Patent Description:
According to a technique called water electrolysis conventionally known, hydrogen (H<NUM>) is produced through electrolysis of water (H<NUM>O). Several types of water electrolysis are prepared in response to electrolytes to be used. One of these types is solid polymer water electrolysis that uses an ion-exchange membrane (electrolyte membrane) as an electrolyte. The solid polymer water electrolysis uses a cell with catalyst layers formed on both surfaces of the electrolyte membrane. During implementation of the water electrolysis, a voltage is applied between an anode-side catalyst layer and a cathode-side catalyst layer and water is supplied to the anode-side catalyst layer. This causes electrochemical reactions as follows at the anode-side catalyst layer and the cathode-side catalyst layer. As a result, hydrogen is output from the cathode-side catalyst layer.

The conventional solid polymer water electrolysis is disclosed in Patent Literature <NUM>, for example.

Patent Literature <NUM> discloses a membrane electrode assembly, comprising an electrode membrane, and a catalyst layer formed on one surface of said electrolyte membrane, wherein said anode catalyst layer includes a catalyst particle, an ionomer and a water-repellent particle.

Patent Literature <NUM> discloses a catalyst layer, wherein said catalyst layer includes a catalyst particle and an ionomer.

As described above, according to the solid polymer water electrolysis, oxygen is to be output from the anode-side catalyst layer. This necessitates supply of water and output of oxygen to and from the anode-side catalyst layer. In some cases, during these supply and output, output of oxygen is hindered by the influence of water supplied to the catalyst layer. In such cases, degradation of the performance of outputting oxygen causes a problem that efficiency of hydrogen production through the solid polymer water electrolysis will be reduced.

According to the solid polymer water electrolysis, water filling the anode-side catalyst layer partially leaks to the cathode-side catalyst layer through the electrolyte membrane. Then, the water having entered the cathode-side catalyst layer may hinder output of generated hydrogen. This causes a problem that efficiency of hydrogen output will be reduced.

The present invention has been made in view of the above-described circumstances, and is intended to provide a technique that achieves improvement of the performance of outputting a substance generated in a catalyst layer.

To solve the above-described problem, a first aspect of the present invention is intended for a membrane electrode assembly comprising: an electrolyte membrane; and an anode catalyst layer formed on one surface of the electrolyte membrane, wherein the anode catalyst layer includes a catalyst particle; an ionomer; and a water-repellent particle, and the water-repellent particle is a ceramic particle with a fluorine group or a metallic particle with a fluorine group.

According to a second aspect of the present invention, in the membrane electrode assembly according to the first aspect, the ratio of the water-repellent particle to the catalyst particle is equal to or greater than <NUM> wt% and equal to or less than <NUM> wt%.

According to a third aspect of the present invention, in the membrane electrode assembly according to the second aspect, the ratio of the water-repellent particle to the catalyst particle is equal to or greater than <NUM> wt% and equal to or less than <NUM> wt%.

According to a fourth aspect of the present invention, in the membrane electrode assembly according to any one of the first to third aspects, the ionomer has an EW value, indicating the dry mass of the ionomer per mol of ion-exchange groups, of equal to or less than <NUM>.

According to a fifth aspect of the present invention, in the membrane electrode assembly according to any one of the first to fourth aspects, the ratio of the ionomer to the catalyst particle is equal to or greater than <NUM> wt% and equal to or less than <NUM> wt%.

A sixth aspect of the present invention is intended for a hydrogen producing device that produces hydrogen through solid polymer water electrolysis, comprising the membrane electrode assembly according to anyone of the first to fifth aspects.

An seventh aspect of the present invention is intended for a method of producing catalyst ink to become an anode catalyst layer of a membrane electrode assembly, comprising: a first step of forming a first preparation liquid by blending a catalyst particle and water; a second step of forming a second preparation liquid by adding an alcohol solution to the first preparation liquid; a third step of forming a third preparation liquid by adding a water-repellent particle to the second preparation liquid; and a fourth step of forming a fourth preparation liquid by adding a solution of an ionomer to the third preparation liquid, wherein the water-repellent particle is a ceramic particle with a fluorine group or a metallic particle with a fluorine group.

According to a eighth aspect of the present invention, in the method of producing the catalyst ink according to the seventh aspect, the ratio of the alcohol solution to the catalyst ink is equal to or greater than <NUM> wt%.

A ninth aspect of the present invention is intended for a method of producing a membrane electrode assembly comprising the step of: applying catalyst ink produced by the producing method according to the seventh or eighth aspect to one surface of an electrolyte membrane and drying the applied catalyst ink, thereby forming the anode catalyst layer.

According to the first to sixth aspects of the present invention, adding the water-repellent particle to the anode catalyst layer achieves improvement of the performance of outputting a substance generated in the anode catalyst layer.

In particular, the second aspect of the present invention achieves improvement of the performance of outputting a substance generated in the anode catalyst layer and achieves reduction in the probability of degradation of electrical conductivity in the anode catalyst layer caused by the influence of the fluorine group.

In particular, the third aspect of the present invention achieves further improvement of the performance of outputting a substance generated in the anode catalyst layer and achieves further reduction in the probability of degradation of electrical conductivity in the anode catalyst layer caused by the influence of the fluorine group.

In particular, according to the fourth aspect of the present invention, the number of ion-exchange groups in a polymer chain of the ionomer is increased. This allows oxonium ions to propagate favorably.

In particular, the fifth aspect of the present invention allows the catalyst particle to be covered with the ionomer favorably. Furthermore, the presence of a void left in the anode catalyst layer achieves favorable output of a substance to be generated.

According to the seventh to ninth aspects of the present invention, the water-repellent particle is added to the catalyst ink to become the anode catalyst layer. This achieves improvement of the performance of outputting a substance generated in the anode catalyst layer. Furthermore, the water-repellent particle is added after addition of the alcohol solution. This allows the water-repellent particle to disperse uniformly.

In particular, the eighth aspect of the present invention allows the water-repellent particle to disperse more uniformly.

A preferred embodiment of the present invention will be described below by referring to the drawings.

<FIG> is a schematic view of a hydrogen producing device <NUM> according to a preferred embodiment of the present invention. The hydrogen producing device <NUM> is a device that produces hydrogen through solid polymer water electrolysis. As shown in <FIG>, the hydrogen producing device <NUM> includes a cell composed of an electrolyte membrane <NUM>, an anode catalyst layer <NUM>, an anode gas diffusion layer <NUM>, an anode gasket <NUM>, an anode separator <NUM>, a cathode catalyst layer <NUM>, a cathode gas diffusion layer <NUM>, a cathode gasket <NUM>, and a cathode separator <NUM>. Of these layers of the cell, the electrolyte membrane <NUM>, the anode catalyst layer <NUM>, and the cathode catalyst layer <NUM> form a stack corresponding to a membrane electrode assembly (MEA) <NUM> according to the preferred embodiment of the present invention.

The electrolyte membrane <NUM> is a membrane like a thin plate having ion conductivity (ion-exchange membrane). A fluorine-based or hydrocarbon-based polymer electrolyte membrane is used as the electrolyte membrane <NUM>. More specifically, a polymer electrolyte membrane containing perfluorocarbon sulfonic acid is used as the electrolyte membrane <NUM>, for example. The electrolyte membrane <NUM> has a thickness from <NUM> to <NUM>, for example.

The anode catalyst layer <NUM> is a layer functioning as an anode-side electrode. The anode catalyst layer <NUM> is formed on an anode-side surface of the electrolyte membrane <NUM>. The anode catalyst layer <NUM> contains a large number of catalyst particles. The catalyst particles are particles of iridium oxide (IrOx), platinum (Pt), an alloy of iridium (Ir) and ruthenium (Ru), or an alloy of iridium (Ir) and titanium dioxide (TiO<NUM>), for example. During use of the hydrogen producing device <NUM>, water (H<NUM>O) is supplied to the anode catalyst layer <NUM>. Then, a voltage is applied between the anode catalyst layer <NUM> and the cathode catalyst layer <NUM> from a power supply <NUM> described later. By doing so, by the actions of the applied voltage and the catalyst particles, the water is electrolyzed into hydrogen ions (H+), oxygen (O<NUM>), and electrons (e-) in the anode catalyst layer <NUM>.

The composition of the anode catalyst layer <NUM> will be described later in more detail.

The anode gas diffusion layer <NUM> is a layer for supplying water uniformly to the anode catalyst layer <NUM> and for transmitting oxygen and electrons generated in the anode catalyst layer <NUM> to the anode separator <NUM>. The anode gas diffusion layer <NUM> is stacked on an outer surface of the anode catalyst layer <NUM>. The anode catalyst layer <NUM> is interposed between the electrolyte membrane <NUM> and the anode gas diffusion layer <NUM>. The anode gas diffusion layer <NUM> has electrical conductivity and is made of a porous material. As an example, carbon paper is used as the anode gas diffusion layer <NUM>.

The anode gasket <NUM> is a layer for preventing leakage of water and oxygen from the anode catalyst layer <NUM> and from the anode gas diffusion layer <NUM> to their surroundings. As shown in <FIG>, the anode gasket <NUM> is formed on the anode-side surface of the electrolyte membrane <NUM> and surrounds the anode catalyst layer <NUM> and the anode gas diffusion layer <NUM>.

The anode separator <NUM> is a layer for supplying water to the anode gas diffusion layer <NUM> and for transmitting electrons coming from the anode catalyst layer <NUM> through the anode gas diffusion layer <NUM> to the power supply <NUM>. The anode separator <NUM> also functions to output oxygen generated in the anode catalyst layer <NUM> to the outside. The anode separator <NUM> is formed on an outer surface of the anode gas diffusion layer <NUM> and on an outer surface of the anode gasket <NUM>. The anode catalyst layer <NUM>, the anode gas diffusion layer <NUM>, and the anode gasket <NUM> are interposed between the electrolyte membrane <NUM> and the anode separator <NUM>.

The anode separator <NUM> has electrical conductivity and is made of a material without permeability to gas. The anode separator <NUM> is provided with a large number of grooves <NUM>. Water is supplied to the anode gas diffusion layer <NUM> through the grooves <NUM> of the anode separator <NUM>. Oxygen generated in the anode catalyst layer <NUM> passes through the anode gas diffusion layer <NUM> and is then output to the outside through the grooves <NUM> of the anode separator <NUM>.

The cathode catalyst layer <NUM> is a layer functioning as a cathode-side electrode. The cathode catalyst layer <NUM> is formed on a cathode-side surface of the electrolyte membrane <NUM> (a surface on the opposite side to the anode catalyst layer <NUM>). The cathode catalyst layer <NUM> contains a large number of carbon particles on which catalyst particles are supported. The catalyst particles are particles of platinum, for example. Alternatively, the catalyst particles may be prepared by mixing a tiny amount of ruthenium or cobalt particles into particles of platinum. During use of the hydrogen producing device <NUM>, hydrogen ions (H+) and electrons (e-) are supplied to the cathode catalyst layer <NUM>. Then, a voltage is applied between the anode catalyst layer <NUM> and the cathode catalyst layer <NUM> by the power supply <NUM> described later. By doing so, by the actions of the applied voltage and the catalyst particles, a reduction reaction is caused in the cathode catalyst layer <NUM> to generate hydrogen gas (H<NUM>) from the hydrogen ions and the electrons.

The cathode gas diffusion layer <NUM> is a layer for transmitting electrons from the cathode separator <NUM> to the cathode catalyst layer <NUM> and for transmitting hydrogen generated in the cathode catalyst layer <NUM> to the cathode separator <NUM>. The cathode gas diffusion layer <NUM> is stacked on an outer surface of the cathode catalyst layer <NUM>. The cathode catalyst layer <NUM> is interposed between the electrolyte membrane <NUM> and the cathode gas diffusion layer <NUM>. The cathode gas diffusion layer <NUM> has electrical conductivity and is made of a porous material. As an example, carbon paper is used as the cathode gas diffusion layer <NUM>.

The cathode gasket <NUM> is a layer for preventing leakage of hydrogen from the cathode catalyst layer <NUM> and from the cathode gas diffusion layer <NUM> to their surroundings. As shown in <FIG>, the cathode gasket <NUM> is formed on the cathode-side surface of the electrolyte membrane <NUM> and surrounds the cathode catalyst layer <NUM> and the cathode gas diffusion layer <NUM>.

The cathode separator <NUM> is a layer for transmitting electrons supplied from the power supply <NUM> to the cathode gas diffusion layer <NUM> and for outputting generated hydrogen to the outside. The cathode separator <NUM> is formed on an outer surface of the cathode gas diffusion layer <NUM> and on an outer surface of the cathode gasket <NUM>. The cathode catalyst layer <NUM>, the cathode gas diffusion layer <NUM>, and the cathode gasket <NUM> are interposed between the electrolyte membrane <NUM> and the cathode separator <NUM>. The cathode separator <NUM> has electrical conductivity and is made of a material without permeability to gas. The cathode separator <NUM> is provided with a large number of grooves <NUM>. Hydrogen from the cathode gas diffusion layer <NUM> passes through the grooves <NUM> and is then output to the outside.

The power supply <NUM> is connected between the anode separator <NUM> and the cathode separator <NUM>. More specifically, the power supply <NUM> has a positive terminal electrically connected to the anode separator <NUM>. The power supply <NUM> has a negative terminal electrically connected to the cathode separator <NUM>. The power supply <NUM> applies a voltage necessary for electrolysis of water between the anode separator <NUM> and the cathode separator <NUM>.

During use of the hydrogen producing device <NUM>, water is supplied from the anode separator <NUM> to the anode catalyst layer <NUM> through the anode gas diffusion layer <NUM>. Then, by the actions of a voltage applied from the power supply <NUM> and the catalyst parties in the anode catalyst layer <NUM>, water is decomposed into hydrogen ions, oxygen, and electrons. The hydrogen ions propagate through the electrolyte membrane <NUM> into the cathode catalyst layer <NUM>. The oxygen passes through the anode gas diffusion layer <NUM> and the anode separator <NUM> and is then output to the outside. The electrons pass through the anode gas diffusion layer <NUM>, the anode separator <NUM>, the power supply <NUM>, the cathode separator <NUM>, and the cathode gas diffusion layer <NUM> and then flow into the cathode catalyst layer <NUM>. Next, at the cathode catalyst layer <NUM>, the hydrogen ions and the electrons are combined with each other to generate hydrogen. The generated hydrogen passes through the cathode gas diffusion layer <NUM> and the cathode separator <NUM> and is then output to the outside. In this way, hydrogen is produced.

The composition of the above-described anode catalyst layer <NUM> will be described next in more detail.

<FIG> is a schematic view conceptually showing the composition of the anode catalyst layer <NUM>. As shown in <FIG>, the anode catalyst layer <NUM> includes multiple catalyst particles <NUM>, an ionomer <NUM>, and multiple water-repellent particles <NUM>.

The catalyst particles <NUM> are particles for causing electrolysis of water. For example, the catalyst particles <NUM> are made of iridium oxide, platinum, an alloy of iridium and ruthenium, or an alloy of iridium and titanium dioxide.

The ionomer <NUM> is an electrolyte polymer covering the catalyst particles <NUM>. The ionomer <NUM> functions to transport hydrogen ions generated through electrolysis of water in the anode catalyst layer <NUM>. For example, nafion (perfluorocarbon sulfonic acid) is used as the ionomer <NUM>. The ionomer <NUM> has a polymer chain with an ion-exchange group such as a sulfone group. The hydrogen ions are combined with water in the cathode catalyst layer <NUM> to become oxonium ions (H<NUM>O+). These oxonium ions propagate through the ion-exchange group of the ionomer <NUM>.

For favorable propagation of the oxonium ions, it is desirable to prepare a large number of ion-exchange groups in the polymer chain of the ionomer <NUM>. More specifically, it is desirable that an EW value indicating the dry mass of the ionomer <NUM> per mol of ion-exchange groups (the reciprocal of the number of ion-exchange groups per unit mass of the ionomer <NUM>) will be set equal to or less than <NUM>. For example, the EW value is desirably set equal to or greater than <NUM> and equal to or less than <NUM>.

If the ratio of the ionomer <NUM> to the catalyst particles <NUM> is too small, it becomes impossible to cover the catalyst particles <NUM> with the ionomer <NUM> sufficiently. This makes it difficult for oxonium ions to propagate through the ionomer <NUM> favorably. On the other hand, if the ratio of the ionomer <NUM> to the catalyst particles <NUM> is too large, voids in the cathode catalyst layer <NUM> are reduced. This becomes hindrance to diffusion of water in the anode catalyst layer <NUM> or to output of oxygen generated in the anode catalyst layer <NUM>.

Thus, the ratio of the ionomer <NUM> to the catalyst particles <NUM> is desirably set to a ratio that allows the catalyst particles <NUM> to be covered with the ionomer <NUM> favorably, and achieves favorable diffusion of water and favorable output of oxygen. More specifically, the ratio (ratio by weight) of the ionomer <NUM> to the catalyst particles <NUM> is desirably set equal to or greater than <NUM> wt% and equal to or less than <NUM> wt%. More desirably, the ratio of the ionomer <NUM> (ratio by weight) to the catalyst particles <NUM> is set equal to or greater than <NUM> wt% and equal to or less than <NUM> wt%.

The water-repellent particles <NUM> are additives for improving the performance of outputting oxygen generated in the anode catalyst layer <NUM>. <FIG> is a conceptual view of the water-repellent particle <NUM>. As shown in <FIG>, the water-repellent particle <NUM> is composed of a body particle <NUM>, and multiple fluorine groups (F) with water repellency provided on a surface of the body particle <NUM>. The body particle <NUM> is a ceramic particle or a metallic particle, for example. The ceramic particle is a particle of titanium oxide (TiO<NUM>), for example. The metallic particle is a particle of a noble metal such as platinum (Pt), silver (Ag), or gold (Au), for example. The water-repellent particle <NUM> has a diameter of equal to or greater than <NUM> and equal to or less than <NUM>, for example.

The anode catalyst layer <NUM> contains water and receives a high voltage of about <NUM> V. Thus, if a carbon particle is used as the body particle <NUM>, oxidation of carbon (electron emission) proceeds in parallel with electrolysis. More specifically, a chemical reaction expressed by the following formula occurs to unintentionally cause disappearance of carbon (C). For this reason, it is desirable to avoid use of carbon and to use a ceramic particle or a metallic particle as the body particle <NUM> as described above.

<FIG> is a graph showing a relationship between the quantity of the water-repellent particles <NUM> added to the anode catalyst layer <NUM> and voltage characteristics of the hydrogen producing device <NUM>. In the graph of <FIG>, a horizontal axis shows the ratio (ratio by weight) of the water-repellent particles <NUM> to the catalyst particles <NUM>. A vertical axis shows a voltage value to be applied from the power supply <NUM> for generating hydrogen of a predetermined amount. The voltage value shown in the graph of <FIG> is determined at a current density of <NUM> A/cm<NUM>.

In response to addition of the water-repellent particles <NUM> to the anode catalyst layer <NUM>, water in the anode catalyst layer <NUM> is repelled by the water-repelling action of the fluorine groups. This reduces a likelihood that movement of oxygen generated in the anode catalyst layer <NUM> will be hindered by water. Thus, it becomes possible to output oxygen efficiently from the anode catalyst layer <NUM>. Improving the performance of outputting oxygen facilitates electrolysis of water further in the anode catalyst layer <NUM>.

Furthermore, adding the water-repellent particles <NUM> to the anode catalyst layer <NUM> reduces a likelihood that water in the anode catalyst layer <NUM> will enter the cathode catalyst layer <NUM> through the electrolyte membrane <NUM>. Thus, movement of hydrogen generated in the cathode catalyst layer <NUM> becomes less prone to hindrance by water. As a result, it becomes possible to output hydrogen efficiently from the cathode catalyst layer <NUM>.

As shown in <FIG>, as a result of the above-described actions, adding the water-repellent particles <NUM> to the anode catalyst layer <NUM> makes it possible to reduce a voltage value to be applied from the power supply <NUM> compared to a case in the absence of addition of the water-repellent particles <NUM>. Specifically, this achieves improvement of the efficiency of producing hydrogen through solid polymer water electrolysis.

However, if the quantity of the added water-repellent particles <NUM> is too large, the fluorine groups having insulating properties exert influence to increase an electrical resistance in the anode catalyst layer <NUM>. Hence, like in a case shown in <FIG> where the ratio by weight of the water-repellent particles <NUM> to the catalyst particles <NUM> is <NUM> wt%, this conversely increases a voltage value to be applied from the power supply <NUM>.

Thus, it is desirable that the water-repellent particles <NUM> will be added to a quantity with which the performance of outputting oxygen generated in the anode catalyst layer <NUM> can be improved and the probability of degradation of electrical conductivity in the anode catalyst layer <NUM> caused by the influence of the fluorine groups can be reduced. More specifically, the ratio (ratio by weight) of the water-repellent particles <NUM> to the catalyst particles <NUM> is desirably set equal to or greater than <NUM> wt% and equal to or less than <NUM> wt%. More desirably, the ratio (ratio by weight) of the water-repellent particles <NUM> to the catalyst particles <NUM> is set equal to or greater than <NUM> wt% and equal to or less than <NUM> wt%. For example, the ratio (ratio by weight) of the water-repellent particles <NUM> to the catalyst particles <NUM> is preferably set to <NUM> wt%.

As described above, in the anode catalyst layer <NUM>, hydrogen ions are combined with water to propagate as oxonium ions. Thus, for increasing the efficiency of propagation of the hydrogen ions, moisture of a certain degree is desirably retained uniformly in the anode catalyst layer <NUM>. However, too much moisture hinders the performance of outputting oxygen generated in the anode catalyst layer <NUM>. For this reason, it is desirable to optimize a moisture content to be retained in the anode catalyst layer <NUM>.

In this regard, reducing the above-described EW value of the ionomer <NUM> contributes to increasing a moisture content in the anode catalyst layer <NUM>. On the other hand, adding the water-repellent particles <NUM> contributes to reducing a moisture content in the anode catalyst layer <NUM>. Thus, by setting the EW value of the ionomer <NUM> to be equal to or less than <NUM> and by adding the water-repellent particles <NUM> as described above, it becomes possible to keep a moisture content retained in the anode catalyst layer <NUM> within an appropriate range. This achieves further improvement of the efficiency of producing hydrogen through solid polymer water electrolysis.

The anode catalyst layer <NUM> is formed by applying catalyst ink in paste form on a surface of the electrolyte membrane <NUM>. The following describes a method of producing the catalyst ink to become the anode catalyst layer <NUM>.

<FIG> is a flowchart showing a procedure of producing the catalyst ink. As shown in <FIG>, for producing the catalyst ink, the catalyst particles <NUM> and water are first blended to form a first preparation liquid (first step S1). In the first step S1, the water is added to prevent the catalyst particles <NUM> from catching fire.

Next, an alcohol solution is added to the first preparation liquid to form a second preparation liquid (second step S2). The alcohol solution is methanol, ethanol, <NUM>-propanol, or <NUM>-propanol, for example.

Next, the water-repellent particles <NUM> are added to the second preparation liquid to form a third preparation liquid (third step S3). The water-repellent particles <NUM> are ceramic particles with fluorine groups or metallic particles with fluorine groups. In the third step S3, the water-repellent particles <NUM> disperse in the alcohol solution added in the second step S2.

Adding the water-repellent particles <NUM> in the above-described first step S1 makes it likely that the water-repellent particles <NUM> will form lumps as a result of being prevented from dispersing in the first preparation liquid by the water-repelling action of the fluorine groups. By contrast, according to the present preferred embodiment, the alcohol solution having a small angle of contact (having high compatibility with the water-repellent particles <NUM>) is added in advance in the second step S2, and then the water-repellent particles <NUM> are added in the third step S3. This allows the water-repellent particles <NUM> to disperse uniformly in the third preparation liquid.

Next, an ionomer solution is added to the third preparation liquid to form a fourth preparation liquid (fourth step S4). The ionomer solution is a solution prepared by dissolving the ionomer <NUM> in water and alcohol. The ionomer solution has a high proportion of water, so that it is added after the water-repellent particles <NUM> are added and disperse in the third step S3.

Next, dispersing process is performed further on the fourth preparation liquid (fifth step S5). In the fifth step S5, the fourth preparation liquid is agitated, for example. This causes the water-repellent particles <NUM> to disperse more uniformly in the fourth preparation liquid. As a result, the catalyst ink is generated. The ratio (ratio by weight) of the alcohol solution to the catalyst ink finally generated is desirably set equal to or greater than <NUM> wt%. This allows the water-repellent particles <NUM> to disperse with still higher performance in the catalyst ink.

A method of producing the membrane electrode assembly <NUM> using the above-described catalyst ink will be described next.

<FIG> is a flowchart showing a procedure of producing the membrane electrode assembly <NUM>. As shown in <FIG>, for producing the membrane electrode assembly <NUM>, the catalyst ink for anode produced by the above-described procedure is applied to one of the surfaces of the electrolyte membrane <NUM> (sixth step S6). Then, the applied catalyst ink is dried (seventh step S7). By doing so, the anode catalyst layer <NUM> is formed on the one surface of the electrolyte membrane <NUM>.

Furthermore, catalyst ink for cathode is applied to the other surface of the electrolyte membrane <NUM> (eighth step S8). Then, the applied catalyst ink is dried (ninth step S9). By doing so, the cathode catalyst layer <NUM> is formed on the other surface of the electrolyte membrane <NUM>. As a result, the membrane electrode assembly <NUM> composed of the electrolyte membrane <NUM>, the anode catalyst layer <NUM>, and the cathode catalyst layer <NUM> is obtained.

Claim 1:
A membrane electrode assembly (<NUM>) comprising:
an electrolyte membrane (<NUM>); and
an anode catalyst layer (<NUM>) formed on one surface of said electrolyte membrane (<NUM>), wherein
said anode catalyst layer (<NUM>) includes:
a catalyst particle (<NUM>);
an ionomer (<NUM>); and
a water-repellent particle (<NUM>), and
said water-repellent particle (<NUM>) is a ceramic particle with a fluorine group or a metallic particle with a fluorine group.