CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to the Singapore application no. 10202250857K filed August 30, 2022, the contents of which are hereby incorporated by reference in their entirety for all purposes.

TECHNICAL FIELD

[0002] This application relates to hydrogen production or water splitting.

BACKGROUND

[0003] The conventional water electrolyzer requires highly purified deionized water to carry out water splitting and generate hydrogen. Impurities in unpurified water, such as dissolved salts, organic molecules, microorganisms, and particulates, can corrode the electrocatalysts, generate parasitic electrochemical reactions, and suppress the water splitting process. For example, chloride anions can pose serious challenges for the anode (the electrode set to oxidative and positive potentials). The chlorine evolution reaction would compete with the oxygen evolution on the anode, while the generated chlorine can corrode components in the electrochemical cell (such as the electrodes, catalysts, and the separator), and even damage the electrolyzer. For the cathode (the electrode is set to reductive and negative potential), the existence of divalent ions, such as Ca ²⁺ and Mg ²⁺ , can form precipitation of carbonaceous (e.g., CaCCh, MgCCh) and hydroxylated species (e.g., Ca(OH)2, Mg(0H)2) on the cathode surface. These precipitates would block the active area of the electrode and catalysts, suppressing the hydrogen evolution reaction on the cathode. Cleaning typically involves the use of acid solutions to dissolve the precipitates. Therefore, most of the easily accessible and abundant water sources, such as seawater and brackish water, cannot be directly utilized by the electrolyzers for hydrogen generation.

SUMMARY

[0004] According to one aspect, the present application discloses a distillate electrolyzer apparatus. The distillate electrolyzer apparatus may be for use with a water source. The distillate electrolyzer apparatus includes: a cell, a membrane, and a baffle. The cell includes: a first electrode, a second electrode, and a separator. The first electrode and the second electrode form an operable pair of an anode and a cathode. The separator is disposed between the first electrode and the second electrode to define a first chamber and a second chamber. The first electrode is disposed in the first chamber and the second electrode is disposed in the second chamber. The first chamber and the second chamber are in fluidic communication with one another exclusively through the separator. The cell is in fluidic communication with the water source exclusively through the membrane. The baffle includes a non-porous panel moveable relative to a major surface of the membrane to expose a variable area of the membrane to the water source.

[0005] A transport of water from the water source across the membrane towards the cell may be enabled at least partially by a vapor pressure difference across the membrane and/or at least partially by an osmotic pressure difference across the membrane. A transport path of water from the water source towards the cell may include any one of the following: (i) a liquid phase transport of liquid water across the membrane responsive to an osmotic pressure difference across the membrane, the membrane including a hydrophilic membrane element, and (ii) a gaseous phase transport of water vapor across the membrane responsive to a vapor pressure difference across the membrane, the membrane including a hydrophobic membrane element. [0006] The membrane may be a hydrophilic membrane or a hydrophobic membrane. The membrane may form a part of a wall of the one or both of the first chamber and the second chamber, or disposed externally of the cell, with the membrane interposing each of one or more transport paths from the water source towards the cell. The distillate electrolyzer apparatus may include an electrolyte storage tank connected externally to the cell in the case where the membrane is disposed externally of the cell.

[0007] The cell may be operable as an alkaline water electrolyzer, a proton exchange membrane water electrolyzer, and/or an anion exchange membrane water electrolyzer.

[0008] The distillate electrolyzer apparatus may include a plurality of cells. The pair of the anode and the cathode of any one of the plurality of cells may be connected in parallel and/or in series with the pair of the anode and the cathode of another one of the plurality of cells.

[0009] In yet another aspect, the present application discloses a method of water splitting. The method includes providing a feed solution to a cell according to any described above. The method may include controlling a variable area of the membrane exposed to a water source by moving a non-porous panel of a baffle relative to a major surface of the membrane, in which the feed solution is in fluidic communication with the water source exclusively through the membrane. The feed solution may be formed by a transport of water from the water source across the membrane towards the cell, in which the transport includes any one of: (i) a liquid phase transport of liquid water across the membrane responsive to an osmotic pressure difference across a hydrophilic membrane element, and (ii) a gaseous phase transport of water vapor responsive to a vapor pressure difference across a hydrophobic membrane element.

[0010] In another aspect, the membrane may define a transport path extending from the feed solution in a feed channel outside the first chamber, across the membrane, and immediately into the first chamber. The transport path may be enabled at least partially by an osmotic pressure difference between the feed solution and a first electrolyte solution in the first chamber, in which the first electrolyte has a higher osmotic pressure than the feed solution. Alternatively, the transport path may be enabled at least partially by a vapor pressure difference across the membrane, the first chamber having a lower vapor pressure than in the feed channel. The distillate electrolyzer apparatus may further include a baffle. The baffle provides a non-porous surface parallel to a major surface of the membrane, wherein the baffle is in slidable engagement relative to the membrane.

[0011] The distillate electrolyzer apparatus may provide the feed solution and the first chamber in fluid communication exclusively through an active area of the membrane, in which a size of the active area is adjustable by sliding the baffle relative to the membrane.

[0012] The transport path may include a liquid phase transport of liquid water across the hydrophilic membrane based on an osmotic pressure difference or a gaseous phase transport of water vapor across the hydrophobic membrane based on a vapor pressure difference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Various embodiments of the present disclosure are described below with reference to the following drawings:

[0014] FIG. 1A is a schematic diagram illustrating a cell according to an alkaline water electrolyzer;

[0015] FIG. IB is a schematic diagram illustrating a cell according to a proton exchange membrane water electrolyzer;

[0016] FIG. 1C is a schematic diagram illustrating a cell according to an anion exchange membrane water electrolyzer;

[0017] FIG. 2A is a schematic block diagram illustrating a transport mechanism according to embodiments of the present disclosure; [0018] FIG. 2B is a schematic block diagram illustrating a transport mechanism according to other embodiments of the present disclosure;

[0019] FIG. 3 schematically illustrates a perspective view of a water electrolyzer apparatus according to various embodiments of the present disclosure;

[0020] FIG. 4A illustrates an alkaline water electrolyzer apparatus according to an embodiment of the present disclosure in which one wall of the anode chamber includes a membrane;

[0021] FIG. 4B illustrates an alkaline water electrolyzer apparatus according to another embodiment of the present disclosure in which one wall of the cathode chamber includes a membrane;

[0022] FIG. 4C illustrates an alkaline water electrolyzer apparatus according to another embodiment of the present disclosure in which each of the anode chamber and the cathode chamber includes a wall formed by a membrane;

[0023] FIG. 4D illustrates the water electrolyzer apparatus in which the membrane is a part of a wall of the anode chamber of a proton exchange membrane water electrolyzer cell;

[0024] FIG. 4E illustrates the water electrolyzer apparatus in which the membrane is a part of a wall of the cathode chamber of an anion exchange membrane water electrolyzer cell;

[0025] FIG. 5 A illustrates a front view of a water electrolyzer apparatus according to various embodiments of the present disclosure, with a baffle moveable to provide a controllable active area of the membrane;

[0026] FIG. 5B illustrates a side view of the water electrolyzer apparatus of FIG. 5 A;

[0027] FIG. 5C illustrates a front view of another water electrolyzer apparatus according to various embodiments of the present disclosure, with a baffle moveable to provide a controllable active area of the membrane;

[0028] FIG. 5D illustrates a side view of the water electrolyzer apparatus of FIG. 5C; [0029] FIG. 6A to FIG. 6C are schematic diagrams illustrating various embodiments of the water electrolyzer apparatus with an external electrolyte storage tank and an external membrane system to supplement water for the electrolyte;

[0030] FIG. 7 A illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are connected in parallel with a closed loop water supply, the water electrolyzer apparatus characterized by an “AFC” (anode chamber of one unit-feed channel-cathode chamber of next unit) configuration;

[0031] FIG. 7B illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are connected in parallel with an open loop water supply, the water electrolyzer apparatus characterized by an “AFC” (anode chamber of one unit-feed channel-cathode chamber of next unit) configuration;

[0032] FIG. 8A illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are alkaline water electrolyzers (AWE) connected in parallel with a closed loop water supply, with the feed channels only on the anode chamber side of the AWE;

[0033] FIG. 8B illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are proton exchange membrane water electrolyzers (PEMWE) connected in parallel with a closed loop water supply, with the feed channels only on the anode chamber side of the PEMWE

[0034] FIG. 9A illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are alkaline water electrolyzers (AWE) connected in parallel with a closed loop water supply, with the feed channels only on the cathode chamber side of the AWE;

[0035] FIG. 9B illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are anion exchange membrane water electrolyzers (AEMWE) connected in parallel with a closed loop water supply, with the feed channels only on the cathode chamber side of the AEMWE;

[0036] FIG. 10 illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are connected in parallel with a closed loop water supply, with the feed channels connected to either the cathode chamber or the anode chamber of each water electrolyzer;

[0037] FIG. 11 illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are connected in parallel with a closed loop water supply, with each feed channel shared by successive water electrolyzers and feeding the cathode chamber one water electrolyzer and the anode chamber of another water electrolyzer;

[0038] FIG. 12 illustrates a water electrolyzer apparatus according to another embodiment of the present disclosure, in which the cells are connected in parallel with a closed loop water supply, with each feed channel shared by successive water electrolyzers and feeding either the cathode chambers or the anode chambers of successive water electrolyzers;

[0039] FIG. 13A illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are connected in series with bipolar assemblies, and in which the feed channel feeds the anode side of the apparatus;

[0040] FIG. 13B illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are connected in series with bipolar assemblies, and in which the feed channel feeds the cathode side of the apparatus;

[0041] FIG. 13C illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are connected in series with bipolar assemblies, and in which the feed channel feeds both the anode side and the cathode side of the apparatus; [0042] FIG. 14A illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, in which the cells are connected in series with bipolar assemblies and in parallel with monopolar assemblies;

[0043] FIG. 14B illustrates a water electrolyzer apparatus according to an embodiment of the present disclosure, the apparatus including combinations of two or more different types of cells, e.g., anion exchange membrane water electrolyzer, proton exchange membrane water electrolyzer, and alkaline water electrolyzer;

[0044] FIG. 15A illustrates plots of water inflow flux (in units of liters per square meter of a membrane per hour) to a cell from sources of simulated wastewater (feed solutions), for an electrolyte (draw solution) in the electrochemical cell of a 1 M (Mole) NaHCCh/lSfeCCh buffer solution at various pH (pH=8.0, 9.5 and 11.3);

[0045] FIG. 15B illustrates plots of water inflow flux to the cell from water sources of simulated seawater (feed solutions), for an electrolyte (draw solution) in the electrochemical cell of a 1 M NaHCCh/lSfeCCh buffer solution at various pH (pH=8.0, 9.5 and 11.3);

[0046] FIG. 16 illustrates a water electrolyzer apparatus with separable modules according to an embodiment of the present disclosure; and

[0047] FIG. 17 is schematic flow diagram of a method of water splitting according to various embodiments of the present disclosure.

DETAILED DESCRIPTION

[0048] The following detailed description is made with reference to the accompanying drawings, showing details and embodiments of the present disclosure for the purposes of illustration. Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments, even if not explicitly described in these other embodiments. Additions and/or combinations and/or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0049] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0050] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance as generally understood in the relevant technical field, e.g., within 10% of the specified value.

[0051] As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

[0052] As used in the present disclosure, the terms “water electrolyzer cell” or "cells" may be used interchangeably with the terms “electrolyzer”, “water electrolyzer unit”, “water electrolysis device”, or “water electrolysis unit”. In referring to the present apparatus, the terms "distillate electrolyzer apparatus" (and/or any cell thereof) and "water electrolyzer apparatus" (and/or any cell thereof) may be used interchangeably. According to various embodiments of the present disclosure, a cell 102 includes a cathode 122 and an anode 132. The cathode 122 is disposed in a cathode chamber 120 and the anode 132 is disposed in an anode chamber 130. The cathode chamber 120 and the anode chamber 130 are separated from one another by a separator 150. In operation, a potential difference (e.g., voltage) 104 is provided across the cathode 122 and the anode 132, such that catalytic electrolysis of water molecules results in the production of hydrogen 20 at the cathode 122 and oxygen 30 at the anode 132. For example, the production of hydrogen 20 and the production of oxygen 30 occur in different chambers 110. In various embodiments, water or a feed solution 70 is fed to one or both chambers 110.

[0053] Advantageously, and as will be described in the following, various embodiments of the water electrolyzer apparatus 100 proposed herein may operate with one or more cells 102 of the following types: alkaline water electrolyzers (AWE), proton exchange membrane water electrolyzers (PEMWE), and/or anion exchange membrane water electrolyzers (AEMWE). In the present disclosure, the AWE refers to a cell 102 as schematically illustrated in FIG. 1A in which both the cathode chamber 120 and the anode chamber 130 contain aqueous solutions 90 provided from a water source 80. The separator 150 between the cathode chamber 120 and the anode chamber 130 serves to separate the hydrogen 20 and the oxygen 30 generated in each of the chambers 110 (at the cathode 122 and the anode 132 respectively). The separator 150 may also allow the transportation of the liquid solution as well as the ions between the two chambers 110.

[0054] In the present disclosure, the PEMWE refers to a cell 102 as schematically illustrated in FIG. IB in which only the anode chamber 130 contains an aqueous solution 90 and in which the separator 150 is a proton exchange membrane (PEM). The PEM separates the two chambers 110 (the cathode chamber 120 and the anode chamber 130) and allows transport of only protons from the anode chamber 130 to the cathode chamber 120. The liquid solution 90 will be rejected by the PEM and remains in the anode chamber 130.

[0055] In the present disclosure, the AEMWE refers to a cell 102 as schematically illustrated in FIG. 1C in which only the cathode chamber 120 contains an aqueous solution 90 and in which the separator 150 is an anion exchange membrane (AEM). The AEM separates the two chambers 110 (the cathode chamber 120 and the anode chamber 130) and allows transport of the anion (OH") from the cathode chamber 120 to the anode chamber 130. The liquid solution will be rejected by the AEM and remains in the cathode chamber 120.

[0056] Solely to aid understanding, the term “water source” 80 may refer to a body of water, for example but not limited to bodies of water such as lakes, reservoirs, rivers, seawater, etc., or to any source of water. In the context of the present disclosure, the water source 80 may be any source of water, including water that is compositionally unknown and/or unsuitable for use in a conventional water electrolyzer. The terms “feed” or “feed solution” 70 refers to the water directed from the water source 80 towards a cell or a plurality of cells 102. In some embodiments, the feed solution 70 may be substantially the same as the water source 80, and in some other embodiments, the feed solution 70 may be a purer form of the water source suitable for use in a water electrolyzer cell 102. For the present disclosure, depending on the type of water electrolyzer apparatus 100, the feed solution 70 may enter the anode chamber 130, the cathode chamber 120, or both anodic and cathodic chambers 110 from one or more feed channels 74. One or more feed channels 74 external to the one or more cells 102 serve to direct the feed solution 70. In some examples, and for ease of reference, the chamber 110 receiving the feed solution 70 directly from the feed channel 74 may be referred to as the "first chamber" 117 or the "draw chamber". Depending on the type of the water electrolyzer cell 102, the first chamber 117 may be the anode chamber 130 (the chamber in which the anode 132 is disposed) or the cathode chamber 120 (the chamber in which the cathode 122 is disposed). Alternatively, both the anode chamber 130 and the cathode chamber 120 may serve as the draw chambers. In some embodiments of the present disclosure, each of the one or more draw chambers provides a pressure difference (osmotic or otherwise) to draw water into the cell 102 across a membrane 200. In some embodiments, the electrolyte or aqueous solution 90 in the draw chamber may serve as a draw solution. In some embodiments, the electrolyte 90 in any one or more of the first chamber 117 and/or draw chambers may be supplied or supplemented by an external membrane system 600 (with or without one or more external electrolyte storage tanks 601).

[0057] The water electrolyzer apparatus 100 according to various embodiments of the present disclosure includes apparatus configured to provide a continuous supply of sufficiently clean or pure water to the one or more water electrolyzers or cells 102 coupled to a water source 80.

[0058] FIG. 2A schematically illustrates a first water transport mechanism by which the water electrolyzer cell 102 may be provided with water in accordance with some embodiments of the present water electrolyzer apparatus. The water electrolyzer apparatus 100 of the present disclosure is capable of drawing directly from a water source 80 or feed solution 70 that may contain impurities, salt ions, organic materials, etc. Water sources 80 such as natural bodies of water, including brackish water, seawater, wastewater, etc., may be used as the feed solution 70. The membrane 200 may be a semipermeable hydrophilic membrane. The driving force for water transport across the membrane 200 includes that based on an osmotic pressure difference across the membrane 200. The liquid 90 in the first chamber 117 (also referred to as the draw solution) has a higher salinity (and a higher osmotic pressure) than that of feed solution 70. The feed solution 70 has a lower salinity (and a correspondingly lower osmotic pressure) than that of the draw solution 90. The osmotic pressure difference between the feed solution 70 and the draw solution 90 across the membrane 200 drives a flow of pure water (in the liquid phase) 77 from the feed solution 70 to the draw solution 90. The draw solution 90 is also the electrolyte solution 90 with electrolyte ions 91 therein. Examples of the electrolyte solution 90 may include electrolyte ions such as KOH, K2CO3, etc. In some examples, the membrane 200 is selected with pore sizes that permit the passage of pure water in the liquid phase 77 while blocking passage of other substances. In some examples, the membrane 200 is selected from hydrophilic membranes. In some examples, the first water transport mechanism may be described as a forward osmosis process.

[0059] FIG. 2B schematically illustrates a second water transport mechanism by which the water electrolyzer cell 102 of the present disclosure may be provided with water. The water electrolyzer apparatus 100 of the present disclosure is capable of drawing directly from a water source 80 or feed solution 70 that may contain impurities, salt ions, organic materials, etc. Water sources 80 such as natural bodies of water, including brackish water, seawater, wastewater, etc., may be used as the feed solution 70. The membrane 200 may be a hydrophobic membrane. The driving force for water transport across the membrane 200 includes that based on a vapor pressure difference across the membrane 200. The draw solution 90 in the first chamber 117 has a higher salinity and a lower vapor pressure than that of feed solution 70. The feed solution 70 has a lower salinity and a correspondingly higher vapor pressure than that of the draw solution 90. The vapor pressure difference between the water vapor in the feed channel 74 and the water vapor in the first chamber 117 (drawing chamber) across the membrane 200 drives a flow of pure water (in the gaseous phase) 79 from the feed channel 74 through the membrane 200 to the first chamber 117. After transporting through the membrane 200, the water vapor condenses into liquid in the first chamber 117. In this scenario, the membrane 200 is hydrophobic. The first chamber 117 is also the electrolyte solution 90 with electrolyte ions 91 therein. Examples of the electrolyte solution 90 may include electrolyte ions such as KOH, K2CO3, etc.

[0060] Various embodiments of the present water electrolyzer apparatus 100 may be operable with various selections of membranes 200. The membrane 200 may be attached to the draw chamber and disposed between the draw chamber and the water source 80. The membrane 200 may be a hydrophobic membrane 220 or a hydrophilic membrane 210. Alternatively described, the membrane 200 may include a hydrophobic membrane element or a hydrophilic membrane element.

[0061] Advantageously, in some embodiments, the present water electrolyzer apparatus 100 is operable with membranes 200 selected from semi-permeable hydrophilic membranes 210 based on polymeric, ceramic, other inorganic materials (e.g., carbon materials, metals, or metal alloys, etc.), and nanomaterials (e.g., graphene, graphene oxide, reduced graphene oxide, metal organic framework, covalent organic framework, etc.). The hydrophilic membrane 210 can be integrally structured asymmetric membranes, thin-film composite membranes, thin-film nanocomposite membranes, etc. The hydrophilic membrane 210 can consist of at least one active layer (dense layer) with small pore size (nanoscale pores) which allows the passage of water molecules but rejects the impurities in feed solution. Flat sheet membranes are preferred as the hydrophilic membrane. Advantageously, the hydrophilic membrane 210 element only allows the permeation of water molecules with high water permeability and has high rejection rates to all the impurities from the various water sources. Advantageously, the rejection rates of the hydrophilic membrane 210 to the salt ions (e.g., Ca ²⁺ , Mg ²⁺ , Cl", etc.), organic molecules and microorganisms are higher than 90%. Advantageously, the hydrophilic membrane 210 is configured to have high rejections (e.g., > 90%) to all the ions in the electrolyte (i.e., draw solution) and retain them within the anode chamber 130. Advantageously, the hydrophilic membrane 210 is capable of preventing the permeation OH" and H ⁺ from electrolyte to the feed solution (water sources). The rejection of the hydrophilic membrane 210 to the impurities in water source and the ions within the electrolysis cell 102 originates from the small pore size on the active layer (dense layer) of the hydrophilic membrane 210. The hydrophilic membrane 210 can be placed with either the active layer facing the feed solution 70 or the active layer facing the electrolyte solution 90. If the feed solution 70 is not clean and can potentially cause fouling or scaling, it is preferred to place the hydrophilic membrane 210 with its active layer facing away from the cathode chamber 120, the anode chamber 130, or both chambers 110, to reduce membrane fouling. If the aqueous solution 90 is clean, it is preferred to place the hydrophilic membrane 210 with its active layer facing the cathode chamber 120, the anode chamber 130, or both chambers 110 to reduce internal concentration polarization and increase water transport flux through the hydrophilic membrane 210. The hydrophilic membrane 210 element is selected to have sufficient mechanical strength to resist the hydraulic pressure in the cell 102 and minimize deformation during recirculation of aqueous water.

[0062] In some other embodiments, the hydrophobic membrane 220 element may be one selected from various types of one or more porous sheets made of one or more hydrophobic materials. Examples of hydrophobic materials include but are not limited to polymers (e.g., polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE), etc.), ceramics (after hydrophobic treatment), other inorganic materials (e.g., graphite, activated carbon, metals, etc.), nanomaterials (e.g., carbon nanotubes, graphene, reduced graphene oxide, etc.), and/or one or composite materials thereof. In this case, water molecules transport in terms of water vapor rather than liquid water pass through the hydrophobic membrane 220 and condense at the electrolyte solution 90. The hydrophobic membrane 220 elements used in this application may possess a porous structure and may be constructed from one or more hydrophobic materials. The hydrophobic membrane 220 may include at least one hydrophobic layer. In some embodiments, the hydrophobic membrane 220 may have an asymmetric structure with a hydrophilic support layer and at least one hydrophobic layer. Flat sheet membranes are preferred for this purpose, although not limited thereto. Advantageously, the hydrophobic layer of the hydrophobic membranes 220 can be porous, with a porosity higher than 50%, and a pore size ranging from 0.01 pm (micrometer) to 0.5 pm. The water contact angle of the hydrophobic layer may be advantageously higher than 120°. Hydrophobic membrane 220 elements may be configured to have sufficient mechanical strength to resist the hydraulic pressure in the first chamber 117/feed channel 74 and minimize deformation during recirculation of aqueous water. Hydrophobic membrane 220 elements are selected to be membranes with the ability to reject involatile compounds present in impure water sources, such as salt ions, particles, microorganisms, and organics. The option to use hydrophobic membrane 220 elements advantageously enables rejection of involatile compounds resulting from the hydrophobic nature of the membrane. Without being limited by theory, hydrophobic membrane 220 elements can theoretically enable 100% rejection of impurities, ensuring that these impurities do not pass through the membrane and contaminate the electrolysis process in the water electrolyzer cell 102. Hydrophobic membranes 220 also demonstrate efficient retention. Without being limited by theory, theoretically, hydrophobic membrane 220 elements can demonstrate 100% retention of electrolyte ions present within the electrolysis cell (water electrolyzer). Electrolyte ions, such as OH- and COs ² ', may be retained to ensure the stability and effectiveness of the hydrogen generation process. In practical applications, even if the performance of the hydrophobic membrane 220 element does not achieve 100% rejection of impurities and/or 100% retention of electrolyte ions, the performance of the water electrolyzer cell 102 is advantageously and significantly improved over the conventional systems.

[0063] FIG. 3 is a schematic diagram illustrating one aspect of the water electrolyzer apparatus 100 or cell 102 of the present disclosure. The membrane 200 forms at least a part of the wall 115 between the draw chamber / first chamber 117 and the feed channel 74. The water electrolyzer apparatus 100 provides for the transport of water in the liquid phase 77 via osmotic pressure difference across the hydrophilic membrane 210 element or the transport of water vapor 79 via a vapor pressure difference across the hydrophobic membrane 220 element. A baffle 300 is in slidable engagement with the wall 115 of the first chamber 117 and/or the membrane 200 such that the active area of the membrane 200 is controllably variable. For example, the baffle 300 may be displaced 303 to cover part of the membrane 200. The baffle 300 is non-porous (e.g., includes a non-porous panel 301) such that the surface area of the exposed membrane 200 (the area exposed to the liquid feed 77 and/or the gaseous feed of water vapor 79 can be controllably set to a desired size. In some examples, the baffle 300 may be disposed such that the membrane 200 is exposed only for one of the liquid water transport 77 and the water vapor transport 79.

[0064] To further illustrate, various examples of the water electrolyzer apparatus 100 including the one or more cells 102 are described with reference to the figures. FIG. 4A shows an alkaline water electrolyzer apparatus 100 including a cell 102. The cathode chamber 120 and the anode chamber 130 are entirely separated from one another by the separator 150. The cathode 122 is disposed in the cathode chamber 120. The anode 132 is disposed in the anode chamber 130. The cathode chamber 120 is sized to contain the catholyte 92, i.e., the electrolyte on the cathode side. The anode chamber 130 is sized to contain the anolyte 93, i.e., the electrolyte on the anode side. The electrolyte 90, including the catholyte and the anolyte, is an aqueous electrolyte that is suitable for water splitting. A power source 104 may be connected to supply an electric current (or voltage) to the electrodes, i.e., to the cathode 122 and the anode 132. A continuous source of water (in the form of liquid water and/or water vapor) may be provided by a feed channel 74. In the example of FIG. 4A, the first chamber 117 is the anode chamber 130. A wall 115 between the first chamber 117 and the feed channel 74 includes a membrane 200. The membrane 200 is disposed between a volume of the electrolyte solution 90 and a volume of the feed solution 70. In the examples where the membrane 200 is essentially a hydrophobic membrane 220, the membrane 200 allows the passage of only the water vapor generated spontaneously from the aqueous feed solutions 70, responsive to a vapor pressure difference across the hydrophobic membrane 220. The water vapor that passes through the hydrophobic membrane 220 condenses to liquid water within an electrolysis cell 102/electrolyte storage tank 601.

[0065] When the power source 104 is connected to the cathode 122 and the anode 132, water in the electrolyte 90 may be consumed and split by the electrochemical reaction, generating hydrogen gas 20 and oxygen gas 30 at the cathode 122 and the anode 132, respectively. The hydrogen gas 20 and the oxygen gas 30 are separated by the separator 150 and extracted from the apparatus 100 / cell 102 through outlets 129/139 of the cathode chamber 120 and the anode chamber 130, respectively. During a water splitting process, the water in the electrolyte 90 is continuously consumed. The electrolyte solution 90 advantageously has a high solute concentration. The osmotic pressure of the electrolyte 90 within the water electrolyzer apparatus 100 is higher than the water source 80. Water is driven by the osmotic pressure difference between the electrolyte 90 and the water source 80 to feed into the anode chamber 130 through the membrane 200. The impurities in the water source 80 are rejected by the membrane 200 and prevented from entering the anode chamber 130. The solutes in the electrolyte can be retained within the anode chamber 130 by the membrane 200. If the consumption rate of the water in the electrolyte 90 by the electrochemical reaction (i.e., water electrolysis reaction) is equal to the water inflow rate from the water source 80 through the membrane 200, the dynamic equilibrium of the electrolyte 90 is achieved. In this case, the water from the unpurified water source 80 is continuously fed into the water electrolyzer apparatus 100 for the production of high-purity hydrogen and oxygen gases 20/30.

[0066] In one example, the membrane 200 is a forward osmosis (FO) membrane. Water supply by forward osmosis is a passive process where water is only driven by the osmotic pressure difference between the electrolyte 90 and the water source 80 without the need to provide external mechanical energy and hydraulic pressure. In another example, the membrane 200 is a hydrophobic membrane 220. Water supply through the hydrophobic membrane 220 is also a passive process where water is only driven by the water vapor pressure difference between the electrolyte 90 and the water source 80 without the need to provide external mechanical energy and hydraulic pressure. The water supply process for the water splitting can be sustainable, consuming nearly zero energy. The minimal energy used in the water supply is only for pumping and recirculating the waters, which is negligible compared to the energy consumption in other pure water production process such as reverse osmosis (RO) and electrodeionization. The power source 104 can be but not limited to various batteries, various types of electric generators, and fossil fuels based electricity. It is advantageous to employ sustainable and renewable power sources, such as solar cells, wind turbines, tidal stream generators, etc., as the power source 104.

[0067] When an electric current 104 is connected to the cathode 122 and the anode 132, an oxygen evolution reaction (OER) would occur at the anode 132 (positive electrode) with the generation of electrons, while a hydrogen evolution reaction (HER) would occur at the cathode 122 (negative electrode) with the consumption of the electrons. The major reactions on the anode 132 and cathode 122 depend on the pH of the electrolyte:

Anode: O ₂ + 2H ₂ O + 4e’

(Acid) O ₂ + 4H ⁺ + de¬

Cathode: (Neutral/Alkaline) 2H2O + 2e’ - H2 + 2OH’

(Acid)

Overall:

[0068] The cathode 122 may be made of any conductive materials, e.g., metals (e.g., Cd, Ti, Zn, Sn, Fe, Co, Ni, Cu, etc.), their alloys, carbon materials (graphite, activated carbon, etc.) and/or any combination thereof. The anode 132 may be made of Ni, Ti, their alloys, and/or any combination thereof. The cathode 122 may contain catalysts for HER and the anode 132 may contain catalysts for OER. The catalysts for the HER on the cathode 122 can be Pt group metals (PGM), such as Pt, Rh, Ir, and non-PGM class including sulfides, phosphides, carbides and borides. The catalysts for the OER on the anode 132 can be PGM, such as Ru, Ir, Rh, Pd, Pt and Au, and their oxides including RuO2 and IrO2. In alkaline and neutral electrolyte, nonprecious-transition metal oxides such as Co’, Ni’, and Fe-based materials can be also used as OER catalysts on anode 132.

[0069] The separator 150 can be made of either porous materials or non-porous materials. The separator 150 is stabilized in the electrolyte and capable of separating the generated gases (i.e., H2 and O2) from the cathode chamber 120 and the anode chamber 130. The porous separator can be a polymer membrane made of, but not limited to, the following materials: polybenzimides, polyphenylene sulphides, sulphonated polymers and composite materials, Zirfon diaphragm (i.e., a polyphenylene sulfide fabric symmetrically coated with a polymer and zirconium dioxide ZrCh), polyvinylidene Fluoride (PVDF), polytetrafluoroethylene (PTFE), glass fiber membranes and ceramic membranes. The nonporous separator, or dense separator, can be ion-exchange membrane and ion-solvating membrane. Ion-exchange membranes utilize the charged functional groups on the organic or inorganic polymer skeleton to allow the transportation of certain dissolved ions and block other ions or neutral molecules. Ion-exchange membranes can be anion exchange membrane, proton exchange membrane and cation exchange membrane. Ion-solvating membrane can swell when imbibed with an aqueous electrolyte and form a homogeneous ternary electrolyte system of polymer/water/electrolyte. Some examples of ion-solvating membranes include polybenzimidazole (PBI) membranes and blend membranes of polysulfone with polyvinylpyrrolidone (PSU-PVP).

[0070] The electrolytes of the water electrolyzer apparatus 100 can be one or more of acidic, neutral, and alkaline aqueous solutions. Advantageously, neutral or near neutral (pH 5-9) buffer solutions (e.g., ftPCh'/HPC ', HCCh’/CCh ² ’) and alkaline solutions (e.g., KOH, NaOH, etc.) may be used as the electrolyte in an alkaline water electrolyzer. The concentration for the electrolyte can be 0.1 to 8 M for the acid or alkaline solutions and 0.1 M to 5 M for the buffer solutions. The osmotic pressure of the electrolyte should be higher than the water source 1080. The osmotic pressure is advantageously larger than 5 bar.

[0071] One side of the water electrolyzer apparatus 100 can be sustainable when the water consumption rate by water electrolysis is equal to the water inflow rate from the water source 80 through the membrane 200. The membrane 200 is embedded in the anode chamber 130 with a frame which can fully replace or partially replace the bipolar plate in conventional water electrolyzers. On each side of the membrane 200, a spacer 76 is preferably placed to support the membrane 200, create flow channels for the feed water or/and the electrolyte solution, and enhance the hydrodynamic conditions (turbulence) on membrane surface. The water inflow rate through the membrane 200 is determined by the intrinsic properties of the membrane 200, the osmotic pressure difference (for hydrophilic membrane) or the vapor pressure difference (for the hydrophobic membrane) between the water source 80 and the electrolyte 90, the active area of the membrane 200 (i.e., the open area of the membrane 200 in contact with the aqueous solution), and the fluid hydrodynamic conditions of the water source 80 and the electrolyte 90. The water consumption rate by the water electrolysis is determined by the current applied to the water electrolyzer 100. Advantageously, the water inflow rate through the membrane 200 can be controlled by the active area of the membrane 200, fluid hydrodynamic conditions (e.g., cross-flow velocity) of the water source 80 and the concentration of the electrolyte 90.

[0072] Water sources 80 can be configured to provide various aqueous solutions for the water electrolyzer apparatus 100, such as seawater, brackish water, industrial wastewater, municipal wastewater, surface water, underground water, reuse water, household water, tap water, etc. The osmotic pressure of the water source 80 can be about 0.5 bar to about 100 bar (e.g., tap water is less than 1 bar; brackish water is around 7 bar; seawater is around 27 bar; shale gas produced water can reach more than 60 bar).

[0073] When employing a hydrophobic membrane 220, water sources 80 could advantageously have higher temperatures than the electrolyte solution 90, typically within the range of about 30°C to about 90 °C. The higher temperature can effectively increase the water vapor pressure of the water sources, resulting in an enhanced water vapor pressure difference across the hydrophobic membrane. This acceleration of water vapor transport facilitates a more efficient supply of fresh water for water electrolysis. To achieve higher water source temperatures, low-grade heat sources, such as waste heat from industries, thermal energy from solar thermal collectors, and geothermal energy, can be utilized. Additionally, interfacial heating hydrophobic membranes, which incorporate an electrical- or photo-thermal layer on the surface, can be also used to heat the water source on the membrane surface using electric energy or solar energy. [0074] FIG. 4B illustrates an alkaline water electrolyzer apparatus 100 according to another embodiment of the present disclosure. The water electrolyzer apparatus 100 includes a cathode chamber 120, a cathode 122, a separator 150, an anode 132, an anode chamber 130, and a membrane 200. The water source 80 may be drawn from natural bodies of water. The various components may be configured as described above with respect to FIG. 4A. The combination of the power source 104, the cathode chamber 120, the cathode 122, the separator 150, the anode 132, and the anode chamber 130 can be referred to as one unit or one cell 102. The membrane 200 may be attached to the cathode chamber 120 instead of the anode chamber 130. [0075] FIG. 4C illustrates an alkaline water electrolyzer apparatus 100 according to another embodiment of the present disclosure. The water electrolyzer apparatus 100 includes a cathode chamber 120, a cathode 122, a separator 150, an anode 132, an anode chamber 130, and two membranes 200, all of which can be configured as described above with respect to FIG. 4A and FIG. 4B. The combination of the power source 104, the cathode chamber 120, the cathode 122, the separator 150, the anode 132, and the anode chamber 130 can be referred to as a water electrolyzer cell 102. Each of the membranes 200 is attached to one of the cathode chamber 120 and the anode chamber 130, respectively.

[0076] FIG. 4D illustrates a proton exchange membrane water electrolyzer apparatus 100 according to another embodiment of the present disclosure. The water electrolyzer apparatus 100 includes a power source 104, a cathode chamber 120, a cathode 122, a separator 150, an anode 132, an anode chamber 130, and a membrane 200 attached to the anode chamber 130, in fluidic communication with a water source 80. Each of the power source 104, the cathode 122, the separator 150, the anode 132, the anode chamber 130, and the membrane 200 can be configured as described above with respect to FIG. 4A. The combination of the power source 104, the cathode chamber 120, the cathode 122, the separator 150, the anode 132, and the anode chamber 130 can be referred to as a water electrolyzer cell 102. The separator 150 is configured to be a proton exchange membrane in this example, which acts as both the separator 150 for the generated gases 20/30 and the electrolyte 90 for the passage of the proton (H ⁺ ) generated on the anode 132. The anode chamber 130 accommodates the anode 132 and an anolyte 93, while the cathode chamber 120 only accommodates the cathode 122 without a liquid phase catholyte. In a preferred example, the electrolyte 90 can be acid solutions, including but not limited to inorganic acid (e.g., H2SO4) and organic acid, while neutral solutions can also be used. A neutral solution electrolyte can avoid acid corrosion and the ions therein can be highly retained within the anode chamber 130 by the membrane 200.

[0077] FIG. 4E illustrates an anion exchange membrane water electrolyzer apparatus 100 according to another embodiment of the present disclosure. The water electrolyzer apparatus 100 includes a power source 104, a cathode chamber 120, a cathode 122, a separator 150, an anode 132, and an anode chamber 130, and a membrane 200 attached to the cathode chamber 120, in fluidic communication with a water source 80. Each of the power source 104, the cathode chamber 120, the cathode 122, the separator 150, the anode 132, and the membrane 200 can be configured as described above with respect to FIG. 4B. The combination of the power source 104, the cathode chamber 120, the cathode 122, the separator 150, the anode 132, and the anode chamber 130 can be referred to as a cell or unit 102. The separator 150 is configured to be an anion exchange membrane in this embodiment, which acts as both separator 150 for the generating gases 20/30 and electrolyte 90 for the passage of the hydroxide ions (OH’ ) generated on the cathode 122. The cathode chamber 120 accommodates the cathode 122 and a catholyte 92, while the anode chamber 130 only accommodates the anode 132 without a liquid phase anolyte. In a preferred example, the electrolyte can be base solutions, including but not limited to inorganic base (e.g., KOH, NaOH, etc.) and organic base, while neutral solutions can also be used. An alkaline electrolyte can avoid acid corrosion and the ions therein can be highly retained within the cathode chamber 120 by the membrane 200. [0078] Any water electrolyzer apparatus 100 described above may further include a baffle 300 attached to a respective membrane 200 thereof. FIG. 5A illustrates a front view of a baffle 300 that may be included in any water electrolyzer apparatus 100 of FIG. 4A to FIG. 4E or in an external water supply device 600, where the baffle 300 is configured for controlling water inflow influx through the respective membrane 200 (and directly or eventually into the water electrolyzer apparatus 100) by changing the active area of the respective membrane 200. In some embodiments, the baffle 300 is disposed in/as a part of the respective water electrolyzer cell 102. In some embodiments, the baffle is disposed in/as part of a water supply device (externally connected to the water electrolyzer cell 102) as shown in FIGS. 6A to 6C. FIG. 5B illustrates a side view of the baffle 300. The baffle 300 can slide along the direction 303 to change the open area of the membrane 200 and adjust the water inflow rate through the membrane 200 according to the real-time water consumption rate within the respective water electrolyzer cell 102. In some embodiments, the water inflow rate through one membrane 200 feeds to a plurality of water electrolyzer cells 102, and the water inflow rate through such a membrane 200 may be adjusted according to a total real-time water consumption rate of the corresponding plurality of water electrolyzer cells 102. Preferably, the water permeate flow rate across the membrane 200 should be greater or equal to the water consumption rate in the respective one or more water electrolyzer cells 102. If the total water permeate flow rate across the membrane 200 is smaller than the water consumption rate in the respective water electrolyzer apparatus 100, additional ultrapure water is needed to directly top up the electrolyze solutions 90 or another external membrane device 600 can be constructed to supply water for the respective water electrolyzer apparatus 100 by using the electrolyte solution 90 as draw solution and recirculate the electrolyte solution 90 in the external membrane device 600.

[0079] FIG. 5C illustrates a front view of a baffle 300 that may be included in any water electrolyzer apparatus 100 of FIG. 4 A to FIG. 4E, or in an external water supply device 600, where the baffle 300 is configured for controlling water inflow influx through the respective membrane 200 into the water electrolyzer apparatus cell 102 by changing the active area of a respective membrane 200, and where the baffle 300 is disposed outside the respective water electrolyzer apparatus cell 102. FIG. 5D illustrates a side view of the baffle 300. The baffle 300 can be configured as described above with respect to FIG. 5 A and FIG. 5B. The baffle 300 can slide along the direction 303 to change the open area of the membrane 200 and adjust the water inflow rate through the membrane 200 according to the real-time water consumption rate within the respective apparatus.

[0080] FIG. 6 A to FIG. 6C illustrate a water electrolyzer apparatus 100 according to another embodiment of the present disclosure when using hydrophobic membrane 220 to supply water for water electrolyzer apparatus 100. In this embodiment, the water electrolyzer unit or cell 102 and the water supply unit (external membrane device) 600 with the hydrophobic membrane 220 are separated. The water electrolyzer unit or cell 102 includes a power source 104, a cathode chamber 120, a cathode 122, a separator 150, an anode 132, and an anode chamber 130. The water supply unit 600 includes a membrane 200 disposed between a water source 80 and an electrolyte chamber 610 (or electrolyte storage tank 601) serving as a draw chamber to draw the feed solution across the membrane 200. The cathode chamber 120, or the anode chamber 130, or both the cathode chamber 120 and anode chamber 130 of the cell 102 is/are connected to an electrolyte storage tank 601 by pipelines 690, as shown in FIG. 6 A, FIG. 6B, and FIG. 6C, respectively. The electrolytes in the electrolyte storage tank 601 are circulated between the cathode chamber 120 and/or the anode chamber 130 and the electrolyte storage tank 601 using the circulation pump continuously or intermittently to sustain the electrolyte concentration in the cathode chamber 120 and/or anode chamber 130 at a relatively stable level. Simultaneously, the electrolyte chamber 610 of the water supply unit 600 is also connected to the electrolyte storage tank 601, and the electrolyte is also circulated between them by pipelines 690 and the circulation pump. Due to the lower water vapor pressure of the electrolyte in the electrolyte chamber 610, the water vapor generated from the water source 80, which has a higher water vapor pressure, can transport through the hydrophobic membrane 220 and condense into liquid water in the electrolyte chamber 610. Subsequently, the water will circulate back to the electrolyte storage tank 601, and then to the cell 102, together with the electrolyte to further supply water for water electrolysis. The membrane 200 can have different configurations such as flat sheet, hollow fiber and tubular configuration. The membrane 200 can be housed in different types of modules such as plate-and-frame module, hollow fiber module, tubular module, spiral wound module. The membrane module can be submerged into the external feedwater source or the external feedwater can circulate through the membrane module.

[0081] Any of the water electrolyzer apparatus 100 described above may be alternatively configured to include two or more cells 102 for large-scale hydrogen production from unpurified water sources 80. As shown in FIG. 7A, the water electrolyzer apparatus 100 includes multiple cells 102 connected in parallel and in the arrangement of “anode chamber of one unit-feed channel-cathode chamber of next unit” (AFC arrangement), and a closed loop water supply established by a pipeline 190 in fluid communication with the water source 80. The water electrolyzer apparatus 100 further includes feed channels 74 disposed between respective cathode chambers 120 and respective anode chambers 130. Various aqueous solutions can be delivered by the pipeline 190 from the water source 80 to respective cathode chambers 120 and corresponding adjacent anode chambers 130 through respective feed channels 74. Water from the water source 80 can be driven by the osmotic pressure difference across respective membranes 200 and so fed into respective cathode chambers 120 and respective anode chambers 130 through respective membranes 200, as is shown in FIG. 7A. The aqueous solution, also referred to as the feed stream, can be recirculated back to the water source 80 through the pipeline 190. [0082] Spacers 76 may be placed in the feed channels 74 to avoid direct contact of the two adjacent membranes 200 from two neighboring cells 102 and create a flow channel for the water source 80. The different geometries of the spacers 76 can affect the fluid/flow dynamics (such as the flow velocity, turbulence, etc.) and mass transfer of the feed stream within the feed channels 74. Different types of spacers 76 are applicable in this disclosure, including net-type, diamond type, ladder type, and any other types which can provide flow channel, enhance mixing and turbulence, and change the hydrodynamic conditions in the feed channels 74.

[0083] The water inflow rate through the membranes 200 from the feed channels 74 to the cells 102 can be also controlled by the active area of the membrane 200, fluid hydrodynamic conditions of the water source 80 and the concentration of the electrolyte. For example, a baffle 300 attached to the membrane 200 (as is shown in FIG. 5A or FIG. 5C) can be used to control the water inflow rate through the membrane 200 by changing the open area (active area or exposed area) of the membrane 200 according to the real-time water consumption rate within the water electrolysis units or cells 102. The cross-flow rate and velocity of the aqueous solution can be adjusted to change the extent of concentration polarization, which can help to adjust water flux.

[0084] In another example shown in FIG. 7B, the water electrolyzer apparatus 100 includes membrane-embedded water electrolysis units or cells 102 connected in parallel and in the arrangement of “anode chamber of one unit-feed channel-cathode chamber of next unit” (AFC arrangement). The water electrolyzer apparatus 100 includes a connection to an open-loop water supply established by a pipeline 190 in fluid communication with the water source 80. The feed stream can be directly discharged from the apparatus 100 after passing through the feed channels 74 without recirculating back to the water source 80.

[0085] FIG. 8 A illustrates a water electrolyzer apparatus 100 according to another embodiment of the present disclosure. The membrane-embedded alkaline water electrolyzer (AWE) cells 102, including cathode chambers 120, anode chambers 130, cathodes 122, separators 150, and anodes 132, are connected in parallel with the feed channels 74 contacting the anode chamber 130 of each cell. The water electrolyzer apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80. FIG. 8B illustrates a water electrolyzer apparatus 100 according to another embodiment of the present disclosure. The membrane-embedded proton exchange membrane water electrolyzer cells (PEMWE) 102, including cathode chambers 120, anode chambers 130, cathodes 122, separators 150, and anodes 132, are connected in parallel with the feed channels 74 contacting the anode chambers 130 of the cells. The water electrolyzer apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80.

[0086] FIG. 9 A illustrates a water electrolyzer apparatus 100 according to an embodiment of the present disclosure. The membrane-embedded alkaline water electrolyzer (AWE) cells 102, including cathode chambers 120, anode chambers 130, cathodes 122, separators 150, and anodes 132, are connected in parallel with the feed channels 74 contacting the cathode chambers 120 of the water electrolysis units. The water electrolyzer apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80. FIG. 9B illustrates a water electrolyzer apparatus 100 according to an embodiment of the present disclosure. The membrane-embedded anion exchange membrane water electrolyzer (AEMWE) cells 102, including cathode chambers 120, anode chambers 130, cathodes 122, separators 150 configured to be anion exchange membranes, and anodes 132, are connected in parallel with the feed channels 74 contacting the cathode chambers 120 of the cells. The apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80. [0087] FIG. 10 illustrates a water electrolyzer apparatus 100 according to an embodiment of the present disclosure. The membrane-embedded water electrolysis units or cells 102, including cathode chambers 120, anode chambers 130, cathodes 122, separators 150, and anodes 132, are connected in parallel with the feed channels 74 connected to either a cathode chamber 120 or an anode chamber 130 of each water electrolysis unit or cell 102. The water electrolyzer apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80.

[0088] FIG. 11 illustrates a water electrolyzer apparatus 100 according to an embodiment of the present disclosure. The membrane-embedded water electrolysis units or cells 102, including cathode chambers 120, anode chambers 130, cathodes 122, separators 150, and anodes 132, are connected in parallel with the feed channels 74 on both the cathode chambers 120 and the anode chambers 130 of the water electrolysis unit or cells 102. The apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80.

[0089] FIG. 12 illustrates an apparatus 100 according to an embodiment of the present disclosure. The membrane-embedded water electrolysis units 102, including cathode chambers 120, anode chambers 130, cathodes 122, separators 150, and anodes 132, are arranged with anode chamber 130 neighboring anode chamber 130 and connected with the feed channels 74 on both the cathode chambers 120 and the anode chambers 130 of the water electrolysis units or cells 102. Each feed channel 74 is only connected to either anode chambers 130 or cathode chambers 120 of the neighboring water electrolysis units 102. The apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80.

[0090] FIG. 13 A illustrates a water electrolyzer apparatus 100 according to an embodiment of the present disclosure. The membrane-embedded water electrolysis units or cells 102, including cathode chambers 120, anode chambers 130, cathodes 122, separators 150, and anodes 132, are connected in series with bipolar assemblies. The feed channel 74 is connected to an outmost anode chamber 130 of the cells 102. One side of each of the cathodes 122 and the anodes 132 acts as a cathode 122 for one cell 102 and the other side acts as an anode 132 for a neighboring cell 102. Separator 150 is placed between the anodes 132 and the cathodes 122 in each cell 102 to separate the oxygen gas 30 and hydrogen gas 20 generated from the electrodes. The water electrolyzer apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80.

[0091] FIG. 13B illustrates a water electrolyzer apparatus 100 according to an embodiment of the present disclosure. The membrane-embedded water electrolysis units or cells 102, including cathode chambers 120, anode chambers 130, cathodes 122, separators 150, and anodes 132, are connected in series with bipolar assemblies described as above with respect to FIG. 13A. The feed channel 74 is connected to an outmost cathode chamber 120 of the water electrolysis unit or cells 102. The water electrolyzer apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80.

[0092] FIG. 13C illustrates a water electrolyzer apparatus 100 according to an embodiment of the present disclosure. The membrane-embedded water electrolysis units or cells 102, including cathode chambers 120, anode chambers 130, cathodes 122, separators 150, and anodes 132, are connected in series with bipolar assemblies described as above with respect to FIG. 13A. The feed channel 74 is connected to both an outmost cathode chamber 120 and an outmost anode chamber 130 of the water electrolysis units or cells 102. The water electrolyzer apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80.

[0093] FIG. 14A illustrates a water electrolyzer apparatus 100 according to an embodiment of the present disclosure. The membrane-embedded water electrolysis units or cells 102, including cathode chambers 120, anode chambers 130, cathodes 122, separators 150, and anodes 132, are connected both in series with bipolar assemblies and in parallel with monopolar assemblies. The water electrolyzer apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80.

[0094] FIG. 14B illustrates a water electrolyzer apparatus 100 according to an embodiment of the present disclosure. The membrane-embedded water electrolysis units or cells 102 include separators 150 in the form of an anion exchange membrane separator, a proton exchange membrane separator, or an alkaline water separator. The cells 102 further include cathode chambers 120, anode chambers 130, cathodes 122, and anodes 132. The water electrolyzer apparatus 100 includes a closed loop water supply established by the pipeline 190 in fluid communication with the water source 80.

[0095] A water electrolyzer apparatus 100 of the present disclosure extracts water from a water source supplying wastewater or seawater as feed solutions. The compositions of the simulated wastewater and simulated seawater are listed in Table 1. FIG. 15A and FIG. 15B illustrate water inflow flux in the unit of L per m ² of a membrane per hour (L m' ² h' ¹ ) to a water electrolyzer apparatus of the present disclosure from water sources (feed solutions) of simulated wastewater and seawater, respectively. The electrolyte in the (electrochemical) cell (draw solutions) is 1 M NaHCO3/Na2CO3 buffer solutions with various pH (pH = 8.0, 9.5, and 11.3). The water inflow fluxes were calculated by the changes in weight of the water electrolyzer recorded automatically by a digital balance. The apparatus 100 can effectively extract pure water from both of the water sources. The pure water fluxes using simulated wastewater as water source were in the range of about 4 to about 6.5 L m' ² h' ¹ (L per m ² of FO membrane per hour). The pure water fluxes using simulated seawater as water source were in the range of about 1.1 to about 1.5 L m' ² h’ ¹ . The electrolyte with more neutral pH (i.e., close to pH = 7) showed higher water fluxes, which can be attributed to the intrinsic properties of the aquaporin in the FO membranes. The water inflow flux into the water electrolyzer apparatus can be further tuned by changing the composition and concentration of electrolytes (draw solution), the hydrodynamic conditions of the source water (e.g., cross-flow velocity, type of spacers), temperatures of solutions, and the type of FO membranes.

Table 1 The compositions of the simulated wastewater and simulated seawater

Simulated Simulated

Composition wastewater seawater unit

NaCl 0.11059 24.53 g/L

MgCh 0.01405 5.2 g/L

Na ₂ SO ₄ 0.09625 4.09 g/L

CaCh 0.07909 1.16 g/L

KC1 N.A 0.695 g/L

NaHCCh 0.01263 0.201 g/L

KBr N.A 0.101 g/L

H ₃ BO ₃ N.A 0.027 g/L

SrCl ₂ N.A 0.025 g/L

Na ₃ PO ₄ 0.01600 N.A g/L

Silica 34wt% 0.03000 N.A g/L pH 7.5 8.2 conductivity 2.175 52.5 ms/cm

[0096] The present disclosure also provides a modularized water electrolyzer apparatus in another aspect. FIG. 16 illustrates a water electrolyzer apparatus 100 with separable modules 700 according to an embodiment of the present disclosure. Each module 700 includes a frame 704 and a plate 706 surrounded by the frame 704. An outlet 708 for gases is disposed on each frame 704. The plate 706 may be a cathode, an anode, or a separator. The modules 700 may be assembled by attaching them together with a water source and a power source (not shown in FIG. 16). The apparatus 100 is easy to assemble and dissemble, e.g., by slotting in appropriate plates or extracting one or more plate to clean and/or for other maintenance.

[0097] In another aspect, and schematically represented in FIG. 17, the present disclosure provides a method 900 of water splitting. The method 900 includes providing a potential difference across a cathode-anode pair, e.g., electrically coupling a cathode and an anode with a power supply 104, the cathode 122 and the anode 132 being electronically separated by a separator 150 disposed between the cathode 122 and the anode 132. The method 900 includes: a step 910 of providing water from a water source 80 in fluid communication with the at least one of the cathode 122 and the anode 132 through a membrane 200 disposed between the water source 80 and the at least one of the cathode 122 and the anode 132 (the membrane 200 allowing water to permeate from a feed solution 70 provided by the water source 80 to the at least one of the cathode 122 and the anode 132); and applying an electrical current between the cathode 122 and the anode 132 with the power supply for water contacting the cathode 122 and the anodel32 to electrochemically split to form hydrogen gas 20 on the cathode 122 and oxygen gas 30 on the anode 132, and separating the hydrogen gas 20 and the oxygen gas 30 with the separator 150. Each of the cathode 122, the anode 132, the separator 150, the power source 104, and the membrane 200 can be configured relative to the water source 80, in accordance with any of the embodiments described above.

[0098] In yet another aspect, a method 900 of the present disclosure includes: providing a feed solution 70 to a cell 102 and a step 920 of controlling a variable area of the membrane 200 exposed to a water source 80. The cell 102 includes: a first electrode and a second electrode, in which the first electrode and the second electrode form an operable pair of an anode 132 and a cathode 122. The cell 102 includes a separator 150. The separator 150 is disposed between the first electrode and the second electrode to define a first chamber 117/110 and a second chamber 118/110. The first electrode is disposed in the first chamber 117/110 and the second electrode is disposed in the second chamber 118/110. The first chamber 117 and the second chamber 118 are in fluidic communication with one another exclusively through the separator 150. Controlling a variable area of the membrane 200 exposed to a water source 80 may be performed by moving a non-porous panel 301 of a baffle 300 relative to a major surface of the membrane 200. The feed solution 70 is in fluidic communication with the water source 80 exclusively through the membrane 200. [0099] In some embodiments, the feed solution 70 is formed by a transport of water from the water source 80 across the membrane 200 towards the cell 102, in which the transport may include any one of: (i) a liquid phase transport 77 of liquid water across the membrane responsive to an osmotic pressure difference across a hydrophilic membrane 210 element, and (ii) a gaseous phase transport 79 of water vapor responsive to a vapor pressure difference across a hydrophobic membrane 220 element. The step 930 of generating hydrogen gas 20 and oxygen gas 30 is based on the water received through the water transport 77/79 described above.

[00100] According to various embodiments of the present disclosure, a water electrolyzer apparatus 100 for use with a feed solution 70 includes: a first electrode; a second electrode; a separator 150; and a membrane 200. The first electrode and the second electrode form an operable pair of an anode 132 and a cathode 122. The separator 150 is disposed between the first electrode and the second electrode to define a first chamber 117/110 and a second chamber 118/110. The first electrode is disposed in the first chamber and the second electrode is disposed in the second chamber. The first chamber 117 and the second chamber 118 are in fluidic communication with one another exclusively through the separator 150. The membrane 200 is a part of a wall 115 of the first chamber. The membrane 200 defines a transport path. The transport path extends from the feed solution 70 in a feed channel 74 outside the first chamber 117, across the membrane 200 and immediately into the first chamber 117. The transport path is enabled at least partially by an osmotic pressure difference between the feed solution and a first electrolyte solution in the first chamber across a hydrophilic membrane 210. The first electrolyte has a higher osmotic pressure than the feed solution 70. The transport path includes a liquid phase transport 77 of liquid water across the hydrophilic membrane 210 based on an osmotic pressure difference. The hydrophilic membrane 210 may consist of at least one active layer (dense layer) with small pore size (nanoscale) which only allows the passage of water molecules. The hydrophilic membrane 210 may reject the impurities in feed solution and prevent electrolyte ions from passing through the membrane 200. In another example, the transport path is enabled at least partially by a vapor pressure difference across a hydrophobic membrane 220, the first chamber having a lower vapor pressure than in the feed channel 74. The transport path includes a water vapor transport 79 across the hydrophobic membrane 220 based on a vapor pressure difference. The hydrophobic membrane 220 may include at least one hydrophobic layer characterized by a water contact angle higher than 120°. The hydrophobic membrane 220 may be characterized by a porosity higher than 50% and pore sizes ranging from 0.01 pm to 0.5 pm. The membrane 200 may be configured to prevent involatile compounds in the feed solution from passing through the membrane 200, and the membrane 200 may be configured to prevent electrolyte ions from passing through the membrane 200.

[00101] The water electrolyzer apparatus 100 includes a baffle 300 providing a non-porous surface 301 parallel to a major surface of the membrane 200, in which the baffle 300 is in slidable engagement relative to the membrane 200.

[00102] The baffle 300 may be in slidable engagement over the major surface facing the feed channel 74. The baffle 300 may be in slidable engagement over the major surface facing away from the feed channel 74.

[00103] The baffle 300 is controllably slidable to expose a variable area of the membrane 200 to the feed channel 74.

[00104] The feed solution 70 and the first chamber 117 are in fluid communication exclusively through an active area of the membrane 200, in which a size of the active area is adjustable by sliding the baffle 300 relative to the membrane 200.

[00105] The separator 150 may include a proton exchange film, with the first electrode being the anode 132. The separator 150 may include an anion exchange film, in which the first electrode is the cathode 122. [00106] The water electrolyzer apparatus 100 in operation is responsive to an electric current provided to the cathode 122 and the anode 132, such that water contacting the cathode 122 and the anode 132 electrochemically splits to generate hydrogen gas 20 on the cathode 122 and oxygen gas 30 on the anode 132, with the hydrogen gas 20 and the oxygen gas 30 being separated by the separator 150.

[00107] In some embodiments, the first electrode is the cathode 122. In other embodiments, the first electrode is the anode 132.

[00108] The water electrolyzer apparatus 100 may further include a second membrane 200. The second membrane 200 may a part of a second wall 115 of the second chamber 118. The second membrane 200 may define a second transport path extending from the feed solution 70 in a second feed channel 74 outside the second chamber 118, across the second membrane 200 and immediately into the second chamber 118. The second transport path 72 is enabled at least partially by an osmotic pressure difference between the feed solution 70 and a second electrolyte solution in the second chamber 118, with the second electrolyte having a higher osmotic pressure than the feed solution 70.

[00109] According to various embodiments, an apparatus 100 includes a plurality of the water electrolyzer cells 102. The pair of the anode 132 and the cathode 122 of one of the plurality of the water electrolyzer cells 102 are connected in parallel with the pair of the anode 132 and the cathode 122 of another one of the plurality of the water electrolyzer cells 102. The apparatus 100 may include a feed channel 74 in fluid communication with the respective first chamber 117 of two of the plurality of the water electrolyzer cells 102.

[00110] According to various embodiments, an apparatus 100 includes a plurality of the water electrolyzer cells 102. The two or more pairs of the anode 132 and the cathode 122 are connected in series. A feed channel 74 is in fluid communication with one or both terminal first chamber of the plurality of the water electrolyzer cells 102. [00111] According to various embodiments of the present disclosure, a method 900 includes: a step 910 of providing the feed solution to the membrane of the water electrolyzer apparatus; and applying an electrical current to the pair of the anode and the cathode of the water electrolyzer apparatus, in which the transport path 72 from the feed solution across the membrane 200 and immediately into the first chamber 117 is enabled at least partially by one or both of an osmotic pressure difference across the hydrophilic membrane 210 and a vapor pressure difference across the hydrophobic membrane 220, and in which the first electrolyte has a higher osmotic pressure than the feed solution, and wherein the first chamber 117 has a lower vapor pressure than in the feed channel 74. The method 900 may further include: a step 920 of varying a size of an active area of the membrane 200 by sliding a non-porous baffle 300 relative to the membrane 200.

[00112] According to one aspect, various embodiments of the present disclosure includes a water electrolyzer apparatus or a distillate electrolyzer apparatus 100 for use with a water source 80. The distillate electrolyzer apparatus 100 includes: a cell 102, a membrane 200, and a baffle 300. The cell 102 includes: a first electrode, a second electrode, and a separator 150. The first electrode and the second electrode form an operable pair of an anode 132 and a cathode 122. The separator 150 is disposed between the first electrode and the second electrode to define a first chamber 117 and a second chamber 118. The first electrode is disposed in the first chamber 117 and the second electrode is disposed in the second chamber 118. The first chamber 117 and the second chamber 118 are in fluidic communication with one another exclusively through the separator 150. The cell 102 is in fluidic communication with the water source 80 exclusively through the membrane 200. The baffle 300 includes a non-porous panel 301 moveable relative to a major surface of the membrane 200 to expose a variable area of the membrane 200 to the water source 80. [00113] In some embodiments, a transport of water from the water source 80 across the membrane 200 towards the cell 102 is enabled at least partially by a vapor pressure difference across the membrane 200.

[00114] In some embodiments, a transport of water from the water source 80 across the membrane 200 towards the cell 102 is enabled at least partially by an osmotic pressure difference across the membrane 200.

[00115] In some embodiments, a transport path 72 of water from the water source 80 towards the cell 102 includes any one of the following: (i) a liquid phase transport 77 of liquid water across the membrane 200 responsive to an osmotic pressure difference across the membrane 200, the membrane 200 including a hydrophilic membrane 210 element, and (ii) a gaseous phase transport 79 of water vapor across the membrane 200 responsive to a vapor pressure difference across the membrane 200, the membrane 200 including a hydrophobic membrane 220 element.

[00116] In some embodiments, the membrane 200 includes at least one hydrophilic membrane 210 element. The at least one hydrophilic membrane 210 element may include at least one active layer with nanoscale pores configured to allow passage of only water molecules.

[00117] In some embodiments, the membrane 200 includes at least one hydrophobic membrane 220 element. The at least one hydrophobic membrane 220 element may include at least one hydrophobic layer characterized by a water contact angle higher than 100°.

[00118] In some embodiments, the at least one hydrophobic membrane 220 element may be characterized by a porosity higher than 50% and pore sizes ranging from 0.01 pm to 0.5 pm.

[00119] In some embodiments, the membrane 200 may form a part of a wall 115 of the one or both of the first chamber 117 and the second chamber 118, with the membrane 200 interposing each of one or more transport paths 72 from the water source 80 to the one or more of the first chamber 117 and the second chamber 118 respectively. [00120] In some embodiments in which the membrane 200 is disposed externally of the cell 102, the membrane 200 is connected externally to the cell 102 with the membrane 200 interposing each of one or more transport paths 72 from the water source 80 towards the cell 102.

[00121] In some embodiments, the water electrolyzer apparatus or the distillate electrolyzer apparatus 100 may include an electrolyte storage tank 601 disposed externally of the cell 102 in the one or more transport paths 72, in which the electrolyte storage tank 601 is in fluidic communication with the water source 80 exclusively through the membrane 200.

[00122] In some embodiments, the membrane 200 may be configured to prevent transport of impurities across the membrane 200. In some embodiments, the membrane 200 may be configured to prevent transport of electrolyte ions 91 across the membrane 200.

[00123] In some embodiments, the non-porous panel 301 may be parallel to the major surface of the membrane 200, in which the panel 301 may be in slidable engagement relative to the membrane 200. In some embodiments, the panel 301 may be in slidable engagement over the major surface facing the water source 80. In some embodiments, the panel 301 may be in slidable engagement over the major surface facing away from the water source 80.

[00124] In some embodiments, the cell 102 is operable as an alkaline water electrolyzer. In some embodiments, the separator 150 includes a proton exchange film, and the cell 102 is operable as a proton exchange membrane water electrolyzer. In some embodiments, the separator 150 includes an anion exchange film, and the cell 102 is operable as an anion exchange membrane water electrolyzer.

[00125] In some embodiments, the distillate electrolyzer apparatus 100 in operation is responsive to an electric current 104 provided to the cathode 122 and the anode 132, in which water contacting the cathode 122 and the anode 132 electrochemically splits to generate hydrogen gas 20 on the cathode 122 and oxygen gas 30 on the anode 132, the hydrogen gas 20 and the oxygen gas 30 being separated by the separator 150.

[00126] According to another aspect, according to various embodiments of the present disclosure, a water electrolyzer apparatus or distillate electrolyzer apparatus 100 for use with a water source 80 includes a plurality of cells 102, a membrane 200, and a baffle 300. Each one of the plurality of cells 102 includes: a first electrode, a second electrode, and a separator 150. The first electrode and the second electrode form an operable pair of an anode 132 and a cathode 122. The separator 150 is disposed between the first electrode and the second electrode to define a first chamber 117 and a second chamber 118. The first electrode is disposed in the first chamber 117 and the second electrode is disposed in the second chamber 118. The first chamber 117 and the second chamber 118 are in fluidic communication with one another exclusively through the separator 150. The plurality of cells 102 are in fluidic communication with the water source 80 exclusively through the membrane 200. The baffle 300 includes a non-porous panel 301 moveable relative to a major surface of the membrane 200 to expose a variable area of the membrane 200 to the water source 80.

[00127] According to some embodiments, a transport of water from the water source 80 across the membrane 200 towards the plurality of cells 102 is enabled at least partially by a vapor pressure difference across the membrane 200. According to some embodiments, a transport of water from the water source 80 across the membrane 200 towards the plurality of cells 102 is enabled at least partially by an osmotic pressure difference across the membrane 200. According to some embodiments, the membrane 200 includes a hydrophilic membrane 210 element configured to enable a liquid phase transport 77 of liquid water from the water source 80 towards the plurality of cells 102 responsive to an osmotic pressure difference across the membrane 200. According to some embodiments, the membrane 200 includes a hydrophobic membrane 220 element configured to enable a gaseous phase transport 79 of water vapor from the water source 80 towards the plurality of cells 102 responsive to a vapor pressure difference across the membrane 200.

[00128] According to some embodiments, the pair of the anode 132 and the cathode 122 of any one of the plurality of cells 102 are connected in parallel with the pair of the anode 132 and the cathode 122 of another one of the plurality of cells 102. According to some embodiments, the pair of the anode 132 and the cathode 122 of any one of the plurality of cells 102 are connected in series with the pair of the anode 132 and the cathode 122 of another one of the plurality of cells 102.

[00129] According to some embodiments, the membrane 200 forms a part of a wall 115 of at least one of the plurality of cells 102, in which the wall 115 is a part of one or both of the first chamber 117 and the second chamber 118, and in which the membrane 200 interposes each of one or more transport paths 72 from the water source 80 towards the plurality of cells 102.

[00130] According to some embodiments, the distillate electrolyzer apparatus 100 further includes an electrolyte storage tank 601, in which the electrolyte storage tank 601 is disposed externally of the plurality of cells 102 and in fluidic communication with the water source 80 exclusively through the membrane 200, and in which the membrane 200 is disposed externally of the plurality of cells 102 and interposes each of one or more transport paths 72 from the water source 80 towards the plurality of cells 102.

[00131] In yet another aspect, embodiments of the present disclosure includes a method 900 of water splitting. The method 900 includes a step 910 of providing a feed solution to a cell 102. The cell 102 includes a first electrode, a second electrode, and a separator 150. The first electrode and the second electrode form an operable pair of an anode 132 and a cathode 122. The separator 150 is disposed between the first electrode and the second electrode to define a first chamber 117 and a second chamber 118. The first electrode is disposed in the first chamber 117 and the second electrode is disposed in the second chamber 118. The first chamber 117 and the second chamber 118 are in fluidic communication with one another exclusively through the separator 150. The method 900 includes a step 920 of controlling a variable area of the membrane 200 exposed to a water source 80 by moving a non-porous panel 301 of a baffle 300 relative to a major surface of the membrane 200, in which the feed solution 70 is in fluidic communication with the water source 80 exclusively through the membrane 200.

[00132] In various embodiments, the feed solution 70 is formed by a transport of water from the water source 80 across the membrane 200 towards the cell 102, in which the transport includes any one of: (i) a liquid phase transport 77 of liquid water across the membrane responsive to an osmotic pressure difference across a hydrophilic membrane 210 element, and (ii) a gaseous phase transport 79 of water vapor responsive to a vapor pressure difference across a hydrophobic membrane 220 element. The water splitting 930 is based on the feed solution 70 supplied by the transport described above.

[00133] All examples described herein, whether of apparatus, methods, materials, or products, are presented for the purpose of illustration and to aid understanding, and are not intended to be limiting or exhaustive. Modifications may be made by one of ordinary skill in the art without departing from the scope of the invention as claimed.