Tuning Thermoelectric Materials for Efficient Power Generation
Researchers discover a new way to tune the transport properties of thermoelectric materials for efficient energy conversion.
Thermoelectric materials are a promising technology for sustainable energy production because they convert heat into electricity directly. This technology can potentially revolutionize energy generation, specifically in remote areas without access to conventional energy sources.
A thermoelectric generator. Image used courtesy of Adobe Stock
Thermoelectric Materials for Energy Production
One of the primary reasons why thermoelectric materials are considered sustainable for energy production is that they are highly efficient. The conversion efficiency of thermoelectric devices is 5% to 10%, comparable to conventional power generation technologies. Additionally, thermoelectric devices can operate at low temperatures, making them ideal for harvesting waste heat from industrial processes, automobile engines, and other sources.
Furthermore, thermoelectric materials are environmentally friendly because they don’t produce any harmful emissions or pollutants during operation. Thus making them an excellent choice for power generation in areas with strict environmental regulations, and the impact of traditional power generation technologies is a concern.
There are numerous approaches to make this energy transformation even more efficient. One of the most effective is increasing the thermoelectric figure of merit (ZT) of the materials used. The ZT factor represents the ratio of electrical conductivity to thermal conductivity and shows how effectively the device converts heat into electricity. Materials with high ZT values are more efficient at converting heat into electricity. So increasing the ZT factor is critical for improving the efficiency of thermoelectric devices.
One way to improve the ZT factor is by using nanostructuring to reduce the material's thermal conductivity. By reducing the size of the material's grains, it is possible to scatter phonons, which are heat-carrying particles, and decrease their thermal conductivity. This increases the temperature gradient within the material, improving the conversion efficiency. Another way is to explore or engineer new promising materials for an optimized device design.
Contributing to the ongoing effort of exploring optimized materials, a team of researchers from Max-Planck-Institut für Eisenforschung (MPIE) tuned a new thermoelectric material for efficient energy conversion.
Grain Boundary Engineering for Better Thermoelectric Properties
Many studies suggest that the composition of grain boundaries is critical for the thermal and electrical conductivity of the materials. Also, one can deduce from the ZT factor relationship that it is desirable to have low thermal conductivity and high electrical conductivity. However, grain boundaries reduce both of these conductivities.
Arrangement of the grain boundary phases. Image used courtesy of Max-Planck-Institut für Eisenforschung GmbH
The researchers from MPIE, Northwestern University, and the Leibniz Institute for Solid State and Materials Research Dresden in Germany focused on modifying grain boundaries such that only thermal conductivity lowers. They used a promising thermoelectric alloy, a Ti-doped NbFeSb half-Heusler intermetallic compound. It has excellent thermoelectric properties, good thermal and mechanical robustness, and abundant elements.
The researchers found that increased grain boundaries significantly reduce electrical conductivity. By doping the new alloy with titanium, the grain boundaries are no longer resistive. In this way, the material offers the low thermal conductivity and high electrical conductivity needed.
Data depicting the effect of grain size on electrical transport properties. Image used courtesy of Max-Planck-Institut für Eisenforschung GmbH
The researchers are now exploring new ways for selectively doping grain boundaries. Moreover, they focus on developing new design principles for such promising materials.