Preparation and electrochemical investigation of the cobalt hydroxide carbonate/activated carbon nanocomposite for supercapacitor applications

Cobalt hydroxide carbonate/activated carbon (AC) composite was successfully synthesized by hydrothermal method. Morphological characterizations of cobalt hydroxide carbonate/AC composite were carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the results show that the cobalt hydroxide carbonate nanorods are well dispersed on the AC. Due to the synergistic effects arising from cobalt hydroxide carbonate nanorods and AC, the electrochemical performances of pure cobalt hydroxide carbonate material is significantly improved by the addition of AC. The composite shows a specific capacitance of 301.44 F g⁻¹ at a current density of 1 A g⁻¹ in 6 M KOH electrolyte and exhibits good cycling stability. Based on the above results, the cobalt hydroxide carbonate/AC composite shows a considerable promise as electrode for electrochemical applications.     

Controllable synthesis of layered Co–Ni hydroxide hierarchical structures for high-performance hybrid supercapacitors

A facile solvothermal method is developed for synthesizing layered Co–Ni hydroxide hierarchical structures by using hexamethylenetetramine (HMT) as alkaline reagent. The electrochemical measurements reveal that the specific capacitances of layered bimetallic (Co–Ni) hydroxides are generally superior to those of layered monometallic (Co, Ni) hydroxides. The as-prepared Co_0.5Ni_0.5 hydroxide hierarchical structures possesses the highest specific capacitance of 1767 F g⁻¹ at a galvanic current density of 1 A g⁻¹ and an outstanding specific capacitance retention of 87% after 1000 cycles. In comparison with the dispersed nanosheets of Co–Ni hydroxide, layered hydroxide hierarchical structures show much superior electrochemical performance. This study provides a promising method to construct hierarchical structures with controllable transition-metal compositions for enhancing the electrochemical performance in hybrid supercapacitors.     

Hydrothermal synthesis of mesoporous Co3O4 nanobelts by means of a compound precursor

In the present work, high surface area mesoporous cobalt oxide (Co₃O₄) nanobelts have been synthesized by thermal treatment of cobalt hydroxide carbonate (CHC) precursors. CHC nanobelts were prepared by a facile hydrothermal method. Control experiments with variations in reaction time, solvent and different cobalt source revealed that temperature and sulfates are key factors in determining the formation of CHC nanobelts. Scanning electron microscopy and transmission electron microscopy images showed that the Co₃O₄ nanobelts consisted of mesoporous nanobelts with the average width of 40 nm. Brunauer–Emmett–Teller (BET) gas adsorption measurement further indicated that the products presented a rather large surface area (172.09 m² g^?1).     

Morphologically controlled preparation of CuO nanostructures under ultrasound irradiation and their evaluation as pseudocapacitor materials

Various morphologies of copper oxide (CuO) nanostructures have been synthesized by controlling the reaction parameters in a sonochemical assisted method without using any templates or surfactants. The effect of reaction parameters including molar ratio of the reactants, reaction temperature, ultrasound exposure time, and annealing temperature on the composition and morphology of the product(s) has been investigated. The prepared samples have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDAX), and thermogravimetric analysis (TGA). It has been found that Cu₂(OH)₃NO₃ nanoplatelets are achieved in mild conditions which can be then converted to various morphologies of CuO nanostructures by either using high concentrations of OH⁻ (formation of nanorods), prolonging sonication irradiation (nanoparticles), or thermal treatment (nanospheres). Application of the prepared CuO nanostructures was evaluated as supercapacitive material in 1 M Na₂SO₄ solution using cyclic voltammetry (CV) in different potential scan rates ranging from 5 to 100 mV s⁻¹. The specific capacitance has been calculated using CV curves. It has been found that the pseudocapacitor performance of CuO can be tuned via employing morphologically controlled samples. Accordingly, the prolonged sonicated sample (nanoparticles) showed the high specific capacitance of 158 F.g⁻¹.     

Characterization of nanoporous carbon fibrous materials obtained by chemical activation of plane tree seed under ultrasonic irradiation

An ultrasonic irradiation was applied for the impregnation by chemical agents in the chemical activation process of new type of active carbon precursor. Plane tree seed, due to the unique fibrous structure and low cost is a promising eco-friendly raw material for the preparation of activated carbon materials. Ultrasonic irradiation was used for the impregnation step allowing the chemical activation by different agents: potassium or sodium hydroxide, hydrogen peroxide and pyrogallol. The porous structures were examined by nitrogen adsorption/desorption isotherms at 77 K and electrochemically by cyclic voltammetry. The textures of these materials were observed by scanning electron microscopy. The application of ultrasonic irradiation in the impregnation step increased surface area of the final material more than two times in comparison to the material which impregnation in the activation process was by conventional stirring. Ultrasonic irradiation enhances the chemical activation process and the activated carbon fibrous materials with nanoporous structure were obtained by impregnation of seeds with alkaline hydroxides. Total surface areas of these samples were 976 m² g⁻¹ and 1130 m² g⁻¹. These fibers have total specific capacitance as high as 125 F g⁻¹ and 53 F g⁻¹ which major fraction in both cases originate from internal micropores structure.     

Electrochemical redox supercapacitors using PVdF-HFP based gel electrolytes and polypyrrole as conducting polymer electrode

Electrochemical redox supercapacitors have been fabricated using polymeric gel electrolytes polyvinylidene fluoride co-hexafluoropropylene (PVdF-HFP)–ethylene carbonate (EC)–propylene carbonate (PC)–MClO₄: M = Li, Na, (C₂H₅)₄N and electrochemically deposited polypyrrole as conducting polymer electrode. The performance of the capacitors have been characterized using a.c impedance spectroscopy, cyclic linear sweep voltammetry and galvanostatic charge–discharge techniques. The capacitors shows larger values of overall capacitance of about 14–25 mF cm^− 2 (equivalent to a single electrode specific capacitance of 78–137 F g^− 1 of polypyrrole), which corresponds to the energy density of 11–19 W h kg^− 1 and power density of 0.22–0.44 kW kg^− 1. The values of capacitance have been found to be almost stable up to 5000 cycles and even more. A comparison indicates that the capacitive behaviour and the capacitance values are not much affected with the size of cations of the salts incorporated in gel electrolytes, rather predominant role of anions is possible at the electrode–electrolyte interfaces. Furthermore the coulombic efficiencies of all the cells were found to be nearly 100% that is comparable to the liquid electrolytes based capacitors.     

SnO2-decorated multiwalled carbon nanotubes and Vulcan carbon through a sonochemical approach for supercapacitor applications

Multiwalled carbon nanotubes (MWCNTs) and Vulcan carbon (VC) decorated with SnO₂ nanoparticles were synthesized using a facile and versatile sonochemical procedure. The as-prepared nanocomposites were characterized by means of transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infra red spectroscopy. It was evidenced that SnO₂ nanoparticles were uniformly distributed on both carbon surfaces, tightly decorating the MWCNTs and VC. The electrochemical performance of the nanocomposites was evaluated by cyclic voltammetry and galvanostatic charge/discharge cycling. The as-synthesized SnO₂/MWCNTs nanocomposites show a higher capacity than the SnO₂/VC nanocomposites. Concretely, the SnO₂/MWCNTs electrodes exhibit a specific capacitance of 133.33 F g⁻¹, whereas SnO₂/VC electrodes exhibit a specific capacitance of 112.14 F g⁻¹ measured at 0.5 mA cm⁻² in 1 M Na₂SO₄.     

Physical,electrochemical and supercapacitive properties of activated carbon pellets from pre-carbonized rubber wood sawdust by CO2 activation

The physical and electrochemical properties of the activated carbon pellet electrodes have been investigated. Activated carbon pellets were prepared from single step carbonization process of pre-carbonized rubber wood sawdust at a temperature of 800 °C that followed with a CO₂ activation process at temperature in the range of 700–1000 °C. The BET characterization on the sample found that the surface area of the carbon pellet increased with the increasing of the activation temperature. The optimum value was as high as 683.63 m² g⁻¹. The electrical conductivity was also found to increase linearly with the increasing of the activation temperature, namely from 0.0075 S cm⁻¹ to 0.0687 S cm⁻¹ for the activation temperature in the range of 700–1000 °C. The cyclic voltammetry characterization of the samples in aqueous solution of 1 M H₂SO₄ also found that the specific capacitance increased with the increasing of the activation temperature. Typical optimum value was shown by the sample activated at 900 °C with the specific capacitance was as high as 33.74 F g⁻¹ (scan rate 1 mV s⁻¹). The retained ratio was as high as 32.72%. The activated carbon pellet prepared from the rubber wood sawdust may found used in supercapacitor applications.     

High surface area monodispersed Fe3O4 nanoparticles alone and on physical exfoliated graphite for improved supercapacitors

Highly conductive, unsophisticated and easy to be obtained physical exfoliated graphite (PHG) supporting well dispersed magnetite, Fe₃O₄/PHG nanocomposite, has been prepared by a one-step chemical strategy and physico-chemical characterized. The nanocomposite, favoured by the a-polar nanoparticles (NPs) capping, results in a self-assembled monolayer of monodispersed Fe₃O₄, covering perfectly the hydrophobic surfaces of PHG. The nanocomposite as an electrode material was fabricated into a supercapacitor and characterized by cyclic voltammetry (CV) and galvanostatic charge–discharge measurements. It shows, after a suitable annealing, significant electrochemical properties (capacitance value of 787 F/g at 0.5 A g⁻¹ and a Fe₃O₄/PHG weight ratio of 0.31) and good cycling stability (retention 91% after 30,000 cycles). Highly monodispersed very fine Fe₃O₄ NPs, covered by organic chains, have been also synthesized. The high surface area Fe₃O₄ NPs, after washing to leave a low content of organic chains able to avoid aggregation without excessively affecting the electrical properties of the material, exhibit remarkable pseudocapacitive activities, including the highest specific capacitance over reported for Fe₃O₄ (300 F/g at 0.5 A g⁻¹).     

Preparation and electrochemical properties of mesoporous Co3O4 crater-like microspheres as supercapacitor electrode materials

Mesoporous Co₃O₄ microspheres with unique crater-like morphology were obtained by utilizing the mesoporous silica material MCM-41 as a template. The analysis results of N₂ adsorption–desorption measurement indicate that the product has a large Brunauer–Emmett–Teller (BET) surface area of 60 m² g⁻¹ and a narrow pore size distribution centering around 3.7 nm. Its electrochemical properties were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The findings reveal that this novel morphology material has a smaller inner resistance of about 0.4 Ω and a higher onset frequency of 550 Hz. This material can provide a high specific capacitance of 102 F g⁻¹ and a large capacity retention of 74% in 500 continuous cycles test at a sweep rate of 3 mV s⁻¹. More significantly, the mass loading of electroactive species can reach as large as 2 mg cm⁻², which is one order of magnitude larger than common amount used.     

Sonochemically synthesized MnO2 nanoparticles as electrode material for supercapacitors

In this study, manganese oxide (MnO₂) nanoparticles were synthesized by sonochemical reduction of KMnO₄ using polyethylene glycol (PEG) as a reducing agent as well as structure directing agent under room temperature in short duration of time and characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM), Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) analysis. A supercapacitor device constructed using the ultrasonically-synthesized MnO₂ nanoparticles showed maximum specific capacitance (SC) of 282 Fg⁻¹ in the presence of 1 M Ca(NO₃)₂ as an electrolyte at a current density of 0.5 mA cm⁻² in the potential range from 0.0 to 1.0 V and about 78% of specific capacitance was retained even after 1000 cycles indicating its high electrochemical stability.     

Hydrophilic polyaniline nanofibrous architecture using electrosynthesis method for supercapacitor application

An electrosynthesis process of hydrophilic polyaniline nanofiber electrode for electrochemical supercapacitor is described. The TGA–DTA study showed polyaniline thermally stable up to 323 K. Polyaniline nanofibers exhibit amorphous nature as confirmed from XRD study. Smooth interconnected fibers having diameter between 120–125 nm and length typically ranges between 400–500 nm observed from SEM and TEM analysis. Contact angle measurement indicated hydrophilic nature of polyaniline fibers. Optical study revealed the presence of direct band gap with energy 2.52 eV. The Hall effect measurement showed room temperature resistivity ∼3 × 10⁻⁴ Ω cm and Hall mobility 549.35 cm⁻²V⁻¹ s⁻¹_. The supercapacitive performance of nanofibrous polyaniline film tested in 1 M H₂SO₄ electrolyte and showed highest specific capacitance of 861 F g⁻¹ at the voltage scan rate of 10 mV/s.     

Improved adsorption performance of nanostructured composite by ultrasonic wave: Optimization through response surface methodology,isotherm and kinetic studies

In this work, ultrasound-assisted adsorption of an anionic dye, sunset yellow (SY) and cationic dyes, malachite green (MG), methylene blue (MB) and their ternary dye solutions onto Cu@ Mn-ZnS-NPs-AC from water aqueous was optimized by response surface methodology (RSM) using the central composite design (CCD). The adsorbent was characterized using Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX) and EDX mapping images. The effects of various parameters such as pH, sonication time, adsorbent mass and initial concentrations of SY, MG and MB were examined. A total 33 experiments were conducted to establish a quadratic model. Cu@ Mn-ZnS-NPs-AC has the maximum adsorption efficiency (>99.5%) when the pH, sonication time, adsorbent mass and initial concentrations of SY, MG and MB were optimally set as 6.0, 5 min, 0.02 g, 9, 12 and 12 mg L⁻¹, respectively. Sonication time has a statistically significant effect on the selected responses. Langmuir isotherm model was found to be best fitted to adsorption and adsorption capacities were 67.5 mg g⁻¹ for SY, 74.6 mg g⁻¹ for MG and 72.9 mg g⁻¹ for MB. Four kinetic models (pseudo-first order, pseudo-second order, Weber–Morris intraparticle diffusion rate and Elovich) were tested to correlate the experimental data and the sorption was fitted well with the pseudo-second order kinetic model.     

Synthesis of defect-rich, (001) faceted-ZnO nanorod on a FTO substrate as efficient photocatalysts for dehydrogenation of isopropanol to acetone

Highly oriented ZnO nanorod was successfully synthesised on Ag nanoseed coated FTO substrate via a microwave hydrolysis approach. It was found that the morphology and the optical properties of the ZnO nanorod are strongly influenced by the power of the microwave irradiation used during the growth process. The aspect ratio of the nanorods changed from high to low with the increasing of microwave power. It was also found that the optical band gap of the ZnO nanorod red shifted with the increasing of the microwave power, reflecting an excellent tune ability of the optical properties of ZnO nanorods. The photocatalytic activity of these unique nanorod was evaluated by a dehydrogenation process of isopropanol to acetone in the presence of ZnO nanorod. It was found that the ZnO nanorod exhibited an excellent catalytic performance by showing an ability to accelerate the production of 0.031 mol L⁻¹ of acetone within only 35 min or 0.9 mmol L⁻¹ min⁻¹ from isopropyl alcohol dehydrogenation. It was almost no conversion from isopropyl alcohol when ZnO nanorods was absence during the reaction. In this report, a detailed mechanism of ZnO nanorod formation and the relationship between morphology and optical energy band gap are described.     

Preparation and characterization of metal-doped carbon aerogel for supercapacitor

Carbon aerogel was prepared by polycondensation of resorcinol and formaldehyde using sodium carbonate as a catalyst with a resorcinol to catalyst ratio of 500. Co-doped carbon aerogels were then prepared by an impregnation method with a variation of cobalt content (1, 3, 5, 7, 10, and 15 wt.%), and their performance for supercapacitor electrode was investigated by measurement of specific capacitance in 1 M H₂SO₄ electrolyte at a scan rate of 10 mV/s. Among the samples prepared, 7 wt.% Co-doped carbon aerogel showed the highest capacitance (100 F/g) and stable cyclability. The enhanced capacitance of Co-doped carbon aerogel was attributed to the faradaic redox reactions of cobalt oxide. On the basis of this result, 7 wt.% Cu-, Fe-, Mn-, and Zn-doped carbon aerogels were also prepared by an impregnation method for use as a supercapacitor electrode. Among the metal-doped carbon aerogels, Mn-doped carbon aerogel showed the highest capacitance (107 F/g) while Cu- and Fe-doped carbon aerogels exhibited the most stable cyclability.     

Optical and physical characteristics of In-doped ZnO nanorods

In this paper the effect of indium dopants on structure, optical, electrical and mechanical properties of ZnO nanorods are studied. The average surface potentials and the surface currents of ZnO:In nanorods were 0.25–0.84 mV and 2.2–200 MΩ-cm, respectively. The turn-on threshold field for the vertical ZnO nanorods was around 2–16 V μm⁻¹. Emission current densities of 3.3–911.4 mA cm⁻² were obtained for an electrical field of 60–160 V μm⁻¹. The photoluminescence (PL) spectrum measured at 15–300 K showed that the intensity of the peak at 2.06 eV increased with decreasing temperature, while the peak at 2.06 eV further red shifted and the peak at 3.39 eV blue shifted.     

Sonocatalyzed decolorization of synthetic textile wastewater using sonochemically synthesized MgO nanostructures

The present study focused on the synthesis of nanostructured MgO via sonochemical method and its application as sonocatalyst for the decolorization of Basic Red 46 (BR46) dye under ultrasonic irradiation. The sonocatalyst was characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray microanalysis (EDX). In the following, the sonocatalytic removal of the dye under different operational conditions was evaluated kinetically on the basis of pseudo first-order kinetic model. The reaction rate of sonocatalyzed decolorization using MgO nanostructures (12.7 × 10⁻³ min⁻¹) was more efficient than that of ultrasound alone (2.0 × 10⁻³ min⁻¹). The increased sonocatalyst dosage showed better sonocatalytic activity but the application of excessive dosage should be avoided. The presence of periodate ions substantially increased the decolorization rate from 14.76 × 10⁻³ to 33.4 × 10⁻³ min⁻¹. Although the application of aeration favored the decolorization rate (17.8 × 10⁻³ min⁻¹), the addition of hydrogen peroxide resulted in a considerable decrease in the decolorization rate (9.5 × 10⁻³ min⁻¹) due to its scavenging effects at specific concentrations. Unlike alcoholic compounds, the addition of phenol had an insignificant scavenging effect on the sonocatalysis. A mineralization rate of 7.4 × 10⁻³ min⁻¹ was obtained within 120 min. The intermediate byproducts were also detected using GC–MS analysis.     

Sonochemical synthesis and characterization of Co3O4 nanocrystals in the presence of the ionic liquid [EMIM][BF4]

For the first time, a sonochemical process has been used to synthesis cobalt oxide Co₃O₄ nanoflowers and nanorods morphology in the presence of the ionic liquid 1-Ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF₄] as reaction media and morphology template. Different sonication time periods and different molar ratios of the ionic liquid (IL) were used to investigate their effects on the structural, optical, chemical and magnetic properties of the produced Co₃O₄ nanoparticles. During synthesis process brown powder contains cobalt hydroxide Co(OH)₂ and cobalt oxyhydroxide (Cobalt hydroxide oxide) CoO(OH) was formed, after calcination in air for 4 h at 400 °C a black powder of Co₃O₄ nanoparticles was produced. The produced Co₃O₄ nanoparticles properties were characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), transmission electron microscopy (TEM), FTIR spectroscopy, UV–vis spectroscopy, and Vibrating Sample Magnetometer (VSM). To explain the formation mechanism of Co₃O₄ NPs some investigations were carried on the brown powder before calcination.     

Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles prepared in the presence of ultrasonic irradiation

In this study, nickle/iron (Ni/Fe) nanoparticles were synthesized by liquid phase reductive method in the presence of 20 kHz ultrasonic irradiation to improve nanoparticles’ disparity and avoid agglomeration. The characterized results showed that this method has obviously modified most of the particles in term of sizes and specific surface areas. Meanwhile, the improved nanoscale Ni/Fe particles were employed for the reductive dechlorination of 2,4-dichlorophenol (2,4-DCP) as a function of some influential factors (Ni content, Ni/Fe nanoparticles dosage, reaction temperature and initial pH values) and degradation path. Experimental results showed that 2,4-DCP was first adsorbed by Ni/Fe nanoparticles, then quickly reduced to o-chlorophenol (o-CP), p-chlorophenol (p-CP), and finally to phenol (P). The application of ultrasonic irradiation for Ni/Fe nanoparticles synthesis was found to significantly enhance the removal efficiency of 2,4-DCP. Consequently, the phenol production rates increased from 68% (in the absence of ultrasonic irradiation) to 87% (in the presence of ultrasonic irradiation) within 180 min. Nearly 96% of 2,4-DCP was removed after 300 min reaction with these optimized conditions: Ni content over Fe⁰ 3 wt%, initial 2,4-DCP concentration 20 mg L⁻¹, Ni/Fe dosage 3 g L⁻¹, initial pH value 3.0, and reaction temperature 25 °C. The degradation of 2,4-DCP followed pseudo-first-order kinetics reaction and the apparent pseudo-first-order kinetics constant was 0.0737 min⁻¹. This study suggested that the presence of ultrasonic irradiation in the synthesis of nanoscale Ni/Fe particles could be a promising technique to enhance nanoparticle’s disparity and avoid agglomeration.     

Application of ZnO nanorods loaded on activated carbon for ultrasonic assisted dyes removal: Experimental design and derivative spectrophotometry method

A method based on application of ZnO nanorods loaded on activated carbon (ZnO-NRs-AC) for adsorption of Bromocresol Green (BCG) and Eosin Y (EY) accelerated by ultrasound was described. The present material was synthesized under ultrasound assisted wet-chemical method and subsequently was characterized by FE-SEM, TEM, BET and XRD analysis. The extent of contribution of conventional variables like pH (2.0–10.0), BCG concentration (4–20 mg L⁻¹), EY concentration (3–23 mg L⁻¹), adsorbent dosage (0.01–0.03 g), sonication time (1–5 min) and centrifuge time (2–6 min) as main and interaction part were investigated by central composite design under response surface methodology. Analysis of variance (ANOVA) was adapted to experimental data and guide the best operational conditions mass by set at 6.0, 9 mg L⁻¹, 10 mg L⁻¹, 0.02 g, 4 and 4 min for pH, BCG concentration, EY concentration, adsorbent dosage, sonication and centrifuge time, respectively. At these specified conditions dye adsorption efficiency was higher than 99.5%. The suitability and well prediction of optimum point was tested by conducting five experiments and respective results revel that RSD% was lower than 3% and high quality of fitting was confirmed by t-test. The experimental data were best fitted in Langmuir isotherm equation and the removal followed pseudo second order kinetics. The experimentally obtained maximum adsorption capacities were estimated as 57.80 and 61.73 mg g⁻¹ of ZnO-NRs-AC for BCG and EY respectively from binary dye solutions. The mechanism of removal was explained by boundary layer diffusion via intraparticle diffusion.