Galvanostatic Charge Discharge Method Research Articles

High cell-potential and high-rate neutral aqueous supercapacitors using activated biocarbon: In situ electrochemical gas chromatography

Electric double layer capacitors (EDLCs) are known for their high-power densities due to the fast mechanism of charge-discharge processes. However, producing eco-friendly and economically viable materials for supercapacitors is one of the most important challenges. Also, a high-rate capability of the supercapacitor is desirable for pulse applications. In the present work, a high cell-potential and high-rate supercapacitor was created using biocarbon derived from a rubberwood-sawdust biomass at three different temperature. Bio-AC carbonized at 900 °C shows a high specific surface area of 1932 m2 g−1 and a pore volume of 1.44 cm3 g−1. A symmetrical supercapacitor of bio-AC(900 °C) with 1.0 M LiTFSI(aq.) displays a high practical cell potential of 1.8 V with an impressive rate up to 100 A g−1. A specific capacitance of ∼100 F g−1 at 0.1 A g−1 was estimated by a galvanostatic charge-discharge method. Besides, an excellent capacitance retention is retained at higher specific currents, for instance, 71% and 49% were estimated at 60 A g−1 and 100 A g−1, respectively. An excellent long-term stability of 84% at 1.8 V was evaluated for the symmetrical supercapacitor in 1.0 M LiTFSI(aq.) after 50,000 cycles at 3.0 A g−1. Also, gas chromatography coupled with the electrochemical cell was employed for the in situ determination of electrolytically generated gases in real time at the positive and negative applied potentials. H2 and CO2 gasses can be generated at too high applied potentials. Understanding the gas evolution in this work may be useful for further development of supercapacitors. Also, high cell-potential and high-rate neutral aqueous supercapacitors using activated biocarbon may be useful for high-power applications.

Nitrate Combustion Synthesis of NVP-Type Cathode Material for Na-Ion Batteries

The synthesis and characterization of a Na3V2(PO4)3 cathode material for room-temperature sodium-ion battery is reported. The NVP material was prepared using a two-step process which proceeded via sol-gel nitrate combustion method for precursor preparation and subsequent pyrolysis under Argon. The materials have been investigated using SEM, EDX, XRD and TOF-SIMS methods. Electrochemical characterization has been carried out using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge method (GCD). The electrode slurry was prepared by mixing the active material, conductive additive (Super P) and polyvinylidene difluoride (PVdF) binder in a 75:15:10 mass ratio. The mixed slurry was cast onto aluminium foil using doctor-blade technique. The cast electrodes were dried under vacuum for 24h. Electrochemical tests were carried out in coin cells, which were assembled in an Argon-filled glovebox (O2 < 0.1 ppm, H2O < 0.1 ppm). Sodium metal was used as the counter electrode and 1M NaPF6 in EC:PC (1:1 vol) as the electrolyte in half-cell measurements. Acknowledgements The present study was supported by European Regional Development Fund (Centres of Excellence TK141 (2014-2020.4.01.15-0011)6, Higher education specialization stipends in smart specialization growth areas 2014-2020.4.02.16-0026), “Institutional development program for research and development and higher education institutions” (ASTRA) (Graduate School of Functional Materials and Technologies, Materials Technology Projects SLOKT12180T and SLOKT12181T, Energy Technology Project SLOKT10209T), Estonian Research Council (Institutional Research Grant IUT20–13 and by NAMUR project 3.2.0304.12-0397. Mr. Väli thanks Estonian Students Fund in USA for financial support.

How to Measure and Calculate Equivalent Series Resistance of Electric Double-Layer Capacitors.

Electric double-layer capacitors (EDLCs) are energy storage devices that have attracted attention from the scientific community due to their high specific power storage capabilities. The standard method for determining the maximum power (Pmax) of these devices uses the relation Pmax = U2/4RESR, where U stands for the cell voltage and RESR for the equivalent series resistance. Despite the relevance of RESR, one can observe a lack of consensus in the literature regarding the determination of this parameter from the galvanostatic charge-discharge findings. In addition, a literature survey revealed that roughly half of the scientific papers have calculated the RESR values using the electrochemical impedance spectroscopy (EIS) technique, while the other half used the galvanostatic charge discharge (GCD) method. RESR values extracted from EIS at high frequencies (>10 kHz) do not depend on the particular equivalent circuit model. However, the conventional GCD method better resembles the real situation of the device operation, and thus its use is of paramount importance for practical purposes. In the latter case, the voltage drop (ΔU) verified at the charge-discharge transition for a given applied current (I) is used in conjunction with Ohm’s law to obtain the RESR (e.g., RESR = ΔU/ΔI). However, several papers have caused a great confusion in the literature considering only applied current (I). In order to shed light on this important subject, we report in this work a rational analysis regarding the GCD method in order to prove that to obtain reliable RESR values the voltage drop must be normalized by a factor of two (e.g., RESR = ΔU/2I).

Misfit-layered cobaltite Ca3Co4O9+δas a new electrode for supercapacitor with excellent cycling stability

One of the major challenges for transition metal used as supercapacitor electrode is their poor electrical conductivity. In this study, misfit-layered cobaltite Ca3Co4O9+δ (CCO) oxide is successfully synthesized using sol-gel method. The structure, morphology and surface composition of the obtained CCO powder are characterized by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy measurement. Herein the CCO exhibits a high electrical conductivity of 62.0 S cm−1 at room temperature. The prepared CCO electrode was characterized by cyclic voltammetry and galvanostatic charge–discharge method to evaluate its electrochemical performances. The CCO electrode displays good capacitance features with a mass specific capacitance of 229.3 F g−1 at a scanning rate of 2 mV s−1, which are mainly due to its high electrical conductivity and unique layered structure. Furthermore, the CCO electrode shows outstanding cycling performance with 107% capacitance retention after 44 000 cycles. More importantly, the bulk CCO can be directly used as free-standing electrode for electrochemical supercapacitors with an area specific capacitance (340 mF cm−2) and excellent cycling stability.

Electrodeposition of polypyrrole on He plasma etched carbon nanotube films for electrodes of flexible all-solid-state supercapacitor

Flexible and portable supercapacitors have been intensively investigated due to their reliable energy storage performance and promising applications in wearable electronic devices. Owing to the unique pseudocapacitance property of conducting polymer and the high conductivity and stability of carbon nanotube film (CNTF), polypyrrole (PPy) was electrodeposited on He plasma etched carbon nanotube film (HCNTF) for electrodes of flexible supercapacitor with high performance. As demonstrated by Raman spectra and contact angle measurement, He plasma etching can produce amorphous carbon on the CNTF and advance the hydrophilicity of the CNTF, which promoted the electrodeposition of PPy onto the CNTFs and improved the adhesion between PPy and CNTF. All-solid-state supercapacitors were fabricated using the PPy/HCNTF electrodes and H3PO4/PVA electrolyte. Cyclic voltammetry tests showed that the capacitive performance of PPy/HCNTF is much higher than that of PPy/CNTF. The specific capacitance of the PPy/HCNTF supercapacitor determined by a galvanostatic charge-discharge method at 0.5 A g−1 is about 414 F g−1, which was maintained 92% after 5000 cycles, reflecting high cycle stability. Moreover, the PPy/HCNTF supercapacitor could remain 96% of the original capacitance when it was bent for 500 times surrounding a cylinder with a diameter of 1.5 cm, showing perfect flexibility and great potential for flexible energy storage devices.

Superb sono-adsorption and energy storage potential of multifunctional Ag-Biochar composite

Silver embedded banana peel biochar (Ag-BBc) composite was tailored effectively by green synthetic route. Azadirachta indica leaf extract was employed for preparation of Ag nanoparticles as reducing agent and biochar was derived from the of banana peel via pyrolysis. The multi-functionality of the fabricated nanocomposite was investigated through its application towards energy storage and environmental remediation. The prepared composite was characterized in detail by various analytical techniques and the electro-chemical aspects were examined by cyclic-voltammetry and galvanostatic charge-discharge methods. The improved specific capacitance of Ag-BBc composite was measured as 655 Fg-1 in 1 M Na2SO4 at a current density of 0.35 Ag-1. The Ag-BBc modified electrode exhibited an excellent cyclic stability of 79.3% after 5000 charge/discharge cycles and displayed high energy and power density of 40 Wh/kg and 490 Wkg−1 respectively, at 1 Ag-1. Furthermore, Ag-BBc composite was used for the ultrasonic assisted adsorption of Congo Red dye with appreciable adsorption efficacy of ∼98% within 5 min of contact time. Langmuir and Freundlich isotherms were considered to describe the equilibrium of dye using ultrasonic assisted adsorption process.

Electrochemical properties of PEDOT/WO3 composite films for high performance supercapacitor application

Tungsten oxide was electrochemically deposited from a metastable acidic solution of isopolytungstate on glassy carbon electrodes coated by the films of a conducting polymer poly-3,4-ethylenedioxythiophene (PEDOT). The formation of PEDOT/WO3 composite films during electrochemical deposition of tungsten oxide into the polymer matrix was gravimetrically monitored by EQCM. The morphology of WO3 deposits was studied using SEM, TEM and EDX analysis, including element mapping and depth concentration profile of main elements. SEM and TEM images of PEDOT/WO3 composites show disperse distribution of WO3 precipitates in the porous matrix of PEDOT, possessing high surface area and pore volume, effective for charge transport. Electrochemical behavior of PEDOT/WO3 was investigated in 0.5 M H2SO4 by cyclic voltammetry, galvanostatic charge-discharge method and electrochemical impedance spectroscopy. The WO3 component in the obtained PEDOT/WO3 composite electrodes exhibited high specific capacitance of 689 F g−1 in the potential range −0.3–0.0 V. The work presents a simple approach for the synthesis of PEDOT/WO3 composites with high values of specific capacitance. The obtained results indicate that PEDOT/WO3 composite could be a promising electrode material for supercapacitor applications.

Получение наноразмерных порошков оксида вольфрама и вольфрама

AbstractNanopowder tungsten oxide and metallic tungsten are obtained via pyrolysis of ammonium metatungstate. Two methods are used for the synthesis of tungsten oxide: the use of a fibrous matrix and pyrolysis of aerosol particles. Tungsten oxide particles are formed during the pyrolysis in air. Metallic tungsten nanoparticles are obtained via subsequent thermal reduction of tungsten oxide in hydrogen. The structure and morphology of the samples are studied with X-ray diffraction and scanning electron microscopy. Tungsten nanopowders with average sizes from 7 to 30 nm are obtained depending on synthesis temperature. The electrochemical characteristics of electrodes coated with tungsten nanoparticles are studied with cyclic voltammetry, impedance spectroscopy, and galvanostatic charge–discharge methods. An electrode with W nanoparticles exhibited a specific low-frequency capacitance of about 90 F/g due to thin tungsten oxide film on the surface of tungsten nanoparticles.

Electrochemical performance of lithium titanate anode fabricated using a water-based binder

A novel anode material based on Li4Ti5O12 prepared using the combination of poly-3,4-ethylenedioxythiophene/polystyrene sulfonate and carboxymethylcellulose for the conducting polymer binder was developed. The comparative study of this material with conventional polyvinylidene fluoride and with the conductive polymer binder by the cyclic voltammetry and galvanostatic charge–discharge methods revealed that the anode material modified with the conductive binder possesses superior properties in terms of higher specific capacity (increase up to 14%), improved high-rate capability, and life cycle stability of battery.

Core–Shell (W@WO3) Nanostructure to Improve Electrochemical Performance

Two different approaches were developed to fabricate core–shell tungsten and tungsten oxide (W@WO3) nanostructures in combination with a hydrogen reduction technique. One is a combination of aerosol and pyrolysis approaches, which produce spherical tungsten oxide nanoparticles with a hexagonal crystal structure. The other is a combination of templating and impregnating approaches, which lead to tungsten oxide with a monoclinic crystalline structure. Subsequent hydrogen reduction lead to the formation of core–shell W@WO3 nanostructures with two different tungsten metallic phases. Structural and morphological characterizations were performed using X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The electrochemical performance of W@WO3 electrodes synthesized by two different approaches was studied using cyclic voltammetry, impedance spectroscopy, and galvanostatic charge–discharge methods. The capacity of core–shell W@WO3 nanostructures can reach 148 F g–1 compared with 2...

Preparation of Nanosized Tungsten and Tungsten Oxide Powders

Nanopowder tungsten oxide and metallic tungsten are obtained via pyrolysis of ammonium metatungstate. Two methods are used for the synthesis of tungsten oxide: the use of a fibrous matrix and pyrolysis of aerosol particles. Tungsten oxide particles are formed during the pyrolysis in air. Metallic tungsten nanoparticles are obtained via subsequent thermal reduction of tungsten oxide in hydrogen. The structure and morphology of the samples are studied with X-ray diffraction and scanning electron microscopy. Tungsten nanopowders with average sizes from 7 to 30 nm are obtained depending on synthesis temperature. The electrochemical characteristics of electrodes coated with tungsten nanoparticles are studied with cyclic voltammetry, impedance spectroscopy, and galvanostatic charge–discharge methods. An electrode with W nanoparticles exhibited a specific low-frequency capacitance of about 90 F/g due to thin tungsten oxide film on the surface of tungsten nanoparticles.

High performance supercapacitor behavior of hydrothermally synthesized CdTe nanorods

CdTe nanorods (NRs) have been prepared by hydrothermal process using ascorbic acid as a reducing agent. X-ray diffraction pattern reveals the formation of CdTe with cubic structure. From transmission electron microscopy the morphology of CdTe is found to be NRs with the length and diameter of 176 and 43 nm respectively. Brunauer–Emmett–Telle and Barrett–Joyner–Halenda analyses show the surface area (12.16 m2/g), pore volume (0.13 cm3/g) and pore diameter (44 nm). A high specific capacitance (438 F/g) is obtained at the current density of 2 mA/cm2 by the galvanostatic charge–discharge method. The excellent cyclic stability (95%) and the Coloumbic efficiency (99.7%) have been achieved even after 5000 cycles. The symmetric supercapacitor device exhibits the specific capacitance of 103 F/g at current density of 2.5 mA/cm2 with an energy density of 20.54 Wh/kg. The high density and electrochemical stability of the prepared CdTe electrode is a promising material for electrochemical energy storage devices.

One-step potentiostatic codeposition and electrochemical studies of poly(1-pyrenyl)-2,5-di(2-thienyl)pyrrole-co-pyrrole) film for electrochemical supercapacitors

In this paper, we report a simple, low-cost, and environmentally friendly electrochemical method to obtain a novel copolymer consisting of 1-pyrenyl-2,5-di(2-thienyl)pyrrole and pyrrole on a pencil graphite electrode (PGE). Poly(1-pyrenyl)-2,5-di(2-thienyl)pyrrole-co-pyrrole) that is P(PyrPy-co-Py) film was prepared by one-step potentiostatic codeposition in an ethanol solution containing PyrPy and Py monomers for supercapacitor applications. The electrodeposition of homopolymer and copolymer modified electrodes was carried out on the surface of the PGE via chronocoulometry. For comparison, P(Py)/PGE and P(PyrPy)/PGE were also electrochemically synthesized under the same reaction conditions. The surface morphologies of all the electrode materials were analyzed by field emission scanning electron microscopy. The capacitive properties of the modified PGEs were investigated in 1 M H 2 role=presentation> 2 2 _{2} SO 4 role=presentation> 4 4 _{4} electrolyte solution by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge methods. Compared with P(Py)/PGE and P(PyrPy)/PGE, the P(PyrPy-co-Py)/PGE composite exhibited the best electrochemical behavior and had the highest specific capacitance value of 397.18 F g − 1 role=presentation> − 1 − 1 ^{-1} in 1 M H 2 role=presentation> 2 2 _{2} SO 4 role=presentation> 4 4 _{4} at a scan rate of 2 mV s − 1 role=presentation> − 1 − 1 ^{-1} . These results indicated that this modified electrode can be used as an electrode material for electrochemical supercapacitors.

Relationships between the Charge-Discharge Methods and the Gas Adsorption Performance of a Supercapacitive Swing Adsorption Module for CO2 Separation

Introduction: Supercapacitive swing adsorption (SSA) is a gas separation technology that is based on selective adsorption and desorption of a gas from a gas mixture upon capacitive charging and discharging activated carbon electrodes.1,2 SSA is a promising technology due to its facile reversibility, significant sorption capacity, complete gas selectivity, and energy efficiency. In this study, we simplified the cell design and enlarged the electrode area of SSA modules. These new cell features are expected to increase the scalability of SSA technology. We defined metrics that allow for a quantitative evaluation of the energetic and adsorption performance of SSA cycles. Using these metrics, we quantitatively determined the influence of different electrical charge-discharge methods on the energetic and CO2 adsorption performance, and identified the most favorable charge-discharge method. Methods: The cross-sectional view of a SSA module is shown in Figure a. The SSA module was operated in gas flow-through mode and fed by a moistened 15% : 85% CO2 : N2 gas mixture serving as a flue gas simulant. In the SSA module, the gas was distributed by radial gas flow system, in which gas flowed from the inlet port in the center to the outlet port in the periphery of the SSA module. This design eliminated the use of gas flow channels, and simplified SSA module configuration. The electrode area was 49 cm2, which was 25 times of that in our previous study2. The CO2 concentration of SSA effluent gas was analyzed and recorded. The electrochemical behavior of the SSA module was controlled and measured using a potentiostat in a two-electrode configuration. Four different charge-discharge methods at voltages between 0 and -1 V were used to evaluate SSA performance, namely GCD (galvanostatic charging-discharging, Figure b), GCD+Pstat (GCD with potentiostatic holding steps between each GCD step, Figure c), GCD+OC (GCD with open-circuit holding steps between each GCD step, Figure d), and Combined (galvanostatic charging followed by holding step at open circuit, and galvanostatic discharging followed by potentiostatic holding step at 0 V, Figure e). Results: We introduced energetic and adsorption metrics to quantitatively evaluate SSA performance for CO2 adsorption. These metrics are specific capacitance, Coulomb efficiency, energy efficiency, energy loss, sorption capacity, electron efficiency, energy consumption, adsorption rate, and time-energy efficiency. Using these metrics, we determined how different charging methods affect the energetic and adsorption performance of SSA module. The galvanostatic charge-discharge method was most time-energy efficient due to its shortest charge time and lowest energy loss. The highest time-energy efficient for CO2 adsorption (7.5 µmol.kJ-1.s-1) was obtained with the galvanostatic charge-discharge methods at 50 mA. Increasing the constant charging current improved the energetic performance but decreased CO2 adsorption capacity. The introduction of holding steps favored CO2 adsorption at the cost of higher energy loss. A holding step of 30 min duration was sufficient for the full completion of CO2 adsorption and desorption. The highest CO2 adsorption capacity (87.5 mmol.kg-1), highest electron efficiency (0.2 molecule.electron-1), lowest energy consumption (109 kJ.mol-1) and highest CO2 adsorption rate (34 µmol.kg-1.s-1) were obtained by Combined method with 30 min holding steps. Conclusions: We demonstrated a simplified SSA module with enlarged electrode area, which is expected to benefit the scale-up of SSA technology for CO2 adsorption and separation. Our results provide systematic method to evaluate SSA performance and improve the understanding of the relationships between energetic properties and gas adsorption performance of SSA. This findings is critical to understanding the mechanism of SSA phenomena and to exploring SSA application. References 1 B. Kokoszka, N. K. Jarrah, C. Liu, D. T. Moore and K. Landskron, Angew. Chemie - Int. Ed., 2014, 53, 3698–3701. 2 C. Liu and K. Landskron, Chem. Commun., 2017, 53, 3661–3664. Figure 1

Development of Nitrate Combustion Synthesized NVP-Type Cathode and Glucose-Derived Hard Carbon Anode for Sodium-Ion Battery Single Cells

The synthesis and characterization of a Na3V2(PO4)3 cathode material for room-temperature sodium-ion battery is reported. The NVP material was prepared by a two-step process via sol-gel nitrate combustion method for precursor preparation and subsequent pyrolysis under Argon. Sodium-ion batteries have emerged as a promising candidate for large-scale energy storage due to sodium’s abundance and low cost of raw materials. However, in order to justify lower energy densities compared to Li-ion systems, Co-containing cathodes have to be avoided.[1,2] The materials have been investigated using SEM, EDX, XRD and TOF-SIMS methods. Electrochemical characterization has been carried out using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge method (GCD). The electrode slurry was prepared by mixing the active material, conductive additive (Super P) and polyvinylidene difluoride (PVdF) binder in a 75:15:10 mass ratio. The mixed slurry was cast onto aluminium foil using doctor-blade technique. The cast electrodes were dried under vacuum for 24h. The half-cells (EL-Cell GmbH) were assembled and electrolyte mixtures prepared in an Argon-filled glovebox (O2 < 0.1 ppm, H2O < 0.1 ppm). Sodium metal was used as counter and reference electrode and 1M NaClO4 in propylene carbonate (PC) as the electrolyte in half-cell measurements. SEM image of the NVP cathode surface in Fig. 1a shows homogeneous distribution of NVP particles and Super P carbon. The NVP particles are of 300 – 500 nm in diameter. The rate-performance of the NVP electrode (Fig. 1b) can be improved by creating a carbon shell around the particles. The results of single cell measurements for optimized NVP cathode and Glucose-derived Hard Carbon [3–5] anode will be discussed. Acknowledgements The present study was supported by European Regional Development Fund (Centres of Excellence TK141 (2014-2020.4.01.15-0011) and TK117 (3.2.0101–0030), TeRa project SLOKT12026T, Higher education specialization stipends in smart specialization growth areas 2014-2020.4.02.16-0026), “Institutional development programme for research and development and higher education institutions” (ASTRA) (Graduate School of Functional Materials and Technologies, Materials Technology Projects SLOKT12180T and SLOKT12181T, Energy Technology Project SLOKT10209T), Estonian Research Council (Institutional Research Grant IUT20–13, Personal Research Grant PUT1033 and by NAMUR project 3.2.0304.12-0397. Mr. Väli thanks Estonian Students Fund in USA for financial support. References British Geological Survey - Risk List 2015, British Geological Survey, (2015) http://nora.nerc.ac.uk/513472/1/Risk_List_2015_FINAL.pdf.Y.-K. Sun, D.-J. Lee, Y. J. Lee, Z. Chen, and S.-T. Myung, ACS Appl. Mater. Interfaces, 5, 11434 (2013).R. Väli, A. Jänes, T. Thomberg, and E. Lust, J. Electrochem. Soc., 163, A1619 (2016).R. Väli, A. Jänes, and E. Lust, J. Electrochem. Soc., 164, E3429 (2017).R. Väli, A. Jänes, T. Thomberg, and E. Lust, Electrochimica Acta, 253, 536 (2017). Figure 1

Binder-free electro-synthesis of highly ordered nickel oxide nanoparticles and its electrochemical performance

In this work, highly ordered nickel oxide nanoparticles were electrochemically synthesized on nickel foam (NiOx NPs/Ni foam) via the formation and subsequent heat treatment of nickel hydroxide. The synthesized NiOx NPs were characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) with elemental analysis and high resolution transmission electron microscopy (HR-TEM). The XRD results revealed the presence of two different oxide phases with high crystallinity. The synthesized NiOx NPs were highly ordered spherical morphology with average size of 7 nm, identified from the FE-SEM images. Further, the electrochemical performance of synthesized NiOx NPs/Ni foam was evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge discharge (GCD) methods. The calculated specific capacity of NiOx NPs/Ni foam was found to be 219 C/g (60.7 mAh/g) at scan rate of 5 mV/s. This present work implies that the electro-synthesized NiOx NPs/Ni foam as a good binder-free, highly stable battery-type material and it can be used as a positive electrode for hybrid-capacitors.

Design of Pt-Supported 1D and 3D Multilayer Graphene-Based Structural Composite Electrodes with Controlled Morphology by Core-Shell Electrospinning/Electrospraying.

Platinum (Pt)-decorated graphene-based carbon composite electrodes with controlled dimensionality were successfully fabricated via core–shell electrospinning/electrospraying techniques. In this process, multilayer graphene sheets were converted into the three different forms, fiber, sphere, and foam, by tailoring the polymer concentration, molecular weight of polymer, and applied voltage. As polymer concentration increased, continuous fibers were produced, whereas decreasing polymer concentration caused the formation of graphene-based foam. In addition, the reduction in polymer molecular weight in electrospun solution led to the creation of three-dimensional (3D) spherical structures. In this work, graphene-based foam was produced for the first time by utilizing core–shell electrospraying technology instead of available chemical vapor deposition techniques. The effect of morphologies and dimensions of carbonized graphene-based carbon electrodes on its electrochemical behavior was investigated by cyclic voltammetry and galvanostatic charge–discharge methods. Among the three different electrodes, Pt-supported 3D graphene-based spheres showed the highest specific capacitance of 118 F/g at a scan rate of 1 mV/s owing to the homogeneous decoration of Pt particles with a small diameter of 4 nm on the surface. After 1000 cycles of charging–discharging, Pt-decorated graphene-based structures showed high cyclic stability and retention of capacitance, indicating their potential as high-performance electrodes for energy storage devices.

Tire Waste Derived Turbostratic Carbon as an Electrode for a Vanadium Redox Flow Battery

For the first time, we report the synthesis of turbostratic carbon derived from tire waste with high surface area and its utilization as an electrode material in vanadium redox flow batteries (VRFBs). The tire waste carbon was initially subjected to acid demineralization followed by KOH activation wherein the carbon to KOH ratio was varied (1:1, 1:2, and 1:5), and the electrochemical performance toward VO2+/VO2+, V3+/V4+, and V2+/V3+ redox reactions was investigated. The turbostratic nature of carbon derived from tire waste was confirmed by high-resolution transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Brunauer–Emmett–Teller (BET) measurements revealed the surface area was as high as 875 m2·g–1 for the 1:5 KOH activated sample. The electrochemical performance of pretreated carbon (TW) and turbostratic carbon (1:1, 1:2, and 1:5) was compared by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge methods. Our results indicated that the...

Investigate the effect of silica on improvement electrochemical storage of hydrogen in ZnAl2O4 spinel

In this work, different morphologies of pure ZnAl2O4 nanostructures and ZnAl2O4/SiO2 nanocomposites were successfully synthesized via a simple co-precipitation method. Two green reagents namely green tea and olive leaf extracts were used to the synthesis of these nanostructures. The products were examined by different analysis such as X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). It was found all samples have pure structures and there are no impurities in the products. The porosity of samples was investigated by BET analysis. The results showed that the reagents have a significant role in the product size and morphology and by changing the extracts, they growth in different directions. Also, it was found that the products are composed of very tiny particles and due to their high active surface area, they aggregated together and some big particles are obtained. The electrochemical hydrogen storage performance of ZnAl2O4 and ZnAl2O4/SiO2 nanocomposite were investigated by the galvanostatic charge-discharge method in 6 M KOH aqueous medium under 1 mA current. The discharge time of ZnAl2O4, ZnAl2O4/SiO2 (synthesized using green tea extract), ZnAl2O4, ZnAl2O4/SiO2 (synthesized using olive leaf extract) is 1750, 2800, 3900 and 5000s, respectively. EIS indicates that the resistance of CU-foam electrodes increases with the addition of samples. The ZnAl2O4 and ZnAl2O4/SiO2 is a good candidate for hydrogen storage due to the electrochemical hydrogen storage performance suitable. The green synthesis and hydrogen storage are very useful for prevent environmental pollution that were used in this work.

Stannous sulfide nanoparticles for supercapacitor application

A facile hydrothermal method has been employed for the synthesis of stannous sulfide nanoparticles for the electrochemical supercapacitor application. The microscopic, optical and surface property of the synthesized material was characterized using different analytical techniques. The electrochemical performance of the synthesized material was reinforced by introducing carbon black. The electro-capacitive properties of the hybrid material were investigated by cyclic-voltammetry and galvanostatic charge-discharge methods where the system exhibited highest specific capacitance value of 201 F g−1 at the current density of 0.1 A g−1.