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Exhibiting a very high surface area, a good electrical conductivity and a high density of active sites, nitrogen-doped graphenic materials are considered as promising catalysts for the oxygen reduction reaction (ORR). Seldom studied in acidic media, N-doped graphenic foams were tested here as the cathode catalysts of a polymer electrolyte membrane fuel cell (PEMFC). The materials were prepared via a solvothermal-based process, by reacting either cyclohexanol and ethanolamine or 1-(2-hydroxyethylethyl) piperidine with metallic sodium, under high pressure and temperature. Membrane electrode assemblies were prepared with a Pt/C anode, 212 Nafion membrane, and an 8 mm disk cathode based on the graphenic materials. The performance exhibited by the PEMFC was evaluated using chronopotentiometry and impedance spectroscopy, depending on the synthesis conditions. The kinetic parameters of the ORR were estimated by interpretation of the experimental data: the high Tafel slope found might express the partial control of oxygen diffusion through the graphenic microporous structure. Relationships between the electrochemical behavior of the materials and their structural properties are discussed. Moderately crystallized materials with a low oxygen content showed the highest catalytic properties, with a current density larger than 30 mA cm−2 and a maximum power density at 2.3 mW cm−2. [ABSTRACT FROM AUTHOR]

Abstract Three-dimensional graphene structures have attracted a great interest these last years. The combination of well-known graphene properties and a large specific surface area developed by their intrinsic porosity is especially interesting for challenging applications such as energy storage and conversion or catalysis. This work is focused on the elaboration of graphene foams by pyrolysis of sodium ethoxide. Whereas the literature mentions the possible elaboration of graphene foams by combustion of sodium ethoxide synthesized by a quite heavy solvothermal-based process, we propose here a thermal treatment consisting in a pyrolysis under a nitrogen flow. Using commercial sodium ethoxide, we show that this treatment leads to the preparation of graphene foams with great structural quality and high specific surface area. This original result is supported by a compared characterization of solvothermal and commercial sodium ethoxide and the proposition of a formation mechanism of the three-dimensional graphene network during the pyrolysis is proposed. This new graphene foam elaboration route is extremely interesting in order to consider a large-scale fabrication of such materials. Graphical abstract Image Highlights • Pyrolysis of commercial sodium ethoxide is sufficient to obtain graphene foams. • The solvothermal sodium ethoxide entraps excess ethanol and water. • The mechanism of formation is based on the interactions between carbon and the sodium-based compounds. [ABSTRACT FROM AUTHOR]

Besides the well-known research concerning graphene, great attention has more recently been paid to three-dimensional graphene structures, motivated by the combination of the properties of graphene and the development of porosity and large specific surface areas. The most current methods of obtaining for this kind of structure start from graphite oxide, which can be thermally treated or assembled in liquid-phase. This work is focused on a little-known and bottom-up method of elaboration, which consists in a solvothermal reaction between metallic sodium and an alcohol, followed by a thermal treatment. The as-obtained graphene foams exhibit very large specific surface areas. More specifically, the length of the carbon chain of the precursor alcohol employed for the solvothermal reaction is found to have a strong influence on the adsorptive properties of the foams, especially on their pore size distribution. The mechanism of formation of such porous structures is discussed through the exploration of the compounds of the carbon-sodium-oxygen system. [ABSTRACT FROM AUTHOR]

Owing to its exceptional properties and a large range of possible applications, graphene gives rise to a great interest. Several major methods, as mechanical cleavage, liquid phase exfoliation of graphite and supported growth, have been developed these last years. However, it remains difficult to yield industrial quantities of graphene-based materials. Besides the research for the improvement of these major ways of synthesis, we focused on a much less common method: solvothermal synthesis. Graphenic powders can be obtained by a solvothermal reaction between ethanol and sodium followed by a thermal treatment step. We performed the solvothermal reaction and pyrolyzed the as-obtained sodium ethoxide with different temperature and time conditions, in order to study the influence of these two parameters on the final carbon-based sample. Various characterization techniques revealed the obtaining of graphenic materials with large aspect ratio, containing multi-layer graphene (MLG) regions. This study shows the strong influence of temperature and time of pyrolysis on purity, crystallinity and thickness of the samples, and goes toward an optimization of the thermal treatment step. [ABSTRACT FROM AUTHOR]

Abstract: The need of interconnect to separate fuel and oxidant gasses and connect individual cells into electrical series in a SOFC stack appears as one of the most important point in fuel cell technology. Due to their high electrical and thermal conductivities, thermal expansion compatibility with the other cell components and low cost, ferritic stainless steels (FSS) are now considered to be among the most promising candidate materials as interconnects in SOFC stacks. Despite the formation at 800°C of a protective chromia Cr2O3 scale, it can transform in volatile chromium species, leading to the lost of its protectiveness and then the degradation of the fuel cell. A previous study demonstrated that in air, the application by metal organic chemical vapour deposition (MOCVD) of a nanometric layer of reactive element oxides (La2O3, Y2O3, Nd2O3) on FSS improved both the electrical conductivity and the oxidation resistance. The beneficial effect of this type of coating on FSS on oxidation resistance in H2/H2O (anode side) is not yet completely understood. So, the goal of this study is to apply reactive element oxide coating (La2O3, Y2O3, Nd2O3) on two FSS (a commercial, Crofer22APU, and a model, Fe30Cr) and to perform oxidation tests in H2/10%H2O. Kinetics was registered for 100h at 800°C and the corrosion products were characterized by SEM, EDX, TEM, SIMS and XRD. [Copyright &y& Elsevier]

Most of alkali metals are well-known to easily intercalate into graphite to form stage-1 graphite intercalation compounds (GIC) whose structure and physical properties have been extensively studied. This work is focused on the intercalation of potassium, sodium and cesium into graphenic foams prepared by a solvothermal-based process. The as-obtained samples are analyzed by means of X-ray diffraction and Raman spectroscopy, and reveal a double phenomenon: the intercalation of alkali metals between the interplanar spaces of the multi-layer graphene stackings, and their sorption into the porosity of the host sample. This kind of behavior has already been reported when studying the reactivity of alkali metals with disordered carbon. Interestingly, our study shows a low stage intercalation in the case of sodium. Moreover, the dispersion of the potassium-intercalated samples into a polar solvent leads to a few-layer graphene dispersion stable for months. Image 1 • The reactivity of potassium, cesium and sodium toward graphenic foams is studied. • Alkali metals are intercalated between graphene layers and sorbed into the porosity. • Low-stage intercalation is observed with sodium. • A dispersion of intercalated foams in a polar solvent gives graphene dispersions. [ABSTRACT FROM AUTHOR]

Extraordinary properties of graphenic materials no longer need to be demonstrated. Nitrogen doping has been known to broaden the graphene application fields, especially for catalysis purposes. The present work reports a solvothermal-based process for the synthesis of a nitrogen-doped graphenic foam with up to 2.6 at.% nitrogen, exhibiting the inherent properties of graphenic materials with high textural properties and surface areas as high as 2243 m2 g−1. This study aims to give a better understanding of the influence of the pyrolysis treatment on the properties of the produced material for optimization of the synthesis in view to fuel cell applications. Several cross-linked techniques such as transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy, nitrogen physisorption at 77 K and X-ray photoelectron spectroscopy have been employed to give a complete, precise characterization of the elaborated N -doped graphenic foams, leading to optimized conditions for the pyrolysis step. Pyrolysis at 850 °C has been found to allow the best compromise in terms of purity, homogeneity and crystallinity, with high fractions of pyrrolic, pyridinic and graphitic N -substitution that are known to greatly enhance the material catalytic properties. An oxidative degradation process was also evidenced for temperatures above 875 °C, leading to far lower graphene amounts. Image 1 • Microporous N -doped graphenic foams possess a very high specific surface area. • Nitrogen is mostly inserted in the graphenic network. • The pyrolysis temperature is a key parameter for the surface N -functions. • N -doped graphenic foam is a promising material for electrocatalytic applications. [ABSTRACT FROM AUTHOR]

For the purpose of synthetizing 3-dimensional nitrogen-doped graphenic materials, which could be used as oxygen reduction catalysts in membrane fuel cells, a solvothermal-based route was successfully carried out. However, the solvothermal reaction between metallic sodium and 1-(2-hydroxyethyl)piperidine (HEP), with the latter as the source of both carbon and nitrogen, is still little understood. The present work was aimed at investigating the solvothermal process under different conditions of temperature and pressure and with different amounts of sodium. Use of in situ mass spectroscopy during the three-day reaction revealed the early formation of dihydrogen, as well as carbon oxides, methane and ammonia, in addition to fragments of ethylpiperidine alkoxide (EP-ONa). XRD measurements evidenced the formation of sodium-based compounds, e.g. hydride, carbonate, hydroxide, and cyanide. Interestingly, Raman spectroscopy revealed the significant presence of large aromatic molecules as well as an sp2 carbon network, an early precursor of graphene. Analysis of the overpressures and reaction yields suggests that the primary compound from the reaction of HEP with sodium is a large sp2 carbon-based network entrapping numerous sodium-based molecules as well as a volatile liquid phase. The suggested reaction mechanism provides information to better tailor the solvothermal products, whose pyrolysis at 850 °C led to very high specific area nitrogen-doped carbon materials. [ABSTRACT FROM AUTHOR]

Graphene-based materials are extensively studied, due to their excellent properties and their wide range of possible applications. Attention has recently been paid to three-dimensional-like graphenic structures, such as crumpled graphene sheets and graphenic foams: these kinds of materials can combine the properties of graphene associating high surface area and porosity, what is particularly interesting for energy or catalysis applications. Most of the synthesis methods leading to such structures are based on graphite oxide exfoliation and re-assembly, but in this work we focus on the preparation of graphenic foams by a solvothermal-based process. We performed a solvothermal reaction between ethanol and sodium at 220°C, during 72 h, under 200 bar, followed by a pyrolysis under nitrogen flow. An extended study of the influence of the temperature (800°C-900°C) of pyrolysis evidences an unexpected strong effect of this parameter on the characteristics of the materials. The optimal conditions provide multi-layer graphene (10 layers) foam with a surface area of 2000 m2·g−1. This work is an important step for the understanding of the mechanisms of the thermal treatment. Post-treatments in different experimental conditions are performed in order to modulate the structure and properties of the graphenic foams. [ABSTRACT FROM AUTHOR]

Functionalization on the carbon material of PEM fuel cells providing them an ionic conductivity, has been thought as a promising way to improve the catalyst activity. Pt/Vulcan catalysts grafted with polystyrene sulfonate (PSSA) groups from 5 to 20 wt.% have been prepared. Owing to the ion-exchange properties of the PSSA grafted on carbon support, we developed less-Nafion electrodes, with only 0.25 or 0.50 mg cm − 2 Nafion loading. The effect of PSSA graft ratio and the Nafion amount was studied in a single cell at 30 °C by polarization curves and impedance measurements. It was found that 5 and 10 wt.% PSSA with 0.50 mg cm − 2 Nafion allow high efficiency, however lower than 10 wt.% grafted Pt/C with 0.25 mg cm − 2 Nafion only. The performance of the various electrodes could be correlated to the overall amount of sulfonate introduced: highest yields were obtained with an overall sulfonate concentration near 0.7–0.8 μmol cm − 2 . [ABSTRACT FROM AUTHOR]

Highlights: [•] Development of preparation procedure for mechanically stable half-cells. [•] Promising use of PSSA-grafted carbon support for PEM fuel cell cathodes. [•] Nafion addition in half-cells could be reduced by 50% by carbon modification. [•] Electrochemical characterization and resistance of half cells with modified carbon. [Copyright &y& Elsevier]

Highly-efficient solid oxide fuel cell (SOFC) systems are gaining increased attention for future energy conversion applications. Many planar SOFC stack designs utilise ferritic stainless steel (FSS) interconnect components. During operation, surface corrosion of FSS interconnects degrades stack operation by increasing electrical resistance and introducing other deleterious material interactions. To minimise these effects, various surface modifications and coatings are currently under investigation. Two of these methods under development for this application are: metal organic chemical vapour deposition (MO-CVD); and, large area filtered arc deposition (LAFAD). SOFC interconnect-relevant corrosion behaviour of an MO-CVD coating on Crofer 22 APU, AL453, Fe30Cr and Haynes230, and complex, amorphous LAFAD AlCrCoMnTiYO coatings on FSS 430 were investigated. Both of these surface modifications and coatings exhibit significantly improved corrosion protection as compared with uncoated FSS samples. [ABSTRACT FROM AUTHOR]

The promising and extraordinary properties of graphene has attracted significant interest from many researchers especially in various electronic applications. The main aim of this work is to develop graphene-based ink with excellent stability and electrical properties for flexible electronics. Graphene foam (GF) was synthesised by using solvothermal method. GF exhibited multi layers of graphene, good in-plane crystallite quality, a low carbon impurity and relatively low sodium carbonate content. GF was further dispersed into various types of solvents. Results showed that GF dispersed in dimethyl sulfoxide (DMF) and N-methylpyrrolidone (NMP) exhibited good stability. However, these solvents suffer from highly toxic which may damage fertility or the unborn child (hazard code = H360). Besides that, GF dispersed in distilled water with an addition of sodium dodecyl sulfate (SDS) as a surfactant presented good stability as compared to GF ink without surfactant and can be further used as the conductive ink for printable electronics. [ABSTRACT FROM AUTHOR]

The activated carbons were prepared from Phoenix dactylifera rachis (PRAC) and Ziziphus jujuba stones (JSAC) using chemical activation by H 3 PO 4. Then, they applied to eliminate a commercial reactive dye BEZAKTIV Red S-Max (BRSM). The resultant carbons PRAC and JSAC were characterized by N 2 adsorption-desorption isotherms, Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM) and Boehm titration method. The BET apparent surface area of the PRAC and JSAC was 1283 and 1896 m2/g, respectively, with predominance acidic character. The effects of initial dye concentration and contact time, pH and temperature on the adsorption were investigated, and it was showed that the elimination percentage decreases as the initial concentration increases, but it rose with the temperature. The experimental equilibrium data were studied using Langmuir, Freundlich and Temkin models, and it was found that the Langmuir model described well the BRSM adsorption (R2 ≥ 0.96), showing a maximum adsorption capacity of BRSM onto PRAC and JSAC of 196.08 and 37.04 mg/g, respectively. The BRSM adsorption kinetic was examined by pseudo-first-order, pseudo-second-order, elovich and intraparticle diffusion models, and it was showed that BRSM adsorption onto used carbons followed pseudo-second-order. The obtained thermodynamic parameters indicated that the phenomenon is spontaneous and endothermic. In addition, the thermal regeneration of the examined carbons revealed that they can be reused on adsorption test. Finally, the results indicated that the Phoenix dactylifera rachis carbon could be considered as low cost material for the elimination of BRSM dye and dyes from dyestuff wastewater (DW). • Activated carbons were produced from Phoenix dactylifera Rachis and Ziziphus jujuba Stones using H 3 PO 4. • Activated carbons were characterized by N 2 adsorption, TGA, EA, Boehm, FTIR and SEM. • PRAC showed maximum monolayer adsorption capacity of 196.08 mg/g at 25 °C. • Thermal regeneration of activated carbons was applied. • Treatment of dyestuff wastewater was tested. [ABSTRACT FROM AUTHOR]

HiPco single-walled carbon nanotube samples contain a non-negligible amount (about 30 wt.%) of metal-based impurities. These impurities are prejudicial to the development of CNT-based applications. In the literature, there is no agreement for their nature and their relative content. Consequently, the standard purification treatments could not be selective enough and they lead to damage the carbon nanotubes. In this work, we have deeply investigated the mineral impurities of a raw HiPco SWCNT sample by means of several techniques. We were able to identify and quantify at least six iron-based phases that coexist in the HiPco SWCNT samples. The raw SWCNTs were submitted to a selective purification treatment involving a high temperature treatment under chlorine. The results show that the efficiency of the metal removal is improved by increasing the temperature of treatment leading to a purification yield of 95.4%, while preserving the structural quality of the SWCNTs. The analysis of the mineral residues in the purified and annealed SWCNT samples allows to propose the chemical mechanisms involved during the chemical treatments. [ABSTRACT FROM AUTHOR]

Abstract: Chromia forming alloys (stainless steels) are among the best candidates for SOFC interconnects. However, problems of decreasing electronic conductivity during high temperature service and volatility of chromium oxide scales need to be solved. Electronically conductive surface coatings, which also reduce oxide scale growth and chromium volatility, are needed to improve stainless steel interconnects. The goal of this study is to investigate combinations of lanthanum oxide (La2O3) and cobalt manganese oxide ((Co,Mn)3O4) coatings on Crofer22APU stainless steel. Thin film coatings of La2O3 (~200 nm) and Co,Mn (1:1) (~2 mm) were deposited via metal organic chemical vapor deposition and magnetron sputtering, respectively. Three types of coatings were investigated: La2O3; (Co,Mn)3O4 (formed by a 100 h, 800 °C air anneal of Co,Mn); and, a combination coating composed of an air annealed La2O3 followed by a (Co,Mn)3O4 layer. Oxidation experiments were performed at 800 °C in air for both 100 and 1000 h and in dual environment (Air+3%H2O/H2 +3%H2O) for 100 h. The combination coatings were observed to inhibit both the formation of chromia (compared to the single (Co,Mn)3O4 layer) and the formation of iron oxide in dual atmosphere (compared to the single La2O3). These and other results and interpretations are presented and discussed here. [Copyright &y& Elsevier]