Tag Archives: nanotubes

Rechargeable Nanotube-Based Solar Energy Storage

[div class=attrib]From Ars Technica:[end-div]

Since the 1970s, chemists have worked on storing solar energy in molecules that change state in response to light. These photoactive molecules could be the ideal solar fuel, as the right material should be transportable, affordable, and rechargeable. Unfortunately, scientists haven’t had much success.

One of the best examples in recent years, tetracarbonly-diruthenium fulvalene, requires the use of ruthenium, which is rare and expensive. Furthermore, the ruthenium compound has a volumetric energy density (watt-hours per liter) that is several times smaller than that of a standard lithium-ion battery.
Alexie Kolpak and Jeffrey Grossman from the Massachusetts Institute of Technology propose a new type of solar thermal fuel that would be affordable, rechargeable, thermally stable, and more energy-dense than lithium-ion batteries. Their proposed design combines an organic photoactive molecule, azobenzene, with the ever-popular carbon nanotube.

Before we get into the details of their proposal, we’ll quickly go over how photoactive molecules store solar energy. When a photoactive molecule absorbs sunlight, it undergoes a conformational change, moving from the ground energy state into a higher energy state. The higher energy state is metastable (stable for the moment, but highly susceptible to energy loss), so a trigger—voltage, heat, light, etc.—will cause the molecule to fall back to the ground state. The energy difference between the higher energy state and the ground state (termed ?H) is then discharged. A useful photoactive molecule will be able to go through numerous cycles of charging and discharging.

The challenge in making a solar thermal fuel is finding a material that will have both a large ?H and large activation energy. The two factors are not always compatible. To have a large ?H, you want a big energy difference between the ground and higher energy state. But you don’t want the higher energy state to be too energetic, as it would be unstable. Instability means that the fuel will have a small activation energy and be prone to discharging its stored energy too easily.

Kolpak and Grossman managed to find the right balance between ?H and activation energy when they examined computational models of azobenzene (azo) bound to carbon nanotubes (CNT) in azo/CNT nanostructures.

[div class=attrib]More from theSource here.[end-div]

Andre Geim: in praise of graphene

[div class=attrib]From Nature:[end-div]

Nobel laureate explains why the carbon sheets deserved to win this year’s prize.

This year’s Nobel Prize in Physics went to the discoverers of the one-atom-thick sheets of carbon known as graphene. Andre Geim of the University of Manchester, UK, who shared the award with his colleague Konstantin Novoselov, tells Nature why graphene deserves the prize, and why he hasn’t patented it.

In one sentence, what is graphene?

Graphene is a single plane of graphite that has to be pulled out of bulk graphite to show its amazing properties.

What are these properties?

It’s the thinnest possible material you can imagine. It also has the largest surface-to-weight ratio: with one gram of graphene you can cover several football pitches (in Manchester, you know, we measure surface area in football pitches). It’s also the strongest material ever measured; it’s the stiffest material we know; it’s the most stretchable crystal. That’s not the full list of superlatives, but it’s pretty impressive.

A lot of people expected you to win, but not so soon after the discovery in 2004. Were you expecting it?

I didn’t think it would happen this year. I was thinking about next year or maybe 2014. I slept quite soundly without much expectation. Yeah, it’s good, it’s good.

Graphene has won, but not that much has actually been done with it yet. Do you think it was too soon?

No. The prize, if you read the citation, was given for the properties of graphene; it wasn’t given for expectations that have not yet been realized. Ernest Rutherford’s 1908 Nobel Prize in Chemistry wasn’t given for the nuclear power station — he wouldn’t have survived that long — it was given for showing how interesting atomic physics could be. I believe the Nobel prize committee did a good job.

Do you think that carbon nanotubes were unfairly overlooked?

It’s difficult to judge; I’m a little afraid of being biased. If the prize had been given for bringing graphene to the attention of the community, then it would have been unfair to take it away from carbon nanotubes. But it was given for graphene’s properties, and I think carbon nanotubes did not deliver that range of properties. Everyone knows that — in terms of physics, not applications — carbon nanotubes were not as successful as graphene.

Why do you think graphene has become so popular in the physics community?

I would say there are three important things about graphene. It’s two-dimensional, which is the best possible number for studying fundamental physics. The second thing is the quality of graphene, which stems from its extremely strong carbon–carbon bonds. And finally, the system is also metallic.

What do you think graphene will be used for first?

Two or three months ago, I was in South Korea, and I was shown a graphene roadmap, compiled by Samsung. On this roadmap were approximately 50 dots, corresponding to particular applications. One of the closest applications with a reasonable market value was a flexible touch screen. Samsung expects something within two to three years.

[div class=attrib]More from theSource here.[end-div]