Catalyst-free soft-template synthesis of ordered mesoporous carbon tailored using phloroglucinol/ glyoxylic acid environmentally friendly precursors

International audienceCarbon porous materials with a periodically ordered pore structure, controlled pore size and geometry and high thermal stability are synthesized using self-assembly of environmentally friendly phloroglucinol/ glyoxylic acid precursors with an amphiphilic triblock copolymer template. Glyoxylic acid, a plant-derived compound, is used for the first time as a substituent of carcinogen formaldehyde usually employed in such a synthesis. Thanks to the double functionality, i.e., aldehyde and carboxylic acid, glyoxylic acid plays not only the role of a cross-linker for the formation of the resin but also the role of a catalyst by creation of H-bonding or specific reactions between the precursors. Hence, no extra catalyst such as strong acids (HCl) or bases (NaOH) is any longer required. Carbon films and powders were successfully prepared with high surface areas (up to 800 m2 g−1), high porous volume (up to 1 cm3 g−1), tunable pore size (0.6 nm to 7 nm) and various pore architectures (hexagonal, cubic, and ink-bottle) by tuning the precursor ratio and by applying different manufacturing engineering strategies. Insights on the synthesis mechanism of the phenolic resin and carbon mesostructures were obtained using several analysis techniques, i.e., nuclear magnetic resonance (13C NMR) and FTIR spectroscopy, temperature programmed desorption coupled with mass spectrometry (TPD-MS) and thermo-gravimetric analysis (TGA)

Insights on the Na+ ion storage mechanism in hard carbon: Discrimination between the porosity, surface functional groups and defects

Sodium ion batteries (SIBs) using hard carbon as negative electrode hold the promise of being low cost alternative to lithium ion batteries (LiBs). However, the Na+ storage mechanism in hard carbons is not fully understood yet and the attribution of Na storage in the sloping and plateau regions of the sodiation/desodiation curves remains still controversial. The current work employs N-2, Kr and CO2 gases to correctly assess the changes in hard carbon porosity induced by different pyrolysis temperature of cellulose. The sloping capacity was found to decrease with the decrease of the specific area of ultramicropores measurable only by CO2 adsorption, while the plateau capacity demonstrated an opposite behavior. The high temperature derived carbons (> 1400 degrees C) present no porosity which disqualifies the attribution of plateau region to the adsorption of Na+ in the nanopores but rather the insertion between the pseudo-graphitic domains. Temperature programmed desorption coupled with mass spectrometry (TPD-MS) was performed to determine the nature and the quantity of oxygen surface functional groups followed by oxygen chemisorptions to assess the amount of carbon edge defects expressed by active surface area (ASA) values. A decrease in the amount of oxygen groups and active surface area with the increase of the pyrolysis temperature was observed which is accompanied by a decrease of the sloping capacity. These results shed light in the storage mechanisms, the sloping region being ascribed mainly to the interaction of Na+ with carbon edge defects and adsorption in the microporosity while the plateau region assigned to the intercalation of Na+ in the pseudo-graphitic nanodomains

Relationship between the carbon nano-onions (CNOs) surface chemistry/defects and their capacitance in aqueous and organic electrolytes

The effect of surface functionalities on the supercapacitors performances has been highlighted often in many works. However, studies devoted to the influence of carbon defects did not gain particular attention due to the difficulty to quantify such parameter. In this context, carbon nano-onions were used as model material in order to understand the influence of the surface chemistry (nature and amount of oxygen groups) and structural defects (active surface area, ASA) on the capacitance. Different types of thermal treatments in oxidizing or reducing atmospheres allowed to finely tune the surface chemistry and the ASA as demonstrated by temperature programmed desorption coupled with mass spectrometry (TPD-MS). For the first time, the presice control of these characteristics independently one of each other allowed to highlight an important influence of the carbon defects on the capacitance in organic and aqueous electrolytes which outbalance the oxygen functional group effect

Comportement en atmosphere oxydante de composites thermostructuraux SiC/C/SiC

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 79575 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Influence des propriétésdu graphite sur le premier cycle d'intercalation du lithium

Les batteries à ions lithium alimentent la plupart des petits appareils électriques, portables. Elles font usage du graphite comme électrode négative. Pour optimiser celle-ci, il faut réduire la perte spécifique de charge du premier cycle d intercalation du lithium. Cette perte est principalement due à la formation d une couche passive par décomposition de l électrolyte. Les propriétés du graphite qui l influencent sont partiellement connues. En particulier, une meilleure compréhension de l exfoliation du graphite, responsable d une grande perte spécifique de charge, est souhaitée. Ce phénomène est provoqué par la co-intercalation de solvant à travers les plans de bord des particules. Des paramètres comme la cristallinité, la chimie de surface et la réactivité du graphite semblent jouer un rôle. Une étude systématique a été entreprise afin de déterminer leur influence sur le premier cycle dans un électrolyte standard à base de carbonate d éthylène et de diméthyle. Il apparaît que les complexes de surface oxygénés ne jouent pas de rôle particulier tandis que les complexes hydrogénés favorisent la co-intercalation de solvant. De plus, les graphites ayant une faible teneur en sites actifs constituant l Active Surface Area (ASA), mesurée par chimisorption d oxygène, sont plus enclins à exfolier. Comme les atomes de bord à deux voisins sont les plus réactifs en raison de la présence d un électron célibataire, la plus grande sensibilité à la co-intercalation de solvant des graphites de faible ASA peut s expliquer par la formation d une couche passive inappropriée sur des plans de bord peu réactifs laissant passer le solvant.In the field of small portable electrical devices, lithium-ion batteries are common. Graphite is used as the negative electrode. To improve its electrochemical performances, the first cycle specific charge loss must be decreased. It is predominantly attributed to the electrolyte reduction into a passivation layer. The graphite properties which influence this charge loss are not clearly identified. In particular, the graphite exfoliation which is responsible for a huge specific charge loss must be better understood. This dramatic phenomenon is due to solvent co-intercalation through the particle edge planes. Many graphite parameters such as crystallinity, surface chemistry and reactivity are thought to play a role. A systematic study was carried out in which the influence of each parameter on the first cycle was assessed in a standard ethylene and dimethyl carbonate based electrolyte. It appears that the presence of oxygen surface complexes does not have any influence whereas C6H bonds cause slight exfoliation. In addition, graphite samples containing low amount of active sites : the so-called Active Surface Area (ASA), quantified by oxygen chemisorption, are more likely to exfoliate. Since graphite active sites are mainly the edge atoms because of unpaired electron presence, low ASA graphite exfoliation can be explained by the formation of inappropriate passivation layer on the edge planes letting solvent molecules co-intercalate.MULHOUSE-SCD Sciences (682242102) / SudocSudocFranceF

Nanoduplication de matrices siliciques hôtes pour l'élaboration de carbones et d'oxydes à porosité et organisé

L'objectif de ce travail concerne la synthèse de matériaux mésoporeux carbonés à porosité organisée et contrôlée obtenus par un procédé original de nanoduplication. Dans un premier temps, un matériau hôte poreux est infiltré par un précurseur carboné converti ultérieurement en carbone. Le matériau mixte résultant est ensuite traité chimiquement pour éliminer sélectivement le matériau hôte. Une réplique carbonée est alors obtenue. Nous avons choisi dans cette étude des matériaux siliciques présentant une mésoporosité organisée (MCM-48, SBA-15) ou vermiculaire (MSU-1). Divers précurseurs carbonés ont été infiltrés, soit par voie gazeuse (propylène), soit par voie liquide (brai de pétrole ou solution aqueuse de sucrose). Nous avons étudié plus particulièrement l'influence de différents paramètres expérimentaux, tels que la nature du précurseur carboné, le type de matériau hôte silicique utilisé et la quantité de carbone infiltré, sur les caractéristiques poreuses des carbones obtenus. Cette étude a mis en évidence la possibilité d'obtenir des matériaux carbonés dont les caractéristiques poreuses peuvent être déterminée " sur mesure " par le choix de conditions opératoires appropriées. Ces matériaux ont par ailleurs été utilisés en tant que moules pour produire des répliques siliciques.The goal of this work is to develop new synthesis routes for the préparation of mesoporous carbon materials with organized and controlled porosity by the nanocasting process. This process consists in the infiltration of a porous material by a carbon precursor which is then converted into carbon. The template is then removed by leaching. We choose in this study, organized mesoporous silica materials (e.g.: MCM-48 and SBA-15) or wormlike porosity (e.g.: MSU-1). Various carbon precursors are used, either by a or wormlike porogaseous route using propylène or by a liquid route using petroleum pitch or a sucrose solution. We focus more particularly on the influence of various expérimental parameters, such as the nature of the carbon precursor, the type of silica host material and the quantity of infiltrated carbon, on the textural and structural characteristics of the carbon replicas. This study highlights the possibility to obtain a wide range of carbon materials with porous features that can be controlled by the choice of the operating conditions. These materials have been used as moulds to produce silica replicas.MULHOUSE-SCD Sciences (682242102) / SudocSudocFranceF

Nanoconfinement of glucose oxidase on mesoporous carbon electrodes with tunable pore sizes

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High cycleability Nano-GeO2/mesoporous-carbon composite as enhanced energy storage anode material in Li-ion batteries

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Carbon spheres prepared from zeolite Beta beads

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