One-step synthesis and electrochemical behavior of LiMnO2 and its composite from MnO2 in the presence of glucose

LiMnO₂ and 0.23Li₂MnO₃·0.77LiMnO₂ were prepared by a convenient one-step solid-state reaction from MnO₂ using glucose as organic carbon resource. The crystal structure and morphology of the as-prepared materials was examined by X-ray powder diffraction and field emission scanning electron microscopy, respectively. The ration of Li to Mn was determined by means of atomic absorption spectrometry and the Li/Mn molar ratio in the products was 1.23. The electrochemical properties were investigated by charge-discharge test and electrochemical impedance measurements. The prepared composite material presented an initial discharge capacity of 45 mAh g^-1 and a good cycling performance with reversible capacity of 218 mAh g^-1 after 30 cycles. On the basis of the experimental results, the discharge efficiency of this composite material more than 100% was also discussed.     

Synthesis and characterization of ZrO2/MnO2/carbon clusters nanocomposite materials

Nano-sized ZrO₂/MnO₂/carbon clusters composite materials has been successfully obtained by the calcination of a Zr(acac)₄/Mn(acac)₃/epoxy resin complex under an oxygen atmosphere. The compositions of the resulting composite materials were determined using inductively coupled plasma (ICP) spectroscopy, elemental analysis and surface characterization by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy (TEM). The ultraviolet–visible (UV–VIS), X-ray photoelectron spectra (XPS) and electron spin resonance (ESR) spectra of the composites were also measured. ESR spectral examinations suggest the possibility of an electron transfer in the process of MnO₂ → carbon clusters → ZrO₂. The visible light-responsive oxidation–reduction ability of the calcined material was also investigated.     

Template-free synthesis of MnO2 nanowires with secondary flower like structure: Characterization and supercapacitor behavior studies

Manganese dioxide (MnO₂) nanowires with diameter about 30-70 nm is achieved via a two-step process: first, template-free cathodic electrodeposition from aqueous solution of Mn(NO₃)₂ on steel substrate and followed by heat treatment. The temperature-annealed sample was studied by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) methods and Fourier transform infrared (FT-IR) spectroscopy. The electrochemical performance of the MnO₂ sample was studied by cyclic voltammetry (CV) and chronopotentiometry in Na₂SO₄ solutions. The sample showed excellent supercapacitive behavior. The specific capacitance (SC) of 237 F g⁻¹ in a potential window of 0-0.9V was obtained at the scan rate of 2 mV s⁻¹. The SC calculated from the chronopotentiometry data is about 246 F g⁻¹. The SC was decreased by 16% after 1000 cycles.     

MnO2/graphite electrodeposited under supergravity field for supercapacitors and its electrochemical properties

MnO₂/graphite electrode material is successfully synthesized by electrodeposition under supergravity field from manganese acetate and graphite suspending solution. X-ray diffraction and field emission scanning electron microscopy show that the obtained composite is γ-MnO₂/graphite. The process of depositing the MnO₂/graphite was shown by the schematic illustration. Galvanostatic charge/discharge and cyclic voltammograms tests are applied to investigate electrochemical performances of the composite electrodes prepared under supergravity fields. MnO₂/graphite synthesized under supergravity field exhibits good discharge capacitance and the specific capacitance is 367.77 F g^?1 at current density of 0.5 A g^?1. It is found that supergravity field has effects on the electrochemical performances of MnO₂/graphite material.     

Preparation and characterization of multiwall carbon nanotube/polypyrrole coaxial fibrils

Multiwall carbon nanotube (MWNT)/polypyrrole (PPy) fibrils were fabricated by template-free in situ electrochemical deposition of PPy over MWNTs, and characterized by electron microscopy and electrical measurements. Scanning and transmission electron microscopy studies reveal that PPy coating on the surface of nanotube is quite uniform throughout the length, with the possibility of forming unique Y-junctions. Current (I)-voltage (V) characteristics at various temperatures show nonlinearity due to tunneling and hopping contributions to transport across the barriers. AC conductivity measurements (300-4.2 K) show that the onset frequency scales with temperature, and the nanoscale connectivity in MWNT/PPy fibrils decreases with the lowering of temperature.     

Preparation of MnO<Subscript>2</Subscript>/WMNT composite and MnO<Subscript>2</Subscript>/AB composite by redox deposition method and its comparative study as supercapacitive materials

The manganese oxide/multi-walled carbon nanotube (MnO₂/MWNT) composite and the manganese oxide/acetylene black (MnO₂/AB) composite were prepared by translating potassium permanganate into MnO₂ which formed the above composite with residual carbon material using the redox deposition method and carbon as a reducer. The products were characterized by X-ray diffraction, Fourier transform infrared, and scanning electron microscope. Electrochemical properties of both the MnO₂/MWNT and MnO₂/AB electrodes were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the MnO₂/MWNT electrode has better electrochemical capacitance performance than the MnO₂/AB electrode. The charge–discharge test showed the specific capacitance of 182.3 F·g⁻¹ for the MnO₂/MWNT electrode, and the specific capacitance of 127.2 F·g⁻¹ for the MnO₂/AB electrode had obtained, within potential range of 0–1 V at a charge/discharge current density of 200 mA·g⁻¹ in 0.5 mol·L⁻¹ potassium sulfate electrolyte solution in the first cycle. The specific capacitance of both the MnO₂/MWNT and MnO₂/AB electrodes were 141.2 F·g⁻¹ and 78.5 F·g⁻¹ after 1,200 cycles, respectively. The MnO₂/MWNT electrode has better cycling performance. The effect of different morphologies was investigated for both MnO₂/MWNT and MnO₂/AB composites.     

Disorder-order phase transition induced by size effect in bulk La2/3Sr1/3MnO3

Bulk La_2/3Sr_1/3MnO₃ ceramic samples prepared by thermal decomposition are investigated using transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). An abnormal phenomenon, where three kinds of La_2/3Sr_1/3MnO₃ phases with different structures and the same composition coexist in the same grain, has been observed. Besides the stable rhombohedral majority phase, the two other phases are a simple cubic structure with a=0.389 nm and a new hexagonal structure with a=0.544 nm, c=0.668 nm. The simple cubic phase is a residual phase of high-temperature due to the size effect and bondage of twin boundary. Image simulations have suggested that the new hexagonal phase is the La-Sr ordered structure with space group , which is converted from the disordered simple cubic phase. The formation mechanism of the ordered phase is explained from volume energy and interface energy considerations.     

Synthesis and characterization of polypyrrole/Sn-doped TiO2 nanocomposites (NCs) as a protective pigment

We have chemically polymerized pyrrole in the presence of Sn-doped TiO₂ nanoparticles (NPs) and TiO₂ (NPs) which act as a protective pigment. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) results show a core-shell structure of pigments in which TiO₂ and Sn-doped TiO₂ NPs have a nucleus effect and caused a homogenous PPy core-shell type morphology leading to coverage of the TiO₂ and Sn-doped TiO₂ NPs by PPy deposit. The XRD results indicate that the crystalline size of polypyrrole/TiO₂ NCs and polypyrrole/Sn-doped TiO₂ NCs were approximately 93.46 ± 0.06 and 23.36 ± 0.06 nm respectively. The electrochemical impedance spectroscopy (EIS) results show that the performance of polypyrrole/Sn-doped TiO₂ NCs is better than polypyrrole/TiO₂ NCs. The results indicate that increasing the area of synthesized polypyrrole in the presence of Sn-doped TiO₂ NPs can increase its ability to interact with the ions liberated during the corrosion reaction of steel in the presence of NaCl. The UV-vis results show that the band gap of TiO₂ NPs increases with doped of Sn in lattice of TiO₂. The increase of the band gap of TiO₂ with doping of Sn can decrease the charge transfer through the coating.     

Enhanced ferromagnetism by preventing antiferromagnetic MnO2 in InP:Be/Mn/InP:Be triple layers fabricated using molecular beam epitaxy

The p-type InP:Be/Mn/InMnP:Be triple epilayers were prepared using MBE to increase T_c (>300 K) by preventing MnO₂. After milling 1–3 nm of epilayers thickness from the top surface, the transmission electron microscopy (TEM) and X-ray diffraction (XRD) revealed no MnO₂ and precipitates, and TEM and XRD results coincide with results of ferromagnetism. The enhanced ferromagnetic transition at >300 K corresponds to InMnP:Be. The increased ferromagnetic coupling without MnO₂ is considered to originate from the increased p–d hybridation. These results demonstrate that InP-based ferromagnetic semiconductor layers having enhanced ferromagnetism can be formed by above process.     

Study of DC conductivity and relative magnetic permeability of nanoparticle NiZnFe2O4/PPy composites

The DC conductivity and the relative magnetic permeability have been measured as functions of temperature for five powder samples of nanoparticle ferrites (Ni_xZn_1−xFe₂O₄; x=0, 0.25, 0.5, 0.75 and 1), a pure polypyrrole (PPy) powder sample and many composite samples prepared by mixing different ratios of the ferrites to PPy. By comparing the results it is found that there is an obvious increase in DC conductivity of the ferrite/PPy composite samples compared to the corresponding pure ferrite samples, whereas compared to the pure PPy sample there is a decrease in DC conductivity. On the contrary, the magnetic permeability of the composites is higher than that of the pure PPy sample and lower than that of the pure ferrite samples as was expected.     

Synthesis and electrochemical properties of Li4Ti5O12/C composite by the PVB rheological phase method

Spinel Li₄Ti₅O₁₂/C powders were synthesized successfully by a simple rheological phase method using polyvinylbutyral (PVB) as both template and carbon source. The structure and morphology characteristics of the composite were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy and transmission electron microscopy. The XRD results showed that the composite had a good crystallinity. Its average particle size was about 2.1 μm with a narrow size distribution as a result of homogeneous mixing of the precursors. The in situ carbon coating produced by decomposition of PVB played an important role in improving electrical conductivity, thereby enhancing the rate capacity of Li₄Ti₅O₁₂ as anode material in Li-ion batteries. The Li₄Ti₅O₁₂/C composite, synthesized at 800 °C for 15 h under argon, containing 0.98 wt% of carbon, exhibited better electrochemical properties in comparison with the pristine Li₄Ti₅O₁₂, which could be attributed to the enhanced electrical conductive network of the carbon coating on the particle surface.     

The electronic behaviors of TiO2/MnO2/carbon clusters composite materials obtained by the calcination of a TiO(acac)2/Mn(acac)3/epoxy resin complex

The calcination of a TiO(acac)₂/Mn(acac)₃/epoxy resin complex under an oxygen atmosphere successfully produced nano-sized TiO₂/MnO₂/carbon clusters composite material. The surface characterizations of the resulting composites indicate that they are composed of nano-sized particles of TiO₂, MnO₂ and carbon clusters. ESR spectral examination suggests the possibility of an electron transfer in the process of MnO₂ → carbon clusters → TiO₂. The visible light-responsive oxidation–reduction function of the composite materials has also been confirmed.     

Microstructural and electromagnetic properties of MnO2 coated nickel particles with submicron size

Nickel particles with submicron size are prepared by using the solvothermal method. These spheres are then coated with a layer of MnO2 using the soft chemical method. The microstructure is characterized by x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Energy x-ray dispersive spectrometry and high-resolution images show that the granular composites have a classical core/shell structure with an MnO2 superficial layer,no more than 10 nm in thickness. The hysteresis measurements indicate that these submicron-size Ni composite powders have small remanence and moderate coercivity. The electromagnetic properties of the powders measured by a vector network analyzer in a frequency range of 2-18 GHz are also reported in detail.     

Hierarchical hollow urchin-like structured MnO2 microsphere/carbon nanofiber composites as anode materials for Li-ion batteries

In this work, novel hollow urchin-like MnO₂ microspheres (u-MnO₂), consisting of a hollow core with nanotubes, are synthesized by a simple hydrothermal process. The morphology of the MnO₂ structures could be tuned from round particles to a hierarchical hollow urchin structure by controlling the hydrothermal reaction time, with no need for surfactant or templates. The nanostructures of the obtained u-MnO₂ are characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The X-ray diffraction (XRD) pattern of the u-MnO₂ reveals a tetragonal structure of α-MnO₂. The carbon nanofibers (CNFs) are uniformly deposited on u-MnO₂ to improve the electrical conductivity and to utilize the hierarchical architecture of u-MnO₂. As the anode electrode of Li-ion batteries, the u-MnO₂/CNFs nanocomposites exhibit discharge capacity of 988 mAh·g⁻¹ after 100 cycles with a good rate capability. The superior electrochemical performances of the u-MnO₂/CNFs nanocomposites can be attributed to the hierarchical urchin-like structures and the superior electrical conductivity of the nanocomposites, which can facilitate fast electron and ion transport and accommodate a large volume change during charge/discharge.     

Electrical transport behavior of La0.67Ca0.33MnO3/Fe3O4 composites

The influence of Fe₃O₄ contents on the electrical transport properties (resistivity and ac susceptibility) of a series of composite samples of La_0.67Ca_0.33MnO₃/Fe₃O₄ is studied. Results show that the Fe₃O₄ phase not only shifts the intrinsic insulator-metal (I-M) transition temperature T_P1 to a lower temperature, but also causes a new I-M transition at a lower temperature T_P2 (T_P2<T_P1). On the basis of an analysis by scanning electron microscopy and X-ray diffraction, we suggest that the decrease of the I-M transition temperature and the formation of the new I-M transition are caused by the segregation of a new phases related to the Fe₃O₄ at grain boundaries or surfaces of the La_0.67Ca_0.33MnO₃ grains.     

Study of alternating current conduction mechanism in polypyrrole-magnesium ferrite hybrid nanocomposite through correlated barrier hopping model

In the present work, both polypyrrole (PPy) and optimized polypyrrole–magnesium ferrite (PPy-MgFe₂O₄) hybrid nanocomposite were synthesized separately by simple oxidative chemical polymerization method and then structurally characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The FTIR spectrum of the composite showed the presence of characteristic absorption bands of both PPy and MgFe₂O₄ in the composite confirming interfacial interaction of PPy with MgFe₂O₄. That this interaction is not affected by crystalline behaviour of predominant MgFe₂O₄ particles but that MgFe₂O₄ has embedded in PPy matrix was confirmed by XRD studies. Agglomerated granular spherical morphology of the composite was confirmed by SEM studies. Decrease in AC conductivity of the composite as compared to PPy due to the formation of interfacial heterojunction barrier between p-type PPy and n-type MgFe₂O₄ was confirmed experimentally and well supported theoretically by calculating binding energy, hopping distance and density of states at Fermi level of PPy and the composite as per CBH model.     

Sonochemically synthesized MnO2 nanoparticles as electrode material for supercapacitors

In this study, manganese oxide (MnO₂) nanoparticles were synthesized by sonochemical reduction of KMnO₄ using polyethylene glycol (PEG) as a reducing agent as well as structure directing agent under room temperature in short duration of time and characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM), Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) analysis. A supercapacitor device constructed using the ultrasonically-synthesized MnO₂ nanoparticles showed maximum specific capacitance (SC) of 282 Fg⁻¹ in the presence of 1 M Ca(NO₃)₂ as an electrolyte at a current density of 0.5 mA cm⁻² in the potential range from 0.0 to 1.0 V and about 78% of specific capacitance was retained even after 1000 cycles indicating its high electrochemical stability.     

Mechanochemical-synthesized Al-doped manganese dioxides for electrochemical supercapacitors

Al-doped MnO₂ as electrode materials for supercapacitor were synthesized by high-energy ball milling. The morphologies and structures of prepared MnO₂ were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Electrochemical investigation indicated that doped MnO₂ presented preferable electrochemical performances than un-doped MnO₂, but there were obvious capacitance decline in the first several dozen of cycles for all doped MnO₂ samples. The Al_0.05/Mn_0.95O₂ electrode, especially, showed the largest capacitance among all prepared MnO₂ samples. Excellent conductivity of Al in doped MnO₂ was considered to be responsible for enhanced electrochemical performances of doped MnO₂.     

Simple microwave synthesis and improved electrochemical performance of Nb-doped MnO<Subscript>2</Subscript>/reduced graphene oxide composite as anode material for lithium-ion batteries

Niobium-doped MnO₂/reduced graphene oxide (Nb-MnO₂/RGO) composite has been successfully synthesized via a simple microwave radiation method. The samples were systematically studied by X-ray diffraction (XRD), thermogravimetric analysis (TG), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and electrochemical measurements. As the anode material for lithium-ion batteries, the Nb-MnO₂/RGO (molar ratio of Mn/Nb?=?50:1) (NMG50) showed an outstanding reversible discharge capacity of 556.6 mAh g^?1 after 50 cycles with a capacity retention of 77% at a charge-discharge rate of 0.1 A g^?1 and the reversible discharge capacity can still retain 223.3 mAh g^?1 at a current of 1 A g^?1, which is much higher than those for Nb-MnO₂/RGO (molar ratio of Mn/Nb?=?10:1) (NMG10) and undoped MnO₂/RGO (MG). The improved electrochemical performance could be attributed to the proper amount of Nb doping, which could enhance both the conductivity and the structure stability of MnO₂.     

Novel synthesis and electrophoretic response of low density TiO-TiO2-carbon black composite

Novel low density TiO-TiO₂-carbon black composite was synthesized, which involved the deposition of inorganic coating on the surface of core-shell latex particles and subsequent removal of latex particles by calcination in high-purity nitrogen. The morphology and interior structure were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The images exhibited the composite had spherical shape and smooth surface, and the interior structure was hollow or porous. X-ray diffraction peaks (XRD) were mostly in agreement with the standard diffraction patterns of rutile TiO₂. In addition, the observed peaks at 2θ of 43.5°, 50.6° and 74.4° can be indexed to (1 1 1), (2 0 0) and (2 2 0) planes of cubic phase TiO. The X-ray photoelectron spectroscopy (XPS) results indicated that composite consisted of carbon black, TiO and TiO₂. The apparent density of the composite was suitable to 1.62 g cm⁻³, due to density matching with suspending media. Glutin-arabic gum microcapsules containing TiO-TiO₂-carbon black composite electrophoretic liquid were prepared via complex coacervation. The particles in the microcapsules showed excellent electrophoretic mobility under a DC field.