Air-tolerant Fabrication and Enhanced Thermoelectric Performance of n-Type Single-walled Carbon Nanotubes Encapsulating 1,1'-Bis(diphenylphosphino)ferrocene

Interface Engineering for High-Performance Thermoelectric Carbon Nanotube Films

Carbon nanotubes (CNTs) stand out for their exceptional electrical, thermal, and mechanical attributes, making them highly promising materials for cutting-edge, lightweight, and flexible thermoelectric applications. However, realizing the full potential of advanced thermoelectric CNTs requires precise management of their electrical and thermal characteristics. This study, through interface optimization, demonstrates the feasibility of reducing the thermal conductivity while preserving robust electrical conductivity in single-walled CNT films. Our findings reveal that blending two functionalized CNTs offers a versatile method of tailoring the structural and electronic properties of CNT films. Moreover, the modified interface exerts a substantial influence over thermal and electrical transfer, effectively suppressing heat dissipation and facilitating thermoelectric power generation within CNT films. As a result, we have successfully produced both p- and n-type thermoelectric CNTs, attaining impressive power factors of 507 and 171 μW/mK2 at room temperature, respectively. These results provide valuable insights into the fabrication of high-performance thermoelectric CNT films.

Molecular Doping Modulation and Applications of Structure-Sorted Single-Walled Carbon Nanotubes: A Review

Single-walled carbon nanotubes (SWCNTs) that have a reproducible distribution of chiralities or single chirality are among the most competitive materials for realizing post-silicon electronics. Molecular doping, with its non-destructive and fine-tunable characteristics, is emerging as the primary doping approach for the structure-controlled SWCNTs, enabling their eventual use in various functional devices. This review provides an overview of important advances in the area of molecular doping of structure-controlled SWCNTs and their applications. The first part introduces the underlying physical process of molecular doping, followed by a comprehensive survey of the commonly used dopants for SWCNTs to date. Then, it highlights how the convergence of molecular doping and structure-sorting strategies leads to significantly improved functionality of SWCNT-based field-effect transistor arrays, transparent electrodes in optoelectronics, thermoelectrics, and many emerging devices. At last, several challenges and opportunities in this field are discussed, with the hope of shedding light on promoting the practical application of SWCNTs in future electronics.

Paper Thermoelectrics by a Solvent-Free Drawing Method of All Carbon-Based Materials

As practical interest in the flexible or wearable thermoelectric generators (TEGs) has increased, the demand for the high-performance TEGs based on ecofriendly, mechanically resilient, and economically viable TEGs as alternatives to the brittle inorganic materials is growing. Organic or hybrid thermoelectric (TE) materials have been employed in flexible TEGs; however, their fabrication is normally carried out using wet processing such as spin-coating or screen printing. These techniques require materials dissolved or dispersed in solvents; thus, they limit the substrate choice. Herein, we have rationally designed solvent-free, all carbon-based TEGs dry-drawn on a regular office paper using few-layered graphene (FLG). This technique showed very good TE parameters, yielding a power factor of 97 μW m-1 K-2 at low temperatures. The p-type only device exhibited an output power of up to ∼19.48 nW. As a proof of concept, all carbon-based p-n TEGs were created on paper with the addition of HB pencil traces. The HB pencil exhibited low Seebeck coefficients (-7 μV K-1), and the traces were highly resistive compared to FLG traces, which resulted in significantly lower output power compared to the p-type only TEG. The demonstration of all carbon-based TEGs drawn on paper highlights the potential for future low-cost, flexible, and almost instantaneously created TEGs for low-power applications.

Ionic Dopant-Encapsulating Single-Walled Carbon Nanotube Films with Metal-Like Electrical Conductivity

Heavy doping is inevitable for utilizing single-walled carbon nanotubes for wiring. However, the electrical conductivity of their films is currently as low as one tenth of the films made from typical metal pastes. Herein we report on metal-comparable electrical conductivity from single-walled carbon nanotube network films. We use ionic liquids and crown ether complexes for p-type and n-type doping, respectively. The encapsulation of counterions into carbon nanotubes promotes the conductivities in the range of 7000 S cm^-1 , approximately ten times larger than those of undoped films.

Magnetic Nanoparticle Supported Ionic Liquid Phase Catalyst for Oxidation of Alcohols

A new magnetic nanoparticle supported ionic liquid phase (SILP) catalyst containing perruthenate anions was prepared by a multistep procedure. The various analytical techniques such as FT-IR spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, thermogravimetric analysis, energy dispersive X-ray analysis, and vibrating sample magnetometer analysis ascertained the successful formation of catalyst. The performance of a magnetically retrievable SILP catalyst was evaluated in the selective oxidation of alcohols. The split test and leaching studies of the SILP catalyst confirmed its heterogeneous nature. In addition, the reusability potential of SILP catalyst was also investigated which revealed its robust activity up to six consecutive cycles.

Enhanced Thermoelectric Properties of Boron-Substituted Single-Walled Carbon Nanotube Films

Atomic doping is the most fundamental approach to modulating the transport properties of carbon nanotubes. In this paper, we demonstrate the enhanced thermoelectric properties of boron-substituted single-walled carbon nanotube (B-SWCNT) films. The developed two-step synthesis of large quantities of B-SWCNTs readily enables the measurements of thermoelectricity of bulk B-SWCNT films. Complementary structural characterization implies the unique configuration of boron atoms at the doping sites of SWCNTs, successfully enabling carrier doping to SWCNTs. The developed boron substitution, in combination with chemical doping, is found to substantially improve the thermoelectric properties.

Surfactant-driven Amphoteric Doping of Carbon Nanotubes

Aqueous surfactant dispersion is the most typical starting step to functionalize materials consisting of carbon nanotubes, but the effects of surfactants on the electronic properties are still unclear. Here we report how the functional groups of surfactants affect the electronic properties of carbon nanotube films. Using spectroscopic and thermoelectric characterization, we demonstrate that anionic and non-ionic surfactants contribute to the formation of p-type and n-type carbon nanotubes, respectively. Additionally, p-type doping with oxygen adsorption is found to compete with surfactants' doping. These findings are useful for designing the srarting carbon nanotube materials exhibiting desirable electronic properties.

Crystallinity-Dependent Thermoelectric Properties of a Two-Dimensional Coordination Polymer: Ni₃(2,3,6,7,10,11-hexaiminotriphenylene)₂

The evaluation of thermoelectric properties has recently become a standard method for revealing the electronic properties of conducting polymers. Herein we report on the thermoelectric properties of a two-dimensional coordination polymer pellets. The pellets of Ni₃(2,3,6,7,10,11-hexaiminotriphenylene)₂, which has recently been developed, show n-type thermoelectric transport, dependent on crystallinity. The present results provide systematic feedback to the guideline for high-performance molecular thermoelectric materials.

Thickness-dependent thermoelectric power factor of polymer-functionalized semiconducting carbon nanotube thin films

The effects of polymer structures on the thermoelectric properties of polymer-wrapped semiconducting carbon nanotubes have yet to be clarified for elucidating intrinsic transport properties. We systematically investigate thickness dependence of thermoelectric transport in thin films containing networks of conjugated polymer-wrapped semiconducting carbon nanotubes. Well-controlled doping experiments suggest that the doping homogeneity and then in-plane electrical conductivity significantly depend on film thickness and polymer species. This understanding leads to achieving thermoelectric power factors as high as 412 μW m-1 K-2 in thin carbon nanotube films. This work presents a standard platform for investigating the thermoelectric properties of nanotubes.

Solvent basicity promotes the hydride-mediated electron transfer doping of carbon nanotubes

This study investigates the hydride-mediated electron transfer doping of single-walled carbon nanotubes using absorption spectroscopy and thermoelectric measurements. Specific solvent basicity is found to be important for the efficient n-type doping of carbon nanotubes. This progress is an essential requirement for the future development of electronic and energy devices.

Carbon-Nanotube-Based Thermoelectric Materials and Devices

Conversion of waste heat to voltage has the potential to significantly reduce the carbon footprint of a number of critical energy sectors, such as the transportation and electricity-generation sectors, and manufacturing processes. Thermal energy is also an abundant low-flux source that can be harnessed to power portable/wearable electronic devices and critical components in remote off-grid locations. As such, a number of different inorganic and organic materials are being explored for their potential in thermoelectric-energy-harvesting devices. Carbon-based thermoelectric materials are particularly attractive due to their use of nontoxic, abundant source-materials, their amenability to high-throughput solution-phase fabrication routes, and the high specific energy (i.e., W g^-1 ) enabled by their low mass. Single-walled carbon nanotubes (SWCNTs) represent a unique 1D carbon allotrope with structural, electrical, and thermal properties that enable efficient thermoelectric-energy conversion. Here, the progress made toward understanding the fundamental thermoelectric properties of SWCNTs, nanotube-based composites, and thermoelectric devices prepared from these materials is reviewed in detail. This progress illuminates the tremendous potential that carbon-nanotube-based materials and composites have for producing high-performance next-generation devices for thermoelectric-energy harvesting.

Synergistic Impacts of Electrolyte Adsorption on the Thermoelectric Properties of Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes are promising candidates for light-weight and flexible energy materials. Recently, the thermoelectric properties of single-walled carbon nanotubes have been dramatically improved by ionic liquid addition; however, controlling factors remain unsolved. Here the thermoelectric properties of single-walled carbon nanotubes enhanced by electrolytes are investigated. Complementary characterization with absorption, Raman, and X-ray photoelectron spectroscopy reveals that shallow hole doping plays a partial role in the enhanced electrical conductivity. The molecular factors controlling the thermoelectric properties of carbon nanotubes are systematically investigated in terms of the ionic functionalities of ionic liquids. It is revealed that appropriate ionic liquids show a synergistic enhancement in conductivity and the Seebeck coefficient. The discovery of significantly precise doping enables the generation of thermoelectric power factor exceeding 460 µW m^-1 K^-2 .

Water-Processable, Air-Stable Organic Nanoparticle-Carbon Nanotube Nanocomposites Exhibiting n-Type Thermoelectric Properties

Water-dispersed organic base nanoparticles are utilized for the highly stable n-type doping of single-walled carbon nanotubes in aqueous dispersion. Long-term stability is often a critical challenge in the application of n-type organic conductors. The present n-type organic materials exhibit almost no degradation in the thermoelectric properties over months, in air.