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.     

Cobalt pyrophosphate nano/microstructures as promising electrode materials of supercapacitor

Cobalt pyrophosphate (Co₂P₂O₇) nano/microstructures (oblong plate, microplate, microflower, and hierarchical architectures) have been successfully synthesized through calcination of NH₄CoPO₄·H₂O nano/microstructures. More importantly, supercapacitive performances of Co₂P₂O₇ nano/microstructures were studied using cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy methods in 3.0 M KOH solution. These results show that Co₂P₂O₇ hierarchical architecture electrodes exhibit high specific capacitance of 367 F?g^?1 at current density of 0.625 A?g^?1 in aqueous KOH solution. Co₂P₂O₇ hierarchical architecture electrodes remain 96.2 % of the initial specific capacitance after 3,000 charge/discharge cycles.     

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.     

碳纳米管在室温熔盐中的电容特性

研究了碳纳米管在室温熔盐二(三氟甲基磺酸酰)亚胺锂(LiTFSI)-乙酰胺中的电容特性. 将碳纳米管制成薄膜电极, 以LiTFSI-乙酰胺为电解液, 装配成模拟电容器, 用循环伏安和恒流充放电法研究其电化学性能. 结果表明, 碳纳米管在室温熔盐中表现出典型的电容特性, 其比电容为22 F•g^-1, 模拟电容器的工作电压可达2.0 V, 具有非常好的循环性能, 循环充放电1000次后容量损失仅10%, 表明室温熔盐是超级电容器非常有前景的新型电解液.     

Self-sustaining hybrid electrode prepared from polyaniline,carbon nanotubes,and carbon fibers: morphological,structural, and electrochemical analyses

The self-sustaining hybrid electrode was prepared via chemical polymerization of aniline in acid medium containing dispersed carbon nanotubes (CNT), using carbon fiber (CF) as conducting substrate. The ternary composites called PAni/CNT/CF were characterized in order to evaluate their morphologies, structures, and thermal properties. The influence of the polyaniline (PAni) layer in the ternary composite properties was studied considering different deposition times on CF samples (30, 60, and 90 min). The ternary composite morphologies were observed by scanning electron microscopy while thermal structural analyses were obtained using thermogravimetric measurements. The structural features were analyzed by Raman scattering spectroscopy and Fourier transform infrared spectroscopy (FTIR). The possible interactions between PAni and CNT were discussed on the basis of Raman and FTIR spectra. These spectroscopic analyses also confirmed that the PAni present in the composite is in the emeraldine (ES) salt form. Furthermore, the ternary composites were also evaluated by electrochemical measurements such as cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) techniques. The results showed good charge storage capacity for ternary composites, in particular, for PAni/CNT/CF obtained with 90 min of deposition time, which exhibited specific capacitance of around 500 F g^?1. Therefore, this electrode was selected to build a prototype of type I supercapacitor. This device presented specific capacitance of around 143 F g^?1 after 3200 charge/discharge cycles.     

Influence of KMnO4 oxidation on the electrochemical performance of pitch-based activated carbons

In this work, activated carbons (ACs) are obtained from petroleum pitch by the combination of a chemical treatment with different potassium permanganate (KMnO₄) amounts, i.e., 0, 0.5, 1.0, and 2.0 g, and a chemical activation with KOH at a constant KOH/pitch ratio of 3/1. The effects of the chemical activating agent on the surface morphology and porosity are evaluated with scanning electron microscopy and N₂ adsorption isotherms at 77 K, respectively. The specific surface area of the pitch-based ACs is increased with increasing the amount of KMnO₄ pre-treatment and showed the highest value of 2,334 m² g^?1 at 2 g of KMnO₄ amount. The electrochemical performance of AC electrodes is examined by cyclic voltammetry and galvanostatic charge/discharge characteristics in 6 M KOH electrolyte. Among the prepared ACs, 2.0 K-ACs possesses a specific capacitance as high as 237 F g^?1 and showed excellent electrochemical performance due to its suitable porous structure and low interface resistance.     

Electrodes and hydrogel electrolytes based on cellulose: fabrication and characterization as EDLC components

In the present work, the cellulose-based materials were manufactured and used as components of electrochemical double layer capacitors (EDLCs). The preparation method of cellulose membranes as well as composite electrodes containing cellulose as a binder was presented. These materials were prepared using for the first time ionic liquid/dimethyl sulfoxide (IL/DMSO) mixture solvent. Obtained components displayed a uniform structure, thermal stability, and good electrochemical properties. The electrochemical performances of these materials were studied in 2-electrode EDLC cells by common electrochemical techniques as cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). The composite electrodes were investigated in three types of electrolytes: aqueous, organic, and ionic liquids. The cellulose membranes were, however, soaked in an aqueous electrolyte and tested as hydrogel polymer electrolytes. All investigated materials show high efficiency in terms of specific capacity. The studied cellulose-based capacitors exhibited specific capacitance values in the range of 20–22 F g^?1, depending on the type of applied electrolyte.     

From nickel oxalate dihydrate microcubes to NiS<Subscript>2</Subscript> nanocubes for high performance supercapacitors

In this study, NiS₂ nanocubes were successfully synthesized by a novel facile solvothermal method using NiC₂O₄·2H₂O microstructures and used as an electrode for high-performance supercapacitors. The electrochemical properties of the prepared NiS₂ electrode were studied using galvanostatic charge–discharge analysis, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) studies. Its maximum specific capacitance was 2077 F g^?1 at a constant current density of about 0.65 A g^?1. Further, the EIS results confirmed the pseudocapacitive nature of the NiS₂ electrode. The experimental results suggested that the NiS₂ electro-active material demonstrates excellent electrochemical performance with high specific capacitance, low resistance, and excellent cycling stability.     

Electrochemical exfoliation and in situ carboxylic functionalization of graphite in non-fluoro ionic liquid for supercapacitor application

Simultaneous electrochemical generation and functionalization of nano-sized graphite from graphite had been carried out in a non-fluoroanion-based ionic liquid, namely, triethylmethylammonium methylsulfate (TEMAMS) containing water and acetonitrile (AN) in different weight ratios. The oxygen-based functional groups attached with the exfoliated material had been identified using Fourier transform infrared spectroscopy (FTIR), and morphological changes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A symmetrical supercapacitor was fabricated using the exfoliated nano-sized graphite, and the influence of surface functionalities on its performance was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge–discharge cycles (CC). The highest specific capacitance (C _sp) value of 140 F g^?1 at 0.25 A g^?1 was obtained in 1.0 M H₂SO₄, followed by aqueous TEMAMS (125 F g^?1), TEMAMS/acetonitrile (115 F g^?1), and TEMAMS (106 F g^?1) at 0.10 A g^?1.     

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.     

A high-performance hybrid supercapacitor with Li4Ti5O12-C nano-composite prepared by in situ and ex situ carbon modification

In this work, we report on the synthesis of in situ and ex situ carbon-modified Li₄Ti₅O₁₂-C (LTO-C) nano-composite and its application in a hybrid supercapacitor constructed using activated carbon (AC) and LTO-C nano-composite as positive and negative electrodes, respectively. The hybrid capacitors are characterized by galvanostatic charge–discharge, cycle life testing, and electrochemical impedance spectroscopy. The results reveal that the AC/LTO-C hybrid capacitors exhibit high rate capability and long cycle life. In the potential range of 1.5–3.0 V, the AC/LTO-C hybrid system can deliver a specific capacitance of 83 F?g^?1 based on the total mass of AC and LTO-C electrodes at a current density of 60 mA g^?1 (2 C rate). At a higher discharge rate of 980 mA g^?1 (32 C), the capacity is 68 F?g^?1, about 82?% of that at 2 C rate. After 9,000 deep cycles at 32 C, the hybrid capacitor still maintains 84?% of its initial capacitance. The specific energy of such hybrid system is 20 Wh kg^?1, which is at least twice that of an AC/AC system. Combining the high energy density with power capability, the AC/LTO-C hybrid supercapacitor has demonstrated high performance for applications needing high power output.     

Supercapacitive behaviors of the nitrogen-enriched activated mesocarbon microbead in aqueous electrolytes

The activated nitrogen-enriched novel carbons (a-NENCs) have been prepared by direct carbonization of polyaniline/activated mesocarbon microbead composites and further activated by 16 M?HNO₃. The electrochemical performances and supercapacitive behaviors of the a-NENCs in 6 M KOH, 1 M?H₂SO₄, and 0.5 M?K₂SO₄ solutions are evaluated by cyclic voltammetry, galvanostatic charge/discharge, electrochemical impedance spectroscopy, cyclic life, leakage current, and self-discharge measurements. The results demonstrate that the supercapacitors perform definitely supercapacitive behaviors; especially in 6 M KOH electrolyte, the supercapacitor represents much better electrochemical performance with more excellent reversibility, shorter relaxation time of 1.11 s, and nearly ideal polarizability. The maximum specific capacitance of the supercapacitors using a-NENCs as active electrode material is 85.1 F?g^?1 at a rate of 500 mA?g^?1 in 6 M?KOH. These outcomes indicate that the 6 M?KOH aqueous solution is a promising electrolyte for the supercapacitor with a-NENCs as electrode material.     

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.     

Chitin and chitin-cellulose composite hydrogels prepared by ionic liquid-based process as the novel electrolytes for electrochemical capacitors

This paper reports on the preparation and electrochemical performance of chitin- and chitin-cellulose-based hydrogel electrolytes. The materials were prepared by a casting solution technique using ionic liquid-based solvents. The method of chitin dissolution in ionic liquid with the assistance of dimethyl sulfoxide co-solvent was investigated. The obtained membranes were soaked with 1-M lithium sulfate aqueous solution. The prepared materials were preliminarily characterized in terms of structural and physicochemical properties. Further, the most promising biopolymer membranes were assembled with activated carbon cloth electrodes in symmetric electrochemical capacitor cells. The electrochemical performances of these devices were studied in a 2-electrode system by commonly known electrochemical techniques, such as cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The devices operated at a maximum voltage of 0.8 V. All the investigated materials have shown high efficiency in terms of specific capacitance, power density, and cyclability. The studied capacitors exhibited specific capacitance values in the range of 92–98 F g⁻¹, with excellent capacitance retention (ca. 97–98%) after 20,000 galvanostatic charge and discharge cycles. Taking into account the above information and the eco-friendly nature of the biopolymer, it appears that the prepared chitin- and chitin-cellulose-based hydrogel electrolytes can be promising components for green electrochemical capacitors.

     

Preparation of polyaniline‐coated mesoporous carbon and its enhanced electrochemical properties

Polyaniline/MC (mesoporous carbon) composite was synthesized by in situ chemical polymerization method and was used as a new electrode material for supercapacitor. The composite was characterized by N₂ adsorption and scanning electron microscope. The electrochemical capacitance performance of the composite was investigated by cyclic voltammetry (CV) and galvanostatic charge–discharge tests with a three‐electrode system in a 10 wt% H₂SO₄ solution. The polyaniline/MC composite electrode shows much higher specific capacitance than pure MC electrode, which is attributed to the incorporation of polyaniline onto the pore surface of MC. Copyright © 2009 John Wiley & Sons, Ltd.     

Coal tar residues-based nanostructured activated carbon/Fe3O4 composite electrode materials for supercapacitors

Oxygen-rich activated carbon with a three-dimensional network structure was prepared by chemical activation of coal tar residues with potassium hydroxide and subsequent carbonization treatment. Nanostructured Fe₃O₄/AC composites were then prepared by simple chemical coprecipitation method and were used as active electrode materials for supercapacitors. The electrochemical behaviors of Fe₃O₄/AC nanocomposites were characterized by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy in 1.0 M Na₂SO₃ electrolyte. It was shown that the specific capacitance of Fe₃O₄/AC nanocomposites reached 150 F g^?1 at a current density of 3.0 A g^?1 and was a great improvement over Fe₃O₄ or AC alone. Furthermore, as-prepared Fe₃O₄/AC nanocomposites exhibited long cycle life without obvious capacitance fading even after 1,000 charge/discharge cycles. Compared with pure Fe₃O₄ and AC, the significant enhanced electrochemical performance of Fe₃O₄/AC nanocomposites could be reasonably attributed to the positive synergetic effect between Fe₃O₄ and AC.     

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.     

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.     

Nickel foam as interlayer to improve the performance of lithium–sulfur battery

In this report, a porous, electronically conductive nickel foam foil (NFF), which is rolled for smooth surface, is introduced as an interlayer placed between the sulfur electrode and the separator to suppress the loss of active material and self-discharge behavior in lithium–sulfur (Li–S) systems. The electrodes are characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge test. The cell with the rolled NFF interlayer shows superior performance in terms of capacity utilization, reversibility, and enhanced rate capability. It exhibits reversible discharge capacity of 604 mAh g^?1 after 80 cycles at 0.2 C, which is much higher than that of pristine sulfur without NFF (424 mAh g^?1). The improvement on electrochemical performance is attributed to the 3D architecture of nickel foam foil as lithium–sulfur batteries interlayer, which can provide a good conductive network with structural stability and the porous architecture accommodating the migrating polysulfide to reduce the shuttling phenomenon during the charge–discharge processes.     

Carbon aerogels with modified pore structures as electrode materials for supercapacitors

Carbon aerogels (CA) with uniform pore structures were prepared by the polycondensation of phloroglucinol, resorcinol, and formaldehyde, using carboxylated chitosan as a soft template. The CA were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and surface area analysis. When carboxylated chitosan was added, the time for wet gel formation was reduced by 60%, and the CA showed a more uniform pore structures. The electrochemical performance of the CA was measured in a three-electrode electrochemical cell. The CA prepared with added carboxylated chitosan showed lower charge transfer resistance on the electrode surface, and the specific capacitances were also enhanced, showing a specific capacitance as high as 135 F/g at a resorcinol-to-carboxylated chitosan mass ratio of 250:1 at a current density of 0.5 A/g. This specific capacitance is much higher than that of the CA without carboxylated chitosan. The capacitance retention under increasing discharge current density was also enhanced by the addition of carboxylated chitosan. The electrochemical performance of the CA in different electrolytes (1 M LiOH, 1 M NaOH, 1 M KOH, 3 M KOH, 6 M KOH, and 9 M KOH) was investigated. The results show that the electrochemical performance in 6 M KOH was better than those in other electrolytes.