JPH025364A - Gas diffusion type oxygen electrode - Google Patents

Abstract

PURPOSE:To obtain high performance gas diffusion type oxygen electrode having remarkable electrode activity, high operating characteristic, good electrode performance and durability by using a perovskite oxide catalyst having a specific composition as an oxide catalyst of a reaction layer. CONSTITUTION:A perovskite oxide catalyst expressed by La1-xGaxMnO3 (however, 0.05<=x<=0.9) or La1-yCayCoO3 (however, 0.05<=y<=0.9) is used as an oxide catalyst of a reaction layer. Ca substitution rate of an oxide catalyst has an influence on battery performance and in case of La1-xCaxMnO3, it is especially preferable that 0.1<=x<=0.3, and particularly preferable that 0.15<=x<=0.25. And in case of La1-yCayCoC3, it is especially preferable that 0.3<=y<=0.5. If the content of oxide catalyst is too small, no catalyst effect can be obtained, and if it is too large, a change occurs in the fine structure inside the electrode with the result that the electrode resistance becomes worse, so that it is advisable the content is within the range of 10-60wt.%, particularly 20-30wt.%. Thereby, the durability of an electrode is improved and a gas diffusion type oxygen electrode which is stable for a long time and has a good operating characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a gas diffusion type oxygen electrode, and particularly to a gas diffusion type oxygen electrode having extremely excellent electrode performance and operating performance.

[Prior Art] Electrochemical reduction reactions of oxygen in aqueous alkaline solutions are extremely important in fuel cells and metal-air cells.

The present inventors have developed a gas diffusion type oxygen electrode for metal-air batteries, particularly a Teflon (polytetrafluoroethylene) bonded gas diffusion type oxygen electrode mainly composed of carbon as an oxygen reduction cathode, that is, a gas diffusion type oxygen electrode for use in metal-air batteries. Various studies have been conducted regarding electrodes.

FIG. 1 is a sectional view showing a general gas diffusion type carbon electrode.

As shown in the figure, the gas diffusion type carbon electrode 1 has two layers: a gas supply layer 2 and a reaction layer 3. The gas supply layer 2 is made of carbon and Teflon, and the reaction layer is made of carbon, Teflon and an oxide catalyst. It becomes more. A conductive wire such as a Ni mesh 4 is embedded in such a gas diffusion type carbon electrode 1 by hot pressing or the like. In use, the gas supply layer 2 is placed on the side of a gas such as oxygen, and the reaction layer 3 is placed on the side of an alkaline aqueous solution such as KOH.

The present inventors have previously discovered that lanthanum-based perovskite-type oxide catalysts represented by the following composition are effective as oxide catalysts used in such gas diffusion type carbon electrodes ("Journal of the Chemical Society of Japan"). J 1986 No. 6
pp. 751-755).

La(1, s S ro4F eo, a Mo, 403
(M=Mn, Co) [Problem to be solved by the invention] In general, electrodes used in various fields are constantly required to improve various properties such as electrode characteristics and durability. Also in electrodes, improvement of current density,
There is a strong demand for further improvements in electrode performance, such as improved electrode activity and potential stabilization, and operating performance.

The present invention has been made in view of the above-mentioned conventional situation,
The purpose of the present invention is to provide a gas diffusion type oxygen electrode with excellent electrode performance and operating performance.

[Means for Solving the Problems] The gas diffusion type oxygen electrode according to claim (1) includes a gas co-supply layer containing carbon and polytetrafluoroethylene, and a reaction layer containing carbon, polytetrafluoroethylene and an oxide catalyst. The gas diffusion type oxygen electrode is characterized in that a belobus-kite type oxide catalyst having the following composition is used as the oxide catalyst.

Lad-x Ca, Mn03 (however, 0.05≦X≦0.9) The gas diffusion type oxygen electrode according to claim (2) includes Lad-, Ca, Mn03 as the oxide catalyst in the gas diffusion type oxygen electrode.
It is characterized by using a perovstite-type oxide catalyst represented by CaO2 (0.05≦y≦0.9).

The present invention will be explained in detail below.

The gas diffusion type oxygen electrode of the present invention uses Lad-xCaxMnO3 (however, 0.05≦X≦0.9) or La + -y Ca y Co O3 (
However, it has the same structure as the conventional gas diffusion type oxygen electrode shown in FIG. 1, except for using a perovstite type oxide catalyst represented by the following formula (0.05≦y≦0.9).

In addition, the Ca substitution rate of the above-mentioned oxide catalyst affects the battery performance, and when the oxide catalyst is L a I-g Ca 11 M n O3, especially 01≦X≦0.3, especially 0.15≦X It is preferable that ≦0.25. Moreover, the oxide catalyst is Lad-,
In the case of CayCOO3, it is particularly preferable that 0,3≦y≦0,5. These oxide catalysts may be used alone or in combination of two types.

If the content of the above-mentioned oxide catalyst in the reaction layer is too small, a sufficient catalytic effect will not be obtained, and even if it is used in excess of a predetermined amount, a commensurate improvement effect on electrode resistance will not be obtained; When a large amount of oxide catalyst is used, the fine structure inside the electrode may change, and the electrode resistance may deteriorate. For this reason, the content of the oxide catalyst is preferably in the range of 10 to 60% by weight, particularly 20 to 30% by weight.

If the content of Teflon in the reaction layer and gas supply layer is too low, the binding of the electrode will deteriorate; on the other hand, if it is too high, 7F
The resistance of the L pole becomes high and the gas diffusivity becomes poor. Therefore, the Teflon content is preferably in the range of 10 to 40% by weight, particularly 20 to 30% by weight in the reaction layer, and 18 to 28% by weight in the gas supply layer.

The gas diffusion type oxygen electrode of the present invention uses carbon and Teflon as the gas supply layer, raw material powder mixed with carbon, Teflon, and an oxide catalyst as the reaction layer, and these two layers are combined with
It can be easily produced by a method such as hot pressing with an i-mesh.

Note that the raw material powder for each layer can be prepared, for example, as follows.

■ Add carbon black to the butanol aqueous solution of raw material powder for the gas supply layer and mix. After dispersing Teflon in this, it is filtered, dried and pulverized (butanol dispersion). Alternatively, a Triton aqueous solution can be used as a mixed system. In this case, it is necessary to perform heat treatment after pulverization to sufficiently remove Triton.

■ The raw carbon powder for the reaction layer and the oxide catalyst were thoroughly mixed in an agate mortar, and the carbon black-Teflon mixed powder obtained by the method (■) was added, mixed in a liquid phase using butanol as a dispersant, filtered, and dried. After that, it is pulverized.

There is no particular restriction on the thickness of the gas diffusion type oxygen electrode of the present invention, but the thinner the electrode, the lower the electrode resistance and the better the performance tends to be. If the thickness becomes too thin, gas oil and liquid leakage will occur, resulting in a decrease in performance. Therefore, in each of the reaction layer and gas supply layer of the TL pole, the amount of raw material powder used for hot pressing is about 5 to tsmg/cm'' per unit area, and especially in the reaction layer, the amount of raw material powder used for hot pressing is about 10 to 12 mg/crn', and the amount of gas Preferably, it is about 9-11' mg/c rn' in the feed layer.

The method for producing the oxide catalyst used in the present invention will be explained below.

Although there are no particular restrictions on the method for producing the perovstokite-type oxide catalyst of the present invention, it can be produced, for example, by the following method (1) or (2).

■ Acetate decomposition method (AD method) (see Figure 2) After evaporating, drying, and decomposing a mixed aqueous solution of each metal acetate with a predetermined molar composition ratio, it is calcined in air at approximately 850°C for approximately 10 hours. .

■ Citric acid precursor method (ACP method) (see Figure 3) After dehydrating and drying a mixed aqueous solution of metal nitrate and citric acid with a predetermined molar composition to obtain an amorphous citric acid precursor,
This is baked in air at about 650°C for about 2 hours.

Particularly, in the present invention, by using a perovstite type oxide catalyst prepared by the ACP method described in (1), a remarkable effect of improving the current density can be obtained. This is A
This is thought to be due to the fact that the calcination temperature of the catalyst prepared by the CP method is about 200° C. lower than that of the AD method, so the surface area is larger and the catalytic activity is higher.

[Function] It is known that in the reduction of oxygen in an alkaline aqueous solution, a four-electron reaction of the following formula (I) and a two-electron reaction of the formula (II) that produces HO2- occur. The generated HO2−
is electrochemically reduced as in formula (III), or
Alternatively, it is catalytically cracked by a catalyst as shown in formula (IV).

02 +2H20+4e-40H-...(1) 02 + H20+26 = HO2-+ OH-...
・(+1) HO2-+ H20+ 2 e = 30 H-...
(III) 2HO2--20H-+02 ・= (IV) The perovstite-type oxide catalyst used in the present invention not only has high activity for the four-electron reduction formula (I) of oxygen, but also has (+'V) Since the hydrogen peroxide decomposition activity of the formula is also high, it is possible to provide a gas diffusion type oxygen electrode having an extremely high current density and excellent electrode performance.

Furthermore, the addition of this perovstite type oxide catalyst greatly improves the durability of the electrode, providing a gas diffusion type oxygen electrode that can operate stably for a long period of time and has extremely excellent operating characteristics.

[Example] The present invention will be described in more detail below with reference to Production Examples, Examples, and Experimental Examples.

Production Example 1: Production of Raw Material Powder for Gas Supply Layer Carbon black, n-butanol, and water were added at a ratio of 1:1:30 (weight ratio) and mixed for 60 minutes using a starter. Teflon was dispersed therein, and after suction and filtration, it was dried at 120° C. for one day and night. This material was pulverized using a mixer to produce a raw material powder with a Teflon content of 23% by weight.

Production Example 2: Production of raw material powder for reaction layer Carbon black and each of the oxide catalysts shown in No. 1 to 4 in Table 1 below were thoroughly mixed in an agate mortar.
Carbon-Teflon raw material powder obtained in the same manner as in Production Example 1 was added, and liquid phase mixing was carried out using n-butanol as a dispersant.
After being filtered and dried, it is pulverized in a mill to obtain a raw material powder (with a Teflon content of 25% by weight and an oxide catalyst content of 25% by weight).
Nos. 1 to 4) were manufactured.

In addition, a raw material powder without catalyst addition (No. 5) was also produced in the same manner.

Table 1 Oxide Catalyst Production Example 3: Production of Gas Diffusion Type Oxygen Electrode The gas obtained in Production Example] was supplied to the hot press molding machine shown in Figure 4, which was made by wrapping a ribbon heater around a 30 mm diameter tablet molding machine. Raw material powder for layer 10 mg/c
Fill rn' with Subatsu Teira and raise it to 360℃ using a ribbon heater (150W). (approx. 1 hour), 424k
A film of about 0.20 mm of the raw material powder for the gas supply layer was created by hot pressing with H/crn'. Next, this film was cut to a predetermined size, and the reaction layer raw material powder NO,I~s (t 1 mg/crn") obtained in Production Example 2 was placed on top of the film.
and Ni mesh, respectively, again at 360°C and 566°C.
Hot pressed at kg/c. Thereafter, the electrodes were taken out after being air-cooled with a hair dryer.

In the figure, 10 is the sample, 11 is the piston, 12 is the cylinder, 13 is the ribbon heater, and 14 is the AC power supply (to
ov) 15 is a thermocouple.

The obtained gas diffusion type oxygen electrode is made of N, as shown in Figure 1.
Gas supply F12 with i-mesh 4 and reaction layer 3 2
It has a layered structure, the thickness of the gas supply layer 2 is 0.2 mm, the thickness of the reaction layer 3 is 0.2 mm, the total thickness t is 0.4 mm, and the length is 15 mm.

Example 1 Each electrode obtained in Production Example 3 was set as shown in Figure 5, and heated in 30 wt% KOH at room temperature (25°C) using a boranediostat while oxygen gas was flowing from the back side. Current density was measured.

In addition, in FIG. 5, 20 is a gas diffusion type oxygen electrode, 21.2
2 is a Teflon holder, 23.24 is an O-ring, 25
is copper wire.

The results are shown in FIGS. 6 and 7.

As is clear from FIGS. 6 and 7, the perovstite-type oxide catalyst of the present invention provides excellent electrode performance. In particular, the perovstite type oxide catalyst produced by the ACP method has a current density that is about four times higher than that of the oxide catalyst produced by the AD method, and excellent electrode performance can be obtained.

Experimental Example 1 The BET surface area was measured for each of perovstite type oxide catalysts No. 1 (ACP method), t No. 2 (AD method), No. 3 (ACP method), and No. 4 (AD method). The results are shown in Table 2.

As is clear from Table 2, both Mn-based and Co-based A
It is recognized that the BET surface area of the catalyst prepared by the CP method is about 9 times larger than that of the AD method, and therefore the catalyst activity is higher.

Example 2 Regarding LaCaCo-based perovstite type oxide catalysts, oxide catalysts were prepared by changing the amount of Ca substitution, and electrodes were manufactured in the same manner as in Production Example 3, and electrodes obtained from each oxide catalyst were prepared. The electrode performance was investigated.

The value of X and current density in Lad-XcaxCo03 (
-125mV vs. Hg/Hgo) is shown in FIG.

As is clear from FIG. 8, in the LaCaCo system, the current density is high in the range of Ca substitution amount x=0.2 to 0.6, and reaches a maximum value at x=0.4.

The performance of this and the end is very high, in terms of RWE, +O,
A high current density of 2.5 A/crn' was obtained during SV.

Experimental Example 2 It is known that when electrochemical reduction of oxygen occurs on carbon, hydrogen peroxide is easily generated due to two-electron reduction. Therefore, when producing an electrode based on carbon, the hydrogen peroxide decomposition activity of the electrode catalyst is extremely important.

Then, using a device like the one shown in Figure 9,
Hydrogen peroxide (I
(202) Degradation activity was measured.

That is, - First, in the Erlenmeyer flask 31, 9 mou/d m'
Approximately 0.02% by weight of oxide catalyst in NaOH aqueous solution
The dispersed liquid 30 was put thereinto, and a 2% by weight hydrogen peroxide solution 32 was dropped into it using a dropping funnel 33. Is this Erlenmeyer flask 31 1ffl? The liquid 30 was placed in an H tank 34 and maintained at 80°C, and the liquid 30 was stirred with a magnetic stirrer 35.

At this time, the generated oxygen is transferred to a container containing water 36 (300
0 cm) 37, water was sent to the graduated cylinder 38, and the rate of oxygen production was measured by a gas replacement method to determine the H2O2 decomposition activity per 1 g of oxide catalyst.

The results are shown in FIG.

As is clear from FIG. 10, the maximum value is reached when the H2022 decomposition active Ca substitution amount x=0.4. This tendency can be seen in Example 2
It corresponds well with the electrode activity result of 8202 of the catalyst.
It is clear that the decomposition activity greatly influences the electrode performance.

Example 3 In Production Example 3, Lao,s produced by the ACP method
A short-term continuous test was conducted at 300 m A / 300 m A / for an electrode manufactured using Cao, 4 COO3 (No. 3) and an electrode manufactured in the same manner without adding a catalyst (No. 5).
The test was carried out at a constant current density of cm', and the change in potential over time was investigated.

The results are shown in FIG.

As is clear from Figure 11, no catalyst added (NO, 5)
The electrode was made of the LaCaCo0a-based catalyst of the present invention (No. 3
), the electrode performance was considerably inferior to that of the electrode with the addition of 30%, and a decrease in potential was observed after 30 hours. On the other hand, the electrode to which the oxide catalyst of the present invention was added continued to be measured.
It operates extremely stably even after hours.

[Effects of the Invention] As detailed above, the gas diffusion type oxygen electrode of the present invention provides a high-performance gas diffusion type oxygen electrode with extremely high electrode activity, operating characteristics, etc., and excellent electrode performance and durability. be done.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the configuration of a gas diffusion type oxygen electrode;
3 and 3 are system diagrams showing a method for preparing an oxide catalyst, FIG. 4 is a schematic cross-sectional view showing an example of the hot press method, FIG. 5 is a schematic cross-sectional view showing a method for measuring electrode characteristics, and FIG. 6 and 7 are graphs showing the results of Example 1, FIG. 8 is a graph showing the results of Example 2, FIG. 9 is a schematic cross-sectional view showing the apparatus of Experimental Example 2, and FIG. 10 is a graph showing the results of Example 2. A graph showing the results of Experimental Example 2, and FIG. 11 is a graph showing the results of Example 3. 1... Gas diffusion type oxygen'gjL pole, 2... Gas supply layer, 3... Reaction layer.

Claims (2)

[Claims] (1) In a gas diffusion type oxygen electrode comprising a gas supply layer containing carbon and polytetrafluoroethylene and a reaction layer containing carbon, polytetrafluoroethylene and an oxide catalyst, a perobst having the following composition as an oxide catalyst A gas diffusion type oxygen electrode characterized by using a kite-type oxide catalyst. La_1_-_xCa_xMnO_3 (0.05≦x≦0.9) (2) In a gas diffusion type oxygen electrode comprising a gas supply layer containing carbon and polytetrafluoroethylene and a reaction layer containing carbon, polytetrafluoroethylene and an oxide catalyst, a perobst having the following composition as an oxide catalyst A gas diffusion type oxygen electrode characterized by using a kite-type oxide catalyst. La_1_−_yCa_yCoO_3 (however, 0.05≦y≦0.9)