Cycle stability of birnessite manganese dioxide for electrochemical capacitors

A combination of step potential electrochemical spectroscopy (SPECS) and electrochemical impedance spectroscopy (EIS) has been used to examine the electrochemical cycling behaviour of a well-characterized birnessite-phase manganese dioxide sample for use in electrochemical capacitors. The resistance and interfacial properties of the macroscopic electrode were found to be irreversible with cycling. However, the corresponding properties for the individual particles were more reversible, although they did show substantial hysteresis in their behaviour during cycling. This behaviour was discussed in terms of the structural, conductivity and morphological characteristics of the birnessite at different depths of discharge.     

A novel method to prepare nanostructured manganese dioxide and its electrochemical properties as a supercapacitor electrode

Nanostructured MnO₂ was synthesized by co-precipitation in the presence of Pluronic P123 surfactant and characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscope (SEM) and transmission electron microscope (TEM). The sample without surfactant was spherical with particle size on the submicron scale, whereas P123-assisted samples were all loose clew shapes, consisting of MnO₂ nanowires, 8-20 nm in diameter and 200-400 nm in length. The electrochemical performances of the as-prepared MnO₂ as the electrode materials for supercapacitors were evaluated by cyclic voltammetry and galvanostatic charge-discharge measurements in a solution of 1 M Na₂SO₄. The sample without surfactant exhibited a relatively low specific capacitance of 77 F g⁻¹, whereas the nanostructured MnO₂ prepared with 0.02% (wt%) P123 exhibited excellent pseudocapacitive behavior, with a maximum specific capacitance of 176 F g⁻¹.     

Facile synthesis and strongly microstructure-dependent electrochemical properties of graphene/manganese dioxide composites for supercapacitors

Graphene has attracted much attention since it was firstly stripped from graphite by two physicists in 2004, and the supercapacitor based on graphene has obtained wide attention and much investment as well. For practical applications of graphene-based supercapacitors, however, there are still many challenges to solve, for instance, to simplify the technological process, to lower the fabrication cost, and to improve the electrochemical performance. In this work, graphene/MnO₂ composites are prepared by a microwave sintering method, and we report here a relatively simple method for the supercapacitor packaging, i.e., dipping Ni-foam into a graphene/MnO₂ composite solution directly for a period of time to coat the active material on a current collector. It is found that the microwave reaction time has a significant effect on the microstructure of graphene/MnO₂ composites, and consequently, the electrochemical properties of the supercapacitors based on graphene/MnO₂ composites are strongly microstructure dependent. An appropriately longer microwave reaction time, namely, 15 min, facilitates a very dense and homogeneous microstructure of the graphene/MnO₂ composites, and thus, excellent electrochemical performance is achieved in the supercapacitor device, including a high specific capacitance of 296 F/g and a high capacitance retention of 93% after 3,000 times of charging/discharging cycles.

PACS

81.05.ue; 78.67.Sc; 88.80.fh     

An electrochemical quartz crystal microbalance study into the deposition of manganese dioxide

An electrochemical quartz crystal microbalance (EQCM) has been used to study the effects of electrolyte composition (MnSO₄ and H₂SO₄ concentrations) and anodic current density on the electrodeposition of manganese dioxide. The EQCM, in tandem with the electrode voltage during deposition, has been used to characterize features of the deposition mechanism such as the relative lifetime of the Mn(III) intermediate, the rate of soluble Mn(III) hydrolysis to form MnOOH, and the porosity of the resultant manganese dioxide deposit as a function of crystal nucleation. The connection between the results obtained here and commercial electrodeposition of manganese dioxide were also discussed.     

Long-term electrochemical behaviors of manganese oxide aqueous electrochemical capacitor under reducing potentials

Long-term electrochemical behaviors of hydrated MnO₂ electrochemical capacitor (EC) electrode in alkali chloride (KCl_(aq)) electrolyte have been studied by using potential cycling for thousands of cycles within different potential windows spanning from 0.8 V (versus Ag/AgCl_(aq)) to varied lower-end potentials below the open-circuit potential. Three potential ranges resulting in different cycling behaviors of the oxide EC have been identified. Range I: cycling above 0.2 V results in no change in either microstructure or surface chemistry of the oxide electrode, and no capacitance reduction has been observed. Range II: cycling down to 0.0 V leads to extensive morphological reconstruction and limited reduction of surface Mn ions, while the electrode capacitance remains stable. Range III: cycling with lower-potential end below 0.0 V results in obvious capacitance reduction, along with different morphological reconstruction and Mn reduction from those in Range II. For each selected lower-end potential in Range III, the capacitance descends to a plateau within first thousand cycles, and the extent of the capacitance reduction increases as the lower-end potential decreases.     

层状二氧化锰材料的制备及其电化学性能研究

以高锰酸钾和5-氨基四唑为原料,采用常压加热法,制备了层状二氧化锰材料。应用X-射线衍射和扫描电镜技术对所得材料的结构和形貌进行表征。结果表明,所得材料具有层状结构,为颗粒状;恒流充放电测试显示,制备材料具有较好的电化学性能,在50 mA/g的电流密度下,首次充电比容量为761 mAh/g,循环50圈后,容量保持率为50%。此外,制备材料具有良好的倍率性能。     

Coating manganese oxide onto graphite electrodes by immersion for electrochemical capacitors

In this study, manganese oxide was coated on a graphite electrode by immersion. Durations for immersion were varied to control the amount of manganese oxide coated onto the electrode surface. Maximum capacitance of 556 mF cm⁻² was obtained in 0.5 M LiCl and with better/superior conditions (immersion time = 80 min and potential scan rate = 10 mV s⁻¹). In addition, cyclic voltammograms of the prepared electrode at different potential scan rates exhibited the approximately rectangular and symmetric current-potential characteristics of a capacitor. Furthermore, the chronopotentiometry (CP) charge-discharge curves of the electrode prepared at 80 min of immersion time with a constant current of 1 mA were symmetric and similar isosceles triangles, which demonstrate its high electrochemical reversibility and good stability. Finally, under scanning electron microscope (SEM), the surface of the electrode prepared at 80 min of immersion time and after 1500 cycles of potential cycling revealed that numerously three-dimensional network of macropores appeared on large spherical grains.     

Capacitive behavior of nanostructured MnO2 prepared by sonochemistry method

Nanostructured manganese dioxide has been successfully prepared by a sonochemical method from an aqueous solution of potassium bromate and manganese sulfate. Changing the proportions of reagents leads either to γ- or layered structures of MnO₂. The capacitive characteristics of the samples were systematically investigated in aqueous electrolytes through means of cyclic voltammetry and chronopotentiometry methods. The electrochemical properties of MnO₂ were strongly affected by the pH of electrolyte employed and this material exhibited ideally capacitive behavior in 0.5 M aqueous Na₂SO₄ solution. A maximum specific capacitance of 344 F g⁻¹ was obtained for the layered structure determined via cyclic voltammetry at a scan rate of 5 mV s⁻¹ in 0.5 M aqueous Na₂SO₄ solution at pH 3.3. Excellent electrochemical reversibility of the materials was also demonstrated.Layered structure MnO₂ showed higher energy density at high power density than the γ-structure material.Impedance spectroscopy studies revealed that charge transfer resistance of the γ-structure oxide has higher value than that of the layered structure.     

Improved electrochemical impedance response induced by morphological and structural evolution in nanocrystalline MnO2 electrodes

The electrochemical cycling behavior of nanocrystalline MnO₂ coatings with a defective antifluorite structure, prepared by anodic electrodeposition, was investigated in terms of morphological and structural evolution. MnO₂ electrodes cycled at 100 mV s⁻¹ exhibited improved electrochemical frequency response, compared with as-prepared electrodes. The improved frequency response is attributed to morphological and structural evolution from equiaxed oxide nanocrystals to petal-shaped, single-crystal nanosheets, which follows a dissolution-redeposition mechanism.     

An RDE and RRDE study into the electrodeposition of manganese dioxide

Electrodeposition of manganese dioxide has been examined using a combination of rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) voltammetry, with the goal of developing an understanding of the electrodeposition mechanism. Experimental variables that have been examined include electrolyte composition (combined changes within the ranges 0.1-1.0 M MnSO₄ and 0.1-5.0 M H₂SO₄), rotation rate (1000-4000 rpm) and temperature (22-98 °C). Voltammetric data (current peak instead of sigmoidal response, and non-proportional current-concentration data) indicates that already deposited manganese dioxide is a poorer catalytic surface compared to Pt. The overall electrodeposition process revolves on the formation of a Mn(III) intermediate, and whether it is soluble for extended periods of time, as in concentrated H₂SO₄ (>1.0 M), or whether it hydrolyzes rapidly to precipitate as a solid Mn(III) species (e.g. MnOOH) as in more dilute H₂SO₄ solutions (<1.0 M). In the more concentrated acid electrolytes most of the Mn(III) was lost to the bulk electrolyte through convection, with what little manganese dioxide that was formed resulting from chemical disproportionation. However, in dilute acid electrolytes, evidence suggests that the solid hydrolysis product underwent solid state oxidation to manganese dioxide. Activation energies extracted from temperature studies supports the different mechanism under different acid concentrations. Experiments examining the effect of rotation rate also indicate that the overall electrodeposition process is not mass transport limited.     

Degradation of tricyclazole by colloidal manganese dioxide in the absence and presence of surfactants

The kinetics of the degradation of tricyclazole by water soluble colloidal MnO₂ in acidic medium (HClO₄) has been studied spectrophotometrically in the absence and presence of surfactants. The experiments have been performed under the pseudo-first-order reaction conditions with respect to MnO₂. To determine the rate constant as functions of [tricyclazole], [MnO₂] and [HClO₄], the pseudo-first-order reaction conditions have been maintained throughout the entire kinetic runs. The degradation has been observed to be first-order with respect to MnO₂ while fractional-order in both tricyclazole and HClO₄. The anionic surfactant, sodium dodecyl sulfate (SDS) has been observed to be ineffective whereas nonionic surfactant, Triton X-100 (TX-100) accelerates the reaction rate. However, the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) causes flocculation with oppositely charged colloidal MnO₂ and therefore could not be studied further. The catalytic effect of TX-100 has been discussed in the light of the mathematical model proposed by Tuncay et al. [25]. The kinetic data have been exploited to generate the various activation parameters for the oxidative degradation of tricyclazole by colloidal MnO₂.     

Synthesis of uniform polycrystalline tin dioxide nanofibers and electrochemical application in lithium-ion batteries

Under optimized synthesis conditions, very large area uniform SnO₂ nanofibers consisting of orderly bonded nanoparticles have been obtained for the first time by thermal pyrolysis and oxidization of electrospun tin(II)2-ethylhexanoate/polyacrylonitrile (PAN) polymer nanofibers in air. The structure and morphology were elaborated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The SnO₂ nanofibers delivered a reversible capacity of 446 mAh g⁻¹ after 50 cycles at the 100 mA g⁻¹ rate and excellent rate capability of 477.7 mAh g⁻¹ at 10.0 C. Owing to the improved electrochemical performance, this electrospun SnO₂ nanofiber could be one of the most promising candidate anode materials for the lithium-ion battery.     

化学二氧化锰制备中粗二氧化锰的氧化研究

在化学二氧化锰的制备过程中,对粗二氧化锰的精制氧化是提高产品的振实密度和锰收率的关键。以氯酸钠为氧化剂,对粗二氧化锰进行精制氧化,考察了各工艺因素对产品振实密度及锰收率的影响,得到了最佳工艺条件:硫酸质量浓度为150 g/L、氯酸钠加料量为理论量的120%、氧化反应时间为3 h、反应体系液固体积比为3∶1。在此优化工艺条件下,溶液中Mn2+几乎全部被氧化成二氧化锰,锰收率达99.8%以上,产品振实密度大于2.0 g/cm3。     

Manganese dioxide nanosheets decorated on MXene (Ti3C2Tx) with enhanced performance for asymmetric supercapacitors

The incorporation of nanosized pseudocapacitive materials and structure design are general strategies to enhance the electrochemical performance of MXene-based materials. Herein, the decoration of manganese dioxide (MnO₂) nanosheets on MXene (Ti₃C₂T_x) surfaces was prepared by a facile liquid phase coprecipitation method. Ti₃C₂T_x is initially modified by polydopamine (PDA) coating to ensure the homogeneous distribution of MnO₂ nanosheets and tight and close connections between MnO₂ and the Ti₃C₂T_x backbone. Due to the obtained three-dimensional (3D) nanostructure, facilitating electron transport within the electrode and promoting electrolyte ion accessibility, the δ-MnO₂@Ti₃C₂T_x-0.06 electrode yields superior electrochemical performances, such as a rather large areal capacity of 1233.1 mF cm^?2 and high specific capacitance of 337.6 F g^?1 at 2 mV s^?1, as well as high cyclic stability for 10000 cycles. Furthermore, δ-MnO₂@Ti₃C₂T_x-0.06 composites are employed as positive electrodes, and activated carbon (AC) materials act as negative electrodes with an aqueous electrolyte of 1 M Na₂SO₄ to assemble asymmetric supercapacitors. The prototype device is reversible at cell voltages from 0 to 1.8 V, and manifests a maximum energy density of 31.4 Wh kg^?1 and a maximum power density of 2700 W kg^?1. These encouraging results show enormous possibilities for energy storage applications.     

Effects of electrochemical-deposition method and microstructure on the capacitive characteristics of nano-sized manganese oxide

The amorphous nano-structured manganese oxide was electrochemically deposited onto a stainless-steel electrode. The structure and surface morphology of the obtained manganese oxide were studied by means of X-ray diffraction analysis and scanning electron microscopy. The capacitive characteristics of the manganese oxide electrodes were investigated by means of cyclic voltammetry and constant current charge-discharge cycling. The morphological and capacitive characteristics of the hydrous manganese oxide was found to be strongly influenced by the electrochemical deposition conditions. The highest specific capacitance value of ca. 410 F g⁻¹ and the specific power of ca. 54 kW kg⁻¹ were obtained at 400 mV s⁻¹ sweep rate of potentiodynamic deposition condition. The cyclic-life data showed that the specific capacitance was highly stable up to 10,000 cycles examined. This suggests the excellent cyclic stability of the obtained amorphous hydrous manganese oxide for supercapacitor application.     

不同基体上电化学法制备二氧化锰电极的研究进展

简要介绍了电化学法制备二氧化锰电极的发展历程.综述了以Pb-Ag、Ti及Ti合金、Ni等金属基体和石墨、直立碳纳米管、导电玻璃复合膜等非金属为基体,用电化学法制备二氧化锰电极的研究现状.指出了电化学法制备二氧化锰电极的研究方向.     

Liquid-phase synthesized mesoporous electrochemical supercapacitors of nickel hydroxide

Electrochemical supercapacitive (ES) properties of liquid-phase synthesized mesoporous (pore size distribution centered ∼12 nm) and of 120 m²/g surface area nickel hydroxide film electrodes onto tin-doped indium oxide substrate are discussed. The amounts of inner and outer charges are calculated to investigate the contribution of mesoporous structure on charge storage where relatively higher contribution of inner charge infers good ion diffusion into matrix of nickel hydroxide. Effect of different electrolytes, electrolyte concentrations, deposit mass and scan rates on the current-voltage profile in terms of the shape and enclosed area is investigated. Specific capacitance of ∼85 F/g at a constant current density of 0.03 A/g is obtained from the discharge curve.     

Morphology evolution in anodically electrodeposited manganese oxide nanostructures for electrochemical supercapacitor applications—Effect of supersaturation ratio

An in-depth study of morphology-controlled growth of manganese oxide nanostructures from acetate-containing aqueous solutions was carried out. By varying the deposition parameters, including solution composition, pH value, deposition temperature and current density, a series of manganese oxide nanostructures, including continuous coatings with equiaxed and fibrous features, petal- and flower-like morphologies, discrete oxide clusters, columnar structures and interconnected nanosheets, were anodically deposited on Au-coated glass. Detailed results on the morphology, chemistry and crystal structure of the as-deposited manganese oxide nanostructures suggest that the rich morphology of manganese oxide obtained is primarily determined by the influence of supersaturation ratio on reaction kinetics in the aqueous solutions. The electrochemical properties (specific capacitance, rate capacity and electrochemical impedance response) of manganese oxide nanostructures are carefully examined. The experimental results show that manganese oxide electrodes with oriented nanostructures, such as a columnar structure and an interconnected nanosheet architecture, exhibit enhanced electrochemcial performance by improving manganese oxide utilization.     

Charge storage mechanism of nanostructured anhydrous and hydrous ruthenium-based oxides

The charge storage mechanism of nanostructured anhydrous and hydrous ruthenium-based oxides was evaluated by various electrochemical techniques (cyclic voltammety, hydrodynamic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy). The effects of various factors, such as particle size, hydrous state, and structure, on the pseudocapacitive property were characterized. The electric double layer capacitance (C_dl), adsorption related charge (C_ad), and the irreversible redox related charge (C_irr) per unit mass and surface area of electrode material has been estimated and the role of structural water within the material either in micropores or interlayer are discussed.     

Nanocomposites of manganese oxides and carbon nanotubes for aqueous supercapacitor stacks

Symmetrical supercapacitors and their serially connected two-cell stacks via a bipolar electrode were constructed with nanocomposites of manganese oxides and carbon nanotubes (MnO_x/CNTs) as the electrode materials. Nanocomposites with different contents of MnO_x were synthesised through the redox reaction between KMnO₄ and CNTs in aqueous solutions. The nanocomposites were characterised by scanning and transmission electron microscopy, BET nitrogen adsorption and X-ray diffraction before being examined in a three-electrode cell with a novel trenched graphite disc electrode by electrochemical means, including cyclic voltammetry, galvanostatic charging-discharging, and electrochemical impedance spectroscopy. The nanocomposites demonstrated capacitive behaviour in the potential range of 0-0.85 V (vs Ag/AgCl) in aqueous KCl electrolytes with less than 9% capacitance decrease after 9000 charging-discharging cycles. Symmetrical supercapacitors of identical positive and negative MnO_x/CNTs electrodes showed capacitive performance in good agreement with the individual electrodes (e.g. 0.90 V, 0.53 F, 1.3 cm²). The bipolarly connected two-cell stacks of the symmetrical cells exhibited characteristics in accordance with expectation, including a doubled stack voltage and reduced internal resistance per cell.