rGO Film Research Articles

A graphene-covalent organic framework hybrid for high-performance supercapacitors

Due to strong van der Waals interactions, graphene nanosheets stack together, resulting in inefficient charge storage, which significantly compromises their performance as electrodes in supercapacitors. Herein, we design a hybrid material by interacting covalent organic frameworks (COFs) into reduced graphene oxide (rGO) films or fibers. The 2D COF nanosheets contain abundant mesopores, which prevents the stacking of rGO nanosheets, enabling the efficient electrolyte ion mass transfer. The optimal COF/rGO hybrid delivers a high gravimetric specific capacitance of 321 ​F ​g−1 and volumetric specific capacitance of 237 ​F ​cm−3 in an aqueous electrolyte measured in the three-electrode configuration, representing a breakthrough in capacitive graphene electrodes. Consequently, the fabricated 2D thin-film and 1D fiber supercapacitors deliver a high device energy density of 10.3 ​Wh kg−1 or 7.9 ​mWh cm−3 in aqueous and gel electrolytes, respectively. Moreover, an ultrahigh stack energy density of 87 ​Wh L−1 ​at the power density of 638 ​W ​L−1 is achieved using an ionic liquid electrolyte, which is superior to most of the carbon-based supercapacitors reported so far, as well as commercial lead-acid and lithium thin-film batteries. Overall, this study demonstrates 2D COFs as a critical enabler to realize high-performance graphene supercapacitors. 2D COFs also have the potential to enable unique architectures for many other 2D materials.

Functionalized reduced graphene oxide with aptamer macroarray for cancer cell capture and fluorescence detection.

Anintegrated aptamer macroarray functionalized with reduced graphene oxide (rGO) to specifically capture and sensitively detect cancer cellsis reported. The capture for cancer cells is based on effective recognition of the modified rGO surface through theaptamer against epithelial cell adhesion molecule (EpCAM). The rough structure of rGO enhances morphologic interactions between rGO film interface and the cancer cells, while super-hydrophilicity of modified rGO hinders nonspecific cell capture. The synergistic interactions offer the aptamer macroarray high efficiency of cancer cell capture. By means of a turn-on fluorescence strategy based on the conformation change of theaptamer induced by the target recognition, the enriched cancer cells can be directly read out at excitation/emission wavelengths of 550/680nm without washing, separation, and dying steps. The working range is1 × 102 to 2 × 104 cells per mL with a detection limit of 22 cells per mL. The results indicate that the aptamer macroarray has a considerable foreground for early diagnosis, therapy, and monitoring of cancer. Graphical abstract.

Si nanoparticles veiled with ultrathin rGO film reduced directly by precoated Ni template: Fabrication and electrochemical performance

Si/graphene composite has been considered as a promising structure to limit the volume expansion and improve poor conductivity of silicon anode. Herein, a novel method to prepare Si/reduced graphene oxide (Si/rGO) composite anode was proposed. With this approach, nickel shell was pre-coated on Si particles via electroless deposition before used as a template to in-situ reduce GO. During the reduction process, the nickel template can as well promote the self-assembly of graphene sheets on the surface of Si nanoparticles. Following these facile and convenient processes, a Si/rGO hybrid-structure can be directly fabricated. Compared with pure Si anode, this Si/rGO composite displays a greatly improved electrochemical performance in both cycling stability and rate capability. It delivers a reversible capacity as high as 975 mA h g−1 and 717 mA h g−1 after 300 cycles under the current densities of 1 A g−1 and 3 A g−1, respectively. Meanwhile, its capacity can still maintain at 602 mA h g−1 even at a rather higher current of 5 A g−1.

Electrochemically deposited graphene oxide thin film supercapacitors: Comparing liquid and solid electrolytes

In the present work, graphene oxide (GO) thin films were prepared on ITO substrates by electrochemical deposition for different voltages and deposition times and were further electrochemically reduced by cyclic voltammetry (CV). Reduced GO films (rGO) were used in the manufacturing of supercapacitors with solid-state electrolyte based on a freeze-thawed PVA-Na2SO4 hydrogel. GO and rGO films were tested using SEM, XRD, RAMAN and XPS techniques for comparative reasons. The specific capacitance of the electrodes and supercapacitors were estimated by electrochemical methods. XRD analysis revealed increase of the rGO interlayer spacing after multiple CV cycles that was assigned to incorporation of the electrolytic agents such as sodium ions of the electrolyte. Raman spectra showed that the ID/IG ratio associated with the graphene matrix defects remained fairly constant even after several CV cycles, meaning that no new defects were added. It was the XPS analysis that confirmed the reduction of GO to rGO as well as the presence of sodium in the rGO films. The optimum value of the electrode capacitance of the constructed model supercapacitor with thin rGO films and PVA-20%Na2SO4 electrolyte was 8.55 mF/cm2 that approaches the electrode capacitance value of 10.67 mF/cm2 measured with liquid Na2SO4 electrolyte.

Fabrication, structural evolutions and properties of large-area orientation reduced graphene oxide films by self-assembly at the air–water interface and thermal treatment

A very facile and efficient method was supplied to fabricate the large-area orientation RGO films by the interface self-assembly and low-temperature thermal reduction. The structural evolutions of RGO films were systematically investigated by AFM, FT-IR, Raman scattering and XPS spectra. The conductivity and wettability of RGO films with temperature changes were quantitatively evaluated by the four-probe measurement and contacted angle testing. As a result, the RGO films could be well reduced in the 200 ~ 300 °C for 2 h under air atmosphere.

Optical properties of graphene oxide thin film reduced by low-cost diode laser

A non-toxic, fast, low-cost, single step and highly efficient reduction method is proposed in this research for the development of high-quality multilayer graphene film using laser diode. Graphene oxide film is irradiated with a diode laser (808 nm, 6 W) for different exposure times (1, 1.5, 2, 2.5, and 3 min.) to reduce it. Surface damage was observed on the graphene oxide (GO) film for exposure time greater than 3 min and at power 6 W. Different measurement techniques (Raman spectroscopy, Uv–visible absorption, photoluminescence and FTIR) are used to study the optical properties of rGO films. After laser irradiation, the Raman spectra of rGO films showed peaks for the D, G, and 2D bands centered at 1335, 1581, and 2710 cm−1, respectively. A small increase in the (ID/IG) ratio was observed and showed that greater reduction occurred after the graphene oxide film exposure time of 3 min. The as-prepared film of graphene oxide that showed absorption peak at 235 nm was red-shifted to 270 nm after 3 min of laser diode irradiation for reduction. The PL measurements were performed, where the sample was excited by Ar-ion laser (488 nm) and the PL signal was amplified using lock in techniques. The photoluminescence emission spectrum was measured at different positions on the graphene oxide film reduced for 3 min to show the effect of the energy spatial distribution of the laser diode beam on the rGO film. The maximum PL peaks gradually blue shifted and the peak intensities decreased as the measurements go toward the center of the reduced film. The FT-IR spectrum revealed that there are no hydroxyl, carboxyl, and epoxy groups and new peaks were found assigned to functional groups such as CH2, C–H by reducing the graphene oxide with laser diode for 3 min.

Impact of enhanced interfacial strength on physical, mechanical and tribological properties of copper/reduced graphene oxide composites: Microstructural investigation

Copper/reduced graphene oxide (rGO) composites were prepared to improve the mechanical and tribological properties of copper without adversely affecting its physical properties in any significant manner. No hazardous chemicals were used for reduced graphene oxide production, which maintained the integrity of layers. For better dispersibility of rGO in the copper matrix, electroless deposition of copper was done on the activated and sensitized rGO surfaces. Different amounts of prepared Copper/rGO nanocomposites were then dispersed in bulk copper using ethanol and finally compacted using spark plasma sintering. The coefficient of friction of copper reinforced with 0.5 wt% of nanocomposite reduced by 77.5% compared to neat copper. The flexural strength of copper reinforced with 0.75 wt% of nanocomposite and modulus of 1 wt% of nanocomposite reinforced copper increased by 15.2% and 31.3%, respectively, with different strengthening mechanisms before and after yield point. The increase in hardness and strength of the material along with thin rGO films in the wear track accounted for the sharp decrease in the coefficient of friction for the composites. There was a minimal and gradual decrease in the physical properties (electrical and thermal conductivities) of the composites with an increase in the amount of reinforcement. The two-step composite fabrication process ensured better dispersion of rGO in the copper matrix, which resulted in even properties throughout the composite.

Reduced graphene oxide nano particle based cryogenic sensor for measurement of liquid level and recording

For nearly a decade, liquid level sensors have been on the market as white food or beverage products, manufacturing, medical, residential, farming, automotive, aerospace, defense and liquid leak detection or level measurement devices. The nano material-resistive sensor based on reduced graphene oxide is highly sensitive and highly reactive to level measurement. This rGO liquid level sensor was developed, and using screen printing process, nano material film is printed on Al2O3 substratum. For safety purposes the sensor film was coated with Parylene-C. The rGO-based nano material was synthesized using Modified Hummer process. A linear relationship between the rGO film’s resistances was observed due to the change in liquid level, which implies fast detection and therefore calibration. With its fast and cost-effective manufacturing process, this liquid level sensor has considerable potential in industries where liquid level sensing is mandatory e.g. pharmaceutical also, space, automotive and even for liquid storage, liquid levels using cryogenic fluids of H2O icewater, LCO2, LN2, LH2, LOX and LHe.

Edge-enriched MoS2@C/rGO film as self-standing anodes for high-capacity and long-life lithium-ion batteries

Restraining the aggregation and polysulfide dissolution of edge-enriched metal sulfides is of significance for their applications as anode materials of lithium-ion batteries (LIBs) with high capacity and long cycle-life. In this work, we have reported the incorporation of MoS2 nanocrystals into amorphous carbon on the surface of reduced graphene oxide (rGO) by balancing the decomposition rates of phenolic resin (PF)-impregnated ammonium thiomolybdate (ATM), which subsequently forms the MoS2@C/rGO film through redispersion and vacuum filtration. Such structural design effectively avoids the aggregation of MoS2 nanocrystals and Li2S loss, and meanwhile ion enrichment in amorphous carbon and diffusion reinforcement can greatly accelerate the electrochemical reaction kinetics. When applied as the self-standing anode, the MoS2@C/rGO film possesses high reversible capacities of 1164 mA h g−1 at the current density of 0.2 A g−1 and 810 mA h g−1 at 6.4 A g−1. It also exhibits quite a high capacity retention after 1000 cycles at 3.2 A g−1. This work develops the formation theory of incorporation structures and promotes their applications in energy storage devices.

The electrochemical behavior of 4-nitrobenzyl bromide and its catalytic activity for reduction of CO2 in the acetonitrile solvent at the Cu/Pd/rGO/GCE surface

In this study, 4-nitrobenzyl bromide was used as a catalyst for reduction of CO2 and as an initial substrate for electrosynthesis of 4-nitrophenylacetic acid. Cu nanoparticles/Pd nanoparticles/reduced graphene oxide nanocomposite modified glassy carbon electrode (Cu/Pd/rGO/GCE) was used to promote electroactivation of CO2. rGO film was fabricated via electrochemical reduction of dispersed GO nanosheets on the GCE surface. Cyclic voltammetry procedure was applied in two steps to deposit Pd and Cu nanoparticles on the rGO/GCE surface. The morphology and structure of the nanocomposites were characterized using FESEM, EDS, AFM and XRD analysis. FTIR, 1H and 13C NMR spectral characteristics were used to identify the final products of the catalytic process. The electrocarboxylation of 4-nitrobenzyl bromide occurs at a potential which is less negative than those reported for other aryl halides. The results indicate that 4-nitrobenzyl bromide, as a catalyst, plays a dual role in the electrosynthesis of 4-nitrophenylacetate. The dual role includes the electrocatalytic reduction of CO2 and reaction of produced CO2•− with 4-nitrobenzyl bromide radical anion. Finally, an EC’C mechanism is proposed for the electrosynthesis of 4-nitrophenylacetate.

Dense Reduced Graphene Oxide Films Obtained by Pressing Create Stable and Compact Capacitive Energy Storage

AbstractIt is generally believed that the re‐stacking of reduced graphene oxide (rGO) sheets limits the electrochemical energy storage. Therefore, rGO based electrodes are usually designed to be non‐compact porous and fluffy structures. However, fluffy structures could reduce the conductance, structure stability, and cycling stability of electrodes. Here, to balance the contradiction, three electrodes with different compactness were studied. Amazingly, dense rGO hydrogel films (DrGO‐HF) achieved by simply pressing filtrated rGO films, show highly stable (92 % capacitance retention after 250 000 cycles) and high‐performance compact capacitive energy storage, which can be attributed to the structural stability and electrical conductivity enhanced by the close contact between graphene sheets. This study clarifies the scientific fact that the re‐stacking of rGO sheets would not degrade the electrochemical energy storage performances, which is of great significance for the design and preparation of supercapacitor electrodes with high volumetric energy density.

Tunable reduction degree of stacked lamellar rGO film for application in flexible all-solid-state supercapacitors

A stacked lamellar rGO film coated on carbon cloth (rGO/CC) was facilely prepared for application in flexible all-solid-state supercapacitors, in which the reduction degree of rGO was tuned to control interlayer spacing and wettability of rGO film. Furthermore, the effect of reduction degree on electrochemical performance of rGO film was investigated in detail. The result showed that the rGO film with higher reduction degree showed larger capacitance of ca. 185.7 F g−1. The enhanced capacitance of rGO film with higher reduction degree was mainly attributed to larger electrochemical active surface area and more channels for diffusion of ions. The work did not only report a new flexible all-solid-state supercapacitors with high performance, but also provided a new method to improve the electrochemical performance and stability of rGO film for various applications.

Fingerprint-inspired graphene pressure sensor with wrinkled structure

Nowadays, flexible pressure sensors have broad applications in healthcare monitoring, wearable electronics and so on. However, conventional fabrications are mostly time-consuming, complicated and even use toxic chemical reagents. It is in urgent need to fabricate pressure sensors with high sensitivity in a facile way. In nature, the fingertip skin of human has many epidermal ridges, which can sense small external stimuli. Here, inspired from the fingerprint, we propose a new type of pressure sensor made with reduced graphene oxide (rGO). The rGO film is designed to form a wrinkled structure by a facile stretching-releasing process, which mimics the morphology of fingertip skin. Owing to the fingertip-skin-like wrinkled structure, the pressure sensor exhibits high sensitivity of 5.77 kPa−1 (0 - 490 Pa). It also has a lot of attractive properties, such as fast response (< 100 ms), small detecting pressure (3 Pa) and good repeatability. We show the ability of the pressure sensor in small pressure detecting, human motion monitoring and motion pattern recognition. Furthermore, a translation system and a multi-touch device with spatially resolved detection based on the pressure sensor are developed. This pressure sensor is hopeful to have potential applications in wearable electronics and human–machine interaction systems.

Solution‐Processed and Transparent Graphene Oxide/TiOx Gas Barrier via an Interfacial Photocatalytic Reduction

AbstractA cost‐effective, flexible, and transparent gas barrier has been a main pursuit of research into plastics electronics. However, it is difficult to realize a high‐performance gas barrier on a plastic substrate via a solution process at low temperature. Here, by introducing an interfacial photocatalytic reduction between TiOx and graphene oxide (GO) films, a solution‐processed and transparent gas barrier film is demonstrated using reduced GO (rGO)/TiOx. A dramatic photochemical reduction of GO occurs at the interface between TiOx and the GO film under ultraviolet irradiation, which allows the fabrication of dense and uniform gas barrier films via a solution process at temperatures below 100 °C. In addition, the closely packed structure in the rGO film results in a decreased water vapor transmission rate (WVTR) of 0.37 g m−2 day−1 even with a thin rGO (&lt;13 nm)/TiOx (7 nm) film, leading to a high transmittance of over 80% in the visible range.

Comparison of temperature dependences of electrical conductivity of composite rGO-SWNT film with rGO and SWNT films

Temperature dependences of electrical conductivity of reduced graphene oxide composite with single-walled nanotubes (rGO-SWNTs) and rGO films has been studied in the temperature range of 25–290 K. Both films were obtained by vacuum filtration of aqueous suspensions. Temperature dependences of conductivity of films were found similar to the conductivity observed in disordered semiconducting systems. It was demonstrated that the behavior of the conductivity temperature dependence of pure rGO, SWNTs and composite film is different. The temperature dependences of the resistance R(T) of the films were analyzed within the framework of the variable range hopping (VRH) transport in which electron motion is due to the thermo-activated quantum tunneling between localized states. Two-dimensional Mott VRH (Mott 2D VRH) and Efros-Shklovskii VRH (ES VRH) models were applied for analysis. Mott 2D VRH was observed for rGO-SWNT film in the interval of 25–200 K. At higher temperatures R(T) of rGO-SWNT was fitted with Arrhenius-like equation describing electron activation from localized states to delocalized ones. R(T) of the rGO film followed the Mott 2D VRH model from 165 to 290 K, however, at lower temperatures ES VRH model was exploited. From approximation of R(T) by these models the parameters of the electron transport in rGO-SWNT and rGO films were estimated. It was suggested that nanotubes in rGO-SWNT composite serve as conductive bridges among rGO sheets enhancing the conductivity as compared to rGO. The conductivity of rGO also influences on the composite properties because 2D character of electron motion is kept in sharp contrast to SWNT film which demonstrated three-dimensional Mott VRH electron transport in the same temperature range.

Structural Properties and Capacitive Performance of Cathodically Deposited Manganese Dioxide Film on Electrophoretically Deposited Reduced Graphene Oxide

The structural properties and capacitive behavior of manganese dioxide (MnO2) films prepared by potentiostatic cathodic deposition were examined in presence and absence of pre-electrophoretically deposited reduced graphene oxide (rGO) film. The FTIR analysis reflects the formation of a MnO2/rGO composite film structure. SEM and TEM characterization show that the MnO2 film deposited on rGO film has finer and less compact nanostructure and grown as sparsely aggregated particles follow the open structure of underlying rGO platelets. The specific capacitance and rate capability of MnO2/rGO film are higher than that of pristine MnO2 film; it exhibits specific capacitance of 292 Fg-1 at 1 mA cm-2 and better cyclic stability at 3 mA cm-2. The presence of 3D underlying defective rGO film creates an open structure with larger area, facilitates the electron transfer and access of the electrolyte ions through the surface of MnO2 film and hence offering the potential of the unique capacitive behavior.

Highly stable multi-layered silicon-intercalated graphene anodes for lithium-ion batteries

Abstract

Direct Growth of Wafer-Scale, Transparent, p-Type Reduced-Graphene-Oxide-like Thin Films by Pulsed Laser Deposition.

Reduced graphene oxide (rGO) has attracted significant interest in an array of applications ranging from flexible optoelectronics, energy storage, sensing, and very recently as membranes for water purification. Many of these applications require a reproducible, scalable process for the growth of large-area films of high optical and electronic quality. In this work, we report a one-step scalable method for the growth of reduced-graphene-oxide-like (rGO-like) thin films via pulsed laser deposition (PLD) of sp2 carbon in an oxidizing environment. By deploying an appropriate laser beam scanning technique, we are able to deposit wafer-scale uniform rGO-like thin films with ultrasmooth surfaces (roughness <1 nm). Further, in situ control of the growth environment during the PLD process allows us to tailor its hybrid sp2-sp3 electronic structure. This enables us to control its intrinsic optoelectronic properties and helps us achieve some of the lowest extinction coefficients and refractive index values (0.358 and 1.715, respectively, at 2.236 eV) as compared to chemically grown rGO films. Additionally, the transparency and conductivity metrics of our PLD grown thin films are superior to other p-type rGO films and conducting oxides. Unlike chemical methods, our growth technique is devoid of catalysts and is carried out at lower process temperatures. This would enable the integration of these thin films with a wide range of material heterostructures via direct growth.

Tuning the optoelectronic properties of the rGO-AuNPs hybrid film by pre-decoration and AuNPs-assisted thermal reduction

Reduced graphene oxide (rGO) decorated with plasmonic gold nanoparticles (AuNPs) is a versatile hybrid material from both aspects of processing and functionality for building the novel optoelectronic and sensor devices. This article presents an alternative way to prepare and tune the optoelectronic properties of the rGO-AuNPs hybrid film by pre-decoration and AuNPs-assisted thermal reduction of graphene oxide (GO). Au was sputtered on GO film for the varied duration before subjected to medium-temperature (MT) reduction of 700 °C and high-temperature (HT) reduction of 1,000 °C. The surface of rGO-MT was decorated by ball AuNPs, while rGO-HT was populated by wire AuNPs and patches of Au thin film after solid-state dewetting. Decoration of AuNPs enhanced the reduction of GO and increased the carrier mobility of rGO-AuNPs hybrid film. The effect was intense for the HT reduction, where the highest hole mobility of 159 ± 5.4 cm2/Vs and the lowest sheet resistance of 325.82 ± 0.32 Ω/sq were measured for the rGO-HT film with 30 s pre-sputtered Au. Without pre-decoration of AuNPs, the reduction results in increased optical constants of the rGO film. This is well expected as the optical absorption of GO within UV–visible–NIR increased due to thermal reduction, resembling the graphene. Remarkably, we found the optical constants of rGO lowered for a longer duration of Au pre-sputtering. The AuNPs directly enhanced the electrical conduction while at the same time tuned the optical constants of rGO more towards GO by incomplete reduction of the embedded layer. The combination of electrically and optically conducting rGO film with the presence of localized surface plasmon resonance from AuNPs in the visible range is prospective for various target applications.

Temperature dependence of charge transport in solid-state molecular junctions based on oligo(phenylene ethynylene)s

The ultimate goal of molecular electronics is to achieve practical applications. For approaching the target, we have successfully fabricated solid-state junctions based on oligo(phenylene ethynylene)s (OPEs) and cruciform OPEs with extended tetrathiafulvalene (TTF) (OPE3 and OPE3-TTF) self-assembled monolayers (SAMs) with a diamine anchoring group. SAMs were confined in micropores with gold substrates to ensure well-defined device surface areas. The transport properties were conducted on a double-junction layout, which the rGO films used for top contacts and interconnects between adjacent SAMs. The solid-state devices based on OPE3-TTF SAMs showed the expected higher conductance under ambient conditions because of the incorporation of a TTF moiety. The two devices displayed varying degrees of temperature dependence with decreasing temperature, which resulted from the cross-conjugated OPE3-TTF molecule exhibiting quantum interference while the linear-conjugated OPE3 molecule did not. This study shows the temperature dependence of the electrical properties of molecular devices based on cruciform OPEs, further enriching the research results of functional molecular devices.