KR100993657B1 - System and method for judging deterioration of fuel cell - Google Patents

Abstract

The present invention relates to a fuel cell deterioration determination apparatus and method, comprising: measuring fluorine ion concentration or pH value in real time with respect to the effluent of a fuel cell stack in a fuel cell vehicle and calculating the fluorine outflow rate therefrom The present invention relates to a device and a method for determining and alerting an electrolyte membrane deterioration of a stack when a speed is outside a set normal range.

Fuel Cell, Stack, MEA, Electrolyte Membrane, Degradation, Fluorine Ion, Fluorine Release Rate

Description

Fuel cell deterioration determination apparatus and method {System and method for judging deterioration of fuel cell}

The present invention relates to an apparatus and method for determining fuel cell deterioration, and more particularly, to an apparatus and method for determining and alarming an electrolyte membrane deterioration by checking an electrolyte membrane state of a fuel cell stack operating in a fuel cell vehicle.

A fuel cell is a kind of power generation device that converts chemical energy of a fuel into electric energy by electrochemically reacting in a fuel cell stack without converting it into heat by combustion.

Currently, as a power source for driving a vehicle, a type of polymer electrolyte membrane fuel cell (PEMFC) having the highest power density among fuel cells is being researched. Fast power conversion response time.

The polymer electrolyte membrane fuel cell evenly distributes the membrane-electrode assembly (MEA) and the reactors with a catalyst electrode layer having an electrochemical reaction on both sides of the polymer electrolyte membrane in which hydrogen ions move. Gas Diffusion Layer (GDL), which transfers energy, gaskets and fasteners to maintain the tightness and proper fastening pressure of the reactor bodies and cooling water, and a separator plate for moving the reactor bodies and cooling water ( bipolar plate).

In the fuel cell having the above-described configuration, hydrogen as fuel and oxygen (air) as oxidant are supplied to the anode and the cathode of the membrane electrode assembly through the flow path of the separator plate, and the hydrogen is the anode ('fuel electrode' or Oxygen (air) is supplied to the cathode (also known as 'air electrode' or 'oxygen electrode' or 'reduction electrode').

Supplied to the anode hydrogen is a hydrogen ion (proton, H ⁺⁾ and electrons by the electrode catalyst constructed on both sides of the electrolyte membrane (electron, e ^-) are decomposed into, passed through only the hydrogen ion in the optional electrolyte membrane cation exchange membrane The electrons are transferred to the cathode through the gas diffusion layer and the separation plate which is a conductor.

In the cathode, hydrogen ions supplied through the electrolyte membrane and electrons transferred through the separator meet with oxygen in the air supplied to the cathode by the air supply device to generate a reaction.

At this time, a flow of electrons is generated due to the movement of hydrogen ions, and current is generated by the flow of electrons.

The electrode reaction of the polymer electrolyte membrane fuel cell is represented as follows.

[Reaction at the ^{_{anode] 2H 2 → 4H + + 4e}} - (1)

[Reaction at ^{_{cathode] O 2 + 4H + + 4e}} - → 2H 2 O (2)

[Total reaction] 2H ₂ + O ₂ → 2H ₂ O + electrical energy + thermal energy (3)

As shown in the reaction formulas (1) to (3), the hydrogen molecules are decomposed at the anode to generate four hydrogen ions and four electrons. The generated electrons move through an external circuit to generate a current, and the generated hydrogen ions move to the cathode through the electrolyte membrane to perform a cathode reaction. At this time, the theoretical potential is 1.23V.

On the other hand, the electrolyte membrane that is responsible for the transfer of hydrogen ions from the anode to the cathode is very important in terms of durability of the fuel cell stack. In particular, it is important to check the electrolyte membrane state of the fuel cell stack in real time and to ensure the durability of the electrolyte membrane during operation of the fuel cell vehicle.

In order to secure the durability performance, it is important to identify and respond to deterioration phenomena that cause the performance of the fuel cell stack and shorten its lifespan.As a cause of degradation of the electrolyte membrane, mechanical degradation due to heat and pressure, ion contamination, electrochemical Deterioration is mentioned.

Among these, electrochemical deterioration is reported by Rod Borup et al. Due to electrolyte membrane attack of hydrogen peroxide and radicals [Rod Borup et al., "Scientific aspects of polymer electrolyte fuel cell durability and degradation", Chem. Rev. 2007 (107) 3904-3951. According to Rod Borup et al., The reaction is:

[Step 1] H ₂ + Pt → Pt-H (at anode) (4)

[Step 2] Pt-H + O ₂ (diffused through PEM to anode) → ㆍ OOH (radical) (5)

[Step 3] ㆍ OOH + Pt-H → H ₂ O ₂ (6)

[Step 4] H ₂ O ₂ + M ² → M ^{+ + 3} + and OH + OH ^- (7)

[Step 5] ㆍ OH + H ₂ O ₂ → H ₂ O + ㆍ OOH (8)

Factors affecting hydrogen peroxide and radical generation include the operating voltage and temperature of the stack, the relative humidity (relative humidity of the reactant gas supplied to the stack), and the partial pressure of gas (the partial pressure of oxygen in the air supplied to the stack). That is, at high voltage, high temperature, low relative humidity, and high gas partial pressure, the rate of hydrogen peroxide and radical generation is high, thereby increasing the film degradation rate.

In general, as a method of checking the state of an electrolyte membrane, an open circuit voltage (OCV) and an OCV decay rate (ODR) of a fuel cell stack are measured, or an LSV (Linear Sweep Voltametry) measurement method and an fluorine ion elution amount are measured in real time by an electrochemical analysis method. And an ion chromatography apparatus that can be measured by the method.

However, in order to prevent stack deterioration due to the formation of a high potential for a stack mounted on a fuel cell vehicle, U.S. Patent No. 7071405 is applied with a driving technology connected with a resistor, so OCV and ODR measurements are performed to check the state of the electrolyte membrane in real time. Is disadvantageous in terms of stack durability performance.

The LSV method, which is an electrochemical analysis method, requires analysis using a unit cell, so it is difficult to be applied to an actual vehicle stack stacked with hundreds of sheets, which is advantageous as a post analysis method of a stack.

In addition, the ion chromatography device for measuring the amount of fluorine ion leaching in real time is very expensive, so it is not suitable for use in mounting the vehicle to check the electrolyte membrane state to prevent degradation. Therefore, it is installed in the stationary fuel cell evaluation equipment and is used as an analysis equipment.

Accordingly, the present invention has been invented in view of the above, and provides an apparatus and a method capable of determining and alarming degradation of an electrolyte membrane by checking the state of the electrolyte membrane in real time with respect to a fuel cell stack of a vehicle in operation. There is a purpose.

In order to achieve the above object, the present invention provides a fluorine ion concentration meter for detecting the fluorine ion concentration in real time with respect to the stack effluent flowing from the fuel cell stack running in the fuel cell vehicle and one of the pH meter for detecting the pH Species or two species;

Flow rate measuring means for measuring a flow rate of the stack effluent;

The fluorine outflow rate is calculated based on the measured fluorine ion concentration or pH value and the flow rate data of the stack effluent to check the electrolyte membrane state of the stack. However, if the fluorine outflow rate is outside the preset normal range, there is a possibility of degradation of the electrolyte membrane. A controller that determines to be;

It provides a fuel cell deterioration determination apparatus comprising a.

In addition, the present invention, (a) measuring the fluorine ion concentration and pH value in real time with respect to the stack effluent from the fuel cell stack using one or two of the fluorine ion concentration meter and pH meter in the fuel cell vehicle, Measuring the flow rate of the stack effluent using a flow rate detecting means;

(b) The controller calculates the fluorine outflow rate based on the measured fluorine ion concentration or pH value and the flow rate data of the stack effluent to check the electrolyte membrane state of the stack, but if the fluorine outflow rate is outside the preset normal range. Determining that there is a possibility of deterioration of the electrolyte membrane;

It provides a fuel cell deterioration determination method comprising a.

Accordingly, according to the fuel cell deterioration determination apparatus and method of the present invention, it is possible to determine the electrolyte membrane deterioration of the stack in real time in the fuel cell vehicle in operation, so that a rapid response for deterioration prevention is possible in the situation where the deterioration is determined. It is effective.

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

The present invention relates to a device and a method for determining and alarming an electrolyte membrane deterioration that causes a decrease in performance and a shortened durability of a fuel cell stack. In particular, the amount of fluorine ions generated during deterioration of an electrolyte membrane or the resulting stack effluent ( The present invention relates to an apparatus and a method for determining and alerting to a deterioration state of an electrolyte membrane by measuring a pH change of a cathode effluent water / anode effluent water in real time.

When the electrolyte membrane is electrochemically degraded in a polymer electrolyte membrane fuel cell mounted in a fuel cell vehicle, fluorine ions flow out of the MEA. At this time, the fluorine emission rate (FER) can be calculated from the membrane degradation rate.

This FER can be calculated from the concentration of fluorine ions eluted in the stack effluent, and the FER can be calculated simply by measuring the pH since the concentration of fluorine ions is closely related to the pH of the effluent discharged from the stack.

1 is a schematic diagram showing the configuration of the electrolyte membrane deterioration determination and warning device according to the present invention, and shows the configuration of a system for checking and alarming the state of the electrolyte membrane for controlling fuel cell degradation.

The electrolyte membrane deterioration determination apparatus according to the present invention is one of a fluorine ion concentration meter for detecting fluorine ion concentration in real time with respect to the stack effluent flowing from the fuel cell stack in operation in a fuel cell vehicle and a pH meter for detecting pH. Or two measuring instruments; Flow rate measuring means for measuring a flow rate of the stack effluent; The fluorine outflow rate is calculated based on the measured fluorine ion concentration or pH value and the flow rate data of the stack effluent to check the electrolyte membrane state of the stack. However, if the fluorine outflow rate is outside the preset normal range, there is a possibility of degradation of the electrolyte membrane. And a controller that determines to be. In addition, the apparatus of the present invention may further include alarm means for driving the control signal output when the controller determines that there is a possibility of degradation of the electrolyte membrane to alert the degradation of the electrolyte membrane.

Referring to FIG. 1, the fuel cell stack 110 is formed by stacking a plurality of unit cells, and hydrogen and air are respectively supplied to the anode (hydrogen electrode) and the cathode (air electrode) at the inlet pipes 110a and 110e and the valve ( 110b and 110f are supplied, and the generated gas of the exhaust gas and the fuel cell reaction, which are reacted at the anode and the cathode, is discharged through the pipes 110c and 110d and the valves 110g and 110h at the outlet end.

The outlet pipes 110c and 110d of the stack are provided with condensers 120 and 130 capable of condensing moisture in the exhaust gas from the gas outlets of the anode and the cathode, and the condenser includes condensed water and condensed water. Fluoride ion concentration measuring instruments 162 and 167 for measuring the fluorine ion concentration of the stack effluent) or pH meters 161 and 166 for measuring the pH are installed.

The condenser (120, 130) collects the condensate condensed by the exhaust gas from the anode and the cathode of the stack 110 and the generated water generated by the fuel cell reaction, the exhaust gas is removed from the condenser is a gas pipe of the condenser outlet end through (g). In addition, each condenser (120, 130) is provided with a drain pipe (w) for discharging the internal water (the condensate and generated water as stack effluent).

In the present invention, the conventional condenser circulating condenser may be used for cooling the exhaust gas. Radiators 121 and 131 are connected to each condenser 120 and 130, and the refrigerant is circulated between the condenser and the radiator. Heat exchange. As an example, a condenser for circulating a refrigerant maintained at a temperature of −3 to 3 ° C. may be installed, and in contact with the exhaust gas of the stack to condense most of the moisture. In the polymer electrolyte membrane fuel cell operating at 65 ~ 80 ℃, the relative humidity of the fuel cell is usually 40 ~ 90%, so if the gas outlet temperature of the stack is at room temperature or slightly higher than normal temperature, water and saturated steam at the gas outlet of the stack Comes out together. Therefore, in order to prevent fluorine ions or other ions in the vapor from flowing out without being measured, heat is exchanged to condense water as much as possible.

The fluorine ion concentration or pH of the water collected in the condenser 120, 130 for a predetermined time is measured by the fluorine ion concentration measuring device (162, 167) and the pH measuring device (161, 166), the fluorine ion concentration measuring device (Ion Selective Electrode, ISE) It can be installed, and at this time, it is preferable to install the one capable of measuring up to a saturation concentration of 1 × 10 ^-7 M in the measuring range of the electrode. The fluorine ion concentration meter and the pH meter both use a product having high sensitivity, chemical resistance, weather resistance, impact resistance.

In the present invention, any one or both (simultaneous use) of the fluorine ion concentration meter (162, 167) and the pH meter (161, 166) can be used to calculate the fluorine outflow rate that becomes the deterioration determination criteria. Since it is expensive, it is possible to reduce the cost for the system configuration when using a pH meter compared to the case of using a fluorine ion concentration meter.

The fluorine ion concentration measuring instruments 162 and 167 and the pH measuring units 161 and 166 detect the fluorine ion concentration and the pH and apply a signal according to the detection value to the controller 140, and the controller 140 controls the fluorine ion concentration measuring instrument or the pH measuring instrument. After calculating the FER (fluorine outflow rate) using the detected value, if it is out of the preset FER normal range, it is determined that the membrane degradation rate is abnormally high and the alarm means 150 alerts and checks the cause of occurrence. Done.

As described above, the criterion for deterioration determination for the electrolyte membrane is the fluorine outflow rate calculated from the fluorine ion concentration or pH, because the membrane area of the stack varies depending on the vehicle specification.

Equation (9) is a formula for calculating the fluorine outflow rate from the fluorine ion concentration, and the fluorine outflow rate is defined as the amount of fluorine ions discharged per unit time per membrane area.

Fluorine Release Rate (FER) = (Fluorine Ion Concentration × Flow Rate) / (Time × Film Area)

= (Fluorine ion concentration × flow rate) / (membrane area) (9)

Here, fluorine ion concentration: ppm (10 ^-6 g / cm 3)

Flow rate: cm 3

Time: min

Membrane Area: ㎠

Flow rate: flow rate / hour → mlpm (cm 3 / min)

to be.

In order to calculate the fluorine outflow rate from the fluorine ion concentration as described above, the amount (flow rate) of the stack effluent (condensate from the exhaust gas and the water produced by the fuel cell reaction) from which the fluorine ion is eluted, and the stack effluent by this amount It is necessary to know the time that is released from the stack.

Since the membrane area in Equation (9) is a unique value according to the stack specification, in the present invention, the fluorine outflow rate is calculated by measuring the fluorine ion concentration and flow rate of the stack effluent in the condenser, or the fluorine measured in a certain amount of stack effluent in the condenser. It is calculated by measuring the ion concentration and the amount of time that the predetermined amount of stack effluent is discharged from the stack (time collected in the condenser).

Here, the flow rate of the stack effluent refers to the rate of generation of the stack effluent in which the fluorine ion concentration is measured, and the controller generates fluorine from the generation rate (= flow rate = flow rate / hour) of the stack effluent in which fluorine ion concentration and fluorine ion are eluted. The outflow rate will be calculated.

The flow rate of the stack effluent is the amount of effluent discharged from the stack to the condenser per unit time and is measured by the flow rate measuring means. In Equation (9), the flow rate is a flow rate concept to be measured as time, and the flow rate measuring method is a method of using a flow meter (flow rate) and a method of measuring a time until a certain volume of water is filled in the condenser ( Flow rate / hour) are all possible.

When using the flow meter (164a, 169a) as the flow rate measuring means, in order to measure the flow rate of the water discharged from the condenser (120, 130) to install the flow meter on the water outlet side of the condenser, that is, the drain port or drain pipe (w) connected thereto After that, the detection value of the tachometer is input to the controller 140.

On the other hand, in the case of measuring a time for filling a certain amount of water, the condenser 120,130 having a drain pipe (w) through which water can be discharged and the electronic open / close valves 164b and 169b installed in the drain pipe. And, using the flow rate measuring means consisting of the upper water level sensor (163a, 168a) and the lower water level sensor (163b, 168b) installed in the condenser (120, 130).

More specifically, first, the upper water level sensors 163a and 168a and the lower water level sensors 163b and 168b are installed in the condenser 120 and 130, and the control of the controller 140 is provided in the drain pipe w through which water is discharged from the condenser. The electronic on-off valves 164b and 169b are installed to be discharged under the condenser.

At this time, in order to calculate the fluorine outflow rate as shown in Equation (9), it is necessary to know the time to fill the water in the condenser 120, 130 by the predetermined volume in addition to the fluorine ion concentration. That is, in Equation (9), the flow rate is a volume (which is a condenser design value) in which water is filled between the lower water level sensors 163b and 168b and the upper water level sensors 163a and 168a in the condenser 120 and 130, and the time is The volume of water is the time to be filled, the controller 140 measures the time the water is filled in a state in which the volume between the lower water level sensor and the upper water level sensor is input in advance, using the volume and time equation (9) Fluorine release rate is calculated.

The electronic on / off valves 164b and 169b are provided to open and close the drain pipe w under the control of the controller 140. The controller 140 has a lower water level sensor through the drain pipe in the state where the electronic on / off valve is opened. After the water is discharged to the water level detected by the water level 163b and 168b, the closing valves 164b and 169b are closed, and the water is filled up to the water level detected by the upper water level sensors 163a and 168a during the stack operation. Will be measured. After the time at which the water is filled up to the level detected by the upper water level sensors 163a and 168a is measured, the controller 140 opens the on / off valves 164b and 169b again to be sensed by the lower water level sensors 163b and 168b. The water will be discharged to the water level. As such, the controller measures the time during which the water is filled by the predetermined volume from the signals of the upper and lower water level sensors, and opens the on / off valve to discharge the water when the water is filled by the predetermined volume. Repeatedly.

In the above method, the flow rate data of the stack effluent is obtained from the time when the water in the condenser is discharged to the lower level sensor and then refilled to the upper level sensor and the volume between the two level sensors. Since the velocity is calculated, the interval between FER data is determined by the volume between the lower and upper level sensors in the condenser.

The flow rate data of the stack effluent can be obtained from the volume and the measured time between the two water level sensors, so that the controller can calculate the fluorine from the fluorine ion concentration (measured value of the fluorine ion concentration meter) measured from the flow rate data and the stack effluent collected in the condenser. The outflow rate can be calculated.

In addition, said fluorine ion concentration has a correlation with pH, and following formula (10) is a formula which shows a correlation between fluorine ion concentration and pH.

^{pH = 4.31 - 0.88log [F -} ] (10)

Here, [F ^-] is a fluorine ion concentration, expression from the pH value detected by the fluorine ion concentration instead of pH measuring devices (161 166) (9) and (10) a fluorine flow rate (FER) can be calculated by using have. That is, since fluorine ion concentration and pH have a close correlation as shown in Equation (10), the fluorine outflow rate can be calculated even by measuring only pH instead of fluorine ion concentration.

In the process of determining the degradation of the electrolyte membrane, the condenser may be installed at either one of the cathode outlet end or the anode outlet end of the stack, or as shown in FIG. 1, provided that both the cathode outlet end and the anode outlet end are both installed. If any of the fluorine outflow rates calculated from the fluorine ion concentrations detected by both condensers is outside the specified range, it is possible to determine and alert that the degradation of the electrolyte membrane is accelerating.

On the other hand, in the present invention, the FER is calculated by measuring the fluorine ion concentration or pH of the stack effluent, and when the FER value is outside the preset normal range, the acceleration and deterioration of the membrane degradation rate is determined and alarmed while the degradation factor is controlled. It is possible to prevent the reduction of the life of the electrolyte membrane by.

In the present invention, the deterioration factor that causes the increase in the film degradation rate may be the operating voltage and temperature, relative humidity, and gas partial pressure of the stack. That is, if it is determined that the deterioration acceleration situation is based on the FER value, driving of the vehicle and the stack so that these deterioration parameters are within the normal range based on the voltage, temperature, relative humidity, and gas partial pressure of the stack measured in real time by the sensor means. To control the condition.

To this end, the electrolyte membrane deterioration determination and warning device according to the present invention, as shown in Figure 1, the voltage sensor 111 for detecting the operating voltage of the fuel cell stack 110, and to detect the operating temperature of the stack Temperature sensor 112, a humidity sensor 113 for detecting the relative humidity of the reaction gas supplied to the stack and a humidity sensor 113 for detecting the relative humidity of the air supplied to the hydrogen supplied to the anode or the cathode, A sensor for measuring the partial pressure of oxygen in the air to be supplied includes an oxygen sensor 114 for detecting the concentration of oxygen in the air supplied to the cathode.

These sensors can be used sensors that are pre-installed in the fuel cell system, the voltage sensor 111 for detecting the operating voltage of the fuel cell stack can use the voltage sensor included in the existing voltage monitoring system, the fuel As the temperature sensor 112 for detecting the operating temperature of the battery stack, a coolant temperature sensor on the stack inlet side may be used (see FIGS. 14 and 15). In addition, the humidity sensor 113 may be an anode inlet side or a cathode inlet side of the humidity sensor (indicated by the reference numerals 113a and 113b in FIGS. 14 and 15), the oxygen sensor 114 as the air blower outlet end The oxygen sensor installed in the can be used (installed between the air blower 106 and the humidifier 107 in Figs. 14 and 15). Examples of the oxygen sensor may include an YSZ sensor (Yittra Stabilized Zirconia sensor), a resistive sensor, and the like.

Accordingly, the controller can check and alert the possibility of deterioration of the electrolyte membrane using the detection value of the fluorine ion concentration meter or the pH meter, and at the same time determine the cause of the deterioration. When the detection value of any one of the relative humidity and the gas partial pressure is out of the preset normal range, a corresponding response is made. That is, the stack operation is performed to reduce the deterioration rate of the electrolyte membrane in order to find a factor that causes deterioration and control the factor to a normal range. For example, if the temperature of the stack is above 90 ° C, the unit cell voltage is above 0.9V, or the relative humidity is 20%, the operation of the vehicle and the stack to maintain the normal temperature, voltage, and relative humidity The condition is controlled. In this case, as described below, the operating conditions are controlled by differentiating the deterioration factors.

The present inventors experimentally examine the effects of stack operating temperature and voltage, relative humidity (relative humidity of reaction gas supplied to the stack), and partial pressure of gas (oxygen partial pressure in the air supplied to the stack) as the deterioration factors of the electrolyte membrane. As it was confirmed, with reference to the accompanying Figures 2 to 11 will be described first.

Stack temperature

In order to deteriorate the electrolyte membrane by accelerated operation after measuring IV performance ('Initial' in FIG. 2) at 80 ° C. of the polymer electrolyte fuel cell stack, the anode is not humidified and the cathode is gas supplied at 65% relative humidity. , 144 hours of operation at OCV state at 90 ° C., after which the performance of the MEA was measured and shown in FIG. 2. The degree of degradation of the polymer electrolyte membrane was confirmed by measuring hydrogen permeability using LSV (Linear Sweep Voltametry) method and FER (fluorine outflow rate) of cathode condensate. The performance decreased as the temperature increased, the FER also increased as shown in FIG. 3, and the hydrogen permeability also increased as the temperature increased as shown in FIG. 4. As such, as the temperature increases, the film degradation rate increases, and it can be seen that the film degradation rate can be confirmed by FER. In the CV (Cyclic Voltametry) results of FIG. 5 measured to investigate the effect of MEA performance reduction due to catalyst deterioration, the effective surface area of the catalyst hardly changed even after the accelerated experiment, and the decrease in MEA performance of FIG. It can be seen that.

Voltage of stack

After the fuel cell stack was maintained at a current density of 10, 40, and 80 mA / cm 2 for 144 hours under constant anode current conditions, I-V performance was measured to measure the voltage difference before and after the evaluation. As shown in FIG. 6, it can be seen that as the current density increases, that is, the lower the voltage, the smaller the voltage difference, the smaller the performance decrease. 7 compares FER values of 144 hours at each current density. As the current density is higher, the FER is smaller, which shows a tendency similar to that of FIG. 6. As shown in FIG. 6, it can be seen that the degradation of the MEA has a large effect due to deterioration of the polymer electrolyte membrane. The lower the current, the higher the voltage, the more advantageous the generation of hydrogen peroxide and oxygen radicals, and the polymer electrolyte by the hydrogen peroxide and oxygen radicals. The film is degraded, resulting in higher FER.

Relative humidity

The fuel cell stack was operated at an operating temperature of 90 ° C. and a cathode relative humidity of 65%, but operated for 144 hours in an OCV state with varying anode relative humidity. 8 shows the difference from the MEA voltage before deterioration at each current value. As the relative humidity of the anode decreases, it can be seen that the MEA deterioration proceeds more because the voltage difference increases. As a result of measuring the hydrogen permeability of the polymer electrolyte membrane, as shown in FIG. 9, the hydrogen permeability increases as the relative humidity decreases. As a result, the lower the relative humidity, the better the membrane degradation, and as a result, the MEA performance decreases.

Oxygen partial pressure

The fuel cell stack was operated at an operating temperature of 90 ° C., a relative humidity anode of 0%, and a cathode of 65%, but oxygen and air were supplied to the cathode for 144 hours in an OCV state. Figure 10 is an I-V performance curve, it can be seen that the performance decreases more rapidly than the case of using air when using oxygen on the cathode side. This is a result of the deterioration of membrane due to the increase of oxygen permeability and the formation of hydrogen peroxide and oxygen radicals due to the increase of oxygen permeability. Figure 11 is a comparison of the fluorine ion outflow rate, since the fluorine ion outflow is severe when using oxygen it can be seen that the performance degradation shown in the I-V performance curve is due to membrane degradation.

12 is data obtained by experimenting the concentration of fluorine ion (ppm) and pH of the anode condensate under various experimental conditions. It can be seen that the concentration of fluorine ions and the pH of the condensed water are proportional to each other. When the electrolyte membrane deteriorates and the fluorine anion (F ⁻ ) flows out, the hydrogen cation corresponding to the anion is followed. Because of this increase, a close correlation is established between the fluorine ion concentration and the pH value as in the above formula (10). Since fluorine ion concentration and pH are correlated as in Eq. (10), it is possible to use a pH meter that is simpler to operate and more widely used than fluorine ion concentration when measuring electrolyte membrane degradation rate (fluorine outflow rate (FER)). .

In the case of the cathode condensate, like the anode condensate, the fluorine ion concentration and the pH of the condensate are proportional to each other. The fluorine ion concentration and the pH of the cathode condensate are measured under various experimental conditions. You can derive a relationship.

Meanwhile, FIG. 13 is a flowchart illustrating a control method for determining electrolyte membrane deterioration and preventing electrolyte membrane deterioration according to the present invention. The controller 140 has the fluorine ion concentration / pH and flow rate of the stack effluent measured by the fluorine ion concentration measuring instrument 162,167 / pH measuring instrument 161,166 and the flow rate measuring means in each condenser 120,130 installed at the outlet end of the anode and the cathode. Are obtained at predetermined sampling intervals and stored in the memory (S101). The fluorine ion concentration and pH can be obtained by using both or only one of both condensers. Since the fluorine ion concentration and the pH also correlate with each other as in the formula (10), only one of them can be obtained and used. Using these acquired values, FER (fluorine outflow rate) is calculated by equation (9) (S103). At this time, the calculated FER value is compared with the set FER value (F1) to check the degradation level of the electrolyte membrane (S105), where FER <F1, there is no need to take measures to prevent membrane degradation without generating degradation determination and alarm. If not, the membrane deterioration is determined to be an abnormal state over a certain level to generate an alarm through the alarm means (S107), and through each sensor means voltage (V), temperature (T), relative humidity (RH), gas partial pressure ( Oxygen partial pressure) (P _O2 ) is measured at regular intervals and accumulated in the memory (S109). Subsequently, voltage, temperature, relative humidity, and gas partial pressure values are compared with the set values V1, T1, RH1, and P _O2 1, respectively, to determine a factor that deepens the film degradation (S111). Here, if all four conditions of V <V1, T <T1, RH> RH1, P _O2 <P _O2 1 are satisfied, the procedure is terminated, and if any of these variables do not satisfy the film stability conditions, that is, the four conditions If any one of the conditions is not satisfied, the driving conditions of the vehicle and the stack are controlled to satisfy the membrane stability condition with respect to the variable, thereby reducing the membrane degradation rate (S113).

Thus, in the present invention, when it is determined that the degradation level of the electrolyte membrane is above a certain level from the fluorine discharge rate, the membrane is checked by checking the state of the voltage, temperature, relative humidity, and gas partial pressure of the stack, which is a deterioration accelerating factor and a deterioration determination and alarm. The control is performed to maintain the stable condition. The driving conditions of the vehicle and the stack are controlled by a predetermined control process for each factor so that the identified deterioration acceleration factor can be controlled within a setting range for film stabilization. This enables a quick response to prevent degradation in situations where degradation is determined and alerted.

Meanwhile, FIG. 14 is a block diagram showing another embodiment of the deterioration determination device, and does not install a separate condenser at the anode outlet of the stack 110, but uses an existing anode side water trap 102. An example is shown.

As shown in Figure 1, by installing a separate condenser 120 on the anode side is possible to measure the fluorine ion concentration and pH for the anode effluent, in this case, in the vehicle for the installation of a separate condenser system (including radiators, etc.) This requires extra space and costs extra.

The water trap 102 is already installed and used in a conventional fuel cell system, and stack effluent (anode effluent) is stored like the condenser of FIG. 1, and unreacted hydrogen and nitrogen from the anode of the stack 110 are stored. In this case, the water contained in the mixed gas including water vapor is separated and collected. The mixed gas from which the droplets are removed from the water trap is transferred to a hydrogen recycle line, mixed with hydrogen supplied from the hydrogen tank, and then re-injected into the stack.

The water trap 102 may be installed with any one or two of the fluorine ion concentration meter 172 and the pH meter 171, and if a certain amount of water is stored, an electronic valve (discharge valve, not shown) at the bottom of the water trap Is released) and release of water takes place. In addition, since the upper water level sensor and the lower water level sensor are basically provided, it is possible to detect that the water is filled with a certain amount of time. The fluorine release rate can be calculated using the measured value of the concentration or pH meter (see equations (9) and (10)).

Thus, using the existing water trap without installing a separate condenser can maximize the space utilization in the vehicle compared to the configuration of Figure 1, it is possible to minimize the installation cost.

In addition, as shown in FIG. 14, the condenser 130 installed at the cathode outlet of the stack 110 may be connected to the humidifier 107. The water collected in the condenser 130 may be sent to the humidifier 107 to blow an air blower. It can be used to humidify the air supplied through 106.

Referring to FIG. 14, a pH meter 113 and a flow meter 174 are installed at the outlet side of the humidifier from which the air supplied from the cathode of the stack 110 and the stack effluent are discharged, and the fluorine discharge rate is measured from these real-time measured values. It is also possible to acquire.

Of course, if the fluorine outflow rate is obtained from the stack effluent collected in the existing water trap as described above, or the fluorine outflow rate from the stack effluent from the humidifier outlet side, it is also possible to delete the condenser installed at the cathode outlet end of the stack.

In order to calculate the fluorine outflow rate, which is a criterion for deterioration, the fluorine ion concentration or pH for the stack effluent (cathode effluent / anode effluent) is measured at the anode outlet stage condenser, the cathode outlet stage condenser, and the existing Water traps, humidifiers, etc. can be in various positions, and selected or all of these positions can be determined as the measurement position.

If a plurality of fluorine ion concentration meter and pH meter are installed in the entire determination device as shown in the illustrated example, if any of the fluorine outflow rate (FER) data calculated from these measured values is out of the normal range, the controller Degradation of the electrolyte membrane is determined to alarm through the alarm means and to control the deterioration generation factor. After checking the state of the electrolyte membrane, the deterioration factor that causes the deterioration is found and a control process for preventing deterioration is performed as described above.

15 is a block diagram showing another embodiment of the deterioration determination device. As shown in FIG. 15, the condenser is not separately installed at the cathode outlet end of the stack 110, but at the outlet side of the existing humidifier 107. It is possible to configure only the measuring device 173 and the flow meter 174.

The pH meter and flow meter at the outlet side of the humidifier are used to measure the pH value and the outflow velocity of the cathode effluent in the stack, and the condenser at the cathode outlet can be removed compared to the configuration of FIG. 1 to maximize and install the space utilization in the vehicle. Minimize costs. In addition, since the fluorine ion concentration meter is relatively expensive, the installation cost can be further reduced when using a pH meter.

16 to 18 are diagrams illustrating other embodiments, and FIG. 16 shows a cathode side (air side) water trap 102a capable of measuring flow rate data of the cathode effluent of the stack 110. In this water trap 102a, a fluorine ion concentration meter 172a or a pH meter 171a (or both meters) is installed, and water is collected using the water trap 102a. A humidification water supply line connected to the stack air supply line and a humidification water pump 132 of the humidification water supply line are installed to control the amount of humidification.

17 and 18, the flow rate data for the cathode effluent is measured at the rear of the humidifier 107 separately from the cathode-side water trap 102a and the condenser 130. The water trap 102b (upper water level sensor and lower water level sensor) And a discharge valve) and one or two of the fluorine ion concentration meter and the pH meter 171c are installed in the water trap 102c to discharge the fluorine to the cathode effluent collected in the water trap 102c. One configuration is shown that allows the speed to be calculated.

As such, in the present invention, the fluorine ion concentration or pH is measured in real time with respect to the effluent discharged from the stack (cathode / anode effluent) during fuel cell operation to calculate the fire propagation rate, and then the fluorine discharge rate is outside the normal range. In this case, degradation of the electrolyte membrane can be determined.

1 is a schematic diagram showing the configuration of an electrolyte membrane deterioration determination and alarm device according to the present invention;

2 is a view showing I-V performance according to stack operation temperature;

3 is a view showing a fluorine ion dissolution rate for each stack operation temperature;

4 is a diagram illustrating hydrogen permeability according to stack operation temperature;

5 is a CV (Cyclic Voltametry) measurement results for each stack operating temperature,

6 is a diagram showing a stack performance reduction rate for each current density;

7 is a view showing the total fluorine ion dissolution rate by current density,

8 is a view showing a stack performance reduction rate according to anode relative humidity;

9 is a view showing the hydrogen permeability according to the relative relative humidity of the anode,

10 is a view showing the I-V performance after the durability evaluation according to the type of gas used on the cathode,

11 is a view showing the fluorine ion dissolution rate for each endurance time according to the type of gas used on the cathode side,

12 is a view showing a proportional relationship between fluorine ion concentration and pH,

13 is a flowchart illustrating a control method for preventing electrolyte membrane degradation and preventing electrolyte membrane degradation according to the present invention;

14 is a configuration diagram of a deterioration determination device and a fuel cell system employing the same according to another embodiment of the present invention;

15 is a configuration diagram of a deterioration determination device and a fuel cell system employing the same according to another embodiment of the present invention;

16 to 18 are structural diagrams of a deterioration determination apparatus and a fuel cell system to which the deterioration determination apparatus according to another embodiment of the present invention is applied.

<Explanation of symbols for main parts of the drawings>

110: stack 120, 130: condenser

161, 166: pH meter 162, 167: fluorine ion concentration meter

140: controller 150: alarm means

Claims (10)

A fluorine ion concentration meter for detecting fluorine ion concentration in real time with respect to the stack effluent flowing out of the fuel cell stack operating in the fuel cell vehicle and a pH meter for detecting pH; Flow rate measuring means for measuring a flow rate of the stack effluent; The fluorine outflow rate is calculated based on the measured fluorine ion concentration or pH value and the flow rate data of the stack effluent to check the electrolyte membrane state of the stack. However, if the fluorine outflow rate is outside the preset normal range, there is a possibility of degradation of the electrolyte membrane. A controller that determines to be; Fuel cell deterioration determination apparatus comprising a. The method according to claim 1, The measuring device is a measuring device for measuring the fluorine ion concentration or pH for the stack effluent collected in the condenser provided on either or both of the anode outlet and the cathode outlet of the stack, collected on the condenser, And the flow rate measuring means is a flow rate meter installed at the water outlet side of the condenser. The method according to claim 1, The measuring device is a measuring device for measuring the fluorine ion concentration or pH for the stack effluent collected in the condenser provided on either or both of the anode outlet and the cathode outlet of the stack, collected on the condenser, The flow rate measuring means includes an upper water level sensor and a lower water level sensor installed in the condenser, an electronic on / off valve installed at the water outlet side of the condenser, And the controller obtains the flow rate data of the stack effluent from the volume between the lower level sensor and the upper level sensor in the condenser and the time at which the water is filled. The method according to claim 1, The measuring device is a measuring device for measuring the fluorine ion concentration or pH for the stack effluent collected in the water trap is installed on either or both of the anode-side water trap and the cathode-side water trap of the stack, The flow rate measuring means includes an upper water level sensor and a lower water level sensor installed in the water trap, an electronic on-off valve installed on the water outlet side of the water trap, And the controller obtains flow rate data of the stack effluent from the volume between the lower level sensor and the upper level sensor in the water trap and the time at which the water is filled. The method according to claim 1, And the pH meter is installed at a humidifier outlet side through which the air supplied from the cathode of the stack and the stack effluent are discharged, and the flow rate measuring means is a flowmeter installed at the outlet side of the humidifier. (a) Measuring the fluorine ion concentration and pH value in real time on the stack effluent from the fuel cell stack using one or two of the fluorine ion concentration meter and the pH meter in the fuel cell vehicle, and using the flow rate detection means. Measuring a flow rate of the stack effluent; (b) The controller calculates the fluorine outflow rate based on the measured fluorine ion concentration or pH value and the flow rate data of the stack effluent to check the electrolyte membrane state of the stack, but if the fluorine outflow rate is outside the preset normal range. Determining that there is a possibility of deterioration of the electrolyte membrane; A fuel cell deterioration determination method comprising a. The method according to claim 6, The fluorine ion concentration and pH value are measured for the stack effluent collected in each condenser installed at either or both of the anode outlet and cathode outlet of the stack, The flow rate of the stack effluent is measured by the flow rate of the water discharged from the condenser. The method according to claim 6, The fluorine ion concentration and pH value are measured for the stack effluent collected in each condenser installed at either or both of the anode outlet and cathode outlet of the stack, And the flow rate of the stack effluent is measured from the volume between the lower water level sensor and the upper water level sensor of the condenser and the time at which the water is filled. The method according to claim 6, The fluorine ion concentration and pH value are measured with respect to the stack effluent collected on either or both of the anode side water trap and the cathode side water trap, The flow rate of the stack effluent is measured from the volume between the lower water level sensor and the upper water level sensor of the water trap and the time the water is filled. The method according to claim 6, And the pH value and the flow rate of the stack effluent are measured at the outlet side of the humidifier from which air supplied from the cathode of the stack and the stack effluent are discharged.

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