Electrodeposition and Capacitive Behavior of Films for Electrodes of Electrochemical Supercapacitors

Polypyrrole films were deposited by anodic electropolymerization on stainless steel substrates from aqueous pyrrole solutions containing sodium salicylate and tiron additives. The deposition yield was studied under galvanostatic conditions. The amount of the deposited material was varied by the variation of deposition time at a constant current density. SEM studies showed the formation of porous films with thicknesses in the range of 0–3 μm. Cyclic voltammetry data for the films tested in 0.5 M Na₂SO₄ solutions showed capacitive behavior and high specific capacitance (SC) in a voltage window of 0.9 V. The films prepared from pyrrole solutions containing tiron showed better capacitive behavior compared to the films prepared from the solutions containing sodium salicylate. A highest SC of 254 F g⁻¹ was observed for the sample with a specific mass of 89 μg cm⁻² at a scan rate of 2 mV s⁻¹. The SC decreased with an increasing film thickness and scan rate. The results indicated that the polypyrrole films deposited on the stainless steel substrates by anodic electropolymerization can be used as electrodes for electrochemical supercapacitors (ES).     

Phase transfer of oxide particles for application in thin films and supercapacitors

This paper reports efficient liquid-liquid extraction strategies for concentrated suspensions of oxide particles and demonstrates the benefits of using such strategies for thin film applications and the fabrication of supercapacitor electrodes. We performed materials synthesis in an aqueous phase and achieved efficient materials transfer to an organic phase, avoiding agglomeration during the drying stage. The metal oxides, suspended in an organic solvent were used directly for the deposition of polymer-titania composite films and fabrication of Mn₃O₄-carbon nanotube composite electrodes for supercapacitors. Strategy E1 involved the modification of particles in-situ during synthesis and a Schiff base reaction with an extractor at the liquid-liquid interface. In the one-step E2 procedure the interface reactions were used for the extraction. We discuss advantages of the E1 and E2 strategies. Both strategies featured a biomimetic approach for the surface modification of the particles, which allowed for strong adsorption of the extractors. The ability to perform efficient extraction using concentrated suspensions allowed for the fabrication of Mn₃O₄–carbon nanotube electrodes with high active mass loading. The electrodes showed a capacitance of 2.63 F cm⁻², good capacitance retention at high charge-discharge rates and low impedance. The results of this investigation pave the way for the agglomerate free processing of various functional materials for applications in advanced films, coatings and devices     

Fe3O4 spinel-Mn3O4 spinel supercapacitor prepared using Celestine blue as a dispersant,capping agent and charge transfer mediator

An asymmetric spinel-spinel supercapacitor is fabricated with negative and positive electrodes respectively consisting of Fe₃O₄ and Mn₃O₄ nanoparticles, where carbon nanotubes (CNT) serve as conductive additives. High performance of the individual electrodes and devices is achieved at a high active mass (AM) loading of 40 mg cm⁻² of the individual electrodes. We implement a conceptually new strategy using multifunctional Celestine blue (CB) dye, which is strongly adsorbed on the spinel phases and CNT, facilitates dispersion, acts as a capping agent and allows for the fabrication of spinel decorated CNT. CB is an efficient charge transfer mediator, which allows for significant improvement of capacitive behavior. The use of CB as a charge transfer mediator allows for good utilization of capacitive properties of spinels at high AM. Mechanisms of spinel-CB-CNT interactions and charge transfer mediation are discussed. The capacitive properties of electrodes with different spinel/CNT mass ratios are tested by cyclic voltammetry, chronopotentiometry and impedance spectroscopy. The areal capacitances of 6.17 and 5.15 F cm⁻² are obtained for Fe₃O₄ and Mn₃O₄ based electrodes, respectively in 0.5 M Na₂SO₄ electrolyte. The high capacitances are achieved for the electrodes that have low resistance. Using these electrodes, an asymmetric device is fabricated that has a capacitance of 2.41 F cm⁻² in a voltage window of 1.6 V.     

Polyaniline/multi-walled carbon nanotube composites with core-shell structures as supercapacitor electrode materials

Composites with core-shell structures consisting of polyaniline and carbon nanotubes were prepared via in situ polymerization of aniline monomers by using multi-walled carbon nanotubes with minimized defects as templates. The strong interaction in such conjugated systems greatly improves the charge-transfer reaction between polyaniline and the carbon nanotube. Influences of the thickness of the polyaniline layer on the surface of the carbon nanotubes on the electrochemical properties of the resulting composites are discussed. The highest specific capacitance of 560 F/g was achieved by using a composite with 66 wt% polyaniline content as the supercapacitor electrode. Additionally, enhancement of the capacity retention was observed, with the composite losing only 29.1% of the maximum capacity after 700 cycles, and then remaining stable.     

ZnCo2O4/CNT composite for efficient supercapacitor electrodes

Due to their combination of enhanced electrical conductivity and high-performance electron and ion transport channels, binary metal oxides with well-morphological optimized electrode materials have been attracted the greatest research attention for high-performance supercapacitor applications. An easy co-precipitation method is used to synthesize ZnCo₂O₄ nanoparticles using NaOH and Urea as precipitation agents. To facilitate electrical conductivity, suitable carbon material such as carbon nanotube (CNT) has been added to make a composite material. The three-electrode system was preferred for estimating specific capacitance of prepared material and optimally efficient ZnCo₂O₄/CNT electrode delivered a moderate 888 F/g capacitance at 1 A/g in 3 M KOH and after 5000 charge discharge cycles 94.72% of cycling stability retained at 5 A/g. This paper presents a little price and simple procedure for preparation of ZnCo₂O₄/CNT electrode that promotes creative sprit for energy storage applications.     

Bi-metallic catalysts of mesoporous Al2O3 supported on Fe,Ni and Mn for methane decomposition: Effect of activation temperature

Methane decomposition reaction has been studied at three different activation temperatures (500 °C, 800 °C and 950 °C) over mesoporous alumina supported Ni–Fe and Mn–Fe based bimetallic catalysts. On co-impregnation of Ni on Fe/Al₂O₃ the activity of the catalyst was retained even at the high activation temperature at 950 °C and up to 180 min. The Ni promotion enhanced the reducibility of Fe/Al₂O₃ oxides showing higher catalytic activity with a hydrogen yield of 69%. The reactivity of bimetallic Mn and Fe over Al₂O₃ catalyst decreased at 800 °C and 950 °C activation temperatures. Regeneration studies revealed that the catalyst could be effectively recycled up to 9 times. The addition of O₂ (1 ml, 2 ml, 4 ml) in the feed enhanced substantially CH₄ conversion, the yield of hydrogen and the stability of the catalyst.     

PAN/SAN/SWNT ternary composite: Pore size control and electrochemical supercapacitor behavior

Single wall carbon nanotubes (SWNT) act as a compatabilizer for polyacrylonitrile (PAN)/styrene-acrylonitrile (SAN) copolymer blends. Carbonization of PAN/SAN/SWNT blend films results in pore widths in the range of 1-200 nm, while carbonized PAN/SAN blend films resulted in pores with typical width of 1-10 μm. Electrochemical supercapacitor behavior of the carbonized PAN/SAN/SWNT films was characterized using 6 M KOH electrolyte. Surface area and pore size distribution were analyzed using nitrogen gas adsorption and the BET and DFT theories. Double layer capacity of the carbonized PAN/SAN/SWNT films was as high as 205 μF/cm² based on the BET surface area.     

Block Copolymer Composite Synthesis in a Mechanistic Approach

Carbon nanotubes-block copolymer composites were synthesized via reversible addition–fragmentation chain transfer living emulsion mechanism, based on zero–one and pseudo-bulk kinetics. In conjunction with multiwalled carbon nanotubes, ab initio reversible addition–fragmentation chain transfer homopolymerization of styrene and butyl acrylate, respectively, was carried out using xanthate-based reversible addition–fragmentation chain transfer agent through ultrasonified macroemulsion and miniemulsion. Then, the second and third monomer were applied at stage II and III, respectively, to produce multiwalled carbon nanotube diblock and triblock copolymer composites such as multiwalled carbon nanotube-b-poly(styrene)-co-polybutyl acrylate-co-polymethyl acrylate and multiwalled carbon nanotube-b-polybutyl acrylate-co-polymethyl acrylate-co-poly(styrene). As multiwalled carbon nanotube-homopolymer proceeds to diblock and triblock, thermal resistance of multiwalled carbon nanotube block composite products is enhanced. A mechanistic approach of reversible addition–fragmentation chain transfer living macroemulsion and miniemulsion polymerizations, with the purified multiwalled carbon nanotubes enables us to control the composite properties such as thermal degradation, mechanical strength, and glass transition temperature of multiwalled carbon nanotube-block copolymer composites, in conjunction with reaction conditions, monomer type, blocking sequence, particle size, and molecular weight.     

Carbon Nanotubes for Supercapacitor

As an electrical energy storage device, supercapacitor finds attractive applications in consumer electronic products and alternative power source due to its higher energy density, fast discharge/charge time, low level of heating, safety, long-term operation stability, and no disposable parts. This work reviews the recent development of supercapacitor based on carbon nanotubes (CNTs) and their composites. The purpose is to give a comprehensive understanding of the advantages and disadvantages of carbon nanotubes-related supercapacitor materials and to find ways for the improvement in the performance of supercapacitor. We first discussed the effects of physical and chemical properties of pure carbon nanotubes, including size, purity, defect, shape, functionalization, and annealing, on the supercapacitance. The composites, including CNTs/oxide and CNTs/polymer, were further discussed to enhance the supercapacitance and keep the stability of the supercapacitor by optimally engineering the composition, particle size, and coverage.     

Preparation of Three-Dimensional Co3O4/graphene Composite for High-Performance Supercapacitors

Here, we developed a simple and efficient route for the preparation of three-dimensional (3D) Co₃O₄-anchored graphene composites using the sacrificial template-assisted method and the subsequent deposition process of Co₃O₄ nanoparticles. As structural guiding materials, polystyrene (PS) spheres provide 3D porous architectures with a high surface area. 3D porous graphene materials serve as conductive supporters for the deposition of Co₃O₄ nanoparticles through precipitation growth. The 3D porous composite structures of Co₃O₄/graphene composites were intensively investigated using scanning electron microscope, transmission electron microscope, and X-ray diffraction. The 3D Co₃O₄/graphene composites show a high specific capacitance of 328?F?g^?1 with efficient and fast charge–discharge process in aqueous 6?M KOH electrolyte. In addition, the composites provide a good cycle lifetime, which retained 98% capacitance retention over 2000 cycles.     

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.     

Nickel and Lanthanum Hydroxide Nanocomposites with Much Improved Electrochemical Performance for Supercapacitors

By developing a facile low temperature hydrothermal process, we demonstrate the direct growth of nickel and lanthanum hydroxide nanocomposites on Ni‐foam substrate. The hydroxide nanocomposites thus derived show much enhanced overall electrochemical capacitance and improved stability of the alpha nickel hydroxide phase in alkaline solution. By adjusting the initial molar ratio between nickel and lanthanum nitrates from 1:0 to 1:2, the electrochemical behavior, such as specific capacitance, shows a dramatic change, while the nickel hydroxide phase evolves from beta nickel hydroxides (1:0) to alpha nickel hydroxide (1:2). Lanthanum hydroxide is not expected to contribute to the pseudocapacitance as it only shows a capacitance of <10 F/g. The specific capacitance is increased from 970 F/g (Ni:La = 1:0) to 1874 F/g (Ni: La = 1:2) at the discharging current of 1 A/g. At high discharging currents (e.g. 10 A/g), the Ni:La = 1:2 sample can retain a capacitance of 1055 F/g. An excellent cycling performance is demonstrated for the Ni:La = 1:2 nanocomposite sample upon 2000 cycles at the discharging current density of 2 A/g, where the stability of alpha nickel hydroxide in the alkaline solution is improved. The low temperature hydrothermal method compares favorably to other previously documented preparation processes, such as chemical coprecipitation and electrochemical deposition, for lanthanum‐doped nickel hydroxides, where the specific capacitance is typically less than 1000 F/g (1 A/g).     

Polyaniline/single-wall carbon nanotube (PANI/SWCNT) composites for high performance supercapacitors

PANI/SWCNT composites were prepared by electrochemical polymerisation of polyaniline onto SWCNTs and their capacitive performance was evaluated by means of cyclic voltammetry and charge-discharge cycling in 1 M H₂SO₄ electrolyte. The PANI/SWCNT composites single electrode showed much higher specific capacitance, specific energy and specific power than pure PANI and SWCNTs. The highest specific capacitance, specific power and specific energy values of 485 F/g, 228 W h/kg and 2250 W/kg were observed for 73 wt.% PANI deposited onto SWCNTs. PANI/SWCNT composites also showed long cyclic stability. Based upon the variations in the surface morphologies and specific capacitance of the composite, a mechanism is proposed to explain enhancement in the capacitive characteristics. The PANI/SWCNT composites have demonstrated the potential as excellent electrode materials for application in high performance supercapacitors.     

Electrochemical activity of a polyaniline/polyaniline-grafted multiwalled carbon nanotube mixture produced by a simple suspension polymerization

A polyaniline (PANi)/PANi-grafted multiwalled carbon nanotube (PANi/PANi-g-MWCNT) mixture was prepared by simple suspension (dynamic interfacial) polymerization. Scanning electron microscopy showed a two-phase mixture of PANi and PANi-g-MWCNTs while transmission electron microscopy of PANi-g-MWCNT showed a core–shell structure with outer PANi layer (5–10 nm). Depending on the doping level, estimated by relative carbon content, the electrical conductivity of PANi/PANi-g-MWCNT was improved by more than four orders of magnitude over that of PANi. The composite also displayed high electrochemical activity with improved stability in an oxygen-saturated acidic solution.     

碳负载型IrO2水合物复合电极材料的制备及电容性能研究

文章以KB600型活性炭和少量氯铱酸为原料,分别采用共沉积法和还原氧化法制备了碳载氧化铱电极材料,通过循环伏安测试和恒流充放电测试对比分析了材料的电化学性能。其中,还原氧化法制备的碳载IrO2电极材料的比电容量高达389.7 F·g-1,具有较好的应用前景。     

超电容器碳纳米管与钼复合电极材料的研究

以碳纳米管（CNTs）为基体材料，用浓硝酸回流处理碳纳米管，TEM（透射电子显微镜）研究表明碳纳米管的端帽被部分打开，通过液相反应对碳纳米管进行表面改性，制备CNTs／Mo复合电极材料，复合电极使电解液和导电材料的接触面积增大，使电极反应的有效表面积增大，反应场所有所增加，从而提高电极电化学反应的活性。基于此复合材料的超电容器具有高比电容、高稳定性、良好的可逆性和长寿命等特点。循环伏安结果表明：CNTs/Mo复合电极的比电容比纯CNTs电极要高出20％。     

Supercapacitive properties of composite electrodes consisting of polyaniline, carbon nanotube, and RuO2

Three types of composite supercapacitor electrodes were prepared; electroactive polyaniline (PANI), PANI/multi-walled carbon nanotube (CNT), and PANI/CNT/RuO₂. Specifically, the PANI and PANI/CNT were prepared by polymerization, and PANI/CNT/RuO₂ was prepared by electrochemical deposition of RuO₂ on the PANI/CNT matrix. Cyclic voltammetry between −0.2 and 0.8 V (vs. Ag/AgCl) at various scan rates was performed to investigate the supercapacitive properties in an electrolyte solution of 1.0 M H₂SO₄. The PANI/CNT/RuO₂ electrode showed the highest specific capacitance at all scan rates (e.g., 441 and 392 F g⁻¹ at 100 and 1,000 mV s⁻¹, respectively). In contrast, the PANI/CNT electrode demonstrated the best capacitance retention (66%) after 10⁴ cycles. Additional analysis including morphology and complex impedance spectroscopy suggested that with small loading of RuO₂, an increase in capacitance was observed, but dissolution and/or detachment of RuO₂ species from the electrode might occur during cycling to reduce the cycle performance.     

Electrochemical supercapacitor material based on manganese oxide: preparation and characterization

A novel class of electrochemical supercapacitor electrode material has been electrochemically synthesized from a manganese halide complex in water-containing acetonitrile electrolyte at room temperature. This material has been physically and chemically characterized by scanning electron microscopy, X-ray photoelectron microscopy (XPS), FT-Raman microscopy and cyclic voltammetry. XPS and FT-Raman characterization suggest that this material is composed of manganese oxide with a chemical composition of Mn₃O₄ and containing a moderate amount of carbon. Cyclic voltammetric characterization indicates that this material has higher electronic conductivity than usually seen for manganese oxide and that it shows fast kinetics for the charge-discharge process in both aqueous and acetonitrile electrolytes. The material provides a large pseudocapacitance over a potential window of about 1 V in aqueous electrolyte and about 2 V in acetonitrile electrolyte. It is therefore a good candidate as a material for an electrochemical supercapacitor electrode.     

A flexible graphene/multiwalled carbon nanotube film as a high performance electrode material for supercapacitors

A flexible graphene/multiwalled carbon nanotube (GN/MWCNT) film has been fabricated by flow-directed assembly from a complex dispersion of graphite oxide (GO) and pristine MWCNTs followed by the use of gas-based hydrazine to reduce the GO into GN sheets. The GN/MWCNT (16 wt.% MWCNTs) film characterized by Fourier transformation infrared spectra, X-ray diffraction and scanning electron microscope has a layered structure with MWCNTs uniformly sandwiched between the GN sheets. The MWCNTs in the obtained composite film not only efficiently increase the basal spacing but also bridge the defects for electron transfer between GN sheets, increasing electrolyte/electrode contact area and facilitating transportation of electrolyte ion and electron into the inner region of electrode. Electrochemical data demonstrate that the GN/MWCNT film possesses a specific capacitance of 265 F g⁻¹ at 0.1 A g⁻¹ and a good rate capability (49% capacity retention at 50 A g⁻¹), and displays an excellent specific capacitance retention of 97% after 2000 continuous charge/discharge cycles. The results of electrochemical measurements indicate that the freestanding GN/MWCNT film has a potential application in flexible energy storage devices.     

Design and synthesis of three-dimensional needle-like CoNi2S4/CNT/graphene nanocomposite with improved electrochemical properties

In this paper, we described a simple two–step method for preparing needle-like CoNi₂S₄/CNT/graphene nanocomposite with robust connection among its ternary components. The prepared CoNi₂S₄/CNT/graphene nanocomposite has been thoroughly characterized by spectroscopic (Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy), X-ray diffraction and thermogravimetric analysis. Microscopy techniques (scanning electron microscopy–energy dispersive spectroscopy and transmission electron microscopy) were employed to probe the morphological structures. The electrochemical properties of the as-prepared 3D architectures were investigated with three and two-electrode systems. In addition to its high specific capacitance (710 F g⁻¹ at 20 A g⁻¹), after charging–discharging for 2000 cycles, the electrode still maintained the capacity retention of about 82%. When used as the active electrode material for supercapacitors, the fabricated CoNi₂S₄–g–CNT nanostructure exhibited excellent specific capacitance and good rate capability, making it a promising candidate for next-generation supercapacitors.