US2871179A

US2871179A - Electrolytic water decomposer

Info

Publication number: US2871179A
Application number: US574675A
Authority: US
Inventors: Zdansky Ewald Arno
Original assignee: Lonza AG
Current assignee: Lonza AG
Priority date: 1955-04-01
Filing date: 1956-03-29
Publication date: 1959-01-27
Anticipated expiration: 1976-01-27

Description

from these surfaces into the electrolyte,

United States ELECTROLYTIC WATER DECOFVIPOSER Ewald Arno Zdansky, Monthey, Switzerland, assignor t Lonza Elektrizitiitswerke und Chemische Fabriken A. G., Basel, Switzerland My invention relates to water electrolysers, and more particularly to water electrolysers of the so-callcd multicell filter-press type, consisting of a pack of consecutively arranged electrolysing cells, each of which being divided by a diaphragm into an anode chamber and a cathode chamber wherein each of said cells is enclosed by the adjacent halves of two metal frames, insulated one from another by a packing ring, and wherein each of said cells is separated from the foregoing and from the following cell by individual metal partitions, each of which partitions acting simultaneously as the anode of one cell and as the cathode of the following cell. Said metal partitions, therefore, are usually termed as bipolar main electrodes; as a rule they are associated with perforated auxiliary electrodes, arranged in a few distance of them on both sides and conductively connected with them by a plurality of metal bridge pieces.

It is an object of my invention to provide within such electrolyser an improved activating layer on the cathode surfaces, said layer reducing the voltage consumption of each cell.

A further object of my invention is to prevent such activating layer on the surfaces of the bipolar main electrodes and to restrict them on the surfaces of the abovenamed auxiliary electrodes.

A further object of my invention is to prevent a hydrogen production on the surfaces of the above-named bipolar main electrodes.

Other objects of my invention will appear from the following description, reference having had to the accompanying drawing.

Different methods are known to activate the electrodes of water electrolysers by the deposition of chromium, tantalum or sponge iron in such a manner that a reduction in the so-called overvoltage takes place. Particular importance is attached in this regard to a reduction of the so-called hydrogen overvoltage arising on the cathode surfaces.

Now we have found that surprising advantages can be obtained if such activation is restricted to the auxiliary electrodes and in particular to the auxiliary cathodes. This specifically reduces the liberation of hydrogen at the bipolarly active electrodes which simultaneously constitute the partition between adjacent cells in such a manner that these partitions are no longer exposed to embrittlement by the absorption of hydrogen. This increases their length of life and specifically in the case of pressure electrolysers leads to a very substantial increase in safety; these pressure electrolysers work at several atmospheres pressure and consequently demand higher security against cracking and gas penetration. The theoretical disadvantage that smaller electrode surfaces are available for the electrolysis has in practice been found negligible; the bipolar main electrodes are in series with an electrolytic path of current of greater length than the auxiliary electrodes, so that already for this reason only a relatively small current component passes If only the atent 2,871,179 Patented Jan. 27, 1959 auxiliary electrodes are activated, this current component becomes practically nil, but despite this diminution of the effective cathode surfaces, the voltage drop across the particular cell decreases under otherwise identical loading.

In order completely to suppress any diffusion of hydrogen into the so-called main electrodes (which in the arrangement according to the invention now act only as partitions) these can be nickel-plated onthe cathode side. As the negative overvoltage on a nickeled cathode is about 0.2 volt higher than on an iron cathode, it is certain that no current will any longer be able to pass from the bipolar main electrodes into the electrolyte.

The application of an activation layer restricted to the auxiliary electrodes is conveniently performed before assembling the cell; most suitably for this purpose the perforated sheet or wire mesh fabric constituting the auxiliary electrode is coated with a noble metal in an appropriate bath. The thus activated auxiliary electrodes can then be attached by spot welding to the contact lugs of the corresponding bipolar main electrode or alternatively placed loosely between the diaphragm and said main electrode; in either case any damage to the sensitive activating coating can easily be prevented.

The invention will now be further described with reference to the accompanying drawing which shows one embodiment by way of example.

Fig. .1 shows in side elevation part of a cell assembly or'pack. built up of consecutive disc-shaped individual cells.

Fig. 2 is'a sectional view showing the construction of the individual cells.

As appears from Fig. 1 the assembly of individual cells 1 is held by strong tierods 2 between an end plate 3 and a second end plate (not shown) of symmetrically identical shape. The cells 1 are traversed at the top by two consecutively parallel gas collector ducts of which the front duct 4 is connected by lateral openings with the cathode compartments K (see Fig. 2) of all cells. This duct or manifold 4 is in communication through a pipe 5 with a gas separator drum 6 which during working of the apparatus is filled with electrolyte up to about the level ab.

Electrolyte carried over by the issuing gas into the gas separator 6 is led through a non-return valve 7, a filter 8 and a pump 9 into a duct 10 which extends longitudinally through the cell assembly and the two ends of which are connected with pipes 10a and 10b. The gas evolved is drawn from the drum 6 (and a further drum for the separation of the oxygen lying concealed behind the drum 6 in Fig. 1) through valves which in known manner are so controlled or adjusted as to maintain in the cells 1 a constant pressure of for instance 25-30 atmospheres.

As shown in Fig. 2 the individual cells are formed by

annular frames

11 and 12, constituting together annular frame means, in each of which a separating plate or disc, 13 and 14, is fitted gastight, and which are electrically insulated from each other by a sealing ring or gasket 15. The disc shaped space of each cell is of a width Z which in practice is restricted to 8 to 15 millimetres. This is divided by a diaphragm 16 into a cathode compartment K and an anode compartment A; for better comprehension, both the diaphragm 16a of the preceding cell on the left, and the diaphragm 16b of the next cell on the right have also been shown. The electrodes are preferably formed of

wire mesh fabric

17 and 18 applied directly to the diaphragm 16 one on either side and the edges of which are gripped together with the edge of the diaphragm between the

frames

11 and 12; to atford space for this the

frames

11 and 12 are provided with corresponding steps or rebates the radial extension of which corresponds to the depth of the clamping region E within which the diaphragm 16 is dripped between the frames. The

sheet metal discs

13, 14 acting as dividing partitions between adjacent cells are each provided with a grid of

studs

19, 20 pressed out to projectalternately on each side of the disc and making contact with the adjacent electrodes of the consecutive cells. The sheet metal disc 13 thus connects by means of its studs 19 the anode 18a of the preceding cell on the left with the cathode 17 of the cell Z representedpsimilarly, the studs 20 on the sheet metal disc 14 connectthe anode 18 of the cell Z represented with the cathode 17b of the next'following cell.

In accordance with the invention only the auxiliary cathodes 17, 17b are activated, preferably by the application of a spongy "layer of noble metal; this is 'indicated-in Fig. 2by the dot-dashed lines P. Furthermore, the so-called bipolar main electrodes '19, 20, which in the actual case are better termed partitions, are coated on both sides, i. e. also on the side towards the cathode compartment K with a dense, firmly adhering plating of nickel. This nickel plating which is suitably applied galvanically is indicated in Fig. 2 by the broken lines N. I

What I claim is:

1. In an electrolytic water decomposer, a plurality of series connected decomposer cells each of which comprises, in combination, an outer annular frame means defining the outer periphery of said cell; a pair of spaced electrically conductive separating plates connected at-their peripheries to said frame means and defining saidcell between themselves, at least one separating plateof each cell also being a separating plate of an adjacent cell so that such separating plate is common to the two cells; a diaphragm connected at its periphery "to said frame means arating plates; and an activating coating covering only said anode .and cathode electrodes.

2. In an electrolytic water decomposer, a plurality of series connected decomposer cells each of which comprises, in combination, an outer annular frame means defining the outer periphery of said cell; a pair of spaced electrically conductive separating plates-connected at their peripheries to saidframe means and defining said cell .between themselves, at least one separating plate of each cell also being a separating plate of an adjacent cell so that such separating plate is common to the two cells; a diaphragm connected at its periphery to said frame means and located between said separating plates so as to divide said cell into anode and cathode chambers; anode and cathode electrodes located in said anode and cathode chambers, respectively, adjacent .said diaphragm and electrically connected to the respective separating plates; a nickel coating covering'both faces of each of said separating plates; and an activating coating covering only said cathode electrode.

References Cited in the file of this patent UNITED STATES PATENTS 22,070,612 Niederreither Feb. 16, 1937 OTHER REFERENCES The Chemical Age, Aug. 19, 1944, pages 173 .to 17.8. The Chemical Age, Aug. 26, 1944, pages 197 to 202.

Claims

1. IN A ELECTROLYTIC WATER DECOMPOSER, A PLURALITY OF SERIED CONNECTED DECOMPOSER CELLS EACH OF WHICH COMPRISES, IN COMBINATION, AN OUTER ANNULAR FRAME MEANS DEFINING THE OUTER PERIPHERY OF SAID CELL; A PAIR OF SPACED ELECTRICALLY CONDUCTIVE SEPARATING PLATES CONNECTED AT THEIR PERIPHERIES TO SAID FRAME MEANS AND DEFINING SSID CELL BETWEEN THEMSELVES, AT LEAST ONE SEPARATING PLATE OF EACH CELL ALSO BEING A SEPARATING PLATE OF AN ADJACENT CELLS SO THAT SUCH SEPARATING PLATE IS COMMON TO THE TWO CELLS; A DIAPHRAGM CONNECTED AT ITS PERIPHERY TO SAID FROME MEANS AND LOCATED BETWEEN SAID SEPARATING PLATES SO AS TO DIVIDE SAID CELL INTO ANODE AND CATHODE CHAMBERS; ANODE AND CATHODE ELECTRODES LOCATED IN SAID ANODE AND CATHODE CHAMBERS, RESPECTIVELY, ADJACENT SAID DIAPHRAGM AND ELECTRICALLY CONNECTED TO THE RESPECTIVE SEPARATING PLATES; A NICKEL COATING COVERING BOTH FACES OF EACH OF SAID SEPARATING PLATES; AND AN ACTIVATING COATING COVERING ONLY SAID ANODE AND CATHODE ELECTRODES.