Note: Descriptions are shown in the official language in which they were submitted.
~2~3~
The present invention relates to an electrolysis cell
for electrolytic processes that produce gas, in particular
for water and chlor-alkali electrolysis, using at least one
electrode with parallel electrode elements that form the
anode and the cathode.
Electrolytic processes that produce gas are extremely
important for the production of different and important
basic chemical materials such as caustic soda, chlorine,
hydrogen, or hydrogen peroxide. The electrodes that are
used during the electrolysis of alkaline solutions, water,
hydrochloric acid or sulfuric acid, which includes both
anodes and cathodes, must meet a number of service
parameters that are in part contradictory. A very important
demand is for the rapid removal of the gases that are
developed from the space between the anodes and the cathodes
in order to avoid a large build up of gas, which increases
the electrical resistance of the electrolyte. This,
however, is contrary to efforts to make maximally effective
use of the structural surfaces that are available for an
electrochemically effective electrode surface.
Furthermore, attempts are being made to arrive at the
most even and finely structured electrode surface that is
possible, in order to provide the conditions for an
homogeneous electrical field. Discontinuities such as, for
example, edges, lead to increases in the field strength and
thus to uneven loading of the electrodes, which causes not
only energy losses, but also premature wear of the electrode
material or the electro-catalytic coating.
Membranes or diaphragms are used to separate the gases
that form on the electrodes. These separator elements are
of relatively high ohmic resistance so that gas separation
is achieved at the cost of high energy consumption.
2 ~ ~ 2 7 ~, ~
An even and small distance between the electrodes is
also important for ensuring an optimal process without
imposing excessive mechanical stress when these membranes
are used, or even damaging them. It should also be ensured
that electrode elements that are of greater thickness do not
exert a high levsl of contact pressure on the membrane and
thus hinder the flow of electrolyte or the ion transport
through the pore system of the membrane.
Two important basic types of gas-generating metal
electrodes are known: first, one uses parallel profile rods
that are supported by current distributors, these being of
circular, tear-drop, or rectangular cross section (DE-OS
3008 116, DE-OS 3325 187, DE-PS 3519 272, DE-OS 3519 573).
However, U-shaped rails that are arranged in spaced rows, as
described in DE-AS 1271 093, are also known. On the other
hand, perforated sheets with vertical and horizontal slits
with segments that are angled with reference to the plane of
the electrode, or deep drawn, perforated sheet metal
electrodes, and metal mesh electrodes are also known (DE-PS
250 026, DE-OS 3625 506, DE-OS 2735 238).
Representatives of the first-named basic type use
electrode elements that are arranged in parallel, and which
are rigidly connected to the current distribution rails and
are of tear-drop cross section (DE-OS 3325 187) or an almost
circular cross section (DE-OS 3008 116). The circular cross
sections have been modified by removing segments that lie in
the plane of the electrodes. Both electrodes are intended
to be used preferably for chlor-alkali electrolysis in
amalgam cells. These electrodes display no significantly
reduced degree of coverage by gas bubbles. The gases are
carried off exclusively by fluid flow and buoyancy. The
particular cross section geometries are not suitable for
assuming an active role during the movement of gas through
the electrodes. It is true that they hinder any overloading
20~27 ?~
of the catalytic coating by avoiding discontinuities,
although this is done by accepting the disadvantages that
result from the uneven spacing of the electrode surfaces
that is caused by their radii.
DE-OS 3519 272 describes an electrode structure that
uses a plurality of parallel electrode elements of
rectangular cross section. A plate-like carrier with bulges
on both sides is used to secure the electrode elements and
as a current distributor. The cross section of the
rectangular electrode elements have in ratio of 1:5. In
order that the trails of gas that is removed do not come
into contact with each other in the area of the gap and
cause turbulence, there is a relatively large gap between
adjacent electrode elements. This leads to a relatively low
use of the available structural surface and to irregular
loading of the electrodes, in particular in the area of the
edges of the rectangular profiles, where increased wear of
the catalytic coating can be anticipated. The selected
shape of the carrier for the electrode elements, which is
simultaneously a current distributor, prevents the
concentration of gas in the space on the far side of the
reactive electrode surface. As a consequence of this, there
is a large amount of gas in the area of the reaction
surface, and there are associated increased electrical
losses.
The electrode that is described in DE-OS 3519 573 is
very similar to the electrode structure described
heretofore. This also consists of electrode elements of
rectangular cross section that are arranged parallel, and
arranged on a current distributor and the spaces between
these electrode elements is in the order of a few
millimetres. In addition, the face sides of the electrode
elements that face the membrane incorporate a plurality of
recesses. The bridge pieces located between these are not
- . .
2Q~27~9 :
electro-catalytically coated and lie upon the membrane.
Thus, the reactive surface that is available only amounts to
approximately 10 per cent of the membrane surface. Because
of the relative movement between the electrode and the
membrane, the bridge pieces can cause localized damage to
the membrane.
- It is an object of the present invention to develop an
electrolysis cell for electrolytic processes that generate
gas, which has significantly altered performance parameters.
It is intended to provide for greatly reduced ohmic power
losses and thus an increase of the specific electrical
loading of the electrodes. However, it is also intended
that the degree of gas enrichment on the electrode surfaces
be greatly reduced, despite the fact that more gas is
produced.
In particular, it is intended to achieve the following:
A reduction of the gas-bubble loading of the
electrolyte between the electrodes and of the degree of gas-
bubble coverage on the reaction surfaces of the electrodes;
The structure of the electrodes is intended to
ensure an appropriately directed movement of the gas during
the process;
Improvement of the ratio of active electrode
surface to the structural surface;
- A reduction of local increases in f eld strength
and the formation of an almost homogeneous electrical field
in order to even out the loading of the electrode surfaces
that are available for the reaction;
The new electrolysis cell is to have gas-
separating characteristics, which will render the use of gas
separating means (membranes, diaphragms, or the like)
unnecessary. When this is done, the spacing between the
electrodes is not to be increased.
According to the present invention, the electrode
elements are of a thickness that is up to three times the
average bubble separation diameter and forms a capillary gap
such that the direction of movement of the gas bubbles
through the electrodes lies essentially either in the
direction or the reverse direction of the electrical field
between the reaction surfaces of the anode and the cathode,
and in that the electrode elements incorporate profilings to
fix the capillary gap. The present invention is also
intended to include electrolysis cells that are built up
from electrode structures with quasi-parallel electrode
elements that form a capillary gap, such as this applies,
for example, to a spiral-wound electrode.
The bubble separation diameter is understood to be the
diameter of a bubble that leaves its formative nucleus under
the given actual process conditions, on an electrode of the
type according to the present invention. The bubbles that
move as a consequence of the adhesion on the electrode
surface are also to be regarded as bubbles that are leaving
their formative nucleus.
As is known, the separation diameters of the gas
bubbles depend to a very considerable extent on the type of
electrolysis and the conditions of the process. According
to Elektrochimika Acta, Vol. 33, No. 6, pp 769 to 779, 1988,
the following bubble diameters can be expected under the
usual conditions of electrolysis:
- for hydrogen: approximately 8 ~m
- for oxygen: approximately 17 ~m
- for chlorine: approximately 110 ~m
Proceeding from the area between the electrode
elements, an electrolysis cell according to claim 1 ensures
that the capillary effect of the electrodes also affects the
bubbles that are formed on the face surfaces, which are
,,
2 ~ 3 ~
mostly rounded, and this then draws them into the capillary
gap if a gap is left between the electrode and the membrane.
It is advantageous that the electrode elements are plates,
bands, or foils with a thickness of at most 450 ~m. The
width of the electrode elements is significantly greater
than their thickness and amounts to at least ten times the
width of the capillary gap. This creates a capillary system
that is effective in two dimensions in the electrode and
this in turn prevents the introduction of turbulence from
the degassing chamber of the electrolyte into the reaction
space between the electrode and the membrane. Thus any
effect on or disruption of the bubble formation process and
the movement of the bubbles into the capillary gap is
precluded. The movement of gas through the electrodes is
effected directionally, essentially transversely to the
plane of the electrodes over the very small distance
corresponding to the width of the electrode elements. The
cause for this is the considerable relative increase in the
volume of the reaction space as a consequence of the bubble
formation process. This leads to an increase of pressure at
this point and a displacement reaction. Electrolyte flows
through the capillary gap without any turbulence to the
reactive surfaces of the electrode to the same extent as the
gas is forced out of the reaction space and the electrode.
The high level of electrolyte exchange prevents ionic
depletion of the electrolyte, even in its boundary layer,
for the movement of liquid caused by capillary forces is
effected directly on the surface of the electrode. The
characteristic flow conditions in the capillary gap prevent
any vertical movement of the gas bubbles to a very large
extent.
Two versions of the electrodes have been found to be
particularly advantageous in order to realize the principle
of the electrolysis cell according to the present invention.
Thus, the alternating folding of continuous sheet material
~27~
permits economic production of capillary gap electrodes,
this being done, most expediently, after all the necessary
work processes such as perforation, profiling, and coating
have been completed in a continuous operation. It is
expedient that these perforations in the area of the fold
edges be evenly distributed. In order to fix the capillary
gap, the electrode elements incorporate profiling. Those
that have a structure that is web-like, and that is
transverse to the plane of the electrode, have also proved
satisfactory; button-surface profiles have also been found
to be useable. But stacking the electrode elements
according to the present invention is also suitable for
producing capillary gap electrodes. The profiling that is
produced in the original shaping process, or by subsequent
shaping, fixes the capillary gap and renders separate
spacers unnecessary.
The lower limit of the thickness of the electrode
elements is determined only by the mechanical stability and
ease of handling of the material, ease with which they can
be machined, which ultimately means the type of material.
In order to be able to exploit the advantages of the
new type of electrolysis cell to its fullest extent, it is
advantageous to seal off the electrode elements that border
the electrode at the sides and the lower end of the
electrode to the inner wall of the cell housing to form a
gap which at most corresponds to the capillary gap. In
addition, the degassing spaces in the upper area of the cell
are to be hermetically sealed by a bulkhead that reaches to
the lowest possible level of the electrolyte within the
reaction space. This prevents any mixing of the gases that
rise into the degassing spaces of the electrolysis cell. If
such a cell construction is used for water electrolysis,
which is to say in a process that requires no separation of
anolyte and catholyte the use of a gas separation system
~&2~
such as, for example, a diaphragm, may be unnecessary or it
may permit the use of a comparatively large-pored element
with a negligible ohmic resistance that, optionally, only
serves to fix the electrode spacing.
In order to prevent coagulation of the gas bubbles that
are formed on the electrode of opposite polarity, a gap that
is equal to at least three times the bubble separation
diameter is to be left between the electrodes. This feature
counteracts any contamination of the gas bubbles that rise
into the degassing spaces and the formation of a mixture of
gases in the reaction space by coagulation of the gas
bubbles.
An advantageous variation of the present invention for
use in water electrolysis, which is to say with identical
anolyte and catholyte, uses a dielectric distance piece that
is resistant to the electrolyte between the anode and the
cathode; in particular, this can be in the structure of a
net, honeycomb or a coarse fabric. Depending on its
thickness, this distance piece guarantees that the anode and
~0 the cathode can be spaced closely together without any
danger of short-circuiting. The great flexibility of the
electrode structure, which can be subjected to extremely
large mechanical loads, ensures electrode spacing that is
even on all sides. In addition, the reaction space is
divided into numerous small reaction cells by this distance
piece. For all practical purposes, no more disruptions
caused by flow conditions and no formation of mixed gas can
occur.
The advantages of electrodes made up of electrode
elements according to the present invention, with a
capillary gap arrangement, are as follows:
~ery little gas-bubble loading of the electrolyte
within the reaction space because of directional gas bubble
-- 8
2~2~
movement within the capillary gap electrode;
- Even and finely structured gas and liquid
permeable electrode structure at a high packing density;
- Because of the foregoing, even current loading and
utilization of the available reaction surface no local
erosion of the electrode surface or, in particular, of the
electro-catalytic coating;
- Mechanically loadable, nevertheless flexible,
electrode structure;
- No great demands with respect to evenness,
distortion, and the like.
The invention will now be described in more detail, by
way of example only, with reference to the accompanying
drawings in which:-
Figure 1 is a cross section through an electrolysis
cell with a capillary gap electrode according to the present
inventlon;
Figure 2 is a perspective and detailed drawing of twocapillary gap electrodes as cathode and anode with an
interposed separating element;
Figure 3 is an enlarged section A of figure 2 (scale
approximately 10:1);
Figure 4 is an enlarged section A of figure 2 (scale
approximately 20:1);
Figure 5 is an electrode coil element in section;
Figure 6 is a cross section through a capillary gap
electrode, consisting of a plurality of electrode coil
elements;
~Q~7~'~
Figure 7 is an enlarged perspective view of electrode
elements of undulating structure (scale approximately 10:1);
Figure 8 is a part of a capillary gap electrode (scale
approximately 10:1) formed from a foil material folded on
alternating sides, in an enlarged perspective view;
Figure 9 is a an enlarged section B of the capillary
gap electrode shown in figure 8;
Figure 10 is an enlarged perspective view of an
electrode element with horizontal bar-like profiling (on one
side);
Figure 11 is an enlarged perspective view of an
electrode element with essentially horizontal bar-like
profiling (on both sides);
Figure 12 is an enlarged perspective view of an
electrode element with local profiling that is made up of
non-directional, staggered button-like elements;
Figure 13 is a section of an electrode having
unprofiled and undulating electrode elements;
Figure 14 is an enlarged perspective view of an
electrode element with grooves arranged on both sides;
Figure 15 is an enlarged perspective view of an
electrode element with grooves arranged on one side; and
Figure 16 is a perspective detailed drawing of two
capillary gap electrodes as cathode and anode with an
interposed distance piece (scale approximately 1:1).
For reasons of clarity, Figures 2 to 16 show only the
-- 10 --
2~2~
electrode elements or the electrodes formed therefrom that
are used in an electrolysis cell.
As can be seen from Figures 1 to 8 and Figure 16, the
electrode is made up of parallel or quasi-parallel electrode
elements 1, la, 28, 29, the thickness 3 of these, and the
distance 4 between them, being one to two orders of
magnitude less than in known electrodes.
According to the present invention, the thickness 3 of
the electrode elements 1, la, lb, lc, ld, 15, 16, 28, 29,
30, 31, which can be bands, foils, or plates, amounts to at
most three times the mean bubble separation diameter.
Between the electrode elements 1, la, lb, lc, ld, 15, 16,
28, 29, 30, 31, there is a gap 4 that causes a capillary
effect. The electrode elements can be fixed to each other,
for example, by a plurality of wires that pass through the
electrode elements. Distance pieces that ensure the
capillary gap can be arranged on the wires between the
electrodes. The use of profiled electrode elements 1, la,
lb, lc, ld, 15, 16, 28, 29, 30, 31 is more advantageous.
These measures permit the simple manufacture of a capillary
gap electrode that is of easily adaptable width, and that is
simple to transport and install.
The production of electrode elements from glass-metal
foil bands that have been produced by the melt-spinning
process is particularly economical. They have smooth
surfaces and edges and are of a thickness 3 of 20 ~m to 100
~m. The preferred range of electrode element thickness lies
about 40 ~m; the bands are approximately 5 mm wide. When
some 40 electrode elements per centimetre are used, there is
an average capillary gap 4 of 200 ~m. An electrode made up
of a number of very flexible single elements represents a
structure that can withstand high mechanical loads and which
is nevertheless completely adaptable to a flat surface and
2 ~ 3? :~
which is in the form of a dense package. No great demands
with regard to flatness, distortion, and the like need be
imposed on these surfaces.
Figure 2 shows two electrodes 8 with electrode elements
1; of these, one forms the cathode and the other forms the
anode, with an interposed separating element 7 such as, for
example, a membrane in the so-called null interval. The
electrode structure permits a constant and small electrode
interval over a large area and this corresponds to the
thickness of the separating element 7. The adaptability of
the electrodes 8 also ensures an even distribution of
pressure across the separating element 7. This does not
restrict the ion flow or the flow of electrolyte, and it
also prevents the separating element 7 from becoming
damaged. The spaces that are adjacent to the electrode
surfaces that are remote from the separating element 7 serve
as degassing spaces for the electrolyte.
Figures 3 and 4 show, at larger scale, the detail
A of the electrode 8 in figure 1. The electrode elements 1
that are used have a thickness 3 of approximately 30 ~m and
a width 5 of approximately 5 mm. The capillary gap 4
between the electrode elements 1 is approximately 200 ~m.
The surfaces 2 of the electrode elements 1 (see figure 4)
represent the areas of high electrolytic reactivity. Their
mass-area conversion corresponds approximately to that on
the face surfaces of the electrode elements 1. These
surfaces 2, which are highly reactive and which play a
significant part in the conversion, extend transversely to
the plane of the electrodes at a depth that corresponds
approximately to the width of the gap 4. For purposes of
improved clarity, the width of the gap 4 has been increased
three-fold in comparison to the thickness and width of the
electrode elements 1.
2~7~
Figure 5 shows another variation of an electrode
structure with a capillary gap, which acts in the same way.
Because of the spiral winding of one pair of electrode
elements, consisting of a smooth electrode element 29 and an
undulating electrode element 28, this is a quasi-parallel
electrode structure. The desired capillary gap can also be
fixed by electrode elements that are profiled in a different
manner; this will be discussed below.
Figure 6 shows an electrode section that consists of a
plurality of electrode coil elements 53. This electrode is
enclosed by a current feed 51. The electrode coil elements
53 are supported by a current distributor 52. Any structure
that ensures sufficient electrical conductivity and which
can be mechanically loaded can be used as a current
distributor 52. In the simplest case, one can use a
perforated metal plate.
Figure 7 shows electrode elements la that are of
undulating structure. The axes 18 of their profiling are
inclined relative to the horizontal. By folding a foil 19
that is profiled in this way on alternate sides on its fold
axes 20 that lie on the vertical axis 17, the profiling on
adjacent electrode elements 15, 16 lie one on top of the
other in point contact. The perforations 21 that are
arranged along the fold axes 20 are of a width 22 that is
oriented to the width of the capillary gap 4 to the degree
of deformation of the foil 19.
Figures 8 and 9 show details of such an electrode. The
foil that is used has a thickness 3 of approximately 25 ~m;
the electrode elements la that are produced by the
alternate-sided folding of the profiled foil 19 have a width
5 of approximately 5 mm and fix the width of the gap 4 at
approximately 200 ~m. The surfaces 2 of the elements la
once again represent areas of a high level of electrolytic
- 13 -
~3~ 2 ~ ? ~
activity. Electrodes that are produced by perforation,
profiling, and folding, are rational to produce, easily
manipulated, and are of a very even and fine structure.
Whereas the electrode element lb that is shown in
figure 10 has horizontal ridge-like profiling 23 on only one
side, on the electrode element lc shown in figure 11 there
are ridge-like profilings 24', 24'' on both sides. The
profiling 24', with the axis 26, on one side, are not
parallel to the profilings 24'', with axis 27, on the other
side of the same electrode element lc. Thus, it is possible
to double the capillary gap between adjacent electrode
elements lc. When electrode elements lc as in figure 11 are
stacked, the profiles 24', 24'' that cross over each other
are in point contact. However, an alternating arrangement
of electrode elements lc with profiling on both sides with
smooth, non-profiled electrode elements is also possible.
Figure 12 shows non-directional button-like profiling
25 on one side of the electrode element ld. However, it is
also possible to provide profiling 25 on both sides of the
electrode element ld. Profilings 23, 24', 24'', 25 shown in
figures 10 to 12 can be made by stamping tools. The
production of the electrode elements lb, lc, ld by the melt-
spin process to form glass-metal foil bands is particularly
economical. These are mostly of a thickness 3 of 20 ~m to
100 ~m and can be produced in the desired width. The
surfaces of the rollers are suitably prepared in order to
generate the profiles 23, 24, 24'', 25.
Figure 13 shows the cross section of part of an
electrode that consists of a package with alternating
profiled and non-profiled electrode elements 28, 29. The
profilings of the electrode elements 28 are of an undulating
structure, which gives rise to a constantly varying
capillary gap. The half gap 34 between two adjacent non-
2~27~
profiled electrode elements 29 can be regarded as the mean
capillary gap width. Because of the spring effect of the
undulating electrode elements 28, the use of this package
permits a very simple variation of the width of the
capillary gap 4, for electrodes can be produced for
different electrolytic processes by using one and the same
profiling.
Figures 14 and 15 show electrode elements 30, 31 with
creased profiling 32 on both or one side, respectively, the
axes 36 of these extending orthogonally to the longitudinal
axis 35 of the electrode elements 30, 31. The electrode
element 30 can be used in this form with non-profiled
electrode elements 1, 29. A combination of these electrode
elements 30 with the axes 36 of the creased profilings 32
that are inclined relative to the horizontal results in
electrode structures that are very similar to those shown in
figures 7 and 8.
The advantages of the electrode elements lie in the
fact that these can be combined to form dense, fine, and
evenly structured packages without separate distance pieces.
The capillary gap between adjacent electrode elements, fixed
by their profilings, ensures a directional movement of the
gas and an intensive electrolyte exchange.
Figure 16 shows two electrodes 8, of which one serves
as the anode, and the other as a cathode, with an interposed
coarse mesh distance element 14. The electrode structure
permits a constant and small electrode interval across a
large surface, this corresponding to the thickness of the
distance element 14. In addition, the adaptability of this
electrode structure ensures that any damage to the distance
element 14 is prevented. The electrodes 8 consist of
electrode elements 1. The bulkhead 13 separates the gases
in the upper area of the cell housing 40.
- 15 -
2~2~
Figure 1 shows the construction of an electrolysis
cell. It incorporates electrodes 8 that are formed from the
electrode elements according to the present invention. In
order to provide for a clearer representation of the gas-
bubble distribution, the path of the gas bubbles has beensimplified in the form of the beaded lines 41 and the
electrolysis cell has a relatively large electrode interval
as well as wide degassing spaces 10, 11. One of the
important requirements for the functioning of the
electrolysis cell according to the present invention are the
electrodes 8 that are formed from the electrode elements
according to the present invention.
The following are indicated by the arrows in figure 1:
- the electrolyte feed 37;
- removal of the gas 38;
- the removal of the mixed gas 39.
The connections between the reaction space 9 and the
degassing spaces 10, 11 are at most of the size of a
capillary gap; complete sealing between these spaces is
better so that no interference caused by the flow can result
from the movement of the electrolyte between the electrodes
8 and the cell housing 40, for such interference would
possibly lead to the separation of gas bubbles 6 from the
electrode reaction surface into the reaction space 9.
This provides a cell structure that divides the
electrolysis cell hydraulically into a common reaction space
9, and separate degassing spaces 9, 10.
The purity of the gases that are generated depends
substantially on the quality of the electrodes. The
distance between the electrodes can also have an effect on
the purity of the gases. In order to prevent any
coagulation of the gas bubbles, a distance that is at least
- 16 -
2~27i~
three times the bubble separation diameter must be left
between the electrodes 8. Coagulation of the gas bubbles
leads to the formation of mixed gas in the reaction space 9.
Thus, every effort must be made to achieve the smallest
possible distance between the electrodes since this reduces
ohmic resistance. Electrolytic exchange between the
degassing spaces 10, 11 and the reaction space 9 is more
intensive the smaller (narrower) the reaction space 9
(electrode interval).
Gas bubbles 6 which leave the electrodes 8 and migrate
into the reaction space 9 lead to the above-discussed
insignificant formation of mixed gas. These bubbles cannot
cause contamination of the pure gas, because, before
reaching the opposite electrode, they would coagulate with
the bubbles that are formed there. Their bubble diameter
would then be too great for movement through the capillary
gap 4 of the electrode 8 or in the sealed area of the
housing wall. The separation of pure gases in the upper
cell area is effected by one or more bulkheads 12 that
extend below the level of the liquid.
Optimal functioning of the electrode 8 is then ensured
if its structure is fine and even. Such properties are best
achieved by tightly packed and evenly profiled electrode
elements 1, la, lb, lc, ld, 28, 29, 30, 31.
An electrolysis cell that is fitted with an electrode
made up of electrode elements according to the present
invention functions as follows:
The large number of electrode elements 1, la, lb, lc,
ld, 28, 29, 30, 31 of the electrode 8 (approximately 40 to
50 electrode elements pex centimetre) represents a high
level of smoothing of the electrode surface. Connected with
- 17 -
:
.
~ ~ ~ 2 7 ~ ~
this is an adequate smoothing of the electrical field and of
the current density loading. Consequently, overloading and
thus premature wear of the electro-catalytic coating is
prevented. Furthermore, it has been made possible to
increase the surface involved in the reaction by a value
greater than the design surface. Under favourable
conditions, the ratio of active reaction surface to
construction surface can lie at a value of approximately 2.
The gas bubbles that are formed on the face surfaces
and on the reactive surfaces 2 of the electrode elements 1,
la, lb, lc, ld, 28, 29, 30, 31 are located in the sphere of
influence of the capillary gap 4. Because of the gas bubble
formation there is a pressure build-up in the reaction space
9, which is the reason for movement of the gas transverse to
the plane of the electrode. Figure 4 shows the path of a
gas bubble 6 through the capillary gap 4 between the
electrode elements 1. To the same extent, the electrolyte
is exchanged between the degassing space 10, 11 and the
reaction space 9. For all practical purposes, there are no
free-moving gas bubbles in the electrolyte of the reaction
space 9. Because of the action of the capillary effect,
they are moved onto the electrode surface and "drawn" into
the capillary gap 4. This results in a significant
reduction of the electrical resistance of the electrolyte.
It should also be pointed out that the width 5 of the
electrode elements 1 can be adapted to the requirements with
reference to the smallest possible ohmic voltage drop in the
electrode material. The same applies to the dimensions of
the capillary gap 4 in order to achieve undisturbed
hydraulic conditions within the reaction space of the
electrolysis cell.
-- 1~ --
