A research team made up of material scientists, chemists and physicists from Northwestern University have discovered a new efficient method for turning heat waste into electricity. They have shown that dispersing nanocrystals of rock salt into lead telluride can create a material able to harness electricity from heat-generating processes, systems and equipment, as well as sunlight. The breakthrough could bring important benefits for industries such as car manufacturing, chemicals, and glass and brick making.

The research, which was published in the journal Nature Chemistry [Biswas et al. Nature Chemistry (2011) doi: 10.1038/nchem.955], showed how the material offers a positive thermoelectric figure of merit that should allow 14 % of heat waste to be converted into electricity, a number never before achieved. The discovery means that any industry that uses heat to manufacture products could improve the efficiency of their system and processes.
Mercouri Kanatzidis, Professor of Chemistry in The Weinberg College of Arts and Sciences and co-author of the study, commented “It has been known for 100 years that semiconductors have this property to harness electricity. To make this an efficient process, all you need is the right material, and we have found a recipe or system to make this material.”
The research team has been working for over a decade to develop new materials that have the ability to convert heat to electricity directly and efficiently. Although previous attempts at this type of nanoscale inclusion in thermoelectric materials have managed to improve the energy conversion efficiency of lead telluride (PbTe), they also increased the scattering of electrons, thus lowering the overall conductivity. However, this study is the first time the use of nanostructures in lead telluride has been able to decrease electron scattering and raise the energy conversion efficiency of the material.
Their new work has shown how the selection and placement of the nanocrystals can be tailored to lower thermal conductivity without having to pay a penalty in terms of electrical conductivity, which offers higher enhancement than ever before. The study provides a recipe for increasing the overall efficiency through the positioning of the nanocrystals endotaxial, which creates a smooth path for the electrons to follow without scattering. It is hoped this method will lead to wide applications and similar advances in many materials systems and higher conversion efficiencies in the future.
Vinayak Dravid, a co-author of the paper, said “These types of structures may have other implications in the scientific community that we haven’t thought of yet, in areas such as mechanical behavior and improving strength or toughness. Hopefully others will pick up this system and use it.”



Laurie Donaldson