scholarly journals Electrochemical Behavior of Carbon Aerogels Derived From Different Precursors

1995 ◽  
Vol 393 ◽  
Author(s):  
R.W. Pekala ◽  
C.T. Alviso ◽  
J.K. Nielsen ◽  
T.D. Tran ◽  
G.A.M. Reynolds ◽  
...  
Keyword(s):  
Cell Structure ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Supercritical Drying ◽  
Inert Atmosphere ◽  
Solid Matrix ◽  
Carbon Aerogels ◽  
Energy Storage Devices ◽  
Electrochemical Double Layer

ABSTRACTThe ability to tailor the structure and properties of porous carbons has led to their increased use as electrodes in energy storage devices. Our research focuses on the synthesis and characterization of carbon aerogels for use in electrochemical double layer capacitors. Carbon aerogels are formed from the sol-gel polymerization of (1) resorcinol-formaldehyde or (2) phenolic-furfural, followed by supercritical drying from carbon dioxide, and subsequent pyrolysis in an inert atmosphere. These materials can be produced as monoliths, composites, thin films, powders, or microspheres. In all cases, the aerogels have an open-cell structure with an ultrafine pore size (<100 nm), high surface area (400-1100 m2/g), and a solid matrix composed of interconnected particles, fibers, or platelets with characteristic dimensions of 10 nm. This paper examines the effects of the carbon precursor and processing conditions on electrochemical performance in aqueous and organic electrolytes.

Carbon Aerogels and Xerogels

1992 ◽  
Vol 270 ◽  
Author(s):  
Richard W. Pekala ◽  
Cynthia T. Alviso
Keyword(s):  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Particle Morphology ◽  
Inert Atmosphere ◽  
Vitreous Carbon ◽  
Carbon Aerogels ◽  
Structure Property ◽  
Microporous Material ◽  
Sol Gel Transition

ABSTRACTThe aqueous polycondensation of resorcinol with formaldehyde proceeds through a sol-gel transition and results in the formation of highly crosslinked, transparent gels. If the solvent is simply evaporated from the pores of these gels, large capillary forces are exerted and a collapsed structure known as a xerogel is formed. In order to preserve the gel skeleton and minimize shrinkage, the aforementioned solvent or its substitute must be removed under supercritical conditions. The microporous material that results from this operation is known as an aerogel. Because resorcinol-formaldehyde aerogels and xerogels consist of a highly crosslinked aromatic polymer, they can be pyrolyzed in an inert atmosphere to form vitreous carbon monoliths. The resultant porous materials are black in color and no longer transparent, yet they retain the ultrafine cell size (< 50 nm), high surface area (600-800 m2 /g), and the interconnected particle morphology of their organic precursors. The thermal, acoustic, mechanical, and electrical properties of carbon aerogels/xerogels primarily depend upon polymerization conditions and pyrolysis temperature. In this paper, the chemistry-structure-property relationships of these unique materials will be discussed in detail.

scholarly journals Resorcinol-Formaldehyde and Carbon Aerogel Microspheres

1996 ◽  
Vol 431 ◽  
Author(s):  
C. T. Alviso ◽  
R. W. Pekala ◽  
J. Gross ◽  
X. Lu ◽  
R. Caps ◽  
...  
Keyword(s):  
Cell Structure ◽  
High Surface ◽  
High Surface Area ◽  
Thermal Characterization ◽  
Supercritical Drying ◽  
Carbon Aerogel ◽  
Solid Matrix ◽  
Attractive Alternative ◽  
Resorcinol Formaldehyde ◽  
Potential Applications

AbstractAerogels are a unique class of materials possessing an open-cell structure with ultrafine cells/pores (<100nm), high surface area (400–1100 m2/g), and a solid matrix composed of interconnected particles, fibers, or platelets with characteristic dimensions of 10nm. Although monolithic aerogels are ideal candidates for many applications (e.g. transparent window insulation), current processing methods have limited their introduction into the commercial marketplace. Our research focuses on the formation of resorcinol-formaldehyde (RF) aerogel microspheres which offer an attractive alternative to monolith production. An inverse emulsion polymerization is used to produce these spherical gel particles which undergo solvent exchange followed by supercritical drying with carbon dioxide. This process yields aerogel microspheres (10–80μ diameter) which can be used as loosely packed powders, compression molded into nearnet shapes using a polymer binder, or used as additives in conventional foaming operations to produce new aerogel composites with superior thermal properties. The emulsification procedure, thermal characterization, mechanical properties, and potential applications of RF aerogel microspheres will be discussed.

Gas permeability of carbon aerogels

1993 ◽  
Vol 8 (12) ◽  
pp. 3100-3105 ◽  
Author(s):  
F-M. Kong ◽  
J.D. LeMay ◽  
S.S. Hulsey ◽  
C.T. Alviso ◽  
R.W. Pekala
Keyword(s):  
Pore Size ◽  
Gas Flow ◽  
Gas Permeability ◽  
High Surface ◽  
High Surface Area ◽  
Supercritical Drying ◽  
Flow Equation ◽  
Carbon Aerogels ◽  
Thin Specimen ◽  
Potential Applications

Carbon aerogels are synthesized via the aqueous polycondensation of resorcinol with formaldehyde, followed by supercritical drying and subsequent pyrolysis at 1050 °C. As a result of their interconnected porosity, ultrafine cell/pore size, and high surface area, carbon aerogels have many potential applications such as supercapacitors, battery electrodes, catalyst supports, and gas filters. The performance of carbon aerogels in the latter two applications depends on the permeability or gas flow conductance in these materials. By measuring the pressure differential across a thin specimen and the nitrogen gas flow rate in the viscous regime, the permeability of carbon aerogels was calculated from equations based upon Darcy's law. Our measurements show that carbon aerogels have permeabilities on the order of 10−12 to 10−10 cm2 over the density range from 0.05–0.44 g/cm3. Like many other aerogel properties, the permeability of carbon aerogels follows a power law relationship with density, reflecting differences in the average mesopore size. Comparing the results from this study with the permeability of silica aerogels reported by other workers, we found that the permeability of aerogels is governed by a simple universal flow equation. This paper discusses the relationship among permeability, pore size, and density in carbon aerogels.

Performance Study and Structure Control of Carbon Aerogel

2013 ◽  
Vol 706-708 ◽  
pp. 897-900 ◽  
Author(s):  
Rui He ◽  
Xuan Liu ◽  
Zhen Fa Liu ◽  
Li Hui Zhang
Keyword(s):  
High Surface ◽  
Sol Gel ◽  
Supercritical Drying ◽  
Carbon Aerogel ◽  
Preparation Condition ◽  
Carbon Aerogels ◽  
Performance Study ◽  
Structure Control ◽  
Sol Gel Process ◽  
Nanopore Structure

In this research the fabrication of carbon aerogel is reported. nanopore carbon aerogels were prepared via a sol-gel process with resorcinol and formaldehyde (RF) aerogels,which were cost-effectively manufacture form Rf wet gels by an ambient drying technique instead of conventional supercritical drying. The key of the work is to fabricate carbon aerogels with controllable nanopore structure, which means sharp pore size distribution and extremely high surface area.The influence of preparation condition of carbon aerogels was studied by scanning electron microscope and Micropore Physisorption Analyzer. The BET surface of the carbon aerogels are from 749m2/g to 1156m2/g .The size of the carbon nanoparticles are in the range of 20nm~40nm. The micro-pore volume and bore diameter can be controlled by gelation conditions such as RF mass fraction.

Determination of the Permeability of Carbon Aerogels by Gas Flow Measurements

1992 ◽  
Vol 270 ◽  
Author(s):  
F-M. Kong ◽  
S.S. Hulsey ◽  
C.T. Alviso ◽  
R.W. Pekala
Keyword(s):  
Pore Size ◽  
Gas Flow ◽  
Cell Structure ◽  
Average Pore Size ◽  
High Surface ◽  
High Surface Area ◽  
Carbon Aerogels ◽  
Average Pore ◽  
Thin Specimen ◽  
Flow Measurements

ABSTRACTCarbon aerogels are synthesized via the polycondensation of resorcinol and formaldehyde, followed by supercritical drying and pyrolysis at 1050 °C in nitrogen. Because of their interconnected porosity, ultrafine cell structure and high surface area, carbon aerogels have many potential applications, such as in supercapacitors, battery electrodes, catalyst supports, and gas filters. The performance of carbon aerogels in the latter two applications depends on the permeability or gas flow conductance in these materials. By measuring the pressure differential across a thin specimen and the nitrogen gas flow rate in the viscous regime, we calculated the permeability of carbon aerogels from equations based upon Darcy's law. Our measurements show that carbon aerogels have apparent permeabilities on the order of 10−12 to 10−10 cm2 for densities ranging from 0.44 to 0.05 g/cm3. Like their mechanical properties, the permeability of carbon aerogels follows a power law relationship with density and average pore size. Such findings help us to estimate the average pore sizes of carbon aerogels once their densities are known. This paper reveals the relationships among permeability, pore size and density in carbon aerogels.

scholarly journals Carbon aerogels with improved flexibility by sphere templating

RSC Advances ◽  
2018 ◽  
Vol 8 (48) ◽  
pp. 27326-27331 ◽  
Author(s):  
Miralem Salihovic ◽  
Nicola Hüsing ◽  
Johannes Bernardi ◽  
Volker Presser ◽  
Michael S. Elsaesser
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Inert Atmosphere ◽  
Carbon Aerogels ◽  
Resorcinol Formaldehyde ◽  
Soft Templating

Using soft templating, mechanically reversible compressible resorcinol–formaldehyde aerogels can be converted into mechanically reversible compressible carbon aerogels with high surface area by carbonization in an inert atmosphere.

scholarly journals A Comparison of the Electrochemical Behavior of Carbon Aerogels and Activated Carbon Fiber Cloths

1996 ◽  
Vol 431 ◽  
Author(s):  
T. D. Tran ◽  
C. T. Alviso ◽  
S. S. Hulsey ◽  
J. K. Nielsen ◽  
R. W. Pekala
Keyword(s):  
Activated Carbon ◽  
Carbon Fiber ◽  
Electrochemical Behavior ◽  
High Surface ◽  
High Surface Area ◽  
Activated Carbon Fiber ◽  
Solid Matrix ◽  
Carbon Aerogels ◽  
Surface Areas ◽  
Cell Structures

AbstractThe electrochemical capacitative behavior of carbon aerogels and selected commercial carbon fiber cloths was studied in 5M potassium hydroxide, 3M sulfuric acid, and 0.5M tetraethylammonium tetrafluoroborate/propylene carbonate electrolytes. The resorcinolformaldehyde based carbon aerogels with a range of density (0.2–0.85 g/cc) have open-cell structures with ultrafine pore sizes (∼5–50 nm), high surface area (400–700 m2/g), and a solid matrix composed of interconnected particles or fibers with characteristic diameters of 10 nm. The commercial fiber cloths in the density range 0.2–0.4g/cc have high surface areas (1000–2500 m2/g). The volumetric capacitances of high-density aerogels are shown to be comparable to or exceeding those obtained from activated carbon fibers. The electrochemical behavior of these types of materials in various electrolytes is compared and related to their physical properties.

scholarly journals Structural Evolution in Carbon Aerogels as a function of Precursor Material and Pyrolysis Temperature

1996 ◽  
Vol 431 ◽  
Author(s):  
J. Gross ◽  
C. T. Alviso ◽  
R. W. Pekala
Keyword(s):  
Pyrolysis Temperature ◽  
Phenol Formaldehyde ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Structural Evolution ◽  
Vitreous Carbon ◽  
Carbon Aerogels ◽  
High Porosity ◽  
Precursor Material

AbstractSeveral organic reactions that proceed through a sol-gel transition have been identified at LLNL. The most-studied reaction involves the aqueous polycondensation of resorcinol (1,3- dihydroxybenzene) with formaldehyde. Recently, we have shown that phenol can be added to this polymerization as a comonomer. The resultant crosslinked gels are supercritically dried from carbon dioxide (Tc=31°C, Pc = 7.4 MPa) to give resorcinol-phenol-formaldehyde (RPF) aerogels. Because RPF aerogels are composed of a highly crosslinked aromatic polymer, they can be pyrolyzed in an inert atmosphere to form vitreous carbon monoliths (CRPF). The resultant aerogels are black in color and no longer transparent, yet they retain the high porosity (40–98 %), ultrafine cell/pore size (< 50 nm), high surface area (600–800 m2/g), and interconnected particle (˜10 nm) morphology of their organic precursors. In this study, we examine the acoustic and mechanical properties of these materials as a function of precursor material and pyrolysis temperature. It is shown that the elastic moduli of RPF and CRPF is higher than that of pure RF / CRF aerogels at a given density. Upon pyrolysis RPF aerogels tend to shrink to a larger extent.

scholarly journals Silica Aerogel: Synthesis and Applications

2010 ◽  
Vol 2010 ◽  
pp. 1-11 ◽  
Author(s):  
Jyoti L. Gurav ◽  
In-Keun Jung ◽  
Hyung-Ho Park ◽  
Eul Son Kang ◽  
Digambar Y. Nadargi
Keyword(s):  
Industrial Development ◽  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Porous Silica ◽  
Supercritical Drying ◽  
Silica Aerogels ◽  
Silica Network ◽  
Molecular Precursors ◽  
Drying Techniques

Silica aerogels have drawn a lot of interest both in science and technology because of their low bulk density (up to 95% of their volume is air), hydrophobicity, low thermal conductivity, high surface area, and optical transparency. Aerogels are synthesized from molecular precursors by sol-gel processing. Special drying techniques must be applied to replace the pore liquid with air while maintaining the solid network. Supercritical drying is most common; however, recently developed methods allow removal of the liquid at atmospheric pressure after chemical modification of the inner surface of the gels, leaving only a porous silica network filled with air. Therefore, by considering the surprising properties of aerogels, the present review addresses synthesis of silica aerogels by the sol-gel method, as well as drying techniques and applications in current industrial development and scientific research.

Inorganic and Organic Aerogels

MRS Bulletin ◽  
1990 ◽  
Vol 15 (12) ◽  
pp. 30-36
Keyword(s):  
High Surface ◽  
Sol Gel ◽  
High Surface Area ◽  
Visible Spectrum ◽  
Supercritical Drying ◽  
Porous Solids ◽  
Metal Alkoxides ◽  
Open Cell Foams ◽  
Sol Gel Transition ◽  
Organic Aerogels

Aerogels are a special class of open-cell foams derived from the supercritical drying of highly cross-linked inorganic or organic gels. These materials have ultrafine cell/pore sizes (less than 1,000 Å), continuous porosity, high surface area (400–1000 m2/g), and a microstructure composed of interconnected colloidal-like particles or polymeric chains with characteristic diameters of 100 Å. This microstructure is responsible for the unusual optical, acoustic, thermal, and mechanical properties of aerogels. For example, aerogels can be prepared as transparent, porous solids because their ultrafine cell/pore size minimizes light scattering in the visible spectrum. Figure 4.1 shows the different aerogels that will be discussed in this article.The hydrolysis and condensation of metal alkoxides is the most common synthetic route for the formation of inorganic aerogels. Inorganic aerogels have been prepared from monomers such as tetraisopropoxy titanate, aluminum secbutylate, and zirconium isopropoxide. Nevertheless, the majority of scientific research has concentrated on the sol-gel polymerization of tetramethoxysilane (TMOS), or the less toxic tetraethoxysilane (TEOS). The resultant silica aerogels are being investigated for applications ranging from window insulation to the collection of hypervelocity partis cles in space.The sol-gel polymerization of a multifunctional monomer in solution, leading to the formation of an aerogel, is not unique to metal alkoxides. Organic reactions that proceed through a sol-gel transition have been discovered recently.

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