碱金属热电转换器（AMTEC）的新技术

介绍了采用熔融合金电极的碱金属热电转换器和采用钾循环工质,以钾－β氧化铝材料作为固体电解质的碱金属热电转换器两种碱金属热电转换器新技术,并与钠工质碱金属热电转换器进行了比较。     

碱金属热电转换器(AMTEC)的电极极化过程分析

从电化学动力学的角度，对碱金属热电转换器的电极极化过程及对其特性的影响进行了讨论。分析认为，阳极极化过电压对碱金属热电转换器输出电压的影响比阴极极化过电压要小得多。影响阴极过电压的因素很多，除电极电流密度的大小外，电极反应本身的性质、BASE本身的性质、电极反应所依附的电极多孔薄膜材料的性质、电极多孔薄膜的形貌等都会对其大小产生影响。选择合适的电极材料，优化电极多孔薄膜的制备工艺，对改善AMTEC的电特性将是十分重要的。     

碱金属热电直接发电装置的热辐射损失

寄生热辐射损失，特别是BASE管外表面的热辐射是影响碱金属热电转换器(AMTEC)高效运行的主要因素之一。为了量化BASE管外表面的热辐射对碱金属热电转换器热电转换效率的影响程度，文章用一简化模型，计算了采用不同层数遮热屏的碱金属热电转换器中的BASE管外表面的净热辐射量。结果表明，恰当设计AMTEC装置的结构，并在BASE管外加数层遮热屏，可使BASE管外单位电极表面的净热辐射损失在其工作温度范围内控制在1W／cm^2以下。     

碱金属热电转换器的循环工质和固体电解质的选择

对碱金属热电转换器所用的循环工质和β″氧化铝固体电解质的选择进行了探讨,对Na-AMTEC、K-AMTEC、NaK-AMTEC3种形式的碱金属热电转换器的热电转换特性进行了比较,认为K-AMTEC和NaK-AMTEC将是两种很有发展前途的碱金属热电转换器形式。     

碱金属热电转换器（AMTEC）理论分析

从理论上分析了碱金属热电转换器的输出电压与电极电流密度之间的关系,最大电极功率密度与工作温度,电极电流密度和BASE面电阻之间的关系,电极效率与工作温度,电极电流密度和BASE面电阻之间的关系。     

钠钾工质碱金属热电转换器发电组件制备关键技术的研究

提出了钠钾工质碱金属热电转换器的概念,论证了开展钠钾工质碱金属热电转换器基础研究的意义,介绍了NaK-BASE管的制备方法,开展了NaK-BASE管—α-Al_2O_3绝缘过渡件—金属法兰之间的活性焊接和NaK-BASE管外表面电极多孔薄膜的制备等关键技术的探索性试验研究。试验结果表明,NaK-BASE管与α-Al_2O_3管以及α- Al_2O_3管与钛合金件之间的钎缝的漏率均达到10~(10)Pa·m~3/s级以上。采用反应性磁控溅射技术,在NaK-BASE管外表面制备了TiN电极多孔薄膜。     

碱金属热电转换器的电极效率

该文计算了碱金属热电转换器在不同的工作温度和不同BASE面电阻下当输入最大电极功率密度时的电极效率，推导出了在给定工作温度和BASE面电阻时取得最大电极效率的条件，并计算了最大电极效率点和最大电极效率，对在给定了工作温度下BASE面电阻和单位面积电极表面的热辐射量对最大电极效率及其工作点位置的影响从理论上进行了推导。     

千瓦级空间堆热离子—碱金属混合式热电转换系统设计及性能

针对空间核电转换系统静态热电转换发电效率低的问题，设计开发了一种新型的热离子-碱金属混合发电系统，即利用热离子转换系统的余热作为碱金属转换器的热源，利用余热进行二次发电以提高转换系统效率，通过建立热离子-碱金属混合发电系统数理模型，研究了热离子热电转换系统接收极功函数和系统电流密度对混合发电系统功率效率的影响，得到了两个参数的最优区间，计算结果表明热离子-碱金属混合发电系统相比于热离子热电转换系统效率约6％~10％，为静态热电转换系统的效率优化提供了理论依据。     

AMTEC与超临界CO_2循环的混合太阳能热发电系统初探

为了进一步提高太阳能热发电效率,以太阳能热为高温热源,将碱金属热电转换器(AMTEC)与在空冷条件下仍有显著热效率优势的超临界CO2循环组成高效的混合太阳能热发电系统,AMTEC冷凝器释放的热量品位高,可以作为余热发电。结果显示,该系统的光电转换效率可达25%以上。     

热电直接转换技术的最新进展

本文列举为止比较成熟和五种热电直接转换技术的原理及发展现状，并且重点介绍了近来在国外研究很热门的碱金属热电直接转换技术。     

氧化钛基半导体热电材料的研究进展

热电材料—即实现热能和电能之间直接相互转换的一类功能材料,提供了一种制冷或发电的新方法—在解决能源和环境危机问题上正在扮演越来越重要的角色。传统的三维材料中,由于几个决定热电性能的关键物理参数相互关联,使得现有热电材料很难获得较高热电优值（ZT）。金属氧化物热电材料由于其良好的耐高温性能,是中高温区使用的理想候选者。如果能提高氧化钛基化合物的热电优值,那么氧化钛基化合物将是一类非常优秀的热电材料,因为其不仅具有优良的化学稳定性和热稳定性,而且原材料丰富、不含有毒元素以及制备工艺简单。纳米化能显著降低材料的热导率,是最近二十年提高热电性能的一条主要途径。同时,通过界面和化学组成调控增加与电学性能相关的功率因子也是一种继续提高热电性能的重要方法。本文综述了我们近期对氧化钛基热电材料的研究成果,包括对钛酸盐纳米管较大赛贝克（Seebeck）系数的实验发现,提出利用一维纳米材料独特的空心结构和纳米管层状特殊构造,将两个相关联的物理参数（热导率和电导率）分别调控;通过合成氧化钛基纳米复合材料,研究界面对载流子和声子散射的作用,提出通过载流子能量过滤效应提高其热电性能;采用尿素燃烧法和高温烧结等方法合成具有纳米结构和化学组成调控的氧化钛基化合物,认识化学组成以及界面对声电输运的作用规律;最后介绍能显著提高热电材料功率因子的载流子非对称迁移的理论。     

Developments in semiconductor thermoelectric materials

A surge in interest in developing alternative renewable energy technologies has been observed in recent years. In particular, thermoelectrics has drawn attention because thermoelectric effects enable direct conversion between thermal and electrical energy, and provide power generation and refrigeration alternatives. During the past decade, the performance of thermoelectric materials has been considerably improved; however, many challenges continue to exist. Developing thermoelectric materials with superior performance means tailoring interconnected thermoelectric physical parameters-electrical conductivities, Seebeck coefficients, and thermal conductivities for a crystalline system. The objectives of this paper are to introduce the recent developments in semiconductor thermoelectric materials, and briefly summarize the applications of such materials.     

Advanced materials for solar thermoelectric transducers

Recent achivements in the creation of advanced thermoelectric materials (the thermoelectric quality factor, cost, and workability) have been analyzed. It has been shown that nanostructured materials (quantum dot superlattices and silicate glasses with nanocrystals) can serve as a basis for the creation of highly efficient and easily accessible for mass application thermoelectric transducers converting solar radiation into electric energy. An advantage of thermoelectric transducers is the nonselective character of conversion and the lower sensitivity to changes in the orientation towards an emission source.     

Numerical Modeling of Thermoelectric Generators With Varing Material Properties in a Circuit Simulator

When a thermoelectric generator (TEG) and its external load circuitry are considered together as a system, the codesign and cooptimization of the electronics and the device are crucial in maximizing the system efficiency. In this paper, an accurate TEG model is proposed and implemented in a SPICE-compatible environment. This model of thermoelectric battery accounts for all temperature-dependent characteristics of the thermoelectric materials to include the nonlinear voltage, current, and electrothermal coupled effects. It is validated with simulation data from the recognized program ANSYS and experimental data from a real thermoelectric device, respectively. Within a common circuit simulator, the model can be easily connected to various electrical models of applied loads to predict and optimize the system performance.      

高效分段温差电单偶仿真设计

由于温差电材料的热电性能随着温度变化而变化,优值系数ZT也随之改变,导致不同温差电材料的只在某一温度区间有较高的效率,因此,分段温差电元件概念被提出,据此可以在很大程度上提高热电转换效率。本文建立了基于P型BiSbTe＼Zn4Sb3＼CeFe4Sb12、N型Bi2Te3＼GoSh3半导体分段温差电单偶模型异进行了ANSYS有限元分析。在对分段温差电元件长度比、截面比及负载电阻均进行优化后,得到在冷端温度为298K,热端温度为973K、873K、773K、673K时的理论转换效率分别为15．2％、13．8％、12．1％、10．6％。     

Thermoelectric transport in graphene and 2D layered materials

ABSTRACT

In early 90s, Hicks and Dresselhaus proposed that low dimensional materials are advantages for thermoelectric applications due to the sharp features in their density-of-states, resulting in a high Seebeck coefficient and, potentially, in a high thermoelectric power factor. Two-dimensional (2D) materials are the latest class of low dimensional materials studied for thermoelectric applications. The experimental exfoliation of graphene, a single-layer of carbon atoms in 2004, triggered an avalanche of studies devoted to 2D materials in view of electronic, thermal, and optical applications. One can mix and match and stack 2D layers to form van der Waals hetero-structures. Such structures have extreme anisotropic transport properties. Both in-plane and cross-plane thermoelectric transport in these structures are of interest. In this short review article, we first review the progress achieved so far in the study of thermoelectric transport properties of graphene, the most widely studied 2D material, as a representative of interesting in-plane thermoelectric properties. Then, we turn our attention to the layered materials, in their cross-plane direction, highlighting their role as potential structures for solid-state thermionic power generators and coolers.     

Nanostructural thermoelectric materials and their performance

In this review, an attempt was made to introduce the traditional concepts and materials in thermoelectric application and the recent development in searching high-performance thermoelectric materials. Due to the use of nanostructural engineering, thermoelectric materials with a high figure of merit are designed, leading to their blooming application in the energy field. One dimensional nanotubes and nanoribbons, two-dimensional planner structures, nanocomposites, and heterostructures were summarized. In addition, the state-of-the-art theoretical calculation in the prediction of thermoelectric materials was also reviewed, including the molecular dynamics (MD), Boltzmann transport equation, and non-equilibrium Green’s function. The combination of experimental fabrication and first-principles prediction significantly promotes the discovery of new promising candidates in the thermoelectric field.     

Parametric study of asymmetric thermoelectric devices for power generation

Thermoelectric devices are considered a promising technique for recycling waste heat. In the present work, a three-dimensional numerical model is developed to study the output performance of thermoelectric devices. A comprehensive analysis is performed based on a conventional π-type thermoelectric couple. The results indicate that the maximum power of thermoelectric devices generally increases with a decrease in height and an increase in cross-sectional area; the maximum efficiency exhibits the opposite trends. The best way to reduce heat losses is by using ceramic plates with higher thermal conductivity. Moreover, the parasitic internal resistance exists in the thermoelements, and its influencing factors are studied. To minimize electric losses, an asymmetric structure is proposed for thermoelectric devices. The results exhibit that the optimal cross-sectional area ratio of the p-type and n-type legs (S_p/S_n) is mainly contingent upon the thermoelectric material parameters; the greater the differences in the parameters of p-type and n-type thermoelectric materials, the greater the gains provided by the asymmetric structure. Furthermore, the experimental data present great consistency with the numerical results. The research results may help guide the design of thermoelectric devices with relatively lower power losses.     

The influence of the Thomson effect on the performance of a thermoelectric cooler

The temperature distribution of a thermoelectric cooler under the influence of the Thomson effect, the Joule heating, the Fourier’s heat conduction, and the radiation and convection heat transfer is derived. The influence of the Thomson effect on the temperature profiles, on the fraction of the Joule’s heat that flows back to the low-temperature side, and consequently on the maximum attainable temperature difference and the maximum allowable heat load are emphasized and explored. The results suggest that the cooling efficiency of a thermoelectric cooler can be improved not only by increasing the figure-of-merit of the thermoelectric materials but also by taking advantage of the Thomson effect. A possible development direction for the thermoelectric materials is thus given.     

Inorganic thermoelectric materials: A review

Thermoelectric generator, which converts heat into electrical energy, has great potential to power portable devices. Nevertheless, the efficiency of a thermoelectric generator suffers due to inefficient thermoelectric material performance. In the last two decades, the performance of inorganic thermoelectric materials has been significantly advanced through rigorous efforts and novel techniques. In this review, major issues and recent advancements that are associated with the efficiency of inorganic thermoelectric materials are encapsulated. In addition, miscellaneous optimization strategies, such as band engineering, energy filtering, modulation doping, and low dimensional materials to improve the performance of inorganic thermoelectric materials are reported. The methodological reviews and analyses showed that all these techniques have significantly enhanced the Seebeck coefficient, electrical conductivity, and reduced the thermal conductivity, consequently, improved ZT value to 2.42, 2.6, and 1.85 for near-room, medium, and high temperature inorganic thermoelectric material, respectively. Moreover, this review also focuses on the performance of silicon nanowires and their common fabrication techniques, which have the potential for thermoelectric power generation. Finally, the key outcomes along with future directions from this review are discussed at the end of this article.