Monolithic bipolar multi-transport electrochemical stack component

Abstract

A monolithic bipolar multi-transport stack component for an electrochemical stack and method for manufacturing such are disclosed. The component comprises a fluidically impermeable and electrically conductive central layer having an anode-side and a cathode-side; recess structures provided on the anode side and on the cathode-side of the central layer, and electrically conductive and fluidically permeable outer layers provided on the recess structures on the anode-side and the cathode-side of the central layer so that the recess structures form flow fields between and parallel to the central layer and the outer layers. The central layer, the recess structures, and the outer layers have been formed via powder processing, adhered together before sintering; and sintered in a single sintering process whereby all layers are monolithically connected. The component is thereby a single monolithic component providing the functionality of a bipolar plate, a flow field, and a porous transport layer for each of two adjacent electrochemical cells. No passivation layers can form between the parts of the component providing the functionalities and therefore no Pt coatings between these parts needed.

Description

[0001] MONOLITHIC BIPOLAR MULTI-TRANSPORT ELECTROCHEMICAL STACK COMPONENT

[0002] FIELD

[0003] The invention involves the technical fields of powder metallurgy and electrochemical stacks.

[0004] BACKGROUND

[0005] Electrochemical stacks are used to convert chemical energy to electricity and vice versa via electrochemical reactions involving an electrolyte, an anode, and a cathode. A stack consists of many independent cells electrically connected with different components. The electrochemical reactions are between reagents provided to the cell and are driven by electrical energy to produce desired products that can then be extracted from the cell, or the reagents react to produce electrical energy and leftover products.

[0006] Water electrolysis is a promising option for carbon-free hydrogen production from renewable and nuclear electricity resources. Nowadays, the two most widely adopted methods for water electrolysis are Alkaline Electrolysis (AEL) and proton exchange membrane electrolysis (PEMEL). Fig. 1 illustrates a schematic of a typical PEMEL cell, highlighting the transport of the involved species and all the constituent components. Fig. 1 shows a cell 10, pure water is fed through the flow channels 16 embedded in the bipolar plates (BPP) 12. At the anode, the anodic porous transport layer (PTL) 18 transports water and electrons to the anodic catalyst layer 4 where the water-splitting reaction takes place. The hydrogen ions travel through a Nation membrane 5 and recombine at the cathode 6 producing hydrogen continuing through cathode PTL 19 and exit the cell via channel in 16 in the next BPP 12. In a practical electrolyser, several of such cells are assembled in series to form a stack, achieving the voltage and power required by the applications.

[0007] PEM electrolysis operates at high voltage (>2V) and in high acidic conditions (pH ~ 0). Given this harsh environment, Titanium is used for both the BPPs and the PTL thanks to its excellent corrosion resistance. The high stability of Titanium is due to the formation of a stable shell of TiO? that protects the core from further oxidation. However, the insulating TiO? shell poses problems at the interfaces between components. Fig. 1 highlights two critical interfaces in a typical PEM cell assembly: 11 is the BPP-PTL interface and I2 is the PTL-CL interface. In both cases, excessive Ti passivation increases the contact resistance and kills the cell performance, this is illustrated in Fig. 2A. Commercial BPPs are machined or hydroformed from Ti sheets while modern PTLs are sintered from Ti powder. To avoid TiO? passivation between the BPP and the PTL, both the BPP and PTL are typically Pt coated before TiO? formation as shown in Fig. 2B, thereby decreasing the contact resistance. The use of Pt coating and the difficulties in BPP manufacturing make the BPP and PTL account to 70-90% of the entire cost of a PEMEL stack.

[0008] Passivation layers and the need for Pt coatings are just some disadvantages of prior art electrochemical cell stacks.

[0009] In prior art method for fabricating electrochemical stack, different parts such as the bipolar plate, flow channels and porous transport layers are different components that are produced separately and successively assembled to form the electrochemical cells. Such separate production and assembly of components increase the costs and complexity of manufacturing. In addition to that, given the hardness of titanium, machining itself requires expensive tools and intensive use of energy.

[0010] US 2023 / 415228 A1 relates to fabrication of bipolar plates made together with porous transport layers so that the porous transport layers are integrally formed with the rest of the bipolar plate. Here, powder pressing techniques are used to form the porous transport layers, which are then placed in a canister as part of an external mould. The external mould is then packed with a titanium powder in an injection moulding process to form a bipolar plate with flow channels next to the porous transport layers. At a subsequent sintering step, the porous transport layers will be integrally formed with the bipolar plate.

[0011] WO 2023 / 242404A1 relates to a process for producing a device for an electrochemical stack. The device comprises a porous layer and a supporting layer comprising channels running in the plane of the supporting layer and being open towards the porous layers. In the process, various green parts are formed and sintered, and thereafter thermically bonded together to form the device. For this reason, the final device is not monolithic.

[0012] SUMMARY

[0013] Accordingly, there is a need for improved components and manufacturing techniques related to electrochemical cells and stacks.

[0014] A method for manufacturing a monolithic bipolar multi-transport stack component for an electrochemical stack is disclosed. The method comprises providing a central layer comprising one or more metallic powder based green layers formed by a layer-forming process, the central layer having an anode-side and a cathode-side. The method comprises providing outer layers at the anode side and on the cathode-side of the central layer, each outer layer comprising one or more metallic powder based green layers formed by a layerforming process. The method comprises providing recess structures between the central layer and each outer layer; wherein the recess structures are formed in one or more metallic powder based green layers at the central layer or at the sides of the outer layers facing the central layer. The method comprises adhering the central layer, the recess structures, and the outer layers together before sintering. The method comprises sintering the central layer, the recess structures, and the outer layers in a single sintering step to form a monolithically connected component wherein the central layer is fluid ically impermeable and electrically conductive, the outer layers are fluidically permeable and electrically conducting, and the recess structures are electrically conductive and define flow fields between and parallel to the central layer and the outer layers.

[0015] In accordance with the method, the one or more powder based green layers forming the central layer are selected to produce a fluidically impermeable and electrically conductive central layer of the component. In accordance with the method, the one or more powder based green layers forming each outer layer are selected to form electrically conducting and fluidically permeable outer layers of the component. In accordance with the method, the one or more powder based green layers forming the recess structure are selected to produce electrically conductive recess structures between the central layer and the out layers of the component.

[0016] A monolithic bipolar multi-transport stack component for an electrochemical stack is disclosed, which is manufactured using the method according to the disclosure.

[0017] A monolithic bipolar multi-transport stack component for an electrochemical stack is disclosed. The multi-transport stack component comprises a fluidically impermeable and electrically conductive central layer having an anode-side and a cathode-side; recess structures provided on the anode side and on the cathode-side of the central layer; and electrically conductive and fluidically permeable outer layers provided on the recess structures on the anode-side and the cathode-side of the central layer. In the multi-transport stack component, the recess structures form flow fields between and parallel to the central layer and the outer layers. In the multi-transport stack component, the central layer, the recess structures, and the outer layers have been formed by layer-forming processes, adhered together before sintering; and sintered in a single sintering process, whereby the recess structures are monolithically connected with the central layer and with the outer layers. An electrochemical cell assembly is disclosed, the electrochemical cell assembly comprising at least two monolithic bipolar multi-transport stack components according to the disclosure, alternatingly stacked with at least two ion-exchange membranes.

[0018] An electrochemical cell stack is disclosed, the electrochemical cell stack comprising a plurality of stacked electrochemical cell assemblies according to the disclosure.

[0019] It is an advantage of the present disclosure that the prior art BPP-PTL interface is eliminated. Thanks to the monolithic grain connection between the central layer and the porous outer layers providing the functionalities of prior art BPPs and PTLs, there is no need for Pt coatings, which considerably reduces cost and improves performance and operational life.

[0020] It is an advantage of the present disclosure that it provides a single manufacturing step for the layers providing the functionalities of prior art BPPs and PTLs. Currently, commercially available BPPs are produced using expensive manufacturing techniques that, together with the need for extensive Pt coating, make the BPP the most expensive component of a PEM electrolyser. In the present disclosure, the separate production step for a BPP can be avoided which considerably reduces cost and simplifies the manufacturing of electrochemical stacks.

[0021] It is an advantage of the present disclosure that the manufacturing of the different layers - such as deposition and shaping - is provided by layer-forming processes such as tape casting, calendaring, and additive manufacturing techniques. In powder pressing and injection moulding techniques such as applied in US 2023 / 415228 A1 , an external mould is filled with a metal powder and binder mixture and pressed to form the shape rather than adding material layer by layer or sheet-wise. In the field of metal powder processing, injection moulding is not a layer forming process.

[0022] In powder pressing and injection moulding, the object is shaped by an external mould or canister, and the ‘building blocks’ - i.e. the powder mixture - does not have an inherent shape. Therefore, the steps of forming, shaping, and assembling different parts of the object are defined solely by the different moulds used to hold powder prior to sintering. After the objects has been removed from the mould, substantial changes in the shapes are not possible. Forming an object using layer-forming processes or mould-free processes means that the manufacturing can be build up and shaped layer-by-layer, and an external mould or canister is not needed to shape the component.

[0023] It is an advantage of the present disclosure that it relies on state-of-the-art production techniques already used for manufacturing of prior arty PTL components. This allows the combined manufacturing of the layers providing the functionalities of prior art BPPs, flow fields, and PTLs at a cost of the same order as currently available PTLs.

[0024] It is an advantage of the present disclosure that the monolithic nature of the component allows a considerable reduction of the stack size. Further, since the BPP, flow field, and PTL functionalities are integrated in a single component, it simplifies stack assembly reducing the manufacturing cost of the stack. This has the further advantage that it allows for the production of considerably smaller stacks for the same power output, reducing cost and the system footprint.

[0025] It is an advantage of the present disclosure that the monolithic nature of the component provides great flexibility for the optimization of channel dimensions and the particle size for the porous parts. This will increase stack performance and reduce the operational cost.

[0026] It is an advantage of the present disclosure that the cost of the stack including component(s) covering the functionalities of BPP, flow fields and PTLs is reduced with respect to conventional multi-component manufacturing and assembly. Even though a metallic powder (for example titanium, or stainless steel or nickel) is more expensive than metal sheets to be machined, the energy intensity of the machining process as well as the tools used (particularly in the case of titanium) necessary for quality finishing, make the final pieces more expensive with respect to a powder metallurgy - sintering route.

[0027] In one or more embodiments, the disclosure uses powder processing to form a multitransport component, where the portions providing the functionality of bipolar plates (BPP), flow fields, and porous transport layers (PTLs) are fabricated in a single sintering step to provide a monolithically connected component with no passivation layers or conductivity changes between the portions. Such a multi-transport component has not been reported in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and other features and advantages of the present disclosure will become readily apparent to those skilled in the art by the following detailed description of examples thereof with reference to the attached drawings, in which:

[0029] Fig. 1 is an illustration of a prior art electrochemical cell,

[0030] Figs. 2A-B are illustrations of parts of prior art electrochemical cells,

[0031] Fig. 3 is an illustration of part of an exemplary component according to the disclosure, Figs. 4 and 5 are illustrations of exemplary components according to the disclosure Figs. 6 and 7 illustrate exemplary methods of manufacturing according to the disclosure Figs. 8A-C illustrate a side-view (9A, a perspective-view (9B), and a top-view (9C) of an exemplary component according to the disclosure.

[0032] Fig. 9 is an illustration of an exemplary electrochemical stack according to the disclosure and an exemplary component according to the disclosure.

[0033] DETAILED DESCRIPTION

[0034] Various exemplary embodiments and details are described hereinafter, with reference to the figures when relevant. It should be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the disclosure or as a limitation on the scope of the disclosure. In addition, an illustrated embodiment needs not to have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated, or if not so explicitly described.

[0035] An electrochemical stack is a stack of electrochemical cells converting chemical energy to electricity and vice versa through electrochemical reactions involving an electrolyte, an anode, and a cathode. A stack consists of many independent cells electrically connected with different components. The electrochemical reactions are between reagents provided to the cell and are driven by electrical energy to produce desired products that can then be extracted from the cell, or the reagents react to produce electrical energy and leftover products.

[0036] A stack typically comprises electrodes, reagent / product inlets / outlets (commonly referred to as ‘flow fields’), multi-species transport layers, electrodes (where the interaction between chemical species and electricity occurs), and membranes (transporting ions). When cells are stacked, neighbouring cells share electrical contacts, made possible by special components also referred to as bipolar plates (BPP). The ‘multi-species transport layer’ refers to layers allowing the transport of chemical species into and from the electrodes (hence excluding the membranes) as well as electrons. A common example of such multi-species transport layer is a sintered porous transport layer (PTL). Metallic felts and foams can also serve the same purpose but are generally not referred to as PTLs.

[0037] For the purpose of nomenclature, a stack, as standard repeating unit (SRU), or a stack component is considered as comprising different layers stacked on top of each other, so that it extends in a vertical / longitudinal direction and the layers extends in horizontal / transverse directions, with a ‘cross-section’ referring to a particular transverse plane within a layer. This way of looking at it does not imply anything related to the order in which the layers are formed or stacked during fabrication. The electrochemical stack can be an electrolyser stack, such as for water electrolysis to generate H2. Examples include proton cells for exchange membrane electrolysis PEMEL, or Alkaline Electrolysis (AEL), and Anion exchange membrane electrolysis (AEM).

[0038] A method for manufacturing a monolithic bipolar multi-transport stack component for an electrochemical stack is disclosed. The method comprises providing a central layer comprising one or more metallic powder based green layers formed by a layer-forming process, the central layer having an anode-side and a cathode-side. Outer layers are provided at the anode side and on the cathode-side of the central layer, each outer layer comprising one or more metallic powder based green layers formed by a layer-forming process. Recess structures are provided between the central layer and each outer layer, with the recess structures being formed in one or more metallic powder based green layers at the central layer or at the sides of the outer layers facing the central layer. The recess structures are preferably formed at, such as in or on, the central layer, or at, such as in or on, the sides of the outer layers facing the central layer, before the central and outer layers are stacked atop of one another.

[0039] In the wider context of metal powder processing, layer-forming processes refer to shaping methods in which a component is built up in a layer- or sheet-wise manner using slurry-, binder-, and powder-based materials. In these processes, the material is either deposited layer by layer to directly form the component (as in additive manufacturing) or formed into separate layers or sheets (as in tape casting or calendaring) that are subsequently laminated to produce the desired thickness or geometry. Layer-forming processes - also referred to as sheet and layer forming techniques - thus encompass tape casting, calendaring, and additive manufacturing techniques such as 3D printing, screen printing, and electrospinning. Within this framework, additive manufacturing denotes deposition- based processes that fabricate parts through sequential layer buildup, whereas tape casting and calendaring are sheet-forming techniques in which discrete sheets are produced and stacked to create the multilayer component. Textbook descriptions of additive manufacturing techniques may be found in e.g. Francis, Lorraine; Materials Processing, Elsevier 2016, Chapter 5. Textbook descriptions of tape casting and calendaring may be found in Mistier and Twiname; Tape casting theory and Practice, American ceramic society, 2000, Chapter 4 and 5.

[0040] In an alternative embodiment, the method comprises providing the central layer and the outer layers as metallic powder based green layers formed by mould-free processes, where mould-free processes is understood to encompass techniques for forming metallic powder based green layers that do not require or use an external mould to shape a powder mixture. In respect to the disclosure, forming a metallic powder based green layer by mould-free processes comprises forming the metallic powder based green layer by tape casting, calendaring, and additive manufacturing techniques comprising binder jetting, electrospinning, screen printing, and 3D printing. Forming a metallic powder based green layer by mould-free processes does not comprise powder pressing techniques requiring an external mould to shape a powder mixture, e.g. injection moulding.

[0041] It is understood that layer-forming processes and mould-free processes both comprise the techniques described in the present disclosure.

[0042] The provided layers are adhering together before sintering the provided layers in a single sintering step to form a monolithically connected component. In the monolithically connected component, the central layer is fluidically impermeable and electrically conductive, the outer layers are fluidically permeable and electrically conducting, and the recess structures are electrically conductive and define flow fields between and parallel to the central layer and the outer layers.

[0043] In accordance with the method, the one or more powder based green layers forming the central layer are selected to produce a fluidically impermeable and electrically conductive central layer of the component. Also, the one or more powder based green layers forming each outer layer are selected to form electrically conducting and fluidically permeable outer layers of the component. Lastly, the one or more powder based green layers forming the recess structure are selected to produce electrically conductive recess structures between the central layer and the out layers of the component. A monolithic bipolar multi-transport stack component for an electrochemical stack manufactured using the above method is disclosed. The component comprises a fluidically impermeable and electrically conductive central layer having an anode-side and a cathodeside; recess structures provided on the anode side and on the cathode-side of the central layer; and electrically conductive and fluidically permeable outer layers provided on the recess structures on the anode-side and the cathode-side of the central layer. In the multitransport stack component, the recess structures form flow fields between and parallel to the central layer and the outer layers. The central layer, the recess structures, and the outer layers have been formed by layer-forming processes such as tape casting, calendaring, and / or additive manufacturing techniques, adhered together before sintering; and sintered in a single sintering process, whereby the recess structures are monolithically connected with the central layer and with the outer layers. That the central layer, the recess structures, and the outer layers have been formed by layer-forming processes can be determined in the final component, since all these techniques involve a layer-wise or sheet-wise material deposition or formation that can be detected by comparing microstructures across the component to determine discontinuous changes in the microstructures. Components formed by injection moulding will not exhibit such discontinuous changes indicating layered deposition or formation.

[0044] Fig 3 illustrates a part 21 of monolithic bipolar multi-transport stack component, showing the central layer 22, recess structure 24, and one outer layer 28. In comparison to the prior art case illustrated in Fig. 2A, the monolithic connection between the central layer 22, recess structure 24, and one outer layer 28 means that, even in the case of TiO? formation, there is no passivation layer hindering electrical conductivity through the component, thus rendering the Pt coating shown in Fig. 2B unnecessary. The terms ‘anode-side’ and ‘cathode-side’ are used merely to distinguish between the two sides of the central layer 22 or of the component as such, when describing the component. Le. the ‘anode-side’ and ‘cathode-side’ are the two sides of the component that will face the anode and cathode in the two neighbouring cells of which the component will be part of if used in an electrochemical cell stack. These terms may be replaced by ‘first side’ and ‘second side’ respectively, but it is found that naming the sides in relation to how an electrochemical cell is built up is more illustrative. The terms do not indicate that the component comprises an anode or a cathode. Later Figs 4 and 8 illustrates the two sides anode-side 43 and cathode-side 44.

[0045] In the present disclosure, a ‘monolithic bipolar multi-transport stack component’ or simply the ‘multi-transport component’ or simply ‘component’ is a descriptive term used in the present disclosure and not a common term in the technical fields of metallurgy or electrochemical stacks, the multi-transport component’ is an electrochemical stack component not previously described in the prior art.

[0046] In the field of metallurgy or powder metallurgy, the term ‘monolithic’ is used as an adjective to specify that a component is a single, structure in which grains have grown coherently at the same time and do not present discontinuities. It is noted that ‘monolithic’ has become a populistic term used in many different fields not relevant to the current disclosure. The term ‘monolithically connected’ means that all the portions of the structure have been formed (such as sintered) at the same time and are therefore formed without the possibility of a passivation layer developing between them. In an alternative wording, ‘monolithically connected’ indicates that there will be no change or variation in the characteristic physical properties throughout the component, such as between different portions of the component. In another alternative wording, ‘monolithically connected’ indicates that all grains used to create the microstructural lattice (crystals) in portions of the component have undergone changes at the same time (such as during sintering).

[0047] In the present disclosure, ‘bipolar’ means that it connects two adjacent, serially connected SRUs and consequently involves a longitudinal voltage potential corresponding to the anode and cathode potentials in the two adjacent electrochemical cells.

[0048] In the present disclosure, multi-transport means that the device allows the transport of multiple phases (liquid (water), gas), chemical species and electricity.

[0049] In the present disclosure, a stack component is a part that has a function in the stack and will be assembled with other components to form the electrochemical stack.

[0050] The central layer is electrically conductive, impermeable to fluids (gas / liquids), and provide BPP functionality to the component. The outer layers are electrically conducting, porous, and permeable, and provide PTL functionality to the component. In one or more embodiments, the recess structures are ribs or elongated walls between the central layer and the outer layers, and related structures are sometimes referred to as channel-forming elements in the prior art. It can be formed on both sides of the central layer, as a separate layer, or on the inner sides of the outer layers. The recess structure provides flow fields in the final component, preferably in transverse directions, and having corresponding inlets and outlets.

[0051] In one or more embodiments, the recess structures are stamped or formed by subtractive material processing in the central layer. In one or more embodiments, the recess structures are stamped or formed by subtractive material processing in the sides of the outer layers facing the central layer. In one or more embodiments, the recess structures are formed by a layer-forming process on the central layer or on the sides of the outer layers facing the central layer. The recess structures define the resulting flow fields between and parallel to the central layer and the outer layers and are also referred to as flow field precursors.

[0052] The flow fields will comprise voids or barrier-free channels so that the flow field can transport a fluid / liquid in transverse directions with relatively low resistance, or alternatively that no impact bodies which induce turbulence in the flow are present in the channels, as it is typically the case for obstacles obliquely to the direction of flow. A channel running in a wave-like manner can therefore be barrier free even if it runs through flow field in a sinusoidal or wave-like manner. A porous layer without defined void channels may provide transverse transport but cannot provide a barrier-free or void flow field. One or more embodiments, the recess structures are formed so that, in a cross-sectional portion within the height of the recess structures (i.e. within the flow field functionality layer), the volume of the void is between 10 - 90%.

[0053] In one or more embodiments, it is advantageous to arrange the recess structures to be predominantly straight and parallel with one another, in order to achieve a smallest possible throughflow resistance. In one or more embodiments, it may be advantageous to form the recess structures with wavy line shapes off set parallel with each one another in such a manner that although a barrier-free passage is maintained, the static support function of the component is increased. Channels of the flow field are then shaped such that they have a preferably straight clear passage, but the side wall is configured in a wave-like manner, in order to achieve this support function.

[0054] In exemplary embodiments, sacrificial void-filler fills the voids of the recess structure before the step of adhering the central layer, the recess structures, and the outer layers together. This has the effect of protecting the shape of the resulting flow field and allow a more efficient adhering process (higher pressure and / or temperature) resulting in a better attachment of the layers. The sacrificial void-filler filling the voids may be deposited before or after the recess structures. In exemplary embodiments, the recess structures are formed, such as by stamping, shaping, or additive material processing in the central or outer layers, whereafter the voids between the recess structures are filled with the sacrificial void-filler to form a flat plane on which further layers can be formed. In such embodiments, the sacrificial void-filler is not used to shape the recess structures since these are already provided, rather they served to protect them during steps such as adhering and pressing. In exemplary embodiments, sacrificial void-filler for defining interstices in the recess structures - i.e. what is to become the voids of the recess structures - are formed before the provision of the recess structures. This sacrificial void-filler thus serves to form the recess structures when further layers are deposited thereon. In these embodiments using a sacrificial void-filler in the voids of the recess structures, the sacrificial void-filler will be enclosed between the central and outer layers so that cutting the sides of the component after adhering (but before debinding) will be required to remove the sacrificial void-filler. The expression sacrificial filler material is used in both procedures as the result - voids or interstices of the recess structures being filled with sacrificial material - is the same.

[0055] In one or more embodiments, the multi-transport component is symmetric around the central layer in terms of the basic functionalities: the central layer being impermeable and electrically conducting and the outer layers being permeable and electrically conducting. However, particular material parameters and dimensions (for example porosity of outer layers and size of flow fields) of the multi-transport component may be either symmetric or asymmetric around the central layer.

[0056] In the field of electrochemical stacks, a Standard (or Single) Repeating Unit is one unit that is repeated in a stack of units. In conventional stack design and nomenclature, an SRU contains all the parts required to make a fully functional electrochemical cell. The component according to the disclosure is part of two neighbouring SRUs.

[0057] In the field of electrochemical stacks BPP (bipolar plate), flow field, and PTL (porous transport layer) are common terms designating separate parts in conventional stack design and nomenclature. In the component according to the disclosure, the ‘BPP’, ‘flow field’, and ‘PTL’ are not used to refer to individual parts, but to refer to nondistinctive or overlapping portions of the component having the functionalities commonly associated with these terms, with these portions are comprised within a single monolithic component.

[0058] The terms BPP / flow field / PTL ‘precursors’ are used to refer to portions of the multi-transport component during manufacturing before they can provide these functionalities, such as at the time of assembly or adhering of green layers. It is an advantageous difference to prior art electrochemical stack components, that all portions that will later provide the BPP / flow field / PTL functionalities are put together before they are monolithically connected (such as before adhering, debinding, and sintering). The precursors will become the portions providing the BPP, flow field and PTL functionalities through the process of being monolithically connected (such as adhering, debinding, and) sintering). That the central layer, the recess structures, and the outer layers are adhered together mean that they are assembled, laminated, densified, or compacted in a way that forms a single, such as a connected, multilayer green body. Common adhering techniques include applying an isostatic pressure (hot isostatic pressing (HIP) or cold isostatic pressing (CIP)) on the assembled green layers, rolling the layers together (dynamic pressure application) or using solvents or heat to melt together their contact surfaces.

[0059] After adhesion, any sacrificial void-filler in the voids of the recess structures is preferably removed prior to sintering.

[0060] The final, such as after-sintering, properties of the different portions of the stack component are at least in part determined by parameters of the green layers used in the precursors, such as particle size distribution of metallic powder, solid loading (i.e. volume ratio between the metallic powder and the total volume of the metallic powder and binder / additives mixture) and pore-forming agent type and content. The final, such as after-sintering, properties of the different portions are also at least in part determined by parameters of the manufacturing process, such as temperature and duration of the different heating steps of the manufacturing. For example, general relations may be that the higher the temperature, the higher the density of the final structure, and the longer the duration, the higher the densification of the final structure. For example, since some parts are desired to be dense and some others are desired to be porous with different porosities, once the temperature and duration are set to achieve desired densification of a layer, it is possible to experiment with the other parameters to obtain the desired final morphology. In the following, more details are provided for selected parameters of the green layers used in the precursors.

[0061] The particle size distribution in the green layers can impact the final properties, but particle size ranges are notoriously difficult to define. In general, the relative ratio between different particles with different sizes affects the final density of the piece. Here, density is the fraction of filled volume in the cross section of a material. With a very uniform distribution and small particles (below 10 microns) the necking process proceeds very uniformly, and the structure is almost 100% dense. With a non-uniform particle size distribution, the relative ratio between small and large particles determines the final structure. In the small ones are enough in volume to occupy all the spaces during the necking process, the structure will be dense, porous otherwise. Here, the necking process is the process where adjacent particles get in contact with each other and their surfaces fuse together as a result of the surface energy reduction potential, driven by temperature. Particle size distribution will typically be measured by laser diffraction techniques. The density during and after manufacturing can be determined with image acquisition tools like scanning electron microscopy, optical microscopy, x-ray computer tomography (3D), and evaluated with image processing techniques.

[0062] The pore forming agent in the green layers can impact the final properties. The pore forming agent functions as a volume void precursor and / or porosity enhancer. It typically comprises hydrocarbon derived materials comprising acrylic, polystyrene (PS), polycarbonate (PC), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polypropylene (PP), epoxy resins, starch, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polymethyl-methacrylate (PMMA), polycaprolactone (PCL), polylactic acid (PLA), wax, carbon or their combinations that is mixed with the powder in the first place. Its function is to occupy a fixed volume portion during the initial forming process (tapecasting, pressing, calendaring), and burn or evaporate away before the sintering (necking) starts. Salts can also be used for the same function, with their extraction leveraging dissolution in a solvent before or after the sintering process. It is a method to influence the microstructural morphology of the component right before sintering. Its content is typically measured in volume ratio with respect to the sintering powder, ranging from 0 - 70 vol%. In one or more preferred embodiments, a content of pore forming agent in the precursors is in the interval 0.01 vol% to 5 vol%. In one or more preferred embodiments, a content of pore forming agent in the precursors is in the interval 5.01 vol% to 45 vol%, such as 20-40 vol%. In one or more preferred embodiments, a content of pore forming agent in the precursors is in the interval 45.01 vol% to 75 vol%.

[0063] Solid loading is the volume ratio of powder (inorganic compounds) with respect to the total volume of powder and binder (poreformer considered coherently). Poreformer can be considered part of the inorganic powder compound or not, see e.g. Mistier and Twiname below. Solid loading is relevant when the forming process involves the shaping of a green matrix or layer, i.e. the use of a mixture of powder and binder, shaped with calendaring, tape casting, or additive manufacturing techniques such as binder 3D printing, electrospinning, screen printing, etc. For these processes, the solid loading is low, such as preferably below 50% The solid loading depends on the density of the powder, particle size and its dispersion and is thus determined by the formulation of the green matrix and not measured after manufacturing. It mainly affects the quality of the forming process with secondary impact on the shrinkage of the sintered piece. Its impact is similar to the one of the poreformer, having influence on the microstructure of the component prior to sintering. Lower solid loading will produce a more porous structure with respect to higher solid loading that will promote a denser structure. Typical values of solid loading are 5-40% for tapecasting and most additive manufacturing processes, and 20-70% for screen printing.

[0064] Manufacturing techniques and further technical terms related thereto are considered known to persons skilled in the art of metal powder processing and powder metallurgy. Some helpful textbook references are included here for completeness:

[0065] Alpien, D., 2001. Particulate processing (powder metallurgy). In: Buschow, K.H., Cahn, R.W., Flemings, M.C., llschner, B. (Eds.), Encyclopaedia of Materials — Science and Technology. Elsevier, New York, NY, pp. 6769-6776.

[0066] German, R.M., 1984. Powder Metallurgy Science. Metal Powder Industries Federation, Princeton, NJ.

[0067] German, R.M., 1996. Sintering Theory and Practice. Wiley Interscience, New York, NY.

[0068] Klar, E. (Ed.), 1984. Metals Handbook, Vol. 7: Powder Metallurgy, ninth ed. ASM International, Materials Park, OH. Powder Processes Chapter | 5409

[0069] Lenel, F.V., 1980. Powder Metallurgy: Principles and Applications. Metal Powder Industries Federation, Princeton, NJ

[0070] (book chapter) Handling And Green Forming Of Fine Powders, D. E. Niesz, L. G. McCoy and R. R. Wills Battelle Columbus Laboratories 505 King Avenue, Columbus, Ohio - 1978

[0071] Tape Casting Theory and Practice, Richard E. Mistier and Eric R. Twiname. Published by The American Ceramic Society, 735 Ceramic Place, Westerville, OH - 2000

[0072] Figs. 4 and 5 illustrate two exemplary multi-transport components 20 and 30. The component comprises three main structural electrically conductive metallic portions:

[0073] A dense inner or central layer 22 designed to prevent the passage of gases and liquids, ensuring a sealed environment within each cell, i.e. a fluid ically impermeable electrically conductive layer.

[0074] Porous outer layers 28 and 29 to each side 43 and 44 of the central layer 22. designed to allow gas and liquid to permeate while providing high electronic contact points per surface unit, i.e. fluidically permeable electrically conductive layers.

[0075] Recess structures 24, 25 formed between the inner layer 22 and outer layers 28 and 29, being electrically conducting and defining flow fields 26, 27 between and parallel to the central layer 22 and the outer layers 28, 29. Recess structures 24 and flow fields 26 are formed between the inner layer 22 and outer layer 28 and recess structures 25 and flow fields 27 are formed between the inner layer 22 and outer layer 29. The flow fields 26, 27b facilitates transverse flow of liquids and gases through the component. Recess structures 24, 25 may have, but do not need, high electronic contact per surface area. Thus, recess structures 24, 25 can be dense like the central layer as shown for component 20 in Fig. 4, or porous like the outer layers 28, 29 as shown for component 30 in Fig. 5. The recess structures may also have a density or porosity different from the central and outer layers.

[0076] The flow field formed by the recess structures and the adjacent central and outer layers serve to lead gas and liquid reagents and products into and out of the multi-transport component, such as electrochemical cells comprising the component. The recess structures may comprise one or more of ribs, pillars, columns, barriers, curved ribs or walls, dividers, etc. The function of the recess structures is to form voids for liquid / gas transport, such as in transverse directions, between the central and outer layers. Depending on the specific shapes of the recess structures, the defined voids providing the flow field may be channels, grids of channels. In general, the dimensions of the channels and, hence, of the ribs are determined by the desired liquid flow resistance, stack thermal management, and thickness of the ‘multi-species layers.’ As an example, to minimize mass-transport losses, the ratio between the thickness of the multi-species layer and the width of the channels could be around 0.5. Typical values of ribs height can be in the order of 0.2 - 2 mm. Typical values of ribs width can vary between 0.2 - 20 mm. The ribs-to-channel width ratio is purely dependent on the flow channel geometry of choice.

[0077] In one or more embodiments, the multi-transport component can be constructed using at least three green layers, such as four or five distinct layers, each characterized by unique physical properties such as binder-to-powder volume ratio, pore-former content, and particle size distribution. Since all the layers are in a green state and will be sintered together, they can be assembled in various configurations using different adhesion and assembly techniques.

[0078] The assembly of the green layers and their adhesion can be carried out in a single step or in multiple sequential steps. However, it is essential that the sintering step is always a single event that causes a uniform change in the density of the entire component and forms monolithic connections between all abutting, parts, structures, or layers in the component.

[0079] The green layers can be produced using a variety of manufacturing methods, such as:

[0080] • Tape Casting

[0081] • Calendaring

[0082] • Screen printing • Extrusion

[0083] • Additive Binder-Based Techniques;

[0084] • Any other binder-based techniques (electrospinning etc)

[0085] These methods can also be combined or integrated with intermediate shaping steps to achieve the desired structure.

[0086] Additionally, the structure can be produced using metal powder bed 3D printing, a technique that does not involve binders or green layers. In this method, microscopic layers of powder are sintered together through precise heating. However, this approach is less scalable compared to green layer methods like tape casting.

[0087] The following presents exemplary embodiments using different green layer assembly methods and descriptions of how each layer can be produced.

[0088] Figure 6 illustrates an exemplary embodiment where three green layers are assembled. In this exemplary embodiment utilizes the minimum number of layers required for the component. Two green outer layers A and C provide a gas / liq uid permeability and high electronic contact points per surface unit, while a third, green central layer B serves a dual purpose, functioning as both a gas / liquid impermeable layer and having recess structures to allow a controller liquid flow.

[0089] The gas / liquid permeable layers with high electronic contact points can be produced using techniques such as:

[0090] • Tape Casting

[0091] • Calendaring

[0092] • Screen Printing

[0093] • Spray Coating

[0094] • Binder Jetting

[0095] • Electrospinning.

[0096] These methods allow for the deposition of a green layer composed of binder and metal powder. The desired porosity can be achieved without the mandatory use of pore-formers, as it can also be controlled by parameters such as the binder-to-powder volume ratio, powder particle size distribution, sintering temperature, time, and atmosphere. Herein, the porosity is defined as the fraction of void in the cross section of a material, i.e. opposite to density. Like density, the porosity can be determined during and after manufacturing with image acquisition tools like scanning electron microscopy, optical microscopy, x-ray computer tomography (3D), and evaluated with image processing techniques.

[0097] The central green layer B, which serves both as the gas / liquid impermeable layer and facilitates high liquid / gas flow, can be produced through two subsequent shaping processes such as tape casting or calendaring, followed by forming or pressing to produce the recess structure of both sides (sides 43 and 44 in Fig 4) of the layer. This layer consists of a binder / powder mixture with physical characteristics (such as particle size distribution and binder-to-powder content) that will create a dense, impermeable microstructure when sintered under the same parameters used for the adjacent porous outer layers A and C.

[0098] The outer green layers A and B, which serve as the gas / liquid permeable layers and thus provide PTL functionality, can be produced by tape casting, calendaring, or additive manufacturing techniques comprising 3D printing, electrospinning, screen printing, and binder jetting followed by adhering in a pressing step. These layers comprise a binder / powder mixture with physical characteristics (such as particle size distribution and binder-to-powder content) that will create a porous, permeable microstructure when sintered under the same parameters used for the adjacent dense central layer B.

[0099] The order of assembly (adhering) can vary and is flexible (e.g., bottom to top, center to sides, or top to bottom). The layers can be adhered in sequential steps or in a single step. Sacrificial materials may be used in the voids between the recess structures and protect the shape during the adhesion process, depending on the chosen method and the acceptable degree of deformation during the process. The green body is finally fired. Sacrificial material can be present or not at the moment of firing. After firing, central green layer B will provide the fluidically impermeable and electrically conductive central layer of the component according to the disclosure, as well as the electrically conductive recess structures defining the flow fields. After firing, the outer green layers A and C will provide the fluidically permeable and electrically conductive outer layers of the component according to the disclosure,

[0100] Figure 7 illustrates an exemplary embodiment where five green layers are assembled. In this process, each layer is produced separately and then assembled before undergoing the adhesion process, which can be completed either in one or multiple steps. The physical properties of the green layer will be consistent with those described in the previous example, where outer green layers A and C serve as gas / liquid-permeable layers with high electronic contact per surface area, and central green layer B functions as a gas / liquid-impermeable barrier. Intermediate, structured green layers D and E can have identical or different physical characteristics in terms of porosity that range from those of the porous layers A and C to the dense layer B or anywhere in between, as well as different rib to channel width ratio, height and channel geometry.

[0101] For layers A, B and C, various production methods such as tape casting, calendaring, screen printing, spraying, spin coating, extrusion or their combinations can be used. In one or more embodiments, tape casting is the preferred method. Intermediate structured green layers D and E can be produced using different approaches, including:

[0102] • Selective casting: Tape casting or screen printing on top of sacrificial void-filling material imposing the voids of the recess structures.

[0103] • Material Removal Techniques: Starting with a precursor green layer without indents, which is then shaped using laser cutting, mechanical tools, blades, or other material removal methods.

[0104] • Material Addition Techniques: Methods like 3D printing or extrusion.

[0105] This approach allows flexibility in how the different layers are created, depending on the specific characteristics required for each one. The order of assembly (adhering) can vary and is flexible (e.g., bottom to top, center to sides, or top to bottom). The layers can be adhered in sequential steps or in a single step. Sacrificial materials may be used to fill the voids between the recess structures in layers D and E and protect the shape during the adhesion process, depending on the chosen method and the acceptable degree of deformation during the process. The green body is finally fired. Sacrificial material can be present or not at the moment of firing.

[0106] One or more exemplary embodiments of the method of manufacturing according to the disclosure can use a combination of the methods described in relation to Figs. 6 and 7. For instance:

[0107] Exemplary embodiment 1 :

[0108] • Tape casting layer A.

[0109] • Producing layers D and B from the same green layer, through plastic deformation of a green tape or green body via pressing.

[0110] • Tape casting layer C.

[0111] • Applying layer E through nozzle extrusion, either on top of layer C or on the flat section of the green layer combining layers D and B.

[0112] Exemplary embodiment 2: • Tape casting a green layer and using material removal techniques to create an indented surface on one side, to form layers D and B.

[0113] • Laser cutting a green layer to form layer E (cut through), then applying it to the flat part of the previously formed layer.

[0114] • Tape casting layers A and C, then applying them to the opposite sides of the previously formed layer.

[0115] Exemplary embodiment 3:

[0116] • Tape casting a green layer and using material removal techniques to create an indented surface on one side, to form layers D and B.

[0117] • Laser cutting a green layer to form layer E, then applying it to the flat surface of the previously formed layer.

[0118] • Filling the voids between the recessed structures (flow field precursors) with sacrificial void-filler to create a smooth surface.

[0119] • Finally, applying layers A and C produced separately and adhered subsequently or directly applied by tape casting, spraying, or screen printing onto the opposite sides of the previously formed layer.

[0120] Exemplary embodiment 4:

[0121] • Produce a green layer through tape casting, calendaring, or additive manufacturing, having the function of layers D and B, or B and E.

[0122] • Laser cutting a green layer to form layer E or D (cut through), then applying it to the flat part of the previously formed layer.

[0123] • Tape casting layers A and C, then applying them to the opposite sides of the previously formed layer.

[0124] For all the above exemplary embodiments 1-4, the order of assembly in green state (adhering) can vary. The layers can be adhered in sequential steps or in a single step. Sacrificial materials may be filling the voids between the recess structures and protect the shape during the adhesion process, depending on the chosen method and the acceptable degree of deformation during the process. The green body is finally fired. Sacrificial material can be present or not at the moment of firing.

[0125] In one or more exemplary embodiments of the method of manufacturing according to the disclosure, the whole multi-transport component can be produced by additive manufacturing techniques using a nozzle such as binder jet 3-d printing of green layers where the final microstructure diversity (permeability I impermeability and porosity grade) is determined by the physical characteristics of the binder / powder mixture deposited by the nozzle. Starting from the bottom, the nozzle can first deposit an outer green layer precursor of the gas / liqu id permeable and high electronic contacting point per surface unit layer. Subsequently the nozzle deposits the recess structures (e.g. ribs). The application of sacrificial material in the voids between the recess structures (binder only or in mixtures with graphite or acrylic powder, that would burn during the sintering, or hydrocarbon mixtures that can be liquified below the binder burning point) can simplify the application of the next layer, if required by the additive manufacturing process chosen. After the nozzle applies the impermeable layer, then the layer of recess structures and the second outer green layer can be applied.

[0126] This additive manufacturing of individual layers can be combined with any of the green layer manufacturing methods discussed in the above in relation to Figs. 6 and 7 as well as exemplary embodiments 1-4.

[0127] In one or more embodiments, formation of the recess structures can be complemented by filling the voids between the recessed structures (flow field precursors) with a sacrificial voidfiller to a) protect the shape during the adhesion process, and to b) create a smooth surface on which to form succeeding layers. As described previously, in exemplary embodiments the sacrificial void-filler can be applied to the interstices or voids in the recess structure after provision of the recess structures, or the sacrificial void-filler is deposited in the shape of the interstices or voids so that adding material thereon will result in the recess structures. Since there is a risk that such sacrificial void-fillers may damage the component during the firing process of the sintering, it may be advantageous to remove it prior thereto. In one or more embodiments, a sacrificial void-filler is applied to the voids between the recessed structures in accordance with the method described in EP appl. No. 23193476.1.

[0128] In all the above approaches, the parameters of the different green layers determine the material properties of the central layer, outer layers, and recess structures in the final component. As the skilled person will be aware, there are a very broad range of green layer parameters that can be applied in different combinations to achieve the characteristics of fluidically impermeable and permeable layers, while respecting the criteria of electrical conductivity and formations of monolithic connections between layers during sintering. Some green layer parameters used to achieve these material characteristics include:

[0129] • Particle size distribution of the metal powder - such as measured by laser diffraction techniques - can range from 100 nm (nanometres) to 400 pm (micrometres).

[0130] • Binder-to-metal powder volume ratio can vary between 10% and 90%, depending on the fabrication technique.

[0131] • Sintering temperature can range from 850°C up to the melting point of the metal (>1650 Celsius degrees). Sintering time and heating rate are variable and cannot be confined to a specific range.

[0132] In one or more embodiments, the selection of the one or more powder based green layers forming the central layer comprises selecting values of at least one of the following parameters to make the sintered central layer fluidically impermeable and electrically conductive: particle size distribution of metallic powder, solids loading, and pore-forming agent.

[0133] In one or more embodiments, the one or more powder based green layers forming the central layer have: a particle size distribution of metallic powder in the interval 0.1 micrometres - 100 micrometres as measured by laser diffraction techniques. solids loading in the interval 5 - 90 vol%; and / or 5 - 30 vol%; and or 20 - 40 vol%; and or 30 - 60 vol%; and / or >60%. a pore forming agent selected from the group consisting of: hydrocarbon derived materials comprising acrylic, starch or similar, wax, salts, carbon and / or any combination of these, with a volume content with respect to the metallic powder below 38 vol%, such as in the interval 1-5%, 5-10%, 10-25%.

[0134] In one or more embodiments, the selection of the powder based green layers forming the outer layers comprises selecting values of at least one of the following parameters to make the sintered outer layers fluidically permeable and electrically conductive: particle size distribution of metallic powder, solids loading, and pore-forming agent. In comparison to the of the powder based green layer(s) forming the central layer, the changes are typically in particle size distribution and poreformer content. The solid loading is determined by the formulation of the green matrix and will typically depend on the production method used.

[0135] In one or more embodiments, powder based green layers forming the outer layers have: a particle size distribution of metallic powder, such as measured by laser diffraction techniques, in the interval 0.1 micrometres - 100 micrometres; solid loading in the interval 5 - 90 vol%; and / or 5 - 30 vol%; and or 20 - 40 vol%; and or 30 - 60 vol%; and / or >60% as determined by the formulation of the green layers in terms of its volume ratio of inorganic powder (typically metals) with respect to the total volume of powder and binder; a pore forming agent selected from the group consisting of: hydrocarbon derived materials comprising acrylic, starch or similar, wax, salts, carbon, and / or any combination of these, with a volume content with respect to the metallic powder above 15 vol%.

[0136] Fig. 8 illustrates an exemplary embodiment of a multi-transport component 20 where the porous outer layers 28 and 29 have a porosity that varies as a function of vertical or longitudinal direction through the component. Such porosity variations are also referred to as porosity or pore-size gradients and are the derivative of the porosity alongside a cross section and shows how fast or mildly the porosity changes across the section of the sample. The porosity or pore-size gradient can be computed with numerical analysis tools starting from porosity or density measurements. Porous outer layers with porosity gradients may be manufactured by multiple green outer layers with different porosities.

[0137] Porosity gradients are necessary for pressurized stack operation. The desired feature of the PTL of having high electronic contact surface, often translates to liquid mass transport limitations that impose very thin components. With reduced thickness, the mechanical stability of the PTL is also compromised, especially during pressurized stack operation. For this reason, a “second PTL” with much smaller contact area (that does not matter because not in contact with the electrode) but more open porosity, can be applied conferring low liquid mass transport resistance with an increased thickness to withstand mechanical stresses. The distinction between the thin and fine porous PTL and the thick and open porosity PTL can be visible or not, in that latter case it is possible to observe the “porosity gradient”.

[0138] Before the sintering step, the density of the component after the final adhering step will fall between the density of the binder (typically ranging from 0.9 g / cm3to 2 g / cm3) and the density of the metal powder (about 4.5 g / cm3 for Ti, up to 8 g / cm3 for stainless steel, about 8.9 g / cm3 for Ni, up to 22 g / cm3 for platinum), depending on their volume ratio. After sintering, the component will reach the density of the metal used (excluding the porosity and cavities). In one or more embodiments, disregarding void between the recess structures and porosity in the component, a density of the component is: a density between 0.8 - 3 g / cm3prior and after the adhering process, prior to sintering a density of 4-5 g / cm3(Titanium) after the adhering process and debinding process (burn out / extraction of the organics and void precursors, preceding the start of sintering) a density of 4-5 g / cm3(Titanium) after sintering. Densities and porosities can be determined with image acquisition tools like scanning electron microscopy, optical microscopy, x-ray computer tomography (3D), and evaluated with image processing techniques.

[0139] Regardless of how the individual layers are formed or assembled, the component manufactured in accordance with the disclosure will exhibit consistent density both before and after sintering, as a consequence of the single firing step. After its shaping in green state, the whole structure goes through the firing process at the same time, meaning organics I precursors I sacrificial materials of the same type leaving the structure at the same time, conferring to the component a continuous density change behaviour when transitioning between green state to sintered piece.

[0140] The disclosure provides a monolithic bipolar multi-transport stack component for an electrochemical stack formed using the method of manufacturing according to the disclosure.

[0141] Figs. 9A-C are different illustration of a monolithic bipolar multi-transport stack component according to an embodiment of the disclosure.

[0142] As illustrated in Fig. 8, the disclosure provides an electrochemical cell assembly 40 comprising at least two monolithic bipolar multi-transport stack components according to the disclosure alternatingly stacked with at least two layers 42 comprising ion-exchange membranes, so that two adjacent components 20 sandwich one ion-exchange membrane.

[0143] As illustrated in Fig. 8, the disclosure provides an electrochemical stack 41 comprising a plurality of monolithic bipolar multi-transport stack components 20 (or 30). In the stack, the components are separated by one or more layers 42 each comprising an ion-exchange membrane and typically comprising an anode catalyst and / or a cathode catalyst. The layer 42 and the opposing halves of the two adjacent multi-transport components 20 form an electrochemical cell. In other words, the opposing sides (anode-side 43 and cathode-side 44) of two adjacent multi-transport components 20 provide parts of different half-cells of an electrochemical cell. In other words, an electrochemical cell stack 41 comprises a plurality of stacked electrochemical cell assemblies 40 according to the disclosure is provided.

[0144] It should be noted that any reference signs do not limit the scope of the claims and that several "means", "units" or "devices" may be represented by the same item. The various exemplary uses, methods, components, and assemblies described herein are described in the general context of method steps or processes, which may be implemented in an automized or a manual process. The particular sequence of use or method steps represents examples of corresponding acts for implementing the functions described in such steps or processes and the order of some steps may be changed.

[0145] Although features have been shown and described, it will be understood that they are not intended to limit the claimed disclosure, and it will be made obvious to those skilled in the art that various changes and modifications may be made without departing from the scope of the claimed disclosure. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense.

Claims

CLAIMS1 . A method for manufacturing a monolithic bipolar multi-transport stack component for an electrochemical stack, the method comprising:- providing a central layer comprising one or more metallic powder based green layers formed by a layer-forming process, the central layer having an anode-side and a cathode-side;- providing outer layers at the anode side and on the cathode-side of the central layer, each outer layer comprising one or more metallic powder based green layers formed by a layer-forming process;- providing recess structures between the central layer and each outer layer; wherein the recess structures are formed by one or more metallic powder based green layers;- adhering the central layer, the recess structures, and the outer layers together before sintering; and- sintering the central layer, the recess structures, and the outer layers in a single sintering step to form a monolithically connected component wherein the central layer is fluid ically impermeable and electrically conductive, the outer layers are fluid ically permeable and electrically conducting, and the recess structures are electrically conductive and define flow fields between and parallel to the central layer and the outer layers; wherein the one or more powder based green layers forming the central layer are selected to produce a fluid ically impermeable and electrically conductive central layer of the component; wherein the one or more powder based green layers forming each outer layer are selected to form electrically conducting and fluidically permeable outer layers of the component; and wherein the one or more powder based green layers forming the recess structure are selected to produce electrically conductive recess structures between the central layer and the out layers of the component.

2. The method according to claim 1 , wherein the layer-forming processes comprises tape casting, calendaring, and / or additive manufacturing techniques comprising binder jetting, electrospinning, screen printing, and 3D printing.

3. The method according to claim 1 or 2, wherein the recess structures are formed at the central layer or at the sides of the outer layers facing the central layer by:- stamping or subtractive material processing in the central layer or in the sides of the outer layers facing the central layer; or- a layer-forming process on the central layer or on the sides of the outer layers facing the central layer.

264. The method according to any of the preceding claims, wherein the one or more powder based green layers forming the recess structure are selected to produce recess structures that are fluidically permeable.

5. The method according to any of claims 1-3, wherein the one or more powder based green layers forming the recess structure are selected to produce recess structures that are fluidically impermeable.

6. The method according to any of the preceding claims, wherein the selection of the one or more powder based green layers forming the central layer comprises selecting values of at least one of the following parameters to make the sintered central layer fluidically impermeable and electrically conductive: particle size distribution of metallic powder, solid loading, and pore-forming agent type and content.

7. The method according to any of the preceding claims, wherein the selected one or more powder based green layers forming the central layer have: a particle size distribution of metallic powder in the interval 0.1 micrometres - 100 micrometres measured by laser diffraction techniques; solid loading in the interval 5 - 90 vol%; and / or 5 - 30 vol%; and or 20 - 40 vol%; and or 30 - 60 vol%; and / or >60% as determined by the formulation of the green layers in terms of its volume ratio of inorganic powder with respect to the total volume of powder and binder; and a pore forming agent selected from the group consisting of: hydrocarbon derived materials comprising acrylic, starch, wax, salts, carbon, and / or any combination of these, with a volume content with respect to the metallic powder below 38 vol%.

8. The method according to any of the preceding claims, wherein the selection of the powder based green layers forming the outer layers comprises selecting values of at least one of the following parameters to make the sintered outer layers fluidically permeable and electrically conductive: particle size distribution of metallic powder, solid loading, and pore-forming agent type and content.

9. The method according to any of the preceding claims, wherein the selected powder based green layers forming the outer layers have: a particle size distribution of metallic powder in the interval 0.1 micrometres - 100 micrometres measured by laser diffraction techniques;solid loading in the interval 5 - 90 vol%; and / or 5 - 30 vol%; and or 20 - 40 vol%; and or 30 - 60 vol%; and / or >60% as determined by the formulation of the green layers in terms of its volume ratio of inorganic powder with respect to the total volume of powder and binder; and a pore forming agent selected from the group consisting of: hydrocarbon derived materials comprising acrylic, starch, wax, salts, carbon, and / or any combination of these, with a volume content with respect to the metallic powder above 15 vol%.

10. The method according to any of the preceding claims, wherein, disregarding void space and porosity in the component, the component has: a density between 0.8 - 3 g / cm3prior and after the adhering process, prior to sintering; a Titanium density of 4-5 g / cm3after the adhering process and debinding process and preceding the start of sintering; and a Titanium density of 4-5 g / cm3after sintering; where the density can be determined with image acquisition tools comprising scanning electron microscopy, optical microscopy, x-ray computer tomography.

11. A monolithic bipolar multi-transport stack component for an electrochemical stack manufactured using the method according to any of claims 1-10.

12. A monolithic bipolar multi-transport stack component for an electrochemical stack, comprising:- a fluidically impermeable and electrically conductive central layer having an anode-side and a cathode-side;- recess structures provided on the anode side and on the cathode-side of the central layer; and- electrically conductive and fluidically permeable outer layers provided on the recess structures on the anode-side and the cathode-side of the central layer; wherein the recess structures form flow fields between and parallel to the central layer and the outer layers; and wherein the central layer, the recess structures, and the outer layers have been: formed by layer-forming processes; adhered together before sintering; and sintered in a single sintering process,whereby the recess structures are monolithically connected with the central layer and with the outer layers.

13. The monolithic bipolar multi-transport stack component according to claim 12, wherein the component has a decreasing porosity gradient in a direction away from the central layer, the pore size gradient being computed from porosity or density determined by image acquisition tools comprising scanning electron microscopy, optical microscopy, and x-ray computer tomography.

14. The monolithic bipolar multi-transport stack component according to any of claims 12-13, wherein the recess structures have a larger porosity than the central layer, the porosity being determined by image acquisition tools comprising scanning electron microscopy, optical microscopy, and x-ray computer tomography.

15. The monolithic bipolar multi-transport stack component according to any of claims 12-14, wherein the recess structures have a smaller porosity than the outer layers, the porosity being determined by image acquisition tools comprising scanning electron microscopy, optical microscopy, and x-ray computer tomography.

16. An electrochemical cell assembly comprising at least two monolithic bipolar multitransport stack components according to any of claims 12-15 alternatingly stacked with at least two ion-exchange membranes.

17. An electrochemical cell stack comprising a plurality of stacked electrochemical cell assemblies according to claim 16.29

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