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

Mechanisms of charge storage, stability, capacitance, morphology and response current of graphene/cerium oxide (CeO₂) nanoparticles as an electrode material for electrochemical capacitors have been investigated. Electrochemical properties of the assembled electrodes were studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques in 3 M NaCl, NaOH and KOH electrolytes. Scanning electron microscopy (SEM) is used to characterize the microstructure and the nature of prepared electrodes. SEM images confirm the layered structure (12 nm thickness) of the used graphene. The proposed electrode shows a maximum specific capacitance as high as 11.09 F g⁻¹ in the potential range between −0.55 and 0.3 (V vs. SCE) at scan rate of 5 mV s⁻¹. The charge/discharge cycling test shows a good reversibility and confirms that capacitance will increase after 500 cycles by 37%.     

Fabrication and performance evaluation of symmetrical supercapacitor based on manganese oxide nanorods–PANI composite

Manganese oxide nanorods distributed over polyaniline (PANI) network was prepared by one step facile synthesis condition. pH of the reactant solution was tuned using sulfuric acid. Effect of pH on the morphology, chemical composition, structure and electrochemical performance of the prepared materials were studied. Thermal investigation reveals the decomposition of PANI at temperatures below 600 °C. Structural details and chemical composition of the compound was obtained from XRD, FTIR and XPS studies. α type MnO₂ was found to be crystallized in the prepared MnO₂–PANI composite. Single crystal manganese oxide nanorods distributed over the PANI network was cognizant from the FESEM and HRTEM investigations. Nanorods of average diameter 82 nm and length 482 nm were obtained without deploying any surfactants or templates. Electrochemical techniques like Cyclic Voltammetry (CV), Chronopotentiometry (CP) and Electrochemical Impedance Spectroscopy (EIS) were utilized. Study results indicate that the composites prepared shows excellent electrochemical performance. Among the prepared materials, MnP-46 exhibits a maximum specific capacitance of 687 Fg⁻¹ at 5 mV s⁻¹ scan rate and a capacitance retention of 95% over 2000 cycling. Promising performance of MnP-46 was further tested in a symmetrical two cell configuration. The cell was operative upto 1 V potential window. MnP-46 in a symmetrical arrangement demonstrates 179 Fg⁻¹ at 5 mV/s scan rate. High conductivity of the electrode material was confirmed from the Nyquist plot.     

Heterostructure of CdO-ZnO nanoparticles intercalated on PANI matrix for better thermal and electrochemical performance

New heterostructure of CdO-ZnO nanoparticles intercalated on PANI matrix (CZP) have been synthesized by two step solution route: firstly, CdO-ZnO heterostructure was prepared by the simple chemical precipitation method and the resulting materials are effectively coupled on PANI by the chemical oxidative polymerization method in acidic medium using APS as oxidant. The resulting respective hybrid materials of CdO, ZnO and PANI matrix were characterized and confirmed (functional groups and crystalline nature) by FTIR, RAMAN and XRD analysis. From the HR-SEM analysis, hybrid materials of CdO-ZnO/PANI matrix has agglomerated hexagonal structure was derived from the granular structure of PANI. Thermo gravimetric analysis showed that CZP hybrid composite has higher thermal stability than ZnO-PANI and PANI matrix. Surface area and pore volume of the hybrid heterostructure obtained to be 54.52 m²/g and 0.14 cm³/g respectively. The electrical properties of CdO-ZnO particles intercalated on PANI matrix are evaluated in three different electrolyte solutions. In the sense, 1 M H₂SO₄ electrolyte solution exhibits better current response than the other electrolyte solution. From the results shows that the hybrid hetero structure of (CZP) exhibited better thermal and electrochemical performances than ZnO-PANI hybrid and the capacitance retention showing 72.6% after 500 cycles at a current density of 0.5 mA g⁻¹, thus the electrode materials possess good specific capacitance and cycle stability. Hence the CZP is a promising material in the field of super capacitor applications.     

Nanostructured nickel oxide ultrafine nanoparticles: Synthesis,characterization, and supercapacitive behavior

Well-dispersed NiO nanoparticles were prepared via cathodic electrodeposition followed by a heat-treatment method. The supercapacitive performance of the prepared nanoparticles was analyzed by means of cyclic voltammetry (CV) and galvanostatic charge–discharge tests at −0.2–0.5 V potential windows in 1 M KOH. The nanoparticles exhibited high specific capacitance (1623.1 F g⁻¹ at the scan rate of 5 mV s⁻¹) and good long-term cycling stability (9.6% capacity decay after 1000 cycling at the current density of 2 A g⁻¹).     

Fabric electrodes coated with polypyrrole nanorods for flexible supercapacitor application prepared via a reactive self-degraded template

Wearable energy storage devices that can be used in the garment industry are strongly required to power E-textiles. In this article, polypyrrole (PPy) nanorods were deposited on cotton fabrics via in situ polymerization of pyrrole in the presence of the fibrillar complex of FeCl₃ and methyl orange as a reactive self-degraded template. The obtained fabrics could be directly used as supercapacitor electrodes, with a maximum specific capacitance of 325 F g⁻¹ and an energy density of 24.7 Wh kg⁻¹ at a current density of 0.6 mA cm⁻². The capacitance remained higher than 200 F g⁻¹ after 500 cycles.     

Porous network of samarium sulfide thin films for supercapacitive application

In the present letter, a novel aqueous chemical method is employed to prepare thin film of Sm₂S₃ material containing porous network of interconnected nanoparticles for supercapacitive application. The orthorhombic phase formation of Sm₂S₃ film is concluded from X–ray diffraction study. The chemical states of samarium and sulfur are determined using X–ray photoelectron spectroscopy study. The pseudocapacitive behavior of Sm₂S₃ showed a maximum specific capacitance of 248 F g⁻¹ in 1.5 M LiClO₄ electrolyte prepared in propylene carbonate electrolyte. The nature of charge and discharge curves confirmed pseudocapacitive behavior of film electrode. The highest power and energy densities of 15.6 kWh kg⁻¹ and 54.6 Wh kg⁻¹, respectively are obtained. An electrochemical stability of 94% is retained after 1500 cycles.     

Iron mediated cathodic electrosynthesis of hausmannite nanoparticles

A novel synthetic route has been proposed to prepare hausmannite nanoparticles. The synthetic route comprises an iron mediated constant current cathodic electrodeposition of manganite and heat treatment of the latter to obtain hausmannite. The obtained nanostructures have been characterized using X-ray Diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and Fourier transform Infrared Spectrometry (FTIR). The role of iron in the formation of manganite precursor has been studied by cyclic voltammetry (CV) and differential thermal analysis (DTA). A formation mechanism based on iron mediated formation of Mn³⁺ and subsequent cathodic reduction of the disproportionated products has been proposed accordingly. The prepared nanoparticles exhibited specific capacitance of 143 F g⁻¹ in 0.5 M Na₂SO₄ solution. The retained specific capacity was 87% after 2000 cycles.     

Deposition of Fe3O4 on oxidized activated carbon by hydrazine reducing method for high performance supercapacitor

Oxidized activated carbon/Fe₃O₄ (AC/Fe₃O₄) composites for supercapacitor electrodes were synthesized by a reduction method. Poly(vinylpyrrolidone) was added as a dispersing agent for homogeneous deposition of Fe₃O₄ on AC. The obtained products were identified as AC/Fe₃O₄ by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. Morphological characterization of AC/Fe₃O₄ was carried out by field emission scanning electron microscopy (FE-SEM); the results clearly showed the formation of Fe₃O₄ nanoparticles about 30 nm in diameter on AC. Moreover, by using N₂ adsorption/desorption isotherm analysis, we confirmed that surface areas and pore volumes decreased with increasing Fe₃O₄ content. We also carried out electrochemical characterization of AC and AC/Fe₃O₄ composites. Remarkably, we found that the value of specific capacitance increased significantly from 99.4 F g⁻¹ of raw AC to 202.6 F g⁻¹ of AC/Fe₃O₄ composites at 10 mV s⁻¹ of scan rate. This result can be ascribed to a synergistic effect of the combination of electrical double-layer capacitance and pseudo-capacitance properties. This research represents a valuable contribution to the application of supercapacitor electrodes in regard to cost effectiveness and simple fabrication.     

Synthesis of samarium telluride thin films by successive ionic layer adsorption and reaction (SILAR) method for supercapacitor application

The present paper deals with synthesis of samarium telluride (Sm₂Te₃) thin films using simple and low cost successive ionic layer adsorption and reaction (SILAR) method for supercapacitor application. The Sm₂Te₃ thin films are characterized by X-ray diffraction (XRD) for structural determination, energy dispersive analysis of X-ray (EDAX) for elemental composition, field emission scanning electron microscopy (FE-SEM) for surface morphological study and contact angle measurement for wettability study. The Sm₂Te₃ exhibits orthorhombic crystal structure with cloud like surface morphology. The film surface showed lyophilic behavior with contact angle of 5.7° for propylene carbonate (PC). Further, electrochemical measurements are carried out in LiClO₄–PC electrolyte using cyclic voltammetry (CV), galvanostatic charge discharge and electrochemical impedance spectroscopy (EIS) techniques. The Sm₂Te₃ film showed maximum specific capacitance and energy density of 144 F g⁻¹ and 10 W h kg⁻¹ respectively. The EIS study showed negligible change in resistive parameters after 1000 electrochemical cycles.     

Synthesis of NiO nanospheres with ultrasonic method for supercapacitors

NiO nanospheres have been synthesized by using magnetic stirring and ultrasound methods. The structure and morphology of synthesized samples were characterized by X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy. The results show the NiO nanospheres prepared by the ultrasonic method are far less than that prepared by the stirring method. Moreover, in the presence of surfactant, the average diameter of NiO nanospheres prepared by the ultrasonic method is only 1–3 nm. The capacitance of NiO electrodes was investigated with cyclic voltammetry. The NiO prepared by the ultrasonic method exhibited higher specific capacitance of ~260 F g⁻¹ at 1 A g⁻¹ current density.     

Effect of aqueous electrolyte on pseudocapacitive behavior of chemically synthesized La2S3 electrode

Lanthanum sulfide electrode (La₂S₃) is prepared by a low cost, simple and room temperature chemical route for energy storage. The surface morphology of La₂S₃ film is revealed through field emission scanning electron microscopy. For the energy storage purpose, the pseudocapacitive behavior of La₂S₃ electrode is studied in 1 M aqueous Na₂SO₄ and 1 M KOH electrolytes. La₂S₃ electrode achieved maximum specific capacitance of 358 F g⁻¹ at 5 mV s⁻¹ scan rate with 78% electrochemical cyclic stability over 1000 cycles in 1 M Na₂SO₄ electrolyte. The galvanostatic charge–discharge study demonstrated the energy density of 35 Wh kg⁻¹ at power density of 1.26 kW kg⁻¹. The electrochemical impedance study showed field assisted charge transfer process with relaxation time of 32 ms in 1 M Na₂SO₄ electrolyte ensuring fast redox reaction.     

Innovative impregnation process for production of γ-Fe2O3–activated carbon nanocomposite

An immobilized superparamagnetic nanocomposite comprising γ-Fe₂O₃ and activated carbon was synthesized via a facile thermal decomposition route. To prepare the magnetically functionalized nanocomposite, treated activated carbon (TAC) loaded with lepidocrocite (γ-FeOOH) nanoparticles (MAC-1) was first produced via a wet chemical method. Then magnetic activated carbon (AC/γ-Fe₂O₃, MAC-2) was fabricated by thermal decomposition of MAC-1 at 250 °C under argon gas for 1 h. Characterization analyses confirmed that superparamagnetic spherical maghemite nanoparticles of 21±2 nm in size were homogeneously dispersed on the TAC. The specific surface area was 643.8 m² g⁻¹ for TAC, 289 m² g⁻¹ for MAC-1, and 303.5 m² g⁻¹ for MAC-2. The industrially friendly nanocomposite was applied as an adsorbent for pollutant removal from aqueous solution.     

Preparation and electrochemical capacitance of MnO2 thin films doped by CuBi2O4

Manganese dioxide (MnO₂) and CuBi₂O₄-doped MnO₂ thin films with different nanostructures were deposited on indium tin oxide (ITO) glass and Ti foil substrates by using a chemical bath deposition (CBD) technique. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron microscopy (XPS). The effects of doping and substrates on electrochemical properties of MnO₂ and CuBi₂O₄-doped MnO₂ thin films on ITO glass and Ti foil were investigated. Capacitive properties of MnO₂ and CuBi₂O₄-doped MnO₂ thin films electrodes were studied using cyclic voltammetry and electrochemical impedance spectroscopy in a three-electrode experimental setup using 0.1 M Na₂SO₄ aqueous solution as electrolyte. Specific capacitance, obtained from electrochemical measurement for the CuBi₂O₄-doped MnO₂, exhibited a higher value of 338 F g⁻¹ compared to the MnO₂ exhibiting value of 135 F g⁻¹. In addition, CuBi₂O₄-doped MnO₂ thin films on an ITO electrode had a better and satisfactory specific capacitance value, and exhibited more excellent electrochemical stability and reversibility than Ti foil substrates.     

Graphene nanosheets as electrode materials for supercapacitors in alkaline and salt electrolytes

Carbon materials have played a significant role in the development of alternative clean and sustainable energy technologies. In particular, we will systematically discuss the applications of graphene nanosheets as an electrode material for supercapacitors. This article summarizes, the effect of size and nature of ions on pseudocapacitance and double layer capacitance of graphene electrode using CV and EIS techniques. The morphology and nature of the prepared electrode was investigated employing a scanning electron microscope. The prepared electrode shows better double layer characteristics in NaOH electrolyte in the potential range between −0.55 and 0.3 V (V vs. SCE) at a scan rate of 100 mV s⁻¹.     

Polypyrrole/reduced graphene oxide coated fabric electrodes for supercapacitor application

Flexible and wearable energy storage devices are strongly demanded to power smart textiles. Herein, reduced graphene oxide (RGO) and polypyrrole (PPy) were deposited on cotton fabric via thermal reduction of GO and chemical polymerization of pyrrole to prepare textile-based electrodes for supercapacitor application. The obtained PPy–RGO-fabric retained good flexibility of textile and was highly conductive, with the conductivity of 1.2 S cm⁻¹. The PPy–RGO-fabric supercapacitor showed a specific capacitance of 336 F g⁻¹ and an energy density of 21.1 Wh kg⁻¹ at a current density of 0.6 mA cm⁻². The RGO sheets served as conductor and framework under the PPy layer, which could facilitate electron transfer between RGO and PPy and restrict the swelling and shrinking of PPy, thus resulting in improved electrochemical properties respect to the PPy-fabric device.     

Synthesis,characterization, and supercapacitor studies of manganese (IV) oxide nanowires

One-dimensional manganese (IV) oxide (MnO₂) (～20 nm in average diameter) were synthesized by cathodic electrodeposition and heat treatment. The mechanism of electrodeposition and nanowire formation were discussed. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR). Nanowires with varying lengths and diameters were found in TEM and SEM images of the sample. The results of N₂ adsorption–desorption analysis indicated that the BET surface area of the MnO₂ nanowires was 157 m² g^?1 and the pore size distributions were 2.5 and 4.5 nm. The electrochemical performances of the prepared MnO₂ as an electrode material for supercapacitors were evaluated by cyclic voltammetry and galvanostatic charge/discharge measurements in a solution of 0.5 M Na₂SO₄. The higher specific capacitance of 318 F g^?1 and good capacity retention of 86% were achieved after 1000 charge–discharge cycles had been observed for the MnO₂ nanowires electrode.     

A study on phase transformation of SnOx thin films prepared by reactive magnetron sputtering

In the paper, SnO_x thin films were deposited by reactive magnetron sputtering from a tin target in O₂ containing working gas. The evolution from Sn-containing SnO to tetravalent SnO₂ films was investigated. The films could be classified into three groups according to their optical band gaps, which are E_g<2.5 eV, E_g=3.0–3.3 eV and E_g>3.7 eV. The electric measurements show that high conductivity can be obtained much easier in SnO₂ than in SnO films. A high electron mobility of 15.7 cm² V⁻¹ s⁻¹, a carrier concentration of 1.43×10²⁰ cm⁻³ and a resistivity of 2.8×10⁻³ Ω cm have been achieved in amorphous SnO₂ films. Films with the optical band gap of 3.0–3.3 eV remain amorphous though the substrate temperature is as high as 300 °C, which implies that °btaining high mobility in p-type SnO is more challenging in contrast to n-type SnO₂ films.     

Synthesis and semiconducting properties of Na2MnPO4F. Application to degradation of Rhodamine B under UV-light

Na₂MnPO₄F is synthesized by hydrothermal route at 453 K and the physical properties and photo-electrochemical characterizations are reported. The compound crystallizes in a monoclinic system (SG: P 2₁/n) with the lattice constants: a=13.7132 Å, b=5.3461 Å, c=13.7079 Å, β=119.97°. The UV–visible spectroscopy shows an indirect optical transition at 2.68 eV; a further direct transition occurs at 3.70 eV, due to the charge transfer O²⁻: 2p → Mn²⁺: e_g. The thermal variation of the electrical conductivity is characteristic of a semiconducting behavior with activation energy of 39 meV and an electron mobility (µ_318 K=5.56×10⁻⁴ cm² V⁻¹ s⁻¹), thermally activated. The flat band potential (+0.47 V_SCE) indicates that the valence band derives mainly from O²⁻: 2p orbital with a small admixture of F⁻ character while the conduction band is made up of Mn²⁺: t_2g orbital. The electrochemical impedance spectroscopy shows the contribution of both the bulk and grains boundaries. The photocatalytic performance of Na₂MnPO₄F for the degradation of Rhodamine B (RhB) is demonstrated on the basis of the energy diagram. 88% of the initial concentration is degraded under UV light and the oxidation follows a first order kinetic with a rate constant of 0.516 h⁻¹. Neither adsorption nor photolysis is observed. The photoactivity results from the electron transition from the hybridized band (O²⁻, F⁻) to the Mn²⁺: e_g orbital, occurring in the UV region. The catalyst was subjected to three successive photocatalytic cycles, thus proving its long term stability.     

The effect of various concentrations of PVDF-HFP polymer gel electrolyte for dye-sensitized solar cell

A PVDF-HFP gel electrolytes based DSSCs were fabricated successfully, where gel electrolytes with 2.5 wt.%, 5 wt.%, 10 wt.% and 15 wt.% PVDF-HFP are included, respectively. Linear sweep voltammetry (LSV), photocurrent–voltage measurements and electrochemical impedance spectra (EIS) were measured. As the results shown, the apparent diffusion coefficient (D_app) of I⁻ and I₃⁻ decreased as PVDF-HFP increased. D_app of I⁻ and I₃⁻ are decreased from 1.87 × 10^− 6 to 0.67 × 10^− 6 cm²/s and 3.28 × 10^− 6 to 0.88 × 10^− 6 cm²/s, respectively. For the solar cell measurements, the short circuit current density (J_sc) were affected by the ion motilities, which was decreased from 11.58 mA/cm² to 8.17 mA/cm², and the energy converting efficiency (η %) was decreased from 5.17% to 2.79%. For electrochemical impedance spectra (EIS) measurements, the ionic diffusion impedance for the redox-couple (I⁻/I₃⁻) in the gel electrolyte was also increased with the concentration of PVDF-HFP from 0.61 Ω to 8.17 Ω. In the Bode Plots, the electron lifetime (τ_e) of the 2.5 wt.% and 5 wt.% PVDF-HFP electrolytes was increased from 40.52 ms to 48.48 ms and 41.29 ms, respectively. However, τ_e was decreased in the concentrations of 10 wt.% and 15 wt.% PVDF-HFP, due to the ion motilities that were decreased by excessing PVDF-HFP polymer. For gel electrolyte, the cell of 2.5 wt.% PVDF-HFP exhibited a better J_SC of 10.89 mA/cm², a higher energy conversion efficiency (η) of 4.75%, a higher fill factor (FF) of 61.26%, and a smaller R of 1.06 Ω than the 15 wt.% PVDF-HFP based cell.     

High electron mobility triazine for lower driving voltage and higher efficiency organic light emitting devices

The triazine compound 4,4′-bis-[2-(4,6-diphenyl-1,3,5-triazinyl)]-1,1′-biphenyl (BTB) was developed for use as an electron transport material in organic light emitting devices (OLEDs). The material demonstrates an electron mobility of ∼7.2 × 10⁻⁴ cm² V⁻¹ s⁻¹ at a field of 8.00 × 10⁵ V cm⁻¹, which is 10-fold greater than that of the widely used material tris(8-hydroxyquinoline) aluminum (AlQ₃). OLEDs with a BTB electron transport layer showed a ∼1.7–2.5 V lower driving voltage and a significantly increased efficiency, compared to those with AlQ₃. These results suggest that BTB has a strong potential for use as an OLED electron transport layer material.