If a practical and inexpensive device can directly convert heat into electricity, then it can certainly change the way of energy utilization from various fields such as automobiles to power plants. The thermoelectric conversion efficiency of the new materials produced by the researchers is 20% higher than that of the previous thermoelectric materials, thus further evolving such equipment toward practical application. More importantly, this material does not require any difficult or expensive manufacturing techniques, and it is made of lead telluride, the price of which is not prohibitively high.
We are now wasting a lot of heat, which is released into the atmosphere through the car's exhaust and the power plant's chimney. Thermoelectric materials can use these heat to generate electricity, but so far, these materials are too expensive and inefficient, and therefore cannot be widely used. Thermoelectric technology currently only gains some niche commercial applications. In addition to generating electrical energy, thermoelectric materials can also have the opposite effect, namely the use of electrical current to transfer heat to cool the portable device, or in the car to heat the seat. They are also used as power sources in space missions.
Unlike the previous thermoelectric materials, the new materials described in the paper published in the journal Nature have sufficient conversion efficiency to make the temperature difference power supply practically valuable. The optimum working temperature for this material is approximately 650°C, which is close to the temperature of the exhaust gas emitted from a car traveling on an expressway at a speed of 65 mph. At this temperature, it can convert about 20% of the energy in the exhaust gas into electricity. The electrical energy thus obtained can be used to charge the battery of a hybrid vehicle, or reduce the burden on the alternator on the vehicle and save fuel.
Thermoelectric materials block the heat that passes through them, but allow the electrons to flow, generating electricity. The new material's heat insulation capability is particularly prominent because it utilizes the microscopic partitions, or grain boundaries, inside the material. At the smallest scale, researchers added dopants to the material to disrupt the regular crystal structure of the material on a single atomic scale. In order to destroy the structure on a larger scale, they mix nano-size pieces of the same material, which are 2 to 10 nanometers wide. Finally, by controlling the crystallization of the material during cooling, they produced tiny grains with diameters of several hundred nanometers. Researchers have previously completed each step of these tasks on their own. "We are all combining these first," said Mercouri Kanatzidis, a chemistry professor at Northwestern University who led the study.
The key to the success of this research is to ensure that the partitions in the material do not block the flow of electrons. The researchers used two methods to achieve this requirement. One was to incorporate impurities that would increase the number of electrons in the material, and the other was to select nanostructured fragments that could be automatically oriented in a large scale in a bulk material. Produce pathways that allow electrons to move unimpeded.
John Fairbanks, head of technology development at the U.S. Department of Energy, called this new material "a great step forward," but he also warned that wanting to commercialize this material may face challenges. He said that a thermoelectric device needs both P-type and N-type materials, and this new material itself is only P-type, so it also needs a partner. He also proposed that regulators in the United States and the European Union would be hesitant to use lead-containing materials in cars, even if they contain less lead than the average motor vehicle battery. This material may also be used in industrial environments or power plants to help collect waste heat.
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