Electrochemically Exfoliated Graphene Research Articles

Electrochemical Biosensors Composed of Polyethylenimine (PEI) and Graphene Derivatives for Rapid Detection of Alzheimer’s Disease

Graphene materials can be used as nanofillers in polymers to take advantage of graphene's suitable properties. Graphene-PEI composites are materials that combine the unique properties of graphene and PEI. These composites are made by combining graphene with PEI through physical or chemical method. The resulting material is characterized by enhanced mechanical properties, improved electrical conductivity and increased stability. By incorporating graphene into biosensor platforms, it can improve overall’s performance, including sensitivity, specificity and response. In this work, the detection of anti-βA40 biomarker was tested. Beta-amyloid peptide (βA1-40) was incorporated into liposomes of Dipalmitoyl Phosphatidylglycerol (DPPG) and was immobilized using Layer-by-Layer self-assembling technique on PEI_graphene derivatives composites. To obtain these composites it was utilized graphene oxide (GO) from Hummers’ method, it’s thermally reduced form (rGO) and also electrochemically exfoliated graphene (EEG). MilliQ water was added to the PEI to obtain a concentration of 2mg/mL and stirred for 30 min at room temperature for complete dissolution of the PEI. Then EEG, GO and rGO were added to PEI solution and subjected to ultrasonication in a Hielscher UP400ST sonicator, using the H14 probe for 30 minutes to obtain a homogeneous and stable dispersion.Carbon microelectrodes modified with PEI-graphene derivatives composites and (DPPG +Aβ-40) were used as biosensors platforms to detect anti-Aβ40 related to Alzheimer's disease. The assembly of the biosensors is shown in Figure 1. Cyclic Voltammetry was performed in three cycles, at a potential of -0.6 V to 0.6 V and scan rate of 0.05 V s-1 to evaluate the sensory response. The electrochemical measurements were performed with saline phosphate buffer solution (PBS). The morphology of PEI and PEI_graphene oxide can be seen in Figure 2. The large surface area of graphene allows for increased binding sites for bioreceptors, which may favor the adsorption of Aβ-40 peptide, improving signal transduction and sensitivity of the biosensor. The wettability of the composites was obtained through measurements of the static contact angle using the Ramé-Hart Contact Angle Goniometer (model 100-25-A). Figure 3 presents the contact angle for a film layer of the composites. All PEI_graphene derivative composites showed hydrophilic behavior (θ < 90°), PEI_EEG composite stood out as less hydrophilic (θ = 68°) among all composites. Hydrophilicity is essential in biosensors because it affects the interactions between the biological recognition elements and the target analytes, as well as the overall stability and reliability of the biosensor. Figure 4 presents the calibration curves using the normalized area obtained from cyclic voltammetry of the biosensors manufactured with 2 bilayers (PEI_graphene derivative/DPPG+Aβ40) and anti-Aβ40 biomarker in concentrations ranging from 1 ng mL to 5 µg mL-1. Among the tested PEI_graphene derivatives composites, the ones with EEG and RGO stood out in relation to pure PEI. Table 1 presents the adjusted R-square of the data in Figure 4. All composites, except PEI_GO, showed excellent linear fit, adjusted R-square close to 1 in the detection range between 1 and 1000 ng mL-1. The PEI_graphene oxide composite can be used in biosensors to enable rapid and efficient transduction of the binding signal, leading to improved detection performance. Figure 1

Emergent high conductivity in size-selected graphene networks

Nanomaterial networks are attractive for a diverse range of printed device applications including electronics, sensing, energy capture and storage. At present, the influence of morphology on the network properties, such as electrical transport, is poorly understood. Here, we develop an understanding of structure-property relationships in these systems by performing size selection from bulk to few-layer graphene. We observe size-dependent electrical conductivity spontaneously during film formation, with the smallest nanosheets realizing electrical conductivity exceeding 105 S/m, a record value for liquid-exfoliated graphene and competitive with electrochemically-exfoliated graphene. Given the high electrical conductivity exhibited by these networks, and the applicability of graphene as a model layered nanosheet system, we explore the use of this size-selected graphene for thermoelectric applications. We interpret our understanding of the high conductivities obtained in terms of nanosheet packing and its influence on the number density and nature of inter-sheet junctions. This work represents an approach to overcome junction-limited electronic transport and enable nanoparticulate networks for printed device applications.

Rational design of nickel‑cobalt sulfide nanorods grown on graphene with high performance for supercapacitors

Nickel cobalt sulfides have exhibited great promise as supercapacitor electrode materials owing to the abundant redox states and considerable theoretical capacities. However, they still suffer from sluggish reaction kinetics, resulting in undesirable capacitance, cyclic and rate performances. Herein, electrochemical exfoliated graphene with high dispensability was utilized as the matrix and uniform nickel‑cobalt sulfide nanorods grown on graphene (Ni-Co-S/G) was achieved by a facile two-step strategy for enhanced capacitive performances. This well-constructed Ni-Co-S/G can provide plentiful active sites for electrochemical reaction, offer more efficient and rapid electron/ion transfer pathways during the charge/discharge process, and the tight contact of nickel‑cobalt sulfide nanorods and graphene can improve the stability. Consequently, the obtained Ni-Co-S/G electrode exhibits a high specific capacity of 1579.68 F g−1 at 1 A g−1, splendid rate capability (1240 F g−1 at 20 A g−1) and excellent cycling stability with capacity retention of 91.5 % after 5000 cycles at 5 A g−1. Additionally, the assembled asymmetric supercapacitor (ASC) device Ni-Co-S/G//AC with Ni-Co-S/G and commercial active carbon as positive and negative electrode displays an energy density of 75.3 W h kg−1 at the power density of 1125 W kg−1, still retaining 50.5 Wh kg−1 even at 16.9 kW kg−1. This work provides a potential strategy to design high-performance nickel‑cobalt sulfides electrode for advanced supercapacitors.

Synthesis and Characterization of Electrochemically Exfoliated Graphene with High Conductivity and Thermal Stability after Reducing Treatment

Graphene is a nanomaterial of great technological interest due to its properties such as high conductivity, lightweight, and excellent mechanical flexibility with potential applications in the most diverse areas as batteries, supercapacitors and electrochemical sensors. The electrochemical exfoliation of graphite technique has great prominence compared to other techniques to produce graphene because of its relative ease, high yield, high quality products and scalability. However, this technique generates products with a high degree of oxidation. To restore the intrinsic properties of graphene, these oxygenated groups must be removed using reduction methods. This work demonstrates the production of high quality graphene derivative with excellent conductivity, low defects density and excellent thermal stability produced by electrochemical exfoliation with reduction treatment (rEEG) using ascorbic acid (AA) and sodium borohydride (SB) as reducing agents. Raman spectroscopy is an excellent tool for the characterization of graphene quality. The ID/IG ratio is an important parameter used as a criterion to identify the degree of disorder in the graphene structure. This technique was employed to quantify the defects in the lyophilized graphene derivatives. Raman spectra of the different graphene produced (Figure 1) shows that freeze-drying process provides graphene with low defects density, since the drying process is conducted under vacuum atmosphere and in very low temperatures (~ -100°C), favorable conditions to preserve the quality of graphene sheets and the degree of oxidation. SB-rEEG stands out for presenting lower defect density which is evidence of great removal of oxygenated groups, confirmed by the C:O ratio observed in Figure 2 (A). On the other hand, the reduction with ascorbic acid resulted in a more oxygenated graphene and with a greater number of defects. Figure 3 shows the AFM image of exfoliated graphene and its corresponding height profile. AFM measurement is a suitable technique to investigate the number of layers and morphology of graphene. Height profile image can be used to get information about the thickness of the graphene layers. Considering the thickness of 0.35 nm for each graphene layer, obtained from X-ray diffraction (XRD) spectrum (Figure 4). AFM height profile of the derivatives graphene obtained shows profiles varying from 4 - 10 nm thickness and from 40 to a few hundred nanometers wide, characterizing them as few layer graphene. Analyzing the conductivity results in Figure 2 (B), SB-rEEG showed a higher conductivity (~2.6 x 105 S m-1) compared to EEG (~7x 103 S m-1) and AA- rEEG (7 x 104 S m-1), demonstrating that sodium borohydride was an effective reducing agent for electrochemically exfoliated graphene (EEG). According to Figure 5 (a) , TGA analysis in an atmosphere of nitrogenshows that EEG presented three main phenomena: (i) water elimination, at temperatures below 100ºC (approximately 10%); (ii) removal of oxygenated groups, between 150ºC to ~250ºC and (iii) pyrolysis of the carbonic chain of the materials accompanied by structural rearrangements of the polyarene network, between 360ºC and 1000ºC. While for SB-rEEG (Figure 5(b)) the same phenomena were observed, but at a lower intensity. The SB-rEEG showed high thermal stability with a weight loss at 1000ºC close to 14%, while the EEG showed a weight loss of 45%. It was possible to restore the conductivity and thermal stability of the electrochemically exfoliated graphene subjected to reduction process, producing graphene derivatives with different chemical and physical properties for different applications. Figure 1

Development of Selective Cortisol Biosensors in the Control of Fatigue and Related Diseases

The study of fatigue becomes complex due to several subjective factors related to its causality, making the relationship between the level of fatigue and the concentration of cortisol in an individual characteristic. However, cortisol is identified as the main element released in response to fatigue, and as such, it can be used as a biomarker for its determination and other associated diseases. Inadequate amounts of cortisol are related to non-specific diseases such as diabetes and osteoporosis. The body's cortisol levels fluctuate throughout the day, with the greatest levels in the morning and the lowest in the evening. To correlate these various fluctuations to the degree of fatigue, is required a real-time determination of cortisol levels with an effective sensory device, which overcomes the demand of costly and time-consuming laboratory analysis. Cortisol, as expressed in sweat, has a wide dynamic concentration range that can be used to monitor fatigue during different activities, being useful in preventing diseases and accidents. Currently, cortisol evaluation may be critical as one of the prospective biomarkers for Covid-19-induced significant inflammatory consequences. Some studies show possible severity between the production of pro-inflammatory cytokines related to viral infection by the new Sars-Cov-2 in people with above-average serum cortisol levels. In this regard, the establishment of a simple and low-cost biosensor with rapid diagnosis and in loco application would be beneficial due to the analytical center's independence and the simplicity with patients positive for the Sars-Cov-2 virus or others may be followed and treated. For the cortisol biosensor development, electrochemically exfoliated graphene (EEG) was used as a current collector nanomaterial in combination with chitosan (CS), a biomaterial derived from discarded crustacean shells. The carbon DropSens were modified with nanocomposite containing CS and EEG prepared using an ultrasonication. 21µL of CS_EEG dispersion by drop casting and exposed for 4 hours by white light, in order to dry the nanocomposite and recover all the working electrode. The material not bounded to electrode was then removed after 3 washes of 50µL of Milli-Q water. 10 µL of glutaraldehyde 1 % solution (GA) was dripped on the electrodes and allowed to react for 15 minutes to guarantee greater interaction of the nanocomposite with the antibody. The wet surface of electrodes was then evaluated for the incorporation of monoclonal antibody solution by IgG type specific for cortisol at varying concentrations. A total of 7.5 µL of diluted IgG solution (3.33 ng mL-1) and pure IgG solution were added to the biosensor immune complex (100 ng mL-1) and allowed to act for 30 minutes. Sensory measurements are performed in standard cortisol dilutions in PBS 7.4 in the following concentrations: 1 ng mL-1, 10ng mL -1, 100ng mL-1, 200ng mL-1, 500ng mL-1 and 1 µg. Then, the electrodes with and without antibody were characterized, via electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), FEG microscopy, Goniometry and Zeta Potential. Goniometry assays showed an increase of hydrophilic profile of the nanocomposites after antibody modification conferring a suit surface for biological elements deposition, Fig 1. FTIR and FEG Microscopy provided the interaction of antibody-nanocomposite and antibody- antigen complex, Fig 2 and 3. Infrared analysis showed bands assigned to methyl groups disappeared after antibody adhesion and this condition may relates to the recovery of heavy chains of IgG on the nanocomposite. The increase in capacitance value after each sensory electrochemical measurement provided a cortisol curve calibration, Fig 4. The zeta potential of the immune complex formation showed an increase of values indicating a high interaction of immune system, mainly for GA condition, Fig 5. The cortisol calibration curve was improved by GA intercalation and the detections were enhanced in concentrated antibody condition, Fig 6. Figure 1

Electrochemical Determination of 4-Bromophenoxyacetic Acid Based on CeO2/eGr Composite.

The determination of plant growth regulators is of great importance for the quality monitoring of crops. In this work, 4-bromophenoxyacetic acid (4-BPA), one of the phenoxyacetic acids, was detected via the electrochemical method for the first time. A CeO2-decorated electrochemical exfoliated graphene (eGr) composite (CeO2/eGr) was constructed as the sensor for sensitive detection of 4-BPA due to the synergistic effect of the excellent catalytic active sites of CeO2 and good electron transference of the eGr. The developed CeO2/eGr sensor displayed a good linearity in a wide range from 0.3 to 150 μmol/L and the lowest detection limit of 0.06 μmol/L for 4-BPA detection. Electrochemical oxidation of 4-BPA follows a mix-controlled process on the CeO2/eGr electrode, which involves 2e in the transference process. This developed CeO2/eGr sensor has excellent repeatability with a relative standard deviation (RSD) of 2.35% in 10 continuous measurements. Moreover, the practical application of the sensor for 4-BPA detection in apple juice has recoveries in the range of 90–108%. This proposed CeO2/eGr sensor has great potential for detecting plant growth regulators in the agricultural industry.

Graphene Wrapped Siox/C Hollow Spheres Composites Via Molecular Polymerization As High Performance Libs Anodes

High-capacity silicon anodes have attracted researchers’ tremendous interest for next generation lithium-ion batteries (LIBs). However, its further application is limited by the large volume expansion during cycling, causing safety issues. Designing nanostructured silicon is an effective strategy to acquire high-performance anodes, but it will face problems of high cost and poor coulombic efficiency. Silicon dioxide and SiOx show relatively higher specific capacity and lower volume expansion than silicon anodes. So, they are now becoming popular among researchers. Structure design of silicon oxide composite is one of the main experimental schemes, like hollow structures. Within the composite materials, graphene becomes one of the main conductive composite matrixes which is ascribed to its superior conductivity and mechanical property since its application in energy storage areas. Hence, SiOx/C composites have been synthesized with carbon and SiOx dispersed uniformly via a simple template-free aldimine condensation between APTMS and dialdehyde. After freeze drying and pyrolysis, the hollow structure can be obtained, in which silicon oxide is derived from APTMS and carbon is derived from carbon chains from dialdehyde. The hollow structure can effectively buffer the volume expansion of silicon oxide during charging and discharging process. Then the hollow particles are wrapped by electrochemical exfoliated graphene. Optimal graphene contents and graphene layers in the composite will be determined to explore its application in LIBs. The introducing of graphene may suppress the volume expansion and improve the conductivity of composites at the same time. Various characterization methods will be conducted to confirm its electrochemical performance and find its potential as anode materials. Figure 1

Fabrication of Wearable Transistor with All-Graphene Electrodes via Hot Pressing.

Textile electronics are ideal for novel electronic devices owing to their flexibility, light weight, and wearability. In this work, wearable organic field-effect transistors (OFETs) with all-graphene electrodes, fabricated using hot pressing, are described. First, highly conductive and flexible electrodes consisting of a cotton textile substrate and electrochemically exfoliated graphene (EEG) were prepared via hot pressing. The EEG/textile electrodes exhibited a low sheet resistance of 1.3 Ω sq−1 and high flexibility; these were used as gate electrodes in the wearable OFETs. In addition, spray-coated EEG was also used as the source/drain (S/D) electrodes of the wearable OFETs, which recorded a sheet resistance of 14.8 Ω sq−1 after hot pressing. The wearable OFETs exhibited stable electrical performance, a field-effect mobility of 13.8 cm2 V−1 s−1, and an on–off current ratio of ~103 during 1000 cycles of bending. Consequently, the fabrication method for wearable transistors developed using textiles and hot-pressed graphene electrodes has potential applications in next-generation wearable devices.

Fabrication of reduced graphene oxide with high electrical conductivity by thermal-assisted photoreduction of electrochemically-exfoliated graphene oxide

Electrochemical exfoliation of graphite is a method for synthesizing graphene oxide (GO) with fewer structural defects than GO synthesized by conventional chemical oxidation. Photoreduction of GO has been focused on due to their facile procedures, and environmental friendliness. In this report, electrochemically-exfoliated graphene oxide (EGO) was irradiated by vacuum ultraviolet (VUV) light at 140 °C under a high vacuum environment, named thermal-assisted VUV light treatment. Conductive atomic force microscopy was used to investigate the electrical characteristics of individual sheets on the nanometer scale. The electrical conductivity of the treated sheet (1.4 × 105 S m−1) was higher than the pristine EGO by an order of magnitude. The chemical and structural analysis showed that the EGO was reduced and their π-conjugated domains were restored through a hybrid of photochemical and thermal treatment. These results indicate that our hybrid approach has the potential for reducing the EGO.

Electric-Field-Triggered Graphene Production: From Fundamental Energy Applications to Perspectives

ConspectusTwo-dimensional sp2-hybridized graphene has been seriously considered and applied in various fields, such as materials science, energy storage/conversion, catalysis, and biomedicine, on account of its unique long-range-ordered and π-conjugated structure as well as excellent thermal and electric conductivity. At present, the adopted methods for graphene synthesis cover micromechanical exfoliation, epitaxial growth, chemical reduction of graphite oxide, chemical vapor deposition, and liquid-phase exfoliation. Nonetheless, a number of issues and challenges still existed in these employed methods in terms of sustainable and green energy chemistry and environmental friendliness. Electrochemical exfoliation is one of the most promising methods for the large-scale production of graphene by virtue of simple/eco-friendly operation and high-efficiency production. Depending on different exfoliation methods (anodic, cathodic, and dual-electrode) and electrochemical exfoliation conditions such as the reaction device, raw material, electrolyte, and power-supply mode, the exfoliated graphene features various and versatile characteristics. The relatively perfect graphene with intrinsic long-range π-conjugated character is accompanied by the fast capability of electron transfer. The defective graphene features the adjustable size and defect density and tunable amphipathicity. As a result, the corresponding graphene has been employed in energy storage/conversion, biology, and medicine fields. In this Account, we summarize the recent progress in the fundamentals of electrochemical exfoliation to produce the graphene and the derivative exfoliation method and their applications in energy-related fields, and the corresponding perspectives are also highlighted. First, we describe the fundamentals for different exfoliation methods and electric-field-induced effects that can help to guide us to prepare and produce graphene with various properties, covering the size, defect density, and surface chemistry. Subsequently, three electric-field-triggered methods (anodic, cathodic, and dual-electrode exfoliation) are discussed in detail. In particular, the effects of various electrolytes and power-supply modes on electrochemically exfoliated graphene (EEG) are systematically underlined in terms of the exfoliation principles and process, which are the significant factors affecting the structure and properties of EEG and the efficiency of intercalation and exfoliation. In addition, the recent progress in multilevel applications of EEG in energy storage/conversion fields such as supercapacitors, secondary batteries, the oxygen evolution reaction, the hydrogen evolution reaction, the carbon dioxide reduction reaction, and so forth is also summarized. Finally, the expectations and future research directions for the EEG in terms of controllably technological parameters and conditions, precise monitoring and in-depth comprehension of the exfoliation processes, multiscale and diverse products (carbon quantum dots, graphene quantum dots, and single-atom catalysts), and large-scale preparation and application are discussed, which hope to provide significant guidance for future research.

Thermally conducting yet electrically insulating epoxy nanocomposites containing aluminum@electrochemically exfoliated graphene hybrid

The development of miniaturized and highly integrated microelectronic products has motivated the current importance of synthesizing heat-dissipation materials with high thermal conductivity and excellent electrical insulation. Although graphene is attractive for improving the thermal conductivity of polymers owing to its high aspect ratio and outstanding thermal conductivity, it significantly deteriorates electrical insulation capability, limiting its practical application in polymer composites for thermal management of electronics and systems. In this work, we used planetary ball milling to synthesize a hybrid powder Al@EEG consisting of electrochemically exfoliated graphene (EEG) and surface-passivated aluminum particles. This ball milling prevents contact between graphene sheets by uniformly dispersing EEG in Al matrices without the conventional surface modification or chemical treatment process of graphene, thereby imparting thermal conductivity and electrical insulation to the hybrid powder. The resulting epoxy composite, containing 35- wt% Al@EEG hybrid, retains an electrical resistance of 1014 Ω·cm or higher and a thermal conductivity of 1.43 W m−1 K−1, which is 499% higher than that of neat epoxy. The as-designed material points the way to polymer-based, thermally conductive, electrically insulating composites for various electronic components such as printed circuit boards and light-emitting diode driver cases.

Optimized electrocatalytic performance of PtZn intermetallic nanoparticles for methanol oxidation by designing catalyst support and fine-tuning surface composition

The electrode performance of fuel cells highly depends on the characteristics of catalysts and catalyst supports. In this work, small PtZn intermetallic (PtZn-i) nanoparticles (< 4 nm) with adjustable surface composition are fabricated on graphene-based nitrogen-doped porous carbon support by pyrolysis of Pt-injected ZIF-8 (ZIF-8@Pt) on electrochemically exfoliated graphene (EEG). This designed two-dimensional porous carbon is capable of providing an electron transfer network and mass transport channels for PtZn-i catalysts. Moreover, in-situ growth of PtZn-i nanoparticles embedded in the carbon wall ensures the small size and high dispersibility of the catalysts, which are beneficial for methanol oxidation on them. Besides, the surface electronic structure of PtZn-i catalysts is fine-tuned by adjusting the mole ratio of Pt to Zn. The results show that PtZn-i catalysts with slightly Zn-rich surface (Pt/Zn = 0.9) exhibit optimized electrocatalytic performance for methanol oxidation. Density functional theory calculations reveal that slightly increasing Zn atoms in the surface can enhance the adsorption of CH2OH* intermediate on PtZn-i catalysts, thereby reducing the reaction free energy of the rate-determining step of methanol oxidation reaction and promoting the electrocatalytic performance of PtZn-i catalysts. This work provides a new perspective to improve the electrocatalytic performance of intermetallic catalysts by surface modification and support design.

Electrochemically Exfoliated Graphite Nanosheet Films for Electromagnetic Interference Shields

Electrochemical exfoliation of graphite is one of the most efficient and easiest processes to produce high-quality graphene materials. In this study, the efficiency of exfoliation methods for graphite to develop graphene-based electromagnetic interference (EMI) shields with high electrical conductivity was investigated. Exfoliation of graphite was performed in four aqueous solutions of inorganic salts of Na2SO4, (NH4)2SO4, NH4NO3, and (NH4)2HPO4, and the electrochemically exfoliated graphene (EEG) was thoroughly screened to separate out the more defective and small sheets. A 30 μm thick film composed of stacked and overlapped co-doped EEG sheets prepared in (NH4)2SO4 had a room-temperature electrical conductivity of 28 400 S/m and an EMI shielding effectiveness (EMI SE) of ∼62 dB in the X-band frequency (8.2–12.4 GHz), without any reduction of EEG sheets. These are both high values compared to values reported in the literature for “graphene” films with comparable thickness. This is an excellent EMI SE for a shield thickness of just 30 μm, compared to the very thick initial graphite sheet’s EMI SE of ≈70 dB with a thickness of 1.5 mm (50 times thicker). An original finding in this paper is that using the (NH4)2HPO4 electrolyte, we were able to prepare thermally stable EEG films with excellent EMI performance (shielding effectiveness of ∼50 dB after 3-day exposure to 500 °C in air). These high values for overall EMI shielding and electrical conductivity confirm the feasibility of electrochemical exfoliationfor high-performance EMI shields; i.e. it is possible to use a method that does not involve treatment with harsh chemicals or oxidizers and does not require high energies or high temperatures.

Scalable activated carbon/graphene based supercapacitors with improved capacitance retention at high current densities.

Scalable, highly stable supercapacitor electrodes were developed from the mixture of a tea factory waste based activated carbon (AC) and a low-cost electrochemical exfoliated graphene (EEG). The hybrid electrodes showed notably enhanced stability at high current densities. The AC sample was prepared by chemical method and exposed to a further heat treatment to enhance electrochemical performance. Graphene used in the preparation of hybrid electrodes was obtained by direct electrochemical exfoliation of graphite in an aqueous solution. Detailed structural characterization of AC, EEG, and hybrid material was performed. The original electrochemical performances of AC and EEG were examined in button size cells using an aqueous electrolyte. The hybrid materials were prepared by mixing AC and EEG at different mass percentage ratios, and tested as supercapacitor electrodes under the same conditions. Capacitance stability of the electrodes developed from AC:EEG (70:30) at high currents increased by about 45% compared to the original AC. The highest gravimetric capacitance (110 F/g) was achieved by this hybrid electrode. The hybrid electrode was scaled up to the pouch size and tested using an organic electrolyte. The organic electrolyte was preferred for scaling up due to its wider voltage ranges. The pouch cell had a gravimetric capacitance of 85 F/g and exhibited as good performance as the coin cell in the organic electrolyte.

Mechanical and Barrier Properties of Bromo–Butyl Elastomers Filled with Electrochemically Exfoliated Graphene

AbstractIn this paper, the effects of graphene loading and processing technique on the morphological, mechanical, thermal, rheological, and barrier properties of bromo–butyl rubber, are explored. Bromo–butyl rubber composites with electrochemically exfoliated graphene (EEG) nanosheet filler are prepared via solvent casting and/or melt blending techniques, and their properties are compared against a carbon black control sample. Even though analysis of the EEG composites via microscopy reveals agglomeration problems not present in the carbon black controls, EEG composite samples are observed to have improved barrier properties over carbon black samples in exchange for slightly reduced stress and strain at break. Extensional rheological analysis of the bromo–butyl rubber composites reveals strain hardening phenomena in all the samples and higher extensional modulus in solvent casted‐melt blended (SCM) samples. As a result of better dispersion over the solely melt‐blended samples, the SCM rubber composites exhibit superior tensile modulus and extensional modulus compared to the samples that are solely melt‐blended.

Electrochemically Exfoliated Graphene for High-Durability Cement Composites.

The development of radically new types of corrosion-resistant cement composites is nowadays compulsory in view of the continuous increase of concrete consumption combined with the intrinsically defective nature of concrete. Among various additives being employed in the concrete technology, carbon nanomaterials have emerged as extremely powerful components capable of remarkably enhancing nano- and microstructures as well as properties of cement-based composites. In this study, we demonstrate that cement mortar incorporating electrochemically exfoliated graphene (EEG) exhibits significantly improved fluid transport properties. The addition of 0.05 wt % of EEG to ordinary Portland cement mortar results in the reduction of initial and secondary sorptivity values by 21 and 25%, respectively. This leads to the outstanding resistance of EEG-cement composites to highly corrosive environments, namely, chloride and sulfate solutions. These observations, combined with the previously reported remarkable enhancement of the tensile strength of EEG-cement mortars, represent a major step toward the development of highly durable graphene-based cement composites.

Reduction of Electrochemically Exfoliated Graphene Films for High-Performance Electromagnetic Interference Shielding.

Two-dimensional graphene is of great interest for electromagnetic interference (EMI) shielding owing to its inherent electrical conductivity, lightweight, and excellent mechanical flexibility even at minor thicknesses. However, the complex synthesis and quality-control difficulties limit its application. In this study, we demonstrate that electrochemically exfoliated graphene (EEG) with post-reduction treatment is a promising candidate for lightweight EMI shielding materials. A facile electrochemical exfoliation approach produces a high-quality multilayer graphene with a high electrical conductivity of ∼600 S cm-1, owing to its low degree of oxidation. The reduction of EEG by three different methods, including chemical, thermal, and microwave treatments, causes the removal of surface functional groups as well as significant changes in the microstructure of the final films. The reduced graphene films by microwaves, which are driven by the improved electrical conductivity and large volume expansion, exhibit an EMI shielding effectiveness of 108 dB at a thickness of 125 μm, one of the largest EMI shielding values ever reported for graphene at comparable thicknesses.

Interlayer Separation in Graphene Paper Comprising Electrochemically Exfoliated Graphene.

The emergence of graphene paper comprising well-stacked graphene flakes has promoted the application of graphene-based materials in diverse fields such as energy storage devices, membrane desalination, and actuators. The fundamental properties of graphene paper such as mechanical, electrical, and thermal properties are critical to the design and fabrication of paper-based devices. In this study, the interlayer interactions in graphene paper were investigated by double cantilever beam (DCB) fracture tests. Graphene papers fabricated by flow-directed stacking of electrochemically exfoliated few-layer graphene flakes were mechanically separated into two parts, which generated force-displacement responses of the DCB sample. The analysis based on fracture mechanics revealed that the interlayer separation energy of the graphene paper was 9.83 ± 0.06 J/m2. The results provided a fundamental understanding of the interfacial properties of graphene papers, which will be useful for developing paper-based devices with mechanical integrity.

Synthesis and Characterization of Graphene Sheets from Graphite through Electrochemical Exfoliation and Microwave Reduction

Graphene as a wonder material has received great attention and importance due to its fascinating properties. Here in this study, we also demonstrate a simple two step process to prepare graphene sheets (GSs) from the electrochemical exfoliated graphene oxide (EE-GO) followed by microwave irradiation reduction. The properties and structure of the resulted product samples were studied by Ultraviolet spectroscopy (UV), Fourier-transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy-dispersive X-ray (EDX or EDS), Raman spectroscopy and Atomic force microscopy (AFM) for validation of their distinguishing characteristics. UV spectra of microwave irradiation reduced graphene oxide (MI-RGO) and EE-GO exhibited an intense and sharp absorption peak concentrated at wavelengths of 236 and 266nm, respectively. The elimination of oxygen functionalities present in the EE-GO plane was illustrated by FTIR as a result of microwave irradiation treatment. The relative layer structures of MI-RGO and EE-GO were confirmed by XRD. Similarly, the Raman spectra revealed the difference in between the EE-GO and MI-RGO characteristic reflection bands. The thin, crumpled and curved type morphology of the obtained graphene sheets (GSs) was also displayed by SEM while the composition of a few layer graphene sheets with atomic mass percents of carbon (75%) and oxygen (25%) was established by EDX. The Synthesis procedure is simple, rapid and eco-friendly with high yield.

High‐density polyethylene reinforced by low loadings of electrochemically exfoliated graphene via melt recirculation approach

AbstractThe purpose of the paper is to demonstrate the effectiveness of high‐aspect ratio electrochemically exfoliated graphene (EEG) as a filler in high‐density polyethylene (HDPE); we use an industrially viable polymer processing technique (melt blending with melt recirculation) to ensure excellent dispersion and reinforcement at low loadings. The effects of nanofiller loading were evaluated for two different HDPE grades with two different melt flow indices (MFI) based on crystallization, tensile, and rheological properties. The findings indicate improvements in mechanical properties (tensile modulus and tensile strength) for all HDPE/EEG nanocomposite samples; however, the reinforcement was more pronounced at 0.2 wt% loading, indicating a transition from excellent dispersion at lower loadings to aggregated at higher loadings. The low and high MFI HDPE/EEG nanocomposites at 0.2 wt% EEG loading displayed an improvement of 31% and 40% in tensile modulus and 19% and 33% in tensile strength, respectively. The improved mechanical response with higher MFI nanocomposites is likely due to enhanced dispersion associated with the lower melt viscosity. Similarly, the rheological results also showed maximum increase in storage and loss modulus at a loading of 0.2 wt% EEG. In conclusion, EEG can be an effective filler if proper dispersion is achieved, which is challenging at high loadings.