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.     

Electrochemical study of perlite-barium ferrite/conductive polymer nano composite for super capacitor applications

Polyaniline/perlite-barium ferrite nanoparticles (PANI/PBF-NPs) composite electrodes were studied in here for super capacitor applications. The PBF-NPs synthesized using hydrothermal technique and then the composite electrode was fabricated electrochemically by cyclic voltammetry (CV) technique. Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller nitrogen adsorption/desorption (BET) and fast Fourier transform infrared spectroscopy (FTIR) were employed to study the morphological and structural properties of the prepared electrodes. Furthermore, various electrochemical techniques were used such as CV, Galvano static charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) to investigate their electrochemical performance as well. SEM graphs show uniform distribution of 60-nm PBF-NPs in the PANI filaments. The specific capacitance of PANI and composite electrodes was obtained to be 225 and 330 F/g, respectively. In addition, inclusion of PBF-NPs in the structure of PANI electrode had significantly increased the conductivity of composite electrodes. Continuous charge-discharge cycles test illustrated the good capability of this nano composite material for use as a charge storage device.     

Capacitance properties of poly(3,4-ethylenedioxythiophene)/polypyrrole composites

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 electrochemical capacitance properties were investigated with cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS) techniques with two- or three-electrode cell configuration. The data showed that the specific capacitance of composite electrodes, due to the synergic effect of poly(3,4-ethylenedioxythiophene) (PEDOT) and PPy, is much higher than the values of either pure PEDOT or pure PPy electrodes. Moreover, the composites prepared on the surface of PPy with horn-like structure allow the specific capacitance up to more than 200 F g⁻¹ and have a good cycleability. This implies that PEDOT/PPy composites are promising to be used as electrode material of supercapacitors.     

First-principles analysis of electrochemical hydrogen storage behavior for hydrogenated amorphous silicon thin film in high-capacity proton battery

Silicon material electrodes as proton carriers for high-capacity proton battery have only been proposed for such a short period of time that their physicochemical properties and electrochemical hydrogen storage behavior during charge and discharge processes remain nearly uncharted territory. Herein, the hydrogenated amorphous silicon (a-Si:H) thin film electrodes are prepared by radio frequency sputtering followed by ex-situ hydrogenation. The electrochemical properties of a-Si:H electrodes are tested experimentally, and the electrochemical hydrogen storage behaviors of a-Si:H electrodes are analyzed by first-principles calculations. The results show that the hydrogenation process significantly increases the electrochemical capacity of the electrodes and reduces the band gap of the electrode structure. The electrode exhibits weak conductivity during the initial charging, but the instability of the electrode electronic structure during the later charging results in a slight fluctuation of the electrochemical charging process. The a-Si:H electrode have better electrochemical hydrogen storage/release reversibility than non-hydrogenated electrodes, but this reversibility is weakened by oxygen atoms covered on the electrode surface. The electrochemical hydrogen storage process is easier to accomplish than the electrochemical desorption process of hydrogen evolution reaction for the a-Si:H electrodes. The a-Si:H thin film electrode is more stable on the Ni(111) substrate surface and the good conductivity of the electrode/substrate interface provides convenient conditions for the free transport of electrons in the electrochemical charge/discharge processes. We believe that these results perfectly explain the microscopic mechanisms responsible for the electrode reaction and electrochemical behavior of a-Si:H electrodes in this type of proton battery, and have a certain reference value in understanding the physicochemical properties and electrochemical hydrogen storage behavior of silicon material electrodes applied to other types of batteries during charge/discharge processes.     

Pd‐Ni/Cd loaded PPy/Ti composite electrode: Synthesis,characterization, and application for hydrogen storage

A wide compositional range of Pd‐Ni/Cd on polypyrrole (PPy)‐modified Ti plates (Pd‐Ni/Cd/PPy/Ti) was fabricated via electrochemical deposition. The hydrogen absorption properties of the prepared Pd‐Ni/Cd/PPy/Ti electrodes were evaluated using cyclic voltammetry and chronoamperometry in acidic media. The optimal Pd₃₆‐Ni₇/Cd₅₇/PPy/Ti electrode achieved a hydrogen storage capacity of 331.3 mC cm^?2 mg^?1 and an H/Pd ratio of 0.77. The enhancement of the hydrogen storage was attributed to a synergistic effect between the Pd‐Ni/Cd catalysts. The surface morphology, crystallinity, and chemical composition of the Pd‐Ni/Cd/PPy/Ti electrode were characterized using scanning electron microscope (SEM), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS), respectively. Hydrogen spillover occurred on the trimetallic catalysts, and secondary hydrogen spillover occurred on the PPy/Ti support. The enhanced hydrogen sorption capacity was due to both the synergistic effect of the trimetallic catalysts and the assistance of PPy, making Pd‐Ni/Cd/PPy/Ti a promising hydrogen storage material.     

Cauliflower‐shaped ternary nanocomposites with enhanced power and energy density for supercapacitors

The present research work aimed to study the electrochemical performance of the rGO/PPY/PANI ternary nanocomposite electrodes for supercapacitor applications. The nanocomposites have been prepared by physical blending of rGO with conducting polymers PANI and PPY in five different ratios. The prepared nanocomposites were examined by XRD, IR, Raman, SEM, and XAS characterizations, and from the results, it was found that ternary nanocomposites formed in cauliflower shape, in which PPY and PANI nanoparticles are decorated on to the rGO matrix. In addition, the electrochemical performance of the prepared nanocomposites were studied using cyclic voltammetry, galvanostatic charge‐discharge, and electrochemical impedance spectroscopic studies. The highest values of capacitance, energy density, and power density values achieved were 317.5 F/g, 254 Wh/kg, and 1508.9 W/kg for nanocomposite, respectively, as expected from the synergistic properties of two types of electrode materials resulting in the nanocomposites with hybrid and improved properties. Further, the cyclic stability was also analyzed by performing 4000 long cycles, and the retained capacitance during such long cycles indicates the high potential of rGO/PPY/PANI ternary nanocomposites as electrodes for future energy requirement.     

Composite sodium p-toluenesulfonate/polypyrrole/TiO2 nanotubes/Ti anode for sodium ion battery

Composite sodium p-toluenesulfonate/polypyrrole/TiO₂ nanotubes/Ti was designed and synthesized for sodium ion battery anode via facile electrochemical methods. The obtained composite sodium p-toluenesulfonate/polypyrrole/TiO₂ nanotubes/Ti (TsONa/PPy/TiO₂NT/Ti) electrode was investigated in terms of SEM, EDX, FTIR, galvanostatic charge/discharge and AC impedance. As expected, the composite TsONa/PPy/TiO₂NT/Ti electrode displayed higher electrochemical performances than the bare TiO₂NT/Ti electrode. For example, the reversible capacity after 50 cycles was still as high as about 200 mAh/g, higher than 170 mAh/g of TiO₂NT/Ti electrode. High Na-storage activities of both TiO₂NT and TsONa/PPy, high conductivity of TsONa-doped PPy and the synergy effect among the various components may be responsible for the improved electrochemical performances.     

Cyclic voltammetry and electrochemical impedance of MmNi3.6Co0.7Mn0.4Al0.3 alloy electrode before and after treatment with a hot alkaline solution containing reducing agent

The hydrogen storage alloy (MmNi_3.6Co_0.7Mn_0.4Al_0.3, Mm=Ce-rich mischmetal) electrodes were treated in an alkaline solution containing a reducing agent (KBH₄ or NaH₂PO₂). Cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) were applied to characterize the electrochemical properties of the alloy electrodes before and after surface treatment. The results show that the charging efficiency and electrochemical reaction activity of metal hydride (MH) electrode were markedly improved by the treating. The reaction of the untreated MH electrode was chiefly controlled by the charge transfer process at the interface of electrode/electrolyte, or by the mixture of the charge transfer and hydrogen diffusion processes, but the reaction of the treated electrode was mainly controlled by hydrogen atom's diffusion in the alloy bulk. The results of EIS measurements indicate that the charge transfer resistance of MH electrode was reduced and its specific surface area augmented after treatment.     

Electrodeposited Pd nanoparticles on polypyrole/nickel foam for efficient methanol oxidation

The present work describes the Ni foam (Ni–F)/polypyrrole (PPy)/palladium (Pd) (Ni–F/PPy/Pd) multilayered catalysts via a facile electrochemical technique. Potentiostatic deposition of PPy on the surface of Ni–F is followed by galvanostatic deposition of Pd nanoparticles on Ni–F/PPy acted as supports for electrochemical deposition of Pd nanoparticles. The produced catalysts are utilized for electrocatalytic methanol oxidation in alkaline media. Chronoamperometry (CA), cyclic voltammetry (CVs), and electrochemical impedance spectroscopy (EIS) techniques are used to examine the electrocatalytic performance of Ni–F/PPy/Pd based electrodes for methanol oxidation. The polypyrrole modification on Ni–F leads to an improvement in the electrocatalytic activity of the Ni-F/PPY-Pd catalysts toward methanol oxidation. As an open-pored, porous metal with high electrical conductivity, nickel foam produces a substantial amount of active area during the modification of Pd and polypyrrole, which results in significant catalytic activity and a rapid rate charge transfer reaction kinetics on methanol oxidation. The Ni–F/PPy/Pd10 catalyst exhibits enhanced specific activity than its counterparts and a reduced onset potential for methanol oxidation, as well as a low Tafel slope. Based on these results, Ni–F/PPy/Pd10 is suggested as a good material for the anode in the electrocatalytic oxidation of methanol.     

Study the effect of conductive fillers on a secondary Zn electrode based on ball-milled ZnO and Ca(OH)2 mixture powders

The active materials of the secondary Zn electrode containing a mixture powder of zinc oxide (ZnO) and calcium hydroxide (Ca(OH)₂) powders were prepared by a ball-milled method. The characteristic properties of active materials of ball-milled ZnO + Ca(OH)₂ mixture powders were examined by scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) system, X-ray diffraction (XRD) analysis, and micro-Raman spectroscopy. The prepared Zn powder electrodes were by using the ball-milled active materials powder +2 wt.% highly electronic conductive fillers, i.e., nano-copper or carbon nanotubes (CNTs) powder. The electrochemical properties of the secondary Zn electrodes without and with the conductive fillers were studied by using cyclic voltammetry (CV) and galvanostatic charge/discharge tests. It was found that the charge/discharge properties of the secondary Zn electrode could be improved when the nano-sized conductive fillers were added into the electrode. In fact, it may be due to the formation of a better electronic conduction path in the electrode matrix. In particular, it was found that the best electrochemical properties were the secondary Zn electrode with 2 wt.% nano-copper fillers. According to the results, it is demonstrated here that the CV method is a quick technique to effectively evaluate the performance of a secondary Zn electrode.     

PPy doped PEG conducting polymer films synthesized on LiFePO4 particles

In this work, polyethyleneglycole (PEG) is introduced into polypyrrole (PPy) film coated on LiFePO₄ powder particles to promote the properties of cathode material for lithium-ion batteries. The enhancement of the electrochemical activity by the substitution of a carbon with electrochemically active polymer is investigated. Films of the PPy doped with the PEG were prepared by the chemical oxidative polymerization of pyrrole (Py) monomer. PEG has been added as an additive during polymerization process to improve mechanical and structural properties of the PPy in final PPy/PEG-LiFePO₄ cathode material. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge measurements were employed to characterize the electrochemical properties of PPy/PEG-LiFePO₄ material. The electrochemical performance of PPy-LiFePO₄ electrodes was greatly improved by introduction of PEG into the PPy films. Charge/discharge measurements confirmed the increase in capacity when applying PEG in PPy. The morphology and particle sizes of the prepared cathode powder material were investigated by scanning electron microscopy (SEM) and particle size analysis (PSA). Distribution of PPy and PPy/PEG films onto the LiFePO₄ particles surface was studied by time of flight secondary ion mass spectrometry (TOF-SIMS). In addition to polymeric coating layer on the surface of PPy-LiFePO₄ composite particles, some PPy unequally distributed between the particles was found. The median diameter value is 4.92 μm for PPy-LiFePO₄ sample. TOF-SIMS measurements and SEM images confirmed that thickness of polypyrrole coating on LiFePO₄ particles is about 100 nm.     

Electrochemical properties of free‐standing polypyrrole/graphene oxide/zinc oxide flexible supercapacitor

We report the preparation of a polypyrrole/graphene oxide/zinc oxide nanocomposite on a nickel foam using a simple and rapid single‐step electrochemical deposition process under ambient conditions. A free‐standing flexible supercapacitor was fabricated by sandwiching a polyvinyl alcohol hydrogel polymer electrolyte between two layers of the as‐prepared ternary nanocomposite electrodes. The electrochemical properties of the free‐standing supercapacitor were analyzed using a two‐electrode system. The supercapacitor achieved a specific capacitance of 123.8 F/g at 1 A/g, which was greater than its single (39.1 F/g) and binary (81.3 F/g) counterparts. This suggests that ZnO acts as a spacer and support that hinders the ternary structure from collapsing and subsequently enhances the diffusion of ions within the matrix. The flexible supercapacitor exhibited remarkable electrochemical stability when subjected to bending at various angles. The cycling stability of the ternary nanocomposite showed a favorable specific capacitance retention of more than 90% after 1000 cycles for mild alkaline electrolytes compared with strong alkali electrolytes. The presence of glycerin in the polymer electrolyte enabled the supercapacitor to perform better under the vigorous cycling condition. The potential of the as‐fabricated supercapacitor for real applications was manifested by its ability to light up a light‐emitting diode after being charged. Copyright © 2014 John Wiley & Sons, Ltd.     

A paste type negative electrode using a MmNi5 based hydrogen storage alloy for a nickel–metal hydride (Ni–MH) battery

Different conducting materials (nickel, copper, cobalt, graphite) were mixed with a MmNi₅ type hydrogen storage alloy, and negative electrodes for a nickel–metal hydride(Ni–MH) rechargeable battery were prepared and examined with respect to the discharge capacity of the electrodes. The change in the discharge capacity of the electrodes with different conducting materials was measured as a function of the number of electrochemical charge and discharge cycles. From the measurements, the electrodes with cobalt and graphite were found to yield much higher discharge capacities than those with nickel or cobalt. From a comparative discharge measurements for an electrode composed of only cobalt powder without the alloy and an electrode with a mixture of cobalt and the alloy, an appreciable contribution of the cobalt surface to the enhancement of charge and discharge capacities was found.     

Contribution of polyaniline coating to the stability and performance of nickel hydroxide based electroactive materials

This study has been conducted for investigating the contribution of polyaniline (PANI) to the electroactivity of nickel hydroxide (NH) by using a combination of electrochemical, structural and morphological characterization techniques. NH, PANI and nickel hydroxide/PANI composite (NHP) electrodes were produced on nickel foam substrates. Electrodeposition and chemical bath deposition methods were used for the preparation of NH and PANI, respectively. All the electrochemical experiments were conducted in alkaline solutions. NH and PANI were used as reference materials and exhibited properties in accordance with the literature. Namely, for NH electrode capacity decayed by cycling because of the phase transformation from α to β-Ni(OH)₂, and particles growth from 350 to 850 nm. Also, flower-like structure of the as prepared Ni(OH)₂ faded after 2000 cycles. On the other hand, PANI electrode although exhibited a decrease in the conductivity because of its degradation retained its capacity over cycling because of swelling and shrinking that led to an increased surface area. Composite electrode consisting of PANI and NH resulted in an improvement of capacity retention. At the beginning of cycling capacitance of the composite electrode was 0.64 F/cm², capacity decreased to 0.47 F/cm² after 500 cycles then, continuously increased and finally reached to 0.54 F/cm² after 2000 cycles. Presence of PANI in combination with NH, limited the particle growth and contributed to the preservation of flower like structure of NH. Contrary to both NH and PANI electrodes, charge transfer resistance of NHP exhibited a decrease with cycling indicating a synergy between NH and PANI in addition to morphological changes.     

Layered NiFe-LDH/MXene nanocomposite electrode for high-performance supercapacitor

Layered double hydroxide (LDH) is potentially excellent supercapacitor (SC) materials, but the low conductivity and easy agglomeration limit the further improvement of their electrochemical properties. Therefore, LDHs are requisite to grow on some conductive substrates to produce high-performance SC. In this paper, the conductive two-dimensional (2D) transition metal carbides, nitrides and carbonitrides (called MXene) were explored as the substrate to directly deposit NiFe-LDH nanosheets by a one-step hydrothermal method, then a three-dimensional (3D) porous NiFe-LDH/MXene electrode was obtained. The morphology and electrochemical performance of the composite electrodes were analyzed and investigated. The results show that the NiFe-LDH/MXene electrode has larger specific capacitance (720.2 F/g) than NiFe-LDH (465 F/g), and the capacitance of the composite electrode retained 86% after 1000 cycles (only 24% for NiFe-LDH), showing excellent cycle stability. The improved electrochemical performance of the composites is caused by the stable sheet-like structure of NiFe-LDH during charge-discharge time and the conductive network formed by the MXene, which can accelerates electron transport. In addition, the asymmetric SC based on NiFe-LDH/MXene positive electrode display a power density of 758.27 W/kg at an energy density of 42.4 Wh/Kg. These results indicate the NiFe-LDH/MXene composites can be applied as the novel candidate of high-performance SC electrodes.     

Synthesis of three-dimensional graphene@Ni(OH)2 nanoflakes on Ni foam by RF magnetron sputtering for application in supercapacitor

Three-dimensional graphene@Ni(OH)₂ nanoflake array grown on Ni foam (G/Ni(OH)₂/NF) as a binder-free electrode of supercapacitor was prepared by combining a one-step hydrothermal approach and Radio frequency (RF) magnetron sputtering technique. Its electrochemical properties were further investigated by the cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectra. The G/Ni(OH)₂/NF showed high specific capacitance (4.0F/cm² at 1.0 mA/cm²), good rate charge-discharge capability and long cycling stability (ca. 90.6% of its initial value). This work provides a new method to prepare 3D porous electrode materials based on graphene for application in electrochemical energy storage.     

Preparation and characterization of copper oxide particles/polypyrrole (Cu2O/PPy) via electrochemical method: Application in direct ethanol fuel cell

The electrocatalytic performance of Polypyrrole-Copper oxide particles modified carbon paste electrode (Cu₂O/PPy/CPE) for electrocatalytic oxidation of ethanol was reported for the first time in alkaline media. The composite Cu₂O/PPy was prepared using a facile approach consisting on the deposition of Polypyrrole film on CPE using galvanostatic mode then followed by the deposition of Copper particles at a constant potential. Scanning electron spectroscopy (SEM), infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the structural and electrochemical properties of the Cu₂O/PPy/CPE and to explain the mechanism of electrooxidation of ethanol. The experimental parameters that influence the electrooxidation of ethanol were investigated and optimized. Our findings suggest that the electrodeposition of Copper particles on Polypyrrole film enhanced the catalytic activity towards the ethanol oxidation with a peak current density of 2.25 mA cm⁻² at 0.8 V vs Ag/AgCl, which is 2.6 times higher than the peak current density obtained by PPy/CPE electrode. It important to note that the saturation limit reaches a value of 5 M. To summarize, the good catalytic activity, stability and easy preparation make the Cu₂O/PPy composite as an excellent electrocatalyst for ethanol oxidation.     

Characterizing capacity loss of lithium oxygen batteries by impedance spectroscopy

Polymer based carbon aerogels were prepared by synthesis of a resorcinol formaldehyde gel followed by pyrolysis at 1073 K under Ar and activation of the resultant carbon under CO₂ at different temperatures. The prepared carbon aerogels were used as active materials in the preparation of cathode electrodes for lithium oxygen cells and the electrochemical performance of the cells was evaluated by galvanostatic charge/discharge cycling and electrochemical impedance measurements. It was shown that the storage capacity and discharge voltage of a Li/O₂ cell strongly depend on the porous structure of the carbon used in cathode. EIS results also showed that the shape and value of the resistance in the impedance spectrum of a Li/O₂ cell are strongly affected by the porosity of carbon used in the cathode. Porosity changes due to the build up of discharge products hinder the oxygen and lithium ion transfer into the electrode, resulting in a gradual increase in the cell impedance with cycling. The discharge capacity and cycle life of the battery decrease significantly as its internal resistance increases with charge/discharge cycling.     

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.