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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]

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]

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]

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]