POWER GENERATOR EQUIPPED WITH MULTIPLE FUEL CELLS

Abstract

POWER GENERATOR WITH MULTIPLE FUEL CELLS A power generator comprises fuel cells with anodic and cathodic output terminals. Frames define a fuel cell receiving window and a through-hole. The frames are stacked one on top of the other, and the through-holes are aligned in a stacking direction. The fuel cells are stacked in the stacking direction between two frames to form an alternating pattern with the through-holes in the stacking direction. Each group of two consecutive fuel cells has two anodic current connectors (4) or two cathodic current connectors as nearest-neighbor current collectors in the stacking direction, said two nearest-neighbor current collectors being supplied by the same supply channel.The frame set defines electrical tracks connecting the anode output terminals and the cathode output terminals (3).

Description

Title of the invention: POWER GENERATOR EQUIPPED WITH MULTIPLE FUEL CELLS technical field

[0001] The invention relates to an electric generator comprising at least one fuel cell. Previous technique

[0002] Conventionally, several fuel cells are combined to form an electrical generator. The multiple fuel cells are connected in series and / or in parallel so as to deliver a desired voltage-current pair.

[0003] Fuel cells are constructed with a more or less complex stacking of layers and have technical constraints related to fuel supply, oxidizer, and the removal of reaction by-products. There are also constraints related to temperature management and compressive stress management to ensure that the multiple layers of the fuel cell are in electrical and thermal contact and that the seal is maintained.

[0004] All these constraints make the formation of an electric generator complex. Furthermore, the issues of compressive stresses applied to the fuel cell stack and heat management result in the need for a heavy metal frame. In a mobile vehicle, the weight of the frame is a drawback. The significant compressive stresses applied to the fuel cells lead to high failure rates, necessitating regular maintenance. Object of the invention

[0005] An object of the invention consists of providing a generator whose configuration is simpler than that of prior art configurations in order to improve its durability and / or performance.

[0006] We tend to solve this problem by means of an energy generator comprising: - a set of fuel cells each having an anodic output terminal and a cathodic output terminal; - a set of frames comprising several frames stacked one on top of the other in a stacking direction, each frame defining a fuel cell receiving window and a through hole, the through holes being aligned in the stacking direction inside the windows; in which one of the several fuel cells is wedged between each of the two successive frames of the set of frames, in which the fuel cells are stacked one on top of the other in the stacking direction between two frames to form an alternation with the through holes in the stacking direction; in which the fuel cells are arranged such that each group of two consecutive fuel cells has two anode current connectors (4) or two cathode current connectors as nearest neighbor current collectors along the stacking direction, said two nearest neighbor current collectors being supplied by the same supply channel; and in which the frame set defines electrical tracks connecting the anode output terminals and the cathode output terminals.

[0007] In a particular configuration, said two nearest neighbor current collectors are separated by an electrically insulating separator elastically deformed by said two nearest neighbor current collectors along the stacking direction.

[0008] Preferably, the electrically insulating separators are porous and / or have dimensions smaller than the dimensions of the windows in directions perpendicular to the stacking direction.

[0009] According to one embodiment, two nearest neighbor cathode current collectors along the stacking direction are each formed by a porous plate, the oxygen precursor supply channel being delimited by the two porous plates.

[0010] Advantageously, said two nearest neighbor current collectors are formed by a metallic foam.

[0011] Advantageously, the frames are connected to each other by at least one fold to form a foldable and unfoldable frame assembly. Brief description of the drawings

[0012] Other advantages and features will become clearer from the following description of particular embodiments and implementations of the invention given by way of non-limiting examples and shown in the accompanying drawings, in which:

[0013] [Fig-1]: schematically illustrates a power generator equipped with a fuel cell fuel;

[0014] [Fig.2]: schematically illustrates an energy generator equipped with several fuel cells;

[0015] [Fig.3]: schematically illustrates an energy generator equipped with a fuel cell mounted on a frame according to the invention.

[0016] [Fig.4]: schematically illustrates an energy generator equipped with several fuel cells mounted on several frames according to the invention. Description of the implementation methods

[0017] Figures 1 to 4 illustrate a fuel cell and a generator equipped with fuel cells. The fuel cell comprises a membrane-electrode assembly which includes a proton exchange membrane 1, an anodic electrode 2, a cathodic electrode 3, an anodic current collector 4 and a cathodic current collector 5.

[0018] The fuel cell is a high-temperature fuel cell, i.e., with an operating temperature above 80°C, preferably above 100°C, and even more preferably above 120°C. The proton exchange membrane 1 can be made of polybenzimidazole (PBI) or any other material suitable for high-temperature operation. Preferably, the operating temperature is above 100°C to obtain water in gaseous form within the pressure range used on the cathode side. Preferably, the degradation temperature of the membrane 1 is above 100°C, or even above 150°C, more preferably above 200°C.

[0019] The proton exchange membrane 1 defines an anodic face and a cathodic face. The anodic face is covered by the anodic electrode 2, while the cathodic face is covered by the cathodic electrode 3. The anodic electrode 2 is located between the proton exchange membrane 1 and the anodic current collector 4. The cathodic electrode 3 is located between the proton exchange membrane 1 and the cathodic current collector 5.

[0020] At least one of the anodic electrode 2 and the cathodic electrode 3 is a nanostructured electrode, i.e., a non-smooth electrode. The nanostructured electrode comprises filamentary nanoelements that extend primarily in the direction connecting the anodic current collector 4 and the cathodic current collector 5 and / or perpendicular to the cathodic or anodic face. The filamentary nanoelements comprise nanotubes and / or nanowires. Nanotubes are hollow filamentary elements, while nanowires are solid filamentary elements.

[0021] The wire nanoelements comprise a catalyst material which may be a cathodic catalyst material or an anodic catalyst material depending on whether the wire nanoelements belong to the cathodic electrode 3 or the anodic electrode 2. The wire nanoelements may be coated by particles of catalyst material or by a continuous layer of catalyst material.

[0022] The wire nanoelements are electrically conductive and are electrically connected to the current collectors to allow electron transfer between the current collector and the catalyst material to carry out the electrochemical reactions. The wire nanoelements can be carbon nanotubes or nanowires of a metallic or other material.

[0023] The use of a nanostructured cathode electrode 3 increases the exchange surface area between the gas and the catalytic material, the site of the electrochemical reaction. The same applies to the use of a nanostructured anodic electrode 2.

[0024] Preferably, the wire nanoelements extend mainly in a direction that is perpendicular to the cathodic face or perpendicular to the anodic face. The extension direction of the wire nanoelements is parallel to the thickness direction of the proton exchange membrane. The thickness direction corresponds to the stacking direction of the membrane-electrode assembly.

[0025] The catalyst material can be selected from chromium, molybdenum, tungsten, manganese, rhenium, iron, copper, silver, zinc, tin, gold, aluminum, osmium, palladium, platinum, iridium, nickel, cobalt, rhodium, and osmium. It is also possible to use several of these elements and / or a mixture thereof.

[0026] Carbon nanotubes preferably have a diameter between a few nanometers and a few tens of nanometers. Preferably, the nanotubes have, on average, a diameter greater than 2 nm, or even greater than 5 nm, or even greater than 10 nm, or even greater than 15 nm. It is advantageous for the nanotubes to have a diameter less than 200 nm, or even less than 150 nm, or even less than 100 nm, or even less than 80 nm, and more preferably less than 50 nm. In a preferred embodiment, the nanotube density is between 10⁹ and 12¹² nanotubes / cm², for a minimum surface area that is preferably greater than or equal to 0.5 mm².

[0027] When the nanowire elements are carbon nanotubes, the carbon nanotubes have inclusions of a catalyst material, or particles of the catalyst material are attached to the carbon nanotubes. Alternatively, the nanostructured surface is formed by a mat of carbon nanotubes coated with a layer of catalyst, preferably platinum. Preferably, the catalyst is deposited by atomic layer deposition (ALD). Advantageously, the thickness of the catalyst layer is less than 15 atomic layers, preferably less than 10 atomic layers. The same can be true for the nanowires.

[0028] The presence of a layer of filamentary nanoelements between the proton exchange membrane 1 and the current collector allows for significant roughness which increases the usable exchange surface area for a given volume. The wire-like nanoelements exhibit good electrical and thermal conductivity, which allows for a layer capable of ensuring good circulation of charge carriers during the redox phase and of ensuring good temperature homogenization along directions parallel to the surface of the cathodic or anodic face.

[0029] The use of wire-like nanoelements allows for good electrical and thermal conduction with the proton exchange membrane. The use of wire-like nanoelements also allows for good heat conduction in a direction perpendicular to the interface between the cathode electrode and the proton exchange membrane 1.

[0030] Preferably, the thickness of the anodic electrode 2 and / or the cathodic electrode 3 is between 5 microns and 200 microns, preferably between 5 microns and 100 microns, preferably between 5 microns and 50 microns.

[0031] To increase the efficiency of the catalyst material present on the wire nanoelements, it is particularly advantageous to use an ionically conductive layer or an ionic conductor that partially covers the wire nanoelements, more preferably a layer of a proton conductor. The ionically conductive layer connects the catalyst material and the proton exchange membrane to transfer the protons involved in the electrochemical reactions.

[0032] In order not to impede the reaction between the catalyst material and the gas, it is advantageous for the ionically conductive layer to be in liquid form. The liquid attaches to the filament nanoelements by capillary action, which allows the use of a small amount of ionically conductive material and the easy formation of a thin layer over a large part of the height of the filament nanoelements, or even over their entire height, to connect the largest possible surface area of ​​catalyst material.

[0033] The use of an ionically conductive layer in liquid form allows for better management of deformations related to differential expansions between the proton exchange membrane 1, the current collector, preferably the cathode current collector, and the wire nanoelements. Depending on temperature changes, the proton exchange membrane 1, the cathode current collector 5, and the wire nanoelements expand or contract. Since the proton exchange membrane 1, the cathode current collector 5, and the wire nanoelements have different coefficients of thermal expansion, the cathode electrode 3 is subjected to different sets of stresses. In order to maintain good performance throughout the fuel cell's lifetime, it is advantageous to have an ionically conductive layer in liquid form that can accommodate the relative deformations between the different layers of the fuel cell.

[0034] Since the fuel cell operates at high temperature, a large portion of the water produced by hydrogen reduction is present in its gaseous form, which tends to limit the dilution of the proton conductor. The proton conductor is preferably an acid, more preferably a strong acid diluted with water, and even more preferably a solution of H3PO4.

[0035] The ionically conductive layer is formed by a first compound in liquid form. The first compound is preferably a copolymer fluoropolymer based on sulfonate tetrafluoroethylene, for example a compound known as Nafion®.

[0036] Preferably, the first compound has an evaporation temperature that is higher than the evaporation temperature of water by at least 20°C, preferably by at least 50°C and more preferably by at least 100°C at the operating pressure of the fuel cell.

[0037] Preferably, the first compound has an evaporation temperature which is higher than the operating temperature of the fuel cell by at least 10°C and more preferably higher than the operating pressure of the fuel cell by at least 50°C.

[0038] It is advantageous to choose the quantity of the first compound so that the thickness of the ionically conductive layer is less than the thickness of the catalyst material particles, so as not to completely cover the catalyst material. Preferably, the filament nanoelements have a coating that exhibits a first surface tension value with the first compound that is greater than a second surface tension value with the catalyst material. This facilitates the release of the catalyst material surface for the electrochemical reaction.

[0039] It is advantageous that the maximum thickness of the ionic conductor be less than 20 microns to form the ionically conducting channels.

[0040] The cathode electrode 3 is a layer that receives oxygen. The cathode electrode 3 is a porous or perforated layer with perforations in one or more directions parallel to the surface of the anodic or cathodic face, allowing for good fluid circulation. This facilitates efficient use of the entire available surface area of ​​the catalyst material.

[0041] The presence of the catalyst material on the surface of the wire nanoelements allows for good heat conduction towards the current collector, in particular the cathode current collector 5. The ionically conductive layer does not form an obstacle to heat dissipation.

[0042] Preferably, the catalyst material can be in the form of particles or a thin porous layer.

[0043] When the filament nanoelement is a carbon nanotube, the catalyst material can be in the form of particles or a thin porous layer. The use of particles prevents excessive reduction in the gas's ability to pass through the carbon nanotube. The same is essentially true when the catalyst material is a porous layer. This configuration allows for a greater number of triple points, i.e., interfaces between the catalyst, the carbon nanotube, and the ionically conductive layer, which are the most efficient points for electrochemical reactions.

[0044] To obtain a thin porous layer, an ALD type deposit is recommended.

[0045] In an advantageous embodiment, wire nanoelements are present on both sides of the cathode current collector 5. First wire nanoelements are arranged between the cathode current layer 5 and the proton exchange membrane 1 to form the cathode electrode 3. Second wire nanoelements are arranged on the opposite face of the cathode current layer 5 to be located in the oxygen precursor gas supply channel. The second wire nanoelements are thermally connected to the cathode current collector 5. The second wire nanoelements are swept by the oxygen precursor gas, which increases the heat exchange surface area between the oxygen precursor gas and the cathode current collector 5.If a portion of the oxygen precursor gas is not used in the electrochemical reaction and instead delivers or absorbs heat to the second wire nanoelement, this electrochemically inactive portion of gas can be used to regulate the temperature of the assembly formed by the proton exchange membrane 1, the cathode electrode 3, and the cathode current collector 5. It is advantageous for the second wire nanoelements to be nanotubes, and preferably carbon nanotubes, in order to achieve good heat exchange with the gas flowing in the feed channel without introducing excessive pressure drop.

[0046] The fuel cell may be equipped with a temperature sensor configured to measure the temperature of the fuel cell, the proton exchange membrane, or the assembly formed by the proton exchange membrane 1, the cathode electrode 3, and the cathode current collector 5. When the temperature exceeds a threshold value, a fuel cell control circuit may inject an excess of cooler oxygen precursor gas. Conversely, when the temperature falls below a second threshold lower than the first threshold, the control circuit may inject warmer oxygen precursor gas.

[0047] For example, if the oxygen precursor gas comes from a pressurized gas, the expansion of the gas out of the tank towards the feed channel 6 can be used to supply a gas whose temperature is below the threshold temperature This allows the cathode current collector 5 to be cooled. Sending a larger quantity of gas allows the current collector 5 to be cooled.

[0048] Sending a larger quantity of gas generates greater electrochemical activity, it is advantageous for the cathode current collector 5 to introduce a charge loss which allows only a small part of the gas to be sent into the cathode electrode, for example less than 70% of the gas beyond its nominal operating point, preferably less than 50% more preferably less than 20%.

[0049] The same may apply to the anodic current collector 4.

[0050] In a preferred embodiment, the cathode current collector 5 is a metallic foam. The metallic foam has open pores such as to define channels connecting the two opposite walls along the thickness direction.

[0051] The use of a metallic foam makes it possible to form a current collector which has good thermal conduction along the thickness direction and good electrical conduction.

[0052] It is advantageous for the cathode current collector 5 to define a wall of the feed channel 6 in oxygen precursor. The oxygen precursor gas flowing in the feed channel 6 passes through the cathode current collector and flows inside the cathode electrode 3 until it comes into contact with the catalyst material.

[0053] The metallic foam advantageously has a porosity ratio between X and Y% by volume.

[0054] The metallic foam has pores on the surface whose average diameter is between X and Y microns.

[0055] The use of a metallic foam is particularly advantageous because it has better compressive strength compared to the carbon felts commonly used in the prior art. The metallic foam compresses less than the carbon felt layer when a given force is applied, which allows less force to be applied to ensure good contact between the cathode electrode 3 and the cathode current collector 5 or between the cathode electrode 3 and the proton exchange membrane 1.

[0056] Since the applied stresses are less severe, it is easier to manage differential expansion between the cathode current collector and the proton exchange membrane. It is also easier to form an electrical generator.

[0057] When the fuel cell has an ionically conductive layer in liquid form, it is advantageous to have a metallic foam whose surface pores have a diameter of less than 10 microns because this makes the passage of the liquid through the metallic foam difficult or even impossible. The passage is This is all the more difficult as the fuel cell is in operation and delivers an oxygen precursor gas which tends to push the liquid towards the proton exchange membrane 1.

[0058] When the ionically conductive layer is formed by a strong acid, the metal foam material is preferably inert to the strong acid and / or the external surface of the metal foam is covered by a protective coating, for example a carbon-based coating deposited by PVD (Physical Vapor Deposition). The coating is electrically conductive.

[0059] The metallic foam may be titanium foam, nickel foam, or preferably Monel nickel and copper foam. Aluminum foam, possibly coated with a protective coating, may also be used. Inconel (nickel-chromium alloy) or Hastelloy (nickel-molybdenum alloy) foam may also be used.

[0060] It is still possible to use a stainless steel foam which is preferably coated with a protective coating, for example a layer of amorphous carbon.

[0061] The metallic foam is preferably free of catalyst material, and any inclusions of catalyst material are devoid of ionically conductive connections with the proton exchange membrane. The metallic foam is used solely as a current collector capable of efficiently conducting electric current and extracting heat, taking advantage of its superior compressive strength compared to carbon felts.

[0062] Alternatively, the metallic foam has a surface containing or coated with catalyst material to increase the electrochemically active surface area. The ionic conductor forms ionically conductive channels to connect the proton exchange membrane and the active part of the cathode current collector 5. The ionically conductive channels are formed by capillary action. The channels can be formed by a suitable coating or texturizing of the cathode current collector 5.

[0063] In a particularly advantageous embodiment, the metal foam is used as a starting substrate for the growth of the wire nanoelements. The wire nanoelements of the cathode electrode 3 are attached to the metal foam, and the installation of the cathode current collector facing the cathode wall of the proton exchange membrane 1 allows the cathode electrode 3 to be connected to the proton exchange membrane 1.

[0064] In another embodiment, the wire nanoelements are made from the cathode wall of the proton exchange membrane 1. The metallic foam is pressed against the wire nanoelements to make the electrical connection between the wire nanoelements and the cathode current collector 5.

[0065] In the cathodic zone, the electrochemical reaction produces water which, depending on the temperature and pressure conditions, can be in liquid or gaseous form. When the ionically conductive layer is in liquid form and contains water, it is advantageous that the fuel cell operating conditions do not significantly alter the composition of the ionically conductive layer, as this would result in a change in the capillary characteristics between the ionically conductive layer and the filament nanoelements. The metallic foam can be coated with a hydrophobic coating, for example, fluorinated polymers or hydrophobic epoxy resins. The surface of the metallic foam can also contain titanium dioxide inclusions to make it hydrophobic. It is also possible to modify the surface texture, and in particular the pore diameter, to make water drainage more or less difficult.

[0066] The surface texture may differ between the anodic current collector 4 and the cathodic current collector 5 in order to exhibit different behavior with respect to water. The cathodic current collector 5 may have areas with different textures to form hydrophobic and less hydrophobic or even hydrophilic areas.

[0067] In a further advantageous embodiment, first filamentary nanoelements are formed on one side of the cathode current collector 5 and have inclusions of catalyst material and / or are coated with catalyst material. On the other side of the cathode current collector 5, second filamentary nanoelements are formed and are located in the oxygen precursor supply channel 6. These second filamentary nanoelements increase the exchange surface area between the oxygen precursor gas and the cathode current collector 5, which allows for better temperature regulation of the cathode current collector 5 and therefore better temperature regulation of the cathode electrode 3 and the proton exchange membrane 1.

[0068] The first and second wire nanoelements can be formed simultaneously from the two opposite faces of the cathode current collector. It is also possible to form them one after the other.

[0069] The second wire nanoelements are devoid of catalyst material and / or are devoid of ionically conductive connection with the proton exchange membrane 1.

[0070] In a particular embodiment, in order to promote the dissipation of heat produced by the cathode electrode 3, it is advantageous to enhance heat dissipation through the cathode current collector 5 and, more preferably, heat dissipation through the oxygen precursor gas. The current collector The cathode current collector 5 exhibits good thermal conductivity along its thickness direction. Preferably, the cathode current collector 5 is made of a metallic material. The cathode current collector 5 has a good thermal connection with the cathode electrode 3; preferably, the cathode electrode 3 is fixed to the cathode current collector 5 or has a large contact surface with the cathode current collector 5.

[0071] As previously mentioned, the fuel cell can be equipped with a temperature sensor configured to measure the temperature of one or more of the fuel cell's constituent elements. Alternatively, the fuel cell is not equipped with such a sensor, and the operating conditions have been studied beforehand to define operating conditions that ensure good temperature control.

[0072] The cathode current collector 5 has an inner face that is in contact with the cathode electrode 3 and an outer face that is opposite it. The gas enters through the outer face and passes through the cathode current collector 5 to reach the cathode electrode 3. The outer face delimits at least part of a first oxygen precursor supply channel 6.

[0073] The anodic current collector 4 has an inner face that is in contact with the anodic electrode 2 and an outer face that is opposite it. The gas enters through the outer face and passes through the anodic current collector 4 to reach the anodic electrode 2. The outer face defines at least part of a second hydrogen precursor supply channel 7. It is advantageous for the supply channel to also serve as an exhaust channel.

[0074] In an advantageous embodiment, the cathode electrode 3 is integral with the proton exchange membrane 1. The deformations of the cathode catalytic layer 3 and the proton exchange membrane 1 are identical or substantially identical in directions perpendicular to the thickness direction. In another advantageous embodiment, the anodic electrode 2 is integral with the proton exchange membrane. The deformations of the anodic catalytic layer 2 and the proton exchange membrane 1 are identical or substantially identical in directions perpendicular to the thickness direction.

[0075] In an even more advantageous embodiment, the cathode electrode 3 is integral with the cathode current collector 5. The deformations of the cathode catalytic layer 3 and the cathode current collector 5 are identical or substantially identical in directions perpendicular to the thickness direction. The use of a cathode electrode 3 that is integral with the cathode current collector 5 allows for good heat and current transfer from the catalytic layer to the current collector, even without The application of a bearing force between the multiple layers of the stack improves the fuel cell's lifespan by limiting the forces along the thickness direction, thus ensuring close contact between the different layers. The same advantageous principle applies to the anodic electrode 2 with the anodic current collector 4.

[0076] A first supply channel 6 connects a first reservoir containing an oxygen precursor and the cathode electrode 3. A second supply channel 7 connects a reservoir containing a hydrogen precursor and the anodic electrode 2.

[0077] The first power supply channel 6 is partially delimited by the cathode current collector 5. The second power supply channel 7 is partially delimited by the anode current collector 4.

[0078] The reaction of the oxygen precursor with the cathode electrode 3 and of the hydrogen precursor with the anode electrode 2 is stoichiometric. At least one gas flow rate is predetermined and delivered to provide a predetermined current value by the fuel cell. It is advantageous for one gas to be delivered under superstoichiometric conditions so that the other gas limits the reaction and defines the amount of current to be delivered. To facilitate the removal of water produced in the cathode zone, it is advantageous for the oxygen precursor to be delivered under superstoichiometric conditions compared to the hydrogen precursor.

[0079] To facilitate the removal of water produced in the cathodic zone, it is advantageous to have a high gas flow rate on the cathodic side. It is advantageous to have an oxygen precursor flow rate that is greater than the stoichiometric flow rate. The excess oxygen allows for a gas flow that ensures the supply of oxygen precursor and the removal of water. Advantageously, the oxygen flow rate in the cathodic electrode 3 is more than twice the stoichiometric flow rate.

[0080] The cathodic current collector 5 and the anodic current collector 4 are openwork layers and they define a pressure drop between the flow which circulates between the supply channel and the associated electrode, i.e. in the direction of the anodic or cathodic electrode.

[0081] The flow rate of the gas emitted by the oxygen precursor reservoir is adapted so that the pressure drop induced by the cathode current collector 5 does not prevent the oxygen precursor flow rate from exceeding the stoichiometric flow rate. Advantageously, the cathode current collector 5 defines a pressure drop that corresponds to a halving of the flow rate between the first feed channel 6 and the cathode electrode 5 within the nominal operating range of the fuel cell.

[0082] Advantageously, the pressure in the first supply channel 6 is greater than 1013 hPa, preferably greater than 2026 hPa. Preferably, the pressure in the first supply channel 6 is less than 10130 hPa. Advantageously, the pressure in the second supply channel 7 is greater than 1013 hPa, preferably greater than 2026 hPa. Preferably, the pressure in the second supply channel 7 is less than 10130 hPa.

[0083] Preferably, the flow rate of the gas emitted by the oxygen precursor reservoir is also adapted to remove a significant amount of heat. The higher the gas flow rate, the greater the amount of heat removed. However, applying too high a flow rate results in the drying out of the proton exchange membrane 1. It is therefore advantageous to transform a very high flow rate in the feed channel 6 into a lower flow rate suitable for supplying the amount of gas necessary for the electrochemical reaction and for removing the water without drying out the proton exchange membrane 1. Advantageously, the cathode current collector 5 defines a pressure drop that corresponds to a fivefold reduction in the flow rate between the first feed channel 6 and the cathode electrode 5.More advantageously, the cathode current collector 5 defines a pressure loss which corresponds to a division by ten of the flow rate between the first feed channel 6 and the cathode electrode 5.

[0084] It is advantageous for the cathode current collector 5 to define a pressure drop which corresponds to a division of the flow rate equal to 2 between the flow rate of the first supply channel and the flow rate in the cathode electrode 3, but no more than a division by 20 of the flow rate in the nominal operating range of the fuel cell.

[0085] Applying a large flow rate in the first supply channel 6 makes it easier to remove heat by means of the gas which circulates against the external face of the cathode current collector 5 which is a good thermal conductor in direct contact with the cathode electrode 3.

[0086] In a particular embodiment, the contact area between the wire nanoelements and the proton exchange membrane 1 is increased so as to enhance heat transfer between the proton exchange membrane 1 and the cathode electrode 3. Alternatively, the contact area between the wire nanoelements and the cathode current collector 5 is increased so as to enhance heat transfer and electrical conduction between the cathode current collector 5 and the cathode electrode 3.

[0087] Preferably, curved wire nanoelements are used. The wire nanoelements have a distal portion fixed to the cathode current collector 5 or to the proton exchange membrane 1, and the proximal portion of the wire nanoelements is in contact with the proton exchange membrane 1 or the cathode current collector 5. The wire nanoelements are curved between the proximal and distal parts.

[0088] The proximal portion extends substantially perpendicularly to the face of the cathode current collector 5 or the face of the proton exchange membrane 1 to which the filament nanoelements are attached. More preferably, the growth of the filament nanoelements has occurred from this face. The proximal portion extends in a direction that is substantially parallel to the face receiving the distal portion.

[0089] Preferably, the distal part is arranged to slide relative to the proton exchange membrane 4 or the cathode current collector 5. During differential deformations between the proton exchange membrane 1 and the cathode current collector 5, the wire nanoelements are able to move and possibly deform to limit the stresses applied within the fuel cell.

[0090] In an alternative embodiment, a portion of the distal part is fixedly mounted to the proton exchange membrane 1 or to the cathode current collector 5. During differential deformations between the proton exchange membrane 1 and the cathode current collector 5, the wire nanoelements are able to deform to limit the stresses applied within the fuel cell.

[0091] At the end of their growth stage, the filament nanoelements do not all have the same length. The greater the desired length, the greater the length variations. The shortest filament nanoelements may not be active if the gap between the filament nanoelement and the proton exchange membrane 1 prevents the formation of an ionically conductive connection. If the filament nanoelement is not in contact with the cathode current collector 5, the catalyst present on the filament nanoelement will not interact electrochemically.

[0092] If the filament nanoelements are straight, a cutting step can be performed to reduce the gap between the longest and shortest filament nanoelements and thus increase the proportion of electrochemically active filament nanoelements. Alternatively, during growth, the filament nanoelements are curved, which increases the contact area of ​​the distal portion with the proton exchange membrane 1 or the cathode current collector 5. The length differences are partially eliminated.

[0093] If the distal portion is in contact with the proton exchange membrane 1 and a liquid ionic conductor is used, all or part of the distal portion may be covered by the liquid ionic conductor. The distal portion allows for significant contact with the proton exchange membrane 1 and with the liquid ionic conductor to ensure good heat transfer. If the distal portion is in contact of the cathode current collector 5, the large contact length allows good heat exchange and good electron transfer.

[0094] The curved wire nanoelements can be nanotubes, for example carbon nanotubes or nanowires, for example silicon nanowires, germanium nanowires or cadmium sulfide nanowires.

[0095] It is particularly advantageous to use curved wire nanoelements when the length of the wire nanoelement is greater than 50 microns, more preferably greater than 100 microns or 200 microns.

[0096] The anodic current collector 4 and the cathodic current collector 5 each define at least one output terminal of the electric current out of the fuel cell.

[0097] Preferably, the porous network is also through-through in at least one direction parallel to the interface between the cathode electrode 3 and the cathode current collector 5.

[0098] It is particularly advantageous that the anodic electrode 2 and the cathodic electrode 3 are fixedly mounted to the proton exchange membrane 1. It is even more advantageous that the anodic current collector 4 and the cathodic current collector 5 are fixedly mounted respectively to the anodic electrode 2 and the cathodic electrode 3.

[0099] The formation of a single-piece assembly extending from the anode current collector 4 to the cathode current collector 5 simplifies the fuel cell configuration by eliminating the means for compressing the stack.

[0100] The cathode current collector 5 can be a metallic layer perforated by holes along its thickness. The size of the holes, their orientation, and their distribution are chosen to obtain the expected pressure drop between the first feed channel 6 and the cathode electrode 5. The pressure drop value depends on the circulation conditions of the oxygen precursor in the feed channel (temperature, pressure, gas composition).

[0101] In a particular embodiment, the oxygen precursor supply channel 6 also forms the outlet channel for excess oxygen precursor and water. Preferably, at least one of the characteristic parameters of the holes is variable depending on the direction of oxygen precursor flow along the first supply channel 6 in order to have a decreasing pressure drop with respect to the direction of oxygen precursor flow and / or to take into account the increase in water content in the gas mixture.

[0102] As an alternative or in addition, the porosity rate along the thickness direction is variable according to the direction of circulation of the oxygen precursor in order to have a decreasing pressure loss along the direction of circulation of the oxygen precursor.

[0103] The cathode current collector 5 may be a metallic foil defining a plurality of through holes. The cathode current collector 5 may be a metallic foam with through pores.

[0104] Since the fuel cell is intended to operate at a temperature above 80°C and more preferably above 100°C or even 120°C, the water can be in a gaseous or liquid form.

[0105] In a particular embodiment, the cathode current collector 5 is formed by a first porous layer and a second porous layer. The first porous layer is disposed between the cathode electrode 3 and the second porous layer. The first porous layer has an average pore size that is smaller than the average pore size of the second porous layer. For example, the first porous layer is a microporous layer and the second porous layer is a macroporous layer. The first porous layer has an average pore size that is less than 5 nanometers and the second porous layer has an average pore size that is greater than 25 nanometers, preferably greater than 50 nanometers. The first porous layer and the second porous layer are good conductors of current and heat.The pore size refers to the pores extending in one or more directions parallel to the interface between the cathode electrode 3 and the cathode current collector 5. Preferably, the first and second porous layers are made of metal, for example, perforated metal or metallic foam. It is also possible to use carbon graphene or a felt formed by nanotubes extending parallel to the surface of the support substrate. The use of a carbon nanotube felt is particularly advantageous when the nanotubes have catalyst inclusions, for example, platinum, and are impregnated with an acid, for example, phosphoric acid.

[0106] The use of large pores in the second layer allows for significant circulation of an oxygen precursor gas, for example, air. This significant gas circulation facilitates heat dissipation by utilizing a large exchange surface area between the gas and the second layer. Reducing the porosity, and preferably the pore size, limits the flow of oxygen precursor in the immediate vicinity of the catalyst. Reducing the air flow prevents the membrane surface from drying out during operation.

[0107] Depending on the desired operating conditions, namely the membrane temperature and the partial pressures of oxygen and hydrogen, it is possible to choose a second layer and a larger or smaller pore diameter.

[0108] The higher the operating temperature, the more the water will tend to be in a gaseous form, which encourages the use of small diameter pores. The higher the oxygen flow rate, the greater the risk of drying out the proton exchange membrane, which encourages the use of small-diameter pores. The higher the pressure or flow rate ratio between the oxygen precursor and the hydrogen precursor, the more advantageous it becomes to use small-diameter pores. A decrease in pore diameter can be offset, or combined with, an increase in the surface area of ​​hydrophobic material.

[0109] In a preferred embodiment, the average porosity in the cathode current collector 5 is less than 50%, more preferably less than 30%.

[0110] The cathode current collector 5 is preferably fixed to the cathode electrode 3, for example by welding, brazing, or bonding. The cathode current collector 5 is fixed by any suitable means that ensures electrical and thermal continuity between the cathode current collector 5 and the cathode electrode 3, independent of deformations of the membrane-electrode assembly due to temperature and / or pressure changes.

[0111] What has been explained for the cathode current collector 5 can be applied to the anodic current collector 4. Preferably, the anodic current collector 4 is identical to the cathode current collector 5.

[0112] In a power generator, the fuel cell is arranged in a housing which partially defines the first supply channel 6 and the second supply channel 7. The housing has a first hood and a second hood which are separated by the membrane-electrode assembly.

[0113] The cathode current collector 5 is surmounted by a first cover 8, and the first cover 8 is advantageously separated from the cathode current collector 5 by a first separator 9. Preferably, the first separator 9 deforms elastically between the first cover 8 and the cathode current collector 5. The elastic deformation of the first separator 9 allows a predetermined force to be applied to one end of the membrane-electrode assembly. The first separator 9 may be in the form of a corrugated plate.

[0114] Advantageously, the anodic current collector 4 is surmounted by a second cover 10, and the second cover 10 is separated from the anodic current collector 4 by a second separator 11. Preferably, the second separator 11 deforms elastically between the second cover 10 and the anodic current collector 4. The elastic deformation of the second separator 11 allows a predetermined force to be applied to the other end of the membrane-electrode assembly. The second separator 11 may be in the form of a corrugated plate.

[0115] In another alternative, the membrane-electrode assembly is fixed to the enclosure by other means. In an example embodiment illustrated in Figures 3 and 4, the enclosure has a frame 12 which defines a through hole. The peripheral portion of a The face of the membrane-electrode assembly rests on the frame 10, allowing a gas to be applied to one face of the assembly through the frame. The seal between the anodic and cathodic faces is ensured by the peripheral portion of the membrane-electrode assembly, which rests on the frame 12.

[0116] It is particularly advantageous for the enclosure to be made of electrically insulating material with a few electrical tracks so as to form an economical and lightweight configuration. The electrical tracks have one end in contact with the anode current collector or the cathode current collector. The other end of the electrical tracks is intended to be connected to an electrical load or other suitable device. The enclosure can be made of plastic material.

[0117] In a particularly advantageous embodiment, an energy generator comprises several fuel cells according to one of the preceding configurations or according to another configuration. Depending on the requirements, the fuel cells are connected in parallel or in series or a mixture of these two arrangements.

[0118] Several fuel cells are mounted opposite each other in a stacking direction that is parallel to the thickness direction of the individual fuel cells. The stacking direction passes through the multiple fuel cells. More specifically, the stacking direction passes through the multiple cathode current collectors 5, the multiple anode current collectors 4, the multiple anodic catalytic layers 2, the multiple cathode catalytic layers 3, and the multiple proton exchange membranes 1. Preferably, each membrane-electrode assembly is mounted on a frame 12, and the multiple frames 12 are stacked one on top of the other.

[0119] The fuel cells are mechanically linked together so that two adjacent fuel cells share the same feed channel. In other words, two adjacent fuel cells have two anode current collectors 4 or two cathode current collectors 5 facing each other, which are nearest neighbor collectors. Such an arrangement facilitates the management of gas flows. It is also advantageous to share a separator, which then becomes common to two adjacent fuel cells. The separator is preferably electrically insulating to offer greater flexibility in the available electrical configurations.

[0120] When the electric generator has three or more than three fuel cells, there are at least two adjacent fuel cells that have two cathode current collectors 5 as nearest neighbors and two adjacent fuel cells that have two anodic current collectors 4 as nearest neighbors.

[0121] Preferably, the fuel cells are mounted on or in frames 12, and the frames 12 are stacked one on top of the other to assemble the fuel cells facing each other. The frames 12 define a window for receiving a fuel cell and a through hole inside the window. Once the frames are stacked one on top of the other, the through holes are aligned along the stacking direction.

[0122] The fuel cells are arranged between the frames so as to form an alternation between a fuel cell and a through hole according to the stacking direction, i.e. a window delimiting the through hole.

[0123] Advantageously, the frames 12 are stacked one on top of the other so as to define oxygen precursor supply channels and hydrogen precursor supply channels, as well as oxygen precursor exhaust channels and hydrogen precursor exhaust channels. The different gases flow from frame to frame. Preferably, the oxygen precursor flows in a channel that is configured to supply the multiple cathode current collectors 5 in parallel.

[0124] When groups of two immediately adjacent fuel cells share the same feed channel to supply two current collectors with the same gas, it is advantageous to form two types of frame 12. [Fig.4] illustrates an embodiment in which the plurality of frames 12 comprises first frames that deliver the oxygen precursor to the cathodic current collectors and second frames that deliver the hydrogen precursor to the anodic current collectors.

[0125] Preferably, the first and second frames 12 are each traversed by the supply and / or discharge channel(s) for the oxygen precursor and the hydrogen precursor. However, a first frame allows only the supply of hydrogen precursor to a second frame, and a second frame allows only the supply of oxygen precursor to a second frame. The same may apply to the discharge channels.

[0126] In one configuration, the first hood 8 and the second hood 10 define an enclosure which encompasses the frame(s) 12. In an alternative, the enclosure is formed by the frame(s) 12 and is terminated at each end by the first hood 8 or the second hood 10.

[0127] In a particular embodiment, each frame 12 of a stack is mechanically linked to the two adjacent frames 12 by a connection that defines a fold zone, with the exception of the end frames. During the manufacture of the power generator, a fuel cell is mounted on or in each frame 12. The frames are arranged one on top of the other by folding the fold zones. The folding of the zones The folding design defines the supply channels as well as the exhaust channels and the sealed portions around the multiple fuel cells.

[0128] Preferably, the frames 12 are provided with electrical tracks 13 which are connected to the anodic current collector 4 or to the cathodic current collector 5. The frames 12 are made of an electrically insulating material, for example an electrically insulating plastic material and are traversed by the electrical tracks.

[0129] All or part of the electrical tracks may pass through the link in order to electrically connect a fuel cell with an adjacent fuel cell of an adjacent frame.

[0130] In one embodiment, at least a portion of the electrical tracks 13 of one frame makes electrical contact with at least a portion of the electrical tracks 13 of an adjacent frame when the two frames are stacked one on top of the other. When the frames are not stacked, the electrical tracks 13 are not in contact.

[0131] The electrical tracks 13 are arranged along the frames 12 to connect the multiple fuel cells in a particular configuration, for example in series, in parallel, or in a more complex arrangement. The electrical configuration of the different fuel cells is defined by the tracks running in the frames before the fuel cells are installed.

[0132] It is particularly advantageous to use frames 12 made of plastic or composite material because this allows for the formation of lightweight frames whose mechanical performance within the operating temperature range of fuel cells ensures good sealing. The power generator can be manufactured economically. Furthermore, the use of a polymer frame is advantageous when the fuel cell contains a strong acid.

[0133] During operation, the redox reaction of the oxygen precursor and the hydrogen precursor occurs at the surface of the anodic electrode and at the surface of the cathodic electrode. A flow of protons passes through the proton exchange membrane 1 from the anodic face to the cathodic face. Electrons flow along the anodic electrode 2 and along the filament nanoelements until they reach the anodic current collector 4. Then, the electrons leave the fuel cell to be used in an electrical charge. Conversely, a flow of electrons enters the fuel cell by means of the cathodic current collector 5 and then reaches the cathodic electrode 3, notably by flowing through filament nanoelements.

Claims

Demands

1. Power generator comprising: - an array of fuel cells each having an anodic output terminal and a cathodic output terminal; - an array of frames comprising several frames stacked one on top of the other in a stacking direction, each frame defining a fuel cell receiving window and a through hole, the through holes being aligned in the stacking direction inside the windows; in which one of the several fuel cells is wedged between each of the two successive frames; the array of frames, in which the fuel cells are stacked one on top of the other in the stacking direction between two frames to form an alternation with the through holes in the stacking direction;in which the fuel cells are arranged so that each group of two consecutive fuel cells has two anode current connectors (4) or two cathode current connectors as nearest neighbor current collectors according to the stacking direction, said two nearest neighbor current collectors being supplied by the same supply channel; and in which the frame set defines electrical traces connecting the anode output terminals and the cathode output terminals.

2. Power generator according to claim 1 wherein said two nearest neighbor current collectors are separated by an electrically insulating separator elastically deformed by said two nearest neighbor current collectors along the stacking direction.

3. Power generator according to claim 2 wherein the electrically insulating separators are porous and / or have dimensions smaller than the dimensions of the windows in directions perpendicular to the stacking direction.

4. Power generator according to any one of claims 1 and 3 wherein two nearest neighbor cathode current collectors along the stacking direction are each formed by a porous plate, the oxygen precursor supply channel being delimited by the two porous plates. 22

5. Power generator according to claim 4 in which said two nearest neighbor current collectors are formed by a metallic foam.

6. Power generator according to any one of claims 1 to 5 wherein the frames are connected to each other by at least one fold to form a foldable and unfoldable frame assembly.

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