Thermoelectric ceramics for generators

Advancements in thermoelectric materials and their performance for thermoelectric generators (TEGs): A short review

Recently, SnSe material with an outstanding high ZT (Figure of merit) of 2.6 has attracted much attention due to its strong applicability for highly efficient thermoelectric devices. Many studies following the first journal publication have been focused on SnSe materials, not on thermoelectric devices. Particularly, to realize highly efficient intermediate-temperature (600~1000 K) thermoelectric modules with this promising thermoelectric material, a more thermally and electrically reliable interface bonding technology needs to be developed so that the modules can stably perform their power generation in this temperature range. In this work, we demonstrate several approaches to develop metallization layers on SnSe thermoelectric legs. The single-layer metallization shows limitations in their electrical contact resistances and elemental diffusions. The Ag/Co/Ti multi-layer metallization results in lowering their electrical contact resistances, in addition to providing more robust interfaces. Moreover, it is found to maintain the interfacial characteristics without any significant degradation, even after heat treatment at 723 K for 20 h. These results can be effectively applied in the fabrication of thermoelectric devices or modules that are made of the SnSe thermoelectric materials.

A large-sized thermoelectric module composed of cement-based composite blocks for pavement energy harvesting and surface temperature reducing

Mg2Si thermoelectric (TE) elements and modules were fabricated using a commercial polycrystalline Mg2Si source. A monobloc plasma-activated sintering technique was used to fabricate the TE elements and Ni electrodes. The TE modules were composed of n-type Mg2Si, using pin–fin structure elements, in order to achieve simple assembly and to realize stable operation at a temperature of ~800 K. The dimensions of each pin–fin element were 4.2 mm × 4.2 mm × 9.8 mm, and the TE module comprised nine pin–fin elements connected in series. The output characteristics of the pin–fin elements and the TE module were evaluated at temperature differences, ΔT, ranging from 100 K to 500 K. The observed values of open-circuit voltage (V OC) and output power (P) of a single pin–fin element were 98.7 mV and 50.9 mW, respectively, at the maximum ΔT of 500 K. The maximum V OC and P values for the TE module were 588 mV and 174.3 mW, respectively, at ΔT = 500 K.

The U.S. military uses large amounts of fuel during deployments and battlefield operations. Consequently, the U.S. military has a strong need to develop technologies that increase fuel efficiency and minimize fuel requirements all along the logistics trail and in all battlefield operations. There are additional requirements to reduce and minimize the environmental footprint of various military equipment and operations and reduce the need for batteries (non-rechargeable) in battlefield operations. The tri-agency SERDP (Strategic Environmental Research and Development Program) office is sponsoring a challenging, high-payoff project to develop a lightweight, small form-factor, soldier-portable advanced thermoelectric generator (TEG) system prototype to recover and convert waste heat from a variety of deployed equipment with the ultimate purpose of obtaining additional power for soldier battery charging, advanced capacitor charging, and other battlefield power applications. The project seeks to achieve power conversion efficiencies of 10% (double current commercial TE conversion efficiencies) in a system with ˜1.6-kW power output for a spectrum of battlefield power applications. In order to meet this objective, the project is taking on the multi-faceted challenges of tailoring LAST/LASTT-based thermoelectric (TE) materials for the proper temperature ranges (300 K – 700 K), fabricating these materials with cost-effective hot-pressed and sintered processes while maintaining their TE properties, measuring and characterizing their thermal fatigue and structural properties, developing the proper manufacturing processes for the TE materials and modules, designing and fabricating the necessary microtechnology heat exchangers, and fabricating and testing the final TEG system. The ultimate goal is to provide an opportunity to deploy these TEG systems in a wide variety of current military equipment. This would help the Army in achieving one of the Office of Secretary of Defense’s major strategic objectives to maintain and enhance operational effectiveness while reducing total force energy demands. The presentation will review the progress made on 1) the performance of LAST / LASTT TE materials and tailoring their temperature dependency; 2) evaluating the structural (Elastic modulus, Poisson’s ratio and mechanical strength) properties of these materials, 3) development of the necessary LAST/LASTT-based TE modules, 4) development of the required hot- and cold-side microtechnology heat exchangers, and 5) the overall system designs for 30 kW and 60 kW TQG applications and potential performance pathways/differences for these two TQG cases. This work leverages critical fundamental research performed by the Office of Naval Research in developing LAST/LASTT materials.

Chapter 8 - New paradigm for efficient thermoelectrics

Lateral comparison of the coupling parameters on the novel hexagonal shaped cross flow thermoelectric generator

A significant number of thermoelectric processes are described with fundamental law of thermodynamics. This paper describes thermoelectric processes in the permeable thermoelements, which are described with the help of relationships of non-equilibrium thermodynamics. The thermoelectric effects, which are described in this work, are laid in the basis of the work of thermoelectric elements, which make up the modules of generators and coolers. Any thermoelectric module can work in refrigerating regime as well as in generator regime. The difference is that, in order to generate energy and to work in the refrigerating regime, the different temperatures and different semiconductors are optimal, which are used in development of thermoelectric modules. The heterogenous materials, which are used to create new thermoelectric modules, can be defined as materials with different sharp heterogeneity of durability from one phase to the other. This heterogeneity of durability may be caused by microstructure of diversity, heterogeneity of the crystal structure or compositional diversity. The size of phases may be in the range from micrometers to millimeters, the geometry of phases may change and create different material systems. The object of this research is the processes in non-equilibrium thermodynamic systems. The subject of the research is the flow of thermodynamic processes in heterogeneous materials, relationship of non-equilibrium thermodynamics in the heterogeneous permeable thermoelements. The methodology of the research is based on the common scientific methods of analysis and synthesis, induction and deduction, observation and abstraction, which are used to systemize results and calculations of thermoelectric systems. The aim of the work is familiarization with the relationship of non-equilibrium thermodynamics, its systematization and calculation of optimal parameters of permeable thermoelement on its basis. This paper describes the physical nature of thermodynamic and thermoelectric phenomenon, based on the newest actual and classic works of the branch of thermoelectricity, non-equilibrium thermodynamics, applied and thermoelectric material science, and their practical application. The analytical review of the literature about the problematics of non-equilibrium thermodynamics in heterogeneous systems was done. We observed the advantages and disadvantages of these systems. The practical part of this work consists of the calculation of parameters of permeable thermoelement made of thermoelectric material on the base of BismuthTtelluride for thermoelectric cooler or, as it used to say in the field of thermoelectricity, thermoelectric heat pump, calculation of dependence of its parameters on amount and size of channels of permeable thermoelement. While investigating the relationship of non-equilibrium thermodynamics, exactly Gibbs’ equation, Boltzmann’s equation, the equation of coolant and heat flow, equation of cooling coefficient, we systemized them and calculated the optimal parameters for the permeable thermoelectric element of cooling on the base of diverse semiconducting alloy Bi2Te3. On the basis of these calculations, we graphically represented the dependence of parameters of semiconducting permeable thermoelectric element on width of its channel, showed optimal definition of width of channel of permeable thermoelectric element. The results of research showed that, by means of the system of channels with the heat carrier, which make changes in the gradient and the temperature’s distribution on the element, is the significant advantage of the cooling factor of the thermoelectric electric over impenetrable.

Traditional thermoelectric power generators consist of thermoelectric elements connected electrically in series and thermally in parallel. Current flowing inside the thermoelectric power generator is conventionally considered to be driven by the Seebeck effect-induced electric field and the output voltage-induced reverse electric field. This paper proposes a more comprehensive model that implies that current is also driven by chemical potential and carrier density variation. Therefore, the thermoelectric power generator can be treated as a current-source power supplier when the current driven by carrier density variation dominates. This paper performs holistic finite element implementation of the new holistic model where a thermoelectric power generator unit behaves like a current-source while the working temperature conditions maintain stability. This result validates that the thermoelectric element shows the behaviors of a current-source power supply under certain conditions. This discovery brings a new perspective on the behaviors of thermoelectric elements, which potentially will lead to the development of novel thermoelectric power generator design.

Abstract

Thermoelectric generators produce electricity by directly converting temperature differences into electrical energy through Seebeck effect. Thermoelectric generators possess many unique features, such as having no moving part and being very reliable with a relatively long lifespan once built. They are solid-state waste heat harvesters. With various waste heat available throughout many industries, thermoelectric generators could offer economically competitive renewable energy. The current state of the art thermoelectric materials includes materials with relatively toxic elements and must work under vacuum, making them quite expensive to produce. Among the various thermoelectric materials, ceramic oxides have been proved to be more chemically stable at high temperatures. Nevertheless, the thermoelectric ceramic oxides do not yet reach the efficiency of the current state of the art materials. Recent efforts have been made to improve the efficiency of ceramic oxide for their potential commercial applications in the waste heat harvester. The present work encompasses the synthesis, characterization, and analysis of p-type thermoelectric Ca3-xCo4O9+δ doped with rare earth elements. The sol-gel chemical solution was applied to synthesize the precursor materials for ceramic oxide with homogeneous chemistry. The results show that to a certain substitution level, doping rare-earth element decreases the thermal conductivity and improves the thermoelectric properties of the oxide thermoelectric materials. Meanwhile, doping also introduces the formation of nano-inclusions that is highly desirable for thermoelectric materials. The formation mechanism of the nano-inclusions and their resultant impact on the electrical and thermal properties of the misfit layered oxide is systematically investigated through this thesis work.

This paper reviews recent advancements in integrated thermoelectric power generation and water desalination technologies, driven by the increasing global demand for electricity and freshwater. The growing population and reliance on fossil fuels for electricity generation pose challenges related to environmental pollution and resource depletion, necessitating the exploration of alternative energy sources and desalination techniques. While thermoelectric generators are capable of converting low-temperature thermal energy into electricity and desalination processes that can utilize low-temperature thermal energy, their effective integration remains largely unexplored. Currently available hybrid power and water systems, such as those combining conventional heat engine cycles (e.g., the Rankine and Kalina cycles) with reverse osmosis, multi-effect distillation, and humidification–dehumidification, are limited in effectively utilizing low-grade thermal energy for simultaneous power generation and desalination, while solid-state heat-to-work conversion technology, such as thermoelectric generators, have low heat-to-work conversion efficiency. This paper identifies a key research gap in the limited effective integration of thermoelectric generators and desalination, despite their complementary characteristics. The study highlights the potential of hybrid systems, which leverage low-grade thermal energy for simultaneous power generation and desalination. The review also explores emerging material innovations in high figure of merit thermoelectric materials and advanced MD membranes, which could significantly enhance system performance. Furthermore, hybrid power–desalination systems incorporating thermoelectric generators with concentrated photovoltaic cells, solar thermal collectors, geothermal energy, and organic Rankine cycles (ORCs) are examined to highlight their potential for sustainable energy and water production. The findings underscore the importance of optimizing material properties, system configurations, and operating conditions to maximize efficiency and output while reducing economic and environmental costs.

Thermoelectric generators: Linking material properties and systems engineering for waste heat recovery applications

Recycling low-temperature waste heat is a key issue to realize de-carbonization in our society. Nevertheless, conventional technologies including thermoelectric generators are incapable of gathering thermal energies from the surrounding environments. Here, we report metamaterial thermoelectric conversion driven by the thermal energies extracted from the surrounding environment, which can be available for energy harvesting. The metamaterial thermoelectric generator can extract thermal energies from the surrounding environment and convert them into electricity. The metamaterial thermoelectric generator consists of a bismuth telluride thermoelectric element loaded with metamaterial-fabricated copper electrode at one edge. The metamaterial arrays fabricated on the copper electrode absorb thermal radiation emitted from the surrounding environment, leading to local heat generation as a consequence of plasmon loss. The local heat propagates to the bismuth telluride thermoelectric element via the copper electrode, resulting in an additional thermal gradient across the thermoelectric element and generation of electricity. Previously, we numerically investigated the metamaterial thermoelectric conversion. In this report, we will show the experimental demonstration of metamaterial thermoelectric conversion.

Patternable and flexible thermoelectric generators based on Bi2Te3/silk fibroin composites for temperature sensing and wearable applications