Multiple density anode for anion exchange membrane water electrolyzers and associated methods

Abstract

An anode for an anion exchange membrane water electrolyzer is provided. The anode includes a multiple density porous transport layer (MDPTL), which may be considered a multiple porosity porous transport layer (MPPTL), and a catalyst layer coupled to the MDPTL. The MDPTL has at least a first portion that has a first density and a second portion that has a second density that is less than the first density. The first portion has a membrane facing side, is proximal the membrane, and is distal the bipolar plate. The second portion has a bipolar plate facing side, is distal the membrane, and proximal the bipolar plate. The catalyst layer, which is proximal to the membrane as compared to the MDPTL, is coupled to the membrane facing side of the first portion. In certain aspects, the MDPTL includes three or more portions with three or more densities.

Description

Attorney Docket No. [569611-8039031] MULTIPLE DENSITY ANODE FOR ANION EXCHANGE MEMBRANE WATER ELECTROLYZERS AND ASSOCIATED METHODS CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] The present application claims priority to United States Provisional Application Serial Number 63 / 651,011, filed May 23, 2024, titled multiple density anode for anion exchange membrane water electrolyzers and associated methods, and to United States Provisional Application Serial Number 63 / 681,417, filed August 9, 2024, titled multiple density anode for anion exchange membrane water electrolyzers and associated methods, the disclosures of which are both incorporated herein as if set out in full for all purposes. BACKGROUND

[0002] Hydrogen storage and water electrolyzers are linked in the context of a hydrogen economy. Water electrolyzers produce hydrogen by splitting water molecules using electricity to obtain hydrogen. The produced hydrogen can then be stored for later use, providing a means of energy storage to balance intermittent renewable energy sources such as wind and solar power. This process enables the conversion of excess renewable energy into hydrogen during periods of low demand, which can be stored and later converted back into electricity, or used as a clean fuel for transportation, heating, and industrial applications.

[0003] Efficient hydrogen production and storage methods are needed to ensure the viability and scalability of hydrogen as an energy management system By storing excess hydrogen generated through water electrolysis, it becomes possible to buffer the intermittent nature of other energy sources, such as, for example, renewable energy sources, and maintain a reliable energy supply. Water electrolyzers are a promising method of producing hydrogen.

[0004] Anion exchange membrane (AEM) water electrolyzers represent an advancement in electrolysis technology. The history of AEM water electrolyzers traces back to the mid-20th century when researchers began exploring various methods to enhance the efficiency and sustainability of hydrogen production. Traditional proton exchange membrane (PEM) 1 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031] electrolyzers dominated the field, but they faced limitations such as high costs associated with noble metal catalysts and susceptibility to corrosion.

[0005] In the early stages of AEM electrolyzer development, the focus was primarily on improving the durability and conductivity of the anion exchange membranes. Researchers have experimented with different polymer structures and chemistries to overcome the challenges posed by harsh electrolysis conditions.

[0006] By the late 20th century, significant progress had been made in the development of AEM water electrolyzers, leading to increased attention from both academia and industry. The improved understanding of membrane properties, coupled with advances in catalyst design and electrode engineering, contributed to the developments of AEM electrolysis systems. These advancements paved the way for scalable and cost-effective hydrogen production, positioning AEM electrolyzers as promising alternatives to conventional technologies.

[0007] In the early 21st century, efforts to optimize AEM water electrolyzers intensified, driven by the growing demand for clean energy solutions and the need to mitigate climate change. Research institutions, government agencies, and private companies have collaborated to further enhance the efficiency, reliability, and scalability of AEM electrolysis technology. Novel approaches such as electrode modification, membrane engineering, and system integration are being explored to unlock the full potential of AEM electrolyzers.

[0008] Recent years have witnessed a surge in the adoption of AEM water electrolyzers for various applications, including renewable hydrogen production, energy storage, and industrial processes. The continuous innovation in materials science, electrochemistry, and process engineering has led to significant improvements in performance and cost reduction. As a result, AEM electrolyzers are increasingly recognized as key enablers of the hydrogen economy, offering a sustainable pathway towards decarbonization and energy transition.

[0009] Looking ahead, ongoing research and development efforts aim to address remaining challenges such as membrane stability, electrode kinetics, and system efficiency. With continued advancements in materials design, manufacturing techniques, and operational strategies, AEM 2 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031] water electrolyzers are poised to play a pivotal role in shaping the future of clean energy infrastructure and driving the widespread adoption of hydrogen as a versatile energy carrier.

[0010] Even with the ongoing work associated with the development of AEM water electrolyzers, there are many components of AEM water electrolyzers that can be improved. For example, there is no "promising" anion exchange membrane electrode assembly, either anode or cathode, for AEM water electrolyzers. Thus, against this background, the technology of the present application provides for an improved anode for AEM water electrolyzers. SUMMARY

[0011] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary, and the foregoing Background, is not intended to identify key aspects or essential aspects of the claimed subject matter. Moreover, this Summary is not intended for use as an aid in determining the scope of the claimed subject matter.

[0012] In certain embodiments, the technology of the present application comprises an anode for an anion exchange membrane (AEM) water electrolyzer. The anode includes a multiple density porous transport layer (MDPTL), which may be considered a multiple porosity porous transport layer (MPPTL), and a catalyst layer coupled to the MDPTL. The MDPTL has at least a first portion that has a first density and a second portion that has a second density that is less than the first density. The first portion has a membrane facing side, is proximal the membrane, and is distal the bipolar plate. The second portion has a bipolar plate facing side, is distal the membrane, and proximal the bipolar plate. The catalyst layer, which is proximal to the membrane as compared to the MDPTL, is coupled to the membrane facing side of the first portion. In certain aspects, the MDPTL includes three or more portions with three or more densities. In certain aspects, the all the densities are different. In certain aspects, the densities in the different portions of the MDPTL decrease from the membrane facing side to the bipolar plate facing side in a gradient, which corresponds to the porosity increasing in the same direction.

[0013] In certain embodiments, the technology provides a method for manufacturing a multiple density porous transport layer (MDPTL). The method includes, among other things, 3 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031] providing a first group of fibrous particles into a form factor and providing a second group of fibrous particles, larger than the first group, on the first group of fibrous particles. The first and second group of fibrous particles are sintered. Once sintered, the first and second group of fibrous particles are densified into a MDPTL. In certain aspects, the first group of fibrous particles and the second group of fibrous particles are obtained by sieving a first batch of fibrous particles into a first group of finer fibrous particles and a second group of larger fibrous particles. In certain aspects, the first and second groups of fibrous particles have an aspect ratio of at least 25, and more preferably, of at least 30. In certain aspects, the method includes providing a third, fourth, or more groups of fibrous particles where each of the third, fourth, or more groups of fibrous particles are larger, or less fine, than earlier groups.

[0014] These and other aspects of the present system and method will be apparent after consideration of the Detailed Description and Figures herein. DRAWINGS

[0015] Non-limiting and non-exhaustive embodiments of the present invention, including the preferred embodiment, are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

[0016] Figure 1 depicts an anion exchange membrane (AEM) water electrolyzer consistent with the technology of the present application.

[0017] Figure 2 depicts a porous transport layer and catalyst layer for the anode of the AEM water electrolyzer of figure 1.

[0018] Figure 3 depicts a chart of fibrous particle size distribution for a batch of fibrous particles that may be used to form the multiple density porous transport layer consistent with the technology of the present application.

[0019] Figure 3A depicts an illustration of a dual density porous transport layer consistent with the technology of the present application.

[0020] Figure 3B depicts images of the membrane facing surface and the bipolar facing surface of the dual density porous transport layer of figure 3A. 4 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031]

[0021] Figure 4 depicts a chart of fibrous particle size distribution for a batch of fibrous particles that may be used to form the multiple density porous transport layer consistent with the technology of the present application.

[0022] Figure 4A depicts an illustration of a multiple density porous transport layer consistent with the technology of the present application. DETAILED DESCRIPTION

[0023] Embodiments are described more fully below with reference to the accompanying figures, which form a part hereof and show, by way of illustration, specific exemplary embodiments. These embodiments are disclosed in sufficient detail to enable those skilled in the art to practice the invention. However, embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. The following detailed description is, therefore, not to be taken in a limiting sense. Moreover, the technology of the present application will be described with relation to exemplary embodiments. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Additionally, unless specifically identified otherwise, all embodiments described herein should be considered exemplary.

[0024] The technology of the present application is described with specific reference to a porous transport layer for use as the anode in an AEM water electrolyzers. However, the technology described herein may be used with applications other than those specifically described herein. Other systems for which the technology of the present application may be useful include, without limitation, other fluid systems where a liquid or gas passes through a material (such as a metallic filter), a carbon dioxide to formic acid system, etc. Still other systems may include electromagnetic pollution material, haptic applications, directional heat flow materials used as, for example, heat wicking material for thermal solar and molten salt applications, neutron absorbing materials, or the like. The technology of the present application also may be applicable to other anodes, to cathodes, sealing applications, or the like. 5 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031]

[0025] The technology of the present application, as mentioned, focuses on using a porous transport layer (PTL) as a portion of the anode in an AEM water electrolyzer. The AEM water electrolyzer uses the PTL coated with a catalyst layer as the anode. Figure 1 shows a diagram of an AEM water electrolyzer 100 consistent with the technology of the present application. From the inside out, the AEM water electrolyzer 100 includes, among other things, an anion exchange membrane 102, an anode 104 and a cathode 106 on opposite sides of the anion exchange membrane 102, opposed flow channels 108, and opposed bipolar plates, 110. A power source 112 supplies power to the anode 104 and the cathode 106. Consistent with the technology as described in the present application, the anode 104 comprises a PTL 114 with a catalyst layer 116. The PTL 114 has a membrane facing side 118 and a bipolar plate facing side 120.

[0026] A detail of the anode 104 is shown in figure 2. Figure 2 shows a PTL 200 in more detail with a catalyst layer 202 and anion exchange membrane 204 in more detail. The catalyst layer 202 couples to the membrane facing side 118 of the PTL 200. The catalyst layer 202 may be coupled to the membrane facing side 118 of the PTL 200 by spray coating, for example.

[0027] During operation, as shown in figures 1 and 2, the power source 112 electrifies the AEM water electrolyzer 100. A water solution 206 entering the AEM water electrolyzer 100 is reacted on by the hydrogen evolution reaction (HER) cathode 106 to produce H2208, at least one spare electron 210, and at least one negative OH ion 212. The negative OH ion 212, and spare electron 210 defuses through the anion exchange member 102 to the oxygen evolution reaction (OER) anode 104 to produce O2212.

[0028] The various parts and components of the AEM water electrolyzer 100 are all important to the efficient and proper operation of the AEM water electrolyzer 100. The AEM water electrolyzer 100 is considered more feasible than either of alkaline electrolyzers and proton exchange membrane electrolyzers for a variety of reasons. For example, the AEM water electrolyzer has reduced corrosion issues as compared to proton exchange membrane electrolyzers allowing for use of less expensive metals. But there has been limited research into the PTL 114, 200.

[0029] There are a number of commercial and proprietary PTL 114, 200 available. The PTL 114, 200 of the AEM water electrolyzer 100 is important for a number of reasons. Although not 6 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031] to be bound by any particular theory of operation, for example, the PTL 114, 200 of the anode influences the water transport into the cell. The PTL 114, 200 of the anode also influences the electron transport to the catalyst. These are but two examples of the influence the PTL 114, 200 may have on the operation of the AEM water electrolyzer 100. Thus, it is apparent, an effective PTL 114, 200 would facilitate the overall operation of the AEM water electrolyzer.

[0030] PTLs 114, 200 are presently available as both commercial and proprietary products, technology. Commercial PTLs including, among others, Ni fiber paper from Dioxide Materials, stainless steel fiber paper from Bekaert, and sintered Ni felt also from Bekaert. Proprietary PTLs are available from, for example, the aforementioned companies as well as other companies such as Technetics Group LLC, who manufacture a series of FELTMETALTMPTLs from Ni, Ni Alloys, and stainless steels, to name but some of the available PTLs.

[0031] PTLs 114, 200, such as those mentioned above and others, have a range of characteristics including, among other things, density and porosity. Generally, the more dense a PTL, the less porous the PTL. Similarly, the more porous a PTL, the less dense the PTL. But the PTL 114, 200’s density and porosity both have advantages for use in AEM water electrolyzer 100. The technology of the present application provides a PTL with multiple densities and porosities to achieve the benefits of density and porosity.

[0032] PTLs for AEM water electrolyzer ideally would have a surface, the membrane facing side 118 identified above, that is sufficiently dense (i.e., a sufficient surface area) such that enough of the catalyst layer adheres to the PTL at a surface position (i.e., not into the depth of one or more pores). The catalyst layer may be adhered to the PTL surface using a number of techniques, such as, for example, spray coating the catalyst layer on the PTL. A dense surface of the PTL may provide sufficient surface area for the catalyst layer such that the catalyst causes an adequate conduction of electrons and current can flow relatively easily. Without sufficient surface area, the catalyst layer may debond or may have insufficient coverage such that the contact resistance will be higher than desirable, which may stop or slow the electrochemical reaction.

[0033] While a dense PTL is an improvement for the catalyst layer, providing better bonding and lower resistances, a dense PTL inhibits mass flow of H2O to the catalyst layer and O27 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031] (oxygen gas) bubbles created at the catalyst which must exit the system through the PTL, which also may slow or stop the electrochemical reaction. Thus, the PTLs for AEMs should have a lower density or higher porosity. At the cathode surface, H2O + electrons react to form H2bubbles and OH- ions (anions). The anions travel thru the membrane to the anode catalyst where the anions OH- react to form O2 gas and H2O water and electrons. The O2 and water must pass through the PTL.

[0034] In view of these divergent requirements, the technology of the present application provides a multiple density PTL for the anode in anion exchange membrane water electrolyzers and associated methods. The multiple density anode comprises a multiple density PTL having a first portion with a first density onto which a catalyst layer may be provided. The PTL has at least a second portion with a second density where the second density is less than the first density. The first portion of the PTL is between the second portion of the PTL and the catalyst layer. The second portion is proximal the bipolar plate of the OER portion of the AEM water electrolyzer 100 and the first portion is distal the bipolar plate of the OER portion of the AEM water electrolyzer 100.

[0035] The technology of the present application provides a multiple density PTL for the anode 104. A multiple density PTL, as used in the present application, comprises a porous transport layer that is formed to have at least two distinct densities, a first density in a first portion and a second density in a second portion, to form a dual density porous transport layer DDPTL) or, as explained further below, a multiple density porous transport layer (MDPTL). A steady density change from a first density to a second density is considered to be at least two distinct densities for the technology of the present application. The first density in the first portion and the second density in the second portion generally are described as the average density in the first, second portions as the density of any PTL may vary across the material. Also, first and second, or other designators, are simply to distinguish the various portions and properties and should not be considered limiting.

[0036] In the alternative, the technology of the present application provides a multiple porosity PTL (MPPTL) where the PTL is formed to have at least two distinct porosities. A first portion of the PTL has a first porosity and the second portion of the PTL has a second porosity 8 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031] distinctly different than the first porosity. A steady porosity change from a first porosity to a second porosity is considered to be at least two distinct porosities for the technology of the present application. The porosity is the average porosity of the porous transport layer as the porosity of the portions of the porous transport layer may have different porosities. In this application, density and porosity are generally used interchangeably as opposite types of properties. But, it is feasible based on material selection, that a MDPTL may have multiple average density portions and a consistent average porosity. Also, it is feasible based on material selection, that a MPPTL may have multiple average porosity portions and a consistent average density. Generally, the present application uses MDPTL and MPPTL interchangeably in context.

[0037] PTLs, in general, may be formed by a matrix of sintered metallic particles. A large number of metals may be used to form PTLs. The technology described herein generally focuses on Ni (Nickel), Fe (Iron including stainless steel), Co (Cobalt), Ti (Titanium), as well as other high strength and high temperature alloys to name but a few. Specific particles include, but are not limited to, austenitic stainless steel (including Stainless Steel 321), Nickel, HastelloyTM, and FeCrAlY. The particles making up a PTL may be a single composition or a mixture of different compositions. For example, as explained above, the MDPTL may have a first portion made of a first composition of particles and a second portion made of a second composition of particles. Also, the metal particles can be the only component of the PTL, but other particles or compositions may be included as well. The particles making up the PTL may be spherical or fibrous in shape. Fibrous particles tend to be elongated members while spherical particles are close to a sphere. The present technology forms PTLs using elongated, or fibrous, particles having a pre-sintered aspect ratio of at least 5.0, but may be in the range of 10 to 100 in some instances. In other embodiments, the aspect ratio may be between about 15 and 50, and in still other embodiments, the aspect ratio is between about 25 and 35, with an aspect ratio of 30 working well. In certain embodiments the aspect ratio is at least 30 and, in other embodiments, the aspect ratio is no more than 50. The aspect ratio is the ratio of the length of the particle over the diameter of the particle. For comparison, a spherical particle has an aspect ratio of 1, or approximately 1. For purposes of the present technology, an aspect ratio below 3 is considered a particle, and an aspect ratio equal to or above 3 is considered a fiber or elongated particle. 9 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031]

[0038] To form the PTLs, the fibrous, or elongated, particles are prepared, deposited, sintered, densified, and finished. The preparation of the particles generally includes cleaning with a solution, drying the fibrous particles, and sizing the fibrous particles. Figure 3 shows a fibrous particle distribution prior to forming the PTL. In this exemplary PTL, the aspect ratio of the fibrous particles was 30, which means the length of the metallic particle is 30 times the diameter of the metallic particle’s cross-sectional diameter. As shown in figure 3, the fibrous particles 300 generally have a distribution across a range of sizes, which could be length or diameter in certain aspects. The batch of fibrous particles 300 has a particle size distribution (PSD) ranging from 38 microns or less to upwards of over 300 microns or more. As is shown in figure 3, PSD of the batch of fibrous particles 300, in this exemplary embodiment, has more than 60% of the fibrous particles with PSD finer than 150 microns and about 20% of the fibrous particles are larger than 212 microns. The remaining fibrous particles have PSD between about 150 microns and 212 microns, although the actual distribution should be considered exemplary and non-limiting. Conventional formation techniques to make PTL would use the batch of fibrous particles 300 together to form the PTL, which would have a generally consistent density and porosity. However, to make the MDPTL, the batch of fibrous particles 300 is first separated into different categories based on the PSD. For example, to form a dual density MDPTL, the fibrous particles 300 may be separated into a first group of fibrous particles 302 with, for example, the finer particles of less than 150 microns and a second group of fibrous particles 304 with the larger particles. The fibrous particles 300 may be separated into the first group of fibrous particles 302 and the second group of fibrous particles 304 using any procedure to separate the particles, such as, for example, sieving the particles. Alternatively, rather than separating a first batch of fibrous particles 300, the first group of fibrous particles 302 may be formed with a first, finer specification and the second group of fibrous particles 304 may be formed with a second, larger specification. The separation may be all fibrous particles finer than 150 microns are in the first group and the remaining fibrous particles are considered larger and in the second group. Alternatively, the first group may be all particles finer than 150 microns are in the first group and all particles larger than 212 microns are in the second group, although the specific dimensions outlined herein are exemplary and not limiting. Thus, a third group of particles between the first group and second group (less fine than the first group, but not as large as the second group) are discarded or repurposed. In other words, the separation does not have to 10 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031] be on a continuum. In certain aspects, the PSD may be based on the cross-sectional diameter of the fibrous particles, such that finer and larger fibrous particles relate to smaller and bigger diameters. In other aspects, the PSD may be based on the length of the fibrous particles, such that the finer and larger fibrous particles relate to shorter and longer fibers. In still other aspects, the PSD may be based on both the cross-sectional diameter and the length of the fibrous particles. As can be appreciated, smaller diameters and shorter lengths allow the fibrous particles to be formed with increased density as compared to larger diameters and longer lengths. While the PSD is described as a range a range from a minimum to a maximum for a wt% of material. The individual particle dimension that is controlling, such as whether or not it falls thru the sieve screen, could be diameter or length, and typically is length. Also, a person of ordinary skill in the art on reading the disclosure would understand that diameter and length are terms relating to the spatial features of the fibrous particles as the particles are often imperfect. Terms relating to the range of diameters and lengths may more appropriately be considered a feret diameter or a chord length as those terms are generally understood.

[0039] Once separated into the first and second group of fibrous particles 302, 304, which may be called a finer or smaller group of particles 302 and a course or larger group of particles 304. For completeness, the finer or smaller fibers generally will have a maximum feret diameter below the median feret diameter. Coarse or larger fibers will have a maximum feret diameter above the median of a given PSD. In one embodiment of the technology, finer fibers are less than 150 microns and coarse fibers are greater than 212 microns. In any event, he first group of fibrous particles 302 is deposited into a sheet form factor, with a low thickness. The second group of fibrous particles 304 is deposited on top of the deposited first group of fibrous particles 302. The second group of fibrous particles 304 is deposited on the sheet form factor, also with a low thickness such that the first and second group of fibrous particles 302, 304 has the same thickness, although the first and second groups of fibrous particles 302, 304 may have different thicknesses in certain aspects. Notice, while called a sheet form factor, the form factor may take many shapes. Generally, a low thickness is considered less than one (1) inch, but in certain applications the thickness of the groups may be a few inches or more.

[0040] Next, the first and second group of fibrous particles are sintered. The first and second group of fibrous particles may be sintered using, for example, a vacuum furnace or other device. 11 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031] The sintering step is performed at a high temperature and low pressure. The high temperature depends on the metals in use, but is generally just less than the metals melting temperature. Similarly, the pressure depends on the material (as well as other conditions of operation) such that the low pressure is typically below atmospheric pressure and, in certain instances, may be a vacuum. This allows the fibrous particles to bond at contact points to unitize the metallic particles and the first and second groups of fibrous particles such that a single, integral MDPTL is formed with a first layer comprising the first group of fibrous particles and a second layer comprising the second group of fibrous particles.

[0041] Once sintered into a unified sheet, the sintered sheet is densified. Densification can be accomplished using any traditional method, such as, for example, roller milling or the like. The densification generally densifies the structure between 20% and 80% dense, although even more or less % dense is possible. As used herein, 20% dense means for any volume 20% of the volume is occupied by the substance and 80% of the volume is occupied by pores (or, said another way, 80% of the volume is space or voids). So, 80% dense would indicate 80% of the volume is occupied by the substance. The density of the MDPTL also may be measured as % density where %density equals (the density of the sintered material / density of a solid block of the alloy (not sintered))*100. For example, a MDPTL made of a layer of 20%density Hastelloy has a 0.2*(the density of solid Hastelloy), which would be 1.4g / cc where solid Hastelloy has a density of 8.22g / cc.

[0042] The depositing, sintering, and densification steps would be similar if the fibrous groups are from two (2) different specified fibrous particles. Different specified fibrous particles means, in certain aspects, altering the lengths, diameter, materials, etc. In other words, for example, instead of separating the fibrous particles into finer and larger particle groups, the fibrous particles are purchased as a finer particle group and a larger particle group.

[0043] Figure 3A shows a cross-sectional view of a dual MDPTL 310. The dual MDPTL 310 has a membrane facing side 312 and a bipolar plate facing side 314. The dual MDPTL has a first portion 316 with a first density. The first portion 316 may be considered a first layer 316. The dual MDPTL 310 also has a second portion 318 with a second density. The second density is less than the first density. The second portion 318 may be considered a second layer 318. Figure 3B 12 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031] shows an image of the membrane facing side 312, which is more dense and less porous, and the bipolar plate facing side 314, which is less dense and more porous.

[0044] In certain embodiments, the first group of fibrous particles 302 may be formed from a first group of metals. The first group of metals may include Ni, Fe, Co, and the like. The second group of fibrous particles 304 may be formed from a second group of metals. The second group of metals may include Ni, Fe, Co, and the like. In certain embodiments, the first group of fibrous particles is formed from the same metal as the second group of fibrous particles. In certain embodiments, the first group of fibrous particles is formed from a different metal than the second group of fibrous particles.

[0045] Alternatively to depositing the first group of fibrous particles 302 and the second group of fibrous particles 304, and subsequently sintering the two groups and densifying the sheet, the MDPTL may be formed by depositing a first group of fibrous particles in a sheet form factor, sintering the first group of fibrous particles, and densifying the first group of fibrous particles into a first PTL layer. The second group of fibrous particles also would be deposited into a sheet form factor (the same form factor as the first group and / or an identical form factor), sintered, and densified into a second PTL layer, where the second PTL layer has a density less than the first PTL layer. The first PTL layer and the second PTL layer may be joined or coupled. The first PTL layer and the second PTL layer may be adhered, welded, pressed together, or the like. When made as separate sintered and densified layers, the first and second PTL layers may be coupled by a further sintering step in some embodiments.

[0046] Figures 3, 3A, 3B and the above describes a dual (two (2)) density porous transport layer (DDPTL). The MDPTL may have more than a first portion with a first density and second portion with a second density. Rather, the MDPTL may have at least three (3) or more portions with three (3) or more densities. Figure 4 shows a PSD with eight (8) different groups, a first (or initial) group of fibrous particles, a second (or intermediate) group of fibrous particles, a third (or intermediate) group of fibrous particles, a fourth (or intermediate) group of fibrous particles, a fifth (or intermediate) group of fibrous particles, a sixth (or intermediate) group of fibrous particles, a seventh (or intermediate) group of fibrous particles, and an eight (or last) group of fibrous particles. Similar to the above, the groups would be deposited in a sheet form factor to a 13 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031] low thickness with the finest group first followed by successively larger, more coarse or less fine, groups until the final layer of the eight group of fibrous particles. The sheet would be sintered and densified such that an eight layer MDPTL was formed. The MDPTL would have an initial portion, six (intermediate) portions, and a final portion. Of course, this is one example of a MDPTL. The MDPTL may have just the initial portion and the final portion (a / k / a DDPTL) or the MDPTL as few as three (3) intermediate portions to as many as are reasonable for the design of the AEM water electrolzyer.

[0047] The eight layer MDPTL also may be formed by sintering and densifying each group of particles individually. The eight layers may subsequently coupled together as described above with the dual density PTL. In some aspect, the layers may be coupled by a lamination step.

[0048] Figure 4A shows a MDPTL 400 with eight layers (or portions) 401-408 including the initial layer 401, intermediate layers 402-407, and final layer 408. The MDPTL 400 has a membrane facing side 409 and a bipolar plate facing side 410, which is opposite the membrane facing side 409. Each of the layers 401-408 have a different density with initial layer 401 being the densest and each intermediate portion 402-407, and final portion 408 being successively less dense. The density may decrease evenly in certain embodiments. In other embodiments, the density decreases may be designed such that the decrease changes from layer to layer.

[0049] It is envisioned that the most dense, least porous layer will be the layer on which the catalyst layer is deposited. It is further envisioned that subsequent layers (outwards from the membrane, closer to the bipolar plates) would be of decreasing density and increasing porosity. However, in certain embodiments, the density / porosity may be approximately the same in successive layers, such as, for example, if there is a material change between layers. Generally, the MDPTL has been described as an ordered arrangement of most dense to least dense layer, which it is envisioned will be beneficial for AEM water electrolyzers. However, in certain embodiments, the MDPTL may have alternative arrangements other than most dense to least dense. In certain aspects, the layers may alternate more or less dense. In still other embodiments, there may be multiple layers that are equally dense. Yet other arrangements are also possible.

[0050] Although the technology has been described in language that is specific to certain structures, materials, and methodological steps, it is to be understood that the invention defined 14 HB: 4925-4241-6709.1Attorney Docket No. [569611-8039031] in the appended claims is not necessarily limited to the specific structures, materials, and / or steps described. Rather, the specific aspects and steps are described as forms of implementing the claimed invention. Since many embodiments of the invention can be practiced without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. Unless otherwise indicated, all numbers or expressions, such as those expressing dimensions, physical characteristics, etc. used in the specification (other than the claims) are understood as modified in all instances by the term “approximately.” At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the claims, each numerical parameter recited in the specification or claims which is modified by the term “approximately” should at least be construed in light of the number of recited significant digits and by applying ordinary rounding techniques. Moreover, all ranges disclosed herein are to be understood to encompass and provide support for claims that recite any and all subranges or any and all individual values subsumed therein. For example, a stated range of 1 to 10 should be considered to include and provide support for claims that recite any and all subranges or individual values that are between and / or inclusive of the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less (e.g., 5.5 to 10, 2.34 to 3.56, and so forth) or any values from 1 to 10 (e.g., 3, 5.8, 9.9994, and so forth). 15 HB: 4925-4241-6709.1

Claims

Attorney Docket No. [569611-8039031] CLAIMS What is claimed is:

1. An anode configured for use with an anion exchange membrane (AEM) water electrolyzer, the anode comprising: a dual density porous transport layer (DDPTL) having a membrane facing surface and a bipolar plate facing surface opposite the membrane facing surface, wherein the porous transport layer comprises a first portion having a first density and a first porosity and a second portion having a second density and a second porosity, wherein the DDPTL is an arranged order of the membrane facing surface, the first portion, the second portion, and the bipolar plate facing surface; and a catalyst layer coupled to the membrane facing surface of the DDPTL.

2. The anode configured for use with the AEM water electrolyzer of claim 1, wherein the DDPTL comprise sintered and densified fibrous metal particles.

3. The anode configured for use with the AEM water electrolyzer of claim 2, wherein the metal particles are selected from the group of metal particles consisting of: nickel, iron, or cobalt.

4. The anode configured for use with the AEM water electrolyzer of claim 2, wherein the first portion is formed from a first group of fibrous metal particles and the second portion is formed from a second group of fibrous metal particles wherein the first group is finer than the second group.

5. The anode configured for use with the AEM water electrolyzer of claim 1, wherein the catalyst layer is spray coated to the membrane facing surface. 16 4925-4241-6709.1Attorney Docket No. [569611-8039031] 6. An anode configured for use with an anion exchange membrane (AEM) water electrolyzer, the anode comprising: a multiple density porous transport layer (MDPTL) having a membrane facing surface and a bipolar plate facing surface opposite the membrane facing surface, wherein the porous transport layer comprises: an initial portion having an initial portion density, the initial portion being proximate the membrane facing surface; an intermediate portion having an intermediate density; a final portion having a final portion density, the final portion being proximate the bipolar plate facing surface, wherein the final density is less than the initial portion density, and the intermediate portion being between the initial portion and the final portion where the intermediate density is between the initial density and the final density; and a catalyst layer coupled to the membrane facing surface of the DDPTL.

7. The anode configured for use with the AEM water electrolyzer of claim 6, wherein the intermediate portion comprises a plurality of intermediate portions.

8. The anode configured for use with the AEM water electrolyzer of claim 7, wherein the plurality of intermediate portions have a plurality of intermediate densities decreasing from the initial density to the final density.

9. The anode configured for use with the AEM water electrolyzer of claim 8, wherein the plurality of intermediate densities decrease evenly from the initial density to the final density.

10. The anode configured for use with the AEM water electrolyzer of claim 6, wherein the MDPTL is formed from sintered and densified metallic fibrous particles.

11. The anode configured for use with the AEM water electrolyzer of claim 10, wherein the metallic fibrous particles are selected from a group of metals consisting of: nickel, iron, cobalt, or a combination thereof. 17 4925-4241-6709.1Attorney Docket No. [569611-8039031] 12. A method of making a multiple density porous transport layer, comprising: obtaining a form factor; layering an initial group of elongate, fibrous particles having an initial diameter in the form factor; layering a final group of elongate, fibrous particles having a final diameter in the form factor on top of the initial group of elongate fibrous particles, wherein the final diameter is greater than the initial diameter; sintering the layered initial group of elongate, fibrous particles and the final group of elongate, fibrous particles to form a sintered sheet having an initial layer and a final layer; and densifying the sintered sheet to form the multiple density porous transport layer.

13. The method of claim 12 comprising providing a first batch of elongate, fibrous particles having a plurality and separating the first batch of elongate, fibrous particles into the initial group of fibrous particles and the final group of fibrous particles.

14. The method of claim 13, wherein the step of separating comprises sieving.

15. The method of claim 12, wherein the initial group of elongate, fibrous particles and the final group of elongate, fibrous particles have an aspect ratio of at least 30.

16. The method of claim 12, comprising layering an intermediate group of elongate, fibrous particles having an intermediate diameter greater than the initial diameter and less than the final diameter subsequently to layering the initial group of elongate, fibrous particles and prior to layering the final group of elongate, fibrous particles.

17. The method of claim 16, wherein layering an intermediate group of elongate, fibrous particles comprises layering a plurality of intermediate group elongate, fibrous particles.

18. A method of making a multiple density porous transport layer, comprising: obtaining a form factor; 18 4925-4241-6709.1Attorney Docket No. [569611-8039031] layering an initial group of elongate, fibrous particles having an initial diameter in the form factor; sintering the initial group of elongate, fibrous particles into an initial sintered sheet; densifying the initial sintered sheet to form a porous transport layer having an initial density; layering a final group of elongate, fibrous particles having a final diameter in the form factor, wherein the final diameter is greater than the initial diameter; sintering the final group of elongate, fibrous particles to form a final sintered sheet; densifying the final sintered sheet to form a porous transport layer having a final density less than the initial density; and coupling the porous transport layer having the initial density to the porous transport layer having the final density to form the multiple density porous transport layer.

19. The method of claim 18 further comprising: layering an intermediate group of elongate, fibrous particles having an intermediate diameter in the form factor, wherein the intermediate diameter is greater than the initial diameter and less than the final diameter; sintering the intermediate group of elongate, fibrous particles to form an intermediate sintered sheet; densifying the intermediate sintered sheet to form a porous transport layer having an intermediate density less than the initial density and greater than the final density; and coupling the porous transport layer having the intermediate density between the porous transport layer having the initial density and the porous transport layer having the final density to form the multiple density porous transport layer.

20. The method of claim 19, wherein the steps are repeated for a plurality of times. 19 4925-4241-6709.1

Images