Articles Comprising Microporous Substrates Having Conformal Coatings, and Methods of Making and Using the Articles - Patent application

Abstract

Improved conductive porous articles and improved methods for making conductive porous articles are provided. [Solution] A composite material comprising a polymer substrate having a microporous structure and a conformal coating disposed around the surface of the polymer substrate, the conformal coating being formed from sintered metal nanoparticles.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63 / 419,695, filed October 26, 2022, and U.S. Provisional Application No. 63 / 417,688, filed October 19, 2022, the entire contents of which are incorporated herein by reference for all purposes.

[0002] This disclosure relates generally to articles comprising a metallized microporous substrate, and more particularly to articles comprising a microporous substrate having a conformal coating formed of sintered metal nanoparticles, and related methods of making and using such articles. [Background technology]

[0003] Conductive articles are used in a variety of contexts, including energy storage and energy conversion applications. Some conductive articles comprise a porous substrate that is conductive or has been treated to impart conductivity (e.g., coated with a conductive material). The porosity of such substrates can serve a variety of important functions, such as enabling mass transport and / or reducing the weight of the conductive article. There is interest in preparing porous conductive materials with specific properties, such as high conductivity, durability, flexibility, and strength.

[0004] With regard to conductive coatings on substrates, some coatings include metals, and the application of such metal coatings can be described as "metallization" of the coated substrate. Some metallization approaches are very time-consuming, use expensive processing aids, and / or leave behind residual contaminants that can cause fitness-for-use issues in certain applications. For example, in electroless plating, it is common to first activate the surface to be metallized using a material such as a palladium / tin activator solution (i.e., deposit a so-called "seed layer"). This adds process complexity and increases costs due to the expense of materials such as palladium. Other metallization processes may require the substrate surface to first be coated with another material, a so-called "adhesion layer." This "adhesion layer" is a layer that can more easily be coated with metal. However, the use of an adhesion layer can have the same drawbacks as those mentioned above, namely, it can complicate the process and leave behind undesirable residues.

[0005] Furthermore, with regard to the metallization of porous substrates, some porous substrates are difficult to metallize due to a variety of detrimental factors. For example, substrates with a complex pore structure can lead to uneven metallization of the interior surface due to the so-called "shadowing" effect when metallization is performed using a substantially line-of-sight technique, such as sputtering or evaporation. For example, substrates that are moderately or highly susceptible to radiation and / or heat damage can lead to reduced properties (e.g., mechanical properties) when metallization is performed using a high-energy technique, such as sputtering. For example, substrates with low surface energy can result in poor adhesion of the resulting coating and a high number of defects and / or uncoated substrate areas. Summary of the Invention [Problem to be solved by the invention]

[0006] There is a need for improved conductive porous articles and improved methods of making conductive porous articles. [Means for solving the problem]

[0007] The present disclosure relates to conductive microporous articles with specific properties (e.g., high conductivity, high durability, and high flexibility) and optimized porosity and pore morphology; and to metallization processes for microporous substrates that are simplified, rapid, require fewer chemicals, can coat the interior surfaces of microporous substrates with intricate pore networks, can apply durable coatings to low surface energy substrates with high coverage and / or low defects, minimize substrate degradation, and / or do not leave undesirable residues (e.g., seed layers or adhesion layers).

[0008] With respect to porous substrates for metallization, microporous polymer substrates (e.g., microporous polymer films) can have desirable properties such as high mechanical strength, tunable morphology, and high surface area. However, such substrates may exhibit some or all of the detrimental factors described in the Background section. One exemplary substrate that may exhibit some or all of these desirable properties and detrimental factors is expanded polytetrafluoroethylene (ePTFE). The present disclosure relates to providing durable conformal metal coatings on surfaces (including interior surfaces) of microporous polymer substrates (e.g., ePTFE), even under the challenging conditions described herein.

[0009] As discussed herein, the porosity of such conductive microporous articles can serve a variety of important functions, such as enabling mass transport and / or reducing the weight of the conductive article. Accordingly, there is interest in optimizing porosity and pore morphology, for example, to provide robust and optimized mass transport. There is also interest in minimizing the amount of conductive coating required, for example, to minimize the weight and / or cost of the conductive article. In some circumstances, it may be desirable to treat a microporous material to be substantially or completely conductive throughout the bulk of the material (e.g., substantially or completely throughout the thickness of a porous, flat sheet).

[0010] The present disclosure provides a microporous polymer substrate having a conformal coating formed of sintered metal nanoparticles. The present disclosure also relates to embodiments in which the microporous polymer substrate having a conformal coating formed of sintered metal nanoparticles is incorporated into an electrode.

[0011] According to one embodiment ("Embodiment 1"), a composite material includes a polymer substrate having a porous structure and a conformal coating disposed about a surface of the polymer substrate, the conformal coating being formed from sintered metal nanoparticles.

[0012] According to yet another embodiment relative to embodiment 1, the surface includes an interior surface defined by a porous structure, and the conformal coating is disposed on the interior surface of the polymer substrate.

[0013] According to yet another embodiment to embodiment 1, the conformal coating is a continuous coating on the surface, including the interior surface, of the polymeric substrate.

[0014] According to yet another embodiment relative to embodiment 1, the porous structure of the polymer substrate comprises nodes and / or fibrils, and the conformal coating is disposed around the nodes and / or fibrils of the polymer substrate.

[0015] According to yet another embodiment to embodiment 1, the porous structure of the polymer matrix is ​​microporous.

[0016] According to yet another embodiment relative to embodiment 1, the conformal coating is selected from one of a platinum coating, an iridium coating, a ruthenium coating, a palladium coating, a gold coating, a silver coating, a copper coating, a nickel coating, an indium coating, combinations thereof, alloys thereof, including alloys with transition metals, and / or oxides thereof.

[0017] According to yet another embodiment to embodiment 1, the polymer substrate is a membrane.

[0018] According to yet another embodiment to embodiment 1, the polymer substrate is expanded polytetrafluoroethylene.

[0019] According to yet another embodiment to embodiment 1, the composite material is between about 1 micrometer and about 100 micrometers thick.

[0020] According to yet another embodiment to embodiment 1, in the composite material, the ratio of the volume of the conformal coating to the volume of the pore phase is 0.001 to 1.0.

[0021] According to yet another embodiment relative to embodiment 1, the composite material has a mean flow pore size at least twice as large as the volume average particle size of the metal nanoparticles.

[0022] According to yet another embodiment relative to embodiment 1, the conformal coating is a conductive coating having a metal retention of greater than 90% by weight.

[0023] According to yet another embodiment ("Embodiment 2") relative to Embodiment 1, the composite material comprises an ion exchange material.

[0024] According to yet another embodiment relative to embodiment 2, the ion exchange material is selected from one of an anion exchange material and a cation exchange material.

[0025] According to yet another embodiment relative to embodiment 2, the ion exchange material is selected from hydrocarbon polymers, fluorocarbon polymers, and perfluorocarbon polymers.

[0026] According to yet another embodiment to embodiment 2, the ion exchange material is perfluorosulfonic acid.

[0027] According to yet another embodiment ("Embodiment 3") to Embodiment 2, there is provided a membrane electrode assembly comprising the composite material of any of the previous embodiments bonded to an electrochemical separator.

[0028] According to yet another embodiment to embodiment 3, the electrochemical separator comprises an ion exchange material.

[0029] According to yet another embodiment relative to embodiment 3, the ion exchange material is selected from one of an anion exchange material and a cation exchange material.

[0030] According to yet another embodiment to embodiment 3, the ion exchange material is selected from hydrocarbon polymers, fluorocarbon polymers, and perfluorocarbon polymers.

[0031] According to yet another embodiment to embodiment 3, the ion exchange material is perfluorosulfonic acid.

[0032] According to another embodiment ("Embodiment 4"), an article comprises the composite material of any of the previous embodiments.

[0033] According to yet another embodiment to embodiment 4, the article is an electrochemical cell.

[0034] According to yet another embodiment to embodiment 4, the article is a fuel cell.

[0035] According to yet another embodiment to embodiment 4, the article is an electrolytic cell.

[0036] According to another embodiment ("Embodiment 5"), an article includes a microporous polymer substrate continuously and conformally coated with sintered metal nanoparticles.

[0037] According to yet another embodiment to embodiment 5, the sintered metal nanoparticles coat the interior surface of the microporous polymer substrate.

[0038] According to yet another embodiment relative to embodiment 5, the microporous polymer substrate comprises a node and fibril microstructure, and the sintered metal nanoparticles coat the nodes and fibrils of the microporous polymer substrate.

[0039] According to another embodiment ("Embodiment 6"), a method of forming a composite material includes providing a polymer substrate having a porous structure, imbibing metal nanoparticles into the polymer substrate, and heating the metal nanoparticles to sinter the metal nanoparticles to form a conformal coating on a surface of the polymer substrate.

[0040] According to yet another embodiment to embodiment 6, the method further comprises preparing a dispersion comprising the metal nanoparticles and a dispersant, and the imbibing comprises wetting the polymer substrate with the dispersion.

[0041] According to yet another embodiment relative to embodiment 6, the step of imbibing into the polymeric substrate comprises heating the polymeric substrate to a first temperature at which the processing aid volatilizes, and the step of heating the metal nanoparticles comprises heating the metal nanoparticles to a second temperature to sinter the metal nanoparticles.

[0042] According to yet another embodiment to embodiment 6, the second temperature at which the nanoparticles are sintered is lower than the melting temperature of the polymer matrix.

[0043] According to yet another embodiment to embodiment 6, the first temperature is about 90°C and the second temperature is about 300°C.

[0044] According to yet another embodiment relative to embodiment 6, the porous structure defines an interior surface, and disposing the metal coating on the interior surface of the polymer substrate defines a continuous metal coating on the porous structure, including the interior surface, of the polymer substrate.

[0045] According to yet another embodiment relative to embodiment 6, the metal coating is selected from one of a platinum coating, an iridium coating, a ruthenium coating, a palladium coating, a gold coating, a silver coating, a copper coating, a nickel coating, an indium coating, combinations thereof, alloys thereof, including alloys with transition metals, and / or oxides thereof.

[0046] According to yet another embodiment to embodiment 6, the polymer substrate is a membrane.

[0047] According to yet another embodiment relative to embodiment 6, the polymer substrate is selected from one of expanded polytetrafluoroethylene and expanded polyethylene. [Brief explanation of the drawings]

[0048] The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification, illustrating embodiments and, together with the description, serve to explain the principles of the disclosure.

[0049] [Figure 1A] 1 is an SEM image showing the microstructure of a conformal gold on ePTFE ("CG / ePTFE") composite, according to certain embodiments of the present disclosure. [Figure 1B] 1 is an SEM image showing the microstructure of a conformal gold on ePTFE ("CG / ePTFE") composite, according to certain embodiments of the present disclosure. [Figure 1C] 1 is an SEM image showing the microstructure of a conformal gold on ePTFE ("CG / ePTFE") composite, according to certain embodiments of the present disclosure.

[0050] [Figure 2] FIG. 1 is a schematic illustration of a membrane electrode assembly according to certain embodiments of the present disclosure.

[0051] [Figure 3] FIG. 1 is a schematic diagram of an apparatus used to measure sheet resistance, according to certain embodiments of the present disclosure.

[0052] [Figure 4] 4 is an exemplary flow diagram illustrating a method 400 of forming a composite material, according to certain embodiments of the present disclosure.

[0053] [Figure 5A] FIG. 1 illustrates a wet flex graining durability test method according to certain embodiments of the present disclosure. [Figure 5B] FIG. 1 illustrates a wet flex graining durability test method according to certain embodiments of the present disclosure. [Figure 5C] FIG. 1 illustrates a wet flex graining durability test method according to certain embodiments of the present disclosure.

[0054] [Figure 6A]1 is an SEM image showing the microstructure of a conformal silver on ePTFE ("CS / ePTFE") composite, according to certain embodiments of the present disclosure. [Figure 6B] 1 is an SEM image showing the microstructure of a conformal silver on ePTFE ("CS / ePTFE") composite, according to certain embodiments of the present disclosure. [Figure 6C] 1 is an SEM image showing the microstructure of a conformal silver on ePTFE ("CS / ePTFE") composite, according to certain embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0055] Those skilled in the art will readily appreciate that the various aspects of the present disclosure may be implemented by any number of methods and apparatuses configured to perform the intended functions. It should also be noted that the accompanying drawings referred to herein are not necessarily drawn to scale and may be enlarged to illustrate various aspects of the present disclosure, and in that regard, the drawings should not be construed as limiting.

[0056] The present disclosure is not intended to be limiting. For example, the terminology used in this application should be interpreted broadly in the context of the meaning that one of ordinary skill in the art would give to that terminology.

[0057] With regard to terminology that includes imprecision, the terms "about" and "approximately" may be used interchangeably to refer to measurements that include the stated measurement as well as measurements that are reasonably close to the stated measurement. A measurement that is reasonably close to the stated measurement deviates reasonably slightly from the stated measurement to an extent that is understood and easily identified by one of ordinary skill in the art. Such deviations may result from, for example, measurement error, differences in calibration of measuring and / or manufacturing equipment, human error in reading and / or setting measurements, minor adjustments made to optimize performance and / or structural parameters to account for differences in measurements associated with other components, specific implementation scenarios, imprecise adjustment and / or manipulation of objects by humans or machines, etc. If it is determined that a person of ordinary skill in the art would not be able to easily identify such a reasonably small difference, the terms "about" and "approximately" may be understood to mean ±10% of the stated value.

[0058] As used herein, the term "conductive" means "electrically conductive" unless otherwise indicated.

[0059] As used herein, the term "porous" is used to describe a structure having voids (e.g., pores) and a solid matrix. Each pore has a pore volume, and a plurality of pores defines the total pore volume of the microporous polymer substrate. A solid matrix refers to the solid portion of the microporous polymer substrate, excluding the pore volume of the microporous polymer substrate.

[0060] As used herein, the term "microporous" is used to describe a material containing pores of a single pore size or a distribution of pore sizes. The average or median pore size may be about 0.05 μm to about 50 μm, or about 0.1 to about 50 μm, or about 0.1 to about 30 μm, or about 0.2 to about 60 μm, or about 0.5 to about 50 μm, or any intermediate range or value subsumed within these ranges. It is understood that a microporous material may contain individual pores outside this average size range, including some macropores. Microporous materials can have a characteristic or nominal pore size characterized by bubble point analysis, as described below, or another suitable test. The average pore size of a material can be characterized, for example, by the mean flow pore size measured by capillary flow porometry.

[0061] As used herein, the term "internal surface" refers to the surfaces of the components (eg, nodes, fibrils, fibers, fiber bundles) that define the walls of the pores of a microporous substrate.

[0062] As used herein, the term "conformal" refers to a coating layer that coats a microporous substrate such that the coating layer substantially conforms to the surface of the microporous substrate, including the exterior and interior surface components (e.g., nodes, fibrils, fibers, fiber bundles) of the substrate.

[0063] As used herein, the term "continuous coating" refers to a coating layer that is substantially electrically continuous along the surface (including the exterior and interior surfaces) of a microporous substrate. A continuous coating can exhibit high conductivity in the cross-plane and in-plane directions relative to the microporous substrate.

[0064] As used herein, the term "imbibition" refers to a process in which a liquid carrier is used to deposit a material into the pores of a microporous substrate, but the imbibed material is not substantially incorporated into the matrix of the microporous substrate, so that the microporous substrate remains largely intact.

[0065] As used herein, the term "electrically conductive material" refers to a material that transports electrons with low resistance, where the electrical resistance of the material does not interfere with its use in the desired application. In practice, this phrase typically refers to a material that has a resistance of about 1×10 -3 It means resistivity in ohms x cm.

[0066] As used herein, the phrases "electrically non-conductive material" and "electrically insulating material" refer to materials that have a high resistivity such that the electrical conductivity of the material does not interfere with its use in the desired application. In practice, these terms typically refer to materials with a resistivity of about 1×10 8 It means a resistivity higher than ohm x cm.

[0067] As used herein, "wetting" refers to the spreading of a fluid on a substrate. In the case of microporous substrates, wetting also refers to the penetration of the fluid into the pores.

[0068] As used herein, "dewetting" refers to the removal of fluid from previously wetted areas of a substrate (e.g., the formation of droplets where the liquid film disappears on the substrate).

[0069] The devices and methods shown and described herein are provided as examples of various features of the devices and methods, and the examples and illustrations thereof are not meant to suggest that the inventive concepts provided herein are limited to fewer features, additional features, or alternative features to one or more of those described with respect to different examples, even if combinations of those illustrated features are clearly within the scope of the invention.

[0070] The articles, devices, and methods discussed herein generally relate to microporous substrates (e.g., expanded polymeric membranes) coated with sintered metal nanoparticles. The metal nanoparticles form a durable metal coating on the microporous substrate, e.g., by sintering the metal nanoparticles. According to some embodiments, the sintered metal nanoparticles form a conformal coating on the microporous substrate, including the exterior and interior surfaces of the microporous substrate. In some embodiments, the sintered metal nanoparticles form a continuous conformal coating on the microporous substrate, including the exterior and interior surfaces. Various features and methods for achieving such a result are discussed throughout. The articles discussed herein maintain their microporous properties after applying a continuous conformal coating to the microporous substrate.

[0071] In one embodiment, a composite material includes a polymer substrate having a microporous structure and a conformal coating disposed about a surface of the polymer substrate, the conformal coating being formed from sintered metal nanoparticles.

[0072] 1A-1C, a composite material 100 is shown. FIGS. 1A-1C provide representative SEM images of a sample of composite material 100. FIG. 1A generally illustrates a cross-section of composite material 100, FIG. 1B illustrates a cross-section of composite material 100 at a node of composite material 100 defined within the microstructure of composite material 100, and FIG. 1C illustrates a cross-section of composite material 100 at a fibril of composite material defined within the microstructure of composite material 100.

[0073] As shown in FIG. 1A, composite material 100 includes a polymer substrate 102. In some embodiments, the polymer substrate can be porous (e.g., having a plurality of pores). In some embodiments, the polymer substrate can be microporous. In certain embodiments, the polymer substrate 102 can be expanded polytetrafluoroethylene (ePTFE). In certain embodiments, the polymer substrate 102 can be a membrane. In certain embodiments, the membrane can be a synthetic polymer membrane.

[0074] According to some embodiments, the polymeric substrate 102 can have a first major exterior surface (e.g., a first surface) and a second major exterior surface (e.g., a second surface) opposite the first surface. In some embodiments, when the polymeric substrate 102 is in the form of a tube, the first and second major exterior surfaces correspond to the inner and outer diameters of the tube. The polymeric substrate 102 can have a thickness that is the distance between the two major exterior surfaces. The plurality of pores have an inner surface defined by an interface with the solid matrix. The inner surface of the pore refers to the surface of the pore that is not present on the outer surface of the substrate. In some embodiments, the polymeric substrate 102 can have a thickness of from about 1 micrometer to about 100 micrometers.

[0075] According to certain embodiments, the microporous polymer substrates described herein may be porous polymer structures that can be configured in various forms, such as webs (i.e., long, thin, flexible materials supplied in roll form), sheets (e.g., flat sheets), or tubes (e.g., circular tubes). In certain embodiments, the porous polymer structures may be thin, flexible, and / or freestanding.

[0076] In some embodiments, a microporous polymer substrate (e.g., polymer substrate 102) can include a continuous layer of material containing pores that form passageways extending from a first surface to a second surface (i.e., from one exterior surface of the layer to the opposite exterior surface of the layer). Such passageways can be referred to as through pores. The pore volume can also include pores that are blind pores (i.e., some pores may not be connected to both exterior surfaces through the pore volume). Pores that are connected to only one exterior surface can be referred to as closed pores, and pores that are not connected to either exterior surface can be referred to as closed-cell pores. In some embodiments, within the pore volume, pores can be interconnected and form a continuous porous network. In certain embodiments, pores can be spaced apart from one another within the pore volume. In some embodiments, there can be some intermediate level of interconnection between pores within the pore volume.

[0077] According to some embodiments, the solid matrix comprises a continuous network of interconnected material elements, and the pores can be void spaces between these material elements. According to certain embodiments, the material elements include a wide variety of structural components that form the building blocks of the overall polymer structure. The material elements are not particularly limited and can include, for example, fibers, fiber bundles, nodes, and fibrils. In some embodiments, the polymer substrates described herein can have a microstructure comprising fibers, fiber bundles, and a plurality of pores, where the fibers and fiber bundles are interconnected, and the plurality of pores are void spaces between the fibers and fiber bundles. In certain embodiments, the polymer substrates described herein can have a microstructure comprising nodes, fibrils, and a plurality of pores, where the nodes are interconnected by fibrils, and the plurality of pores are void spaces between the nodes and fibrils.

[0078] In some embodiments, the polymer substrates described herein support and mechanically reinforce the composite material, thereby improving its structural integrity and durability. In some embodiments, the polymer substrate may enable thinner and / or larger-area composite membranes while retaining handleability and other desirable properties. In certain embodiments, the polymer substrate is thermally, chemically, and / or electrochemically stable in the environment in which the composite membrane will be used. In certain embodiments, the polymer substrate can withstand any manufacturing steps required in the production of the composite membrane and / or the subsequent storage, transportation, and handling of the composite membrane.

[0079] In certain embodiments, the polymeric substrates described herein can be stable at very high pH (e.g., a pH greater than about 10, or a pH greater than about 11, or a pH greater than about 12, or a pH greater than about 13, or a pH greater than about 14). In some embodiments, the polymeric substrates can be stable at very low pH (e.g., a pH less than about 5, or a pH less than about 4, or a pH less than about 3, or a pH less than about 2, or a pH less than about 1).

[0080] According to some embodiments, the polymer substrate described herein can be formed by any method suitable for the application. The method for manufacturing the polymer substrate is not particularly limited, and any method known in the art can be used to form the polymer substrate. In some embodiments, suitable processing methods can include roll-to-roll processing, paste processing, gel processing, and stretching. Depending on the manufacturing method, the polymer substrate can have a machine direction (MD) and a transverse direction (TD), where the MD is perpendicular to the TD. In certain embodiments, the MD and TD are each perpendicular to the thickness direction. In some embodiments, for example, when the polymer substrate is in the form of a web, the MD can correspond to the length direction, and the TD can correspond to the width direction.

[0081] According to certain embodiments, the polymeric substrates described herein can be formed from any material suitable for the application. The material is not particularly limited, and any material known in the art can be used to form the polymeric substrate. For example, the polymeric substrate can include a polymeric material. In some embodiments, the polymeric material can include a polymer or a mixture of polymers. In some embodiments, the polymeric material can include a homopolymer or a copolymer. In some embodiments, the polymeric material can include an inorganic polymeric material and / or an organic polymeric material. In certain embodiments, the polymeric material can include fluorine and / or other heteroatoms. In certain embodiments, the polymeric material can include aromatic and / or non-aromatic (e.g., aliphatic or olefinic) portions. In certain embodiments, the polymeric material can include side chains and / or functional groups. In some embodiments, the polymeric material can include a fibrillizable polymer (e.g., PTFE).

[0082] According to some embodiments, the polymer substrates described herein can be formed from any one selected from a non-fluorinated polymer (e.g., a hydrocarbon polymer), a partially fluorinated polymer, a perfluorinated polymer, and any combination thereof. In some embodiments, the polymer substrates described herein can include a polyolefin such as polyethylene (PE) or polypropylene (PP). In some embodiments, the polymer substrates described herein can include any one selected from polytetrafluoroethylene (PTFE), polyethylene (PE), or a copolymer of PTFE and PE. In certain embodiments, the polymer substrates described herein can include expanded polytetrafluoroethylene (ePTFE) or expanded polyethylene (ePE).

[0083] Non-limiting examples of materials suitable for use as the polymer substrate 102 include expanded polytetrafluoroethylene (ePTFE). In at least one embodiment, the polymer substrate 102 is a microporous synthetic polymer membrane, such as a microporous fluoropolymer membrane having a node and fibril microstructure, where the nodes are interconnected by fibrils and the pores are voids or spaces located between the nodes and fibrils throughout the polymer substrate. An exemplary node and fibril microstructure is described in U.S. Pat. No. 3,953,566 to Gore. The nodes and fibrils of the microporous microstructure have surfaces that define the interior surface of the polymer substrate.

[0084] The polymer substrates described herein are approximately 2.0 m 2 / cm 3 Super, about 4.0m 2 / cm 3 Super, about 6.0m 2 / cm 3 Super, about 8.0m 2 / cm 3 Super, about 10m 2 / cm 3 Super, about 20m 2 / cm 3 Super, about 30m 2 / cm 3 Super, about 40m 2 / cm 3 Super, about 50m 2 / cm 3 Super, about 60m 2 / cm 3 Super, about 70m 2 / cm 3 Super, about 80m 2 / cm 3 Super, about 90m 2 / cm 3 Over 100m 2 / cm 3 The surface area per unit volume can be up to 1000 nm, where the surface area per unit volume is determined based on the skeletal volume rather than the apparent volume.

[0085] In some embodiments, the surface area per unit volume is about 2.0 m 2 / cm 3 ~approx. 100m 2 / cm 3 , or approximately 3.0 m 2 / cm 3 ~about 90m 2 / cm 3 , or approximately 4.0 m 2 / cm 3 ~about 80m 2 / cm 3 , or approximately 5.0 m 2 / cm 3 ~about 70m 2 / cm 3 , or approximately 6.0 m 2 / cm 3 ~about 60m 2 / cm 3 , or approximately 7.0 m 2 / cm 3 ~approx. 50m 2 / cm 3 , or approximately 7.5 m 2 / cm 3 ~about 40m 2 / cm 3 , or approximately 8.0 m 2 / cm 3 ~about 30m 2 / cm 3 , or approximately 8.5 m 2 / cm 3 ~about 20m 2 / cm 3 , or approximately 9.0 m 2 / cm 3 ~about 10m 2 / cm 3 or any other range included between these endpoints.

[0086] In some embodiments, the surface area per unit volume is about 2.0 m 2 / cm 3 ~about 3.0m 2 / cm 3 , or approximately 3.0 m 2 / cm 3 ~about 5.0m 2 / cm3 , or approximately 5.0 m 2 / cm 3 ~about 10m 2 / cm 3 , or about 10m 2 / cm 3 ~about 20m 2 / cm 3 , or about 20m 2 / cm 3 ~about 30m 2 / cm 3 , or about 30m 2 / cm 3 ~about 40m 2 / cm 3 , or about 50m 2 / cm 3 ~about 60m 2 / cm 3 , or about 60m 2 / cm 3 ~about 70m 2 / cm 3 , or about 70m 2 / cm 3 ~about 80m 2 / cm 3 , or about 80m 2 / cm 3 ~about 90m 2 / cm 3 , or about 90m 2 / cm 3 ~approx. 100m 2 / cm 3 or any other range included between these endpoints.

[0087] Additionally, the majority of the fibrils in the polymeric substrate can have a diameter of less than about 1.0 μm, or from about 0.1 μm to about 1.0 μm, from about 0.3 μm to about 1.0 μm, from about 0.5 μm to about 1.0 μm, or from about 0.7 μm to about 1.0 μm, or any other range included within these endpoints. Furthermore, the polymeric substrate can be thin, having a thickness of from about 1 μm to about 100 μm, or from about 1.1 μm to about 75 μm, or from about 1.2 μm to about 50 μm, or from about 1.3 μm to about 35 μm, or from about 1.4 μm to about 25 μm, or from about 1.5 μm to about 10 μm, or from about 1.6 μm to about 5 μm, or from about 1.7 μm to about 4 μm, or from about 1.8 μm to about 3 μm, or any other thickness within any other range included within these endpoints.

[0088] In some embodiments, the polymeric substrate can have a conformal coating disposed about the surface of the polymeric substrate, the conformal coating being formed of sintered metal nanoparticles. In some embodiments, the conformal coating can be disposed about the interior surface of the polymeric substrate. In certain embodiments, the metal nanoparticles can be sintered. Non-limiting examples of conformal coatings can include metal nanoparticles such as platinum group metals (PGMs, e.g., platinum, iridium, ruthenium, palladium), gold, silver, copper, nickel, indium, combinations thereof, alloys thereof (e.g., alloys with transition metals), and / or oxides thereof.

[0089] The composite material 100 may also include a conformal coating 104 formed of sintered metal nanoparticles dispersed about the surface of the polymer substrate 102. The coating 104 may be formed of sintered metal nanoparticles.

[0090] In some embodiments, for example, as shown in Figures 1B-1C, the microporous structure defines an interior surface, and a conformal coating 104 formed of sintered metal nanoparticles is disposed on the interior surface of the polymer substrate 102. In certain embodiments, the conformal coating 104 formed of sintered metal nanoparticles is a continuous coating on the surface of the polymer substrate 102, including the interior surface.

[0091] In some examples, the polymer substrate 102 includes a microstructure having a plurality of nodes 106 (e.g., as shown in FIG. 1B) and fibrils 108 (e.g., as shown in FIG. 1C). A conformal coating 104 formed of sintered metal nanoparticles is disposed around the nodes 106 and fibrils 108 of the polymer substrate 102.

[0092] In certain examples, the conformal coating 104 formed of sintered metal nanoparticles is selected from one of a platinum coating, an iridium coating, a ruthenium coating, a palladium coating, a gold coating, a silver coating, a copper coating, a nickel coating, an indium coating, combinations thereof, alloys thereof (e.g., alloys including transition metals), and / or oxides thereof.

[0093] According to some embodiments, the coated polymer substrate comprises a microporous polymer continuously and conformally coated with sintered metal nanoparticles. In some embodiments, the sintered metal nanoparticles coat the interior surface of the polymer substrate. According to certain embodiments, the polymer substrate comprises a node and fibril microstructure, and the sintered metal nanoparticles coat the nodes and fibrils of the polymer substrate. In certain embodiments, the sintered metal nanoparticles form a continuous conformal coating on the interior surface of the polymer substrate. In some embodiments, the polymer substrate can have a microstructure. The microstructure can include, for example, nodes and / or fibrils. In some examples, the thickness of the conformal coating formed on the nodes can be similar to the thickness of the conformal coating formed on the fibrils. In some examples, the thickness of the conformal coating formed on the nodes can be different from the thickness of the conformal coating formed on the fibrils. In some embodiments, the thickness of the conformal coating formed on one node can be substantially similar to the thickness of the conformal coating formed on another node. In some embodiments, the thickness of the conformal coating formed on one fibril can be similar to the thickness of the conformal coating formed on another fibril.

[0094] According to the present disclosure, durable, conformal metal coatings can be formed on the interior surface and throughout the thickness of polymeric substrates (e.g., ePTFE) with intricate pores and low surface energy by absorption and sintering of metal nanoparticles.

[0095] As noted above in the Background section with regard to the third aggravating factor, one of the historical obstacles to conformal coating is the difficulty of producing thin metal coatings on polymeric substrates (e.g., ePTFE) that have high surface areas and low surface energies. This difficulty can be exacerbated when there is a significant mismatch in surface energy between the coating and the polymeric substrate. In general, metals tend to have much higher surface energies than polymers, particularly low-surface-energy polymers such as polytetrafluoroethylene (PTFE). As an illustrative example, metals such as gold and platinum have surface energies of approximately 1500 mJ / m2 each. 2 , about 2400mJ / m 2 whereas PTFE has a surface energy of approximately 20 mJ / m 2 (two orders of magnitude lower).

[0096] While not wishing to be bound by theory, it is generally understood that surfaces tend toward their lowest energy state, and therefore, materials with higher surface energy tend not to "wet" low-energy surfaces, particularly those with large surface areas. Furthermore, materials with high surface energy tend to "dewet" low-energy surfaces when possible and tend to accumulate or agglomerate to minimize their surface area. It is also generally understood that metal nanoparticles can be sintered at temperatures well below the melting point of the bulk metal. This sintering is believed to occur due to melting point depression, for example, via the Gibbs-Thomson effect. Therefore, sintering metal nanoparticles disposed on a low-energy surface would be expected to result in substantial "dewetting" of the metal from the low-energy surface of the target polymer substrate, with the metal nanoparticles accumulating or agglomerating in accessible pore spaces. Furthermore, metal coatings can be expected to have relatively poor adhesion to low-energy surfaces. However, the present disclosure demonstrates articles and methods for producing such articles that achieve substantially uniform and conformal metal coatings of low-energy surfaces of polymer substrates. Additionally, the conformal coating durably adhered to the polymer substrate, as demonstrated by the results of the wet bending particle testing described below. The present disclosure demonstrates embodiments and methods for fusing metal nanoparticles into a relatively thin, dense metal coating that substantially conforms to the interior surface of a polymer substrate (e.g., ePTFE), where the metal nanoparticles are spread over a relatively large surface area.

[0097] The mechanical durability of metal coatings on polymer substrates (e.g., adhesion of the metal coating to the polymer substrate) can be measured using an in-house wet flex particulation test, described in more detail below. In some embodiments, the particulation level of the conductive coating can be less than 0.01% by weight of the conductive coating (i.e., corresponding to greater than 99.99% by weight conductive coating retention). In some embodiments, the conductive coating retention can be greater than 99.9% by weight. In some embodiments, the conductive coating retention can be greater than 99% by weight. In some embodiments, the conductive coating retention can be greater than 90% by weight.

[0098] Thus, the present disclosure relates to providing conformal metal coatings, including on the interior surfaces of polymeric substrates, despite the challenges associated with, for example, surface energy and other exacerbating factors discussed herein. In some embodiments, metal nanoparticles (e.g., gold) are deposited and processed to form a conformal and continuous coating around the polymeric substrate. Without wishing to be bound by theory, this is achieved by delivering the metal nanoparticles substantially uniformly to the surface of the microporous substrate and inducing fusion of the metal nanoparticles by sintering (e.g., rapid sintering) within the pores of the polymeric substrate to form a conformal coating on the surface of the polymeric substrate (e.g., ePTFE). In some examples, the conformal coating can completely surround microstructural elements such as nodes and / or fibrils, thereby enhancing the durability of the conductive coating (e.g., as measured by a wet bending particle test). In some examples, substantially all surfaces of the substrate (including the exterior and interior surfaces) are coated with the conformal coating. In some examples, at least a portion of the exterior and interior surfaces of the substrate are coated with the conformal coating.

[0099] 1A-1C show representative SEM images of an example of a composite with conformal gold on ePTFE, i.e., a CG / ePTFE composite. Figure 1A shows the composite cross section, Figure 1B shows its node cross section, and Figure 1C shows its fibril cross section. CG is visible around the nodes and fibrils of the ePTFE membrane.

[0100] In one embodiment, cross-sectional SEM images reveal that the sintered metal nanoparticles conform to the surface topography of the polymer substrate components (e.g., nodes) (see, e.g., FIG. 1B). In some embodiments, the polymer substrate fibrils are coated with metal nanoparticles around their entire periphery (see, e.g., FIG. 1C).

[0101] It is understood that the articles and methods described herein can be implemented in a variety of settings. In one non-limiting example, a polymer substrate having a conformal coating of sintered metal nanoparticles can be implemented in an electrochemical cell or a device including an electrochemical cell, for example, for energy storage and conversion. In one embodiment, the conformally coated polymer substrate can be configured as a component of an electrochemical cell, such as an electrode. In another embodiment, the conformally coated polymer substrate can be configured as part of a membrane electrode assembly.

[0102] For example, referring now to FIG. 2 , a schematic illustration of a membrane electrode assembly 200 using the composite materials and / or polymer substrates described herein is shown. As shown, the membrane electrode assembly 200 can have multiple layers, including a cathode layer 202, an anode layer 204, and a separator layer 206. The membrane electrode assembly 200 can be integrated into a single structure, as shown in FIG. 2 , or can be a separate structure. In one embodiment, the article can include a separator layer 206 attached to an electrode, where the electrode comprises a polymer substrate having a conformal coating of sintered metal nanoparticles. The membrane electrode assembly can include both electrodes or only one of them. As will be appreciated by those skilled in the art, the size, shape, orientation, compliance, flexibility, and other attributes of the membrane electrode assembly 200 can vary.

[0103] In some embodiments, the cathode layer 202 and / or the anode layer 204 may be electrically conductive. In some examples, the cathode layer 202 and / or the anode layer 204 may include a catalyst. In some examples, the cathode layer 202 and / or the anode layer 204 may include an electrocatalyst. In some examples, the cathode layer 202 may include an electrocatalyst for a reduction reaction. In some examples, the anode layer 204 may include an electrocatalyst for an oxidation reaction. In some examples, the electrocatalyst may have an extended surface. In such cases, it is of interest to prepare conductive materials with specific properties, such as high catalytic activity, high current density, stable mass transport, and high durability.

[0104] In some embodiments, when a polymer substrate having a conformal coating formed of sintered metal nanoparticles is configured as an electrode, the electrode may be modified to enable ion conduction. For example, the electrode may be configured to enable the transport of cations and / or anions. In certain embodiments, the electrode may become ionically conductive when wetted or swollen with a liquid electrolyte. In certain embodiments, the electrode may comprise an ion exchange material (e.g., at least one ion exchange polymer). In certain embodiments, the ion exchange material may comprise a hydrocarbon ion exchange material. In certain embodiments, the ion exchange material may comprise a fluorocarbon ion exchange material. In certain embodiments, the ion exchange material may comprise a perfluorocarbon ion exchange material. In certain embodiments, the ion exchange material may comprise an anion exchange material (e.g., an anion exchange polymer). In certain embodiments, the ion exchange material may comprise a cation exchange material (e.g., a cation exchange polymer). In certain embodiments, the ion exchange material may comprise a perfluorosulfonic acid. As will be readily understood by one of ordinary skill in the art, the ionic conductivity of a porous electrode can be quantified using electrochemical impedance spectroscopy (e.g., modeled using an equivalent circuit incorporating a "transmission line" mechanism).

[0105] When used as a component of an electrochemical cell (e.g., as a component such as an electrode or as part of a membrane electrode assembly), conformally coated polymer substrates can have certain advantages over conventional materials. According to some embodiments, the membrane electrode assembly 200 can exhibit greater durability compared to conventional membrane electrode assemblies that use conventional "ink-based" electrodes with carbon-supported PGM-based catalysts. Also, according to some embodiments, the membrane electrode assembly 200 can exhibit more stable performance (i.e., higher performance over a wider operating range) than conventional membrane electrode assemblies.

[0106] The separator layer 206 can be disposed between the cathode layer 202 and the anode layer 204. In some examples, the separator layer 206 can be an ionically conductive and electrically insulating layer that allows ions to be transported between the anode layer 204 and the cathode layer 202 through the separator layer 206, while allowing electrons to travel around an external circuit. In certain embodiments, the separator layer 206 can be an electrochemical separator that becomes ionically conductive when wetted with a liquid electrolyte. The electrochemical separator can be configured to allow the transport of cations and / or anions. In certain embodiments, the separator layer 206 can be an electrochemical separator that includes an ion exchange material (e.g., at least one ion exchange polymer). In certain embodiments, the ion exchange material can include a hydrocarbon ion exchange material. In certain embodiments, the ion exchange material can include a fluorocarbon ion exchange material. In certain embodiments, the ion exchange material can include a perfluorocarbon ion exchange material. In certain embodiments, the ion exchange material can include an anion exchange material (e.g., an anion exchange polymer). In certain embodiments, the ion exchange material can include a cation exchange material (e.g., a cation exchange polymer). In certain embodiments, the ion exchange material can include perfluorosulfonic acid. As will be readily understood by one of ordinary skill in the art, the ionic conductivity of an electrochemical separator can be quantified using electrochemical impedance spectroscopy (e.g., by examining the real part of the impedance at an appropriate high frequency, such as where the data intersects the x-axis of a Nyquist plot).

[0107] In one example of a conductive article, such as that shown in Figure 2, the microporous electrocatalytic electrode can be used in energy storage and conversion applications, such as fuel cells and / or electrolyzers. In some examples, the fuel cell can be a proton exchange membrane fuel cell (PEMFC). In some examples, the electrolyzer can be a proton exchange membrane water electrolyzer (PEMWE).

[0108] According to certain embodiments, in a conformally coated polymer substrate, the ratio of the volume of the conformal coating to the volume of the pore phase (V コーティング / V 細孔 ) is about 0.001 to about 1.0, or about 0.01 to about 0.9, or about 0.02 to about 0.8, or about 0.03 to about 0.7, or about 0.04 to about 0.6, or about 0.05 to about 0.5, or about 0.06 to about 0.4, or about 0.07 to about 0.3, or about 0.08 to about 0.25, or about 0.09 to about 0.2, or about 0.1 to about 0.15, 0.001 to about 0.01, or about 0.01 to about 0.02, or about 0.02 to about 0.03, or about 0.03 to about It may have a ratio in the range of 0.04, or from about 0.04 to about 0.06, or from about 0.06 to about 0.8, or from about 0.08 to about 0.1, or from about 0.1 to about 0.2, or from about 0.2 to about 0.3, or from about 0.3 to about 0.4, or from about 0.4 to about 0.5, or from about 0.5 to about 0.6, or from about 0.6 to about 0.7, or from about 0.7 to about 0.8, or from about 0.8 to about 0.9, or from about 0.9 to about 1.0, or any other range encompassed by these endpoints.

[0109] According to some embodiments, the conformally coated polymeric substrate can have a porosity of about 25% to about 95% by volume, or about 30% to about 94% by volume, or about 35% to about 93% by volume, or about 40% to about 92% by volume, or about 45% to about 91% by volume, or about 50% to about 90% by volume, or any other range encompassed by these endpoints. In one exemplary embodiment, the conformally coated polymeric substrate has a porosity of about 55% to about 95%.

[0110] Quantitative characterization of pore size in porous materials with complex or irregular pore geometries is notoriously difficult. Pore size in this case can be considered a population property that is inherently polydisperse and can be represented by a pore size distribution. A variety of standard characterization methods are available to those skilled in the art, including quantitative image analysis, BET / BJH analysis, capillary flow porometry (including bubble point analysis), and liquid / liquid porometry. Each of these quantification methods makes simplifying assumptions about pore geometry. Most of these quantification methods generate a pore size distribution from which characteristic pore size (e.g., pore size d) parameters can be extracted, such as the median or mode pore size (e.g., by BET / BJH analysis) or the largest through-hole pore (e.g., by bubble point measurement). In some embodiments, capillary flow porometry can be used to measure the mean flow pore size.

[0111] Similarly, the difficulty of characterizing particle size (e.g., mean or median particle size D) is complex and well known to those skilled in the art. Various standard means, such as dynamic light scattering, are available, but care must be taken to avoid data bias due to agglomeration. Another method used to measure particle size is direct microscopic observation of the nanoparticles before sintering, or when the conformal coating itself is minimally sintered and the initial particle size is still evident. Alternatively, the specific surface area (SSA, m) of the unsintered or minimally sintered particles can be measured. 2 / g, as determined by BET), and if the density (ρ) of the particle is known or measured (e.g., by helium pycnometry), the volume of the sphere (V) based on the diameter (D) of the sphere can be determined, e.g., 球体 ) and area (A 球体 ) can be used to calculate the typical sphere diameter. The relevant equation is:

number

[0112] According to some embodiments, the uncoated or conformally coated polymer substrate has a characteristic pore size (e.g., volume mean pore size determined by quantitative image analysis or mean flow pore size determined by capillary flow porometry) that is significantly larger than the characteristic particle size (e.g., volume mean particle size) of the nanoparticles used to generate the conformal coating. For example, the pore size can be at least about 2 times larger, at least about 3 times larger, at least about 4 times larger, at least about 5 times larger, at least about 10 times larger, at least about 20 times larger, at least about 30 times larger, at least about 40 times larger, at least about 50 times larger, at least about 100 times larger, at least about 200 times larger, at least about 300 times larger, at least about 400 times larger, at least about 500 times larger, at least about 1000 times larger, at least about 2000 times larger, at least about 3000 times larger, at least about 4000 times larger, at least about 5000 times larger, at least about 10,000 times larger, or at least about 100,000 times larger. In some embodiments, the pore size can be from about 2 times larger to about 100,000 times larger, or any other range included between these endpoints.

[0113] According to some embodiments, the conformally coated polymer substrate has a coating weight of about 1 g / m 2 ~about 100g / m 2 , or about 2 g / m 2 ~about 90g / m 2 , or about 3 g / m 2 ~about 85g / m 2 , or about 4 g / m 2 ~about 80g / m 2 , or about 5 g / m 2 ~about 75g / m 2 , or about 6 g / m 2 ~about 70g / m 2 , or about 7 g / m 2 ~about 65g / m 2, or approximately 8 g / m 2 ~about 60g / m 2 , or approximately 9 g / m 2 ~about 50g / m 2 , or approximately 10 g / m 2 ~about 50g / m 2 , or approximately 15 g / m 2 ~about 50g / m 2 , or about 1 g / m 2 ~about 5g / m 2 , or about 5 g / m 2 ~about 10g / m 2 , or approximately 10 g / m 2 ~about 15g / m 2 , or approximately 15 g / m 2 ~about 20g / m 2 , or approximately 20 g / m 2 ~About 30g / m 2 , or approximately 30 g / m 2 ~about 40g / m 2 , or approximately 40 g / m 2 ~about 50g / m 2 , or approximately 50 g / m 2 ~about 60g / m 2 , or approximately 60 g / m 2 ~about 70g / m 2 , or approximately 70 g / m 2 ~about 80g / m 2 , or approximately 80 g / m 2 ~about 90g / m 2 , or approximately 90 g / m 2 ~about 100g / m 2 or any other range included between these endpoints. In some embodiments, the conformally coated polymer substrate has a mass / area of ​​about 15 g / m 2 , or approximately 20 g / m 2 , or approximately 46 g / m 2 It has a mass / area of

[0114] According to some embodiments, the conformally coated polymer substrate has a resistivity of from about 0.1 Ω / sq. to about 0.5 Ω / sq., or from about 0.11 Ω / sq. to about 0.49 Ω / sq., or from about 0.12 Ω / sq. to about 0.48 Ω / sq., or from about 0.13 Ω / sq. to about 0.47 Ω / sq., or from about 0.14 Ω / sq. to about 0.46 Ω / sq., or may have a sheet resistance of about 0.15 Ω / sq. to about 0.45 Ω / sq., or about 0.16 Ω / sq. to about 0.44 Ω / sq., or about 0.17 Ω / sq. to about 0.43 Ω / sq., or about 0.18 Ω / sq. to about 0.42 Ω / sq., or about 0.19 Ω / sq. to about 0.41 Ω / sq., or about 0.2 Ω / sq. to about 0.4 Ω / sq.

[0115] According to some embodiments, the conformally coated polymer substrate has a resistivity of from about 0.5 Ω / sq. to about 1.0 Ω / sq., or from about 0.51 Ω / sq. to about 0.99 Ω / sq., or from about 0.52 Ω / sq. to about 0.98 Ω / sq., or from about 0.53 Ω / sq. to about 0.97 Ω / sq., or from about 0.54 Ω / sq. to about 0.96 Ω / sq., or from about 0.55 Ω / sq. to about 0.98 Ω / sq. The sheet resistance may be about 0.95 Ω / sq., or about 0.56 Ω / sq. to about 0.94 Ω / sq., or about 0.57 Ω / sq. to about 0.93 Ω / sq., or about 0.58 Ω / sq. to about 0.92 Ω / sq., or about 0.59 Ω / sq. to about 0.91 Ω / sq., or about 0.6 Ω / sq. to about 0.9 Ω / sq., or about 0.7 Ω / sq. to about 0.8 Ω / sq.

[0116] In some embodiments, the polymer substrate comprises a microporous membrane having a continuous conformal coating of metal nanoparticles throughout the thickness of the microporous membrane. In certain embodiments, the sheet resistance measured on one side of the composite sheet is within about 1% to about 30%, or about 5% to about 25%, or about 10% to about 20%, or about 11% to about 19%, or about 12% to about 18%, or about 13% to about 17%, or about 14% to about 16% of the sheet resistance measured on the other side. In one embodiment, the sheet resistance measured on one side of the composite sheet is within about 15% of the sheet resistance measured on the other side.

[0117] FIG. 4 is an illustrative flow diagram showing a method 400 of forming a composite material according to certain embodiments of the present disclosure. This diagram is merely an example. Those skilled in the art will recognize many variations, alternatives, and modifications. The method 400 of forming a composite material includes processes 402, 404, 406, and 408. While the above is illustrated using selected processes for the method 400 of forming a composite material, many alternatives, modifications, and variations may exist. For example, some of the processes may be expanded and / or combined. Other processes may be inserted into the processes described above. Depending on the embodiment, the order of the processes may be interchanged with others being substituted. Further details of these processes are provided throughout this disclosure.

[0118] According to some embodiments, in process 402, method 400 includes providing a polymer substrate having a microporous structure. In some embodiments, the polymer substrate can be selected from one of expanded polytetrafluoroethylene and expanded polyethylene. In particular embodiments, the polymer substrate is a membrane. In some examples, the polymer substrate includes a microporous structure having nodes and fibrils that define an interior surface.

[0119] According to certain embodiments, in process 404, method 400 includes preparing a dispersion of metal nanoparticles in a liquid carrier. The liquid carrier can be considered a processing aid. In some examples, the liquid carrier can be organic and / or aqueous. The dispersion can also include other processing aids, such as dispersants, so that the metal nanoparticles are stably dispersed in the solvent. Non-limiting examples of dispersants include oleylamine and polyvinylpyrrolidone.

[0120] In some embodiments, in process 406, method 400 includes imbibing a solution containing metal nanoparticles into a polymer substrate. In some embodiments, process 406 can include delivering the metal nanoparticles substantially uniformly to a surface of the microporous substrate. In some embodiments, process 406 can include delivering the metal nanoparticles substantially or completely throughout the bulk of the material. In certain embodiments, process 406 includes fixing the polymer substrate to substantially prevent dimensional change.

[0121] In process 408, method 400 includes heating the polymer substrate to sinter the metal nanoparticles to form a metal coating on the surface of the polymer substrate. Generally, the temperature required for sintering depends on the composition of the nanoparticles (e.g., which one or more metals are included), the size of the nanoparticles, and the sintering time. Generally, metal nanoparticles have a different melting temperature than non-nanoparticulate forms of the same metal. Metal nanoparticles tend to have a lower melting temperature than larger particle sizes of the same metal. Generally, longer sintering times allow for the use of lower sintering temperatures.

[0122] Process 408 can include heating the polymer substrate to a first temperature at which the liquid carrier evaporates and deposits the metal nanoparticles around the surface of the polymer substrate, and to a second temperature at which the nanoparticles sinter. The first temperature can be controlled so that the liquid carrier and processing aids, such as a dispersant (if present), volatilize and the metal nanoparticles are deposited around the surface of the polymer substrate.

[0123] In certain embodiments, the second temperature at which the nanoparticles are sintered is below the melting temperature of the polymer substrate. The second temperature at which the nanoparticles are sintered is below the melting temperature of the polymer substrate, thereby substantially preserving the structure of the microporous substrate upon formation. In one exemplary embodiment, the first temperature is about 90°C and the second temperature is about 300°C. In certain embodiments, the polymer substrate is fixed during process 408 to substantially prevent dimensional change.

[0124] The formed metal coating is disposed on the interior surface of the polymeric substrate, thereby defining a continuous metal coating on the microporous structure, including the interior surface of the polymeric substrate. In some embodiments, the metal coating is selected from one of a platinum coating, an iridium coating, a ruthenium coating, a palladium coating, a gold coating, a silver coating, a copper coating, a nickel coating, an indium coating, a combination thereof, an alloy thereof (e.g., an alloy including a transition metal), and / or an oxide thereof. Test Method

[0125] Although specific methods and equipment are described below, it should be understood that other methods or equipment may alternatively be utilized as determined appropriate by one skilled in the art. Non-contact thickness

[0126] Non-contact thickness was measured using a laser micrometer (Keyence, Model No. LS-7010, Mechelen, Belgium) using the following technique: A metal cylinder was positioned between the laser micrometer transmitter and receiver so that a first shadow of the top of the cylinder was projected onto the receiver. The position of the first shadow was then set as the "zero" reading on the laser micrometer. A single layer of the test article was then draped, without overlapping or wrinkles, over the surface of the metal cylinder, which projected a second shadow onto the receiver. The laser micrometer then indicated the change in position between the first and second shadows as the thickness of the sample. Each thickness was measured three times and averaged for each sample. Bubble Point

[0127] Bubble point pressure was measured using a Capillary Flow Porometer (Model 3 Gzh, manufactured by Quantachrome Instruments, Boynton Beach, Florida) using Silwick Silicone Fluid (20.1 dyne / cm; microporous Materials Inc.) according to ASTM F31 6-03. The values ​​presented for bubble point pressure are the average of two measurements. Matrix tensile strength measurement

[0128] The specimens were cut using ASTM D412-Dogbone F. When the specimen contained an ePTFE membrane, the "machine direction" was the direction of extrusion, and the "cross direction" was perpendicular to it. The specimen was positioned on a cutting table to ensure that the area where the specimen was to be cut was wrinkle-free. A die was then placed on the specimen so that its long axis was parallel to the test direction. After the die was positioned, pressure was applied to cut the specimen. After the pressure was removed, the dogbone specimens were inspected to ensure there were no edge defects that could affect the tensile test. At least three specimens were prepared in the machine direction and three specimens in the cross direction in this manner. Once the dogbone specimens were prepared, they were weighed using a Mettler Toledo scale, model AG204, to determine their mass.

[0129] The tensile break load was measured using an INSTRON® 5500R (Illinois Tool Works Inc., Norwood, MA) tensile tester equipped with a rubber-coated faceplate and a serrated faceplate, with each end of the sample held between one rubber-coated faceplate and one serrated faceplate. The pressure applied to the gripping plates was approximately 552 kPa. The gauge length between the grips was set to 58.9 mm, and the crosshead speed (pulling rate) was set to 508 mm / min. These measurements were performed using a 500 N load cell, and data were collected at a rate of 50 points / second. The laboratory temperature was maintained between 20 and 22.2 °C to ensure comparable results. If the sample broke at the grip interface, the data were discarded. At least three samples were successfully pulled (without slippage or fracture at the grips) to characterize the material in a given direction (e.g., machine direction or cross direction). Kawabata Flexibility Test

[0130] Low-force bending behavior was measured using a Kawabata Pure Bending Tester (KES-FB2-Auto-A; Kato Tech Co., Ltd., Kyoto, Japan). Samples were cut to a width of 7 cm. The sensitivity of the instrument was set to 10. The instrument automatically tightened the grips and moved the sample 2.5 cm in both directions. -1 The applied load was recorded while bending the specimen to a curvature of 0.5-1.5 cm. The reported average B values ​​ranged from 0.5-1.5 cm. -1 and -0.5 to -1.5 cm -1 The bending stiffness is the average value of the bending stiffness of the laminated sample when bent at a constant flexure. The bending stiffness is expressed in gf cm. 2 Reported in / cm. ATEQ Airflow

[0131] ATEQ Airflow is a test method that measures the laminar volumetric flow rate of air through a membrane sample. For each membrane, the sample is clamped between two plates and a 2.99 cm diameter airflow is measured across the flow channel. 2The air flow rate (L / hr) through each membrane sample was measured using an ATEQ® (ATEQ Corp., Livonia, Michigan) Premier D Compact Flow Tester by forcing an air pressure differential of 1.2 kPa (12 mbar) across the membrane. Gurley air permeability

[0132] Gurley air permeability test: 100cm 3 of air expands to 1 square inch (approximately 6.45 cm) at a water pressure of 0.177 psi (approximately 1.22 kPa). 2 The time in seconds for the sample to flow is measured. The samples were measured on a GURLEY™ Densometer and Smoothness Tester Model 4340 (Gurley Precision Instruments, Troy, NY). Reported values ​​are the average of three measurements and are in seconds. Capillary Flow Porometry (CFP) Testing

[0133] Measurements were performed using a Quantachrome Porometer 3G zH. The wetting fluid was silicone oil with a nominal surface tension of 19.78 dyne / cm. The pressure range was 0.255 psig to 394 psig. The sample size was 10 mm in diameter. Wet bending particle test

[0134] This durability test was developed to evaluate the tendency of composite materials to shed particles. For the test to be valid, the specimen must have a low enough bending stiffness to allow full bending motion under the test conditions. To perform the test, a 2.125 inch by 0.5 inch specimen was cut from the composite material. The specimen was loaded into test fixture 500 by sandwiching it between two pieces of engineering plastic cut to the shape shown in FIG. 5A. Test fixture body 502 includes notches 504a and 504b to allow for the placement of O-rings, a window 506 to allow specimen bending, an ablation groove 508 to enhance specimen retention, an O-ring location 510 to establish an interference fit within the centrifuge tube, and O-ring locations 512a and 512b to securely hold the specimen in place.

[0135] As shown in Figure 5B, the sample was loaded with a controlled amount of deflection and held in place by O-rings 514a and 514b. For scale, the window allowing sample bending measured 24.5 mm long x 14.1 mm wide x 2.7 mm thick. The test fixture containing the sample was then loaded into a standard 50 mL centrifuge tube, which was then filled with 40 mL of isopropanol (hereafter referred to as "test fluid"). Isopropanol was chosen because it readily wets the sample under test, is reasonably inert to the sample under test (e.g., negligible corrosion or dissolution of the sample was expected), and has a low enough viscosity to allow for the desired fluid dynamics within the tube, as described below. Alternative test fluids may be selected depending on the needs of the sample under test and the intended application. The centrifuge tube was then capped and sealed with tape to prevent leakage.

[0136] Next, as shown in Figure 5C, the centrifuge tube 516 was loaded into the Intelli-Mixer (#RM-2L) with the plane of the test fixture parallel to the axis of rotation. This orientation allowed for sample flexing. The Intelli-Mixer was set to rock the sample at 20 rpm + / - 99° for the desired time (typically 1-7 days). Each time the sample rocked, it also flexed due to the fluid dynamics inside the tube. Flexing refers to the deflection within the sample switching from one side of the test fixture to the other. After rocking for the desired time, the liquid inside the tube was extracted with a pipette and analyzed using inductively coupled plasma mass spectrometry (ICP-MS) to confirm the presence of metals that may have been released from the composite material. Sheet resistance

[0137] A 2.125 inch x 0.5 inch sample was die cut from a sheet of the material to be tested. The sample was placed flat on a closed-cell silicone sponge sheet (½ inch thick, Bellofoam #7704). Resistance was measured using a Keithley 2750 Digital Multimeter with a four-point probe 300, as shown in Figure 3. The probe 300 was made of gold-plated stainless steel. Each of the four probes 302a-d had a width of approximately 1.2 inches and a length of approximately 1.5 inches. The four probes 402a-d had an average distance of approximately 0.5 inches from each other, with a PTFE spacer 304 connecting them.

[0138] The four-point probe 300 was connected to the Multimeter in a standard four-point probe configuration (i.e., voltage sensing leads on the inner two terminals and input leads on the outer two terminals). After gently placing the four-point probe 300 on the sample to be measured, a 330 gram weight was placed on top of the probe 300 to ensure good, uniform contact between the probe 300 and the sample. Care was taken to ensure good contact between the probe 300 and the conductive phase of the sample. The weight was insulated with a plastic sheet to prevent it from shorting out the probe 300. The Keithley Multimeter was operated in four-point probe mode with "OCOMP" four-wire offset compensation enabled. For each measurement, the system was allowed to stabilize for approximately 10 seconds before recording the resistance value. Data was reported in units of ohms per square area. Example 1: Preparation of conformal gold / ePTFE composites

[0139] This example describes the preparation of an ePTFE membrane composite incorporating a conformal gold coating ("CG / ePTFE composite").

[0140] First ePTFE membrane ("target membrane") (3-5 g / m 2 A second ePTFE membrane ("introduction membrane") (3-5 g / m2) was placed in a 4-inch diameter metal hoop (mass / area; bubble point 1.5 psi; non-contact thickness 92 μm; W.L. Gore & Associates) and tensioned by hand to remove wrinkles. 2A 6-inch diameter metal hoop (mass / area; bubble point 40 psi; non-contact thickness 18 μm; WL Gore & Associates) was secured within the hoop and manually tensioned to remove wrinkles. The delivery membrane was placed on top of the target membrane so that the two membranes were in physical contact and approximately concentric. 0.75 mL of gold nanoparticle ink (#UTDAu60X; UTDots, Inc.) was pipetted onto the surface of the delivery membrane and spread evenly using a disposable pipette bulb until the imbibing solution completely wetted both the delivery membrane and the target membrane (<30 seconds). Excess ink was removed by wiping the upper surface of the delivery membrane with a lint-free cloth. The two imbibed membranes were then separated by separating their respective hoops. The delivery membrane was discarded. The resulting membrane was then dried using a heat gun set at 93° C. and then heated in a standard convection oven at 300° C. for 1 hour. The CG / ePTFE composite was obtained.

[0141] This CG / ePTFE composite has a mass of 46 g / m 2 and had a sheet resistance of about 0.2-0.4 Ω / sq. using the four-point probe sheet resistance test method described above and illustrated in Figure 3. The sheet resistance of the composite was nearly identical (specifically, within about 15% of the less resistive surface) whether measured on the top or bottom surface, indicating that the metal was coated continuously and conformally throughout the intended film thickness.

[0142] The samples were stress tested using the "Wet Flex Graining Test" for a period of 7 days. Inductively Coupled Plasma (ICP) analysis of the test fluid revealed that gold was undetectable in all samples (i.e., gold present at levels below the detection threshold of the instrument), corresponding to a minimum metal retention of >99.99 wt%. Example 2: Preparation of conformal silver / ePTFE composites

[0143] This example describes the preparation of an ePTFE membrane composite incorporating a conformal silver coating ("CS / ePTFE composite").

[0144] First ePTFE membrane ("target membrane") (3-5 g / m 2 A second ePTFE membrane ("introduction membrane") (3-5 g / m2) was placed in a 4-inch diameter metal hoop (mass / area; bubble point 1.5 psi; non-contact thickness 92 μm; W.L. Gore & Associates) and tensioned by hand to remove wrinkles. 2 A 6-inch diameter metal hoop (mass / area; bubble point 40 psi; non-contact thickness 18 μm; WL Gore & Associates) was secured within the hoop and manually tensioned to remove wrinkles. The transfer membrane was placed on top of the target membrane so that the two membranes were in physical contact and approximately concentric. A mixture was prepared using 0.39 g of silver nanoparticle ink (#UTDAg60X; UTDots, Inc.) and 0.58 g of xylene. Approximately 1 mL of this mixture was pipetted onto the surface of the transfer membrane and evenly spread using a disposable pipette bulb until the imbibing solution completely wetted both the transfer membrane and the target membrane (<30 s). Excess ink was removed by wiping the upper surface of the transfer membrane with a lint-free cloth. The two imbibed membranes were then separated by separating their respective hoops. The transfer membrane was discarded. The resulting membrane was then dried using a heat gun set at 93° C. and then heated in a standard convection oven at 200° C. for 1 hour. The CS / ePTFE composite was obtained.

[0145] This CS / ePTFE composite has a mass of 15.6 g / m 2and had a sheet resistance of about 0.7-0.8 Ω / sq. using the four-point probe sheet resistance test method described above and illustrated in Figure 3. The sheet resistance of the composite was nearly identical (specifically, within about 15% of the less resistive surface) whether measured on the top or bottom surface, indicating that the metal was coated continuously and conformally throughout the intended film thickness.

[0146] Figures 6A-6C are representative SEM images showing the microstructure of the CS / ePTFE composite of Example 2. Figures 6A-6B show cross-sections of the CS / ePTFE composite at various nodes of material defined within the microstructure of the CS / ePTFE composite, and Figure 6C shows a general cross-section of the CS / ePTFE composite material.

[0147] As shown, the composite material 600 can also include a conformal coating 604 formed of sintered metal nanoparticles dispersed about the surface of the polymer substrate 602. The coating 604 can be formed of sintered metal nanoparticles.

[0148] 6A-6B, the microporous structure defines an interior surface, and a conformal coating 604 formed of sintered metal nanoparticles is disposed on the interior surface of the polymer substrate 602. In certain embodiments, the conformal coating 604 formed of sintered metal nanoparticles is a continuous coating on the surface of the polymer substrate 602, including the interior surface.

[0149] In some examples, the polymer substrate 602 includes a microstructure having a plurality of nodes 606 (e.g., those shown in FIGS. 6A-B) and fibrils 608 (e.g., those shown in FIG. 6C). A conformal coating 604 formed of sintered metal nanoparticles is disposed around the nodes 606 and fibrils 608 of the polymer substrate 602.

[0150] For metallized polymer substrates, the conformal coating formed by the pore phase and sintered metal nanoparticles disposed on the surface of the polymer substrate can be characterized by calculating various volume ratios based on the properties of each component listed in Table 1 and a mass / area ratio of ePTFE of 4 g / m. 2 Assuming that, the ratio can be calculated as follows:

[0151] V コーティング / V 基材 =2.2cc / m 2 / 1.8cc / m 2 =1.22

[0152] V 細孔 / V 基材 =31cc / m 2 / 1.8cc / m 2 =17.2

[0153] V コーティング / V 細孔 =2.2cc / m 2 / 31cc / m 2 =0.07

[0154] V 細孔 / V 合計 =31cc / m 2 / 35cc / m 2 =0.89=89% by volume = "porosity" [Table 1] [Table 2]

[0155] The present invention of this application has been described above in general terms and with reference to specific embodiments. It will be apparent to those skilled in the art that various modifications and changes can be made in the embodiments without departing from the scope of the present disclosure. Therefore, it is intended that the embodiments cover the modifications and variations of the present invention and their equivalents, provided they fall within the scope of the appended claims.

Claims

1. A composite material, the composite material comprising: a polymer substrate having a porous structure; a conformal coating disposed about a surface of the polymer substrate; wherein the conformal coating is formed from sintered metal nanoparticles.

2. 10. The composite material of claim 1, wherein the surface comprises an interior surface defined by the porous structure, and the conformal coating is disposed on the interior surface of the polymeric substrate.

3. 3. The composite material of claim 1, wherein the conformal coating is a continuous coating on the surfaces, including the interior surfaces, of the polymer substrate.

4. 4. The composite material of claim 1, wherein the porous structure of the polymer substrate comprises nodes and / or fibrils, and the conformal coating is disposed around the nodes and / or fibrils of the polymer substrate.

5. The composite material according to any one of claims 1 to 4, wherein the porous structure of the polymer substrate is microporous.

6. 6. The composite material of any one of claims 1 to 5, wherein the conformal coating is selected from one of a platinum coating, an iridium coating, a ruthenium coating, a palladium coating, a gold coating, a silver coating, a copper coating, a nickel coating, an indium coating, combinations thereof, alloys thereof including alloys with transition metals, and / or oxides thereof.

7. The composite material of any one of claims 1 to 6, wherein the polymer substrate is a membrane.

8. The composite material of any one of claims 1 to 7, wherein the polymer substrate is expanded polytetrafluoroethylene.

9. The composite material of any one of claims 1 to 8, wherein the composite material is from about 1 micrometer to about 100 micrometers thick.

10. 9. The composite material according to claim 1, wherein the ratio of the volume of the conformal coating to the volume of the pore phase in the composite material is from 0.001 to 1.

0.

11. 9. The composite material of claim 1, wherein the composite material has a mean flow pore size at least twice as large as the volume average particle size of the metal nanoparticles.

12. The composite material of any one of claims 1 to 11, wherein the composite material comprises an ion exchange material.

13. 13. The composite material of claim 12, wherein the ion exchange material is selected from one of an anion exchange material and a cation exchange material.

14. 14. The composite material of claim 13, wherein the ion exchange material is selected from hydrocarbon polymers, fluorocarbon polymers, and perfluorocarbon polymers.

15. 14. The composite material of claim 13, wherein the ion exchange material is perfluorosulfonic acid.

16. A membrane electrode assembly comprising the composite material of any one of claims 1 to 15 bonded to an electrochemical separator.

17. 17. The membrane electrode assembly of claim 16, wherein the electrochemical separator comprises an ion exchange material.

18. 18. The membrane electrode assembly of claim 17, wherein the ion exchange material is selected from one of an anion exchange material and a cation exchange material.

19. 20. The membrane electrode assembly of claim 18, wherein the ion exchange material is selected from hydrocarbon polymers, fluorocarbon polymers, and perfluorocarbon polymers.

20. 20. The membrane electrode assembly of claim 18, wherein the ion exchange material is perfluorosulfonic acid.

21. An article comprising the composite material of any one of claims 1 to 20.

22. 22. The article of claim 21, wherein the article is an electrochemical cell.

23. 22. The article of claim 21, wherein the article is a fuel cell.

24. 22. The article of claim 21, wherein the article is an electrolytic cell.

25. 1. A method of forming a composite material, comprising: Providing a polymer substrate having a porous structure; imbibing metal nanoparticles into the polymeric substrate; heating the metal nanoparticles to sinter them to form a conformal coating on the surface of the polymer substrate; A method comprising:

26. 26. The method of claim 25, further comprising preparing a dispersion comprising the metal nanoparticles and a dispersing agent, wherein the imbibing step comprises wetting the polymer substrate with the dispersion.

27. 27. The method of any one of claims 25 and 26, wherein the step of absorbing into the polymeric substrate comprises heating the polymeric substrate to a first temperature at which the processing aid volatilizes, and wherein the step of heating the metal nanoparticles comprises heating the metal nanoparticles to a second temperature to sinter the metal nanoparticles.

28. 28. The method of claim 27, wherein the second temperature at which the nanoparticles are sintered is less than the melting temperature of the polymer substrate.

29. 29. The method of any one of claims 27 and 28, wherein the first temperature is about 90°C and the second temperature is about 300°C.

30. 30. The method of any one of claims 25 to 29, wherein a porous structure defines an interior surface, and wherein disposing a metal coating on the interior surface of the polymeric substrate defines a continuous metal coating on the porous structure, including the interior surface of the polymeric substrate.

31. 31. The method of any one of claims 25 to 30, wherein the metal coating is selected from one of a platinum coating, an iridium coating, a ruthenium coating, a palladium coating, a gold coating, a silver coating, a copper coating, a nickel coating, an indium coating, combinations thereof, alloys thereof including alloys with transition metals, and / or oxides thereof.

32. The method of any one of claims 25 to 31, wherein the polymer substrate is a membrane.

33. The method of any one of claims 25 to 32, wherein the polymer substrate is selected from one of expanded polytetrafluoroethylene and expanded polyethylene.

34. 10. The composite material of claim 1, wherein the conformal coating is a conductive coating having greater than 90% by weight metal retention.

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