Synthesis and electrochemical properties of three-dimensional graphene/polyaniline composites for supercapacitor electrode materials

To improve the specific capacitance and rate capability of electrode material for supercapacitors, a three-dimensional graphene/polyaniline(3DGN/PANI) composite is prepared via in situ polymerization on GN hydrogel. PANI grows on the GN surface as a thin film, and its content in the composite is controlled by the concentration of the reaction monomer. The specific capacitance of the 3DGN/PANI composite containing 10 wt% PANI reaches 322.8 F·g-1at a current density of1 A·g-1, nearly twice as large as that of the pure 3DGN(162.8 F·g-1). The capacitance of the composite is 307.9 F·g-1at 30 A·g-1(maintaining 95.4%), and 89% retention after 500 cycles. This study demonstrates the exciting potential of3DGN/PANI with high capacitance, excellent rate capability and long cycling life for supercapacitors.     

Synthesis and characterization of nitrogen-doped graphene hollow spheres as electrode material for supercapacitors

Recently, the rapid development of graphene industry in the world, especially in China, provides more opportunities for the further extension of the application field of graphene-based materials. Graphene has also been considered as a promising candidate for use in supercapacitors. Here, nitrogen-doped graphene hollow spheres (NGHS) have been successfully synthesized by using industrialized and pre-processed graphene oxide (GO) as raw material, SiO₂ spheres as hard templates, and urea as reducing-doping agents. The results demonstrate that the content and pretreatment of GO sheets have important effect on the uniform spherical morphologies of the obtained samples. Industrialized GO and low-cost urea are used to prepare graphene hollow spheres, which can be a promising route to achieve mass production of NGHS. The obtained NGHS have a cavity of about 270 nm, specific surface area of 402.9 m² g^?1, ultrathin porous shells of 2.8 nm, and nitrogen content of 6.9 at.%. As electrode material for supercapacitors, the NGHS exhibit a specific capacitance of 159 F g^?1 at a current density of 1 A g^?1 in 6 M KOH aqueous electrolyte. Moreover, the NGHS exhibit superior cycling stability with 99.24% capacitive retention after 5000 charge/discharge cycles at a current density of 5 A g^?1.     

Enhanced electrochemical performance of porous activated carbon by forming composite with graphene as high-performance supercapacitor electrode material

In this work, a novel activated carbon containing graphene composite was developed using a fast, simple, and green ultrasonic-assisted method. Graphene is more likely a framework which provides support for activated carbon (AC) particles to form hierarchical microstructure of carbon composite. Scanning electron microscope (SEM), transmission electron microscope (TEM), Brunauer–Emmett–Teller (BET) surface area measurement, thermogravimetric analysis (TGA), Raman spectra analysis, XRD, and XPS were used to analyze the morphology and surface structure of the composite. The electrochemical properties of the supercapacitor electrode based on the as-prepared carbon composite were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), charge/discharge, and cycling performance measurements. It exhibited better electrochemical performance including higher specific capacitance (284 F g^?1 at a current density of 0.5 A g^?1), better rate behavior (70.7% retention), and more stable cycling performance (no capacitance fading even after 2000 cycles). It is easier for us to find that the composite produced by our method was superior to pristine AC in terms of electrochemical performance due to the unique conductive network between graphene and AC.     

Synthesis of NiCo2S4 nanospheres/reduced graphene oxide composite as electrode material for supercapacitor

The NiCo₂S₄ nanospheres arrayed on the surface of reduced graphene oxide (rGO) was fabricated via one-step hydrothermal method. The effect of initial feeding mass of Ni(NO₃)₂·6H₂O and Co(NO₃)₂·6H₂O to rGO on the microstructure and electrochemical performance of the as-prepared composites was studied. The results indicated that the specific capacitances of the composites were first increased and then reduced due to the aggregation of NiCo₂S₄ nanospheres. NiCo₂S₄ nanospheres/rGO composites exhibited a remarkable specific capacitance of 1406 F/g and excellent cyclic stability of 82.36% at the current density of 1 A/g, which were better than those of individual NiCo₂S₄ (792 F/g and 64.77%) counterpart. These results showed that the as-prepared NiCo₂S₄ nanospheres/rGO composites were outstanding candidate for electrode material of supercapacitors.     

Electrochemical properties of Mn-doped activated carbon aerogel as electrode material for supercapacitor

Carbon aerogel (CA) was prepared by a sol-gel polymerization of resorcinol and formaldehyde, and it was activated with KOH to obtain activated carbon aerogel (ACA). Specific capacitance of carbon aerogel and activated carbon aerogel was measured by cyclic voltammetry and galvanostatic charge/discharge methods in 6 M KOH electrolyte. Activated carbon aerogel showed higher specific capacitance than carbon aerogel (136 F/g vs. 90 F/g). In order to combine excellent electrochemical performance of activated carbon aerogel with pseudocapacitive property of manganese oxide, 7 wt% manganese oxide was doped on activated carbon aerogel by an incipient wetness impregnation method. For comparison, 7 wt% manganese oxide was also doped on carbon aerogel by an incipient wetness impregnation method. It was revealed that 7 wt% Mn-doped activated carbon aerogel (Mn/ACA) showed higher specific capacitance than 7 wt% Mn-doped carbon aerogel (Mn/CA) (168 F/g vs. 98 F/g). The enhanced capacitance of 7 wt% Mn-doped activated carbon aerogel was attributed to the outstanding electric properties of activated carbon aerogel as well as the faradaic redox reactions of manganese oxide.     

Study on the electrochemical behavior of vanadium nitride as a promising supercapacitor material

Vanadium nitride (VN) powder was synthesized by calcining V₂O₅ xerogel in a furnace under an anhydrous NH₃ atmosphere at 400 °C. The structure and surface morphology of the obtained VN powder were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The supercapacitive behavior of VN in 1 M KOH electrolyte was studied by means of cyclic voltammetry (CV), constant current charge-discharge cycling (CD) and electrochemical impedance spectroscopy (EIS). The XRD result indicates that the obtained VN belongs to the cubic crystal system (Fm3m [2 2 5]) with unit-cell parameter 4.15 Å. SEM images show the homogeneous surface of the obtained VN. The CV diagrams illustrate the existence of fast and reversible redox reactions on the surface of VN electrode. The specific capacitance of VN is 161 F g⁻¹ at 30 mV s⁻¹. Furthermore, the specific capacitance remains 70% of the original value when the scan rate increases from 30 to 300 mV s⁻¹. CD experiments show that VN is suitable for CD at high current density, and the slow and irreversible faradic reactions exist during the charge-discharge process of the VN electrode. The experimental results indicate that VN is a promising electrode material for electrochemical supercapacitors.     

Electrochemical performance of CeO<Subscript>2</Subscript> nanoparticle-decorated graphene oxide as an electrode material for supercapacitor

Cerium oxide nanoparticles and cerium oxide nanoparticle-decorated graphene oxide (GO) are synthesized via a facile chemical coprecipitation method in the presence of hexadecyltrimethylammonium bromide (CTAB). Nanostructure studies and electrochemical performances of the as-prepared samples were systematically investigated. The crystalline structure and morphology of the nanocomposites were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM), Raman spectrum, and X-ray photoelectron spectroscopy (XPS). Electrochemical properties of the CeO₂ electrode, the GO electrode, and the nanocomposites electrodes were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. The CeO₂ nanoparticle-decorated GO (at the mole ratio of CeO₂/GO = 1:4) electrode exhibited excellent supercapacitive behavior with a high specific capacitance of 382.94 F/g at the current density of 3.0 A/g. These superior electrochemical features demonstrate that the CeO₂ nanoparticle-decorated GO is a promising material for next-generation supercapacitor systems.     

Synthesis of carbon-coated Fe3O4 nanorods as electrode material for supercapacitor

Carbon-coated Fe₃O₄ and pure Fe₃O₄ nanorods are synthesized via hydrothermal reaction and subsequent sintering procedure. The as-prepared products characterized by X-ray diffraction and scanning electron microscopy analysis indicate that carbon coating does not affect the structure and morphology of Fe₃O₄. Transmission electron microscope shows that Fe₃O₄ nanorods are homogeneously coated by carbon layer with a thickness of approximately 2 nm. The electrochemical properties measured by cyclic voltammetry, galvanostatic charge–discharge cycling and electrochemical impedance spectroscopy tests show that carbon-coated Fe₃O₄ (Fe₃O₄/C) nanorods present improved electrochemical performance due to the carbon layer. A specific capacitance of 275.9 F?g^?1 is achieved at a current density of 0.5 A g^?1 in 1 M Na₂SO₃ aqueous solution for the Fe₃O₄/C nanorods in comparison to that of 208.6 F?g^?1 for pure Fe₃O₄.     

Potato starch-based activated carbon spheres as electrode material for electrochemical capacitor

Potato starch-based activated carbon spheres (PACS) were prepared from potato starch by stabilization, carbonization followed by activation with KOH. The obtained PACS are hollow and retain the original morphology of potato starch with decrease in size, as shown by scanning electron microscopy. Modification of textural properties of the PACS was achieved by varying the carbonization temperature and the ratio of KOH/PCS. The results of N₂ adsorption isotherms indicate that the samples prepared are mainly microporous. The electrochemical behaviors of the hollow PACS were studied by galvanostatic charge-discharge, cyclic voltammetry, and impedance spectroscopy. The results indicate that high specific capacitance of 335 F/g is obtained at current density 50 mA/g for PACS with specific surface area 2342 m²/g. Only a slight decrease in capacitance, to 314 F/g, was observed when the current density increases to 1000 mA/g, indicating a stable electrochemical property.     

Synthesis of nanofiber-composed dandelion-like CoNiAl triple hydroxide as an electrode material for high-performance supercapacitor

In this work, CoNiAl triple hydroxide with nanofiber-composed dandelion-like morphology was synthesized on nickel foam by a hydrothermal route. This delicate nanostructure was initiated from the rolling up of hydroxide nanosheets. The hierarchical nanostructure and optimized molar ratio of Co, Ni, and Al guarantees the high electrochemical performance of obtained samples. The maximum specific capacitance of 2,791 F g^?1 for the as-prepared CoNiAl hydroxides was achieved at scan rate of 5 mV s^?1 in 3 M KOH aqueous solution. The capacitance of material still remained 85 % after 2,000 charge–discharge cycles. These results demonstrated that the as-prepared CoNiAl triple hydroxide can be applied as a high-performance electrode material for supercapacitor.     

Facile synthesis of nitrogen-doped reduced graphene oxide as an efficient counter electrode for dye-sensitized solar cells

A nitrogen-doped reduced graphene oxide (N-RGO) nanosheet was synthesized by a simple hydrothermal method and characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electrode microscopy. After being deposited as counter electrode film for dye-sensitized solar cells (DSSCs), it is found that the synthesized N-RGO nanosheet has smaller charge-transfer resistance and better electrocatalytic activity towards reduction of triiodide than the reduced graphene oxide (RGO) nanosheet. Consequently, the DSSCs based on the N-RGO counter electrode achieve an energy conversion efficiency of 4.26%, which is higher than that of the RGO counter electrode (2.85%) prepared under the same conditions, and comparable to the value (5.21%) obtained with the Pt counter electrode as a reference. This N-RGO counter electrode offers the advantages of not only saving the cost of Pt itself but also simplifying the process of counter electrode preparation. Therefore, an inexpensive N-RGO nanosheet is a promising counter electrode material to replace noble metal Pt.

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Graphical abstract A nitrogen-doped reduced graphene oxide nanosheet was synthesized by a simple hydrothermal method, which is a promising counter electrode material to replace noble metal Pt.

     

Silver nanoparticles decorated on a three-dimensional graphene scaffold for electrochemical applications

Silver metal nanoparticles were decorated by electron beam evaporation on graphene foam (GF) grown by chemical vapour deposition. X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy, and atomic force microscopy were used to investigate the structure and morphology of the graphene foam/silver nanoparticles (GF/Ag). Both samples were tested as electrodes for supercapacitors. The GF/Ag exhibited a significantly higher capacitive performance, including a specific capacitance value of (~110 Fg⁻¹) and excellent cyclability in a three-electrode electrochemical cell. These results demonstrate that graphene foam could be an excellent platform for metal particles for investigating improved electrochemical performance.     

Electrochemical synthesis of flower like Mn-Co mixed metal oxides as electrode material for supercapacitor application

In the present work flower like Mn-Co mixed metal oxide electrode materials were successfully synthesized by simple, low cost electrodeposition method on stainless steel substrates. Different volume ratio of Mn-Co was used to attempt enhancement in the supercapacitive properties of electrode material. Structural, morphological and wettability properties of synthesized electrodes were carried out using XRD, RAMAN, FE-SEM and Contact Angle Measurement techniques. Electrochemical properties of electrodeposited Mn-Co mixed metal oxide at three different volume variation such as 50-50, 60-40 and 70-30 electrodes were analyzed by using cyclic voltammetry, galvonostatic charge discharge and electrochemical impedance spectroscopy in 1 M NaOH aqueous electrolyte. The Mn-Co:60-40 composition shows maximum specific capacitance which is 679 F/g at scan rate 5 mV/sec. Charge discharge studies gives 95% columbic efficiency. Impedance spectroscopy reveals capacitive behavior and gives series resistance ∼0.19 ohm and combined internal resistance ∼0.89 ohm. The 80% retention of specific capacitance after the 1000 cycles. The synergistic effect of Mn-Co mixed metal oxide electrode having good conductivity, large surface area and improved charge transportation than individual electrode material leads to enhancing supercapacitor performance of electrode material for its practical application.     

Mn-doped activated carbon aerogel as electrode material for pseudo-capacitive supercapacitor: Effect of activation agent

Carbon aerogel (CA) was prepared by a sol-gel polymerization of resorcinol and formaldehyde, and a series of activated carbon aerogels (ACA-X, X = H₃PO₄, K₂CO₃, KOH, and ZnCl₂) were then prepared by a chemical activation using different activation agent (X represented an activation agent). Specific capacitances of activated carbon aerogels were measured by cyclic voltammetry and galvanostatic charge/discharge methods in 6 M KOH electrolyte. Among the samples prepared, ACA-K₂CO₃ showed the highest specific capacitance (152 F/g). In order to combine excellent electrochemical performance of activated carbon aerogel with pseudo-capacitive property of manganese oxide, 7 wt% manganese oxide was doped on activated carbon aerogels (Mn/ACA-X) by an incipient wetness impregnation method. Capacitance measurements revealed that Mn/ACA-K₂CO₃ showed the highest specific capacitance (189 F/g). The enhanced capacitance of Mn/ACA-K₂CO₃ was attributed to the fine pore structure and outstanding electric properties of activated carbon aerogel as well as the faradaic redox reactions of manganese oxide.     

Lithium-enriched polypyrrole as a prospective cathode material for Li-ion cells

Lithium substitution in polypyrrole can be accomplished by a variety of approaches and the present work introduces one of the cost-effective techniques using a relatively less expensive lithium salt, n-butyllithium in hexanes (n-BuLi), as the dopant. Chemical oxidative polymerization method is employed to synthesize polypyrrole (PPy) using anhydrous ferric chloride as the oxidant and it is dedoped using NH₄OH solution in the fully reduced state. The dedoped polypyrrole is treated with n-butyllithium in hexanes (n-BuLi) in an argon-filled glove box to get the lithiated form of polypyrrole (PPyL) and the concentration of n-BuLi is varied to improve metalation. The lithiated PPy is characterized by FTIR spectroscopy, XRD, FESEM, and TEM techniques to understand the structural and the morphological details. The lithium content in the lithiated samples is estimated using ICP-AES analysis. The thermal studies using the TGA technique show that the lithiated polypyrrole has good thermal stability. Coin cells are assembled in the argon-filled glove box using Li-substituted polypyrrole as the cathode, lithium metal foil as the anode, and lithium hexafluorophosphate (LiPF₆) as the electrolyte. The assembled cells are electrochemically characterized using cyclic voltammetry and charge–discharge cycling techniques and it is seen that the Li-substituted polypyrrole-based Li-ion cells are electrochemically active.     

N-doped graphene as a nanostructure adsorbent for carbon monoxide: DFT calculations

ABSTRACT

This work reports the physisorption of carbon monoxide (CO) on the surface of N-doped graphene. To study the adsorption of CO on N-doped graphene, some quantum chemical calculations were used through density functional theory. Based on our results, it can be found that the CO molecule could be adsorbed on the surface of N-doped graphene physically with the adsorption energies (E_ads) of ?2.9 and ?0.8 kcal mol^?1 (depends on the kind of configuration) while positive adsorption energies were calculated upon adsorption of CO on pristine graphene. We used the charge analysis for calculation of the net transferred charge of adsorbed CO on pristine and N-doped graphene sheets to evaluate the sensing ability of surface. The global indices of reactivity were calculated from the differences of the lowest unoccupied molecular orbital and highest occupied molecular orbital energies. Graphs for density of states point to some orbital hybridisation between CO molecule and N-doped graphene. Consequently, the N-doped graphene transforms the existence of CO molecules into electrical signal, and it may be potentially used as a sensor for CO.     

Synthesis of graphene oxide nanosheets and its application to construct a modified carbon paste electrode as a hydroxylamine electrochemical sensor

Ionics - A ferrocene-derivative compound, 2, 7-bis (ferrocenyl ethynyl) fluoren-9-one (2,7-BFE), was synthesized and used to construct a modified graphene paste electrode. The electrooxidation of...     

Performance evaluation of polyacrylamide/silver composite as electrode material in electrochemical capacitor

In this research, polyacrylamide/Ag composite is synthesized and used as an electrode in an electrochemical capacitor (EC). The characterization of the composite is performed by X-ray diffraction, scanning electron microscopy, and cyclic voltammetry methods. The electrochemical characterization is conducted in an electrolytic solution of KOH and an electrolytic solution of Na₂SO₄. The capacitance of the polyacrylamide/Ag composite is associated mainly with the reduction/oxidation of Ag. The specific capacitance of the EC using the KOH electrolyte is 950 Fg^?1, which is better than the capacitance in the Na₂SO₄ electrolyte. This behavior is explained by the respective physical characteristics of the two electrolytes.     

Converting of the 2D graphene to its 3D by chicken red blood cells as sheets separator for construction supercapacitor electrode

Here, we report on a facile green and scalable method for the fabrication of porous 3D graphene as a well-known carbon-based material used in many energy storage devices. Chicken red blood cells were used as sheets spacer and heteroatom sources in the construction of 3D graphene. First, the red blood cells were separated from the blood and mixed with graphene oxide. Then, the mixture was freeze-dried and carbonized at 700 °C. The resulted 3D graphene containing heteroatoms was used as a supercapacitor electrode modifier on a glassy carbon electrode and tested with various electrochemical techniques. The supercapacitor electrode showed a specific capacitance of 330 F g⁻¹ at a current density of 1 A g⁻¹, maximum power density of 1958 W kg⁻¹, and maximum energy density of 85 Wh kg⁻¹. Furthermore, the supercapacitive performances were tested in a two-electrode symmetrical system which exhibited a specific capacitance of 238 F g⁻¹ for 1 A g⁻¹. It also showed a power density of 2200 W kg⁻¹ and an appreciable energy density of 160 Wh kg⁻¹. The excellent electrochemical behavior of 3D graphene indicates the promising abilities of the composite for other applications such as biosensors, batteries, electrocatalysts, etc.