Poly(3,4-ethylenedioxythiophene)-tosylate (PEDOT-Tos) electrodes in thermogalvanic cells

Effect of heat treatment with different heat transfer modes on the polymerization of tosylate-doped poly(3,4-ethylenedioxythiophene) films

In this work, tosylate-doped poly(3,4-ethylenedioxythiophene) (PEDOT:Tos) films are prepared by thermally assisted oxidative polymerization either on a hot plate or in a convection oven. The main difference between these heat treatments is the way heat is transferred (conduction or convection) during polymerization. The surface morphology and structure, doped state, chemical composition, and the changes in the physical and chemical properties of the differently heat-treated films are analyzed using various instrumental methods. The hot plate-treated films exhibit a smooth and dense surface morphology with a low root-mean-square roughness of ~ 5 nm. The films have a quinoid-prevalent thiophene structure with a high electrical conductivity of 575 S/cm. By contrast, the oven-treated films show a rough and porous morphology with a surface roughness ranging from 30 to 80 nm depending on the scanning area, which yields high absorption capacity of more than 90% in the near-infrared range. The oven-treated films show a benzenoid-prevalent structure that provides relatively low electrical conductivity of 244 ± 45 S/cm. As a demonstration of these noticeable changes, PEDOT:Tos films are examined as a photothermal conversion layer to convert light energy to thermal energy, which is converted to electrical energy using a thermoelectric device by covering the films on the device.

Understanding PEDOT doped with tosylate

Now in their 5th decade of research and development, conducting polymers represent an interesting class of materials to underpin new wearable or conformable electronic devices. Of particular interest over the years has been poly(3,4-ethylenedioxythiophene), commonly known as PEDOT, owing to its ease of fabrication and relative stability under typical ambient conditions. Understanding PEDOT from a variety of fundamental and applied perspectives is important for how it can be enhanced, modified, functionalised, and/or processed for use in commercial products. This feature article highlights the contribution of the research team at the University of South Australia led by Professor Evans, and their collaborators, putting their work into the broader context of conducting polymer research and application. This review focuses on the vapour synthesis of PEDOT doped with the tosylate anion, the benefits of controlling its morphology/structure during synthesis, and its application as an active material interacting with secondary anions in sensors, energy devices and drug delivery.

Material Nanoarchitectonics of Functional Polymers and Inorganic Nanomaterials for Smart Supercapacitors

Smart supercapacitors are a promising energy storage solution due to their high power density, long cycle life, and low-maintenance requirements. Functional polymers (FPs) and inorganic nanomaterials are used in smart supercapacitors because of the favorable mechanical properties (flexibility and stretchability) of FPs and the energy storage properties of inorganic materials. The complementary properties of these materials facilitate commercial applications of smart supercapacitors in flexible smart wearables, displays, and self-generation, as well as energy storage. Here, an overview of strategies for the development of suitable materials for smart supercapacitors is presented, based on recent literature reports. A range of synthetic techniques are discussed and it is concluded that a combination of organic and inorganic hybrid materials is the best option for realizing smart supercapacitors. This perspective facilitates new strategies for the synthesis of hybrid materials, and the development of material technologies for smart energy storage applications.

Thermoelectrochemical Cells Based on Ferricyanide/Ferrocyanide/Guanidinium: Application and Challenges

Ferricyanide/ferrocyanide/guanidinium-based thermoelectrochemical cells have been investigated under different loading conditions in this work. Compared with ferricyanide/ferrocyanide-based devices, the device with guanidinium-added electrolytes shows higher power and energy densities. We observed that the enhanced performance is not due to the ionic Seebeck effect of guanidinium but because of the configuration entropy change resulting from the selective binding of Gdm+ to Fe(CN)64-. However, the device with guanidinium-added electrolyte does not show steady-state operation. The two possible reasons include (1) the difficult diffusion of Fe(CN)63- into the crystal layer of (Gdm+)n[Fe(CN)64-] at the hot electrode and (2) the difficult precipitation of (Gdm+)n[Fe(CN)64-] formed at the cold side upon the binding of the reduced Fe(CN)64- with Gdm+. Nevertheless, the performance recovers once the device is disconnected from the external loading. Due to the high thermopower after adding guanidinium, we successfully fabricate self-powered sensors by connecting four flexible cells in series. The sensors can transfer humidity, temperature, and air pressure data wirelessly using body heat. Therefore, ferricyanide/ferrocyanide/guanidinium is a promising electrolyte material for applications of low-grade energy harvesting.

All-polymer wearable thermoelectrochemical cells harvesting body heat

Wearable thermoelectrochemical cells have attracted increasing interest due to their ability to turn human body heat into electricity. Here, we have fabricated a flexible, cost-effective, and 3D porous all-polymer electrode on an electrical conductive polymer substrate via a simple 3D printing method. Owing to the high degree of electrolyte penetration into the 3D porous electrode materials for redox reactions, the all-polymer based porous 3D electrodes deliver an increased power output of more than twice that of the film electrodes under the same mass loading using either n-type or p-type gel electrolytes. To realize the practical application of our thermocell, we fabricated 18 pairs of n-p devices through a series connection of single devices. The strap shaped thermocell arrangement was able to charge up a commercial supercapacitor to 0.27 V using the body heat of the person upon which it was being worn and in turn power a typical commercial lab timer.

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A compatible high electrical conductivity polymer film works as underlying substrate

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3D printable polymer ink with suitable rheological properties

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A serial 18 pairs of n-p devices charged supercapacitor to power a lab timer

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3D-printed all-polymer electrode thermocell device for harvesting body heat

Unconventional Thermoelectric Materials for Energy Harvesting and Sensing Applications

Heat is an abundant but often wasted source of energy. Thus, harvesting just a portion of this tremendous amount of energy holds significant promise for a more sustainable society. While traditional solid-state inorganic semiconductors have dominated the research stage on thermal-to-electrical energy conversion, carbon-based semiconductors have recently attracted a great deal of attention as potential thermoelectric materials for low-temperature energy harvesting, primarily driven by the high abundance of their atomic elements, ease of processing/manufacturing, and intrinsically low thermal conductivity. This quest for new materials has resulted in the discovery of several new kinds of thermoelectric materials and concepts capable of converting a heat flux into an electrical current by means of various types of particles transporting the electric charge: (i) electrons, (ii) ions, and (iii) redox molecules. This has contributed to expanding the applications envisaged for thermoelectric materials far beyond simple conversion of heat into electricity. This is the motivation behind this review. This work is divided in three sections. In the first section, we present the basic principle of the thermoelectric effects when the particles transporting the electric charge are electrons, ions, and redox molecules and describe the conceptual differences between the three thermodiffusion phenomena. In the second section, we review the efforts made on developing devices exploiting these three effects and give a thorough understanding of what limits their performance. In the third section, we review the state-of-the-art thermoelectric materials investigated so far and provide a comprehensive understanding of what limits charge and energy transport in each of these classes of materials.

How Long are Polymer Chains in Poly(3,4-ethylenedioxythiophene):Tosylate Films? An Insight from Molecular Dynamics Simulations

Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most important conductive polymers utilized in a variety of applications in organic electronics and bioelectronics and energy storage. PEDOT chains are believed to be rather short, but detailed knowledge of their length is missing because of the challenges in its experimental determination due to insolubility of PEDOT films. Here, we report a molecular dynamics (MD) study of in situ oxidative chemical polymerization and simultaneous crystallization of molecularly doped PEDOT focusing on the determination of its chain lengths at different polymerization temperatures. We find the average chain length to be 6, 7, and 11 monomers for 298, 323 and 373 K, respectively. At the same time, the length distribution is rather broad, for example, between 2 and 16 monomer units for T = 323 K. We demonstrate that the limiting factor determining the chain length is the diffusivity of the reactants (PEDOT monomers and oligomers). We also study the polymer film formation during solvent evaporation, and we find that although crystallization starts and proceeds already during the polymerization and doping phases, it mostly occurs during the evaporation phase. Finally, we believe that our results providing the oligomer chain length and polymerization and crystallization mechanisms obtained by means of MD "computational microscopy" provide an important insight into the morphology of PEDOT that cannot be obtained by other means.

Carbon Nanomaterials Embedded in Conductive Polymers: A State of the Art

Carbon nanomaterials are at the forefront of the newest technologies of the third millennium, and together with conductive polymers, represent a vast area of indispensable knowledge for developing the devices of tomorrow. This review focusses on the most recent advances in the field of conductive nanotechnology, which combines the properties of carbon nanomaterials with conjugated polymers. Hybrid materials resulting from the embedding of carbon nanotubes, carbon dots and graphene derivatives are taken into consideration and fully explored, with discussion of the most recent literature. An introduction into the three most widely used conductive polymers and a final section about the most recent biological results obtained using carbon nanotube hybrids will complete this overview of these innovative and beyond belief materials.

Thermosensitive crystallization-boosted liquid thermocells for low-grade heat harvesting

Low-grade heat (below 373 kelvin) is abundant and ubiquitous but is mostly wasted because present recovery technologies are not cost-effective. The liquid-state thermocell (LTC), an inexpensive and scalable thermoelectric device, may be commercially viable for harvesting low-grade heat energy if its Carnot-relative efficiency (η_r) reaches ~5%, which is a challenging metric to achieve experimentally. We used a thermosensitive crystallization and dissolution process to induce a persistent concentration gradient of redox ions, a highly enhanced Seebeck coefficient (~3.73 millivolts per kelvin), and suppressed thermal conductivity in LTCs. As a result, we achieved a high η_r of 11.1% for LTCs near room temperature. Our device demonstration offers promise for cost-effective low-grade heat harvesting.

Oxidative Spin-Spray-Assembled Coordinative Multilayers as Platforms for Capacitive Films

The spin-spray-assisted layer-by-layer (LbL) assembly technique was used to prepare coordinative oxidative multilayers from Ce(IV), inorganic polyphosphate (PP), and graphene oxide (GO). The films consist of successive tetralayers and have a general structure (PP/Ce/GO/Ce)n. Such oxidative multilayers have been shown to be a general platform for the electrodeless generation of conducting polymer and melanin-type films. Although the incorporation of GO enhances the film growth, the conventional dip LbL method is very time consuming. We show that the spin-spray method reduces the time required to grow thick multilayers by the order of magnitude and the film growth is linear from the beginning, which implies a stratified structure. We have deposited poly(3,4-ethylenedioxothiophene), PEDOT, on the oxidative multilayers and studied these redox-active films as models for melanin-type capacitive layers for supercapacitors to be used in biodegradable electronics, both before and after the electrochemical reduction of GO to rGO. The amount of oxidant and PEDOT scales linearly with the film thickness, and the charge transfer kinetics is not mass transfer-limited, especially after the reduction of GO. The areal capacitance of the films grows linearly with the film thickness, reaching a value of ca. 1.6 mF cm-2 with 20 tetralayers, and the specific volumetric (per film volume) and mass (per mass of PEDOT) capacitances are ca. 130 F cm-3 and 65 F g-1, respectively. 5,6-Dihydroxyindole can also be polymerized to a redox-active melanin-type film on these oxidative multilayers, with even higher areal capacitance values.

Interplay between synthetic conditions and micromorphology in poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:Tos): an atomistic investigation

A systematic analysis was performed to elucidate the role played by proton scavengers in PEDOT chain length distribution and micromorphology.

Bulk electronic transport impacts on electron transfer at conducting polymer electrode-electrolyte interfaces

Electrochemistry is an old but still flourishing field of research due to the importance of the efficiency and kinetics of electrochemical reactions in industrial processes and (bio-)electrochemical devices. The heterogeneous electron transfer from an electrode to a reactant in the solution has been well studied for metal, semiconductor, metal oxide, and carbon electrodes. For those electrode materials, there is little correlation between the electronic transport within the electrode material and the electron transfer occurring at the interface between the electrode and the solution. Here, we investigate the heterogeneous electron transfer between a conducting polymer electrode and a redox couple in an electrolyte. As a benchmark system, we use poly(3,4-ethylenedioxythiophene) (PEDOT) and the Ferro/ferricyanide redox couple in an aqueous electrolyte. We discovered a strong correlation between the electronic transport within the PEDOT electrode and the rate of electron transfer to the organometallic molecules in solution. We attribute this to a percolation-based charge transport within the polymer electrode directly involved in the electron transfer. We show the impact of this finding by optimizing an electrochemical thermogalvanic cell that transforms a heat flux into electrical power. The power generated by the cell increased by four orders of magnitude on changing the morphology and conductivity of the polymer electrode. As all conducting polymers are recognized to have percolation transport, we believe that this is a general phenomenon for this family of conductors.

Conflicting effect of chemical doping on the thermoelectric response of ordered PEDOT aggregates

Poly(3,4-ethylenedioxythiophene) (PEDOT) semiconductor plays a relevant role in the development of organic thermoelectric (TE) devices for low-power generation.