Researchers from Hokkaido University, along with their coworkers in Taiwan and Japan, have enhanced the ability of a material to convert wasted heat into usable electrical energy by confining the movement of spread electrons to a narrow space.
Conceptual drawing of the superlattice in which spread electrons are confined to a narrow space to enhance thermoelectric conversion. (Image credit: Hokkaido University)
The study, which has been reported in the journal
Nature Communications, could make it possible to lower the amount of wasted heat, and therefore wasted fossil fuel, in industries and everyday activities.
Over 60% of energy generated by fossil fuels is lost as waste heat. This problem can be addressed by converting the wasted heat into electricity, called thermoelectric energy conversion. Conversely, it has been difficult to improve the conversion rate due to a trade-off association between the preferred properties inside the material.
When there is a difference in temperature, thermoelectric materials transform heat into electricity. This phenomenon is called the Seebeck effect. In order to improve conversion rates, researchers have been exploring various means to restrict electrons to a narrow space. Later in 2007, scientists designed an artificial superlattice that contained conducting ultrathin layers packed closely by thick insulating layers. While this approach produced a higher voltage, it failed to enhance conversion rates. It has been predicted by researchers that if electrons with longer de Broglie wavelength, meaning they are more spread, are restricted to a narrow conducting layer, performance can be considerably enhanced. However, this method is yet to be proven experimentally.
Headed by Hiromichi Ohta of Hokkaido University, the researchers built a superlattice wherein electrons are spread 30% wider when compared to earlier experiments. This not only led to a relatively higher voltage but also doubled the rate of thermoelectric conversion recorded from previous techniques.
This is a significant step forward towards reducing the amount of heat wasted by power plants, factories, automobiles, computers, and even human bodies,” says Hiromichi Ohta of Hokkaido University.