Three-dimensional Reduced Graphene Oxide Network Research Articles

N doping porous carbon embedded in self-assembled three-dimensional reduced graphene oxide networks for electrochemical hydrogen storage

Electrochemical hydrogen storage can realize reversible hydrogen absorption and desorption at room temperature and pressure, which has attracted extensive attention recently. A nanosheet-like reduced graphene oxide (rGO)-porous carbon composite with N-doping defect is prepared via a facile annealing, followed by hydrothermal and freeze-drying process. After N-doping, the porous carbon materials exhibit rich pore structure, and high pyridine nitrogen and pyrrolic nitrogen content. Adding them into the graphene self-assembly process, the aggregation tendency of graphene sheets can be reduced, the composite shows a free-standing 3D porous structure. Benefit from the synthetic effect between the rGO conductive network, the hierarchical porous structure, and the doping of N atoms, the rGO-N800 delivers a high hydrogen storage capacity of 266.3 mAh g−1 at 200 mA g−1 after 100 cycles. Moreover, the reversible capacities of the composite can reach 288.4, and 267.1 mAh g−1 at 1000 mA g−1 and 2000 mA g−1, respectively. The outstanding electrochemical performance of the composite demonstrates a promising direction for design carbon-based hydrogen storage materials.

Fabrication of a membrane-less non-enzymatic glucose-air fuel cell with graphene‑cobalt oxide nanocomposite anode and Fe, N-doped biomass carbon cathode

Abiotic glucose air fuel cell possess higher durability and power density than its enzyme-based counterparts, thereby offering new paradigms towards their commercialization. Till date, noble metal electrocatalysts dominate the area of abiotic glucose-air fuel cells. We here provide the synthetic strategy to develop highly efficient non-noble metal based carbonaceous hybrid structures as both anode and cathode catalysts in the fuel cell. The anode catalyst for glucose oxidation, consists of Co3O4 nanoparticles supported on three-dimensional reduced graphene oxide networks, directly grown on a nickel foam substrate (Co3O4-3DrGO/Nif) via coelectrodeposition. On the other hand, nitrogen and iron doped biowaste derived activated carbon (N,Fe-PSAC) material, synthesized via simple pyrolysis technique is employed as a cathode for oxygen reduction reaction. Excellent O2-insensitivity and glucose tolerance are observed for Co3O4-3DrGO/Nif and N,Fe-PSAC, respectively in the experimental electrolyte, 0.1 M KOH under air atmosphere. Therefore, a single compartment fuel cell, without any separator, containing only 10 mM glucose is developed with these electrodes. The as-fabricated cell exhibits an open circuit voltage (OCV) of 0.442 V and delivers the highest power delivery of 12.81 μW cm−2. Such low-cost abiotic glucose-air fuel cell has tremendous scope to be optimized and miniaturized for real-time applications as alternative power sources.

Freeze-drying assisted fabrication of highly homogenized reduced graphene oxide/alumina metacomposites with negative permittivity

Graphene oxide (GO) was used to fabricated the highly homogenization reduced graphene oxide (RGO)/alumina (Al2O3) metacomposites with low percolation threshold and adjustable negative permittivity by spark plasma sintering method. Compared to the dry grinding method used for the graphene(GR)/Al2O3 and GR/AlN metacomposites reported in our previous work, the highly homogenization RGO/Al2O3 metacomposites were obtained based on freeze-drying. The microstructures and phase composition of the RGO/Al2O3 metacomposites were investigated by field emission scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The dielectric properties including permittivity (ε′ and ε′′), dielectric loss tangent (tan δ), alternating current conductivity (σac) and reactance (Z′′) were discussed in detail. The percolation phenomenon of σac was observed when the content of RGO increased from 13.50 to 15.38 wt%, and the percolation threshold fitted by the power law was 14.31 wt%, which appeared earlier than the reported GR/Al2O3 and GR/AlN metacomposites. What's more, the negative permittivity behavior was observed when the content of RGO reached 13.50 wt%, which was ascribed to the formation of continuous three-dimensional RGO network among the metacomposites. The RGO13.50/Al2O3 and RGO15.38/Al2O3 metacomposites realized the ε′ transition from negative to positive at 501 and 299 MHz, corresponding to the capacitive-inductive conversion.

High-performance flexible supercapacitors based on electrochemically tailored three-dimensional reduced graphene oxide networks

A simple approach for growing porous electrochemically reduced graphene oxide (pErGO) networks on copper wire, modified with galvanostatically deposited copper foam is demonstrated. The as-prepared pErGO networks on the copper wire are directly used to fabricate solid-state supercapacitor. The pErGO-based supercapacitor can deliver a specific capacitance (Csp) as high as 81±3 F g−1 at 0.5 A g−1 with polyvinyl alcohol/H3PO4 gel electrolyte. The Csp per unit length and area are calculated as 40.5 mF cm−1 and 283.5 mF cm−2, respectively. The shape of the voltammogram retained up to high scan rate of 100 V s−1. The pErGO-based supercapacitor device exhibits noticeably high charge-discharge cycling stability, with 94.5% Csp retained even after 5000 cycles at 5 A g−1. Nominal change in the specific capacitance, as well as the shape of the voltammogram, is observed at different bending angles of the device even after 5000 cycles. The highest energy density of 11.25 W h kg−1 and the highest power density of 5 kW kg−1 are also achieved with this device. The wire-based supercapacitor is scalable and highly flexible, which can be assembled with/without a flexible substrate in different geometries and bending angles for illustrating promising use in smart textile and wearable device.

Controlled synthesis of three-dimensional reduced graphene oxide networks for application in electrode of supercapacitor

Three-dimensional reduced graphene oxide network deposition on Ni foam (3D rGO/NF) was successfully synthesized by a new process. Here, the structure and loading of rGO deposition on Ni foam could be easily controlled by the synthesis conditions. Furthermore, it was directly applied as the electrode of supercapacitor, in which the electrochemical behaviors of 3D rGO/NF with various structures were further compared in detail. As a result, the rGO film deposition on backbones of Ni foam electrode delivered a higher specific capacitance comparing to rGO aerogel deposition on Ni foam. The result was attributed to that the direct and close contact between rGO film and Ni foam was beneficial to the enhanced conductivity of the electrode, as well as the improvement of ion diffusion/transport into the electrode for the rGO film deposition on backbones of Ni foam. The works provided a new way to controlled synthesis of rGO network at large scale for in various applications.

Approaching the theoretical capacitance of graphene through copper foam integrated three-dimensional graphene networks

A facile and cost-effective approach to fabricate all-in-one supercapacitor electrodes is achieved with copper foam integrated three-dimensional reduced graphene oxide networks. The resulting electrodes display high specific capacitance close to the theoretical value of graphene and good charging–discharging stability.

Experimental study of transient boiling characteristics on three-dimensional reduced graphene oxide networks

We report nucleate pool boiling experiments using reduced graphene oxide (RGO) colloidal suspensions on a silicon dioxide plate surface, in order to describe a kind of quasi-transition boiling phenomenon, whereby the wall temperature gradually increased as a function of time without a rapid increase in temperature at the critical heat flux (CHF). Under boiling conditions, the RGO flakes formed a three-dimensional (3D) graphene structure at the surface, so that the RGO colloidal suspension exhibited a larger boiling heat transfer coefficient and larger CHF with the quasi-transition boiling phenomenon than when the working fluid was deionized water. To evaluate the effect of the heat flux conditions on the phenomenon, various heat fluxes were investigated, and the transient behavior of the boiling heat transfer characteristics was observed. We found that the rate of change of the wall temperature in the quasi-transition boiling regime was proportional to the heat flux, even if the higher heat flux was applied following the onset of the increase in the wall temperature.

Enhanced rate capability of LiMn0.9Mg0.1PO4 nanoplates by reduced graphene oxide/carbon double coating for Li-ion batteries

The reduced graphene oxide (RGO)/carbon double-coated LiMn0.9Mg0.1PO4 (LMP) nanoplates are introduced as a cathode material for Li-ion batteries with excellent rate capability. The double coating of RGO and carbon simultaneously brings the unique advantages of conformal carbon layer on each particle surface, and soft RGO sheets connecting the nanoplates to each other, thereby provides easy conduction pathways for the whole LMP aggregates. In particular, the simple self-assembly process driven by the electrostatic interactions enables conducting RGO sheets effectively to wrap the carbon-coated LMP, establishing three-dimensional RGO network. The RGO/C/LMP nanocomposites exhibit remarkably enhanced rate capability compared to the only C- or RGO-coated LMP, which is well explained by the reduced charge-transfer resistance achieved from electrochemical impedance spectroscopy.

Mesoporous anatase TiO2 submicrospheres embedded in self-assembled three-dimensional reduced graphene oxide networks for enhanced lithium storage

A novel composite of mesoporous TiO2 submicrospheres embedded in three-dimensional (3D) reduced graphene oxide networks (denoted as MTO/3D-GN) as an electrode material for Li-ion batteries (LIBs) was prepared via a facile hydrothermal self-assembly strategy. The as prepared MTO/3D-GN composite shows monolithic 3D interconnected networks of reduced graphene oxide sheets with well-dispersed mesoporous submicrospheres composed of small-size anatase TiO2 nanocrystals. The novel composite integrates the advantages of mesoporous structure, submicrometer-sized spherical morphology and reduced graphene oxide, thereby providing a high contact area between the electrolyte and electrode, favorable diffusion kinetics for both electrons and lithium ions, and double protection against the volume changes of electroactive TiO2 materials and excellent electrical conductivity of the overall electrode during electrochemical processes. The evaluation of its electrochemical performance for lithium storage demonstrates that the prepared MTO/3D-GN composite has greatly improved lithium storage properties. In particular, the unique hybrid material has the ability to deliver high reversible capacities with superlative cyclic capacity retention at different current rates for prolonged cycling, and exhibit excellent high-rate performance at a current rate as high as 20 C. The embedded reduced graphene oxide composite with designed mesoporous structure and advanced chemical composition can be used for high-performance LIB negative-electrode materials and other important applications such as solar cells and photocatalysis.