Articles having microporous substrates with conformal coatings and methods of making and using same

Abstract

A composite material includes a polymer substrate having a microporous structure and a conformal coating disposed on a surface of the polymer substrate, wherein the conformal coating is formed from sintered metal nanoparticles.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of Provisional Application No. 63 / 419,695, filed on October 26, 2022, and Provisional Application No. 63 / 417,688, filed on October 19, 2022, which are hereby incorporated by reference in their entireties for all purposes. Technical field

[0003] The present disclosure generally relates to articles having a metallized microporous substrate. More specifically, the present disclosure relates to articles having a microporous substrate with a conformal coating containing sintered metal nanoparticles, and related methods of making and using such articles. Background art

[0004] Conductive articles can be used in a variety of applications, including energy storage and energy conversion applications. Some conductive articles include a porous substrate that has conductivity or has been treated to have conductivity (e.g., coated with a conductive material). The pores 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 characteristics such as high conductivity, high durability, high flexibility, high strength, etc.

[0005] Regarding conductive coatings on substrates, some coatings include metals, and the application of such metal coatings can be described as "metallizing" the coated substrate. Some metallization methods can be very time - consuming, use expensive processing aids, and / or leave residual contaminants, which may cause applicability problems in certain applications. For example, in electroless plating, the surface to be metallized is typically first activated with a material such as a platinum / tin activator solution (i.e., depositing a so - called "seed layer"). This complicates the process and increases the cost due to the expense of materials such as palladium. Other metallization processes may require first coating the substrate surface with another material, a so - called "tie layer", to which the metal can be more easily coated. However, the use of a tie layer may bring similar drawbacks as described above - it complicates the process and leaves undesirable residues.

[0006] In addition, with respect to the metallization of porous substrates, some porous substrates may be difficult to metallize due to various exacerbating factors. As a first example of an exacerbating factor, when a substrate having a tortuous pore phase is metallized using a basic line-of-sight technique such as sputtering or evaporation, non-uniform metallization of the inner surface may occur due to the so-called "shadowing" effect. As a second example of an exacerbating factor, when metallization is carried out by a high-energy technique such as sputtering, substrates that are moderately or highly susceptible to radiation and / or thermal damage may result in a degradation of properties such as mechanical properties. As a third example of an exacerbating factor, substrates with a low surface energy may result in poor coating adhesion and a large number of defects and / or uncoated substrate areas.

[0007] There is a need to improve conductive porous articles and methods of making conductive porous articles. SUMMARY OF THE INVENTION

[0008] The present disclosure relates to conductive microporous articles having specific characteristics such as high conductivity, high durability, and high flexibility, and optimized porosity and pore morphology; and a method for metallizing a microporous substrate, wherein the method is simple, fast, requires fewer chemicals, can coat the inner surface of a microporous substrate having a tortuous pore diameter, can apply a durable coating to a low surface energy substrate with a high coverage rate and / or a low defect rate, minimizes degradation of the substrate, and / or does not leave undesired residues such as a seed layer or a tie layer.

[0009] With respect to porous substrates for metallization, microporous polymer substrates such as microporous polymer membranes can have desired properties such as mechanical strength, customizable morphology, and a high surface area. However, they may exhibit some or all of the exacerbating factors described in the background section. An exemplary substrate that can exhibit some or all of these desired properties and exacerbating factors is expanded polytetrafluoroethylene (ePTFE). Despite the challenges described herein, the present disclosure still relates to providing a durable conformal metal coating on the surface (including the inner surface) of a microporous polymer substrate such as ePTFE.

[0010] As described herein, the pores of such conductive microporous articles can play a variety of important roles, such as enabling mass transport and / or reducing the weight of the conductive article. Accordingly, there is interest in optimizing the porosity and pore morphology, such as providing robust and optimized mass transport. There is also interest in minimizing the amount of the required conductive coating, such as minimizing the weight of the conductive article and / or reducing costs. In some cases, it may be necessary to treat the microporous material to make it conductive throughout the bulk of the material (e.g., substantially or completely through the thickness of a porous plate).

[0011] 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 implemented for an electrode.

[0012] According to one embodiment (“Embodiment 1”), a composite material comprising a polymer substrate having a porous structure and a conformal coating disposed on a surface of the polymer substrate, wherein the conformal coating is formed of sintered metal nanoparticles.

[0013] According to another embodiment of Embodiment 1, the surface includes an inner surface defined by the porous structure, and the conformal coating is disposed on the inner surface of the polymer substrate.

[0014] According to another embodiment of Embodiment 1, the conformal coating is a continuous coating on a surface of the polymer substrate, the surface including an inner surface.

[0015] According to another embodiment of Embodiment 1, the porous structure of the polymer substrate includes nodes and / or fibrils, wherein the conformal coating is located at the nodes and / or fibrils of the polymer substrate.

[0016] According to another embodiment of Embodiment 1, the porous structure of the polymer substrate is microporous.

[0017] According to another embodiment of Embodiment 1, the conformal coating is selected from the group consisting 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.

[0018] According to another embodiment of Embodiment 1, the polymer substrate is a membrane.

[0019] According to another embodiment of Embodiment 1, the polymer substrate is expanded polytetrafluoroethylene.

[0020] According to another embodiment of Embodiment 1, the thickness of the composite material is from about 1 micron to about 100 microns.

[0021] According to another embodiment of Embodiment 1, the volume ratio of the conformal coating of the composite material to the volume of the pore phase is from 0.001 to 1.0.

[0022] According to another embodiment of Embodiment 1, the composite material has a median flow pore size that is at least 2 times larger than the volume average particle size of the metal nanoparticles.

[0023] According to another embodiment of Embodiment 1, the conformal coating is a conductive coating having a metal retention rate greater than 90 wt%.

[0024] According to another embodiment of Embodiment 1 (“Embodiment 2”), the composite material includes an ion exchange material.

[0025] According to another embodiment of Embodiment 2, the ion exchange material is selected from one of an anion exchange material and a cation exchange material.

[0026] According to another embodiment of Embodiment 2, the ion exchange material is selected from hydrocarbon polymers, fluorocarbon polymers, and perfluorocarbon polymers.

[0027] According to another embodiment of Embodiment 2, the ion exchange material is perfluorosulfonic acid.

[0028] According to another embodiment of Embodiment 2 (“Embodiment 3”), a membrane electrode assembly includes the composite material according to any one of the foregoing embodiments in combination with an electrochemical separator.

[0029] According to another embodiment of Embodiment 3, the electrochemical separator includes an ion exchange material.

[0030] According to another embodiment of Embodiment 3, the ion exchange material is selected from one of an anion exchange material and a cation exchange material.

[0031] According to another embodiment of Embodiment 3, the ion exchange material is selected from hydrocarbon polymers, fluorocarbon polymers, and perfluorocarbon polymers.

[0032] According to another embodiment of Embodiment 3, the ion exchange material is perfluorosulfonic acid.

[0033] According to another embodiment (“Embodiment 4”), an article includes the composite material according to any one of the foregoing embodiments.

[0034] According to another embodiment of Embodiment 4, the article is an electrochemical cell.

[0035] According to another embodiment of Embodiment 4, the article is a fuel cell.

[0036] According to another embodiment of Embodiment 4, the article is an electrolyzer.

[0037] According to another embodiment (“Embodiment 5”), an article includes a microporous polymer substrate, and the microporous polymer substrate is continuously and conformally coated with sintered metal nanoparticles.

[0038] According to another embodiment of Embodiment 5, the inner surface of the microporous polymer substrate is coated with sintered metal nanoparticles.

[0039] According to another embodiment of Embodiment 5, the microporous polymer substrate includes a node and fibril microstructure, wherein the sintered metal nanoparticles coat the nodes and fibrils of the microporous polymer substrate.

[0040] According to another embodiment (“Embodiment 6”), a method of forming a composite material includes providing a polymer substrate having a porous structure; absorbing metal nanoparticles into the polymer substrate; and heating the metal nanoparticles to sinter the metal nanoparticles, thereby forming a conformal coating on the surface of the polymer substrate.

[0041] According to another embodiment of Embodiment 6, the method further includes preparing a dispersion comprising metal nanoparticles and a dispersant, wherein absorbing includes wetting the polymer substrate with the dispersion.

[0042] According to another embodiment of Embodiment 6, absorbing the polymer substrate includes heating the polymer substrate to a first temperature at which processing aids volatilize, and wherein heating the metal nanoparticles includes heating the metal nanoparticles to a second temperature to sinter the metal nanoparticles.

[0043] According to another embodiment of Embodiment 6, the second temperature for sintering the nanoparticles is lower than the melting temperature of the polymer substrate.

[0044] According to another embodiment of Embodiment 6, the first temperature is about 90 degrees Celsius and the second temperature is about 300 degrees Celsius.

[0045] According to another embodiment of Embodiment 6, the porous structure defines an inner surface, and the metal coating is located on the inner surface of the polymer substrate to define a continuous metal coating on the porous structure (including the inner surface) of the polymer substrate.

[0046] According to another embodiment of Embodiment 6, the metal coating is selected from one of the following groups: platinum coating, iridium coating, ruthenium coating, palladium coating, gold coating, silver coating, copper coating, nickel coating, indium coating, combinations thereof, alloys thereof, including alloys with transition metals, and / or oxides thereof.

[0047] According to another embodiment of Embodiment 6, the polymer substrate is a film.

[0048] According to another embodiment of Embodiment 6, the polymer substrate is selected from one of expanded polytetrafluoroethylene and expanded polyethylene. Description of the Drawings

[0049] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0050] Figure 1A - 1C is an SEM image that shows the microstructure of a conformal-gold-on-ePTFE (“CG / ePTFE”) composite according to an embodiment of certain embodiments of the present disclosure;

[0051] Figure 2 is a schematic diagram of a membrane electrode assembly according to certain embodiments of the present invention;

[0052] Figure 3 is a schematic diagram of a device for measuring sheet resistance according to certain embodiments of the present disclosure;

[0053] Figure 4 illustrates an illustrative flowchart of a method 400 for forming a composite material according to certain embodiments of the present disclosure;

[0054] Figure 5A - 5C illustrates a wet bending granulation durability test method according to certain embodiments of the present disclosure;

[0055] Figure 6A - 6C is an SEM image that shows the microstructure of a conformal-silver-on-ePTFE (“CS / ePTFE”) composite according to an embodiment of certain embodiments of the present disclosure. DETAILED DESCRIPTION

[0056] Those skilled in the art will readily appreciate that various aspects of the present disclosure can be implemented by any number of methods and devices configured to perform the desired functions. It should also be noted that the drawings referred to herein are not necessarily drawn to scale and may be enlarged to illustrate various aspects of the present disclosure, and in this regard, the drawings should not be considered limiting.

[0057] The present disclosure is not intended to be construed in a limiting manner. For example, the terms used in this application should be construed broadly in the context of the meanings given to such terms in the art.

[0058] For imprecise terms, the terms "about" and "approximately" are used interchangeably and are intended to mean that a measured value includes the recited value and also includes any measured value that is reasonably close to the recited value. As would be understood and readily determined by one of ordinary skill in the relevant art, a measured value that is reasonably close to the recited value is one that deviates from the recited value by a relatively small amount. Such deviation may be attributable to measurement error, differences in measurement and / or manufacturing equipment calibration, human error in reading and / or setting measurements, fine tuning for measurement differences associated with other components to optimize performance and / or structural parameters, particular implementation scenarios, imprecise adjustment and / or operation of objects by people or machines, etc. If it is determined that a person of ordinary skill in the relevant art cannot readily determine the value of such a reasonably small difference, the terms "about" and "approximately" may be understood to mean plus or minus 10% of the recited value.

[0059] As used herein, unless otherwise specified, the term "conductive" means "electrically conductive".

[0060] 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 the plurality of pores define the total pore volume of the microporous polymer substrate. The solid matrix refers to the solid portion of the microporous polymer substrate in addition to its pore volume.

[0061] As used herein, the term "microporous" is used to describe a material that includes pores having a single pore size or pore size distribution. The average or median pore size can be from about 0.05 μm to about 50 μm, or from about 0.1 to about 50 μm, or from about 0.1 to about 30 μm, or from about 0.2 to about 60 μm, or from about 0.5 to about 50 μm, or any intermediate range or value encompassed by these ranges. It should be understood that the microporous material may include individual pores outside of this average size range, including some macropores. The microporous material may have a characteristic or nominal pore size characterized by bubble point analysis or other suitable tests, as shown below. The average pore size of the material can be characterized, for example, by the mid-flow average pore size determined by capillary flow porometry.

[0062] As used herein, the term "inner surface" refers to the surface of the features (e.g., nodes, fibrils, fibers, fiber bundles) that define the pore walls of the microporous substrate.

[0063] As used herein, the term "conformal" refers to a coating applied to a microporous substrate such that the coating substantially presents the surface profile of the microporous substrate, including the outer and inner surface features (e.g., nodes, fibrils, fibers, fiber bundles) of the substrate.

[0064] As used herein, the term "continuous coating" refers to a coating that is substantially electrically continuous along the surface of the microporous substrate (including the outer and inner surfaces). The continuous coating can exhibit high conductivity relative to the microporous substrate in the through-plane and in-plane directions.

[0065] As used herein, the term "absorption" refers to the process of depositing a material within the pores of a microporous substrate using a liquid carrier, but substantially without incorporating the absorbed material into the matrix of the microporous substrate, such that the microporous substrate remains substantially intact.

[0066] As used herein, the phrase "conductive material" refers to a material that transports electrons with low resistance such that the resistance of the material does not render it unsuitable for the desired application. In practice, this phrase generally refers to materials having a resistivity of less than about 1 x 10 -3 ohm×cm.

[0067] As used herein, the phrases "non-conductive material" and "electrically insulating material" refer to materials having a high resistance such that the conductivity of the material does not render it unsuitable for the desired application. In practice, this phrase generally refers to materials having a resistivity greater than about 1 x 10 8 ohm×cm.

[0068] As used herein, "wetting" refers to the spreading of a fluid over a substrate. In the case of a microporous substrate, wetting also refers to the penetration of the fluid into the pores.

[0069] As used herein, "dewetting" describes the expulsion of a fluid (e.g., droplets formed when a liquid film breaks on a substrate) from a previously wetted area of the substrate.

[0070] The devices and methods shown and described herein are provided as examples of various features of such devices and methods, and although combinations of these shown features are clearly within the scope of the invention, this example and its description are not meant to imply that the inventive concepts provided herein are limited to fewer features, additional features, or alternative features, but rather one or more of these features are described for different examples.

[0071] The articles, devices, and methods described herein generally relate to a microporous substrate (e.g., an expanded polymer film) coated with sintered metal nanoparticles. For example, by sintering the metal nanoparticles, a durable metal coating is formed on the microporous substrate. According to some embodiments, the sintered metal nanoparticles form a conformal coating on the microporous substrate, including the outer and inner surfaces of the microporous substrate. According to some embodiments, the sintered metal nanoparticles form a continuous conformal coating on the microporous substrate, including the outer and inner surfaces. Various features and methods for achieving such results are discussed herein. After applying a continuous, conformal coating to the microporous substrate, the articles described herein still retain their microporous characteristics.

[0072] According to one embodiment, a composite material includes a polymer substrate having a microporous structure and a conformal coating disposed on a surface of the polymer substrate, wherein the conformal coating is formed from sintered metal nanoparticles.

[0073] Reference is now made toFigure 1A - 1C , shows the composite material 100. Figure 1A - 1C Provides a representative SEM image of a sample of the composite material 100. Figure 1A Shows the overall cross-section of the composite material 100, Figure 1B Shows the cross-section of the composite material 100 at the nodes of the composite material 100 defined within the microstructure of the composite material 100, Figure 1C Shows the cross-section of the composite material 100 at the fibrils of the composite material 100 defined within the microstructure of the composite material 100.

[0074] As Figure 1A Shown, the composite material 100 includes a polymer substrate 102. In some embodiments, the polymer substrate may be porous (e.g., having a plurality of pores). In some embodiments, the polymer may be microporous. In certain embodiments, the polymer substrate 102 may be expanded polytetrafluoroethylene (ePTFE). In certain embodiments, the polymer substrate 102 may be a film. In certain embodiments, the film may be a synthetic polymer film.

[0075] According to some embodiments, the polymer substrate 102 may have a first major outer surface (e.g., a first surface) and a second major outer surface (e.g., a second surface) opposite the first surface. In some embodiments, where the polymer substrate 102 is a tubular member, the first and second major outer surfaces correspond to the inner diameter and outer diameter of the tubular member. The polymer substrate 102 may have a certain thickness, i.e., the distance between the two major outer surfaces. The plurality of pores have inner surfaces defined by their interfaces with the solid matrix. The inner surface of a pore refers to the surface of the pore that is not on the outer surface of the substrate. In some embodiments, the thickness of the polymer substrate 102 may be from about 1 micron to about 100 microns.

[0076] According to certain embodiments, the microporous polymer substrate described herein may be a porous polymer structure, which may be configured in a variety of forms, such as a mesh (i.e., a long, thin, flexible material provided in a roll form), a sheet (e.g., a flat plate) or a tubular member (e.g., a round tube). In certain embodiments, the porous polymer structure may be thin, flexible and / or freestanding.

[0077] In some embodiments, the microporous polymer substrate (e.g., polymer substrate 102) can include a continuous layer of material that includes pores forming channels that extend from a first surface to a second surface (i.e., from one outer surface of the layer to the opposite outer surface of the layer). Such channels can be referred to as through-holes. The pore volume can also include pores that are not through-holes (i.e., some pores may not connect through the pore volume to both outer surfaces). A pore that is connected to only one outer surface can be referred to as a dead-end pore, and a pore that is not connected to any outer surface can be referred to as a closed pore. In some embodiments, within the pore volume, the pores can be interconnected and can form a continuous porous network. In certain embodiments, within the pore volume, the pores can be isolated from each other. In some embodiments, within the pore volume, there can be any intermediate level of interconnectivity between the pores.

[0078] According to some embodiments, the solid matrix includes a continuous network of interconnected material elements, and the pores can be the void spaces between these material elements. According to certain embodiments, the material elements include a variety of structural components that form the structural units of an integral polymer structure. The material elements are not particularly limited, but can include, for example, fibers, fiber bundles, nodes, and fibrils. In some embodiments, the polymer substrates described herein can have a microstructure that includes fibers, fiber bundles, and a plurality of pores, wherein the fibers and fiber bundles are interconnected, and the plurality of pores are the void spaces between the fibers and fiber bundles. In certain embodiments, the polymer substrates described herein can have a microstructure that includes nodes, fibrils, and a plurality of pores, wherein the nodes are interconnected by fibrils, and the plurality of pores are the void spaces between the nodes and fibrils.

[0079] In some embodiments, the polymer substrates described herein can support and mechanically reinforce the composite material, enhancing its structural integrity and durability. In some embodiments, the polymer substrate can enable the composite film to be thinner and / or larger in area while maintaining operability and other desired properties. In certain embodiments, the polymer substrate has thermal, chemical, and / or electrochemical stability in the environment in which the composite film is used. In certain embodiments, the polymer substrate can withstand any manufacturing steps required in the production of the composite film and / or the subsequent storage, transportation, and handling of the composite film.

[0080] In certain embodiments, the polymer substrates described herein can be stable at very high pH (e.g., above about pH 10, or above about pH 11, or above about pH 12, or above about pH 13, or above about pH 14). In some embodiments, the polymer substrate can be stable at very low pH (e.g., below about pH 5, or below about pH 4, or below about pH 3, or below about pH 2, or below about pH 1).

[0081] According to some embodiments, the polymer substrates described herein can be formed by any method suitable for the intended application. The method of manufacturing the polymer substrates is not particularly limited, and any method known in the art can be used to form the polymer substrates. In some embodiments, suitable processing methods may include roll-to-roll processing, paste processing, gel processing, and swelling. Depending on the manufacturing method, the polymer substrates may have a machine direction (MD) and a transverse direction (TD), where MD is orthogonal to TD. In certain embodiments, MD and TD are respectively orthogonal to the thickness direction. In some embodiments, for example, when the polymer substrate is in the form of a mesh, its MD can be aligned with the length direction and TD can be aligned with the width direction.

[0082] According to certain embodiments, the polymer substrates described herein can be formed from any material suitable for the intended application. The material is not particularly limited, and any material known in the art can be used to form the polymer substrates. For example, the polymer substrates may include polymer materials. In some embodiments, the polymer materials may include polymers, mixtures of polymers. In some embodiments, the polymer materials may include homopolymers or copolymers. In some embodiments, the polymer materials may include inorganic polymer materials and / or organic polymer materials. In certain embodiments, the polymer materials may contain fluorine and / or other heteroatoms. In certain embodiments, the polymer materials may contain aromatic moieties and / or non-aromatic (e.g., aliphatic or olefinic) moieties. In certain embodiments, the polymer materials may contain side chains and / or functional groups. In some embodiments, the polymer materials may include fibrillatable polymers (e.g., PTFE).

[0083] According to some embodiments, the polymer substrates described herein can be formed from any one selected from the group consisting of non-fluorinated polymers (e.g., hydrocarbon polymers), partially fluorinated polymers, fully fluorinated polymers, and any combination thereof. In some embodiments, the polymer substrates described herein may include polyolefins, such as polyethylene (PE) or polypropylene (PP). In some embodiments, the polymer substrates described herein may include any one selected from the group consisting of polytetrafluoroethylene (PTFE), polyethylene (PE), or a copolymer of PTFE and PE. In certain embodiments, the polymer substrates described herein may include expanded polytetrafluoroethylene (ePTFE) or expanded polyethylene (ePE).

[0084] Non-limiting examples of materials suitable for use as the polymeric substrate 102 include expanded polytetrafluoroethylene (ePTFE). In at least one embodiment, the polymeric substrate 102 is a microporous synthetic polymer membrane, such as a microporous fluoropolymer membrane having a nodular and fibrillar microstructure, where the nodes are interconnected by fibrils and the pores are located in the voids or spaces between the nodes and fibrils throughout the polymeric substrate. U.S. Patent No. 3,953,566 to Gore describes an exemplary nodular and fibrillar microstructure. The nodes and fibrils of the microporous microstructure have surfaces that define the inner surface of the polymeric substrate.

[0085] The volume specific surface area of the polymeric substrate described herein is greater than about 2.0 m 2 / cm 3 , greater than about 4.0 m 2 / cm 3 , greater than about 6.0 m 2 / cm 3 , greater than about 8.0 m 2 / cm 3 , greater than about 10 m 2 / cm 3 , greater than about 20 m 2 / cm 3 , greater than about 30 m 2 / cm 3 , greater than about 40 m 2 / cm 3 , greater than about 50 m 2 / cm 3 , greater than about 60 m 2 / cm 3 , greater than about 70 m 2 / cm 3 , greater than about 80 m 2 / cm 3 , greater than about 90 m 2 / cm 3 , and up to about 100 m 2 / cm 3 . As used herein, the volume specific surface area is defined based on the skeletal volume, rather than the encapsulated volume.

[0086] In some embodiments, the volume specific surface area is from about 2.0 m 2 / cm 3 to about 100 m 2 / cm 3 , or from about 3.0 m 2 / cm 3 to about 90 m 2 / cm 3 , or from about 4.0 m 2 / cm 3 to about 80 m2 / cm 3 , or about 5.0 m 2 / cm 3 to about 70 m 2 / cm 3 , or about 6.0 m 2 / cm 3 to about 60 m 2 / cm 3 , or about 7.0 m 2 / cm 3 to about 50 m 2 / cm 3 , or about 7.5 m 2 / cm 3 to about 40 m 2 / cm 3 , or about 8.0 m 2 / cm 3 to about 30 m 2 / cm 3 , or about 8.5 m 2 / cm 3 to about 20 m 2 / cm 3 , or about 9.0 m 2 / cm 3 to about 10 m 2 / cm 3 , or may have a volume specific surface area within any other range covered by these endpoints.

[0087] In some embodiments, the volume specific surface area is about 2.0 m 2 / cm 3 to about 3.0 m 2 / cm 3 , or about 3.0 m 2 / cm 3 to about 5.0 m 2 / cm 3 , or about 5.0 m 2 / cm 3 to about 10 m 2 / cm 3 , or about 10 m 2 / cm 3 to about 20 m 2 / cm 3 , or about 20 m 2 / cm 3 to about 30 m 2 / cm 3 , or about 30 m 2 / cm 3 to about 40 m 2 / cm3 , or about 50 m 2 / cm 3 to about 60 m 2 / cm 3 , or about 60 m 2 / cm 3 to about 70 m 2 / cm 3 , or about 70 m 2 / cm 3 to about 80 m 2 / cm 3 , or about 80 m 2 / cm 3 to about 90 m 2 / cm 3 , or about 90 m 2 / cm 3 to about 100 m 2 / cm 3 , or may have a volume specific surface area within any other range encompassed by these endpoints.

[0088] In addition, most of the fibrils in the polymeric substrate have a diameter of less than about 1.0 μm, or about 0.1 μm to about 1.0 μm, or about 0.3 μm to about 1.0 μm, or about 0.5 μm to about 1.0 μm, or about 0.7 μm to about 1.0 μm, or may have a diameter within any other range encompassed by these endpoints. Additionally, the polymeric substrate can be thin, having a thickness of about 1 μm to about 100 μm, or about 1.1 μm to about 75 μm, or about 1.2 μm to about 50 μm, or about 1.3 μm to about 35 μm, or about 1.4 μm to about 25 μm, or about 1.5 μm to about 10 μm, or about 1.6 μm to about 5 μm, or about 1.7 μm to about 4 μm, or about 1.8 μm to about 3 μm, or may have a thickness within any other range encompassed by these endpoints.

[0089] In some embodiments, a conformal coating of the polymeric substrate can be disposed on the surface of the polymeric substrate, the conformal coating being formed of sintered metal nanoparticles. In some embodiments, the conformal coating can be disposed on the inner surface of the polymeric substrate. In certain embodiments, the metal nanoparticles can be sintered. Non-limiting examples of the conformal coating can include metal nanoparticles such as platinum group metals (PGM, such as platinum, iridium, ruthenium, palladium), gold, silver, copper, nickel, indium, combinations thereof, alloys thereof (such as alloys including transition metals), and / or oxides thereof.

[0090] Composite 104 may further include a conformal coating 104 formed of sintered metal nanoparticles dispersed on the surface of polymeric substrate 102. Coating 104 can be formed of sintered metal nanoparticles.

[0091] In some embodiments, such as as shown in Figure 1B - 1C , the microporous structure defines an inner surface, and a conformal coating 104 formed of sintered metal nanoparticles is disposed on the inner surface of the polymeric substrate 102. In certain embodiments, the conformal coating 104 formed of sintered metal nanoparticles is a continuous coating on the surface (including the inner surface) of the polymeric substrate 102.

[0092] In some cases, the polymeric substrate 102 includes a microstructure having a plurality of nodes 106 (such as as shown in Figure 1B ) and fibrils 108 (such as as shown in Figure 1C ). The conformal coating 104 formed of sintered metal nanoparticles is located at the nodes 106 and fibrils 108 of the polymeric substrate 102.

[0093] In certain cases, the conformal coating 104 formed of sintered metal nanoparticles is selected from one of the following groups: platinum coating, iridium coating, ruthenium coating, palladium coating, gold coating, silver coating, copper coating, nickel coating, indium coating, combinations thereof, alloys thereof (such as alloys including transition metals), and / or oxides thereof.

[0094] According to some embodiments, the coated polymeric substrate includes a microporous polymer continuously and conformally coated with sintered metal nanoparticles. In some embodiments, the sintered metal nanoparticles coat the inner surface of the polymeric substrate. According to certain embodiments, the polymeric substrate includes a node and fibril microstructure, wherein the sintered metal nanoparticles coat the nodes and fibrils of the polymeric substrate. In certain embodiments, the sintered metal nanoparticles form a continuous conformal coating on the inner surface of the polymeric substrate. In some embodiments, the polymer may have a microstructure. The microstructure may include, for example, nodes and / or fibrils. In some cases, the thickness of the conformal coating formed on the nodes may be similar to the thickness of the conformal coating formed on the fibrils. In some cases, the thickness of the conformal coating formed on the nodes may 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 may 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 may be similar to the thickness of the conformal coating formed on another fibril.

[0095] According to the present disclosure, by absorbing and sintering metal nanoparticles, a durable conformal metal coating can be formed on the inner surface and throughout the thickness of a polymeric substrate (such as ePTFE) having tortuous pores and low surface energy.

[0096] As described regarding the third exacerbating factor in the background art above, a historical obstacle faced by conformal coatings is the difficulty in producing thin metal coatings on polymer substrates (such as ePTFE) with high surface area and low surface energy. This challenge can be exacerbated when there is a large surface energy difference between the coating and the polymer substrate. Generally, the surface energy of metals is much higher than that of polymers, especially low surface energy polymers such as polytetrafluoroethylene (PTFE). As an illustrative example, the surface energies of metals such as gold and platinum are approximately 1500 mJ / m 2 and approximately 2400 mJ / m 2 , while the surface energy of PTFE is approximately 20 mJ / m 2 (two orders of magnitude lower).

[0097] Without wishing to be bound by theory, it is generally understood that surfaces tend towards the lowest energy state, and thus materials with higher surface energy do not tend to "wet" low energy surfaces, especially those with large surface areas. Additionally, materials with high surface energy tend to "dewet" low surface energy surfaces as much as possible and accumulate or aggregate in a manner that minimizes their surface area. It is also generally understood that metal nanoparticles can sinter at temperatures far below the melting point of bulk metal. This sintering is believed to occur through a lowering of the melting point, such as through the Gibbs-Thomson effect. Thus, it can be expected that the sintering of metal nanoparticles located on a low energy surface will cause the metal to "dewet" substantially from the low energy surface of the target polymer substrate, causing the metal nanoparticles to accumulate or aggregate in the available pore space. Additionally, it can be expected that the adhesion of the metal coating to the low energy surface will be relatively poor. However, the present disclosure demonstrates articles and methods for preparing those articles that achieve a substantially uniform conformal metal coating on the low surface energy surface of a polymer substrate. Additionally, the conformal coating adheres persistently to the polymer substrate, as shown by the results of the wet bend particle test described below. The present disclosure demonstrates embodiments and methods in which metal nanoparticles fuse into a relatively thin and dense metal coating that substantially conforms to the inner surface of a polymer substrate (such as ePTFE), where the metal nanoparticles are dispersed over a relatively large surface area.

[0098] The mechanical durability of the metal coating on the polymer substrate (such as the adhesion of the metal coating to the polymer substrate) can be measured by the internal wet bend particle test detailed below. In some embodiments, the level of granulation of the conductive coating can be less than 0.01 wt% of the conductive coating (i.e., corresponding to a retention rate of the conductive coating greater than 99.99 wt%). In some embodiments, the retention rate of the conductive coating can be greater than 99.9 wt%. In some embodiments, the retention rate of the conductive coating can be greater than 99 wt%. In some embodiments, the retention rate of the conductive coating can be greater than 90 wt%.

[0099] Accordingly, despite the difficulties associated with, for example, surface energy and other exacerbating factors as described herein, the present disclosure relates to providing a conformal metal coating on an inner surface of a polymeric substrate. In some embodiments, metal nanoparticles (e.g., gold) are deposited and processed to form a conformal and continuous coating on 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 the metal nanoparticles to sinter (e.g., rapidly sinter) together within the pores of the polymeric substrate to form a conformal coating on the surface of the polymeric substrate (e.g., ePTFE). In some cases, the conformal coating can completely surround the microstructural features (e.g., nodes and / or fibrils), which can enhance the durability of the conductive coating (e.g., as measured by a wet bend particle test). In some cases, all surfaces of the substrate (including outer and inner surfaces) are substantially coated with the conformal coating. In some cases, at least a portion of the outer and inner surfaces of the substrate are coated with the conformal coating.

[0100] According to one embodiment as Figure 1A - 1C shown, a representative SEM image of a conformal-gold-ePTFE CG / ePTFE composite example is shown. Figure 1A A cross-section of the composite is shown, Figure 1B a cross-section of its nodes is shown, Figure 1C a cross-section of its fibrils is shown. CG can be seen at the nodes and fibrils of the ePTFE membrane.

[0101] In one embodiment, according to the cross-sectional SEM image, the sintered metal nanoparticles exhibit a surface topography that conforms to the features of the polymeric substrate (e.g., nodes) (see, for example, Figure 1B ). In some embodiments, the fibrils of the polymeric substrate are wrapped by the metal nanoparticles within their entire circumference (see, for example, Figure 1C ).

[0102] It should be understood that the articles and methods described herein can be implemented in various environments. In one non-limiting example, a polymeric substrate having a conformal coating of sintered metal nanoparticles can be implemented in an electrochemical cell or a device that includes an electrochemical cell, such as with respect to energy storage and conversion. In one embodiment, the conformally coated polymeric substrate can be configured as a component of an electrochemical cell, such as an electrode. In another embodiment, the conformally coated polymeric substrate can be configured as part of a membrane electrode assembly.

[0103] For example, now referring to Figure 2, which is a schematic diagram of a membrane electrode assembly 200 incorporating the composite materials and / or polymer substrates described herein. 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 Figure 2 shown, or can be separate structures. In one embodiment, the article can include a separator layer 206 adhered to an electrode, where the electrode includes a polymer substrate with a conformal coating of sintered metal nanoparticles. The membrane electrode assembly can include two electrodes or only one electrode. As will be understood by one of ordinary skill in the art, the size, shape, orientation, compliance, flexibility, and other properties of the membrane electrode assembly 200 can vary.

[0104] In some embodiments, the cathode layer 202 and / or the anode layer 204 can be conductive. In some cases, the cathode layer 202 and / or the anode layer 204 can include a catalyst. In some cases, the cathode layer 202 and / or the anode layer 204 can include an electrocatalyst. In some cases, the cathode layer 202 can include an electrocatalyst for a reduction reaction. In some cases, the anode layer 204 can include an electrocatalyst for an oxidation reaction. In some cases, the aforementioned electrocatalyst can have an extended surface. In such cases, there is interest in preparing conductive materials with specific characteristics such as high catalytic activity, high current density, robust mass transport, high durability, etc.

[0105] In some embodiments, when a polymer substrate with a conformal coating formed from sintered metal nanoparticles is configured as an electrode, the electrode can be modified to enable ion conduction. For example, the electrode can be configured to permit the transport of cations and / or anions. In certain embodiments, the electrode can become ionically conductive when wetted or swollen with a liquid electrolyte. In certain embodiments, the electrode can include 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 a porous electrode can be quantified using electrochemical impedance spectroscopy (e.g., using equivalent circuit modeling incorporating "transmission line" features).

[0106] When used as a component of an electrochemical cell (e.g., as a component of an electrode or as part of a membrane electrode assembly), the conformally coated polymer substrate may have certain advantages compared to conventional materials. According to some embodiments, the membrane electrode assembly 200 may exhibit higher durability compared to a conventional membrane electrode assembly with a carbon-supported PGM-based catalyst in a traditional "ink-based" electrode. Additionally, according to some embodiments, the membrane electrode assembly 200 may exhibit more robust performance (i.e., high performance over a wider operating range) compared to traditional membrane electrode assemblies.

[0107] The separator layer 206 may be located between the cathode layer 202 and the anode layer 204. In some cases, the separator layer 206 may be ionically conductive and an electrically insulating layer that allows ions to pass through the separator layer 206 for transport between the anode layer 204 and the cathode layer 202, but forces electrons to travel around through an external circuit. In certain embodiments, the separator layer 206 may be an electrochemical separator that becomes ionically conductive when wetted with a liquid electrolyte. The electrochemical separator may be configured to allow the transport of cations and / or anions. In certain embodiments, the separator layer 206 may 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 may include a hydrocarbon ion exchange material. In certain embodiments, the ion exchange material may include a fluorocarbon ion exchange material. In certain embodiments, the ion exchange material may include a perfluorocarbon ion exchange material. In certain embodiments, the ion exchange material may include an anion exchange material (e.g., an anion exchange polymer). In certain embodiments, the ion exchange material may include a cation exchange material (e.g., a cation exchange polymer). In certain embodiments, the ion exchange material may include perfluorosulfonic acid. As will be readily understood by one of ordinary skill in the art, the ionic conductivity of the electrochemical separator can be quantified using electrochemical impedance spectroscopy (e.g., by examining the real part of the impedance at an appropriately high frequency, such as where the data intersects the x-axis of a Nyquist plot).

[0108] In one example of a conductive article, such as Figure 2 shown, the microporous electrocatalytic electrode can be used in energy storage and conversion applications, such as fuel cells and / or electrolyzers. In some cases, the fuel cell can be a proton exchange membrane fuel cell (PEMFC). In some cases, the electrolyzer can be a proton exchange membrane water electrolyzer (PEMWE).

[0109] According to certain embodiments, the ratio of the conformal coating volume to the pore phase volume of the conformally coated polymeric substrate is from about 0.001 to about 1.0, or from about 0.01 to about 0.9, or from about 0.02 to about 0.8, or from about 0.03 to about 0.7, or from about 0.04 to about 0.6, or from about 0.05 to about 0.5, or from about 0.06 to about 0.4, or from about 0.07 to about 0.3, or from about 0.08 to about 0.25, or from about 0.09 to about 0.2, or from about 0.1 to about 0.15, 0.001 to about 0.01, or from about 0.01 to about 0.02, or from about 0.02 to about 0.03, or from about 0.03 to about 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 may have a ratio within any other range encompassed by these endpoints.

[0110] According to some embodiments, the porosity of the conformally coated polymeric substrate is from about 25 vol% to about 95 vol%, or from about 30 vol% to about 94 vol%, or from about 35 vol% to about 93 vol%, or from about 40 vol% to about 92 vol%, or from about 45 vol% to about 91 vol%, or from about 50 vol% to about 90 vol%, or may have a porosity within any other range encompassed by these endpoints. In an exemplary embodiment, the porosity of the conformally coated polymeric substrate is from about 55% to about 95%.

[0111] It is well known that quantitatively characterizing the pore size of a porous material with a complex or irregular pore geometry is a challenge. In such cases, the pore size can be considered an inherently polydisperse population property and can be described by a pore size distribution. For those of ordinary skill in the art, there are a variety of standard evaluation methods, such as quantitative image analysis, BET / BJH analysis, capillary flow porometry (including bubble point analysis), and liquid / liquid porosimetry. Each quantification method makes a simplified assumption about the pore geometry. Most of these quantification methods produce a pore size distribution from which characteristic pore size (e.g., pore diameter, d) parameters such as median or mode pore size (e.g., by BET / BJH analysis), or maximum through hole (e.g., by bubble point determination) can be extracted. In some embodiments, capillary flow porometry can be used to determine the median flow average pore size.

[0112] Similarly, as is well known to those of ordinary skill in the art, the challenges of characterizing particle size (e.g., average or median particle size, D) are also complex. There are a variety of standard tools available, such as dynamic light scattering, in which case care must be taken to prevent data distortion due to agglomeration. Another method for determining particle size is to directly microscopically observe the nanoparticles before sintering, or when the conformal coating itself only undergoes minimal sintering and the initial particle size is still clearly visible. Alternatively, the specific surface area (SSA, in units of m 2 / g, measured by BET) of the unsintered or minimally sintered particles can be measured, and if the particle density (ρ) is known or has been measured (e.g., by helium pycnometry), then standard equations based on, for example, the volume (V 球体 ) and area (A 球体 ) of a sphere based on the sphere diameter (D) can be used to calculate a representative spherical particle size. The relevant equations are as follows:

[0113] A 球体 = πD 2

[0114]

[0115] According to some embodiments, the characteristic pore size (e.g., the volume average pore size determined by quantitative image analysis or the middle flow average pore size determined by capillary flow porometry) of the polymer substrate before coating or the conformally coated polymer substrate is significantly larger than the characteristic particle size (e.g., the volume average particle diameter) of the nanoparticles used to produce the conformal coating. For example, the aforementioned 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 aforementioned pore size can be from about 2 times to about 100,000 times larger, or can be within any other range encompassed by these endpoints.

[0116] According to some embodiments, the mass / area of the conformally coated polymer substrate is from about 1 g / m 2 to about 100 g / m 2 , or from about 2 g / m 2 to about 90 g / m 2 , or from about 3 g / m 2 to about 85 g / m 2 , or from about 4 g / m 2to about 80 g / m 2 ,or about 5 g / m 2 to about 75 g / m 2 ,or about 6 g / m 2 to about 70 g / m 2 ,or about 7 g / m 2 to about 65 g / m 2 ,or about 8 g / m 2 to about 60 g / m 2 ,or about 9 g / m 2 to about 50 g / m 2 ,or about 10 g / m 2 to about 50 g / m 2 ,or about 15 g / m 2 to about 50 g / m 2 ,or about 1 g / m 2 to about 5 g / m 2 ,or about 5 g / m 2 to about 10 g / m 2 ,or about 10 g / m 2 to about 15 g / m 2 ,or about 15 g / m 2 to about 20 g / m 2 ,or about 20 g / m 2 to about 30 g / m 2 ,or about 30 g / m 2 to about 40 g / m 2 ,or about 40 g / m 2 to about 50 g / m 2 ,or about 50 g / m 2 to about 60 g / m 2 ,or about 60 g / m 2 to about 70 g / m 2 ,or about 70 g / m 2 to about 80 g / m 2 ,or about 80 g / m 2 to about 90 g / m 2 ,or about 90 g / m 2 to about 100 g / m 2 ,or may have a mass / area within any other range encompassed by these endpoints. In some embodiments, the mass / area of the conformally coated polymeric substrate is about 15 g / m 2 ,or about 20 g / m 2 ,or about 46 g / m 2 。

[0117] According to some embodiments, the sheet resistance of the conformally coated polymer substrate is from about 0.1 ohms per square to about 0.5 ohms per square, or from about 0.11 ohms per square to about 0.49 ohms per square, or from about 0.12 ohms per square to about 0.48 ohms per square, or from about 0.13 ohms per square to about 0.47 ohms per square, or from about 0.14 ohms per square to about 0.46 ohms per square, or from about 0.15 ohms per square to about 0.45 ohms per square, or from about 0.16 ohms per square to about 0.44 ohms per square, or from about 0.17 ohms per square to about 0.43 ohms per square, or from about 0.18 ohms per square to about 0.42 ohms per square, or from about 0.19 ohms per square to about 0.41 ohms per square, or from about 0.2 ohms per square to about 0.4 ohms per square.

[0118] According to some embodiments, the sheet resistance of the conformally coated polymer substrate is from about 0.5 ohms per square to about 1.0 ohms per square, or from about 0.51 ohms per square to about 0.99 ohms per square, or from about 0.52 ohms per square to about 0.98 ohms per square, or from about 0.53 ohms per square to about 0.97 ohms per square, or from about 0.54 ohms per square to about 0.96 ohms per square, or from about 0.55 ohms per square to about 0.95 ohms per square, or from about 0.56 ohms per square to about 0.94 ohms per square, or from about 0.57 ohms per square to about 0.93 ohms per square, or from about 0.58 ohms per square to about 0.92 ohms per square, or from about 0.59 ohms per square to about 0.91 ohms per square, or from about 0.6 ohms per square to about 0.9 ohms per square, or from about 0.7 ohms per square to about 0.8 ohms per square.

[0119] In some embodiments, the polymer substrate includes a microporous membrane having a continuous and 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 in the range of 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.

[0120] Figure 4Illustrative flowchart of a method 400 for forming a composite material in accordance with certain embodiments of the present disclosure is shown. This figure is merely an example. Those of ordinary skill in the art will recognize many variations, changes, and modifications. The method 400 for forming a composite material includes processes 402, 404, 406, and 408. Although a selected set of processes for forming a composite material using the method 400 has been shown above, there can be many changes, modifications, and variations. For example, some processes can be extended and / or combined. Other processes can be inserted into the processes described above. According to embodiments, the order of the processes can be interchanged or replaced by other processes. Further details of these processes can be found throughout the present disclosure.

[0121] According to some embodiments, at process 402, the method 400 includes providing a polymeric substrate having a microporous structure. In some embodiments, the polymeric substrate can be selected from one of expanded polytetrafluoroethylene and expanded polyethylene. In certain embodiments, the polymeric substrate is a film. In some cases, the polymeric substrate includes a microporous structure having nodes and fibrils defining an inner surface.

[0122] According to certain embodiments, at process 404, the method 400 includes preparing a dispersion comprising metal nanoparticles in a liquid carrier. The liquid carrier can be considered a processing aid. In some cases, the liquid carrier can be organic and / or aqueous. The dispersion can also include other processing aids, such as a dispersant, such that the metal nanoparticles are stably dispersed in the solvent. Non-limiting examples of the dispersant include oleylamine and polyvinylpyrrolidone.

[0123] In some embodiments, at process 406, the method 400 includes causing the polymeric substrate to absorb a solution comprising metal nanoparticles. In some embodiments, process 406 can include delivering the metal nanoparticles substantially uniformly to the surface of the microporous substrate. In some embodiments, process 406 can include delivering the metal nanoparticles substantially or completely through most of the material. In certain embodiments, process 406 includes restricting the polymeric substrate to substantially prevent dimensional changes.

[0124] At process 408, the method 400 includes heating the polymeric substrate to sinter the metal nanoparticles to form a metal coating on the surface of the polymeric substrate. Generally, the temperature required for sintering depends on the composition of the nanoparticles (e.g., which metal is included), the size of the nanoparticles, and the sintering time. Generally, metal nanoparticles have different melting temperatures compared to the same metal in non-nanoparticle form. The melting temperature of metal nanoparticles tends to be lower compared to the same metal with a larger particle size. Generally, the longer the sintering time, the lower the sintering temperature used.

[0125] Process 408 may include heating the polymeric substrate to a first temperature at which the liquid carrier evaporates and the metal nanoparticles are deposited on the surface of the polymeric substrate, and heating to a second temperature at which the nanoparticles are sintered. The first temperature can be controlled such that processing aids [such as the liquid carrier and dispersant (if present)] volatilize and the metal nanoparticles are deposited on the surface of the polymeric substrate.

[0126] In certain embodiments, the second temperature at which the nanoparticles are sintered is below the melting temperature of the polymeric substrate. The second temperature at which the nanoparticles are sintered is below the melting temperature of the polymeric substrate so that the structure of the microporous substrate is substantially retained during formation. In an exemplary embodiment, the first temperature is about 90 degrees Celsius and the second temperature is about 300 degrees Celsius. In certain embodiments, the polymeric substrate is restricted during process 408 to substantially prevent dimensional changes.

[0127] The formed metal coating can be disposed on the inner surface of the polymeric substrate to define a continuous metal coating over the microporous structure (including the inner surface) of the polymeric substrate. In some embodiments, the metal coating is selected from one of the following groups: platinum coating, iridium coating, ruthenium coating, palladium coating, gold coating, silver coating, copper coating, nickel coating, indium coating, combinations thereof, alloys thereof (such as alloys including transition metals), and / or oxides thereof.

[0128] Testing methods

[0129] It should be understood that while certain methods and apparatuses are described below, other methods or apparatuses determined to be applicable by one of ordinary skill in the art may alternatively be employed.

[0130] Non-contact thickness

[0131] The non-contact thickness is measured using the following technique with a laser micrometer (Keyence LS-7010 model, Mechelen, Belgium). A metal cylinder is aligned between the laser micrometer source and the laser micrometer receiver such that the first shadow of the top of the cylinder is projected onto the receiver. The position of the first shadow is then set as the "zero" reading of the laser micrometer. Then a single-layer test article is placed over the surface of the metal cylinder without overlap and wrinkles, which projects a second shadow onto the receiver. The laser micrometer then indicates the change in position between the first and second shadows as the thickness of the sample. The thickness of each sample is measured three times and averaged.

[0132] Bubble point

[0133] The bubble point pressure was measured in accordance with ASTM F316-03 using a capillary flow porometer (Model 3Gzh from Quantachrome Instruments, Boynton Beach, Florida) and using Silwick silicone fluid (20.1 dynes / cm; Microporous Materials, Inc.). The bubble point pressure value is the average of two measurements.

[0134] Matrix Tensile Strength Determination

[0135] Samples were cut using ASTM D412 - Dogbone F. In the case where the sample includes an ePTFE membrane, the "machine direction" refers to the extrusion direction, and the "transverse direction" refers to the direction perpendicular to this. The sample was placed on the cutting table such that the area to be cut was free of wrinkles. Then the die was placed on the sample such that its long axis was parallel to the direction to be tested. Once the die was aligned, pressure was applied to cut the sample. After the pressure was removed, the dogbone-shaped sample was inspected to ensure that it had no edge defects that could affect the tensile test. At least 3 samples in the machine direction and at least 3 samples in the transverse direction were prepared in this way. Once the dogbone-shaped samples were prepared, they were measured using an AG204 model balance from Mettler Toledo to determine their mass.

[0136] Using a 5500R tensile testing machine [from Illinois Tool Works Inc., Norwood, Massachusetts] to measure the tensile break load, which is equipped with rubber-coated panels and serrated panels such that each end of the sample was clamped between a rubber-coated plate and a serrated plate. The pressure applied to the clamping plates was approximately 552 kPa. The gauge length between the clamps was set to 58.9 mm, and the crosshead speed (pulling speed) was set to a speed of 508 mm / min. These measurements were made using a 500 N load cell, and data was collected at a rate of 50 points per second. The laboratory temperature was between 20 and 22.2 °C to ensure the comparability of the results. If the sample broke at the clamp interface, the data was discarded. To characterize the material in a given direction (e.g., machine direction or transverse), at least three samples (without slipping or breaking at the clamps) were successfully pulled out.

[0137] Kawabata Flexibility Measurement

[0138] The low-force bending behavior was measured using a Kawabata pure bending tester (KES-FB2-Auto-A; Kato Tech Co., Ltd., Kyoto, Japan). The sample was cut to a width of 7 cm. The machine sensitivity was set to 10. The machine automatically tightened the clamps and bent the sample in two directions to a curvature of 2.5 cm -1 while recording the applied load. The reported B-average value is for the laminated sample at 0.5 to 1.5 cm -1 and -0.5 to -1.5 cm-1 The average flexural stiffness when bent between. The unit of flexural stiffness is gram-force centimeter 2 / cm.

[0139] ATEQ air flow

[0140] Air flow is a test method for measuring the laminar volume flow rate of air through a membrane sample. For each membrane, the sample is clamped between two plates in such a way that it seals a flow channel with an area of 2.99 cm 2 The area. Using (ATEQ Corporation, Livonia, Michigan) Premier D Miniature Flow Meter, the air flow rate (liters per hour) through each membrane sample is measured by applying an air pressure difference of 1.2 kPa (12 mbar) to the membrane.

[0141] Gurley air flow

[0142] The Gurley air flow test measures the time (in seconds) required for 100 cm 3 of air to flow through a 1 in 2 (~6.45 cm 2 ) sample at a water pressure of 0.177 psi (~1.22 kPa). The sample is measured in a GURLEY TM Density Tester and Smoothness Tester Model 4340 (Gurley Precision Instruments, Troy, New York). The reported value is the average of 3 measurements and is in seconds.

[0143] Capillary Flow Porometry (CFP) test

[0144] Measurements are made using a Porometer 3G zH from Quantachrome Instruments. The wetting fluid is silicone oil with a nominal surface tension of 19.78 dynes / cm. The pressure range is from 0.255 psig to 394 psig. The sample size is 10 mm in diameter.

[0145] Wet flexural particle test

[0146] This durability test is designed to evaluate the tendency of the composite material to shed particles. For the test to be valid, the sample must have a low enough flexural stiffness to be able to undergo full bending motion under the test conditions. To conduct this test, a 2.125” x 0.5” sample is cut from the composite material. By clamping the sample between two pieces cut as Figure 5ABetween the engineering plastics of the shown shape, the sample is loaded into the test fixture 500. The main body 502 of the test fixture includes: cutouts 504a and 504b for mounting O-rings, a window 506 that allows the sample to bend, ablation grooves 508 that enhance the adhesion of the sample, O-ring positions 510 for establishing an interference fit in a centrifuge tube, and O-ring positions 512a and 512b for firmly fixing the sample.

[0147] The sample is loaded with a controlled slack and fixed in place by O-rings 514a and 514b as Figure 5B shown. For the dimensions, the window that allows the sample to bend has a size of 24.5 mm long x 14.1 mm wide x 2.7 mm thick. Then the test fixture with the sample is loaded into a standard 50 mL centrifuge tube, and then 40 mL of isopropyl alcohol (hereinafter referred to as "test fluid") is added to the centrifuge tube. Isopropyl alcohol is chosen because it easily wets the sample to be tested, is relatively inert to the sample to be tested (for example, it is expected that the corrosion or dissolution of the sample can be ignored), and has a low enough viscosity to achieve the required hydrodynamics in the tube, as described below. Other test fluids can be selected according to the needs of the sample to be tested and the target application. Then the centrifuge tube is capped and sealed with tape to prevent leakage.

[0148] As Figure 5C shown, then the centrifuge tube 516 is loaded into an Intelli-Mixer (#RM-2L) such that the plane of the test fixture is parallel to the axis of rotation. This orientation enables the sample to bend. The Intelli-Mixer is set to shake the sample at a speed of 20 rpm by + / - 99 degrees for the required time (usually 1 - 7 days). Each time the sample is shaken, they also bend due to the hydrodynamics inside the tube. Bending means that the slack part of the sample transfers from one side of the test fixture to the other side. After the required time of shaking, the liquid in the tube is extracted with a pipette and analyzed using inductively coupled plasma mass spectrometry (ICP-MS) to check for the presence of metals that may have detached from the composite material.

[0149] Sheet resistance

[0150] A 2.125” x 0.5” sample is die-cut from the material sheet to be tested. The sample is placed flat on a closed-cell silicone sponge sheet [1 / 2 inch thick, Bellofoam #7704]. Using a Keithley 2750 digital multimeter, the resistance is measured using a 4-point probe 300 as Figure 3 shown. The probe 300 is made of gold-plated stainless steel. Each of the 4 probes 302a - d has a thickness of approximately 1.2 inches and a length of approximately 1.5 inches. The average distance between the 4 probes 402a - d is approximately 0.5 inches, and they are connected by PTFE spacers 304.

[0151] The four-point probe 300 is connected to a multimeter in a standard four-point probe configuration (i.e., the voltage sensing leads are connected to the two innermost terminals, and the input leads are connected to the two outermost terminals). After gently placing the four-point probe 300 on the sample to be measured, a 330 g weight is placed on top of the probe 300 to ensure reliable and uniform contact between the probe 300 and the sample. Note to ensure sufficient contact between the probe 300 and the conductive phase of the sample. Insulate the weight with a plastic sheet to ensure that it does not short-circuit the probe 300. The Keithley multimeter operates in four-point probe mode and enables "OCOMP" four-wire offset compensation. For each measurement, the system needs to stabilize for about 10 seconds before recording the resistance. The data is reported in ohms per square area.

[0152] Example 1: Preparation of conformal gold / ePTFE composite

[0153] This example describes the preparation of an ePTFE membrane composite combined with a conformal gold coating ("CG / ePTFE composite").

[0154] The first layer of ePTFE membrane ("target membrane") (3 - 5 g / m 2 mass / area; 1.5 psi bubble point; 92 μm non-contact thickness; W.L. Gore & Associates, Inc.) is confined in a 4" diameter metal ring and hand-tensioned to remove wrinkles. The second layer of ePTFE membrane ("inlet membrane") (3 - 5 g / m 2 mass / area; 40 psi bubble point; 18 μm non-contact thickness; W.L. Gore & Associates, Inc.) is confined in a 6" diameter metal ring and hand-tensioned to remove wrinkles. The inlet membrane is placed on top of the target membrane such that the two membranes are in physical contact and roughly concentric. 0.75 mL of gold nanoparticle ink (#UTDAu60X; UTDots, Inc.) is pipetted onto the surface of the inlet membrane and spread evenly with a disposable pipette ball until the absorption solution completely wets the inlet membrane and the target membrane (<30 seconds). Wipe the upper surface of the inlet membrane with a lint-free cloth to remove excess ink. Then, the two wetted membranes are separated by separating their respective rings. Discard the inlet membrane. Then, the target membrane is dried using a hot air gun set at 93 °C and subsequently heated in a standard convection oven at 300 °C for one hour. The resulting product is the CG / ePTFE composite.

[0155] According to the sheet resistance test method of the four-point probe described above (as Figure 3 shown), the mass / area of the CG / ePTFE composite is 46 g / m 2, the sheet resistance is about 0.2 - 0.4 ohms per square. To demonstrate that the metal is continuously and conformally coated over the entire thickness of the target film, the sheet resistance of the composite material is approximately the same when measured on either the top or bottom surface (specifically, within about 15% of the surface with the lower resistance).

[0156] The samples were subjected to a 7 - day pressure test using the "wet bent particle test". Inductively coupled plasma (ICP) analysis of the test fluid showed that no gold was detected in either sample (i.e., the content of any gold present was below the detection limit of the instrument), corresponding to a minimum metal retention rate > 99.99 wt%.

[0157] Example 2: Preparation of Conformal Silver / ePTFE Composite

[0158] This example describes the preparation of an ePTFE membrane composite material combined with a conformal silver coating ("CS / ePTFE composite").

[0159] The first layer of ePTFE membrane ("target membrane") (3 - 5 g / m 2 mass / area; 1.5 psi bubble point; 92 μm non - contact thickness; W.L. Gore & Associates, Inc.) was confined within a 4" diameter metal ring and hand - tensioned to remove wrinkles. The second layer of ePTFE membrane ("inlet membrane") (3 - 5 g / m 2 mass / area; 40 psi bubble point; 18 μm non - contact thickness; W.L. Gore & Associates, Inc.) was confined within a 6" diameter metal ring and hand - tensioned to remove wrinkles. The inlet membrane was placed on top of the target membrane such 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 inlet membrane and spread evenly with a disposable pipette bulb until the absorption solution completely wetted the inlet membrane and the target membrane (< 30 seconds). The upper surface of the inlet membrane was wiped with a lint - free cloth to remove excess ink. Then, the two wetted membranes were separated by detaching their respective rings. The inlet membrane was discarded. Then, the target membrane was dried using a hot air gun set to 93 °C and subsequently heated in a standard convection oven at 200 °C for one hour. The resulting product was the CS / ePTFE composite.

[0160] According to the four - point probe sheet resistance test method described above (as Figure 3 shown), the mass / area of the CS / ePTFE composite is 15.6 g / m 2, The sheet resistance is about 0.7 - 0.8 ohms per square. To demonstrate that the metal is continuously and conformally coated over the entire thickness of the target film, the sheet resistance of the composite material is substantially the same whether measured on the top or bottom surface (specifically, within about 15% of the surface with the lower resistance).

[0161] Figure 6A - 6C Figure is a representative SEM image showing the microstructure of the CS / ePTFE composite material of Example 2. Figure 6A - 6B Figure

[0161] shows a cross - section of the CS / ePTFE composite material at various nodes of the material defined within the microstructure of the composite material. Figure 6C Figure Figure 6A - 6C shows an overall cross - section of the CS / ePTFE composite material.

[0162] As shown, the composite material 600 may also include a conformal coating 604 formed by sintered metal nanoparticles dispersed on the surface of the polymer substrate 602. The coating 604 may be formed by sintered metal nanoparticles.

[0163] In some embodiments, for example, as shown in Figure 6A - 6B Figure , the microporous structure defines an inner surface, and the conformal coating 604 formed by sintered metal nanoparticles is disposed on the inner surface of the polymer substrate 602. In certain embodiments, the conformal coating 604 formed by sintered metal nanoparticles is a continuous coating on the surface (including the inner surface) of the polymer substrate 602.

[0164] In some cases, the polymer substrate 602 includes a microstructure having a plurality of nodes 606 (such as shown in Figure 6A Figure

[0163] -B) and fibrils 608 (such as shown in Figure 6C Figure Figure 6A - 6B ). The conformal coating 604 formed by sintered metal nanoparticles is located at the nodes 606 and fibrils 608 of the polymer substrate 602.

[0165] For a metallized polymer substrate, its pore phase and the conformal coating formed by sintered metal nanoparticles disposed on the surface of the polymer substrate can be characterized by calculating various volume ratios. Based on the properties of the components listed in Table 1, assuming the mass / area of ePTFE is 4 g / m 2 , the ratios can be calculated as follows:

[0166] V 涂层 / V 基材 = 2.2 cc / m 2 / 1.8 cc / m 2 = 1.22

[0167] V 孔 / V 基材 = 31 cc / m 2 / 1.8 cc / m2 = 17.2

[0168] V 涂层 / V 孔 = 2.2 cc / m 2 / 31 cc / m 2 = 0.07

[0169] V 孔 / V 总计 = 31 cc / m 2 / 35 cc / m 2 = 0.89 = 89 vol% = “porosity”

[0170] Table 1. Characteristics of the gold / ePTFE composite in Example 1

[0171]

[0172] Table 2. Characteristics of the silver / ePTFE composite in Example 2

[0173]

[0174] The invention of the present application has been generally described above and in connection with specific embodiments. It will be apparent to those skilled in the art that various modifications and changes can be made to the embodiments described herein without departing from the spirit and scope of the invention. Accordingly, the embodiments are intended to cover such modifications and changes to the invention as long as they are within the scope of the appended claims and their equivalents.

Claims

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

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

3. The composite material according to any one of claims 1 and 2, wherein the conformal coating is a continuous coating on the surface of the polymeric substrate including the inner surface.

4. The composite material according to any one of claims 1-3, wherein the porous structure of the polymeric substrate comprises nodes and / or fibrils, and wherein the conformal coating is located at the nodes and / or fibrils of the polymeric substrate.

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

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

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

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

9. The composite material according to any one of claims 1-8, wherein the thickness of the composite material is about 1 micron to about 100 microns.

10. The composite material according to any one of claims 1-8, wherein the ratio of the volume of the conformal coating of the composite material to the volume of the pore phase is 0.001 to 1.

0.

11. The composite material according to any one of claims 1-8, wherein the median flow pore diameter of the composite material is at least 2 times the volume average particle diameter of the metal nanoparticles.

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

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

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

15. The composite material according to claim 13, wherein the ion exchange material is perfluorosulfonic acid.

16. A membrane electrode assembly, comprising the composite material according to any one of claims 1-15 in combination with an electrochemical separator.

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

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

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

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

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

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

23. The article according to claim 21, wherein the article is a fuel cell.

24. The article according to claim 21, wherein the article is an electrolyzer.

25. A method of forming a composite material, comprising: providing a polymeric substrate having a porous structure; causing the polymeric substrate to absorb metal nanoparticles; and heating the metal nanoparticles to sinter the metal nanoparticles, thereby forming a conformal coating on the surface of the polymeric substrate.

26. The method according to claim 25, further comprising preparing a dispersion comprising metal nanoparticles and a dispersant, wherein the absorbing comprises wetting the polymeric substrate with the dispersion.

27. The method according to any one of claims 25 and 26, wherein causing the polymeric substrate to absorb comprises heating the polymeric substrate to a first temperature at which processing aids volatilize, and wherein heating the metal nanoparticles comprises heating the metal nanoparticles to a second temperature to sinter the metal nanoparticles.

28. The method according to claim 27, wherein the second temperature at which the nanoparticles are sintered is lower than the melting temperature of the polymeric substrate.

29. The method according to any one of claims 27 and 28, wherein the first temperature is about 90 degrees Celsius and the second temperature is about 300 degrees Celsius.

30. The method according to any one of claims 25 - 29, wherein the porous structure defines an inner surface, and the metal coating is located on the inner surface of the polymeric substrate to define a continuous metal coating on the porous structure of the polymeric substrate including the inner surface.

31. The method according to any one of claims 25 - 30, wherein the metal coating is selected from the group consisting 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, the alloys including alloys with transition metals, and / or oxides thereof.

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

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

34. The composite material according to claim 1, wherein the conformal coating is a conductive coating having a metal retention rate of greater than 90 wt%.

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