Cell arrangement for a filter press type stack of cells

An electrical contact to a porous metal layer forming an anode of a diaphragm cell in a stack of such cells, is established by sintering a plurality of metal platelets into the porous metal layer. Preferably, the sintering-in of the platelets takes place simultaneously with the sintering of the porous metal layer. Each platelet is provided with an electrical contact metal pin extending out of the porous metal layer.

FIELD OF THE INVENTION 
The invention relates to a cell arrangement for a filter press type stack 
of cells. More specifically, the invention relates to an anode 
construction for such a cell for supplying electrical current to the 
porous anode of a bi-polar plate forming such a cell, for example, in a 
stack of cells arranged in a filter press type stack, whereby the anode is 
a porous metal layer formed by reduction sintering of a metal oxide 
coating or layer. 
DESCRIPTION OF THE PRIOR ART 
The electrodes of conventional bi-polar plates or cells suitable for such a 
cell stack are formed by screen or perforated sheet metal members, whereby 
an electrical contact for the current supply may be formed either by point 
welding or by pressing a contact element against the screen or perforated 
member. 
German Patent Publication (DE-OS) No. 3,224,555 discloses the production of 
porous metal layers by a reduction sintering of a metal oxide layer to 
form electrodes. It has been found that it is possible to assure a 
sufficient current supply and also a satisfactory current distribution in 
connection with such electrodes by merely pressing one or several 
distributed contacts against such a porous metal layer forming a cathode. 
However, in connection with porous metal layers which were produced by a 
reduction sintering to form an anode, a satisfactory current supply and 
distribution is not possible. 
OBJECTS OF THE INVENTION 
In view of the foregoing it is the aim of the invention to achieve the 
following objects singly or in combination: 
to provide a bi-polar plate or cell with such an anode structure that a 
satisfactory current supply and distribution is achieved even if the anode 
is produced by a reduction sintering of a metal oxide layer; 
to provide a cell structure suitable for stacking in the manner of a filter 
press stack while assuring a satisfactory current supply to all anodes in 
the stack; and 
to provide a method for producing such an anode construction. 
SUMMARY OF THE INVENTION 
According to the invention a cell arrangement for a filter press type stack 
comprises a diaphragm, a porous metal layer forming an anode on one side 
of the diaphragm, a cathode on the opposite side of the diaphragm also in 
the form of a porous metal layer, and means for supplying electrical 
current to the anode including at least one metal platelet sintered into 
the porous metal layer forming the anode. Thus, the anode construction 
according to the invention includes a porous metal layer which is formed 
by a reducing sintering from a metal oxide layer, and at least one metal 
platelet sintered into the porous metal layer, preferably together with 
the sintering of the metal oxide layer forming the anode. 
According to the invention the anode with its current supply means is 
formed as follows. A first coating of a reducible metal oxide is applied 
to one surface of a diaphragm. At least one conductor metal platelet is 
inserted into the first coating or into the recess or recesses. 
Thereafter, the conductor metal platelet or platelets on or in the first 
coating are covered with a sinterable second coating which, at least after 
the sintering, becomes electrically conducting. Preferably, but not 
necessarily, at least one recess is formed in the first coating which will 
be transformed into a porous metal layer to form the anode. A plurality of 
such recesses may be provided in the first coating. In the last step the 
first and second coatings are simultaneously sintered to form the porous 
metal layer as the anode and to simultaneously bond the conductor metal 
platelets to the anode and to simultaneously bond the conductor metal 
platelets to the anode or into the recesses of the anode, whereby a good 
electrical contact surface for the platelets and thus for the anode is 
achieved. 
By embedding the conductor metal platelets and/or by sintering the 
conductor metal platelets into the porous anode layer, during the 
reductive sintering of the porous anode layer, a crystalline metallic 
bonding is achieved between the porous anode layer and the metal platelet, 
whereby good electrical contacts result for the anode because the 
formation of a high ohmic resistance as a result of a barrier oxide layer 
between the porous anode layer and the metal platelet is prevented. 
By giving the metal platelets a polygonal configuration, preferably a 
star-shape, an improved current distribution is achieved, whereby any 
voltage drop across the anode is further reduced. Thus, according to the 
invention, very high currents may be introduced into the anode even if the 
anodes are rather thin, for example having a thickness of about 0.2 to 
about 0.5 mm. Such anodes in the form of sintered metal electrodes are 
used for the advanced alkaline water electrolysis and in fuel cells, for 
example.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE 
OF THE INVENTION 
Referring to FIG. 1, the stack comprises a plurality of bi-polar cells 1 
arranged between end plates 2 and 3. The end plate 2 forms an anode since 
it is connected through a copper rail 4 to the positive terminal of a d.c. 
power supply not shown. The end plate 3 forms a cathode connected through 
a copper rail 5 to the negative terminal of the d.c. power supply. 
Spacings 15 are provided between neighboring cells 1 and between the end 
plates and the respective neighboring cell. Contact improving perforated 
contact members 11 in the form of corrugated sheet metal members are 
inserted in these spacings. 
Referring to FIGS. 2 and 3, the contact corrugated sheet metal members 11 
have perforations 14 arranged in valleys 12 between ridges 13. 
Each bi-polar plate or cell comprises a diaphragm 6 in the form of a 
cermet, a cathode 7, and an anode 8 in the form of porous metal layers 
formed by a reducing sintering of a metal oxide layer or coating. 
According to the invention polygonal, for example star-shaped conductor 
metal platelets 9, are embedded in the anode layer 8. Each platelet is 
provided with a contact pin 10 which is secured in a conventional manner 
to the platelet, for example by brazing, or as a result of the sintering. 
The sheet metal corrugated contact member 11 contacts with its valley 
bottoms, the anode 8, whereby the contact pins 10 of the platelets 9 
extend through the perforations 14. The pins 10 fit snuggly into the 
perforations 14 to provide a good electrical contact. The ridges 13 then 
contact the neighboring cathode 7 of the neighboring cell in the stack. 
Preferably, the pins 10 are welded to the member 11 after the member 11 is 
placed in position with the pins extending through the apertures 14 to 
further improve the electrical contact. The sheet metal member 11, due to 
its corrugation, has a certain springiness to assure a good electrical 
contact between neighboring anodes and cathodes in the stack. The above 
mentioned spacings 15 in which the contact sheet metal members 11 are 
received, provide also space for the electrolyte. 
The anode 8 is formed, for example, by applying a reducible metal oxide 
paste to one surface of the diaphragm layer 6, whereby a screen printing 
method may be used. The screen printing is performed according to the 
invention in such a way that preferably recesses are formed in the metal 
oxide layer for receiving the conductor metal platelets 9. The recesses 
will have the same configuration as the polygonal configuration of the 
platelets, for example, in a star-shaped configuration as shown in FIG. 2. 
Such screen printing may be directly applied to the diaphragm layer 6. 
After the platelets 9 have been inserted into the recesses of the screen 
printed metal oxide layer, the platelets 9 are also covered with a second 
sinterable metal coating or with a second sinterable metal oxide coating, 
such as a metal oxide paste so that in the subsequent reducing type of 
sintering a homogeneous bonding between the anode layer 8 and the 
platelets 9 is assured. The reducible metal oxide paste of the above 
mentioned first coating and the second sinterable metal coating comprise a 
metal selected from the group including metals from the first, second, and 
eighth subgroup of the periodic table. The second coating may also be a 
metal oxide which is reducible by the sintering step. A metal powder or 
metal oxide powder may be used for the second coating. Reducible metal 
oxides such as nickel oxide, cobalt oxide, and iron oxide are suitable and 
so are mixtures of these metal oxides. 
The configuration and distribution of the metal platelets 9 in the anode 
layer 8 depends on the desired current density and/or the desired current 
distribution. For example, the metal platelets 9, as shown in FIGS. 2 and 
3, may, for an improved electrical contact, be connected to the sheet 
metal member 11 through the mentioned contact pins 10. However, such 
contact pins are not indispensible. It is also possible to contact the 
metal platelets 9 directly with the contact member 11. For this purpose, 
certain surface portions of the platelets 9 are not coated with the metal 
coating or with the metal oxide paste coating so that a sufficiently good 
electrical contact may be achieved by simply pressing the contact sheet 
metal member 11 onto these uncoated portions of the platelets 9. 
Although the invention has been described with reference to specific 
example embodiments, it will be appreciated, that it is intended to cover 
all modifications and equivalents within the scope of the appended claims.