Porous carbons prepared from deoiled asphalt and their electrochemical properties for supercapacitors

Porous carbon was prepared from deoiled asphalt by conventional NaOH activation process and by the combination of nano-sized MgO template method and NaOH activation process. The electrochemical properties used as supercapacitors electrode material were evaluated in 7 M KOH aqueous solution. Porous carbon sample obtained by NaOH activation possessed more micropores and higher specific surface area, resulting in a higher specific capacitance of 235 F g^− 1 at low charge-discharge current of 50 mA g^− 1. For the combination method, the resultant carbons possessed higher capacitance and good capacitance maintaining at high current, with a capacitance of nearly twice as that of the former at current density of 10 A g^− 1, due to their abundant mesopores.     

Preparation of activated carbon from sorghum pith and its structural and electrochemical properties

The cost effective activated carbon (AC) has been prepared from sorghum pith by NaOH activation at various temperatures, including 300 °C (AC1), 400 °C (AC2) and 500 °C (AC3) for the electrodes in electric double layer capacitor (EDLC) applications. The amorphous nature of the samples has been observed from X-ray diffraction and Raman spectral studies. Subsequently, the surface functional groups, surface morphology, pore diameter and specific surface area have been identified through FT-IR, SEM, histogram and N₂ adsorption/desorption isotherm methods. The electrochemical characterization of AC electrodes has been examined using cyclic voltammetry technique in the potential range of −0.1-1.2 V in 1.0 M H₂SO₄ electrolyte at different scan rates (10, 20, 30, 40, 50 and 100 mV/s). The maximum specific capacitances of 320.6 F/g at 10 mV/s and 222.1 F/g at 100 mV/s have been obtained for AC3 electrode when compared with AC1 and AC2 electrodes. Based on the characterization studies, it has been inferred that the activated carbon prepared from sorghum pith may be one of the innovative carbon electrode materials for EDLC applications.     

Pore size control and electrochemical capacitor behavior of chemically activated polyacrylonitrile – Carbon nanotube composite films

Activated polyacrylonitrile (PAN)/carbon nanotube (CNT) composite film based electrodes have been prepared by chemical activation with potassium hydroxide for electrochemical capacitors. This paper analyses the following aspects of specific capacitance, pore size distribution and surface area: influence of activation temperature, molarity of activating agent, composition of PAN/carbon nanotube precursor films and electrolytes. A maximum value of specific capacitance of ∼302 Fg⁻¹ was achieved for the samples activated at 800 °C. Energy density for PAN/CNT 80/20 sample when tested with ionic liquid/organic electrolyte system was as high as ∼22 W h kg⁻¹. Pore size control predominantly below 5 nm was observed in these activated PAN samples. Data analysis showed that micropores make a significant contribution to the capacitance performance of these materials in both 6 M KOH as well as in BMIMBF₄/acetonitrile electrolytes.     

Protective YSZ-based thin films deposited by RF magnetron sputtering

Protective Zr(Y)O_2−δ-based films sputter-deposited onto apatite-type lanthanum silicate ceramics were appraised for potential applications in solid oxide fuel cells with silicate-based solid electrolytes, where the performance may suffer from surface decomposition processes in reducing atmospheres. Dense and crystalline coatings were deposited using radio-frequency magnetron sputtering from an yttria-stabilized zirconia target. On the basis of microstructural analysis and profile measurements, a sputtering power of 300 W was selected in order to achieve deposition rates in the range 0.50-0.75 μm/h. The surface morphology studies using an atomic force microscope revealed typical film structures with small (<50 nm) grains. The polarization of model electrochemical cells with cermet anodes comprising Ni, yttria-stabilized zirconia and Ce_0.8Gd_0.2O_2−δ (50:30:20 wt.%), deposited onto the protective zirconia films, was found quite similar to that of copper-zirconia cermets without interlayers, suggesting that the electrochemical reaction is essentially governed by the oxygen anion transfer from zirconia phase and/or hydrogen oxidation in the vicinity of zirconia film surface.     

Removal of acid orange 7 by guava seed carbon: A four parameter optimization study

The preparation of carbon from waste materials is a recent and economic alternative for the removal of dyes. In this study four samples of carbon were obtained by thermal treatment at 1000 °C using as precursor the guava seed with different particle sizes. The Taguchi method was applied as an experimental design to establish the optimum conditions for the removal of acid orange 7 in batch experiments. The chosen experimental factors and their ranges were: pH (2–12), temperature (15–35 °C), specific surface area (50–600 m² g⁻¹) and adsorbent dosage (16–50 mg ml⁻¹). The orthogonal array L₉ and the larger the better response category were selected to determine the optimum removal conditions: pH 2, temperature 15 °C, S_esp 600 m² g⁻¹ and dosage 30 mg ml⁻¹. Under these conditions a total removal of acid orange 7 was achieved. Moreover, the most significant factors were the carbon specific surface area and the pH. The influence of the different factors on the adsorption of acid orange 7 from solution is explained in terms of electrostatic interactions by considering the dye species and the character of the surface.     

Influence of the pitch fluoride on the electrical conductivity of the activated carbon cloth as electrodes of the supercapacitor

Fluorinated activated carbon cloth was prepared by impregnating a commercial activated carbon cloth in a pitch fluoride solution followed by carbonization. The surface properties of samples before and after treatment were characterized by X-ray Photoelectron Spectroscopy. Electrochemical Impedance Spectroscopy, Constant Current Charge-Discharge were employed to investigate the electrochemical properties of the samples. After the fluorination, the element fluorine was introduced to the surface of the activated carbon cloth. The electrical conductivity was improved from 2.51 to 33.21 Scm^− 1. As the electrodes of a supercapacitor, the equivalent series resistance of as-prepared sample was substantially decreased compared with the pristine material. The improvement of conductivity is ascribed to the creation of ionic fluorine-carbon bonds after fluorination, indicating the high power characteristics of this material.     

Facile synthesis and electrochemical properties of Mn3O4 nanoparticles with a large surface area

Mn₃O₄ nanoparticles were prepared by a novel oxidation-precipitation method at a low temperature. The crystal phase, microstructure, surface area and electrochemical properties of the products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N₂ adsorption-desorption isotherms and cyclic voltammetry (CV). The results indicate that the addition of citric acid and tartaric acid remarkably reduced the particle size and increased the specific surface area of Mn₃O₄ nanoparticles. The samples prepared by the addition of citric acid and tartaric acid have a narrow particle size distribution of 5-10 nm, a surface area of 119 and 122 m²/g, and a capacitance of 171 and 172 F g⁻¹, respectively.     

Microporous carbon derived from polyaniline base as anode material for lithium ion secondary battery

Microporous carbon with large surface area was prepared from polyaniline base using K₂CO₃ as an activating agent. The physicochemical properties of the carbon were characterized by scanning electron microscope, X-ray diffraction, Brunauer-Emmett-Teller, elemental analyses and X-ray photoelectron spectroscopy measurement. The electrochemical properties of the microporous carbon as anode material in lithium ion secondary battery were evaluated. The first discharge capacity of the microporous carbon was 1108 mAh g⁻¹, whose first charge capacity was 624 mAh g⁻¹, with a coulombic efficiency of 56.3%. After 20 cycling tests, the microporous carbon retains a reversible capacity of 603 mAh g⁻¹ at a current density of 100 mA g⁻¹. These results clearly demonstrated the potential role of microporous carbon as anode for high capacity lithium ion secondary battery.     

La0.67Ca0.33MnO3 thin films on Si (1 0 0) by DC magnetron sputtering technique using nanosized powder compacted target

La_0.67Ca_0.33MnO₃ (LCMO) thin films were successfully fabricated by a DC magnetron sputtering technique on Si (1 0 0) substrates from chemically synthesized compacted powders. Powders of proper stochiometry composites were synthesized by a novel chemical technique [D.R. Sahu, B.K. Roul, P. Pramanik, J.L. Huang, Physica B 369 (2005) 209] and were found to be nanosized (≈40-50 nm). The sinterability of the powders were improved significantly due to their large surface area with a reduction of sintering temperature (up to 500 °C) as compared to the powders prepared by other solid-state reaction route. Bulk LCMO targets were prepared and preliminary structural and magnetic properties of target were investigated for colossal magnetoresistance (CMR) properties. Films deposition parameters like DC power, gas flow rate, deposition time, etc., were critically optimized to achieve desired thickness of film using above LCMO target by DC magnetron sputtering. LCMO films fabricated on Si (1 0 0) substrates showed enhanced magnetoresistance (MR) at low temperature. Maximum MR of about 1000% was observed at 100 K. Paramagnetic to ferromagnetic transitions were observed in films below room temperature and were found at approximately 240 K. However, as compared to bulk target prepared by a chemical route, it was found that Curie temperature (T_c) and MR response of bulk target were higher than the thin films. Preliminary point chemical analysis revealed the deficiency of Ca²⁺ ions in CMR films.     

Synthesis and characterization of nanofiber-structured Ba0.5Sr0.5Co0.8Fe0.2O3−δ perovskite oxide used as a cathode material for low-temperature solid oxide fuel cells

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) was synthesized in two forms: as a powder (by the sol-gel combined citrate-EDTA complexing (CC-EDTA) method) and as nanofibers (by electrospinning). Both forms were sintered at 950 °C for 5 h in air before their morphology and structure were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and specific surface area analysis based on the BET theory. Moreover, the mass loss and heat flow of as-electrospun BSCF nanofibers were analyzed by differential thermal analysis (DTA) and thermogravimetric analysis (TG). The results showed that these materials had a perovskite oxide crystal structure. The CC-EDTA method yielded BSCF in powder form, with a particle size of 1-10 μm and a specific surface area of 1.0 m²/g. On the other hand, BSCF obtained by the electrospinning technique was in the form of highly porous nanofibers with diameters in the range of 100-200 nm and a specific surface area of 2.4 m²/g. To demonstrate the potential applications of BSCF as a cathode material in low-temperature solid oxide fuel cells (LT-SOFCs), the electrochemical properties of the samples were determined using electrochemical impedance spectroscopy (EIS). The area specific resistance (ASR) of the BSCF nanofiber cathode was determined to be 0.094 Ω cm² at 600 °C, whereas that of the BSCF powder cathode was 0.468 Ω cm² under similar conditions.     

The evolution of the structural, electrical and optical properties in indium-tin-oxide thin film on glass substrate by DC reactive magnetron sputtering

The evolution of the structural, electrical and optical properties in indium-tin-oxide (ITO) thin film on glass substrate prepared by DC reactive magnetron sputtering was investigated. The variation of the structural, electrical and optical properties could be largely divided into two regions of (i) the initial region I roughly up to the critical film thickness of 50 nm and (ii) the stable region II above the critical thickness. As the film thickness grew, X-ray diffraction (XRD) peak intensities of both (2 2 2) and (4 0 0) planes increased continuously and the film morphology became clear. The peak intensity ratio of I₂₂₂/I₄₀₀ decreased gradually with the thickness, implying a preferred orientation along the (4 0 0) plane at a higher thickness.In the region II over the critical film thickness of 50 nm, where the structural evolution was clearly observable, the carrier density also increased over 9.0×1020/cm³ and the specific resistivity was lower than 140 μΩ cm.     

Preparation and characterization of La0.9Sr0.1Ga0.8Mg0.2O3−δ thin film electrolyte deposited by RF magnetron sputtering on the porous anode support for IT-SOFC

Thin films of solid electrolyte La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) were deposited by RF magnetron sputtering onto porous La_0.7Sr_0.3Cr_0.5Mn_0.5O_3−δ (LSCM) anode substrates. The effects of substrate temperature, sputtering power density and sputtering Ar gas pressure on the LSGM thin film density, flatness and morphology were systematically investigated. RF sputtering power density of 7.8 W cm⁻², substrate temperature of 300 °C and sputtering Ar gas pressure of 5 Pa are identified as the best technical parameters. In addition, a three-electrode half cell configuration was selected to investigate the electrochemical performance of the thin film. The LSGM film deposited at optimum conditions exhibited a lower area specific ohmic resistance of 0.68 Ω cm⁻² at 800 °C, showing that the practicability of RF magnetron sputtering method to fabricate LSGM electrolyte thin film on porous LSCM anode substrates.     

Preparation and characterization of nanostructured NiO/MnO2 composite electrode for electrochemical supercapacitors

Nanostructured nickel-manganese oxides composite was prepared by the sol-gel and the chemistry deposition combination new route. The surface morphology and structure of the composite were characterized by scanning electron microscope and X-ray diffraction. The as-synthesized NiO/MnO₂ samples exhibit higher surface area of 130-190 m² g⁻¹. Cyclic voltammetry and galvanostatic charge/discharge measurements were applied to investigate the electrochemical performance of the composite electrodes with different ratios of NiO/MnO₂. When the mass ratio of MnO₂ and NiO in composite material is 80:20, the specific capacitance value of NiO/MnO₂ calculated from the cyclic voltammetry curves is 453 F g⁻¹, for pure NiO and MnO₂ are 209, 330 F g⁻¹ in 6 mol L⁻¹ KOH electrolyte and at scan rate of 10 mV s⁻¹, respectively. The specific capacitance of NiO/MnO₂ electrode is much larger than that of each pristine component. Moreover, the composite electrodes showed high power density and stable electrochemical properties.     

Effect of Fe on the synthesis and electrochemical performance of nanostructured MnO2

Different MnO₂ nanostructures were synthesized in stoichiometric KMnO_4/MnSO₄ aqueous solutions in the absence/presence of Fe³⁺ at temperature ranging from 30 °C to 180 °C. The phase structures, morphologies and electrochemical properties of the as-prepared MnO₂ products were investigated using X-ray powder diffraction, scanning electron microscope, N₂ physical adsorption and cyclic voltammetry techniques. The results showed that the presence of Fe³⁺ addition had a significant effect on the phase structural evolution, morphological features and electrochemical properties of the MnO₂ products. Fe³⁺ was found to greatly prevent the epitaxial growth and crystallization of MnO₂ nucleus, which in turn influenced textual characteristics. The electrochemical performance of the nanostructured MnO₂ products had a complex relationship with the phase structures, specific surface area as well as pore characteristics. MnO₂ prepared in the presence of Fe³⁺ (KMF-MnO₂) showed relatively higher specific capacitance compared to that of MnO₂ prepared in the absence of Fe³⁺ (KM-MnO₂). Maximum capacitance of 214 F g⁻¹ was obtained for KMF-MnO₂ prepared at 30 °C at a scan rate of 2 mV s⁻¹ in 0.1 M Na₂SO₄ electrolyte.     

Physical and electrochemical properties of cobalt doped (Ti,Ru)O2 electrode coatings

The physical and electrochemical properties of ternary oxides Ti_0.7Ru_0.3−xCo_xO₂ (x = 0.093 and x = 0) have been investigated and compared. Samples of three different thicknesses were prepared by spin-coating onto polished titanium to achieve uniform and well-defined coatings. The resulting electrodes were characterized with a variety of methods, including both physical and electrochemical methods. Doping with cobalt led to a larger number of micrometer-sized cracks in the coating, and coating grains half the size compared to the undoped samples (10 instead of 20 nm across). This is in agreement with a voltammetric charge twice as high, as estimated from cyclic voltammetry. There is no evidence of a Co₃O₄ spinel phase, suggesting that the cobalt is mainly incorporated in the overall rutile structure of the (Ti,Ru)O₂. The doped electrodes exhibited a higher activity for cathodic hydrogen evolution compared to the undoped electrodes, despite the fact that one third of the active ruthenium was substituted with cobalt. For anodic chlorine evolution, the activity was similar for both electrode types.     

Synthesis of carbon foam covered with carbon nanofibers as catalyst support for gas phase catalytic reactions

Mesophase pitch based carbon foam (MPCF) covered with a layer of carbon nanofibers (CNFs) was prepared as catalyst support for gas phase catalytic reactions. Owing to the CNF layer, the specific surface area of MPCF increases from 40 to 198 m²/g. This kind of catalyst support plays an important role in the enhancement of mass/heat transfer due to the large external surface area, high porosity and high thermal conductivity. When selective catalytic NO reduction was taken as a model reaction, more than 90% NO conversion could be achieved in a wide temperature range of 180-220 °C over MnO_x-CeO₂/MPCF-CNF catalyst.     

Interaction of highly dissociated low pressure hydrogen plasma with W-C thin film deposits

Thin film deposits of carbon and tungsten on stainless steel substrate were prepared by RF sputtering of a tungsten target in acetylene atmosphere. At the target bias of − 1700 V and the target current of 30 mA cm^− 2, a rather uniform film containing 50 at.% of C and 50 at.% of W was deposited. The thickness of the deposited film was about 1 μm. Samples were exposed to highly dissociated hydrogen plasma created by a microwave discharge at the power of 1000 W. Some samples were heated additionally by concentrated solar radiation. After plasma treatment, the samples were characterized by X-Ray Diffraction and Auger Electron Spectroscopy. The results showed that aggressive hydrogen plasma allows for the removal of carbon from the deposits at moderated temperatures. Prolonged treatment showed formation of highly crystalline pure tungsten, and finally the tungsten film interacted with the substrate forming a thin film rich of Fe₇W₆ compound. The range of temperature and/or treatment time for the removal of carbon from the W-C film was found very narrow.     

Sensitive and selective imprinted electrochemical sensor for p-nitrophenol based on ZnO nanoparticles/carbon nanotubes doped chitosan film

A sensitive and selective molecularly imprinted electrochemical sensor for p-nitrophenol detection has been developed based on ZnO nanoparticles/multiwall carbon nanotubes (MWNTs)-chitosan (CTS) nanocomposite. This nanocomposite was dripped onto an indium tin oxide electrode and then imprinted sol-gel solution was electrodeposited onto the modified electrode to construct the proposed sensor. The morphologies and electrochemical behaviors of the imprinted sensor were characterized by scanning electron microscope, X-ray diffraction, electrochemical impedance spectroscopy, square wave voltammetry and cyclic voltammetry. The imprinted sensor displayed excellent selectivity towards the target molecule p-nitrophenol. Meanwhile, the introduced nanocomposite increased surface area and active sites for electron transfer, thus remarkably enhancing the sensitivity of the imprinted sensor. Under optimal conditions, the peak current was linear to p-nitrophenol concentration ranging from 1.0 × 10^− 8 to 2.0 × 10^− 4 mol·L^− 1 with a detection limits of 1.0 × 10^− 9 mol·L^− 1 (S/N = 3). This proposed sensor was applied to the detection of p-nitrophenol in various water samples successfully.     

Effect of annealing temperature on structural, electrical and optical properties of B-N codoped ZnO thin films

The B-N codoped p-type ZnO thin films have been prepared by radio frequency magnetron sputtering using a mixture of nitrogen and oxygen as sputtering gas. The effect of annealing temperature on the structural, electrical and optical properties of B-N codoped films was investigated by using X-ray diffraction, Hall-effect, photoluminescence and optical transmission measurements. Results indicated that the electrical properties of the films were extremely sensitive to the annealing temperature and the conduction type could be changed dramatically from n-type to p-type, and finally changed to weak p-type in a range from 600 °C to 800 °C. The B-N codoped p-type ZnO film with good structural, electrical and optical properties can be obtained at an intermediate annealing temperature region (e.g., 650 °C). The codoped p-type ZnO had the lowest resistivity of 2.3 Ω cm, Hall mobility of 11 cm²/Vs and carrier concentration of 1.2 × 10¹⁷ cm^− 3.     

Synthesis of carbon hollow particles by a simple inverse-emulsion method

Morphology-controlled carbon hollow particles have been successfully prepared via carbonization of the resorcinol-formaldehyde (RF) hollow particles synthesized from O/W/O inverse-emulsion system. Various morphologies of carbon hollow particles such as hollow spheres, bowl-like structure, and capsules were tailored by adjusting the pH values of RF precursor. The obtained carbon hollow particles exhibited similar microporous properties with specific surface areas of 526-659 m² g^− 1 and pore volumes of 0.26-0.43 cm³ g^− 1. Based on these results, it was proposed that the low initial pH value of RF precursor and the stability of inverse-emulsion system were crucial in fabricating morphology-controlled carbon hollow particles.