JPH11329461A - Phosphoric acid fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an internal resistance and perform a stable operation for a long period by interposing a mixture of heat resisting phosphoric fine particle and phosphoric acid between at least one of a fuel electrode and an oxidizer electrode and an electrolytic matrix layer. SOLUTION: A cell (unit cell) of a fuel cell has an electrolytic matrix layer 1 impregnated with and retaining phosphoric acid as electrolyte and a fuel electrode 2 and oxidizer electrode 3 arranged with this inbetween. Catalyst layers 4, 5 are formed on the electrolytic matrix layer 1 surfaces of the fuel electrode 2 and oxidizer electrode 3, respectively, and a mixture of heat resisting phosphoric fine particle with electrode or phosphoric acid is interposed between the catalyst layer 4 of the fuel electrode 2 and the electrolytic matrix layer 1. The heat resisting phosphoric fine particle means a particle excellent in resistance to the corrosive property of phosphoric acid in high-temperature state, and carbon black is used as the material. The constituting material of the electrolytic matrix layer consists of silicon carbide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphoric acid fuel cell in which a plurality of cells each having a fuel electrode, an oxidant electrode, and an electrolyte matrix layer sandwiched between these electrodes are stacked.

[0002]

2. Description of the Related Art FIG. 10 is a schematic view showing a cell of a conventional phosphoric acid fuel cell. In the figure, a cell (unit cell) of a fuel cell includes an electrolyte matrix layer 1 impregnated and holding phosphoric acid as an electrolyte, and a fuel electrode 2 and an oxidant electrode 3 arranged with the electrolyte matrix layer 1 interposed therebetween. It is composed of Catalyst layers 4 and 5 are formed on the surfaces of the fuel electrode 2 and the oxidant electrode 3 on the electrolyte matrix layer 1 side, respectively.

Generally, an electrolyte matrix layer 1 of a phosphoric acid type fuel cell is formed into a sheet by dispersing fine particles of a material having excellent heat-resistant phosphoric acid such as silicon carbide with a binder having excellent heat-resistant phosphoric acid such as fluororesin. It is made by molding. The electrolyte matrix layer 1 thus produced is impregnated with an electrolyte during assembly, and is integrated with the fuel electrode 2 and the oxidant electrode 3 which are also impregnated with the electrolyte.

In such a phosphoric acid type fuel cell, the fuel electrode 2 supplies H ₂ → 2H ⁺ by supplying a fuel gas and an oxidizing gas from opposite surfaces of the catalyst layers on which the electrodes 2 and 3 are formed.
+ 2e ⁻ , and at the oxidant electrode 3 １ ／ O ₂ + 2H ⁺ + 2e ⁻ →
The electrochemical reaction of H ₂ O progresses, and electric power can be taken out.

[0005]

However, in the conventional phosphoric acid fuel cell, a gap is formed at the contact interface between the electrodes 2 and 3 and the electrolyte matrix layer 1 depending on the surface condition of the fuel electrode 2 and the oxidant electrode 3. Therefore, when the electrolyte is not sufficiently impregnated, or when the electrolyte mass in the cell decreases, the electrolyte is locally depleted, the interface resistance increases, and the cell voltage decreases.
That is, there is a problem that power generation efficiency is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a low internal resistance by keeping an electrolyte stable at an interface between an electrode and an electrolyte matrix layer for a long period of time. It is an object of the present invention to obtain a phosphoric acid type fuel cell which can be operated stably for a long period of time.

[0007]

According to a first aspect of the present invention, there is provided a phosphoric acid fuel cell comprising a fuel cell, an oxidizer electrode, and a plurality of cells having an electrolyte matrix layer sandwiched between these electrodes. In this case, a mixture of heat-resistant phosphoric acid fine particles and phosphoric acid is interposed between at least one of the fuel electrode and the oxidant electrode and the electrolyte matrix layer.

In the phosphoric acid type fuel cell according to the second aspect of the present invention, the heat-resistant phosphoric acid fine particles are made of the same material as the electrolyte matrix layer, and the particle diameter of the heat-resistant phosphoric acid fine particles is adjusted to the particle size of the constituent material of the electrolyte matrix layer. It is smaller than the diameter.

The phosphoric acid fuel cell according to the third aspect of the present invention uses silicon carbide as a constituent material of the electrolyte matrix layer.

A phosphoric acid fuel cell according to a fourth aspect of the present invention uses carbon black as the heat-resistant phosphoric acid fine particles.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. FIG. 1 is a configuration diagram schematically showing a phosphoric acid type fuel cell according to an embodiment of the present invention. In the figure, a cell (unit cell) of a fuel cell includes an electrolyte matrix layer 1 impregnated and holding phosphoric acid as an electrolyte,
It has a fuel electrode 2 and an oxidant electrode 3 arranged with the electrolyte matrix layer 1 interposed therebetween. Catalyst layers 4 and 5 are formed on the surfaces of the fuel electrode 2 and the oxidant electrode 3 on the electrolyte matrix layer 1 side, respectively. A mixture 6 of heat-resistant phosphoric acid fine particles and an electrolyte, that is, phosphoric acid, is interposed between the catalyst layer 4 of the fuel electrode 2 and the electrolyte matrix layer 1. Here, the heat-resistant phosphoric acid fine particles are fine particles having excellent resistance to the corrosiveness of phosphoric acid in a high temperature state.

In order to examine the battery characteristics of a small single cell having such a structure, two types of small single cells A, having the structure shown in FIG.
B was assembled, and a small single cell C having the structure of FIG. 10 was assembled as a comparative example. As the heat-resistant phosphoric acid fine particles, silicon carbide having an average particle size of 1 μm is used in the small single cell A, and carbon black (acetylene black) is used in the small single cell B. A mixed paste of these and phosphoric acid is used as the fuel electrode 2. It was interposed between the electrolyte matrix layer 1 and each.

As a result of the above experiment, each cell A, B,
FIG. 2 shows the change over time of the cell voltage of C, and FIG. 3 shows the change over time of the internal resistance. As shown in the figure, in the cells A and B having the structure of FIG. 1, the cell voltage decreases at a rate of about 5 mV / 1000.
h, whereas in the cell C having the conventional structure, about 10 mV
/ 1000h. The rate of increase of the internal resistance was almost constant in the cells A and B, while the cell C of the conventional structure tended to increase with the operation time. It is considered that such a difference in the cell voltage decreasing rate is caused by a difference in internal resistance, that is, an interface resistance between the fuel electrode 2 and the electrolyte matrix layer 1.

That is, in the phosphoric acid type fuel cell having the structure as shown in FIG. 1, the gap at the contact interface between the fuel electrode 2 and the electrolyte matrix layer 1 is filled with the mixture 6 of the heat-resistant phosphoric acid fine particles and phosphoric acid. The interface resistance between the fuel electrode 2 and the electrolyte matrix layer 1 is reduced, and stable operation can be performed for a long time.

Embodiment 2 Next, FIG. 4 is a configuration diagram schematically showing a phosphoric acid type fuel cell according to Embodiment 2 of the present invention. In the first embodiment, the mixture 6 is interposed between the catalyst layer 4 of the fuel electrode 2 and the electrolyte matrix layer 1, but in the second embodiment, the mixture 6 is interposed between the catalyst layer 5 of the oxidant electrode 3 and the electrolyte matrix layer 1. The mixture 7 of the heat-resistant phosphoric acid fine particles and phosphoric acid is interposed between them.

In order to examine the battery characteristics of the small single cell having such a structure, two types of small single cells C and C having the structure shown in FIG.
D was assembled and compared with the battery characteristics of the small single cell C having the structure of FIG. As the heat-resistant phosphoric acid fine particles, silicon carbide having an average particle diameter of 1 μm is used in the small single cell D, and carbon black (acetylene black) is used in the small single cell E. And the electrolyte matrix layer 1.

As a result of the above experiment, each cell D, E,
FIG. 5 shows the change over time of the cell voltage of C, and FIG. 6 shows the change over time of the internal resistance. As shown in the figure, in the cells D and E having the structure of FIG. 4, the rate of decrease in cell voltage is about 5 mV / 1000.
h, whereas in the cell C having the conventional structure, about 10 mV
/ 1000h. Also, the rate of increase of the internal resistance was almost constant in the cells D and E, while the cell C of the conventional structure tended to increase with the operation time. It is considered that such a difference in cell voltage reduction rate is caused by a difference in internal resistance, that is, an interface resistance between the oxidant electrode 3 and the electrolyte matrix layer 1.

That is, in the phosphoric acid type fuel cell having the structure as shown in FIG. 4, the gap at the contact interface between the oxidant electrode 3 and the electrolyte matrix layer 1 is filled with the mixture 7 of the heat-resistant phosphoric acid fine particles and phosphoric acid. In addition, the interfacial resistance between the oxidant electrode 3 and the electrolyte matrix layer 1 is reduced, and the device can be stably operated for a long time.

Embodiment 3 Next, FIG. 7 is a configuration diagram schematically showing a phosphoric acid type fuel cell according to Embodiment 3 of the present invention. In this example, a mixture 6 of the heat-resistant phosphoric acid fine particles and phosphoric acid is provided between the catalyst layer 4 of the fuel electrode 2 and the electrolyte matrix layer 1 and between the catalyst layer 5 of the oxidant electrode 3 and the electrolyte matrix layer 1. A mixture 7 of heat-resistant phosphoric acid fine particles and phosphoric acid is interposed.

In order to examine the battery characteristics of the small single cell having such a structure, two types of small single cells F, having the structure shown in FIG.
G was assembled and compared with the battery characteristics of the small single cell C having the structure of FIG. Note that, as the heat-resistant phosphoric acid fine particles, silicon carbide having an average particle size of 1 μm was used in the small single cell F, and carbon black (acetylene black) was used in the small single cell G.

As a result of the above experiment, each cell F, G,
FIG. 8 shows the change over time of the cell voltage of C, and FIG. 9 shows the change over time of the internal resistance. As shown in the figure, in the cells F and G having the structure of FIG. 7, the cell voltage decreases at a rate of about 5 mV / 1000.
h, whereas in the cell C having the conventional structure, about 10 mV
/ 1000h. Also, the rate of increase of the internal resistance was almost constant in the cells F and G, while the cell C of the conventional structure tended to increase with the operation time. It is considered that such a difference in the cell voltage decreasing rate is caused by a difference in internal resistance, that is, an interface resistance between the electrodes 2 and 3 and the electrolyte matrix layer 1.

That is, in the phosphoric acid type fuel cell having the structure shown in FIG. 7, a mixture of heat-resistant phosphoric acid fine particles and phosphoric acid is used.
Thereby, the gaps at the contact interfaces between the electrodes 2 and 3 and the electrolyte matrix layer 1 are filled, and the interface resistance between the electrodes 2 and 3 and the electrolyte matrix layer 1 is reduced, respectively.
It can be operated stably for a long time.

[0023]

As described above, in the fuel cell according to the first aspect of the present invention, the heat-resistant phosphoric acid fine particles and the phosphoric acid are interposed between at least one of the fuel electrode and the oxidant electrode and the electrolyte matrix layer. Since the mixture is interposed, the interface resistance between the electrode and the electrolyte matrix layer can be reduced, and high power generation performance can be maintained for a long time.

In the phosphoric acid type fuel cell according to the second aspect of the present invention, the heat-resistant phosphoric acid fine particles are made of the same material as the electrolyte matrix layer, and the particle diameter of the heat-resistant phosphoric acid fine particles is adjusted to the particle diameter of the constituent material of the electrolyte matrix layer. Since the following conditions are satisfied, the overall structure can be inexpensively formed while the internal resistance is more reliably reduced.

In the phosphoric acid fuel cell according to the third aspect of the present invention, since silicon carbide is used as a constituent material of the electrolyte matrix layer, the entire structure can be inexpensively formed while the internal resistance is more reliably reduced.

In the phosphoric acid type fuel cell according to the fourth aspect of the present invention, since carbon black is used as the heat-resistant phosphoric acid fine particles, the particle size is made smaller, and the gap at the contact interface between the electrode and the electrolyte matrix layer is made more reliable. Can be buried in
The interface resistance can be more reliably reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a phosphoric acid type fuel cell according to Embodiment 1 of the present invention.

FIG. 2 is a relationship diagram showing a change over time of a cell voltage in the phosphoric acid fuel cell of FIG.

FIG. 3 is a relationship diagram showing a change over time of internal resistance in the phosphoric acid type fuel cell of FIG.

FIG. 4 is a configuration diagram schematically showing a phosphoric acid type fuel cell according to Embodiment 2 of the present invention.

FIG. 5 is a relationship diagram showing a change over time of a cell voltage in the phosphoric acid type fuel cell of FIG.

FIG. 6 is a relationship diagram showing a change over time of internal resistance in the phosphoric acid fuel cell of FIG.

FIG. 7 is a configuration diagram schematically showing a phosphoric acid type fuel cell according to Embodiment 3 of the present invention.

8 is a relationship diagram showing a change over time of a cell voltage in the phosphoric acid fuel cell of FIG.

9 is a relationship diagram showing a change over time of internal resistance in the phosphoric acid type fuel cell of FIG.

FIG. 10 is a configuration diagram schematically showing a cell of a conventional fuel cell.

[Explanation of symbols]

1 electrolyte matrix layer, 2 fuel electrode, 3 oxidant electrode, 6,7 mixture.

Claims (4)

[Claims] 1. A phosphoric acid fuel cell in which a fuel electrode, an oxidant electrode, and a cell having an electrolyte matrix layer sandwiched between these electrodes are stacked in a plurality of stages. A phosphoric acid-type fuel cell, wherein a mixture of heat-resistant phosphoric acid fine particles and phosphoric acid is interposed between at least one of them and the electrolyte matrix layer. 2. The phosphoric acid-resistant fine particles according to claim 1, wherein the heat-resistant phosphoric acid fine particles are made of the same material as the electrolyte matrix layer, and have a particle size equal to or smaller than a particle size of the constituent material of the electrolyte matrix layer. Acid type fuel cell. 3. The phosphoric acid fuel cell according to claim 2, wherein the constituent material of the electrolyte matrix layer is silicon carbide. 4. The phosphoric acid fuel cell according to claim 1, wherein the heat-resistant phosphoric acid fine particles are carbon black.