New Device Converts Vehicle Exhaust Heat Into Electricity

September 25, 2017
Maximum diesel gas exhaust temperatures can reach up to 1,089 F

Researchers at Washington State University have announced the creation of a new multi-layer semi-conductor, called the van der Waals Schottky diode, that coverts heat into electricity three times more efficiently than silicon, another semi-conductor material.

The new thermoelectric device is still in an early stage of development. (Thermoelectric devices are based on materials that create a charge through changes in temperature. NASA's Curiosity Rover is using a thermoelectric propulsion system.)

Yi Gu, an associate professor in WSU’s Department of Physics and Astronomy said, “In the future, one layer could be attached to something hot like a car exhaust or a computer motor and another to a surface at room temperature. The diode would then use the heat differential between the two surfaces to create an electric current that could be stored in a battery and used when needed.”

Maximum diesel gas exhaust temperatures can reach up to 1,089 F

Research by the U.S. Department of Agriculture shows maximum diesel gas exhaust temperatures before the cooler on truck tractors can reach up to 1,089 F, making cars and heavy vehicles a prime source for heat harvesting.

How it works

Schottky diodes are used to guide electricity in a specific direction, similar to how a valve in a water main directs the flow of liquid going through it. They are made by attaching a conductor metal like aluminum to a semiconductor material like silicon.

Instead of combining a common metal like aluminum or copper with a conventional semiconductor material like silicon, Gu’s diode is made from a multilayer of microscopic, crystalline Indium Selenide. He and a team of graduate students used a simple heating process to modify one layer of the Indium Selenide to act as a metal and another layer to act as a semiconductor. The researchers then used a new kind of confocal microscope developed by Klar Scientific, a start-up company founded in part by WSU physicist Matthew McCluskey, to study their materials’ electronic properties.

Unlike its conventional counterparts, Gu’s diode has no impurities or defects at the interface where the metal and semiconductor materials are joined together. The smooth connection between the metal and semiconductor enables electricity to travel through the multilayered device with almost 100 percent efficiency.

“When you attach a metal to a semiconductor material like silicon to form a Schottky diode, there are always some defects that form at the interface,” said McCluskey, a co-author of the study. “These imperfections trap electrons, impeding the flow of electricity. Gu’s diode is unique in that its surface does not appear to have any of these defects. This lowers resistance to the flow of electricity, making the device much more energy efficient.”