Waste heat to be turned into electricity with new thermoelectric material

Researchers from Japan have made a new system that can convert waste heat into electricity. The new candidate, the mixed-semimetal MoSi2, can be used to develop efficient thermoelectric devices.

“We wanted to explore new transverse thermoelectric materials. Recently, the presence of axis-dependent conduction polarity (ADCP) in a material has been recognized as an indicator for TTE generation ability,” explains Dr. Okazaki.

“Mixed-metal conductors like MoSi2 are potential ADCP candidates, but their thermopower generation ability has not been thoroughly investigated.”

Thermoelectric conversion devices offer a promising route for heat-to-energy conversion

The research team revealed that thermoelectric conversion devices offer a promising route for sustainable heat-to-energy conversion.

They are particularly attractive for recovering energy from waste heat, such as that produced by conventional fossil fuel-based engines, improving their overall energy efficiency.

Around 20-50% of the input energy is lost as waste heat in industries. This could be used as a source by thermoelectric conversion devices.

These devices also have the potential to enable portable power generation, for example, to run small sensors in remote locations, according to a press release.

Thermoelectric transport of molybdenum disilicide MoSi2

Published in the journal Communications Materials, the study reveals that the research team investigated the thermoelectric transport of molybdenum disilicide MoSi2 and found that MoSi2 is an ideal transverse thermoelectric material without a magnetic field.

Experimental and first-principles studies confirm that MoSi2 exhibits axis-dependent conduction polarity (ADCP) in both the Seebeck and Hall coefficients.

“Electronic band structure calculations and the following Peltier conductivity calculations show that the mixed-dimensional Fermi surfaces play a crucial role in the emergence of ADCP,” said researchers in the study.

The team revealed that they measured the transport properties of MoSi2 using both experiments and first-principles calculations.

Specifically, they examined the temperature dependence of resistivity and thermal conductivity, as well as longitudinal thermopower, along the material’s two crystallographic axes.

Thermopower measurements demonstrated clear ADCP, which was further confirmed through Hall resistivity measurements.

Currently, most thermoelectric devices rely on the longitudinal thermoelectric effect, in which electricity is generated in the same direction as heat flow.

Such devices generally consist of alternating layers of p- and n-type semiconductors connected in series. p- and n-type semiconductors generate electricity in opposite directions.

When a temperature difference is applied across the device, the charge carriers in these materials move from the hot side to the cold side, generating a voltage. However, stacking many layers increases the electrical contact resistance at their interfaces, which leads to energy losses and limits overall efficiency, as per the release.

The team pointed out that by utilizing a thin film of MoSi2 as an ideal material for TTE applications, a large heat source area could be covered to produce voltage.

Overall, this study represents a new direction for finding TTE materials, paving the way for efficient waste heat recovery systems for a greener future.