JP6981883B2 - Fuel cell aging method - Google Patents

Description

The present invention relates to a method for aging a fuel cell.

The fuel cell supplies fuel gas (for example, hydrogen) and oxidant gas (for example, air) to the anode-side electrode (hereinafter, may be simply referred to as an anode) and the cathode-side electrode (hereinafter, which may be simply referred to as a cathode). It is a system that obtains electrical energy (electronode) by electrochemically reacting.

For example, a cell of a solid polymer fuel cell (sometimes referred to as a fuel cell or a single cell) has an ionic conductive electrolyte membrane, an anode-side catalyst layer (electrode layer) sandwiching the electrolyte membrane, and a cathode-side catalyst. A membrane electrode assembly (MEA) composed of a layer (electrode layer) is provided. Gas diffusion layers (GDL) are formed on both sides of the MEA to provide fuel gas or oxidant gas and to collect electricity generated by an electrochemical reaction. MEA in which GDL is arranged on both sides is called MEGA (Membrane Electrode & Gas Diffusion Layer Assembly), and MEGA is sandwiched by a pair of separators. Here, MEGA is the power generation unit of the fuel cell, and when there is no gas diffusion layer, MEA is the power generation unit of the fuel cell.

A fuel cell (sometimes referred to as a fuel cell stack) is used by stacking a plurality of cells having the above-mentioned configurations on top of each other and mounting them on a vehicle such as an automobile, for example.

In this type of polymer electrolyte fuel cell, the initial power generation performance is low due to reasons such as insufficient water content of the electrolyte membrane immediately after assembly. Therefore, in order to bring out the desired power generation performance after assembling the fuel cell, a preliminary operation (break-in operation) called an aging operation (simply also referred to as aging) of the fuel cell is usually performed. This aging operation is such that the performance of the cell can exhibit the desired ability by preliminarily generating power after assembling the fuel cell. In addition, not only after manufacturing, but also when regenerating power (at the time of restarting) after the fuel cell is paused (particularly after a long-term pause), or when the fuel cell is generated for a long period of time, the output characteristics such as electromotive force are affected. Even when the fuel cell is lowered, the output characteristics of the fuel cell may be restored by performing the aging operation described above.

As a method for shortening the aging time in the aging (break-in operation) of such a solid polymer fuel cell, the fuel cell is forcibly energized, a periodically fluctuating electric load is applied, or the fuel cell is subjected to a periodic electric load. A method of periodically varying the load current is known (see, for example, Patent Documents 1 to 3 below).

Japanese Unexamined Patent Publication No. 2006-040869 Japanese Unexamined Patent Publication No. 2005-340022 Japanese Unexamined Patent Publication No. 2007-066666

By the way, as requirements necessary for promoting aging leading to shortening of aging time, removal of toxic substances (contaminated substances) on the catalyst surface of the membrane electrode assembly, removal of the oxide film on the catalyst surface, and electrolyte resin in the electrolyte membrane and the catalyst layer. Wetness is mentioned. Here, in general, the removal of the oxide film on the catalyst surface and the wetting of the electrolyte resin are performed in a shorter time than the removal of the poisonous substance. Therefore, in order to shorten the aging time (promote aging), how efficiently the poisonous substance can be used. It is important to remove it.

However, for example, in the prior art described in Patent Document 3, it is necessary to sweep a high current (high current density) in order to realize a low potential by a load current. In this case, the amount of generated water increases due to the high current sweep, but on the other hand, the amount of heat generated increases, so the amount of liquid water (the amount of liquid water for washing away and discharging the toxic substance on the catalyst surface) decreases, and aging. May interfere with the necessary wetting for promotion. That is, controlling the load current as described above has a contradictory effect on aging.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel cell aging method capable of effectively shortening the aging time.

In order to solve the above problems, the fuel cell aging method according to the present invention is a fuel cell aging method including an anode, a cathode, and an anode and an electrolyte membrane sandwiched between the cathodes, and is supplied to the cathode. It is characterized in that the potential of the fuel cell is periodically changed in the range of 0.4 V or less by periodically changing the flow rate of the inert gas mixed with the oxidizing agent gas.

It is preferable to periodically change the potential of the fuel cell in a wavy potential pattern by periodically changing the flow rate of the inert gas in a serrated flow pattern.

According to the present invention, by setting the potential of the fuel cell in the range of 0.4 V or less, it is possible to efficiently remove the poisonous substance that takes the longest time during aging, and the fuel cell by adjusting the flow rate of the inert gas. By controlling the potential of the fuel cell, it is possible to prevent a decrease in the amount of liquid water and secure the wetting required for promoting aging, so that the aging time can be effectively shortened.

It is a figure which shows an example of the fuel cell (fuel cell stack) to which the aging method of the combustion battery by this invention is applied, (A) is the main part sectional view, (B) is an overall external view. It is a schematic diagram explaining the aging mechanism. It is a time chart which shows the relationship between the flow rate of nitrogen gas at the time of aging, and the potential of a fuel cell. (A) is a power generation pattern of an example, and (B) is a time chart showing a power generation pattern of a comparative example.

Hereinafter, the configuration of the present invention will be described in detail based on an example of an embodiment shown in the drawings. In the following, as an example, a case where the present invention is applied to a fuel cell mounted on a fuel cell vehicle or a fuel cell system including the present invention will be described as an example, but the scope of application is not limited to such an example. ..

[Fuel cell (fuel cell stack) configuration]
FIG. 1 is a diagram showing an example of a fuel cell (fuel cell stack) to which the aging method for a combustion battery according to the present invention is applied. FIG. 1 (A) is a cross-sectional view of a main part, and FIG. 1 (B) is an overall view. It is an external view.

First, to outline the internal configuration of a fuel cell (solid polymer fuel cell) with reference to FIG. 1A, the fuel cell (fuel cell stack) 10 contains a cell (single cell) 1 which is a basic unit. Multiple layers are stacked. Each cell 1 is a solid polymer fuel cell that generates an electromotive force by an electrochemical reaction between an oxidant gas (for example, air) and a fuel gas (for example, hydrogen). The cell 1 includes a MEGA 2 and a separator (fuel cell separator) 3 that contacts the MEGA 2 so as to partition the MEGA 2. In this embodiment, MEGA2 is sandwiched by a pair of separators 3 and 3.

The MEGA 2 is a combination of a membrane electrode assembly (MEA) 4 and gas diffusion layers 7 and 7 arranged on both sides thereof. The membrane electrode assembly 4 includes an electrolyte membrane 5 and a pair of electrodes 6 and 6 bonded so as to sandwich the electrolyte membrane 5. The electrolyte membrane 5 is made of a proton-conducting ion exchange membrane made of a solid polymer material, and the electrode 6 is made of, for example, a porous carbon material carrying a catalyst such as platinum. The electrode 6 arranged on one side of the electrolyte membrane 5 serves as an anode, and the electrode 6 on the other side serves as a cathode. The gas diffusion layer 7 is formed of a gas-permeable conductive member such as a carbon porous body such as carbon paper or carbon cloth, or a metal porous body such as a metal mesh or foamed metal.

In the present embodiment, the MEGA 2 is the power generation unit of the fuel cell 10, and the separator 3 is in contact with the gas diffusion layer 7 of the MEGA 2. When the gas diffusion layer 7 is omitted, the membrane electrode assembly 4 is the power generation unit, and in this case, the separator 3 is in contact with the membrane electrode assembly 4. Therefore, the power generation unit of the fuel cell 10 includes the membrane electrode assembly 4 and comes into contact with the separator 3.

The separator 3 is a plate-shaped member based on a metal having excellent conductivity and gas impermeableness, and one side thereof is in contact with the gas diffusion layer 7 of MEGA2, and the other side is adjacent to another separator. It is in contact with the other surface side of 3.

In the present embodiment, each separator 3 is formed in a wavy or uneven shape. The shape of the separator 3 is such that the shape of the wave is an isosceles trapezoid, the top of the wave is flat, and both ends of the top are angular at equal angles. That is, each separator 3 has substantially the same shape when viewed from the front side and the back side. The top of the separator 3 is in surface contact with one gas diffusion layer 7 of MEGA 2, and the top of the separator 3 is in surface contact with the other gas diffusion layer 7 of MEGA 2.

The gas flow path 21 defined between the gas diffusion layer 7 on the one electrode (that is, the anode) 6 side and the separator 3 is a flow path through which the fuel gas flows, and is on the other electrode (that is, the cathode) 6 side. The gas flow path 22 defined between the gas diffusion layer 7 and the separator 3 is a flow path through which the oxidizing agent gas flows. When the fuel gas is supplied to one of the gas flow paths 21 facing each other via the cell 1 and the oxidant gas is supplied to the gas flow path 22, an electrochemical reaction occurs in the cell 1 to generate an electromotive force.

Further, one cell 1 and another cell 1 adjacent thereto are arranged so that the electrode 6 serving as an anode and the electrode 6 serving as a cathode face each other. Further, the top of the back side of the separator 3 arranged along the electrode 6 which is the anode of a certain cell 1 and the top of the back side of the separator 3 arranged along the electrode 6 which is the cathode of another cell 1. And are in surface contact. Water as a refrigerant for cooling the cell 1 flows through the space 23 defined between the separators 3 and 3 that are in surface contact with each other between the two adjacent cells 1.

Further, a gasket (not shown) as a sealing member for sealing a fuel gas (for example, hydrogen) or an oxidant gas (for example, air) or cooling water is held between the ends of two adjacent cells 1. Has been done.

Further, as shown in FIG. 1 (B), the above-mentioned fuel cell 10 includes a cell monitor cable (not shown) for monitoring the voltage (cell voltage) between each cell, and a gas on the electrode (anode) 6 side. A gas pipe 11 for supplying / discharging fuel gas to the flow path 21, a gas pipe 12 for supplying / discharging oxidant gas to the gas flow path 22 on the electrode (cathode) 6 side, and water as a refrigerant in the space 23. A cooling water pipe 13 or the like for supplying / discharging (cooling water) is connected and configured.

[Aging method for fuel cell (fuel cell stack)]
In the fuel cell 10 having the above-described configuration, in order to stabilize the power generation performance (output characteristics), for example, aging (break-in operation) is performed after the fuel cell 10 is assembled.

Here, in the above-mentioned aging, the catalyst surface of the membrane electrode assembly 4 is mainly washed (removal of toxic substances (contamination substances)) through steps 1 to 3 shown in FIG.
<Process 1>: A state in which a poisonous substance adheres to the surface of the catalyst.
<Process 2>: Toxic substances adhering to the catalyst surface are floated (separated) from the catalyst surface.
<Process 3>: The toxic substance floating from the surface of the catalyst is washed away with liquid water or the like generated by the electrochemical reaction of the fuel cell, and discharged from the inside of the cell.

The poisonous substances adhering to the catalyst surface are various kinds of organic substances having a low molecular weight to a high molecular weight used in the electrode process, the cellification process, and the like, and it is necessary to efficiently remove these organic substances. That is, it is indispensable to efficiently perform the process 2 before the process 3 of rinsing with liquid water.

Therefore, in the present embodiment, various types of poisonous substances are removed in a short time by varying the potential of the fuel cell between 0V and 0.4V, which promotes and accelerates the aging. _{Specifically, an inert gas (for example, nitrogen N 2} ) mixed with the oxidizing agent gas supplied from the gas pipe 12 to the electrode (cathode) 6 by using, for example, a flow control valve arranged in the gas pipe 12. By periodically changing the flow rate of the gas), the potential of the fuel cell 10 is periodically changed in the range of 0.4 V or less, and the aging is carried out.

_{More specifically, as shown in FIG. 3, the flow rate of the inert gas (for example, nitrogen N 2} gas) mixed with the oxidizing agent gas supplied to the electrode (cathode) 6 is periodically changed in a serrated flow pattern. The aging is carried out by periodically changing the potential (cell average voltage) of the fuel cell 10 in a wavy (sine wavy) potential pattern within the range of 0.1 V to 0.4 V.

Hereinafter, the action and effect of the aging (potential control in) of the present embodiment described above will be described.

<Effect of generating electricity to shorten the aging time of the fuel cell>
For example, in the method of washing by flowing hot water or the like without power generation, the effect of removing the toxic substance adhering to the catalyst surface is small, and a sufficient aging effect cannot be obtained.

It has a surface potential (surface energy) peculiar to the catalyst species depending on the potential applied in power generation and the environment inside the electrode, and the toxic substance can be separated or combined by the interaction between the surface energy and the toxic substance. , The poisonous substance on the surface of the catalyst can be effectively removed.

<Effect of cyclically changing the potential of each cell constituting the fuel cell between 0 and 0.4V (so that the cycle is 0.4V → 0V → 0.4V)>
Most of the poisonous substances adhering to the catalyst surface are anionic, and by setting the potential to 0V to 0.4V, the poisonous substances can be effectively separated from the catalyst surface.

Furthermore, there are often multiple types of poisonous substances (types of poisonous substances), and the potential that can be effectively deviated from the catalyst surface differs depending on the poisonous substance species, so the potential is cycle-variable from 0.4V → 0V → 0.4V. This makes it possible to efficiently remove all poisonous species.

In addition, by changing the potential cycle, the action of the poisonous substance to easily deviate from the surface of the catalyst increases. In this case, it may be combined with a constant potential.

<Action and effect of controlling the fluctuation of the potential of the fuel cell by changing the mixed flow rate of the _{inert gas (for example, nitrogen N 2 gas) to the cathode>}
The aging effect differs depending on the power generation environment (temperature and amount of water produced) in each cell, but mixing the inert gas can promote aging with almost no change in the power generation environment in each cell. can.

As described above, in the present embodiment, by setting the potential of the fuel cell 10 in the range of 0.4 V or less, it is possible to efficiently remove the poisonous substance, which takes the longest time during aging, and it is inactive. By controlling the potential of the fuel cell 10 by adjusting the flow rate of the gas, it is possible to prevent a decrease in the amount of liquid water and secure the wetting required for promoting aging, so that the aging time can be effectively shortened.

[Experiments and results evaluating the power generation performance and aging time of fuel cells (fuel cell stack)]
The present inventors have produced a fuel cell (fuel cell stack) as described with reference to FIG. 1, and have hydrogen and oxidation as fuel gas via a gas pipe for fuel gas and a gas pipe for oxidant gas. Air as an agent gas was supplied to the anode side electrode and the cathode side electrode to perform aging power generation (Examples and Comparative Examples), and the power generation performance (output characteristics) and aging time at that time were evaluated.

<Aging method of Examples and Comparative Examples>
As shown in FIGS. 4A and 4B, the power generation patterns of the examples and comparative examples during aging power generation are stepped patterns from 0 to 600A (specifically, the current is 0 → 150A → 300A →). The pattern is the same as 450A → 600A, which gradually increases in steps), but in the example, nitrogen gas was started to be mixed with air as an oxidant gas after a certain period of time after reaching 600A. The amount of nitrogen gas in the examples was varied several times from zero (the potential at this time corresponds to about 0.4 V) to the upper limit, with the amount when the voltage reached almost 0 V as the upper limit.

On the other hand, in the comparative example, nitrogen gas was not mixed.

In the examples and comparative examples, the flow rate of air as the oxidant gas was set to 1.2 for each current value.

Further, here, the aging times of the examples and the comparative examples are the same (aging time T).

<Evaluation result of output after aging>
As a result of measuring the outputs of the examples and the comparative examples after the above-mentioned aging, as shown in Table 1 below, the outputs of the examples and the comparative examples are the outputs of the fuel cells after the aging is sufficiently carried out (that is, each of them). , Target output), 96% and 93%.
<Table 1>

From this experimental result, it was demonstrated that in the example, the same power generation performance can be obtained in a shorter aging time than in the comparative example, in other words, the aging time can be shortened.

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and there are design changes and the like within a range that does not deviate from the gist of the present invention. Also, they are included in the present invention.

1 ... cell (fuel cell), 2 ... MEGA, 3 ... separator, 4 ... membrane electrode junction (MEA), 5 ... electrolyte membrane, 6 ... electrode (anode, cathode), 7 ... gas diffusion layer, 10 ... fuel Battery (fuel cell stack), 11, 12 ... gas pipe, 13 ... cooling water pipe, 21,22 ... gas flow path, 23 ... space for water to flow

Claims (2)

A method for aging a fuel cell including an anode, a cathode, and the anode and an electrolyte membrane sandwiched between the cathodes.
A fuel cell characterized in that the potential of the fuel cell is periodically changed in the range of 0.4 V or less by periodically changing the flow rate of the inert gas mixed with the oxidant gas supplied to the cathode. Aging method. The method for aging a fuel cell according to claim 1, wherein the potential of the fuel cell is periodically changed in a wavy potential pattern by periodically changing the flow rate of the inert gas in a serrated flow pattern.

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