Water electrolyzer

Abstract

To provide a novel water electrolyzer, electrolyzer materials, and related methods that significantly reduce the cost of industrial water electrolysis while maintaining high current density.SOLUTION: The water electrolyser is an anion exchange membrane water electrolyser (or AEMEL) using a solid polymer anion exchange membrane and pure water and comprises a plurality of end plates between which "n" electrochemical cells, each comprising a gas diffusion layer, a membrane and a porous transport layer, are arranged, separated from each other by bipolar plates.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] INCORPORATION BY REFERENCE OF RELATED APPLICATIONS This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 63 / 062,041, filed August 6, 2020, the entire contents of which are incorporated herein by reference in their entirety.

[0002] The field to which the invention belongs This application relates to water electrolyzers, such as those incorporating anion exchange membranes. This application also relates to materials incorporated into water electrolyzers, and approaches for manufacturing water electrolyzers, and methods of using water electrolyzers. [Background technology]

[0003] Water electrolysis, also known as "water splitting," is the decomposition of liquid water (HO) into oxygen gas (O) and hydrogen gas (H). At a high level, water electrolysis is achieved by passing an electric current through water with a voltage of at least 1.23 V applied between an anode and a cathode. Hydrogen gas is produced at the cathode, and oxygen gas is produced at the anode. Hydrogen gas plays an important role in industrialized society as both a direct (alternative) energy source and a reagent in many important industrial processes, including the Haber process (to produce ammonia, used to make most agricultural fertilizers). Oxygen gas may also be used as an oxidizer or simply as a component of breathable air. For example, astronauts residing on the International Space Station (ISS) rely on water electrolysis to maintain their life-sustaining oxygen supply.

[0004] However, simple water electrolysis using only pure water and metal electrodes does not efficiently produce hydrogen and oxygen because the current density allowed by this design is too low for practical use. As a result, two primary water electrolysis approaches are currently in use: alkaline electrolysis and proton exchange membrane (PEM) electrolysis, which allow for much higher current densities and produce much more gaseous products. However, both approaches have significant drawbacks. Alkaline electrolyzers are less efficient than PEM approaches, require the use of liquid electrolytes, increase initial capital expenditures and balance of plant (support components and auxiliary systems), and require larger plants to produce the same material output. While PEM electrolyzers are more efficient than alkaline electrolyzers and can use pure water, they operate in acidic environments, requiring much more expensive anode and cathode materials and catalysts (e.g., platinum group metal electrodes and catalysts), significantly increasing initial capital expenditures. Other water electrolysis technologies also exist, such as anion exchange membrane electrolyzers (AEMEL), which utilize corrosive electrolytes such as KOH or NaHCO3. Due to the need for corrosive electrolytes, such systems do not significantly improve upon the current state of the art in industrially used systems. As a result, the majority of commercial hydrogen is not produced using water electrolysis approaches. Instead, most industrial hydrogen is produced by non-renewable methods such as steam reforming of natural gas, partial oxidation of methane, and coal gasification.

[0005] In contrast to these non-renewable approaches, water electrolysis can be carried out in a completely carbon-neutral manner and can produce 100% renewable hydrogen energy. Furthermore, water electrolysis can produce hydrogen domestically without the use of fossil fuels, which means that water electrolysis can significantly reduce or eliminate dependence on foreign energy sources and / or the need to utilize strategic fossil fuel reserves. However, current water electrolysis technologies are not economically efficient enough to compete with non-renewable approaches, so there is a strong need to develop improved water electrolysis approaches. Summary of the Invention

[0006] Recognizing the need for improved water electrolysis, the inventors of the present application have developed novel water electrolyzers, electrolyzer materials and related methods that significantly reduce the cost of industrial water electrolysis while maintaining high current densities.

[0007] Thus, in one aspect, the present application provides a water electrolyzer. In a preferred embodiment of the present application, the water electrolyzer is an anion exchange membrane water electrolyzer (or AEMEL) that uses a solid polymer anion exchange membrane and pure water, and therefore does not require a liquid electrolyte (e.g., does not require an alkaline electrolyte such as KOH or NaHCO3), as shown in FIG. 1. A preferred structure of such an AEMEL includes multiple end plates, as shown in FIG. 2, between which are disposed "n" electrochemical cells, each with a gas diffusion layer, a membrane, and a porous transport layer, separated from each other by bipolar plates (sometimes known as middle plates). The number of cells "n" can be one (known as a single cell) or multiple (known as a stack).

[0008] The water electrolyzers of the present application eliminate the drawbacks of current approaches. First, because these water electrolyzers utilize pure water without a liquid electrolyte and do not operate in an acidic environment, they can be constructed using low-cost materials such as stainless steel and nickel, unlike PEMEL. Second, because they do not use a liquid electrolyte, the water electrolyzers of the present application have a simple balance of plant (support components and auxiliary systems) and can produce pressurized hydrogen gas (Figure 3), unlike alkaline water electrolyzers (Figure 4). Third, unlike alkaline water electrolyzers, the water electrolyzers of the present application can operate at high current densities and can be constructed into space-saving, efficient stacks. Fourth, the water electrolyzers of the present application use non-precious metals such as molybdenum, tin, cobalt, nickel, copper, and iron, compared to current industrial electrolyzers such as PEMELS, which rely on precious metals such as platinum, iridium, ruthenium, and silver. Fifth, the cell flow field in the water electrolyzer of the present application is designed as a simpler quadrilateral pocket with optimized thickness, which is different from the complex flow field designs (e.g., single serpentine, multi-serpentine, parallel, pin-type / grid) for current industrial PEM electrolyzers or fuel cells, improving molecular flow while also reducing manufacturing steps and costs.

[0009] Further objects, features, and advantages of the present application will become apparent from the detailed description set forth below. [Brief explanation of the drawings]

[0010] [Figure 1] Figure 1 shows the general structure of the anion exchange membrane water electrolyzer (single cell diagram) of the present application. As shown, water is supplied only at the anode side. [Figure 2] FIG. 2 shows the general structure of a water electrolyzer stack. [Figure 3] FIG. 3 shows a process flow diagram of AEMEL according to the present application. [Figure 4] Figure 4 shows a typical AEL process flow diagram. [Figure 5]FIG. 5 shows two common ink spray coating methodologies in forming electrodes for anion exchange membrane water electrolyzers. [Figure 6] Figure 6 shows two styles of pocket flow fields: (a) Two current collectors and one pocket flow field. This flow field allows water and / or gas to flow from the inlet to the outlet through an open space occupied only by the diffusion layer (PTL or GDL). No flow patterns are observed. (b) A simple pocket flow field, where water can flow in (in the case of the anode) or nothing (in the case of the cathode) and hydrogen can flow out (in the case of the cathode) or a mixture of oxygen and water can flow out (in the case of the anode). No flow patterns are observed. [Figure 7] FIG. 7 shows a process flow diagram of the non-precious metal catalyst preparation strategy for AEMEL. [Figure 8] FIG. 8 shows voltage data over time for an AEMEL cell functioning in pure water and maintaining a dry cathode. DETAILED DESCRIPTION OF THE INVENTION

[0011] definition The term "AEL" as used in this application refers to an alkaline water electrolyte. The term "AEM" as used in this application refers to an anion exchange membrane. The term "AEMEL" as used in this application refers to an anion exchange membrane water electrolyzer. The term "ionomer" as used in this application refers to a polymer that can be cast to produce an AEM and can also be used to produce ink to make electrodes. The term "GDL" as used in this application refers to a gas diffusion layer. The term "PEM" as used in this application refers to a proton exchange membrane. The term "electrode substrate" as used in this application refers to a PTL or GDL when coated with ink. The term "PEMEL" as used in this application refers to a proton exchange membrane water electrolyzer. The term "PTL" as used in this application refers to a porous transport layer. The term "ink" as used in this application refers to the mixture of ionomer, catalyst, additives, and solvent used to coat the AEM, PTL, and / or GDL. The term "CCM" as used in this application refers to a catalyst-coated membrane (the method by which the ink is coated onto the membrane). The term "CCE" as used in this application refers to a catalyst-coated electrode (the method by which the ink is coated onto the PTL or GDL). The term "CCS" as used in this application refers to a catalyst-coated substrate (the method by which the ink is coated onto the PTL or GDL). CCE and CCS are identical, and the words can be used interchangeably. The term "FeNiO" refers to iron-nickel oxide, and Ni is the metal content depending on the amount of each metal. y Fe 1-y O x It can also be written as:

[0012] It should be understood that the term "electrode" can refer to either the anode or cathode of the electrolyzer, or both. Furthermore, if the ink is coated on the GDL and / or PTL, the electrode can also, as a matter of fact, encompass those layers.

[0013] water electrolyzer In one aspect, the present application provides a water electrolyzer. In a preferred embodiment of the present application, the water electrolyzer of the present application is in the form of an anion exchange membrane (AEM) water electrolyzer, or AEMEL, which uses a solid polymer anion exchange membrane electrolyte and pure water, and therefore does not require a liquid electrolyte (e.g., does not require an alkaline electrolyte such as KOH or NaHCO). A generic and simplified example of an AEMEL is shown in Figure 1.

[0014] The AEMEL of the present application includes an anode and a cathode between which a voltage is applied to electrolyze water. Disposed between the bipolar plates are multiple additional layers, including, in some embodiments, gas diffusion layers, membranes, and / or porous transport layers, all of which may be coated with ink (although none are required). An example of a preferred configuration of the AEMEL of the present application is shown in FIG. 2, where the repeat symbol indicates multiple cells arranged in series in an electrolyzer stack.

[0015] In one embodiment, the AEMEL of the present application includes an anode plate, a cathode plate, and multiple bipolar plates (also known as intermediate plates). One purpose of these plates is to transport liquids and gases into and out of the cell. In one embodiment, a single element can act as both an anode plate and a cathode plate, particularly in a series of stacked AEMEL cells, and is called a bipolar plate or intermediate plate. In another embodiment, there can be separate elements for each cell that are an anode plate and a cathode plate.

[0016] In one embodiment, the intermediate plate (or bipolar plate) is made from metal. In some embodiments, the intermediate plate is made from coated or uncoated aluminum, nickel, copper, zinc, and / or stainless steel (e.g., SS304, SS316, SS430, SSA-286, etc.). In some embodiments, the intermediate plate may be coated with a layer of metal including nickel, gold, titanium, platinum, steel, ruthenium, iridium, silver, aluminum, copper, zinc, or another metal or a combination thereof. In some embodiments, the intermediate plate is made from a non-metallic component (e.g., ceramic or plastic) coated with one metal or multiple layers of multiple metals as described above.

[0017] In a preferred embodiment, the intermediate plate, also known as a bipolar plate, constitutes a single element with pocket flow fields on both sides for transporting liquids and gases. In a preferred embodiment, the intermediate plate is made of stainless steel, most preferably stainless steel type 316, although other types of stainless steel (or other metals) may be used depending on engineering and material considerations (e.g., thermal expansion coefficient, electrical resistance, etc.).

[0018] In one embodiment, the anode plate is made of metal. In some embodiments, the anode is made of coated or uncoated aluminum, nickel, copper, zinc, and / or stainless steel (e.g., SS304, SS316, SS430, SSA-286, etc.). In some embodiments, the anode plate may be coated with a layer of metal including nickel, gold, titanium, platinum, steel, ruthenium, iridium, silver, aluminum, copper, zinc, or another metal, or a combination thereof.

[0019] In a preferred embodiment, the anode plate is a stainless steel plate with pocket flow fields for transporting liquids and gases, most preferably stainless steel type 316, although other types of stainless steel (or other metals) may be used depending on engineering and material considerations (e.g., thermal expansion coefficient, electrical resistance, etc.).

[0020] In one embodiment of the present application, water is supplied to the AEMEL. In a preferred embodiment, the water is supplied on the anode side. Thus, in certain embodiments, the anode plate can have a flow field to allow water to be supplied to the AEMEL on the anode side. The flow field and / or inlets may be machined directly on the anode plate or may be provided as a separate structure that can be attached to the anode plate. The flow field may simply be pockets through which water can be randomly distributed within the porous transport layer. In the AEMEL, oxygen gas is generated at the anode. In certain embodiments, the anode may have a pocket flow field arranged for oxygen in the anode plate with an outlet that allows oxygen to exit the AEMEL on the anode side. The flow field (either pocket or another specific pattern) and / or outlet may be machined on the anode plate or may be provided as a separate structure that can be attached to the anode plate. The flow fields for water and oxygen may be connected or separate.

[0021] In one embodiment, the cathode plate is also made of metal. In another embodiment, the cathode plate is made of graphite. In some embodiments, the cathode plate is made of coated or uncoated aluminum, nickel, copper, zinc, and / or stainless steel (e.g., SS304, SS316, SS430, SSA-286, etc.). In some embodiments, the cathode plate may be coated with a layer of metal including nickel, gold, titanium, platinum, steel, ruthenium, iridium, silver, aluminum, copper, zinc, or another metal, or a combination thereof.

[0022] In a preferred embodiment, the cathode plate is a stainless steel plate with pocket flow fields for transporting liquids and gases, most preferably stainless steel type 316, although other types of stainless steel (or other metals) may be used depending on engineering and material considerations (e.g., thermal expansion coefficient, electrical resistance, etc.).

[0023] In the AEMEL, hydrogen gas is produced at the cathode. The cathode in the AEMEL of the present application can be configured as a dry cathode, so that hydrogen can be produced at the cathode at a pressure higher than ambient pressure (e.g., 1 atmosphere above sea level). In one embodiment, the cathode can have a flow field therein with an outlet that allows hydrogen to exit the AEMEL on the cathode side. Hydrogen can exit the cathode at a pressure higher than ambient pressure, facilitating easy storage in a dedicated container that can be pressurized. The hydrogen flow field and / or outlet can be machined onto the cathode or provided as a separate structure that can be attached to the cathode plate. In a preferred embodiment, the cathode is a dry cathode. In a dry cathode, no liquid other than water is present.

[0024] In one embodiment, the anode plate, middle plate, and cathode plate can have a serpentine flow field design, a multi-serpentine channel design, a parallel flow field design, an interdigitated flow field design, a pocket flow field design, or a combination thereof. In all cases, these fields are used to transport liquids and gases into and out of the cell. A pocket flow field does not have a machined pattern to direct the liquid and gas flow. In other words, the flow direction is not constrained by grooves (as in a serpentine-pattern flow field). Instead, it contains a diffusion layer (PTL or GDL), allowing gas and / or liquid flow to occur only through the pores of these diffusion layers, as illustrated in Figure 6. When properly positioned, multiple water inlets can actively create a constant flow across the active area.

[0025] In a preferred embodiment, the anode, intermediate and cathode plates have pocket flow fields designed to optimize fluid flow through the diffusion layer, minimize pressure drop and maximize cell life.

[0026] In a preferred embodiment of the present application, the AEMEL includes multiple layers disposed between the anode and cathode. The multiple layers include a gas diffusion layer, a porous transport layer, and / or an anion exchange membrane. Those skilled in the art will understand that each of these layers may itself be composed of multiple layers of material. An example of the arrangement of these layers in an AEMEL according to the present application is shown in Figure 2.

[0027] In one embodiment of the AEMEL according to the present application, a gas diffusion layer is present and disposed adjacent to the cathode to facilitate gas transport. Thus, the gas diffusion layer can facilitate transport of hydrogen gas, among other things. In some embodiments, the gas diffusion layer is made of titanium, aluminum, carbon (e.g., carbon paper, carbon fiber composite, graphite felt, graphene, carbon cloth, etc.), nickel, copper, zinc, stainless steel (e.g., SS304, SS316, SS316L, SS430, SSA-286, etc.), other materials, or combinations thereof. In some embodiments, the gas diffusion layer may be coated or uncoated. In some embodiments, the gas diffusion layer may be waterproofed to increase its hydrophobicity. In some embodiments, the gas diffusion layer may include a microporous layer to improve water repellency and catalyst adhesion. In some embodiments, the gas diffusion layer has a nanostructure or microstructure. In some embodiments, the gas diffusion layer is formed of nanowires, microfibers, or fabric. In some embodiments, the gas diffusion layer is formed using a foam. In some embodiments, the gas diffusion layer is electrically connected to the cathode material so as to effectively form part of the cathode. In some embodiments, multiple layers with different porosities may be stacked to maximize water and gas transport in the gas diffusion layer. In some embodiments, the gas diffusion layer may include additives such as fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer resin (PFA), or polyvinylidene difluoride (PVDF).

[0028] In preferred embodiments, the gas diffusion layer comprises carbon paper (such as formed graphite laminate or carbon fiber) or nickel sheet (foam or fiber) or stainless steel sheet (foam or fiber).

[0029] In the AEMEL of the present application, a porous transport layer is present to facilitate the transport of liquids and gases and is disposed adjacent to the anode. Therefore, the porous transport layer can particularly facilitate the transport of water and ions dissolved in the water, as well as generated oxygen. In some embodiments, the porous transport layer is made of titanium, aluminum, carbon (e.g., carbon paper, carbon fiber composite, graphite felt, graphene, carbon cloth, etc.), nickel, copper, zinc, stainless steel (e.g., SS304, SS316, SS316L, SS430, SSA-286, etc.), other materials, or combinations thereof. In some embodiments, the porous transport layer may be coated or uncoated. In some embodiments, the porous transport layer may be waterproofed to increase its hydrophobicity. In some embodiments, the porous transport layer may include additives such as fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer resin (PFA), or polyvinylidene difluoride (PVDF). In some embodiments, the porous transport layer may include a microporous layer to improve water repellency and improve catalyst adhesion. In some embodiments, the porous transport layer has a nanostructure or microstructure. In some embodiments, the porous transport layer is formed of nanowires, microfibers, or fabrics. In some embodiments, the porous transport layer is formed using foam. In some embodiments, the porous transport layer is electrically connected to the anode material so as to effectively form part of the anode. In some embodiments, multiple layers with different porosities may be stacked to maximize water and gas transport in the porous transport layer.

[0030] In a preferred embodiment, the porous transport layer comprises nickel foam or microfiber felt.

[0031] In the AEMEL of this application, the anion exchange membrane (AEM) is a membrane that exchanges anions (OH -Anion exchange membranes are semipermeable membranes designed to allow the flow of oxygen (such as argon) and water, while preventing the flow of gases (such as H2 and O2 produced at the cathode and anode). Anion exchange membranes are made by casting an ionomer solution. As described below, certain embodiments of the present application also use ionomers as resins for catalyst inks. The catalyst and / or catalyst ink (described in more detail below) also include an ionomer.

[0032] Thus, in some embodiments, the ionomer used in this application is a polymer. In one embodiment, the ionomer constitutes approximately 45% by weight (or less) of the catalyst ink (defined as the mixture of catalyst, ionomer, and additives, excluding solvent or water). In one embodiment, the ionomer of the AEM and / or catalyst ink is a polymer based on poly(arylpiperidinium), which consists of either piperidone monomers or 3-oxo-6-azoniaspiro[5.5]undecane salt monomers, as well as aromatic and optional trifluoroacetophenone monomer groups. It may also be functionalized with quaternary ammonium cation groups, such as trimethylammonium or methylpiperidinium cations. In one embodiment, the ionomer of the AEM and / or catalyst ink is an ionomer or polymer based on styrene-butadiene block copolymer (SEBS) with quaternary ammonium groups tethered via aromatic rings. In one embodiment, the ionomer of the AEM and / or catalyst ink is a multi-block copolymer containing one or more norbornene-based hydrophilic blocks and one or more norbornene-based or alkene-based hydrophobic blocks, functionalized with a quaternary ammonium cation group (such as trimethylammonium). In one embodiment, the ionomer of the AEM and / or catalyst ink is a trimethyl- or benzyltrimethylammonium-functionalized polystyrene ionomer containing different mole percentages of quaternized benzylammonium. In one embodiment, the ionomer of the AEM and / or catalyst ink is composed of hexamethyltrimethylammonium-functionalized Diels-Alder polyphenylene (HTMA-DAPP). In one embodiment, the ionomer of the AEM and / or catalyst ink is an ionomer using a tetrakis(dialkylamino)phosphonium cation as the functional group.In one embodiment, the ionomer of the AEM and / or catalyst ink is a polyethylene-based triblock copolymer and polychloromethylstyrene-b-polyethylene-b-polychloromethylstyrene (PCMS-b-PE-b-PCMS) quaternized with either trimethylammonium cations or methylpiperidinium cations. In one embodiment, the ionomer of the AEM and / or catalyst ink is an ionomer or polymer containing cationic benzimidazolium or imidazolium-containing moieties. In one embodiment, the ionomer of the AEM and / or catalyst ink is an ionomer based on hexamethyl-p-terphenyl poly(benzimidazolium). In one embodiment, the ionomer of the AEM and / or catalyst ink is an ionomer or polymer having a 3M-PFSA (EW798) precursor containing a copolymer of tetrafluoroethylene (PTFE) and trifluoroethylene functionalized with perfluorinated sulfonyl fluorocarbon chains. The trimethylammonium or imidazolium cation is linked to the sulfonamide via a six-carbon alkyl spacer chain. In another embodiment, the AEM and / or catalyst ink of the present application may include a PPN (polyphenylene) ionomer or membrane, or a PAP (polyarylpiperidinium) ionomer or membrane. In one embodiment, the ionomer of the AEM and / or catalyst ink is made of ethylene tetrafluoroethylene (ETFE), low-density polyethylene (LDPE), or high-density polyethylene (HDPE) that has been irradiated with an electron beam. It may be tethered by a quaternary ammonium cation group, such as trimethylammonium, benzyltrimethylammonium, N-methylpyrrolidine, or N-methylpiperidine. The polymer may be grafted with vinylbenzyl chloride (VBC) or other vinyl alkyl chlorides or aromatic chlorides.

[0033] In a preferred embodiment, the AEM and / or catalyst ink comprises a poly(arylpiperidinium)-based polymer, which consists of either piperidone monomers or 3-oxo-6-azoniaspiro[5.5]undecane salt monomers, as well as aromatic groups and optional trifluoroacetophenone monomer groups.

[0034] In another preferred embodiment, the AEM and / or catalyst ink comprises a multi-block copolymer comprising one or more norbornene-based hydrophilic blocks and one or more norbornene-based or alkene-based hydrophobic blocks.

[0035] In another preferred embodiment, the AEM and / or catalyst ink comprises a polymer based on styrene-butadiene block copolymer (SEBS) with quaternary ammonium groups tethered via aromatic rings.

[0036] In another preferred embodiment, the AEM and / or catalyst ink comprises an e-beam irradiated ETFE, LDPE or HDPE based polymer that may be tethered with quaternary ammonium cationic groups.

[0037] In one embodiment, the AEMEL of the present application includes one or more catalysts. In some embodiments, the catalyst is present to increase the reaction rate of a half-reaction occurring at the cathode, the anode, or both electrodes. Thus, the catalyst can increase the rate of formation of hydrogen gas, oxygen gas, or both. In some embodiments, the catalyst is an oxide, a combination of metals, a perovskite, a pure metal, or another material. In some embodiments, the catalyst is supported or unsupported. In some embodiments, platinum group metals can be used as catalysts. In some embodiments, non-platinum group metals can be used as catalysts.

[0038] In some embodiments, the anode catalyst is selected from RuO2, IrO2, spinel oxides, e.g., Al 0.5 Mn2.5 O4, PbRuO x , Fe x Ni y OOH, IrRuO2, Perovskite, Mo (direct deposition), MoP, IrO x / NbO x , IrRuO2 / NbO x , NiFeCo, NiCe@NiFe / NF, Fe-CoP / NF, Co3O4, Fe 0.33 Co 0.66 P, Fe(PO3)2 / Ni2P, (Ni,Fe)OOH, Ni-Fe-OH@Ni3S2 / NF, Ni(Fe)O x H y , Ni x Fe y O z , NiFeO x , Co x Fe 3-x O4 / CFP, and combinations thereof (including alloys), where x, y, and z can be (0, 0.1, . . . , 2.0, 2.1, . . . ). In some embodiments, the cathode catalyst is Ni x Mo y , Pt / C, Pt alloy / ECS, Pt / ECS, Pt black, Pt alloy, Ni alloy, NiZn, NiMo, MoS2 / Ni3S2 / NF, a-MoS x / CC, Co-Co2P@NPC / rGO, Ni 2(1-x) Mo 2x P / NF, Co 2.90 B 0.73 P 0.27 / NF, F-Co2P / Fe2P / IF, Ni2P / NF, CoP / Ni5P4 / CoP, P-Fe3O4 / IF, A-NiCo LDH / NF, and combinations thereof, where ECS refers to engineered catalyst support. In some embodiments, atomic layer deposition (ALD) can be used to deposit the cathode catalyst, the anode catalyst, or both.

[0039] In some embodiments, one or more catalysts can be incorporated into the catalyst ink. The catalyst ink can be prepared by mixing the catalyst with an ionomer resin, a solvent, water, and additives. In some embodiments, additives (e.g., polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), polydimethylsiloxane (PDMS), polyamide (nylon), polyethylene (PE), ethylene tetrafluoroethylene (ETFE), and / or others) can be used to modify the mechanical and chemical properties of the catalyst ink. In some embodiments, non-ionic surfactants such as polyoxyethylene alkyl ethers can also be used. Three commercially available examples of these chemicals are Teflon® PTFE DISP30, Teflon® PFAD335D, and Teflon® FEPD121 fluoropolymer dispersions (all from Chemours). In some embodiments, the amount of additive can be as much as 50% by weight in the catalyst ink mixture (defined as catalyst, ionomer, and additive, excluding solvent and water). In some embodiments, the catalyst ink may be coated onto an anion exchange membrane, a porous transport layer, a gas diffusion layer, or a combination thereof. In some embodiments, the ink forms a moldable clay-like layer that can be pressed onto the diffusion layer and / or membrane. When coated onto an anion exchange membrane, the catalyst ink may be referred to as a catalyst-coated membrane (or CCM). When coated onto a gas diffusion layer and / or a porous transport layer, the catalyst ink may be referred to as a catalyst-coated electrode (or CCE) or catalyst-coated substrate (or CCS). This is illustrated in FIG. 5. In some embodiments, the catalyst ink may be independently molded (instead of coated) using additives that create a clay-like layer. This layer may then be pressed onto the diffusion layer and / or membrane. In some embodiments, the catalyst layer may be produced by atomic layer deposition (ALD).

[0040] In a preferred embodiment, with the addition of additives such as non-ionic surfactants and / or PTFE, the catalyst ink is a moldable clay-like layer that is pressed onto the diffusion layer and / or membrane.

[0041] In some embodiments, a catalyst layer can be grown on the porous transport layer by etching (hydrothermal deposition, electrodeposition, etc.) a metal foam, fiber, or mesh in an aqueous solution containing copper, lithium, iron, cerium, cobalt, zinc, or nickel cations, or a combination thereof, and including a dopant such as phosphorus, boron, fluorine, cobalt, or others. An example of such a method is shown in Figure 7. The catalyst layer can contain molybdenum, nickel, cobalt, cerium, iron, tin, sulfur, phosphorus, fluorine, oxygen, oxides, hydroxides, dihydroxides, and other materials, or combinations thereof. In some embodiments, the catalyst may be supported on a conductive carbon support, such as carbon, vulcan, or ketjen black. In some embodiments, the catalyst may be supported on a nonionic or ionic polymer binder, such as PTFE, PVA, PAA, PE, ETFE, or PVDF. In some embodiments, the catalyst may be supported by an ionic polymer binder containing cationic protons or anionic hydroxide ions.

[0042] In another aspect, the AEMEL of the present application may be configured into a stack containing multiple cells, as shown in FIG. 2. In some embodiments, bipolar plates can be shared between cells, meaning they have flow fields machined on both sides. In some embodiments, multiple cells share the same water supply and gas exhaust. In some embodiments, the first and last flow field plates are called end plates and can have attachments that connect to the balance of the plant. In some embodiments, the bipolar plates and end plates may be cooled or heated.

[0043] structure The AEMEL of the present application can be made by hot pressing the membrane / electrode assembly, roll-to-roll coating the membrane, spray coating the membrane or electrodes, electrochemically growing a catalyst on the electrodes, etc. The torque applied to the stack bolts, the temperature and purity of the water, the thickness of the different components, and the amount of ionomer in the ink all play a function in the manufacturing process. In some embodiments, the catalyst ink may be coated onto an anion exchange membrane, a porous transport layer or a gas diffusion layer, or a combination thereof.

[0044] In some embodiments, the catalyst can be grown on a gas diffusion layer and / or a porous transport layer. For example, a metal porous substrate can be immersed in HCl or H2SO4 or other acid to remove residual oxides, and then rinsed with water to remove such acids. At this point, a nitrate (such as iron nitrate hexahydrate) and a dopant (such as sodium fluoride) can be dissolved in water. The substrate is then immersed in the solution while oxygen is bubbled through. After several hours, the desired iron-based self-supported catalyst is formed.

[0045] How to use The AEMEL of the present application can be operated by applying a voltage between the anode and cathode. For electrolysis to occur, the voltage must be at least 1.23 V. However, in certain embodiments, the applied voltage is as high as 3 V per cell. In certain embodiments, the voltage is between 1.23 V and 3 V. In certain embodiments, the voltage is 1.3 V, 1.4 V, 1.5 V, 1.6 V, 1.7 V, 1.8 V, 1.9 V, 2.0 V, 2.1 V, 2.2 V, 2.3 V, 2.4 V, 2.5 V, 2.6 V, 2.7 V, 2.8 V, 2.9 V, or 3.0 V. The voltage recorded over time is shown in Figure 8.

[0046] An AEMEL according to the present application may be used as shown in the process flow diagram shown in Figure 3. Such a process is much simpler than the process flow diagram of a typical alkaline water electrolyzer (AEL) as shown in Figure 4. The construction of an AEMEL according to the present application as described above also makes such an AEMEL substantially cheaper than a PEMEL while retaining high current density.

[0047] In another aspect, the AEMEL of the present application includes a highly conductive anion exchange membrane that has high chemical stability in pure water. Compared to other AEMELs, the AEMEL of the present application can operate for a longer life even when operated at a higher voltage. In particular, the AEMEL of the present application can operate at a current density of 0.5 Ampere / cm. 2 When operated at a current density above 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or 2.5 Amps / cm, the anion exchange membrane can operate for at least 1000 hours before needing replacement. In some embodiments, the electrolyzer is 2 In some embodiments, the electrolyzer is operated at 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900 or 950 mA / cm 2 It is operated by.

[0048] Further embodiments 1.1 an anode containing an amount of an anode catalyst; a cathode including an amount of a cathode catalyst; and an anion exchange membrane interposed between the anode and the cathode; Water electrolyzer including: The water electrolyzer uses tap water or purified water that does not contain additives such as salts, acids, and bases.

[0049] 1.2 1.1 Water electrolyzer, wherein the anion exchange membrane comprises a material selected from (a) a polymer based on poly(arylpiperidinium) containing either a piperidone monomer or a 3-oxo-6-azoniaspiro[5.5]undecane salt monomer, an aromatic group, and an optional trifluoroacetophenone monomer group; (b) a multiblock copolymer containing one or more norbornene-based hydrophilic blocks and one or more norbornene-based or alkene-based hydrophobic blocks; (c) a polymer based on styrene-butadiene block copolymer (SEBS) having quaternary ammonium groups tethered via aromatic rings; and (d) a polymer based on electron beam irradiated ETFE, LDPE, or HDPE, which can be tethered by quaternary ammonium cation groups.

[0050] 1.3 The water electrolyzer according to any one of 1.1 to 1.2, wherein the cathode is a dry cathode.

[0051] 1.4 The water electrolyzer according to any one of 1.1 to 1.3, further comprising an anode catalyst and a cathode catalyst.

[0052] 1.5 The water electrolyzer according to any one of 1.1 to 1.4, wherein the anode catalyst contains one or more metal catalysts, and the metals are metals other than Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, and Au.

[0053] 1.6 The water electrolyzer according to any one of 1.1 to 1.5, wherein the anion exchange membrane has a thickness of 1 to 200 μm.

[0054] 1.7 The water electrolyzer according to any one of 1.1 to 1.6, further comprising a porous transport layer and a gas transport layer.

[0055] 1.8 The water electrolyzer according to any one of 1.1 to 1.7, wherein the anode plate comprises a stainless steel plate having a pocket-shaped flow field and optionally coated.

[0056] 1.9 The water electrolyzer according to any one of 1.1 to 1.8, wherein the cathode plate comprises a stainless steel plate having a pocket-shaped flow field and optionally coated.

[0057] 1.10 The water electrolyzer according to any one of 1.1 to 1.9, further comprising a bipolar plate, the bipolar plate comprising an optionally coated stainless steel plate having pocket-shaped flow fields on both sides.

[0058] 1.11 The water electrolyzer according to any one of 1.7 to 1.10, wherein the porous transport layer comprises a nickel material.

[0059] 1.12 The water electrolyzer according to any one of 1.7 to 1.10, wherein the gas diffusion layer contains a nickel material.

[0060] 1.13 The water electrolyzer according to any one of 1.1 to 1.12, further comprising a catalyst ink containing (1) an anode catalyst or a cathode catalyst, (2) an ionomer, (3) a solvent and / or water, and (4) an additive.

[0061] 1.14 1.13 water electrolyzer, wherein the ionomer is selected from the group consisting of: (1) a polymer based on poly(arylpiperidinium) containing either a piperidone monomer or a 3-oxo-6-azoniaspiro[5.5]undecane salt monomer, and an aromatic group and an optional trifluoroacetophenone monomer group; (2) a multiblock copolymer containing one or more norbornene-based hydrophilic blocks and one or more norbornene-based or alkene-based hydrophobic blocks; (3) a polymer based on styrene-butadiene block copolymer (SEBS) having quaternary ammonium groups tethered via aromatic rings; and (4) a polymer based on electron beam irradiated ETFE, LDPE, or HDPE, which can be tethered by quaternary ammonium cation groups.

[0062] 1.15 1.13 Water electrolyzer, wherein the additive is selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), polydimethylsiloxane (PDMS), polyamide (nylon), polyethylene (PE), ethylene tetrafluoroethylene (ETFE) and / or non-ionic surfactants (such as polyoxyethylene alkyl ethers).

[0063] 1.16 1.15 water electrolyzer, where the additive gives the ink the mechanical properties of a clay-like material that can be molded, rolled and / or hot pressed.

[0064] 2.1 Providing a water electrolyzer according to any one of 1.1 to 1.16; and A method of operating a water electrolyzer comprising providing a voltage between the anode and the cathode.

[0065] 2.2 The method of 2.1, wherein the voltage is less than 2.5 V per cell.

[0066] 2.3 2. The method of claim 2, wherein the anion exchange membrane is capable of operating for at least 1000 hours before requiring replacement. [Example]

[0067] Example 1 - AEMEL according to the present application AEMEL was constructed to demonstrate hydrogen generation using pure deionized water and low-cost plates. The specifications of the AEMEL are as follows: (a) Single cell structure (not multi-cell stack). (b) The anode plate is made of nickel and the cathode plate is made of graphite. (c) The PTL is made of nickel foam, and the GDL is made of carbon paper. (d) The anion exchange membrane and ionomer were selected to be poly(arylpiperidinium)-based polymers. (e) Using an electrical energy source, a voltage of less than 2.2 V was applied between the anode and cathode of each cell.

[0068] The membrane / electrode assembly was fabricated as follows: first, the cathode catalyst Pt / C was mixed with an ionomer solution to set the ionomer weight percentage below 40% and the final catalyst loading at 5 mg / cm. 2 This ink was then coated onto the membrane (CCM). Second, the anode catalyst IrO2 was mixed with the ionomer solution to keep the ionomer weight percentage below 40% and the final catalyst loading at 5 mg / cm. 2 The ink was then coated onto a substrate (CCE). The entire membrane / electrode assembly was pressed for a few minutes before assembly. The cell was 25 cm 2 The active area was 1000 Å and operated at 90° C. Pure deionized water was flowed only on the anode side.

[0069] This water electrolyzer operates at 200mA / cm for extended periods below 2.2V. 2The inventors believe that this example is the most stable pure water AEMEL developed to date.

[0070] Example 2 - AEMEL according to the present application To demonstrate hydrogen production from an AEM electrolyzer stack using pure deionized water, low-cost plates, and a low-cost catalyst, an AEMEL was constructed with the following specifications: (a) AEMEL with a four-cell stack. (b) The anode, bipolar, and cathode plates are made of stainless steel 316. (c) Stainless steel was used as the PTL and carbon paper was used as the GDL. (d) The anion exchange membranes and ionomers were selected to be multi-block copolymers containing one or more norbornene-based hydrophilic blocks and one or more norbornene-based or alkene-based hydrophobic blocks. (e) A voltage of less than 2.2 V was applied between the anode and cathode using an electrical energy source.

[0071] The membrane / electrode assembly was fabricated as follows: first, the cathode catalyst, nickel alloy, was mixed with an ionomer solution to set the ionomer weight percentage below 50% and the final catalyst loading at 5 mg / cm. 2 This ink was then coated onto a membrane (CCM). Second, a molybdenum-based anode catalyst was mixed with an ionomer solution to keep the ionomer weight percentage below 50% and the final catalyst loading at 5 mg / cm. 2 The ink was then coated onto a decal (PTFE coated fiberglass) and thermally laminated to coat it on the anode side. The cell was 25 cm 2 The water electrolyzer had an active area of ​​1.5 m / s and was operated at 90°C. Pure deionized water was flowed only on the anode side. The water electrolyzer was operated at 200 mA / cm per cell for extended periods below 2.2 V. 2 showed.

[0072] Example 3 - AEMEL according to the present application To demonstrate hydrogen production from an AEM electrolyzer using pure deionized water and different coating technologies, an AEMEL was constructed with the following specifications: (a) Single cell structure (not multi-cell stack). (b) The anode plate is made of nickel and the cathode plate is made of graphite. (c) The PTL is made of nickel foam, and the GDL is made of carbon paper. (d) The anion exchange membrane and ionomer were selected to be polymers based on styrene-butadiene block copolymer (SEBS) with quaternary ammonium groups tethered via aromatic rings. (e) A voltage of less than 2.2 V was applied between the anode and cathode using an electrical energy source.

[0073] The membrane / electrode assembly was fabricated as follows: first, the cathode catalyst Pt / C was mixed with an ionomer solution to set the ionomer weight percentage below 40% and the final catalyst loading at 5 mg / cm. 2 The ink was then coated onto PTL (CCE). Second, the anode catalyst was electrochemically grown on nickel foam at 5 mg / cm. 2 The final catalyst loading was less than 25 cm. 2 The water electrolyzer had an active area of ​​1.5 m / s and was operated at 60°C. Pure deionized water was flowed only on the anode side. The water electrolyzer was operated at 200 mA / cm for extended periods below 2.2 V. 2 showed.

[0074] The above examples are merely illustrative and are not intended to be an exhaustive list of all possible embodiments, applications, or modifications of the present electrochemical device. Accordingly, various modifications and variations of the described methods and systems of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the present invention has been described in connection with specific embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described embodiments for carrying out the present invention that are apparent to those skilled in the chemical or related fields are intended to be within the scope of the appended claims.

[0075] Example 4 - AEMEL according to the present application AEMEL was constructed to demonstrate hydrogen production using pure water and low-cost plates. The specifications of AEMEL are as follows: (f) Single cell structure (not multi-cell stack). (g) The anode and cathode plates are made of stainless steel 316. (h) The PTL and GDL consist of nickel foam with similar porosity. (i) The anion exchange membranes and ionomers were selected to be multi-block copolymers containing one or more norbornene-based hydrophilic blocks and one or more norbornene-based or alkene-based hydrophobic blocks. (j) Using an electrical energy source, a voltage of less than 2.2 V was applied between the anode and cathode of each cell.

[0076] The membrane / electrode assembly was fabricated as follows: First, the cathode catalyst, NiMo on carbon, was mixed with an ionomer solution, keeping the ionomer weight percentage below 40%. Additives such as PTFE, PAA, PVA, and PFA were also added. This clay-like ink was then molded and pressed onto the GDL. Second, the anode catalyst, NiMo, was mixed with the ionomer solution, keeping the ionomer weight percentage below 40%. x Fe y O zwas mixed with the ionomer solution, keeping the ionomer weight percent below 40%. This clay-like ink was then molded and pressed onto the PTL.

[0077] Before assembly, the entire membrane / electrode assembly was pressed. The cell was 25 cm 2 The water electrolyzer had an active area of ​​1000 mA / cm² and was operated at 60°C. Pure water was flowing only on the anode side. The water electrolyzer was operated at 500 mA / cm² for extended periods below 2.5V. 2 showed.

[0078] Example 5 - AEMEL according to the present application An AEMEL was constructed to demonstrate hydrogen production using pure deionized water, low-cost plates, and a low-cost OER catalyst. The specifications of the AEMEL are as follows: (k) Single cell structure (not multi-cell stack). (l) The anode plate is made of stainless steel and the cathode plate is made of graphite. (m) The PTL is made of nickel foam and the GDL is made of carbon paper. (f) Anion exchange membranes and ionomers were selected to be polymers based on multi-block copolymers containing one or more norbornene-based hydrophilic blocks and one or more norbornene-based or alkene-based hydrophobic blocks. (n) An electrical energy source was used to apply a voltage of less than 2.2 V between the anode and cathode of each cell.

[0079] The membrane / electrode assembly was fabricated as follows: First, the anode PTL was immersed in Fe(III) solution for 96 hours. The PTL was then air-dried overnight. Second, the cathode catalyst PtNi / C was mixed with the ionomer solution to adjust the ionomer weight percentage to less than 40% and the final catalyst loading to 5 mg / cm. 2 The ink was then coated onto a carbon substrate (CCE). The entire membrane / electrode assembly was pressed for a few minutes before assembly. The cell was 25 cm 2The active area was 1000 Å and operated at 70° C. Pure deionized water was flowed only on the anode side.

[0080] This water electrolyzer operates at 200mA / cm for extended periods below 2.2V. 2 showed.

[0081] Example 6 - AEMEL according to the present application To demonstrate hydrogen production from an AEM electrolyzer stack using pure deionized water, low-cost plates, and a low-cost catalyst, an AEMEL was constructed with the following specifications: (g) AEMEL with a four-cell stack. (h) The anode, bipolar, and cathode plates are made of stainless steel 316. (i) Stainless steel was used as the PTL and carbon paper as the GDL. (j) The anion exchange membranes and ionomers were selected to be multi-block copolymers containing one or more norbornene-based hydrophilic blocks and one or more norbornene-based or alkene-based hydrophobic blocks. (k) A voltage of less than 2.2 V was applied between the anode and the cathode using an electrical energy source.

[0082] The membrane / electrode assembly was fabricated as follows: first, the cathode catalyst PtNi / C was mixed with an ionomer solution to set the ionomer weight percentage below 50% and the final catalyst loading at 5 mg / cm. 2 The ink was then coated onto a substrate (CCE). The anode PTL and Ni foam were then immersed in an ethanol solution of Fe(III) for 8-16 hours. The PTL was then immersed in another ethanol solution of Fe(III) with NH4HCO3 at 30°C with mechanical stirring. The cell was 25 cm 2 The water electrolyzer had an active area of ​​1.5 m / s and was operated at 70°C. Pure deionized water was flowed only on the anode side. The water electrolyzer was operated at 200 mA / cm per cell for extended periods below 2.2 V. 2 showed.

[0083] The above examples are merely illustrative and are not intended to be an exhaustive list of all possible embodiments, applications, or modifications of the present electrochemical device. Accordingly, various modifications and variations of the described methods and systems of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the present invention has been described in connection with specific embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described embodiments for carrying out the present invention that are apparent to those skilled in the chemical or related fields are intended to be within the scope of the appended claims.

Claims

1. an anode comprising an anode catalyst; a cathode including a cathode catalyst; and an anion exchange membrane interposed between the anode and the cathode; Water electrolyzer including: The water electrolyzer uses tap water or purified water that does not contain additives such as salts, acids, or bases.

2. 2. The water electrolyzer of claim 1, wherein the anion exchange membrane comprises a material selected from the group consisting of: (a) a polymer based on poly(arylpiperidinium) containing either a piperidone monomer or a 3-oxo-6-azoniaspiro[5.5]undecane salt monomer, an aromatic group, and an optional trifluoroacetophenone monomer group; (b) a multiblock copolymer containing one or more norbornene-based hydrophilic blocks and one or more norbornene-based or alkene-based hydrophobic blocks; (c) a polymer based on styrene-butadiene block copolymer (SEBS) having quaternary ammonium groups tethered via aromatic rings; and (d) a polymer based on electron beam irradiated ETFE, LDPE, or HDPE that can be tethered by quaternary ammonium cation groups.

3. 3. The water electrolyzer according to claim 1, wherein the cathode is a dry cathode.

4. The water electrolyzer according to any one of claims 1 to 3, further comprising an anode catalyst and a cathode catalyst.

5. The water electrolyzer according to any one of claims 1 to 4, wherein the anode catalyst comprises one or more metal catalysts, and the metal is a metal other than Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, and Au.

6. The water electrolyzer according to any one of claims 1 to 5, wherein the anion exchange membrane has a thickness of 1 to 200 µm.

7. The water electrolyzer of any one of claims 1 to 6, further comprising a porous transport layer and a gas transport layer.

8. 8. The water electrolyzer according to any one of claims 1 to 7, wherein the anode plate comprises a stainless steel plate having a pocket-shaped flow field and optionally coated.

9. 9. The water electrolyzer according to any one of claims 1 to 8, wherein the cathode plate comprises a stainless steel plate having a pocket-shaped flow field and optionally coated.

10. 10. The water electrolyzer according to any one of claims 1 to 9, further comprising a bipolar plate, the bipolar plate comprising an optionally coated stainless steel plate having pocket-shaped flow fields on both sides.

11. The water electrolyzer according to any one of claims 7 to 10, wherein the porous transport layer comprises a nickel material.

12. The water electrolyzer according to any one of claims 7 to 10, wherein the gas diffusion layer comprises a nickel material.

13. The water electrolyzer according to any one of claims 1 to 12, further comprising a catalyst ink containing (1) an anode catalyst or a cathode catalyst, (2) an ionomer, (3) a solvent and / or water, and (4) an additive.

14. 14. The water electrolyzer according to claim 13, wherein the ionomer is selected from the group consisting of: (1) a polymer based on poly(arylpiperidinium) containing either a piperidone monomer or a 3-oxo-6-azoniaspiro[5.5]undecane salt monomer, an aromatic group, and an optional trifluoroacetophenone monomer group; (2) a multi-block copolymer containing one or more norbornene-based hydrophilic blocks and one or more norbornene-based or alkene-based hydrophobic blocks; (3) a polymer based on styrene-butadiene block copolymer (SEBS) having quaternary ammonium groups tethered via aromatic rings; and (4) a polymer based on electron beam irradiated ETFE, LDPE, or HDPE that can be tethered by quaternary ammonium cation groups.

15. 14. The water electrolyzer according to claim 13, wherein the additive is selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), polydimethylsiloxane (PDMS), polyamide (nylon), polyethylene (PE), ethylene tetrafluoroethylene (ETFE), and / or a non-ionic surfactant (such as a polyoxyethylene alkyl ether).

16. 16. The water electrolyzer of claim 15, wherein the additive imparts to the ink the mechanical properties of a clay-like material that can be molded, rolled and / or hot pressed.

17. A method of operating a water electrolyzer, comprising providing a water electrolyzer according to any one of claims 1 to 16, and providing a voltage between the anode and cathode.

18. 17. The method of claim 16, wherein the voltage is less than 2.5 V per cell.

19. 18. The method of claim 17, wherein the anion exchange membrane is capable of operating for at least 1000 hours before requiring replacement.

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