KR20210069135A - Fuel cell deterioration diagnosis system and diagnosis method - Google Patents

Abstract

a fuel cell stack in which a plurality of unit cells are stacked to generate electric power by receiving fuel gas and oxidizing gas; a potential control unit for controlling a potential between electrodes included in the fuel cell stack; a current sensing unit for measuring the current of one or a plurality of unit cells in a state where the potential is varied in the potential control unit; and a deterioration determination unit for determining the degree of deterioration of one or a plurality of unit cells based on the magnitude of the current measured by the current sensing unit;

Description

Fuel cell deterioration diagnosis system and method {FUEL CELL DETERIORATION DIAGNOSIS SYSTEM AND DIAGNOSIS METHOD}

The present invention relates to a system and method for diagnosing deterioration of a fuel cell, and to a technology for detecting deterioration of a membrane-electrode assembly included in a fuel cell stack.

A fuel cell converts chemical energy into electrical energy by using the oxidation-reduction reaction of hydrogen and oxygen supplied from a hydrogen supply device and an air supply device, respectively. A fuel cell stack that produces electrical energy and a cooling system for cooling the same contains

That is, hydrogen is supplied to the anode side of the fuel cell, and the oxidation reaction of hydrogen proceeds at the anode to generate hydrogen ions (Protons) and electrons (Electrons). At this time, the generated hydrogen ions and electrons are respectively transferred to the cathode through the electrolyte membrane. Move. At the cathode, electric energy is generated through an electrochemical reaction in which hydrogen ions and electrons moved from the anode and oxygen in the air participate.

As the fuel cell continues to generate power or is exposed to high potential, a membrane-electrode assembly (MEA) included in the fuel cell stack is deteriorated. When deterioration occurs in the membrane-electrode assembly, the power generation performance of the fuel cell is significantly reduced, and the stability of the fuel cell also occurs.

Therefore, while it is important to operate a fuel cell to prevent deterioration of the stack of the fuel cell, a technology for diagnosing deterioration occurring in the stack of the fuel cell is required.

The matters described as the above background art are only for improving the understanding of the background of the present invention, and should not be taken as acknowledging that they correspond to the prior art already known to those of ordinary skill in the art.

KR 10-2011-0062130 A

The present invention has been proposed to solve this problem, and an object of the present invention is to provide a technology for detecting deterioration of a fuel cell by detecting the amount of gas crossover between the membrane-electrode assemblies of the fuel cell stack.

According to an aspect of the present invention, there is provided a fuel cell deterioration diagnosis system comprising: a fuel cell stack in which a plurality of unit cells are stacked to generate electric power by receiving fuel gas and oxidizing gas; a potential control unit for controlling a potential between electrodes included in the fuel cell stack; a current sensing unit for measuring the current of one or a plurality of unit cells in a state where the potential is varied in the potential control unit; and a deterioration determining unit that determines the degree of deterioration of one or a plurality of unit cells based on the magnitude of the current measured by the current sensing unit.

The current sensing unit may measure the current of one or a plurality of unit cells in a state in which the oxidizing gas is removed from the cathode of the fuel cell.

Further comprising; a gas supply unit for supplying fuel gas to the anode of the fuel cell; in the current sensing unit, the gas supply unit measures the current of one or a plurality of unit cells in a state in which the fuel gas is supplied by pressurizing the fuel gas to the anode of the fuel cell can do.

In the current sensing unit, one or a plurality of unit cells are divided into a plurality of positions, each current is measured at the divided positions, and the deterioration determining unit determines the degree of deterioration at the divided positions based on the measured current, respectively. can judge

The potential control unit may control the potential between the electrodes by a linear scanning potential method so that the potential between the electrodes is constantly increased or decreased at a predetermined rate.

The deterioration determining unit may determine the degree of deterioration based on a magnitude of a peak current that is a peak value of the current measured by the current sensing unit or a magnitude of a peak potential that is a potential value from the peak current.

According to an aspect of the present invention, there is provided a method for diagnosing deterioration of a fuel cell, the method comprising: varying a potential between electrodes included in a fuel cell stack; measuring the current of one or a plurality of unit cells included in the fuel cell stack in a state in which the potential between the electrodes is varied; and determining the degree of deterioration of one or a plurality of unit cells based on the magnitude of the measured current.

The method may further include, before the step of varying the potential between the electrodes, removing the oxidizing gas from the cathode of the fuel cell.

Prior to the step of varying the potential between the electrodes, the method may further include a step of supplying the fuel gas by pressurizing the fuel gas to the anode of the fuel cell.

In the step of varying the potential between the electrodes, the potential between the electrodes may be controlled by the linear scanning potential method so that the potential between the electrodes is constantly increased or decreased at a predetermined rate.

In the step of measuring the current of the unit cell, in the step of dividing one or a plurality of unit cells into a plurality of positions, measuring the current at each of the divided positions, and determining the degree of deterioration of the unit cell, the measured current is It is possible to determine the degree of deterioration at the positions divided based on each.

In the step of determining the degree of degradation of the unit cell, the degree of degradation may be determined based on the magnitude of the peak current that is the peak value of the current measured by the current sensing unit or the magnitude of the peak potential that is the potential value from the peak current.

According to the fuel cell deterioration diagnosis system and method of the present invention, it is possible to diagnose whether a pinhole is generated and a specific location of an electrolyte membrane included in the fuel cell.

In addition, the fuel cell durability is improved by improving the fuel cell operation precision, and it is possible to determine the degree of deterioration of the electrolyte membrane.

1 is a block diagram of a fuel cell deterioration diagnosis system according to an embodiment of the present invention.
2 illustrates a potential change with time according to an embodiment of the present invention.
3 illustrates a change in current according to a change in potential according to an embodiment of the present invention.
4 is a diagram illustrating a current distribution measured by a current sensing unit according to an embodiment of the present invention.
5 is a flowchart of a method for diagnosing deterioration of a fuel cell according to an embodiment of the present invention.

Specific structural or functional descriptions of the embodiments of the present invention disclosed in the present specification or application are only exemplified for the purpose of describing the embodiments according to the present invention, and the embodiments according to the present invention may be implemented in various forms. and should not be construed as being limited to the embodiments described in the present specification or application.

Since the embodiment according to the present invention can have various changes and can have various forms, specific embodiments are illustrated in the drawings and described in detail in the present specification or application. However, this is not intended to limit the embodiment according to the concept of the present invention with respect to a specific disclosed form, and should be understood to include all changes, equivalents or substitutes included in the spirit and scope of the present invention.

Terms such as first and/or second may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another, for example, without departing from the scope of rights according to the inventive concept, a first component may be termed a second component, and similarly The second component may also be referred to as the first component.

When a component is referred to as being “connected” or “connected” to another component, it is understood that the other component may be directly connected or connected to the other component, but other components may exist in between. it should be On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that no other element is present in the middle. Other expressions describing the relationship between elements, such as "between" and "immediately between" or "neighboring to" and "directly adjacent to", should be interpreted similarly.

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprises" or "have" are intended to designate that the described features, numbers, steps, operations, components, parts, or combinations thereof exist, and include one or more other features or numbers. , it should be understood that it does not preclude the existence or addition of steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as meanings consistent with the context of the related art, and unless explicitly defined in the present specification, they are not to be interpreted in an ideal or excessively formal meaning. .

Hereinafter, the present invention will be described in detail by describing preferred embodiments of the present invention with reference to the accompanying drawings. Like reference numerals in each figure indicate like elements.

1 is a block diagram of a fuel cell deterioration diagnosis system according to an embodiment of the present invention.

Referring to FIG. 1 , a fuel cell deterioration diagnosis system according to an embodiment of the present invention includes a fuel cell stack 10 in which a plurality of unit cells are stacked to generate electric power by receiving fuel gas and oxidizing gas; a potential control unit 20 for controlling a potential between electrodes included in the fuel cell stack 10; a current sensing unit 30 for measuring the current of one or a plurality of unit cells in a state where the potential is varied in the potential control unit 20; and a deterioration determining unit 40 that determines the degree of deterioration of one or a plurality of unit cells based on the magnitude of the current measured by the current sensing unit 30 .

The fuel cell stack 10 may be formed by stacking a plurality of unit cells. A membrane-electrode assembly is positioned inside the unit cell, and an anode and a cathode may be separated by the membrane-electrode assembly.

Hydrogen as a fuel gas may be supplied to the anode of the fuel cell stack 10 , and air containing oxygen as an oxidizing gas may be supplied to the cathode. Specifically, when the fuel cell generates electric power, hydrogen is oxidized at the anode of the fuel cell stack 10 and separated into hydrogen ions and electrons, the hydrogen ions are moved to the cathode through the electrolyte membrane, and oxygen and hydrogen ions are generated at the cathode. Water can be produced by absorbing electrons.

The fuel cell stack 10 includes a membrane-electrode assembly, and electrodes may be positioned on both sides of the electrolyte membrane, respectively. When the fuel cell generates electric power, a potential may be formed between the electrodes.

The potential control unit 20 controls the potential between the electrodes included in the fuel cell stack 10 . In particular, the potential control unit 20 may form a potential between the electrodes inside the unit cell.

In one embodiment, the potential control unit 20 may be a separate power source connected to the fuel cell outside the fuel cell. That is, when the fuel cell is separated and diagnosed in a state in which power generation of the fuel cell is stopped, the potential control unit 20 may connect a separate power source to the fuel cell.

In another embodiment, the potential control unit 20 may be a power storage device such as a high-voltage battery or a supercapacitor that charges or discharges power generated by the fuel cell to assist the required power of the fuel cell. That is, when the fuel cell is mounted on a vehicle and the fuel cell is diagnosing deterioration in a state in which power generation of the fuel cell is temporarily stopped, a potential can be applied between the electrodes of the fuel cell by discharging the high voltage battery.

The current sensing unit 30 is a current sensor, and may measure a current of a unit cell included in the fuel cell stack 10 . In particular, the current sensing unit 30 may measure each current flowing through each unit cell.

The current sensing unit 30 is located inside the fuel cell stack 10 , and is arranged in parallel with the individual unit cells to measure the current flowing at each position of the individual unit cells.

The deterioration determining unit 40 may determine the degree of deterioration of the unit cell by using the current measured by the current sensing unit 30 .

Specifically, deterioration of the electrolyte membrane is classified into chemical deterioration and mechanical deterioration. Chemical degradation means that radicals/hydrogen peroxide generated in the cell attack the polymer membrane and the electrolyte membrane deteriorates. As the electrolyte membrane deteriorates, a pinhole is partially formed as the thickness of the membrane decreases, and thus, hydrogen permeability through the electrolyte membrane increases.

The deterioration determination unit 40 determines the degree of crossover of hydrogen injected into the anode of the fuel cell stack 10 toward the cathode, and measures the magnitude of the current resulting from oxidation of the hydrogen crossover toward the cathode. deterioration can be judged. For example, the potential control unit 20 may apply a reverse voltage to the electrode of the fuel cell so that hydrogen is oxidized on the cathode side.

In an embodiment, the current sensing unit 30 may measure the current of one or a plurality of unit cells in a state in which the oxidizing gas is removed from the cathode of the fuel cell.

The fuel gas may be supplied to the anode of the fuel cell and the oxidizing gas may be supplied to the cathode of the fuel cell. However, when power generation of the fuel cell is stopped, the oxidizing gas may be removed from the cathode of the fuel cell.

In particular, it is possible to remove the oxidizing gas inside the cathode through COD (Cathode Oxygen Depletion) control. In COD control, the voltage of the fuel cell stack 10 can be lowered while charging the high voltage battery with the power of the fuel cell stack 10 or by connecting the fuel cell stack 10 with a COD resistor to remove the oxidizing gas inside the cathode. have.

In another embodiment, the gas supply unit 50 may supply nitrogen to the cathode of the fuel cell. In a state in which oxygen is removed from the inside of the cathode by supplying separately stored nitrogen to the cathode, or by supplying nitrogen from the air to the cathode and deoxygenated air is supplied to the cathode, one or a plurality of unit cells current can be measured.

In addition, it further includes a gas supply unit 50 for supplying fuel gas to the anode of the fuel cell, and in the current sensing unit 30, the gas supply unit 50 pressurizes the fuel gas to the anode of the fuel cell and supplies it. can measure the current of one or a plurality of unit cells.

The gas supply unit 50 may control a hydrogen supply system for supplying hydrogen to the anode of the fuel cell or an air supply system for supplying air to the cathode of the fuel cell. The gas supply unit 50 may pressurize and supply hydrogen to the anode of the fuel cell, and the current sensing unit 30 may measure the current of one or a plurality of unit cells while hydrogen is pressurized to the anode.

That is, it induces the pressurized hydrogen of the anode to cross over to the cathode from which oxygen has been removed, and the current sensing unit 30 detects the current according to the oxidation of hydrogen crossed over to the cathode to estimate the crossover amount of hydrogen. have. The deterioration determining unit 40 may determine that the deterioration of the fuel cell has progressed as the estimated hydrogen crossover amount increases.

In the current sensing unit 30, one or a plurality of unit cells are divided into a plurality of positions, each current is measured at the divided positions, and in the deterioration determining unit 40, the position is divided based on the measured current. The degree of deterioration in each can be determined.

The current sensing unit 30 may be a current sensor plate having regions separated in a horizontal direction and a vertical direction of the unit cell. The current sensing unit 30 may measure currents at a plurality of positions of the unit cell, respectively.

That is, the current sensing unit 30 can measure a current density distribution (CDD) of the unit cell, and accordingly, the deterioration determining unit 40 determines the current of the unit cell measured by the current sensing unit 30 . According to the density, it is possible to determine the degree of deterioration according to the position of the unit cell. Accordingly, it is possible to determine the degree of deterioration for each location according to the current density for each location of the unit cell included in the fuel cell, and to sense the deteriorated area of the unit cell.

FIG. 2 shows a change in potential with time according to an embodiment of the present invention, and FIG. 3 shows a change in current according to a change in potential according to an embodiment of the present invention.

2 to 3 , the potential control unit 20 may control the potential between the electrodes to be constantly increased or decreased at a preset rate using a linear sweep voltammetry (LSV).

The linear scanning potential method (LSV) is a method of measuring a current-potential curve by changing the potential between electrodes at a constant speed V[V/sec] in the positive or negative direction from the initial potential (Ei).

The deterioration determining unit 40 may determine the degree of deterioration based on the magnitude of the peak current that is the peak value of the current measured by the current sensing unit 30 or the magnitude of the peak potential that is the potential value at the peak current.

Specifically, in the case of a reversible electrode reaction, the peak current ip is given by the following equation.

Here, n is the number of electrons participating in the electrode reaction, F is the Faraday constant (96487 C/moL), C is the concentration of the active species, V is the potential scanning rate, and D is the diffusion coefficient of the active species.

Here, the active species means a chemical species that controls catalysis in the catalyst.

The peak current ip is proportional to the square root of the scanning dislocation speed V, and the peak current ip increases as the scanning dislocation speed increases.

In addition, the relationship between the peak potential Ep and the half-peak potential Ep/2 and the half-wave potential E1/2 of DC polarography is as follows.

Here, T is arranged on the assumption that the temperature of the fuel cell is 25 [℃].

That is, by measuring the peak current ip and the peak potential Ep, quantitative and qualitative analysis of the electrode active material is possible.

The deterioration determining unit 40 may determine the deterioration degree of the unit cell or the fuel cell including the unit cell based on the peak current or the peak potential. In particular, the deterioration determining unit 40 may determine the degree of deterioration according to the position of the unit cell.

In one embodiment, the deterioration determining unit 40 may determine that the electrolyte membrane is damaged when the peak current measured by the current sensing unit 30 is 2.0 [mA/cm2] or more. Alternatively, when the peak current is 0.2 [A] or more in the local 1/64 region based on the area of the unit cell, it may be determined that the electrolyte membrane is damaged.

In addition, when the peak current is 0.4 [A] or more in the local 1/64 region based on the area of the unit cell, it can be determined that the electrolyte membrane is seriously damaged. In particular, when the deterioration determination unit 40 determines that the electrolyte membrane is seriously damaged, the gas supply unit 50 may reduce the air supply flow rate of the fuel cell and limit the power generation of the fuel cell. In particular, when the fuel cell is mounted on a vehicle, maintenance of the vehicle may be induced while limiting the vehicle speed or acceleration of the vehicle.

4 illustrates a current distribution measured by the current sensing unit 30 according to an embodiment of the present invention.

Referring further to FIG. 4 , in the case of a new MEA, when ODT (Open Circuit Decay Time) is measured, the ODT is 108 seconds, which is a state in which deterioration of the electrolyte membrane hardly occurs. It can be seen that the new MEA generates a very low peak current at all positions of the unit cell.

Therefore, in the new MEA, it is determined that hydrogen crossover from the anode to the cathode is very small, and it can be determined that there is almost no damage to the electrolyte membrane.

In contrast, the deteriorated MEA was measured with an ODT of 6.7 seconds, indicating that the electrolyte membrane was greatly deteriorated. In the deteriorated MEA, it can be confirmed that the peak current is measured locally in the unit cell. In particular, in the deteriorated MEA, it can be determined that a pinhole is generated in the upper right part of the unit cell, considering that the peak current is greatly measured at the upper right part of the unit cell.

Therefore, in the deteriorated MEA, it is determined that hydrogen crossover from the anode to the cathode is relatively large, and damage to the electrolyte membrane can be determined to be large.

5 is a flowchart of a method for diagnosing deterioration of a fuel cell according to an embodiment of the present invention.

Referring further to FIG. 5 , the method for diagnosing deterioration of a fuel cell according to an embodiment of the present invention includes the steps of varying a potential between electrodes included in the fuel cell stack 10 ( S300 ); measuring the current of one or a plurality of unit cells included in the fuel cell stack 10 in a state in which the potential between the electrodes varies ( S400 ); and determining the degree of deterioration of one or a plurality of unit cells based on the magnitude of the measured current (S500).

Before the step of varying the potential between the electrodes ( S300 ), removing the oxidizing gas from the cathode of the fuel cell ( S100 ); may further include.

Before the step (S300) of varying the potential between the electrodes, the step of supplying the fuel gas by pressurizing the fuel gas to the anode of the fuel cell (S200); may further include.

In the step of varying the potential between the electrodes ( S300 ), the potential between the electrodes may be controlled by a linear scanning potential method so that the potential between the electrodes is constantly increased or decreased at a predetermined rate.

In the step of measuring the current of the unit cell (S400), one or a plurality of unit cells are divided into a plurality of positions, the current is measured at each of the divided positions, and in the step of determining the degree of deterioration of the unit cell, the measurement is performed. It is possible to determine the degree of deterioration in each of the divided positions based on one current.

In the step of determining the degree of degradation of the unit cell (S500), the degree of degradation is determined based on the magnitude of the peak current that is the peak value of the current measured by the current sensing unit 30 or the magnitude of the peak potential that is the potential value at the peak current. can do.

Although shown and described with respect to specific embodiments of the present invention, it is within the art that the present invention can be variously improved and changed without departing from the spirit of the present invention provided by the following claims. It will be obvious to one of ordinary skill.

10: fuel cell stack 20: potential control unit
30: current sensing unit 40: deterioration determination unit
50: gas supply unit

Claims (12)

a fuel cell stack in which a plurality of unit cells are stacked to generate electric power by receiving fuel gas and oxidizing gas;
a potential control unit for controlling a potential between electrodes included in the fuel cell stack;
a current sensing unit for measuring the current of one or a plurality of unit cells in a state where the potential is varied in the potential control unit; and
A fuel cell deterioration diagnosis system comprising a; a deterioration determination unit for determining the degree of deterioration of one or a plurality of unit cells based on the magnitude of the current measured by the current sensing unit. The method according to claim 1,
The current sensing unit measures the current of one or a plurality of unit cells in a state in which the oxidizing gas is removed from the cathode of the fuel cell. The method according to claim 1,
It further includes; a gas supply unit for supplying fuel gas to the anode of the fuel cell,
The current sensing unit measures the current of one or a plurality of unit cells while the fuel gas is supplied by pressurizing the fuel gas to the anode of the fuel cell by the gas supply unit. The method according to claim 1,
In the current sensing unit, one or a plurality of unit cells are divided into a plurality of positions, and each current is measured at the divided positions,
The deterioration diagnosis system of the fuel cell, characterized in that the deterioration determination unit determines the degree of deterioration at the divided positions based on the measured current. The method according to claim 1,
The fuel cell deterioration diagnosis system, characterized in that the electric potential controller controls the electric potential between the electrodes by a linear scanning electric potential method so that the electric potential between the electrodes is constantly increased or decreased at a predetermined rate. The method according to claim 1,
The deterioration diagnosis system of a fuel cell, wherein the deterioration determination unit determines the degree of deterioration based on the magnitude of the peak current that is the peak value of the current measured by the current sensing part or the magnitude of the peak potential that is the potential value from the peak current. varying an electric potential between electrodes included in the fuel cell stack;
measuring the current of one or a plurality of unit cells included in the fuel cell stack in a state in which the potential between the electrodes is varied; and
Determining the degree of deterioration of one or a plurality of unit cells based on the magnitude of the measured current; A method for diagnosing deterioration of a fuel cell comprising a. 8. The method of claim 7,
The method for diagnosing deterioration of a fuel cell, further comprising: removing an oxidizing gas from a cathode of the fuel cell before the step of varying the potential between the electrodes. 8. The method of claim 7,
The method for diagnosing deterioration of a fuel cell, further comprising the step of supplying the fuel gas by pressurizing the fuel gas to the anode of the fuel cell before the step of varying the potential between the electrodes. 8. The method of claim 7,
The method for diagnosing deterioration of a fuel cell, characterized in that in the step of varying the potential between the electrodes, the potential between the electrodes is controlled by a linear scanning potential method so that the potential between the electrodes is constantly increased or decreased at a predetermined rate. 8. The method of claim 7,
In the step of measuring the current of the unit cell, one or a plurality of unit cells are divided into a plurality of positions, and the current in the divided positions is measured, respectively,
In the step of determining the degree of deterioration of the unit cell, the deterioration diagnosis method of a fuel cell, wherein the degree of deterioration at the divided positions is determined based on the measured current, respectively. 8. The method of claim 7,
In the step of determining the degree of degradation of the unit cell, the degree of degradation is determined based on the magnitude of the peak current that is the peak value of the current measured by the current sensing unit or the magnitude of the peak potential that is the potential value from the peak current. A method for diagnosing battery deterioration.

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