Laser-Reduced Graphene Oxide with Ultralow Defect Density for Paper-Supported Electrochemical Capacitors.

Reduction of graphene oxide on polyethylene terephthalate surface by using transmission femtosecond laser

Facile laser fabrication of high quality graphene-based microsupercapacitors with large capacitance

Graphene oxide (GO) films are deposited on flexible Kapton substrates and selectively modified to conductive reduced graphene oxide (rGO) electrodes using laser patterning. Based on this, we design, fabricate, and test a flexible sensor integrating laser-reduced GO with silver plasmonic nanostructures. The fabricated device results in dual transduction channels: for electrochemical and plasmonic nanostructure-based surface-enhanced Raman spectroscopy (SERS) detection. The spectroscopic analysis verifying the formation of rGO and the modification by silver nanostructures is performed by Raman, energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The morphological investigation is followed by optical and scanning electron microscopy imaging. In addition to pristine silver nanostructures, the Raman spectroscopy results show the formation of species such as Ag2O, Ag2CO3, and Ag2SOx. A dual-channel sensor device based on electrochemical and plasmonic detection is fabricated as a demonstration of our Ag-rGO flexible concept architecture. The dual-channel device performance is successfully demonstrated in the electrochemical and SERS detection of 4-nitrobenzenethiol (4-NBT) using the same device. Our results show that without Ag nanostructures the sensitivity in the electrochemical and optical channels is not sufficient to detect 4-NBT. The performance and stability of the silver modified device are also verified. This work demonstrates an inexpensive, highly efficient, and greener way that is compatible with solution-processing technology for the production of flexible GO-based electrochemical and SERS detection devices integrated with plasmonic nanostructures.

In this work, a simple, single-step electrochemical method is used to decorate a ternary Polypyrrole-Cu2O-MoO3 (PPy-Cu2O-MoO3) nanocomposite on Graphene Oxide (GO) nanosheets formed on a Graphite Foil Electrode (GFE). The characterization confirmed successful synthesis of ternary nanocomposite, and electrochemical tests showed the electrode performed well as both a supercapacitor and a hydrogen evolution reaction (HER). The investigation of the hydrogen production reaction by the PPy-Cu2O-MoO3/GO/GFE shows that this electrode has a smaller Tafel slope and overpotential. Additionally, the PPy-Cu2O-MoO3/GO/GFE has a specific capacitance of 1010.30 mF cm-2 at 1mA cm-2 in a 0.5 M H2SO4 electrolyte solution. The evaluation of the fabrication of a symmetric solid-state supercapacitor device shows that the constructed device has an excellent capacitance of 596.5 mF cm-2 at 1mA cm-2 and a cyclic stability of 82.4% after 6000 GCD cycles. For hydrogen evolution reaction, the electrode demonstrated an overpotential of 361 mV at 10mA cm-2 and a Tafel slope of 142 mV dec-1, indicating favorable electrocatalytic activity. These results highlight the potential of the synthesized nanocomposite as a multifunctional electrode material for both energy storage and clean energy production.

Two-dimensional atomically thick materials, reduced graphene oxide (RGO), and layered molybdenum disulfide (MoS2 ) have been investigated as potential novel energy storage materials because of their distinct physicochemical properties. These materials suffer, however, from rapid capacity decay and low rate capability. This study describes a facile, binder-free approach to fabricate large-scale, 3D network structured MoS2 @carbon nanotube (CNT)/RGO composites for application in flexible supercapacitor devices. The as-obtained composites possess a hierarchical porosity, and an interconnected framework. The electrochemical supercapacitive measurements of the MoS2 @CNT/RGO electrode show a high specific capacitance of 129 mF cm-2 at 0.1 mA cm-2 . The symmetric supercapacitor devices based on the as-obtained composites exhibit a long lifetime (94.7 % capacitance retention after 10 000 cycles), and a high electrochemical performance (29.7 mF cm-2 ). The present experimental findings will lead to scalable, binder-free synthesis of MoS2 @CNT/RGO hybrid electrodes, with enhanced, flexible, supercapacitive performance, in portable and wearable energy storage devices.

This study presents a novel slit evaporation self-assembly method for fabricating freestanding sulfuric acid-treated reduced graphene oxide/commercial graphene films (S-ATrGO/CG). The unique capillary slit-induced self-assembly process facilitates the alignment and stacking of graphene flakes, resulting in a well-ordered, laminated film. The treatment of graphene oxide (GO) with sulfuric acid facilitates the ring-opening of inert functional groups, converting them into active functional groups. Sulfuric acid-treated graphene oxide (ATGO) can serve as an effective binder for adhering commercial graphene flakes. X-ray photoelectron spectroscopy was used to quantitatively analyze the oxygen-containing functional groups in GO, ATGO, and S-ATrGO/CG. A series of electrochemical tests were conducted to investigate the behavior of the S-ATrGO/CG films, which exhibited well-defined redox peaks, indicating the contribution of unreduced oxygen-containing groups to redox reactions and pseudocapacitance. The S-ATrGO/CG films exhibit superior electrochemical performance, with an ultra-high area-specific capacitance of 1,589.78 mF cm-2 at a scan of 5 mV s-1 and an impressive initial capacitance retention of 99.80% after 20,000 cycles at a current density of 50 mA cm-2. This study highlights the potential of S-ATrGO/CG films as high-performance electrodes for supercapacitors, contributing to the advancement of sustainable energy storage systems.

A low voltage, flexible, graphene-based electrothermal heater for wearable electronics and localized heating applications

Graphene Oxide (GO) has been prepared by modified Hummers method and it has been reduced using an IR bulb (800-2000 nm). Both as grown GO and reduced graphene oxide (RGO) have been characterized using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Raman spectra shows well documented Dband and G-band for both the samples while blue shift of G-band confirms chemical functionalization of graphene with different oxygen functional group. The XPS result shows that the as-prepared GO contains 52% of sp 2 hybridized carbon due to the C=C bonds and 33% of carbon atoms due to the C-O bonds. As for RGO, increment of the atomic % of the sp 2 hybridized carbon atom to 83% and rapid decrease in atomic % of C=O bonds confirm an efficient reduction with infrared radiation. UV-Visible absorption spectrum also confirms increment of conjugation with increased reduction. Non-linear optical properties of both GO and RGO are measured using single beam open aperture Z-Scan technique in femtosecond regime. Intensity dependent nonlinear phenomena are observed. Depending upon the intensity, both saturable absorption and two photon absorption contribute to the non-linearity of both the samples. Saturation dominates at low intensity (~ 127 GW/cm 2 ) while two photon absorption become prominent at higher intensities (from 217 GW/cm 2 to 302 GW/cm 2 ). We have calculated the two-photon absorption co-efficient and saturation intensity for both the samples. The value of two photon absorption co-efficient (for GO~ 0.0022-0.0037 cm/GW and for RGO~ 0.0128-0.0143 cm/GW) and the saturation intensity (for GO~57 GW/cm 2 and for RGO~ 194GW/cm 2 ) is increased with reduction. Increase in two photon absorption coefficient with increasing intensity can also suggest that there may be multi-photon absorption is taking place.

Unveiling a novel mechanism: Reduction of graphene oxide by Lysinibacillus sp. through secretion of l-ascorbic acid

This research work aims to explore the potential usage of post-consumer waste expanded polystyrene (EPS) for the fabrication of self-standing electrodes by incorporating reduced graphene oxide (rGO) into it via a facile cost-effective mechanical mixing process. The π-π interaction between the expanded polystyrene and rGO is evidenced from FT-IR and Raman analysis. The elevated thermal stability of the EPS/rGO composite from thermogravimetric analysis (TGA) further confirms the interconnection between the rGO and EPS. This π-π stacking interaction between the rGO and the polystyrene molecules present in the polymer matrix enable the composite material to be interconnected throughout which is beneficial for the charge transport process. The symmetric coin cell supercapacitor fabricated using the EPS/rGO composite electrode can be operated with a high operating voltage of 1.6 V in aqueous KOH and Na2SO4 electrolytes. The devices fabricated with KOH and Na2SO4 electrolytes deliver an areal capacitance of 11.9 mF cm-2 and 10 mF cm-2 at the discharge current density of 0.1 mA cm-2. Further, the devices fabricated with the KOH and Na2SO4 electrolytes demonstrated remarkable rate capability of 87.1% and 99.5% after 10 000 continuous charge discharge cycles. This facile method of preparation without consuming energy or polluting the environment is a novel approach which can be scaled-up to large-scale fabrication of self-standing plastic electrodes for low-cost energy storage applications.

Here we report a highly conductive polypropylene-graphene nonwoven composite via direct coating of melt blown polypropylene (PP) nonwoven fabrics with graphene oxide (GO) dispersions in N,N-dimethylformamide (DMF), followed by the chemical reduction of GO with hydroiodic acid (HI). GO as an amphiphilic macromolecule can be dispersed in DMF homogeneously at a concentration of 5 mg/mL, which has much lower surface tension (37.5 mN/m) than that of GO in water (72.9 mN/m, at 5 mg/mL). The hydrophobic PP nonwoven has a surface energy of 30.1 mN/m, close to the surface tension of GO in DMF. Therefore, the PP nonwoven can be easily wetted by the GO/DMF dispersion without any pretreatment. Soaking PP nonwoven in a GO/DMF dispersion leads to uniform coatings of GO on PP-fiber surfaces. After chemical reduction of GO to graphene, the resulting PP/graphene nonwoven composite offers an electrical conductivity of 35.6 S m-1 at graphene loading of 5.2 wt %, the highest among the existing conductive PP systems reported, indicating that surface tension of coating baths has significant impact on the coating uniformity and affinity. The conductivity of our PP/graphene nonwoven is also stable against stirring washing test. In addition, here we demonstrate a monolithic supercapacitor derived from the PP-GO nonwoven composite by using a direct laser-patterning process. The resulted sandwich supercapacitor shows a high areal capacitance of 4.18 mF/cm2 in PVA-H2SO4 gel electrolyte. The resulting highly conductive or capacitive PP/graphene nonwoven carries great promise to be used as electronic textiles.

Graphene oxide (GO) and reduced graphene oxide (rGO) synthesised from GO, has a promising future in fields ranging from electronics to energy technologies[1]. GO may be synthesized by the modified Hummer’s method[2], where a mixture of potassium permanganate and concentrated sulfuric acid forms the ground pillar for the oxidation of graphite to GO. rGO can be synthesized by a broad range of methods, with the chemical and the thermal reduction routes being very common[3]. The synthesis mechanism of GO by the modified Hummer’s method is still unknown, even though the active oxidizing species dimanganese heptoxide has been suggested as the main redox active specie[4]. The mechanism of the thermal reduction of GO to rGO is also unknown. We present results from i n situ synchrotron X-ray diffraction (XRD) experiments of syntheses and thermal reduction of GO. The in situ synthesis of GO was performed by placing a mixture of permanganate and sulphuric acid in a capillary next to graphite. The synthesis was then initiated by gently pushing the fluid mixture into the powder with N2 gas. The in situ XRD of the GO synthesis showed how the oxidation reaction proceeds in three separate stages, as seen in Figure 1. The first stage was the dissolution of potassium permanganate, followed by an intercalation stage and subsequent formation of crystalline material. The GO 001 diffraction peak was observed early during the synthesis, in the second stage, and the intensity of the 001 diffraction increased during the third stage. The in situ XRD results of the thermal reduction of GO to rGO showed a dependence on the temperature ramping and addition of diamond powder. Syntheses were measured at 1, 5, 10, 20 and 50 °/min temperature ramps. The syntheses were performed in a capillary with GO being heated by a hot air blower under constant N2 flow. Three stages were observed for the reduction process; a GO stage, an amorphous stage and a rGO stage. The change in stage was defined from the changing of the d-value of the initial 001 GO peak, see Figure 2. The initial GO diffraction pattern changed during the heating and more diffraction peaks were observed. The results showed that the nature of the rGO material depends heavily on both temperature and additives. These in situ XRD studies revealed the crystalline intermediates and final product of synthesis by a modified Hummer’s method and the diffractional change during the thermal reduction of GO. The stages observed for both syntheses illuminate how important it is to consider the experimental parameters dependent on the application; they might even have to be optimized separately. As the future use of GO and rGO is expanding and the commercialization of these products are enhanced, the syntheses mechanisms may be of increasing interest. [1] M. Segal, Nat Nano, 4 (2009) 612-614. [2] Hummer and Offeman, J. Am. Chem. Soc. (1958) 1339-1339 [3] Pei and Cheng, Carbon (2012) 3210-3228 [4] Dreyer, Park, Bielawski and Ruoff, Chem. Soc. Rev. (2010) 228-240 Figure 1

An easy ionothermal method is proposed to deoxygenate graphene oxide (GO) for preparation of graphene by using a choline chloride (ChCl)/urea mixture-based ionic liquid. In the synthesis process, the urea portion in the ionic liquid breaks up to release NH3 at around 100 °C. This reacts with the oxygen functional groups of the GO sheets, leading to the formation of graphene. The ionothermal method is an environmentally-friendly and attractive strategy for reducing GO because both ChCl and urea are naturally biocompatible compounds. X-Ray photoelectron spectroscopy indicates that nitrogen atoms can be doped into the graphene skeleton accompanied by the reduction of GO. As an electrode for an electrochemical double layer capacitor in aqueous KOH, the ionothermally reduced GO exhibits a gravimetric capacitance of 155 F g−1 at a current density of 0.2 A g−1 and good cycling performance, which is comparable to the hydrazine reduced GO. We expect that the ionothermal method will have implications for the use of ionic liquids in the large-scale synthesis of graphene-based materials.

Graphene oxide/polyvinylpyrrolidone composite coating on 316L SS with superior antibacterial and anti-biofouling properties

In-depth understanding of the photoreduction of graphene oxide to reduced-graphene oxide on TiO2 surface: Statistical analysis of X-ray photoelectron and Raman spectroscopy data