Novel mixed method for the electrochemical deposition of thick layers of Bi2+xTe3−x with controlled stoichiometry

Comprehensive Review on Thermoelectric Electrodeposits: Enhancing Thermoelectric Performance Through Nanoengineering

Thermoelectric devices based power generation and cooling systemsystem have lot of advantages over conventional refrigerator and power generators, becausebecause of solid-state devicesdevices, compact size, good scalability, nono-emissions and low maintenance requirement with long operating lifetime. However, the applications of thermoelectric devices have been limited owingowing to their low energy conversion efficiency. It has drawn tremendous attention in the field of thermoelectric materials and devices in the 21st century because of the need of sustainable energy harvesting technology and the ability to develop higher performance thermoelectric materials through nanoscale science and defect engineering. Among various fabrication methods, electrodeposition is one of the most promising synthesis methods to fabricate devices because of its ability to control morphology, composition, crystallinity, and crystal structure of materials through controlling electrodeposition parameters. Additionally, it is an additive manufacturing technique with minimum waste materials that operates at near room temperature. Furthermore, its growth rate is significantly higher (i.e., a few hundred microns per hour) than the vacuum processes, which allows device fabrication in cost effective matter. In this paper, the latest development of various electrodeposited thermoelectric materials (i.e., Te, PbTe, Bi₂Te₃ and their derivatives, BiSe, BiS, Sb₂Te₃) in different forms including thin films, nanowires, and nanocomposites were comprehensively reviewed. Additionally, their thermoelectric properties are correlated to the composition, morphology, and crystal structure.

Nanostructured Inorganic Chalcogenide-Carbon Nanotube Yarn having a High Thermoelectric Power Factor at Low Temperature

As power-conversion devices, flexible thermoelectrics that enable conformal contact with heat sources of arbitrary shape are attractive. However, the low performance of flexible thermoelectric materials, which does not exceed those of brittle inorganic counterparts, hampers their practical applications. Herein, we propose inorganic chalcogenide-nanostructured carbon nanotube (CNT) yarns with outstanding power factor at a low temperature using electrochemical deposition. The inorganic chalcogenide-nanostructured CNT yarns exhibit the power factors of 3425 and 2730 μW/(m·K²) at 298 K for the p- and n-type, respectively, which is higher than those of previously reported flexible TE materials. On the basis of excellent performance and geometry advantage of the nanostructured CNT yarn for modular design, all-CNT based thermoelectric generators have been easily fabricated, showing the maximum power densities of 24 and 380 mW/m² at ΔT = 5 and 20 K, respectively. These results provide a promising strategy for the realization of high-performance flexible thermoelectric materials and devices for flexible/or wearable self-powering systems.

Synthesis and Evaluation of Thick Films of Electrochemically Deposited Bi₂Te₃ and Sb₂Te₃ Thermoelectric Materials

This paper presents the results of the synthesis and evaluation of thick thermoelectric films that may be used for such applications as thermoelectric power generators. Two types of electrochemical deposition methods, constant and pulsed deposition with improved techniques for both N-type bismuth telluride (Bi₂Te₃) and P-type antimony telluride (Sb₂Te₃), are performed and compared. As a result, highly oriented Bi₂Te₃ and Sb₂Te₃ thick films with a bulk-like structure are successfully synthesized with high Seebeck coefficients and low electrical resistivities. Six hundred-micrometer-thick Bi₂Te₃ and 500-µm-thick Sb₂Te₃ films are obtained. The Seebeck coefficients for the Bi₂Te₃ and Sb₂Te₃ films are −150 ± 20 and 170 ± 20 µV/K, respectively. Additionally, the electrical resistivity for the Bi₂Te₃ is 15 ± 5 µΩm and is 25 ± 5 µΩm for the Sb₂Te₃. The power factors of each thermoelectric material can reach 15 × 10⁻⁴ W/mK² for Bi₂Te₃ and 11.2 × 10⁻⁴ W/mK² for Sb₂Te₃.

Preparation of Bismuth Telluride Films with High Thermoelectric Power Factor

Highly conductive n-type Bi₂Te₃ films on a flexible substrate were prepared via electrodeposition followed by a transfer process using an adhesive substrate. The growth of the Bi₂Te₃ crystals was precisely controlled by an electrochemical deposition potential (V_dep), which was critical to the preferred orientation of the crystal growth along the (110) direction and thus to the properties of a flexible thermoelectric generator (FTEG). A Bi₂Te₃ film prepared under V_dep of 0.02 V showed high electrical conductivity (691 S cm^-1) with a maximum power factor of 1473 μW m^-1 K^-2, which is the highest among the Bi₂Te₃ films prepared by the electrodeposition methods. As-prepared FTEG was bendable, showing only a small resistance change after 300 repeated bending cycles. Combined with the n-type Bi₂Te₃ FTEG, a prototype p-n-type flexible thermoelectric (pn-FTEG) was prepared using p-type poly(3,4-ethylene dioxythiophene)s. The pn-FTEG (5-couples) generated an output voltage of 5 mV at ΔT = 12 K with high output power of 56 nW (or 105 nWg^-1). These results indicate that the FTEG can reproducibly work well in a bent state and has high application potential for harvesting thermal energy from curved sources such as human body temperature.

Facile production of thermoelectric bismuth telluride thick films in the presence of polyvinyl alcohol

Bismuth telluride is currently the best performing thermoelectric material for room temperature operations in commercial thermoelectric devices. We report the reproducible and facile production of 600 micron thick bismuth telluride (Bi2Te3) layers by low cost and room temperature pulsed and potentiostatic electrodeposition from a solution containing bismuth and tellurium dioxide in 2 M nitric acid onto nickel in the presence of polyvinyl alcohol (PVA). This was added to the electrolyte to promote thick layer formation and its effect on the structure, morphology and composition of the electrodeposits was investigated by SEM and EDX. Well adherent, uniform, compact and stoichiometric n-type Bi2Te3 films with a high Seebeck coefficient of up to -200 μV K(-1) and a high electrical conductivity of up to 400 S cm(-1) resulting in a power factor of 1.6 × 10(-3) W m(-1) K(-2) at film growth rates of 100 μm h(-1) for potentiostatic electrodeposition were obtained. The films also exhibited a well defined hexagonal structure as determined by XRD.

Fully automated measurement setup for non-destructive characterization of thermoelectric materials near room temperature

A measurement setup is presented that allows for a complete and non-destructive material characterization of electrochemically deposited thermoelectric material. All electrical (Seebeck coefficient α, electrical conductivity σ), thermal (thermal conductivity λ), and thermoelectric (figure of merit ZT) material parameters are determined within a single measurement run. The setup is capable of characterizing individual electrochemically deposited Bi(2+x)Te(3-x) pillars of various size and thickness down to a few 10 μm, embedded in a polymer matrix with a maximum measurement area of 1 × 1 cm(2). The temperature range is limited to an application specific window near room temperature of 10 °C to 70 °C. A maximum thermal flux of 1 W/cm(2) can be applied to the device under test (DUT) by the Peltier element driven heat source and sink. The setup has a highly symmetric design and DUTs can be mounted and dismounted within few seconds. A novel in situ recalibration method for a simple, quick and more accurate calibration of all sensors has been developed. Thermal losses within the setup are analysed and are mathematically considered for each measurement. All random and systematic errors are encountered for by a MATLAB routine, calculating all the target parameters and their uncertainties. The setup provides a measurement accuracy of ±2.34 μV/K for α, ±810.16 S/m for σ, ±0.13 W/mK for λ, and ±0.0075 for ZT at a mean temperature of 42.5 °C for the specifically designed test samples with a pillar diameter of 696 μm and thickness of 134 μm, embedded in a polyethylene terephthalate polymer matrix.