A team of physicists last week announced their creation of a device that converts car exhaust into renewable energy. The scientists are based at Washington State University, and their efforts represent a big step in the burgeoning field of thermoelectrics, the use of converted heat to generate alternative forms of energy. Heat harvesting for a number of different purposes is creating considerable interest.
The device uses a new type of diode—the van der Waals Schottky diode—that basically turns heat into electricity at a rate three times more efficiently than silicon. The heat can be kept as a kind of storable current. Conversion of storable battery power from heat the team envisions is another related project. This area of thermoelectrics addresses issues related to the difficulty of fully harnessing the heat that is created from everything from cars to appliances.
Heat conversion is typically done through the use of diodes, devices made for the purpose of conducting electric current flow in one direction. The two most common types are light emitting diodes, or LED, and the Schottky diodes, which involves a semiconductor material being joined with a metal to achieve heat conversion through conducting electricity flow. Although both types of diodes are industry standards, study co-author Matthew McCluskey was quick to point out their limitations when it comes to heat conversion:
“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...These imperfections trap electrons, impeding the flow of electricity.” The name van der Waals Schottky, therefore is a nod to the Schottky diode, but also an improvement on something which the team acknowledge is already working fairly well.
The key distinguishing feature is that in place of silicon for the diode, the team used a crystalline compound known as indium selenide (InSe), which meant that one layer could function as a metal and the other as a semiconductor, essentially combining the process into one.
On the subject of important future implications, WSU team lead physicist Yi Gu sounded very optimistic:
“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,” said Yi Gu, who led the WSU study. “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.”
The need for renewable power is urgent, and with this big step, physicists are hopeful that future work in the area will be very fruitful.