CNT-based metamaterial turns heat into light: Page 2 of 2

July 17, 2019 //By Julien Happich
Researchers from Rice University have leveraged the anisotropic properties of carbon nanotubes (CNTs) to design a novel type of metamaterial that can take intense heat and channel broadband thermal photons into a narrow bandwidth IR light, which could then be focused onto a photovoltaic cell to generate electricity from waste heat.

Today, waste heat accounts for 67% of all energy used in direct energy production in the United States, note the authors. And today, the most efficient way to turn heat back into electricity is to use turbines, and steam or some other liquid to drive them, with a conversion efficiency under 50%. "Instead of going from heat directly to electricity, we go from heat to light to electricity," explains Naik. "It seems like two stages would be more efficient than three, but here, that's not the case."

A Rice University simulation shows an array of cavities
patterned into a film of aligned carbon nanotubes. When
optimized, the film absorbs thermal photons and emits
light in a narrow bandwidth that can be recycled as electricity.
Illustration by Chloe Doiron.

The new metamaterial could prove to be also much more cost effective than today’s large heat-transfer and turbines installations. Designed on a thin-film substrate, they could also be used to harvest extra energy from untapped industrial heat. Naik estimates that adding the so-called hyperbolic thermal emitters to standard solar cells could boost their efficiency from the current peak of about 22%. "By squeezing all the wasted thermal energy into a small spectral region, we can turn it into electricity very efficiently," he said. "The theoretical prediction is that we can get 80% efficiency."

A proof-of-concept CNT-based device designed at the lab was shown to operate at up to 700ºC and output narrow-band IR light.

Rice University -

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