Reduced Graphene Oxide‐Tailored CuFe2O4 Nanoparticles as an Electrode Material for High‐Performance Supercapacitors

Design of hierarchical porous carbon nanofibrous membrane for better electrochemical performance in solid-state flexible supercapacitors

Nowadays, the energy sector is receiving significant attention and extensive research as the need for energy efficiency and sustainable growth continues to rise, especially in the field of energy storage. This study successfully approached the development of iron-modified carbon aerogel derived from water hyacinth as electrode materials for supercapacitors, aiming to enhance energy storage capacity compared to conventional carbon aerogel materials. The materials were synthesized using two different impregnation methods: incorporating the metal precursor into the initial mixture (Method 1) and wet impregnation (Method 2). Physical properties of the materials were analyzed using Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), and Brunauer–Emmett–Teller (BET) to specify the optimal sample of each technique. Furthermore, the electrochemical properties were conducted in order to identify the best suitable sample for energy storage and supercapacitor application. The electrical behavior and performance of the optimally prepared samples via both techniques were examined using Electrochemical Impedance Spectroscopy (EIS) with frequency from 1 Hz to 10000 Hz, Cyclic Voltammetry (CV) technique with a scan rate at 10 mV/s and Galvanostatic Charge-Discharge (GCD) with 5 varying current densities (0.25 A/g, 0.5 A/g, 1A/g, 2 A/g, 4 A/g) in H 2 SO 4 and KOH electrolyte. The results showed that Fe-doped carbon aerogels exhibited a well-structured porous system with enhanced surface area characteristics, leading to enhanced charge storage capacity. Electrochemical measurements of Fe-doped carbon aerogels demonstrated superior capacitive behavior in both solution electrolytes compared to the carbon aerogel blank. These findings demonstrate that activated carbon derived from water hyacinth biomass holds great promise as an eco-friendly and high-performance electrode material for supercapacitors.

Capacitance performance of Ti3C2Tx MXene nanosheets on alkaline and neutral electrolytes

Metal organic frameworks (MOF's) have gained considerable attention in the field of energy storage and supercapacitors applications. Herein, we synthesized copper oxide (CuO) through the precipitation method and concurrently derived from the solvothermal prepared copper-benzene dicarboxylate (Cu-BDC) by calcination. The integration of MOF-derived nanostructures with traditional CuO to form a hybrid electrode material, has not been extensively explored. The synthesized materials were characterized using x-ray Diffractometry, FTIR, XPS, Brunauer, Emmett, and Teller and morphological analysis was conducted using scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) affirming the composite's nature. Electrochemical impedance spectroscopy, galvanostatic charge-discharge, and cyclic voltammetry were used to evaluate the electrochemical properties of electrode material. With a specific capacitance of 691 Fg-1for CuO obtained from Cu-BDC (benzene dicarboxylic acid) and 236 Fg-1for CuO via the precipitation method, measured at a scan rate of 5 m Vs-1in 6 M KOH was found to be the optimal performance solution for the electrode material. The mesoporous structures are crucial for their absorption ability and improved ion transport, resulting in optimized electrochemical performance. Finally, we demonstrate significant improvements in specific capacitance and cycling stability compared to pure CuO-based electrodes, highlighting the potential of this composite structure for advanced supercapacitor applications.

Transition metal sulfides have been suggested as promising materials for efficient energy storage with superior electrochemical performances. Compound NiMoS4-A was synthesized by a facile chemical co-precipitation process, followed by calcining at 450°C in Ar. The as-prepared NiMoS4-A electrode exhibits a high specific capacity of 313 C g−1 at 1 A g−1 and good rate capability (83% retention at 10 A g−1). Electrochemical impedance spectroscopy (EIS) results indicate that the good performances could be attributed to the low internal and charge transfer resistances. Additionally, the quantitative charge storage analysis reveals that the faradaic redox process dominates at lower scan rates (78% at 1 mV s−1), while the capacitive effect dominates at higher scan rates (56% at 20 mV s−1). Furthermore, a hybrid supercapacitor (HSC), with NiMoS4-A as the positive electrode and activated carbon (AC) as the negative electrode, displays a high energy density of 35 Wh kg−1 at an average power density of 400 W kg−1. Meanwhile, the HSC exhibits excellent cycle stability, maintaining 82% of the initial capacitance after 10000 charge-discharge cycles even at a high current density of 5 A g−1. These good electrochemical performances indicate that NiMoS4-A is a promising positive electrode material for hybrid supercapacitors.

In order to improve the pseudocapacitance properties and cycle stability of polyaniline (PANI), reduced graphene oxide–silica (rGOS) is used to modify the polyaniline material. Ternary composites of reduced graphene oxide–silica–polyaniline (rGOSP) are prepared by chemical polymerization of aniline using ammonium persulfate oxidant with various amounts of rGOS in aq. 1 M H2SO4 solution. Morphology analysis of rGOSP composite revealed that the nano fibers form of polyaniline is intercalated in the graphene layers and also covered the rGOS. Symmetric supercapacitor cell is fabricated in CR2032 coin cell with rGOSP composite as electrode and its electrochemical performance is evaluated from cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy techniques. rGOSP composite yielded a higher capacitance and lower ESR value compared to that of its individual components, PANI and rGOS. The energy density of the composite is found to be 10 W h kg−1 at a power density of 2310 W kg−1. Furthermore, over 75.2 % of the original capacitance is retained after 6000 galvanostatic charge–discharge cycles at 0.8 A g−1.

Nickel-cobalt phosphate/graphene foam as enhanced electrode for hybrid supercapacitor

We report a simple and low-cost technique to prepare a composite comprising of activated carbon and few layers of graphene sheets and fabricated as electrode material for supercapacitor (SC) applications. The composite is characterised by using Raman spectroscopy, powder X-ray diffraction (XRD), scanning electron microscope (SEM) and current-voltage (I-V) measurements. The synthesized composite is investigated by using galvanostatic chargedischarge (GCD) and cyclic voltammetry (CV) measurements in 3M KOH aqueous electrolyte to evaluate its electrochemical performance. The composite results high specific capacitance from 173 to 564 F/g at different scan rates (100-5 mV/s), analysed by CV and the capacitances resulted in GCD measurement were 196 to 587 F/g at various current densities (5-1 A/g). The cycle stability of the as-prepared AC/graphene composite is also tested and observed that 89% of capacitance is retained even after 5000 cycles which reveals the excellent long term chargedischarge stability of the prepared composite. Therefore, the composite performs very well in storage as well as life cycling. The obtained results suggest that AC/graphene composite can be a suitable electrode material for high-performance SC.

With the ongoing global energy crisis, producing reliable and efficient methods of energy storage remains an integral part of cutting-edge materials research. Within this topic, 3D-printing (also known as additive manufacturing) is evolving from a niche hobby to a reliable scientific tool for materials science research [1-3]. 3D-printing energy storage materials provides unparalleled levels of customisation [4-9] and freedom of design, while also eliminating waste material during the manufacturing process.3D-printing energy storage materials has been widely covered, but usually just focuses on one method of 3D-printing. Directly comparing more than one 3D-printing method within a single energy storage study is far more seldom researched. This work directly compares the electrochemical performances of symmetric carbon-based supercapacitor devices made using two 3D-printing techniques, SLA (stereolithography) and FDM (fused deposition modelling). Two cell types are made in this study, one with gold-sputtered SLA-printed current collectors, the other with conductive PLA (polylactic acid) FDM-printed current collectors. Carbon-based electrode (various combinations of SWCNT, GNP, Super-P, PVDF) slurries and aqueous 6M KOH electrolyte are implemented in these cells. The benefits and limitations of these 3D-printing methods are directly compared, with the electrochemical performance of the supercapacitor cells being analysed using cyclic voltammetry and galvanostatic charge-discharge tests.The sputtered conductive SLA current collector cells display better conductivity and more ideal rectangular cyclic voltammetry curves for electronic double-layer capacitors (EDLCs) but suffer from poor cycle life in initial experiments (~5,000 charge-discharge cycles before losing all specific capacitance). The FDM current collector cells have poorer conductivity, less ideal cyclic voltammetry curves, and are less structurally sound (causing some electrolyte leakage over long term cycling) but offer extremely stable cycle life for supercapacitor cells, retaining most of their specific capacitance after 100,000 charge-discharge cycles. The cycle lives of the gold-sputtered SLA current collector cells are greatly improved after several changes made during the study, such as reducing the voltage window from 0.0-1.0 V to 0.2-0.7 V, and exploring additives for the carbon-based slurry electrodes, such as Super-P and PVDF (polyvinylidene fluoride).

For the goal of synthesizing high performance supercapacitor electrode materials to meet the pressing requirements of energy storage, nitrogen doped activated graphene (N-AG) was successfully synthesized by employing two steps as KOH activating and following nitrogen doping using a hydrothermal method. Continuously increased ID/IG ratios were observed in Raman spectra after KOH activation and N-doping process, indicating increased defects due to the etching effect of KOH and the introduced nitrogen defects on graphene sheet. Stacked graphene with damaged sheets on the surface was clearly seen in transmission electron microscopy (TEM) image after the KOH etching. The successful dopant of N was demonstrated by X-ray photoelectron spectroscopy (XPS) spectra and energy-dispersive X-ray spectroscopy (EDS) mapping, confirming this effective hydrothermal N doping method. The N-AG exhibited largely enhanced capacitance (186.63 F/g) and cycling stability compared with that of nitrogen doped graphene (N-G, 50.88 F/g) and activated graphene (AG, 58.38 F/g) due to the combined positive effects of KOH activation and N-doping. This facile hydrothermal method is of great significance of scaling the production and the synthesized N-AG through combining the KOH activation and nitrogen doping processes represents a promising alternative candidate to commonly used electrode materials in supercapacitor. Experimental Graphite oxide (GO) was synthesized following the modified Hummers method.1 For the synthesis of nitrogen doped graphene (N-G) and KOH activated graphene (AG), 26.0 g homogeneous GO solution (0.338 g GO) was first transferred to a 40 mL teflon lined hydrothermal autoclave, 3 mL NH4OH solution or well dissolved KOH solution (4.05 g KOH, mass KOH : GO = 12:1) was added, the solution was diluted to 40 mL by DI water and sealed maintaining at 150 ºC for 3 hrs. After cooling down, the precipitates were collected by filtration and washed with water for 3 times, the products were dried naturally for 72 hours. Reduced graphene oxide (RGO) was also obtained following the same procedure using simple GO solutions as a control experiment. For the synthesis of N-AG, 0.2 g synthesized AG powders were uniformly grinded and dissolved in 30 mL water, which undergo a 30 min sonication to achieve a uniform distribution, the AG solution was then transferred to a 40 mL autoclave added with 1.80 mL NH4OH solution (same NH4OH/AG ratio as that of NH4OH/GO). Similar procedures were following proceeded to obtain the N-AG powder products. Results and Discussion The Raman spectroscopy and TEM have successfully demonstrated the increased defects and edge parts on graphene after the activation with KOH. Typical N peaks deconvoluted from XPS and uniform distribution of N observed from EDS mapping clearly indicate the successful doping of N using this facile hydrothermal method. Activation and N-doping processes can both contribute to the enhancement of energy storage through increasing active electronic sites and surface area. Increased capacitance, energy and power densities as well as cycling stability after the activation and N-doping processes are confirmed by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements,2demonstrating the effectiveness of this hydrothermal method and potential of this N-AG for practical energy storage applications. Conclusion A facile hydrothermal synthesis method combining KOH activation and N-doping was successfully employed to synthesize nitrogen doped activated graphene, which is economically and effectively at a very high yield, implying feasibility for mass production. The synthesized N-AG exhibited relatively decreased oxygen containing groups with increased defects due to the etching nature of KOH and N containing defects were also introduced with this effective N doping method. These unique properties endow them as promising electrodes for supercapacitors with high capacity, excellent rate capability, and long-term stability. Due to the possibility of scalable synthesis and prominent properties, the N-AG can offer attractive opportunities for both fundamental study and potential industrial applications in catalysis, adsorption, energy storage, and energy conversion systems. Acknowledgments The financial supports from University of Tennessee Knoxville are kindly acknowledged. Figure 1. Charge−discharge of RGO, N-G, AG and N-AG with a current density as 1 A/g. Background is a schematic representation of the synthesis process.

Bifunctional PAni@Bi/Ce metal organic framework-Chitosan composite for electrochemical sensing and energy storage applications

Investigation of the capacitive performance of tobacco solution reduced graphene oxide

Green synthesis of Ag and Au NPs decorated rGO nanocomposite for high impedimetric electrochemical sensor as well as enhanced antimicrobial performance against foodborne pathogens

Hybrid supercapacitors have gained significant attention in recent years due to their potential to combine the advantages of both batteries and capacitors. In this study, we investigate the use of metal oxides materials in a hybrid supercapacitor using a dendritic gold current collector, the device was implanted on a silicon wafer. Metal oxide materials, such as iron Oxide (Fe2O3) and manganese oxide (Mn2O3), are known for their high pseudo-capacitance and excellent electrochemical performance in water based electrolyte.By integrating dendritic gold current collectors with these materials, we aim to enhance its energy storage capacity and cycling stability. The silicon substrate provides mechanical support and pave the way for on-chip application, while the dendritic gold current collector offers a high surface area for efficient ion adsorption and desorption along the electrode-electrolyte interface. The metal oxide is coated onto the porous gold electrode using a simple and low cost-effective method, the electroplating, by mean of a solution based on FeSO4. The performance of the hybrid supercapacitor is evaluated through various electrochemical tests, including cyclic voltammetry, galvanostatic charge-discharge cycling, and electrochemical impedance spectroscopy, adopting neutral water based electrolyte. The results show that the enhanced hybrid supercapacitor with metal oxide materials exhibits significantly improved electrochemical performance compared to the device with a flat metal oxide electrode. The Fe-coated dendritic electrode exhibits a high specific capacitance over 20 mF cm-2, while the MnO2-coated flat electrode demonstrates similar specific capacitance over 25 mF cm-2. Additionally, the hybrid supercapacitor shows excellent cycling stability with negligible capacitance loss after 1000 cycles.In conclusion,the results suggest that mixing micro-structured current collectors with metal oxides can lead to simplified area's balancing technique for planar electrochemical cells, destinated to the development of on-chip devices with large operating voltage window, high energy storage capability and efficiency. Figure 1

Freestanding hierarchical NiO/MnO2 core/shell nanocomposite arrays for high-performance electrochemical energy storage