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Among the environmental issues, plastic waste is one of the most significant problems, and thus, searching for ways to solve it is critical. In the present work, a green process is proposed for synthesizing RGO nanosheets from recycled plastic waste for efficient supercapacitor applications. The suggested approach consists of the transformation of plastic waste into GO using a direct and reproducible strategy and then the transformation of GO to RGO via an eco-friendly reducing agent. The synthesized RGO nanosheets possessed desirable electrochemical characteristics such as a specific capacitance of 104F/g at 0.5A/g, 90% capacitance retention after 5000 cycles, and good rate capability. The RGO nanosheets were further employed as electrode materials for the supercapacitor devices which has been evidenced with high energy density and power density. Physical properties have been characterized by XRD, Raman spectroscopy and transmission electron microscope have clearly observed the structure and the morphology of Graphene nanosheets has been established. The electrochemical properties of RGO have been examined and demonstrated to be regular. The proposed structure exhibits a nearly rectangular shape within the range of the potential window, conforming to the standard characteristics of an ideal capacitor. The findings of this study represent a viable and techno-economically feasible strategy to address the global issue of plastic waste and generate high-value graphene materials for energy storage technologies.

Nano-composite materials of reducing graphene oxide (RGO), polyaniline (Pani), and Prussian blue (PB) were prepared. RGO was prepared by the hammer oxidation method followed by reduction with olive leaf extract (OLE). Pani was prepared by chemical oxidation with ammonium persulfate (APS). PB was prepared by mixing two equal volumes of the same concentration of Fe(NO${}_3{)}_3$ and K₄Fe(CN)₆. These three materials were ground with black activated carbon as filler and wetted with a binder to produce a slurry. A surgical blade was used to coat the GC substrate with the slurry and allowed to stand for two days. A comparative study of single, binary, and ternary components was performed. Fourier-transform-infrared (FTIR) spectroscopy was used to characterize the ternary composite and the SEM pattern was used to study the morphology of the nanomaterials. The electrochemical tests were performed using cyclic voltammetry and demonstrated high specific capacitance, high reversibility, and excellent stability, up to 98.2% of the initial value after 1000 cycles. Charge/discharge time which also demonstrates high-rate capability and high specific capacity, up to 850 F/g at 0.1 A/g was investigated. Finally, the resistance of the electrode/electrolyte interface based on the measurements obtained using electrochemical impedance spectroscopy was considered. Achieved Made a prototype of a supercapacitor with a hybrid solid-state gel electrolyte using a Cu–Al foil folding current collector, which was tested using a rotating little fan.

The development of composite materials is a key area of research for enhancing the electrochemical performance of electrode materials. In this study, NiCo–S nanostructured hybrid electrode materials were prepared on nickel foam (NF) by using binary metal–organic frameworks (MOFs) as the sacrificial template through a two-step hydrothermal method. Ni–MOF was then deposited on the surface of NiCo–S/NF through the hydrothermal method and subsequently converted into Ni(OH)₂ through a subsequent alkalization treatment. The duration of the Ni–MOF hydrothermal process was varied as a parameter. NiCo–S@Ni–MOF/NF was prepared through hydrothermal reaction for 6h, 9h and 12h, followed by heating in a 6M KOH solution at 75${}^{\circ }$C for 6h in a water bath. The electrode materials with the best morphology and electrochemical properties were obtained when the hydrothermal reaction time was 6h. The optimized electrode had a specific capacity of 2533.2F$\cdot$g${}^{-1}$ at 1A$\cdot$g${}^{-1}$ and a capacity retention rate of 60.8% at 10A$\cdot$g${}^{-1}$, which indicated good rate performance. Additionally, the electrode material demonstrated excellent cycling stability, with a capacity retention rate of 95.3% after 5000 cycles at 50mV$\cdot$s${}^{-1}$. The energy density of the hybrid supercapacitor device assembled from this electrode material was 33.5Wh$\cdot$kg${}^{-1}$ when the power density was 849.89W$\cdot$kg${}^{-1}$ at a current density of 1A$\cdot$g${}^{-1}$.

The performance of supercapacitor electrode materials was greatly affected by the specific surface area. The urchin-like NiCo₂O₄ was transformed into porous NiCo₂O₄ (AA-NiCo₂O${}_4)$ using the acid–alkali treatment method. The specific surface area of AA-NiCo₂O₄ was 165.0660 m²/g, which was about three times larger than that of NiCo₂O₄. The specific capacitance of the AA-NiCo₂O₄ was enhanced significantly (1700 F/g at 1 A/g), and AA-NiCo₂O₄ possesses good rate capacitance (1277 F/g at 10 A/g). This is mainly attributed to the larger specific surface area, fast and convenient electron–ion transport and redox reaction. Therefore, AA-NiCo₂O₄ is a promising high-performance supercapacitor electrode material.

MnCo₂O₄/g-C₃N₄ composite material was synthesized by the hydrothermal method, compared with MnCo₂O₄ without g-C₃N₄, it has excellent electrochemical performance. The composite material can reach a specific capacitance of 350 Fg${}^{-1}$ at 1 Ag${}^{-1}$. The capacity retention rate is 96% after 1000 cycles at the rate of 2 Ag${}^{-1}$. Experiments show that g-C₃N₄ can effectively disperse and improve the conductivity of urchin-like MnCo₂O₄, and the composite of sufficient g-C₃N₄ can give full play to the performance of urchin-like MnCo₂O₄, provide faster electronic transport channels, effectively improve the ion migration rate, and make urchin-like MnCo₂O₄ increase the rate performance under high charge and discharge rates.

In this research, manganese cobaltite (MCO) nanoparticles with different morphologies were synthesized by a simple hydrothermal method with excellent electrochemical properties. To investigate the physical features of prepared samples, XRD analysis was used to study the crystalline structure. The SEM and TEM proved that the morphology of synthesized materials formed as flake and nanoplane structures. The electrode of samples was prepared using the hydrothermal method and the electrochemical properties of samples were investigated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), electrochemical impedance spectroscopy (EIS) and cyclic stability analysis. Results showed that the flake structures of nanoparticles revealed the highest capacitance of 1971.98$\mathrm{\text{F}}\cdot {\mathrm{\text{g}}}^{-1}$ at 0.5Ag${}^{-1}$ as well as longer stability compared to the others with the nanoplane structure. The high cyclic stability of 91.47% after 5000 cycles introduces this electrode as a durable and promising electrode for use in energy storage devices.

Modifications with different acids (HNO₃, H₂SO₄, HCl and HF, respectively) were introduced to treat the activated carbons (ACs) surface. The microstructures and surface chemical properties were discussed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), ASAP, Raman spectra and Fourier transform infrared (FTIR) spectra. The ACs electrode-based supercapacitors were assembled with 6 mol ⋅ L${}^{-1}$ KOH electrolyte. The electrochemical properties were studied by galvanostatic charge–discharge and cyclic voltammetry. The results indicated that although the BET surface area of modified ACs decreased, the functional groups were introduced and the ash contents were reduced on the surface of ACs, receiving larger specific capacitance to initial AC. The specific capacitance of ACs modified with HCl, H₂SO₄, HF and HNO₃ increased by 31.4%, 23%, 21% and 11.6%, respectively.

In this work, electrochemical double layer supercapacitors were fabricated using multiwalled carbon nanotube (MWCNT) composite microfilm as electrode. To improve the electrochemical properties, MWCNTs were functionalized with −COOH by acid treatments. CNT/PVA films have been deposited on different current collectors by spin coating to drastically enhance the electrode performance. Electrode fabrication involved various stages preparing of the CNT composite, and coating of the CNT/PVA paste on different substrates which also served as current collector. Al, Ni and graphite were used and compared as current collectors. The surface morphology of the fabricated electrodes was investigated with scanning electrode microscopy (SEM). Overall cell performance was evaluated with a multi-channel potentiostat/galvanostat analyzer. Each supercapacitor cell was subjected to charge–discharge cycling study at different current rates from 0.2Ag${}^{-1}$ to 1Ag${}^{-1}$. The results showed that graphite-based electrodes offer advantages of significantly higher conductivity and superior capacitive behavior compared to thin film electrodes formed on Ni and Al current collectors. The specific capacitance of graphite based electrode is found to be 29Fg${}^{-1}$.

The cobalt oxide and boron-doped cobalt oxide thin films were produced by spray deposition method. All films were obtained onto glass and fluorine-doped tin oxide (FTO) substrates at 400${}^{\circ }$C and annealed at 550${}^{\circ }$C. We present detailed analysis of the morphological and optical properties of films. XRD results show that boron doping disrupts the structure of the films. Morphologies of the films were investigated by using a scanning electron microscopy (SEM). Optical measurements indicate that the band gap energies of the films change with boron concentrations. The electrochemical supercapacitor performance test has been studied in aqueous 6 M KOH electrolyte and with scan rate of 5 mV/s. Measurements show that the largest capacitance is obtained for 3% boron-doped cobalt oxide film.

Novel unique fabrication of ZnO nanoparticles decorated graphene beaded carbon nanofibers (G-CNF) encapsulated by polyaniline (PANI) nanocomposites through three steps by electrospinning, hydrothermal and in-situ polymerization is reported. As-synthesized G-CNF/ZnO/PANI and CNF/ZnO/PANI nanocomposites were comparatively studied by scanning electron microscopy and electrochemical characterizations for supercapacitor application. Electrochemical measurements of G-CNF/ZnO/PANI electrode revealed the maximum specific capacitance, discharge time, energy density and power density as compared to that of CNF/ZnO/PANI indicating the increase in surface area due to graphene incorporation in electrospinning of carbon nanofibers. The combination of electric double layer charge (EDLC) capacitance from high surface area of G-CNF and pseudo-capacitance from PANI and ZnO nanoparticles facilitates the synergistic effect of ternary components to enhance the electrochemical performance of G-CNF/ZnO/PANI nanocomposite.

The micro/nano blocks of Ni/MnO composites were synthesized by a facile microwave-assisted solvothermal method. The results indicated that the morphology changed from irregular block to polyhedron and then to the sphere with the increase of ethylene glycol (EG) ratio in the solvent. The results indicated the specific capacitance of the obtained material increased as the EG ratio increased, but when the EG ratio exceeded 60%, the change of specific capacitance was not obvious (less than 5%). For the Ni/MnO material synthesized in pure EG, its specific capacitance reached 860 F/g at 1 A/g and the capacitance retention maintained 58% after 6500 cycles. The micro/nano structure of Ni/MnO material formed in EG solvent increased the surface area and provided more transfer channels for the electrolyte ion, which were all beneficial to improve the electrochemical properties. The high capacitance and good cycle stability especially after a period of cycles demonstrated the obtained Ni/MnO materials had a potential application for the supercapacitor electrode material.

A structured carambola-like CoWO₄ was fast prepared by a microwave-assisted hydrothermal method with the help of urea and NH₄F. Physical characterization indicated that the as-obtained CoWO₄ displayed a large specific surface area, high dispersion and self-selected orientation of crystal growth. Further electrochemical tests presented a high specific capacity of 492.0 C⋅g${}^{-1}$ at 1 A⋅g${}^{-1}$, low internal resistance and excellent cycle stability as 137.3% capacity maintenance after 8000 cycles at 20 A⋅g${}^{-1}$. These excellent electrochemical properties for the as-obtained material indicate that CoWO₄ has great potential as hybrid supercapacitor electrode materials. This work also provides a new and effective solution for regulating the morphology of CoWO₄-based hybrid supercapacitor materials to further improve the electrochemical performance.

A circuit for adiabatically charging and discharging a supercapacitor was designed. A microprocessor sets the duty ratio of the switching transistors that control the inductor current. Changing the duty ratio in a stepwise fashion causes the output voltage to change in a similar fashion. Stepwise voltage changes enable adiabatic charging and discharging. Current measurements showed that the eight-step charging and discharging of a supercapacitor reduced the energy dissipation to one-eighth of that for a constant-voltage process. The circuit enables precise voltage control in small steps.

A simple hydrothermal growth process was developed to deposit conformal manganese oxide nanospheres with a diameter of 10 to 20 nm on mesoporous carbon paper. The coating of nanospheres increased the cyclic-voltammogramic response of carbon paper by a factor of 5 with a slight dependence on the scan rate. For comparison, a related chemistry was also developed to fabricate a dense packing of manganese oxide nanorods with a diameter of 20 to 50 nm and a length of approximately 500 nm. The nanorods also increased the cyclic-voltammogramic response of carbon paper but only by a factor of approximately 3.

Potentiostatic two step anodizing of titanium utilized for preparation of self organized titania nanotubes arrays with diameter of 150 nm. Then the new alginate method has been applied for incorporation of NiO into the nanotubes. The prepared hybrid materials have been characterized by various methods including field emission scanning electron microscopy, X-ray diffractometry and cyclic voltammetry analyses. The X-ray diffraction patterns of samples were also studied by Rietveld's method. Results showed that the prepared electrode containing anatase, rutile and NiO phases with fraction of 70, 8, and 22%, respectively. It was found that by application of the new method, porous NiO uniformly coated on nanotubes surface and great enhancement of specific capacitance from 0.14 to 3.8 mF cm^-2 could be obtained. The prepared nanocomposites are promising materials for supercapacitance application and also for solar energy harvesting systems.

A novel and simple approach for preparing nanoporous binder free Sn:Pb composite metal foam has been demonstrated. The anodized metallic composite block was functionalized and also found a nanoporous structure. A scanning electron microscopy (SEM) result shows that the nanoflake-like arrangement has synthesized. The X-ray diffraction (XRD) results confirm the nanoporous structure of the Sn/Pb foam after etching with 6 M NaOH. The prepared Sn:Pb metal foam is able to be used as a super capacitors electrode to offer large areal capacitance with regards to the synergic integration of Sn and Pb metals and the unique nanoporous structure.

Facing the challenge of low energy density of conventional electric double layer supercapacitors, researchers have long been focusing on the development of novel pseudocapacitive electrode materials with higher energy densities. Since capacitive charge storage reaction mostly occurs on the interface of electrode and electrolyte, the interface chemistry determines the achievable power and energy densities of a supercapacitor. Consequently, understanding of surface–interface reaction mechanism is a key towards efficient design of high-performance supercapacitor electrode materials. In this paper, we have reviewed the recent advances in the understanding of surfaces–interfaces in the system of pseudocapacitive supercapacitors. With significant research advancements in the understanding of surface–interface of supercapacitors, novel colloidal electrode materials with improved surface–interface structures have been developed in our previous work, which have the potential to deliver both high energy and power densities. This review aims to provide an in-depth analysis on the surface–interface control approaches to improve the energy and power densities of supercapacitors.

Metal oxide-carbon composites (MOCCs) derived from sodium alginate gels were prepared through a facile and green ionic gelation method. Various polyvalent cations (Mn${}^{2+}$, Fe${}^{3+}$, and Zn${}^{2+})$ were used to crosslink sodium alginate to produce gels, following which the gels were carbonized under nitrogen flow to yield MOCCs. X-ray diffraction, scanning electron microscopy, and Raman spectra can character the as-prepared materials’ structural and morphological characters and thermogravimetric analysis. The electrochemical behavior of the as-prepared materials was studied by applying to cyclic voltammetry, galvanostatic charge–discharge measurements, and electrochemical impedance spectroscopy in 6M KOH electrolyte. The highest specific capacitance (161F g${}^{-1}$ at 0.5A g${}^{-1})$ was obtained for the Fe oxide-doped carbon material (MOCC-Fe), which displayed a good life cycle with only a 10% capacitance decline after 2000 cycles.

We report here the development of MnO₂ nanostructure electrode for electrochemical energy storage application. MnO₂ nanoparticles synthesized by a facile and efficient precipitation approach have been investigated for supercapacitor application. The structures and morphologies of MnO₂ nanoparticles were systematically studied using X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The synthesized nanoparticles are observed spherical in shape with uniform size distribution. The electrochemical properties were studied in two-electrode configuration by cyclic voltammetry process. A specific capacitance of 52.8F/g has been obtained for MnO₂ nanoparticles at scan rate of 100mV/s. The electrode is able to deliver a power density of 0.66kW/kg and energy density of 1.8Wh/kg.

Nitrogen-doped porous carbon materials are a new type of electrode material with safety, nontoxicity, high conductivity and good electrochemical performance, which have recently attracted extensive attention due to its wide application in supercapacitors. In this work, carbon-based materials named ZBK-$n$ were prepared (where $n$ represents the different ratios of KNO₃ used in the synthesis), using the nitrogen-containing organic molecule benzotriazole as a carbon and nitrogen source, and ZnCl₂ and KNO₃ as activators. These materials were mixed and heated at 350^∘C for 1h and 750^∘C for 2h under N₂ to prepared porous carbon materials with a higher nitrogen content. The result had shown that material (ZBK-4) had a larger specific surface area (2292.47m²/g) and higher nitrogen and oxygen contents (4.88%N and 5.99% O). At the current density of 1A/g, the specific capacitance of ZBK-4 was 300F/g, indicating good rate capability. In addition, the specific capacitance of the material after 8000 cycles remained at 93.05%, indicating good cycle stability. Therefore, these experimental results have confirmed that the obtained nitrogen-doped porous carbon material has good electrochemical performance, and good prospects for application in the field of supercapacitors.