Lignin-Derived Ionic Conducting Membranes for Low-Grade Thermal Energy Harvesting

Wood-based ionic conductive membranes have emerged as a new paradigm for low-grade thermal energy harvesting applications due to their unique andtailorable structures. Herein, a lignin-derivedionic conducting membrane with hierarchical aligned channels is synthesized viaa double network crosslinking approach. Their excellent thermal stability andsuperior swelling ratio allow their optimization as low-grade heat recovery technologies. Several vertically aligned nanoscaleconfinements are found in the synthesized membranes, contributing towardenhanced ionic diffusion. Among all the combinations, the membrane comprising69.2 wt.% of lignin and infiltrated with 0.5 m KOH exhibits anexceptional ionic figure of merit (ZTi) of 0.25, relatively higher ionic conductivity(51.5 mS cm^‒1), lower thermal conductivity(0.195 W m^‒1·K), and a remarkable ionic Seebeck coefficientof 5.71 mV K^‒1 under the application of an axialtemperature gradient. A numerical model is also utilized to evaluate theveracity of experimental observations and to gain a better understanding of thefundamental mechanisms involved in attaining such values. These results displaythe potential of lignin-basedmembranes for future thermal energy harvesting applications and are a new facetin thermoelectric energy conversion which is certain to pave the way forfurther investigations on sustainable ionic conductive membranes.     

Complementary n‐Type and p‐Type Graphene Films for High Power Factor Thermoelectric Generators

Solution‐phase exfoliated graphene has always been an attractive material for flexible thermoelectric applications, but traditional oxidative routes suffer from poor flake quality and a lack of quality doping techniques to make complementary n‐type and p‐type films. Here, it is demonstrated that by changing the adsorbed surfactant during the intercalation‐exfoliation process (polyvinylpyrrolidone for n‐type, pyrenebutyric acid for p‐type), both extremely high electrical conductivity (3010 and 2330 S cm^?1) and high Seebeck coefficients (53.1 and ?45.5 µV K^?1) can be achieved. The result is that both of these films show remarkable power factors, over 600 µW m^?1 K^?2 at room temperature, which is over an order of magnitude better than that in previous works demonstrating complementary n‐type and p‐type graphene thermoelectric films. Based on these films, a full all‐graphene thermoelectric device is constructed as a proof of concept, where a peak power of 5.0 nW is recorded at a temperature difference of 50 K.     

High Thermopower of Agarose-Based Ionic Thermoelectric Gel Through Micellization Effect Decoupling the Cation/Anion Thermodiffusion

Ionic thermoelectric (i-TE) gels can have a high thermopower, if the thermodiffusion of mobile cation/anion is decoupled, attracting increasing attentions. Herein, it is shown a high p-type i-TE thermopower of 41.8 mV K⁻¹ in agarose-based ionic thermoelectric gels of AG-x Na:DBS (AG: agarose, Na:DBS: sodium dodecyl benzene sulfonate). The exclusively high thermopower is relative to the successfully decoupling the thermodiffusion of cation Na⁺ and anion DBS⁻. A unique porous structure is formed due to the micellization of the amphiphilic DBS⁻ with the hydrophilic benzenesulfonic group attached to the hydrous agarose gel chains, while the hydrophobic alkyl chain point to the pore centers. As a result, the DBS⁻ micelles are almost immobile as compared with Na⁺, which can be reconsidered as a part of the gel matrix. The work shines a light on decoupling of cation/anion thermodiffusion through tailoring the microstructure of the quasi-solid i-TE materials.     

芯片冷却中热电制冷器性能的实验研究

设计了电子芯片冷却实验装置,对热电制冷器在电子芯片冷却中的冷却效果和制冷性能进行了研究。实验结果表明,不仅热电制冷片热端冷却水流量是影响冷却效果的重要因素,而且热电电流和芯片功率与热电冷却性能也有着密切的关系。实验结果对热电冷却器的最佳冷却性能的确定具有一定的参考意义。     

Contrasting Cu Roles Lead to High Ranged Thermoelectric Performance of PbS

To obtain high-performance PbS-based thermoelectric materials, this study introduces Cu with different contrasting roles in p-type PbS, which can effectively decrease the lattice thermal conductivity and simultaneously optimize the electrical transport properties. Experimental results illustrate that Cu substitutions and Cu interstitials can improve carrier mobility through lowering effective mass (m*) and carrier concentration (n_H) in a low temperature range (300–450 K), and further optimize temperature-dependent n_H in a high temperature range (450–823 K). Both decreased m* and n_H shift the peak power factor to low temperature range, leading to an ultrahigh power factor ≈23 µW cm⁻¹ K⁻² at 423 K for Pb_0.99Cu_0.01S-0.01Cu. Additionally, the special dynamic-doping behaviors of Cu can continuously promote n_H to approach the temperature-dependent relationship of (n_{H, opt}) ≈ (m*T)^1.5, which brings about an eminent average power factor (PF_ave) ≈ 18 µW cm⁻¹ K⁻² among 300–823 K in Pb_0.99Cu_0.01S-0.01Cu. Furthermore, the microstructure characterizations unclose that the atomic and nanoscale Cu-containing defects can effectively intensify the phonon scattering and suppress the lattice thermal conductivity. Consequently, both high ZT (≈0.2 at 300 K) and peak ZT (≈1.2 at 773 K) result in a record-high average ZT (ZT_ave) of ≈0.79 at 300–823 K for Pb_0.99Cu_0.01S-0.01Cu.     

Approach to the Practical Use of Thermoelectric Power Generation

The results of research and development in the Japanese national project “Development for Advanced Thermoelectric Conversion Systems” are summarized, and the approaches to practical use of advanced thermoelectric modules and power generation systems are presented. The 5-year national project was successfully completed in March 2007. Three kinds of high- efficiency cascaded thermoelectric modules and two kinds of innovative Bi-Te thermoelectric modules were successfully developed. Heat cycle tests for three types of modules were also completed. Moreover, four types of advanced thermoelectric power generation systems were experimentally demonstrated for recovery of waste heat from the industrial and private sectors. In order to proceed further, thermoelectric power generation systems using practical heat sources were followed after installation of the developed modules. In parallel, various approaches for practical use by private companies, as well as plans for the next-phase project by the National Institute of Advanced Industrial Science and Technology (AIST) and the Engineering Advancement Association (ENAA), were also followed. The scenarios to proceed to the commercial phase of thermoelectric power generation are discussed on the basis of the results of the national project.     

Atomic Disorders Induced by Silver and Magnesium Ion Migrations Favor High Thermoelectric Performance in α‐MgAgSb‐Based Materials

Thermoelectric devices can directly convert thermal energy to electricity or vice versa with the efficiency being determined by the materials’ dimensionless figure of merit (ZT). Since the revival of interests in the last decades, substantial achievements have been reached in search of high‐performance thermoelectric materials, especially in the high temperature regime. In the near‐room‐temperature regime, MgAgSb‐based materials are recently obtained with ZT ≈ 0.9 at 300 K and ≈1.4 at 525 K, as well as a record high energy conversion efficiency of 8.5%. However, the underlying mechanism responsible for the performance in this family of materials has been poorly understood. Here, based on structure refinements, scanning transmission electron microscopy (STEM), NMR experiments, and density function theory (DFT) calculations, unique silver and magnesium ion migrations in α‐MgAg_0.97Sb_0.99 are disclosed. It is revealed that the local atomic disorders induced by concurrent ion migrations are the major origin of the low thermal conductivity and play an important role in the good ZT in MgAgSb‐based materials.     

Analysis of Nanostructuring in High Figure‐of‐Merit Ag1–xPbmSbTe2+m Thermoelectric Materials

Thermoelectric materials based on quaternary compounds Ag_1?xPb_mSbTe_2+m exhibit high dimensionless figure‐of‐merit values, ranging from 1.5 to 1.7 at 700 K. The primary factor contributing to the high figure of merit is a low lattice thermal conductivity, achieved through nanostructuring during melt solidification. As a consequence of nucleation and growth of a second phase, coherent nanoscale inclusions form throughout the material, which are believed to result in scattering of acoustic phonons while causing only minimal scattering of charge carriers. Here, characterization of the nanosized inclusions in Ag_0.53Pb₁₈Sb_1.2Te₂₀ that shows a strong tendency for crystallographic orientation along the {001} planes, with a high degree of lattice strain at the interface, consistent with a coherent interfacial boundary is reported. The inclusions are enriched in Ag relative to the matrix, and seem to adopt a cubic, 96 atom per unit cell Ag₂Te phase based on the Ti₂Ni type structure. In‐situ high‐temperature synchrotron radiation diffraction studies indicated that the inclusions remain thermally stable to at least 800 K.     

A Versatile Method to Fabricate Highly In‐Plane Aligned Conducting Polymer Films with Anisotropic Charge Transport and Thermoelectric Properties: The Key Role of Alkyl Side Chain Layers on the Doping Mechanism

A general method is proposed to produce oriented and highly crystalline conducting polymer layers. It combines the controlled orientation/crystallization of polymer films by high‐temperature rubbing with a soft‐doping method based on spin‐coating a solution of dopants in an orthogonal solvent. Doping rubbed films of regioregular poly(3‐alkylthiophene)s and poly(2,5‐bis(3‐dodecylthiophen‐2‐yl)thieno[3,2‐b ]thiophene) with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄TCNQ) yields highly oriented conducting polymer films that display polarized UV–visible–near‐infrared (NIR) absorption, anisotropy in charge transport, and thermoelectric properties. Transmission electron microscopy and polarized UV–vis–NIR spectroscopy help understand and clarify the structure of the films and the doping mechanism. F₄TCNQ^? anions are incorporated into the layers of side chains and orient with their long molecular axis perpendicular to the polymer chains. The ordering of dopant molecules depends closely on the length and packing of the alkyl side chains. Increasing the dopant concentration results in a continuous variation of unit cell parameters of the doped phase. The high orientation results in anisotropic charge conductivity (σ) and thermoelectric properties that are both enhanced in the direction of the polymer chains (σ = 22 ± 5 S cm^?1 and S = 60 ± 2 µV K^?1). The method of fabrication of such highly oriented conducting polymer films is versatile and is applicable to a large palette of semiconducting polymers.     

Positive Effect of Ge Vacancies on Facilitating Band Convergence and Suppressing Bipolar Transport in GeTe‐Based Alloys for High Thermoelectric Performance

Because the intrinsic Ge vacancies in GeTe usually lead to high hole concentration beyond the optimal range, many previous studies tend to consider Ge vacancies as negative effects on increasing the figure of merit ZT of GeTe‐based alloys, and consequently have proposed various approaches to suppress Ge vacancies. However, in this work, it is demonstrated that the Ge vacancies can have great positive effects on enhancing the ZT of GeTe‐based alloys when the hole concentration falls into the optimal range. First, hole concentration of GeTe is reduced close to the optimal range by co‐alloying of Pb and Bi, and then the Ge vacancies are increased by adding excess Te into the Ge_0.8Pb_0.1Bi_0.1Te_1+x. The Ge vacancies can cause lattice shrinkage and promote rhombohedral‐to‐cubic phase transition. As revealed by first‐principle calculations, theoretical simulations, and experimental tests, Ge vacancies can facilitate the band convergence, suppress the bipolar transport at higher temperature range, and reduce the lattice thermal conductivity. Combining these effects, a peak ZT of 1.92 at 637 K and an average ZT of 1.34 within 300–773 K in Ge_0.8Pb_0.1Bi_0.1Te_1.06 can be obtained, demonstrating the great significance of utilizing vacancy‐type defects for enhancing ZT.     

Rational Manipulation of Epitaxial Strains Enabled Valence Band Convergence and High Thermoelectric Performances in Mg3Sb2 Films

Strain engineering is demonstrated to effectively regulate the functionality of materials, such as thermoelectric, ferroelectric, and photovoltaic properties. As the straightforward approach of strain engineering, epitaxial strain is usually proposed for rationally manipulating the electronic structure and performances of thermoelectric materials, but has rarely been verified experimentally. In this study, tunable and large epitaxial strains are demonstrated, as well as the resulting valence band convergence can be achieved in the Mg₃Sb₂ epi-films with the choice of substrates. The large epitaxial strains up to 8% in Mg₃Sb₂ films represent one of the most striking results in strain engineering. The angle-resolved photoemission spectroscopy measurements and the theoretical calculations reveal the vital role of epitaxial strain in tuning the crystal field splitting and the band structure of Mg₃Sb₂. Benefiting from the appropriate manipulation of the crystal field effect via in-plane compressive strain, the valence band convergence is unambiguously discovered in the strained Mg₃Sb₂ film grown on InP(111) substrate. As a result, a state-of-the-art thermoelectric power factor of 0.94 mWm⁻¹K⁻² is achieved in the strain-engineered Mg₃Sb₂ film, well exceeding that of the strain-relaxed Mg₃Sb₂. The work paves the way for effectively manipulating epitaxial strain and band convergence for Mg₃Sb₂ and other thermoelectric films.     

Engineering of Graphene Layer Orientation to Attain High Rate Capability and Anisotropic Properties in Li‐Ion Battery Electrodes

Novel carbon films with different graphene layer orientations are investigated as electrode materials for Li‐ion batteries. It is demonstrated that engineering the crystallographic orientation with graphene layers oriented perpendicular to the surface substantially alters stress evolution during Li insertion. With this crystallographic orientation the intercalating/de‐intercalating Li‐ions also have direct access to the graphene interlayer spaces, resulting in higher capacity at faster electrochemical cycling, compared to carbon films with graphene layers parallel to the film surface. Electrodes with perpendicular alignment are prepared by supramolecular synthesis using either spin coating or bar coating of chromonic liquid crystal precursors into precursor organic films followed by in situ carbonization. These materials are compared with in situ stress measurements during lithiation/delithiation cycles, and the bar‐coated films exhibit a highly anisotropic stress which is consistent with long‐range alignment of the graphene layers. In contrast, the in‐plane stresses in the spin‐coated films are isotropic, which is consistent with the presence of randomly oriented domains (still with graphene layers oriented perpendicular to the surface). Overall, the use of thin film graphitic materials with controlled crystallographic orientations provides a valuable platform for investigating the impact of graphene structure on the properties of Li‐ion battery electrode materials.     

Directional Reconstruction of Iron Oxides to Active Sites for Superior Water Oxidation

Rationally constructing and manipulating the in situ formed catalytically active surface of catalysts remains a tremendous challenge for a highly efficient water electrolysis. Herein, an anion and cation co-induced strategy is presented to modulate in situ catalyst dissolution-redeposition and to achieve the directional reconstruction of Zn and S co-doped Fe₂O₃ and Fe₃O₄ on iron foams (Zn,S-Fe₂O₃-Fe₃O₄/IF), for oxygen evolution reaction (OER). Benefiting from Zn, S co-doping and the presence of Fe₃O₄, a directionally reconstructed surface is obtained. The Fe₂O₃ in the Zn,S-Fe₂O₃-Fe₃O₄/IF is directionally reconstructed into FeOOH (Zn,S-Fe₃O₄-FeOOH/IF), in which the S leaching promotes the Fe dissolution and the Zn co-deposition regulates the activity of the obtained FeOOH. Moreover, the presence of Fe₃O₄ provides a stable site for FeOOH deposition, and thus causes more FeOOH active components to be formed. Directionally reconstructed Zn,S-Fe₃O₄-FeOOH/IF outperformes many state-of-the-art OER catalysts and demonstrates a remarkable stability. The experimental and density functional theory (DFT) calculation results show that the introduction of Zn-doped FeOOH with abundant oxygen vacancies through directional reconstruction has activated lattice O atoms, facilitating the OER process on the heterojunction surface following the lattice oxygen mechanism (LOM) pathway. This work makes a stride in co-induced strategy modulating directional reconstruction.     

Supplementary Networking of Interpenetrating Polymer System (SNIPSy) Strategy to Develop Strong & High Water Content Ionic Hydrogels for Solid Electrolyte Applications

To synthesize hydrogels that possess tensile strength and modulus together in MPas along with extensibility at high equilibrium water content (≥90 wt%) is challenging but important from the application perspective. Especially, such hydrogel compositions are useful for fabricating flexible electronics devices for subsea applications, where underwater risk-free implementation and optimum device performance at low temperature (≈0 °C) and high hydrostatic pressure (≤20 bar) conditions is desirable. The high water content of hydrogel is necessary to facilitate ion transportation, and mechanical strength is desirable to maintain a stable electrode–electrolyte interface under load. In this study, supplementary networking of an interpenetrating polymer system strategy is utilized to develop ionic hydrogels with tensile strength and Young's modulus values up to 2 and 1.67 MPa, respectively, at high equilibrium water content value up to 96%. Cost-effective, durable, rechargeable, and flexible batteries are fabricated using the Zn & Li ion soaked hydrogel as solid electrolyte without barrier. These batteries display minimal loss in capacity when immersed in water, deformed, exposed to flame, put under high load, and operated under low-temperature conditions suggesting the viability for subsea application.     

Ion-Bolometric Effect in Grain Boundaries Enabled High Photovoltage Response for NIR to Terahertz Photodetection

The excellent performance of bolometers in the infrared and terahertz regions has attracted great attention. Understanding the transport process of charged particles is an efficient approach to determine detector performance. However, the lack of studies on the fine-scale spatial motion of microscopic particles in bolometers has prevented a full understanding of the physical process. Herein, using micro-nano-scale optoelectronic performance correlation measurements, it is described how prevalent defect states at the grain boundaries (GBs) decrease current responses. Ions at the GBs of the polycrystalline perovskite bolometer contribute to the photocurrent via thermal excitons. In addition, the built-in electric field established by ion migration fluctuates periodically with the strength of the light-heating process due to the interaction between the bolometric effect and the Coulomb force. Additionally, the first ion-bolometric detector is demonstrated with a significant photovoltage response to infrared and THz waves (75.3 kV W⁻¹ at 1064 nm and 2.3 kV W⁻¹ at 0.22 THz). An examination of the THz images shows the potential for large-area THz imaging applications. The ion-bolometric effect combines the broad spectral characteristics of the bolometer effect with the temperature sensitivity due to ion migration and provides a unique perspective on detector technology.     

Utilization of the Antiferromagnetic IrMn Electrode in Spin Thermoelectric Devices and Their Beneficial Hybrid for Thermopiles

The thermoelectric effect in various magnetic systems, in which electric voltage is generated by a spin current, has attracted much interest owing to its potential applications in energy harvesting, but its power generation capability has to be improved further for actual applications. In this study, the first instance of the formation of a spin thermopile via a simplified and straightforward method which utilizes two distinct characteristics of antiferromagnetic IrMn is reported: the inverse spin Hall effect and the exchange bias. The former allows the IrMn efficiently to convert the thermally induced spin current into a measurable voltage, and the latter can be used to control the spin direction of adjacent ferromagnetic materials. It is observed that a thermoelectric signal is successfully amplified in spin thermopiles with exchange‐biased IrMn/CoFeB structures, where an alternating magnetic alignment is formed using the IrMn thickness dependence of the exchange bias. The scalable signal on a number of thermopiles allowing a large‐area application paves the way toward the development of practical spin thermoelectric devices. A detailed model analysis is also provided for a quantitative understanding of the thermoelectric voltages, which consist of the spin Seebeck and anomalous Nernst contributions.     

Flexible and Transparent Nanocomposite of Reduced Graphene Oxide and P(VDF‐TrFE) Copolymer for High Thermal Responsivity in a Field‐Effect Transistor

A new class of temperature‐sensing materials is demonstrated along with their integration into transparent and flexible field‐effect transistor (FET) temperature sensors with high thermal responsivity, stability, and reproducibility. The novelty of this particular type of temperature sensor is the incorporation of an R‐GO/P(VDF‐TrFE) nanocomposite channel as a sensing layer that is highly responsive to temperature, and is optically transparent and mechanically flexible. Furthermore, the nanocomposite sensing layer is easily coated onto flexible substrates for the fabrication of transparent and flexible FETs using a simple spin‐coating method. The transparent and flexible nanocomposite FETs are capable of detecting an extremely small temperature change as small as 0.1 °C and are highly responsive to human body temperature. Temperature responsivity and optical transmittance of transparent nanocomposite FETs were adjustable and tuneable by changing the thickness and R‐GO concentration of the nanocomposite.     

用于SPICE模拟高频互连效应的RLC电路模型

提出了一个用于ＳＰＩＣＥ模拟高频互连 应的ＰＣＬ互连电路模型,该模型考虑了频率对互连电感、电阻的影响,适用于从芯片间互连到芯片内互连高频效应的分析。基于所提出的互连模型,对频率达１０００ＭＨｚ时芯片内长互连线的延迟、串扰、过冲等互连寄生效应进行了分析,并指出了抑制互连效应的技术途径。     

调整峰值功放电流响应提高效率的LTE-A Doherty 功放*

介绍了一种利用宽带输入匹配网络调整峰值功放输出电流,改善Doherty 功放负载调制效果和带内 效率的设计方法。理论分析表明,Doherty功放中峰值功放C 类偏置情况下带来的带内不一致开启特性会影响输出 电流和负载调制效果。通过引入宽带输入匹配网络,能有效改善它的开启不一致性。为验证分析结果设计了具有 宽带(采用简易实频技术)和窄带两种不同输入匹配网络,用于2.15GHz 频段LTE-A 的Doherty功放。仿真和测试 结果表明,功放的输出功率超过49dBm,在7dB 回退功率处,宽带输入匹配Doherty 功放的带内效率达到42% 以上, 效率波动由10%降低到2%。使用100MHz 宽带LTE-A 信号经过线性化改善后,在40dBm 输出时,宽带输入匹配网 络的Doherty功放上下边带ACLR(adjacent channel leakage ratio)指标为-45.1/-44.9dBc,效率为40.5%,均优于窄带输入匹配网络的Doherty功放。     

Recent Progress of Methods to Enhance Photovoltaic Effect for Self-Powered Heterojunction Photodetectors and Their Applications in Inorganic Low-Dimensional Structures

An important class of photoelectronic devices, self-powered photodetectors, has attracted worldwide attention because of its crucial role in both basic scientific research and commercial/public applications. Thanks to a special synergistic effect, excellent photoelectric properties, and outstanding mechanical stability, the study of heterojunction devices can provide valuable insights and new possibilities for the future of self-powered photodetectors. This paper reviews the recent years of fundamental research of photovoltaic efficiency based on the ferroelectric-enhanced photovoltaic effect, the pyro-phototronic effect, and the piezo-phototronic effect. It also highlights important topics related to heterojunctions and materials that are suitable for self-powered photodetectors. The article concludes with an outlook of the future development in this important and rapidly advancing field.