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Abstract This work aims at shedding light on how the microporous texture of porous carbons influences their electrochemical behavior when used as anodes for Li-ion batteries. To this aim, a synthetic hard carbon (carbon xerogel, CX), prepared from a resorcinol-formaldehyde precursor gel, underwent several post-synthesis treatments in order to modulate its micropore to total pore volume ratio. The micropore volume was either expanded by physical activation or decreased using chemical vapor deposition (CVD) of a carbon layer. Several variables other than the micropore texture of the obtained carbons, which could influence their behavior as anode active materials for Li-ion batteries, such as the particle size or the electrode characteristics, were carefully controlled. The thickness of electrode coatings and the pore texture of the active material-binder composite were analyzed. It was shown that CX-binder composites resulting from water-based slurries preserve the microporosity of the starting materials. Detailed electrochemical characterization of the electrodes prepared with carbon xerogels displaying various defined micropore textures was performed. A clear linear dependency could be evidenced between the Li+ insertion and de-insertion in half-cell configuration with the increase of the volume of supermicropores (0.7–2 nm), demonstrating the effect of micropore enlargement by activation on the storage capacity, provided the maximum charge potential value is set at 3.0 V vs. Li+/Li. Graphical abstract Image 1 Highlights • The microporosity of a macroporous carbon xerogel was selectively modulated. • The micropore texture was characterized by combined N 2 and CO 2 adsorption measurements. • Using a water-soluble binder to prepare electrodes allows for keeping the micropores accessible. • The volume of supermicropores strongly influences Li+ ions insertion and de-insertion. [ABSTRACT FROM AUTHOR]

N-doped carbon xerogels (CXs) were synthesized from melamine-resorcinol-formaldehyde aqueous gels by evaporative drying and pyrolysis at 800 °C. The pore texture of these N-doped CXs ranged from micro-mesoporous to micro-macroporous depending on the initial pH of the precursors solution. For different pH values, while the specific surface area varied slightly from 500 to 600 m 2 g −1 , the total void volume changed from 0.6 to 1.6 cm 3 g −1 . Furthermore, N-doped CXs showed a wide interval of average pore diameters ranging from 19 to 1200 nm. The nitrogen amount in N-doped CXs varied from 4 to 11 wt. % and XPS analysis showed that nitrogen was mainly incorporated into the carbon network as pyridine or quaternary nitrogen groups. These results indicate that this doping approach is suitable to tune the pore texture, pore size and chemical composition by adjusting the initial pH value or the amount of nitrogen precursor. Taking into account the properties mentioned above, N-doped CXs can be tailored to find applications as adsorbents, catalyst supports, materials for energy generation and storage. [ABSTRACT FROM AUTHOR]

Highlights: [•] OMC were prepared via a rapid aqueous soft-templating route. [•] Influence of preparation temperature on structure and texture was investigated in detail. [•] Highly ordered materials can be prepared in the temperature range 72–115°C. [•] OMC show excellent cycling stability as anode materials for Li-ion batteries. [ABSTRACT FROM AUTHOR]

This work aims at understanding the effect of the mesopore volume of ordered mesoporous carbons (OMCs) on their behavior as anodes for Li-ion batteries. To that purpose, the hard-templating method was used as an enabling tool, with the controlled partial etching of the silica template to prepare a series of OMCs with a wide range of mesopore volumes. The formed carbon-silica hybrids were processed into electrodes using a water-based ink preparation route in the presence of xanthan gum as a binder, which retained access to the pores after formation of the electrodes. The pore texture of the latter was compared to that of the starting powders. A very good linear relationship could be evidenced between the mesopore volume of the electrodes and the first insertion capacity of Li-ions. The lithium de-insertion also followed a linear trend, but its behavior was dependent on the final applied potential. Indeed, the higher the mesopore volume, the higher the contribution of de-insertion at elevated voltages. This study further points out the importance of the textural characterization of electrodes (instead of just the starting material) as well as the conditions at which the electrochemical measurements are carried out, especially the maximum applied de-insertion voltage. Image 1 • OMCs with increasing mesopore volumes were obtained by partial etching of the silica template. • Using a water-soluble binder to prepare electrodes allows for preserving porosity. • Li+ insertion is directly correlated with the mesopore volume. • Higher de-insertion potentials are needed to recover Li+ ions for OMCs with high mesopore volumes. [ABSTRACT FROM AUTHOR]

Carbon xerogels (CX) with varying nodule sizes, from 50 nm to 2 μm, are synthesized via polycondensation of resorcinol with formaldehyde in water, followed by pyrolysis at 800 °C to investigate their electrochemical properties as negative electrode material in Na-ion batteries. All samples exhibit high specific surface areas (∼600 m2 g-1 by N 2 physisorption) due to the presence of a large volume of micropores. Chemical Vapor Deposition (CVD) is used to fill or mask the micropores to mitigate the typical detrimental effects of high surface areas on the Initial Coulombic Efficiency (ICE). Larger nodules correlate with increased Na+ storage capacity and ICE (up to 80 %), independently of the measured specific surface area. Notably, the sample displaying 2 μm nodule size reach a reversible capacity of 248 mAh g-1 and 80 % ICE at C/20 cycling rate. CVD-deposited carbon layers show a graphitic-like structure and completely block the micropores, reducing the specific surface area and improving both reversible capacity and ICE up to 298 mAh g-1 and 84 %, respectively. Such materials composed of two different carbons show great promise in the advancement of carbon-based materials for Na-ion batteries. [Display omitted] [ABSTRACT FROM AUTHOR]

The electrochemical performances of lithium-ion batteries depend to a great extent on the method used to prepare the electrodes and on the pore texture of the active material. In the present study, carbon xerogels with different pore sizes and pore volumes were synthesized by means of microwave heating. These carbonaceous materials were used to prepare lithium-ion battery anodes. Generally, electrodes are prepared by coating a slurry made of an active material, a binder and N -methyl-2-pyrrolidone as organic solvent. The disadvantage of this solvent is that it is both toxic and costly. In this work, the use of water instead of the organic solvent and water-soluble binders yielded electrodes with similar electrochemical performances making the battery assembly process more economic and environmentally friendly. The results of this study also confirm that the use of an aqueous preparation pathway does not undermine the interdependence between the electrochemical properties of the cells and the porous properties of the carbon xerogels. [ABSTRACT FROM AUTHOR]

Abstract: The wet impregnation of ammonium heptamolybdate onto silica–alumina is used to prepare MoO3/SiO2–Al2O3 heterogeneous metathesis catalysts. The preparation is inspected in details in conjunction with physico-chemical characterization tools with the aim to identify the parameters that dictate the genesis of active and inactive metathesis species. The effects of the MoO3 loading and of the calcination temperature are systematically explored. The samples are characterized by N2-physisorption, ICP-AES, XRD, Raman, 27Al MAS-NMR and XPS and evaluated in the metathesis of propene to butene and ethene. Particular attention is brought to the interaction of the mesoporous silica–alumina support with the active component, to the decomposition of the precursor salt and to the location of the molybdenum oxide phase with respect to the pores of the support. It is shown that the temperature of calcination influences markedly the performances of the catalyst. High temperature treatments are necessary to decompose efficiently the Mo salt precursor. In the metathesis of propylene, the performances are levelling off when the MoO3 loading is increased above ∼8wt.%. This effect is correlated to the build up of MoO3 crystals and of Al2(MoO4)3 at relatively high loading. [Copyright &y& Elsevier]