Electrochemical Capacitive Properties Research Articles

Holey Graphene Nanomanufacturing: Structure, Composition, and Electrochemical Properties

Topology is critical for properties and function of 2D nanomaterials. Membranes and films from 2D nanomaterials usually suffer from large tortuosity as a result from dense restacking of the nanosheets and thus have limited utility in applications such as electrodes for supercapacitor and batteries, which require ion transport through the nanosheet thickness. In comparison with conventional porous 2D nanomaterials, introducing holes through the nanosheets to create holey 2D nanomaterials with retention of the 2D‐related properties is a more viable approach to improve molecular transport. Here, graphene is used as a model to study the fundamental structure‐property relationship as a result from defect‐enabled hole creation. Specifically, the correlation of electrochemical capacitive properties with structure and composition for holey graphene materials is prepared using a highly scalable controlled air oxidation process. The presence of holes on graphene sheets is not sufficient to account for the observed capacitance improvement. Rather, the improvement is achieved through the combination of an enhanced mesopore fraction with simultaneous oxygen doping while retaining the graphitic carbon network with minimal damage. The detailed understanding might be further applied to other 2D materials toward a broader range of both energy‐related and other applications.

Electrochemical double layer near polar reduced graphene oxide electrode: Insights from molecular dynamic study

Reduced graphene oxide (rGO) has emerged as an attractive choice for electrochemical double layer capacitors. Based on the accurate atomic partial charge distribution determined by density functional theory calculations, the electrochemical double layer structural and capacitive properties at the rGO/NaCl aqueous electrolyte interface are studied using the molecular dynamic simulations. Due to the charge redistribution mainly around oxygen functional groups, rGO will form a strong polar surface. It will significantly change the arrangement of surrounding water molecules through a hydrogen bond like interaction. The change of dipole orientation of water will induce corresponding net charge redistribution, leading to a change of potential of zero charge of rGO electrode. The polarization interaction also restricts the orientation of electrolyte molecules and weakens their mobility, resulting in the decrease of integral capacitance value of rGO with increasing of functional groups concentration. This work about electrochemical double layer near polar rGO electrode could offer a reasonable guidance for future performance improvements of electrochemical double layer capacitors.

Preparation of NiO Microspheres by Hydrothermal Method and its Electrochemical Capacitive Properties

The precursor Ni (OH)2 was synthesized by a simple hydrothermal method with hexamethylenetetramine ((CH2)6N4) as precipitant and template, and then NiO was gained after calcination. The phase and morphology of the synthesized product were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), and the electrochemical capacitive characterization was performed using cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS) in a 6mol/L KOH aqueous solution electrolyte. The result shows that spherical NiO without impurity was synthesized, the average diameter of the spheres is 5 um and these spheres were constructed by the interactive arrangement of many nanoflakes in three dimensions. This kind of NiO shows the typical electrochemical characteristics of pseudo capacitance with high specific capacity and excellent rate capability. The specific capacity can reach 515F/g at the current density of 1A/g

Preparation of Nickel and Manganese Dioxide by Co-Precipitation and its Electrochemical Capacitive Properties

The precursor nickel and manganese carbonates were synthesized by co-precipitation with sodium carbonate as precipitant, and then nickel and manganese oxides were gained after calcination. The phase and morphology of the synthesized product were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), and the electrochemical characterization was performed using cyclic voltammetry (CV), galvanostatic charge–discharge tests (GCD) and electrochemical impedance spectroscopy (EIS) in a 6mol/L KOH aqueous solution electrolyte. The result showed that the products were the mixture of nickel and manganese oxides and solid solution. nanoparticles and spherical particles were gained by controlling the molar ratio of nickel and manganese. All of the samples exhibited typical Faradic redox capacitance. The specific capacitance was different with the change of nickel and manganese molar ratio. The specific capacitance (Cs) reached 130F/g at 1A/g when the ratio was 2:1.

Synthesis and electrochemical capacitive properties of nitrogen-doped porous carbon micropolyhedra by direct carbonization of zeolitic imidazolate framework-11

Nitrogen-doped porous carbon micropolyhedra (N-PCMPs) were successfully prepared by direct carbonization of ZIF-11 polyhedra and further activated with fused KOH to obtain N-PCMPs-A. The morphology and microstructure of samples were examined by scanning electron microscopy, X-ray diffraction, and micropore and chemisorption analyzer. Electrochemical properties were characterized by cyclic voltammetry and galvanostatic charge/discharge method in 1.0M H2SO4 aqueous solution on a standard three-electrode system. Results show that, compared with N-PCMPs, N-PCMPs-A has higher specific surface area (2188m2g−1) and exhibits improved electrochemical capacitive properties (307Fg−1 at 1.0Ag−1). The mass specific capacitance of N-PCMPs-A is also higher than that of most MOF-derived carbons, some carbide-derived carbons and carbon aerogel-derived carbons. In addition, the capacitance of the N-PCMPs-A retains 90% after 4000 cycles even at a high current density of 10Ag−1. These imply that N-PCMPs-A is the promising materials for the construction of a high-performance supercapacitor.

Facile electrochemical polymerization of 2-(thiophen-2-yl)furan and the enhanced capacitance properties of its polymer in acetonitrile electrolyte containing boron trifluoride diethyl etherate

ABSTRACT In this study, a new simple hybrid poly(2-(thiophen-2-yl)furan) (PTFu) was easily electrodeposited by direct anodic oxidation of 2-(thiophen-2-yl)furan in acetonitrile solution containing 0.1 M lithium perchlorate (LiClO 4 ). The oxidation onset potential of 2-(thiophen-2-yl)furan monomer in this medium was measured to be 0.90 V, which was lower than those of thiophene (1.47 V) and furan (1.28 V). The structure and morphology of PTFu were characterized by Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermal analysis. The electrochemical capacitance properties of PTFu electrode in three electrolytes were also investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscope techniques. The electrochemical results showed that the specific capacitance of PTFu electrode was enhanced to 392.0 F g −1 from 249.4 F g −1 at 5 A g −1 and the cycling stability was also enhanced to 67.0% retention from 25.5% retention after 500 cycles when the equivalent boron trifluoride diethyl etherate (BFEE) was added into the acetonitrile electrolyte. Furthermore, the PTFu electrode in ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF 6 ) showed a lower specific capacitance value (209.4 F g −1 at 5 A g −1 ) and an improved stability (67.6% retention after 600 cycles). These results indicated that the conducting polymers based on furan should be a promising electrode material for supercapacitor applications when the electrolyte based-BFEE is used.

Enhanced electrosorption capacity for lead ion removal with polypyrrole and air‐plasma activated carbon nanotube composite electrode

ABSTRACTPolypyrrole (PPy) and air‐plasma activated carbon nanotube (CNT) composites (P‐CNT‐PPy) prepared via in situ chemical oxidative polymerization are studied to improve the electrosorption capacity of CNT‐based electrodes for the removal of lead ions. For comparison, the PPy prepared on the CNTs without plasma activation is labeled as CNT/PPy. The morphology of the composite was observed by scanning electron microscopy (SEM), and pore structures were studied by N2 adsorption‐desorption isotherms. The electrochemical capacitance properties of the composite were measured by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge‐discharge in lead solutions. With plasma‐activation, the specific surface area of the P‐CNT‐PPy composite is larger than that of CNT/PPy. Additionally, the P‐CNT‐PPy composites exhibit excellent electrochemical performance in lead solution, with a higher specific capacitance and smaller charge transfer resistance than that of CNT/PPy. XPS elemental analysis and electrosorption and regeneration results show that the electrosorption and desorption process is reversible under a voltage of 450 mV. The electrosorption kinetics of P‐CNT‐PPy electrodes abide by pseudo‐second‐order model reaction. The lead ion electrosorption experiments agree with the Langmuir model, and the equilibrium electrosorption capacity of the P‐CNT‐PPy electrodes is 3.6 and 1.3 times higher than that of the CNT and CNT/PPy, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41793.

Back Cover: Engineering the Electrochemical Capacitive Properties of Graphene Sheets in Ionic-Liquid Electrolytes by Correct Selection of Anions (ChemSusChem 11/2014)

Back Cover: Engineering the Electrochemical Capacitive Properties of Graphene Sheets in Ionic-Liquid Electrolytes by Correct Selection of Anions (ChemSusChem 11/2014)

Influence of annealing temperature on the morphology and the supercapacitance behavior of iron oxide nanotube (Fe-NT)

The article demonstrates the influence of annealing temperature on the supercapacitance behavior of iron oxide nanotube synthesized on pure iron substrate by electrochemical anodization process. Anodization was performed in an ethylene glycol solution containing 3% H2O and 0.5 wt. % NH4F. The as-anodized nanotubes were annealed in an ambient atmosphere at various temperatures ranging from 200 to 700 °C for a fixed duration of time (2 h). The morphology and crystal phases developed after anodization and subsequent annealing processes were examined using field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and X-ray photospectroscopy (XPS). Cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) experiments were performed in 1 M Li2SO4 to evaluate the electrochemical capacitance properties of the oxide nanotube electrodes. It was found that the electrode annealed at 300 °C exhibited superior electrochemical capacitance compared to the electrodes annealed at other temperatures. The highest specific capacitance achieved after annealing at 300 °C was about 314 mF cm−2. The electrodes annealed at 200, 500, 600 and 700 °C displayed much lower specific capacitance compared to those annealed at 300 and 400 °C. Galvanostatic charge–discharge experiments conducted on some of the annealed electrodes demonstrated excellent cycle stability with more than 80% capacitance retention after 1000 charge–discharge cycles.

Engineering the electrochemical capacitive properties of graphene sheets in ionic-liquid electrolytes by correct selection of anions.

Graphene sheet (GS)-ionic liquid (IL) supercapacitors are receiving intense interest because their specific energy density far exceeds that of GS-aqueous electrolytes supercapacitors. The electrochemical properties of ILs mainly depend on their diverse ions, especially anions. Therefore, identifying suitable IL electrolytes for GSs is currently one of the most important tasks. The electrochemical behavior of GSs in a series of ILs composed of 1-ethyl-3-methylimidazolium cation (EMIM(+)) with different anions is systematically studied. Combined with the formula derivation and building models, it is shown that the viscosity, ion size, and molecular weight of ILs affect the electrical conductivity of ILs, and thus, determine the electrochemical performances of GSs. Because the EMIM-dicyanamide IL has the lowest viscosity, ion size, and molecular weight, GSs in it exhibit the highest specific capacitance, smallest resistance, and best rate capability. In addition, because the tetrafluoroborate anion (BF4(-)) has the best electrochemical stability, the GS-[EMIM][BF4] supercapacitor has the widest potential window, and thus, displays the largest energy density. These results may provide valuable information for selecting appropriate ILs and designing high-performance GS-IL supercapacitors to meet different needs.

Electrochemical synthesis, characterization and capacitive properties of novel thiophene based conjugated polymer

In this paper, a novel thiophene based monomer, 1-(pyren-1-yl)-2,5-di(thiophen-2-yl)-1H-pyrrole, PThP, was synthesized and characterized by 1H NMR and 13C NMR spectroscopic methods. The electrochemical behavior and electropolymerization of this novel monomer were performed on pencil graphite electrode (PGE) by cyclic voltammetry. The effect of solvent, dopant, scan number and scan rate on the electropolymerization and properties of the conjugated polymer films were investigated. The capacitive properties of the poly(PThP) films were tested by electrochemical impedance spectroscopy (EIS). The highest specific capacitance value was calculated for the conjugated polymer modified PGE that was obtained in 0.1M tetrabutylammonium perchlorate/dichloromethane solution for 30 cycles at 25mV/s scan rate as 25.45mFcm−2. The surface morphologies of the conjugated polymer modified electrodes were determined by scanning electron microscopy (SEM).

Ordered nitrogen doped mesoporous carbon assembled under aqueous acidic conditions and its electrochemical capacitive properties

With urea as nitrogen source, soluble phenol–urea–formaldehyde (PUF) resin is synthesized under basic conditions, and then an N-containing mesophase is obtained by co-assembly of the obtained PUF resin and block copolymer of F127 in acidic aqueous solution. The pyrolysis of the resultant mesophase in inert atmosphere produces a nitrogen-doped mesoporous carbon, which possesses a well-defined ordered mesoporous structure, large surface area (up to 537m2/g), uniform pore size (∼3.6nm) and large pore volume (∼0.49cm3/g). Multi-techniques, such as elemental analysis, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS) are performed to characterize the samples; these analytic results indicate that the doped nitrogen mainly exists as pyridinic and pyrrolic nitrogen is successfully and homogeneously introduced into the skeleton of the mesoporous carbon. And more, the nitrogen content in the final ordered mesoporous carbon can be easily adjusted up to 3.85 wt.% by increasing the original ratio of urea to phenol. Electrochemical measurements show the nitrogen doped mesoporous carbon presents a higher specific capacitance (up to 225F/g) than nitrogen-free ones (169F/g) and exhibits a good electrochemical stability even after 1000 cycles at current density of 5.0A/g.

In Situ Synthesis and Characterization of Polypyrrole/Graphene Conductive Nanocomposites via Electrochemical Polymerization and Chemical Reduction

Polypyrrole/graphene sheets (PPy/GNs) nanocomposite electrodes were in- situ synthesized via electrochemical polymerization and chemical reduction from pyrrole (Py) and graphene oxide (GO). The surface morphologies of the nanocomposites were observed by scanning electron microscopy (SEM). The SEM results showed graphene sheets (GNs) scattered on the surface of the polypyrrole (PPy), and the morphologies of PPy/GNs nanocomposites manufactured by pulse current (PC-PPy/GNs) or direct current (DC-PPy/GNs) were smoother than that of PC-PPy. The electrochemical capacitance properties of the nanocomposite films were measured by cyclic voltammetry (CV), galvanostatic charge and discharge (GC), and electrochemical impedance spectroscopy (EIS) techniques in 3 mol·L−1 KCl aqueous solutions. The results indicated that the specific capacitance of the DC-PPy/GNs nanocomposite was 13.5% higher than that of a PC-PPy electrode. Comparison of the electrochemical performance of the nanocomposites indicated that the PC-PPy/GNs nanocomposite had higher specific capacitance and better charging/discharging capability than that of the DC-PPy/GNs nanocomposite. The specific capacitance of the PC-PPy/GNs nanocomposite could reach to 280 F·g−1 at a scanning rate of 100 mV·s−1.

Effect of the electrochemical oxidation/reduction cycle on the electrochemical capacitance of graphite oxide

Reduction largely affects the properties of graphene oxide (GO), because the content of each functional group changes by the oxidation degree. So far no study about re-oxidation and re-reduction of GO has been carried out. Herein, we report the effects of oxidation/reduction cycle of graphite oxide (GtO, multilayered GO) on its composition and electrochemical capacitance property. Electrochemical oxidation and reduction of glassy carbon (GC) were conducted at potentials of +2.0 and −1.1V (vs. Ag/AgCl), respectively, and then the electrochemical capacitances were measured. According to X-ray photoelectron spectroscopy (XPS) analysis, CC bonds were produced from CH defects of the reduced graphite oxide (rGtO) by the electrochemical re-oxidation. The conductivities of the reduced samples, with CH defects, and re-oxidized samples, with newly produced CC bonds, were high and low, respectively. The high electrochemical capacitance observed for the rGtO electrodes is caused by the activity of the CH defects and good conduction.

Electrochemical synthesis and capacitance properties of a novel poly(3,4-ethylenedioxythiophene bis-substituted bithiophene) electrode material

A novel EDOT-bithiophene-EDOT based comonomer, 5,5′-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2,2′-bithiophene (BEDOT-BT), was synthesized, and further, it was electrodeposited into PBEDOT-BT on platinum electrode as an active electrode material for supercapacitor. As-formed PBEDOT-BT film was characterized by FTIR, SEM and thermal analysis. The electrochemical performances of the PEDOT-BT electrode with good thermal stability were also investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy techniques. The electrochemical results showed that PBEDOT-BT electrode afforded a specific capacitance of 171 F g−1 at a current density of 1 A g−1 and good cycling stability in ACN-Bu4NPF6 electrolyte solution. The specific energy of the PEDOT-BT electrode reached 23.76 Wh/kg at a specific power of 0.49kW/kg. These results indicated that the PBEDOT-BT is a promising electrode material for supercapacitor applications.

Electrochemical Synthesis and Capacitance Properties of a Novel Poly (3,4-ethylenedioxythiophene) Derivative-Based Electrode Material

not Available.

Three-dimensional nanoporous TiO2 network films with excellent electrochemical capacitance performance

The three-dimensional (3D) nanoporous hydrogenated TiO2 (denoted as H-TiO2) network film on titanium substrate was fabricated by a novel and controllable method. The fabrication process involved dealloying, alkaline reflux and hydrogenation. The dealloying produced the 3D nanoporous titanium film with open pores and interconnected nanoflakes nearly perpendicular to the substrate. The oxidation of the 2D titanium nanoflakes in the alkaline reflux resulted in the formation of the TiO2 nanotubes with an inner diameter of 5–10nm and a length larger than 1.5μm. The 3D nanoporous TiO2 network film was formed by the self assembly of these long and thin TiO2 nanotubes. Hydrogenation induced the formation of oxygen vacancies and more hydroxyl groups on the H-TiO2 surface. The 3D nanoporous H-TiO2 network film presented a capacitance of 1.05mFcm−2 at the scanning rate of 100mVs−1. Furthermore, the H-TiO2 network film electrode also showed remarkable rate capability as well as excellent electrochemical cycling stability with a capacitance reduction of less than 7% after 1000 charge–discharge cycles at the current density of 100μAcm−2. The prominent electrochemical capacitance properties of the 3D H-TiO2 network film electrode could be attributed to its unique structural characteristics.

Mesoporous Polyaniline Films for High Performance Supercapacitors

High surface area mesoporous polyaniline (M-PANI) films can be produced on the surface of glassy carbon electrodes by the electrochemical polymerization from a composite made by mixing a Brij 98 surfactant with a water solution of aniline and sulfuric acid. The surfactant serves as a structure directing agent. When the quantity of Brij 98 in the composite was 45% by weight, it formed a hexagonal phase that comprises a template of cylinders arranged on a hexagonal lattice with a hydrophilic core. The aniline monomer infiltrated the core of the templates. When the potential of the glassy carbon electrode was cycled, the polymerization occurred inside the hollow core and cast it with the PANI film. Subsequently, the Brij 98 template was removed by a thorough washing with water to produce a well-ordered M-PANI film. The structure and the surface morphology of the M-PANI films were fully characterized by a scanning electron microscope and a transmission electron microscope. The electrochemical capacitance properties were investigated using electrochemical techniques, e.g., cyclic voltammetry, galvanostatic cycling and electrochemical impedance. The data showed a significant increase in the specific capacitance (as high as 532 F g−1) of the M-PANI films when compared with a non M-PANI electrode, which delivered a specific capacitance of 228 F g−1.

Post-heating effects on the physical and electrochemical capacitive properties of reduced graphene oxide paper

We report combined electrochemical double-layer capacitance (EDLC) and pseudocapacitance in reduced graphene oxide (rGO) thick film like paper due to annealing temperature variations. The influence of annealing temperature (from room temperature (RT) to 1000 °C) on the structural, morphological, electrical, and electrochemical properties of rGO paper was evaluated. Upon increasing the annealing temperature, shifting of the dominant (002) X-ray diffraction (XRD) peak to a higher degree, volume expansion, and red-shifting of the G band in Raman spectra were observed. High-resolution transmission electron microscopy (HRTEM) images showed a reduction in the interlayer distance in rGO sheets from 0.369 to 0.349 nm as the annealing temperature increased from RT to 1000 °C; these results were congruent with the XRD results. According to X-ray photoelectron spectroscopy (XPS), the presence of hydroxyl, carboxyl, and other oxygen-containing groups decreased in samples annealed at higher temperatures. The attached functional groups, the electrical conductivity, and the supercapacitance of rGO papers were found to be mutually interrelated and could be tuned by varying the annealing temperature. The rGO paper annealed at 200 °C in a 1 M H2SO4 electrolyte at a scan rate of 50 mV s−1 exhibited a maximum specific capacitance of 198 F g−1.

Tailoring of Single-Crystalline Complex Ta5Si3 Nanostructures: From Networked Nanowires to Nanosheets

Single-crystalline Ta5Si3 nanostructures with a complex morphology were synthesized through a catalyst-free, chemical vapor deposition method under low pressures. The morphology, structure, and composition of deposited nanostructures were studied by scanning electron microscopy, X-ray diffraction, and high-resolution transmission electron microscopy. These nanostructures have lengths of up to several tens of micrometers and an average thickness of 13 nm. It was found that the formation of networked Ta5Si3 nanostructures is highly sensitive to the vapor pressure of tantalum chloride and silica and is based on a vapor–solid mechanism. Results indicate that, with the decrease of silica vapor pressure, the Ta5Si3 networked nanowires evolve into networked nanoribbons and nanosheets via two-dimensional growth. Cyclic voltammetry measurements of the Ta5Si3 nanostructures show superior electrochemical capacitance properties of nanosheets compared to nanowires. It is expected that these nanostructures have great p...