Influence of silver-decorated multi-walled carbon nanotubes on electrochemical performance of polyaniline-based electrodes

In this work, silver (Ag) nanoparticles were deposited on multi-walled carbon nanotubes (MWNTs) by chemical reduction while Ag-decorated MWNTs (Ag-MWNTs)/polyaniline (PANI) composites were prepared by oxidation polymerization. The effect of the Ag incorporated into the interface of the composites on the electrochemical performance of the MWNTs/PANI was investigated. It was found that highly dispersed Ag nanoparticles were deposited onto the MWNTs, and the Ag-MWNTs were successfully coated by PANI. According to cyclic voltammograms, the Ag-MWNTs/PANI exhibited significantly increased electrochemical performances compared to MWNTs/PANI and the highest specific capacitance obtained of MWNTs/PANI and 0.15 M Ag-MWNTs/PANI was 162 F/g and 205 F/g, respectively. This indicated that Ag nanoparticles that were deposited onto the MWNTs caused an enhanced electrochemical performance of the MWNTs/PANI due to their high electric conductivity, which resulted in an increase of the charge transfer between the MWNTs and PANI by a bridge effect.     

Impedance study of thiolated polyaniline

Covalent attachment of thiolated probes to conducting polymers such as polyaniline (PANI) is a promising approach towards the development of electrochemical sensors and biosensors. However, thiolation alters the conjugated polymer backbone and influences the electrochemical behavior of the conducting polymer. PANI studied in this work was electropolymerized on glassy carbon (GC) electrodes from a solution of 0.1 M aniline in 0.5 or 1.0 M H₂SO₄. The GC/PANI electrodes were then functionalized by covalent attachment of 2-mercaptoethanol to the PANI backbone. The progress of thiolation was studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Thiolation of PANI was found to cause an initial decrease in electroactivity at 0–0.25 V and an increase in electroactivity at 0.25–0.6 V. However, prolonged thiolation caused a loss of electroactivity of PANI, which could be seen from EIS measurements as a dramatic decrease in the bulk redox capacitance of PANI.     

Electrochemical polymerization of polyaniline doped with Zn2+ as the electrode material for electrochemical supercapacitors

Polyaniline doped with Zn²⁺ (PANI/Zn²⁺) films was synthesized by cyclic voltammetric method on stainless steel mesh substrates in 0.2 mol L^?1 aniline and 0.5 mol L^?1 sulfuric acid electrolyte with various concentrations of zinc sulfate (ZnSO₄·7H₂O). The structure and morphology of PANI and PANI/Zn²⁺ films were characterized by Fourier transform infrared, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques, respectively. The electrochemical properties of PANI and PANI/Zn²⁺ films were investigated by cyclic voltammetry, galvanostatic charge–discharge test, and electrochemical impedance spectroscopy in 0.5 mol L^?1 H₂SO₄ electrolyte in a three-electrode system. The results show that the surface morphology of PANI/Zn²⁺ is more rough than that of pure PANI. The specific capacitance of the PANI/Zn²⁺ film displays a larger specific capacitance of 738 F g^?1, lower resistance, and better stability as compared with the pure PANI film. Thus, good capacitive performance demonstrates its potential superiority for supercapacitors.     

季铵盐掺杂聚苯胺电极的电容性能

采用循环伏安法,在铂电极表面聚合制备了季铵盐[CnH2n+1N(CH3)3]Cl(n=12,14,16,18)掺杂的聚苯胺修饰电极。 利用扫描电子显微镜、红外光谱以及X射线衍射对复合电极的表面形貌和结构进行了表征。 用循环伏安法、交流阻抗和恒电流充放电测试对电极的电化学性质和电容行为进行了系统研究。 结果表明,其中[C18H37N(CH3)3]Cl季铵盐掺杂的聚苯胺复合电极比表面积大,电容性能好,在2×10-3 A的充电电流下,初始比电容高达329.6 F/g,未掺杂电极比电容为199.0 F/g。 而且,复合电极的循环稳定性良好,经30次循环后比电容保持为252.4 F/g。     

Facile controlled synthesis of MnO2 nanowires for supercapacitors

In this report, a simple and facile method was developed for preparation of MnO₂ nanowires by calcinations of MnOOH nanowires previously synthesized under hydrothermal conditions, using hexamethylenetetramine as a reducing agent, without any template. The as-prepared MnO₂ nanowires displayed an enhanced specific capacitance (262.7 F g^?1) and good cycling stability (e.g., no loss within 1,500 cycles), showing good electrochemical performances as electrode material for supercapacitors.     

Nanostructured ferrite/graphene/polyaniline using for supercapacitor to enhance the capacitive behavior

Graphene nanosheets, polyaniline (PANI), and nanocrystallites of transition metal ferrite {Fe₃O₄ (Mag), NiFe₂O₄ (NiF), and CoFe₂O₄ (CoF)} have been prepared and characterized via XRD, FTIR, SEM, TEM, UV–vis spectroscopy, cyclic voltammetry, galvanostatic charge discharges, and impedance spectroscopy. Electrochemical measurements showed that supercapacitances of hybrid electrodes made of the ternary materials are higher than that of hybrid electrode made of binary or single material. The ternary hybrid CoF/graphene (G)/PANI electrode exhibits a highest specific capacitance reaching 1123 Fg^?1, an energy density of 240 Wh kg^?1 at 1 A g^?1, and a power density of 2680 Wkg^?1 at 1 A g^?1 and outstanding cycling performance, with 98.2% capacitance retained over 2000 cycles. The extraordinary electrochemical performance of the ternary CoF/G/PANI hybrid can be attributed to the synergistic effects of the individual components. The PANI conducting polymer enhances an electron transport. The Ferrite nanoparticles prevent the restocking of the carbon sheets and provide Faradaic processes to increase the total capacitance.     

Fabrication and the electrochemical activation of network-like MnO<Subscript>2</Subscript> nanoflakes as a flexible and large-area supercapacitor electrode

Porous network-like MnO₂ thick films are successfully synthesized on a flexible stainless steel (SS) mesh using a simple and low-cost electrodeposition method followed by an electrochemical activation process. Morphology, chemical composition, and crystal structure of the prepared electrodes before and after the activation process are determined and compared by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses. The results show that the implementation of the electrochemical activation process does not change the chemical composition and crystal structure of the films, but it influences the surface morphology of the MnO₂ thick layer to a flaky nanostructure. Based on the electrochemical data analysis, the maximum specific capacitance of 1400 mF (381 F g^?1) and 3700 mF (352 F g^?1) are measured for small (2.6 cm²) and large (10 cm²) surface area electrodes, respectively. In addition, a flexible symmetric MnO₂//MnO₂ solid-state supercapacitor shows a capacitance of 0.3 F with about 98% retention at different bending angles from 0 to 360°.     

Co-electrodeposition of MnO2/graphene oxide coating on carbon paper from phosphate buffer and the capacitive properties

MnO₂/graphene oxide sheet composite (MnO₂/GOS) has been co-electrodeposited on the thermally treated carbon paper (TTCP) in phosphate buffer solution containing GOS and KMnO₄. The resulted samples have been characterized by scanning and transmission electron microscopy, Raman, X-ray diffraction, and X-ray photoelectron energy spectroscopy. The results show that the synthesized MnO₂ may be δ-MnO₂ and the morphology of MnO₂/GOS is very different from that of MnO₂, indicating that the introduction of GOS in electrolyte can influence the morphology during the deposition. The capacitive properties of the samples are investigated by using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The specific capacitance of MnO₂ for MnO₂/GOS can reach about 829 F g^?1 at discharged current density of 1.0 A g^?1 in 1 M Na₂SO₄ aqueous solution, which is larger than that of MnO₂ deposited on TTCP. The composite of MnO₂/GOS also exhibits excellent cyclic stability with a decrease of 18.5 % specific capacitance after 1,500 cycles.     

Preparation of 3D MnO2/Polyaniline/Graphene Hybrid Material via Interfacial Polymerization as High‐Performance Supercapacitor Electrode

MnO₂/polyaniline/graphene composite as a supercapacitor electrode material was synthesized through an interfacial polymerization approach in the interface of oil/water phase. The as‐synthesized MPG is characterized by infrared spectroscopy, XRD, XPS, SEM and TEM, and its electrochemical performance is measured by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The 3D nanostructure of MPG and loose nanorod structure of polyaniline (PANI) coated with round MnO₂ pellets could be clearly observed. The maximum energy density of MPG is 45.4 Wh/kg (at a power density of 67.8 kW/kg) and the highest power density is 229.2 kW/kg (at an energy density of 25.7 Wh/kg). The capacitance retentions after 500 cycles at the scan rate of 5 mV/s for MGP composite and PANI/graphene are 70.4% and 59.1%, respectively, and the capacitance values after 500 cycles are 158.4 F/g and 114.8 F/g, respectively. The improved performance of MPG is due to the 3D nanostructure, loose nanorod structure of PANI and stable support of graphene, which prevent the mechanical deformation effectively during the fast charge/discharge process and facilitate the diffusion of the electrolyte ions into the inner region of active materials. The composite material is very promising for the next generation of high‐performance supercapacitors electrode.     

Enhanced electrochemical performance of nano-MnO2 modified by Ni(OH)2 as electrode material for supercapacitor

Ni(OH)₂ was compounded to MnO₂ in an easy liquid phase process to improve the diffusion process of the electrode. The as-prepared materials were a mixture of amorphous and nanocrystalline with aggregated nanoparticles forming slit-shaped pore structures. The composite has higher specific surface area and smaller pore volume compared with pristine MnO₂. Electrochemical properties of the electrodes were carried out with cyclic voltammetry (CV), galvanostatic charge–discharge tests, and electrochemical impedance spectroscopy (EIS). The MnO₂/Ni(OH)₂ composites exhibited enhanced electrochemical properties than that of pristine MnO₂. Remarkably, the composite which contains 3 % Ni(OH)₂ exerted the best discharged specific of 408 F g^?1 under 0.2 A g^?1, much higher than 247 F g^?1 of pristine MnO₂ at the same current density. Better rate capability and cycling stability were also realized by the same composite in comparison.     

Flexible asymmetric supercapacitor based on MnO2 honeycomb structure

By controlling the electroplating time of solution containing Mn(Ac)₂, the MnO₂ nanosheets were self-assembled to the honeycomb structure and showed an excellent electrochemical performance in 1 mol/L Na₂SO₄ electrolyte. Via pairing with activated carbon as negative electrode, the capacitor could deliver a maximum energy density of 43.84 Wh/kg and a maximum power density of 6.62 kW/kg.     

Electrodeposition of MnO2 nanowires on carbon nanotube paper as free-standing,flexible electrode for supercapacitors

MnO₂ nanowires were electrodeposited onto carbon nanotube (CNT) paper by a cyclic voltammetric technique. The as-prepared MnO₂ nanowire/CNT composite paper (MNCCP) can be used as a flexible electrode for electrochemical supercapacitors. Electrochemical measurements showed that the MNCCP electrode displayed specific capacitances as high as 167.5 F g⁻¹ at a current density of 77 mA g⁻¹. After 3000 cycles, the composite paper can retain more than 88% of initial capacitance, showing good cyclability. The CNT paper in the composite acted as a good conductive and active substrate for flexible electrodes in supercapacitors, and the nanowire structure of the MnO₂ could facilitate the contact of the electrolyte with the active materials, and thus increase the capacitance.     

Asymmetric supercapacitors based on stabilized α-Ni(OH)2 and activated carbon

In this work, stabilized Al-substituted α-Ni(OH)₂ materials were successfully synthesized by a chemical coprecipitation method. The experimental results showed that the 7.5% Al-substituted α-Ni(OH)₂ materials exhibited high specific capacitance (2.08?×?10³ F/g) and excellent rate capability due to the high stability of Al-substituted α-Ni(OH)₂ structures in alkaline media, suggesting its potential application in electrode material for supercapacitors. To enhance energy density, an asymmetric type pseudo/electric double-layer capacitor was considered where α-Ni(OH)₂ materials and activated carbon act as the positive and negative electrodes, respectively. Values for the maximum specific capacitance of 127 F/g and specific energy of 42 W·h/kg were demonstrated for a cell voltage between 0.4 and 1.6 V. By using the α-Ni(OH)₂ electrode, the asymmetric supercapacitor exhibited high energy density and stable power characteristics. The hybrid supercapacitor also exhibited a good electrochemical stability with 82% of the initial capacitance over consecutive 1,000 cycle numbers.     

Electrochemical storage properties of polyaniline-, poly(N-methylaniline)-, and poly(N-ethylaniline)-coated pencil graphite electrodes

Three types of conducting polymers, polyaniline (PANI), poly(N-methylaniline) (PNMA), poly(N-ethylaniline) (PNEA) were electrochemically deposited on pencil graphite electrode (PGE) surfaces characterized as electrode active materials for supercapacitor applications. The obtained films were electrochemically characterized using different electrochemical methods. Redox parameters, electro-active characteristics, and electrostability of the polymer films were investigated via cyclic voltammetry (CV). Doping types of the polymer films were determined by the Mott-Schottky method. Electrochemical capacitance properties of the polymer film coating PGE (PGE/PANI, PGE/PNMA, and PGE/PNEA) were investigated by the CV and potentiostatic electrochemical impedance spectroscopy (EIS) methods in a 0.1 M H₂SO₄ aqueous solution. Thus, capacitance values of the electrodes were calculated. Results show that PGE/PANI, PGE/PNMA, and PGE/PNEA exhibit maximum specific capacitances of 131.78 F g^?1 (≈ 436.50 mF cm^?2), 38.00 F g^?1 (≈ 130.70 mF cm^?2), and 16.50 F g^?1 (≈ 57.83 mF cm^?2), respectively. Moreover, charge-discharge capacities of the electrodes are reported and the specific power (SP) and specific energy (SE) values of the electrodes as supercapacitor materials were calculated using repeating chronopotentiometry.     

The effect of the polyaniline morphology on the performance of polyaniline supercapacitors

The polyaniline (PANI) prepared by the pulse galvanostatic method (PGM) or the galvanostatic method on a stainless steel substrate from an aqueous solution of 0.5 mol/l H₂SO₄ with 0.2 mol/l aniline has been studied as an electroactive material in supercapacitors. The electrochemical performance of the PANI supercapacitor is characterized by cyclic voltammetry, a galvanostatic charge–discharge test and electrochemical impedance spectroscopy in NaClO₄ and HClO₄ mixed electrolyte. The results show that PANI films with different morphology and hence different capacitance are synthesized by controlling the synthesis methods and conditions. Owing to the double-layer capacitance and pseudocapacitance increase with increasing real surface area of PANI, the capacitive performances of PANI were enhanced with increasing real surface area of PANI. The highest capacitance is obtained for the PANI film with nanofibrous morphology. From charge–discharge studies of a nanofibrous PANI capacitor, a specific capacitance of 609 F/g and a specific energy density of 26.8 Wh/kg have been obtained at a discharge current density of 1.5 mA/cm². The PANI capacitor also shows little degradation of capacitance after 1,000 cycles. The effects of discharge current density and deposited charge of PANI on capacitance are investigated. The results indicate that the nanofibrous PANI prepared by the PGM is promising for supercapacitors.     

Synthesis of vanadium oxides nanosheets as anode material for asymmetric supercapacitor

Vanadium oxides (V₂O₅) have been intensely investigated for advanced supercapacitors due to its extensive multifunctional properties of typical layered structure and multiple stable oxide states of vanadium in its oxides. In this study, V₂O₅ nanosheets are synthesized via V₂O₅ xerogel solvothermal reaction in ethanol solvent at 200 °C for 12 h. The V₂O₅ nanosheets facilitate the easy accessibility of ions and can provide more area available for electrochemical reactions. We have achieved the highest specific capacitance of 298 F/g and good rate discharge for V₂O₅ electrodes. Notably, the capacitance still retains a high retention rate of 85% after 10,000 cycles at 200 mV/s. Furthermore, asymmetric supercapacitors is assembled based on V₂O₅ nanosheets and active carbon electrode, and a specific capacitance of 13.2 F/g is obtained at 1 A/g, with a energy density of 4.7 Wh/kg at a power density of 0.798 kW/kg and remains 2.28 Wh/kg at 7.992 kW/kg. Based on these results, the asymmetric supercapacitor exhibits a good cycle life with 77.3% capacitance retention after 3000 cycles. It suggests that the V₂O₅ nanosheets are promising electrode material for electrochemical supercapacitors.     

Facile and scalable fabrication of graphene/polypyrrole/MnO<Subscript>x</Subscript>/Cu(OH)<Subscript>2</Subscript> composite for high-performance supercapacitors

In this study, to improve the specific capacitance of graphene-based supercapacitor, novel quadri composite of G/PPy/MnO_x/Cu(OH)₂ was synthesized by using a facile and inexpensive route. First, a two-step method consisting of thermal decomposition and in situ oxidative polymerization was employed to fabricate graphene/polypyrrole/manganese oxide composites. Second, Cu(OH)₂ nanowires were deposited on Cu foil. Afterwards, for the electrochemical measurements, composite powders were deposited on Cu(OH)₂/Cu foil substrate as working electrodes. The synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR) spectroscopy, and Raman spectroscopy. The XRD analysis revealed the formation of PPy/graphene, Mn₃O₄/graphene, and graphene/polypyrrole/MnO_x. In addition, the presence of polypyrrole and manganese oxides was confirmed using FT-IR and Raman spectroscopies. Graphene/polypyrrole/MnO_x/Cu(OH)₂ electrode showed the best electrochemical performance and exhibited the largest specific capacitance of approximately 370 F/g at the scan rate of 10 mV/s in 6 M KOH electrolyte. In addition, other electrochemical measurements (charge–discharge, EIS and cyclical performance) of the G/Cu(OH)₂, G/PPy/Cu(OH)₂, G/Mn₃O₄/Cu(OH)₂, and G/PPy/MnO_x/Cu(OH)₂ electrodes suggested that the G/PPy/MnO_x/Cu(OH)₂ composite electrode is promising materials for supercapacitor application.     

Synthesis and performance evaluation of novel cobalt hydroxychlorides for electrochemical supercapacitors

Co₂(OH)₃Cl has been prepared by a facile one pot sol-gel process. Two different solvents, ethylene glycol and glycerol, are used for the synthesis. The resulting samples are studied for their morphology, structure, and electrochemical stability upon cycling. The sample with ethylene glycol as solvent exhibits three-dimensional porous interconnected xerogel morphology, whereas that with glycerol shows a crystalline and non-porous nanoparticulate structure. The specific capacitance of the Co₂(OH)₃Cl prepared with ethylene glycol is 434 F/g, when the electrodes are cycled in 3 M KOH at a specific current 2 A/g, and with that of glycerol, it is 252 F/g. Interestingly, at a high current density of 25 A/g, Co₂(OH)₃Cl with ethylene glycol and glycerol showed 143 and 72 F/g, respectively. Ethylene glycol significantly modified the structure and morphology so as to attain a mesoporous Co₂(OH)₃Cl with high surface area, which in turn influenced its remarkable electrochemical behavior. With a significant specific capacity and electrochemical stability, the synthesized material is a novel potential candidate for supercapacitors.     

原位化学沉积法制备碳/聚苯胺复合材料作为超级电容器材料的研究

Polyaniline （PA） film was chemically deposited onto the surface of activated carbon （AC） uniformly. Chemical deposition was carried out in 0.1 mol/L aniline plus 0.5 mol/L H2SO4 solution adopting V2O5·nH2O coated on the surface of activated carbon as oxidant. The surface morphologies and structures of the composite materials were characterized by scanning electron microscopy and FT-IR spectra. The electrochemical properties of the composite material electrodes were studied by cyclic voltammetry and constant current charge/discharge tests in 1 molFL H2SO4 solutions. The specific capacitance of composite materials was exhibited as high as 237.5 F/g at a current density of 1.0 A/g compared with a value of 120 F/g for pure carbon electrode. Good power characteristic and good stability of composite electrodes were also demonstrated.     

Effect of alkaline and alkaline–earth cations on the supercapacitor performance of MnO2 with various crystallographic structures

The electrochemical performances of the α-, γ-, and δ-MnO₂ with different crystallographic structures were systematically investigated in 0.5 mol/L Li₂SO₄, 0.5 mol/L Na₂SO₄, 1 mol/L Ca(NO₃)₂, and 1 mol/L?Mg(NO₃)₂ electrolytes. The results showed that the electrochemical performances of the manganese dioxides depended strongly on the crystallographic structures of MnO₂ as well as the cation in the electrolytes. Because the δ-MnO₂ consists with layers of structure and the interlayer separation is 7 Å, which is suitable for insertion/extraction of some alkaline and alkaline–earth cations, the δ-MnO₂ electrode showed the higher specific capacitance than that of α-MnO₂ and γ-MnO₂. We also found that the α-, γ-, and δ-MnO₂ electrodes in the Mg(NO₃)₂ electrolyte showed a higher specific capacitance, while all the α-, γ-, and δ-MnO₂ electrodes in the Li₂SO₄ electrolyte exhibited a better cycle life. The reason for the different behavior of Li⁺ and Mg²⁺ during the charge/discharge process can be ascribed to the charge effect of the cations in the electrolytes. The ex situ X-ray diffraction (XRD) and long-time cyclic voltammogram measurements were used to systematically study the energy storage mechanism of MnO₂-based electrodes. A progressive crystallinity loss of the materials is also observed upon potential cycling at the oxidized states. A reasonable charge/discharge mechanism is proposed in this work.