From graphene oxide (GO) to reduced graphene oxide (rGO) films: A hybrid approach combining film transfer and vapor reduction for enhanced structural and optical properties

ABSTRACTGraphene is a strong contender as a material to replace indium tin oxide as the transparent conductor of choice for electronic applications due to its exceptional electrical and optical properties. In this work, we present a study of graphene oxide (GO) films produced by inkjet-printing. The printed GO films are reduced using hydriodic acid (HI) and acetic acid vapour at low temperature. The reduced GO (rGO) films displayed good optical and electrical properties with a sheet resistance 6.8 kΩ/□ at a transmittance of 80%. In addition, we show that the conductivity of rGO films is related to both the size of individual GO sheets in the ink and the thickness of printed films. The rGO films using large size GO sheets displayed a thickness-independent conductivity of ∼ 4 × 104S/m, while the rGO films using small size GO sheets showed a thickness-independent conductivity of ∼ 1.7 × 104S/m. These properties are comparable to graphene films produced by solvent exfoliation. In summary, we demonstrate a scalable and potentially low-cost technique to produce rGO transparent films and a route to improve the conductivity of rGO films by controlling size of GO sheets in the ink.

We have synthesized free-standing films of graphene oxide (GO), reduced graphene oxide (rGO) and graphene oxide-manganese oxide composite (GMC) for humidity and hydrogen peroxide sensing applications. Structural and morphological characterizations of these free-standing films were performed using X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The presence of anionic sites in the form of oxygen functional groups (OFGs) at the surface of GO along with its hydrophilic nature makes GO a unique candidate as a suitable material for humidity and hydrogen peroxide sensing. In contrast, rGO has a relatively lower fraction of OFGs, higher electrical conductivity and hydrophobicity compared to GO. We estimate the response time, recovery time and stability of free-standing films over multiple sensing-degassing cycles of the as chemically prepared GO, rGO and GMC films for humidity sensing. We observed a dramatic improvement in both the response and recovery times for rGO and GMC films compared to GO film at relatively low humidity, while at higher humidity percentages, rGO film has the best response and recovery times compared to GMC and GO films. Regarding stability, GO was found to be more stable over multiple sensing cycles compared to rGO and GMC at high humidity values. In addition to this, we observed that the addition of metal oxide to GO makes GMC film more selective for hydrogen peroxide sensing in comparison to GO and rGO film at a lower concentration.

Materials that combine high stiffness with effective damping are in high demand across various industries. While polymers excel in damping, they often lack stiffness and thermal stability. Conversely, metals and ceramics boast high mechanical and thermal properties but lack damping. This study demonstrates that graphene oxide (GO) and reduced graphene oxide (rGO) films can achieve exceptional viscoelastic properties across a wide temperature range. Furthermore, it explains the damping mechanisms and structural characteristics that influence the unique viscoelastic behavior of GO and rGO films. Through comprehensive characterizations, this study correlates the structure and spatial variation in local strain (measured with in situ Raman microscopy) of GO and rGO films with their storage and loss moduli. This correlation links these properties to the water loss as a function of the temperature rise. GO and rGO films exhibited a damping coefficient of 0.2-0.4 while maintaining stiffness values of 10-20 GPa in the 30-120 °C range. These high damping values were attributed to intermittent slippage and hydrogen bond density between the constituent sheets. Numerical modeling was conducted to further elucidate the mechanisms responsible for the properties noted in these films. This study enhances our understanding of the viscoelastic properties of GO films and offers a new potential material for applications across various fields.

Facile formation of porous, multilayer reduced graphene oxide electrodes using electrophoretic deposition and flash sintering

A highly efficient synthetic process of graphene films with tunable optical properties

We report the performance of supercapacitor device model based on double layer reduced graphene oxide (rGO) films as electrode in 1 M KCl. Graphene oxide (GO) films were deposited on ITO-glass use an electrochemical deposition method using 1 mg/ml GO dispersed in water. The film’s thicknesses were controlled by number deposition cycles. rGO films were obtained by thermally reduced the GO films at 200°C for 1 hour under argon flowing. A pair of 1 cm2 rGO/ITO electrodes was employed as double layer electrodes of supercapacitor device model using a filter paper which was soaked in 1 M KCl as a separator. Performance of the supercapacitor model was investigated using cyclic voltammetry (CV) in a voltage range of 0.0 volts to +0.9 volts with varied scan rate range of 25mV/s to 125mV/s. The highest specific capacitance of 20 F/kg and specific power of 0.825 W/kg was obtained using device with rGO films that deposited for three voltage cycles.

The chemical oxidation method can be used to mass-produce graphene oxides (GOs) from highly oriented pyrolytic graphite. However, numerous oxygen-containing functional groups (hydroxyl, epoxy, carbonyl, etc.) exist in typical GO surfaces, resulting in serious electrical losses. Hence, GO must be processed into reduced graphene oxide (rGO) by the removal of most of the oxygen-containing functional groups. This research concentrates on the reduction efficiency of GO films that are manufactured using atmospheric-pressure and continuous plasma irradiation. Before and after sessions of plasma irradiation with various irradiation times, shelters, and working distances, the surface, physical, and electrical characteristics of homemade GO and rGO films are measured and analyzed. Experimental results showed that the sheet resistance values of rGO films with silicon or quartz shelters were markedly lower than those of GO films because the rGO films were mostly deprived of oxygen-containing functional groups. The lowest sheet resistance value and the largest carbon-to-oxygen ratio of typical rGO films were approximately 90 Ω/sq and 1.522, respectively. The intensity of the C–O bond peak in typical rGO films was significantly lower than that in GO films. Moreover, the intensity of the C–C bond peak in typical rGO films was considerably higher than that in GO films.

Graphene oxide (GO) films have great potential for aerospace, electronics, and renewable energy applications. GO sheets are low-cost and water-soluble and retain some of Graphene’s exceptional properties once reduced. GO or reduced GO (rGO) sheets within a film interact with each other via secondary bonds and cross-linkers. These interfacial interactions include non-covalent bonds such as hydrogen bonding, ionic bonding, and π-π stacking. Stress transfer and failure mechanisms in GO and rGO films, specifically how linkers affect them, are not well understood. The present study investigates the influence of inter-particle interactions and film structures, focusing on hydrogen bonds introduced via cellulose nanocrystals (CNC), on failure and stress-transfer of the GO and rGO films. To this end, GO films with CNC crosslinkers were made, followed by a chemical reduction. The few-micron thick films were characterized using tensile testing. All tested films exhibited a brittle failure and achieved tensile strengths and modulus in the ~40-85 MPa and ~3.5-9 GPa ranges, respectively. To reveal stress transfer mechanisms in each sample, tensile in-situ Raman spectroscopy testing was carried out. By monitoring the changes in bandwidth and position of Raman bands while stretching the film, useful information such as sheet slippage and cross-linker interactions were gathered. The addition of CNC enhanced modulus but degraded strength for both GO and rGO films. Interestingly, the Raman G-peak shift at failure, indicative of stress transfer to individual GO/rGO particles, is commensurate with the films’ strengths. Correlating these results with the structure and composition of different films reveals new understanding of stress transfer between GO/rGO particles, paving the way for the scalable manufacturing of strong and stiff GO-based films.

ABSTRACTIn this study, the reduced graphene oxide (rGO) films were fabricated at room temperature using capacitively coupled CH4 plasma treatment of the spin-coated graphene oxide (GO) films. The variations of the rGO films were evaluated according to the treatment positions (bulk plasma region (Rb) and sheath region (Rs)) and the treatment time. The reduction of the GO films began immediately after the CH4 plasma was exposed to both regions. However, as the treatment time increased, the physical properties of rGO films became different. The reduction in the Rb was effective to modify the rGO films for transparent conducting films.

Controllable preparations and anti-corrosion properties of reduced graphene oxide films by binder-free electrophoretic deposition

The capacities of graphene oxide (GO) and reduced graphene oxide (rGO) films grown on silicon substrate to cause the aniline to azobenzene oxidation reaction were compared by using Raman spectroscopy, high-resolution photoemission spectroscopy (HRPES), and work function measurements as well as scanning electron microscopy (SEM). The oxygen carriers’ existence on GO film, which includes a lot of oxygen carriers, can facilitate the aniline to azobenzene oxidation reaction with slightly partial conversion of aniline to nitrobenzene, as determined by the Raman shifts and core-level spectra resulting from exposure to aniline. The work function of the GO film was found to change dramatically in comparison with rGO film, indicating that aniline exposed to a GO film produced n-type doping characteristics by electron charge transfer from GO to aniline. These results indicate that the oxygen carriers on a GO film oxidize aniline to azobenzene and show that GO film prefers to act as a reaction reagent rather than rGO.

The flexible reduced graphene oxide (rGO) films are prepared by treating the graphene oxide (GO) films assembled in the presence of urea and p-phenylenediamine (PPD) with hydroiodic acid firstly and then heating at 165 °C. The addition of urea can overcome the aggregation of GO sheets induced by the PPD, and the formed microcrystallines of urea and PPD can act as the templates to regulate the structure of GO films during the drying process. Compared with the rGO films obtained from pure GO films, measurements based on the two-electrode system reveal that the capacitive performance of the films can be dramatically improved when the GO films are assembled in the presence of urea and PPD. The selected flexible film exhibits a specific capacitance of about 430 F g−1 in 1.0 mol L−1 H2SO4 electrolyte, and the cells fabricated by the films exhibit a maximum energy density of 8.96 Wh kg−1 at the power density of 100.42 W kg−1, and maximum power density of 1.70 kW kg−1 at the energy density of 7.92 Wh kg−1 based on the active materials, and can retain about 85% of its initial capacitance after 10,000 cycles. This novel strategy may be developed as a route to prepare flexible N-doped rGO electrode materials with high-performance.

Highly reduced graphene oxide (rGO) films are fabricated by combining reduction with smeared hydrazine at low temperature (e.g., 100 degrees C) and the multilayer stacking technique. The prepared rGO film, which has a lower sheet resistance ( approximately 160-500 Omega sq(-1)) and higher conductivity (26 S cm(-1)) as compared to other rGO films obtained by commonly used chemical reduction methods, is fully characterized. The effective reduction can be attributed to the large "effective reduction depth" in the GO films (1.46 microm) and the high C1s/O1s ratio (8.04). By using the above approach, rGO films with a tunable thickness and sheet resistance are achieved. The obtained rGO films are used as electrodes in polymer memory devices, in a configuration of rGO/poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM)/Al, which exhibit an excellent write-once-read-many-times effect and a high ON/OFF current ratio of 10(6).

Graphene oxide (GO) presents the advantage of being easily dispersed in water, which facilitates the assembly of nano and microstructures by numerous methods, in order to form uniform and thickness-controlled functional coatings. For example, the electrophoretic deposition (EPD) is one of the most used techniques to produce anticorrosive coatings onto metals, including GO and reduced graphene oxide (rGO) coatings. We have used a variation of the EPD process of GO, which consisted in changing the GO’s charge to positive values allowing the electrophoretic deposition of GO onto the cathode (cEPD). The coating diminished by three times the corrosion rate of carbon steel. The preparation of these coatings also implies the understanding of the mechanism through which the electrochemical reduction of the GO is carried out.1 An electrochemical reduction mechanism of GO involving hydrogenation/hydrogenolysis reactions is suggested as the main reason to achieve an effective anticorrosive-coating by cEPD in comparison to the films produced by an anodic EPD. For this reason, we studied the electrochemical reduction of GO in aqueous and organic media containing H+ donor, to investigate the role of H+ in the reduction mechanism. In aqueous electrolyte, in both acid and basic pH, the H+ enhanced the removal of oxygenated groups by electrochemical reduction and promoted the loss of some sp2 domains due to hydrogenation reactions of the graphitic domains. The electrochemical reduction of GO in organic media, free of H+, resulted in the restoration, to some degree, of the sp2 domains. However, the removal of the oxygenated groups seemed hindered when compared to the same process in presence of H+ donor, in the organic solvent, at the same potential intervals. Considering that through these studies it is possible to choose a route for the preparation of functional films, recently we proceeded to modify electrochemically the rGO through with 5-membered alkyne chains. The resulting rGO film presented lower conductivity, due to the loss of graphitic domains, and an increased hydrophobicity. The modified rGO film was evaluated as an anticorrosive coating for carbon steel, showing a better protection from corrosion in comparison to the protection granted by the regular rGO film. [1] J.A. Quezada-Rentería, L.F. Chazaro-Ruiz, J.R. Rangel-Mendez, Synthesis of reduced graphene oxide (rGO) films onto carbon steel by cathodic electrophoretic deposition: Anticorrosive coating, Carbon 122 (2017) 266-275.

Hydrogen-assisted pulsed KrF-laser irradiation for the in situ photoreduction of graphene oxide films