Self-Healable and Stretchable PAAc/XG/Bi_(2)Se_(0.3)Te_(2.7) Hybrid Hydrogel Thermoelectric Materials

Thermoelectric power generators have attracted increasing interest in recent years owing to their great potential in wearable electronics power supply.It is noted that thermoelectric power generators are easy to damage in the dynamic service process,resulting in the formation of microcracks and performance degradation.Herein,we prepare a new hybrid hydrogel thermoelectric material PAAc/XG/Bi_(2)Se_(0.3)Te_(2.7)by an in situ polymerization method,which shows a high stretchable and self-healable performance,as well as a good thermoelectric performance.For the sample with Bi_(2)Se_(0.3)Te_(2.7)content of 1.5 wt%(i.e.,PAAc/XG/Bi2Se0.3Te27(1.5 wt%)),which has a room temperature Seebeck coefficient of-0.45 mV K^(-1),and exhibits an open-circuit voltage of-17.91 mV and output power of 38.1 nW at a temperature difference of 40 K.After being completely cut off,the hybrid thermoelectric hydrogel automatically recovers its electrical characteristics within a response time of 2.0 s,and the healed hydrogel remains more than 99%of its initial power output.Such stretchable and self-healable hybrid hydrogel thermoelectric materials show promising potential for application in dynamic service conditions,such as wearable electronics.

Frictional contact analysis of a rigid solid with periodic surface sliding on the thermoelectric material

Understanding and characterizing rough contact and wavy surfaces are essential for developing effective strategies to mitigate wear,optimize lubrication,and enhance the overall performance and durability of mechanical systems.The sliding friction contact problem between a thermoelectric(TE)half-plane and a rigid solid with a periodic wavy surface is the focus of this investigation.To simplify the problem,we utilize mixed boundary conditions,leading to a set of singular integral equations(SIEs)with the Hilbert kernels.The analytical solutions for the energy flux and electric current density are obtained by the variable transform method in the context of the electric and temperature field.The contact problem for the elastic field is transformed into the second-kind SIE and solved by the Jacobi polynomials.Notably,the smoothness of the wavy contact surface ensures that there are no singularities in the surface contact stress,and ensures that it remains free at the contact edge.Based on the plane strain theory of elasticity,the analysis primarily examines the correlation between the applied load and the effective contact area.The distribution of the normal stress on the surface with or without TE loads is discussed in detail for various friction coefficients.Furthermore,the obtained results indicate that the in-plane stress decreases behind the trailing edge,while it increases ahead of the trailing edge when subjected to TE loads.

Recent Progress of Two-Dimensional Thermoelectric Materials

Thermoelectric generators have attracted a wide research interest owing to their ability to directly convert heat into electrical power.Moreover,the thermoelectric properties of traditional inorganic and organic materials have been significantly improved over the past few decades.Among these compounds,layered two-dimensional(2D)materials,such as graphene,black phosphorus,transition metal dichalcogenides,IVA–VIA compounds,and MXenes,have generated a large research attention as a group of potentially high-performance thermoelectric materials.Due to their unique electronic,mechanical,thermal,and optoelectronic properties,thermoelectric devices based on such materials can be applied in a variety of applications.Herein,a comprehensive review on the development of 2D materials for thermoelectric applications,as well as theoretical simulations and experimental preparation,is presented.In addition,nanodevice and new applications of 2D thermoelectric materials are also introduced.At last,current challenges are discussed and several prospects in this field are proposed.

Surface contact behavior of functionally graded thermoelectric materials indented by a conducting punch

The contact problem for thermoelectric materials with functionally graded properties is considered.The material properties,such as the electric conductivity,the thermal conductivity,the shear modulus,and the thermal expansion coefficient,vary in an exponential function.Using the Fourier transform technique,the electro-thermoelastic problems are transformed into three sets of singular integral equations which are solved numerically in terms of the unknown normal electric current density,the normal energy flux,and the contact pressure.Meanwhile,the complex homogeneous solutions of the displacement fields caused by the gradient parameters are simplified with the help of Euler’s formula.After addressing the non-linearity excited by thermoelectric effects,the particular solutions of the displacement fields can be assessed.The effects of various combinations of material gradient parameters and thermoelectric loads on the contact behaviors of thermoelectric materials are presented.The results give a deep insight into the contact damage mechanism of functionally graded thermoelectric materials(FGTEMs).

Electronic structure engineering in organic thermoelectric materials

Electronic structures, which play a key role in determining electrical and optical properties of π-conjugated organic materials, have attracted tremendous interest. Efficient thermoelectric (TE) conversion of organic materials has rigorous requirements on electronic structures. Recently, the rational design and precise modulation of electronic structures have exhibited great potential in exploring state-of-the-art organic TE materials. This review focuses on the regulation of electronic structures of organic materials toward efficient TE conversion. First, we present the basic knowledge regarding electronic structures and the requirements for efficient TE conversion of organic materials, followed by a brief introduction of commonly used methods for electronic structure characterization. Next, we highlight the key strategies of electronic structure engineering for high-performance organic TE materials. Finally, an overview of the electronic structure engineering of organic TE materials, along with current challenges and future research directions, are provided.

Thermoelectric properties of porous (Bi_(0.15)Sb_(0.85))_2Te_3 thermoelectric materials

In order to obtain thermoelectric materials with high figure of merit, theconcept of Hollow (Vacuum) Quantum Structure or Effect and related thermoelectric materials designwere proposed. To demonstrate the theory, the materials of (Bi_(0.15)Sb_(0.85))_2Te_3 with porousstructure have been fabricated. Their thermoelectric properties and the microstructure wereinvestigated and compared with their density structure. It was found that the porous structure couldimprove their properties greatly.

An Overview of Advanced Chalcogenide Thermoelectric Materials and Their Applications

Thermoelectricity is a strong scientific and technological interest due to its wide application ranging from clean energy producing to photon sensing devices.Recent developments in theoretical studies on the thermoelectric(TE)effects as well as the newly discovered thermoelectric materials provide new opportunities for several applications.Though the scale of production is limited,thermoelectric technology provides an alternative to traditional methods of power generation,heating and cooling systems.TE technologies can be used in power generation,heating and cooling applications.They potentially offer significant energy savings through waste heat recovery and augmented cooling.This article critically discusses the current progress in chalcogenide TE materials and the advantages and limitations associated with the TE technologies.The need for new materials discoveries from the point of view of achieving higher figure-of-merit combined with thermal stabilities in intermediate-and hightemperature Peltier and Seebeck effects applications is also emphasized.Besides,this article aims to evaluate the main features of recently characterized multicomponent chalcogenide ionic compounds with high thermal stabilities as potential TE materials to harvest electric power from high-temperature heat flux via thermoelectricity.

Thermoelectric field for a coated hole of arbitrary shape in a nonlinearly coupled thermoelectric material

We study the thermoelectric field for an electrically and thermally insulated coated hole of arbitrary shape embedded in an infinite nonlinearly coupled thermoelectric material subject to uniform remote electric current density and uniform remote energy flux.A conformal mapping function for the coating and matrix is introduced,which simultaneously maps the hole boundary and the coating-matrix interface onto two concentric circles in the image plane.Using analytic continuation,we derive a general solution in terms of two auxiliary functions.The general solution satisfies the insulating conditions along the hole boundary and all of the continuity conditions across the perfect coating-matrix interface.Once the two auxiliary functions have been obtained in the elementary-form,the four original analytic functions in the coating and matrix characterizing the thermoelectric fields are completely and explicitly determined.The design of a neutral coated circular hole that does not disturb the prescribed thermoelectric field in the thermoelectric matrix is achieved when the relative thickness parameter and the two mismatch parameters satisfy a simple condition.Finally,the neutrality of a coated circular thermoelectric inhomogeneity is also accomplished.

Optimization of p-type Segmented Bi_2Te_3/CoSb_3 Thermoelectric Material Prepared by Spark Plasma Sintering

A kind of p-type segmented Bi2 Te3/CoSB3 thermoetectric material was preparea oy sparse ptasma sintering（ SPS ） . When the segmented materials were used at the temperature ranging from 300 K to 800 K, the junction temperature was optimized, which is about 500 K, and the corresponding length ratio of CoSb3 to Bi2 Te3 is about 15 ： 2. The measured maximum power output of segmented materials is abont 320 W·m^-2, which is about 1.8 times as high as that of monolithic material CoSb3 under the same measuring conditions.

Research status and performance optimization of medium-temperature thermoelectric material SnTe

Thermoelectric materials have the ability to directly convert heat into electricity,which have been extensively studied for decades to solve global energy shortages and environmental problems.As a medium temperature(400-800 K)thermoelectric material,SnTe has attracted extensive attention as a promising substitute for PbTe due to its non-toxic characteristics.In this paper,the research status of SnTe thermoelectric materials is reviewed,and the strategies to improve its performance are summarized and discussed in terms of electrical and thermal transport properties.This comprehensive discussion will provides guidance and inspiration for the research on SnTe.

Grain size and structure distortion characterization of α-MgAgSb thermoelectric material by powder diffraction

Nanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg0.97Sb0.99, with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. Here, we report the average grain size of 24–28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron x-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg0.97Sb0.99.

Thermoelectric properties of BiSb_x (x=0.6-0.8) thermoelectric materials fabricated by different processing

In order to improve the thermoelectric properties, hot-pressing sintering andultra high pressure sintering methods were adopted to fabricate BiSb_x. The phase and crystalstructures were determined by X-ray diffraction analysis (XRD). The thermoelectric properties weremeasured at 303 K along the direction parallel to the pressing direction. The electric conductivityof the samples was measured at 303 K by the four-probe technique. To measure the Seebeckcoefficient, heat was applied to the samples placed between two Cu discs. The thermoelectricelectromotive force (E) was measured upon applying small temperature differences (DELTA T<2 deg C)between the both ends of the samples. The Seebeck coefficient of the samples was determined from thevalue of E/DELTA T. The results indicate that the thermoelectric properties of the samplesfabricated by UHPS (ultra high pressure sintering) method are much higher than that by HPS (hotpressing sintering) method and have the highest values at x=0.7.

Thermoelectric Properties of N-typer Bi_2Te_3-PbTe Graded Thermoelectric Materials with Different Barriers

In order to investigate the adaptability of thermoelectric materials system with different barriers to functional graded thermoelectric materials, n-type Bi2Te, and PbTe two segments graded thermoelectric materials (GTM) with different barriers were fabricated by conventional hot pressing method. Metals Cu, Al, Fe, Co and Ni were used as barriers between two segments. The effects of different barriers on thermoelectric properties of GTM were investigated. The phase and crystal structures were determined by x-ray diffraction analysis (XRD). The distributions of different compositions were analyzed by electron microprobe analysis (EMA). The thermoelectric properties were measured at 303 K along the direction parallel to the pressing direction. The electric conductivity of samples was measured at 303 K by the four-probe technique. To measure the Seebeck coefficient, heat was applied to the samples, which were placed between two Cu discs. The thermoelectric electromotive force (E) was measured upon applying small temperature differences (DeltaT<275 K) between the both ends of the samples. The Seebeck coefficient of the samples was determined from the E/&UDelta;T.

Thermoelectric properties of p-type Bi-Sb-Te compositionally graded thermoelectric materials with different barriers

In order to find more suitable materials as barriers and to improve the thermoelectric properties, p-type (Bi1-xSbx) 2Te3 (x = 0.85, 0.9) two segments compositionally graded thermoelectric materials (CGTM) with different barriers were fabricated by conventional hot pressure method. Metals Fe, Co, Cu and Al were used as barriers between two segments. The effects of different barriers on thermoelectric properties of CGTM were investigated. The results show that metal Fe is more stable and suitable as the barrier.

An engineering roadmap for the thermoelectric interface materials

Thermoelectric generators(TEGs)are renowned for powering deep space exploration due to their simple system structure,long-term stability,and vibration-less operation^([1-4]).However,the extensive commercial application of TEGs remains stagnant due to the challenges in designing reliable electrode contact inter-faces,especially the interface between thermoelectric interface ma-terials(TEiMs)and thermoelectric conversion materials(TEcMs)^([5]).

High-entropy alloys in thermoelectric application:A selective review

Since the superior mechanical,chemical and physical properties of high-entropy alloys(HEAs)were discovered,they have gradually become new emerging candidates for renewable energy applications.This review presents the novel applications of HEAs in thermoelectric energy conversion.Firstly,the basic concepts and structural properties of HEAs are introduced.Then,we discuss a number of promising thermoelectric materials based on HEAs.Finally,the conclusion and outlook are presented.This article presents an advanced understanding of the thermoelectric properties of HEAs,which provides new opportunities for promoting their applications in renewable energy.

Processing of advanced thermoelectric materials

Last two decades have witnessed significant progress in thermoelectric research, to which materials processing has crucial contributions. Compared with traditional zone-melting method used for fabricating bismuth telluride alloys, new powder-based processes have more freedom for manipulating nanostructnres and nanocomposites. Thermoelectric performance enhancement is realized in most thermoelectric materials by introducing fine-grained and nano-composite structures with accurately controlled compositions. This review gives a comprehensive summary on the processing aspects of thermoelectric materials with three focuses on the powder synthesis, advanced sintering process and the formation of nanostructures in bulk materials.

Low-cost and environmentally benign selenides as promising thermoelectric materials

Developing high-efficiency materials with earth-abundant and low-toxicity elements has become a popular trend in the field of thermoelectrics.Among these compounds,oxides and sulfides,the lighter,cheaper and green analogies of tellurides,have been extensively investigated and summarized as well defined classes.Nonetheless,the vast family of selenides with better electrical performance,lower thermal conductivity and higher thermoelectric efficiency have not been specially discussed.Here in this review,we present recent advances in binary and multinary selenide thermoelectric materials,covering traditional PbSe,liquid-like Cu_(2)Se,layered SnSe,diamond-like and disordered multinary compounds.The features of selenides are discussed based on both environmental concerns and from the perspective of chemical bonding,transport properties and performance.Emphasis is put on the“compositionstructure-processing-performance”relationship,and some interesting issues are addressed.Finally,challenges for thermoelectric selenides are discussed,and possible optimization strategies are also suggested.

Heat Conduction in Multilayered Thermoelectric Materials with Multiple Cracks

Multilayer thin-film thermoelectric materials are of technological importance. This paper describes a method to analyze the heat conduction in a multilayered thermoelectric plate containing some non-collinear cracks. The material properties in one layer may be different from those in another even though each layer may still be homogeneous. Using the Fourier integral transforms, the boundary value problem is reduced to a system of general singular integral equations. The model is sufficiently general to account for any number of layers and any number of cracks. As a numerical illustration, the electric flux intensity factor, energy flux intensity factor and thermal flux intensity factor for a three-layer plate specimen with two cracks are presented. The effects of strip width on the electric flux intensity factor and thermal flux intensity factor are studied.

When thermoelectric materials come across with magnetism

Nowadays,thermoelectric materials have attracted a lot of attention as they can directly convert heat into electricity and vice versa.However,while strenuous efforts have been made,those conventional strategies are still inevitably going to meet their performance optimization limits.For this reason,brand new strategies are badly needed to achieve further enhancement.Here,the roles played by magnetism in recent advances of thermoelectric optimization are concluded.Firstly,magnetic thermoelectric materials can just be treated like other normal materials because the use of universal optimization strategies can still get good results.So,it is not a situation which is all or nothing and the tactics of using magnetism for thermoelectric optimization can coexist with other strategies.Besides,through magnetic doping,we can introduce and adjust magnetism in materials for further optimization.Magnetism provides more possibilities in thermoelectric optimization as it can directly influence the spin states in materials.Furthermore,in the form of magnetic secondphase nanoclusters,magnetism can be introduced to thermoelectric materials to conquer the dilemma that the solid solubility of many magnetic ions in thermoelectric materials is too low to have any significant effect on thermoelectric properties.Finally,when exposed to an external magnetic field,topological materials can rely on its unique band structures to optimize.