n-type thermoelectric material Mg ₂ Sn _0.75 Ge _0.25 for high power generation

Abstract

Thermoelectric power generation is one of the most promising techniques to use the huge amount of waste heat and solar energy. Traditionally, high thermoelectric figure-of-merit, ZT, has been the only parameter pursued for high conversion efficiency. Here, we emphasize that a high power factor (PF) is equivalently important for high power generation, in addition to high efficiency. A new n-type Mg 2 Sn-based material, Mg 2 Sn 0.75 Ge 0.25 , is a good example to meet the dual requirements in efficiency and output power. It was found that Mg 2 Sn 0.75 Ge 0.25 has an average ZT of 0.9 and PF of 52 μW·cm ·K−2 over the temperature range of 25-450°C, a peak ZT of 1.4 at 450°C, and peak PF of 55 μW·cm·K −2 at 350°C. By using the energy balance of one-dimensional heat flow equation, leg efficiency and output power were calculated with T h = 400°C and T c = 50°C to be of 10.5% and 6.6 W·cm −2 under a temperature gradient of, respectively.thermoelectrics | magnesium | tin | power factor | output power T hermoelectric power generation from waste heat is attracting more and more attention. Potential fuel efficiency enhancement by recovering the waste heat is beneficial for automobiles and many other applications (1, 2). In addition, solar thermoelectric generator provides an alternative route to convert solar energy into electrical power besides the photovoltaic conversion (3). Thermoelectric generator (TEG) can be regarded as a heat engine using electrons/holes as the energy carrier. The conversion efficiency of a TEG is related to the Carnot efficiency and the material's average thermoelectric figure of merit ZT (4):where ZT = (S 2 σ/κ)T, and S, σ, κ, and T are Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. Pursuing high ZT has been the focus of the entire thermoelectric community by applying various phonon engineering via nanostructuring approaches to reduce the thermal conductivity (5-7), or by exploring new compounds with intrinsically low thermal conductivity, such as compounds having complex crystalline structure, local rattlers, liquid-like sublattice, and highly distorted lattice (8-11). However, for practical applications, efficiency is not the only concern, and high output power density is as important as efficiency when the capacity of the heat source is huge (such as solar heat), or the cost of the heat source is not a big factor (such as waste heat from automobiles, steel industry, etc.). The output power density ω is defined as the output power W divided by the cross-sectional area A of the leg, i.e., ω = W/A, which is related to power factor PF = S 2 σ by the following:Eq. 2 contains two main parts: square of the temperature difference divided by leg length, and material power factor PF = S 2 σ.Clearly, to achieve higher power density for a given heat source, we have to either increase the power factor PF or decrease the leg length. However, decreasing the leg length could cause severe consequences such as increase of large heat flux that will incr...

Achieving high power factor and output power density in p-type half-Heuslers Nb 1-x Ti x FeSb

“…One effective approach to enhance ZT is through nanostructuring that can significantly enhance phonon scattering and consequently result in a much lower lattice thermal conductivity compared with that of the unmodified bulk counterpart (2). This approach works well for many inorganic TE materials, such as Bi 2 Te 3 (2), IV-VI semiconductor compounds (3,4), lead-antimony-silver-tellurium (LAST) (5), skutterudites (6), clathrates (7), CuSe 2 (8), Zintl phases (9), half-Heuslers (10-12), MgAgSb (13,14), Mg 2 (Si, Ge, Sn) (15,16), and others.…”

Lithium Doping to Enhance Thermoelectric Performance of MgAgSb with Weak Electron–Phonon Coupling

“…[ 24,25 ] Recently, Liu et al further stressed the signifi cance of high power factor in thermoelectric materials for power generation. [ 26 ] High-output power density, defi ned as the output power W divided by the cross-sectional area A of the leg, namely ω = W / A , should be as impEEortant as effi ciency when the heat source is unlimited (such as solar heat), or heat source is free (such as waste heat from automobiles, steel industry, etc.).…”

Relationship between thermoelectric figure of merit and energy conversion efficiency

“…1 cannot be reliable. To overcome the inadequacy, complicated numerical simulations based on the finite difference method were carried out to calculate the efficiency while accounting for the temperature dependence over a large temperature difference between the cold and hot sides (23)(24)(25). The efficiency by Eq.…”