JP5428496B2 - Determination of catalyst poisoning status of fuel cell system - Google Patents

Description

  The present invention relates to determination of a catalyst poisoning state in a fuel cell system.

  In a fuel cell system, a technology for determining a catalyst deterioration state by comparing a detected voltage drop amount with a deterioration judgment reference value (electromotive voltage drop amount) stored in a memory in advance, a measurement voltage of a single cell stack, A technique for estimating the flooding state, dry-up state, and catalyst poisoning state of a fuel cell based on the measured temperature and the inclination of the measured temperature with respect to time is known.

JP 2008-311080 A JP 2004-241201 A JP 2005-85662 A JP-A-1-122570 JP 2007-103115 A

  The prior art described above has room for improvement in terms of accuracy in determining the catalyst poisoning state in the fuel cell system.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the determination accuracy of the catalyst poisoning state in the fuel cell system.

In order to solve at least a part of the above problems, the present invention can be realized as the following forms or application examples. For example, the present invention is a method for determining a catalyst poisoning state of a fuel cell system, and (a) prediction of a low load voltage that is a voltage of the fuel cell system in a load region lower than a preset load threshold. Obtaining a value; and (b) reducing the voltage of the fuel cell system to a value smaller than a voltage threshold preset as a voltage value at which the oxide film adhering to the cathode electrode catalyst surface is removed, A step of actually measuring the low load voltage of the fuel cell system; and (c) determining a catalyst poisoning state of the fuel cell system based on a comparison result between the predicted value of the low load voltage and the actually measured value. It is possible to implement | achieve as a method provided with these. In addition, the present invention can be realized as the following forms or application examples.

Application Example 1 A method for determining a catalyst poisoning state of a fuel cell system,
(A) obtaining a predicted value of a low load voltage that is a voltage of the fuel cell system in a load region lower than a preset load threshold;
(B) measuring the low load voltage of the fuel cell system after reducing the voltage of the fuel cell system to a value smaller than a preset voltage threshold;
(C) determining a catalyst poisoning state of the fuel cell system based on a comparison result between the predicted value of the low load voltage and the measured value.

  In this method, a predicted value of the low load voltage of the fuel cell system is acquired, and after the voltage of the fuel cell system is reduced to a value smaller than a preset voltage threshold, the low load voltage is measured and the predicted low load voltage is estimated. The catalyst poisoning state of the fuel cell system is determined based on the comparison result between the value and the actual measurement value. The process of reducing the voltage of the fuel cell system to a value smaller than a preset voltage threshold value removes the oxide film adhering to the catalyst surface, thereby suppressing the influence of the oxide film on the actually measured value of the low load voltage. . Therefore, according to this method, the determination accuracy of the catalyst poisoning state in the fuel cell system can be improved.

Application Example 2 An apparatus for determining a catalyst poisoning state of a fuel cell system,
A predicted value acquisition unit that acquires a predicted value of a low load voltage, which is a voltage of the fuel cell system in a low load region lower than a preset load threshold;
An actual value acquisition unit for acquiring an actual value of the low load voltage of the fuel cell system after reducing the voltage of the fuel cell system to a value smaller than a preset voltage threshold;
And a determination unit that determines a catalyst poisoning state of the fuel cell system based on a comparison result between the predicted value of the low load voltage and the actual measurement value.

  Note that the present invention can be realized in various modes. For example, a fuel cell system, a catalyst poisoning state determination method for a fuel cell system, a catalyst poisoning state determination device for a fuel cell system, a fuel cell vehicle, and the like It is realizable with the aspect of.

It is explanatory drawing which shows schematically the structure of the fuel cell vehicle 10 in the Example of this invention. It is a flowchart which shows the flow of operation control of a fuel cell system. It is explanatory drawing which shows the prediction curve of a low load voltage. It is explanatory drawing which shows the method of a catalyst washing process.

  Next, embodiments of the present invention will be described based on examples.

A. Example:
FIG. 1 is an explanatory diagram schematically showing the configuration of a fuel cell vehicle 10 in an embodiment of the present invention. The fuel cell vehicle 10 includes a fuel cell system 100 and a control unit 200. The control unit 200 is configured by a computer having a CPU, a RAM, a ROM, and the like, and controls the entire fuel cell vehicle 10 including the fuel cell system 100.

  The fuel cell system 100 is a system that generates power using an electrochemical reaction between hydrogen and oxygen. The fuel cell system 100 includes a fuel cell (not shown). The fuel cell of this example is a polymer electrolyte fuel cell that is relatively small and excellent in power generation efficiency.

  The fuel cell has a stack structure in which a plurality of MEAs (Membrane Electrode Assemblies (membrane / electrode assemblies)) are sandwiched between separators. The MEA has an electrolyte membrane, an anode electrode disposed on one surface of the electrolyte membrane, and a cathode electrode disposed on the other surface of the electrolyte membrane. The electrolyte membrane has good proton conductivity in a wet state. The anode electrode is a reaction field where the anode-side electrode reaction proceeds, and contains a catalyst (for example, platinum) that promotes the electrode reaction in the vicinity of the contact surface with the electrolyte membrane. The cathode electrode is a reaction field where the cathode side electrode reaction proceeds, and contains a catalyst in the vicinity of the contact surface with the electrolyte membrane, similarly to the anode electrode. A fuel gas containing hydrogen gas is supplied to the anode electrode of the fuel cell via a fuel gas supply manifold, and air is supplied to the cathode electrode via an oxidizing gas supply manifold. The supplied fuel gas and air are used for power generation by an electrochemical reaction in the MEA.

  Under the control of the control unit 200, the electric power generated by the fuel cell system 100 is output to an inverter (not shown) and used to drive the travel motor of the fuel cell vehicle 10. Further, for example, when the amount of power generation is larger than the power necessary for running the fuel cell vehicle 10, the surplus power is stored in the secondary battery via the DC / DC converter and used when power is insufficient such as during rapid acceleration. Is done.

  FIG. 2 is a flowchart showing a flow of operation control of the fuel cell system. In the operation control of the fuel cell system 100 in the present embodiment, as described in detail below, determination of the poisoning state of the electrode catalyst (determination of whether or not the electrode catalyst is poisoned) is performed. Electrocatalyst poisoning is due to the influence of outside air, fuel, materials that enter the cell together with battery constituent materials during operation, elution from battery constituent materials, decomposition products of battery constituent materials, etc. This is a phenomenon in which the power generation reaction is hindered and the power generation performance decreases. Since catalyst poisoning does not occur regularly and is difficult to predict, in this embodiment, the poisoning state of the electrode catalyst is determined, and the electrode catalyst is considered to be poisoned. The electrode catalyst cleaning process is executed.

  In the fuel cell vehicle 10, the normal operation of the fuel cell system 100 is performed under the control of the control unit 200 (step S110 in FIG. 2). Measurement of the low load voltage of the fuel cell system 100 is performed regularly or at any time, and the measured value of the low load voltage is acquired by the control unit 200 (step S120). The low load voltage is a cell voltage in a low load region where the load is equal to or less than a predetermined threshold (for example, 0.2 A / cm 2), and is an index value indicating the surface area of the cathode electrode catalyst (correlated with the surface area of the cathode electrode catalyst). Index value). In this embodiment, the voltage when the load is 0.1 A / cm 2 is actually measured as the low load voltage. The actual measurement of the low load voltage is performed, for example, by monitoring the voltage of the fuel cell system 100 during operation.

  Here, in the present embodiment, a process for reducing the cell voltage of the fuel cell system 100 to 0.5 V or less is executed in order to remove the oxide film adhering to the cathode electrode catalyst surface before the actual measurement of the low load voltage. Is done. Generally, when the fuel cell system 100 is operated for a certain period of time, an oxide film adheres to the surface of the cathode electrode catalyst. The oxide film adhering to the cathode electrode catalyst surface can cause a voltage drop in the fuel cell system 100. In this embodiment, the process of removing the oxide film attached to the surface of the cathode electrode catalyst by reducing the cell voltage of the fuel cell system 100 to 0.5 V or less is executed, so that the measured value of the low load voltage due to the oxide film is obtained. The influence of is suppressed.

  When the acquisition of the measured value of the low load voltage is completed, a comparison determination between the measured value Z of the low load voltage and the predicted value Zx of the low load voltage is executed (step S130). The low load voltage predicted value Zx to be compared is determined based on a prediction curve indicating the low load voltage predicted value Zx for each operation time (or travel distance). FIG. 3 is an explanatory diagram showing a prediction curve of a low load voltage. As shown in FIG. 3, the prediction curve for the low load voltage is a downward-sloping curve in which the value of the low load voltage decreases as the operation time increases. This is because during the operation of the fuel cell system 100, the dissolution and deposition of the catalyst is repeated due to fluctuations in the electrode potential, and the surface area of the cathode electrode catalyst decreases (the form changes).

  The control unit 200 (FIG. 1) of the fuel cell vehicle 10 includes a prediction system that sets a prediction curve for a low load voltage based on a simulation using a driving load. A simulation for setting a prediction curve is a known simulation method (for example, “RM Darling and JP Meyers: J. Electrochem. Soc., 150, A1523-A1527, (2003)”). The method described in (1) can be executed. Since the influence of catalyst poisoning on the low load voltage is difficult to predict, the prediction simulation of the low load voltage is executed without considering the influence of catalyst poisoning. The control unit 200 acquires the predicted value Zx based on the prediction curve of the low load voltage set by the prediction system, and compares and determines the measured value Z of the low load voltage and the predicted value Zx.

  The comparison determination (step S130) between the actual measurement value Z and the predicted value Zx of the low load voltage corresponds to the determination of the poisoning state of the electrode catalyst. That is, when the measured value Z of the low load voltage is smaller than the predicted value Zx of the low load voltage (see timing T1 in FIG. 3), the cathode electrode is a cause of lowering the measured value Z of the low load voltage below the predicted value Zx. Catalytic poisoning is considered. On the other hand, when the actual measurement value Z is not smaller than the predicted value Zx, it is considered that catalyst poisoning of the cathode electrode has not occurred.

  If it is determined that the actual measured value Z of the low load voltage is smaller than the predicted value Zx (step S130 in FIG. 2: Yes), it is considered that the catalyst poisoning of the cathode electrode has occurred. A catalyst cleaning process for the cathode electrode is performed (step S140). In consideration of errors in actual measurement and prediction, the catalyst cleaning process for the cathode electrode may be executed only when the difference between the actual measurement value Z and the predicted value Zx of the low load voltage is equal to or greater than a predetermined threshold value. .

  FIG. 4 is an explanatory view showing a method of catalyst cleaning treatment. As shown in FIG. 4, in the catalyst cleaning process, when the fuel cell system 100 is started at the timing T1 (ignition-on), a predetermined time (with a high current value I1 equal to or higher than a predetermined threshold value regardless of the user's accelerator operation) Power generation (current sweep) is performed for a period from time T1 to time T2. By this current sweep, the substance that poisons the catalyst is decomposed and removed, and the power generation performance is recovered (increased). The processing current value I1 and the processing time (time from the timing T1 to T2) vary depending on the constituent material of the fuel cell and the cell configuration / shape, and therefore experimentally obtained values are used in advance. The Electric power obtained during this period (current sweeping) is charged in the secondary battery. During this period, “Ready” is not displayed, and the fuel cell vehicle 10 is not driven (motor drive). Note that the fuel cell vehicle 10 may travel during this period. In this case, the fuel cell vehicle 10 travels using power obtained from the fuel cell or power from the secondary battery. After the preset timing T2, the normal operation (step S110 in FIG. 2) is executed in which the output is changed according to the user's accelerator operation.

  When it is determined that the measured value Z is not smaller than the predicted value Zx in the comparison determination (step S130 in FIG. 2) between the measured value Z of the low load voltage and the predicted value Zx (step S130: No), the cathode electrode Since it is considered that the catalyst is not poisoned, the control unit 200 performs a normal operation (step S110).

  As described above, in the fuel cell system 100 of the present embodiment, the determination of the poisoning state of the electrode catalyst is executed by comparing the measured value Z of the low load voltage with the predicted value Zx. Since the voltage recovery process can be performed at an optimal timing at which the output can be reliably recovered by determining the poisoning state of the electrode catalyst, a decrease in the output of the fuel cell system 100 can be suppressed, and drivability can be improved. Here, in this embodiment, since the process of lowering the cell voltage to 0.5 V or less is performed in order to remove the oxide film adhering to the cathode electrode catalyst surface before the actual measurement of the low load voltage, the oxide film The influence of the low load voltage on the actual measurement value Z is suppressed. Therefore, in this embodiment, it is possible to improve the accuracy of determination of the poisoning state of the electrode catalyst in the fuel cell system 100.

B. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

B1. Modification 1:
In the above embodiment, the low load voltage is used as the index value representing the surface area of the cathode electrode catalyst, but the surface area of the cathode electrode catalyst itself may be used. That is, the surface area of the cathode electrode catalyst is measured, and the determination of the poisoning state of the electrode catalyst may be executed by comparing the measured value of the surface area of the cathode electrode catalyst with the predicted value. The actual measurement of the surface area of the cathode electrode catalyst is performed using an electrochemical method such as cyclic voltammetry. In the actual measurement of the surface area of the cathode electrode catalyst, the cell voltage is reduced and the oxide film attached to the surface of the cathode electrode catalyst is removed, so that the measurement accuracy of the surface area of the cathode electrode catalyst can be improved. As a result, the accuracy of determination of the poisoning state of the electrode catalyst in the fuel cell system 100 can be improved.

  Simulations to set the prediction curve for low load voltage (or cathode electrode catalyst surface area) show catalyst particle size distribution, catalyst particles where the total weight of particles with the same particle size is the same at each particle size And a simulation method using a modeling method for expressing the distribution of the catalyst particles using the interval between the particle sizes of the representative points.

  Each step of the operation control (FIG. 2) of the fuel cell system 100 is not necessarily executed by the control unit 200. For example, the acquisition of the measured value of the low load voltage (step S120) and the comparison determination with the predicted value (step S130) may be executed by an external computer other than the control unit 200. Further, the control unit 200 does not need to have a prediction system for simulation, and a prediction curve of a low load voltage (or a surface area of the cathode electrode catalyst) is set in advance by simulation using an external computer. It may be stored.

B2. Modification 2:
The configuration of the fuel cell system 100 in the above embodiment is merely an example, and other configurations can be employed. In the above embodiment, the fuel cell system 100 is used in the fuel cell vehicle 10. However, the present invention is also applicable to other fuel cell systems such as a stationary fuel cell system. It is possible.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell vehicle 100 ... Fuel cell system 200 ... Control part

Claims (2)

A method for determining a catalyst poisoning state of a fuel cell system, comprising:
(A) obtaining a predicted value of a low load voltage that is a voltage of the fuel cell system in a load region lower than a preset load threshold;
(B) After the voltage of the fuel cell system is lowered to a value smaller than a voltage threshold set in advance as a voltage value at which the oxide film attached to the cathode electrode catalyst surface is removed , the low load of the fuel cell system Measuring voltage, and
(C) determining a catalyst poisoning state of the fuel cell system based on a comparison result between the predicted value of the low load voltage and the measured value. An apparatus for determining a catalyst poisoning state of a fuel cell system,
A predicted value acquisition unit that acquires a predicted value of a low load voltage, which is a voltage of the fuel cell system in a low load region lower than a preset load threshold;
The actual measurement of the low load voltage of the fuel cell system after the voltage of the fuel cell system is lowered to a value smaller than a voltage threshold set in advance as a voltage value for removing the oxide film adhering to the cathode electrode catalyst surface. An actual value acquisition unit for acquiring values;
And a determination unit that determines a catalyst poisoning state of the fuel cell system based on a comparison result between the predicted value of the low load voltage and the actual measurement value.

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