KR20100130785A - Method for evaluating the performance of fuel cell - Google Patents

Abstract

PURPOSE: A performance evaluating method of a fuel cell is provided to obtain a return value reliable for a determinant of the performance of the fuel cell, and to improve the performance of the fuel cell. CONSTITUTION: A performance evaluating method of a fuel cell comprises the following steps: activating the fuel cell; determining the gathering time for results capable of obtaining the power density for the activated fuel cell, stabilized at a constant voltage; and evaluating the performance of the fuel cell by the temperature. The activation process of the fuel cell includes a step of operating the fuel cell while repeating the increase and the decrease of the temperature.

Description

Method for evaluating the performance of fuel cell

Disclosed is a method for evaluating the performance of a fuel cell, and more specifically, by providing a certain criterion for the performance evaluation of a fuel cell, a fuel that can derive an optimized fuel cell in a short time by using an experimental design method with reliable results. Disclosed is a method for evaluating performance of a battery.

Recently, with the development of science and technology, the need for a high capacity power supply is increasing. However, the existing secondary battery does not satisfy this need, and has the disadvantage of having a short time and a long life of recharging. . As a solution to this, environmentally friendly, high energy density and long life fuel cells are attracting attention as the next generation power source.

Such fuel cells are polymer electrolyte membrane fuel cells (PEMFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC) depending on the type of electrolyte used. cell), solid oxide fuel cell (SOFC), etc., depending on the electrolyte used, the operating temperature of the fuel cell and the material of the components are different. A typical example of a direct fuel supply type is a direct methanol fuel cell (DMFC), and a direct methanol fuel cell generally uses an aqueous methanol solution as a fuel and a hydrogen ion conductive polymer electrolyte membrane as an electrolyte. DMFC also belongs to PEMFC. PEMFCs can achieve high power density, even at small and light weights. Moreover, the use of PEMFCs simplifies the construction of power generation systems.

The basic structure of a fuel cell typically includes an anode (fuel electrode), a cathode (oxidant electrode), and a polymer electrolyte membrane disposed between the anode and the cathode. The anode is provided with a catalyst layer for promoting the oxidation of the fuel, and the cathode is provided with a catalyst layer for promoting the reduction of the oxidant. In the anode, the fuel is oxidized to produce hydrogen ions and electrons, the hydrogen ions are transferred to the cathode through the electrolyte membrane, and the electrons are transferred to the external circuit (load) through the conductor (or current collector). In the cathode, water is generated by combining hydrogen ions transferred through the electrolyte membrane, electrons transferred from an external circuit through a conductor (or current collector), and oxygen. At this time, the movement of electrons via the anode, the external circuit and the cathode is power. In order to improve the performance of such a fuel cell, it is necessary to further refine performance determining factors. The membrane electrode assembly can be further subdivided according to the type of material (catalyst, membrane, binder, gas diffusion layer, etc.) and the physical properties (density, active area of active metal, film thickness, gas permeability, etc.) of each material. There is a direct correlation, and depending on the method of manufacturing the membrane electrode assembly, the performance has various values. In addition, the performance of the fuel cell may vary greatly depending on the type of material, the physical properties, the bonding method, and the operating conditions (fuel, temperature, humidity, etc.) of the configured fuel cell. This is an indication that there are too many factors to consider because the reaction in a fuel cell is due to a combination of factors. However, to this day, only individual research activities on each material, joining method, and operating conditions are changed, and the interpretation of numerous cumulative results studied over the world for a long time does not have a certain reference point, so the results of each other There is a difficulty in mutual trust, and thus, duplicate experiments are being conducted for the same experimental direction. This suggests that in the context of complex performance determinants, studies in each field do not obtain reliable evaluations of their findings in a complex integrated environment.

One aspect of the present invention is to obtain a reliable result for the determinants of the performance of the fuel cell, and based on these results can provide the design of the fuel cell of the optimum conditions and the performance improvement of the fuel cell in a short time. It is to provide a method for evaluating the performance of a fuel cell.

According to one aspect of the invention,

Activating the fuel cell;

Determining a result collection time for the activated fuel cell to obtain a stabilized power density at a predetermined voltage; And

According to the determined result collection time is provided a method for evaluating the performance of the fuel cell comprising the step of evaluating the performance of the activated fuel cell for each temperature.

The activating of the fuel cell may include driving the fuel cell while repeating the temperature increase and the decrease in temperature at a temperature of 30 ° C. to 100 ° C. at room temperature.

Determining the result collection time,

Determining a target temperature, a target voltage, and a voltage variation measurement time;

Setting a current value at the target voltage of the activated fuel cell as a reference current value;

Measuring a change amount of the voltage at the reference current value according to the voltage change amount measurement time; And

It may include the step of setting the time the amount of change in the measured voltage is 0.01 to 1.0 mV / s as a result collection time.

The method may further include verifying the result collection time, after the determining of the result collection time and before evaluating the performance of the activated fuel cell for each temperature.

The step of verifying the result collection time may be a step of measuring a change in current at each voltage while changing the voltage during the result collection time, and evaluating whether the measured change amount of the current is 1% or less.

Evaluating the performance of the fuel cell for each temperature may include determining a measurement temperature; And measuring the power density according to the voltage after the operation temperature of the fuel cell reaches the measurement temperature and the result collection time has elapsed.

After evaluating the temperature-specific performance of the fuel cell, the method may further include evaluating the durability of the fuel cell.

The method for evaluating the performance of a fuel cell according to an embodiment of the present invention provides a standard for evaluating the performance of a fuel cell composed of different components and comparing the results with each other. It provides compatibility of research results between countries and efficiency of production, which can shorten the time for commercialization of fuel cells.

Hereinafter, the present invention will be described in more detail.

Method for evaluating the performance of a fuel cell according to an embodiment of the present invention comprises the steps of activating the fuel cell; Determining a result collection time for the activated fuel cell to obtain a stabilized power density at a predetermined voltage; And evaluating temperature-specific performance of the activated fuel cell according to the determined result collection time.

In the present invention, the activation step is a step of activating the battery in an atmosphere that minimizes the deterioration factor in order to see the optimum performance of the component material that can act as a performance determinant. Examples of the performance deterioration factor include drying the electrolyte membrane and methanol cross-over to the cathode. In the process of manufacturing the electrode membrane assembly (MEA), since the electrolyte membrane is dried to a certain level by hot-press, it is necessary to keep the electrolyte membrane sufficiently wet for optimum performance. In addition, in the electrode layer in the electrode membrane assembly, a passage through which fuel and hydrogen charges can move is smoothly formed within the microstructure of the catalyst and the binder.

To this end, the step of activating the fuel cell includes the step of operating the fuel cell while repeating the temperature increase and temperature decrease in a temperature range of a certain range.

The temperature section in which the temperature increase and the temperature reduction are repeated for the fuel cell is, for example, 30 to 100 ° C, 30 to 80 ° C, and 30 to 70 ° C. If the lower limit of the temperature range is less than 30 ℃ activation efficiency is lowered, if the upper limit is more than 100 ℃ fuel efficiency may be lowered by the evaporation of the solution used as fuel.

The number of times the temperature increase and the temperature reduction are repeated, for example, 3 to 10 times, 3 to 8 times, 3 to 5 times. If the number is less than 3 times, the activation becomes poor and it is difficult to determine the performance of the fuel cell.

As a result, it is possible to form a passage for charge by fuel, and at this time, the amount of fuel injected into the cathode can be lowered to a small amount, for example, 50cc or less, in order to prevent drying of the electrolyte membrane.

Specifically, for example, by injecting a fuel of an air electrode capable of maintaining a voltage of 0.3 to 0.55 V, a natural chemical reaction in the catalyst layer can be induced.

If the voltage maintained during the cathode fuel injection is less than 0.3V, methanol fuel may have a relatively large amount of supply compared to air, resulting in a disadvantage of methanol crossover. If the voltage is more than 0.5V, the electrolyte membrane may be dried.

As the temperature and the temperature of the battery are repeated while the amount of the cathode is controlled, the charge transfer passage in the electrode is smoothly formed, and the electrolyte membrane can also be maintained in a condition that does not dry, thereby creating an atmosphere that can exhibit optimal performance. .

One specific embodiment of the step of activating the fuel cell is as follows.

That is, the temperature increase and the temperature reduction are repeated five times in a state in which the air supply is reduced from room temperature to 80 ° C. The repeated process of the temperature increase and temperature decrease, after reaching 80 ° C., is maintained for 30 minutes, the temperature is naturally reduced to room temperature, the fuel supply is stopped at room temperature, the fuel outlet is blocked, the operation is stopped for 20 minutes, and the temperature is increased again in the same process. Repeat the temperature and temperature. In this case, when the temperature is changed, the injection amount of air is 10 cc / min, the injection amount of methanol is 1 cc / min, when the temperature is maintained, the injection amount of air is 50 cc / min, the injection amount of methanol can be adjusted to 1 cc / min.

The determining of the result collection time may include determining a target temperature, a target voltage, and a voltage variation measurement time; Setting a current value of the activated fuel cell as a reference current value at the target voltage; Measuring an amount of change in voltage at the reference current value according to the voltage change amount measuring time; And setting the time for which the amount of change in the measured voltage becomes 1.0 mV / s as the result collection time.

Determining the result collection time for obtaining a stabilized power density at a constant voltage of the fuel cell may provide compatibility between individuals, companies, and countries that can use evaluation results obtained from fuel cells having different configurations or operating conditions. To be able. As a result, the importance is important in that it can bring economic effects by reducing the unnecessary time and material consumption required for fuel cell development.

That is, in the evaluation of the fuel cell, the current and voltage values to be measured differ according to the collection time of the current and voltage values. For example, when a reference voltage of a battery desired to be used is 0.4V, if the current amount based on 0.4V at a fixed temperature is measured, the current amount can change over time. This can be said to be a property that can have a different value for each electrode membrane assembly manufactured according to the amount of fuel supplied and the chemical reaction rate in the electrode membrane assembly. In the case of measuring the amount of current at a certain voltage, if the resultant value at the stabilization point cannot be selected, sharing of the selected resultant value with each other may be meaningless.

From this point of view, the activation step is followed by the determination of the result collection time in the temperature for use.

For example, the target temperature may be set within 30 to 100 ° C, 40 to 80 ° C, and 50 to 70 ° C. When the target temperature is less than 30 ° C, it is difficult to determine an accurate result by generating internal heat according to the reaction of the battery. It becomes difficult, and if it is over 100 ° C, there may be a deterioration in fuel loss.

For example, the target voltage may be set within 0.3 to 0.5V. If the target voltage is out of this range, it is difficult to obtain stable power of a desired fuel cell.

In addition, the voltage change measurement time can be arbitrarily determined, for example, it can be determined in less than 1 second. If the voltage variation measurement time exceeds 1 second, an error may increase in the result collection time.

The time for which the amount of change in the measured voltage becomes, for example, 1.0 mV / s or less is defined as the result collection time.

If the measured voltage change amount is greater than 1.0 mV / s, the voltage change amount is large and it is difficult to see a stable result.

The method may further include verifying the result collection time, after the determining of the result collection time and before evaluating the performance of the activated fuel cell for each temperature.

The step of verifying the result collection time may include measuring a change in current at each voltage while changing the voltage during the result collection time, and evaluating whether or not the measured current change amount is, for example, 1% or less. . When the measured amount of change in the current is more than 1%, the stabilization step is performed again.

Referring to Figure 1 will be described the step of determining the result collection time. In this case, the matters shown in FIG. 1 are merely to help a clear understanding of the present invention, and the scope of the present invention is not limited to the embodiment of FIG. 1.

First, the target temperature for use of the fuel cell is set to 60 ° C and the target voltage is 0.4V, and the voltage change amount of the fuel cell is measured when the temperature of the activated fuel cell is stabilized to 60 ° C. At this time, the current amount selected as the reference point is fixed after taking the current amount at 0.4V as a reference point, and the change amount of the voltage is measured as a time for measuring the voltage change amount, for example, 0.5 seconds to 1 second. (See the graph on the left in Figure 1)

Subsequently, the change in the voltage value for 300 seconds is measured based on the current value at 0.4 V, and the time for which the time-varying voltage change value of the measured voltage value becomes 1 mV / s is determined as the result collection time. See center graph)

According to the determined result collection time, a current-voltage curve result can be obtained in a low voltage direction (forward direction) at a high voltage, and a current-voltage curve according to a result collection time determined in a high voltage direction (reverse direction) at a low voltage You can get the result.

At this time, by confirming that the current value at the specific voltage obtained in the forward direction is not different from the current value at the same specific voltage obtained in the reverse direction, it is possible to verify whether the result collection time is valid.

The graph on the right side of Fig. 1 measures the current value according to the result collection time determined by gradually decreasing the voltage in the direction of 0.8V to 0.2V, and then increases the voltage in the direction of 0.2V to 0.8V again. It shows the process of measuring the current value according to the collection time.

The finally determined result collection time means the time when the change of voltage disappears while the current is fixed, and after the result, the fuel cell shows a stable power value (voltage X current).

After the verification of the result collection time, the performance of the fuel cell according to the temperature change is evaluated.

Evaluating the performance of the fuel cell for each temperature may include determining a measurement temperature; And measuring the power density according to the voltage after the operation temperature of the fuel cell reaches the measurement temperature and the result collection time has elapsed.

The measurement of the power density according to the temperature change is performed in the same manner as the fuel injection of the activation step, and the unmeasured interval between the temperature increase and the temperature decrease of the air is controlled by adjusting the amount of air so that a voltage between 0.3V and 0.5V is formed. Before the measurement is started by injecting fuel according to the fuel equivalent ratio. That is, only the minimum air flow rate is supplied in order to prevent performance degradation due to drying of the electrolyte membrane due to excessive air injection into the fuel electrode.

In order to measure each temperature step, the measurement should be carried out after stabilizing time for a certain time after reaching the measurement temperature, and the fuel is supplied with reduced air supply at the temperature raising and lowering of the temperature. The fuel set as the standard is supplied and the result value is collected by the result collection time.

According to an embodiment of the present invention, the method for evaluating the performance of the fuel cell may further include evaluating the durability of the fuel cell after the step of evaluating the performance of each fuel cell for each temperature.

Endurance evaluation consists of repeating the process of measuring the current value by operating the fuel cell for operation time required, for example, 29 minutes and 30 seconds, and then stopping the operation for 30 seconds. Ending the durability assessment when it is more than 10% of the initial measured value.

By using the method for evaluating the performance of a fuel cell according to an embodiment of the present invention, obtaining and analyzing result values according to changes in various operating conditions of the fuel cell, and applying the analyzed results to the experimental design method, It is possible to efficiently provide fuel cells with optimal conditions.

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.

Figure 1 illustrates the step of determining the result collection time according to an embodiment of the present invention.

Claims (7)

Activating the fuel cell; Determining a result collection time for the activated fuel cell to obtain a stabilized power density at a predetermined voltage; And And evaluating performance of the activated fuel cell for each temperature according to the determined result collection time. In claim 1, The step of activating the fuel cell is a method of evaluating the performance of a fuel cell comprising the step of operating the fuel cell while repeating the temperature increase and temperature reduction at a temperature of 30 ℃ to 100 ℃ at room temperature. In claim 1, Determining the result collection time, Determining a target temperature and a target voltage; Setting a current value at the target voltage of the activated fuel cell as a reference current value; Measuring an amount of change in voltage at the reference current value; And And setting the time for which the amount of change in the measured voltage becomes 1.0 mV / s or less as a result collection time. In claim 1, And after the determining of the result collection time, before the evaluating performance of the activated fuel cell for each temperature, verifying the result collection time. In claim 4, The step of verifying the result collection time may include measuring a change in current at each voltage while changing the voltage during the result collection time, and evaluating whether the measured change amount of the current is 1% or less. Method for evaluating performance of fuel cell. In claim 1, Evaluating performance of each fuel cell for each temperature may include determining a measurement temperature; And measuring the power density according to the voltage after the operation temperature of the fuel cell reaches the measurement temperature and the result collection time has elapsed. In claim 1, After the step of evaluating the temperature-specific performance of the fuel cell, the performance evaluation method of the fuel cell, characterized in that further comprising the step of evaluating the durability of the fuel cell.

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