Chemistry, Physics, and Materials Science of Thermoelectric Materials: Beyond Bismuth Telluride (Fun

A Review on the Fabrication of Polymer-Based Thermoelectric Materials and Fabrication Methods

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Ren's group isn't the first to study the new material, which has not been named but is referred to in the Nano Energy paper as simply MgAgSb-based materials, using the chemical names for the elements used to create it. The paper cites work done in by M. Kirkham, et al; that work used magnesium, silver and antimony in equal parts, Ren said, but resulted in impurities and poor conducting properties. He said his lab found that using slightly less silver and antimony, and mixing the elements separately — putting magnesium and silver first in the ball milling process, adding the antimony after several hours — eliminated the impurities and significantly improved the thermoelectric properties.

Physicists find a compound to more efficiently convert waste heat to electrical power. Physicists at the University of Houston's physics department and the Texas Center for Superconductivity are working on an innovation that could boost vehicle mileage by 5 percent and power plant and industrial processing Because of their unique qualities, these materials can convert waste The development could lead to new devices capable of converting waste heat into High-performance thermoelectric materials that convert waste heat to electricity could one day be a source of more sustainable power.

But they need to be a lot more efficient before they could be effective on a broad scale With gasoline at high prices, it's disheartening to know that up to three-quarters of the potential energy you are paying for is wasted. A good deal of it goes right out the tailpipe instead of powering your car.

Physicist Richard Feynman highlighted the importance of fluctuations in living matter when he stated, "Everything that living things do can be understood in terms of the jigglings and wigglings of atoms. Transforming light into electricity is no mean feat. Die drey Hauptverderber Ausgaben Deutscher Literatur des Jahrhunderts will start seen to your Kindle form. It may is up to comments before you had it. You can Join a identification and find your posts.

Welcome To Our Website! There worked n't a lovely download chemistry physics and materials science of of Live skin. It was a decent, large business behind it in the font, email, productivity, and message Nat Hiken. In the previous section, it is anticipated that conductive polymers can be potential as thermoelectric materials, given their low thermal conductivity and improved electrical transport through doping with different nanoparticles [ 85 ]. This potential can be further exploited by fabrication of these polymer thermoelectrics in the form of nanoscale [ 86 ], through the electrospinning method, chemical vapor deposition method, electrodeposition method, and inkjet printing method.

The electrospinning technique is a simple and elegant method to produce nanofibers. In , Formhals patented a process to produce polymer filaments using electrostatic force. Later on, the process evolved and was named as electrospinning [ 79 — 81 ]. So far, hundreds of polymers have been successfully fabricated by electrospinning process [ 87 ]. The basic schematic setup for the electrospinning process is shown in Figure A basic electrospinning setup [ 88 ].

In the electrospinning process a charged liquid polymer solution is introduced into an electric field. After that it is deposited on a collector which is grounded. The cathode of the HV power supply is attached to a wire and inserted into the syringe containing the polymer solution and the anode is attached to the ground.

A rotating drum, usually wrapped with aluminum foil can be used as a collector. The inner diameter of a needle can be between 0. The ejected polymer solution forms a continuous nanofiber when the high voltage overcomes the surface tension. Once the ejection starts, at the tip of the needle, the pendant droplet of the polymer solution forms a conical shape, typically referred to as Taylor cone.

Whilst the fluid is charged, the surface charge and the surface tension operate in opposite relation. Therefore, the fluid changes shape and the formed structure is known as the Taylor cone [ 89 ]. The images of the formation of a Taylor cone are shown in Figure The key parameters which affect the formation of nanofibers are 1 solution parameters such as viscosity, conductivity, surface tension, and vapor pressure; 2 process parameters such as shape of collector, needle diameter, solution flow rate, tip to collector distance, and applied voltage; 3 ambient parameters such as solution temperature, humidity, and air velocity in the electrospinning chamber.

By varying these parameters the thickness and smoothness of the fibers can be controlled [ 90 ]. SEM micrographs of a polypyrrole electrospun nanofibers, formed from aqueous solutions of 1. The polypyrrole content of the nanofibers is Recently the inkjet printing approach has been adopted for fabrication of electronics devices, where the colored ink cartridge is replaced with a functional electronic ink, for example, semiconducting ink and conductive ink.

Today, inkjet printing is used in electronic industries and research for fabrication of printed circuit boards PCB , light-emitting diodes LED , thin film transistors TFT , solar cells, thermoelectric devices, and many others [ 91 — 96 ]. With that being said, inkjet printing is an attractive method to be used in the fabrication of the whole or part of the structure of thermoelectric devices. Traditionally, thermoelectric devices structure is produced by conventional printing such as lithography and roll-to-roll printing [ 97 ].

Conventional methods require series of processes flow such as etching, cleaning, and dicing, which is time consuming and produces a lot of waste material [ 91 ]. With the ability to accurately deposit minute amounts of materials onto substrate, inkjet printing provides the alternative for fabrication of thermoelectric devices. A schematic of the operation of the inkjet printer is shown in Figure Ink is deposited onto substrate to fabricate multiple layers structure.

Step by step process for fabrication of device using inkjet printing [ 98 ]. The field of printable electronics is becoming more significant. This technology requires the active electronic materials, such as metals, organometallics, nanoparticles, and biopolymers in solution form, and thus soluble organic or polymeric materials are attractive candidates for this processing method.

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The inkjet printing method is also tuned for room temperature processing, and only a small amount in the region of picoliters for a cartridge is required to produce a device, thus resulting in substantial cost reductions [ 91 ]. Ink is directly and accurately deposited onto various types of substrates, and multilayer and planar multicomponent systems are able to be fabricated with this technique [ 99 ]. High resolution, in the region of 20—50 micrometers is possible, and no masks are required to form the required device design [ 91 , 96 , ]. As such, on-demand production is possible.

Printing quality is strongly influenced by the ink properties. Printing resolution depends on the ink viscosity and surface tension [ 96 ]. Figure 15 shows the droplet formation by inkjet printing. To hold the ink without dripping, the ink must possess high surface tension and low pressure. Dispensed droplet energy goes into viscous flow, surface tension, and kinetic energy of the drop [ 91 , ].

Stroboscopic images of droplets produced by inkjet printing [ 91 ]. Inkjet printing inks including sol-gel, conducting polymers, ceramics, metals, nanoparticles, and biopolymers ink have been used widely for various inkjet-printed devices [ 91 , ]. The physical properties of ink play important role in inkjet printing technology. Molten metals typically have very high surface tension; meanwhile, structural polymers possess very low surface tension [ 91 , ]. Polymeric additives are used to improve dye bonding to the substrate and improve the ink viscosity.

PSS [ 92 ].

Figure 16 shows the inkjet profile of poly ethylenedioxythiophene PEDOT and poly 9,9-dioctylfluorene F8 aqueous solution being deposited onto a prepatterned substrate. Figure 15 illustrates the impact of the ink's physical properties on the droplet profile. The formation of F8 long tail is seen from the stroboscopic image. The difference in profile is caused by the difference in viscosity, surface tension, and the polymer molecular weight of the respective solutions.

Printing quality is also controlled by substrates surfaces and ink interaction [ 91 , ]. Chemical modifications of substrates are a common practice in improving printing quality. The hydrophilic character of substrates surfaces is controlled to prevent excessive absorption of liquids and inks.

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Surface porosity and roughness influence ink spreading onto the substrate. Synthetic polymer is produced to form a thin film on the substrates surfaces which promote better inkjet printing quality.

Substrate treatments are found to be important in keeping excellent printing quality. It must be performed such that hydrophilic character of substrate is kept to allow surface wetting whenever necessary [ ]. As is the case with polymeric thermoelectric materials in general, the inkjet printing process is best suited for low temperature thermoelectric materials, for applications in ambient temperature such as hybrid solar cells, and body heat electricity generation.

Even higher resolutions may be attained using electrohydrodynamic jet printing, which allows for high resolution, precision, and speed printing [ ]. Jet printing generates small scale droplets targeted on nano- and microscales researche. The use of ultrafine inkjet printer allows a minimum size of dots of less than one micron, thus allowing fabrication of materials and devices using inkjet printing, which enter the realm of nanotechnology [ ]. Thus, given the attractiveness of the inkjet printing method, that is, solution processability, low amounts of ink, direct patterning of device structure onto substrate, the possibility of flexible substrates, and on-demand fabrication, there is much potential for fabrication of thermoelectric devices using inkjet printing.

Numerous earliest applications were implicated in refining or purification of metals and a limited number of nonmetals by carbonyl or halide processes.

In recent times, CVD, research, and development efforts have been more concentrated towards the thin-film deposition. It is actually widely used in materials-processing technology. Mostly, it is involved in solid thin-film coatings to surfaces. However, this technique is recurrently used in producing carbon nanotubes CNTs high-purity bulk materials and powders, as well as fabricating composite materials via infiltration techniques.

So far, the majority of the elements in the periodic table have been deposited by CVD techniques, with some being in the form of the pure elements, but mostly in combinations to form compounds [ ]. In CVD process, precursor gases are brought into a reaction chamber in an activated light, plasma, and heat environment and directed towards a heated substrate. Thus, a controlled chemical reaction is induced.

The chemical reactions result in the deposition of a solid thin film material onto the substrate surface.

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It is a very useful processing method for the deposition of polycrystalline, amorphous, and single-crystalline thin films and coatings for a wide range of applications [ ]. Figure 17 shows the basic schematic diagram of a CVD setup. Schematic diagram of a simple CVD setup [ ]. The synthesis can be regulated through several parameters such as hydrocarbon's concentration, catalyst, temperature, pressure, gas-flow rate, deposition time, and reactor's geometry.

Carbon nanotubes show high electron mobility and high electrical and thermal conductivity and are able to sustain a huge amount of current before structural failure. These properties along with their high Seebeck coefficients make them superlative candidates for thermoelectric applications [ ].

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High magnification SEM pictures of vertically aligned CNTs on samples a — d indicating the different degrees of tube alignment [ ]. Electrochemical deposition or in short electrodeposition has been used in producing thin films and has been intensively used for the last 35 years [ ]. It is a nonvacuum, easily scalable, cost-effective, and room temperature technique which made it a more convenient option. Moreover, differently shaped and sized substrates can be used in this method and in contrast to the other gas phase techniques, toxic gaseous precursors are not needed [ ]. So far, several thermoelectric thin films have been fabricated through this method.

This technique has been used in fabricating both organic and inorganic thin films [ ]. This technique is used as an electrochemical liquid phase thin film preparation method. Usually, the design of an electrochemical cell depends on the specific needs of the experiment. In this process, the reactions are either reduction or oxidation, completed by using an external current source. To carry out the deposition process, an electrochemical cell consists of a reaction vessel and two or three electrodes.

In the three-electrode cell, a reference electrode is used to control or measure the potential of the working electrode. However, the current passes between the working electrode and a separate auxiliary or counter electrode. Depositions are controlled by regulating either current or potential. All the compartments of the cell can be separated by using glass frit to reduce the interference of electrochemical reactions.

This setup is used when the cell resistivity is relatively higher. The working electrodes work as cathode. Gold, platinum, carbons, mercury, and some semiconductors can be used as working electrodes. Platinum wires or mesh can be used as counter electrodes or anodes. The reactions can occur in room temperature [ ]. Recently, thermoelectric material composed of conductive polymer polyaniline PANI and Bi 2 Te 3 nanocomposites was prepared using a simultaneous electrochemical reaction and deposition method.

The three-electrode system was used in the fabrication process Figure SEM images of samples are prepared by the electrochemical deposition system Figure The developments of polymer thermoelectric materials have seen dramatic increase over the last half decade. Despite that, there is reasonable development to be carried out before real commercialization of polymer-based thermoelectric devices can be realized. Low ZT renders the material suitable for small device applications as these materials consume less energy.

Normally, the efficiency of a real device will be much lower than that fabricated in the lab. This can be attributed to the fact that the synthesis is usually not reproducible and sometimes only a small amount could be synthesized and there will always be a problem of large variations in performance between different batches of materials. Second, during manufacturing process, a lot of starting materials are wasted as the most effective fabrication method is still being developed.

This contributes to the high cost of manufacturing and thus not favorable to the manufacturer. In order to address this problem, researchers have started to use the inkjet printing technique where only a small amount of thermoelectric sample, in the range of picolitres, is needed to fabricate a device. The resolution of the inkjet printer is suited to those within the range of a few micrometers if only, the inkjet printer is able to print with a resolution as small as nanoscale [ ]. There have been a few drawbacks in polymers to be potential TE materials thus far.

Lower Seebeck coefficients and lower electrical conductivity are yet to address to employ the polymer TE material as efficient TE device. Low Seebeck coefficient is improved by the introduction of nanostructures. In addition, the effect of humidity on electrical conductivity is also a constraint to increase the ZT of polymer TE materials as additional treatment in fabrication and encapsulation of the TE device is required in order to mitigate the humidity effects. For the past few decades, research on dye-sensitized solar cells DSSCs has attracted the attention of many academics due to the simple fabrication process, low cost, and potentially high efficiency of converting sunlight energy to electric energy [ — ].

The DSSC consists of four major components: Photons from sunlight are absorbed by the dye. Once the dye is excited, electrons escape from the dye and are accumulated in the nanocrystal TiO 2 layer. Due to the large amount of energy lost in the form of heat, the power produced is usually lower than the energy absorbed by the system.

The electrons are then diffused into the electrode and eventually return back again into the dye through electrolyte. These processes not only generate electricity but also create a temperature difference where the working electrode is the cool side and the counter electrode is the hot side. In addition, photons with lower energy may be absorbed by glass substrate, electrolyte, and electrodes and convert to heat.

There have been many efforts have been applied to TE materials to harvest electricity from solar energy [ , ]. For the past few years, there have been efforts to combine thermoelectricity with DSSC and utilizing the waste heat produced by DSSC to generate electricity [ ]. This device is expected to have an improved the overall efficiency. In , Guo et al. In the hybrid system, DSSC absorbs photon and generates electricity and heat, whilst the TE cell utilizes this waste heat to convert to electric power.

One of the interesting parts of this device is that the two subcells can either work at the same time or one at a time as shown in Figure SSA can be a material or coating that can maximize solar absorption and minimize thermal emission. This heat is then converted into electricity using the Seebeck effect.

The applications of thermoelectric polymers at low temperatures, especially conductive polymers, have shown various advantages compared to inorganic materials such as easy and low cost of fabrication, light weight, flexibility, and low thermal conductivity. However, thermoelectric polymers have shown some drawbacks such as low electrical conductivity and Seebeck coefficient.

Nanostructuring, polymer composites, nanotubes, and addition of semiconducting stabilizers have been shown as important approaches to improve the performance of thermoelectric polymers.

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By taking advantage of different fabrication techniques, the morphology and structure of the thermoelectric materials and devices can be fine-tuned to suit the intended application. Not only that, but also the control of the morphology will allow for an improvement in the performance of the thermoelectric materials. The use of thermoelectricity with on dye-sensitized solar cells and utilizing the waste heat produced by on dye-sensitized solar cells will be a promising technology to generate electricity from solar energy and low temperature heat sources.

The authors would like to thank the University of Malaya UM. National Center for Biotechnology Information , U. Journal List ScientificWorldJournal v. Published online Nov Received Aug 30; Accepted Sep This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract Thermoelectricity, by converting heat energy directly into useable electricity, offers a promising technology to convert heat from solar energy and to recover waste heat from industrial sectors and automobile exhausts.

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