Apparatuses for water electrolysis and methods for their manufacturing and operation

Abstract

Disclosed are apparatuses, cells, and stacks for water electrolysis, where electrolyte and electrodes are compartmentalized in a sealed compartment and separated from the water feedstock by a porous non-wettable, gas and vapor permeable interface. The electrochemical reactions are thus fed by the water vapor crossing from the liquid water feed through the non- wettable interface and condensing in the sealed compartment. The hydrogen and oxygen gases generated by electrolysis move in the opposite direction, through the non-wettable interface, and away from the sealed reaction compartment. No liquid flow contact exists between the sealed compartment and the environment, allowing the use of low-quality water with neutral pH as feedstock.

Description

APPARATUSES FOR WATER ELECTROLYSIS AND METHODS FOR THEIR MANUFACTURING AND OPERATIONTECHNICAL FIELD

[0001] The present invention relates to the field of water electrolysis for electrochemical generation of hydrogen from water.BACKGROUND

[0002] Hydrogen is a valuable industrial gas, widely used in manufacturing of ammonia fertilizer, methanol, and other useful chemicals, as well as in the petrochemical industry for hydrogenation of heavy hydrocarbons. Recently, hydrogen has been increasingly used as a fuel since it bums cleanly, with water as the only by-product, without emission of carbon dioxide or other greenhouse gases. Hydrogen powered fuel cells are increasingly being used to generate electric mobility in vehicles and in other applications.

[0003] Hydrogen can be generated from water using electricity in a process known as electrolysis, which has been first demonstrated in 1789, with the first industrial electrolyzers appearing in 1888. Water electrolysis is a conceptually simple process where electricity is applied between two electrodes and water is electrochemically split into hydrogen generated at the cathode and oxygen generated at the anode. Compensating ionic current flows between the electrodes in an electrolyte medium.

[0004] The most commonly used method for electrolysis of liquid water is alkaline water electrolysis (AWE), performed with strong alkali electrolytes and cost-effective electrodes made from non-precious metals, such as nickel or nickel-iron alloys.

[0005] AWE uses strong alkali electrolyte, such as highly concentrated potassium hydroxide (KOH) or sodium hydroxide (NaOH) dissolved in high-purity deionized water. While KOH and NaOH are inexpensive reagents, their solutions strongly absorb carbon dioxide from the atmosphere, leading to formation of carbonates, which reduce electrolytic performance. In addition, KOH and NaOH solutions are highly corrosive, and their use requires that the electrolyzer and the supporting systems are made from high quality corrosion-resistant materials and that extra care is taken to avoid contact of KOH with the environment and thepersonnel.

[0006] The electrodes in some AWE systems must be separated by a gap that can be several millimeters in length, to prevent the crossover of the hydrogen and oxygen gasses that are generated at the electrodes. The ionic resistance in the gap between electrodes creates polarization and a significant IR loss in the process. More advanced AWE methods use a solid separator between the electrodes, made for example from polysulfone and zirconium oxide (such as Ziffron membrane), which eliminates the gap but introduces additional cost and resistance. In general, AWE cannot operate at high differential pressures, since the oxygen and hydrogen gases cross over between the electrodes and mix, which therefore requires that the hydrogen product is compressed post-production.

[0007] Another common method for water electrolysis is Proton Exchange Membrane Water Electrolysis (PEMWE), which is based on a proton-conducting solid electrolyte membrane. PEMWE systems are fed ultrapure water, which can be with neutral pH. However, the oxidation of neutral water at the anode to gaseous oxygen proceeds with generation of strong acid, which is even more corrosive than KOH or NaOH. This strong acid can corrode the bipolar plates used for connecting the PEMWE cells into stacks and degrade the performance of the system. For this reason, PEMWE cells connected in stacks require expensive acid-resistant bi-polar plates made from titanium alloys or gold-plated steel, to protect against acid corrosion.SUMMARY

[0008] Briefly, the invention comprises apparatuses, cells, and stacks of cells for water electrolysis, where electrolyte and electrodes are compartmentalized in a sealed compartment and separated from the water feedstock by a porous non-wettable, gas and vapor permeable interface . The electrochemical reactions are thus fed by the water vapor crossing from the liquid water feed through the non-wettable interface and condensing in the sealed compartment. The hydrogen and oxygen gases generated by electrolysis move in the opposite direction, through the non-wettable interface, and away from the sealed reaction compartment.

[0009] The sealed compartment is under high pressure, facilitating the escape of the produced gases out of the sealed compartment and allowing production of pressurized hydrogen.

[0010] The present invention also provides for integrated electrode structures and methods for their manufacture, as well as other methods to achieve electrical connection between theelectrochemically-active metal electrodes, which reside inside the sealed compartment and the electric current carrying structures (bi-polar plates or pre-electrodes) that are outside the sealed compartment.

[0011] The apparatuses of the present invention can be used both for AWE and PEMWE.

[0012] When applied as an AWE system the apparatuses and methods of the present invention make use of common components employed in AWE - KOH or NaOH electrolyte and nonprecious metal electrodes - while at the same time eliminating most of AWE downsides: i. Allow use of water feedstocks of low quality and purity, including seawater (low-grade water), eliminating the need for high purity water and the associated demineralization systems and costs. ii. Eliminate the handling of highly corrosive alkali hydroxides outside of the sealed reaction compartment, allowing all the feeding, output and other auxiliary systems to be made from affordable materials and reducing the health, safety and environmental risk of concentrated KOH or NaOH solutions. iii. Allow the production of high-purity and high-pressure hydrogen product directly in the electrolyzer, reducing the costs of post-processing. iv. Eliminate the contact of KOH or NaOH solutions to atmospheric air, leading to reduced absorption of carbon dioxide and improved performance. v. Reduce the resistance of the interelectrode separator, thus reducing the electrical IR losses and allowing operation at higher current densities.

[0013] When applied as a PEMWE system, the apparatuses and methods of the present invention make use of the common components employed in PEMWE - membranes, catalyst electrode materials, and porous transport layers (PTLs) — usually assembled into membraneelectrode assemblies (MEAs) — while at the same time eliminating some PEMWE downsides: i. Eliminate the leakage of anode -generated acid to the bi-polar plates (BPPs), allowing construction of BPPs from inexpensive materials such as stainless steel. ii. Allow use of low-grade water feedstocks, eliminating the need for high purity water and the associated demineralization systems and costsBRIEF DESCRIPTION OF THE DRAWINGS

[0014] Certain details of the present disclosure are presented in the following drawings, in addition to and as clarifying illustrations to the features that are apparent from the description, the claims and the examples.

[0015] Throughout the various drawings, like reference numerals are used to designate like elements and they are referenced accordingly in the detailed description.

[0016] FIG. 1. is a schematic diagram of the layers in an electrolysis cell of the present invention with a sealed compartment 10. The cell comprises of a first pre-electrode 106, a second pre-electrode 107, and a sealed compartment 10, which sealed compartment is comprising of a first electrode 102, a second electrode, 103, an optional separator 100, seals or gaskets 101, and two non-wettable interfaces 104. The electrodes 102 and 103 are contacted to the pre-electrodes 106 and 107 throughout the periphery with peripheral metal contacts 105, ensuring electrical connectivity between them.

[0017] FIG. 2 is a schematic diagram of the layers in a three-layer integrated electrode structure with conductive tacks, comprising of a pre-electrode 111, non-wettable interface 110 and electrode 108, where the electrical contact between the electrodes and the pre-electrodes is achieved via conductive non-permeable tacks 109.

[0018] FIG. 3a is a schematic diagram of the layers in an integrated electrode structure with protrusions, comprising a pre-electrode 111, plated protrusions 113, protruding from the pre- electrode through the non-wettable porous interface 112 into the sealed compartment. FIG. 3b represents the integrated electrode structure 114 with protrusions 113.

[0019] FIG. 4 is a schematic diagram of a single inner electrolytic cell in a AWE stack, comprising of a sealed compartment 11, which sealed compartment is comprising of an integrated anode structure with protrusions 115, an integrated cathode structure with protrusions 116, an optional separator 100, and seals or gaskets 101. The electrolytic cell with the sealed compartment is contacted in series through bi -polar plates 117 and 118 to adjacent cells (not shown). The stack arrangement of layers with gaskets and seals incorporates feeding line for water 117a and outlet line for brine and oxygen gas 118a which lines are open in the space between the BPP 117 and the integrated anode structure 115, an additional (optional)water feed line 118b and outlet line for hydrogen gas 117b, which lines are open in the space between the BPP 118 and the integrated cathode structure 116, as well as electrolyte fill-in, make-up and exchange inlet line 117c and outlet line 118c, which lines only open inside the sealed compartment 11. The BPPs feature protruding ridges 117d for making electrical contact to the integrated electrode structures and indented valleys 117e as channels for the flow of water and gases.

[0020] FIG. 5 is a schematic diagram of a single inner electrolytic cell in a AWE stack, comprising of a sealed compartment 12, with peripheral conductive contacts 105. The numbered elements are described in the descriptions of FIG. 1 and FIG. 4

[0021] FIG. 6 is a schematic diagram of a single inner electrolytic cell in a PEMWE stack, comprising of a sealed compartment 13, which sealed compartment is comprising of a membrane-electrode assembly (MEA) 119, porous transport layers (PTLs) 120, seals or gaskets 101, and non-wettable interfaces 104. The PTLs 120 are connected to the BPPs 117 and 118 through electrically conductive peripheral contacts 105, which surround the sealed compartment. The stack incorporates feeding and outlet lines that are similar to the lines of the AWE stack described in FIG. 4 and FIG. 5. One difference is that the inlet 117c and outlet 118c lines, which open inside the sealed compartment 13 are used to wet the MEA 119 inside 13 with ultra-pure water, instead of alkaline electrolyte solution.DETAILED DESCRIPTION

[0022] The present invention comprises an electrolytic cell or a stack of cells with a sealed compartment separated from the water feed by a non-wettable, gas and vapor permeable interface.AWE Electrolytic Cells with Sealed Compartments

[0023] In the AWE cells of the present invention shown on FIG. 1, the sealed compartment comprises of a first electrode (anode) 102, a second electrode (cathode) 103, seals or gaskets 101, and two porous, non-wettable interfaces 104. and may include an optional separator 100, between the anode and cathode.

[0024] Throughout this disclosure “non-wettable” means to be generally impermeable to liquidwater and aqueous solutions, but permeable to gases and vapors, while “sealed compartment means a compartment without liquid flow contact to and from the environment outside.

[0025] The sealed compartment is sealed with alkaline electrolyte inside, so that the electrolyte is not in contact with the environment outside the sealed compartment. Since the sealed compartment is bordered by non-wettable interfaces 104 on each side, the liquid electrolyte cannot wet the interphase and escape the sealed compartment. At the same time water vapors are able to enter, and produced gases are able to exit the sealed compartment through the pores of the non-wettable interface.

[0026] In addition to the sealed compartment, the electrolytic cell includes a first pre-electrode 106 and a second pre-electrode 107. The pre-electrodes are electrically contacted to the electrodes inside the sealed compartment 10, so that electric currents can pass from the preelectrodes to the electrodes, as described below. While the electrodes and pre-electrodes are electrically connected, they are separated from each other by the non-wettable interfaces, so that only electrical current can pass between, but no liquids such as water or electrolyte.Electrodes and Pre-electrodes

[0027] The electrodes 102 and 103 are compositions made from non-precious metals or metal alloys that are effective in alkaline water electrolysis and are well known in the art. Such metal and metal alloy materials include nickel, stainless steel, nickel-iron alloys, nickel-cobalt alloys, nickel-molybdenum alloys, or others. Certain metal or metal alloy electrode materials may incorporate non-metal atoms (heteroatoms) such as phosphorus.

[0028] The electrode materials typically have a high electrochemical surface area (ECSA) to provide for high electrochemical performance. Metal electrode materials with high ECSA such as Raney Nickel are well known in the art. The electrode material structure is not monolithic, so that liquids and gases can pass through it. Examples of non-monolithic structures for electrodes are metal meshes, metal papers, metal foams, metal felts or others.

[0029] The pre-electrodes 106 and 107 are electrically conductive structures with pores, holes or other openings that allow passage of water and gases. In preferred embodiments the pre- electrodes are in the form of woven or non-woven stainless steel meshes, grids or perforated stainless steel sheets or expanded sheets. The function of the pre-electrodes is to evenly distribute the electric currents, reduce electrical resistance and provide electrical contact to thebipolar plates in electrolytic stacks.

[0030] The electrodes and the pre -electrodes must be connected electrically. In certain embodiments this is done through contact on their periphery as shown in FIG. 1, where a conductive peripheral contact is represented as the 105 elements. These conductive contact elements 105 surround and encompass the sealed compartment 10 and are in integral continuity with the solid non-porous borders of the electrodes 102 and 103 and the pre-electrodes 106 and 107, respectively. The 105 elements in FIG. 1 are shown as separate layers for clarity, however, they can be an integral raised part of the electrodes 102 and 103 or the pre-electrodes 106 and 107.

[0031] In certain other embodiments the electrodes and pre-electrodes are contacted through the non-wettable interphase to improve the electrical conductivity between them and reduce resistive electrical losses. An example of such contact is shown on FIG. 2 and is referred to as “contact with conductive tacks”. The contact with conductive tacks 109 is achieved through a perforation of the non-wettable interface 110 separating the electrode 108 from the preelectrode 111, and application of conductive paint in and across the perforation to: (i) contact and bind the electrode to the pre-electrode through the perforation, and (ii) to seal the perforation so that that the non-wettable integrity of the non-wettable membrane is restored. Conductive paints or waxes are well-known in the arts and typically consist of metal flakes or particles resuspended in a polymer solution, to be applied, followed by solidification through drying and / or curing.Integrated Electrode Structures with Protrusions

[0032] A subject of the present invention is “integrated electrode structures”, which comprise protrusions from the pre-electrodes, traversing the non-wettable interphase, as shown schematically on FIG. 3. FIG. 3a is a schematic diagram of the layers in an integrated electrode structure with protrusions, comprising a pre-electrode 111, plated protrusions 113, protruding from the pre-electrode through the non-wettable porous interface 112 into the sealed compartment. FIG. 3b represents the integrated electrode structure 114 with protrusions 113. The protrusions 113 are the effective electrochemical electrodes that carry the electrochemical splitting of water into hydrogen and oxygen inside the sealed compartment, and they represent a more economical substitute to the separately manufactured free-standing electrodes, such as102 and 103 in FIG. 1.

[0033] In a preferred embodiment the protrusions are made of nickel or other metal that is plated onto the stainless-steel pre-electrode through the pores of the non-wettable interphase.

[0034] The invention of these protrusions was brought about by the realization that: (i) certain hydrophobic membranes or porous films are wettable by organic solvents, such as alcohols, and by water-solvent mixtures even though they are impenetrable to liquid water and liquid aqueous solutions, and (ii) plating of metals can be accomplished from organic solvents or water-solvent mixtures.

[0035] The making of protrusions can be done either through electroplating or through electroless plating methods.

[0036] In the electroplating methods, the pre-electrode is used as a cathode and another material is used as anode, with current flowing between the anode and cathode, through an electroplating bath solution containing a dissolved salt of the metal that is being plated. The pre-electrode / cathode is covered with a non-wettable hydrophobic membrane which is pressed firmly against it to ensure good contact between them. In addition to the dissolved salts, the electroplating bath contains a solvent, which allows the wetting of the hydrophobic membrane.

[0037] In certain embodiments the metal protrusions are made from electroplated nickel, and correspondingly the electroplating bath contains dissolved nickel salts such as nickel chloride, nickel sulfate, nickel sulfamate, nickel ammonium sulfate or other salts. In addition, the electroplating bath contains an organic solvent to allow wetting of the membrane, such as isopropyl alcohol, ethanol, methanol, ethylene glycol, glycerol, acetone, or another organic solvent. In certain embodiments the electroplating bath contains a surfactant as a wetting agent, instead of organic solvent.

[0038] In electroless plating an anode is not required and the metal protrusions are plated from a bath containing a reducing agent. The pre-electrode is covered with a non-wettable hydrophobic membrane which is pressed firmly against it to ensure good contact between them and an electroless bath is applied over the membrane. The metal is plated onto the pre-electrode and protrudes through the membrane to form metal protrusions.

[0039] In certain other embodiments the metal protrusions are made from electroless nickel,and correspondingly the electroless bath contains dissolved nickel salts such as nickel chloride, and a reducing agent such as sodium hypophosphite. In addition, the electroless bath contains an organic solvent to allow wetting of the membrane, such as isopropyl alcohol, ethanol, methanol, ethylene glycol, glycerol, or others. In certain embodiments the electroless bath contains a surfactant as a wetting agent, instead of organic solvent.Non-wettable interface

[0040] The non-wettable surface interface of the present invention is a hydrophobic porous polymer fdm or coating that is generally non-wetted by water or by aqueous solutions, and is made from polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), polyvinylidene fluoride PVDF), polyetherimide (PEI) or another hydrophobic polymer or polymers.

[0041] In certain embodiments the non-wettable interface is a manufactured porous hydrophobic non-wettable membrane. Such membranes are well known in the art and can be produced by a variety of methods such as: dry stretching of PP, expansion of PTFE, phase inversion techniques, such as TIPS (temperature-induced phase separation), of fiber spinning techniques. Some of these non-wettable membranes are marketed under the brand names Celgard (dry-stretched PP), Gore-Tex (expanded PTFE) or others.

[0042] The wettability of these membranes by a given liquid depends on several factors: the surface tension of the liquid, the liquid-membrane contact angle, and the size and geometry of the pores. Theoretical models have been developed to estimate the pressure under which the liquid will enter the membrane, known as Liquid Entry Pressure (LEP). Membranes with sufficiently small pore sizes (less than 100 nanometers) can withstand multiple atmospheres of hydrostatic pressure from aqueous solutions without wetting. Therefore, using such hydrophobic membranes allows operation of the electrolysis apparatus of this invention with pressure differentials across the non-wettable membrane, between the reaction compartment and the feed and product compartments.

[0043] In other embodiments the non-wettable interface is achieved by direct coating of a porous electrode or a porous current collector with a hydrophobic polymer to obtain a nonwettable porous coating, which has similar pore architecture and function as the premanufactured membranes described above.

[0044] Sealings. Electrode Separation and Electrolytes

[0045] Sealing of the sealed compartment is accomplished with water-tight seals or gaskets. The seal or gasket material can be chosen from among a variety of thermoplastic polymers such as polyethylene, polypropylene, PEEK, or thermoplastic elastomers such as isobutylene, or other elastomers or rubbers that are well known in the arts for its water-tight sealing properties. The function of the seal or gasket is to prevent liquid contact between the edges of the sealed compartment and the outside environment.

[0046] Another function of the seal or gasket is to provide for separation between the cathode and the anode, which has two purposes: (i) to prevent electrical contact and short-circuit between the electrodes, and (ii) to prevent crossover of produced oxygen and hydrogen gases, which would lead to either loss of hydrogen product into the oxygen outlet, or contamination of hydrogen product with oxygen.

[0047] In certain embodiments the separation between the anode and cathode is provided solely by the gap between them. In other embodiments the separation between the anode and cathode is provided or complemented by a solid separator. The separator can be a macroporous separator such as non-woven or woven polymer mesh or paper. In other embodiments the separator can be a microporous separator. In other embodiments the separator can be an anion- exchange membrane (AEM) separator.

[0048] The separation gap is filled with electrolyte, and when the separation is enhanced by a solid separator, the separator is also impregnated with electrolyte. The electrolyte is a concentrated solution of a strong base such as 30% KOH or 30% NaOH. Such alkaline electrolytes are well-known and used in the AWE art.AWE Stacks of Cells

[0049] In a preferred embodiment, two or more of the electrolysis cells of the present invention can be connected into stacks, using conductive solid bi-polar plates (BPPs). Stacking of electrolytic cells is well-known in the arts.

[0050] In a preferred embodiment the cells are electrically connected in series to form a stack, using BPPs. In that configuration the bi-polar plates are made of conductive material, such as stainless steel or other metal. The bi-polar plates are positioned between cells so that one side(cathode-side) of the bi-polar plate is contacted to the cathode pre-electrode / electrode of a cell (cell 1) and the other side (anode-side) of the bi-polar plate is contacted to the anode pre- electrode / electrode of the next cell (cell 2) and so on.

[0051] The sides of the bi-polar plates are not flat but are machined with extending ridges to make electrical contact with the pre-electrodes, as well as indented valleys to create channels for the in-flow of feed water and outflow of produced gases to the corresponding lines.

[0052] FIG. 4 is a schematic diagram of a single inner electrolytic cell in a AWE stack, comprising of a sealed compartment 11, which sealed compartment is comprising of an integrated anode structure with protrusions 115, an integrated cathode structure with protrusions 116, an optional separator 100, and seals or gaskets 101. The electrolytic cell with the sealed compartment is contacted in series through bi-polar plates 117 and 118 to adjacent cells (not shown).

[0053] The stack arrangement of layers with gaskets and seals incorporates a feeding line for water 117a and an outlet line for brine and oxygen gas 118a, which lines are open in the space between the BPP 117 and the integrated anode structure 115; an outlet line for hydrogen gas 117b and an additional (optional) water feed line 118b, which lines are open in the space between the BPP 118 and the integrated cathode structure 116. The BPPs feature extending ridges 117d for making electrical contact to the integrated electrode structures and indented valleys 117e as channels for the flow of water and gases.

[0054] In certain embodiments electrolyte fdl-up, make-up and exchange lines are also included in the stack and are shown on FIG. 4 as inlet line 117c and outlet line 118c, which lines only open inside the sealed compartment 11.

[0055] In certain other embodiments of an AWE stack, free-standing, pre-manufactured electrodes are employed instead of protrusions. FIG. 5 is a schematic diagram of a single inner electrolytic cell in an AWE stack, comprising of a sealed compartment 12 with peripheral conductive contacts 105 between the free-standing electrodes 102 and 103, and the preelectrodes 106 and 107, respectively (see FIG 1 as well). The designations for the inlet and outlet lines, as well as the BPPs, are the same as in FIG 4.

[0056] Whenever the cells are arranged in stacks, the sealing takes into consideration the natureof the electrodes and pre-electrodes that are used. In the case of integrated electrode structures with protrusions, a simple seal or gasket is sufficient between the two non-wettable films (FIG. 4). In the cases where the electrode is a separate free-standing structure (metal mesh or grid or foam), additional sealing is applied to the electrode, on the inner periphery of the cell, inside of the metal -to-metal electrical contact on the outer periphery (FIG 5).Differential Pressure Operation

[0057] The AWE apparatuses of the present invention can be operated with a differential pressure between the water feed line and the hydrogen product line, allowing the water to be fed into the apparatus with low pressure, that is close to atmospheric pressure with only slight overpressure sufficient to overcome the hydraulic resistances in the flowpath, while producing high-pressure hydrogen product and reducing the requirements for post-production compression.

[0058] This capability is based on the discovery that the sealed compartment that is the subject of the present invention becomes pressurized on its own during operation. Without claiming to have an exhaustive scientific explanation of this discovery, we believe that it is based on the low vapor pressures over concentrated KOH and NaOH solutions, which draw and condense water vapors from the feed water, leading to an expansion of the liquid volume in the sealed compartment. Since the liquid cannot penetrate and escape the non-wettable interfaces, this excess liquid volume results in a sharp increase in the pressure inside the sealed compartment.

[0059] The differential pressure operation method of the present invention is enabled by pressure control valves in the product outlet lines in the electrolyzer stacks, which can be adjusted to the desired output pressure. For a given electrolyzer configuration with a particular interelectrode separation, there is a maximum output pressure (breakthrough pressure), which allows operation without significant crossover and loss of hydrogen product into the inlet line. The breakthrough pressure is higher for electrolyzers with solid ion-exchange separators and lower for liquid gap separation without solid separator.PEMWE Electrolytic Cells and Stacks of Cells with Sealed Compartments

[0060] The electrolytic cells with a sealed compartment of the present invention can be implemented as PEMWE cells and stacks of cells, where the non-wettable interface preventsthe leakage of corrosive acid from the anode and allows operation of the electrolyzer with low- grade water feed.

[0061] FIG. 6 is a schematic diagram of a single inner electrolytic cell in a PEMWE stack, comprising of a sealed compartment 13, which sealed compartment is comprising of a Proton Exchange Membrane (PEM)-catalyst layer 119, porous transport layers (PTLs) 120, seals or gaskets 101, and non-wettable interfaces 104. The PTLs 120 are connected to the BPPs 117 and 118 through electrically conductive peripheral contacts 105, which surround the sealed compartment. The PEM-catalyst layer 119 and the PTLs 120 are commonly referred in the arts as membrane-electrode assemblies (MEA).

[0062] The stack incorporates inlet and outlet lines, which are similar to the lines of the AWE stack described in FIG. 4 and FIG. 5 and are identified with the same numerals. One difference is that the inlet 117c and outlet 118c lines, which open inside the sealed compartment 13, are used to wet the MEA (119, 120) inside 13 with ultra-pure water, instead of alkaline electrolyte solution.

[0063] MEAs, PEMs and PTLs are well-known in the PEMWE art. PEMs are electrically insulating proton-conducting membranes, usually made from sulfonated fluropolymers (brand name Nafion). The electrode catalyst material is usually platinum or another platinum-group metal, and is usually bound to the PEM and the GTLs with the help of ionomer binders, which are similar in chemical composition to the PEM. PTLs are generally found on both sides of the MEA and their function is to deliver and distribute electrical current to the catalyst. PTLs are often made from carbon paper or carbon cloth.

[0064] The non-wettable interphases 104 for PEMWE cells in FIG. 6 are essentially the same as the ones for AWE cells described above.

[0065] In a preferred embodiment the non-wettable interphases 104 for PEMWE stacks are positioned between the PTLs 120 and the BPPs 117 and 118, as shown on FIG. 6, and low- grade feed water is supplied between the BPP and the sealed compartment 13. In such an arrangement, the strong acid generated at the PEMWE anodes stays inside the sealed compartment and cannot corrode the BPPs. Consequently, the BPPs can be made from inexpensive materials, such as stainless steel.

[0066] Electrical contact between the BPPs and the PTLs of the PEMWE stack is accomplished in the same way as the contact between pre-electrode and electrode in the AWE stacks. More specifically, in certain embodiments the electrical contact 105 is on the outer periphery of the stack, outside the sealed compartment 13, as shown on FIG. 6. In other embodiments the electrical contact is achieved with conductive tacks made of non-permeable conductive paint between the BPP and the PTL and through the non-wettable interface (see FIG. 2). In other embodiments, metal protrusions are plated onto the BPP ridges, going through the non-wettable interface and contacting the PTL (see FIG 3).

[0067] Sealing is required between the PTLs and the non-wettable interphases to prevent the flow of low-grade water from the water inlet line into the sealed compartment from the edge of the stack.

[0068] A separate inlet line 117c, and an outlet line 118c in the stack have openings only inside the sealed compartments of the cells and are used to provide small amounts of high-purity water for initial wetting of the MEAs inside the sealed compartment. The seals of the stack are arranged so that there is no contact between the low-grade feed water and the high-purity water for wetting line.EXAMPLE: Electrolysis with a sealed compartment and tap water.

[0069] A simple electrolysis device was assembled with 4 sq. cm. active area, using Ni-paper electrodes with low ECSA (purchase from Dioxide Materials, Inc.) and an anion-exchange separator (FAS-PK membrane from FumaSep). In the Test experiment the electrodes were enclosed in a sealed compartment using stretched polypropylene membrane (Celgard), while in the Control experiment it was absent.

[0070] In the control experiment on the Left, 0.1M KOH electrolyte was used as feed (pH 13), in the KDI experiment on the right - with the sealed compartment - the feed was tap water (pH 6). 40 mA amperostatic current was applied, and electrolysis voltage and gas production were monitored.

[0071] Both electrolysis reactions proceeded with the expected gas generation rates (> 99% coulombic efficiency within measurement error). In the KOH experiment the voltage plateaued at 2.078 V, while in the KDI experiment at 2.098 V.

Claims

WHAT IS CLAIMED IS:

1. Water electrolysis cell with a sealed compartment, comprising of:Liquid alkaline electrolyte solution;A first electrode and a second electrode contacted electrically to electrical circuit elements outside the sealed compartment;A first porous non-wettable interface and a second porous non-wettable interface, constructed and arranged in such a way that the sealed compartment is sealed with the electrodes and the electrolyte inside, so that no liquid flow contact exists with the environment outside the sealed compartment2. The electrolysis cell of Claim 1, further comprising a separator between the first and the second electrode inside the sealed compartment.

3. The electrolysis cell of Claim 1, further comprising pre-electrodes, which are outside the sealed compartment and are in electrical contact with the first and second electrode.

4. The electrolysis cell of Claim 1, further comprising pre-electrodes, which are outside the sealed compartment and are in electrical contact with the first and second electrode via conductive tacks.

5. A multitude of the electrolysis cells of Claim 1, connected electrically via bipolar cells and arranged in an electrolysis stack.

6. Integrated electrode structure comprising of: a. A layer of electrically conductive material with pores, holes or other openings b. a porous non-wettable interface in contact with the electrically conductive layer c. metal protrusions protruding from the electrically conductive layer through the pores of the porous non-wettable interface7. The integrated electrode structure of Claim 5 where the protrusions are electroplated through the pores of the porous non-wettable interface8. The integrated electrode structure of Claim 5 where the protrusions are electrolessly plated through the pores of the porous non- wettable interface9. Water electrolysis cell with a sealed compartment comprising of:Liquid alkaline electrolyte solution;A first integrated electrode structure with protrusions and a second integrated electrode structure with protrusions;10. The electrolysis cell of Claim 9, further comprising a separator between the first and the second integrated electrode structure.

11. A multitude of the electrolysis cells of Claim 9, connected electrically via bipolar cells and arranged in an electrolysis stack.

12. Water electrolysis cell with a sealed compartment, comprising of:Membrane -electrode assembly with a proton-exchange membrane, catalyst and porous transport layers.A first porous non-wettable interface and a second porous non-wettable interface, constructed and arranged in such a way that the membrane electrode assemblies are sealed inside the sealed compartment.

13. A multitude of the electrolysis cells of Claim 12, connected electrically via bipolar cells and arranged in an electrolysis stack.

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