JP5533800B2 - FUEL CELL AND FUEL CELL INSPECTION METHOD - Google Patents

Description

  The present invention relates to a fuel cell and a fuel cell inspection method.

  Conventionally, it is known that a fuel cell that generates power by reacting a fuel gas and an oxidant gas generates a so-called negative voltage when starting at below freezing point, resulting in a decrease in power generation efficiency and performance. . Specifically, when a fuel cell stack in which a plurality of fuel cells are stacked is stopped in an environment below freezing, the gas flow paths of some fuel cells are blocked due to freezing of residual water. When the fuel cell system is started in this state, the fuel cell (cell) whose gas flow path is closed becomes in a state where the fuel gas is deficient, and the potential of the anode rises to a negative voltage. Since the negative voltage fuel cell does not work to the outside, the power generation efficiency of the entire fuel cell stack may be reduced. Further, in this negative voltage fuel cell, oxidation of carbon constituting the catalyst may occur in order to pass the same current as other fuel cells. When carbon oxidation occurs, the performance of the fuel cell deteriorates due to a decrease in the catalyst area or the like. In connection with the problem of the negative voltage, a technique for relaxing the negative voltage by attaching a diode unit outside the fuel cell stack has been known (Patent Document 1).

JP 2010-212025 A JP 2011-003477 A

  However, there is still room for improvement in the technology for suppressing the decrease in power generation efficiency and performance of the fuel cell due to the generation of negative voltage.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve a technique for suppressing a decrease in power generation efficiency and a performance when a fuel cell becomes a negative voltage.

  In order to solve at least a part of the above problems, the present invention can be realized as the following aspects or application examples.

[Application Example 1]
A fuel cell,
A power generation member configured to include a membrane electrode assembly;
A pair of separators respectively disposed on both sides of the power generation member;
A heating circuit disposed between the pair of separators, having both ends electrically connected to the pair of separators, and generating heat by a current flowing when a negative voltage is generated between the pair of separators. ,
The heat generating circuit is a fuel cell that is disposed at a position where a gas flow path formed between the power generation member and the separator can be heated.

  According to this configuration, even when a negative voltage is generated in the fuel cell due to freezing of residual water, the ice that closes the gas flow path can be melted due to the heat generation circuit generating heat due to the negative voltage. Thus, the negative voltage state can be eliminated at an early stage to suppress a decrease in power generation efficiency.

[Application Example 2]
In the fuel cell described in Application Example 1,
The pair of separators includes an anode separator that contacts the anode side of the membrane electrode assembly, and a cathode separator that contacts the cathode side of the membrane electrode assembly,
The heat generation circuit includes a diode arranged so that a current flows from the anode side separator to the cathode side separator.

  According to this configuration, the ice blocking the gas flow path can be melted by the heat generated by the diode, so that the negative voltage state can be eliminated at an early stage to suppress a decrease in power generation efficiency.

[Application Example 3]
In the fuel cell according to Application Example 1 or Application Example 2,
The power generation member includes a support member formed on an outer peripheral portion of the membrane electrode assembly,
The heat generating circuit is a fuel cell, wherein the heat generating circuit is disposed at a position where the gas flow path formed between the separator and the support member can be heated.

  According to this configuration, in the gas flow path, the portion where the residual water is likely to freeze can be heated, so that the negative voltage state can be eliminated at an early stage to suppress a decrease in power generation efficiency.

[Application Example 4]
In the fuel cell described in Application Example 3,
The fuel cell, wherein the heat generating circuit is disposed on each side of a gas flow path formed between the separator and the support member.

  According to this configuration, in the gas flow path, the portion where the residual water is likely to freeze can be heated from both sides, so that the negative voltage state can be eliminated at an early stage and the reduction in power generation efficiency can be suppressed.

[Application Example 5]
In the fuel cell according to Application Example 1 or Application Example 2,
The separator includes a refrigerant flow path forming portion for forming a refrigerant flow path on a surface opposite to a surface in contact with the power generation member,
The heat generating circuit is a fuel cell, wherein the heat generating circuit is disposed at a position capable of heating a gas channel in which the refrigerant channel is not formed on the opposite surface of the gas channel.

  According to this configuration, in the gas flow path, the portion where the residual water is likely to freeze can be heated, so that the negative voltage state can be eliminated at an early stage to suppress a decrease in power generation efficiency.

[Application Example 6]
In the fuel cell according to any one of Application Examples 1 to 5,
The fuel cell, wherein a negative voltage between the pair of separators when a current flows through the heat generating circuit is larger than a voltage when a water electrolysis reaction occurs in an anode of the membrane electrode assembly.

  According to this configuration, even if a negative voltage is generated between the pair of separators due to the lack of fuel gas, a current flows through the heat generating circuit, so that the voltage between the separators causes an oxidation reaction of carbon at the anode. Since the voltage does not drop to the voltage, it is possible to suppress the deterioration of the performance of the fuel cell due to catalyst deterioration.

[Application Example 7]
A method for inspecting a fuel cell,
A fuel cell comprising a membrane electrode assembly, a pair of separators disposed on both sides of the membrane electrode assembly, and a heating circuit that generates heat due to a current flowing when a negative voltage is generated between the pair of separators. A preparation process;
Drying the membrane electrode assembly until a resistance value between the pair of separators is a predetermined value or more;
The state of the fuel cell is determined depending on whether or not a negative voltage between the pair of separators when a current is passed between the pair of separators of the fuel cell after drying the membrane electrode assembly is greater than or equal to a predetermined value. And a step of determining.

  According to this configuration, in a fuel cell including a heat generation circuit that generates heat when a negative voltage occurs, it can be easily inspected whether or not catalyst deterioration can be suppressed when a negative voltage occurs.

  It should be noted that the present invention can be realized in various modes, for example, a form of a fuel cell system including the fuel cell, a vehicle equipped with the fuel cell, a method of manufacturing the fuel cell, etc. Can be realized.

It is explanatory drawing for demonstrating schematic structure of the fuel cell which concerns on 1st Example. It is explanatory drawing for demonstrating schematic structure of a separator. It is explanatory drawing for demonstrating schematic structure of sealing member integrated MEA. It is explanatory drawing which illustrated the B-B 'cross section of FIG. 2 and FIG. It is explanatory drawing for demonstrating the electric power generation state of the fuel cell at the time of normal. It is explanatory drawing for demonstrating the electric power generation state of the fuel cell at the time of hydrogen deficiency. It is explanatory drawing for demonstrating the equivalent circuit of the fuel cell of a present Example. 6 is an explanatory diagram illustrating the relationship between a forward voltage and a forward current of a diode D. FIG. It is explanatory drawing for demonstrating the bypass voltage Vcb. It is explanatory drawing which showed the evaluation result of the water electrolysis reaction generation voltage Vcw in a fuel cell. It is explanatory drawing which illustrated the flow of the inspection method of a fuel cell. It is explanatory drawing for demonstrating the installation position of the diode chip which concerns on 2nd Example. 12 is an explanatory diagram for explaining an installation position of a diode chip according to Modification 1. FIG.

A. First embodiment:
FIG. 1 is an explanatory diagram for explaining a schematic configuration of the fuel cell according to the first embodiment. FIG. 1 illustrates a cross-sectional configuration of the fuel cell stack 10 and corresponds to a cross section taken along the line AA ′ of FIGS. 2 and 3 described later. The fuel cell stack 10 has a configuration in which a plurality of fuel cells 100 are stacked. The fuel cell stack 10 is mounted on a moving body such as a vehicle and used as a power source for the moving body. It is also used as a stationary power source. The fuel cell 100 is a polymer electrolyte fuel cell that generates power by receiving supply of hydrogen and oxygen.

  The fuel cell 100 includes a seal member integrated MEA (Membrane-Electrode Assembly) 200, separators 310 and 330, and a diode chip 500. The fuel cell 100 has a configuration in which a seal member integrated MEA 200 is sandwiched between separators 310 and 330.

  The seal member-integrated MEA 200 includes an MEA 210 and a seal member 220, and a frame-shaped seal member 220 is formed on the outer periphery of the substantially rectangular MEA 210. In the MEA 210, the anode side catalyst layer 214 and the anode side gas diffusion layer 410 are laminated in this order on one surface of the electrolyte membrane 212, and the cathode side catalyst layer 215 and the cathode side gas diffusion layer 430 are laminated in this order on the other surface. It has a configuration. The seal member 220 of the present embodiment corresponds to a “power generation member” in the claims.

  The electrolyte membrane 212 is composed of a polymer electrolyte membrane (Nafion (registered trademark)) formed of a fluorine-based sulfonic acid polymer as a proton conductive solid polymer material. The polymer electrolyte membrane is not limited to Nafion (registered trademark), and other fluorine-based sulfonic acid membranes such as Aciplex (registered trademark) and Flemion (registered trademark) may be used. Further, for example, a fluorine-based phosphonic acid film, a fluorine-based carboxylic acid film, a fluorine-hydrocarbon-based graft film, a hydrocarbon-based graft film, an aromatic film, or the like may be used.

  The anode-side catalyst layer 214 and the cathode-side catalyst layer 215 include, for example, carbon particles (catalyst-supported carrier) supporting a catalyst metal (for example, platinum) that progresses an electrochemical reaction, and a polymer electrolyte having proton conductivity (for example, (Fluorine resin). As the conductive carrier, in addition to carbon particles, for example, carbon materials such as carbon black, carbon nanotubes, carbon nanofibers, carbon compounds represented by silicon carbide, and the like can be used. In addition to platinum, for example, platinum alloy, palladium, rhodium, gold, silver, osmium, iridium and the like can be used as the catalyst metal.

  The seal member 220 is a member for supporting the MEA 210 and is formed by injection molding using silicone rubber. In addition to the cathode gas supply through-hole 223 and the anode exhaust gas discharge through-hole 312 shown in FIG. 1, the seal member 220 includes a plurality of through-holes described later with reference to FIG. Each through hole constitutes a manifold for supplying and discharging reaction gas and cooling water together with through holes formed in the separators 310 and 330, respectively. The seal member 220 of the present embodiment corresponds to a “support member” in the claims.

  The gas diffusion layers 410 and 430 are layers that diffuse reaction gases (anode gas and cathode gas) used for the electrode reaction along the surface direction of the electrolyte membrane 212, and are constituted by a porous diffusion layer base material. Yes. As the base material for the diffusion layer, for example, a carbon porous body such as carbon paper or carbon cloth, or a metal porous body such as a metal mesh or foam metal can be used. In order to obtain water repellency, the gas diffusion layers 410 and 430 may be formed by coating a diffusion layer base material with a water repellent paste (water repellent treatment).

  Separator 310,330 is comprised by the member which has gas interruption | blocking property and electronic conductivity. The anode-side separator 310 has one main surface in contact with the anode-side gas diffusion layer 410 of the seal member-integrated MEA 200 and the other main surface in contact with the cathode-side separator 330. The cathode-side separator 330 has one main surface in contact with the cathode-side gas diffusion layer 430 of the seal member-integrated MEA 200 and the other main surface in contact with the anode-side separator 310. Each of the separators 310 and 330 includes a plurality of openings for forming a manifold. Specific shapes and configurations of the separators 310 and 330 will be described in detail with reference to FIG.

  The diode chip 500 includes a silicon diode composed of P-type silicon 510 and N-type silicon 530. The diode chip 500 is connected in parallel with the fuel cell 100. Specifically, P-type silicon 510 is electrically connected to anode-side separator 310, and N-type silicon 530 is electrically connected to cathode-side separator 330. The silicon diode used in the diode chip 500 has a characteristic that the forward drop voltage is about 0.6 V and the resistance to the reverse voltage is high. The mounting position of the diode chip 500 in the separators 310 and 330 will be described in detail with reference to FIG. The diode chip 500 of this embodiment corresponds to a “heat generation circuit” in the claims.

  FIG. 2 is an explanatory diagram for explaining a schematic configuration of the separator. FIG. 2 illustrates the main surface of the anode-side separator that comes into contact with the seal member integrated MEA 200. The shape of the cathode side separator 330 is the same as that of the anode side separator 310 shown in FIG.

  The anode-side separator 310 is formed of a thin metal plate such as stainless steel, titanium, aluminum, or copper having a substantially rectangular shape. The anode separator 310 includes a gas flow path forming portion 317 for forming a gas flow path between the seal member-integrated MEA 200 by a plurality of grooves in the vicinity of the center portion, and a plurality of gas flow path forming portions 317 for forming a manifold at both ends. Openings (through holes) 311 to 316 are provided. Hereinafter, the openings 311 to 316 are respectively formed as an anode gas supply through hole 311, an anode exhaust gas discharge through hole 312, a cathode gas supply through hole 313, a cathode exhaust gas discharge through hole 314, and a cooling water supply through hole 315. Also referred to as a cooling water discharge through hole 316.

  The gas flow path forming unit 317 forms a gas flow path for circulating the anode gas and the anode exhaust gas between the anode side separator 310 and the seal member integrated MEA 200. The gas flow path forming portion 317 has two portions, a power generation region portion 317Ag that is a portion facing the MEA 210 and a non-power generation region portion 317An that is a portion facing the seal member 220. The power generation region portion 317Ag has a substantially rectangular shape corresponding to the MEA 210, and is a region used for conduction of electrons during power generation. The non-power generation region portion 317An is a region formed between the power generation region portion 317Ag and the anode gas supply through hole 311 and between the power generation region portion 317Ag and the anode exhaust gas discharge through hole 312. In the non-power generation region portion 317An, a plurality of convex portions 318 that are in contact with the seal member 220 are formed, but the convex portions 318 may not be provided. Hereinafter, the gas flow path formed between the non-power generation region portion 317An and the seal member 220 is also referred to as a non-power generation region gas flow path GCn. The non-power generation region gas flow path GCn of the present embodiment corresponds to “a gas flow path formed between the separator and the support member” in the claims.

  The diode chip 500 is disposed at a position where the non-power generation region gas flow path GCn can be heated. Specifically, as will be described later, when a negative voltage is generated in the fuel cell 100, the diode chip 500 generates heat when a current flows. The position of the diode chip 500 is set at an arbitrary position close to the non-power generation region gas flow path GCn to such an extent that the heat generation can heat the non-power generation region gas flow path GCn. The installation position of the diode chip 500 is set to a position where the non-power generation region gas flow path GCn can be heated. The non-power generation region gas flow path GCn is a place where heat generated by the power generation of the fuel cell 100 is difficult to be transmitted. This is because sometimes ice is difficult to melt.

  Here, the diode chips 500 are respectively disposed on both sides of the non-power generation region gas flow path GCn. The diode chip 500 may be arranged so that only the non-power generation region gas flow path GCn connected to the anode exhaust gas discharge through-hole 312 can be heated, or connected to the anode gas supply through-hole 221. The non-power generation region gas flow path GCn may be arranged so as to be heatable.

  FIG. 3 is an explanatory diagram for explaining a schematic configuration of the seal member integrated MEA. The seal member-integrated MEA 200 has a MEA 210 disposed in the vicinity of the center of a seal member 220 having a substantially rectangular shape, and includes a plurality of openings (through holes) 221 to 226 for constituting a manifold at both ends. Hereinafter, the openings 221 to 226 are respectively formed as an anode gas supply through hole 221, an anode exhaust gas discharge through hole 222, a cathode gas supply through hole 223, a cathode exhaust gas discharge through hole 224, and a cooling water supply through hole 225. Also referred to as a cooling water discharge through hole 226.

  The seal member integrated MEA 200 has a position where the diode chip 500 is disposed when the anode-side separator 310 of FIG. 2 is stacked in addition to the openings (through holes) 221 to 226 for forming a manifold. An insertion port (through hole) 220b for inserting the diode chip 500 is provided at a corresponding position. In the present embodiment, the insertion port 220 b is formed in the seal member 220.

  FIG. 4 is an explanatory view illustrating the B-B ′ cross section of FIGS. 2 and 3. As shown in FIG. 4, the diode chip 500 is connected to the anode side separator 310 and the cathode side separator 330 through the insertion port 220b. When a negative voltage is generated in the fuel cell 100 and the potential of the anode side separator 310 becomes higher than the potential of the cathode side separator 330, current flows from the anode side separator 310 toward the cathode side separator 330 via the diode chip 500. Flowing. When the current flows through the diode chip 500, the diode chip 500 generates heat and heats the non-power generation region gas flow path GCn.

  In general, when a fuel cell is stopped in a sub-freezing environment, the gas flow path of the fuel cell may be blocked due to freezing of a liquid such as residual water. When the fuel cell is started in this state, the fuel cell whose gas flow path is closed becomes deficient in fuel gas (hydrogen), the anode potential rises, and the anode potential becomes a negative voltage higher than the cathode potential. Since the negative voltage fuel cell does not work to the outside, there is a problem that the power generation efficiency of the entire fuel cell is lowered. In addition, in the negative voltage fuel cell, there is a problem that the oxidation of carbon constituting the catalyst is generated and the performance of the fuel cell is deteriorated in order to pass the same current as that of other adjacent fuel cells.

  However, in the fuel cell 100 according to the present embodiment, when a negative voltage is generated by starting in a sub-freezing environment, a current flows through the diode chip 500 before dropping to a voltage at which the carbon oxidation reaction occurs. Occurrence can be suppressed. When a current flows through the diode chip 500, the non-power generation region gas flow path GCn is heated by the diode chip 500, so that the ice inside the non-power generation region gas flow path GCn can be melted. Thereby, the blockage | closure of a gas flow path can be eliminated earlier and a negative voltage state can be eliminated early. Below, the flow of electrons when the fuel cell 100 is deficient in hydrogen, the chemical reaction that occurs at the anode and the cathode, and the like will be described.

  5 and 6 are explanatory diagrams for explaining the power generation state during normal operation (normal time) and when the fuel cell is deficient in the fuel cell. FIG. 5 shows the power generation state of the fuel cell 100 at normal time, and FIG. 6 shows the power generation state of the fuel cell 100 at the time of hydrogen deficiency. 5 and 6, for convenience of explanation, the fuel cell stack 10 is shown as a configuration in which three fuel cells 100 (100a, 100b, 100c) are stacked. Each fuel cell 100a, 100b, 100c is indicated by an electrolyte membrane m, a cathode c, an anode a, and a separator s. For example, the fuel cell 100a is indicated by a part of the separator s0, the cathode c1, the electrolyte membrane m1, the anode a1, and a part of the separator s1. A part of the separator s0 corresponds to the cathode-side separator 330 in FIG. The cathode c1 corresponds to the cathode side gas diffusion layer 430 and the cathode side catalyst layer 215. The electrolyte membrane m1 corresponds to the electrolyte membrane 212. The anode a1 corresponds to the anode side catalyst layer 214 and the anode side gas diffusion layer 410. The separator s1 corresponds to a laminate of the anode side separator 310 and the cathode side separator 330.

  As shown in FIG. 5, during normal power generation (normal time) of the fuel cell 100, that is, hydrogen gas and air are sufficiently supplied to the fuel cells 100a, 100b, and 100c, and the fuel cells 100a, 100b, and 100c When power generation is performed, a reaction represented by the following formula (1) occurs at the anode. Further, the reaction shown in the following formula (2) occurs at the cathode. At this time, the voltage of each fuel cell 100a, 100b, 100c (voltage between separators of each fuel cell 100: cell voltage Vc) is approximately + 1.0V. Reactions of the following formulas (1) and (2) can occur when the voltages of the fuel cells 100a, 100b, and 100c are higher than 0V.

  The cell voltage Vc of the fuel cell 100 that is a single cell is determined as shown in the following formula (3). In Equation (3), Vc is the cell voltage, Ec is the cathode potential, Ea is the anode potential, and IR is the voltage due to the resistance of the single cell (electrolyte membrane resistance, wiring contact resistance, etc.). Each means a descent. In addition, the cell voltage Vc means a potential difference between two fuel cells (between single cells) with one fuel cell interposed therebetween. For example, the cell voltage Vc of the fuel cell 100b means a potential difference between the fuel cell 100a (anode a1) and the fuel cell 100c (cathode c3).

  When the fuel cell 100b is normal (that is, when the cell voltage Vc is 0 V or higher), a reverse bias is applied to the diode chip 500, so that almost no current flows. The state in which no current flows through the diode chip 500 is not limited to when the fuel cell 100b is normal (in the case of 0 ≦ Vc), but the cell voltage Vc of the fuel cell 100b becomes a negative voltage, and its absolute value is the diode chip. This can also occur when the forward voltage Vf (eg, 0.6 V) of the diode included in 500 is smaller (−Vf <Vc <0).

  When the amount of hydrogen gas supplied to the fuel cell 100 is smaller than the amount necessary for power generation (when hydrogen is deficient), the anode potential Ea in the above equation (3) rises, so the cell voltage Vc is a negative voltage ( Vc <0). As described above, the hydrogen deficiency is caused by an electrochemical reaction in a sub-freezing environment, in addition to the case where the generated water accumulated in the fuel gas channel and the anode catalyst layer 214 freezes and the gas channel is blocked. It may occur when water (product water) accumulates in the fuel gas flow path and the pressure loss in the fuel gas flow path is increased by the generated water.

  FIG. 6 shows a state where hydrogen deficiency occurs in the fuel cell 100b and the cell voltage Vc is a negative voltage. At this time, since the other fuel cells 100a and 100c generate power normally, the fuel cell 100b also tries to generate current (that is, try to exchange electrons). However, due to the lack of hydrogen, the reaction represented by the above formula (1) does not occur at the anode a2 of the fuel cell 100b, and the reactions represented by the following formula (4) and the following formula (5) may occur. The water electrolysis reaction of Formula (4) can occur when the cell voltage Vc is approximately −0.7 V or less. The carbon oxidation reaction of Formula (5) can occur when the cell voltage Vc is approximately −1.5V or less. In the cathode c2, a reaction represented by the following formula (2) occurs. Hereinafter, the cell voltage Vc when the water electrolysis reaction of Formula (4) occurs is also referred to as the water electrolysis reaction generation voltage Vcw, and the cell voltage Vc when the carbon oxidation reaction of Formula (5) occurs is also referred to as the carbon oxidation reaction generation voltage Vcc. Call.

  Here, the reaction shown in Formula (5) means oxidation of carbon contained in the catalyst constituting the anode a2. That is, at the time of hydrogen deficiency, the catalyst may be deteriorated by the reaction shown in the formula (5) at the anode a2. However, in the fuel cell 100b of this embodiment, since the diode chip 500 is disposed, the cell voltage Vc becomes a negative voltage, and the absolute value thereof is larger than the forward voltage Vf of the diode included in the diode chip 500 ( If Vc <−Vf <0), even if electrons are not supplied from the anode a2 to the cathode c3 of the fuel cell 100c, the electrons generated at the anode a1 of the fuel cell 100a via the diode chip 500 are generated in the fuel cell 100c. Supplied to the cathode c3. Therefore, even if the fuel cell 100b is in a hydrogen-deficient state, the occurrence of reactions shown in the above formulas (4) and (5) at the anode a2 is suppressed. Therefore, the occurrence of catalyst deterioration of the anode a2 is suppressed.

  The fuel cell 100 of this embodiment is configured such that the bypass voltage Vcb, which is the cell voltage Vc when a current flows through the diode chip 500, is greater than the water electrolysis reaction generation voltage Vcw (Vcw <Vcb <0). . In this way, when the cell voltage Vc drops to a negative voltage state (Vc <0), a current flows through the diode chip 500, so that the cell voltage Vc is changed to the water electrolysis reaction generation voltage Vcw or the carbon oxidation. It is possible to suppress a drop to the reaction generation voltage Vcc. A specific configuration of the fuel cell 100 for the bypass voltage Vcb to be greater than the water electrolysis reaction generation voltage Vcw will be described with reference to FIGS.

FIG. 7 is an explanatory diagram for explaining an equivalent circuit of the fuel cell of the present embodiment. As shown in the upper part of FIG. 7, here, the thickness of the anode-side separator 310 and the cathode-side separator 330 is t _s (m), respectively, and the thickness of the adhesive between the diode chip 500 and the separators 310 and 330 is set. Are each t _b (m). The total contact area between the diode chip 500 and the separators 310 and 330 is S (m ² ). S (m ² ) is equal to the total cross-sectional area of the diode chip 500. The total current flowing through the diode chip 500 is I (A). Further, the electrical resistivity of the separator is ρ _s (Ω · m), and the electrical resistivity of the adhesive is ρ _b (Ω · m).

The equivalent circuit of the fuel cell 100 can be expressed as shown in the lower part of FIG. 7 by the power generation unit G, the diode D, and the combined resistance Rs of the separator and the adhesive. The power generation unit G is a part used for power generation in the fuel cell 100, specifically, a part where the MEA 210, the anode side separator 310, and the cathode side separator 330 are stacked. The diode D is a diode included in the diode chip 500. The combined resistance Rs (Ω) is a resistance obtained by combining the resistance of the separator and the resistance of the adhesive, and the electrical resistivity ρ _s (Ω · m) of the separator, the thickness t _s (m) of the palator, Using the contact area S (m ² ), the electrical resistivity ρ _b (Ω · m) of the adhesive, and the thickness t _b (m) of the adhesive, it can be expressed as the following formula (6).

  FIG. 8 is an explanatory diagram illustrating the relationship between the forward voltage and the forward current of the diode D. The vertical axis in FIG. 8 represents the forward voltage (bias voltage) Vf (V) of the diode D, and the horizontal axis represents the forward current I (A) of the diode D. FIG. 8 shows the relationship between the forward voltage Vf and the current I when the temperature Tc of the diode D is 150 ° C. and 25 ° C. FIG. 8 shows a typical value (TYP value) and a maximum value (MAX value). It can be seen that the forward voltage Vf of the diode D decreases as the temperature Tc of the diode D increases, and increases as the current I increases.

FIG. 9 is an explanatory diagram for explaining the bypass voltage Vcb. The bypass voltage Vcb is the current I, the forward voltage Vf of the diode D, the electrical resistivity ρ _s (Ω · m) of the separator constituting the combined resistor Rs, the thickness t _s (m) of the palator, Using the contact area S (m ² ), the electrical resistivity ρ _b (Ω · m) of the adhesive, and the thickness t _b (m) of the adhesive, it can be expressed as the following formula (7). .

FIG. 10 is an explanatory diagram showing the evaluation result of the water electrolysis reaction generation voltage Vcw in the fuel cell. The horizontal axis in FIG. 10 indicates the current density Dc (A / cm ² ) of the current flowing through the MEA, and the vertical axis indicates the cell voltage Vc (V). FIG. 10 shows the water electrolysis reaction generation voltage in each state where the temperature and current density of the fuel cell are different. In order to obtain the evaluation result of FIG. 10, in a fuel cell that does not include the diode chip 500, the cell voltage Vc when a water electrolysis reaction occurs when current is swept from the outside with nitrogen flowing through the anode and air flowing through the cathode. (= Water electrolysis reaction generation voltage) was measured. There are three fuel cell temperatures: 40 ° C., 60 ° C., and 80 ° C., and the relative humidity is 100%. The current density when the cell voltage Vc is measured is 0.05, 0.1, 0.2, 0.3, 0.4 (A / cm ² ). FIG. 10 shows that the water electrolysis reaction generation voltage Vcw increases as the temperature of the fuel cell increases and increases as the current density decreases.

  Therefore, the water electrolysis reaction generation voltage Vcw used for evaluating the bypass voltage Vcb of the fuel cell 100 is, for example, the water electrolysis reaction generation voltage Vcw when the temperature of the fuel cell is high and the current flowing through the fuel cell is small. The safety side can be evaluated. In this example, the water electrolysis reaction generation voltage Vcw used for evaluating the bypass voltage Vcb was set to −0.6V. This is because, as shown in FIG. 10, when the cell voltage Vc is larger than −0.6 V, the water electrolysis reaction does not occur regardless of the temperature and current of the fuel cell.

In the fuel cell 100 of this example, the current I, the electrical resistivity ρ _s (Ω · m) of the separator, the thickness t _s (m) of the palator, The resistivity ρ _b (Ω · m) and the adhesive thickness t _b (m) are designed so as to satisfy the relationship of the following formula (8).

  In Expression (8), Vcc is a cell voltage Vc when the carbon oxidation reaction of Expression (5) occurs, and Vcw is a design water electrolysis reaction generation voltage. If the fuel cell 100 is designed so that the relationship of the above formula (8) is established, the occurrence of a carbon oxidation reaction can also be suppressed. As a method for examining the bypass voltage Vcb of the fuel cell 100, in addition to the method using the above formula (7), for example, from the both sides of the fuel cell 100 in a state where the MEA 210 is sufficiently dried to be regarded as an insulator. The bypass voltage Vcb can be examined by the cell voltage Vc when a current is passed. Alternatively, the bypass voltage Vcb may be examined by making a fuel cell 100 with an insulator sandwiched in place of the MEA 210 and passing a current from both sides of the fuel cell 100. If the cell voltage Vc is measured in a state where the MEA 210 is dried, the bypass voltage Vcb can be specified non-destructively with respect to the assembled fuel cell 100, so that the bypass voltage Vcb is water electrolysis as designed. Whether or not the reaction generation voltage Vcw becomes larger can be inspected at the time of shipment of the product. The flow of this inspection method will be described below.

  FIG. 11 is an explanatory diagram illustrating the flow of a fuel cell inspection method. The produced fuel cell 100 is prepared, and the MEA 210 is first dried (step S110). The MEA 210 is dried until the resistance value in the stacking direction of the fuel cell 100 becomes a predetermined value or more (step S120: NO). The predetermined value is a resistance value in the stacking direction of the fuel cell 100 when the MEA 210 is dried and becomes almost an insulator. As this predetermined value, for example, 100 (Ω) can be set.

  When the resistance value of the fuel cell 100 becomes equal to or higher than a predetermined value due to drying of the MEA (step S120: YES), an electric current is supplied to the fuel cell 100 in the direction from the anode to the cathode using an external power source (step S130). Then, it is determined whether or not the cell voltage Vc (<0) is larger than a value (here, −0.6 V) preset as the water electrolysis reaction generation voltage Vcw (step S140).

  When the cell voltage Vc (<0) is larger than the water electrolysis reaction generation voltage Vcw (step S140: YES), the bypass voltage Vcb of the fuel cell 100 is larger than the water electrolysis reaction generation voltage Vcw. Can be shipped. On the other hand, when the cell voltage Vc (<0) is equal to or lower than the water electrolysis reaction generation voltage Vcw (step S140: NO), the bypass voltage Vcb of the fuel cell 100 may be equal to or lower than the water electrolysis reaction generation voltage Vcw. For example, it can be discarded as a failure. Further, when the inspection fails, the manufacturing method of the fuel cell 100 can be reviewed. By performing such an inspection, the fuel cell 100 in which a current flows in the diode chip 500 before the water electrolysis reaction occurs when a negative voltage is generated can be shipped.

  According to the fuel cell 100 of the first embodiment described above, when a negative voltage is generated during start-up in a sub-freezing environment, a current flows through the diode chip 500, so that the cell voltage reaches a voltage at which a carbon oxidation reaction occurs. Since it does not decrease, a decrease in fuel cell performance due to the occurrence of a carbon oxidation reaction can be suppressed. Further, when a current flows through the diode chip 500, the internal ice is melted by heating the diode chip 500, so that the state in which the power generation efficiency is lowered can be quickly eliminated.

  2. Description of the Related Art Conventionally, a fuel cell including a control unit that detects a negative voltage and controls a current flowing through the fuel cell is known. However, if this fuel cell generates electricity with a large current in order to quickly increase the temperature when starting below freezing, the voltage drop rate when the negative voltage is generated is fast, and the control unit detects the negative voltage and executes control such as current limiting A carbon oxidation reaction or the like may occur before the treatment. In addition, in order to perform the above control, it is necessary to install a cell monitor for detecting the negative voltage of each fuel cell, and there is a problem that the cost increases. According to the fuel cell 100 of the present embodiment, since the bypass voltage Vcb is designed to be higher than the water electrolysis reaction generation voltage Vcw, the generation of the carbon oxidation reaction can be suppressed. Moreover, since it is not necessary to install a cell monitor for detecting the negative voltage of each fuel cell, an increase in cost can be suppressed.

  Conventionally, a fuel cell in which ice inside a gas flow path is melted by a heater is known. However, in the configuration in which the heater is heated after detecting a negative voltage at the start, the ice cannot be sufficiently melted, and the occurrence of the carbon oxidation reaction cannot be sufficiently avoided. Moreover, since electric power for generating heat from the heater is required, the supply efficiency of generated power may be reduced. According to the fuel cell 100 of the present embodiment, the diode chip 500 generates heat as the negative voltage is generated, so that the time required for heat generation can be shortened. In addition, since power is supplied to the diode chip 500 using a negative voltage, it is possible to suppress a decrease in power usage efficiency.

B. Second embodiment:
Although the diode chip 500 of the first embodiment has been described as being disposed at a position where the non-power generation region gas flow path GCn can be heated, the diode chip 500 of the second embodiment is other than the non-power generation region gas flow path GCn. It arrange | positions in the position which can heat this gas flow path.

  FIG. 12 is an explanatory diagram for explaining an installation position of the diode chip according to the second embodiment. FIG. 12 shows an anode side separator 310b and a diode chip 500 of the separator of the second embodiment. FIG. 12 corresponds to FIG. 2 of the first embodiment. In FIG. 12, the display of ribs in the gas flow path forming portion 317 is omitted. On the other hand, in FIG. 12, the position of the groove-shaped cooling water flow path forming portion formed on the main surface opposite to the main surface on which the gas flow path forming portion 317 is formed (hereinafter also referred to as “rear surface”) is indicated by a broken line BL. Is shown. The cooling water flow path forming unit forms a cooling water flow path through which cooling water flows when the anode side separator 310 and the cathode side separator 330 are stacked.

  The gas flow path forming section 317 includes two parts, a cooling water flow area portion 317Aw where the cooling water flow path is formed on the back surface and a cooling water non-flow flow area portion 317Ac where the cooling water flow path is not formed on the back surface. Has one part. Here, a gas flow path formed between the cooling water non-circulation region portion 317Ac and the MEA 210 or between the cooling water non-circulation region portion 317A and the seal member 220 is referred to as a cooling water non-circulation region gas flow path GCc. Also called. The cooling water non-circulation region gas flow path GCc of the present embodiment corresponds to “a gas flow path in which no refrigerant flow path is formed on the opposite surface” in the claims.

  The diode chip 500 is disposed at a position where the cooling water non-circulation region gas flow path GCc can be heated. The position of the diode chip 500 is a position close to the cooling water non-circulation region gas flow path GCc to such an extent that the cooling water non-circulation region gas flow path GCc can be heated by the heat generated when the negative voltage is generated. Either inside or outside the gas flow path may be used. As long as the cooling water non-circulation region gas flow path GCc can be heated, the position of the diode chip 500 may be the power generation region portion 317Ag (FIG. 2) or the non-power generation region portion 317An. The installation position of the diode chip 500 is set to a position where the cooling water non-circulation region gas flow path GCc can be heated. The cooling water non-circulation region gas flow path GCc is a place where heat from the cooling water is difficult to be transmitted. This is because ice is difficult to melt at the start.

  According to the fuel cell 100 of the second embodiment described above, the position of the diode chip 500 is the same as when the non-power generation region gas flow path GCn (FIG. 2) is disposed at a position other than the position where heating is possible. However, when a negative voltage is generated by starting under a freezing environment, a current flows through the diode chip 500, so that the cell voltage does not decrease to a voltage at which a carbon oxidation reaction occurs. A decrease in performance can be suppressed. Further, when a current flows through the diode chip 500, the internal ice is melted by heating the diode chip 500, so that the state in which the power generation efficiency is lowered can be quickly eliminated.

C. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

C-1. Modification 1:
The diode chip 500 may be installed at a position other than the above-described position as long as the portion where the ice is difficult to melt at the time of starting below the freezing point can be heated. In addition, the number, position, and range of the diode chips 500 described in the present embodiment are examples, and the number, position, and range of the diode chips 500 may be configured other than the embodiment.

  FIG. 13 is an explanatory diagram for explaining an installation position of the diode chip according to the first modification. It is explanatory drawing. As illustrated in FIG. 13A, the diode chip 500 may be disposed at a position facing the non-power generation region gas flow path GCn, the ribs such as the convex portion 318, and the like. As shown in FIG. 13B, a plurality of diode chips 500 may be arranged at positions facing the ribs such as the convex portions 318, respectively. When the installation position of the diode chip 500 is as described above, it is preferable to cover the surface of the diode chip 500 with gold plating or the like in order to suppress corrosion of the diode chip 500.

C-2. Modification 2:
Instead of the diode chip 500 shown in this embodiment, a diode may not be included, and a heating circuit configured by a resistor, a control unit capable of controlling the amount of current, or the like may be used. Even in this configuration, since the cell voltage does not decrease to the voltage at which the carbon oxidation reaction occurs due to the current flowing through the heat generating circuit, it is possible to suppress a decrease in the performance of the fuel cell due to the occurrence of the carbon oxidation reaction. Further, when a current flows through the heating element, the internal ice is melted by heating the heating element, so that the state in which the power generation efficiency is reduced can be quickly eliminated.

C-3. Modification 3:
In the present embodiment, the gas flow path is described as being formed between the gas flow path forming portion 317 formed in the anode separator 310 and the seal member integrated MEA 200. However, the gas flow path is formed on the anode side. It may be formed by a gas flow path forming member disposed between the separator 310 and the seal member integrated MEA 200. The gas flow path forming member can be made of, for example, a foam metal such as titanium, stainless steel, nickel, or copper, or an expanded metal formed of stainless steel.

C-4. Modification 4:
The fuel cell stack 10 is not limited to a configuration in which only the fuel cell 100 including the diode chip 500 is stacked, and may partially include a fuel cell that does not include the diode chip 500.

C-5. Modification 5:
In this embodiment, the polymer electrolyte fuel cell is used as the fuel cell, but various fuel cells such as a phosphoric acid fuel cell, a molten carbonate fuel cell, and a solid oxide fuel cell can be used.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell stack 100 ... Fuel cell 200 ... Sealing member integrated MEA
210 ... MEA
DESCRIPTION OF SYMBOLS 212 ... Electrolyte membrane 214 ... Anode side catalyst layer 215 ... Cathode side catalyst layer 220 ... Seal member 220b ... Insertion port 221 ... Through-hole for anode gas supply 222 ... Through-hole for anode exhaust gas discharge 223 ... Through-hole for cathode gas supply 224 ... Cathode exhaust gas discharge through hole 225 ... Cooling water supply through hole 226 ... Cooling water discharge through hole 310 ... Anode-side separator 311 ... Anode gas supply through hole 312 ... Anode exhaust gas discharge through hole 313 ... Cathode gas supply through hole Hole 314 ... Cathode exhaust gas discharge through hole 315 ... Cooling water supply through hole 316 ... Cooling water discharge through hole 317 ... Gas flow path forming portion 318 ... Projection 330 ... Cathode side separator 410 ... Anode side gas diffusion layer 430 ... Cathode side gas diffusion layer 500 ... Diode chip

Claims (7)

A fuel cell,
A power generation member configured to include a membrane electrode assembly;
A pair of separators respectively disposed on both sides of the power generation member;
A heating circuit disposed between the pair of separators, having both ends electrically connected to the pair of separators, and generating heat by a current flowing when a negative voltage is generated between the pair of separators. ,
The heat generating circuit is a fuel cell that is disposed at a position where a gas flow path formed between the power generation member and the separator can be heated. The fuel cell according to claim 1, wherein
The pair of separators includes an anode separator that contacts the anode side of the membrane electrode assembly, and a cathode separator that contacts the cathode side of the membrane electrode assembly,
The heat generation circuit includes a diode arranged so that a current flows from the anode side separator to the cathode side separator. The fuel cell according to claim 1 or 2,
The power generation member includes a support member formed on an outer peripheral portion of the membrane electrode assembly,
The heat generating circuit is a fuel cell, wherein the heat generating circuit is disposed at a position where the gas flow path formed between the separator and the support member can be heated. The fuel cell according to claim 3, wherein
The fuel cell, wherein the heat generating circuit is disposed on each side of a gas flow path formed between the separator and the support member. The fuel cell according to claim 1 or 2,
The separator includes a refrigerant flow path forming portion for forming a refrigerant flow path on a surface opposite to a surface in contact with the power generation member,
The heat generating circuit is a fuel cell, wherein the heat generating circuit is disposed at a position capable of heating a gas channel in which the refrigerant channel is not formed on the opposite surface of the gas channel. The fuel cell according to any one of claims 1 to 5,
The fuel cell, wherein a negative voltage between the pair of separators when a current flows through the heat generating circuit is larger than a voltage when a water electrolysis reaction occurs in an anode of the membrane electrode assembly. A method for inspecting a fuel cell,
A fuel cell comprising a membrane electrode assembly, a pair of separators disposed on both sides of the membrane electrode assembly, and a heating circuit that generates heat due to a current flowing when a negative voltage is generated between the pair of separators. A preparation process;
Drying the membrane electrode assembly until a resistance value between the pair of separators is a predetermined value or more;
The state of the fuel cell is determined depending on whether or not a negative voltage between the pair of separators when a current is passed between the pair of separators of the fuel cell after drying the membrane electrode assembly is greater than or equal to a predetermined value. And a step of determining.

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