Symmetric redox supercapacitor based on micro-fabrication with three-dimensional polypyrrole electrodes

To achieve higher energy density and power density, we have designed and fabricated a symmetric redox supercapacitor based on microelectromechanical system (MEMS) technologies. The supercapacitor consists of a three-dimensional (3D) microstructure on silicon substrate micromachined by high-aspect-ratio deep reactive ion etching (DRIE) method, two sputtered Ti current collectors and two electrochemical polymerized polypyrrole (PPy) films as electrodes. Electrochemical tests, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatical charge/discharge methods have been carried out on the single PPy electrodes and the symmetric supercapacitor in different electrolytes. The specific capacitance (capacitance per unit footprint area) and specific power (power per unit footprint area) of the PPy electrodes and symmetric supercapacitor can be calculated from the electrochemical test data. It is found that NaCl solution is a good electrolyte for the polymerized PPy electrodes. In NaCl electrolyte, single PPy electrodes exhibit 0.128 F cm⁻² specific capacitance and 1.28 mW cm⁻² specific power at 20 mV s⁻¹ scan rate. The symmetric supercapacitor presents 0.056 F cm⁻² specific capacitance and 0.56 mW cm⁻² specific power at 20 mV s⁻¹ scan rate.     

A new high-performance supercapacitor electrode of strategically integrated cerium vanadium oxide and polypyrrole nanocomposite

Herein we show a construction of high-performance supercapacitor electrode made of cerium vanadate uniformly glazed over polypyrrole (CeVO₄/Ppy) nanostructures by a simple hydrothermal method, which was characterized by various analytical techniques. Electrochemical studies on CeVO₄/Ppy/Ni foam with 1 M KOH show a maximum specific capacitance of 1236 F/g at a current density of 0.75 A/g. These salient features, together with smart interactions between the interconstituents, CeVO₄ and Ppy, lead to high conductivity, specific capacitance, and cycling stability with retention of 92.6% capacitance in 10,000 cycles of GCD curves. Additionally, the asymmetric supercapacitor based on activated carbon (AC), AC//CeVO₄/Ppy device delivers a high specific capacitance of 116 F/g and energy density of 52.2 Wh/Kg at power density of 675.9 W/kg along with high capacity retention of 77.80% after 10,000 cycles. This system could be scaled up to large-scale production of high power devices, which opens up lot of opportunities in modern electronic industrial applications.     

Electrochemical supercapacitor electrode material based on poly(3,4-ethylenedioxythiophene)/polypyrrole composite

Poly (3,4-ethylenedioxythiophene)/polypyrrole composite electrodes were prepared by electropolymerization of 3,4-ethylenedioxythiophene (EDOT) on the surface of polypyrrole (PPy) modified tantalum electrodes. The morphology observation of PPy and poly(3,4-ethylenedioxythiophene)/polypyrrole composite (PEDOT/PPy) was performed on Field Emission Scanning Electron Microscope (SEM). The electrochemical capacitance properties of the composite were investigated with cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS) techniques in the two- or three-electrode cell system. The results show that the PEDOT/h-PPy (PPy with horn-like structure) composite films were characterized with highly porous structure, which leads to their specific capacitance as 230 Fg⁻¹ in 1 M LiClO₄ aqueous solutions and even 290 Fg⁻¹ in 1 M KCl aqueous solutions. Moreover, the composite exhibits a rectangle-like shape of voltammetry characteristics even at scanning rate 100 mV s⁻¹, a linear variation of the voltage with respect to time without a clear ohm-drop phenomenon in galvanostatic charge–discharge process and almost ideal capacitance behavior in low-frequency in 1 M KCl solutions. Furthermore, specific power of the composite would reach 13 kW kg⁻¹ and it had good cycle stability. All of the above imply that the PEDOT/h-PPy composites were an ideal electrode material of supercapacitor.     

Fabrication and properties of a carbon/polypyrrole three-dimensional microbattery

The carbon-microelectromechanical systems (C-MEMS) microfabrication process offers a promising method for fabricating three-dimensional (3D) battery architectures. In the current study, this approach was extended to the fabrication of positive electrode arrays and their assembly in a 3D lithium-ion microbattery. The positive electrode array was fabricated by electrochemical deposition of dodecylbenzenesulfonate-doped polypyrrole (PPYDBS) on an array of carbon rods. Electrochemical measurements show that the electrodeposited PPYDBS electrode array reversibly intercalates lithium with better gravimetric capacity than that of 2D electrodeposited films. The prototype carbon/PPYDBS 3D battery was based on an interdigitated electrode array configuration. It functioned as a secondary battery but the performance was limited because of electrical shorting. These initial results with the 3D interdigitated battery help to identify the needs associated with different electrode fabrication approaches and specific 3D designs.     

Polypyrrole/carbon aerogel composite materials for supercapacitor

Polypyrrole (PPy)/carbon aerogel (CA) composite materials with different PPy contents are prepared by chemical oxidation polymerization through ultrasound irradiation and are used as active electrode material for supercapacitor. The morphology of PPy/CA composite is examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that PPy is deposited onto the surface of CA. As evidenced by cyclic voltammetry, galvanostatic charge/discharge test and EIS measurements, PPy/CA composites show superior capacitive performances to CA, moreover, the results based on cyclic voltammograms show that the composite material has a high specific capacitance of 433 F g⁻¹, while the capacitance of CA electrode is only 174 F g⁻¹. Although the supercapacitor used PPy/CA as active electrode material has an initial capacitance loss due to the instability of PPy, the specific capacitance after 500 cycles stabilizes nearly at a fixed value.     

A high-performance three-dimensional micro supercapacitor based on self-supporting composite materials

This paper introduces a silicon three-dimensional (3D) micro supercapacitor, featured by using self-supporting nano porous composite materials and interdigital electrodes with high-aspect-ratio. A way to prepare self-supporting materials has been developed, and composites that contain an activated carbon as the active component have been studied and designed to meet the requirements for adequate specific capacitance, good conductivity and strong structure. By combining the designed composite with microfabrication techniques, a micro supercapacitor with high-aspect-ratio interdigital electrodes has been achieved. Electrochemical characterization results of the prototype with NaNO₃ electrolyte demonstrate that the 3D supercapacitor exhibits an outstanding overall performance. A large capacitance of 90.7 mF cm⁻² and a fast power of 51.5 mW cm⁻² are calculated. Robust stability and high charge/discharge efficiency are also observed. Moreover, this study provides a scalable device built by compatible fabrication method, which is applicable to the integration of high-performance supercapacitors on chip.     

One step electrodeposition of V2O5/polypyrrole/graphene oxide ternary nanocomposite for preparation of a high performance supercapacitor

A new ternary nanocomposite based on graphene oxide (GO), polypyrrole (PPy) and vanadium pentoxide (V₂O₅) is obtained via one-step electrochemical deposition process. Electrochemical deposition of V₂O₅, PPy and GO on a stainless steel (SS) substrate is conducted from an aqueous solution containing vanadyl acetate, pyrrole and GO to get V₂O₅/PPy/GO nanocomposite. Characterization of the electrode material is carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The electrochemical performance of the as-prepared nanocomposite is evaluated by different electrochemical methods including cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) in 0.5 M Na₂SO₄ solution. Remarkably, V₂O₅/PPy/GO nanocomposite shows a specific capacitance of 750 F g^?1 at a current density of 5 A g^?1, which is far better than PPy (59.5 F g^?1), V₂O₅/PPy (81.5 F g^?1) and PPy/GO (344.5 F g^?1). Furthermore, V₂O₅/PPy/GO maintains 83% of its initial value after 3000 cycles, which demonstrates good electrochemical stability of the electrode during repeated cycling. These results demonstrate that the combination of electrical double layer capacitance of GO and pseudocapacitive behavior of the PPy and V₂O₅ can effectively increase the specific capacitance and cycling stability of the prepared electrode. Also, a symmetric supercapacitor device assembled by V₂O₅/PPy/GO nanocomposite yielded a maximum energy density of 27.6 W h kg^?1 at a power density of 3600 W kg^?1, and a maximum power density of 13680 W kg^?1 at an energy density of 22.8 W h kg^?1.     

Polypyrrole-coated tape electrode for flexible supercapacitor applications

A non-conductive tape was covered with graphite by the attachment of tape on bulk graphite and subsequently peeled off from the surface. Flexible tape with thin graphite coating was designed as the current collector. Polypyrrole film was synthesized potentiostatically on the flexible tape electrode surface from pyrrole monomer in sulfuric acid medium. Topographical, morphological, compositional and electrochemical properties of polypyrrole films were investigated by AFM, SEM, FTIR and potentiostatic/galvanostatic techniques, respectively. Polypyrrole flexible electrodes, electroplated in acidic medium, were cycled in aqueous and non-aqueous electrolyte environments, specifically, acetonitrile and ionic liquid. The capacitance retention rate of the polypyrrole-based electrode cycled in deep eutectic solvent increased by 11% after 3000 scans. The highest specific capacitance of the electropolymerized polypyrrole-based electrode was 545 F g⁻¹ in aqueous electrolyte, that is, water containing 1 M LiClO₄, at scan rate 100 mV s⁻¹. Polypyrrole-based electrodes can be synthesized on flexible tapes as a cheap and easy method for supercapacitor applications.     

Frequency,thermal and voltage supercapacitor characterization and modeling

A simple electrical model has been established to describe supercapacitor behaviour as a function of frequency, voltage and temperature for hybrid vehicle applications. The electrical model consists of 14 RLC elements, which have been determined from experimental data using electrochemical impedance spectroscopy (EIS) applied on a commercial supercapacitor.     

A novel capacitor material based on Nafion-doped polypyrrole

The electrochemical characteristics of polypyrrole doped with either perchlorate or Nafion are determined. Polypyrrole doped with Nafion ions or perchlorate ions exhibits a specific capacitance of 344 or 355 F g⁻¹, respectively. Cycle life experiments reveal that the Nafion-doped material retains 98% of the original capacitance after 3000 cycles whereas that doped with perchlorate retains only 70% over this period. Scanning electron microscopy (SEM) before and after long-term cycling, reveals some mechanical degradation.     

Multilayered electrode materials based on polyaniline/activated carbon composites for supercapacitor applications

The supercapacitor multilayered electrode materials were prepared potentiodynamically based on polyaniline/activated carbon composite materials. The multilayers comprised of various combinations of activated carbon and doped polyaniline layers using three dopants such as sulphuric acid, camphor-10-sulphonic acid and p-toluene sulphonic acid. These composite materials were characterized using SEM, BET Surface area and FTIR. The supercapacitive properties of the fabricated symmetrical supercapacitors were analyzed by cyclic voltammetry, ac impedance and galvanostatic charge–discharge techniques. Based on the electrochemical results best one was chosen for fabricating the symmetrical supercapacitor and it showed the highest specific capacitance of 549.5 F/g. Further, it was found that these multilayered electrode materials gave higher capacitance than their single layered counter parts.     

Electrochemically synthesized nanocrystalline spinel thin film for high performance supercapacitor

Spinels are not known for their supercapacitive nature. Here, we have explored electrochemically synthesized nanostructured NiCo₂O₄ spinel thin-film electrode for electrochemical supercapacitors. The nanostructured NiCo₂O₄ spinel thin film exhibited a high specific capacitance value of 580 F g⁻¹ and an energy density of 32 Wh kg⁻¹ at the power density of 4 kW kg⁻¹, accompanying with good cyclic stability.     

Flexible supercapacitor based on polyaniline nanowires/carbon cloth with both high gravimetric and area-normalized capacitance

Flexible supercapacitor is successfully fabricated using polyaniline nanowires/carbon cloth (PANI-NWs/CC) nanocomposite. High gravimetric capacitance of 1079 F g⁻¹ at a specific energy of 100.9 Wh kg⁻¹ and a specific power of 12.1 kW kg⁻¹ is obtained. Moreover, this approach also offers an exceptionally high area-normalized capacitance of 1.8 F cm⁻². The diffusion length of protons within the PANI-NWs is estimated to be about 60 nm by electrochemical impedance analysis, which indicates that the electrochemical performance of the electrode is not limited by the thickness of PANI-NWs. The electrochemical performance of PANI-NWS/CC remains without any deterioration, even when the cell is bent under high curvature. These results clearly present a cost-effective and simple method of fabrication of the nanostructured polymers with enormous potential in flexible energy storage device applications.     

Carbon-supported,nano-structured,manganese oxide composite electrode for electrochemical supercapacitor

Carbon-supported MnO₂ nanorods are synthesized using a microemulsion process and a manganese oxide/carbon (MnO₂/C) composite is investigated for use in a supercapacitor. As shown by high-resolution transmission electron microscopy the 2 nm × 10 nm MnO₂ nanorods are uniformly dispersed on the carbon surface. Cyclic voltammograms recorded for the MnO₂/C composite electrode display ideal capacitive behaviour between −0.1 and 0.8 V (vs. saturated calomel electrode) with high reversibility. The specific capacitance of the MnO₂/C composite electrode found to be 165 F g⁻¹ and is estimated to be as high as 458 F g⁻¹ for the MnO₂. Based on cyclic voltammetric life-cycle tests, the MnO₂/C composite electrode gives a highly stable and reversible performance for up to 10,000 cycles.     

Supercapacitor with superior electrochemical properties derived from symmetrical manganese oxide-carbon fiber coated with polypyrrole

A supercapacitor electrode comprising conducting polypyrrole (PPy) coated on manganese oxide-carbon fiber (CNFMnO₂) was successfully synthesized using electrospinning, followed by carbonization and in-situ polymerization. A non-uniform distribution of PPy on the surface of CNFMnO₂ was observed via FESEM analysis. The chemical bonding of CNFMnO₂/PPy and the valence state of manganese were revealed via FTIR, Raman spectroscopy, XRD and XPS measurements. CNFMnO₂/PPy composite possessed high specific capacitance and specific energy of 315.80 Fg^?1 and 13.68 Wh/kg, respectively. In addition, good electrochemical reversibility was proven upon CNFMnO₂/PPy even at higher sweep rate (5–200 mV/s). Moreover, this one-dimensional electrode achieved an excellent long-term cycling stability (82.46%) over 2000 CV cycles with low charge transfer resistance (4.61 Ω). The modification of CNFMnO₂/PPy contributes to good synergistic effects among the material which improve the electrochemical behavior of manganese oxide-based fiber composite for future supercapacitor.     

Electrochemical properties of leucoemeraldine, emeraldine, and pernigraniline forms of polyaniline/multi-wall carbon nanotube nanocomposites for supercapacitor applications

We report on the synthesis and electrochemical properties of leucoemeraldine base, emeraldine salt and pernigraniline base forms of polyaniline (PANI) in the form of nanocomposites with MWNTs. The oxidation state of PANI in the composite is controlled by doping and dedoping of the emeraldine salt form of PANI/MWNT composite, which is prepared through chemical polymerization, using oxidizing and reducing agents without changing the morphology of PANI in the composite and is confirmed by ultraviolet-visible spectroscopy (UV-vis) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The electrochemical and pseudocapacitive properties of the composites are investigated using cyclic voltammetry and analyzed with respect to the oxidation state of polyaniline. The PANI/MWNT nanocomposites show specific capacitance values of 217 F g⁻¹, 328 F g⁻¹ and 139 F g⁻¹ for leucoemeraldine base, emeraldine salt and pernigraniline base, respectively. Electrochemical impedance spectroscopy is performed to explain the different electrochemical properties of PANI in different oxidation states.     

Pulsed laser deposition of manganese oxide thin films for supercapacitor applications

Thin films of manganese oxides have been grown by the pulsed laser deposition (PLD) process on silicon wafer and stainless steel substrates at different substrate temperatures and oxygen gas pressures. By proper selection of processing parameters such as temperature and oxygen pressure during the PLD process, pure crystalline phases of Mn₂O₃, Mn₃O₄ as well as amorphous phase of MnO_x were successfully fabricated as identified by X-ray diffraction. The pseudo-capacitance behaviours of these different phases of manganese oxides have also been evaluated by the electrochemical cyclic voltammetry measured in 0.1 M Na₂SO₄ aqueous electrolyte at different scan rates. Their specific current and capacitance determined by electrochemical measurements were compared and the results show that crystalline Mn₂O₃ phase has the highest specific current and capacitance, while the values for crystalline Mn₃O₄ films are the lowest. The specific current and capacitance values of the amorphous MnO_x films are lower than Mn₂O₃ but higher than Mn₃O₄. The specific capacitance of Mn₂O₃ films of 120 nm thick reaches 210 F g⁻¹ at 1 mV s⁻¹ scan rate with excellent stability and cyclic durability. This work has demonstrated that PLD is a very promising technique for screening high performance active materials for supercapacitor applications due to its excellent flexibility and capability of easily controlling chemical composition, microstructures and phases of materials.     

Electrocatalytic properties of monometallic and bimetallic nanoparticles-incorporated polypyrrole films for electro-oxidation of methanol

Oxidative electrochemical polymerization of pyrrole at indium-doped tin oxide (ITO) is accomplished from a neat monomer solution with a supporting electrolyte (0.3 M n-tetrabutyl ammonium tetrafluoroborate) by multiple-scan cyclic voltammetry. Polypyrrole (Ppy) films containing nanometer-sized platinum and Pt/Pd bimetallic particles are electro-synthesized on ITO glass plates by voltammetric cycling between −0.1 and +1 V (versus Ag/AgCl/3 M NaCl). The electrocatalytic oxidation of methanol on the nanoparticle-modified polypyrrole films is studied by means of electrochemical techniques. The modified electrode exhibits significant eletrocatalytic activity for methanol oxidation. The enhanced electrocatalytic activities may be due to the uniform dispersion of nanoparticles in the polypyrrole film and a synergistic effect of the highly-dispersed metal particles so that the polypyrrole film reduces electrode poisoning by adsorbed CO species. The monometallic (Pt) and bimetallic (Pt/Pd) nanoparticles are uniformly dispersed in polypyrrole matrixes, as confirmed by scanning electron microscopic and atomic force microscopic analysis. Energy dispersive X-ray analysis is used to characterize the composition of metal present in the nanoparticle-modified electrodes.     

Fabrication and electrochemical characterization of two-dimensional ordered nanoporous manganese oxide for supercapacitor applications

A nanoporous manganese oxide (MnO₂) film was fabricated via a polystyrene templated electrodeposition in the solution containing MnSO₄. The nanoporous MnO₂ film obtained has been characterized by field emission scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge methods. The specific capacitance of 1018 F g⁻¹ was observed at a low current density of 500 mA g⁻¹. When the current density increased to 30.0 A g⁻¹, the specific capacitance of 277 F g⁻¹ remained. The high capacitance retention at high rates makes the prepared MnO₂ a promising candidate for supercapacitor applications.     

KOH modified graphene nanosheets for supercapacitor electrodes

Chemical modification of graphene nanosheets by KOH was examined as a way to enhance the specific capacity of graphene nanosheets in supercapacitor. Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy were used to investigate the effects of the treatment on the surface of the graphene nanosheets. The specific capacitance of 136 F g⁻¹ was obtained for KOH treated graphene by integration of the cyclic voltammogram, an increase of about 35% compared with that for the pristine graphene nanosheets.