Graphene-like Carbon Material Research Articles

High-performance asymmetric supercapacitor assembled with three-dimensional, coadjacent graphene-like carbon nanosheets and its composite

In our work, the porous carbon nanosheets (PCNs) are successfully prepared using one-step activation and carbonization of the naturally hollow tube-like dandelion fluffs. The dandelion fluff with hollow tube structure is composed of aligned nanocellulose, enabling the facile activating agent (KOH) permeation, which can activate the dandelion fluff into porous interconnected carbon nanosheets. The obtained porous interconnected graphene-like structure of the activated carbon material contributes to the electrolyte permeation and electron transfer, which is beneficial to enhance the electrochemical performances, especially the rate capability. Manganese dioxide (MnO2) modified PCNs composited with MnO2 is prepared as the positive electrode for asymmetric supercapacitor using in-situ microwave deposition method. The conformally coated MnO2 on PCNs can facilitate the ion diffusion and the electron transport, which contribute to the enhancement of the rate performance. Herein, the assembly asymmetric supercapacitor based on PCNs and MnO2/PCNs composite displays an energy density as high as 28.2 Wh kg−1 at the power density of 899.36 W kg−1 and a good capacitance retention of 89% after 10,000 cycles. These results present that the graphene-like cross-linked carbon material is a promising electrode material for high-efficiency electrochemical energy storage and conversion.

Multivariate modeling via artificial neural network applied to enhance methylene blue sorption using graphene-like carbon material prepared from edible sugar

Graphene-like carbon (GLC) material was facile synthesized from edible sugar by a thermal dehydration method, used an adsorbent for methylene blue (MB) removal. The purity and physicochemical properties, including surface morphology, textural property, surface elemental composition and nanostructure of as synthesized GLC was investigated by microscopy and spectroscopy techniques. These results confirmed the formation of nano size (50–100) aggregated plate GLC by showing high specific surface area, 674.593 m2/g and 0.278 cm3/g pore volume. The adsorptive removal of MB onto the GLC increased with increases of the dosages of adsorbent and the pH of the solution; however, as the initial concentration of MB was increased, its removal efficiency was decreased. From batch studies, initial concentration of 10 mg/L, pH of 8 and dosage of 4.0 g/L were found to be the optimum experimental conditions for maximum amount of MB removal. The optimized isotherm parameters were evaluated by a differential evaluation optimization (DEO) approach suggesting that the Langmuir model better describe the MB adsorption. This result indicates the adsorption process is a monolayer adsorption on homogeneous surface. The kinetic study demonstrated that the adsorption of dye onto GLC followed the pseudo-second-order kinetic. Further, the adsorption process variables were optimized using multivariate modeling via artificial neural network (ANN). The maximum adsorption capacity (qm) of GLC for MB is around 20 mg/g. This may attributed to the high surface area of GLC and due to multiple adsorption mechanisms, including pore filling, and electrostatic interactions between MB and GLC. The overall results demonstrate the suitability of GLC for organic dye, MB removal from water. In addition, the present study confirms the viability and quantifiability of the use of GLC by comparison with other graphene/carbon based adsorbents for MB removal.

Highly microporous nitrogen doped graphene-like carbon material as an efficient fuel cell catalyst

Nitrogen-doped carbon materials are known to be promising candidates as oxygen reduction reaction electrocatalysts used in fuel cells. However, developing metal-free catalysts with high performance and stability still remains a big challenge. Herein we report a new route by using the Maillard reaction, to caramelize ribose in a dispersing salt matrix, followed by carbonization of this caramel to synthesize metal-free catalysts. This catalytic material has the morphology of microporous nitrogen doped graphene-like carbon, and a highest surface area of 1261 m2 g−1 with a large amount of micropores. Such microporous structure offers numerous defects that generate a large number of reactive sites. As a result, when used as the cathode materials in fuel cells, the fuel cell shows a high power density of 547 mW cm−2 under 1.0 atm back pressure with good stability with only 12.5% loss after 250 h. Such catalyst has good performance in the class of metal-free oxygen reduction reaction catalysts, and is possible for commercial use.

Silk-Derived Graphene-like Carbon Material with High Electrocatalytic Activity for Oxygen Reduction Reaction

Natural silk-derived, graphene-like carbon fiber (GF) assisted by K intercalation shows high catalytic activity for the oxygen reduction reaction (ORR). The enhancement in ORR activity results from the formation of a porous structure composed of nitrogen-containing graphene, which not only increases the specific surface area but also leads to more active nitrogen species within the carbon network being exposed to the electrolyte.

Silk-derived graphene-like carbon with high electrocatalytic activity for oxygen reduction reaction

A facile method to prepare graphene-like carbon material from a natural silk fiber was developed by a potassium intercalation and carbonization procedure. The as-synthesized graphene-like fiber exhibited impressive oxygen reduction activity.

Facile synthesis of nitrogen and sulfur co-doped graphene-like carbon materials using methyl blue/montmorillonite composites

Heteroatom-doped carbon materials are currently drawing increasing interest because they show remarkable performance when applied in lithium-ion batteries, supercapacitors, and fuel cells. In this work, a facile method was developed to synthesize N and S co-doped graphene-like carbon materials using montmorillonite (Mt) after the adsorption of methyl blue (MB). The MB–Mt composites were pyrolyzed in a N2 atmosphere to carbonize the adsorbed MB within the interspace of Mt. The resulting pyrolyzed carbon/Mt composite showed a basal spacing value of approximately 0.44 nm, close to the thickness of a single graphene sheet, suggesting the formation of graphene-like carbon materials within the interspace of Mt. Then, the carbon/Mt composite was demineralized by acid washing to liberate the carbon materials. Transmission electron microscopy and atomic force microscopy results directly showed the morphology of the resulting carbon material, i.e., the stacking of thin carbon sheets. Raman spectra showed the simultaneous presence of both a D-band and G-band for the obtained carbon materials, and their intensity ratio decreased with increasing pyrolysis temperature. X-ray photoelectron spectroscopy results indicated the presence of C, S, and N atoms in the carbon materials, and the doping sites of the S and N atoms were proposed. Finally, the obtained carbon materials showed interesting electrocatalytic activity for the oxygen reduction reaction, suggesting their potential application as efficient metal-free electrocatalysts in fuel cells. Our work synthesized N and S co-doped graphene-like materials with interesting electrocatalytic activity, which proved that the templated synthesis method could be a facile approach to synthesize various heteroatom-doped graphene-like carbon materials.

Preparation and Capacitive Properties of Graphite-like Porous Carbon Based on Coal Extracts

By using extracts of lignites as carbon precursors, MgO as isolation agent, and KOH as activator, porous graphene-like carbon materials were prepared at 800°C under an inert atmosphere. Porous carbon materials were characterized by FTIR, XRD, TEM and Raman. Further, electrochemical capacitive properties of porous carbons before and after activation as the electrodes were evaluated by cyclic voltammetry, galvanostatic charge-discharge and impedance spectroscopic techniques. Results indicate that carbon materials after activation exhibit porous film-like shape. The specific surface areas of carbon materials before and after activation are 138.4 m/g and 1396 m/g, respectively. Specific capacitances of carbon materials after activation reach 533 F/g and 390 F/g at 1 A/g and 4 A/g, respectively, while those of carbon materials before activation at same conditions are 366 F/g and 198 F/g. After 8000 cycles at a current density of 5 A/g, the capacitance retentions of carbon materials before and after activation are 72.5% and 40 无 机 材 料 学 报 第 31卷 89.6%, respectively. Accordingly, after KOH activation, the specific capacitance and electrochemical stability of carbon materials are significantly improved. This study verifies that the use of the isolation agent and the activator can obtain highly flexible graphene-like porous carbon with high capacitance performance.

Templated synthesis of nitrogen-doped graphene-like carbon materials using spent montmorillonite

This work provided a method that can recycle the spent montmorillonite and synthesize heteroatom-doped graphene-like materials.

Porous layer-stacking carbon derived from in-built template in biomass for high volumetric performance supercapacitors

Two-dimensional (2D) porous graphene-based materials such as graphene nanomesh, activated graphene and curved graphene, possess high gravimetric performances due to their high surface area and short ion transport path. However, their poor volumetric performances come from low density and/or high pore volume of the electrode materials, as well as their high manufacturing cost, which would limit their further applications. In this work, densely porous graphene-like carbon (PGC) materials were greenly synthesized through hydrothermal treatment of fungus (Auricularia) and subsequent carbonization process. Layer-stacking PGC derived from cell walls of fungus has high surface area (1103m2g−1), high bulk density (about 0.96g cm−3), and hierarchically interconnected porous framework, which can provide more storage sites and short transport paths for electrolyte ions, and enhance the overall conductivity of the electrode. As a result, the PGC electrode shows ultra-high volumetric capacitance of 360F cm−3 and excellent cycling stability with 99% capacitance retention after 10000 cycles. More importantly, the as-assembled symmetric supercapacitor delivers superior volumetric energy density of 21WhL−1 and excellent cycling stability (96% specific capacitance retention after 10000 cycles). These exciting results suggest a low-cost and environmentally friendly design of electrode materials for high volumetric-performance supercapacitors.

Fast and non-catalytic growth of transparent and conductive graphene-like carbon films on glass at low temperature

This article presents the synthesis and systematic study of graphene-like carbon thin films directly grown on commercial glass by using remote electron cyclotron resonance plasma-assisted chemical vapour deposition. The fabrication process is extremely rapid and performed on 2 inch scale dielectric substrate at relatively low temperature (<550 °C) without using metal catalyst. This method avoids damaging and expensive transfer processes of graphene based films and improves compatibility with current fabrication technologies. Nanostructural characterization by transmission electron microscopy indicates the formation of layered graphene-like carbon material. Raman spectroscopy shows that the film consists of nanocrystals with a mean domain size close to 2 nm, probably interconnected by amorphous material. These graphene-like carbon based films are transparent and conductive. Functional optoelectric characterization of these films confirms their high transparency over 95% and relative high conductivity around 5 kΩ, exceeding the properties of non-doped small domain graphene based films grown at low temperatures reported so far.

Preparation of Graphene-Like Carbon Materials as Electrodes of Electric Double Layer Capacitors

Graphene-like carbon materials (GCMs) are prepared by the carbonization of liquid acrylonitrile oligomer (LANO) at 600-1400 °C for 4 h in an Ar atmosphere. LANO undergoes thermal oxidative dehydrogenation and preliminary cyclization by pre-process in air at low temperature (120 °C) and high temperature (220 °C) before the carbonization. Surface chemistry，crystalline and pore structures of the GCMs are characterized by scanning electron microscope (SEM), power X-ray diffraction (XRD) and N2 adsorption respectively. Comparison of the effect of various carbonization temperatures on the electrochemical performance of the electric double layer capacitors (EDLCs) is specifically investigated. The GCMs carbonized at 1300 °C for 4 h shows a fairly good electrochemical performance. The BET surface area of GCM1300 is 81.58 m2/g and the specific capacitance of the GCM1300 is 22.52 F/g in 1 mol/ L Et4NBF4/PC electrolytes.

Theoretical Study of Hydrogen Chemisorption to Nitrogen-Substituted Graphene-Like Compounds

Abstract Interaction between nitrogen-substituted graphene-like compounds and hydrogen was investigated using ab initio molecular orbital methods to assess hydrogen storage. We adopted coronene as a model molecule for fragmented graphene-like carbon materials and compared the chemisorption energies of hydrogen on pure and N-substituted coronens by changing nitrogen positions. Among the assumed 19 N-substituted models with different substitution sites, three representative models were selected and closely examined to reveal the dependences on both nitrogen-substitution and hydrogen-adsorption positions. Optimized structures of the chemisorbed products are largely stabilized by N-substitution at a certain position. Positive or negative energy gain was apparent depending on both substituted sites of N and adsorbing position of H2. The results suggest that it is possible to improve hydrogen storage properties of graphene-like materials by N-substitution.

Theoretical Study on N Doping in Carbon Materials for Hydrogen Storage

AbstractInteraction between nitrogen-substituted graphene-like compounds and hydrogen was investigated using ab initio molecular orbital method in the aspect of hydrogen storage. We adopted coronene as a model compound for fragmented graphene-like carbon materials and compared the interaction between hydrogen and pure or N-substituted coronenes by changing nitrogen positions. Among the assumed 19 N-substituted models, polarozabilities and HOMO–LUMO gaps were compared to evaluate physisorption and chemisorption energies. As for chemisorption, two N-substituted models were selected and closely examined to reveal the dependence on both nitrogen-substitution and hydrogen-adsorption positions. Potential energy surfaces as a function of H–H bond length and H2–coronen distance showed that the barrier height for hydrogen chemisorption strongly depends on N-substitution positions. The chemisorbed products of N-substituted coronenes are stabilized or destabilized compared with the pure carbon case depending on the sites of N-substitution and H-adsorption. These results suggest that N-substitution at certain positions possibly improve hydrogen storage properties of graphene-like materials.