JP2007335268A - Fuel cell system and operation method of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress degradation in power generation performance of a fuel cell caused by water and oxides remained in a fuel electrode after operation in a fuel-deficient state. <P>SOLUTION: The fuel cell system is provided with a fuel cell unit cell for carrying out power generation by reacting the fuel supplied to the fuel electrode installed at one face side of an electrolyte membrane with oxidizer supplied to an oxidizer electrode installed at the other face side of the electrolyte membrane. At least at one of the fuel cell unit cells, a means is provided which generates hydrogen by the fuel electrode of the fuel cell unit cell when supply of the fuel is returned from the fuel-deficient state during the operation of the fuel cell. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system and a fuel cell operating method.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle, and thus exhibit high energy conversion efficiency. A fuel cell is usually formed by laminating a plurality of single cells having a basic structure of a membrane / electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes. Among them, a solid polymer electrolyte fuel cell using a solid polymer electrolyte membrane as an electrolyte membrane has advantages such as easy miniaturization and operation at a low temperature. It is attracting attention as a power source for the body.

In a solid polymer electrolyte fuel cell using hydrogen as a fuel and oxygen as an oxidant, the reaction of formula (1) proceeds at the fuel electrode (anode) during normal power generation.
2H ₂ → 4H ⁺ + 4e ⁻ (1)
The electrons generated by the equation (1) reach the oxidant electrode (cathode) after working with an external load via an external circuit. The proton generated in the formula (1) moves from the fuel electrode to the oxidant electrode side in the solid polymer electrolyte membrane in a hydrated state with water.

On the other hand, the reaction of the formula (2) proceeds at the oxidant electrode.
4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O (2)
That is, as a whole battery,
2H ₂ + O ₂ → 2H ₂ O (3)
The reaction proceeds to generate electricity.

However, it is known that if the fuel electrode is deficient in fuel such as hydrogen (hereinafter referred to as fuel shortage) due to some cause, for example, gas channel blockage or flooding, the battery characteristics will deteriorate. Yes. In a single cell in which an abnormality occurs in the fuel supply state and fuel shortage occurs, protons and electrons generated by fuel oxidation are insufficient. In order to replenish these deficient protons and electrons, in the single cell, the water present in the fuel electrode or the water electrolysis of the electrolyte membrane and the oxidant electrode (H ₂ O → 2H ⁺ + 2e ⁻ + 1 / 2O ₂ ) proceeds. At this time, the potential of the fuel electrode of the single cell rises to the electrolysis potential of water, and as a result, the potential of the fuel electrode (anode) and the oxidant electrode (cathode) is reversed.

While the electrolysis of water in the fuel electrode can sufficiently supply protons and electrons, the potential of the fuel electrode is stable, but the electrolysis of water alone does not secure enough protons and electrons. In this case, the potential of the fuel electrode further increases, and the oxidation reaction (C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e) of the carbon material constituting the electrode (for example, carbon particles supporting the electrode catalyst). ^- ) Progresses and replenishes electrons and protons. In this oxidative corrosion of the carbon material, the surface of the carbon material is covered with an oxide film, and as a result, the carbon material is decomposed and lost.

  Surface oxidation or disappearance of the carbon material, which is a conductive material, lowers the conductivity of the cell and causes an increase in resistance due to poor contact. In addition, the surface oxidation or disappearance of the carbon material, which is a water repellent material, reduces the water repellency of the cell and easily causes flooding that hinders the supply of the reaction gas. In addition, due to decomposition or disappearance of the carbon material carrying the electrode catalyst, the electrode catalyst is lost or moved, and the effective catalyst surface area is reduced. Thus, due to the oxidative corrosion of the carbon material, the power generation performance of the fuel cell is greatly reduced, and stable power generation performance cannot be expressed.

Since the oxidation of the carbon material at the fuel electrode as described above is an irreversible reaction, the performance of the fuel cell does not return to the state before the fuel shortage even if the fuel shortage is eliminated. Examples of a technique for solving the problem caused by such a fuel shortage state include those described in Patent Document 1 and Patent Document 2.
Patent Document 1 discloses an anode used in a fuel cell having improved resistance to voltage reversal, wherein the anode is a first catalyst composition for electrochemically oxidizing fuel for the anode. And an anode comprising a second catalyst composition for generating oxygen from water is disclosed.

Patent Document 2 discloses that a fuel electrode of a solid polymer electrolyte fuel cell that promotes a fuel cell reaction that oxidizes fuel introduced through a diffusion layer is in contact with a solid polymer electrolyte membrane and performs the fuel cell reaction. A fuel for a solid polymer electrolyte fuel cell, comprising: at least one reaction layer to be advanced; and at least one water decomposition layer that is in contact with the diffusion layer and electrolyzes water in the fuel electrode The pole is disclosed.
The techniques described in Patent Document 1 and Patent Document 2 try to suppress the oxidative corrosion of the carbon material by causing the electrode to contain a water electrocatalyst and accelerating the electrolysis of water in the electrode when the fuel runs out. Is.

Special table 2003-508877 gazette JP 2004-22503 A JP 2004-311348 A

After the fuel shortage state is eliminated, there is another problem that the power generation performance is lowered due to oxides or water remaining on the surface of the electrode catalyst in the fuel electrode, the surface of the conductive particles carrying the electrode catalyst, or the like. The fuel electrode is exposed to a strong oxidizing atmosphere due to an increase in the potential of the fuel electrode in the absence of fuel (for example, 1.5 to 1.7 V), and the surface of the electrode catalyst in the fuel electrode and the surface of the conductive particles carrying the electrode catalyst. As a result, an oxide is formed. Formation of an oxide on the surface of the electrode catalyst decreases the activity of the electrode catalyst, and generation of an oxide on the surface of the conductive particles that are the support of the electrode catalyst decreases the conductivity of the conductive particles.
Further, when the fuel electrode is exposed to a high potential state, hydrophilic groups such as a carboxy group and a quinone group are generated on the surfaces of the electrode catalyst and the conductive particles, so that the hydrophilicity of the electrode catalyst and the conductive particles is increased. As a result, water is strongly adsorbed on the surface of the electrode catalyst and conductive particles in the fuel electrode, and the supply of the reaction gas to the electrode catalyst is hindered, resulting in a decrease in power generation performance.

  If a water electrocatalyst is arranged on the fuel electrode as in Patent Document 1 or Patent Document 2, it is possible to suppress the oxidative corrosion of the carbon material, but the above-described electrode catalyst or oxidation on the surface of the conductive particles is possible. It is difficult to prevent product generation and water adsorption, and it is impossible to prevent a decrease in power generation performance due to these.

As a fuel cell system capable of removing moisture in the fuel cell, Patent Document 3 discloses a solid state in which hydrogen is supplied to the fuel electrode and oxygen supplied to the oxidant electrode is electrochemically reacted to generate power. A fuel cell system including a polymer electrolyte fuel cell, comprising a power supply device capable of supplying power to the fuel cell, and after the power generation operation of the fuel cell is stopped, the oxidation from the power supply device to the fuel cell A fuel cell system is disclosed in which a voltage is applied such that the agent electrode side has a higher potential than the fuel electrode side.
The fuel cell system of Patent Document 3 is intended to solve the problem that moisture remaining in the electrode freezes when the fuel cell is stopped, and the battery cannot be restarted. However, in the fuel cell system of Patent Document 3, if a voltage sufficient to remove moisture in the electrode is applied, there is a possibility that the material constituting the fuel cell is adversely affected. In addition, this fuel cell system removes water in the electrode after stopping the power generation operation, and removes water in the electrode and removes oxides during operation after the fuel shortage state is resolved. Is not considered.

  The present invention has been accomplished in view of the above circumstances, and aims to suppress a decrease in power generation performance of a fuel cell due to moisture and oxide remaining in the fuel electrode after operation in a fuel-deficient state. To do.

The fuel cell system of the present invention reacts a fuel supplied to a fuel electrode provided on one side of an electrolyte membrane and an oxidant supplied to an oxidant electrode provided on the other side of the electrolyte membrane. A fuel cell system comprising a fuel cell unit cell for generating power, wherein at least one of the fuel cell unit cells returns when the fuel supply is restored from the fuel-deficient state during fuel cell operation. And a means for generating hydrogen (H ₂ ) at the fuel electrode of the single fuel cell.

In the fuel cell system of the present invention, the oxide generated on the surface of the electrode catalyst contained in the fuel electrode or the catalyst carrier supporting the electrode catalyst during the operation in the fuel shortage state is operated in the fuel shortage state. Thereafter, it can be reduced by generating hydrogen at the fuel electrode. Therefore, it is possible to suppress a decrease in catalyst activity due to the oxide, a decrease in conductivity of the fuel electrode, and the like.
Further, since the hydrophilic group generated on the surface of the electrode catalyst or the catalyst carrier is removed by the reducing action of the generated hydrogen gas, the hydrophilicity of the fuel electrode is lowered and water adsorption can be suppressed. Furthermore, by generating hydrogen at the fuel electrode, there is an effect that oxides and water are physically removed by hydrogen gas, unlike when hydrogen gas is simply circulated through the fuel electrode.

  As a specific configuration of the fuel cell system of the present invention, at least one of the water electrocatalyst contained in the oxidizer electrode and the single fuel cell cell is in a state where the fuel is deficient during the fuel cell operation. When the fuel supply returns, (1) water supply means for controlling the amount of water in the oxidant electrode, and (2) the oxidant so that water electrolysis proceeds in the oxidant electrode. There is a first fuel cell system provided with a voltage applying means for applying a voltage between the electrode and the fuel electrode.

In the first fuel cell system, electrolysis of water proceeds at the oxidizer electrode by voltage control by the water electrolysis catalyst and voltage applying means, and the generated protons move through the electrolyte membrane to the fuel electrode. In the fuel electrode, hydrogen gas is generated from the protons and electrons generated by electrolysis of water in the oxidant electrode and transferred to the fuel electrode.
In the first fuel cell system, the voltage applied between the oxidant electrode and the fuel electrode by the voltage applying means may be about +1.4 to + 2.0V. The water electrocatalyst contained in the oxidizer electrode includes at least one selected from IrO ₂ , RuO ₂ , Pt, TiO ₂ , and a solid solution containing two or more of these.

  As another configuration of the fuel cell system according to the present invention, when at least one of the fuel cell single cells returns to the supply of the fuel from the fuel deficient state during the fuel cell operation, (1) Means for supplying hydrogen gas to the oxidant electrode; and (2) a voltage is applied between the oxidant electrode and the fuel electrode so that a hydrogen oxidation reaction (protonation reaction) proceeds in the oxidant electrode. And a voltage applying means for applying the second fuel cell system.

In the second fuel cell system, the hydrogen gas supplied to the oxidant electrode is oxidized by voltage control by the voltage application means. Then, the generated protons and electrons move to the fuel electrode, and hydrogen gas is generated at the fuel electrode.
In the second fuel cell system, the voltage applied between the oxidant electrode and the fuel electrode by the voltage applying means may be about −0.2 to +0.1 V (excluding 0 V).

  Furthermore, as another configuration of the fuel cell system according to the present invention, when at least one of the fuel cell single cells returns from the state where the fuel is deficient during the fuel cell operation, 1) means for supplying hydrogen gas to the oxidant electrode; (2) means for supplying inert gas to the fuel electrode; and (3) a hydrogen oxidation reaction (protonation reaction) proceeds at the oxidant electrode. As described above, there is a third fuel cell system including short-circuit means for electrically connecting and short-circuiting the oxidant electrode and the fuel electrode.

  In the third fuel cell system, first, the inert gas is supplied to the fuel electrode to lower the hydrogen gas concentration in the fuel electrode, and the hydrogen gas is supplied to the oxidant electrode to sandwich the electrolyte membrane. A hydrogen gas concentration difference is formed between the fuel electrode and the oxidant electrode. At this time, the oxidant electrode and the fuel electrode are electrically connected and short-circuited to cause an oxidation reaction in which hydrogen is decomposed into protons and electrons at the oxidant electrode. Then, protons and electrons generated by the hydrogen slope reaction at the oxidant electrode move to the fuel electrode, and react with each other at the fuel electrode to generate hydrogen gas.

  In the fuel cell system of the present invention, the fuel electrode preferably contains a water electrocatalyst having catalytic activity for water electrolysis. By including a water electrocatalyst in the fuel electrode, the electrolysis of water at the fuel electrode when fuel runs out is promoted, and protons and electrons replenished by water electrolysis increase, so that the carbon material such as the catalyst carrier It is possible to suppress oxidative corrosion.

The fuel cell operating method of the present invention includes a fuel supplied to a fuel electrode provided on one side of an electrolyte membrane, an oxidant supplied to an oxidant electrode provided on the other side of the electrolyte membrane, In a fuel cell comprising a fuel cell single cell that generates electricity by reacting with the fuel cell, when at least one of the fuel cell single cells is in operation of the fuel cell, when the supply of the fuel is restored from the fuel-deficient state, Hydrogen (H ₂ ) is generated at the fuel electrode of the single fuel cell.

As a specific aspect of the method for operating a fuel cell according to the present invention, the oxidant electrode contains a water electrocatalyst having catalytic activity for water electrolysis, and at least one of the fuel cell single cells. The oxidant electrode and the fuel electrode so that the electrolysis of water present in the oxidant electrode proceeds when the fuel supply is restored from the fuel-deficient state during fuel cell operation. An operation method in which a voltage is applied between the two is mentioned.
The voltage applied between the oxidant electrode and the fuel electrode by the voltage applying means may be about +1.4 to + 2.0V. Examples of the water electrocatalyst include at least one selected from IrO ₂ , RuO ₂ , Pt, TiO ₂ , and solid solutions containing two or more of these.

Further, as another aspect of the method of operating the fuel cell according to the present invention, in at least one of the fuel cell single cells, when the fuel supply is restored from the fuel deficient state during the fuel cell operation, An operation in which a hydrogen gas is supplied to the oxidant electrode and a voltage is applied between the oxidant electrode and the fuel electrode so that a hydrogen oxidation reaction (protonation reaction) proceeds in the oxidant electrode. A method is mentioned.
The voltage applied between the oxidant electrode and the fuel electrode by the voltage applying means may be about −0.2 to +0.1 V (excluding 0 V).

  Furthermore, as another aspect of the method of operating the fuel cell according to the present invention, in at least one of the fuel cell single cells, when the supply of the fuel returns from the fuel-deficient state during the fuel cell operation, There is an operation method in which hydrogen gas is supplied to the oxidant electrode, an inert gas is supplied to the fuel electrode, and the oxidant electrode and the fuel electrode are electrically connected and short-circuited.

  In the fuel cell operation method of the present invention, the fuel electrode preferably contains a water electrocatalyst having catalytic activity for water electrolysis.

  The fuel cell system and the fuel cell operation method of the present invention is a fuel cell system and a fuel cell operation method that remain in the fuel electrode after a fuel shortage operation and cause moisture or oxidation to cause a decrease in gas diffusibility and conductivity in the fuel electrode and catalytic activity of the electrode catalyst. Things can be removed. Therefore, according to the fuel cell system and the fuel cell operation method of the present invention, the power generation performance can be maintained even after the operation in the fuel-deficient state.

The fuel cell system of the present invention reacts a fuel supplied to a fuel electrode provided on one side of an electrolyte membrane and an oxidant supplied to an oxidant electrode provided on the other side of the electrolyte membrane. A fuel cell system comprising a fuel cell unit cell for generating power, wherein at least one of the fuel cell unit cells returns when the fuel supply is restored from the fuel-deficient state during fuel cell operation. A means for generating hydrogen (H ₂ ) at the fuel electrode of the fuel cell single cell is provided.

  Hereinafter, the fuel cell system and the fuel cell operating method of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing an embodiment of a fuel cell single cell that is provided in the fuel cell system of the present invention or to which the fuel cell operating method of the present invention can be applied.

In FIG. 1, a fuel cell single cell (hereinafter sometimes simply referred to as a single cell) 100 includes a fuel electrode (an anode in this embodiment) 2 on one surface of an electrolyte membrane 1 and an oxidant electrode (an anode in the present embodiment). In this embodiment, a membrane / electrode assembly 6 provided with a cathode 3 is provided. In the present embodiment, the fuel electrode 2 and the oxidant electrode 3 are respectively in order from the electrolyte membrane side, the fuel electrode side catalyst layer 4a and the fuel electrode side gas diffusion layer 5a, and the oxidant electrode side catalyst layer 4b and the oxidant electrode side gas. The diffusion layer 5b has a laminated structure.
The catalyst layers 4a and 4b of each electrode (fuel electrode and oxidant electrode) contain an electrode catalyst (not shown) having catalytic activity for the electrode reaction, and serve as an electrode reaction field. The gas diffusion layers 5 a and 5 b are for increasing the diffusibility of the reaction gas to the catalyst layer 4.
In the present invention, the structure of each electrode is not limited to that shown in FIG. 1, and may be a structure including only a catalyst layer or a structure including layers other than the catalyst layer and the gas diffusion layer.

The membrane / electrode assembly 6 is sandwiched between the fuel electrode side separator 7 a and the oxidant electrode side separator 7 b to constitute the fuel cell single cell 100. The separator 7 defines a flow path 8 (8a, 8b) for supplying reaction gas (fuel gas, oxidant gas) to the electrodes 2 and 3, gas seals between the single cells, and as a current collector Also works. The fuel electrode 2 is supplied with a fuel gas (a gas containing hydrogen or generating hydrogen, usually hydrogen gas) from the flow path 8a, and the oxidant electrode 3 is supplied with an oxidant gas (including oxygen) from the flow path 8b. Or a gas that generates oxygen (usually air). The fuel cell generates power by the reaction between the fuel and the oxidant. The fuel and the oxidant are not limited to gas and may be liquid.
The fuel cell unit cell 100 is normally stacked in a plurality and stacked in a fuel cell.

  As the electrolyte membrane, those used in general fuel cells can be used. For example, Nafion (trade name, manufactured by DuPont), Flemion (trade name, manufactured by Asahi Glass), Aciplex (trade name) (Manufactured by Asahi Kasei Co., Ltd.) and other fluorinated electrolyte resin membranes represented by perfluorocarbon sulfonic acid resins, and hydrocarbon resins such as polyethersulfone, polyimide, polyetherketone, polyetheretherketone, and polyphenylene. , Boronic acid groups, phosphonic acid groups, hydroxyl resin groups, electrolyte polymer membranes such as hydrocarbon polymer electrolyte membranes introduced with proton conductive groups, polybenzimidazole, polypyrimidine, polybenzoxazole, etc. Examples include a composite electrolyte membrane of a basic polymer in which a molecule is doped with a strong acid and a strong acid. Although the thickness of the electrolyte membrane is not particularly limited, it is usually about 10 to 100 μm.

  The gas diffusion layer that constitutes the electrode has gas diffusibility and conductivity that can efficiently supply gas to the catalyst layer, and has the strength required as a material constituting the gas diffusion layer, such as carbon paper, Carbon porous materials such as carbon cloth, carbon felt, titanium, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, silver, aluminum alloy, zinc alloy, lead alloy, titanium, niobium, tantalum, iron Further, it can be formed using a gas diffusion layer sheet made of a conductive porous material such as a metal mesh made of metal such as stainless steel, gold or platinum, or a metal porous material. The thickness of the conductive porous body is preferably about 50 to 300 μm.

  The gas diffusion layer sheet may be composed of a single layer of the conductive porous body as described above, but a water repellent layer may be provided on the side facing the catalyst layer. The water-repellent layer usually has a porous structure containing conductive particles such as carbon particles and carbon fibers, water-repellent resin such as polytetrafluoroethylene (PTFE), and the like. The method for forming the water-repellent layer on the conductive porous body is not particularly limited. For example, conductive particles such as carbon particles, a water-repellent resin, and other components as necessary, ethanol, propanol, A water-repellent layer ink mixed with an organic solvent such as propylene glycol, water or a solvent such as a mixture thereof is applied to at least the side facing the catalyst layer of the conductive porous body, and then dried and / or baked. Good. In addition, the conductive porous body is formed by impregnating and applying a water-repellent resin such as polytetrafluoroethylene to the side facing the catalyst layer with a bar coater or the like, so that the moisture in the catalyst layer is efficiently removed from the gas diffusion layer. You may process so that it may be discharged well.

The catalyst layer usually contains an electrolyte resin in addition to the electrode catalyst having catalytic activity for the electrode reaction. The electrode catalyst is not particularly limited as long as it has catalytic activity for the electrode reaction, and those generally used as electrode catalysts can be used. Usually, metals such as platinum, ruthenium, iridium, rhodium, palladium, osnium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, or alloys thereof can be used. Preferred are platinum alloys such as platinum and platinum-ruthenium alloys. The amount of the electrode catalyst per unit area 0.01 to 10 mg / cm ² of electrode, particularly preferably a 0.01 to 1 mg / cm ^2.

Electrocatalysts are usually supported on conductive particles with a large actual surface area so that electrons can be exchanged smoothly in electrode reactions with the electrode catalyst and to ensure dispersibility of the electrode catalyst in the electrode. Is done. Examples of the conductive particles include carbon particles such as graphitized carbon, and metal particles such as titanium oxide (TiO ₂ ) and metal carbide. The conductive particles are not limited to spherical shapes, and include particles having a relatively large aspect ratio such as a fibrous shape.

  The electrolyte resin is not particularly limited, and those commonly used in polymer electrolyte fuel cells can be used. For example, hydrocarbons such as polyethersulfone, polyimide, polyetherketone, polyetheretherketone, polyphenylene as well as fluorine-based electrolyte resins such as perfluorocarbonsulfonic acid resin represented by Nafion (trade name, manufactured by DuPont) A hydrocarbon electrolyte resin into which a proton conductive group such as a sulfonic acid group, a boronic acid group, a phosphonic acid group, a hydroxyl group, or a carboxyl group is introduced can be used. In addition to the conductive particles carrying the electrode catalyst and the electrolyte resin, the catalyst layer contains other components such as a water-repellent polymer (for example, polytetrafluoroethylene) and a binder as necessary. You may make it contain.

The fuel cell system of the present invention comprises the above fuel cell single cell. In at least one of such fuel cell single cells, if the fuel becomes deficient during the operation of the fuel cell, the fuel electrode of the fuel cell single cell electrolyzes water to capture the insufficient protons and electrons. Progresses. At this time, the potential of the fuel electrode rises to the electrolysis potential of water (for example, about 1.5 to 1.7 V). If protons and electrons are not sufficiently ensured only by electrolysis of water, the potential of the fuel electrode further increases, and the carbon material constituting the electrode (for example, carbon particles carrying an electrode catalyst) Oxidation reaction (C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ ) occurs to replenish electrons and protons. The oxidative corrosion of the carbon material that is the electrode catalyst carrier is one of the major factors that reduce the electric power generation performance of the fuel cell by lowering the electroconductivity and water repellency of the electrode as well as lowering the catalytic activity.

Further, the increase in the potential of the fuel electrode in the fuel shortage state makes the fuel electrode a strong oxidizing atmosphere, and generates oxide on the surface of the electrode catalyst in the fuel electrode and the surface of the conductive particles carrying the electrode catalyst. Oxide formation on the electrode catalyst surface reduces the activity of the electrode catalyst. Moreover, the production | generation of the oxide on the electroconductive particle surface which is a support | carrier of an electrode catalyst reduces the electroconductivity of electroconductive particle.
In addition, the increase in the potential of the fuel electrode generates hydrophilic groups such as carboxyl groups and quinone groups on the surfaces of the electrode catalyst and conductive particles, and the hydrophilicity of the electrode catalyst and conductive particles becomes high. As a result, water is strongly adsorbed on the surfaces of the electrode catalyst and the conductive particles, the supply of the reaction gas to the electrode catalyst is hindered, and the power generation performance is reduced.

  Oxides generated at the fuel electrode due to battery operation in the fuel shortage state and water adsorbed in the fuel electrode remain in the fuel electrode even after the fuel supply is restored and the fuel shortage state is resolved. Therefore, even if the fuel shortage state is resolved, the problem of performance degradation caused by oxides and moisture remaining in the fuel electrode cannot be resolved.

Therefore, in the present invention, by removing the oxides and moisture remaining in the fuel electrode after the operation in the above-mentioned fuel shortage state, the performance deterioration of the fuel cell due to these oxides and moisture is prevented. Specifically, hydrogen (H ₂ ) is generated at the fuel electrode when the fuel supply is restored in the fuel cell single cell in the fuel shortage state after operation in the fuel shortage state.

By flowing hydrogen gas through the fuel electrode, oxides and hydrophilic groups remaining in the fuel electrode are reduced and removed. As a result, the decrease in the catalytic activity of the electrode catalyst and the decrease in the conductivity of the conductive material are suppressed, and the adsorption of moisture that has been strongly adsorbed on the conductive material as the electrode catalyst or catalyst carrier by the hydrophilic group is weakened. Can do. In addition, in the present invention, hydrogen gas is not circulated through the fuel electrode, but hydrogen gas is generated at the fuel electrode. A removal effect due to the action can be obtained. That is, when hydrogen gas is generated (2H ⁺ + 2e ⁻ → H ₂ ) on the surface of the electrode catalyst contained in the fuel electrode, oxides attached to the surface of the electrode catalyst or the surface of the conductive particles, etc. Moisture is effectively removed by physical action.

As described above, the fuel cell system of the present invention generates hydrogen gas at the fuel electrode of the single cell in which the fuel shortage state occurs after operation in the fuel shortage state (hereinafter simply referred to as hydrogen gas generation processing). Therefore, it is possible to efficiently remove oxides generated in the fuel electrode due to operation in a fuel-deficient state and moisture adsorbed on the fuel electrode.
Also, in the case of a fuel cell system that supplies hydrogen gas as fuel, the efficiency of returning the fuel supply state in the single fuel cell after the hydrogen generation process is good due to the generation of hydrogen gas at the fuel electrode by the hydrogen generation process. There is also an effect.

In the fuel cell system of the present invention, in the case where a plurality of fuel cell single cells are provided, the single cell that is in a fuel-deficient state is removed from the hydrogen cell in a state in which the electrical connection with other fuel cell single cells is released. On the other hand, it is preferable that other fuel cell single cells except for the single cell that performs the hydrogen generation treatment are connected by a circuit different from that during normal power generation to generate power (3B in FIG. 3). 5B in FIG. 5 and 7B in FIG. 7). This is because the hydrogen generation process can be performed only for the single cells that require the hydrogen generation process while generating power in the single cell that does not perform the hydrogen generation process. Then, after the hydrogen generation treatment, power generation may be performed by returning the single cell subjected to the hydrogen generation treatment and another single cell to the connection state during normal power generation (3C in FIG. 3, 5C in FIG. 5, FIG. 5). 5C).
Further, the hydrogen generation treatment may be performed on only one single cell, or may be performed simultaneously on a plurality of single cells. Even when there are multiple single cells that need to be subjected to hydrogen generation treatment, in order to maintain the power generation performance of the entire fuel cell during the hydrogen generation treatment, the single cell group that needs to undergo hydrogen generation treatment is divided into a plurality of Hydrogen generation treatment may be performed.

The fuel cell system of the present invention is provided with means for sensing that the supply of fuel has recovered from a fuel shortage condition at the fuel electrode. As a means for detecting the return of fuel, for example, a voltage sensor is provided in a single cell, and if the E value of the voltage sensor, that is, the cell voltage is 0 V <E (V), it can be considered that the fuel has returned. . Alternatively, an oxygen sensor and / or a CO ₂ sensor is provided at the gas discharge port of the fuel electrode, and O ₂ and CO ₂ are concentration values below a specified value (O ₂ concentration and CO ₂ concentration at normal power generation of the single cell). If it is theoretically zero), it can be regarded as a return.

Hereinafter, a first fuel cell system, which is one of preferred embodiments of the fuel cell system of the present invention, will be described with reference to FIGS.
In the first fuel cell system, when at least one of the water electrocatalyst contained in the oxidizer electrode and the fuel cell unit cell returns to the fuel supply from the fuel-deficient state during the fuel cell operation. (1) water supply means for controlling the amount of water in the oxidant electrode; and (2) between the oxidant electrode and the fuel electrode so that electrolysis of water proceeds in the oxidant electrode. Voltage applying means for applying a voltage.

  In FIG. 2, the oxidant electrode 3 provided on one surface of the electrolyte membrane 1 contains a water electrolysis catalyst (not shown) having catalytic activity for electrolysis of water. Further, the oxidant electrode 3 can supply water as needed when the fuel is returned from the operation in the fuel-deficient state by the water supply means for controlling the amount of water in the oxidant electrode 3. It has become. Further, between the fuel electrode 2 and the oxidant electrode 3 provided on the other surface of the electrolyte membrane 1, the electrolysis of water at the oxidant electrode 3 proceeds by the voltage application means (power source 9). It is possible to apply a voltage.

In the fuel cell single cell provided in the first fuel cell system, when the fuel shortage occurs and the operation in the fuel shortage state is performed, when the fuel supply is restored, the catalyst by the water electrolysis catalyst By the action, voltage application by the voltage application means, and water supply by the water supply means, electrolysis of water (H ₂ O → 1 / 2O ₂ + 2H ⁺ + 2e ⁻ ) proceeds at the oxidizer electrode 3. Protons and electrons generated at the oxidizer electrode by electrolysis of water move to the fuel electrode through the electrolyte membrane and the external circuit, respectively, and generate hydrogen at the fuel electrode (2H ⁺ + 2e ⁻ → H ₂ ). . That is, in the first fuel cell system, a reaction opposite to that during normal power generation occurs at each electrode of the fuel electrode and the oxidant electrode, and hydrogen gas is generated at the fuel electrode.

  The water electrocatalyst contained in the oxidant electrode has a higher catalytic activity for water electrolysis than the electrode catalyst contained in the electrode (oxidant electrode) together with the water electrocatalyst. The magnitude of the catalytic activity for electrolysis of water can be defined by an oxygen generation current value at 1.4 V (vs. RHE) in a sulfuric acid aqueous solution at 25 ° C. Is larger than the electrode catalyst.

As described above, since platinum or a platinum alloy is normally used as the electrode catalyst, the water electrocatalyst usually has a higher catalytic activity for electrolysis of water than platinum or a platinum alloy. Used. Examples of such a water electrocatalyst include RuO ₂ , IrO ₂ , Pt, TiO ₂ , and solid solutions containing two or more of these. Among these, from the viewpoint of water splitting activity and electrochemical stability, solid solutions of IrO ₂ and RuO ₂ —IrO ₂ are preferably used.

The water electrocatalyst is preferably supported on conductive particles from the viewpoint of efficient electron transfer. Examples of the conductive particles for supporting the water electrocatalyst include carbon particles such as graphitized carbon, metal particles such as titanium oxide (TiO ₂ ), and metal carbide. The conductive particles are not limited to a spherical shape, and include particles having a relatively large aspect ratio such as a fibrous shape.

The content of water electrolysis catalyst in the oxidant electrode, per unit area 0.01 to 10 mg / cm ² of the oxidant electrode, particularly preferably a 0.01 to 1 mg / cm ^2. When the amount of the water electrocatalyst per unit area of the oxidizer electrode is less than 0.01 mg / cm ² , there are few protons and electrons generated by water electrolysis, and oxide and water are removed by hydrogen gas generated at the fuel electrode. The effect may be reduced. On the other hand, when the amount of the water electrocatalyst per unit area of the oxidant electrode is more than 10 mg / cm ² , the gas diffusibility in the oxidant electrode may be lowered.

  The water electrocatalyst may be contained in the catalyst layer in the oxidizer electrode, may be contained in the gas diffusion layer, or may be contained in both the catalyst layer and the gas diffusion layer. Further, a water electrolysis layer containing a water electrolysis catalyst may be additionally provided. From the viewpoint of easy release of oxygen gas generated by water electrolysis, the water electrocatalyst is preferably contained in the water electrolysis layer.

The position at which the water electrolysis layer containing the water electrocatalyst is provided is not particularly limited, and the water electrolysis layer can be provided at any position such as the interface between the electrolyte membrane and the oxidant electrode and the interface between the catalyst layer and the gas diffusion layer. From the viewpoint of easy release of oxygen gas generated by water electrolysis, the water electrolysis layer is preferably provided at the interface between the catalyst layer and the gas diffusion layer.
In addition to the water electrocatalyst, the water electrolysis layer may contain components such as an electrolyte resin and a water repellent resin. From the viewpoint of the conductivity of protons generated by water electrolysis to the fuel electrode side, it is usually preferable to contain an electrolyte resin in the water electrolysis layer. As the electrolyte resin contained in the water electrolysis layer, the same electrolyte resin as that contained in the catalyst layer can be used.

The method for forming the water electrolysis layer is not particularly limited, and for example, the water electrolysis layer can be formed using a water electrolysis catalyst ink containing a water electrocatalyst and an electrolyte resin. The formation of the water electrolysis layer with the water electrolysis catalyst ink can be performed in the same manner as the method for forming the catalyst layer with the catalyst ink.
Although the thickness of a water electrolysis layer is not specifically limited, Usually, what is necessary is just to be about 1-20 micrometers.

  When the water electrocatalyst is contained in the catalyst layer, the water electrocatalyst is mixed in the catalyst ink forming the catalyst layer of the oxidizer electrode, and the resulting water electrocatalyst containing catalyst ink is used in a general method. A catalyst layer may be formed in accordance with this. That is, a method of directly applying the catalyst ink to the electrolyte membrane or the gas diffusion layer sheet and drying, or applying the catalyst ink to the base film of the transfer film and drying, and then transferring the catalyst ink to the electrolyte membrane or the gas diffusion layer sheet. It is done.

  Examples of the solvent for the catalyst ink include alcohols such as methanol, ethanol, propanol, and propylene glycol, N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, and N, N-diethylacetamide. Etc., or a mixture thereof or a mixture with water can be used, but is not limited thereto. Of these, ethanol and methanol are preferably used from the viewpoint of catalyst poisoning prevention and viscosity stability.

  As a method for containing a water electrocatalyst in the gas diffusion layer, the conductive porous body that forms the gas diffusion layer sheet as described above is used in a water electrocatalyst solution in which the water electrocatalyst is dispersed in a solvent such as ethanol or methanol. And a method of applying a water electrocatalyst solution to a conductive porous body. Alternatively, a water electrocatalyst solution mixed with an electrolyte resin such as perfluorocarbon sulfonic acid resin is coated on a substrate and dried to produce a water electrolysis catalyst sheet. The water electrolysis catalyst sheet and the gas diffusion layer sheet are The method of hot pressing is also mentioned. Moreover, a method of impregnating and applying a water electrocatalyst to the conductive porous body together with the water repellent resin may be included in the water repellent layer ink.

The water supply means for controlling the amount of water in the oxidant electrode is such that the electrolysis of water that generates protons and electrons for generating a sufficient amount of hydrogen gas at the fuel electrode proceeds at the oxidant electrode. The configuration is not particularly limited as long as water can be supplied to the electrode.
For example, the thing etc. which humidify oxidizing agent (generally air) gas and supply to an oxidizing agent electrode are mentioned. When supplying a humidified gas, the amount of H ₂ gas generated [H ₂ O → 1 / 2O ₂ + 2e ⁻ + 2H ^{+ is} generated from H ⁺ generated from H ⁺ (2H ⁺ + 2e ⁻ → H ₂ ). The temperature and flow rate are controlled based on the amount of water to compensate for.

  The water supply means does not necessarily need to be operated in a single cell operated in a fuel-deficient state. For example, a sufficient amount of water exists in the oxidizer electrode, and even if this is used, the performance of the fuel cell is reduced. If there is no possibility of occurrence of water, it is not necessary to supply water to the oxidizer electrode by the water supply means.

  Whether or not water is supplied to the oxidizer electrode by the water supply means and the supply amount can be determined by the exhaust gas humidity of the oxidizer or the cell resistance value.

The voltage application means for applying a voltage between the oxidant electrode and the fuel electrode paired with the oxidant electrode so that the electrolysis of water proceeds at the oxidant electrode is not particularly limited, and an external power source Alternatively, the fuel cell system may be used as a power source for the voltage applying means.
A power source as a voltage applying means is connected in series with a single cell that has become in a fuel-deficient state after fuel shortage operation (see 3B in FIG. 3), so that the fuel electrode and oxidant of the single cell are connected. A desired voltage can be applied to the pole. As shown in 3B of FIG. 3, in the fuel cell including a plurality of single cells, the single cell in the fuel shortage state is disconnected from the other single cells and serves as a voltage application unit. By connecting to a power source and electrically connecting the single cells except for the single cell, the hydrogen gas generation process of the single cell that has become fuel shortage while generating power as a whole fuel cell It can be carried out.

  In the present invention, since the water electrocatalyst is contained in the oxidant electrode, the electrolysis of water in the oxidant electrode proceeds without applying an excessive voltage. If the water electrocatalyst is not contained, it is necessary to apply a high potential, for example, a potential of 1.6 to 2.4 V, and there is a risk of deteriorating members constituting the single cell. On the other hand, in the fuel cell system of the present invention, the electrolysis of water at the oxidant electrode usually proceeds by applying a potential of 1.4 to 2.0 V between the fuel electrode and the oxidant electrode. To do. When the applied voltage is lower than 1.4V, the electrolysis of water hardly proceeds at the oxidizer electrode. On the other hand, when the applied voltage is higher than 2.0 V, there is a possibility that the members constituting the single cell, in particular, the electrolyte membrane, the electrolyte resin, the carbon, and the catalyst may be deteriorated. The applied voltage between the fuel electrode and the oxidant electrode is particularly preferably 1.5 to 1.8V.

  In the first fuel cell system, the time for performing the hydrogen generation process is the degree of adhesion of oxides and moisture due to the lack of fuel in the fuel cell single cell performing the hydrogen generation process, the hydrogen generation process conditions, the fuel cell single cell Although it depends on the configuration and the like, usually, it may be about 1 to 30 minutes, preferably 1 to 15 minutes, particularly preferably 5 to 10 minutes.

Next, a second fuel cell system, which is one of the preferred embodiments of the fuel cell system of the present invention, will be described with reference to FIGS.
In the second fuel cell system, in at least one of the fuel cell single cells, when the fuel supply is restored from the fuel deficient state during the fuel cell operation, (1) hydrogen gas is supplied to the oxidant electrode. Means for supplying, and (2) voltage applying means for applying a voltage between the oxidant electrode and the fuel electrode so that an oxidation reaction (protonation reaction) of hydrogen proceeds at the oxidant electrode. It is.

In the second fuel cell system, it is possible to supply hydrogen gas to the oxidant electrode 3 provided on one surface of the electrolyte membrane 1 when the fuel is recovered from the fuel-deficient operation ( (See FIG. 4). Further, between the fuel electrode 2 and the oxidant electrode 3 provided on the other surface of the electrolyte membrane 1, a voltage application means (power source 9) is used to oxidize hydrogen (protonation reaction) at the oxidant electrode 3. : H ₂ → 2H ⁺ + 2e ⁻ ) can be applied.

In the fuel cell single cell provided in such a second fuel cell system, when the operation in the fuel shortage state is performed, when the supply of fuel is restored, hydrogen gas is supplied to the oxidant electrode, By the voltage application by the voltage application means, the oxidation reaction of hydrogen proceeds at the oxidant electrode 3. Protons and electrons generated at the oxidant electrode by the oxidation reaction of hydrogen move to the fuel electrode through the electrolyte membrane and the external circuit, respectively, and generate hydrogen at the fuel electrode (2H ⁺ + 2e ⁻ → H ₂ ). . That is, in the second fuel cell system, hydrogen gas is generated at the fuel electrode by utilizing an electrochemical hydrogen pump function generated from the difference in H ₂ concentration.

When supplying hydrogen gas to the oxidant electrode, the supply of the oxidant to the oxidant electrode is stopped from the viewpoint of securing the hydrogen gas concentration and preventing damage to the single cell due to the combustion of hydrogen gas.
The hydrogen gas supplied to the oxidant electrode may contain components other than hydrogen as long as it does not interfere with the hydrogen oxidation reaction at the oxidant electrode and does not adversely affect the oxidant electrode. Usually, the hydrogen concentration is preferably 50 vol% or more, particularly preferably 80 vol% or more.

The supply of hydrogen gas to the oxidant electrode varies depending on the configuration (electrode area) of the fuel cell unit cell, the hydrogen concentration of the hydrogen gas, and the like, and is not specifically limited. However, the amount of H ₂ gas generated [H ₂ The hydrogen supply amount is determined based on the amount of hydrogen that compensates for the amount of hydrogen (2H ⁺ + 2e ⁻ → H ₂ ) generated from H ⁺ generated by 2e ⁻ + 2H ⁺ .

The voltage application means for applying a voltage between the oxidant electrode and the fuel electrode so that the oxidation reaction of hydrogen proceeds at the oxidant electrode is not particularly limited, and an external power source is used or the present fuel cell is used. The system may be used as a power source for the voltage applying means. The power source as the voltage application means is connected in series with the unit cell that has become in a fuel-deficient state after hydrogen shortage operation (see 5B in FIG. 5), so that the fuel electrode and oxidant of the unit cell are connected. A desired voltage can be applied to the pole.
As shown in 5B of FIG. 5, in a fuel cell including a plurality of single cells, the single cells that have run out of fuel are disconnected from the other single cells and serve as voltage application means. By connecting to a power source and electrically connecting the single cells except for the single cell, the hydrogen gas generation process of the single cell that has become fuel shortage while generating power as a whole fuel cell It can be carried out.

  In a single fuel cell that performs hydrogen generation treatment, the voltage applied between the fuel electrode and the oxidant electrode is not particularly limited as long as the oxidation reaction of hydrogen proceeds at the oxidant electrode. Since many of the electrode catalysts contained in the oxidizer electrode usually have catalytic activity also for the oxidation reaction of hydrogen, a potential of about −0.2 to +0.1 V is usually applied. For example, an oxidation reaction of hydrogen can occur at the oxidant electrode. When the applied voltage is higher than +0.1 V, the hydrogen gas generation reaction hardly proceeds at the fuel electrode. The applied voltage between the fuel electrode and the oxidant electrode is particularly preferably in the range of −0.2 to +0.05 V, more preferably −0.1 to +0.05 V.

  In the second fuel cell system, the time for performing the hydrogen generation treatment is the degree of adhesion of oxides and moisture due to the lack of fuel in the fuel cell single cell performing the hydrogen generation treatment, the hydrogen generation treatment condition, the fuel cell single cell Although it depends on the configuration and the like, usually, it may be about 1 to 30 minutes, preferably 1 to 15 minutes, particularly preferably 5 to 10 minutes.

Next, a third fuel cell system, which is one of the preferred embodiments of the fuel cell system of the present invention, will be described with reference to FIGS.
The third fuel cell system provides (1) supply of hydrogen gas to the oxidizer electrode when at least one of the fuel cell single cells returns from the fuel-deficient state during fuel cell operation. (2) a means for supplying an inert gas to the fuel electrode; (3) the oxidant electrode and the fuel electrode so that a hydrogen oxidation reaction (protonation reaction) proceeds in the oxidant electrode. And a short-circuit means for electrically connecting and short-circuiting each other.

  In the third fuel cell system, when the fuel is recovered from the fuel-deficient operation, hydrogen gas is supplied to the oxidant electrode 3 provided on one surface of the electrolyte membrane 1, and the other of the electrolyte membrane 1 is supplied. It is possible to supply an inert gas to the fuel electrode 2 provided on the surface (see FIG. 6). In addition, the fuel electrode 2 provided with the oxidant electrode 3 and the electrolyte membrane 1 interposed therebetween is electrically connected between these electrodes by a short-circuit means (external circuit 10) when the fuel returns from the operation in the fuel-deficient state. It is possible to short-circuit by connecting to.

In such a single fuel cell system provided in the third fuel cell system, when operation is performed in a fuel-deficient state, hydrogen gas is supplied to the oxidizer electrode when the fuel supply is restored. Then, an inert gas is supplied to the fuel electrode (see FIG. 6). As a result, in the fuel electrode 2, the concentration of hydrogen gas decreases due to the supply of the inert gas. On the other hand, in the oxidant electrode 3 that faces the fuel electrode 2 with the electrolyte membrane 1 interposed therebetween, hydrogen gas is supplied. The gas concentration increases, and a hydrogen gas concentration distribution is formed between the fuel electrode 2 and the oxidant electrode 3 in the single fuel cell. At this time, when the fuel electrode 2 and the oxidant electrode 3 are electrically connected by the short-circuit means, the oxidation reaction of hydrogen proceeds in the oxidant electrode 3. The oxidation reaction of hydrogen in the oxidant electrode 3 is usually promoted by the electrode catalyst contained in the oxidant electrode 3. Then, the generated protons pass through the electrolyte membrane, and the electrons move to the fuel electrode 2 by the short-circuiting means to generate hydrogen at the fuel electrode (2H ⁺ + 2e ⁻ → H ₂ ). That is, in the third fuel cell system, hydrogen gas is generated at the fuel electrode by utilizing an electrochemical hydrogen pump function generated from the difference in H ₂ concentration.

Also in the third fuel cell system, as in the second fuel cell system, when supplying hydrogen gas to the oxidizer electrode, from the viewpoint of securing the hydrogen gas concentration and preventing damage to the single cell due to the combustion of hydrogen gas, etc. Supply of the oxidizing agent to the oxidizing agent electrode is stopped.
The hydrogen gas supplied to the oxidant electrode may contain components other than hydrogen as long as it does not interfere with the hydrogen oxidation reaction at the oxidant electrode and does not adversely affect the oxidant electrode. Usually, the hydrogen concentration is preferably 50 vol% or more, particularly preferably 80 vol% or more.

The supply of hydrogen gas to the oxidant electrode varies depending on the configuration (electrode area) of the fuel cell unit cell, the hydrogen concentration of the hydrogen gas, and the like, and is not specifically limited. However, the amount of H ₂ gas generated [H ₂ The hydrogen supply amount is determined based on the amount of hydrogen that compensates for the amount of hydrogen (2H ⁺ + 2e ⁻ → H ₂ ) generated from H ⁺ generated by 2e ⁻ + 2H ⁺ .

The inert gas supplied to the fuel electrode is not particularly limited, and for example, nitrogen gas, argon gas, helium gas, or the like can be used. If the flow rate of the inert gas is small, there is a possibility that a sufficient amount of H ₂ gas is not generated at the fuel electrode.

As a short-circuit means for electrically connecting the oxidant electrode and the fuel electrode so that the oxidation reaction of hydrogen proceeds at the oxidant electrode, the oxidant electrode and the fuel electrode can be electrically connected. It is not particularly limited if possible.
As shown in 7B of FIG. 7, in a fuel cell including a plurality of single cells, the single cell that has become in a fuel-deficient state is disconnected from the other single cells and is externally connected as a short-circuit means. By connecting to the circuit, and the unit cells other than the unit cell are electrically connected, the power generation of the entire fuel cell is performed, and the hydrogen gas generation processing of the unit cell that is in a fuel-deficient state is performed. It can be carried out.

  In the third fuel cell system, the time for performing the hydrogen generation treatment is the degree of adhesion of oxides and moisture due to the lack of fuel in the fuel cell single cell performing the hydrogen generation treatment, the hydrogen generation treatment condition, the fuel cell single cell Although it depends on the construction, etc., usually it may be about 1 to 30 minutes, preferably 1 to 15 minutes, particularly preferably 5 to 10 minutes.

In the fuel cell system of the present invention, the fuel electrode preferably contains a water electrocatalyst having a catalytic action for electrolysis of water. By disposing the water electrocatalyst at the fuel electrode, the electrolysis of water is promoted when the fuel runs out. This is because by making more protons and electrons replenished by electrolysis of water, the progress of the oxidative corrosion reaction of the carbon material at the time of fuel shortage can be suppressed.
As the water electrocatalyst to be contained in the fuel electrode, the same one as the oxidant electrode in the first fuel cell system can be used. Further, the content of the water electrocatalyst in the fuel electrode can be made the same as in the first fuel cell system.

(Manufacture of single fuel cell)
1 g of platinum-supported carbon black (Pt / C catalyst, Pt support ratio: 45 wt%), 0.55 g of perfluorocarbon sulfonic acid resin (trade name: Nafion, manufactured by Aldrich), ethanol, and water are mixed with stirring. A catalyst ink was prepared.

On the other hand, 1 g of carbon black carrying a water electrocatalyst RuO ₂ (RuO ₂ / C catalyst, RuO ₂ loading: 30 wt%), 0.7 g of perfluorocarbon sulfonic acid resin (trade name: Nafion, manufactured by Aldrich), Water and ethanol were mixed with stirring to prepare a water electrocatalyst ink.

The catalyst ink was spray-coated on both sides of a fluorine-based electrolyte membrane (trade name: Gore Select membrane, manufactured by Japan Gore-Tex, Inc., film thickness: 45 μm, 7 cm × 7 cm). At this time, the catalyst ink was applied so that the amount of Pt per unit area of the catalyst layer was 0.2 mg / cm ² . The ink was dried to form a catalyst layer (3.6 cm × 3.6 cm).
Next, the water electrolysis catalyst ink was spray-coated on the catalyst layers formed on both surfaces of the electrolyte membrane. At this time, the water electrolysis catalyst ink was applied so that the amount of RuO ₂ per unit area of the water electrolysis layer was 0.1 mg / cm ² . The ink was dried to form a water electrolysis layer (3.6 cm × 3.6 cm).

The electrolyte membrane in which the catalyst layer and the water electrolysis layer are formed is sandwiched between carbon papers for gas diffusion layers (thickness: 250 μm) and thermocompression bonded (pressing pressure: 3 MPa, pressing temperature: 140 ° C.) to form a membrane / electrode joint Got the body.
The obtained membrane electrode assembly was sandwiched between two separators (made of carbon) to produce a single cell.

(Reference experiment example)
The single cell produced as described above was operated under the following conditions, and a power generation performance evaluation test was performed. The results are shown in FIG.

<Power generation performance evaluation test>
Fuel electrode: hydrogen gas 500 cm ³ / min (1 atm, constant condition at 25 ° C., humidity 100% RH)
Oxidant electrode: Air 1000 cm ³ / min (1 atm, constant condition at 25 ° C., humidity 100% RH)
Cell temperature: 80 ° C

Example 1
A single cell produced in the same manner as described above was operated for 1 hour in the following hydrogen deficient state, and then hydrogen was generated at the fuel electrode under the following hydrogen generation treatment conditions. Thereafter, a power generation performance evaluation test was performed in the same manner as described above. The results are also shown in FIG.

<Histogenous state>
Fuel electrode: nitrogen gas 500 cm ³ / min (1 atm, 25 ° C. constant condition, humidity 100% RH)
Oxidant electrode: Air 500 cm ³ / min (1 atm, constant condition at 25 ° C., humidity 100% RH)
Current density: 0.1 A / cm ²
Cell temperature: 80 ° C
<Hydrogen generation treatment conditions>
Fuel electrode: nitrogen gas 500 cm ³ / min (1 atm, 25 ° C. constant condition, humidity 100% RH)
Oxidant electrode: hydrogen gas 500 cm ³ / min (1 atm, constant condition at 25 ° C., humidity 100% RH)
Fuel electrode / oxidant electrode voltage: -0.02 V control Hydrogen treatment time: 10 minutes

(Comparative Example 1)
A single cell produced in the same manner as described above was operated for 1 hour in the same hydrogen deficient state as above. Thereafter, a power generation performance evaluation test was performed in the same manner as described above without performing the hydrogen generation treatment. The results are shown in FIG.

  As shown in FIG. 8, the fuel cell single cell of Example 1 in which hydrogen generation processing for generating hydrogen at the fuel electrode after operation in a hydrogen deficient state was slightly inferior to the power generation performance before the hydrogen deficient state, Compared with the fuel cell single cell of Comparative Example 1 in which the hydrogen generation treatment was not performed, the voltage drop accompanying the increase in current density was small, and the power generation performance was excellent.

It is a figure which shows one example of the fuel cell single cell with which the fuel cell system of this invention is equipped. It is a key map explaining the 1st fuel cell system concerning the present invention. It is a key map explaining the 1st fuel cell system concerning the present invention. It is a conceptual diagram explaining the 2nd fuel cell system which concerns on this invention. It is a conceptual diagram explaining the 2nd fuel cell system which concerns on this invention. It is a conceptual diagram explaining the 3rd fuel cell system concerning the present invention. It is a conceptual diagram explaining the 3rd fuel cell system concerning the present invention. It is a graph which shows the experimental result in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Fuel electrode 3 ... Oxidant electrode 4 ... Catalyst layer (4a: Fuel electrode side catalyst layer, 4b: Oxidant electrode side catalyst layer)
5. Gas diffusion layer (5a: fuel electrode side gas diffusion layer, 5b: oxidant electrode side gas diffusion layer)
6 ... Membrane / electrode assembly 7 ... Separator (7a: fuel electrode side separator, 7b: oxidant electrode side separator)
8 (8a, 8b) ... gas flow path 9 ... power supply (voltage applying means)
10 ... External circuit (short-circuit means)
100 ... Fuel cell single cell

Claims (16)

A fuel cell unit that generates electricity by reacting a fuel supplied to a fuel electrode provided on one side of the electrolyte membrane with an oxidant supplied to an oxidant electrode provided on the other side of the electrolyte membrane. A fuel cell system comprising a cell,
At least one of the single fuel cell units generates hydrogen (H ₂ ) at the fuel electrode of the single fuel cell unit when the fuel supply is restored from the fuel depleted state during fuel cell operation. A fuel cell system comprising means for causing A water electrocatalyst contained in the oxidant electrode;
In at least one of the fuel cell single cells, when the fuel supply is restored from the fuel deficient state during fuel cell operation,
(1) water supply means for controlling the amount of water in the oxidizer electrode;
(2) voltage applying means for applying a voltage between the oxidant electrode and the fuel electrode so that electrolysis of water proceeds at the oxidant electrode;
The fuel cell system according to claim 1, comprising:   The fuel cell system according to claim 2, wherein a voltage applied between the oxidant electrode and the fuel electrode by the voltage applying unit is +1.4 to + 2.0V. 4. The fuel cell system according to claim ₂ , wherein the water electrocatalyst is at least one selected from IrO ₂ , RuO ₂ , Pt, TiO ₂ , and a solid solution containing two or more thereof. In at least one of the fuel cell single cells, when the fuel supply is restored from the fuel deficient state during fuel cell operation,
(1) means for supplying hydrogen gas to the oxidant electrode;
(2) voltage applying means for applying a voltage between the oxidant electrode and the fuel electrode so that a hydrogen oxidation reaction (protonation reaction) proceeds in the oxidant electrode;
The fuel cell system according to claim 1, comprising:   6. The fuel cell system according to claim 5, wherein a voltage applied between the oxidant electrode and the fuel electrode by the voltage application unit is −0.2 to +0.1 V (excluding 0 V). 7. . In at least one of the fuel cell single cells, when the fuel supply is restored from the fuel deficient state during fuel cell operation,
(1) means for supplying hydrogen gas to the oxidant electrode;
(2) means for supplying an inert gas to the fuel electrode;
(3) short-circuit means for electrically connecting and short-circuiting the oxidant electrode and the fuel electrode;
The fuel cell system according to claim 1, comprising:   The fuel cell system according to any one of claims 1 to 7, wherein the fuel electrode contains a water electrocatalyst having catalytic activity for electrolysis of water. A fuel cell unit that generates electricity by reacting a fuel supplied to a fuel electrode provided on one side of the electrolyte membrane with an oxidant supplied to an oxidant electrode provided on the other side of the electrolyte membrane. In a fuel cell comprising a cell,
At least one of the single fuel cell units generates hydrogen (H ₂ ) at the fuel electrode of the single fuel cell unit when the fuel supply is restored from the fuel depleted state during fuel cell operation. A method for operating a fuel cell, comprising:   The oxidant electrode contains a water electrocatalyst having catalytic activity for water electrolysis, and supply of the fuel from a state where the fuel is deficient during operation of the fuel cell in at least one of the fuel cell single cells. The fuel cell according to claim 9, wherein a voltage is applied between the oxidant electrode and the fuel electrode so that electrolysis of water existing in the oxidant electrode proceeds when the oxidant returns. how to drive.   The method of operating a fuel cell according to claim 10, wherein a voltage applied between the oxidant electrode and the fuel electrode by the voltage applying means is +1.4 to + 2.0V. The method of operating a fuel cell according to claim 10 or 11, wherein the water electrocatalyst is at least one selected from IrO ₂ , RuO ₂ , Pt, TiO ₂ , and a solid solution containing two or more thereof.   In at least one of the fuel cell single cells, when the fuel supply is restored from the fuel depleted state during fuel cell operation, hydrogen gas is supplied to the oxidant electrode, and the oxidant electrode The method of operating a fuel cell according to claim 9, wherein a voltage is applied between the oxidant electrode and the fuel electrode so that a hydrogen oxidation reaction (protonation reaction) proceeds.   14. The fuel cell according to claim 13, wherein a voltage applied between the oxidant electrode and the fuel electrode by the voltage application unit is −0.2 to +0.1 V (excluding 0 V). how to drive.   In at least one of the fuel cell units, when the fuel supply is restored from the fuel-deficient state during fuel cell operation, hydrogen gas is supplied to the oxidant electrode, and the fuel electrode is supplied to the fuel electrode. The method for operating a fuel cell according to claim 9, wherein an inert gas is supplied, and the oxidant electrode and the fuel electrode are electrically connected and short-circuited.   The method for operating a fuel cell according to any one of claims 9 to 15, wherein the fuel electrode contains a water electrocatalyst having catalytic activity for water electrolysis.

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