Free-standing Single-walled Carbon Nanotube Films Research Articles

Large thermoelectric power factor in wafer-scale free-standing single-walled carbon nanotube films

Single-walled carbon nanotubes (SWCNTs) have the potential for application in thermoelectric energy generators owing to their advantages, such as good charge-carrier transport properties, mechanical flexibility and robustness, and tunability of polarity. However, the fabrication of SWCNTs still remains a problem due to its complexity and high cost. In this paper, we propose an approach for the direct formation of free-standing SWCNT films from as-grown SWCNT mats without any dispersion or separation processes. We used this approach to develop high-performance SWCNT-based thermoelectric leg materials. The as-grown SWCNT mats were synthesized by an enhanced direct injection pyrolytic synthesis (eDIPS) method. The selectivity of the tube diameter for the eDIPS method clarified the dependence of the thermoelectric performance of the free-standing SWCNT films on the tube diameter. The Seebeck coefficients and thermal conductivities were found to correlate with the tube diameter and agreed with the theoretical predictions. Owing to the dispersion-free film formation, our SWCNT films afforded large thermoelectric power factors. In particular, a power factor of 350 μW/(m K2) was obtained for the mean tube diameter of 1.7 nm without any semiconductor extraction or doping treatments. Our approach allowed the fabrication of thermoelectric legs with an arbitrary size; thus, it offers a useful strategy for the simpler, cheaper, and low-waste manufacturing of high-performance organic thermoelectric devices.

Highly efficient thermophones based on freestanding single-walled carbon nanotube films

We present the state-of-the-art performance of air-coupled thermophones made of thin, freestanding films of randomly oriented single-walled carbon nanotubes (SWCNTs).

Texture and light-induced anisotropic terahertz properties of free-standing single-walled carbon nanotube films with random networks

We present an anisotropic property investigation of the free-standing single-walled carbon nanotube (SWCNT) random networks by terahertz time-domain spectroscopy (THz-TDS). Strongly anisotropic transmission in the spectral region 0.3–2.5 THz is observed. The experimental observation implies that our pristine SWCNT networks show preferential order in micrometer scale, which are attributed to the formation of the texture pattern. Modulation of this exceptional anisotropy by mechanical stretching and light illuminating indicates that the anisotropic response can be enhanced. The light-induced anisotropic property shows a hyperbolic tangent dependence with the pump power. The results suggest the potential applications and manipulations of SWCNT networks for THz electro-optical and polarized devices.

Fabrication and electrochemical properties of free-standing single-walled carbon nanotube film electrodes

An easily manipulative approach was presented to fabricate electrodes using free-standing single-walled carbon nanotube (SWCNT) films grown directly by chemical vapor deposition. Electrochemical properties of the electrodes were investigated. In comparison with the post-deposited SWCNT papers, the directly grown SWCNT film electrodes manifested enhanced electrochemical properties and sensitivity of sensors as well as excellent electrocatalytic activities. A transition from macroelectrode to nanoelectrode behaviours was observed with the increase of scan rate. The heat treatment of the SWCNT film electrodes increased the current signals of electrochemical analyser and background current, because the heat-treatment of the SWCNTs in air could create more oxide defects on the walls of the SWCNTs and make the surfaces of SWCNTs more hydrophilic. The excellent electrochemical properties of the directly grown and heat-treated free-standing SWCNT film electrodes show the potentials in biological and electrocatalytic applications.

Compact-designed supercapacitors using free-standing single-walled carbon nanotube films

We reported the realization of assembling compact-designed supercapacitors using large-scaled free-standing and flexible single-walled carbon nanotube (SWCNT) films as both anode and cathode. A prototype of the processing procedures was developed to obtain the uniform spreading of the SWCNT films onto the separators serving as both electrodes and charge collectors without metallic current collectors, leading to a simplified and lightweight architecture. The area of SWCNT film on a separator can be scaled up and its thickness can be extended. High energy and power densities (43.7 Wh kg−1 and 197.3 kW kg−1, respectively) were achieved from the prepared SWCNT film-based compact-designed supercapacitors with small equivalent series resistance. The specific capacitance of this kind of compact-designed SWCNT film supercapacitor is about 35 F g−1. These results clearly show the potential application of free-standing SWCNT film in compact-designed supercapacitor with enhanced performance and significantly improved energy and power densities.

Effects of ozonolysis and subsequent growth of quantum dots on the electrical properties of freestanding single-walled carbon nanotube films

A significant challenge exists in probing the transport behavior of chemically modified single-walled carbon nanotubes (SWNTs). Thin films of SWNTs offer one facile approach to integration of these materials into electronics and sensing applications. Data on bulk resistivities of ‘bucky paper’ films created from HiPco SWNTs that were initially ozonized and subsequently decorated with CdTe quantum dots have been collected via 4-point probe measurements. Both the oxidation process and addition of CdTe nanocrystals result in increased bulk resistivities, presumably due to the introduction of additional scattering centers in tube sidewalls as well as charge traps in the CdTe functionalized tubes.

Growth of novel carbon phases by methane infiltration of free-standing single-walled carbon nanotube films

High-temperature methane infiltration of thin, free-standing films of acid-treated single-walled carbon nanotubes (SWCNT) has been studied by means of scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. In the early stages of infiltration, carbon nuclei form predominantly at SWCNT bundle intersections. Further growth proceeds via the formation of graphite nanosheets – without further influence of the nanotube support. Both sheet edges and their structural imperfections act as reaction centers for subsequent deposition, likely giving rise to autocatalytic deposition kinetics. In contrast, infiltration with a H 2:CH 4 (24:1) mixture leads to the reductive activation of residual Ni/Co impurities embedded in the precursor SWCNT-felt. This is associated with a different predominant carbon deposition mode in which multiwalled carbon nanotubes grow out from the substrate.