Highly flexible and excellent performance continuous carbon nanotube fibrous thermoelectric modules for diversified applications

A highly flexible and continuous fibrous thermoelectric (TE) module with high-performance has been fabricated based on an ultra-long single-walled carbon nanotube fiber, which effectively avoids the drawbacks of traditional inorganic TE based modules. The maximum output power density of a 1-cm long fibrous TE module with 8 p-n pairs can reach to 3436 μW·cm^-2, the power per unit weight to 2034 μW·g^-1, at a steady-state temperature difference of 50 K. The continuous fibrous TE module is used to detect temperature change of a single point, which exhibits a good responsiveness and excellent stability. Because of its adjustability in length, the flexible fibrous TE module can satisfy the transformation of the temperature difference between two distant heat sources into electrical energy. Based on the signal of the as-fabricated TE module, a multi-region recognizer has been designed and demonstrated. The highly flexible and continuous fibrous TE module with excellent performance shows a great potential in diversified applications of TE generation, temperature detection, and position identification.     

平板集热太阳热电器件建模及结构优化

太阳能热电转换是光伏效应外另一种直接将太阳辐射转变为电能的途径, 近年来已经成为太阳能利用的热点之一. 本文以Bi₂Te₃材料为基础构建平板集热太阳热电器件模型, 采用有限元法分析AM1.5辐射条件下器件温度分布情况, 并结合基于温度的物性参数计算集热比、热臂截面积与长度变化等因素对器件的开路电压、 最大输出功率及转化效率的影响. 研究发现: 集热比与热臂长度的变化对器件性能有显著影响, 热臂截面积的变化对器件转化效率影响相对较弱; 在这一模型中, 平板集热太阳热电器件的转化效率达到1.56%.     

Recent advances in organic,inorganic, and hybrid thermoelectric aerogels

The thermoelectric(TE)materials and corresponding TE devices can achieve direct heat-to-electricity conversion,thus have wide applications in heat energy harvesting(power generator),wearable electronics and local cooling.In recent years,aerogel-based TE materials have received considerable attention and have made remarkable progress because of their unique structural,electrical and thermal properties.In this review,the recent progress in both organic,inorganic,and composite/hybrid TE aerogels is systematically summarized,including the main constituents,preparation method,TE performance,as well as factors affecting the TE performance and the corresponding mechanism.Moreover,two typical aerogel-based TE devices/generators are compared and analyzed in terms of assembly modes and output performance.Finally,the present challenges and some tentative suggestions for future research prospects are provided in conclusion.     

半导体温差发电过程的模型分析与数值仿真

本文提出一种新型的半导体温差发电模型,在温差发电过程的数值模拟中考虑了热电单元之间封闭腔体内空气传热的影响.同时进一步运用有限元的数值计算方法对不同电臂对数和不同型号温差发电模型的温度场、电压场进行了数值仿真计算,并对仿真结果进行分析.结果表明:采用127对热电单元模型计算的能量转换效率随冷热端温差增大而迅速提高,与采用1对热电单元模型计算的能量转换效率之差从冷热端温差为20℃的0.39%提高到冷热端温差为220℃时的5.16%,能量转换效率比1对热电单元平均高出3.02%.冷端温度恒定在30℃时,温差发电芯片的输出电压、功率以及能量转换效率均随着电偶臂的横截面积的增大而提高,且电偶臂冷热两端的温差越大提高幅度也越大,而温差发电芯片内阻则与电偶臂横截面积成反比关系,当温差为220℃时对应的输出功率最高达28.9 W.     

Detection of internal cracks and ultrasound characterization of nanostructured Bi₂Te₃-based thermoelectrics via acoustic microscopy

The search for thermoelectric (TE) materials for highly efficient devices aims at improving the TE efficiency and broadening their areas of applications. We created nanostructured thermoelectric Bi-Sb-Te-family materials by high energy (ball milling) pre-treatment of the parent materials followed by high-pressure/high-temperature treatment. Bi_0.5Sb_1.5Te₃ compositions with the superfluous maintenance of tellurium was used for the synthesis of the samples with p-type electrical conductivity. Acoustic microscopy was used to study elastic properties and bulk irregularities and to detection of internal cracks both in the parent materials and in the created nanostructured samples. The data has been used for optimization of parameters of synthesis of nanostructured thermoelectrics.     

Bi2Te3 合金低温热电性能及冷能发电研究

利用机械合金化和冷压烧结法制备得到n型和p型Bi₂Te₃基热电材料,在80—300 K温度范围测量了电导率、Seebeck系数,结果表明其具有良好的低温热电性能.采用Bi₂Te₃基热电材料制备出半导体热电器件,并配合附属设备搭建出一套半导体温差发电装置.利用液氮汽化时释放的冷能,对半导体热电器件的发电性能进行实验研究,得出这种半导体热电器件输出电压、输出功率与电流关系式,测得最大的输出功率达到1.33 W,从而证明了冷     

Flexible thermoelectric module based on zinc oxide thin film grown via SILAR

In this work, we used the low temperature solution growth Successive Ionic Layer Adsorption and Reaction (SILAR) for a deposition of the nanostructured undoped and indium doped (ZnO and ZnO:In) thin films on flexible polyimide (PI) substrates for their use as cheap non-toxic thermoelectric materials in the flexible thermoelectric modules of planar type to power up portable and wearable electronics and miniature devices. The use of a zincate solution in the SILAR method allows to obtain ZnO:In film, which after post-growth annealing at 300 °C has low resistivity ρ ≈ 0.02 Ω m, and high Seebeck coefficient −147 μV/K and thermoelectric power factor ~1 μW K⁻² m⁻¹ at near-room temperatures. As evidence of the operability of the manufactured films as the basis of the TE device, we have designed and tested experimental lightweight thin-film thermoelectric module. This TE module is able to produce specific output power 0.8 μW/m² at ΔT = 50 K.     

N-type core-shell heterostructured Bi2S3@Bi nanorods/polyaniline hybrids for stretchable thermoelectric generator

With the growing need on distributed power supply for portable electronics,energy harvesting from environment becomes a promising solution.Organic thermoelectric(TE)materials have advantages in intrinsic flexibility and low thermal conductivity,thus hold great prospect in applications as a flexible power generator from dissipated heat.Nevertheless,the weak electrical transport behaviors of organic TE materials have severely impeded their development.Moreover,compared with p-type organic TE materials,stable and high-performance n-type counterparts are more difficult to obtain.Here,we developed a n-type polyaniline-based hybrid with core-shell heterostructured Bi;S;@Bi nanorods as fillers,showing a Seebeck coefficient-159.4μV/K at room temperature.Further,a couple of n/p legs from the PANI-based hybrids were integrated into an elastomer substrate forming a stretchable thermoelectric generator(TEG),whose function to output stable voltages responding to temperature differences has been demonstrated.The in situ output performance of the TEG under stretching could withstand up to 75%elongation,and stability test showed little degradation over a one-month period in the air.This study provides a promising strategy to develop stable and high thermopower organic TEGs harvesting heat from environment as long-term power supply.     

硒化亚铜薄膜热电性能研究进展

热电材料可以实现热能和电能的相互转换,它是一种环境友好的功能性材料.当前,热电材料的热电转换效率低,这严重制约了热电器件的大规模应用,因此寻找更加优异热电性能的新材料或提高传统热电材料的热电性能成为热电研究的主题.与块状材料相比,薄膜具有二维的宏观性质和一维的纳米结构特性,方便研究材料的物理机制与性能的关系,还适用于制备可穿戴电子设备.本文总结了Cu₂Se薄膜5种不同的制备方法,包括电化学沉积、热蒸发、旋涂、溅射以及脉冲激光沉积.另外,结合典型事例,总结了薄膜的表征手段,并从Cu₂Se的电导率、塞贝克系数和热导率等参数出发,讨论了各个参数对热电性能的影响机制.最后介绍了Cu₂Se薄膜热电的热门应用方向.     

Thermoelectric properties in Mn-doped Bi2Se3

Using n-type and p-type Mn-doped Bi₂Se₃ single crystals, a thin-film-type thermoelectric (TE) module was fabricated and the TE characteristics were investigated. The Seebeck coefficient at room temperature was about 100 μV K⁻¹ with different sign for both materials. From the Seebeck coefficient and resistivity values, the electric power of our TE module was evaluated to be 90 μW for a single couple at the temperature difference of 10 K. This value is compared to that (∼21 μW) of commercialized TE device. Nevertheless, the actual power was measured to be quite small around 0.74 μW, which is much higher than other homemade TE power level. This small power is attributed to the high electrical contact resistance between the TE material and the heat source and sink. Assuming the contact resistance level ∼0.1 Ω similar to that of commercialized TE devices, the electric power should be about 41 μW, which is almost 2 times higher than that in commercialized TE devices. These results propose that the Mn-doped Bi₂Se₃ system is another promising TE material, which can be replaced with the commercialized Bi₂Te₃ system.     

热电制冷LED自然对流散热的设计与优化

为提升高热流密度下LED灯具的自然对流散热性能,以一款基于热电制冷（TEC）的单颗LED小型灯具模组为研究对象,在采用实验测量和回归拟合准确获得TEC性能参数的基础上,建立了有无TEC参与散热的等效热路模型,并选择合理的数学公式对其进行性能描述,进而遵循本文设计的计算流程快速得到各种散热性能数据。LED模组的散热分析表明：在恒定的LED热功率下,施加最佳的TEC电流可获得最高的散热性能;LED热功率越低,安装TEC的散热性能越比常规方法优异。经遗传算法优化前后的性能对比分析表明：优化后结构中TEC的合理工作区明显增大,能满足LED更高功率的散热需求;当LED为0.493 W时,优化后结构的最佳结温仅为15.66℃,远低于30℃的环境温度。基于TEC实验数据建立的等效热路模型,能为装配TEC的LED模组提供快速完整的散热设计分析与结构优化的合理方案。     

Strategies for discovery and optimization of thermoelectric materials: Role of real objects and local fields

Thermoelectric materials provide a renewable and eco-friendly solution to mitigate energy shortages and to reduce environmental pollution via direct heat-to-electricity conversion. Discovery of the novel thermoelectric materials and optimization of the state-of-the-art material systems lie at the core of the thermoelectric society, the basic concept behind these being comprehension and manipulation of the physical principles and transport properties regarding thermoelectric materials. In this mini-review, certain examples for designing high-performance bulk thermoelectric materials are presented from the perspectives of both real objects and local fields. The highlights of this topic involve the Rashba effect, Peierls distortion, local magnetic field, and local stress field, which cover several aspects in the field of thermoelectric research. We conclude with an overview of future developments in thermoelectricity.     

Generating power of a thermoelectric generator under periodically alternating temperature gradients

The thermo-emf ΔV and thermoelectric current ΔI generated by imposing a temperature gradient alternating at a period of T on a thermoelectric (TE) generator were measured as a function of t, where t is the lapsed time and 1/T was varied from 0 to 1/30 s^-1. A TE generator was sandwiched between two Peltier modules connected in series. The alternating temperature gradients were produced by imposing an alternating voltage V on two Peltier modules, where V was varied from 1.0 to 3.7 V. Both ΔV and ΔI generated by the TE generator oscillate at a period of T but their amplitudes tend to increase monotonically with an increase of V. The effective thermo-emf ΔV_eff and current ΔI_eff calculated from ΔV and ΔI increase abruptly with an increase of 1/T and have a local maximum at 1/T=1/120 or 1/240 s^-1. The generating power ΔW_eff(=ΔV_effΔI_eff) tends to increase proportionally with an increase of input power W_input, owing to the increase in the temperature difference. The rate of ΔW_eff to W_input at 1/T=1/240 s^-1 reached approximately 3.2 times as large as that obtained for the steady temperature gradient corresponding to 1/T=0 s^-1. It was thus found that the generating power of the TE generator operating under the temperature gradient alternating at an optimum period is remarkably increased compared to that of a TE generator working under a conventional steady temperature gradient. PACS 72.15.Jf; 84.60.Rb; 85.30De     

Recent advances on thermoelectric materials

By converting waste heat into electricity through the thermoelectric power of solids without producing greenhouse gas emissions, thermoelectric generators could be an important part of the solution to today’s energy challenge. There has been a resurgence in the search for new materials for advanced thermoelectric energy conversion applications. In this paper, we will review recent efforts on improving thermoelectric efficiency. Particularly, several novel proof-of-principle approaches such as phonon disorder in phonon-glass-electron crystals, low dimensionality in nanostructured materials and charge-spin-orbital degeneracy in strongly correlated systems on thermoelectric performance will be discussed.      

太阳能光伏-温差发电驱动的新型冰箱模型设计与热力学分析

结合太阳能电池温度特性和温差发电特点,设计了一套新的太阳能光伏发电-温差发电驱动的冰箱模型,该模型包括太阳能光伏电池、半导体温差发电模块、电源控制系统等.根据负载用电需求,做出了光伏发电系统的设计方案.采用热力学基本理论,对该模型进行了工作效率及 火 用 效率的分析.结果发现:能效比COP达到了2.73(一般 冰箱COP为2左右), 火 用 效率也达到42.5%.同时,该系统模型环境效益明显,可以减排CO₂ 1394.2 kg,SO₂     

稳态平板法在热电器件热电转换效率测试中的应用

将稳态平板法测导热系数的实验应用于热电器件热电转换效率的测试,通过测量输入器件的传热速率和负载的输出电功获得热电器件的热电转换效率。研究发现,稳态平板法可以测量工作温度在室温到100℃范围内热电器件的热电转换效率。     

Electronic and thermoelectric properties of Mg_2Ge_xSn-_(1-x)(x=0.25,0.50,0.75) solid solutions by first-principles calculations

The electronic structure and thermoelectric(TE) properties of Mg_2Ge_xSn_(1-x)(x = 0.25, 0.50, 0.75) solid solutions are investigated by first-principles calculations and semi-classical Boltzmann theory. The special quasi-random structure(SQS) is used to model the solid solutions, which can produce reasonable band gaps with respect to experimental results.The n-type solid solutions have an excellent thermoelectric performance with maximum zT values exceeding 2.0, where the combination of low lattice thermal conductivity and high power factor(PF) plays an important role. These values are higher than those of pure Mg_2Sn and Mg_2Ge. The p-type solid solutions are inferior to the n-type ones, mainly due to the much lower PF. The maximum zT value of 0.62 is predicted for p-type Mg_2Ge_(0.25)Sn_(0.75) at 800K. The results suggest that the n-type Mg_2Ge_xSn_(1-x) solid solutions are promising mid-temperature TE materials.     

基于梯度翅片换热器的热电发电系统性能研究

本文建立了热电发电系统(TEG)多物理场数值模型,并充分考虑换热器流体影响,综合研究了具有不同热侧换热器翅片结构的TEG系统性能。在雷诺数为1000~10000范围内,分析了流体沿程温度分布特征、泵功及热电发电模块的能量转换特性.所研究的三种翅片结构包括:全流道等高度直翅片(Fin-1)、下游强化梯度翅片(Fin-2)以及上游强化梯度翅片(Fin-3).研究表明,通道长高比及热电材料覆盖率一定,热电发电功率及转换效率随流量呈二次曲线变化关系,存在最匹配流量使得系统发电性能最佳。等高度直翅片对流量的变化敏感,随流量增大,则压损增大,导致系统净输出功率及发电效率无收益.而梯度翅片可以在更大范围内产生正收益;下游强化梯度翅片具有最佳的流体沿程温度均匀性,但沿程局部热阻却最大.综合考虑沿程局部热阻分布及泵功消耗,上游强化梯度翅片TEG系统净转换效率最高,因此局部热阻分布及泵功综合因素应为TEG内的换热器合理设计的关键。     

Investigations on thermoelectric power of lanthanum oxide doped ferroelectric sodium vanadate

The thermoelectric power of ferroelectric sodium vanadate doped with different concentrations of lanthanum oxide has been measured in the temperature range covering their transition temperatures. It has been observed that the thermoelectric power increases with temperature, attains maximum value and with further increase in the temperature decreases to zero, indicating Curie temperature of the respective samples; however, it changes the sign for higher temperature. The thermoelectric power of sodium vanadate increases to maximum with increase in doping concentration of lanthanum oxide from 0.025 to 0.1 mol%; however, it decreases for higher concentrations. Pure as well as lanthanum oxide doped sodium vanadate samples showp-type behaviour in the ferroelectric region andn-type behaviour in the paraelectric region.     

高光谱吸收微纳结构表面提高太阳能温差发电性能的研究

采用飞秒激光等离子体丝（飞秒光丝）在金属铝箔表面以不同飞秒光丝扫描速度（5,15,25,35和45 mm·s-1）制备了微纳结构表面,并在太阳光能量主要覆盖的光谱范围（330～890 nm）内对其进行了反射率测量,发现飞秒光丝制备的微纳结构表面具有显著的高光谱吸收特性,并且飞秒光丝扫描速度越慢,光谱吸收率越强,5 mm·s-1条件下微纳结构表面光谱吸收率达97%以上。将制备的高光谱吸收微纳结构表面作为温差发电片（TEG）光吸收体,以此为基础构建了考虑太阳光辐照及温差发电模块（即TEG模块：结合微纳结构表面的TEG）散热情况的仿真实验环境并进行发电功率测量。研究结果表明,具有微纳结构的铝表面（5 mm·s-1制备条件下）与抛光铝箔或裸发电片相比,光电转化效率（发电效率）可分别提高43.3和10.7倍。进一步研究了TEG模块的温差发电的过程与机理,将TEG模块的温差发电过程分为光热（光能转化为热能）与热电（热能转化为电能）两个转化过程分析：首先在光热转化过程中,微纳结构表面增强了太阳光吸收效率,为光热转化提供更多的光子能量,实现了其在表面更多的热量沉积,进而在之后的热电转化过程中,更多的热能沉积使得TEG模块的载流子迁移率得到了很大提升,这样在同样的温差（发电片冷热端的温度差值）条件下,微纳结构表面与普通表面相比可以获得更高的热电转化效率。因此,微纳结构表面的高光谱吸收性能使得TEG模块经光热转化后得到的高热能沉积使载流子迁移率得到了提高,进而显著提升了TEG模块发电性能,这是微纳结构表面增强TEG温差发电效率的主要原因。这一机理的揭示,为TEG模块发电性能的进一步优化和提升提供了理论依据,对TEG模块的实际应用具有重要的意义。