Potentiodynamical co-deposited manganese oxide/carbon composite for high capacitance electrochemical capacitors

Manganese oxide/carbon composite materials were prepared by introducing the carbon powders into the potentiodynamical anodic co-deposited manganese oxide in 0.5 mol L^− 1 MnSO₄ and 0.5 mol L^− 1 H₂SO₄ mixed solution at 40 °C. The surface morphology and structure of the composite material were examined by scanning electron microscope and X-ray diffraction. Cyclic voltammetry tests and electrochemical impedance measurements were applied to investigate the performance of the composite electrodes with different ratios of manganese oxide and carbon. These composite materials with rough surface, which consisted of approximately amorphous manganese oxide, were confirmed to possess the ideal capacitive property. The highest specific capacitance of manganese oxide/carbon composite electrode was up to 410 F g^− 1 in 1.0 mol L^− 1 Na₂SO₄ electrolyte at the scan rate 10 mV s^− 1. The synthesized composite materials exhibited ideal capacitive behavior indicating a promising electrode material for electrochemical supercapacitors.     

Self-assembled manganese dioxide nanowires as electrode materials for electrochemical capacitors

The microstructure and morphology of sol-gel derived manganese dioxide (MnO₂) xerogels were affected by the synthesis conditions and post synthesis heat treatment. Manganese dioxide nanoparticles in sol that were dialyzed to more acidic pH (pH 5.7) value were observed to self-assemble into nanowires, whereas non-dialyzed sols remained nanoparticulate in nature. MnO₂ xerogels of disordered nanowire network exhibited comparatively higher porosity and BET surface areas. The electrochemical properties of both MnO₂ nanowire and nanoparticle thin-film electrodes were evaluated using cyclic voltammetry in a mild aqueous electrolyte (0.1 M Na₂SO₄). The charge capacities of MnO₂ nanowire-based thin-film electrodes were substantially higher (~ 800 F/g) than those of nanoparticulate thin-film electrodes (~ 700 F/g).     

纳米二氧化锰的可控制备及其电化学储能机理研究

通过添加十二烷基溴化氨(CTAB)利用液相沉淀法制备了不同形貌的纳米二氧化锰,用扫描电镜、X射线衍射、孔结构以及循环伏安法等分析研究了CTAB添加量对二氧化锰形貌和电化学性能的影响.结果表明,随着CTAB添加量的增加,二氧化锰形貌从长棒状到均匀球状发生规律变化,此外随着颗粒尺寸变小,二氧化锰比容量从162F/g提高到了...     

掺锰活性炭的制备及其电化学性能

分别采用催化法和物理法制得含锰氧化物的中孔活性炭(AC-Mn)和普通活性炭(AC),表征了活性炭的孔容、孔径分布、碘值和亚甲兰值等主要结构、性能指标,并对以这两种活性炭为原料制得的电极进行循环伏安、定电流充放电和交流阻抗测定.结果表明:AC-Mn的收率和碘值分别比AC降低了28.9%和12.4%,但业甲兰吸附值提高了19.8%.AC-Mn的中孔率显著提高,其中3.4nm-4.2nm的中孔增长率最大.AC-Mn电极比电容达93.8F/g.比末负载金属Mn的AC电极高近140%,显示出相对较高的能量密度和良好的准电容特性.     

Chemical synthesis of nanosized oxides

Fine powder of single and binary mixed oxides can be produced by decomposition of the respective metal nitrates and polyvinyl alcohol (PVA) or, a mixture of PVA and polyacrylic acids. These mixtures, after spray drying, yield a brown fluffy mass, which is spontaneously combustible and the heat liberated is sufficient for the crystallization of the desired oxide phase. The rate of combustion controls the growth of the particles. This can be manifested by combustion of the mixture in controlled atmosphere. The nanoparticles of the oxide system studied are: spinels [MFe₂O₄ where M = Ni(II), Co(II), Zn(II), Mg(II)]; orthoferrites [MFeO₃ where M = Gd(III), Sm(III)]; LaAlO₃, NdGaO₃, CaO/MgO/Y₂O₃ stabilized zirconia (ZrO₂); lead zirconate titanate (PZT), lanthanum modified lead zirconate titanate (PLZT) and BaTiO₃.     

Bacterial cellulose as source for activated nanosized carbon for electric double layer capacitors

A nanosized carbonaceous material was derived from bacterial cellulose (BC). BC, which is produced by bacteria as nanosized material, possesses high degree of crystallinity of 90 %, was pyrolysed at 950 °C and physically activated with CO₂ to produce a nanosized activated carbon material. The pyrolysis of BC yielded a carbonaceous material (carbon yield of between 2 and 20 %) with a relatively low D- to G-band ratio (between 2.2 and 2.8), indicating that the carbonaceous material possesses a graphitic structure. Two different BC materials were pyrolysed—a loose fibrous (freeze-dried) and dense paper form. It was observed that a carbon nanofibre-like material was produced by the pyrolysis of the loose fibrous form of BC. The electric double layer (EDL) capacitance and the area-normalised specific capacitance in K₂SO₄ solution were as high as 42 F g^?1 and 1,617 F cm^?2, respectively. The EDL capacitance was also compared to commercially available activated carbon (YP-50F).     

Measuring the capacitance of capacitors with large losses

Conclusions The application range of the beating method and similar methods for measuring capacitances with large losses are limited by errors which are inherent in these methods and are due to the loss resistances affecting the measurement results (12).The effect of losses on the capacitance measurements is completely eliminated in measuring circuits with modulated parameters. The utilization of circuits with an external modulation serves to raise the sensitivity of capacitance measurements. The automation of these circuits makes them very promising for designing commercial instruments.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 58–61, August, 1968.     

Reactions of manganese oxides with sulfuric acid solutions studied by kinetic and electrochemical methods

Reactions of manganese oxides of various compositions with sulfuric acid solutions have been studied by kinetic and electrochemical methods. The surface composition of the manganese oxides has been shown to vary during the dissolution process. We present mathematical dependences of the dissolution rate on kinetic parameters of the electrolyte solution for the oxides of various compositions and interpret the behavior of the manganese oxide with various compositions during dissolution in sulfuric acid solutions of various concentrations.     

A simple route to electrophoretic deposition of transition metal-coated nickel oxide films for electrochemical capacitors

Nickel hydroxide films coated with transition metals such as nickel and cobalt were fabricated directly by a one-step electrophoretic deposition (EPD) in the presence of charging additives (transition metal salts). A nickel hydroxide particle with a weakly charged surface in an isopropanol solution was found to be detrimental to EPD and dispersion. When a small amount of charging additive was added to the suspension, the adsorption of dissolved metal ions on the nickel hydroxide resulted in a more positively charged particle surface, facilitating EPD and dispersion. When nickel hydroxide particles migrated to the negative electrode during the EPD process, the metal ions adsorbed on the particle were reduced electrochemically to form a metal layer. The as-deposited nickel hydroxide film converted to nickel oxide following heat treatment at 300 °C. Our results revealed that nickel oxide films coated with nickel and cobalt showed better capacitive behavior than the bare film. The improved capacitive behavior was attributed to the co-deposition of transition metals, which provided additional active sites on the nickel oxide surface for the electrochemical reaction to occur.     

Simultaneous synthesis of high crystalline manganese oxides with layered and tunnel structures

High crystalline manganese oxides with birnessite-type (H-BirMO) and large 2 × 4 tunnel-type (Na-2 × 4) were synthesized simultaneously using a low crystalline Na-form birnessite (NaBir) as a precursor in a 2 M NaOH solution at low temperature (150 °C) and autogenous pressure. The weight ratio of the obtained Na-2 × 4 to H-BirMO was about 50. Elemental analyses indicated that Na-2 × 4 had a formula in one unit cell of Na₈Mn₂₇O₅₃·9H₂O, and the manganese average oxidation state was 3.63. H-BirMO had a formula of Na_0.31Mn_2.04O₄·0.66H₂O and the manganese average oxidation state of 3.77. H-BirMO contained a set of basal reflections with d values that correspond to a minimum periodicity along c equal to 7.06 Å. H-BirMO belonged to a monoclinic system, and the lattice parameters were a = 5.18 Å, b = 2.85 Å, c = 7.35 Å, and β = 103.3°, respectively. Na-2 × 4 showed that the first peak appeared at a d spacing of 12.07 Å in the [0 0 2] direction, and the second peak had a similar d spacing of 7.16 Å in the [2 0 0] direction with Na-birnessite in the [1 0 0] direction. FE-SEM image of H-BirMO showed a very large plate-like morphology, while SEM photograph of Na-2 × 4 consisted of nanofibers with a thickness of about 80 nm and lengths ranging between 6 and 10 μm.     

Microwave-assisted route for synthesis of nanosized metal oxides

Microwave-assisted route for the synthesis of nanomaterials has gained importance in the field of synthetic technology because of its faster, cleaner and cost effectiveness than the other conventional and wet chemical methods for the preparation of metal oxide nanoparticles. In the present work, synthesis of metal oxide nanoparticles viz., γ-Fe₂O₃, NiO, ZnO, CuO and Co-γ-Fe₂O₃ were carried out by microwave-assisted route through the thermal decomposition of their respective metal oxalate precursors employing polyvinyl alcohol as a fuel. The metal oxide nanoparticles are then characterized for their size and γ to α (in γ-Fe₂O₃) transition and structure by employing powder X-ray diffraction (XRD) pattern, high-temperature X-ray diffraction (HTXRD) pattern and Fourier transform infrared (FT-IR) spectral studies. The morphology of the samples ranged from nanorods to irregular-shaped particles for different metal oxide samples on the basis of scanning electron microscopy and transmission electron microscopy images. Frequency-dependent dielectric study of the ferrite samples (γ-Fe₂O₃ and Co-Fe₂O₃) showed a similar behaviour, where the dielectric constant decreased rapidly with increase in frequency. Possible explanation for this behaviour is given.     

Microwave-assisted route for synthesis of nanosized metal oxides

Microwave-assisted route for the synthesis of nanomaterials has gained importance in the field of synthetic technology because of its faster, cleaner and cost effectiveness than the other conventional and wet chemical methods for the preparation of metal oxide nanoparticles. In the present work, synthesis of metal oxide nanoparticles viz., γ-Fe₂O₃, NiO, ZnO, CuO and Co-γ-Fe₂O₃ were carried out by microwave-assisted route through the thermal decomposition of their respective metal oxalate precursors employing polyvinyl alcohol as a fuel. The metal oxide nanoparticles are then characterized for their size and γ to α (in γ-Fe₂O₃) transition and structure by employing powder X-ray diffraction (XRD) pattern, high-temperature X-ray diffraction (HTXRD) pattern and Fourier transform infrared (FT-IR) spectral studies. The morphology of the samples ranged from nanorods to irregular-shaped particles for different metal oxide samples on the basis of scanning electron microscopy and transmission electron microscopy images. Frequency-dependent dielectric study of the ferrite samples (γ-Fe₂O₃ and Co-Fe₂O₃) showed a similar behaviour, where the dielectric constant decreased rapidly with increase in frequency. Possible explanation for this behaviour is given.     

Graphene sheets anchored with ZnO nanocrystals as electrode materials for electrochemical capacitors

An efficient approach consisted of modified Hummers' method, pulse microwave heating, and homogenizing dispersion has been demonstrated to prepare ZnO/graphene hybrid as electrode material for electrochemical capacitors (ECs). Highly-crystalline ZnO nanoparticles are anchored with graphene sheets, forming three-dimensional framework. The electrochemical properties of ZnO/graphene hybrids are characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge cycling. The EC equipped with ZnO/graphite hybrid (1:5 in w/w) exhibit the improved performance in terms of specific capacitance, high rate capability, and excellent cycling stability, as compared with blank graphene electrode. The maximum energy and power densities of ZnO/graphite capacitor can be obtained as high as 66 Wh kg⁻¹ and 15.2 kW kg⁻¹, respectively. The improved performance can be ascribed to the insertion of ZnO nanocrystals between individual graphite sheets, creating a conducting framework that provides more active sites for the formation of electric double layer. The unique framework allows the electrolyte ions to diffuse easily into the interior channels, leading to small inner resistance.     

Nanoparticulate magnetite thin films as electrode materials for the fabrication of electrochemical capacitors

Magnetite nanoparticles in stable colloidal suspension were prepared by the co-precipitation method. Nanoparticulate magnetite thin films on supporting stainless steel plates were prepared by drop-coating followed by heat treatment under controlled conditions. The effects of calcination temperature and atmosphere on the microstructure and electrochemical properties of nanoparticulate magnetite thin films were investigated. Nanoparticulate magnetite thin films prepared under optimized conditions exhibited a specific capacitance value of 82 F/g in mild aqueous 1.0 M Na₂SO₄ solution. Due to their high charge capacity, good cycling reversibility, and stability in a mild aqueous electrolyte, nanoparticulate magnetite thin films appear to be promising electrode materials for the fabrication of electrochemical capacitors.     

Hydrothermal stability of some manganese oxides

Hydrothermal phase reaction studies in the systemsβ-MnO₂-H₂O,γ-Mn₂O₃H₂O andγ-MnO₂-H₂O have been carried out. Based on the experimental data and the reported phase diagrams in Mn₂O₃-H₂O and MnO-H₂O systems, hydrothermal stability temperature of some of the manganese oxide minerals has been defined.     

Enhanced electrochemical capacitance of polyaniline/graphene hybrid nanosheets with graphene as templates

Polyaniline/graphene nanocomposites (PANi/GR) were prepared via PANi covalent grafting from the surface of GR. The unique structure of hybrid nanosheets was formed with uniform PANi layer coating GR without phase separation appearing when the weight ratio of aniline-to-graphene was 1:1. The unique PANi/GR hybrid nanosheets as electrode material for supercapacitors have a specific capacitance as high as 922 F/g at 10 mV/s and still retain a specific capacitance of 106 F/g at a high scan rate of 1 V/s due to synergistic effect between PANi and GR. The capacitance retention was ∼90% after 1000 cycles, which is much better than that of pure PANi or other PANi nanocomposites. The enhanced capacitive performance of PANi/GR hybrid nanosheets makes them have potential application in developing high performance energy storage devices.