JPS5842181A - Fuel battery - Google Patents

Abstract

PURPOSE:To reduce the decrease of the voltage associated with increase of the current density and reduce the decrease of voltage associated with the lapse of time for electric discharge by using the matrix for holding electrolyte which is stable for phosphoric acid at high temperature and possesses a large holding power for phosphoric acid. CONSTITUTION:The aqueous solution is added into silicon carbide powder, of chloride or hydroxide of Zr, Sn, Ti, Si, or Al and mixed, and further phosphoric acid is added. The above mixture is heated, until the reaction is completed, and then water is removed to obtain the substance having a high viscosity. A gaseous diffusion electrode is coated with the above highly-viscous substance, so as to form the matrix for holding electrolyte. As phosphoric acid which is free against silicon carbide is contained in the matrix, said phosphoric acid in free form acts as the electrolyte of the fuel cell.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel cell, in particular, a fuel cell comprising a pair of gas diffusion electrodes and a matrix for retaining phosphorous as an electrolyte (hereinafter referred to as a phosphoric acid s'Jit retaining matrix). It is related to fuel cells.

Figure 1 shows the basic structure of a fuel cell that uses hydrogen as the fuel, oxygen in the air as the oxidant, and phosphoric acid as the electrolyte. 1 is the anode (gas diffusion electrode), 2 is the cathode (gas diffusion electrode). Diffusion electrode), 3 indicates a phosphoric acid electrolyte holding matrix, hydrogen is in contact with the anode 1, and air is in contact with the cathode 2.

``Conventionally, phenolic resin fiber cloth or a mixture of silicon carbide powder and polytetrafluoroethylene mixed with an organic binder has been used as a matrix for holding phosphoric acid electrolyte. When using phenolic resin fiber cloth as the matrix material, the operating temperature of the fuel cell is 1301
：At higher temperatures, the phenolic resin gradually carbonizes,
You will not be able to drive for a long period of time. In order to eliminate this problem, it is possible to lower the operating temperature of the battery, but
In this case, a new problem arises in that the output of the battery gradually decreases. In addition, when a mixture of silicon carbide powder and an organic binder, polytetrafluoroethylene, is used as the matrix material, the operating temperature of the fuel cell is set to 190 to 200 C1! However, organic binders generally have high water repellency, and in particular, electrified fluororesins such as polytetrafluoroethylene have high water repellency and lack affinity with phosphoric acid. There is a drawback. As a result, the ability to hold phosphoric acid in the electrolyte holding matrix (phosphoric acid holding capacity) is small, and this rounding causes the problem of deterioration of the performance of the fuel cell (b-).

This A1m removes the Zhao point during these times, and the high temperature phosphorus 11
It is possible to provide a fuel cell having an electrolyte retention matrix that is stable and has a high p1 phosphate retention capacity,
The fuel cell has a pair of gas diffusion electrodes and a matrix holding phosphoric acid as an electrolyte, and the matrix is made of a phosphoric acid-resistant material fixed with an inorganic binder.

The conditions that the phosphate electrolyte retention matrix should meet are as follows:
α) It must be stable in phosphoric acid at a temperature of 190 to 200 C', (2) It must be an insulator with no electronic conductivity, (3)
) It has a high affinity with phosphoric acid and has a large holding power, and (the pore volume that can contain phosphoric acid is large).

The present invention was obtained as a result of various studies on matrices for retaining phosphoric acid electrolytes that satisfy these conditions. It uses various inorganic proboscises such as titanium.

For example, among oxides, composite oxides containing zirconium as the main component, such as zircon, tantalum pentoxide, etc.
Carbides include silicon carbide and tantalum carbide, and nitrides include boron titanide. However, when silicon carbide is used, an Arashi bond is obtained.

When we investigated binders for fixing these powders, it became clear that various phosphoric acid compounds were suitable as binders. In particular, silium,
Phosphate compounds of tin, titanium, silicon, and aluminum are preferred; these substances have a high affinity with phosphoric acid and are highly effective as binders. For example, it is mixed with silicon carbide in advance, or mixed with silicon carbide in the form of a salt solution in an oxide, and then phosphoric acid is added and reacted to form a phosphoric acid compound. In the present invention, the latter method is particularly preferred, and has a large action as a binder@Vh*.Examples will be described below.

Example α) An aqueous solution of a chloride or hydroxide of zirconium, tin, titanium, silicon or aluminum was added to and mixed with silicon carbide powder having an average particle size of 0.3 μm, and phosphoric acid was further added thereto. The mixing ratio of silicon carbide and zirconium, tin, titanium, silicon, or aluminum salt solution is 70% by weight of silicon carbide and 30% by weight of the phosphoric acid compound produced by the reaction of the aforementioned metal salt/acid. % by weight, and the amount of phosphoric acid is, in addition to the amount required for making the phosphoric acid compound, 60% by weight based on silicon carbide.
Circle. Then, these mixtures were heated at 200 C for 15 hours to complete the anti-Ct reaction and remove moisture, thereby making it possible to obtain a highly viscous material.

This highly viscous material is coated on the gas diffusion electrode to constitute an electrolyte holding matrix, and this matrix contains 60% by weight of free phosphoric acid based on the silicon carbide mentioned above. Therefore, this free phosphoric acid acts as an electrolyte in the fuel cell. Table 1 shows the electrolyte retention matrix obtained in this example and the conventional method, that is, mixing 5% by weight of polytetrafluoroethylene with silicon carbide, and then adding 60% by weight of phosphoric acid.
This table shows a comparison of the viscosity of 17% sulfuric acid electrolyte retaining matrix. The viscosity was determined by applying a load of 50 kg to 5 g of each phosphoric acid electrolyte holding matrix on a flat plate, and measuring its spread area. Table 1 shows that by using an inorganic binder it is possible to obtain binding properties comparable to those of polytetrafluoroethylene.

The phosphoric acid electrolyte holding matrix of the 5AIlIA example has a softness of 17
)/A substance having acid retention ability was obtained.

Example e) 1 t of zirconium oxychloride A (zrocz, a 8HmO) was added to 26 g of V% nine-silicon carbide (example value).
A solution of -2 g dissolved in water s〇- was mixed, 1 g of phosphoric acid was added, and the mixture was heated at 200 C for 15 hours to prepare an electrolyte holding matrix. This wjrix was applied onto a known gas diffusion electrode to a thickness of α3cm, and the other gas diffusion electrode was stacked and integrated to assemble a fuel cell. The gas diffusion electrode is made by coating carbon powder carrying a small amount of platinum on carbon paper.

Figures 2 and 3 respectively show the current density-voltage characteristics of a fuel cell using the phosphoric acid electrolyte retention matrix of this example, and the characteristics when continuously discharged at a current of 200 mA/al''. The change in battery voltage over time was measured using a conventional electrolyte retention matrix, i.e., silicon carbide with polytetrafluoroethylene as a binder.
This is shown in comparison with the characteristics of a fuel cell.The horizontal axes of Figures 2 and 3 vA respectively indicate the current density (mA/
a++'') and discharge time Φ), and the vertical axis of both figures shows the voltage M (j), A and C are for the embodiment, and B and D are for the conventional example.

As is clear from FIGS. 2 and 3, implementation.

When using the phosphoric acid electrolyte retention matrix in the example, there is less voltage drop as the current density increases and voltage drop as the discharge time elapses, resulting in superior round performance compared to the conventional case. It will be done. This improvement in performance is based on the fact that the phosphoric acid compound used as the binder has good affinity with phosphoric acid and has a high ability to retain phosphoric acid. Furthermore, in Figures 2 and 3, the operating temperature is 190C.
This figure shows the results at K, indicating that stable results can be obtained even at high temperatures when the phosphoric acid electrolyte holding matrix of the example is used.

In addition, in Example (2), an example was shown in which a zirconium salt was used to generate a phosphorus@electrolyte holding matrix.
A similar effect can be obtained by using a liquid.

As described above, the fuel cell of the present invention makes it possible to provide a fuel cell having an electrolyte retention matrix that is stable to high-temperature phosphoric acid and has a large phosphoric acid retention capacity, and has industrial effects. It is a great thing.

[Brief explanation of the drawing]

FIG. 111 is a sectional view showing the basic structure of a fuel cell having a phosphoric acid electrolyte holding matrix, and FIGS. 2 and 3.
The figure is a characteristic diagram showing the characteristics of an embodiment of the fuel cell of the present invention in comparison with the characteristics of a conventional fuel cell. 1...Anode, 2-...Cathode, 3-...Phosphate electrolyte (1 other person) 1st Figure 1 Figure 2 Melo (t' FJ name σ bow (Continuation of page 1) @ Applicant Hitachi Chemical Co., Ltd. 2-1-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo

Claims (1)

[Claims] 1. A fuel cell having a pair of gas diffusion electrodes and a matrix holding phosphoric acid as an electrolyte, characterized in that the matrix is made of a phosphoric acid-resistant material fixed with an inorganic binder. fuel cell. 2. vIJ The inorganic binder is zirconium or tin. The fuel cell according to claim 1, which is at least one phosphoric acid compound selected from the group consisting of titanium, silicon, and aluminum. 3. The fuel cell according to claim 11 [or claim 2], wherein the phosphoric acid-resistant substance is silicon carbide.