System and method for thermal regulation of a solid or polymer electrolyte in an electrochemical device

Abstract

A thermal regulation system (100) comprising: - an electrochemical device (1) comprising two electrodes (3, 4) and a solid or polymer electrolyte (2), - a heating element (5) configured to heat the electrolyte (2), - a control device (6) configured to control the heating power (P) of the heating element (5) and, - a measuring device (7) configured to apply, between the electrodes (3, 4), a sinusoidal voltage signal (U(F)) at a predetermined reference frequency (F), and to measure in response a sinusoidal intensity signal (I(F)), the control device (6) being configured to determine a resistance measurement (R(F)) of the electrolyte (2), and if the resistance measurement (R(F)) is lower than a predetermined minimum threshold (Smin(F)) corresponding to a maximum acceptable temperature of the electrolyte (2), reduce the value of the heating power (P) of the heating element (5). Abstract figure: Figure 3

Description

Title of the invention: System and method for thermal regulation of a solid or polymer electrolyte in an electrochemical device Technical field

[0001] The present invention relates to the field of thermal regulation of a solid or polymer electrolyte in an electrochemical device.

[0002] As is known, the integration of a solid or polymer electrolyte into an electrochemical device, such as an electrochemical sensor or a fuel cell, has the advantage of making the electrochemical device more heat resistant. Indeed, liquid or gel electrolytes present a risk of drying and chemical decomposition at high temperature, which can lead to overheating. The use of solid electrolytes therefore makes it possible to reduce this risk and increase safety during its use.

[0003] In practice, it is necessary to heat the electrolyte to ensure the proper functioning of the electrochemical device, namely to generate a representative measurement of a gaseous element for an electrochemical sensor or to produce sufficient electricity in the case of a fuel cell. The temperature to be reached to obtain sufficient electrical conductivity of the electrolyte varies according to the material of the electrolyte, from 25°C up to 200°C for a polymer and up to 900°C for certain solid electrolytes.

[0004] In a known manner, heating is traditionally carried out by a resistive circuit mounted in contact with one face of the electrolyte, which ensures constant heating of the electrolyte. In practice, such heating does not make it possible to maintain the electrolyte at a constant temperature because the electrolyte is subject to variable heat losses depending on the temperature of the outside air. Such temperature differences have the effect of modifying the electrical conductivity of the electrochemical device, which can undesirably disrupt the measurements of an electrochemical sensor or the electricity production of a fuel cell.

[0005] To avoid this drawback, one solution would be to integrate a temperature sensor to take into account the external temperature in determining the heating power of the resistive circuit. Such a temperature sensor would, however, increase the cost and complexity of the electrochemical device in an undesirable manner.

[0006] The invention thus aims to regulate in a simple, precise and reliable manner the temperature of the solid or polymer electrolyte in an electrochemical device. PRESENTATION OF THE INVENTION

[0007] The invention relates to a system for thermal regulation of a solid or polymer electrolyte comprising: • at least one electrochemical device comprising at least two electrodes and at least one solid or polymer electrolyte electrically connecting the electrodes, • at least one heating element configured to heat the electrolyte and • at least one control device configured to control the heating power of the heating element,

[0008] The invention is remarkable in that: • the thermal regulation system comprises at least one measuring device configured to: • applying, between the electrodes, one of at least one sinusoidal voltage or current signal at at least one predetermined reference frequency, and • measure in response, between the electrodes, the other of at least one sinusoidal intensity or voltage signal at said reference frequency, and • the control device being electrically connected to the measuring device, the control device being configured to: • determine at least one measurement of the resistance of the electrolyte at said reference frequency from the sinusoidal voltage signal and the sinusoidal intensity signal, • compare the resistance measurement to a predetermined minimum threshold at said reference frequency and corresponding to a maximum acceptable temperature of the electrolyte, and • if the resistance measurement is lower than the said minimum threshold, reduce the heating power value of the heating element, to reduce the temperature of the electrolyte.

[0009] The invention advantageously makes it possible to promote the performance of an electrochemical device with a solid or polymer electrolyte, by maintaining the temperature of the electrolyte within an optimal and constant operating range. The thermal regulation system advantageously makes it possible to determine the resistance of the electrolyte precisely and reliably, taking into account the heat losses that the electrolyte undergoes. The temperature is advantageously controlled in a simple manner via the measurement of the electrical resistance, which is sensitive to small variations in temperature. Thanks to the invention, the operational use of the electrochemical device remains efficient despite variations in external temperature.

[0010] According to one aspect of the invention, the control device is configured to: • compare the resistance measurement to a predetermined maximum threshold at said reference frequency and corresponding to a minimum acceptable temperature of the electrolyte, and • if the resistance measurement is higher than the said maximum threshold, increase the heating power value of the heating element, to increase the temperature of the electrolyte.

[0011] The control device advantageously makes it possible to maintain the temperature of the electrolyte in a simple and practical manner within an optimal and constant operating range defined between a minimum threshold and a maximum threshold.

[0012] According to one aspect of the invention, the reference frequency is between 10Hz and 1MHz, preferably between 1kHz and 1MHz, preferentially between 10kHz and 1MHz. Such high frequencies make it possible to distinctly measure the resistive electrical behavior of the electrolyte, without including that of the electrodes.

[0013] According to a first aspect of the invention, the electrochemical device is in the form of an electrochemical sensor of at least one gaseous element. The invention advantageously makes it possible to improve the precision and reliability of measurement of electrochemical sensors with solid or polymer electrolyte. The measurement of a gaseous element is thus independent of external temperature conditions.

[0014] According to a second aspect of the invention, the electrochemical device is in the form of a fuel cell. The invention advantageously makes it possible to promote the electrical production of a fuel cell.

[0015] According to one aspect of the invention: • the measuring device is configured to: • applying, between the electrodes, one of at least one sinusoidal voltage or current signal at a plurality of predetermined reference frequencies and • measure in response, between the electrodes, the other of at least one sinusoidal intensity or voltage signal at each reference frequency, and • the control device is configured to: • determine at least one measurement of electrolyte resistance for each reference frequency, • compare each resistance measurement to a predetermined minimum threshold of the same reference frequency, and • if at least one resistance measurement is lower than the minimum threshold of the same reference frequency, reduce the heating power value of the heating element, to reduce the temperature of the electrolyte.

[0016]

[0017]

[0018] According to a preferred aspect of the invention, the control device is configured to: • compare each resistance measurement to a predetermined maximum threshold of the same reference frequency, and • if at least one resistance measurement is higher than the maximum threshold of the same reference frequency, increase the heating power value of the heating element, to increase the temperature of the electrolyte. A plurality of measuring points at different reference frequencies enables more precise and reliable temperature control. The invention also relates to a method for thermal regulation of a solid or polymer electrolyte by means of a thermal regulation system as described above, said method comprising: • at least one step of applying, between the electrodes, one of a sinusoidal voltage or intensity signal at at least one predetermined reference frequency, • at least one measurement step in response, between the electrodes, to the other of a sinusoidal intensity or voltage signal at said reference frequency, • at least one step of determining a measurement of the resistance of the electrolyte at said reference frequency, from the sinusoidal voltage signal and the sinusoidal intensity signal, • at least one step of comparing the resistance measurement to a predetermined minimum threshold at said reference frequency and corresponding to a maximum acceptable temperature of the electrolyte, and • if the resistance measurement is lower than said minimum threshold, a step of reducing the value of the heating power of the heating element, to reduce the temperature of the electrolyte.

[0019] Such a method is advantageously practical and quick to implement, by simply measuring the resistive electrical behavior of the electrolyte and comparing it to a predetermined threshold. The resistance of the electrolyte is sensitive to small variations in temperature, which allows precise control, without requiring an overly expensive and complex temperature sensor.

[0020] According to one aspect of the invention, the method further comprises: • at least one step of comparing the resistance measurement to a predetermined maximum threshold at said reference frequency and corresponding to a minimum acceptable temperature of the electrolyte, • if the resistance measurement is higher than said maximum threshold, a step of increasing the value of the heating power of the heating element, to increase the temperature of the electrolyte.

[0021] According to one aspect of the invention, the method is repeated until the resistance measurement is between the minimum threshold and the maximum threshold. The minimum threshold and the maximum threshold make it possible to maintain the electrolyte in an optimal operating range for the operational use of the electrochemical device.

[0022] According to a preferred aspect, the method comprises: • at least one step of applying, between the electrodes, one of a sinusoidal voltage or intensity signal at a plurality of predetermined reference frequencies, • at least one measurement step in response, between the electrodes, to the other of a sinusoidal intensity or voltage signal at each reference frequency, • at least one step of determining a measurement of the resistance of the electrolyte at each reference frequency, from the sinusoidal voltage signal and the sinusoidal intensity signal, • at least one step of comparing each resistance measurement to a predetermined minimum threshold of the same reference frequency and corresponding to a maximum acceptable temperature of the electrolyte, and • if at least one resistance measurement is lower than said minimum threshold of

[0023]

[0024]

[0025] same reference frequency, a step of decreasing the value of the heating power of the heating element, to decrease the temperature of the electrolyte. According to a preferred aspect, the method further comprises: • at least one step of comparing each resistance measurement to a predetermined maximum threshold of the same reference frequency and corresponding to a minimum acceptable temperature of the electrolyte, • if at least one resistance measurement is greater than said maximum threshold of the same reference frequency, a step of increasing the value of the heating power of the heating element, to increase the temperature of the electrolyte. According to one aspect of the invention, the method comprises at least one waiting phase between two phases of operational use of the electrochemical device, said method being implemented during a waiting phase. The thermal regulation method is advantageously implemented when the electrochemical device is in the waiting phase to avoid any interference which could distort the measurement of the resistance or impact the operational use of the electrochemical device. According to a preferred aspect, the method further comprises, initially during a calibration phase: • at an optimum temperature of the electrolyte, at least one step of application, between the electrodes, of one of a voltage or sinusoidal intensity signal calibration at a plurality of calibration frequencies, • at the optimum temperature of the electrolyte, at least one measurement step in response, between the electrodes, to a calibration sinusoidal intensity or voltage signal at each calibration frequency, • at least one step of selecting at least one reference frequency from among the calibration frequencies, • at least one step of determining, from the sinusoidal voltage signal and the sinusoidal intensity signal at the selected reference frequency and at the optimal temperature, a resistance measurement defining a minimum threshold.

[0026] According to a preferred aspect, the determining step also comprises, from the sinusoidal voltage signal and the sinusoidal intensity signal at the selected reference frequency and at the optimal temperature, the determination of a resistance measurement defining a maximum threshold.

[0027] According to a preferred aspect, the selection step is implemented by: • determining, at the optimal temperature, a measurement of the impedance for each calibration frequency from the pair of voltage and current signals of the same calibration frequency, • determining the Nyquist diagram of the impedance measurement, • selecting a reference frequency greater than or equal to a characteristic frequency defined as the minimum frequency for which the Nyquist diagram presents a local minimum.

[0028] Such a selection makes it possible to determine a reference frequency making it possible to distinctly measure the electrical behavior of the electrolyte, without including that of the electrodes. PRESENTATION OF FIGURES

[0029] The invention will be better understood on reading the description which follows, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0030] [Fig.l] is a schematic representation of a thermal regulation system for the solid or polymer electrolyte of an electrochemical sensor according to a first embodiment of the invention.

[0031] [Fig.2] is a schematic representation of the thermal regulation system of [Fig.l] during an operational use phase of the electrochemical sensor.

[0032] [Fig. 3] is a schematic representation of the thermal control system of [Fig. 1] during the implementation of the thermal control method during a electrochemical sensor waiting phase.

[0033] [Fig.4] is a schematic representation of the thermal control system of [Fig.l] during an initial calibration phase of the thermal control process.

[0034] [Fig.5] is a schematic representation of an electrochemical system with integrated thermal regulation according to a second embodiment of the invention with a fuel cell.

[0035] [Fig.6] is a schematic representation of the initial calibration, functional use and standby phases of the electrochemical sensor of the electrochemical system of [Fig.l].

[0036] [Fig.7] is a schematic representation of the method of thermal regulation of the solid or polymer electrolyte of an electrochemical system according to one embodiment of the invention.

[0037] [Fig.8] is a schematic representation of the initial calibration phase of the thermal regulation method of [Fig.7] according to one embodiment of the invention.

[0038] [Fig.9] is a schematic representation of the step of selecting a reference frequency during the initial calibration phase of [Fig.8].

[0039] It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0040] With reference to figures 1 and 3, the invention relates to a thermal regulation system 100 of an electrolyte 2 of solid or polymer type in an electrochemical device 1. The thermal regulation system 100 according to the invention comprises: • an electrochemical device 1 comprising two electrodes 3, 4 and a solid or polymer electrolyte 2 electrically connecting the electrodes 3, 4, • a heating element 5 configured to heat the electrolyte 2, • a control device 6 configured to control the heating power P of the heating element 5, and • a measuring device 7 electrically connected to the control device 6.

[0041] According to the invention and as illustrated in [Fig. 3], the measuring device 7 is configured to apply, between the electrodes 3, 4, a sinusoidal voltage signal U(F) at a predetermined reference frequency F, and to measure in response a sinusoidal intensity signal I(F) at said reference frequency F, or vice versa.

[0042] Still according to the invention and as illustrated in [Fig.3], the control device 6 is configured to: • determine a measurement of resistance R(F) of the electrolyte 2 at said frequency reference F from the sinusoidal voltage and current signals U(F), I(F), • compare the R(F) resistance measurement to: • a minimum threshold Smin(F) predetermined at said reference frequency F and corresponding to a maximum acceptable temperature of the electrolyte 2, and • preferably, a maximum threshold Smax(F) predetermined at said reference frequency F and corresponding to a minimum acceptable temperature of the electrolyte 2, and • if the resistance measurement R(F) is lower than the minimum threshold Smin(F), reduce the value of the heating power P of the heating element 5, to reduce the temperature of the electrolyte 2. • preferably, if the resistance measurement R(F) is greater than the maximum threshold Smax(F), increase the value of the heating power P of the heating element 5, to increase the temperature of the electrolyte 2.

[0043] In the example illustrated in Figures 1 to 3, the electrochemical device 1 is in the form of an electrochemical sensor of one or more gaseous elements 10, such as an amperometric sensor or a potentiometric sensor. The electrodes 3, 4 of the electrochemical sensor 1 are usually called “working electrode 3” and “counter electrode 4”. The electrochemical sensor 1 also conventionally comprises a reference electrode (not shown). The working electrode 3, the counter electrode 4 and the reference electrode are conventionally immersed in the electrolyte 2 which ensures the ionic conductivity. With reference to [Fig.2], the working electrode 3 is configured to react chemically with one or more gaseous elements 10, causing a variation in potential or intensity which is measured by a calculation member 9 and makes it possible to provide a measurement of the concentration of the gaseous element 10.The operation of an electrochemical sensor 1 is known per se to those skilled in the art and is therefore not described further.

[0044] In the example illustrated in [Fig. 5], the electrochemical device 1' is in the form of a fuel cell. The fuel cell 1' usually comprises several electrochemical cells (only one is shown in [Fig. 5]). Each electrochemical cell comprises electrodes 3, 4 usually called "anode 3" and "cathode 4" separated by an electrolyte 2 usually called "ion exchange membrane". The anode 3 and the cathode 4 are configured to be supplied with reactants so as to generate a redox reaction, so as to produce electricity which drives a motor 9'. The operation of a fuel cell 1' is known per se to those skilled in the art and is therefore not described further.

[0045] The term “electrochemical device 1, 1'” is used indiscriminately hereinafter. to designate an electrochemical sensor 1 or a fuel cell 1'.

[0046] With reference to [Fig. 1], the invention is limited to electrolytes 2 of solid type or polymer type. An electrolyte 2 is said to be solid if it comprises a solid physical state. A solid electrolyte 2 comprises, for example, a ceramic material, such as yttrium oxide-stabilized zirconia (known by the abbreviation “YSZ”), gadolinium-doped cerium oxide (known by the abbreviation “GDC”), lanthanum strontium cobalt ferrite (known by the abbreviation “LSCF”) and / or strontium-doped lanthanum manganite (known by the abbreviation “LSM” or “LSMO”).

[0047] An electrolyte 2 is said to be polymeric if it comprises at least one polymer material. A polymer electrolyte 2 is for example in the form of a gel. A polymer electrolyte 2 comprises for example polyethylene glycol, polyvinyl alcohol, polymethyl methacrylate, polycaprolactone, chitosan, polyvinylpyrrolidone, polyvinyl chloride, polyvinylidene fluoride, and / or polyimide.

[0048] Such solid or polymer electrolytes 2, as opposed to liquid or gel electrolytes, are more heat resistant and thus reduce the risk of overheating during their use. This eliminates the disadvantage of the risk of drying or chemical decomposition of liquid or gel electrolytes. The integration of solid or polymer electrolytes 2 in an electrochemical device 1,1' makes it possible in particular to increase safety during its use. To ensure satisfactory ionic conductivity, such electrolytes 2 need to be heated to a temperature usually ranging from 25°C up to 200°C for polymers and up to 900°C for certain solid electrolytes.

[0049] With reference to [Fig. 1], the heating element 5 is for example in the form of a resistive circuit mounted in contact with one face of the electrolyte 2. This makes it possible to ensure mainly conductive heating. The resistive circuit comprises for example one or more successive U-shaped resistive wires. The resistive circuit comprises a conductive material, such as platinum, iron, copper, nickel, chromium and / or palladium, in pure or alloy form.

[0050] With reference to [Fig.l], the measuring device 7 is mounted so as to define an electrical loop 8 with the electrodes 3, 4 and the electrolyte 2. The measuring device 7 is for example in the form of an RLC meter. According to a first aspect of the invention, the measuring device 7 is configured to emit a sinusoidal voltage signal U(F) and measure in response a sinusoidal intensity signal I(F) of the same reference frequency F. According to a second aspect of the invention, the measuring device 7 is configured to emit a sinusoidal intensity signal I(F) and measure in response a sinusoidal voltage signal U(F) of the same reference frequency F. The measuring device is preferably a high-frequency voltage generator whose reference frequency F is between 10Hz and 1MHz, preferably between 1kHz and 1MHz, preferably between 10kHz and 1MHz.

[0051] Still with reference to [Fig.l], the control device 6 is presented by way of example in the form of a microcontroller, associated with a database configured to store the minimum threshold Smin(F) and the maximum threshold Smax(F). The microcontroller is configured to carry out calculation operations from the data provided by the measuring device 7 and control operations of the heating element 5. The control device 6 may be presented in a unitary or modular form, integrated or not in the measuring device 7. The control device 6 is presented in any form within the scope of the invention.

[0052] With reference to figures 3 and 7, the invention also relates to a method for thermal regulation of the electrolyte 2 in an electrochemical device 1. The method is implemented by means of the thermal regulation system 100 and comprises: • a step of applying El, between the electrodes 3, 4, a sinusoidal voltage signal U(F) at a predetermined reference frequency F, • a measurement step E2, between the electrodes 3, 4, of a sinusoidal intensity signal I(F) at said reference frequency (F) in response to the sinusoidal voltage signal U(F), • a step E3 of determining a measurement of resistance R(F) of the electrolyte 2 at said reference frequency F, from the sinusoidal voltage signal U(F) and the sinusoidal intensity signal I(F), • a comparison step E4 of the resistance measurement R(F) to: • a minimum threshold Smin(F) predetermined at said reference frequency F and corresponding to a maximum acceptable temperature of the electrolyte 2, and • preferably, a maximum threshold Smax(F) predetermined at said reference frequency F and corresponding to a minimum acceptable temperature of the electrolyte 2, and • if the resistance measurement R is lower than the minimum threshold Smin(F), a step E5 of reduction of the value of the heating power P of the heating element 5, to reduce the temperature of the electrolyte 2. • if the resistance measurement R is greater than the maximum threshold Smax(F), a step E6 of increasing the value of the heating power P of the heating element 5, to increase the temperature of the electrolyte 2.

[0053] According to an equivalent variant of the invention, the method comprises: • a step of applying El, between the electrodes 3, 4, a sinusoidal intensity signal I(F) at a predetermined reference frequency F, and • a measurement step E2, between electrodes 3, 4, of a voltage signal if sinusoidal U(F) at said reference frequency F in response to the sinusoidal intensity signal I(F), • the other steps remaining unchanged.

[0054] As illustrated in Figures 3 and 6, the thermal regulation method is preferably implemented during a waiting phase E between two operational use phases M of the electrochemical device 1. As illustrated in [Fig.2], in the case of an electrochemical sensor 1, an operational use phase M corresponds to a phase of measuring the concentration of one or more gaseous elements 10. In the case of a fuel cell 1', an operational use phase M corresponds to a phase of producing electrical energy. The thermal regulation method is thus implemented during a waiting phase E, namely a phase of non-operational use of the electrochemical device 1,1', to avoid any interference which could hinder or even distort both the temperature regulation and the measurement of gaseous concentration or the production of electrical energy.

[0055] As illustrated in [Fig. 6], the reference frequency F, the minimum threshold Smin(F) and the maximum threshold Smax(F) are preferably determined initially during a calibration phase C (described below). The calibration phase C precedes in practice an alternation of operational use phases M ([Fig. 2]) and waiting phases E ([Fig. 3]). Note that a waiting phase E can be defined passively, by detecting the more or less prolonged non-operational use of the electrochemical device 1, 1', or actively, by causing the interruption of the operational use M of the electrochemical device 1, 1'.

[0056] With reference to Figures 3 and 7, the step of applying El a sinusoidal voltage signal U(F) at the reference frequency F is implemented by the measuring device 7 between the electrodes 3, 4. Similarly, the step of measuring E2 a sinusoidal intensity signal I(F) of the same reference frequency F in response is implemented by the measuring device 7. According to one aspect of the invention, the steps of applying El and measuring E2 are repeated several times for several different predetermined reference frequencies F, in order to obtain several measurement points for more precise and more reliable thermal regulation. According to one aspect of the invention, the steps of applying El and measuring E2 are repeated several times for the same reference frequency F. The measurement redundancy also allows more reliable thermal regulation.At the end of the application steps E1 and measurement steps E2, the sinusoidal voltage and current signals U(F), I(F) are transmitted to the control device 6. In an equivalent alternative manner, steps E1 and E2 can be implemented by emitting a sinusoidal current signal I(F) and measuring a sinusoidal voltage signal U(F).

[0057] With reference to figures 3 and 7, the step E3 of determining a measurement of re resistance R(F) is then implemented by the control device 6. From a pair of sinusoidal voltage and current signals U(F), I(F) of the same reference frequency F, the control device 6 calculates the impedance Z(F) of the electrolyte 2 at the reference frequency F in the following manner: Z(F) = U(F) / I(F). The control device 6 then calculates the resistance measurement R(F) of the electrolyte 2 at the reference frequency F in the following manner: R(F) = Re(Z(F)), where Re denotes the real part of the impedance Z(F).

[0058] At the end of the determination step E3, a resistance measurement R(F) is determined for each pair of sinusoidal voltage and current signals U(F), I(F) of the same reference frequency F. As will be seen later with the calibration phase C, each reference frequency F is chosen to be sufficiently high so as to represent the electrical behavior of the electrolyte 2 considered separately from the electrodes 3, 4. Each resistance measurement R(F) is thus representative, at a given frequency F, of the electrical resistance of the electrolyte 2 alone.

[0059] With reference to Figures 3 and 7, during the comparison step E4, the control device 6 compares each resistance measurement R(F) to a minimum threshold Smin(F) and to a maximum threshold Smax(F) of the same reference frequency F. Each minimum threshold Smin(F) and each maximum threshold Smax(F) is stored beforehand in the database associated with the control device 6. In practice, at a fixed frequency F, the temperature of the electrolyte 2 is strongly linked to the electrical resistance R(F) of the electrolyte 2 and varies inversely proportionally with the electrical resistance R(F) of the electrolyte 2. Thus, for a given frequency F, a minimum threshold Smin(F) corresponds to a maximum acceptable temperature to ensure sufficient ionic conductivity of the electrolyte 2. Similarly, for a given frequency F, a maximum threshold Smax(F) corresponds to a minimum acceptable temperature to ensure sufficient ionic conductivity of the electrolyte 2.

[0060] With reference to Figures 3 and 7, for a given frequency F, the minimum threshold Smin(F) and the maximum threshold Smax(F) thus define a limited range of electrical resistances corresponding to an acceptable operating temperature for the electrolyte 2. If the resistance measurement R(F) verifies Smin(F) < R(F) < Smax(F), this indicates that the temperature of the electrolyte 2 allows satisfactory operational use M of the electrochemical device 1, 1' and the thermal regulation method is terminated. Preferably, the difference between the minimum threshold Smin(F) and the maximum threshold Smax(F) is small to maintain the temperature of the electrolyte within a restricted range. A restricted range allows greater measurement accuracy.

[0061] With reference to [Fig.7], if the resistance measurement R(F) is lower than the minimum threshold Smin(F), this indicates that the temperature of the electrolyte 2 is too high. The comparison step E4 is then followed by a reduction step E5 of the heating power P of the heating element 5, in the form of a setpoint transmitted by the control device 6. With reference to [Fig.7], if the resistance measurement R(F) is greater than the maximum threshold Smax(F), this indicates that the temperature of the electrolyte 2 is too low. The comparison step E4 is then followed by a step E6 of increasing the heating power P of the heating element 5, in the form of a setpoint transmitted by the control device 6.

[0062] According to a preferred aspect of the invention, the decreasing step E5 and the increasing step E6 are implemented respectively by removing and adding a fixed increment to the heating power P. The thermal regulation method is then repeated until the resistance measurement R(F) is between the minimum threshold Smin(F) and the maximum threshold Smax(F). According to another preferred aspect, the increment is variable and determined as a function of the difference between the resistance measurement R(F) and the threshold Smin(F), Smax(F). The thermal regulation method is then preferably repeated to verify that the resistance measurement R(F) is between the minimum threshold Smin(F) and the maximum threshold Smax(F).

[0063] According to a preferred aspect illustrated in Figures 4 and 8, each reference frequency F, each minimum threshold Smin(F) and each maximum threshold Smax(F) are initially determined during a calibration phase C. The calibration phase C precedes an operational use phase M to avoid any interference in a manner analogous to previously. The following steps are preferably implemented during the calibration phase C: • at an optimal temperature Topt of the electrolyte 2, a step of application Cl, between the electrodes 3, 4, of a sinusoidal calibration voltage signal Uopt(Fcal) at several calibration frequencies Fcal, • at the optimum temperature Topt of the electrolyte 2, a measurement step C2, between the electrodes 3, 4, of a sinusoidal calibration intensity signal lopt(Fcal) at each calibration frequency Fcal in response to the sinusoidal calibration voltage signal Uopt(Fcal), • a selection step C3 of one or more reference frequencies F from among the calibration frequencies Fcal, • a C4 determination step: • from the sinusoidal voltage signal Uopt(Fcal) and the sinusoidal intensity signal lopt(Fcal) at the selected reference frequency F and at the optimal temperature Topt, a resistance measurement defining a minimum threshold Smin(F), and preferably a resistance measurement defining a maximum threshold Smax(F).

[0064] Alternatively, steps C1 and C2 can be implemented by emitting a calibration sinusoidal intensity signal lopt(Fcal) and measuring a calibration sinusoidal voltage signal Uopt(Fcal).

[0065] With reference to Figures 4 and 8, the steps C1 of applying a voltage signal, and C2 of measuring a current signal in response differ from the steps E1, E2 of the same name previously described in that they are implemented for several calibration frequencies Fcal and at a known optimal temperature Topt of the electrolyte 2, for example measured by a temperature sensor. The optimal temperature Topt is preferably indicated by the manufacturer of the electrochemical device or determined during the calibration phase C. Preferably, the steps C1, C2 are implemented over a frequency range Fcal of between 10Hz and 1MHz, preferably between 1kHz and 1MHz, preferentially between 10kHz and 1MHz.

[0066] According to a preferred aspect illustrated in [Fig.9], the selection step C3 is implemented by the control device 6 by: • determining, at the optimal temperature Topt, a measurement of the impedance Zopt(Fcal) for each calibration frequency Fcal from the pair of voltage and current signals Uopt(Fcal), lopt(Fcal) of the same calibration frequency Fcal, • determining the Nyquist diagram of the impedance Zopt(Fcal), of which the real part Re(Zopt(Fcal)) is on the abscissa and the imaginary part Im(Zopt(Fcal)) on the ordinate, • selecting a reference frequency F greater than or equal to a characteristic frequency F2 defined as the minimum frequency for which the Nyquist diagram presents a local minimum.

[0067] Conventionally and as illustrated in [Fig. 9], the Nyquist diagram of the electrochemical device 1, 1' has three concave portions and two local minima of frequencies F1, F2. The first concave portion at lower frequency Fcal (on the right in [Fig. 9]) represents the electrical behavior of the electrodes 3, 4 while the two following concave portions at higher frequency Fcal represent the electrical behavior of the electrolyte 2. The selection step C3 thus makes it possible to determine one or more reference frequencies F (only one shown as an example in [Fig. 9]) representative of the electrical behavior of the electrolyte 2 distinctly from the electrodes 3, 4.

[0068] Following the selection step C3, the determination step C4 is preferably implemented by determining: • in a manner analogous to the determination step E3 previously described, a measurement of the resistance Ropt(F) of the electrolyte (2) at the optimum temperature Topt, from the sinusoidal voltage and current signals Uopt(F) and lopt(F) at the reference frequency F and • the maximum threshold Smax(F) at the minimum acceptable temperature being defined as follows: Smax(F) = Ropt(F) + e, where e denotes a predetermined acceptable deviation, for example of the order of 1%. • the minimum threshold Smin(F) at the maximum acceptable temperature being defined as follows: Smin(F) = Ropt(F) - e.

[0069] At the end of the calibration phase C, the reference frequency F, the maximum threshold Smax(F) and the minimum threshold Smin(F) are stored in the database associated with the control device 6. The calibration phase C advantageously makes it possible to determine a reference frequency F and thresholds Smin(F), Smax(F) specific to the electrochemical device 1,1', for precise and reliable thermal regulation.

Claims

Claims

1. Thermal regulation system (100) of a solid or polymer electrolyte (2) comprising: • at least one electrochemical device (1, 1') comprising at least two electrodes (3, 4) and at least one solid or polymer electrolyte (2) electrically connecting the electrodes (3, 4), • at least one heating element (5) configured to heat the electrolyte (2) and • at least one control device (6) configured to control the heating power (P) of the heating element (5), • the thermal regulation system (100) being characterized in that it comprises at least one measuring device (7) configured to: • applying, between the electrodes (3, 4), one of at least one sinusoidal voltage or intensity signal (U(F), I(F)) at at least one predetermined reference frequency (F), the reference frequency (F) being between 10kHz and 1MHz, and • measure in response, between the electrodes (3, 4) the other of at least one sinusoidal intensity or voltage signal (I(F), U(F)) at said reference frequency (F), • the control device (6) being electrically connected to the measuring device (7), the control device (6) being configured to: • determine at least one resistance measurement (R(F)) of the electrolyte (2) at said reference frequency (F) from the sinusoidal voltage signal (U(F)) and the sinusoidal intensity signal (I(F)), • compare the resistance measurement (R(F)) to a minimum threshold (Smin(F)) predetermined at said reference frequency (F) and corresponding to a maximum acceptable temperature of the electrolyte (2), and • if the resistance measurement (R(F)) is lower than said minimum threshold (Smin(F)), reduce the value of the heating power (P) of the heating element (5), to reduce the temperature of the electrolyte (2).

2. Thermal regulation system (100) according to claim 1, wherein the control device (6) is configured to: • compare the resistance measurement (R(F)) with a maximum threshold (Smax(F)) predetermined at said reference frequency (F) and corresponding to a minimum acceptable temperature of the electrolyte (2), and • if the resistance measurement (R(F)) is greater than said maximum threshold (Smax(F)), increase the value of the heating power (P) of the heating element (5), to increase the temperature of the electrolyte (2).

3. Thermal regulation system (100) according to one of claims 1 to 2, in which the electrochemical device (1) is in the form of an electrochemical sensor of at least one gaseous element.

4. Thermal regulation system (100) according to one of claims 1 to 2, in which the electrochemical device (F) is in the form of a fuel cell.

5. Thermal regulation system (100) according to one of claims 1 to 4, wherein: • the measuring device (7) is configured to: • apply, between the electrodes (3, 4), one of at least one sinusoidal voltage or current signal (U(F), I(F)) at a plurality of predetermined reference frequencies (F) and • measure in response, between the electrodes (3, 4), the other of at least one sinusoidal voltage or current signal (I(F), U(F)) at each reference frequency (F), • the control device (6) being configured to: • determine at least one resistance measurement (R(F)) of the electrolyte (2) for each reference frequency (F), • compare each resistance measurement (R(F)) to a minimum threshold (Smin(F)) predetermined with the same reference frequency (F), and • if at least one resistance measurement (R(F)) is lower than the minimum threshold (Smin(F)) with the same reference frequency (F), reduce the value of the heating power (P) of the heating element (5), to reduce the temperature of the electrolyte (2).

6. Method for thermal regulation of a solid or polymer electrolyte (2) by means of a thermal regulation system (100) according to one of claims 1 to 5, said method comprising: • at least one step of application (El), between the electrodes (3, 4), of one of a sinusoidal voltage or intensity signal (U(F), I(F)) at at least one predetermined reference frequency (F), • at least one step of measurement (E2) in response, between the electrodes (3, 4), of the other of a sinusoidal voltage or intensity signal (I(F), U(F)) at said reference frequency (F), • at least one step of determination (E3) of a resistance measurement (R(F)) of the electrolyte (2) at said reference frequency (F), from the sinusoidal voltage signal (U(F)) and the sinusoidal intensity signal (I(F)),• at least one step of comparing (E4) the resistance measurement (R(F)) to a minimum threshold (Smin(F)) predetermined at said reference frequency (F) and corresponding to a maximum acceptable temperature of the electrolyte (2), • if the resistance measurement (R) is lower than said minimum threshold (Smin(F)), a step of reducing (E5) the value of the heating power (P) of the heating element (5), to reduce the temperature of the electrolyte (2).,

7. Thermal regulation method according to claim 6, further comprising: • at least one step of comparing (E4) the resistance measurement (R(F)) to a maximum threshold (Smax(F)) predetermined at said reference frequency (F) and corresponding to a minimum acceptable temperature of the electrolyte (2), • if the resistance measurement (R(F)) is greater than said maximum threshold (Smax(F)), a step of increasing (E6) the value of the heating power (P) of the heating element (5), to increase the temperature of the electrolyte (2).

8. A thermal regulation method according to claim 7, which is repeated until the resistance measurement (R(F)) is between the minimum threshold (Smin(F)) and the maximum threshold (Smax(F)).

9. Thermal regulation method according to one of claims 6 to 8, comprising at least one waiting phase (E) between two operational use phases (M) of the electrochemical device (1), said method being implemented during a waiting phase (E).

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