Catalyst coating layers and electrically conductive layers within electrochemical cells

Abstract

The following disclosure relates to catalyst coating layers and electrically conductive layers for electrochemical cells. In certain examples, the catalyst coating layer is a cathode catalyst coating layer positioned on a surface of a membrane of an electrochemical cell, including an ionomer and a catalyst composition comprising platinum. The cathode catalyst coating layer composition includes 0.1 mg Pt / cm2 to 2 mg Pt / cm2 of the cathode catalyst coating layer composition. In other examples, the catalyst coating layer includes an ionomer, a catalyst comprising a plurality of crystallites, and an acid-stable support material having a plurality of pores with an average opening diameter greater than an average diameter of individual crystallites of the catalyst, such that individual crystallites of the catalyst are embedded within the pores of the support material. The catalyst coating layers advantageously provide cost savings over the current state of the art by reducing the amount of catalyst needed.

Description

CATALYST COATING LAYERS AND ELECTRICALLY CONDUCTIVE LAYERS WITHIN ELECTROCHEMICAL CELLS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 673,852, filed July 22, 2024, and U.S. Provisional Patent Application No. 63 / 710,683, filed October 23, 2024, which are hereby incorporated by reference in their entireties.FIELD

[0002] The following disclosure relates to electrochemical cells and components thereof. More specifically, the following disclosure relates to catalyst coating layers and electrically conductive layers within electrochemical cells that are advantageous in improving cell performance.BACKGROUND

[0003] Hydrogen has been considered as an ideal energy carrier to store renewable energy. Proton exchange membrane water electrolysis (PEMWE) as a means for hydrogen production offers high product purity, fast load response times, small footprints, high efficiencies, and low maintenance efforts. It is regarded as a promising technology, especially when coupled with renewable energy sources.

[0004] An electrochemical cell or system uses electrical energy to drive a chemical reaction. For example, water is split to form hydrogen and oxygen. The products may be used as energy sources for later use. In recent years, improvements in operational efficiency have made electrolyzer systems competitive market solutions for energy storage, generation, and / or transport. For example, the cost of generation may be below $6 per kilogram of hydrogen in some cases. Increases in efficiency and / or improvements in operation will continue to drive the installation of electrolyzer systems.

[0005] Various challenges are present with operation at or near the membrane of an electrochemical cell. For example, ion exchange membrane (IEM) performance may be related to the thickness of the membrane. That is, a thinner membrane may conduct more protons / current for a given overpotential. However, thin membranes may be problematic because of an increased risk of loss of mechanical and chemical integrity due to degradation during operation.

[0006] It is specifically desired for improved performance properties within electrochemical cells, including improved catalyst coating layers for the ion exchange membranes as well as additional layers within the electrochemical cell positioned adjacent to the membrane or a catalyst coating layer.SUMMARY

[0007] In one embodiment, a cathode catalyst coating layer is provided for an electrochemical cell. The cathode catalyst coating layer includes a cathode catalyst coating layer composition having an ionomer and a catalyst composition including platinum (Pt). The cathode catalyst coating layer composition includes 0.1 mg Pt / cm2to 2 mg Pt / cm2of the cathode catalyst coating layer composition, and the cathode catalyst coating layer is configured to be positioned on a surface of a membrane of the electrochemical cell such that the cathode catalyst coating layer is positioned between a cathode flow field and the membrane of the electrochemical cell.

[0008] In another embodiment, a catalyst coating layer configured to coat a membrane surface of an electrochemical cell is provided. The catalyst coating layer includes an ionomer, a catalyst comprising a plurality of crystallites, and an acid-stable support material having a plurality of pores. The plurality of pores has an average opening diameter that is greater than an average diameter of individual crystallites of the crystal such that individual crystallites of the catalyst are embedded within the pores of the support material.

[0009] In another embodiment, a catalyst coated membrane is provided, wherein the catalyst coated membrane includes a membrane of an electrochemical cell and a catalyst coating layer, wherein the catalyst coating layer is positioned on a surface of the membrane, wherein the catalyst coating layer includes an ionomer, a catalyst including a plurality of crystallites, and an acid-stable support material having a plurality of pores. The plurality of pores has an average opening diameter that is greater than an average diameter of individual crystallites of the crystal such that individual crystallites of the catalyst are embedded within the pores of the support material.

[0010] In another embodiment, an electrochemical cell is provided, wherein the cell includes an anode flow field, a cathode flow field, a membrane positioned between the anode flow field and the cathode flow field. The cell further includes a cathode catalystcoating layer positioned on a surface of the membrane and between the cathode flow field and the membrane, wherein the cathode catalyst coating layer includes a cathode catalyst coating layer composition having an ionomer and a catalyst composition including platinum (Pt). The cathode catalyst coating layer composition includes 0.1 mg Pt / cm2to 2 mg Pt / cm2of the cathode catalyst coating layer composition.

[0011] In another embodiment, an electrochemical cell is provided, wherein the cell includes an anode flow field, a cathode flow field, a membrane positioned between the anode flow field and the cathode flow field, a catalyst coating layer positioned between the membrane and the anode flow field or the cathode flow field, and an electrically conductive layer positioned between the membrane and the catalyst coating layer.

[0012] In another embodiment, an electrochemical cell is provided, wherein the cell includes an anode flow field, a cathode flow field, a membrane positioned between the anode flow field and the cathode flow field, and a catalyst coating layer. The electrochemical cell further includes the catalyst coating layer positioned on a surface of the membrane, wherein the catalyst coating layer includes an ionomer, a catalyst including a plurality of crystallites, and an acid-stable support material having a plurality of pores. The plurality of pores has an average opening diameter that is greater than an average diameter of individual crystallites of the crystal such that individual crystallites of the catalyst are embedded within the pores of the support material.

[0013] In another embodiment, a method for forming a catalyst coating layer is provided. The method includes providing a gel composition having a catalyst support precursor including a metal chloride. The method further includes heating the gel composition to a calcination temperature to oxidize the catalyst precursor metal chloride to form an acid-stable support material comprising a metal oxide or metal oxo-acid salt and a plurality of pores. The method further includes mixing the acid-stable support material with a catalyst containing a plurality of crystallites wherein the plurality of pores of the acidstable support material has an average opening diameter that is greater than an average diameter of individual crystallites of the catalyst such that individual crystallites of the catalyst are embedded within the pores of the acid-stable support material during the mixing to provide a mixed catalyst-support material composition. The method furtherincludes drying the mixed catalyst-support material composition to provide a catalystsupport material powder. The method further includes combining the catalyst-support material powder with an ionomer to form the catalyst coating layer.

[0014] 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 is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Exemplary embodiments are described herein with reference to the following drawings.

[0016] Figure 1 depicts an example of an electrochemical system including an electrochemical stack having a plurality of electrochemical cells.

[0017] Figure 2 depicts an example of an electrochemical cell.

[0018] Figure 3 depicts an additional example of an electrochemical cell.

[0019] Figure 4 depicts an example of improved cell efficiency via a reduced voltage requirement at a fixed current density.

[0020] Figure 5 depicts examples of operating power (kWh) per mass of hydrogen gas generation (kg) as a function of current density for ionomers within the cathode catalyst coating layer with varying equivalent weights (EW).

[0021] Figure 6 depicts an example a portion of an electrochemical cell having an electrically conductive layer positioned between a catalyst coating layer and a membrane of the cell.

[0022] Figure 7 depicts an alternative example a portion of an electrochemical cell having an electrically conductive layer, wherein the catalyst coating layer is positioned between the electrically conductive layer and the membrane of the cell.

[0023] Figure 8 depicts an example of performance data for various catalyst coating layers.

[0024] Figure 9 depicts a flow chart describing a method for forming a catalyst coating layer.DETAILED DESCRIPTION

[0025] The following disclosure describes improved catalyst coating layers adjacent to the membrane, cathode catalyst coating layers, and / or the addition of an electrically conductive layer adjacent to the membrane or catalyst coating layer. The inclusion of such a layer or layers within the electrochemical cell may provide improved efficiency within the electrolytic reaction while achieving cost savings. This may further lead to reduction in the amount of power required to run the electrochemical reaction, therein leading to a reduction in the cost of producing hydrogen gas.

[0026] Specifically, the following disclosure describes an improved cathode catalyst coating layer having a higher loading of active catalyst (e.g., platinum) within the catalyst coating composition, contrary to the current teaching in the art. This larger catalyst loading, while in certain cases maintaining a same catalyst coating structure on the anode side of the electrochemical cell, may lead to improved cell performance / efficiency, including the ability to run the electrochemical reaction within the cell / stack / plant under a fixed high current density with a lowered voltage (and thus overall lower power requirement) in comparison to the state of the art. This advantageously may lead to an overall reduced kWh / kg cost of producing hydrogen gas. The improved cathode catalyst coating layer may provide additional advantages as well, such as increased / improved cell durability / life, increased / improved membrane durability or life, the ability to include a thinner membrane to the cell leading to lower operation resistance losses, and / or other benefits ultimately responsible for an increase in hydrogen efficiency or an overall reduced kWh / kg cost of producing hydrogen gas.

[0027] Additionally, the following disclosure describes the inclusion of an electrically conductive layer that may be positioned adjacent to the membrane or a catalyst coating layer of the membrane to provide additional operating efficiency improvements when combined with the cathode catalyst coating layer, or on its own independent of the inclusion of such an improved catalyst coating layer. The efficiency improvements may relate to the reduced kWh / kg operating cost of producing hydrogen gas, increased / improved cell life, increased / improved membrane durability or life, the ability to include a thinner membrane to the cell leading to a more efficient electrolysis system.

[0028] Additionally, the following disclosure describes an improved catalyst coating layer (e.g., an anode catalyst coating layer) having a lower loading amount of catalyst (i.e., iridium) within the catalyst coating composition while achieving similar performance results as current teaching in the art. This lower catalyst loading may lead to better dispersing of catalyst and improved utilization of the catalyst active sites, as well as a reduction in the amount of catalyst purchased for manufacturing. Additionally, this lower catalyst loading may lead to creating a more stable catalyst reaction by allowing the sintering to occur more slowly or be less prone to poisoning and deactivation. This advantageously may lead to an overall reduced cost of producing hydrogen gas. The improved catalyst coating layer may provide additional advantages as well, such as increased / improved cell durability / life, increased / improved membrane durability or life, the ability to include a thinner membrane to the cell leading to lower operation resistance losses, and / or other benefits ultimately responsible for an increase in hydrogen efficiency or an overall reduced kWh / kg cost of producing hydrogen gas.Electrochemical Cells and Systems

[0029] Figure 1 depicts an example of an electrochemical system including an electrochemical stack having a plurality of electrochemical cells. In certain examples, the electrochemical stack may contain 50-1000 cells, 50-100 cells, 500-700 cells, or more than 1000 cells. Any number of cells may make up a stack. The electrochemical cells within the electrochemical stack may be configured to operate with 200 mV or less of pure resistive loss when operating at a high current density (e.g., at least 3 Amps / cm2, at least 4 Amps / cm2, at least 5 Amps / cm2, at least 6 Amps / cm2, at least 7 Amps / cm2, at least 8 Amps / cm2, at least 9 Amps / cm2, at least 10 Amps / cm2, at least 11 Amps / cm2, at least 12 Amps / cm2, at least 13 Amps / cm2, at least 14 Amps / cm2, at least 15 Amps / cm2, at least 16 Amps / cm2, at least 17 Amps / cm2, at least 18 Amps / cm2, at least 19 Amps / cm2, at least 20 Amps / cm2, at least 25 Amps / cm2, at least 30 Amps / cm2, in a range of 1-30 Amps / cm2, in a range of 3-20 Amps / cm2, in a range of 3-15 Amps / cm2, in a range of 3-10 Amps / cm2, or in a range of 10-20 Amps / cm2). In additional examples, the amount of water (e.g., deionized (DI) water) transferred to or circulated through each cell of the stack may may be less than 5 mL / Amp / cell / min, less than 1 mL / Amp / cell / min, less than 0.5 mL / Amp / cell / min, less than0.1 mL / Amp / cell / min, less than 0.05 mL / Amp / cell / min. In other examples, the amount of water transferred to or circulated through each cell of the stack may be in a range of 0.05- 0.1 mL / Amp / cell / min, 0.05-0.25 mL / Amp / cell / min, 0.05-0.5 mL / Amp / cell / min, 0.05-1 mL / Amp / cell / min, 0.05-5 mL / Amp / cell / min, 0.1-1 mL / Amp / cell / min, 0.1-5 mL / Amp / cell / min, 0.25-1 mL / Amp / cell / min, in a range of 0.25-5 mL / Amp / cell / min, or in a range of 0.5-1 mL / Amp / cell / min.

[0030] As illustrated in the system of Figure 1, water (H2O) may be supplied to the anodic inlet of an electrolytic cell stack 12. In some embodiments, only the anodic inlet of the cell stack 12 may receive water. In these embodiments, the cathode side of the cell stack 12 may not receive water (e.g., a dry cathode side may be used). In another embodiment, a cathode inlet may also receive water, wherein the water may be supplied to the cathode inlet to cool the cell stack 12 during electrolysis.

[0031] The water supplied to the anodic inlet flows to an anodic inlet manifold that distributes the water to the anode side of the plurality of cells contained with the cell stack 12. In embodiments where water is supplied to the cathode inlet, water supplied to the cathode inlet flows to a cathodic inlet manifold that distributes the water to the cathode side of the plurality of cells in the cell stack 12. In certain examples, the amount of water (e.g., deionized (DI) water) transferred to or circulated through each cell of the stack may be in a range of 0.25-5 mL / Amp / cell / min.

[0032] During electrolysis, oxygen (O2) is produced at the anode side of the electrolytic cells and hydrogen ( H 2) is produced at the cathode side of the electrolytic cells. Specifically, a water splitting electrolysis reaction is configured to take place within each individual cell in the cell stack 12. Each cell includes one interface (the anode side of the cell) configured to run an oxygen evolution reaction (OER) and another interface (the cathode side of the cell) configured to run a hydrogen evolution reaction (HER) (such as depicted in Figure 2).

[0033] During electrolysis, some of the water supplied to the anode side of an electrolytic cell may not be converted into oxygen. Accordingly, a two-phase flow of oxygen and unreacted water is outlet from each of the anode sides of the cells into an anodic outlet manifold 13. The two-phase flow of oxygen and unreacted water flows from out of the cell stack 12 through the anodic outlet manifold 13. This stream within the anodic outletmanifold 13 may be configured to be transferred to a gas detection and conditioning system, such as described in greater detail below, for analysis of the composition within the stream. Specifically, this anodic stream may be analyzed to identify if any undesirable hydrogen gas has leaked (i.e., cross-leaked) across the membranes from the cathode sides of the cells to the anode sides of the cells within the cell stack.

[0034] Additionally, in some embodiments, water may be supplied to the cathode side of the cell stack as a coolant. Accordingly, a two-phase flow of hydrogen and water is outlet from each of the cathode sides of the cells to a cathodic outlet manifold 14. The two-phase flow of hydrogen and water flows out of the cell stack 12 through the cathodic outlet manifold 14. Similarly, this particular stream within the cathodic outlet manifold 14 may be configured to be transferred to a gas detection and conditioning system (separate from the anodic gas detection and conditioning system) for analysis of the composition within the stream. Specifically, this cathodic stream may be analyzed to identify if any undesirable oxygen gas has leaked (i.e., cross-leaked) across the membranes from the anode sides of the cells to the cathode sides of the cells within the cell stack.

[0035] Figure 2 depicts an example of an electrochemical or electrolytic cell for hydrogen gas and oxygen gas production through the splitting of water. The electrochemical cell within Figure 2 may be one of the plurality of cells within the electrochemical stack in Figure 1. The electrochemical cell includes a cathode, an anode, and a membrane positioned between the cathode and anode. The membrane may be a proton exchange membrane (PEM) that may have a catalyst coating on one or both surfaces of the PEM. In other examples, the membrane may be positioned within an electrochemical cell having a catalyst coating on an adjacent supporting layer within the cell (e.g., a gas diffusion layer or porous transport layer near or abutting the membrane).

[0036] Proton Exchange Membrane (PEM) electrolysis involves the use of a solid electrolyte or ion exchange membrane. Within the water splitting electrolysis reaction, one interface runs an oxygen evolution reaction (OER) while the other interface runs a hydrogen evolution reaction (HER). For example, the anode reaction is H2O->2H++>2O2+2e and the cathode reaction is 2H++2e->H2.

[0037] Figure 3 depicts an additional example of an electrochemical or electrolytic cell. Specifically, Figure 3 depicts a portion of an electrochemical cell 300 having a cathode flow field 302, an anode flow field 304, and a membrane 306 positioned between the cathode flow field 302 and the anode flow field 304.

[0038] In certain examples, the membrane 306 may be a catalyst coated membrane (CCM) having a cathode catalyst layer 305 and / or an anode catalyst layer 307 positioned on respective surfaces of the membrane 306. Alternatively, the membrane may not include a catalyst coating layer on one or both sides of the membrane. In certain examples, the cell may still include a cathode catalyst layer and / or anode catalyst layer, but one or both of these layers may be coated or positioned on an adjacent supporting layer within the cell (e.g., the gas diffusion layer or the porous transport layer).

[0039] In certain examples, the thickness of the membrane 306 may be less than 1000 microns, less than 500 microns, less than 100 microns, less than 50 microns, less than 10 microns, less than 5 microns, less than 2 microns, less than 1 micron, in a range of 1-1000 microns, in a range of 2-500 microns, in a range of 5-100 microns, or in a range of 10-50 microns. As used herein, a "thickness" by which is layer is characterized refers to the distance, or median measured distance, between the top and bottom faces of a film in a direction perpendicular to the plane of the film layer. As used herein, the top and bottom faces of a film layer refer to the sides of the film extending in a parallel direction of the plane of the film having the largest surface area.

[0040] In certain examples, additional layers may be present within the electrochemical cell 300. For example, one or more additional layers 308 may be positioned between the cathode flow field 302 and membrane 306. In certain examples, this may include a gas diffusion layer (GDL) 308 positioned between the cathode flow field 302 and membrane 306. This may be advantageous in providing a hydrogen diffusion barrier adjacent to the cathode on one side of the multi-layered membrane to assist in transferring or releasing the generated hydrogen gas toward the cathode flow field and out of the cell.

[0041] In certain examples, the GDL is made from a carbon paper or woven carbon fabrics. The GDL is configured to allow the flow of hydrogen gas to pass through it. The thickness of the GDL may be within a range of 100-1000 microns, for example. The thicknessmay affect the mass transport within the cell as well as the durability / deformability and electrical / thermal conductivity of the GDL. In other words, a thinner GDL may provide better mass transport, lower resistance, and a reduction in durability (e.g., greater chance for localized deformation).

[0042] In certain examples, a microporous layer (MPL) may be positioned between the GDL 308 and the cathode catalyst layer 305. In certain examples, the MPL is coated on the surface of the cathode catalyst layer 305 facing or positioned adjacent to the GDL.Additionally, or alternatively, a microporous layer (MPL) may be positioned between the PTL 310 and the anode catalyst layer 307. In certain examples, the MPL is coated on the surface of the anode catalyst layer 307 facing or positioned adjacent to the PTL. Such an MPL within the electrochemical cell may be advantageous in providing or improving some of the above benefits in addition to further improving durability by protecting the membrane against stress or shorts.

[0043] In certain examples, the composition of the MPL may include a carbon-based compound and a binder. Additional components, such as additional additive or filler compounds, may also be included within the MPL composition. In certain examples, the carbon-based composition may be a carbon powder. In certain examples, the carbon powder is a graphitic carbon. In some examples, the binder within the MPL composition is a polymeric binder. Any polymer with good binding properties may be used.

[0044] Additionally, the MPL includes pores or openings within the layer allowing the transport of fluids (i.e., water and gas) through the layer. The average size of the pores may be on a micrometer or nanometer scale. For example, the average pore size may be less than 50 microns, less than 10 microns, less than 1 micron, less than 100 nm, less than 50 nm, less than 10 nm, less than 5 nm, in a range of 1-1000 nm, in a range of 1-100 nm, in a range of 1-50 nm, in a range of 1-10 nm, or in a range of 1-5 nm.

[0045] In some examples, a cathode catalyst coating layer 305 may be positioned between the cathode flow field 302 and the GDL 308. The overall thickness of the cathode catalyst coating layer may be less than 25 microns, less than 10 microns, less than 1 micron, in a range of 0.01-25 microns, in a range of 0.01-10 microns, in a range of 0.01-5 microns, or in a range of 0.01-1 micron.

[0046] Detailed descriptions of various cathode catalyst coating layers 305 are discussed in greater detail below.

[0047] S imilarly, one or more additional layers 310 may be present in the electrochemical cell between the membrane 306 and the anode flow field 304. In certain examples, this may include a porous transport layer (PTL) positioned between the membrane 306 (e.g., the anode catalyst layer of the membrane 306) and the anode flow field 304.

[0048] In certain examples, the PTL is made from a titanium mesh / felt. Similar to the GDL, the PTL is configured to allow the transportation of the reactant water to the anode catalyst layers, remove produced oxygen gas, and provide good electrical conductivity for effective electron conduction. The thickness of the PTL may be within a range of 100-1000 microns, for example. The thickness may affect the mass transport within the cell as well as the durability / deformability and electrical / thermal conductivity of the PTL. In other words, a thinner PTL may provide better mass transport and a reduction in durability (e.g., greater chance for localized deformation).

[0049] In some examples, an anode catalyst coating layer 307 may be positioned between the anode flow field 304 and the PTL 310. The overall thickness of the anode catalyst coating layer may be less than 25 microns, less than 10 microns, less than 1 micron, in a range of 0.01-25 microns, in a range of 0.01-10 microns, in a range of 0.01-5 microns, or in a range of 0.01-1 micron.

[0050] The cathode 302 and anode 304 of the cell may individually include a flow field plate composed of metal, carbon, or a composite material having a set of channels machined, stamped, or etched into the plate to allow fluids to flow inward toward the membrane or out of the cell.Cathode Catalyst Coating Layers

[0051] As noted above with reference to Figure 3, an electrochemical cell may include a catalyst coating layer 305 positioned on the cathode side of the cell 300, i.e., a cathode catalyst coating layer. Such coating layers may be positioned on a surface of the membrane 306 of the electrochemical cell such that the cathode catalyst coating layer is positioned between a cathode flow field 302 and the membrane 306 of the electrochemical cell 300. Insome embodiments described in greater detail below, an intermediate layer (i.e., an electrically conductive layer) may be positioned between the cathode catalyst coating layer and the membrane.

[0052] In certain examples, the cathode catalyst coating layer may have a composition that includes an ionomer and a catalyst composition. The catalyst composition may include an active catalyst such as platinum.

[0053] In certain examples, the platinum may be pure platinum metal (e.g., platinum black) mixed with the ionomer. Alternatively, the platinum may be supported on a carbon substrate (otherwise referred to as Pt / C).

[0054] Specifically, regardless of whether the platinum refers to a pure platinum metal or a Pt / C composition, the overall amount of platinum (by weight percent) loaded within the catalyst coating layer composition is larger than described in the state of the art (i.e., a catalyst loading of less than or equal to 0.1 mg Pt / cm2). In other words, this higher Pt loading is contrary to the known art, which suggests a lower catalyst loading due to the cost of platinum and cell performance.

[0055] Nevertheless, it has been discovered that the amount of active catalyst loading may be increased and still achieve an overall cost reduction due to the added costs of platinum being offset by greater cost reductions in operating efficiency within the electrochemical cell / stack / plant. In other words, the efficiency gains in cell / stack / plant operation may provide a cost reduction that exceeds the added cost of a larger platinum loading.

[0056] For example, the platinum loading may be at least 0.2 mg Pt / cm2, at least 0.3 mg Pt / cm2, at least 0.5 mg Pt / cm2, at least 0.75 mg Pt / cm2, at least 1 mg Pt / cm2, at least 1.5 mg Pt / cm2, at least 2 mg Pt / cm2, in a range of 0.2-2 mg Pt / cm2, in a range of 0.2-1.5 mg Pt / cm2, in a range of 0.2-1 mg Pt / cm2, in a range of 0.2-0.75 mg Pt / cm2, or in a range of 0.2-0.5 mg Pt / cm2.

[0057] At such higher platinum loadings, the efficiency gains within the electrochemical cell / stack / plant may include: operating the cell / stack at a lower voltage while achieving a similar hydrogen production output (in comparison to the current state of the art having lower Pt catalyst loadings, e.g., less than 0.1 mg Pt / cm2such as 0.05 mg Pt / cm2); operatingthe cell / stack at a same voltage as the current state of the art cell with lower Pt catalyst loading (e.g., less than 0.1 mg Pt / cm2) and achieving an increase in hydrogen production; increased / improved cell life; increased / improved membrane durability or life.

[0058] Specifically, the cathode catalyst coating layer, as described herein, may advantageously assist in reducing an operating voltage of the electrochemical cell by at least 5%, at least 10%, at least 15%, or at least 20% in comparison to an operating voltage of the similar electrochemical cell with the lower platinum loading, while still achieving the same amount of hydrogen gas generation at a defined or fixed current density. That is, a lower operating voltage may be provided to the cell / stack to effectively run the electrochemical reaction, split water, and generate a similar amount of hydrogen gas product.

[0059] Figure 4 depicts such an improvement in cell efficiency. In this example, the operating voltages for two different cells are shown as a function of current density. As current density increases, each cell shows an increase in the required operating voltage. The improvement of the presently disclosed cathode catalyst coating layer is identified in one of the cells as current density increases. Specifically, the required operating voltage for the catalyst coating layer having a higher Pt loading is less than the current state of the art. Specifically, at certain current densities, the operating voltage of the electrochemical cell with the improved cathode catalyst coating layer may be at least 10 mV, at least 20 mV, at least 30 mV, at least 40 mV, or at least 50 mV less than a similarly configured cell having a lower Pt catalyst loading.

[0060] Alternatively, or additionally, the cathode catalyst coating layer, when positioned within the electrochemical cell, may advantageously assist in providing an improvement in cell efficiency in comparison to a similar electrochemical cell having a cathode catalyst coating layer having less than 0.1 mg Pt / cm2(e.g., 0.05 mg Pt / cm2), wherein the improvement in cell efficiency relates to a reduction of power per weight of hydrogen gas generation over the current state of the art (i.e., lower Pt catalyst loading). For instance, the improvement in cell efficiency may be in a range of 0.1 to 5 kWh per kilogram of hydrogen gas generation (kWh / kg), in a range of 0.1-2 kWh / kg, in a range of 0.2 to 1 kWh / kg, in a range of 0.3 to 1 kWh / kg, or in a range of 0.5 to 0.8 kWh / kg.

[0061] It should be noted that these efficiency gains in cell / stack / plant operation may occur without any modification to the anode catalyst coating layer on the anode side of the cell. In other words, the active catalyst loading within an anode catalyst coating layer (e.g., iridium oxide or IrOx) does not need to be modified (i.e., the same anode catalyst coating layer and same iridium oxide loading may be provided). Alternatively, in certain examples, the efficiency gains achieved on with an increased platinum catalyst loading may be offset by a reduced anode catalyst loading such that the overall result is an operation of the cell / stack / plant at a same voltage or power as the current state in the art. This may be advantageous in a reduction in the amount of iridium required within the electrochemical cell. As such, the increased cost from an increased platinum loading and the lowered cost from a lowered iridium loading may equate to an overall cost savings due to the higher costs of iridium.

[0062] Returning to the composition of the cathode catalyst layer, as noted above, in certain examples, the platinum within the catalyst composition may be supported on a carbon substrate (otherwise referred to as Pt / C).

[0063] The carbon support within the composition may be an activated carbon composition. In certain examples, the carbon may have mesoporous structure, e.g., having pore sizes in a range of 2-50 nanometers. In some examples, the pore size distribution is wide, e.g., the largest pore size is at least 10 times greater or at least 20 times greater than the smallest pore size within the mesoporous structure. In other examples, the pore size distribution is narrow, e.g., the largest pore size is less than 10 times greater or less than 5 times greater than the smallest pore size within the mesoporous structure.

[0064] Another variable affecting kinetics, cell voltage, and other metrics is the type of carbon support which can range from Ketjen black to Vulcan XC-72, for example.

[0065] Additionally important is the surface area of the carbon and how the catalyst (e.g., Pt) is dispersed on it. In certain examples, the Pt / C catalyst powder may be annealed onto the surface of the carbon at a temperature in a range of 500°C to 1000°C to induce necking, particle growth, and further stabilization of the Pt on the carbon.

[0066] The ratio of platinum to carbon within the platinum on carbon composition is configurable. In certain examples, the composition may range from 10 wt.% platinum and90 wt.% carbon to 90 wt.% Pt and 10 wt.% C. In other examples, the composition may range from 20 wt.% Pt and 80 wt.% C to 80 wt.% Pt and 20 wt.% C. In other examples, the composition may range from 30 wt.% Pt and 70 wt.% C to 70 wt.% Pt and 30 wt.% C. In other examples, the composition may range from 40 wt.% Pt and 60 wt.% C to 60 wt.% Pt and 40 wt.% C. Alternatively described, the weight ratio of platinum to carbon within the catalyst coating layer may be in a range of 1:10 to 10:1 platinum wt.%:carbon wt.%, in a range of 1:5 to 5:1 platinum wt.%:carbon wt.%, in a range of 1:3 to 3:1 platinum wt.%:carbon wt.%, or in a range of 1:2 to 2:1 platinum wt.%:carbon wt.%.

[0067] As noted above, the cathode catalyst coating composition includes at least one ionomer composition. The presence of the ionomer in the catalyst coating layer may be advantageous in reducing an overall amount of catalyst (e.g., platinum) needed by exposing a larger fraction of the catalyst to the hydrogen gas, while also acting as a binding agent to hold the catalyst coating layer together with the adjacent membrane layer and / or gas diffusion layer. Further, the ionomer within the catalyst coating layer may be provided to advantageously prevent a short circuit within the cell and function as a triple phase boundary within the electrochemical cell for the catalyst-chemical species (ions, gases) and electrolyte (ionomer and membrane) for the electrolysis reactions.

[0068] In certain examples, the ionomer may be any polymeric composition having ionized units covalently bonded to a polymer backbone. The ionomer may include long side chain (LSC) ionomers, medium side chain (MSC) ionomers, short side chain (SSC) ionomers, or a combination thereof to promote physical linkage of polymer layers and a mix of properties. Similarly, the ionomers may be a blend of different EW (equivalent weight).

[0069] In additional examples, the ionomer may include one or more perfluorinated polymers such as perfluoroalkyl substances (PFAS). PFAS refer to a class of long and short chain fluorinated organic molecules. Examples of PFAS include perfluorosulfonic acid (PFSA), perfluorooctanoic acid (PFOA), and perfluorooctanesulfonic acid (PFOS). As used herein, PFAS will refer to all perfluoroalkyl substances, including PFSA, PFOA, and PFOS. Further, when referring to PFSA, PFOA, or PFOS herein, the term will refer to the single species / compound example of the larger genus of PFAS. These highly fluorinated substances are advantageously unique in their hydrophobic and lipophobic / oleophobic properties, aswell as their general chemical and thermal stability. As such, PFAS compounds such as PFSA within the ionomer layer of the membrane may advantageously provide structural support for the catalyst coating layer while assisting in the flow of water to the reaction sites within the membrane and hydrogen gas from the reaction sites to the cathode outlet channels / flow fields of the ce I l / stack.

[0070] In certain examples, the ionomer includes a medium or long side chain chemically stabilized perfluorosulfonic acid (MSC- or LSC-PFSA) ionomer and polytetrafluoroethylene (PTFE), such as commercially available in D1021 Nation™ Dispersion. In other examples, the ionomer includes a short side chain chemically stabilized perfluorosulfonic acid (SSC-PFSA) ionomer and copolymer of tetrafluoroethylene (TFE) and sulfonyl fluoride vinyl ether (SFVE), such as commercially available in Aquivion® D72-25BS.

[0071] In one embodiment, the ionomer is lower than 1000 equivalent weight (EW) to advantageously promote faster proton transport. In another embodiment, the ionomer in the solution is above 1000 equivalent weight to advantageously limit swelling and water transport and hence slow hydrogen transport in the catalyst coating layer. The ionomer EW selection may be based on a desired or planned current density operation within the electrochemical cell / stack / plant. For example, a lower EW ionomer may operate more efficiency at a higher current density than at a lower current density. Such an example is depicted in Figure 5.

[0072] The ratio of ionomer to carbon within the cathode catalyst coating layer composition is configurable. In certain examples, the weight ratio of ionomer to carbon within the cathode catalyst coating layer may be in a range of 0.1:1 to 1:1 ionomer wt.%: carbon wt.%, in a range of 0.5:1 to 1:1, or in a range of 0.6:1 to 0.8:1.

[0073] While these examples of catalyst coating layer compositions reference ionomers and platinum on carbon compositions, additional additives and / or catalysts may also be present within the catalyst coating layer. In certain non-limiting examples, the additional additive or catalyst may include a scavenging agent such as Zirconia, Ceria / Ceria yttria- stabilized Zirconia, Cerium, Tungsten carbide, Cerium phosphate, Zirconium phosphate, a mixed metal oxide, or a combination thereof. Additionally, or alternatively, the additive within the catalyst coating layer may include a conducting additive such as poly(3,4-ethlenedioxythiophene) (PEDOT), low / medium / high surface area carbon, graphene, carbon black powder such as Super P®, or combinations thereof, which advantageously may improve conductivity or charge transport properties while, in some cases, also lowering hydrogen crossover.Electrically Conductive Layers

[0074] In addition to or in the alternative of the inclusion of an improved cathode catalyst coating layer as described above, cell performance and efficiency may also be improved through the addition of an electrically conductive layer within the electrochemical cell.

[0075] Figures 6 and 7 depict certain examples of the location of such an electrically conductive layer within the electrochemical cell.

[0076] Specifically, Figure 6 depicts a portion of an electrochemical cell 600 such as identified in Figure 3. In this excerpt, the cell 600 includes a membrane 306 such as described above. The cell 600 additionally includes a catalyst coating layer 305, 307. This may refer to a cathode catalyst coating layer 305 such as described herein or an anode catalyst coating layer 307 positioned between the membrane and the anode flow field.

[0077] In the example of Figure 6, an additional electrically conductive layer 612 is positioned between the membrane and the catalyst coating layer 305, 307.

[0078] Figure 7 depicts a similar example of an excerpt of an electrochemical cell 700 having a membrane 306 and a catalyst coating layer 305, 307 such as described above. Again, the catalyst coating layer may be a cathode catalyst coating layer 305 or an anode catalyst coating layer 307. In this particular embodiment in Figure 6, the electrically conductive layer 612 is positioned on an opposite surface of the catalyst coating layer 305, 307 in comparison to Figure 6, such that the catalyst coating layer 305, 307 is positioned between the electrically conductive layer 612 and the membrane 306.

[0079] In certain examples, the thickness of the electrically conductive layer may be in a range of 0.01-20 microns, in a range of 0.01-10 microns, or in a range of 0.01-5 microns.

[0080] In certain examples, the electrically conductive layer may refer to any conductive composition that has an electrical conductivity of at least 10 siemens (S) per centimeter (cm), at least 100 S / cm, at least 1000 S / cm, at least 5000 S / cm, in a range of 10 siemens (S)per centimeter (cm) to 10000 S / cm, in a range of 100 S / cm to 10000 S / cm, in a range of 100 S / cm to 5000 S / cm, in a range of 1000 S / cm to 10000 S / cm, in a range of 1000 S / cm to 5000 S / cm, or in a range of 5000 S / cm to 10000 S / cm.

[0081] In certain examples, the electrically conductive layer includes a composition including carbon. The composition may include one or more additional components such as an ionomer (such as those described above), as well as one or more additives such as titanium oxide (TiCh) or zirconium oxide (ZrOj). Specifically, in certain examples, the electrically conductive layer is devoid of any active catalyst composition (e.g., platinum or iridium oxide).

[0082] The carbon may be graphene, graphene oxide, or reduced graphene oxide (RGO). In certain examples, the electrically conductive layer includes a reduced graphene oxide, which advantageously has a high electrical conductivity of at least 5000 S / cm, a high surface area of at least 2500 m2 / g, a higher mechanical strength over graphene oxide, a higher Young's modulus over graphene oxide, and a hydrophobic behavior.

[0083] Such a graphene oxide layer or a reduced graphene oxide (RGO) layer may be advantageous in its inclusion within the electrochemical cell as such a composition is advantageously thermally compatible within the cell at the operating conditions of the cell. Further, such compositions are chemically stable, and electrically conductive. Additionally, the inclusion of such a graphene oxide or RGO layer is advantageous in providing similar properties to graphene, but without the added costs and challenges of fabrication.

[0084] Additionally, as noted above, such an electrically conductive layer including graphene oxide or RGO in particular, may assist in efficiency and performance improvements when positioned within the electrochemical cell, such as a reduced kWh / kg operating cost of producing hydrogen gas, an increased / improved cell life, an increased / improved membrane durability or life, and / or an improved hydrogen crossover protection.

[0085] Further, with reference to the example in Figure 6, the positioning of the electrically conductive between the membrane and the catalyst coating composition (i.e., the cathode catalyst coating composition) may advantageously shift the hydrogenproduction away from the membrane interface and improve kinetics of hydrogen evolution and transport.

[0086] Further, this electrically conductive layer may flood with liquid water coming from the anode to cathode by electroosmotic drag (EOD). The flooding may fill the pores of the layer, therein creating a barrier between the membrane and cathode catalyst coating layer, further advantageously isolating the cathode catalyst coating layer from the membrane. Additionally, protons have to move through the electrically conductive layer to the cathode catalyst coating layer, therein pulling water with the protons. This water flux should promote hydrogen transport from the HER sites to the cathode outlet.

[0087] Additionally, the composition within the electrically conductive layer may not exhibit the micellular / backbone structure of a bulk ionomer film such as within the membrane, and as such, again facilitate the transport route discussed above.

[0088] Further, through the addition of such an electrically conductive layer within the cell, the benefits of the layer may advantageously allow for a thinner membrane to be included within the cell without detriment to cell operation, durability, or membrane life. This inclusion of a thinner membrane may lead to lower operation resistance losses in comparison to a thicker membrane used in the current state of the art, therein additionally leading to more efficient operation and lower operational costs.

[0089] Additionally, in certain iterations, the cathode catalyst coating layer as described herein may additionally prevent supersaturation and spiking of hydrogen concentration in the ionomer / liquid phases, therein adding additional benefits to those described above for this electrically conductive layer.Additional Catalyst Coating Layers

[0090] In certain examples, the electrochemical cell may include an alternative or additional catalyst coating layer (e.g., to those described above) positioned on a surface of the membrane or between the membrane and one of the flow fields of the electrochemical cell 300.

[0091] The catalyst coating layers disclosed herein may advantageously provide improved mechanical properties over the state of the art including improved durability and stability during operation of the electrochemical cell / stack / plant. For example, a thickercatalyst layer or modified properties of the catalyst layer composition (discussed herein) may provide better / improved mechanical properties over the state of the art, such as, but not limited to, improved cohesion within the catalyst layer and improved adhesion to other layers such as the membrane.

[0092] In certain examples, the catalyst coating layer may be an anode catalyst coating layer 307 positioned on a surface of the membrane 306 of the electrochemical cell such that the catalyst coating layer is positioned between anode flow field 304 and the membrane 306 of the electrochemical cell 300. The anode catalyst coating layer may be an additional catalyst coating layer to the cathode catalyst coating layers described above.

[0093] Alternatively, the catalyst coating layer may be a cathode catalyst coating layer 305 positioned on a surface of the membrane 306 of the electrochemical cell such that the catalyst coating layer is positioned between cathode flow field 302 and the membrane 306 of the electrochemical cell 300, wherein the cathode catalyst coating layer is a different embodiment from those cathode catalyst coating layers described above.

[0094] In certain examples, the catalyst coating layer may have a composition that includes an ionomer, an active catalyst composition (herein "a catalyst"), and a support material having a plurality of pores. The catalyst may include a plurality of crystallites having defined sizes, crystal phase, and compositions.

[0095] In certain examples, the composition of the catalyst coating layer may be configured to be electrically conductive.

[0096] In certain examples, the addition or presence of the support material within the catalyst coating layer may be advantageous in reducing the amount of active catalyst needed within the coating layer. In other words, the support material may advantageously act as a substitute or replacement for active catalyst within the coating layer without negatively affecting the performance qualities of the catalyst coating layer within the electrochemical cell. This therein provides an advantageous reduction in cost for the coating layer, as the support material may be less expensive than the active catalyst composition.

[0097] In certain examples, the catalyst coating layer is configured to be arranged such that the catalyst (e.g., the catalyst crystallites) are positioned within pores or openings of the support material. This may provide several advantages including allowing for betterdispersion of active catalyst, a reduction in the amount of active catalyst required, and protecting the active catalyst from undesirable agglomeration or aggregation of the active catalyst sites or destruction from exposure on an outer surface of the catalyst layer.

[0098] In certain examples, the plurality of pores of the support material has an average opening diameter that is greater than an average diameter of individual crystallites of the catalyst such that at least a portion of the individual crystallites of the catalyst (e.g., at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99%, at least 99.9%, or 100% of the individual crystallites of the catalyst) are embedded within the pores of the support material. In certain examples, the average opening diameter of the plurality of pores of the acid-support material may be at least 3 nm, at least 4 nm, at least 5 nm, at least 6 nm, at least 7 nm, at least 8 nm, at least 9 nm, at least 10 nm. The sizes of the pores may be defined or identified by any known process in the state of the art. For example, the pore sizes may be determined or measured by ASTM 4222, ASTM 4284, ASTM 4365, and / or ASTM 4641.

[0099] The average diameter of the individual crystallites of the catalyst may be less than the average diameter of the plurality of pores, such as less than 4 nm, less than 3 nm, less than 2 nm, less than 1 nm, in a range of 1-4 nm, or in a range of 2-4 nm. Similarly, the sizes of the individual crystallites may be defined or identified by any known process in the state of the art. For example, the crystal sizes may be determined or measured by ASTM 4222, ASTM 4284, ASTM 4365, and / or ASTM 4641.

[0100] In certain examples, the catalyst may be a cathode catalyst composition for a cathode catalyst coating layer. The cathode catalyst composition may include platinum (e.g., platinum supported on carbon).

[0101] Alternatively, the catalyst may be an anode catalyst composition for an anode catalyst coating layer. For example, the anode catalyst composition may include iridium oxide (IrOz).

[0102] In certain examples, the anode catalyst coating layer may include less than 1 mg of IrOz per cm2of the catalyst coating layer, less than 0.75 mg of lrC>2 per cm2, less than 0.5 mg of I rC>2 per cm2, less than 0.25 mg of I rC>2 per cm2, or less than 0.1 mg of I rCh per cm2.Alternatively, the anode catalyst coating layer may include 0.01-1 mg of I rOj per cm2of the catalyst coating layer, 0.1-1 mg of I rO? per cm2, or 0.1-0.5 mg of IrCh per cm2.

[0103] In certain examples, the support material of the catalyst coating layer may be an "acid-stable" support composition. As defined herein, the term "acid-stable" may refer to a composition that is configured to remain structurally stable within the electromagnetic cell during an electrolysis reaction within the electrochemical cell. That is, the composition is configured to remain structurally stable within the acidic operating conditions at the anode of the electrochemical cell during the generation of oxygen gas from the water splitting reaction. Alternatively, the term "acid-stable" may refer to a composition configured to remain structurally stable within an acidic environment having a pH of less than 7, less than 6, less than 5, less than 4, less than 3, less than 2, in a range of 1-7, in a range of 2-6, or in a range of 3-5.

[0104] In certain examples, the acid-stable support material may include a metal oxide or a metal oxo-acid salt. The metal may include a transition metal such as a Group IV, V, or VI metal. In other examples, the metal may include an alkali metal or an alkaline earth metal. In certain specific examples, the acid-stable support material may include niobium oxide, sodium niobate, tantalum oxide, sodium tantalate, tungsten oxide, sodium tungstate, zirconium oxide, or sodium zincate.

[0105] As noted above, the catalyst coating layer composition may include at least one ionomer composition. The presence of the ionomer in the catalyst coating layer may be advantageous in reducing an overall amount of catalyst (e.g., iridium) needed by exposing a larger fraction of the catalyst to the hydrogen gas, while also acting as a binding agent to hold the catalyst coating layer together with the adjacent membrane layer and / or porous transport layer. Further, the ionomer within the catalyst coating layer may be provided to advantageously prevent a short circuit within the cell and function as a triple phase boundary within the electrochemical cell for the catalyst-chemical species (ions, gases) and electrolyte (ionomer and membrane) for the electrolysis reactions.

[0106] In certain examples, the ionomer may be any polymeric composition having ionized units covalently bonded to a polymer backbone. The ionomer may include long side chain (LSC) ionomers, medium side chain (MSC) ionomers, short side chain (SSC) ionomers,or a combination thereof to promote physical linkage of polymer layers and a mix of properties. Similarly, the ionomers may be a blend of different EW (equivalent weight).

[0107] In additional examples, the ionomer may include one or more perfluorinated polymers such as perfluoroalkyl substances (PFAS). PFAS refer to a class of long and short chain fluorinated organic molecules. Examples of PFAS include perfluorosulfonic acid (PFSA), perfluorooctanoic acid (PFOA), and perfluorooctanesulfonic acid (PFOS). As used herein, PFAS will refer to all perfluoroalkyl substances, including PFSA, PFOA, and PFOS. Further, when referring to PFSA, PFOA, or PFOS herein, the term will refer to the single species / compound example of the larger genus of PFAS. These highly fluorinated substances are advantageously unique in their hydrophobic and lipophobic / oleophobic properties, as well as their general chemical and thermal stability. As such, PFAS compounds such as PFSA within the ionomer layer of the membrane may advantageously provide structural support for the catalyst coating layer while assisting in the flow of water to the reaction sites within the membrane and hydrogen gas from the reaction sites to the cathode outlet channels / flow fields of the cell / stack.

[0108] In certain examples, the ionomer includes a medium or long side chain chemically stabilized perfluorosulfonic acid (MSC- or LSC-PFSA) ionomer and polytetrafluoroethylene (PTFE), such as commercially available in D1021 Nation™ Dispersion. In other examples, the ionomer includes a short side chain chemically stabilized perfluorosulfonic acid (SSC-PFSA) ionomer and copolymer of tetrafluoroethylene (TFE) and sulfonyl fluoride vinyl ether (SFVE), such as commercially available in Aquivion® D72-25BS.

[0109] The ratio of ionomer to a combination of the catalyst and the support material is configurable. In certain examples, the weight ratio of ionomer to a combination of the catalyst and the support material may be in a range of 10 parts by weight ionomer:l part by weight catalyst / support material to 1 part by weight ionomer: 10 parts by weight catalyst / support material. In other examples, the amount of ionomer in the catalyst coating layer (i.e., dried, following removal of any solvent present during formulation of the layer) may be in a range of 1-50 wt.% of the catalyst coating layer, in a range of 1-40 wt.%, in a range of 1-30 wt.%, in a range of 2-20 wt.%, or in a range of 5-15 wt.%, wherein the remaining amount of the catalyst coating layer may be formed by the catalyst and thesupport material (ignoring any impurities or further additives present). That is, the amount of combined catalyst and support material within the catalyst coating layer may be in a range of 50-99 wt.% of the catalyst coating layer, in a range of 60-99 wt.%, in a range of 70- 99 wt.%, in a range of 80-98 wt.%, or in a range of 85-95 wt.% of the catalyst coating layer (ignoring any impurities or additional additives present).

[0110] Further, within the combination of catalyst and support material, the catalyst may make up at least 1 wt.% of the catalyst / support material composition, at least 5 wt.%, at least 10 wt.%, at least 25 wt.%, less than 90 wt.%, less than 80 wt.%, less than 70 wt.%, less than 60 wt.%, less than 50 wt.%, in a range of 1-90 wt.% of the catalyst / support material composition, in a range of 1-80 wt.%, in a range of 1-70 wt.%, in a range of 1-60 wt.%, in a range of 5-50 wt.%, in a range of 10-50 wt.%, or in a range of 25-50 wt.% of the catalyst / support material composition.

[0111] While these examples of catalyst coating layer compositions reference ionomers, additional additives and / or catalysts may also be present within the catalyst coating layer. In certain non-limiting examples, an additional additive or catalyst composition may include a scavenging agent such as Zirconia, Ceria / Ceria yttria-stabilized Zirconia, Cerium, Tungsten carbide, Cerium phosphate, Zirconium phosphate, a mixed metal oxide, or a combination thereof. Additionally, or alternatively, the additive within the catalyst coating layer may include a conducting additive such as poly(3,4-ethlenedioxythiophene) (PEDOT), low / medium / high surface area carbon, graphene, carbon black powder such as Super P®, or combinations thereof, which advantageously may improve conductivity or charge transport properties while, in some cases, also lowering hydrogen crossover.

[0112] Figure 8 depicts an example of certain performance data comparing an improved catalyst coating layer as described within this disclosure versus a conventional catalyst coating layer. Specifically, Figure 4 depicts a curve showing voltage in relation to current density for two different catalyst coatings. The improved coating includes a loading of 0.68 mg iridium oxide per cm2(with added support material) versus a conventional coating having a loading of 1.7 mg iridium oxide per cm2(with no support material). As noted within the figure, the lower catalyst loading / support material composition has a similar performance to the conventional formulation, therein providing support that the loweredamount of catalyst (with all its advantages including cost savings) may be employed in an electrochemical cell with expectations of a similar operating performance known in the art. Methods of Making

[0113] Various processes may be employed to form an electrochemical cell or various layers of an electrochemical cell having a catalyst coating layer as described herein.

[0114] In one permutation, the method of forming an electrochemical cell, or at least a portion of the electrochemical cell, may include providing a membrane layer. A cathode catalyst coating composition may be subsequently adhered or deposited onto a surface of the membrane layer that would be adjacent to the cathode of the cell. In certain examples, an electrically conductive layer may be adhered or deposited onto an exposed surface of the cathode catalyst coating composition. Subsequently, a gas diffusion layer (GDL) may be adhered to the exposed surface of the electrically conductive composition. In some alternative examples in which the electrically conductive layer is not present, the gas diffusion layer (GDL) may be adhered to the exposed surface of the cathode catalyst coating composition.

[0115] In certain examples, a microporous layer including carbon, ionomer, and / or PTFE may be coated onto the exposed surface of the cathode catalyst coating composition prior to the addition of the GDL, for the benefits discussed above.

[0116] Alternatively, following the providing of the membrane layer, the electrically conductive layer may be adhered or deposited onto the surface of the membrane layer that would be adjacent to the cathode of the cell. Subsequently, a cathode catalyst coating composition may be subsequently adhered or deposited onto the exposed surface of the electrically conductive layer. In some examples, the gas diffusion layer (GDL) may subsequently be adhered to exposed surface of the cathode catalyst coating composition.

[0117] In another permutation of forming the electrochemical cell, the method may include beginning with a substrate layer on one side of the membrane or cell and subsequently adding each additional layer of the membrane or cell on top of the existing formation.

[0118] For example, this process could include providing one of the electrodes (e.g., the anode or cathode) as the substrate. The method would then continue by applying each layer(or a group of pre-formed layers) to the substrate in order. This could include applying a porous transport layer (PTL) to the anode substrate. This may be followed by the application of an anode catalyst coating composition to the exposed PTL surface. This may subsequently be followed by the application of an electrically conductive layer (if present on the anode side of the cell). This may subsequently be followed by the application of the membrane layer to the anode catalyst coating composition / PTL / anode substrate. In this sequential process, the process may continue with the application of the cathode catalyst coating composition, gas diffusion layer, and ending with the adhering of the opposing cathode to complete the cell formation. Further, as noted above, in certain alternative embodiments, an electrically conductive layer may be added to the membrane before the cathode catalyst coating composition (or the electrically conductive layer may be added to the cathode catalyst coating composition before the addition of the GDL.

[0119] Additional or alternative methods of formation are also possible to create such an electrochemical, as long as the end result is the inclusion of a (e.g., cathode) catalyst coating composition and / or an electrically conductive layer as described herein.

[0120] Figure 5 depicts a flowchart describing a method for forming a catalyst coating layer. In act S201, if present within the method, a micelle forming agent may be mixed with a catalyst-support precursor to create a critical micellar concentration. A plurality of micelles in the micelle forming agent may be distributed between metal chloride compounds of the catalyst support precursor. The micelle forming agent may include pluronic-123, cetyltrimethylammonium bromide, or a combination thereof.

[0121] In act S202, if present within the method, the critical micellar concentration solution may be dried to create a gel composition.

[0122] In act S203, the gel composition is provided having a catalyst-support precursor. The catalyst support precursor may contain a metal chloride. The metal chloride may include a transition metal such as a Group IV, V, or VI metal. In certain specific examples, the metal chloride may include niobium chloride, tantalum chloride, tungsten chloride, or zirconium chloride.

[0123] In act S204, the gel composition is heated to a calcination temperature to oxidize the catalyst precursor metal chloride to form an acid-stable support material. In certainexamples, in the heating to the calcination temperature, micelles present within the gel composition may also be burned off to form a plurality of pores in the acid-stable support material. The acid-stable support material may then contain a metal oxide or metal oxo-acid salt and a plurality of pores as described herein. In certain examples, the metal oxide may include niobium oxide, tantalum oxide, tungsten oxide, or zirconium oxide. Alternatively, the metal oxo-acid salt may include niobium oxide, sodium niobate, sodium tantalate, sodium tungstate, or sodium zincate.

[0124] The acid-stable support material may remain structurally stable within the electrochemical cell during an electrolysis reaction within the electrochemical cell. The acidstable support material may remain structurally stable within an acidic environment have a pH of less than 7.

[0125] In act S205, the acid-stable support material is mixed with a catalyst containing a plurality of crystallites. The mixing process may be one of conventional means known in the art. As noted above, the plurality of pores of the acid-stable support material may have an average opening diameter that is greater than an average diameter of individual crystallites of the catalyst such that individual crystallites of the catalyst are configured to be embedded within the pores of the acid-stable support material during the mixing to provide a mixed catalyst-support material composition. As noted above, in certain examples, the average opening diameter of the plurality of pores of the support material may be at least 5 nm, while the average diameter of the individual crystallites of the catalyst may be less than 4 nm. In certain examples, the catalyst may be an anode catalyst composition and include iridium oxide ( IrOz) .

[0126] In act S206, the mixed catalyst-support material composition is dried to provide a catalyst-support material powder. The drying of the mixed catalyst-support material composition may be conducted via a spray drier process to form the catalyst-support material power.In act S207, the catalyst support material is combined with an ionomer to create a catalyst coating layer. This mixing process of ionomer and catalyst / support-material is also one of conventional means known in the art. As noted above, the amount of overall active catalyst material within the catalyst coating layer described herein (e.g., due to the inclusion of thesupport material) is advantageously less than catalyst loadings known in the art. For instance, the catalyst coating layer may include less than 1 mg of iridium oxide per cm2of catalyst coating layer. Alternatively, in another example, the catalyst coating layer may include 0.1-1 mg of iridium oxide per cm2of catalyst coating layer.

[0127] One or more embodiments of the disclosure may be referred to herein, individually and / or collectively, by the term "invention" merely for convenience and without intending to voluntarily limit the scope of this application to any particular invention or inventive concept. Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all subsequent adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, are apparent to those of skill in the art upon reviewing the description.

[0128] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0129] As used herein, "for example," "for instance," "such as," or "including" are meant to introduce examples that further clarify more general subject matter. Unless otherwise expressly indicated, such examples are provided only as an aid for understanding embodiments illustrated in the present disclosure and are not meant to be limiting in any fashion. Nor do these phrases indicate any kind of preference for the disclosed embodiment.

[0130] The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b) and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed toless than all of the features of any of the disclosed embodiments. Thus, the following claims are incorporated into the Detailed Description, with each claim standing on its own as defining separately claimed subject matter.

[0131] It is intended that the foregoing detailed description be regarded as illustrative rather than limiting and that it is understood that the following claims including all equivalents are intended to define the scope of the disclosure. The claims should not be read as limited to the described order or elements unless stated to that effect. Therefore, all embodiments that come within the scope and spirit of the following claims and equivalents thereto are claimed as the disclosure.

Claims

CLAIMS1. A cathode catalyst coating layer for an electrochemical cell, the cathode catalyst coating layer comprising: a cathode catalyst coating layer composition having: an ionomer; and a catalyst composition comprising platinum (Pt), wherein the cathode catalyst coating layer composition comprises 0.1 mg Pt / cm2to 2 mg Pt / cm2of the cathode catalyst coating layer composition, and wherein the cathode catalyst coating layer is configured to be positioned on a surface of a membrane of the electrochemical cell such that the cathode catalyst coating layer is positioned between a cathode flow field and the membrane of the electrochemical cell.

2. The cathode catalyst coating layer of claim 1, wherein the platinum is supported on carbon.

3. The cathode catalyst coating layer of claim 2, wherein a weight ratio of platinum to carbon within the cathode catalyst coating layer is in a range of 1:10 to 10:1 platinum wt.%:carbon wt.%, in a range of 1:5 to 5:1 platinum wt.%:carbon wt.%, in a range of 1:3 to 3:1 platinum wt.%:carbon wt.%, or in a range of 1:2 to 2:1 platinum wt.%:carbon wt.%.

4. The cathode catalyst coating layer of claim 2, wherein the carbon comprises activated carbon.

5. The cathode catalyst coating layer of claim 4, wherein the activated carbon comprises a mesoporous structure having a pore size distribution in a range of 2-50 nanometers.

6. The cathode catalyst coating layer of claim 2, wherein a weight ratio of ionomer to carbon within the cathode catalyst coating layer is in a range of 0.1:1 to 1:1 ionomer wt.%: carbon wt.%, in a range of 0.5:1 to 1:1, or in a range of 0.6:1 to 0.8:1.

7. The cathode catalyst coating layer of claim 1, wherein the cathode catalyst coating layer is configured to, when positioned within the electrochemical cell, assist in generating a same amount of hydrogen gas at a defined current density, while operating at a lower voltage, in comparison to a similar electrochemical cell having a cathode catalyst coating layer with a platinum loading of less than 0.1 mg Pt / cm2.

8. The cathode catalyst coating layer of claim 7, wherein an operating voltage of the electrochemical cell is at least 5%, at least 10%, at least 15%, or at least 20% less than an operating voltage of the similar electrochemical cell with the platinum loading of less than 0.1 mg Pt / cm2to achieve the same amount of hydrogen gas generation at the defined current density.

9. The cathode catalyst coating layer of claim 1, wherein the cathode catalyst coating layer is configured to, when positioned within the electrochemical cell, assist in providing an improvement in cell efficiency in comparison to a similar electrochemical cell having a cathode catalyst coating layer with a platinum loading of less than 0.1 mg Pt / cm2.

10. The cathode catalyst coating layer of claim 9, wherein the improvement in cell efficiency is a reduction of 0.1-5 kWh per kilogram of hydrogen gas generation (kWh / kg), 0.1-2 kWh / kg, 0.2-1 kWh / kg, 0.3-1 kWh / kg, or 0.5-0.8 kWh / kg.

11. The cathode catalyst coating layer of claim 1, wherein the ionomer comprises a chemically stabilized perfluorosulfonic acid (PFSA) ionomer and polytetrafluoroethylene (PTFE).

12. The cathode catalyst coating layer of claim 1, wherein the ionomer comprises a chemically stabilized perfluorosulfonic acid (PFSA) ionomer and copolymer of tetrafluoroethylene (TFE) and sulfonyl fluoride vinyl ether (SFVE).

13. The cathode catalyst coating layer of claim 1, wherein the ionomer comprises a long side chain (LSC) ionomer, a medium side chain (MSC) ionomer, a short side chain (SSC) ionomer, or a combination thereof.

14. The cathode catalyst coating layer of claim 1, wherein a thickness of the cathode catalyst coating layer within the electrochemical cell is less than 25 microns, less than 10 microns, less than 1 micron, in a range of 0.01-25 microns, in a range of 0.01-10 microns, in a range of 0.01-5 microns, or in a range of 0.01-1 micron.

15. An electrochemical cell comprising: an anode flow field; a cathode flow field; a membrane positioned between the anode flow field and the cathode flow field; a catalyst coating layer positioned between the membrane and the anode flow field or between the membrane and the cathode flow field; and an electrically conductive layer positioned between the membrane and the catalyst coating layer.

16. The electrochemical cell of claim 15, wherein the catalyst coating layer is a cathode catalyst coating layer positioned between the membrane and the cathode flow field, and wherein the electrically conductive layer is positioned between the membrane and the cathode catalyst coating layer.

17. The electrochemical cell of claim 16, wherein the cathode catalyst coating layer has a cathode catalyst coating layer composition as claimed in any of claims 1-14.

18. The electrochemical cell of claim 15, wherein the catalyst coating layer is an anode catalyst coating layer positioned between the membrane and the anode flow field, and wherein the electrically conductive layer is positioned between the membrane and the anode catalyst coating layer.

19. The electrochemical cell of claim 15, wherein the electrically conductive layer comprises reduced graphene oxide.

20. The electrochemical cell of claim 15, wherein a thickness of the electrically conductive layer is in a range of 0.01-20 microns, in a range of 0.01-10 microns, or in a range of 0.01-5 microns.

21. The electrochemical cell of claim 15, wherein the electrically conductive layer comprises an electrical conductivity in a range of 1000 siemens (S) / cm to 10000 S / cm.

22. A catalyst coating layer configured to coat a surface of a membrane of an electrochemical cell, the catalyst coating layer comprising: an ionomer; a catalyst comprising a plurality of crystallites; and an acid-stable support material having a plurality of pores, wherein the plurality of pores has an average opening diameter that is greater than an average diameter of individual crystallites of the catalyst such that individual crystallites of the catalyst are embedded within the pores of the acid-stable support material.

23. The catalyst coating layer of claim 22, wherein the catalyst comprises iridium oxide (lrO2).

24. The catalyst coating layer of claim 23, wherein the catalyst coating layer comprises less than 1 mg of iridium oxide per cm2of the catalyst coating layer.

25. The catalyst coating layer of claim 23, wherein the catalyst coating layer comprises 0.1-1 mg of iridium oxide per cm2of the catalyst coating layer.

26. The catalyst coating layer of claim 22, wherein the acid-stable support material is configured to remain structurally stable within the electrochemical cell during an electrolysis reaction within the electrochemical cell.

27. The catalyst coating layer of claim 22, wherein the acid-stable support material is configured to remain structurally stable within an acidic environment having a pH of less than 7, less than 6, less than 5, less than 4, less than 3, less than 2, in a range of 1-7, in a range of 2-6, or in a range of 3-5.

28. The catalyst coating layer of claim 22, wherein the acid-stable support material comprises a metal oxide or a metal oxo-acid salt.

29. The catalyst coating layer of claim 28, wherein the acid-stable support material comprises niobium oxide, sodium niobate, tantalum oxide, sodium tantalate, tungsten oxide, sodium tungstate, zirconium oxide, or sodium zincate.

30. The catalyst coating layer of claim 22, wherein an amount of ionomer within the catalyst coating layer is in a range of 1-50 wt.%, and an amount of combined catalyst and support material within the catalyst coating layer is in a range of 50-99 wt.%.

31. The catalyst coating layer of claim 30, wherein an amount of catalyst within the combined catalyst and support material is in a range of 5-50 wt.%.

32. The catalyst coating layer of claim 22, wherein the catalyst coating layer has a thickness in a range of 1 to 20 micrometers.

33. The catalyst coating layer of claim 22, wherein the catalyst coating layer is electrically conductive.

34. The catalyst coating layer of claim 22, wherein the ionomer comprises one or more perfluoroalkyl substances (PFAS).

35. The catalyst coating layer of claim 22, wherein the catalyst coating layer is configured to be positioned on an anode side of the membrane of the electrochemical cell.

36. The catalyst coating layer of claim 22, wherein the average opening diameter of the plurality of pores of the acid-stable support material is at least 5 nm, and wherein the average diameter of the individual crystallites of the catalyst is less than 4 nm.

37. A catalyst coated membrane comprising: a membrane of an electrochemical cell; and a catalyst coating layer as recited in any of claims 22-36, wherein the catalyst coating layer is positioned on a surface of the membrane.

38. A method of forming a catalyst coating layer, the method comprising: providing a gel composition having a catalyst support precursor comprising a metal chloride; heating the gel composition to a calcination temperature to oxidize the metal chloride to form an acid-stable support material comprising a metal oxide or a metal oxoacid salt and a plurality of pores; mixing the acid-stable support material with a catalyst containing a plurality of crystallites, wherein the plurality of pores of the acid-stable support material has an averageopening diameter that is greater than an average diameter of individual crystallites of the catalyst such that individual crystallites of the catalyst are embedded within the pores of the acid-stable support material during the mixing to provide a mixed catalyst-support material composition; drying the mixed catalyst-support material composition to provide a catalyst-support material powder; and combining the catalyst-support material powder with an ionomer to form the catalyst coating layer.

39. The method of claim 38, wherein the gel composition is formed by: mixing a micelle forming agent with the catalyst support precursor to create a critical micellar concentration solution, wherein a plurality of micelles in the micelle forming agent are distributed between metal chlorides compounds of the catalyst support precursor; and drying the critical micellar concentration solution to create the gel composition, wherein the heating of the gel composition to the calcination temperature burns the plurality of micelles to form the plurality of pores in the acid-stable support material.

40. The method of claim 39, wherein the micelle forming agent comprises pluronic- 123, cetyltrimethylammonium bromide, or a combination thereof.

41. The method of claim 38, wherein the drying of the mixed catalyst-support material composition is conducted via a spray dryer process to form the catalyst-support material powder.

42. The method of claim 38, wherein the catalyst comprises iridium oxide ( I rC ).

43. The method of claim 42, wherein the catalyst coating layer comprises less than 1 mg of iridium oxide per cm2of the catalyst coating layer.

44. The method of claim 42, wherein the catalyst coating layer comprises 0.1-1 mg of iridium oxide per cm2of the catalyst coating layer.

45. The method of claim 38, wherein the acid-stable support material is configured to remain structurally stable within an electrochemical cell during an electrolysis reaction within the electrochemical cell.

46. The method of claim 38, wherein the acid-stable support material is configured to remain structurally stable within an acidic environment having a pH of less than 7, less than 6, less than 5, less than 4, less than 3, less than 2, in a range of 1-7, in a range of 2-6, or in a range of 3-5.

47. The method of claim 38, wherein the acid-stable support material comprises niobium oxide, sodium niobate, tantalum oxide, sodium tantalate, tungsten oxide, sodium tungstate, zirconium oxide, or sodium zincate.

48. The method of claim 38, wherein an amount of ionomer within the catalyst coating layer is in a range of 1-50 wt.%, and an amount of combined catalyst and acid-stable support material within the catalyst coating layer is in a range of 50-99 wt.%.

49. The method of claim 48, wherein an amount of catalyst within the combined catalyst and acid-stable support material is in a range of 5-50 wt.%.

50. The method of claim 38, wherein the catalyst coating layer has a thickness in a range of 1 to 20 micrometers.

51. The method of claim 38, wherein the catalyst coating layer is electrically conductive.

52. The method of claim 38, wherein the ionomer comprises one or more perfluoroalkyl substances (PFAS).

53. The method of claim 38, wherein the catalyst coating layer is configured to be positioned on an anode side of a membrane of an electrochemical cell.

54. The method of claim 38, wherein the average opening diameter of the plurality of pores of the acid-stable support material is at least 5 nm, and wherein the average diameter of the individual crystallites of the catalyst is less than 4 nm.

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