Electrolysis apparatus and method

Abstract

An electrolyser apparatus is provided comprising an enclosure having containing walls defining a fuel space, and an inlet for receiving input fuel such as H2O to be contained in said fuel space. Electrochemical cells located substantially within said enclosure at least partially convert fuel such as H2O into first and second products such as hydrogen and oxygen. The cells are exposed to fuel in the fuel space. There is a first exhaust pathway to receive the first product produced by the electrochemical cells and transport it to the exterior of the enclosure and a second exhaust pathway to receive the second product and transport it to the exterior of the enclosure. The arrangement of each cell in an array preferably defines an active fuel volume adjacent to a fuel side of the cell. At least part of the active fuel volume is open to the fuel space defined by the enclosure. In this way, fuel such as steam may be present between multiple cell stacks and all around the cells, in equal concentration at all points in the fuel volume.

Description

[0001] Electrolysis Apparatus and Method

[0002] Field of the Disclosure

[0003] This disclosure relates to an electrolysis apparatus and method, for separating a consumable product (referred to herein as "fuel") such as water (H2O) or carbon dioxide into elements such as hydrogen and oxygen through the application of an electric voltage.

[0004] Background

[0005] EP4070399A1 describes solid oxide electrolyser cell units that can separate hydrogen and oxygen from water, or carbon monoxide and oxygen from carbon dioxide. They may be tubular or planar in configuration. Planar cell units may be arranged overlying one another in a stack arrangement, for example 100-300 cell units in a stack. Each cell comprises a metal-support with electrochemically active cell layers deposited on and supported by a metal support plate that has a porous region surrounded by a non-porous region with the active layers being deposited upon the porous region so that gases may pass through the pores from one side of the metal support plate to the opposite side to access the active layers coated thereon.

[0006] Summary

[0007] According to a first aspect of the invention there is provided an electrolyser apparatus comprising: an enclosure having containing walls defining a fuel space, and an inlet for receiving input fuel including a reactant to be contained in said fuel space; a plurality of electrochemical cells adapted to at least partially convert the reactant into a first product and a second product, wherein said electrochemical cells are located substantially within said enclosure; a first exhaust pathway adapted to receive the first product produced by said electrochemical cells and transport it to the exterior of the enclosure; and a second exhaust pathway adapted to receive the second product produced by said electrochemical cells and transport it to the exterior of the enclosure.

[0008] Typically the reactant is H2O (usually in the form of steam) and the first product is hydrogen and the second product is oxygen. The example of H2O electrolysis simplifies nomenclature and aids understanding, and therefore the terms "steam", "hydrogen" and "oxygen" may be used in the specification as indicative of the reactant, the first product and the second product respectively, and should be construed accordingly. Other reactants which may undergo electrolysis however include carbon dioxide and nitrogen dioxide. In some cases multiple reactants can be electrolysed together (e.g. co-electrolysis of H2O and carbon dioxide). Each cell of the plurality of electrochemical cells may be adapted to at least partially convert the reactant into the first product and the second product. As discussed, the reactant - or fuel - is preferably a gas as are the first and second products.

[0009] According to embodiments of this aspect of the invention, there is no need to provide an inlet manifold, or inlet channels or pathways, for fuel (typically steam) to feed the individual cells. Rather the walls of the enclosure serve to contain a volume of fuel, and the cells are located substantially within, and surrounded by that fuel volume. In this way, there is a better distribution of fuel across the cells and less risk of blockage. Additionally the design of the cells and all their supporting structure can be simplified.

[0010] A plurality of cells are typically grouped or arranged together in arrays, or stacks, according to preferred embodiments. Such stacks or arrays preferably provide physical support to maintain the spatial arrangement of cells, and preferably define active fluid volumes adjacent to the surfaces of the cells, in which reactants or products of the electrolysis process are consumed or produced respectively.

[0011] Preferably a plurality of cell arrays are included in the enclosure. In this way more than one cell array is substantially located within the volume of fuel provided by the enclosure, and therefore differences in pressure and temperature between arrays associated with inlet manifolds are reduced. Furthermore, an increased number of cells can be provided with a common fuel supply mechanism (i.e. the enclosure) and it will be understood that this allows reduced materials costs and a more compact form factor with fewer components used.

[0012] In embodiments the cells are thin planar structures having a first side and a second side. In embodiments the first side is designed to be exposed to a reactant or fuel stream such as steam, and the second side produces oxygen through the electrolysis process (powered by application of an electric current / voltage). The cells can be formed on a porous support or can be self-supporting. In preferred embodiments the cells are substantially flat, however other geometries are possible such as curved planar structures e.g. tubes.

[0013] Where cells are grouped in an array, or stack, such array or stack preferably defines for each cell, an active fuel volume to which the first side (fuel side) of said cells are exposed. Said active fuel volume, in use, guides fuel across the first surface of the cells (where electrolysis may occur), towards the first exhaust pathway. In preferred embodiments, at least a part of said active fuel volume is open to said enclosure, i.e. there is no dedicated component or components designed to guide the flow of fuel from the enclosure into the active fuel volume. Advantageously this reduces the risk of blockage as there are fewer constrictions in the fuel path to the active fuel volume(s). The active fuel volume may be adjacent to a fuel side of each cell in the array (i.e., in fluidic communication with the fuel electrode, also referred to as a cathode for electrolysers). In other words, the active fuel volume may comprise a volume in fluidic communication with the fuel electrode, and at least partially enclosed by the cell unit, or at least partially enclosed by a cell unit and a neighboring cell unit.

[0014] The active fuel volume is typically elongate having an entry end and an exit end. In embodiments, the entry end is open to the enclosure, and the exit end is closed to the enclosure but feeds into the first exhaust pathway.

[0015] There is preferably provided a first exhaust manifold. Such manifold is adapted to collect and combine the first product (and possibly unused fuel) produced from multiple cells and transport it to the exterior of the enclosure. At least part of the first exhaust pathway may comprise the first exhaust manifold. In embodiments where cells are grouped in stacks, each cell stack is provided with a first exhaust manifold, and the first exhaust manifold may be integrated with the array or stack, or mounted to it, and is substantially contained within the enclosure. It is possible that the first exhaust manifold constitutes the first exhaust pathway, for example where a cell array is mounted directly to or integral with a wall of the enclosure.

[0016] Such stack or array preferably also defines an active oxygen volume to which said second side of said cells are exposed (i.e. this is the volume in which oxygen is generated during electrolysis of steam). Said active oxygen volume, in use, guides oxygen produced (and possibly also any sweep gas if present) from the surface of the cells, towards the second exhaust pathway. In preferred embodiments, said active oxygen volume is fl uidically sealed from said enclosure.

[0017] There is preferably provided a second exhaust manifold. Such manifold is adapted to collect and combine oxygen (and possibly also any sweep gas if present) produced from multiple cells and transport it to the exterior of the enclosure. At least part of the second exhaust pathway may comprise the second exhaust manifold. The second exhaust manifold may be integrated with the array or stack, or mounted to it, and is substantially contained within the enclosure. It is possible that the second exhaust manifold constitutes the second exhaust pathway, for example where a cell array is mounted directly to or integral with a wall of the enclosure.

[0018] The first and second exhaust pathways preferably maintain separation of produced first product (e.g., hydrogen) and second product (e.g., oxygen) respectively from said fuel in said enclosure. In this way the products of electrolysis can be prevented from mixing with fuel in the enclosure. Stacks or arrays of cells may further include electrical connections and pathways for providing current to the cells. Each array may have dedicated power connection terminals to provide power to cells of that array. The terminals allow feed lines or bus bars routing electrical power from outside the enclosure to be connected to each array. In embodiments therefore, the enclosure includes feed throughs in the enclosure walls, to allow an electrical conductor to pass through, while maintaining a fluidic seal. The enclosure however is preferably electrically inactive, which is to say it is electrically isolated from the cells. As part of the structure of the array, cells are typically arranged in series in a stack, and arrays typically comprise cells or cell units in electrical contact with one another to allow current from the terminals to travel through cells of an array.

[0019] According to embodiments, the enclosure is a pressure vessel, capable of maintaining the enclosed fuel at elevated pressures, i.e. sealed from, and at a pressure above its surroundings, which are typically at atmospheric pressure. The enclosure may be adapted to be pressurized to approximately 1.1 bar or greater, 1.2 bar or greater, 1.5 bar or greater, 2 bar or greater, 3 bar or greater, or 5 bar or greater, depending on the application. In most cases, it is considered that pressures above 10 bar offer no significant advantage, and so the enclosure is preferably adapted to maintain a pressure of 10 bar or less, 8 bar or less, or 6 bar or less. The enclosure is configured such that the pressure within it can be maintained substantially constant during use (or steady state use outside of startup and shut down operations) of the electrolyser system.

[0020] In embodiments the array or stack is contained substantially within the enclosure, although some parts of the array or stack may be in contact with, or integral with part of the enclosure walls. Preferably the pressure in the enclosure (but not necessarily in the stack or array, or the active fuel or oxygen volumes) is substantially uniform throughout in use. Because in embodiments, the active fuel volume is open to said enclosure there is very little or substantially no pressure drop between the fuel in the enclosure and the fuel entering the active fuel volume. Furthermore, the pressure experienced by each active fuel volume is substantially equal.

[0021] In embodiments, the inlet is adapted to receive input fuel at elevated pressure from a pressurized fuel source, such as a steam generator. The pressure in the enclosure is preferably maintained by regulating the flow of exhaust products exiting the enclosure, for example using a back pressure regulator. It is however possible that alternative embodiments use a pressure reducing regulator at the enclosure input (i.e. a regulator which control downstream pressure).

[0022] Separate back pressure regulators can be used for both the first exhaust pathway and the second exhaust pathway, however it has been found to be advantageous to provide an arrangement whereby both pathways are controlled relative to a common reference pressure. The pressure regulator may be an arrangement having a single reference pressure biased diaphragm regulating the first and second outlets, or whereby separate diaphragms are employed but controlled by a common reference pressure. In such embodiments, the pressure upstream of both pathways can be accurately maintained equal (even if there is variance in the absolute pressure upstream of the regulator, a pressure differential is avoided). In arrangements having stacks or arrays of cells defining active fuel and oxygen volumes, balancing pressure of these two active volumes has been found to reduce degradation and / or improve reliability of the electrochemical cells. This is particularly useful for solid oxide cells (i.e., solid oxide electrolyser cells, SOEC), and more particularly useful for metal supported solid oxide cells.

[0023] In embodiments, an oxygen source (or source of air, nitrogen, or inert gas), is connected to the second outlet, upstream of the pressure regulator. The oxygen source is preferably adapted to provide oxygen at a pressure at or above the reference pressure of the pressure regulator. The oxygen source can be used to ensure balanced pressure between the outlets when there is insufficient production of oxygen by the cells to maintain the appropriate pressure at the second outlet.

[0024] In embodiments, depending on the conversion rate of electrolysis, hydrogen in the first exhaust pathway may be mixed with fuel (typically steam). Preferably however there is only a single inlet to the enclosure, or at least in steady state operation no reactant or fluid is provided to the enclosure and cells other than fuel / steam). In this way, the electrolyser system can be simplified as it does not require any manifolding upstream of the cells. In such cases, output fluid in the second exhaust pathway is substantially pure oxygen, or at least 90% pure by weight.

[0025] Conductors to allow current to be supplied to the cells may pass through the enclosure walls in embodiments, but the enclosure is preferably electrically inactive, which is to say it does not have any electrical functionality, and is preferably electrically isolated from the cells. In embodiments where the enclosure is made of a conductor such as metal, it is preferably electrically isolated from the input current to the electrolyser.

[0026] Preferably the cells are solid oxide cells, and more preferably metal supported solid oxide cells. Advantageously the cells are adapted to operate at approximately 400 to 650 degrees C, preferably 450 to 600 degrees C, more preferably 500 to 600 degrees C.

[0027] Examples and embodiments will now be described, by way of example only, with reference to the drawings. Brief Description of the Drawings

[0028] Figure 1 is a schematic diagram of an electrolysis cell as is known in the art.

[0029] Figure 2 is a schematic diagram of an electrolysis cell in accordance with the present disclosure.

[0030] Figure 3 is a cross-section elevation of a multi-stack array of electrolysis cells in accordance with the present disclosure.

[0031] Figure 4 is a cross section, in plan view, of the array of Figure 3.

[0032] Figure 5 is an exploded perspective view of a cell in accordance with the present disclosure.

[0033] Figure 6 is an exploded perspective view of an alternative cell array in accordance with the present disclosure.

[0034] Figure 7 is a schematic diagram of a control system in accordance with the present disclosure.

[0035] Detailed Description

[0036] In the following description, references to water, steam and fuel may be interchangeable. Water (in the form of steam) may be referred to as "fuel" in the sense that it is used up in the electrolysis reaction. Alternative fuels can be used such as carbon dioxide or nitrogen dioxide, and the fuel may comprise more than one of said water, carbon dioxide or nitrogen dioxide.

[0037] Figure 1 shows a typical electrolysis cell 103, having a steam inlet 101, an air inlet 102, a hydrogen (H2) gas outlet 105 and an oxygen (O2) gas outlet 106.

[0038] In operation of the cell 103, steam enters the inlet 101 and air is able to enter the inlet 102. After undergoing electrolysis in the cell 103, the products released are F and O2 at the respective outlets.

[0039] Figure 2 shows an electrolysis apparatus having an electrolysis cell 204. The cell 204 has a steam inlet 201, a hydrogen (H2) gas outlet 207 and an oxygen (O2) gas outlet 208. The cell is contained within a vessel 203 having a purge / sweep inlet 202 (for air, O2, N2 or the like) and a steam inlet 210. The cell 204 is fully enclosed within the vessel 203.

[0040] The vessel 203 may be a pressure vessel, adapted to be pressurized to approximately 1.2 bar (120k Pascals or about 1.2 atmospheres) or greater, 1.5 bar or greater, 2 bar or greater, 3 bar or greater, or 5 bar or greater, depending on the application. In most cases, it is considered that pressures above 10 bar offer no significant advantage, and so the vessel is preferably adapted to maintain a pressure of 10 bar or less, 8 bar or less, or 6 bar or less. The enclosure is configured such that the pressure within it can be maintained substantially constant during use (or steady state use outside of start-up and shut-down operations) of the electrolyser system.

[0041] At steady operating pressure, the steam at the steam inlet 201 is the only input into the vessel 203 and the cell 204. When the cell comprises an oxygen ion conducting electrolyte and when voltage is applied to the cell and the cell performs electrolysis, hydrogen is generated and emerges from the H2 outlet 207. Oxygen is output from outlet 208.

[0042] Figure 3 shows a cross sectional view of an electrolyser apparatus 300 comprising a multi stack array, within a vessel 309 having, a H2O inlet 301, a first stack 312 of electrolysis cells and a second stack 322 of electrolysis cells. The vessel 309 has walls 302 and 303, a floor 305 and a lid 323. Within the vessel, between and generally in contact with the walls (and generally, the floor and the lid) is a volume that will be referred to as a fuel volume 324. The cells of the or each stack of cells are located substantially within and surrounded by the fuel volume 324.

[0043] A cell stack may have a large number of cells stacked vertically on top of each other, for example from 10 to 300 cells (but could have fewer or more, for example from 4 to 50 cells, or upwards of 50, 100, or 150 cells). Top and bottom plates may be provided (not shown) and means (such as tie bars, not shown) may be provided for holding the cells together in the stack and applying pressure to keep the cells in place and maintain integrity of seals around each cell. Vertical stacking is not essential - the cells can be stacked horizontally.

[0044] The first stack has steam inlets 311, an oxygen outlet 315 and a hydrogen outlet 316. The second stack has steam inlets 321, an oxygen outlet 325 and a hydrogen outlet 326. The oxygen and hydrogen outlets 315, 325, 316, 326 extend through the floor 305 of the vessel 309 (but they could equally extend through a wall 302, 303 or the lid 323, or some could extend through the floor and others out through the lid).

[0045] The outlets (ports) of adjacent cells are aligned and form a chimney within the cell stack. Each chimney has inter-cell seals (described below), preventing any mixing between the products from the electrolysis process. The inlet 301 allows steam to enter the vessel 309. The inlet 301 is shown at the top in the lid 323, but could enter the vessel 309 through the floor or a wall. This steam flows through the steam (H2O) inlets 311, 321 and is processed by the electrolysis cells. By application of an electric voltage to cells each comprising an oxygen ion conducting electrolyte, electrolysis causes oxygen ions to be removed from the water in the steam and to be transported through oxygen ion conducting electrolyte each cell. H2 is generated on the same side of the cell as the input steam and emerges (mixed with steam) from the hydrogen outlets 316, 326. Pure O2 is generated on the opposite side of each cell and emerges from the oxygen outlets 315, 325.

[0046] Figure 4 shows six cell stacks 312, 322, within the fuel volume 324 of the vessel 309. There may be more or fewer cell stacks. This may, for example, be 2, 4, 6, 8, 12, 16 or 24 such cell stacks.

[0047] The cell stacks are in side-by-side arrangement such that steam is present between the cell stacks and all around the cells. Steam pressure and distribution is substantially equal at all points in the fuel volume 324. The vessel 309 is preferably lagged (insulated) to prevent steam condensation. A drain (not shown) can be provided to remove any condensate.

[0048] Figure 5 shows an exploded view of a cell in schematic outline, with an additional separator (upper layer 542) to exemplify how cell units are stacked. The figure shows a lower layer 502, with a first hole (port) 503 at one end and a second hole (port) 504 at the other end. The lower layer may be referred to as a separator plate. It separates the cell from an adjacent cell (not shown).

[0049] On top of the lower layer 502 is a first gasket 512 that functions as a first peripheral separator and also as a first peripheral seal. A fuel volume 520 is defined between the first layer 502, a supporting layer 522 and the surrounding first gasket 512. The first gasket 512 can be referred to as a first peripheral separator. The first gasket 512 does not fully surround the gap between the lower layer 502 and the supporting layer 522. The first gasket 512 has a gap 527 (shown on the left-hand side) at an end of the cell. In this way, the fuel volume 520 is open to the fuel volume 324 of the surrounding vessel 309.

[0050] The supporting layer 522 is a substrate with electrochemical layers 525 deposited thereon. In the figure, they are preferably deposited on the upper side, but they could be deposited on the underside. An annular seal 513 is located around the first hole 503.

[0051] Above the lower layer 502 is a supporting layer (substrate) 522. The supporting layer has holes 523 and 524 at respective ends, coinciding with holes 503 and 504. An area between the holes 523 and 524 accommodates chemistry layer 525. This area of the supporting layer has holes or is porous for fluidic communication between the fuel volume 520 and the chemistry layer nearest to the supporting layer. It is illustrated in dotted outline and it is the active region of the cell.

[0052] A second gasket 532 is provided above the supporting layer 522 and extends around the entire perimeter of the supporting layer 522. The second gasket 532 functions as a second peripheral separator and as a second peripheral seal. It may be referred to as a second peripheral separator. An annular seal 533 is also located on top of the supporting layer 522, around the hole 524.

[0053] Seals 513, 533 are preferably compressible gaskets that can withstand high compressive forces in the vicinity of the holes (e.g. 503, 522). Compression means such as tie bars can be provided from one end of a cell stack to an opposite end, to maintain compression in the stack. The gaskets are sized to prevent hydrogen and oxygen that may be travelling through the ports / chimneys in the stack from leaking into external areas. This prevents mixing of the fluid inside the cell stack.

[0054] The gaskets may also provide electrical insulation between a first fuel cell unit and a second fuel cell unit, so as to prevent a short circuit. The gaskets may be any suitable fuel cell gaskets (sealing rings), such as, for example, Vermiculite (trade mark).

[0055] An upper layer 542, similar to the lower layer 502 and which may be considered part of a neighboring cell unit in a stack or array, is mounted on top of the gasket 532 and seal 533. It has holes 543 and 544 corresponding to holes 523 and 524 in the layer below. Seal 533 surround the underside of hole 544. Hole 543 has no seal below (but can have another seal above, identical to seal 513, for a next cell above in the stack). The upper layer can be referred to as a second peripheral separator. It separates the substrate (supporting layer 522) from an adjacent cell unit (not shown).

[0056] An electrical connector 552 is connected to the supporting layer 522. A further connector (not shown) may connect to the upper side of the chemistry layer 525. These connectors can be formed as part of the cells. The cells themselves can be shaped to provide the necessary contacts to the anode and cathode sides of the chemistry layer 525. E.g. layer 542 can have suitable bumps, buttons or other shapes to connect to the upper side of the chemistry layer 525 (or these can be provided in layer 502 if the chemistry layer is on the underside of layer 522).

[0057] Layers 502, 522 and 542 can have suitable touching or interconnecting flanges, rims, buttons or other shapes to connect them together as appropriate for serial or parallel connection and to provide electric current / voltage to the electrochemical cells of the cell array.

[0058] Preferably, the chemistry layer 525 has a cathode below and anode above and is formed on top of the supporting layer 522, but it can be positioned on the underside. In each case, a closed volume is created above the supporting layer, within the second gasket 532 and between the supporting layer

[0059] 522 and the upper layer 542. This volume can be referred to as an oxygen collection volume. In this arrangement, hole 503 is an oxygen outlet (part of an oxygen chimney that includes seal 513, hole

[0060] 523 and hole 543) and hole 504 is a hydrogen outlet (part of a hydrogen chimney that includes hole 524, seal 533 and hole 544).

[0061] In the operation of the cell, steam enters the gap 527 in the first gasket 512. The steam undergoes electrolysis at the chemistry layer 525 located on the supporting layer 522. During electrolysis, oxygen is generated at the anode and released to the oxygen volume formed by the gasket 532. The oxygen passes up through hole 543 and / or down through hole 523 and emerges from an oxygen outlet.

[0062] Hydrogen is generated at the cathode and collects in a second volume (fuel volume 520) between the lower layer 502 and the supporting layer 522. The hydrogen passes through hole 524 (and hole 544) and / or down through hole 504 to a hydrogen outlet.

[0063] In some embodiments supporting layer 522 is a metal support plate with a porous region, and the (active) fuel cell chemistry layers 525 take the form of an electrochemically active layer comprising of a cathode, an electrolyte and an anode formed (e.g. coated or deposited) onto the metal support plate over the porous region. This arrangement with the (non-self-supporting, thin) chemistry layers provided directly on the metal support plate requires the minimum number of components. The metal support plate thus performs a dual function of supporting the cell chemistry and defining the fluid volume (together with the annular peripheral seals and annular gaskets). Steam first reacts at the cathode, resulting in the formation of hydrogen gas and negatively charged oxygen ions. The electrolyte is an oxygen ion conducting electrolyte, and so allows oxygen ions transport from the cathode to the anode. At the anode, oxygen ions combine to form oxygen gas (O2). The hydrogen is released at the cathode (i.e., same side of the chemistry layer as the fuel input).

[0064] In some embodiments, it is possible that one or other exhaust products from the cells are extracted by being allowed to mix with fuel in the enclosure, having a direct outlet enclosure. In other words an exhaust manifold or dedicated pathway is not provided. In such cases the product (e.g. hydrogen) could be separated from the fuel (steam) in a downstream process.

[0065] A "cell unit" may be considered to comprise the lower layer 502, the supporting plate 522, the electrochemical layers 525 and the two peripheral separators (gaskets 512 and 532), in which case the upper layer 542 is part of a next adjacent cell unit. Alternatively, a "cell unit" may be considered to comprise the supporting plate 522, the electrochemical layers 525, the two peripheral separators and the upper layer 542. In such case, the lower separator plate 502 may be part of a next adjacent cell unit. In each case, a cell unit is a repeatable unit. A lower end plate or an upper end plate is provided for a lowermost cell unit of a stack or uppermost cell unit of a stack, as necessary.

[0066] Thus, an electrolyser apparatus has been described that has electrochemical cells grouped into at least one cell array comprising a plurality of cell units. Each cell unit comprises a substrate (supporting layer 522) having electrochemical layers 525 extending across a region thereof to provide an active region. At least first and second openings 524, 523 are provided for first and second products (e.g. hydrogen and oxygen) respectively. A plate (e.g. lower layer 502) faces a first side of the substrate to define a first volume 520 between the substrate and the plate. A first peripheral separator 512 separates the substrate from the plate. A second peripheral separator 532 separates the substrate from a further plate that may be part of an adjacent cell unit. One of the first and second peripheral separators (e.g. second peripheral separator 532) extends around the entire periphery of the cell unit and the other one of the first and second peripheral separators (e.g. separator 512) is open to the exterior of the cell unit. This allows fluidic communication between cell unit and exterior thereof. Either one or both of the peripheral separators can be integrated into an adjacent separator plate.

[0067] A first annular seal 533 within the second peripheral separator preferably surrounds the first opening 524 and a second annular seal within the first peripheral separator 512 preferably surrounds an underside of the second opening 523. Figure 6 shows an alternative stack arrangement in which the electrochemical cells are tubular, as opposed to the planar arrangement described above. Tubular structures or tubes 603 support or comprise the active electrochemical layers, and define a fuel volume within the tube, or at least on the inner surface (it will be understood that if order of anode and cathode are reversed relative to that exemplified, then the fuel volume may be bounded by the outer surface of the tubes). Structures 603 abut an end plate 602 at an inlet end, holes in the endplate providing fuel inlets. When the stack is situated in a fuel enclosure, the end plate is directly adjacent to and open to the fuel in the enclosure. As fuel passes through the tubular structures, it is (at least partially) converted by electrolysis to hydrogen. The far end of the tubes abut a first chamber 606 having a plurality of holes formed on a connecting wall to allow fluid exiting the tubes to enter the chamber. Thus in use, fuel within the enclosure enters the tubes via end plate 602, passes through the tubes where it undergoes electrolysis, and hydrogen (and any unreacted steam) exits the tubes via holes into chamber 606. An outlet 608 in the wall of chamber 606 allows the hydrogen to be output from the stack, and from the chamber, possibly via further manifolding (not shown).

[0068] When assembled the tubes 603 are located within a second chamber defined by the inlet plate 602, shroud 605 and a wall of the connecting wall of the first chamber. Oxygen produced by electrolysis evolves from the outer surface of the tubes, and collects in the second chamber. A second outlet 607 in a wall of the shroud 605 allows the oxygen to be output from the stack, and from the chamber, possibly via further manifolding (not shown)

[0069] Fuel in the enclosure, and hence fuel entering tubes 603 will typically be pressurized, and in order to balance pressure on the internal and external surfaces of the tubes, pressures of the outlet fluids are controlled to be substantially equal.

[0070] Figure 7 shows a control system for an electrolyser comprising a plurality of electrochemical cells within a vessel 701, having external F manifold 702, external O2 manifold 703, an oxygen reservoir 712, a pressure control valve 711 for the oxygen reservoir 712, an O2 pressure control valve 721 for the O2 output, a H2 pressure control valve 722 for the H2 output, a controller 731, a controller 741, a pressure control valve 751, and steam (fuel) source 752. Arrows used within Figure 7 are used to describe the direction of flow. In the operation of the control system, hydrogen is exhausted from the cells within the vessel 701, through to the external hydrogen manifold 702. Oxygen is exhausted from the cells within the vessel 701 through to the external oxygen manifold 703.

[0071] Oxygen pressure is measured and controlled by the oxygen pressure control valve 721. Hydrogen pressure is measured and controlled by the hydrogen pressure control valve 722. The oxygen pressure control valve 721 and hydrogen pressure control valve 1 2. are connected to the controller 731, which ensures that the pressures of oxygen and hydrogen are substantially equal.

[0072] Pressure information from the controller 731 is used by controller 741. Controller 741 determines the pressure that the pressure control valve 751 allows from the steam source 752. The resulting steam goes from the pressure control valve 751 as an input into the vessel 701. Note that an input pressure control valve is not necessary. Control valves 721 and 1 2. can control the pressure to maintain the pressure source above the vessel pressure (by back pressure regulation).

[0073] Oxygen reservoir 712 and pressure control valve 711 allow pressure at control valve 721 to be equalized as necessary with pressure at control valve 722. The pressure control valve 711 allows oxygen reservoir 712 to release oxygen into the system or take in oxygen from the system, depending on the pressure of the oxygen in the external oxygen manifold 703 relative to the pressure in the hydrogen manifold 702.

[0074] Because, in embodiments, the active fuel volume of each cell is open to the enclosure, there is substantially no pressure drop between the fuel in the enclosure and the fuel entering the active fuel volume. Furthermore, the pressure experienced by each active fuel volume is substantially equal.

[0075] The pressure in the enclosure is preferably maintained by regulating the flow of exhaust products exiting the enclosure. It is however possible that alternative embodiments use a pressure reducing regulator at the enclosure input (i.e. a regulator which control downstream pressure)

[0076] Separate regulators can be used for both the first exhaust pathway and the second exhaust pathway, however it has been found to be advantageous to provide an arrangement whereby both pathways are controlled relative to a common reference pressure. The pressure regulator may be an arrangement having a single reference pressure biased diaphragm regulating the first and second outlets, or whereby separate diaphragms are employed but controlled by a common reference pressure. In such embodiments, the pressure upstream of both pathways can be accurately maintained equal (even if there is variance in the absolute pressure upstream of the regulator, a pressure differential is avoided).

[0077] In arrangements having stacks or arrays of cells defining active fuel and oxygen volumes, balancing pressure of these two active volumes has been found to reduce degradation and / or improve reliability of the electrochemical cells. This is particularly useful for solid oxide cells (i.e., solid oxide electrolyser cells, SOECs), and more particularly useful for metal supported solid oxide cells.

[0078] In embodiments, an oxygen source (reservoir 712) is connected to the second outlet, upstream of the pressure regulator. The oxygen source is preferably adapted to provide oxygen at a pressure at or above the reference pressure of the pressure regulator. The oxygen source can be used to ensure balanced pressure between the outlets when there is insufficient production of oxygen by the cells to maintain the appropriate pressure at the second outlet.

[0079] It is however possible that alternative embodiments use a pressure reducing regulator at the enclosure input (i.e. a regulator which control downstream pressure)

[0080] In embodiments, depending on the conversion rate of electrolysis, hydrogen in the first exhaust pathway may be mixed with fuel (typically steam). Preferably there is only a single inlet to the enclosure, or at least in steady state operation no reactant or fluid is provided to the process other than fuel / steam). In this way, the electrolyser system can be simplified as it does not require any manifolding upstream of the cells. In such cases, oxygen in the second exhaust pathway is substantially pure, or at least highly concentrated.

[0081] Conductors to allow current to be supplied to the cells may pass through the enclosure walls in embodiments, but the enclosure is preferably electrically inactive, which is to say it does not have any electrical functionality, and is preferably electrically isolated from the cells. In embodiments where the enclosure is made of a conductor such as metal, it is preferably electrically isolated from the input current to the electrolyser.

[0082] More than one array or stack of cells may be included in the enclosures, according to some embodiments. Providing multiple stack or arrays in a single enclosure creates efficiencies as an increased number of cells can be provided with a common fuel supply mechanism (i.e. the enclosure) it will be understood that this allows reduced materials costs and a more compact form factor. Furthermore, the pressure experienced by different stacks will be substantially the same.

[0083] Alternative arrangements and shapes will also be within the scope of the present invention, for example in which each cell has more than one first exhaust pathway and / or more than one second exhaust pathway, and / or the active region extends partway around the holes in the substrate and / or there is more than one active region on a substrate. The electrolysis cell unit may take shapes other than the generally flat rectangular shape shown in the diagrams. There may be other arrangements of electrochemically active layers and the arrangement of the elements for enabling fluid flow into and out of the fuel volume within the electrolysis cell unit may take different forms. These and other features of the present invention have been described above purely by way of example. Modifications in detail may be made to the invention within the scope of the claims.

Claims

CLAIMS1. An electrolyser apparatus comprising: an enclosure having containing walls defining a fuel space, and an inlet for receiving input fuel including a reactant to be contained in said fuel space; a plurality of electrochemical cells adapted to at least partially convert the reactant into a first product and a second product, wherein said electrochemical cells are located substantially within said enclosure and are exposed to fuel in said fuel space; a first exhaust pathway adapted to receive the first product produced by said electrochemical cells and transport it to the exterior of the enclosure; and a second exhaust pathway adapted to receive the second product produced by said electrochemical cells and transport it to the exterior of the enclosure.

2. An electrolyser apparatus according to claim 1, wherein the reactant comprises H2O, the first product is hydrogen and the second product is oxygen.

3. An electrolyser apparatus according to claim 1 or 2, wherein the electrochemical cells are grouped into at least one cell array.

4. An electrolyser apparatus according to claim 3, wherein a plurality of cell arrays are located substantially within said enclosure.

5. An electrolyser apparatus according to claim 3 or claim 4, wherein each cell array is provided with a first exhaust manifold adapted to collect and combine the first product produced from cells of the array.

6. An electrolyser apparatus according to any one of claims 3 to 5, wherein each cell array is provided with a second exhaust manifold adapted to collect and combine the second product produced from cells of the array.

7. An electrolyser apparatus according to claim 5 or claim 6, wherein said first and / or second exhaust manifolds are connected to or integral with said first and second exhaust pathways respectively.

8. An electrolyser apparatus according to any one of claims 3 to 7, wherein the arrangement of each cell in an array defines an active fuel volume adjacent to a fuel side of the cell, and wherein at least part of said active fuel volume is open to said fuel space defined by said enclosure.

9. An electrolyser apparatus according to claim 8, wherein said active fuel volume is elongate having an entry end and an exit end, and wherein the entry end is open to the enclosure.

10. An electrolyser apparatus according to claim 9, wherein the exit end of said active fuel volume is closed to the enclosure and feeds into the first exhaust pathway.

11. An electrolyser apparatus according to any of claims 3 to 10, wherein each cell array includes electrical connectors for supplying electrical current from a power source to cells of that array.

12. An electrolyser apparatus according to any preceding claim wherein said enclosure is a pressure vessel adapted to maintain said fuel space at elevated pressure.

13. An electrolyser apparatus according to claim 12, wherein said inlet is adapted to receive input fuel at elevated pressure from a pressurized fuel source.

14. An electrolyser apparatus according to claim 12 or claim 13, further comprising a pressure regulator adapted to regulate the pressure of said first and / or second outlets.

15. An electrolyser apparatus according to claim 14, wherein said pressure regulator is adapted to regulate the pressure of the first and second outlets to be substantially equal.

16. An electrolyser apparatus according to any one of claims 12 to 15, wherein said pressure vessel is adapted to contain fuel in said fuel space at a pressure of 1.2 bar or greater.

17. An electrolyser apparatus according to any one of claims 12 to 16, wherein said pressure vessel is adapted to contain fuel in said fuel space at a pressure of 2 bar or greater.

18. An electrolyser apparatus according to any preceding claim, wherein the electrochemical cells are grouped into at least one cell array comprising a plurality of cell units, each cell unit comprising a substrate having electrochemical layers extending across a region thereof to provide an active region and having at least first and second openings for first and second product respectively;a first plate is provided facing a first side of the substrate with a first volume between the substrate and the first plate; a first peripheral separator separates the substrate from the first plate; a second peripheral separator separates the substrate from an adjacent second plate, wherein one of the first and second plates is part of an adjacent cell unit; and wherein one of the first and second peripheral separators extends around the entire periphery of the cell unit and the other one of the first and second peripheral separators is open to the exterior of the cell unit.

19. An electrolyser apparatus according to claim 18, wherein the first peripheral separator extends around the entire periphery of the cell unit, enclosing the first volume, and enclosing the electrochemical layers, and wherein the second peripheral separator is located on a side of the substrate opposite to the electrochemical layers, for separating the substrate from an adjacent cell unit, the second peripheral seal extending around less than the entire periphery of the cell, to provide an opening for fluidic communication.

20. A method of operating an electrolyser comprising a fuel enclosure and a plurality of electrochemical cells substantially located in said fuel enclosure, the method comprising: providing fuel including a reactant to said fuel enclosure, walls of said fuel enclosure containing said fuel, whereby said electrochemical cells are exposed to the contained fuel; providing an electric current to said electrochemical cells to facilitate at least partial conversion of the reactant into a first product and a second product; collecting the first product from said plurality of cells and transporting it out of said fuel enclosure via a first dedicated pathway; and collecting the second product from said plurality of cells and transporting it out of said fuel enclosure via a second dedicated pathway.

21. A method according to claim 20, wherein the reactant is H2O, the first product is hydrogen and the second product is oxygen.

22. A method according to claim 20 or 21, wherein the electrochemical cells are grouped into at least one cell array.

23. A method according to claim 22, wherein a plurality of cell arrays are located substantially within said enclosure.

24. A method according to any one of claims 20 to 23, wherein providing electric current to said electrochemical cells comprises providing current via a dedicated electrical connector to each array of cells.

25. A method according to any one of claims 20 to 24, wherein said fuel enclosure is a pressure vessel and wherein said enclosure walls contain said fuel at an elevated pressure.

26. A method according to any one of claims 20 to 25, wherein fuel is provided to said fuel enclosure at elevated pressure from a pressurized fuel source.

27. A method according to any one of claims 20 to 26, further comprising regulating the pressure at an outlet of said first dedicated pathway and / or an outlet of said second dedicated pathway.

28. A method according to any one of claims 20 to 27, further comprising regulating the pressure of the first and second outlets to be substantially equal.

29. A method according to any one of claims 20 to 28, comprising maintaining fuel in the fuel enclosure at a pressure of 1.2 bar or greater.

30. A method according to any one of claims 20 to 29, comprising maintaining fuel in the fuel enclosure at a pressure of 2 bar or greater.

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