Mesoporous carbons and polymers

A mesoporous material prepared by polymerizing a resorcinol/formaldehyde system from an aqueous solution containing resorcinol, formaldehyde and a surfactant and optionally pyrolyzing the polymer to form a primarily carbonaceous solid. The material has an average pore size between 4 and 75 nm and is suitable for use in liquid-phase surface limited applications, including sorbent, catalytic, and electrical applications.

CROSS-REFERENCE TO RELATED APPLICATIONS
 Not applicable.
 TECHNICAL FIELD OF THE INVENTION
 The present invention relates generally to mesoporous organic polymers and
 more particularly to mesoporous carbon structures that are particularly
 useful as catalyst supports, sorbents, and electrodes.
 BACKGROUND OF THE INVENTION
 Mesoporous Materials
 Materials whose structures allow fluids to flow through the materials are
 porous. Porous materials can be characterized by their pore sizes. Very
 small pores having diameters &lt;2 nm are called micropores, while very
 large pores (&gt;50 nm) are called macropores. Most high surface area
 carbons, such as activated carbons, are primarily microporous, and have
 pores that are too small to be readily accessible to liquids. Pores of
 intermediate size (between 2 and 50 nm) are called mesopores and form the
 subject of the present invention. One aspect of mesopores is that they
 have pores that are large enough to readily allow liquids to enter the
 material. At the same time, large pores do not provide as much surface
 area in a given volume of material as do smaller pores. Thus, mesoporous
 materials provide liquid access to more surface area per unit volume of
 material than either microporous or macroporous materials. As used herein
 the term "mesopore" will be used to refer to pores in the desired size
 range, namely to pores having diameters between approximately 2 and 50 nm.
 Uses for Mesoporous Materials
 Because of their large liquid-accessible surface areas, mesoporous
 materials are useful in many liquid phase applications, including as
 sorbents, electrical materials and catalyst supports. For example,
 catalytic reactions are typically surface reactions, i.e. the surface of
 the catalyst serves as an active site for the combination or separation of
 reactive species. The larger the surface area of catalyst, the more active
 sites there will be and the more rapidly the catalyzed reaction will
 proceed. Catalytic reactions can occur in the gas or liquid phase; in
 either case, it is desirable to maximize the amount of catalyst surface
 area. One common way to do this is to provide the catalyst as a thin
 coating on the surface of a support material. The support material
 provides the structure for the catalyst and thus determines its shape and
 the amount of surface area per unit volume. Hence, the porosity and
 surface area of the support become rate-limiting factors. Mesoporous
 materials provide optimal support structures for certain catalytic
 systems.
 Similarly, pore size is an important aspect of sorbent technology. Sorption
 typically involves a solid phase (the sorbent) and a liquid or gas phase.
 The liquid phase can comprise a solvent containing a dissolved species to
 be sorbed, or an emulsion or other mixture of two liquids, one of which is
 to be sorbed. Examples of common sorbent applications currently include
 polymers and carbons in powdered, granular, and pelletized form for
 environmental applications associated with energy production, by-product
 recoveries, and waste incineration, as well as water purification and
 wastewater cleanup. An example of a sorbent application that involves a
 gas phase is air purification. A variety of other uses are known or are
 being developed. For each desired application, the sorbent is selected
 such that the sorbent has an affinity for the sorbate species, so that it
 is attracted into the solid and held there by one of various surface
 mechanisms. The efficacy of a sorbent material depends on how much sorbate
 it can attract and retain. Hence, the pore size and available surface area
 are critical in this context as well.
 Similarly, certain electrical applications involve liquid phase,
 surface-limited reactions. One example of such an application is an
 ultracapacitor. Like batteries, ultracapacitors are energy storage
 devices. Ultracapacitors are notable for their ability to store and
 deliver energy at high power densities, and to be cycled virtually
 indefinitely without degradation. In contrast, batteries store large
 amounts of energy, but function most efficiently at low power densities
 and degrade quickly if they are deeply cycled. The characteristics of
 ultracapacitors make them particularly suitable to meet the power
 requirements of various emerging technologies, including electric
 vehicles, electronics (cellular telephones, and digital communications)
 and clean power (uninterrupted power sources, filters, etc.).
 An ultracapacitor typically comprises a pair of electrodes separated by a
 non-conductive porous separator. The space between the electrodes is
 filled with a liquid electrolyte, which can be aqueous or organic-based.
 Because there are no chemical reactions taking place during the
 charge/discharge cycle, capacitors can be cycled many times without
 degradation, unlike batteries. However, previously known ultracapacitors
 lacked sufficient energy storage capacity to make them commercially
 practical. One key to improving the energy storage capacity of
 ultracapacitors is to optimize the interaction between the electrodes and
 the electrolyte.
 There are two major categories of electrolytes for double layer devices:
 aqueous and organic, each of which has advantages and disadvantages.
 Aqueous electrolytes such as potassium hydroxide and sulfuric acid have
 low resistance (0.2 to 0.5 ohms/cm.sup.2) and can be charged and
 discharged very quickly. However, they can only be cycled through a
 potential range of one volt due to the voltage limits of aqueous
 electrolytes; this sharply limits their energy storage density (which is
 proportional to voltage squared). Organic electrolytes such as propylene
 carbonate have much higher breakdown voltages (up to three volts) and
 therefore have much greater energy storage densities (in theory, by a
 factor of nine). However, because they have much higher resistance (1-2
 ohms/cm.sup.2), they cannot be cycled as quickly. The type of electrolyte
 that is desirable depends on the nature of the application.
 The mechanism for energy storage devices of this type is based on the
 double-layer capacitance at a solid/solution interface. More specifically,
 double-layer ultracapacitors typically consist of high surface area carbon
 structures that store energy in a polarized liquid layer. The polarized
 liquid layer forms at the interface between an ionically conducting liquid
 electrolyte and an electronically conducting electrode, namely the carbon
 structure. As illustrated in FIG. 1, the separation of charge in the ionic
 species at the interface (called a double layer) produces a standing
 electric field. Thus, the capacitive layer, while only a few angstroms
 thick, has a very is large area. The larger the area of the interface is,
 the more energy can be stored. Hence, the capacitance of this type of
 capacitor is proportional to the surface area of the electrode.
 At the same time, electrodes having pores smaller than about 2 nm do not
 exhibit increased capacitance. It is believed that pores smaller than
 about 2 nm are too small to allow entry of most nonaqueous electrolytes
 and therefore cannot be fully wetted, with the result that a portion of
 the potential interface area is not realized. Hence, it is believed that
 mesoporous materials are optimal for use in this type of capacitor.
 While some carbon structures having pore sizes in the mesoporous range have
 been extensively investigated for use in ultracapacitors because of their
 low cost and potential for high-energy storage densities, none of them
 have proved entirely satisfactory. Since the capacitance of the material
 increases linearly with the specific surface area, a carbon material with
 a capacitance of 20 .mu.F/cm.sup.2 and a surface area of 1000 M.sup.2 /g
 would have a capacitance of 200 F/g if all of the surface were
 electrochemically accessible. However, since high surface area porous
 carbons typically have a high fraction of micropores, only a fraction of
 the surface of the carbon is effectively utilized (wetted); most of the
 surface therefore does not contribute to the double-layer capacitance of
 the electrode and the measured capacitance values of prior carbon
 structures are therefore only about 20% of theoretical. For carbon-based
 ultracapacitors to approach their theoretical performance, they should
 have a high pore volume (&gt;50%) and a high fraction of continuous pores
 with diameters of greater than 2 nm to allow the electrolyte access to the
 carbon surface.
 In sum, the major drawbacks of the carbons now used in double-layer
 ultracapacitors are: low capacitance (due to pores that are too large or
 too small), low density (which increases the size of the ultracapacitor),
 and high costs (due to materials and processing costs).
 In addition, the electrical conductivity low conductivity (due to
 resistance at particle/particle interfaces) of the electrode itself
 affects the efficiency of the capacitor. Thus, for ultracapacitor
 electrodes, monolithic carbon is more desirable than particulate carbons
 or compacts of particulate carbon, which have high surface areas, but
 which suffer from high internal resistance because of the
 particle-particle interfaces.
 Another example where a monolithic polymer is advantageous is in high
 performance liquid chromatography (HPLC), a commonly used technique for
 separating and quantifying the constituents of a mixture. HPLC is often
 used to separate chemicals and biological molecules that have very similar
 properties and are difficult if not impossible to separate by other
 conventional means. The major disadvantage of HPLC is, because the columns
 are packed with small porous beads, the high flow rates required to
 maximize the throughput in preparatory scale separations result in
 channeling of the solution around the particles, thereby degrading the
 separation. Since separation is a major cost of chemical processing, the
 development of high capacity monolithic columns could greatly reduce the
 cost of manufacturing pharmaceuticals and their precursors. The mesoporous
 polymers described herein may be prepared by polymerization within a
 suitable structure (e.g., a glass or metal tube) to form a stationary
 phase for chromatography.
 Manufacture of Mesoporous Materials
 In order to introduce larger pores into polymers and carbon, and thus
 increase its porosity, several groups have tried to form polymeric gels
 around liquid emulsions. This usually results in a mixture of pore sizes,
 and both the polymers and the carbons formed therefrom are mostly
 macroporous (&gt;50 nm) rather than mesoporous (LeMay et al. 1990, Even
 and Gregory 1994). In an alternative approach, pyrolysis of aerogels
 prepared by supercritical fluid extraction of RF gels produces carbons
 with a mixture of meso- and micropores (Pekala et al. 1994), but because
 of the need for supercritical extraction, aerogels are very expensive to
 make. Hence, an effective method for producing a mesoporous carbon that
 does not involve supercritical extraction is particularly desirable.
 On another front, since the invention of a new family of mesoporous silica
 materials, designated M41S, by scientists at Mobil Oil Corporation (Kresge
 et al. 1992, Beck et al. 1992), there have been numerous publications
 describing the use of surfactants to produce mesoporous metal oxides (Beck
 et al. 1994, Huo et al. 1994). This has dramatically expanded the range of
 pore sizes in metal oxides from the micropore to the mesopore regime.
 These mesoporous metal oxides are produced by gelation of metal alkoxides
 around a template made from micelles or liquid crystals formed by
 surfactants. Once the structure has formed, the surfactant is removed by
 high temperature oxidation, leaving a mesopore. The pore sizes can be
 adjusted by changing the length and the structure of the surfactants used.
 Cationic, anionic, and nonionic surfactants have been used to make a
 variety of mesoporous metal oxides (Luca et al. 1995).
 Hence, it is desired to provide an improved mesoporous polymer and carbon
 structure. The desired polymer structure should be simple and inexpensive
 to manufacture and should have a high pore volume and a high fraction of
 mesopores. When intended for use as electrodes for ultracapacitors, the
 desired carbon structure should have high volumetric capacitance, high
 density, and high conductivity.
 BRIEF SUMMARY OF THE INVENTION
 The present invention comprises mesoporous materials that are suitable for
 use as catalyst supports, sorbents, and materials for separations. In
 electrical applications, the present carbons can be used as electrodes in
 double-layer capacitors. The present invention further comprises a method
 for making the novel mesoporous materials.
 The present invention comprises polymer structures that have high
 mesoporosity, high density, and are simple and inexpensive to manufacture.
 The present invention also includes carbon structures having a relatively
 narrow pore size distribution in which the pores are large enough for the
 electrolyte solution to easily enter. Hence, the present carbon structures
 have high volumetric capacitance and high conductivity, and provide more
 wetted carbon surface in which a fully charged double layer can develop.
 The present monolithic carbons also offer increased density and
 conductivity as compared to compacts formed by pressing together a mass of
 carbon particles.
 According to one preferred embodiment, a mesoporous polymer is formed by
 polymerizing resorcinol-formaldehyde (RF) and/or
 resorcinol-phenol-formaldehyde (RPF) in the presence of a cationic
 surfactant. It has been discovered the desired structures can be formed
 using a method of emulsion polymerization in which a phenol-formaldehyde
 polymer is formed around surfactant micelles. The size of the micelles
 controls the pore size of the material. It has been found that by
 adjusting the initial formulation, polymers and carbons having a narrow
 distribution of pore sizes can be prepared. More specifically, it is
 possible to produce pores with diameters ranging from 4 nm to micron size.
 The polymer formed in this manner is pyrolyzed to give a porous carbon
 structure, which is then activated to increase the fraction of mesopores
 therein. The present method yields a mesoporous carbon that has many
 desired properties.

DETAILED DESCRIPTION OF THE INVENTION
 To address the shortcomings of the prior art, we have developed low-cost
 monolithic mesoporous polymers and carbons and a method for making same.
 The polymers are particularly useful as sorbents for liquid phase
 separations. While the present carbons can be used advantageously in a
 variety of applications, including in particular liquid phase,
 surface-limited reactions, they are particularly suited for use as thin
 film electrodes for use in ultracapacitors. These materials are made from
 inexpensive materials, and do not require expensive and time-consuming
 manufacturing processes.
 Material Composition
 According to a preferred embodiment, the present invention comprises
 polymerizing a suitable organic compound that is initially present as a
 microemulsion containing micelles of a surfactant. The resulting
 monolithic solid polymer is a porous solid with pores having a desirable
 size distribution range. Pyrolysis of said polymer produces a monolithic
 solid consisting primarily of elemental carbon, also having a desired pore
 size distribution and other desirable electrical properties.
 The polymer preferably has pore sizes between 2-1000 nm, a density of 0.1
 to 1.0 g/cc, and a surface area between 50-500 m.sup.2 /g. For purposes of
 experimentation, the well-known resorcinol/formaldehyde (RF) composition
 was used and is discussed below. One skilled in the art will understand
 that references herein to an RF system are exemplary only, and that the
 present invention can be practiced with a range of polymer systems,
 including but not limited to: hydroquinone/resorcinol/formaldehyde,
 phloroglucinol/resorcinol/formaldehyde, catechol/ resorcinol/formaldehyde,
 polyvinyl chloride, phenol/formaldehyde, epoxidized phenol/ formaldehyde,
 polyvinyl chloride, phenol/benzaldehyde, oxidized polystyrene,
 polyfurfuryl alcohol, polyvinyl alcohol, polyacrylonitrile, polyvinylidene
 chloride, cellulose, polybutylene, cellulose acetate,
 melamine/formaldehyde, polyvinyl acetate, ethyl cellulose, epoxy resins,
 acrylonitrile/styrene, polystyrene, polyamide, polyisobutylene,
 polyethylene, polymethyl-methacrylate, and divinylbenzene/styrene.
 The surfactant is preferably any surfactant that is capable of stabilizing
 the electrostatic interactions between the monomer and surfactant. The
 surfactant may be cationic, anionic or nonionic depending on the polymer
 system in question. The best surfactant is related to the solvent,
 catalyst (if any) and monomers that are used. Examples of suitable
 surfactants include cetyltrimethylammonium chloride and
 cetyltrimethylammonium bromide (cationic), sodium dodecylbenzenesulfonic
 acid and sodium bis-2-ethylhexylsulfosuccinate (anionic), and Brij 30
 (nonionic, poly-(ethyleneoxy) polar group).
 Depending on the polymer, the preferred solution may also include an amount
 of a catalyst sufficient to catalyze the reaction within a desired period
 of time at the desired reaction temperature. Suitable catalysts include
 Na.sub.2 CO.sub.3 for RF and AIBN (2,2'-azobisisobutyronitrile) for
 divinylbenzene/styrene.
 Experimental Procedure
 To test the possibilities of using surfactants to introduce mesopores into
 monolithic carbon materials, RF gels were initially prepared in the
 presence of various surfactants. In this polymerization, resorcinol serves
 as a tri-functional monomer capable of adding formaldehyde in the 2, 4,
 and 6 positions of the ring. This monomer is particularly reactive because
 of the electron-donating effects of the attached hydroxyl groups. The
 substituted resorcinol rings condense with each other to form 30-200
 angstrom clusters in solution. The size of the clusters is regulated by
 the catalyst concentration (Na.sub.2 CO.sub.3) in the RF solution. The
 resulting structure is shown in FIG. 2.
 The surfactants used for these experiments were cetyltrimethylammonium
 chloride (CTAC, cationic), the sodium salt of dodecylbenzenesulfonic acid
 (anionic), and Brij 30 (nonionic, poly-(ethyleneoxy) polar group). Only
 the cationic surfactant was effective with the preferred system.
 The mole ratio of monomer, surfactant, and water was 10:1:560 as described
 for the preparation of metal oxides with nonionic surfactants (Bagshaw et
 al. 1995). The test procedure was to add to a tube with Teflon stoppers:
 water (8 mL), sodium carbonate (5 mg), surfactant (0.91 mmol), resorcinol
 (1.0 g, 9.1 mmol), and 37% formaldehyde in water (18.2 mmol). The tubes
 were stoppered and held at 90.degree. C. for 3 days. The gels were dried
 in air at ambient temperature for 1 day, followed by 3 hours at
 100.degree. C.
 After heating for 3 days, the CTAC gel was orange and opaque. Drying the
 gel did not shrink it noticeably. The dried gel was heated at 800.degree.
 C. under a nitrogen atmosphere for 2 hours to carbonize the polymer and
 decompose the surfactant. The material shrank by approximately 40% but did
 not powder. The density of the product was 0.19 g/mL and the BET surface
 area was 467 m.sup.2 /g. The carbon material was analyzed by Hg
 porosimetry (Micromeritics, Norcross, Ga.). The median pore size was 2
 .mu.m and the porosity 86.5%. Although this material was largely
 macroporous (pore diameter &gt;50 nm) the result nevertheless shows a
 potential for making porous carbons by this method. A control sample with
 no surfactant experienced considerable shrinkage during drying and
 carbonization for a density of 0.98 g/mL. The control sample also had a
 high surface area (500 m.sup.2 /g) but contained only micropores.
 Following the success of the screening experiments using a surfactant to
 control pore sizes, various types of surfactant were contemplated. For
 example a nonionic surfactant (Brij 56) that has better solubility in
 water was tried and found to be no more effective than Brij 30. Since CTAC
 is commercially available only as an aqueous solution (25 wt.%), while
 CTAB (cetyltrimethylammonium bromide) is available as a pure solid, CTAB
 (cetyltrimethyl-ammonium bromide) was substituted for CTAC in some of the
 formulations in order to decrease the amount of water in the total
 formulation. Compounds formulated according to the preferred embodiment
 are therefore referred to herein as RF/CTA, where CTA is either CTAB or
 CTAC.
 In the examples discussed below, the parameters varied were the ratio of
 surfactant, solvent, and catalyst to resorcinol. It has been shown that
 the ratio of monomer to catalyst significantly affects the density,
 surface area and mechanical properties of RF aerogels; therefore we
 examined monomer to catalyst (Na.sub.2 CO.sub.3) ratios of 0.02 to 0.005
 (Pekala et al. 1992). In our experiments, we found that in the presence of
 CTA, the higher catalyst concentration resulted in the formation of a
 precipitate; for this reason we maintained a catalyst/monomer molar ratio
 of 0.005 (5:1000). A preferred catalyst/monomer ratio is in the range of
 from about 0.001 to about 0.007. Elemental analysis of a sample carbonized
 at 500.degree. C. was C=83.36%, H=3.61% and N=0.23% showing that most of
 the nitrogen was gone but a considerable amount of hydrogen remained. When
 the sample was carbonized at 900.degree. C., the elemental analysis was
 C=95.44%, H=0.73%, and N=0.40% showing that the sample consisted mainly of
 carbon.
 The specific surface area and the pore size distribution were analyzed by
 nitrogen adsorption on a Micromeritics Gemini instrument and by mercury
 porosimetry on a Micromeritics Autopore II 9220. FIG. 3 shows a
 representative isotherm using nitrogen as an adsorbate showing a type 4
 isotherm that is characteristic for mesoporous solids (Gregg and Sing
 1982). FIG. 4 shows typical pore size distribution data for our mesoporous
 carbons as calculated by the BJH method (Barrett ct al. 1951).
 Examples
 In the sample that follows we prepared resorcinol/formaldehyde polymer in
 an aqueous solution. Mixing the desired ingredients together in the
 presence of water formed the aqueous polymer solution. The polymer
 solution was then added to a glass mold that could be sealed to prevent
 evaporation. The solution was gelled by heating at 70 .degree. C. for 24
 hours. The gelled polymer was removed from the mold and dried to remove
 the water. At this point the polymer can either be used as is, or the
 surfactant can be removed by washing with methanol, depending on the
 application. Because the present carbons are intended for use in
 ultracapacitors, the sample preparation method included an additional step
 in which the polymer was heated under an inert atmosphere (nitrogen or
 argon) to 1000.degree. C. for 2 h at a ramp rate of 1.degree. C./minute.
 This step carbonized the polymer and decomposed the surfactant as desired.
 The samples produced in this manner were measured using conventional
 mercury porosimetry and nitrogen desorption techniques. Table 1 gives the
 measured values for the median pore diameter (MPD), total pore area (TPA),
 desorption pore diameter (DPD), desorption pore area (DPA), and BET
 surface area (BET), for twenty-five exemplary formulations.
 Example
 Using formulation #20 from Table 1 as an example, the steps followed in
 preparing each sample are as follows:
 The polymer solution is added to a glass mold that can be sealed to prevent
 evaporation.
 In sample #20, the solution has a composition in terms of moles of
 component per mole resorcinol:
 2 moles formaldehyde as a 37 wt. % aqueous solution
 0.005 moles Na.sub.2 CO.sub.3 as a 0.4 M aqueous solution
 0.06 moles CTAC as a 25 wt. % aqueous solution
 The solution is gelled by heating at 70 .degree. C. for 24 hours.
 The polymer is removed from the mold and dried to remove the water. At this
 point the polymer can either be used as is or the surfactant can be
 removed by extracting the polymer with 2% HCl in EtOH.
 To prepare the mesoporous carbons, the polymer is heated under an inert
 atmosphere (nitrogen or argon) to 1000 .degree. C. for 2 h at a ramp rate
 of 1 .degree. C. /minute. This step carbonizes the polymer and decomposes
 the surfactant.
 TABLE 1
 Formulation and properties of TDA's RF/CTA porous carbons.
 Measured Properties
 Den-
 .sup.1 Molar sity
 Sam- Ratios (g/ .sup.2 MPD .sup.3 TPA .sup.4 DPD .sup.5 DPA BET
 ple CTA .sup.7 H.sub.2 O cm.sup.3) (nm) (m.sup.2 /g) (nm) (m.sup.2
 /g) (m.sup.2 /g)
 1 0.10 56 0.19 2000 52 446
 3 0.10 19 0.51 248 49 67 446
 4 0.10 14 0.62 139 62 95 465
 8 0.02 14 0.50 25 33 24 161 540
 10 0.14 56 0.20 1612 10 25 441
 15 0.02 11 0.75 18 199 18 334 644
 16.sup.6 0.02 0 0.89 8 224 9 348 621
 17.sup.6 0.06 0 1.2 5 134 4 214 386
 19 0.02 0 0.70 9 190 9 290 570
 20 0.06 0 0.71 24 142 28 172 453
 22 0.10 0 0.53 374 32 97 501
 23 0.03 0 0.80 13 162 10 312 653
 24 0.04 0 0.80 16 143 11 301 661
 25 0.05 0 0.78 23 99 12 218 580
 Experimental Conditions:
 .sup.1 molar ratios are with respect to resorcinol (x/resorcinol), Na.sub.2
 CO.sub.3 /resorcinol = 0.005, gelled at 95.degree. C. for 1-4 days,
 carbonized at 800.degree. C. for 2 h (1.degree. C./min.) Hg porosimetry
 data:
 .sup.2 MPD = Median Pore Diameter (Volume)
 .sup.3 TPA = Total Pore Area
 Nitrogen desorption data:
 .sup.4 DPD = Desorption Pore Diameter
 .sup.5 DPA = Desorption Pore Area
 .sup.6 CTAB instead of CTAC.
 .sup.7 Indicates the amount of additional water; does not include water
 present in original reagent solutions.
 Samples using alkyl-trimethyl-ammonium surfactants were prepared in which
 the only the length of the alkyl chain of the surfactant. Table 2 shows
 how the length of the alkyl chain affects pore size of the carbon; longer
 alkyl chains result in larger pores.
 TABLE 2
 Effect of surfactant chain length on carbon pore size
 (as determined by nitrogen desorption).
 Surfactant Chain
 Length Pore
 C.sub.n H.sub.2n+1 (CH.sub.3).sub.3 N.sup.+
 Diameter
 where n = (nm)
 12 13
 14 16
 16 18
 Samples were also prepared in which the length of the alkyl chain was kept
 constant (hexadecyl) and the other substituents on the nitrogen were
 varied. Table 3 shows that different substituents on the nitrogen do
 affect the resultant pore size. The hexadecyldimethyl head group is the
 least sterically demanding because both hexadecyl substituents are
 directed into the micelle leaving only the two methyl groups; as expected
 this surfactant gives the smallest pores. From Table 3, it is observed
 that as the steric bulk of the head group is increased, the measured pore
 size of the carbon is also increased.
 TABLE 3
 Effect of head group substituents on the carbon pore size
 (as determined by nitrogen desorption)
 Head Group of
 Hexadecyl Ammonium Pore Diameter
 Surfactant (nm)
 Hexadecyldimethyl 16
 Trimethyl 18
 Benzyldimethyl 28
 Pyridinium 39
 Formulations in which a percentage of the resorcinol was replaced with
 phenol are shown in Table 4. It was found that up to 70% of the resorcinol
 content could be replaced with phenol. Beyond 70%, the solution does not
 gel properly resulting in precipitate formation. It appears that slightly
 more surfactant is needed for RPF carbons than is needed for the RF
 carbons in order to obtain the same pore size.
 TABLE 4
 Formulation and properties of RPF/CTA porous carbons.
 .sup.1 Molar Ratios Phenol Density Pore diameter BET
 Sample CTA H.sub.2 O (%) (g/cm.sup.3) (nm) (m.sup.2 /g)
 29 0.08 0 50 1.03 17 209
 30 0.10 0 50 0.57 80 362
 56 0.10 0 70 100 718
 Experimental Conditions:
 .sup.1 molar ratios are with respect to phenol content (x/resorcinol +
 phenol),
 Na.sub.2 CO.sub.3 /resorcinol + phenol = 0.005, gelled at 50.degree. C. for
 1-3 days, carbonized at 1000.degree. C. for 2 hours (1.degree. C./min.).
 We have also analyzed the structure of the polymer precursor to the carbons
 and found that the pores are approximately twice the size of those
 measured in the carbonized materials (Table 5). In the polymers, primarily
 the mesopores are present and the overall and mesoporous surface areas are
 the same. This is in contrast to the carbons, in which there are always
 some micropores produced due to gas evolution during carbonization.
 TABLE 5
 Properties of the RF/CTA polymers
 (pre-carbonization)
 Pore diameter BET
 Sample (nm) (m.sup.2 /g)
 20 38 64
 24 22 165
 For our work with divinylbenzene/styrene we did the polymerization in an
 organic solvent (toluene) rather than water, because the divinylbenzene
 (DVB) and styrene are not sufficiently soluble in water. Therefore, in
 these systems the pore formation will be around reverse micelles as shown
 in FIG. 5 (that is, the orientation of the surfactant is opposite to its
 orientation in water, with the ionic head group in the center of the
 micelle and the alkyl chains pointing out; Myers 1988). The surfactant
 that we used was sodium bis-2-ethylhexylsulfosuccinate (AOT), since this
 surfactant readily forms stable reverse micelles (Kurumada et al. 1996).
 In this system styrene and divinylbenzene (1 :1 molar ratio) in toluene
 were polymerized with a free radical initiator (AIBN), surfactant (AOT)
 and heat (Dhal and Khisti 1993). After polymerization, the polymer was
 washed with methanol to remove the surfactant and any unreacted monomer,
 and then dried. In this case we found that the polymers with and without
 AOT had a high surface area (530 and 313 m.sup.2 /g respectively) but the
 polymer without AOT had a broad range of pore sizes varying from 10 nm to
 micropores, whereas the polymer prepared with AOT had a sharp peak
 centered at 28 nm. We also prepared polymers without any added solvent
 (toluene). In this case the polymer with AOT had a surface area of 13
 m.sup.2 /g and pore size of 15 nm, while the polymer without AOT had a
 surface area of 0.8 m.sup.2 /g and no measurable pores. We did not prepare
 carbons of DVB/styrene polymers because they decompose upon heating,
 although it should be possible to form carbon if they are heated in air at
 220.degree. C. before pyrolysis.
 In another system, we prepared carbons from polyvinylidene chloride (PVDC).
 Once again we prepared the polymer in an organic solvent using AOT as the
 surfactant. The general procedure was to dissolve vinylidene chloride, the
 free radical initiator AIBN with a initiator/substrate molar ratio of
 0.0028 and various surfactant/substrate molar ratios of AOT in toluene
 (2.5 mL). The solution was purged with argon for 5 minutes and then heated
 at 55.degree. C. for 24 hours. During this step the a powdery white solid
 was formed. The polymer was then carbonized at 1000.degree. C. for 2 hours
 (ramp rate 1.degree. C./min). As expected the polymer prepared without any
 AOT (Sample 7) did not show any pores in the mesopore range. The addition
 of AOT did add mesoporosity to the carbon with a sharp peak centered at
 3.8 nm. In conclusion, our approach of adding a surfactant to PVDC
 formulations to add mesoporosity to the resulting carbon was successful.
 A problem with PVDC/AOT is that it is a powdery solid and not suitable for
 preparing monolithic carbons. In order to produce monolithic carbons,
 divinylbenzene (DVB) was added to the solution as a crosslinking agent.
 The addition of 10% DVB to the solution resulted in white homogeneous
 solids. Unfortunately, pyrolysis of this material resulted in the loss of
 the DVB component. The reason for this is that DVB does not form a char
 and instead decomposes upon heating. To overcome this problem, the polymer
 was heated in air at 220.degree. C. for 16 hours before carbonization.
 This step stabilized the polymer structure and successfully produced a
 mesoporous monolithic carbon (Jenkins and Kawamura 1976).
 Formation Mechanism
 The pore size of the materials was mainly controlled by the surfactant
 concentration used in the formulation. This observation is in contrast to
 phenomena observed in studies relating to mesoporous metal oxides. In
 mesoporous metal oxides, the concentration of the surfactant to monomer
 can be varied over a large range without affecting the resulting pore
 sizes (Beck et al. 1992; Bagshaw et al. 1995). In addition, varying the
 chain length of the surfactant can modify pore sizes in the present
 invention.
 According to the present invention, it is possible to prepare carbons
 having pore sizes ranging from mesoporous (4 nm) to macroporous (2000 nm),
 depending on the formulation. We observed that the RF gels with small pore
 sizes (samples 16 and 17) were transparent, indicating that the pores
 formed during polymerization were smaller than the wavelength of visible
 light (200-800 nm), whereas the gels of large pore carbons were opaque.
 The overall surface area (BET) is always greater than the liquid
 accessible surface area (&gt;2 nm) as measured by nitrogen adsorption
 (DPA) and Hg porosimetry (MPD), indicating the presence of micropores
 formed by gas evolution during the carbonization process. From the data,
 we find that the amount of water and surfactant have the greatest effect
 on the pore sizes. Generally, the pore sizes decrease as we use less water
 and less surfactant, although this is not true in every case (see 16 and
 17). When the molar ratio of surfactant to resorcinol is &lt;0.2, the
 surfactant is no longer effective in controlling the pore size.
 Hence, the present invention provides an inexpensive route to high surface
 area monolithic mesoporous polymers. This technique also allows control
 over the pore size of the resultant carbon in the mesopore range, a result
 that has not been possible with previous methods.
 Activation
 To further increase the surface area of the materials, the samples can be
 activated. When samples are activated, they are heated at high
 temperature, most commonly in the present of carbon dioxide, steam or
 aqueous base (Kinoshita 1988). This is a known method for preparing high
 surface area carbons. As discussed above, increasing the surface area of
 the carbon structure improves the efficacy of the material in a variety of
 applications, including sorbent, catalysis, and electrical applications.
 Carbon dioxide reacts with free carbon sites (C.sub.f) according to the
 equation:
EQU CO.sub.2 +C.sub.f .revreaction.CO(g)+(CO)
 The surface complex (CO) desorbs as CO leaving a new free carbon site.
EQU (CO).fwdarw.CO(g)+C.sub.f
 Oxidation by carbon dioxide can increase the microporosity and surface area
 of the carbon, but the nature of the carbon precursor determines to a
 large extent the final pore texture. For relatively nonporous carbons,
 such as graphites, only a small increase in surface area is evident, with
 an increase in burnoff due to the unavailability of pores that provide
 additional surface area. For a carbon such as the present mesoporous
 carbons, which contain fine pores, the surface area increases dramatically
 with CO.sub.2 activation. This new surface area is only exposed by the
 gaseous activation and is not created by it.
 Three of the present RF carbon formulations were activated with CO.sub.2.
 They contained molar ratios of CTAC/resorcinol of 0.02 (sample 19), 0.04
 (24) and 0.06 (sample 20) respectively. After pyrolysis, the samples were
 activated in carbon dioxide at 850.degree. C. or 900.degree. C. The
 porosity measurements showed that the median pore size pattern did not
 change, but the total surface area and the mesopore surface area have
 increased considerably. Table 6 shows how the surface area of the present
 mesoporous carbon stricture increases after being heated in CO.sub.2.
 TABLE 6
 Comparison of the properties of RF/CTA carbon.
 CO.sub.2 Activation BET Mesopore Pore
 Temperature Surface Area Surface Area Diameter
 Sample (.degree. C.) (m.sup.2 /g) (m.sup.2 /g) (nm)
 24 no activation 524 150 28
 24 850 891 211 28
 24 900 1361 377 28
 20 no activation 503 82 75
 20 850 947 130 75
 19 no activation 543 223 11
 19 850 1081 340 11
 The reason that the mesopore diameter does not measurably increase during
 activation is that, to a first approximation, both the micropores and
 mesopores are etched away at the same rate during activation. Hence, the
 removal of a few layers of carbon in the mesopores will not result in a
 significant increase in the pore size (e.g. 28 nm to 28.5 nm), while
 increasing the pore diameter of a micropore from 1 nm to 1.5 nm is a
 significant increase. In addition, activation can open up closed pores and
 extend the length of existing pores, as illustrated in FIG. 6.
 As described in the next section, activation by carbon dioxide results in a
 dramatic increase in capacitance, which is likely due either to increased
 accessibility to the micropore surface area or to changes in the surface
 properties of the carbon, or a combination of the two.
 To support this hypothesis, one of the present RF carbon samples was sent
 to Micromeritics to measure the micropore size distribution before and
 after activation on their ASAP2010 instrument. In FIG. 7, the micropore
 size distribution of one of the present RF carbons as produced is compared
 with the micropore size distribution after activation with carbon dioxide.
 The range of the instrument is limited to 5 angstroms (indicated by the
 sharp cutoff of the peaks), but from the shoulder that we can see, the
 micropore distribution has been expanded from a limit of approximately 12
 angstroms to about 20 angstroms. From this data we believe that the
 dramatic increase in capacitance that observed in the present samples
 after activation is due to the increase in the micropore size and surface
 area.
 Testing Methods
 The present activated and unactivated mesoporous carbons were screened by
 measuring their capacitance and generating a charge discharge curve for
 each in aqueous and nonaqueous electrolytes. A typical discharge curve is
 shown in FIG. 9. The charge discharge curves for the present films were
 obtained by applying a constant current pulse and following the voltage
 response with time using a VersaStat potentiostat, manufactured by EG&G of
 Oak Ridge Tennessee, interfaced to an IBM-compatible computer. EG&G Model
 270 software was used for application of the waveform function and data
 acquisition. The capacitance was measured in farads (F) and the cell
 resistance in ohms from the charge/discharge curve according to known
 procedures (Burke and Miller 1992) and the following equation:
EQU C=It/(V.sub.1 -V.sub.2)
 The internal resistance (ER) is evaluated from the initial voltage drop
 (V.sub.1 -V.sub.0) as expressed by equation
EQU ER=(V.sub.0 -V.sub.1)/I
 The charge/discharge curves are an efficient way to quickly measure the
 capacitance of porous carbons and are routinely used to measure
 double-layer capacitance. To compare the performance of different samples,
 this value is divided by either the volume (F/cm.sup.3) or the mass (F/g)
 of the sample.
 Capacitance Results for RF Carbons
 In Table 7, gravimetric (F/g), and volumetric (F/cc) capacitance (C.sub.d)
 of the present unactivated carbons in 4 M KOH are tabulated. In addition,
 the density, pore diameter, and BET surface area of our different carbon
 formulations are given and compared to the values for carbon aerogels and
 woven carbon fibers (Tran et al. 1996). Our best data in 4 M KOH is 116
 F/g for the RF carbon and 80 F/g for the RPF carbon. The capacitance is
 tabulated for an individual electrode or half-cell because this is the
 usual and accepted practice in most of the relevant literature. That is,
 since we are using two identical pieces of carbon as the anode and the
 cathode it would be more technically accurate to divide the given
 capacitance by the weight or volume of the pair (which would cut the
 reported values in half), but this approach would not be consistent with
 usual practice in the industry. The weight values are for the dry
 electrode, i.e. the weight of the electrolyte is not included.
 TABLE 7
 Capacitance values for RF/CTA carbons in 4 M KOH.
 Pore BET
 C.sub.d C.sub.d Density Diameter Surface
 Sample (F/g) (F/cc) (g/cm.sup.3) (nm) Area (m.sup.2 g)
 1 60 12 0.19 2000 446
 8 52 26 0.50 55 540
 15 102 77 0.75 18 644
 16 25 23 0.89 9 621
 17 16 19 1.2 4 386
 19 90 63 0.70 9 570
 20 116 82 0.71 28 453
 22 76 40 0.53 374 501
 23 103 82 0.80 10 653
 24 110 88 0.80 11 661
 25 100 78 0.78 12 580
 29 80 82 1.03 17 209
 30 75 43 0.57 80 362
 56 68 100 718
 CA.sup.1 70 52 0.74 3 600
 ACFC.sup.1 80 22 0.27 &lt;3 1690
 CA = carbon aerogel, ACFC = carbon fiber cloth. .sup.1 (Tran et al. 1996)
 From this data, a number of observations can be made. First, a comparison
 of the capacitance of our best materials versus the theoretical
 double-layer capacitance shows that essentially all of the surface area is
 accessible. That is, for a carbon with a specific surface area of 500
 m.sup.2 /g, the theoretical capacitance of the electrode if all of the
 surface area is electrochemically active is 100 F/g, and several of our
 samples (20, 23, 24, 25) are at or close to the theoretical number.
 Second, a comparison of the mesopore diameter versus the overall
 capicitance shows a strong correlation. As shown in FIG. 8, as the pore
 size is increased from 4 nm to 28 nm the capacitance increases and above
 this value begins to drop off. This clearly shows that the mesapore
 content and size dramatically influences the double-layer capacitance of
 porous carbon electrodes and the optimum pore diameter appears to be
 between 10 and 30 nm for aqueos KOH interestingly, the capacitance of the
 carbon is more strongly influenced by the size of the mesopores rather
 than the overall surface area of the material. Since these mesopore sizes
 are much greater than necessary for the electrolyte to enter the pores, it
 is believed that the large mesopores allow easier ion transport.
 A comparison of our materials with data for carbon aerogels and woven
 carbon fibers shows that TDA's carbon outperforms these carbons in
 gravimetric capacitance because of the size of the pores. Our electrodes
 also have considerable volumetric capacitance advantage over conventional
 carbon fiber and particulate carbon electrode because our carbons are much
 denser. This can be especially important in applications where space can
 be at a premium.
 We also tested some of our samples using 1 M H.sub.2 SO.sub.4 as the
 electrolyte (Table 8) and found that the capacitance was improved over
 aqueous KOH. This was expected because most carbon samples give slightly
 better capacitance in sulfuric acid, but oxidation of the carbon and
 corrosion of the current collectors can be a problem, especially at higher
 voltages, requiring the use of expensive noble metals (Eisenmann 1995).
 TABLE 8
 Capacitance in 1 M sulfuric acid.
 Sample C.sub.d (F/g) C.sub.d (F/cc)
 8 82 39
 20 135 88
 Table 9 shows the capacitance data for the same RF/CTA formulations
 described in Table 8. The as-produced carbons showed relatively low
 capacitance in organic electrolytes (&lt;10 F/g), but their capacitance
 increased dramatically upon activation with CO.sub.2. The mesopore
 distribution varies from 11 to 75 nm between these three samples and the
 data indicate that the optimum pore size is within this range. A preferred
 range for the pore size is from about 15 nm to about 25 nm. The samples
 show similar gravimetric capacitance regardless of whether they are
 activated at 850 or 900.degree. C. The main difference is that a higher
 activation temperature tends to lower the density (0.65 g/mL for
 850.degree. C. vs 0.50 g/mL for 900.degree. C). Therefore, the sample
 activated at 850.degree. C. gives a preferred balance of high capacitance
 and high density.
 TABLE 9
 Comparison of the capacitance of activated and non-activated
 mesoporous monolithic carbon
 CO.sub.2 BET Pore
 Activation Gravimetric Volumetric Surface Di-
 Temperature Capacitance Capacitance Area ameter
 Sample (.degree. C.) (F/g) (F/cc) (m.sup.2 /g) (nm)
 24 No activation 5 8 524 28
 24 850 57 37 891 28
 24 900 54 27 1361 28
 20 No activation 1 1 503 75
 20 850 40 28 947 75
 19 No activation 7 6 543 11
 19 850 47 32 1081 11
 CA No activation 16 10 600 3
 ACFC No activation 40 12 1690 &lt;3
 CA-Carbon aerogel
 ACFC-activated carbon fiber cloth
 If all of the surface area of the best sample (#24 activated at 850.degree.
 C.) were electrochemically accessible, its theoretical capacitance would
 be about 180 F/g (based on surface area of 900 m.sup.2 /g and a
 capacitance of 20 .mu.F/cm.sup.2). An experimental value of 57 F/g was
 achieved, which indicates a 32% effective utilization of the surface area.
 Similar results have been obtained for PVDC derived carbons.
 In Table 10, the results of the carbon electrodes prepared according to
 this invention are set out and compared those for other carbons that are
 currently being used in ultracapacitors, namely carbon acrogels developed
 at Lawrence Livemore National Laboratories, now being commercialized by
 PowerStor, and woven carbon fiber cloths. These results show that that the
 present materials exceed the performance of the prior art carbons. Not
 only does capacitance exceed that of the known carbon aerogels, but
 through the use of low-cost starting materials and elimination of the
 expensive supercritical extraction processing step, the present materials
 are considerably less expensive to produce. Also, because of the much
 greater densities possible for monolithic carbons, the volumetric energy
 density is much better than is possible with particulate carbon
 electrodes.
 TABLE 10
 Comparison of the capacitance of ultracapacitor electrodes
 (0.65 M NEt.sub.4 BF.sub.4 in propylene carbonate).
 Gravimetric Volumetric
 Capacitance Density Capacitance
 Porous carbon (F/g) (g/cc) (F/cc)
 TDA 57 0.65 37
 CA.sup.1 16 0.62 10
 ACFC.sup.1 40 0.30 12
 Calculations are based on the dry weight of a single carbon electrode
 CA = carbon aerogel,
 ACFC = activated carbon fiber cloth.
 .sup.1 (Tran et al. 1996)
 Finally, we measured the conductivity of our porous carbons using the four
 probe van der Pauw method. The results and comparison to other carbons arc
 shown in Table 11. As expected, the conductivity is not as good as
 non-porous carbons, but is considerably better than other highly porous
 carbons.
 TABLE 11
 Comparison of conductivity of carbons.
 Carbon Type Conductivity (Scm.sup.-1)
 Graphite 1400.sup.1
 glassy carbon 200.sup.1
 TDA's porous carbon 70
 carbon aerogel 20.sup.2
 Reticulated vitreous carbon 0.7
 .sup.1 Kinoshita 1988,
 .sup.2 Lu et al. 1993
 Capacitor Preparation
 While the foregoing discussion discloses the formation of the present
 monolithic, high surface area carbon films in general, we have also
 prepared these materials as monolithic free-standing thin films. The
 present materials are ideal for double-layer capacitors because they have
 high conductivity, high surface areas, high mesoporosity and most
 importantly high capacitance. Very thin carbon electrodes give increased
 power because they allow more rapid transport of ions in and out of the
 carbon. Also, thin films can easily be packed into an array of electrodes
 to produce a compact device.
 According to one preferred embodiment, thin films are prepared by casting
 the present polymer solution between two Teflon covered flat aluminum
 plates with a thin silicone gasket around the edges. After curing, the
 film can be cut into any desired shape with a high-speed blade or if the
 film is thin enough, it can be cut with a scissors. Using this procedure,
 after pyrolysis thin film carbon electrodes have been produced that are as
 thin as 200 microns.
 The preferred thin film carbon electrodes can in turn be used in the
 assembly of a capacitor. For example, according to the preferred
 embodiment illustrated in FIG. 10, an ultracapacitor 10 consists of two or
 more pairs of the mesoporous carbon electrodes 12 separated by a porous,
 electrically insulating material 14. Current collectors 16 supply
 electrical contacts to the electrodes to provide electrical connection to
 the voltage source (not shown). The preferred carbon pore size will depend
 on the electrolyte that is used. The components are preferably sealed in a
 polymeric housing or package 18. An example of a suitable device comprises
 electrodes made from the present carbon film, a glass fiber paper
 separator, and aluminum foil current collectors, with a liquid electrolyte
 (0.65 M NEt.sub.4 BF.sub.4 in propylene carbonate (PC)), sealed in a
 metallized film bag. After the electrodes, separator and electrolyte are
 placed in the bag, it can be sealed with an epoxy inside an argon filled
 glovebox.
 Conclusions
 In sum, the mesopores that are introduced by the present surfactant
 templating synthesis produce predominantly mesoporous polymers of any
 desired pore size by simply adjusting the initial formulation. These
 polymers can be pyrolyzed to produce monolithic carbons that contain
 mesopores that provide a passageway to the micropores that contain the
 surface area needed in a variety of applications. With the combination of
 surfactant templating and activation, it is possible to produce monolithic
 carbons with a desired pore size range.
 Using the present technology, it is also possible to prepare monolith
 polymers with the desired pore size distribution of for high-throughput
 chromatography.