Facile and green synthesis of nitrogen-doped polymer and carbon porous spheres

The development of green, sustainable and simple synthesis pathways for the design of polymer and carbonaceous materials with well controlled features is of great importance for many fields of applications. Herein, we report a green synthesis method for polymer and carbon particles with well-defined shape and size. This approach involves the use of green precursors, water as solvent, no templates under ambient temperature and pressure conditions, simultaneously. Green polymer resins (phloroglucinol-glyoxylic acid) and a catalyst/nitrogen source (triethylenediamine) are dissolved in water at room temperature resulting in polymer particles which by subsequent thermal treatment transforms in carbon particles. Mainly spherical carbon particles with controlled size from 500 nm to 10 µm were obtained by simply adjusting the experimental conditions, i.e., the synthesis time and the molar ratio between the precursors or solvent. In some conditions, flower-like morphology was obtained as well. The synthesis mechanism from polymer resin spheres formation to their conversion into carbon sphere was determined by several techniques, i.e., 13C NMR spectroscopy, SEM, XPS and TPD-MS (temperature programmed desorption coupled by mass spectrometer)

Insights on the synthesis mechanism of green phenolic resin derived porous carbons via a salt-soft templating approach

International audienceA combined salt-soft template approach to synthesize porous carbon materials is reported along with their synthesis mechanism. This consists in the evaporation induced self-assembly (EISA) of aqueous solutions containing green phenolic resins, a triblock copolymer template and a metallic salt, followed by thermal treatment and washing. The increase of pH up to 5 using NaOH, induces significant improvement in the carbon microporosity but in the detrimental of mesoporosity. As suggest by 13 C and 1 H NMR, the mesoporosity lost is caused by the decrease of H-bonding and self-assembly between the phenolic resin and the template due to the strong "salting-out" effect of eOH ions. For higher pH (pH-9), the porosity start to decrease and graphene-sheet like morphology is formed. The microporosity varies with the salt in the following order: KCl > NaCl > LiCl, while the mesoporosity in the opposite way. The structure changes as well from smooth turbostatic (KCl) to defective graphitic one (NaCl, LiCl). These textural and structural modifications are explained in terms of cation hydration enthalpy and cation-p binding energy and by the competition between the metal salt cations and the Na ions (used to regulate the pH) for water or phenolic resin aromatic ring sites

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

Direct synthesis of graphitic mesoporous carbon from green phenolic resins exposed to subsequent UV and IR laser irradiations

International audienc

Eco-Friendly Synthesis of Nitrogen-Doped Mesoporous Carbon for Supercapacitor Application

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Self-supported binder-free hard carbon electrodes for sodium-ion batteries: insights into their sodium storage mechanisms

Hard carbons are one of the most promising negative electrode materials for sodium-ion batteries (NIBs). In contrast to most of the published works employing powder-like electrodes containing binders, additives and solvents, we report herein an innovative way to prepare binder-free electrodes by simple impregnation of cellulose and cotton filter papers with a phenolic resin solution. The latter enables improvement of the poor mechanical properties and thermal stability observed for pristine hard carbon self-standing electrodes (SSEs) along with the carbon yield. A high reversible specific capacity and long-term stability were observed for cellulose compared to those of cotton-based SSEs in NIBs, i.e., 240 mAh·g-1 vs. 140 mAh·g-1, respectively, for C/10 rate and high mass loading (~5.2 mg·cm-2). This could be ascribed to the larger amount of defects on cellulose than cotton as quantified by temperature programmed desorption coupled with mass-spectrometry (TPD-MS), the structure and porosity being similar for both materials. Furthermore, the addition of a conductive sputter coating on the cellulose SSE surface improved the reversible specific capacity (to ~300 mAh·g-1) and initial coulombic efficiency (ICE) (to 85%). Operando X-ray diffraction (XRD) was performed to provide additional insights on the Na storage mechanisms. Although no shift was noticed for the graphite (002) diffraction peak, clear evidence of sodium intercalation was observed in the plateau region appearance of a new diffraction peak (~28.0° 2θ) likely associated with a sodium intercalation compound. Consequently, the sloping region could be related to the Na+ adsorption on hard carbon defects and pores

Ultrasmall MgH_2 Nanoparticles Embedded in an Ordered Microporous Carbon Exhibiting Rapid Hydrogen Sorption Kinetics

MgH_2 nanoparticles with different average sizes have been prepared as ordered microporous carbon by tuning the Mg amount from 15 to 50 wt %. Ultrasmall particles with mean sizes of 1.3 and 3.0 nm have been obtained for 15 and 25 wt % Mg contents, respectively. The hydrogen desorption properties strongly depend on the nanoparticle size, as evidenced by different thermal analysis techniques. The onset temperature of hydrogen desorption for MgH_2 nanoparticles below 3 nm occurs at a temperature about 245 K lower than for microcrystalline material. Two distinct hydrogen desorption peaks are noticed for nanoparticles with mean sizes of 1.3 and 3.0 nm, as confirmed by TDS and HP-DSC. 1H NMR investigations suggest the presence of two MgH_2 populations with enhanced hydrogen mobility, as compared to the microcrystalline hydride. The short hydrogen diffusion path and the enhanced hydrogen mobility may explain the increased desorption kinetics of these ultrasmall nanoparticles

Eco-friendly synthesis of SiO2 nanoparticles confined in hard carbon: A promising material with unexpected mechanism for Li-ion batteries

Times Cited: 3Nita, Cristina Fullenwarth, Julien Monconduit, Laure Le Meins, Jean-Marc Fioux, Philippe Parmentier, Julien Ghimbeu, Camelia MateiGhimbeu, Camelia/N-7855-2015Ghimbeu, Camelia/0000-0003-3600-587731873-3891A fast, simple and environmentally friendly one-pot route to obtain carbon/SiO2 hybrid materials is reported in this work. This consists in simple mixture of carbon and silica precursors, followed by thermal annealing at different temperatures. An interpenetrating hybrid network composed of hard carbon and amorphous SiO2 nanoparticles (2–5 nm) homogeneously distributed was achieved. Increasing the annealing temperature from 600 °C up to 1200 °C, the material porosity and oxygen functional groups are gradually removed, while the amorphous nature of SiO2 is conserved. This allows to diminish the irreversible capacity during the first charge-discharge cycle and to increase the reversible capacity. An excellent cycling capability, with a reversible capacity up to 535 mA h/g at C/5 constant current rate was obtained for C/SiO2 materials used as anodes for Li-ion batteries. An atypical increase of the capacity during the first 50 cycles followed by a stable plateau up to 250 cycles was observed and related to electrolyte wettability limitation through the materials, particularly for those annealed at high temperatures which are more hydrophobic, less porous and the SiO2 nanoparticles less accessible. The SiO2 lithiation mechanism was evaluated by XRD, TEM and XPS post-mortem analyses and revealed the formation of reversible lithium silicate phases