Method of Producing Electrocatalyst Coated Electrode by Electrochemical Oxidation

The production of hydrogen gas (H) can play an important role because Hgas is required for many chemical processes. As of 2022, roughly 75 million tons of hydrogen is produced annually worldwide for various uses, such as oil refining, in the production of ammonia (through the Haber process), in the production of methanol (though reduction of carbon monoxide), or as a fuel in transportation.

Historically, a large majority of Hgas (˜95%) has been produced from fossil fuels (e.g., by steam reforming of natural gas, partial oxidation of methane, or coal gasification). Other methods of hydrogen production include biomass gasification, low- or no-COemission methane pyrolysis, and electrolysis of water. Electrolysis uses electricity to split water molecules into Hgas and oxygen gas (O). To date, electrolysis systems and methods have been generally more expensive than fossil-fuel based Hgas production. However, the fossil-fuel based methods can be more environmentally damaging, generally resulting in increased COemissions. Therefore, there is a need for cost-competitive and environmentally friendly methods of hydrogen gas producing electrolysis systems and methods.

Electrolysis systems typically include one or more electrolysis cells with a cathode and an anode, wherein Hgas is formed at the cathode and Ogas is optionally formed at the anode. Typically, one or both of the cathode and the anode include an electrically conductive substrate coated with one or more materials that act as a catalyst for the Hforming half reaction or the Oforming half reaction.

The present disclosure describes a catalyst coated electrode for use in an electrochemical device, such as a water electrolyzer for the production of hydrogen gas (H). In an example, the catalyst comprises a metal compound (e.g., an oxide of a metallic element), that has been formed by first coating a slurry comprising particles of one or more precursor compounds (e.g., a metal hydroxide) and then electrochemically oxidizing the one or more precursor compounds to one or more catalyst compounds (such as a mixed metal oxide).

In an example, the present disclosure describes a method comprising applying a slurry to one or more surfaces of a conductive substrate to form a precursor coating and provide a precursor coated substrate, wherein the slurry includes precursor particles comprising one or more precursor compounds in a slurry medium, and electrochemically oxidizing the one or more precursor compounds to chemically convert the one or more precursor compounds to one or more catalyst compounds and form catalyst particles adhered to the one or more surfaces of the conductive substrate to provide a catalyst coated substrate.

The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments, which are also referred to herein as “examples,” are described in enough detail to enable those skilled in the art to practice the invention. The example embodiments may be combined, other embodiments may be utilized, or structural, and logical changes may be made without departing from the scope of the present invention. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.

References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a recited range of values of “about 0.1 to about 5” should be interpreted to include not only the explicitly recited values of about 0.1 and about 5, but also all individual concentrations within the indicated range of values (e.g., 1, 1.23, 2, 2.85, 3, 3.529, and 4, to name just a few) as well as sub-ranges that fall within the recited range (e.g., 0.1 to 0.5, 1.21 to 2.36, 3.3 to 4.9, or 1.2 to 4.7, to name just a few). The statement “about X to Y” has the same meaning as “about X to about Y,” unless indicated otherwise. Likewise, the statement “about X, Y, or about Z” has the same meaning as “about X, about Y, or about Z,” unless indicated otherwise.

In this document, the terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. Unless indicated otherwise, the statement “at least one of” when referring to a listed group is used to mean one or any combination of two or more of the members of the group. For example, the statement “at least one of A, B, and C” can have the same meaning as “A; B; C; A and B; A and C; B and C; or A, B, and C,” or the statement “at least one of D, E, F, and G” can have the same meaning as “D; E; F; G; D and E; D and F; D and G; E and F; E and G: F and G; D, E, and F; D, E, and G; D, F, and G; E, F, and G; or D, E, F, and G.” A comma can be used as a delimiter or digit group separator to the left or right of a decimal mark; for example, “0.000,1” is equivalent to “0.0001.”

In the methods described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Furthermore, specified steps can be carried out concurrently unless explicit language recites that they be carried out separately. For example, a recited act of doing X and a recited act of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the process. Recitation in a claim to the effect that first a step is performed, and then several other steps are subsequently performed, shall be taken to mean that the first step is performed before any of the other steps, but the other steps can be performed in any suitable sequence, unless a sequence is further recited within the other steps. For example, claim elements that recite “Step A, Step B, Step C, Step D, and Step E” shall be construed to mean step A is carried out first, step E is carried out last, and steps B, C, and D can be carried out in any sequence between steps A and E (including with one or more steps being performed concurrent with step A or Step E), and that the sequence still falls within the literal scope of the claimed process. A given step or sub-set of steps can also be repeated.

Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed step of doing X and a claimed step of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

The term “about” as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, within 1%, within 0.5%, within 0.1%, within 0.05%, within 0.01%, within 0.005%, or within 0.001% of a stated value or of a stated limit of a range, and includes the exact stated value or range.

The term “substantially” as used herein refers to a majority of, or mostly, such as at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or 100%.

In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

Hydrogen gas (H) can be formed electrochemically by a water-splitting reaction where water is split into Hgas and (optionally) oxygen gas (O) at a cathode and an anode of an electrochemical cell, respectively. Examples of such electrochemical processes include, without limitation, proton electrolyte membrane (PEM) electrolysis and alkaline water electrolysis (AWE). In such electrochemical reactions, the operating energy necessary to drive the water-splitting electrolysis reaction is high due to additional energy costs as a result of various energy inefficiencies. For example, to reduce unwanted migration of ionic species between the electrodes, the cathode and the anode may be separated by a separator, such as a membrane, which can reduce migration of the ionic species. Although the separator can improve the overall efficiency of the cell, it can come at a cost of additional resistive losses in the cell, which in turn increases the operating voltage. Other inefficiencies in water electrolysis can include solution resistance losses, electric conduction inefficiencies, and/or electrode over-potentials, among others.

is a schematic diagram of an example water electrolyzer cellthat converts water (HZO) into hydrogen gas (H) and oxygen gas (O) with electrical power. In an example, the electrolyzer cellcomprises a housing, e.g., an overall chassis structure that defines and at least partially encloses an interior of the cell. The housing can divide the cellinto two half cells: a first half celland a second half cell. In an example, the first and second half cells,are separated by a separator, such as a membrane. In an example, the separatorcomprises a porous membrane (e.g., a microporous membrane or a nanoporous membrane), an ion-exchange membrane, or an ion solvating membrane. In examples wherein the separatorcomprises an ion-exchange membrane, the membrane can be of different types, such as an anion exchange membrane (AEM), a cation exchange membrane (CEM), a proton exchange membrane (PEM), or a bipolar ion exchange membrane (BEM).

In examples where the separatoris a cation exchange membrane, the cation exchange membrane can be a conventional membrane such as those available from, for example, Asahi Kasei Corp. of Tokyo, Japan, or from Membrane International Inc. of Glen Rock, NJ, USA, or from The Chemours Company of Wilmington, DE, USA. Examples of cation exchange membranes include, but are not limited to, the membrane sold under the N2030WX trade name by The Chemours Company and the membrane sold under the F8020/F8080 or F6801 trade names by the Asahi Kasei Corp. Examples of materials that can be used to form a cationic exchange membrane include, but are not limited to, a perfluorinated polymer containing anionic groups, for example sulphonic and/or carboxylic groups. It may be appreciated, however, that in some examples, depending on the need to restrict or allow migration of a specific cation or an anion species between the electrolytes, a cation exchange membrane that is more restrictive and thus allows migration of one species of cations while restricting the migration of another species of cations may be used. Similarly, in some embodiments, depending on the need to restrict or allow migration of a specific anion species between the electrolytes, an anion exchange membrane that is more restrictive and thus allows migration of one species of anions while restricting the migration of another species of anions may be used. Such restrictive cation exchange membranes and anion exchange membranes are commercially available and can be selected by one ordinarily skilled in the art.

In some examples, the separatorcan be selected so that it can function in an acidic and/or an alkaline electrolytic solution, as appropriate. Other properties for the separatorthat may be desirable include, but are not limited to, high ion selectivity, low ionic resistance, high burst strength, and high stability in electrolytic solution in a temperature range of room temperature to 150° C. or higher.

In an example, the separatoris stable in a temperature range of from about 0° C. to about 150° C., for example from about 0° C. to about 100° C., such as from about 0° C. to about 90° C., for example from about 0° C. to about 80° C., such as from about 0° C. to about 70° C., for example from about 0° C. to about 60° C., such as from about 0° C., to about 50° C., for example from about 0° C. to about 40° C., or such as from about 0° C. to about 30° C.

It may be useful to use an ion-specific ion exchange membrane that allows migration of one type of ion (e.g., cation for a CEM and anion for an AEM) but not another, or migration of one type of ion and not another, to achieve a desired product or products in the electrolyte solution.

In an example, the first half celldefines a first chamberthat at least partially houses a first electrodeand a first electrolyte solutionand the second half celldefines a second chamberthat at least partially houses a second electrodeand a second electrolyte solution. In an example, described in more detail below, each electrode,can comprise a high surface area metal, such as a fine metal mesh. In an example, each electrode,comprises a nickel mesh. Examples of solutions that can comprise the first electrolyteand the second electrolyteinclude, but are not limited to, one or more of: a solution of potassium hydroxide (KOH) in water, a solution of sodium hydroxide (NaOH) in water, and a solution of lithium hydroxide (LiOH) in water.

In an example, the first and second electrodes,are positioned proximate to the separator, such as by being abutted against a corresponding face of the separator. In an example, the first electrodeis positioned proximate to (e.g., abutted against) a first separator face on a first side of the separatorand the second electrodeis positioned proximate to (e.g., abutted against) a second separator face on a second side of the separatorthat opposes the first separator face.

In an example, the first electrodeis the anode for the electrolyzer celland the second electrodeis the cathode for the electrolyzer cell. Therefore, for the sake of simplicity of identification, the first half cellmay also be referred to as “the anode half cell,” the first electrodemay also be referred to as “the anode,” the first electrolyte solutionmay also be referred to as “the anode electrolyte solution” or as “the anolyte,” the second half cellmay also be referred to as “the cathode half cell,” the second electrodemay also be referred to as “the cathode,” and the second electrolyte solutionmay also be referred to as “the cathode electrolyte solution” or as “the catholyte.”

The electrodes,are the locations of the cellwhere electron transfer half reactions occur, e.g., by reacting with one or more components of the electrolyte solutions,in the chambers,to generate Ogas and/or Hgas, respectively. Each of the electrodes,can be coated with one or more electrocatalysts to speed reaction toward Hgas and/or toward Ogas. In a typical example, one of both of the electrodes,comprises a conductive substrate, such as a nickel substrate body, with or without an electrocatalyst material coated onto one or more surfaces of the conductive substrate. One or more binders can be used to adhere an electrocatalyst material onto the conductive substrate of one or both of the electrodes,. The electrocatalyst material can lower the activation energy for the electrochemical reaction so that the reaction can proceed without the electrocatalyst being consumed by the reaction. By lowering the activation energy, an electrocatalyst is able to facilitate specific reactions at the electrode so that the electrochemical device has a reduced energy demand and lower operating costs. Examples of electrocatalyst materials include, but are not limited to, metals, metal alloys, metal-metalloid alloys, metal oxides, metal phosphides, and metal sulfides. Further details of specific examples of electrocatalyst materials that can be applied to one or both electrodes,are described in more detail below.

Each of the electrodes,can be configured for a particular electrochemical half reaction, such as the half reactions for the overall water electrolysis process described below. For example, the first electrodecan be configured to perform a first electrochemical half reaction and the second electrodecan be configured to perform a second electrochemical half reaction. The actual half reactions that take place at each electrode,can depend on the type of local environment that is present at each electrode,during operation of the electrolyzer cell, and in particular on the alkalinity (e.g., pH) of the anolyteat the anodeand of the catholyteat the cathode. Half Reaction [1], below, is an example of a reaction that can take place at the anodewhen the anolyteis alkaline (e.g., with a pH>7):

4OH→O+2HO+4  [1]

Half Reaction [1] is also referred to as the “Oxygen Evolution Reaction [1]” or “the OER [1].” The Ogas that is generated by the OER [1] can form oxygen bubblesin the anolytewithin the anode chamber, as shown in.

Half Reaction [2], below, is an example of a reaction that can take place at the cathodewhen the catholyteis alkaline (e.g., with a pH>7):

2+2HO→H+2OH  [2]

Half Reaction [2] is also referred to as the “Hydrogen Evolution Reaction [2]” or “the HER [2].” The Hgas that is generated by the HER [2] can form hydrogen bubblesin the catholytewithin the cathode chamber, as shown in.

In an example, the anodeis electrically connected to an external positive conductive lead(also referred to as “the anode lead”) and the cathodeis electrically connected to an external negative conductive lead(also referred to as “the cathode lead”). In an example, when the separatoris wet and is in electrolytic contact with the electrodes,, and an appropriate voltage is applied across the leadsand, Half Reactions [1] and [2] are activated. As noted above, in OER [1], OHions are oxidized at the anode, which generates Ogas (e.g., as the Obubblesin the anolyte) and forms additional HO molecules in the anolyte. In HER [2], HO is reduced at the cathode, which generates Hgas (e.g., as the Hbubblesin the catholyte) and forms additional OHions in the catholyte. In some examples, at least a portion of the OHions pass through the separator(e.g., if the separatoris an anion exchange membrane) so that they are available to be oxidized via OER [1] at the anode.

The electrolyzer cellcan be configured so that the electrolyte solutions,flow through the chambers,so that each electrolyte solution,can pick up the gas generated by its corresponding electrode,and carry the produced gas out of the electrolyzer cell. For example, the anolytecan flow into the anode half cellthrough an anolyte inletand can exit the anode half cellthrough an anolyte outlet. Similarly, the catholytecan flow into the cathode half cellthrough a catholyte inletand can exit the cathode half cellthrough a catholyte outlet. In an example, the flow of the anolytethrough the anode chamberpicks up the produced Ogas as the Obubblesand exits the anode chamberthrough the anolyte outletand the flow of the catholytethrough the cathode chamberpicks up the produced Hgas as the Hbubblesand exits the cathode chamberthrough the catholyte outlet. One or both of the gases can be separated from their respective electrolyte solution,downstream of the electrolyzer cellwith one or more appropriate separators. In an example, the produced Hgas is separated from the catholyte, dried, and harvested into high pressure canisters or fed into further process elements. The produced Ogas can be allowed to simply vent into the atmosphere or can be stored for other uses. In an example, the electrolyte solutions,are recycled from the electrolyte outlets,back to the electrolyte inlets,, as needed.

In an example, a typical voltage across the electrolyzer cell(e.g., the voltage difference between the anode leadand the cathode lead) is from 1.5 volts (V) to 3.0 V. In an example, an operating current density for the electrolyzer cellis from 0.1 A/cmto 3 A/cm. Each cellhas a size that is sufficiently large to produce a sizeable amount of Hgas when operating at these current densities. In an example, an active area of each cell(e.g., a width multiplied by a height for a rectangular cell) is from 0.25 square meters (m) to 15 m, such as from 1 mto 5 m, for example from 2 mto 4 m, such as from 2.25 mto 3 m, such as from 2.5 mto 2.9 m. In an example, the total volume of each cell (e.g., a width multiplied by a height multiplied by a depth) is from 0.1 cubic meter (m) to 2 m, such as from 0.15 mto 1.5 m, for example from 0.2 mto 1 m, such as from 0.25 mto 0.5 m, for example from 0.275 mto 0.3 m. In a non-limiting example, the total volume of the entire electrolyzer system (e.g., the combined volume of all the cells in all the stacks in the plant) is from 1 mto 25,000 m, such as from 5 mto 2,500 m, for example from 10 mto 100 m, such as from 25 mto 75 m, for example from 30 mto 50 m.

The efficiency of an electrolyzer cell can depend on resistive losses between the anode and cathode, also referred to as ohmic resistance. The ohmic resistance of the separatorcan affect the voltage drop across the anodeand the cathode(and thus, the overall efficiency of the cell). For example, as the ohmic resistance of the separatorincreases, the voltage across the anodeand the cathodethat is required may also increase, and vice versa. In an example, the separatorhas a relatively low ohmic resistance and a relatively high ionic mobility. In an example, the separatorhas a relatively high hydration characteristics that increase with temperature, and thus decreases the ohmic resistance. By selecting a separatorwith lower ohmic resistance known in the art, the voltage drop across the anodeand the cathodeat a specified temperature can be lowered.

One parameter that can affect the ohmic resistance between electrodes in an electrolyzer cell is the distance between the anode and the cathode, with a larger gap between the electrodes resulting in a correspondingly larger resistance compared to a smaller gap. Therefore, in an example, an electrolyzer cell can be configured so that the space or gap between the anode and the cathode is as small as possible. In one example configuration, one or both of the anode and the cathode are positioned so that the electrode is in contact with the separator, which is also referred to as a “zero-gap” configuration. In an example of a zero gap configuration, one face or surface of the anode is in contact with a first surface of the separator and one face or surface of the cathode is in contact with an opposing second surface of the separator.

shows an example of a cell assemblythat can provide for a zero gap architecture for an electrolyzer cell, e.g., with one or both electrodes compressed against a separator. The example cell assemblyofcan form part of the electrolyzer cellof.

In an example, the cell assemblyincludes a housing that at least partially encloses a cell interior, wherein a first electrode, a second electrode, and a separatorare enclosed within the cell interior. In an example, each electrode,can be part of a corresponding half cell. For example, the first electrodecan be included as part of a first half cell and the second electrodecan be included as part of a second half cell. In a non-limiting example, the first electrodeis the anode of the cell assemblyand the second electrodeis the cathode of the cell assembly, such that the first and second electrodes,may also be referred to as “the anode” and “the cathode,” respectively, and the corresponding half cells will also be referred to as the anode half cell (i.e., the half-cell associated with the anode) and the cathode half cell (i.e., the half-cell associated with the cathode). There are also instances when the anodeand the cathodeare referred to more generically as “the electrode,” or “the electrodes,.”

The separatorcan be situated between the anode half cell and the cathode half cell, for example by being positioned between the anodeand the cathode. As discussed above, the separatorcan be configured to reduce migration of certain species between the electrodes,while allowing one or more other species to pass from the anode half cell to the cathode half cell and/or from the cathode half cell to the anode half cell. In an example, the separatorcomprises a diaphragm, a membrane electrode assembly (MEA), or a membrane, such as an ion exchange membrane (IEM) (e.g., an anion exchange membrane (AEM), a cation exchange membrane (CEM), or a proton exchange membrane (PEM)), a bipolar ion exchange membrane (BEM), an ion solvating membrane (ISM), or a microporous or nanoporous membrane. In some examples, the separatorcan comprise more than one type of separator, e.g., more than one type of membrane (as is the case with a bipolar ion exchange membrane), and/or can be part of a composite structure (such as a membrane electrode assembly (MEA)), which can also include one or more separator components (e.g., to separate an anion exchange membrane (AEM) from a cation exchange membrane (CEM)), or one or more support structures to provide mechanical integrity to the one or more separators. In addition to these components, individual gaskets or gasket tape may be provided in between and along the outer perimeter of the components to seal the compartments from fluid leakage.

As discussed above, in an example, each of the electrodes,is situated in a “zero-gap” configuration relative to the separator. Although the term “zero-gap” would typically imply that one or both electrodes,are in actual physical contact with the separator, in the present disclosure, the term “zero-gap” is expanded to mean that all structures between the two current collectors,(described below) are in mechanical contact with no space for the liquid electrolyte to congregate. In other words, there could be one or more spacer materials inserted between one or both of the current collectors,and the separator, and the overall structure would still be considered a “zero-gap architecture,” as that term is being used herein, so long as there is not a liquid electrolyte gap between the two current collectors,.

The housing of the cell assemblycan comprise a pan assembly,for one or both of the half cells, such as an anode-side pan assemblyfor the anode half cell and a cathode-side pan assemblyfor the cathode half cell (also referred to as “the anode pan assembly” and “the cathode pan assembly,” respectively). In an example, each pan assembly,includes a pan,with an interior for receiving an electrolyte solution. For example, the anode pan assemblycan comprise an anode-side pan(also referred to as “the anode pan”) for receiving an anolyte and the cathode pan assemblycan comprise a cathode-side pan(also referred to as “the cathode pan”) for receiving a catholyte. The pan assemblies,can be configured so that the electrolyte flowing through each pan,will come into contact with its corresponding electrode,, e.g., so that Hgas can be evolved from the cathodeand so that Ogas can be evolved from the anode. Each pan assembly,can also include an inlet for receiving electrolyte into the interior of the pan,, and one or more outlets so that electrolyte and evolved gas can exit the pan,(not shown in, but could be similar to the electrolyte solution inlets,and outlets,for the electrolyzer cellof).

In an example, each electrode,is electrically connected to its corresponding pan,so that electrical current can flow from the pan,to the electrode,(as is the case for current flowing from an anode panto an anode) or from the electrode,to the pan,(as is the case for current flowing from a cathodeto a cathode pan). Each half cell can include one or more additional structures to provide for the electrical connection between the electrodes,and the pans,. For example, one or both of the electrodes,can be part of a corresponding electrode assembly comprising the electrode,and one or more additional structures. For example, the first electrode(e.g., the anode) can be part of a first electrode assembly(which will also be referred to herein as “the anode assembly”) and the second electrode(e.g., the cathode) can be part of a second electrode assembly(which will also be referred to herein as “the cathode assembly”).

One or both of the electrode assemblies,can include its corresponding electrode,, a current collector, and an optional elastic element (also sometimes referred to as a “mattress”). For example, the anode assemblycan include the anode, an anode-side current collector(also referred to simply as “the anode current collector”), and an optional anode-side elastic element(also referred to simply as “the anode elastic element”). Similarly, the cathode assemblycan include the cathode, a cathode-side current collector(also referred to simply as “the cathode current collector”), and an optional cathode-side elastic element(also referred to simply as “the cathode elastic element”).

Each electrode assembly,is coupled to its respective pan,, i.e., so that there is an electrical connection between the anodeand the anode panand between the cathodeand the cathode pan. In an example, one or both of the electrodes,comprise a fine mesh structure, such as a fine woven mesh, for example the woven mesh electrode shown in(described in more detail below). A fine mesh, such as a woven mesh, have been found to make an excellent electrode for electrolyzer cells because it provides a high relative surface area, a relatively large open area for electrolyte and gas flow to and from the electrode, and are readily available in sizes that are large enough for a large commercial electrolyzer cell, e.g., with an active area of at least 1 m, such as from 1 mto 4 m.

In an example, a differential fluid pressure can be applied across the separator(e.g., with a pressure on the cathode side of the separatorbeing larger than on the anode side, or vice versa). The differential pressure, in addition to or in place of one or both of the elastic elements,, can act to load the electrodes,and create effective electrical contact between the electrode,and the separatoracross the active area of the electrodes,without requiring welding to couple the electrodes,to other structures in the cell assembly, particularly with fine mesh electrodes.

As described in more detail below, in an example, the woven mesh of one or both of the electrodes,can comprise a network of sets of crossing wires, which can be perpendicular or angled relative to one another, that alternative cross and bend over one another. For example, any particular wire alternates between passing under an adjacent cross wire and then over the next cross wire. In an example, one or both of the electrodes,can comprise a woven wire mesh electrode formed from wires having a wire diameter of 0.18 mm diameter with openings in the mesh of 0.44 mm and with an open area of from about 50% to about 60%, such as from about 50% to about 55%. In an example, one or both of the electrodes,is formed from an expanded mesh wherein one or both of the electrodes,are fabricated from a sheet of material that is 0.13 mm thick with a long way of the diamond shape (LWD) of about 2 mm and a short way of the diamond (SWD) of about 1 mm.

In an example, one or both of the anodeand the cathodeis made primarily or entirely from nickel. Fabricating both the anodeand the cathodeout of nickel enables the use of non-welded electrodes fabricated from fine woven meshes for both electrodes,, for example because nickel has a very low contact resistance. In an example, one or both of the anodeand the cathodeis coated with one or more catalyst materials, e.g., in the form of one or more catalyst coating layers on the electrode,. In an example, the one or more catalyst materials can be electrically conducting.

The current collector,of each electrode assembly,acts to distribute current flowing into or out of its respective electrode,. In an example, the current collector,of each electrode assembly,comprises a rigid structure, such as a rigid metal plate or mesh, which is electrically connected to its corresponding electrode,, either directly or indirectly. In an example, each current collector,can comprises an expanded metal sheet, such as an expanded nickel sheet.

In an example, each elastic element,, if present, comprises a compressible and expandable structure that provides a controlled load when compressed. For example, the elastic element,can be compressed between the separatorand the current collector,, and the resulting load that results as the elastic element,tries to expand back to its fully expanded state biases its corresponding electrode,toward the separatorto provide a zero-gap configuration between the electrode,and the separator. In an example, the elastic element,is also electrically conductive (e.g., the elastic element,is made from or is coated with an electrically conductive material, such as nickel) so that the elastic element,will conduct electricity from the current collector,to the electrode,or vice versa. In an example, each of the one or more elastic elements,comprise one or more electrically conductive filaments that are woven together into an elastic layer that can expand and collapse to apply the controlled load when the elastic layer is compressed. In some examples, one or both of the elastic elements,can be a corrugated knitted mesh having a pre-load of 2 pounds per square inch at about 3 mm of compression. In an example, an uncompressed thickness of one or both of the elastic elements,can be from about 5 mm to about 7 mm. One or both of the elastic elements,can have a corrugation pitch of about 10 mm. In an example, one or both of the elastic elements,are formed from wire having a wire diameter of 0.15 mm.

In the example shown inboth the anode assemblyand the cathode assemblyinclude an elastic element,, e.g., such that the anode elastic elementprovides a first loading force to bias the anodetoward a first side of the separatorand the cathode elastic elementprovides a second loading force to bias the cathodetoward an opposing second side of the separator. In other examples (not shown in the Figures), there is an elastic element on only one side of the separator(e.g., with only the anode assemblyhaving the elastic elementand with the cathode assemblyomitting the elastic element, or vice versa with only the cathode assemblyhaving the elastic elementand with the anode assemblyomitting the elastic element). In such a configuration, the elastic element on only one side of the separatorcan produce sufficient compressive load so that both electrodes,are compressed against the opposing sides of the separator.

In an example, the current collectors,can be coupled to their respective pans,, e.g., so that the current collector,is electrically connected to its corresponding pan,, which provides part of the electrical path between an electrode,and its corresponding pan,. In order to accommodate this electrical connection between the current collector,and its corresponding pan,, in an example, each pan assembly,includes one or more ribs that extend between the electrode assembly,and a back wall of the pan. For example, the anode pan assemblycan include one or more ribsthat extend between a back wallof the anode panand the anode assembly, while the cathode pan assemblycan include one or more ribsthat extend between a back wallof the cathode panand the cathode assembly. The one or more ribscan be welded to the back wallof the anode panwhile the one or more ribscan be welded to the back wallof the cathode pan.