Carbon porous surface layers and methods of making the same

Abstract

A porous surface layer formed on a surface of a porous transport layer (PTL) includes carbon particles between 95% and 100% by weight of the porous surface layer. The porous surface layer is functionalized to control a degree of hydrophobicity or hydrophilicity and has a contact angle between 0° and 150°.

Description

FIELD OF INVENTION

[0001] This disclosure relates generally to physical structures and manufacturing processes for forming a porous surface layer that is applicable for electrode materials and more specifically for porous transport or separator layers designed for fuel cells, electrolyzers, or battery applications. These porous surface layers can also be used in carbon dioxide (CO2) capture, filtration, or other separation processes such as capacitive deionization and electrostatic precipitation.BACKGROUND

[0002] Hydrogen-based energy conversion and storage devices offer significant advantages over traditional technologies like internal combustion engines and lithium-ion batteries, including higher energy density, greater operational efficiency, improved reactant utilization, and extended operational lifetimes. These devices, e.g., fuel cells, electrolyzers, batteries, etc., are designed to store and release energy derived from renewable sources without the generation and release of greenhouse gases such as CO2. A fuel cell typically generates energy by converting chemical potential energy into electrical energy, whereas an electrolyzer utilizes electrical energy to split water into oxygen and hydrogen gases, while a battery can both store chemical energy (charging) or convert chemical energy to electricity (discharge). In all these devices there are a pair of electrodes for collecting current and a porous transport layer (PTL) or a gas diffusion layer (GDL) for transporting fluids and gases. The term PTL is used in electrolyzer applications and the term GDL is used in fuel cell applications. The properties and functionalities of the PTL or GDL are critical to the operation and efficiency of a system.

[0003] Conventionally, PTLs or GDLs used in these industries have a porous surface layer (sometimes colloquially referred to as a microporous layer or MPL) that is generally comprised of some combination of carbon particles and a non-conductive, hydrophobic polymer binder, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc. that can survive extreme temperatures and harsh operating environments. The polymer binder is necessary for stability of the porous surface layer and preventing wear and / or carbon washout during operation. However, the use of polymer binders in conventional PTLs or GDLs results in poor electrical conductivity, which is a major limitation. Polymers, such as PTFE or PVDF, are electrical insulators which hinder the efficiency of energy storage and conversion devices.SUMMARY

[0004] In one embodiment, a porous surface layer formed on a surface of a porous transport layer (PTL) includes carbon particles between 95% and 100% by weight of the porous surface layer. The porous surface layer is functionalized to control a degree of hydrophobicity or hydrophilicity and has a contact angle between 0° and 150°.

[0005] In another embodiment, a method of forming a porous transport layer on a porous transport layer (PTL) includes forming a coating ink comprising carbon particles and applying the coating ink to a surface of the PTL. The method includes applying heat or both heat and pressure to the porous transport layer coated with the coating ink to form a composite. The method includes heat treating the composite in an inert atmosphere or in vacuum to form the porous surface layer. The method includes functionalizing the porous surface layer to control a degree of hydrophobicity or hydrophilicity. The porous surface layer has a contact angle between 0° and 150.BRIEF DESCRIPTION OF THE DRAWING

[0006] In the accompanying drawings, structures are illustrated that, together with the detailed description provided below, describe example embodiments of the disclosed systems, methods, and apparatus. Where appropriate, like elements are identified with the same or similar reference numerals. Elements shown as a single component can be replaced with multiple components. Elements shown as multiple components can be replaced with a single component. The drawings may not be to scale. The proportion of certain elements may be exaggerated for the purpose of illustration.

[0007] FIG. 1A shows an exemplary method for forming a porous surface layer on a surface of a substrate.

[0008] FIG. 1B shows an exemplary process diagram for forming a porous surface layer on a surface of a substrate.

[0009] FIG. 1C shows another exemplary process diagram for forming a porous surface layer on a surface of a substrate.

[0010] FIG. 1D shows another exemplary process diagram for forming a porous surface layer on a surface of a substrate.

[0011] FIG. 2 is a scanning electron microscope image of a cross section of an exemplary conventional porous surface layer.

[0012] FIG. 3 is a scanning electron microscope image of a cross section of an exemplary hydrophobic porous surface layer formed by the method of FIG. 1A.

[0013] FIG. 4 is a scanning electron microscope image of a cross section of an exemplary hydrophilic porous surface layer formed by the method of FIG. 1A.

[0014] FIG. 5A shows surface images and FIG. 5B shows corresponding measured surface roughness values of conventional porous surface layers on substrates under different compressive loads.

[0015] FIG. 6A shows surface images and FIG. 6B shows corresponding measured surface roughness values of porous surface layers on substrates formed by the method of FIG. 1A under different compressive loads.

[0016] FIG. 7 shows a contact angle (θ) measurement on a hydrophobic porous surface layer formed by the method of FIG. 1A coated on a substrate.

[0017] FIG. 8 shows a contact angle (θ) measurement on a hydrophilic porous surface layer formed by the method of FIG. 1A coated on a substrate.

[0018] FIG. 9 and FIG. 10 show contact angle (θ) measurements at time=0 second and after 30 seconds, respectively, on a hydrophobic polymer layer coated hydrophilic porous surface layer on a substrate.DETAILED DESCRIPTION

[0019] The apparatus, systems, arrangements, and methods disclosed in this document are described in detail by way of examples and with reference to the figures. It will be appreciated that modifications to disclosed and described examples, arrangements, configurations, components, elements, apparatus, methods, materials, etc. can be made and may be desired for a specific application. In this disclosure, any identification of specific techniques, arrangements, method, etc. are either related to a specific example presented or are merely a general description of such a technique, arrangement, method, etc. Identifications of specific details or examples are not intended to be and should not be construed as mandatory or limiting unless specifically designated as such.

[0020] Disclosed herein are manufacturing processes for forming a porous surface layer structure on a substrate, which can be a PTL or GDL. More specifically, disclosed herein are physical structures and manufacturing processes for forming a less compressible, hydrophilic porous surface layer that is applicable for electrode materials and more specifically for porous transport or separator layers designed for fuel cells, electrolyzers, and battery applications. These porous surface layers can also be used in carbon dioxide (CO2) capture, filtration, or other separation processes that require water or electricity such as capacitive deionization or electrostatic precipitation.

[0021] More specifically, disclosed herein are methods for manufacturing a hydrophilic or hydrophobic porous surface layer coated on the surface of a substrate, e.g., PTL or GDL, for use in electrochemical systems (e.g., electrolyzer, fuel cell, etc.). PTL plays a crucial role in facilitating the efficient mass transport of reactant and product gases, managing water within the electrolyzer, maintaining optimal pressure and gas distribution, and providing mechanical support to the electrode assembly. In case of a fuel cell, GDL is an essential component of the polymer electrolyte membrane water electrolysis (PEMWE). With the multi-function of electrical and mass transport, PTL or GDL must deal with surface passivation during long-term operation, acidic environment, and high operating temperature. It should be noted that the PTL or GDL is not coated with catalyst.

[0022] FIG. 1A shows an exemplary method 100 for forming a porous surface layer on a substrate, e.g., a PTL or GDL. Method 100 includes (step 102) forming a coating ink and (step 104) applying the coating ink to a surface of a substrate at a controlled thickness. Method 100 includes (step 106) applying heat or both heat and pressure to the ink coated substrate to form a composite. Step 106 is designed to dry or advance curing of a porous surface layer on the substrate. Optionally, step 106 is followed by (step 108) heat treating the composite in an inert atmosphere, e.g., argon (Ar), helium (He), nitrogen (N2), or in vacuum. Alternatively, step 106 may be omitted, and method 100 proceeds from step 104 to step 108.

[0023] Optionally, method 100 may include (step 110) applying a hydrophobic polymer to the composite (the composite formed in step 106 or step 108) after carbonization to provide a hydrophobic effect. Specifically, the porous surface layer may be altered from hydrophilic to hydrophobic by applying a hydrophobic polymer (e.g., PTFE, PVDF, or a combination thereof) at a very low concentration level (e.g. <1% by weight of the porous surface layer). Unexpectedly, the introduction of the hydrophobic polymer does not reduce the overall electrical conductivity of the porous surface layer. Without being bound by the theory, since the elemental carbon serves as the primary binder in the porous surface layer, there is no need for a significant amount of hydrophobic polymer to maintain the network connectivity, e.g., only minimal amount of hydrophobic polymer is added in step 110. Because the hydrophobic polymer is only present at a low concentration and because the porous surface layer has a highly connected structure via the carbon bonds formed in steps 106 and / or 108, the added hydrophobic polymer does not disrupt the carbon-carbon connectivity and does not reduce the overall electrical conductivity of the porous surface layer. The incorporation of a low concentration of hydrophobic polymer results in a hydrophobic porous surface layer that provides a resistance to repel the water.

[0024] In summary, a porous surface layer disclosed herein may be formed by steps 102, 104, and 108 with or without step 110, or by steps 102, 104, 106, and 108 with or without step 110. In all of the above examples, the porous surface layer has a relatively low roughness.

[0025] In step 102, the coating ink is formed from a mixture of carbonizable binder or polymer, carbon or graphite particles, viscosity agent(s), pore formers, and solvent, and optionally an activator. The total suspended solid (or non-volatile) content can range between 5% and 35% by weight of the coating ink.

[0026] The carbonizable binder is comprised of a polymer resin, or a blend of different polymer resins, and may contain different particles (carbon, metals, ceramics, etc.) as filler. The carbonizable binder may include any suitable polymer which yields a pyrolyzed carbon char of >5% of the initial polymer mass. The carbonizable binder may include polyvinyl pyrrolidone, polyimide, polyvinyl chloride, polyethylene, polyvinyl alcohol, thermosetting resins such as phenolic or melamine resin, or a combination thereof. The filler can be carbon or graphite particles, carbon black, synthetic or flake graphite of various shapes or forms (e.g., crystalline or amorphous).

[0027] The viscosity agents may include a form of hydrolyzed methylcellulose and / or other forms of fibrillated cellulose. The viscosity agents can include one or more of polyvinyl alcohol, polyvinyl pyrrolidone, carboxymethyl cellulose and / or other cellulose derivatives, as well as the carbon / graphite particles themselves when formulated with a solids content >15% by weight of the coating ink. Increasing the weight percentage of carbon / graphite particles in the mixture can increase the viscosity of the ink to a certain extent, e.g., above a given threshold. When the solid content in the ink is low (e.g., below 15 wt. %), additional carbon / graphite particles do not increase the viscosity substantially. However, as the solid content in the ink increases, the carbon / graphite particles will form complexes with the viscosity agents and this can increase the viscosity more effectively than with the viscosity agents alone. In an embodiment absent of viscosity agents, the binders, carbon / graphite particles, and pore formers contribute to the suspended solids and the amount of water is adjusted to control / adjust the viscosity.

[0028] The pore formers are formulated for the formation of a porous carbonizable binder. Pore formers used herein may include one or more of solid polymeric particles such as polymethyl methacrylate, liquid polymers surfactants, or metallic particles such as zinc, which could be subsequently removed during heat treatment. The pore formers are thermally decomposed during the heat treatment process leaving behind slightly larger pores than the size of the beads. The pore formers may be specifically sized spherical poly(methyl methacrylate) (PMMA) beads that are coated and then removed through thermal processing.

[0029] The solvents may be selected depending on the type of polymer used. The solvents may be selected from water, any polar protic organic solvent such as isopropyl or ethyl alcohol, and water-soluble alcohol (in small quantities).

[0030] The coating ink may optionally include an activator that allows the binder material to partially cure during the drying process (step 106) and provides additional stability for the porous surface layer prior to or in lieu of further heat treatment. The activator is a material that acts as a catalyst to thermally cure the material prior to carbonization which increases the char yield. For example, hexamethylenetetramine may be added at between about 3 wt. % and about 15 wt. % of the total weight of the coating ink to catalyze the cure rate of phenolic resin in the process.

[0031] In step 104, the coating ink is applied to the surface of the substrate through a coating process. The coating process may be a slot die coating process or modified slot die coating process, a curtain coating process, a spray coating process, a film transfer process, or any similar, uniform surface coating method. The coating ink may be applied to the surface of the substrate as a film or via a decal transfer method. Regardless of the coating method, control of the thickness and basis weight, e.g., weight per unite area, gram per square meter (g / m2) of the layer is critical for optimal performance.

[0032] In steps 106 and / or 108, parameters and process conditions are designed to modify the physical properties of the porous surface layer. In step 106, the heat treatment temperature range is between about 300 degree Celsius (° C.) and about 700° C. or between about 300° C. and about 800° C. In step 106, the heat treatment is done in air or an oxygenated environment. In step 108, the heat treatment temperature range is between about 700° C. and about 2600° C., between about 800° C. and about 3000° C., or between about 1700° C. and about 3000° C. In step 108, the heat treatment is done in an inert atmosphere and / or in vacuum.

[0033] In one example, in step 106, heating is done in an oxygenated environment, e.g., in air, at a temperature between 300° C. and 800° C. such that the composite structure is not fully carbonized (carbon content is between 80% and 100%, between 80% and 99.5%, or between 88% and 99%, between 95% and 99.5% by weight or atomic % of the entire porous surface layer), which results in a hydrophilic porous surface layer. In some embodiments, heating may be done in an environment with an oxygen concentration higher than in air. Higher concentrations of oxygen increase the activation of the surface and increase hydrophilicity, but this may also lead to less uniformity and risks of damaging the carbon. In step 106, heating can be applied under a pressure higher than an atmospheric pressure. The pressure may be applied by a press with piece parts at pressure ranging from about 50 pounds per inch (psi) to about 750 psi or may be applied continuously through a calender (e.g., a series of hard pressure rollers) or through a double belt bonder with pressures ranging from about 0.5 pounds per linear inch (PLI) to about 10 PLI. Carbonization under pressure can produce carbon materials with different structures (e.g., micro and / or nano texture or structures) and in higher yields under atmospheric pressure. Carbonization under pressure can also produce carbon from precursors that wouldn't produce carbon under atmospheric pressure.

[0034] In one example, in step 108, heating is done in an inert atmosphere between about 700° C. and about 2600° C. such that the composite structure is fully carbonized (carbon content equal to or greater than 95%, for example, between about 95% and about 100%, or between about 95% and about 99.5% by weight or atomic percent of the entire porous surface layer), which also results in a hydrophilic porous surface layer.

[0035] In another example, in step 108, the heat treatment is done at about 1000° C. in an inert atmosphere and subsequently at about 1700° C. to about 3000° C. in vacuum. Carbonization of a hydrophilic coating at 1000° C. in inert atmosphere results in a hydrophilic porous surface layer. After carbonization, the porous surface layer is graphitized in vacuum at about 1700° C. to about 3000° C. Graphitization crystallizes the elemental carbon binder (decreases the d-spacing of the adjacent carbon layers in the crystal structure) making this carbon more hydrophobic. The net result is that after graphitization the water contact angle on the porous surface layer is close to 90° C. (neutral) whereas the water contact angle is significantly smaller than 900 after carbonization. Graphitization occurs in vacuum such that there is no atmosphere.

[0036] In another example, in step 108, the heat treatment is done at above 700° C. in an inert atmosphere, to fully carbonize the binder and create a hydrophilic porous surface layer structure on top of the substrate.

[0037] Steps 106 and / or 108 may be performed in a furnace having one or more zones. Controlling the uniformity of the temperature distribution and atmosphere composition in each zone of the furnace results in formation of pores within the binder structure, yielding a strong layer with a smooth surface, high porosity, and a uniform thickness profile, which is also thermally and electrically conductive and chemically stable. There may be multiple zones, e.g., 8 zones, that are located at different points down a length of the furnace and each zone can be set with different temperature and / or atmospheric set points. Each zone may contain one or more inert gas valves (e.g., Ar, He, and / or N2 valves) that can be set at different flow rates to change the atmospheric conditions. The inert gas valves may be configured to remove the off gassing quickly or slowly as well as controlling the rate of inert gas passing through the material to control the impacts on the formation of pores within the material (e.g., rate of pore former dissolution, rate of carbonization of the binder, etc.). The settings on each of these zones as well as the total balance of gas flow in the furnace to achieve desirable impacts on the porous surface layer (e.g., under a positive flow an inert gas is pushing out of the furnace vs. under a negative flow trace amounts of air are drawn into the furnace).

[0038] The porous surface layers formed via method 100 exhibit improved properties over that formed via conventional methods. A porous surface layer formed via a conventional method typically contains carbon black particles and a polymer binder, typically PTFE, which is sintered to fuse the PTFE with the carbon particles. The PTFE acts as a binder for carbon and makes the layer hydrophobic, which is a functional requirement for traditional PEM fuel cells.

[0039] Different from a conventional porous surface layer, the porous surface layer disclosed herein may be hydrophilic, which promotes better contact between the catalyst layer and membrane and prevents the formation of gas bubbles at the cathode of an electrolyzer that could otherwise create mass transport limitations. Fuel cell applications utilizing self-humidification or otherwise operating in very hot or dry conditions operating in ambient temperature conditions would also benefit from a hydrophilic porous surface layer. Additionally, the binder in the hydrophilic porous surface layer disclosed herein is carbonized, resulting in a higher electrical conductivity that is beneficial for any electrochemical cells, fuel cells, electrolyzers, or battery technologies. Specifically, the polymer binder is fully carbonized through the heat treatment process in steps 106 and / or 108 (e.g., fusing the carbon particles to each other with a carbonized polymer). Carbonization of the polymer and graphitization further improve the electrical conductivity and alters the hydrophilicity. The porous surface layer disclosed herein may also show minimal deformation or swelling during water absorption / drying that would be advantageous in many applications where such layers could be damaged by cyclic swelling / drying events such as in batteries, fuel cells, or electrolyzers. The structure of the porous surface layer disclosed herein is much more rigid than comparable layers, so as it absorbs water the material resists swelling compared to other materials. With minimal swelling property, the porous surface layer is less affected by cyclic swelling / drying, and thus contributes to better long-term stability.

[0040] Method 100 may include (step 112) functionalizing the composite (from step 106, 108, or 110) to form a functionalized porous surface layer. In one example, the porous surface coating includes carbon particles (i.e., at greater than 95 wt. % carbon) that are functionalized to control the hydrophobic nature, where the porous surface layer has a contact angle (θ) between about 0° and about 150°. The composite (from step 106, 108, or 110) may be functionalized through a thermal or electrochemical process which adds elements to the composite that can alter the contact angle θ. For example, adding oxygen groups to the composite can provide an “activated” surface that is more hydrophilic. For example, adding fluorinated groups to the composite can make the surface hydrophobic. In another example, the porous surface layer may include one or more type of functional additives to determine structural, electrical, or thermal properties of the carbon composite paper or substrate. Examples of functional additives may include catalytically active particles such as platinum, ruthenium, ruthenium oxide, nickel, copper, nickel copper alloys, nitrogen doped carbons, or metal oxides such as cerium oxide or mixed metal oxides that are catalytically active in applications such as redox flow batteries, PEM / alkaline anion-exchange membrane (AEM) fuel cells, water electrolysis, or air breathing battery cathodes. The functional additives are designed to tune the final properties of the porous surface layer.

[0041] The carbon filler can be amorphous, turbostratic, or graphitized and can range in size from nano range (i.e., 0 nanometer (nm)-100 nm) to micro range (i.e., 100 nm-1 micrometer (μm)) to macro range (i.e., greater than 1 μm), which can be used to alter the pore size and structure of the porous surface layer.

[0042] The pore size of the porous surface layers may range from pore sizes within the range of nano-sized pores, micro-sized pores, meso-sized pores, macro-sized pores, or any combination thereof. The pores may have different functions within the porous surface layer / substrate. For example, large macro pores may effectively transport water, while small micropores (particularly hydrophobic pores) may keep the PTL dry and may be used for transporting reactant gases. The porous surface layer disclosed herein is designed to have a good distribution of pores typically centered around a reasonable number of macropores (>15 μm) and a reasonable number of micropores (<5 μm, typically more in the nm scale). This ensures good liquid and gas transport within the layer.

[0043] In the porous surface layer, post carbonization, the ratio of carbonized binder to carbon and graphite particles by mass is between is 0.1-3. The carbonized binder is configured to support the porous surface layer and may be an amorphous form, a turbostratic form, or a graphitized form.

[0044] The speciation of the carbon and the average pore size can be tuned to optimize the water contact angle to range from hydrophilic (0<θ<90) to hydrophobic (θ≥90). In certain embodiments, the thickness of the porous surface layer can be adjusted to control the total pore volume available within the porous surface layer for water retention or to minimize the path length for gaseous transport. The porous surface layer may be as thin as possible while adequately covering the surface fibers of the PTL or GDL to prevent roughness. The thickness of the porous surface layer may be configured to control a total pore volume available within the porous surface layer for water retention or to minimize a path length for gaseous transport. The thickness of the porous surface layer may be about 10 μm-100 μm for most applications, and in some embodiments, a thinner porous surface layer is preferred.

[0045] In certain embodiments, the porous surface layer disclosed herein may be applied such that the surface roughness as measured by an optical profilometer or other suitable device is ≤10 μm. The porous surface layer may be arranged such that the porous surface layer does not noticeably swell or deform during repeated wetting and drying cycles. No noticeable swelling refers to less than or equal to 5% change in thickness of the porous surface layer, e.g., less than or equal to 5% swelling or contracting of the porous surface layer during repeated wetting and drying cycles, no permanent deformation, and no cracking. The porous surface layer may be arranged so that the porous surface layer reduces the permanent compression set when pressed between about 7.3 psi and 450 psi (3.1 MPa) or between about 7.3 psi and 150 psi (1.0 MPa). In one embodiment, a permanent compression set is less than or equal to 30% when compressed between 7.3 psi and 450 psi. The “compression set” of material is the permanent deformation remaining after compressing it. The porous surface layer may be configured to be compressible and is able to spring back close to the original thickness, e.g., like an elastic sponge. In certain embodiments, the porous surface layer can be arranged with a porosity greater than 50% and a resistivity of less than 10 mΩ-cm.

[0046] In certain embodiments, the addition of a hydrophobic polymer or agent (PTFE, PVDF, etc.) may be used to subsequently transition to the porous surface layer from hydrophilic to hydrophobic. For example, (referring to step 110 in FIG. 1) a thin coating on either one or both surfaces of the porous surface layer without altering the center of the layer, such that there can be a transition zone from hydrophobic on the surface to hydrophilic in the center. The hydrophobic polymer or agent (e.g., PTFE, PVDF, etc.) may be coated over the surface layer to increase the contact angle (θ>90) and in this case, the quantity of the hydrophobic polymer or agent is significantly reduced (compared to that in a conventional porous layer) as the hydrophobic polymer or agent in the present disclosure is not required as a binder and the electrical resistivity of the PTL with the porous surface layer disclosed herein is low (≤10 mΩ-cm).

[0047] The porous surface layer disclosed herein exhibits the benefit of having a high strength and low compressibility. The required loading is reduced due to the presence of the binder in the porous surface layer. Furthermore, the overall electrical conductivity is much higher than that in conventional designs due to better contact between the porous surface layer and substrate (GDL or PTL) as well as lower polymer amounts (<5% by wt.) necessary for the hydrophobic properties. The amount of polymer or polymer binder in the porous surface layer disclosed herein is about 0.01 wt. %-about 5 wt. %, about 0.01 wt. %-about 4.5 wt. %, about 0.01 wt. %-about 3 wt. %, about 0.01 wt. %-about 2.5 wt. %, about 0 wt. %-about 2.0 wt. %, about 0.01 wt. %-about 2 wt. %, about 0.01 wt. %-about 1.5 wt. %, about 0.01 wt. %-about 1.0 wt. %, or about 0.01 wt. %-about 0.5 wt. % of the porous surface layer.

[0048] The improved strength of the porous surface layer enables the use of a thinner (e.g. lower weight) coating of polymer (particles are held together via sp2 hybridized carbon bonds rather than the polymer itself). Because the usage of binder is less / thinner, the conductive carbon particles in the porous surface layer are in better contact without discontinuities from the polymer binder. The conductive carbon fibers with less overall hydrophobic polymer disclosed herein lead to less contact resistance and better overall conductivity (parallel circuit vs. series circuit).

[0049] FIG. 1B shows an exemplary process diagram for forming a porous surface layer on a surface of a substrate. Specifically, the diagram shows a continuous slot die or modified slot die coating process for forming a uniform porous surface layer on a substrate (GDL or PTL). The substrate (GDL or PTL) may be in a form of a roll of sheet. A hydrophilic ink is applied as a porous surface layer coating on top of the substrate. The coated substrate is then subjected to a drying / heat treatment. A GDL or PTL with hydrophilic porous surface layer is obtained after the drying / heat treatment as a final product. In one example, the process shown in FIG. 1B may be set up using a sheet roll conveyor belt process involving feeding large sheets of materials like paper or metal, onto a specialized conveyor belt designed to smoothly transport the rolled sheets from one point to another or from one treatment to another.

[0050] FIG. 1C shows another exemplary process diagram for forming a porous surface layer on a surface of a substrate. The substrate may be a roll of carbon paper. A hydrophilic ink is applied as a porous surface layer coating on top of the substrate. In the illustrated example, the roll of substrate passes through or is dipped in the ink. The coated substrate is subsequently subjected to a drying / heat treatment. A GDL or PTL with hydrophilic porous surface layer is obtained after the drying / heat treatment as a final product. In one example, the process shown in FIG. 1C may be set up using a sheet roll conveyor belt process involving feeding large sheets of materials like paper or metal, onto a specialized conveyor belt designed to smoothly transport the rolled sheets from one point to another or from one treatment to another.

[0051] FIG. 1D shows another exemplary process diagram for forming a porous surface layer on a surface of a substrate. The substrate (GDL or PTL) may be in the form of a roll of sheet. A hydrophobic ink is applied as a porous surface layer coating on top of the substrate. The ink is formulated to form a hydrophobic porous surface layer with enhanced strength and minimized PTFE content. The coated substrate is then subjected to a drying / heat treatment. A GDL or PTL with hydrophobic porous surface layer then passes through or dips in a pool of PTFE (e.g., PTFE saturation), and subsequently a PTFE sintering treatment. Obtained after the PTFE sintering treatment is a final product of GDL or PTL with porous surface layer. In the PTFE saturation step, a solution of PTFE is formulated at a given concentration and a full dip of the hydrophobic porous surface coated GDL or PTL through the PTFE saturation tank and squeezed to remove the excess solution and then a dry / sintering step makes it hydrophobic. In one example, the process shown in FIG. 1D may be set up using a sheet roll conveyor belt process involving feeding large sheets of materials like paper or metal, onto a specialized conveyor belt designed to smoothly transport the rolled sheets from one point to another or from one treatment to another.Results and Comparisons

[0052] FIG. 2 shows a scanning electron microscope image 200 of a cross section of an exemplary porous surface layer formed according to a conventional coating approach essentially including three steps: (step 1) substrate teflonation; (step 2) microporous layer (MPL) coating; and (step 3) sintering. In step 1, a surface of a substrate 202 is covered by a polytetrafluoroethylene (PTFE) film 204 and. In step 2, a MPL coating 206 is applied to the teflonated substrate. In step 3, the composite (including the substrate 202, the PTFE film 204, and the MPL coating 206) is sintered. There appears to be delamination at the PTFE interface (between the MPL coating 206 and the teflonated substrate 202) in the porous surface layer formed via the conventional coating approach. The conventional coating approach results in a high electrical resistivity, characterized by Equation 1, due to the distinct PTFE interface 204 between the substrate 202 and the MPL coating 206. In Equation 1, RMPL, RPTFF Interface, and Rsubstrate represent the electrical resistivity of the MPL coating 206, the PTFE film 204, and the substrate 202, respectively, and Rcomposite represents the electrical resistivity of the composite (including the layers 202, 204, and 206).Rcomposite=RMPL+RPTFF⁢ Interface+Rsubstrate(Equation⁢ 1)

[0053] FIG. 3 shows a scanning electron microscope image 300 of a cross section of an exemplary porous surface layer formed according to method 100. The composite shown in the image 300 is formed by coating a substrate 302 with a MPL coating 304 (see steps 102 and 104 of method 100) and drying and / or applying heat treatment to the MPL coated substrate (see steps 106 and optionally 108 of method 100). Chemical bonding appears to occur at the interface 306 between the substrate 302 and the MPL layer 304, specifically pi-pi bonding between the carbon fibers in the substrate and the carbon powder of the porous layer. These pi-pi bonds eliminate the typical PTFE interface seen in commercial GDLs (e.g., the PTFE interface 204 in FIG. 2) and increase the cross-sectional area of the interface. This increased contact area between the fiber and the porous surface layer yields higher conductivity and reduces the possibility of delamination. The coating approach (method 100) disclosed herein results in a significantly lower electrical resistivity, characterized by Equation 2, and better mechanical strength due to the pi-pi bonding between the substrate 302 and the MPL coating 304 as well as sp2 hybridization bonds between the carbon particles themselves. In Equation 2, Rcomposite, RMPL, and Rsubstrate represent the electrical resistivity of the composite (including the layers 302, 304, and 306), the MPL coating 304, and the substrate 302, respectively.1Rcomposite=1RMPL+1Rsubstrate(Equation⁢ 2)

[0054] FIG. 4 shows a scanning electron microscope image of a cross section of an exemplary hydrophilic porous surface layer formed according to method 100. As shown in regions indicated by arrows 400, the hydrophilic porous surface layer conforms to high and low spots on the substrate, which are formed by x-y directionality in carbon veil. As shown in regions indicated by arrows 402, the hydrophilic porous surface layer is attached to the substrate surface via pi-pi bonding. The high and low spots refer to areas where there are dips in the surface of the substrate. As shown in FIG. 4, both high and low spots are covered by the porous surface layer and the porous surface layer has a wavy profile rather than a smooth profile. These characteristics indicate that the porous surface layer has a uniform thickness, as opposed to having a thicker surface layer in the low spots and thinner layer in the high spots. Having a uniform porous surface layer is important for mass transport and limiting the mean transport length to maximize performance.

[0055] FIG. 5A shows image of surfaces and FIG. 5B shows measured surface roughness of conventional MPLs under different compressive loads. For comparison, results of PTLs formed according to method 100 are shown in FIGS. 6A and 6B. The PTLs formed according to method 100 have a lower surface roughness (FIGS. 6A and 6B) in comparison to that of the conventional MPLs (FIGS. 5A and 5B). The surface roughness of the PTLs (FIGS. 6A and 6B) does not change significantly as the compressive stress increases.

[0056] FIGS. 7 and 8 show contact angle measurements on exemplary porous surface layers formed according to method 100. Measurements based on FIG. 7 show no wicking into substrate and the contact angle is well over 140°, indicating the porous surface layer is highly hydrophobic. Measurements based on FIG. 8 show that water is instantly wicked into surface, and a contact angle cannot be determined, indicating the porous surface layer is highly hydrophilic.

[0057] FIGS. 9 and 10 show contact angle measurements on a porous surface layer formed according to method 100 at two different times; time=0 second and after 30 seconds. Measurements based on FIG. 9 show wicking into the substrate initially (time=0 second), the sample is initially hydrophobic, e.g., contact angle, θ>90°, about 116.3° and about 123.2° in this case. There are signs of the water droplet starting to wick into the substrate on the edges (due to the hydrophilic nature of the substrate). Measurements based on FIG. 10 show that after 30 seconds (time=30 seconds), the water droplet has been almost completely absorbed into the surface of the hydrophilic substrate. The results from FIGS. 9 and 10 verify that water can wick into the porous surface layer even if the underlying substrate is hydrophobic.

[0058] This written description sets forth the best mode of practicing the claimed invention, and describes the invention so as to enable a person of ordinary skill in the art to make and use the invention, by presenting examples of the elements recited in the claims. The detailed descriptions of those examples do not impose limitations that are not recited in the claims.

[0059] As used herein, the term “or” may be construed in either an inclusive or exclusive sense. Moreover, the description of resources, operations, or structures in the singular shall not be read to exclude the plural. Conditional language, such as, among others, “can,”“could,”“might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and / or steps.

[0060] Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. Adjectives such as “conventional,”“traditional,”“normal,”“standard,”“known,” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. The presence of broadening words and phrases such as “one or more,”“at least,”“but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent.

[0061] The foregoing description of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments. Many modifications and variations will be apparent to the practitioner skilled in the art. The modifications and variations include any relevant combination of the disclosed features. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical application, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalence.

[0062] In one aspect, a method may include an operation, an instruction, and / or a function and vice versa. In one aspect, a clause or a claim may be amended to include some or all of the words (e.g., instructions, operations, functions, or components) recited in other one or more clauses, one or more words, one or more sentences, one or more phrases, one or more paragraphs, and / or one or more claims.

[0063] To illustrate the interchangeability of hardware and software, items such as the various illustrative blocks, modules, components, methods, operations, instructions, and algorithms have been described generally in terms of their functionality. Whether such functionality is implemented as hardware, software or a combination of hardware and software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application.

[0064] The functions, acts or tasks illustrated in the Figures or described may be executed in a digital and / or analog domain and in response to one or more sets of logic or instructions stored in or on non-transitory computer readable medium or media or memory. The functions, acts or tasks are independent of the particular type of instructions set, storage media, processor or processing strategy and may be performed by software, hardware, integrated circuits, firmware, microcode and the like, operating alone or in combination. The memory may comprise a single device or multiple devices that may be disposed on one or more dedicated memory devices or disposed on a processor or other similar device. When functions, steps, etc. are said to be “responsive to” or occur “in response to” another function or step, etc., the functions or steps necessarily occur as a result of another function or step, etc. It is not sufficient that a function or act merely follow or occur subsequent to another. The term “substantially” or “about” encompasses a range that is largely (anywhere a range within or a discrete number within a range of ninety-five percent and one-hundred and five percent), but not necessarily wholly, that which is specified. It encompasses all but an insignificant amount.

[0065] As used herein, the phrase “at least one of” preceding a series of items, with the terms “and” or “or” to separate any of the items, modifies the list as a whole, rather than each member of the list (e.g., each item). The phrase “at least one of” does not require selection of at least one item; rather, the phrase allows a meaning that includes at least one of any one of the items, and / or at least one of any combination of the items, and / or at least one of each of the items. By way of example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” each refer to only A, only B, or only C; any combination of A, B, and C; and / or at least one of each of A, B, and C.

[0066] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Phrases such as an aspect, the aspect, another aspect, some aspects, one or more aspects, an implementation, the implementation, another implementation, some implementations, one or more implementations, an embodiment, the embodiment, another embodiment, some embodiments, one or more embodiments, a configuration, the configuration, another configuration, some configurations, one or more configurations, the subject technology, the disclosure, the present disclosure, other variations thereof and alike are for convenience and do not imply that a disclosure relating to such phrase(s) is essential to the subject technology or that such disclosure applies to all configurations of the subject technology. A disclosure relating to such phrase(s) may apply to all configurations, or one or more configurations. A disclosure relating to such phrase(s) may provide one or more examples. A phrase such as an aspect or some aspects may refer to one or more aspects and vice versa, and this applies similarly to other foregoing phrases.

[0067] A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Underlined and / or italicized headings and subheadings are used for convenience only, do not limit the subject technology, and are not referred to in connection with the interpretation of the description of the subject technology. Relational terms such as first and second and the like may be used to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. All structural and functional equivalents to the elements of the various configurations described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the subject technology. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description. No claim element is to be construed under the provisions of 35 U.S.C. § 112(f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”

[0068] While this specification contains many specifics, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of particular implementations of the subject matter. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0069] The subject matter of this specification has been described in terms of particular aspects, but other aspects can be implemented and are within the scope of the following claims. For example, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. The actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the aspects described above should not be understood as requiring such separation in all aspects, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[0070] The title, background, brief description of the drawings, abstract, and drawings are hereby incorporated into the disclosure and are provided as illustrative examples of the disclosure, not as restrictive descriptions. It is submitted with the understanding that they will not be used to limit the scope or meaning of the claims. In addition, in the detailed description, it can be seen that the description provides illustrative examples and the various features are grouped together in various implementations for the purpose of streamlining the disclosure. The method of disclosure is not to be interpreted as reflecting an intention that the claimed subject matter requires more features than are expressly recited in each claim. Rather, as the claims reflect, inventive subject matter lies in less than all features of a single disclosed configuration or operation. The claims are hereby incorporated into the detailed description, with each claim standing on its own as a separately claimed subject matter.

[0071] The claims are not intended to be limited to the aspects described herein, but are to be accorded the full scope consistent with the language claims and to encompass all legal equivalents. Notwithstanding, none of the claims are intended to embrace subject matter that fails to satisfy the requirements of the applicable patent law, nor should they be interpreted in such a way.

Examples

Embodiment Construction

[0019]The apparatus, systems, arrangements, and methods disclosed in this document are described in detail by way of examples and with reference to the figures. It will be appreciated that modifications to disclosed and described examples, arrangements, configurations, components, elements, apparatus, methods, materials, etc. can be made and may be desired for a specific application. In this disclosure, any identification of specific techniques, arrangements, method, etc. are either related to a specific example presented or are merely a general description of such a technique, arrangement, method, etc. Identifications of specific details or examples are not intended to be and should not be construed as mandatory or limiting unless specifically designated as such.

[0020]Disclosed herein are manufacturing processes for forming a porous surface layer structure on a substrate, which can be a PTL or GDL. More specifically, disclosed herein are physical structures and manufacturing proces...

FIELD OF INVENTION

[0001] This disclosure relates generally to physical structures and manufacturing processes for forming a porous surface layer that is applicable for electrode materials and more specifically for porous transport or separator layers designed for fuel cells, electrolyzers, or battery applications. These porous surface layers can also be used in carbon dioxide (CO2) capture, filtration, or other separation processes such as capacitive deionization and electrostatic precipitation.BACKGROUND

[0002] Hydrogen-based energy conversion and storage devices offer significant advantages over traditional technologies like internal combustion engines and lithium-ion batteries, including higher energy density, greater operational efficiency, improved reactant utilization, and extended operational lifetimes. These devices, e.g., fuel cells, electrolyzers, batteries, etc., are designed to store and release energy derived from renewable sources without the generation and release of greenhouse gases such as CO2. A fuel cell typically generates energy by converting chemical potential energy into electrical energy, whereas an electrolyzer utilizes electrical energy to split water into oxygen and hydrogen gases, while a battery can both store chemical energy (charging) or convert chemical energy to electricity (discharge). In all these devices there are a pair of electrodes for collecting current and a porous transport layer (PTL) or a gas diffusion layer (GDL) for transporting fluids and gases. The term PTL is used in electrolyzer applications and the term GDL is used in fuel cell applications. The properties and functionalities of the PTL or GDL are critical to the operation and efficiency of a system.

[0003] Conventionally, PTLs or GDLs used in these industries have a porous surface layer (sometimes colloquially referred to as a microporous layer or MPL) that is generally comprised of some combination of carbon particles and a non-conductive, hydrophobic polymer binder, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc. that can survive extreme temperatures and harsh operating environments. The polymer binder is necessary for stability of the porous surface layer and preventing wear and / or carbon washout during operation. However, the use of polymer binders in conventional PTLs or GDLs results in poor electrical conductivity, which is a major limitation. Polymers, such as PTFE or PVDF, are electrical insulators which hinder the efficiency of energy storage and conversion devices.SUMMARY

[0004] In one embodiment, a porous surface layer formed on a surface of a porous transport layer (PTL) includes carbon particles between 95% and 100% by weight of the porous surface layer. The porous surface layer is functionalized to control a degree of hydrophobicity or hydrophilicity and has a contact angle between 0° and 150°.

[0005] In another embodiment, a method of forming a porous transport layer on a porous transport layer (PTL) includes forming a coating ink comprising carbon particles and applying the coating ink to a surface of the PTL. The method includes applying heat or both heat and pressure to the porous transport layer coated with the coating ink to form a composite. The method includes heat treating the composite in an inert atmosphere or in vacuum to form the porous surface layer. The method includes functionalizing the porous surface layer to control a degree of hydrophobicity or hydrophilicity. The porous surface layer has a contact angle between 0° and 150.BRIEF DESCRIPTION OF THE DRAWING

[0006] In the accompanying drawings, structures are illustrated that, together with the detailed description provided below, describe example embodiments of the disclosed systems, methods, and apparatus. Where appropriate, like elements are identified with the same or similar reference numerals. Elements shown as a single component can be replaced with multiple components. Elements shown as multiple components can be replaced with a single component. The drawings may not be to scale. The proportion of certain elements may be exaggerated for the purpose of illustration.

[0007] FIG. 1A shows an exemplary method for forming a porous surface layer on a surface of a substrate.

[0008] FIG. 1B shows an exemplary process diagram for forming a porous surface layer on a surface of a substrate.

[0009] FIG. 1C shows another exemplary process diagram for forming a porous surface layer on a surface of a substrate.

[0010] FIG. 1D shows another exemplary process diagram for forming a porous surface layer on a surface of a substrate.

[0011] FIG. 2 is a scanning electron microscope image of a cross section of an exemplary conventional porous surface layer.

[0012] FIG. 3 is a scanning electron microscope image of a cross section of an exemplary hydrophobic porous surface layer formed by the method of FIG. 1A.

[0013] FIG. 4 is a scanning electron microscope image of a cross section of an exemplary hydrophilic porous surface layer formed by the method of FIG. 1A.

[0014] FIG. 5A shows surface images and FIG. 5B shows corresponding measured surface roughness values of conventional porous surface layers on substrates under different compressive loads.

[0015] FIG. 6A shows surface images and FIG. 6B shows corresponding measured surface roughness values of porous surface layers on substrates formed by the method of FIG. 1A under different compressive loads.

[0016] FIG. 7 shows a contact angle (θ) measurement on a hydrophobic porous surface layer formed by the method of FIG. 1A coated on a substrate.

[0017] FIG. 8 shows a contact angle (θ) measurement on a hydrophilic porous surface layer formed by the method of FIG. 1A coated on a substrate.

[0018] FIG. 9 and FIG. 10 show contact angle (θ) measurements at time=0 second and after 30 seconds, respectively, on a hydrophobic polymer layer coated hydrophilic porous surface layer on a substrate.DETAILED DESCRIPTION

[0019] The apparatus, systems, arrangements, and methods disclosed in this document are described in detail by way of examples and with reference to the figures. It will be appreciated that modifications to disclosed and described examples, arrangements, configurations, components, elements, apparatus, methods, materials, etc. can be made and may be desired for a specific application. In this disclosure, any identification of specific techniques, arrangements, method, etc. are either related to a specific example presented or are merely a general description of such a technique, arrangement, method, etc. Identifications of specific details or examples are not intended to be and should not be construed as mandatory or limiting unless specifically designated as such.

[0020] Disclosed herein are manufacturing processes for forming a porous surface layer structure on a substrate, which can be a PTL or GDL. More specifically, disclosed herein are physical structures and manufacturing processes for forming a less compressible, hydrophilic porous surface layer that is applicable for electrode materials and more specifically for porous transport or separator layers designed for fuel cells, electrolyzers, and battery applications. These porous surface layers can also be used in carbon dioxide (CO2) capture, filtration, or other separation processes that require water or electricity such as capacitive deionization or electrostatic precipitation.

[0021] More specifically, disclosed herein are methods for manufacturing a hydrophilic or hydrophobic porous surface layer coated on the surface of a substrate, e.g., PTL or GDL, for use in electrochemical systems (e.g., electrolyzer, fuel cell, etc.). PTL plays a crucial role in facilitating the efficient mass transport of reactant and product gases, managing water within the electrolyzer, maintaining optimal pressure and gas distribution, and providing mechanical support to the electrode assembly. In case of a fuel cell, GDL is an essential component of the polymer electrolyte membrane water electrolysis (PEMWE). With the multi-function of electrical and mass transport, PTL or GDL must deal with surface passivation during long-term operation, acidic environment, and high operating temperature. It should be noted that the PTL or GDL is not coated with catalyst.

[0022] FIG. 1A shows an exemplary method 100 for forming a porous surface layer on a substrate, e.g., a PTL or GDL. Method 100 includes (step 102) forming a coating ink and (step 104) applying the coating ink to a surface of a substrate at a controlled thickness. Method 100 includes (step 106) applying heat or both heat and pressure to the ink coated substrate to form a composite. Step 106 is designed to dry or advance curing of a porous surface layer on the substrate. Optionally, step 106 is followed by (step 108) heat treating the composite in an inert atmosphere, e.g., argon (Ar), helium (He), nitrogen (N2), or in vacuum. Alternatively, step 106 may be omitted, and method 100 proceeds from step 104 to step 108.

[0023] Optionally, method 100 may include (step 110) applying a hydrophobic polymer to the composite (the composite formed in step 106 or step 108) after carbonization to provide a hydrophobic effect. Specifically, the porous surface layer may be altered from hydrophilic to hydrophobic by applying a hydrophobic polymer (e.g., PTFE, PVDF, or a combination thereof) at a very low concentration level (e.g. <1% by weight of the porous surface layer). Unexpectedly, the introduction of the hydrophobic polymer does not reduce the overall electrical conductivity of the porous surface layer. Without being bound by the theory, since the elemental carbon serves as the primary binder in the porous surface layer, there is no need for a significant amount of hydrophobic polymer to maintain the network connectivity, e.g., only minimal amount of hydrophobic polymer is added in step 110. Because the hydrophobic polymer is only present at a low concentration and because the porous surface layer has a highly connected structure via the carbon bonds formed in steps 106 and / or 108, the added hydrophobic polymer does not disrupt the carbon-carbon connectivity and does not reduce the overall electrical conductivity of the porous surface layer. The incorporation of a low concentration of hydrophobic polymer results in a hydrophobic porous surface layer that provides a resistance to repel the water.

[0024] In summary, a porous surface layer disclosed herein may be formed by steps 102, 104, and 108 with or without step 110, or by steps 102, 104, 106, and 108 with or without step 110. In all of the above examples, the porous surface layer has a relatively low roughness.

[0025] In step 102, the coating ink is formed from a mixture of carbonizable binder or polymer, carbon or graphite particles, viscosity agent(s), pore formers, and solvent, and optionally an activator. The total suspended solid (or non-volatile) content can range between 5% and 35% by weight of the coating ink.

[0026] The carbonizable binder is comprised of a polymer resin, or a blend of different polymer resins, and may contain different particles (carbon, metals, ceramics, etc.) as filler. The carbonizable binder may include any suitable polymer which yields a pyrolyzed carbon char of >5% of the initial polymer mass. The carbonizable binder may include polyvinyl pyrrolidone, polyimide, polyvinyl chloride, polyethylene, polyvinyl alcohol, thermosetting resins such as phenolic or melamine resin, or a combination thereof. The filler can be carbon or graphite particles, carbon black, synthetic or flake graphite of various shapes or forms (e.g., crystalline or amorphous).

[0027] The viscosity agents may include a form of hydrolyzed methylcellulose and / or other forms of fibrillated cellulose. The viscosity agents can include one or more of polyvinyl alcohol, polyvinyl pyrrolidone, carboxymethyl cellulose and / or other cellulose derivatives, as well as the carbon / graphite particles themselves when formulated with a solids content >15% by weight of the coating ink. Increasing the weight percentage of carbon / graphite particles in the mixture can increase the viscosity of the ink to a certain extent, e.g., above a given threshold. When the solid content in the ink is low (e.g., below 15 wt. %), additional carbon / graphite particles do not increase the viscosity substantially. However, as the solid content in the ink increases, the carbon / graphite particles will form complexes with the viscosity agents and this can increase the viscosity more effectively than with the viscosity agents alone. In an embodiment absent of viscosity agents, the binders, carbon / graphite particles, and pore formers contribute to the suspended solids and the amount of water is adjusted to control / adjust the viscosity.

[0028] The pore formers are formulated for the formation of a porous carbonizable binder. Pore formers used herein may include one or more of solid polymeric particles such as polymethyl methacrylate, liquid polymers surfactants, or metallic particles such as zinc, which could be subsequently removed during heat treatment. The pore formers are thermally decomposed during the heat treatment process leaving behind slightly larger pores than the size of the beads. The pore formers may be specifically sized spherical poly(methyl methacrylate) (PMMA) beads that are coated and then removed through thermal processing.

[0029] The solvents may be selected depending on the type of polymer used. The solvents may be selected from water, any polar protic organic solvent such as isopropyl or ethyl alcohol, and water-soluble alcohol (in small quantities).

[0030] The coating ink may optionally include an activator that allows the binder material to partially cure during the drying process (step 106) and provides additional stability for the porous surface layer prior to or in lieu of further heat treatment. The activator is a material that acts as a catalyst to thermally cure the material prior to carbonization which increases the char yield. For example, hexamethylenetetramine may be added at between about 3 wt. % and about 15 wt. % of the total weight of the coating ink to catalyze the cure rate of phenolic resin in the process.

[0031] In step 104, the coating ink is applied to the surface of the substrate through a coating process. The coating process may be a slot die coating process or modified slot die coating process, a curtain coating process, a spray coating process, a film transfer process, or any similar, uniform surface coating method. The coating ink may be applied to the surface of the substrate as a film or via a decal transfer method. Regardless of the coating method, control of the thickness and basis weight, e.g., weight per unite area, gram per square meter (g / m2) of the layer is critical for optimal performance.

[0032] In steps 106 and / or 108, parameters and process conditions are designed to modify the physical properties of the porous surface layer. In step 106, the heat treatment temperature range is between about 300 degree Celsius (° C.) and about 700° C. or between about 300° C. and about 800° C. In step 106, the heat treatment is done in air or an oxygenated environment. In step 108, the heat treatment temperature range is between about 700° C. and about 2600° C., between about 800° C. and about 3000° C., or between about 1700° C. and about 3000° C. In step 108, the heat treatment is done in an inert atmosphere and / or in vacuum.

[0033] In one example, in step 106, heating is done in an oxygenated environment, e.g., in air, at a temperature between 300° C. and 800° C. such that the composite structure is not fully carbonized (carbon content is between 80% and 100%, between 80% and 99.5%, or between 88% and 99%, between 95% and 99.5% by weight or atomic % of the entire porous surface layer), which results in a hydrophilic porous surface layer. In some embodiments, heating may be done in an environment with an oxygen concentration higher than in air. Higher concentrations of oxygen increase the activation of the surface and increase hydrophilicity, but this may also lead to less uniformity and risks of damaging the carbon. In step 106, heating can be applied under a pressure higher than an atmospheric pressure. The pressure may be applied by a press with piece parts at pressure ranging from about 50 pounds per inch (psi) to about 750 psi or may be applied continuously through a calender (e.g., a series of hard pressure rollers) or through a double belt bonder with pressures ranging from about 0.5 pounds per linear inch (PLI) to about 10 PLI. Carbonization under pressure can produce carbon materials with different structures (e.g., micro and / or nano texture or structures) and in higher yields under atmospheric pressure. Carbonization under pressure can also produce carbon from precursors that wouldn't produce carbon under atmospheric pressure.

[0034] In one example, in step 108, heating is done in an inert atmosphere between about 700° C. and about 2600° C. such that the composite structure is fully carbonized (carbon content equal to or greater than 95%, for example, between about 95% and about 100%, or between about 95% and about 99.5% by weight or atomic percent of the entire porous surface layer), which also results in a hydrophilic porous surface layer.

[0035] In another example, in step 108, the heat treatment is done at about 1000° C. in an inert atmosphere and subsequently at about 1700° C. to about 3000° C. in vacuum. Carbonization of a hydrophilic coating at 1000° C. in inert atmosphere results in a hydrophilic porous surface layer. After carbonization, the porous surface layer is graphitized in vacuum at about 1700° C. to about 3000° C. Graphitization crystallizes the elemental carbon binder (decreases the d-spacing of the adjacent carbon layers in the crystal structure) making this carbon more hydrophobic. The net result is that after graphitization the water contact angle on the porous surface layer is close to 90° C. (neutral) whereas the water contact angle is significantly smaller than 900 after carbonization. Graphitization occurs in vacuum such that there is no atmosphere.

[0036] In another example, in step 108, the heat treatment is done at above 700° C. in an inert atmosphere, to fully carbonize the binder and create a hydrophilic porous surface layer structure on top of the substrate.

[0037] Steps 106 and / or 108 may be performed in a furnace having one or more zones. Controlling the uniformity of the temperature distribution and atmosphere composition in each zone of the furnace results in formation of pores within the binder structure, yielding a strong layer with a smooth surface, high porosity, and a uniform thickness profile, which is also thermally and electrically conductive and chemically stable. There may be multiple zones, e.g., 8 zones, that are located at different points down a length of the furnace and each zone can be set with different temperature and / or atmospheric set points. Each zone may contain one or more inert gas valves (e.g., Ar, He, and / or N2 valves) that can be set at different flow rates to change the atmospheric conditions. The inert gas valves may be configured to remove the off gassing quickly or slowly as well as controlling the rate of inert gas passing through the material to control the impacts on the formation of pores within the material (e.g., rate of pore former dissolution, rate of carbonization of the binder, etc.). The settings on each of these zones as well as the total balance of gas flow in the furnace to achieve desirable impacts on the porous surface layer (e.g., under a positive flow an inert gas is pushing out of the furnace vs. under a negative flow trace amounts of air are drawn into the furnace).

[0038] The porous surface layers formed via method 100 exhibit improved properties over that formed via conventional methods. A porous surface layer formed via a conventional method typically contains carbon black particles and a polymer binder, typically PTFE, which is sintered to fuse the PTFE with the carbon particles. The PTFE acts as a binder for carbon and makes the layer hydrophobic, which is a functional requirement for traditional PEM fuel cells.

[0039] Different from a conventional porous surface layer, the porous surface layer disclosed herein may be hydrophilic, which promotes better contact between the catalyst layer and membrane and prevents the formation of gas bubbles at the cathode of an electrolyzer that could otherwise create mass transport limitations. Fuel cell applications utilizing self-humidification or otherwise operating in very hot or dry conditions operating in ambient temperature conditions would also benefit from a hydrophilic porous surface layer. Additionally, the binder in the hydrophilic porous surface layer disclosed herein is carbonized, resulting in a higher electrical conductivity that is beneficial for any electrochemical cells, fuel cells, electrolyzers, or battery technologies. Specifically, the polymer binder is fully carbonized through the heat treatment process in steps 106 and / or 108 (e.g., fusing the carbon particles to each other with a carbonized polymer). Carbonization of the polymer and graphitization further improve the electrical conductivity and alters the hydrophilicity. The porous surface layer disclosed herein may also show minimal deformation or swelling during water absorption / drying that would be advantageous in many applications where such layers could be damaged by cyclic swelling / drying events such as in batteries, fuel cells, or electrolyzers. The structure of the porous surface layer disclosed herein is much more rigid than comparable layers, so as it absorbs water the material resists swelling compared to other materials. With minimal swelling property, the porous surface layer is less affected by cyclic swelling / drying, and thus contributes to better long-term stability.

[0040] Method 100 may include (step 112) functionalizing the composite (from step 106, 108, or 110) to form a functionalized porous surface layer. In one example, the porous surface coating includes carbon particles (i.e., at greater than 95 wt. % carbon) that are functionalized to control the hydrophobic nature, where the porous surface layer has a contact angle (θ) between about 0° and about 150°. The composite (from step 106, 108, or 110) may be functionalized through a thermal or electrochemical process which adds elements to the composite that can alter the contact angle θ. For example, adding oxygen groups to the composite can provide an “activated” surface that is more hydrophilic. For example, adding fluorinated groups to the composite can make the surface hydrophobic. In another example, the porous surface layer may include one or more type of functional additives to determine structural, electrical, or thermal properties of the carbon composite paper or substrate. Examples of functional additives may include catalytically active particles such as platinum, ruthenium, ruthenium oxide, nickel, copper, nickel copper alloys, nitrogen doped carbons, or metal oxides such as cerium oxide or mixed metal oxides that are catalytically active in applications such as redox flow batteries, PEM / alkaline anion-exchange membrane (AEM) fuel cells, water electrolysis, or air breathing battery cathodes. The functional additives are designed to tune the final properties of the porous surface layer.

[0041] The carbon filler can be amorphous, turbostratic, or graphitized and can range in size from nano range (i.e., 0 nanometer (nm)-100 nm) to micro range (i.e., 100 nm-1 micrometer (μm)) to macro range (i.e., greater than 1 μm), which can be used to alter the pore size and structure of the porous surface layer.

[0042] The pore size of the porous surface layers may range from pore sizes within the range of nano-sized pores, micro-sized pores, meso-sized pores, macro-sized pores, or any combination thereof. The pores may have different functions within the porous surface layer / substrate. For example, large macro pores may effectively transport water, while small micropores (particularly hydrophobic pores) may keep the PTL dry and may be used for transporting reactant gases. The porous surface layer disclosed herein is designed to have a good distribution of pores typically centered around a reasonable number of macropores (>15 μm) and a reasonable number of micropores (<5 μm, typically more in the nm scale). This ensures good liquid and gas transport within the layer.

[0043] In the porous surface layer, post carbonization, the ratio of carbonized binder to carbon and graphite particles by mass is between is 0.1-3. The carbonized binder is configured to support the porous surface layer and may be an amorphous form, a turbostratic form, or a graphitized form.

[0044] The speciation of the carbon and the average pore size can be tuned to optimize the water contact angle to range from hydrophilic (0<θ<90) to hydrophobic (θ≥90). In certain embodiments, the thickness of the porous surface layer can be adjusted to control the total pore volume available within the porous surface layer for water retention or to minimize the path length for gaseous transport. The porous surface layer may be as thin as possible while adequately covering the surface fibers of the PTL or GDL to prevent roughness. The thickness of the porous surface layer may be configured to control a total pore volume available within the porous surface layer for water retention or to minimize a path length for gaseous transport. The thickness of the porous surface layer may be about 10 μm-100 μm for most applications, and in some embodiments, a thinner porous surface layer is preferred.

[0045] In certain embodiments, the porous surface layer disclosed herein may be applied such that the surface roughness as measured by an optical profilometer or other suitable device is ≤10 μm. The porous surface layer may be arranged such that the porous surface layer does not noticeably swell or deform during repeated wetting and drying cycles. No noticeable swelling refers to less than or equal to 5% change in thickness of the porous surface layer, e.g., less than or equal to 5% swelling or contracting of the porous surface layer during repeated wetting and drying cycles, no permanent deformation, and no cracking. The porous surface layer may be arranged so that the porous surface layer reduces the permanent compression set when pressed between about 7.3 psi and 450 psi (3.1 MPa) or between about 7.3 psi and 150 psi (1.0 MPa). In one embodiment, a permanent compression set is less than or equal to 30% when compressed between 7.3 psi and 450 psi. The “compression set” of material is the permanent deformation remaining after compressing it. The porous surface layer may be configured to be compressible and is able to spring back close to the original thickness, e.g., like an elastic sponge. In certain embodiments, the porous surface layer can be arranged with a porosity greater than 50% and a resistivity of less than 10 mΩ-cm.

[0046] In certain embodiments, the addition of a hydrophobic polymer or agent (PTFE, PVDF, etc.) may be used to subsequently transition to the porous surface layer from hydrophilic to hydrophobic. For example, (referring to step 110 in FIG. 1) a thin coating on either one or both surfaces of the porous surface layer without altering the center of the layer, such that there can be a transition zone from hydrophobic on the surface to hydrophilic in the center. The hydrophobic polymer or agent (e.g., PTFE, PVDF, etc.) may be coated over the surface layer to increase the contact angle (θ>90) and in this case, the quantity of the hydrophobic polymer or agent is significantly reduced (compared to that in a conventional porous layer) as the hydrophobic polymer or agent in the present disclosure is not required as a binder and the electrical resistivity of the PTL with the porous surface layer disclosed herein is low (≤10 mΩ-cm).

[0047] The porous surface layer disclosed herein exhibits the benefit of having a high strength and low compressibility. The required loading is reduced due to the presence of the binder in the porous surface layer. Furthermore, the overall electrical conductivity is much higher than that in conventional designs due to better contact between the porous surface layer and substrate (GDL or PTL) as well as lower polymer amounts (<5% by wt.) necessary for the hydrophobic properties. The amount of polymer or polymer binder in the porous surface layer disclosed herein is about 0.01 wt. %-about 5 wt. %, about 0.01 wt. %-about 4.5 wt. %, about 0.01 wt. %-about 3 wt. %, about 0.01 wt. %-about 2.5 wt. %, about 0 wt. %-about 2.0 wt. %, about 0.01 wt. %-about 2 wt. %, about 0.01 wt. %-about 1.5 wt. %, about 0.01 wt. %-about 1.0 wt. %, or about 0.01 wt. %-about 0.5 wt. % of the porous surface layer.

[0048] The improved strength of the porous surface layer enables the use of a thinner (e.g. lower weight) coating of polymer (particles are held together via sp2 hybridized carbon bonds rather than the polymer itself). Because the usage of binder is less / thinner, the conductive carbon particles in the porous surface layer are in better contact without discontinuities from the polymer binder. The conductive carbon fibers with less overall hydrophobic polymer disclosed herein lead to less contact resistance and better overall conductivity (parallel circuit vs. series circuit).

[0049] FIG. 1B shows an exemplary process diagram for forming a porous surface layer on a surface of a substrate. Specifically, the diagram shows a continuous slot die or modified slot die coating process for forming a uniform porous surface layer on a substrate (GDL or PTL). The substrate (GDL or PTL) may be in a form of a roll of sheet. A hydrophilic ink is applied as a porous surface layer coating on top of the substrate. The coated substrate is then subjected to a drying / heat treatment. A GDL or PTL with hydrophilic porous surface layer is obtained after the drying / heat treatment as a final product. In one example, the process shown in FIG. 1B may be set up using a sheet roll conveyor belt process involving feeding large sheets of materials like paper or metal, onto a specialized conveyor belt designed to smoothly transport the rolled sheets from one point to another or from one treatment to another.

[0050] FIG. 1C shows another exemplary process diagram for forming a porous surface layer on a surface of a substrate. The substrate may be a roll of carbon paper. A hydrophilic ink is applied as a porous surface layer coating on top of the substrate. In the illustrated example, the roll of substrate passes through or is dipped in the ink. The coated substrate is subsequently subjected to a drying / heat treatment. A GDL or PTL with hydrophilic porous surface layer is obtained after the drying / heat treatment as a final product. In one example, the process shown in FIG. 1C may be set up using a sheet roll conveyor belt process involving feeding large sheets of materials like paper or metal, onto a specialized conveyor belt designed to smoothly transport the rolled sheets from one point to another or from one treatment to another.

[0051] FIG. 1D shows another exemplary process diagram for forming a porous surface layer on a surface of a substrate. The substrate (GDL or PTL) may be in the form of a roll of sheet. A hydrophobic ink is applied as a porous surface layer coating on top of the substrate. The ink is formulated to form a hydrophobic porous surface layer with enhanced strength and minimized PTFE content. The coated substrate is then subjected to a drying / heat treatment. A GDL or PTL with hydrophobic porous surface layer then passes through or dips in a pool of PTFE (e.g., PTFE saturation), and subsequently a PTFE sintering treatment. Obtained after the PTFE sintering treatment is a final product of GDL or PTL with porous surface layer. In the PTFE saturation step, a solution of PTFE is formulated at a given concentration and a full dip of the hydrophobic porous surface coated GDL or PTL through the PTFE saturation tank and squeezed to remove the excess solution and then a dry / sintering step makes it hydrophobic. In one example, the process shown in FIG. 1D may be set up using a sheet roll conveyor belt process involving feeding large sheets of materials like paper or metal, onto a specialized conveyor belt designed to smoothly transport the rolled sheets from one point to another or from one treatment to another.Results and Comparisons

[0052] FIG. 2 shows a scanning electron microscope image 200 of a cross section of an exemplary porous surface layer formed according to a conventional coating approach essentially including three steps: (step 1) substrate teflonation; (step 2) microporous layer (MPL) coating; and (step 3) sintering. In step 1, a surface of a substrate 202 is covered by a polytetrafluoroethylene (PTFE) film 204 and. In step 2, a MPL coating 206 is applied to the teflonated substrate. In step 3, the composite (including the substrate 202, the PTFE film 204, and the MPL coating 206) is sintered. There appears to be delamination at the PTFE interface (between the MPL coating 206 and the teflonated substrate 202) in the porous surface layer formed via the conventional coating approach. The conventional coating approach results in a high electrical resistivity, characterized by Equation 1, due to the distinct PTFE interface 204 between the substrate 202 and the MPL coating 206. In Equation 1, RMPL, RPTFF Interface, and Rsubstrate represent the electrical resistivity of the MPL coating 206, the PTFE film 204, and the substrate 202, respectively, and Rcomposite represents the electrical resistivity of the composite (including the layers 202, 204, and 206).Rcomposite=RMPL+RPTFF⁢ Interface+Rsubstrate(Equation⁢ 1)

[0053] FIG. 3 shows a scanning electron microscope image 300 of a cross section of an exemplary porous surface layer formed according to method 100. The composite shown in the image 300 is formed by coating a substrate 302 with a MPL coating 304 (see steps 102 and 104 of method 100) and drying and / or applying heat treatment to the MPL coated substrate (see steps 106 and optionally 108 of method 100). Chemical bonding appears to occur at the interface 306 between the substrate 302 and the MPL layer 304, specifically pi-pi bonding between the carbon fibers in the substrate and the carbon powder of the porous layer. These pi-pi bonds eliminate the typical PTFE interface seen in commercial GDLs (e.g., the PTFE interface 204 in FIG. 2) and increase the cross-sectional area of the interface. This increased contact area between the fiber and the porous surface layer yields higher conductivity and reduces the possibility of delamination. The coating approach (method 100) disclosed herein results in a significantly lower electrical resistivity, characterized by Equation 2, and better mechanical strength due to the pi-pi bonding between the substrate 302 and the MPL coating 304 as well as sp2 hybridization bonds between the carbon particles themselves. In Equation 2, Rcomposite, RMPL, and Rsubstrate represent the electrical resistivity of the composite (including the layers 302, 304, and 306), the MPL coating 304, and the substrate 302, respectively.1Rcomposite=1RMPL+1Rsubstrate(Equation⁢ 2)

[0054] FIG. 4 shows a scanning electron microscope image of a cross section of an exemplary hydrophilic porous surface layer formed according to method 100. As shown in regions indicated by arrows 400, the hydrophilic porous surface layer conforms to high and low spots on the substrate, which are formed by x-y directionality in carbon veil. As shown in regions indicated by arrows 402, the hydrophilic porous surface layer is attached to the substrate surface via pi-pi bonding. The high and low spots refer to areas where there are dips in the surface of the substrate. As shown in FIG. 4, both high and low spots are covered by the porous surface layer and the porous surface layer has a wavy profile rather than a smooth profile. These characteristics indicate that the porous surface layer has a uniform thickness, as opposed to having a thicker surface layer in the low spots and thinner layer in the high spots. Having a uniform porous surface layer is important for mass transport and limiting the mean transport length to maximize performance.

[0055] FIG. 5A shows image of surfaces and FIG. 5B shows measured surface roughness of conventional MPLs under different compressive loads. For comparison, results of PTLs formed according to method 100 are shown in FIGS. 6A and 6B. The PTLs formed according to method 100 have a lower surface roughness (FIGS. 6A and 6B) in comparison to that of the conventional MPLs (FIGS. 5A and 5B). The surface roughness of the PTLs (FIGS. 6A and 6B) does not change significantly as the compressive stress increases.

[0056] FIGS. 7 and 8 show contact angle measurements on exemplary porous surface layers formed according to method 100. Measurements based on FIG. 7 show no wicking into substrate and the contact angle is well over 140°, indicating the porous surface layer is highly hydrophobic. Measurements based on FIG. 8 show that water is instantly wicked into surface, and a contact angle cannot be determined, indicating the porous surface layer is highly hydrophilic.

[0057] FIGS. 9 and 10 show contact angle measurements on a porous surface layer formed according to method 100 at two different times; time=0 second and after 30 seconds. Measurements based on FIG. 9 show wicking into the substrate initially (time=0 second), the sample is initially hydrophobic, e.g., contact angle, θ>90°, about 116.3° and about 123.2° in this case. There are signs of the water droplet starting to wick into the substrate on the edges (due to the hydrophilic nature of the substrate). Measurements based on FIG. 10 show that after 30 seconds (time=30 seconds), the water droplet has been almost completely absorbed into the surface of the hydrophilic substrate. The results from FIGS. 9 and 10 verify that water can wick into the porous surface layer even if the underlying substrate is hydrophobic.

[0058] This written description sets forth the best mode of practicing the claimed invention, and describes the invention so as to enable a person of ordinary skill in the art to make and use the invention, by presenting examples of the elements recited in the claims. The detailed descriptions of those examples do not impose limitations that are not recited in the claims.

[0059] As used herein, the term “or” may be construed in either an inclusive or exclusive sense. Moreover, the description of resources, operations, or structures in the singular shall not be read to exclude the plural. Conditional language, such as, among others, “can,”“could,”“might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and / or steps.

[0060] Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. Adjectives such as “conventional,”“traditional,”“normal,”“standard,”“known,” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. The presence of broadening words and phrases such as “one or more,”“at least,”“but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent.

[0061] The foregoing description of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments. Many modifications and variations will be apparent to the practitioner skilled in the art. The modifications and variations include any relevant combination of the disclosed features. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical application, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalence.

[0062] In one aspect, a method may include an operation, an instruction, and / or a function and vice versa. In one aspect, a clause or a claim may be amended to include some or all of the words (e.g., instructions, operations, functions, or components) recited in other one or more clauses, one or more words, one or more sentences, one or more phrases, one or more paragraphs, and / or one or more claims.

[0063] To illustrate the interchangeability of hardware and software, items such as the various illustrative blocks, modules, components, methods, operations, instructions, and algorithms have been described generally in terms of their functionality. Whether such functionality is implemented as hardware, software or a combination of hardware and software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application.

[0064] The functions, acts or tasks illustrated in the Figures or described may be executed in a digital and / or analog domain and in response to one or more sets of logic or instructions stored in or on non-transitory computer readable medium or media or memory. The functions, acts or tasks are independent of the particular type of instructions set, storage media, processor or processing strategy and may be performed by software, hardware, integrated circuits, firmware, microcode and the like, operating alone or in combination. The memory may comprise a single device or multiple devices that may be disposed on one or more dedicated memory devices or disposed on a processor or other similar device. When functions, steps, etc. are said to be “responsive to” or occur “in response to” another function or step, etc., the functions or steps necessarily occur as a result of another function or step, etc. It is not sufficient that a function or act merely follow or occur subsequent to another. The term “substantially” or “about” encompasses a range that is largely (anywhere a range within or a discrete number within a range of ninety-five percent and one-hundred and five percent), but not necessarily wholly, that which is specified. It encompasses all but an insignificant amount.

[0065] As used herein, the phrase “at least one of” preceding a series of items, with the terms “and” or “or” to separate any of the items, modifies the list as a whole, rather than each member of the list (e.g., each item). The phrase “at least one of” does not require selection of at least one item; rather, the phrase allows a meaning that includes at least one of any one of the items, and / or at least one of any combination of the items, and / or at least one of each of the items. By way of example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” each refer to only A, only B, or only C; any combination of A, B, and C; and / or at least one of each of A, B, and C.

[0066] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Phrases such as an aspect, the aspect, another aspect, some aspects, one or more aspects, an implementation, the implementation, another implementation, some implementations, one or more implementations, an embodiment, the embodiment, another embodiment, some embodiments, one or more embodiments, a configuration, the configuration, another configuration, some configurations, one or more configurations, the subject technology, the disclosure, the present disclosure, other variations thereof and alike are for convenience and do not imply that a disclosure relating to such phrase(s) is essential to the subject technology or that such disclosure applies to all configurations of the subject technology. A disclosure relating to such phrase(s) may apply to all configurations, or one or more configurations. A disclosure relating to such phrase(s) may provide one or more examples. A phrase such as an aspect or some aspects may refer to one or more aspects and vice versa, and this applies similarly to other foregoing phrases.

[0067] A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Underlined and / or italicized headings and subheadings are used for convenience only, do not limit the subject technology, and are not referred to in connection with the interpretation of the description of the subject technology. Relational terms such as first and second and the like may be used to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. All structural and functional equivalents to the elements of the various configurations described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the subject technology. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description. No claim element is to be construed under the provisions of 35 U.S.C. § 112(f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”

[0068] While this specification contains many specifics, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of particular implementations of the subject matter. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0069] The subject matter of this specification has been described in terms of particular aspects, but other aspects can be implemented and are within the scope of the following claims. For example, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. The actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the aspects described above should not be understood as requiring such separation in all aspects, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[0070] The title, background, brief description of the drawings, abstract, and drawings are hereby incorporated into the disclosure and are provided as illustrative examples of the disclosure, not as restrictive descriptions. It is submitted with the understanding that they will not be used to limit the scope or meaning of the claims. In addition, in the detailed description, it can be seen that the description provides illustrative examples and the various features are grouped together in various implementations for the purpose of streamlining the disclosure. The method of disclosure is not to be interpreted as reflecting an intention that the claimed subject matter requires more features than are expressly recited in each claim. Rather, as the claims reflect, inventive subject matter lies in less than all features of a single disclosed configuration or operation. The claims are hereby incorporated into the detailed description, with each claim standing on its own as a separately claimed subject matter.

[0071] The claims are not intended to be limited to the aspects described herein, but are to be accorded the full scope consistent with the language claims and to encompass all legal equivalents. Notwithstanding, none of the claims are intended to embrace subject matter that fails to satisfy the requirements of the applicable patent law, nor should they be interpreted in such a way.

Examples

Embodiment Construction

[0019]The apparatus, systems, arrangements, and methods disclosed in this document are described in detail by way of examples and with reference to the figures. It will be appreciated that modifications to disclosed and described examples, arrangements, configurations, components, elements, apparatus, methods, materials, etc. can be made and may be desired for a specific application. In this disclosure, any identification of specific techniques, arrangements, method, etc. are either related to a specific example presented or are merely a general description of such a technique, arrangement, method, etc. Identifications of specific details or examples are not intended to be and should not be construed as mandatory or limiting unless specifically designated as such.

[0020]Disclosed herein are manufacturing processes for forming a porous surface layer structure on a substrate, which can be a PTL or GDL. More specifically, disclosed herein are physical structures and manufacturing proces...

Claims

1. A porous surface layer formed on a surface of a porous transport layer (PTL), comprising carbon particles between 95% and 100% by weight of the porous surface layer, wherein the porous surface layer is functionalized to control a degree of hydrophobicity or hydrophilicity and has a contact angle between 0° and 150°2. The porous surface layer of claim 1 is configured to be applied to the surface of the PTL as a coating by a coating method selected from at least one of slot die coating, modified slot die coating, curtain coating, and spray coating.

3. The porous surface layer of claim 1 is configured to be applied to the surface of the PTL as a film or via a decal transfer method.

4. The porous surface layer of claim 1, comprising at least one functional additives configured to control at least one of structural, electrical, and thermal properties of the porous surface layer.

5. The porous surface layer of claim 1, wherein the carbon particles comprise carbon fillers in an amorphous form, a turbostratic form, or a graphitized form.

6. The porous surface layer of claim 5, wherein the carbon fillers are in a nano-size range between 0 nanometers (nm) and 100 nm, a micro-size range between 100 nm and 1 micrometer (μm), or a macro-size range greater than 1 μm tunned to alter pore size and structure of the porous surface layer.

7. The porous surface layer of claim 1, wherein the carbon particles comprise carbonized binders configured to support the porous surface layer, and the carbonized binders are in an amorphous form, a turbostratic form, or a graphitized form.

8. The porous surface layer of claim 1 has an average pore size within nano range, micro range, meso range, or macro range.

9. The porous surface layer of claim 8, wherein a form of the carbon particle and the average pore size are tuned to optimize a water contact angle (θ) ranging from hydrophilic (0°<θ<90°) to hydrophobic (θ≥90°).

10. The porous surface layer of claim 1 has a thickness that is configured to control a total pore volume available within the porous surface layer for water retention or to minimize a path length for gaseous transport.

11. The porous surface layer of claim 1 has a surface roughness equal to or less than 10 μm.

12. The porous surface layer of claim 1 does not noticeably swell or deform during repeated wetting and drying cycles.

13. The porous surface layer of claim 1 has a permanent compression set of less than or equal to 30% when pressed between 7.3 psi and 450 psi.

14. The porous surface layer of claim 1 has a porosity greater than 50% and an electrical resistivity less than 10 mΩ-cm.

15. The porous surface layer of claim 1 comprises a hydrophobic agent coated on a surface of the porous surface layer configured to increase a contact angle (θ) to greater than 90°.

16. The porous surface layer of claim 1 is heated in an oxygenated environment at a temperature between 300 degree Celsius (° C.) and 800° C. such that the porous surface layer is carbonized with a carbon content between 80% and 99% by weight of the porous surface layer.

17. The porous surface layer of claim 1 is heated in an inert atmosphere at a temperature between 700° C. and 2600° C. such that the porous surface layer is carbonized with a carbon content equal to great than 95% by weight of the porous surface layer.

18. A method of forming a porous transport layer on a porous transport layer (PTL), comprising:forming a coating ink comprising carbon particles;applying the coating ink to a surface of the PTL;applying heat or both heat and pressure to the porous transport layer coated with the coating ink to form a composite;heat treating the composite in an inert atmosphere or in vacuum to form the porous surface layer; andfunctionalizing the porous surface layer to control a degree of hydrophobicity or hydrophilicity, wherein and the porous surface layer has a contact angle between 0° and 15019. The method of claim 18, further comprising applying a hydrophobic polymer to the composite.

20. The method of claim 18, wherein the carbon particles are between 95% and 100% by weight of the porous surface layer,

Images