Ru oxide/carbon fabric composites for supercapacitors

Ru oxide/carbon fabric composites (Ru oxide/CF) were prepared by impregnating carbon fabric (CF) with a hydrous RuO₂ suspension. Their properties were characterized by scanning electron microscopy, impedance spectroscopy, cyclic voltammetry, and constant current discharging. Specific capacitance increased with increasing loading of Ru oxide. The apparent average specific capacitance of the Ru oxide component reached 1,085 F g⁻¹ for a 9.15% loading, with a peak of 1,984 F g⁻¹ at approximately 0.3 V vs Ag/AgCl. The presence of Ru oxide decreases the ionic resistance of the CF and appears to increase its specific capacitance by generating additional electroactive surface functionality.     

The preparation of PANI/CA composite electrode material for supercapacitors and its electrochemical performance

Polyaniline (PANI)/carbon aerogel (CA) composite electrode materials were prepared by chemical oxidation polymerization. The morphology of PANI/CA composite was examined by scanning electron microscopy. The results showed that PANI was uniformly deposited onto the surface of porous CA and filled big inner pores of the CA. Electrochemical performance of the composite electrode was studied by cyclic voltammograms and galvanostatic charge/discharge measurements. The results indicated that the PANI/CA composite electrode had much better electrochemical performance, high reversibility, and high charge/discharge properties than CA. Moreover, the results based on cyclic voltammograms showed that the composite material has a high specific capacitance of 710.7 F g⁻¹, while the capacitance of CA electrode was only 143.8 F g⁻¹. Besides, the supercapacitor using the PANI/CA composite as electrode active material showed a stable cycle life in the potential range of −0.2–0.8 V.     

Electropolymerized composite film of polypyrrole and functionalized multi-walled carbon nanotubes: effect of functionalization time on capacitive performance

The composite film of polypyrrole and functionalized multi-walled carbon nanotubes (PPy/F-MWNTs) was prepared by electropolymerization. MWNTs were functionalized by sonicating with a concentrated solution of H₂SO₄/HNO₃ (3/1, volume ratio) in a water bath for different times. The carbon nanotubes (CNTs) are cut into smaller portions with more functional groups introduced on their surface when the sonicating time (nominated as functionalization time hereafter) is increased. However, the specific capacitance of the composite film reaches a maximum of 240 F g⁻¹ at the scanning rate of 10 mV s⁻¹ when MWNTs are functionalized for 24 h, which is about 205 F g⁻¹, 225 F g⁻¹ and 232 F g⁻¹, respectively, when MWNTs are functionalized for 6 h, 12 h and 48 h. At a current load of 1.0 A g⁻¹, PPy/F-MWNT composite film functionalized for 24 h (PPy/F-MWNTs (24 h)) retains 93.49% of its initial capacitance after 1,000 cycles of galvanostatic charge/discharge, and the discharge efficiency is higher than 98.15% during cycling. High specific capacitance, good rate performance, fast charge/discharge ability and long cycling life are ascribed to the synergistic effect of the two components to form a porous composite film as well as the easy accessibility of counter ions into the film. Therefore, PPy/F-MWNT (24 h) composite film is a kind of promising electrode material for supercapacitors. The mechanism of underfunctionalization and overfunctionalization of carbon nanotubes is also discussed.     

Preparation and electrochemical performance of activated carbon thin films with polyethylene oxide-salt addition for electrochemical capacitor applications

The effect of polymer–salt addition in the activated carbon electrode for electric double-layer capacitor (EDLC) has been investigated. A series of composite thin film electrode consisting of activated carbon, carbon black, polytetrafluoroethylene and polymer–salt complex (polyethyleneoxide–LiClO₄) with an appropriate weight ratio were prepared and examined their performance for EDLCs using 1 mol L⁻¹ LiClO₄ in ethylene carbonate:diethylcarbonate electrolyte solution. The electrochemical capacitance performances of these electrodes with different compositions were characterized by cyclic voltammetry, galvanostatic charge–discharge cycling, and AC impedance measurements. By comparison, the best results were obtained with a composite electrode rich in polymer–salt additive (132 F g⁻¹ at 100 mA g⁻¹ of galvanostatic experiment). In general, the polymer–salt-containing electrode had shown improved performance over activated carbon electrodes without polymer–salt at high current density.     

Study of capacitive properties in supercapacitor for copolymer of aniline with m-phenylenediamine

The copolymers were synthesized with different molar ratios of m-phenylenediamine to aniline (R for short) by a chemical oxidation method. The products were first used as electrochemical activity materials of the supercapacitor. Capacitive behaviors of the prepared copolymers in 1 mol·L⁻¹ H₂SO₄ electrolyte were examined by electrochemical impedance spectroscopy, cyclic voltammeter, and galvanostatic charge/discharge. The relationship of molar ratios with capacitive property of the prepared products was investigated too. The results showed that the product with R of 2:98 displayed better electrochemical properties than that of the other products. Compared with the synthesized polymer in the absence of m-phenylenediamine, the polymerized copolymer with R of 2:98 exhibited the initial specific capacitance value of 475 F·g⁻¹, which increased by nearly 10.1% than that of the former at a current density of 200 mA·g⁻¹ in 1 mol·L⁻¹ H₂SO₄ electrolyte in the potential range of −0.3 to 0.7 V. The discharge specific capacitance value of the copolymer remained 300 F·g⁻¹ after 1,000 cycles, exhibiting a good cycling performance and the structure stability.     

Electrochemical capacitance of nickel oxide nanotubes synthesized in anodic aluminum oxide templates

Nickel oxide (NiO) nanotubes for supercapacitors were synthesized by chemically depositing nickel hydroxide in anodic aluminum oxide templates and thermally annealing at 360 °C. The synthesized nanotubes have been characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The capacitive behavior of the NiO nanotubes was investigated by cyclic voltammetry, galvanostatic charge–discharge experiment, and electrochemical impedance spectroscopy in 6 M KOH. The electrochemical data demonstrate that the NiO nanotubes display good capacitive behavior with a specific capacitance of 266 F g⁻¹ at a current density of 0.1 A g⁻¹ and excellent specific capacitance retention of ca. 93% after 1,000 continuous charge–discharge cycles, indicating that the NiO nanotubes can become promising electroactive materials for supercapacitor.     

Characterization and electrochemical applications of a carbon with high density of surface functional groups produced from beer yeast

Carbon materials enriched with nitrogen and oxygen surface functional groups were obtained by pyrolyzing strained beer yeast at 750 °C under an inert atmosphere. Physical and surface properties of the carbon obtained were characterized by X-ray powder diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, Raman spectrometry, and X-ray photoelectron spectroscopy. Results show that the carbon possesses an amorphous structure, a spherical morphology, and a high density of surface functional groups. Electrochemical properties were evaluated by cyclic voltammetry, a galvanostatic charge–discharge technique, and electrochemical impedance spectroscopy. The carbon has 989.65 mAh·g⁻¹ of initial discharge capacity and a stable cycle performance for a Li–C cell. A specific capacitance of 120 F·g⁻¹ was obtained for a single carbon electrode and good cycle performance was achieved for a symmetrical supercapacitor fabricated using this carbon. These carbons derived from strained beer yeast have promising applications in energy storage and conversion systems.     

Immersion enthalpy and the constants of Langmuir model in the 3-chloro phenol adsorption on activated carbon

The adsorption process of 3-chloro phenol from aqueous solution on a activated carbon prepared from African palm stone and which presents a specific surface area of 685 m² g⁻¹, a greater quantity of total acid groups and a pH_PZC of 6.8 is studied. The adsorption isotherms are determined at pH values of 3, 5, 7, 9 and 11. The adsorption isotherms are fitted to the Langmuir model and the values of the maximum quantity adsorbed that are between 96.2 and 46.4 mg g⁻¹ are obtained along with the constant K_L with values between 0.422 and 0.965 L mg⁻¹. The maximum quantity adsorbed diminishes with the pH and the maximum value for this is a pH of 5. The immersion enthalpies of the activated carbon in a 3-chloro phenol solution of constant concentration, of 100 mg L⁻¹, are determined for the different pH levels, with results between 37.6 and 21.2 J g⁻¹. Immersion enthalpies of the activated carbon in function of 3-chloro phenol solution concentration are determined to pH 5, of maximum adsorption, with values between 28.3 and 38.4 J g⁻¹, and by means of linearization, the maximum immersion enthalpy is calculated, with a value of 41.67 J g⁻¹. With the results of the immersion enthalpy, maximum quantity adsorbed and the constant K_L, establish relations that describe the adsorption process of 3-chloro phenol from aqueous solution on activated carbon.     

Electrochemical performance of Co–Al layered double hydroxide nanosheets mixed with multiwall carbon nanotubes

Regular hexagonal Co–Al layered double hydroxides (Co–Al LDH) were synthesized by urea-induced homogeneous precipitation. This material proved to be nanosheets by scanning electron microscopy and X-ray diffraction measurements. The electrochemical capacitive behavior of the nanosheets in 1 M KOH solution were evaluated by constant current charge/discharge and cyclic voltammetric measurements, showing a large specific capacitance of 192 F·g⁻¹ even at the high current density of 2 A·g⁻¹. When multiwall carbon nanotubes (MWNTs) were mixed with the Co–Al LDH, it was found that the specific capacitance and long-life performance of all composite electrodes at high current density are superior to pure LDH electrode. When the added MWNTs content is 10 wt%, the specific capacitance increases to 342.4 F·g⁻¹ and remains at a value of 304 F·g⁻¹ until the 400th cycle at 2 A·g⁻¹, showing that this is a promising electrode material for supercapacitors working at heavy load. According to the electrochemical impedance spectra, MWNTs greatly increase the electronic conductivity between MWNTs and the surface of Co–Al LDH, which consequently facilitates the access of ions in the electrolyte and electrons to the electrode/electrolyte interface.     

Electrochemical capacitive properties of CNT fibers spun from vertically aligned CNT arrays

Due to their lightweight, large surface area; excellent electrical conductivity; and mechanical strength, carbon nanotube (CNT) fibers show great potentials in serving as both electrode materials and current collectors in supercapacitors. In this paper, the capacitive properties of both as-spun CNT fibers and electrochemically activated CNT fibers have been investigated using cyclic voltammetry and electrochemical impedance spectroscopy. It is found that the as-spun CNT fibers exhibit a very low specific capacitance of 2.6 F g⁻¹, but electrochemically activated CNT fibers show considerably improved specific capacitance. The electrochemical activation has been realized by cyclic scanning in a wide potential window. Different electrolytes have also been examined to validate the applicability of our carbon materials and the activation mechanism. It is believed that such an activation process can significantly improve the surface wetting of the CNT fibers by electrolyte (aqueous Na₂SO₄ solution). The cycling stability and rate-dependence of the capacitance have been studied, and the results suggest practical applications of CNT fibers in electrochemical supercapacitors.     

RuO2/Co3O4 thin films prepared by spray pyrolysis technique for supercapacitors

RuO₂/Co₃O₄ thin films with different RuO₂ content were successfully prepared on fluorine-doped tin oxide coated glass plate substrates by spray pyrolysis method, and their capacitive behavior was investigated. Electrochemical property was performed by cyclic voltammetry, constant current charge/discharge, and electrochemical impedance spectra. The capacitive performance of RuO₂/Co₃O₄ thin films with different RuO₂ content corresponded to a contribution from a main pseudocapacitance and an additional electric double-layer capacitance. The specific capacitance of pure Co₃O₄, 15.5%, 35.6%, and 62.3% RuO₂ composites at the current density of 0.2 A g⁻¹ were 394 ± 8, 453 ± 9, 520 ± 10, and 690 ± 14 F g⁻¹, respectively; 62.3% RuO₂ composite presented the highest specific capacitance value at various current densities, whereas 35.6% RuO₂ composite exhibited not only the largest specific capacitance contribution from RuO₂ (C _sp ^RuO2) at the current density of 0.5, 1.0, 1.5, and 2.0 A g⁻¹ but also the highest specific capacitance retention ratio (46.3 ± 2.8%) at the current density ranging from 0.2 to 2.0 A g⁻¹. Electrochemical impedance spectra showed that the contact resistance dropped gradually with the decrease of RuO₂ content, and the charge-transfer resistance (R _ct) increased gradually with the decrease of RuO₂ content.     

Electrochemical performance of LiVPO<Subscript>4</Subscript>F/C composite cathode prepared through amorphous vanadium phosphorus oxide intermediate

LiVPO₄F/C composites with better electrochemical performance were prepared by calcination of LiF and amorphous vanadium phosphorus oxide (VPO) intermediate synthesized by a sol–gel method using H₃PO₄, V₂O₅ and citric acid as raw materials. The properties of LiVPO₄F/C composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The analysis of XRD patterns and Fourier transform infrared spectra (FTIR) reveal that VPO intermediate prepared by sol–gel method is amorphous and VPO₄ may exist in VPO intermediate. The compositions of LiVPO₄F/C composites are related to the calcination temperature for preparation of amorphous VPO/C intermediate and LiVPO₄F/C composite prepared by VPO/C synthesized at 700°C consists of a single crystal phase of LiVPO₄F. The electrochemical tests show that LiVPO₄F/C composite prepared by VPO/C synthesized at 700°C exhibits higher discharge capacity and excellent cycle performance. This LiVPO₄F/C composite displays discharge capacity of 133 mAh g⁻¹ at 0.5 C (78 mA g⁻¹) and remains capacity retention of 96.8% after 30 cycles, even at a high rate of 5 C, the composite exhibits high discharge capacity of 115 mAh g⁻¹ and capacity retention of 97% after 100 cycles.     

Synthesis and supercapacitance of flower-like Co(OH)<Subscript>2</Subscript> hierarchical superstructures self-assembled by mesoporous nanobelts

A facile hydrothermal strategy was first proposed to synthesize flower-like Co(OH)₂ hierarchical microspheres. Further physical characterizations revealed that the flower-like Co(OH)₂ microspherical superstructures were self-assembled by one-dimension nanobelts with rich mesopores. Electrochemical performance of the flower-like Co(OH)₂ hierarchical superstructures were investigated by cyclic voltammgoram, galvanostatic charge–discharge and electrochemical impedance spectroscopy in 3 M KOH aqueous electrolyte. Electrochemical data indicated that the flower-like Co(OH)₂ superstructures delivered a specific capacitance of 434 F g⁻¹ at 10 mA cm⁻² (about 1.33 A g⁻¹), and even kept it as high as 365 F g⁻¹ at about 5.33 A g⁻¹. Furthermore, the SC degradation of about 8% after 1,500 continuous charge–discharge cycles at 5.33 A g⁻¹ demonstrates their good electrochemical stability at large current densities.     

壳聚糖基多孔碳材料的制备及其超级电容性能

以胶态SiO₂纳米粒子为模板,壳聚糖为碳源,ZnCl₂为活化剂,制备了具有不同比表面积和孔体积的氮掺杂介孔碳。采用多种表征手段对碳材料的微观形貌、比表面积和孔道结构进行了表征,探究了壳聚糖与SiO₂纳米粒子的比例以及ZnCl₂活化剂对碳材料孔体积和比表面积的影响。结果表明,在未使用活化剂时碳材料(CSi-1.75)的孔体积高达4.53 cm³·g^-1,但其比表面积最小(729 m²·g^-1);使用ZnCl₂作为活化剂制备的碳材料(CSi-1.75-Zn)比表面积为1 032 m²·g^-1,但其孔体积下降到1.99 cm³·g^-1,且具有最多的吡啶氮和吡咯氮。在以6.0 mol·L^-1KOH为电解液的三电极体系中,当电流密度为0.5 A·g^-1时,CSi-1.75...     

Enthalpic characterization of activated carbons obtained from <Emphasis Type="Italic">Mucuna Mutisiana</Emphasis> with different burn-offs

Immersion enthalpies of activated carbon samples obtained by activation with steam at temperatures between 600 and 900 °C and activation times between 1 and 10 h were determined. The calorimetric liquids of immersion are CCl₄, water, NaOH, and HCl 2 M solutions, and the values of the immersion enthalpies are related to other properties of the activated carbons such as the surface area B.E.T., the micropore volume, the content of acid, and basic surface groups. The highest values for the immersion enthalpies take place for the polar solvent CCl₄ and for HCl solution, with values between 4.0 and 75.2 J g⁻¹ and 9.15 and 48.3 J g⁻¹, respectively.     

Structural and electrochemical behavior of Mn–V oxide synthesized by a novel precipitation method

Manganese–vanadium oxide had been synthesized by a novel simple precipitation technique. Scanning electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller, thermogravimetric analysis/differential scanning calorimetry, and X-ray photoelectron spectroscopy were used to characterize Mn–V binary oxide and δ-MnO₂. Electrochemical capacitive behavior of the synthesized Mn–V binary oxide and δ-MnO₂ was investigated by cyclic voltammetry, galvanostic charge–discharge curve, and electrochemical impedance spectroscope methods. The results showed that, by introducing V into δ-MnO₂, the specific surface area of the mixed oxide increased due to a formation of small grain size. The specific capacitance increased from 166 F g⁻¹ estimated for MnO₂ to 251 F g⁻¹ for Mn–V binary oxide, and the applied potential window extended to −0.2–1.0 V (vs. saturated calomel electrode). Through analysis, it is suggested that the capacitance performance of Mn–V binary oxide materials may be improved by changing the following three factors: (1) small grain and particle size and large activity surface area, (2) appropriate amount of lattice water, and (3) chemical state on the surface of MnO₂ material.     

Influence of addition of cobalt oxide on microstructure and electrochemical capacitive performance of nickel oxide

Ni–Co oxide nanocomposite was prepared by thermal decomposition of the precursor obtained via a new method—coordination homogeneous coprecipitation method. The synthesized sample was characterized physically by X-ray diffraction, scanning electron microcopy, energy dispersive spectrum, transmission electron microscope, and Brunauer–Emmett–Teller surface area measurement, respectively. Electrochemical characterization of Ni–Co oxide electrode was examined by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance measurements in 6-mol L⁻¹ KOH aqueous solution electrolyte. The results indicated that the addition of cobalt oxide not only changed the morphology of NiO but also enhance its electrochemical capacitance value. A specific capacitance value of 306 F g⁻¹ of Ni–Co oxide nanocomposite with n _Co = 0.5 (n _Co is the mole fraction of Co with respect to the sum of Co and Ni) was measured at the current density of 0.2 A g⁻¹, nearly 1.5 times greater than that of pure NiO electrode. Lower resistance and better rate capability can also be observed.     

壳聚糖基多孔碳材料的制备及其超级电容性能

以胶态SiO₂纳米粒子为模板,壳聚糖为碳源,ZnCl2为活化剂,制备了具有不同比表面积和孔体积的氮掺杂介孔碳。采用多种表征手段对碳材料的微观形貌、比表面积和孔道结构进行了表征,探究了壳聚糖与SiO₂纳米粒子的比例以及ZnCl2活化剂对碳材料孔体积和比表面积的影响。结果表明,在未使用活化剂时碳材料(CSi-1.75)的孔体积高达4.53 cm³·g^-1,但其比表面积最小(729 m²·g^-1);使用ZnCl₂作为活化剂制备的碳材料(CSi-1.75-Zn)比表面积为1032 m²·g^-1,但其孔体积下降到1.99 cm³·g^-1,且具有最多的吡啶氮和吡咯氮。在以6.0 mol·L^-1 KOH为电解液的三电极体系中,当电流密度为0.5 A·g^-1时,CSi-1.75-Zn的比电容为344 F·g^-1,而CSi-1.75的比电容仅为255 F·g^-1。这表明碳材料的比表面积对超级电容性能影响最大,而孔体积影响较小。电容贡献分析结果表明,相对于CSi-1.75,CSi-1.75-Zn的双电层电容和赝电容都得到了提高,这表明更大的比表面积和更多的吡啶氮和吡咯氮有利于提高碳材料的超级电容性能。     

Hybrid materials for supercapacitor application

In the present study, a manganese oxide obtained by the acid treatment of LiMn₂O₄ spinel has been used as a positive electrode of supercapacitor. Removal of lithium from a spinel allowed to obtain MnO₂ compound with the pores partly distributed in atomic scale, hence, an efficient use of its pseudocapacitive properties could be reached. On the other hand, residual lithium remaining in the structure preserved layered framework of MnO₂ with pathways for ions sorption. Physical properties, morphology, and specific surface area of electrode materials were studied by scanning and transmission electron microscopy, and nitrogen sorption measurements. Voltammetry cycling, galvanostatic charge/discharge, and impedance spectroscopy measurements performed in two- and three-electrode cells have been applied in order to measure electrochemical parameters. Neutral Li₂SO₄ aqueous solution has been selected for electrolytic medium. Extension of operating voltage for supercapacitor has been realized through asymmetric configuration with an activated carbon as a negative electrode. The asymmetric capacitor was operating within a voltage range up to 2.5 V (limited to 2.0 V for cycling tests) and was able to deliver a specific capacitance of 60 Fg⁻¹ per capacitor at 100 mA g⁻¹ current density. High specific energy of 36 Wh kg⁻¹ was reached but with a moderate power density.     

Preparation and electrochemical performance of nano-structured Li<Subscript>2</Subscript>Mn<Subscript>4</Subscript>O<Subscript>9</Subscript> for supercapacitor

Nano-structured spinel Li₂Mn₄O₉ powder was prepared via a combustion method with hydrated lithium acetate (LiAc·2H₂O), manganese acetate (MnAc₂·4H₂O), and oxalic acid (C₂H₂O₄·2H₂O) as raw materials, followed by calcination of the precursor at 300 °C. The sample was characterized by X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopy techniques. Electrochemical performance of the nano-Li₂Mn₄O₉ material was studied using cyclic voltammetry, ac impedance, and galvanostatic charge/discharge methods in 2 mol L⁻¹ LiNO₃ aqueous electrolyte. The results indicated that the nano-Li₂Mn₄O₉ material exhibited excellent electrochemical performance in terms of specific capacity, cycle life, and charge/discharge stability, as evidenced by the charge/discharge results. For example, specific capacitance of the single Li₂Mn₄O₉ electrode reached 407 F g⁻¹ at the scan rates of 5 mV s⁻¹. The capacitor, which is composed of activated carbon negative electrode and Li₂Mn₄O₉ positive electrode, also exhibits an excellent cycling performance in potential range of 0–1.6 V and keeps over 98% of the maximum capacitance even after 4,000 cycles.