KR102124755B1 - Diagnosis function for detecting membrane defects at pem-fuel cells - Google Patents

Abstract

The present invention is a method for inspecting a polymer electrolyte membrane-fuel cell for detecting defects in a polymer electrolyte membrane separating a hydrogen-guided anode system and an air-guided cathode system from each other, the anode system and the cathode system during a certain operating state of the fuel cell. Variation in the pressure difference 1 between is carried out, detection of hydrogen partial pressure or hydrogen amount 3, 4 during the variation in the pressure difference 1 and/or nitrogen partial pressure 2 during the variation in the pressure difference or It relates to a method for inspecting a polymer electrolyte membrane-fuel cell, in which the amount of nitrogen is detected.

Description

Diagnosis function for detecting membrane defects in polymer electrolyte membrane-fuel cells {DIAGNOSIS FUNCTION FOR DETECTING MEMBRANE DEFECTS AT PEM-FUEL CELLS}

The present invention relates to a method for inspecting a polymer electrolyte membrane-fuel cell for detecting defects in a polymer electrolyte membrane separating a hydrogen-guided anode system and an air-guided cathode system from each other.

A polymer electrolyte membrane (PEM) separates a hydrogen-guided anode and an air-guided cathode from a polymer electrolyte membrane-fuel cell (PEM-fuel cell). The task of the membrane is to enable the flow of protons, but not to pass electrons, so that protons can act as currents. Due to aging and undesirable operating conditions, the polymer electrolyte membrane (PEM) between the anode and the cathode is thinned. Thus, the ingress of hydrogen from the anode to the cathode or the infiltration of nitrogen and oxygen from the cathode to the anode may appear. When the holes are large, the battery completely fails and the battery potential falls to zero. In this case, operation of the PEM-fuel cell or fuel cell-stack (multiple PEM-fuel cells are integrated to form one stack) is no longer possible.

Hydrogen permeation to the cathode increases consumption, and heat release by direct oxidation in the presence of oxygen causes water and thus accelerates potential membrane aging, and increases H ₂ -release when hydrogen is not oxidized. An increase in nitrogen penetration accelerates N2-concentration in the anode system. Oxygen forms water with the hydrogen present in the anode. If oxygen does not react, in the worst case an explosive mixture can form. To prevent this, the anode is normally operated with excess pressure in relation to the cathode. In all cases, membrane errors should be detected as early as possible to avoid critical operating conditions.

From electrochemistry, methods are known for detecting membrane errors in PEM-fuel cells, such as cyclovoltametry. These methods are unsuitable for conducting on-board diagnostics in automobiles and require very complex measurement techniques in service. In addition, in the above-described known method, there is a disadvantage that this method cannot be applied because there is no access to individual cell voltages in the fuel cell stack.

In DE 10 2009 026 590 A1 a method of operation of a fuel cell system is known, in which the operating state of the fuel cell is controlled based on the mass flow and the pressure difference before and after the cell, an operational failure based on the type of deviation The type of is estimated. However, in this method, it is impossible to detect individual film defects.

US 2004/0018404 A1 discloses a fuel cell system with a device for measuring the pressure difference between the anode and the cathode and hydrogen in the cathode exhaust gas. If the measured values are outside the predetermined setting range, the abnormal state of the fuel cell is estimated, and the operating state of the fuel cell is changed to prevent further damage to the fuel cell.

In JP 2006 269 337 A, a fuel cell system is known which is inspected by controlling the pressure difference between the cathode and the anode and the hydrogen concentration in the cathode exhaust gas while driving in a vehicle. When the hydrogen concentration in the cathode exhaust gas exceeds the limit, the pressure difference between the anode and the cathode fluctuates by the control device until the water concentration in the cathode exhaust gas again becomes below the limit.

The disadvantage of the known method is that it is impossible to detect defects in the polymer electrolyte membrane in the category of factory diagnostics and in the category of on-board diagnostics of automobiles. Further, detection of membrane defects in the polymer electrolyte membrane fuel cell stack is not possible by known methods.

An object of the present invention is a method for inspecting a polymer electrolyte membrane-fuel cell for detecting a defect in a polymer electrolyte membrane, which enables detection of membrane defects in the category of factory diagnosis and in the category of on-board diagnostics of automobiles without additional sensors. Is to provide.

The above object is achieved by the method according to claim 1. Preferred embodiments of the invention are presented in the dependent claims.

A method for inspecting a polymer electrolyte membrane-fuel cell for detecting defects in a polymer electrolyte membrane separating a hydrogen-guided anode system and an air-guided cathode system from each other, the method comprising: between the anode system and the cathode system during a certain operating state of the fuel cell according to the present invention Variation in pressure difference is carried out, and detection of hydrogen partial pressure or amount of hydrogen during variation of the pressure difference and/or detection of nitrogen partial pressure or amount of nitrogen during variation of pressure difference is performed.

The expression anode system includes at least the anode of a polymer electrolyte membrane-fuel cell. In addition, the expression anode system may include a suitable sensor for detecting a small fractional pressure or hydrogen content in the anode system. The expression cathode system includes at least the cathode of a polymer electrolyte membrane-fuel cell. In addition, suitable sensors for detecting the hydrogen partial pressure or amount of hydrogen in the cathode system may be included.

According to one aspect of the invention, detection of hydrogen partial pressure, amount of hydrogen and/or hydrogen gradient in the anode system during fluctuations in pressure difference can be carried out. Alternatively or additionally, detection of the hydrogen partial pressure or amount of hydrogen and/or hydrogen gradient in the cathode system during fluctuations in the pressure difference can be carried out. In addition, alternatively or additionally, detection of the nitrogen partial pressure or nitrogen amount or nitrogen gradient in the anode system during fluctuations in the pressure difference can be carried out.

The fuel cell for this purpose comprises a corresponding sensor for the measurement of the hydrogen partial pressure or amount of hydrogen and/or for the measurement of the nitrogen partial pressure or amount of nitrogen. In addition, an evaluation unit may be provided that determines the material slope from the measurements and/or performs monitoring of the measurement and/or material slope to a predetermined threshold. The evaluation unit may be a component part of a control device typically provided in a fuel cell system.

When the pressure difference between the anode and the cathode in the intact polymer electrolyte membrane-fuel cell (PEM-fuel cell) fluctuates, a series of system sizes that can be determined directly or indirectly, such as the amount of hydrogen in the anode system or the hydrogen partial pressure or within the anode system The effect of nitrogen or nitrogen partial pressure and the amount of hydrogen in the exhaust gas of the cathode can be neglected.

On the other hand, if the pressure difference between the anode and the cathode fluctuates in the case of a membrane defect, a large influence on the system size is observed.

With one side fluctuation of the anode pressure, for example by fluctuation of the set pressure upon adjustment of the anode pressure, or by one side fluctuation of the cathode pressure, for example if the cathode pressure is regulated, for example, by a throttle valve disposed in the outlet of the cathode, By varying the pressure difference between the cathodes, membrane defects can be detected from the system sizes, such as the amount of hydrogen or partial hydrogen in the anode system, the amount of nitrogen or partial nitrogen in the anode system and the amount of hydrogen in the exhaust gas of the cathode or its slopes. Can be. Specifically, measures described below or a combination thereof are possible according to the availability of the system size.

An increase in the pressure difference between the anode and the cathode increases the hydrogen partial pressure or amount of hydrogen in the anode system regardless of the membrane state. The increase can be detected by pressure and hydrogen sensors in the anode system or indirectly from available system information and by a corresponding evaluation of the system information. In addition, an increase in the pressure difference between the anode and the cathode in the case of a membrane defect increases the amount of hydrogen in the exhaust gas of the cathode, and the amount of hydrogen is monitored by a hydrogen sensor connected after the cathode in the cathode system, that is, the amount of hydrogen in the exhaust gas of the cathode It can be detected by a hydrogen sensor arranged to. In addition, an increase in the pressure difference between the anode and the cathode causes a decrease in the nitrogen amount or nitrogen partial pressure in the anode system, and the nitrogen amount or nitrogen partial pressure can be detected by the pressure and hydrogen sensor in the anode system.

In addition, defects in the polymer electrolyte membrane of the PEM-fuel cell can be estimated from the inverse fluctuation of the pressure difference between the anode and the cathode. When the pressure difference between the anode and the cathode falls to an excess pressure on the cathode side at the time of a membrane defect, the fractional partial pressure or amount of hydrogen in the anode system drops, and the hydrogen partial pressure or amount of hydrogen decreases in the anode system and the hydrogen sensor in the anode system It can be detected by. In addition, when the pressure difference between the anode and the cathode drops to an excess pressure on the cathode side in the case of a membrane defect, the amount of hydrogen in the exhaust gas of the cathode decreases to zero, and the decrease in the amount of hydrogen is detected by a hydrogen sensor disposed in the cathode system. The hydrogen amount in the exhaust gas of the cathode is measured by the hydrogen sensor. In addition, when the pressure difference between the anode and the cathode drops to an excess pressure on the cathode side in the case of a membrane defect, the nitrogen amount or nitrogen partial pressure in the anode system increases. The increase in nitrogen amount or nitrogen partial pressure in the anode system can be detected by pressure measurement in the anode system and hydrogen sensor in the anode system.

The change in partial pressure and material amount can be determined by the pressure and hydrogen sensors in each system area, or by corresponding evaluation methods from indirectly available system information.

In the method according to the invention, an evaluation of the absolute value of the hydrogen partial pressure or the amount of hydrogen and/or the hydrogen gradient in the anode and/or cathode system is preferably made. In particular, limit monitoring is carried out. As an alternative or additionally, an evaluation of the nitrogen partial pressure or the amount of nitrogen in the anode system and/or the absolute value of the nitrogen gradient can be made, in particular limit monitoring can be carried out.

Variations in the pressure difference between the anode system and the cathode system can be caused by variations in the hydrogen pressure in the anode system. As an alternative, fluctuations in the pressure difference between the anode system and the cathode system can be caused by fluctuations in the air pressure in the cathode system or can be caused by a combination of fluctuations in hydrogen pressure in the anode system and fluctuations in air pressure in the cathode system. have.

Basically, two different measures are possible. On the one hand, fluctuations in the pressure difference between the anode system and the cathode system can be caused by an increase in the pressure difference from the anode system to the cathode system. As an alternative, fluctuations in the pressure difference between the anode system and the cathode system can also be caused by a drop in pressure difference from the anode system to the cathode system up to the excess pressure on the cathode system side.

The essence of the present invention is that fluctuations in the pressure difference between the anode system and the cathode system in the event of a membrane defect directly cause changes in the amount of hydrogen and nitrogen in the anode and cathode systems.

For factory diagnostics, a test operation can be initiated via a diagnostic tester with a corresponding operating state, such as a minimum load of the fuel cell system. The pressure difference is then varied and the available measurements are recorded, such as the hydrogen partial pressure or amount of hydrogen in the anode system and/or the amount of hydrogen in the exhaust gas of the cathode and/or nitrogen or nitrogen partial pressure in the anode system. By comparing the recorded measurement value with a predetermined limit value, detection of a film defect when the limit is exceeded is simply possible.

Thus, a PEM-fuel cell in the category of on-board diagnostics of a vehicle or initiates fluctuations in the pressure difference by corresponding triggering at a constant load point during system operation, such as in no-load condition when the vehicle is stopped or in subsequent operation of the system. It is possible to obtain the inspection results of the PEM-fuel cell stack.

Application in the category of automotive on-board diagnostics is a particularly desirable application. However, in general, the method according to the invention for inspecting PEM-fuel cells can be applied to other mobile and stationary applications and is not limited to automobiles. In the method according to the invention for the inspection of a polymer electrolyte membrane-fuel cell, it is particularly preferred that the fuel cell stack as well as the individual fuel cells can be inspected, since the membrane defects of the individual fuel cells are reliably detected even in the fuel cell stack. This is because only sensors corresponding to individual PEM-fuel cells in the fuel cell stack need to be provided.

According to the present invention, a method for inspecting a polymer electrolyte membrane-fuel cell for detecting a defect in a polymer electrolyte membrane, which enables detection of membrane defects in the category of factory diagnosis and in the category of on-board diagnostics of automobiles without additional sensors, Is provided.

An embodiment of the invention is illustrated in the drawings and described in detail below.
1 is a graph showing the change over time of different system parameters when the pressure difference in a PEM-fuel cell fluctuates in the presence of a membrane defect.

1 shows the change over time of different system parameters in the event of fluctuations in the pressure difference 1 between the anode and the cathode and in the presence of membrane defects in the PEM-fuel cell. Time t is shown on the abscissa. The vertical axis shows the quantitative change of the pressure difference 1 between the anode and the cathode. In addition, the vertical axis shows the quantitative variation of the nitrogen partial pressure 2 in the anode system, the amount of hydrogen 3 in the anode system and the amount of hydrogen 4 in the cathode exhaust gas.

System parameters are shown during the implementation of the method according to the invention. It appears that the pressure difference 1 between the anode and the cathode descends step by step from the time t1 starting from the original operating state. Based on the changes in the system parameters shown, it is shown how other system parameters change due to the drop in the pressure difference 1 between the anode and the cathode and due to the presence of membrane defects in the PEM-fuel cell. Due to the drop in the pressure difference 1 between the anode and the cathode, the nitrogen partial pressure 2 in the anode system rises. It is also observed that during the stepwise drop in the pressure difference 1 between the anode and the cathode, the amount of hydrogen 3 in the anode system decreases rapidly. In addition, the amount of hydrogen 3 in the cathode exhaust gas drops to zero, because the drop in the pressure difference 1 between the anode and the cathode is carried out to the excess pressure at the cathode side. The excess pressure at the cathode side causes a drop in the amount of hydrogen 3 in the cathode exhaust gas to a zero value.

By observing and evaluating changes in the nitrogen partial pressure 2 at the anode side and the amount of hydrogen 3 in the anode system and the amount of hydrogen in the cathode exhaust gas 4, membrane defects in the PEM-fuel cell can be reliably detected. . This can be done on the one hand by monitoring the limits of one or more of the above system parameters or by detecting and evaluating the slope, especially because the amount of hydrogen 3 in the anode system and the amount of hydrogen in the cathode exhaust gas 4 This is because a sudden drop of each amount due to fluctuations in the pressure difference (1) between the anode and the cathode is observed.

Thus, membrane defects can be detected by threshold monitoring and by tilt monitoring. Combination of limit monitoring and slope monitoring is also possible. In addition, a feasibility check can be carried out by monitoring a number of system parameters.

At time t2, the pressure difference 1 between the anode and the cathode rapidly returns to the original operating state again, and it is shown how the system parameter approaches the starting value again. The nitrogen partial pressure 2 in the anode system gradually returns back to the original value taken before the fluctuation of the pressure difference. Likewise, the measured amount of hydrogen 3 in the anode system and the amount of hydrogen 4 in the cathode exhaust gas return back to the value before the fluctuation of the pressure difference 1 between the anode and the cathode.

1 pressure difference
2 Nitrogen partial pressure
3, 4 hydrogen levels

Claims (10)

A method for inspecting a polymer electrolyte membrane-fuel cell for detecting defects in a polymer electrolyte membrane separating a hydrogen-guided anode system and an air-guided cathode system from each other,
During the constant operating state of the fuel cell, fluctuations in the pressure difference 1 between the anode system and the cathode system are carried out, and during the fluctuation in the pressure difference 1, hydrogen partial pressure or hydrogen amount in the anode system and the cathode system During the detection and fluctuation of the pressure difference, the nitrogen partial pressure 2 or the amount of nitrogen is detected in the anode system,
The variation of the pressure difference (1) between the anode system and the cathode system is caused by the drop of the pressure difference (1) from the anode system to the cathode system. The method according to claim 1, wherein the hydrogen partial pressure or the hydrogen amount in the anode system, or the hydrogen gradient, or the hydrogen partial pressure or the hydrogen amount and the absolute value of the hydrogen gradient, or the hydrogen partial pressure in the cathode system, Evaluation of the hydrogen amount, or the hydrogen gradient, or the hydrogen partial pressure or the absolute value of the hydrogen amount and the hydrogen gradient, or the hydrogen partial pressure or the hydrogen amount in the anode system and the cathode system, or the hydrogen gradient, or the hydrogen A method of inspecting a polymer electrolyte membrane-fuel cell, characterized in that the partial pressure, the amount of hydrogen, and the absolute value of the hydrogen slope are evaluated, and in particular, threshold monitoring is performed. The method according to claim 1, wherein the nitrogen partial pressure (2) or the nitrogen amount in the anode system, or the nitrogen gradient, or the absolute value of the nitrogen partial pressure or the nitrogen amount and the nitrogen gradient is carried out, and in particular, threshold monitoring is performed. A polymer electrolyte membrane-inspection method of a fuel cell, characterized in that. Method according to claim 1, characterized in that the fluctuation of the pressure difference (1) between the anode system and the cathode system is caused by fluctuations in the hydrogen pressure in the anode system. Method according to claim 1, characterized in that the fluctuation of the pressure difference (1) between the anode system and the cathode system is caused by fluctuations in air pressure in the cathode system. Method according to claim 1, characterized in that the pressure difference (1) is caused by a drop from the anode system to the cathode system to an excess pressure on the cathode system side. delete delete delete delete

Images