Galvanostatic Charge-discharge Studies Research Articles

Superior electrochemical performance of SnSe-PPy nanocomposites for supercapacitor application

Recently, Metal chalcogenides have received considerable interest in the field of energy storage devices. In this work, tin selenide-polypyrrole (SnSe-PPy) nanocomposite has been synthesized by hydrothermal method and its supercapacitive behavior is investigated. The synthesized SnSe-PPy nanocomposite is analyzed by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and electrochemical characterization. XRD confirms the existence of orthorhombic SnSe, and the FTIR result reveals the presence of polypyrrole. The supercapacitive behavior of SnSe-PPy nanocomposite is studied by cyclic voltammetry and galvanostatic charge-discharge studies. SnSe-PPy nanocomposite delivers the specific capacitance of 223 F g-1 at 10 mV sec -1. The addition of polypyrrole increases the conductivity of the material and improves its supercapacitive behavior.

Incredible electrochemical performance of ZnWO4/PANI as a favorable electrode material for supercapacitor

Abstract ZnWO4/PANI was synthesized through the in-situ polymerization technique, revealing the wolframite monoclinic phase in its XRD pattern. The distinctive morphology of ZnWO4/PANI observed in the SEM image, exhibits enhanced redox sites, thereby improving its electrochemical performance. Cyclic voltammetry and galvanostatic charge-discharge studies confirm the pseudocapacitive behavior of ZnWO4/PANI, showcasing an impressive capacitance of 908 F g−1 at 1 A g−1 in 1 M KOH, along with a capacitive retention of 94 % over 5000 cycles. The robust conductivity of PANI and the narrow ion transport channels along with multiple oxidation states of ZnWO4 contribute to the higher specific capacity, guiding the movement of electrons and ions. This study suggests a synergistic effect in ZnWO4/PANI, resulting in remarkable electrochemical performance enhancements.

Sustainable Synthesis of Porous Biomass-Derived Carbon from Tecoma capensis for High Performance Supercapacitors: Characterization and Electrochemical Evaluation

Biowaste carbon products possess interesting physico-chemical properties and are cost-effective due to their remarkable characteristics. Biomass carbon derived from Tecoma capensis (TCL) was processed using pyrolysis at a controlled temperature in an eco-friendly, innovative and sustainable way to develop biomass-derived carbon material. The aim of this study is to demonstrate the facile synthesis of porous carbon compounds from biowaste and evaluate their use in supercapacitors. Various analytical methods, such as structural analysis, morphological studies and electrochemical studies, have been employed to characterize the carbon material generated from biomass. Electrochemical performance evaluation was conducted through cyclic voltammetry and galvanostatic charge-discharge studies utilizing 1 M H2SO4 and 1 M KOH aqueous electrolyte, which exhibited a specific capacitance of 238 F g-1. The outcomes of the studies suggested that the eco-friendly, straightforward process can be utilized to prepare biomass carbon for the electrochemical energy storage applications in an efficient and sustainable manner.

Development of surfactant integrated polyaniline based electrode material towards supercapacitor application

Tailoring electrode material is always important for fabricating high-performance energy storage devices. Polyaniline (PANI) is one of the most-explored electrode materials due to its electroactivity, redox property, easy and cost-effective synthesis and reasonable capacitance. Herein, PANI has been integrated with surfactants (cetyltrimethylammonium bromide, dioctyl sodium sulfosuccinate, sodium lauryl sulphate, Tween-80) via chemical oxidative polymerization pathway and utilized as the electrode material for supercapacitor. Chemical nature, crystallinity and morphology of surfactant integrated PANI samples were evaluated by FTIR, UV–Visible, X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques while electrochemical properties were investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy studies. Among the different PANI samples, PANI integrated with cetyltrimethylammonium bromide (PMC) afforded 2.3 times higher capacitance (528 F/g) than PANI synthesized without surfactants (PM) (229 F/g). Due to the influence of CTAB, PMC displayed higher pore volume and lesser particle size as investigated by Brunauer-Emmett-Teller and dynamic light scattering analyses. Furthermore, PMC displayed two times higher electroactive surface area as compared to PM as investigated by cyclic voltammetry studies. It has been observed that the surfactant not only improved the processability of the polymer but also assisted in enhancing the capacitance of the electrode material significantly.

Modified 3D Graphene for Sensing and Electrochemical Capacitor Applications.

Less defective, nitrogen-doped 3-dimensional graphene (N3DG) and defect-rich, nitrogen-doped 3-dimensional graphene (N3DG-D) were made by the thermal CVD (Chemical Vapor Deposition) process via varying the carbon precursors and synthesis temperature. These modified 3D graphene materials were compared with pristine 3-dimensional graphene (P3DG), which has fewer defects and no nitrogen in its structure. The different types of graphene obtained were characterized for morphological, structural, and compositional assessment through Scanning Electron Microscopy (SEM), Raman Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS) techniques. Electrodes were fabricated, and electrochemical characterizations were conducted to evaluate the suitability of the three types of graphene for heavy metal sensing (lead) and Electric Double-Layer Capacitor (EDLC) applications. Initially, the various electrodes were treated with a mixture of 2.5 mM Ruhex (Ru (NH3)6Cl3 and 25 mM KCl to confirm that all the electrodes underwent a reversible and diffusion-controlled electrochemical process. Defect-rich graphene (N3DG-D) revealed the highest current density, followed by pristine (P3DG) and less-defect graphene (N3DG). Further, the three types of graphene were subjected to a sensing test by square wave anodic stripping voltammetry (SWASV) for lead detection. The obtained preliminary results showed that the N3DG material provided a great lead-sensing capability, detecting as little as 1 µM of lead in a water solution. The suitability of the electrodes to be employed in an Electric Double-Layer Capacitor (EDLC) was also comparatively assessed. Electrochemical characterization using 1 M sodium sulfate electrolyte was conducted through cyclic voltammetry and galvanostatic charge-discharge studies. The voltammogram and the galvanostatic charge-discharge (GCD) curves of the three types of graphene confirmed their suitability to be used as EDLC. The N3DG electrode proved superior with a gravimetric capacitance of 6.1 mF/g, followed by P3DG and N3DG, exhibiting 1.74 mF/g and 0.32 mF/g, respectively, at a current density of 2 A/g.

Construction of a binder-free PANI-CQD-Cu electrode via an electrochemical method for flexible supercapacitor applications.

In recent years, flexible hybrid supercapacitors (FSCs) have played a significant role in energy storage applications owing to their superior flexibility and electrochemical properties. In this study, carbon quantum dots (CQDs) were prepared from ascorbic acid via a hydrothermal method and physical and chemical characterizations were performed. Then, the carbon quantum dots (CQDs) were doped with polyaniline (PANI) and copper (Cu) to form a PANI-CQD-Cu composite coated on carbon cloth (CC) using an electropolymerization method. In the polymerization process, CQDs bind with the PANI chain and form a PANI-CQD-Cu composite. The prepared electrode's functional group and surface morphology were characterized through XRD, Raman, BET, XPS and SEM with EDAX studies. The electrochemical properties of the PANI-CQD-Cu electrode were investigated using cyclic voltammetry, impedance spectroscopy and galvanostatic charge-discharge study. The capacitance value of PANI-CQD-Cu was 1070 mF cm-2 at 5 mA cm-2 (1070 F g-1 at 1 A g-1), which was higher than that of PANI (775 mF cm-2). Moreover, a flexible asymmetric supercapacitor (FASC) based on an activated carbon/PVA-H2SO4/PANI-CQD-Cu device was fabricated, which exhibited outstanding energy and power densities of 23.10 μW h cm-2 and 0.978 mW cm-2, respectively. The capacitance value remained at 92% after 3000 cycles. The outcome results indicated that the PANI-CQD-Cu-coated CC electrode material can be a promising electrode material for practical energy storage applications.

Sputtered vanadium carbon nitride (VCN) thin films: a potential electrode for supercapacitors

The preparation of efficient thin film-based electrode materials is a vital prerequisite for practical energy storage devices. Herein, we have prepared unique vanadium carbon nitride (VCN) thin films on FTO substrates by pulsed DC magnetron sputtering technique for competent supercapacitor electrodes. XRD analysis confirmed the crystalline nature of VCN thin films. SEM and AFM revealed a smooth morphology with an average grain size of 30 nm. Raman spectra showed two broad peaks around 1346 and 1589 cm−1, belonging to the D-band and G-band of VCN. The surface electronic states of VCN were investigated by XPS analysis, which confirmed the formation of pure VCN films without any impurities. The electrochemical performance of the thin film electrode was evaluated using cyclic voltammetry (CV), Galvanostatic charge–discharge (GCD), and Electrochemical impedance analysis (EIS). The electrochemical results showed the VCN thin films exhibited super capacitive behaviours. The maximum specific capacitance (Cs) value of 78.2 F g−1 was obtained from GCD studies. A variation in charge transfer resistance is detected from the EIS study, which arises due to the partial oxidation of the active nitride component. The VCN electrode showed good cycling stability, retaining 87% of its capacitance at a current density of 5 A g−1 even after 2000 cycles. The sputtered VCN films have been demonstrated as potential thin film electrodes for electrochemical supercapacitors for practical energy storage devices.

Tunable capacitive charge storage of NiCoLDH@rGO for high-energy capacitor: Performance of flexible solid-state capacitor

The compositionally tunned pristine nickel cobalt layered double hydroxides (NiCoLDHs) and NiCoLDH@reduced graphene-oxide (NiCoLDH@rGO) composites generated via the simple single-pot solvothermal method. The synthesized NiCoLDH and the NiCoLDH@rGO composites were characterized through powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transformed infra-red (FT-IR) spectroscopy, scanning electron microscope (SEM) equipped with energy dispersive X-ray analysis (EDAX), high-resolution transmission electron microscope (HR-TEM), and X-ray photoelectron spectroscopy (XPS) techniques. The XRD, Raman and FT-IR data confirmed the formation of the NiCoLDH with presence of carbonate and nitrate ions in the basal space. Enhanced basal length was observed for the NiCoLDH@rGO composites. The three-electrode system was constructed to analyse the cyclic voltammetry and Galvanostatic charge-discharge studies in 1 M KOH confirmed that the pristine LDHs and the composites are electrochemically active, and the capacity could be tuned by varying (Ni2+/Co3+) mole ratio or the rGO content. The charge storage kinetics in NiCoLDH@rGO was performed through Dunn's approaches and the Power Law, affirmed as the (Ni2+/Co3+) ratio or the rGO content is increased in the composite the capacitive contribution is increased for the charge storage. The NC@RG10 (NiCoLDH with 10 wt% rGO) composite electrode could deliver an enhanced specific capacity of 963C g−1 at a current rate of 1.5 A g−1. Consequently, pristine LDH or composites as positive electrode and rGO as negative electrode was fabricated using the CR-2032 coin-type hybrid capacitor. The laboratory prototype pristine hybrid capacitor (NiCoLDH|1 M KOH|rGO) delivered an enhanced specific energy of 56 Wh kg−1 at specific power of 810 W kg−1, whereas the composite hybrid device (NC@RG10|1 M KOH|rGO) having NC@RG10 electrode delivered an enhanced specific energy of 166 Wh kg−1 at specific power of 638 W kg−1. The NC@RG10 composite-based hybrid device exhibited excellent stability with coulombic efficiency as high as 99 % even at the 10,000th charge−discharge cycle. Reduced aggregation and enhanced conductivity leading to significant capacitive contribution in the NC@RG10 composite is due to the existence of rGO and responsible for the excellent charge storage performance. The fabricated hybrid capacitor powered a red LED on a single charge for 40 min. Fascinatingly, a flexible solid-state hybrid capacitor was also fabricated that delivered an impressive specific energy of 28 Wh kg−1 at a specific power of 553 W kg−1 at a 180° bent angle.

Design Strategies for High Reflectivity Contrast and Stability Adaptive Camouflage Electrochromic Supercapacitors.

The integration of an electrochromic (EC), energy storage, and adaptive camouflage system into a multifunctional electronic device is highly desirable and yet challenging. In this work, two carbazole-based conjugated polymers were prepared to achieve a reversible color change from transparent to yellow, green, and blue-green by easy electrochemical polymerization. Due to its dendritic geometry, the conjugated polymer p3CBCB exhibits a loosely packed structure with a relatively higher specific surface area than pCBCB, as well as a relatively better ionic conductivity. The kinetic and galvanostatic charge-discharge (GCD) study reveals that p3CBCB has superior properties with larger optical contrast and volumetric capacitance. Moreover, EC supercapacitors (ECSCs) are constructed with p3CBCB as the EC layer and ZnO@PEDOT:PSS as the ion storage layer. The dual function of a ZnO interface layer on improvement in reflectivity contrast (ΔR% > 35.1%) and cycling stability (over 40,000 cycles) using ZnO as a reflective and protective layer is demonstrated in an ion storage layer. Additionally, patterned prototype devices based on the design of double-sided ITO glass were successfully assembled, which can simulate conditions of various natural environments including forests, wilderness, and deserts. This study provides new ideas not only for the preparation of conjugated polymers that can simultaneously realize reversible transparent-yellow-green conversion but also for the achievement of high coloration efficiency, high reflectivity contrast, and good stability of ECSCs for adaptive camouflage.

Studies of reduced graphene oxide (rGO)/CuS nanocomposite for supercapacitor applications

We have prepared CuS and CuS-rGO nanocomposites via the hydrothermal method. The physical properties of the synthesized materials were studied through x-ray diffraction and scanning electron microscopy. The supercapacitor characteristics were evaluated by cyclic voltammetric and galvanostatic charge–discharge studies. The cyclic voltammetric studies conform the pseudocapacitive nature of CuS and CuS-rGO electrodes. The specific capacitance of CuS was obtained as 207, 150, and 97 F/g at a current density of 0.5, 5, and 20 A/g, respectively. The rGO-CuS nanocomposite showed improved specific capacitance of 350, 251, and 149 F/g at current densities of 0.5, 5, and 20 A/g, respectively.

Elucidating the Role of Copper-Induced Mixed Phases on the Electrochemical Performance of Mn-Based Thin-Film Electrodes.

Manganese oxide is a fascinating material for use as a thin-film electrode in supercapacitors. Herein, the consequences of copper incorporation on spray pyrolyzed manganese oxide thin films and their electrochemical performance were investigated. The Cu-incorporated manganese oxide thin films were deposited by spray pyrolysis, and their structural and electrochemical properties were thoroughly evaluated. The formation of the spinel Mn3O4 phase with effective Cu incorporation was confirmed by X-ray diffraction investigation. Through Raman studies, it was noticed that mixed phases of manganese oxide tend to form after Cu incorporation, and this result was also reflected in X-ray photoelectron spectroscopic studies. The surface morphology and roughness were also altered by the addition of copper. However, electrochemical measurements implied a reduction in the specific capacitance upon copper inclusion. The cyclic voltammetry test indicated a specific capacitance of 132 F/g for Mn3O4 electrodes, but a substantial drop for copper-incorporated samples due to the mixed manganese phase. The decremental tendency was further supported by galvanostatic charge-discharge studies and electrochemical impedance spectroscopic measurements. These results provide valuable insights into the effects of copper addition in manganese oxide thin-film-based electrodes for energy storage applications.

A Comparative Cyclic Voltammetry Study of Amorphous Carbon-Transition Metal Oxide Hybrid System: Selection for the Best Capacitor

The present study addresses the synthesis of various amorphous carbon nanostructures-transition metal hybrid systems by a simple, low-temperature chemical route. Electron microscopic images of the pure and hybrid systems confirmed that different functionalized samples have significantly different morphologies. The Fourier-transformed infrared spectroscopic analysis provided ideas about different bonds present in all the samples, whereas the Raman spectra quantified the carbon content with different hybridization states. Thermal analysis confirmed that all the samples are thermally well-stable. Whereas energy dispersive X-ray was used to perform quantitative еlеmеntal analysisWhen cyclic-voltammetry (CV) and galvanostatic charge-discharge (GCD) studies of all the samples were performed, it was seen that among all the hybrids, the manganese-based system gave the best result with specific capacitance values over 530F/g.When Nyquist plots of all the samples were done in order to study the electrochemical impedance spectra, it was confirmed that the manganese based system shows the ideal capacitive nature with the lowest value of internal resistance. It was seen that when a-CNTs were functionalized with MnO2, the specific capacitance increased almost 7 times, whereas other samples gave much inferior results. Efforts have been made to explain the variation of the results from the point of view of the fundamentals of electrochemistry. It has been shown that the change in surface area, porosity, ion transport, and clustering of the foreign nanostructures are the key parameters behind the result.

Incorporation of photonic material BNNT into the PANI@MgO matrix to boost energy density for supercapacitor application

Supercapacitors have garnered significant interest in the realm of electrical energy storage due to their remarkable attributes of high power density and extended cycle life. The electroactive electrode materials embedded within these systems play a crucial role in augmenting both energy density and capacitance. This study presents a novel exploration into the intercalation and distinct characteristics of hexagonal boron nitride (h-BN) within different ratios of MgO/PANI (PANI/MgO/h-BN) composite using a one-pot oxidative polymerization method for supercapacitor applications. The compositional analysis of the composite was comprehensively conducted through techniques such as X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge studies (GCD), and Electrochemical Impedance Spectroscopy (EIS). The average crystallite sizes computed for PANI/MgO/h-BN, denoted as A (1:1:1), B (1:1:2), C (1:1:3), and D (1:1:4), were 26 nm, 22 nm, 20 nm, and 18 nm, respectively. The specific capacitance values obtained from GCD were found to be 437F/g, 1609F/g, 1695F/g, and 2105F/g, accompanied by energy densities of 10.1 Wh/kg, 19.3 Wh/kg, 32.2 Wh/kg, and 42.9 Wh/kg, respectively. The outcomes underscore that the composite exhibits a propensity for elevated specific capacitance as the loading capacity of h-BN is escalated, displaying a notable absence of saturation.

Facile synthesis of SnO2/graphene and Bi–SnO2/graphene-based nanocomposites as electrode materials for energy storage devices

Graphene-based nanocomposites are widely investigated as cathode materials for energy storage device. Herein, tin oxide-modified graphene (SnO2/G) and bismuth-doped SnO2/G (Bi–SnO2/G) nanocomposites with nanorod-like morphology were synthesized by the combination of electrochemical and wet chemical methods. The as-prepared nanocomposites were characterized using Raman spectroscopy, X-ray diffraction, fourier-Transform spectroscopy, and scanning electronic microscopy. Further, electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge (GCD) curves, and cyclic voltammetry (CV) were utilized to assess the ultra-capacitor properties of SnO2/G and Bi–SnO2/G nanocomposites.The electrochemical performance of SnO2/G and Bi–SnO2/G nanocomposites demonstrated exceptional specific capacitance of 487 F/g and 174 F/g, respectively, at 5 mV/s compared to as-prepared pristine graphene (108 F/g) and SnO2 nanoparticles (117 F/g). While, the GCD study confirmed the cyclic stability of these electrodes. Overall, the SnO2/G and Bi–SnO2/G nanocomposites have shown good electrochemical properties in all assays.

Ceramic Fillers for Improved Lithium-Sulfur Batteries

With the decarbonization of transportation, the demand for electric vehicles (EVs) and batteries that can power these EVs has been increasing. Lithium-ion-based batteries are already well-established and are considered the main chemistries to power current EVs. However, limited specific energy (< 300 Wh/kg) prevents these batteries from having high mileage vehicles. Lithium-sulfur batteries are considered the most promising next-generation energy storage system as they high theoretical capacity (~1675 mAhg-1), low cathode materials cost, and cell energy densities that can exceed 700 Wh/kg [1,2]. However, some major drawbacks prevent the Li-S battery system from being applicable in energy devices and hinder its commercialization, that include low power density and rapid capacity degradation during their cycling life. In addition, the lithium metal anode in Li-S batteries bring various issues to the forefront such as continuous solid electrolyte interface growth, dendrite formation, and loss of active lithium and electrolyte. These issues are further exacerbated at high C-rates which increases the possibility of an internal short-circuit and sudden cell failure [3]. In order to promote longer life cycles and prevent sudden cell failure, a thorough understanding of the cell’s electrochemical behavior is crucial for the development of a stable and practical Li-S battery system. The introduction of oxide fillers such TiO2, Al2O3, SiO2, etc. has been previously studied in various lithium-ion systems and has been shown to improve the cell’s lithium-ion transport properties, which in turn improve the performance of Li-S cells [4]. When used as interlayers they can also trap soluble polysulfides diffusing out of the cathode and reduce their crossover to the anode which helps reduce the shuttle effect of said polysulfides.In the present study, the use of a polysulfide immobilizing system to reduce sulfur loss and improve capacity retention has been demonstrated. The galvanostatic charge-discharge cycling study shows that cells retain higher capacity during the course of cycling. The initial capacity for Li-S cells with the filler average 1300+ mAh/g (C/10) while the capacity stabilizes around 1000 mAh/g after 3 cycles (C/5). The capacity retention at C/5 after 75 cycles was approximately 875 mAh/g which represents a rate 0.17% drop per cycle. When compared to control cells, the cells containing no fillers had lower initial capacity that averaged 1050 mAh/g and that rapidly declined to stabilize around 650 mAh/g. However, after this major drop, the cells remained stable no with measurable drop after 75 cycles. The behavior indicates that the cells with fillers delayed the effect of sulfur loss experienced in cells without fillers; however, the slow capacity drop that ensued, indicates that while polysulfide trapping was efficient it was unable to fully prevent it. The effect of fillers on the Coulombic efficiency (CE) also supports the polysulfide “trapping” mechanism and shows the ability of the cell to reduce the shuttle effect that contributes to lower CE values. Further electrochemical studies have been performed to understand the mechanisms of the improvement of the cell.

Ion conduction property and electrochemical characteristics of Ag-ion gel polymer electrolyte

Ag-ion gel polymer electrolyte (GPE) based on Poly (vinyl Alcohol) and Silver tetrafluoroborate (AgBF4) was prepared using solution casting technique. The prepared GPE was characterised using XRD and FTIR techniques to determine its complex formation. The optical characteristic of the synthesised membrane was analysed through UV–Vis spectroscopy. The Ag-ion conductivity of the synthesised membrane was further analysed by AC impedance, and its dielectric property was studied using impedance data. Results of the AC impedance analysis show an ionic conductivity of up to 1.28 × 10-5Scm-1. The electrochemical characteristics of Ag-ion GPE were analysed, exhibiting an electrochemical working voltage of up to 1.1 V. On this basis, the oxidation–reduction reaction of the membrane was studied by fabricating a cell (Ag//Ag-ion GPE//Zn) using the synthesised membrane as electrolyte. This study confirms the electrochemical behaviour of the electrolyte. Galvanostatic charge–discharge studies were conducted, and the results indicate that the charging and discharging process in the cell occurred successfully.

Structure-Electrochemical Property Relationship of F vs 2F Substituents in Low Bandgap Conjugated Polymers

Two alternating copolymers bearing fluorinated benzothiadiazole as a strong acceptor unit and dithienopyrrole as a strong donor unit were designed and synthesized to discuss the effect of the number of fluorine atom substitution. The polymers were characterized via cyclic voltammetry, spectroelectrochemistry, electrochemical impedance spectroscopy and galvanostatic charge discharge studies. Besides a red shift in absorption spectra, an anodic shift was also observed in the oxidation potentials when number of fluorine atom increases in the polymer backbone. Galvanostatic charge-discharge (GCD) studies revealed that difluorinated polymer exhibited enhanced area specific capacitance compared to mono fluorinated polymer.

High electrochemical performance of rGO-CNTs composites as an electrode material for supercapacitors applications

The objective of this work was to improve the capacitive behavior of rGO-CNTs composite electrode. The prepared composite has been examined for electric double layer capacitor (EDLCs) devices. The structural and chemical properties of the composite has been validated by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscope (SEM). We performed the cyclic voltammetry (CV) and measured specific capacitance of 54 Fg−1at 10 ​mV/s for 1 ​M ​H2SO4 and 36.25 ​F ​g−1 for 1 ​M KOH liquid electrolyte. From galvanostatic charge-discharge (GCD) studies, 1 ​M H2SO4 electrolytes we obtained the energy density and power density as 10.67 ​Wh kg−1 and 2400 ​W ​kg−1 respectively at 6 A/g. However, 1 ​M KOH electrolytes has an energy density and power density of 1.7 ​Wh kg−1 and 1600 ​W ​kg−1 at 4 A/g. Therefore, the performance of 1 ​M ​H2SO4 electrolytes shows better results as compared to the 1 ​M KOH. Hence, we conclude that rGO-CNTs electrode is an interesting material for supercapacitor applications.

Synthesis of hydrothermally derived boron and sulfur-incorporated reduced graphene oxide sheets for supercapacitor applications

The combination of boron and sulfur incorporated reduced graphene oxide (B/S-rGO) was synthesized by a simple hydrothermal technique using a novel and single source of thiophene-2 boronic acid pinacol ester. Structural and functional groups of the synthesized materials were analyzed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy analysis. The Raman analysis revealed the defective structure after incorporating sulfur and boron elements into rGO. The morphological and the presence of elements in the synthesized material were analyzed by scanning electron microscopy, transmission electron microscopy and elemental mapping analysis. The chemical states and chemical composition of B/S-rGO were observed by X-ray photoelectron spectroscopy (XPS) analysis. The electrochemical performance of the prepared material was studied using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance analysis. GCD studies were performed for B/S-rGO electrode material in an aqueous 1 M H2SO4 electrolyte. The prepared material showed a high specific capacitance of 345 Fg−1 at 1 Ag−1 in a three-electrode configuration. B/S-rGO based device exhibited 97 Fg−1 of specific capacitance at 1 Ag−1 in a symmetric two-electrode configuration. B/S-rGO based symmetric device showed a high energy density of 13.4 Whkg−1 at 249 Wkg−1 and more than 96% capacity retention after 5000 cycles.

Rational designed Cu-MOF@1D carbon nanofibers as free-standing and flexible electrode for robust electrochemical energy storage

The present study reported the performance of free-standing carbon nanofibers decorated with copper-metal-organic frameworks (Cu-MOFs). A green electrospinning technique was utilized to obtain nanofiber sheets that were carbonized and activated to produce activated carbon nanofiber sheets (ACNFs). These ACNFs consist of inherent oxygen functionalities of the lignin that can aid the growth of MOF structure on it in a single step, which motivated us to do this work. Cu-MOF particles were in-situ grown over the surface of ACNFs using a hydrothermal-assisted technique. The developed materials were characterized using FESEM, Raman Spectroscopy and BET analysis in order to identify morphological, porosity, and surface area transformations. Along with these, Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and Galvanostatic Charge-Discharge (GCD) studies were performed to compare the electrochemical performance of the Cu-MOF, ACNF, and Cu-MOF@ACNF as electrode materials for supercapacitors. Among three electrodes, the Cu-MOF@ACNF sheet reveals a higher specific capacitance of 303.2 F/g compared to ACNF (203.3 F/g) and Cu-MOF (68.2 F/g) at the same current density of 1 A/g. Based on the higher performance of Cu-MOF@ACNF two types of symmetrical devices, i.e., aqueous (using electrolyte-impregnated filter paper) and solid-state devices (using a polymeric gel electrolyte), were fabricated. The all-solid-state supercapacitor device was found to feature high flexibility, stand-alone characteristics, and excellent performance as an electrode with a working potential window of 0–2.0 V. The device demonstrates a high energy density of 78.71 Wh/kg and a power density of 1050.0 W/kg, along with high coulombic efficiency (99.8 %) after 10,000 cycles. The achieved performance is superior to many published reports, revealing that the developed composite materials hold prospect for applications in green and high-performance flexible energy storage devices.