Graphene-based precursor structures

Abstract

A method of improving catalyst accessibility of a carbon precursor, the method comprising: accelerating a plurality of electrocatalyst clusters to a graphene-based multilayer precursor structure by applying a voltage such that the graphene-based multilayer precursor structure is exposed to the clusters, so as to produce both: mechanical defects in the surface of the graphene-based multilayer precursor structure; and a population of deposited electrocatalysts of near uniform size at a near uniform depth in the graphene-based multilayer precursor structure.

Description

Technical Field

[0001] This disclosure relates to graphite precursor structures for use in the manufacture of catalyst support components (e.g., for fuel cells), and methods for modifying said graphite precursor structures to alter one or more properties. Background Technology

[0002] Hydrogen technologies such as fuel cells and electrolyzers are gaining popularity due to their ability to convert stored chemical energy into electricity or vice versa using water and hydrogen as a medium. However, many challenges remain and pose obstacles to their large-scale production. Besides the harsh environments of fuel cells and electrolyzers posing material selection challenges, the degradation of components such as catalysts and membranes needs to be addressed, as degradation affects the efficiency of hydrogen devices. Similarly, functional reliability and manufacturing economics need improvement. Summary of the Invention

[0003] In one embodiment, a method for improving catalyst accessibility to carbon precursors is disclosed. The method may include accelerating multiple electrocatalyst clusters toward a graphene-based multilayer precursor structure by applying a voltage, such that the graphene-based multilayer precursor structure is exposed to the clusters, to generate both: mechanical defects in the surface of the graphene-based multilayer precursor structure; and a nearly uniformly sized group of deposited electrocatalysts at a nearly uniform depth within the graphene-based multilayer precursor structure. The electrocatalyst clusters may be monodisperse, generated by an iso-energy beam. The electrocatalyst clusters may be polydisperse, generated by an iso-velocity beam. The method may also include selecting multiple electrocatalysts based on a target cluster size of less than 100 atoms. The method may also include selecting multiple electrocatalysts based on a target cluster diameter of about 2 to 5 nanometers. The voltage may be in the range of about 1 to 10 megavolts and from tens of kiloelectron volts per atom to tens of megaelectron volts per atom. The mechanical defects may include exposed lattice portions, resulting in increased porosity of the graphene-based multilayer precursor structure.

[0004] In another embodiment, a method for improving catalyst accessibility to carbon precursors is disclosed. The method may include repeatedly bombarding a graphene-based multilayer precursor structure with a set of electrocatalyst clusters selected based on at least one predetermined value to gradually increase the porosity of the structure while depositing the electrocatalyst clusters within the structure, the repeated bombardment comprising applying a constant ionization energy. The at least one predetermined value may include a target cluster size of less than 100 atoms. The at least one predetermined value may include a target cluster diameter of about 2 to 5 nanometers. The constant ionization energy may include a constant energy per atom. The constant ionization energy may include an energy constant regardless of the cluster size. The electrocatalyst clusters may be monodisperse clusters.

[0005] In an alternative embodiment, a method for depositing an electrocatalyst onto a carbon precursor is disclosed. The method may include providing electrocatalyst particle clusters based on the uniformity of cluster size. The method may further include accelerating the electrocatalyst particle clusters toward a graphene-based multilayer precursor structure by applying a voltage field in the range of about 1 to 10 megavolts and from tens of kiloelectron volts per atom to tens of megaelectron volts per atom. The method may also include colliding the accelerated electrocatalyst particle clusters with the graphene-based multilayer precursor structure to deposit the electrocatalyst particle clusters based on a depth deposition criterion. The uniformity of cluster size may include nearly uniformly sized clusters with a deviation of approximately ±1-5% of the average cluster size. The depth deposition criterion may include nearly uniformly sized deposited catalyst groups at nearly uniform depths within the carbon structure. The depth deposition criterion may also include non-uniformly sized deposited catalyst groups at multiple non-uniform depths. The clusters may be monodisperse. The method may also include increasing the number of mechanical defects in the carbon precursor. Attached Figure Description

[0006] Figure 1 A schematic diagram of a non-limiting example, a proton exchange membrane fuel cell, is shown; and Figure 2A , Figure 2B and Figure 2C Non-limiting examples of complex graphite structures according to one or more embodiments disclosed herein are shown. Detailed Implementation

[0007] Embodiments of this disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples, and other embodiments may take various and alternative forms. The drawings are not necessarily drawn to scale; certain features may be exaggerated or minimized to show detail of particular components. Therefore, the specific structural and functional details disclosed herein should not be construed as limiting, but should only serve as a representative basis for teaching those skilled in the art to employ these embodiments in various ways. As will be understood by those skilled in the art, the various features shown and described with reference to any of the drawings may be combined with features shown in one or more other drawings to produce embodiments not explicitly shown or described. The combinations of features shown provide representative embodiments for typical applications. However, various combinations and modifications of features consistent with the teachings of this disclosure may be desired for particular applications or implementations.

[0008] Unless explicitly indicated by example or otherwise, all numerical values ​​in this specification representing amounts of material or reaction conditions and / or conditions of use should be understood as being modified by the word “about” when describing the widest scope of this disclosure. Practice within these numerical limits is generally preferred. Furthermore, unless explicitly stated otherwise: percentages, “parts”, and ratio values ​​are by weight; descriptions of a suitable or preferred group or class of materials for a given purpose relating to this disclosure mean that a mixture of any two or more members of that group or class is equally suitable or preferred; descriptions of components in chemical terms refer to the components as they are added to any combination specified in the specification and do not necessarily preclude chemical interactions between the components of the mixture once mixed. Unless otherwise stated, weight percentages (wt.%) are based on the total weight of the substrate, and volume percentages (vol.%) are based on the total volume of the substrate.

[0009] The initial definition of an acronym or other abbreviation applies to all subsequent uses of the same abbreviation herein, with necessary modifications to apply to normal grammatical variations of the abbreviation as originally defined. Unless explicitly stated otherwise, the measurement of a property is determined by the same technique referenced previously or later for the same property.

[0010] It must also be noted that, as used in the specification and appended claims, the singular forms “a / an,” “an / an,” and “the” include plural objects unless the context clearly indicates otherwise. For example, referring to a component in the singular is intended to include multiple components.

[0011] As used herein, the terms “substantially,” “generally,” or “about” mean that the quantity or value in question may be a specific value or some other value in its vicinity. Typically, the term “about” indicating a value is intended to indicate a range within ±5% of that value. As an example, the phrase “about 100” indicates a range of 100 ± 5, i.e., from 95 to 105. Generally, when the term “about” is used, it can be expected that similar results or effects according to this disclosure can be obtained within ±5% of the indicated value. The term “substantially” may modify a value or relative characteristic disclosed or claimed in this disclosure. In such cases, “substantially” may indicate that the modified value or relative characteristic is within ±0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or 10% of that value or relative characteristic.

[0012] It should also be understood that an integer range explicitly includes all integers in between. For example, the integer range from 1 to 10 explicitly includes 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Similarly, the range from 1 to 100 includes 1, 2, 3, 4, ..., 97, 98, 99, and 100. Similarly, when any range is required, the intermediate number, which is the increment between the difference between the upper and lower limits divided by 10, can be considered an optional upper or lower limit. For example, if the range is 1.1 to 2.1, the following numbers could be chosen as the lower or upper limit: 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2.0. Likewise, whenever a list of integers is provided in this document, it should also be understood that the list explicitly includes the range of any two integers in that list.

[0013] In the examples described herein, concentrations, temperatures, and reaction conditions (e.g., pressure, pH, flow rate, etc.) can be implemented using values ​​plus or minus 50%, rounded or truncated to two significant figures. In an improved embodiment, concentrations, temperatures, and reaction conditions (e.g., pressure, pH, flow rate, etc.) can be implemented using values ​​plus or minus 30%, rounded or truncated to two significant figures. In another improved embodiment, concentrations, temperatures, and reaction conditions (e.g., pressure, pH, flow rate, etc.) can be implemented using values ​​plus or minus 10%, rounded or truncated to two significant figures.

[0014] As used herein, the term “and / or” means that all or only one element of the group may be present. For example, “A and / or B” means “A only, or B only, or both A and B”. In the case of “A only”, the term also covers the possibility that B is not present, i.e., “A only, but not B”.

[0015] It should also be understood that this disclosure is not limited to the specific embodiments and methods described below, as specific components and / or conditions may vary. Furthermore, the terminology used herein is for the purpose of describing particular embodiments of this disclosure only and is not intended to be limiting in any way.

[0016] The term "comprising" is synonymous with "including," "having," "containing," or "characterized by." These terms are inclusive and open-ended and do not exclude additional, unlisted elements or methodological steps. The term "comprising" may cover the phrases "comprising," "consisting of," or "substantially consisting of."

[0017] The phrase "consisting of..." excludes any element, step, or component not specified in the claim. When this phrase appears in a clause of the body of a claim rather than immediately following the preamble, it only limits the element set forth in that clause; other elements are not excluded from the claim as a whole.

[0018] The phrase “consistent essentially of…” limits the scope of the claim to the specified material or step, plus the material or step that does not substantially affect one or more basic and novel features of the claimed subject matter.

[0019] With regard to the terms “comprising,” “consisting of,” and “substantially composed of,” one of these three terms is used herein, and the subject matter of this disclosure may include the use of either of the other two terms.

[0020] The term "one or more" means "at least one," and the term "at least one" means "one or more." The terms "one or more" and "at least one" include "multiple" as a subset.

[0021] A description of a group or class of materials applicable to a given purpose in relation to one or more embodiments means that a mixture of any two or more members of that group or class is suitable. Furthermore, a description of a group or class of materials applicable to a given purpose in relation to one or more embodiments means that the group or class of materials may “comprise” any or all of the members of that group or class of materials, “consist of any or all of the members of that group or class of materials,” and / or “consist substantially of any or all of the members of that group or class of materials.” The initial definition of acronyms or other abbreviations applies to all subsequent uses of the same abbreviations herein, with necessary modifications to the normal grammatical variations applicable to the initially defined abbreviations. Unless expressly stated to the contrary, measurements of properties are determined by the same techniques referenced previously or later for the same property.

[0022] Chemical and electrochemical systems using hydrogen as a fuel source, whether in direct hydrogen combustion engines or fuel cells, are considered energy systems of the future. These hydrogen production devices are becoming increasingly popular due to their ability to generate clean energy. Such systems may include fuel cells, electrolyzers, and battery cells. Fuel cells, or electrochemical cells, convert the chemical energy of fuel (e.g., hydrogen) and oxidant into electricity through a pair of electrochemical half-reduction reactions (redox reactions), and have become an increasingly popular hydrogen fuel production technology. Fuel cells are now a promising alternative transportation technology capable of operating without toxic or greenhouse gas emissions. An electrolyzer is an electrochemical device designed to convert electricity and water into hydrogen and oxygen, which can then be used for energy storage. Electrolyzers utilize electrolysis to produce hydrogen. Besides fuel cells, electrolyzers can be used in other applications, including industrial, residential, and military applications, as well as in technologies focused on energy storage, such as grid stabilization using dynamic power sources including wind turbines and solar cells, or localized hydrogen production.

[0023] Non-limiting examples of fuel cells include proton exchange membrane fuel cells (PEMFCs). Utilizing the electrochemical reaction of H2 and O2 gases, PEMFCs offer a practical energy efficiency exceeding 60%, with H2O being the only product. The rapid diffusion of H- ions allows PEMFCs to operate at relatively low temperatures of around 100°C. In contrast, solid oxide fuel cells and molten carbonate fuel cells operate at around 600°C and above.

[0024] exist Figure 1 A non-limiting example of a fuel cell, a PEMFC, is shown in the figure. Figure 1As shown, PEMFC 110 includes an anode catalyst support 112 coated with an anode catalyst layer 114 formed of an anode catalyst material and a cathode catalyst support 16 coated with a cathode catalyst layer 118 formed of a cathode catalyst material. A polymer electrolyte material (PEM) 120 extends between the anode catalyst support 112 and the cathode catalyst support 116. The cathode catalyst material may be dispersed at the interface between the PEM 120 and a current collector (not shown) supported by the cathode catalyst support 118. The current collector may be a porous carbon current collector. The anode catalyst layer 114 is positioned between the anode catalyst support 112 and the PEM 120. The cathode catalyst layer 118 is positioned between the cathode catalyst support 116 and the PEM 120. Anode 122 may generally refer to the anode catalyst support 112 and the anode catalyst layer 114. Cathode 124 may generally refer to the cathode catalyst support 116, the cathode catalyst layer 118, and the current collector (not shown). PEMFC 110 also includes first and second gas diffusion layers (GDL) (not shown). The first GDL is adjacent to the outer surface 126 of the anode catalyst support 112, and the second GDL is adjacent to the outer surface 128 of the cathode catalyst support 116.

[0025] Despite their advantages, PEMFCs' high production cost and relatively poor durability limit their application in energy plants and more affordable transportation technologies. For example, the cost of platinum (Pt) / carbon (C) electrocatalysts in PEMFC cathodes is at least half the production cost of PEMFCs, while the electrochemically active surface area (ECSA) of Pt catalysts deteriorates significantly during cycling (e.g., 50% or more).

[0026] Optimizing the microstructure of catalyst supports is a promising step towards improving the durability and reducing the cost of PEMFCs. Various forms of carbon have been explored and tested for applications in PEMFCs, including catalyst support materials. While many types of supports are carbon-based, studies have confirmed that differences in carbon structure, morphology, allotropic forms, etc., affect the properties and capabilities of the support. Therefore, not only the type of carbon, but also production conditions and variations can influence its suitability for specific applications. For example, many graphene and graphite structures have been identified and can differ significantly in properties such as electrical conductivity, elasticity, tensile strength, and thermal conductivity.

[0027] Optimizing the carbon support for Pt catalysts is a promising step towards improving the durability and reducing the cost of PEMFCs and other electrochemical devices employing carbon-based electrocatalyst supports. In the optimization process, the correlation between the surface area of ​​the carbon support and the ECSA of the Pt catalyst deposited on it can be considered. For example, when applying the same weight percentage of Pt loading, a larger surface area of ​​the carbon support results in a larger ECSA for the Pt catalyst deposited on it. This trend may be due to the uniformly small (e.g., average diameter of approximately 3 nm) size of Pt nanoparticles and their uniform distribution on carbon supports with relatively large surface areas. Although Pt / C electrocatalysts with large surface area carbon (HSAC) achieve relatively high ECSA at lower Pt loadings, they still suffer from the same or similar severe ECSA degradation during cycling as Pt / C electrocatalysts with small surface area carbon (LSAC). One suggestion for improving the cycling stability of Pt / C is to replace oxidizing amorphous carbon with less reactive graphitized carbon.

[0028] One proposed method for fabricating graphitic carbon with very large surface areas involves a silver template approach. According to this method, mesoporous carbon nanodendritic (MCND) structures are synthesized with primary particles containing bubble-like hollow graphitic carbon nanoparticles (HGCNs) exhibiting surface pores. While typical HGCNs have wall thicknesses exceeding 5 nanometers (e.g., more than 10 graphite layers), MCND structures can have monolayer graphene walls, resulting in very large surface areas (e.g., 1,610 m² / g).

[0029] However, preparing carbon precursors for the fabrication of low-reactivity graphitized carbon with large surface areas, such as amorphous carbon clusters with diameters less than 2 nanometers, has proven difficult. The difficulties in graphene production are generally related to scalability and the requirement for defect-free graphene materials. Specifically, producing graphene with various configurations using scalable basic mechanical and chemical methods remains a challenge.

[0030] In one or more embodiments, a method for producing a carbon precursor for manufacturing a graphitized carbon catalyst support is disclosed. In one non-limiting embodiment, the process (described in detail below) includes the steps of utilizing defective graphene sheets, modifying these graphene sheets with additional carbon structures, optionally introducing additional defects, and wrinkling the modified graphene sheets into a carbon precursor.

[0031] The resulting carbon precursors may include wrinkled, modified graphene structures. The resulting carbon precursors may include graphitic carbon nanoparticles having a monolayer graphite structure (e.g., a shell or wall). These precursors may include monolayer structures. These precursors may include two-dimensional materials, near-two-dimensional materials, or a combination of both. These precursors may include graphitic nanoparticles having one or more graphitic materials (e.g., carbon atom crystals formed in a hexagonal structure), amorphous carbon structures, nanoclusters, or carbon materials having one or more dimensions in the nanoscale range of 1 to 100 nanometers, onion-like graphitic carbon mesostructures, hollow irregular-shaped mesostructures, or combinations thereof. These carbon precursors may include crystalline structures, amorphous materials, or combinations thereof. These carbon structures may include complex structures with tortuous geometries, where multiple bends and turns within a wavy surface topology result in pockets, cavities, curvature, and different orientations of the inner and outer surfaces.

[0032] These carbon precursors can include nanoscale, mesoscale, and microscale (ranging from nanometers (10⁻⁻⁴)). 9 From meters to micrometers (10⁻) 6 The structures, or combinations thereof, can be irregular, asymmetrical, curved, have one or more curvatures, undulations, holes, voids, defects, or combinations thereof. These structures may include an irregular number of pentagons and heptagons throughout the structure or at its edges. The non-limiting example structures disclosed herein... Figure 2A , 2B As shown in 2C.

[0033] These carbon precursors may have very large surface areas in the range of about 500 to 3000, 800 to 2500, or 1000 to 1400 square meters per gram. This very large surface area may be about or at least about 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, or 3000 square meters per gram.

[0034] These carbon precursors may have densities of about 0.7–3.5, 0.9–3.2, or 1.2–3.0 g / cm³. This density may be about, at least about, or at most about 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3.0 g / cm³.

[0035] These carbon precursors can be used to produce one or more components of chemical or electrochemical devices, for example Figure 1 The PEMFC is schematically depicted herein. Non-limiting examples of uses for carbon precursors manufactured according to one or more embodiments disclosed herein may include large surface area carbon applications, carbon supports for electrocatalysts in fuel cell cathodes and anode materials, carbon materials for supercapacitors, lithium-ion batteries, lithium-air batteries, CO2 reduction batteries, etc.

[0036] Unlike many previously explored applications, these carbon structures can be defective, and these defects are intentionally used as part of the manufacturing process disclosed herein.

[0037] The process may include multiple steps. The first step may include obtaining graphene as a single-layer atomic carbon two-dimensional material, a low-number multilayer graphene material (including a few-layer graphene sheet with no more than 10 layers), or a combination thereof. Graphene is a two-dimensional carbon material in which each carbon atom is spaced 2s, 2p... x and 2p y The orbital's sp² hybridization is bonded to the three nearest-neighbor carbon atoms, and the 2p orbital... z The orbitals form delocalized π and π* bands perpendicular to the graphene plane. Graphene is a two-dimensional crystal, a solid material consisting of a single layer of atoms arranged in an ordered pattern. Due to its two-dimensional nature, graphene exhibits strong bending wave properties, characterized by ripples and wrinkles. Primitive graphene is nonmagnetic and has a zero band gap.

[0038] The process may include the step of exfoliating graphite to obtain multiple graphene flakes. This exfoliation can be mechanical exfoliation, liquid phase exfoliation, layer-engineered exfoliation, large-scale chemical vapor deposition, etc.

[0039] These graphene sheets may include one or more structural defects, such as topological defects, single vacancies, multiple vacancies, multilayer exfoliation, foreign atoms, substituted impurities (e.g., boron (B), nitrogen (N)), line defects, grain boundaries, stacking faults, lattice breaks, Stone-Wales defects or crystallographic defects (including rotation of double-bonded carbon atoms that cause distortion of the hexagonal network), lattice irregularities, edge defects, edge reconstructions, grain boundaries, dislocations, distortions, dangling bonds, analogs, or combinations thereof. These defects may be two-dimensional, three-dimensional, or both. These defects may be intrinsic, intriguing, or both.

[0040] This process can utilize exfoliated graphene flakes with and / or without defects. This utilization can be indiscriminate, thus utilizing any or all graphene flakes obtained in the exfoliation step. Alternatively, the process can utilize more than 25%, 50%, or 75% defective graphene flakes, with the remainder being defect-free. The process can utilize only defect-free pristine graphene flakes. However, defective graphene flakes are more preferred. The process can utilize only graphene flakes with a specific type of defect as described above.

[0041] The process may include selecting graphene flakes based on one or more parameters, such as the final target density of the precursor (e.g., in the range of 1 to 3.5 g / cm³). In one non-limiting example, if the target precursor structure is to be an onion-like graphitic carbon mesostructure, a higher density exfoliated graphene flake close to 3.5 g / cm³ may be selected. In another non-limiting example, if the target precursor structure is a monolayer graphitic carbon mesostructure, a lower density exfoliated graphene flake close to 1 g / cm³ may be selected. Another parameter may be the size of the graphene flakes, which affects the final size of the precursor structure. These graphene flakes may be from about 0.005 to 500 x 10⁻⁶. 4 0.05 to 500 x 10³, or 0.5 to 500 x 10² µm².

[0042] In subsequent steps, the process may include modifying these graphene flakes. This process may include decorating the graphene flakes with one or more deposited structures. Decoration involves the deposition of material. Decoration may be performed to ensure specific length scales, preventing graphene and graphene-like flakes from stacking into higher layers (layers that do not anneal to the desired structure), to target the specific amorphous structure density disclosed above, or a combination thereof. The deposited material may aggregate on the surface of the graphene flakes. This deposition step results in the introduction of heterogeneity in the pore size distribution of the graphene flakes, and ultimately in the pore size distribution of the graphite precursor structure. In turn, the heterogeneity of the pore size distribution can provide preferred pathways for water and gas transport in the PEMFC catalyst layer. For example, large pores are preferred for water accumulation, while nanopores can be used for gas transport.

[0043] The deposited structures may include non-graphene carbon structures. Non-limiting examples of structures may include nanostructures, fullerenes or fullerene-like carbon spheres, such as C60 (a football-shaped molecule composed of 60 carbon atoms) to C80, Buckminster fullerenes, linked spherical dimers, heterofullerenes, endohedral metallofullerenes, fullerols, buckyball clusters, carbon nanorods, carbon nanotubes (single-walled and multi-walled, with armchair or zigzag configurations), spherical carbon nanoparticles, or combinations thereof. Fullerenes are allotropes of carbon whose molecules consist of carbon atoms linked by single and double bonds, forming closed or partially closed network structures with fused rings or five to seven atoms. Carbon nanorods are elongated particles ranging from about 10 to 120 nanometers in size, with a specific surface area of ​​about 30-70 m² / g. Carbon nanotubes are allotropes of carbon, tubes made of carbon having nanoscale diameters and regular hexagonal lattices. These non-graphene carbon structures may include one or more defects disclosed herein. Based on the total amount of non-graphene carbon structures deposited, at least about 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% may include at least one defect.

[0044] Because graphene and graphene-like structures typically exhibit high rigidity or stiffness, the process may include a secondary modification step. This secondary modification step can be performed to enhance the effect of subsequent wrinkling steps. The secondary modification step may include introducing or inducing additional defects in the graphene and graphene-like structures. These additional defects are designed to enable the graphene sheet to bend. The secondary modification step may include etching the graphene structure with acid, water vapor, plasma, or a combination thereof. The process may include controlling the density of additional defects to control the shape of the carbon nanostructure. For example, introducing a high defect density may result in a small primary structure, while a low defect density may result in a larger primary structure. These additional defects may further serve as catalyst attachment sites, improve ionomer interactions of the catalyst, thereby improving the catalyst layer quality, or both.

[0045] The process may then include the step of wrinkling the modified graphene sheets disclosed above. Wrinkling can refer to a process of structural deformation of graphene, which may result in the formation of wrinkles within the graphene structure, deformation from a two-dimensional to a three-dimensional structure, wrinkled shapes, folds, etc. Wrinkled graphene includes graphene sheets bonded by weak van der Waals forces.

[0046] The wrinkling step may include decorative graphene sheets with or without defects, undecorated graphene sheets with or without defects, or mixtures thereof. Wrinkling may be induced by the presence of a polar solvent (i.e., water, alcohol, or acetone) (because the polar interaction between the solvent and graphene induces wrinkling in unsupported graphene), charging of the graphene layer, alteration of the polarity / interaction of the solvent by additives (e.g., organic or inorganic salts), mechanical methods (i.e., ball milling or wet / dry mixing), or combinations thereof. This wrinkling step produces wrinkled modified graphene or graphene-like precursor materials as disclosed herein.

[0047] As described in this paper, the presence of defects (primary and additional) can provide additional sites that are easily deformable during the wrinkling step. Due to the presence of defects, the graphene hexagonal lattice may have structural deviations that weaken its strength, so the defect sites may deform in a way that differs from the rest of the lattice, potentially contributing to the generation of additional bending, folding, or deformation within the wrinkled structure.

[0048] These wrinkled structures can then be annealed. Annealing is a post-processing step performed for various reasons, such as to remove any residues generated during solvent application. Annealing can be thermal annealing, rapid thermal annealing, electro-annealing, etc. Annealing can be performed at approximately 200-2800, 500-1500, or 800-1200 degrees Celsius. 0 Annealing is performed at a temperature of C. Annealing can be performed under high vacuum or a reducing gas atmosphere (such as argon (Ar), hydrogen (H2), nitrogen (N2), or a combination thereof).

[0049] The process may include one or more verification steps to verify the defect density in unmodified graphene sheets, the defect density in modified graphene sheets, the defect density in the resulting wrinkled precursor structure, the density of the carbon precursor, the porosity of the carbon precursor, similar parameters, or combinations thereof. This verification may be performed, for example, by transmission electron microscopy, Raman spectroscopy, or electron energy loss spectroscopy.

[0050] The process may include steps of changing, adjusting, increasing, maintaining, or preserving the density, defect density, porosity, surface area, or combinations thereof of the graphene flakes or the resulting carbon precursor. The process may therefore include setting predetermined target values ​​for the density, defect density, surface area, porosity, or combinations thereof of the graphene flakes or the resulting carbon precursor, measuring or evaluating these target values ​​during and / or after the manufacturing process, monitoring whether the predetermined target values ​​are reached during the process, and correcting the target values ​​by adjusting the process, such as repeating one or more steps, taking corrective actions to achieve the predetermined values, or combinations thereof.

[0051] The process may include introducing a predetermined amount of defects and / or additional defects into the graphene flakes. This predetermined amount may relate to the percentage of the flakes affected by the defects and / or additional defects. Based on the total amount of graphene flakes available for the process, this percentage may be about, at least about, or at most about 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%. This predetermined amount may involve any number of defective graphene flakes, which are generated due to a deliberate step including defective graphene flakes or due to a deliberate step including not removing or excluding defective graphene flakes from the graphene flakes to be decorated, wrinkled, or both.

[0052] The above process steps can be performed prior to any catalyst deposition. Therefore, the resulting carbon precursor may not contain any catalyst material, such as noble metals, particularly platinum (Pt), palladium (Pd), their oxides, or combinations thereof. The catalyst can be deposited onto the precursor in subsequent processing stages.

[0053] The modifications to graphene disclosed herein affect the arrangement, structure, and properties of the resulting precursor structures. The wrinkled, modified graphene precursors disclosed herein may include undulations, pockets, recesses, shapes, and folds due to the processes disclosed herein, configured to capture and retain electrocatalysts. For example, the precursor may include wrinkled, partially closed fused carbon rings, pentagonal and heptagonal rings within a hexagonal lattice, wavy portions, hexagon-dominant networks (with interruptions, such as trenches, throughout the network), deformed portions forming a predominantly flat graphene lattice, including spherical protrusions, lumps, waves, pores, holes, similar structures, or combinations thereof.

[0054] Compared to unmodified wrinkled graphene and planar graphene sheets, the number of such catalyst retention sites within the precursor structure is enhanced. Therefore, the wrinkled structures disclosed herein may include multiple sites with high affinity for electrocatalysts.

[0055] Typically, the structures used as precursors for manufacturing carbon-based components are characterized by relatively low accessibility, such as the accessibility of their internal surfaces to catalysts. While the aforementioned preparation methods help to increase topological bias, thereby generating more sites with high affinity for electrocatalysts than normal, there is still a need to develop a method to improve the accessibility of the internal surfaces of carbon precursors prepared by alternative or conventional methods.

[0056] Furthermore, the problem of insufficient site accessibility is more severe for structures with multilayered configurations (such as onion-like layered mesostructures). This problem may arise if multilayered graphene is used instead of single-layered graphene in the precursor fabrication process.

[0057] Conversely, the overall activity of the electrochemical cell may be affected due to insufficient deposited catalyst quantity and / or higher catalyst concentrations being confined to a smaller support region. Consequently, catalyst particles may be more prone to agglomeration and the formation of larger, undesirable catalyst agglomerates or aggregates with a smaller electrochemical active surface area per unit volume.

[0058] Therefore, there is a need to develop a method to achieve better distribution of the catalyst within the available surface of the carbon precursor.

[0059] In at least one embodiment, a method for increasing the accessibility of the inner surface of a graphite carbon precursor structure is disclosed. The graphite structure can be the structure described above, or any graphite or graphene-based structure used as a precursor for manufacturing carbon components in electrochemical or chemical devices (such as PEMFCs). These structures can be defect-free, including defects, topological anomalies of the lattice, have an amorphous configuration, be irregular, asymmetric, or curved, and have one or more curvatures, undulations, pores, voids, etc. These structures can have nanoscale, mesoscale, or microscale dimensions, ranging from nanometers (10⁻⁻⁴). 9 From meters to micrometers (10⁻) 6 (meters). These structures can have large surface areas, densities, and other properties disclosed herein.

[0060] This method may include one or more steps described herein. At least some steps may be repeated once or multiple times. This method may include one or more loops. This method may include 1-10, 2-8, or 3-6 loops.

[0061] This method may include utilizing the unique volume-temperature properties of water, particularly its anomalous expansion. It is well known that at 4... 0 Above a certain temperature (°C), the volume of water increases with increasing temperature, but at a certain temperature (°C), the volume of water increases. 0 Below 4°C, the volume of water increases as the temperature decreases. Therefore, when the temperature drops to 4°C... 0 Below C and reaching 0 0 At temperature C, water expands rather than contracts. This behavior makes water less dense, and at 0°C... 0 At temperature C, water reaches its maximum volume as ice. In other words, between -10 and ±10 °C... 0 Within the range of C, the minimum volume of water (or the maximum density of water) is 4. 0 Implemented in C. Therefore, in 4 0 Below a certain temperature (°C), water confined within a space will expand and may disrupt the boundaries of the enclosed space containing the water.

[0062] In the initial step, the method may include wetting the precursor or providing water to a volume containing the low-accessibility precursor. This volume may be completely or partially enclosed in a container. Provision may include submerging, filling with liquid water, supplying water vapor, steam, spraying, or a combination thereof. Provision may mean accumulating water until at least a portion or all of the precursor is submerged in water. This provision may occur in approximately 4... 0 C occurs at the point of maximum density of water. This provision is customizable and includes selecting predetermined regions of the precursor to be opened or made more accessible to catalysts, electrolytes, analogues, or combinations thereof. Wetting may include wetting the inner surface, outer surface, or both of the structure.

[0063] This method may include one or more ways to reduce the surface tension of water. For example, the method may include using a surface tension greater than 4. 0 Water at temperature C is preferred because higher temperatures mean lower surface tension. In another example, the method may include the use of one or more additives specified for this purpose, such as one or more surfactants. In yet another example, the method may include electrowetting or applying a voltage to the system, resulting in a change in the wettability of the water caused by the applied electricity.

[0064] In subsequent steps, the method may include rapid cryowetting of the precursor. This step may also include thawing, melting, or sublimation without thawing or melting. Temperature fluctuations may be around -200°C. 0 C to approximately 10 0 C, Approximately -195 0 C to approximately 4 0 C or approximately -150 0 C to approximately 0 0 The system's freezing and thawing temperatures can be approximately, at least approximately, or at most approximately -200, -190, -180, -175, -170, -165, -160, -150, -145, -140, -135, -130, -125, -120, -115, -110, -105, -100, -95, -90, -85, -80, -75, -70, -65, -60, -55, -50, -45, -40, -35, -30, -25, -20, -15, -10, -5, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. 0 C. The method may include rapid freezing, flash freezing, external freezing, using liquid nitrogen or other methods to rapidly freeze-wet the precursor. Flash freezing involves rapid freezing, which involves low temperature or -196°C. 0Direct contact with liquid nitrogen at C. Rapid freezing can involve instantaneous freezing over a period of several seconds to approximately 30 to 60 seconds. Therefore, rapid freezing can be approximately 1 to 90 seconds, 10 to 60 seconds, or 20 to 30 seconds. Rapid freezing can be approximately or at most approximately 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89 or 90 seconds.

[0065] Freezing causes the water inside and around the precursor to expand. The size of the ice crystals formed is a function of the freezing rate. Faster freezing may produce smaller ice crystals, which are desirable for inducing small fractures in the precursor material. Therefore, rapid freezing causes ice crystals to grow throughout the structure, including inaccessible regions, which are the primary target of the process disclosed herein. Conversely, a slow freezing process may lead to the growth of large crystals and potentially ice crystals growing on the exterior of pores and cavities in the precursor structure, which is undesirable.

[0066] Therefore, the method may include steps of adjusting, maintaining, regulating, or changing the freezing rate to obtain ice crystals with a predetermined or target size. The target size may be at the nanoscale, microscale, or both.

[0067] The method may then include thawing or heating the frozen precursor. Thawing may be rapid, slow, one-time, staged, steady, or gradual, occurring approximately 25%, 50%, 60%, 70%, 80%, or 90% slower than freezing. Preferably, thawing is steady and slow. Alternatively, the method may include a sublimation step or a step of converting the frozen liquid into a gaseous state (without the fluid becoming liquid).

[0068] Changes in water volume caused by temperature variations are used to disrupt inaccessible structures, breaking them down and making them more open or accessible, leading to the formation of mechanical defects. Cracking and fracturing caused by flash freezing can expose previously inaccessible areas. Cracking and fracturing can alter the shape of the structure, including changes in the number and / or size of pores, angles between structural sections, lattice fracture, formation of trenches and pores within the lattice, increased spacing between layers in multilayer structures, and similar or combinations thereof. This process can increase porosity, decrease density, or both.

[0069] Rapid freezing and heating can be repeated multiple times. For example, freezing and thawing cycles can be repeated once, twice, three times, four times, five times, six times, seven times, eight times, nine times, ten times, or more. Repetition is particularly useful for precursors that may be more difficult to access through a single flash freezing procedure (such as multilayered onion-like graphite shells). Repeated cycles can progressively make the graphitic carbon structure more accessible. The final heating stage can be extended in time to facilitate the removal of water from the system.

[0070] This method may include removing water from the structure. Removal may include drainage, drying, similar methods, or a combination thereof. Removal may be rapid or slow.

[0071] Water is a suitable fluid for implementation in this method for several reasons. First, there is the aforementioned anomaly in water's expansion. Second, the presence of water is normal during fuel cell operation, thus minimizing the risk of contamination. Other fluids that expand in volume upon freezing, such as gallium, are also considered. However, the suitability of some substances may not be suitable for the fuel cell environment.

[0072] The type of water used in this method can be customized based on the desired outcome. For example, a large volume of pure or deionized water can be used to submerge the structure, resulting in the formation of crystals on the order of a few micrometers. The water can be tap water or filtered or otherwise relatively mineral-free. Water containing minerals is also considered, although the presence of minerals may lower the freezing point. The water may include additional components such as glycerol, glycerol, analogues, or combinations thereof.

[0073] After freezing and thawing, crystals may fracture at the microscale. Alternatively, water mixed with glycerol can induce even smaller crystals at the nanoscale, and thus smaller cracks in the carbon structure at the nanoscale. Furthermore, the structure can be initially exposed to vapor to partially wet it with pure water, thereby inducing fracture only in portions of the structure. Therefore, the method can include the steps of selecting and determining which portions of the structure to open or make more accessible, selecting and determining which crack sizes are desired, or both. Thus, the method allows for application-specific customization of results.

[0074] Furthermore, the method may include selecting, measuring, evaluating, inspecting, managing, or changing the porosity of a structure based on predetermined values. The method may include repeatedly checking the pore distribution, density, or both throughout the process. If the porosity should be increased to meet a predetermined target value, the method may include adding another freeze / thaw cycle. The method may include evaluating the initial porosity and increasing the porosity of the structure based on the initial porosity value.

[0075] As disclosed above, because the graphene-like structure of the precursor is very rigid, the method may include a step of introducing defects. More defective structures are more readily wetted. Therefore, the method may include increasing the incidence of defects within the structure through one or more steps disclosed herein.

[0076] Accessibility of the structures under discussion can be increased by alternative methods described herein. These alternative methods can be used in place of or in combination with freeze-thaw methods. The methods may include one or more steps described herein. The methods may include voltage-induced bombardment of the structure with platinum ions.

[0077] This method may include preparing the atoms of an electrocatalyst. The electrocatalyst may be platinum (Pt), palladium (Pd), its oxides, alloys, or combinations thereof. The preparation may include depositing or growing catalyst atoms into aggregates or clusters comprising nanoclusters, clusters, small nanoparticles with a size of less than about 250 atoms, or combinations thereof. Although the term "aggregate" is used herein, aggregates, clusters, nanoclusters, and small nanoparticles with a size of less than about 250 atoms, or combinations thereof, are equally covered by this disclosure. These aggregates or clusters may be monodisperse or nearly monodisperse, referring to relatively small size variations between aggregates. The size distribution may vary between about tens and hundreds of atoms. In a non-limiting example, the size distribution may include aggregates or clusters with a size of less than 25 atoms to more than 100 atoms. These aggregates or clusters may also be polydisperse, such that the size distribution of the aggregates or clusters is larger than the size distribution in the monodisperse group.

[0078] Once aggregates or clusters are formed, the method may include classifying or selecting aggregates or clusters based on one or more criteria. These criteria may include the objectives disclosed herein. Furthermore, the criteria may include factors to consider, such as efficiency. For example, smaller aggregates or clusters, such as those with tens of atoms, are easier to classify due to their smaller mass and easier to accelerate due to lower voltage requirements.

[0079] This method may include applying a voltage to aggregates or clusters to accelerate the catalyst aggregates or clusters toward a precursor structure. In a non-limiting example, the voltage may be provided by an electrostatic, van der Graff accelerator. This acceleration may result in bombardment of the structure with the aggregates or clusters. This bombardment may cause at least a portion of the aggregates or clusters to penetrate the surface and mass of the structure. This penetration may reach a specific depth discussed below. This bombardment may cause significant mechanical deformation and defects in the structure, thereby causing lattice deformation, the formation of pores, trenches, increased spacing between layers of the structure, etc., and consequently increasing surface accessibility to the catalyst.

[0080] The energy applied to the aggregates or clusters can be constant (regardless of the size of the aggregates or clusters) or constant per atom. The method may include ionizing the structure. Therefore, the method may include generating isoenergy beams of ions to produce constant energy (regardless of the size of the aggregates or clusters), or generating isovelocity beams to produce constant energy per atom. In the case of nearly monodisperse aggregates or clusters, isoenergy equals isovelocity because the aggregates or clusters consist of nearly the same number of atoms. In the case of polydisperse aggregates or clusters, isoenergy does not equal isovelocity. The term "equi" is related to the term "equal" derived from the Latin term "aequi". Alternatively, the aggregates or clusters may be monodisperse, but can be generated by the high-voltage glow discharge or arc discharge disclosed herein.

[0081] Non-limiting examples of voltage and energy / atom ranges can be approximately 1 to 10, 2-8, or 3-7 megavolts (MV) and tens of kiloelectron volts per atom (10s of keV / atom) to tens of megaelectron volts per atom (10s of MeV / atom), for example, 10 kiloelectron volts to 99 megaelectron volts / atom, 30 kiloelectron volts to 70 megaelectron volts / atom, or 40 kiloelectron volts / atom to 60 megaelectron volts / atom. The voltage and energy / atom can be approximately, at least approximately, or at most approximately 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 10 megavolts and 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1 250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 15000, 20000, 30000, 35000, 40000, 45000, 50000, 55000, 60000, 65000, 70000, 75000, 80000, 85000, 90000, 95000, or 99000 kiloelectron volts per atom.

[0082] The depth to which an aggregate or cluster stops during its journey through a carbon structure is a function of the aggregate's or cluster's energy. Therefore, the following is relevant: (A) Monodisperse aggregates or clusters and isoenergetic (or isovelocity) bombardment. In this case, the bombardment of aggregates or clusters will produce a nearly uniformly sized deposited catalyst population at a nearly uniform depth within the carbon structure; (B) Polydisperse aggregates or clusters and isoenergies. In this case, non-uniformly sized deposited catalyst masses are deposited at nearly uniform depths within the carbon structure; and (C) Polydisperse and isotropic. In this case, a non-uniformly sized group of deposited catalysts is deposited at non-uniform depths within the carbon structure.

[0083] The term "nearly uniform" can refer to a deviation from the average value of approximately ±1 to 5%. For example, a nearly uniform size population can refer to an average size of approximately ±1 to 5% of the average size. Similarly, a nearly uniform depth can refer to the average depth of sedimentary aggregates of approximately ±1 to 5% of the average depth, thus encompassing additional aggregates or clusters within the deviation range.

[0084] This method may include providing or selecting one or more predetermined depths at which agglomerates or clusters should be deposited. The predetermined target may be set based on several factors, such as the desired degree, number, and location of mechanical defects, the target porosity value of the carbon structure, the target number and location of catalysts within the carbon structure, the distribution of catalysts within the carbon structure, similar factors, or combinations thereof. Non-limiting examples of the target size for depositing agglomerates or clusters may be from about several hundred to several thousand atoms, for example, in the range of 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, or 9500 atoms. Non-limiting examples of deposited agglomerates or clusters may have a target diameter of about 2 to 5, 2.2 to 4.8, or 2.5 to 4.5 nanometers. This diameter may be about, at least about, or at most about 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, or 5 nanometers.

[0085] This method may further include evaluating, measuring, and scanning the penetration quality, quantity, and depth. When a uniform depth of penetration is achieved in a structure, voltage scanning can be used to approach progressively deeper / stronger regions of the structure. The term "stronger" refers to more difficult-to-access regions in a multilayer configuration.

[0086] The steps of applying voltage and bombarding the carbon structure with agglomerates or clusters can be repeated, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more times. This repetition can be performed using the same or different agglomerates or clusters, which differ in their particle distribution, chemical composition, and average size. This repetition can be performed using the same or different energy and velocity as the previous application. This repetition can continue until one or more predetermined objectives are met.

[0087] This repetition may include bombarding a carbon precursor and forming an electrocatalyst layer on the precursor. The method may further include additional deposition of the carbon precursor, followed by additional bombardment with the electrocatalyst. This process may be repeated until a desired number of layers and / or electrocatalyst loading are achieved.

[0088] This method may include annealing to increase the fluidity of deposited catalyst agglomerates or clusters, promoting the coalescence of small agglomerates or clusters into larger agglomerates or clusters until a desired target size is reached, repairing any damage to the crystal structure of the agglomerates or clusters, similar purposes, or combinations thereof.

[0089] Although exemplary embodiments have been described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the language used in this specification is descriptive rather than restrictive, and it should be understood that various changes can be made without departing from the spirit and scope of the invention. Furthermore, features of various embodiments can be combined to form other embodiments of the invention.

Claims

1. A method for improving the accessibility of a catalyst to carbon precursors, the method comprising: By applying a voltage to accelerate the process of multiple electrocatalyst clusters toward a graphene-based multilayer precursor structure, the graphene-based multilayer precursor structure is exposed to the clusters, thereby producing both of the following: Mechanical defects on the surface of the graphene-based multilayer precursor structure; as well as A nearly uniformly sized group of electrocatalysts deposited at a nearly uniform depth in the graphene-based multilayer precursor structure.

2. The method as described in claim 1, wherein, The electrocatalyst clusters are monodisperse and generated by an isoelectric beam.

3. The method as described in claim 1, wherein, The electrocatalyst clusters are monodisperse and generated by isokinetic beams.

4. The method of claim 1, wherein, The electrocatalyst clusters are polydisperse and generated by isoelectric beams.

5. The method of claim 1, further comprising selecting the plurality of electrocatalysts based on the target cluster size of less than 100 atoms.

6. The method of claim 1, further comprising selecting the plurality of electrocatalysts based on a target cluster diameter of about 2 to 5 nanometers.

7. The method of claim 1, wherein, The voltage is in the range of approximately 1 to 10 megavolts and from tens of kiloelectron volts per atom to tens of megaelectron volts per atom.

8. The method of claim 1, wherein, The mechanical defects include exposed lattice portions, leading to increased porosity in the graphene-based multilayer precursor structure.

9. A method for improving the accessibility of a catalyst to carbon precursors, the method comprising: A graphene-based multilayer precursor structure is repeatedly bombarded with a set of electrocatalyst clusters selected based on at least one predetermined value to gradually increase the porosity of the structure while depositing the electrocatalyst clusters within the structure. The repeated bombardment involves applying a constant ionization energy.

10. The method of claim 9, wherein, The at least one predetermined value includes a target cluster size of less than 100 atoms.

11. The method of claim 9, wherein, The at least one predetermined value includes a target cluster diameter of approximately 2 to 5 nanometers.

12. The method of claim 9, wherein, The constant ionization energy includes a constant energy per atom.

13. The method of claim 9, wherein, The constant ionization energy includes energy that remains constant regardless of the size of the cluster.

14. The method of claim 9, wherein, The electrocatalyst clusters are monodisperse clusters.

15. A method for depositing an electrocatalyst onto a carbon precursor, the method comprising: Electrocatalyst particle clusters are provided based on the uniformity of cluster size. By applying a voltage field ranging from approximately 1 to 10 megavolts and from tens of kiloelectron volts per atom to tens of megaelectron volts per atom, the electrocatalyst particle clusters are accelerated toward a graphene-based multilayer precursor structure; and The accelerated electrocatalyst particle clusters are collided with the graphene-based multilayer precursor structure to deposit the electrocatalyst particle clusters based on depth deposition standards.

16. The method of claim 15, wherein, The uniformity of cluster size includes clusters with a near-uniform size that deviates from the average cluster size by approximately ±1-5%.

17. The method of claim 15, wherein, The depth deposition criterion includes a nearly uniformly sized group of deposited catalysts at a nearly uniform depth within the carbon structure.

18. The method of claim 15, wherein, The depth deposition criterion includes a group of deposited catalysts of non-uniform size at multiple non-uniform depths.

19. The method of claim 15, wherein, The clusters are monodisperse.

20. The method of claim 15, further comprising increasing the number of mechanical defects in the carbon precursor.

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