Single-walled Carbon Nanotube Electrodes Research Articles

In Situ Synchrotron X-ray Diffraction Studies of Single-walled Carbon Nanotubes for Electric Double-layer Capacitors

In situ synchrotron X-ray diffraction experiments of SWCNT (single-walled carbon nanotube) electrode in alkali halide aqueous electrolyte at several applied potentials were performed, and the change in the diffraction pattern of SWCNTs was observed. It was found that the position of the 100 diffraction peak does not change with applied potential while the peak intensity decreases with anion adsorption. It was concluded that the space inside the tube would be the important ion adsorption site for the well-grown SWCNT bundles.

Mediated Electron Transfer at Vertically Aligned Single-Walled Carbon Nanotube Electrodes During Detection of DNA Hybridization.

Vertically aligned single-walled carbon nanotube (VASWCNT) assemblies are generated on cysteamine and 2-mercaptoethanol (2-ME)-functionalized gold surfaces through amide bond formation between carboxylic groups generated at the end of acid-shortened single-walled carbon nanotubes (SWCNTs) and amine groups present on the gold surfaces. Atomic force microscopy (AFM) imaging confirms the vertical alignment mode of SWCNT attachment through significant changes in surface roughness compared to bare gold surfaces and the lack of any horizontally aligned SWCNTs present. These SWCNT assemblies are further modified with an amine-terminated single-stranded probe-DNA. Subsequent hybridization of the surface-bound probe-DNA in the presence of complementary strands in solution is followed using impedance measurements in the presence of Fe(CN)63−/4− as the redox probe in solution, which show changes in the interfacial electrochemical properties, specifically the charge-transfer resistance, due to hybridization. In addition, hybridization of the probe-DNA is also compared when it is attached directly to the gold surfaces without any intermediary SWCNTs. Contrary to our expectations, impedance measurements show a decrease in charge-transfer resistance with time due to hybridization with 300 nM complementary DNA in solution with the probe-DNA attached to SWCNTs. In contrast, an increase in charge-transfer resistance is observed with time during hybridization when the probe-DNA is attached directly to the gold surfaces. The decrease in charge-transfer resistance during hybridization in the presence of VASWCNTs indicates an enhancement in the electron transfer process of the redox probe at the VASWCNT-modified electrode. The results suggest that VASWCNTs are acting as mediators of electron transfer, which facilitate the charge transfer of the redox probe at the electrode–solution interface.

Does Electronic Type Matter when Single‐Walled Carbon Nanotubes are Used for Electrode Applications?

Single‐walled carbon nanotube (SWNT) electrodes that are chemically and mechanically robust are fabricated using a simple drop cast method with thermal annealing and acid treatment. An electronic‐type selective decrease in sheet resistance of SWNT electrodes with HNO3 treatment is shown. Semiconducting SWNTs show a significantly higher affinity toward hole doping in comparison to metallic SWNTs; a ≈12‐fold and a ≈fivefold drop in sheet resistance, respectively. The results suggest the insignificance of the electronic type of the SWNTs for the film conductivity after hole doping. The SWNT films have been employed as transparent hole extracting electrodes in bulk heterojunction (BHJ) organic photovoltaics. Performances of the devices enlighten the fact that the electrode film morphology dominates over the electronic type of the doped SWNTs with similar sheet resistance and optical transmission. The power conversion efficiency (PCE) of 4.4% for the best performing device is the best carbon nanotube transparent electrode incorporated large area BHJ solar cell reported to date. This PCE is 90% in terms of PCEs achieved using indium tin oxide (ITO) based reference devices with identical film fabrication parameters indicating the potential of the SWNT electrodes as an ITO replacement toward realization of all carbon solar cells.

Novel single wall carbon nanotube electrode system capable of quantitative detection of CD4+ T cells (TECH2P.909)

Abstract We developed a fully-integrated SWCNT-based immunosensor capable of selective capture and linear quantification of CD4+ T cells by employing the two-step O2 plasma treatment processes. These processes overcome the current hurdle in the quantification of a specific subset of lymphocytes by removing the byproduct of spray-coated SWCNTs that hinders charge transfer and by creating large number of anchoring sites for anti-CD4 antibodies for stable cell binding. As a result, a linear range of electrochemical signal is generated by SWCNT electrode in proportion to the bound CD4+ T cells. Our CD4+ T cell-immunosensor provides a simple and low-cost platform which can fulfill the requirement for the development of point of care diagnostic technologies for HIV patients in the resource-limited countries.

Study of Adenine and Guanine Oxidation Mechanism by Surface-Enhanced Raman Spectroelectrochemistry

Metal nanoparticles are systems largely employed in surface-enhanced Raman spectroscopy (SERS). In particular, gold nanoparticles are one of the best substrates used in this field. In this work, the optimal conditions for gold nanoparticles electrodeposition on single-walled carbon nanotubes electrodes have been established to obtain the best SERS response. Using this substrate and analyzing the changes of in situ Raman spectra obtained at different potentials, we have been able to explain simultaneously the oxidation mechanism of purine bases, differentiating the oxidation intermediates and their orientation during the different oxidation steps. Adenine orientation hardly changes during the whole oxidation; the molecule maintains a parallel configuration and only shows a slightly tilted orientation after the first oxidation step. On the other hand, guanine orientation changes completely during its oxidation. Initially, guanine is perpendicular respect to gold nanoparticles, changing its orientation after...

Highly stretchable reduced graphene oxide (rGO)/single-walled carbon nanotubes (SWNTs) electrodes for energy storage devices

We report on the fabrication of reduced graphene oxide/single-walled carbon nanotubes (rGO/SWNTs) electrodes deposited onto stretchable polyurethane via spray coating. The electrochemical properties of the rGO/SWNTs electrodes were compared to pure rGO and SWNT electrodes. The highest capacitance value obtained for the unstretched rGO/SWNTs electrode was 265Fg−1 in 1M H2SO4 at 5mVs−1, which decreased to 219 and 162Fg−1 after 50 and 100 stretching cycles (at 100% strain), respectively. The rGO/SWNTs composite electrode also retained approximately 75% of its initial capacitance under constant 100% strain. Further characterization, including galvanostatic charge/discharge measurements and electrochemical impedance spectroscopy (EIS), showed that the rGO/SWNTs electrode retained a well-defined capacitive response after repetitive stretching to 100% strain. Overall, the rGO/SWNTs composite electrode showed enhanced electrochemical properties in comparison to rGO and SWNTs electrodes. Approximately 65% of the initial capacitance for the rGO/SWNTs composite electrode is retained after 100 stretching cycles and then maintained up to the 3000th CV cycle, making the electrodes a potential option for stretchable energy storage applications.

Controlled functionalisation of single-walled carbon nanotube network electrodes for the enhanced voltammetric detection of dopamine

Voltammetric studies of dopamine (DA) oxidation on pristine and acid-treated single-walled carbon nanotube (SWNT) network electrodes were undertaken in order to investigate both the effect of network density and acid treatment times on the voltammetric characteristics for DA oxidation and the susceptibility of the electrodes to fouling. Through careful control of catalysed chemical vapour deposition growth parameters, multiply interconnected and randomly oriented SWNT networks of two significantly different densities were grown (high density, HD, coverage ≫10 μm length of SWNT per μm(-2) and low density, LD, coverage = 5 (±1) μmSWNTμm(-2)). Acid treatment was performed to provide materials with different electrochemical properties and SWNT coverage, as determined by field emission-scanning electron microscopy, atomic force microscopy and micro-Raman spectroscopy. A high concentration of DA (100 μM) was deliberately employed to accelerate the fouling phenomenon associated with DA oxidation in order to evaluate the lifetime of the electrodes. HD pristine SWNT networks were found to promote more facile electron transfer (ET) and were less susceptible to blocking, compared to LD pristine SWNT networks. Acid treatment resulted in both a further enhancement of the ET rate and a reduction in susceptibility towards electrode fouling. However, lengthy acid treatment detrimentally affected ET, due to a decrease in network density and significant damage to the SWNT network structure. These studies highlight the subtle interplay between SWNT coverage and degree of acid functionalisation when seeking to achieve the optimal SWNT electrode for the voltammetric detection of DA.

The study of capacitive deionization behavior of a carbon nanotube electrode from the perspective of charge efficiency.

In this work, the capacitive deionization (CDI) performance of a single-walled carbon nanotube (CNT) electrode has been studied from the point view of charge efficiency theory. It is revealed here that the charge efficiency of a CNT electrode is strongly dependent upon the cell voltage and solution concentration. Either the high cell voltage or the low ionic strength results in a high charge efficiency, implying that CDI is expected to be a promising technique for an aqueous solution with low ionic strength. Additionally, it is found that the high decay constant and high electrical double-layer capacity are beneficial to enhance electrosorption performance.

Electrochemical and Electron Paramagnetic Resonance Study of the Mechanism of Oxidation of Phenazine-di-N-oxide in the Presence of Isopropyl alcohol at Glassy Carbon and Single-Walled Carbon Nanotube Electrodes

The mechanism of oxidation of phenazine-di-N-oxide in the presence of isopropyl alcohol was studied by cyclic voltammetry at glassy carbon (GC) and single-walled carbon nanotubes (SWCNT) electrodes in 0.1M LiClO4 solutions in acetonitrile. The adsorption of phenazine-di-N-oxide at SWCNT electrode in 0.1M LiClO4 solution in acetonitrile was investigated by measurement of the dependence of the differential double layer capacitance of the electrode C on potential E. The effect of isopropyl alcohol on the shape of cyclic voltammograms (CVs) of phenazine-di-N-oxide and the intensity of Electron Paramagnetic Resonance (EPR) signal of its radical cation was investigated. The catalytic currents were recorded at the oxidation of phenazine-di-N-oxide at SWCNT and GC electrodes in the presence of isopropyl alcohol. The results were explained in terms of the E1C1E2C2 mechanism of two-stage electrode process characterized by catalytic current recorded at the second electrode stage. The overall two-electron catalytic oxidation of isopropyl alcohol in complex with the phenazine-di-N-oxide radical cation was assumed to occur. It was shown that SWCNT electrodes can be used in the electrocatalytic oxidation of organic compounds in the presence of electrochemically generated phenazine-di-N-oxide radical cation.

A comparative study of different protein immobilization methods for the construction of an efficient nano-structured lactate oxidase-SWCNT-biosensor

We constructed lactate biosensors by immobilization of lactate oxidase (LOx) onto a single-walled carbon nanotube (SWCNT) electrode. The first step of the sensor construction was the immobilization of oxidized SWCNT onto a platinum electrode modified with 4-aminothiophenol (4-ATP). Two enzyme immobilization methods were used to construct the biosensors, i.e., covalent immobilization using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and physical adsorption. Atomic force microscopy (AFM) experiments confirmed the immobilization of SWCNT during the biosensor construction and X-ray photoelectron spectroscopy (XPS) experiments confirmed covalent immobilization of LOx onto the SWCNT in the first method. The biosensor based on covalent enzyme immobilization showed a sensitivity of 5.8μA/mM, a linearity up to 0.12mM of l-lactate, and a detection limit of 4.0μM. The biosensor based on protein adsorption displayed a sensitivity of 9.4μA/mM, retaining linearity up to 0.18mM of l-lactate with a detection limit of 3.0μM. The difference in the biosensor response can be attributed to protein conformational or dynamical changes during covalent immobilization. The stability of the biosensors was tested at different temperatures and after different storage periods. The thermostability of the biosensors after incubation at 60°C demonstrated that the biosensor with covalently immobilized LOx retained a higher response compared with the adsorbed protein. Long-term stability experiments show a better residual activity of 40% for the covalently immobilized protein compared to 20% of residual activity for the adsorbed protein after 25d storage. Covalent protein immobilization was superior compared to adsorption in preserving biosensor functionality over extended time period.

Conductance switching in single light-sensitive molecular device with carbon nanotube electrodes

By applying nonequilibrium Green's function formalism combined first-principles density functional theory, a new mechanism for optical switch of single molecular device with carbon nanotube electrodes is proposed. The molecule comprises the switch can convert between enol and keto isomers upon photoinduced excited state hydrogen transfer in the molecular bridge. Theoretical results show that these two isomers exhibit very different current-voltage characteristics both in armchair and zigzag junction, which can realize the on and off states of the molecular switch. Meantime, the chirality of the single-walled carbon nanotube (SWCNT) electrodes strongly affects the switching characteristics of the molecular junctions. The maximum value of on-off ratio can reach 72 at 1.6 V for the switch with zigzag SWCNT electrodes, suggesting potential applications of this junction in future design of light-driven molecular switches.

Electron Transport and CO Sensing Characteristics of Fe(II) Porphyrin with Single-Walled Carbon Nanotube Electrodes

Electron transport and carbon monoxide (CO) sensitive characteristics of Fe(II) porphyrin (PP-Fe) with two single-walled carbon nanotube electrodes (SWCNTs) were studied using nonequilibrium Green’s function (NEGF) formalism combined first-principles density functional theory (DFT). When PP-Fe is connected to SWCNT electrodes in diagonal configuration, owing to the fact that the electron passes through the Fe center, it shows higher CO sensitivity than that in para connection mode. Meanwhile, the PP-Fe sensor with armchair SWCNTs is more sensitive to CO than that in zigzag junction, since the coupling interaction between central molecule and armchair SWCNT electrodes is stronger. The PP-Fe sensor anchored on armchair SWCNTs in diagonal configuration can reach a current on–off ratio of 2.1 × 104 in response to the chemisorption of CO, showing better CO sensitive characteristics than that with zigzag SWCNTs and metallic electrodes. With the development of experimental techniques, it is completely possible t...

Comparative Electrocatalytic Performance of Single-Walled and Multiwalled Carbon Nanotubes for Zinc Bromine Redox Flow Batteries

Carbon nanotubes (CNTs) have been employed as electrode materials in rechargeable zinc bromine redox flow batteries (ZBB) owing to their high electrocatalytic activity, remarkable electrical conductivity, and excellent mechanical strength with high Young’s modulus. The electrocatalytic effect of single-walled carbon nanotube (SWCNT) and multiwalled carbon nanotube (MWCNT) electrodes for the 2Br–/Br2 redox couple has been investigated for zinc bromine redox flow battery application. The anodic peak current density of SWCNT electrode is found to be about 16 mA cm–2, which is almost 50% higher than that of MWCNT, indicating the enhanced electrocatalytic effect of SWCNT perhaps due to a large amount of basal planes. The peak separation between the anodic and cathodic process at SWCNT and MWCNT electrodes is 201 and 126 mV, respectively, demonstrating the quasireversible nature of the 2Br–/Br2 redox reaction. Moreover, the peak separation for the MWCNT electrode is 37% less compared to that on the SWCNT electr...

Structural and Electrochemical Characterization of Ethylenediaminated Single-Walled Carbon Nanotubes Prepared from Fluorinated SWCNTs

We prepared ethylenediaminated single-walled carbon nanotubes (SWCNTs) from fluorinated SWCNTs by substituting fluorine groups with ethylenediamine groups. The ethylenediaminated SWCNTs were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman scattering spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area measurement by nitrogen adsorption, contact angle measurement, zeta potential analysis, and thermogravimetry. In addition, the properties of 30 wt % sulfuric acid aqueous electrolyte-based electric double-layer supercapacitors (EDLSCs) with free-standing ethylenediaminated SWCNT electrodes were investigated. The degree of ethylenediamine functionalization was 0.603 mmol/g and 1.46 μmol/m2, and the specific surface area was ∼413.3 m2/g. From HRTEM observation, isolated nanotubes disentangled from the bundled SWCNTs were present in many observed areas, and the structures retained a nanotube sk...

Micropatterned single-walled carbon nanotube electrodes for use in high-performance transistors and inverters.

We demonstrated the solution-processed single-walled carbon nanotube (SWNT) source-drain electrodes patterned using a plasma-enhanced detachment patterning method for high-performance organic transistors and inverters. The high-resolution SWNT electrode patterning began with the formation of highly uniform SWNT thin films on a hydrophobic silanized substrate. The SWNT source-drain patterns were then formed by modulating the interfacial energies of the prepatterned elastomeric mold and the SWNT thin film using oxygen plasma. The SWNT films were subsequently selectively delaminated using a rubber mold. The patterned SWNTs could be used as the source-drain electrodes for both n-type PTCDI-C8 and p-type pentacene field-effect transistors (FETs). The n- and p-type devices exhibited good and exactly matched electrical performances, with a field-effect mobility of around 0.15 cm(2) V(-1) s(-1) and an ON/OFF current ratio exceeding 10(6). The single electrode material was used for both the n and p channels, permitting the successful fabrication of a high-performance complementary inverter by connecting a p-type pentacene FET to an n-type PTCDI-C8 FET. This patterning technique was simple, inexpensive, and easily scaled for the preparation of large-area electrode micropatterns for flexible microelectronic device fabrication.

Effect of carbon nanotubes chirality on the E–C photo-isomerization switching behavior in moelcular device

Applying nonequilibrium Green's function formalism in combination with the first-principles density functional theory, we investigate the electronic transport properties of optical molecular switch based on the fulgide molecule with two different single-walled carbon nanotube (SWCNT) electrodes. The molecule that comprises the switch can convert between E isomer and C isomer by ultraviolet or visible irradiation. Theoretical results show that these two isomers exhibit very different conductance properties both in armchair and zigzag junction, which can realize the on and off states of the molecular switch. Meantime, the chirality of the SWCNT electrodes strongly affects the switching characteristics of the molecular junctions, which is useful for the design of functional molecular devices.

Capacitive behavior of latex/single-wall carbon nanotube stretchable electrodes

In this report single-wall carbon nanotubes (SWNTs) were coated onto latex using spray coating to produce a stretchable electrode. The electrochemical properties of the electrode were determined using cyclic voltammetry and electrochemical impedance spectroscopy and galvanostatic charge/discharge tests were also carried out. The impedance and charge/discharge curves of the latex/SWNTs electrode showed good capacitive behavior even after repetitive stretching to 100% strain. The highest capacitance value obtained for the unstretched SWNTs electrode was 119 F g−1 in 1M Na2SO4 at 5mV s−1. After the 100th stretch ≈ 80% of the original capacitance value was retained.

Effects of Taiwan Roselle anthocyanin treatment and single-walled carbon nanotube addition on the performance of dye-sensitized solar cells

This study investigates the relationship between the performance of a dye-sensitized solar cell (DSSC) sensitized by a natural sensitizer of Taiwan Roselle anthocyanin (TRA) and fabrication process conditions of the DSSC. A set of systematic experiments has been carried out at various soaking temperatures, soaking periods, sensitizer concentrations, pH values, and additions of single-walled carbon nanotube (SWCNT). An absorption peak (520 nm) is found for TRA, and it is close to that of the N719 dye (518 nm). At a fixed concentration of TRA and a fixed soaking period, a lower pH of the extract or a lower soaking temperature is found favorable to the formation of pigment cations, which leads to an enhanced power conversion efficiency (η) of DSSC. For instance, by applying 17.53 mg/100ml TRA at 30 for 10 h, as the pH of the extract decreases to 2.00 from 2.33 (the original pH of TRA), the η of DSSC with TiO2+SWCNT electrode increases to 0.67% from 0.11% of a traditional DSSC with TiO2 electrode. This performance improvement can be explained by the combined effect of the pH of sensitizer and the additions of SWCNT, a first investigation in DSSC using the natural sensitizer with SWCNT.

Research on automatic spraying of single-walled carbon nanotubes and detection of spraying effects

Single-walled carbon nanotubes (SWNTs) have been introduced as compliant electrodes for dielectric elastomers (DEs) due to fault tolerance. To acquire a better electrostrictive strain and longer lifetime, it is essential to obtain a certain and uniform width of the SWNT electrode. To ensure uniform width manually, a small flux and longer time are necessary. Moreover, it is difficult to control the width of the electrode for the randomness of manual spraying. Therefore, a new type of automatic spraying process is presented in this paper. The width and homogeneity of the electrode can be easily controlled by certain parameters of the process. Two methods for detecting the homogeneity of the electrode are introduced in this paper: Measurement of surface resistance and luminosity. The coefficient of variation (CV) values detected by the two methods are virtually equal and less than 8%, which shows the feasibility of the detection method and homogeneity of automatic spraying. The speed of automatic spraying is 102 mm2/s, which is higher than that of manual spraying. The spraying process and the method used to detect homogeneity in this paper provide a reference for the relevant processes.

Mechanical integrity and environmental reliability of a single wall carbon nanotube as a flexible transparent conducting electrode

We investigated a single wall carbon nanotube (SWCNT) electrode as a potential flexible transparent conducting electrode. The mechanical integrity of an SWCNT electrode spray-coated onto a polyethylene terephthalate substrate was investigated via outer/inner bending, twisting, stretching, and adhesion tests. In particular, its environmental reliability under high-temperature and high-humidity conditions was characterized. The spray-coated SWCNT electrode showed a sheet resistance of 200 Ω/square and a transparency of 83%. The SWCNT electrode showed a constant resistance change (ΔR/R0) within an outer and inner bending radius of 2.5 mm. The bending fatigue test showed that the SWCNT electrode can withstand 10,000 bending cycles at a bending radius of 5 mm. Furthermore, the resistance change of the stretched SWCNT electrode was fairly constant up to a strain of 5%, which is quite stable compared with the resistance change of conventional amorphous indium tin oxide electrodes. The SWCNT electrode also showed good adhesion strength. The environmental storage test at a high temperature (85 °C) indicated that change in the electrical resistance of the SWCNT electrode is less than 9% after 100 h test. In the environmental reliability tests at 85% relative humidity (RH) and 60 °C/90% RH, the ΔR/R0 of the SWCNT electrode was very small. These results indicate that the SWCNT electrode has good environmental stability.