WO2021233822A1

WO2021233822A1 - Method for activating a fuel cell

Info

Publication number: WO2021233822A1
Application number: PCT/EP2021/062984
Authority: WO
Inventors: Benoit GUENOT; André RAKOTONDRAINIBE; Yacine Hammadi
Original assignee: Alstom Hydrogène Sas
Priority date: 2020-05-18
Filing date: 2021-05-17
Publication date: 2021-11-25
Also published as: FR3110289B1; CA3177755A1; FR3110289A1

Abstract

The activation method comprises a hydration step comprising supplying a fuel compartment (22) and an oxidant compartment (24) with hydrated inert gas while measuring high-frequency impedance on a group of electrochemical cells (10) of the fuel cell (4), so as to monitor the evolution of a high-frequency impedance, with the end of the hydration step being controlled as a function of the measured high-frequency impedance, then an electrochemical preconditioning step comprising supplying the fuel compartment (22) with combustible fluid and/or supplying the oxidant compartment (24) with oxidising fluid while imposing a current produced by the fuel cell (4).

Description

Method of activating a fuel cell

The present invention relates to a method of activating a fuel cell, in particular a fuel cell using hydrogen as fuel and oxygen as oxidizer.

A fuel cell is an electrochemical reactor that performs an electrochemical reaction between a fuel and an oxidizer to produce electrical energy.

A fuel cell uses, for example, hydrogen as fuel and oxygen as oxidizer. In this case, in addition to the electricity it generates, the fuel cell produces heat and rejects water resulting from the electrochemical reaction between hydrogen and oxygen. The sum of the electrical energy and the heat produced is equal to the chemical energy associated with the combustion of hydrogen.

A fuel cell is for example of the ion exchange membrane type, in particular, in the case of a fuel cell using dihydrogen as fuel and a polymer membrane of the proton exchange membrane type (or of the “PEM” type. "For" Proton Exchange Membrane "), allowing the exchange of hydrogen ions or" protons "between the hydrogen fuel and the oxygen oxidant.

An ion exchange membrane fuel cell comprises at least one electrochemical cell, and generally several electrochemical cells, each electrochemical cell comprising a fuel chamber for the circulation of the combustible fluid containing the fuel and an oxidizer chamber for the circulation of the fluid oxidizer containing the oxidizer, the fuel chamber and the oxidizer chamber being separated in a fluidtight manner by a membrane-electrode assembly comprising an ion exchange membrane sandwiched between two electrodes, one defining an anode and the another defining a cathode, the membrane-electrode assembly allowing the passage of ions from one side to the other. The electrodes preferably contain catalytic layers containing catalysts suitable for promoting the electrochemical reaction.

In operation, combustible fluid circulates in the fuel chamber and oxidizing fluid circulates in the oxidizer chamber of each electrochemical cell, and ions pass through the membrane-electrode assembly while a voltage appears between the electrodes of the assembly. membrane-electrode, and that a voltage appears at the terminals of each electrochemical cell, and thus at the terminals of the fuel cell. Before the integration of an ion exchange membrane fuel cell, in particular with a proton exchange membrane, in an electricity production system and its operation, an electrochemical activation should be carried out (also called preconditioning). or running-in) to allow better use of the intrinsic electrochemical performance of the fuel cell. A proton exchange membrane dihydrogen fuel cell that has undergone the electrochemical activation process has better electrochemical performance compared to that of a fuel cell that has not undergone electrochemical activation.

Electrochemical activation amounts, on the one hand, to promoting the hydration of each ion exchange membrane by using hydrated inert gas (hydrated nitrogen, hydrated argon) and / or hydrated reactive gases (hydrated dihydrogen, hydrated dioxygen, hydrated air), and, on the other hand, to carry out an electrochemical pretreatment to activate the catalytic layers of the membrane-electrode assemblies. This electrochemical activation makes it possible on the one hand to eliminate surface oxides and impurities blocking the active sites of the catalytic layers and on the other hand to promote the accessibility of the active sites to hydrogen by imposing a preprogrammed charge profile controlled under form of profile of electric current intensity or electric voltage at the terminals of the fuel cell.

The electrochemical activation of a fuel cell depends on the charge profile. It is very time consuming and results in a high consumption of inert hydrated gases and / or hydrated reactive gases, and a high consumption of electricity. These consumptions are all the higher for high-power fuel cells, for which the electrical voltages and the intensities of electrical current to be applied can be very high and require a set of electrical control devices specific to high electrical power, expensive or not readily available.

The activation of fuel cells constitutes a technological lock in an industrial production line of fuel cells and fuel cell systems, in particular of the proton exchange membrane type.

One of the aims of the invention is to provide an activation method which can be carried out efficiently and quickly, in particular for fuel cells or combinations of high power fuel cells.

To this end, the invention provides a method of activating a fuel cell, the fuel cell comprising at least one electrochemical cell, each electrochemical cell comprising a fuel chamber and an oxidizer chamber separated by a membrane assembly. electrode including an ion exchange membrane sandwiched between two electrodes, the fuel cell comprising an fuel compartment for the circulation of a combustible fluid including the fuel chamber of each electrochemical cell and an oxidizer compartment for the circulation of an oxidizing fluid including the oxidizer chamber of each electrochemical cell, the activation method comprising:

- a hydration step comprising supplying the fuel compartment and the oxidizer compartment with hydrated inert gas (s) while performing a high-frequency impedance measurement on a group of electrochemical cells of the fuel cell so as to monitor the evolution of a high frequency impedance, the end of the hydration step being controlled as a function of the measured high frequency impedance, then

- an electrochemical preconditioning step comprising supplying the fuel compartment with combustible fluid and / or supplying the oxidizer compartment with oxidizing fluid while imposing a current produced by the fuel cell.

According to particular embodiments, the activation method comprises one or more of the following optional characteristics, taken individually or in any technically possible combination:

- during the hydration step, the fuel compartment and the oxidizer compartment are supplied with the same hydrated inert gas, for example from the same source of hydrated inert gas;

- during the hydration step, the fuel compartment is supplied with a hydrated inert gas having a relative humidity level equal to or greater than 50% and / or the oxidizer compartment is supplied with a hydrated inert gas having a relative humidity level equal to or greater than 50%;

- during the hydration step, the fuel compartment is supplied with an inert gas hydrated at a temperature equal to or greater than 50 ° C and / or at a temperature equal to or less than 90 ° C, and / or the oxidizer compartment is supplied with an inert gas hydrated at a temperature equal to or greater than 50 ° C and / or at a temperature equal to or less than 90 ° C;

- the group of electrochemical cells on which the high-frequency impedance measurement is carried out includes all the electrochemical cells of the fuel cell;

the group of electrochemical cells on which the high-frequency impedance measurement is carried out includes a fraction of the electrochemical cells of the fuel cell; - the hydration step is stopped when the average surface high frequency impedance, determined as a function of the measured high frequency impedance, of the number of electrochemical cells of the group of electrochemical cells on which the measurement is carried out and of the surface area of the ion exchange membrane of each electrochemical cell is equal to or greater than 50 mQ.cm ² , in particular equal to or greater than 100 mQ.cm ² , and / or equal to or less than 200 mQ.cm ² , in particular equal or less than 150 mQ.cm ² ;

the preconditioning step comprises a first sub-step comprising supplying the fuel compartment with combustible fluid and supplying the oxidizer compartment with oxidizing fluid by requiring the production by the fuel cell of a current d 'substantially constant intensity, then a second sub-step comprising continuing the supply of the fuel compartment with combustible fluid and the supply of the oxidizer compartment with oxidizing fluid by requiring the production by the fuel cell of a current variable so as to vary the voltage at the terminals of the fuel cell, so that the voltage of each electrochemical cell varies within a predetermined voltage range;

- the predetermined voltage range is the range from 0.3 V to 0.8 V;

- the intensity of the current imposed during the first sub-step corresponds to a current density through the ion exchange membrane of each electrochemical cell between 0.4 A / cm ² and 0.6 A / cm ² , in in particular a current density of about 0.5 A / cm ² ;

- the first sub-step is implemented for a period of between 5 minutes and 20 minutes, in particular a period of about 10 minutes;

the preconditioning step comprises a deprivation step comprising a first phase of supplying the fuel compartment with combustible fluid and supplying the oxidizer compartment with oxidizing fluid while requiring production, by the fuel cell, of an imposed current of determined intensity, then a second phase of continuing the supply of the fuel compartment with combustible fluid by interrupting the supply of the oxidizer compartment with oxidizing fluid and by maintaining the production of the current imposed by the cell fuel, for a fixed period of deprivation.

The invention and its advantages will be better understood on reading the description which follows, given solely by way of non-limiting example, and made with reference to the accompanying drawings, in which:

- Figure 1 is a schematic view of a fuel cell integrated into an electricity production system; - Figures 2 to 4 are views of the fuel cell of Figure 1 during different steps of a method of activating the fuel cell.

The power generation system 2 shown in Figure 1 comprises a fuel cell 4 configured to perform an electrochemical reaction between a fuel and an oxidizer to produce electricity.

The fuel cell 4 is fluidly connected to a source of combustible fluid 6 for its supply of combustible fluid containing the fuel, and is fluidly connected to a source of oxidizing fluid 8 for its supply of oxidizing fluid containing the oxidant.

The fuel fluid source 6 is for example a fuel fluid reservoir or a fuel fluid distribution network.

The source of oxidizing fluid 8 is for example an oxidizing fluid reservoir or an oxidizing fluid distribution network. If the oxidant fluid is air, the oxidizer source 8 is for example an air collection device (air compressors, fans or blowers) ...

The fuel cell 4 is of the ion exchange membrane type.

The fuel cell 4 comprises at least one electrochemical cell 10, each electrochemical cell 10 comprising a fuel chamber 12 for the circulation of the combustible fluid and an oxidizer chamber 14 for the circulation of the oxidizing fluid, separated in a fluidtight manner by a membrane-electrode assembly 16 comprising an ion exchange membrane 18 sandwiched between two electrodes 20.

The membrane-electrode assembly 16 (also designated by the acronym “AME” or the acronym “MEA” for “Membrane Electrode Assembly” according to English terminology) is a multilayer complex comprising several layers including the ion exchange membrane 18 and the two electrodes 20 sandwiching the ion exchange membrane 18.

The membrane-electrode assembly 16 is impermeable to fluids and adapted to allow passage of ions from one side to the other of the membrane-electrode assembly 16.

Preferably, the membrane-electrode assembly 16 of each electrochemical cell 10 comprises catalytic layers (not shown) containing catalysts suitable for promoting the electrochemical reaction between the fuel and the oxidant.

For reasons of simplification of the drawings, a single electrochemical cell 10 is shown in Figures 1 to 4. Preferably, the fuel cell 4 comprises several electrochemical cells 10, the fuel chambers 12 of the electrochemical cells 10 being fluidly connected to one another, for example in parallel or in series, for the circulation of the combustible fluid, and the oxidizer chambers 14 electrochemical cells 10 being fluidly connected to one another, for example in parallel or in series, for the circulation of the oxidizing fluid.

Preferably, the fuel chambers 12 of the electrochemical cells 10 of the fuel cell 4 are fluidly connected in parallel for the circulation of the fuel fluid, and / or the oxidizer chambers 14 of the electrochemical cells 10 of the fuel cell 4 are connected. fluidly in parallel for the circulation of the oxidizing fluid.

The electrochemical cells 10 are for example stacked forming a stack or “stack” according to English terminology.

The fuel cell 4 comprises a fuel compartment 22 for the circulation of the oxidizing fluid, and an oxidizing compartment 24 for the circulation of the oxidizing fluid.

The fuel compartment 22 includes the fuel chamber 12 of each electrochemical cell 10, and the oxidizer compartment 24 includes the oxidizer chamber 14 of each electrochemical cell 10.

As illustrated in Figure 1, in the operating configuration of the fuel cell 4, the fuel compartment 22 is fluidly connected to the fuel source 6 and the oxidizer compartment 24 is fluidically connected to the oxidizer source 8.

In operation, the fuel compartment 22 is supplied with combustible fluid and the oxidizer compartment 24 is supplied with oxidizing fluid. In each electrochemical cell 10, ions are generated and pass through the membrane-electrode assembly 16, and the electrons thus released are collected by the electrodes 20.

Each electrochemical cell 10 generates an electrical voltage (or "voltage" hereinafter) between the electrodes 20 of its membrane-electrode assembly 16.

When the fuel cell 4 comprises a single electrochemical cell 10, the voltage across the terminals of the fuel cell 4 is the voltage across the terminals of the single electrochemical cell of the fuel cell 4.

When the fuel cell 4 comprises several electrochemical cells 10, the electrochemical cells 10 are electrically connected to each other in series. The voltage at the terminals of the fuel cell 4 is equal to the sum of the voltages at the terminals of the electrochemical cells 10. For a given voltage at the terminals of the fuel cell 4, the average voltage of the electrochemical cells 10 is equal to the voltage at the terminals of the fuel cell 4 referred to (or "divided by the") number of electrochemical cells 10 of the fuel cell 4.

The fuel cell 4 uses for example dihydrogen (H ₂ ) as fuel and dioxygen (0 ₂ ) as oxidizer.

In operation, such a fuel cell 4 produces electricity and water resulting from the electrochemical reaction between dihydrogen (H ₂ ) and dioxygen (0 ₂ ). The combustible fluid is for example dihydrogen (H ₂ ) and the oxidizing fluid is for example dioxygen (0 ₂ ) or air.

In this case, each ion exchange membrane 18 is more precisely a proton exchange membrane. The fuel cell 4 is then said to be of the PEM type for “Proton Exchange Membrane” or PEMFC for “Proton Exchange Membrane Fuel Celle” according to English terminology.

An electric load 26 is electrically connected to the terminals of the fuel cell 4, so as to be supplied with electricity by the fuel cell 4. The electric load 26 is a device consuming electricity, such as for example an electrical installation of a building.

When an electric current passes through the fuel cell 4, this current passes through each electrochemical cell 10, and in particular the ion exchange membrane 18 of each electrochemical cell 10.

The electrochemical cells 10 of the fuel cell 4 are substantially identical. In particular, the ion exchange membranes 18 of the electrochemical cells 10 have substantially the same area.

The current density passing through the ion exchange membrane 18 of each electrochemical cell 10 is the intensity of the electric current passing through the ion exchange membrane 18 per unit area, ie the intensity of the electric current divided by the area of the ion exchange membrane 18. The current density is expressed for example in amperes per square centimeter (A / cm ² ).

A method of activating the fuel cell 4 of Figure 1 will now be described with reference to Figures 2 to 4 which illustrate different steps of the activation method.

As illustrated in Figure 2, the activation method comprises a hydration step aimed at hydrating each ion exchange membrane 18 of the fuel cell 4. The hydration step comprises supplying the fuel compartment 22 with a hydrated inert gas and supplying the oxidizer compartment 24 with a hydrated inert gas.

The hydration step makes it possible to hydrate the ion exchange membrane 18 of each electrochemical cell 10 of the fuel cell 4. This is necessary for the subsequent proper functioning of the fuel cell 4.

Preferably, the fuel compartment 22 is supplied with a hydrated inert gas having a relative humidity level equal to or greater than 50%, and / or the oxidizer compartment 24 is supplied with a hydrated inert gas having a humidity level. relative equal to or greater than 50%.

Preferably, the fuel compartment 22 is supplied with an inert gas hydrated at a temperature equal to or greater than 50 ° C, in particular at a temperature equal to or greater than 60 ° C, and / or at a temperature equal to or less than 90 ° C. ° C, especially at a temperature of 80 ° C or less.

Preferably, the oxidizer compartment 24 is supplied with an inert gas hydrated at a temperature equal to or greater than 50 ° C, in particular at a temperature equal to or greater than 60 ° C, and / or at a temperature equal to or less than 90 ° C. ° C, especially at a temperature of 80 ° C or less.

More preferably, the fuel compartment 22 and the oxidizer compartment 24 are supplied with inert hydrated gases having the same temperature and / or the same relative humidity.

In an advantageous example of implementation, the fuel compartment 22 and the oxidizer compartment 24 are supplied with the same hydrated inert gas.

Advantageously, the fuel compartment 22 and the oxidizer compartment 24 are supplied with hydrated inert gas by the same source of hydrated inert gas 28 fluidly connected to the fuel compartment 22 and to the oxidizer compartment 24.

Preferably, as illustrated in Figure 2, the fuel compartment 22 and the oxidizer compartment 24 are fluidly connected in parallel to the same source of hydrated inert gas 28.

As a variant, they are fluidly connected in series to the same source of hydrated inert gas 28. In this case, the fuel compartment 22 is located upstream of the oxidizer compartment 24, the hydrated inert gas first circulating in the combustion compartment. fuel 22 then in the oxidizer compartment 24, or alternatively, the oxidizer compartment 24 is located upstream of the combustion compartment. fuel 22, the hydrated inert gas circulating first in the oxidizer compartment 24 and then in the fuel compartment 22.

Feeding the fuel compartment 22 and the oxidizer compartment 24 using the same source of hydrated inert gas 28, in particular in parallel, facilitates balancing of the pressures in the fuel compartment 22 and the oxidizer compartment. 24, which limits the risk of damaging the ion exchange membrane 18 of each electrochemical cell 10 during the hydration step.

The hydration step comprises carrying out a high-frequency impedance measurement on the fuel cell 4, and controlling the end of the hydration step, ie the end of the supply of inert gas ( s) hydrated, as a function of said high frequency impedance measurement.

The high frequency impedance measurement is carried out using an impedance measuring device 30. The impedance measuring device 30 is for example a milliohmmeter, in particular an alternating milliohmmeter, or an impedance spectrometer. . High frequency impedance is expressed, for example, in milliohms (mO).

The high-frequency impedance measurement is carried out simultaneously with the supply of the fuel compartment 22 and the oxidizer compartment 24 with hydrated inert gas (s), so as to follow the evolution of the impedance measurement. high frequency over time during the hydration step, ie during the supply of the fuel compartment 22 and the oxidizer compartment 24 with hydrated inert gas.

The high-frequency impedance measurement is performed by imposing an alternating current across the group of electrochemical cells 10 whose high-frequency impedance is measured, and the measured high-frequency impedance depends on the frequency of the alternating current.

The high frequency impedance measurement is performed at at least one measurement frequency. Preferably, each measurement frequency is included in the measurement frequency range between 100 Hz and 10 kHz. In particular, the high frequency impedance measurement is carried out at a measurement frequency of 1 kHz, for example using a milliohmmeter.

The high-frequency impedance measurement is performed on a group of electrochemical cells 10 of the fuel cell 4. The group of electrochemical cells comprises a single electrochemical cell 10 or more electrochemical cells 10 electrically connected in series.

In an exemplary implementation, the group of electrochemical cells 10 comprises for example all the electrochemical cells 10 of the fuel cell 4. In this case, the high frequency impedance measurement is for example carried out at the terminals of the fuel cell 4, as illustrated in FIG. 2.

In another example of implementation, the group of electrochemical cells 10 comprises a fraction of the electrochemical cells 10 of the fuel cell 4, ie a number of electrochemical cells 10 strictly lower than the total number of electrochemical cells 10 of the fuel cell. 4.

The high frequency impedance of each electrochemical cell 10 is representative of the high frequency impedance of the ion exchange membrane 18 of this electrochemical cell 10.

The high frequency impedance of the group of electrochemical cells 10 is representative of the sum of the high frequency impedances of the electrochemical cells 10 constituting the group, and therefore of the sum of the high frequency impedances of the ion exchange membranes 18 of the electrochemical cells 10 of the group .

In particular, the high frequency impedance of the fuel cell 4 is representative of the sum of the high frequency impedances of all the electrochemical cells 10 of the fuel cell 4, and therefore of the sum of the high frequency impedances of the exchange membranes. of ions 18 from all the electrochemical cells of the fuel cell 4.

Furthermore, the high frequency impedance of each ion exchange membrane 18 is a function of its hydration.

The hydration of the ion exchange membrane 18 promotes the transport of ionic charges, in particular protons (H ⁺ ). The more the ion exchange membrane 18 is hydrated, the more its ionic conductivity, and in particular proton, increases, and the more its high frequency impedance decreases.

Thus, the high frequency impedance measured is a function of the hydration of the ion exchange membrane 18 of each electrochemical cell 10 of the group, and can be considered as representative of the hydration of the ion exchange membrane 18 of each. electrochemical cell 10 of the fuel cell 4.

On the other hand, the surface high frequency impedance of an ion exchange membrane 18 is the high frequency impedance of this ion exchange membrane 18 multiplied by the area (or area) of the ion exchange membrane 18.

The surface high frequency impedance is expressed for example in milliohms square centimeters (mO.cm ² ).

The activation method comprises stopping the hydration step as a function of the high frequency impedance measurement carried out on the fuel cell 4 during supplying the fuel compartment 22 and the oxidizer compartment 24 with hydrated inert gas (s).

The activation method comprises, for example, stopping the hydration step as a function of an average surface high frequency impedance of the ion exchange membranes 18 of the electrochemical cells 10 of the group of electrochemical cells 10 whose high impedance frequency is measured.

The average area high frequency impedance is determined as a function of the measured high frequency impedance and the area of the ion exchange membrane 18 of each electrochemical cell 10 of the group of electrochemical cells 10 whose high frequency impedance is measured.

The average surface high frequency impedance of the ion exchange membranes 18 of the electrochemical cells 10 of the electrochemical cell group 10 is in principle equal to the sum of the surface high frequency impedances of the ion exchange membranes 18, divided by the number of cells. electrochemical 10.

The average surface high frequency impedance is expressed in principle according to the following formula:

OR

"N" is the number of electrochemical cells 10 in the group whose high frequency impedance is being measured;

"Rsurface average" is the average surface high frequency impedance of the ion exchange membranes 18 of the electrochemical cells 10 of the group;

"Rsurfaciquei" is the surface high frequency impedance of the ion exchange membrane 18 of the i ^th electrochemical cell 10 of the group;

"Rmembrane," is the surface high frequency impedance of the ion exchange membrane 18 of the i ^th electrochemical cell 10 of the group;

“Smembrane, ·” is the surface of the ion exchange membrane 18 of the i ^th electrochemical cell 10 of the group.

Considering that the ion exchange membranes 18 have an average surface area, it is possible to determine the average surface high frequency impedance as the sum of the high frequency impedances of the exchange membranes. of ions 18, multiplied by the average area of ion exchange membranes 18 and divided by the number of electrochemical cells 10 in that group.

Thus, considering that the ion exchange membranes 18 have an average surface area, the average surface high frequency impedance is expressed according to the following formula:

OR

"N" is the number of electrochemical cells 10 in the group of electrochemical cells 10 whose high frequency impedance is being measured;

"Smaverage" is the average area of ion exchange membranes 18 of electrochemical cells 10 of electrochemical cell group 10 whose high-frequency impedance is measured.

The measured high frequency impedance is representative of the sum of the high frequency impedances of the ion exchange membranes 18 of the electrochemical cells 10 of the group of electrochemical cells 10 whose high frequency impedance is being measured.

Thus, in an exemplary embodiment, the average surface high frequency impedance is determined as the measured high frequency impedance multiplied by the average surface area of the ion exchange membranes 18 of the electrochemical cells 10 of the group of electrochemical cells 10 whose impedance high frequency is measured, divided by the number of 10 electrochemical cells in that group.

The average surface high frequency impedance is then determined according to the following formula:

OR "N" is the number of electrochemical cells 10 in the group of electrochemical cells 10 whose high frequency impedance is being measured;

"Rmeasured" is the high frequency impedance measured for electrochemical cell group 10;

"Smoy" is the average area of the ion exchange membranes 18 of the electrochemical cells 10 of the electrochemical cell group 10 whose high-frequency impedance is being measured.

In a particular exemplary embodiment, when the high frequency impedance measurement is carried out on the fuel cell 4 as a whole, ie on a group including all the electrochemical cells 10 of the fuel cell 4, the surface high frequency impedance average of the ion exchange membranes 18 of the fuel cell 4 is determined as equal to the measured high frequency impedance multiplied by the average area of the ion exchange membranes 18 and divided by the number of electrochemical cells 10 of the fuel cell. fuel 4.

In a particular exemplary implementation, the activation method comprises controlling the stopping of the hydration step when the average surface high frequency impedance of the ion exchange membranes 18 of the electrochemical cell group 10 is located within a predetermined impedance range.

In a particular exemplary implementation, the activation method comprises controlling the stopping of the hydration step when the average surface high frequency impedance of the ion exchange membranes 18 of the electrochemical cell group 10 is equal to or greater than 50 mQ.cm ² , in particular equal to or greater than 100 mQ.cm ² , and / or equal or less than 200 mQ.cm ² , in particular equal to or less than 50 mQ.cm ² , preferably for a measurement frequency of between 100 Hz and 10 kHz, in particular a measurement frequency of approximately 1 kHz.

The range of the average surface high frequency impedance value depends on the average thickness of the exchange membranes. A very fine or fine or moderately fine membrane corresponds respectively to an impedance range greater than or equal to 50 mQ.cm ² , greater than or equal to 100 mQ.cm ² and greater than or equal to 150 mQ.cm ² .

For a fuel cell 4 using hydrogen as the fuel fluid and air as the combustion fluid, these average surface high frequency impedance values of the ion exchange membranes 18 correspond approximately to a voltage at the start of the fuel cell 4 greater than or equal to 0.6 V per cell electrochemical 10 and a starting current density greater than or equal to 0.5 A / cm ² through the ion exchange membrane 18 of each electrochemical cell 10, at ambient temperature and at low pressure.

The duration of the hydration step is a function, on the one hand, of the temperature and pressure of hydrated inert gas, of the flow of hydrated inert gas, of the dew point, of the number of electrochemical cells 10 to hydrated. , and, on the other hand, the characteristics of the materials of the membrane-electrode assembly 16 of each electrochemical cell 10 with respect to water (thicknesses, porosities, hydrophobicities, etc.), and in particular of the nature and the physicochemical characteristics of the ion exchange membrane 18 (thickness of the ion exchange membrane 18, intrinsic ionic conductivity, ionic charge capacity, water absorption rates).

The duration of the hydration step is for example equal to or less than two hours, in particular less than or equal to one hour.

The activation method includes an electrochemical preconditioning step implemented after the hydration step. The hydration step and the electrochemical preconditioning step are carried out sequentially.

In an exemplary embodiment, the electrochemical preconditioning step comprises two sub-steps performed sequentially, namely a first sub-step and a second sub-step.

The first sub-step comprises supplying the fuel compartment 22 with combustible fluid and supplying the oxidizer compartment 24 with oxidizing fluid by controlling the current produced by the fuel cell 4, so as to impose a current of intensity constant.

The first sub-step comprises, for example, the connection of a programmable load 32 to the terminals of the fuel cell 4 in order to force the production of a current of constant intensity by the fuel cell 4.

In an exemplary implementation, the substantially constant intensity of the current produced by the fuel cell 4 corresponds to a current density located in a predetermined current density range through the ion exchange membranes 18 of the electrochemical cells 10. fuel cell 4.

The predetermined current density range is for example between 0.4 A / cm ² and 0.6 A / cm ² . The constant current is for example chosen so that the current density is approximately equal to 0.5 A / cm ² .

In an exemplary embodiment, this first sub-step is carried out for a period of between 5 minutes and 20 minutes, in particular a period of approximately 10 minutes. The second sub-step comprises supplying the fuel compartment 22 with combustible fluid and supplying the oxidizer compartment 24 with oxidizing fluid by controlling the current produced by the fuel cell 4 so as to impose a variable voltage across the terminals of the fuel cell 4, such that the average voltage of the electrochemical cells 10 varies within a predetermined voltage range. The predetermined voltage range is for example between 0.3 V and 0.8 V.

The control of the current produced by the fuel cell 4 is obtained for example by connecting a programmable load 34 to the terminals of the fuel cell 4, in particular a programmable electronic load or a programmable resistive load.

The variable voltage imposed on the terminals of the fuel cell 4 is for example cyclic. The voltage at the terminals of each electrochemical cell 10 is then also cyclic.

The second sub-step makes it possible to reduce the oxides and impurities which would be trapped in each membrane-electrode assembly 16 of the fuel cell 4, in particular in any catalytic layers, in order to maximize their electro-catalytic activities vis-à-vis fuel and oxidizer.

In another exemplary embodiment, as illustrated in FIG. 4, the electrochemical preconditioning step comprises a deprivation step comprising a first phase of supplying the fuel compartment 22 and the oxidizer compartment 24 with oxidizing fluid while imposing the production of an imposed current, then a second phase of maintaining the supply of the fuel compartment 22 with combustible fluid while interrupting the supply of the oxidizer compartment 24 with oxidizing fluid and by maintaining the production of the imposed current for one fixed duration, for example a few seconds.

The current imposed during the deprivation step is, for example, a current of constant intensity.

The current produced by the fuel cell 4 is imposed, for example, by means of a programmable load 32 connected to the terminals of the fuel cell 4, in particular a programmable electronic load configured in an imposed current operating mode.

Stopping the supply of oxidizer causes a drop in the voltage across each electrochemical cell 10 to low values while remaining in current density domains through the ion exchange membrane 18 of each electrochemical cell. 10 between 0.2 A / cm ² and 0.7 A / cm ² .

The current imposed at the terminals of the fuel cell 4 corresponds for example to a current density through the ion exchange membrane 18 of each cell electrochemical 10 between 0.4 A / cm ² and 0.6 A / cm ² , in particular a current density of about 0.5 A / cm ^2. As illustrated in Figure 4, the second phase of the the deprivation step is carried out for example by fluidly connecting the oxidizer compartment 24 with the fuel compartment 22 so that the oxidizer compartment 24 is supplied with the combustible fluid which has passed through the fuel compartment 22, and not with oxidizing fluid .

The second phase of the deprivation stage is implemented for a specified deprivation period. Preferably, the determined duration is between 5 seconds and 30 seconds. Deprivation by oxidizing under current causes the voltage of the fuel cell 4 to drop very rapidly in order to electrochemically reduce the oxides and / or the impurities present in the active layers of the electrodes 20. The maximum deprivation time would correspond to a final cell voltage. equal to 0 V.

The total duration of the electrochemical preconditioning step is for example less than 2 hours, in particular less than 1 hour.

The electrochemical preconditioning step is carried out for example individually on the fuel cell 4, in particular on a fuel cell test bench, or simultaneously on several fuel cells 4 electrically connected in series. This allows the electrochemical preconditioning step to be carried out simultaneously on several fuel cells, thereby reducing costs.

The proposed activation method makes it possible to reduce the activation time of a fuel cell 4 or of a group of fuel cells 4, while limiting the time required to achieve this activation.

The activation method comprises two distinct steps carried out sequentially, comprising a step of hydration of the ion exchange membrane 18 of each electrochemical cell 10 by circulation of hydrated inert gas (s) then a step of preconditioning. electrochemical.

The proposed activation method makes it possible both to control the state of hydration of each ion exchange membrane 18 but also to control the quality of each ion exchange membrane 18 and the ohmic losses on the scale of each electrochemical cell 10 of fuel cell 4, in particular when the high frequency impedance measurement is carried out on fuel cell 4, ie on all of the electrochemical cells 10.

The measurement of an impedance depends on two quantities, namely the value of the impedance and the value of the phase shift between the current and the voltage. For an ion exchange membrane 18, a high frequency impedance measurement makes it possible to carry out an impedance measurement with an electric current which is in phase with the voltage, and the measured impedance corresponds to the ionic resistance, and in particular proton resistance (ie to the resistance to the passage of ions, in particular protons, through each ion exchange membrane 18).

The proposed activation method makes it possible to consider reducing the duration of activation of a fuel cell 4 using hydrogen as fuel fluid and air as combustion fluid to less than two hours before its use in a fuel cell. fuel cell system for power generation.

The proposed activation method also limits the consumption of reactive gases, the hydration step being carried out using inert gas (s).

The activation method is applicable to a fuel cell 4 individually or a set of several fuel cells 4 electrically connected to each other.

The activation method can be used as a preliminary step in a chain of industrial production and quality control of fuel cells before their implementation.

During the hydration step, the high-frequency impedance measurement is preferably carried out on the fuel cell 4, ie on all the electrochemical cells 10 of the fuel cell 4. This makes it possible to take into account in the measurement hydration of the ion exchange membrane 18 of each electrochemical cell 10.

In another exemplary implementation, the high-frequency impedance measurement is carried out on a group of electrochemical cells 10 comprising a fraction of all the electrochemical cells 10 of the fuel cell 4. The high-frequency impedance measurement only takes into account the ion exchange membranes 18 of the electrochemical cells 10 of the group on which the high-frequency impedance measurement is carried out, but it is possible to consider that this is representative of all the electrochemical cells.

In a particular example of implementation, the high frequency impedance measurement is carried out on a group of electrochemical cells 10 comprising a single electrochemical cell 10 among a plurality of electrochemical cells 10 of the fuel cell 4.

The activation method applies to the case of a fuel cell comprising a single electrochemical cell (or “single-cell” fuel cell), in which case the group of electrochemical cells 10 on which the measurement of d is carried out. The high frequency impedance necessarily comprises a single electrochemical cell 10.

It should be noted that the activation method is particularly advantageous for a high power fuel cell comprising a plurality of cells. electrochemical 10, for example at least 20, at least 40, see at least 100 electrochemical cells 10.

Thus, preferably, the fuel cell 4 comprises at least 20, at least 40, or even at least 100 electrochemical cells 10. During the hydration step, the high frequency impedance measurement is carried out for example on a single group. electrochemical cells 10.

In another exemplary embodiment, the high-frequency impedance measurement is carried out on several groups of electrochemical cells 10, each group of electrochemical cells 10 comprising at least one electrochemical cell 10. This nevertheless requires the availability of several measuring devices. high frequency impedance for measuring high frequency impedance, each high frequency impedance measuring device performing the measurement on a respective electrochemical cell group 10.

Claims

1. Method of activating a fuel cell (4), the fuel cell (4) comprising at least one electrochemical cell (10), each electrochemical cell (10) comprising a fuel chamber (12) and a chamber. of oxidizer (14) separated by a membrane-electrode assembly (16) including an ion exchange membrane (18) sandwiched between two electrodes (20), the fuel cell (4) comprising a fuel compartment (22) for the circulation of a combustible fluid including the fuel chamber (12) of each electrochemical cell (10) and an oxidizer compartment (24) for the circulation of an oxidizer fluid including the oxidizer chamber (14) of each cell electrochemical (10), the activation method comprising:

- a hydration step comprising supplying the fuel compartment (22) and the oxidizer compartment (24) with hydrated inert gas (s) while performing a high frequency impedance measurement on a group of cells electrochemical (10) of the fuel cell (4) so as to monitor the evolution of a high frequency impedance, the end of the hydration step being controlled as a function of the measured high frequency impedance, then

- an electrochemical preconditioning step comprising supplying the fuel compartment (22) with combustible fluid and / or supplying the oxidizer compartment (24) with oxidizing fluid while imposing a current produced by the fuel cell ( 4).

2. Activation method according to claim 1, wherein, during the hydration step, the fuel compartment (22) and the oxidizer compartment (24) are supplied with the same hydrated inert gas, for example. from the same source of inert hydrated gas.

3. Activation method according to claim 1 or 2, wherein, during the hydration step, the fuel compartment (22) is supplied with a hydrated inert gas having an equal or greater relative humidity. at 50% and / or the oxidizer compartment (24) is supplied with a hydrated inert gas having a relative humidity level equal to or greater than 50%.

4. Activation method according to any one of the preceding claims, wherein, during the hydration step, the fuel compartment (22) is supplied with an inert gas hydrated at a temperature equal to or greater than 50. ° C and / or at a temperature equal to or less than 90 ° C, and / or the oxidizer compartment (24) is fed with an inert gas hydrated at a temperature of 50 ° C or greater and / or at a temperature of 90 ° C or less.

5. Activation method according to any one of the preceding claims, in which the group of electrochemical cells (10) on which the high frequency impedance measurement is carried out includes all the electrochemical cells (10) of the fuel cell (4). ).

6. Activation method according to any one of claims 1 to 4, in which the group of electrochemical cells (10) on which the high frequency impedance measurement is carried out includes a fraction of the electrochemical cells (10) of the battery. fuel (4).

7. Activation method according to any one of the preceding claims, in which the hydration step is stopped when the average surface high frequency impedance, determined as a function of the measured high frequency impedance, of the number of electrochemical cells. (10) of the group of electrochemical cells (10) on which the measurement is carried out and the surface area of the ion exchange membrane (18) of each electrochemical cell (10) is equal to or greater than 50 mQ.cm ² , in particular equal to or greater than 100 mQ.cm ² , and / or equal to or less than 200 mQ.cm ² , in particular equal to or less than 150 mQ.cm ² .

8. Activation method according to any one of the preceding claims, wherein the preconditioning step comprises:

- a first sub-step comprising the supply of the fuel compartment (22) with combustible fluid and the supply of the oxidizer compartment (24) with oxidizing fluid by requiring the production by the fuel cell (4) of a current of substantially constant intensity, then

- a second sub-step comprising the continuation of the supply of the fuel compartment (22) with combustible fluid and the supply of the oxidizer compartment (24) with oxidizing fluid by imposing the production by the fuel cell (4) of a variable current so as to vary the voltage at the terminals of the fuel cell (4), so that the voltage of each electrochemical cell (10) varies within a predetermined voltage range.

9. The activation method according to claim 8, wherein the predetermined voltage range is the range from 0.3 V to 0.8 V.

10. Activation method according to claim 8 or claim 9, wherein the intensity of the current imposed during the first sub-step corresponds to a current density through the ion exchange membrane (18) of each cell. electrochemical (10) between 0.4 A / cm ² and 0.6 A / cm ² , in particular a current density of about 0.5 A / cm ² .

11. Activation method according to any one of claims 8 to 9, wherein the first sub-step is implemented for a period of between 5 minutes and 20 minutes, in particular a period of about 10 minutes.

12. Activation method according to any one of the preceding claims, in which the preconditioning step comprises a deprivation step comprising a first phase of supplying the fuel compartment (22) with combustible fluid and of supplying it. of the oxidizer compartment (24) with oxidizing fluid while requiring the production, by the fuel cell (4), of an imposed current of determined intensity, then a second phase of continuing the supply of the fuel compartment ( 22) with combustible fluid by interrupting the supply to the oxidizer compartment (24) with oxidizing fluid and by maintaining the production of the current imposed by the fuel cell (4), for a determined deprivation period.