New material aids energy conversion

Researchers have created a new material capable of converting waste heat to electricity with high levels of efficiency.

The scientists modified a compound made of niobium, iron and antimony, substituting between four and five percent of the niobium with titanium. Using hot pressing – a high pressure, low strain rate technique using metallic powders – at 1373°K (1100°C) they created a material with an unusually high power output.

Professor Zhifeng Ren, from the University of Houston and lead author said: “For most thermoelectric materials, a power factor of 40 is good. Many have a power factor of 20 or 30.” The new material has a power factor of 106 at room temperature and an output density of 22 watts per cm². This is far higher than the five or six watts typically produced by these materials.

Thermoelectric materials produce electricity by taking advantage of heat flowing from a warm to a cool area. Their efficiency rate is calculated as a measure of how well the material converts heat into power – however a high efficiency rate doesn’t guarantee a high power output.

The international group of researchers of the study published in Proceedings of the National Academy of Science, wrote: “The majority of industrial energy input is lost as waste heat. Converting some of the waste heat into useful electrical power will lead to the reduction of fossil fuel consumption and CO₂ emission.”

The excess heat converted into electricity was from industrial smokestacks, power generating plants and even car tailpipes. "This aspect of thermoelectrics needs to be emphasised," Dr Ren said. "You can't just look at the efficiency. You have to look also at the power factor and power output."

The team of researchers were from the University of Houston, Berkeley National Laboratory, Morgan State University and universities in China.