Morphology Of MnO2 Research Articles

Effect of poly(3,4-ethylenedioxythiophene) (PEDOT) on the pseudocapacitive properties of manganese oxide (MnO2) in the PEDOT/MnO2/multiwall carbon nanotube (MWNT) composite

The effect of the presence of poly(3,4-ethylenedioxythiophene) (PEDOT) on the pseudocapacitive properties of manganese oxide (MnO2) is investigated using PEDOT/MnO2/multiwall carbon nanotube-based (MWNT) coaxial composites containing different PEDOT contents. To prepare these PEDOT/MnO2/MWNT coaxial composites, a nanometer-thick outer layer of PEDOT was electrochemically polymerized onto the MnO2/MWNT composite, without affecting the morphology of MnO2. The pseudocapacitive properties of the MnO2/MWNT and PEDOT/MnO2/MWNT composites were evaluated by cyclic voltammetry. By analysis of the voltammetric charge, the outermost PEDOT layer on the MnO2/MWNT composite was found to improve the rate capability mainly through acting as an electrically conductive layer, rather the specific capacitance of the MnO2/MWNT composite.

Facile synthesis of hollow sphere amorphous MnO2: the formation mechanism, morphology and effect of a bivalent cation-containing electrolyte on its supercapacitive behavior

Nearly X-ray amorphous hollow sphere manganese oxides (hollow sphere MnO2) have been synthesized by a carboxylic acid-mediated system containing KMnO4 and Na2S2O4 under ambient conditions for supercapacitor applications. The product was characterized by powder XRD, Raman spectroscopy and thermal analysis. SEM and TEM were used to investigate the morphology of MnO2. The as-prepared MnO2 was X-ray amorphous and had particles in the size range 0.1–1 μm. A mechanism has been proposed for the formation of hollow sphere structures in the micro-emulsion medium. Upon annealing the sample at temperatures greater than 500 °C, the amorphous MnO2 transforms into Mn2O3. Cyclic voltammetry and galvanostatic charge–discharge cycling were used to evaluate the electrochemical performance. The initial discharge capacities were found to be 283 and 188 F g−1 in 0.1 M Ca(NO3)2 and 0.1 M Na2SO4, respectively, at a current density of 0.5 mA cm−2. The higher specific capacitance in the electrolyte with a bivalent cation is attributed to the reduction of two Mn4+ to Mn3+ by each of the bivalent cations present in the electrolyte.

Morphology Control of the Nano-MnO<sub>2</sub> by Microwave Hydrothermal Synthesis

In this paper, KMnO4 was used as raw material, nano-MnO2 with different morphologies such as flowers globular, hollow tubular and rodlike were obtained by the microwave assisted hydrothermal synthesis under the acidic condition. The crystal structure and morphology of the resultant MnO2 were characterized by X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM), respectively. The elements and content of samples were tested by Energy Dispersive Spectrometer (EDS). The influence of reaction temperature and holding time on crystal forms and morphologies of the MnO2 was analyzed.

Development of redox deposition of birnessite-type MnO2 on activated carbon as high-performance electrode for hybrid supercapacitors

Birnessite-type MnO2/activated carbon nanocomposites have been synthesized by directly reducing KMnO4 with activated carbon in an aqueous solution. It is found that the morphologies of MnO2 grown on activated carbon can be tailored by varying the reaction ratio of activated carbon and KMnO4. An asymmetric supercapacitor with high energy density was fabricated by using MnO2/activated carbon (MnO2/AC) nanocomposite as positive electrode and activated carbon as negative electrode in 1 M Na2SO4 aqueous electrolyte. The asymmetric supercapacitor can be cycled reversibly in the cell voltage of 0–2 V, and delivers a specific capacitance of 50.6 F g−1 and a maximum energy density of 28.1 Wh kg−1 (based on the total mass of active electrode materials of 9.4 mg), which is much higher than that of MnO2/AC symmetric supercapacitor (9.7 Wh kg−1).

Self-assembled spongy-like MnO2 electrode materials for supercapacitors

Mesoporous spongy-like MnO2 has been synthesized via a facile and biphasic wet method, accompanied with tetraoctylammonium bromide (TOAB) as a soft template under ambient condition. A well-defined spongy morphology of MnO2 with uniform filament diameters 10–20nm have been observed by FESEM, TEM, HRTEM, XRD, FT-IR,TGA-DSC studies. Further physical characterizations revealed that MnO2 sponges owned a large surface area of 155m2g−1 with typical mesoporous appearance. A specific capacitance value as high as 336Fg−1 was obtained. This improved capacitive behavior was attributed to the large surface area, morphology nature of nano-MnO2, and its broad pore size distribution.

Rapid sonochemical synthesis of mesoporous MnO2 for supercapacitor applications

Mesoporous MnO2 samples with average pore-size in the range of 2–20 nm are synthesized in sonochemical method from KMnO4 by using a tri-block copolymer, namely, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) as a soft template as well as a reducing agent. The MnO2 samples are found to be poorly crystalline. On increasing the amplitude of sonication, a change in the morphology of MnO2 from nanoparticles to nanorods and also change in porosity are observed. A high BET surface area of 245 m2 g−1 is achieved for MnO2 sample. The MnO2 samples are subjected to electrochemical capacitance studies by cyclic voltammetry (CV) and galvanostatic charge–discharge cycling in 0.1 M aqueous Ca(NO3)2 electrolyte. A maximum specific capacitance (SC) of 265 F g−1 is obtained for the MnO2 sample synthesized in sonochemical method using an amplitude of 30 μm. The MnO2 samples also possess good electrochemical stability due to their favourable porous structure and high surface area.

Facile Controlled Synthesis of Pt/MnO2 Nanostructured Catalysts and Their Catalytic Performance for Oxidative Decomposition of Formaldehyde

Pt/MnO2 nanostructured catalysts with cocoon-, urchin-, and nest-like morphologies were synthesized by a facile method. The synthesized MnO2 nanostructures and Pt/MnO2 catalysts were characterized by means of X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). TEM analyses showed that Pt nanoparticles of 1–4 nm were evenly dispersed on the surface of three MnO2 nanostructures, and no Pt nanoparticle agglomeration occurred in the Pt/MnO2 catalysts. These Pt/MnO2 catalysts showed much higher catalytic activities than the corresponding MnO2 nanostructures for oxidative decomposition of formaldehyde. Comparison of Pt/MnO2 catalysts with varied Pt loadings and MnO2 morphologies revealed that 2 wt % is the optimal Pt loading, and 2 wt % Pt/nest-like MnO2 showed the highest catalytic activity for oxidative decomposition of formaldehyde (temperature for complete decomposition of HCHO is 70 °C). The high dispersion and small size of Pt ...

Controllable Fabrication of δ-MnO<sub>2</sub> Microspheres and α-MnO<sub>2</sub> Nanorods

MnO2 nanostructure was synthesized via a redox reaction of potassium permanganate in hydrochloric acid solution below 100°C at open environment. The effects of pH value in solution and reaction temperature on the crystal structure and morphology of MnO2 were investigated. It was revealed that layer folded δ-MnO2 microspheres were obtained at low reaction temperature and low HCl concentration, whereas α-MnO2 single-crystal nanorods were fabricated with increasing reaction temperature and HCl concentration. The possible formation mechanism of δ-MnO2 microspheres and α-MnO2 nanorods is suggested.

Controlled Morphology of One-Dimensional Manganese Dioxide with Dramatic Enhancing Removal Efficiency to Heavy Metal Ions in Aqueous Solution

To examine the effects of morphologies of one-dimentional metal oxides on their surface properties, two typical morphologies of manganese dioxide (one is nanorod, the other is nanofiber) as a model of metal oxide were prepared with hydrothermal approach under similar conditions. The adsorption properties of Pb2+ in aqueous solution were carried out by using surface active group of MnO2 with different morphologies. The results indicated that the sorption capacities for Pb2+ were dramaticly increased via tailoring the morphology of MnO2. The products were characterized with SEM (Scanning Electron Microscopy), XRD (X-ray Diffraction), FTIR (Fourier-Transform Infrared), atomic absorption spectrophotometer, and so on. These results illustrated that it was feasible to improve the removal efficiency of heavy metal ions dramatically in aqueous solution by tailoring the morphology of nanostructured MnO2.

One-step electrochemical approach to the synthesis of Graphene/MnO2 nanowall hybrids

We have demonstrated a one-step and effective electrochemical method to synthesize graphene/MnO2 nanowall hybrids (GMHs). Graphene oxide (GO) was electrochemically reduced to graphene (GN), accompanied by the simultaneous formation of MnO2 with a nanowall morphology via cathodic electrochemical deposition. The morphology and structure of the GMHs were systematically characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Raman spectroscopy. The resulting GMHs combine the advantages of GN and the nanowall array morphology of MnO2 in providing a conductive network of amorphous nanocomposite, which shows good electrochemical capacitive behavior. This simple approach should find practical applications in the large-scale production of GMHs. Open image in new window

MnO2/graphene composite electrodes for supercapacitors: the effect of graphene intercalation on capacitance

MnO2/graphene composites were prepared for the electrode material of supercapacitors. MnO2 was synthesized on a gold plate by the electrodeposition method. Graphene prepared by thermal CVD was transferred onto the MnO2 layer. These processes were repeated to make multilayer structures. The optimal performance of the MnO2/graphene composite was examined as a function of the number of graphene layers in MnO2. The morphology of MnO2 on graphene was confirmed by SEM and TEM, and the capacitance of the electrode was investigated by cyclic voltammetry and galvanostatic charge/discharge test. The graphene layer provides the electro-conductivity of MnO2, and then leads to enhancement of the capacitance of MnO2.

Evaluation of the Porosity and the Nano-structure Morphology of MnO2 Prepared by Pulse Current Electrodeposition

Evaluation of the Porosity and the Nano-structure Morphology of MnO2 Prepared by Pulse Current Electrodeposition

HYDROTHERMAL SYNTHESIS OF NANOCRYSTAL MNO2 UNDER PULSED MAGNETIC FIELD

Nanocrystal MnO 2 was successful synthesized by hydrothermal method under pulsed magnetic field. The effect of pulsed magnetic field on the nucleation and growth of MnO 2 was studied by XRD and SEM analysis. It was found that the morphology of MnO 2 has been changed comparing without magnetic field. However, there were no different phases presented when pulsed magnetic field was applied.

Shape-Controlled Synthesis of 3D Hierarchical MnO2 Nanostructures for Electrochemical Supercapacitors

A simple hydrothermal method has been used to fabricate sea urchin shaped α-MnO2 without using any template and surfactant. When other conditions were kept the same and Al3+ exists in the solution, the product is α-MnO2 nanorods clusters; when Al3+ was substituted by Fe3+ in the solution, the phase of the products was transformed from α-MnO2 to ε-MnO2; relatively, the morphology of the product was changed from urchinlike clusters to 3D clewlike. The sea urchin shaped α-MnO2 and α-MnO2 nanorods clusters consist of radially grown single crystalline MnO2 nanorods of ca. 30−40 nm in diameter and ca. 0.87−1.2 μm in length. The 3D clewlike ε-MnO2 nanostructures are composed of nanosheets with a thickness of about 17 nm. The electrochemical properties of the prepared MnO2 materials were studied using cyclic voltammetry (CV) and ac impedance measurements in aqueous electrolyte. 3D clewlike ε-MnO2 nanostructures have a specific capacitance of 120 F g−1 and lower charge-transfer resistance. The results indicate that metal ions (Fe3+, Al3+) have great effects on the structure and morphology of MnO2.

Surfactant stabilized nanopetals morphology of α-MnO2 prepared by microemulsion method

α-Manganese dioxide is synthesized in a microemulsion medium by a redox reaction between KMnO4 and MnSO4 in presence of sodium dodecyl sulphate as a surface active agent. The morphology of MnO2 resembles nanopetals, which are spread parallel to the field. The material is further characterized by powder X-ray diffraction, energy dispersive analysis of X-ray, and Brunauer–Emmett–Teller surface area. Supercapacitance property of α-MnO2 nanopetals is studied by cyclic voltammetry and galvanostatic charge–discharge cycling. High values of specific capacitance are obtained.

A new type of MnO 2· xH 2O/CRF composite electrode for supercapacitors

In this paper, MnO 2· xH 2O/carbon aerogel (CRF) composite electrode materials were prepared by a chemical co-precipitation method. The structure and morphology of MnO 2· xH 2O/CRF were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that carbon aerogel was an amorphous material with a pearly network structure, the MnO 2· xH 2O powders possessed, a nanoscaled structure, and thus the MnO 2· xH 2O/CRF composite materials were nano-sized particles with a relatively high specific surface area. Electrochemical performance of the composite electrodes with different ratio's was studied by cyclic voltammetry and galvanostatic charge/discharge measurements. The results indicated that MnO 2· xH 2O/CRF composite electrodes had good electrochemical performance, high reversibility and high charge–discharge properties. Moreover, when the loading amount of MnO 2· xH 2O was 60%, the composite material has a high specific capacitance of 226.3 F g −1, while the capacitance of carbon aerogel electrode alone was 112 F g −1. Besides, MnO 2· xH 2O/CRF composite supercapacitors showed a stable cycle life in the potential range of 0–1.0 V and retained 90% of initial capacitance over 400 cycles.

Effect of synthesis conditions on the morphology of MnO2 (α-, β-, γ-) synthesized by the hydrothermal-electrochemical method

The morphology and particle size of various MnO2 compounds synthesized by the hydrothermal-electrochemical method is presented. Individual crystals as well as bundles of fibers were obtained, with diameters ranging from several tens of nanometers to several microns. The effects of the solution pH, synthesis temperature and the applied current density are discussed. Two very different morphologies were found for α-MnO2 synthesized under different conditions. Various morphologies were also found for γ-MnO2 and γ/β-MnO2 compounds. The relationship between the synthesis parameters, γ-MnO2 structural parameters and the morphology is discussed.