I am a PhD Researcher that focuses on characterising the microstructural behaviour of superalloys.
Follow this pinboard to understand the science behind thermoelectrcs
In 10 Seconds? Energy efficiency is a worldwide concern; it is generally known that the largest loss of energy is through wasted heat – which is why so much research is being carried out to improve the properties of thermoelectric materials. The basic principle behind thermoelectricity is that the thermoelectric material must be within a temperature gradient (temperature difference) i.e. one side hot and the other side cold.
Don’t believe it? Review the pinned articles to observe the novel research that is being done to improve the conversion efficiency – one particular paper focuses on charged colloidal particles, which showed positive results for future research.
Where are they used? Thermoelectric modules can be found extensively within the automotive industry – where the waste heat is converted into an electrical output. Similarly, they can be found in power plants doing the same job.
The science behind thermoelectric modules
These thermoelectric modules consist of two thermoelectric materials - one to form the n-type semiconductor and the other to form the p-type semiconductor, which are all contained within a temperature gradient.
To allow for a successful conversion of heat to electricity one particular material property is critical – low thermal conductivity. This is because it is crucial to retain the temperature gradient. Therefore, having a low thermal conductivity means the heat will not pass through the material to the cooler section of the module.
Abstract: Phonon scattering by nanostructures and point defects has become the primary strategy for minimizing the lattice thermal conductivity (κL) in thermoelectric materials. However, these scatterers are only effective at the extremes of the phonon spectrum. Recently, it has been demonstrated that dislocations are effective at scattering the remaining mid-frequency phonons as well. In this work, by varying the concentration of Na in Pb0.97Eu0.03Te, it has been determined that the dominant microstructural features are point defects, lattice dislocations, and nanostructure interfaces. This study reveals that dense lattice dislocations (≈4 × 1012 cm−2) are particularly effective at reducing κL. When the dislocation concentration is maximized, one of the lowest κL values reported for PbTe is achieved. Furthermore, due to the band convergence of the alloyed 3% mol. EuTe the electronic performance is enhanced, and a high thermoelectric figure of merit, zT, of ≈2.2 is achieved. This work not only demonstrates the effectiveness of dense lattice dislocations as a means of lowering κL, but also the importance of engineering both thermal and electronic transport simultaneously when designing high-performance thermoelectrics.
Pub.: 11 Apr '17, Pinned: 22 Apr '17
Abstract: Currently, liquid thermocells are receiving increasing attention as an inexpensive alternative to conventional solid-state thermoelectrics for low-grade waste heat recovery applications. Here we present a novel path to increase the Seebeck coefficient of liquid thermoelectric materials using charged colloidal suspensions; namely, ionically stabilized magnetic nanoparticles (ferrofluids) dispersed in aqueous potassium ferro-/ferri-cyanide electrolytes. The dependency of thermoelectric potential on experimental parameters such as nanoparticle concentration and types of solute ions (lithium citrate and tetrabutylammonium citrate) is examined to reveal the relative contributions from the thermogalvanic potential of redox couples and the entropy of transfer of nanoparticles and ions. The results show that under specific ionic conditions, the inclusion of magnetic nanoparticles can lead to an enhancement of the ferrofluid's initial Seebeck coefficient by 15% (at a nanoparticle volume fraction of ∼1%). Based on these observations, some practical directions are given on which ionic and colloidal parameters to adjust for improving the Seebeck coefficients of liquid thermoelectric materials.
Pub.: 23 Mar '17, Pinned: 22 Apr '17
Abstract: Ternary copper tin sulfide (Cu-Sn-S) compounds have been investigated for decades as promising candidates of earth-abundant thin film solar cell absorbers. Cu2SnS3 is a representative member of this material system, and is highly expected to be a potential thermoelectric material by the first-principles calculations. In this work, Cu2SnS3 bulk materials were synthesized by the mechanical alloying (MA) combined with spark plasma sintering (SPS), and their crystal structures, electronic transport properties and enhanced thermoelectric performance were systematically investigated. We found that pristine Cu2SnS3 is a p-type thermoelectric material with a relatively high thermopower up to 300 μV/K and low thermal conductivity below 1.0 W/m K above 700 K. It revealed that In doping is an effective means to improve the electrical transport properties, which leads to a figure of merit (ZT) of Cu2Sn0.9In0.1S3 close to 0.6 at the relatively low temperature (773 K).
Pub.: 26 Feb '16, Pinned: 22 Apr '17
Abstract: Cu2SnS3 is an attractive earth abundant material for not only solar cells but also thermoelectrics because high thermoelectric performance is predicted by the first principle calculation. In our previous work, Cu2SnS3 is successfully synthesized by solid phase reaction with binary compounds and obtained a high Seebeck coefficient and a low thermal conductivity. However, a low electric conductivity results in a low figure of merit (ZT) of less than 0.1. In this work, CuS and In2S3 are added to starting materials to enhance the electrical conductivity and it has been improved by one order of magnitude.CuS and In2S3 addition enhance electrical conductivities.
Pub.: 27 Feb '17, Pinned: 22 Apr '17
Abstract: The issue of how to improve the thermoelectric figure of merit (ZT) in oxide semiconductors has been challenging for more than 20 years. In this work, we report an effective path to substantial reduction in thermal conductivity and increment in carrier concentration, and thus a remarkable enhancement in the ZT value is achieved. The ZT value of In2O3 system was enhanced 4-fold by nanostructuing (nano-grains and nano-inclusions) and point defect engineering. The introduction of point defects in In2O3 results in a glass-like thermal conductivity. The lattice thermal conductivity could be reduced by 60%, and extraordinary low lattice thermal conductivity (1.2 W m(-1) K(-1) @ 973 K) below the amorphous limit was achieved. Our work paves a path for enhancing the ZT in oxides by both the nanosturcturing and the point defect engineering for better phonon-glasses and electron-crystal (PGEC) materials.
Pub.: 15 Jan '15, Pinned: 22 Apr '17
Abstract: The study of the lead chalcogenides system has been extended throughout the history of thermoelectrics due to their extraordinary physical and chemical properties. Compared with PbTe, PbSe has been drawing increased attention because it combines several attractive features, such as higher melting point, lower cost, and higher operation temperatures. The all-scale hierarchical structures were successfully applied to p-type PbSe systems, and a fascinating ZT value was achieved by effectively reducing the lattice thermal conductivity, which could be attributed to phonon scattering with a spectrum of wavelengths. However, the lattice thermal conductivity also reached about 1.0 W m−1 K−1 in the n-type PbSe system, which is very high compared with p-type PbSe that has been reported. In this study, by means of introducing mesostructures, the lattice thermal conductivity was efficaciously lowered from ∼1.3 W m−1 K−1 to ∼1.2 W m−1 K−1 at room temperature and ∼0.9 W m−1 K−1 to ∼0.6 W m−1 K−1 at 923 K for the n-type PbSe–PbS system. Correspondingly, a marked increase in ZT value from ∼1.3 to ∼1.5 at 923 K was observed, which indicated that the applications with superior conversion efficiencies on a large scale could be achieved from systems consisting of abundant and inexpensive chemical elements.
Pub.: 08 Feb '17, Pinned: 22 Apr '17
Abstract: Oxides based thermoelectrics have the advantage over other materials due to their low processing cost, better temperature stability and environmental friendly nature. However, it is difficult to achieve good electrical conductivity along with high Seebeck coefficient in oxides. Recently double perovskites based oxides have shown great potential to optimize various thermoelectric (TE) parameters in order to achieve high figure-of-merit, ZT values for TE power generations. In the present work we investigated the effect of Ba-doping on the high temperature thermoelectric properties of double perovskite Sr2TiMoO6 (STM), which exhibits metal like conductivity (∼105 S/m). Dense ceramic samples of BaxSr2-xTiMoO6 with 0 ≤ x ≤ 2.0 were synthesized using solid-state reaction route. Rietveld refinement of XRD data confirmed the cubic crystal structure in these double perovskites with space-group <img height="14" border="0" style="vertical-align:bottom" width="41" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0925838817310666-si1.gif">Pm3¯m. It is shown in this paper that complete substitution of barium in place of strontium actually increases the Seebeck coefficient without compromising much in electrical conductivity values, resulting better thermoelectric power factor in Ba2TiMoO6 (BTM) compared to STM composition. Thermopower (S) measurement showed the conductivity switching from p-type to n-type behavior in all the compositions at higher temperature although the switching temperature decreases with increase in Ba-concentration. Temperature dependent Seebeck coefficient was further explained using an analytical model for coexistence of both types of charge carriers in these oxides. Conductivity mechanism of these double perovskites was found to be governed by small polaron hopping model.
Pub.: 27 Mar '17, Pinned: 22 Apr '17
Abstract: Alloy anodes possessed of high theoretical capacity show great potential for next generation advanced lithium ion battery. Even though huge volume change during lithium insertion and extraction leads to severe problems, such as pulverization and unstable Solid-Electrolyte Interphase (SEI), various nanostructures including nanoparticles, nanowires and porous networks can address related challenges to improve electrochemical performance. However, the complex and expensive fabrication process hinders the widespread application of nanostructured alloy anodes, which generate urgent demand of low cost and scalable processes to fabricate building blocks with fine controls of size, morphology and porosity. Here, we demonstrate a scalable and low cost process to produce porous yin-yang hybrid composite anode with graphene coating through high energy ball-milling and selective chemical etching. With void space to buffer the expansion, the produced functional electrodes demonstrate stable cycling performance of 910 mAh g-1 over 600 cycles at a rate of 0.5C for Si-graphene "yin" particles and 750 mAh g-1 over 300 cycles at 0.2C for Sn-graphene "yang" particles. Therefore, we open up a new approach to fabricate alloy anode materials at low cost, low energy consumption and large scale. This type of porous silicon or tin composite with graphene coating can also potentially play a significant role in thermoelectrics and optoelectronics applications.
Pub.: 18 Apr '17, Pinned: 22 Apr '17
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