Carbon Oxygen Groups Research Articles

Effect of the carbon surface chemistry on the metal speciation in Ru/C catalysts. Impact on the transformation of levulinic acid to γ-valerolactone

A set of Ru/C catalysts prepared using a commercial active carbon and a series of carbon materials derived from it (treatment in N2 flow, at 300, 600 or 900 °C that selectively removes surface oxygen complexes), of similar textural properties and different surface chemistry, were used, without reduction treatment, in the aqueous phase transformation of levulinic acid (LA) to γ-valerolactone (GVL) at 70 °C. The prepared Ru/C catalysts were active, being activity and selectivity strongly dependent on the support surface chemistry. It was confirmed that the supported Ru species became reduced under reaction conditions, and this process was more efficient in catalysts prepared with the heat treated supports, due to the different interactions created between Ru species and the support surface. In a cleaner carbon surface, the anchorage of the Ru species on carbon oxygen groups was limited, and they were more prone to be reduced and to move, forming more defined metallic structures. The carbon surface chemistry determined the Ru speciation (reduced and oxidized species), and the proportion of reduced Ru drived the H spill over process, which was related to the creation of protonic acid sites, proposed to be key point to explain the trend in selectivity to GVL.

Facile preparation of polyvinyl chloride/activated carbon thin-film composites and study of their microwave absorption at Ka-band frequencies

Poly(vinyl chloride) (PVC) and activated carbon (AC) powders were hot-pressed into (PVC)100– x /(AC) x thin-film composites (TFCs), where x = 0.2–30 wt%. The nanostructure, morphology, and composition of AC were investigated by TEM, SEM, and EDX. The thermal stability and surface carbon-oxygen groups of the AC filler were determined by thermolysis in air and vacuum. The AC effect on the (PVC)100– x /(AC) x TFCs transparency to the electromagnetic radiation (EMR) was demonstrated at Ka-band microwave frequencies. Characteristically, the EMR reflection of the TFCs increases with the x value. For reduced EMR reflection, these TFCs should contain only 0.2 wt% AC.

(Invited) Enabling High Quality Dielectric Passivation on Monolayer WS2 Using a Sacrificial Graphene Oxide Template

Two-dimensional transition metal dichalcogenides (2D TMDC’s) hold a wide variety of applications, among which microelectronic devices. 2D TMDC’s are promising alternatives for today’s silicon-based technology but suffer from various integration challenges. Among others, direct dielectric growth on the 2D surface occurs poorly due to their self-passivated surfaces resulting in island-like growth initiated at defect sites. This work focuses on enabling uniform high-k dielectric nucleation and growth on 2D TMDC’s via a sacrificial, graphene oxide-based buffer layer. Essentially, the role of the sacrificial graphene buffer layer is twofold: 1) serve as a passivation layer, protecting the underlying 2D TMDC (i.e., WS2) during processing and 2) act as a nucleation layer, enabling uniform atomic layer deposition (ALD) high-k dielectric (i.e,. HfO2) growth. A graphene layer is transferred on monolayer WS2, after which polymeric transfer residues are cleaned via a combination of wet treatments and a dry hydrogen downstream plasma exposure. The cleaned graphene is functionalized via a dry UV/O3 oxidative treatment, which enriches its basal plane with carbon-oxygen single bond functionalities by sacrificing its π-network. This way, the graphene carbon lattice itself remains intact and retains its passivation properties. Moreover, a substrate dependency is observed where graphene transferred on WS2 requires longer UV/O3 exposure to ensure functionalization compared to a SiO2 substrate and can be explained by UV-light induced, ultrafast charge transfer between the graphene and WS2 monolayer. The carbon-oxygen groups formed on graphene’s basal plane act as nucleation sites during a subsequent HfO2 ALD process. A constant roughness is noted for the HfO2 film grown on the graphene oxide capped WS2, indicating uniform material deposition even in the early stages of the ALD process. This is in sharp contrast when HfO2 is directly grown on the WS2 monolayer, whose roughness stabilizes only after many ALD cycles (up to 256), demonstrating the poor, island-like growth mechanism. In addition, a similar hafnium areal density is measured for the graphene oxide capped WS2 compared bare SiO2, which was selected to represent a well-functionalized surface and thus confirming the efficiency of the graphene oxide-based nucleation layer. For devices incorporating the graphene oxide buffer layer concept, a crucial question is to what extent the graphene oxide layer gives rise to leakage currents by providing a conductive path between source and drain. Electrical evaluation of a GFET by means of I-V measurements reveal a significant shift in Dirac point towards positive gate voltage for transferred graphene, which is typically associated with p-type doping originating from the polymeric transfer residues still present on the surface. The Dirac point shifts towards 0-point voltage after final hydrogen downstream plasma cleaning, confirming the effectiveness of the established cleaning protocol. Moreover, Graphene’s conductivity is suppressed after UV/O3 to the nA range, as caused by the formation of carbon-oxygen functionalities and associated sacrifice of its π-network. The residual current may be further suppressed by extending the UV/O3 treatment, but nevertheless demonstrates that the graphene oxide buffer layer will not give rise to significant leakage currents.

Physicochemical characteristics of three-phase products of low-rank coal by hydrothermal carbonization: experimental research and quantum chemical calculation

In this paper, the distribution characteristics of gas, liquid, and solid products of low-rank coal by hydrothermal carbonization (HTC) at different temperatures are studied. Advanced testing methods are used to explore changing rules of physicochemical characteristics. Reaction properties of different regions are explained based on the mechanism of quantum chemistry. Experimental results showed that as the temperature increases, the volatile content decreases, the fixed carbon content increases, and impurities are removed in the form of gas or ions. The coal aliphatic properties are reduced, whereas the aromatization degree is significantly enhanced. Meanwhile, the specific surface area after upgrading is reduced, but the average pore diameter is increased, and the pore structure density is enhanced. The content of carbon-containing groups increases but that of carbon-oxygen groups decreases, which corresponds to the O/C ratio. Theoretical calculation results demonstrate that the more negative and positive areas of the surface electrostatic potential (ESP), the smaller distribution proportion. The ESP value in the vicinity of oxygen-containing group is relatively negative, indicating that it is more reactive, which is a good proof of the experiment's conclusions. In summary, low-rank coal obtained after HTC meets the blast furnace injection requirements and can be used for injection.

Tailoring Coordination in Conventional Ether-Based Electrolytes for Reversible Magnesium-Metal Anodes.

Rechargeable magnesium (Mg) batteries based on conventional electrolytes are seriously plagued by the formation of the ion-blocking passivation layer on the Mg metal anode. By tracking the Mg2+ solvation sheath, this work links the passivation components to the Mg2+ -solvents (1,2-dimethoxyethane, DME) coordination and the consequent thermodynamically unstable DME molecules. On this basis, we propose a methodology to tailor solvation coordination by introducing the additive solvent with extreme electron richness. Oxygen atoms in phosphorus-oxygen groups compete with that in carbon-oxygen groups of DME for the coordination with Mg2+ , thus softening the solvation sheath deformation. Meanwhile, the organophosphorus molecules in the rearranged solvation sheath decompose on the Mg surface, increasing the Mg2+ transport and electrical resistance by three and one orders of magnitude, respectively. Consequently, the symmetric cells exhibit superior cycling performance of over 600 cycles with low polarization.

Effects of Chromic Treatment on the Surface Properties of Polypropylene (PP) Wood Composites

The moisture sensitivity of wood–polymer composites (WPCs) is mainly related to their hydrophilic wood components. Coatings are among the alternatives that improve the dimensional stability of these composites. However, the adhesion of most coatings to the WPC surface is generally poor. Thus, chemical and/or mechanical treatments should be applied to the WPC surface to improve the coating adhesion. Therefore, the main objective of this study was to improve the adhesion coating of polypropylene (PP) WPCs through a chromic treatment. PP was reinforced by three different pulp fibers (kraft, thermomechanical (TMP), and chemothermomechanical (CTMP)) at three fiber contents (50, 60, and 70% w/w). A chromic treatment was applied to the PP-based WPCs to activate the surface of the composites and alter their roughness parameters, creating a higher interfacial zone that improved the bonding of the epoxy coating to the surface of the PP composites. The chromic treatment increased the roughness of the surface. An increase in profile and surface parameters was observed after treatment. This treatment modified the chemical composition of the surface by creating polar carbon–oxygen groups and increasing the carbonyl and hydroxyl indexes.

Systematic comparison of various oxidation treatments on diamond surface

It is known that surface terminations contribute significantly to diamond properties. As one of the most commonly studied types, oxygen-terminated diamond surface possesses a positive electron affinity (PEA) and hydrophilicity, making it suitable for electronic device fabrication and bioapplications. Various oxidation methods have been reported on diamond, but a systematic comparison is still lacking. Herein, we present a comparative study on the oxidation of microcrystalline diamond powder (DP) and polycrystalline diamond film (PCD) by wet chemical treatments, including various acid mixtures, as well as by dry processes, including O2 plasma and UV ozone. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) results reveal that H2SO4/HNO3 5:1 at 360 °C demonstrates the best oxidation performance on DP and PCD compared to other wet chemical methods, while the PCD treated by O2 plasma exhibits the highest oxygen content among all the treated samples. Besides, the concentration of carbon-oxygen groups on diamond surfaces is found largely determined by oxidation methods. These experimental results can be attributed to the corresponding oxidation mechanism of different treatments and agree well with theoretical simulations. Finally, we investigated the sp2 bonded carbon concentration and surface roughness of oxidized PCD, suggesting the optimized diamond surface cleaning conditions.

Chemical feature of the soot emissions from a diesel engine fueled with methanol-diesel blends

The chemistry of soot particles has high affinity with the concentration and accessibility of potential radical sites for the reactions regarding to soot growth and oxidation behaviors during in-cylinder combustion, and thus affects the particle emissions of the engines. The addition of methanol in diesel fuel is widely believed to transform the soot formation and oxidation behaviors. However, the instinctive explanation on these transformation by soot chemistry is not well understood. In this study, the chemical feature of soot emissions from a methanol-diesel blend fueled diesel engine was characterized, using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR), respectively. Results showed that epoxy, ether and C vacancy as well as ester groups were the dominant surface species, while the carboxyl and carbonyl groups exerted less contribution amongst the carbon–oxygen groups on soot surfaces for both of pure diesel fuel and methanol-diesel blends. At low engine load conditions, the increase in methanol blending content led to an increase–decrease-increase behavior of C-O epoxy concentration, which was opposite with the C vacancy contribution. At the higher engine load, increasing methanol content in fuel blends led to higher increment in the hydroxyl species with respect to the epoxy groups on soot surfaces, especially for the 5% and 10% methanol addition. The predominant groups within the bulk of soot particles consisted of aliphatic C–H (methyl and methylene), carbonyl-like CO, aromatic C–H groups and C–O bonds in phenols, anhydrides, esters and ether-like groups for both diesel and methanol blending fuels. Relative to the aromatic CC, the concentration of aliphatic C–H reduced with the increasing methanol content in the fuel blends. The lower-volume-proportion addition of methanol at low engine load led to an increase in the aromatic C–H with respect to aromatic CC. While different, the addition of methanol exerted no significant influence on the aromatic C–H concentration within the soot particles at high engine load condition.

Thermal and chemical activation methods applied to DFAFC anodes prepared by magnetron sputtering

Anodes consisting of Pd and bimetallic PdCu catalysts deposited directly on a carbon cloth by magnetron sputtering have been tested in a direct formic acid fuel cell. Current-voltage measurements showed that a bimetallic Pd-based catalyst temperature-treated to 300 °C exhibits the highest catalytic activity. Chemical and structural information from the surface of the catalysts was revealed by X-ray photoelectron spectroscopy (XPS) and by scanning electron microscopy (SEM). Increasing the temperature of the anode together with hydrogen peroxide (H2O2) treatment of the catalyst surface was proposed as an additional treatment method. In this method, the highest catalytic activity was achieved (P = 56 mW mg−1) for a monometallic Pd catalyst.The enhanced catalytic efficiency after these methods had been applied was attributed to the decrease in the content of metal oxide forms, carbon-oxygen groups, and PdCx surface contamination, where the PdCx surface content played a major role.

Surface Study of Fe3O4 Nanoparticles Functionalized With Biocompatible Adsorbed Molecules.

Surfaces of iron oxide of ferrimagnetic magnetite (Fe3O4) nanoparticles (MNPs) prepared by Massart's method and their functionalized form (f-MNPs) with succinic acid, L-arginine, oxalic acid, citric acid, and glutamic acid were studied by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR-S), UV-vis, thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and reflection electron energy loss spectroscopy (REELS). The XPS analysis of elements and their chemical states at the surface of MNPs and f-MNPs revealed differences in chemical bonding of atoms, content of carbon–oxygen groups, iron oxide forms, iron oxide magnetic properties, adsorbed molecules, surface coverage, and overlayer thickness, whereas the Auger parameters (derived from XPS and Auger spectra) and elastic and inelastic scattering probabilities of electrons on atoms and valence band electrons (derived from REELS spectra) indicated modification of surface charge redistribution, electronic, and optical properties. These modified properties of f-MNPs influenced their biological properties. The surfaces biocompatible for L929 cells showed various cytotoxicity for HeLa cells (10.8–5.3% of cell death), the highest for MNPs functionalized with oxalic acid. The samples exhibiting the largest efficiency possessed smaller surface coverage and thickness of adsorbed molecules layers, the highest content of oxygen and carbon–oxygen functionalizing groups, the highest ratio of lattice O2− and OH− to C sp2 hybridizations on MNP surface, the highest ratio of adsorbed O− and OH− to C sp2 hybridizations on adsorbed molecule layers, the closest electronic and optical properties to Fe3O4, and the lowest degree of admolecule polymerization. This high cytotoxicity was attributed to interaction of cells with a surface, where increased content of oxygen groups, adsorbed O−, and OH− may play the role of additional adsorption and catalytic sites and a large content of adsorbed molecule layers of carboxylic groups facilitating Fenton reaction kinetics leading to cell damage.

The effect of diesel emulsification using sodium petroleum sulfonate on carbon flotation from fly ash

It is critical to separate carbon from fly ash due to its increasing amount being produced per year and component requirements for secondary utilizations. Flotation is an efficient technique to fulfill this task. Effects of diesel emulsification using sodium petroleum sulfonate on unburned carbon flotation from a fly ash sample were studied. Flotation tests showed that carbon recovery was increased from 41% to 86% using the emulsified collector at the same dosage level (0.5 kg/ton) as diesel. Zeta potential measurements indicated that both the carbon and emulsified collector droplets carried negative charges within the studied pH range. For fly ash particles with high carbon content, adsorption bands of carbonyl bond (CO) were detected in the FTIR spectra, which agreed with the XPS characterization findings. XPS analysis indicated that the emulsified diesel (ED) collector interacted more intensively with the surface carbon-oxygen groups relative to the normal diesel collector. Finally, the improved efficiency of ED is proved to be related to its polar groups and reduced oil droplet size. The polar groups of ED (mainly sulfonate) interacted with the surface oxygen containing groups (e.g., CO and COOH) through hydrogen bonding and Lewis acid base interaction.

Improved Surface and Adhesion Properties of Wood-Polyethylene Composite by Treatment with Argon–Oxygen Low Pressure Plasma

Ar:O2 low pressure plasma (Ar:O2 LPP) surface treatment is proposed for increasing the surface energy and improve the adhesion of wood-polyethylene composite. The treatment time was varied between 20 and 90 s and the configuration of the shelves inside the plasma chamber (direct and secondary downstream) was also changed. Ar:O2 LPP treatment during 30–40 s created new surface carbon–oxygen groups, increased the surface energy, mainly its polar component, reduced roughness and caused ablation of wood-polyethylene composite, irrespective of the configuration of the shelves inside the plasma chamber. The increase of the treatment time above 40 s did not cause additional surface modifications. Adhesion of the wood-polyethylene composite was noticeably increased when was treated with Ar:O2 LPP. The surface modifications of Ar:O2 LPP treated wood-polyethylene composite were partially lost during 24 h after treatment.

Theoretical and Experimental Evidence for the Carbon-Oxygen Group Enhancement of NO Reduction.

The relation between a catalytic center and the surrounding carbon-oxygen groups influences the catalytic activity in various reactions. However, the impact of this relation on catalysis is usually discussed separately. For the first time, we proved that carbon-oxygen groups increased the reducibility of Fe-C bonds toward NO reduction. Experimentally, we compared the reductive activities of materials with either one or both factors, i.e., carbon-oxygen groups and Fe-C bonds. As a result, graphene oxide-supported Fe (with both factors) showed the best activity, duration of activity, and selectivity. This material reduced 100% of NO to N2 at 300 °C. Moreover, theoretical calculations revealed that the adsorption energy of graphene for NO increased from -13.51 (physical adsorption) to -327.88 kJ/mol (chemical adsorption) after modification with Fe-C. When the graphene-supported Fe was further modified with carboxylic acid groups, the ability to transfer charge increased dramatically from 0.109 to 0.180 |e-|. Therefore, the carbon-oxygen groups increased the reducibility of Fe-C. The main results will contribute to the understanding of NO reduction and the design of effective catalysts.

Metal-organic frameworks as selectivity regulators for hydrogenation reactions.

Owing to the limited availability of natural sources, the widespread demand of the flavouring, perfume and pharmaceutical industries for unsaturated alcohols is met by producing them from α,β-unsaturated aldehydes, through the selective hydrogenation of the carbon-oxygen group (in preference to the carbon-carbon group). However, developing effective catalysts for this transformation is challenging, because hydrogenation of the carbon-carbon group is thermodynamically favoured. This difficulty is particularly relevant for one major category of heterogeneous catalyst: metal nanoparticles supported on metal oxides. These systems are generally incapable of significantly enhancing the selectivity towards thermodynamically unfavoured reactions, because only the edges of nanoparticles that are in direct contact with the metal-oxide support possess selective catalytic properties; most of the exposed nanoparticle surfaces do not. This has inspired the use of metal-organic frameworks (MOFs) to encapsulate metal nanoparticles within their layers or inside their channels, to influence the activity of the entire nanoparticle surface while maintaining efficient reactant and product transport owing to the porous nature of the material. Here we show that MOFs can also serve as effective selectivity regulators for the hydrogenation of α,β-unsaturated aldehydes. Sandwiching platinum nanoparticles between an inner core and an outer shell composed of an MOF with metal nodes of Fe3+, Cr3+ or both (known as MIL-101; refs 19, 20, 21) results in stable catalysts that convert a range of α,β-unsaturated aldehydes with high efficiency and with significantly enhanced selectivity towards unsaturated alcohols. Calculations reveal that preferential interaction of MOF metal sites with the carbon-oxygen rather than the carbon-carbon group renders hydrogenation of the former by the embedded platinum nanoparticles a thermodynamically favoured reaction. We anticipate that our basic design strategy will allow the development of other selective heterogeneous catalysts for important yet challenging transformations.

In Situ Synthesis of Ti3+ Self-Doped TiO2/N-Doped Carbon Nanocomposites and its Visible Light Photocatalytic Performance

Ti[Formula: see text] self-doped TiO2 (TiO[Formula: see text])/N-doped carbon nanostructure composites were prepared via a facile one-step hydrothermal method to optimize the use of visible light and reduce recombination of photogenerated electrons and holes. The composites were characterized by X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The amounts of carbon and nitrogen sources affect the morphology and photocatalytic performance. At low amounts of the sources, the N-doped carbon nanostructure is an amorphous film and is well-combined with TiO[Formula: see text] nanoparticles through surface carbon–oxygen groups. At high amounts of the sources, N-doped carbon quantum dots (NCQDs) were obtained, and carbon atoms could substitute for oxygen atoms in the TiO2 lattice to form Ti–C structures, which are responsible for the high photocatalytic activity under visible light illumination. Transient photocurrent response and electrochemical impedance spectroscopy results indicate that the amorphous hybrid film becomes a trap for electrons and that NCQDs can accelerate electron transfer. The improved visible light photocatalytic property for the TiO[Formula: see text]/NCQDs composite can be attributed to the enhancement of light absorption and inhibition of the photogenerated electron–hole recombination of anchored NCQDs.

Fabrication of carbon quantum dots modified granular SnO2 nanotubes for visible light photocatalysis

The C QDs modified granular SnO2 nanotubes are prepared via a simple technical route through which SnO2 nanotubes are dispersed in C QDs solution, then dried at 80°C. The results of X-ray photoelectron spectroscopy, Fourier-transform infra-red spectroscopy, transmission electron microscopy indicated that SnO2 nanotubes are well combined with C QDs through surface carbon–oxygen groups. By degradation of Rhodamine B under visible light irradiation, it demonstrates that the photocatalytic performance of these composites significantly enhanced. Furthermore, the unique up-converted photoluminescence behaviour of the carbon dots and the remarkable granular, tube-shape structure of the SnO2 are considered as the main reasons of this enhancement.

Activated Carbon Fiber Treated at Different Temperatures as Supercapacitor Electrodes: Electrochemical Characterization

Introduction Nowadays, carbon-based materials have been used as electrodes for supercapacitors due to their physical and chemical properties. Among the different carbon-based materials, carbon fiber (CF) offer the advantage for using as electrodes because is not necessary any substrates or binders. Besides, it is believed that may be a plausible strategy to maximize the energy density of supercapacitors. Currently, many researches reported that the incorporation of heteroatoms like oxygen and nitrogen into carbon-based materials improved the specific capacitance. These materials containing numerous electroactive heteroatoms may be appropriate for the production of electrodes with better capacitance because the heteroatoms are responsible to induce pseudocapacitive behavior and to increase their polar properties [1]. It is known that different oxygen-containing groups are produced using various techniques or exposures. The result of the oxidation process as a function of both the amount of oxygen as well as the type of carbon-oxygen groups may also depend on the CF surface nature. In this work were proposed two pre-treatments for the CF surface activation, electrochemical and chemical oxidation. The samples were evaluated electrochemically, aiming their performance as electrodes in supercapacitors. Experimental Part The CF samples were produced from polyacrylonitrile (PAN) precursor at different heat treatment temperature (HTT) of 1000 ºC, 1500 ºC and 2000 ºC using temperature steps of 330 ºC/h under inert atmosphere of nitrogen, reaching the maximum during 30 min up to its cooling down to room temperature. The CF samples were cut in size 1 cm2 and previously weighed. For the chemical treatment the CFs samples were dispersed in boiling acetone for 5 min. Subsequently, these were washed with distilled water, immersed in H2SO4/K2Cr2O7 and sonicated for 5 min. For electrochemical oxidation, the CFs were anodically polarized using as electrolyte 0.5 mol L-1 H2SO4 in a fixed potential of 2.0 V for 30min using a conventional three electrode cell. The electrochemical characterization of the electrodes was studied by Electrochemical Impedance Spectroscopy (EIE), Cyclic Voltammetry (CV), and Charge/Discharge tests. All measurements have been performed in 1.0 mol L-1 H2SO4 solution. Results and discussion The CV of all sample electrodes obtained between -0.1 and 0.8 V, recorded at scan rates of 1 at 100 mV s-1, using 1.0 mol L-1 H2SO4 as an electrolyte, showed a small distortion of the current response at the switching potential which may be attributed to electrolyte and electrode resistance. How this effect is usually dependent on the scan rate, this distortion is more pronounced between 50 and 100 mV s-1. However, the three materials exhibit the characteristic rectangular shape typical of the electric double-layer capacitors. The charge-discharge profile of the CF electrodes at HTT submitted at two treatment oxidation, carried out at a current density of 0.5, 0.75 and 1 mA cm-1, showed linear charge/discharge profile which indicates that capacitance is mainly due to electric double layer formation. The EIE analysis in the present work it is observed for all samples after the two pre-treatment that the vertical lines are close to the imaginary axis, which indicates supercapacitor behavior is very close to ideal capacitor. After two pre-treatment used it was observed an insignificant increase in internal resistance of materials. This behavior may be associated to the heteroatoms incorporation, becoming the ionic transport pathway more tortuous, which result in the diffusion phenomena more evidenced. Conclusion The CF samples submitted a different HTT were available for application as electrode materials in supercapacitors. The two pre-treatments contributed to the increase specific capacitance. Particularly, the CF 1000 ºC electrodes electrochemically treated exhibited better performance in general terms for possible application as electrodes for supercapacitors. Acknowledgments This work was supported by CNPq-170141/2014-4. References Yun,Y. S., Lee, M. E., Joo, M. J., Jin, H.-J. Journal of Power Sources 246 (2014) 540-547.

Investigation of chemical and electrochemical reactions mechanisms in a direct carbon fuel cell using olive wood charcoal as sustainable fuel

Direct carbon fuel cell (DCFC) is a high temperature fuel cell using solid carbon as fuel. The use of environmentally friendly carbon material constitutes a promising option for the DCFC future. In this context, this paper focuses on the use of biomass-derived charcoal renewable fuel. A practical investigation of Tunisian olive wood charcoal (OW-C) in planar DCFCs is conducted and good power density (105 mW cm−2) and higher current density (550 mA cm−2) are obtained at 700 °C. Analytical and predictive techniques are performed to explore the relationships between fuel properties and DCFC chemical and electrochemical mechanisms. High carbon content, carbon–oxygen groups and disordered structure, are the key parameters allowing the achieved good performance. Relatively complex chain reactions are predicted to explain the gas evolution within the anode. CO, H2 and CH4 participation in the anodic reaction is proved.

Carboxyl Group Enhanced CO Tolerant GO Supported Pt Catalysts: DFT and Electrochemical Analysis

The effect of residual oxygen species in as-prepared Pt nanoparticle on partially reduced graphene oxide (Pt/PRGO) and partially reduced carboxylated-GO (Pt/PR(GO–COOH)) supports was investigated using electrochemical CO stripping and density functional theory (DFT) analysis. Pt/PRGO and Pt/PR(GO–COOH) revealed a clear negative shift in CO-stripping onset potential compared to commercial Pt/carbon black. DFT analysis confirmed that the presence of a −COOH group provides the most resistance for CO adsorption. This CO-Pt binding energy is significantly lower than that observed in the presence of an −OH group, which is the most abundant oxygen group in carbon supports. The Pt-CO dissociation energies (on a 42-atom graphene sheet) in the presence of various oxygen groups, in descending order, were OH > C═O ≈ C–O–C > COOH. Although single-bonded carbon–oxygen groups (−OH and C–O–C) are more abundant on the GO basal plane and play an important role in Pt nanoparticle nucleation and distribution on graphene sheets, the double-bonded carbon–oxygen (C═O and COOH) groups are more abundant residual species post Pt nanoparticle growth and play a vital role in enhancing CO tolerance.

Preparation of graphene oxide and characterisation using electron spectroscopy

Graphene oxide was prepared from commercial graphene powder (G) platelets of 8nm thickness by oxidation in ozone (G-O3) and low-energy (cold) glow air plasma in a pink region (G-PP). X-ray photoelectron spectroscopy (XPS) was applied for chemical characterisation of the atomic content and for obtaining quantitative information on C hybridisation. Reflection electron energy loss spectroscopy (REELS) was used for characterising the surface structure including the content of surface and bulk carbon atoms of sp2 and sp3 hybridisation.The G-O3 and G-PP graphene oxide samples contain a low amount of C sp3 bonds and carbon–oxygen groups in comparison to graphene oxide prepared by the “wet” chemical methods. Oxidation of commercial graphene platelets powder, especially in air plasma, leads to increasing surface C sp3 and significantly bulk C sp3 contributions, indicating intercalation by oxygen groups. The intensity ratio of the REELS π+σ C sp2 bulk to the C sp2 surface energy loss peaks, decreasing in the order G>G-O3>G-PP, indicates exfoliation of layers in G-O3 and G-PP by oxygen functional groups and water with decreasing average number of layers in graphene oxide nanostructures due to oxidation. Although, the “wet” chemical methods are more effective for oxidation leading to a larger amount of C sp3 and oxygen groups, the proposed methods of oxidation by ozonation and in air plasma are inexpensive, safe, effective, environmentally friendly and do not result in toxic chemical waste products.