KR101007153B1 - Optimal Purge Method for Securing Fuel Cell System's Durability in Sub-zero Conditions - Google Patents

Abstract

The present invention relates to an optimal purge method for securing the durability of a fuel cell system in sub-zero conditions. The object of the present invention is to provide a durability after operation of a fuel cell system. In consideration of this, it is to provide a purge method under the maximum energy efficiency to allow sufficient water removal with less energy.

The configuration of the present invention is a purge method for removing residual moisture in a fuel cell system under sub-zero conditions, wherein the temperature of the fuel cell system is higher than that of the general operating state of the fuel cell system to remove internal residual moisture when the fuel cell system is stopped. By purging while controlling the flow rate or purge time of the purge gas supplied while maintaining the temperature range of ℃, the optimal purge method for securing the durability of the fuel cell system in the subzero condition to have the maximum system efficiency and the minimum residual water content It features.

Fuel cell, purge, subzero condition, durability, purge temperature

Description

Optimized purge method for the durable fuel cell systems in below zero temperature condition

The present invention relates to an optimal purge method for securing durability of a fuel cell system in sub-zero conditions. Specifically, the fuel cell system shuts down after operation to remove the remaining reactive gas and to remain in the cell. It is possible to remove enough water with less energy by considering both the water removal level and the additional energy consumed when removing the water in purging operation to remove the moisture in the liquid to ensure the durability of the cell. The present invention relates to an optimal purge method for purging.

A fuel cell refers to a cell that directly converts chemical energy generated by oxidation of fuel into electrical energy. This is a kind of power generation device, and it is basically the same as a normal chemical cell, such as using an oxidation-reduction reaction, but is different from a chemical cell that performs a battery reaction in a closed system. Continuously supplied from this outside, the reaction product is continuously removed out of the system.

Gas fuels using fossil fuels such as methane and natural gas in addition to hydrogen and liquid fuels such as methanol (methyl alcohol) and hydrazine have emerged. The thing below about 300 degreeC is called low temperature type, and the higher one is called high temperature type. In addition, the second generation of high-temperature molten carbonate fuel cells, which are intended to improve power generation efficiency, but do not use precious metal catalysts, are the third generation fuel cells. do.

Looking at the type of such fuel cells, there are phosphate (PAFC), alkali (AFC), polymer electrolyte (PEFC), molten carbonate (MCFC), solid oxide (SOFC) battery and the like.

Among the fuel cells described above, the fuel cell related to the present invention is a polymer fuel cell. The basic structure of a conventional polymer electrolyte fuel cell has a form in which a porous anode, a cathode, and a gas diffusion layer are attached to both sides of the polymer electrolyte membrane, as shown in FIG. 10.

In more detail, the main components of the polymer electrolyte fuel cell include a polymer electrolyte membrane, an electrode (anode, cathode), a gas diffusion layer, and a separator for forming a stack. In particular, the hot-pressing method of attaching two electrodes, an anode and a cathode, to a polymer electrolyte membrane is called a polymer electrolyte membrane electrode assembly (MEA). It is the core of this polymer electrolyte fuel cell.

A fuel cell stack is composed by stacking dozens or hundreds of unit cells in which electrochemical reactions occur. A unit cell or stack may tie both end plates to reduce contact resistance between components. It is pressed by rod or air pressure. Both end plates are provided with connections for the outlet and inlet coolant circulation ports of the reactor body and for the electrical power output.

11 shows a conceptual diagram of a ballard polymer electrolyte fuel cell stack. Of course, in addition to this stack, the actual system consists of a fuel reformer, an air compressor, a heat and water processor, and a power converter.

The polymer electrolyte fuel cell has the advantages of low operating temperature of less than 100 ℃ and high corrosion resistance of electrolyte and high corrosion resistance of electrolyte, and it has few restrictions on installation place, simplifies the structure of structure and enables small installation (water kW installation), and high repetition. It has the advantages of operational safety (convenient operation safety), room temperature operation and short start-up time (emergency and military power supply), so it is suitable for industrial use from 250 kW class module to several tens of kW commercial, several kW residential, 80 kW class. It can be applied to a wide range of products from passenger cars, buses around 150 kW to small fuel cells below 1 kW, as well as subwatt IT applications.

FIG. 12 is an exploded perspective view illustrating the structure of the fuel cell described with reference to FIGS. 10 and 11 in more detail. Current collectors are disposed at both ends, and a polymer electrolyte membrane electrode assembly is disposed at the center. MEA), and gas diffusion layers are located between the current collector and the polymer electrolyte membrane electrode assembly (MEA). In addition, each current collector (Current collector) can be seen that the separator and the gas inlet and outlet tubes are formed.

In addition, the cross-sectional structure of a general fuel cell is composed of a separator engraved with a flow path, a gas diffusion layer, a catalyst layer, and an electrolyte membrane as shown in FIG. 13, through which a reaction gas such as oxygen and hydrogen is supplied and supplied. The reacted gas passes through a gas diffusion layer having a large number of pores, diffuses into the catalyst layer, and a reaction occurs in the catalyst layer. The gas diffusion layer existing between the reaction gas and the catalyst layer is made of a porous medium having a high porosity so that the reaction gas and the product water can pass smoothly.

Among the problems with the conventional polymer fuel cell having such a structure, the most important issue is the uniformity of reaction and water discharge. In order to solve these problems, various types of separator flow paths have been developed, for example, a serpentine channel, a parallel channel and a parallel-serpentine channel.

14 shows a single meandering flowpath with only one flow path. Single serpentine channels are known to have good water discharge performance. Because in a single meander flow path, the reaction gas passes through only one flow path, so that a relatively high flow rate can be maintained, and as a result, the momentum of the gas increases, which is very advantageous to discharge condensed water droplets in the flow path. Because.

FIG. 15 shows a parallel meandering flow path, which is intended to solve the problem of a single meandering flow path, in which a parallel flow path and a meandering flow path are mixed with each other. Parallel meandering flow paths are arranged in parallel with a number of meandering flow paths, which can reduce the length and the number of bends to an appropriate level.

The conventional polymer electrolyte fuel cell as described above is spotlighted as an environment-friendly energy conversion technology having a high power generation efficiency and output density. In order to commercialize this polymer electrolyte fuel cell, low cost and durability are known to be the biggest challenges. In particular, proper water management in a fuel cell is one of the important factors in securing performance and durability of the polymer electrolyte fuel cell.

In addition, as described above, since the polymer electrolyte fuel cell is generally operated at 100 ° C. or lower, the liquid and gaseous water always coexist in the cell. At this time, the liquid water causes a floating phenomenon or a dry phenomenon in the cell according to the absolute amount and the temperature of the fuel cell, which causes the performance of the fuel cell to be degraded. In particular, in the case of automobiles inevitably experience freezing conditions in winter, in this case, if the moisture remaining in the fuel cell stack is frozen, it may adversely affect the performance of the fuel cell. The performance deterioration problem caused by the freezing can be seen as a problem that must be solved for the commercialization of fuel cell vehicles.

Therefore, when the actual fuel cell system is shut down after operation, a purge process is generally performed. The purpose is to remove the reaction gas remaining in the cell, and also to remove the remaining liquid gas. To get rid of moisture.

The purge process has little effect on performance or durability if the amount of remaining water is within a certain level under normal imaging conditions, but may affect cell breakage and operating characteristics under subzero conditions where water freezes. In particular, when the amount of remaining moisture is large, physical breakage occurs in the cell due to the formation of ice, which results in poor performance and durability. Thus, when the fuel cell system is operated under sub-zero conditions, an appropriate purge is required to remove water when the device is stopped.

In particular, research on the deterioration of fuel cells (cells) under subzero freezing conditions has been actively conducted, and the number of reports on this has been increasing recently. The main causes of the deterioration are the physical breakdown of the electrode or the gap between the electrolyte membrane and the electrode layer. We report by tally, etc.

For example, as reported by Los Alamos National Lab., The cause of performance degradation is the increase in cell resistance due to interfacial peeling.

In addition, a report presented by Fraunhofer ISE, Germany, revealed a situation where the surface of an electrode that had experienced subzero conditions was physically damaged. Even when the electrode layer was damaged, GDM (Gas Diffusion Media) itself did not show any visible damage. I'm reporting.

In addition, the report published by Los Alamos National Lab. Reported that the degree of performance degradation under freezing conditions may vary according to the type of GDM. In the case of carbon cloth, the degree of performance deterioration is much lower than that of carbon paper. I'm reporting. In addition, when the temperature change rate at the time of freezing is faster, performance degradation is reported to be more severe. (Conference Information: 3rd Annual International Conference on Fuel Cells Durability & Performance, November 15-16, 2007, Mianmi, FL, USA.)

According to the existing reports and patents (US 6,479,177, etc.) to solve the performance degradation or durability problems of the stack of the fuel cell or the unit cell constituting the stack, the condition lower than the general operating temperature of the stack (75 ℃-85 ℃) It is reported that it is advantageous to remove moisture remaining inside. Particularly preferred temperature ranges from 15 ° C. to 30 ° C. are presented.

For reference, the reason why the polymer electrolyte fuel cell stack is mainly operated at about 70 ° C. to 80 ° C. is easy to control at the system level to minimize cell floating or dry during normal operation. Because it is a condition. In other words, when a condition in which the relative humidity condition of the cell is about 100% is created, the performance of the cell can be maximized, which is a temperature condition of the cell that is easy to meet.

However, according to the results of the present invention to be described later, it was experimentally found that the water purge process at a higher temperature than the low temperature is much more efficient in removing residual moisture. When the water removal process is performed in the conventional manner, more water is retained when the same flow rate and time are required, which may act as a major factor in deteriorating fuel cell performance. In addition, to achieve the same level of water removal effect, more energy is consumed, which may be disadvantageous in terms of energy efficiency of the entire fuel cell system.

However, since the optimized purge method has not been proposed in consideration of the above-mentioned conventional problems, many problems are caused in fuel cell performance under subzero conditions.

An object of the present invention for solving the above problems is to remove enough water with less energy considering both the water removal level when purging water and the additional energy consumed when removing water in order to have durability after operation of the fuel cell system. It is to provide a purge method in a situation where the energy efficiency is the maximum to enable.

Another object of the present invention is to provide a purge method having an optimal purge condition (flow rate, time, temperature) range for purging water to have durability after operation of the fuel cell system.

Another object of the present invention is that the conventional purge condition is performed at 15 ° C.-30 ° C., which is lower than the average 70 ° C.-80 ° C. level, which is the temperature of the general operating state of the stack constituting the fuel cell. It is to provide a purge method to minimize the residual moisture in the stack or cell by purging the water at a temperature of 75 ℃-95 ℃ higher than the temperature level.

The present invention, which achieves the object as described above and the problem to eliminate the conventional defects in the purge method for removing residual moisture in the fuel cell system under sub-zero conditions, the internal residual moisture is removed when the fuel cell system is stopped In order to purge while controlling the flow rate or purge time of the purge gas supplied while maintaining the temperature range of 75 ℃ to 95 ℃ to ensure the maximum system efficiency and the minimum amount of residual water fuel It is achieved by providing an optimal purge method for ensuring durability of the battery system.

The flow rate of the purge gas is controlled to 600 ~ 1200 mA / cm ² based on the active area of the unit cell constituting the stack of the fuel cell system.

The total flow rate of the purge gas is determined by multiplying the number of unit cells constituting the stack by a value of 600 to 1200 mA / cm ² .

The purge time is controlled to be 30 to 60 seconds based on the time the purge gas passes through the stack of the fuel cell system.

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The gas is characterized in that any one or more than one selected from nitrogen, air, hydrogen, reforming gas.

The object to which residual moisture is to be removed in the fuel cell system is characterized by including a manifold of the stack, a separator flow channel, a gas diffusion layer, an electrode catalyst layer, and an electrolyte membrane constituting the unit cell.

The flow rate of the purge gas is characterized in that it is supplied so as to have a value range of 70 to 80% and 40 to 50% of the utilization rate, respectively, based on the anode and the cathode as the electrode catalyst layer.

The purge condition is characterized in that the purge irrespective of whether the idling operation is stopped after the normal operation of the fuel cell system.

The purge condition may be purged regardless of whether any kind of stopping process for stopping the fuel cell system is performed before or after the purging process.

The system efficiency is characterized in that the amount of water remaining in the unit cell compared to the amount of additional electrical energy consumed for purging.

The present invention provides a range of optimal purge conditions (flow rate, time, temperature) considering both the water removal level when purging water and the additional energy consumed when water is removed to ensure durability when the fuel cell system is applied under sub-zero operating conditions. By having enough energy to remove enough water with less energy, the energy efficiency is high,

It is a useful invention that is expected to be used industrially as a useful invention having the advantage of minimizing the amount of residual water in the stack or the cell than by the conventional purge for purging moisture at a higher temperature of the stack than the conventional purge method.

The present invention purges for the purpose of minimizing the amount of water remaining in the unit cell in order to reduce the degree of performance degradation of the stack and the unit cell constituting the stack when the fuel cell system is stopped at subzero conditions. When purging, it relates to the fuel cell system shut-down process and conditions for obtaining maximum system efficiency and minimum residual water content.

In particular, the present invention can fully achieve the desired effect only if the temperature, flow rate, and time factors satisfy a condition of a certain level or more. In particular, the temperature conditions are for purging water at 75 ℃-95 ℃ higher than the average 70 ℃-80 ℃ level of the general operating state of the stack, unlike the purge temperature (15 ℃-30 ℃) disclosed in the prior art Promoting purge is the main point. That is, although the prior art discloses that a purge condition of a low temperature range is preferable, the present invention is characterized in that the temperature of the purge is set to a temperature higher than that of the conventional general operation.

The fuel cell system according to the present invention refers to the above-described polymer fuel cell system. In particular, the main object of removing moisture in the configuration of the fuel cell system according to the present invention is a manifold of the stack among the elements constituting the conventional polymer fuel cell system. And a separation plate flow path, a gas diffusion layer, an electrode catalyst layer (refer to the air electrode and the fuel electrode), and the electrolyte membrane constituting the unit cell.

At this time, the purge condition may use a predetermined predetermined condition (flow rate, temperature, time) regardless of the idling operation condition after the normal operation. If an appropriate purge condition is applied to the actual system according to the idling operation conditions, the complexity of the equipment may be increased. In the present invention, the same purge regardless of the idling operation condition (operation history immediately before the device stops) may be applied. Apply the conditions. Specific conditions will be described later.

The purge condition may be effectively applied to any kind of stopping process for stopping the fuel cell system before or after the purging process. If the stop process is to be applied to the actual system for each of the rough conditions before and after the purge process, the complexity of the equipment may be increased, the present invention applies the same purge conditions irrespective of the stop conditions.

In the present invention, the efficiency of the fuel cell system refers to the concept of comparing the amount of moisture remaining in the fuel cell (Cell) against the amount of additional electrical energy consumed for purging.

The gas used for purging in the present invention may be nitrogen, air, hydrogen and reformed gas (gas consisting of 40 to 80% hydrogen, 15 to 25% oxygen dioxide, 5 to 10% nitrogen and a small amount of carbon monoxide and hydrocarbon) can be used. have. The reason for choosing such a gas is because it is highly likely to be used in an actual system, and the spreading body may be mounted inside the fuel cell system or supplied through a separate supply line from the outside of the system.

In the present invention, the purge flow rate purges to have a flow rate range of 600 to 1200 mA / cm ² based on the active area of the unit cell. The reason for limiting the numerical value is that if it is smaller than the lower limit, there is a problem that the pressure resistance value generated between the inlet and outlet of the separator flow path is not sufficient, and there is a high possibility that the water present in the cell cannot be discharged sufficiently. This is because there is a problem that excessive energy is consumed for the operation of the blower, etc. in the process.

Therefore, when the flow rate of the unit cells as described above, the flow rate for purging the stack may be determined by multiplying the number of cells constituting the stack by a value of 600 to 1200 mA / cm ² .

If the purge conditions (flow rate, temperature, time) for such a unit cell are determined, sufficient moisture removal is also possible for components such as a manifold, a separator flow path, a gas diffusion layer, an electrode catalyst layer, and an electrolyte membrane of the stack. In other words. The ultimate goal is to minimize the amount of water present in the components, and the conditions of the invention for achieving these conditions are flow rate, time and temperature conditions, in particular temperature conditions being an important factor.

In the present invention, the flow rate is expressed as a current density value (mA / cm ² ) as a unit indicating the magnitude of the current produced in the fuel cell is directly proportional to the amount of fuel (hydrogen or air) to be supplied. That is, the amount of fuel supplied to obtain 100A is 100 times the amount of fuel supplied to obtain 1A. In fact, to obtain a current of 1A, a flow rate of about 7 ml / min is required based on hydrogen. In addition, the magnitude of the current obtainable from the fuel cell is proportional to the area of the electrode. That is, there can be obtained a 1A in an area of 1 cm ^2, it is possible to obtain the A 100 of the electrode 100 cm ² area. Therefore, if simply expressed in units of flow rate (L / min), since the supply flow rate should be changed according to the capacity of each system, it can be represented by the area-based flow rate uniformly.

In addition, the flow rate preferably has a value range of 70 to 80%, and 40 to 50%, respectively, on the basis of the anode and the cathode, which are the electrode catalyst layers. Here, the concept of utilization rate is different from the theoretical value in the actual system, the fuel cell does not use 100% of the fuel supplied. Therefore, when operating a real fuel cell, it is somewhat excessively supplied. For example, the concept of 80% utilization rate theoretically adds 20 fuels where necessary for 80 fuels and 100 fuels in actual operation. At this point, 20 will not be consumed and will come out of the stack. If the utilization rate is 50%, it is a case where two times the theoretical flow rate is required.

The reason for limiting the numerical value can be explained in common with the anode and the cathode. If the value is smaller than the lower limit, the performance may not be sufficiently obtained, and it may be a major cause of deterioration of fuel cell durability. Large energy is needed to supply fuel and air, which contributes to low energy efficiency in terms of the overall fuel cell system.

In addition, the purge time of the stack constituting the fuel cell or the unit cell constituting the stack according to the present invention preferably has a value between 30 to 60 seconds based on the time that the fluid (purge gas) passes through the stack.

The reason for limiting the value for time as described above is that if it is smaller than the lower limit, there is a problem that the remaining moisture content is still maintained at a high level, as shown in the experimental results to be described later. Even if the water removal effect is not noticeable, there is a problem that the energy efficiency is reduced at the system level.

In addition, the purge start temperature in the above it is advantageous to maintain a high temperature in the range that the stack or the unit cell constituting the stack is not very dry, preferably 75 to 95 ℃ range.

The reason for limiting the value of the purge initiation temperature is that if the lower limit is lower than the lower limit, even if purging is performed for the same flow rate and time, there is a problem in that the water removal efficiency existing in the stack is lowered. This is because performance and durability may be degraded due to excessive drying of the catalyst layer.

In addition, in order to obtain a temperature higher than the general operating temperature of 70 ℃ in the above, it is more preferable to stop the refrigerant for stack cooling first in the process of stopping the fuel cell system. That is, since the electrochemical reaction of the fuel cell is thermodynamically exothermic, if the stack cooling refrigerant is stopped during operation, the stack temperature can be sufficiently increased without additional external heat supply.

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

1 is a graph showing the concept of an experiment to find the optimum water removal condition by checking the change in the amount of water remaining in the fuel cell under various purge conditions, the amount of water removal in the initial conditions during the purge process to remove residual water In many cases, as the purge condition increases, the water removal efficiency can be expected to decrease gradually. In other words, when the amount of water removal reaches a certain level, it is not necessary to continue the water removal process by consuming additional energy, and for practical application, it is necessary to find a combination of individual conditions for high efficiency water removal purge. The general trend according to the process is a graph showing the temperature and purge time of the fuel cell according to the concept of confirming as shown in the figure.

Since the purpose of the water purge after stopping the fuel cell system is directly linked to the durability check under the freezing condition, in the embodiment of the present invention, after confirming the activation and basic performance evaluation of the fuel cell, as shown in FIG. Through the conditions, the freezing / thawing process was repeated, and the change of fuel cell performance according to the amount of residual water was confirmed.

Table 1 below shows measurement conditions for performing FIG. 2. The fuel cell was maintained at 80 ° C, the operating condition of a typical fuel cell system, and the basic performance was measured at 80% relative humidity. At this time, the utilization rate of the fuel was maintained at 75% and 50%, respectively. In the freezing / thawing test, the range of sub-zero 40 ° C. or minus 30 ° C. to 80 ° C. was repeated for a predetermined number of times, and the retention time was controlled to 30 minutes under sub-zero conditions.

Table 1: Measurement Conditions

3 is a graph of an experimental design for comparing the effect of the idle mode on the residual moisture after stopping the fuel cell system after operation.

(A) of FIG. 3 is a graph of a case in which the fuel cell system stops immediately without going through an idle mode after operation of a general fuel cell system, and (b) shows an idle state under a condition of 40 mA / cm ² , which is a low current density range before purging. idle) mode, and (c) is a graph showing the experimental design for the operation stop after going idle mode at the current density value of 160 mA / cm ² before purging.

This experiment is to check the effect of the idle mode (Idle) mode after the three types of (idle) experiments, and to check the difference in the residual moisture content after purge (purge) under the same conditions. According to these results, there is almost no difference in the amount of residual water because the idle process can be removed from the experimental variables to confirm the water removal effect.

In this case, the idle mode refers to a state in which the fuel cell maintains a mode that consumes the minimum power without following the load according to the driving of the fuel cell system such as a fuel cell vehicle. A typical car, for example, is similar to a situation where the engine is running at its default rpm and has not been pressed down.

It can be seen that the idle mode variable according to the experimental design can be removed. That is, after the experiment progress according to the experimental design according to Figure 3, as a result of confirming the standard deviation and the uncertainty of the residual water amount, it was confirmed that even if this variable is removed almost does not affect the overall results. Table 2 below shows such results.

(Table 2. Comparison of Water Residuals after Purging with Children)

4 is a graph showing a change in performance level when freezing / thawing of a fuel cell that does not undergo a purge process, that is, when residual moisture is not removed, and FIG. 5 illustrates freezing / thawing of a fuel cell having a purge process according to the present invention. This is a graph showing the change in performance degradation level according to the removal of residual moisture.

As shown in FIG. 4, the freeze / thaw cycle experiment was performed without purging after removing the fuel cell. After about 50 evaluations, the performance decreased from the initial 10 times, and the performance decreased as the number of tests increased. Appeared constantly.

In addition, the water removal purge for the fuel cell according to FIG. 5 did not show any noticeable performance degradation during 50 freeze / thaw cycles.

6 is an exemplary view showing a device configuration for measuring the effect of the purge condition on the fuel cell on the residual water in accordance with the present invention, the main cause of the fuel cell performance deterioration in the freezing conditions is residual as measured with this device configuration It can be determined that the moisture, and to what extent the residual moisture can be tolerated, it is possible to experimentally determine the residual moisture according to the purge conditions.

In the measurement method, the fuel cell is prepared first, as shown in the drawing, and then water is supplied, the fuel cell is closed, the wet cell is kept at 80 ° C. for one hour, and then the fuel cell is purged according to each condition. Purge conditions are temperature, flow rate (Q is flow rate equivalent to 160 mA / cm ² ), time

7 is a test result of residual moisture amount according to a purge flow rate of a fuel cell according to an exemplary embodiment of the present invention. In this experiment to check the effect of the purge flow rate, the temperature of the fuel cell was fixed at 70 ° C., the purge time was 5 seconds, the flow rate was changed, and the residual water content was measured. When GDL 1 was used in the fuel cell, which had a little degree of waterproofing, and the PTFE used in the waterproofing was about twice as high, the residual water removal effect was confirmed under the same conditions. Basically, when the PTFE content was high, it was confirmed that the absolute amount of residual moisture was kept small. Particularly noteworthy, as shown, when the flow rate increases, the residual water content is rapidly decreased initially, but it can be seen that there is no great water removal effect any more than 4Q. In view of the energy efficiency, it can be seen that the flow rate according to the present invention is sufficient if the flow rate of 4Q ~ 7.5Q level. The upper limit of the flow rate is limited to 7.5Q because a larger flow rate is not desirable given the limit capacity and energy efficiency of the air supply device mounted in the actual system.

8 is a graph showing the results of experiments to determine the residual moisture amount according to the purge temperature of the fuel cell according to an embodiment of the present invention, it can be seen that the higher the purge start temperature, the better the water removal. It can be seen that this result is the opposite of the existing patents (US 6,479,177, etc.) and reports. In the existing patent, it is advantageous to proceed purge at a temperature lower than the temperature of a general operating state, and the temperature below 30 ° C is a more preferable condition. However, according to the embodiment of the present invention, it can be seen that the water removal effect is rather insignificant at the stack temperature of 60 ° C. or lower, and the water removal effect is very large as the purge start temperature is increased. In particular, when the flow rate is large at a high temperature, it can be seen that the water removal effect is greater. According to the above results, the purge temperature according to the present invention was found to be advantageous to purge at a stack temperature of 75 ~ 95 ℃.

If the purge temperature is less than 75 ℃, even if purging for the same flow rate and time, there is a problem that the efficiency of water removal existing in the stack is lowered, and limiting the purge temperature to less than 95 ℃ is due to excessive moisture removal and high temperature Since it may cause physical damage to the electrolyte membrane, it is necessary to limit the maximum temperature during purging to ensure durability of the stack.

9 is a graph showing the results of experiments to confirm the residual moisture amount according to the purge time of the fuel cell according to an embodiment of the present invention, as shown in the figure, it can be seen that the amount of moisture remaining decreases with the purge time at a constant flow rate. . However, if the purge proceeds for about 30 seconds or more at a predetermined flow rate, it can be seen that the water removal effect by purge is no longer great. Preferred purge times according to the invention range from 30 to 60 seconds. When purging in the time range of 30 seconds or less, there is no sufficient level of water removal effect, and even if unfolding is performed for more than about 60 seconds, the water removal effect is small compared to the power consumption, and thus the overall energy efficiency of the fuel cell system. In view of the upper limit for the purge time can be limited as in the embodiment of the present invention.

The present invention is not limited to the above-described specific preferred embodiments, and various modifications can be made by any person having ordinary skill in the art without departing from the gist of the present invention claimed in the claims. Of course, such changes will fall within the scope of the claims.

1 is a graph showing the concept of an experiment to find the optimum water removal conditions by checking the change in the amount of water remaining inside the fuel cell under various purge conditions,

2 is a graph confirming the change in fuel cell performance according to the residual water content after a specific purge condition and repeating the freezing / thawing process after the operation of the fuel cell after confirming the activation and basic performance evaluation,

3 is a graph designed to compare the effect of the idle mode after the operation of the fuel cell system before the stop on the residual water content,

4 is a graph showing a change in performance degradation level when freezing / thawing of a fuel cell that has not been purged, that is, when residual moisture is not removed.

5 is a graph showing a change in performance degradation level according to the presence or absence of residual moisture during freezing / thawing of a fuel cell having a purge process according to the present invention,

6 is an exemplary view showing a device configuration for measuring the effect of the purge conditions for the fuel cell on the residual water in accordance with the present invention,

7 is a test result of residual moisture amount according to a purge flow rate of a fuel cell according to an exemplary embodiment of the present invention.

8 is a graph showing the results of experiments to determine the residual moisture amount according to the purge temperature of the fuel cell according to an embodiment of the present invention,

9 is a graph showing the results of experiments to determine the residual moisture amount according to the purge time of the fuel cell according to an embodiment of the present invention,

10 is a basic structural diagram of a conventional polymer electrolyte fuel cell,

11 is a conceptual diagram of a conventional polymer electrolyte fuel cell stack,

12 is an exploded perspective view showing the structure of a conventional fuel cell.

13 is a structural diagram showing a cross section of a typical fuel cell,

14 is an exemplary view showing a structure of a single meandering flow path in a separator plate form of a conventional fuel cell,

15 is an exemplary view showing a parallel meandering channel structure of a separator plate of a conventional fuel cell.

Claims (11)

A purge method for removing residual moisture in a fuel cell system under subzero conditions, The fuel cell system purges while controlling the flow rate or purge time of the supplied purge gas while maintaining the temperature range of 75 ° C to 95 ° C to remove internal residual water when the fuel cell system is stopped. Optimal purge method for securing durability of fuel cell system under subzero condition, characterized in that the method. The method according to claim 1, The purge gas flow rate is controlled based on the active area of the unit cell constituting the stack of the fuel cell system 600 ~ 1200 mA / cm ² characterized in that the optimum purge method for ensuring the durability of the fuel cell system under sub-zero conditions. The method according to claim 2, The total flow rate of the purge gas is determined by multiplying the number of unit cells constituting the stack by a value of 600 ~ 1200 mA / cm ² value, the optimum purge method for securing the durability of the fuel cell system in sub-zero conditions. The method according to claim 1, The purge time is controlled to be 30 to 60 seconds based on the time the purge gas passes through the stack of the fuel cell system, the optimum purge method for ensuring the durability of the fuel cell system in sub-zero conditions. delete The method according to claim 1, The gas is an optimum purge method for securing the durability of the fuel cell system in sub-zero conditions, characterized in that any one or more selected from nitrogen, air, hydrogen, reforming gas. The method according to claim 1, Residual moisture to be removed in the fuel cell system includes a manifold of a stack, a separator flow channel constituting a unit cell, a gas diffusion layer, an electrode catalyst layer, and an electrolyte membrane. Optimal purge method for The method according to claim 1, The flow rate of the purge gas is an optimum purge method for securing durability of the fuel cell system at subzero conditions, characterized in that the supply rate has a value range of 70 to 80% and 40 to 50%, respectively, based on the anode and the cathode as the electrode catalyst layer. . The method according to claim 1, The purge condition is an optimal purge method for securing the durability of the fuel cell system in the sub-zero condition, characterized in that the purge irrespective of whether or not idling operation when the fuel cell system is stopped after normal operation. The method according to claim 1, The purge condition is purged irrespective of whether or not any kind of stopping process for stopping the fuel cell system before or after the purge process, the optimum purge method for securing the durability of the fuel cell system in sub-zero conditions. The method according to claim 1, The system efficiency is an optimal purge method for securing the durability of the fuel cell system in sub-zero conditions, characterized in that the amount of water remaining in the unit cell compared to the amount of additional electrical energy consumed for purging.

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