MWCNT Electrode Research Articles

Electrochemical Determination of Uric Acid Using a Nanocomposite Electrode with Molybdenum Disulfide/Multiwalled Carbon Nanotubes (MoS2@MWCNT).

This paper presents an application for a molybdenum disulfide nanomaterial with multiwalled carbon nanotubes (MoS2@MWCNT/E) in a modified electrode substrate for the detection of uric acid (UA). The modified electrode generates a substantial three-fold increase in the anodic peak current for UA compared to the unmodified MWCNT electrode (MWCNT/E). The MoS2@MWCNT/E surface was characterized by cyclic voltammetry (CV), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and electrochemical impedance spectroscopy (EIS). The achieved detection limit stood at 0.04 µmol/L, with a relative standard deviation (RSD) of 2.0% (n = 10). The method's accuracy, assessed through relative error and percent recovery, was validated using a urine standard solution spiked with known quantities of UA.

Solid–Liquid–Gas Management for Low-Cost Hydrogen Gas Batteries

Aqueous nickel-hydrogen gas (Ni-H2) batteries with excellent durability (>10,000 cycles) are important candidates for grid-scale energy storage but are hampered by the high-cost Pt electrode with limited performance. Herein, we report a low-cost nickel-molybdenum (NiMo) alloy as an efficient bifunctional hydrogen evolution and oxidation reaction (HER/HOR) catalyst for Ni-H2 batteries in alkaline electrolytes. The NiMo alloy demonstrates a high HOR mass-specific kinetic current of 28.8 mA mg-1 at 50 mV as well as a low HER overpotential of 45 mV at a current density of 10 mA cm-2, which is better than most nonprecious metal catalysts. Furthermore, we apply a solid-liquid-gas management strategy to constitute a conductive, hydrophobic network of NiMo using multiwalled carbon nanotubes (NiMo-hydrophobic MWCNT) in the electrode to accelerate HER/HOR activities for much improved Ni-H2 battery performance. As a result, Ni-H2 cells based on the NiMo-hydrophobic MWCNT electrode show a high energy density of 118 Wh kg-1 and a low cost of only 67.5 $ kWh-1. With the low cost, high energy density, excellent durability, and improved energy efficiency, the Ni-H2 cells show great potential for practical grid-scale energy storage.

Incorporation of ZIF-67 derived Co-N/C core-shell nanoparticles on functionalized MWCNT as a highly efficient electrocatalyst for nonenzymatic H2O2 sensor

This work focuses on the fabrication of zero-dimensional (0D) and one-dimensional (1D) based nanocomposite materials for hydrogen peroxide (H2O2) sensing applications. We demonstrate an environmentally friendly synthesis approach for ZIF-67 growth on CTAB functionalized MWCNT using deionized water as a solvent medium (ZIF-67@CT-MWCNT). The pyrolysis treatment effectively formed a 0D/1D composite structure consisting of core-shell Co/N dual-doped carbon nanospheres and a CT-MWCNT network (referred to as Co-N/C@CT-MWCNT). The characteristic properties of composite materials were clearly investigated by SEM, TEM, XRD, micro-Raman, and XPS analysis. The electrocatalytic properties of Co-N/C@CT-MWCNT toward H2O2 reduction are also examined by cyclic voltammetry and amperometry techniques. The results indicated that the Co-N/C@CT-MWCNT modified electrode shows fast electron transfer kinetics for reduction of H2O2 in pH 7 electrolyte compared to other control electrodes. It mainly depends on the high catalytic activity of Co-Nx active species and the high electron conductive carbon network in the composite structure. Amperometry determination of H2O2 reduction on Co-N/C@CT-MWCNT electrode was performed at − 0.4 V (vs. Ag/AgCl), which shows rapid H2O2 sensing response time within 2 s, resulting in a wide linear range (0.5 μM - 25.74 mM) with the detection limit of 0.18 μM. The Co-N/C@CT-MWCNT sensor also showed excellent sensitivity (868.88 μA mM−1 cm−2), operational stability, and selectivity to H2O2 sensing. Thus, our proposed hybrid electrocatalyst material could be able to fabricate with commercial screen-printed carbon electrodes for the real-time H2O2 sensing application.

ZIF-8-derived ZnO/C decorated hydroxyl-functionalized multi-walled carbon nanotubes as a new composite electrode for supercapacitor application

Due to the poor conductivity of metal-organic frameworks (MOFs), it is challenging to directly employ MOFs as electrode materials for supercapacitors. Herein, hydroxyl-functionalized multi-walled carbon nanotube (f-MWCNT) was used to decorate ZnO/C obtained from the prior calcination of pristine zeolitic imidazolate framework-8 (ZIF-8) and applied as electrode material for supercapacitor application. The resulting ZnO/C@f-MWCNT electrode exhibits excellent storage performance, as confirmed by the specific capacitance of 650 F/g at 1 A/g and a superior energy/power density compared to the single electrode. Additionally, the composite electrode displayed remarkable cycling stability of 70% after 5000 cycles and retained 75% of its initial capacitance at 10 A/g, demonstrating good rate cyclability. The exceptional performance of ZnO/C@f-MWCNT was attributed to the synergistic effects offered by f-MWCNT which improved its electrical conductivity and ZnO/C that provided sufficient redox-active sites and structural stability. This work may promote the design of advanced MOF-based nanocomposites for energy storage application.

High performance flexible micro-supercapacitor for powering a vertically integrated skin-attachable strain sensor on a bio-inspired adhesive

We report on the fabrication of a high performance flexible micro-supercapacitor (MSC) for powering a vertically integrated skin-attachable strain sensor on a gecko-inspired micro-structured adhesive. Combined utilization of the mixed manganese/vanadium (Mn/V) oxide grown on MWCNT electrode and the sulfone-based electrolyte, PC/SL/LiClO4/PMMA, enhances both the capacitance and operation voltage up to 2 V of MSC. Thus, the fabricated MSC exhibits excellent electrochemical performance with an areal capacitance of 11.8 mF cm−2 and an areal energy density of 6.58 µWh cm−2 at an areal power density of 200 µW cm−2. The MSC shows mechanical stability over 1000 repetitive bends at a bending radius of 3.7 mm. The strain sensor made of fragmentized graphene foam embedded in PDMS film provides a high gauge factor of 12.6 up to 50% strain to detect strains due to various bio-signals. Our gecko-inspired adhesive made of PDMS micropillars inked with a mixture of PDMS and Silbione to have spatula tips exhibits not only high adhesion property but also high durability over repeated cycles of attachment-detachment and negligible skin irritation. After vertical integration of the MSC, strain sensor, and the adhesive film, bio-signals such as an arterial pulse, swallowing, and frowning of the brow are successfully detected using energy stored in the MSC.

Effect of carbon material additives on hydrogen evolution at rechargeable alkaline iron battery electrodes

In recent years a renewed interest in developing iron electrode for iron based accumulators has risen, govern by the progress in nano-materials research that could bring iron based accumulators nearer to their theoretical energy density and capacity. In this aspect, Iron-Air battery chemistry is best suited for current energy crisis in combination with the cost effectiveness, eco-friendliness, recyclability, non-toxicity of the iron materials. The possibility of Iron-Air battery to function as a rechargeable battery makes this electrochemical systems for engaging development. However, some challenges related to the performance of iron electrode needs to be addressed such as the passivation of the iron electrode on discharge due to the accumulation of iron hydroxide and the low efficiency due to the parasitic hydrogen evolution that occurs during the charging. So the proper engineering and the formulation of iron electrodes are necessary to attain the maximum efficiency for Iron-Air battery. In this exertion, different Fe2O3/Carbon (Fe/C) composites are tested as electrodes for Iron air battery. In addition to this, the prepared materials were comprehensively characterized by X-ray diffraction (XRD). The electrochemical effectiveness of the prepared samples were tested in a three electrode configuration.Fe2O3/MWCNT electrode show the best electrochemical performance exhibits a specific capacity of about 350 mAhg−1 at 10 mA cm−2 compared to the Fe2O3/Graphene of 300 mAhg−1, Fe2O3/Acetylene black of 225 mAhg−1 and Fe2O3/Vulcan carbon of 180 mAhg−1.

Electrochemical Evaluation of Choline Oxidase on Modified Bamboo-Like CNTs Electrode: from Nano-Chemistry Towards Biotechnological Application

Carbon nanotube (CNT) can be considered as one of the best materials for enzyme nanobiosensor. In this study, we investigated comprehensively electron transfer properties in three kinds of carbon nanotubes for finding the best supporting material for comprising of the electrochemistry and electrocatalysis of enzymes in nano-dimension. Choline oxidase was selected as a sample enzyme for evaluating the performance of the electrodes. The enzyme was absorbed on modified SWCNT, MWCNT and Bamboo-like CNTs electrode in ionic liquid. Electron transfer and electroanalytical responses were investigated by Metrohm Autolab. Functionalization was studied by Raman spectroscopy and FTIR and also, the morphological evaluation was conducted by SEM. Raman spectroscopy showed that Bamboo-like CNTs had better properties in loading enzyme and other electrochemical properties for electron transfer. FTIR spectroscopy showed that Bamboo-like CNTs had high covalent binding on the surface wall of nanotubes. High loading of the enzyme was detected in Bamboo-like CNTs in comparison to two other nano-tubes by SEM. The electrochemical and amperometric response showed that Bamboo-like CNTs had a better response in different scan rates, wide linear range and detection limit. ChOx/RTIL/Bamboo-like CNTs/GC electrodes showed the high amounts of enzyme loading, high enzyme-substrate affinity, low detection limit, best sensitivity and wider linear range.

Characteristics of Nitric Acid‐Modified Carbon Nanotubes and Desalination Performance in Capacitive Deionization

AbstractMultiwalled carbon nanotubes (MWCNTs) were treated by nitric acid to probe the effect of nitric acid modification on their properties and desalination performance in capacitive deionization (CDI). The nitric acid modification exerts a slight influence on the morphologies, specific surface area, and pore properties of the MWCNTs but can increase the amount of oxygen‐containing functional groups and then obviously enhance the specific capacitance of the electrodes. Thus, the desalination efficiency can be significantly improved as the modified MWCNTs serve as electrodes in CDI. The adsorption of salt ions on the original and modified MWCNT electrode is fitted well by the Freundlich isotherm other than the Langmuir isotherm.

Coaxial-nanostructured MnFe2O4 nanoparticles on polydopamine-coated MWCNT for anode materials in rechargeable batteries.

MnFe2O4@PDA-coated MWCNT coaxial nanocables are successfully designed via a simple one-pot process by utilizing the adhesion property of polydopamine (PDA) with cations in aqueous solutions and employing a modified co-precipitation synthesis at a low temperature. The incorporation of the PDA coating layer on the MWCNT leads to the well-dispersed state of the MWCNTs in the aqueous solution due to the hydrophilic functional group of the PDA coating layer. In addition, the catechol-based functional group of the PDA coating layer effectively anchors the Mn and Fe ions from the aqueous solution before the co-precipitation process, eventually resulting in the preferential and homogeneous formation of MnFe2O4 nanoparticles on the MWCNT. The final MnFe2O4@PDA-coated MWCNT electrode exhibits excellent power characteristics such as a high rate capacity of around of 367 mA h g-1 at a 5C-rate condition (= 4585 mA g-1). Cycling tests reveal that the stable performance of the MnFe2O4@PDA-coated MWCNT electrode persists even after 350 cycles.

A binder‐free Ir0.4Ru0.6‐oxide/functionalized multi‐walled carbon nanotube electrode for possible applications in supercapacitors

An initial study on a simple and inexpensive method to form an Ir0.4Ru0.6‐oxide (MMO) coating onto high‐area plasma functionalized multi‐walled carbon nanotubes (f‐MWCNTs) at the bench‐scale for possible supercapacitor (SC) applications is presented. f‐MWCNT electrodes are prepared in a two‐step process combining the growth of MWCNTs directly onto a 316 stainless steel mesh by thermal‐chemical vapour deposition (t‐CVD), followed by the addition of oxygen‐containing functionalities to their surface by plasma functionalization. The plasma functionalization step is done to: (i) improve electrode wettability and (ii) improve capacitive properties through the addition of pseudocapacitive oxygen functionalities. A simple dip‐dry method is then employed to coat the f‐MWCNTs with the desired MMO coating (Ir0.4Ru0.6‐oxide) prepared initially in a liquid precursor mixture. f‐MWCNT electrodes are suspended and dipped into the precursor then heated in air to evaporate the solvent while building the oxide layer. The resulting MMO/f‐MWCNT electrode exhibits excellent stability in 4 mol/L KOH electrolyte, yielding larger specific capacitance values than those obtained on bare f‐MWCNT electrodes; at a charging/discharging current density of 0.5 mA cm−2, the MMO/f‐MWCNT and f‐MWCNT electrodes achieve specific capacitances of 664 ± 7 and 190 ± 30 F g−1 in a 3‐electrode cell, respectively. The MMO/f‐MWCNT electrodes show good rate capability performance up to 10 mA · cm−2 and excellent stability.

Simultaneous recording of the action potential and its whole-cell associated ion current on NG108-15 cells cultured over a MWCNT electrode

It is well known that, in excitable cells, the dynamics of the ion currents (Ii) is extremely important to determine both the magnitude and time course of an action potential (Ap). To observe these two processes simultaneously, we cultured NG108-15 cells over a multi-walled carbon nanotubes electrode (MWCNTe) surface and arranged a two independent Patch Clamp system configuration (Bi-Patch Clamp). The first system was used in the voltage or current clamp mode, using a glass micropipette as an electrode. The second system was modified to connect the MWCNTe to virtual ground. While the Ap was recorded through the micropipette electrode, the MWCNTe was used to measure the underlying whole-cell current. This configuration allowed us to record both the membrane voltage (Vm) and the current changes simultaneously. Images acquired by atomic force microscopy (AFM) and scanning electron microscopy (SEM) indicate that cultured cells developed a complex network of neurites, which served to establish the necessary close contact and strong adhesion to the MWCNTe surface. These features were a key factor to obtain the recording of the whole-cell Ii with a high signal to noise ratio (SNR). The experimental results were satisfactorily reproduced by a theoretical model developed to simulate the proposed system. Besides the contribution to a better understanding of the fundamental mechanisms involved in cell communication, the developed method could be useful in cell physiology studies, pharmacology and diseases diagnosis.

Selective electrochemical detection of ascorbic acid in canned juice using aniline/N-(1-naphthyl)ethylene-diamine modified MWCNT electrode

Selective electrochemical detection of ascorbic acid in canned juice using aniline/N-(1-naphthyl)ethylene-diamine modified MWCNT electrode

Poly(3,4-ethylenedioxythiophene) growth on the surface of horizontally aligned MWCNT electrode

The process of conjugated polymer deposition on the surface of horizontally aligned multi-walled carbon nanotube, HA-CNT, electrode is described. Poly(3,4-ethylenedioxythiophene), PEDOT, was grown electrochemically under variable conditions in both aqueous and non-aqueous solutions of selected electrolytes. It is shown that the mechanism of nucleation highly depends on the reaction environment. The presence of a surfactant or non-aqueous medium favors the process of progressive nucleation in which the polymer growth is uniform and a homogeneous film of PEDOT is formed. It is demonstrated that the conditions make it is possible to cover the outer walls of individual HA-CNTs instead of forming thick polymer layer. The application of overpotential is proven to be a necessary condition to generate radical cations and cause relatively fast growth of polymer layer.

Improved electrochemical performance of CoS2-MWCNT nanocomposites for sodium-ion batteries.

A CoS2/multi-walled carbon nanotube (MWCNT) nanocomposite was synthesized and its sodium storage performances in ether-based electrolyte and commonly used carbonate-based electrolyte were investigated for the first time. A high capacity of 568 mA h g(-1) after 100 cycles in ether-based electrolyte can be achieved.

Photovoltaic Characterization and Electrochemical Impedance Spectroscopy Analysis of Dye-Sensitized Solar Cells Based on Composite TiO2–MWCNT Photoelectrodes

Dye-sensitized solar cells (DSSCs) use the effect of light on dye molecules to generate electricity through a photoelectrochemical mechanism. The aim of this study is to synthesize nanostructured DSSCs based on titania–multiwalled carbon nanotube (TiO2–MWCNT) composite photoelectrodes and improve their performance and efficiency. DSSCs were fabricated based on single-layer TiO2–MWCNT photoelectrodes with various weight percentages of multiwalled carbon nanotubes and bilayer TiO2/TiO2–2%MWCNT photoelectrodes. The microstructure and thickness of the anodic layers were characterized by field-emission scanning electron microscopy and optical microscopy. Also, to compare the conversion efficiency and determine the electron behavior in the electrical equivalent circuit of these cells, photovoltaic characterization and electrochemical impedance spectroscopy (EIS) analysis were used. The DSSC based on a single-layer TiO2–2%MWCNT electrode, compared with other single-layer DSSCs in this study, had the highest conversion efficiency of 3.9% (for anodic layer thickness of 9 μm). The efficiency of the solar cell with the bilayer TiO2/TiO2–2%MWCNT photoelectrode, in comparison with the single-layer solar cell with the TiO2–2%MWCNT electrode, showed a 23% increase from 4.33% to 5.35% (for anodic layer thickness of 18 μm). EIS analysis indicated that the charge-transport resistance of the DSSC based on the bilayer photoelectrode, in comparison with the single-layer TiO2 and TiO2–2%MWCNT solar cells, was decreased by 68% and 57%, respectively.

Sol–gel synthesis and impedance characteristics of networked nanocrystalline olivine cathode for Li-ion full cells

A sol–gel synthesis using adipic acid yielded small particles of around 20 nm in size of olivine LiFePO4/C cathode materials. In the characterization of cathode system(s), solid state impedance spectra of the pristine LiFePO4/C cathode revealed clear localization of charge through charge build-up. When networked with MWCNT, this material facilitates enhancement in charge mobility, eventually explaining the capacity enhancement of the LiFePO4/C–MWCNT electrode, which yields a high capacity of 163 mA h g−1 at C/10. On the other hand, the lower capacity of 125 mA h g−1 found for the pristine LiFePO4/C electrode material can be explained in terms of charge becoming localized/trapped in the vicinity of inter- and intra-granular regions of the cathode particles. To get a broader view of the application potential (in terms of cell voltages of ∼3 V, 2 V, and safety aspects) of the networked cathode materials, two kinds of Li-ion full cells using mesocarbon microbeads (MCMB) and Li4Ti5O12 as anodes were fabricated, which yielded capacities of 1.94 and 2.1 mA h respectively.

Behavior of NiO–MnO 2/MWCNT composites for use in a supercapacitor

NiO–MnO 2/MWCNT composite was formed by a simple chemical precipitation method using a chelating agent and Ni and Mn hydroxides on MWCNT. The NiO–MnO 2/MWCNT was pretreated by ultrasonication, followed by thermal annealing at 300 °C. The material obtained was applied as an electrode in a supercapacitor. FT-IR, EDS, XRD, FE-SEM and FE-TEM were used to characterize the structural features. The results show that a nanosized NiO–MnO 2 layer covered the surface of the MWCNT, and the original structure of the MWCNT was retained during the coating process. The capacitive behavior of the NiO–MnO 2/MWCNT electrode was investigated by cyclic voltammetry and galvanostatic charge/discharge methods in a 6 M KOH aqueous solution. The cyclic voltammetry curves demonstrated that the maximum specific capacitance of the NiO–MnO 2/MWCNT electrode was 193.50 F g −1, which is significantly higher than that of an MWCNT electrode. The results show that both the MWCNT and NiO–MnO 2/MWCNT electrodes exhibited capacitive behaviors, and the NiO–MnO 2 layer increased the capacitance of the supercapacitor.

Electropolymerization of a poly(3,4-ethylenedioxythiophene) and functionalized, multi-walled, carbon nanotubes counter electrode for dye-sensitized solar cells and characterization of its performance

Composite films of poly(3,4-ethylenedioxythiophene) and functionalized, multi-walled, carbon nanotubes (PEDOT–MWCNT) were fabricated by a simple oxidative electropolymerization method. These films were formed on fluorine-doped, tin oxide, glass substrates as counter electrodes (CEs) of platinum-free, dye-sensitized solar cells (DSSCs). The surface morphology, formation mechanism and electrochemical nature of PEDOT–MWCNT films were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), cyclic voltammetry (CV) and alternating current (AC) impedance spectroscopy. The SEM and AFM images showed that PEDOT–MWCNT films were more porous than PEDOT films. CV and AC impedance spectroscopy revealed that the PEDOT–MWCNT electrode had higher electrocatalytic activity for the I 3 −/I − redox reaction and a smaller charge transfer resistance than the PEDOT electrodes. The energy conversion efficiency of the DSSC with a PEDOT–MWCNT CE was 13.0% higher than with a PEDOT CE using the same conditions with a ruthenium sensitizer.

Characterization of a manganese dioxide/carbon nanotube composite fabricated using an in situ coating method

An in situ coating technique was developed to prepare a manganese dioxide/multi-walled carbon nanotube (MnO 2/MWCNT) composite, which exhibits excellent energy storage capacity. An alkaline KMnO 4 solution was first used to oxidize and open the ends of pristine MWCNT, and citric acid was then added as a reductant to form the composite. TEM, HR-TEM, XRD, TG–DSC, FT-IR, Raman and XPS methods were used to characterize the structural features. Cyclic voltammetry and electrochemical impedance spectroscopy measurements were used to investigate the electrochemical behavior of the samples. Results show that a nanosized ε-MnO 2 uniform layer covered the surface of the MWCNT and the original structure of the pristine MWCNT was retained during the coating process. The cyclic voltammetry curves demonstrate that the specific capacitance of the composite electrode reaches 250.5 F/g, which is significantly higher than that of a pure MWCNT electrode. The favorable capacitance performance is confirmed by the impedance spectra.