Thermoelectrics take center stage and nanotech can play a part

In a feature article in this monthâ''s Spectrum, which can be found online here, inventor Lonnie Johnson, who was previously best known for his invention of a high-powered squirt gun, has developed a thermoelectric generator that could operate as an entirely self-contained system, recirculating hydrogen within the generator to be cooled and then heated again in a continuous loop. The beauty of the system is that its design is all-solid-state thereby eliminating the moving parts such as turbines and pistons that result in parasitic losses.

With thermoelectric systems, the basic principle is that the difference between temperatures generates electricity, and in Lonnie Johnsonâ''s proposed system the difference in temperatures could be extreme with the hot side reaching 1100 °Celsius while the cool side remaining at room temperature, 25 °Celsius. This extreme temperature difference imparts high conversion efficiencies for changing the heat difference to electricity of 78 percent Carnot efficiency. This compares rather favorably to both photovoltaic devices that have net conversion efficiencies in the teens and thermionic (or thermoelectric) chips reach only a little higher than 20 percent of Carnot.

This story coincides with recent reports (which can be found here in Spectrum online and was originally reported in the journal Science) of two researchers from MIT and Boston College, Gang Chen of MIT and Zhifeng Ren of BC, who employed the low-tech process of ball milling to the common thermoelectric material bismuth antimony telluride (BiSbTe) and were able to break up the material into random nanostructures that increased the materialâ''s figure of merit, or ZT of the alloy, by 40% from 1 to 1.4.

US Government laboratories over the last 10 years have been focusing on research to develop and improve thermoelectrics, and the results of this work seems to be coming fast and furious.

Everything from computers that power themselves from their own heat generation to automobiles that can power their electrical systems through exhaust heat are being discussed as possibilities. And perhaps most importantly, a technology that can more efficiently than photovoltaics turn the energy from the sun into electricity.

Richard Smalley in his final years took it upon himself to see if nanotechnology could be used to fend off the worldâ''s developing energy crisis. If he could see recent developments, he certainly would be encouraged in general and pleased to see the role nanotechnology is playing.


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