Electrical conductivity of oxidized-graphenic nanoplatelets obtained from bamboo: effect of the oxygen content

Synthesis of Sustainable Lignin Precursors for Hierarchical Porous Carbons and Their Efficient Performance in Energy Storage Applications

Lignin-derived porous carbons have great potential for energy storage applications. However, their traditional synthesis requires highly corrosive activating agents in order to produce porous structures. In this work, an environmentally friendly and unique method has been developed for preparing lignin-based 3D spherical porous carbons (LSPCs). Dropwise injection of a lignin solution containing PVA sacrificial templates into liquid nitrogen produces tiny spheres that are lyophilized and carbonized to produce LSPCs. Most of the synthesized samples possess excellent specific surface areas (426.6-790.5 m2/g) along with hierarchical micro- and mesoporous morphologies. When tested in supercapacitor applications, LSPC-28 demonstrates a superior specific capacitance of 102.3 F/g at 0.5 A/g, excellent rate capability with 70.3% capacitance retention at 20 A/g, and a commendable energy density of 2.1 Wh/kg at 250 W/kg. These materials (LSPC-46) also show promising performance as an anode material in sodium-ion batteries with high reversible capacity (110 mAh g-1 at 100 mA g-1), high Coulombic efficiency, and excellent cycling stability. This novel and green technique is anticipated to facilitate the scalability of lignin-based porous carbons and open a range of research opportunities for energy storage applications.

Basic physical properties and potential application of graphene oxide fibers synthesized from rice husk

The synthesis method and correlation between compositional, vibrational, and electrical properties in graphene oxide fibers (GOF) are presented and discussed here, as well as a potential application through the development of a heater device based on GOF. The GOF samples were synthesized from rice husk (RH), via a thermal decomposition method, employing an automated pyrolysis system with a controlled nitrogen atmosphere, varying carbonization temperature (TCA) from 773 to 1273 K. The compositional analysis shows peaks in the XPS spectrum associated with C1s and O1s, with presence of hydroxyl and epoxy bridges; the oxide concentration (OC) of samples varied from 0.21 to 0.28, influenced by TCA. The GOF samples exhibit fiber morphology, vibrational characteristics which are typical of graphene oxide multilayers, and electrical behavior that scales with OC. The electrical response shows that OC decreases and increases electrical conductivity at the polycrystalline phase, possibly attributed to the desorption of some oxides and organic compounds. In addition, physical correlations between OC and its vibrational response showed that decreasing OC increases edge defect density and decreases crystal size as a result of thermal decomposition processes. The correlation between OC and physical properties suggests that by controlling the OC in GOF, it was possible to modify vibrational and electrical properties of great interest in fabrication of advanced electronics; consequently, we show a potential application of GOF samples by developing an electrically controlled heater device.

Temperature dependence of electrical conductivity and variable hopping range mechanism on graphene oxide films

The rapid development of optoelectronic applications for optical-to-electrical conversion has increased the interest in graphene oxide material. Here, graphene oxide films (GOF) were used as source material in an infrared photodetector configuration and the temperature dependence of the electrical conductivity was studied. GOF were prepared by the double-thermal decomposition (DTD) method at 973 K, with a fixed carbonization temperature, in a pyrolysis system, under a controlled nitrogen atmosphere, over quartz substrates. Graphene oxide films were mechanically supported in a photodetector configuration on Bakelite substrates and electrically contacted with copper wires and high-purity silver paint. Morphological images from the GOF's surface were taken employing a scanning electron microscope and observed a homogeneous surface which favored the electrical contacts deposition. Vibrational characteristics were studied employing Raman spectroscopy and determined the typical graphene oxide bands. GOF were used to discuss the effect of temperature on the film's electrical conductivity. Current-voltage (I-V) curves were taken for several temperatures varying from 20 to 300 K and the electrical resistance values were obtained from 142.86 to 2.14 kΩ. The GOF electrical conductivity and bandgap energy (E_g) were calculated, and it was found that when increasing temperature, the electrical conductivity increased from 30.33 to 2023.97 S/m, similar to a semiconductor material, and E_g shows a nonlinear change from 0.33 to 0.12 eV, with the increasing temperature. Conduction mechanism was described mainly by three-dimensional variable range hopping (3D VRH). Additionally, measurements of voltage and electrical resistance, as a function of wavelength were considered, for a spectral range between 1300 and 3000 nm. It was evidenced that as the wavelength becomes longer, a greater number of free electrons are generated, which contributes to the electrical current. The external quantum efficiency (EQE) was determined for this proposed photodetector prototype, obtaining a value of 40%, similar to those reported for commercial semiconductor photodetectors. This study provides a groundwork for further development of graphene oxide films with high conductivity in large-scale preparation.

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The effective removal of chemisorbed water in graphene oxide by oxidized carbon nanotubes via cooperatively strengthened OH···OC hydrogen bonds.

Owing to their great significance for energy storage and sensing applications, multi-layer papers consisting of graphene oxide–carbon nanotube (GO–CNT) hybrid sheets were prepared by in situ exfoliation of graphite oxide in the presence of oxidized CNTs (oCNTs). For the first time we elucidate the influence of oCNTs on chemisorbed water (CW), i.e. the water molecules inherently bound to the oxygen functional groups (OFGs) of graphene oxide (GO) and responsible for irreversible structural damage upon thermal reduction processes. We show that oCNTs self-assemble onto GO sheets during the liquid phase processing steps by forming cooperatively strengthened OH···OC hydrogen bonds between the carboxylic groups of the oCNTs and OFGs of GO. At oCNT amounts of about 10 to 15 wt% this leads to the displacement of considerable amounts of CW without altering the original chemical composition of GO. The thermally reduced GO–CNT (rGO–CNT) papers reveal improved sp² character and an enhancement of the specific capacitance by 75% with respect to thermally reduced GO (rGO), largely due to the effective removal of CW by oxidized CNTs. These findings disclose the relevance of the cooperative hydrogen bonding phenomena in graphene oxide paper/film electrodes for the development of improved electrochemical energy storage and sensing devices.