New fuel cell electrodes made from graphene nanosheets and their nanocomposites

The production of novel catalyst support materials could open up new ways to enhance the catalytic activity by reduced catalyst loadings. Nanocomposites composed of conducting polymers reinforced with graphene nanosheets (GNS) or graphite oxide (GO) sheets can be potential fuel cell electrodes as an alternative to commercial fuel cell electrodes

Structural characterization of semicokes produced from the pyrolysis of petroleum pitches

Semicokes obtained from the pyrolysis of petroleum pitches are important materials that are used in the manufacture of many carbonaceous products. Therefore, new structural information of the semi-cokes will extend their utilization. The structural analysis of anisotropic semicokes of the pyrolysis of petroleum pitches obtained under various experimental conditions of temperature and time was investigated. The overall objective is to provide further detailed information of factors which influence formation of anisotropy or turbostratic structures in resultant semicokes. Experiments were carried out under an argon atmosphere at the temperature range of 500-1000 degrees C for 30, 60 and 120 min in a tube furnace. FTIR, H-1-NMR, and C-13 NMR results showed that the aromatic structure of the semicokes was increasing with respect to increasing temperature as well as increasing time. Aromaticity of the semicokes was calculated as 0.54 and 0.64, for Pitch A at 500 degrees C after 120 min, and Pitch B at 600 degrees C after 120 min, respectively. The intensity ratio between Raman "D" and "G" peaks, I-D/I-G (commonly used to characterize disorder in graphene structures) was observed to increase approximately linearly from 0.65 to 0.92 when the pyrolysis temperature of Pitch A was increased from 500 degrees C to 900 degrees C. XRD patterns of the semicokes showed the formation of some crystalline material with time and temperature. The average number of layers, calculated by the Debye-Scherer technique using the XRD patterns of the semicokes, was between 5 and 10. SEM images of the semicokes indicated the presence of turbostratic structures. All the results of characterizations were consistent and indicated the formation of highly amorphous hydrocarbon materials that contain turbostratic structures. Treatments at higher temperatures increased formations of aromatic structure with increased crystallinity. Temperature seemed to be the dominating parameter of the pyrolysis reactions. As the pyrolysis temperature was increased, aromatic structure formation was favored with increased crystallinity in the semicokes. We expect that findings of the present work will open new uses for the anisotropic semicokes obtained from petroleum pitches. The pitches can be widely applied to the templating synthesis of carbon nanostructures and other carbon nanomaterials

Synthesis of mesoporous MCM-41 materials with low power microwave heating

Crystalline, high surface area, hexagonal mesoporous MCM-41 having uniform pore sizes and good thermal stability was successfully synthesized at 90-120oC in 30 minutes using low power microwave irradiation. This appears to be the first comprehensive and quantitative investigation of the comparatively rapid synthesis of mesoporous MCM-41 using low power microwave heating of 80W (90oC) and 120W (120oC). The influence of reaction temperature and the duration of heating were carefully investigated and the calcined MCM-41 materials were characterized by XRD, SEM, TEM, nitrogen adsorption, TGA and FTIR. The mesoporous MCM-41 product synthesized in 30 minutes at 120W and calcined at 550oC had a very high surface area of 1438 m2/g and was highly ordered, contained uniform pores with diameters in the range of 3.5-4.5 nm. The wall thickness of the materials highly depended on the power of the microwave energy used during the synthesis. Synthesis of the mesoporous MCM-41 products at 120oC resulted with a structure having thinner walls. The mesoporous MCM-41 materials synthesized in the present work had good thermal stability

Synthesis and characterization of iron-impregnated pre-oxidized activated carbon prepared by microwave radiation for As(V) removal from water

One of the most efficient ways to treat water is probably by adsorption and catalytic oxidation. Surely, for such a process to be economical, the catalyst and the adsorber should have a high catalytic activity and adsorption capacity, and be inexpensive. One of these materials is iron oxide, which is studied and used in areas like catalysis and environmental applications. It is known that synthesizing iron oxides in nano size enhances the catalytic activity. Pre-oxidized activated carbons impregnated with iron-based nanoparticles are prepared in a single step under hydrothermal conditions with microwave radiation. The hydrothermal treatment provides an important advantage by forming fine particles that can easily impregnate deep in to the porous support by the help of water. Their efficiency for the removal of As(V) from water was compared with the pure pre-oxidized activated carbon and iron oxide nanoparticles impregnated without microwave radiation. The synthesized nanomaterials with different iron oxide loadings were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area analyzer. Iron loadings were calculated using flame atomic absorbance. Microwave radiation provided much faster iron impregnation on the active carbon surface. At the first stage of microwave radiation iron oxide impregnation is low but after 6 minutes, iron oxide nanoparticles of 100 nm size started to cover the surface homogeneously. Further treatment with microwave increased the size of particles and the amount of surface coverage. Additionally, with microwave hydrothermal treatment, relatively higher iron oxide loadings were achieved within 10 minutes. From the XRD characterization it was seen that at the first stage of radiation, iron deposited in the form of -FeOOH, but after the first stage the structure became Fe2O3. While radiation increased the surface area of the material during the first stages, at the last stage the surface area did not increase because of complete surface coverage. Laboratory experiments were carried out to analyze removal capacities of the adsorbents, and also to achieve adsorption isotherms and kinetic parameters. The adsorption was strongly dependent on pH, adsorbent dose and As(V) concentration. Percentage removal of As(V) increased with the decrease in pH value of solution and in order to obtain an effective arsenate removal, the adsorption experiments would require pH values between 3 and 5 for the adsorbent materials. According to kinetic sorption data, for all adsorbent materials, higher regression coefficients (R2) were obtained after the application of pseudo-second order to the experimental data of As(V)’s initial concentrations. The results indicated that iron-impregnated pre-oxidized activated carbon is one of the appropriate adsorbents which can be used for water contaminated with arsenic

Nafion-coated LiNi0.80Co0.15Al0.05O2(NCA) cathode preparation and its influence on the Li-ion battery cycle performance

One of the main problems of LiNi0.80Co0.15Al0.05O2(NCA) materials is the sidereactions occurring during battery cycling. These side reactions result in capac-ity fading, which in turn decreases the life span of the battery. Conventionally,for nickel-rich cathodes, an inorganic layer is used as a protective layer. Apply-ing these layers may require additional complicated steps. To overcome thisproblem, we focused on coating the NCA electrode with a polymeric ion con-ductive layer that can easily be applied. For this purpose, using an ion-conductive polymer is a novel approach. We used Nafion as the protectivelayer on NCA electrodes. While the Nafion layer can protect the surfaceagainst the side reactions, it does not prevent the Li+ion flow. Following thispurpose, we synthesized NCA by a modified co-precipitation method followedby sintering at 750C. After the preparation of the NCA cathodes, we coatedthe surfaces with a more straightforward drip coating. The Nafion-coated elec-trodes delivered a superior electrochemical performance with 100% of dis-charge capacity retention even after 100 cycles at 0.1C. The electrochemicalimpedance spectroscopy revealed that the Nafion coating could effectively pre-vent passive layer formation, which causes capacity fading

Fundamental open questions on engineering of "super" hydrogen sorption in graphite nanofibers: relevance for clean energy applications

Herein, some fundamental open questions on engineering of “super” hydrogen sorption (storage) in carbonaceous nanomaterials are considered, namely: 1) on thermodynamic stability and related characteristics of some hydrogenated graphene layers nanostructures: relevance to the hydrogen storage problem; 2) determination of thermodynamic characteristics of graphene hydrides; 3) a treatment and interpretation of some recent STM, STS, HREELS/LEED, PES, ARPS and Raman spectroscopy data on hydrogensorbtion with epitaxial graphenes; 4) on the physics of intercalation of hydrogen into surface graphene-like nanoblisters in pyrolytic graphite and epitaxial graphenes; 5) on the physics of the elastic and plastic deformation of graphene walls in hydrogenated graphite nanofibers; 6) on the physics of engineering of “super” hydrogen sorption (storage) in carbonaceous nanomaterials, in the light of analysis of the Rodriguez-Baker extraordinary data and some others. These fundamental open questions may be solved within several years

Biogasification and combustion reactions of Turkish lignites: adsorption behavior and biogasification of Soma lignite and co-combustion of Beypazari lignite with biomass

In this study, our primary objective is to understand CBM capacity of the Soma coal basin. For this reason, porosity of the coal samples must be determined. Usually, surface area and the porosity of the materials can be calculated through the N2 physical sorption experiment, in this method entire relative pressure range (10-8 to 1) can be analyzed without using high pressure equipments. However, for microporous materials like carbon materials and zeolites physical sorption occurs at very low relative pressure ranges (10-8 to 10-3) and experiments that are conducted with N2 are less reliable due to the low diffusion rate and adsorption equilibrium in the pores between 0,5 to 1 nm at 77 K. It is also known that specifically for carbon materials experiments that are conducted at low temperatures such as N2 sorption causes pore shrinkage that leads to the low sorption equilibrium