MWCNTs/metal (Ni, Co, Fe) oxide nanocomposite as potential material for supercapacitors application in acidic and neutral media

Supercapacitive properties of synthesised metal oxides nanoparticles (MO where M = Ni, Co, Fe) integrated with multi-wall carbon nanotubes (MWCNT) on basal plane pyrolytic graphite electrode (BPPGE) were investigated. Successful modification of the electrode with the MWCNT-MO nanocomposite was confirmed with spectroscopic and microscopic techniques. Supercapacitive properties of the modified electrodes in sulphuric acid (H₂SO₄) and sodium sulphate (Na₂SO₄) electrolytes were investigated using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic constant current charge–discharge (CD) techniques. The specific capacitance values followed similar trend with that of the cyclic voltammetry and the electrochemical impedance experiments and are slightly lower than values obtained using the galvanostatic charge–discharge cycling. MWCNT-NiO-based electrode gave best specific capacitance of 433.8 mF?cm^?2 (ca 2,119 F?g^?1) in H₂SO₄. The electrode exhibited high electrochemical reproducibility with no significant changes over 1,000 cyclic voltammetry cycles.     

Electrochemical behaviour of conducting polymers obtained into clay-catalyst layers. An in situ Raman spectroscopy study

In this paper we present the study of the electrochemical properties of the following conducting polymers: poly(o-anisidine), polyaniline and copolymers of aniline and o-anisidine obtained by a new synthetic method. The polymers are synthesized in free-of-acid conditions, using an activated montmorillonitic clay catalyst, known as Maghnite-H⁺ (Mag-H) as proton source. The electrochemical behaviour of poly(o-anisidine) created using Mag-H (PoANI-MagH) and their copolymers with aniline is quite different of those polymers created in HCl solution. In situ Raman data suggest that the structure of PoANI-MagH is a mixture of conducting (polyaniline-type) and redox (phenoxazine or phenazine-type) segments.     

Synthesis of Poly(<Emphasis Type="Italic">o</Emphasis>-anisidine)/H<Subscript>2</Subscript>SO<Subscript>4</Subscript> Film for the Development of Glucose Biosensor

The poly(o-anisidine)–sulfuric acid–glucose oxidase (POA–H₂SO₄–GOx) electrode has been investigated in the present work. Platinum electrode was used for the synthesis of poly (o-anisidine)–sulfuric acid (POA–H₂SO₄) film using galvanostatic method with 0.2 M o-anisidine, 1.0 M H₂SO₄ solution, 1.0 pH and 2 mA/cm² applied current density. The synthesized film was characterized using electrochemical technique, conductivity measurement, UV–visible spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. GO_X was immobilized on synthesized POA–H₂SO₄ film by cross-linking via glutaraldehyde in phosphate and acetate buffer. The Michaelis–Menten constant ( K_\textm￠K_{\text{m}}^\prime ) was determined for the immobilized enzyme. The glucose oxidase electrode shows the maximum current response at pH 5.5 and potential 0.6 V. The sensitivity of POA–H₂SO₄–GO_X electrode in phosphate and acetate buffer has been recorded. The results of this study reveal that the phosphate buffer gives fast response as compared to acetate buffer in amperometric measurements.     

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.     

Electrochemical and chemical synthesis of nanostructure copoly(aniline-o-anisidine-o-toluidine) and study of its electrochemical behavior in organic sulfonic acid media

Terpolymerization of aniline, o-anisidine and o-toluidine was carried out by electrochemical and interfacial chemical polymerization. All homopolymers and terpolymer thin films have been synthesized through electropolymerization at room temperature in aqueous solutions containing 0.5 M of organic sulfonic acid, such as p-toluene sulfonic acid, methane sulfonic acid, sulfosalicylic acid, dodecylbenzene sulfonic acid, and 0.1 M of aniline, o-anisidine and o-toluidine monomers, using cyclic voltammetry method, applying a sequential linear potential scan at a rate of 25 mV s^?1 between ?0.1 and 0.9 V. The electrochemical terpolymerization has been performed at various mole ratios of monomers. Nanoparticles obtained from conjugation of homo- and terpolymer with organic sulfonic acids, were prepared by a chemical oxidation via interfacial chemical polymerization. SEM micrographs, FTIR spectra and conductivity measurements using four-probe method were applied for the characterization of the products. Terpolymer was characterized by higher conductivity than poly-o-toluidine and lesser than polyaniline and poly-o-anisidine. The solubility of terpolymers was dependent on the monomers mole ratio.     

Synthesis of ternary polypyrrole/Ag nanoparticle/graphene nanocomposites for symmetric supercapacitor devices

In this study, novel ternary synthesis of reduced graphene oxide (rGO) sheets via intercalation of Ag nanoparticles (Ag) and polypyrrole (PPy) was obtained for supercapacitor evaluations. The synthesis procedure of nanocomposite is simple, cheap, and ecologically friendly. The nanocomposites were analyzed by Fourier transform infrared-attenuated transmission reflectance (FTIR-ATR) and scanning electron microscopy-energy dispersion X-ray analysis (SEM-EDX). In addition, electrochemical performances of electrode active materials (rGO/Ag/PPy) of the samples were tested by means of galvanostatic charge/discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The highest specific capacitance and energy density of rGO/Ag/PPy nanocomposite were obtained as C_sp = 1085.22 F/g and E = 36.92 Wh/kg for [rGO]_o/[Py]_o = 1/5 at 4 mV/s in 1 M H₂SO₄ solution. Under the optimized preparation conditions in different initial feed ratios ([rGO]_o/[Py]_o = 1/1, ½, 1/5, and 1/10) of rGO/Ag/PPy, nanocomposites acquired a high Coulombic efficiency, and a retention of 66% of its initial capacitance for [rGO]_o/[Py]_o = 1/10 after 1000 cycles. GCD and EIS measurements of rGO/Ag/PPy nanocomposite electrode active material allowed for supercapacitor applications.     

A Novel V<Subscript>2</Subscript>AlC Electrode Material for Supercapacitors

A novel V₂AlC electrode material for supercapacitors was investigated in this study. The structure and surface morphology were examined using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The formation of irregularly shaped V₂AlC with different particle size distribution was confirmed by XRD and FESEM. The electrochemical measurements were performed by cyclic voltammetry (CV), galvanostatic charge discharge and electrochemical impedance spectroscopy (EIS). V₂AlC electrode exhibited 27.6 F g^–1 of specific capacitance at the current density of 0.5 A g^–1. The specific capacitance of V₂AlC electrode remained 93.8% of the first cycle after 2000 cycles. V₂AlC has great potential for application in supercapacitors.     

Conformal Surface Coatings to Enable High Volume Expansion Li‐Ion Anode Materials

An alumina surface coating is demonstrated to improve electrochemical performance of MoO₃ nanoparticles as high capacity/high‐volume expansion anodes for Li‐ion batteries. Thin, conformal surface coatings were grown using atomic layer deposition (ALD) that relies on self‐limiting surface reactions. ALD coatings were tested on both individual nanoparticles and prefabricated electrodes containing conductive additive and binder. The coated and non‐coated materials were characterized using transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, electrochemical impedance spectroscopy, and galvanostatic charge/discharge cycling. Importantly, increased stability and capacity retention was only observed when the fully fabricated electrode was coated. The alumina layer both improves the adhesion of the entire electrode, during volume expansion/contraction and protects the nanoparticle surfaces. Coating the entire electrode also allows for an important carbothermal reduction process that occurs during electrode pre‐heat treatment. ALD is thus demonstrated as a novel and necessary method that may be employed to coat the tortuous network of a battery electrode.     

The electrochemical synthesis of poly(o-phenylenediamine) on stainless steel and its corrosion protection ability in 3.5 % NaCl solution

In this study, electrochemical synthesis of poly(o-phenylenediamine) (PoPDA) on 316L stainless steel and its corrosion inhibition effect were studied. Electropolymerization of o-phenylenediamine (oPDA) was carried out by a potentiodynamic method using 0.5 M H₂SO₄ solution containing 0.05 M oPDA monomer. The corrosion protection ability of the PoPDA in 3.5 % NaCl was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, and change of open circuit potential with immersion time (E_OCP ? t). The results showed that PoPDA acted as a protective layer on stainless steel against corrosion in 3.5 % NaCl solution.     

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.     

Electrochemical corrosion resistance performance of sustainable resource-based nanoconducting polymer composites in alkaline medium

The corrosion resistance performance of poly (otoluidine) (POT)-dispersed castor oil-polyurethane, (COPU) nanocomposite coatings, POT/COPU, with three different compositions (i.e. 0.25, 0.5 and 1.0 wt%) in alkaline medium is studied. The coatings are applied on mild steel specimens by brushing. Corrosion resistance behaviour of these coatings is investigated using potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS) and by weight loss. The morphological behaviour of corroded and uncorroded coated specimens is investigated by scanning electron microscopy (SEM). It is interesting to report that the presence of conducting polymer nanoparticles in POT/COPU coatings suppresses the saponification of COPU in an alkaline environment. These investigations show that the dispersion of POT in COPU remarkably improves the corrosion resistance performance of COPU in alkaline media. POT/COPU (1.0 wt%) coatings have potential as anticorrosive-coating materials in alkaline media at higher pH. These coatings have a higher resistance to alkaline medium in comparison to other compositions.     

Composite layers consisting of polyaniline and poly(o-phenylenediamine): Electrochemical deposition, electrochromic and electrocatalytic properties

The composite polymer layers consisting of polyaniline (PANI) and poly(o-phenylenediamine) (poly(o-PDA)) were electrodeposited on a platinum electrode by simultaneous electrochemical oxidation of corresponding monomers from aquaeous hydrochloric solutions. The growth of PANI and poly(o-PDA) occurs separately resulting in layers with two distinct, finely distributed phases. The first deposited layers are composed mainly of poly(o-PDA) and become richer in PANI as the electropolymerization proceeds. The aniline/o-PDA copolymer was not formed during electrodeposition, as evidenced by cyclic voltammetry and Fourier-transformed IR spectroscopy. It was demonstrated that the electrochromic properties of resulting composite layers are the combination of yellow/brown-reddish and green/dark blue observable color transitions which are characteristics of poly(o-PDA) and PANI, respectively. Electrocatalytic properties of the electrosynthesized composite layers were investigated on quinone/hydroquinone (Q/H₂Q) redox system and it was shown that the composite layers increase the heterogeneous electron transfer rate with a magnitudes ranging from those obtained on pure poly(o-PDA) to those obtained on pure PANI layer.     

Solid electrolyte interphase (SEI) electrode: Part III. Deposition-dissolution process of lithium in thionyl-chloride solution

The deposition-dissolution mechanism of lithium on stainless steel and calcium electrodes in 1 M LiAlCl₄ -thionyl-chloride solution is studied by pulse galvanostatic and ac techniques. The metal -solution interfacial capacitance of the stainless steel electrode is about 30 μF cm^?2 which is higher by an order of magnitude than the capacitance of lithium-coated stainless steel and either pure or lithium-coated calcium. The lower capacitance is attributed to the existence of a solid electrolyte interphase (SEI) on the coated stainless steel or the calcium electrode.Significantly different is observed upon deposition of lithium on stainless steel or calcium. Deposition on stainless steel takes place only after prior formation of a SEI on the electrode (by passage of about 20 mC cm^?2), while deposition on calcium starts immediately after the electrode capacitance has been charged (by about 5 μC cm^?2). Furthermore, deposition of about 3% of a monolayer of lithium on calcium is enough to stabilize its potential at 0.0 V vs. LiRE.On the lithium-coated stainless steel electrode, a linear relationship between the current and over-potential is observed for up to 700 mV. This indicates a Tafel slope > V. During lithium deposition on stainless steel, the SEI resistivity is about 1.5 × 10⁷ Ω-cm and its thickness is about 10 nm.Under open circuit potential, the deposited lithium corrodes at an apparent rate of 100 μA cm^?2. Rapid fluctuations of the electrode potential during the corrosion or dissolution process are accounted for by a break and repair mechanism of metallic contact between lithium deposited within the SEI and the current collector.     

Electropolymerization,characterization and corrosion protection evolution of poly(4-aminomethyl-5-hydroxymethyl-2-methylpyridine-3-ol) on steel and copper

The electrochemical synthesis of poly(4-aminomethyl-5-hydroxymethyl-2-methyl pyridine-3-ol) on steel and copper electrodes was achieved in both sulfuric acid and oxalic acid by cyclic voltammetry technique. Characterization of the polymer films were achieved by Fourier transforms infrared spectroscopy technique (FTIR) and scanning electron microscope (SEM). Corrosion performance of coatings was investigated in 0.1 M H₂SO₄ by potentiodynamic polarization and electrochemical impedance (EIS) spectroscopy techniques.     

Enhancing effect of boron trifluoride diethyl etherate electrolytes on capacitance performance of electropolymerized poly[poly(<Emphasis Type="Italic">N</Emphasis>-vinyl-carbazole)] films

In this paper, poly[poly(N-vinyl-carbazole)] (PPVK) films electrodeposited in tetrahydrofuran (THF) containing 12 % boron trifluoride diethyl etherate (BFEE) were studied as electrode active material for supercapacitors. The morphology and thermal property were characterized by SEM, atomic force microscopy (AFM), and thermogravimetry (TG), respectively. The electrochemical capacitive behaviors of the PPVK films were also investigated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The electrochemical results showed that the specific capacitance of PPVK films in CH₃CN solution was about 126 mF cm^?2 at 1.5 mA cm^?2 and the capacitance retention was only 14.4 % after 1000 cycles. It was exciting to improve the specific capacitance up to 169.3 mF cm^?2 at 1.5 mA cm^?2 and to make the cyclic stability increase to 81.8 % capacitance retention after 5000 cycles when the equivalent BFEE was added into the CH₃CN solution containing 0.05 M Bu₄NBF₄ electrolyte. These results clearly demonstrated that BFEE was an efficient promoter for the enhancement of the capacitance performance of PPVK films. Therefore, with the help of BFEE electrolyte, the PPVK films have potential application as capacitive materials in high-performance energy storage devices.     

Cobalt ion-doped polyaniline,poly(N-methylaniline), and poly(N-ethylaniline): electrosynthesis and characterisation using electrochemical methods in acidic solutions

Cobalt ion (Co²⁺)-doped polyaniline (PANI-Co), poly(N-methylaniline) (PNMA-Co), and poly(N-ethylaniline) (PNEA-Co) films were synthesised electrochemically on a pencil graphite electrode (PGE) and their electrochemical properties were investigated for supercapacitor applications. The polymer film-coated electrodes (PGE/PANI-Co, PGE/PNMA-Co, and PGE/PNEA-Co) thus obtained were characterised by scanning electron microscopy (SEM) and different electrochemical methods. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were employed in 0.1 M H₂SO₄ solution to calculate the specific capacitance (C _S) values of the electrodes. The maximum C _S of 192.94 F g^?1, 139.83 F g^?1, and 47.12 F g^?1 were achieved for PGE/PANI-Co, PGE/PNMA-Co, and PGE/PNEA-Co at 1 mV s^?1, respectively. On the other hand, the charge/discharge stability of the electrodes was analysed using the repeating chronopotentiometry (RCP) method. The RCP measurements indicate that the electrodes could be used as an electrode active material for low voltage supercapacitor applications.     

Indirect Transformation of Coordination‐Polymer Particles into Magnetic Carbon‐Coated Mn3O4 (Mn3O4@C) Nanowires for Supercapacitor Electrodes with Good Cycling Performance

Carbon‐coated Mn₃O₄ nanowires (Mn₃O₄@C NWs) have been synthesized by the reduction of well‐shaped carbon‐coated bixbyite networks and characterized by TEM, X‐ray diffraction, X‐ray photoelectron spectroscopy, and electrochemical experiments. To assess the properties of 1D carbon‐coated nanowires for their use in supercapacitors, cyclic voltammetry and galvanostatic charging–discharging measurements were performed. Mn₃O₄@C NWs could be charged and discharged faster and had higher capacitance than bare Mn₃O₄ nanostructures and other commercial materials. The capacitance of the Mn₃O₄@C NWs was 92 % retained after 3000 cycles at a charging rate of 5 A g^?1. This improvement can be attributed to the carbon shells, which promote fast Faradaic charging and discharging of the interior Mn₃O₄ core and also act as barriers to protect the inner core. These Mn₃O₄@C NWs could be a promising candidate material for high‐capacity, low‐cost, and environmentally friendly electrodes for supercapacitors. In addition, the magnetic properties of the as‐synthesized samples are also reported to investigate the influence of the carbon coating.     

Novel poly(1H-benzo[g]indole)/TiO2 nanocomposites for high-performance electrochromic supercapacitor application

Poly(1H-benzo[g]indole) (PBIn)/TiO₂ nanocomposites with core-shell nanorod array morphology are successfully prepared via simply hydrothermal synthesis combined with electrochemical polymerization. The synergistic effect between PBIn and TiO₂ and the matched energy level distribution make PBIn/TiO₂ nanocomposites have a specific capacitance of 29.65 mF cm⁻². At the same time, it can reversibly change between light yellow and light green and show excellent cycling stability (86% retention after 3000 cycles). Thus, the electrochromic supercapacitor device (ESD) is also constructed based on PBIn/TiO₂ nanocomposite and poly(3,4-ethylenedioxythiophene). This ESD shows a good specific capacitance (13.2 mF cm⁻²) and high-coloring efficiency (487 cm² C⁻¹). In the charging and discharging stage, the color of ESD can reversibly change between yellow and dark blue. Thus, the accumulated energy state of the ESD can be simply judged by monitoring the color or transmittance value of the device. To verify the good energy storage and actual application, this ESD can light up the Light Emitting Diode (LED) after charging, which provides new possibilities for the application of intelligent supercapacitors in the future.     

Effect of thermal annealing of poly(3-octylthiophene) films covered stainless steel on corrosion properties

The effect of thermal annealing of poly(3-octylthiophene) (P3OT) coatings on the corrosion inhibition of stainless steel in an NaCl solution was investigated. P3OT was synthesized by direct oxidation of the 3-octylthiophene monomer with ferric chloride (FeCl₃) as oxidant. P3OT films were deposited by drop-casting technique onto 304 stainless steel electrode (304SS). 304SS coated with P3OT films were thermally annealed during 30 h at different temperatures (55°C, 80°C, and 100°C). The corrosion resistance of stainless steel coated with P3OT in 0.5 M NaCl aqueous solution at room temperature was investigated by using potentiodynamic polarization curves, linear polarization resistance, and electrochemical impedance spectroscopy. The results indicated that the thermal treatment at 80°C and 100°C of P3OT films improved the corrosion resistance of the stainless steel in NaCl solution; the speed of corrosion diminished in an order of magnitude with regard to the 304SS. In order to study the temperature effect in the morphology of the coatings before and after the corrosive environment and correlate it with corrosion protection, atomic force microscopy and scanning electron microscopy were used. Morphological study showed that when the films are heated, the grain size increased and a denser surface was obtained, which benefited the barrier properties of the film.     

Electropolymerization of Mefenamic Acid on Copper and Copper Based Alloy as a New Strategy to Control the Release of Copper Ions from Copper Containing Devices

Poly-2-(2,3-dimethylanilino) benzoic acid (PMF) coatings on copper and brass alloy were synthesized by electrochemical oxidation of 2-(2,3-dimethylanilino) benzoic acid in the presence of oxalic acid as the reaction medium. Electrodeposition was carried out using the cyclic voltammetry technique using a silver/silver-chloride standard electrode, with a scan rate of 600 mV min^–1. Smooth and well adhered PMF coatings were electrosynthesized during sequential scanning of the potential in the range–500 mV to 1400 mV on copper and brass alloy. The electrodeposited coatings were characterized by recording the oxidation peaks at 122 mV for Cu and–0.7 mV for brass, in cyclic voltammetry and using scanning electron microscopy (SEM). Corrosion inhibition efficiency of coated copper and brass alloy was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The impedance results showed that the inhibition efficiency of coated copper is 89% and for coated brass 79.4% compared to the uncoated copper and brass in 0.1 M H₂SO₄.