FR2969827A1 - Fuel cell for supplying electric current to e.g. motor vehicle, has circulation systems provided with reversal systems and circulating oxidizing and reducing fluids along sides of membrane based on different flow directions, respectively - Google Patents

Abstract

The cell has a compartment (10) comprising an ion exchange membrane that separates oxidizing fluid and reducing fluid. Oxidizing and reducing fluid circulation systems (50, 52) circulate the oxidizing fluid and the reducing fluid along sides of the membrane based on different flow directions, respectively. The oxidizing and reducing fluid circulation systems have reversal systems (68, 78) that reverse the fluid flow directions in a cathodic fluid exchange pipe and an anodic fluid exchange pipe (16), respectively. An independent claim is also included for a method for supplying oxidizing fluid and reducing fluid to a fuel cell.

Description

FIELD OF THE INVENTION The present invention relates to a fuel cell for generating an electric current from a redox reaction between a fluid and a fluid exchange system adapted to reverse the flow direction of the fluids. oxidant and a reducing fluid, the fuel cell comprising at least one cell comprising an ion exchange membrane separating the oxidizing and reducing fluids, the fuel cell comprising an oxidizing fluid circulation system for circulating the oxidizing fluid. along a first side of the membrane of the or each cell and a reducing fluid circulating system for circulating the reducing fluid along a second side of the membrane of the or each cell. Such a fuel cell is for example intended to power a motor vehicle, a boat, or any device requiring a transportable energy source. The operating principle of such a fuel cell is based on a redox reaction of the oxidizing and reducing fluids, reaction resulting in the formation of water molecules. Generally, positive ions are exchanged between the two sides of the membrane through the ion exchange membrane, the negative charges transiting, in the form of electrons, by an electrical circuit. Each side of the membrane constitutes an electrode of the fuel cell. The ion exchange membrane that separates the oxidizing and reducing fluids requires, for optimal operation, to be properly hydrated. Indeed, in case of too low hydration of the membrane, it can not fulfill its ion exchange function, damage and risk of breaking. On the contrary, in the event of excessive hydration of the membrane, the electrodes are flooded, the reactive fluids can no longer reach the ion exchange membrane and the reaction is stopped.

However, due to the production of water during the reaction occurring on both sides of the membrane, the oxidizing and reducing fluids are generally more humid at the stack outlet than at the inlet. This results in an imbalance of hydration of the ion exchange membrane between the fluid inlet zone and the outlet zone. Systems have been devised to allow more satisfactory hydration of the ion exchange membrane. Document US 2007 264 538 describes a fuel cell equipped with one of these systems. In this document, it is described that the incoming fluids are wetted by the outgoing fluids. Such a system, however, is not entirely satisfactory. Indeed, if one thus limits a too pronounced dewatering of the membrane in the zone of entry of the fluids, the hydration of the membrane remains nevertheless unbalanced. In addition, such humidifier systems are expensive and complex to implement.

An object of the invention is therefore to provide a fuel cell such that the ion exchange membrane is satisfactorily hydrated and has little hydration heterogeneity, while limiting the complexity and the cost of the battery. fuel.

For this purpose, the subject of the invention is a fuel cell of the aforementioned type, characterized in that the oxidizing fluid circulation system is adapted to circulate the oxidizing fluid along the first side of the membrane of the or each cell. in different flow directions. According to particular embodiments of the invention, the fuel cell according to the invention also comprises one or more of the following characteristic (s), taken individually or according to any combination (s). ) technically possible (s): - the reducing fluid circulating system is adapted to circulate the reducing fluid along the second side of the membrane of the or each cell in different flow directions, - at least one of the systems circulation device comprises at least one fluid exchange conduit along the membrane of the or each cell and at least one system for reversing the direction of flow of the fluid in the or each exchange conduit; at least one of the circulation systems comprises a fluid inlet duct, a fluid outlet duct, a first connection duct at one end of at least one exchange duct, a second duct for connection to the duct; another end of the or each exchange conduit and a reversal system of the fluid flow direction, the inversion system being adapted to switch between a first configuration in which the fluid inlet conduit is placed in communication fluidic with the first connecting conduit, and the second connecting conduit is in fluid communication with the fluid outlet conduit, and a second configuration, wherein the fluid inlet conduit is in fluid communication with the second conduit connection, and the first connecting conduit is in fluid communication with the fluid outlet conduit; the fluid flow direction inversion system comprises a first three-way valve connected to the fluid inlet duct, the fluid outlet duct and the first connection duct, the inversion system comprising a second valve three channels connected to the fluid inlet duct, the fluid outlet duct and the second connecting duct; the fluid flow direction inversion system comprises a four-way inversion valve arranged to selectively connect the inlet duct to the first connecting duct and the outlet duct to the second connecting duct, or connect the duct to the duct; inlet duct to the second connecting duct and the outlet duct to the first connecting duct; the fuel cell comprises a plurality of cells and a plurality of fluid flow direction inversion systems, each fluid flow direction reversal system being specific to a single cell or a respective group of cells; the oxidizing fluid is pure dioxygen, and the reducing fluid is pure dihydrogen. The subject of the invention is also a method for supplying an oxidizing and / or reducing fluid fuel cell, the fuel cell comprising at least one cell comprising an ion exchange membrane separating the oxidizing and reducing fluids. , each oxidizing and reducing fluid flowing along the ion exchange membrane, characterized in that the direction of flow of the oxidizing fluid along the membrane of the or each cell is reversed during operation of the cell. The method according to the invention may also comprise one or more of the following characteristic (s), taken individually or according to any combination (s) technically possible (s): - the direction of circulation reducing fluid along the membrane of the or each cell is inverted during the operation of the cell - the moisture of at least one membrane is measured during the operation of the cell, the flow direction of the oxidizing fluid and / or reducing fluid being inverted as a function of the measured humidity; the directions of circulation of the oxidizing and reducing fluids are reversed simultaneously. the oxidizing fluid is pure dioxygen, and the reducing fluid is pure dihydrogen.

Other characteristics and advantages of the invention will emerge more clearly on reading the following description, given solely by way of example and with reference to the appended drawings, in which: FIG. 1 is a diagrammatic view of a cell of a fuel cell according to the invention; Figure 2 is a schematic representation of a fuel cell according to the invention; Figure 3 is a schematic view of a first embodiment of a fluid circulation system of the fuel cell of Figure 2; Figure 4 is a schematic view of a second embodiment of a fuel cell fluid circulation system of Figure 2, a valve of the fluid circulation system being in a first position; and Figure 5 is a view similar to that of Figure 4, the valve being in a second position. The cell 10 of the fuel cell according to the invention, shown in FIG. 1, comprises an ion exchange membrane 12, a cathodic exchange conduit 14, an anode exchange conduit 16, a cathode 18 and an anode 20. The ion exchange membrane 12 separates the oxidizing and reducing fluids. It is adapted to leave only charged ions, preferably cations, through it. The ion exchange membrane 12 is generally a proton exchange membrane, adapted to allow only protons to pass through it. The membrane 12 is typically made of polymeric material and generally contains platinum. The cathode exchange duct 14 extends along a first side 22 (on the left in FIG. 1) of the membrane 12. It is adapted to circulate an oxidizing fluid, symbolized by the arrows 24, along the first side 22 of the membrane 12.

Generally, the oxidizing fluid 24 comprises dioxygen. The oxidizing fluid 24 is typically pure dioxygen, that is to say a fluid having a concentration of oxygen molecules greater than 90%. The anode exchange duct 16 extends along a second side 26 (on the right in FIG. 1) of the membrane 12. It is adapted to circulate a reducing fluid, symbolized by the arrows 28, along the second side 26 of the membrane 12. Generally, the reducing fluid comprises hydrogen atoms in the form of dihydrogen molecules or methanol. The reducing fluid 28 is typically pure dihydrogen, i.e., a fluid having a concentration of dihydrogen molecules greater than 90%.

The cathode 18 is interposed between the cathode exchange conduit 14 and the membrane 12. It is made of electrically conductive material. It is connected to a first terminal of a load 30 intended to be supplied with electricity by the fuel cell. The anode 20 is interposed between the anode exchange conduit 16 and the membrane 12. It is made of electrically conductive material. It is connected to the other terminal of the load 30.

A method of producing electricity by means of the cell 10 will now be described, still referring to FIG. 1. The reducing fluid 28, comprising dihydrogen molecules, is brought to the level of the exchange duct 16. On contact membrane 12 and anode 20, the dihydrogen molecules are split into protons and electrons. The protons, symbolized by the arrow 32, pass through the membrane 12 towards the first side 22, while the electrons, symbolized by the arrow 34, are picked up by the anode 20 and pass through the charge 30 towards the cathode 18. At the first side 22, the protons 32 and the ions 34 react with the oxygen molecules of the oxidizing fluid 24 to give water molecules. The electrons 34, passing through the load 30, supply said load with electric current. The fuel cell comprises a plurality of elementary cells such as the cell 10 described above. These cells are grouped together in a stack 40, commonly referred to as a "stack", visible in FIG. 2.

The fuel cell also comprises an oxidizing fluid circulation system 50 and a reducing fluid circulation system 52. The oxidizing fluid circulation system 50 is connected to the first side 22 of each cell 10 of the stack 40, and the system Reducing fluid circulation 52 is connected to the second side 26 of each cell 10 of the stack 40. These circulation systems 50, 52 are shown in FIG. 2. The oxidizing fluid circulation system 50 comprises the cathodic exchange ducts 14 of FIG. each cell 10, an inlet duct 60 of the oxidant fluid in the fuel cell, an outlet duct 62 of the oxidant fluid out of the fuel cell, a first cathode connection duct 64, in fluid communication with each duct of cathode exchange 14, via a first end of each thereof, a second cathode connection conduit 66, in fluid communication with each conduit of cathode 14 changes, via the other second end of each thereof, and a reversing system 68 of the flow direction of the oxidant fluid into the cathode exchange conduits 14.

Likewise, the reducing fluid circulating system 52 comprises the anode exchange ducts 16 of each cell 10, an inlet duct 70 of the reducing fluid in the fuel cell, an outlet duct 72 of the reducing fluid out of the fuel cell, a first anode connecting conduit 74, in fluid communication with each anode exchange conduit 16, via a first end thereof, a second anode connecting conduit 76, in fluid communication with each conduit; anodic exchange 16, via the other second end of each of them, and an inversion system 78 of the flow direction of the oxidizing fluid in the anode exchange ducts 16. Each inversion system, respectively 68 , 78, the direction of fluid flow is interposed between the inlet duct, respectively 60, 70, and the outlet duct, respectively 62, 72, on the one hand, and the first connecting duct, respectively 64, 74, and the second connecting duct, respectively 66, 76, on the other hand. Each inversion system 68, 78 is adapted to switch between first and second configurations. In FIG. 2, the inversion system 68 of the flow direction of the oxidizing fluid is shown tilted in the first configuration, while the reversal system 78 of the flow direction of the reducing fluid is shown tilted in the second configuration. . In the first configuration of each inversion system, respectively 68, 78, the fluid inlet duct, 60, 70 respectively, is placed in fluid communication with the first connecting duct, respectively 64, 74, and the second duct 66, 76, is in fluid communication with the fluid outlet conduit, respectively 62, 72. In the second configuration of each inverting system, respectively 68, 78, the fluid inlet duct, respectively 60, 70, is in fluid communication with the second connecting duct, respectively 66, 76, and the first connecting duct, respectively 64, 74, is in fluid communication with the fluid outlet duct, respectively 62, 72. The circulation systems 50, 52 are analogous. Embodiments of the oxidant fluid flow system 50 will now be described with reference to Figures 3 to 5.

As can be seen in FIG. 3, in a first embodiment, the inversion system 68 comprises two three-way valves 80, 82 and a control module 84 of said two three-way valves 80, 82. Such three-way valves are known. of the skilled person. A first three-way valve 80 is connected to the fluid inlet duct 60, the fluid outlet duct 62, and the first connecting duct 64. A second three-way valve 82 is connected to the fluid inlet duct 60, the fluid outlet duct 62 and the second connecting duct 66. The first valve 80 is adapted to switch between a first position, in which it puts in fluid communication the fluid inlet duct 60 with the first connecting duct 64, when the inversion system 68 is in its first configuration, and a second position, in which it puts in fluid communication the second connecting duct 66 with the fluid outlet duct 62, when the inversion system 68 is in its second configuration. The second valve 82 is adapted to switch between a first position, in which it puts in fluid communication the second connecting duct 66 with the fluid outlet duct 62, when the inverting system 68 is in its first configuration, and a second position, in which it fluidly communicates the fluid inlet duct 60 with the second connecting duct 66, when the inverting system 68 is in its second configuration. In Fig. 3, the solid arrows represent the path of the oxidizing fluid when the inverting system 68 is in its first configuration, and the dotted arrows represent the path of the oxidizing fluid when the inverting system 68 is in its second configuration. . The control module 84 is adapted to control a simultaneous switching of the valves 80, 82 between their first and second respective positions.

The control module 84 is connected to a humidity sensor 86 of the stack 40. The humidity sensor 86 is adapted to measure the humidity of the membrane 12 of at least one cell 10 of the stack 40, for example of all the cells 10 of the stack 40. In a second embodiment, visible in FIGS. 4 and 5, the inversion system 68 comprises a four-way reversing valve 88 instead of the two three-way valves 80, 82. such four-way inversion valves are known to those skilled in the art. The inverting system 68 further comprises a control module 90, similar to the control module 84 described in the first embodiment. The four-way reversing valve 88 is arranged to selectively connect the inlet duct 60 to the first connecting duct 64 and the second connecting duct 66 to the outlet duct 62, or connecting the inlet duct 60 to the second duct 62. The four-way inverting valve 88 comprises four ports 92, 94, 96, 98 connected in pairs. A first port 92 is connected to a second port 94 and a third port 96 is connected to a fourth port 98. The valve 88 is adapted to switch between a first position, shown in Figure 4, wherein the input port fluid 60 and the first connecting pipe 64 are connected to ports, respectively 92, 94, connected to each other, the fluid outlet duct 62 and the second connecting duct 66 being connected to other ports, respectively 96, 98 connected to each other, and a second position, shown in FIG. 5, in which the fluid inlet duct 60 and the second connecting duct 66 are connected to ports, respectively 94, 92, connected to each other, the duct fluid outlet 62 and the first connecting pipe 64 being connected to other ports, respectively 98, 96, connected to each other. The valve 88 is in its first position when the reversing system 68 is in its first configuration, and it is in its second position when the inverting system 68 is in its second configuration. The valve 88 is adapted to rotate about an axis of rotation A-A '. In Figures 4 and 5, this axis is shown orthogonal to the plane of the sheet.

The four ports 92, 94, 96, 98 are successively distributed around the periphery of the valve 88, in a plane orthogonal to the axis of rotation A-A '. The tilting of the valve 88 between its first and second positions is effected by a rotation of substantially 90 ° of the valve 88 around its axis of rotation A-A ', so as to put each of its ports 92, 94, 96 98, opposite one of the conduits 60, 62, 64, 66. In FIGS. 4 and 5, the tilting of the valve 88 from its first position to its second position is illustrated by a rotation of the valve 88 of substantially 90.degree. ° in a first direction (here the opposite direction of the needles of a watch). In a first variant, the valve 88 is adapted to rotate in only one direction. The tilting of the valve 88 from its second position to its first position is then done by a rotation thereof of substantially 90 ° about the axis A-A ', in the same direction as above, so that the first port 92 is opposite the fluid outlet duct 62, the second port 94 is opposite the second connecting duct 66, the third port 96 is facing the fluid inlet duct 60 and the fourth port 98 is in position. view of the first connecting pipe 64.

In a second variant, the valve 88 is adapted to change the direction of rotation. The tilting of the valve 88 from its second position to its first position is then done by a rotation thereof of substantially 90 ° in a second direction (here the clockwise direction) about the axis A- A ', so that the valve 88 returns to the same first position as that shown in FIG. 4.

The control module 90 is adapted to control the rotation of the valve 88 about its axis A-A ', and thus to control the tilting thereof between its first and second positions. The control module 90 is connected to the same humidity sensor 86 of the stack 40 as that described in the first embodiment.

Preferably, the inversion systems 68 and 78 are made according to the same embodiment. In a variant, the inversion system 68 is made according to one embodiment and the inversion system 78 is made according to another embodiment. The method of supplying the oxidant fluid fuel cell and the method of supplying the reducing fluid fuel cell are analogous. The method for supplying oxidizing fluid will now be described, with reference to FIGS. 3 to 5. The inversion system 68 is in its first configuration, the first connecting duct 64 being supplied with incoming oxidizing fluid coming from the duct. 60, and the second connecting duct 66 being supplied with oxidant fluid leaving the stack 40. The oxidizing fluid 24 then circulates in a first direction of circulation in each exchange duct 14, along each membrane 12. humidity 86 measures the humidity of the membrane 12 of at least one cell 10, for example of each cell 10, of the stack 40. During the operation of the battery, when the control module, respectively 84, 90, of the reversing system 68 detects, by means of the humidity sensor 86, excessive dewatering and / or wetting of at least one region of at least one membrane 12 of a cell of the stack 40, the control module, respectively 84, 90, d triggers the tilting of the inversion system 68 from its first to its second configuration. The flow direction of the oxidizing fluid 24 along the membrane 12 of each cell 10 of the stack 40 is then reversed. Alternatively, the control module, respectively 84, 90, controls the switching of the inverting system 68 after a predetermined time. In the first embodiment, when switching the inverting system 68 from its first configuration to its second configuration, the control module 84 controls the simultaneous switching of the two three-way valves 80, 82 from their first to their respective second positions. . In the second embodiment, the control module 90 controls the rotation of the reversing valve 88 in the first direction. Preferably, the flow directions of the oxidizing fluids 24 and reducing agents 26 are reversed simultaneously. Thanks to the invention, humification imbalances of the cell membranes of the fuel cell are largely limited and the membranes are maintained at satisfactory hydration. In addition, fluid flow direction inversion systems are simple and inexpensive.

The description given above describes two preferred embodiments of the invention. However, many other fluid flow direction reversal systems may be contemplated without departing from the scope of the invention. Finally, instead of using a single inversion system for each of the oxidizing and reducing fluids, as described above, it can be envisaged to use several systems for reversing the flow direction of the reducing fluid and several systems. reversing the flow direction of the oxidant fluid, each inversion system being specific to a single cell, or to a respective group of cells.

Claims (1)

CLAIMS 1. Fuel cell for generating an electric current from a redox reaction between an oxidizing fluid (24) and a reducing fluid (28), the fuel cell comprising at least one cell (10) comprising an ion exchange membrane (12) separating the oxidant (24) and reductant fluids (26), the fuel cell having an oxidizing fluid circulation system (50) for circulating the oxidant fluid (24) therein along a first side (22) of the membrane (12) of the or each cell (10) and a reducing fluid circulating system (52) for circulating the reducing fluid (28) along a second side (26) of the membrane (12) of the or each cell (10), characterized in that the oxidizing fluid circulation system (50) is adapted to circulate the oxidizing fluid (24) along the first side (22). ) of the membrane (12) of the or each cell (10) in different flow directions. 2. Fuel cell according to claim 1, characterized in that the reducing fluid circulating system (52) is adapted to circulate the reducing fluid (28) along the second side (26) of the membrane (12). of the or each cell (10) in different flow directions. 3.- fuel cell according to claim 1 or 2, characterized in that at least one of the circulation systems (50, 52) comprises at least one fluid exchange conduit (14, 16) along the membrane (12) of the or each cell (10) and at least one inversion system (68, 78) of the flow direction of the fluid in the or each exchange conduit (14, 16). 4. Fuel cell according to claim 3, characterized in that at least one of the circulation systems (50, 52) comprises a fluid inlet duct (60, 70), a fluid outlet duct (62) , 72), a first connecting duct (64, 74) at one end of at least one exchange duct (14, 16), a second connecting duct (66, 76) at the other end of the duct each exchange duct (14, 16) and an inversion system (68, 78) of the fluid flow direction, the inversion system (68, 78) being adapted to switch between a first configuration in which the fluid inlet duct (60,70) is in fluid communication with the first connecting duct (64,74), and the second connecting duct (66,76) is in fluid communication with the duct outlet (64,74). fluid (62, 72), and a second configuration, wherein the fluid inlet conduit (60, 70) is in fluid communication with the fluid x connecting duct (66, 76), and the first connecting duct (64, 74) is in fluid communication with the fluid outlet duct (62, 72). 5. Fuel cell according to claim 4, characterized in that the inversion system (68, 78) of the fluid flow direction comprises a first three-way valve (80) connected to the fluid inlet duct ( 60, 70), the fluid outlet duct (62, 72) and the first connecting duct (64, 74), the inverting system (68, 78) having a second three-way valve (82) connected to the duct fluid inlet (60, 70), the fluid outlet conduit (62, 72) and the second conduit (64, 74). 6. Fuel cell according to claim 4, characterized in that the inversion system (68, 78) of the fluid flow direction comprises a four-way reversing valve (88) arranged to selectively connect the conduit. (60, 70) to the first connecting duct (64, 74) and the outlet duct (62, 72) to the second connecting duct (66, 76), or connecting the inlet duct (60, 70). ) to the second connecting duct (66, 76) and the outlet duct (62, 72) to the first connecting duct (64, 74). 7. Fuel cell according to any one of claims 3 to 6, characterized in that it comprises several cells (10) and several inversion systems (68, 78) of the direction of fluid flow, each system inversion (68, 78) of the fluid flow direction being specific to a single cell (10) or group of cells (10) respectively. 8.- Fuel cell according to any one of the preceding claims, characterized in that the oxidizing fluid (24) is pure oxygen and in that the reducing fluid (28) is pure dihydrogen. 9. A method for supplying a fuel cell with an oxidizing fluid (24) and / or a reducing fluid (28), the fuel cell comprising at least one cell (10) comprising an ion exchange membrane (12). ) separating the oxidant (24) and reducing (28) fluids, each oxidizing fluid (24) and reducing agent (28) flowing along the ion exchange membrane (12), characterized in that the flow direction of the oxidizing fluid (24) along the membrane (12) of the or each cell (10) is inverted during operation of the cell. 10. A method of supply according to claim 9, characterized in that the direction of flow of the reducing fluid (28) along the membrane (12) of the or each cell (10) is reversed during the operation of the battery. 11. A method of supply according to claim 10, characterized in that the flow directions of the oxidizing fluid (24) and reducing (28) are reversed simultaneously. 10 12. A method of supply according to any one of claims 9 to 11, characterized in that the moisture of at least one membrane (12) is measured during operation of the battery, the direction of circulation of the fluid oxidant (24) and / or reducing fluid (28) being inverted depending on the measured humidity. 15 13. A method of feeding according to any one of claims 9 to 12, characterized in that the oxidizing fluid (24) is pure oxygen and in that the reducing fluid (28) is pure dihydrogen. 20