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 for 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 that generates electricity through an electrochemical reaction between a fuel, which is dihydrogen, and an oxidant, which is dioxygen, for example, dioxygen from the air. This discussion focuses on proton exchange membrane fuel cells with a solid electrolyte – also known as PEMFCs – which typically comprise a stack of several unit cells, each constituting an electrochemical generator.

[0003] In the following 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 a solid electrolyte is interposed 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, together with the corresponding membrane, delimits a reactive compartment. One of the two compartments, called the cathodic compartment, houses a cathodic element, formed by a cathodic 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 referred to as an "MEA".

[0005] For two adjacent cells, a separator of one of the two cells is located back-to-back with a separator of 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 oxygen-containing air supply, and the anodic compartment is supplied with fuel, i.e., dihydrogen. Each reactive compartment also generally includes a gas diffusion layer, located between the separator bipolar and catalytic layer, allowing good circulation of dioxygen and dihydrogen from the separator to the catalytic layer.

[0007] When the fuel cell is operating, 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 the terminals of each cell, referred to as the "cell voltage." All the cells of the fuel cell are electrically connected in series, so that the voltage delivered across the terminals of the fuel cell is equal to the sum of the cell voltages of all the unit cells.

[0008] A common problem when using such a fuel cell is that, when the fuel cell is shut down, reactants remain present in the cathode and anode compartments of each cell, 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 if its terminals are connected, which is dangerous for a fuel cell user. To mitigate these drawbacks, it is known to perform a shutdown procedure aimed, on the one hand, at reducing the amount of oxygen present in the cathode compartment and, on the other hand, at reducing the voltage delivered to the fuel cell terminals, i.e., at depolarizing the fuel cell.Such a shutdown procedure is, for example, described by FR-A-2307111. Following such a shutdown procedure, the anodic compartment consists mainly of dihydrogen and the cathodic compartment consists mainly of nitrogen.

[0009] After the shutdown procedure is complete, due to the permeability of the membrane, the gas composition of the anodic and cathodic compartments tends to equilibrate: hydrogen diffuses from the anodic compartment to the cathodic compartment, and nitrogen diffuses from the cathodic compartment to the anodic compartment. Following a medium-duration shutdown of the fuel cell, a mixture of hydrogen and nitrogen is therefore observed in the anodic compartment of each cell.

[0010] In the event of a prolonged shutdown of the fuel cell, the gas composition of the anodic and cathodic compartments first equilibrates, resulting in a mixture of dihydrogen and nitrogen. Then, subsequently, dioxygen enters the cathodic compartment of each cell. This influx of dioxygen is primarily due to leaks and sealing defects in the air supply circuit. Furthermore, it is observed in In each cell, oxygen diffuses from the cathode compartment to the anode compartment via diffusion across the membrane. The oxygen migrating into the anode compartment then reacts with hydrogen in a combustion reaction until the hydrogen in the anode compartment of each cell is completely depleted. Thus, after a prolonged shutdown of the fuel cell, the composition of the anode and cathode compartments of each cell consists of nitrogen and oxygen.

[0011] The presence of dioxygen in the anodic compartment during the shutdown leads, when the fuel cell is refueled with dihydrogen at the beginning of its restart, to further combustion between dihydrogen and dioxygen molecules, until the dioxygen in the anodic compartment of each cell is completely depleted. Thus, following this combustion of dioxygen, the anodic compartment of each cell contains a mixture of dihydrogen and nitrogen, as after a medium-duration shutdown of the fuel cell.

[0012] When the fuel cell is started, i.e., normally supplied with dihydrogen and dioxygen, the presence of a mixture of dihydrogen and nitrogen in the anodic compartment of each cell leads to a lack of dihydrogen, preventing the electrochemical reactions necessary for the fuel cell to deliver the required voltage and current. This phenomenon is known as "fuel starvation" and leads to irreversible degradation of the fuel cell, notably by causing a higher electrochemical potential than during normal operation in the anodic and cathodic catalytic layers of each cell, resulting in degradation of the anodic and cathodic catalytic layers and thus a decrease in the fuel cell's performance.

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

[0014] For example, EP-B-1665427 proposes measuring the dihydrogen content in the anodic compartment of each cell. If the sensor detects a dihydrogen content that is too low, the anodic compartment of each cell is purged with dihydrogen to obtain a sufficient proportion of dihydrogen to start the fuel cell without risking damage. Such a starting procedure has the disadvantage of high dihydrogen consumption, since the dihydrogen used to purge the anodic compartment of each cell is redirected to the atmosphere and is therefore lost. This increased dihydrogen consumption raises the operating cost of the fuel cell. Furthermore, purging hydrogen in this way is not compatible with certain automotive safety standards, such as the GTR13 standard, which imposes a maximum limit on the hydrogen content in the gases purged from a fuel cell.

[0015] The aim of the invention is therefore to propose a fuel cell starting procedure that allows the anodic compartment of each cell to be purged with dihydrogen, while addressing these drawbacks

[0016] 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 anodic compartment and a cathodic compartment separated by a proton exchange membrane; - an anodic inlet supplying the anodic compartment of each fuel cell with dihydrogen and an anodic outlet removing the dihydrogen from the anodic compartment of each fuel cell; and - a cathode ray inlet supplying air to the cathode ray compartment of each battery cell and a cathode ray outlet expelling air from the cathode ray compartment of each battery cell,

[0017] the electrochemical system comprising a filter including: - an input connected to the anode output of the battery; - a recirculation output connected to the battery's anodic input; and - a purge outlet.

[0018] 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.

[0019] According to the invention, the fuel cell starting method comprises at least: - supply the anodic compartment of each fuel cell with dihydrogen through the anodic inlet of the fuel cell and evacuate the gas from the anodic compartment of each fuel cell through the anodic outlet of the fuel cell to the inlet of the filter; - using the filter, filter the dihydrogen contained in the gas feeding the filter inlet and deliver the filtered dihydrogen to the recirculation outlet; - simultaneously with the filtration of dihydrogen, measure an electrical quantity representative of the filter's operation; and - when the measured electrical quantity reaches a reference value, supply the cathode compartment of each fuel cell with air through the cathode cell inlet.

[0020] Thanks to the invention, the dihydrogen used to purge the anodic compartment of each cell is filtered by the filter, thus allowing its reuse and preventing its loss. Furthermore, monitoring the electrical quantity representing the filter's operation makes it possible to quantify the evolution of the dihydrogen purging of the anodic compartment of each cell, preventing this purging from continuing for longer than necessary. Thus, as soon as the dihydrogen content in the anodic compartment of each cell is sufficient, the cathodic compartment of each cell is supplied with air, allowing the fuel cell to start.

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

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

[0023] - During the filtering of the dihydrogen contained in the gas from the The anodic compartment of each battery cell, using the electrochemical filter, draws a nearly constant electrical current. Furthermore, the electrical quantity representing the operation of the electrochemical filter is the voltage across its terminals. In addition, the reference value is a reference voltage value.

[0024] - During the filtering of the dihydrogen contained in the gas from the using the electrochemical filter, the electrical voltage across the terminals of the electrochemical filter decreases in the anodic compartment of each battery cell.

[0025] - The starting method further includes, when the electrical quantity When the representative of the filter's operation is measured and the reference value is reached, stop the filter.

[0026] - The electrochemical system further comprising a purge valve located between the anodic 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 anodic input of the battery.

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

[0029] - The gas feeding the filter inlet, after filtration of dihydrogen by the filter, is purged from 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 fuel cell stacks, each fuel cell comprising an anodic compartment and a cathodic compartment separated by a proton exchange membrane; • an anodic inlet supplying the anodic compartment of each fuel cell with dihydrogen and an anodic outlet removing the dihydrogen from the anodic compartment of each fuel cell; and • a cathode ray inlet supplying air to the cathode ray compartment of each battery cell and a cathode ray outlet removing air from the cathode ray compartment of each battery cell, - a filter, comprising: • an input connected to the battery's anode output; • a recirculation output connected to the battery's anodic input; and • a purge outlet, - a control unit.

[0031] Furthermore, the filter is adapted to be electrically powered to filter dihydrogen contained in a gas feeding 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 process 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 become clearer upon reading the following description of an embodiment of an electrochemical system and a method for starting a fuel cell, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0034] [Fig-1] Fig. 1 is a schematic diagram of an electrochemical system conforming to the invention comprising a fuel cell.

[0035] [Fig.2] The [Fig.2] is a functional diagram of a method for starting the fuel cell of the electrochemical system of the [Fig.1], the starting method being in accordance with the invention.

[0036] Fig. 1 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 enabling the production of 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 which powers an electric motor which provides propulsion for the vehicle.

[0038] The fuel cell 20 is a proton exchange membrane fuel cell and comprises a stack of electrochemical cells (not shown). The fuel cell comprises, for example, between 60 and 500 cells. In [Fig. 1], for clarity, 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 allow, in particular, for the stack of cells to be kept compressed, i.e., squeezed along a compression axis, and for the supply of dihydrogen in gaseous form, and air in gaseous form, and, where applicable, the circulation of a heat transfer fluid for a cell cooling circuit.

[0040] The invention is described more particularly 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 solid electrolyte ion-exchange membrane fuel cells having different constructions.

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

[0042] Each cell of the fuel cell 20, referred to as a "fuel cell", comprises an anodic compartment 21, a cathodic compartment 24 and a proton exchange membrane 27 which separates the anodic compartment from the cathodic compartment.

[0043] The fuel cell 20 includes a fuel cell anodic inlet 22 supplying the anodic compartment 21 of each fuel cell with dihydrogen and a fuel cell anodic outlet 23 removing the dihydrogen from the anodic compartment of each fuel cell.

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

[0045] The electrochemical system 10 includes a dihydrogen supply circuit, enabling the fuel cell 20 to be supplied with dihydrogen. In [Fig. 1], this dihydrogen supply circuit is represented in a simplified manner by - an inlet valve 30, which is connected to the anodic inlet of the fuel cell 22 and which controls a flow of dihydrogen from a reservoir not shown and delivered to the anodic inlet of the fuel cell 22, and - a purge valve 32, which is connected to the anodic outlet of the pile 23 and which allows the gas from the anodic compartment 21 of each pile cell to be evacuated.

[0046] The electrochemical system 10 includes an air supply circuit, which supplies the fuel cell 20 with dioxygen. In [Fig. 1], this air supply circuit is represented in a simplified manner by - a compressor 34, which is connected to the cathode inlet of pile 25 and which controls a flow of air from the atmosphere delivered to the cathode inlet of pile 25, and - a regulating valve 36, which is connected on one side to the cathode outlet of the fuel cell 26 and on the other side to the outside of the electrochemical system 10. The regulating valve 36 allows the gas from the cathode compartment 24 of each fuel cell to be vented. Preferably, the regulating valve 36 is a proportional valve that allows the pressure within the cathode compartment 24 of each fuel cell to be increased.

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

[0048] The electrochemical filter 40 comprises a stack of filter cells, each filter cell having an anodic compartment 41 and a cathodic 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 includes 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, which vents the gas 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 anodic compartment 21 of each cell stack via the anodic outlet 23.

[0051] In a non-represented variant of the invention, the cathode outlet of filter 46 is connected to the control 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 stack cell.

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

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

[0054] In the example, the recirculation circuit 50 comprises a conduit 52 connecting the anodic outlet of filter 43 to the anodic inlet of battery 22, a valve 54, mounted on the conduit 52 and operated to prevent gas circulation from the anodic inlet of battery 22 to the anodic outlet of filter 43 and a drive member 56 causing the recirculation of a gas from the anodic outlet of filter 43 to the anodic inlet of battery 22. In a non-shown variant of the invention, the valve 54 is replaced by a check valve.

[0055] In the example, the drive element 56 is a pump, also referred to as a recirculation pump. In a non-shown variant of the invention, the drive element 56 is an ejector, in particular a Venturi-type ejector.

[0056] The electrochemical system 10 also includes 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 in this example is suitable for delivering a constant direct current to the electrochemical filter 40. In this example, the power supply 60 is dedicated to The power supply for the electrochemical filter 40. In an alternative configuration not shown, the power supply 60 also supplies other electrical loads. For example, when the electrochemical system 10 is installed in an electric vehicle, the power supply 60 is a vehicle battery that also powers 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 cathodic compartment 44 and the anodic compartment 41 of each filter cell tends to cause the movement of protons H+, or cations, across the proton exchange membrane 47, from the cathodic compartment 44 to the anodic compartment 41 of each filter cell. In practice, these protons originate from dihydrogen molecules H2, present in the cathodic compartment 44 of each filter cell and undergoing an oxidation reaction: H2 = 2H+ + 2e-.

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

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

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

[0062] The electrochemical filter 40, when it is supplied with electrical energy by the power supply 60 and receives a gas in the cathodic 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 anodic 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 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, that is, on 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 voltage measured across 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 consists solely of dihydrogen.A particularly advantageous feature is that measuring the voltage across the electrochemical filter 40 allows for the measurement of the proportion of dihydrogen in the gas present in the cathode compartment 44 of each filter cell. The voltage across the electrochemical filter 40, denoted U40, thus corresponds to an electrical quantity representative of the electrochemical filter's operation. Furthermore, the voltage U40 across the electrochemical filter 40 is proportional to the voltage supplied by the power supply 60 to the electrochemical filter. In practice, the power supply 60 has imperfect efficiency, resulting in the voltage U40 across the electrochemical filter 40 being lower than the voltage supplied by the power supply.

[0064] Advantageously, since the voltage U40 across the electrochemical filter 40 is proportional to the voltage supplied 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 voltage supplied by the power supply to the electrochemical filter and thus allows the voltage U40 to be deduced, taking into account the efficiency of the power supply. Measuring the voltage supplied by the power supply to the electrochemical filter is therefore equivalent to measuring the voltage U40.

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

[0066] In practice, the evolution of the electrical voltage measured across 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 dihydrogen proportion observed during the start-up of the fuel cell 20, that is to say in a range of dihydrogen proportion from 50% to 100% dihydrogen.

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

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

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

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

[0071] Before the start-up process begins, the fuel cell 20 is at a standstill, i.e. it is not supplied with air or dihydrogen.

[0072] In the case where the stop prior to the start of the fuel cell 20 is a medium-duration stop, for example less than 120 minutes, the anodic compartment 21 of each fuel 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 long-duration shutdown, for example, exceeding 120 minutes, the anodic compartment 21 of each fuel cell contains a gas that is essentially a mixture of oxygen and nitrogen. Furthermore, the anodic compartment 21 of each fuel cell also contains water, notably from the combustion reaction occurring between the oxygen diffusing into the anodic compartment of each cell and the hydrogen previously present there. This water is formed in the form of vapor and tends to condense.

[0074] The fuel cell start-up method 20 is implemented indifferently following a medium-term stop or a long-term stop.

[0075] The start-up process begins with a first step 100, during which a start instruction is received by the control unit 70. This start 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 embedded. In such an example, the start instruction is issued, for instance, in conjunction with a vehicle start instruction.

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

[0077] The start-up process then includes a step 110, during which the hydrogen supply circuit of the electrochemical system 10 is operated by opening the inlet valve 30 to supply the anodic inlet of the fuel cell 22 with hydrogen. Simultaneously, the drain valve 32 is opened to allow the gas present in the anodic compartment 21 of each fuel cell to be renewed by the hydrogen supplied through the inlet valve 30. Thus, as soon as the inlet valve 30 and drain valve 32 are opened, the gases present in the anodic compartment 21 of each fuel cell are progressively renewed by hydrogen, while being discharged via the drain valve 32 to the cathodic inlet of the filter 45.

[0078] In the case where the start-up process follows a long-term shutdown of the fuel cell, the hydrogen supplying the anodic compartment 21 of each fuel cell reacts with the oxygen present in the anodic compartment of each fuel cell in a combustion reaction producing water, until all the oxygen is consumed. This oxygen consumption occurs over a very short period, for example, less than 1 second. Afterward, the anodic compartment 21 of each fuel cell contains a mixture of hydrogen and nitrogen, as after a medium-term shutdown of the fuel cell. Thus, whether the start-up process is implemented after a medium-term or long-term shutdown of the fuel cell, a mixture of hydrogen and nitrogen is purged from the fuel cell 20 to the electrochemical filter 40.Following a prolonged shutdown, water is also purged from the fuel cell to the electrochemical filter. This mixture comprises, for example, a proportion of dihydrogen approximately equal to 50% and a proportion of nitrogen approximately equal to 50%.

[0079] The start-up process continues with the switching on 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 valves 30 and purge valves 32, or shortly after the opening of the inlet valves 30 and purge valves 32, for example less than 50 milliseconds after the opening of the inlet valves 30 and purge valves 32.

[0081] Thus, the gas present in the anodic compartment 21 of each fuel cell is purged to the cathodic compartment 44 of each filter cell of the filter The electrochemical filter 40 operates by filtering the hydrogen contained in the purged gas and transferring it through the proton exchange membrane 47 to the anodic compartment 41 of each filter cell. Starting with a gas containing a mixture of hydrogen, nitrogen, and possibly water, the electrochemical filter 40 separates some or all of the hydrogen, corresponding to a filtrate or permeate, from the nitrogen and possibly water in gaseous and liquid forms, corresponding to a retentate or concentrate.

[0082] The filtered dihydrogen, collected in the anodic compartment 41 of each filter cell, is then recirculated to the anodic inlet of the fuel cell 22 using the recirculation circuit 50 via the filter anodic outlet 43, which is thus a recirculation outlet. In this way, the dihydrogen is reused, thereby reducing the dihydrogen 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] Furthermore, the gases not filtered by the electrochemical filter 40, i.e., the retentate or condensate, essentially nitrogen, unfiltered dihydrogen, and possibly water in gaseous form, but also any liquid water present in the cathode compartment 44 of each filter cell, are purged from the filter 40 through 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 anodic compartment of each fuel cell 21, or even zero, which reduces dihydrogen losses and facilitates compliance with automotive safety standards, such as, for example, the GTR13 standard, which imposes a maximum limit on the dihydrogen content in the purged gases of a fuel cell.In a non-shown variant of the invention, this retentate, or condensate, is redirected to the control valve 36 to be evacuated with the purged gases from the cathode compartment 24 of each fuel cell coming from the cathode outlet of the fuel cell 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 gases contained in the anodic compartment 21 of each fuel cell leads to a progressive increase in the dihydrogen content in the anodic compartment of each fuel cell.

[0086] During the 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 process. Due to the increase in the dihydrogen content in the anodic compartment 21 of each fuel cell, and therefore in the cathodic 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 across the terminals of the electrochemical filter 40 when the proportion of dihydrogen in the gas purged from the anodic compartment 21 of each fuel cell, i.e. in the gas supplied to the cathodic 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 intensity of the 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 high enough to ensure efficient filtering of the dihydrogen contained in the gas supplied to the cathode compartment 44 of each filter cell and thus to limit the duration of the start-up process of the fuel cell 20. Indeed, the higher the intensity of the electric current supplying the electrochemical filter 40, the more efficient and rapid the filtering of the dihydrogen by the electrochemical filter.

[0089] This reference voltage value Urefest is also chosen based on 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 electrochemical filter 40 is greater than the reference voltage value Uref, the filtering of the purged gases from the anodic compartment 21 of each fuel 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 electrochemical filter 40 during measurement step 130 reaches the reference voltage value Uref, or even falls below the reference voltage value Uref, the hydrogen content within the anodic compartment 21 of each fuel cell is sufficient to allow the fuel cell 20 to start safely. It is therefore no longer necessary to purge the anodic compartment 21 of each fuel cell or to filter the purged gases from the anodic compartment of each fuel cell using the electrochemical filter 40.

[0092] Thus, when the voltage U4 measured across the terminals of the electrochemical filter 40 during the measurement step 130 reaches the reference voltage value Uref, the start-up process continues with the stopping of the electrochemical filter 40, during a stop step 140.

[0093] In parallel, the start-up process continues with a step 150 during which the air supply to the fuel cell 20 is restored, that is, during which the cathode compartment 24 of each fuel cell is supplied with air containing dioxygen through the fuel 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, that is, it is supplied with dihydrogen and dioxygen so as to produce an electric current consumed by the electrical load. Before step 150, the fuel cell 20 is said to be stopped because it is not connected to an electrical load, that is, it is in an open circuit, and produces no electric current.

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

[0095] The start-up process continues with a normal operating step 160 of the fuel cell 20, the fuel cell 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 vehicle battery.

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

[0097] This filtration is, for example, carried out by the electrochemical filter 40, which then remains operational 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 means of filtration. Preferably, when this filtration is carried out by the electrochemical filter 40, the start-up process does not include the shutdown step 140 of the electrochemical filter 40, which thus remains operational.

[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 dioxygen and dihydrogen to the fuel cell and is, for example, carried out as described in FR-A-2307111.

[0099] Once the fuel cell 20 has stopped, a new fuel cell starting process 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 allows both the measurement of the proportion of dihydrogen in the gases purged from the anodic compartment of each cell and the filtering of this dihydrogen, the start-up method makes it possible to purge the anodic compartment 21 of each fuel cell without wasting dihydrogen, the purged dihydrogen being recirculated to the anodic inlet of the fuel cell 22.Furthermore, measuring the proportion of dihydrogen in the purged gases allows for a precise shutdown condition, preventing excessively long purging of the anodic compartment of each fuel cell. This avoids wasting dihydrogen and delaying the start-up of the fuel cell 20, while ensuring that the anodic compartment of each fuel cell contains a sufficient proportion of dihydrogen to allow the fuel cell to start without risk of damage.

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

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

[0103] In a non-shown embodiment of the invention, the electrochemical filter 40 is not supplied 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 an embodiment, the electrical quantity representative of the filter's operation measured during step 130 is not the electrical voltage across the electrochemical filter, but, for example, the current Lo consumed by the electrochemical filter. This current is compared to a reference value Iref.

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

[0105] In a non-shown variant of the invention, the purge valve 32 is also connected to the conduit 52 so as to selectively allow gas recirculation either from the anodic outlet of the cell 23 to the electrochemical filter 40, or from the anodic outlet of the cell 23 to the anodic inlet of the cell 22 without passing through the electrochemical filter 40. In such a variant, the gases purged from the anodic compartment 21 of each cell of the cell during the normal operating step 160 are either redirected to the anodic inlet of the cell 22, or redirected to the electrochemical filter 40.

[0106] In a non-shown embodiment of the invention, the purge valve 32 is connected to the control valve 36 so as to selectively allow either gas recirculation from the anodic outlet of the fuel cell 23 to the electrochemical filter 40, or the purging of gases from the anodic outlet of the fuel cell 23 to the outside of the electrochemical system 10 by first mixing them with the gases purged from the cathodic compartment of each fuel cell. Such a mixture dilutes any dihydrogen present at the outlet of the electrochemical filter 40 and thus reduces the proportion of dihydrogen in the gases purged to the outside of the electrochemical system 10, thereby facilitating compliance with automotive safety standards such as the GTR13 standard.In such a variant, the gases purged from the anodic compartment 21 of each fuel cell during the normal operating step 160 are either purged to the outside of the electrochemical system 10, i.e. to the atmosphere, or redirected to the electrochemical filter 40.

[0107] Any feature described for an embodiment or variant in the foregoing may be implemented for the other embodiments and variants described above, provided that it is technically feasible.

Claims

1. Demands 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 dihydrogen and dioxygen, the fuel cell (20) comprising: - a stack of battery cells, each battery cell comprising an anodic compartment (21) and a cathodic compartment (24) separated by a proton exchange membrane (27); - an anodic inlet (22) supplying the anodic compartment (21) of each fuel cell with dihydrogen and an anodic outlet (23) removing the dihydrogen from the anodic compartment of each fuel cell; and - a cathode ray inlet (25) supplying air to the cathode ray compartment (24) of each battery cell and a cathode ray outlet (26) expelling air from the cathode ray compartment of each battery cell, the electrochemical system (10) comprising a filter (40) including: - an input (45) connected to the anode output of the battery (23); - a recirculation outlet (43) connected to the battery anodic input (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 fuel cell starting method (20) comprises at least: - supply (110) the anodic compartment (21) of each cell of the fuel cell (20) with dihydrogen through the anodic inlet of the cell (22) and evacuate the gas from the anodic compartment of each cell through the anodic outlet of the cell (23) to the inlet (45) of the filter (40); - 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 dihydrogen, measure (130) an electrical quantity (U40; I40) representative of the operation of filter (40); and - when the measured electrical quantity (U40; I40) reaches a reference value (Uref; Iref), supply (150) the cathode compartment (24) of each fuel cell (20) with air through the cathode cell inlet (25).

2. A starting method according to claim 1, the filter (40) being an electrochemical filter of the hydrogen pump type with a proton exchange membrane and comprising: - a stack of filter cells, each filter cell having an anodic compartment (41) and a cathodic compartment (44) separated by a proton exchange membrane (47); - a filter cathodic inlet (45), corresponding to the inlet of the electrochemical filter (40), supplying the cathodic compartment (44) of each filter cell with gas from the anodic compartment (21) of each cell; - a filter cathodic outlet (46), corresponding to the purge outlet of the electrochemical filter (40), venting the gases from the cathodic compartment (44) of each filter cell to the outside;and - an anodic outlet of the filter (43), corresponding to the recirculation outlet of the electrochemical filter (40), evacuating dihydrogen from the anodic compartment (41) of each filter cell to the anodic inlet of the cell (22), the electrochemical filter (40) being electrically powered to filter the dihydrogen contained in the gas supplying the cathodic inlet of the filter (45) through the proton exchange membrane (47) of each filter cell and to deliver the filtered dihydrogen to the anodic outlet of the filter (43).

3. A starting method according to claim 2, wherein, during the filtering (120) of the dihydrogen contained in the gas from the anodic compartment (21) of each fuel 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 electrical 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 from the anodic compartment (21) of each fuel cell using the electrochemical filter (40), the electrical voltage (U40) across the terminals of the electrochemical filter (40) decreases.

5. A starting method according to any one of claims 1 to 4, further comprising: - when the electrical quantity (U40; I40) representing 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 anodic outlet of the cell (23) and the inlet (45) of the filter, in which, during the starting method of the fuel cell (20) the purge valve (32) is opened.

7. A starting method according to any one of claims 1 to 6, wherein the filtered dihydrogen (120) by the filter (40) is recirculated from the recirculation outlet (43) to the anodic inlet of the fuel cell (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 anodic inlet of the fuel cell (22) is driven by a drive element (56) such as a pump or an ejector.

9. A start-up method according to any one of claims 1 to 8, wherein the gas feeding the inlet (45) of the filter (40), after filtration of dihydrogen by the filter, is purged out of 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 anodic compartment (21) and a cathodic compartment (24) separated by a proton exchange membrane (27); • an anodic inlet (22) supplying the anodic compartment (21) of each fuel cell with dihydrogen and an anodic outlet (23) removing the dihydrogen from the anodic compartment of each fuel cell; and • a cathode ray inlet (25) supplying air to the cathode ray compartment (24) of each battery cell and a cathode ray outlet (26) removing air from the cathode ray 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 anodic input (22); and • a purge outlet (46), - a control unit (70), in which the filter (40) is adapted to be electrically powered to filter dihydrogen contained in a gas feeding 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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