Preparation of activated carbon from Turbinaria turbinata seaweeds and its use as supercapacitor electrode materials

Turbinaria turbinata brown seaweeds were tested as carbon electrode material in symmetric, electrochemical supercapacitors. The electrochemical properties of the carbon materials were characterised for their application as supercapacitors using cyclic voltammetry, galvanostatic charge/discharge method and electrochemical impedance spectroscopic analyses. Our initial results showed that the optimal behaviour was obtained for the sample prepared by pyrolysis at 800 °C. The average surface area of the carbon was 812 m²/g. Electrochemical tests with an organic electrolyte gave the following interesting results: a capacitance of 74.5 F/g, a specific series resistance of 0.5 Ω cm² and an ionic resistivity of 1.3 Ω cm². These results show the promising capacitive properties of carbon derived from seaweeds and their application in electrochemical supercapacitors.     

Nanocrystalline FeWO4 as a pseudocapacitive electrode material for high volumetric energy density supercapacitors operated in an aqueous electrolyte

Iron tungstate (FeWO₄) has been synthesized using two low-temperature synthetic routes and investigated as a new pseudocapacitive electrode material for supercapacitors operating in a neutral aqueous electrolyte. Its electrochemical properties are clearly related to the specific surface area and seem to originate from Fe^3 +/Fe^2 + fast surface reactions. For FeWO₄ obtained by polyol-mediated synthesis, a high volumetric capacitance of 210 F·cm^− 3 (i.e. more than two times higher than that of activated carbon) was measured at 20 mV·s^− 1 with less than 5% fade over 10,000 cycles. Furthermore, unlike most of the previously investigated iron based electrodes, a unique pseudocapacitive behavior is observed, thus emphasizing the role of the crystallographic structure on the electrochemical signature.     

Nitrogen enriched mesoporous carbon spheres obtained by a facile method and its application for electrochemical capacitor

A kind of mesoporous carbon spheres (MCS) containing in-frame incorporated nitrogen has been prepared by a facile polymerization-induced colloid aggregation method. As the electrode material for electric double layer capacitor (EDLC) in 5 mol/L H₂SO₄, the MCS products present excellent specific capacitance as 211 F/g much larger than that of the most popularly applied activated carbon at a high discharge current density of 1 A/g. Its specific capacitance can still remain 200 F/g at 20 A/g. The superior electrochemical performance of MCS is associated with the following characteristics: high specific surface area (∼1330 m²/g) contributed mainly by the mesopores, uniform pore size as large as 29 nm and moderate content of nitrogen (10 wt%), which are the requirements for ideal supercapacitors.     

Preparation of monodisperse carbon nanospheres for electrochemical capacitors

The efficiently hydrothermal route using sucrose without any catalysts is employed to prepare the uniform carbon spheres. The monodisperse 100–150 nm carbon spheres are obtained with the activation treatment in molten KOH. The carbon spheres are characterized by transmission electron microscope, X-ray diffraction, N₂ adsorption, Raman spectroscopy and electrochemical techniques. The relationships of specific capacitance and surface properties of carbon spheres are investigated. A single electrode of carbon nanosphere materials performs excellent specific capacitance (328 F g⁻¹), area capacitance (19.2 μF cm⁻²) and volumetric capacitance (383 F cm⁻³).     

Structural and electrochemical properties of a porous nanostructured SnO2 film electrode for lithium-ion batteries

A B₂O₃-doped SnO₂ thin film was prepared by a novel experimental procedure combining the electrodeposition and the hydrothermal treatment, and its structure and electrochemical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, energy dispersive X-ray (EDX) spectroscopy and galvanostatic charge–discharge tests. It was found that the as-prepared modified SnO₂ film shows a porous network structure with large specific surface area and high crystallinity. The results of electrochemical tests showed that the modified SnO₂ electrode presents the largest reversible capacity of 676 mAh g^?1 at the fourth cycle, close to the theoretical capacity of SnO₂ (790 mAh g^?1); and it still delivers a reversible Li storage capacity of 524 mAh g^?1 after 50 cycles. The reasons that the modified SnO₂ film electrode shows excellent electrochemical properties were also discussed.     

A study of ion charge transfer on electrochemical behaviors of poly(vinylidene fluoride)-derived carbon electrodes

In this work, porous carbon with a high specific surface area as electrode materials for supercapacitors are obtained by a carbonization process at various temperatures from 700 °C to 1000 °C without activation process using poly(vinylidene fluoride) (PVDF) as a carbon precursor. The electrochemical performance is characterized by cyclic voltammetry and galvanostatic charge–discharge cycling performance using two-electrode system in 6.0 M KOH as an aqueous electrolyte. The results indicate that carbonization temperature significantly affected the specific surface area and pore volume of the PVDF-derived carbons and their capacitive behavior. In particular, the electrochemical performance of the prepared PVDF-derived carbon is determined by both the electric double-layer capacitance and the pseudo-capacitance resulting from the residual surface functional groups on PVDF-derived carbons.     

Determination of concentrated hydrogen peroxide at single-walled carbon nanohorn paste electrode

Single-walled carbon nanohorn (SWCNH) paste electrode was used for amperometric determination of concentrated hydrogen peroxide, and was compared with other carbon electrodes. The calibration plots are linear from 0.5 to 100 mM at activated SWCNH paste electrode and edge plane graphite (EPG) electrode. In contrast, the calibration plots are linear only at concentrations lower than 45 mM at graphite paste electrode, multi-walled carbon nanotube paste electrode, and glassy carbon electrode. Our results show that SWCNH paste electrode and EPG electrode are interesting alternatives to high surface area platinum electrode for determination of concentrated hydrogen peroxide. Because of its high-purity, metal-free SWCNH is a user-friendly and attractive material for electrochemical study.     

Worm-like mesoporous carbon synthesized from metal–organic coordination polymers for supercapacitors

A green and efficient route has been employed to synthesize a worm-like mesoporous carbon with high specific surface area (2587 m² g^?1) and large pore volume (3.14 cm³ g^?1). Three electrochemical methods have been used to measure its electrochemical performance. Worm-like mesoporous carbon performs the high specific capacitance (344 F g^?1) at constant-current densities of 50 mA g^?1.     

Tube-covering-tube nanostructured polyaniline/carbon nanotube array composite electrode with high capacitance and superior rate performance as well as good cycling stability

The combination of a vertically aligned carbon nanotube array (CNTA) framework and electrodeposition technique leads to a tube-covering-tube nanostructured polyaniline (PANI)/CNTA composite electrode with hierarchical porous structure, large surface area, and superior conductivity. PANI/CNTA composite electrode has high specific capacitance (1030 F g⁻¹), superior rate capability (95% capacity retention at 118 A g⁻¹), and high stability (5.5% capacity loss after 5000 cycles). Energy storage characteristics of the PANI/CNTA composite are presented in this paper.     

Electrodeposited PbO2 thin film on Ti electrode for application in hybrid supercapacitor

PbO₂ thin films were prepared by pulse current technique on Ti substrate from Pb(NO₃)₂ plating solution. The hybrid supercapacitor was designed with PbO₂ thin film as positive electrode and activated carbon (AC) as negative electrode in the 5.3 M H₂SO₄ solution. Its electrochemical properties were determined by cyclic voltammetry (CV), charge–discharge test and electrochemical impedance spectroscopy (EIS). The results revealed that the PbO₂/AC hybrid supercapacitor exhibited large specific capacitance, high-power and stable cycle performance. In the potential range of 0.8–1.8 V, the hybrid supercapacitor can deliver a specific capacitance of 71.5 F g^?1 at a discharge current density of 200 mA g^?1(4 mA cm^?2) when the mass ratio of AC to PbO₂ was three, and after 4500 deep cycles, the specific capacitance remains at 64.4 F g^?1, or 32.2 Wh Kg^?1 in specific energy, and the capacity only fades 10% from its initial value.     

Modification of carbon electrode in ionic liquid through the reduction of phenyl diazonium salt. Electrochemical evidence in ionic liquid

Electrochemical reduction of the 4-nitrophenyl diazonium salt in ionic liquid media has been investigated at carbon electrode. The ionic liquid chosen for this study was 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI]. The cyclic voltammetry study demonstrated the possibility of the electrochemical grafting of the nitrophenyl groups onto carbon electrode after the reduction of its corresponding diazonium in ionic liquid. The electrochemical characterization of the modified electrode achieved on ionic liquid displays the presence of the nitrophenyl group at the carbon surface. Moreover, the surface concentration of the attached group obtained in this media was found to be around 1.7 × 10⁻¹⁰ mol cm⁻², this value may suggest the possibility of the formation of monolayer. Furthermore, the characterization of the modified electrode in [EMIM][TFSI] showed the conversion of some NO₂-phenyl groups to NHOH-phenyl. This observation could indicate the presence of surface interaction between the reduced NO₂-phenyl and the ionic liquid cation, thanks to the presence of acidic proton in the ionic liquid cation.     

An activated carbon with high capacitance from carbonization of a resorcinol–formaldehyde resin

A polymeric activated carbon (PAC) was synthesized from the carbonization of a resorcinol–formaldehyde resin with KOH served as an activation agent. The nitrogen adsorption–desorption at 77 K, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared PAC. Compared with the commercial activated carbon (Maxsorb: Kansai, Japan), PAC shows superior capacitive performance in terms of specific capacitance, power output and high energy density as electrode materials for supercapacitors. PAC presents a high specific capacitance of 500 F g^?1 in 6 mol l^?1 KOH electrolyte at a current density of 233 mA g^?1 which remained 302 F g^?1 even at a high current density of 4.6 A g^?1. The good electrochemical performance of the PAC was ascribed to well-developed micropores smaller than 1.5 nm, the presence of electrochemically oxygen functional groups and low equivalent series resistance.     

Camphoric carbon nanobeads – A new electrode material for supercapacitors

For the first time activated carbon nanobeads have been synthesized for supercapacitor applications by a simple pyrolysis technique. TEM analysis suggests the size of the carbon nanobeads are around 40 nm and XRD measurement reveals an amorphous structure. The average surface area of the nanobeads by BET studies is measured to be 79.6 m²/g, which is higher than the previously reported values. This cell shows an excellent cycleability successfully cycled more than 100,000 cycles and with minimum IR drop. It is suggested that this carbon nanobeads may be used as an active electrode material for supercapacitor applications.     

High performance electrochemical sensor based on modified screen-printed electrodes with cost-effective dispersion of nanostructured carbon black

A novel sensor based on a screen-printed electrode (SPE) modified with a stable dispersion of commercially available carbon black (CB) N220 was developed. This probe showed significantly enhanced electrochemical activity relative to a bare SPE when tested with ferricyanide, epinephrine, norepinephrine, benzoquinone and NADH. When challenged in amperometric batch mode with NADH, the response was stable and revealed a linear dependence up to 2·10^?4 mol L^?1 with a detection limit of 3·10^?7 mol L^?1. The analytical performance, coupled with the low cost of the CB nanomaterial, suggests that this sensor holds promise for electrochemical applications.     

Microwave plasma chemical vapor deposition of nano-composite C/Pt thin-films

Composite carbon–platinum thin-films of nano-crystalline graphitic carbon decorated with uniformly-dispersed 2–4 nm Pt nano-particles have been synthesized from a solid organic precursor by a one-step microwave plasma chemical vapor deposition (MPCVD). The fast Ar-plasma discharge and the presence of microwave radiation accelerate the formation of sites suitable for in situ heterogeneous nucleation, and consequently, the fine dispersion of metal in the carbonaceous matrix. The electrochemical response of the 2 μm C/Pt thin-film electrode displays electrochemical activity, which is attributed to the high ca. 18 m²/g effective surface area of Pt nano-particles.     

Constructing a hierarchical graphene–carbon nanotube architecture for enhancing exposure of graphene and electrochemical activity of Pt nanoclusters

Stacking of individual graphene sheets (GS) is effectively inhibited by introducing one-dimensional carbon nanotubes to form a 3-D hierarchical structure which enhances the utilization of GS-based composites. From SEM images, CNTs are useful nanospacers for diminishing the face-to-face aggregation of GS. The specific electrochemically active surface area (SECSA) and specific double-layer capacitance (C_S,DL) of Pt/GS–CNTs (127.9 m²/g, 171.3 F/g) is much higher than that of Pt/GS (105.4 m²/g, 104.7 F/g) and Pt/CNTs (51.5 m²/g, 37.1 F/g), revealing the synergistic effects between GS and CNTs on enhancing the electrochemical activity of Pt nanoparticles and electrolyte-accessible surface area.     

A high-performance carbon derived from polyaniline for supercapacitors

Activated carbon derived from rod-shaped polyaniline (the diameter of 170 nm) was synthesized by carbonization and subsequent activation with KOH. The obtained activated carbon exhibits a high specific capacitance (455 F g^?1) and remarkable rate capability due to its high specific surface area (1976 m² g^?1), narrow pore size distribution (< 3 nm) as well as short diffusion length. It is indicated that the promising synthetic method used in this work can pave the way for designing new carbon based materials from different polymers for high-performance energy applications.     

Fully electrochemical hyphenated flow system for preconcentration,cleanup, stripping,capillary electrophoresis with stacking and contactless conductivity detection of trace heavy metals

Successful coupling of electrochemical preconcentration (EPC) to capillary electrophoresis (CE) with contactless conductivity detection (C⁴D) is reported for the first time. The EPC–CE interface comprises a dual glassy carbon electrode (GCE) block, a spacer and an upper block with flow inlet and outlet, pseudo-reference electrode and a fitting for the CE silica column, consisting of an orifice perpendicular to the surface of a glassy carbon electrode with a bushing inside to ensure a tight press fit. The end of the capillary in contact with the GCE is slant polished, thus defining a reproducible distance from the electrode surface to the column bore. First results with EPC–CE–C⁴D are very promising, as revealed by enrichment factors of two orders of magnitude for Tl, Cu, Pb and Cd ion peak area signals. Detection limits for 10 min deposition time fall around 20 nmol L^?1 with linear calibration curves over a wide range. Besides preconcentration, easy matrix exchange between accumulation and stripping/injection favors procedures like sample cleanup and optimization of pH, ionic strength and complexing power. This was demonstrated for highly saline samples by using a low conductivity buffer for stripping/injection to improve separation and promote field-enhanced sample stacking during electromigration along the capillary.     

Gelatin-functionalized carbon nanotubes for the bioelectrochemistry of hemoglobin

In this paper, we compared the use of gelatin-functionalized carbon nanotubes (CNTs) as substrates for Hemoglobin (Hb) immobilization and as electrodes for electrochemical reduction of the absorbed Hb. The non-covalently gelatin-functionalized CNTs possessed an improved solubility in aqueous solution and may have an enhanced biocompatibility with Hb. The characteristics of Hb/gelatin-CNTs composite films were studied by using UV–vis spectroscopy, FTIR spectroscopy and electrochemical methods. The immobilized Hb showed a couple of quasi-reversible redox peaks with a formal potential of −0.35 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffer solution (PBS). The surface concentration of electroactive Hb immobilized on gelatin-CNT/GC electrode was about 4.34 × 10⁻¹⁰ mol cm⁻².     

Selective determination of trichloroacetic acid using silver nanoparticle coated multi-walled carbon nanotubes

Silver nanoparticle coated multi-walled carbon nanotubes (Ag/MWCNT) were prepared and used to fabricate a modified electrode. The Ag/MWCNT composites were observed by a transmission electron microscope (TEM), and the electrochemical properties of the Ag/MWCNT composite modified glassy carbon electrode were characterized by electrochemical measurements. The results showed that these composites had a favorable catalytic ability for the reduction of trichloroacetic acid (TCAA). Square wave voltammetric (SWV) technique was applied to detect TCAA. Under optimum conditions, the voltammetric determination of TCAA was performed with a linear range of 5.0 × 10^? 6–1.2 × 10^? 4 mol L^? 1 and a detection limit of 1.9 × 10^? 6 mol L^? 1 (S/N = 3).