Carbon Nanotubes MnO2 Research Articles

Hybridization of Carbon Nanotube Tissue, MnO2 Catalyst and CFx as an Advanced Air Cathode in Metal–Air Batteries

We first present the utilization of hybrid carbon nano-tube (CNT) – manganese dioxide (MnO2) tissues as air electrodes in nonaqueous aluminum- and lithium-based battery systems. The CNT tissues are impregnated with α-manganese dioxide nanoparticles via a straightforward binder-free ultrasonic treatment, thereby enabling an improved oxygen reduction reaction (ORR) catalytic activity. Half-cell potentiodynamic measurements along with full-cell discharge evaluations of Li- and Al-based battery systems are reported. Higher discharge potentials and capacities were obtained from generic and advanced hybrid CNT–MnO2 air cathodes. The discharge products obtained on the air cathode surface were studied using high-resolution scanning electron microscopy. Their chemical compositions were evaluated using elemental mapping energy-dispersive X-ray spectroscopy. The stability of the α-MnO2 catalyst was studied using X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy, thereby indicating the ongoing formation of an outer MnF2 shell layer, which affected the α-MnO2 functionality, as an efficient ORR catalyst. We conclude this part of the talk by showing that the function of the metal–air battery is enabled by using porous carbon nanotube (CNT)-based tissue substrates loaded with MnO2 catalyst.In contrast, fluorinated graphite (CFx) coating on the CNT substrate provides an additional discharge process, enhancing discharge capacity. Two CFx loadings are investigated, and their performances are compared with that of a pristine CNT tissue. Electrochemical evaluations, including half- and full-cell measurements, are performed to examine the effect of the coating layer thickness on the ability of the cell to function at high discharge rates.

Hybridization of carbon nanotube tissue and MnO2 as a generic advanced air cathode in metal–air batteries

This paper presents the utilization of hybrid carbon nano-tube (CNT) – manganese dioxide (MnO2) tissues as air electrodes in nonaqueous aluminum- and lithium-based battery systems. The CNT tissues are impregnated with α-manganese dioxide nanoparticles via a straightforward binder-free ultrasonic treatment, thereby enabling an improved oxygen reduction reaction (ORR) catalytic activity. Half-cell potentiodynamic measurements along with full-cell discharge evaluations of Li- and Al-based battery systems are reported. Higher discharge potentials and capacities were obtained from generic and advanced hybrid CNT–MnO2 air cathodes. The discharge products obtained on the air cathode surface were studied using high-resolution scanning electron microscopy. Their chemical compositions were evaluated using elemental mapping energy-dispersive X-ray spectroscopy. We complemented our analysis with density functional theory calculations of oxygen adsorption on MnO2 and graphene. The modifications obtained for the discharge products in both systems, along with their improved distribution within the cathode surface, supported longer discharge processes without clogging the O2 penetration pathways at the air cathode. The stability of the α-MnO2 catalyst was studied using X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy, thereby indicating the ongoing formation of an outer MnF2 shell layer, which affected the α-MnO2 functionality, as an efficient ORR catalyst.

Controllable preparation of Ti/TiO2-NTs/PbO2–CNTs–MnO2 layered composite materials with excellent electrocatalytic activity for the OER in acidic media

High oxygen evolution overpotential and low corrosion resistance are the main challenges for oxygen evolution materials in acidic media. In this study, a novel composite material, Ti/TiO2-NTs/PbO2–CNTs–MnO2, with high oxygen evolution electrocatalytic activity was successfully prepared. First, TiO2 nanotubes (TiO2-NTs) were synthesized in situ on a Ti sheet via anodization and used as an intermediate layer. Subsequently, the adhesion and conductivity of the TiO2-NTs layer were increased through additional anodization, annealing, and electrochemical reduction. Finally, PbO2 was electrodeposited with a constant current in a lead acetate medium and doped with carbon nanotubes (CNTs) and MnO2. The surface morphology, phase composition, and electrochemical performance of the composite materials were investigated. Notably, in an acidic electrolyte (150 g/L H2SO4), Ti/TiO2-NTs/PbO2–CNTs–MnO2 exhibited good stability (30 h) and a low oxygen evolution overpotential of 410 mV at 50 mA/cm2, which is almost equivalent to that of precious metals (RuO2 and IrO2) and 499 mV lower than that of the industrial Pb–0.76 wt% Ag alloy. The outstanding performance is mainly attributed to the high aspect ratio of the TiO2-NT structure, synergistic effects of the active particles, and inherently good electrochemical properties of the active particles. Therefore, this study provides a new synthetic route for oxygen evolution materials in acidic media.

Structural, Optical and Electrical Properties of MnO2 / MWCNTs/PVA Nanocomposite

Manganese dioxide/multi-walled carbon nanotubes MnO2/ MWCNTs nanocomposite are synthesized by hydrothermal method. The crystallographic information of the acid-treated MWCNTs and the MnO2/ modified MWCNTs nanocomposite were characterized by X-ray diffraction (XRD),Transmission electron microscope (TEM )and FT-IR spectra. Optical and electrical properties of MnO2 / MWCNTs / PVA nanocomposite thin film with different concentration were studied .UV-VIS absorption spectra shift, at different exposing time , indicated the sensitivity to UV radiation. Optical band gap decreases with increasing time of radiation. Electrical properties of MnO2 / MWCNTs / PVA nanocomposite thin films with different concentration according to different frequency and exposing time of UV radiation showed semiconducting properties and sensitivity to UV radiation.

Low-temperature synthesis of manganese oxide–carbon nanotube-enhanced microwave-absorbing nanocomposites

Noting that the dielectric properties of manganese oxide make it a promising microwave-absorbing material, a low-temperature method to deposit crystalline MnO2 over carbon nanotubes (CNTs) is developed. Adjusting the pH of the precursor solution allows control over the phases and morphologies of the synthesized manganese oxides MnO2 and Mn3O4 that have minimum reflection losses of − 11 dB and − 6 dB, respectively. The synthesized CNT–MnO2 and CNT–Mn3O4 nanocomposites are superior microwave absorbers than simpler physical mixtures of CNTs and manganese oxides, with reflection losses as high as − 19 dB at 9.5 GHz and − 34 dB at 4 GHz, and have wider absorption bands than pure manganese oxides. Coating CNTs with manganese oxide not only increases dielectric and magnetic losses, but also improves the impedance match between free space and the absorber. The addition of CNTs to pure MnO2 and Mn3O4 improves impedance matching by enhancing the relaxation polarization and conductivity losses, magnetic loss, including contributions form eddy current and natural resonance. This facile, low-cost, scalable, high-yield method produces an enhanced microwave-absorbing nanocomposite.

Rational design of coaxial structured carbon nanotube–manganese oxide (CNT–MnO2) for energy storage application

Recently, there has been great research interest in the development of composites (core–shell structures) of carbon nanotubes (CNTs) with metal oxides for improved electrochemical energy storage, photonics, electronics, catalysis, etc. Currently, the synthetic strategies for metal oxides/hydroxides are well established, but the development of core–shell structures by robust, cost-effective chemical methods is still a challenge. The main drawbacks for obtaining such electrodes are the very complex synthesis methods which ultimately result in high production costs. Alternatively, the solution based method offers the advantages of simple and cost effective synthesis, as well as being easy to scale up. Here, we report on the development of multi-walled carbon nanotube–manganese oxide (CNT–MnO2) core–shell structures. These samples were directly utilized for asymmetric supercapacitor (ASC) applications, where the CNT–MnO2 composite was used as the positive electrode and ZIF-8 (zeolitic imidazolate framework, ZIF) derived nanoporous carbon was used as the negative electrode. This unconventional ASC shows a high energy density of 20.44 W h kg−1 and high power density of 16 kW kg−1. The results demonstrate that these are efficient electrodes for supercapacitor application.

Assembling fabrication and capacitance of manganese oxide nanosheets and functionalized carbon nanotubes hybrid material

The manganese oxide nanosheets (MnO2) with negative charge and the functionalized carbon nanotubes (CNTs) with positive charge are selected as assembling blocks, and the manganese oxide nanosheets and functionalized carbon nanotubes hybrid material (CNTs–MnO2 hybrid material) is fabricated by an assembling flocculation method. The restacking process of the manganese oxide nanosheets is effectively prevented due to the existence of CNTs, and manganese oxide nanosheets exist in nearly exfoliation state in CNTs–MnO2 hybrid material. The morphology and structure of the obtained materials are investigated by FTIR, XRD, SEM and TEM. A unique flaky appearance is observed for hybrid material. The capacitance of the CNTs–MnO2 hybrid material is investigated by cyclic voltammetry (CV) and Nyquist plots. A strong synergistic effect between the functionalized CNTs and exfoliated MnO2 is observed. The doped CNTs not only increase the utilization of manganese oxide nanosheets in the active cathode material, but also improve its performance at the high rate charge and discharge. The capacitance of CNTs–MnO2 hybrid material electrode is about 285Fg−1 at 5mVs−1. A relative high specific capacitance of 151Fg−1 can be maintained even at 100mVs−1.

Development of new nanocomposite based on nanosized-manganese oxide and carbon nanotubes for high performance electrochemical capacitors

Abstract We report the synthesis of a new composite electrode based on nanosized-manganese oxide and carbon nanotubes (CNTs) by electrophoretic deposition of CNTs on a stainless steel (SS) substrate followed by direct spontaneous reduction of MnO4− ions to MnO2 to form the multi-scaled SS–CNT–MnO2 electrode. The resulting material was characterized by scanning electron microscopy, energy dispersive X-ray analysis, cyclic voltammetry and galvanostatic charge–discharge in a 0.65 M K2SO4 aqueous solution. The binderless SS–CNT–MnO2 nanocomposite electrode shows a very high specific capacitance of 869 F/g of CNT–MnO2 and good stability during long galvanostatic charge–discharge cycling. To the best of our knowledge, this is one of the highest capacitance for manganese oxide electrode ever reported. In addition to its applicability in electrochemical capacitors, this methodology could be extended to develop other high performance nanocomposite material electrodes based on carbon nanotubes and metal oxide for the future generation of electrochemical power sources.