Templated mesoporous carbons for supercapacitor application

Mesoporous carbons prepared by an inverse replica technique have been used as electrodes for electrochemical capacitors. Such well-sized carbons were prepared from mesostructured SBA-16 silica materials that served as templates whereas polyfurfuryl alcohol was the carbon precursor. Two highly mesoporous carbons characterized by 3 and 8 nm average pore diameter were tested in various electrolytic solutions (acidic, alkaline and aprotic).It can be concluded that templated mesoporous carbons with tailored pore size distribution are very promising materials to be used as electrodes in supercapacitors. The design of their pore size allows suiting the dimensions of electrolyte ions and efficient charging of the electrical double layer is achieved especially at high current load. Definitively better capacitance performance has been found for carbon with 3 nm pores range, however, cycling performance depends not only on the pore size.     

Hierarchically porous phenolic resin-based carbons obtained by block copolymer-colloidal silica templating and post-synthesis activation with carbon dioxide and water vapor

A series of hierarchically porous carbons was synthesized by self-assembly of polymeric carbon precursors and block copolymer template in the presence of tetraethyl orthosilicate (TEOS) and colloidal silica under acidic conditions. Resorcinol and formaldehyde were used as carbon precursors, poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer was employed as a soft template, and TEOS-generated silica and colloidal silica were used as hard templates. The carbon precursors were polymerized in hydrophilic domains of block copolymer, followed by carbonization and silica dissolution. This resulted in carbons possessing cylindrical (∼12 nm) and spherical (20 or 50 nm) mesopores created by thermal decomposition of the soft template and by the dissolution of colloidal silica, respectively; fine pores were also formed by the dissolution of the TEOS-generated silica (∼2 nm). A further increase in fine porosity was achieved by post-synthesis activation of the carbons with carbon dioxide and/or water vapor, which resulted in hierarchical carbons with a surface area and pore volume approaching 2800 m²/g and 6.0 cm³/g, respectively.     

Colloidal templating synthesis and adsorption characteristics of microporous–mesoporous carbons from Kraft lignin

Microporous–mesoporous carbons were synthesized via colloidal silica templating using Kraft lignin as a carbon precursor, which is a waste byproduct from paper industry. A unique feature of these carbons are uniform spherical mesopores achieved after dissolving colloidal silica used as a hard template, while micropores were created by post-synthesis CO₂ activation. The resulting activated lignin-based carbons possessed high specific surface area (up to 2000 m²/g) and microporosity and mesoporosity easily tunable by adjusting activation conditions and optimizing the amount and particle size of the colloidal silica used. The total pore volumes of activated carbons obtained by using 20 and 13 nm silica colloids as a hard template exceeded 1 and 2 cm³/g, respectively.     

The effect of Mo2C derived carbon pore size on the electrical double-layer characteristics in propylene carbonate-based electrolyte

Carbide-derived carbon (CDC) was synthesised from molybdenum carbide by extracting Mo atoms in a high-temperature chlorine atmosphere. A systematic study of the influence of pore size on the electrical double layer (EDL) performance was carried out with carbons synthesised in the temperature interval of 500-900 °C. Strong effect of chlorination conditions on the pore-size distribution was noticed that gives wide possibilities to vary the pore structure of Mo₂C derived carbons. An average pore size of carbons varied between 1 nm and 2 nm depending on chlorination temperature. The relationships were established between the pore-size distribution and the electrochemical performance of micro/mesoporous carbons. The EDL characteristics of carbon materials in a propylene carbonate solution of triethylmethylammonium tetrafluoroborate were obtained using the cyclic voltammetry at ΔE of 3.8 V and the constant current methods in a 3-electrode test cell. A novel test method was developed to demonstrate the power characteristics of the electrode materials. The results of this study affirmed the great potential of Mo₂C derived carbons, whose EDL capacitance reaches ∼65 F cm⁻³ and 132 F g⁻¹ and the 20-s discharge power density is 2.1 W cm⁻³.     

Carbon spheres prepared from zeolite Beta beads

Porous carbon beads were prepared from macroporous anion-exchange resin beads preliminary converted into resin-zeolite Beta composite or pure zeolite Beta spheres. Two synthesis procedures were used depending on the initial template employed. In a series of experiments, the resin from the resin-zeolite Beta composite was directly carbonized into carbon. In another series of experiments, the resin was removed by oxidation at 600 °C leaving behind self-bonded zeolite Beta beads, which were filled with carbon by chemical vapor deposition (CVD) of propylene. As a final step for both procedures, the zeolite was dissolved in hydrofluoric acid. All the carbons prepared inherited the macroscopic spherical shape of the template spheres as well as the morphology of the primary particles building up the beads. The synthesis procedure and the carbonization temperature or the temperature for CVD of carbon employed influenced the ordering and the pore structure of the produced carbons. The carbons prepared by direct carbonization showed relatively low surface areas, less than 1000 m² g⁻¹, and no zeolite structural regularity. The samples obtained via CVD maintained the zeolite ordering with a periodicity of 11.7 Å and had surface areas of over 2000 m² g⁻¹.     

Direct fabrication of mesoporous carbons using in-situ polymerized silica gel networks as a template

Mesoporous carbons were synthesized by in-situ polymerized silica gel networks as a template. The co-condensation of carbon precursor (sucrose) and silica precursor (sodium silicate) followed by heat treatment generated a carbon/silica nanocomposite. After etching the silica template, mesoporous carbons were obtained. Under optimum synthesis conditions a mesoporous carbon with a high surface area of >800 m²/g and a narrow pore size distribution centered at 3 nm was produced. The three-dimensionally interconnected silica structures effectively functioned as the template for the porous carbon materials.     

PtCo supported on ordered mesoporous carbon as an electrode catalyst for methanol oxidation

A catalyst for methanol oxidation, PtCo supported on graphitized mesoporous carbon, has been synthesized and its electrochemical activity for methanol oxidation has been investigated. The graphitized mesoporous carbon support with ordered pore structure and high surface area of 585 m² g⁻¹ was prepared by one-step melt casting method using Al doped hexagonal mesoporous silica as hard templates and mineral pitches as carbon precursors followed by carbonization at 800 °C. The materials were characterized by X-ray diffraction, Raman spectra, field emission scanning electron microscopy, transmission electron microscopy and nitrogen sorption techniques. Cyclic voltammetry and amperometric i-t tests were adopted to characterize the electro-catalytic activities of the materials for methanol oxidation. The results show that the graphitized mesoporous carbon exhibits large electrochemical capacitance and good electric property. After supported with 20 wt%Pt or 20 wt%PtCo nanoparticles, the resultant mesostructured composites show 26-97% higher electrochemical catalytic activity for methanol oxidation than commercial catalyst 20 wt%Pt/C in mass activity (mA mg Pt⁻¹).     

Optimisation of supercapacitors using carbons with controlled nanotexture and nitrogen content

In order to optimize the performance of supercapacitors, the capacitance of the carbon materials used as electrodes was strictly related to their pores size and also to their redox properties. Well-sized carbons have been elaborated through a template technique using mesoporous silica. For a series of template carbons, a perfect linear dependence has been found for the capacitance values versus the micropore volume determined by CO₂ adsorption. The redox properties of carbons were enhanced by substituting nitrogen for carbon up to ca. 7 wt.%. For carbons with similar nanotextural characteristics, the electrochemical measurements showed a proportional increase of the specific capacitance with the nitrogen content in acidic electrolyte. For an activated carbon from polyacrylonitrile with a specific surface area of only 800 m² g⁻¹, but with a nitrogen content of 7 wt.%, the capacitance reaches 160 F g⁻¹, with very little fading during cycling.     

Some aspects of the direct synthesis of platinum containing carbons by template assisted routes

Several aspects of the direct synthesis of noble metal containing carbons by template assisted routes are discussed. Commercial available silica as well as in situ formed silica were used as templates. The synthesis solutions consisted in different carbon precursors such as sucrose, pyrrole and polyvinyl alcohol (PVA), and hexachloro platinum acid as the metal source. The resulting materials are characterized by nitrogen adsorption at 77 K, X-ray diffraction and X-ray photoelectron spectroscopy. The results are discussed regarding pore system development, metal particle size, and surface composition.     

Quenched solid density functional theory and pore size analysis of micro-mesoporous carbons

We present a new model of adsorption on micro-mesoporous carbons based on the quenched solid density functional theory (QSDFT). QSDFT quantitatively accounts for the surface geometrical inhomogeneity in terms of the roughness parameter. We developed the QSDFT models for pore size distribution calculations in the range of pore widths from 0.4 to 35 nm from nitrogen at 77.4 K and argon at 87.3 K adsorption isotherms. The QSDFT model improves significantly the method of adsorption porosimetry: the pore size distribution (PSD) functions do not possess gaps in the regions of ∼1 nm and ∼2 nm, which are typical artifacts of the standard non-local density functional theory (NLDFT) model that treats the pore walls as homogeneous graphite-like plane surfaces. The advantages of the QSDFT method are demonstrated on various carbons, including activated carbons fibers, coal based granular carbon, water purification adsorbents, and mirco-mesoporous carbon CMK-1 templated on MCM-48 silica. The results of PSD calculations from nitrogen and argon are consistent, however, argon adsorption provides a better resolution of micropore sizes at low vapor pressures than nitrogen adsorption.     

A green process for the synthesis of controllable mesoporous silica materials

The synthesis, characterization, and application of mesoporous silicas have attracted a lot of attention for over two decades, which stems from their fascinating structures, formation mechanisms and prospects of their applications. Various methods have been developed for the synthesis of these silicas with a tunable pore diameter and a narrow pore size distribution. In this paper, mesoporous silica materials with controllable pore diameters (3-9 nm), narrow pore size distributions, high surface area (>700 m² g⁻¹) and pore volume (>1 cm³ g⁻¹) were prepared by a green template, amphiphilic dendritic polyamidoamine. The resulting silica materials were characterized by ¹H, ¹³C NMR spectroscopy; thermogravimetic analysis; nitrogen adsorption; transmission electron microscope. It was shown that the template could be completely removed and recycled from the silica in an environmentally friendly way by means of a simple water extraction. Furthermore, it was shown that the pore diameter of these materials could be controlled by dendritic polyamidoamine with different generations and functional groups. Meanwhile, the porous framework showed strong thermal stability. Thus, a new environmentally friendly pathway for the controllable synthesis of this fascinating silicas has been proposed.     

Hierarchical porous carbons with controlled micropores and mesopores for supercapacitor electrode materials

Various porous carbons were prepared by CO₂ activation of ordered mesoporous carbons and used as electrode materials for supercapacitor. The structures were characterized by using X-ray diffraction, transmission electron microscopy and nitrogen sorption at 77 K. The effects of CO₂ treatment on their pore structures were discussed. Compared to the pristine mesoporous carbons, the samples subjected to CO₂ treatment exhibited remarkable improvement in textural properties. The electrochemical measurement in 6 M KOH electrolyte showed that CO₂ activation leads to better capacitive performances. The carbon CS15A6, which was obtained after CO₂ treatment for 6 h at 950 °C using CMK-3 as the precursor, showed the best electrochemical behavior with a specific gravimetric capacitance of 223 F/g and volumetric capacitance of 54 F/cm³ at a scan rate of 2 mV/s and 73% retained ratio at 50 mV/s. The good capacitive behavior of CS15A6 may be attributed to the hierarchical pore structure (abundant micropores and interconnected mesopores with the size of 3-4 nm), high surface area (2749 m²/g), large pore volume (2.09 cm³/g), as well as well-balanced microporosity and mesoporosity.     

Carbide-derived-carbons with hierarchical porosity from a preceramic polymer

Synthesis of carbon by extraction of metals from carbides has been successfully used to produce a variety of micro-porous carbide-derived carbons (CDCs) with narrow pore size distributions and tunable sorption properties. This approach is of limited use when larger mesopores are targeted, however, because the relevant synthesis conditions yield broad pore size distributions. Here we demonstrate the porosity control in the 3-10 nm range by employing preceramic polymer-derived silicon carbonitride (SiCN) precursors. Polymer pyrolysis in the temperature range 600-1400 °C prior to chlorine etching yields disordered or graphitic CDC materials with surface area in the range 800-2400 m² g⁻¹. In the hierarchical pore structure formed by etching SiCN ceramics, the mesopores originate from etching silicon nitride (Si₃N₄) nano-sized crystals or amorphous Si-N domains, while the micropores come from SiC domains. The etching of polymer-derived ceramics allows synthesis of porous materials with a very high specific surface area and a large volume of mesopores with well controlled size, which are suitable for applications as sorbents for proteins or large drug molecules, and supports for metal catalyst nanoparticles.     

Monodispersed nanoporous starburst carbon spheres and their three-dimensionally ordered arrays

Controlled syntheses of highly monodispersed nanoporous carbon spheres via a nanocasting route are described. Previously reported monodispersed super-microporous or mesoporous silica spheres with hexagonally ordered pore channels were used as sacrificial templates, and the effect of pore sizes of the templates on the porous properties of the nanocast carbon spheres was comprehensively studied. The resultant carbon spheres exhibited a unique starburst structure derived from radially-aligned pore channels in the silica template, and had a BET surface area of over 1000 m²g^?1. It was found out that the radial alignment and sufficiently large pore size of hexagonally ordered pore channels in the silica spheres were effective to enhance the degree of order of the starburst structure in the nanocast carbon spheres and that ordered nanoporous carbon spheres could be obtained even from the MCM-41-type mesoporous silica. The diameters of the nanoporous carbon spheres were controlled in the sub-micrometer range by changing the sizes of silica templates. Furthermore, three-dimensionally ordered arrays consisting of nanoporous carbon spheres were successfully fabricated via the self-assembly of mesoporous silica/carbon composite spheres and the subsequent dissolution of the silica templates.     

Bimodal, templated mesoporous carbons for capacitor applications

Several high capacitance ordered mesoporous carbon (OMC) materials, containing a bimodal pore distribution, were synthesized directly using hexagonal mesoporous silicas (HMS) as the template material. The HMS templates were formed using amine surfactants (C_nH_2n+1NH₂) with hydrophobic chain lengths containing 8-16 carbons (n = 8-16). These HMS structures were found to have an interconnected wormhole structure, high textural mesoporosity, a surface area ranging from 910 to 1370 m²/g, and a total pore volume of 1.09-1.83 cm³/g. Also, evidence for a change in structure from hexagonally ordered to layered (for surfactants of chain length with n > 12) was found. The resulting OMCs, formed using sucrose as the carbon precursor, contain bimodal pores 1.6-1.8 and 3.3-3.9 nm in diameter and have a very high surface area (980-1650 m²/g). The OMCs were evaluated as electrode materials for electrochemical capacitors using cyclic voltammetry in 0.5 M H₂SO₄ solution, giving a tunable gravimetric capacitance that increased linearly with BET area (and surfactant chain length), up to 260 F/g, among the highest yet reported for ordered carbon formed from an HMS templated precursor. All OMCs studied in this work displayed a specific capacitance of ∼0.15 F/m².     

The effect of silica template structure on the pore structure of mesoporous carbons

We have synthesized two kinds of mesoporous carbons using a spherical silica sol (SMC1 carbon) and an elongated silica sol (SMC3 carbon) as templates. Nitrogen isotherms and electrochemical experiments were performed to investigate the effect of the silica template structure on the pore structure of the resulting mesoporous carbons. When carbons produced using the same silica to resorcinol molar ratio were compared, both nitrogen isotherms and electrochemical studies revealed that the SMC3 carbons exhibit simpler pore connectivity than SMC1 carbons.     

Synthesis of ultra-large mesoporous carbons from triblock copolymers and phloroglucinol/formaldehyde polymer

Ultra-large mesoporous carbon materials were synthesized with the use of triblock copolymers and phloroglucinol/formaldehyde polymer as filler under acid conditions. The carbons obtained by employing F127 as template and carbonizing at 600 °C exhibit large mesopores with a narrow pore-size distribution centered at 19.2 nm. With the assistance of decane as a swelling agent, the pore size of the P123-templated 600 °C-carbonized carbons could be enlarged from 11.5 to 14.7 nm. It is demonstrated that the low synthesis temperature and high reactivity of phloroglucinol are two key factors for the formation of large mesopores.     

Adsorption capacity and removal efficiency of heavy metal ions by Moso and Ma bamboo activated carbons

In order to understand the adsorption capacity and removal efficiency of heavy metal ions by Moso and Ma bamboo activated carbons, the carbon yield, specific surface area, micropore area, zeta potential, and the effects of pH value, soaking time and dosage of bamboo activated carbon were investigated in this study. In comparison with once-activated bamboo carbons, lower carbon yields, larger specific surface area and micropore volume were found for the twice-activated bamboo carbons. The optimum pH values for adsorption capacity and removal efficiency of heavy metal ions were 5.81–7.86 and 7.10–9.82 by Moso and Ma bamboo activated carbons, respectively. The optimum soaking time was 2–4 h for Pb²⁺, 4–8 h for Cu²⁺ and Cd²⁺, and 4 h for Cr³⁺ by Moso bamboo activated carbons, and 1 h for the tested heavy metal ions by Ma bamboo activated carbons. The adsorption capacity and removal efficiency of heavy metal ions of the various bamboo activated carbons decreased in the order: twice-activated Ma bamboo carbons > once-activated Ma bamboo carbons > twice-activated Moso bamboo carbons > once-activated Moso bamboo carbons. The Ma bamboo activated carbons had a lower zeta potential and effectively attracted positively charged metal ions. The removal efficiency of heavy metal ions by the various bamboo activated carbons decreased in the order: Pb²⁺ > Cu²⁺ > Cr³⁺ > Cd²⁺.     

Magnetically separable bimodal mesoporous carbons with a large capacity for the immobilization of biomolecules

A method for the fabrication of carbon-based mesoporous magnetic composites with a large capacity for the adsorption/immobilization of biomolecules is presented. The composites consist of iron oxide spinel nanoparticles inserted into the pores of templated unimodal or bimodal mesoporous carbons. The deposition of the magnetic iron oxide nanoparticles was carried out following two synthetic routes: (1) the direct incorporation of nanoparticles into the pores of the templated carbons and (2) the insertion of nanoparticles into the mesopores of the carbon-silica composite followed by the selective removal of silica framework. The carbon-iron oxide magnetic composites prepared according to route 2 were found to have better textural properties (larger BET surface areas and pore volumes) and significantly higher capacity for the adsorption of hemoglobin and immobilization of lysozyme. The amounts of hemoglobin or lysozyme adsorbed/immobilized by these materials were 176 mg hemoglobin g⁻¹ support and 131 mg lysozyme g⁻¹ support using route 1 and 430 mg hemoglobin g⁻¹ support and 322 mg lysozyme g⁻¹ support by route 2. Furthermore, we have demonstrated that, when no inorganic nanoparticles are deposited, the bimodal mesoporous carbon shows exceptionally a large immobilization capacity for hemoglobin (830 mg g⁻¹ support) and lysozyme (510 mg g⁻¹).     

A combined salt–hard templating approach for synthesis of multi-modal porous carbons used for probing the simultaneous effects of porosity and electrode engineering on EDLC performance

A new approach, based on a combination of salt and hard templating for producing multi-modal porous carbons is demonstrated. The hard template, silica nanoparticles, generate mesopores (∼22 nm), and in some cases borderline-macropores (∼64 nm), resulting in high pore volume (∼3.9 cm³/g) while the salt template, zinc chloride, generates borderline-mesopores (∼2 nm), thus imparting high surface area (∼2100 m²/g). The versatility of the proposed synthesis technique is demonstrated using: (i) dual salt templates with hard template resulting in magnetic, nanostructured-clay embedded (∼27% clay content), high surface area (∼1527 m²/g) bimodal carbons (∼2 and 70 nm pores), (ii) multiple hard templates with salt template resulting in tri-modal carbons (∼2, 12 and 28 nm pores), (iii) low temperature (450 °C) synthesis of bimodal carbons afforded by the presence of hygroscopic salt template, (iv) easy coupling with physical activation approaches. A selected set of thus synthesized carbons were used to evaluate, for the first time, the simultaneous effects of carbon porosity and pressure applied during electrode fabrication on EDLC performance. Electrode pressing was found to be more favorable for carbons containing hard-templated mesopores (∼87% capacitance retention at current density of 40 A/g) as compared to those without (∼54% capacitance retention).