Tuesday, February 5, 2008

Nanotechnology and Climate Change

If Dustin Hoffman’s film the Graduate was set today, the one word Mr. McGuire says to Ben would be “nanotechnology” rather than “plastics.” Nanotechnology has potential applications in fields as varied as cancer treatment and new materials for aircraft manufacture, as well as a number of interesting possibilities for combating climate change. This is a quick review of some of these possibilities, following a nanotechnology conference I attended a week or so ago. I will try to come back to some of them in more detail in later postings.

Nanotechnology is the science of very small particles, from 1 to 10 nanometers, a nanometer being an American billionth (10 to the power -9) of a meter. These have interesting properties because this is small enough for quantum mechanical effects to emerge and also because the ratio of surface area to volume gets greater as the size of the particles gets smaller. Both these aspects of nanotechnology present exciting possibilities in the fight against climate change.

The first four applications below relate to two major problems with renewable energy: since renewable sources of electricity like wind and sun tend not to be constantly available, we need an efficient way to store the electricity; and since they may also not be available in the place where they are needed, we also need to be able to transmit the electricity efficiently.

The high surface area to volume ratio raises the possibility of creating “ultracapacitors” to replace chemical batteries. A capacitor is just a couple of charged conductors separated by an insulator (or “dielectric”). Connecting the two plates completes a circuit, discharging the plates and releasing the stored energy. The amount of energy which can be stored depends upon the surface area, the distance between the plates, and the type of dielectric. Conventional capacitors are used in electronic circuitry for example, but cannot hold a significant amount of energy like a battery of a similar size can. This all changes at the nano level because of the high surface area to volume ratio. Work at MIT's Laboratory for Electromagnetic and Electronic Systems (LEES) has demonstrated the use of vertically aligned single-wall carbon nanotubes.

[Nanotechnology seems to be closer than I thought! After I had prepared this post, I came across an article in this week's Economist about a prototype hybrid which uses ultracapacitors for regenerative braking. The car was exhibited at the Detroit Auto Show by AFS Trinity and is based upon a Sauturn Vue. I then found it on the web. See for example http://business2-cnet.com.com/8300-10784_3-7-0.html?categoryId=2047.]

Nanotechnology also has applications in chemical batteries. For example, Toshiba has a prototype lithium-iron battery where the surface area of the lithium is dramatically increased and the battery can be safely charged in minutes. This may have application for electric cars, making it feasible to recharge at a roadside station like we currently fill up with gas. (Though a lower tech solution is just to switch out the battery as Israel is planning. I hope to post on electric car news on the next two Wednesdays.) Also, Stanford University announced a new process that may allow lithium-ion batteries, using silicon instead of carbon as the anode, to store 10 times as much energy as current batteries.

Instead of storing energy in the form of electricity or chemically in a battery, there is the possibility of storing hydrogen and using this to generate electricity in a fuel cell. Fuel cells rely on catalysts, and the high area to volume ratio of nanomaterials greatly increases the efficiency of fuel cells.

High Temperature Superconductivity (HTSC) offers the possibility of loss-free transmission of electricity over long distances. Current power grids lose about 20% of the energy, so this could be a huge benefit even with the present generation system. Imagine however the possibility of being able to transmit power to Hamburg from a solar power station in the Sahara! Superconductivity was first observed at temperatures close to absolute zero. Later, materials were found which exhibited HTSC, but “high temperature” is relative; we were still talking about -200 degrees centigrade. A cable made of carbon nanotubes exhibits superconductivity at normal temperatures.

HTSC also offers the possibility of better electric motors. Making the windings superconductive would not only eliminate the losses, making them more energy-efficient, but because there is no heat to dissipate the motors can also be made smaller and lighter.

Quantum dots are semiconductor nanostructures which promise much cheaper and more efficient photovoltaic materials. (Current solar panels typically convert only about 15% of the sun’s energy into electricity.)

The extremely high strength of some nanomaterials, including carbon nanotubes, has obvious advantages in reducing the weight, and hence energy efficiency, of cars, planes, etc. One thing which might not be so obvious is that it will enable us to make flywheels which will run at much higher speeds without disintegrating, which means that for any given size they can store more energy. One possible application of this is in regenerative braking. Current hybrids use a generator to convert kinetic energy recovered from braking into electricity which is stored in the battery, but the energy could also be stored kinetically in a flywheel. The Federation International de l’Automobile (FIA) has recently endorsed the use of such a Kinetic Energy Recovery System (KERS) for Formula 1 racing in 2009. I will probably post more on this.

Finally, GE has announced plans to produce a more efficient incandescent light bulb based on photonic band gap technology, which utilizes a nanostructured mix of materials of different refractive index materials to concentrate the radiation into the visible spectrum. Compared to CFLs this technology promises lower prices, familiar shape and size, and no disposal problems.

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