Thermoelectric Nanomaterials Research Articles

Bi2Te3/Carbon Nanotube Hybrid Nanomaterials as Catalysts for Thermoelectric Hydrogen Peroxide Generation

Harnessing waste heat from environmental or industrial sources presents a promising approach to eco-friendly and sustainable chemical synthesis. In this study, we introduce a thermoelectrocatalytic (TECatal) system capable of utilizing even small amounts of heat for hydrogen peroxide (H2O2) production. We developed a nanohybrid structure, combining carbon nanotubes (CNTs) and Bi2Te3 nanoflakes (Bi2Te3/CNTs), through a one-pot synthesis method. Bi2Te3, as a thermoelectric (TE) material, generates charge carriers under a temperature gradient via the Seebeck effect, enabling them to participate in surface redox reactions. However, the rapid recombination of these charge carriers greatly limits the TECatal activity. In the Bi2Te3/CNTs nanohybrid system, the introduction of CNTs substantially enhances the efficiency of H2O2 production, as the strong bonding between CNTs and Bi2Te3, along with the excellent conductivity of CNTs, facilitates charge carrier separation and transport, as confirmed by TE electrochemical tests. This study underscores the significant potential of thermoelectric nanomaterials for converting waste heat into green chemical synthesis.

Size and surface-dependent phase transition temperature in Cu2Se nanobridges

The critical phase transition temperature (Tc) of Cu2Se thermoelectric nanomaterials has been a focal point of extensive research, yet the quantification of surface energy on Tc is frequently ignored. In this paper, we systematically investigate the impact of both the width/thickness and surface configuration of Cu2Se nanobridges (NBs) on Tc. We find that the Tc decreases with size reduction, which becomes particularly accelerated when the size decreases to a few nanometers. Additionally, the NBs with higher energy surfaces exhibit lower Tc. Then we propose an optimized thermodynamic model to quantify the combined effect of size and surface energy on Tc in Cu2Se NBs, which provides an approach to predict Tc in Cu2Se and other thermoelectric nanomaterials. Our study facilitates the understanding of the dependence of Tc on size and surface in Cu2Se, with an eye towards the stable room temperature thermoelectric applications of Cu2Se nanomaterials.

Development of Thermoelectric Nanomaterials with Photothermal Effect to Enhance Thermalcatalysts Sterilization Applications

Reactive oxygen species (ROS) are widely used in environmental and health-related fields due to their high reactivity. Among them, hydrogen peroxide (H2O2) is the most mild, stable, and environmentally friendly oxidant with only H2O and O2 as the decomposition products. Therefore, it is widely used in bleaching, wastewater treatment, fuel cells, and medical which can using on sterilization or infective wound healing and so on. However, the traditional anthraquinone method for producing H2O2 requires precious metal catalysts、high energy consumption and produces a large amount of wastewater. In addition, the catalytic production of H2O2 is mainly achieved by photocatalysis, piezocatalysis, or electrocatalysis procresses, which limits the application environment. To solve this problem, thermocatalysis based on temperature difference by using thermoelectric materials is a promising solution. However, the current H2O2 production efficiency is still low, which limits the application scenarios. Therefore, we propose to use Au nanoparticles and MoS2 nanosheets with Bi2Te3 nanoplates as the thermocatalytic material. Bi2Te3 nanoplates have high Seebeck coefficient at room temperaturea and high specific surface area. Moreover, Au nanoparticles and MoS2 nanosheets are known as great photothermal property materials which can be used to increase the temperature difference of the material to improve the H2O2 production efficiency. The temperature difference is the most common environmental factor in daily life, which makes thermoelectric nanomaterials have great potential for practical applications in the field of thermalcatalysts.

Harvesting Thermal Energy through Pyroelectric and Thermoelectric Nanomaterials for Catalytic Applications

The current scenario sees over 60% of primary energy being dissipated as waste heat directly into the environment, contributing significantly to energy loss and global warming. Therefore, low-grade waste heat harvesting has been long considered a critical issue. Pyroelectric (PE) materials utilize temperature oscillation to generate electricity, while thermoelectric (TE) materials convert temperature differences into electrical energy. Nanostructured PE and TE materials have recently gained prominence as promising catalysts for converting thermal energy directly into chemical energy in a green manner. This short review provides a summary and comparison of catalytic processes initiated by PE and TE effects driven by waste thermal energy. The discussion covers fundamental principles and reaction mechanisms, followed by the introduction of representative examples of PE and TE nanomaterials in various catalytic fields, including water splitting, organic synthesis, air purification, and biomedical applications. Finally, the review addresses challenges and outlines future prospects in this emerging field.

General Syntheses of High-Performance Thermoelectric Nanostructured Solids without Post-Synthetic Ligand Stripping.

Ligand-assisted wet chemical synthesis is a versatile methodology to produce controllable nanocrystals (NCs). The post-treatment of ligands is significant for the performance of functional devices. Herein, a method that retains ligands of colloidal-synthesized nanomaterials to produce thermoelectric nanomaterials is proposed, which differs from the conventional methods that strip ligands using multistep cumbersome processes. The ligand-retention method can control the size and dispersity of nanocrystals during the consolidation of the NCs into dense pellets, in which retained ligands are transformed into organic carbon within the inorganic matrices, establishing clear organic-inorganic interfaces. Characterizations of the nonstripped and stripped samples confirm that this strategy can affect electric transport slightly but reduce the thermal conductivity largely. As a result, the materials (e.g., SnSe, Cu2-xS, AgBiSe2, and Cu2ZnSnSe4) with ligands retained achieve higher peak zT and better mechanical properties. This method can be applied to other colloidal thermoelectric NCs and functional materials.

Recent advances in silicon-based nanostructures for thermoelectric applications

In this work, implementations of silicon-based thermoelectric nanomaterials are reviewed. Approaches ranging from nanostructured bulk—i.e., macroscopic materials presenting nanoscale features—to more complex low-dimensional materials are covered. These implementations take advantage of different phonon scattering mechanisms and eventual modifications of the electronic band-structure for the enhancement of the thermoelectric figure of merit. This work is focused on the recent advances in silicon and silicon-based thermoelectric nanomaterials of the last decade—at both the theoretical and experimental level—with the spotlight on the most recent works. Different nanostructures and their fabrication methods are detailed, while the thermoelectric performances and the feasibility of their integration into functional micro-harvester generators are compared and discussed. This Research Update first covers the advances in nanostructured bulk, such as nanometric-sized polycrystals or defect-induced materials. Subsequently, it reviews low-dimensional materials, namely, thin films and nanowires. Later, other complex structures based on nanoporosity, superlattices, or core–shell schemes are detailed. Finally, it is devoted to present examples of the successful implementation of nanostructured silicon into functional thermoelectric devices.

Enhancement in figure of merit in N-type Bi(R)-Te thermoelectric nanomaterials

In this paper, we reported the cerium (Ce) doped thermoelectric materials with composition Bi2−xRxTe3 (R = Ce, x = 0.0, 0.1, and 0.2), which were prepared by using different wet chemical methods. The selected synthesis methods that were used included a simplified sol-gel method (Without Water and Surfactants-WOWS) and the Composite Mediated Hydrothermal Method (CMHM). The structural analysis of the samples showed rhombohedral and hexagonal structures. In addition, the surface morphology revealed a flower-like structure for the synthesized samples. The thermal stability was determined using differential scanning calorimetry and thermogravimetric analysis. The electrical conductivity of the samples with a doping ratio of x = 0.1 showed maximum conductivity of (19.10 × 103 (S/cm))-WOWS; (9.10 × 103 (S/cm)) – (CMHM) as compared to than that of other samples (x = 0.0 and 0.2). Interestingly, the doping of Ce increased the Seebeck effect, which also increased the power factor. The power factor of the samples x = 0.1 was higher than that of the undoped samples, which had a magnitude of 12.30 μW/cm.K2 (WOWS) and 7.02 μW/cm.K2 (CMHM). Moreover, we measured the thermal conductivity of the samples using the Advantageous Transient Plane Source (ATPS) method. Therefore, we found the higher figure of merit (ZT) value (0.41) at x = 0.1, which was prepared using a simplified sol-gel method, which is among the highest values that was reported for Bi2−xRxTe3 at room temperature. Because of its potential applications this material has great interest as a thermoelectric material and chip cooling sensing.

Energy-Saving Pathways for Thermoelectric Nanomaterial Synthesis: Hydrothermal/Solvothermal, Microwave-Assisted, Solution-Based, and Powder Processing.

The pillars of Green Chemistry necessitate the development of new chemical methodologies and processes that can benefit chemical synthesis in terms of energy efficiency, conservation of resources, product selectivity, operational simplicity and, crucially, health, safety, and environmental impact. Implementation of green principles whenever possible can spur the growth of benign scientific technologies by considering environmental, economical, and societal sustainability in parallel. These principles seem especially important in the context of the manufacture of materials for sustainable energy and environmental applications. In this review, the production of energy conversion materials is taken as an exemplar, by examining the recent growth in the energy‐efficient synthesis of thermoelectric nanomaterials for use in devices for thermal energy harvesting. Specifically, “soft chemistry” techniques such as solution‐based, solvothermal, microwave‐assisted, and mechanochemical (ball‐milling) methods as viable and sustainable alternatives to processes performed at high temperature and/or pressure are focused. How some of these new approaches are also considered to thermoelectric materials fabrication can influence the properties and performance of the nanomaterials so‐produced and the prospects of developing such techniques further.

Self-Assembled Nanocomposites and Nanostructures for Environmental and Energy Applications

Self-assembled nanocomposites are attracting considerable attention owing to their controllable architectures and self-assembly processes, as well as the increase in worldwide environmental effects and energy needs. Further understanding of the self-assembly procedure for improving environmental and energy applications would advance the design and manufacture of nanomaterials for various applications. These materials can be grouped into major categories for various application fields, including powder photocatalysts, membrane photocatalysts, and thin-film thermoelectric nanomaterials. These self-assembled nanomaterials can be used for environmental and energy applications, such as wastewater purification, hydrogen production by water splitting, energy storage, and energy harvesting. In this review, a brief introduction to the definitions and classifications of self-assembled nanocomposites is provided. We aim to provide a summary of the recent research related to self-assembled nanocomposites and nanostructures used for environmental and energy applications. Moreover, typical examples and discussions are aimed at demonstrating the advantages of self-assembled nanostructures. At the end of each section, the structural properties and the application of the nanocomposite or nanostructure are summarized. Finally, we provide perspectives for future research on the design and fabrication of self-assembled nanocomposites and nanostructures.

Polymer-Inorganic Thermoelectric Nanomaterials: Electrical Properties, Interfacial Chemistry Engineering, and Devices.

Though solar cells are one of the promising technologies to address the energy crisis, this technology is still far from commercialization. Thermoelectric materials offer a novel opportunity to convert energy between thermal and electrical aspects, which show the feasibility to improve the performance of solar cells via heat management and light harvesting. Polymer–inorganic thermoelectric nanocomposites consisting of inorganic nanomaterials and functional organic polymers represent one kind of advanced hybrid nanomaterials with tunable optical and electrical characteristics and fascinating interfacial and surface chemistry. During the past decades, they have attracted extensive research interest due to their diverse composition, easy synthesis, and large surface area. Such advanced nanomaterials not only inherit low thermal conductivity from polymers and high Seebeck coefficient, and high electrical conductivity from inorganic materials, but also benefit from the additional interface between each component. In this review, we provide an overview of interfacial chemistry engineering and electrical feature of various polymer–inorganic thermoelectric hybrid nanomaterials, including synthetic methods, properties, and applications in thermoelectric devices. In addition, the prospect and challenges of polymer–inorganic nanocomposites are discussed in the field of thermoelectric energy.

An Approach toward the Realization of a Through-Thickness Glass Fiber/Epoxy Thermoelectric Generator.

The present study demonstrates, for the first time, the ability of a 10-ply glass fiber-reinforced polymer composite laminate to operate as a structural through-thickness thermoelectric generator. For this purpose, inorganic tellurium nanowires were mixed with single-wall carbon nanotubes in a wet chemical approach, capable of resulting in a flexible p-type thermoelectric material with a power factor value of 58.88 μW/m·K2. This material was used to prepare an aqueous thermoelectric ink, which was then deposited onto a glass fiber substrate via a simple dip-coating process. The coated glass fiber ply was laminated as top lamina with uncoated glass fiber plies underneath to manufacture a thermoelectric composite capable of generating 54.22 nW power output at a through-thickness temperature difference οf 100 K. The mechanical properties of the proposed through-thickness thermoelectric laminate were tested and compared with those of the plain laminates. A minor reduction of approximately 11.5% was displayed in both the flexural modulus and strength after the integration of the thermoelectric ply. Spectroscopic and morphological analyses were also employed to characterize the obtained thermoelectric nanomaterials and the respective coated glass fiber ply.

Microwave Irradiation to Produce High Performance Thermoelectric Material Based on Al Doped ZnO Nanostructures

Microwave irradiation is found to be effective to provide highly crystalline nanostructured materials. In this work, this technique has been used to produce highly improved thermoelectric (TE) material based on aluminum (Al) doped zinc oxide (ZnO) nanostructures (NSs). The effect of Al dopant at the concentration range 0.5–3 mol % on the structural and TE properties has been investigated in more details. The optimum concentration of Al for better TE performance is found to be 2 mol %, which could significantly increase the electrical conductivity and reduce the thermal conductivity of ZnO NSs and thus enhance the TE performance. This concentration showed almost metallic conductivity behavior for ZnO NSs at low temperatures, e.g., below 500 K. The electrical conductivity reached 400 S/m at room temperature, which is around 200 times greater than the value recorded for the pure ZnO NSs. Remarkably, the measured room temperature thermal conductivity of the microwave synthesized ZnO NSs was very low, which is around 4 W/m·K. This value was further reduced to 0.5 W/m·K by increasing the Al doping to 3 mol %. The figure of merit recorded 0.028 at 675 K, which is 15 times higher than that of the pure ZnO NSs. The output power of a single leg module made of 2 mol % Al doped ZnO NSs was 3.7 µW at 485 K, which is higher by 8 times than that of the pure sample. These results demonstrated the advantage of the microwave irradiation rout as a superior synthetic technique for producing and doping promising TE nanomaterials like ZnO NSs.

Optical and transport properties of few quintuple-layers of Bi2-xSbxSe3 nanoflakes synthesized by hydrothermal method

Hydrothermal synthesis as a commonly bottom-up growth method has considerable advantages for manufacturing thermoelectric nanomaterials with advanced thermoelectric properties. However, the hydrothermally synthesized thermoelectric nanostructures often show a low thermoelectric performance due to their low power factor. In this work, we report on using a hydrothermal method for the growth of n-type Bi2-xSbxSe3 nanoflakes with a fixed thickness of ∼16 quintuple-layers. The controlling of the stoichiometric composition, phase purity and crystallinity of the Bi2-xSbxSe3 nanoflakes are demonstrated by the X-ray diffraction, Raman spectroscopy, and high resolution transmission electron microscopy. We further prove that adding of antimony into Bi2Se3 compound mostly influences the in-plane vibration mode. The optical energy gap is sharply increased as the Sb content increases. The effect of the antimony incorporation on the electrical conductivity, Seebeck coefficient and power factor of Bi2-xSbxSe3 nanoflakes is systematically investigated. The Bi1.92Sb0.08Se3 sample is found to have the highest power factor ∼13.17 μW/cm.K2 at 470 K which is much higher than those published for other various nanostructured or bulk Bi2Se3 compounds. The results propose a great prospect for further enhancing the thermoelectric power factor of the Bi2Se3 nanostructures synthesized by this hydrothermal method. Taking into consideration the progress in Bi–Se compounds, the results of this work advocate the promise of Bi–Se nanostructures towards producing high performance thermoelectric devices.

Large-area and adaptable electrospun silicon-based thermoelectric nanomaterials with high energy conversion efficiencies

Large amounts of waste heat generated in our fossil-fuel based economy can be converted into useful electric power by using thermoelectric generators. However, the low-efficiency, scarcity, high-cost and poor production scalability of conventional thermoelectric materials are hindering their mass deployment. Nanoengineering has proven to be an excellent approach for enhancing thermoelectric properties of abundant and cheap materials such as silicon. Nevertheless, the implementation of these nanostructures is still a major challenge especially for covering the large areas required for massive waste heat recovery. Here we present a family of nano-enabled materials in the form of large-area paper-like fabrics made of nanotubes as a cost-effective and scalable solution for thermoelectric generation. A case study of a fabric of p-type silicon nanotubes was developed showing a five-fold improvement of the thermoelectric figure of merit. Outstanding power densities above 100 W/m2 at 700 °C are therefore demonstrated opening a market for waste heat recovery.

Complete Genome Sequence of Bacillus cereus CC-1, A Novel Marine Selenate/Selenite Reducing Bacterium Producing Metallic Selenides Nanomaterials.

Metallic selenides nanomaterials are widely used in many fields, especially for photothermal therapy and thermoelectric devices. However, the traditional chemogenic methods are energy-intensive and environmentally unfriendly. In this study, the first complete genome data of a metallic selenides producing bacterium Bacillus cereus CC-1 was reported. This strain can not only reduce selenite and selenate into elemental selenium nanoparticles (SeNPs), but also synthesize several metallic selenides nanoparticles when adding metal ions (Pb2+, Ag+ and Bi3+) and selenite simultaneously. The size of the genome is 5,308,319bp with 36.07% G+C content. Several putative genes responsible for heavy metal resistance, salt resistance, and selenate reduction were found. This genome data provide fundamental information, which support the use of this strain for the production of biocompatible photothermal and thermoelectric nanomaterials under mild conditions.

N-type Bi-doped SnSe Thermoelectric Nanomaterials Synthesized by a Facile Solution Method.

An n-type Bi-doped SnSe was synthesized by a facile solution method followed by spark plasma sintering. We used bismuth(III) 2-ethyhexanoate as a cationic dopant precursor, which can absorb on the powder surface and then diffuse into the lattice to realize the substitution of Sn by Bi. A strip structure with low-angle boundary was constructed for effective phonon scattering. With increasing content of Bi, the carrier concentration decreased from 1.35 × 1019 cm-3 (p-type) in undoped SnSe to 4.7 × 1014 cm-3 (n-type) in Sn0.99Bi0.01Se and then increased to 1.3 × 1015 cm-3 (n-type) in Sn0.97Bi0.03Se. The Seebeck coefficient changed from positive to negative and presented n-type conducting behavior in the whole measured temperature range from 300 to 773 K, reaching a maximum absolute value of ∼900 μV K-1 at room temperature and ∼300 μV K-1 at 773 K. Considering the rich variety of metal 2-ethylhexanoates, higher thermoelectric performance is expected by different cationic doping in solution-synthesized nanomaterials.

Ce-doped Bi<sub>2</sub>O<sub>3</sub> nanorods and thermoelectric properties

Nowadays, the problem of environmental pollution and energy shortage caused by the burning of a large number of fossil fuels (coal, oil and gas) is becoming more and more serious. Finding an efficient, green, low-cost and sustainable energy material is the focus of energy science research now. Thermoelectric technology is able to generate a temperature gradient by collecting waste heat from factories, cars and so on and converts it into electricity through the Seebeck effect, and through the Peltier effect, it can be used for refrigeration. Thermoelectric material is the key to the thermoelectric technology. Therefore, the performance research of thermoelectric materials will play an important role in solving energy problems in the future. As a green environmental material, Bi2O3 possesses a low cost and high Seebeck coefficient of thermoelectric materials. Due to poor electrical conductivity; however, the power factor (PF) of Bi2O3 has so far been less than 1.05×10−3 W K−2 m. It is one of the most important way to improve the efficiency of thermoelectric conversion to obtain counterpart nanomaterials. In this paper, through a simple chemical vapor deposition (CVD), Ce x Bi2− x O3 ( x =0%, 0.1%, 0.2%, 0.3%) nanorods were successfully fabricated. As for the chemical composition, morphology, and microstructure analysis, conventional X-ray diffraction (XRD) pattern/small grazing incident X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS) were used to prove to be the Ce x Bi2− x O3 sample. Through scanning/transmission electron microscope, it was found that products were dispersed uniformly nanorods, and counterpart samples cold be pressed into a round piece. Based on Seebeck coefficient/electrical resistivity measurement system using thermoelectric performance testing system (ZEM-3), electrical transport properties of the samples were characterized. Laser thermal conductivity meter (LASER FLASH DLF-1) and EXSTAR differential scanning calorimeter (6200) were used to test the thermal conductivity of the sample. The obtained results showed that the power factor (PF) and ZT value of the sample (Ce0.2Bi1.8O3) arrived at 1.265×10−2 W K−2 m−1 and 0.57×10−2 at 479 K, respectively, which is far higher than that of the un-doped samples. So Ce-doped Bi2O3 thermoelectric nanomaterials have a good application prospect for energy, material and devices.

Gram-scale solution-based synthesis of SnSe thermoelectric nanomaterials

Gram-scale SnSe nanomaterials have been prepared by exploiting a simple wet-chemical route at ambient environments in which a transparent NaHSe solution was mixed with SnCl2 and sodium ascorbate, followed by hydrothermal heating for 24 h. It is notable that phase-pure crystalline SnSe nanorods having aspect ratios of ∼5 were obtained within a short period of time and without any sophisticated instruments or inert environment. The key steps and conditions to obtain pure SnSe nanorods in the synthesis process were identified and discussed. The SnSe powder was sintered using a facile spark plasma sintering method to form polycrystalline pellets for thermoelectric property measurements. According to the thermopower measurement results, the pristine SnSe pellets are p-type, and showed slightly higher electrical conductivities compared to that of single crystalline SnSe. The counterpart n-type SnSe pellets were also fabricated by doping Bi with a high energy ball milling process. The thermal conductivity of our polycrystalline SnSe was found to be in between that of single crystalline SnSe along a- and b- axis (or c-axis) direction. The facile and new synthesis route, high reproducibility and cost-effectiveness are easily adaptable for the formation of other doped and un-doped metal selenide nanomaterials with a short reaction time for various applications beyond thermoelectrics.

Growth of epitaxial FeGeγ nanocrystals with incommensurate Nowotny chimney-ladder phase on Si substrate

We developed the growth technique of epitaxial nanocrystals of FeGeγ (γ ∼ 1.52), a recently-found new crystal with incommensurate Nowotny chimney-ladder phase, on Si(001) substrates. This bulk material is promising for thermoelectric application, and now their films and nanostructures are expected to be fabricated. However, it was difficult to grow single phase epitaxial FeGeγ directly on Si substrates by conventional growth method. On the other hand, we successfully formed almost single phase epitaxial FeGeγ nanocrystals on Si substrates covered with ultrathin SiO2 films with nanowindows. Reflection high energy electron diffraction indicated that the nanocrystals had the Nowotny chimney-ladder structure, the lattice constants of which were approximately consistent with those of FeGeγ bulk. This indicated strain relaxation in nanocrystals due to the hemispherical shape. This will open a road to realize high performance thermoelectric nanomaterials on Si substrates.

Skutterudite (CoSb3) thermoelectric nanomaterials fabricated by Pulse Plasma in Liquid

In this work, we present a new fabrication method of thermoelectric nanomaterials using Pulsed Plasma in Liquid (PPL) with a low-energy spark discharge. Thermoelectric (TE) materials can be used for direct energy conversion from heat into electricity. They are of particular interest as a result of enabling both clean energy transformation and waste heat energy harvesting. The efficiency of the conversion process depends on the Carnot cycle and the material’s properties, described by the thermoelectric figure-of-merit (ZT). This parameter is based on electrical conductivity, Seebeck coefficient and thermal conductivity. One can increase the ZT value by reducing the thermal conductivity e.g. through the nano-structuring of TE materials and, at the same time, conserving their electrical properties. CoSb3, which is a state-of-the-art TE material from the skutterudite family known as a narrow-band gap semiconductor with a parabolic bottom of the conduction band, was studied in the present work.Binary skutterudite CoSb3 polycrystalline ingots were synthesized by a direct fusion technique from pure elements. The densified materials with a cylindrical shape were used as substrates in the fabrication process of CoSb3 nanoparticles via the modified Pulse Plasma in Liquid method. The nanopowders were consolidated using rapid Spark Plasma Sintering (SPS) with the processing time in minutes. X-ray diffraction (XRD), scanning electron microscopy (SEM/EDS) and scanning transmission electron microscopy (STEM) were used to characterize the synthesized powders and sinters. Thermal conductivity was determined by the laser flash technique (LFA). Electrical properties such as resistivity and Seebeck coefficient were measured by the four probe technique, as a function of temperature.