Showing papers on "Cyclic voltammetry published in 2011"

Carbon coated textiles for flexible energy storage

Abstract: This paper describes a flexible and lightweight fabric supercapacitor electrode as a possible energy source in smart garments. We examined the electrochemical behavior of porous carbon materials impregnated into woven cotton and polyester fabrics using a traditional printmaking technique (screen printing). The porous structure of such fabrics makes them attractive for supercapacitor applications that need porous films for ion transfer between electrodes. We used cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy to study the capacitive behaviour of carbon materials using nontoxic aqueous electrolytes including sodium sulfate and lithium sulfate. Electrodes coated with activated carbon (YP17) and tested at ∼0.25 A·g−1 achieved a high gravimetric and areal capacitance, an average of 85 F·g−1 on cotton lawn and polyester microfiber, both corresponding to ∼0.43 F·cm−2.

Graphene Nanosheet/Ni2+/Al3+ Layered Double-Hydroxide Composite as a Novel Electrode for a Supercapacitor

Abstract: A hybrid chemically converted graphene nanosheet/Ni2+/Al3+ layered double-hydroxide (GNS/LDH) composite for supercapacitor material has been fabricated by a hydrothermal method. Scanning electron microscopy and transmission electron microscopy results reveal that Ni2+/Al3+ LDH platelets homogeneously grew onto the surfaces of the GNSs as spacers to keep the neighboring sheets separate. Electrochemical properties were characterized by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy. The composite exhibits a maximum specific capacitance of 781.5 F/g and excellent cycle life with an increase of the specific capacitance of 38.07% after 50 cycle tests. Even after 200 cycle tests, the increase of the capacitance is 22.56% compared with the initial capacitance.

Facile synthesis of large-area manganese oxide nanorod arrays as a high-performance electrochemical supercapacitor

Abstract: Large-area manganese oxide nanorod arrays (MONRAs) and herringbones (MOHBs) were successfully synthesized on F-doped SnO2 coated glass (FTO) substrates by a simple electrochemical method. Cyclic voltammetry (CV) and galvanostatic charge/discharge measurements demonstrated that the MONRAs and MOHBs exhibited excellent specific capacitance and good cycling stability in 0.5 M Na2SO4 aqueous solution. For example, the specific capacitance of the MONRAs achieves as high as 660.7 F g−1 at a scan rate of 10 mV s−1 and 485.2 F g−1 at a current density of 3 A g−1, respectively. Furthermore, the presented method may be extended to allow similar MONRs with a specific capacitance of 583.6 F g−1 to grow on flexible Ti foil, which may have great potential application in fabricating flexible supercapacitors.

Low-cost dye-sensitized solar cell based on nine kinds of carbon counter electrodes

Abstract: Nine kinds of carbon materials were introduced into dye-sensitized solar cells (DSCs) system as counter electrodes (CEs). We also compared the electrochemical catalytic activity of these carbon materials with Pt for the reduction of triiodide to iodide by measuring cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel-polarization curve. The nine kinds of carbon materials in this work included synthesized well-ordered mesoporous carbon (Com), activated carbon (Ca), carbon black (Cb), conductive carbon (Cc), carbon dye (Cd), carbon fiber (Cf), carbon nanotube (Cn), discarded toner of a printer (Cp) and fullerene (C60). All carbon materials showed electrochemical catalytic activity for triiodide reduction in the DSCs system. In particular, the synthesized Com showed excellent electrochemical catalytic activity which can be comparable to the performance of Pt. After optimizing the proportion of TiO2 added into the carbon paste and the spray time of the carbon paste, the DSCs based on these carbon CEs achieved energy conversion efficiencies of 2.8–7.5%. The results demonstrate that carbon material is a promising substitute for the expensive Pt CE for low-cost DSCs.

Intercalation of mesoporous carbon spheres between reduced graphene oxide sheets for preparing high-rate supercapacitor electrodes

Abstract: A method for preparing three-dimensional (3D) carbon-based architectures consisting of mesoporous carbon spheres intercalated between graphene sheets is demonstrated in this paper. Colloidally dispersed negatively charged graphene oxide (GO) sheets strongly interacted with positively charged mesoporous silica spheres (MSS) to form a MSS–GO composite. The MSS were then used as template for replicating mesoporous carbon spheres (MCS) via a chemical vapor deposition process, during which the GO sheets were reduced to reduced graphene oxide (RGO). Removal of the silica spheres left behind a 3D hierarchical porous carbon architecture with slightly crumpled graphene sheets intercalated with MCS. The 3D carbon structure contained a low amount of oxygen (3.2% of atomic ratio of O/C) than a RGO sample (10.1%), which was prepared by using the chemical reduction method with hydrazine as the reducing agent. Thermal annealing of the 3D carbon structure in ammonia atmosphere further reduced the O/C atomic ratio to 1.6%. The capacitive performance of the samples as supercapacitor electrodes was investigated using the cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy techniques. The 3D carbon structure showed a substantially lower equivalent series resistance and a higher power capability than the RGO electrode. In addition, the 3D carbon electrode exhibited an excellent electrochemical cyclability with 94% capacitance retention after 1000 cycles of galvanostatic charge–discharge. The method demonstrated in this work opens up a new route to the preparation of 3D graphene-based architectures for supercapacitor applications.

Graphene-encapsulated Fe3O4 nanoparticles with 3D laminated structure as superior anode in lithium ion batteries.

Abstract: Fe3O4-graphene composites with three-dimensional laminated structures have been synthesised by a simple in situ hydrothermal method. From field-emission and transmission electron microscopy results, the Fe3O4 nanoparticles, around 3-15 nm in size, are highly encapsulated in a graphene nanosheet matrix. The reversible Li-cycling properties of Fe3O4-graphene have been evaluated by galvanostatic discharge-charge cycling, cyclic voltammetry and impedance spectroscopy. Results show that the Fe3O4-graphene nanocomposite with a graphene content of 38.0 wt% exhibits a stable capacity of about 650 mAh g(-1) with no noticeable fading for up to 100 cycles in the voltage range of 0.0-3.0 V. The superior performance of Fe3O4-graphene is clearly established by comparison of the results with those from bare Fe3O4. The graphene nanosheets in the composite materials could act not only as lithium storage active materials, but also as an electronically conductive matrix to improve the electrochemical performance of Fe3O4.

Flexible graphene/MnO2 composite papers for supercapacitor electrodes

Abstract: Graphene/manganese dioxide (MnO2) composite papers (GMCP) are fabricated via a simple three-step route: preparation of graphene oxide/MnO2 composite (GOMC) dispersion, subsequent vacuum filtration of GOMC dispersion to achieve graphene oxide/MnO2 composite paper (GOMCP), and finally thermal reduction of GOMCP to generate GMCP. The morphology and microstructure of the prepared samples are characterized by field-emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transformation infrared spectroscopy, thermal gravimetric analysis and X-ray photoelectron spectroscopy. Moreover, as a binder-free and flexible electrode material for supercapacitors, the electrochemical properties of the prepared GMCP are evaluated by cyclic voltammetry and galvanostatic charge/discharge tests. As a result, the specific capacitance of the GMCP with the MnO2 weight ratio of 24% (GMCP-24) reaches 256 F g−1 at a current density of 500 mA g−1 and also shows good cycle stability, indicating a promising potential application as an effective electrode material for supercapacitors.

Rapid Synthesis of Li4Ti5O12 Microspheres as Anode Materials and Its Binder Effect for Lithium-Ion Battery

Abstract: Li4Ti5O12 microspheres composed of nanoflakes were synthesized within 1 h by a combination of a microwave-assisted hydrothermal method and a microwave postannealing process. The Li4Ti5O12 microspheres were characterized by X-ray diffraction, Brunauer–Emmett–Teller N2 adsorption, scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy. Sodium carboxymethyl cellulose (CMC) was also investigated as a low-cost green binder. The electrochemical tests, including constant current charge–discharge, cyclic voltammetry, and electrochemical impedance spectroscopy, demonstrated that the electrode using CMC as binder had better high-rate capability than the one with polyvinylidene fluoride (PVDF) binder. The electrode using CMC and PVDF as binder had the same lithium diffusion coefficient. The electrode using CMC as binder showed much lower charge transfer resistance, lower apparent activation energy, and lower apparent diffusion activation energy than for the electrode using PVDF as the...

Electrochemistry at Chemically Modified Graphenes

Abstract: Electrochemical applications of graphene are of great interest to many researchers as they can potentially lead to crucial technological advancements in fabrication of electrochemical devices for energy production and storage, and highly sensitive sensors. There are many routes towards fabrication of bulk quantities of chemically modified graphenes (CMG) for applications such as electrode materials. Each of them yields different graphene materials with different functionalities and structural defects. Here, we compare the electrochemical properties of five different chemically modified graphenes: graphite oxide, graphene oxide, thermally reduced graphene oxide, chemically reduced graphene oxide, and electrochemically reduced graphene oxide. We characterized these materials using transmission electron microscopy, Raman spectroscopy, high-resolution X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry, which allowed us to correlate the electrochemical properties with the structural and chemical features of the CMGs. We found that thermally reduced graphene oxide offers the most favorable electrochemical performance among the different materials studied. Our findings have a profound impact for the applications of chemically modified graphenes in electrochemical devices.

Highly dispersed Fe3O4 nanosheets on one-dimensional carbon nanofibers: Synthesis, formation mechanism, and electrochemical performance as supercapacitor electrode materials

Abstract: Highly dispersed Fe3O4 nanosheets on one-dimensional (1D) carbon nanofibers (CNFs) were firstly fabricated by combining the versatility of the electrospinning technique and solvent-thermal process. The electrochemical performances of the Fe3O4/CNFs nanocomposites as the electrode materials for supercapacitors were evaluated by cyclic voltammetry (CV) and galvanostatic charge–discharge measurement in 1 M Na2SO3 electrolyte. At different scan rates, the sample showed excellent capacitance behavior. The high capacitive behavior could be ascribed to the high electrical conductivity and the one-dimensional properties of the CNFs in Fe3O4/CNFs nanocomposites, which could decrease the charge transfer resistance of the Fe3O4. At the same time, the high specific surface area and high level exposure of the Fe3O4 nanosheets on the surface of the CNFs increased the electrochemical utilization of Fe3O4. Moreover, in comparison to the pure Fe3O4 (83 F g−1), the as-prepared Fe3O4/CNFs nanocomposites electrode exhibited a higher specific capacitance (135 F g−1). Meanwhile, the supercapacitor devices of the Fe3O4/CNFs nanocomposites exhibited excellent long cycle life along with 91% specific capacitance retained after 1000 cycle tests. Finally, a possible mechanism for the formation of the Fe3O4 nanosheets on the surface of CNFs was suggested.

Hierarchical micro- and mesoporous carbide-derived carbon as a high-performance electrode material in supercapacitors.

Abstract: Ordered mesoporous carbide-derived carbon (OM-CDC) materials produced by nanocasting of ordered mesoporous silica templates are characterized by a bimodal pore size distribution with a high ratio of micropores. The micropores result in outstanding adsorption capacities and the well-defined mesopores facilitate enhanced kinetics in adsorption processes. Here, for the first time, a systematic study is presented, in which the effects of synthesis temperature on the electrochemical performance of these materials in supercapacitors based on a 1 M aqueous solution of sulfuric acid and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid are reported. Cyclic voltammetry shows the specific capacitance of the OM-CDC materials exceeds 200 F g(-1) in the aqueous electrolyte and 185 F g(-1) in the ionic liquid, when measured in a symmetric configuration in voltage ranges of up to 0.6 and 2 V, respectively. The ordered mesoporous channels in the produced OM-CDC materials serve as ion-highways and allow for very fast ionic transport into the bulk of the OM-CDC particles. At room temperature the enhanced ion transport leads to 75% and 90% of the capacitance retention at current densities in excess of ∼10 A g(-1) in ionic liquid and aqueous electrolytes, respectively. The supercapacitors based on 250-300 μm OM-CDC electrodes demonstrate an operating frequency of up to 7 Hz in aqueous electrolyte. The combination of high specific capacitance and outstanding rate capabilities of the OM-CDC materials is unmatched by state-of-the art activated carbons and strictly microporous CDC materials.

Graphene-Encapsulated Hollow Fe3O4 Nanoparticle Aggregates As a High-Performance Anode Material for Lithium Ion Batteries

Abstract: Graphene-encapsulated ordered aggregates of Fe3O4 nanoparticles with nearly spherical geometry and hollow interior were synthesized by a simple self-assembly process. The open interior structure adapts well to the volume change in repetitive Li+ insertion and extraction reactions; and the encapsulating graphene connects the Fe3O4 nanoparticles electrically. The structure and morphology of the graphene-Fe3O4 composite were confirmed by X-ray diffraction, scanning electron microscopy, and high-resolution transmission microscopy. The electrochemical performance of the composite for reversible Li+ storage was evaluated by cyclic voltammetry and constant current charging and discharging. The results showed a high and nearly unvarying specific capacity for 50 cycles. Furthermore, even after 90 cycles of charge and discharge at different current densities, about 92% of the initial capacity at 100 mA g–1 was still recoverable, indicating excellent cycle stability. The graphene-Fe3O4 composite is therefore a capab...

Graphene oxide nanosheets/multi-walled carbon nanotubes hybrid as an excellent electrocatalytic material towards VO2+/VO2+ redox couples for vanadium redox flow batteries

Abstract: A graphene oxide nanosheets/multi-walled carbon nanotubes (GO/MWCNTs) hybrid with excellent electrocatalytic redox reversibility towards VO2+/VO2+ redox couples for vanadium redox flow batteries (VRFB) has been prepared by an electrostatic spray technique after efficient ultrasonic treatment. The structures and electrochemical properties of GO/MWCNTs are investigated by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and cyclic voltammetry. GO/MWCNTs are shown to be cross-linked and form an electrocatalytic hybrid with an effective mixed conducting network, leading to efficiently fast ion and electron transport characteristics. Compared with the pure GO nanosheets and MWCNTs, GO/MWCNTs deliver a much better electrocatalytic redox reversibility towards the positive VO2+/VO2+ couple, especially for the reduction from VO2+ to VO2+. The excellent experimental results demonstrate that the newly developed hybrid material holds great promise in the application of VRFB.

Nanoscale morphology dependent pseudocapacitance of NiO: Influence of intercalating anions during synthesis

Abstract: Three nano-porous NiO samples with high specific surface area were prepared by a simple hydrothermal method under homogeneous precipitation conditions using CTAB as a template and urea as the hydrolysis controlling agent. This study was done to determine the effect of different anions (acetate, nitrate and chloride) present in the precursor salts on the morphology and pseudocapacitance behavior of NiO. The samples were characterized by thermogravimetry (TG), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), Brunauer–Emmet–Teller (BET) isotherm and field emission scanning electron microscopy (FESEM). The final NiO samples showed different hierarchical surface morphologies and their effect on the electrochemical pseudocapacitance behavior was carefully studied by cyclic voltammetry, galvanostatic charge–discharge cycles (chronopotentiometry) and impedance spectroscopic techniques. The specific capacitance of NiO sample synthesized by NO3− ion intercalation showed higher surface area, intermediate porosity and a novel pine-cone morphology with nano-wire surface attachments. This sample exhibits the highest pseudocapacitance of 279 F g−1 at a scan rate of 5 mV s−1, calculated from the cyclic voltammetry measurements. The sample synthesized by Cl− intercalation shows a nano-flower morphology with lower surface area, porosity and pseudocapacitance behaviour. The NiO sample prepared in the presence of CH3COO− ions showed a honeycomb type surface morphology with an intermediate pseudocapacitance value but higher reversibility. The galvanostatic charge–discharge and impedance spectroscopic measurements on these NiO electrodes were consistent with CV results. The Coulombic efficiency of all the three NiO samples was found to be high (∼85 to ∼99%) after 100 galvanostatic charge–discharge cycles. This study shows that the surface morphology and porosity of NiO are strongly influenced by the anions in the precursor salts, and in turn affect significantly the pseudocapacitance behavior and the power performance of NiO powders.

Morphology-controllable synthesis of cobalt oxalates and their conversion to mesoporous Co3O4 nanostructures for application in supercapacitors.

Abstract: In this work, one-dimensional and layered parallel folding of cobalt oxalate nanostructures have been selectively prepared by a one-step, template-free, water-controlled precipitation approach by simply altering the solvents used at ambient temperature and pressure. Encouragingly, the feeding order of solutions played an extraordinary role in the synthesis of nanorods and nanowires. After calcination in air, the as-prepared cobalt oxalate nanostructures were converted to mesoporous Co(3)O(4) nanostructures while their original frame structures were well maintained. The phase composition, morphology, and structure of the as-obtained products were studied in detail. Electrochemical properties of the Co(3)O(4) electrodes were carried out using cyclic voltammetry (CV) and galvanostatic charge-discharge measurements by a three-electrode system. The electrochemical experiments revealed that the layered parallel folding structure of mesoporous Co(3)O(4) exhibited higher capacitance compared to that of the nanorods and nanowires. A maximum specific capacitance of 202.5 F g (-1) has been obtained in 2 M KOH aqueous electrolyte at a current density of 1 A g(-1) with a voltage window from 0 to 0.40 V. Furthermore, the specific capacitance decay after 1000 continuous charge-discharge cycles was negligible, revealing the excellent stability of the electrode. These characteristics indicate that the mesoporous Co(3)O(4) nanostructures are promising electrode materials for supercapacitors.

Facile preparation and enhanced capacitance of the polyaniline/sodium alginate nanofiber network for supercapacitors.

Abstract: A porous and mat-like polyaniline/sodium alginate (PANI/SA) composite with excellent electrochemical properties was polymerized in an aqueous solution with sodium sulfate as a template. Ultraviolet–visible spectra, X-ray diffraction pattern, and Fourier transform infrared spectra were employed to characterize the PANI/SA composite, indicating that the PANI/SA composite was successfully prepared. The PANI/SA nanofibers with uniform diameters from 50 to 100 nm can be observed on scanning electron microscopy. Cyclic voltammetry and galvanostatic charge/discharge tests were carried out to investigate the electrochemical properties. The PANI/SA nanostructure electrode exhibits an excellent specific capacitance as high as 2093 F g–1, long cycle life, and fast reflect of oxidation/reduction on high current changes. The remarkable electrochemical characteristic is attributed to the nanostructured electrode materials, which generates a high electrode/electrolyte contact area and short path lengths for electronic t...

LiNi1/3Co1/3Mn1/3O2–Graphene Composite as a Promising Cathode for Lithium-Ion Batteries

Abstract: The use of graphene as a conductive additive to enhance the discharge capacity and rate capability of LiNi1/3Co1/3Mn1/3O2 electrode material has been demonstrated. LiNi1/3Co1/3Mn1/3O2 and its composite with graphene (90:10 wt %) were prepared by microemulsion and ball-milling techniques, respectively. The structural and morphological features of the prepared materials were investigated with powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Characterization techniques depict single-phase LiNi1/3Co1/3Mn1/3O2 with particle sizes in the range of 220–280 nm. Electrochemical studies on LiNi1/3Co1/3Mn1/3O2 and LiNi1/3Co1/3Mn1/3O2–graphene were conducted using cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy methods by constructing a lithium half-cell. Cyclic voltammograms show the well-defined redox peaks corresponding to Ni2+/Ni4+. Charge–discharge tests were performed ...

Facile Synthesis of Nanocrystalline TiO2 Mesoporous Microspheres for Lithium-Ion Batteries

Abstract: TiO2 mesoporous nanocrystalline microspheres assembled from uniform nanoparticles were synthesized by a facile and template-free hydrolytic precipitation route in normal solvent media The phase structure, morphology, and pore nature were analyzed by X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and BET measurements The electrochemical properties were investigated by cyclic voltammetry, constant current discharge−charge tests, and electrochemical impedance techniques Microspheres with diameters ranging from 02 to 10 μm were assembled by aggregation of nanosized TiO2 crystallites (∼8−15 nm) and yielded a typical type-IV BET isotherm curve with a surface area of ∼1169 m2 g−1 and a pore size of ∼54 nm A simplified model was proposed to demonstrate the nanoparticle packing modes to form the mesoporous structure The initial discharge capacity reached 265 mAh g−1 at a rate of 006 C and 234 mAh g−1 at a rate of 012 C The samples demonstrated high rat