DE102021207855A1 - Method of monitoring an electrochemical cell unit - Google Patents

Abstract

Method for monitoring an electrochemical cell unit (1, 49, 53) for converting electrochemical energy into electrical energy as a fuel cell unit (1) and/or for converting electrical energy into electrochemical energy as an electrolytic cell unit (49) with stacked electrochemical cells (2, 50, 52 ) as a cell stack (61) with the steps: operating the electrochemical cell unit (1, 49, 53) with the operating parameters necessary for operation, so that electrochemical energy is converted into electrical energy or electrical energy into electrochemical energy, detecting a cell parameter separately for each a cell (2, 50, 52) of the cell stack (61) of the electrochemical cell unit (1, 49, 53) with sensors, transmission of the cell parameters recorded separately for the individual cells (2, 50, 52) to a computing unit, determination of a cell state as a temporary operational impairment or as damage to one cell each (2, 50, 52) in Depending on the cell parameters recorded separately for each cell (2, 50, 52) by means of the computing unit (62, 63), at least one operating parameter of the electrochemical cell unit (1, 49, 53) changing over a period of time, in particular differing from that for the Operating parameters required for operation, for which monitoring is changed to at least one monitoring operating parameter and the electrochemical cell unit (1, 49, 53) is operated with the at least one monitoring parameter during the change period and the cell parameters are recorded before and/or during and/or after the change period for determining the cell state separately for each cell (2, 50, 52) of the cell stack (61) of the electrochemical cell unit (1, 49, 53) is designed with sensors.

Description

The present invention relates to a method for monitoring an electrochemical cell unit according to the preamble of claim 1 and an electrochemical cell unit according to the preamble of claim 14.

State of the art

Fuel cell units as galvanic cells convert continuously supplied fuel and oxidizing agent into electrical energy and water by means of redox reactions at an anode and cathode. Fuel cells are used in a wide variety of stationary and mobile applications, for example in houses without a connection to a power grid or in motor vehicles, in rail transport, in aviation, in space travel and in shipping. In fuel cell units, a multiplicity of fuel cells are arranged in a fuel cell stack as a fuel cell stack. Inside each fuel cell there is a gas space for oxidizing agent, ie a flow space for conducting oxidizing agent, such as air from the environment with oxygen, through. The oxidant gas space is formed by channels on the bipolar plate and by a gas diffusion layer for a cathode. The channels are thus formed by a corresponding channel structure of a bipolar plate and the oxidizing agent, namely oxygen, reaches the cathode of the fuel cells through the gas diffusion layer. A gas space for fuel is present in an analogous manner.

Electrolytic cell units made up of stacked electrolytic cells, analogous to fuel cell units, are used, for example, for the electrolytic production of hydrogen and oxygen from water. Furthermore, fuel cell units are known which can be operated as reversible fuel cell units and thus as electrolytic cell units. Fuel cell units and electrolytic cell units form electrochemical cell units. Fuel cells and electrolytic cells form electrochemical cells.

In electrochemical cell units, process fluids are used to convert electrochemical energy into electrical energy and/or to convert electrical energy into electrochemical energy. During operation of the electrochemical cell units, there may be deviations in the cell parameters of the electrochemical cells due to the processes taking place, particularly when the electrochemical cell units are in operation for a longer period of time. For example, in a PEM fuel cell, water, in particular water of reaction, can be deposited or collected as process fluid in the anodes, cathodes and gas diffusion layers as well as the channels for fuel and oxidant. These deposits have negative effects on operation, in particular leading to a reduction in efficiency and accelerated aging in the PEM fuel cell, so that the voltage in each fuel cell is reduced as a cell parameter of a damaged fuel cell. In addition, the proton exchange membrane can also become enriched with carbon monoxide, which has negative effects. Carbon deposits can form in the channels in a SOFC fuel cell.

It is already known to use a CVM device (cell voltage monitoring device) to detect damage to individual fuel cells. In this case, the cell parameter of the voltage of the fuel cells is detected during normal operation of the fuel cell unit with operating parameters by means of the CVM device. However, these operating parameters generally only show very small changes during operation, so that there are no changes or only minor changes that are difficult to detect in the cell parameters as the voltages of the fuel cells. As a result, damage to fuel cells can only be detected, in a disadvantageous manner, when individual fuel cells have generally only been substantially and irreparably damaged. The service life of such fuel cell units is disadvantageously short because measures to extend the service life can only be initiated very late.

Disclosure of Invention

Advantages of the Invention

Method according to the invention for monitoring an electrochemical cell unit for converting electrochemical energy into electrical energy as a fuel cell unit and/or for converting electrical energy into electrochemical energy as an electrolysis cell unit with stacked electrochemical cells as a cell stack, with the steps: operating the electrochemical cell unit with the operating parameters necessary for operation, see above that electrochemical energy is converted into electrical energy or electrical energy into electrochemical energy, detecting a cell parameter separately for each cell of the cell stack of the electrochemical cell unit with sensors, transmitting the cell parameters detected separately for the individual cells to a computing unit, determining a cell state as a temporary impairment of operation or as damage to one cell depending on the cell parameters recorded separately for each cell by means of the computing unit, with at least one operating parameter of the electrochemical cell unit in a change period, in particular deviating from the operating parameters necessary for operation, for the monitoring is changed to at least one monitoring operating parameter and the electrochemical cell unit is operated with the at least one monitoring parameter during the change period and before and/or during and/or after the change period the cell parameters for determining the damage are recorded separately for each cell of the cell stack of electrochemical cell unit is running with sensors.

In a further embodiment, before and/or during and/or after the change period, the cell parameter is detected separately for each cell of the cell stack of the electrochemical cell unit with sensors at different, chronologically consecutive points in time.

In a supplementary variant, the determination of the cell status of one cell each is carried out in the computing unit as a function of the cell parameters recorded separately for each cell by using the mathematical methods of statistics to determine the cell parameters of the cells, particularly those recorded during the change period, at a particular point in time and/or stochastics are evaluated.

In an additional embodiment, a statistical and/or stochastic value of the cell parameter is determined from the recorded cell parameters of the cells for a particular point in time.

A reference deviation from the statistical and/or stochastic value of the cell parameter is preferably determined or specified for each point in time, and if the cell parameter exceeds and/or falls below and/or deviates from the reference deviation, a cell status index is generated for each cell during each point in time for this one point in time for which one cell is assumed. The cell condition index is therefore an indication or an indicator of the temporary operational impairment and/or the deficiency and/or the damage as the cell condition of one cell in each case. For example, given the arithmetic mean as the statistical and/or stochastic value, the reference deviation is a range larger and smaller than the arithmetic mean. The reference deviation is thus at least a value and/or a range of the cell parameter.

In a further embodiment, the cell parameters and/or cell state indicators for at least 80%, 90% or 95% of the cells, in particular all cells, are recorded separately at each point in time.

In an additional variant, the at least one operating parameter is changed to the monitoring operating parameter as a positive and/or negative jump and/or as a Dirac pulse and/or as a periodic change, in particular a change corresponding to the sine function.

In an additional embodiment, the determination of the cell state is carried out on one cell at a time by dividing the number of cell state indicators of each cell at the different points in time by the total number of recorded points in time and, once a limit value of the result of this division has been exceeded, the cell state of the per cell is determined. The temporary impairment or damage for each cell is thus determined or recorded as the cell state from when a limit value of the result of this division is exceeded.

In a supplementary variant, the reference deviation and/or the limit value of the proportion index is changed using algorithms depending on the operating parameters and/or monitoring operating parameters and/or cell parameters and/or proportion indices and/or the operating time determined in the past. In these algorithms, for example, the aging of a cell is taken into account so that after many hours of operation, i. H. a long operating time, the reference deviation is increased, so that larger deviations in the cell parameters that occur due to aging do not or only slightly lead to a higher number of cells with damage or temporary impairments. In addition, the reference deviation and/or the limit of the share index are also a function of the operating parameter and monitor operating parameter, i. H. the larger the operating parameter is changed to the monitoring operating parameter, the larger are also the changes in cell parameters and this must be taken into account for an effective determination of cells with the cell state. Artificial intelligence methods can also be used here.

The statistical and/or stochastic value of the cell parameter is expediently the mean, in particular the arithmetic and/or geometric and/or harmonic mean, and/or which is the standard deviation of the cell parameters and/or at least one statistical moment of a higher order, for example the skewness, for each point in time.

In an additional configuration, the at least one operating parameter and/or monitoring operating parameter is the current conducted through the cell stack and/or the volume flow of the cathode gas conducted through the cell stack and/or the volume flow of the anode gas conducted through the cell stack and/or the concentration of the gas in the cell stack introduced fuel in the anode gas and/or the temperature of the coolant introduced into the cell stack and/or the volume flow of the coolant conducted through the cell stack and/or the volume flow of the electrolyte conducted through the cell stack at the anodes and/or the volume flow of the through the cell stack conducted electrolyte at the cathodes.

The cell parameter is preferably the voltage on each cell and/or the distribution of a magnetic field on each cell.

In a further variant, the control and/or regulation of the electrochemical cell unit is changed with the cell state as a function of the number of cells determined. For example, monitoring operating parameters can be determined in which a predetermined larger number of cells with a cell condition as temporary impairment and / or damage and / or deficiency and then these operating parameters are no longer used in normal operation, for example a very rapid and strong increase in current .

Electrochemical cell unit according to the invention for converting electrochemical energy into electrical energy as a fuel cell unit and/or for converting electrical energy into electrochemical energy as an electrolysis cell unit, comprising electrochemical cells arranged stacked and the electrochemical cells each comprising layered components arranged stacked, the components of the electrochemical cells preferably proton exchange membranes, anodes , Cathodes, preferably membrane electrode arrangements, preferably gas diffusion layers and bipolar plates are channels for the passage of process fluids, wherein a method described in this patent application can be carried out with the electrochemical cell unit.

In an additional variant, the electrochemical cell unit comprises at least one measuring device for detecting the cell parameter of the voltage separately for each cell, in particular for all cells of the cell stack, and/or Hall sensors on the cells for detecting the magnetic field and/or the distribution of the magnetic field separately for one cell each, in particular for all cells of the cell stack.

The operating parameters are preferably the voltage applied to the electrolytic cell unit and/or the current applied to the electrolytic cell unit and/or the pressure and/or volumetric flow of the cathode gas introduced into the fuel cell stack and/or the pressure and/or the volumetric flow of the anode gas introduced into the fuel cell stack and/or the pressure and/or the volume flow of the coolant introduced into the fuel cell stack.

In an additional embodiment, the statistical and/or stochastic value of the cell parameter for each point in time is the standard deviation. The standard deviation is a measure of the spread of the cell parameters at each point in time of the cells around the arithmetic mean of the cell parameters of the cells at each point in time. When using the standard deviation, the reference deviation can also be taken as the standard deviation and if a cell parameter is within the standard deviation for any given point in time, i.e. H. no deviation from the reference deviation as the standard deviation occurs, no cell state indices for that one point in time are assumed for this cell unit and if a cell parameter is outside the reference deviation as the standard deviation for one point in time, a cell state indices for that one point in time are assumed for that cell unit. Deviating from this, when using the standard deviation statistical and/or stochastic value, the procedure described above for determining the cell condition index can be changed with a determination of the reference deviation by first determining the standard deviation using the known method and then adding a positive and negative value to this standard deviation is added, whereby a positive value is added to the larger value of the standard deviation and a negative value is added to the smaller value of the standard deviation and this range, increased by the negative and positive value on both sides of the standard deviation, is specified as the reference deviation.

In a further variant, the cell parameters and/or the cell state indicators of the cells are determined at all points in time.

In a further variant, the determination of the cell status of one cell each is carried out as a function of the cell parameters recorded separately for each cell in the computing unit by determining the differences in the cell parameters of each cell before the change period on the one hand and during and/or after the change period on the other hand Change period are determined and these differences are evaluated quantitatively based on reference differences.

The reference differences are expediently determined as a function of the at least one operating parameter and the at least one monitoring operating parameter.

In an additional embodiment, after the change period, the change in the at least one operating parameter to the at least one change parameter is reversed again, essentially to the value before the change period. Substantially means with a deviation of less than 30%, 20% or 10%.

In a further variant, the duration of the change period is between 10 ms and 100 s (seconds), in particular between 100 ms and 10 s.

In an additional variant, a positive and/or negative jump in an operating parameter is a change in the operating parameter by at least 30%, 50%, 100%, 200%, 300% or 500%.

In an additional variant, the determination of the cell status of one cell each is carried out in the computing unit as a function of the cell parameters recorded separately for each cell by changing the cell parameters of the cells at one point in time during several change periods using the mathematical methods of statistics and/or stochastics be evaluated.

The method for determining the cell state is preferably carried out on one cell each with a plurality of change periods. For example, the cell state index is thus determined for each cell with a number of change periods.

In a supplementary embodiment, at least one operating parameter of the electrochemical cell unit is changed in a change period, deviating from the operating parameters necessary for the operation, only for the monitoring to at least one monitoring operating parameter. During the change period, the electrochemical cell unit is thus operated with at least one monitoring operating parameter, which is only carried out for the monitoring in this variable.

In a supplementary variant, the at least one operating parameter is changed by at least 100%, 300%, 500% or 700% to the at least one monitoring operating parameter as an increase, in particular as a maximum during the change period.

In a supplementary variant, the at least one monitoring operating parameter is changed to less than 90%, 70%, 50%, 30% or 10% of the value of the at least one operating parameter as a reduction, in particular as a minimum during the change period.

In a further variant, the method is carried out during operation of the electrochemical cell unit by changing at least one operating parameter on a monitoring parameter during the change period, or the method is carried out during maintenance of the electrochemical cell unit. The method for monitoring the electrochemical cell unit can thus be carried out both during operation of the electrochemical cell unit and during maintenance of the electrochemical cell unit.

In an additional embodiment, the time required for maintenance of the electrochemical cell unit is determined as a function of the detected number of cells with the specific cell condition.

In a further embodiment, an error message is output as a function of the detected number of cells with the specific cell status.

The invention also includes a computer program with program code means, which are stored on a computer-readable data carrier, in order to carry out a method described in this patent application, when the computer program is carried out on a computer or a corresponding computing unit.

The invention also includes a computer program product with program code means that are stored on a computer-readable data carrier in order to carry out a method described in this property right application when the computer program is carried out on a computer or a corresponding processing unit.

In an additional embodiment, the electrochemical cell unit is a fuel cell unit as a fuel cell stack for converting electrochemical energy into electrical energy and/or an electrolytic cell unit for converting electrical energy into electrochemical energy.

The bipolar plates are expediently designed as separator plates and an electrical insulation layer, in particular a proton exchange membrane, is arranged between each anode and each cathode, and preferably the electrolysis cells each include a third channel for the separate passage of a cooling fluid as the third process fluid.

In an additional variant, the electrolytic cell unit is additionally designed as a fuel cell unit, in particular a fuel cell unit described in this patent application, so that the electrolytic cell unit forms a reversible fuel cell unit.

In a further variant, the first substance is oxygen and the second substance is hydrogen.

In a further variant, the electrolytic cells of the electrolytic cell unit are fuel cells.

In a further variant, the electrochemical cell unit comprises a housing and/or a connection plate. The cell stack is enclosed by the housing and/or the connection plate.

Fuel cell system according to the invention, in particular for a motor vehicle, comprising a fuel cell unit as a fuel cell stack with fuel cells, a compressed gas store for storing gaseous fuel, a gas delivery device for delivering a gaseous oxidizing agent to the cathodes of the fuel cells, the fuel cell unit being a fuel cell unit described in this patent application and/or Electrolytic cell unit is formed.

Electrolysis system and/or fuel cell system according to the invention, comprising an electrolysis cell unit as an electrolysis cell stack with electrolysis cells, preferably a pressurized gas store for storing gaseous fuel, preferably a gas delivery device for delivering a gaseous oxidizing agent to the cathodes of the fuel cells, a storage container for liquid electrolyte, a pump for delivering the liquid Electrolytes, wherein the electrolytic cell unit is designed as an electrolytic cell unit and/or fuel cell unit described in this patent application.

In a further embodiment, the fuel cell unit described in this patent application also forms an electrolytic cell unit and preferably vice versa.

In a further variant, the electrochemical cell unit, in particular the fuel cell unit and/or the electrolytic cell unit, comprises at least one connecting device, in particular a plurality of connecting devices, and tensioning elements.

Components for electrochemical cells, in particular fuel cells and/or electrolytic cells, preferably insulation layers, in particular proton exchange membranes, preferably membrane electrode arrangements, anodes, cathodes, preferably gas diffusion layers and bipolar plates, in particular separator plates, are expedient.

In a further embodiment, the electrochemical cells, in particular fuel cells and/or electrolysis cells, each preferably comprise an insulating layer, in particular a proton exchange membrane, an anode, a cathode, preferably membrane electrode arrangements, preferably at least one gas diffusion layer and at least one bipolar plate, in particular at least one separator plate.

In a further embodiment, the connecting device is designed as a bolt and/or is rod-shaped and/or is designed as a tension belt.

The clamping elements are expediently designed as clamping plates.

In a further variant, the gas conveying device is designed as a blower and/or a compressor and/or a pressure vessel with oxidizing agent.

In particular, the electrochemical cell unit, in particular a fuel cell unit and/or an electrolytic cell unit, comprises at least 3, 4, 5 or 6 connecting devices.

In a further embodiment, the tensioning elements are plate-shaped and/or disk-shaped and/or flat and/or designed as a lattice.

Preferably the fuel is hydrogen, hydrogen rich gas, reformate gas or natural gas.

The fuel cells and/or electrolytic cells are expediently designed to be essentially flat and/or disc-shaped.

In a supplementary variant, the oxidizing agent is air with oxygen or pure oxygen.

Preferably, the fuel cell unit is a PEM fuel cell unit with PEM fuel cells, or a SOFC fuel cell unit with SOFC fuel cells, or an alkaline fuel cell (AFC).

character list

• 1 eine stark vereinfachte Explosionsdarstellung eines elektrochemischen Zellensystems als Brennstoffzellensystem und Elektrolysezellensystem mit Komponenten einer elektrochemischen Zelle als Brennstoffzelle und Elektrolysezelle,
• 2 eine perspektivische Ansicht eines Teils einer Brennstoffzelle und Elektrolysezelle,
• 3 einen Längsschnitt durch elektrochemische Zellen als Brennstoffzelle und Elektrolysezelle,
• 4 eine perspektivische Ansicht einer elektrochemischen Zelleneinheit als Brennstoffzelleneinheit und Elektrolysezelleneinheit als Brennstoffzellenstapel und Elektrolysezellenstapel,
• 5 eine Seitenansicht der elektrochemischen Zelleneinheit als Brennstoffzelleneinheit und Elektrolysezelleneinheit als Brennstoffzellenstapel und Elektrolysezellenstapel,
• 6 eine perspektivische Ansicht einer Bipolarplatte und
• 7 ein erstes oberes Diagramm mit dem Strom als einen Betriebs- und Veränderungsparameter der Brennstoffzelleneinheit aufgetragen an der Ordinate und der Zeit aufgetragen an der Abszisse und ein zweites unteres Diagramm mit der Spannung der Zellen aufgetragen an der Ordinate und der Zeit aufgetragen an der Abszisse und
• 8 ein Diagramm mit dem Volumenstrom des in die Brennstoffzelleneinheit eingeleiteten Oxidationsmittel aufgetragen an der Ordinate und der Zeit aufgetragen an der Abszisse in einem ersten Ausführungsbeispiel,
• 9 ein Diagramm mit dem Volumenstrom des in die Brennstoffzelleneinheit eingeleiteten Oxidationsmittel aufgetragen an der Ordinate und der Zeit aufgetragen an der Abszisse in einem zweiten Ausführungsbeispiel und
• 10 ein stark vereinfachtes Ablaufdiagramm eines Verfahrens zur Überwachung der elektrochemischen Zelleneinheit.

Exemplary embodiments of the invention are described in more detail below with reference to the attached drawings. It shows:

• 1 a greatly simplified exploded view of an electrochemical cell system as a fuel cell system and electrolysis cell system with components of an electrochemical cell as a fuel cell and electrolysis cell,
• 2 a perspective view of part of a fuel cell and electrolytic cell,
• 3 a longitudinal section through electrochemical cells as fuel cells and electrolytic cells,
• 4 a perspective view of an electrochemical cell unit as a fuel cell unit and electrolytic cell unit as a fuel cell stack and electrolytic cell stack,
• 5 a side view of the electrochemical cell unit as a fuel cell unit and electrolytic cell unit as a fuel cell stack and electrolytic cell stack,
• 6 a perspective view of a bipolar plate and
• 7 a first upper diagram with the current as an operating and changing parameter of the fuel cell unit plotted on the ordinate and time plotted on the abscissa and a second lower diagram with the voltage of the cells plotted on the ordinate and time plotted on the abscissa and
• 8th a diagram with the volume flow of the oxidizing agent introduced into the fuel cell unit plotted on the ordinate and the time plotted on the abscissa in a first exemplary embodiment,
• 9 a diagram with the volume flow of the oxidizing agent introduced into the fuel cell unit plotted on the ordinate and the time plotted on the abscissa in a second exemplary embodiment and
• 10 a highly simplified flow chart of a method for monitoring the electrochemical cell unit.

In the 1 until 3 the basic structure of a fuel cell 2 is shown as a PEM fuel cell 3 (polymer electrolyte fuel cell 3). The principle of fuel cells 2 is that electrical energy or electrical current is generated by means of an electrochemical reaction. Hydrogen H ₂ is passed as a gaseous fuel to an anode 7 and the anode 7 forms the negative pole. A gaseous oxidizing agent, namely air with oxygen, is fed to a cathode 8, ie the oxygen in the air provides the necessary gaseous oxidizing agent. A reduction (acceptance of electrons) takes place at the cathode 8 . The oxidation as electron release is carried out at the anode 7 .

• Kathode: O₂ + 4 H⁺ + 4 e^- --» 2 H₂O
• Anode: 2 H₂ --» 4 H⁺ + 4 e^-
• Summenreaktionsgleichung von Kathode und Anode: 2 H₂ + O₂ --» 2H₂O

The redox equations of the electrochemical processes are:

• Cathode: O ₂ + 4 H ⁺ + 4 e ^- --» 2 H ₂ O
• Anode: 2 H ₂ --» 4 H ⁺ + 4 e ^-
• Summation reaction equation of cathode and anode: _{2H2 +} O2 --» _2H2O

The difference between the normal potentials of the pairs of electrodes under standard conditions as a reversible fuel cell voltage or no-load voltage of the unloaded fuel cell 2 is 1.23 V. This theoretical voltage of 1.23 V is not reached in practice. In the idle state and with small currents, voltages of over 1.0 V can be reached and when operating with larger currents, voltages between 0.5 V and 1.0 V are reached. The series connection of several fuel cells 2, in particular a fuel cell unit 1 as a fuel cell stack 61 of several stacked fuel cells 2, has a higher voltage, which corresponds to the number of fuel cells 2 multiplied by the individual voltage of each fuel cell 2.

The fuel cell 2 also includes a proton exchange membrane 5 (proton exchange membrane, PEM), which is arranged between the anode 7 and the cathode 8 . The anode 7 and cathode 8 are layered and disk-shaped, respectively educated. The PEM 5 acts as an electrolyte, catalyst support and separator for the reaction gases. The PEM 5 also acts as an electrical insulator and prevents an electrical short circuit between the anode 7 and cathode 8. In general, 12 μm to 150 μm thick, proton-conducting foils made from perfluorinated and sulfonated polymers are used. The PEM 5 conducts the H ⁺ protons and essentially blocks ions other than H ⁺ protons, so that the charge transport can take place due to the permeability of the PEM 5 for the H ⁺ protons. The PEM 5 is essentially impermeable to the reaction gases oxygen O ₂ and hydrogen H ₂ , ie blocks the flow of oxygen O ₂ and hydrogen H ₂ between a gas space 31 at the anode 7 with fuel hydrogen H ₂ and the gas space 32 at the cathode 8 with air or oxygen O ₂ as the oxidizing agent. The proton conductivity of the PEM 5 increases with increasing temperature and increasing water content.

The electrodes 7 , 8 as the anode 7 and cathode 8 lie on the two sides of the PEM 5 , each facing towards the gas chambers 31 , 32 . A unit made up of the PEM 5 and the electrodes 7, 8 is referred to as a membrane electrode assembly 6 (membrane electrode assembly, MEA). The electrodes 7, 8 are pressed with the PEM 5. The electrodes 7, 8 are platinum-containing carbon particles bonded to PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene-propylene copolymer), PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride) and/or PVA (polyvinyl alcohol) and embedded in microporous carbon fiber, Glass fiber or plastic mats are hot-pressed. A catalyst layer 30 (not shown) is normally applied to each of the electrodes 7, 8 on the side facing the gas chambers 31, 32. The catalyst layer 30 on the gas space 31 with fuel on the anode 7 comprises nanodisperse platinum-ruthenium on graphitized soot particles bound to a binder. The catalyst layer 30 on the gas space 32 with oxidizing agent on the cathode 8 analogously comprises nanodispersed platinum. For example, Nation®, a PTFE emulsion or polyvinyl alcohol are used as binders.

Deviating from this, the electrodes 7, 8 are constructed from an ionomer, for example Nation®, platinum-containing carbon particles and additives. These electrodes 7, 8 with the ionomer are electrically conductive due to the carbon particles and also conduct the protons H ⁺ and also function as a catalyst layer 30 due to the platinum-containing carbon particles. Membrane electrode assemblies 6 with these electrodes 7, 8 comprising the ionomer form membrane electrode assemblies 6 as a CCM (catalyst coated membrane).

On the anode 7 and the cathode 8 there is a gas diffusion layer 9 (gas diffusion layer, GDL). The gas diffusion layer 9 on the anode 7 distributes the fuel from fuel channels 12 evenly onto the catalyst layer 30 on the anode 7. The gas diffusion layer 9 on the cathode 8 distributes the oxidant from oxidant channels 13 evenly onto the catalyst layer 30 on the cathode 8. The GDL 9 also withdraws reaction water in the reverse direction to the direction of flow of the reaction gases, i. H. in one direction each from the catalyst layer 30 to the channels 12, 13. Furthermore, the GDL 9 keeps the PEM 5 wet and conducts the current. The GDL 9 is constructed, for example, from hydrophobic carbon paper as the carrier and substrate layer and a bonded carbon powder layer as the microporous layer.

A bipolar plate 10 rests on the GDL 9 . The electrically conductive bipolar plate 10 serves as a current collector, for water drainage and for conducting the reaction gases as process fluids through the channel structures 29 and/or flow fields 29 and for dissipating the waste heat, which occurs in particular during the exothermic electrochemical reaction at the cathode 8. In order to dissipate the waste heat, channels 14 are incorporated into the bipolar plate 10 as a channel structure 29 for conducting a liquid or gaseous coolant as the process fluid. The channel structure 29 in the gas space 31 for fuel is formed by channels 12 . The channel structure 29 in the gas space 32 for the oxidizing agent is formed by channels 13 . Metal, conductive plastics and composite materials and/or graphite, for example, are used as the material for the bipolar plates 10 .

In a fuel cell unit 1, several fuel cells 2 are stacked in alignment to form a fuel cell stack 61 ( 4 and 5 ). The fuel cell stack 61 is enclosed by a housing (not shown) and a connection plate. In 1 is an exploded view of two aligned stacked fuel cells 2 shown. Seals 11 seal the gas chambers 31, 32 or channels 12, 13 in a fluid-tight manner. In a compressed gas accumulator 21 ( 1 ) hydrogen H ₂ is stored as a fuel at a pressure of, for example, 350 bar to 700 bar. From the compressed gas reservoir 21, the fuel is passed through a high-pressure line 18 to a pressure reducer 20 to reduce the pressure of the fuel in a medium-pressure line 17 from approximately 10 bar to 20 bar. The fuel is routed to an injector 19 from the medium-pressure line 17 . At the injector 19, the pressure of the fuel is reduced to an injection pressure of between 1 bar and 3 bar. From the injector 19, the fuel is supplied to a supply line 16 for fuel ( 1 ) fed and from the supply line 16 to the channels 12 for fuel, which form the channel structure 29 for fuel. As a result, the fuel flows through the gas space 31 for the fuel. The gas space 31 for the fuel is formed by the channels 12 and the GDL 9 on the anode 7 . After flowing through the channels 12 , the fuel not consumed in the redox reaction at the anode 7 and any water from controlled humidification of the anode 7 are discharged from the fuel cells 2 through a discharge line 15 .

A gas conveying device 22, embodied for example as a fan 23 or a compressor 24, conveys air from the environment as oxidizing agent into a supply line 25 for oxidizing agent. The air is supplied from the supply line 25 to the channels 13 for oxidizing agent, which form a channel structure 29 on the bipolar plates 10 for oxidizing agent, so that the oxidizing agent flows through the gas space 32 for the oxidizing agent. The gas space 32 for the oxidizing agent is formed by the channels 13 and the GDL 9 on the cathode 8 . After the oxidizing agent 32 has flowed through the channels 13 or the gas space 32, the oxidizing agent not consumed at the cathode 8 and the water of reaction formed at the cathode 8 due to the electrochemical redox reaction are discharged from the fuel cells 2 through a discharge line 26. A supply line 27 is used to supply coolant into the channels 14 for coolant and a discharge line 28 is used to discharge the coolant conducted through the channels 14 . The supply and discharge lines 15, 16, 25, 26, 27, 28 are in 1 shown as separate lines for reasons of simplification. At the end area in the vicinity of the channels 12, 13, 14 are in the stack as a cell stack 61 of the fuel cell unit 1 aligned fluid openings 41 on sealing plates 39 as an extension at the end area 40 of the bipolar plates 10 ( 6 ) and membrane electrode assemblies 6 (not shown) are formed. The fuel cells 2 and the components 5, 6, 7, 8, 9, 10, 30, 51 of the fuel cells 2 are disk-shaped and span imaginary planes 59 aligned essentially parallel to one another. The aligned fluid openings 41 and seals (not shown) in a direction perpendicular to the notional planes 59 between the fluid openings 41 thus form an oxidant supply duct 42, an oxidant discharge duct 43, a fuel supply duct 44, a fuel discharge duct 45, a Supply channel 46 for coolant and a discharge channel 47 for coolant. The supply and discharge lines 15, 16, 25, 26, 27, 28 outside of the cell stack 61 of the fuel cell unit 1 are designed as process fluid lines. The supply and discharge lines 15, 16, 25, 26, 27, 28 outside the cell stack 61 of the fuel cell unit 1 open into the supply and discharge channels 42, 43, 44, 45, 46, 47 within the stack of the fuel cell unit 1. The fuel cell stack 1 together with the compressed gas reservoir 21 and the gas delivery device 22 forms a fuel cell system 4.

The fuel cells 2 are arranged as clamping plates 34 between two clamping elements 33 in the fuel cell unit 1 . A first clamping plate 35 lies on the first fuel cell 2 and a second clamping plate 36 lies on the last fuel cell 2 . The fuel cell unit 1 comprises approximately 200 to 400 fuel cells 2, not all of which are shown in 4 and 5 are shown. The clamping elements 33 apply a compressive force to the fuel cells 2, ie the first clamping plate 35 rests on the first fuel cell 2 with a compressive force and the second clamping plate 36 rests on the last fuel cell 2 with a compressive force. The fuel cell stack 61 is thus braced as a fuel cell stack 61 in order to ensure the tightness of the fuel, the oxidizing agent and the coolant, in particular due to the elastic seals 11, and also to keep the electrical contact resistance within the fuel cell stack 61 as a cell stack 61 as small as possible. To brace the fuel cells 2 with the tensioning elements 33, four connecting devices 37 are designed as bolts 38 on the fuel cell unit 1, which are subjected to tensile stress. The four bolts 38 are connected to the chipboards 34 .

In 6 the bipolar plate 10 of the fuel cell 2 is shown. The bipolar plate 10 includes the channels 12, 13 and 14 as three separate channel structures 29. The channels 12, 13 and 14 are in 6 not shown separately but only in simplified form as a layer of a channel structure 29. The fluid openings 41 on the sealing plates 39 of the bipolar plates 10 ( 6 ) and membrane electrode assemblies 6 are arranged stacked in alignment within the fuel cell unit 1, so that feed and discharge channels 42, 43, 44, 45, 46, 47 are formed. Seals (not shown) are arranged between the sealing plates 39 for fluid-tight sealing of the supply and discharge channels 42, 43, 44, 45, 46, 47 formed by the fluid openings 41.

Since the bipolar plate 10 also separates the gas chamber 31 for fuel from the gas chamber 32 for oxidizing agent in a fluid-tight manner and also seals the channel 14 for coolant in a fluid-tight manner, the term separator plate 51 for the fluid-tight separation or separation of process fluids can also be selected for the bipolar plate 10 . Thus, under the term bipolar plate 10 also subsumed under the term separator plate 51 and vice versa. The channels 12 for fuel, the channels 13 for oxidizing agent and the channels 14 for coolant of the fuel cell 2 are also formed on the electrochemical cell 52 as an electrolytic cell 50, but with a different function.

The fuel cell unit 1 can also be used and operated as an electrolytic cell unit 49, ie forms a reversible fuel cell unit 1. A number of features that allow the fuel cell unit 1 to be operated as an electrolytic cell unit 49 are described below. A liquid electrolyte, namely highly diluted sulfuric acid with a concentration of approximately c(H ₂ SO ₄ ) = 1 mol/l, is used for the electrolysis. A sufficient concentration of oxonium ions H ₃ 0 ⁺ in the liquid electrolyte is necessary for the electrolysis.

• Kathode: 4 H₃O⁺ + 4 e^- → 2 H₂ + 4 H₂O
• Anode: 6 H₂O → O₂ + 4 H₃O⁺ + 4 e^-
• Summenreaktionsgleichung von Kathode und Anode: 2 H₂O → 2 H₂ + O₂

The following redox reactions take place during electrolysis:

• Cathode: 4H3O ⁺ + 4e ^- → _{2H2 + 4H2O}
• Anode: 6 H ₂ O → O ₂ + 4 H ₃ O ⁺ + 4 e ^-
• Summation reaction equation of cathode and anode: 2H2O → _{2H2 + O2}

The polarity of the electrodes 7, 8 with electrolysis when operating as an electrolytic cell unit 49 is reversed (not shown) as when operating as a fuel cell unit 1, so that in the channels 12 for fuel, through which the liquid electrolyte is conducted, at the cathodes Hydrogen H ₂ is formed as a second substance and the hydrogen H ₂ is taken up by the liquid electrolyte and transported in dissolved form. Analogously, the liquid electrolyte is conducted through the channels 13 for oxidizing agent and oxygen O ₂ is formed as the first substance at the anodes in or at channels 13 for oxidizing agent. The fuel cells 2 of the fuel cell unit 1 function as electrolytic cells 50 during operation as an electrolytic cell unit 49. The fuel cells 2 and electrolytic cells 50 thus form electrochemical cells 52. The oxygen O ₂ formed is absorbed by the liquid electrolyte and transported in dissolved form. The liquid electrolyte is stored in a storage tank 54 . In 1 For reasons of simplification in the drawing, two storage tanks 54 of the fuel cell system 4 are shown, which also functions as an electrolytic cell system 48 . The 3-way valve 55 on the fuel supply line 16 is switched over during operation as an electrolytic cell unit 49, so that the liquid electrolyte is introduced into the fuel supply line 16 from the storage tank 54 with a pump 56 and not fuel from the compressed gas storage tank 21 . A 3-way valve 55 on the supply line 25 for oxidant is switched over during operation as an electrolytic cell unit 49, so that the liquid electrolyte with the pump 56 from the storage tank 54 is fed into the supply line 25 for oxidant rather than oxidant as air from the gas delivery device 22 is initiated. The fuel cell unit 1, which also functions as an electrolytic cell unit 49, has optional modifications to the electrodes 7, 8 and the gas diffusion layer 9 compared to a fuel cell unit 1 that can only be operated as a fuel cell unit 1: for example, the gas diffusion layer 9 is not absorbent, so that the liquid electrolyte easily drains completely or the gas diffusion layer 9 is not formed or the gas diffusion layer 9 is a structure on the bipolar plate 10. The electrolytic cell unit 49 with the storage tank 54, the pump 56 and the separators 57, 58 and preferably the 3-way valve 55 forms a electrochemical cell system 60.

A separator 57 for hydrogen is arranged on the discharge line 15 for fuel. The separator 57 separates the hydrogen from the electrolyte with hydrogen and the separated hydrogen is introduced into the compressed gas reservoir 21 with a compressor (not shown). The electrolyte discharged from the hydrogen separator 57 is then returned to the electrolyte storage tank 54 through a pipe. A separator 58 for oxygen is arranged on the discharge line 26 for fuel. The separator 58 separates the oxygen from the electrolyte with oxygen, and the separated oxygen is introduced with a compressor (not shown) into a compressed gas reservoir (not shown) for oxygen. The oxygen in the compressed gas reservoir for oxygen, not shown, can optionally be used to operate the fuel cell unit 1 by using a line, not shown, to slide the oxygen into the supply line 25 for oxidizing agent when operating as a fuel cell unit 1. The electrolyte derived from the separator 58 for oxygen is then fed back to the storage tank 54 for the electrolyte with a line. The channels 12, 13 and the discharge and supply lines 15, 16, 25, 26 are designed in such a way that after use as an electrolytic cell unit 49 and the pump 56 has been switched off, the liquid electrolyte runs back completely into the storage container 54 due to gravity. Optional is after use as electrolytic cell unit 49 and before use as fuel cells An inert gas is passed through the unit 1 through the channels 12, 13 and the discharge and supply lines 15, 16, 25, 26 for the complete removal of the liquid electrolyte before the passage of gaseous fuel and oxidant. The fuel cells 2 and the electrolytic cells 2 thus form electrochemical cells 52. The fuel cell unit 1 and the electrolytic cell unit 49 thus form an electrochemical cell unit 53. The channels 12 for fuel and the channels for oxidizing agent thus form channels 12, 13 for the passage of the liquid electrolyte during operation as an electrolytic cell unit 49 and this applies analogously to the supply and discharge lines 15, 16, 25, 26. An electrolytic cell unit 49 does not normally require any channels 14 for the passage of coolant for process-related reasons. In an electrochemical cell unit 49, the channels 12 for fuel also form channels 12 for passing fuel and/or electrolyte and the channels 13 for oxidant also form channels 13 for passing fuel and/or electrolyte.

In a further exemplary embodiment, which is not shown, the fuel cell unit 1 is designed as an alkaline fuel cell unit 1 . Potassium hydroxide solution is used as a mobile electrolyte. The fuel cells 2 are stacked. A monopolar cell structure or a bipolar cell structure can be formed. The potassium hydroxide solution circulates between an anode and cathode and transports reaction water, heat and impurities (carbonates, dissolved gases) away. The fuel cell unit 1 can also be used as a reversible fuel cell unit 1, i. H. as an electrolytic cell unit 49.

The operation, control, regulation and monitoring of the electrolytic cell unit 49, namely the fuel cell unit 1 described above, is carried out with a computing unit 62, ie a control and/or regulation unit 63. Each bipolar plate 10 is electrically conductively connected to a power line 65 and the power lines 65 of the cell stack 61 as the fuel cell stack 61 are connected to a measuring device 66 for separately detecting the voltages on the fuel cells 2 for each fuel cell 2 . The measuring device 66 and the power lines 65 thus form a sensor 64 for detecting a cell parameter of the fuel cells 2, namely the voltage of the fuel cells 2. A separate measuring device 66 can be provided for each fuel cell 2 ( 3 ) and the cell parameters detected by this measuring device 66 are then transmitted as data to the computing unit 62, for example by means of a bus system. Deviating from this (not shown), the fuel cell unit 1 has a central measuring device 66 for all fuel cells 2 and the power lines 65 are routed to this central measuring device 66 . In addition, a Hall sensor 67 can also be present on each of the fuel cells 2 as a sensor 64 for quantitatively detecting the magnetic field and/or the distribution of the magnetic field on the fuel cells 2 as a further cell parameter of the fuel cells 2.

During normal operation of the fuel cell unit 1 for converting the electrochemical energy of the hydrogen fuel into electrical energy, the fuel cell unit 1 is operated with specific and variable operating parameters 68. These operating parameters are, for example, the current conducted through the fuel cell stack 61, the volume flow of the anode gas, H. of the fuel hydrogen, which is introduced into the fuel cell unit 1, the volume flow of the cathode gas, d. H. of the oxidant air introduced into the fuel cell unit 1 and the temperature and volume flow of the coolant introduced into the fuel cell unit 1 .

To monitor the fuel cell unit 1 as the electrochemical cell unit 53, a change, i. H. an increase and/or a reduction of at least one operating parameter or several operating parameters to a monitoring parameter or several monitoring parameters. After the change period 74 has ended, the fuel cell unit 1 is operated again with the normal operating parameters required for operation.

in the in 7 The diagram shown above shows the time t on the abscissa and the current I, which is conducted through the fuel cell unit 1, on the ordinate. The beginning of the change period 74 is the time t ₁ and the end of the change period 74 is the time t ₂ . From time t ₁ , the current jumps negatively as a very rapid reduction in current I, and shortly before time t ₂ , ie still during the change period 74, the current jumps positively as a very rapid increase in current I back to the original value of the current I as the operating parameter for the normal operation of the fuel cell unit 1.

In 8th the time t is plotted on the abscissa and the volume flow Q of the oxidizing agent air as the cathode gas, which is introduced into the fuel cell unit 1, is plotted on the ordinate. During the change period 74 a positive jump in the volume flow Q is first carried out as a very rapid increase in the volume flow Q and immediately afterwards a negative jump in the volume flow Q is carried out as a very rapid reduction in the volume flow Q. Overall, therefore, lies in 8th as the change in the volume flow Q of the oxidant air as the cathode gas during the short change period 74 as a sawtooth.

9 differs from 8th in that during the variation period 74 a periodic variation according to the sine function of the volume flow Q of the oxidant air as the cathode gas is carried out.

During an initial phase of the change period 74, the cell parameters of all fuel cells 2 are detected 70 at different, consecutive points in time t _x . The cell parameters are recorded as the voltages separately for each fuel cell 2 with the measuring device 66 and this is carried out for all of the different, chronologically consecutive points in time t _x . The data from these cell parameters as the voltages are then transmitted to the arithmetic unit 62 and the arithmetic mean value is determined 71 for each point in time t _x as a statistical value of the cell parameter of the voltage. In a fictitious fuel cell unit 1 with 3 fuel cells 2, in which the voltages 0.9 V, 1.0 V and 0.6 V were determined at a point in time t _x , the arithmetic mean value of the cell parameter of the voltage at this point in time is t _x about 0.83 V.In 7 Deviating from this exemplary embodiment, the course of the voltages in some fuel cells 2 is shown during the change period 74 . In 7 below, the voltage U is plotted on the ordinate and the time t is plotted on the abscissa, the voltage U being plotted as two lines for two fuel cells 2 as a function of the time t.

A comparison 72 of the cell parameters as a voltage of the fuel cells 2 with a reference deviation is then carried out. The reference deviation is determined by increasing the arithmetic mean for the time t _x by a positive value of 0.2 V and decreasing it by a negative value of -0.2 V and the range in between is the reference deviation. If there is a deviation in a cell parameter for each fuel cell 2 from the reference deviation during a point in time t _x , a cell state index is assumed. The reference deviation is a range of voltage from +/- 0.2 V to the arithmetic mean of 0.83 V, i.e. a range of voltage between 0.63 V and 1.03 V. The first fuel cell 2 with the voltage of 0 .9 V is thus within the reference deviation, and the first fuel cell 2 is thus not assigned a cell condition index as the temporary deterioration or damage. The second fuel cell 2 has a voltage of 1.0 V and this is also within the reference deviation, so that no cell state index is assigned to the second fuel cell 2 either. At time t _x , the third fuel cell 2 has a voltage of 0.6 V and this is outside the reference deviation, so that a cell state index is assigned to the third fuel cell 2 for this time t _x . This process is carried out for all points in time t _x , so that for each point in time t _x it has been determined for all fuel cells 2 whether or not a cell condition index has been assigned to each fuel cell 2 in accordance with the procedure described above. For example, the method is executed during the change period 74 with 3, 15 or 20 points in time t _x . The number of determinations for the fuel cells 2 as to whether or not a cell condition index is present thus corresponds to the result of the multiplication of the number of fuel cells 2 of the fuel cell unit 1 by the number of times t _x .

The determination 73 of the cell state of the fuel cells 2 is then carried out by dividing the number of cell state indicators of each fuel cell 2 during the change period 74 by the total number of recorded times t _x and, once a limit value has been exceeded, the result of this division as a proportion indicator Cell state of each fuel cell 2 is determined. The cell state is a property of a fuel cell 2 that is negative for the operation, in the form of damage or a temporary operational impairment. If the total number of points in time t _x is 10 and the limit value is 9%, the cell state of a fuel cell 2 is assigned to and determined from just one cell state index at only one point in time t _x of a fuel cell 2 . If the total number of points in time t _x is 10 and the limit value is 29%, the cell state is assigned to and determined from a cell state index of at least three points in time t _x for each fuel cell 2 of this fuel cell 2 . If the total number of times t _x is 3 and the limit value is 30%, the cell state of a fuel cell 2 is assigned to and determined from just one cell state index at just one point in time t _x of this fuel cell 2 because 33% is greater than 30%.

The method described above can also be combined in such a way that the cell condition indicators and/or the determined cell condition of fuel cells 2 become different Change periods 74 is determined with different monitoring operating parameters. For example, a fuel cell 2 is only assigned a cell state if a cell state results for this fuel cell 2 for the separate determination of the two different change periods 74 with the different monitoring operating parameters. In addition, two or more of the operating parameters can also be changed to the monitoring operating parameters during the change period 74 .

If the voltage of the fuel cells 2 is used as a cell parameter and the fuel cell unit 1 and the fuel cell system 4 have a CVM device (CVM: cell voltage monitoring) and the changing 69 of operating parameters to monitoring parameters by means of the computing unit 62 as the control and/or control unit 63, it is possible for the method according to the invention to be carried out by means of a software-based improvement on an electrochemical cell unit 53.

Overall, the method according to the invention for monitoring the electrochemical cell unit 53 and the electrochemical cell unit 53 according to the invention have significant advantages. Temporary impairments, damage and defects as the cell condition of the fuel cell 2 can only be detected early with difficulty during normal operation of the fuel cell unit 1 with the necessary operating parameters, because the individual fuel cells 2 only have minor changes in the cell parameters that are difficult to detect. For this reason, during the change period 74, a significant and large change in at least one operating parameter to the at least one monitoring parameter is carried out, so that there are also larger, easily detectable changes in the cell parameters on the fuel cells 2 and thus even small and low cell levels as damage, temporary impairments and defects in fuel cells 2 can be determined. In this way, a cell state of a fuel cell 2 can advantageously be detected at an early stage and then measures for controlling and/or regulating the electrochemical cell unit 53 can be initiated automatically in order to keep further deterioration of the cell state of fuel cells 2 as low as possible. If, for example, the cell parameters recorded in the past show that problems and damage will occur for certain extreme monitoring operating parameters for individual fuel cells 2 when controlling and/or regulating the electrochemical cell unit 53, attempts are made to avoid certain extreme operating parameters as far as possible in normal operation as well. As a result, the service life of an electrochemical cell unit 53, i. H. the fuel cell unit 1 and the electrolytic cell unit 49, are extended.

Claims (15)

Method for monitoring an electrochemical cell unit (1, 49, 53) for converting electrochemical energy into electrical energy as a fuel cell unit (1) and/or for converting electrical energy into electrochemical energy as an electrolytic cell unit (49) with stacked electrochemical cells (2, 50, 52 ) as a cell stack (61) with the steps: - operating the electrochemical cell unit (1, 49, 53) with the operating parameters necessary for operation, so that electrochemical energy is converted into electrical energy or electrical energy into electrochemical energy, - detecting a cell parameter separately for one electrochemical cell (2, 50, 52) of the cell stack (61) of the electrochemical cell unit (1, 49, 53) with sensors (64), - transmitting the separately recorded for the individual electrochemical cells (2, 50, 52). cell parameters to a computing unit (62, 63), - determination of a cell state as a temporary operational impairment or as damage to one cell (2, 50, 52) depending on the cell parameters recorded separately for each cell (2, 50, 52) by the computing unit (62, 63), characterized in that at least one operating parameter of the electrochemical cell unit (1, 49, 53) in a change period, in particular deviating from the operating parameters necessary for operation, for which monitoring is changed to at least one monitoring operating parameter and the electrochemical cell unit (1, 49, 53) during the change period (74). the at least one monitoring parameter is operated and before and/or during and/or after the change period (74) the detection of the cell parameters for determining the cell state separately for each one electrochemical cell (2, 50, 52) of the cell stack (61) of electrochemical cell unit (1, 49, 53) with sensors (64). procedure after claim 1 , characterized in that before and/or during and/or after the change period (74) the cell parameter is detected separately for each one electrochemical cell (2, 50, 52) of the cell stack (61) of the electrochemical cell unit (1, 49, 53) with sensors (64) on various consecutive points in time (t _x ) is executed. procedure after claim 2 , characterized in that the determination of the cell state of each electrochemical cell (2, 50, 52) as a function of the cell parameters recorded separately for each electrochemical cell (2, 50, 52) is carried out in the computing unit (62, 63). in that the cell parameters of the electrochemical cells (2, 50, 52) recorded in particular during the change period (74) are evaluated at a point in time (t _x ) using the mathematical methods of statistics and/or stochastics. procedure after claim 3 , characterized in that from the detected cell parameters of the electrochemical cells (2, 50, 52) a statistical and / or stochastic value of the cell parameter for a time (t _x ) is determined. procedure after claim 4 , characterized in that a reference deviation from the statistical and/or stochastic value of the cell parameter is determined or specified for a point in time (t _x ) and when the cell parameter is exceeded and/or undershot and/or a deviation is generated for each cell (2nd , 50, 52) during each point in time (t _x ) from the reference deviation, a cell state index for each point in time (t _x ) for which one cell (2, 50, 52) each is assumed. Method according to one or more of the preceding claims, characterized in that the cell parameters and/or cell condition indicators for at least 80%, 90% or 95% of the electrochemical cells (2, 50, 52), in particular all cells (2, 50, 52) , the cell stack (61) are recorded separately at each point in time. Method according to one or more of the preceding claims, characterized in that the change in the at least one operating parameter to the monitoring operating parameter as a positive and / or negative jump and / or as a Dirac pulse and / or as a periodic change, in particular change according to the sine function, is executed. Method according to one or more of the Claims 5 until 7 , characterized in that the cell state is determined for one cell (2, 50, 52) each by dividing the number of cell state indicators of each cell (2, 50, 52) at the different points in time (t _x ) by the total number of detected points in time (t _x ) is divided and when a limit value of the result of this division is exceeded, the cell state of each cell (2, 50, 52) is determined as a proportion index. Method according to one or more of the Claims 5 until 8th , characterized in that the reference deviation and/or the limit value for the proportion index is changed by means of algorithms depending on the operating parameters and/or monitoring operating parameters and/or cell parameters and/or proportion indices and/or operating time determined in the past. Method according to one or more of the Claims 4 until 9 , characterized in that the statistical and/or stochastic value of the cell parameter is the mean, in particular the arithmetic and/or geometric and/or harmonic mean, and/or the standard deviation of the cell parameters and/or at least one statistical moment of a higher order, for example the skewness , for which is a point in time (t _x ). Method according to one or more of the preceding claims, characterized in that the at least one operating parameter and/or monitoring operating parameter is the flow conducted through the cell stack (61) and/or the volume flow of the cathode gas conducted through the cell stack (61) and/or the volume flow of the anode gas conducted through the cell stack (61) and/or the concentration of the fuel introduced into the cell stack (61) in the anode gas and/or the temperature of the coolant introduced into the cell stack (61) and/or the volume flow of the through the cell stack (61 ) coolant conducted and/or the volume flow of the electrolyte conducted through the cell stack (61) to the anodes (7) and/or the volume flow of the electrolyte conducted to the cathodes through the cell stack (61). Method according to one or more of the preceding claims, characterized in that the cell parameter is the voltage on each cell (2, 50, 52) and/or the distribution of a magnetic field on each cell (2, 50, 52). Method according to one or more of the preceding claims, characterized in that the control and/or regulation of the electrochemical cell unit (1, 49, 53) is changed with the cell state depending on the number of specific cells (2, 50, 52). Electrochemical cell unit (1, 49, 53) for converting electrochemical energy into electrical energy as a fuel cell unit (1) and/or for converting electrical energy into electrochemical energy as an electrolysis cell unit (49), comprising - stacked electrochemical cells (2, 50, 52) and the electrochemical cells (52) each comprise stacked layered components (5, 6, 7, 8, 9, 10, 30, 51), - the components (5, 6, 7, 8, 9, 10, 30, 51 ) of the electrochemical cells (2, 50, 52) are preferably proton exchange membranes (5), anodes (7), cathodes (8), preferably membrane electrode arrangements (6), preferably gas diffusion layers (9) and bipolar plates (10), - channels (12, 13, 14) for conducting process fluids, characterized in that a method according to one or more of the preceding claims can be carried out with the electrochemical cell unit (1, 49, 53). Electrochemical cell unit according to Claim 14 , characterized in that the electrochemical cell unit (1, 49, 53) has at least one measuring device (65, 66) for detecting the cell parameter of the voltage separately for each cell (2, 50, 52), in particular for all cells (2, 50 , 52) of the cell stack (61), and/or Hall sensors (67) on the cells (2, 50, 52) for detecting the magnetic field and/or the distribution of the magnetic field separately for each cell (2, 50, 52), in particular for all cells (2, 50, 52) of the cell stack (61).

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