JP2001167780A - Cell for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cell for a fuel cell that can precisely detect reduction of hydrogen concentration damaging the electrodes of the fuel cell, and can monitor the hydrogen concentration with a small size and simple device for a safe operation of the fuel cell. SOLUTION: The cell consists of a high polymer film, and an electrode carbon metal and a separator provided at both sides of the high polymer film, respectively. A reaction gas path is formed to a gas outlet from a gas inlet in the cell, and a hydrogen concentration detector is provided just in front of the gas outlet of the reaction gas path.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel cell having a hydrogen concentration detector, and more particularly to a fuel cell capable of measuring the hydrogen concentration in each cell of a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art In a polymer electrolyte fuel cell body, a large number of cells are stacked to form a stack, and each cell is supplied with a reaction gas. Each cell usually consists of a hydrogen-side separator, a polymer membrane, and an oxygen-side separator, and it is necessary to distribute hydrogen gas and oxygen gas evenly in each cell. Ability (performance) is determined. As described above, there are two gas systems, one is a system in which hydrogen gas is supplied and discharged, and the other is a system in which oxygen gas is supplied and discharged. A polymer film is provided at the center of these separators.

FIG. 3 is a diagram showing a flow path of a reaction gas on a cell / separator surface, and FIG. 4 is a diagram schematically showing a change in hydrogen concentration from an inlet side to an outlet side in a cell. . Normally, when the reaction gas flows from the gas inlet side to the gas outlet side on the surface of the separator, the reaction gas enters from the supply manifold 9. Here, if the gas does not flow uniformly and a sufficient flow rate cannot be obtained, the absolute flow rate of hydrogen is insufficient. In FIG. 4, the hydrogen concentration from the gas inlet side to the gas outlet side decreases as shown in FIG. On the other hand, in the case of an abnormality, the way of decreasing the hydrogen concentration becomes sharp, and the situation as shown in FIG. Then, on the hydrogen side of the separator, there is a lower limit of the supply of the hydrogen gas concentration for the reaction gas. When the fuel cell is generating power and current is flowing, if hydrogen is insufficient, instead of consuming hydrogen, water (H ₂ O) is electrolyzed to generate oxygen (O ₂ ). With the oxygen generated,
The carbon material forming the cell itself reacts (combines) with it and burns, possibly resulting in carbon dioxide or carbon monoxide. If the use of the fuel cell is continued below the lower limit of the hydrogen concentration, which is a hydrogen deficient state, the cell may be damaged and may become unusable.

On the other hand, measurement of hydrogen concentration in a cell is usually
Since the measuring instrument has a fixed volume, there is a problem that the apparatus itself becomes large or extremely complicated. When these devices are incorporated, the cost tends to be high. On the other hand, when the hydrogen concentration measurement is not performed at all as described above, since power is generated even when the hydrogen concentration is reduced, carbon, which is a main material of the electrode base material, is consumed instead of hydrogen, Destruction of the electrode substrate itself may occur. Further, this hydrogen concentration detection is desirably measured for each cell, but it is difficult to install a normal measuring instrument in view of downsizing and weight saving of the measuring instrument.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present inventors have been able to accurately detect a decrease in hydrogen concentration that causes damage to an electrode in a fuel cell, and to provide a small and simplified device. The intense study was conducted to develop a cell that enables safe fuel cell operation by monitoring the hydrogen concentration. As a result, the present inventors have found that such a problem can be solved by providing a hydrogen concentration monitor immediately before the hydrogen gas outlet so that the hydrogen concentration in the reaction gas groove of the cell can be constantly monitored. The present invention has been completed from such a viewpoint.

[0006]

That is, the present invention relates to a cell comprising a polymer film, an electrode carbon member and a separator on both sides of the polymer film, and a gas outlet from a gas inlet side to a gas outlet in the cell. The present invention provides a fuel cell, characterized in that a reaction gas flow path is provided toward the side, and a hydrogen concentration detector is provided immediately before a gas outlet of the reaction gas flow path. As the hydrogen concentration detection unit, an insulator (B) provided on a part of the electrode carbon member on both sides of the polymer film, and provided on a part of the separator on both sides by being laminated on the insulator (B). It is preferable that the insulator (A) be provided and lead wires connecting the separator portions insulated by the insulator on both sides of the polymer film. The width of the insulator in the surface direction of the cell is 100 μm or more and 1 μm or more.
It is preferably not more than 000 μm. The electrode carbon member is desirably carbon paper or carbon cloth. The present invention also provides a fuel cell stack characterized by stacking any one of the fuel cell cells described above, and usually stacks 10 to 500 cells.

In the present invention, in order to prevent an electrode destruction accident due to insufficient hydrogen concentration, a hydrogen concentration detector is provided immediately before the gas outlet so that the hydrogen concentration in the reaction gas groove of the cell can be constantly monitored. Here, examples of the hydrogen concentration monitor include a normal hydrogen concentration detection device and a semiconductor detector. However, in the present invention, the hydrogen concentration monitor is compact from the viewpoint of weight reduction and simplification of the device and further cost reduction. As a simple auxiliary device, a hydrogen concentration detector is provided in the cell. In the present invention, the actual hydrogen concentration in the gas flow path in each cell can be ascertained by monitoring the amount of power generation.

In a preferred embodiment of the present invention, the periphery of a part of the cell is insulated (isolated), and electricity is supplied to the insulating part for monitoring. The insulating part is provided on the outlet side of the gas flow path in the separator, and is located immediately before the discharge manifold. It is preferable that each cell of the stacked stack is provided with a hydrogen concentration detecting unit (monitor). If necessary, for example, from the viewpoint of cost, a mode in which a fuel cell stack is configured using the cell of the present invention in combination with a cell having no hydrogen concentration detection unit is also possible. An apparatus for measuring the hydrogen concentration of the discharged gas as a whole system may be separately provided.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The fuel cell of the present invention is made of PE
An FC hydrogen concentration monitor is provided at the last part on the outlet side in the gas flow path of the cell. In the fuel cell stack, a monitor (concentration detection unit) is required for each cell, and it is not possible to determine whether or not an abnormality has occurred in each cell by measuring the flow from a plurality of stacked cells as a whole. . That is, after mixing with the gas flowing from the other cells, a decrease in the hydrogen concentration in each cell cannot be detected. For example, when there is a cell in which the reaction gas flow path is clogged with dust and the flow path is blocked, an abnormality can be detected only by measuring each cell. On the other hand, if a normal hydrogen detector is provided for each cell, the structure becomes complicated and expensive.

On the other hand, if the cell of the present invention is used, it is not necessary to separately provide a special hydrogen detector for measuring the hydrogen concentration, and the hydrogen concentration can be measured using the function of the battery as it is. In the present invention, hydrogen concentration can be detected by providing an insulator and connecting a lead wire to the insulated portion. Hereinafter, specific embodiments of the fuel cell according to the present invention will be described in detail with reference to the accompanying drawings.

Embodiment FIG. 1 shows an example of a fuel cell according to the present invention. In this embodiment, as shown in FIG. 1, a part of the electrode immediately before the outlet is made electrically independent, and the hydrogen concentration is calculated by measuring the current flowing through the insulating part. Do not fall below the lower limit. Here, carbon paper or the like serving as an electrode is adhered to both surfaces of the polymer membrane 1 (ion exchange membrane) by a compression press or the like. It is preferable to use carbon paper, carbon cloth, or the like as the electrode carbon member. Separators having reaction gas grooves 11 are provided on both sides thereof, and these constitute a cell integrally. The stack of these cells is a stack. If the electromotive force generated in one cell is, for example, 0.7 V, a stack of about 70 V is obtained by stacking 100 cells. A platinum catalyst is applied to both sides of the polymer film 1, and an electrode carbon member is provided outside the catalyst.

FIG. 2 is a sectional view of a hydrogen concentration detecting section in which a lead wire is provided at a portion (insulating section) insulated by an insulator. In the cell of FIG. 2, carbon paper 6 is provided below the hydrogen-side separator 2 on the upper surface, carbon paper 6 is provided on the oxygen-side separator 3 on the lower surface, and the polymer film 1 is provided at the center thereof. In the present embodiment, as shown in FIG. 2, the separator of the hydrogen concentration detecting section is electrically insulated by the insulator A. Similarly, in carbon paper 6,
It is electrically insulated by the insulator B. By measuring the current with respect to the lead wire connecting the insulating portion from the outside, the hydrogen concentration in the insulating portion can be measured. That is, by providing the insulating portion on the surface having the reaction gas flow path as the power generation portion, it is possible to measure the hydrogen concentration immediately before the gas outlet while isolating only this portion. The reason immediately before the gas outlet is that the portion is a portion where the hydrogen concentration is reduced most by the reaction in the cell. is necessary.

Here, the separator and the carbon paper can be relatively easily insulated, but it is difficult to insulate the polymer film 1 in the manufacturing process or the gas sealing process, and the cost is high. Therefore, it is usually used without insulation. For this reason, it is conceivable that protons from surrounding non-insulated portions may sneak in at the time of measuring the hydrogen concentration in the insulated portion, making it impossible to accurately measure and control the hydrogen concentration. Therefore, it is necessary to make the width W of the insulator wide so as not to be affected by the wraparound of the protons. That is, a flow of electricity occurs in the polymer membrane 1, and the movement of protons occurs. At this time, there are protons generated outside the insulating part and protons generated inside the insulating part. Protons generated outside the insulating part may flow into the inside (r _{2 in} FIG. ₂ ). And such r ₂ routes, since an error becomes large concentration measurement becomes impossible to separate the r ₁ route, it is necessary to ensure insulation A, the distance of the width W of the B well. On the other hand, if the width W is too large, the original role of the cell may be impaired, which is not preferable.

The width W of the insulator is calculated as follows from the ionic conductivity (electrical resistance) in the polymer film in order to insulate it from the surrounding non-insulating portions. That is, the sheet resistance [Ω · cm ² ] of the polymer film at a temperature of 80 ° C. can be expressed by the following equation. r _N = {1 / σ (80 ° C.)} × t _N [cm] In the formula, σ indicates ionic conductivity, and t _N indicates a distance traveled by protons. Then, assuming that the width of an insulator for separating protons between the hydrogen detection unit (monitor unit) and the power generation unit is W,
The ratio between the resistances r ₂ and r ₁ when protons flow around from the surroundings can be expressed by the following equation.

[0015]

(Equation 1) Here, assuming that an error of up to 10% is accepted, the solution of equation (1) is 0.1 or less,

(Equation 2) Assuming that an error of 1% is accepted, the solution of equation (1) is 0.01 or less,

(Equation 3) Becomes In the formula, r ₁ indicates the sheet resistance when the proton goes straight through the polymer membrane, and r ₂ indicates the minimum value of the sheet resistance of the proton wrapping around from outside the insulating portion.

Although the thickness of the polymer film 1 is not particularly limited, it is usually in the range of 10 to 100 μm, preferably 30 to 80 μm. It is. When this is applied to the above equation in which an error of up to 10% is recognized, about 100 μm is obtained.
It is understood that it is preferable to have an insulator width W of m or more.

The hydrogen concentration monitored in each cell having such a hydrogen concentration detecting section is determined by a determination processor in relation to the current density of the fuel cell stack, and is determined to be a normal concentration or an excessive state, or a hydrogen deficient state. Is determined for each cell. On the basis of this determination result, in the fuel cell main body, operation control such as an emergency stop or a hydrogen supply line flow rate adjustment is performed by an emergency stop means or an electric load removing means. As described above, when the fuel cell body stack is manufactured using the cells of the present invention, the hydrogen concentration in each cell of the operating fuel cell can be monitored, so that the safe operation of the fuel cell can be performed. it can.
Hereinafter, examples of the fuel cell operation control using the cells of the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[0018]

Embodiment 1 FIG. 6 is a block diagram showing an operation control method according to this embodiment, and FIG. 7 is a flowchart showing signals in a determination processor in this embodiment. Here, the voltage value of the hydrogen detector in each cell (Xn) described above is sent to the determination processor A together with the current density of the fuel cell stack. In the determination processor A, based on the standard IV curve as shown in FIG. 5, it is determined whether each cell is above (a) or below (b) the curve. Normally, if the hydrogen concentration is above (a) or above the curve (including the error range), it is determined that the hydrogen concentration in the cell is normal or in an excessive state. On the other hand, standard IV
If it exists below the curve (b), it is determined that the hydrogen concentration in the cell is in an insufficient state. In a case where such a shortage is determined for at least one cell, in this embodiment, an electrical load removal signal or an emergency stop signal for the entire fuel cell is issued in order to avoid danger in the cell. . As a result, the fuel cell main body can be controlled to enable safe operation.

Embodiment 2 FIG. 8 is a block diagram showing an operation control method according to this embodiment, and FIG. 9 is a flowchart showing signals in a determination processor in this embodiment. Here, the same signal as in the first embodiment is sent to the determination processor B. In the decision processor B, based on the standard IV curve as shown in FIG.
Is determined. Below the standard IV curve (b)
If not, it is checked whether the hydrogen flow rate of the reformer provided in front of the fuel cell body is normal, and if it is normal, the operation is continued in that state. Since there is, a hydrogen production reduction signal is sent to the reformer. On the other hand, if the cell is below (b) the standard IV curve, it is checked whether or not all the cells are below (b) the curve. If at least one cell is down (b) but not all cells are in the down (b) state, some of the cells may be in a hydrogen deficient state and an electrical unload signal, an emergency stop signal, or a modified A signal to open the fuel gas supply line bypass from the plasterer, and the like. On the other hand, when all the cells are in the state (b) below the curve, the entire fuel cell is in a hydrogen-deficient state,
First, it is confirmed whether or not the hydrogen flow rate of the former reformer is normal. If it is normal, an electrical load removal signal or an emergency stop signal is issued. If not,
It emits a signal to increase hydrogen production. By these signal controls, the condition of insufficient hydrogen concentration in each cell in the fuel cell body can be resolved, and the fuel cell system can be operated safely and efficiently.

[0020]

According to the present invention, it is possible to monitor the reduction of the concentration of hydrogen which causes electrode damage in a fuel cell by using an extremely small and simplified device.
Further, since the hydrogen concentration in each cell of the fuel cell during operation can be monitored, safe operation of the fuel cell can be realized.

[Brief description of the drawings]

FIG. 1 is a layout diagram showing an outline of a structure in which a cell of the present invention is disassembled.

FIG. 2 is a sectional view of a hydrogen concentration detecting portion according to the present embodiment.

FIG. 3 is a diagram showing gas flow paths flowing inside the cells / separators when they are stacked.

FIG. 4 is a diagram schematically showing a change in hydrogen concentration from an inlet side to an outlet side in a cell.

FIG. 5 shows a standard I for hydrogen concentration in each cell.
It is a figure which shows a -V curve.

FIG. 6 is a block diagram illustrating an operation control method according to the first embodiment.

FIG. 7 is a flowchart illustrating signals in a determination processor according to the first embodiment.

FIG. 8 is a block diagram showing an operation control method according to the second embodiment.

FIG. 9 is a flowchart illustrating signals in a determination processor according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polymer film 2 Hydrogen side separator 3 Oxygen side separator 4 Insulator A 5 Insulator B 6 Electrode carbon paper 7 Hydrogen flow path 8 Oxygen flow path 9 Supply manifold 10 Discharge manifold 11 Gas groove

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takuya Moriga 4-22, Kannonshinmachi, Nishi-ku, Hiroshima-shi, Hiroshima F-term in Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd. 5H026 AA06 CC03 CC08 CX03 CX04 HH03 5H027 AA06 BA01 KK31 KK51 KK56

Claims (5)

[Claims] 1. A cell comprising a polymer film, an electrode carbon member and a separator on both sides of the polymer film,
A fuel cell, wherein a reaction gas flow path is provided in the cell from the gas inlet side to the gas outlet side, and a hydrogen concentration detection unit is provided immediately before the gas outlet of the reaction gas flow path. 2. Insulators wherein said hydrogen concentration detectors are respectively provided on a part of an electrode carbon member on both sides of a polymer film.
(B), the insulator (A) which is laminated on the insulator (B) and provided on a part of the separator on both sides, and the separator portions insulated by the insulator on both sides of the polymer film are connected. The fuel cell according to claim 1, further comprising a lead wire. 3. The fuel cell according to claim 2, wherein a width of the insulator in a plane direction of the cell is 100 μm or more. 4. The fuel cell according to claim 1, wherein the electrode carbon member is carbon paper or carbon cloth. 5. A fuel cell stack comprising the fuel cell according to claim 1 stacked thereon.