KR20180095987A - Method for activating the membrabne-electrode assembly of the fuel cell - Google Patents

Abstract

The present invention relates to a method for activating a fuel cell membrane-electrode assembly. The method for activating a fuel cell membrane-electrode assembly comprises supplying a flow rate of a reaction fuel calculated according to a stoichiometric ratio in consideration of an output value of current density, thereby shortening a time required for an activation process by controlling the flow rate of the fuel supplied according to the output value.

Description

[0001] The present invention relates to a method for activating a fuel cell membrane-electrode assembly,

The present application relates to a method for activating a fuel cell membrane-electrode assembly.

A fuel cell is a cell that converts chemical energy generated when a fuel such as hydrogen reacts with oxygen into electrical energy, and this energy conversion takes place in a Membrane-Electrode Assembly (MEA) of the fuel cell. The membrane-electrode assembly can be divided into a hydrocarbon-based membrane-electrode assembly and a fluorine-membrane-electrode assembly according to the constituents contained in the electrolyte membrane, for example, the basic components of an ion exchange membrane.

The hydrocarbon-based membrane-electrode assembly has a lower unit cost and lower gas permeability than the fluorine-based membrane-electrode assembly, but has a disadvantage in that it is difficult to maintain moisture in the humidified state. And the activation time of the hydrocarbon-based membrane-electrode assembly is generally longer than the activation time of the fluorine-membrane electrode assembly. The longer activation time is fuel consumption and the higher process cost, so commercialization requires shorter activation time. On the other hand, in the case of the fluorine-based membrane-electrode assembly, activation is not performed well in a low humidification state, and therefore it is necessary to shorten the time required for the activation process when activated under low humidification conditions.

One object of the present invention is to provide a method of activating a membrane-electrode assembly in which the activation process time is shortened.

Another object of the present application is to provide a method of activating a membrane-electrode assembly capable of reducing fuel consumption and reducing the process cost.

The above and other objects of the present application can be all solved by the present application, which is described in detail below.

In one example of the present application, the method of activating the membrane-electrode assembly may be a method performed while changing the voltage applied to the battery at predetermined time intervals.

In another example of the present application, the method of activating the membrane-electrode assembly may be a method of supplying the reacted fuel at a flow rate calculated in accordance with the stoichiometric ratio in consideration of the output value of the current density.

In another example of the present application, the method of activating the membrane-electrode assembly includes a method of supplying the reacted fuel at a flow rate calculated from the time when the output value of the current density has a value larger than a predetermined current density value, Lt; / RTI >

In another example of the present application, the method of activating the membrane-electrode assembly may be a method of supplying the reactant fuel at a fixed flow rate until a time when the current density output value has a value smaller than a predetermined current density value.

In another example of the present application, the voltage applied during the method of the present application may be a constant voltage.

In another example of the present application, the applied voltage applied in performing the method of the present application may be a plurality of constant voltages of different magnitudes.

In another example of the present application, the plurality of applied constant voltages applied in performing the method of the present application can be selected from the operating voltage of the fuel cell and the constant voltage of the size smaller or larger than the operating voltage.

In another example of the present application, one of the voltages applied in performing the method of the present application may be an open circuit voltage.

In another example related to the present application, the times at which each of the plurality of applied constant voltages are held may be set equal to each other, or may be set differently from each other.

In another example of the present application, the method of activating the membrane-electrode assembly may be performed on a unit cell including a membrane-electrode assembly, or on a fuel cell stack in which a plurality of unit cells are stacked.

In another example of the present application, a method of activating the membrane-electrode assembly can be performed on a unit cell or a fuel cell stack including a hydrocarbon-based membrane-electrode assembly.

The method of activating the membrane-electrode assembly according to the present application can shorten the time required for the activation process of the fuel cell, thereby reducing the amount of fuel consumed in the activation process and the operation cost.

FIG. 1 is a graph comparing the time required for the activation process according to each of the examples and the comparative examples.
FIG. 2 is a graph showing the time to reach a specific current density while performing the same activation process as in FIG.
FIG. 3 is a graph showing a change in resistance of the fuel cell with time while the same activation process as in FIG. 1 is performed.

Hereinafter, a method of activating the membrane electrode assembly according to one embodiment of the present application will be described in detail with reference to the accompanying drawings.

The term " activated " as used in the present application means that the battery is provided with a predetermined performance (output) until the fuel cell stack in which a unit cell or a plurality of unit cells are stacked starts to operate normally And the like. The activation can remove the impurities in the electrode to expose the reaction site, and at the same time ensure the movement path of the reaction product and the product. In addition, the hydration in the electrolyte membrane due to the activation makes it possible to humidify the dried electrolyte membrane and to secure the movement path of hydrogen ions. The completion time of the activation process may be a time point at which a predetermined output set in consideration of the specification or use of the battery or the like appears. For example, if the measured current density value at a specific voltage application shows a convergence to a current density of a commercially required level, it can be seen that the activation is completed, that is, the activation is completed. This activation process may be performed on a unit cell or a cell stack in which a plurality of unit cells are stacked.

Unless specifically mentioned in the present application, a unit cell constituting a fuel cell may include a membrane-electrode assembly (MEA) in which an electrochemical reaction takes place. The unit cell includes a gas diffusion layer (GDL) for transferring a reactive gas, a separator plate for supplying a fuel and a flow path formed to discharge water generated by the reaction, and a gasket for preventing leakage of the reaction gas and the cooling water And a gasket. The membrane-electrode assembly (MEA) may include an anode, a cathode, and an electrolyte membrane provided between the two electrodes. In addition, the configuration of the fuel cell is not particularly limited, but a fuel cell configured to exhibit a commercially required level of performance may be used. A fuel cell having a commercially required level of performance is, for example, a fuel which is configured such that a current density of about 1 A / cm ² to about 2 A / cm ² can be output when a voltage of about 0.6 V is applied, Battery.

The term " fluorine-based membrane-electrode assembly " in the present application means a membrane-electrode assembly in which the main constituent used for forming the electrolyte membrane of the membrane-electrode assembly, for example, an ion exchange membrane or the like is configured to contain a halogen element such as fluorine It can mean. Alternatively, the membrane-electrode assembly in which the main constituent of the electrolyte membrane is made of a hydrocarbon-based polymer may be referred to as a " hydrocarbon-based membrane-electrode assembly ".

Further, unless otherwise specified in the present application, the term " reactive fuel " may mean a material used to generate chemical energy that can be converted into electrical energy in the fuel cell. For example, the reactive fuel may be meant to include hydrocarbons such as hydrogen, methanol, butane, and air (oxygen).

In one example of the present application, the present application relates to a method of activating membrane-electrode assemblies. The activation method can shorten the time required for the activation process by controlling the flow rate of the fuel supplied according to the output value. The output may be, for example, a current density measured according to an applied constant voltage.

Regarding the current density measured at the time of applying the constant voltage, the battery before the normal operation has a commercially required output level, that is, an output of a commercially required level due to impurities in the electrode, unexamination of the reaction site, The current density can not be displayed at the time of applying the voltage. This is also the case for a battery that has been put into the activation process. Therefore, even when a constant voltage is applied for a predetermined time, a desired level of current density can not be obtained at a time. For example, as shown in FIG. 1, the current density measured during the application of the constant voltage may show a tendency to increase from a small initial output to a large value. After a certain period of time when the constant voltage is applied, Can converge to a specific current density at the considered level.

As described above, since it takes a considerable time to complete the activation, that is, to converge the current density to a specific value, in the related art, the reaction of the fuel cell is rapidly induced by supplying the excessive amount of the reactive fuel for a predetermined time, And to reduce the time required for the increase. However, the excessive supply of the reactive fuel acts as a large load on the equipment, and the reactive fuel at the excessive flow rate can rapidly dry the membrane-electrode assembly and hinder the hydration in the electrolyte membrane, Lt; / RTI > In view of this, the activation method of the present application can be performed in consideration of the stoichmetric ratio relationship between the current density and the flow rate of the reactive fuel. For example, an increase in the current density measured over time can mean an increase in the response, which may mean that more reactive fuel, for example, more air (oxygen) and hydrogen is required Therefore, in the present application, the flow rate of the supplied reactive fuel is controlled in an amount corresponding to the current density changing in real time, or in an amount necessary for a chemical reaction that may occur at the current density.

In one example, the method of activating the membrane-electrode assembly according to the present application is performed while changing the voltage applied to the battery at predetermined time intervals, and considering the stoichiometric ratio according to the output value of the current density, And may be a method for controlling the flow rate. Accordingly, the present application can avoid the inhibition factor of the activation by the supply of the reactive fuel at the flow rate. On the other hand, as mentioned above, since not only the current density value is increased until the completion of the activation but also the voltage applied in the present application can be changed in size at predetermined time intervals, It can mean that the flow rate of the fuel can be changed in real time. The stoichiometric ratio can be calculated by a person skilled in the art or by computerized means widely known to those skilled in the art.

In one example, the applied voltage may be a constant voltage. The magnitude of the constant voltage is not particularly limited, but may be determined in consideration of, for example, the following operation voltage.

In another example, the applied voltage may be a plurality of constant voltages of different magnitudes. More specifically, the plurality of constant voltages may be selected from an operating voltage and a constant voltage having a magnitude smaller than or greater than the operating voltage. Here, the operation voltage means a voltage applied at the time of actual battery operation after completion of the activation process, and may be in the range of about 0.5 V to 1.0 V in consideration of the commercial demand level.

In one example, one of the applied voltages may be an open circuit voltage. The size of the open circuit voltage is not particularly limited and may vary depending on the configuration of the battery or other conditions. In one example, the open circuit voltage may have the same magnitude as the magnitude of the operating voltage, or it may have a value that is greater or less than the magnitude of the operating voltage.

In one example, the constant voltage may be changed in size at a predetermined time interval. More specifically, the time at which each of the plurality of constant voltages is held may be set to the same or different from each other. In the case of the holding time, though not particularly limited, it is preferable that the holding time is selected in the range of several seconds to several tens of minutes in consideration of the fuel consumption amount and the activation efficiency.

The order in which the plurality of positive voltages are applied is not particularly limited. In one example, an operating voltage, a voltage less than the operating voltage, and an open circuit voltage (OCV) may be applied in sequence, and then thereafter the operating voltage, a voltage less than the operating voltage, OCV) may be applied in order. In addition, the above-described application period can be repeated a plurality of times until the activation completion time point.

In one example, the method of activating the membrane-electrode assembly according to the present application can control the flow rate of the fuel in different ways according to the output value of the current density. More specifically, in the activation method of the present application, one current density value is predetermined, and when the output, that is, the measured current density value has a value larger than the predetermined current density value, the flow rate calculated according to the stoichiometric ratio And when the measured current density value is smaller than the predetermined current density value, the reactive fuel may be supplied at a fixed flow rate. In the early stage of activation, a very small level of output is observed, so that the degree of the chemical reaction that can be generated is very small, and sufficient activation can not be expected. Therefore, in the method of the present application, when a stoichiometric ratio is taken into account at the initial stage of activation, a rather excessive amount of the reaction fuel is supplied at a fixed flow rate to induce sufficient activation, The flow rate of the reaction fuel can be controlled in real time in consideration of the stoichiometric ratio. At this time, the predetermined current density value compared with the output value is not particularly limited as a value that can be set in consideration of the performance required for the battery, the conditions under which the activation process is performed, and the like.

The activation method of the membrane-electrode assembly of the present application can shorten the activation time because it can prevent the activation inhibition by the excessive supply of the reactive fuel, while leading to a sufficient activation process. Particularly, when the method of the present application is carried out for a fuel cell having a hydrocarbon-based membrane-electrode assembly in which water retention is not easy even in a high humidity condition where the relative humidity is 80% or more, the activation time shortening effect can be remarkable. In addition, even in the case of the fluorine-based membrane-electrode assembly having a relatively high moisture-retaining function, the fuel cell having the fluorine-based membrane-electrode assembly can not be used under low humidification conditions It is advantageous to shorten the activation time by using the activating method of the present application. Figs. 1 to 3 specifically show the effects of the activation method of the present application as follows.

FIG. 1 is a graph comparing the activation time between an application example of the activation process according to an example of the present application and an application example of the activation process in which excess reaction fuel is supplied. Specifically, 0.6 V was applied for 5 minutes, and then 0.4 V was applied for 15 seconds, and OCV (open circuit voltage) was maintained for 15 seconds. The constant current was repeatedly applied, As shown in FIG. At this time, 0.5 V to 0.6 V is the voltage at which the output of the fuel cell used is the maximum, and 0.6 V is the operating voltage of the used battery. In addition, 0.4V, not the operating voltage, is a constant voltage given in consideration of a severe condition. In Fig. 1, the comparative example is a case where hydrogen (H ₂ ) is supplied at 1 slpm and air is supplied at 3 slpm. The flow rate ratio of hydrogen: air was fixed at 1.5: 2.0 until the current density of 0.2 A / cm ² was measured. When the measured current density value exceeded 0.2 A / cm ² , And the ratio of hydrogen to air is controlled according to the stoichiometric ratio. Both Example and Comparative Example were performed on a fuel cell configured to include a hydrocarbon-based membrane-electrode assembly. It can be seen from FIG. 1 that when the method of the present embodiment is used, the time point at which the current density measured at the operating voltage converges to a value of about 2.0 A / cm ² is twice or more shorter than that of the comparative example.

2 compares the time required to reach a specific current density while performing the same activation process as in Fig. It can be seen that the arrival times for all of the specified current densities are observed more rapidly in the examples.

3 is a graph showing changes in resistance of the fuel cell over time while the same activation process as that of FIG. 1 is performed. In the case of the embodiment, it can be seen that the degree of change of the resistance as well as the absolute value of the resistance is small compared with the comparative example. This means that the example process provides faster hydration and shorter activation times than the comparative process.

The examples of the present application described above are only disclosed for illustrative purposes. Those skilled in the art will appreciate that various modifications, changes, and / or additions may be made to the examples of the present application within the spirit and scope of the present application. Such modifications, alterations, and additions should be regarded as falling within the scope of the claims of the present application.

Claims (9)

A method for activating a membrane-electrode assembly performed while changing a voltage applied to a cell at predetermined time intervals,
Wherein the reaction fuel is supplied at a flow rate calculated in accordance with the stoichiometric ratio in consideration of the output value of the current density.
The method of claim 1,
Wherein the reaction fuel is supplied at a flow rate calculated according to a stoichiometric ratio from a point at which the output value of the current density has a value larger than a predetermined current density value.
3. The method of claim 2,
Wherein the reactive fuel is supplied at a fixed flow rate until a time when the current density output value has a value smaller than a predetermined current density value.
The method for activating a membrane-electrode assembly according to claim 1, wherein the applied voltage is a constant voltage.
5. The fuel cell system according to claim 4, wherein the applied voltage is a plurality of constant voltages having different magnitudes, and the plurality of constant voltages are selected from an operating voltage of the fuel cell and a constant voltage of a magnitude smaller than or greater than the operating voltage. - Activation of the electrode assembly.
5. The method of claim 4, wherein one of the applied voltages is an open circuit voltage.
6. The method according to claim 5, wherein the times at which the plurality of applied positive voltages are held are set to be equal to each other or set differently from each other.
The method of claim 1, wherein the method is performed on a unit cell including a membrane-electrode assembly, or is performed on a plurality of stacked fuel cell stacks.
9. The method of claim 8, wherein the method is performed on a unit cell or fuel cell stack comprising a hydrocarbon-based membrane-electrode assembly.

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