DE1240571B - Method for reducing the polarization at a gas diffusion electrode in a fuel element and an arrangement for carrying out the method - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY Int. Cl .:

HOIm

! GERMAN

PATENT OFFICE

EDITORIAL

Deatsche Kl .: 21 b -14/01

Number: 1240571

File number: A41467 VI b / 21 b

Filing date: October 25, 1962

Open date: May 18, 1967

A fuel element for generating electrical energy by reacting between a continuously supplied fuel, e.g. B. hydrogen gas, and a continuously supplied oxidizing Substance, e.g. oxygen gas, air or halogen, in its simplest form can be derived from a liquid Electrolytes and two porous electrodes are made, one of which is between the electrolyte and the fuel and the other between the electrolyte and the oxidizing substance

The electrode reaction in the fuel elements takes place in the contact points between the electrolyte, Fuel and oxidizing substance and electrode. These contact points are at the points in the Pores of the electrodes where the electrolyte and fuel or oxidizing substance meet. the The result is that only a very small part of the pore area the electrodes are used for the reaction taking place there and the concentration polarization becomes significant.

The fuel can, however, also be dispersed or dissolved in the electrolyte. This is with elements the case for liquid fuel. Certain oxidizing agents, e.g. B. hydrogen peroxide, can be dissolved in the electrolyte. Combination forms between elements with gaseous and liquid fuel are also conceivable, e.g. B. fuel elements with a fuel that consists of dissolved Methanol and gaseous hydrogen gas are made up, both of which are attached to the porous fuel electrode react. In galvanic elements it was previously known to use polarization in porous electrodes Help an arrangement to diminish the continuous circulation of the electrolyte in one Direction worried.

The present invention relates to a method for reducing the polarization on the electrode and to improve the utilization of the pore surface of the electrode for the reaction which takes place there with a porous electrode in a fuel element, on one side of which a liquid electrolyte is arranged, at least partially the Fills pores of the electrode and passes through the pores of the electrode with one on the other side of the Electrode arranged, at the electrode reacting gas forms contact.

The method according to the invention is characterized in that that the electrolyte in the pores of the electrode with the aid of a pulsation device and is moved.

Electrolyte and gas form interfaces in the pores at least during the pulsation. If both methods of reducing polarization
on a gas diffusion electrode in one
Fuel element and an arrangement for
Carrying out the procedure

Applicant:

Allmänna Svenska Elektriska Aktiebolaget,

Västeräs (Sweden)

Representative:

Dipl.-Ing. H. Missling, patent attorney,

Giessen, Bismarckstrasse. 43

Named as inventor:

Dr. Olle Lindström, Västeräs (Sweden)

Claimed priority:

Sweden October 28, 1961 (10 738)

a5 fuel as well as oxidizer from an porous If there are gases located in the electrodes, the movement of the electrolyte at both can of course Electrodes take place at the same time. In the case where the fuel or oxidizer is in the electrolyte triggered, the described movement of the interface between electrolyte and gaseous Substance can only be made on the one electrode where gas is present. For these movements of the Electrolytes can be a pulsing device, e.g. B. a pulse generator can be used on the electrolyte compartment the fuel cell is connected. The pulse generator can consist of a piston, which gives the electrolyte a reciprocating motion in a cylinder, or from a Membrane that acts in an analogous manner on the electrolyte. By the movements of the electrolyte an effective stirring of the electrolyte takes place in the pores, which the conversion of in- and emerging reaction products accelerated in the pore system, so that the composition of the electrolyte in the pore system is kept more constant and the concentration polarization is reduced will.

When the interface between electrolyte and gas moves back and forth in the pores, comes an effect of particularly great importance is added. When the electrolyte is drawn from the pores,

709 580/96

3 4

namely, a liquid film remains on the surfaces part through the valves 12 and 13 for pressure

of the pore system of the electrode in question, the same container 14 out. When the

which is quickly saturated with the gas present. Piston 15 closes the check valve 12 and öff *

When the electrolyte is returned, the net will be the check valve 10. The throttle valve Ii

Removed reaction products, and the liquid film 5 is adjusted so that the electrolyte, which in the vpr-

is renewed when the electrolyte drops. With previous forward movement of the piston 15 in the

Using air as an oxidizing agent, electrodes have been pressed, thereby being sucked back

also achieved the particular advantage that. that will. A regulation of the differential pressure between

Nitrogen gas is vented out. the gas spaces 5 and 7 and the electrolyte space 4

The conditions for the pulsation depend in io can be established with pressure-sensitive organs 16 and 17

primarily on the diameter of the pores. The follow which are the mean value for the pressure differences

Pore diameters are often of the order of magnitude and the regulator valves 19 and 20 for the gas

1 to 30 μ. With these pore diameters, you can control the supply with. These are well-known pressure

Advantage of a pulsation with a frequency of 10 sensitive organs, which are preferably used

up to 200 vibrations per minute can be used 15 to generate a pneumatic or electrical safety

and such a large amplitude as to be given in consideration of the gnal, so that the pressure difference on elec-

Pressure drop, mechanical strength of the fuel transferring way to another organ that

cell, especially the electrodes, and the power requirement of the valves. In the one shown in the figure

for pulsation is possible. The amplitude for the arrangement is used by the pulsating device 9 at the same time

The pulsation is much greater than the pore size as a circulation pump for the electrolyte. the

knife. Electrodes 2 and 3 can be shaped so that

Several embodiments of the invention are pulsation mainly in the more reactive

in the following on the basis of the schematic drawing electrode takes place in that the resistance

described in more detail. In the drawing shows for the liquid flow in this lower

F i g. 1 an arrangement for carrying out the invention is made (larger pore diameter) than in FIG

according to the method in which the electrolyte between others.

see two porous electrodes arranged from In the case described above, the elec-

one of which on the outside in contact with trode2 consists of an active nickel electrode;

a gaseous fuel and the other to the in a known manner by pressing and sintering

Outside in contact with a gaseous oxy- 30 a powder mixture of 30 weight percent AIu-

dation agent stands, minium-nickel alloy, the same parts of the

F i g. 2 shows an arrangement in which the fuel contains both metals, and 70 percent by weight

Electrolyte is dissolved, one of which is made of carbonyl nickel, after which the sintered

Electrodes completely and the other partially filled, product by leaching out the aluminum with

where the oxidizing agent is activated in the form of a gas on an alkali, and in which the pores

the outside is arranged. have a diameter of about 2 to 4 μ and the

The fuel cell! contains according to FIG. 1 two porosity is about 50%. The electrode3 can

porous electrodes 2 and 3. Between the electrodes consist of a silver electrode, which in analog

the electrolyte is in the electrolyte compartment 4. and also, as is known, from a powder

Outside the electrode 2 there is a gas mixture made up of 30 percent by weight

space 5, which contains a gaseous fuel, the silver-aluminum alloy, the same parts of the

is supplied via the supply line 6. Outside contains both metals, and 70 percent by weight

the electrode 3 is also a gas carbonyl nickel is made and in which the pores

Space 7, which contains a gaseous oxidizing agent, have a diameter of about 3 to 5 μ and the

which is supplied via the supply line 8. The 45 porosity is about 50%. The electrolyte can run out

Pulsing will in principle consist of the pulsing device - potassium hydroxide solution, which contains 300 g of KOH per liter,

device 9 in conjunction with a non-return The operating temperature is about 80 ° C. The gas conveying

valve 10 and throttle valve 11 reached, both before moderate fuel can consist of hydrogen gas

the fuel cell are arranged, and with one and the gaseous oxidizing agent from oxygen

second check valve 12 and throttle valve 13, the 50 gas. The pulsation takes place at a frequency of

both are arranged behind the fuel cell. At 20 oscillations per minute and with one amplitude

the electrolyte space 4 of the fuel cell is a place that a mean shift of the boundary

Circulatory system 18 arranged, which has a vessel 14 for area in the pores of about 0.3 mm in each elec-

Contains pressure equalization and pressure maintenance. This trode corresponds.

Circulatory system contains the above-mentioned return 55 Instead of the fuel cell described

impact and throttle valves, and the Pulsiervorrich- according to Fig. 1, a fuel cell with Nickelelek-

Device 9 is used in a branch line 21 to this electrode. These are known in

arranges. The pulse generator can also be operated directly on the elec-

troly space 4 of the fuel cell has its own weight percent ammonium bicarbonate and 80 weight

connected. The liquid in the 60 weight percent carbonyl nickel, type B, at high

Circulatory system and the pulsing device is made the-temperature, after which a thin layer

same as in the fuel cell, i.e. H. the electrolyte. of carbonyl nickel, type A, on the pressed elec-

When the piston 15 of the pulsing device is in trode by a sedimentation process.

Moved towards the fuel cell, closes is brought. This gives a so-called double

the check valve 10 and opens the check 65 pelschichtelectrode in which the first made

valve 12. Due to the resistance in the throttle layer pores with a largest diameter of

valve 13 is a part of the pulsating volume about 30 μ and the last layer attached pores

picked up by the porous electrodes and has a largest diameter of about 16 μ.

To increase the conductivity of the oxygen electrode, it can be impregnated with a lithium compound. The fuel can be hydrogen gas . Each electrode is arranged so that the layer with the finer pores faces the electrolyte and the layer with the coarser pores faces the gaseous fuel or the gaseous oxidizing agent. The electrolyte can consist of potassium hydroxide solution, which contains 300 g KOH per liter. The operating temperature is around 200 ° C and the operating pressure is around 40 atm. The pulsation can take place with a frequency of 100 oscillations per minute and with an amplitude which corresponds to a mean displacement of the interface in the pores of about 0.3 mm in each electrode.

In the fuel cell in the arrangement according to FIG. 2, none is arranged in a gas space Fuel used. Instead, the fuel is dissolved in the electrolyte. The electrolyte fills up the pores in the electrode 2 completely and moves back and forth in the pores with the pulsation. Outside the electrode 3, a gaseous oxidizing agent is arranged in the gas space 7, as before. The electrode 2 can consist of a known platinized nickel electrode with a diameter of the pores of about 10 μ and the electrode 3 from the earlier described silver nickel electrode with a diameter the pores consist of about 3 to 5 μ. The gaseous oxidizing agent can be oxygen gas. The electrolyte can consist of a potassium hydroxide solution containing 100 g KOH per liter. In this is the fuel Methanol dissolved in a concentration of about 100 g / l. The operating temperature is appropriate 80 ° C. The pulsation can be carried out with a frequency of 60 oscillations per minute and with an amplitude corresponding to a mean displacement of the electrolyte in the pores of about 0.5 mm in the electrode 2 corresponds. After the fuel in the electrolyte has been consumed, will the electrolyte is replaced with a new and new fuel containing one.

If an acidic electrolyte is used instead of potassium hydroxide in the arrangement described last is, carbon dioxide formed in the arrangement 14 can be exhausted during operation of the fuel cell and fuel, d. H. in the cited case methanol, likewise in the arrangement 14 continuously are fed.

Following the description of FIG. Electrodes, fuels, oxidizers and electrolytes shown in FIGS. 1 and 2 are only examples of suitable material. It is evident that the invention can be used in all fuel cells with porous electrodes and liquid electrolytes in contact with a gaseous fuel or gaseous oxidizing agent.

Claims (4)

Patent claims: 1. A method for reducing the polarization at a gas diffusion electrode in a fuel element, which is in contact on one side with the liquid electrolyte and on the other side with the gas, characterized in that the (electrolyte in the pores of the electrode with the aid of a pulsing machine \ is moved back and forth. 2. The method according to claim 1, characterized in that the movement of the electrolyte in the pores of the electrode with a frequency of 10 to 200 oscillations per minute is carried out. 3. The method according to claim 1, characterized in that the pulsing device (9) acts on the electrolyte space (4) of the fuel element (1). 4. Arrangement for performing the method according to claims 1 to 3, characterized in that that a circulatory system (18) is connected to the electrolyte space (4), that the pulsing device (9) is connected to the supply line the circulatory system (18) to the electrolyte space (4) between the latter and a check valve (10) is connected that in the supply and discharge line of the circulatory system one check valve (10, 12) and one throttle valve (U, 13) are arranged in series with one another and that there is a pressure equalization tank (14) in the circulatory system. 1 sheet of drawings 709 580/96 5.67 © Bundesdruckerei Berlin