Investigations on electrochemical supercapacitors using polypyrrole redox electrodes and PMMA based gel electrolytes

Polypyrrole based solid state electrochemical redox supercapacitors have been fabricated using the polymeric gel electrolytes comprising of poly methyl methacrylate (PMMA)-propylene carbonate (PC)-ethylene carbonate (EC)-perchlorate salts of different cations [Li⁺, Na⁺ and (C₂H₅)₄N⁺ (TEA⁺)]. A comparative study has been carried out using linear sweep reversal voltammetry, complex impedance spectroscopy and constant current charge-discharge tests. The capacitance values of the cells have been observed to be in the range of 15.3-22.5 mF cm⁻² (equivalent to single electrode specific capacitance of 120-178 F g⁻¹ of polypyrrole). This corresponds to the values of energy density 16.7-24.7 Wh kg⁻¹ and power density 1.6-2.8 kW kg⁻¹ calculated for the working voltage of 1.0 V limited for polypyrrole based redox capacitors. Substantial improvements in the coulombic efficiency of the cells have been observed (close to 100%) due to the application of gel electrolytes showing flexible and liquid like behaviour. Further, the types and sizes of the cations in the gel electrolytes do not play any dominant role in the capacitive behaviour of the redox cells.     

Investigations by electrochemical quartz crystal impedance system-electrodeposition of silver and polyaniline

An electrochemical quartz crystal impedance system (EQCIS) which allows rapid and simultaneous measurements of admittance spectra of piezoelectric quartz crystal resonance during electrochemical processes was developed by combining an HP 4395A Network/Spectrum/Impedance analyzer with an EG & G M283 potentiostat. Non-linear least square regression analyses of simultaneously acquired conductance and susceptance data were discussed in detail, giving that R_m, C_s, 1/C_m (or L_m) and of as estimation parameters is the best choice among various fitting routines. Equivalent electrical circuit parameters of quartz crystal resonance during electrodeposition of silver and polyaniline and electrochemical processes of the deposits were obtained and discussed according to changes in electrode mass, electrode surface roughness and film conductivity etc. The significant changes of motional resistance R_m and static capacitance C, observed in the silver case was believed to result mainly from changes in electrode surface roughness and the linear relationship between them was well explained by the following equation, C_s = C_q+ C_e = ε_qA_q/ h_q + ε_ek²R_m/[h_e(ωρ_Lη_L]1/2.     

Resorcinol-formaldehyde carbon spheres/polyaniline composite with excellent electrochemical performance for supercapacitors

Well-dispersed resorcinol-formaldehyde-based carbon spheres (RFCs) have been prepared by the polycondensation of resorcinol and formaldehyde with ammonia as catalyst and subsequent carbonization of the obtained polymer. In situ polymerization of the aniline occurred in the suspension of the RFC, and RFC was surrounded by the polyaniline (PANI) wires. The PANI and RFC hybrid network (PRFC) formed gradually. In a three-electrode mode, the specific capacitance (C _sp) of PRFC reaches 315 F g^?1 at a current density of 1 A g^?1 in 2 M H₂SO₄, much higher than that of pure PANI (225 F g^?1) and RFC (121.7 F g^?1). Furthermore, the C _sp of PRFC retains 80.0 % after 1000 charge-discharge processes at a current density of 5 Ag^?1. The enhanced electrochemical performance of the PRFC came from its homogeneous three-dimensional hierarchical network structure, good electric conductivity of the PANI around the RFC, and the synergistic effect between the RFC and PANI.     

Three-dimensional manganese dioxide-functionalized carbon nanotube electrodes for electrochemical supercapacitors

Three-dimensional manganese dioxide (MnO₂)-functionalized multiwalled carbon nanotube (MWCNT) electrodes have been produced by a simple and scalable thermal decomposition process. The electrodes are prepared by treating planar MWCNT sheets with manganese(II) nitrate (Mn(NO₃)₂) solution and annealing at low temperature (200–300 °C) and ambient pressure. The morphology, chemical composition, and structure of the resulting matrices have been investigated with scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction. Supercapacitors assembled with three-dimensional electrodes exhibit a 14-fold increase in specific capacitance (C _sp) in comparison to those containing pristine, two-dimensional MWCNT electrodes. C _sp varies linearly with Mn(NO₃)₂ thermal decomposition temperature (from 100 to 61 F/g at 0.2 A/g), a trend that is discussed in the context of nitrate reaction chemistry and MWCNT structure. This efficient and promising approach allows for simultaneous enhancement of electrode–electrolyte contact area and incorporation of redox-based charge storage within electrochemical capacitors.     

Mechanochemically prepared polyaniline and graphene-based nanocomposites as electrodes of supercapacitors

Conductive nanocomposites based on polyaniline and graphene (PAni/Gr) were prepared by cheap and efficient mechanochemical method. The uniform distribution of Gr nanoparticles in the polymer matrix and the ordering of the polymer chains due to the action of mechanical shear stresses, which were established by TEM, stipulated high specific capacitance about 920 F g^?1 in ??0.2–1.0 V vs. Ag/AgCl potential range. PAni/Gr-based electrodes are able to provide the specific capacitance of ~?750 F g^?1 at 2 A g^?1 in symmetric supercapacitors (SSC) and stably cycle at the operating voltage V?=?0.65 V for 10,000 charge-discharge cycles with 96% capacitance retention, whereas the increasing of V leads to the loss of stability as a result of the cathode degradation. PAni/Gr-based SSC possessed improved self-discharge showed high rate capability, and the specific power of such SSC could reach ~?10 kW kg^?1 at the specific energy of ~?18 W h kg^?1.     

Synthesis of polyaniline/HF partially etched-hierarchical porous TiO2 microspheres composite with high electrochemical performance for supercapacitors

Journal of Solid State Electrochemistry - A novel electrode material of polyaniline/HF partially etched-hierarchical porous TiO2 microspheres (PANI/F-HPTM) composite has been designed and...     

Direct electrochemical redox of tyrosinase at silver electrodes

The direct electron transfer reactions between tyrosinase and silver electrode were investigated by using cyclic voltammetry and potential-step chronoamperometry as well as current-step chronopotentiometry techniques. The kinetics of these reactions is quasi-reversible with two electron transfer reactions and 0.030 s(-1) apparent electrode reaction rate constant. The results demonstrate that neither electrode surface modification nor the inclusion of mediators is necessary to study the electron transfer reactions of tyrosinase at silver electrodes. Moreover, both the anodic and the cathodic currents are linear relationship with the tyrosinase concentration in the range of 1 x 10(-9) approximately 5 x 10(-8)moll(-1). It is possible to be used as a method of analyzing tyrosinase concentration.     

Graphene oxide doped polyaniline for supercapacitors

A novel high-performance electrode material based on fibrillar polyaniline (PANI) doped with graphene oxide sheets was synthesized via in situ polymerization of monomer in the presence of graphene oxide, with a high conductivity of 10 S cm^?1 at 22 °C for the obtained nanocomposite with a mass ratio of aniline/graphite oxide, 100:1. Its high specific capacitance of 531 F/g was obtained in the potential range from 0 to 0.45 V at 200 mA/g by charge–discharge analysis compared to 216 F/g of individual PANI. The doping and the ratio of graphene oxide have a pronounced effect on the electrochemical capacitance performance of the nanocomposites.     

Carbon nanotube/dendrimer hybrids as electrodes for supercapacitors

Journal of Solid State Electrochemistry - Carbon nanotubes (CNTs) were surface-modified by a glycodendrimer with four glucose units (4-Gl). Electrodes for supercapacitors based on CNT/4-Gl hybrids...     

Biomass-derived electrodes for flexible supercapacitors

At present, supercapacitors constitute, along with batteries, one of the most promising electrochemical energy storage technology. The recent emerging generation of bendable portable electronic devices has boosted the research of new materials, new processing techniques and new designs that can meet the demands in terms of mechanical stability upon bending or stretching, without compromising their electrochemical performance, at an acceptable cost. Among all the electrode materials currently explored, biomass-derived carbons hold a great potential, due to their low-cost, easy processing techniques, stability and versatility. Here we introduce the range of renewable precursors available and current state-of-the-art performances, and explore the challenges regarding flexibility and sustainability.     

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.     

Graphene-based electrochemical supercapacitors

Graphenes prepared by three different methods have been investigated as electrode materials in electrochemical supercapacitors. The samples prepared by exfoliation of graphitic oxide and by the transformation of nanodiamond exhibit high specific capacitance in aq. H₂SO₄, the value reaching up to 117 F/g. By using an ionic liquid, the operating voltage has been extended to 3·5 V (instead of 1 V in the case of aq. H₂SO₄), the specific capacitance and energy density being 75 F/g and 31·9 Wh kg⁻¹ respectively. This value of the energy density is one of the highest values reported to date. The performance characteristics of the graphenes which are directly related to the quality, in terms of the number of layers and the surface area, are superior to that of single-walled and multi-walled carbon nanotubes.     

Synthesis and high electrochemical performance of polyaniline/MnO2-coated multi-walled carbon nanotube-based hybrid electrodes

Multi-layered electrodes which consist of polyaniline (PANI)/manganese dioxide (MnO₂)-multi-walled carbon nanotubes (MWNTs) are prepared as the electrode materials for supercapacitors. MnO₂-MWNTs are made by the in situ direct coating method to deposit MnO₂ onto MWNTs; the core/shell structure of multi-layered fibrous electrodes can also be obtained by PANI coating onto the MnO₂-MWNTs. The effect of PANI coating on the electrochemical performance and cyclic stability of MnO₂-MWNTs is investigated. From the cyclic voltammograms, the PANI/MnO₂-MWNTs show remarkably enhanced specific capacitance and cycle stability compared to MnO₂-MWNTs, where the highest specific capacitance (350 F/g) is obtained at a current density of 0.2 A/g for the PANI/MnO₂-MWNTs as compared to 92 F/g for pristine MWNTs and 306 F/g for MnO₂-MWNTs. This indicates that the improved electrochemical performance of PANI/MnO₂-MWNTs is due to the enhanced electrical properties by nano-scale-coated MnO₂ onto MWNTs and the PANI coating that leads to the increased cycle stability by delaying the dissolution of MnO₂ during charge/discharge tests.     

Silver nanowires-copper sulfide core/shell nanostructure for electrochemical supercapacitors

This paper reports the synthesis of a new hybrid core (silver nanowires (AgNWs))/shell (copper sulfide (Cu₂S)) nanostructure using simple and inexpensive drop casting and successive ionic layer adsorption and reaction (SILAR) methods. The effects of the thickness of the Cu₂S shell on the Ag NW core on the electrochemical properties of the nanocomposite were studied by varying the number of SILAR cycles from one to four. The structure and microstructure of the prepared composite nanostructure electrode materials were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The AgNW/Cu₂S exhibited a high specific capacitance of 603 Fg^?1 (stainless steel substrate) and 707 Fg^?1 (Ni foam substrate) at a scan rate of 10 mVs^?1 with an energy density of 10.01 Whkg^?1 and 25.33 Whkg^?1 at an applied current of 0.2 mA. This study provides a simple and cost-effective strategy for the fabrication of nanostructured electrodes for supercapacitor applications.     

A high-performance carbon derived from polyaniline for supercapacitors

Activated carbon derived from rod-shaped polyaniline (the diameter of 170 nm) was synthesized by carbonization and subsequent activation with KOH. The obtained activated carbon exhibits a high specific capacitance (455 F g^?1) and remarkable rate capability due to its high specific surface area (1976 m² g^?1), narrow pore size distribution (< 3 nm) as well as short diffusion length. It is indicated that the promising synthetic method used in this work can pave the way for designing new carbon based materials from different polymers for high-performance energy applications.     

Electrochemical characterization on cobalt sulfide for electrochemical supercapacitors

High capacitance at a high charge–discharge current density of 50 mA/cm² for a new type of electrochemical supercapacitor cobalt sulfide (CoS_x) have been studied for the first time. The CoS_x was prepared by a very simply chemical precipitation method. The electrochemical capacitance performance of this compound was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge tests with a three-electrode system. The results show that CoS_x has excellent electrochemical capacitive characteristic with potential range −0.3 ∼ 0.35 V (versus SCE) in 6 M KOH solution. Charge–discharge behaviors have been observed with the highest specific capacitance values of 475 F/g at the current density of 5 mA/cm², even at the high current density of 50 mA/cm², CoS_x also shows the high specific capacitance values of 369 F/g.     

Carbon electrodes with high pseudocapacitance for supercapacitors

Electrochemical properties of electrodes on the basis of CH900-20 activated carbon (AC) cloth were studied in concentrated H₂SO₄ solutions in a wide range of potentials from −0.8 to +1 V RHE. Cyclic voltammetric curves measured in two ranges of potentials were analyzed: in the reversibility range (from 0.1 to 0.9 V) and in the deep cathodic charging range (from −0.8 to 1 V). Electric double layer (EDL) charging occurs in the reversibility range, while faradaic processes of hydrogen chemisorption and its intercalation into carbon take place in the range of negative potentials (<−0.1 V). The intercalation process is controlled by slow solid-phase hydrogen diffusion. For the first time, the maximum value of specific discharge capacity of 1560 C/g was obtained, which is much higher than the values known from the literature for carbon electrodes. On the basis of this value and Faraday’s law, it was assumed that the compound of C₆H is formed in the limiting case of AC deep cathodic charging. The specific charge value grows at an increase in the concentration of H₂SO₄. The mechanism of double intercalation of sulfuric acid and hydrogen into the AC is suggested. The data obtained are used to develop a mathematical charging-discharge model for an AC electrode taking into account the EDL charging, chemisorption, and hydrogen intercalation.     

MnO2/polyaniline hybrid nanostructures on carbon cloth for supercapacitor electrodes

Journal of Solid State Electrochemistry - A facile two-step strategy is developed for synthesis of MnO2/polyaniline (PANI) hybrid nanostructures on carbon cloth (CC). Vertically aligned PANI...     

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.     

Ni-NiO core-shell inverse opal electrodes for supercapacitors

A general template-assisted electrochemical approach was used to synthesize three-dimensional ordered Ni core-NiO shell inverse opals (IOs) as electrodes for supercapacitors. The Ni-NiO IO electrodes displayed pseudo-capacitor behavior, good rate capability and cycling performance.