Composite bipolar plates and methods of making and use thereof

Abstract

The present disclosure generally relates to electrically conductive composites for a variety of purposes, including as materials for bipolar plates, and related methods. In certain aspects, the composite comprises a substrate comprising a plurality of fibers (e.g., carbon fibers) aligned substantially orthogonal to the substrate. The composite may also comprise one or more chemically resistant polymers and one or more conductive materials (e.g., a conductive metal, alloy, carbon-based material, and / or polymer, etc.). In certain aspects, the composite is configured to provide a desirable electrical conductivity, gas permeability, and mechanical strength. Other aspects are generally directed to methods of making or using such materials.

Description

[0001] COMPOSITE BIPOLAR PLATES AND METHODS OF MAKING AND USE THEREOF

[0002] RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 511,534, filed June 30, 2023, entitled “Composite Bipolar Plates and Methods of Making and Use Thereof’; and of U.S. Provisional Patent Application Serial No. 63 / 513,403, filed July 13, 2023, entitled “Composite Bipolar Plates and Methods of Making and Use Thereof.” Each of these is incorporated herein by reference in its entirety.

[0004] FIELD

[0005] The present disclosure generally relates to electrically conductive composites for a variety of purposes, including as materials for bipolar plates, and related methods.

[0006] BACKGROUND

[0007] Bipolar plates are a component of proton exchange membrane (PEM) fuel cells that serve multiple functions. Bipolar plates, for example, may be used to uniformly distribute reactant gases and byproducts, conduct electrical current from cell to cell, provide heat and water management, prevent leakage of reactant gases and coolant, or provide overall dimensional stability to each cell. However, conventional bipolar plates can be problematic as they are often heavy components of fuel cells. For example, a bipolar plate may contribute 80% of the weight, 50% of the volume, and 40% of the cost of the overall fuel cell.

[0008] Common materials for bipolar plates include, for example, coated metallics or polymers. Metallics provide lower relative cost, high mechanical strength, ease of manufacturing, better durability to shocks and vibration, and little to no gas permeability. The surface of metallic bipolar plates, however, are often coated to prevent corrosion during cyclic usage of the fuel cell. These coatings incur significant expense. Polymer composites offer good mechanical properties, thermal management, and cost-effective manufacturing processing. The materials also provide improved corrosion resistance without requiring additional coatings as compared to metallics. Polymer composites, however, provide relatively low electrical conductivity, high gas permeability, and lower mechanical integrity as compared to metallics.

[0009] Accordingly, improved bipolar plates are needed.

[0010] SUMMARY

[0011] The present disclosure generally relates to electrically conductive composites for a variety of purposes, including as materials for bipolar plates, and related methods. The subject matter of the present disclosure involves, in some cases, interrelated products, alternative solutions to a particular problem, and / or a plurality of different uses of one or more systems and / or articles.

[0012] According to certain embodiments, a composite is described, the composite comprising a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate. In some embodiments, the composite further comprises a first region and a second region, the first region having a first average areal specific resistance and the second region having a second average areal specific resistance, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 1 : 1 and less than or equal to 10: 1.

[0013] In some embodiments, a composite comprises a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate. In certain embodiments, the composite further comprises a first region and a second region, the first region having a first average areal specific resistance of greater than or equal to 1 ohm-cm2and the second region having a second average areal specific resistance of less than or equal to 1 ohm-cm2.

[0014] According to some embodiments, a composite comprises a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate. In some embodiments, the composite further comprises a first region and a second region, the first region having a first polymer weight percent (wt.%) versus a total weight of the composite and the second region having a second polymer wt.% versus the total weight of the composite that is less than the first polymer wt.%.

[0015] In certain embodiments, a composite comprises a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate. In some embodiments, the composite further comprises a surface having a plurality of features, wherein a first portion of the plurality of features has a first average areal specific resistance and a second portion of the plurality of features has a second average areal specific resistance, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 1 : 1 and less than or equal to 10: 1.

[0016] According to certain embodiments, a composite comprises a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate. In some embodiments, the composite further comprises a surface having a plurality of features, wherein a first portion of the plurality of features has a first average areal specific resistance of greater than or equal to 0.001 ohm-cm2and a second portion of the plurality of features has a second average areal specific resistance of greater than or equal to 0.001 ohm-cm2. In some embodiments, a device is described, the device comprising a bipolar plate separating two cells of a fuel cell, the bipolar plate comprising a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate.

[0017] According to some embodiments, a method of modifying a composite is described. In certain embodiments, the method comprises: providing the composite, wherein the composite comprises a substrate, the substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate, wherein the composite further comprises a first region and a second region; and modifying the first region such that the first region has a first average areal specific resistance and the second region has a second average areal specific resistance, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 1:1 and less than or equal to 10:1.

[0018] In certain embodiments, a method of modifying a composite comprises: providing the composite, wherein the composite comprises a substrate, the substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate, wherein the composite further comprises a surface comprising a plurality of features, the plurality of features comprising a first portion and a second portion; and modifying a surface of the second portion of the plurality of features such that a surface of the first portion of the plurality of features has a first average areal specific resistance and the surface of the second portion of the plurality of features has a second average areal specific resistance, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 1 : 1 and less than or equal to 10: 1.

[0019] According to some embodiments, a composite comprises a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate. In certain embodiments, the composite further comprising a first region and a second region, the first region having a first average areal specific resistance and the second region having a second average areal specific resistance, wherein the second average areal specific resistance is the same as or less than the first average areal specific resistance.

[0020] Other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments of the disclosure when considered in conjunction with the accompanying figures.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure. In the figures:

[0023] FIG. 1 is, according to certain embodiments, a schematic top-view diagram of a composite;

[0024] FIG. 2 is, according to certain embodiments, a schematic cross-sectional diagram of a composite;

[0025] FIG. 3 is, according to certain embodiments, a schematic cross-sectional diagram of a composite comprising a surface having a plurality of features;

[0026] FIGS. 4A-4E is, according to certain embodiments, schematic diagrams representing a method of making a composite;

[0027] FIG. 5 is, according to certain embodiments, a local microstructure of a composite comprising aligned carbon fibers;

[0028] FIG. 6 is, according to certain embodiments, a cross-sectional view of a composite comprising aligned carbon fibers; and

[0029] FIG. 7 is, according to certain embodiments, a top-view of a composite showing a polymer-rich perimeter region (left) and a conductive interior region (right).

[0030] DETAILED DESCRIPTION

[0031] The present disclosure generally relates to electrically conductive composites for a variety of purposes, including as materials for bipolar plates, and related methods. In certain aspects, the composite comprises a substrate comprising a plurality of fibers (e.g., carbon fibers) aligned substantially orthogonal to the substrate. The composite may also comprise one or more chemically resistant polymers and one or more conductive materials (e.g., a conductive metal, alloy, carbon-based material, and / or polymer, etc.). In certain aspects, the composite is configured to provide a desirable electrical conductivity, gas permeability, and mechanical strength. Other aspects are generally directed to methods of making or using such materials.

[0032] Certain aspects are directed to composites having different electrically conductive regions. For example, the composite may comprise a first region (e.g., a perimeter region) and a second region (e.g., an interior region), wherein the first region substantially surrounds the interior region. Both the first region and the second region may advantageously be electrically conductive, in some aspects, such that the entirety of the composite is electrically conductive and has a low electrical resistance (e.g., a low areal specific resistance). In certain aspects, the electrical conductivity of the second region (e.g., the interior region) may be higher than the electrical conductivity of the first region (e.g., the perimeter region). In other embodiments, the electrical conductivity of the first region (e.g., the perimeter region) and the second region (e.g., the interior region) may be substantially the same.

[0033] A surface of the composite may also comprise a plurality of features (e.g., in the second, interior region) having a first portion (e.g., valleys) and a second portion (e.g., peaks) that are both advantageously electrically conductive, such that the entirety of the plurality of features has a low electrical resistance (e.g., a low areal specific resistance). The electrical conductivity of the second portion of features (e.g., the peaks) may be higher than the electrical conductivity of the first portion of features (e.g., valleys), in some aspects. In other embodiments, the electrical conductivity of the first portion of features (e.g., valleys) and the second portion of features (e.g., peaks) may be substantially the same. As mentioned, such composites, with various electrically conductive regions, can be used for various applications, including, but not limited to, materials or components for use in bipolar plates.

[0034] Methods of making and / or modifying composites are also described herein. In certain aspects, for example, a composite may be fabricated by providing one or more substrates (e.g., comprising a plurality of carbon fibers, which may be aligned substantially orthogonal to the substrate) and disposing one or more layers and / or films of a conductive material and one or more layers and / or films of a polymer on at least a portion of the substrate. However, it should be understood that aligned fibers may not necessarily be present in some embodiments. The resulting material may be thermally infused, pressed, and / or stamped to provide the composite. By discretely positioning the one or more polymer layers and / or films in the first region (e.g., the perimeter region) of the composite, the polymer content of the perimeter region may increase, which may lower the conductivity of the perimeter region as compared to the interior region. The perimeter region therefore can provide mechanical integrity to the composite in certain embodiments, while the interior region can provide desirable conductivity and low gas permeability.

[0035] The plurality of features (e.g., peaks and valleys) may be formed on a surface of the composite by stamping, molding, forming, and the like. After fabricating the plurality of features, a surface of the second portion of features (e.g., peaks) may be modified by decreasing a polymer content of the surface of the second of portion of features. For example, in some aspects, the surface of the second portion of features may be ablated (e.g., using techniques such as machining, sanding, laser ablation, sand blasting, etc.) to expose conductive material, which may result in an interior region with a first portion of the features (e.g., valleys) having a lower conductivity than a second portion of the features (e.g., peaks).

[0036] Configuring the composite as described herein results in a material having a low weight density (e.g., 1.3-1.8 g / cm3), a low thickness (e.g., less than 250 micrometers), a low electrical resistance (e.g., an average areal specific resistance of less than 1 ohm-cm2), a low gas permeability (e.g., a gas transmission rate of less than 200 (cm3 / m224 h 0.1 MPa)), and / or desirable mechanical properties (e.g., a flexural strength greater than 40 MPa). The composite may be utilized, for example, in fuel cells (e.g., as a bipolar plate), in heat exchangers, or other applications.

[0037] Turning to the figures, certain specific non-limiting embodiments are described in further detail. It should be understood that the various systems, components, features, and methods described relative to these embodiments may be used either individually and / or in any desired combination as the disclosure is not limited to only the specific embodiments described herein.

[0038] FIG. 1 is, according to certain embodiments, a top-view schematic diagram of composite 100a. In some embodiments, composite 100a comprises first region 102a (e.g., a perimeter region). First region 102a of composite 100a may, in some embodiments, be defined as the area (e.g., surface area) of composite 100a between first perimeter 104 of first region 102a and second perimeter 106 of first region 102a. Without wishing to be bound by theory, the first region may advantageously provide the composite with desirable mechanical properties (e.g., flexural strength) in certain embodiments, as explained herein in greater detail.

[0039] First region 102a may, in certain embodiments, comprise one or more holes 112 passing through composite 100a (e.g., from a first surface of composite 100a to a second surface of composite 100a that is substantially opposite the first surface). In some embodiments, the plurality of holes may be configured to provide a fluidic pathway for one or more fluids (e.g., gases and / or liquids). In certain embodiments wherein the composite is used in a bipolar plate, the plurality of holes may be configured to connect with one or more adjacent bipolar plates. Embodiments in which the composite (e.g., the first region of the composite) does not comprise any holes are also contemplated, however, as the present disclosure is not limiting in this regard.

[0040] In certain embodiments, composite 100a comprises second region 108a (e.g., an interior region). Second region 108a of composite 100a may, in some embodiments, be defined as the area (e.g., surface area) of composite 100a within perimeter 110 of second region 108a. Without wishing to be bound by theory, the second region may advantageously provide the composite with desirable electrical conductivity and / or gas permeability properties under certain circumstances, as explained herein in greater detail.

[0041] In some aspects, second region 108a comprises plurality of features 120. Plurality of features 120 are explained herein in greater detail with respect to FIG. 3.

[0042] The second region may be non-porous, according to certain embodiments (although it may be porous in other embodiments). In some embodiments, for example, the second region may be impermeable to fluids (e.g., gases and / or liquids).

[0043] In some embodiments, as shown in FIG. 1, first region 102a substantially surrounds second region 108a. In some cases, the first region may substantially surround the second region such that, when viewed from at least one angle, the two-dimensional convex hull of the first region completely surrounds the second region. In addition, the two-dimensional convex hull of a given view of an article may refer to the smallest two-dimensional convex set that contains the article. The convex hull is also sometimes referred to in the field of geometry as the two-dimensional convex envelope or the two-dimensional convex closure, and it can be immediately visualized as the shape enclosed by a rubber band stretched around a two-dimensional view of an object. Using FIG. 1 as an illustrative example, first region 102a substantially surrounds second region 108a because, when viewed from the angle illustrated in FIG. 1, the first perimeter 104 (e.g., the outer perimeter) of first region 102a (which also corresponds to the two-dimensional convex hull of first region 102a as shown in FIG. 1) completely surrounds second region 108a.

[0044] According to some embodiments, the composite (e.g., a first region and / or a second region of the composite) comprises a substrate. FIG. 2 is, according to certain embodiments, a schematic cross-sectional diagram of composite 100a taken along dotted line 2 shown in FIG. 1. As shown in FIG. 2, composite 100a (e.g., first region 102a and second region 108a of composite 100a) comprises substrate 202. The substrate may be in the form of a layer and / or film, in certain embodiments, although other configurations are also possible as the present disclosure is not limiting in this regard.

[0045] In some embodiments, the substrate spans a distance of the composite. Referring to FIG. 2, for example, substrate 202 spans a length of composite 100a from first end 114 of composite 100a to second end 116 of composite 100a. In other embodiments, the substrate does not span a distance of the composite.

[0046] According to some embodiments, although not shown in the figures, the composite may comprise a plurality of substrates (e.g., two substrates, three substrates, four substrates, five substrates, etc.), where some or all of the substrates are configured as described herein. In some such embodiments, some or all of the substrates may be in the form of a layer and / or film. In certain embodiments, the plurality of substrates may be arranged in a stacked configuration and / or adjacent to one another (e.g., arranged end-to-end), or in other suitable configurations. In some embodiments wherein a plurality of substrates are arranged end-to- end, an end of a first substrate may directly abut an end of a second substrate and / or an end of a first substrate may not directly abut an end of a second substrate such that there is a gap between the first substrate and the second substrate. In certain embodiments, for example, first region 102a and / or second region 108a of composite 100a may comprise at least two substrates, at least three substrates, at least four substrates, at least five substrates, etc., in a stacked, end-to-end, or other suitable configuration.

[0047] The substate may, in certain embodiments, comprise a plurality of fibers (e.g., carbon fibers). In some embodiments, the plurality of fibers are a plurality of discontinuous fibers (e.g., discontinuous carbon fibers). The plurality of fibers may be aligned substantially orthogonal to the substrate, in some aspects. Further details regarding the substrate and the plurality of fibers are explained herein in greater detail, including, for example, various types of suitable fibers, suitable lengths of fibers, suitable diameters of fibers, suitable methods for producing the substrate, etc.

[0048] In some embodiments, the composite (e.g., a first region and / or second region of the composite) comprises a polymer. As shown in FIG. 2, for example, composite 100a (e.g., first region 102a of composite 100a) may comprise polymer 204, in some aspects.

[0049] The polymer may be present within various composites, such as those described herein, in the form of a layer and / or film. In other embodiments, the polymer may be in the form of a coating. Embodiments in which the composite comprises a polymer in the form of a layer and / or film and in the form of a coating are also envisioned, as the present disclosure is not limiting in this regard.

[0050] According to certain embodiments, at least a portion of the substrate and at least a portion of the polymer may be in direct contact with each other. In some embodiments, for example, the polymer (e.g., polymer layer and / or film, polymer coating) may be disposed (e.g., directly disposed) on at least a portion of one or more surfaces of the substrate. For example, in some embodiments, a polymer may be disposed on a surface of the substrate (e.g., a surface of the substrate in the first region of the composite). In other embodiments, a polymer may be disposed on a first surface of the substrate (e.g., a first surface of the substrate in the first region of the composite), and polymer may be disposed on a second surface of the substrate (e.g., a second surface of the substrate in the first region of the composite) that is substantially opposite the first surface.

[0051] In some embodiments, although not shown in the figures, the second region of the composite may comprise a polymer (e.g., a polymer layer and / or film, a polymer coating). For example, the polymer may span a distance (e.g., a length) of the composite, in some embodiments, such that the first region and the second region of the composite comprise a polymer. In other embodiments, the second region of the composite may comprise a polymer without the polymer spanning a distance of the composite. The polymer may, in certain embodiments, be disposed on a surface of the substrate in the second region of the composite. In other embodiments, the polymer is disposed on a first surface of the substrate in the second region of the composite and on a second surface of the substrate in the second region of the composite that is substantially opposite the first surface.

[0052] Although not necessarily shown in the figures, the composite may comprise a plurality of polymer layers and / or films (e.g., two polymer layers and / or films, three polymer layers and / or films, four polymer layers and / or films, five polymer layers and / or films, etc.) disposed on a first surface of the substrate and / or a plurality of polymer layers and / or films (e.g., two polymer layers and / or films, three polymer layers and / or films, four polymer layers and / or films, five polymer layers and / or films, etc.) disposed on a second surface of the substrate that is substantially opposite the first surface, where some of all of the polymer layers and / or films are configured as described herein. In certain embodiments, the plurality of polymer layers and / or films may be arranged in a stacked configuration and / or adjacent to one another (e.g., arranged end-to-end), or in other suitable arrangements. In certain embodiments, for example, the first region and / or the second region of the composite may comprise at least two polymer layers and / or films, at least three polymer layers and / or films, at least four polymer layers and / or films, at least five polymer layers and / or films, etc., disposed on a first surface of the substrate and / or the composite may comprise at least two polymer layers and / or films, at least three polymer layers and / or films, at least four polymer layers and / or films, at least five polymer layers and / or films, etc., disposed on a second surface of the substrate that is substantially opposite the first surface, each polymer layer and / or film in a stacked, end-to-end, or other suitable configuration.

[0053] Any of a variety of suitable polymers may be employed. For example, in certain embodiments, the composite comprises a thermoplastic polymer (e.g., a thermoplastic resin), a thermoset polymer (e.g., a thermoset resin), a liquid crystal polymer, an elastomer, and / or combinations thereof. In some embodiments, for example, the polymer comprises a phenolic polymer, an epoxy, a vinyl ester, and / or a furan ester. Non-limiting examples of polymers include polyetherimide (PEI), polyethersulfone (PES), polyvinylidene fluoride (PVDF), polypropylene (PP), polyphenylene sulfide (PPS), polyurethane (PUR), polypyrrole (Ppy), polyaniline (Pani), poly(3,4-ethylenedioxythiophene) (PEDOT), polyetheretherketone (PEEK), polyaryletherketone (PAEK), and / or combinations of these and / or other polymers. Other polymers are also possible as the present disclosure is not limiting in this regard.

[0054] In certain embodiments, the composite (e.g., a first region and / or a second region of the composite) comprises a conductive material. Referring to FIG. 2, for example, composite 100a (e.g., second region 108a of composite 100a) comprises conductive material 206.

[0055] In various embodiments, the conductive material may be in the form of a layer and / or film. In other embodiments, the conductive material may be in the form of a coating. Embodiments in which the composite comprises a conductive material in the form of a layer and / or a film and in the form of a coating are also envisioned, as the present disclosure is not limiting in this regard.

[0056] In some embodiments, at least a portion of the substrate and at least a portion of the conductive material may be in direct contact with each other. For example, in certain embodiments, the conductive material (e.g., conductive material layer and / or film, conductive material coating) may be disposed (e.g., directly disposed) on at least a portion of one or more surfaces of the substrate. In certain embodiments, for example, the conductive material is disposed on a first surface of the substrate (e.g., a first surface of the substrate in the second region of the composite). Although not shown in figures, the conductive material may be disposed on a second surface of the substrate (e.g., in the second region of the composite) that is substantially opposite the first surface, as the present disclosure is not limiting in this regard. In some embodiments, at least a portion of the conductive material may be in direct contact with one or more fibers (e.g., carbon fibers) of the substrate.

[0057] In some embodiments, at least a portion of the polymer and at least a portion of the conductive material may be in direct contact with each other. For example, in certain embodiments, the conductive material (e.g., conductive material layer and / or film, conductive material coating) may be disposed (e.g., directly disposed) on at least a portion of one or more surfaces of the polymer.

[0058] According to some embodiments, although not necessarily shown in the figures, the first region of the composite may comprise a conductive material (e.g., a conductive material layer and / or film, a conductive material coating). In certain embodiments, for example, the conductive material may be disposed on a surface of the substrate and / or polymer in the first region of the composite. In other embodiments, the conductive material may be disposed on a first surface of the substrate and / or polymer in the first region of the composite and on a second surface of the substrate and / or polymer in the first region of the composite that is substantially opposite the first surface.

[0059] Although not shown in the figures, the composite may comprise a plurality of conductive material layers and / or films (e.g., two conductive material layers and / or films, three conductive material layers and / or films, four conductive material layers and / or films, five conductive material layers and / or films, etc.) disposed on a first surface of the substrate and / or polymer, and / or a plurality of conductive material layers and / or films (e.g., two conductive material layers and / or films, three conductive material layers and / or films, four conductive material layers and / or films, five conductive material layers and / or films, etc.) disposed on a second surface of the substrate and / or polymer that is substantially opposite the first surface, where some or all of the conductive material layers and / or films are configured as described herein. The plurality of conductive material layers and / or films may be arranged in a stacked configuration and / or adjacent to one another (e.g., arranged end-to-end), or in other suitable arrangements, in some embodiments. For example, in certain embodiments, the first region and / or the second region of the composite may comprise at least two conductive material layers and / or films, at least three conductive material layers and / or films, at least four conductive material layers and / or films, at least five conductive material layers and / or films, etc., disposed on a first surface of the substrate and / or polymer, and / or the composite may comprise at least two conductive material layers and / or films, at least three conductive material layers and / or films, at least four conductive material layers and / or films, at least five conductive material layers and / or films, etc., disposed on a second surface of the substrate and / or polymer that is substantially opposite the first surface, each conductive material layer in a stacked, end-to-end, or other suitable configuration.

[0060] Any of a variety of suitable conductive materials may be employed. In some embodiments, for example, the conductive material comprises a metal, an alloy, a carbonbased material, a conductive polymer, and / or combinations thereof. In certain embodiments, the conductive material may be disposed in one or more polymers (e.g., a matrix of one or more polymers).

[0061] The composite may comprise any of a variety of suitable metals and / or alloys. In certain embodiments, for example, the metal and / or alloy comprises aluminum (Al), titanium (Ti), nickel (Ni), zirconium (Zr), niobium (Nb), tantalum (Ta), hafnium (Hf), stainless steel (SS), and / or combinations thereof. In some embodiments, the metal and / or alloy comprises a metal and / or alloy foil. In certain embodiments, the metal and / or alloy comprises metal and / or alloy particles. Other metals and / or alloys are also possible as the present disclosure is not meant to be limiting in this regard.

[0062] The composite may comprise any of a variety of suitable carbon-based materials. In some embodiments, for example, the carbon-based material comprises graphite, graphene, a carbon nanostructure (e.g., carbon nanotubes, carbon nanowires, etc.), carbon black, and / or combinations thereof. The carbon-based material may be a powder (e.g., carbon and / or graphite powder) or a fiber (e.g., carbon and / or graphite fibers), in some aspects. Other carbon-based materials are also possible as the present disclosure is not limiting in this regard.

[0063] The first region may be electrically conductive, in some embodiments, such that the first region has a low electrical resistance. For example, the first region may have any of a variety of suitable areal specific resistances. The average areal specific resistance of the first region may be advantageously low, in some aspects. In some embodiments, for example, the first region has an average areal specific resistance of less than or equal to 10 ohm-cm2, less than or equal to 5 ohm-cm2, less than or equal to 4 ohm-cm2, less than or equal to 3 ohm-cm2, or less than or equal to 2 ohm-cm2. In certain embodiments, the first region has an average areal specific resistance of greater than or equal to 1 ohm-cm2, greater than or equal to 2 ohm-cm2, greater than or equal to 3 ohm-cm2, greater than or equal to 4 ohm-cm2, or greater than or equal to 5 ohm-cm2. Combinations of the above recited ranges are possible (e.g., the first region has an average areal specific resistance of less than or equal to 10 ohm-cm2and greater than or equal to 1 ohm-cm2, the first region has an average areal specific resistance of less than or equal to 5 ohm-cm2and greater than or equal to 4 ohm-cm2). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0064] In certain embodiments, the areal specific resistance of the first region is determined by placing a sample of the first region between two copper platens such that the sample is sandwiched between two layers of carbon paper (e.g., Toray Carbon Paper TGP-H-060), compressing the two copper platens together at a suitable pressure (e.g., 140 PSI), and measuring the areal specific resistance across the sample of the first region. In some embodiments, the average areal specific resistance of the first region is determined by determining the areal specific resistance of multiple samples of the first region as described above and averaging the areal specific resistances.

[0065] In certain embodiments, the second region may be electrically conductive such that the second region has a low electrical resistance. For example, the second region may have any of a variety of suitable areal specific resistances. The average areal specific resistance of the second region may be advantageously low, in some aspects. In some embodiments, for example, the second region has an average areal specific resistance of less than or equal to 1 ohm-cm2, less than or equal to 0.5 ohm-cm2, less than or equal to 0.1 ohm-cm2, less than or equal to 0.05 ohm-cm2, less than or equal to 0.01 ohm-cm2, or less than or equal to 0.005 ohm-cm2. In certain embodiments, the second region has an average areal specific resistance of greater than or equal to 0.001 ohm-cm2, greater than or equal to 0.005 ohm-cm2, greater than or equal to 0.01 ohm-cm2, greater than or equal to 0.05 ohm-cm2, greater than or equal to 0. 1 ohm-cm2, or greater than or equal to 0.5 ohm-cm2. Combinations of the above recited ranges are possible (e.g., the second region has an average areal specific resistance of less than or equal to 1 ohm-cm2and greater than or equal to 0.001 ohm-cm2, the second region has an average areal specific resistance of less than or equal to 0.1 ohm-cm2and greater than or equal to 0.05 ohm-cm2). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0066] In certain embodiments, the areal specific resistance of the second region is determined by placing a sample of the second region between two copper platens such that the sample is sandwiched between two layers of carbon paper (e.g., Toray Carbon Paper TGP-H-060), compressing the two copper platens together at a suitable pressure (e.g., 140 PSI), and measuring the areal specific resistance across the sample of the second region. In some embodiments, the average areal specific resistance of the second region is determined by determining the areal specific resistance of multiple samples of the second region as described above and averaging the areal specific resistances.

[0067] In some embodiments, the average areal specific resistance of the second region may be less than the average areal specific resistance of the first region, such that the second region has a higher conductivity than the first region.

[0068] The average areal specific resistance of the first region and the average areal specific resistance of the second region may have any of a variety of suitable ratios. In certain embodiments, for example, the ratio of the average areal specific resistance of the first region to the average areal specific resistance of the second region is less than or equal to 10:1, less than or equal to 10:2, less than or equal to 10:3, less than or equal to 10:4, less than or equal to 10:5, less than or equal to 10:6, less than or equal to 10:7, or less than or equal to 10:8. In some embodiments, the ratio of the average areal specific resistance of the first region to the average areal specific resistance of the second region is greater than or equal to 10:9, greater than or equal to 10:8, greater than or equal to 10:7, greater than or equal to 10:6, greater than or equal to 10:5, greater than or equal to 10:4, greater than or equal to 10:3, or greater than or equal to 10:2. Combinations of the above recited ranges are possible (e.g., the ratio of the average areal specific resistance of the first region to the average areal specific resistance of the second region is less than or equal to 10: 1 and greater than or equal to 10:9, the ratio of the average areal specific resistance of the first region to the average areal specific resistance of the second region is less than or equal to 10:4 and greater than or equal to 10:6). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0069] According to certain embodiments, the average areal specific resistance of the first region and the average areal specific resistance of the second region may be the same or substantially the same. In some embodiments, for example, the ratio of the average areal specific resistance of the first region to the average areal specific resistance of the second region is 1:1.

[0070] According to some embodiments, the first region may have a polymer wt.% versus a total weight of the composite (e.g., a first polymer wt.%) and the second region may have a polymer wt.% versus the total weight of the composite (e.g., a second polymer wt.%), wherein the polymer wt.% of the first region versus the total weight of the composite is different than the polymer wt.% of the second region versus the total weight of the composite. In some embodiments, for example, the polymer wt.% of the second region versus a total weight of the composite may be less than the polymer wt.% of the first region versus a total weight of the composite. Configuring the composite in this manner may, in some embodiments, advantageously provide a first region having a first electrical resistance and a second region having a second electrical resistance, wherein the second electrical resistance (e.g., the electrical resistance of the second region) is lower than the first electrical resistance (e.g., the electrical resistance of the first region).

[0071] The polymer wt.% of the first region versus the total weight of the composite (e.g., the first polymer wt.%) and the polymer wt.% of the second region versus the total weight of the composite (e.g., the second polymer wt.%) may have any of a variety of suitable ratios. In some embodiments, for example, the ratio of the first polymer wt.% to the second polymer wt.% is less than or equal to 10:1, less than or equal to 10:2, less than or equal to 10:3, less than or equal to 10:4, less than or equal to 10:5, less than or equal to 10:6, less than or equal to 10:7, or less than or equal to 10:8. In certain embodiments, the ratio of the first polymer wt.% to the second polymer wt.% is greater than or equal to 10:9, greater than or equal to 10:8, greater than or equal to 10:7, greater than or equal to 10:6, greater than or equal to 10:5, greater than or equal to 10:4, greater than or equal to 10:3, or greater than or equal to 10:2. Combinations of the above recited ranges are possible (e.g., the ratio of the first polymer wt.% to the second polymer wt.% is less than or equal to 10: 1 and greater than or equal to 10:9, the ratio of the first polymer wt.% to the second polymer wt.% is less than or equal to 10:4 and greater than or equal to 10:6). Other combinations are also possible as the present disclosure is not limiting in this regard.

[0072] According to certain embodiments, the polymer wt.% of the first region versus the total weight of the composite (e.g., the first polymer wt.%) and the polymer wt.% of the second region versus the total weight of the composite (e.g., the second polymer wt.%) may the same or substantially the same. In some embodiments, for example, the ratio of the first polymer wt.% to the second polymer wt.% is 1:1.

[0073] As described herein, the composite may comprise a surface having a plurality of features. For example, FIG. 3 is, according to certain embodiments, a schematic cross- sectional diagram of composite 100b comprising surface 302 having plurality of features 120. In certain embodiments, plurality of features 120 comprise first portion of features 304. First portion of features 304 may, in some embodiments, comprise one or more valleys, as shown, for example, in FIG 3. In some embodiments, plurality of features 120 comprise second portion of features 306. In certain embodiments, as shown in FIG. 3, second portion of features 306 comprise one or more peaks.

[0074] The plurality of features of a composite as discussed herein may be configured to transport one or more fluids (e.g., one or more liquids and or gases). In certain embodiments, for example, the plurality of features may function as a channel for the flow of one or more fluids along the composite. It should be noted that the plurality of features may not be limited to valleys and peaks. In certain embodiments, for example, the plurality of features may comprise any of a variety of suitable structures, including, but not limited to, crests, troughs, pillars, posts, and / or particles.

[0075] At least a portion of the plurality of features may be patterned on the surface of the composite, in some embodiments. In other embodiments, the plurality of features are randomly oriented on the surface of the composite. Methods of forming the plurality of features on the surface of the composite are described herein in greater detail.

[0076] The first portion of features and the second portion of features may be electrically conductive, in some embodiments, such that the first portion of features and the second portion of features have a low electrical resistance. For example, a surface of the first portion of features and / or the second portion of features may have any of a variety of suitable areal specific resistances. The average areal specific resistance of the surface of the first portion of features and / or the surface of the second portion of features may be advantageously low, in some aspects. In some embodiments, for example, the surface of the first portion of the plurality of features and / or the surface of the second portion of the plurality of features has an average areal specific resistance of less than or equal to 1 ohm-cm2, less than or equal to 0.5 ohm-cm2, less than or equal to 0.1 ohm-cm2, less than or equal to 0.05 ohm-cm2, less than or equal to 0.01 ohm-cm2, or less than or equal to 0.005 ohm-cm2. In certain embodiments, the surface of the first portion of the plurality of features and / or the surface of the second portion of the plurality of features has an average areal specific resistance of greater than or equal to 0.001 ohm-cm2, greater than or equal to 0.005 ohm-cm2, greater than or equal to 0.01 ohm- cm2, greater than or equal to 0.05 ohm-cm2, or greater than or equal to 0.1 ohm-cm2, or greater than or equal to 0.5 ohm-cm2. Combinations of the above recited ranges are possible (e.g., the surface of the first portion of the plurality of features and / or the surface of the second portion of the plurality of features has an average areal specific resistance of less than or equal to 1 ohm-cm2and greater than or equal to 0.001 ohm-cm2, the surface of the first portion of the plurality of features and / or the surface of the second portion of the plurality of features has an average areal specific resistance of less than or equal to 0. 1 ohm-cm2and greater than or equal to 0.05 ohm-cm2). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0077] In certain embodiments, the average areal specific resistance of the surface of the first portion of the plurality of features and / or the surface of the second portion of the plurality of features is measured by placing a sample of the first portion of the plurality of features and / or the second portion of the plurality of features between two copper platens such that the sample is sandwiched between two layers of carbon paper (e.g., Toray Carbon Paper TGP-H- 060), compressing the two copper platens together at a suitable pressure (e.g., 140 PSI), and measuring the areal specific resistance across the sample of the first portion of the plurality of features and / or the second portion of the plurality of features. In some embodiments, the average areal specific resistance of the first portion of the plurality of features and / or the second portion of the plurality of features is determined by determining the areal specific resistance of multiple samples of the first portion of the plurality of features and / or the second portion of the plurality of features as described above and averaging the areal specific resistances.

[0078] In some embodiments, the average areal specific resistance of the surface of the second portion of features may be less than the average areal specific resistance of the surface of the first portion of features, such that the surface of the second portion of features has a higher conductivity than the surface of the first portion of features.

[0079] The average areal specific resistance of the surface of the first portion of features and the average areal specific resistance of the surface of the second portion of features may have any of a variety of suitable ratios. In certain embodiments, for example, the ratio of the average areal specific resistance of the surface of the first portion of the plurality of features to the average areal specific resistance of the surface of the second portion of the plurality of features is less than or equal to 10: 1, less than or equal to 10:2, less than or equal to 10:3, less than or equal to 10:4, less than or equal to 10:5, less than or equal to 10:6, less than or equal to 10:7, or less than or equal to 10:8. In some embodiments, the ratio of the average areal specific resistance of the surface of the first portion of the plurality of features to the average areal specific resistance of the surface of the second portion of the plurality of features is greater than or equal to 10:9, greater than or equal to 10:8, greater than or equal to 10:7, greater than or equal to 10:6, greater than or equal to 10:5, greater than or equal to 10:4, greater than or equal to 10:3, or greater than or equal to 10:2. Combinations of the above recited ranges are possible (e.g., the ratio of the average areal specific resistance of the surface of the first portion of the plurality of features to the average areal specific resistance of the surface of the second portion of the plurality of features is less than or equal to 10:1 and greater than or equal to 10:9, the ratio of the average areal specific resistance of the surface of the first portion of the plurality of features to the average areal specific resistance of the surface of the second portion of the plurality of features is less than or equal to 10:4 and less than or equal to 10:6). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0080] According to certain embodiments, the average areal specific resistance of the surface of the first portion of features and the average areal specific resistance of the surface of the second portion of features may be the same or substantially the same. In some embodiments, for example the ratio of the average areal specific resistance of the surface of the first portion of features to the average areal specific resistance of the surface of the second portion of the plurality of features is 1: 1.

[0081] In some aspects, the composite may be electrically conductive such that the composite has a low electrical resistance. For example, the composite may have any of a variety of suitable areal specific resistances. In some embodiments, the average areal specific resistance of the composite may be advantageously low. In certain embodiments, for example, the composite has an average areal specific resistance of greater than or equal to 0.001 ohm-cm2, greater than or equal to 0.005 ohm-cm2, greater than or equal to 0.01 ohm- cm2, greater than or equal to 0.05 ohm-cm2, greater than or equal to 0.1 ohm-cm2, greater than or equal to 0.5 ohm-cm2, greater than or equal to 1 ohm-cm2, or greater than or equal to 2 ohm-cm2. In some embodiments, the composite has an average areal specific resistance of less than or equal to 5 ohm-cm2, less than or equal to 2 ohm-cm2, less than or equal to 1 ohm- cm2, less than or equal to 0.5 ohm-cm2, less than or equal to 0. 1 ohm-cm2, less than or equal to 0.05 ohm-cm2, less than or equal to 0.01 ohm-cm2, or less than or equal to 0.005 ohm-cm2. Combinations of the above recited ranges are possible (e.g., the composite has an average areal specific resistance of greater than or equal to 0.001 ohm-cm2and less than or equal to 5 ohm-cm2, the composite has an average areal specific resistance of greater than or equal to 0.05 ohm-cm2and less than or equal to 1 ohm-cm2). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0082] In some embodiments, the areal specific resistance of the composite may be determined by placing a sample of the composite (e.g., a sample of the first region of the composite, a sample of the second region of the composite) between two copper platens such that the sample is sandwiched between two layers of carbon paper (e.g., Toray Carbon Paper TGP-H-060), compressing the two copper platens together at a suitable pressure (e.g., 140 PSI), and measuring the areal specific resistance across the sample of the composite. In some embodiments, the average areal specific resistance of the composite is determined by determining the areal specific resistance of multiple samples of the composite as described above and averaging the areal specific resistances.

[0083] The composite may have any of a variety of suitable gas permeabilities. The gas permeability of the composite may be advantageously low, in some aspects. In certain embodiments, for example, the composite has an average gas transmission rate of less than or equal to 200 (cm3 / m224 h 0.1 MPa), less than or equal to 150 (cm3 / m224 h 0.1 MPa), less than or equal to 100 (cm3 / m224 h 0. 1 MPa), less than or equal to 50 (cm3 / m224 h 0.1 MPa), less than or equal to 10 (cm3 / m224 h 0. 1 MPa), less than or equal to 1 (cm3 / m224 h 0. 1 MPa), or less than or equal to 0.1 (cm3 / m224 h 0.1 MPa). In some embodiments, the composite has an average gas transmission rate of greater than or equal to 0.01 (cm3 / m224 h 0.1 MPa), greater than or equal to 0.1 (cm3 / m224 h 0.1 MPa), greater than or equal to 1 (cm3 / m224 h 0.1 MPa), greater than or equal to 10 (cm3 / m224 h 0.1 MPa), greater than or equal to 50 (cm3 / m224 h 0.1 MPa), greater than or equal to 100 (cm3 / m224 h 0.1 MPa), or greater than or equal to 150 (cm3 / m224 h 0.1 MPa). Combinations of the above recited ranges are possible (e.g., the composite has an average gas transmission rate of less than or equal to 200 (cm3 / m224 h 0.1 MPa) and greater than or equal to 0.01 (cm3 / m224 h 0.1 MPa), the composite has an average gas transmission rate of less than or equal to 50 (cm3 / m224 h 0.1 MPa) and greater than or equal to 10 (cm3 / m224 h 0.1 MPa)). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0084] In some embodiments, the average gas transmission rate of the composite may be determined by ASTM DI 434 using O2 gas.

[0085] The composite may have any of a variety of suitable corrosion current densities. The corrosion current density of the composite may be advantageously low, in some aspects. In certain embodiments, for example, the composite has an average corrosion current density of less than or equal to 1 microamps / cm2, less than or equal to 0.5 microamps / cm2, less than or equal to 0.1 microamps / cm2, or less than or equal to 0.05 microamps / cm2. In some embodiments, the composite has an average corrosion current density of greater than or equal to 0.01 microamps / cm2, greater than or equal to 0.05 microamps / cm2, greater than or equal to 0.1 microamps / cm2, or greater than or equal to 0.5 microamps / cm2. Combinations of the above recited ranges are possible (e.g., the composite has an average corrosion current density of less than or equal to 1 microamps / cm2and greater than or equal to 0.01 microamps / cm2, the composite has an average corrosion current density of less than or equal to 0.5 microamps / cm2and greater than or equal to 0.05 microamps / cm2). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0086] In some embodiments, the average corrosion current density of the composite may be determined by placing the composite in an electrolyte, polarizing the composite with a potential difference, measuring the resulting current, and calculating the corrosion current density based on Faraday’s law of electrolysis.

[0087] The composite may have any of a variety of suitable flexural strengths. The flexural strength of the composite may be advantageously high, in some aspects, such that the composite is mechanically robust. In certain embodiments, for example, the composite has an average flexural strength of greater than or equal to 30 MPa, greater than or equal to 40 MPa, greater than or equal to 50 MPa, greater than or equal to 60 MPa, greater than or equal to 70 MPa, greater than or equal to 80 MPa, or greater than or equal to 90 MPa. In some embodiments, the composite has an average flexural strength of less than or equal to 100 MPa, less than or equal to 90 MPa, less than or equal to 80 MPa, less than or equal to 70 MPa, less than or equal to 60 MPa, less than or equal to 50 MPa, or less than or equal to 40 MPa. Combinations of the above recited ranges are possible (e.g., the composite has an average flexural strength of greater than or equal to 30 MPa and less than or equal to 100 MPa, the composite has an average flexural strength rate of greater than or equal to 60 MPa and less than or equal to 70 MPa). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0088] In some embodiments, the average flexural strength of the composite may be determined by ASTM D790.

[0089] The composite may have any of a variety of suitable thermal conductivities. The thermal conductivity of the composite may be advantageously high, in some aspects. In certain embodiments, for example, the composite has an average thermal conductivity of greater than or equal to 3 W / m-K, greater than or equal to 5 W / m-K, greater than or equal to 10 W / m-K, greater than or equal to 50 W / m-K, greater than or equal to 100 W / m-K, greater than or equal to 300 W / m-K, greater than or equal to 500 W / m-K, greater than or equal to 700 W / m-K, or greater than or equal to 900 W / m-K. In some embodiments, the composite has an average thermal conductivity of less than or equal to 1000 W / m-K, less than or equal to 900 W / m-K, less than or equal to 700 W / m-K, less than or equal to 500 W / m-K, less than or equal to 300 W / m-K, less than or equal to 100 W / m-K, less than or equal to 50 W / m-K, less than or equal to 10 W / m-K, or less than or equal to 5 W / m-K. Combinations of the above recited ranges are possible (e.g., the composite has an average thermal conductivity of greater than or equal to 3 W / m-K and less than or equal to 1000 W / m-K, the composite has an average thermal conductivity of greater than or equal to 100 W / m-K and less than or equal to 300 W / m-K). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0090] In some embodiments, the average thermal conductivity of the composite may be determined by ASTM El 461.

[0091] The composite may have any of a variety of suitable densities. The density of the composite may be advantageously low, in some aspects. In certain embodiments, for example, the composite has an average density of less than or equal to 2 g / cm3, less than or equal to 1.9 g / cm3, less than or equal to 1.8 g / cm3, less than or equal to 1.7 g / cm3, less than or equal to 1.6 g / cm3, less than or equal to 1.5 g / cm3, less than or equal to 1.4 g / cm3, less than or equal to 1.3 g / cm3, less than or equal to 1.2 g / cm3, or less than or equal to 1.1 g / cm3. In some embodiments, the composite has an average density of greater than or equal to 1 g / cm3, greater than or equal to 1.1 g / cm3, greater than or equal to 1.2 g / cm3, greater than or equal to 1.3 g / cm3, greater than or equal to 1.4 g / cm3, greater than or equal to 1.5 g / cm3, greater than or equal to 1.6 g / cm3, greater than or equal to 1.7 g / cm3, greater than or equal to 1.8 g / cm3, or greater than or equal to 1.9 g / cm3. Combinations of the above recited ranges are possible (e.g., the composite has an average density of less than or equal to 2 g / cm3and greater than or equal to 1 g / cm3, the composite has an average density of less than or equal to 1.8 g / cm3and greater than or equal to 1.6 g / cm3). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0092] In certain embodiments, the average density of the composite may be determined by ASTM D792.

[0093] The composite may have any of a variety of suitable thicknesses. Referring to FIG. 2, for example, composite 100a may have thickness 210, in certain embodiments.

[0094] The thickness of a composite such as is described herein may be advantageously low, in certain aspects. In some embodiments, for example, the composite has an average thickness of less than or equal to 250 micrometers, less than or equal to 200 micrometers, less than or equal to 150 micrometers, or less than or equal to 100 micrometers. In some embodiments, the composite has an average thickness of greater than or equal to 50 micrometers, greater than or equal to 100 micrometers, greater than or equal to 150 micrometers, or greater than or equal to 200 micrometers. Combinations of the above recited ranges are possible (e.g., the composite has an average thickness of less than or equal to 250 micrometers and greater than or equal to 50 micrometers, the composite has an average thickness of less than or equal to 150 micrometers and greater than or equal to 100 micrometers). Other ranges are also possible as the present disclosure is not limiting in this regard.

[0095] According to certain embodiments, a composite as described herein may comprise one or more additives and / or fillers. In some embodiments, for example, the additive and / or filler may comprise one or more secondary conductive materials dispersed in one or more components of the composite (e.g., dispersed in the substrate, the polymer, and / or the conductive material). In certain embodiments, at least a portion of the additive and / or filler is in electrical contact with at least a portion of the substrate (e.g., the plurality of carbon fibers of the substrate).

[0096] Any of a variety of suitable additives and / or fillers may be employed. In some embodiments, for example, the additive and / or filler comprises a carbon-based material. Suitable carbon-based materials include, but are not limited to, graphite, graphene, a carbon nanostructure (e.g., carbon nanotubes, carbon nanowires, etc.), carbon black, and / or combinations thereof. The carbon-based material may be a powder (e.g., carbon and / or graphite powder) or a fiber (e.g., carbon and / or graphite fibers), in some aspects. Other carbon-based materials are also possible. In some embodiments, the additive and / or filler comprises a metal and / or alloy. Suitable metals and / or alloys comprise aluminum (Al), titanium (Ti), nickel (Ni), stainless steel (SS), and / or combinations thereof.

[0097] In certain embodiments, the additive and / or filler comprises a polymer (e.g., a conductive polymer, a non-conductive polymer).

[0098] In some embodiments, the additive and / or filler comprises a colorant and / or dye.

[0099] Other additives and / or fillers are also possible.

[0100] Various methods of making and / or modifying composites are described herein. FIGS. 4A-4E show, according to certain embodiments, schematic diagrams representing a method of making a composite. Referring to FIG. 4A, the method, in some embodiments, comprises providing substrate 202 (e.g., a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate).

[0101] The substrate may be provided, in some embodiments, in the form of a layer and / or film. According to some embodiments, certain methods may comprise providing more than one substrate (e.g., two substrates, three substrates, four substrates, five substrates, etc.), each substrate configured as described herein. In some such embodiments, each substrate in the plurality of substrates may be in the form of a layer and / or film.

[0102] In certain embodiments, certain methods may comprise disposing a conductive material on one or more surfaces of the substrate. Referring to FIG. 4B, for example, one embodiment may comprise disposing conductive material 206 on first surface 402a of substrate 202.

[0103] In some embodiments, e.g., as discussed herein, the conductive material may be disposed on the one or more surfaces of the substrate in the form of a layer and / or film. The conductive material may be disposed on the one or more surfaces of the substrate in the form of a coating, according to some embodiments.

[0104] Although not shown in the figures, the conductive material may be disposed on more than one surface of the substrate. In certain embodiments, for example, the conductive material may be disposed on a first surface of the substrate and on a second surface of the substrate substantially opposite the first surface.

[0105] The methods may comprise, in certain embodiments, disposing more than one conductive material (e.g., two conductive materials, three conductive materials, four conducive materials, five conductive materials, etc.) on one or more surfaces of the substrate. For example, in certain embodiments, two or more conductive materials (e.g., in the form of a layer and / or film, in the form of a coating) may be disposed on one surface of the substrate. In some embodiments, two or more conductive materials (e.g., in the form of a layer and / or film, in the form of a coating) may be disposed on a first surface of the substrate, and two or more conductive materials (e.g., in the form of a layer and / or film, in the form of a coating) may be disposed on a second surface of the substrate substantially opposite the first surface.

[0106] The conductive material may be disposed on one or more surfaces of the substrate by any of a variety of suitable techniques. In some embodiments, the conductive material may be plated, coated, deposited, etc., or otherwise applied on the one or more surfaces of the substrate. For example, in certain embodiments, the conductive material may be applied on one or more surfaces of the substrate via electroplating, electroless plating, conformal coating, lamination, dip coating, spray coating, extrusion, infiltration, etc. Other methods of applying the conductive material are also possible, as the present disclosure is not limiting in this regard.

[0107] According to some embodiments, after disposing the conductive material on one or more surfaces of the substrate, the substrate and the conductive material may be thermally infused, pressed, stamped, pressurized, or the like.

[0108] In some embodiments, after thermally infusing, pressing, stamping, and / or pressurizing the substrate and the conductive material, the conductive material may be at least partially embedded within the substrate. In certain embodiments, the conductive material is completely embedded within the substrate.

[0109] In certain embodiments, various methods may comprise disposing a polymer on one or more surfaces of the substrate and / or on one or more surfaces of the conductive material. Referring to FIG. 4C, for example, a method comprises disposing polymer 204a on first surface 402a of substrate 202. In some embodiments, a method comprises disposing polymer 204b on second surface 402b of substrate 202 substantially opposite of first surface 402a, as shown in FIG. 4D.

[0110] In some embodiments, e.g., as discussed herein, the polymer may be disposed on the one or more surfaces of the substrate and / or conductive material in the form of a layer and / or film. In certain embodiments, the polymer may be disposed on the one or more surface of the substrate and / or conductive material in the form of a coating.

[0111] Certain methods as discussed herein may comprise disposing more than one polymer layer and / or film (e.g., two polymer layers and / or films, three polymer layers and / or films, four polymer layers and / or films, five polymers layer and / or films, etc.) on a first surface of the substrate and / or conductive material, and disposing more than one polymer layer and / or film (e.g., two polymer layers and / or films, three polymer layers and / or films, four polymer layers and / or films, five polymer layers and / or films, etc.) on a second surface of the substrate and / or conductive material substantially opposite the first surface. For example, in certain embodiments, two or more polymer layers and / or films may be disposed on one surface of the substrate and / or conductive material. In some embodiments, two or more polymer layers and / or films may be disposed on a first surface of the substrate and / or conductive material, and two or more polymer layers and / or films may be disposed on a second surface of the substrate and / or conductive material substantially opposite the first surface.

[0112] The polymer may be disposed on the one or more surfaces of the substrate and / or conductive material by any of a variety of suitable techniques. In some embodiments, for example, the polymer is disposed by overmolding, injection molding, additive manufacturing, etc. Other methods of disposing the polymer are also possible, as the present disclosure is not meant to be limiting in this regard.

[0113] According to some embodiments, after disposing the polymer on one or more surfaces of the substrate and / or conductive material, the substrate, the conductive material, and the polymer may be thermally infused, pressed, stamped, pressurized, or the like.

[0114] In certain embodiments, thermally infusing, pressing, stamping, and / or pressurizing the substrate, the conductive material, and the polymer, the polymer may be at least partially embedded within the substrate and / or the conductive material. In some embodiments, the polymer is completely embedded within the substrate and / or the conductive material.

[0115] In some embodiments, the polymer may be disposed on one or more surfaces of the substrate prior to disposing the conductive material on one or more surfaces of the substrate, as the present disclosure is not limiting in this regard.

[0116] According to some embodiments, as a result of disposing the polymer on one or more surfaces of the substrate and / or on one more surfaces of the conductive material, the resulting composite structure may comprise a first region and second region, e.g., as described herein. Referring, for example, to FIG. 4E, as a result of disposing polymer 204a on first surface 402a of substrate 202 and polymer 204b on second surface 402b of substrate 202 substantially opposite first surface 402a, composite 100c may comprise first region 102b (e.g., a perimeter region) and second region 108b (e.g., an interior region).

[0117] According to some embodiments, the resulting composite structure may be modified by disposing the polymer on one or more surfaces of the substrate and / or on one or more surfaces of the conductive material. For example, in certain embodiments, as a result of disposing the polymer on one or more surfaces of the substrate and / or on one or more surfaces of the conductive material, a polymer content of the first region is increased such that the first region has a polymer wt.% versus a total weight of the composite (e.g., a first polymer wt.%) and the second region has a polymer wt.% versus the total weight of the composite (e.g., a second polymer wt.%) that is less than the polymer wt.% of the first region versus the total weight of the composite. Referring, for example, to FIG. 4E, as a result of disposing polymer 204a on first surface 402a of substrate 202 and polymer 204b on second surface 402b of substrate 202 substantially opposite first surface 402a, a polymer content of first region 102b is increased such that first region 102b has a polymer wt.% versus a total weight of composite 100c and second region 108b has a polymer wt.% versus the total weight of composite 100c that is less than the polymer wt.% of the first region versus the total weight of the composite.

[0118] In addition, in some embodiments, after the modifying, a ratio of the polymer wt.% of the first region versus the total weight of the composite (e.g., the first polymer wt.%) to the polymer wt.% of the second region versus the total weight of the composite (e.g., the second polymer wt.%) is less than or equal to 10:1 and greater than or equal to 10:9, as explained herein in greater detail.

[0119] In some embodiments, after the modifying, the polymer wt.% of the first region versus the total weight of the composite (e.g., the first polymer wt.%) may be the same or substantially the same as the polymer wt.% of the second region versus the total weight of the composite (e.g., the second polymer wt.%). According to some embodiments, for example, after the modifying, a ratio of the polymer wt.% of the first region versus the total weight of the composite (e.g., the first polymer wt.%) to the polymer wt.% of the second region versus the total weight of the composite (e.g., the second polymer wt.%) is 1:1.

[0120] In certain embodiments, as a result of disposing the polymer on one or more surfaces of the substrate and / or on one more surfaces of the conductive material, the first region may have a first average areal specific resistance and the second region may have a second average areal specific resistance that is less than the first average areal specific resistance. Referring to FIG. 4E, for example, as a result of disposing polymer 204 on surface 402 of substrate 202, the resulting material (e.g., composite 100c) may be modified such that first region 102b has a first average areal specific resistance and second region 108b has a second average areal specific resistance that is less than the first average areal specific resistance.

[0121] In addition, in certain embodiments, after the modifying, a ratio of the average areal specific resistance of the first region (e.g., the first average areal specific resistance) to the average areal specific resistance of the second region (e.g., the second average areal specific resistance) is less than or equal to 10:1 and greater than or equal to 10:9, as described herein. In some embodiments, after the modifying, the average areal specific resistance of the first region (e.g., the first average areal specific resistance) may be the same or substantially the same as the average areal specific resistance of the second region (e.g., the second average areal specific resistance). According to some embodiments, for example, after the modifying, a ratio of the average areal specific resistance of the first region (e.g., the first average areal specific resistance) to the average areal specific resistance of the second region (e.g., the second average areal specific resistance) is 1:1.

[0122] According to certain embodiments, certain methods comprise forming a plurality of features on at least one surface of the resulting composite structure. In some embodiments, the plurality of features can be formed on at least one surface of the resulting composite structure by stamping, compression molding, pressure forming, vacuum forming, thermoforming, injection molding, insert molding, overmolding, embossing, machining, or the like. Other methods of shaping the composite (e.g., to form a plurality of features) are also possible, as the present disclosure is not limiting in this regard. In some embodiments, the plurality of features may comprise a first portion of features (e.g., valleys) and a second portion of features (e.g., peaks), as described herein. Other features are also possible, however, as the present disclosure is not limiting in this regard. The plurality of features may patterned and / or randomly oriented on the surface of the composite, in some embodiments.

[0123] According to certain aspects, methods of modifying the composites may comprise modifying a surface of the second portion of the plurality of features (e.g., peaks) such that the average areal specific resistance of the surface of the second portion of the plurality of features is less than the average areal specific resistance of a surface of the first portion of the plurality of features (e.g., valleys).

[0124] In some embodiments, modifying the surface of the second portion of the plurality of features (e.g., peaks) comprises decreasing a polymer content of the surface of the second portion of the plurality of features. In certain embodiments, for example, modifying the surface of the second portion of the plurality of features comprises ablating the surface of the second portion of the plurality of features. Any of a variety of ablating techniques may be employed, as the present disclosure is not limiting in this regard. In certain embodiments, for example, ablating comprises machining, laser ablating, sand blasting, sanding (e.g., using sandpaper), or other suitable ablation techniques.

[0125] In certain embodiments, as result of decreasing the polymer content of the surface of the second portion of the plurality of features (e.g., peaks), the surface of the second portion of the plurality of features may comprise a higher content of one or more conductive materials, e.g., as compared to the surface of the first portion of the plurality of features (e.g., valleys). In certain embodiments, after the modifying, a ratio of the average areal specific resistance of the surface of the first portion of the plurality of features to the average areal specific resistance of the surface of the second portion of the plurality of features is greater than or equal to 10:9 and less than or equal to 10: 1, as described herein.

[0126] In some embodiments, after the modifying, the average areal specific resistance of the surface of the first portion of features may be the same or substantially the same as the average areal specific resistance of the surface of the second portion of features. According to some embodiments, for example, after the modifying, a ratio of the average areal specific resistance of the surface of the first portion of features to the average areal specific resistance of the surface of the second portion of features is 1: 1.

[0127] According to certain embodiments, various devices are described. In some embodiments, a device comprises a bipolar plate for an electrochemical cell, although other devices are also contemplated. The bipolar plate may, in some embodiments, be or comprise a composite as described herein (e.g., a composite comprising a substrate, wherein the substrate comprises a plurality of carbon fibers aligned substantially orthogonal to the substrate).

[0128] The bipolar plate may be configured to separate two components of the device, in some embodiments. For example, in certain embodiments, the device is a fuel cell (e.g., a proton exchange membrane fuel cell), and the bipolar plate is configured to separate two cells of the fuel cell.

[0129] Other devices are also possible, however, as the present disclosure is not limiting in this regard. In some embodiments, for example, the device may be a heat exchanger, and the material used as a component of the heat exchanger.

[0130] As described herein, the composite may include a plurality of fibers (e.g., discontinuous fibers), in various aspects. In some cases, the fibers may be substantially aligned, e.g., defining a substrate. In some embodiments, at least 20 vol.%, at least 30 vol.%, at least 40 vol.%, at least 50 vol.%, at least 60 vol.%, at least 70 vol.%, at least 80 vol.%, at least 90 vol.%, at least 95 vol.%, at least 97 vol.%, at least 99 vol.%, etc. of the substrate may contain fibers. In addition, at least 20 vol.%, at least 30 vol.%, at least 40 vol.%, at least 50 vol.%, at least 60 vol.%, at least 70 vol.%, at least 80 vol.%, at least 90 vol.%, at least 95 vol.%, at least 97 vol.%, at least 99 vol.%, etc. of the substrate may be formed from fibers.

[0131] The fibers (e.g., discontinuous fibers) may be formed or include any of a wide variety of materials, and one or more than one type of material may be present. For example, the fibers may comprise materials such as carbon (e.g., carbon fibers), basalt, silicon carbide, silicon nitride, aramid, zirconia, nylon, boron, alumina, silica, borosilicate, mullite, nitride, boron nitride, graphite, glass, a polymer (including any of those described herein), or the like. The fibers may include any natural and / or any synthetic material, and may be magnetic and / or non-magnetic.

[0132] In certain embodiments, the fibers (e.g., discontinuous fibers) may be formed from a material having a relatively high electrical conductivity. For instance, in some embodiments, the fibers have electrical conductivities of at least 100 S / m, at least 1,000 S / m, at least 10,000, at least 100,000 S / m, etc.

[0133] In addition, in some cases, the fibers (e.g., discontinuous fibers) may be formed from materials having relatively a high thermal conductivity. For instance, in various embodiments, the fibers may have thermal conductivities of at least 5 W / m K, at least 10 W / m K, at least 100 W / m K, at least 200 W / m K, at least 250 W / m K, at least 300 W / m K, at least 350 W / m K, at least 400 W / m K, at least 450 W / m K, at least 500 W / m K, at least 600 W / m K, at least 750 W / m K, at least 900 W / m K, at least 1000 W / m K, etc.

[0134] The fibers (e.g., discontinuous fibers), in some embodiments, may be at least substantially aligned within the substrate. Methods for aligning fibers are discussed in more detail herein. Various alignments are possible, and in some cases, can be determined, for example, optically or microscopically. Thus, in some cases, the alignment may be determined qualitatively. However, it should be understood that the alignment need not be perfect. In some cases, at least 5%, at least 10%, at least 25%, at least 50%, at least 75%, at least 85%, at least 90%, or at least 95% of the fibers may be substantially aligned, or may exhibit an alignment that is within 20°, within 15°, within 10°, or within 5° of the average alignment of the plurality of the fibers, e.g., within a sample of the substrate. In other embodiments, the fibers are not substantially aligned within the substrate, as the present disclosure is not limiting in this regard.

[0135] In addition, in some cases, the average alignment of the fibers (e.g., discontinuous fibers) may be oriented to be at least 45°, at least 60°, at least 65°, at least 70°, at least 75°, at least 85°, or at least 87° relative to the plane of the substrate at that location. Without wishing to be bound by any theory, it is believed that alignment of the fibers substantially orthogonal to the substrate may advantageously serve to provide structural reinforcement of the substrate. This may improve the strength of the substrate, e.g., when subjected to forces in different directions. For instance, fibers within the substrate may run in substantially orthogonal directions in three dimensions, thereby providing strength to the substrate regardless of the direction of force that is applied. The fibers may also limit degradation of the surface, e.g., with interlaminar micro-cracks, through-ply fissures, or the like.

[0136] In addition, without wishing to be bound by theory, it is believed that alignment of the fibers (e.g., discontinuous fibers) substantially orthogonal to the substrate may advantageously enhance the ability to transfer electrical current preferentially in a direction along the direction of the fibers, e.g., such that the substrate may exhibit anisotropic electrical conductivity. For example, the substrate may exhibit an electrical conductivity in one direction of at least 100 S / m, at least 1,000 S / m, at least 10,000 S / m, at least 100,000 S / m, etc. For instance, this may be in a direction defined by the average alignment of the fibers, or a through-thickness direction of a substrate, e.g., substantially perpendicular to the plane of the substrate.

[0137] Furthermore, without wishing to be bound by theory, it is believed that alignment of the fibers (e.g., discontinuous fibers) substantially orthogonal to the substrate may advantageously enhance the ability to transfer heat preferentially in a direction along the direction of the fibers, e.g., such that the substrate may exhibit anisotropic heat conductivity. For instance, the substrate may exhibit a heat conductivity in one direction of at least 3 W / m K, at least 5 W / m K, at least 10 W / m K, at least 30 W / m K, at least 50 W / m K, at least 100 W / m K, 250 W / m K, at least 500 W / m K, at least 750 W / m K, etc. For instance, this may be in a direction defined by the average alignment of the fibers, or a through-thickness direction of a substrate, e.g., substantially perpendicular to the plane of the substrate. In some embodiments, this may allow improved heat transfer, e.g., away from a heat source.

[0138] While others have suggested packing fibers in a substrate, it is believed that higher fiber volume fractions were previously unachievable, e.g., in composites. Without wishing to be bound by any theory, it is believed that this may be due to higher electrostatic interactions that cause fiber agglomeration, and / or higher viscosities of polymer resins that can prevent consistent dispersion. Accordingly, certain embodiments as discussed herein are generally directed to fiber volume fractions (e.g., of substantially aligned fibers such as those discussed herein) of at least 40% fiber volume, at least 45% fiber volume, at least 50% fiber volume, at least 55% fiber volume, at least 60% fiber volume, at least 65% fiber volume, at least 70% fiber volume, etc.

[0139] A variety of techniques may be used to align the fibers (e.g., discontinuous fibers) in various embodiments, including magnetic fields, shear flow, or the like, as are discussed in more detail below. As a non-limiting example, magnetic particles, including those discussed herein, can be attached to the fibers, and a magnetic field may then be used to manipulate the magnetic particles. For instance, the magnetic field may be used to move the magnetic particles into a substrate, and / or to align the fibers within the substrate. The magnetic field may be constant or time-varying (e.g., oscillating), for instance, as is discussed herein. For example, an applied magnetic field may have a frequency of 1 Hz to 500 Hz and an amplitude of 0.01 T to 10 T. Other examples of magnetic fields are described in more detail below.

[0140] In some cases, the fibers (e.g., discontinuous fibers) may have any of a variety of suitable lengths. In some embodiments, for example, the fibers have an average length, or characteristic dimension, of at least 1 nm, at least 3 nm, at least 5 nm, at least 10 nm, at least 30 nm, at least 50 nm, at least 100 nm, at least 300 nm, at least 500 nm, at least 1 micrometer, at least 3 micrometers, at least 5 micrometers, at least 10 micrometers, at least 20 micrometers, at least 30 micrometers, at least 50 micrometers, at least 100 micrometers, at least 200 micrometers, at least 300 micrometers, at least 500 micrometers, at least 1 mm, at least 2 mm, at least 3 mm, at least 5 mm, at least 10 mm, at least 15 mm, etc. In certain embodiments, the fibers may have an average length, or characteristic dimension, of no more than 5 cm, no more than 3 cm, no more than 2 cm, no more than 1.5 cm, no more than 1 cm, no more than 5 mm, no more than 3 mm, no more than 2 mm, no more than 1 mm, no more than 500 micrometers, no more than 300 micrometers, no more than 200 micrometers, no more than 100 micrometers, no more than 50 micrometers, no more than 30 micrometers, no more than 20 micrometers, no more than 10 micrometers, no more than 5 micrometers, no more than 3 micrometers, no more than 1 micrometers, no more than 500 nm, no more than 300 nm, no more than 100 nm, no more than 50 nm, no more than 30 nm, no more than 10 nm, no more than 5 nm, etc. Combinations of any of these are also possible. For example, the plurality of fibers may have an average length of between 1 mm and 5 mm.

[0141] In addition, the fibers (e.g., discontinuous fibers) may also have any suitable average diameter. For instance, the fibers may have an average diameter of at least 5 micrometers, at least 10 micrometers, at least 20 micrometers, at least 30 micrometers, at least 50 micrometers, at least 100 micrometers, at least 200 micrometers, at least 300 micrometers, at least 500 micrometers, at least 1 mm, at least 2 mm, at least 3 mm, at least 5 mm, at least 1 cm, at least 2 cm, at least 3 cm, at least 5 cm, at least 10 cm, etc. In certain embodiments, the fibers may have an average diameter of no more than 10 cm, no more than 5 cm, no more than 3 cm, no more than 2 cm, no more than 1 cm, no more than 5 mm, no more than 3 mm, no more than 2 mm, no more than 1 mm, no more than 500 micrometers, no more than 300 micrometers, no more than 200 micrometers, no more than 100 micrometers, no more than 50 micrometers, no more than 30 micrometers, no more than 20 micrometers, no more than 10 micrometers, no more than 5 micrometers, etc. Combinations of any of these are also possible. For example, the fibers may have an average diameter of between 5 micrometers and 50 micrometers, 10 micrometers and 100 micrometers, between 50 micrometers and 500 micrometers, between 100 micrometers and 5 mm, etc.

[0142] In certain embodiments, the fibers (e.g., discontinuous fibers) may have a length that is at least 10 times or at least 50 times its thickness or diameter, on average. In some cases, the fibers may have an average aspect ratio (ratio of fiber length to diameter or thickness) of at least 3, at least 5, at least 10, at least 30, at least 50, at least 100, at least 300, at least 500, at least 1,000, at least 3,000, at least 5,000, at least 10,000, at least 30,000, at least 50,000, or at least 100,000. In some cases, the average aspect ratio of the fibers may be less than 100,000, less than 50,000, less than 30,000, less than 10,000, less than 5,000, less than 3,000, less than 1,000, less than 500, less than 300, less than 100, less than 50, less than 30, less than 10, less than 5, etc. Combinations of any of these are also possible in some cases; for instance, the aspect ratio may be between 5, and 100,000.

[0143] In some instances, the fibers (e.g., discontinuous fibers) may comprise a relatively large portion of the composite. For example, in certain embodiments, the fibers may comprise at least 1%, at least 2%, at least 3%, at least 4%, at least 5%, at least 7%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 97% of the mass or volume of the composite. In some cases, the fibers comprise no more than 97%, no more than 95%, no more than 90%, no more than 85%, no more than 80%, no more than 70%, no more than 60%, no more than 50%, no more than 40%, no more than 30%, no more than 20%, or no more than 10% of the mass or volume of the composite. Combinations of any of these are also possible.

[0144] At least some of the fibers (e.g., discontinuous fibers) may be uncoated. In some cases, however, some or all of the fibers (e.g., discontinuous fibers) may be coated. The coating may be used, for example, to facilitate the adsorption or binding of particles, such as magnetic particles, onto the fibers, or for other reasons.

[0145] As one non-limiting example, at least some of the fibers are coated with sizing. Some examples of coatings or sizings include, but are not limited to, polypropylene, polyurethane, polyamide, phenoxy, polyimide, epoxy, or the like. These can be introduced, for example, as a solution, dispersion, emulsion, etc. As other examples, the fibers may be coated with a surfactant, a silane coupling agent, an epoxy, glycerine, polyurethane, an organometallic coupling agent, or the like. Non-limiting examples of surfactants include oleic acid, sodium dodecyl sulfate, sodium lauryl sulfate, etc. Non-limiting examples of silane coupling agents include amino-, benzylamino-, chloropropyl-, disulfide-, epoxy-, epoxy / melamine-, mercapto-, methacrylate-, tertasulfido-, ureido-, vinyl-, isocynate-, and vinly-benzyl-amino- based silane coupling agents. Non-limiting examples of organometallic coupling agents include aryl- and vinyl-based organometallic coupling agents.

[0146] As mentioned, in one set of embodiments, at least some of the fibers (e.g., discontinuous fibers) may be carbon fibers (e.g., discontinuous carbon fibers). The carbon fibers may be aligned in a magnetic field directly or indirectly, e.g., using magnetic particles or other techniques such as those discussed herein. For instance, some types of carbon fibers are diamagnetic and can be directly moved using an applied magnetic field. Thus, certain embodiments are directed to fibers that are substantially free of paramagnetic or ferromagnetic materials and could still be aligned using an external magnetic field. For example, if any paramagnetic or ferromagnetic materials are present, they may form less than 5%, less than 1%, less than 0.5%, less than 0.3%, less than 0.1%, less than 0.05%, less than 0.03%, less than 0.01%, less than 0.005%, less than 0.003%, or less than 0.001% (by mass) of the material.

[0147] A variety of carbon fibers may be obtained commercially, including diamagnetic carbon fibers. In some cases, carbon fibers can be produced from polymer precursors such as polyacrylonitrile (PAN), rayon, pitch, or the like. In some cases, carbon fibers can be spun into filament yarns, e.g., using chemical or mechanical processes to initially align the polymer atoms in a way to enhance the final physical properties of the completed carbon fibers. Precursor compositions and mechanical processes used during spinning filament yams may vary. After drawing or spinning, the polymer filament yams can be heated to drive off non-carbon atoms (carbonization or pyrolization), to produce final carbon fiber. In some embodiments, such techniques may be used to produce carbon fiber with relatively high carbon content, e.g., at least 90%, or other contents as described herein.

[0148] Non-limiting examples of carbon fibers include, for instance, pitch- and / or polymer- based (e.g., ex-PAN or ex-Rayon) variants, including those commercially-available. In some cases, these may include intermediate / standard modulus (greater than 200 GPa) carbon fibers, high modulus (greater than 300 GPa), or ultra-high modulus (greater than 500 GPa) carbon fibers. In one set of embodiments, the carbon fibers have a relatively high carbon content. Without wishing to be bound by any theory, it is believed that such fibers may exhibit diamagnetic properties that allows them to be oriented with low-energy magnetic fields. In general, diamagnetism is the repulsion of a material to an applied magnetic field by generation of an induced magnetic field that is opposite in direction to the applied magnetic field. A material is typically categorized as diamagnetic if it lacks noticeable paramagnetic or ferromagnet contributions to the overall magnetic response. In many cases, the magnetic response of diamagnetic materials is very weak and negligible. However, relatively high magnetic fields can induce a noticeable physical response in such diamagnetic materials.

[0149] Thus, in some cases, carbon fibers exhibiting relatively highly-oriented molecular structures may exhibit anisotropic, high-diamagnetism diamagnetic properties. Such diamagnetic properties may allow them to be oriented with relatively weak magnetic fields, such as is described herein. For example, in one set of embodiments, an applied magnetic field may generate a strong induced magnetic field in the C-C bonds of a carbon fiber in the opposite direction of the applied magnetic field. Certain types of carbon fibers may possess a high degree of C-C bonds parallel to the in-fiber direction, which may create an anisotropic diamagnetic response. Thus, such carbon fibers can be subjected to a magnetic torque that is neutralized when the carbon fiber aligns fully-parallel to the applied magnetic field. Accordingly, by applying a suitable magnetic field, the carbon fibers may be aligned due to such diamagnetic properties. This response may be sufficient to overcome gravitational, viscous, and / or interparticle steric effects.

[0150] For instance, in certain embodiments, the carbon fibers may have a carbon content of greater than 80%, greater than 90%, greater than 92%, greater than 94%, greater than 95%, greater than 96%, greater than 97%, greater than 98% greater than 99%, or greater than 99.5% by mass. Such carbon fibers may be obtained commercially in some cases. For example, the carbon fibers may be produced pyrolytically e.g., by “burning” or oxidizing other components that can be removed (e.g., by turning into a gas), leaving behind a carbon fiber with a relatively high carbon content. Other methods of making carbon fibers are also possible, e.g., as discussed in detail herein.

[0151] The carbon fibers may also exhibit substantial alignment of the C-C bonds within the carbon fibers in some instances. For instance, at least 50%, at least 60%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95% of the carbon fibers may exhibit substantial alignment of the C-C bonds. Such alignment may be determined, for example, using wide angle x-ray diffraction (WAXD), or other techniques known to those of ordinary skill in the art.

[0152] In one set of embodiments, the carbon fibers (or other fibers) may have a relatively high modulus (tensile modulus, which is a measure of stiffness). Typically, higher modulus fibers are stiffer and lighter than low modulus fibers. Carbon fibers typically have a higher modulus when force is applied parallel to the fibers, i.e., the carbon fibers are anisotropic. In some embodiments, the carbon fibers (or other fibers) may have a modulus (e.g., when force is applied parallel to the fibers) of at least 100 GPa, at least 200 GPa, at least 300 GPa, at least 400 GPa, at least 500 GPa, at least 600 GPa, at least 700 GPa, etc. It is believed that more flexible carbon fibers may exhibit less alignment, i.e., carbon fibers having a low modulus may have subtle physical responses to magnetic fields, or have no response, rather than align within an applied magnetic field.

[0153] In one set of embodiments, the carbon fibers (or other fibers) may exhibit an anisotropic diamagnetic response when free-floating within a liquid (e.g., water, oil, polymer resin, polymer melt, metal melt, an alcohol such as ethanol, or another volatile organic compound), and a magnetic field is applied. For example, in some cases, the carbon fibers may align when a suitable magnetic field is applied, i.e., indicative of a diamagnetic response. In some cases, the magnetic field may be at least 100 mT, at least 200 mT, at least 300 mT, at least 500 mT, at least 750 mT, at least 1 T, at least 1.5 T, at least 2 T, at least 3 T, at least 4 T, at least 5 T, at least 10 T, etc. In some cases, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90%, of the free-floating carbon fibers within the liquid may exhibit alignment when a suitable magnetic field is applied.

[0154] Typically, a fiber has a shape such that one orthogonal dimension (e.g., its length) is substantially greater than its other two orthogonal dimensions (e.g., its width or thickness). The fiber may be substantially cylindrical in some cases. As mentioned, the carbon fibers may be relatively stiff, in some instances; however, a carbon fiber need not be perfectly straight (e.g., its length may still be determined along the fiber itself, even if it is curved).

[0155] In one set of embodiments, the carbon fiber may have a dimension (e.g., a characteristic dimension) that is substantially the same, or smaller, than the thickness of the substrate. For example, at least some carbon fibers within a substrate may have an average length that substantially spans the thickness of the substrate. However, in other cases, the characteristic dimension of the carbon fiber may be greater than the thickness.

[0156] As mentioned, in one set of embodiments, particles such as magnetic particles may be added, for example, to align the fibers (e.g., discontinuous fibers), or for other applications. The particles may be adsorbed or otherwise bound to at least some of the fibers. In some cases, the particles may coat some or all of the fibers. This may be facilitated by a coating of material as discussed herein, although a coating is not necessarily required to facilitate the adsorption of the particles.

[0157] If the particles are magnetic, the particles may comprise any of a wide variety of magnetically susceptible materials. For example, the magnetic materials may comprise one or more ferromagnetic materials, e.g., containing iron, nickel, cobalt, alnico, oxides of iron, nickel, cobalt, rare earth metals, or an alloy including two or more of these and / or other suitable ferromagnetic materials. In some cases, the magnetic particles may have a relative permeability of at least 2, at least 5, at least 10, at least 20, at least 40, at least 100, at least 200, at least 500, at least 1,000, at least 2,000, at least 5,000, or at least 10,000.

[0158] However, it should be understood that not all of the particles are necessarily magnetic. In some cases, non-magnetic particles may be used, e.g., in addition to and / or instead of magnetic particles. Non-limiting examples of nonmagnetic particles include glass, polymer, metal, or the like. In addition, in some embodiments, no particles are present.

[0159] The particles (if present) may be spherical or non- spherical, and may be of any suitable shape or size. The particles may be relatively monodisperse or come in a range of sizes. In some cases, the particles may have a characteristic dimension, on average, of at least 10 micrometers, at least 20 micrometers, at least 30 micrometers, at least 50 micrometers, at least 100 micrometers, at least 200 micrometers, at least 300 micrometers, at least 500 micrometers, at least 1 mm, at least 2 mm, at least 3 mm, at least 5 mm, at least 1 cm, at least 1.5 cm, at least 2 cm, at least 3 cm, at least 5 cm, at least 10 cm, etc. The particles may also have an average characteristic dimension of no more than 10 cm, no more than 5 cm, no more than 3 cm, no more than 2 cm, no more than 1.5 cm, no more than 1 cm, no more than 5 mm, no more than 3 mm, no more than 2 mm, no more than 1 mm, no more than 500 micrometers, no more than 300 micrometers, no more than 200 micrometers, no more than 100 micrometers, no more than 50 micrometers, no more than 30 micrometers, no more than 20 micrometers, no more than 10 micrometers, etc. Combinations of any of these are also possible. For example, the particles may exhibit a characteristic dimension of or between 100 micrometer and 1 mm, between 10 micrometer and 10 micrometer, etc. The characteristic dimension of a nonspherical particle may be taken as the diameter of a perfect sphere having the same volume as the nonspherical particle.

[0160] In addition, in some aspects, the substrate may further comprise fillers or additional materials, e.g., in addition to fibers (e.g., discontinuous fibers). For instance, in certain embodiments, the substrate may further comprise one or more ceramics, such as boron nitride, alumina, titania, or the like. In addition, in some embodiments, the substrate may further comprise one or more metals, such as aluminum, copper, silver, tin, gold, etc. In addition, in one embodiment, such materials present within the substrate may be formed by fusing particles together, e.g., during formation of the substrate. Other materials may also be present in the substrate in some cases as well.

[0161] In one set of embodiments, a binder is also present within the substrate, e.g., which may be used to bind the fibers (e.g., discontinuous fibers), e.g., within the substrate. For example, the binder may facilitate holding the fibers in position within the substrate. However, it should be understood that the binder is optional and not required in all cases. In some cases, the binder may comprise a resin. The binder may include, for example, a thermoset, thermoplastic, and / or a vitrimer. In certain embodiments, the binder may comprise a thermoplastic solution, a thermoplastic melt, thermoplastic pellets, a thermoset resin, a volatile compound such as a volatile organic compound, water, or an oil. Additional non-limiting examples of binders include an epoxy, polyester, vinyl ester, polyethylenimine, polyetherketoneketone, polyaryletherketone, polyether ether ketone, polyphenylene sulfide, polyethylene terephthalate, a polycarbonates, poly (methyl methacrylate), acrylonitrile butadiene styrene, polyacrylonitrile, polypropylene, polyethylene, nylon, a silicone rubber, polyvinylidene fluoride, styrene butadiene rubber, or a pre-ceramic monomer, a siloxane, a silazane, or a carbosilane. In some cases, a binder may comprise a covalent network polymer prepared from an imine-linked oligomer and an independent crosslinker comprising a reactive moiety. Non-limiting examples of reactive moieties include epoxy, isocyanate, bismaleimide, sulfide, polyurethane, anhydride, and / or polyester. Examples of vitrimers include, but are not limited to, epoxy resins based on diglycidyl ether of bisphenol A, aromatic polyesters, polylactic acid (poly lactide), polyhydroxyurethanes, epoxidized soybean oil with citric acid, polybutadiene, etc. The binder may also include mixtures including any one or more of these materials and / or other materials, in certain embodiments.

[0162] In some embodiments, the binder may comprise at least 1%, at least 2%, at least 3%, at least 4%, at least 5%, at least 7%, at least 10%, at least 15%, at least 20%, or at least 25% of the mass of the substrate, and / or no more than 25%, no more than 20%, no more than 15%, no more than 10%, no more than 7%, no more than 5%, no more than 4%, no more than 3%, no more than 2%, or no more than 1% of the mass of the substrate.

[0163] As discussed, certain aspects are generally directed to composites. In some cases, the composite is generally planar, and / or may contain one (or more) substrates. However, it should be understood that the composite or the substrate need not be a mathematically-perfect planar structure (although they can be); for instance, a composite, or a substrate, may also be at least partially deformable, curved, bent, folded, rolled, creased, or the like. Also, the substrate may be rigid, in some cases.

[0164] Another aspect is generally directed to systems and methods for making substrates such as those described herein. In one set of embodiments, such substrates can be prepared from a liquid. The liquid may be, for example, a slurry, a solution, an emulsion, or the like. The liquid may contain fibers (e.g., discontinuous fibers) such as discussed herein. The fibers may then be aligned as discussed herein, and the liquid may be then be removed, e.g., to create a fiber-containing material. After alignment, the final substrate may be formed, for example, by applying heat and / or pressure, e.g., to remove the liquid and / or to embed the fibers into the substrate. In some cases, the substrate can be set or hardened, e.g., with a binder, which may be used to immobilize or fix the fibers within the substrate. The composite may be relatively stiff or flexible in various embodiments.

[0165] In one set of embodiments, the liquid is able to neutralize the electrostatic interactions between the fibers (e.g., discontinuous fibers), for example using aqueous liquids. This may be useful, for example, to allow the fibers to be dispersed within the liquid at relatively high fiber volumes without agglomeration. In some cases, surfactants and / or alcohols can be introduced into the slurry to reduce electrostatic interactions between the fibers. High shear mixing and flow also may help reduce agglomeration / flocculation in certain cases.

[0166] In some embodiments, the liquid phase may include, for example, a thermoplastic or a thermoset, e.g., a thermoplastic solution, thermoplastic melt, thermoset, volatile organic compound, water, or oil. Non-limiting examples of thermosets include polyethylenimine, polyetherketoneketone, polyaryletherketone, polyether ether ketone, polyphenylene sulfide, polyethylene terephthalate, a polycarbonates, poly (methyl methacrylate), acrylonitrile butadiene styrene, polyacrylonitrile, polypropylene, polyethylene, nylon, polyvinylidene fluoride, phenolics, epoxies, bismaleimides, cyanate esters, polyimides, etc. Non-limiting examples of elastomers include silicone rubber and styrene butadiene rubber, etc. Nonlimiting examples of thermoplastics include epoxy, polyester, vinyl ester, polycarbonates, polyamides (e.g., nylon, PA-6, PA- 12, etc.), polyphenylene sulfide, polyetherimide, poly etheretherketone, polyetherketoneketone, etc. Non-limiting examples of ceramic monomers include a siloxane, a silazane, or a carbosilane, etc. In some cases, for example, one or more of these may be added to assist in homogenously dispersing the fibers within the liquid. Examples of volatile organic compounds include, but are not limited to, isopropanol, butanol, ethanol, acetone, toluene, or xylenes.

[0167] Any suitable amount of fibers (e.g., discontinuous fibers) may be present in the slurry or other liquid. For instance, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, or at least 80% of the volume of the slurry may be fibers. In some cases, no more than 85%, no more than 80%, no more than 75%, no more than 70%, no more than 65%, no more than 60%, no more than 55%, no more than 50%, no more than 45%, no more than 40%, no more than 35%, no more than 30%, no more than 25%, no more than 20%, no more than 15%, or no more than 10% may be fibers. Combinations of any of these are also possible in some cases. For example, a slurry or other liquid may contain between 70% and 80%, between 75% and 85%, between 50% and 90%, etc. fibers.

[0168] For example, after preparation of the slurry or other liquid, it may be applied to or exposed to a surface, e.g., to form a substrate. Any suitable method may be used to apply the slurry or other liquid to the surface. As non-limiting examples, the liquid may be poured, coated, sprayed, or painted onto the surface, or the surface may be immersed partially or completely within the liquid. The liquid may be used to wet, coat, and / or surround the surface.

[0169] A magnetic field may be applied to manipulate the fibers (e.g., discontinuous fibers), directly or indirectly, as discussed herein, according to one set of embodiments. Any suitable magnetic field may be applied. In some cases, the magnetic field is a constant magnetic field. In other cases, the magnetic field may be time-varying; for example, the magnetic field may oscillate or periodically change in amplitude and / or direction, e.g., to facilitate manipulation of the fibers. The oscillation may be sinusoidal or another repeating waveform (e.g., square wave or sawtooth). The frequency may be, for example, at least 0.1 Hz, at least 0.3 Hz, at least 0.5 Hz, at least 1 Hz, at least 3 Hz, at least 5 Hz, at least 10 Hz, at least 30 Hz, at least 50 Hz, at least 100 Hz, at least 300 Hz, at least 500 Hz, etc., and / or no more than 1000 Hz, no more than 500 Hz, no more than 300 Hz, no more than 100 Hz, no more than 50 Hz, no more than 30 Hz, no more than 10 Hz, no more than 5 Hz, no more than 3 Hz, etc. For example, the frequency may be between 1 Hz to 500 Hz, between 10 Hz and 30 Hz, between 50 Hz and Hz, or the like. In addition, the frequency may be held substantially constant, or the frequency may vary in some cases.

[0170] The magnetic field, whether constant or oscillating, may have any suitable amplitude. For example, the amplitude may be at least 0.001 T, at least 0.003 T, at least 0.005 T, at least 0.01 T, at least 0.03 T, at least 0.05 T, at least 0.1 T, at least 0.3 T, at least 0.5 T, at least 1 T, at least 3 T, at least 5 T, at least 10 T, etc. The amplitude in some cases may be no more than 20 T, no more than 10 T, no more than 5 T, no more than 3 T, no more than 1 T, no more than 0.5 T, no more than 0.3 T, no more than 0.1 T, no more than 0.05 T, no more than 0.03 T, no more than 0.01 T, no more than 0.005 T, no more than 0.003 T, etc. The amplitude may also fall within any combination of these values. For instance, the amplitude may be between 0.01 T to 10 T, between 1 T and 3 T, between 0.5 T and 1 T, or the like. The amplitude may be substantially constant, or may vary in certain embodiments, e.g., within any range of these values.

[0171] In some embodiments, the magnetic field direction (i.e., direction of maximum amplitude) may vary by + / - 90°, + / - 85°, + / - 80°, + / -75°, + / -700, + / -65°, + / -600, + / -55°, + / -500, + / -45°, + / -400, + / -35°, + / -300, + / -25°, + / -200, + / -15°, + / -100, + / -5° about a mean direction.

[0172] A variety of different devices for producing suitable magnetic fields may be obtained commercially, and include permanent magnets or electromagnets. In some cases, an oscillating magnetic may be created by attaching a magnet to a rotating disc and rotating the disc at an appropriate speed or frequency. Non-limiting examples of permanent magnets include iron magnets, alnico magnets, rare earth magnets, or the like.

[0173] In one set of embodiments, shear flow may be used to align or manipulate the fibers (e.g., discontinuous fibers). For example, a shearing fluid may be applied to the substrate to cause at least some of the plurality of fibers to align, e.g., in the direction of shear flow. Examples of shearing fluids that may be used include water, or another liquid, such as oil, an alcohol such as ethanol, an organic solvent (e.g., such as isopropanol, butanol, ethanol, acetone, toluene, or xylenes), or the like. In certain embodiments, the shearing fluid may have a viscosity of at least 1 cP. In addition, in some cases, the shearing fluid may be a gas, such as air. The linear flow rate of the shearing fluid, may be, for example, at least 10 mm / min, at least 20 mm / min, at least 30 mm / min, at least 50 mm / min, at least 100 mm / min, at least 200 mm / min, at least 300 mm / min, etc.

[0174] For example, in one set of embodiments, the fibers can be added to a liquid, including an alcohol, solvent, or resin, to form a slurry. The slurry can be flowed to align the fibers in some cases, e.g., wherein the slurry is used as a shearing fluid. In other cases, however, the slurry may first be applied to a substrate, then a shearing fluid used to align the fibers.

[0175] In addition, in some embodiments, mechanical vibration may be used to manipulate the fibers (e.g., discontinuous fibers), e.g., in addition to and / or instead of magnetic manipulation and / or shear flow. For example, mechanical vibration can be used to move fibers into or on the substrate, e.g., into pores or holes within the substrate, and / or at least to substantially align the fibers within the substrate, e.g., as discussed herein. In one set of embodiments, mechanical vibration may be applied to cause motion of the fibers of at least 1 micrometer, at least 2 micrometers, at least 3 micrometers, at least 5 micrometers, at least 10 micrometers, at least 20 micrometers, at least 30 micrometers, at least 50 micrometers, at least 100 micrometers, at least 200 micrometers, at least 300 micrometers, at least 500 micrometers, at least 1,000 micrometers, at least 2,000 micrometers, at least 3,000 micrometers, at least 5,000 micrometers, or at least 10,000 micrometers.

[0176] In addition, in some cases, the mechanical vibrations may be time-varying; for example, the mechanical vibrations may periodically change in amplitude and / or direction, e.g., to facilitate manipulation of the fibers (e.g., discontinuous fibers). The oscillation may be sinusoidal or another repeating waveform (e.g., square wave or sawtooth). The frequency may be, for example, at least 0.1 Hz, at least 0.3 Hz, at least 0.5 Hz, at least 1 Hz, at least 3 Hz, at least 5 Hz, at least 10 Hz, at least 30 Hz, at least 50 Hz, at least 100 Hz, at least 300 Hz, at least 500 Hz, etc., and / or no more than 1000 Hz, no more than 500 Hz, no more than 300 Hz, no more than 100 Hz, no more than 50 Hz, no more than 30 Hz, no more than 10 Hz, no more than 5 Hz, no more than 3 Hz, etc. For example, the frequency may be between 1 Hz to 500 Hz, between 10 Hz and 30 Hz, between 50 Hz and Hz, or the like. In addition, the frequency may be held substantially constant, or the frequency may vary in some cases. If applied in conjunction with an oscillating magnetic field, their frequencies may independently be the same or different.

[0177] During and / or after alignment, the fibers (e.g., discontinuous fibers) may be set or fixed with the substrate, in some embodiments, e.g., to prevent or limit subsequent movement of the fibers. Non -limiting examples of techniques include, but are not limited to solidifying, hardening, gelling, melting, heating, evaporating, freezing, lyophilizing, or pressing the liquid or the slurry. In another set of embodiments, a material, such as a thermosetting polymer, may be cured to harden the substrate.

[0178] In some cases, the liquid may comprise a relatively volatile solvent, which can be removed by heating and / or evaporation (e.g., by waiting a suitable amount of time, or allowing the solvent to evaporate, e.g., in a fume hood or other ventilated area). Non-limiting examples of volatile solvents include isopropanol, butanol, ethanol, acetone, toluene, or xylenes. Other examples of methods of removing solvents include applying vacuum, lyophilization, mechanical shaking, or the like. In one set of embodiments, heating may be applied to the fibers (e.g., discontinuous fibers), for example, to dry the liquid or remove a portion of the solvent. For example, the fibers may be heated to a temperature of at least about 30 °C, at least about 35 °C, at least about 40 °C, at least about 45 °C, at least about 50 °C, at least about 55 °C, at least about 60 °C, at least about 65 °C, at least about 70 °C, at least about 75 °C, at least about 80 °C, at least about 90 °C, at least about 100 °C, at least about 125 °C, at least about 150 °C, at least about 175 °C, at least about 200 °C, at least about 250 °C, at least about 300 °C, at least about 350 °C, at least about 400 °C, at least about 450 °C, at least about 500 °C, etc. Any suitable method of applying heat may be used, for example, a thermoelectric transducer, an Ohmic heater, a Peltier device, a combustion heater, or the like. In some cases, the viscosity of the liquid may decrease as a result of heating. The heating may be applied, for example, prior, concurrent or subsequent to the application of magnetic field and / or mechanical vibration. In some cases, heating may be used to prevent or initiate cross-linking or curing of a thermosetting prepolymer.

[0179] In one set of embodiments, pressure may be applied to the substrate, e.g., to partially or completely embed the fibers (e.g., discontinuous fibers) into the substrate, e.g., to form the substrate. In some cases, the pressure may be used to also remove some of the liquid from the substrate. Examples include, but are not limited to, hot-pressing, calendaring, vacuum infusion, or the like. The pressure, may be, for example, at least 15 psi (gauge), at least 30 psi, at least 45 psi, etc. (1 psi = 6895 Pa)

[0180] A binder may also be applied in one set of embodiments, e.g., before, during, and / or after hardening of the substrate and / or removal of at least a portion of the liquid. In some embodiments, the binder may be used to produce a pre-impregnated composite ply material, e.g., by wetting dry ply material.

[0181] The following documents are incorporated herein by reference in their entireties: Int. Pat. Apl. Pub. No. WO 2018 / 175134, entitled “Fiber-Reinforced Composites, Methods Therefore And Articles Comprising The Same”; Int. Pat. Apl. Pub. No. WO 2020 / 123334, entitled “Systems and Methods for Carbon Fiber Alignment and Fiber-Reinforced Composites”; Int. Pat. Apl. Pub. No. WO 2021 / 007381, entitled “Systems and Methods for Forming Short-Fiber Films, Composites Comprising Thermosets, and Other Composites”; Int. Pat. Apl. Pub. No. WO 2021 / 007389, entitled “Compositions and Methods for Carbon Fiber-Metal Composites”; U.S. Pat. Apl. Ser. No. 63 / 511,534, filed June 30, 2023, entitled “Composite Bipolar Plates and Methods of Making and Use Thereof’; and U.S. Pat. Apl. Ser. No. 63 / 513,403, filed July 13, 2023, entitled “Composite Bipolar Plates and Methods of Making and Use Thereof.”

[0182] The following examples are intended to illustrate certain embodiments of the present disclosure, but do not exemplify the full scope of the disclosure.

[0183] EXAMPLE 1

[0184] The following example describes the fabrication of bipolar plates.

[0185] In a first embodiment, a graphite / polyetherimide composite film (75 micrometer thickness) was pressed on one surface of a dry ZRT™ film (150 micrometer thickness). The graphite / polyetherimide composite film and the dry ZRT™ film were thermally infused. A first polyetherimide film (25 micrometer thickness) was then added to a perimeter region of the resulting material by pressing the first poly etherimide film on a first surface of the perimeter region of the resulting material. A second polyetherimide film (25 micrometer thickness) was then added to the perimeter region of the resulting material by pressing the second polyetherimide film on a second surface of the perimeter region of the resulting material substantially opposite the first surface. The thermally infused graphite / polyetherimide composite film-dry ZRT™ film and the polyetherimide films were then thermally stamped and pressurized to form the composite bipolar plate (see FIGS. 5-6).

[0186] In a second embodiment, a first graphite / polyetherimide composite film (50 micrometer thickness) was pressed on a first surface of a dry ZRT™ film (150 micrometer thickness), and a second graphite / polyetherimide composite film (25 micrometer thickness) was pressed on a second surface of the dry ZRT™ film substantially opposite the first surface. The graphite / polyetherimide composite films and the dry ZRT™ film were thermally infused. A first polyetherimide film (25 micrometer thickness) was then added to a perimeter region of the resulting material by pressing the polyetherimide film on a first surface of the perimeter region of the resulting material. A second polyetherimide film (25 micrometer thickness) was then added to the perimeter region of the resulting material by pressing the polyetherimide film on a second surface of the perimeter region of the resulting material substantially opposite the first surface. The thermally infused graphite / polyetherimide composite films -dry ZRT™ film and the poly etherimide films were then thermally stamped and pressurized to form the composite bipolar plate.

[0187] In a third embodiment, two graphite / polyetherimide composite films (25 micrometer thicknesses) were pressed on a first surface of a dry ZRT™ film (150 micrometer thickness), and another graphite / polyetherimide composite film (25 micrometer thicknesses) was pressed on a second surface of the dry ZRT™ film substantially opposite the first surface. The graphite / polyetherimide composite films and the dry ZRT™ film were thermally infused. A first polyetherimide film (25 micrometer thickness) was then added to a perimeter region of the resulting material by pressing the polyetherimide film on a first surface of the perimeter region of the resulting material. A second polyetherimide film (25 micrometer thickness) was then added to the perimeter region of the resulting material by pressing the polyetherimide film on a second surface of the perimeter region of the resulting material substantially opposite the first surface. The thermally infused graphite / polyetherimide composite films-dry ZRT™ film and the polyetherimide films were then thermally stamped and pressurized to form the composite bipolar plate.

[0188] The first, second, and third embodiments were repeated by substituting polyetherimide with polypropylene, polyvinylidene fluoride, polyethersulfone, and polyphenylene sulfide.

[0189] EXAMPLE 2

[0190] The following example describes an alternative fabrication of bipolar plates.

[0191] In a first embodiment, a graphite / fluoroelastomer composite film (75 micrometer thickness) was pressed on one surface of a dry ZRT™ film (150 micrometer thickness). The graphite / fluoroelastomer composite film and the dry ZRT™ film were thermally infused. A first polyetherimide film (25 micrometer thickness) was then added to a perimeter region of the resulting material by pressing the first poly etherimide film on a first surface of the perimeter region of the resulting material. A second polyetherimide film (25 micrometer thickness) was then added to the perimeter region of the resulting material by pressing the second polyetherimide film on a second surface of the perimeter region of the resulting material substantially opposite the first surface. The thermally infused graphite / fluoroelastomer-dry ZRT™ film and the polyetherimide films were then thermally stamped, pressurized, and thermally cured to form the composite bipolar plate.

[0192] In a second embodiment, a graphite / fluoroelastomer composite film (50 micrometer thickness) was pressed on one surface of a dry ZRT™ film (150 micrometer thickness). The graphite / fluoroelastomer composite film and the dry ZRT™ film were thermally infused. A first polyetherimide film (25 micrometer thickness) was then added to a perimeter region of the resulting material by pressing the first poly etherimide film on a first surface of the perimeter region of the resulting material. A second polyetherimide film (25 micrometer thickness) was then added to the perimeter region of the resulting material by pressing the second polyetherimide film on a second surface of the perimeter region of the resulting material substantially opposite the first surface. The thermally infused graphite / fluoroelastomer-dry ZRT™ film and the polyetherimide films were then thermally stamped, pressurized, and thermally cured to form the composite bipolar plate.

[0193] In a third embodiment, a graphite / fluoroelastomer composite film (25 micrometer thickness) was pressed on one surface of a dry ZRT™ film (150 micrometer thickness). The graphite / fluoroelastomer composite film and the dry ZRT™ film were thermally infused. A first polyetherimide film (25 micrometer thickness) was then added to a perimeter region of the resulting material by pressing the first poly etherimide film on a first surface of the perimeter region of the resulting material. A second polyetherimide film (25 micrometer thickness) was then added to the perimeter region of the resulting material by pressing the second polyetherimide film on a second surface of the perimeter region of the resulting material substantially opposite the first surface. The thermally infused graphite / fluoroelastomer-dry ZRT™ film and the polyetherimide films were then thermally stamped, pressurized, and thermally cured to form the composite bipolar plate.

[0194] The first, second, and third embodiments were repeated by substituting graphite / fluoroelastomer with an epoxy resin, a vinyl ester resin, a furan ester resin, an acrylic resin, a phenolic resin, a polyimide resin, and Arkema Elium® Resin.

[0195] EXAMPLE 3

[0196] The following example describes yet another alternative fabrication of bipolar plates.

[0197] In a first embodiment, a polyetherimide film (75 micrometer thickness) was pressed on one surface of a dry ZRT™ film (150 micrometer thickness). The polyetherimide film and the dry ZRT™ film were thermally infused by pressing at 380° C for 1 minute and held in a double belt press. The thermally infused poly etherimide film-dry ZRT™ film was then thermally stamped to form the composite bipolar plate geometry. Next, a fluoroelastomer / graphite formulation was sprayed on one surface of an interior region of the resulting material to form the final composite bipolar plate.

[0198] In a second embodiment, a polyetherimide film (50 micrometer thickness) was pressed on one surface of a dry ZRT™ film (150 micrometer thickness). The polyetherimide film and the dry ZRT™ film were thermally infused by pressing at 380° C for 1 minute and held in a double belt press. The thermally infused poly etherimide film-dry ZRT™ film was then thermally stamped to form the composite bipolar plate geometry. Next, a fluoroelastomer / graphite formulation was sprayed on one surface of an interior region of the resulting material to form the final composite bipolar plate.

[0199] In a third embodiment, a polyetherimide film (25 micrometer thickness) was pressed on one surface of a dry ZRT™ film (150 micrometer thickness). The polyetherimide film and the dry ZRT™ film were thermally infused by pressing at 380° C for 1 minute and held in a double belt press. The thermally infused poly etherimide film-dry ZRT™ film was then thermally stamped to form the composite bipolar plate geometry. Next, a fluoroelastomer / graphite formulation was sprayed on one surface of an interior region of the resulting material to form the final composite bipolar plate.

[0200] The first, second, and third embodiments were repeated by substituting polyetherimide with polypropylene, polyvinylidene fluoride, polyethersulfone, and polyphenylene sulfide.

[0201] EXAMPLE 4

[0202] The following example describes yet another alternative fabrication of bipolar plates.

[0203] In a first embodiment, a polyetherimide film (75 micrometer thickness) was pressed on a first surface of a dry ZRT™ film (150 micrometer thickness), and a second polyetherimide film (25 micrometer thickness) was pressed on a second surface of the dry ZRT™ film substantially opposite the first surface. The polyetherimide films and the dry ZRT™ film were thermally infused by pressing at 380° C for 1 minute and held in a double belt press. The resulting material was thermally stamped and pressurized. Next, a surface of the interior region of the resulting material was partially ablated to remove between 5-15 micrometers of material from the surface (see, for example, FIG. 7). A nickel (Ni) film (1-5 micrometer thickness) and a non-porous graphite coating (less than 1 micrometer thickness) were then either electroplated or deposited by physical vapor deposition on the interior region of surface of the interior region of the resulting material to form the composite bipolar plate.

[0204] In a second embodiment, a polyetherimide film (50 micrometer thickness) was pressed on a first surface of a dry ZRT™ film (150 micrometer thickness), and a second polyetherimide film (50 micrometer thickness) was pressed on a second surface of the dry ZRT™ film substantially opposite the first surface. The polyetherimide films and the dry ZRT™ film were thermally infused by pressing at 380° C for 1 minute and held in a double belt press. The resulting material was thermally stamped and pressurized. Next, a surface of the interior region of the resulting material was partially ablated to remove between 5-15 micrometers of material from the surface. A nickel (Ni) film (1-5 micrometer thickness) and a non-porous graphite coating (less than 1 micrometer thickness) were then either electroplated or deposited by physical vapor deposition on the interior region of surface of the interior region of the resulting material to form the composite bipolar plate.

[0205] In a third embodiment, a polyetherimide film (75 micrometer thickness) was pressed on a first surface of a dry ZRT™ film (150 micrometer thickness), and a second polyetherimide film (50 micrometer thickness) was pressed on a second surface of the dry ZRT™ film substantially opposite the first surface. The polyetherimide films and the dry ZRT™ film were thermally infused by pressing at 380° C for 1 minute and held in a double belt press. The resulting material was thermally stamped and pressurized. Next, a surface of the interior region of the resulting material was partially ablated to remove between 5-15 micrometers of material from the surface. A nickel (Ni) film (1-5 micrometer thickness) and a non-porous graphite coating (less than 1 micrometer thickness) were then either electroplated or deposited by physical vapor deposition on the interior region of surface of the interior region of the resulting material to form the composite bipolar plate.

[0206] The first, second, and third embodiments were repeated by substituting nickel with titanium (Ti) and stainless steel (SS).

[0207] EXAMPLE 5

[0208] The following example describes yet another alternative fabrication of bipolar plates.

[0209] In an embodiment, a polyetherimide film (75 micrometer thickness) was pressed on a first surface of a dry ZRT™ film (150 micrometer thickness), and a graphite coated aluminum foil (10 micrometer thickness) was pressed on a second surface of the dry ZRT™ film substantially opposite the first surface. The polyetherimide film, dry ZRT™ film, and the graphite coated aluminum foil were thermally infused by pressing at 380° C for 1 minute and held in a double belt press to form the bipolar plate.

[0210] The embodiment was repeated by substituting the aluminum foil with nickel foil, titanium foil, and stainless steel foil.

[0211] While several embodiments of the present disclosure have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the present disclosure. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the teachings of the present disclosure is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the disclosure described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the disclosure may be practiced otherwise than as specifically described and claimed. The present disclosure is directed to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the scope of the present disclosure.

[0212] In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control. If two or more documents incorporated by reference include conflicting and / or inconsistent disclosure with respect to each other, then the document having the later effective date shall control.

[0213] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0214] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0215] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and / or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0216] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.”

[0217] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0218] When the word “about” is used herein in reference to a number, it should be understood that still another embodiment of the disclosure includes that number not modified by the presence of the word “about.”

[0219] It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

[0220] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

CLAIMSWhat is claimed is:

1. A composite, comprising: a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate, the composite further comprising a first region and a second region, the first region having a first average areal specific resistance and the second region having a second average areal specific resistance, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 1:1 and less than or equal to 10:1.

2. The composite of claim 1, wherein the ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 10:9 and less than or equal to 10:1.

3. The composite of any one of claims 1-2, wherein the first average areal specific resistance is greater than or equal to 1 ohm-cm2and less than or equal to 10 ohm-cm2.

4. The composite of any one of claims 1-3, wherein the second average areal specific resistance is greater than or equal to 0.001 ohm-cm2and less than or equal to 1 ohm-cm2.

5. The composite of any one of claims 1-4, wherein the composite comprises a polymer.

6. The composite of claim 5, wherein the polymer comprises a thermoplastic polymer, a thermoset polymer, a liquid crystal polymer, and / or an elastomer.

7. The composite of any one of claims 5-6, wherein the polymer comprises polyetherimide (PEI), polyethersulfone (PES), polyvinylidene fluoride (PVDF), polypropylene (PP), polyphenylene sulfide (PPS), polyurethane (PUR), polypyrrole (Ppy), polyaniline (PAni), poly(3,4-ethylenedioxythiophene) (PEDOT), polyetheretherketone (PEEK), polyaryletherketone (PAEK), and / or combinations thereof.

8. The composite of any one of claims 1-7, wherein the first region has a first polymer weight percent (wt.%) versus a total weight of the composite and the second region has a second polymer wt.% versus a total weight of the composite that is less than the first polymer wt.%.

9. The composite of claim 8, wherein a ratio of the first polymer wt.% to the second polymer wt.% is greater than or equal to 10:9 and less than or equal to 10:1.

10. The composite of any one of claims 1-9, wherein the first region substantially surrounds the second region.

11. The composite of any one of claims 1-10, wherein the first region comprises one or more holes passing from a first surface of the composite to a second surface of the composite that is substantially opposite the first surface.

12. The composite of any one of claims 1-11, wherein the composite comprises a conductive material.

13. The composite of claim 12, wherein the conductive material comprises a metal and / or an alloy.

14. The composite of claim 13, wherein the metal and / or the alloy comprises aluminum (Al), titanium (Ti), nickel (Ni), stainless steel (SS), and / or combinations thereof.

15. The composite of claim 12, wherein the conductive material comprises a carbonbased material.

16. The composite of claim 15, wherein the carbon-based material comprises graphite, graphene, a carbon nanostructure, carbon black, a carbon fiber and / or mixtures thereof.

17. The composite of any one of claims 1-16, wherein the composite has an average thickness of greater than or equal to 50 micrometers and less than or equal to 250 micrometers.

18. The composite of any one of claims 1-17, wherein the composite is a bipolar plate.

19. A composite, comprising: a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate, the composite further comprising a first region and a second region, the first region having a first average areal specific resistance of greater than or equal to 1 ohm-cm2and the second region having a second average areal specific resistance of less than or equal to 1 ohm-cm2.

20. The composite of claim 19, wherein the first average areal specific resistance is less than or equal to 10 ohm-cm2.

21. The composite of any one of claims 19-20, wherein the second average areal specific resistance is greater than or equal to 0.001 ohm-cm2.

22. The composite of any one of claims 19-21, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 1:1 and less than or equal to 10:1.

23. The composite of claim 22, wherein the ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 10:9 and less than or equal to 10:1.

24. The composite of any one of claims 19-23, wherein the composite comprises a polymer.

25. The composite of claim 24, wherein the polymer comprises a thermoplastic polymer, a thermoset polymer, a liquid crystal polymer, and / or an elastomer.

26. The composite of any one of claims 24-25, wherein the polymer comprises polyetherimide (PEI), polyethersulfone (PES), polyvinylidene fluoride (PVDF), polypropylene (PP), polyphenylene sulfide (PPS), polyurethane (PUR), polypyrrole (Ppy),polyaniline (PAni), poly(3,4-ethylenedioxythiophene) (PEDOT), polyetheretherketone (PEEK), polyaryletherketone (PAEK), and / or combinations thereof.

27. The composite of any one of claims 19-26, wherein the first region has a first polymer weight percent (wt.%) versus a total weight of the composite and the second region has a second polymer wt.% versus a total weight of the composite that is less than the first polymer wt.%.

28. The composite of claim 27, wherein a ratio of the first polymer wt.% to the second polymer wt.% is greater than or equal to 10:9 and less than or equal to 10:1.

29. The composite of any one of claims 19-28, wherein the first region substantially surrounds the second region.

30. The composite of any one of claims 19-29, wherein the first region comprises one or more holes passing from a first surface of the composite to a second surface of the composite that is substantially opposite the first surface.

31. The composite of any one of claims 19-30, wherein the composite comprises a conductive material.

32. The composite of claim 31, wherein the conductive material comprises a metal and / or an alloy.

33. The composite of claim 32, wherein the metal and / or the alloy comprises aluminum (Al), titanium (Ti), nickel (Ni), stainless steel (SS), and / or combinations thereof.

34. The composite of claim 31, wherein the conductive material comprises a carbonbased material.

35. The composite of claim 34, wherein the carbon-based material comprises graphite, graphene, a carbon nanostructure, carbon black, a carbon fiber, and / or mixtures thereof.

36. The composite of any one of claims 19-35, wherein the composite has an average thickness of greater than or equal to 50 micrometers and less than or equal to 250 micrometers.

37. The composite of any one of claims 19-36, wherein the composite is a bipolar plate.

38. A composite, comprising: a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate, the composite further comprising a first region and a second region, the first region having a first polymer weight percent (wt.%) versus a total weight of the composite and the second region having a second polymer wt.% versus the total weight of the composite that is less than the first polymer wt.%.

39. The composite of claim 38, wherein a ratio of the first polymer wt.% to the second polymer wt.% is greater than or equal to 10:9 and less than or equal to 10:1.

40. The composite of any one of claims 38-39, wherein the first region has a first average areal specific resistance and the second region has a second average areal specific resistance, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance greater than or equal to 1: 1 and less than or equal to 10: 1.

41. The composite of claim 40, wherein the first average areal specific resistance is greater than or equal to 1 ohm-cm2and less than or equal to 10 ohm-cm2.

42. The composite of any one of claims 40-41, wherein the second average areal specific resistance is greater than or equal to 0.001 ohm-cm2and less than or equal to 1 ohm-cm2.

43. The composite of any one of claims 40-42, wherein the ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 10:9 and less than or equal to 10:1.

44. The composite of any one of claims 38-43, wherein the composite comprises a thermoplastic polymer, a thermoset polymer, a liquid crystal polymer, and / or an elastomer.

45. The composite of any one of claims 38-44, wherein the composite comprises polyetherimide (PEI), polyethersulfone (PES), polyvinylidene fluoride (PVDF), polypropylene (PP), polyphenylene sulfide (PPS), polyurethane (PUR), polypyrrole (Ppy), polyaniline (PAni), poly(3,4-ethylenedioxythiophene) (PEDOT), and / or combinations thereof.

46. The composite of any one of claims 38-45, wherein the first region substantially surrounds the second region.

47. The composite of any one of claims 38-46, wherein the first region comprises one or more holes passing from a first surface of the composite to a second surface of the composite that is substantially opposite the first surface.

48. The composite of any one of claims 38-47, wherein the composite comprises a conductive material.

49. The composite of claim 48, wherein the conductive material comprises a metal and / or an alloy.

50. The composite of claim 49, wherein the metal and / or the alloy comprises aluminum (Al), titanium (Ti), nickel (Ni), stainless steel (SS), and / or combinations thereof.

51. The composite of claim 48, wherein the conductive material comprises a carbonbased material.

52. The composite of claim 51, wherein the carbon-based material comprises graphite, graphene, a carbon nanostructure, carbon black, a carbon fiber, and / or mixtures thereof.

53. The composite of any one of claims 38-52, wherein the composite has an average thickness of greater than or equal to 50 micrometers and less than or equal to 250 micrometers.

54. The composite of any one of claims 38-53, wherein the composite is a bipolar plate.

55. A composite, comprising: a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate, the composite further comprising a surface having a plurality of features, wherein a first portion of the plurality of features has a first average areal specific resistance and a second portion of the plurality of features has a second average areal specific resistance, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 1:1 and less than or equal to 10:1.

56. The composite of claim 55, wherein the ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 10:9 and less than or equal to 10:1.

57. The composite of any one of claims 55-56, wherein the first average areal specific resistance is greater than or equal to 0.001 ohm-cm2and less than or equal to 1 ohm-cm2.

58. The composite of any one of claims 55-57, wherein the second average areal specific resistance is greater than or equal to 0.001 ohm-cm2and less than or equal to 1 ohm-cm2.

59. The composite of any one of claims 55-58, wherein the composite comprises a polymer.

60. The composite of claim 59, wherein the polymer comprises a thermoplastic polymer, a thermoset polymer, a liquid crystal polymer, and / or an elastomer.

61. The composite of any one of claims 59-60, wherein the polymer comprises polyetherimide (PEI), polyethersulfone (PES), polyvinylidene fluoride (PVDF), polypropylene (PP), polyphenylene sulfide (PPS), polyurethane (PUR), polypyrrole (Ppy), polyaniline (PAni), poly(3,4-ethylenedioxythiophene) (PEDOT), polyetheretherketone (PEEK), polyaryletherketone (PAEK), and / or combinations thereof.

62. The composite of any one of claims 55-61, wherein the composite comprises a conductive material.

63. The composite of claim 62, wherein the conductive material comprises a metal and / or an alloy.

64. The composite of claim 63, wherein the metal and / or the alloy comprises aluminum (Al), titanium (Ti), nickel (Ni), stainless steel (SS), and / or combinations thereof.

65. The composite of claim 62, wherein the conductive material comprises a carbonbased material.

66. The composite of claim 65, wherein the carbon-based material comprises graphite, graphene, a carbon nanostructure, carbon black, a carbon fiber, and / or mixtures thereof.

67. The composite of any one of claims 55-66, wherein the composite has an average thickness of greater than or equal to 50 micrometers and less than or equal to 250 micrometers.

68. The composite of any one of claims 55-67, wherein the first portion of the plurality of features comprise one more valleys.

69. The composite of any one of claims 55-68, wherein the second portion of the plurality of features comprise one or more peaks.

70. The composite of any one of claims 55-69, wherein the composite is a bipolar plate.

71. A composite, comprising: a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate, the composite further comprising a surface having a plurality of features, wherein a first portion of the plurality of features has a first average areal specific resistance of greater than or equal to 0.001 ohm-cm2and a second portion of the plurality of features has a second average areal specific resistance of greater than or equal to 0.001 ohm-cm2.

72. The composite of claim 71, wherein the first average areal specific resistance is less than or equal to 1 ohm-cm2.

73. The composite of any one of claims 71-72, wherein the second average areal specific resistance is greater than or equal to 1 ohm-cm2.

74. The composite of any one of claims 71-73, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 1:1 and less than or equal to 10:1.

75. The composite of claim 74, wherein the ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 10:9 and less than or equal to 10:1.

76. The composite of any one of claims 71-75, wherein the composite comprises a polymer.

77. The composite of claim 76, wherein the polymer comprises a thermoplastic polymer, a thermoset polymer, a liquid crystal polymer, and / or an elastomer.

78. The composite of any one of claims 76-77, wherein the polymer comprises polyetherimide (PEI), polyethersulfone (PES), polyvinylidene fluoride (PVDF), polypropylene (PP), polyphenylene sulfide (PPS), polyurethane (PUR), polypyrrole (Ppy), polyaniline (PAni), poly(3,4-ethylenedioxythiophene) (PEDOT), polyetheretherketone (PEEK), polyaryletherketone (PAEK), and / or combinations thereof.

79. The composite of any one of claims 71-78, wherein the composite comprises a conductive material.

80. The composite of claim 79, wherein the conductive material comprises a metal and / or an alloy.

81. The composite of claim 80, wherein the metal and / or the alloy comprises aluminum (Al), titanium (Ti), nickel (Ni), stainless steel (SS), and / or combinations thereof.

82. The composite of claim 79, wherein the conductive material comprises a carbonbased material.

83. The composite of claim 82, wherein the carbon-based material comprises graphite, graphene, a carbon nanostructure, carbon black, carbon fiber, and / or mixtures thereof.

84. The composite of any one of claims 71-83, wherein the composite has an average thickness of greater than or equal to 50 micrometers and less than or equal to 250 micrometers.

85. The composite of any one of claims 71-84, wherein the first portion of the plurality of features comprise one more valleys.

86. The composite of any one of claims 71-85, wherein the second portion of the plurality of features comprise one or more peaks.

87. The composite of any one of claims 71-86, wherein the composite is a bipolar plate.

88. A device, comprising: a bipolar plate separating two cells of a fuel cell, the bipolar plate comprising a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate.

89. The device of claim 88, wherein the bipolar plates further comprises an additive and / or filler that is in electrical contact with at least a portion of the plurality of carbon fibers.

90. The device of claim 89, wherein the additive and / or filler comprises a metal and / or an alloy.

91. The device of claim 90, wherein the metal and / or the alloy comprises aluminum (Al), titanium (Ti), nickel (Ni), stainless steel (SS), and / or combinations thereof.

92. The device of claim 89, wherein the additive and / or filler comprises a carbon-based material.

93. The device of claim 92, wherein the additive and / or comprises graphite, graphene, a carbon nanostructure, carbon black, a carbon fiber, and / or mixtures thereof.

94. A method of modifying a composite, comprising: providing the composite, wherein the composite comprises a substrate, the substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate, wherein the composite further comprises a first region and a second region; and modifying the first region such that the first region has a first average areal specific resistance and the second region has a second average areal specific resistance, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 1:1 and less than or equal to 10:1.

95. The method of claim 94, wherein the ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 10:9 and less than or equal to 10:1.

96. The method of any one of claims 94-95, wherein modifying the first region comprises increasing a polymer content of the first region such that the first region has a first polymer weight percent (wt.%) versus a total weight of the first region and the second region has a second polymer wt.% versus a total weight of the second region that is less than the first polymer wt.%.

97. The method of claim 96, wherein a ratio of the first polymer wt.% to the second polymer wt.% is greater than or equal to 10:9 and less than or equal to 10:1.

98. A method of modifying a composite, comprising: providing the composite, wherein the composite comprises a substrate, the substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate, wherein the composite further comprises a surface comprising a plurality of features, the plurality of features comprising a first portion and a second portion; andmodifying a surface of the second portion of the plurality of features such that a surface of the first portion of the plurality of features has a first average areal specific resistance and the surface of the second portion of the plurality of features has a second average areal specific resistance, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 1: 1 and less than or equal to 10:1.

99. The method of claim 98, wherein the ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 10:9 and less than or equal to 10:1.

100. The method of any one of claims 98-99, wherein modifying the surface of the second portion of the plurality of features comprises decreasing a polymer content of the surface of the second portion of the plurality of features.

101. The method of any one of claims 98-100, wherein modifying the surface of the second portion of the plurality of features comprises ablating the surface of the second portion of the plurality of features.

102. The method of claim 101, wherein ablating comprises machining, sanding, laser ablating, and / or sand blasting.

103. The method of any one of claims 98-102, wherein the first portion of the plurality of features comprise one or more valleys.

104. The method of any one of claims 98-103, wherein the second portion of the plurality of features comprise one or more peaks.

105. A composite, comprising: a substrate comprising a plurality of carbon fibers aligned substantially orthogonal to the substrate, the composite further comprising a first region and a second region, the first region having a first average areal specific resistance and the second region having a second averageareal specific resistance, wherein the second average areal specific resistance is the same as or less than the first average areal specific resistance.

106. The composite of claim 105, wherein the first average areal specific resistance is greater than or equal to 1 ohm-cm2and less than or equal to 10 ohm-cm2.

107. The composite any one of claims 105-106, wherein the second average areal specific resistance is greater than or equal to 0.001 ohm-cm2and less than or equal to 1 ohm-cm2.

108. The composite of any one of claims 105-107, wherein a ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 1:1 and less than or equal to 10:1.

109. The composite of claim 103, wherein the ratio of the first average areal specific resistance to the second average areal specific resistance is greater than or equal to 10:9 and less than or equal to 10:1.

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