KR101519667B1 - Method for accelerating activation of fuel cell - Google Patents

Abstract

The present invention relates to a method for accelerating the activation of a fuel cell, and more particularly, to a fuel cell acceleration activation method capable of reducing the activation process time and hydrogen consumption amount of the fuel cell stack and reducing the production cost of the fuel cell as compared with the conventional constant current output method and pulse discharge method The purpose of that is to provide. In order to achieve the above object, there is provided a method for controlling a fuel cell, comprising the steps of: discharging and holding a fuel cell such that a current output of a predetermined current density is performed in a loaded state; and stopping the supply of the reactive gas to maintain the fuel cell in a shutdown state A method of activating fuel cell acceleration comprising the steps of:

Fuel Cell, Stack, Activation, Acceleration, Pulse Discharge, Constant Current Output, OCV, Shutdown

Description

[0001] The present invention relates to a method for accelerating activation of fuel cells,

The present invention relates to a fuel cell acceleration activation method, and more particularly, to a fuel cell acceleration activation method capable of shortening an activation process time of a fuel cell stack and reducing a hydrogen consumption amount to reduce fuel cell production cost.

Polyether Electrolyte Membrane Fuel Cells (PEMFC) are more efficient than other types of fuel cells and have high current density and power density, short startup time, and fast response to load changes.

In particular, polymer electrolyte membrane fuel cells are less sensitive to changes in the pressure of reactive gases (hydrogen and oxygen in the air) and can produce a wide range of output. For this reason, it can be applied to a variety of fields such as a power source for pollution-free vehicles, a self-generated power source, a mobile power source, and a military power source.

Polymer Electrolyte Membrane A fuel cell is a device that generates electricity by reacting hydrogen and oxygen electrochemically to generate water. The supplied hydrogen is separated into hydrogen ions and electrons in the anode catalyst, and the separated hydrogen ions are passed through the electrolyte membrane And to the cathode.

At this time, the oxygen in the air supplied to the cathode combines with the electrons entered into the cathode through the external conductor to generate water and generates electric energy. The theoretical potential at this time is 1.23 V, and the reaction formula is as shown in the following reaction formula 1.

A negative electrode _{(Anode): H 2 → 2H} + + 2e -

Cathode: 1/2 O ₂ + 2H ⁺ + 2e ^- → H ₂ O

On the other hand, in order to obtain a necessary electric potential in an actual vehicle, unit cells should be stacked by a required potential, and stacks of unit cells are called a stack (= fuel cell stack).

Each of the unit cells includes a membrane electrode assembly (MEA), and the membrane electrode assembly includes an anode in which hydrogen (H ₂ ) is supplied to both sides of an electrolyte membrane through which hydrogen ions (H ⁺ ) are transferred, (Oxygen) is supplied.

A gas diffusion layer is disposed on the outside of the anode and the cathode including the catalyst layer, and the fuel cell stack in which the membrane electrode assembly, the separation plate formed with the reaction gas and the cooling water flow path are sequentially laminated.

In the fuel cell stack which essentially includes the above-described structure, by causing hydrogen to be an anode fuel and air containing oxygen or oxygen as an oxidant to flow, an electrochemical reaction is caused to generate a high- .

That is, the electrochemical reaction by the reaction gas takes place in the catalyst layer inside the fuel cell, and the generated hydrogen ions move through the electrolyte and the electrolyte membrane in the catalyst layer.

Since the hydrogen ions moving through the electrolyte or the electrolyte membrane travel through the water existing in the electrolyte membrane, the electrolyte and the electrolyte membrane in the catalyst layer must be hydrated sufficiently for the fuel cell to exhibit better performance. In addition, Gas must be smoothly reached to the catalyst layer.

In the fuel cell stack, electrodes such as a cathode and an anode are formed as a catalyst layer by mixing a hydrogen ion transport material such as Nafion with a catalyst such as platinum, The reason for this is as follows.

First, because the reaction path of the reactant is clogged and can not reach the catalyst,

Second, the hydrogen ion transporter, which forms the three phase interface like the catalyst, is not easily hydrolyzed at the beginning of operation,

Third, the continuous mobility of hydrogen ions and electrons is not ensured.

For this reason, in order to secure the steady-state performance after assembling the fuel cell, an activation process for securing the electrode reaction area of three phases, removing impurities from the polymer electrolyte membrane or the electrode, and improving the ion conductivity of the polymer electrolyte membrane is required do.

1 is a view showing the structure of the electrolyte membrane 3 in a wet state.

The purpose of fuel cell activation, also referred to as pre-conditioning or break-in, is to activate a catalyst that does not participate in the reaction, sufficiently hydrate the electrolyte membrane and the electrolyte contained therein, It is in securing the passage.

In general, the activation process performed to reach the maximum performance after assembling the fuel cell may take several hours or several days depending on the operating conditions, and the fuel cell may be operated without reaching the maximum performance due to improper activation.

This inadequate activation procedure reduces the production rate in mass production of fuel cells, causes a large amount of hydrogen use, increases the unit cost of the stack, and maintains low stacking performance.

The activation of the fuel cell is carried out by the fuel cell manufacturers in various different ways, but the main activation method is to operate for a long time under a constant voltage.

As an example, AISIN SEIKI Co. Ltd. Japanese Patent Application No. 2003-143126 discloses a method of activating a solid polymer fuel cell. This method includes activating a fuel cell stack at a low voltage for a long time to a portion where the stacking performance is no longer improved. However, in this case, the activation procedure is simple, but there is a drawback in that it takes a very long time to exhibit the highest performance of the fuel cell.

Korean Patent Application No. 2005-0120743 by the applicant of the present application discloses a method of activating a polymer electrolyte fuel cell to which a step voltage operation is applied in which a voltage cycle is applied to a stack, And a voltage cycle of OCV (1 min) → 0.4 V (5 min) is applied to the stack at a high relative humidity (RH 100%) to shorten the fuel cell activation time to about 3 hours or less. In this case, The efficiency of the fuel cell is deteriorated due to the long time until the maximum output is achieved, and excessive consumption of hydrogen and air during the operation may cause a disadvantage to the price competition of the fuel cell in the future.

FIG. 2 is a view for explaining an example of an activation process according to the related art. The activation process using the pulse discharge method, which is a cycle operation method in which fuel cells are alternately switched to a load state and a no-load state using a load device, FIG. Cell voltage distribution over time during the activation process.

As shown in the figure, the discharge is maintained for 3 minutes under the load state of the high current density (current output per unit area of the electrode) with the reference output of 1.2 or 1.4 A / cm 2, and the system is maintained for 20 seconds in the no-load OCV (Open Circuit Voltage) state . In this case, it takes about 1 hour and 30 minutes to 2 hours for the fuel cell stack having 220 cells.

As compared with the conventional constant current output method, the activation process using the pulse discharge method has a merit that the activation speed is increased by shortening the activation time and the hydrogen consumption by changing the water flow in the fuel cell, Based on the stack composed of 220 cells, the total activation time is about 107 minutes and the hydrogen usage is 20.7 m3. Therefore, there is a need to improve the process time, hydrogen consumption, and the cost accordingly.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above-described problems, and it is an object of the present invention to provide a fuel cell system capable of shortening the activation process time of the fuel cell stack and reducing the amount of hydrogen used, And a method for activating fuel cell acceleration.

In order to achieve the above object, the present invention provides a method for controlling a fuel cell, comprising the steps of: discharging and holding a fuel cell such that a current output of a predetermined current density is performed in a loaded state; and maintaining the fuel cell in a shutdown state by shutting off the reaction gas supply The method comprising the steps of:

In a preferred embodiment, the discharge sustaining step and the shutdown sustaining step are repeated once for each repetition cycle.

Further, in a preferred embodiment, the step of repeating the step of performing the step of holding the discharge for each repetition cycle by a predetermined number of times and then maintaining the step in the shutdown state is repeatedly performed.

Here, the step of maintaining the discharge may be performed by connecting a load device to maintain a load state in which a current output is generated from the fuel cell, disconnecting the load device, and then switching to a no-load state. In the shutdown state, When the cell voltage rises to a certain level in the no-load state, the supply of the reaction gas is completely cut off, thereby shutting down the operation of the fuel cell.

Accordingly, in the fuel cell acceleration activation method of the present invention, the steps of discharging and maintaining the fuel cell in such a manner that a current output of a predetermined current density is achieved in a loaded state, and maintaining the fuel cell in a shutdown state by shutting off the reaction gas supply It is possible to shorten the activation process time of the fuel cell stack and reduce the amount of hydrogen used to reduce the production cost of the fuel cell compared to the conventional constant current output method and pulse discharge method.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be easily understood by those skilled in the art.

FIGS. 3 and 4 are diagrams for explaining a fuel cell acceleration activation method according to the present invention, showing a pulse discharge method of the present invention in which a shutdown process for completely stopping pulse discharge and reaction gas supply is applied.

In order to exhibit the steady-state performance after assembling the fuel cell stack, an activation process for securing the electrode reaction area of the three phases, removing impurities from the polymer electrolyte membrane or the electrode, and improving ion conductivity of the polymer electrolyte membrane is required as described above . Improvement of ionic conductivity through change of the surface structure inside the electrolyte membrane among the three internal structure changes through the activation process is an important activation accelerator.

Therefore, in the present invention, it is intended to obtain an activation acceleration effect by effectively changing the surface structure of the electrolyte membrane through wetting of water during activation to improve ionic conductivity. That is, a method for dramatically shortening the process time required for actual activation by effectively improving the ion conductivity of the electrolyte membrane compared to the conventional activation process.

In the conventional activation process, pulse discharge consisting of a high current density (1.2 or 1.4 A / cm 2) discharge and an OCV state is performed. In this case, the process time of about 1 hour and 30 minutes to 2 hours . In this activation method using pulse discharge, not only the process time is still large, but also the amount of hydrogen used is excessive.

In the present invention, the conventional pulse discharge is improved and a shutdown (pausing) process in which the supply of the reaction gas (air containing hydrogen and oxygen) is completely stopped, instead of applying the OCV state maintenance as no load to the middle of the pulse discharge Lt; / RTI >

That is, the acceleration activation method of the present invention includes the steps of: maintaining the fuel cell in a discharged state to maintain a current output of a predetermined current density in a loaded state; and interrupting the supply of the reactive gas to maintain the fuel cell in a shutdown state repeatedly And the process of proceeding.

At this time, it is practicable to repeatedly perform the step of holding the discharge in each repetition cycle and the step of maintaining it in the shutdown state once. Or performing the step of holding the discharge for each cycle repeated at a predetermined number of times and then maintaining the shutdown state once.

Here, the discharge sustaining step may be performed by connecting a load device to maintain a load state in which a current output is generated from the fuel cell stack for a predetermined time, and then disconnecting the load device to switch to a no-load state.

Referring to FIG. 3, the cell voltage distribution over time during the activation process is shown. The cell voltage distribution is maintained for 3 minutes under a high current density (current output per unit area of the electrode) of 1.2 or 1.4 A / And the pulse discharge in which the rear shutdown process is held for 5 minutes, the pulse discharge is repeatedly performed once for 3 minutes pulse discharge and once for 5 minutes shutdown.

The apparatus for performing the fuel cell activating process of the pulse discharge method including the shutdown process can use an activating device having the same configuration as the conventional one. In the method, the supply of the reactive gas The shutdown state, which completely blocks the shutdown state, is maintained for a predetermined period of time.

For example, a basic constituent element for operating the fuel cell stack can be configured in combination. A hydrogen supply device (hydrogen storage device such as a hydrogen tank, a high-voltage / low-voltage regulator, a hydrogen supply device (Including air blowers, humidifiers, etc.) for supplying air containing oxygen, which is an oxidizing agent, to the fuel cell stack, and the inlet and the outlet of the air side (cathode) of the fuel cell stack A load device for controlling the current state of the fuel cell stack, a cooling device for cooling the fuel cell stack, a voltage detector for monitoring the cell voltage of the fuel cell stack, and the like.

Here, the load device is a component for controlling the current output state of the fuel cell stack. The load device includes an electronic load connected to a current output terminal of the fuel cell stack, And an open / close switch for turning on and off the switch.

The cooling device may include a cooling water pump for circulating the cooling water, a heat exchanger for cooling the cooling water circulating the stack, and the like, for cooling the stack by circulating the cooling water through the cooling water channel in the fuel cell stack have.

The 3-minute discharge maintenance is performed by connecting the load device and maintaining the load state for current output from the fuel cell stack for 3 minutes and then disconnecting the load device to switch to a no-load state. After that, When the cell voltage rises, the supply of the reaction gas is completely cut off and the operation of the fuel cell is shut down for 5 minutes.

In the embodiment of FIG. 3, the discharge and the shutdown were repeatedly performed as described above, and the time required for the activation to be completed was reduced to 68 minutes and the hydrogen consumption to 6.6 m 3.

Table 1 below shows the time required for the one-time discharge and the one shutdown application of FIG. 3 and the amount of hydrogen used in comparison with the conventional pulse discharge method.

Referring to FIG. 4, the step of discharging is performed at a constant current density, a shutdown step for completely shutting off the supply of the reactive gas, a step for restarting the supply of the reactant gas and outputting the discharge again, and a shutdown step for completely shutting off the supply of the reactant gas repeatedly Thereby increasing the ionic conductivity of the process of the present invention.

When the discharge is performed at a constant current density (1.2 A / cm < 2 >) in the activation process of the present invention, an electro-osmotic drag of water molecules for inducing a vapor state of water, Back diffusion of water by physical drag force such as concentration difference or pressure difference is performed.

Also, according to the shutdown process inserted in the middle of the pulse discharge, it is possible to induce the condensation of the water in the vapor state easily, and at the same time, the water generated at the high current density can be easily diffused into the sub micropore structure of the electrolyte membrane to improve the ion conductivity do.

Particularly, since the electrolyte membrane can easily be swelled through repetition of high-rate discharge and shutdown, the volume expansion of this electrolyte membrane favor the absorption of water in the membrane pores.

In the conventional OCV condition, the flow of water in the membrane is limited. However, in shutdown, condensation occurs in high-rate discharge or condensed water is freely diffused in various directions, and wetting the pore structure of the membrane through various paths, The movement becomes easy.

Therefore, the surface structure of the film suitable for the migration of hydrogen cations can be formed by the infiltration by the expansion of the film, so that the activation accelerating effect and the performance improvement can be achieved.

(B) shows an activation process in which three times of 3-minute pulse discharges and one minute of shutdown are repeated, FIG. 5 (c) shows an activation process of 3 A minute pulse discharge and a 10-minute shutdown are repeated.

By introducing the shutdown process as described above, the amount of hydrogen used in the present invention can be reduced to about 30% as compared with the conventional pulse discharge activation process (OCV process in FIG. 2), and shutdown is repeated once after three pulse discharges (b), the process time can be shortened to about 50% (from 107 minutes to 56 minutes).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the present invention is not limited to the disclosed exemplary embodiments. Modified forms are also included within the scope of the present invention.

1 is a view showing the structure of the electrolyte membrane 3 in a wet state.

2 is a view for explaining an example of an activation process according to the prior art.

3 and 4 are views for explaining a fuel cell acceleration activation method according to the present invention.

5 is a diagram illustrating various embodiments of the activation process of the present invention using a shutdown.

Claims (7)

The method comprising the steps of: maintaining the fuel cell in a discharged state such that a current output of a predetermined current density is obtained in a loaded state; and repeating the step of shutting off the reaction gas supply to maintain the fuel cell in a shutdown state Way. The method according to claim 1, Wherein the step of maintaining the discharge and the step of maintaining the shutdown state are repeated once for each repetition cycle. The method of claim 2, Wherein the fuel cell is repeatedly subjected to a three minute pulse discharge once and a five minute shutdown once in such a manner that a discharge is maintained at a current density of 1.2 or 1.4 A / cm < 2 > for 3 minutes and then a shutdown state is maintained for 5 minutes. Way. The method of claim 2, Wherein the fuel cell is repeatedly subjected to a 3-minute pulse discharge once and a 10-minute shutdown once in such a manner that a discharge is maintained for 3 minutes at a current density of 1.2 or 1.4 A / cm < 2 >, and the shutdown state is maintained for 10 minutes. Way. The method according to claim 1, And performing the step of maintaining the discharge for each of the repeated cycles at a predetermined number of times and then maintaining the shutdown state once. The method of claim 5, The discharge is maintained for three minutes at a current density of 1.2 or 1.4 A / cm < 2 > for three times, and then the shutdown state is maintained for one minute. The three-times pulse discharge and the one-minute shutdown are repeated A method for activating fuel cell acceleration. The method according to any one of claims 1 to 6, Wherein the step of maintaining the discharge continues in a step of connecting the load device to maintain the load state in which the current output from the fuel cell is maintained, Wherein the step of maintaining the reactor in the shutdown state completely shut off the supply of the reaction gas when the cell voltage rises to a certain level in the no-load state to shut down the operation of the fuel cell.

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