Functionalized graphene oxide-reinforced electrospun carbon nanofibers as ultrathin supercapacitor electrode

Graphene oxide has been used widely as a starting precursor for applications that cater to the needs of tunable graphene. However, the hydrophilic characteristic limits their application, especially in a hydrophobic condition. Herein, a novel non-covalent surface modification approach towards graphene oxide was conducted via a UV-induced photo-polymerization technique that involves two major routes; a UV-sensitive initiator embedded via pi-pi interactions on the graphene planar rings, and the polymerization of hydrophobic polymeric chains along the surface. The functionalized graphene oxide successfully achieved the desired hydrophobicity as it displayed the characteristic of being readily dissolved in organic solvent. Upon its addition into a polymeric solution and subjected to an electrospinning process,non-woven random nanofibers embedded with graphene oxide sheets were obtained. The prepared polymeric nanofibers were subjected to two-step thermal treatments that eventually converted the polymeric chains into a carbon-rich conductive structure. A unique morphology was observed upon the addition of the functionalized graphene oxide, whereby the sheets were embedded and intercalated within the carbon nanofibers and formed a continuous structure. This reinforcement effectively enhanced the electrochemical performance of the carbon nanofibers by recording a specific capacitance of up to 140.10 F/g at the current density of 1 A/g, which was approximately three folds more than that of pristine nanofibers.It also retained the capacitance up to 96.2% after 1000 vigorous charge/discharge cycles. This functionalization technique opens up a new pathway in tuning the solubility nature of graphene oxide towards the synthesis of a graphene oxide-reinforced polymeric structure.     

Heterogeneous nanostructured electrode materials for electrochemical energy storage

In order to fulfil the future requirements of electrochemical energy storage, such as high energy density at high power demands, heterogeneous nanostructured materials are currently studied as promising electrode materials due to their synergic properties, which arise from integrating multi-nanocomponents, each tailored to address a different demand (e.g., high energy density, high conductivity, and excellent mechanical stability). In this article, we discuss these heterogeneous nanomaterials based on their structural complexity: zero-dimensional (0-D) (e.g. core-shell nanoparticles), one-dimensional (1-D) (e.g. coaxial nanowires), two-dimensional (2-D) (e.g. graphene based composites), three-dimensional (3-D) (e.g. mesoporous carbon based composites) and the even more complex hierarchical 3-D nanostructured networks. This review tends to focus more on ordered arrays of 1-D heterogeneous nanomaterials due to their unique merits. Examples of different types of structures are listed and their advantages and disadvantages are compared. Finally a future 3-D heterogeneous nanostructure is proposed, which may set a goal toward developing ideal nano-architectured electrodes for future electrochemical energy storage devices.     

Activated carbon/graphene composites with high-rate performance as electrode materials for electrochemical capacitors

Glucose-derived activated carbon (GAC)/reduced graphene oxide (RGO) composites are prepared by pre-carbonization of the precursors (aqueous mixture of glucose and graphene oxide) and KOH activation of the pyrolysis products. The effect of the mass ratio of graphene oxide (GO) in the precursor on the electrochemical performance of GAC/RGO composites as electrode materials for electrochemical capacitors is investigated. It is found that the thermally reduced graphene oxide sheets serves as a wrinkled carrier to support the activated carbon particles after activation. The pore size distribution and surface area are depended on the mass ratio of GO. Besides, the rate capability of GAC is improved by the introduction of GO in the precursor. The highest specific capacitance of 334 F g^?1 is achieved for the GAC/RGO composite prepared from the precursor with a GO mass ratio of 3 %.     

Nano-graphite functionalized mesocellular carbon foam with enhanced intra-penetrating electrical percolation networks for high performance electrochemical energy storage electrode materials

Mesocellular carbon foam (MSU-F-C) is functionalized with hollow nanographite by a simple solution-phase method to enhance the intrapenetrating electrical percolation network. The electrical conductivity of the resulting material, denoted as MSU-F-C-G, is increased by a factor of 20.5 compared with the pristine MSU-F-C. Hollow graphite nanoparticles are well-dispersed in mesocellular carbon foam, as confirmed by transmission electron microscopy (TEM), and the d spacing of the (002) planes is 0.343 nm, which is only slightly larger than that of pure graphite (0.335 nm), suggesting a random combination of graphitic and turbostratic stacking. After nanographitic functionalization, the BET surface area and total pore volume decreased from 928 m(2) g(-1) and 1.5 cm(3) g(-1) to 394 m(2) g(-1) and 0.7 cm(3) g(-1), respectively. Thermogravimetric analysis in air shows that the thermal stability of MSU-F-C-G is improved relative to that of MSU-F-C, and the one-step weight loss indicates that the nanographite is homogeneously functionalized on the MSU-F-C particles. When the resulting mesocellular carbon materials are used as electrode materials for an electric double layer capacitor (EDLC), the specific capacitances (C(sp)) of the MSU-F-C and MSU-F-C-G electrodes at 4 mV s(-1) are 109 F g(-1) and 93 F g(-1), respectively. The MSU-F-C-G electrode exhibited a very high area capacitance (C(area), 23.5 μF cm(-2)) compared with that of the MSU-F-C electrode (11.7 μF cm(-2)), which is attributed to the enhanced intraparticle conductivity by the nanographitic functionalization. MSU-F-C-G exhibited high capacity retention (52%) at a very high scan rate of 512 mV s(-1), while only a 23% capacity retention at 512 mV s(-1) was observed in the case of the MSU-F-C electrode. When applied as an anode in a lithium ion battery, a significant increase in the initial efficiency (44%), high reversible discharge capacity (580 mA h g(-1)) in the lower voltage region, and a higher rate capability were observed. The high rate capability of the MSU-F-C-G electrode as charge storage was due to the low resistance derived from the nanographitic functionalization.     

Oligochitosan-modified three-dimensional graphene free-standing electrode for electrochemical detection of imidacloprid insecticide

A simple sensor based on an oligosaccharide-modified three-dimensional graphene (OCS-3D-G) free-standing electrode was developed for the electrochemical determination of the insecticide imidacloprid (IDP). OCS can interact with graphene oxide sheets by π–π and electrostatic interactions, leading to graphene oxide sheets arranged as regular and dense porous structures. T herefore, compared with other modifier carbohydrates, OCS-3D-G is more suitable for electrochemical sensing. OCS-3D-G was synthesized by a hydrothermal method and then fabricated as an electrochemical sensor, and its characterization was done and electrochemical behavior studied in detail. T he optimized sensor showed good reproducibility, selectivity, and stability, and responded linearly over a wide concentration range (1.0–50.0 μM) w ith a limit of detection (LOD) of 0.51 μM. F inally, the proposed sensor was used for the determination of IDP in brown rice, and the results were in line with those obtained from high-performance liquid chromatography (HPLC). It is thereby shown that the developed free-standing electrode is simple and cheap and can be used as a disposable electrode.     

Functionalized N-doped graphene quantum dots for electrochemical determination of cholesterol through host-guest inclusion

Functionalized nitrogen-doped graphene quantum dots (N-GQD) with mean particle size of 8.5?±?0.5 nm were covalently linked to β-cyclodextrin (β-CD) to form a β-CD@N-GQD nanoprobe. The probe is shown to enable voltammetric determination of cholesterol via selective host-guest recognition and by using ferrocene (FC) as the redox indicator. FC is first included in β-cyclodextrin. Cholesterol has a higher affinity for β-CD (in comparison to FC). It forms a strong inclusion complex with β-CD and can replace FC from its cavities. The quantity of released FC is proportional to the concentration of cholesterol. The differential pulse voltammetric signal for FC (with a peak at typically 0.22 V vs Ag/AgCl) increases linearly in the 0.5–100 μM cholesterol concentration range, with a limit of detection as low as 80 nM. The assay is found to be highly selective over 15 potentially interfering species. The method was successfully applied to the detection of cholesterol in spiked serum samples which gave recoveries between 96 and 101%. The probe can be stored for at least 28 days after which the activity still is 87%.

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Graphical abstract This scheme illustrates the detection of cholesterol by differential pulse voltammetry (DPV) technique. The β-cyclodextrin functionalized nitrogen-doped graphene quantum dot (β-CD@N-GQD) probe was developed to enable voltammetric determination of cholesterol using selective host-guest recognition.

     

An improved solution-tight electrode holder for variable temperature electrochemical studies

With the help of oscillopolarographic methods, the formation of additional adsorption-desorption peaks or incisions in the curves i=f(E) and dE/dt=f(E) was observed for saturated solutions of higher fatty acids in 1 M H₂SO₄. In virtue of the analysis of the first and second polarization cycle, it was found, that, a previous electrode polarization to the adsorption potentials was necessary, if the additional peaks were to be formed. A supposition was made, that the additional peaks originate in the desorption and adsorption of the dimerized molecules of the acids.     

Efficient electrode material for electrochemical energy storage from organic waste

Journal of Solid State Electrochemistry - Heteroatom functionalities in activated carbons have a positive effect on their electrochemical properties. High surface area, reasonable heteroatom...     

Unusual metals as electrode materials for electrochemical sensors

Although noble metals are still widely used in electroanalysis, a plethora of different nonconventional metals is now enriching the panorama of materials acting as the electrochemical transducer in sensing systems. In particular, Ti, Cu, Co, Fe, Mo, Ta, W, Rh, Bi, Sb, Te and Pb are discussed here in view of their peculiar physicochemical properties and of the interesting electrocatalytic activities ascribable to these elements and to the relevant metal oxide ultrathin films that spontaneously form at the electrode–solution interface. This behaviour, exploitable in electroanalysis for the detection of a number on analytes, is often accompanied by low price and high resistance to corrosion and to abrasion characterising these materials. These peculiarities encourage the possible use of the cited metals in a wide number of analytical frames, ranging from process control to bioimplantable sensing systems.     

One step simultaneous electrochemical synthesis of NiO/multilayer graphene nanocomposite as an electrode material for high performance supercapacitors

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Functionalized boranes for hydrogen storage

Using density functional theory, the generalized gradient approximation for the exchange‐correlation potential and Møller–Plesset perturbation theory we study the hydrogen uptake of Li‐ and Mg‐doped boranes. Specifically, we calculate the structures and binding energies of hydrogen molecules sequentially attached to LiB₆H₇, LiB₁₂H₁₃, Li₂B₆H₆, Li₂B₁₂H_12, MgB₆H₆, and MgB₁₂H₁₂. Up to three H₂ molecules can be bound quasi‐molecularly to each of the metal cations with binding energies per H₂ molecule ranging between 0.07 eV and 0.27 eV. The corresponding gravimetric densities lie in the range of 3.49 to 12 wt %, not counting the H atoms bound chemically to the B atoms.     

Electrodeposited nanogold decorated graphene modified carbon ionic liquid electrode for the electrochemical myoglobin biosensor

In this paper, a carbon ionic liquid electrode (CILE) was fabricated using ionic liquid 1-hexylpyridinium hexafluorophosphate as modifier, which was further in situ electrodeposited with graphene (GR) and gold nanoparticles step by step to get an Au/GR nanocomposite modified CILE. Myoglobin (Mb) was further immobilized on the Au/GR/CILE surface with Nafion film to get the modified electrode denoted as Nafion/Mb/Au/GR/CILE. Cyclic voltammetric experiments indicated that a pair of well-defined quasi-reversible redox peaks appeared in pH 3.0 phosphate buffer solution with the formal potential (E ^0′) located at ?0.197 V (vs. saturated calomel electrode), which was the typical characteristics of Mb heme Fe(III)/Fe(II) redox couples. Thus, the direct electron transfer rate between Mb and the modified electrode was promoted due to the high conductivity and increased surface area of Au/GR nanocomposite present on electrode surface. Based on the cyclic voltammetric data, the electrochemical parameters of Mb on the modified electrode were calculated. The Mb-modified electrode showed excellent electrocatalytic activities towards the reduction of trichloroacetic acid and H₂O₂ with wider linear range and lower detection limit. Using GR and Au nanoparticles modified CILE, a new third-generation electrochemical Mb biosensor was constructed with good stability and reproducibility.     

Nickel phosphide-embedded graphene as counter electrode for dye-sensitized solar cells

Nickel phosphide-embedded graphene, prepared by the hydrothermal reaction of red phosphorus, nickel chloride, and graphene oxide in a mixture of ethylene glycol-water, is investigated as the counter electrode of DSSCs. It is demonstrated that the DSSC with the nickel phosphide-embedded graphene as the new counter electrode presents an excellent performance competing with that of the Pt electrode.     

Self-standing rationally functionalized graphene as high-performance electrode materials for supercapacitors

Supercapacitors（SCs） have attracted much attention as one of the alternative energy devices due to their high power performance,long cycle life,and low maintenance cost.Graphene is considered as an innovative and promising material due to its large theoretical specific surface area,high electrical conductivity,good mechanical properties and chemical stability.Herein,we report an effective strategy for elaborately constructing rationally functionalized self-standing graphene（SG） obtained from giant graphene oxide（GGO） paper followed by an ultrarapid thermal-processing.This treatment results in both the exfoliation of graphene sheets and the reduction of GGO by elimination of oxygencontaining groups.The as-prepared SG electrode materials without additive and conducting agent provide an excellent combination of the electrical double layer capacitor（EDLC） and pseudocapacitor（PC） functions and exhibit superior electrochemical performance,including high specific capacitance,good rate capability and excellent cycling stability when investigated in three-electrode electrochemical cells.     

Polycationic oxides as potential electrode materials for aqueous-based electrochemical capacitors

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Controllable deposition of a platinum nanoparticle ensemble on a polyaniline/graphene hybrid as a novel electrode material for electrochemical sensing

We demonstrate for the first time an interfacial polymerization method for the synthesis of high-quality polyaniline-modified graphene nanosheets (PANI/GNs), which represents a novel type of graphene/polymer heterostructure. The interfacial polymerization at a liquid-liquid interface allows PANI to grow uniformly on the surface of the GNs. An ultra-high loading of Pt nanoparticles was then controllably deposited on the surface of the PANI/GNs to form a Pt/PANI/GNs hybrid. The obtained composites were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The Pt/PANI/GNs hybrid shows excellent electrocatalytic activity toward methanol oxidation and oxygen reduction. H(2)O(2) and glucose were used as two representative analytes to demonstrate the sensing performance of a Pt/PANI/GNs-modified electrode. It is found that this sensing element shows high sensitivity and a low detection limit for H(2)O(2) and glucose. The results demonstrate that the Pt/PANI/GNs hybrid may be an attractive and advanced electrode material with potential applications in the construction of electrochemical sensors and biosensors.     

Functionalized carbon nanotubes as sensitive materials for electrochemical detection of ultra-trace 2,4,6-trinitrotoluene

This report demonstrates a novel electrochemical method for fast and sensitive detection of ultra-trace 2,4,6-trinitrotoluene (TNT) based on modified electrodes by functionalized MWCNTs. To fabricate new kind of functionalized MWCNTs material sensitive to TNT, our work first theoretically investigated the interaction between triphenylene (TP) and TNT by calculating their electrostatic potentials, and secondly characterized this interaction by the fluorescence spectra. The functionalized MWCNTs of TP-MWCNTs were thoroughly characterized by fluorescence and UV-visible spectra, and by analysing these results, the interaction between TP and MWCNTs was also examined. Electrochemical experiment suggests, compared to MWCNTs- and TP- modified electrodes, TP-MWCNTs-modified electrodes result in both fast response and enhanced sensitivity to TNT detection. These results show the attachment of TP on MWCNTs leads to better sensing unit with more receptor site to TNT, associated with the coordinative recognition of TP and MWCNTs to TNT, finally result in the improvement of response and sensitivity. And this improved recognition process is attributed to the geometric and electrostatic complementarity between TP and TNT. The present study demonstrates TP-MWCNTs-modified electrode holds promising and important implications for the detection of ultra-trace TNT.     

Evaluation of polyketones with N-cyclic structure as electrode material for electrochemical energy storage: case of pyromellitic diimide dilithium salt

Pyromellitic diimide dilithium salt was selected to complete our database on redox-active polyketones with a N-cyclic structure. Although never reported to date, such a lithiated salt was readily synthesized making its electrochemical evaluation in a Li battery possible. Preliminary data show that this novel material reversibly inserts two Li per formula unit at a relatively low potential giving a stable capacity value of 200 mAh g(-1).     

Functionalized polypyrrole nanotube arrays as electrochemical biosensor for the determination of copper ions

A novel electrochemical biosensor based on functionalized polypyrrole (PPy) nanotube arrays modified with a tripeptide (Gly-Gly-His) proved to be highly effective for electrochemical analysis of copper ions (Cu²⁺). The vertically oriented PPy nanotube arrays were electropolymerized by using modified zinc oxide (ZnO) nanowire arrays as templates which were electrodeposited on indium–tin oxide (ITO) coated glass substrates. The electrodes were functionalized by appending pyrrole-α-carboxylic acid onto the surface of polypyrrole nanotube arrays by electrochemical polymerization. The carboxylic groups of the polymer were covalently coupled with the amine groups of the tripeptide, and its structural features were confirmed by attenuated total reflection infrared (ATR-IR) spectroscopy. The tripeptide modified PPy nanotube arrays electrode was used for the electrochemical analysis of various trace copper ions by square wave voltammetry. The electrode was found to be highly sensitive and selective to Cu²⁺ in the range of 0.1–30 μM. Furthermore, the developed biosensor exhibited a high stability and reproducibility, despite the repeated use of the biosensor electrode.     

DMF-exfoliated graphene for electrochemical NADH detection

The electrochemical detection of NADH is of considerable interest because it is required as a cofactor in a large number of dehydrogenase-based biosensors. However, the presence of oxygenated functionalities on the electrode often causes fouling due to the adsorption of the oxidised form, NAD(+). Here we report an electroanalytical NADH sensor based on DMF-exfoliated graphene. The latter is shown to have a very low oxygen content, facilitating the exceptionally stable and sensitive detection of this important analyte.