JPH0724223B2 - Fuel cell - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a fuel cell having stable performance over a long period of time.

[Technical background of the invention and its problems]

BACKGROUND ART Conventionally, a fuel cell has been known as a device for directly converting the energy of fuel into electrical energy. In this fuel cell, a pair of porous electrodes are placed across the electrolyte, and a fluid fuel such as hydrogen is brought into contact with the back surface of one electrode and a fluid oxidant such as oxygen is brought into contact with the back surface of the other electrode. By utilizing the electrochemical reaction that occurs at this time, electric energy is taken out from between the electrodes, and electric energy is taken out with high conversion efficiency as long as the fuel and the oxidant are supplied. Is something that can be done.

By the way, the unit cell of a fuel cell based on the above principle, in particular, using phosphoric acid as an electrolyte is usually constructed as shown in FIG. 3 (a) or (b), and a plurality of unit cells may be stacked. As a result, the entire fuel cell device is constructed as shown in FIG.

That is, in FIG. 3 (a), the unit cell has electrodes 2 and 3 (generally made of carbon material) formed of a porous body and having a catalyst added on both sides of the matrix 1 impregnated with the electrolyte. Further, the matrix 1 of both electrodes 2 and 3 and the plate 6 having ribs 4 and 5 on the back surface respectively (generally composed of a mixed binder of Claffite and thermosetting resin. Hereinafter referred to as interconnector). .) Has been placed. On the surface of the interconnector 6 located on the side of each of the electrodes 2 and 3, a plurality of grooves 7 and 8 are regularly provided in parallel so as to be orthogonal to each other by ribs 4 and 5, respectively. Flow passages for fluid fuel and fluid oxidizer are formed in 7 and 8, respectively. Similarly, on the opposite surface of the interconnector 6, grooves 7 and 8 are provided by the ribs 4 and 5 so as to serve as flow passages for the fluid fuel and the fluid oxidant in the unit cells which are adjacent to each other in a direction orthogonal to each other. ing. The matrix 1, the electrodes 2 and 3 and the interconnector 6 are stacked in this way, and in this state, the end faces of each stack are hermetically sealed leaving only the openings at both ends of the grooves 7 and 8 of the interconnector 6 to form a unit cell. I am configuring.

A plurality of unit cells configured as shown in FIG. 3 (a) are stacked, and as shown in FIG. 4, a manifold 10 having a fuel supply port 9 on one of the opposite end faces of this stack, A manifold 12 having a fuel discharge port 11 on the other side is applied, and a manifold 14 having an oxidant supply port 13 on the other end face and a manifold 16 having an oxidant discharge port 15 on the other side. And the manifolds 110, 12, 14, 16 are tightened with bolts or the like to be kept airtight, and thereby the fuel cell device 17 is constituted. Therefore, according to the fuel cell device 17, when the fluid fuel is supplied from the fuel supply port 9, the fuel is shunted through the plurality of grooves 7 which are the flow passages of each unit cell and is in contact with the back surface of the porous electrode 2. flow,
After that, the fuel is discharged from the fuel discharge port 11. Also the oxidant supply port
When the fluid oxidant is supplied from 13, the oxidant shunts the plurality of grooves 8 which are the flow passages of each unit cell, and the porous electrode 3
Flow while coming into contact with the back surface of the oxidant, and then discharged from the oxidant discharge port 15. The fluid fuel and the fluid oxidant are supplied to the porous electrodes 2 and 3 by diffusion to generate electric energy as a fuel cell. The output terminals are omitted in the figure.

Further, a fuel cell unit cell configured as shown in FIG. 3 (b) is considered as an improved type. In FIG. 3 (b), 18 is a separator, 19 is a ribbed electrode, and other elements having the same operation as in FIG. 3 (a) are designated by the same reference numerals. That is, the interconnector 6 shown in FIG. 3A is divided into a parator 18 and ribs 4 and 5, and the ribs 4 and 5 are integrated with the electrodes 2 and 3, respectively, to form ribbed electrodes 19. It is configured.

The characteristic of this improved type is that the separator 18 prevents the mixing of the fluid fuel and the fluid oxidant and also serves as a current collector for the unit cell stacking. Further, in this improved fuel cell, the weight is reduced to about half of that of the interconnector type shown in FIG. 3 (a), and the rib portion is porous, so that it overflows from the matrix layer. It has a so-called "reservoir function" that absorbs phosphoric acid and replenishes the stored phosphoric acid when the phosphoric acid in the matrix layer decreases. That is, the ribbed electrode 19 has sufficient permeability of the reaction fluids for the reaction fluids of the fluid fuel and the fluid oxidant to reach the catalyst layer, respectively, and has good electrical conductivity and thermal conductivity, and has a good stacking load. It has the strength to endure.

By the way, the conventional fuel cell electrode as described above is
% Of the conductive particles carrying the catalyst on a carbon paper or carbon sintered substrate (hereinafter referred to as an electrode substrate) having a porosity of 100% by kneading with a hydrophobic polymer and a solvent, followed by drying and firing. Manufactured.
However, as a result of the examination in the conventional electrode,
It has become clear that there are the following problems.

(A) As the catalyst-supporting zone, it is required to use a material having improved corrosion resistance even with the same carbon material, for example, fine particles of acetylene black or graphite. The material having improved corrosion resistance itself has strong water repellency. Therefore, the water repellency of the catalyst layer becomes abnormally strong and repels the electrolyte, resulting in insufficient contact between the catalyst and the electrolyte, thus reducing the reaction area which is the contact interface between the electrolyte and the catalyst and the reaction gas, and The resistance increases and the battery performance decreases significantly.

(B) Volume change of the electrolyte is inevitably accompanied by operating conditions such as operating temperature, operating pressure, negative electrode, and humidity in reaction gas. That is, phosphoric acid as an electrolyte is a reaction product part of water and phosphorus pentoxide and a desiccant having a strong hygroscopic property as shown in the following reaction formula.

3H ₂ O + 1 / 2P ₄ O ₁₀ 2H ₃ PO ₄ Therefore, the reaction proceeds to the left under high temperature and dry conditions, and to the right under low temperature and high humidity conditions. Here, although the explanation is simplified, there are many complex condensates of phosphoric acid as the intermediate products. However, regarding the progress of those reactions, the same tendency as described above is the same. On the other hand, when a load is applied, water is produced as an electrochemical reaction product. Moreover, since the humidity is determined by the ratio of the partial pressure of water vapor to the total pressure, the equilibrium of the above reaction also moves depending on the operating pressure. Here, if the water repellency of the catalyst layer is too large, the electrolyte overflowing from the matrix layer, which is the electrolyte holding layer, is forced out through the catalyst layer due to the water repellency of the catalyst and is extruded onto the electrode substrate. Although it reaches and is occluded, when the electrolytic mass in the matrix layer is reduced, the overflowed electrolyte supplies the electrolyte to the matrix layer again, and as a result, a so-called constant amount of electrolyte is always retained in the matrix layer. The "reservoir function" is hindered, and the electrolyte once overflowed remains isolated and held in the electrode plate due to the strong water repellency of the catalyst layer. As a result, the electrolyte in the matrix layer gradually decreases, and the voids increase, and the reaction gas of the fuel cell, that is, the separator function of preventing the mixing of the fuel gas and air, disappears, and the mixing of the two reaction gases occurs. A so-called “crossover” phenomenon occurs, which significantly reduces battery performance and causes an explosion.

(C) In order to improve the performance, the support is required to be fine particles of several tens of microns or less, but the finer the particles, the smaller the pore size of the catalyst layer, and the phosphorus in the penetration direction of the catalyst layer. Acid transfer is significantly excluded, and the above (a) and (b)
The phenomenon of is accelerated.

[Object of the Invention]

The present invention has been made to solve the above problems, and its object is to improve the contact between the catalyst layer and the electrolyte and to provide a conductive electrode substrate made of a porous carbon material that is a support of the catalyst layer. An object of the present invention is to provide a fuel cell capable of effectively utilizing the electrolyte reservoir function and exhibiting stable performance for a long time.

[Summary of the Invention] In order to achieve the above object, the present invention includes a fluid fuel flow passage and a fluid oxidant flow passage that are in contact with a pair of electrodes that are arranged to face each other through an electrolyte matrix, and each flow passage has In a fuel cell that outputs electric energy under the condition that a fuel and an oxidant are flowing, the electrode side of the pair of electrodes, which serves as the anode, has a conductive particulate R1 volume percent carrying a catalyst and the conductive particulate. A mixture layer of 100% by volume of the phosphorous acid-philic particles R2 having a phosphoric acid resistance of the same particle size or larger than that of 100% by volume is formed on the conductive electrode substrate.

[Examples of the Invention] The present invention is to form a mixture layer of electroconductive fine particles carrying a catalyst and phosphoric acid-philic particles of the same or larger particles as the fine particles on an electrode substrate. The one in which the dissolution medium is supported on the fine particles having an average particle diameter of 1 μm or less is
It is known to have a very good catalytic activity.

That is, in the fuel cell electrode of the present invention, on the anode electrode side, conductive fine particles R1 (67 ≦ R1 <
80) vol% and the parent phosphoric acid particles R2 having phosphoric acid resistance of particles equal to or larger than the conductive fine particles
(20 <R2 ≦ 33) and a mixture layer consisting of 100% by vol%
It is formed on a conductive electrode substrate.

In this case, vol% is represented by a value calculated by the respective bulk (apparent) densities and is represented by the following equation.

Where x is the conductive fine particle weight [g], a is the conductive fine particle bulk density [g / cm ³ ], y is the phosphorus-philic acidic particle weight [g],
β is the bulk density [g / cm ³ ] of the parent phosphoric acid particles.

As a result, the electrolyte has a water repellency sufficient to prevent contact with the electrolyte and the catalyst from being immersed in the electrolyte, has a passage through which the electrolyte can freely pass, and has a sufficient electrolyte reservoir function of the electrode substrate. It can be utilized.

This point can be considered as follows, and FIG. 1 (a)
An explanation will be given using (b). That is, as shown in FIG.
The conductive fine particles 26 are fixed by the hydrophobic polymer 27,
The layers are in contact with each other and are electrically connected as a whole. This structure is the same as that of the conventional catalyst layer. Further, phosphorophilic acid particles 28, which are larger than the conductive fine particles 26, are fixed between the conductive fine particles 26 by the hydrophobic polymer 27. This is the greatest feature point of the configuration of the present invention.

That is, the large phosphoric acid-philic particles 28 determine the size of the micropores that become the phosphoric acid transfer passages of the catalyst layer, and the phosphoric acid-philic particles 28 communicate with each other in the thickness direction of the catalyst layer, and the phosphoric acid transfer path is Secured and allows phosphoric acid to easily migrate through the catalyst layer. It has been experimentally understood that the size of the parent phosphoric acid particles 28 is about 5 μm in order to form an appropriate phosphoric acid transfer path.

Thus, the phosphorus-philic acid particles 28 are three-dimensionally arranged in the catalyst layer so that the phosphorus-philic acid portions communicate with each other in the thickness direction, and the electrolyte 29 can freely pass through the highly water-repellent catalyst layer. Phosphophilic acidic particles are required to be stable materials in high temperature and in phosphoric acid and air, and can be used as matrix materials such as ZrO ₂ , Ta ₂ O ₅ , (ZrO ₂ ) ₂ P ₂ O ₇ Is desirable. These matrix materials are non-electroconductive materials, and the electrophilic phosphorous acid particles have a volume ratio of 1/5 or more with respect to the electroconductive fine particles, and the electroconductivity of the catalyst layer decreases.

Next, a specific embodiment of the present invention based on the above concept will be described.

In this example, the average particle diameter of platinum loading 8wt% is 0.03μ,
Carbon black carrier particles, which are conductive fine particles having a bulk density of 0.1 g / cm ³ , have an average particle size of 5 which is a phosphoric acid acidic particle.
μ, bulk density 0.6g / cm ³ Silicon Carbide (SiC)
Mix the particles. To a liquid obtained by suspending these mixtures in water, with respect to the weight of the carrier, a dispersion containing 36% of polytetrafluoroethylene solid content which is a hydrophobic polymer was added, and kneaded with a mixer to give a thickness of 2 mm. It was applied on the flat side of the electrode base material with ribs, dried and fired to manufacture an electrode. FIG. 2 shows the performance of a battery manufactured using this electrode as shown in FIG.

From FIG. 3, regarding the mixing ratio of the carbon black carrier particles which are the conductive fine particles carrying the catalyst and the silicon carbide particles which are the phosphoric acid acidic particles, the anode electrode is
Carbon black support is R1 (67 ≦ R1 <80) vol%, S
It can be seen that the highest value of the battery voltage, which is the battery performance, can be obtained when the iC powder forms a mixture layer of R2 (20 <R2 ≦ 33) vol% and 100 vol%.

As described above, the conductive fine particles are R1 (67 ≦ R1 <80) vol%
And parent phosphoric acid particles are R2 (20 <R2 ≤ 33) vol% and 100 vo
It can be seen that the battery performance is best when the mixture layer of 1% is formed.

In the above, a hydrophobic polymer is used for the conductive fine particles.
Although 40 wt% or 36 wt% is added, 25-50 wt% of hydrophobic polymer may be added to 50-75 wt% of conductive fine particles for the anode electrode.

Therefore, with such an electrode structure, as shown in FIG. 2, due to the action of the silicon carbide particles which are the phosphorus-philic acid particles of the catalyst layer, the catalyst layer is appropriately wetted with the electrolyte to improve the contact, and the catalyst-gas-phosphorus The three-phase interface of the acid is three-dimensionally formed, and therefore, the number of points contributing to the reaction is increased to improve and maintain the battery performance. In addition, in FIG.
It shows the battery characteristics at normal pressure after 100 hours. In addition, the difference between the anode electrode and the cathode electrode is that, in principle, water, which is a reaction product, is generated from the cathode side, so that the cathode electrode tends to get wet over time when a load is applied. As a result, oxygen diffusion may be hindered and battery performance may deteriorate. Therefore, the hydrophilic phosphoric acid particles to be added to the catalyst layer on the cathode side are not added.

Thus, the catalyst layer is in good contact with the electrolyte, and the catalyst-phosphoric acid-reaction gas three-phase interface is also three-dimensionally formed to increase the area, so that the internal resistance of the battery is reduced and improved, and the three-phase interface is Since the phosphorus-philic acid particles stabilize, the battery performance can be stably ensured for a long time.

As described above, in the fuel cell of the present embodiment, of the pair of electrodes, the electrode side serving as the anode has conductive fine particles R1 (67 ≦ R1 <80) in which the catalyst is carried, and the conductive fine particles are Formed on a conductive electrode substrate, a mixture layer comprising phosphoric acid-philic particles R2 (20 <R2≤33) having a phosphoric acid resistance of the same or larger particles and having a volume percentage of 100% by volume. Is.

Therefore, even if fine catalyst particles are used, a catalyst layer having a target micropore structure is formed by mixing phosphorophilic acid particles having the same size as or larger than the conductive fine particles in the catalyst layer. Further, by using, as the phosphoric acid-philic particles, phosphoric acid-resistant particles having phosphoric acid resistance, the micropore structure can be stably maintained for a long period of time.

As a result, the phosphoric acid in the porous carbon plate and the electrolyte matrix can move freely without being blocked by the catalyst layer having strong water repellency, so that the phosphoric acid amount in the electrolyte matrix can be kept constant over a long period of time. It is possible to make effective use of reserved acid and ensure the affinity between the catalyst layer and phosphoric acid, and as a result, it is possible to improve the performance and extend the life of the fuel cell.

Even when the present invention is applied to a battery using an interconnector type carbon paper as an electrode as shown in FIG. 3 (a), the same effect as the above case can be obtained.

[Effects of the Invention] As described above, according to the present invention, a fluid fuel flow passage and a fluid oxidant flow passage are provided so as to be in contact with a pair of electrodes that are opposed to each other via an electrolyte matrix, and the fuel is provided in each flow passage. And a fuel cell that outputs electric energy under conditions in which an oxidant is flowing, among a pair of electrodes,
The electrode side, which will be the anode, is a conductive fine particle carrying a catalyst.
100% by volume of R1 (67 ≤ R1 <80) volume percent and R2 (20 <R2 ≤ 33) volume percent of parent phosphoric acid particles having the same or larger phosphoric acid resistance than the conductive fine particles. Since a mixture layer consisting of the following is formed on the conductive electrode substrate, the phosphoric acid particles are mixed in the catalyst layer to facilitate the phosphoric acid penetrating transfer of the catalyst layer and increase the phosphoric acid amount of the electrolyte matrix. A fuel that enables the effective utilization of reserveduric acid over a period of time and ensures the affinity between the catalyst layer and phosphoric acid, thereby achieving high performance and long life of the fuel cell. Batteries can be provided.

[Brief description of drawings]

1 (a) and 1 (b) are views showing an embodiment of the present invention, and FIG.
FIG. 3 is a diagram for explaining the effect of the present invention, FIGS. 3 (a) and 3 (b) are exploded perspective views showing a unit cell of a conventional fuel cell device, and FIG. 4 is a fuel cell incorporating the same cell. It is a perspective view which shows an apparatus. 1 ... Matrix, 2, 3 ... Electrode, 2 ', 3' ... Catalyst layer, 4, 5
... rib, 6 ... interconnector, 18 ... separator, 19 ... ribbed electrode, 21 ... anode electrode substrate, 22 ... anode catalyst, 23 ... matrix layer, 24 ... cathode electrode substrate, 25 ...
Cathode catalyst, 26 ... Conductive fine particles (support), 27 ... Hydrophobic polymer, 28 ... Phosphophilic acidic particles.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Katsunori Sakai, 2-1, Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa, Ltd. Inside the Hamakawasaki Plant, Toshiba Corporation (56) Reference Japanese Patent Laid-Open No. 60-95862 Kai 58-166645 (JP, A) JP 58-166639 (JP, A) JP 59-224067 (JP, A)

Claims (1)

[Claims] 1. A condition in which a fluid fuel flow passage and a fluid oxidant flow passage are provided so as to contact a pair of electrodes arranged to face each other via an electrolyte matrix, and the fuel and the oxidant flow through the respective flow passages. In the fuel cell that outputs electric energy in the pair of electrodes, the electrode side that serves as an anode is a conductive fine particle R1 volume percent carrying a catalyst, and is the same as or larger than the conductive fine particles. Phosphophilic acid-resistant particles with phosphoric acid resistance R2 and 100% by volume percent
A fuel cell, characterized in that a mixture layer comprising a volume percentage is formed on a conductive electrode substrate. 67 ≤ R1 <80 20 <R2 ≤ 33