Enhanced thermoelectric properties of PEDOT:PSS composites by functionalized single wall carbon nanotubes

This contribution investigates the utilization of carboxylic acid and hydroxyl functionalized single wall carbon nanotubes (SWNTs) for enhancing thermoelectric (TE) performances of the composites prepared with an inherently conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Our results indicated an atypical thermoelectric property which is a simultaneous increase in electrical conductivity and the Seebeck coefficient which leads a greater power factor (PF) up to 22 μW m⁻¹ K⁻² while it is only 0.7 μW m⁻¹ K⁻² for the sample prepared with pristine SWNT. The functionalities on the carbon nanotube walls facilitate blend dispersion in aqueous media without requiring any surfactants and also enhance PFs as a result of improved charge transport routes. The improvement in the thermoelectric performance can be ascribed to hydrogen bonds with the -COOH or -OH groups on the nanotube walls which help induce the polymer chains to adopt an extended conformation.     

Thermoelectric properties of porous SiC/C composites

We developed a porous SiC/C composite by oxidizing a SiC/C composite made from a mixed powder of wood charcoal and SiO₂ (32–45 μm) by pulse current sintering at 1600 and 1800 °C under a N₂ atmosphere. The microstructures of the porous SiC/C composites with oxidation and the SiC/C composites without oxidation were analyzed by Raman spectroscopy and scanning electron microscopy (SEM). Raman spectra revealed the disappearance of excess carbon and the presence of β-SiC. The porous microstructure was monitored by SEM observation as a function of the heat treatment temperature. The thermoelectric properties of porous SiC/C composites with oxidation and SiC/C composites without oxidation were investigated by measuring the Seebeck coefficient, the electrical conductivity and thermal conductivity. The Seebeck coefficient of all samples revealed n-type conduction, and the absolute value of the Seebeck coefficient for the porous SiC/C samples with oxidation was much larger than that for the SiC/C samples without oxidation. For the electrical conductivity the reverse is true. Only the thermal conductivity of the SiC/C sample heated to 1800 °C without oxidation was high initially and stayed rather high. In general, the thermoelectric properties improved at higher measurement temperatures indicating their suitability for high-temperature thermoelectric conversion. A maximum figure of merit of 2.01×10⁻⁵ K⁻¹ was obtained at 700 °C in porous SiC/C samples sintered at 1800 °C with oxidation.     

Phonon phase stability,structural, mechanical,electronic, and thermoelectric properties of two new semiconducting quaternary Heusler alloys CoCuZrZ (Z = Ge and Sn)

For meeting the energy demand, the development of new and novel thermoelectric (TE) materials for power generation is very vital. In this draft, we have theoretically investigated two new quaternary CoCuZrZ (Z = Ge and Sn) Heusler alloys for their structural, mechanical, electronic, and TE properties. In the energy minimization process, the alloys are found to be non-magnetic in the ground state. Based on calculated phonon dispersion curves, formation energy, and elastic constants, we propose that both CoCuZrGe and CoCuZrSn are stable. Furthermore, the mechanical properties indicate that CoCuZrGe (CoCuZrSn) has a brittle (ductile) nature. The electronic properties examined in Perdew-Burke-Ernzerhof (PBE), PBEsol, and modified Becke-Johnson (mBJ) potential, all predict that reported systems are narrow-gap semiconductors (SCs). In addition, the temperature dependent TE properties have been studied by calculating the electronic thermal conductivity (κ), Seebeck coefficient (S), power factor (PF) and electrical conductivity (σ/τ). The obtained positive value of S conveys the materials as p-type SCs, with a maximum value of 26.2 μV/K for CoCuZrGe and 28 μV/K for CoCuZrSn. The σ/τ, κ, and PF show increasing trends with rising temperature. The PF is found to be 1.55 × 10¹² WK⁻²m⁻¹s⁻¹ for CoCuZrGe and 1.38 × 10¹² WK⁻²m⁻¹s⁻¹ for CoCuZrSn. The proposed semiconducting Heusler alloys may receive attention for a range of TE and spintronic applications.     

Proton conductivity of the azole composites based on BEA zeolites with different pore systems

There is a need for a stable and economical solid proton-conducting electrolyte capable of operating at elevated temperatures (>373 K), suitable for high-performance hydrogen fuel cells. In its search, imidazole (Im) or 1,2,4-triazole (Tri) is introduced into the channels of BEA zeolites with different porosity (i.e. the conventional microporous BEA (BEA-O) and two hierarchical materials with structural (BEA-C) or interparticle (BEA-TF) mesoporosity). The proton conductivity of obtained composites increases with increasing azole loading and temperature. The generation of mesopores in BEA zeolites leads to a decrease in the activation energy of proton conductivity in composites and favors the dispersion of a large amount of azoles. Zeolites with structural porosity (BEA-C) allow to introduce the highest amount of the azole molecules (0.29 wt% of imidazole), however the highest proton conductivity and the lowest activation energy is recorded for BEA-TF-0.25Im (σ = 5.86 × 10⁻⁴ S cm⁻¹ at 393 K). A comparison of azole composites (with Im and Tri) of equal azole loadings shows that imidazole-containing materials exhibit significantly higher proton conductivity, regardless of the type of zeolite matrix.     

Thermoelectric properties of P‐doped and V‐doped Fe2O3 for renewable energy conversion

The effect of P and V contents on the microstructure and thermoelectric properties of Fe_2‐xM_xO₃ (M: P and V; 0 ≤ x ≤ 0.01) is studied. Higher P and V contents result in increases of both the grain size and density, thus increasing the electrical conductivity. The absolute values of the Seebeck coefficients of the Fe_2‐xP_xO₃ and Fe_2‐xV_xO₃ increase with increasing P and V contents up to x = 0.0075 and 0.005, respectively, and then decrease with further increase of its concentration. The addition of a small amount of V (0.005) to Fe₂O₃ leads to a marked increase in both the electrical conductivity and Seebeck coefficient. This means that the introduction of a small amount of V is highly effective for improving the thermoelectric properties of Fe₂O₃. Copyright © 2013 John Wiley & Sons, Ltd.     

Design of a thermoelectric generator with fast transient response

Thermoelectric modules are currently used both in Peltier cooling and in Seebeck mode for electricity generation. The developments experienced in both cases depend essentially on two factors: the thermoelectric properties of the materials that form these elements (mainly semiconductors), and the external structure of the semiconductors. Figure of Merit Z is currently the best way of measuring the efficiency of semiconductors, as it relates to the intrinsic parameters of the semiconductor: Seebeck coefficient, thermal resistance, and thermal conductivity. When it comes to evaluating the complete structure, the Coefficient of Performance (COP) is used, relating the electrical power to the thermal power of the module. This paper develops a Thermoelectric Generator (TEG) structure which allows minimising the response time of the thermoelectric device, obtaining short working cycles and, therefore, a higher working frequency.     

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.     

Characterisation of zirconium and titanium phosphates and direct methanol fuel cell (DMFC) performance of functionally graded Nafion(R) composite membranes prepared out of them

Pure layered phosphates of varying crystalline phases and crystallinity and composites of gradient layers of zirconium phosphate in Nafion 117-membranes have been prepared. The proton conductivity and, in case of the composites, also the dynamic mechanical properties of these materials were measured under different conditions of temperature and humidity. Membrane-electrode assemblies with low platinum catalyst loading of 0.4 mg cm⁻² Pt at the cathode and 1.9 mg cm⁻² Pt–Ru at the anode were examined in a direct methanol fuel cell (DMFC) at medium temperatures (130 °C). The conductivity of the layered zirconium phosphates is superior to the titanium phosphates and increases with decreasing crystallite size. The electrical performance of the composites in a DMFC-environment is slightly decreased as compared to the unmodified membrane but taking the reduced methanol crossover into account, higher efficiencies can be reached with the zirconium phosphate modified membrane. Furthermore, the mechanical properties are significantly improved by the presence of the inorganic compound.     

磁控溅射法制备Si1−xGex/B多层薄膜及其热电性能研究

本文通过磁控溅射法制备了一种独特的SiGe/B五层结构薄膜材料,每层结构包含60 nm的Si60Ge40层和0.55 nm的B层。实验考察了薄膜材料的热电性能,结果表明：B掺杂的溅射时间最佳为30 s;当退火温度为650℃时,薄膜的致密性最好,且在此温度下具有较高的Seebeck系数,最大值为6.75 × 10−4 V/K,电阻率最小值为1.6 × 10−5 Ω•m,其功率因子最大值为0.026 W/(m?K2)。     

Preparation of Cu atom doped LaFeO3/activated porous carbon composites and their electrocatalytic nitrogen reduction performance

The electrocatalytic N₂ reduction reaction (NRR) under ambient conditions is a green and sustainable method for ammonia (NH₃) synthesis, and the development of efficient electrocatalysts for NRR is a top priority. In recent years, LaFeO₃ has been widely used in the field of catalysis because of its high stability, low cost, and green advantages. Through strategies such as heteroatom doping and carbon loading, we can effectively increase the content of oxygen vacancies and improve the electrical conductivity of the material to produce composites with unique electronic structures and excellent catalytic properties. In the present work, we prepared single-atom doped LaFeO₃/activated porous carbon composites (LFC/AC) for electrocatalytic NRR. The NH₃ yield and Faraday efficiency of LFC/AC were the highest at 23.876 μg h⁻¹ mg⁻¹ and 6.53% in 0.1 M Na₂SO₄ electrolyte solution, both of which were higher than those of LFC. A series of characterizations and tests have shown that LFC/AC has excellent stability, electrical conductivity, and electrocatalytic properties. The density flooding theory (DFT) simulations were performed to explore the main mechanisms to improve the NRR performance of the materials.     

Enhancement of an IT-SOFC cathode by introducing YSZ: Electrical and electrochemical properties of La0.6Ca0.4Fe0.8Ni0.2O3-δ-YSZ composites

La_0.6Ca_0.4Fe_0.8Ni_0.2O_3-δ (LCFN) is synthesized by liquid mixed method. Its crystalline structure is investigated by using X-ray diffraction. The results show that it has an orthorhombic perovskite structure with Pnma space group symmetry. The 8 mol % Y₂O₃-Stabilized ZrO₂ (YSZ) is physically mixed with various weight percentages of LCFN to form composite cathodes. High-temperature 4-probe conductivity measurements are performed to investigate the electrical behavior of the system. Electrochemical impedance spectroscopy is carried out using symmetric cells with YSZ substrates under equilibrium condition from 850 °C to room temperature. The electrical conductivity is reduced from 271.3 S cm⁻¹ to 49.5 S cm⁻¹ for LCFN and 10 wt % of YSZ-added LCFN (LCFN-YSZ-9010), respectively. The best area specific resistance among all fabricated composites is 0.0080(1) Ω.cm² at 850 °C for LCFN-YSZ-9010 which exhibits almost 50% lower value than LCFN. The YSZ-based composites appear to be suitable than the other low temperature electrolyte based composite cathodes.     

Synthesis of porous flower-like Ni-Co-Mo-S nanostructures on Ni foam for battery-supercapacitor hybrid devices

The synergistic effects of multiple components and unique nanostructures were contributed to prepare the high-performance battery-type electrode materials. In this work, Mo element was introduced to form the ternary transition metal oxides/hydroxides of Ni-Co to improve conductivity, and then charge transfer was accelerated to enhance the capacity storage. After sulfidation, the electrical conductivity was further improved, and a porous flower-like nanostructure was formed. Except for that, the composites of transition metal oxides/hydroxides and sulfides were formed via sulfidation. With the help of the synergistic effects of multiple components and a porous flower-like nanostructure, more Faradic redox reactions occurred. Therefore, the as-prepared porous flower-like Ni-Co-Mo-S nanostructures on Ni foam exhibited an excellent areal capacitance of 7.22 C·cm⁻² at 5 mA·cm⁻² and long-cycle stability (96.9% retention after 5000 cycles). Furthermore, a coin-type battery-supercapacitor hybrid (BSH) device was assembled, which achieved 54.54 Wh·kg⁻¹ at 540 W·kg⁻¹ and displayed 74.8% capacitance retention after 3500 cycles. All mentioned above demonstrated that ternary transition metal oxides/hydroxides precursors via sulfidation can form special structures and the composites of transition metal oxides/hydroxides and sulfides to prepare high-performance battery-type electrodes for energy storage.     

Evaluation of efficiency factors and internal resistance of thermoelectric materials

It is well known that the figure of merit (ZT) is unreliable in calculating the efficiency (?) of micro thermoelectric generators system level and unrealistic when comparing the performance of thermoelectric (TE) materials in the same metric units. To solve this problem, we have used COMSOL multiphysics to design a single leg of micro thermoelectric generators model for computing efficiency factors (? ) and internal resistance using TE materials' constants, such as electrical conductivity (σ ), TE conductivity (K ), and Seebeck coefficient (α ). The TE materials were placed between two copper electrodes, and the first data analyzed were the voltages per meter and electric currents per meter. The internal resistances were calculated by taking the ration of voltages to electric currents, and at the same time, the electric powers were calculated from the products of electric currents and voltages yielding power per unit area in μW cm^?2. The ? were calculated using changes in power (ΔP ), temperature gradient (ΔT ), and the surface area (A ). The obtained results showed that the TE materials with highest ? when the temperatures are between 375 and 550 K are n‐type SiGe and p‐type SiGe. When the temperatures are between 550 and 780 K, the TE materials with the highest ? are PbTe‐Pbl₂, PbTe‐CdTe, and PbTe‐SrTe‐Na. We noted that the ? obtained from eight TE materials in this work are within the range as those reported in the literature between 0.001 and 0.091 μW cm^?2 K^?2. The TE materials with high internal resistances such as PbS, PbTe, and PbSe have ? that is <0.0001 μW cm^?2 K^?2, and those with low internal resistances have ? in the range between 0.002 and 0.0091 μW cm^?2 K^?2. This work has shown that COMSOL multiphysics is a powerful computational tool that can be used to analyze internal resistances and ? of TE materials in the same temperature ranges. Copyright © 2016 John Wiley & Sons, Ltd.     

Solvothermal synthesis of flower-like structure Cu-Mn bimetallic sulfide on Ni-foam for high-performance symmetric supercapacitors

Although transition metal sulfides have gotten extensive attention due to their high electrical conductivity, fast charge transfer kinetics, outstanding mechanical stability, the performances of them applied separately to supercapacitors are not satisfactory, and one solution is to hybridize with other metal sulfide materials. Therefore, in the study, the flower-like structure Cu-Mn bimetallic sulfide on Ni-foam (CuS/MnS@NF) was firstly synthesized by a hierarchical two-step solvothermal reaction to our knowledge, which was directly utilized as electrodes without binders or conductive agents. The CuS/MnS@NF electrode possesses flower-like morphology, superior electrical conductivity, and there are the synergistic effect and intense interaction between CuS and MnS. They can display higher specific capacitance of 1517.07 F g⁻¹ at 1 A g⁻¹ and excellent cyclic stability with specific capacity retention of 115.6% at 10 A g⁻¹ after 3000 cycles, which is more admirable than their individual metal sulfide electrodes (CuS@NF and MnS@NF) and other recently reported metal-based electrodes. In short, the CuS/MnS@NF electrodes are promising candidate when used in battery-type supercapacitors.     

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。     

Ni-YSZ cermets for solid oxide fuel cell anodes via two-step firing

The electrochemical performance and dimensional stability of Ni-YSZ cermets, conventionally used as solid oxide fuel cell anodes, depend strongly on their microstructure and therefore fabrication conditions. This work was focused on the assessment of a less common two-step firing procedure for fabrication of Ni-YSZ cermets with comparatively low nickel fraction of 30 vol.%. The impact of different firing parameters including peak temperature (1623–1723 K), heating/cooling rate (4–10 K/min), and isothermal treatment temperature (1473–1573 K) and time (2–8 h), on the porosity and electrical conductivity of cermets was assessed employing Taguchi experimental planning. The applied procedure yielded Ni-YSZ composites with porosity 26–35% and electrical conductivity ranging from 170 to 420 S/cm at 873–1173 K in 10%H₂–N₂ atmosphere. Microstructural studies indicated that the conductivity is determined mainly by Ni particle size distribution. Analysis of results suggests that, for the studied range of sintering parameters, a higher peak temperature and ramp rate are favorable for the improvement of conductivity, whereas isothermal dwell temperature and time have a rather minor effect on the conductivity level.     

Multilevel N-doped carbon nanotube/graphene supported cobalt phosphide nanoparticles for electrocatalytic hydrogen evolution reaction

Electrochemical water splitting plays an important role in alternative energy studies, since it is highly efficient and environment-friendly. Accordingly, it is an ideal way of providing alternative to meet the urgent need of finding sustainable and clean energy. This study presents the fabrication of CoP attached on multilevel N-doped CNT/graphene (CoP–CNT/NG) hybrids. The multilevel carbon structure can enhance electrical conductivity efficiently and increase the reaction active area immensely. The obtained electrocatalyst exhibits great electronic conductivity (17.8 s cm⁻¹) and HER activity with low overpotential (155 mV at 10 mA cm⁻²), low Tafel slope (69.1 mV dec⁻¹) in 0.5 M H₂SO₄. In addition, the CoP–CNT/NG displays prominent electrochemical durability after 18 h.     

Thermoelectric e.m.f. of battery grade manganese dioxide

Measured Seebeck coefficients of 5 battery grade manganese dioxide powder samples against solid graphite are reported. Temperature: 10 and 50 °C, respectively. Pressure: 7.5 megapascal (1 MPa ? 10 bar). All samples exhibit n-type semiconductivity with very high carrier concentration and very low mobility. Apparently, close correlations exist between thermoelectric behaviour, powder conductivity, water content, and electrode potential.     

The role of synthesis method in hydrogen evolution activity of Ce doped ZnO/CNTs photocatalysts: A comparative study

Cerium doped zinc oxide/carbon nanotubes (Ce doped ZnO/CNTs) composites are synthesized using sol-gel, hydrothermal deposition and one-pot hydrothermal methods. These composites are tested for photocatalytic hydrogen evolution from water-methanol mixture to check the effect of synthesis method on photocatalytic activity of these composites. Each synthesis method induces unique physiochemical properties in composite and hydrogen evolution rates. The composite prepared by one-pot hydrothermal method shows highest hydrogen evolution of 759 μmolh⁻¹g⁻¹ under sunlight. This hydrogen evolution rate is significantly higher than the sol-gel synthesized photocatalyst (579 μmolh⁻¹g⁻¹) and hydrothermal deposition method (621 μmolh⁻¹g⁻¹). The high hydrogen evolution activity of the prepared composites can be attributed to small crystallite size, low recombination of charge carriers, large active surface area, short diffusion pathway for photoinduced electrons and high oxidation potential of photogenerated holes. Focused on different methods, this study provides a pathway for production of efficient semiconductor photocatalysts for environmental applications.     

Thermoelectric e.m.f. of battery grade manganese dioxide

Measured Seebeck coefficients of 5 battery grade manganese dioxide powder samples against solid graphite are reported. Temperature: 10 and 50 °C, respectively. Pressure: 7.5 megapascal (1 MPa ? 10 bar). All samples exhibit n-type semiconductivity with very high carrier concentration and very low mobility. Apparently, close correlations exist between thermoelectric behaviour, powder conductivity, water content, and electrode potential.