JP2021128868A - Fuel cell aging method - Google Patents

Abstract

To provide a fuel cell aging method by which the corrosion of a metal separator can be suppressed without extending an aging time.SOLUTION: A method for aging a fuel cell, which includes a membrane-electrode assembly having an anode, a cathode, and an electrolyte membrane held between the anode and cathode, and a metal separator disposed on at least one side outside of the membrane-electrode assembly, comprises: a start-of-power generation step of supplying the anode with fuel, and the cathode with an oxidizer, thereby starting the power generation of the fuel cell; and an aging step of applying an electric load for causing a voltage to periodically fluctuate upward and downward to the fuel cell caused to start power generation, thereby stabilizing an output characteristic of the fuel cell. The aging step includes at least two or more successive steps; an upper limit voltage in the initial first aging step is made lower than an upper limit voltage in the second or later aging step.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to a fuel cell aging method.

In a solid polymer fuel cell, electric energy is generated by supplying an oxidant gas containing oxygen and a fuel gas containing hydrogen to a fuel cell stack in which a plurality of cells are stacked and causing a chemical reaction. The cell, which is the basic unit, is generally provided with MEA (Membrane Electrode Assembly: Membrane Electrode Assembly) in which electrode catalyst layers are formed on both sides of a solid polymer electrolyte membrane, a diffusion layer on the outside thereof, and a gas flow path on the outside thereof. And the separator is arranged.
At the fuel electrode (anode), hydrogen supplied from the flow path / diffusion layer is protonated by the catalytic action of the catalyst layer, passes through the electrolyte membrane, and moves to the oxidant electrode (cathode). The electrons generated at the same time work through an external circuit and move to the cathode. Oxygen supplied to the cathode reacts with protons and electrons on the cathode to produce water.
The generated water gives an appropriate humidity to the electrolyte membrane, and the excess water permeates the diffusion layer and is discharged to the outside of the system through the flow path.

After manufacturing, the fuel cell needs to be aged until it reaches a predetermined output voltage designed as a battery characteristic. The performance of the fuel cell immediately after production is often lower than the design performance, and aging is performed as a process for ensuring the initial performance of the fuel cell. Therefore, it is difficult to quickly evaluate the quality of the fuel cell after manufacturing, and shortening the aging time is a big issue.

For example, in Patent Document 1, the step of starting the power generation of the fuel cell and the fuel cell that started the power generation are periodically changed by supplying fuel to the anode and supplying the oxidizing agent to the cathode. A method for aging a fuel cell, which comprises a step of stabilizing the output characteristics of the fuel cell by applying an electric load, is disclosed.

Further, in Patent Document 2, the step of gradually increasing the output current Ifc of the fuel cell from 0 to Ih11 and then gradually decreasing it to 0 is repeatedly executed. Then, after t15 when the output voltage of the fuel cell rises to a predetermined level, the output current Ifc of the fuel cell is gradually increased from 0 to Ih12 (> Ih11) and then gradually decreased to 0 again. A technique is disclosed in which the voltage is repeatedly executed until the voltage rises to a predetermined aging end level.

Further, in Patent Document 3, a polymer electrolyte fuel cell stack 1 to be preliminarily operated is prepared (S1), and a loader 21 is connected to the polymer electrolyte fuel cell (S2). An aging method for preliminarily operating a polymer electrolyte fuel cell by passing a load current whose magnitude periodically fluctuates with the passage of time from the fuel cell to the loader is disclosed (S3).

Japanese Unexamined Patent Publication No. 2005-3400022 Japanese Unexamined Patent Publication No. 2005-251396 Japanese Unexamined Patent Publication No. 2007-066666

During fuel cell power generation, especially in the initial stage of power generation such as an aging process, sulfate ions, which are decomposition products from the electrolyte membrane damaged in the heat treatment process during cell production, flow out and the in-plane pH of the cell decreases.
On the other hand, metal separators such as stainless steel are being studied in order to reduce the cost of fuel cells, but in systems using metal separators such as stainless steel, high potential is achieved when the pH is lowered as described above. In this state, there is a high possibility that the separator will be corroded, such as elution of metal components (iron ions, etc.).
Therefore, in order to prevent corrosion of the metal separator by the above-mentioned conventional technique, it is necessary to apply a low potential cycle so as not to have a high potential, but there is a problem that the aging time is long in the low potential cycle.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a fuel cell aging method capable of suppressing corrosion of a metal separator without extending the aging time.

In the present disclosure, a membrane electrode assembly having an anode, a cathode, and an anode and an electrolyte membrane sandwiched between the anode and the cathode, and a metal separator arranged on at least one side outside the membrane electrode assembly. A method of aging fuel cells, including
A power generation start step of starting power generation of the fuel cell by supplying fuel to the anode and supplying an oxidizing agent to the cathode.
It has an aging step of stabilizing the output characteristics of the fuel cell by applying an electric load that periodically fluctuates the voltage up and down to the fuel cell that has started power generation.
The fuel cell has at least two consecutive steps, and the upper limit voltage in the first first aging step is lower than the upper limit voltage in the second and subsequent aging steps. Provides an aging method for.

The present disclosure can provide a fuel cell aging method capable of suppressing corrosion of a metal separator without prolonging the aging time.

It is a figure which shows an example of the relationship between the power generation time and the pH in the cell surface of a fuel cell. It is a figure which shows an example of the voltage control method at the time of aging. It is a figure which shows another example of the voltage control method at the time of aging. It is a figure which shows the result of the aging completion time and the elution amount of Fe contained in a stainless steel separator.

In the present disclosure, a membrane electrode assembly having an anode, a cathode, and an anode and an electrolyte membrane sandwiched between the anode and the cathode, and a metal separator arranged on at least one side outside the membrane electrode assembly. A method of aging fuel cells, including
A power generation start step of starting power generation of the fuel cell by supplying fuel to the anode and supplying an oxidant to the cathode.
It has an aging step of stabilizing the output characteristics of the fuel cell by applying an electric load that periodically fluctuates the voltage up and down to the fuel cell that has started power generation.
The fuel cell has at least two consecutive steps, and the upper limit voltage in the first first aging step is lower than the upper limit voltage in the second and subsequent aging steps. Provides an aging method for.

FIG. 1 is a diagram showing an example of the relationship between the power generation time and the pH in the cell surface of the fuel cell.
As shown in FIG. 1, in the initial stage of power generation, sulfate ions come out from the electrolyte membrane, and the pH drops. If the pH is 4 or less, the stainless steel separator will dissolve.
In the initial stage of fuel cell power generation, sulfate ions, which are film decomposition products, flow out from the electrolyte membrane damaged in the heat treatment process during cell manufacturing, and the in-plane pH of the cell drops. Accelerates corrosion.
In the prior art, 1) a load (current / voltage) is applied periodically, and 2) a low current may be applied stepwise. It is necessary to apply a low-potential cycle so as not to reach a potential, but the low-potential cycle takes a long time for aging. That is, it is not possible to achieve both corrosion of the metal separator and shortening of the aging time.

According to the present disclosure, the aging time is extended by lowering the upper limit voltage in the early stage of power generation where sulfate ions flow out and lowering the pH, and raising the upper limit voltage after the middle stage of power generation when pH> 4. Corrosion of the metal separator can be suppressed without this.
The term “aging” refers to, for example, power generation in which a fuel cell is manufactured and then its output characteristics reach a designed predetermined output characteristic.

The fuel cell aging method of the present disclosure includes (1) a power generation start step and (2) an aging step. Hereinafter, each step will be described in order.

(1) Power generation start step In the power generation start step, the power generation of the fuel cell is started by supplying fuel to the anode and supplying an oxidizing agent to the cathode.

The fuel cell includes a membrane electrode assembly having an anode, a cathode, and an anode and an electrolyte membrane sandwiched between the anode and the cathode, and a metal separator arranged on at least one side outside the membrane electrode assembly. ,including.
The metal separator may be arranged on at least one side of the outside of the membrane electrode assembly, and may be arranged on both sides, and the membrane electrode assembly may be sandwiched by two metal separators.
The metal separator may be, for example, an iron separator, a stainless steel separator, or the like.
The fuel cell may be a fuel cell stack in which a plurality of single cells are stacked.
The anode and the cathode are not particularly limited, and conventionally known anodes can be used.
The electrolyte membrane is not particularly limited, and a perfluorocarbon sulfonic acid membrane (PFSA membrane) or the like can be used.
The anode may be composed of an anode catalyst layer, a diffusion layer, or the like, and the cathode may be composed of a cathode catalyst layer, a diffusion layer, or the like. Examples of the anode catalyst and the cathode catalyst include Pt (platinum) and Ru (ruthenium), and examples of the base material and the conductive material supporting the catalyst include carbon materials such as carbon. Examples of the ionic conductor include the above-mentioned perfluorocarbon sulfonic acid and the like.
The metal separator may have a gas flow path.
The fuel supplied to the fuel cell is not particularly limited, and may be at least one selected from, for example, hydrogen and methanol. The oxidizing agent supplied to the fuel cell is not particularly limited, and may be, for example, a gas containing oxygen.
The method of supplying fuel to the anode and the method of supplying the oxidizing agent to the cathode are not particularly limited, and conventionally known methods can be adopted.

(2) Aging Step The aging step is a step of stabilizing the output characteristics of the fuel cell by applying an electric load that periodically fluctuates the voltage up and down to the fuel cell that has started power generation. ..
The method of applying a periodically fluctuating electrical load to the fuel cell that has started power generation is not particularly limited. For example, a load may be connected to the fuel cell and the magnitude of the load may be changed periodically. More specifically, for example, the fuel cell may be connected to a resistor such as a fixed resistor or a variable resistor (or an aggregate of the resistors), and the magnitude of the resistor may be changed periodically.
The voltage control method is not particularly limited, and a conventionally known method can be adopted. For example, the voltage may be controlled by adjusting the supply amounts of the fuel and the oxidizing agent.
The aging step has at least two consecutive steps, that is, a first first aging step and a second and subsequent aging steps, and the upper limit voltage (V1) in the first first aging step is set to the second. It is lower (V1 <Vn) than the upper limit voltage (Vn) in the subsequent aging step.
The aging step can suppress the elution of metal components such as Fe from the metal separator and shorten the aging time.

FIG. 2 is a diagram showing an example of a voltage control method during aging.
In the aging step shown in FIG. 2, the first first aging step (first step) of lowering the upper limit voltage (V1) at the initial stage of power generation in which the in-plane pH of the fuel cell is lowered so that the upper limit voltage is V1 <V2. ) And a second aging step (second step) for raising the upper limit voltage (V2).

FIG. 3 is a diagram showing another example of the voltage control method during aging.
In the aging step shown in FIG. 3, not only the first aging step of the upper limit voltage V1 (first step) and the second aging step of the upper limit voltage V2 (second step), but also V1 <V2 <V3. It has a third aging step (third step) of the upper limit voltage V3 such that
In this case, a suitable aging method is obtained by providing the first step and the second step so as to further divide the first step in the first embodiment described later. In that case, the elution amount of the metal component such as Fe in the metal separator is slightly increased, but the aging completion time can be shortened as compared with Example 1.
Further, it may have a third aging step (third step) of the upper limit voltage V3 such that V1 <V3 <V2.

The upper limit voltage in one process may or may not be constant. For example, the values of the upper limit voltages V1, V2 and V3 are as long as V1 <V2 and V1 <V3 are satisfied. , Each value does not have to be constant.
The execution time of each step of the first first aging step and the second and subsequent aging steps is not particularly limited, and the relationship between the power generation time of the fuel cell and the pH in the cell plane is shown in advance by experiments or the like. A data group may be prepared, and the execution time of each step may be determined from the data group.

(Example 1)
A fuel cell including an anode, a cathode, a membrane electrode assembly having the anode and an electrolyte membrane sandwiched between the cathodes, and two stainless steel separators sandwiching the membrane electrode assembly was prepared. ..
Then, the fuel was supplied to the anode of the fuel cell and the oxidizing agent was supplied to the cathode to start the power generation of the fuel cell (power generation start process).
After that, the aging step was carried out under the following conditions.
V1 = 0.7V, V2 = OCV (open circuit voltage), V1 <V2, and in the first aging step, aging was performed in a cycle of 0V⇔0.7V for 5 minutes at a predetermined cycle, and then the second aging step was performed. In the aging step of No. 1, aging was carried out in a cycle of 0V⇔OCV in a predetermined cycle until the desired output characteristics of the fuel cell were obtained. After the aging was completed, the amount of Fe eluted in the stainless steel separator was measured. The results of the aging completion time and the elution amount of Fe contained in the stainless steel separator are shown in FIG.

(Comparative Example 1)
Aging was carried out in the same manner as in Example 1 except that aging was carried out under the following conditions in the aging step.
With V1 = V2 = OCV, aging was carried out in a cycle of 0V⇔OCV in a predetermined cycle until the desired output characteristics of the fuel cell were obtained. The results of the aging completion time and the elution amount of Fe contained in the stainless steel separator are shown in FIG.

(Comparative Example 2)
Aging was carried out in the same manner as in Example 1 except that aging was carried out under the following conditions in the aging step.
With V1 = V2 = 0.7V, aging was carried out in a cycle of 0V⇔0.7V at a predetermined cycle until the desired output characteristics of the fuel cell were obtained. The results of the aging completion time and the elution amount of Fe contained in the stainless steel separator are shown in FIG.

FIG. 4 is a diagram showing the results of the aging completion time and the elution amount of Fe contained in the stainless steel separator.
An aging method in which the aging completion time is short and the amount of Fe contained in the stainless steel separator is small is suitable as an aging method for a fuel cell using a stainless steel separator.
As shown in FIG. 4, in Comparative Example 1, the aging completion time (here, the time when 95% of the maximum output is reached is referred to as the aging completion time) is the fastest, but the amount of Fe eluted from the stainless steel separator is the largest. Further, in Comparative Example 2, the elution amount of Fe contained in the stainless steel separator is the smallest, but the aging completion time is the slowest.
On the other hand, Example 1 is a preferable example because the aging completion time is the same as that of Comparative Example 1 and the Fe elution amount can be reduced by 80% or more.

Claims (1)

Includes an anode, a cathode, and a membrane electrode assembly having the anode and an electrolyte membrane sandwiched between the cathodes and a metal separator located on at least one outer side of the membrane electrode assembly. It ’s a fuel cell aging method.
A power generation start step of starting power generation of the fuel cell by supplying fuel to the anode and supplying an oxidizing agent to the cathode.
It has an aging step of stabilizing the output characteristics of the fuel cell by applying an electric load that periodically fluctuates the voltage up and down to the fuel cell that has started power generation.
The fuel cell has at least two consecutive steps, and the upper limit voltage in the first first aging step is lower than the upper limit voltage in the second and subsequent aging steps. Aging method.

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