Graphene Oxide Composite Films Research Articles

Free-standing Sandwich Structure MoO3-rGO Composite Film Electrode for Flexible Supercapacitors

ABSTRACTThe research of high-performance flexible supercapacitors is urgent due to the rapid development of wearable and portable electronics. The key challenge is the preparation of flexible electrodes with high areal capacitance since electrodes are the most important part of supercapacitors. Compared to those conventional electrodes loading with typical flexible substrates such as textile, PET, paper et al, free-standing electrodes have many advantages such as more efficient capacity contribution, solidly embedded active materials and thinner thickness. Herein, we have successfully fabricated a novel sandwich-like structure free-standing MoO3-rGO (reduced graphene oxide) composite film electrode for flexible supercapacitors using simple vacuum filtration method followed by HI reduction process. The obtained MoO3-rGO composite film electrode shows excellent electrochemical performance, whose areal specific capacitance reaches 8972 mF·cm-2 (1.5 mA·cm-2). Here, MoO3 provides pseudocapacitance and rGO provides double-layer capacitance. After cycling for 2000 cycles, the capacity retention is 86.7%, showing good cycle stability. Besides, the as-prepared composite film has good flexibility and will not break easily during following bending, rolling, folding or twisting steps. This study has been approved to be an important step for the high-performance electrode design for free-standing flexible supercapacitors.

VO2(B) nanobelts/reduced graphene oxide composites for high-performance flexible all-solid-state supercapacitors

Vanadium oxide has attracted extensive attention for electrochemical capacitors due to its wide range of versatility. However, due to the relative poor conductivity and chemical stability of vanadium oxide, severe losses of capacitance often occur during charge and discharge processes. Herein, a free-standing vanadium dioxide (VO2(B)) nanobelts/reduced graphene oxide (VO2/rGO) composite film was fabricated by assembly of VO2(B) nanobelts and rGO for supercapacitors. The flexible rGO sheets and VO2(B) nanobelts intertwined together to form a porous framework, which delivered a 353 F g−1 specific capacitance at 1 A g−1, and after 500 cycles, the specific capacitance retention rate was 80% due to the enhanced conductivity of the VO2(B) nanobelts by rGO and increased transport of ions and electrons by the porous structures. An all-solid-state symmetrical supercapacitor was assembled from the VO2/rGO composites, which exhibited good energy storage performance with a maximum voltage of 1.6 V. The maximum power density is 7152 W kg−1 at the energy density of 3.13 W h kg−1, ranking as one of the highest power densities for reported materials. In addition, after 10000 cycles, it still has a specific capacitance retention rate of 78% at 10 A g−1.

Sol-gel synthesized spin coated GO: ZnO composite thin films: optical, structural and electrical studies

In the present work, we report on the structural, optical and electrical properties of solution-processed transparent conducting Graphene Oxide and Zinc oxide (GO: ZnO) composite thin films. Eco-friendly top-down modified Hummer’s method was adopted for the synthesis of GO. The ZnO and GO:ZnO thin films were grown on the glass substrates employing a simple and cost-effective spin coating technique. To get a stable solution for spin coating, an efficient solvent, 2-methoxyethanol is used to disperse GO. The structural properties of the GO: ZnO thin films were analyzed using XRD pattern wherein the average crystallite size decreases with the increase in GO% in ZnO. UV–vis spectroscopy studies showed that the optical band gap and the transmittance (>80%) of thin films are decreased with the increment of GO% in ZnO. FESEM and XRD data revealed a decrease in the particle size. GO: ZnO composite thin films exhibit an ohmic nature when silver is used as a contact with increase in current in composite thin films compared to ZnO thin film. The increase in current is due to the removal of oxygen moieties in GO and partial restoration of the graphene structure occurred during the pre and post-annealing of thin films. Thus, the reduced graphene oxide (rGO) acts as a conductive frame for ZnO. The optical and electrical parameters procured for GO: ZnO composite thin films propel the possibility of using composite thin films for transparent conducting electrode applications.

Enhanced corrosion protective performance of graphene oxide-based composite films on AZ31 magnesium alloys in 3.5 wt% NaCl solution

Constructing the film with a green corrosion inhibitor is the key to metal corrosion protection. This study reports an environmentally friendly graphene oxide (GO) and carboxymethyl cellulose (CMC) composite films (CMC@GO) with enhanced corrosion protection performance. The CMC@GO composite film was grown on AZ31 magnesium alloy by the layer-by-layer (LbL) assembly method. Fourier transform infrared (FT-IR) spectroscopy and the solid-state NMR Spectrometer reveal the successful modification of CMC on the surface of GO nanosheets. The chemical states and the surface morphology of the CMC@GO composite film were obtained from X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electrochemical measurements and equivalent circuit fitting results demonstrate that the film containing GO composites has higher corrosion resistance than the film of undoped GO. The CMC@GO composite film exerted the corrosion inhibition effect of GO, owing to the synergistic protective effect of GO and CMC.

ZnO/carbon nanotube/reduced graphene oxide composite film as an effective interlayer for lithium/sulfur batteries

The application of lithium/sulfur (Li/S) batteries is negatively affected by the insulation of sulfur and large volumetric change during the cycles as well as the polysulfides dissolution. To solve the above problems, we fabricated a composite interlayer for Li/S batteries using ZnO nanocrystals anchored on connected carbon nanotube and graphene. The preparation of ZnO/carbon nanotube/reduced graphene oxide (ZnO/CNT/RGO) composite film was inspired from the combination of a one-step sol-gel synthetic technique and vacuum-assisted filtration. The ZnO/CNT/RGO interlayer showed effective adsorption of polysulfides during diffusion experiments. This ZnO/CNT/RGO interlayer can efficiently increase sulfur utilization by immobilizing soluble intermediate polysulfides. When used as a composite interlayer in Li/S batteries, an impressive high capacity of 768 mAh g−1 at 0.2C was achieved after 150 cycles and improved rate performance of 597 mAh g−1 at 2C was obtained. This study offers a facile method to improve the electrochemical performance of the Li/S batteries.

A novel H1.6Mn1.6O4/reduced graphene oxide composite film for selective electrochemical capturing lithium ions with low concentration

A novel lithium ion separation composite film consisting of H1.6Mn1.6O4 nanoparticle and reduced graphene oxide (rGO) is successfully fabricated by using vacuum filtration. Based on the great selective adsorption for lithium ions of H1.6Mn1.6O4 and good conductivity of rGO, the H1.6Mn1.6O4/rGO composite film is applied for selective electrochemical extraction of low concentration lithium ions from aqueous solutions using an electrochemically switched ion exchange (ESIX) technique. As a result, the lithium ion adsorption capacity of the H1.6Mn1.6O4/rGO composite film reaches 38.78 mg·g−1 with an adsorption equilibrium time of 5 h. The lithium ion adsorption capacity of the H1.6Mn1.6O4/rGO composite film still retain 99% comparing with the initial value after 5 cycles. In particular, the selectivity factors for Li+/Na+ and Li+/Mg2+ reach 10.39 and 10.23 when the initial molar ratios of Li+/Na+ and Li+/Mg2+ are 1:1. This composite film could be applied for the extracting of low concentration lithium ions in future.

Facile preparation of binder–free electrode for electrochemical capacitors based on reduced graphene oxide composite film

Binder-free electrode based on reduced graphene oxide (rGO) is attracting attention for electrochemical capacitors. Here the binder-free electrodes have been fabricated by activating the composite films of GO and carbonized cornstalk-cores. In the composites, the rGO sheets are found to be tightly adhered to the activated bio‑carbon which is intercalated between the rGO sheets to prevent them from stacking. Moreover, the influences of the mass ratios of GO to bio‑carbon on the electrochemical performance have been systematically investigated. The optimal binder-free electrode (rGO/ACCS1/1) prepared from the composite films with 1:1 mass ratio of GO to bio‑carbon exhibits a specific capacitance as high as 278Fg−1 at scan rate of 1mVs−1 and shows excellent stability in 6M KOH electrolyte. Furthermore, the optimal electrode can retain 47.8% of the initial specific capacitance even at current density of 100Ag−1, indicating a fast charge-discharge capability. This work provides a simple method to prepare binder-free composite electrodes by introducing renewable and inexpensive biomass based carbon into activated rGO films.

Electrical Resistance Response of Reduced Graphene Oxide - Aramid Nanofiber Films to Bending-Induced Strain

Structural energy storage is a field associated with the combination of important functions such as structural reliability, energy storage, and energy delivery. The combination of said functions ensures savings in the overall volume and mass of the system. Reduced graphene oxide (rGO) and aramid nanofibers (ANF) composite film electrodes were developed for the purpose of structural energy storage. Graphene is studied due to its remarkable mechanical properties, electrical conductivity and electrochemical surface area. Furthermore, Kevlar® aramid nanofibers enhance the structural properties of the composite due to their excellent mechanical properties. However, external strains are expected on the composite film due to its structural function, and the response of the electrical properties to external strain needs to be evaluated. In this work, the change in electrical resistance was measured under bending-induced strain, using a home-built instrument that allows for accurate strain measurements using image analysis. We show that the resistance of the film decreases under bending via a mechanism we called “mechanical annealing.” This mechanism may be the effect of improved stacking of rGO sheets. The degree of mechanical annealing was also correlated to the amount of bending strain, as well as the amount of ANF loading. Our results demonstrate an improvement, rather than deterioration of the electrical resistance of rGO/ANF composite films under strain, making them suitable for structural energy storage applications.

Self-supporting lithium titanate nanorod/carbon nanotube/reduced graphene oxide flexible electrode for high performance hybrid lithium-ion capacitor

A Li4Ti5O12 nanorod/carbon nanotube/reduced graphene oxide self-supporting and flexible composite film is prepared through a facile vacuum filtration approach. The Li4Ti5O12 nanorod/carbon nanotube/reduced graphene oxide composite film electrode is able to deliver a reversible specific capacity of 207 mAh g−1, and retains a capacity retention of 90% after 1000 cycles at the current density of 0.35 A g−1. Moreover, a hybrid lithium ion capacitor consisting of an active carbon/carbon nanotube/reduced graphene oxide composite film cathode and the as-prepared Li4Ti5O12 nanorod/carbon nanotube/reduced graphene oxide composite film anode presents high energy density of 67 Wh kg−1 and power density of 1589 W kg−1, respectively. The hierarchically structured Li4Ti5O12 nanorod/carbon nanotube/reduced graphene oxide composite film electrode is lightweight, flexible, conductive additive/binder free, which is a highly desirable feature for wide applications in the wearable energy storage devices.

Eco-Friendly Electrochemical Biosensor based on Sodium Carboxymethyl Cellulose/Reduced Graphene Oxide Composite

Reduced graphene oxide (GO) and carboxymethyl cellulose sodium (CMC) composite film was prepared by a simple solution blending method. The obtained composite film was used to modify glassy carbon electrode (GCE) to detect Vitamin B6 (VB6) with electrochemical measurements. Morphologies and stucture of the composite were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). The electrochemistry performances of the GCE modified by GO/CMC composite were investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The results revealed that CMC and GO were able to form a homogeneous mixture, and the modified GCE presented extremely strong sensitivity towards VB6 such as high detection sensitivity, low detection limit, small Ret value, certain stability and excellent reversibility. The good performance might be attributed to high electrical conductivity and large surface-to-volume ratio of GO which could accelerate electron transfer between the surface of GCE and VB6. The test results showed that GO/CMC composite was a novel electrochemical biosensor for the detection of VB6.

Layer-by-layer MoS2:GO composite thin films for optoelectronics device applications

With reference of our previous report (Appl. Surf. Sci. 474(2019)227), the molybdenum disulphide (MoS2) thin film were prepared by the dip-coating technique at different temperatures (400 °C–450 °C) using methanolic solution of ammonium molybdate and ammonium thiocyanate that are used as bare-substrate for the deposition of graphene oxide (GO) thin films. For the deposition of graphene oxide (GO), commercially purchased GO (0.5 mg in 10 mL aqueous solution) was deposited by dip-coating technique on dip-deposited MoS2 thin film to make layer-by-layer MoS2:GO composite thin films and hence studied their electronic and electrical behaviours. The micro-structural and surface morphology were studied using Raman spectroscopy, X-ray diffraction (XRD) and field emission scanning electron microscopy, whereas optical band estimated from the optical absorption spectra. The electronic structure and their bonding properties were studied using X-ray photoelectron spectroscopy and the electrical behaviours were observed from the current-voltage (I-V) characteristic curve. The formation of different phases of MoS:GO thin films show an enhanced electronic and electrical performance due to their unique-structure and the synergetic effect of MoS2:GO nanosheets when compared to those of bare MoS2.

A flexible pressure sensor by induced ordered nano cracks filled with multilayer graphene oxide composite film as a conductive fine-wire network for higher sensitivity

Inspired by the structure of skin, a flexible pressure sensor is proposed here, which consists of a flexible Kapton/polydimethylsiloxane (PDMS) substrate, a sensing structural layer of a fine-wire connected conductive network and a protective layer of PDMS. Notably, cracks, often referred to as defects, were utilized to fabricate the conductive network in this work. The ordered nano cracks were induced by changing the temperature of the patterned photoresist film suddenly to form the regular hexagonal array nano-channel network. Then the Ni/multilayer graphene oxide/Ni sandwich composites were introduced to obtain the conductive fine-wire connected network by electroplating and graphene oxide electrodeposition. When the sensor is under pressure, the strain effect of the bottom Ni network, the change of intermediate multilayer graphene oxide microstructure, and the breaks of electron transport paths owing to the top wrinkled Ni cracking, contribute to the resistance change together. As a result, the fabricated flexible pressure sensor shows a maximum sensitivity as high as 4953.15 kPa−1 at 52.27 kPa. In addition, the sensor has a fast response (47 ms) and good repeatability, which are essential for practical applications. Furthermore, the pressure sensor was demonstrated to have good potential in e-skin application, such as pulse detection, laughter and swallowing movement recognition. This work provides a new and convenient approach to fabricate a conductive network with nanowires by induced cracks.

Hydrophilic Fluoro‐Functionalized Graphene Oxide / Polyvinylidene Fluoride Composite Films with High Dielectric Constant and Low Dielectric Loss

AbstractA novel and facile method, to synthesize high‐quality fluoro‐functionalized graphene oxide (F‐GO) and polyvinylidene fluoride (PVDF) composite (F‐GO/PVDF) films prepared by solution blending of F‐GO and PVDF in solution was proposed. The fabricated F‐GO/PVDF nanocomposites with different mass fractions exhibited high dielectric constant and low dielectric loss. Meanwhile, Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy and raman spectroscopy verified the functional groups in the F‐GO. The microstructure analysis using X‐ray diffraction and field‐emission scanning electronmicroscopy were performed to investigate the morphology of F‐GO and F‐GO/PVDF composite films. The thermal, hydrophilic and electrical characterization properties of F‐GO/PVDF composites were investigated by thermal gravimetric analysis, contact angle, and dielectric constant. These results indicate their potential applications for dielectric devices storage devices.

One‐Step Synthesis of Vacancy‐Rich MnO2−x/Reduced Graphene Oxide Composite Film for High Electrochemical Performance

AbstractHigh electrochemical performance is important to achieve practical application of energy storage devices. It has been found recently that it is hard to achieve high capacity and high stability simultaneously using a single electrode material. Thus, constructing composite electrode materials which can combine the advantages of different materials together is an efficient approach to improve the electrochemical properties. In this work, we have built a vacancy‐rich MnO2−x/reduced graphene oxide (rGO) composite film through a facile one‐step route. In the synthesis process, GO nanosheets were reduced into rGO to improve the electronic conductivity, while Mn2+ was oxidized to MnO2 with vacancies. The obtained vacancy‐rich MnO2−x/rGO composite showed a superior electrochemical performance: The specific capacitance reached 675.5 F/g at a current density of 0.5 A/g and the material demonstrated high capacitance retention (96.1 % after 10000 cycles). Besides, the symmetric electrochemical capacitor based on the vacancy‐rich MnO2−x/rGO composite electrode can achieve a high energy density (8.42 mWh/cm3) and power density (3.78 W/cm3) as well as excellent stability.

Gamma irradiated poly (methyl methacrylate)-reduced graphene oxide composite thin films for multifunctional applications

Poly (methyl methacrylate) (PMMA)-Reduced Graphene Oxide (rGO) (PrGO) composite films were fabricated by solvent evaporation technique and exposed to gamma radiation at different dosages viz. 25 kGy, 50 kGy and 100 kGy. The XRD analysis revealed the phases of PMMA and rGO and further confirmed the semi-crystalline nature of PMMA. The irradiation also decreased the peak intensities of the functional groups of PMMA and rGO. At 50 kGy irradiation, lamellar structures were formed on the surface of the films (50 kGy) due to the thermal fluctuations whereas, at higher dosage (100 kGy), pores were formed. The surface roughness and contact angle were enhanced on 50 kGy sample. The drug impregnated PrGO50 and PrGO100 samples showed sustained and burst release of drug respectively and in addition exhibited a better zone of inhibition against E. coli bacteria. All the samples were hemocompatible in nature. Fibroblast proliferation was enhanced with no cytotoxic effect on 50 kGy samples. Hence, the gamma irradiated samples could be an excellent candidate for biosensing and biomedical applications.

Fabrication of poly(pyrrole-3-carboxylic acid)/graphene oxide composite thin film for glucose biosensor

An electrochemical glucose biosensor based on poly(pyrrole-3-carboxylic acid)/graphene oxide (PP3C/GO) composite thin film was developed by immobilizing glucose oxidase (GOx) onto the surface of composite thin film via covalent linkages. The PP3C/GO composite thin film was fabricated on indium tin oxide (ITO) coated glass substrate by electrochemical polymerization. The glucose biosensor was constructed with immobilization of GOx on PP3C/GO composite thin film by covalent attachment. The developed glucose biosensor was characterized by cyclic voltammetry, scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and amperometry. It was found that the presented functionalized polypyrrole/graphene oxide composite thin film showed good electroactivity in neutral PBS solution and could be applied to the detection of biomolecule. The presented biosensor exhibited a high sensitivity and selectivity for the detection of glucose with a wide detection linear range from 1 to 20 mM, correlation coefficient of r2 = 0.9957, response time ∼5 s, and low detection limit (S/N = 3) of 0.05 mM. It also exhibited high stability and specificity to glucose. Therefore, it can be concluded that an electrochemically fabricated PP3C/GO composite thin film is a promising candidate as smart material for amperometric glucose biosensor.

Temperature-induced amperometric glucose biosensor based on a poly(N-vinylcaprolactam)/graphene oxide composite film.

A temperature-induced sensing film consisting of poly(N-vinylcaprolactam) (PVCL), graphene oxide (GO) and glucose oxidase (GOD) was fabricated and used to modify a glassy carbon electrode (GCE). The PVCL/GO/GOD/GCE composite film was characterized by electrochemical impedance spectroscopy (EIS). The morphological properties of the composite were investigated by scanning electron microscopy (SEM). The direct electron transfer (DET) of GOD was achieved. GOD at PVCL/GO/GOD/GCE exhibited a couple of well-defined redox peaks with a formal potential of -0.432 V (vs. Ag/AgCl). The composite film showed temperature-induced catalytic activity towards glucose. Large peak currents were observed by amperometry at -0.39 V (vs. Ag/AgCl) when the temperature was above the lower critical solution temperature (LCST) of PVCL, and then disappeared when it was below the LCST. The modified electrode displayed an excellent electrocatalytic response to glucose. The detection of glucose with the composite film ranged from 0.1 to 1.7 mmol L-1 above 35 °C. The constructed biosensor also possesses good stability, reproducibility and anti-interference ability.

Photonic actuators with predefined shapes.

Developing actuators with multi-responsibility, large deformation, and predefined shapes is critical for the application of actuators in the field of artificial intelligence. Herein, we report the preparation of a new type of unimorph actuators containing phenol-formaldelyde resin (PFR) and graphene oxide (GO) using the chiral nematic structure of cellulose nanocrystals (CNCs) as the template. The so-obtained PFR/GO films have a unimorph structure with an asymmetric distribution of GO across the film. They exhibit synchronous responses of both photonic properties and actuation to humidifying/dehumidifying. Moreover, PFR/GO films can be forged into desired shapes by aldehyde treatment, and thereby are able to produce complex movements. In addition, the objects with predetermined shapes show good shape recovery capability upon many wetting-drying cycles, especially through the treatment with formaldehyde. A mechanism model for shape predetermination by aldehyde treatment is suggested based on experimental details. By further designing the predetermined shapes and patterns, such PFR/GO actuators may hold great promise for smart actuation devices of highly complex movements.

Reversible Switched pH‐Responsive Hydroquinone Electrochemical Sensor Based on Composite Film of Polystyrene‐b‐Poly (Acrylic Acid) and Graphene Oxide

AbstractThe detection of some environmental pollutants remains still a great challenge and the current methods suffer from low sensitivity, reproducibility and require sophisticated instruments. Here, a simple, sensitive and pH‐responsive electrochemical sensor for the detection of hydroquinone (HQ) was developed based on a pH‐responsive block copolymer polystyrene‐b‐poly(acrylic acid) (PS‐b‐PAA) and graphene oxide (GO) composite film (PG) modified glassy carbon electrode (GCE). The electrochemical behaviors of HQ at the modified GCE (PG/GCE) electrode were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The peak current of the PG/GCE electrode toward HQ was significantly enhanced at pH 7.0 and greatly suppressed below pH 6.0, which are caused by swelling and shrinking of pH‐responsive block copolymer and the synergistic effect with GO. The PG/GCE exhibited a reversible “On/Off” switch for the HQ electrochemical behaviors between pH 4.0 and pH 7.0. When the pH of the medium is 7.0, the PG complex film on the PG/GCE is in the “On” state, the linear detection range of HQ is from 16 μM to 104 μM with a detection limit as low as 0.34 μM. Furthermore, the PG/GCE can also successfully detect the HQ concentration of the lake water sample with satisfactory recovery, indicating that the pH‐responsive block copolymer/GO‐functionalized sensor provided a powerful avenue for simple, sensitive and convenient detection of HQ, which can be translated into practical application.

High sensitivity detection of nitrogen oxide gas at room temperature using zinc oxide-reduced graphene oxide sensing membrane

Using thermal annealing process, graphene oxide (GO) films were synthesized into reduced graphene oxide (rGO) composite films. Compared with the NO2 gas sensors using ZnO and rGO sensing membranes, the performances of the NO2 gas sensors using ZnO-rGO sensing membrane were improved. The improvement mechanisms were attributed to the removal of oxygen-containing functional groups, the supply of electrons from the oxygen vacancies of ZnO material, and the formation of COZn bonds. To study the dependence of sensing performances on the ZnO/GO ratio, various ZnO/GO ratios in the ZnO-rGO sensing membrane were used in the NO2 gas sensors. For the best ratio of 0.08, the sensing responsivity, response time, and recovery time of the ZnO-rGO NO2 gas sensors were respectively improved to 47.4%, 6.2 min, and 15.5 min compared with 19.0%, 10.3 min, and 75.9 min of the rGO NO2 gas sensors operated under 100 ppm NO2 environment at room temperature. Furthermore, the minimum detective NO2 concentration of 5 ppm and linear sensing responsivity from 10 ppm to 100 ppm were achieved using the ZnO-rGO gas sensors operated at room temperature.