Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Hydrogen sensors are faster, more sensitive

31.05.2005


The same kind of chemical coating used to shed rainwater from aircraft and automobile windows also dramatically enhances the sensitivity and reaction time of hydrogen sensors. Hydrogen sensor technology is a critical component for safety and other practical concerns in the proposed hydrogen economy. For example, hydrogen sensors will detect leaks from hydrogen powered cars and fueling stations long before the gas becomes an explosive hazard.



The discovery was made by a team led by Zhili Xiao, a physicist in the Materials Science Division at the U.S. Department of Energy’s Argonne National Laboratory and an associate professor of physics at Northern Illinois University. The scientists demonstrated that the enhanced sensor design shows a rapid and reversible response to hydrogen gas that is repeatable over hundreds of cycles. A report on the team’s research was published in May in Applied Physics Letters.

The sensor material is made by depositing a discontinuous palladium thin film on a glass slide coated with a grease-like self-assembled monolayer of siloxane anchored to the surface.


"By adding the siloxane self-assembled monolayer, we have changed the thin film dynamics," said Michael Zach, a chemist and holder of the Glenn Seaborg Postdoctoral Fellowship at Argonne. "Other sensors have a response time of several seconds upon exposure to 2 percent hydrogen; ours works in tens of milliseconds." Also, the scientists reported that the enhanced sensors are sensitive enough to detect hydrogen levels as low as 25 parts per million (ppm), far below hydrogen’s lower explosive limit around 40,000 ppm. Their sensitivity and speed are superior to any available commercial sensors.

Palladium is an ideal material for hydrogen sensing because it selectively absorbs hydrogen gas and forms a chemical species known as a palladium hydride. Thick-film hydrogen sensor designs rely on the fact that palladium metal hydride’s electrical resistance is greater than the metal’s resistance. In such systems, the absorption of hydrogen is accompanied by a measurable increase in electrical resistance.

However, a palladium thin-film sensor is based on an opposing property that depends on the nanoscale structures within the thin film. In the thin film, nanosized palladium particles swell when the hydride is formed, and in the process of expanding, some of them form new electrical connections with their neighbors. The increased number of conducting pathways results in an overall net decrease in resistance.

Palladium is good at "wetting" bare glass surfaces – it spreads across the glass in puddle-like clusters a few nanometers thick and tens of nanometers across. After pre-coating the glass with the siloxane monolayer, the Argonne scientists saw a remarkable shift in the size and spatial distribution of the palladium. Like water beading on the surface of a freshly waxed car, the palladium formed granular clusters just a few nanometers across. The gaps between neighboring palladium clusters on the siloxane-coated glass were more numerous and ten times smaller on average than the gaps between the much larger, spread-out clusters on the bare glass.

"The shorter gap distance is important for giving you a fast, sensitive response," said Tao Xu, a chemist and the first inventor of the submitted patent application on fast hydrogen sensors. Even a slight swelling of the clusters produces many more new electrical contacts between neighbors and links together many new pathways for an electrical current to travel.

The scientists also have evidence that the surface treatment of the glass reduces the adhesion – or "stiction" – between the metal and glass that hinders the expansion and contraction of the palladium nanoparticles on bare glass. This effect contributes to the increased speed of the sensor response.

The scientists spent nearly a year optimizing the procedure to make the palladium films on coated glass, and they developed a new test system that could inject hydrogen quickly enough to test the sensors on a millisecond time scale. They say their approach to making sensors is easily scalable to an industrial level. "We are using techniques that the semiconductor industry already uses," Zach said.

The sensor will be affordable too. Although palladium is an expensive precious metal, Zach estimated that the amount in each sensor is so small that the metal cost is less than a penny.

Several outstanding questions include whether the sensors can be made to withstand poisonous contaminants in the air and whether the sensors will stand up to long-term operation. Wai-Kwong Kwok, leader of the Superconductivity and Magnetism group in the Materials Science Division, expressed confidence that these issues can be handled on an engineering level. The sensors are being developed for commercial use by an industrial partner in collaboration with Argonne.

Catherine Foster | EurekAlert!
Further information:
http://www.anl.gov

More articles from Physics and Astronomy:

nachricht CCNY-Yale researchers make shape shifting cell breakthrough
12.12.2018 | City College of New York

nachricht Electronic evidence of non-Fermi liquid behaviors in an iron-based superconductor
11.12.2018 | Science China Press

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Lethal combination: Drug cocktail turns off the juice to cancer cells

A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.

The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...

Im Focus: New Foldable Drone Flies through Narrow Holes in Rescue Missions

A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.

Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...

Im Focus: Topological material switched off and on for the first time

Key advance for future topological transistors

Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...

Im Focus: Researchers develop method to transfer entire 2D circuits to any smooth surface

What if a sensor sensing a thing could be part of the thing itself? Rice University engineers believe they have a two-dimensional solution to do just that.

Rice engineers led by materials scientists Pulickel Ajayan and Jun Lou have developed a method to make atom-flat sensors that seamlessly integrate with devices...

Im Focus: Three components on one chip

Scientists at the University of Stuttgart and the Karlsruhe Institute of Technology (KIT) succeed in important further development on the way to quantum Computers.

Quantum computers one day should be able to solve certain computing problems much faster than a classical computer. One of the most promising approaches is...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

ICTM Conference 2019: Digitization emerges as an engineering trend for turbomachinery construction

12.12.2018 | Event News

New Plastics Economy Investor Forum - Meeting Point for Innovations

10.12.2018 | Event News

EGU 2019 meeting: Media registration now open

06.12.2018 | Event News

 
Latest News

New discoveries predict ability to forecast dementia from single molecule

12.12.2018 | Health and Medicine

CCNY-Yale researchers make shape shifting cell breakthrough

12.12.2018 | Physics and Astronomy

Pain: Perception and motor impulses arise in the brain independently of one another

12.12.2018 | Health and Medicine

VideoLinks
Science & Research
Overview of more VideoLinks >>>