The three Laws of Thermodynamics are sometimes simplified as “You Can’t Win, You Can’t Break Even, and Can’t Quit the Game.” The second Law says that energy inevitably leaks out of a system. One obvious example is a car engine; it converts fuel to mechanical motion, but a lot of the energy is lost as heat. In fact, heat is a by-product of many systems, from light bulbs to the human body. It would be wonderful if we could recapture some of that “lost” heat as energy that could do useful work, but most systems require a large differential between two states — think “steam engine” — and it’s difficult to harvest energy from small temperature differentials.
Researchers at Washington State University may have developed a new solution to this problem. They have created a new type of diode for energy harvesting from a heat source. A diode is a solid-state device that only lets electricity flow in one direction in an electrical circuit. This new diode is a multilayered composite of indium selenide, instead of the typical combination of metal and semi-conductor materials. The indium selenide is treated specially to form layers with different properties; one layer acts as a metal, while the next acts as a semi-conductor. The junction between the layers is free of defects, making the device far more effective than traditional diodes. Attach one side to a warmer surface, and the other to a cooler surface, and it produces electricity.
Plenty of obstacles remain before this can be a commercial product. The researchers are looking at ways to synthesize larger quantities of the material so that they can move beyond small scale lab demonstrations. In time, however, this new approach could lead to wearable devices that are powered simply by body heat, and never need recharging or new batteries.