DE102023132470A1 - DEVICE AND METHOD FOR DETERMINING A CONDITION OF A FUEL CELL - Google Patents

Abstract

A method according to the invention includes determining data which represent a first polarization curve, which reflects an expected state of the fuel cell at the start of operation, after a certain period of operation or at the end of operation, deriving a deviation between measurement data and the first polarization curve and determining the state of the fuel cell based on the deviation.

Description

AREA

The present invention relates to a device and a method for determining a state of a fuel cell.

BACKGROUND

Fuel cells are subject to an aging process, which typically leads to a change in the polarization curve of the fuel cell during operation.

DESCRIPTION

A method according to the invention includes determining data which represent a first polarization curve, which reflects an expected state of the fuel cell at the start of operation, after a certain period of operation or at the end of operation, deriving a deviation between measurement data and the first polarization curve and determining the state of the fuel cell based on the deviation.

In this context, the term “polarization curve”, as used in the context of the present description and the claims, is to be understood in particular as a curve which shows the dependence of the electrical voltage generated by the at least one fuel cell between the anode and cathode on the Current density describes. Said polarization curve typically shifts to lower voltages due to aging processes during the operation of the fuel cell at the same current densities. In this respect, determining the polarization curve of the fuel cell at a certain point in the life cycle of the fuel cell allows a prediction of the aging or health status (“State of Health, SoH”) at that point in time.

The aging or state of health can be determined from the deviation of the specific polarization curve from a reference polarization curve (determined by measurement or analysis), which reflects an expected state of the fuel cell at the start of operation, after a certain period of operation or at the end of operation. It is understood that the fuel cell is not subject to any or only insignificant signs of aging at the start of operation and that the signs of aging increase as the fuel cell continues to operate.

If the polarization curve of the fuel cell is used as a reference at the start of operation, the greater the deviation, the greater the aging and the lower the health. However, if the polarization curve of the fuel cell is used as a reference at the end of operation, the smaller the deviation, the greater the aging and the lower the health. Of course, the deviation of the specific polarization curve from the reference polarization curve can also be derived during operation without complete (or possibly partial) detection of the polarization curve by otherwise determining to what extent the measurement data fit the reference polarization curve.

Taking into account the state of the fuel cell, electrical and thermodynamic conditions to which the fuel cell is exposed during further operation can then be adjusted. By adapting the electrical and thermodynamic conditions, an improved operating strategy can be achieved with regard to the aging expected during operation.

The measurement data can include a voltage value of the fuel cell associated with a reference current density value.

The reference current density value can be chosen so that it lies in an ohmic region of the polarization curve. This can depend on the respective use of the fuel cell and can, for example, be in the range of 40% to 70% of the nominal load.

The measurement data may include a series of current density values and voltage values associated with the current density values.

The current/voltage value pairs can be used to derive a second polarization curve. For example, the second polarization curve can be derived from the value pairs using a fitting method.

The method may further include deriving the second polarization curve based on the measurement data, wherein the deviation between the measurement data and the first polarization curve includes a comparison of the first polarization curve and the second polarization curve.

The derivation of the second polarization curve can be based on an analytical model of the fuel cell, preferably the Kulikovsky model.

For example, the analytical model can be used to derive the polarization curve from the value pairs using a fitting process by deriving boundary conditions from the model.

A device according to the invention comprises a non-volatile memory in which data is stored which represents a first polarization curve which reflects an expected state of the fuel cell at the start of operation, after a certain period of operation or at the end of operation, a sensor set up to record measurement data, and a processor , set up to derive a deviation between the measurement data and the first polarization curve and to determine the state of the fuel cell based on the deviation.

The measurement data can include a voltage value of the fuel cell associated with a reference current density value.

The measurement data may include a series of current density values and voltage values associated with the current density values.

The processor can further be set up to derive a second polarization curve based on the measurement data, the derivation of the deviation between the measurement data and the first polarization curve being based on a comparison of the first polarization curve and the second polarization curve.

The derivation of the second polarization curve can be based on an analytical model of the fuel cell, preferably the Kulikovsky model.

The device can be designed as a control device for controlling electrical and thermodynamic conditions to which the fuel cell is subject during operation of the fuel cell.

Furthermore, a computer program according to the invention can include instructions which, when the program is executed by a computer, cause it to carry out the method according to the invention.

BRIEF DESCRIPTION OF DRAWINGS

• 1 eine schematische Darstellung einer Brennstoffzelle;
• 2 eine schematische Darstellung eines Brennstoffzellenstapels;
• 3 eine schematische Darstellung der Auswirkung von Alterungsprozessen auf die Polarisationskurve der Brennstoffzelle;
• 3a das Ableiten eines Verlaufes der Polarisationskurve zu einem bestimmten Zeitpunkt auf Basis eines zu einem Referenzstromdichtewert zugehörigen Spannungswertes;
• 3b das Ableiten eines Verlaufes der Polarisationskurve zu einem bestimmten Zeitpunkt auf Basis einer Reihe an Stromdichtewerten und zu den Stromdichtewerten zugehörigen Spannungswerten;
• 4 ein Steuergerät zur Steuerung elektrischer und thermodynamischer Gegebenheiten, denen die Brennstoffzelle während des Betriebs unterliegt; und
• 5 eine schematische Darstellung des Ablaufs eines computerimplementierten Verfahrens zum Bestimmen eines Zustandes der Brennstoffzelle zeigt.

The invention is explained below in the detailed description using exemplary embodiments, with reference being made to drawings in which:

• 1 a schematic representation of a fuel cell;
• 2 a schematic representation of a fuel cell stack;
• 3 a schematic representation of the effect of aging processes on the polarization curve of the fuel cell;
• 3a deriving a course of the polarization curve at a specific point in time based on a voltage value associated with a reference current density value;
• 3b deriving a course of the polarization curve at a specific point in time based on a series of current density values and voltage values associated with the current density values;
• 4 a control device for controlling electrical and thermodynamic conditions to which the fuel cell is subject during operation; and
• 5 shows a schematic representation of the sequence of a computer-implemented method for determining a state of the fuel cell.

In the drawings, the same or functionally similar elements are identified by the same reference numerals.

DETAILED DESCRIPTION

1 shows a schematic representation of a fuel cell 10. The fuel cell 10 comprises a cathode 12, a cathode-side catalyst layer 14, a polymer membrane 16, an anode-side catalyst layer 18 and an anode 20.

As in 2 shown, several fuel cells 10 can be arranged in a stack 22, wherein a bipolar plate 24 can be arranged between two fuel cells 10 arranged next to one another.

3 shows a schematic representation of the influence of operational aging of the fuel cell 10 on its polarization curve 26. As in 3 shown, the polarization curve 26 shifts from its initial course 28 towards a lower voltage due to aging processes with the same current density.

Said shift can, as in 3a indicated, can be determined by measuring a voltage value associated with a reference current density value Jref.

Said shift can also be made as in 3b indicated, can be determined by measuring a series of current density values and voltage values associated with the current density values and fitting the polarization curve. The Kulikovsky model can be used to determine the boundary conditions under which the fitting is carried out.

The shift can be determined in relation to an initial state, a final state (which represents the end of the life of the fuel cell 10) or a state lying between the initial and final states. The shift can also be used to determine the aging state of the fuel cell 10.

4 shows a control device 30 for controlling electrical and thermodynamic conditions to which the fuel cell 10 is subject during operation. The control device 30 can be provided with a processor, a non-volatile memory and a computer program stored in the non-volatile memory, which includes instructions that cause the method to be carried out when the program is executed by the processor. In particular, the control unit 30 can be set up to adapt at least a first electrical or thermodynamic condition to which the fuel cell 10 is subject during operation from the specific time t1 in order to extend the service life of the fuel cell 10.

5 shows the process flow. This begins at step 32 with determining data which represents the polarization curve 28, which reflects an expected state of the fuel cell at the start of operation. Instead of the in 3 , 3a or 3b The polarization curve 28 shown can of course also be used as a polarization curve which reflects the expected state of the fuel cell 10 after a certain period of operation or at the end of operation. The method then continues at step 34 with the derivation of a deviation between the measurement data and the polarization curve 28. As in connection with 3a and 3b described, the measurement data may include a voltage value of the fuel cell 10 associated with a reference current density value Jref or a series of current density values and voltage values associated with the current density values.

The method then ends at step 36 with determining the state of the fuel cell 10 based on the deviation. For example, it can be determined that the deviation of the specific polarization curve 26 from the initial polarization curve 28 suggests a specific remaining operating time. In particular, a measure of the displacement can be used which correlates with the aging state of the fuel cell 10.

REFERENCE SYMBOL LIST

10

Fuel cell

12

cathode

14

Catalyst layer

16

membrane

18

Catalyst layer

20

anode

22

Fuel cell stack

24

Bipolar plate

26

Polarization curve (initial)

28

Polarization curve (after aging of the polymer electrolyte fuel cell)

30

Control unit

32

Step

34

Step

36

Step

Claims (10)

Method for determining a state of a fuel cell (10), comprising: Determining data which represents a first polarization curve (28) which reflects an expected state of the fuel cell (10) at the start of operation, after a certain period of operation or at the end of operation; Deriving a deviation between measurement data and the first polarization curve (28); and Determining the state of the fuel cell (10) based on the deviation. Procedure according to Claim 1 , wherein the measurement data includes a voltage value of the fuel cell (10) associated with a reference current density value. Procedure according to Claim 1 , wherein the measurement data includes a series of current density values and voltage values associated with the current density values. Procedure according to Claim 3 , further comprising: deriving a second polarization curve (26) based on the measurement data, wherein the deviation between the measurement data and the first polarization curve (28) comprises a comparison of the first polarization curve (28) and the second polarization curve (26). Procedure according to Claim 4 , wherein the derivation of the second polarization curve (26) is based on an analytical model of the fuel cell (10), preferably the Kulikovsky model. Device comprising: a non-volatile memory in which data is stored which has a first polarization represent curve (28) which represents an expected state of the fuel cell (10) at the start of operation, after a certain period of operation or at the end of operation; a sensor set up to record measurement data; and a processor configured to derive a deviation between the measurement data and the first polarization curve (28) and to determine the state of the fuel cell (10) based on the deviation. Device according to Claim 6 , wherein the measurement data includes a voltage value of the fuel cell (10) associated with a reference current density value. Device according to Claim 6 , wherein the measurement data includes a series of current density values and voltage values associated with the current density values. Device according to Claim 8 , wherein the processor is further set up to derive a second polarization curve (26) based on the measurement data, the derivation of the deviation between the measurement data and the first polarization curve (28) being based on a comparison of the first polarization curve (28) and the second polarization curve (26 ) based. Device according to Claim 9 , wherein the derivation of the second polarization curve (26) is based on an analytical model of the fuel cell (10), preferably the Kulikovsky model.

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