Electrochemical Properties Of Graphene Research Articles

Effect of alkane adsorption on the electrochemical properties of graphene

The surface characteristics of graphene, such as hydrophilicity and adsorptivity, have clear impact on the surface charged state and the transport of electrons.

Fabrication of high-performance symmetric pseudocapacitor by synthesizing ionic liquid-modified graphene/MoS2 NS binary electrode

The combination of graphene with metal sulfides has always been getting attention from researchers due to the compatibility in their two-dimensional structure with active sites on their edges and their exceptional optical, magnetic, and physiochemical properties. Herein, we synthesize highly efficient pseudocapacitive electrode material using ionic liquid-modified graphene (IL-rGO) and ultrathin MoS2 nanosheets (MoS2 NS). The electrochemical properties of graphene were tuned by modifying its surface with green solvents such as ionic liquids. Modification of the graphene surface with IL increased the number of active sites at the edges, and provided a more compact arrangement to the graphene layers which enabled them to accommodate MoS2 NSs between them. Among the synthesized binary electrodes, 1.5 g IL-modified rGO loaded with 15 wt% of MoS2 NS electrode, the PIRM15 binary electrode, exhibits a high specific capacitance of 955 F/g. TEM micrographs of the PIRM15 electrode delineated the intercalation of MoS2 NSs between the graphene layers. The PIRM15 electrode displayed 93.7 % of pseudocapacitance and 6.7 % electrical double-layer capacitance. The symmetric pseudocapacitor integrated with the PIRM15 binary electrode possesses 97 % capacitance retention and 87 % coulombic efficiency at 0.008 A. The pseudocapacitor's calculated energy and power densities are 25 Wh/kg and 3333 W/kg at a current of 0.003 A and 0.05 A, respectively.

Plasma‐Based Synthesis of Freestanding Graphene from a Natural Resource for Sensing Application

AbstractAtmospheric pressure microwave plasma has the lead in synthesizing freestanding and scalable graphene within seconds without the need for high vacuum and temperature. However, the process is limited in utilizing chemical sources for synthesis, such as methane and ethanol. Herein, the usage of an extract of a sustainable precursor, that is, Melaleuca alternifolia, commonly known as tea tree, is for the first time reported to synthesize graphene nanosheets in atmospheric pressure microwave plasma. The synthesis is carried out in a single step at a remarkably low microwave power of 200 W. The morphology, structure, and electrochemical properties of graphene are studied using state‐of‐the‐art characterization techniques such as Raman spectroscopy, X‐ray diffraction, transmission electron microscopy (TEM) and electrochemical impedance spectroscopy. The TEM images reveal the presence of a combination of nanostructures such as nano‐horns, nano‐rods, or nano‐onions consisting of multi‐layer graphitic architectures. An excellent sensing capability of as‐synthesized graphene is demonstrated through the detection of diuron herbicide. A commendable linear range of 20 µm to 1 mm and a limit of detection of 5 µm of diuron is recorded.

Effect of Environmental Contaminants on the Interfacial Properties of Two-Dimensional Materials

ConspectusThe surface of 2D materials can spontaneously adsorb and react with molecules in the environment during their processing and storage. This effect, while having a significant impact on many properties of 2D materials, is not always recognized and accounted for in the research involving them. This Account summarizes our recent work in understanding how the ambient environment impacts the properties of 2D materials and its mitigation strategies. We highlight graphene and hydrocarbons in our discussion and complement it with selected studies involving other 2D materials as well as water and oxygen.When graphene and graphite are exposed to air and water, their surfaces adsorb the residue hydrocarbons, typically at part-per-trillion to part-per-billion levels, in the environment. The adsorption of hydrocarbons reduces the surface energy of graphene and graphite and creates a barrier between them and the electrolyte. As a result, the wettability and electrochemical properties of graphene and graphite can be significantly altered by mere exposure to the ambient environment. These changes can be very significant yet highly variable depending on the local environment: several hours of air exposure can increase the water contact angle of graphene by up to 40° and reduce the double-layer capacitance of graphite by up to 50%! The high hydrophobicity and poor electrochemical performance of pristine graphitic carbons, once believed to be intrinsic properties of these materials, are largely due to unintentional surface contamination. The same type of hydrocarbon adsorption was reported for many other 2D materials, such as MoS2, hexagonal BN, and mica. In the case of mica, which is highly ionic in nature, the adsorption of hydrocarbons disrupts its interaction with ionic liquid and alters the self-assembly structure of ionic liquid at the mica surface. Similarly, water also impacts the surface properties of graphene in several ways. Water vapor can compete with hydrocarbons for adsorption onto the surface of graphene, thus reducing the rate of hydrocarbon contamination. Water can intercalate between graphene and some of its supporting substrate, altering their interactions. Finally, water enhances the doping of 2D materials by O2 by promoting an electrochemical doping mechanism involving the O2/H2O redox couple.Reducing and reversing the surface contamination of 2D materials can greatly enhance material and device performances. While completely stopping the contamination is still challenging, a high-humidity environment is shown to reduce the rate of contamination, as mentioned above. For samples already contaminated by airborne hydrocarbons, their surface properties can be partially restored by treatment in high-vacuum, high-temperature, or mildly oxidative environments.

WAYS OF CHANGING THE STRUCTURAL-MORPHOLOGICAL, PHYSICO-CHEMICAL AND ELECT­RICAL PROPERTIES OF GRAPHENES

A literature analysis of sources on synthesis methods and their influence on the structural-morphological, physico-chemical, and electrochemical properties of graphene and graphene-like structures was carried out. It was established that these properties have a clear dependence on the synthesis method, starting materials, and the composition of the synthesis medium.
 The main ways of changing graphene's structural-morphological, physico-chemical and electrical properties are changes in the synthesis method and conditions that affect the formation of σ-bonds and π-bonds. The presence of these bonds regulates the number of graphene layers and the formation of van der Waals interactions between them, as well as the formation of edge structural defects responsible for electrokinetic and catalytic properties. Changing the gas medium to a liquid one greatly simplifies the synthesis of graphene. Still, in the case of a liquid nitrogen medium, simultaneously with a 2-dimensional structure, it is possible to form 3-dimensional particles up to tens of nanometers in size. Aqueous medium and plasma-arc synthesis methods are the most attractive for obtaining materials with electron-donor conductivity, which have attractive electrochemical and catalytic properties for use in chemical current sources and fuel cells. Using an aqueous environment requires mandatory further heat treatment at temperatures above 250 0C to se­parate chemisorbed water from the structure, which complicates the synthesis procedure. The advantage of the plasma-arc method for the synthesis of graphene and other carbon nanostructures is its ability to shorten the stages of the synthesis of graphene, the possibility of modifying them directly during the synthesis process by changing the environment, easy management, and obtaining a clean final pro­duct. In the modern practice, this method is limited to obtaining coatings on a solid carrier.

Physical and Electrochemical Properties of Graphene Decorated with ZnO Hollow Spheres for Supercapacitor Applications

Single-layer graphene-ZnO hollow sphere (SLG-ZnO(HS)) composites were successfully prepared through facile one-step solvothermal synthesis route. The morphological structures of the samples were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Hollow spheres consisting of ZnO nanoparticles with a diameter of approximately 30 nm are decorated to both sides of the SLG sheets. The electrochemical performances were tested by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance (EIS). The SLG-ZnO(HS) composite electrode synthesized at a concentration of 0.25 mM Zn precursor exhibited an enhanced specific capacitance of 34.7 F/g at a scan rate of 1 mV/s with energy and power densities of 5.39 W h/kg and 1.73 kW/kg, respectively.

A Brief Description of Cyclic Voltammetry Transducer-Based Non-Enzymatic Glucose Biosensor Using Synthesized Graphene Electrodes

The essential disadvantages of conventional glucose enzymatic biosensors such as high fabrication cost, poor stability of enzymes, pH value-dependent, and dedicated limitations, have been increasing the attraction of non-enzymatic glucose sensors research. Beneficially, patients with diabetes could use this type of sensor as a fourth-generation of glucose sensors with a very low cost and high performance. We demonstrate the most common acceptable transducer for a non-enzymatic glucose biosensor with a brief description of how it works. The review describes the utilization of graphene and its composites as new materials for high-performance non-enzymatic glucose biosensors. The electrochemical properties of graphene and the electrochemical characterization using the cyclic voltammetry (CV) technique of electrocatalysis electrodes towards glucose oxidation have been summarized. A recent synthesis method of the graphene-based electrodes for non-enzymatic glucose sensors have been introduced along with this study. Finally, the electrochemical properties such as linearity, sensitivity, and the limit of detection (LOD) for each sensor are introduced with a comparison with each other to figure out their strengths and weaknesses.

A Computational Study of Graphene as a Prospective Material for Microelectrodes in Retinal Prosthesis and Electric Crosstalk Analysis.

The computational model plays a vital role in the design and optimization of microelectrodes for efficient electrical stimulation and recording in the retinal prosthesis. Moreover, the material choice acts decisively in ensuring that the electronic device delivers sufficient stimulating current to the retina without harming the neighboring tissue. Recently, due to the enhanced electrical and electrochemical properties of graphene, it has become a viable material in biomedical applications. In this study, we analyzed the computational model for the retinal prosthesis by the novel use of graphene-based microelectrodes. For this, different topologies of the electrode arrangement were investigated. The most suitable configuration involves the arrangement of electrodes serving as the ground in a hexagonal fashion around the central stimulating electrode. We observed that the performance of graphene as the stimulating electrodes is comparable to the existing noble metal-based electrodes. Moreover, we found that optimizing the microelectrode design resulted in uniform electric potential distribution, and this eventually led to an increased electric field intensity at the desired activation point. Additionally, we analyzed the crosstalk phenomenon, and we observed from the results that it is better to implant such an electrode array in the vicinity of the targeted volume to minimize the effect of crosstalk.Clinical relevance- The present study can help in the improvement of the retinal prosthesis by analyzing the quantitative and qualitative effects of graphene-based microelectrodes on producing the threshold electric field in the retina tissue. The results obtained can be used to optimize the implantable microelectrode design and thus is a step forward in finding a cure to vision impairment diseases.

Promotion of the performance of nitrogen-doped graphene by secondary heteroatoms doping in energy transformation and storage

The depletion of conventional fossil fuel is one of the most serious problems nowadays. To develop new materials for efficient energy transformation or storage are great challenges for the researchers. Due to the unique two-dimensional structure, high surface area, excellent electrical conductivity, and easy modification, graphene (GR) has attracted great attention in the energy-related fields. It has been proved that doping with nitrogen can significantly enhance the electrochemical properties of GR. Recently, more researches have shown that modifying the nitrogen-doped GR (N-GR) further by introducing a second heteroatom, such as boron, sulfur, and phosphorus, greatly improved electrochemical properties which could be obtained compared with mono-nitrogen-doped GR. This should be originated from the redistributed surface charge and abundant active sites led by the synergistic co-doping effect. This review will focus on the synthesis of nitrogen and a second heteroatom co-doped GR for energy-related applications, including energy transformation and storage. The enhanced mechanism by adding the secondary heteroatoms will also be discussed. We expected that this review will provide enriched information to harvest the excellent special properties of dual-doped GR materials for solving the energy problems.

Synthesis of Boron‐Doped Graphene by Supercritical Fluid Processing and its Application in Symmetric Supercapacitors using Various Electrolytes

AbstractDoping of heteroatoms on graphene networks is an efficient way of modifying both, chemical and electrochemical properties of graphene. Here, the preparation of boron doped graphene was achieved by supercritical fluid processing using sodium tetraborate as a boron source. The phase purity, structure and surface morphology of all the prepared materials were characterised by XRD, Raman spectra, FE‐SEM and HR‐TEM. The presence of boron bearing functionalities and type of B‐doping are determined by FT‐IR spectroscopy and XPS, respectively. From the different weight combination of B‐source along with graphene oxide, the B‐doped graphene obtained from B‐source and graphene oxide are in 1 : 2 weight ratio showed an enhanced capacitive behaviour over reduced graphene oxide with an improved specific capacitance value of 270 F/g at 1 A/g and revealed a superior cycling stability of 93 % retention over 10000 cycles at 10 A/g. To appreciate the device performance, the full cell studies was performed in three different electrolytes and the energy density obtained using 1‐ethyl‐3‐methyl imidazolium tetrafluoroborate (EMIMBF4) as ionic liquid electrolyte is found to be 39.3 Wh/kg which is higher than both 20 % KOH solution (5.1 Wh/kg) and 1 M TEABF4 in acetonitrile (18.6 Wh/kg).

Investigation of cyclic voltammetry, impedance spectroscopy and electrical properties of thermally exfoliated biomass-synthesized graphene

In this paper we have reported the synthesis of graphene by a novel and facile thermal exfoliation process of Allium cepa (Onion) and was characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy to investigate the morphological and structural properties and chemical networks present on it. The AFM and SEM images revealed the formation of thin strip-like layered structure of graphene with the thickness of 1.1 nm. The electrochemical properties of graphene were characterized by cyclic voltammeter, impedance spectroscopy, Tafel plot, Nyquist plot, Bode plot, and voltage-dependent impedance using 0.5 M H2SO4 electrolyte as an illustrative standard material. The cyclic voltammetric curve of graphene electrodes determined a quasi-reversible electrochemical behavior under linear diffusion control square shape at higher process temperature. The ratio of atomic % C-to-O varied from 7.57 to 24.04 indicating a decrease in the oxygen content for the graphene processed at higher temperature. The areal capacitance and voltage-dependent impedance varied from 8.59 × 10− 5 to 18.8 × 10− 5 F/cm2 and 15.79 to 7.7 Ohm, respectively, with the process temperature varying from 600 to 1000 °C. The corrosion potential (Ecorr) and corrosion current density (Icorr) values are − 0.12 V and − 9.1A/cm2, respectively, for the graphene processed at 1000 °C.

Synthesis of CoFe2O4/graphene composite as a novel counter electrode for high performance dye-sensitized solar cells

A novel nanocomposite of CoFe2O4 nanoparticles with graphene nanosheet (CoFe2O4/GN) is prepared as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). The size of CoFe2O4 nanoparticles is about 3 nm, and the influence of CoFe2O4 on the electrochemical properties of graphene is studied. The CoFe2O4 nanoparticles anchored on graphene nanosheets can serve as spacers to prevent graphene aggregations and thereby provide efficient diffusion pathways and more active surface area for electrolyte molecules. Also, the CoFe2O4 nanoparticles with substantial catalytic activity accelerate the reduction of triiodide. Meanwhile the graphene improves charge transfer during the catalytic process. Compared with CoFe2O4, graphene, and Pt electrodes, the CoFe2O4/GN electrode displays higher catalytic activity because of its minimal charge transfer resistance. The DSSCs fabricated with CoFe2O4/GN demonstrate an improved photoelectric conversion efficiency of 9.04% in comparison to Pt electrodes (6.54%). This study suggests that CoFe2O4/GN can replace expensive Pt electrodes for large-scale fabrication of low cost and high efficiency DSSCs.

Effect of uniaxial stress on the electrochemical properties of graphene with point defects

We report a calculational study of electron states and the resulting electrochemical properties of uniaxially strained graphene with point defects. For this study the reduction of ferricyanide to ferrocyanide serves as a benchmark electrochemical reaction. We find that the heterogeneous electron transfer activity of the perfect graphene electrode rises under uniaxial strain. However, evolution of the cathodic reaction rate depends on the direction of strain. For moderate lattice deformations, the zigzag strain improves electrochemical performance better than the armchair strain. Standard rate constant increases by 50% at the zigzag strain of 10%. Vacancies, covalently bonded moieties, charged adatoms and substitutional impurities in the zigzag strained graphene induce changes in the shape of the curve of the cathodic reaction rate. However, this changes do not translate into the electrocatalytic activity. Vacancies and covalently bonded moieties at concentration of 0.1% do not affect the electrochemical performance. Charged adatoms and substitutional impurities give a slight increase in the standard rate constant by, respectively, 2.2% and 3.4%.

Synthesis of Multifunctional Electrically Tunable Fluorine-Doped Reduced Graphene Oxide at Low Temperatures.

Doping with heteroatoms is a well-established method to tune the electronic properties and surface chemistry of graphene. Herein, we demonstrate the synthesis of a fluorine-doped reduced graphene oxide (FrGO) at low temperatures that offers multiple opportunities in applied fields. The as-synthesized FrGO product shows a better electrical conductivity of 750 S m-1 than that of undoped rGO with an electrical conductivity of 195 S m-1. To demonstrate the multifunctional applications of the as-synthesized FrGO, it was examined for electromagnetic interference shielding and electrochemical sensing of histamine as an important food biomarker. A laminate of FrGO delivered an EMI shielding effectiveness value of 22 dB in Ku band as compared with 11.2 dB for an rGO laminate with similar thickness. On the other hand, an FrGO modified sensor offered an excellent sensitivity (∼7 nM), wide detection range, and good selectivity in the presence of similar biomarkers. This performance originates from the better catalytic ability of FrGO as compared with rGO, where fluorine atoms play the role of catalytic active sites owing to their high electronegativity. The fluorination reaction also helps to improve the reduction degree of the chemically synthesized graphene, consequently enhancing the electrical conductivity, which is a prime requirement for increasing the electromagnetic and electrochemical properties of graphene.

Electrochemical Properties of Graphene Oxide/Resol Composites as Electrode Materials for Supercapacitor Applications.

RGO/Resol carbon composites were prepared from a mixture of reduced GO and a low-molecular-weight phenolic resin (Resol) solution. The effects of the calcination temperature, amount of Resol added and KOH treatment on the electrochemical performance of the RGO/Resol composites were investigated. The physical and electrochemical properties of the composite materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer, Emmett and Teller (BET) surface areas measurements, and cyclic voltammetry (CV). The relationships between their physical properties and their electrochemical performance were examined for use as super-capacitors (SCs). The RGO/Resol composite calcined at 400 degrees C after the KOH loading showed dramatically improved electrochemical properties, showing a high BET surface and capacitance of 2190 m2/g and 220 F/g, respectively. The RGO/Resol composites calcined after the KOH treatment showed much better capacitor performance than those treated only thermally at the same temperature without KOH impregnation. The fabrication of high surface electrodes was essential for improving the SCs properties.

On adatomic-configuration-mediated correlation between electrotransport and electrochemical properties of graphene

The electron-transport properties of adatom–graphene system are investigated for different spatial configurations of adsorbed atoms: when they are randomly-, correlatively-, or orderly-distributed over different types of high symmetry sites with various adsorption heights. The results are obtained numerically using the quantum-mechanical Kubo–Greenwood formalism. A band gap may be opened only if ordered adatoms act as substitutional atoms, while there is no band gap opening for adatoms acting as interstitial atoms. The type of adsorption sites strongly affect the conductivity for random and correlated adatoms, but practically does not change the conductivity when they form ordered superstructures with equal periods. Depending on electron density and type of adsorption sites, the conductivity for correlated and ordered adatoms is found to be enhanced in dozens of times as compared to the cases of their random positions. The correlation and ordering effects manifest weaker or stronger depending on whether adatoms act as substitutional or interstitial atoms. The conductivity approximately linearly scales with adsorption height of random or correlated adatoms, but remains practically unchanged with adequate varying of elevation of ordered adatoms. Correlations between electron transport properties and heterogeneous electron transfer kinetics through potassium-doped graphene and electrolyte interface are investigated as well.

Supercapacitors based on ternary nanocomposite of TiO2&Pt@graphenes

The electrochemical properties of graphene can be significantly enhanced due to the incorporating of hetero-atoms into the graphene. In this article Crumpled-like TiO2–Pt/graphene nanocomposite from graphene oxide (GO), titanium (III) chloride (TiCl3) and Hydrogen hexa chloro palatinate (H2PtCl6) was synthesized via a simple reflux strategy and employed as a simple capacitor electrode material. The nanocomposite was characterized by XRD, XPS, FESEM, HRTEM and the electrochemical properties were investigated by cyclic voltammetry (CV). Electrochemical characterization for introduced nanocomposite indicated that the corresponding specific capacitance is 160 F/g (at 5 mV/s) with good stability. The high electrochemical performance is recognized to the presence of Pt nanoparticles on the nanocomposite and graphene distinct characteristics. To the best of our knowledge this is the first report on TiO2–Pt/graphene nanocomposite as an electrical double layer capacitor material.

Sub-20 nm anatase particles uniformly anchored on graphene oxide and reduced graphene oxide nanosheets and their photocatalytic oxidation and Li-ion storage capabilities

Nanosized anatase TiO2 particles anchored on nanocarbon substrates have great potential for practical applications in high-performance lithium ion batteries and efficient photocatalysts. The synthesis of this material usually utilizes calcination to crystallize amorphous titania, which normally causes the formation of aggregates and some side effects. In this work, we demonstrated that sub-20nm anatase particles uniformly anchored on graphene oxide and reduced graphene oxide nanosheets in aqueous solution at a temperature of 90°C and atmospheric pressure, without further calcination. The photocatalytic oxidation activity and electrochemical properties of graphene oxide/anatase TiO2 (GO/A) and reduced graphene oxide/anatase TiO2 (RGO/A) were comparatively investigated. We found that GO/A showed higher photocatalytic oxidation activity than RGO/A under UV light irradiation. Graphene oxide accepted electrons and suffered reduction, which finally decreased GO/A’s photocatalytic oxidation activity to an extent similar to RGO/A. We also found that, as anode material for Li-ion battery, the specific capacity of RGO/A was nearly three times that of GO/A at the same current rate. This study will inspire better design of metal oxide/nanocarbon nanocomposites for high performance lithium ion battery and photocatalysis applications.

Mesomeric Effects of Graphene Modified with Diazonium Salts: Substituent Type and Position Influence its Properties.

In the last decade, graphene and graphene derivatives have become some of the most intensively studied materials. Tuning of the electronic and electrochemical properties of graphene is of paramount importance. In this study, six diazonium-modified graphenes containing different functional groups according to the diazonium salt precursor were investigated. These diazonium moieties have a strong mesomeric (resonance) effect and act as either electron-donating or -withdrawing species. Different graphene precursors, such as thermally and chemically reduced graphenes were studied. All the products were characterized in detail by elemental combustion analysis, FTIR spectroscopy, Raman spectroscopy, high-resolution X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry. Resistivity and zeta potential measurements were consistent with theoretical (DFT) calculations. The results show that chemical modification of graphene by diazotation strongly influences its properties, creating a huge application potential in microelectronics, energy storage and conversion devices, and electrocatalysis.

Residual metallic contamination of transferred chemical vapor deposited graphene.

Integration of graphene with Si microelectronics is very appealing by offering a potentially broad range of new functionalities. New materials to be integrated with the Si platform must conform to stringent purity standards. Here, we investigate graphene layers grown on copper foils by chemical vapor deposition and transferred to silicon wafers by wet etching and electrochemical delamination methods with respect to residual submonolayer metallic contaminations. Regardless of the transfer method and associated cleaning scheme, time-of-flight secondary ion mass spectrometry and total reflection X-ray fluorescence measurements indicate that the graphene sheets are contaminated with residual metals (copper, iron) with a concentration exceeding 10(13) atoms/cm(2). These metal impurities appear to be partially mobile upon thermal treatment, as shown by depth profiling and reduction of the minority charge carrier diffusion length in the silicon substrate. As residual metallic impurities can significantly alter electronic and electrochemical properties of graphene and can severely impede the process of integration with silicon microelectronics, these results reveal that further progress in synthesis, handling, and cleaning of graphene is required to advance electronic and optoelectronic applications.