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Fuel cells get a boost
Thursday, 15 October 2009 00:00
Fuel cells, devices that can produce electricity from hydrogen or other fuels without burning them, are considered a promising new way of powering everything from homes and cars to portable devices like cellphones and laptop computers. Their big advantage — the prospect of eliminating emissions of greenhouse gases and other pollutants — has been outweighed by their very high cost, and researchers have been trying to find ways to make the devices less expensive.

Now, an MIT team led by Associate Professor of Mechanical Engineering and Materials Science and Engineering Yang Shao-Horn has found a method that promises to dramatically increase the efficiency of the electrodes in one type of fuel cell, which uses methanol instead of hydrogen as its fuel and is considered promising as a replacement for batteries in portable electronic devices. Since these electrodes are made of platinum, increasing their efficiency means that much less of the expensive metal is needed to produce a given amount of power.

The key to the boost in efficiency, the team found, was to change the surface texture of the material. Instead of leaving it smooth, the researchers gave it tiny stairsteps. This approximately doubled the electrode's ability to catalyze oxidation of the fuel and thus produce electric current. The researchers believe that further development of these surface structures could end up producing far greater increases, yielding more electric current for a given amount of platinum.

Their results are reported Oct. 13 in the Journal of the American Chemical Society. The paper's eight authors include chemical engineering graduate student Seung Woo Lee and mechanical engineering postdoctoral researcher Shuo Chen, along with Shao-Horn and other researchers at MIT, the Japan Institute of Science and Technology, and Brookhaven National Laboratory.

"One of our research focuses is to develop active and stable catalysts," Shao-Horn says, and this new work is a significant step toward "figuring out how the surface atomic structure can enhance the activity of the catalyst" in direct methanol fuel cells.

Resolving a controversy

In their experiments, the team used platinum nanoparticles deposited on the surface of multi-wall carbon nanotubes. Lee says that many people have been experimenting with the use of platinum nanoparticles for fuel cells, but the results of the particle size effect on the activity so far have been contradictory and controversial. "Some people see the activity increase, some people see a decrease" in activity as the particle size decreases. "There has been a controversy about how size affects activity."

The new work shows that the key factor is not the size of the particles, but the details of their surface structure. "We show the details of surface steps presented on nanoparticles and relate the amount of surface steps to the activity," Chen says. By producing a surface with multiple steps on it, the team doubled the activity of the electrode, and the team members are now working on creating surfaces with even more steps to try to increase the activity further. Theoretically, they say, it should be possible to enhance the activity by orders of magnitude.

Shao-Horn suggests that the key factor is the addition of the edges of the steps, which seem to provide a site where it's easier for atoms to form new bonds. The addition of steps creates more of those active sites. In addition, the team has shown that the step structures are stable enough to be maintained over hundreds of cycles. That stability is key to being able to develop practical and effective direct methanol fuel cells.

Team members also hope to understand whether the steps enhance the other part of the process that takes place in a fuel cell. This study looked at the enhancement of oxidation, but the other side of a fuel cell undergoes oxygen reduction. Does the addition of steps to the surface also enhance the oxygen reduction? "We need to find why it does, or why it doesn't," Shao-Horn says. The researchers expect to have answers to that question in the next few months.

 
Silicon brittle? Not this kind!
Wednesday, 14 October 2009 20:04
(PhysOrg.com) -- Silicon, the most important semiconductor material of all, is usually considered to be as brittle and breakable as window glass. On the nanometer scale, however, the substance exhibits very different properties, as Empa researchers from Switzerland have shown by creating minute silicon pillars. If the diameters of the columns are made small enough, then under load they do not simply break off, as large pieces of silicon would, but they yield to the pressure and undergo plastic deformation, as a metal would. This discovery opens the way for completely new design techniques from a materials point of view for mechanical microsystems and in the watch industry.

 
Researchers uncover recipe for controlling carbon nanotubes
Wednesday, 14 October 2009 16:50
(PhysOrg.com) -- Carbon nanotubes hold promise for delivering medicine directly to a tumor; acting as sensors so keen they detect the arrival or departure of a single electron; replacing costly platinum in fuel cells; or as energy-saving transistors and wires, but building them with the right structure has been a challenge.

 
Scientist increase the efficiency of a type of solar cell by incorporating ionic salts
Wednesday, 14 October 2009 07:40
A group of scientists are working on the optimisation of a type of photovoltaic cell (Grätzel cell) that artificially mimics photosynthesis.

 
How Perfect Can Graphene Be?
Tuesday, 13 October 2009 13:11
(PhysOrg.com) -- Physicists have investigated the purest graphene to date, and have found that the material possesses unprecedented high electronic quality. The discovery has raised the bar for this relatively new material, and challenges scientists to find out just how perfect graphene can be.

 
Winzige Kontakte im Visier (source: nanowerk.com)
Tuesday, 13 October 2009 06:17
Dr. Regina Hoffmann vom Physikalischen Institut des KIT untersucht die Struktur und die elektronischen Eigenschaften von Nanokontakten in der Nanoelektronik und konnte fuer ihr Projekt erstmals fuer Karlsruhe einen begehrten ERC Starting Grant des European... (source: nanowerk.com) - RSS widgets and RSS feeds on Feedzilla.com

 
Thermal noise highlights viscoelasticity in micro-cantilever (source: Nanotechweb.org)
Tuesday, 13 October 2009 06:17
Custom-built interferometric AFM deflection sensor captures dissipation process (source: Nanotechweb.org) - RSS widgets and RSS feeds on Feedzilla.com

 
Carbon nanotube components boost satellite lifetimes through improved propulsion (source: nanowerk.com)
Tuesday, 13 October 2009 06:17
Researchers at the Georgia Institute of Technology have won a $6.5 million grant to develop improved components that will boost the efficiency of electric propulsion systems used to control the positions of satellites and planetary probes. (source: nanowerk.com) - News widgets and RSS feeds on Feedzilla.com

 
Sensor biochips could aid in cancer diagnosis and treatment (source: nanowerk.com)
Tuesday, 13 October 2009 06:17
Researchers at the Heinz Nixdorf Chair for Medical Electronics at the Technische Universitaet Muenchen have developed a new test process for cancer drugs. With the help of microchips, they can establish in the laboratory whether a patient's tumor cells wil... (source: nanowerk.com) - News widgets and RSS feeds on Feedzilla.com

 
Graphene Used As Floating-Molecular Carpet To Ornament It With 24-Carat Gold 'Snowflakes'
Monday, 12 October 2009 19:15
(PhysOrg.com) -- In an effort to make graphene more useful in electronics applications, Kansas State University engineers made a golden discovery -- gold "snowflakes" on graphene.

 
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