Electrochemical cell layer with electrical insulation

Abstract

A cell layer for an electrochemical cell unit and a method of manufacturing the same. The cell layer comprising a support structure having first and second sides, the support structure comprising a fluid communication region providing fluidic communication between the sides and a fluid blocking region. The second side of the support structure carrying a first electrode, an electrolyte and a counter-electrode provided and forming an electrochemically active cell region (EACR) over at least a portion of the fluid communication region. The support structure has a greater extent than the EACR thereby forming an electrochemically inactive region (EIR). An electrically insulating layer (EIL) is provided on the second side of the support structure across at least a portion of the EIR and is not provided across the EACR.

Description

[0001] ELECTROCHEMICAL CELL LAYER WITH ELECTRICAL INSULATION

[0002] Field of the Invention

[0003] The present invention relates to a cell layer for use in electrochemical cell units, in particular fuel cell units and electrolyser cell units, electrochemical cell units comprising said cell layer, stacks containing such electrochemical cell units, methods for manufacturing said cell layers, electrochemical cell units, and stacks thereof, and the use of such cell units. The cell units of the present invention include cells of solid oxide, polymer electrolyte membrane. The present invention more specifically relates to solid oxide fuel cell (SOFC) and solid oxide electrolyser cell (SOEC) units, and these may include metal-supported solid oxide fuel cell (MS-SOFC) or electrolyser cell (MS-SOEC) units.

[0004] Background to the Invention

[0005] Some electrochemical cell units can produce electricity by using an electrochemical conversion process that oxidises fuel to produce electricity. Some electrochemical cell units can also, or instead, operate as regenerative fuel cells (or reverse fuel cells) units, often known as electrolyser cell units, for example to produce hydrogen and oxygen from water, or carbon monoxide and oxygen from carbon dioxide. They may be tubular or planar in configuration. Planar electrochemical cell units may be arranged overlying one another in a stack arrangement, for example 100 to 200 or more electrochemical cell units in a stack, with the individual electrochemical cell units arranged, for example, electrically in series. For convenience, "cell units" is used to refer to "electrochemical cell units" including fuel or electrolyser cell units.

[0006] A solid oxide fuel cell (SOFC) that produces electricity is based upon a solid oxide electrolyte that conducts negative oxygen ions from a cathode to an anode located on opposite sides of the electrolyte. For this, a fuel, or reformed fuel, contacts the anode (fuel electrode) and an oxidant, such as air or an oxygen rich fluid, contacts the cathode (oxygen electrode). Conventional ceramic-supported (e.g. anode-supported) SOFCs have low mechanical strength and are vulnerable to fracture. Hence, metal-supported SOFCs have been developed which have the active fuel cell component layer supported on a metal substrate. In these cells, the ceramic layers can be very thin since they only perform an electrochemical function: that is to say, the ceramic layers are not self-supporting but rather are thin coatings / films laid down on and supported by the metal substrate. Such metal supported SOFC stacks are more robust, lower-cost, have better thermal properties than ceramic-supported SOFCs, and can be manufactured using conventional metal welding techniques.

[0007] A solid oxide electrolyser cell (SOEC) may have a similar structure to an SOFC but operating to achieve the electrolysis fuel. For example, electrolysis of water by input of electrical energy and using the solid oxide electrolyte (or other electrolytes as listed above) to produce hydrogen gas and oxygen.

[0008] Each cell unit in a stack of cell units typically includes a cell layer comprising an electrochemically active cell region (EACR) and an interconnect. An interconnect typically contacts one side of the cell layer of a cell unit and, in a stack of cell units, and may also contact an opposite side of a cell layer of an adjacent cell unit. Some interconnects are also configured to separate fluid volumes disposed to opposite sides of said interconnect (e.g. a fuel volume and an oxidant volume).Figure 1 shows an exploded perspective view of a cell unit taken from GB 2603665 A, which discusses an electrochemical cell unit and a stack comprising a plurality of such electrochemical cell units. The cell unit 10 of Figure 1 comprises a flat (i.e. planar) metal support plate 14 and an interconnect 12. The interconnect 12 is shown to have flanged perimeter 18 around its perimeter. The flanged perimeter 18 extends out of the predominant plane of the sheet, as found at a central fluid volume area, to create a concavity in the interconnect (and a convexity to the outside surface). The concavity forms a fluid volume within cell unit. The cell unit 10 has a fluid port 22 towards each end in both the interconnect 12 and the metal support plate 14. Around the fluid ports of the interconnect 12, shaped port features 24 are provided. The shaped port features 24 are provided as multiple elements in the form of dimples extending out of the plane of the interconnect a distance corresponding to that of the height of the flanged perimeter 18 - to have a common height therewith. This is so that they will mechanically contact the opposing surface of the metal support plate 14, just like the flanged perimeter 18, when the cell unit 10 is assembled. As a result, when the flanged perimeter 18 is joined to the metal support plate 14, for example by welding, the shaped port features 24 will likewise contact the metal support plate 14.

[0009] In a central portion of the cell unit 10, an electrochemically active area 50 is provided on the metal support plate. In this example it is located outside of the enclosed fluid volume. The electrochemically active area 50 includes an fuel electrode, an oxygen electrode, and an electrolyte positioned between the fuel electrode and oxygen electrode (not explicitly shown). The fuel electrode, oxygen electrode and electrolyte may together be referred to as the electrochemically active layer 50, active electrochemical cell layer, or electrochemically active cell region. The electrolyte conducts either oxygen ions between the fuel electrode and the oxygen electrode. A stack may comprise a plurality of cell units positioned one atop another.

[0010] Figure 2 shows an exploded perspective underside view of the cell unit of Figure 1. The metal support plate 14 is provided with multiple small holes or pores 48 to enable fluid communication between the (enclosed) fluid volume and the electrode (of the electrochemical layers) that is closest to the metal support plate 14. These form a porous region bounded by a non-porous region. The fuel electrode layer is located adjacent the small holes / pores with the (enclosed) fluid volume within the cell unit comprising a fuel flow volume supplied by fuel entering and exiting via the fluid ports 22, which are thus fuel ports 22. The oxygen electrode layer is on the opposite side of electrochemically active layer 50, i.e. on its outer face. Figure 2a shows a simplified cross-section of the arrangement shown in Figures 1 and 2.

[0011] The interconnect has a first side 13a and a second side 13b. The interconnect may be provided with central area having upward protrusions 32 and downward protrusions 36, extending between the internal opposed surfaces of the two plates and an outer surface of the electrochemically active layer of the cell unit adjacent to the outward protrusions. The upward protrusions 32 define fluid pathways between them for fuel, the pathways being through the enclosed fluid volume between fluid ports at opposed ends of the cell unit. The downward protrusions 36 define fluid pathways between them for oxygen through the fluid volume defined between the outer surface of the electrochemically active layer of the cell unit adjacent to the downward protrusions. The upward protrusions 32 are convex on the second side 13b of the interconnect and configured to contact the support plate 14 of the cell layer, to provide mechanical support (i.e., to contact the first side 15a of the cell layer / support plate).The downward protrusions 36 are convex on the first side 13a of the interconnect and configured to contact the second side 15b of the cell layer, specifically to contact the EACR 50 of the cell layer (the cell layer is usually that of a neighboring cell unit), in order to electrically connect the interconnect (via its first side) to the outer layer of the EACR 50).

[0012] Each gasket, for example gasket 34 (also referred to as a "seal"), provides a primary sealing function and will usually be a compressible gasket that is subjected to compressive forces in the vicinity of the ports. These gaskets, each of which typically surrounds a respective fluid port and is thus typically annular in shape, may also provide electrical insulation between a first cell unit 10 and an adjacent cell unit 10. The gaskets may be any suitable material such as, for example, vermiculite-based gaskets. The gaskets 34 may be relatively thick, for example approximately 0.5 mm in thickness. Relatively thick gaskets, along with downward dimples / protrusions 36, are advantageous in spacing apart neighbouring cell units and may be used for fuel cell units in which excess fluid flow is often provided as a coolant in the oxygen volume. However, it is advantageous to reduce the height of the downward dimples 36 (and gasket thickness), to bring the first side 13a of the interconnect and the second side 15b of the cell layer closer together to reduce the size of stacks of cell units, especially electrolyser cell units in which coolant is not required.

[0013] Further, while it is the function of the downward dimples 36 of the interconnect (protrusions on the first side 13a of the interconnect 12) to make electrical contact with the outermost layer of the EACR of the cell layer, no other electrical contact should be made between the first side 13a of the interconnect and the metal support plate. Misalignment between dimples 36 and the EACR, or features elsewhere on the interconnect or cell layer (outside of the EACR) may increase risk of contact between the first side 13a of the interconnect and the cell layer outside of the EACR, which may cause damage and / or a short circuit.

[0014] There is a risk that deformation (e.g. flexing) of the interconnect and / or the cell layer may occur, causing unintended and unwanted contact between the interconnect and the cell layer outside of the EACR. Such contact may result in application of voltage outside of the EACR, which may short circuit the cell and / or apply a voltage across layers outside of the EACR which may cause damage to said layers.

[0015] The present disclosure seeks to address, overcome or mitigate at least one of the prior art disadvantages.

[0016] Summary

[0017] It is herein disclosed, to improve the reliable functioning of an electrochemical cell unit and the corresponding cell stack (for electrolysis or fuel cell operation), the introduction of an insulation means, such as at least one insulating layer, on the cell layer in one or more area(s) that correspond to area(s) that are outside of the active cell area.

[0018] According to an aspect there is provided a cell layer for an electrochemical cell unit. The cell layer may be for use in an electrochemical cell stack. The cell layer comprising:

[0019] a support structure having first and second sides, the support structure comprising a fluid communication region providing fluidic communication between the sides and a fluid blocking region,the second side of the support structure carrying a first electrode, an electrolyte and a counterelectrode provided and forming an electrochemically active cell region (EACR) over at least a portion of the fluid communication region,

[0020] wherein the support structure has a greater extent than the EACR thereby forming an electrochemically inactive region (EIR), and

[0021] wherein an electrically insulating layer (EIL) is provided on the second side of the support structure across at least a portion of the EIR and is not provided across the EACR.

[0022] The EIL prevents cell to cell shorting when the cell layer is used in a stack of electrochemical cell units. As electrochemical cell units increase in size to meet power and fluid production demands, risk of cel I-to-cell shorting due to slight bends of cell layers and cell units increases. The EIL is particularly advantageous for electrolyser cell units wherein the height of oxygen volume may be relatively low (in comparison to fuel cell units), thereby leading to an increased risk of cell-to-cell shorting.

[0023] The EIL may prevent application of voltage difference across electrolyte in regions which are not part of the EACR, e.g., because they are not above the fluid communication region (i.e., may not be substantially supplied with fuel by the fluid communication region). Such conditions can cause damage to the electrolyte, especially over thermal or on / off (load) cycles. It will usually be desirable to avoid cell-to-cell contact outside of the EACR, but such contact is possible, resulting in application of voltage to those areas, due to bending of cell layers and cell units, dimples in neighboring components of a stack which contact the (second side of the) cell layer outside the EACR, and / or support dimples in neighboring components of a stack which contact the (second side of the) cell layer (which may be used to counteract any bending). The EIL is particularly advantageous for electrolyser cell units where electrical current and voltage may be relatively high (in comparison to fuel cell units) in steady state operation. As the EIL may prevent application of voltage difference across electrolyte in regions which are not part of the EACR (and the EIL may extend past the electrolyte, or layers thereof), it will be appreciated that the electrolyte is not the EIL.

[0024] The fluid blocking region blocks fluid communication between sides. The fluid blocking region may bound (or surround) the fluid communication region.

[0025] In some examples, the first electrode, electrolyte and counter-electrode are coated or deposited on the support structure. Alternatively, a laminate formed by the first electrode, electrolyte and counterelectrode may be self-supporting (e.g., electrode or electrolyte supported) and attached to the support structure, in which case the fluid communication region may be a porous region of the support structure or may be a single opening therethrough. The layers of the first electrode, electrolyte, functional layer (where present), and counter-electrode may be deposited sequentially on the support structure by any suitable method. Each of these layers may be comprised of multiple sub-layers (sublayers may have varying compositions).

[0026] The second side of the support structure carries the first electrode, electrolyte and counter-electrode provided and forming the electrochemically active cell region (EACR) over at least a portion of the fluid communication region - in other words, the EACR is the region of the cell layer capable of electrochemical activity, i.e., by being provided with all three of the first electrode, electrolyte and counter-electrode and in fluidic communication with the fluid communication region of the support structure. Preferably, the EACR is provided over the entirety of the fluid communication region. Preferably, the EACR is a region over which each of the first electrode, electrolyte and counterelectrode exist over fluid communication region.The electrochemically inactive region (EIR) may be a region over which one or more of the first electrode, electrolyte and counter-electrode do not extend and / or a region in which there is no supply or exhaust of fluid via the fluid communication region.

[0027] In some examples, the EIL extends over the EIR (i.e., over substantially the entirety of the EIR) and / or extends over the fluid blocking region (i.e., over substantially the entirety of the fluid blocking region), and in doing so may extend over or under one or more of the first electrode, the electrolyte and the counter-electrode. In some examples the extent of the EIL is at least coincident with an extent of the at least one of the first electrode, the electrolyte and the counter-electrode across the fluid blocking region.

[0028] In some examples, the electrically insulating layer (EIL) is coated or deposited. Alternatively, in some examples (where the EIL is not between the support structure and another layer) the EIL may comprise a separate component, for example a vermiculite strip.

[0029] In some examples, the fluid communication region is a porous region of the support structure and the fluid blocking region is a non-porous region of the support structure. The support structure may be a support plate, e.g., a metal support plate, optionally the metal support plate may comprise a steel support plate, optionally a stainless steel support plate. The support plate may also be referred to as a substrate. The porous region of the support structure may comprise drilled holes (optionally laser drilled holes) through the support plate in the porous region. Alternatively, the porous region may comprise an inherently porous substrate / support plate, which may be attached to a peripheral non-porous support.

[0030] Where a support plate is used, the support plate may comprise a metal support plate, optionally the metal support plate may comprise a steel support plate, optionally a stainless steel support plate. The support plate may also be referred to as a substrate. The porous region of the support plate may comprise drilled holes through the support plate in the porous region, optionally may comprise laser drilled holes through the support plate in the porous region. Alternatively, the porous region may comprise an inherently porous substrate / support plate, which may be attached to a peripheral non-porous support. Optionally, the support plate may comprise a barrier layer on at least one surface thereof. The barrier layer may be a layer to prevent / reduce corrosion of the support by oxygen. The support structure may comprise a barrier layer on at least one surface thereof. The barrier layer may be a layer to prevent / reduce corrosion of the support by oxygen.

[0031] The electrolyte may be disposed between the electrodes. The electrolyte may be disposed between the counter-electrode and the support structure. The first electrode may be proximal to and / or may form part of the support structure.

[0032] In some examples, at least one of the first electrode, the electrolyte and the counter-electrode extends past an edge of the fluid communication region and at least partially across the fluid blocking region. Preferably, the electrolyte extends past the edge of the fluid communication region. The EIL prevents application of a voltage difference across a layer which extends past an edge of the fluid communication region and resulting damage to the layer. Further, it prevents electrical shorting, for example where the first electrode extends past the edge of the fluid communication region and is exposed opposing surface (e.g., if it is not covered by the electrolyte).

[0033] In some examples, the EIL contacts the electrolyte.In some examples, the EIL is disposed between the electrolyte and the support structure. In other words, the EIL is beneath the electrolyte. The EIL prevents application of a voltage difference to the parts of the electrolyte under which the EIL extends.

[0034] In some examples, the first electrode is disposed between the EIL and the support structure - at least for some extent of EIL - i.e., the EIL can extend past edge of first electrode. The EIL may extend past a boundary of the first electrode, over the fluid blocking region.

[0035] In some examples, the EIL surrounds (and may abut) the first electrode. The boundaries of the first electrode and EIL may be coincident. This may reduce stresses in the cell layer and improve isolation provided by the EIL. Further, it may simplify manufacturing of the cell layer wherein the first electrode and EIL may be co-sintered and / or the first printed layer (i.e., one of EIL and first electrode) may form a stencil around which to print the second printed layer (i.e., the other one of EIL and first electrode). In some examples, the EIL and the first electrode are disposed on the support structure, and the EIL has substantially the same thickness (e.g., within 15% of each other) as the first electrode. Typically, the electrolyte sits on top of the first electrode and extends past a boundary of the first electrode to seal it. As a result of the substantially the same thicknesses of the EIL and first electrode, there is no significant step in the electrolyte as it sits thereon, thereby reducing stress in the electrolyte and improving quality and reliability of the same.

[0036] In some examples, the electrolyte is disposed between the EIL and the support structure. In other words the EIL is disposed on top of electrolyte. The EIL may extend past a boundary of the electrolyte to cover parts of the fluid blocking region which are not themselves covered by the electrolyte. In such cases, the EIL may not contact the counter-electrode. This may maximise the size of the EACR. Alternatively, the EIL may surround (and may abut) the counter-electrode. The boundaries of the counter-electrode and EIL may be coincident. This may reduce stresses in the cell layer and improve isolation provided by the EIL. Further, it may simplify manufacturing of the cell layer wherein the counter-electrode and EIL may be co-sintered and / or the first printed layer (i.e., one of EIL and counter-electrode) may form a stencil around which to print the second printed layer (i.e., the other one of EIL and counter-electrode).

[0037] In some examples, the EIL may be disposed over the counter-electrode but not over the fluid communication region of the support structure (i.e., part of the counter-electrode disposed between the EIL and the fluid blocking part of the support structure).

[0038] In some examples, the counter-electrode does not overlap the EIL. This reduces cost by not extending the counter-electrode further than necessary.

[0039] In some examples, the counter-electrode is disposed between the EIL and the electrolyte. The counter-electrode may be between EIL and support structure (preferably only the fluid blocking region thereof). In other words, the EIL is disposed on top of the counter-electrode.

[0040] In some examples, the EIL may be disposed on the counter-electrode in some areas, on the electrolyte in others, and on the (fluid blocking region of the) support structure in yet others.

[0041] In examples where the EIL overlaps the electrolyte (or one or more layers thereof), it may contribute mechanical support to the edges of the electrolyte, improving robustness of the cell layer.

[0042] The EIL does not conduct electrons, preferably the EIL also does not conduct ions. In other words it is ionically non-conductive in addition to electrically non-conductive. Thus transport of ions through the EIL is blocked which forces ion transport though the EACR, which in turn may improve the efficiency of the cell layer.In some examples, an or the extent of EIL is at least coincident with an extent of electrolyte across fluid blocking region. In other words, the EIL overlies or underlies the electrolyte across parts of the cell layer where the electrolyte extends across the fluid bocking region. In some examples, the first electrode and / or the counter electrode do (does) not overlie or underlie the EIL.

[0043] In some examples, the EIL begins within 3 mm, optionally within 1 mm, optionally within 0.7 mm, optionally within 0.5 mm of a boundary between the fluid communication region and the fluid blocking region and extends over the at least a portion of the fluid blocking region. This ensures that the EIL prevents application of voltage to the cell layer in regions where there is no substantial communication with the fluid communication region. In some cases, the EIL overlaps the fluid communication region, which ensures robustness. Preferably the EIL begins between boundary of fluid communication region and a location over the fluid blocking region and within 3 mm, optionally within 1 mm, optionally within 0.7 mm, optionally within 0.5 mm of the boundary of the fluid communication region.

[0044] In some examples, the first electrode does not extend past the boundary between fluid communication region and fluid blocking region.

[0045] In some examples, the electrolyte comprises (and may comprise at least one electrolyte layer comprising) ceria, preferably doped ceria. Ce is preferable due to its relatively low operating temperature (e.g., 400-700 °C).

[0046] In some examples, the electrolyte is multi-layered, and comprises a main electrolyte layer and a functional layer. The functional layer may have at least one of the following functions: to block electron transport through the electrolyte, to block transport of chemical species from the first electrode or counter-electrode to the main electrolyte layer, and to provide for interfacial bonding between the main electrolyte layer and the first electrode or the counter-electrode. The functional layer may comprise one or both of a Zr-based layer and / or an Sr-blocking layer. The Sr-blocking layer may block migration of Sr from the counter-electrode, and may comprise doped ceria. The Zr-based layer may block electron transport through the electrolyte. The functional layer may be disposed between the electrolyte and the counter-electrode. Alternatively, the electrolyte is multi-layered, and comprises main electrolyte and a functional layer (e.g., a Zr-based layer) disposed between the electrolyte and the first electrode.

[0047] In some examples, the functional layer is disposed between the EIL and the main electrolyte layer. In other words the EIL is disposed on the functional layer. Alternatively in some examples, the EIL may be disposed between the functional layer and the main electrolyte layer.

[0048] The electrolyte may comprise at least one electrolyte layer comprising rare earth doped ceria. The rare earth doped ceria may comprise ceria doped with at least one rare earth element selected from Y, Sc or a lanthanide (Ln). The rare earth doped ceria may be selected from samarium-doped ceria (SDC), gadolinium-doped ceria (GDC), praseodymium doped ceria (PDC), samaria gadolinia doped ceria (SGDC) and mixtures thereof. Gd and Sm are advantageous and may yield higher ionic conductivities. The dopant concentration in the ceria may be in the range 45 atom % or lower, optionally 40 atom % or lower, optionally 20 atom % or lower. The dopant concentration in the ceria may be 3 atom % or higher, optionally 5 atom % or higher, optionally 10 atom % or higher.

[0049] Thus, the dopant concentration in the ceria may be in the range 3 to 45 atom %, optionally 5 to 40 atom %, optionally 10 to 20 atom %. The electrolyte has a primary purpose of facilitating oxygen ion diffusion from one electrode to another and may advantageously provide a mechanically stable layer having very low or no gas permeability and having ionic resistance that is as low as possible. The advantage of the use of a doped ceria electrolyte includes relatively low temperature operation (butrelatively good ionic conductivity). The electrolyte may have a thickness of 17 pm or lower. Optionally, the electrolyte may have a thickness of 15 pm or lower, optionally 12 pm or lower.

[0050] The electrolyte may have a thickness of 4 pm or greater. Optionally, the electrolyte may have a thickness of 5 pm or greater, 6 pm or greater or 7 pm or greater. Thus, the electrolyte may have a thickness in the range 4 pm to 17 pm, a thickness in the range 5 pm to 15 pm, or a thickness in the range 6 pm to 12 pm.

[0051] In some examples, the electrically insulating layer (EIL) comprises a dielectric layer or a ceramic layer. In some examples, EIL comprises one or more of zirconia (e.g., YSZ), hafnium, alumina, glass-ceramic, an alumina-zirconia composite.

[0052] In some examples, the EIL comprises a ceramic material and is co-sintered with at least one of the electrolyte and the counter-electrode. In some examples the EIL comprises a ceramic or alumina material and is co-sintered with the first electrode (optionally also with the electrolyte) or is cosintered with counter-electrode when EIL is above electrolyte and / or counter-electrode (optionally also with the electrolyte). In each case, co-sintering the EIL with one or more of the other layers reduces processing time and the number of thermal processes, thereby reducing cost and reducing the potential for damage to layers in multiple sintering processes. Preferably, the EIL is co-sintered with the first electrode and electrolyte, particularly where the EIL comprises zirconia. The counterelectrode may be sintered separately. In some cases, when EIL is above electrolyte and / or counterelectrode, it may be preferable to co-sinter the EIL with at least the counter-electrode (optionally also the electrolyte), particularly where the EIL comprises alumina. An alumina-based EIL may sinter at a relatively low temperature and so is adapted for co-sintering with (or sintering after) the counterelectrode whereas a zirconia-based EIL may sinter at a relatively high temperature and so is adapted for co-sintering with (or sintering before) the first electrode and / or electrolyte.

[0053] In some examples, the EIL comprises an alumina-zirconia composite, preferably disposed above the electrolyte (specifically above the functional layer thereof). In such cases, the EIL is sintered with the counter-electrode, reducing the number of thermal processes, thereby reducing cost and reducing the potential for damage to layers in multiple sintering processes. Preferably, the composite does not comprise a sintering aid. A thickness of the composite may be between 60 and 150 micrometers. In some examples, the EIL comprises YSZ, optionally 3YSZ, optionally alumina (AI2O3). YSZ is usually sintered at a temperature higher than that of some counter-electrode materials (especially when the counter-electrode is the oxygen electrode), so it is preferred to co-sinter the EIL with one or both of the electrolyte and first electrode. Further, YSZ adheres well to ceria-containing layers as preferably used for the electrolyte and first electrode.

[0054] In some examples, the electrically insulating layer (EIL) has a thickness of between 0.5 micrometer and 500 micrometers, preferably between 1 micrometer and 100 micrometers, preferably between 1 micrometer and 50 micrometers, preferably between 1 micrometer and 10 micrometers. A hafnium-based EIL may have a thickness of between 1 micrometer and 10 micrometers, preferably between 1 micrometer and 5 micrometers. A YSZ-based EIL may have a thickness of between 1 micrometer and 100 micrometers, preferably between 1 micrometer and 50 micrometers. The electrically insulating layer (EIL) may be thicker than the functional layer (where present).

[0055] In some examples, the first electrode is a fuel electrode. As a result, electrolyte which overlaps the fluid blocking region may not be substantially fuelled (if lateral fluid communication in the first electrode is not significant) or may not be as well fuels as electrolyte which overlaps the fluid communication region. In such examples, the counter-electrode is the oxygen electrode.The fuel electrode may comprise at least one layer comprising doped ceria, optionally at least one layer of the fuel electrode may comprise ceria gadolinium oxide (CGO). The fuel electrode may be a cermet, which may be Zr or Ce-based, and / or may comprise a material as found in the electrolyte or interlayer. As a result, electrical conductivity of the fuel electrode may be greater than if the electrode were a ceramic. This may enable improved electrical connection to the fuel electrode (outermost electrode relative to the support plate), said electrical connection typically via interfacial contact. The greater electrical conductivity means that losses in the electrical connection may be reduced relative to a lower conductivity electrode. The fuel electrode may comprise at least one layer comprising a source of transition metal or metal oxide. The transition metal (or oxide thereof) may be one or more of nickel, iron, cobalt, or copper, preferably nickel. Thus, the fuel electrode may comprise at least one layer comprising a source of nickel, optionally the source of nickel may comprise nickel oxide. The fuel electrode may comprise at least one layer comprising a transition metal (including metal oxide) CGO cermet. The fuel electrode may comprise at least one layer comprising nickel CGO cermet. The fuel electrode may have a thickness of 3 pm or higher, optionally 5 pm or higher, optionally 10 pm or higher, optionally 15 pm or higher. The fuel electrode may have a thickness of 60 pm or lower, 50 pm or lower, optionally 45 pm or lower, optionally 40 pm or lower, optionally 35 pm or lower, optionally 30 pm or lower, optionally 25 pm or lower, optionally 20 pm or lower optionally 15 pm or lower. Thus, the fuel electrode may have a thickness in the range 3 pm to 60 pm, 5 pm to 50 pm, optionally 15 pm to 25 pm. In use, the fuel electrode may be contacted by a fuel gas that may comprise, for example, steam and / or CO2 and / or NO2.

[0056] The oxygen electrode may comprise a material that is electrically conductive, optionally the oxygen electrode may comprise a material that is an electrically conductive ceramic material. The oxygen electrode may comprise a material that is selected from lanthanum cobaltite, lanthanum ferrite, lanthanum nickel ferrite, Lao.ggCoo^Nio.eOp-s) (LCN60), praseodymium strontium cobaltite, praseodymium doped ceria, lanthanum strontium manganese, lanthanum strontium cobaltite and mixtures thereof. In the formula for Lao.ggCoo.4Nio.60(3-6) (LCN60), 6 indicates the degree of oxygen deficiency. The oxygen electrode may comprise or further comprise doped ceria, optionally the oxygen electrode may comprise or further comprise doped ceria gadolinium oxide (CGO).

[0057] The oxygen electrode may comprise a Pr / Ln"1material of composition Pr(i-q)LnlllqO(2-5), wherein Ln" is selected from at least one rare earth metal, optionally Ln1" is selected from La, Nd, Sm, Eu, Gd, preferably Gd or Sm, more preferably Sm, 6 is the degree of oxygen deficiency, and 0.01 < q < 0.4. Such a Pr / Ln"1material has excellent activity and other properties and does not need to contain alkaline earth metal oxides (e.g. strontium oxide). Alkaline earth metal oxides (e.g. Sr) may be problematic in electrochemical cells because they may react, in particular, with zirconia-based electrolytes.

[0058] In the Pr / Ln"1material, q may be selected to achieve a balance between oxygen vacancy concentration and ion-mobility e.g. 0.02 to 0.25. Advantageously, q may be in the range 0.02<x<0.3; 0.03<x<0.3; 0.04<x<0.3; 0.05<x<0.3; 0.05<x<0.27; 0.05<x<0.25; 0.05<x<0.25; or 0.05<x<0.3. Suitably the Pr / Ln1" material may be of formula Pro.9Lno.1O11.95-6), Pro.85Lno.i50(i.925-6), Pro.8Lno.20(i.9.6) or mixtures thereof; wherein Ln is selected from one or more of La, Nd, Sm, Eu, Gd, or Yb; preferably Sm.

[0059] Advantageously, the Pr / Ln"1material may have a cubic crystalline structure; preferably a fluorite crystalline structure. The first oxygen electrode layer may essentially comprise or consist of a single phase having a cubic fluorite structure, or of two or more phases having a cubic fluorite structure. The fluorite structure of the Pr / Ln1" material may also be advantageous because it may provide good interfacial interaction with an electrolyte layer comprising a material with a fluorite structure.

[0060] Suitably the Pr / Ln1" material may be of formula Pro.9Lno.1O11.95-6), Pro.85Lno.i50(i.925-6), Pro.8Lno.2O11.9_6) or mixtures thereof; wherein Ln is selected from one or more of La, Nd, Sm, Eu, Gd, or Yb; preferably Sm,may be in direct contact with the electrolyte. In such cases, the resulting cells may exhibit improved electronic leakage, in turn improving performance particularly at high temperatures.

[0061] The oxygen electrode may further comprise a material that is also comprised in the electrolyte (e.g., Ce, Zr). The oxygen electrode may comprise multiple sub-layers. For example, the oxygen electrode may comprise a bulk electrode and an active electrode (each of which may comprise multiple sublayers). In other cases, there may only be an active electrode. Either or both of the active and bulk (where present) electrodes may comprise Pr. If a bulk oxygen electrode is present, it may comprise a Cr or S getter.

[0062] In some examples, the second side of the support structure bounds an oxygen volume and the first side of the support structure bounds a fuel volume.

[0063] In some examples, the cell layer is for an electrolysis cell unit.

[0064] In some examples, the fluid blocking region comprises at least one fluid port for delivery fluid to or exhaust of fluid from the first electrode or the counter-electrode. In such cases, the EIL may be provided between the EACR and the at least one fluid port. Such an EIL may prevent electrical shorting between the cell layer and component(s) that facilitate fluid delivery from the at least one port to the EACR and vice-verse.

[0065] In some examples, the EIL is provided between the at least one fluid port and a perimeter of the cell layer.

[0066] In some examples, the fluid blocking region surrounds fluid communication region and the EIR may be provided between the fluid communication and edge of cell layer.

[0067] In some examples, the electrochemically active cell region comprises a solid oxide electrolyte.

[0068] According to an aspect, a cell layer for an electrochemical cell unit is provided. The cell layer may comprise:

[0069] an electrochemically active cell region (EACR) comprising a first electrode, an electrolyte, and a counter electrode, wherein the EACR is supported by a support structure, the support structure comprising a support plate with a fluid communication region, first electrode or electrolyte;

[0070] wherein the support structure has a greater extent than the EACR thereby forming an electrochemically inactive region; and

[0071] wherein an electrically insulating layer (EIL); is provided on the second side of the support structure across at least a portion of the EIR and is not provided across the EACR.

[0072] Features of the preceding aspect may be combined with this aspect.

[0073] According to an aspect there is provided an electrochemical cell unit, i.e., a repeat unit for a stack of electrochemical cell units. The electrochemical cell unit comprises the cell layer of one of the above aspects and an interconnect, the interconnect having a first side and a second side, wherein the second side of the interconnect faces the first side of the support structure or the first side of the interconnect faces the second side of the support structure (any in such cases typically also faces the EACR).In some examples, the interconnect comprises dimples (i.e., a plurality of dimples) which form protrusions on the first side and which contact the EACR of the cell layer of the cell unit or which are configured to contact a cell layer of a neighboring cell unit in a stack of cell units. Such dimples are protrusions formed in the interconnect to protrude towards and / or away from the cell layer. In some cases, the interconnect is pressed or formed to form the dimples, such that a protrusion on one side of the interconnect forms a depression on the other side of the interconnect. The dimples provide an electrical connection function and / or a support function, to transmit compression force through a stack of cell units.

[0074] In some examples, at least one dimple contacts or is configured to contact EIL. Such at least one dimple may be a bridge dimple or a support dimple, to provide support outside the EACR. The EIL prevents transfer of electrical current via the at least one dimple.

[0075] In some examples, the interconnect has at least one bridge dimple that forms a protrusion on the first side of the interconnect and a corresponding depression on the second side of the interconnect, the depression for fluid guidance on the second side of the interconnect and the electrically insulating layer is provided on (i.e., at least on) the (second side of the) cell layer at a location which faces the at least one bridge dimple (the first side of the interconnect) of the electrochemical cell unit or which is configured to face an at least one bridge dimple of a neighboring electrochemical cell unit in a stack of electrochemical cell units. The fluid guidance may be in a first fluid volume formed between the second side of the interconnect and the first side of the cell layer (of the electrochemical cell unit, or of a neighboring cell unit in a stack). The EIL in such cases faces the convex side of the bridge dimple(s). The depression may be for fluid delivery to and / or exhaust from the fluid communication region. The depression (a volume formed thereby) may be in fluidic communication with the at least one port and / or a first fluid volume enclosed between the (second side of the) interconnect and the (first side of the) cell layer (substrate). The depression (a volume formed thereby) may allow fluidic communication between the at least one port and the first fluid volume and / or fluid communication region.

[0076] In some examples, the at least one fluid port is in fluidic communication with a first fluid volume provided (i.e., defined) between the second side of the interconnect and the first side of the support structure, the electrochemical cell unit further comprising a fluid guidance insert disposed in the first fluid volume, said fluid guidance insert comprising a plurality of elongate slots formed therein, said elongate slots defining a fluid channel system for conveying fluid between the at least one fluid port and the first fluid volume via the at least one bridge dimple (LE., the second side of the interconnect, via the depression (volume formed by the depression) of the at least one bridge dimple). The bridge dimple protrudes towards the second side of a cell layer, reducing a gap between the interconnect and cell layer. The EIL on the second side of the cell layer is configured to prevent current transfer via the bridge dimple.

[0077] In some examples, the elongate slots each have a distal end section wherein the distal end section of at least one of the elongate slots is closed by a web of the fluid guidance insert, and wherein the at least one bridge dimple extends away from the fluid guidance insert and spans said web to form a fluid bypass around the web (i.e., for conveying fluid between the at least one fluid port and the first fluid volume via the at least one bridge dimple). In other words, the second side of interconnect faces the fluid guidance insert and so the depression of the at least one bridge dimple faces the insert. In other words the bridge dimple allows fluidic communication between the slot and the first fluid volume. The proximal end section may be proximal to the fluidic port and in fluidic communication therewith (it may be referred to as being open or not closed by the web). The distal end section may be distal from the proximal end section (and port). Preferably, the at least one fluid port is providedby a through-hole extending through the interconnect, the fluid guidance insert and the support structure (i.e., said ports outside the central, electrochemically active area - between said area and periphery). In some cases, the distal end section of at least one of the elongate slots is open (in other words, it is not closed by a web).

[0078] In some examples, the first side of the interconnect is electrically conductive in an area that is adapted to face the electrochemically active cell region. Preferably, this is a central area of the interconnect. In some examples, the area comprises conductive features, such as conductive protrusions, adapted to contact the electrochemically active cell region and space the interconnect from the electrochemically active cell region. Preferably, the protrusions comprise dimples which are pressed or formed in the interconnect, said dimples adapted to contact the electrochemically active cell region. Such pressing or forming is relatively cost-effective and may be executed at the same time as pressing or forming other features of the interconnect. Alternatively or additionally, the protrusions comprise features printed or deposited on - and / or machined or etched into a printed or deposited layer on - the first side of the interconnect. The height of such features may be easy to control, and may be manufactured with relative ease. Alternatively, said area comprises a porous layer (of a given thickness across the area of the electrochemically active cell region) adapted to contact the electrochemically active cell region and space the interconnect from the electrochemically active cell region. The second side of the interconnect may be adapted to be exposed to a first fluid volume for a first fluid (e.g. fuel, for example hydrocarbon or Hz for a fuel cell, steam for an electrolyser cell), and the first side of the interconnect may be adapted to be exposed to a second fluid volume for a second fluid (e.g. oxidant / oxygen / sweep gas) that is different to the first fluid. Preferably, the interconnect is adapted to separate said fluids. The electrochemical cell unit may be configured to constrain the first fluid in a first fluid volume (e.g., between the second side of the interconnect and the first side of the cell layer (support structure), preferably enclosed by the interconnect and cell layer (support structure) of a cell unit) and to constrain the second fluid in a second fluid volume (e.g., between the first side of the interconnect and the second side of the cell layer / support plate). A cross-sectional area of the second fluid volume may be smaller than a cross-sectional area of the first fluid volume. In some examples, the electrochemical cell unit is an electrolysis cell unit, more preferably a solid oxide electrolysis cell (SOEC) unit. Electrolysis cell units may have a lower oxidant flow rate requirement than fuel cell units, and so the height of an oxidant side (e.g., the fluid volume disposed to the first side of the interconnect, e.g., defined by height of dimples in the interconnect) of an interconnect for an electrolysis cell unit may be reduced relative to the height of an oxidant side of an interconnect for a fuel cell unit. Such lower heights may increase the chance that the first side of the interconnect contacts the cell layer in undesirable locations (e.g., outside the electrochemically active cell area). The electrically insulating coating may prevent such contact.

[0079] Preferably, the second side of the interconnect and the cell layer (in some cases, the first side of the support structure) are spaced from one another to provide a first fluid volume therebetween and are joined around their periphery or perimeter and electrically connected thereto. Protrusions or features on the second side of the interconnect may contact the cell layer to maintain the spacing between the interconnect and cell layer, and thus said fluid volume. In a stack of such cell units, gaskets may be provided (e.g., around port(s)) between the first side of the interconnect of a first cell unit and the second side of the cell layer of a second, adjacent cell unit. Alternatively, the first side of the interconnect and the cell layer are spaced from one another to provide a first fluid volumetherebetween, and having at least one gasket provided therebetween. Said gasket may be electrically insulating, albeit that it need not be electrically insulating if said gasket is provided upon the electrically insulating layer. Protrusions or features on the first side of the interconnect may contact the cell layer to maintain the spacing between the interconnect and cell layer, and thus said fluid volume.

[0080] According to an aspect there is provided an electrochemical cell stack. The electrochemical cell stack comprise a plurality of electrochemical cell units each according to the above aspect, wherein the first side of the interconnect of a first electrochemical cell unit (i.e., of the plurality of cell electrochemical units) faces the second side of the support structure of a second, neighboring (i.e., stacked / overlaid on or below the first cell unit), electrochemical cell unit. Alternatively, the first side of the interconnect of the first electrochemical cell unit faces the first side of the support structure of the second, neighboring, electrochemical cell unit. In such stacks, the EIL prevents current flow or voltage application between the second side of the cell layer and the first side of the interconnect through the stack, thereby preventing electrical shorting and / or damage to the electrolyte.

[0081] According to an aspect there is provided a method of manufacturing a cell layer for an electrochemical cell unit. The method comprises:

[0082] providing a support structure having first and second sides, the support structure comprising a fluid communication region providing fluidic communication between the sides and a fluid blocking region, the second side of the support structure carrying a first electrode, or precursor therefor, provided over at least the fluid communication region, wherein the support structure has a greater extent than the first electrode thereby forming an electrochemically inactive region (EIR); and applying a material on at least part of the fluid blocking region as a precursor for, and to form, an electrically insulating layer (EIL) on the second side of the support structure across at least a portion of the EIR.

[0083] In some cases, the second side of the support structure further carries an electrolyte, or precursor therefor, provided over at least the first electrode or precursor therefor. This may also be over at least the porous region.

[0084] In some cases, applying the material as a precursor for, and to form, the EIL is applied by screen printing.

[0085] In some cases, the EIL comprises a ceramic material, the method further comprising sintering the material as a precursor for, and to form, the EIL.

[0086] In some cases, sintering the EIL comprises co-sintering the EIL with at least the first electrode. In some cases, the sintering the EIL comprises co-sintering the EIL with at least the electrolyte (optionally also the first electrode).

[0087] In some cases, the method comprises, subsequent to the sintering, applying a material on at least part of the electrolyte as a precursor for, and to form, a counter-electrode on the EL.

[0088] In some cases, the method comprises co-sintering the first electrode and the electrolyte, and applying the material as a precursor for, and to form, an electrically insulating layer subsequent to said sintering (optionally also subsequent to application of a functional layer).

[0089] In some cases, the method comprises co-sintering the EIL with the counter-electrode.Preferably, the EIL is co-sintered with the first electrode and electrolyte, particularly where the EIL comprises zirconia. The counter-electrode may be sintered separately. Alternatively, in some cases, when EIL is above electrolyte and / or counter-electrode, it may be preferable to co-sinter the EIL with at least the counter-electrode (optionally also the electrolyte), particularly where the EIL comprises alumina. An alumina-based EIL may sinter at a relatively low temperature and so is adapted for cosintering with (or sintering after) the counter-electrode whereas a zirconia-based EIL may sinter at a relatively high temperature and so is adapted for co-sintering with (or sintering before) the first electrode and / or electrolyte.

[0090] In some cases, the support structure may be provided with an electrolyte or precursor therefor in addition to the first electrode, or precursor therefor, prior to applying the material as a precursor for and to form the EIL. In some cases, the support structure may be provided with a counter-electrode or precursor therefor in addition to the first electrode and electrolyte, or respective precursors therefor, prior to applying the material as a precursor for and to form the EIL.

[0091] In some cases, the method comprises applying a material on the first electrode, or precursor therefor, as a precursor for, and to form, an electrolyte on the first electrode. In some cases, the method comprises applying a material on the electrolyte, or precursor therefor, as a precursor for, and to form, a counter-electrode on the electrolyte. Such steps of applying the respective materials for the first electrode, electrolyte, and counter-electrode may be prior to or subsequent to the step of applying a material as a precursor for, and to form, an electrically insulating layer.

[0092] According to a further aspect, there is provided a method of manufacturing an electrochemical cell unit. The method comprises providing the cell layer according to (or manufactured using) one of the aspects above and an interconnect, and joining the cell layer and interconnect to one another around their perimeter. Said joining may be by welding.

[0093] According to a further aspect, there is provided a method of manufacturing an electrochemical cell stack of electrochemical cell units comprising providing at least two cell units each according to one of the aspects above and overlaying said cell units over one another in a stacking direction wherein the first side of a first interconnect faces the second side of a first support structure (e.g., forming a first fluid volume therebetween, the first fluid volume in fluidic communication with the first electrode via the fluid communication region) and the first side of the first interconnect faces the second side of a second support structure (the first interconnect may contact the EACR on the second support structure). The first interconnect and the first support structure may be part of (or form) a first electrochemical cell unit. The second support structure may be part of a second electrochemical cell unit (also comprising a second interconnect). A second fluid volume may be formed between the first side of the first interconnect and the second side of a second support structure, in fluidic communication with the counter-electrode.

[0094] In this specification, the terms "rare earth", "rare earth metal" or "rare earth element" refer to metals selected from Y, Sc, and lanthanoid. "Lanthanoid", "lanthanide" and "Ln" are used interchangeably and mean the metallic chemical elements with atomic numbers 57-71. The term "dopant" as used herein is not intended to be restricted to a maximum percentage of elements, ions or compounds added to chemical structures. Similarly, the term "doping" is intended to mean the addition of a certain amount of elements, ions or compounds to a material. It is not limited to a maximum quantity of material, after which, further addition of material no longer constitutes doping.

[0095] Metal oxides including mixed metal oxides may exhibit non-stoichiometry with the oxide being deficient in oxygen. In this specification, 6 indicates the degree of oxygen deficiency of a material. 6may vary depending on the environment and history of the material. As would be understood by the skilled person, values of 6 are usually small.

[0096] The term "source of" an element, compound or other material refers to a material comprising the element, compound or other material whether or not chemically bonded in the source. The source of the element, compound or other material may be an elemental source (e.g. Ln, Ni or 02) or may be in the form of a compound or mixture comprising the element, compound or other material including one or more of those elements, compounds or materials.

[0097] The various features of aspects / examples of the disclosure as described herein may be used in combination with any other feature in the same or other aspect / example of the disclosure, if needed with appropriate modification, as would be understood by the person skilled in the art. Furthermore, although all aspects / examples of the invention or disclosure preferably "comprise" the features described in relation to that aspect, it is specifically envisaged that they may "consist" or "consist essentially" of those features outlined in the claims.

[0098] It will be understood that each layer may be comprised of multiple sub-layers (and those sub-layers may have varying compositions).

[0099] In order that the present invention be more readily understood, various aspects of specific embodiments will now be described in conjunction with the attached drawings.

[0100] Brief Description of the Drawings

[0101] Figures 1 and 2 are exploded perspective views of a cell unit and two gaskets.

[0102] Figure 2a is a simplified cross-section of the cell unit of Figures 1 and 2.

[0103] Figure 3 is a schematic cross-sectional view of a cell unit and an interconnect.

[0104] Figure 4 is a schematic plan view of a cell layer of a cell unit.

[0105] Figure 5 is an exploded perspective view of a cell unit.

[0106] Figure 6A is a plan view of an example cell layer.

[0107] Figure 6B is an exploded perspective view of two cell units each including a cell layer corresponding to Figure 6A.

[0108] Figures 6C and 6D are cross-sectional views through the cell units of Fig. 6B

[0109] Figures 7A to 7C are an exploded perspective view and two cross-sectional views of two cell units each including a further example cell layer.

[0110] Figures 8A to 8C are an exploded perspective view and two cross-sectional views of two cell units each including a further example cell layer.

[0111] Figure 9 is a plan view of another example cell layer.

[0112] Figure 10 is a plan view of another example cell layer.

[0113] Figure 11 illustrates a method of manufacturing a cell layer for an electrochemical cell stack.

[0114] Figures 12A and 12B are exploded perspective and cross-sectional views of another example cell unit comprising a fluid guidance insert.

[0115] Figure 13 is a schematic cross-sectional view of an example cell layer and interconnect forming a cell unit.

[0116] Figures 14 to 25 are schematic cross-sectional views of example cell layers alternative to the cell layer of Fig. 13.Detailed Description

[0117] The drawings are included for illustrative purposes only. Some of the figures only indicate one or two electrochemical cell units (each hereafter referred to simply as a "cell unit") in a stack. In various embodiments, multiple cells are provided. In further embodiments (not shown) multiple electrochemical cell stacks are provided, and in still further embodiments multiple electrochemical cell stacks each comprising multiple electrochemical cells are provided. It will be appreciated that the fuel volume and oxygen volume inlets, outlets (off-gas), ducting, and manifolding, and their configuration are modified as appropriate for such embodiments, and will be readily apparent to a person of ordinary skill in the art.

[0118] The cell units described with reference to Figures 3 to 25 may be fuel cell units, such as SOFC units, or electrolyser cell units, such as SOEC units.

[0119] Figure 3 shows a simplified schematic of a cell unit (comprising a cell layer and interconnect) and an interconnect. It depicts a cell layer 314 and two adjacent interconnects 312a and 312b. It will be appreciated that these three components are for explanation of stacking of cell units, that a cell unit (i.e. a repeat unit) is constructed from one cell layer 314 and one interconnect (sometimes referred to as a separator plate) 312 - whether a cell layer with an interconnect above (312b) or below (312a) it - and that plural cell units may be stacked one upon the next to form a stack of cell units.

[0120] The cell layer includes an electrochemically active cell area (EACR) 350. That electrochemically active cell area 350 may be self-supporting (e.g., fuel electrode-supported or electrolyte-supported) or may be supported by a support structure. In the latter case, and as shown in Fig. 3, the support structure, e.g., support plate, has a fluid communication region provided by a porous region 355 for fluidic communication between the electrochemically active cell area 350 and the first fluid flow region. Where the EACR is self-supporting it typically has a support structure extending past a boundary of the EACR which it is fixed to, handled with, and supported by, that support structure having a region (e.g., through-hole or porous region) allowing fluidic communication with one of the electrodes of the EACR. The EACR 350 comprises a first electrode, an electrolyte, and a counter-electrode. The first electrode may be between the electrolyte and the support structure, and may be a fuel electrode (the counter-electrode therefore being an oxygen electrode when the electrolyte is an oxygen ion conductor). The EACR 350 is a region configured to be in fluidic communication with separate fluid volumes (first and second fluid volumes) on respective sides of the EACR 350 and cell layer 300. The EACR 350 may be a region of the cell layer 300 in which each of the first electrode, electrolyte, and counter-electrode overlay the fluid communication region of the support structure.

[0121] The cell layer 314 and the interconnects 312a, 312b each have a first side and a second side. The first side 313a of each interconnect 312 faces the second side 315b of each cell layer 314. The second side 313b of each interconnect 312 faces the first side 315a of each cell layer 314.

[0122] A first fluid volume (or flow region) 360 is defined between the first side 315a of the cell layer 314 and the second side 313b of the interconnect 312. A second fluid volume (flow region) 365 is defined between the second side 315b of the cell layer 314 and the first side 313a of the interconnect 312.The first fluid volume 360 may be for delivery of first fluid (e.g., fuel) to the first side of the cell layer 314, i.e. to a layer of the electrochemically active cell area 350 which is in fluidic communication with the first fluid flow region 360. In this case, the first fluid volume is in fluidic communication with the EACR 350 (specifically, the first electrode thereof) via the porous region 355 of a support plate in cases where the cell layer 314 comprises a support plate supporting the electrochemically active cell area 350. The first fluid volume 360 may also exhaust a product of an electrochemical reaction at the electrochemically active cell area 350 (and exhausts any unused fuel).

[0123] The second fluid volume 365 may be for delivery of second fluid (e.g., oxidant or sweep gas) and / or for exhaust of a product of the electrochemical reaction at the electrochemically active cell area 350. In the case of electrolysis cell operation, only a sweep gas may be supplied (and exhausted) via the second fluid volume, to assist in exhaust of a second product of the electrochemical cell reaction. The sweep gas may, for example, be oxygen, oxidant, air, or another suitable gas.

[0124] Figure 3 depicts the height (and cross-section) of the second fluid volume 365 as being smaller than the cross-sectional area of the first fluid volume 360. This cross-sectional area difference may be defined by the height h2366 of the second fluid volume 365 being smaller than the height hl 361 of the first fluid volume 360.

[0125] A cell unit (i.e. a repeat unit, plural units form a stack) comprises one cell layer 314 and one interconnect 312. In an example, cell units 300 are formed from the cell layer 314 and the interconnect 312a, such that said components enclose the first fluid volume 360 between the second side 313b of the interconnect and the first side of the cell layer 315a. When two cell units 300 are stacked, the second fluid flow volume 365 is bounded between the second side 315b of the cell layer 314 of a first cell unit 300 and the first side 313a of the interconnect 312b of a second, neighbouring (i.e. adjacent) cell unit 300, and may be referred to as the second fluid volume.

[0126] In an alternative example, cell units 370 are formed from the cell layer 314 and the interconnect 312b, such that said components enclose the second fluid volume 365 between the first side 313a of the interconnect 312b and the second side 315b of the cell layer 314. When two cell units 370 are stacked, the first fluid volume 360 is bounded between the first side 315a of the cell layer 314 of a first cell unit 300 and the second side 313b of the interconnect 312a of a second, neighbouring (i.e. adjacent) cell unit 370.

[0127] The cell layer is typically (substantially) planar, at least within the plan view area of the electrochemically active cell area 350. The interconnect is typically formed from a planar sheet, for example a metal sheet.

[0128] Conductive features are preferably formed on the first side 313a of the interconnect 312. For example, they are conductive protrusions. Such protrusions may be printed features, or features formed by pressing a metal sheet, for example. Protrusions may take the form of discrete dimples; alternatively, they may take the form of ribs or otherwise. They protrude into the corresponding fluid volume 365, and conductively contact the electrochemically active cell region 350 of the cell layer 314 (the second side 315b thereof) while at the same time performing the role of spacing the cell layer 314 from the interconnect 312b above.Instead of protrusions (e.g. dimples), the conductive features may comprise a porous layer formed (e.g. deposited or coated) on the first side of 313a of the interconnect. Alternatively or additionally, a porous layer may be formed (e.g. deposited coated) on the second side 315b of the cell layer 314, specifically on the electrochemically active cell area 350. Such a porous layer may also be provided as a component in its own right (e.g. an expanded metal sheet or mesh) in the stack. Protrusions or other features may be provided on the second side 313b of the interconnect 312, as can be seen in some illustrated examples below. Protrusions or porous layers may also serve the purpose of transferring compression force through or between cell units in a stack.

[0129] Figure 4 shows a simplified schematic plan view of the second side of a cell layer 400 in its full extent, this second side corresponding to second side 313a of Figure 3. Said second side of the cell layer may be exposed to (form a boundary of) the second fluid volume, which may be for air or oxidant, and configured to face the first side of an interconnect.

[0130] In this example, four first fluid ports 440 (described further below) are shown, which are through-holes through the cell layer 400, although other numbers (at least one) of ports are possible. The cell layer 400 which has an outer perimeter 430, The cell layer 400 has an EACR 450, similar to the EACR 350 described above, supported by a support structure. The EACR 450 is provided across a central area of the cell layer 400.

[0131] The area 420 on the cell layer 400 outside the EACR 450 is shaded in Figure 4; they are exclusive of each other. In other words, this area 420 is between the central EACR 450 and the perimeter 430 of the cell layer 400, and may be described as a periphery or electrochemically inactive region (EIR) 420 of the (support structure and the) cell layer 400. The ports 440 are formed in the EIR 420.

[0132] Referring back to schematic Figure 3, the EACR 450 in the central area of the cell layer 400 of Figure 4 corresponds to the portion electrochemically active cell area 350 of the cell layer 314 that overlays the porous region 355. The EIR 420 corresponds to the remainder of the second side 315b of the cell layer 314 which faces the first side 313a of the interconnect 312b outside of the electrochemically active cell area 350 of the cell layer 314.

[0133] As above mentioned, it is undesirable for any part of the interconnect to get into electrical contact with the cell layer except where such electrical contact is intended, namely between the electrochemically active cell area of the cell layer and the central part of the interconnect. Such undesirable contact may happen if the interconnect undergoes deformation or flexing for any reason during operation, or if the height 366 of the second fluid volume is particularly small, resulting in a short circuit. Dimples or other features protruding from the first side 313a of the interconnect may also be positioned outside of the area configured to contact the EACR, for example as a result of manufacturing tolerances or intentionally for support or to reduce flexing, or for fluid transfer purposes. As mentioned above, it is undesirable for these to contact the cell layer outside of the EACR. It is herein disclosed that at least one electrically insulating means, such as an insulating layer, may be provided on the cell layer, on at least a portion of the second side 315b, for example across at least part of the EIR 420.This is advantageous in electrically insolating the interconnect from the cell layer (except at the active area), particularly if spacing therebetween is small. This is particularly the case for electrolyser cells (e.g. SOECs), in which the first side of the interconnect is adapted to be exposed to oxidant / oxygen volume, in which case oxidant volume may be reduced in size compared to fuel cell (e.g. SOFC) operation. The oxidant volume may be smaller compared to fuel side of fuel cells because the only fluid in the oxidant volume may be that produced by the electrolysis cell reaction (plus, optionally, a sweep gas).

[0134] The insulation layer may be, but is not limited to, a dielectric layer. It is preferably an insulating material with a relative permittivity less than 25, preferably less than 20, more preferably less than 15, more preferably less than 10, more preferably less than 5. It may comprise, for example, a glass ceramic. Further examples for the material of the insulation layer or coating include alumina, hafnium oxide, silica, zirconia, ceria, aluminium silicate (or magnesium silicate) based glasses.

[0135] The insulation layer may have a thickness of between approximately 1 micrometer and 500 micrometers, for example. A smaller range of between preferably between 1 micrometer and 100 micrometers may be preferred, more preferably between 1 micrometer and 50 micrometers, more preferably between 5 micrometers and 20 micrometers. For example, an alumina coating that is approximately 1 micron (e.g. 0.5 to 2 micron) thick on steel has insulating effect. The upper limit of the thickness of the insulation layer may correspond to the applicable cell unit design, for example, to correspond to the height of a dimple on an interconnect.

[0136] It is noted that such insulation means is provided on / in the cell layer rather than the interconnect. Although applying an insulating layer on the cell layer airside incurs additional manufacturing costs, it provides an effective way of preventing or reducing the risk of shorting of cells and cell stacks. Additional manufacturing costs are mitigated by the fact that the cell layer already has one or more layers of the EACR coated or deposited thereon, and some manufacturing steps can be shared between layers of the EACR and insulation. Further, in some cases the insulation may be used as a template for coating / deposition of a subsequent layer of the EACR or vice-versa.

[0137] Insulating layers can be deposited using various methods, such as:

[0138] • wet deposition methods, such as screen printing, tape casting, transfer printing of inks; • physical or chemical vapour deposition methods (e.g. CVD, PVD, sputtering);

[0139] • wet spraying or plasma spraying methods.

[0140] Screen printing may be a particularly preferred route, because of ease of use.

[0141] After deposition, further heat treatment may be needed. For example, a firing or sintering process and / or heat treatment may be carried out, to increase the density of the insulating layer and enhance its adhesion to the cell layer (support structure or other layer which it is deposited on). Said heating may involve heating the interconnect to a temperature of at least 300°C, preferably at least 500°C, more preferably at least 800°C and at a temperature of less than 1200°C, preferably less than 1000°C, more preferably less than 900°C.In a cell unit, the interconnect may contain electrical contact features, for example dimples. The interconnect may comprise upward features that protrude (are convex) on the first side 313a of the interconnect to contact the second side 315b of the cell layer, primarily across the EACR to provide electrical connection and mechanical support therebetween. Some features may not contact the EACR and therefore the EIL provides electrical insulation between the first side 313a of the interconnect and the second side 315b of the cell layer outside of the EACR. The interconnect may comprise downward features that protrude (are convex) on the second side 313b of the interconnect to contact the first side 315a of the cell layer, primarily across the EACR to provide electrical connection and mechanical support therebetween. Said mechanical support maintains the height of the respective fluid volumes. The electrical contact features may comprise conductive protrusions or dimples, for example, adapted to contact said electrochemically active cell region and space the interconnect therefrom. The conductive protrusions may comprise dimples which are pressed or formed in the interconnect, said dimples adapted to contact the electrochemically active cell region (the second side thereof for protrusions extending from the first side of the interconnect and the first side thereof - directly or via the support structure - for protrusions extending from the second side of the interconnect. Alternatively or additionally, they may comprise features printed or deposited on this first side of the interconnect. Preferably, the protrusions do not confine fluid flow, i.e. they are not or do not form channels. In such cases, each protrusion preferably has an aspect ratio (length-width in plan view) of less than 5, more preferably less than 2, and are preferably oval or circular in (plan view) cross section. Preferably, the at least one port(s) 440 or through-hole(s), are disposed to each side of EACR. They may be for fluid delivery of a first fluid or second fluid, typically to a first or second fluid volume enclosed by the interconnect and cell layer. The interconnect may have corresponding at least one port(s) so that respective ports in the cell layer and interconnect line up to form a chimney.

[0142] An electrically insulating layer (or a section thereof) may be provided between the port(s) 440 and the EACR 450. Additionally or alternatively, it may be provided between the port(s) 440 and the perimeter 430 of the cell layer / support structure. Additionally or alternatively, it may be provided in another location of the interconnect as long as it is away from the EACR 450. In principle an insulating layer may be provided to location(s) where there is a risk of unwanted contact happening. Note that an insulating layer can be provided under a gasket (i.e. between the cell layer (support structure) and a gasket). This can be seen in the following examples.

[0143] The second side of the interconnect may be electrically conductive. However, the second side of the interconnect is often electrically insulating, with the exception that current flows through segments (e.g. welded segments) at the perimeter or edge of the interconnect where it is joined to the cell layer to form the cell unit. For example, there may be an insulating coating on the second side of the interconnect, such as an alumina coating. Protrusions or dimples thereon, which contact the cell layer (on its first side / substrate), are thus electrically insulating.

[0144] The cell layer is adapted to be provided with a gasket to surround a respective each of the at least one port, to be positioned between cell units of the electrochemical cell stack. The gasket(s) are provided on the second side of the cell layer (and thus contact the first side of the interconnect). In cases where the cell layer is provided with an electrically insulating coating surrounding the port(s), the gasket(s) contact the electrically insulating coating. This advantageously helps to prevent corrosion at theinterface between the gaskets and cell layer. Further, in such cases, the gasket(s) do not need to be electrically insulating thereby allowing a greater range of choice of gasket materials.

[0145] Figure 5, included as a simplified perspective view of a cell unit Fig. 5 is a modified version of Figure 2, where an exemplary insulating layer 590 is shown (illustrated as a hatched area), positioned on the second side of the cell layer between the port 22 and the central area carrying the EACR.. Only one such insulating section is shown here for simplicity; preferably, other sections of the interconnect will be also provided with an insulating layer or coating. The interconnect 12 of Figure 5 has a flanged edge / perimeter, and the cell layer (e.g., metal support plate) and interconnect are (sealingly) joined around the flanged perimeter, for example by welding, such that the second side of the interconnect contacts the first side of the cell layer (metal support plate) around the perimeter. It will be understood that the metal support plate may instead have a flanged perimeter. Alternatively, both the metal support plate and the interconnect may have flanged perimeters extending towards and contacting one another to provide the full height of the volume enclosed between the second side of the interconnect and first side of the cell layer. The electrically insulating layer may not cover the flanged perimeter - indeed it often need not do so since the flanged perimeter results in a relatively greater spacing between the second side of the cell layer and the first side of the interconnect at the flanged perimeter.

[0146] Aspects of the present disclosure are now described with reference to several examples of cell units and respective cell layers and interconnects.

[0147] Figure 6A is a plan view of a cell layer 600, with perimeter 630, viewed from the second side. Figure 6B is an exploded perspective view corresponding to Figure 6A, comprising two cell units, each comprising a cell layer 600 and an interconnect 612, in a stacked arrangement. Figures 6C and 6D show cross-sections A-A and B-B, respectively, through the stacked cell units, A-A and B-B indicated in Fig. 6B. The interconnect design of Fig. 6 comprises protrusions on both sides (dimples which are pressed or formed). Four fluid ports 640 in the periphery or EIL 620, are shown. The periphery may also be referred to as a peripheral area.

[0148] As mentioned, an electrically insulating layer 690 (e.g. in the form of a coating) may be provided outside EACR 450 . This layer 690 may be in one continuous area, or provided in several discrete portions or sections. For example:

[0149] • a coating 690a may be provided in the peripheral area 620 between two ports 640;

[0150] • a coating 690b may be provided in the peripheral area 620 between a port 640 and the perimeter 630;

[0151] • a coating 690c (not hashed, for clarity) may be provided in the peripheral area 620 to surround and / or cover a port 640;

[0152] • a coating 690d may be provided in the peripheral area 620 between a port 640 and the EACR 450;

[0153] • a coating 690e may be provided in the peripheral area 620 between the EACR 450 and the perimeter 630.

[0154] It is appreciated that all of these coatings, or sections thereof, can be included, or only one or some of them, on a cell layer in accordance with the present disclosure. In other words, the aboveindividually described areas with insulation means may be provided alternative or additional to one other on one cell layer. In cases where multiple of the coatings 690a to 690e are provided, it will be appreciated that they are preferably continuous (gaps between areas indicated for coatings 690a to 690e being shown for clarity) and are preferably deposited or formed in the same step. It is preferable that corners of the cell layer, and / or areas distal from support by gaskets and dimples via the EACR are provided with the insulation means. In the perspective view, only one example of each coating is indicated in the figure for clarity, but it will be understood that there would usually be consistent coverage by the layer 690 across the cell, e.g. if 690c is present it will usually be present around each port.

[0155] Gaskets 670 may be provided between an interconnect and a neighbouring cell layer, on the first side of the interconnect and the second side of the cell layer. Each of the above-described "types" of insulating coating portion 690 is illustrated (for clarity, only one of each type 690a-e is illustrated). It will be noted that there are dimples surrounding the port(s) 640 form protrusions on the second side of the interconnect, directed towards the cell layer 600. The coating 690c surrounds the port(s) and concave side of the dimples surrounding the ports, and the gasket(s) 670 contact the planar part of the interconnect surrounding the ports.

[0156] The cell layer 600 in this case comprises a metal support plate acting as the support structure. A second side of the metal support plate carries, or has deposited / coated thereon, the electrochemically active cell region 450. A porous region, similar to porous region 48 previously described, is provided in the metal support plate to allow fluidic communication between a first side of the metal support plate (which faces the second side of the interconnect) and the electrochemically active cell region -specifically a first electrode, typically the fuel electrode, which is carried by, coated on or deposited on the second side of the metal support plate. An outermost face of the outermost electrode (counter-electrode), typically oxygen electrode, of the electrochemically active cell region and the second side of the metal support plate together form the second side of the cell layer 600. The electrochemically active cell region 450 is provided in a central area of the cell layer 600 (corresponding to the porous region), which is surrounded by a periphery of the cell layer which is electrochemically inactive. The electrically insulating coating on the second side of the cell layer (supports structure) faces (e.g., aligns with when seen in plan view) at least a portion of the interconnect outside the EACR. In this way, the electrically insulating coating prevents electrical contact (and associated current flow / voltage application) between the first side of the interconnect and the second side of the cell layer - more specifically in this case between the periphery of the first side of the interconnect and the periphery of the second side of the cell layer.

[0157] Dimples which form protrusions on the first side of the interconnect protrude towards (and, in a stack of cell units, contact) the second side of a cell layer, to space said components thereby providing a second fluid volume, typically for oxygen. Dimples which form protrusions on the second side of the interconnect protrude towards (and, in a stack of cell units, contact) the first side of a cell layer - in the case of Figure 6b, the metal support plate - to space said components thereby providing a first fluid volume, typically for fuel. The ports through the interconnect and cell layer typically supply and exhaust first fluid from this first fluid volume. Said dimples are provided in a central area of the interconnect, surrounded by a periphery between the central area and the perimeter of the interconnect. Said central area of the interconnect generally corresponds to (e.g., aligns with in planview) the electrochemically active cell region of the cell layer. Said dimples of Figure 6 take the form of pressed or formed features in the interconnect (i.e., they protrude out of the general plane (which may be an original / unbent plane) of the interconnect). Note that these protrusions may also comprise at least one of: a plurality of ribs extending from the second side of the interconnect toward the first side of the cell layer, a plurality of discrete protrusions extending from the second side of the interconnect toward the first side of the cell layer, or a porous layer.

[0158] Figs. 6C and 6D are cross-sectional views of the two cell units of Fig. 6B (shown exploded in Fig. 6B), the cross-sections being along the lines A-A and B-B, respectively, of Fig. 6B. The EIL 690 is between a boundary of the EACR and the perimeter of the cell units, on the second side of the support structure (across the EIR thereof). As a result, the EIL prevents electrical shorting between neighboring cell units by prevention of contact between conductive parts of the interconnect and cell layer outside of the EACR. In this example (and in other examples herein) the one or more of the layers which form the EACR may extend over or under the EIL, outside of the porous region as discussed in detail Figs. 13-25.

[0159] Fig. 7 depicts a further example cell unit: Fig. 7A is an exploded perspective view of two cell units and Figs. 7B and 7C are cross-sectional views along A-A and B-B, respectively, of Fig. 7A. The cell units of Fig. 7 are similar to those of Fig. 6 except that the protrusions which extend from the first side of the interconnect (by being pressed or formed therein) are replaced by protrusions 794 on the second side of the cell layer 700. Specifically, these protrusions are on the outermost face of the EACR. These protrusions 794 may be printed or deposited on the outermost face of the EACR. Alternatively, they may be formed from a homogeneous outermost layer of the EACR (e.g., the counter-electrode or a sacrificial layer thereon) which is selectively machined or etched to create the protrusions. Such protrusions 794 can alternatively be provided on the first side of the interconnect 712. Upward protrusions 792 (dimples, pressed or formed in the interconnect) in the second side of the interconnect are also shown.

[0160] Similar to Fig. 6, an electrically insulating layer 790 (e.g. in the form of a coating) is provided in the periphery or EIL of the cell layer outside the EACR 450. This layer 790 may be in one continuous area, or provided in several discrete portions or sections. For example:

[0161] • a coating 790a may be provided in the peripheral area 720 between two ports 740;

[0162] • a coating 790b may be provided in the peripheral area 720 between a port 740 and the perimeter 730;

[0163] • a coating 790c (not hashed, for clarity) may be provided in the peripheral area 720 to surround and / or cover a port 740;

[0164] • a coating 790d may be provided in the peripheral area 720 between a port 740 and the EACR 450;

[0165] • a coating 790e may be provided in the peripheral area 720 between the EACR 450 and the perimeter 730.

[0166] In the perspective view, only one example of each coating is indicated in the figure for clarity, but it will be understood that there would usually be consistent coverage by the layer 690 across the cell, e.g. if 670c is present it will usually be present around each port.In the cross-sectional views of Figs. 7B and 7C, thick hashed areas show where insulating layer portions 790a, 790e are included. Other layer portions such as 790b / c / d may be additionally or alternatively included, but not shown in the cross-sections of Figs. 7B and 7C.

[0167] Fig. 8 depicts a further example cell unit: Fig. 8A is an exploded perspective view of two cell units and Figs. 8B and 8C are cross-sectional views along A-A and B-B, respectively, of Fig. 8A. The cell units of Fig. 8 are similar to those of Fig. 6 except that except that the protrusions which extend from the first side of the interconnect (by being pressed or formed therein) are replaced by protrusions 894 on the first side of the interconnect 812 which are printed, deposited and / or machined / etched like the protrusions 794 of Fig. 7. Further, the interconnect 812 does not have a flanged edge / perimeter, instead there is provided a spacer plate 880.

[0168] Similar to in Figures 6 and 7, an electrically insulating layer 890 (e.g. in the form of a coating) may be provided in the periphery 820 outside the EACR 450. This layer 890 may be in one continuous area, or provided in several discrete portions or sections. For example:

[0169] • a coating 890a may be provided in the peripheral area 820 between two ports 840;

[0170] • a coating 890b may be provided in the peripheral area 820 between a port 840 and the perimeter 830;

[0171] • a coating 890c (not hashed, for clarity) may be provided in the peripheral area 820 to surround and / or cover a port 840;

[0172] • a coating 890d may be provided in the peripheral area 820 between a port 840 and the EACR 450;

[0173] • a coating 890e may be provided in the peripheral area 820 between the EACR 450 and the perimeter 830.

[0174] Instead of the interconnect having a flanged perimeter, a spacer plate 880 is provided in each cell unit, to help space the plates apart and define a fluid volume therebetween. The interconnect, spacer, and cell layer (metal support plate) are (sealingly) joined around their perimeter, for example by welding through the three plates. In this case the second side of the interconnect faces and is spaced from (except for the protrusions which contact) the first side of the cell later (metal support plate), said spacing provided by the spacer plate which contacts the second side of the interconnect and the first side of the cell layer (metal support plate). Gaskets 870 may be provided between an interconnect and a neighbouring cell layer, on the first side of the interconnect and second side of the cell layer. Each of the above-described "types" of insulating coating portion 890 is illustrated (for clarity, only one of each type 890a-e is illustrated).

[0175] Figures 7 and 8 show protrusions on the second side of the cell layer and first side of the interconnect, respectively, which are printed or deposited. It will be understood that such printed or deposited protrusions may additionally or alternatively be provided on both of the second side of the cell layer and first side of the interconnect.

[0176] Figures 9 and 10 show further example cell layer and cell unit configurations.

[0177] Figure 9 illustrates an cell layer 900 with a perimeter 930 and six fluid ports 940 (which may be for supplying to and exhausting from the first fluid volume, enclosed between the second side of theinterconnect and first side of the cell layer, for example for fuel). Corresponding fluid ports are provided in the interconnect and a respective gasket for the ports are provided. Similar to the previous examples, in the peripheral region 920 outside of the EACR 450, one or more insulating layer portions 990 are provided. Portions 990a / b / c / d / e each corresponds (in terms of their locations relative to other interconnect features) to 690a / b / c / d / e, 790a / b / c / d / e and 890a / b / c / d / e, respectively, and are not again described in detail here.

[0178] Figure 10 illustrates an cell layer 1000 with a perimeter 1030 and two fuel / fluid ports 1040; unlike the other examples, the ports 1040 are not provided at corners of the interconnect, but instead towards the centre of the width of the interconnect (similar to Figure 5). Corresponding fluid ports are provided in the interconnect and a respective gasket for the ports are provided. Similar to the previous examples, in the peripheral region 1020 outside of the central region 1010, one or more insulating layer portions 1090 are provided. Portions 1090b / c / d / e each corresponds (in terms of their locations relative to other interconnect features) to 690b / c / d / e, 790b / c / d / e and 890b / c / d / e, respectively, and are not again described in detail here.

[0179] The cell layers as described in the examples above, each comprising an electrically insulating layer (as integral layer, or as a plurality of disconnected portions i.e. islands), form electrochemical cell units with corresponding interconnects. Multiple electrochemical cell units are stacked one atop another along a stacking direction to form an electrochemical stack such as those shown, in part, in Figures 7 and 8.

[0180] An electrochemical cell unit, and an electrochemical cell stack, according to aspects of the present disclosure, are hereby described further.

[0181] An electrochemical cell unit for an electrochemical cell stack comprises a cell layer as described above along with an interconnect. The cell layer and the interconnect overlie one another to form the electrochemical cell unit, in a spaced relationship to form a fluid volume for a first fluid therebetween. The cell layer may have a central area carrying the electrochemically active cell region. It also comprises a periphery between the electrochemically active cell region and a perimeter of the cell layer, which may be described as a region outside of the active cell region or an electrochemically inactive region. The portion of the second side of the cell layer upon which the electrically insulating layer is provided is aligned with (a portion of) the peripheral area of the interconnect (e.g. faces the first side of (a portion of) the peripheral area of the interconnect of a neighbouring cell unit).

[0182] The cell layer can also be described to comprise an electrochemically inactive region that is outside of (e.g. surrounds) a central area in which the electrochemically active cell region is provided. This electrochemically inactive region may be provided with the EIL.

[0183] The electrochemically active cell region of the cell layer may comprise a solid oxide electrolyte. For example, the electrochemical cell unit is a solid oxide electrolysis cell (SOEC) unit. The cell layer may further comprise a metal support plate carrying the electrochemically active cell region provided (e.g. coated or deposited upon) over a central porous region of the metal support plate. The central porous region of the metal support plate may be surrounded by a periphery between the central porous region and a perimeter of the metal support plate. The portion of the second side of the cell layerupon which the electrically insulating layer is provided is aligned with or faces a portion of the periphery of the interconnect.

[0184] The metal support plate has a first side and a second side. The second side carries the electrochemically active cell region, and the first side faces the second side of an interconnect. The porous region provides fluidic communication between the first side and the second side of the metal support plate.

[0185] Preferably, the second side of the interconnect and the cell layer (the first side of the metal support plate) are spaced from one another to provide, and preferably enclose, a (first) volume therebetween, preferably a fluid volume for fuel; they are also directly or indirectly, e.g. via a flanged perimeter or a spacer plate, respectively, joined around their periphery or perimeter (e.g. by welding around the perimeter) and are electrically connected thereto.

[0186] The first side of the interconnect and the cell layer (the second side of the metal support plate) are spaced from one another to provide a (second) volume with at least one electrically insulating gasket provided therebetween. This fluid volume may be for oxygen.

[0187] An electrochemical cell stack may comprise a plurality of electrochemical cell units overlaying one another in a stacking direction. The first side of an interconnect of a first cell unit faces an outermost layer of the electrochemically active cell region (e.g. the second side a cell layer) of a neighbouring cell unit in a spaced relationship, to form a (second) fluid volume for a (second) fluid therebetween. This second fluid may be oxidant and / or oxygen.

[0188] The stack of cell units may further comprise one or more gaskets between neighbouring cell units, said gasket(s) contacting the first side of the interconnect and (the second side of) the cell layer (second side of the metal support plate), preferably the gasket(s) contact the electrically insulating layer on said second side of the cell layer.

[0189] The interconnect and cell layer / metal support plate may be provided with ports / through-holes for delivery of fluid to and exhaust from the first fluid volume. These ports are preferably aligned in the stacking direction and surrounded by respective gaskets.

[0190] Figure 11 shows a further example cell unit comprising a cell layer provided with an electrically insulating layer 1190, 1191. Two examples of the EIL are shown - a first example in the form of three islands 1190 and a second example in the form of a single, larger, island 1191 performing the same function. The EIL is provided on the second side of the cell layer across an area which faces protrusions on the first side of the interconnect which protrude towards the second side of the cell layer, locally reducing the distance between the second side of the cell layer and the first side of the interconnect in this area. It will be understood that a given cell unit is either provided with the single island 1191 or the multiple islands 1190, and that the cell unit in Fig. 11, depicted with both, is for brevity.

[0191] Fig. 11A shows a lower and an upper exploded perspective view. Fig. 11B shows a cross section (Z-Z as depicted in the exploded view) of one cell unit. In this example each cell unit has two fluid ports, similar to Fig. 5, but may have other numbers of fluid ports (e.g., 1, 3, 4, 6 etc). However, in contrast to Fig. 5 a fluid guidance insert 1153 surrounds a respective fluid port and is provided with at least one elongate slot 1154 (also referred to as a channel, and in this case three slots or channels but there1

[0192] may be more or fewer, e.g., 2, 4, 5) for fluidic communication with the (first) fluid volume enclosed between the second side of the interconnect and the first side of the cell layer.

[0193] One fluid guidance insert 1153 is associated with a fluid inlet port. This fluid guidance insert 1153 is arranged such that the hole 1156 contributes to forming a through-hole through the cell unit, i.e. the fluid inlet port. The fluid guidance insert 1153 associated with the fluid inlet port is configured to convey a fluid from the fluid inlet port to the fluid volume. Specifically, a fluid may pass from the fluid inlet port through the elongate slots 1154 of the insert 1153 to the enclosed fluid volume. The fluid guidance insert 1153 may spread the fluid along a direction perpendicular to that between inlet and exhaust ports. Thus, the fluid guidance insert 1153 associated with the fluid inlet port may support a uniform distribution of the fluid in the fluid volume, i.e. across the width extent of the cell unit. A second fluid guidance insert 1153 is associated with a fluid exhaust port (also referred to as an outlet port). It will be understood that multiple ports for inlet and exhaust may be provided, each of which may be associated with a fluid guidance insert or multiple ports may be associated with a single fluid guidance insert (e.g., one fluid guidance insert for multiple inlet ports and a second fluid guidance insert for multiple exhaust ports).

[0194] The fluid guidance insert 1153 is configured flat (i.e., planar and as e.g., as a separate plate or component). In the assembled cell unit, a first surface of the fluid guidance insert 1153 is in direct contact with an opposed surface (first side) of the cell layer, i.e. the support plate 1114. A second surface of the fluid guidance insert 1153 is in direct contact with an opposed surface (second side) of the interconnect 1112. Thus, the fluid guidance inserts 1253 may transfer compression forces (represented by arrows in Fig. 11) between the cell layer and the interconnector plate 1112. This may increase the mechanical stability of the cell unit. Specifically, the fluid guidance inserts 1153 may prevent a deformation of the cell layer and the interconnect 1112.

[0195] In this example, the proximal end sections of the elongate slots 1154 are open. That is to say, the proximal end sections open into the hole 1156. In this example the distal end sections of the elongate slots 1154 are closed by a respective web 1162. This increases the mechanical stability of the fluid guidance insert 1153. The interconnect 1112 comprises several bridge dimples 1168 that extend away from the fluid guidance insert 1153 and that span a respective one of the webs 1162 to form a fluid bypass around that web 1162. Thus, the bridge dimples 1168 fluidically connect the respective elongate slot 1154 with the enclosed fluid volume around the respective web 1162. In this example, each one of the elongate slots 1154 is associated with a respective bridge dimple 1168. Alternatively, several webs 1162 may be associated with a common bridge dimple 1168 or several bridge dimples 1168 may be associated with a common web 1162. It will be understood that one elongate slot may be open at the distal end without compromising structural integrity of the fluid guidance insert 1153. In such cases no bridge dimple is needed for fluid communication between the port and the enclosed fluid volume via an elongate slot with an open distal end.

[0196] In this example, the bridge dimples 1168 are formed or pressed in the interconnect 1112. Preferably, the bridge dimples 1168 are formed or pressed at the same step as the upward protrusions 32 and downward protrusions 36 of the interconnect 1112 and / or the flanged perimeter of the tub-shaped interconnect 1112. Alternatively, the bridge dimples may be formed or pressed in the support plate 1114.On the first side of the interconnector plate 1112 (that is facing away from the enclosed fluid volume), the bridge dimples 1168 form protrusions that extend away from the enclosed fluid volume. The gaskets 34 are positioned directly adjacent to the protrusions of the bridge dimples 1168. The outer perimeter of the gaskets 34 is in direct contact with the protrusions. Thus, the protrusions restrict movement of the gaskets 34.

[0197] On the first side of the interconnector plate 1112 (that is the side facing away from the fluid guidance insert), the bridge dimples 1168 form protrusions that extend away from the fluid guidance insert and towards the second side of the cell layer, specifically in this example the second side of the support plate 1114, of a neighboring cell unit in a stack of cell units. The cell layer 1114 is provided with an insulating layer 1190, 1191 on the second side of the cell layer 1114 at least in locations facing the bridge dimples 1168 of the interconnect 1112 (the outwardly protruding, i.e., convex side of the bridge dimples). As discussed above, the EIL may take the form of one or more islands 1190, each island configured to face a corresponding bridge dimple (e.g., two islands facing corresponding two bridge dimples, three islands facing corresponding three bridge dimples, and so forth up to a maximum number of bridge dimples / islands (and channels) e.g., 8, 10, or 14 associated with each port). Alternatively, the EIL may take the form of a single island 1191 covering an area over which the cell layer is configured to face the bridge dimple(s). In this way, the island may correspond to coatings 690d, 790d, 890d, 990d, 1090d of the preceding examples. In some cases only the area of the cell layer facing the bridge dimples may be coated with the insulating layer 1190, 1191 because the convex side of the bridge dimples (i.e., first side of the interconnect) are the closest part of the interconnect, outside of the down protrusions 36, to the second side of the cell layer. However, an insulating layer may also be provided on other parts of the second side of the cell layer as described with reference to previous Figures.

[0198] In accordance with an aspect of the present disclosure, a method 1200 of manufacturing a cell layer for an electrochemical cell unit is hereby described, with reference to Figure 12. The method 1200 comprises providing a support structure having first and second sides, the support structure comprising a fluid communication region providing fluidic communication between the sides and a fluid blocking region, the second side of the support structure carrying a first electrode, or precursor therefor, provided over at least the fluid blocking region, wherein the support structure has a greater extent than the first electrode thereby forming an electrochemically inactive region (step 1210). The method further comprises applying a material on at least part of the fluid blocking region as a precursor for, and to form, an electrically insulating layer on the second side of the support structure across at least a portion of the EIR (step 1230). The insulating layer may be provided by coating or depositing it on said portion.

[0199] In some cases, the step of providing 1210 comprises providing a support structure wherein the second side of the support structure is further carrying an electrolyte, or precursor therefor, provided over at least the first electrode or precursor therefor. Alternatively, the method comprises a step 1220 of applying a material on at least part of the first electrode or precursor therefor, to form an electrolyte, or precursor therefor. Said electrolyte, or precursor therefor, may be applied over at least the fluid communication region and may extend across at least a portion of the EIR. Preferably, it surrounds the first electrode, or precursor therefor. Step 1220 may precede step 1230 where the electrolyte is disposed between the EIL and the support structure. Alternatively, step 1220 may follow step 1230where the EIL is disposed between the electrolyte and the support structure. If the electrolyte and EIL do not overlay one another then step 1220 may precede step 1230 and vice-versa.

[0200] In some examples, the method 1200 further comprises a step 1240 of sintering the material as a precursor for, and to form, the EIL, wherein the EIL comprises a ceramic material. The material as a precursor for the EIL may be co-sintered (step 1250) with one or both of the first electrode or the electrolyte (or respective precursors therefor). Where the electrolyte is not co-sintered with the EIL, the electrolyte or a precursor therefor may be deposited or coated upon the support structure (on the first electrode and EIL) after the step 1240 / 1250. Subsequently a functional layer and / or counterelectrode, or precursor therefor, may be coated or deposited on the support structure and sintered. Providing an electrically insulating layer may comprise using at least one of: (a) a wet deposition method such as screen printing, (b) a physical or chemical vapour deposition method, and (c) a wet spraying or plasma spraying method, to deposit the electrically insulating layer on a portion of the second side of the cell layer.

[0201] Sintering or co-sintering may comprise heating the cell layer to a temperature of at least 300°C, preferably at least 500°C, more preferably at least 800°C and at a temperature of less than 1200°C, preferably less than 1000°C, more preferably less than 900°C. Said heating step may be executed in an oxidising environment. (Co-)Sintering of the EIL and / or electrolyte and / or first electrode may be conducted at a higher temperature than sintering of the counter-electrode.

[0202] Providing the cell layer may comprise providing at least one port in the periphery, wherein the electrically insulating layer is provided between at least one of: (a) the at least one port and the EACR, and (b) the at least one port and the perimeter of the cell layer. The electrically insulating layer surround the at least one port.

[0203] The electrically insulating layer may comprise a dielectric layer. The electrically insulating layer may have a thickness of between 1 micrometer and 500 micrometers, , preferably between 1 micrometer and 100 micrometers, preferably between 1 micrometer and 50 micrometers, more preferably between 5 micrometers and 20 micrometers.

[0204] Using the cell layer, an electrochemical cell unit may be manufactured by providing the cell layer of and an interconnect, and joining (e.g., welding) the cell layer and interconnect to one another around their perimeter. The cell layer and interconnect together enclose a first fluid volume (where the cell unit is formed by the first side of the cell layer facing the second side of the interconnect) or second fluid volume (where the cell unit is formed by the second side of the cell layer facing the first side of the interconnect) therebetween.

[0205] Additional steps or preferable aspects in this method may include one or more of:

[0206] • Providing an interconnect may comprise providing, in the area that is adapted to face the electrochemically active cell region, conductive protrusions adapted to contact the electrochemically active cell region and space the interconnect from the electrochemically active cell region. Providing the conductive protrusions may comprise pressing or forming the interconnect to provide dimples on the first side of the interconnect, and / or printing or depositing conductive features on the first side of the interconnect. Providing theinterconnect may additionally or alternatively comprise providing a porous layer on the first side of the interconnect.

[0207] • The second side of the interconnect may be adapted to be exposed to a first fluid, and first side of the interconnect is adapted to be exposed to a second fluid different to the first fluid.

[0208] • The interconnect may be configured for use in an electrolysis cell unit or electrolysis cell stack. Using the electrochemical cell unit, an electrochemical cell stack of electrochemical cell units may be manufactured by providing at least two cell units and overlaying said cell units over one another in a stacking direction wherein the first side of a first interconnect faces the second side of a first support structure (e.g., forming a first fluid volume therebetween, the first fluid volume in fluidic communication with the first electrode via the fluid communication region) and the first side of the first interconnect faces the second side of a second support structure (the first interconnect may contact the EACR on the second support structure). The first interconnect and the first support structure may be part of (or form) a first electrochemical cell unit. The second support structure may be part of a second electrochemical cell unit (also comprising a second interconnect). A second fluid volume may be formed between the first side of the first interconnect and the second side of a second support structure, in fluidic communication with the counter-electrode.

[0209] Figs. 13-25 are schematic cross-sectional views which show detail of the boundary between the EACR and the EIL, wherein the EIL may (in some cases) overlay or underlay at least one of the layers which form the EACR. Such overlay or underlay of the EIL across at least one of the layers of the EACR is typically across at least part of the EIR, and may only be across the fluid blocking region of the support structure. In other words, it is preferable that the EIL terminates at a boundary between the EACR and the EIL. Accordingly, the EIL may terminate at a boundary between the fluid communication region and the fluid blocking region, or within a threshold distance therefrom. Said threshold distance may be at most 5 mm, optionally 3 mm, optionally 1 mm, optionally 0.7 mm, optionally 0.5 mm, optionally 0.3mm. Said threshold distance may be dependent upon lateral fluidic transfer properties of the first electrode, which are derivable by analysing pore size, pore alignment, pore connectivity in the first electrode and thickness thereof. Alternatively, when the fluid communication region is provided by a porous region, the threshold distance may be taken as an average distance between pores in the porous region. Preferably, the EIL does not overlay or extend over the fluid communication region. The electrically insulating layer (EIL) comprises a dielectric layer or a ceramic layer. In some examples, EIL comprises one or more of zirconia (e.g., YSZ), hafnium, alumina, glass-ceramic.

[0210] Fig. 13 is a schematic cross-sectional view through a cell unit comprising a cell layer 1314 and an interconnect 1312. The interconnect is depicted in simplified form, but may be similar to that described previously, for example with respect to Fig. 5, but could alternatively comprise a spacer and interconnect as in Fig. 8. The cell layer 1314 comprises a support structure, in this case a (e.g., metal) support plate with a porous region 1302 and a non-porous region 1301. The porous region provides fluid communication between the first and second sides of the support structure (upward and downward facing, respectively, in Fig. 13). The non-porous region blocks fluid communication between the first and second sides of the support structure. The support structure carries a first electrode 1315, an electrolyte 1320, and a counter-electrode 1325. Areas of the first electrode 1315, electrolyte 1320, and counter-electrode 1325 which overlay the porous region 1302 (and, as discussed above, may be within the threshold distance of the boundary between the porous and non-porousregions) are referred to as the EACR 1305. The EIR 1310 is outside the EACR 1305, across areas where the EACR does not cover. In Fig. 13, the first electrode 1315 and the electrolyte 1320 partially extend across the EIR 1310 - across the non-porous region 1301. The electrolyte 1320 overlays and surrounds the first electrode 1315 to provide a fluid barrier between a first fluid volume (e.g., fuel volume) in fluidic communication with the fuel electrode 1315 via the porous region 1302. The electrolyte may be a multilayer electrolyte such as described with reference to the subsequent figures. Each of the layers may be comprised of multiple sub-layers (sub-layers may have varying compositions). The electrolyte comprises doped ceria, preferably rare earth (e.g., one or more of Gd, Pr, or Sm) doped ceria. The counter-electrode 1325 is depicted as having substantially the same extent as the porous region 1302 (i.e., a boundary or edge of the counter-electrode 1325 is aligned with the boundary or edge of the porous region 1302)), however it may have a smaller or larger extent than the porous region. For example, a boundary of the counter-electrode 1325 may be within the threshold distance of the boundary between the porous region 1302 and the non-porous region 1301.

[0211] An EIL 1390 is disposed across the EIR 1310. The EIL 1390 is provided on the second side of the support structure, in some areas over layer(s) between the EIL 1390 and the support structure itself. Over part of the EIR 1310, the electrolyte 1320 is disposed between the EIL 1390 and the support structure. The EIL 1390 contacts the electrolyte 1320 in these areas. Over part of the EIR 1310, the first electrode 1315 (and the electrolyte) is disposed between the EIL 1390 and the support structure. The EIL 1390 extends to an edge or perimeter of the support structure (and cell layer 1314) - for part of its extent the electrolyte 1320 is not between the EIL 1390 and the support structure, and in these areas the EIL 1390 may sit on the support structure or on a further layer (not shown) which underlies the EACR, extension of the layer(s) of the EACR over the EIR 1310, and the EIL 1390. The EIL 1390 extends to and abuts the counter-electrode 1325 - this may be achieved through accurate printing methods or may be achieved by first depositing the EIL 1390 using the EIL 1390 as a stencil for depositing the counterelectrode 1325 or by first depositing the counter-electrode 1325 and using the counter-electrode 1325 as a stencil for depositing the EIL 1390. In some cases, the EIL 1390 may not abut the counter-electrode 1325 due design or to manufacturing tolerances associated with different methods for depositing the respective layers. As with the previous examples, the EIL 1390 is electrically insulating. It may also be ionically insulating (e.g., it may also block oxygen or hydrogen ions). The EIL 1390 is preferably non-porous, e.g., having a similar porosity to the electrolyte. The EIL 1390 of Fig. 13 sits on the electrolyte and so may comprise may be co-sintered with the counter-electrode, in which case it preferably comprises alumina due to the relatively low sintering temperature of alumina. However, the EIL may comprise other materials (e.g., zirconia) to match the sintering temperature of the counter-electrode. Alternatively, the EIL may be co-sintered with at least one of the electrolyte and the first-electrode. Fig. 14 is a schematic cross-sectional view through an example cell layer 1414. No interconnect is shown in Fig. 14 and the subsequent Figures, but it will be understood that a similar interconnect to that described with reference to Fig. 13 may be attached to the cell layer described with reference to Fig. 14 (and subsequent Figures) to form a cell unit. Cell layer 1414 is generally similar to cell layer 1314 and only differences will be described. The cell layer 1414 comprises a multi-layer electrolyte, formed from a main electrolyte layer 1420 and a functional layer, also referred to as an interlayer (which together may simply be referred to as "electrolyte"). The main electrolyte layer 1420 may be generally similar to the electrolyte 1320 of cell layer 1314. The main electrolyte is ionically conductive - i.e., it may allow oxygen ions to pass but block molecular transport and preferably electronictransport. The functional layer may itself comprise one or both of a first layer 1421 and a second layer 1422. The first layer 1421 is an electron-blocking layer, and comprises Zr. The second layer 1422 is an interfacial layer between the electrolyte and the counter-electrode, which may promote adhesion therebetween and prevent diffusion of species (e.g., Sr from the counter-electrode) from the counterelectrode to the electrolyte (e.g., first layer 1421 or the main electrolyte 1420) and / or vice-versa, and may comprise doped ceria. The electrolyte (i.e., main electrolyte plus functional layer) of cell layer 1414 extends across the whole of the EIR 1310, as does the EIL 1390. The EIL 1390 is disposed on the electrolyte, specifically on the functional layer (second layer 1422 thereof).

[0212] In the subsequent examples, a multilayer electrolyte comprising the functional layer is described. However, the skilled person will understand that the functional layer (or one sub-layer thereof) is not necessary in all examples.

[0213] Fig. 15 is a schematic cross-sectional view through an example cell layer 1514. Cell layer 1414 is generally similar to the previously described cell layers and only differences will be described. In cell layer 1514, the functional layer (depicted as first layer 1421 and second layer 1422) extend across the EACR 1305 but do not extend across the full extent of the (main) electrolyte 1420. The electrolyte 1420 extends across a portion of the EIL 1310 but the functional layer extends over a lesser extent of the EIL 1310 than the electrolyte 1420. The EIL 1390 extends to an edge or perimeter of the support structure (and cell layer 1514) - for part of its extent the electrolyte 1420 is not between the EIL 1390 and the support structure, and in these areas the EIL 1390 may sit on the support structure or on a further layer (not shown) which underlies the EACR, extension of the layer(s) of the EACR over the EIR 1310, and the EIL 1390. The EIL sits on the functional layer across the functional layer's extent in the EIR 1310, and sits on top of the electrolyte 1420 where the functional layer is not present. Further, and merely as an example of variations described with respect to Fig. 13, the counter-electrode 1325 has a lesser extent than the porous region 1305 (but their boundaries may be within a threshold distance of one another).

[0214] Fig. 16 is a schematic cross-sectional view through an example cell layer 1614. Cell layer 1614 is generally similar to the previously described cell layers and only differences will be described. Similar to cell layer 1514, the EIL 1390 of cell layer 1614 extends over the main electrolyte 1420 but does not extend across the area covered by the functional layer. Its termination is at the step of the electrolyte 1420 over the first electrode 1315.

[0215] Fig. 17 is a schematic cross-sectional view through an example cell layer 1714. Cell layer 1714 is generally similar to the previously described cell layers and only differences will be described. The EIL 1390 of cell layer 1714 is disposed between the (main) electrolyte 1420 and the functional layer (specifically the first layer 1421 thereof). The EIL 1390 is above the (main) electrolyte 1420 over the portion of the main electrolyte which extends outside the EACR 1305 and across the EIR 1310 (which may correspond to the non-porous region 1301, as shown).

[0216] Fig. 18 is a schematic cross-sectional view through an example cell layer 1814. Cell layer 1814 is generally similar to the previously described cell layers and only differences will be described. The counter-electrode 1325 of cell layer 1814 extends past the boundary of the porous region 1302 and partially across the non-porous region 1301 (and EIR 1310). In these areas, the EIL 1390 overlays the counter-electrode 1325. In other words, the counter-electrode 1325 is between the EIL 1390 and thesupport structure. The EIL of cell layer 1814 prevents electrical contact outside of the EACR and may be relatively straightforward to apply, since it may overlay the layers of the EACR and their extensions in to the EIR 1310. Cell layer 1814 may also increase the effective area of the EACR. However, the functionality of prevention of application of a voltage to the electrolyte 1420 outside of the EACR 1305 may be partially diminished in cases where the counter-electrode exhibits lateral conductivity.

[0217] Fig. 19 is a schematic cross-sectional view through an example cell layer 1914. Cell layer 1914 is generally similar to the previously described cell layers and only differences will be described. Cell layer 1914 comprises a two-part support structure, formed from a non-porous plate (e.g., metal plate) 1901 and a first-electrode 1915 (e.g., fuel electrode) supported EACR 1305. The EACR 1305 is disposed above a hole through the non-porous plate - in other words, the plate forms a frame around the edge of the first electrode 1915. The first electrode is self-supporting and so can be handled (e.g., with the electrolyte 1320 and counter-electrode 1325 above) independently of the plate 1901 until attached to said plate. It will be understood that the electrolyte may instead be self-supporting with the electrodes deposited thereon. As with previous examples, the EIL 1390 covers the extension of the electrolyte 1320 and first electrode 1915 outside of the EACR 1305, with the first electrode 1915 and in some areas electrolyte 1320 between the EIL 1390 and the support structure. Preferably, the EIL is non-porous and extends across and surrounds the entirety of the first electrode's extent over the fluid blocking region, to seal the first electrode and prevent fluidic communication (via the first electrode's porosity) between the two sides of the cell layer. The EIL 1390 may also cover the exposed face of the plate 1901 (not shown).

[0218] Fig. 20 is a schematic cross-sectional view through an example cell layer 2014. Cell layer 2014 is generally similar to the previously described cell layers (particularly Figs. 13-18) and only differences will be described. The functional layer (first layer 1421 and second layer 1422) extends to the perimeter of the cell layer -i.e., over the EIR 1310- whereas the electrolyte 1420 only partially extends towards the perimeter (e.g., merely surrounding the first electrode 1315 and contacting the EIR 1310 / non-porous region 1301 of the support structure to seal the first electrode and porous region). The EIL 1390 is disposed above the functional layer. In other words the functional layer is disposed between the EIL 1390 and the support structure (across the EIR 1310). The functional layer is disposed on the support structure (or another layer beneath all layers including the EACR) towards the perimeter of the cell layer. The counter-electrode 1325 is depicted as overlapping the EIL 1390 at the interface therebetween partly because the extent of the counter-electrode 1325 is greater than the extent of the first electrode 1315. As with other examples, this need not be the case - the counterelectrode may have its boundary approximately at or within the boundary of the first electrode 1315 or porous region 1302. In latter cases, the counter-electrode 1325 does not overlap the EIL 1390. Figs. 13 to 20 are examples in which the electrolyte is between the EIL 1390 and the support structure, over at least part of the extent of the EIL 1390. Figs. 21 to 25 are examples in which the EIL 1390 is disposed between the electrolyte (at least one layer thereof) and the support structure, over at least part of the extent of the electrolyte (at least one layer thereof).

[0219] Fig. 21 is a schematic cross-sectional view through an example cell layer 2114. Cell layer 2114 is generally similar to the previously described cell layers and only differences will be described. The electrolyte (multilayered in the example, comprising main electrolyte 1420, and functional layer itself comprising first layer 1421 and second layer 1422) of the cell layer 2114 extends to the perimeter ofthe cell layer 2114. Outside of the EACR 1305, the EIL 1390 is disposed between the (main) electrolyte 1420 and the supports structure, specifically the non-porous region 1301 of the support structure. The EIL 1390 abuts the first electrode 1315 - i.e., their boundaries coincide. The EIL 1390 prevents application of a voltage across the electrolyte 1420. A thickness of the EIL 1390 may be substantially equal to a thickness of the first electrode 1315, in turn meaning that the electrolyte (and functional layer) has substantially no step therein, thereby reducing mechanical stress in said layers. The EIL in this example (and subsequent examples in Figs. 22-25) may be non-porous to seal the first electrode and prevent fluidic communication (via the first electrode's porosity) between the two sides of the cell layer. Fig. 21 is an example in which the EIL sits between the electrolyte and the support structure, and so the EIL may be co-sintered with one or both of the first electrode and the electrolyte. A zirconiabased EIL may be preferable due to sintering with the first electrode and / or first electrode, which may typically sinter at a higher temperature than the counter-electrode.

[0220] Fig. 22 is a schematic cross-sectional view through an example cell layer 2214. Cell layer 2214 is similar to cell layer 2114 of Fig. 21 except that the (main) electrolyte 1420 does not extend to the perimeter of the cell layer 2214. As a result, the functional layer sits on the EIL 1390 across part of the EIR 1310. Fig. 23 is a schematic cross-sectional view through an example cell layer 2314. Cell layer 2314 is generally similar to the previously described cell layers and only differences will be described. The electrolyte 1315 of cell layer 2314 substantially ends at the boundary between the EACR 1305 and the EIR 1310. The first layer 1421 of the functional layer extends partially across the EIR 1310, while the second layer 1422 substantially ends at the boundary between the EACR 1305 and the EIR 1310. The EIL 1390 is between the first layer 1421 and the support structure across the portion of the EIR 1310 covered by the first layer 1421. The EIL 1390 extends to the perimeter of the cell layer 2314.

[0221] Fig. 24 is a schematic cross-sectional view through an example cell layer 2414. Cell layer 2414 is generally similar to the previously described cell layers and only differences will be described. The functional layer substantially ends at the boundary between the EACR 1305 and the EIR 1310. The functional layer does not overlay the EIR. The (main) electrolyte 1420 extends past the boundary of the EACR 1305 and the EIR 1310 - and at least partially over the EIR 1310 and the non-porous region 1301. In this way, the EIL 1390 is disposed between the electrolyte 1315 and the support structure. Fig. 25 is a schematic cross-sectional view through an example cell layer 2514. Cell layer 2514 is generally similar to the previously described cell layers and only differences will be described. In this example, the (main) electrolyte 1420 and the functional layer (both of first layer 1421 and second layer 1422) extend to the perimeter of the cell layer 2514. The counter-electrode 1325 extends at least partially across the EIR 1310 and the non-porous region 1301. The EIL 1390 extends to the perimeter of the cell layer 2514 and acts to prevent application of voltage across the electrolyte outside of the EACR.

[0222] The present invention is not to be limited by the above-described aspects and examples, and that many variations are within the scope of the appended claims. The various aspects and examples may be combined if necessary and appropriate. The drawings serve as exemplary illustrations of the invention only, to aid understanding of the invention.

Claims

35CLAIMS1. A cell layer for an electrochemical cell unit comprising:a support structure having first and second sides, the support structure comprising a fluid communication region providing fluidic communication between the sides and a fluid blocking region, the second side of the support structure carrying a first electrode, an electrolyte and a counter-electrode provided and forming an electrochemically active cell region (EACR) over at least a portion of the fluid communication region;wherein the support structure has a greater extent than the EACR thereby forming an electrochemically inactive region (EIR); andwherein an electrically insulating layer (EIL) is provided on the second side of the support structure across at least a portion of the EIR and is not provided across the EACR.

2. The cell layer of claim 1, wherein at least one of the first electrode, the electrolyte and the counter-electrode extends past an edge of the fluid communication region and at least partially across the fluid blocking region.

3. The cell layer of claim 2, wherein the electrolyte extends past the edge of the fluid communication region.

4. The cell layer of claim 3, wherein an extent of the EIL is at least coincident with an extent of the electrolyte across the fluid blocking region.

5. The cell layer of any one of the preceding claims, wherein the EIL contacts the electrolyte.

6. The cell layer of any one of the preceding claims, wherein the EIL is disposed between the electrolyte and the support structure.

7. The cell layer of claim 6, wherein the first electrode is disposed between the EIL and the support structure.

8. The cell layer of claim 6, wherein the EIL surrounds the first electrode.

9. The cell layer of any one of claims 1 to 5, wherein the electrolyte is disposed between the EIL and the support structure.

10. The cell layer of claim 9, wherein the EIL does not contact the counter-electrode.

11. The cell layer of claim 9, wherein the EIL surrounds the counter-electrode.

12. The cell layer of any one of the preceding claims, wherein the counter-electrode does not overlap the EIL.

13. The cell layer of any one of claims 1 to 5 and 9, wherein the counter-electrode is disposed between the EIL and the electrolyte.

14. The cell layer of any one of the preceding claims, wherein the EIL begins within 5 mm of a boundary between fluid communication region and fluid blocking region and extends over the at least a portion of the fluid blocking region.

15. The cell layer of any one of the preceding claims, wherein the first electrode does not extend past the boundary between fluid communication region and fluid blocking region.

16. The cell layer of any one of the preceding claims, wherein the electrolyte comprises doped ceria.

17. The cell layer of any one of the preceding claims, wherein the electrolyte is multi-layered, and comprises a main electrolyte layer and a functional layer.

18. The cell layer of claim 17 when dependent on one of claims 9 to 11, wherein the functional layer is disposed between the EIL and the main electrolyte layer.

19. The cell layer of any one of the preceding claims, wherein the electrically insulating layer comprises a dielectric layer or a ceramic layer.

20. The cell layer of claim 19, wherein the EIL comprises a ceramic material and is co-sintered with at least one of the electrolyte and the counter-electrode.

21. The cell layer of any one of the preceding claims, wherein the first electrode is a fuel electrode.3622. The cell layer of any one of the preceding claims, wherein the fluid blocking region comprises at least one fluid port for delivery of fluid to or exhaust of fluid from the first electrode or the counter-electrode.

23. The cell layer of claim 22, wherein the EIL is provided between the EACR and the at least one fluid port.

24. The cell layer of claim 22 or 23, wherein the EIL is provided between the at least one fluid port and a perimeter of the cell layer.

25. An electrochemical cell unit comprising the cell layer of any one of the preceding claims and an interconnect, the interconnect having a first side and a second side, wherein the second side of the interconnect faces the first side of the support structure or the first side of the interconnect faces the second side of the support structure.

26. The electrochemical cell unit of claim 25, wherein the interconnect comprises dimples which form protrusions on the first side and which contact the EACR of the cell layer of the cell unit or which are configured to contact a cell layer of a neighboring cell unit in a stack of cell units.

27. The electrochemical cell unit of claim 25 or 26, wherein the interconnect has at least one bridge dimple that forms a protrusion on the first side of the interconnect and a corresponding depression on the second side of the interconnect, the depression for fluid guidance on the second side of the interconnect and the electrically insulating layer is provided on the cell layer at a location which faces the at least one bridge dimple of the cell unit or which is configured to face an at least one bridge dimple of a neighboring cell unit in a stack of cell units.

28. The electrochemical cell unit of claim 27 when dependent claim 24, wherein the at least one fluid port is in fluidic communication with a first fluid volume provided between the second side of the interconnect and the first side of the support structure, the electrochemical cell unit further comprising a fluid guidance insert disposed in the first fluid volume, said fluid guidance insert comprising a plurality of elongate slots formed therein, said elongate slots defining a fluid channel system for conveying fluid between the at least one fluid port and the first fluid volume via the at least one bridge dimple.

29. The electrochemical cell unit of claim 28, wherein the elongate slots each have a distal end section wherein the distal end section of at least one of the elongate slots is closed by a web of the fluid guidance insert, and wherein the at least one bridge dimple extends away from the fluid guidance insert and spans said web to form a fluid bypass around the web.

30. An electrochemical cell stack comprising a plurality of electrochemical cell units each according to any one of claims 25 to 29, wherein the first side of the interconnect of a first electrochemical cell unit faces the second side of the support structure of a second, neighboring, electrochemical cell unit or the first side of the interconnect of the first electrochemical cell unit faces the first side of the support structure of the second, neighboring, electrochemical cell unit.

31. A method of manufacturing a cell layer for an electrochemical cell unit comprising providing a support structure having first and second sides, the support structure comprising a fluid communication region providing fluidic communication between the sides and a fluid blocking region, the second side of the support structure carrying a first electrode, or precursor therefor, provided over at least the fluid communication region, wherein the support structure has a greater extent than the first electrode thereby forming an electrochemically inactive region (EIR); andapplying a material on at least part of the fluid blocking region as a precursor for, and to form, an electrically insulating layer (EIL) on the second side of the support structure across at least a portion of the EIR.

32. The method of claim 31, wherein the second side of the support structure further carries an electrolyte, or precursor therefor, provided over at least the first electrode or precursor therefor.

33. The method of claim 31 or 32, wherein the EIL comprises a ceramic material, the method further comprising sintering the material as a precursor for, and to form, the EIL.

34. The method of claim 33, wherein the sintering the EIL comprises co-sintering the EIL with at least the first electrode.

35. The method of claim 33 or 34 when dependent on claim 32, wherein the sintering the EIL comprises co-sintering the EIL with at least the electrolyte.

36. A method of manufacturing an electrochemical cell unit comprising providing the cell layer of any one of claims 1 to 24 or the cell layer as manufactured by any one of claims 31 to 35 and an interconnect, and joining the cell layer and interconnect to one another around their perimeter.

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