, possibly, a change in the target's board. Video provided by TheStreet
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:
from the past week

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