JPH08138696A - Fuel cell - Google Patents

Abstract

PURPOSE: To achieve stabilization of large output by promoting drainage in a fuel cell. CONSTITUTION: An oxidized gas passing groove 18 formed on a collector 17 on a cathode 16 side is so formed that its depth may be gradually increased toward a gas discharging port 18b from a gas introducing port 18a. Accordingly, output can be prevented from being decreased caused by blockage of the gas passage caused by the accumulation of formed water since the formed water can be prevented from being accumulated in the oxidized gas passing groove 18 by discharging the formed water to be generated in the oxidized gas passing groove 18 by gravity. Since the contact area of the collector with the electrode is not reduced, the contact resistance between both sides can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell, and more particularly to a gas flow channel for supplying a reaction gas to electrodes of a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art Among various types of fuel cells, a polymer electrolyte fuel cell is a fuel cell that can be started at room temperature with high output, and that provides safe and stable output. Attention has been paid. The electrolyte of this polymer electrolyte fuel cell uses a cation exchange resin membrane as a cation conductive membrane, and this conductive membrane contains protons (hydrogen ions) in the molecule.
It has an exchange group, and when it is saturated with water, it exhibits a specific resistance of 20 Ω · cm or less at room temperature and functions as a proton conductive electrolyte.

The saturated water content of the polymer electrolyte membrane reversibly changes depending on the temperature, but during operation of the fuel cell, in order to prevent evaporation from the polymer electrolyte membrane, the saturated water content in the fuel gas and the oxidizing gas is reduced. A saturated state is always maintained by the humidified water added in the form of water vapor and the water generated by the electrochemical reaction on the cathode side. However, the amount of water generated on the cathode side increases, or the fuel gas and the oxidizing gas are consumed and the water vapor in the residual gas becomes supersaturated and the water condenses.
If the supply of water becomes excessive, the polymer electrolyte membrane will be soaked in water, resulting in a so-called flooding state, the gas contact area will decrease, and further, the supply of oxygen gas to the cathode will be obstructed, and the generated voltage will decrease. There was a problem.

Therefore, conventionally, various measures have been taken to prevent retention of generated water, condensed water, etc. in the gas flow grooves. For example, FIGS. 5 to 7 show a plan view and a sectional view of the gas separator plate 1 on the cathode side of the conventional polymer electrolyte fuel cell disclosed in Japanese Patent Laid-Open No. 5-251097, which has a rectangular shape. A plurality of oxidizing gas flow grooves 2 are formed on one surface of the formed gas separator plate 1 at a constant depth and in parallel with each other. Oxidizing gas such as air supplied from the outside is supplied from the introducing manifold 3 to the gas separator plate 1, and the separator plate 1
It is distributed and supplied from the internal manifold 4 to the plural oxidizing gas flow grooves 2. Further, the excess oxidizing gas is collected by the internal manifold 5 on the opposite side and discharged from the discharge manifold 6 to the outside of the apparatus.

Each of the oxidizing gas flow grooves 2 formed in the gas separator plate 1 has a groove width on the downstream side in order to prevent the generated water generated in each groove from being accumulated and blocked. Is widely formed. That is, a plurality of oxidizing gas flow grooves 2 are formed on one surface of the gas separator plate 1 so as to connect the introducing manifold 3 and the discharging manifold 6, which are formed along two opposite sides, respectively. These oxidizing gas flow grooves 2 are adjacent to each other in the section from the almost center thereof to the discharge manifold 6 on the downstream side, where every other partition wall portion separating the grooves is removed. By connecting the grooves 2 and 2 at the side portions thereof, the wide groove 2a is formed by expanding the width of the partition wall (see FIGS. 6 and 7). In this way, by expanding the groove width on the downstream side of each oxidizing gas passage groove 2 to form the wide groove 2a, generated water and the like generated on the cathode side stays in the oxidizing gas passage groove 2 and is blocked. To prevent it.

[0006]

In the above-mentioned conventional polymer electrolyte fuel cell, the groove width is expanded by forming the wide groove 2a on the downstream side (outlet side) of the oxidizing gas flow groove 2. Therefore, when the gas separator plate 1 is vertically arranged and each of the oxidizing gas flow grooves 2 is formed in the vertical direction, the generated water or the like naturally falls due to gravity and the discharge manifold 6 It is possible to prevent the stagnation in the oxidant gas flow groove 2 by flowing inward. However, when the gas separator plate 1 is horizontally arranged, it is not possible to expect natural flow of the generated water in each of the oxidizing gas flow grooves 2 toward the discharge manifold 6, and therefore the groove width on the downstream side. Although the generated water and the like are less likely to stay due to the wider width, the generated water and the like in the oxidizing gas flow groove 2 could not be actively drained.

Further, the partition wall defining the oxidizing gas flow groove 2 also serves as a current collecting portion. However, if a part of the partition wall is removed as described above, the current collecting area decreases and the resistance increases. There is inconvenience.

The present invention has been made in view of the above circumstances, and the generated water or the like in each oxidizing gas flow groove is positively discharged to reduce the groove of the generated water or the like without reducing the current collecting area. An object of the present invention is to provide a fuel cell in which the gas passage is prevented from being blocked by internal retention and accumulated water.

[0009]

As a means for solving the above problems, the present invention comprises an anode and a cathode with an electrolyte membrane sandwiched therebetween, and a collector which also serves as a gas separator on the anode side and the cathode side. A current collector is provided, and a fuel gas flow groove through which a fuel gas flows is provided on a surface of the current collector facing the anode, and an oxidizing gas flow groove through which an oxidizing gas flows is provided on a surface of the current collector facing the cathode. In each of the fuel cells that are formed to obtain an electromotive force by reacting hydrogen ions in the fuel gas with oxygen in the oxidizing gas through the electrolyte membrane, the oxidizing gas flow groove has a gas from its gas inlet port. It is characterized in that the depth is gradually increased toward the discharge port.

Further, the oxidizing gas flow groove is formed in the electrode reaction region in a shallow depth and a substantially constant depth in the electrode reaction region instead of the above-mentioned structure, and in the portion deviated from the electrode reaction region. The depth can be gradually increased toward the gas inlet or the gas outlet.

[0011]

As described above, the oxidizing gas flow groove formed on the surface of the current collector, which also functions as the gas separator disposed on the cathode side of the electrolyte membrane, facing the cathode, is provided with a gas inlet port and a gas outlet port. Since it is formed so that the depth thereof gradually becomes deeper, the cross-sectional area of the flow path due to the oxidizing gas flow groove becomes wider on the downstream side, and therefore the generated water generated in the oxidizing gas flow groove and The flow resistance to excess water such as condensed water is reduced on the discharge side, and as a result, the excess water is positively discharged without staying in the oxidizing gas flow channel. In particular,
When installed horizontally, the oxidizing gas flow groove is arranged so that the discharge side gradually lowers and the surplus water is allowed to flow down naturally, so that the generation water etc. is prevented from accumulating in the oxidizing gas flow groove. A stable generated voltage is maintained. Further, since the width of the oxidizing gas flow groove is not widened, the current collecting area of the current collector is not reduced, and thus the contact resistance is prevented from increasing.

Further, the oxidizing gas flow groove is formed so as to have a shallow depth and a substantially constant depth in the electrode reaction region facing the cathode, and the gas introduction is performed at a portion outside the electrode reaction region. If the depth is gradually increased toward the mouth or the gas outlet, the oxidizing gas flow groove is formed shallow in the electrode reaction region, so the flow passage cross-sectional area is Gradually becomes narrower, and as a result, it functions as an ejector to accelerate the gas flow rate, thereby increasing the oxidizing gas density to promote the reaction and prevent the backflow of the generated water toward the gas inlet. In addition, in the part deviated from the electrode reaction region to the downstream side, since the bottom part is inclined so as to spread toward the discharge port side, excess water such as generated water and condensed water generated in this oxidizing gas flow groove is The water is positively discharged to the discharge port side to prevent the generated water and the like from accumulating in the reaction region, and a stable generated voltage is maintained. Also in this case, since the width of the oxidizing gas flow groove is not widened, the current collecting area of the current collector is not reduced, and thus the contact resistance is prevented from increasing.

[0013]

EXAMPLE An example in which the present invention is applied to a polymer electrolyte fuel cell will be described below with reference to FIGS.

FIG. 1 shows a first embodiment of a polymer electrolyte fuel cell according to the present invention, in which a catalyst reaction layer 12 is provided on the upper surface of a polymer electrolyte membrane 11 arranged substantially horizontally. An anode (fuel electrode) 13 is formed as a result, and a carbon current collector 14 formed on a gas impermeable plate and serving also as a gas separator is provided on the upper side of the anode 13 with its lower surface in close contact. Then, on the lower surface of the carbon current collector 14 facing the anode 13 side, a fuel gas flow groove 14a for flowing hydrogen gas (H ₂ ) as a fuel gas,
The depth is 1 mm and the width is 1 mm, and a plurality of them are formed at 1 mm intervals.

A cathode (oxygen electrode) 16 is formed on the lower surface of the polymer electrolyte membrane 11 via a catalytic reaction layer 15.
Is formed. Below the cathode 16, a plate-shaped carbon current collector 17 also serving as a gas separator is formed.
The upper surface is closely attached. Then, on the upper surface of the carbon current collector 17 facing the cathode side, a plurality of oxidizing gas flow grooves 18 for circulating air serving as an oxidizing gas are provided in a direction orthogonal to the formation direction of the fuel gas flow grooves 14a. The gas inlet 18a is formed at the left end in FIG. 1 and the gas outlet 18b is opened at the other end.

The plurality of oxidizing gas flow grooves 18 are provided.
Are formed with a width of 1 mm and at intervals of 1 mm, and the depth is 0.5 mm at the end on the gas inlet 18a side and the depth on the gas outlet 18b side when the electrode area is within 10 cm square. The bottom surface 18c is formed so as to be inclined so that the depth of the end portion becomes 2.5 mm and the gas discharge port 18b side becomes lower. The oxidizing gas flow groove 18 may be formed with an inclination angle of 1 degree or more.

Further, as the polymer electrolyte membrane 11,
A fluorine-based cation exchange membrane having a film thickness of 130 μm is used, and a catalytic reaction layer (for example, Pt 20% supported carbon 0.
Carrying 4 mg / cm ² + cation exchange resin, carbon ratio 50
%) And gas diffusion layer (water-repellent treated carbon containing 50% Teflon) are applied to a carbon cloth (thickness 0.3 mm) as an electrode material by hot pressing (120 ° C. × 100 kg /
cm ² ) is used.

Further, in FIG. 1, the carbon collector 14 on the upper side and the carbon collector 17 on the lower side are the same member,
Although not shown, a plurality of oxidizing gas flow grooves are formed on the upper surface of the upper carbon current collector 14 at a predetermined inclination in a direction orthogonal to the fuel gas flow groove 14a. Further, a plurality of fuel gas flow grooves are formed on the lower surface of the lower carbon current collector 17 in a direction orthogonal to the oxidizing gas flow grooves 18.

In the polymer electrolyte fuel cell constructed as described above, a plurality of single cells having the same structure are stacked in the vertical direction, and the carbon current collectors 14 on the anode 13 side which are vertically adjacent to each other, The carbon current collector 17 on the cathode 16 side is brought into contact with and electrically connected in series to form a stack, and further, a plurality of stacks are electrically connected in series, parallel or series-parallel to achieve high output. Used in the state. In FIG. 1, reference numeral 19
Is a tension frame that sandwiches the four sides of the polymer electrolyte membrane 11, and reference numeral 20 is a sealing agent that hermetically seals the polymer electrolyte fuel cell (single cell).

Next, the operation of the unit cell of this embodiment configured as described above will be explained. Hydrogen gas (H ₂ ) is introduced into the fuel gas flow groove 14a on the anode 13 side of the polymer electrolyte fuel cell. Supplied. Further, the polymer electrolyte membrane 11 is hydrated in a saturated state so as to function as a proton conductive electrolyte having a specific resistance of 20 Ω · cm or less at room temperature, in the hydrogen gas supplied through the fuel gas flow groove 14a, and Water vapor is mixed into the air supplied through the oxidizing gas flow groove 18 to prevent evaporation of water from the polymer electrolyte membrane 11.

When air containing oxygen (O ₂ ) is supplied to the oxidizing gas flow groove 18 on the cathode 16 side, H ₂ = 2H ⁺ + 2e in the catalytic reaction layer 12 on the anode 13 side.
Reaction occurs, and the catalytic reaction layer 15 on the cathode 16 side
Then, the reaction of 1 / 2O ₂ + 2H ⁺ + 2e = H ₂ O occurs.

That is, in the anode 13, the hydrogen gas (H ₂ ) flowing through the fuel gas flow groove 14a produces protons (2H ⁺ ) and electrons (2e). The generated protons move in the polymer electrolyte membrane 11 which is an ion exchange membrane toward the cathode 16, and the electrons pass from the carbon current collector 14 on the anode side through an external circuit (not shown) to the cathode 16 side. Move to the carbon current collector 17.

In the cathode 12, oxygen in the air flowing through the oxidizing gas flow groove 18, the protons moving from the anode 12 in the polymer electrolyte membrane 11 and the electrons moving through the external circuit. Reacts with water (H ₂
O) is generated.

The hydrogen gas supplied to the fuel gas flow groove 14a and the air supplied to the oxidizing gas flow groove 18 are consumed, so that the proportion of water vapor mixed increases. A supersaturated state occurs, and dew condensation occurs on the outlet side of the fuel gas flow groove 14a and the oxidizing gas flow groove 18 (in the vicinity of the gas discharge port 18b in the oxidizing gas flow groove 18) to generate condensed water.

As a result, in the oxidizing gas flow groove 18, a large amount of water is produced by the water produced by the oxidation reaction and the condensed water of the steam for humidification, but in the present embodiment, the oxidizing gas flow is generated. The flow groove 18 is shallow on the gas introduction port 18a side,
Since the gas discharge port 18b side is deeply formed, the generated water generated on the cathode 16 side smoothly flows down without retention, and even if condensed water generated near the gas discharge port 18b is added, this gas discharge Since the groove is formed deep in the vicinity of the outlet 18b and the cross-sectional area of the flow passage is enlarged, a space for discharging excess air can be secured in the upper part of the groove. In addition, each current collector 1 is used to expand the flow passage cross-sectional area.
Since the contact area between the electrodes 4 and 17 and the electrode is not reduced, the contact resistance between them can be reduced.

Next, when an instrument was connected between both carbon current collectors 14 and 17 of this polymer electrolyte fuel cell to evaluate the cell performance, the results are shown in FIGS. 3 and 4. From the line III showing the current-voltage characteristic of the conventional polymer electrolyte fuel cell, the line I showing the current-voltage characteristic of the first embodiment always shows a high value, so that the improvement of the performance can be confirmed. It was confirmed that the voltage stability was improved when the product was kept in a high current density region where a large amount of produced water was generated. Further, it was confirmed that the improvement of the dischargeability of the generated water and the like prevents the generation of the generated water and the like from blocking the oxidant gas flow groove 18. Therefore, it is possible to prevent the output reduction due to the gas diffusion inhibition resulting from this. It is also possible to prevent hydrogen gas from entering the cathode 16 side as the output voltage decreases due to gas diffusion inhibition. In FIG. 3, the vertical axis represents cell voltage (V),
A plot of current density (A / cm ² ) on the abscissa, and a plot of cell voltage (V) on the ordinate and holding time (Hr) on the abscissa in FIG. 4. Is.

FIG. 2 shows a second embodiment of the polymer electrolyte fuel cell according to the present invention. The same components as those of the first embodiment are designated by the same reference numerals and their detailed description will be omitted. Description will be omitted, and description will be given below with reference to the drawings.

In this polymer electrolyte fuel cell, an anode 13 is formed on the upper surface of a polymer electrolyte membrane 11 arranged substantially horizontally with a catalytic reaction layer 12 interposed therebetween.
A carbon current collector 24 is provided on the upper side of 3, and a fuel gas flow groove 24a is provided on the lower surface of the carbon current collector 24.
A plurality of hydrogen gas (H ₂ ) is formed at a depth of 1 mm and a width of 1 mm at intervals of 1 mm, and hydrogen gas (H ₂ ) circulates in the fuel gas flow groove 24a so as to come into contact with the anode 13.

A cathode 16 is formed on the lower surface of the polymer electrolyte membrane 11 via a catalytic reaction layer 15.
A carbon current collector 27 is provided on the lower side of the cathode 16, and a plurality of oxidizing gas flow grooves 28 are formed on the upper surface of the carbon current collector 27 in a direction orthogonal to the fuel gas flow grooves 24a. This is formed and the gas inlet 2 is at the left end in FIG.
8a, and the gas discharge port 28b is opened at the other end.

Then, the plurality of oxidizing gas flow grooves 28 are provided.
Are formed with a width of 1 mm at intervals of 1 mm, and the depth thereof is set to a high gas flow velocity (preferably 0.5 m / sec or more) in the electrode reaction region facing the central cathode 16, and the electrode (cathode is In order to suppress the decrease in oxygen partial pressure in the portion facing 16), the groove in the electrode reaction region is formed shallow to ensure high performance. In this embodiment, when the electrode area is 10 cm square, the groove depth is
0.5 mm in the electrode reaction area (flow rate approx. 1 m / se when theoretical flow rate x 2 at a current density of 0.5 A / cm ²⁾
As c), from the electrode end of the cathode 16 to the gas inlet 2
An inclined bottom surface 28d having an inclination angle of 3 degrees is formed up to 8a, and similarly between the electrode end portion and the gas discharge port 28b,
An inclined bottom surface 28e having an inclination angle of 3 degrees is formed.

In the polymer electrolyte fuel cell of this embodiment having the above-described structure, hydrogen gas is supplied to the fuel gas flow groove 24a and the oxidizing gas flow groove 28 is formed, as in the first embodiment. It is operated by supplying air to each. And
On the cathode 16 side, the oxidizing gas flow groove 28 in the electrode reaction region is formed shallower than the gas introduction port 28a side to function as an ejector, and the gas flow velocity is accelerated to prevent a decrease in oxygen partial pressure. The reaction efficiency is improved.
In addition, the water generated in the oxidizing gas flow groove 28 is prevented from flowing back toward the gas inlet port 28a by the flow of the supplied air, and the inclined bottom surface 28e is formed toward the gas outlet port 28b. As a result, gravity flows down naturally, preventing retention of generated water in the electrode reaction region. Also, condensed water is added near the gas outlet 28b,
Since the groove is formed deep in the vicinity of the gas discharge port 28b and the cross-sectional area thereof is enlarged, a space for discharging excess air can be secured in the upper part of the groove. Therefore, it is possible to prevent the diffusion of the gas from being hindered by blocking the oxidizing gas flow groove 28 with the generated water or the like. In addition, also in the second embodiment, each current collector 24, 27 and electrode 13,
A sufficient contact area with 16 can be secured.

Next, an instrument was connected between both carbon current collectors 24 and 27 of the polymer electrolyte fuel cell of this example, and the cell performance was evaluated in the same manner as in the case of the first example. However, the results shown in FIGS. 3 and 4 were obtained. That is, it was confirmed that the current-voltage characteristics were improved as compared with the case of the first embodiment, and the voltage stability was also improved when held in the high current density region where a large amount of produced water was generated. Further, it was confirmed that the improvement of the dischargeability of the generated water and the like prevents the generation of the generated water and the like from clogging the oxidizing gas flow groove 28, so that the output reduction due to the gas diffusion inhibition due to this can also be prevented.

In both of the above embodiments, the case where the plurality of oxidizing gas flow grooves 18, 28 are formed in a linear shape has been described, but the case where these grooves are formed in a grid shape is also described. The same effect can be obtained. Further, if the inner surfaces of the oxidizing gas flow grooves 18, 28 are subjected to a hydrophilic treatment or a water repellent treatment, the drainage property can be further improved.

As another example of the polymer electrolyte membrane,
Polystyrene cation exchange resin membrane with sulfonic acid group, which can be used as a cation conductive membrane, for example, a mixed membrane of fluorocarbon sulfonic acid and polyvinylidene fluoride, or trifluoroethylene grafted to a fluorocarbon matrix Things are suitable.

Further, the present invention is not limited to a fuel cell in which the electrolyte membrane is installed horizontally, but can be applied to a fuel cell of a type in which the electrolyte membrane is arranged vertically.

[0036]

As described above, in the fuel cell of the present invention, the oxidizing gas passage groove formed on the side of the current collector also serving as the gas separator on the cathode side facing the cathode is the same as the oxidizing gas passage groove. Since the depth is gradually increased from the gas inlet side toward the gas outlet side, the flow passage cross-sectional area of the oxidizing gas flow groove is enlarged without reducing the contact area between the current collector and the electrode. Therefore, the generated water and the like generated in the oxidizing gas flow groove can be positively discharged without staying and the drainage is excellent, and the blocking of the oxidizing gas flow groove due to the retention of the generated water and the like can be prevented. Particularly in a horizontally installed type fuel cell, it becomes possible to positively perform drainage by gravity, so that the effect becomes remarkable. Therefore, even when continuously operating in a high current density region where a large amount of generated water is generated, the generated water can be efficiently discharged, so the voltage is stable,
A stable output can be continuously obtained.

Further, the electrode reaction region of the oxidizing gas flow groove is formed to have a shallow and constant depth, and the portion deviated from the electrode reaction region is gradually deepened toward the gas introduction port side and the gas discharge port side. If each is formed so that the gas flow velocity in the electrode reaction region of the oxidizing gas flow groove is increased, the oxygen partial pressure in this region can be prevented from lowering and the reaction efficiency is improved, so that a higher voltage can be stabilized. Can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional side view showing a polymer electrolyte fuel cell according to a first embodiment of the present invention.

FIG. 2 is a sectional side view showing a polymer electrolyte fuel cell according to a second embodiment of the present invention.

FIG. 3 shows currents between the polymer electrolyte fuel cells of the first and second embodiments and the conventional polymer electrolyte fuel cell.
It is a diagram which shows a voltage characteristic.

FIG. 4 is a diagram showing the relationship between the voltage and the holding time of the polymer electrolyte fuel cells of the first and second embodiments and the conventional polymer electrolyte fuel cell.

FIG. 5 is a plan view of a gas separator plate in a conventional polymer electrolyte fuel cell.

FIG. 6 is a sectional view taken along line VI-VI of FIG. 5;

7 is a sectional view taken along line VII-VII in FIG.

[Explanation of symbols]

 11 Polymer Electrolyte Membrane 13 Anode 14 Carbon Current Collector 14a Fuel Gas Flow Groove 16 Cathode 17 Carbon Current Collector 18 Oxidizing Gas Flow Channel 18a Gas Inlet 18b Gas Outlet 18c Sloping Bottom 24 Carbon Current Collector 24a Fuel Gas Flow groove 27 Carbon current collector 28 Oxidizing gas flow groove 28a Gas inlet port 28b Gas discharge port 28c Horizontal bottom surface 28d Sloping bottom surface 28e Sloping bottom surface

Claims (2)

[Claims] 1. A current collector having an anode and a cathode with an electrolyte membrane sandwiched therebetween, and a current collector that also functions as a gas separator is provided on the anode side and the cathode side, and a fuel is provided on a surface of the current collector facing the anode. A fuel gas flow groove through which a gas flows, and an oxidizing gas flow groove through which an oxidizing gas flows is formed on the surface of the current collector facing the cathode, and hydrogen gas in the fuel gas and hydrogen ions in the fuel gas flow through the electrolyte membrane. In a fuel cell that obtains an electromotive force by reacting with oxygen in an oxidizing gas, the oxidizing gas flow groove is formed such that its depth gradually increases from the gas inlet to the gas outlet. Fuel cell characterized by being 2. An anode and a cathode are provided with an electrolyte membrane sandwiched therebetween, and a current collector also serving as a gas separator is provided on the anode side and the cathode side, and a fuel facing surface of the current collector faces the anode. A fuel gas flow groove through which a gas flows, and an oxidizing gas flow groove through which an oxidizing gas flows is formed on the surface of the current collector facing the cathode, and hydrogen gas in the fuel gas and hydrogen ions in the fuel gas flow through the electrolyte membrane. In a fuel cell for obtaining electromotive force by reacting with oxygen in oxidizing gas, the oxidizing gas flow groove is formed to have a shallow depth and a substantially constant depth in the electrode reaction region facing the cathode. In addition, in the part outside this electrode reaction area,
A fuel cell, characterized in that the fuel cell is formed so that the depth thereof gradually increases toward the gas inlet or the gas outlet.