Patent Description:
A fuel cell conventionally known generates electric power through an electrochemical reaction between hydrogen (H<NUM>) in a fuel and oxygen (O<NUM>) in the air. Several types of fuel cell are prepared in response to electrolytes to be used. One of these types is a polymer electrolyte fuel cell that uses an ion-exchange membrane (electrolyte membrane) as an electrolyte. The polymer electrolyte fuel cell is capable of operating at ordinary temperature and capable of being reduced in size and weight, so that it is used for various purposes of use such as for automobiles, portable equipment, houses, etc..

The polymer electrolyte fuel cell has a configuration with catalyst layers formed on both surfaces of an electrolyte membrane. During use of the polymer electrolyte fuel cell, hydrogen gas is supplied to an anode-side catalyst layer and oxygen gas is supplied to a cathode-side catalyst layer. This causes electrochemical reactions as follows at the anode-side catalyst layer and the cathode-side catalyst layer to generate electric power.

(cathode side)     <NUM>/2O<NUM> + <NUM>+ + 2e- → H<NUM>O.

The conventional polymer electrolyte fuel cell is disclosed in Patent Literature <NUM>, for example.

As described above, in the polymer electrolyte fuel cell, water is generated in the cathode-side catalyst layer. This necessitates supply of oxygen gas and output of water to and from the cathode-side catalyst layer. In some cases, during these supply and output, poor performance of outputting water makes it difficult for oxygen gas to diffuse in the catalyst layer. This causes a problem of degradation of the voltage characteristics of the fuel cell.

In this regard, in Patent Literature <NUM> mentioned above, a fibrous material such as a carbon nanotube or a carbon nanofiber is provided at the cathode-side catalyst layer to improve the performance of outputting water from the catalyst layer. However, as an electrolyte membrane of the polymer electrolyte fuel cell is considerably thin, providing the fibrous material might cause damage on the electrolyte membrane. Hence, in the method of Patent Literature <NUM>, implementing a leak test on the electrolyte membrane is considered to be required in a manufacturing step. <CIT> discloses a method of producing catalyst ink to become a cathode catalyst layer of a membrane electrode assembly, comprising thoroughly mixing a graphite intercalation compound, carbon supporting Pt, solid polymer electrolyte and a solvent for dissolving the solid polymer electrolyte. <CIT> discloses that a catalyst layer preferably contains a polymer electrolyte with a small EW, preferably an EW of <NUM>/mol or less, more preferably an EW of <NUM>/mol or less, and particularly preferably and EW of <NUM>/mol or less. <CIT> discloses that the ratio ionomer/carbon (I/C) should be between <NUM>/<NUM> - <NUM>/<NUM>. <CIT> discloses a first step of forming a first preparation liquid by blending a carbon particle, a catalyst particle and water, a second step of forming a second preparation liquid by adding an alcohol solution to said first preparation liquid and a solution of an ionomer.

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 water from a catalyst layer without use of a fibrous material such as that used in Patent Literature <NUM>.

A first aspect of the present invention is intended for a method of producing catalyst ink to become a cathode catalyst layer of a membrane electrode assembly, comprising: a first step of forming a first preparation liquid by blending a carbon particle, 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 carbon particle with a fluorine group 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.

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

A third 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 first or second aspect to one surface of an electrolyte membrane and drying the applied catalyst ink, thereby forming the cathode catalyst layer.

According to the first to third aspects of the present invention, the water-repellent carbon particle is added to the catalyst ink to become the cathode catalyst layer. This achieves improvement of the performance of outputting water from the cathode catalyst layer. Furthermore, the water-repellent carbon particle is added after addition of the alcohol solution. This allows the water-repellent carbon particle to disperse uniformly.

In particular, the second aspect of the present invention allows the water-repellent carbon 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 cell <NUM> as one of cells of a polymer electrolyte fuel cell (PEFC) according to an embodiment not belonging to the present invention. The polymer electrolyte fuel cell has a configuration with a plurality of the cells <NUM> shown in <FIG> stacked in series in multiple layers. Alternatively, the polymer electrolyte fuel cell may be composed of the single cell <NUM>.

As shown in <FIG>, the cell <NUM> of the polymer electrolyte fuel cell includes 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 <NUM>, 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 (negative electrode) of the polymer electrolyte fuel cell. 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 a platinum alloy, for example. As an example, the platinum alloy is an alloy of at least one type of metal selected from a group including ruthenium (Ru), palladium (Pd), nickel (Ni), molybdenum (Mo), iridium (Ir), and iron (Fe), and platinum (Pt). During use of the polymer electrolyte fuel cell, hydrogen gas (H<NUM>) is supplied to the anode catalyst layer <NUM>. Then, by the action of the catalyst particles in the anode catalyst layer <NUM>, the hydrogen is decomposed into hydrogen ions (H+) and electrons (e-).

The anode gas diffusion layer <NUM> is a layer for supplying hydrogen gas uniformly to the anode catalyst layer <NUM> and for causing electrons generated in the anode catalyst layer <NUM> to flow 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 hydrogen gas 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 hydrogen gas to the anode gas diffusion layer <NUM> and for outputting electrons coming from the anode catalyst layer <NUM> through the anode gas diffusion layer <NUM> to an external circuit <NUM>. 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>. The hydrogen gas is supplied to the anode gas diffusion layer <NUM> through the grooves <NUM> of the anode separator <NUM>.

The cathode catalyst layer <NUM> is a layer functioning as a cathode-side electrode (positive electrode) of the polymer electrolyte fuel cell. 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 polymer electrolyte fuel cell, oxygen gas (O<NUM>), hydrogen ions (H+), and electrons (e-) are supplied to the cathode catalyst layer <NUM>. Then, by the action of the catalyst particles in the cathode catalyst layer <NUM>, water (H<NUM>O) is generated from the oxygen gas, hydrogen ions, and electrons.

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

The cathode gas diffusion layer <NUM> is a layer for supplying oxygen gas uniformly to the cathode catalyst layer <NUM> and for causing electrons to flow from the cathode separator <NUM> to the cathode catalyst layer <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 oxygen gas and water 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 supplying oxygen gas to the cathode gas diffusion layer <NUM> and for causing electrons supplied from the external circuit <NUM> to flow into the cathode gas diffusion layer <NUM>. 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>. The oxygen gas passes through the grooves <NUM> of the cathode separator <NUM> and is then supplied to the cathode gas diffusion layer <NUM>.

The external circuit <NUM> is connected between the anode separator <NUM> and the cathode separator <NUM>. More specifically, the external circuit <NUM> has a negative terminal electrically connected to the anode separator <NUM>. The external circuit <NUM> has a positive terminal electrically connected to the cathode separator <NUM>.

During use of the polymer electrolyte fuel cell, hydrogen gas is supplied as fuel from the anode separator <NUM> to the anode catalyst layer <NUM> through the anode gas diffusion layer <NUM>. Then, by the action of the catalyst particles in the anode catalyst layer <NUM>, hydrogen atoms are decomposed into hydrogen ions and electrons. The hydrogen ions propagate through the electrolyte membrane <NUM> into the cathode catalyst layer <NUM>. The electrons pass through the anode gas diffusion layer <NUM>, the anode separator <NUM>, the external circuit <NUM>, the cathode separator <NUM>, and the cathode gas diffusion layer <NUM> and then flow into the cathode catalyst layer <NUM>. On the cathode side of the cell <NUM>, oxygen gas is supplied from the cathode separator <NUM> to the cathode catalyst layer <NUM> through the cathode gas diffusion layer <NUM>. Then, by the action of the catalyst particles in the cathode catalyst layer <NUM>, water is generated from the oxygen gas, hydrogen ions, and electrons. The generated water passes through the cathode gas diffusion layer <NUM> and the cathode separator <NUM> and is then output to the outside.

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

<FIG> is a schematic view conceptually showing the composition of the cathode catalyst layer <NUM>. As shown in <FIG>, the cathode catalyst layer <NUM> includes catalyst supporting carbon <NUM>, an ionomer <NUM>, and a water-repellent carbon particle <NUM>.

The catalyst supporting carbon <NUM> includes a large number of carbon particles <NUM> and multiple catalyst particles <NUM> supported on the carbon particles <NUM>. The catalyst particles <NUM> are particles of platinum (Pt), for example. Alternatively, the catalyst particles <NUM> may be prepared by mixing a tiny amount of ruthenium or cobalt particles into particles of platinum.

If the ratio of the platinum to the carbon particles <NUM> is too small in the catalyst supporting carbon <NUM>, it becomes impossible to achieve sufficient catalysis. Conversely, the quantity of the carbon particles <NUM> is required to be increased for achieving sufficient catalysis and this unintentionally causes increase in the thickness of the cathode catalyst layer <NUM>. On the other hand, if the ratio of the platinum to the carbon particles <NUM> is too large, distances between particles of the platinum are reduced. In this case, the platinum particles fuse with each other during electric power generation to cause a problem of reducing the performance of generating electric power.

Thus, the ratio of the platinum to the carbon particles <NUM> is desirably set to a ratio with which the thickness of the cathode catalyst layer <NUM> is restrained and with which the distances between the platinum particles are maintained in such a manner as to prevent fusion between the platinum particles. More specifically, the ratio (ratio by weight) of the platinum to the carbon 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 platinum to the carbon particles <NUM> is set equal to or greater than <NUM> wt% and equal to or less than <NUM> wt%.

The ionomer <NUM> is an electrolyte polymer covering the catalyst supporting carbon <NUM>. The ionomer <NUM> functions to transport hydrogen ions supplied from the electrolyte membrane <NUM> in the cathode catalyst layer <NUM>. For example, nafion (perfluorocarbon sulfonic acid) is used as the ionomer <NUM>. The ionomer <NUM> has a polymer chain structure with an ion-exchange group such as a sulfone group. The hydrogen ions supplied from the electrolyte membrane <NUM> 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 supporting carbon <NUM> is too small, it becomes impossible to cover the catalyst supporting carbon <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 supporting carbon <NUM> is too large, voids in the cathode catalyst layer <NUM> are reduced. This becomes hindrance to diffusion of oxygen gas in the cathode catalyst layer <NUM> or to output of water generated in the cathode catalyst layer <NUM>.

Thus, the ratio of the ionomer <NUM> to the catalyst supporting carbon <NUM> is desirably set to a ratio with which the catalyst supporting carbon <NUM> is covered with the ionomer <NUM> favorably and with which oxygen gas is caused to diffuse and water is output favorably. More specifically, the ratio (ratio by weight) of the ionomer <NUM> to the catalyst supporting carbon <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 ionomer <NUM> to the catalyst supporting carbon <NUM> is set equal to or greater than <NUM> wt% and equal to or less than <NUM> wt%. Still more desirably, the ratio (ratio by weight) of the ionomer <NUM> to the catalyst supporting carbon <NUM> is set equal to or greater than <NUM> wt% and equal to or less than <NUM> wt%.

The water-repellent carbon particle <NUM> is an additive for improving the performance of outputting water from the cathode catalyst layer <NUM>. <FIG> is a conceptual view of the water-repellent carbon particle <NUM>. As shown in <FIG>, the water-repellent carbon particle <NUM> has a surface provided with multiple fluorine groups (F) with water repellency. The water-repellent carbon particle <NUM> has a diameter of equal to or greater than <NUM> and equal to or less than <NUM>, for example. The water-repellent carbon particle <NUM> has a specific surface area of equal to or greater than <NUM><NUM>/g and equal to or less than <NUM><NUM>/g, for example.

<FIG> is a graph showing a relationship between the quantity of the water-repellent carbon particles <NUM> added to the cathode catalyst layer <NUM> and the voltage characteristics of the polymer electrolyte fuel cell. In the graph of <FIG>, a horizontal axis shows the ratio (ratio by weight) of the water-repellent carbon particles <NUM> to the catalyst supporting carbon <NUM>. A vertical axis shows an output voltage obtained from the polymer electrolyte fuel cell. A voltage value shown in the graph of <FIG> is determined at a current density of <NUM> A/cm<NUM>. The voltage characteristics shown in the graph of <FIG> are determined in two cases including one case where the relative humidity of supplied gas is <NUM>% RH and the other case where this relative humidity is <NUM>% RH.

Adding the water-repellent carbon particle <NUM> to the cathode catalyst layer <NUM> allows water generated in the cathode catalyst layer <NUM> to be output efficiently by means of the water-repelling action of the fluorine groups. Thus, voids are reserved in the cathode catalyst layer <NUM> to allow oxygen gas to be supplied efficiently. As a result, as shown in <FIG>, adding the water-repellent carbon particle <NUM> to the cathode catalyst layer <NUM> achieves improvement of the voltage characteristics of the polymer electrolyte fuel cell compared to the absence of addition of the water-repellent carbon particle <NUM>.

However, if the quantity of the added water-repellent carbon particles <NUM> is too large, the fluorine groups having insulating properties exert influence to increase an electrical resistance in the cathode catalyst layer <NUM>. Hence, like in a case shown in <FIG> where the ratio by weight of the water-repellent carbon particles <NUM> to the catalyst supporting carbon <NUM> is <NUM> wt%, this conversely degrades the voltage characteristics of the polymer electrolyte fuel cell.

Thus, it is desirable that the water-repellent carbon particles <NUM> will be added to a quantity with which the performance of outputting water from the cathode catalyst layer <NUM> is improved and with which the probability of degradation of electrical conductivity in the cathode catalyst layer <NUM> caused by the influence of the fluorine groups is reduced. More specifically, the ratio (ratio by weight) of the water-repellent carbon particles <NUM> to the catalyst supporting carbon <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 carbon particles <NUM> to the catalyst supporting carbon <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 carbon particles <NUM> to the catalyst supporting carbon <NUM> is preferably set to <NUM> wt%.

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

In this regard, reducing the above-described EW value of the ionomer <NUM> contributes to increasing a moisture content in the cathode catalyst layer <NUM>. On the other hand, adding the water-repellent carbon particles <NUM> contributes to reducing a moisture content in the cathode catalyst layer <NUM>. Thus, by setting the EW value of the ionomer <NUM> equal to or less than <NUM> and by adding the water-repellent carbon particles <NUM> as described above, it becomes possible to keep a moisture content retained in the cathode catalyst layer <NUM> within an appropriate range. This achieves further improvement of the voltage characteristics of the polymer electrolyte fuel cell.

The cathode 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 cathode 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 carbon particles <NUM>, 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 carbon 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 carbon particles <NUM> with fluorine groups are added to the second preparation liquid to form a third preparation liquid (third step S3). In the third step S3, the water-repellent carbon particles <NUM> disperse in the alcohol solution added in the second step S2. Adding the water-repellent carbon particles <NUM> in the above-described first step S1 makes it likely that the water-repellent carbon 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 carbon particles <NUM>) is added in advance in the second step S2, and then the water-repellent carbon particles <NUM> are added in the third step S3. This allows the water-repellent carbon 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 carbon 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, the fourth preparation liquid is agitated, for example. This causes the water-repellent carbon 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 carbon 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 cathode 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 cathode catalyst layer <NUM> is formed on the one surface of the electrolyte membrane <NUM>.

Furthermore, catalyst ink for anode 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 anode 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.

Order of implementation may be reversed between formation of the cathode catalyst layer <NUM> including the sixth step S6 and the seventh step S7 and formation of the anode catalyst layer <NUM> including the eighth step S8 and the ninth step S9.

The preferred embodiment described above is intended for the membrane electrode assembly <NUM> used in the polymer electrolyte fuel cell. However, the membrane electrode assembly of the present invention may be used for purpose other than the polymer electrolyte fuel cell.

According to one exemplary technique, an organic hydride (methylcyclohexane, for example) prepared by hydrogenating an aromatic compound such as toluene is used as a carrier for transporting hydrogen. <FIG> shows an example of a device of generating the organic hydride according to this technique. The device of <FIG> uses the membrane electrode assembly <NUM> including the electrolyte membrane <NUM> and the cathode catalyst layer <NUM> formed on one surface of the electrolyte membrane <NUM>. The composition of the cathode catalyst layer <NUM> is the same as that in the above-described case of the polymer electrolyte fuel cell.

Sulfuric acid is stored in a reservoir <NUM> on the anode side. Toluene is stored in a reservoir <NUM> on the cathode side. By applying a voltage between the cathode catalyst layer <NUM> and an anode electrode <NUM> and supplying electrons (e-) to the cathode catalyst layer <NUM>, the following electroreduction reaction is caused in the cathode catalyst layer <NUM>. By doing so, methylcyclohexane (MCH) as an organic hydride can be obtained.

C<NUM>H<NUM> + <NUM>+ + 6e- → C<NUM>H<NUM>.

Claim 1:
A method of producing catalyst ink to become a cathode catalyst layer (<NUM>) of a membrane electrode assembly (<NUM>), comprising:
a first step (S1) of forming a first preparation liquid by blending a carbon particle (<NUM>), a catalyst particle (<NUM>), and water;
a second step (S2) of forming a second preparation liquid by adding an alcohol solution to said first preparation liquid;
a third step (S3) of forming a third preparation liquid by adding a water-repellent carbon particle (<NUM>) with a fluorine group to said second preparation liquid; and
a fourth step (S4) of forming a fourth preparation liquid by adding a solution of an ionomer (<NUM>) to said third preparation liquid.