Method for starting a fuel cell and electrochemical system comprising a fuel cell

Abstract

Method for starting a fuel cell and electrochemical system comprising a fuel cell The present invention relates to a method for starting a fuel cell (20) belonging to an electrochemical system (10) also comprising a filter (40) adapted to be electrically powered to filter dihydrogen contained in a gas feeding the filter and to deliver the filtered dihydrogen to a recirculation outlet (43) of the filter.The process comprises: supplying the anodic compartment (21) of the fuel cell with dihydrogen and venting the gas from the anodic compartment to the filter; using the filter, filtering the dihydrogen contained in the gas feeding the filter and delivering the filtered dihydrogen to the recirculation outlet; simultaneously with the filtration of the dihydrogen, measuring an electrical quantity representative of the filter's operation; and when the measured electrical quantity reaches a reference value, supplying the cathodic compartment (24) of the fuel cell with air. Figure for the abstract: 1.

Description

Title of the invention: Method for starting a fuel cell and electrochemical system comprising a fuel cell

[0001] The present invention relates to a method of starting a fuel cell and an electrochemical system comprising a fuel cell started using such a starting method.

[0002] A fuel cell is a device for generating electricity by electrochemical reaction between a fuel, which is dihydrogen, and an oxidant, which is dioxygen, for example dioxygen contained in the air. We are interested here in fuel cells of the solid electrolyte proton exchange membrane type - also called PEMFC in English -, which usually comprise a stack - called "stack" in English - of several unit cells each constituting an electrochemical generator.

[0003] In the remainder of the description, the terms nitrogen and dinitrogen, hydrogen and dihydrogen, as well as oxygen and dioxygen are used interchangeably.

[0004] Schematically, each unit cell comprises two separators, also called polar plates, between which is interposed a solid electrolyte in the form of a proton exchange membrane. The membrane is made for example of a sulfonated perfluorinated polymer material. Within each cell, each separator delimits with the corresponding membrane a reactive compartment. One of the two compartments, called the cathode compartment, houses a cathode element, formed by a cathode catalytic layer located on the surface of the membrane, while the other compartment, called the anodic compartment, houses an anodic element, formed by an anodic catalytic layer located on the surface of the membrane. The assembly of the membrane and the anodic and cathodic catalytic layers forms a membrane-electrode assembly, generally called "AME".

[0005] For two neighboring cells, a separator from one of the two cells is back-to-back with a separator from the other cell. These two separators together form a bipolar separator, also called a bipolar plate.

[0006] Generally, in a unit cell, the cathode compartment is supplied with oxidant, i.e. dioxygen, most often in the form of an air supply containing dioxygen, and the anode compartment is supplied with fuel, i.e. dihydrogen. Each reactive compartment also generally comprises a gas diffusion layer, located between the bipolar separator and the catalytic layer, allowing good circulation of dioxygen and dihydrogen from the separator to the catalytic layer.

[0007] When the fuel cell is in operation, the electrochemical reaction creates an electrical potential difference between the two separators of each unit cell. The electrical potential difference between the two separators of each unit cell creates a voltage across each cell, referred to as the "cell voltage." All of the cells in the fuel cell are electrically connected together in series, so that the voltage delivered across the fuel cell is equal to the sum of the cell voltage of all of the unit cells.

[0008] A common problem when using such a fuel cell is that, when the fuel cell is shut down, reactants are still present in the cathode compartment and in the anode compartment of each cell after the fuel cell has been shut down and the electrochemical reaction therefore continues to occur within each cell. The fuel cell thus continues to generate an electrical voltage at its terminals, which is detrimental to its longevity, and remains capable of spontaneously delivering electrical power in the event of electrical connection of its terminals, which is dangerous for a user of the fuel cell. In order to limit these drawbacks, it is known to carry out a shutdown procedure aimed, on the one hand, at reducing the quantity of oxygen present in the cathode compartment and, on the other hand, at reducing the voltage delivered to the terminals of the fuel cell, i.e. at depolarizing the fuel cell.Such a shutdown procedure is, for example, described by FR-A-2307111. At the end of such a shutdown procedure, the anode compartment essentially comprises dihydrogen and the cathode compartment essentially comprises nitrogen.

[0009] After the end of the shutdown procedure, due to the permeability of the membrane, the gas composition of the anode and cathode compartments tends to equilibrate: a diffusion of dihydrogen from the anode compartment to the cathode compartment and a diffusion of nitrogen from the cathode compartment to the anode compartment are observed. At the end of a medium-term shutdown of the fuel cell, a mixture of dihydrogen and nitrogen is therefore observed in the anode compartment of each cell.

[0010] In the event of a long-term shutdown of the fuel cell, a balancing of the gas composition of the anode and cathode compartments is first observed, i.e. a mixture of dihydrogen and nitrogen. Then, in a second stage, an arrival of dioxygen is observed in the cathode compartment of each cell. This arrival of dioxygen is notably linked to leaks and sealing defects present in the air supply circuit. In addition, a diffusion of dioxygen from the cathode compartment to the compartment is observed in each cell. anode, by diffusion through the membrane. The oxygen migrating into the anode compartment then reacts with the hydrogen in a combustion reaction, until the hydrogen in the anode compartment of each cell is completely depopulated. Thus, after a long shutdown of the fuel cell, a composition comprising nitrogen and oxygen is observed in the anode and cathode compartments of each cell.

[0011] This presence of oxygen in the anode compartment during the shutdown causes, when the fuel cell is re-supplied with hydrogen at the start of its restart, new combustions between the hydrogen molecules and the oxygen molecules, until the oxygen in the anode compartment of each cell is completely depopulated. Thus, at the end of this combustion of oxygen, the anode compartment of each cell contains a mixture of hydrogen and nitrogen, as after a medium-term shutdown of the fuel cell.

[0012] When the fuel cell is started, that is to say normally supplied with dihydrogen and dioxygen, the presence of a mixture of dihydrogen and nitrogen in the anode compartment of each cell results in a lack of dihydrogen to allow the electrochemical reactions necessary for the fuel cell to deliver the voltage and supply the required current to take place. This phenomenon is known as "fuel starvation" and leads to irreversible degradation of the fuel cell, in particular by causing the appearance of a higher electrochemical potential than in normal operation at the level of the anodic and cathodic catalytic layers of each cell, resulting in degradation of the anodic and cathodic catalytic layers and thus a reduction in the performance of the fuel cell.

[0013] To avoid these drawbacks, it is known to carry out a start-up procedure aimed at purging the gases present in the anode compartment of each cell and replacing them with dihydrogen.

[0014] For example, EP-B-1665427 proposes measuring the hydrogen content in the anode compartment of each cell. If the sensor detects a hydrogen content that is too low, the anode compartment of each cell is purged with hydrogen so as to obtain a sufficient proportion of hydrogen to start the fuel cell without risking damage to it. Such a start-up procedure has the disadvantage of high hydrogen consumption, because the hydrogen used to purge the anode compartment of each cell is redirected to the atmosphere and is therefore lost. This increased consumption of hydrogen increases the operating cost of the fuel cell. Furthermore, purging hydrogen in this way is not compatible with certain automotive safety standards, such as

[0015]

[0016]

[0017]

[0018]

[0019] such as the GTR13 standard, which imposes a maximum limit on the di-hydrogen content in the gases purged from a fuel cell. The aim of the invention is therefore to propose a procedure for starting a fuel cell making it possible to purge the anode compartment of each cell with dihydrogen, while addressing these drawbacks. To this end, the invention relates to a method for starting a fuel cell belonging to an electrochemical system, the fuel cell being adapted to generate electricity by electrochemical reaction between dihydrogen and dioxygen, the fuel cell comprising: - a stack of battery cells, each battery cell comprising an anode compartment and a cathode compartment separated by a proton exchange membrane; - a battery anode inlet supplying the anode compartment of each battery cell with hydrogen and a battery anode outlet discharging hydrogen from the anode compartment of each battery cell; and - a battery cathode inlet supplying air to the cathode compartment of each battery cell and a battery cathode outlet discharging air from the cathode compartment of each battery cell, the electrochemical system comprising a filter comprising: - an input connected to the anode output of the battery; - a recirculation outlet connected to the battery anode inlet; and - a purge outlet. In addition, the filter is adapted to be electrically powered to filter dihydrogen contained in a gas supplied to the inlet of the filter and to deliver the filtered dihydrogen to the recirculation outlet of the filter. According to the invention, the method for starting the fuel cell comprises at least: - supplying the anode compartment of each fuel cell of the fuel cell with hydrogen through the anode inlet of the fuel cell and discharging the gas from the anode compartment of each fuel cell through the anode outlet of the fuel cell to the inlet of the filter; - using the filter, filter the hydrogen contained in the gas supplying the filter inlet and deliver the filtered hydrogen to the recirculation outlet; - simultaneously with the filtration of the dihydrogen, measure an electrical quantity representative of the operation of the filter; and - when the measured electrical quantity reaches a reference value, supply the cathode compartment of each fuel cell with air via the fuel cell cathode inlet.

[0020] Thanks to the invention, the dihydrogen used to purge the anode compartment of each cell is filtered by the filter, which allows its reuse and therefore avoids its loss. In addition, monitoring the electrical quantity representative of the operation of the filter makes it possible to quantify the evolution of the dihydrogen purge of the anode compartment of each cell, avoiding continuing this purge longer than necessary. Thus, as soon as the dihydrogen content in the anode compartment of each cell is sufficient, the cathode compartment of each cell is supplied with air, allowing the fuel cell to be started.

[0021] According to other advantageous aspects of the invention, the starting method comprises one or more of the following characteristics, taken individually or in all technically possible combinations:

[0022] - the filter being an electrochemical filter of the membrane hydrogen pump type proton exchange membrane and comprises: a stack of filter cells, each filter cell having an anode compartment and a cathode compartment separated by a proton exchange membrane; a filter cathode inlet, corresponding to the inlet of the electrochemical filter, supplying the cathode compartment of each filter cell with gas from the anode compartment of each battery cell; a filter cathode outlet, corresponding to the purge outlet of the electrochemical filter, discharging gas from the cathode compartment of each filter cell to the outside; and a filter anode outlet, corresponding to the recirculation outlet of the electrochemical filter, discharging dihydrogen from the anode compartment of each filter cell to the battery anode inlet.In addition, the electrochemical filter is electrically powered to filter the hydrogen contained in the gas supplying the filter cathode inlet through the proton exchange membrane of each filter cell and to deliver the filtered hydrogen to the filter anode outlet.

[0023] - During the filtering of the dihydrogen contained in the gas coming from the com anode compartment of each battery cell using the electrochemical filter, the electrochemical filter consumes a substantially constant electric current. In addition, the electrical quantity representative of the operation of the electrochemical filter is an electrical voltage across the terminals of the electrochemical filter. In addition, the reference value is a reference voltage value.

[0024] - During the filtering of the dihydrogen contained in the gas coming from the com anode compartment of each battery cell with the help of the electrochemical filter, the electrical voltage across the electrochemical filter decreases.

[0025] - The starting method further comprises, when the electrical quantity represents If the measured filter operation indicator reaches the reference value, stop the filter.

[0026] - The electrochemical system further comprising a purge valve located between the anode outlet of the cell and the inlet of the filter and during the fuel cell start-up process the purge valve is opened.

[0027] - The dihydrogen filtered by the filter is recirculated from the recirculation outlet to the anode input of the battery.

[0028] - Recirculation of the dihydrogen filtered by the filter from the recirculation outlet to the anode inlet of the battery is driven by a drive member such as a pump or an ejector.

[0029] - The gas feeding the filter inlet, after filtration of the dihydrogen by the filter, is purged out of the electrochemical system via the purge outlet.

[0030] According to another aspect, the invention also relates to an electrochemical system comprising: - a fuel cell, adapted to generate electricity by electrochemical reaction between dihydrogen and dioxygen and comprising: • a stack of battery cells, each battery cell comprising an anode compartment and a cathode compartment separated by a proton exchange membrane; • a battery anode inlet supplying hydrogen to the anode compartment of each battery cell and a battery anode outlet discharging hydrogen from the anode compartment of each battery cell; and • a battery cathode inlet supplying air to the cathode compartment of each battery cell and a battery cathode outlet discharging air from the cathode compartment of each battery cell, - a filter, comprising: • an input connected to the battery anode output; • a recirculation outlet connected to the battery anode inlet; and • a purge outlet, - a control unit.

[0031] Furthermore, the filter is adapted to be electrically powered to filter dihydrogen contained in a gas supplying the inlet of the filter and to deliver the filtered dihydrogen to the recirculation outlet of the filter and the control unit is configured to implement the start-up method described above.

[0032] This electrochemical system induces the same advantages as those mentioned above regarding the starting method of the invention.

[0033] The invention will appear more clearly on reading the following description of an embodiment of an electrochemical system and a starting method. of a fuel cell, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0034] [Fig.l] [Fig.l] is a diagram of an electrochemical system according to the invention comprising a fuel cell.

[0035] [Fig.2] [Fig.2] is a block diagram of a method of starting the battery at fuel of the electrochemical system of [Fig.l], the starting method being in accordance with the invention.

[0036] [Fig.l] illustrates an electrochemical system 10 comprising a fuel cell 20. This electrochemical system 10 is intended to be installed in an electrical system, the fuel cell making it possible to produce electricity supplying an electrical load of the electrical system.

[0037] The electrochemical system 10 is for example intended to be installed in a vehicle, the fuel cell 20 thus producing electricity supplying an electric motor ensuring the propulsion of the vehicle.

[0038] The fuel cell 20 is of the proton exchange membrane fuel cell type and comprises a stack (not shown) of electrochemical cells. The fuel cell comprises, for example, between 60 and 500 cells. In [Fig.l], for clarity of the drawing, the fuel cell is shown as comprising only one cell.

[0039] The stack of cells of the fuel cell 20 is held between two end plates, which are not shown in [Fig. 1]. These end plates make it possible in particular to keep the stack of cells compressed, that is to say clamped along a compression axis, and to supply the stack with dihydrogen in gaseous form, and with air in gaseous form, and, if necessary, the circulation of a heat transfer fluid for a cell cooling circuit.

[0040] The invention is more particularly described in the context of a common construction in which each cell comprises a membrane-electrode assembly and two bipolar plates, arranged on either side of the membrane-electrode assembly. However, the invention is also applicable in the context of fuel cells of the ion exchange membrane type with solid electrolyte having different constructions.

[0041] It is considered that, for a given fuel cell 20, all the cells of the fuel cell are identical to each other, therefore having identical characteristics.

[0042] Each cell of the fuel cell 20, called a “battery cell”, comprises an anode compartment 21, a cathode compartment 24 and a proton exchange membrane 27 which separates the anode compartment from the cathode compartment.

[0043] The fuel cell 20 comprises a cell anode inlet 22 supplying the anode compartment 21 of each cell with dihydrogen and a cell anode outlet 23 discharging the dihydrogen coming from the anode compartment of each cell.

[0044] The fuel cell 20 comprises a cell cathode inlet 25 supplying the cathode compartment 24 of each cell with air containing oxygen and a cell cathode outlet 26 discharging air from the cathode compartment of each cell.

[0045] The electrochemical system 10 comprises a dihydrogen supply circuit, making it possible to supply the fuel cell 20 with dihydrogen. In [Fig.l], this dihydrogen supply circuit is represented in a simplified manner by - an inlet valve 30, which is connected to the anode inlet of the cell 22 and which controls a flow of dihydrogen coming from a reservoir not shown and delivered to the anode inlet of the cell 22, and - a purge valve 32, which is connected to the anode outlet of the battery 23 and which allows the gas coming from the anode compartment 21 of each battery cell to be evacuated.

[0046] The electrochemical system 10 comprises an air supply circuit, making it possible to supply the fuel cell 20 with oxygen. In [Fig.l], this air supply circuit is represented in a simplified manner by - a compressor 34, which is connected to the cathode inlet of cell 25 and which controls a flow of air coming from the atmosphere and delivered to the cathode inlet of cell 25, and - a regulating valve 36, which is connected on the one hand to the battery cathode outlet 26 and on the other hand to the outside of the electrochemical system 10. The regulating valve 36 makes it possible to evacuate the gas coming from the cathode compartment 24 of each battery cell. Preferably, the regulating valve 36 is a proportional valve making it possible to increase the pressure within the cathode compartment 24 of each battery cell.

[0047] The electrochemical system 10 also comprises a filter 40, which is in the example an electrochemical filter of the hydrogen pump type with proton exchange membrane, also referred to as a proton pump.

[0048] The electrochemical filter 40 comprises a stack of filter cells, each filter cell comprising an anode compartment 41 and a cathode compartment 44 separated by a proton exchange membrane 47.

[0049] The electrochemical filter 40 comprises, for example, between 2 and 30 cells. In [Fig. 1], for clarity of the drawing, the electrochemical filter 40 is shown as comprising only one cell.

[0050] The electrochemical filter 40 comprises a filter cathode inlet 45, supplying the cathode compartment 44 of each filter cell with gas and a filter cathode outlet 46, or purge outlet, discharging the gases from the cathode compartment of each filter cell out of the electrochemical filter. The filter cathode inlet 45 is connected to the purge valve 32, so that the cathode compartment 44 of each filter cell is supplied with the gas purged from the anode compartment 21 of each cell via the cell anode outlet 23.

[0051] In a variant of the invention not shown, the filter cathode outlet 46 is connected to the regulating valve 36. Thus, the gases purged from the cathode compartment of each filter cell are purged with the gases purged from the cathode compartment of each battery cell.

[0052] The electrochemical filter 40 includes an anode filter outlet 43, or recirculation outlet, discharging gases from the anode compartment 41 of each filter cell out of the electrochemical filter.

[0053] The electrochemical system 10 also comprises a recirculation circuit 50, which connects the filter anode output 43 to the battery anode input 22.

[0054] In the example, the recirculation circuit 50 comprises a conduit 52 connecting the filter anode outlet 43 to the cell anode inlet 22, a valve 54, mounted on the conduit 52 and operated to prevent a circulation of gas from the cell anode inlet 22 to the filter anode outlet 43 and a drive member 56 causing the recirculation of a gas coming from the filter anode outlet 43 to the cell anode inlet 22. In a variant of the invention not shown, the valve 54 is replaced by a non-return valve.

[0055] In the example, the drive member 56 is a pump, also referred to as a recirculation pump. In a variant of the invention not shown, the drive member 56 is an ejector, in particular a Venturi type ejector.

[0056] The electrochemical system 10 also comprises a power supply 60, which is electrically connected to the electrochemical filter 40. The power supply 60 is preferably a direct current power supply, which is in the example adapted to deliver a constant direct electric current to the electrochemical filter 40. In the example, the power supply 60 is dedicated to the electrical supply of the electrochemical filter 40. In a variant not shown, the power supply 60 also supplies other electrical loads. For example, when the electrochemical system 10 is on board an electric vehicle, the power supply 60 is a battery of the vehicle which also supplies an electric motor of the vehicle.

[0057] The power supply 60 thus generates a voltage in each filter cell of the electrochemical filter 40. More precisely, the power supply 60 generates a positive charge within the cathode compartment 44 of each filter cell and generates a negative charge within the anode compartment 41 of each filter cell. In other words, the power supply 60 generates a potential difference between the cathode compartment 44 and the anode compartment 41 of each filter cell.

[0058] This potential difference between the cathode compartment 44 and the anode compartment 41 of each filter cell tends to cause the movement of protons H^, or cations, through the proton exchange membrane 47, from the cathode compartment 44 to the anode compartment 41 of each filter cell. In practice, these protons come from molecules of dihydrogen H2, present in the cathode compartment 44 of each filter cell and undergoing an oxidation reaction: H2 = 2H^ + 2e^.

[0059] The protons thus transferred into the anode compartment 41 of each filter cell then combine with each other to form molecules of dihydrogen H2, according to a reduction reaction occurring in the anode compartment of each filter cell: 2H^ + 2e^ = 1¾.

[0060] It is thus understood that the electrical power supply 60, by generating a potential difference between the anode 41 and cathode 44 compartments of each filter cell, makes it possible to force the oxidation and reduction reactions resulting in the filtration and displacement of dihydrogen from the cathode compartment to the anode compartment.

[0061] It is also noted that the nitrogen present in the cathode compartment 44 of each filter cell, present in the form of dinitrogen molecules, is inert and is therefore not oxidized by the oxidation reactions.

[0062] The electrochemical filter 40, when supplied with electrical energy by the power supply 60 and receives a gas in the cathode compartment 44 of each filter cell via the filter inlet 45, therefore makes it possible to filter the dihydrogen present in the received gas and to move this dihydrogen to the anode compartment 41 of each filter cell.

[0063] In practice, when the power supply 60 provides the electrochemical filter 40 with a constant electric current, the electric voltage delivered by the power supply to the electrochemical filter depends on the proportion of dihydrogen in the gas present in the cathode compartment 44 of each filter cell, i.e. the partial pressure of dihydrogen. Thus, at constant current, when the proportion of dihydrogen increases in the gas present in the cathode compartment 44 of each filter cell, the electric voltage measured at the terminals of the electrochemical filter 40 decreases, until it reaches a minimum value when the gas present in the cathode compartment 44 of each filter cell is made up solely of dihydrogen. Particularly advantageously, measuring the voltage across the electrochemical filter 40 therefore makes it possible to measure the proportion of dihydrogen in the gas present in the cathode compartment 44 of each filter cell. The voltage across the electrochemical filter 40, designated U40, thus corresponds to an electrical quantity representative of the operation of the electrochemical filter. Furthermore, the voltage U40 across the electrochemical filter 40 is proportional to the voltage delivered by the power supply 60 to the electrochemical filter. In practice, the power supply 60 has imperfect efficiency, leading the voltage U40 across the electrochemical filter 40 to be lower than the voltage delivered by the power supply.

[0064] Advantageously, since the voltage U40 across the terminals of the electrochemical filter 40 is proportional to the electrical voltage delivered by the power supply 60 to the electrochemical filter, the voltage U40 is measured by a voltage measuring device 65, such as a voltmeter, integrated into the power supply. The voltmeter 65 measures the electrical voltage delivered by the power supply to the electrochemical filter and therefore makes it possible to deduce the voltage U40 therefrom, taking into account the efficiency of the power supply. Measuring the electrical voltage delivered by the power supply to the electrochemical filter therefore amounts to measuring the voltage U40.

[0065] In a non-shown variant of the invention, the electrochemical system 10 comprises a voltage measuring device, such as a voltmeter, separate from the electrical power supply 60, configured to measure the voltage U40 at the terminals of the electrochemical filter 40.

[0066] In practice, the change in the electrical voltage measured at the terminals of the electrochemical filter 40 as a function of the proportion, or partial pressure, of dihydrogen is approximately linear, in the range of proportion of dihydrogen observed during the start-up of the fuel cell 20, that is to say in a range of proportion of dihydrogen going from 50% to 100% of dihydrogen.

[0067] Furthermore, it has been observed using experiments that the decrease, or decay, of the electrical voltage measured at the terminals of the electrochemical filter 40 over time, when the proportion of dihydrogen in the gas present in the cathode compartment 44 of each filter cell increases, is an exponential decay.

[0068] The electrochemical system 10 also comprises a control unit 70, which controls the operation of the fuel cell 20, the electrochemical filter 40, the electrical power supply 60, the valves 32, 36 and 54, the compressor 34 and the drive member 56 and which collects the measurements of the voltage U40 carried out by the voltmeter 65.

[0069] A method of starting the fuel cell is now described with reference to [Fig. 2]. fuel 20, for example implemented during a start-up of a vehicle in which the electrochemical system 10 is embedded. This start-up method aims to purge the anode compartment 21 of each battery cell in order to achieve a proportion of dihydrogen within the anode compartment of each battery cell that is sufficiently high to allow the fuel cell to start without risk of damage.

[0070] In the example, the method for starting the fuel cell 20 is implemented by the control unit 70.

[0071] Before the start of the start-up process, the fuel cell 20 is stopped, that is to say it is not supplied with air or dihydrogen.

[0072] In the case where the shutdown preceding the start-up of the fuel cell 20 is a shutdown of medium duration, for example less than 120 minutes, the anode compartment 21 of each cell comprises a gas which is essentially a mixture of dihydrogen and nitrogen.

[0073] In the case where the shutdown preceding the start-up of the fuel cell 20 is a shutdown of long duration, for example greater than 120 minutes, the anode compartment 21 of each cell comprises a gas which is essentially a mixture of oxygen and nitrogen. In addition, the anode compartment 21 of each cell also comprises water, originating in particular from the combustion reaction occurring between the oxygen diffusing into the anode compartment of each cell and the hydrogen which is previously present there. This water is formed in the form of vapor and tends to condense.

[0074] The method for starting the fuel cell 20 is implemented regardless of whether it is following a medium-term shutdown or a long-term shutdown.

[0075] The starting method begins with a first step 100, during which a starting instruction is received by the control unit 70. This starting instruction is for example issued by an operator of the electrochemical system 10, such as a driver of a vehicle in which the electrochemical system is on board. In such an example, the starting instruction is for example issued jointly with an instruction to start the vehicle.

[0076] At the beginning of the fuel cell 20 startup process, the fuel cell is not connected to any electrical load, i.e., the fuel cell is in open circuit. Thus, the fuel cell does not produce any electrical current.

[0077] The start-up method then comprises a step 110, during which the dihydrogen supply circuit of the electrochemical system 10 is operated by opening the inlet valve 30, to supply the anode inlet of the cell 22 with dihydrogen. Simultaneously, the purge valve 32 is opened in order to allow the renewal of the gas present in the anode compartment 21 of each cell of battery by the dihydrogen supplied through the inlet valve 30. Thus, as soon as the inlet 30 and purge 32 valves are opened, the gases present in the anode compartment 21 of each battery cell are progressively renewed by dihydrogen, while being evacuated via the purge valve 32 towards the cathode inlet of filter 45.

[0078] In the case where the starting method follows a long-term shutdown of the fuel cell, the dihydrogen supplying the anode compartment 21 of each cell reacts with the dioxygen present in the anode compartment of each cell in a combustion reaction producing water, until all the dioxygen is consumed. This consumption of the dioxygen takes place in a very short time, for example less than 1 second. Then, the anode compartment 21 of each cell comprises a mixture of dihydrogen and nitrogen, as at the end of a medium-term shutdown of the fuel cell. Thus, whether the starting method is implemented after a medium-term shutdown or a long-term shutdown of the fuel cell, a mixture of dihydrogen and nitrogen is purged from the fuel cell 20 to the electrochemical filter 40.Following a long-term shutdown, water is also purged from the fuel cell into the electrochemical filter. This mixture, for example, comprises a proportion of approximately 50% hydrogen and a proportion of approximately 50% nitrogen.

[0079] The start-up process continues with the start-up of the electrochemical filter 40 during a step 120.

[0080] In practice, the electrochemical filter 40 is started simultaneously with the opening of the inlet 30 and purge 32 valves, or quickly after the opening of the inlet 30 and purge 32 valves, for example less than 50 milliseconds after the opening of the inlet 30 and purge 32 valves.

[0081] Thus, the gas present in the anode compartment 21 of each battery cell is purged to the cathode compartment 44 of each filter cell of the electrochemical filter 40. The operation of the electrochemical filter 40 then makes it possible to filter the dihydrogen contained in this purged gas and to transfer this dihydrogen through the proton exchange membrane 47 to the anode compartment 41 of each filter cell. From a gas comprising a mixture of dihydrogen, nitrogen and possibly water, the electrochemical filter 40 thus makes it possible to separate part or all of the dihydrogen, corresponding to a filtrate or a permeate, from the nitrogen and possibly water in gaseous form and in liquid form, corresponding to a retentate or a concentrate.

[0082] The filtered dihydrogen, collected in the anode compartment 41 of each filter cell, is then recirculated to the cell anode inlet 22 using the recirculation circuit 50 via the filter anode outlet 43, which is thus a recirculation outlet. Thus, this hydrogen is reused, which makes it possible to reduce the hydrogen consumption of the electrochemical system 10. This recirculation is carried out either continuously or intermittently, depending on the design of the recirculation circuit 50.

[0083] In addition, the gases not filtered by the electrochemical filter 40, that is to say the retentate or condensate, essentially nitrogen, dihydrogen that has not been filtered and possibly water in gaseous form, but also water in liquid form possibly present in the cathode compartment 44 of each filter cell, are purged out of the filter 40 by the filter cathode outlet 46, which is thus a purge outlet. This retentate, or condensate, has a dihydrogen content lower than that of the gas discharged from the anode compartment of each cell of the battery 21, or even zero, which reduces the losses of dihydrogen and facilitates compliance with automobile safety standards, such as for example the GTR13 standard, which imposes a maximum limit on the dihydrogen content in the gases purged from a fuel cell.In a variant of the invention not shown, this retentate, or condensate, is redirected towards the control valve 36 to be evacuated with the gases purged from the cathode compartment 24 of each battery cell coming from the battery cathode outlet 26.

[0084] It is noted that the presence of water in the cathode compartment 44 of each filter cell does not prevent the operation of the electrochemical filter 40 and on the contrary allows the proton exchange membrane 47 to be moistened, improving its operation.

[0085] The progressive purging of the gases contained in the anode compartment 21 of each battery cell results in a progressive increase in the dihydrogen content in the anode compartment of each battery cell.

[0086] During operation of the electrochemical filter 40, the voltage U40 across the terminals of the electrochemical filter 40 is regularly measured by the voltmeter 65 and compared to a reference voltage value Uref, during a measurement step 130 of the start-up method. Due to the increase in the dihydrogen content in the anode compartment 21 of each battery cell, and therefore in the cathode compartment 44 of each filter cell, the voltage U40 measured across the terminals of the electrochemical filter 40 tends to decrease over time.

[0087] The reference voltage value Urefest is chosen to correspond to a voltage measured at the terminals of the electrochemical filter 40 when the proportion of dihydrogen in the gas purged from the anode compartment 21 of each battery cell, i.e. in the gas supplied to the cathode compartment 44 of each filter cell, is greater than 99%, preferably greater than 99.97%.

[0088] In practice, this reference voltage value Uref depends on the current intensity electric current supplied by the power supply 60 to the electrochemical filter 40. The intensity of this electric current is preferably chosen to be as low as possible, so as not to degrade the electrochemical filter, while being sufficiently high to ensure effective filtering of the dihydrogen contained in the gas supplied to the cathode compartment 44 of each filter cell and therefore to limit the duration of the starting process of the fuel cell 20. Indeed, the higher the intensity of the electric current supplying the electrochemical filter 40, the more effective and rapid the filtering of the dihydrogen by the electrochemical filter.

[0089] This reference voltage value Urefest is also chosen as a function of the floor value corresponding to the voltage value when the gas present in the cathode compartment 44 of each filter cell consists solely of dihydrogen.

[0090] As long as the voltage U40 measured across the terminals of the electrochemical filter 40 is greater than the reference voltage value Uref, the filtering of the gases purged from the anode compartment 21 of each battery cell continues and the measurement is regularly repeated. For example, the measurement is carried out at regular intervals, with an interval between two measurements of between 10 milliseconds and 100 milliseconds, or the measurement is carried out continuously.

[0091] When the voltage U40 measured across the terminals of the electrochemical filter 40 during the measurement step 130 reaches the reference voltage value Uref, or is even lower than the reference voltage value Uref, the dihydrogen content within the anode compartment 21 of each battery cell is sufficient to allow the fuel cell 20 to start up without risk. It is thus no longer necessary to purge the anode compartment 21 of each battery cell or to filter the gases purged from the anode compartment of each battery cell using the electrochemical filter 40.

[0092] Thus, when the voltage U40 measured at the terminals of the electrochemical filter 40 during the measurement step 130 reaches the reference voltage value Uref, the starting method continues with the stopping of the electrochemical filter 40, during a stopping step 140.

[0093] In parallel, the starting method continues with a step 150 during which the air supply to the fuel cell 20 is restored, i.e. during which the cathode compartment 24 of each cell is supplied with air containing oxygen via the cell cathode inlet 25, using the air supply circuit, and during which the fuel cell is connected to an electrical load. At the end of this step, the fuel cell 20 is started, i.e. it is supplied with hydrogen and oxygen so as to produce an electrical current consumed by the electrical load. Before step 150, the fuel cell fuel 20 is said to be off because it is not connected to an electrical load, that is to say it is in open circuit, and does not produce any electrical current.

[0094] Reaching the reference voltage value Urefest is therefore a criterion for stopping the purging of the anode behavior 21 of each cell of the battery and a criterion for starting the normal start-up of the fuel cell 20.

[0095] The starting method continues with a normal operating step 160 of the fuel cell 20, the fuel cell then being normally supplied with air containing oxygen and hydrogen. During the normal operating step 160, the fuel cell 20 is connected to an electrical load and used to power the electrical load. The electrical load powered by the fuel cell is, for example, a battery of a vehicle.

[0096] During the normal operating step 160 of the fuel cell 20, the gases purged from the anode compartment 21 of each cell are preferably filtered to isolate the dihydrogen, which is then recirculated to the cell anode inlet 22.

[0097] This filtration is for example carried out by the electrochemical filter 40, which then remains in operation during the operation of the fuel cell, or by a Venturi type ejector calibrated to allow only the recirculation of dihydrogen, or by any other filtration means. Preferably, when this filtration is carried out by the electrochemical filter 40, the start-up method does not include the step 140 of stopping the electrochemical filter 40, which thus remains in operation.

[0098] The normal operating step 160 of the fuel cell 20 ends when a shutdown of the fuel cell 20 is required, during a shutdown step 170. This shutdown step aims to interrupt the supply of oxygen and hydrogen to the fuel cell and is, for example, carried out as described in FR-A-2307111.

[0099] Once the fuel cell 20 is stopped, a new method of starting the fuel cell begins with the first step 100 when a start instruction is received.

[0100] The start-up method of the invention is particularly advantageous for minimizing the operating costs of the electrochemical system 10. Indeed, thanks to the use of the electrochemical filter 40, which makes it possible both to measure the proportion of dihydrogen in the gases purged from the anode compartment of each cell and to filter this dihydrogen, the start-up method makes it possible to purge the anode compartment 21 of each cell without wasting dihydrogen, the purged dihydrogen being recirculated to the anode inlet of the cell 22. In addition, the measurement of the proportion of dihydrogen in the purged gases makes it possible to benefit from a precise shutdown condition making it possible to avoid excessively long purging of the compartment anode compartment of each cell of the fuel cell, which avoids wasting dihydrogen and delaying the start-up of the fuel cell 20, while ensuring that the anode compartment of each cell of the fuel cell contains a sufficient proportion of dihydrogen to allow start-up of the fuel cell without risk of damage.

[0101] Furthermore, this dual function of the electrochemical filter 40 facilitates the design of the electrochemical system 10 and in particular avoids having to have the sensors after the anode output of the battery 23.

[0102] In a variant of the invention not shown, the electrical quantity representative of the operation of the filter measured during step 130 is not the electrical voltage U4o at the terminals of the electrochemical filter 40, but the electrical voltage delivered by the electrical power supply 60 to the electrochemical filter.

[0103] In a variant of the invention that is not shown, the electrochemical filter 40 is not powered by the power supply 60 with a constant current, but with a variable current, and the power supply 60 then preferably delivers a constant voltage to the electrochemical filter. In such a variant, the electrical quantity representative of the operation of the filter measured during step 130 is not the electrical voltage across the terminals of the electrochemical filter, but for example the current Eo consumed by the electrochemical filter. This current is compared to a reference value Iref.

[0104] In a variant of the invention that is not shown, the hydrogen filtered by the electrochemical filter 40 is not directly recirculated to the cell anode inlet 22, but is collected in a hydrogen reservoir. Preferably, this reservoir is itself connected to the cell anode inlet 22, so that the filter anode outlet 43 is connected to the cell anode inlet 22 via the reservoir, i.e. indirectly connected to the cell anode inlet.

[0105] In a variant of the invention that is not shown, the purge valve 32 is also connected to the conduit 52 so as to selectively allow gas recirculation either from the cell anode outlet 23 to the electrochemical filter 40, or from the cell anode outlet 23 to the cell anode inlet 22 without passing through the electrochemical filter 40. In such a variant, the gases purged from the anode compartment 21 of each cell during the normal operating step 160 are either redirected to the cell anode inlet 22, or redirected to the electrochemical filter 40.

[0106] In a variant of the invention not shown, the purge valve 32 is connected to the control valve 36 so as to selectively allow either a recirculation of gas from the anode outlet of the cell 23 to the electrochemical filter 40, or a purge of the gases coming from the anode outlet of the cell 23 to the outside of the electrochemical system 10 by mixing them beforehand with the gases purged from the cathode compartment of each cell of the cell. Such a mixture makes it possible to dilute the dihydrogen even actually present at the outlet of the electrochemical filter 40 and therefore to reduce the proportion of dihydrogen in the gases purged towards the outside of the electrochemical system 10, thus facilitating compliance with automotive safety standards such as the GTR13 standard. In such a variant, the gases purged from the anode compartment 21 of each battery cell during the normal operating step 160 are either purged towards the outside of the electrochemical system 10, i.e. towards the atmosphere, or redirected towards the electrochemical filter 40.

[0107] Any feature described for one embodiment or variation in the foregoing may be implemented for the other embodiments and variations described above, as long as technically feasible.

Claims

Claims

1. Method for starting a fuel cell (20) belonging to an electrochemical system (10), the fuel cell being adapted to generate electricity by electrochemical reaction between di-hydrogen and dioxygen, the fuel cell (20) comprising: - a stack of battery cells, each battery cell comprising an anode compartment (21) and a cathode compartment (24) separated by a proton exchange membrane (27); - a battery anode inlet (22) supplying the anode compartment (21) of each battery cell with dihydrogen and a battery anode outlet (23) discharging the dihydrogen coming from the anode compartment of each battery cell; and - a battery cathode inlet (25) supplying the cathode compartment (24) of each battery cell with air and a battery cathode outlet (26) discharging air from the cathode compartment of each battery cell, the electrochemical system (10) comprising a filter (40) comprising: - an input (45) connected to the battery anode output (23); - a recirculation outlet (43) connected to the battery anode inlet (22); and - a purge outlet (46), the filter (40) being adapted to be electrically powered to filter dihydrogen contained in a gas supplying the inlet (45) of the filter (40) and to deliver the filtered dihydrogen to the recirculation outlet (43) of the filter (40), characterized in that the method of starting the fuel cell (20) comprises at least: - supply (110) the anode compartment (21) of each fuel cell stack cell (20) into dihydrogen through the stack anode inlet (22) and discharge gas from the anode compartment of each stack cell through the stack anode outlet (23) to the inlet (45) of the filter (40);

2. - using the filter (40), filter (120) the dihydrogen contained in the gas supplying the inlet (45) of the filter and deliver the filtered dihydrogen to the recirculation outlet (43); - simultaneously with the filtration (120) of the dihydrogen, measure (130) an electrical quantity (U40; I4o) representative of the operation of the filter (40); and - when the measured electrical quantity (U40; I4o) reaches a reference value (Uref; Iref), supply (150) the cathode compartment (24) of each cell of the fuel cell (20) with air via the cell cathode inlet (25). Method for controlling an electrochemical system (10) according to claim 1, the filter (40) being an electrochemical filter of the hydrogen pump type with proton exchange membrane and comprising: - a stack of filter cells, each filter cell comprising an anode compartment (41) and a cathode compartment (44) separated by a proton exchange membrane (47); - a filter cathode inlet (45), corresponding to the inlet of the electrochemical filter (40), supplying the cathode compartment (44) of each filter cell with gas coming from the anode compartment (21) of each battery cell; - a filter cathode outlet (46), corresponding to the purge outlet of the electrochemical filter (40), evacuating the gases coming from the cathode compartment (44) of each filter cell to the outside; and - an anode filter outlet (43), corresponding to the recirculation outlet of the electrochemical filter (40), discharging dihydrogen from the anode compartment (41) of each filter cell to the anode battery inlet (22), the electrochemical filter (40) being electrically powered to filter the dihydrogen contained in the gas supplying the filter cathode inlet (45) through the proton exchange membrane (47) of each filter cell and to deliver the filtered dihydrogen to the filter anode outlet (43).

3. A starting method according to claim 2, wherein, during the filtering (120) of the dihydrogen contained in the gas coming from the anode compartment (21) of each battery cell using the electrochemical filter (40), the electrochemical filter consumes a substantially constant electric current, wherein the electrical quantity representative of the operation of the electrochemical filter (40) is an electric voltage (U40) across the terminals of the electrochemical filter, and wherein the reference value (Uref) is a reference voltage value.

4. A starting method according to claim 3, wherein, during the filtering (120) of the dihydrogen contained in the gas coming from the anode compartment (21) of each battery cell using the electrochemical filter (40), the electrical voltage (U40) across the terminals of the electrochemical filter (40) decreases.

5. Starting method according to any one of claims 1 to 4, further comprising: - when the electrical quantity (U40; ^representative of the operation of the filter (40) measured (130) reaches the reference value (Uref; Iref), stopping (140) the filter.

6. A starting method according to any one of claims 1 to 5, the electrochemical system (10) further comprising a purge valve (32) located between the cell anode outlet (23) and the filter inlet (45), wherein during the fuel cell (20) starting method the purge valve (32) is open.

7. A starting method according to any one of claims 1 to 6, wherein the dihydrogen filtered (120) by the filter (40) is recirculated from the recirculation outlet (43) to the cell anode inlet (22).

8. A starting method according to claim 7, wherein the recirculation of the filtered dihydrogen (120) by the filter (40) from the recirculation outlet (43) to the cell anode inlet (22) is driven by a drive member (56) such as a pump or an ejector.

9. A starting method according to any one of claims 1 to 8, during which the gas supplying the inlet (45) of the filter (40), after filtration of the dihydrogen by the filter, is purged from the electrochemical system (10) via the purge outlet (46).

10. Electrochemical system (10) comprising: - a fuel cell (40), adapted to generate electricity by electrochemical reaction between dihydrogen and dioxygen and comprising: • a stack of battery cells, each battery cell comprising an anode compartment (21) and a cathode compartment (24) separated by a proton exchange membrane (27); • a battery anode inlet (22) supplying the anode compartment (21) of each battery cell with dihydrogen and a battery anode outlet (23) discharging the dihydrogen from the anode compartment of each battery cell; and • a battery cathode inlet (25) supplying the cathode compartment (24) of each battery cell with air and a battery cathode outlet (26) evacuating air from the cathode compartment of each battery cell, - a filter (40), comprising: • an input (45) connected to the battery anode output (23); • a recirculation outlet (43) connected to the battery anode inlet (22); and • a purge outlet (46), - a control unit (70), wherein the filter (40) is adapted to be electrically powered to filter dihydrogen contained in a gas supplying the inlet (45) of the filter (40) and to deliver the filtered dihydrogen to the recirculation outlet (43) of the filter, and wherein the control unit (70) is configured to implement the starting method of any one of claims 1 to 9.

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