MnO2 Nanotubes Research Articles

Flexible supercapacitors based on carbon nanotube/MnO2nanotube hybrid porous films for wearable electronic devices

To meet the requirement of clean and efficient energy storage system for practical applications, supercapacitors (SCs) to be promising candidates for the next-generation energy storage devices have received tremendous attentions. In fact, the SCs can have broader potential if they are designed as flexible power supplies for wearable electronic devices. Herein, we develop the first flexible, low-cost and high-performance hybrid electrode based on MnO2 nanotubes (NTs) and carbon nanotubes (CNTs) by employing a facile vacuum-filtering method. The superior mechanical and electrochemical performance of these flexible electrodes is attributed to: (1) the ultra-long one-dimensional nanotube morphology, (2) the synergistic effects between pseudocapacitive MnO2 NTs and conductive CNTs, (3) hierarchical porous structure of the freestanding film, and (4) high mass loading of MnO2 (4 mg cm−2). Subsequently, the as-synthesized freestanding CNT/MnO2 NT hybrid electrodes are assembled in the form of solid-state SC devices using polyvinyl alcohol (PVA)/LiCl as gel electrolyte. The device exhibits an excellent volumetric capacitance of 5.1 F cm−3 and a high energy density of 0.45 mW h cm−3 for the entire SC volume. Finally, these SCs are integrated in a flexible power band that can drive watches and LEDs. The solid-state SC devices with outstanding flexibility and stability clearly demonstrate their broad applications as flexible, low-cost, high-performance power supplies in wearable electronic devices.

MnO2/polypyrrole nanotubular composites: reactive template synthesis, characterization and application as superior electrode materials for high-performance supercapacitors

A novel MnO2/polypyrrole (PPy) heterogeneous composite with nanotubular structure is reported by a facile preparation of in situ chemical polymerization via a reactive template of MnO2. MnO2 nanotubes are found to be served as both appropriate oxidants and scaffolds to polymerize conducting PPy nanocoatings on the surface, thus constructing a unique coaxial configuration. The electrochemical measurements show that both components in the hybrid nanocomposites exhibit highly pseudocapacitive behavior in neutral KCl aqueous electrolyte. MnO2/PPy nanocomposites prepared from an initial MnO2/pyrrole ratio (3:1) deliver a maximum specific capacitance of 337 F g−1 at 0.5 A g−1 with good rate capability and long-term cycling stability, demonstrating their promising applications in high-performance supercapacitors. Moreover, the synthetic methodology may provide a generic guideline in developing different nanostructured MnO2/PPy electrode materials for electrochemical energy storage.

Kirkendall Effect Induced One-Step Fabrication of Tubular Ag/MnOx Nanocomposites for Supercapacitor Application

One-dimensional (1D) tubular Ag/MnOx nanocomposites were synthesized by the solvothermal method via the Kirkendall effect between potassium permanganate (KMnO4) and Ag nanowire templates. The morphology and electrochemical performance of Ag/MnOx composites were tuned by varying the pH levels. Tubular MnOx nanosheets with ultrafine Ag nanoparticles were formed in an acidic environment (pH 0.76), whereas the Ag nanoparticles entrapped in amorphous MnO2 nanotubes were prepared in a neutral environment (pH 7.00). Based on a series of volume-dependent experiments, it was confirmed that the Kirkendall effect was involved in the formation of these morphologies. When tested as an electrode for supercapacitors, the hierarchical tubular Ag/MnOx nanosheet composites prepared in an acidic environment exhibited an optimized electrochemical performance, with specific capacitance of 180 F g–1 at current density of 0.1 A g–1, and still maintained 80% of initial capacity after 1000 cycles at current density of 1 A g–1. Th...

Carbon/MnO2Double-Walled Nanotube Arrays with Fast Ion and Electron Transmission for High-Performance Supercapacitors

The novel carbon (C)/MnO2 double-walled nanotube arrays (DNTAs) are designed and fabricated via template-assisted electrodeposition. The unique DNTA architectures of C/MnO2 composites with high weight fraction of MnO2 allow high electrode utilization ratio and facilitate electron and ion transmission. In the half-cell test, the hybrid C/MnO2 DNTAs as electrodes show a large specific capacitance (Csp) of 793 F/g at the scan rate of 5 mV/s, high energy/power densities, and much enhanced long-term cycle stability. After 5,000 cycles, the Csp retention of C/MnO2 DNTAs keeps ∼97%, which is much larger than 69% of the MnO2 nanotube arrays (NTAs). The symmetrical supercapacitors (SSCs) composed of C/MnO2 DNTAs also show the predominant performance, such as large Csp of 161 F/g and high energy density of ∼35 Wh/kg, indicating that the C/MnO2 DNTAs is a potential electrode for supercapacitors. The high order pore passages, double-walled structures, hollow structures, and high conductivity are responsible for the superior performance of C/MnO2 DNTAs. Such hybrid C/MnO2 DNTAs may bring new opportunities for the development of supercapacitors with superior performance.

Template assisted fabrication of free-standing MnO2 nanotube and nanowire arrays and their application in supercapacitors

In this Letter, an innovative technique is reported to control the fabrication of free-standing MnO2 nanotube and nanowire arrays. The synthesis is based on a three-step process, using porous anodic aluminum oxide as a template, and enables the selective fabrication of vertically aligned MnO2 nanotubes or nanowires on large areas. The as-prepared MnO2 nanotube and nanowire arrays are investigated as electrode materials for supercapacitor applications and show a good electrochemical performance with specific capacitances of 210 F g−1 at 1.9 A g−1 and 231 F g−1 at 0.5 A g−1, respectively. The investigation of the rate capability of both structures indicates a superior performance of the nanotube arrays.

Self-Assembly of Mesoporous Nanotubes Assembled from Interwoven Ultrathin Birnessite-type MnO2 Nanosheets for Asymmetric Supercapacitors

Porous nanotubes comprised of MnO2 nanosheets were fabricated with a one-pot hydrothermal method using polycarbonate membrane as the template. The diameter and thickness of nanotubes can be controlled by choice of the membrane pore size and the chemistry. The porous MnO2 nanotubes were used as a supercapacitor electrode. The specific capacitance in a three-electrode system was 365 F g−1 at a current density of 0.25 A g−1 with capacitance retention of 90.4% after 3000 cycles. An asymmetric supercapacitor with porous MnO2 nanotubes as the positive electrode and activated graphene as the negative electrode yielded an energy density of 22.5 Wh kg−1 and a maximum power density of 146.2 kW kg−1; these values exceeded those reported for other MnO2 nanostructures. The supercapacitor performance was correlated with the hierarchical structure of the porous MnO2 nanotubes.

Nanotubular MnO2/graphene oxide composites for the application of open air-breathing cathode microbial fuel cells

Nanotubular shaped α-MnO2/graphene oxide nanocomposites were synthesized via a simple, cost and time efficient hydrothermal method. The growth of hollow structured MnO2 nanotubes preferentially occurred along the [001] direction as evidenced from the morphological and structural characterizations. The tunnels of α-MnO2 nanotubes easily accommodated the molecular oxygen and exhibited excellent catalytic activity towards the oxygen reduction reaction over the rod structure and was further enhanced with the effective carbon support graphene oxide. The MnO2 nanotubes/graphene oxide nanocomposite modified electrode exhibited a maximum power density of 3359mWm−2 which is 7.8 fold higher than that of unmodified electrode and comparable with the Pt/C modified electrode. The microbial fuel cell equipped with MnO2 nanotubes/graphene oxide nanocomposite modified cathode exhibited quick start up and excellent durability over the studied electrodes and is attributed to the high surface area and number of active sites. These findings not only provide the fundamental studies on carbon supported low-dimensional transition-metal oxides but also open up the new possibilities of their applications in green energy devices.

Effect of morphology of α-MnO2 nanocrystals on electrochemical detection of toxic metal ions

Three different morphologies of α-MnO2 (nanoparticles, nanobowls and nanotubes) have been prepared for the electrochemical determination of Zn(II), Cd(II), Pb(II), Cu(II) and Hg(II). The three different morphologies of MnO2-modified electrodes offered an obvious regularity in individual electrochemical determination of Zn(II), Pb(II), Cu(II) and Hg(II): MnO2 nanobowls>MnO2 nanotubes>MnO2 nanoparticles. This study indicates the effect of morphology of MnO2 on its electrochemical detection of toxic metal ions.

Synthesis and property of novel MnO2@polypyrrole coaxial nanotubes as electrode material for supercapacitors

Novel MnO2@polypyrrole (PPy) coaxial nanotubes have been prepared via a simple and green approach without any surfactant and additional oxidant. Under the acidic condition, MnO2 nanotubes act as both template and oxidant to initiate the polymerization of pyrrole monomers on its fresh-activated surface. Fourier transform infrared spectra (FT-IR), X-ray diffraction patterns (XRD), thermo-gravimetric analysis data (TG) and X-ray photoelectron spectra (XPS) suggest the formation of composite structure of MnO2@PPy. Also, FESEM and TEM images intuitively confirm that the PPy shell is coated uniformly on the surface of MnO2 nanotubes. Adjusting the concentrations of sulfuric acid or adding oxidant can modulate the morphology of the products accordingly. Due to the synergic effect between MnO2 core and PPy shell, the MnO2@PPy coaxial nanotubes possess better rate capability, larger specific capacitance of 380 F g−1, doubling the specific capacitance of MnO2 nanotubes, and good capacitance retention of 90% for its initial capacitance after 1000 cycles.

One-pot facile synthesis of hierarchical hollow microspheres constructed with MnO2 nanotubes and their application in lithium storage and water treatment

Semiconductor α-MnO2 hierarchical hollow microspheres constructed with nanotubes have been facilely synthesized through a bubble template-based self-scrolling solution route. An energy-minimizing-driven self-assembly of α-MnO2 nanoparticles on the base of O2 bubbles is responsible for the formation of hierarchical hollow microsphere structure. The as-obtained α-MnO2 products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and UV-vis-NIR spectrophotometry. The Li ion storage and water treatment performances of these α-MnO2 hierarchical hollow microspheres constructed with nanotubes were tested. A discharge capacity as high as 983 mA h g−1 during the 30th cycle has been delivered at a current density of 300 mA g−1. These as-prepared samples were also used as adsorbents in water treatment, and showed an excellent ability to remove organic pollutants without any other additives.

Surface modification of MnO2 and carbon nanotubes using organic dyes for nanotechnology of electrochemical supercapacitors

Efficient dispersion and electrophoretic deposition (EPD) of multiwalled carbon nanotubes (MWCNTs) was achieved using organic dyes, such as pyrocatechol violet (PV) and m-cresol purple (CP). The problem of MnO2 nanoparticle dispersion in concentrated suspensions was addressed by the use of PV as a dispersant. The analysis and comparison of experimental data for PV and CP provided insight into the influence of chemical structures of the dyes on their adsorption on MWCNTs and MnO2. The adsorption of PV on MWCNTs and MnO2 was attributed to π–π interactions and catecholate type bonding, respectively. The EPD yield can be varied by the variation of the PV concentration in the suspensions, deposition voltage and time. It was found that PV can be used as a co-dispersant for EPD of MWCNTs and MnO2 and the fabrication of MnO2–MWCNT composites. The proposed approach offers advantages of uniform distribution of individual components and low binder content in the composite. MnO2–MWCNT films were prepared by EPD for thin film electrodes of electrochemical supercapacitors (ES). Bulk MnO2–MWCNT electrodes with a material loading of 40 mg cm−2 were obtained by the impregnation of Ni foam current collectors. The highest specific capacitance of 5.9 F cm−2 (148 F g−1) was achieved. The composite materials are promising for ES applications.

Facile synthesis of polyaniline nanotubes using reactive oxide templates for high energy density pseudocapacitors

A remarkable energy density of 84 W h kg(cell)−1 and a power density of 182 kW kg(cell)−1 have been achieved for full-cell pseudocapacitors using conducting polymer nanotubes (polyaniline) as electrode materials and ionic liquid as electrolytes. The polyaniline nanotubes were synthesized by a one-step in situ chemical polymerization process utilizing MnO2 nanotubes as sacrificial templates. The polyaniline-nanotube pseudocapacitors exhibit much better electrochemical performance than the polyaniline-nanofiber pseudocapacitors in both acidic aqueous and ionic liquid electrolytes. Importantly, the incorporation of ionic liquid with polyaniline-nanotubes has drastically improved the energy storage capacity of the PAni-nanotube pseudocapacitors by a factor of ∼5 times compared to that of the PAni-nanotube pseudocapacitors in the acidic aqueous electrolyte. Furthermore, even after 10 000 cycles, the PAni-nanotube pseudocapacitors in the ionic liquid electrolyte maintain sufficient high energy density and can light LEDs for several minutes, with only 30 s quick charge.

Performance loss of aqueous MnO2/carbon supercapacitors at elevated temperature: cycling vs. storage

Birnessite MnO2 nanotubes of high specific surface area have been used as one electrode material in supercapacitors with a commercial-carbon-based second electrode ((NH4)2SO4(aq.) electrolyte). Assembled cells have been subjected to full electrochemical testing at temperatures ≤80 °C. At elevated temperatures, specific capacitance as high as 700 F g−1 has been observed. The increase in specific capacitance with temperature has been found to be at a cost to cycling performance. Furthermore, the time spent at elevated temperatures “at rest” has been shown to have a major effect on device lifetime. It has been found that at 80 °C, without cycling, such devices lose all significant capacitance after 21 days. The findings herein are believed to have major implications for transport, storage lifetime and ultimate utilization of such systems.

Co3O4 nanoparticle-modified MnO2 nanotube bifunctional oxygen cathode catalysts for rechargeable zinc–air batteries

We report the preparation of MnO2 nanotubes functionalized with Co3O4 nanoparticles and their use as bifunctional air cathode catalysts for oxygen reduction reaction and oxygen evolution reaction in rechargeable zinc-air batteries. These hybrid MnO2/Co3O4 nanomaterials exhibit enhanced catalytic reactivity toward oxygen evolution reaction under alkaline conditions compared with that in the presence of MnO2 nanotubes or Co3O4 nanoparticles alone.

One-dimensional manganese oxide nanostructures as radical scavenger to improve membrane electrolyte assembly durability of proton exchange membrane fuel cells

One-dimensional manganese oxide (MnO2) scavengers are proposed to minimize the radical degradation of membrane electrode assembly (MEA) in fuel cells. The synthesized MnO2 nanotubes and MnO2 nanowires are ca. 5–8 nm in diameter and more than 100 nm in length, respectively. Water retention of the hydrophilic MnO2 reduces the humidity sensitivity of the fuel cells. At 75 RH% humidify levels of inlet gas at 60 °C, single cells assembled by catalyst layer with MnO2 nanotubes and nanowires as the cathodes have peak power densities of 599.3 and 536.8 mW cm−2, respectively. Radical scavenger MnO2 in the cathode catalyst is effective in minimizing the radical degradation in proton exchange membrane (PEM) fuel cells. After the OCV degradation, the hydrogen crossover of cell assembled by catalyst layer with MnO2 nanowires or MnO2 nanotubes in anode and traditional catalyst layer in cathode are about 5.3 and 4.9 mA cm−2, respectively. As a comparison, single cell with conventional catalyst layer in both anode and cathode, the hydrogen crossover through the MEA is increased to 14.7 mA cm−2.

Oxidation-Etching Preparation of MnO2 Tubular Nanostructures for High-Performance Supercapacitors

1D hierarchical tubular MnO(2) nanostructures have been prepared through a facile hydrothermal method using carbon nanofibres (CNFs) as sacrificial template. The morphology of MnO(2) nanostructures can be adjusted by changing the reaction time or annealing process. Polycrystalline MnO(2) nanotubes are formed with a short reaction time (e.g., 10 min) while hierarchical tubular MnO(2) nanostructures composed of assembled nanosheets are obtained at longer reaction times (>45 min). The polycrystalline MnO(2) nanotubes can be further converted to porous nanobelts and sponge-like nanowires by annealing in air. Among all the types of MnO(2) nanostructures prepared, tubular MnO(2) nanostructures composed of assembled nanosheets show optimized charge storage performance when tested as supercapacitor electrodes, for example, delivering an power density of 13.33 kW·kg(-1) and a energy density of 21.1 Wh·kg(-1) with a long cycling life over 3000 cycles, which is mainly related to their features of large specific surface area and optimized charge transfer pathway.

Manganese dioxide nanotube and nitrogen-doped carbon nanotube based composite bifunctional catalyst for rechargeable zinc-air battery

Abstract A composite bifunctional catalyst (MnO2–NCNT) was prepared from manganese dioxide (MnO2) nanotubes and nitrogen-doped carbon nanotubes (NCNT) for the purpose of oxygen reduction (ORR) and evolution (OER) catalysis in the rechargeable zinc-air battery. From the half cell test, the MnO2–NCNT composite illustrated excellent activities towards ORR and OER in alkaline conditions. Based on the battery test, the composite catalyst displayed outstanding discharge and charge performance while maintaining good stability. In both cases, the marked performance improvements from MnO2–NCNT compared favourably to the NCNT and MnO2, which are the constituents of the composite. In particular, MnO2–NCNT exhibited improved half wave potential by 220 mV compared to MnO2 and much superior OER stability compared to NCNT based on the rotating ring disk voltammetry results. According to battery test, MnO2–NCNT decrease the battery resistance by 34% and concurrently improved the durability, discharge and charge performance in comparison to the MnO2 nanotubes.

Inorganic nanotubes reinforced polyvinylidene fluoride composites as low-cost electromagnetic interference shielding materials

Novel polymer nanocomposites comprising of MnO2 nanotubes (MNTs), functionalized multiwalled carbon nanotubes (f-MWCNTs), and polyvinylidene fluoride (PVDF) were synthesized. Homogeneous distribution of f-MWCNTs and MNTs in PVDF matrix were confirmed by field emission scanning electron microscopy. Electrical conductivity measurements were performed on these polymer composites using four probe technique. The addition of 2 wt.% of MNTs (2 wt.%, f-MWCNTs) to PVDF matrix results in an increase in the electrical conductivity from 10-16S/m to 4.5 × 10-5S/m (3.2 × 10-1S/m). Electromagnetic interference shielding effectiveness (EMI SE) was measured with vector network analyzer using waveguide sample holder in X-band frequency range. EMI SE of approximately 20 dB has been obtained with the addition of 5 wt.% MNTs-1 wt.% f-MWCNTs to PVDF in comparison with EMI SE of approximately 18 dB for 7 wt.% of f-MWCNTs indicating the potential use of the present MNT/f-MWCNT/PVDF composite as low-cost EMI shielding materials in X-band region.

Polyaniline–MnO2 nanotube hybrid nanocomposite as supercapacitor electrode material in acidic electrolyte

Herein, we report a preparation method of a novel binary hybrid nanocomposite based on polyaniline (PANI) and α-MnO2 nanotubes (MNTs) by in situpolymerization. The polymerization is carried out in acidic medium using α-MnO2 nanotubes as oxidant. A symmetrical supercapacitor is fabricated and the electrochemical performance of the supercapacitor is investigated by cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) techniques using 1.0 M H2SO4 as electrolyte. The nanocomposite shows maximum specific capacitance of 626 F g−1 and corresponding energy density of 17.8 W h kg−1, as calculated from the charge–discharge curve at a specific current density of 2 A g−1 in the potential range 0–0.7 V.

Synthesis of Birnessite Type MnO2 Nanotubes and Their Application in Aqueous Supercapacitors

Potassium birnessite nanotubes have been made through a templated hydrothermal route with specific surface areas and pore volumes as high as 110 m2 g-1 and 0.54 cm3 g-1 respectively. After casting into electrode films and assembling into hybrid supercapacitor cells, good cyclability has been demonstrated, with high coulombic efficiencies, with changes in the electrodes during cycling being monitored through electrochemical impedance spectroscopy. High specific capacitances have been observed, with values approaching 350 F g-1 at current densities of 0.1 A g-1. Energy densities approaching 90 W h g-1 have been achieved at low current densities, with power densities over 75000 W kg-1 at high current densities.