Researchers report new thermoelectric material with high power factors

Researchers report new thermoelectric material with high power factors
SEM images of the material hot-pressed at a) 1123 K, b)1173 K, c) 1273 K, and d)1373 K. Credit: University of Houston

With energy conservation expected to play a growing role in managing global demand, materials and methods that make better use of existing sources of energy have become increasingly important.

Researchers reported this week in the Proceedings of the National Academy of Sciences that they have demonstrated a step forward in converting waste heat - from industrial smokestacks, or even automobile tailpipes - into electricity.

The work, using a thermoelectric compound composed of niobium, titanium, iron and antimony, succeeded in raising the material's density dramatically by using a very hot pressing temperature - up to 1373 Kelvin, or about 2,000 degrees Fahrenheit - to create the material.

"The majority of industrial energy input is lost as waste heat," the researchers wrote. "Converting some of the waste heat into useful electrical will lead to the reduction of fossil fuel consumption and CO2 emission."

Thermoelectric materials produce electricity by exploiting the flow of heat current from a warmer area to a cooler area, and their efficiency is calculated as the measure of how well the material converts heat - often waste heat generated by power plants or other industrial processes - into power. For example, a material that takes in 100 watts of heat and produces 10 watts of electricity has an efficiency rate of 10 percent.

That's the traditional way of considering thermoelectric materials, said Zhifeng Ren, MD Anderson Professor of Physics at the University of Houston and lead author of the paper. But having a relatively high conversion efficiency doesn't guarantee a high power output, which measures the amount of power produced by the material rather than the rate of the conversion.

Because is an abundant - and free - source of fuel, the conversion rate is less important than the total amount of power that can be produced, said Ren, who is also a principal investigator at the Texas Center for Superconductivity at UH. "In the past, that has not been emphasized."

In addition to Ren, researchers involved in the project include Ran He, Jun Mao, Qing Jie, Jing Shuai, Hee Seok Kim, Yuan Liu and Paul C.W. Chu, all of UH; Daniel Kraemer, Lingping Zeng and Gang Chen of the Massachusetts Institute of Technology; Yucheng Lan of Morgan State University, and Chunhua Li and David Broido of Boston College.

The researchers tweaked a compound made up of niobium, iron and antimony, replacing between 4 and 5 percent of the niobium with titanium. Processing the new compound at a variety of high temperatures suggested that a very high temperature - 1373 Kelvin - resulted in a material with an unusually high .

"For most , a power factor of 40 is good," Ren said. "Many have a power factor of 20 or 30."

The new material has a power factor of 106 at room temperature, and researchers were able to demonstrate an output power density of 22 watts per square centimeter, far higher than the 5 to 6 watts typically produced, he said.

"This aspect of thermoelectrics needs to be emphasized," he said. "You can't just look at the efficiency. You have to look also at the power factor and power output."


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More information: Achieving high power factor and output power density in p-type half-Heuslers Nb1-xTixFeSb, Proceedings of the National Academy of Sciences,
www.pnas.org/cgi/doi/10.1073/pnas.1617663113
Citation: Researchers report new thermoelectric material with high power factors (2016, November 14) retrieved 26 June 2019 from https://phys.org/news/2016-11-thermoelectric-material-high-power-factors.html
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Nov 15, 2016
This stuff sounds like it has some serious possibilities compared to the regular materials.

Nov 15, 2016
https://en.wikipe...r_factor
Materials with a high power factor are able to 'generate' more energy (move more heat or extract more energy from that temperature difference) in a space-constrained application, but are not necessarily more efficient in generating this energy.


Thermoelectrics are still practically useless because of the low conversion efficiency. Now they're just useless in a smaller package.

In most applications, such as drawing electricity out of the waste heat of a powerplant, the size is not at a premium. The efficiency is low because the waste heat comes out at under 100 C and there's only a small temperature difference across the device: 50-60 degrees or so against the ambient conditions. In that situation, even a theoretically perfect converter can only reach 15-16% efficiency. The practical thermoelectric converter does about 4-5% and the energy recovered is neglible at best.


Nov 15, 2016
Don't convert, Capture! Don't aim to distribute energy, aim to reuse it in house. Not enough people using common sense now days. For example, a water generator could convert 50% of the heat into power. Water could then transfer the remainer to wherever the plant could use heat. Create something to take advantage of the remaining heat rather than letting go to waste.
In the distance future maybe powerlines could be replaced by fibre optics; infrared or otherwise. That won't happen until somebody figures out how to economically make electrons out of mostly photons.

Nov 15, 2016
Really, I'm waiting on a method to distribute heat in the grid. Skip the conversion, everyone needs heat right.

Nov 16, 2016
Really, I'm waiting on a method to distribute heat in the grid. Skip the conversion, everyone needs heat right.


https://en.wikipe..._heating

It is common in Europe. It's just a well-insulated water pipe, and the buildings tap into it through a heat exchanger. Both open and closed loops exist - the older tend to be open loop and dump the leftover heat out the other end.

The downside is that wind and solar energy don't play well with the heating grid, because the electricity and heat generation from a co-generation plant are linked and cannot change arbitrarily in a hurry. They're characteristically baseload powerplants because of the large amount of thermal mass in the system, and they become inefficient if you force them to throttle.

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