KR101349022B1 - Catalyst deterioration jundging method for fuel cell - Google Patents

Abstract

The present invention calculates the cell voltage deviation of a stack using a moving average method even in an operating state of an actual fuel cell vehicle in which a fuel cell stack is mounted, and makes a determination of deterioration of a catalyst layer, thereby making it possible to determine a specific cell among a plurality of cells constituting the stack. It is an object of the present invention to provide a method for diagnosing catalyst deterioration of a fuel cell stack to facilitate diagnosis of catalyst layer deterioration.

Description

CATALYST DETERIORATION JUNDGING METHOD FOR FUEL CELL}

The present invention relates to a method for diagnosing catalyst deterioration of a fuel cell stack, and more particularly, to a catalyst of a fuel cell stack capable of diagnosing catalyst deterioration of a specific cell using a moving average method of cell voltage deviation during operation of the fuel cell stack. It relates to a method for diagnosing deterioration.

A fuel cell refers to a device that generates heat and electrical energy as reaction products while converting chemical energy into electrical energy using oxidation and reduction reactions of reaction gases (hydrogen and oxygen in the air) continuously supplied. Stacking hundreds of cells each of the fuel cells is called a fuel cell stack.

Looking at the cell unit configuration of the fuel cell stack, an electrode including a polymer electrolyte membrane capable of moving hydrogen cations and an anode and a fuel electrode, which are catalyst layers coated to react hydrogen and oxygen on both surfaces of the electrolyte membrane. Membrane-Electrode Assembly (MEA) is located inside, Gas Diffusion Layer (GDL) and Gasket (Layer) are sequentially stacked on the outside of the cathode and anode, and fuel is deposited outside of the gas diffusion layer. A separation plate is formed in which a flow field is formed to supply and discharge the water generated by the reaction.

Since the cell voltage variation occurs due to damage of the catalyst layer, that is, the air electrode and the fuel electrode during the construction of the fuel cell stack, a failure diagnosis method for measuring corrosion resistance of the catalyst layer forming the air electrode and the fuel electrode by quantitatively measuring the amount of catalyst loss due to deterioration is required. It is becoming.

Cyclic voltage-current method (CV) is used in the corrosion resistance evaluation method with respect to the conventional catalyst.

That is, the cyclic voltage-current method of oxidizing or reducing the potential of the working electrode from the initial potential, converting the original potential through the reduction limit potential or the oxidation limit potential over time, and measuring the current value corresponding to the potential change. Using (CV), the failure of the catalyst layer is diagnosed along with the corrosion resistance evaluation of the catalyst layer.

delete

Thus, the smaller the platinum effective active surface area (Spt) reduction rate of the catalyst layer measured using the cyclic voltammetry method, the more resistant to corrosion resistance, and the larger the platinum effective active surface area (Spt) reduction rate of the catalyst layer, the more determined the failure of the catalyst layer. do.

However, the above-described conventional cyclic voltammetry is only suitable for experimentation because an artificial voltage must be applied to the catalyst layer, and is not applicable during the operation of an actual fuel cell vehicle equipped with a fuel cell stack.

The present invention has been made in view of the above, and in order to determine the deterioration of the catalyst layer by calculating the cell voltage deviation of the stack using a moving average method even in a driving state of an actual fuel cell vehicle equipped with a fuel cell stack. Accordingly, an object of the present invention is to provide a method for diagnosing catalyst deterioration of a fuel cell stack, which facilitates diagnosing catalyst layer deterioration of a specific cell among a plurality of cells constituting the stack.

In order to achieve the above object, the present invention calculates a difference between a stack average voltage and a minimum cell voltage in a specific current range generated in a fuel cell stack, but differs between a stack average voltage and a minimum cell voltage in two or more representative current ranges. Calculating a; Calculating a difference between the average stack voltage and the minimum cell voltage in the low current range and calculating the average value (average DV1); Calculating a difference between the average stack voltage and the minimum cell voltage in the high current range and calculating the average value (average DV2); When average DV2> average DV1 + b, failure determination as deterioration of the catalyst of the specific cell in which the minimum cell voltage has occurred; It provides a method for diagnosing catalyst degradation of a fuel cell stack, characterized in that consisting of.

Through the above-mentioned means for solving the problems, the present invention provides the following effects.

According to the present invention, there is no need for a separate test for diagnosing the condition of the catalyst layer of the fuel cell stack, the catalyst diagnosis time is short, and the diagnosis can be performed during actual vehicle operation. to provide.

In addition, controller memory allocation for catalyst status diagnosis can be minimized.

1 is a current-voltage curve for a normal cell and a catalyst loss cell among a plurality of cells constituting a fuel cell stack;
2 is a current-voltage curve for a normal cell and a catalyst loss cell of a plurality of cells in operation of a stack mounted in an actual fuel cell vehicle.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a current-voltage curve obtained by measuring a current-voltage of a normal cell and a catalyst loss cell among a plurality of cells constituting the fuel cell stack using predetermined evaluation equipment.

As shown in FIG. 1, it can be seen that the voltage difference between the damaged cell and the normal cell increases as the current increases, and the voltage deviation between the normal cell and the damaged cell measured at a specific current is very small or large, so that each current It is preferable to determine the failure of the catalyst cell by comparing the degree of the cell voltage drop at.

FIG. 2 shows actual operation data of current-voltage measured for a normal cell and a catalyst loss cell among a plurality of cells during operation of a stack mounted in an actual fuel cell vehicle, and the average voltage of the stack (blue) and the catalyst are damaged. The minimum cell voltage is shown.

As shown in FIG. 2, it can be seen that the current in the stack operation mounted on the fuel cell vehicle is changed randomly, and also the number of times the specific current is driven is small, and each cell voltage at the same current has a dispersion. .

Therefore, when determining the catalyst loss cell using the actual operation data as described above, the voltage difference in a specific current range, that is, the difference between the stack average voltage and the catalyst loss cell voltage (hereinafter, referred to as a specific cell voltage or minimum cell voltage). Should be calculated.

For example, when the current generated during stack operation of a fuel cell vehicle is 0.6, when the stack average voltage and the specific cell voltage difference DV are calculated, that is, the difference between the stack average voltage and the minimum cell voltage (stack average voltage − When calculating the minimum cell voltage), calculate the data using the data when the current range is 0.6-a <current <0.6 + a.
Here, a means a margin value arbitrarily set by a measurement operator to determine a current range of a specific current at this time when calculating a voltage difference using a specific current (representative current).
As described above, since the current varies randomly during operation of the actual fuel cell stack, and the number of operating at a specific current is not large, and the cell voltages are scattered at the same current, the actual operating data is used. In the case of determining the catalyst loss cell, the current range is determined by giving a "+" and a "-" margin value (a) to a specific current (such as 0.6 or 0.4) and calculating a voltage difference in the current range. .

More preferably, the difference between the stack average voltage and the minimum cell voltage may be calculated using two or more representative currents generated during stack operation of the fuel cell vehicle, for example, the current range is 0.6-a <current < Calculate using data from 0.6 + a and with current range 0.4-a <current <0.4 + a.

More specifically, when the specific current range 0.4-a <current <0.4 + a, the difference between the stack average voltage and the minimum cell voltage (DV1 = stack average voltage-minimum cell voltage) is obtained, respectively, and the average value (average DV1) is obtained. Calculate the difference between the stack average voltage and the minimum cell voltage (DV2 = stack average voltage-minimum cell voltage) when the specific current range is 0.6-a <current <0.6 + a, and calculate the average value (average DV2). Calculate

In other words, when 0.4-a <current <0.4 + a, if the number of times operated within this current range is n times, the average voltage of the stack of hundreds of cells at 0.4-a <current <0.4 + a Calculate the average DV1 = (stack average voltage-minimum cell voltage) / n as the difference from the minimum cell voltage, and when the number of times of operation within this current range is n times when 0.6-a <current <0.6 + a The average DV2 = (average voltage-minimum cell voltage) / n is calculated as the difference between the average cell voltage and the minimum cell voltage of a stack of several hundred cells at 0.6-a <current <0.6 + a.

Therefore, when average DV2> average DV1 + b, failure determination is made that the catalyst of the minimum cell (specific cell) has deteriorated.
Here, b is a predetermined set value for determining the failure of the catalyst, and when the value of the average DV2 is larger than the sum of b plus the average DV1, the failure is judged to be deteriorated.
That is, the average DV1 is compared with the average DV2, and if the difference (average DV2-average DV1) is larger than the set value b, it is determined that the catalyst has failed.

As shown in FIG. 2, in the case of a damaged cell, the voltage decreases as the current of the stack increases, and the voltage difference between the normal cell and the damaged cell increases with increasing current, and as the damage of the catalyst increases, The difference is even larger due to the increase in diffusion resistance due to the reduction of the surface area of the catalyst.

Therefore, the DV2, which is the difference in the voltage of the average voltage-catalyzed damaged cell at high current, is larger than the DV1, the difference in the voltage of the average voltage-catalyzed damaged cell at low current, and the greater the catalyst damage, the greater the difference.

Thus, the difference between the stack average voltage and the voltage of the cell to be damaged at high current indicates the degree of catalyst damage more than the difference between the stack average voltage and the voltage at the cell to be damaged at low current, wherein the specific voltage value b is added to DV1. If DV2 is greater than the value, it is determined that the failure of the catalyst requires repair of the stack.

Here, the catalyst degradation diagnosis method of the fuel cell stack according to the present invention will be described in more detail.

In calculating the average cell voltage difference (DV), which represents the difference between the stack average voltage and the minimum cell voltage, in the specific current range produced by the stack, use the most frequent cell voltage difference, and the second most frequent cell voltage difference. Save temporarily.

When the minimum cell voltage does not occur more than N times in the same cell among a plurality of cells, the temporary storage cell voltage is calculated as the average cell voltage difference DV, and the number and DV of the current minimum voltage generating cell are temporarily stored.

In this case, the position of the cell where the minimum cell voltage occurs in a specific current range may be the same or may be a cell of another position, for example, cell 10 of the 180 sampling data was the minimum voltage 100 times in a specific current range, 20 If the burncell was at the minimum voltage of 80, then cell 10 would be the most frequent cell.

In addition, if the voltage sampling is performed once per second, the operation time is 180 seconds, and it is operated only at a specific current, the minimum voltage of the 10th cell occurs 100 times and the minimum voltage of the 20th cell occurs 80 times. The frequency number is 10 cells, the number is 100 times, the second frequency is 20 cells, the number is 80 times, and stored in the memory.

In addition, when the operation time is 300 seconds and it is operated only at a specific current, if the minimum voltage of the 10th cell is generated 120 times and the minimum voltage of the 20th cell is generated 180 times, the number of the first frequency is 20th cell, the number of times Number 180 is the second frequency, number 10, and number 120 is stored in memory.

In this way, when the operation time increases and the number of the most frequent cell is changed, the position of the cell can be known at that time.

Meanwhile, the average cell voltage difference calculation (DV) process using the moving average method is performed by calculating N sample moving averages DV using the following equation.

As described above, when calculating the average voltage difference in a specific current range by using the moving average method, the average DV, the previous average DV, DV, the number of operations in the specific current range (N) for the memory allocation of the controller Need

When calculating the average voltage difference in a general manner, the number of operation (N) DVs, the average DV, DV, and the number of operation (N) in a specific current range should be allocated to the controller memory.

Therefore, in the present invention, the memory allocation of the controller can be minimized when calculating the average DV using the moving average method.

That is, the number of times of operation (N) in a specific current range is 1000 times, and since 1000 data are needed as the voltage value for calculating the average DV, the controller needs 1000 data storage places to calculate the average. As the operation time increases, the memory should be allocated as it increases. However, according to the present invention, when the DV is calculated using the moving average method, the previous average DV, the number of times operated in a specific current range (N), and the current DV value Since only memory needs to be allocated, only three data storage locations are required, thus minimizing the memory allocation of the controller.

Claims (3)

Calculating a difference between the stack average voltage and the minimum cell voltage in a specific current range generated in the fuel cell stack, wherein calculating a difference between the stack average voltage and the minimum cell voltage in at least two representative current ranges;
Calculating a difference between the average stack voltage and the minimum cell voltage in the low current range and calculating the average value (average DV1);
Calculating a difference between the average stack voltage and the minimum cell voltage in the high current range and calculating the average value (average DV2);
If average DV2> average DV1 + b, failing to determine that the catalyst of the particular cell in which the minimum cell voltage has occurred has deteriorated;
A catalyst degradation diagnostic method of a fuel cell stack, characterized in that consisting of.
Here, DV1 is the difference between the stack average voltage and the minimum cell voltage at low current, DV2 is the difference between the stack average voltage and the minimum cell voltage at high current, and b is a predetermined set value for determining the failure of the catalyst. .
The method according to claim 1,
The current range of the low current is 0.4-a <current <0.4 + a, the current range of the high current is 0.6-a <current <0.6 + a catalyst degradation diagnostic method of the fuel cell stack, characterized in that.
Here, a is a margin value arbitrarily set in order to determine the current range of the current.
The method according to claim 1,
The average DV1 and DV2 is

A method for diagnosing catalyst degradation of a fuel cell stack, wherein n is a number of operations in a high current or low current range, and DV is a difference between a stack average voltage and a minimum cell voltage.

Images