rGO Electrode Research Articles

A Pyrene-Substituted Tris(bipyridine)osmium(II) Complex as a Versatile Redox Probe for Characterizing and Functionalizing Carbon Nanotube- and Graphene-Based Electrodes

We report the functionalization of nanostructured graphene-based electrode with an original (bis(2,2'-bipyridine)(4,4'-bis(4-pyrenyl-1-ylbutyloxy)-2,2'-bipyridine]osmium(II) hexafluorophosphate complex bearing pyrene groups. Graphene oxide (GO) and chemically reduced graphene oxide (c-RGO) paper electrodes were prepared by the flow-directed filtration method. After film transfer via the soluble membrane technique, the homogeneous and stable GO electrode was electrochemically reduced in water to achieve electrochemically reduced graphene oxide (e-RGO) film on the electrode. The electrochemical properties of GO, c-RGO, and e-RGO electrodes were characterized by scanning electron microscopy and electrochemistry. Cyclic voltammetry of the Ru(NH3)6(2+/3+) redox probe underlines the important influence of the RGO preparation method on electrochemical properties. We finally achieved the flexible functionalization of graphene-based electrodes using either supramolecular binding of the Os(II) complex bearing pyrene groups or its electropolymerization via the irreversible oxidation of pyrene. The properties of these functionalized graphene paper electrodes were compared to glassy carbon (GC) and multiwalled carbon nanotube (MWCNT) electrodes. Thanks to its divalent binding sites, the Os(II) complex constitutes a useful tool to probe the π-extended graphitic surface of RGO and MWCNT films. The Os(II) complex interacts strongly via noncovalent π-π interactions, with π-extended graphene planes, thus acting as a marker to quantify the electroactive surface of both MWCNT and RGO electrodes and to illustrate their ease of functionalization.

Manganese oxide nanorod–graphene/vanadium oxide nanowire–graphene binder-free paper electrodes for metal oxide hybrid supercapacitors

In this study MnO2 nanorodes (MNR) were fabricated on reduced graphene oxide (rGO) sheets using a facile hydrothermal synthesis route. As prepared binder free MNR-rGO electrodes exhibited promising electrochemical performance. A similar approach was employed to prepare V2O5 nanowire (VNW) on rGO electrodes as anodes for supercapacitor applications. The VNW-rGO anode and MNR-rGO cathode were combined to form a novel hybrid supercapacitor. The hybrid supercapacitor exhibited excellent electrochemical performance reflecting the synergistic effect of combining the MNR-rGO electrode and VNW-rGO electrode. This novel hybrid supercapacitor delivered an energy density of ~15Wh/kg with a specific capacitance of 36.9F/g. These results suggest that the binder free flexible MNR-rGO electrode is a promising cathode material for asymmetric supercapacitors and also for hybrid devices, which incorporate metal oxide anodes.

High power density microbial fuel cell with flexible 3D graphene–nickel foam as anode

The structure and electrical conductivity of anode play a significant role in the power generation of microbial fuel cells (MFCs). In this study, we developed a three-dimensional (3D) reduced graphene oxide-nickel (denoted as rGO-Ni) foam as an anode for MFC through controlled deposition of rGO sheets onto the nickel foam substrate. The loading amount of rGO sheets and electrode surface area can be controlled by the number of rGO loading cycles. 3D rGO-Ni foam anode provides not only a large accessible surface area for microbial colonization and electron mediators, but also a uniform macro-porous scaffold for effective mass diffusion of the culture medium. Significantly, at a steady state of the power generation, the MFC device with flexible rGO-Ni electrodes produced an optimal volumetric power density of 661 W m(-3) calculated based on the volume of anode material, or 27 W m(-3) based on the volume of the anode chamber. These values are substantially higher than that of plain nickel foam, and other conventional carbon based electrodes (e.g., carbon cloth, carbon felt, and carbon paper) measured in the same conditions. To our knowledge, this is the highest volumetric power density reported for mL-scale MFC device with a pure strain of Shewanella oneidensis MR-1. We also demonstrated that the MFC device can be operated effectively in a batch-mode at least for a week. These new 3D rGO-Ni electrodes show great promise for improving the power generation of MFC devices.

Synthesis of carbon coated Li3V2(PO4)3/reduced graphene oxide composite for high-performance lithium ion batteries

The carbon coated Li3V2(PO4)3/reduced graphene oxide (LVP@C/rGO) composite is successfully synthesized by a conventional solid-state reaction, which is easily scaled up. LVP grains coated with a thin layer (∼8nm) of carbon are adhered to the surface of the rGO layer and/or enwrapped into the rGO sheets, which can facilitate the fast charge transfer within the whole electrode and to the current collector. As a cathode material, the LVP@C/rGO electrode delivers an initial discharge capacity of 177mAhg−1 at 0.5C with capacity retention of 96% during the 50th cycle in a wide voltage range of 3.0–4.8V. A superior rate capability is also achieved, e.g., exhibiting a discharge capacity of 96mAhg−1 at a high C rate of 10C.

Electrically tunable organic bioelectronics for spatial and temporal manipulation of neuron-like pheochromocytoma (PC-12) cells

BackgroundOrganic bioelectronic devices consisting of alternating poly(3,4-ethylenedioxythiophene) (PEDOT) and reduced graphite oxide (rGO) striped microelectrode arrays were fabricated by lithography technology. It has been demonstrated that the organic bioelectronic devices can be used to spatially and temporally manipulate the location and proliferation of the neuron-like pheochromocytoma cells (PC-12 cells). MethodsBy coating an electrically labile contact repulsion layer of poly(l-lysine-graft-ethylene glycol) (PLL-g-PEG) on the PEDOT electrode, the location and polarity of the PC-12 cells were confined to the rGO electrodes. ResultsThe outgrowth of spatially confined bipolar neurites was found to align along the direction of the 20μm wide electrode. The location of the PC-12 cells can also be manipulated temporally by applying electrical stimulation during the neurite differentiation of PC-12 cells, allowing the PC-12 cells to cross over the boundary between the PEDOT and the rGO regions and construct neurite networks in an unconfined manner where the contact repulsive coating of PLL-g-PEG was removed. ConclusionsThis adsorption and desorption of the PLL-g-PEG without and with electrical stimulation can be attributed to the tunable surface properties of the PEDOT microelectrodes, whose surface charge can switch from being negative to positive under electrical stimulation. General significanceThe electrically tunable organic bioelectronics reported here could potentially be applied to tissue engineering related to the development and regeneration of mammalian nervous systems. The spatial and temporal control in this device would also be used to study the synapse junctions of neuron–neuron contacts in both time and space domains. This article is part of a Special Issue entitled Organic Bioelectronics — Novel Applications in Biomedicine.

A reduced graphene oxide based electrochemical biosensor for tyrosine detection

In this paper, a ‘green’ and safe hydrothermal method has been used to reduce graphene oxide and produce hemin modified graphene nanosheet (HGN) based electrochemical biosensors for the determination of l-tyrosine levels. The as-fabricated HGN biosensors were characterized by UV–visible absorption spectra, fluorescence spectra, Fourier transform infrared spectroscopy (FTIR) spectra and thermogravimetric analysis (TGA). The experimental results indicated that hemin was successfully immobilized on the reduced graphene oxide nanosheet (rGO) through π–π interaction. TEM images and EDX results further confirmed the attachment of hemin on the rGO nanosheet. Cyclic voltammetry tests were carried out for the bare glass carbon electrode (GCE), the rGO electrode (rGO/GCE), and the hemin–rGO electrode (HGN/GCE). The HGN/GCE based biosensor exhibits a tyrosine detection linear range from 5 × 10−7 M to 2 × 10−5 M with a detection limitation of 7.5 × 10−8 M at a signal-to-noise ratio of 3. The sensitivity of this biosensor is 133 times higher than that of the bare GCE. In comparison with other works, electroactive biosensors are easily fabricated, easily controlled and cost-effective. Moreover, the hemin–rGO based biosensors demonstrate higher stability, a broader detection linear range and better detection sensitivity. Study of the oxidation scheme reveals that the rGO enhances the electron transfer between the electrode and the hemin, and the existence of hemin groups effectively electrocatalyzes the oxidation of tyrosine. This study contributes to a widespread clinical application of nanomaterial based biosensor devices with a broader detection linear range, improved stability, enhanced sensitivity and reduced costs.

One-step synthesis of Pt nanoparticles/reduced graphene oxide composite with enhanced electrochemical catalytic activity

A one-step electrochemical approach for synthesis of Pt nanoparticles/reduced graphene oxide (Pt/RGO) was demonstrated. Graphene oxide (GO) and chloroplatinic acid were reduced to RGO and Pt nanoparticles (Pt NPs) simultaneously, and Pt/RGO composite was deposited on the fluorine doped SnO2 glass during the electrochemical reduction. The Pt/RGO composite was characterized by field emission-scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy, which confirmed the reduction of GO and chloroplatinic acid and the formation of Pt/RGO composite. In comparison with Pt NPs and RGO electrodes obtained by the same method, results of cyclic voltammetry and electrochemical impedance spectroscopy measurements showed that the composite electrode had higher catalytic activity and charge transfer rate. In addition, the composite electrode had proved to have better performance in DSSCs than the Pt NPs electrode, which showed the potential application in energy conversion.

Alkaline deoxygenated graphene oxide for supercapacitor applications: An effective green alternative for chemically reduced graphene

Graphene is a promising electrode material for energy storage applications. The most successful method for preparing graphene from graphite involves the oxidation of graphite to graphene oxide (GO) and reduction back to graphene. Even though different chemical and thermal methods have been developed to reduce GO to graphene, the use of less toxic materials to generate graphene still remains a challenge. In this study we developed a facile one-pot synthesis of deoxygenated graphene (hGO) via alkaline hydrothermal process, which exhibits similar properties to the graphene obtained via hydrazine reduction (i.e. the same degree of deoxygenation found in hydrazine reduced GO). Moreover, the hGO formed freestanding, binder-free paper electrodes for supercapacitors. Coin cell type (CR2032) symmetric supercapacitors were assembled using the hGO electrodes. Electrochemical characterization of hGO was carried out using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and ethylmethylimidazolium bis-(trifluoromethanesulfonyl)imide (EMITFSI) electrolytes. The results for the hGO electrodes were compared with the hydrazine reduced GO (rGO) electrode. The hGO electrode exhibits a energy density of 20 W h kg−1 and 50 W h kg−1 in LiTFSI and EMITFSI respectively, while delivering a maximum power density of 11 kW kg−1 and 14.7 kW kg−1 in LiTFSI and EMITFSI, respectively.

Reduction of graphene oxide by an in-situ photoelectrochemical method in a dye-sensitized solar cell assembly

Reduction of graphene oxide [GO] has been achieved by an in-situ photoelectrochemical method in a dye-sensitized solar cell [DSSC] assembly, in which the semiconductor behavior of the reduced graphene oxide [RGO] is controllable. GO and RGO were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, high-resolution transmission electron microscope, and Fourier-transform infrared spectroscopy. It was found that the GO film, which assembled in the DSSC assembly as the counter electrode, was partly reduced. An optimized photoelectrochemical assembly is promising for modulating the reduction degree of RGO and controlling the band structure of the resulting RGO. Moreover, this method appeared to be a green progress for the production of RGO electrodes.

Étude par imagerie radioisotopique du dépôt facial d’un aérosol nébulisé par masque

Graphene-based materials have shown significant potential for biomedical applications including biosensors, cell scaffolds and drug delivery. However, the interaction of complex biomacromolecules like proteins with graphene and its derivatives, graphene oxide (GO) and reduced (r)GO, remains poorly understood. Here, we demonstrate that the quartz-crystal microbalance with dissipation monitoring (QCM-D) technique can be used to systematically study the interaction dynamics of a typical protein, bovine serum albumin (BSA), with graphene materials of varying degrees of functionalisation. We find significant differences in molecular orientation and confirmation, mass adsorption and biochemical functionality of BSA on different graphene surfaces, determined by both the population of functional groups of GO and the protein concentration. The dominant forces during the adsorption of biomolecules onto GO and rGO are shown to be hydrophilic and hydrophobic interactions, respectively. The GO surface yielded higher BSA adsorption than both rGO and control standard gold electrodes due to the high density of functional groups. The biochemical functionality of adsorbed BSA was investigated through the interaction with its anti-BSA antibody counterpart. BSA on GO can retain its binding sites while, in contrast, a denatured ad-layer of BSA forms on the rGO followed by further binding of active BSA molecules, depending on the concentration of the protein. Intermediate conformations are observed for partially-reduced GO. These results also suggest that QCM-D is a viable readout technique for graphene-based biosensors. This QCM-D approach could be further extended to study the interaction of a host of biomolecules and their assemblies, including whole cells, with 2-dimensional materials.

Facile Patterning of Reduced Graphene Oxide Film into Microelectrode Array for Highly Sensitive Sensing

In this study, we develop a new technique to fabricate a reduced graphene oxide (rGO)-based microelectrode array (MEA) with low-cost soft lithography. To prepare patterned rGO, a polydimethylsiloxane (PDMS) mold with an array of microwells on its surface is fabricated using soft lithography, and GO is assembled on an indium tin oxide (ITO) electrode with a layer-by-layer method. The rGO pattern is formed by closely contacting the assembled GO film onto the ITO electrode with the PDMS mold filled with hydrazine solution in the microwells to selectively reduce the localized GO into the rGO. The MEA with patterned rGO as the microelectrode is characterized with Kelvin probe force microscopy (KFM), atomic force microscopy (AFM), and cyclic voltammetry (CV) with ferricyanide in aqueous solution as the redox probe. The KFM and AFM results demonstrate that each rGO pattern prepared under the present conditions is 3 μm in diameter, which is close to that of the PDMS mold we use. The CV results show that the rGO patterned onto the ITO exhibits a sigmoid-shaped voltammogram up to 200 mVs(-1) with a microampere level current response, suggesting that the rGO-based electrode fabricated with soft lithography behalves like a MEA. To demonstrate the potential electroanalytical application of the rGO-based MEA, prussian blue (PB) is electrodeposited onto the rGO-based MEA to form the PB/rGO-based MEA. Electrochemical studies on the formed PB/rGO-based MEA reveal that MEA shows a lower detection limit and a larger current density for the detection of H(2)O(2), as compared with the macroscopic rGO electrode. The method demonstrated here provides a simple and low-cost strategy for the fabrication of graphene-based MEA that are useful for electroanalytical applications.

Nucleation Mechanism of Electrochemical Deposition of Cu on Reduced Graphene Oxide Electrodes

The nucleation mechanism of electrochemical deposition of Cu on reduced graphene oxide (rGO) electrodes has been systematically studied on the basis of the cyclic voltammetry, Tafel plot, and chronoamperometry. Our results show that the experimental parameters including electrolyte concentration, deposition potential, solution pH, and the presence of background electrolyte can determine the nucleation mechanism. Scanning electron microscopy is employed to study the nucleation and growth of Cu on rGO electrodes. This study is significant in development of the electrochemical method in practical applications based on the rGO electrodes.

Transparent, Flexible, All-Reduced Graphene Oxide Thin Film Transistors

Owing to their unique thickness-dependent electronic properties, together with perfect flexibility and transparency, graphene and its relatives make fantastic material for use in both active channel and electrodes in various electronic devices. On the other hand, the electronic sensors based on graphene show high potential in detection of both chemical and biological species with high sensitivity. In this contribution, we report the fabrication of all-reduced graphene oxide (rGO) thin film transistors by a combination of solution-processed rGO electrodes with a micropatterned rGO channel, and then study their applications in biosensing. Our all-rGO devices are cost-effective, highly reproducible, and reliable. The fabricated electronic sensor is perfectly flexible with high transparency, showing good sensitivity in detecting proteins in the physiological buffer. As a proof of concept, fibronectin as low as 0.5 nM was successfully detected, which is comparable with the previously reported protein sensors based on single-layer pristine graphene obtained from mechanical cleavage. The specific detection of avidin by using biotinylated all-rGO sensor is also successfully demonstrated.

Label-free, electrochemical detection of methicillin-resistant staphylococcus aureus DNA with reduced graphene oxide-modified electrodes

Reduced graphene oxide (rGO)-modified glassy carbon electrode is used to detect the methicillin-resistant Staphylococcus aureus (MRSA) DNA by using electrochemical impedance spectroscopy. Our experiments confirm that ssDNA, before and after hybridization with target DNA, are successfully anchored on the rGO surface. After the probe DNA, pre-adsorbed on rGO electrode, hybridizes with target DNA, the measured impedance increases dramatically. It provides a new method to detect DNA with high sensitivity (10 −13 M, i.e., 100 fM) and selectivity.

Electrochemical deposition of Cl-doped n-type Cu2O on reduced graphene oxide electrodes

Reduced graphene oxide (rGO) electrodes can be applied for the electrochemical deposition of various semiconductor oxides. In this study, we demonstrate the electrochemical deposition of Cl-doped n-type Cu2O (Cl–Cu2O) on rGO electrodes. The structure and properties of the deposited Cl–Cu2O have been investigated extensively. Moreover, the effect of Cl doping on the carrier concentration and photocurrent of Cl–Cu2O has also been investigated. Our study shows significant implications in tailoring the properties of materials deposited on rGO electrodes by using electrochemical methods.

High-Performance Supercapacitors Based on Poly(ionic liquid)-Modified Graphene Electrodes

We report a high-performance supercapacitor incorporating a poly(ionic liquid)-modified reduced graphene oxide (PIL:RG-O) electrode and an ionic liquid (IL) electrolyte (specifically, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide or EMIM-NTf(2)). PIL:RG-O provides enhanced compatibility with the IL electrolyte, thereby increasing the effective electrode surface area accessible to electrolyte ions. The supercapacitor assembled with PIL:RG-O electrode and EMIM-NTf(2) electrolyte showed a stable electrochemical response up to 3.5 V operating voltage and was capable of yielding a maximum energy density of 6.5 W·h/kg with a power density of 2.4 kW/kg. These results demonstrate the potential of the PIL:RG-O material as an electrode in high-performance supercapacitors.

Organic Photovoltaic Devices Using Highly Flexible Reduced Graphene Oxide Films as Transparent Electrodes

The chemically reduced graphene oxide (rGO) was transferred onto polyethylene terephthalate (PET) substrates and then used as transparent and conductive electrodes for flexible organic photovoltaic (OPV) devices. The performance of the OPV devices mainly depends on the charge transport efficiency through rGO electrodes when the optical transmittance of rGO is above 65%. However, if the transmittance of rGO is less than 65%, the performance of the OPV device is dominated by the light transmission efficiency, that is, the transparency of rGO films. After the tensile strain (∼2.9%) was applied on the fabricated OPV device, it can sustain a thousand cycles of bending. Our work demonstrates the highly flexible property of rGO films, which provide the potential applications in flexible optoelectronics.

Bulk Heterojunction Polymer Memory Devices with Reduced Graphene Oxide as Electrodes

A unique device structure with a configuration of reduced graphene oxide (rGO) /P3HT:PCBM/Al has been designed for the polymer nonvolatile memory device. The current-voltage (I-V) characteristics of the fabricated device showed the electrical bistability with a write-once-read-many-times (WORM) memory effect. The memory device exhibits a high ON/OFF ratio (10(4)-10(5)) and low switching threshold voltage (0.5-1.2 V), which are dependent on the sheet resistance of rGO electrode. Our experimental results confirm that the carrier transport mechanisms in the OFF and ON states are dominated by the thermionic emission current and ohmic current, respectively. The polarization of PCBM domains and the localized internal electrical field formed among the adjacent domains are proposed to explain the electrical transition of the memory device.