JP7396196B2 - Laminate for fuel cells - Google Patents

Description

The present invention relates to a laminate for fuel cells.

Fuel cells are known that generate electricity by chemically reacting an anode gas such as hydrogen and a cathode gas such as oxygen.

In a fuel cell, an anode gas (fuel gas) such as hydrogen and a cathode gas (oxidant gas) such as oxygen are supplied to two electrically connected electrodes, and the fuel is electrochemically oxidized. This directly converts chemical energy into electrical energy.

At the anode (fuel electrode) to which hydrogen is supplied as anode gas, the reaction of formula (a) below proceeds.
H ₂ → 2H ⁺ + 2e ^-... (a)

The electrons (e ⁻ ) generated in the above formula (a) pass through an external circuit, do work with an external load, and then reach the cathode (oxidant electrode). On the other hand, the protons (H ⁺ ) generated in the above formula (a), while hydrated with water, move from the anode side to the cathode side within the electrolyte membrane sandwiched between the anode and the cathode by electroosmosis. do.

On the other hand, at the cathode, protons (H ⁺ ) generated by the above formula (a) that have passed through the electrolyte membrane, oxygen supplied as cathode gas, and electrons (e) generated by the above formula (a) via an external circuit. ^- ) causes the reaction of the following formula (b) to proceed.
2H ⁺ + 1/2O ₂ + 2e ^- → H ₂ O ... (b)

Therefore, the chemical reaction shown in the following formula (c) proceeds in the entire battery, generating an electromotive force and performing electrical work on the external load.
H ₂ + 1/2O ₂ → H ₂ O...(c)

Such fuel cells are usually constructed by stacking a plurality of single cells each having a basic structure of a membrane electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes. Among these, solid polymer electrolyte fuel cells that use solid polymer electrolyte membranes as electrolyte membranes have advantages such as being easy to downsize and operating at low temperatures, so they are particularly popular in mobile devices and other devices. It is expected to be used as a power source for mobile devices such as portable devices and electric vehicles.

Here, the configuration of a single cell of a solid polymer electrolyte fuel cell includes, for example, an anode-side separator, an anode-side gas diffusion layer, an anode-side catalyst layer, an electrolyte membrane, a cathode-side catalyst layer, a cathode-side gas diffusion layer, and A laminate in which cathode-side separators are stacked in this order is known.

The gas diffusion layer is a laminate in which a microporous layer (MPL) is laminated on the surface of a conductive porous diffusion layer base material layer such as carbon paper or carbon cloth. The microporous layer (MPL) is formed by applying a material paste to the surface of the diffusion layer base layer. The gas diffusion layer in which MPL is formed has excellent gas diffusion properties.

In such fuel cells, hydrogen peroxide may be generated during the reaction process. The generated hydrogen peroxide then decomposes the ionomer, which is an electrolyte component. As a result, the electrolyte membrane containing the ionomer as a main component and the catalyst layer containing the ionomer as a component deteriorate, causing problems in battery durability.

On the other hand, it is known to use a cerium-containing substance as an electrolyte membrane constituting a fuel cell. Cerium ions released from a cerium-containing substance function as a catalyst for decomposing hydrogen peroxide.

However, cerium ions (Ce ³⁺ ) are adsorbed to sulfonic acid groups (-SO ₃ ⁻ ) in the ionomer contained in the electrolyte membrane or the catalyst layer, and when the adsorption rate is high, proton conduction is inhibited. Therefore, if the concentration of cerium ions (Ce ³⁺ ) is too high, the power generation performance of the fuel cell may deteriorate.

Figure 6 shows the substitution rate when cerium ion (Ce ³⁺ ) adsorbs to the sulfonic acid group (-SO ₃ ⁻ ) in the ionomer constituting the electrolyte membrane and replaces the proton (H ⁺ ) of the sulfonic acid group. and the proton resistance value (relative value) of the electrolyte membrane at a relative humidity of 30%. As shown in FIG. 6, it can be seen that when the cerium ion (Ce ³⁺ ) substitution rate in the electrolyte membrane is too high, the proton resistance value of the electrolyte membrane increases, and the degree of inhibition of proton conduction increases.

Further, FIG. 7 shows the relationship between the substitution rate of protons (H ⁺ ) of sulfonic acid groups (-SO ₃ ⁻ ) in the electrolyte membrane with cerium ions (Ce ³⁺ ) and the output of the fuel cell. As shown in FIG. 7, it can be seen that as the cerium ion (Ce ³⁺ ) substitution rate in the electrolyte membrane increases, the output of the fuel cell decreases.

Therefore, it has been proposed to add a cerium-containing compound only to the microporous layer (MPL) that constitutes the gas diffusion layer in the initial state when the fuel cell is started to be used after manufacturing (see Patent Document 1). ).

According to Patent Document 1, after the use of the battery is started, the cerium-containing compound is ionized and releases cerium ions, and the cerium ions are eluted from the microporous layer (MPL) and pass through the catalyst layer to the electrolyte. Move to the membrane. The cerium ions that reach the electrolyte membrane function as a catalyst to decompose hydrogen peroxide by moving within the ionomer in the membrane due to wetting and drying and electric potential, thereby preventing thinning of the electrolyte membrane. Improve the chemical durability of fuel cells.

Japanese Patent Application Publication No. 2018-190584

However, in the embodiment in which a cerium-containing compound is added only to the microporous layer (MPL), cerium ions are not present in the electrolyte membrane in the initial state at the start of use after manufacture. It has been found that thinning of the electrolyte membrane may not be avoided for some time afterwards.

The present invention has been made in view of the above-mentioned background, and is capable of suppressing film thinning of an electrolyte membrane immediately after manufacturing a fuel cell and starting use, and realizing a highly durable fuel cell. The purpose of the present invention is to provide a laminate for fuel cells.

The present inventor conducted extensive research to solve the above problems. Then, when producing a fuel cell, an appropriate amount of cerium ions are present in the electrolyte membrane, and when used, the cerium ions eluted from the microporous layer are guided to the electrolyte membrane. The present inventors have discovered that it is possible to suppress thinning of the electrolyte membrane immediately after manufacture and immediately after the start of use, and to realize a fuel cell with excellent durability, leading to the completion of the present invention. That is, the present invention is as follows.

A stacked body for a fuel cell in which a gas diffusion layer, a catalyst layer, and an electrolyte membrane are stacked in this order,
The gas diffusion layer includes a microporous layer and a diffusion layer base material layer stacked in this order from the catalyst layer side,
The microporous layer includes a cerium-containing oxide,
The catalyst layer and the electrolyte membrane include an ionomer having a sulfonic acid group,
In the initial state when a stack for a fuel cell is formed, some of the protons of the sulfonic acid group are substituted with cerium ions,
The substitution rate of the cerium ions in the catalyst layer is greater than the substitution rate of the cerium ions in the electrolyte membrane.
Laminate for fuel cells.

According to the laminate for a fuel cell of the present invention, since the electrolyte membrane has cerium ions in the initial state at the time of starting use of the fuel cell after manufacturing, the electrolyte membrane has cerium ions immediately after the start of use of the fuel cell. Membrane thinning can be suppressed.

In addition, in the fuel cell stack of the present invention, in the initial state at the time of starting use after manufacturing the fuel cell, there is a concentration gradient of the cerium ion substitution rate between the ionomers contained in each of the catalyst layer and the electrolyte membrane. By having this, it becomes possible to guide cerium ions eluted from the microporous layer to the electrolyte membrane side during use of the fuel cell.

Therefore, even if cerium ions in the electrolyte membrane are lost little by little along with generated water etc. over a long period of use, it is possible to replenish the electrolyte membrane with cerium ions little by little from the microporous layer, resulting in a concentration of cerium ions in the electrolyte membrane. This makes it possible to suppress a sudden rise in . As a result, it is possible to suppress thinning of the electrolyte membrane immediately after the start of use of the fuel cell, and to suppress an increase in the proton resistance value of the electrolyte membrane, and it is possible to maintain the output performance of the fuel cell for a long period of time.

FIG. 1 is a cross-sectional view of a stack for a fuel cell according to one embodiment. FIG. 3 is a diagram showing the cerium ion replacement rate in an initial state of a fuel cell stack according to an embodiment of the present invention. It is a graph showing the relationship between the durability time of a fuel cell and the concentration of cerium ions in an electrolyte membrane. 3 is a diagram showing the cerium ion substitution rate in each layer of the fuel cell stack of Comparative Example 1. FIG. FIG. 3 is a diagram showing the cerium ion substitution rate in each layer of the fuel cell stack of Example 1. It is a graph showing the relationship between the substitution rate to cerium ions and the proton resistance value of the electrolyte membrane. It is a graph showing the relationship between the substitution rate to cerium ions and the output of the fuel cell.

Embodiments of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments, but can be implemented with various modifications.

《Laminated body for fuel cells》
The laminate for a fuel cell of the present invention is at least a part of a laminate that constitutes a fuel cell, and is a laminate in which a gas diffusion layer, a catalyst layer, and an electrolyte membrane are laminated in this order. In the gas diffusion layer, a microporous layer and a diffusion layer base material layer are laminated in this order from the catalyst layer side.

In the fuel cell laminate of the present invention, in the initial state after forming the fuel cell laminate, the microporous layer contains a cerium-containing oxide, and the catalyst layer and the electrolyte membrane have sulfonic acid groups. A portion of the protons in the ionomer are substituted with cerium ions, and the substitution rate in the catalyst layer and the substitution rate in the electrolyte membrane have a specific relationship.

In the fuel cell laminate of the present invention, the electrolyte membrane has cerium ions in the initial state when the fuel cell is started to be used, so that the electrolyte membrane can be thinned immediately after the fuel cell starts to be used. can be suppressed.

In addition, in the fuel cell stack of the present invention, the cerium ion substitution rate of the ionomer contained in each of the catalyst layer and the electrolyte membrane has a specific relationship in the initial state at the time of starting use after manufacturing the fuel cell. By having this, it becomes possible to guide cerium ions eluted from the microporous layer to the electrolyte membrane side during use of the fuel cell.

Therefore, even if cerium ions in the electrolyte membrane are lost little by little along with generated water etc. over a long period of use, it is possible to replenish the electrolyte membrane with cerium ions little by little from the microporous layer, resulting in a concentration of cerium ions in the electrolyte membrane. This makes it possible to suppress a sudden rise in . As a result, it is possible to suppress thinning of the electrolyte membrane immediately after the start of use of the fuel cell, and to suppress an increase in the proton resistance value of the electrolyte membrane, and it is possible to maintain the output performance of the fuel cell for a long period of time.

The laminate for a fuel cell of the present invention may include other layers as long as it includes a gas diffusion layer, a catalyst layer, and an electrolyte membrane as essential components. Examples of other layers include, but are not limited to, separators.

Furthermore, the laminate for a fuel cell of the present invention may include an electrolyte membrane, an anode side catalyst layer, and an anode side gas diffusion layer, or an electrolyte membrane, a cathode side catalyst layer, and a cathode side gas diffusion layer. Alternatively, it may be a membrane electrode gas diffusion layer assembly (MEGA) including both an anode side and a cathode side.

The structure of the laminate stored in a typical fuel cell includes, for example, an anode separator, an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, a cathode gas diffusion layer, and a cathode gas diffusion layer. A laminate in which side separators are laminated in this order can be mentioned.

FIG. 1 is a sectional view of a laminate for a fuel cell of the present invention according to one embodiment. The laminate 100 according to one embodiment includes an anode gas diffusion layer 10 in which an anode diffusion layer base material layer 11 and an anode microporous layer 12 are laminated, an anode catalyst layer 15, an electrolyte membrane 30, and a cathode catalyst layer. 25, and the cathode gas diffusion layer 20 in which the cathode diffusion layer base material layer 21 and the cathode microporous layer 22 are laminated in this order.

In the laminate 100 shown in FIG. 1, the microporous layer in the gas diffusion layer faces the catalyst layer on each of the anode side and the cathode side.

<Gas diffusion layer>
In the fuel cell laminate of the present invention, the gas diffusion layer is an essential constituent layer. In the laminate of the present invention, the gas diffusion layer is adjacent to the catalyst layer.

The gas diffusion layer has the function of diffusing and making the supplied reaction gas uniform, and spreading the gas to adjacent catalyst layers.

In the present invention, the gas diffusion layer is a laminate in which a microporous layer is laminated on a diffusion layer base material layer. Then, the microporous layer is arranged so as to face the adjacent catalyst layer.

(Diffusion layer base material layer)
The diffusion layer base material layer in the gas diffusion layer is a porous layer that supplies reactive gas to the adjacent catalyst layer. The diffusion layer base material layer is preferably made of a material that is gas permeable and electrically conductive.

In the fuel cell laminate of the present invention, any material that is commonly used as a diffusion layer base material can be used without particular limitation. For example, carbon porous materials such as carbon paper or carbon cloth can be used. or a metal porous body such as a metal mesh or a metal foam. Note that the carbon porous body such as carbon paper or carbon cloth may be made of, for example, carbon fibers and a binder such as a resin that is carbonized by firing.

In the present invention, the pore diameter, density, thickness, etc. of the diffusion layer base material layer constituting the gas diffusion layer are not particularly limited, regardless of whether it is on the anode side or the cathode side. It can be set as appropriate depending on the required performance of the fuel cell.

(Microporous layer (MPL))
The microporous layer in the gas diffusion layer is a layer that exists on the diffusion layer base material layer and is disposed on the catalyst layer side. By forming MPL in the gas diffusion layer constituting the stacked body for fuel cells, gas diffusivity in the fuel cell is improved.

The method for manufacturing the microporous layer (MPL) is not particularly limited, but for example, a slurry for forming the MPL is applied to the surface of the diffusion layer base material using a die coater, or a paste for forming the MPL is applied. An example of this method is to apply the coating by discharging it from a processing head, and then drying and baking it.

The gas diffusion layer constituting the laminate for a fuel cell of the present invention may be on either the anode side or the cathode side, but in either case, the microporous layer (MPL) is In the initial state when the laminate is formed, it contains a cerium-containing oxide that generates cerium ions, which are hydrogen peroxide decomposition catalysts.

Therefore, in the fuel cell laminate of the present invention, the MPL forming slurry or MPL forming paste for forming the microporous layer (MPL) may be used on either the anode side or the cathode side. This results in a composition containing a cerium-containing oxide as an essential component.

The cerium-containing oxide is not particularly limited, and includes, for example, cerium oxide (CeO ₂ ).

Further, other components constituting the microporous layer in the gas diffusion layer are not particularly limited, but generally include carbon particles and water-repellent resin as main components.

Examples of the carbon particles include particles of carbon black, graphene, graphite, and the like.

The average primary particle size of the carbon particles may be 25 nm to 70 nm. The average primary particle diameter of the carbon particles may be 25 nm or more, 45 nm or more, or 65 nm or more, and may be 70 nm or less, 60 nm or less, or 50 nm or less.

Note that the average primary particle diameter of carbon particles is calculated using an electron microscope such as a transmission electron microscope (TEM) or a scanning electron microscope (SEM). This value is the arithmetic average of the measured values obtained.

Examples of the water-repellent resin include fluorine-based polymer materials such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer, polypropylene, Examples include polyethylene.

In the fuel cell laminate of the present invention, the thickness of the microporous layer (MPL) constituting the gas diffusion layer is not particularly limited, regardless of whether it is on the anode side or the cathode side. It can be set as appropriate depending on the required performance of the fuel cell. For example, it may be 20 μm or more.

<Catalyst layer>
The catalyst layer is an essential constituent layer in the fuel cell stack of the present invention. In the fuel cell stack of the present invention, the catalyst layer is arranged between the gas diffusion layer and the electrolyte membrane.

The stack for fuel cells of the present invention may be on either the anode side or the cathode side, but in either case, the catalyst layer is in the initial state when forming the stack for fuel cells. , contains an ionomer having a sulfonic acid group, and a portion of the protons (H ⁺ ) of the sulfonic acid group are substituted with cerium ions.

In the fuel cell laminate of the present invention, the material constituting the catalyst layer is the above-mentioned ionomer containing a sulfonic acid group, and a portion of the protons (H ⁺ ) of the sulfonic acid group are substituted with cerium ions. Other components are not particularly limited as long as they contain an ionomer, and any known catalyst layer forming material can be used.

When the catalyst layer in the laminate of the present invention is the catalyst layer on the anode side, it has a function of decomposing hydrogen (H ₂ ), which is a reaction gas, into protons (H ⁺ ) and electrons (e ⁻ ). On the other hand, the catalyst layer on the cathode side has the function of generating water (H ₂ O) from protons (H ⁺ ), electrons (e ⁻ ), and oxygen (O ₂ ).

The catalyst layers on the anode side and the cathode side can be formed of similar materials. For example, a conductive carrier supporting a catalyst such as platinum or a platinum alloy is used, and more specifically, a catalyst-supported carbon carrier in which a catalyst is supported on carbon particles such as carbon black that functions as a conductive substance is used. Examples include a layer composed of particles and an electrolyte component that exhibits proton conductivity through ion exchange groups, which is a component of the electrolyte membrane described above. The layer may be formed by coating catalyst-supported carbon particles with an electrolyte component such as an ionomer having proton conductivity.

In the laminate of the present invention, the thickness of the catalyst layer is not particularly limited, and can be appropriately set depending on the required performance of the fuel cell to be formed.

<Electrolyte membrane>
The electrolyte membrane is an essential constituent layer in the fuel cell stack of the present invention, and is disposed adjacent to the catalyst layer. The electrolyte membrane has the function of blocking the flow of electrons and gas and moving protons (H ⁺ ) generated at the anode from the anode catalyst layer to the cathode catalyst layer.

The electrolyte membrane in the fuel cell laminate of the present invention contains an ionomer having a sulfonic acid group in the initial state after forming the fuel cell laminate, and some of the protons (H ⁺ ) of the sulfonic acid group are , is substituted with cerium ion.

In the fuel cell laminate of the present invention, the electrolyte membrane has cerium ions in the initial state when the fuel cell is started to be used, so that the electrolyte membrane can be thinned immediately after the fuel cell starts to be used. can be suppressed.

In the fuel cell laminate of the present invention, the material constituting the electrolyte membrane is the above-mentioned ionomer containing a sulfonic acid group, and a portion of the protons (H ⁺ ) of the sulfonic acid group are replaced with cerium ions. Other components are not particularly limited as long as they contain an ionomer, and materials known as electrolyte membranes used in fuel cells can be used.

Examples of the ionomer containing a sulfonic acid group include a polymer electrolyte resin having ion conductivity such as perfluorosulfonic acid (PFSA) ionomer. Furthermore, examples of materials having groups other than sulfonic acid groups include resins containing other ion exchange groups (electrolyte components) such as phosphoric acid groups and carboxylic acid groups.

The thickness of the electrolyte membrane is not particularly limited, and can be appropriately set depending on the required performance of the fuel cell to be formed. The thickness of the electrolyte membrane may be, for example, 10 μm or less.

<Other layers>
The laminate for a fuel cell of the present invention may include other layers as long as it includes a gas diffusion layer, a catalyst layer, and an electrolyte membrane as essential components. Examples of other layers include, but are not limited to, separators.

<Relationship of cerium ion replacement rate in the fuel cell stack in the initial state>
In the fuel cell laminate of the present invention, in the initial state at the beginning of use after manufacturing the fuel cell, the catalyst layer and the electrolyte membrane contain an ionomer having a sulfonic acid group, and one of the protons of the sulfonic acid group is part is substituted with cerium ion.

The cerium ion substitution rate in the catalyst layer is greater than the cerium ion substitution rate in the electrolyte membrane.

In the present invention, the "substitution rate" in which the protons of the sulfonic acid groups in the ionomer are substituted with cerium ions can be determined as the ratio of the total amount of cerium ions to the total amount of sulfonic acid groups.

FIG. 2 shows a membrane electrode gas diffusion layer assembly in which the laminate for a fuel cell of the present invention is composed of an anode side gas diffusion layer, an anode side catalyst layer, an electrolyte membrane, a cathode side catalyst layer, and a cathode side gas diffusion layer. (MEGA), the protons ( This is an example showing the substitution rate, which is the rate at which cerium ions (H ⁺ ) are substituted with cerium ions.

In the laminate shown in FIG. 2, the cerium ion substitution rate in the electrolyte membrane is smaller than the cerium ion substitution rate in the catalyst layers on the anode side and the cathode side.

In the laminate shown in FIG. 2, the cerium ion substitution rates in the anode and cathode catalyst layers are almost the same, but the present invention is applied to both the anode and cathode catalyst layers. In this case, the cerium ion substitution rates may be the same or different. In addition, if they are different, the substitution rate of either catalyst layer may be large, but it is preferable that the substitution rate of the cathode side catalyst layer is large.

In the fuel cell stack of the present invention, in the initial state at the time of starting use after manufacturing the fuel cell, the cerium ion substitution rate of the ionomer contained in the catalyst layer is the same as the cerium ion substitution rate of the ionomer contained in the electrolyte membrane. By being larger than , it becomes possible to guide cerium ions eluted from the microporous layer to the electrolyte membrane side during use of the fuel cell.

Therefore, over a long period of use, it becomes possible to replenish the electrolyte membrane with cerium ions little by little, and it becomes possible to suppress a rapid increase in the cerium ion concentration in the electrolyte membrane, thereby increasing the proton resistance of the electrolyte membrane. This makes it possible to suppress the increase in fuel cell output and maintain the output performance of the fuel cell for a long period of time.

Hereinafter, the present invention will be explained in more detail by showing experimental results.

<Example 1>
In Example 1, a membrane electrode gas diffusion layer assembly (MEGA) was prepared in which the anode side gas diffusion layer/anode side catalyst layer/electrolyte membrane/cathode side catalyst layer/cathode side gas diffusion layer were laminated in this order. By sandwiching them between a pair of separators, a laminate that would become a fuel cell was fabricated.

The anode-side and cathode-side gas diffusion layers were arranged such that their respective microporous layers (MPLs) faced the adjacent anode-side and cathode-side catalyst layers, respectively.

The microporous layer (MPL) in the anode side gas diffusion layer and the microporous layer (MPL) in the cathode side gas diffusion layer used in Example 1 contained cerium oxide (CeO ₂ ).

In addition, the anode side catalyst layer, the electrolyte membrane, and the cathode side catalyst layer contain an ionomer having a sulfonic acid group, and in the initial state when forming a stack for a fuel cell, protons (H ⁺ ) of the sulfonic acid group A part of is replaced with cerium ions, so that the cerium ion substitution rate in the catalyst layer is greater than the cerium ion substitution rate in the electrolyte membrane.

<Comparative example 1>
In Comparative Example 1, a membrane electrode gas diffusion layer assembly (MEGA) was produced with the same configuration as in Example 1, and sandwiched between a pair of separators to produce a laminate that would become a fuel cell.

As in Example 1, the anode-side and cathode-side gas diffusion layers were arranged such that their respective microporous layers (MPLs) faced the adjacent anode-side and cathode-side catalyst layers, respectively.

The microporous layer (MPL) in the anode side gas diffusion layer and the microporous layer (MPL) in the cathode side gas diffusion layer used in Comparative Example 1 contained cerium oxide (CeO ₂ ) as in Example 1. .

However, although the anode side catalyst layer, electrolyte membrane, and cathode side catalyst layer used in Comparative Example 1 contain an ionomer having a sulfonic acid group, the protons (H ⁺ ) of the sulfonic acid group are replaced by cerium ions. It was assumed that the That is, in the fuel cell stack produced in Comparative Example 1, none of the anode-side catalyst layer, electrolyte membrane, and cathode-side catalyst layer contains cerium ions in the initial state of forming the stack.

<Battery evaluation>
A fuel cell was produced using the fuel cell stack produced in Example 1 and Comparative Example 1, and a durability test was conducted. As a durability test, a temperature change durability test was conducted, in which the temperature was repeatedly raised and lowered a specific number of times while sweeping the current at a constant low current density.

(Cerium ion concentration in electrolyte membrane)
Regarding the fuel cells produced in Example 1 and Comparative Example 1, the cerium ion (Ce ³⁺ ) concentration in the electrolyte membrane was evaluated in a temperature change durability test.

FIG. 3 shows the relationship between the durability time of the fuel cells produced in Example 1 and Comparative Example 1 and the cerium ion concentration in the electrolyte membrane. In FIG. 3, the broken line is the fuel cell produced in Example 1, and the solid line is the fuel cell produced in Comparative Example 1.

The horizontal axis in FIG. 3 indicates the endurance time after the start of use of the fuel cell, and the vertical axis indicates the cerium ion (Ce ³⁺ ) concentration in the electrolyte membrane in relative concentration. Note that the line C on the vertical axis is a line where membrane thinning of the electrolyte membrane occurs.

As shown in FIG. 3, the fuel cell manufactured in Comparative Example 1 has a certain durability time because cerium ions are not present in the electrolyte membrane in the initial state at the time of starting use after manufacturing the fuel cell. It can be seen that membrane thinning of the electrolyte membrane continues to occur until the process progresses.

On the other hand, in the fuel cell manufactured in Example 1, cerium ions are already present in the electrolyte membrane in the initial state at the time of starting use after manufacturing the fuel cell. This exceeds the criteria for thinning to occur, and it can be seen that membrane thinning of the electrolyte membrane has been avoided from the beginning of use.

(Cerium ion substitution rate in each layer)
Regarding the fuel cells produced in Example 1 and Comparative Example 1, the sulfonic acid group in the ionomer was found in the electrolyte membrane, the cathode side catalyst layer, and the cathode side microporous layer in the initial state at the time of starting use after production of the fuel cell. The substitution rate at which protons (H+) were replaced with cerium ions was determined. Similarly, the cerium ion substitution rate in the electrolyte membrane, the cathode catalyst layer, and the cathode microporous layer after the temperature change durability test was determined.

The cerium ion substitution rate was calculated from the total amount of cerium ions relative to the total amount of sulfonic acid groups per unit area.

Figure 4 shows the cerium ion substitution rate in the electrolyte membrane, cathode side catalyst layer, and cathode side microporous layer in the initial state and the respective cerium ion substitution rates after the durability test for the fuel cell fabricated in Comparative Example 1. This is a graph showing .

The horizontal axis in FIG. 4 indicates each layer, and the vertical axis indicates the cerium ion replacement rate. Line C on the vertical axis is a line where thinning of the electrolyte membrane occurs.

Note that since the microporous layer does not contain an ionomer, the cerium substitution rate, which is calculated as the total amount of cerium ions relative to the total amount of sulfonic acid groups, was expressed as infinite.

From FIG. 4, in the fuel cell fabricated in Comparative Example 1, cerium ions eluted from the microporous layer during use of the fuel cell move to the electrolyte membrane and until a sufficient relaxation rate is reached, cerium ions in the electrolyte membrane It is understood that the ion concentration is insufficient, which causes thinning of the electrolyte membrane.

FIG. 5 shows the cerium ion substitution rate in the electrolyte membrane, cathode side catalyst layer, and cathode side microporous layer in the initial state and the respective cerium ion substitution rates after the durability test for the fuel cell fabricated in Example 1. This is a graph showing .

The horizontal axis in FIG. 5 indicates each layer, and the vertical axis indicates the cerium ion replacement rate. Note that the line C on the vertical axis is a line where membrane thinning of the electrolyte membrane occurs.

As shown in FIG. 5, in the fuel cell manufactured in Example 1, the electrolyte membrane has cerium ions in the initial state at the beginning of use after manufacturing the fuel cell. It can be seen that the criteria for membrane thinning to occur is exceeded, and membrane thinning of the electrolyte membrane can be avoided.

In addition, in the fuel cell produced in Example 1, in the initial state at the time of starting use after manufacturing the fuel cell, the catalyst layer and the electrolyte membrane contain cerium ions, and the catalyst layer contains cerium ions. The cerium ion substitution rate, in which the protons (H ⁺ ) of the sulfonic acid groups in the ionomer are replaced with cerium ions, is greater than the cerium ion substitution rate in the electrolyte membrane, and fuel cell durability tests have shown that the microporous layer It can be seen that the cerium ions eluted from the sample were guided to the electrolyte membrane.

In other words, in the fuel cell fabricated in Example 1, even if cerium ions in the electrolyte membrane are gradually lost along with generated water etc. during long-term use, cerium ions are gradually replenished from the microporous layer to the electrolyte membrane. This suppresses membrane thinning of the electrolyte membrane immediately after the start of use of the fuel cell, prevents a sudden increase in the cerium ion concentration in the electrolyte membrane, and maintains the output performance of the fuel cell for a long period of time. It can be predicted that it will be possible.

100 Laminated body 10 Anode side gas diffusion layer 11 Anode side diffusion layer base material layer 12 Anode side microporous layer 15 Anode side catalyst layer 20 Cathode side gas diffusion layer 21 Cathode side diffusion layer base material layer 22 Cathode side microporous layer 25 Cathode Side catalyst layer 30 Electrolyte membrane

Claims (1)

A stacked body for a fuel cell in which an anode side gas diffusion layer, an anode side catalyst layer, an electrolyte layer, a cathode side catalyst layer, and a cathode side gas diffusion layer are stacked in this order,
The anode side gas diffusion layer and the cathode side gas diffusion layer include a microporous layer and a diffusion layer base material layer stacked in this order from the anode side catalyst layer side and the cathode side catalyst layer side, respectively,
The microporous layer includes a cerium-containing oxide,
The anode side catalyst layer, the cathode side catalyst layer, and the electrolyte membrane include an ionomer having a sulfonic acid group,
In the initial state of forming a laminate for a fuel cell, some of the sulfonic acid groups are cerium ion-substituted sulfonic acid groups in which protons of the sulfonic acid groups are replaced with cerium ions,
In the initial state of forming a fuel cell stack, the rate of substitution of the sulfonic acid groups with cerium ions in the anode side catalyst layer and the cathode side catalyst layer is determined by the substitution rate of the sulfonic acid groups with cerium ions in the electrolyte membrane. greater than the replacement rate,
The substitution rate of the sulfonic acid groups with cerium ions in the cathode side catalyst layer is higher than the substitution rate of the sulfonic acid groups with cerium ions in the anode side catalyst layer.
Laminate for fuel cells.

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