Method for the generation of electricity or hydrogen

Abstract

The system comprises a fuel cell including a pair of electrodes including an anode and a cathode separated by an electrolyte, a first inlet for introducing hydrogen into said fuel cell at said anode, and a second inlet for introducing oxygen into said fuel cell at said cathode. The cathode may comprise protrusions facing the electrolyte.

Description

[0001] METHOD FOR THE GENERATION OF ELECTRICITY OR HYDROGEN

[0002] The present disclosure is directed to a fuel cell and a method for generating electricity by means of a fuel cell. The fuel cell may be also operate in reverse and consume electricity for producing a chemical such as hydrogen.

[0003] Leaking electrolyte through electrodes of a fuel cell may be disadvantageous, because electrolyte is deplenished. However, in order to avoid leaking electrolyte a complicated construction of the fuel cell may arise. It is an object of the present disclosure to operate a fuel cell with leaking electrolyte.

[0004] A first aspect of the present disclosure is:

[0005] A system for generating electricity, said system comprising: a fuel cell including: a pair of electrodes including an anode and a cathode separated by an electrolyte, a first inlet for introducing hydrogen into said fuel cell at said anode, a second inlet for introducing oxygen into said fuel cell at said cathode.

[0006] A second aspect of the present disclosure is:

[0007] A method for generating electricity comprising: providing a fuel cell including a pair of electrodes including an anode and a cathode separated by an electrolyte, a first inlet for introducing hydrogen into said fuel cell at said anode, a second inlet for introducing oxygen into said fuel cell at said cathode,

[0008] - inletting said hydrogen and said oxygen into said fuel cell by means of said first inlet and said second inlet, - connecting a pair of wires to said pair of electrodes for transporting current through a load as electrons move between said pair of electrodes when said hydrogen being oxidized.

[0009] In the following the “fuel cell” part of the system is to be understood as where the reaction happens, e.g. the pair of electrodes and the space between the pair of electrodes where ions flow from one electrode to the other through the electrolyte. At the same time electrons move between the pair of electrodes in an electric circuit including a load.

[0010] In the present context replenishing / new electrolyte refers to substituting the electrolyte that may have reacted with carbon dioxide in the air and can therefore not function as electrolyte for the generation of electric current / electric energy.

[0011] The term “pipe” is to be understood as a passageway for conveying. It may include several pipe sections connected to each other and it may have corners or bends. It may also include a pump for example.

[0012] In the following specific examples according to aspects of the present disclosure will be explained in more detail with reference to the accompanying drawings. The present disclosure may, however, be embodied in different forms than depicted below, and should not be construed as limited to any examples set forth herein. Rather, any examples are provided so that the disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout. Like elements will, thus, not be described in detail with respect to the description of each figure.

[0013] Fig. 1 shows a schematic of a fuel cell for generating electricity.

[0014] The specific example show an alkaline fuel cell, e.g. a fuel cell that consumes hydrogen and oxygen. However, other types of fuel cells using another fuel and another oxidizing agent may be contemplated.

[0015] The fuel cell comprises a pair of electrodes including an anode 10 and a cathode 12. The pair of electrodes are separated by a distance and a fuel cell space is thus defined between the pair of electrodes.

[0016] A pair of wires (not shown) are connected to the electrodes such that an electric current can flow between the pair of electrodes through a load.

[0017] The space (electrolyte chamber) between the two electrodes is filled with an electro- lyte / aqueous alkaline solution. In the specific example the electrolyte is potassium hydroxide KOH. However, other electrolytes may be contemplated such as sodium hydroxide NaOH or another compound where a hydroxide is present in the electrolyte, e.g. another metal such as an alkali metal may be used for binding the hydroxide.

[0018] Hydrogen H2 is introduced into the fuel cell (into an anode chamber) at a (hydrogen) inlet 14 for oxidizing the hydrogen at the anode.

[0019] Oxygen / air 02 is introduced into the fuel cell (into a cathode chamber) at an (oxy- gen / air) inlet 16 at the cathode, and the fuel cell produces power through a redox reaction between the hydrogen and the oxygen. The air may be introduced into the cathode chamber by a fan.

[0020] There is also shown an inlet 18 for electrolyte into the fuel (into the electrolyte chamber). This may compensate for a potential loss of electrolyte during operation.

[0021] It is contemplated that the fuel cell may be mobile, e.g. used to power a vehicle such as an airplane or a truck. In such a case the vehicle may comprise a fuel tank for containing fuel for the fuel cell. It may also comprise a tank for containing an oxidizing agent and / or a tank for containing electrolyte.

[0022] The electrolyte (in the electrolyte chamber) between the two electrodes are to be maintained at a higher pressure than the fluid in the cathode chamber. This may reduce the complexity of the fuel cell, e.g. making the fuel cell less costly. It may also allow the fuel cell to be used in systems for capturing carbon dioxide in the air. It may also keep the electrodes from each other, e.g. reducing the risk that the electrodes may have a connection creating a short circuit (especially for cells having a short distance between the electrodes). In general, the pressure difference may be such that the electrolyte pressure may be 5 % higher than the than the fluid in the cathode chamber, such as 10 % higher or 20 %, or 35 %, or 50 %, or 75 % or 100 % higher. As a specific example the pressure of the fluid in the cathode chamber may be 1 bar and the pressure of the electrolyte may be 1.5 bar.

[0023] There may be the same pressure difference with respect to the fluid in the anode chamber. Alternatively, the pressure difference between the electrolyte and the fluid in the anode chamber may be smaller than the pressure difference between the electrolyte and the fluid in the cathode chamber in order to have a reduced flow of electrolyte into the anode chamber.

[0024] It is contemplated that the cathode (and / or anode) is permeable (ability of a material to transmit fluid) such that electrolyte may flow through the cathode - when there is a higher pressure on one side of the cathode than on the other.

[0025] The electrodes are naturally also contemplated to be electric conductive.

[0026] An example of a porosity of a permeable electrode may be random distributed holes having a (average) diameter in the range 5 -100 urn (micro meter) such as 5 - 75, or 5 - 50, or 5 - 35, or 15 - 100, or 15 - 75, or 15 - 50, or 15 to 35 urn. As a specific example the porosity may be 30 um. Together with a pressure difference of 0.5 bar this has shown to be efficient, e.g. not too much electrolyte is lost and the cell is still efficient.

[0027] The average diameter may be different between the two electrodes, e.g. the average diameter hole size may be smaller in the anode than in the cathode, such as at least 10 % smaller, or at least 15, or 20, or 25 or 35 or 50 or 100 % smaller.

[0028] Such a higher pressure may also allow for the two electrodes to be kept separated without the need for electrode spacer(s). Since the electrodes need to be electrically isolated from each other a spacer is to have an insulating material property. It also needs to withstand high temperatures. It is therefore desirable to have a spacer-free fuel cell.

[0029] An electrode (the anode and / or the cathode) may have a width of 12 cm and a height of 12 cm (0.12 by 0.12 m) which equals an area of 0.0144 m2. The electrolyte flow may be 10 mL per second (0.01 L per second).

[0030] This gives a flow per area per second of 0.01 10.0144 = 0.6944 L / m2 / s.

[0031] Per hour this is 2500 L / m2.

[0032] For the whole area it is 0.0144 * 2500 = 36 L per hour.

[0033] Other areas of the electrodes or one of them, such as the cathode, may be 0.01 m2 to 2 m2, or 0.05 m to 1 m2.

[0034] In another example the electrolyte flow may be 1 mL per second (0.001 L per second).

[0035] This gives a flow per area per second of 0.001 10.0144 = 0.06944 L / m2 / s.

[0036] Per hour this is 250 L / m2.

[0037] In general, the flow rate of the electrolyte through an electrode may be 0.02 - 5000 L / m2 per hour such as 0.02 - 2500, or 0.02 - 1000, or 0.02 - 500, or 0.02 - 250, or 0.02 - 100, or 0.02 - 50, or 2 - 5000, or 2 - 2500, or 2 - 1000, or 5 - 5000, or 5 - 2500, or 5 - 1000, 10 - 5000, or 10 - 2500, or 10 - 1000, 50 - 5000, or 50 - 2500, or 50 - 1000, L / m2 per hour.

[0038] There may be the same flow rate of electrolyte through the anode and the cathode. Alternatively, the flow rate of electrolyte through the anode may be smaller than the flow rate of electrolyte through the cathode in order to have a reduced flow of electrolyte into the anode chamber, e.g. the electrodes may be designed with a different permeability such that the flow of electrolyte to the hydrogen side / into the hydrogen chamber may be smaller than the flow of electrolyte to the air side / into the air chamber.

[0039] The height of the fuel cell may be greater than 12 cm such as greater than 20 cm or 30 cm or 40 cm or 50 cm. Several fuel cells may be stacked together by means of bipolar plates, e.g. a bipolar plate is used to provide the physically and electrically conductive connection between the anode of a cell and the cathode of its neighboring cell.

[0040] Fig. 1 shows that the fuel cell has an anode chamber outlet 20, an electrolyte chamber outlet 22, and a cathode chamber outlet 24.

[0041] At the end of each outlet is a container where liquid may be collected, e.g. the system may comprise a first container (may also be termed reservoir or compartment) for containing electrolyte from the anode chamber outlet. A second container for containing electrolyte from the electrolyte chamber outlet may be comprised. And a third container for containing electrolyte from the cathode chamber outlet may be comprised.

[0042] Between each outlet and container may be a pipe, e.g. a first pipe between the first outlet and the first container. The pipe may be omitted such that the outlet constitutes an opening into the container.

[0043] The system may comprise a first pump for pumping electrolyte that has been outlet through the electrolyte chamber outlet.

[0044] A second pump for pumping electrolyte that has been outlet through the anode chamber outlet may be comprised.

[0045] And a third pump for pumping electrolyte that has been outlet through the cathode chamber outlet may be comprised.

[0046] The purpose of a pump such as the first pump is to pump electrolyte back into the fuel cell, e.g. the first pump is connected to the electrolyte chamber inlet. The same with the second pump and the third pump.

[0047] The fluid that comes from the air side (and into the container in fluid communication with the air side chamber) comprises electrolyte that has been transported through the electrode from the electrode chamber to the chamber where air is inlet. This fluid is depleted electrolyte, because the electrolyte has reacted with the carbondioxide in the air. This fluid can be handled separately (when having a container for that fluid and a pump in fluid communication with that container), e.g. independent from the fluid pumped by other pumps in the system, such as the pump pumping electrolyte from the container having received electrolyte from the electrolyte chamber. For example, the depleted electrolyte can be pumped to a reactor for producing new electrolyte to be pumped back into the electrolyte chamber.

[0048] There may be a pump at the outlet of each container. This may prevent fluid being pumped from one container to come into one of the other containers through the outlet of one of these other containers. A cross valve or similar may also be used, e.g. it is a rectifying function / means such that fluid may not flow back into a container.

[0049] It is contemplated that electrolyte that has transported through an electrode drips down into an outlet, e.g. electrolyte that has flowed into the cathode chamber drips down into the cathode outlet 24 and collected into a first container 26.

[0050] Electrically insulating hoses may be used between the chambers and the containers.

[0051] Each container may have an outlet such as a first container outlet 28.

[0052] Each container outlet may be connected to the same pipe 30 for circulating electrolyte back to the electrolyte chamber, e.g. there may be a manifold combining the fluids in the three containers.

[0053] There may be a first valve 32 for outputting fluid from the first container or the pipe 30 to a carbon dioxide capturing system. This output option is not necessary if the system is to operate as an electrolysis cell instead of a fuel cell.

[0054] There may be a second valve 34 for adding water to the collected electrolyte in the pipe 30.

[0055] It is illustrated that the collected electrolyte is led back to the electrolyte chamber via a heat exchanger 36. In such a case the heated electrolyte may be used as residential heating, e.g. for generating warm water in a household for example.

[0056] % material parameter At least one of the pair of electrodes may have a material parameter changing as a function of height.

[0057] Such a varying material parameter may be arranged such that an electrolyte pressure at the top of the fuel cell causing a first flow rate at the top, and a higher pressure at the bottom of the fuel cell causing a second flow rate no more than 25 % different than said first flow rate.

[0058] In fig. 1 it is illustrated that it is the thickness of both of the two electrodes that varies as a function of height, e.g. the thickness of both of the two electrodes are greater at the bottom of the cell than at the top of the cell. Specifically, both of the two electrodes are illustrated as wedge shaped, e.g. the side facing the electrolyte is straight and the side facing the opposite direction than the electrolyte is inclined. Other shapes may be contemplated.

[0059] In general, the cathode and / or anode may have a thickness at the bottom at least 10 % greater than the thickness at the top, such as greater than 25, or 50, or 75, or 100 or 150 %, e.g. there may be a thickness ratio defining a bottom thickness relative to a top thickness. This thickness ratio may be greater than 1.

[0060] Specifically, the cathode and / or anode may have a thickness in the range 0,1 - 1 mm such as 0,2 - 0,4 mm at the top.

[0061] The material parameter of the cathode may be different than the material parameter of the anode, e.g. the thickness ratios of the two electrodes may be different from each other - for example the anode may have a higher thickness ratio than the cathode or vice versa.

[0062] In addition, or as an alternative, the porosity may be varying as a function of height. For example, the average diameter hole size may decrease towards the bottom of the cathode and / or anode. This may compensate for a higher pressure at the bottom than at the top of the cell, e.g. the pressure increases towards the bottom due to gravity.

[0063] There may be a porosity ratio defining a top porosity relative to a bottom porosity. This thickness ratio may be greater than 1. The porosity of the cathode may be different than the porosity of the anode - such that there is a higher flow of electrolyte through the cathode than the anode (all other things equal). For example, the anode may have a higher porosity ratio than the cathode or vice versa.

[0064] % electric isolation

[0065] It is contemplated that in general there should be an electric isolation between a fuel cell chamber, such as the electrolyte chamber, and a container.

[0066] For example, the outlet (of a fuel cell chamber) may be electrically connected to the fuel cell, but not to a container, e.g. the outlet may comprise an edge of an electrically insulating material (such as plastic), or there may simply be a physical distance / sepa- ration between the edge of the outlet and the edge of the pipe leading to the container (or the edge of the inlet of the container).

[0067] Alternatively, the pipe and / or container may be made of an electrically insulated material.

[0068] % drip solution

[0069] In another alternative, there may be a filter 27 above the surface of the liquid inside a container such that electrolyte drips down into the liquid in the container.

[0070] Fig. 1b illustrates such a filter in a container.

[0071] The filter provides an electric isolation.

[0072] The filter may be a grate for example.

[0073] In certain electrochemical systems — such as batteries, electolysis, fuel cells, or other stacked cell configurations — it is critical to maintain sufficiently high overall electrical conductivity for ion transport (e.g., OH“ in alkaline electrolytes), while simultaneously minimizing resistance to avoid excessive power losses. Indeed, the power loss in such systems is proportional to U2 / R, so higher voltages in a stack can lead to disproportionately higher losses. A conventional strategy to mitigate these losses is to split the overall voltage into two separate stacks, thereby reducing the power loss to one quarter for each half-voltage stack. Further subdivision, however, creates complexity in the associated power electronics. It is called a stacked configuration, because it is a stack of compartment, e.g. anode compartment, and a cathode compartment with the electrolysis chamber in between.

[0074] Another known approach involves minimizing the fluidic cross-sectional area to increase resistance and reduce shunt currents between cells. This solution, however, compromises cooling capacity because smaller channels cannot maintain high flow rates at a given pressure. In contrast, the disclosed drip-based system addresses both shunt-current reduction and cooling requirements simultaneously. By allowing the electrolyte to drip into the reservoir, a high flow rate can be sustained for cooling, while the drip mechanism itself breaks the conductive path and substantially increases electrical resistance. Shunt currents are therefore minimized without requiring excessive channel restriction. This arrangement may be implemented with one or more pumps, thereby preserving cooling performance and system reliability across the entire stack.

[0075] The pipe leading to the inlet of a container may have a larger diameter than the pipe leading away from the outlet of a container.

[0076] The pipe leading to the inlet of a container may have a diameter such that electrolyte flows along the pipe’s inner or outer surface.

[0077] % electrode protrusions

[0078] Fig. 2 shows a close up of part of the fuel cell, specifically the part of an electrode facing the electrolyte. The part may alternatively face the gas side, e.g. the air side and fuel side respectively.

[0079] The electrode comprises a surface that is non-planar, e.g. having topographical pattern, also referred to as a corrugated / textured surface. It may be grooves / ridges, or pillars, or wells, e.g. protrusions (defining a pattern of ridges and valleys) including a first protrusion / ridge 40.

[0080] It may both of the electrodes or only be one of the electrodes that has such as corrugated / textured surface. It may be both sides or only one of the sides of an electrode that has a topographic pattern. The protrusions of the cathode may be different from the protrusions of the anode.

[0081] The triple phase boundary / triple-point of the fuel cell may be closer to the top of a protrusion than to the base of a protrusion, e.g. in general the triple point / the location of the triple point in the fuel cell can be controlled (when having protrusions) - it will be in the valley between two neighbouring protrusions. This is important, because for the present disclosure there is a pressure difference between the two sides of an electrode. It is contemplated that this pressure difference may result in an uncontrollable triple point - unless having an electrode with protrusions for “trapping’Varranging the (location of the) triple point with respect to the protrusions.

[0082] In fig. 2 the protrusions are illustrated as parallel wedges. However, other geometries may be contemplated such as tetrahedrons.

[0083] The protrusions may increase the area of the electrode. The cathode may have protrusions such that the total area of the cathode is greater than the area of the anode.

[0084] An increased area of the cathode may increase capture of carbon dioxide.

[0085] An electrode may also comprise flow channels (not shown) for the flow of electrolyte across the electrode, e.g. an electrode may be moulded / produced with integrated flow channels and / or protrusions.

[0086] In addition, the bipolar plates (when using the fuel cell according to the present disclosure in a stacked configuration) may have a substantially planar surface on each side, e.g. devoid any flow channels. With substantially planar is meant within production tolerances.

[0087] Fig. 3 shows another example of an electrode.

[0088] The electrode is made of the two plates shown in the figure put on top of one another.

[0089] The plate shown to the left comprises elongated cutouts. The plate to the right is permeable. The electrode may be sintered metal, e.g. compacted metal particles. The diameter of the particles may be in the range 10 - 50 micrometer.

[0090] When the two plates are put together they form an electrode that has protrusions and is permeable.

[0091] The height difference / distance between the tip of a protrusion and the base of a protrusion (no matter how the specific geometry of the protrusion) define a space for the triple phase boundary for the fuel cell. The position of the triple phase boundary may thereby be controlled. This also makes it easier to handle / control the Balance of Plant for the fuel cell.

[0092] It is preferred that the protrusions do not define a channel for flow of electrolyte parallel to an electrode, e.g. for example a vertical channel. With channel is meant a valley define by two ridges extending at least 25 % of the height or width of a electrode.

[0093] The permeability / porosity of an electrode may be a function of the thickness of an electrode. For example, in the case with two plates being put together and making up an electrode the two plates may have different permeability / porosity. Thus, the permeability may not only be a function of the height of an electrode, but also a function of the thickness.

[0094] For example, the plate with the holes may have a different permeability than the other plate. The plate with the holes may have a greater permeability than the other or vice versa.

[0095] Along the edge of an electrode (or both electrodes) the density of the electrode may be greater than the density of the electrode closer to the center of the electrode, e.g. the permeability may be less at the edge of the electrode than away from the edge (closer to the center than to the edge). This may allow for a recess along the edge of the electrode in which a seal (O-ring) may fit.

[0096] Fig. 4 illustrates a stacked configuration, e.g. a system comprising more than one cell.

[0097] In a stacked configuration so called bipolar plates are between the cells. The illustrated stack comprises an end plate, an electrode 10, an electrolyte chamber, an electrode 12, a bipolar plate 13, an electrode, an electrolyte chamber and so forth, e.g. the sequence is repeated until the stack ends with an end plate. The stack has six cells.

[0098] Thus, a stack with at least two cells comprises at least a first electrode, a second electrode, a bipolar plate, a third electrode, and a fourth electrode. Between the first and second electrodes is a first electrolyte chamber, between the third and fourth electrodes is a second electrolyte chamber, and between the second and third electrode is a bipolar plate.

[0099] As mentioned the bipolar plate may be substantially planar.

[0100] The top of the protrusions of the electrodes contact the bipolar plate such that an electric current can pass through the stack.

[0101] To summarize, the present disclosure discloses a fuel cell, specifically an alkaline fuel cell using air where at least one of the electrodes is permeable to electrolyte and has a topographic surface, and the electrolyte is at a pressure causing a flow of electrolyte through the electrode.

[0102] The fuel cell system may comprise a controller and a pump for controlling the fuel cell such that the electrolyte is maintained at a pressure causing the electrolyte to flow through the electrode to the air side of the fuel cell, e.g. having a higher pressure on the electrolyte side than on the air side.

[0103] The flow of electrolyte out of the electrolyte chamber may be balanced with a flow of electrolyte into the electrolyte chamber, e.g. over time the flow in and the flow out should equal each other.

[0104] The fuel cell may be membrane-less, e.g. not having a membrane adjacent an electrode.

[0105] The fuel cell is reversible, e.g. the cell may operate as a fuel cell or an electrolysis cell.

[0106] This is also called a regenerative fuel cell or reverse fuel cell. Thus, during low production of electricity from wind turbines or solar panels the fuel cell may produce electricity and during high production of electricity from wind turbines or solar panels it may produce hydrogen, e.g. water is let into the cell and electricity is used to split the water into oxygen and hydrogen, which may be stored for when there is low production of electricity from wind turbines or solar panels.

[0107] Now follows a set of items, which constitute aspects of the present disclosure which may be considered independently patentable and as such the following sets form basis for possible future sets of claims:

[0108] 1. A system for generating electricity or hydrogen comprising: a cell including a first electrode and a second electrode, a first inlet for inletting hydrogen into said cell. a second inlet for inletting air into said cell.

[0109] 2. The system according to any of the preceding items, comprising: a third inlet for inletting electrolyte into said cell.

[0110] 3. The system according to any of the preceding items, said first electrode and / or said second electrode being permeable to said electrolyte for transporting electrolyte through said first electrode.

[0111] 4. The system according to any of the preceding items, said second electrode being permeable to said electrolyte for transporting electrolyte through said second electrode.

[0112] 5. The system according to any of the preceding items, comprising: an electrolyte chamber between said first electrode and said second electrode.

[0113] 6. The system according to any of the preceding items, said first electrode and / or said second electrode having a side comprising protrusions.

[0114] 7. The system according to any of the preceding items, said side facing said electrolyte chamber or away from said electrolyte chamber.

[0115] 8. The system according to any of the preceding items, comprising: a controller for controlling said cell such that the pressure at an electrolyte side of said first electrode being higher than the pressure of an air side of said first electrolyte such that said electrolyte flow through said first electrode.

[0116] 9. The system according to any of the preceding items, said first and second electrode separated by an electrolyte.

[0117] 10. The system according to any of the preceding items, said first electrode constituting the anode of said cell.

[0118] 11. The system according to any of the preceding items, said second electrode constituting the cathode of said cell.

[0119] 12. The system according to any of the preceding items, said first inlet arranged at said first electrode.

[0120] 13. The system according to any of the preceding items, said second inlet at said second electrode.

[0121] 14. The system according to any of the preceding items, said electrolyte having a higher pressure than said oxygen during intended operational use of said system such that electrolyte being transported through one or both of said pair of electrodes, such as through said cathode and / or said anode.

[0122] 15. The system according to any of the preceding items, said first electrode and / or said second electrode comprising a porous material.

[0123] 16. The system according to any of the preceding items, at least one of said pair of electrodes having a material parameter changing as a function of height.

[0124] 17. The system according to any of the preceding items, said material parameter arranged such that a pressure at the top of said fuel cell causing a first flow rate at the top, and a higher pressure at the bottom of said fuel cell causing a second flow rate no more than 25 % different than said first flow rate.

[0125] 18. The system according to any of the preceding items, said first electrode and / or said second electrode having a material parameter such that said fuel cell having a flow rate of electrolyte through said cathode in the range 500 - 5000 L / m2 per hour.

[0126] 19. The system according to any of the preceding items, said first electrode and / or said second electrode having an area in the range 0.01 m2 to 2 m2 or 0.05 m to 1 m2.

[0127] 20. The system according to any of the preceding items, said material parameter being a thickness or a porosity or a permeability.

[0128] 21. The system according to any of the preceding items, said first electrode and / or said second electrode having an increasing thickness in the direction from the top of said fuel cell towards the bottom of said fuel cell.

[0129] 22. The system according to any of the preceding items, said first electrode and / or said second electrode having a thickness in the range 0,1 — 1 mm such as 0,2 - 0,4 mm at the top of said first electrode and / or said second electrode.

[0130] 23. The system according to any of the preceding items, said first electrode and / or said second electrode having a thickness at the bottom of first electrode and / or said second electrode at least 10 % greater than said thickness at the top of said first electrode and / or said second electrode, such as greater than 25, or 50, or 75, or 100 or 150 %.

[0131] 24. The system according to any of the preceding items, said anode having an increasing thickness in the direction from the top of said fuel cell towards the bottom of said fuel cell.

[0132] 25. The system according to any of the preceding items, said fuel cell comprising a first chamber for air or oxygen on an opposite side of an electrode than said electrolyte chamber.

[0133] 26. The system according to any of the preceding items, said fuel cell comprising a second chamber for hydrogen.

[0134] 27. The system according to any of the preceding items, comprising a fan or compressor for transporting air or oxygen into said first chamber.

[0135] 28. The system according to any of the preceding items, said first electrode being different from said second electrode such that a flow of electrolyte through said first electrode being different than a flow of electrolyte through said second electrode.

[0136] 29. The system according to any of the preceding items, said fuel cell having a height greater than 20 cm or 30 cm or 40 cm or 50 cm.

Claims

CLAIMS1. A method for generating electricity or hydrogen comprising: providing a cell including a first electrode and a second electrode separated by an electrolyte,- a first inlet for inletting hydrogen into said cell,- a second inlet for inletting air into said cell,- a third inlet for inletting electrolyte into said cell, said first electrode being permeable to said electrolyte and having a side comprising protrusions, said method comprising controlling said cell such that the pressure at an electrolyte side of said first electrode being higher than the pressure of an air side of said first electrolyte such that said electrolyte flow through said first electrode.

2. The method according to any of the preceding claims, said protrusions arranged on the air side of said first electrode.

3. The method according to any of the preceding claims, said first electrode comprising a porous or sintered metal.

4. The system according to any of the preceding claims, comprising: controlling said cell such that said flow being in the range 5 - 500 L / m2 per hour.

5. The method according to any of the preceding claims, comprising: providing a fan or compressor for transporting oxygen into said cell.

6. The method according to any of the preceding claims, comprising: providing a pump for pumping electrolyte into said cell.

7. The method according to any of the preceding claims, comprising: controlling said cell such that said flow being greater than a flow through said second electrode.

8. The method according to any of the preceding claims,said cell being membrane-less.

9. The method according to any of the preceding claims, comprising: providing a fourth inlet for inletting water into an electrolyte chamber.

10. The method according to any of the preceding claims, comprising: providing a first outlet for outletting hydrogen.

11. The method according to any of the preceding claims, comprising: providing a second outlet for outletting oxygen.

12. The method according to any of the preceding claims, comprising: passing an electric current through said electrolyte for splitting said water into hydrogen and oxygen.

13. The method according to any of the preceding claims, comprising: providing a second cell, and stacking said first cell and said second cell with a bipolar plate between said first cell and said second cell.

14. The method according to any of the preceding claims, said bipolar plate having a substantially planar surface on both sides of said bipolar plate.

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