A comprehensive study of Bi2Sr2Co2Oy misfit layered oxide as a supercapacitor electrode material

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.

In this paper, we studied the VOPO4·2H2O as an electrode material for supercapacitors. A systematic comparison of VOPO4·2H2O prepared by reflux and hydrothermal methods was carried out through detailed analyses that included power X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Their electrochemical performances were also investigated by using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). Meanwhile, we proposed a possible charge storage mechanism on the VOPO4·2H2O electrode surface. The material synthesized by reflux method had better performance in the capacitance than that by hydrothermal method, and its specific capacitance was up to 202 F/g at 2 mV/s. A total of 67.4 % of capacitance was maintained for the VOPO4·2H2O synthesized by reflux method when current density changed from 0.2 to 2 A/g, much higher than those obtained from the hydrothermal-synthesized VOPO4·2H2O supercapacitor of 42.5 %. The energy density of VOPO4·2H2O supercapacitor synthesized by reflux method was 18.7 Wh/kg at 290 W/kg and maintained 6.2 Wh/kg at 1,421 W/kg, much higher than the hydrothermal-synthesized VOPO4·2H2O supercapacitor. Our work confirms that VOPO4·2H2O is a potential electrode material for supercapacitors.

The incorporation of cobalt ions into hydroxyapatite nanostructure for a novel range of electrochemical energy storage applications

Electrochemical capacitors can provide both high energy storage capacity and fast charge-discharge speed, and are thus seen as a promising technology to fill in the gaps in energy needs not covered by devices such as batteries. Among the most widely investigated materials, transition metal oxides have been shown to exhibit high specific capacitance because of Faradaic redox activity, and long cyclic life due to their robust crystal structure. Cationic substitutions in ternary oxides have shown dramatic improvements over binary analogues, but the peak stoichiometry is often arrived at by heuristic chance. To fully optimize mixed-metal oxides there is an unmet need to understand how cationic substitution affects supercapacitor performance. Transition metal oxides are also hampered by low electronic conductivity, requiring the use of conducting additives such as carbon black. Organic-solution phase colloidal nanoparticle synthesis is seen as the prized method to integrate nano-engineered materials into industry because of the ability of its ability to finely control size dispersion and to easily produce a large amount of nanocrystals through industrially-friendly, scalable solution processing. However, conventional methods for incorporating colloidal nanoparticles into electrochemical storage electrodes involves additives such as polymeric binders to create strong attachments between the particles and current collector, and conductive carbon to increase electronic conductivity. The addition of binders and conductive carbon increases the weight by ~10%‒40% and reduces the porosity of the electrode, which diminishes the ability of the electrolytes to homogeneously percolate through the network. In this talk I will report on the effect of cationic substitutions in Co3-xMnxO4nanoparticles on electrochemical Li-ion energy storage, in electrodes assembled without polymeric or conducting additives. We employ colloidal synthesis to produce Co-Mn oxide nanoparticles with various ratios of Co/Mn. The nanoparticles are assembled on copper substrates as supercapacitor electrodes using Electrophoretic Deposition. Using this technique, we successfully fabricate electrochemical capacitors with additive-free and binder-free transition metal oxides electrodes. We find that the sample with a Co/Mn ratio of unity (i.e., Co1.5Mn1.5O4) has an anomalous increase in performance, outperforming all other stoichiometries by up to 20× for specific capacitance. The Co1.5Mn1.5O4 eletrode shows an energy density of 26.6 Wh/Kg with a specific capacitance of 173.6 F/g. This nanoparticle electrode delivers the highest power density of 3.8 kW/Kg at a 5 A/g constant current discharge. The energy density and power density delivered by the optimal mixture is ~6× and ~3× higher, respectively, than that of pure Co3O4 electrodes. The specific capacitance for the Co-Mn mixture is also ~4× better than the pure Co3O4 supercapacitor. The Co1.5Mn1.5O4composition also exceeds the Mn-rich composition performance in energy density (~16×), power density (~12×), and specific capacitance (~20×). This composition shows excellent stability with greater than 80% capacitance retention over 300 cycles. To understand this anomalous increase in performance we analyze the mechanisms behind the charge storage. The cyclic voltamogram and charge-discharge analyses indicate that the capacitive charge storage is the significant contribution for total charge storage for the Co1.5Mn1.5O4 electrode in all sweep rates. This is in contrast to Co3O4 electrodes which show that a majority of charge storage is diffusion-controlled. By characterizing the impedance behavior of the samples we find that the Co1.5Mn1.5O4 exhibits higher charge transfer kinetics and better capacitor performance than both the Co3O4 and the Mn-rich end composition. Based on these impedance results the Co1.5Mn1.5O4 electrode delivers its stored energy almost two times faster than Co3O4, and operates in a much more capacitive mode than does the Co3O4sample and the Mn-rich x=2.54 sample. Finally, we measure the oxidation states through XPS for the Mn and Co 2+ and 3+ ions. We find that the top-performing sample (Co1.5Mn1.5O4) has both a high Co3+/Co2+ ratio and a high Mn3+/Mn2+ ratio, compared to other samples. We posit that this composition could be displaying peak performance because it maximizes the 3+ to 2+ redox activity of the cations, and also the ratio is not too high as to overwhelm electronic conduction that relies on equal 3+ and 2+ ions on equivalent sites to mediate polaron hopping. Our work reveals a method to test cationic substitution in transition-metal oxides for nanoparticle supercapacitors, and shows how to assemble high-performing electrochemical electrodes without the use of additives, providing a new pathway for materials research towards supercapacitors S.D. Perera, X. Ding, A. Bhargava, R. Hovden, A. Nelson, L.F. Kourkoutis, R.D. Robinson, “Enhanced supercapacitor performance for equal Co-Mn stoichiometry in colloidal Co3-xMnxO4 nanoparticles, in additive-free electrodes,” Chem. Mater. 27, 7861 (2015) 10.1021/acs.chemmater.5b02106 Figure 1

The increasing consumption of fossils fuel accompanied by related carbon emissions and complex set of issues associated with the generation and use of electricity has raised an urgent need for reliable, renewable and sustainable energy alternatives [1]. Remarkable progress made in nanoscience and nanotechnology brought inspiration for further development of new technologies in electrochemical energy storage. Supercapacitors (SCs) have emerged as a fast-rising class of energy storage technology and have received tremendous attention for potential applications in high-power sources [1,2]. Thus, manipulation of nanostructured materials became an important approach for the improvement of energy storage properties in SCs. Up to now, various synthetic methods have been established to improve the electrode materials for SC applications. Carbon nanomaterials such as carbon nanotubes (CNTs), graphene and graphene oxide (GO) have been widely used and modified to enhance their energy storage performance in SCs. Recently, much interest has been devoted to the doping of carbon materials to improve the performance of SC devices. Manganese oxide-based electrode materials characterized by their high theoretical specific surface area (1370 m2 g-1), high theoretical specific capacitance (1100 to 1300 F g-1), low-cost, abundance and environmentally friendly in nature, have attracted significant interest as active electrode materials for SCs. Although intensive study has been done on the MnO2-based pseudocapacitor, tetragonal hausmannite manganese oxide, Mn3O4, has received limited attention in SCs application [3]. Among various synthetic methods of synthesizing carbon/metal oxides nanohybrids, hydrothermal reduction of metal salts in the presence of carbon material is widely used, due to the simple operation and the low cost. This work present, one-pot synthesis of nitrogen-doped reduced graphene oxide decorated with hausmannite manganese oxide (N-rGO/Mn3O4 nanohybrid) and the study of its electrochemical energy storage performance for supercapacitor application. The microscopic and spectroscopic characterization of N-rGO/Mn3O4 nanohybrid and its precursor materials were acquired using SEM, EDX, Raman and XRD whereas the electrochemical characterization were acquired using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS).

Electrodeposited molybdenum selenide sheets on nickel foam as a binder-free electrode for supercapacitor application

Ternary structured magnesium cobalt oxide/graphene/polycarbazole nanohybrids for high performance electrochemical supercapacitors

The demand for regenerative energy and electric automotive applications has grown in recent decades. Supercapacitors have multiple applications in consumer alternative electronic products due to their excellent energy density, rapid charge/discharge time, and safety. CuFe2O4-incorporated three-dimensional graphene sheet (3DGS) nanocomposites were studied by different characterization studies such as X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The electrochemical studies were based on cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. As prepared, 3DGS/CuFe2O4 nanocomposites exhibited an excellent surface area, high energy storage with appreciable durability, and excellent electrocatalysis properties. A supercapacitor with 3DGS/CuFe2O4-coated nickel foam (NF) electrodes exhibited an excellent specific capacitance of 488.98 Fg−1, a higher current density, as well as a higher power density. After charge–discharge cycles in a 2.0 M KOH aqueous electrolyte solution, the 3DGS/CuFe2O4/NF electrodes exhibited an outstanding cyclic stability of roughly 95% at 10 Ag−1, indicating that the prepared nanocomposites could have the potential for energy storage applications. Moreover, the 3DGS/CuFe2O4 electrode exhibited an excellent electrochemical detection of chloramphenicol with a detection limit of 0.5 µM, linear range of 5–400 µM, and electrode sensitivity of 3.7478 µA µM−1 cm−2.

NiFe2O4/SiO2 nanostructures as a potential electrode material for high rated supercapacitors

Electrochemical synthesis of hybrid nanostructure of nickel cobalt phosphide/molybdenum disulfide on nickel foam as an effective electrode material in supercapacitor

In the recent years, the development of electrochemical energy storage device has been widely investigated. Supercapacitors are known for their excellent power density and superb cycling stability but restricted by low charge storage capacity, on the other hand batteries provide high energy density, limited by low power density. Here, olivine-structured LiXPO4 (X=Mn,Fe,Co) possessing high energy storage capability is used as a positive electrode. Our recent research demonstrated that Fe2O3-based Fractal-like structures supported on Ni Foam exhibit extremely high specific capacitance of ~2708 F g-1 at 1 A g-1 in 1 M KOH electrolyte, when used as negative electrode [1]. Hence, the Fractal-like Fe2O3 is used as the negative electrode for the envisaged hybrid supercapacitor device. The flexibility is imparted to these devices by employing carbon cloth as the current collector. The choice of suitable electrolyte is crucial for supercapacitor applications as it decides the working potential window, electrode-electrolyte interaction, and ionic conductivity. Here, PVA based gel polymer electrolyte (GPE) is used due to the ease in gel formation and non-toxicity to make flexible hybrid supercapacitor device. Different PVA based GPEs are synthesized using H3PO4, H2SO4 and KOH with Ionic liquids viz. EMIMBF4 and EMIMCl. The role of GPEs in the performance of LiXPO4 (X=Mn,Fe,Co)//GPE//Fe2O3 hybrid supercapacitors is understood through charge storage mechanisms deciphered from galvanostatic charge-discharge (GCD) experiments, Electrochemical Impedance Spectroscopy (EIS).

The intermittent nature of many renewable energy sources such as wind and solar, coupled with fluctuations in energy demand, creates a pressing need for efficient, low-cost energy storage technologies. Supercapacitors are promising candidates to play a role in next-generation energy storage systems. They have a higher power density and better cycle life (although lower energy density) than batteries making them ideal for rapid energy storage and deployment [1]. Activated carbon is a favoured electrode material due to high surface area, although low conductivity requires use of a conductive additive (often carbon black), reducing available surface area for charge storage. In contrast, the high conductivity and specific surface area of graphene has made it a promising material for electrochemical double layer supercapacitors (EDLCs) [2], however, performance is limited by restacking of the graphene sheets, reducing available surface area.In this work, high-shear exfoliated few layer graphene (FLG) [3] is investigated both as an electrode material and as a conductive additive/interfacial layer for EDLCs. FLG suspensions were produced under a variety of exfoliation conditions, with platelet thickness and linear dimension determined from Raman spectroscopy based on metrics developed by Backes et al. [4] and through scanning electron microscopy (SEM).The FLG suspensions were used in three ways: i) to create thin ‘graphene paper’ electrodes; ii) as a conductive additive, mixed into the activated carbon electrode material; iii) deposited onto the back of (and diffused within) activated carbon electrodes. These electrodes were investigated by Raman spectroscopy and Scanning Electron Microscopy, before being assembled into symmetric two-terminal aqueous cells then evaluated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS), and their electrochemical performance related to structure and composition.As expected, pure FLG electrodes often showed excellent low series resistance values, however specific capacitance was low, due to restacking. Directly mixing 5% FLG into activated carbon as a conventional conductive additive led to a specific capacitance of 63 F/g (from CV at 10 mV/s), and a series resistance of 19 W (from GCD at 1 A/g) - markedly inferior to those with 5% carbon black as a conductive additive (95 F/g and 2 Ohm) and inferior even to electrodes with no conductive additive (87 F/g and 10 Ohm).However, post fabrication deposition/infusion of FLG offers comparable performance to carbon black (90 F/g and 1 Ohm) at 7% FLG by weight. As the quantity of FLG is increased the specific capacitance decreases sharply. This behaviour is attributed to FLG restacking on the rear of the electrode, so adding mass whilst providing limited additional capacitance, and compression of the electrode.Adding high-shear exfoliated FLG to activated carbon electrodes shows promise for obtaining the benefits of both materials. At present, FLG/activated carbon electrodes can match the performance of those produced from activated carbon with a carbon black conductive additive and, with further optimization, we expect will be able to exceed them.Figure: a) Cross sectional SEM image of activated carbon electrode with graphene interfacial layer; b) magnified cross sectional SEM image of graphene interfacial layer; c) cyclic voltammograms at 10 mV/s of the different electrodes mentioned in the abstract.

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.

Electrochemical investigation of graphene/cerium oxide nanoparticles as an electrode material for supercapacitors

Transition metal oxide‐based magnetic nanocomposites attract great attention due to their unique properties and applications in the field of energy storage. Herein, we present a facile microwave procedure for the synthesis of CuFe2O4 (CF) and CuFe2O4 incorporated with reduced graphene oxide CuFe2O4/rGO (CG) as potential electrode materials for hybrid supercapacitor. The structure and morphology of CF and CG nanoparticles are examined. The electrochemical performance is studied in 6 M aqueous KOH electrolyte using cyclic voltammetry (CV), galvanostatic charge‐discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques. The attractive CG nanocomposite exhibits high specific capacity of 800 C/g at a current density of 2 A/g and better cycling stability when compared to pure CF, due to the formation of nanostructure composed of ferrite nanoparticles homogeneously incorporated onto rGO sheets. Furthermore, the practicability of CG electrode is investigated by the fabrication of CG and activated carbon. The hybrid supercapacitor device shows excellent electrochemical performance with specific energy of 18.3 Wh/kg and a specific power of 455 W/kg. It is noteworthy that the cyclic stability is excellent with a capacity retention of ~98% after 3000 cycles manifesting the superiority of CG electrode. The proposed device demonstrates the potential to fabricate other metal oxides with activated carbon via a facile synthesis method for promoting application in energy storage materials and promoting new opportunities of binary nanocomposite.