JPS5945190B2 - Hydrogen storage electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a hydrogen storage electrode, particularly a cathode used in a storage battery that generates electrical energy by electrochemically reacting hydrogen stored in the electrode with oxygen.

Batteries such as conventional lead-lead oxide batteries, nickel-cadmium batteries, etc. have relatively low energy storage capacity per unit of weight or volume due to their oxide electrodes.

Therefore, in order to improve the energy storage capacity, an electrode that absorbs hydrogen has been proposed as a cathode. For example, JP-A-51-13934 proposes LhM3 alloy as a hydrogen absorbent composition. Ln can be one or a mixture of lanthanide metals from lanthanum to lutetium (atomic numbers 57-71). M represents either nickel, cobalt or a mixture of both. This type of Ln-based alloy is very expensive, and therefore a cathode material that has a large discharge capacity, is relatively easy to manufacture, and is also inexpensive is desired. In view of the above, an object of the present invention is to provide a hydrogen storage cathode that is inexpensive and has a large discharge capacity.

The hydrogen storage electrode of the present invention includes, as an alloy that stores hydrogen,
It uses an alloy represented by the formula CaxNi3 (where x is 0.85 to 1.15), and LnM, an alloy such as L
Compared to aNi6, it is cheaper and has a higher hydrogen storage capacity. The present invention will be explained below with reference to Examples.

FIG. 1 shows the relationship between the composition of alloy CaxNi6 and the amount of hydrogen storage at 20±2°C.

The value of x indicates the number of Ca atoms, and the value of x is 0.8 to 1.3.
If the hydrogen storage capacity is increased to approximately 150Tnt/g
In the case of LaNi and alloys, it is about 160Tlij8k. Figure 2 shows the discharge capacity for each alloy composition.

The electrode has an alloy composition of CaO and 8Nis, where calcium is 0.8 atoms relative to nickel (5 atoms), and the alloy active material l
The discharge capacity per gram is O, 133Ah/g. Similarly, electrodes with alloy compositions with x values of 0.9, 1.0, 1.1, and 1.211.3 have discharge capacities per 1' of alloy active material of O, 3, O, 35, O, and O, respectively. 3, O, 22.0.1
2Ah/g, and the discharge capacity reaches its maximum value when the value of x is around 1.0.

The reason why peaks are formed in the discharge capacity as shown in FIG. 2 depending on the amount of calcium is considered to be due to the following reasons.

First, as a result of X-ray diffraction, only the hexagonal Cacu5 type crystal structure was detected in the range of x = 0.8 to 1.1, but the mixed crystal structure in the range of x = 1.2 to 1.3. It was observed. That is, it means that a crystal structure other than CaCu type is formed. On the other hand, due to the relationship between the hydrogen storage component and the equilibrium pressure, the width of the flat equilibrium pressure becomes smaller when the value of x becomes larger than 1.1. This is considered to be due to a clear decrease in the Cacu5 type crystal structure and an increase in other crystal structures. Therefore, even though the amount of hydrogen storage increases as the value of x increases, the amount of hydrogen released at room temperature and pressure decreases. In other words, once the hydrogen is occluded, it is not easily released. Therefore, when the storage battery is discharged, the amount of hydrogen released decreases, and the electrode capacity decreases. Also, x
In the composition range where the value of
．． As it becomes larger than 8, it becomes larger. This clearly indicates that the CaCu type crystal structure gradually becomes sharper. Therefore, the value of x is 0
．． As the ratio increases from 8 to 1.0, the amount of hydrogen released at normal temperature and pressure also increases. The value of x is 0.8
When , the amount of hydrogen storage is small, so naturally the electrode capacity is also low. As the amount of hydrogen storage increases, the electrode capacity also increases, and when the value is 1.0, the discharge capacity is maximum. Generally, an alkaline storage battery has no characteristics as a practical battery unless its discharge capacity as a cathode is 0.25AV9 or more.

For CaxNi alloys, as is clear from Figure 2, the alloy is effective when the value of x is in the range of 0.85 to 1.15, that is, in the range of 0.17 to 0.23 atomic ratio of calcium to 1 atom of nickel. Within the composition range, the above conditions can be fully satisfied. Example 1 Calcium metal with a purity of 99.5% or higher and nickel metal with a purity of 99.5% or higher (CaxNi) with x values of 0.8, 0.9, 1.0, 1.
1, 1.2, and 1.3, respectively, and put them into an arc melting furnace and melt them at 10-4 to 10-5 t0rr. After vacuuming to
Dissolve in the state of c$N,O.

The sample was inverted several times to homogenize the alloy composition. The button-shaped alloy sample thus obtained was crushed in a dry box in an argon atmosphere and sieved to prepare particles with a particle size of about 40 μm or less.

This CalCNi5 alloy powder is mixed with an aqueous dispersion of fluororesin as a binder at a solid content of 10% by weight to form a paste, which is then pressure-filled into a nickel foam and heated to a pressure of about 200 degrees. Pressure was applied to form an electrode. The size of this electrode is 40 x 40 mm and the thickness is 111 mm, and the amount of the alloy powder, which is the active material, is about 39 mm. FIG. 3 shows a storage battery in which the above electrode is combined as a cathode and a known nickel oxide electrode as an anode.

In the figure, 1 is an anode, 2 is a cathode, 3 is a separator, 4 is an alkaline electrolyte, 5 is a battery container, 6 is an anode terminal, 7 is a cathode terminal, 8
is the liquid injection port. The battery was charged and discharged using an electrode using a CaxNi5 alloy having a different composition as the cathode.
As a result of measuring the discharge capacity with a discharge current of 00 mA, the following was found.

That is, as shown in Figure 2, in the CaxNi5 alloy composition, as the value of x increases, the discharge capacity per unit weight of the alloy increases, and when the value of x is 1.0, the maximum discharge capacity is 0.35A. T, and as the value of X further increased, on the contrary, the discharge capacity decreased. The discharge capacity as an alkaline storage battery cathode is 0.25Ah/f! If it is not above, it has no characteristics as a practical battery, but in CaxNi, alloy, x
A value of 0.85 to 1.15 is an effective alloy composition range,
It is extremely advantageous for use in storage battery electrodes.

Furthermore, alloy materials are also less expensive than Ln-based materials. For example, Ca, . ONi, an alloy, is less expensive than LaNi, an alloy. Furthermore, it has a fast hydrogen absorption rate and is relatively lightweight, allowing an electrode to be constructed that is 30 to 60% lighter than a LaNi alloy. Also LaNi. The discharge capacity of the alloy is about 0.17 AVS, which is about 1 A, which is the maximum discharge capacity of the CaONi alloy. Thus, according to the present invention,
A practically important effect of high reversible capacity can be obtained, and a relatively inexpensive and lightweight storage battery can be provided. Example 2 In the same manner as in Example 1, the amount of alloy powder packed was about 20 g, the size was 80 x 80 m, the length was 1.51 cm, and the thickness was 1.51 cm! We created an electrode, used it as a hydrogen electrode, and combined it with an oxygen electrode to construct an oxygen-hydrogen fuel cell power generation device.

FIG. 4 shows the same device, where 9 is a fuel cell and 10 is an electrolyte tank. The electrolyte in the tank is supplied from a pipe 12 equipped with a pump 11 to the battery 9, and via a pipe 13 to the tank 10. taken back inside. 14 is a load connected to the output terminal of the battery 9 via a constant voltage device 15.

Note that 16 is a pipe that supplies oxygen to the oxygen chamber of the battery, and 17
18 is a pipe for supplying hydrogen to the hydrogen chamber of the battery, and 19 is the same discharge pipe. Note that, like the oxygen electrode, the hydrogen electrode is incorporated into the battery as a gas diffusion type electrode, with one side facing the hydrogen chamber and the other side in contact with the electrolyte.
Therefore, it normally works in the same way as a conventional hydrogen electrode, but since it can store hydrogen, when the supply of hydrogen is stopped, the stored hydrogen acts as an active material. In the power generating device having the above configuration using the cathode of the present invention, even if the fuel cell has an accident and the supply of fuel is stopped, electric power can be extracted from the hydrogen stored in the cathode. Moreover, its discharge capacity is C
a.

ONi, alloy 0.35Ah x 20: 7Ay
If it is autumn and the load is 1A, it is possible to discharge for 7 hours. Therefore, it is very effective when used as a backup power source.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the x value of CaxNi and the alloy and the amount of absorbed hydrogen, Figure 2 is a diagram showing the relationship between the X value and discharge capacity,
FIG. 3 is a schematic vertical cross-sectional view of a storage battery using the electrode of the present invention, and FIG. 4 is a schematic view of a fuel cell power generation device.

Claims (1)

[Claims] 1. A hydrogen storage electrode whose constituent element is an alloy that stores hydrogen, wherein the alloy has the formula Ca_xNi_5 (however, x
is 0.85 to 1.15).