Carbon Textural Properties Research Articles

Carbons Derived from Agave tequilana Fibers as Efficient Sulfur Supports for High‐Performance Lithium–Sulfur Batteries

The fabrication of cathodes with carbonized Agave tequilana bagasse for Li–S batteries is performed for the first time. Three porous carbonaceous structures are developed and studied to elucidate the best carbon textural properties in terms of their surface area and pore size distribution: hierarchical porosity, highly microporous, and nonporous material, for sulfur hosting in Li–S cathodes. N2 physorption, scanning electron microscopy, infrared spectroscopy, and potentiometric titrations analysis are performed to determine the textural, morphology, and physicochemical properties. The fabricated coin cells, CR2032, with cathodes made of mesoporous carbons, display a high discharge current (≈1600 mAh g−1), superior performance, and cyclability up to 250 cycles. The performance of batteries is found to be strongly influenced by surface area and pore size of the carbon materials. The carbonized tequila bagasse hosting sulfur can be very useful to fabricate cathodes for Li–S batteries with high initial capacity and cycling stability.

Toward better porous carbon-based electrodes by investigation of the viscoelastic properties of carbon suspension

In this article, an electrode slurry based on activated carbon, which is used to form electrodes of electrochemical capacitors, was assigned to a given group of rheological fluids. The interactions between the textural properties of carbon, the components of the slurry and their impact on the flow nature were explained. Moreover, the viscosity window and optimal ratio between components have been specified, which are necessary to form the right coating on the stainless steel foil as a current collector. The equation that correlates electrode thickness, viscosity, and composition of the slurry (mass of solid materials, solvent, and ratio between components) was obtained by mathematical consideration. Electrochemical measurements were performed to verify the impact of coating quality and thickness on device performance. Finally, the effect of the microstructure formed after slurry preparation and the phenomena accompanying the selected mixing technique are discussed. The paper ends with an economic analysis of electrode slurry production.

Carbon-Based Materials as Catalyst Supports for Fischer–Tropsch Synthesis: A Review

The use of carbon-based materials as catalyst supports for Fischer–Tropsch synthesis (FTS) is thoroughly reviewed. The main factors to consider when using a carbonaceous catalyst support for FTS are first discussed. Then, the most relevant and recent literature on the topic from the last 2 decades is reviewed, classifying the different examples according to the carbon structure and shape. Some aspects such as the carbon textural properties, carbon support modification (functionalization and doping), catalyst preparation methods, metal particle size and location, catalyst stability and reducibility, the use of promoters, and the catalyst performance for FTS are summarized and discussed. Finally, the main conclusions, advantages, limitations, and perspectives of using carbon catalyst supports for FTS are outlined.

Link between Alkali Metals in Salt Templates and in Electrolytes for Improved Carbon-Based Electrochemical Capacitors.

Various alkali metal (Li+, Na+, K+, Rb+, and Cs+) chlorides with Pluronic F127 were used as a soft-salt template for tuning the textural and structural properties of carbon. Highly conductive metal hydroxide solutions, where the cations are the same as those in the salt template, have been used as electrolytes. By increasing the size of the cation in the template, the textural properties of carbon, such as the specific surface area, micropore volume, and pore size, were remarkably enhanced. It directly translates to an increase in the specific capacitance of the electrode material. For a constant current charge/discharge at 0.1 A g–1, the electrode composed of LiCl-T and operating with 1 mol L–1 LiOH demonstrates the capacitance of 124 F g–1, whereas CsCl-T with the same electrolyte has a capacitance of 216 F g–1. Moreover, the materials show the highest capacitance retention (up to 75%) vs. the current regime applied when the cation used during synthesis matches the cation present in the electrolyte (i.e., LiCl-T with LiOH). Interestingly, capacitance normalized by specific surface area has been found to be the highest when LiOH solution is applied as an electrolyte. Thus, for this metric, the size of ions seems to be a crucial parameter. The importance of mesoporosity is highlighted as well by using materials with a similar fraction of micropores and with or without mesopores. Briefly, the presence of mesopore fraction proved to be essential for improved capacity retention (69% vs. 30%). Besides textural properties, the graphitization degree impacts the electrochemical performance as well. It increases among the samples, in accordance with cation-π binding energy, e.g., LiCl-T is the most “graphitic-like” material and CsCl-T is the most disordered. Thus, the more graphitic-like materials demonstrate higher rate capability and cycle stability.

Synthesis and Characterization Ru–C/SiO2 Aerogel Catalysts for Sugar Hydrogenation Reactions

Synthesis of materials with combined chemistry and textural properties of carbon and silica aerogels was studied. The synthesized support was modified with ruthenium using evaporation impregnation and deposition–precipitation methods. The ruthenium modification methods were observed to influence the particle size, dispersion, surface area, pore volume and acidity of Ru–C–SiO2 catalysts. Ruthenium particles of 1–2 nm were obtained with a simple impregnation–evaporation method, while deposition precipitations technique gave ruthenium particles ranging from 1 to 8 nm. Small Ru nanoparticles (1–2 nm) were stable even after being exposed at 700 °C or washed with ethanol for regeneration. Furthermore, the catalytic properties of Ru–C–SiO2 catalysts in sugar hydrogenation were also observed to be influenced by the synthesis methods. The catalysts were tested in hydrogenation of sugars with different molecule sizes (i.e. glucose and cellobiose). d-Glucose was more reactive than d-cellobiose when they were studied separately. For the mixture of sugars higher reactivity of both sugars was observed in comparison with neat substrates for the catalyst made by evaporation-impregnation. On the contrary no significant differences between kinetics of the separated sugars and their mixture were observed for the catalyst prepared by deposition–precipitation. The results can be attributed to acidity and a combination of meso and microporosity of the catalysts. The support composite material could also be produced as a monolith, being a promising candidate for future industrial applications.

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

A sustainable and simple synthesis procedure involving the co-assembly of green phenolic resin and amphiphilic polymer template in water/ethanol mixture at room temperature to synthesize nitrogen doped mesoporous carbon is reported herein. Guanine is proposed as a novel nitrogen-based precursor which is able to create H-bondings both with the phenolic resin and the template allowing the formation of mesoporous carbons with nitrogen atoms uniformly distributed in their framework. The influence of the synthesis procedure, template amount and annealing temperature on the carbon textural properties, structure and surface chemistry were investigated. For several conditions, carbon materials with ordered pore size and high nitrogen content (up to 10.6 at %) could be achieved. The phase separation procedure combined with optimal amount of template favor the formation of ordered mesoporous carbons with higher specific surface area while the increase in the temperature induces a decrease in the surface area and amount of heteroatoms (N and O). The electrochemical performances as electrode in supercapacitors were evaluated in acidic medium and the capacitance was closely related to the material conductivity and surface chemistry.

Synthesis of large pore sized ordered mesoporous carbons using triconstituent self-assembly strategy under different acidic conditions and ratios of carbon precursor to structure directing agent

This study was aimed at the synthesis of ordered mesoporous carbons with large pores. A triconstituent self-assembly strategy was employed, where resorcinol and formaldehyde were used as carbon source, tetraethyl orthosilicate was used as silica source, and triblock copolymer Pluronic F127 was used as structure directing agent. The effects of hydrochloric acid (HCl) concentration on the composite yield and the textural properties of carbons were investigated. The composite yield was seen to increase until a HCl concentration of 0.66 M. The effect of carbon source (resorcinol-formaldehyde (RF)) to Pluronic F127 ratio (RF/F127) was also investigated. The pore sizes slightly varied around 6 nm at low RF/F127 ratios, while the RF/127 = 2 ratio gave a 8.1-nm pore size and 711-m2/g surface area. The resultant carbons are promising for use in areas such as fuel cells, where diffusion limitations affect the performance.

Facile and rapid one-pot microwave-assisted synthesis of Pd-Ni magnetic nanoalloys confined in mesoporous carbons

An easy and rapid one-pot microwave-assisted soft-template synthesis method for the preparation of Pd-Ni nanoalloys confined in mesoporous carbon is reported. This approach allows the formation of mesoporous carbon and the growth of the particles at the same time, under short microwave irradiation (4 h) compared to the several days spent for the classical approach. In addition, the synthesis steps are diminished and no thermopolymerization step or reduction treatment being required. The influence of the Pd-Ni composition on the particle size and on the carbon characteristics was investigated. Pd-Ni solid solutions in the whole composition range could be obtained, and the metallic composition proved to have an important effect on the nanoparticle size but low influence on carbon textural properties. Small and uniformly distributed nanoparticles were confined in mesoporous carbon with uniform pore size distribution, and dependence between the nanoparticle size and the nanoalloy composition was observed, i.e., increase of the particle size with increasing the Ni content (from 5 to 14 nm). The magnetic properties of the materials showed a strong nanoparticle size and/or composition effect. The blocking temperature of Pd-Ni nanoalloys increases with the increase of Ni amount and therefore of particle size. The magnetization values are smaller than the bulk counterpart particularly for the Ni-rich compositions due to the formed graphitic shells surrounding the particles inducing a dead magnetic layer.

Enhanced ammonia adsorption on functionalized nanoporous carbons

Nanoporous carbons were synthesized and treated with nitric acid after which the change in their propensities for ammonia adsorption was determined. The adsorbents had mean pore sizes ranging from 0.5 to 12 nm and they included polyfurfuryl alcohol (PFA)-derived carbons, commercial activated carbons, and both soft and hard-templated mesoporous carbons. The carbons were treated with concentrated nitric acid at elevated temperatures (e.g. 90 °C) and for time spans between 15 and 240 min. The textural properties of carbons, before and after nitric acid treatment, were determined using CO2 adsorption at 0 °C. Ammonia adsorption uptakes were measured at 25 °C and at pressures up to 9.5 bar. The highest total uptake of ammonia on the native carbons, that is prior to nitric acid treatment, was ∼10 mmol/g at 1 bar and 25 °C; this was obtained on a microporous carbon derived from the pyrolysis of polyfurfuryl alcohol and polyethylene glycol blends followed by CO2 oxidation. Nitric acid treatment of this carbon significantly increased its total uptake of ammonia to 17 mmol/g. This sample provided a reversible uptake of 14 mmol/g after it was outgassed at 160 °C and 10−5 bar under dynamic vacuum. This is 2 mmol/g higher than state-of-the-art ammonia adsorbents such as COF-10. An x-ray photoelectron spectrum (XPS) showed that the oxygen content of the carbon increased from 3 at.% to 16.4 at.% after the nitric acid treatment. Heats of adsorption profiles, calculated from adsorption isotherms, started from 165 kJ/mol and quickly dropped to 40 kJ/mol with ammonia loading. This showed that the isosteric heat of adsorption on the remaining surface was still higher than the native carbon sample resulting in high reversible adsorption uptake, even after excluding the irreversible adsorption on the very high energy sites.

Effect of the Porous Texture of Activated Carbons on the Electrochemical Properties of Molecule-Grafted Carbon Products in Organic Media

Two commercial activated carbons, different from their texture, were grafted with electroactive molecules and tested for determining what texture is well-suited for the grafting. Microporous and mesoporous carbons, having approximately the same BET surface area, were selected. The electroactive molecule consists in a naphthalimide compound having an amine as surface attachment group. The present work was divided in two parts. In a first part, the modified carbons were characterized by thermal gravimetric analysis, X-ray photoelectron spectroscopy, elemental chemical analysis and nitrogen gas adsorption measurements have been used for studying the impact of the grafting on the textural properties of carbons. In a second part, the electrochemical properties of the modified carbons were studied in propylene carbonate +1 M Bu4NBF4. Results show that the grafting ruins the performances of the microporous carbon, while the mesoporous carbon appears well-suited for the grafting, showing a good compromise between electrolyte-accessibility and ionic transportation.

Preparation of activated carbons from cocoa shells and siriguela seeds using H3PO4 and ZnCL2 as activating agents for BSA and α-lactalbumin adsorption

The aim of this work was to prepare activated carbons from cocoa shells and siriguela seeds and to evaluate the whey protein adsorption on produced activated carbon. The residues were impregnated with ZnCl2 and H3PO4. DTA/TG and FTIR were performed with this material. Carbonization was performed under nitrogen flow for 40min at 500 °C and the obtained activated carbons were washed, dried and stored. The resulting carbons were characterized regarding their textural properties. Additionally, an adsorption study was performed, using BSA and α-lactalbumin. The activated carbons showed surface areas higher than 642 m2·g−1. Impregnation with H3PO4 was more effective in modifying the structure of the precursors and carbon textural properties and this action was favorable for the adsorption of the protein α-lactalbumin. Impregnation with ZnCl2 resulted in activated carbons which were more effective in the adsorption of BSA. In both cases, use of the siriguela seed as a precursor in the production of activated carbon was favorable. The pseudo second-order model was fitted satisfactorily to the time equilibrium experimental data, for both proteins. The Toth model represents most efficiently α-lactalbumin adsorption experimental data and the Langmuir model was considered the most satisfactory for the adsorption of BSA.

Inverse Opal Carbons As Li-O2 Cathodes with an Ionic Liquid-Based Electrolyte: Effect of Macropore Size on Capacity, Rate Capability and Reversibility

Inverse opals are beautiful macroporous materials prepared by template synthesis and presenting a well-defined arrangement of pores of tunable monodisperse size. Thus, they are ideal model systems for studying the effect of macropore size in lithium-oxygen electrodes.In this work, inverse opal carbons were prepared by using poly(styrene-co-methacrylic acid) (PS-MAA) spheres of different size as templates via a resorcinol-formaldehyde sol-gel process. These were used in cathodes for Li-O2 batteries using different cell configurations and an ionic liquid electrolyte (LiTFSI in PYR14TFSI). The high porosity and open channels with low tortuosity allowed remarkable capacities of over 3000 mAh/g at 0.1 mA/cm2.We could relate the carbon textural properties to the capacity, rate capability and reversibility. We observed better rate capability for discharge with the largest macropores (500 nm diameter), evidencing a mass transport limitation. However, charge profiles denoted a remarkable asymmetry respect to discharge, with low coulomb efficiency. Instead, when macropores were smaller than 100 nm we obtained a remarkable symmetry in time-limited discharge-charge profiles. This proves that confinement of discharge products in small pores effectively prevents the electrode passivation. Acknowledgement The research leading to these results has received funding from the European Union’s Seventh Framework Programme under EC-GA No. 265971 ‘LABOHR’, and from the Spanish Government under contract MAT2012-39199-C02-01. M.O. acknowledges CSIC for a JAE-DOC research contract.

Zero-valent iron supported on nitrogen-containing activated carbon for catalytic wet peroxide oxidation of phenol

Zero-valent iron supported catalysts were prepared through modifying an activated carbon (AC) support with different nitrogen containing precursors; (ethylenediamine, urea and melamine) and impregnating it with 3wt% of iron. The supports were characterized by N2 adsorption at −196°C, elemental analysis (EA), the pH at the point of zero charge (pHPZC) and temperature programmed desorption (TPD). The iron catalysts were also characterized by temperature programmed reduction (TPR). Subsequently, the catalysts were tested in the adsorption and wet peroxidation of phenol. The results from the different characterization techniques demonstrate that the nitrogen-containing groups are successfully introduced into the carbon surface via all the precursors used. The tests of the different modified carbons as adsorbents/catalysts indicated that the adsorption capacity and the efficiency in phenol oxidation are governed by the specific surface area and functional groups present. Both surface chemistry and textural properties of carbons are influenced by the nitrogen source and the type of oxygen functionalities preexisting on the surface. The modified carbon-supported iron catalysts revealed significantly enhanced phenol removal efficiency, reaching over 85% conversion after 3h, and showed interesting catalytic stability.

Grape seed carbons for studying the influence of texture on supercapacitor behaviour in aqueous electrolytes

Microporous carbon materials having a negligible contribution of mesopores have been synthesised by cyclic oxidation/desorption of grape seeds char using air, ozone and HNO3 as oxidant agents. By adequate selection of the operating conditions (oxidation procedure and number of cycles), it is possible to tune the volume and pore size distribution (PSD) of carbon materials and therefore determine the influence of carbon textural properties on the electrochemical behaviour of carbon–carbon symmetric supercapacitors operating in different aqueous electrolytes. The results confirm that although energy density can be improved using neutral electrolytes because of their higher stability potential window compared to acidic or basic electrolytes, it is important to adapt the textural properties of the carbon materials to improve the ions’ diffusion inside the porosity for assuring the charging of the double layer at high current densities to reach high power densities.

Preparation of mesoporous activated carbons from coal liquefaction residue for methane decomposition

Mesoporous activated carbons were prepared from direct coal liquefaction residue (CLR) by KOH activation method, and the experiments were carried out to investigate the effects of KOH/CLR ratio, solvent for mixing the CLR and KOH, and carbonization procedure on the resultant carbon texture and catalytic activity for catalytic methane decomposition (CMD). The results showed that optimal KOH/CLR ratio of 2: 1; solvent with higher solubility to KOH or the CLR, and an appropriate carbonization procedure are conductive to improving the carbon pore structure and catalytic activity for CMD. The resultant mesoporous carbons show higher and more stable activity than microporous carbons. Additionally, the relationship between the carbon textural properties and the catalytic activity for CMD was also discussed.

Ultrahigh surface area polypyrrole-based carbons with superior performance for hydrogen storage

Ultrahigh surface area carbons (3000–3500 m2 g−1) have been obtained via chemical activation of polypyrrole with KOH. The carbon materials exhibit large pore volumes (up to ∼2.6 cm3 g−1) and possess two pore systems: one of pores in the micropore range (∼1.2 nm) and the other in the small mesopore range (2.2–3.4 nm). Some carbons also possess a significant proportion of 0.6 nm pores. Tuning of the carbon textural properties was achieved through the control of the activation parameters (temperature and amount of KOH). The carbons achieve an excellent hydrogen storage capacity of up to 7.03 wt% at −196 °C and 20 bar, which is the highest ever reported for one-step activated carbons and amongst the best for any porous material. The gravimetric hydrogen uptake of the carbons translates to a very attractive volumetric density of up to 37 g H2 L−1 at 20 bar. These carbons exhibit excellent gravimetric and volumetric capacity due to the fact that their high porosity is not at the detriment of packing density.