MX2008002720A - Activated carbon fibers, methods of their preparation, and devices comprising activated carbon fibers - Google Patents

Abstract

Catalytically activated carbon fibers and methods for their preparation are described. The activated carbon fibers are engineered to have a controlled porosity distribution that is readily optimized for specific applications using metal-containing nanoparticles as activation catalysts. The activated carbon fibers may be used in all manner of devices that contain carbon materials, including but not limited to various electrochemical devices (e.g., capacitors, batteries, fuel cells, and the like), hydrogen storage devices, filtration devices, catalytic substrates, and the like.

Description

ACTIVATED CARBON FIBERS, METHODS FOR PREPARATION AND DEVICES COMPRISING ACTIVATED CARBON FIBERS TECHNICAL FIELD The present invention relates to activated carbon fibers, preferably nanofibres, and to methods for their preparation. The activated carbon fibers are engineered to have a controlled porosity and can be used in all kinds of devices containing activated carbon materials, including without limitation various electrochemical devices (eg capacitors, batteries, fuel cells and the like) , hydrogen storage devices, filtration devices, catalytic substrates, and the like.

BACKGROUND OF THE INVENTION In many emerging technologies, such as in research aimed at the development of electric and hybrid vehicles thereof, there is a pressing need for capacitors with high energy and high energy density. Although capacitors have been known since the invention of the Leyden jar in 1745, there is still a need for a capacitor that has an energy density that is sufficient for applications such as the automotive industry.

The electric capacitors of double layer (EDLC's or ultracapacitors) and pseudocapacitores (PC's or supercapacitors) are two types of capacitors that have been studied for automotive applications. The main challenges in advancing these technologies include improving energy density, reducing the internal impedance of the device (modeled as resistance in equivalent series or ESR), and reducing the cost. These two capacitive phenomena are presented briefly below. The double-layer electric capacitor designs are based on very large electrode surface areas, which are usually made of "nanoscale" metal oxide or activated carbons that line a current collector made of a good conductor such as thin film of aluminum or copper, to store charge by physically separating ions from a conductive electrolyte salt into a region known as the Helmholtz layer. This layer of Helmholtz, which forms a few Angstroms beyond the surface of the electrode, normally corresponds to the first two or three molecules from the surface. There is no distinct physical dielectric in an EDLC, which is provided in its place by the electromagnetically determined Helmholtz layer. However, the capacitance is still based on a physical charge separation through an electric field. As the electrodes on each side of the cell store identical ionic charges on their surfaces while the electrolyte is exhausted between them (but beyond the Helmholtz layer), and in effect it becomes the opposite plate of a conventional capacitor, this technology HE denominates electric capacitance of double layer. The electrodes are placed in series, operate together at twice their individual voltage and capacitance, and are physically separated by a porous thin-film spacer similar to electrolytic capacitors or lithium-ion batteries. Current EDLC's have frequency response constants (response curve or RC) that vary from milliseconds to seconds. However, commercial EDLC's (sometimes called ultracapacitors) are currently too expensive and of insufficient energy density for applications such as hybrid vehicles, and are mostly used in consumer electronics for fail-soft memory backup. It is generally accepted that the pore size of the EDLC should be at least about 1-2 nm for an aqueous electrolyte, or about 2-3 nm for an organic electrolyte, to accommodate the solvation spheres of the respective electrolyte ions so that the pores contribute to the available surface for the capacitance of the Helmholtz layer. The pores should also be opened to the surface for electrolyte exposure and wet, instead of being closed and internal. At the same time, the more total open pores there are above this size threshold it will be better, since this maximizes the total surface area. Substantially larger pores are undesirable because they comparatively decrease the total available surface. Research by other authors has shown that the capacitance improves as the average pore size increases from approximately 4 nm to approximately 28 nm, and that the optimum pore size with organic electrolytes ranges from about 15 nm to about 25 nm. The conventional activated carbons used in such EDLC devices have many electrochemically unusable micropores (ie, less than 2 nm according to the IUPAC definition). The pore size should be approximately the electrolyte ion solvation sphere, or larger, for the Helmholtz layer to form. For organic electrolytes, these pores should ideally be greater than 3-4 nm; it has been shown experimentally that micropores smaller than 2 nm almost do not contribute to the capacitance. In the best highly activated electrochemical carbons reported in the literature, the actual measured EDLC is less than 20% theoretical due to suboptimal pore size distributions, being a large fraction (usually more than one third to half) of micropores that they can not contribute to the capacitance, and an increasing fraction of macropores (depending on the degree of activation) that reduce the overall surface area. A problem separated from the highly activated carbons in electrochemical devices is the increase in their fragility; they tend to form small irregular particles that contribute to higher electrode ESR due to the many poor contact grain boundaries, with reported conductivity as low as 7 S / cm. Pseudo-capacitors can be constructed based on electrochemical pseudocapacitancy in one of three ways: adsorption of electrolyte ions on the surface of an electrode, a reaction of oxidation / reduction (redox) on the surface of the electrode, or doping / ion depletion of a conductive polymer. Pseudo-capacitors tend to have CR constants slower than EDLC's due to the reversible electrochemical nature of charge storage mechanisms, and thus are more like a battery than a capacitor. Current PCs have RC constants that vary from fractions of seconds to hundreds of seconds. Redox pseudocapacitancy devices (so-called supercapacitors) have been commercially developed for military use, but are very expensive due to the cost of constituent ruthenium oxide (RuO) and other rare earth metals. Commercial EDLC's are currently too expensive and insufficient energy density for applications in hybrid vehicles. PCs are also too expensive for many uses. Although the two load storage mechanisms can coexist in the two types of capacitors, one or the other predominates in current commercial devices. If the two mechanisms can be inexpensively combined in a large scale in a device, the device would have the characteristics of both an energy capacitor and a battery, and could find substantial markets in applications such as hybrid electric vehicles. Until now, such practical hybrid devices have not been produced. Kyotani, Carbon, 2000, 38: 269-286, has summarized the available methods for obtaining mesoporous coal. Lee et al., Chem. Commun., 1999, 2177-2178, described a mesoporous carbon film for used with double-layer electrochemical capacitors. Oya et al., Carbón, 1995, 33 (8): 1085-1090, mixed cobalt acetylacetonate with phenolic resin, then spun, cured, carbonized and activated large diameter fibers to obtain brittle carbon fibers of moderate surface area in Comparison with conventional activation, but with some large mesopores (several 10s of nm) generated by cobalt, together with a preponderance of micropores. In these experiments, the best total surface resulting from materials mixed with cobalt was less than 1000 square meters / g compared to up to 1900 square meters / g without cobalt. The total area of mesoporous as a proportion of the total area does not exceed 27% (170 square meters / g) in the best case, even at 40% of consumption. Oya found problems with the activated fibers because they became very fragile due to the catalytic graphitization of the material inside the coal. Oya did not consider or report the cobalt particle sizes that result from his procedure. Hong et al., Korean J. Chem. Eng., 2000, 17 (2), 237-240, described a second activation of previously activated carbon fibers by additional catalytic gasification. Hong started with commercially available conventional activated carbon fibers that have only 11.9% mesopores and a surface area of 1711 square meters / g (thus, mainly micropores less than 2 nm). Hong used cobalt chloride precursor to catalytically produce a material with 56% mesoporum volume compared to approximately 23% for a second comparable activation without cobalt. However, the additional mesoporous size distribution had a maximum at approximately 2 nm and there was no appreciable difference in the mesoporous production above 4 nm according to its figure 6. Therefore, the total surface area only increased to 1984 square meters / g compared to 1780 square meters / g after the second activation without the cobalt, and 1711 square meters / g before the second activation. Hong specifically found that the fragility does not increase, unlike the result of Oya. Hong does not consider or report the size of the cobalt particles formed by his procedure, but they must have been mainly less than 2 nm, given the resulting mesoporous distribution in his data. Trimmel et al., New Journal of Chemistry 2002 26 (2), 759-765, made nanoparticles of nickel oxide of various average diameters, from 3 nm to several nm, of various organometallic precursors varying the precursor conditions. The Japanese organization ÑIRE reported on its website in March 2001 that its researchers were able to form several metal oxide nanoparticles with diameters ranging from 5 nm to 10 nm, using metal organometallic acetylacetonates coating particulate lignite, which catalyzed mesopores in the particles resulting from activated carbon.

BRIEF DESCRIPTION OF THE INVENTION The scope of the present invention is defined solely by the appended claims and is not affected to any extent by the claims of this brief description. One embodiment of the present invention is a method of preparing a carbon fiber, comprising electrowinning a polymer fiber with a diameter of less than about 1 μm from a polymeric material; carbonization of at least a portion of the polymer fiber to provide a polymer fiber; and catalytic activation of at least a portion of the carbon fiber with catalytic nanoparticles larger than micropore to form one or more pores on the surface of the carbon fiber. A second embodiment of the present invention is a method of preparing a carbon fiber, which comprises adding the catalytic material before or after electrospinning a polymer fiber; electrospinning the polymer fiber with a diameter less than about 1 μm of a polymeric material; carbonizing at least a portion of the polymer fiber to provide a carbon fiber; and catalytically activating at least a portion of the carbon fiber with catalytic nanoparticles larger than micropore to form one or more pores on the surface of the carbon fiber. A third embodiment of the present invention is a method of preparation of a carbon fiber, comprising electrospinning a polymer fiber with a diameter less than about 1 μm of a polymeric material; coating at least a portion of the fiber with a precursor of catalytic material before or after carbonizing at least a portion of the polymer fiber, and before activating, converting the precursor of catalytic material to catalytic particles of larger size than micropore; and catalytically activating at least a portion of the carbon fiber with said catalytic nanoparticles to form one or more pores on the surface of the carbon fiber. A fourth embodiment of the present invention is a method of preparing a carbon fiber, comprising electrospinning a polymer fiber with a diameter of about 1 μm of a polymeric material; carbonizing at least a portion of the polymer fiber to provide a carbon fiber; catalytically activating at least a portion of the carbon fiber with catalytic nanoparticles larger than micropore to form one or more pores on the surface of the carbon fiber; and breaking at least a portion of the carbon fiber to provide a plurality of carbon fiber fragments. Another embodiment of the present invention are carbon fibers with diameters less than 1 μm, with one or more mesopores, and with one or more metal-containing nanoparticles in the mesopores. Another embodiment of the present invention is a fibrous material comprising a plurality of the carbon fibers of the present invention. invention or fragments thereof. Another embodiment of the present invention is an electrode comprising a current collector; and the fibrous material of the present invention in electrical contact with the current collector. Another embodiment of the present invention is a capacitor comprising one or more of the carbon fibers of the present invention, or fragments thereof.

DETAILED DESCRIPTION OF THE INVENTION Mesoporous activated carbon fibers and nanofibers constructed with precision by engineering have been discovered and are described herein. Fibers and nanofibers have superior surface area properties especially suitable for use in capacitors, and can be prepared by methods that include spinning, electroheating, carbonization, catalytic activation using nanoparticles with an average diameter greater than 2 nm, and optionally grinding into fragments as described further below. The preparation methods described herein provide control over the total porosity and the pore size distribution on the surface of the fibers and nanofibers, and also the porosity of some fibrous materials. Activated carbons with fiber geometries according to this invention have features designed for specific applications including, without limitation, capacitors. Further, by the addition of the metal oxide catalyst nanoparticles, these materials have the additional advantage of optionally contributing to the pseudocapacitancy of the metal oxides, in addition to the capacitance of the Helmholtz layer of the activated carbon surface; thus increasing the energy density of a hybrid capacitor cell. The present inventor has found that the nanofibers, a porosity of upper total fiber of open surface mesopores (usually measured by the BET method for surface per unit weight in m2 / g), a maximization of the mesoporous size distribution above about 3 nm and below about 30 nm, and the optimization of void density to volume (equivalently, porosity and usually measured by weight of carbon per unit volume), in porous activated carbon materials made from said fibers, contribute to obtain larger total effective surface areas and can improve the performance of the EDLC device. Throughout this description and the appended claims the following definitions are understood as follows: The term "mesoporous", used with respect to a fiber or carbon nanofiber describes a surface pore size distribution, wherein at least about 50% of the total pore volume has a size of about 2 nm to about 50 nm. The phrase "catalytically activated" used with respect to a carbon fiber or nanofiber refers to its surface containing pore, in where the pores have been introduced by a catalytically controlled activation process (for example, chemical etching). In some embodiments, metal oxide particles of a chosen average size serve as suitable catalysts, and at least a portion of the metal oxides remain in or on the nanofibers after the activation process. The term "fiber" used with respect to polymers and carbon refers to filamentous material of fine diameter, for example diameters less than about 20 microns, and preferably less than about 10 microns, for example as the type obtainable using methods of conventional spinning. The term "nanofiber" with respect to polymers and carbon refers to a filamentous material of very fine diameter less than one miera, and preferably nanoscale (diameter of 100 nanometers or less), such as the type obtainable using a electrohilament process. The term "nanoparticle" used with respect to catalytic particles means a nanoscale material, preferably a metal or metal oxide with an average particle size greater than 2 nm. As an introduction, a method of preparing activated carbon nanofibers incorporating the features of the present invention, includes electrospinning a polymer fiber with a diameter less than about 1 μm from a polymeric material; carbonizing at least a portion of the polymer fiber to provide a carbon fiber; Y catalytically activating at least a portion of the carbon fiber with catalytic nanoparticles of minimum diameter of at least mesoporous to form one or more pores on the surface of the carbon fiber. In the presently preferred embodiments, the polymeric material is polyacrylonitrile or PAN. Although a fiber or carbon nanofiber made by carbonizing PAN filaments is conventionally desirable, the present invention is not limited thereto, but comprises any polymer or combination of polymers capable of being spun into thin, charred and activated filaments. In some embodiments, a metal-containing material, such as a metal oxide nanoparticle or a precursor thereof, is introduced during one or more processing steps to provide catalytic surface sites for subsequent chemical etching of surface pores during the process. activation stage, or to provide a desired electrochemical activity. The metal or metals of the metal-containing materials are selected based on their catalytic or electrochemical activity. In some embodiments, the metal-containing material comprises a metal oxide nanoparticle or a combination of different metal oxide nanoparticles. In some embodiments, metal oxide nanoparticles have diameters up to about 10 nm, inclusive, in other embodiments up to about 8 nm, inclusive, in other embodiments up to about 6 nm, inclusive, in other embodiments up to 4 nm, inclusive , in other modalities up to about 3 nm, inclusive, and in other modalities up to about 2 nm, inclusive. In some embodiments, the metal oxide nanoparticles comprise oxides of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum or combinations thereof. In some embodiments, the metal oxide nanoparticles comprise nickel oxide. In some embodiments, the metal-containing material comprises an organometallic metal oxide precursor or a mixture of said precursors. In some embodiments, the metal oxide precursor comprises a metal acetylacetonate. In some embodiments, the metal oxide precursor comprises nickel acetylacetonate. In some embodiments, the metal oxide precursor comprises metal acetate with an alcohol as the solvent. In some embodiments, the precursor is nickel acetate. For embodiments in which an organometallic metal oxide precursor (for example nickel acetylacetonate), a mixture of said precursors or a mixture of said precursors and one or more metal oxide nanoparticles are used, the organometallic precursors can be converted into metal oxides of suitable particle size during the carbonization of spun fibers or nanofibers (for example, using temperature controlled treatments). In some embodiments, the metal-containing material is introduced after spinning and before carbonization or activation. TO As an example, a network of electroheated nanofibers can be coated with an organometallic complex (or equivalent metal oxide precursors) in a solvent to any desired degree of dilution and other precursor conditions. In a subsequent step, for example before or at the beginning of the carbonization of the coated nanofibers, a controlled temperature hydrolysis or other controlled chemical reaction can be performed to convert the complex or complexes into metal oxide coatings into nanoparticles of a size and desired coverage density on the surface of the nanofiber before activation. The doping at a controlled density of metal oxide nanoparticles of controlled size distribution (or in preferred embodiments their organometallic precursors), in or preferably on controlled diameter carbonaceous fiber material (preferably 100 nm or less), which then catalytically activates in a controlled manner, depending on the catalyst, nanoparticle size and activation conditions, provides a mesoporous fibrous material with a very high surface area, suitable for applications in capacitors. Unlike conventional activation, most of the pores in said material are created by the mesoscale catalytic nanoparticles, and therefore are substantial mesopores at least as large as the catalyst nanoparticles. As described above, although it is possible to directly add metal oxide nanoparticles of suitable size obtained separately, preferably these nanoparticles are created during the carbonization / activation phases from mixed or preferably coated precursor sols, such as the acetylacetonate complexes of metal and metal acetate known in the art. The organometallic complexes, such as nickel acetylacetonate (or their equivalents), in a suitable solvent, can be applied as a coating on the surfaces of the fiber, or preferably nanofiber, of PAN, spun and polymerized, at any desired dilution; then the solvent is removed (for example by evaporation) and the organometallic residue is converted to metal oxide nanoparticles of a reasonably controlled nanoparticle size distribution, which covers the surface of the fiber or nanofiber to a desired degree using the known processes . This preferred approach has the advantages of being technically straightforward and of ensuring that all the resulting metal oxide nanoparticles are on the surface to catalyze open surface mesopores, as opposed to being indoors where they do not have pore forming activity. of surface, but can catalyze the coal into fragile graphite, resulting in fragility. In some embodiments, nickel oxide is a desirable metal oxide due to the lower catalytic activity reported on the carbon, as compared for example with iron or cobalt; If the catalytic activity of a metal oxide is too large, the activation may result in the complete breaking of a nanofiber, instead of the desired mesoporous etching. In addition, nickel oxide has a proven ability to form particles of approximately 3 nm to several nm in size (ideal for initial mesopores), from several precursor organometallic sols, as shown by another work with nickel organometals. In addition, it is known that nickel oxide exhibits a good pseudocapacitancy. Notwithstanding the advantages of nickel, other metals such as cobalt may be useful for the methods according to the present invention, depending on the optimization of the activation process. Cobalt also contributes to a good pseudocapacitance and is more reactive as a catalyst. Mixtures of various metal oxides can also be used, although these can complicate manufacturing processes by requiring separate depositions depending on the chemistry of the precursor. For example, larger pores created by more reactive catalysts can be used to dissect nanofibers, break them down by chemical grinding to produce nanofiber fragments with low to moderate aspect ratios, which can be used to form fibrous non-woven materials well packaged The carefully controlled carbonization (and depending on the details of the process, the simultaneous conversion of the precursor materials to metal oxide nanoparticles in the same heating step), followed by activation (for example steam treatment in a relatively inert atmosphere of N2 at 750 ° C or more, approximately, carbon monoxide treatment, treatment with carbon dioxide, or any combination of such treatments), will create a preponderance of open fiber surface mesoporos, all substantially above 2 nm, preferably above 5 nm, as is desirable for EDLC's. The final pore density (and total surface porosity) with average pore size above the size of the catalyst nanoparticle is a function of the metal oxide type (catalytic power), particle size, particle charge and carbon activation conditions, such as temperature, pressure and duration. Nickel oxide is cheap compared to cobalt or ruthenium, and can conveniently be used as a pseudo-capacitive pore catalyst that has been seen to be less reactive than iron or cobalt during carbon activation. In this way, nickel oxide may be susceptible to higher nanoparticle loading for a higher total surface activation, and for higher pseudocapacitancy. Others have shown that the oxide nanoparticles will remain for the most part exposed in the pores of the carbon fiber they create, and will therefore be available to contribute to pseudocapacitancy with organic or aqueous electrolytes. Nickel oxide is one of at least three metal oxides (Co, Fe, and Ni) that can be used to catalytically control the creation of mesoporum in activated bulk lignite carbons (the term "mesoporous" being defined here as according to the IUPAC standard as between 2 nm and 50 nm). Previous work in the Asian coal industry has shown that hard coal in precursor particles can be coated, and The temperature and duration of the conventional steam activation process can be controlled to provide metal oxide nanoparticles of 5-10 nm in diameter and mesoporous volume ratios of up to 76% (using iron), in the resulting activated carbon particles, with substantially all mesopores larger than their causative nanoparticles. Because of the intrinsic nature of the process, all these mesopores are open. The total porosity of the resulting particulate carbon depends on the metal catalyst and the activation conditions used. The BET surfaces vary from approximately 600 m2 / g to more than 950 m2 / g, depending on the catalyst and the activation conditions. This compares very favorably with Hong, which achieved only 44.5% additional mesopores by a second catalytic activation, with a mesoporous distribution with a maximum of 2 nm, and minimal additional surface attributable to these additional cobalt-derived mesopores of only 204 m / g. The brittleness of the resultant activated carbon fiber or nanofiber is a consideration for electrodes of electrochemical devices, since it is intended to be attached as a very thin uniform layer of porous fibrous material (in some embodiments less than about 100 microns thick) to the electrodes. Thin metal sheet current collectors. In some embodiments, the nanofibers can be electro-wound directly onto the current collectors, thus eliminating an assembly step in manufacturing. The densification of the "felt" spun during manufacture (for example by pressure lamination after the polymerization or after carbonization), can further reduce the open space between the fibers, reducing the porosity of void to volume of the fibrous material, and efficiently increase the total surface area for a given thickness of material regardless of the BET surface of the fibers. A brittle graphitized material would fracture into many small particles along the planes of the graphite sheet, potentially with aspect ratios less than 1 (creating fiber wafers), and results in a material that more closely resembles the conventional particles. When this occurs with the nanofibers, the resulting material of submicron particles would pack more densely than conventional activated carbons with their distribution of micron size particles, potentially reducing the usable surface area as shown by the example below. Alternatively, fibers or nanofibers can be fractured or broken by various chemical or mechanical processes. As described above, the fibers can be activated with a first catalyst for mesopores, and simultaneously with a second catalyst that forms macropores that dissect the fiber (chemical milling). Alternatively, mechanical methods such as grinding can be used to create short fragments of a desired average aspect ratio. These fiber fragments can be used to create fibrous material using solvent coating processes analogous to papermaking. Said suspension of fibrous powder has the advantage of being directly replaceable in the manufacturing processes currently used for particulate activated carbon electrodes. Conventional finished carbon coatings on electrode particles are ideally of a thickness of less than 100 microns to minimize ESR. This limitation may not apply to fibrous activated carbon materials with different interfiber pore geometries. The comparatively larger conductive fibers or fiber fragments have less grain boundaries and the material has elongated pores. More of the particles can make direct electrical contact with the current collector, and they can also be completely exposed to the electrolyte. These characteristics reduce the ESR and increase the capacitance thus producing a more dense energy device. The work of other authors suggests the potential benefit of densification of materials for optimum ratios from hollow to volume (porosity of material), for electrode materials. For example, it has been shown that the performance is improved by applying pressure to EDLC electrodes of experimental carbon nanotube (constructed by deposition of multilayer carbon nanotube stream over thin sheets of current collector). Carbon nanotubes are not brittle but have high aspect ratios and therefore are packaged randomly in a very porous material; the pressure results in closer proximities and reduced porosity in the nanotube mat, in other words, densification. In some embodiments, the electrohilated nanofibers of the fibrous material comprise diameters of approximately 300 nm or less, in other embodiments of approximately 250 nm or less, in other embodiments of approximately 200 nm or less, in other embodiments of approximately 150 nm or less, in other embodiments of approximately 100 nm or less , and in other modalities of approximately 75 nm or less. In some embodiments, the nanofibers comprise diameters of about 50 nm or less. The preferred diameter depends on the process used to create the fibrous material; With some processes, the aspect ratio of the fiber strongly affects the porosity of the material. Conventional electroheating processes already result in mats or "nets" of conventionally activated carbon fiber, with fibers of average diameter from 50 nm, compared to an average of about 10-20 nm for carbon nanotubes of all types (varying from less than 2 nm to approximately 40 nm in diameter). Thinner diameter fibers per unit volume improve yield simply because of the larger total surface area, provided they can be compacted into a properly dense interwoven material. However, with such fine fibers, finally a substantial number of conventional high-activation macropores would cut the fibers completely into particle fragments during activation. By using carbon nanofibers coated with catalytic nanoparticles (such as nickel oxide), the activation of mesopores can be controlled at average pore that keep most fibers intact above a certain diameter threshold, sufficiently larger than the average mesoporum created by the specifications of the chosen parameters of the activation process. As an example, if the real (relatively soft) activation conditions produce 65% of mesopores less than 40 nm thick, mainly of catalytic nanoparticles, and only 5% of pores larger than 75 nm, mainly of the general degree of consumption , then an average fiber diameter of 75 nm would leave about 95% of the fiber intact. Such activated nanofibers have individual fiber surface porosities that further increase the total effective surface, unlike smooth carbon nanotubes. And unlike carbon nanotubes, they can be milled into chosen aspect ratio fragments by solvent deposition to produce fibrous materials with maximum random packing and minimum porosity, to further increase the total surface area in the resulting material. In case of requiring nanofiber fragments for further processing, an additional advantage of the catalytic activation of nanoparticles can be obtained by choosing the catalysts, their sizes and charges, in such a way that the fibers are selectively cut by the nanoparticle catalysts causing the pores more large and the fastest growth during activation. This presents an alternative of chemical milling to the mechanical means to produce a powder of Fragment of fiber. By way of example, the addition of a small amount of iron or cobalt in or on an organometallic nanoparticle precursor, mainly nickel, results in a small designed proportion of non-nickel, more reactive nanoparticles distributed over the fiber. In any given activation condition, the few extra active sites, with pores that grow more rapidly, will cut the nanofibers into fragments long before nickel can do so, while at the same time nickel produces mesopores on the surface of the nanofiber. By varying the dilution of the most reactive catalyst, and consequently the space distribution of its resulting nanoparticles on the surface of the fiber, and then controlling the activation conditions, any average length distribution of fiber fragment can be obtained in principle. This method, for example, can produce, from suitably coated precursor carbon nanofibers, a particulate submicron powder of mesoporous activated carbon nanofiber fragments with an aspect ratio distribution of 3 to 5, which provides nearly optimal aspect ratios for packaging random maximum of the fibers in at least the porous fibrous material, with advantageous elongated interfiber pore structures. Significantly, chiral problems are not involved in creating carbon nanofibers, unlike carbon nanotubes. The latter exist in several chiral forms, the individual production of which currently can not be controlled and only one of which is responsible for metallic conduction, unlike semiconduction. In some embodiments, activation of the carbon fibers comprises controlled vapor activation. In some embodiments, activation of the carbon fibers comprises controlled activation of carbon monoxide. In some embodiments, activation of the carbon fibers comprises controlled activation of carbon dioxide. In some embodiments, activation of the carbon fibers comprises a combination of one or more of the treatments described above. The activation allows the maximization of the mesoporosity of total fiber surface, obtaining a desired pore size distribution of the nanoparticles on the surface of the fibers. In some embodiments, activation provides carbon fibers having a total consumption of at least about 15%, in some embodiments of at least about 30%, and in some embodiments of at least about 40%. The size of pores introduced on the surface of the nanofiber during the activation depends on the catalytic activity of the metal oxide catalysis, its quantity or the size of its nanoparticles, as well as the conditions of its activation. In general, it is desirable to select pore sizes large enough to accommodate the particular electrolyte used, but not substantially larger to prevent unnecessary reductions in the total fiber surface area. In some modalities, at least approximately 40% of the number Total pore has a particle size of about 2 nm to about 50 nm. In some embodiments, at least about 50% of the total number of pores has a size ranging from about 2 nm to about 50 nm. In some embodiments, at least about 60% of the total number of pores have a size ranging from about 2 nm to about 50 nm. In some embodiments, at least about 70% of the total number of pores have a size ranging from about 2 nm to about 50 nm. In some embodiments, no more than about 35% of the total number of pores have a size greater than about 50 nm. In some embodiments, no more than about 25% of the total number of pores have a size greater than about 50 nm. In some embodiments, no more than about 20% of the total number of pores have a size greater than about 50 nm. In some embodiments, no more than about 15% of the total number of pores have a size greater than about 50 nm. In some embodiments, at least about 40% of the total number of pores have a size ranging from about 2 nm to about 35 nm. In some embodiments, at least about 50% of the total number of pores have a size ranging from about 2 nm to about 35 nm. In some embodiments, at least approximately 60% of the total number of pores they have a size ranging from about 2 nm to about 35 nm. In some embodiments, at least about 70% of the total number of pores have a size ranging from about 2 nm to about 35 nm. In some embodiments, no more than about 35% of the total number of pores have a size greater than about 35 nm. In some embodiments, no more than about 25% of the total number of pores have a size greater than about 35 nm. In some embodiments, no more than about 20% of the total number of pores have a size greater than about 35 nm. In some embodiments, no more than about 15% of the total number of pores have a size greater than about 35 nm. In some embodiments, at least about 40% of the total number of pores have a size ranging from about 3 nm to about 25 nm. In some modalities, at least about 50% of the total number of pores have a size ranging from about 3 nm to about 25 nm. In some embodiments, at least about 60% of the total number of pores have a size ranging from about 3 nm to about 25 nm. In some embodiments, at least about 70% of the total number of pores have a size ranging from about 3 nm to about 25 nm. In some embodiments, no more than about 35% of the total number of pores are larger than approximately 25 nm. In some embodiments, no more than about 25% of the total number of pores have a size greater than about 25 nm. In some embodiments, no more than about 20% of the total number of pores have a size greater than about 25 nm. In some embodiments, no more than about 15% of the total number of pores have a size greater than about 25 nm. In some embodiments, the polymeric material (and optionally any metal oxide nanoparticles or metal oxide precursors) is electrospinned directly onto a thin sheet of current collector (e.g., aluminum, copper, gold, silver, platinum, palladium or the like). ), thus eliminating a manufacturing step in the assembly of an electrode. In some embodiments, the density of the fibrous material can be further increased (for example by simple lamination under pressure to a desired thickness or the like). In some embodiments, the density increases before carbonization or activation, and in other embodiments the density increases after carbonization or activation. In some embodiments, the thickness of the dense fibrous material is less than or equal to about 200 microns, in other embodiments less than or equal to about 150 microns, and in other embodiments less than or equal to about 100 microns. As an alternative to the preparation of woven cloths or non-woven nets made of cardboard fibers, the carbon nanofibers that incorporate the features of the present invention can be broken into shorter fragments (for example after carbonization and during or after activation), and then applied to a substrate (for example as a suspension), to form a non-woven layer of paper type. A particle-size short fiber fragment powder can be made from the dough by grinding, milling, shredding, chemical grinding, etc., with a length distribution of engineered fragment, for subsequent coating on a substrate (for example a electrode surface). The distribution of the aspect ratio of the resulting fibrous powder will result in a material of average fiber density and porosity according to the principles of random packing. This type of additional processing can be performed to provide a material in accordance with the present invention, compatible with conventional particulate carbon coating processes, as described in US Pat. UU Nos. 6,627,252 and 6,631,074, the entire contents of which are incorporated herein by reference, except that in the case of any disclosure or definition inconsistent with the present application, the disclosure or definition herein is considered prevailing. The electrode manufacturing process described in the aforementioned patents includes two steps: first, a conductive carbon (graphite) is placed on a thin sheet of current collector by means of a suspension with binder, and dried or cured; Secondly, a second coating of the coal dust is placed activated on the first coating layer, possibly mixed with some conductive carbon to increase the conductivity and reduce the ESR, to a final particle to volume ratio of less than 25% to 35%. This is conventionally achieved with activated carbon powders having a wide dispersion of irregularly shaped particle sizes from 3 microns to 30 microns, which follows the principles of random packing with particles at least twice as large or smaller than other particles in the same random packaging. Such conventional procedures for particulate activated carbon can be easily adapted for use with carbon fiber fragments encompassing the features of the present invention. By way of example, a mass of polymer fibers can be coated with organometallic precursors, carbonized and activated as described above to produce mesoporous fiber surfaces. Then, the fibers can be finely ground. Depending on the graphitization of the fiber, the degree of grinding and the exact grinding process used, the fibers would preferably break along their longitudinal axes into shorter fiber fragments, respectively. Grinding devices that can be used include, without limitation, machines that produce conventional pieces of ground carbon fiber. An example of a machine capable of producing particles with finer distributions of 50% of 3 microns, and therefore adequately low aspect ratios for finely spun carbon fibers, is the MaxxMill stirred medium mill from Noli Gmbh, with an advanced air classifier. Chemical milling, for example using differentially potent catalysts in selected proportions during activation, would also produce such nanofiber fragments. Optionally you can also perform screening / selection / additional classification to control the final distributions of aspect ratio, or to eliminate fines as with other commercial fine powders. The final result would be analogous to bulk paper pulp, except for the much finer geometries of the materials involved in activated carbon fiber. The resulting density of the "paper-like" fibrous material, such as by coating a thin sheet of current collector, is an engineered property of the length of the nanofiber fragments as compared to their diameter (their aspect ratio), the distribution of the lengths compared to the average diameter, and optionally the subsequent densification of deposition (for example by means of pressure). If the length approaches the diameter, then the diameters will be more like conventional particles and will pack more densely with less porosity in the resulting material. If the length is much larger than the diameter, then the aspect ratio will be high and the packing will be less dense (that is, a more porous material in its ratio of hollow to volume). The average aspect ratio of length to diameter can be adjusted or mixtures of different ratios can be used to provide any desired porosity of material (hollow ratio / volume), within the limits of the packaging principles random. In some embodiments, at least about 50% of the total number of carbon fiber fragments have a length ranging from about 5 microns to about 30 microns, equivalent to some activated carbon particle materials. In other modalities at least about 50% of the total number of fragments have aspect ratios less than 50. In other modalities the average aspect ratios are less than 20. In other modalities the average aspect ratios are less than 10. In other embodiments In embodiments where the diameters of the nanofiber fragment are 100 nm or less are more closely resembling the carbon nanotubes, at least about 50% of the total number of carbon nanofiber fragments are less than one length in length with ratios of aspect less than 20. The above-described processing can be applied to carbon fibers or carbon nanofibers, and is independent of the manner in which the precursor fiber was produced. By way of non-limiting example, electrospinning can be conveniently used for nanofibers below about 1 miera, and preferably below 100 nm, while conventional spinning can be used to obtain material with diameters normally above 1 miera approximately, more regularly with finer diameters of about 5 to 10 microns. For embodiments involving electrospinning, the nature of the polymeric material or combination of said materials subjected to Electrohilatura is not limited, although the materials must be susceptible to electrospinning and carbonization. All kinds of polymeric materials that meet these criteria are contemplated for use according to the present invention. In some embodiments, the polymeric material comprises polyacrylonitrile or PAN. Wound fibrous materials, comprised of catalytically mesoporous activated carbon nanofibers according to the present invention, can have an engineered aspect ratio ranging from symmetric particle type (aspect ratio 1) to very filamentous (aspect ratio above) of one hundred and even thousands), a porosity of material from hollow to volume constructed by engineering resulting from the packing of fibers, and also a pore size distribution of surface built by engineering. Electrohilated nanofibers catalytically activated can approximate carbon nanotubes in diameter, but unlike nanotubes they can contribute to more mesoporous activated surface area. Unlike nanotubes, they can be manufactured in arbitrary length distributions by chemical milling, mechanical milling, or simply without milling. Therefore they represent a full scale of engineering choices to produce an activated carbon material optimized for a purpose in a particular device. An electrode incorporating the features of the present invention, suitable for use in a capacitor or other electrochemical devices, includes a thin sheet of current collector, cover with a fibrous material of substantially mesoporous activated carbon fiber, nanofiber, or fragments with suitable aspect ratio in electrical contact with the current collector. As used herein, the term "mesoporous" refers to pores between about 2 nm and about 50 nm, inclusive. Preferably, the nanofibers comprise diameters that are preferably about 100 nm or less, with aspect ratios of 20 or less, and the resulting fibrous material preferably comprises a thickness of about 100 microns or less, and preferably with a random packing porosity of hollow volume of 65% or less. In some embodiments, at least a portion of the nanofiber surfaces comprises one or more pores comprising maximum sizes ranging from about 3 nm to about 30 nm. EDLC electrodes are usually made of activated carbon bonded directly or indirectly over a metal sheet thin current collector, although metal oxides can be used. In accordance with the present invention, activated carbon materials prepared by the methods described herein can be applied to current collectors together with additional metal oxides or the like, for hybrid characteristics including improved pseudocapacitancy. A capacitor incorporating the features of the present invention includes at least one electrode of a type described herein. In some embodiments, the capacitor also comprises an electrolyte, which in some modalities are aqueous, in other modalities it is organic. In some embodiments, the capacitor exhibits double layer electrical capacitance. In some embodiments, particularly when residual metal oxide is present on the surface of the activated carbon fibrous material, the capacitor also exhibits pseudocapacitancy. Conventional carbon EDLC's with organic electrolytes use propylene carbonate or organic acetonitrile solvents and a standard fluoroborate salt. Some commercial carbon and metal oxide EDLC's use aqueous electrolytes based on sulfuric acid (H2SO) or potassium hydroxide (KOH). Any of these electrolytes or the like can be used according to the present invention. Since organic electrolytes have a lower conductivity than aqueous electrolytes, they have slower RC characteristics and higher ESR contributions. However, since they have breaking voltages greater than 3 V compared to 1 V of aqueous electrolytes, organics produce higher total energy density since the total energy is a function of the voltage to the square. The pores optimized for organics would optionally also work ideally for aqueous electrolytes, since the aqueous solvation spheres are smaller. This would allow to design devices for the requirements of the RC without importing the manufacture of the electrode, changing the electrolyte. Hybrid devices would naturally have a broader scale of total RC characteristics, since they combine the EDLC with the phenomenon capacitive PC The practical scale for use in hybrid electric vehicles is less than about 1 second to more than about 15 seconds, and for distributed energy less than about 0.01 seconds to more than about 1 second. The mesoporous carbon fibers or nanofibers, or their respective fragments, which incorporate the characteristics of the present invention, can be incorporated in all kinds of devices that incorporate conventional activated carbon materials or that it could be advantageous to modify them to incorporate activated mesoporous carbon materials. . Representative devices include, without limitation, all kinds of electrochemical devices (e.g. capacitors; batteries, including without limitation one side of a nickel hydride battery cell, or both sides of lithium ion battery cells; fuel cells, etc.). Such devices can be used without restriction in all kinds of applications including, without limitation, those that could potentially benefit from high energy and high energy density capacitors or the like. By way of illustration, the devices containing activated carbon fibers incorporating the characteristics of the present invention can be included in all kinds of vehicles (for example as elements in capacitors or batteries, or electrical combinations thereof, which optionally can be coupling with one or more additional components including, without limitation, capacitors, batteries, fuel cells or the like); electronic devices (eg computers, mobile phones, assistants personal digital, electronic games and the like); any device for which a combination of battery and capacitor (combining the energy density of the batteries with the energy densities of the capacitors) is desirable, including an uninterruptible power supply (UPS) to accommodate transient power surges and power failure stabilizations, wireless drills, and the like; any device that can advantageously contain a conventional batcap device (i.e., a device system that provides a capacitor to handle the energy density and a battery to provide power density, wired in parallel); and similar. In some embodiments, a device incorporating the features of the present invention comprises a capacitor used in a vehicle, including without limitation an electric vehicle and hybrids thereof. Representative vehicles for use in accordance with the present invention include, without limitation, automobiles, motorcycles, scooters, boats, airplanes, helicopters, airships, space shuttles, human carriers such as those sold by Segway LLC (Manchester, NH) under the trademark. SEGWAY, and similar. The individual processing actions used in the methods embodying the features of the present invention-spinning, electrospinning, organometallic solvent coating, carbonization, activation and grinding-are well understood in the art and have been fully described in the references cited herein. Each of the patents, patent publications and other references of the literature cited is it is incorporated herein by reference in its entirety, except that in the case of any disclosure or inconsistent definition of the present application, it is considered that the disclosure or definition of the present application prevails. The electrospinning technique, which usually includes the creation of an electric field on the surface of a liquid, allows the production of very fine fibers that can be collected and formed into networks. This technique, well known, and the representative apparatuses for its realization, have been described for example in the US patents. UU Nos. 6,753,454, Smith and others; 6,713,011, by Chu et al .; 6,790,528, by Wendorff et al .; and 6,616,435, by Lee et al., as well as in the US patent publication. UU No. 2005/0025974 A1, by Lennhoff. Additional information can be found in the Journal of Raman Spectroscopy, 2004, 35, No. 11, 928-933; Journal of Applied Polymer Science, 2005, 96, No. 2, 557-569; Applied Physics Letters, 2003, 83, No. 6, 1216-1218; and IEEE Transactions on Nanotechnology, 2003, 2, No. 1, 39-43. Alternatively, nanofibers can be prepared by decomposition of methyl alcohol, as described in Applied Physics Letters 2002, 81, No. 3, 526-528. The carbonization and activation techniques described above can be carried out using any of the known techniques described in the literature. By way of example, various methods that may be used in accordance with the present invention include, without limitation, those described in US Pat. UU Nos. 6,737,445, Bell and others; 5,990,041, Chung et al .; 6,024,899, by Peng et al .; 6,248,691, of Gadkaree and others; 6,228,803, by Gadkaree et al .; 6,205,016, by Niu; 6,491, 789, de Niu; 5,488,023, from Gadkaree et al .; and also in the US patent publications. UU Nos. 2004/0047798 A1, from Oh et al., 2004/0091415 A1, from Yu et al., And 2004/0024074 A1, from Tennison et al. Additional information can be found in Chemical Communications, 1999, 2177-2178; and Journal of Power Sources, 2004, 134, No. 2, 324-330. As an illustration of the utility of the invention described herein, it is known that the total capacitance of an ELDC is a direct linear function of the adequate available surface area, defined as the total surface area greater than the solvating sphere., or approximately 3 nm for organic electrolytes. The equation that governs this is: C / A = e / (4 * p * d) (Eq 1) where C is the capacitance, A is the usable surface area, e is the relative dielectric constant of the electrolyte, and d is the distance from the surface to the center of the ionic layer (Helmholtz) in the electrolyte. For any given electrolyte and salt solvent, e and d are fixed, so that the right side of the equation is true constant k. Substituting and rearranging, C = kA (Eq.2) In this way, doubling the usable surface area effectively doubles the capacitance. For any fibrous material, the total surface area in a given volume is: S = N * A (Eq. 3) where S is the total area in square units, N is the number of fibers in the volume, and A is the surface area per fiber in square units. This equation is an approximation for the ELDC capacitors, since the points of contact of the individual particles may not satisfy the requirement to be greater than the solvation sphere of the electrolyte. The importance of this depends on the geometry of the material as shown below. The surface area of the fiber, in turn, depends on whether it is smooth (ie carbon nanotube or inactivated carbon fiber) or rough (activated carbon fiber). The number of fibers in a volume depends on its geometry and the filling conditions of the volume. The density of the fibers packaged in parallel is much higher than the randomly packaged fibers themselves. With current methods of manufacturing capacitor electrodes, solvent deposition or suspension of random fiber fragments is possible, as an extension of particulate carbon deposition (see for example U.S. Patent No. 6,627,252). This was also the reported method for the experimental carbon nanotube capacitor electrodes made at U. Cal. Davis, at Georgia Tech, and at the Posnan University in Poland. The proportion of any volume (cubic units) occupied randomly by the particles of a material of a certain geometry is known as its random packing density. The porosity of this volume of material is 1 - random packing density. Both are dimensionless volume / volume relationships. There are many theoretical and empirical studies on random packing density. For straight fibers, the ideal form of approach is a cylinder of a certain diameter D and length /, with an aspect ratio "a" defined as L / D. There is no perfect analytical solution of random packaging. An approximation commonly used for minimum porosity, based on excluded volume considerations, is: Porosity > 1 - 11 / (2a + 6 + (TT / 2a)) (Eq.4) In this way, the lower aspect ratios represent a more dense packing to a certain extent. Several independently derived mathematical models suggest minimum porosity and maximum density at fiber aspect ratios of around 2 to 5. At the opposite extreme, the previous approximation suggests the zero trend of the random packing density as the aspect ratio tends to infinite. This has been mathematically tested and verified empirically. The density of random packing is a purely geometric phenomenon and therefore invariable of the scale. The only variable that matters is the aspect ratio of the cylinder. For a general reference see "Predicting Packing Characteristics of Particles of Arbitrary Shape", by Gan et al., KONA, 2004, 22: 82-90. This idealization is not strictly true for carbon fibers, since microphotographs of carbon nanotubes and Carbon nanofibers show a considerable curvature of long filaments. For any fiber stiffness measured by the modulus of elasticity (or Young's modulus), the lower the aspect ratio, the more comparatively rigid the fiber will be (since the maximum leverage of one force on the fiber is reduced proportionally ), and the approach to a rigid cylinder will become truer. For example, carbon nanotubes are very rigid but also very thin, with high aspect ratios that allow them to bend them with reasonable forces despite their comparative rigidity. The Young's modulus of the single wall carbon nanotube is 1054 Gpa (gigapascals). For multipared carbon nanotubes it is almost 1200 Gpa. Comparatively, for the diamond it is 1200, for steel 190-210, for high strength concrete approximately 30, for oak 11, for nylon 3 and for rubber 0.01. A conventional commercial PAN-activated carbon fiber with an average diameter of 7-9 um (AGM-94 and AGM-99 from Asbury Graphite Mills, Inc.), has a Young's modulus that varies from 180 to 260, depending on the degree of Activation and purity of coal. Several sources report actual average diameters and lengths (and thus aspect ratios) for multi-wall carbon nanotubes. The ANI defines multipared carbon nanotubes as 1 to 50 nm in diameter and 10 to 100 um in length. Mitsui Chemical (in Minatec 2003 in Grenoble, France) reported the bulk production of multipared carbon nanotubes with average diameters of 20 to 50 nm and an average length of several um, by means of a chemical vapor deposition (CVD) process .

Nanocyl in Belgium offers experimental quantities of multipared carbon nanotubes with diameters ranging up to 40 nm with average lengths of up to 50 um, produced by their CVD process. Therefore, with the current production methods, the typical aspect ratios of carbon nanotubes are substantially greater than 100, and these can practically not be ground to lower aspect ratios with any currently known technology, given their resistance to very high tension. This implies that a low random packing density, a porosity of high fibrous material and a correspondingly reduced total surface area per unit volume of material can be achieved, as compared to what could be obtained with shorter fibers of similar diameter. Mitsui reported that its multipared carbon nanotube material had a measured bulk density of 0.01 to 0.03 g / cm3, compared to a "true" density of 1.9 to 2.0 g / cm3 (the equivalent volume of graphite). Single walled carbon nanotubes have a calculated ideal maximum density of 1.33 g / cm3, caused by the nature of the carbon bonds that produce the smallest possible cylinder diameter. This value is approximate, since it is dependent on chirality. This means that the smallest diameter of single wall carbon nanotubes is about 2/3 of the carbon (the rest is the middle hole). The multipared carbon nanotubes of smaller diameter are denser, since they have more carbon walls that wrap around the same tubular hole. In materials of fibrous carbon nanotube, the interfiber porosity will dominate the intrafiber gaps, given the three orders of magnitude difference in the scale. The randomly packaged interfiber porosity of the Mitsui product, corrected for the minimum intrafiber cupping of the single-wall carbon nanotube, is from 99.2% to 97.7%, based on its reported measurements, precisely as mathematical models of cylinder packing prediction. high aspect This, in turn, demonstrates that a rigid cylinder model, while not allowing bending, is a reasonable approximation for real carbon nanotubes. Not surprisingly, Frackowiak and others reported that ELDC devices made using multilayer carbon nanotube mesoporous "entanglement" had a capacitance that varied widely from 4 to 135 F / g, highly dependent on the density of the multipared carbon nanotube and of post-processing (densification) (Applied Physics Letters, October 9, 2000, 77 (15): 2421-2423). Indeed, the inability to pack randomly (by means of solvent deposition) such comparatively rigid fibers with high aspect ratios, counteracts the advantage of more surface of finer fibers. Experimentally there should be different real random packaging in different small samples, as reported by Frackowiak. For fibrous materials according to the present invention, an appropriate volume of materials for comparative performance analysis is equivalent to that set forth for example in U.S. Pat. UU Do not. 6,627,252, using thicknesses of 0.1 mm or 100 μm carbon film. A cubic reference volume of electrode carbon material for an ELDC (above the metal current collector) is 100 cubic cubic meters, or (1 E + 2) ** 3, or 1 cubic E + 6 cubic meters. To apply the cylinder randomization model to equation 3, the volume (V) of a cylinder approximated by a fiber of radius r is: V = (tt * (r) ** 2) * L (eq. The total surface area (A) of the cylinder including the ends (which count for the capacitance) is: A = 2 * rr * r * L + 2 * rr * r ** 2 (ec 6) With a catalytic activation using metal oxide nanoparticles with a diameter greater than the minimum mesopore size, the resulting pores can be idealized as truncated inverted cones, with the widest part on the surface of the fiber and the narrowest part of the particle to penetrate deeper below the surface. The particle does not catalyze a tubular "cavity" since ordinary activation will continue to erode the coal sides of the pit, even as the depth of the pit increases due to the catalytic activation of the particle. The resulting pore volume idealized as an inverted truncated cone is simply the partially larger imaginary cone volume, minus the volume of the imaginary cone not recorded below the nanoparticle in the truncation. The formula for the volume of any cone is: V = 1/3 * p * (r ** 2) * h (eq 7) where h is the height of the cone (sometimes called altitude) in the center (not the height of the slope). This height is a function of the rate of catalytic activation by the metal oxide nanoparticle compared to the uncatalyzed activation rate of carbon exposed on the walls of the hole made, and computable by simple caltion of any respective rate of activation and size of particle. This summed volume for all pores approximates the degree of engraving (percentage of eroded coal (weight equivalent to volume in a uniform material), or percentage of activation consumption). The surface area of the idealized inverted truncated cone "pore" is the surface of the largest cone minus the surface of the tip cone not completed, plus the cross-sectional area in the truncation. The surface area of a cone that excludes the base is: A = p * r * ((r ** 2 + h ** 2) 1/2) (Eq. 8) The area of the truncated cone side is due add the area of the circle in the narrow background of the truncation, given by: A = tr * (r ** 2) (eq.9) which is the transverse nanoparticle area assuming a spherical particle with cirr cross section. The additional total surface area to which said idealized pores contribute depends on how the pores populate the surface, and also the depth and radius of the pore. The limit case is that of non-overlapping pores of arbitrary depth (approximately ideal oxide spacing for any activation condition can be imagined as a function of the absolute size of trapped organometallic complexes, or of the degree of uniform dilution in solvent as contemplated in this invention). For idealized truncated cones, it is approximated by its circle bases of a certain radius, covering the fiber cylinder surface as much as possible (but not overlapping), which when unwound is a certain rectangle. The actual coverage percentage depends on whether the circles are of the same radius or not. With the actual processing, they would not be the same. Furthermore, with the actual processing, the pores would randomly overlap to a certain degree as a function of the uneven distribution of particles at the nanoscale, and would therefore create less total surface area than the idealized model. But as a first approximation using ordinary coverage of equal circle diameters (coins on a flat surface), in a 3d area by 3d there can be only 7 full circles of diameter d. This means that the coverage density is limited by: Covered ratio = 7 * 77/36, since d / 2 is equal to ary 3d * 3d = (3 * 2 * r) ** 2 Proportion not covered residual = (36- 7 * p) / 36 (Eq. 10) For any idealized cone "pore" and cylinder "fiber", these equations allow a computable estimate of the proportion of total area covered by non-overlapping pores, the total number of pores (the area divided by the area of a single pore base) and, for application of the volume and surface equations for arbitrary truncated cones, the eroded volume of material and therefore the degree of activation and the resulting total surface area per fiber.

Caltion Examples Metal oxide nanoparticles of 10 nm diameter and a 2x or 5x ratio of catalytic / non-catalytic activation rate were modeled to demonstrate the increase in surface area of fibers and fibrous materials made by means of the present invention . These particle sizes and reaction rates are reported or inferred from the Asian coal research. The pore diameter modeled at the base of the idealized cone (surface of the fiber) is 30 nm. This is approximately the optimal maximum pore size of ELDC that has been reported experimentally. The total surface area of the modeled material of commercially available multi-wall carbon nanotubes, such as those evaluated above, is compared with the total surface areas of materials made of 100-nm electrospun fibers ground into fragments with two aspect ratios, 20 (length 2 μm) and 10 (length 1 μm), with and without idealized activation. These are aspect ratios higher than the optimally dense ones, but are obtainable with the current milling equipment, such as the MaxxMill agitated mill from Noli Gmbh with advanced air classifier, which can achieve a d50 of 3 microns at speeds of production of 150 kg / h of raw materials of 2 mm fries. The actual packing of ground fiber fragments would be denser than calculated (a potential benefit) due to the proportion of fines with lower aspect ratios, in addition to the potential contribution of bending. Also, surfaces of conventionally rotated activated carbon fibers with a diameter of 5 microns (approximately the lower limit of the diameters of conventional technology) were analyzed, because the maximum aspect ratio of random packing can be easily modified by grinding. Below are shown in the table the total available surface areas modeled (in total square micras per 100 cubic microns of fibrous material).

In this way, due to the better random packing density, even the largest diameter non-activated electrospun fibers, but substantially lower aspect ratio than the "commercial" multilayer carbon nanotubes, offer 1,534x or 2,095x the area of total area per unit volume and therefore capacitance, compared to currently available nanotubes deposited by means of equivalent procedures. The non-activated fiber spun conventionally (5 microns) is only about 6% of multipared carbon nanotubes even with optimum aspect ratios for maximum random packing, and therefore would work only from % to 35% as well as conventional highly activated particles. Since it has been experimentally demonstrated in several laboratories that the multipared carbon nanotube material deposited by solvent is 5 to 8 times better than the best conventional activated particulate carbon electrodes, even inactivated, the carbon fibers electrohilated in relation to lower aspect offer an improvement of 8 to 16 times over conventional electrode materials, when processed in fragmented fibrous material with suitable aspect ratios as contemplated by this invention. As a further benefit of the electrode materials made in accordance with this invention, the fibrous packing creates porosity through many large interconnected channels, such that the total depth of the material is essentially available to the electrolyte and therefore is utility. The packing of irregular particles of different size distributions creates a denser material with many more points of contact, rendering a non-negligible fraction of the interior particle surface geometrically useless, as well as flow "blocker" into the finely packed material, which it is part of it inaccessible to the electrolyte. Ground fragments of electrohilated activated carbon fibers are molded to have up to 2000x the proportional total surface area and capacitance of multi-walled carbon nanotubes, and more than three orders of magnitude better performance than particulate carbons. As a further advantage of the invention, the relatively light activation (less than 20 percent consumption) takes less time, therefore is less expensive, subjects the fiber to less graphitization and fragility, and allows the fiber to remain more conductive than with conventional high degrees of activation in the consumption scale of 30-60%. The mesoporous fiber fragments of conventional diameter catalytically activated modeled in accordance with this invention, due to their greater mesoporous surface area and almost optimal packing density, are modeled to be from 76x to 160x the area and the capacitance of carbon nanotubes of multipared, and therefore more than two orders of magnitude better than conventional particulate activated carbon materials. Extremely gentle modeling activation (around 1% consumption) suggests that even more total mesoporous surface could be created with moderate activation (on the 20% consumption scale), easily obtainable by means of higher temperatures or longer activation times. This computational result also suggests another reason why Hong had little success with the additional catalytic activation of previously activated carbon fiber, regardless of the increased cost of that proposal. The second activation of 20-30% of consumption, using a coating of very fine particles of size smaller than 2 nm as inferred from its experimental method and results, destroys surface characteristics of the initial activation (surface reduction), at the same time that adds new but very small mesopores to the macro features (surface increase). Therefore, its catalytic result was only 11% more of total surface than with simple additional ordinary activation, achieved with a mesoporous distribution that does not vary significantly in mesopores of 5 nm or larger than non-catalyzed comparison activations. As another aspect of the invention, a greater surface roughness can be created by means of a mixture of catalysts with two or more different proportions, preferably also with different sizes of nanoparticle (larger particles for faster catalysts), using a consumption of total activation less than that required for the chemical grinding of fiber fragments. Computational models suggest that such differential catalytic activation would be particularly useful for maximizing the useful area of conventionally spun fibers of several microns in diameter. The above detailed description has been provided by way of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments illustrated herein will be apparent to those skilled in the art and remain within the scope of the appended claims and their equivalents.

Claims (31)

NOVELTY OF THE INVENTION CLAIMS

1. A method of preparing a carbon fiber, comprising: spinning a fiber of less than 10 microns in diameter, or electrospinning a polymer fiber with a diameter of less than about one millimeter of a polymeric material; carbonizing at least a portion of the polymer fiber to provide a carbon fiber; and catalytically activating at least a portion of the carbon fiber with catalytic nanoparticles of at least 2 nm average size, to form one or more mesopores on the surface of the carbon fiber.

2. The method according to claim 1, further characterized in that it comprises adding the catalytic material before or after forming the polymer fiber.

3. The method according to claim 1, further characterized in that the catalytic material is metal oxide nanoparticles.

4. The method according to claim 1, further characterized in that the metal oxide nanoparticles comprise nickel, iron, cobalt, ruthenium oxides, or combinations thereof.

5. The method according to claim 1, further characterized in that the diameter of the polymer fiber is less than about 100 nm.

6. The method according to claim 1, further characterized in that it comprises adding the catalytic material before or after carbonizing the polymer fiber.

7. The method according to claim 1, further characterized in that it comprises coating at least a portion of the polymer fiber or carbon fiber with a precursor of catalytic material and, before activation, converting the material precursor catalytic in the catalytic material.

8. The method according to claim 7, further characterized in that the catalytic material precursor is a metal acetylacetonate or metal acetate.

9. The method according to claim 1, further characterized in that the activation comprises treating the carbon fiber with steam, carbon monoxide, carbon dioxide, or a combination thereof.

10. The method according to claim 1, further characterized in that the activation produces a carbon fiber having at least about 50% of the pore volume with a size ranging from about 2 nm to about 50 nm, and not more than about 25% of the pore volume with a size greater than about 50 nm.

11. - The method according to claim 1, further characterized in that the activation produces a carbon fiber with a volume of porosity comprised of more than about 35% mesopores.

12. The method according to claim 1, further characterized in that the polymeric material comprises polyacrylonitrile.

13. The method according to claim 1, further characterized in that it comprises breaking at least a portion of the carbon fiber to provide a plurality of carbon fiber fragments.

14. The method according to claim 13, further characterized in that the breaking comprises catalytically activating the carbon fibers with an additional catalyst different from the catalytic nanoparticles, in such a way that some of the pores dissect the fibers.

15. The method according to claim 14, further characterized in that at least about 50% of the carbon fiber fragments have aspect ratios of less than 20.

16. The method according to claim 1, further characterized because the electrohilatura step is done on a current collector. 17.- A carbon fiber with a smaller diameter of about 10 microns, with one or more mesopores, and with one or more mesoscale nanoparticles containing metal in the pores. 18. The carbon fiber according to claim 17, further characterized in that the metal-containing nanoparticle comprises a transition metal. 19. The carbon fiber according to claim 17, further characterized in that the metal-containing nanoparticle comprises a metal oxide. 20. The carbon fiber according to claim 19, further characterized in that the metal oxide comprises a nickel, iron, cobalt, or ruthenium oxide. 21. The carbon fiber according to claim 20, further characterized in that the metal oxide is nickel oxide. 22. A fibrous material comprising a plurality of the carbon fibers prepared by means of the method claimed in claim 1, or fragments thereof, wherein said material is woven or non-woven. 23. The fibrous material according to claim 22, further characterized in that it exhibits pseudocapacitancy. 24. The fibrous material according to claim 22, further characterized by being randomly packed with a suspension or solvent deposition. 25. A fibrous material comprising a plurality of the carbon fibers of claim 17, or fragments thereof, wherein said material is woven or non-woven. 26. The fibrous material according to claim 25, further characterized in that it exhibits pseudocapacitancy. 27. The fibrous material according to claim 25, further characterized in that it is randomly packaged from a suspension or solvent deposition. 28. An electrode comprising: a current collector; and the fibrous material of claim 22 in electrical contact with the current collector. 29. An electrode comprising: a current collector; and the fibrous material of claim 25 in electrical contact with the current collector. 30. A capacitor comprising one or more carbon fibers prepared by means of the method of claim 1, or fragments thereof. 31. A capacitor comprising one or more of the carbon fibers of claim 17, or fragments thereof.