HU207612B - Primary or rechargeable closed electrochemical cell - Google Patents

Abstract

In rechargeable or primary, electrochemical cells, hydrogen may evolve. The invention concerns the use of an auxiliary electrode material to catalyse the recombination of pressurized hydrogen, for example, hydrogen at pressures ranging from 5 to 15 psig up to pressure relief of the cell. The cell is a sealed cell having a metal oxide cathode (12), a zinc anode (14) and an aqueous alkaline electrolyte contacting both anode and cathode. The auxiliary electrode material, which may be mixed with the cathode material or be formed into a discrete auxiliary cathode (28), comprises a porous substrate for the absorption of pressurized hydrogen by the electrolyte. The substrate may be carbon, graphite or metal. The catalyst may be carbon, catalytically active noble metals, salts or oxides of lead, nickel, titanium, lanthanum, chromium, tantalum, and alloys of the metals, or mixtures of carbon with the salts or oxides.

Description

Danubia Patent and Trademark Office Ltd., Budapest (54) Primary or rechargeable sealed electrochemical cell (57)

BACKGROUND OF THE INVENTION The present invention relates to a primary or rechargeable electrochemical cell having a manganese dioxide cathode, a zinc anode, and an aqueous alkaline electrolyte in contact with the anode, in which hydrogen can be generated during operation and a cathode is provided in the cell. The auxiliary cathode material according to the invention has a porous support and a catalyst which absorbs hydrogen under pressure in the presence of an electrolyte, and the auxiliary cathode material is partially wetted and the auxiliary cathode material and the cathode are in direct contact. The support may consist of carbon, graphite or metal, and the catalyst may be a catalytically active noble metal, or a salt or oxide of lead, nickel, titanium, lanthanum, chromium, tantalum or their alloys, or mixtures of carbon with precious metal oxides or salts.

The sealed cell has a manganese dioxide cathode (12), a zinc anode (14), and the auxiliary cathode material may be mixed with the cathode material or formed as a separate auxiliary cathode (28).

CU

HU 207 612

Description: 8 pages (including 2 pages)

HU 207 612 Β

The present invention relates to a primary or rechargeable sealed electrochemical cell, such as an alkaline zinc manganese dioxide cell, having a cathode, a zinc anode and an aqueous alkaline electrolyte in contact with the anode and cathode in which hydrogen can be generated during operation. More particularly, the present invention relates to porous electrodes useful in the cathode of fuel cells, wherein a catalyst is provided with a porous electrically conductive support for reabsorption of hydrogen.

Many people have been addressing the problem of reducing or avoiding water loss in galvanic cells using aqueous electrolyte to prevent excessive gas pressure in the sealed cell. During charging or standby, many electrode materials, such as aluminum, magnesium, zinc, iron, lead, and so on. is accompanied by the development of hydrogen gas. Generally, the electrodes are not capable of recombining the resulting hydrogen, so the gas is removed, which results in water loss and, in the case of hermetically sealed cells, the internal pressure is increased. In closed cells, depending on the rate of gas evolution and the amount of hydrogen, high gas pressures can occur which can break the safety valve and result in electrolyte loss, resulting in cell failure or at least electrolyte leakage. It has been previously found that cells having a porous manganese dioxide cathode are capable of recombining hydrogen when catalytically active substances are added to the cathode electrode.

Attempts to overcome this problem have two main approaches:

1. Hydrogen and oxygen are catalytically recombined inside or outside a battery. In the latter case, it is ensured that the resulting water is recycled to the electrolyte compartment. Such solutions are disclosed in U.S. Patent Nos. 3,630,778 (1971), 3598653 (1971), 3622398 (1971), and 3701691 (1972).

2. Auxiliary (third) electrode is used as an overflow recombination reactor as described by P. Ruetschi and J. B. Ockerman in Electrochem. Technol. 4, 383 (1966).

U.S. Patent No. 4,242,384 to Kordesch et al. Discloses excellent hydrogen gas absorption properties of dry manganese dioxide powder catalyzed by salts or oxides of platinum, palladium, ruthenium, rhodium, arsenic and lead. However, the hydrogen uptake rate of these materials is not significant when used in wetted manganese dioxide matrix and at near atmospheric pressure.

In U.S. Patent No. 2,104,973, there is specifically a need to serially insert a resistor between the main electrode and the auxiliary electrode. U.S. Pat. No. 3,893,470 discloses the use of a hydrogen absorbent extruded material which is contained in a membrane impermeable to the electrolyte but permeable to hydrogen. In other words, the alkaline electrolyte cannot even partially moisten the auxiliary cathode material. British Patent No. 1226220, like US Patent No. 2104973, requires resistance between the main electrode and any auxiliary electrode. Even in the case of a non-linear characteristic, such resistance elements form a series impedance and adversely affect the operation of the auxiliary cathode. Finally, Japanese Patent Publication No. 5324539 relates specifically to zinc silver oxide electrolytic cells, whereas the present invention is directed to modified manganese dioxide zinc cells. The function of silver oxide-zinc cells is different from that of manganese dioxide-zinc cells, the difference being in lower cell voltage and different electrochemical processes.

It is an object of the present invention to recombine hydrogen produced during storage, charging and use with the active mass of the electrolyte. This allows you to avoid water loss and reduce the risk of overpressure in the cell.

Surprisingly, it has been found that many materials already used in electrochemical cells have a hydrogen recombination property when the gas pressure is increased (for example, in the range 35,000 to 105,000 Pa) and its potential is adjusted to that of the active manganese dioxide.

Accordingly, the present invention provides a primary or rechargeable sealed electrochemical cell having a manganese dioxide cathode, a zinc anode and an aqueous alkali metal hydroxide electrolyte in contact with the anode and the cathode in which hydrogen is generated during operation.

The cathode comprises a metal oxide and auxiliary cathode material, the latter being a porous support and a catalyst for absorbing hydrogen under pressure in the electrolyte. The auxiliary cathode material is at least partially wetted by the electrolyte due to its placement.

The support may be carbon, graphite or metal, and the catalyst may be a catalytically active noble metal, or a salt or oxide of lead, nickel, titanium, lanthanum, chromium, tantalum or alloys thereof, or a mixture of precious metal or carbon with salts or oxides of precious metals. Precious metals include platinum, palladium, ruthenium, rhodium or silver.

The auxiliary cathode material may be used, or by mixing it with a metal oxide jacket, preferably in a ratio of 30:70, or a separate auxiliary electrode may be provided which is electrically conductive in contact with the metal oxide cathode.

When the auxiliary cathode material is formed as a separate auxiliary electrode and the metal oxide cathode is cylindrically surrounded by an inner anode core, the auxiliary electrode is preferably ring or disc shaped in size and is in contact with one end of the anode.

The present invention provides an economical and efficient solution for removing hydrogen in galvanic cells. Precious metals such as platinum, palladium,

Radium, iridium, ruthenium and osmium have a high catalytic effect on the oxidation of hydrogen. In alkaline electrolytes, nickel and alloys of nickel with other metals (such as titanium and lanthanum) have been found to be active catalysts. Gas diffusion electrodes may also be used in the present invention. The use of such electrodes is particularly advantageous at higher recombination current densities.

The invention will now be described in more detail with reference to the drawings, in which: The drawing shows:

Figure 1 is a vertical sectional view of a first embodiment of the invention, a

Figure 2 is a vertical sectional view of another embodiment of the invention, a

Figure 3 is a diagram comparing the performance of known cells according to the present invention with that of Example 2, a

4 and 5

Figures 3 to 5 are diagrams comparing the performance of known cells according to the invention with that of Example 3.

Figures 1 and 2 show two different embodiments of the cell according to the invention. In either case, the housing of the cell is formed by a steel cup (10) with a metal oxide (12) of conventional design inside. The bulge (11) formed at the bottom of the cup (10) contacts the cathode cylindrical around the anode (14). The cathode (12) comprises finely divided manganese dioxide and graphite, which is separated from the anode (14) containing zinc dust by a separator (16) permeable to the electrolyte. The electrolyte, preferably an aqueous solution of potassium hydroxide, penetrates through the separator (16) into the zinc powder in the anode (14) and into the cathode (12).

As depicted in the drawing, the anode (14) is contained in a basket (18), and the basket (18) can be made of polyvinyl acetate, e.g. Optionally, the basket (18) may be used to accommodate an oxygen re-absorbing catalyst. The basket (18) is closed, for example, by a brass cap (20), which is separated from the bottom of the cup (10) by an insulating disk (15) on the islands. The cathode (12) is held in a cylindrical shape by a mesh and a sealing ring (23) made of plastic.

A current outlet pin 24 extends into the anode (14) through the cover (25), the head (26) of which is outside the cover (25) and forms the outlet of the anode. The cup (10) is sealed by the lid (25) since its end is bent by a flange.

Fig. 1 shows a separate auxiliary cathode disk (28) made of catalytically activated carbon located below the insulating disk (15) at the bottom of the cup (10).

Physical and electrical contact is formed between the auxiliary cathode disk (28) and the cathode (12), and the material of the cathode disk (28) is also wetted by the electrolyte in the cup (10).

The embodiment outlined in Figure 2 differs therein

Referring to Fig. 1, an auxiliary cathode ring (30) is located underneath the plastic sealing ring (23) instead of the auxiliary cathode disk (28). The auxiliary cathode ring 30 may comprise, for example, silver oxide and there is physical and electrical contact between it and the cathode 12 and the cathode ring 30 will be wetted by the electrolyte in the cup 10.

Each of the embodiments outlined in Figures 1 and 2 has a separate auxiliary cathode. If the auxiliary cathode material is mixed with the metal oxide jacket, the cell according to the invention will have the same configuration as outlined in FIGS. 1 or 2, but neither the cathode ring (28) nor the cathode ring (30) will be found. 12) cathode already contains auxiliary material.

Example 1

A conventional, refillable manganese dioxide zinc cell as described in U.S. Patent No. 4,384,029 was prepared using a metal cage to receive the active weight of the cathode. The cathode mixture was formed, pressed into rings, and placed into three cups with metal casing, sized to fit D-type cells, and centered in separator baskets (made of this type of polyvinyl acetate).

Cathode composition:

90.0 parts 84.11% EMD TRONA "D"

9.5 parts 8.9 wt% Lonza KS-44 graphite 7.0 parts 6.5 wt% 9 N potassium hydroxide 0.5 parts 0.5 wt% acetylene carbon

Total weight: 87.5 g

This known cell was modified according to the present invention by preparing a catalytically active cathode mixture by replacing 3, 12, 20 and 30 percent by weight of EMD (manganese dioxide) material with silver oxide, and then producing D-size cells in the peak range of the cell. the cathode material was enriched with 4 g of silver oxide.

The zinc anode gelled in the middle region was extruded and the cell was covered with a polyethylene disc through a current outlet made of a brass tap, and the cup was sprayed onto the disc for sealing.

Anode composition:

61.41% New Jersey 1205 zinc containing 3% mercury

2.0% Zinc Oxide (ZnO)

1.01% magnesium oxide (MgO)

0.8t% 70/30 CMC / 940

34.8% by weight of 9% KOH and 8% by weight of ZnO

Gross weight: 21 g

To demonstrate the hydrogen recombination properties of the present invention, a series of D cells containing 3, 12, 20 and 30% substituted EMD was subjected to a storage study at 65 ° C. Because of the high temperature, gas formation was felt, causing hydrogen to overpress in the cells. The test results are given in the table below:

3% Ag ₂ O 12% Ag ₂ O 20% Ag ₂ O 30% Ag ₂ O l.hét65 C 6/6 good 6/6 good 6/6 good 6/6 good Week 2 65 ° C 3/4 good 2/4 good 3/4 good 4/4 good Week 3 65 ° C 1/1 good 0 1/1 good 2/2 good

HU 207 612 Β

Typical cells with 0% Ag ₂ O had an error rate of 50% at 65 ° C after 2 weeks (in this case, the error means cell leakage), compared with an improvement in all substituted cells and no error at all in 30% substituted cells. It was not.

Example 2

A conventional porous manganese dioxide cathode used in primary alkaline or rechargeable alkaline manganese dioxide zinc cells was fabricated, pressed into rings, and three were placed into metal C-sized cups and placed in the center of the C-cell. A separator basket of the described material was introduced.

Cathode composition:

84.11% EMDTRONA "D"

8.9t% Lonza KS-44 Graphite

6.5% 9N potassium hydroxide 0.51% acetylene carbon black

Total weight: 37.5 g

This known cell was modified according to the present invention by preparing a catalytically active cathode mixture by replacing 0 and 30% by weight of EMD (manganese dioxide) with silver oxide, then producing C-size cells and 4 g of silver at the open end of the cell. oxide-enriched cathode ring was placed.

In order to illustrate the hydrogen recombination properties of the cell of the invention, two half cells were made from C-size cells, one with the catalytically active cathode ring and the other without. Both open cells were placed vertically in a tube, the negative electrode was filled with 9N potassium hydroxide to the height of the polyethylene spacer, and a spiral nickel wire was immersed in the electrolyte. The cells were galvanically discharged (at 50 mA for 20 hours) to remove 1 A of stored energy from the positive electrode (total capacity approximately 8 A). The cells were covered with a suitable cover, and then, through sealed tubing and flexible tubes, the cells were led to U-shaped tubes filled with water. After flanging, the cells became gas-tight and any pressure changes were detected with manometers.

Both cells were electroplated at 10 and 25 mA until the pressure reached 300 psi (3,000 Pa). Under normal atmospheric pressure, no detectable hydrogen recombination was observed in any of the cells.

Subsequently, the U-shaped tubes were replaced with a precision manometer (with a total gas volume of 2.0 ml at normal temperature and pressure) and both cells were filled at room temperature with a current of 50 mA until the cell pressure reached 210000 Pa. The positive electrode reaction involves the conversion of MnO (OH) _{2 to} MnO ₂ . and in the counter-reaction, hydrogen is formed on the surface of the nickel coil wire inserted into the negative electrode cavity. The evolution of hydrogen gas at a current of 50 mA occurred at a rate of 20 ml / h. The results are summarized in Figure 3.

Figure 3 shows the time evolution of hydrogen evolution and reflects that pressure in the conventional cell (diagram A) develops faster than that in Ag ₂ O. It also shows that the cell containing the catalytically active disk undergoes a significant degree of hydrogen recombination. After the power supply has been switched off, the pressure in the cell containing the active catalyst is reduced significantly faster than in the reference.

Example 3

A conventional porous manganese dioxide cathode used in primary alkaline or rechargeable alkaline manganese dioxide zinc cells was fabricated, pressed into rings, and three were placed into metal C-sized cups and placed in the center of the C-cell. A separator basket of the described material was introduced.

Cathode composition:

84.1% w / w EMDTRONA "D"

8.9t% Lonza KS-44 Graphite

6.5% 9N potassium hydroxide 0.5% acetylene carbon black

Total weight: 37.5 g

A gas diffusion electrode was prepared according to the present invention using a Pd / Rh blend as a reagent adsorbing hydrogen, and a 400 micron blend was prepared by mixing with a carbon blend of "Black Pearls 2000" and polytetrafluoroethylene to to get a foil. Alternatively, a carbon / poly (tetrafluoroethylene) film containing 70% carbon and 30% polytetrafluoroethylene was printed on one side with a separator sheet (type Dexter C1235) and on the other side with a nickel mesh. A 25 mm outer diameter ring and a 14 mm inner diameter ring were cut from the foil and this carbon ring was placed on top of the cathode so that the separator side faces the cathode. After placing the perforated polyethylene ring, the structure is pressed into the cathode bushing.

The purpose of the separator disk is to absorb the electrolyte, which promotes partial wetting of the carbon ring and creates ionic contact between the hydrogen and the manganese dioxide electrode. The carbon ring is electrically contacted with the metal sleeve and the metal cage and can thus be considered as a "hydrogen manganese short circuit element".

To illustrate the reabsorption of hydrogen, two C-size cells were prepared and one provided with a catalytic carbon ring and the other not. Both open cells were placed vertically in a tube, the cathode chamber was filled with 9N potassium hydroxide to the height of the polyethylene spacer, and a spiral nickel wire was immersed in the electrolyte as a counter electrode. The cells were galvanically discharged (at 50 mA for 20 hours) to remove 1 A of stored energy from the positive electrode (total capacity approximately 8 A). Sealed tube connections to the cell cover were mounted and connected to a manometer (their gas volume was 2 ml).

HU 207 612 Β

Both cells were electroplated at room temperature with a current of 50 raA. The positive electrode reaction involves the oxidation of MnO (OH) _{2 to} MnO ₂ . In the opposite reaction, hydrogen is formed on the surface of the nickel coil wire, which is inserted into the negative electrode cavity. The evolution of hydrogen gas at a current of 50 mA occurred at a rate of 20 ml / h. The resulting pressure curves are shown in Figure 4.

A cell containing a catalytically active ring as described above recombined the resulting hydrogen, thereby providing a cell volume of about 10%. maintained pressure at 28,000 Pa for four hours (curve D). With an overflow of 50 mA for 4 hours, the 3.5 cm ² disk has recombined more than 80 ml of hydrogen (normal temperature and pressure), keeping the pressure constant.

A current of 12 mA was passed through the cell for 12 hours, and the current was increased to 25.50 and 100 mA at 12 hour intervals. Figure 5 shows that, over a 48 hour period within which more than 900 ml of hydrogen was produced, the internal pressure of the cell remained below 75,000 Pa due to recombination.

The maximum recombination rate of hydrogen gas was above 145 mL of hydrogen per hour (with a 3.5 cm ² ring electrode) and was equivalent to a 100mA hydrogen generating current. For the type C cell used, this value is significantly higher than what may occur under "realistic conditions of use".

To study the long-term behavior of the electrode, the electrode described above was placed in a half cell and continuously operated at a current density of 50 mA / cm ² for more than 1000 hours. The test was terminated when the total hydrogen consumption exceeded 20 liters (normal temperature and pressure). The following table provides operational data when the electrolyte was 6N potassium hydroxide and the reaction gas was hydrogen at room temperature.

Time (Hours) Hydrogen Consumption (1) Current density (mA / cm ² ) Rb free potential (mV relative to Zn) 0 0 50 22 163 3.4 50 10 307 6.4 50 25 475 9.9 50 30 691 14.3 50 46 859 17.8 50 47 1003 20.8 50 49

The internal resistance (Rb) -free potential was measured in a standard laboratory method and expressed in mV relative to the reversible hydrogen electrode.

Claims (13)

PATENT CLAIMS A primary or rechargeable sealed electrochemical cell having a manganese dioxide cathode, a zinc anode, an anode and an aqueous alkaline electrolyte in contact with the cathode, wherein hydrogen is formed during operation and the auxiliary cathode material is present in the cell, the cathode material having a porous support and a catalyst which absorbs hydrogen under pressure in the presence of the electrolyte, and the auxiliary cathode material is at least partially wetted and the auxiliary cathode material and the cathode are in direct contact with each other. 2. A primary or rechargeable cell according to claim 1, wherein the hydrogen absorber catalyst has an active pressure range from 35,000 to 105,000 Pa. The primary or rechargeable cell of claim 2, wherein the auxiliary cathode carrier comprises carbon, graphite, or metal, and the catalyst is carbon, catalytically active metals, or lead, nickel, titanium, lanthanum, chromium, tantalum or the like. or alloys thereof, or a mixture of carbon and these metals, salts or oxides thereof. The primary or rechargeable cell of claim 3, wherein the catalytically active metal is a noble metal. The primary or rechargeable cell of claim 4, wherein the noble metal is platinum, palladium, ruthenium, rhodium, iridium, osmium or silver. The primary or rechargeable cell of claim 3, wherein the catalytically active metal is nickel or an alloy of nickel with lanthanum or titanium. The primary or rechargeable cell of claim 3, wherein the auxiliary cathode material is mixed with the manganese dioxide cathode. The primary or rechargeable cell of claim 4, wherein the amount of noble metal oxide in the cathode relative to the manganese dioxide is substantially 30:70. A primary or rechargeable cell according to claim 3, characterized in that the auxiliary cathode material is formed as a separate electrode and has an electrical contact between it and the metal oxide cathode. A primary or rechargeable cell according to claim 9, characterized in that the auxiliary active ingredient is a ring of a mixture of carbon with palladium and radium, which is located on the top of the metal oxide. 11. The primary or rechargeable cell of claim 1, wherein the manganese dioxide cathode is mixed with 5-201% of a graphite carrier. 12. The primary or rechargeable cell of claim 1, wherein the anode comprises zinc powder bound in the electrolyte gel. 13. The primary or rechargeable cell of claim 1, wherein the anode is a zinc powder paste. HU 207 612 ínin.Cl. ⁵ : Η 01 Μ6 / 04