Synthesis and electrochemical performance of bismuth–vanadium oxyfluoride

Bismuth–vanadium oxyfluoride (Bi₂VO₅F) has been synthesized using a simple, solid-state reaction process at different sintering temperatures. The structure and performance of the samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge experiments. The results show that bismuth–vanadium oxyfluoride belongs to a tetragonal crystal system with space group I4mm. The sample that was synthesized at 550 °C (P550) exhibits relatively good electrochemical properties. Sample P550 shows a high, initial discharge capacity of 222 mAh g⁻¹ at a rate of 100 mA g⁻¹ between 1.4 and 3.5 V. Sample P550 also shows acceptable electrochemical cycling properties. After the first cycle, the discharge specific capacity remains between 106 and 155 mAh g⁻¹, which plateaus between 2.1 and 1.9 V during the first 15 cycles.     

Lithium storage performance and interfacial processes of three dimensional porous Sn–Co alloy electrodes for lithium-ion batteries

Three-dimensional porous Cu film is prepared for the first time by electroless plating. Sn–Co alloy is electrodeposited on the porous Cu film to fabricate porous Sn–Co alloy electrode. SEM images evidence that porous Sn–Co alloy electrode presents a three-dimensional porous structure. XRD results show that the Sn–Co alloy electrode comprises pure Sn and CoSn₂ phases. Electrochemical discharge/charge results show that the three-dimensional porous Sn–Co alloy electrode exhibits much better cycleability than planar Sn–Co alloy electrode, with first discharge capacity and charge capacity of 636.3 and 528.7 mAh g⁻¹, respectively. After 70th cycling, capacity retention is 83.1% with 529.5 mAh g⁻¹. The lithiation and delithiation processes during first discharge and charge were investigated by electrochemical impedance spectroscopy (EIS). EIS results together with differential capacity curves describe the process of SEI formation, charge transfer and phase transformation in the alloy electrode in the first discharge, and phase transformation during charge at delithiation potential.     

Preparation of high surface area nickel electrodeposit using a liquid crystal template technique

We show in this work that template electrodeposition of nickel at room temperature from a nickel sulphamate bath prepared in a new hexagonal liquid crystalline phase of water-Triton X-100-poly (acrylic acid) results in a highly porous surface. The roughness factor value of about 3620 obtained for this coating is the highest value reported in the literature for any electrodeposited nickel. The scanning electron microscopy (SEM) and scanning tunneling microscopy (STM) pictures show the formation of porous deposit with granular features in between the pores. The single electrode double layer capacitance value measured for the deposit is 338 mF cm⁻², which translates into a specific capacitance of 50 F g⁻¹ without any post-thermal treatment of the electrode, suggesting its utility in super capacitors. Electrochemical studies using cyclic voltammetry (CV), Tafel plots and electrochemical impedance spectroscopy (EIS) and comparison of these results with some existing high surface area Ni catalysts show that the material has potential application as an excellent hydrogen evolving cathode.     

Preparation and electrochemistry of NiO/SiNW nanocomposite electrodes for electrochemical capacitors

This paper studies nickel oxide/silicon nanowires (NiO/SiNWs) as composite thin films in electrodes for electrochemical capacitors. The SiNWs as backbones were first prepared by chemical etching, and then the Ni/SiNW composite structure was obtained by electroless plating of nickel onto the surface of the SiNWs. Next, the NiO/SiNW nanocomposites were fabricated by annealing Ni/SiNW composites at different temperatures in an oxygen atmosphere. Once the electrodes were constructed, the electrochemical behavior of these electrodes was investigated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In 2 M KOH solution, the electrode material was found to have novel capacitive characteristics. Finally, when the NiO/SiNW composites were annealed at 400 °C, the maximum specific capacitance value was found to be as high as 681 F g⁻¹ (or 183 F cm⁻³), and the probing of the cycling life indicated that only about 3% of the capacity was lost after 1000 charge/discharge cycles. This study demonstrated that NiO/SiNW composites were the optimal electrode choice for electrochemical capacitors.     

Porous polythiophene as a cathode material for lithium batteries with high capacity and good cycling stability

Polythiophene (PTh) has been synthesized by chemical oxidative polymerization and used as an active cathode material in lithium batteries. The lithium batteries are characterized by cyclic voltammetry (CV), galvanostatic charge/discharge cycling and electrochemical impedance spectroscopic studies (EIS). The lithium battery with the PTh cathode exhibits a discharge voltage of 3.7 V compared to Li⁺/Li and excellent electrochemical performance. PTh can provide large discharge capacities above 50 mA h g⁻¹ and good cycle stability at a high current density 900 mA g⁻¹. After 500 cycles, the discharge capacity is maintained at 50.6 mA h g⁻¹. PTh is a promising candidate for high-voltage power sources with excellent electrochemical performance.     

Facile preparation of electrodes based on WO3 nanostructures modified with C and S used as anode materials for Li-ion batteries

An appropriate morphological and structure matrix configuration where lithium ions could insert and de-insert is essential for lithium-ion batteries (LiB). Tungsten oxides (WO₃) are especially attractive materials for this aim. In this research, the effects of the morphology and composition of WO₃ nanostructures on the charge/discharge behavior for Li-ion batteries are methodically examined. On the one hand, nanostructured WO₃ thin film was effectively synthesized by an electrochemical procedure. Then, an annealing treatment at 600°C in air environment for 4 h was carried out. In the second electrode synthesized, a carbon layer was uniformly deposited on WO₃ nanostructures to obtain a WO₃/C electrode. Finally, WO₃/WS₂ electrodes were prepared by means of in situ sulfurization of WO₃ one-step solid-state synthesis using tungsten trioxide (WO₃) and thiourea as precursor material. By using X-ray photoelectron spectroscopy, X-ray diffraction analysis, transmission electron microscopy, Raman spectra, and field-emission scanning electron microscopy, the three electrodes have been morphologically characterized. Electrochemical properties were analyzed by cyclic voltammogram, galvanostatic charge/discharge cycling, and electrochemical impedance spectroscopy. Among all the synthesized samples, WO₃/C nanostructures reveal the best performance as they exhibit the greatest discharge capacity and cycle performance (820 mA h g⁻¹).     

A new high-performance cathode material for rechargeable lithium-ion batteries: Polypyrrole/vanadium oxide nanotubes

Polypyrrole/vanadium oxide nanotubes (PPy/VOx-NTs) as a new high-performance cathode material for rechargeable lithium-ion batteries are synthesized by a combination of hydrothermal treatment and cationic exchange technique. The morphologies and structures of the as-prepared samples are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetry and differential scanning calorimeter (TG-DSC) and X-ray powder diffraction (XRD). The results indicate that the organic templates are mainly substituted by the conducting polymer polypyrrole without destroying the previous nanotube structure. Their electrochemical properties are evaluated via galvanostatic charge/discharge cycling, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It is found that PPy/VOx-NTs exhibit high discharge capacity and excellent cycling performance at different current densities compared to vanadium oxide nanotubes (VOx-NTs). After 20 cycles, the reversible capacity of PPy/VOx-NTs (159.5 mAh g⁻¹) at the current density of 80 mA g⁻¹ is about four times of magnitude higher than that of VOx-NTs (37.5 mAh g⁻¹). The improved electrochemical performance could be attributed to the enhanced electronic conductivity and the improved structural flexibility resulted from the incorporation of the conducting polymer polypyrrole.     

Influence of the reaction temperature on polyaniline morphology and evaluation of their performance as supercapacitor electrode

The polyaniline (PANI) nanostructures of tubular, spherical, and granules morphologies were synthesized by chemical oxidation approach in different reaction temperatures and used as the active electrode materials of symmetric redox supercapacitors. X‐ray diffraction and scanning electron microscopy techniques are employed for characterization of these PANIs. With the initial and reaction temperature increase, the morphology of PANI turned from block to spherical and tubular. Electrochemical properties of these PANI electrodes are studied by cyclic voltammetry (CV), agalvanostatic charge–discharge test, and electrochemical impedance spectroscopy (EIS) in 1M H₂SO₄ aqueous solution. The highest electrochemical properties are obtained on the PANI with tubular morphology. The initial specific capacitance of tubular, spherical, and granules PANI are about 300, 300, and 290 F g^?1 at a constant current of 5 mA. Meanwhile, the retention of the tubular PANI capacitance after 500 charge–discharge cycles was 75%, whereas the spherical and granules PANI was only 35% and 57%. The results indicate that tubular PANI electrodes have potential applications as high‐performance supercapacitors electrode materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3753–3758, 2013     

A novel EDOT–nonylbithiazole–EDOT based comonomer as an active electrode material for supercapacitor applications

A novel EDOT–nonylbithiazole–EDOT based bis(3,4-ethylene-dioxythiophene)-(4,4′-dinonyl-2,2′-bithiazole) comonomer was synthesized and was electrochemically deposited onto carbon fiber electrode as an active electrode material. An electrochemical impedance study on the prepared electrodes is reported in this paper. Capacitive behavior of the carbon fiber microelectrode/poly(3,4-ethylene-dioxythiophene)-(4,4′-dinonyl-2,2′-bithiazole) system was investigated with cyclic voltammetry (CV) experiments and electrochemical impedance spectroscopy. Variation of capacitance values by scan rate and specific capacitance values at different potentials are presented. Specific capacitance value for a galvanostatically prepared polymer film with a charge of 5 C cm⁻² was obtained about 340 mF cm⁻². Effect of the solvent and the deposition charge on the capacitive behavior of the film was investigated using electrochemical impedance spectroscopy. An equivalent circuit model was proposed and the electrochemical impedance data were fitted to find out numerical values of the proposed components. The galvanostatic charge/discharge characteristic of a film was investigated by chronopotentiometry and the morphology of the films electrodeposited at different deposition charges were monitored using FE-SEM.     

Porous ZnO nanosheets grown on copper substrates as anodes for lithium ion batteries

Porous ZnO nanosheets are grown directly on copper substrates by a chemical bath deposition technique followed by a heat treatment. The materials are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Their electrochemical properties as anodes of lithium ion batteries are examined by cyclic voltammetry (CV) and galvanostatic discharge–charge tests. The results show that porous ZnO nanosheets exhibit higher reversible capacities and better cyclabilities than those of commercial ZnO powders. When cycled at 0.05 A g⁻¹, these nanosheets deliver initial discharge and charge capacities of 1120 and 750 mAh g⁻¹, and at 0.5 A g⁻¹, they keeps stable capacities of 400 mAh g⁻¹ up to 100 cycles, in addition, they also exhibit good rate capabilities. It is believed that the porous sheet nanostructure plays an important role in the electrochemical performance.     

Hierarchical NiO nanoflake coated CuO flower core–shell nanostructures for supercapacitor

In this work, we developed a simple and cost-effective approach to prepare the hierarchical NiO/CuO nanocomposite without any surfactant. The morphology and structure of the hybrid nanostructure was examined by focus ion beam scanning electron microscopy (FIB/SEM), X-ray diffraction spectroscopy (XRD) and high-resolution transmission electron microscopy (HRTEM). Furthermore, the electrochemical properties of the hierarchical NiO/CuO nanocomposite electrodes were elucidated by cyclic voltammograms, galvanostatic charge/discharge tests and electrochemical impedance spectroscopy in 6 M KOH electrolyte. The electrochemical results demonstrated that this unique NiO/CuO nanostructure exhibited a specific capacitance of 280 F g⁻¹ and excellent cycling stability (91.4% retention after 3000 cycles). The remarkable electrochemical performance coupled with the facile synthesis of the hierarchical NiO/CuO nanocomposite indicated the great application potential in supercapacitors.     

Performance evaluation of CNT/polypyrrole/MnO2 composite electrodes for electrochemical capacitors

A ternary composite of CNT/polypyrrole/hydrous MnO₂ is prepared by in situ chemical method and its electrochemical performance is evaluated by using cyclic voltammetry (CV), impedance measurement and constant-current charge/discharge cycling techniques. For comparative purpose, binary composites such as CNT/hydrous MnO₂ and polypyrrole/hydrous MnO₂ are prepared and also investigated for their physical and electrochemical performances. The specific capacitance (SC) values of the ternary composite, CNT/hydrous MnO₂ and polypyrrole/hydrous MnO₂ binary composites estimated by CV technique in 1.0 M Na₂SO₄ electrolyte are 281, 150 and 35 F g⁻¹ at 20 mV s⁻¹ and 209, 75 and 7 F g⁻¹ at 200 mV s⁻¹, respectively. The electrochemical stability of ternary composite electrode is investigated by switching the electrode back and forth for 10,000 times between 0.1 and 0.9 V versus Ag/AgCl at 100 mV s⁻¹. The electrode exhibits good cycling stability, retaining up to 88% of its initial charge at 10,000th cycle. A full cell assembled with the ternary composite electrodes shows a SC value of 149 F g⁻¹ at a current loading of 1.0 mA cm⁻² during initial cycling, which decreased drastically to a value of 35 F g⁻¹ at 2000th cycle. Analytical techniques such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), Brunauer-Emmet-Teller (BET) surface area measurement and inductively coupled plasma-atomic emission spectrometry (ICP-AES) are also used to characterize the composite materials.     

Electrochemical performance of Li[Co0.1Ni0.15Li0.2Mn0.55]O2 modified by carbons as cathode materials

To enhance specific capacity, cycle performance and rate-capability of lithium-ion battery cathode materials, the Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ (LCMNO) is modified by coating them with amorphous carbons and by preparing nanocomposites with nanostructured carbons (carbon nanotube and graphene). The carbon-treated LCMNO powders and their cathodes are characterized by morphological observation, crystalline property analysis, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. The LCMNO nanocomposite shows a superior discharge capacity of ca. 290 mAh g⁻¹ at low C-rates, due to a greater number of active sites embedded by nanostructured carbon species. In contrast, the carbon-coated LCMNO shows higher discharge capacity in high rate regions due to the carbon-coated layer in the carbon-coated LCMNO, suppressing the side reactions and enhancing the electrical conductivity.     

A Facile Preparation of Zinc Cobaltite (ZnCo2O4) Nanostructures for Promising Supercapacitor Applications

Hybrid nanocomposites have shown their excellent potential in energy storage devices particularly in electrochemical supercapacitors to meet the forthcoming demand in the energy sector applications. Novel hybrid composited displayed the dual nature of electrochemical double layer and pseudocapacitive behaviour, which makes them more advantageous in supercapacitor device fabrication. Zinc cobaltite (ZnCo₂O₄) nanostructures have been prepared by precipitation route and the structural, optical and electrochemical properties of the final product were analyzed. X-ray pattern showed the spinal cubic phase structure with fine nano-crystallites. The FTIR and Raman spectrum confirmed the presence of surface functional groups and confirmed the formation of high-quality ZnCo₂O₄ nanocrystals. XPS and EDX spectrum showed the high purity and good crystallinity nature of the as-prepared ZnCo₂O₄ nanocrystal. FE-SEM and TEM analysis exhibits the bundle like morphology of the final product. Finally, the as-prepared ZnCo₂O₄ nanostructure was investigated by cyclic voltammetry (CV), galvanic charge–discharge analysis (GCD) and electrochemical impedance spectroscopy (EIS) to check its suitability. The electrochemical investigation demonstrated the highest capacitance of 159 F g^?1 at 2 mA cm^?2 in 2 M KOH electrolyte and the long cyclic test showed the 92% initial capacitance retention over 2500 cycles. It reveals/demonstrated that the spinel ZnCo₂O₄ nanostructures own a promising usage in devices for electrochemical energy storage.

     

Enhanced rate performance of carbon-coated LiNi0.5Mn1.5O4 cathode material for lithium ion batteries

Conductive carbon has been coated on the surface of LiNi_0.5Mn_1.5O₄ cathode material by the carbonization of sucrose for the purpose of improving the rate performance. The effect of carbon coating on the physical and electrochemical properties is discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), cycling and rate tests. Results demonstrate that the carbon coating can greatly enhance the discharge capacity, rate capability and cycling stability of the LiNi_0.5Mn_1.5O₄ without degrading the spinel structure. The sample modified with 1 wt.% sucrose displays the best performance. A large capacity of 130 mAh g⁻¹ at 1 C discharge rate with a high retention of 92% after 100 cycles and a stable 114 mAh g⁻¹ at 5 C discharge rate can be delivered. The remarkably improved rate properties of the carbon-coated samples are due to the suppression of the solid electrolyte interfacial (SEI) layer development and faster kinetics of both the Li⁺ diffusion and the charge transfer reaction.     

Supercapacitor device performances of polycarbazole/graphene and polycarbazole/nanoclay/graphene nanocomposites

In this study, graphene oxide (GO) is chemically reacted with sodium borohydride (NaBH₄) to form reduced graphene oxide (rGO). rGO, polycarbazole (PCz)/rGO and PCz/nanoclay/rGO materials were obtained by chemical polymerisation method. These three materials were characterised by Fourier-transform infra-red spectroscopy-attenuated transmission reflectance, scanning electron microscopy, energy-dispersive X-ray analysis, cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy. The PCz/nanoclay/rGO nanocomposite shows significantly improved capacitance (C_sp?=?187.78?F?g^?1) compared to that of PCz/rGO (C_sp?=?74.18?F?g^?1) and rGO (C_sp?=?20.78?F?g^?1) at the scan rate of 10?mV?s^?1 by CV method. The supercapacitor device performance results show high power density (P?=?1057.81?W?kg^?1) and energy density (E?=?1.7?Wh?kg^?1) obtained from Ragone plot for PCz/nanoclay/rGO material. Stability tests were also examined by the CV method for 1000 cycles.     

Hexavalent chromium synthesized polyaniline nanostructures: Magnetoresistance and electrochemical energy storage behaviors

In this work, the oxidant Cr(VI) dose was observed to have influenced the polyaniline (PANI) nanostructures as well as the crystallization structure. The temperature dependent resistivity study revealed a quasi 3-dimensional variable range hopping (VRH) electrical conduction mechanism. The permittivity was found to be affected by the PANI nanostructures. The observed positive MR at room temperature in the synthesized PANI samples was analyzed by the wave-function shrinkage model. The electrochemical energy storage was investigated using the cyclic voltammetry (CV) and galvanostatic charge–discharge measurements. The highest gravimetric capacitance of 298.5 F g⁻¹ was obtained in the prepared PANI sample using 3 mmol K₂Cr₂O₇ derived from the CV at a scan rate of 5 mV s⁻¹ and the maximum value of gravimetric capacitance of 330.2 F g⁻¹ was achieved in the galvanostatic charge–discharge measurements at a current density of 0.5 A g⁻¹. After applying an external magnetic field, the capacitance decreased due to the observed positive magnetoresistance phenomenon. The cyclic stability studies revealed that the synthesized PANI samples exhibited good durability and retained around 80% of the capacitance even after 1000 charge–discharge galvanostatic cycles.     

Nickel foam-supported porous Ni(OH)2/NiOOH composite film as advanced pseudocapacitor material

A porous net-like β-Ni(OH)₂/γ-NiOOH composite film is prepared by a chemical bath deposition. The as-prepared porous composite film shows a highly porous structure built up by many interconnected nanoflakes with a thickness of about 20 nm. The pseudocapacitive behavior of the porous composite film is investigated by cyclic voltammograms (CV) and galvanostatic charge–discharge tests in 1 M KOH. The porous β-Ni(OH)₂/γ-NiOOH composite film exhibits a noticeable pseudocapacitance with 1420 F g⁻¹ at 2 A g⁻¹ and 1098 F g⁻¹ at 40 A g⁻¹, respectively, much higher than those of the dense Ni(OH)₂ film (897 F g⁻¹ at 2 A g⁻¹ and 401 at 40 A g⁻¹). The porous architecture is responsible for the enhancement of the electrochemical properties, and it increases electrochemical reaction area, shortens ions diffusion paths and relaxes volume change caused by the electrochemical reactions.     

Bi2O3 modified cobalt hydroxide as an electrode for alkaline batteries

Manganese dioxide electrode shows reversible charge storage capacity, if the charge-discharge process is limited to 0.3e⁻ exchange. Addition of small amount of Bi₂O₃ to manganese dioxide induces reversibility with an exchange of 2e⁻/Mn. Nickel hydroxide is known to reversibly exchange 1e⁻. In spite of isostructural relationship between the cobalt hydroxide, nickel hydroxide and manganese dioxide, cobalt hydroxide does not show any electrochemical activity. Bi₂O₃ modified cobalt hydroxide electrodes exchanges 0.3-0.5e⁻/Co during the charge discharge process. The oxidation-reduction process in cobalt hydroxide and Bi₂O₃ modified cobalt hydroxide electrodes were monitored using the PXRD patterns.     

Co3O4 thin film prepared by a chemical bath deposition for electrochemical capacitors

Co₃O₄ thin film is synthesized on ITO by a chemical bath deposition. The prepared Co₃O₄ thin film is characterized by X-ray diffraction, and scanning electron microscopy. Electrochemical capacitive behavior of synthesized Co₃O₄ thin film is investigated by cyclic voltammetry, constant current charge/discharge and electrochemical impedance spectroscopy. Scanning electron microscopy images show that Co₃O₄ thin film is composed of spherical-like coarse particles, together with some pores among particles. Electrochemical studies reveal that capacitive characteristic of Co₃O₄ thin film mainly results from pseudocapacitance. Co₃O₄ thin film exhibits a maximum specific capacitance of 227 F g⁻¹ at the specific current of 0.2 A g⁻¹. The specific capacitance reduces to 152 F g⁻¹ when the specific current increases to 1.4 A g⁻¹. The specific capacitance retention ratio is 67% at the specific current range from 0.2 to 1.4 A g⁻¹.