Thermoelectrics

High-performance wearable thermoelectric generator  

Lower-cost thermoelectrics Thermoelectric materials convert heat to electricity, making them attractive for heat harvesting or cooling applications. However, many high-performance thermoelectrics are made of expensive or toxic materials. He  et al.  found that a material composed of primarily tin and sulfur could be optimized to have relatively good thermoelectric properties. Introducing about 10% selenium to tin sulfide helped tune these properties by electronic band manipulation. This material is a step toward more earth-abundant, less toxic, and lower-cost thermoelectrics than the telluride-based materials currently in use. Source: High thermoelectric performance in low-cost SnS0.91Se0.09 crystals

BY  SAHNGKI HONG ,  YUE GU ,  JOON KYO SEO ,  JOSEPH WANG ,  PING LIU ,  Y. SHIRLEY MENG ,  SHENG XU ,  RENKUN CHEN SCIENCE ADVANCES 17 MAY 2019:  EAAW0536 Wearable thermoelectrics offers personalized thermoregulation with higher energy efficiency and enhanced thermal comfort.

... Efficiency is a very important factor when thermoelectric materials are used in applications.  The ‘Best Thermoelectric Material’ should have a large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. Mobile app: Thermoelectrics - Apps on Google Play Enter the parameters to estimate the ZT.

Researchers have reported the discovery of a new half-Heusler compound TaFeSb, which demonstrates a record ZT of ~ 1.52 at 973 K. The results are published in  nature COMMUNICATIONS. ( volume 10, Article 270 (2019)) Article: Discovery of TaFeSb-based half-Heuslers with high thermoelectric performance Researchers have found a promising thermoelectric performance in reduced graphene oxide (RGO) nanosheets. A high power factor S2σ = 54.5 µW/cm K2 is achieved. RGO nanosheets can be printable, lightweight and useful for making flexible films. The results are published in nature energy . ( volume 3, pages 148–156 (2018)) Article:  Thermoelectric properties and performance of flexible reduced graphene oxide films up to 3,000 K Researchers from Northwestern University ( Zhao et al. ) have observed exceptionally very low lattice thermal conductivity ~0.23 W/mK at 973 K in SnSe. Such a low thermal conductivity resulted in a record high ZT of 2.6 at 923 K. The work is pu...

..... Measuring the Seebeck coefficient (which is also called "thermopower") is basically very easy. But it requires a proper measuring instrument to do the task.     Seebeck coefficient is the ratio between the potential difference developed ( dV ) and the temperature gradient applied ( dT ).       So, a temperature gradient must be created between the two points/sides of the sample and the resulting voltage ( dV ) must be measured by taking electrical connections from those two points. Meanwhile, the temperatures at the HOT and COLD points must also be measured and then temperature difference be calculated ( dT= Thot - Tcold ). Finally, the ratio dV/dT is nothing but the Seebeck coefficient. The sign of the Seebeck coefficient indicates whether the sample is a p-type or n-type conductor. The positive sign indicates p-type, negative indicates n-type material.

..... The below values are approximate Seebeck coefficient of some of the common metals. All the data is in ( uV/K ) ( Microvolts per Kelvin ) The data is obtained from different sources. These values just give an idea of the magnitude of the Seebeck coefficient in different metals. For exact values please refer standard Thermoelectric Books or respective literature sources. Copper (Cu):    +1.8 Gold (Au):         +2.0 Silver (Ag):       +1.5 Lead (Pb):         -1.2 Nickel (Ni):        -18 Platinum (Pt):   -5.0 Bismuth (Bi):     -70 to -75 Antimony (Sb):  +41 Aluminum (Al):  -1.7 Tellurium (Te):   +500