U.S. patent application number 17/292885 was filed with the patent office on 2021-12-30 for electrode for electrolytic evolution of gas.
The applicant listed for this patent is INDUSTRIE DE NORA S.P.A.. Invention is credited to Alice GARGIULO, Toshikazu HAYASHIDA.
Application Number | 20210404076 17/292885 |
Document ID | / |
Family ID | 1000005883909 |
Filed Date | 2021-12-30 |
United States Patent
Application |
20210404076 |
Kind Code |
A1 |
GARGIULO; Alice ; et
al. |
December 30, 2021 |
ELECTRODE FOR ELECTROLYTIC EVOLUTION OF GAS
Abstract
An electrode for evolution of gas in electrolytic processes
having a substrate of valve metal and a catalytic coating having
two layers. A first layer having oxides of valve metal, ruthenium
and iridium and a second layer having one or more metals chosen
from amongst elements of the platinum group.
Inventors: |
GARGIULO; Alice; (Milan,
IT) ; HAYASHIDA; Toshikazu; (Fujisawa City, Kanagawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INDUSTRIE DE NORA S.P.A. |
Milan |
|
IT |
|
|
Family ID: |
1000005883909 |
Appl. No.: |
17/292885 |
Filed: |
December 3, 2019 |
PCT Filed: |
December 3, 2019 |
PCT NO: |
PCT/EP2019/083448 |
371 Date: |
May 11, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 1/26 20130101; C25B
13/00 20130101; C25B 9/23 20210101; C25B 11/093 20210101 |
International
Class: |
C25B 11/093 20060101
C25B011/093; C25B 1/26 20060101 C25B001/26; C25B 9/23 20060101
C25B009/23; C25B 13/00 20060101 C25B013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 2018 |
IT |
102018000010760 |
Claims
1. An electrode for gas evolution in electrolytic processes
comprising a valve metal substrate and a coating comprising a first
catalytic layer formed on said substrate containing a mixture of
iridium, ruthenium, tin and platinum or their oxides or
combinations thereof, obtained from precursors containing said
iridium, ruthenium and tin in the form of organometallic complexes,
and a second catalytic layer formed on said first catalytic layer
containing platinum and tin or their oxides or combinations
thereof, wherein said tin of the said second catalytic layer is
present in a decreasing concentration from the interface with said
first catalytic layer and wherein said platinum of the said first
catalytic layer is present in a decreasing concentration from the
interface with said second catalytic layer.
2. An electrode for gas evolution in electrolytic processes
comprising a valve metal substrate and a coating comprising a first
catalytic layer formed on said substrate containing a mixture of
iridium, ruthenium, tin and platinum or their oxides or
combinations thereof and a second catalytic layer formed on said
first catalytic layer containing platinum and tin or their oxides
or combinations thereof, wherein said first layer is obtained from
a platinum-free first precursor solution comprising a mixture of
iridium, ruthenium and tin, applied said substrate and subjected to
a heat treatment, wherein said platinum-free first precursor
solution contains said iridium, ruthenium and tin in the form of
organometallic complexes, and wherein said second catalytic layer
is obtained from a tin-free second catalytic composition containing
platinum, applied said substrate and subjected to a heat
treatment.
3. The electrode according to claim 1, wherein said second
catalytic layer contains Pt=48-96% in the form of metal, or its
oxides, in molar percentage referred to the metal element.
4. The electrode according to claim 1, wherein said second
catalytic layer contains Pd=0-24% or Rh=0-24%, in the form of
metal, or their oxides, or combinations thereof, in the form of
metals or their oxides in molar percentage referred to the metal
elements.
5. The electrode according to claim 1, wherein said second
catalytic layer contains Sn=4-12% in the form of metal or its
oxides, in average molar percentage referred to the metal
element.
6. The electrode according to claim 1, wherein said iridium,
ruthenium and tin oxides of said first catalytic layer are present
in molar percentages Ru=24-34%, Ir=3-13%, Sn=30-70% referring to
the metal elements.
7. The electrode according to claim 1, wherein said first catalytic
layer also contains titanium oxides in molar percentage Ti=30-40%
referred to the metal element.
8. The electrode according to claim 1, wherein said first catalytic
layer contains Pt=3-10% in the form of metal or its oxides, in
average molar percentage referred to the metal element.
9. The electrode according to claim 1, wherein the valve metal
substrate is selected from the group consisting of titanium,
tantalum, zirconium, niobium, tungsten, aluminium, silicon, or
their alloys.
10. A method for the production of an electrode as defined in claim
1, comprising the following steps: applying to a valve metal
substrate a platinum-free first solution comprising a mixture of
iridium, ruthenium and tin, subsequently drying at 50-60.degree. C.
and carrying out decomposition of said first solution by heat
treatment at 400-650.degree. C. for a time of 5 to 30 minutes,
wherein said first solution contains said iridium, ruthenium and
tin in the form of organometallic complexes; repeating the previous
step until a desired specific load of noble metal is reached;
applying a tin-free second catalytic solution containing platinum
and subsequently drying at 50-60.degree. C. and carrying out
decomposition of said second solution by heat treatment at
400-650.degree. C. for a time of 5 to 30 minutes; repeating the
previous step until a desired specific load of noble metal is
reached.
11. The method according to claim 10, wherein the temperature of
said thermal decomposition in steps a) and c) is between 480 and
550.degree. C.
12. (canceled)
13. A cell for the electrolysis of solutions of alkaline chlorides
comprising an anodic compartment and a cathodic compartment wherein
the anodic compartment is equipped with the electrode according to
claim 1.
14. A cell for electrolysis according to claim 13 wherein said
anodic compartment and said cathodic compartment are separated by a
diaphragm or an ion-exchange membrane.
15. An electrolyzer for the production of chlorine and alkali from
alkali chloride solutions comprising a modular arrangement of
cells, wherein each cell is the cell according to claim 13.
16. The electrode according to claim 2, wherein said second
catalytic layer contains Pt=48-96% in the form of metal, or its
oxides, in molar percentage referred to the metal element.
17. The electrode according to claim 2, wherein said second
catalytic layer contains Pd=0-24% or Rh=0-24%, in the form of
metal, or their oxides, or combinations thereof, in the form of
metals or their oxides in molar percentage referred to the metal
elements.
18. The electrode according to claim 2, wherein said second
catalytic layer contains Sn=4-12% in the form of metal or its
oxides, in average molar percentage referred to the metal
element.
19. The electrode according to claim 2, wherein said iridium,
ruthenium and tin oxides of said first catalytic layer are present
in molar percentages Ru=24-34%, Ir=3-13%, Sn=30-70% referring to
the metal elements.
20. The electrode according to claim 2, wherein said first
catalytic layer also contains titanium oxides in molar percentage
Ti=30-40% referred to the metal element.
21. The electrode according to claim 2, wherein said first
catalytic layer contains Pt=3-10% in the form of metal or its
oxides, in average molar percentage referred to the metal element.
Description
FIELD OF THE INVENTION
[0001] The invention relates to an electrode for evolution of gas
in electrolytic processes comprising a valve metal substrate and a
catalytic coating comprising two layers. A first layer comprising
valve metal, ruthenium and iridium oxides and a second layer
comprising one or more metals chosen from amongst the elements of
the platinum group.
BACKGROUND OF THE INVENTION
[0002] The field of the invention relates to the preparation of a
catalytic coating for electrodes used in brine electrolysis
processes. This coating is applied to a metal substrate, typically
titanium or other valve metal.
[0003] Over the years, the technology of brine electrolysis has
undergone innovations towards an efficient implementation from the
energy point of view and from the cost/benefit of the use of
resources. In this ever more challenging context, the optimization
of the anode plays a key role. In particular, numerous efforts have
been made in order to reduce the over-voltage of the anode in the
generation of chlorine and in order to reduce the concentration of
oxygen in the gaseous chlorine generated and thus to produce
gaseous chlorine with a high purity.
[0004] A further difficulty resides in the obtaining of an
electrode capable of maintaining higher performance for a long
period of time.
[0005] Generally speaking, the processes for electrolysis of
brines, for example alkaline chloride brines such as sodium
chloride, for the production of chlorine and caustic soda, are
carried out with anodes made of titanium or another valve metal,
activated with a superficial layer of ruthenium dioxide (RuO2)
optionally mixed with tin dioxide (SnO2) and another noble metal,
such as for example described in EP0153586. Accordingly, it is
possible to obtain a decrease in the over-voltage of the chlorine
evolution anodic reaction and thus in the overall energy
consumption.
[0006] The formulation just described, together with the other
formulations containing tin, has however the problem of also
reducing the over-voltage of the concurrent oxygen development
reaction, leading to the production of chlorine gas contaminated
with an excessive quantity of oxygen.
[0007] Another partial improvement in the performance is obtained
by applying to a metal substrate a formulation based on RuO2 and
SnO2 combined with a reduced quantity of IrO2 such as for example
described in WO2016083319. A similar formulation allows optimum
values of cell potential and moderate quantities of oxygen to be
obtained.
[0008] Other coatings of the prior art, such as for example the
formulation described in WO2012081635 comprising two catalytic
coatings, the first containing titanium and noble metal oxides and
the second containing a platinum and palladium alloy, also allow
optimum values of cell potential and reduced quantities of oxygen
in chlorine gas to be obtained; however, they do not endow the
electrode with an optimum resistance capable of maintaining higher
levels of performance, with regard to catalytic activity and
selectivity, for an adequate period of time.
[0009] US 2013/0186750 A1 describes an electrode suitable for
chlorine evolution which has alternate layers of two distinct
compositions, namely one type of layers comprising iridium,
ruthenium and valve metals and another type of layer comprising
oxides of iridium, ruthenium and tin.
[0010] US 2013/0334037 A1 describes an electrode for electrolysis
including a conductive substrate, a first layer formed on the
conductive substrate containing at least one oxide selected from
ruthenium oxide, iridium oxide and titanium oxide and a second
layer formed on the first layer containing an alloy of platinum and
palladium.
[0011] U.S. Pat. No. 4,626,334 describes an anode comprising an
electroconductive substrate provided with a (Ru--Sn)O2 solid
solution coating for brine electrolysis.
[0012] JP S62243790 describes an electrode having a first coating
layer comprising a mixture of platinum and iridium oxide and a
second coating layer comprising a mixture of ruthenium oxide and
tin oxide.
[0013] The need is thus apparent to identify a new catalytic
coating for electrodes for evolution of gaseous products in
electrolytic cells in brine electrolysis processes, characterized
by a higher level of catalytic activity and by a high resistance
capable of sustaining higher levels of performance for a long
period of time under the usual operating conditions with respect to
the formulations of the prior art.
SUMMARY OF THE INVENTION
[0014] Various aspects of the present invention are described in
the appended claims. The present invention relates to an electrode
for evolution of gaseous products in electrolytic cells, for
example for evolution of chlorine in alkaline brine electrolysis
cells, comprising a catalytic coating applied on a metal substrate.
In the present context, the term catalytic coating indicates two
different catalytic layers with different catalytic compositions in
which the first catalytic layer formed on the substrate comprises
at least a mixture of iridium, of ruthenium, of tin and of platinum
or their oxides or respective combinations and a second catalytic
layer formed on the first catalytic layer comprises platinum and
tin or their oxides or respective combinations thereof. The tin of
the second catalytic layer is present in a concentration decreasing
from the interface with said first catalytic layer towards the
upper surface of the second catalytic layer, i.e. surface opposite
the interface with the first catalytic layer, and the platinum of
the said first catalytic layer is present in a concentration
decreasing from the interface with said second catalytic layer
towards the substrate.
[0015] The present invention also relates to an electrode for
evolution of gaseous products in electrolytic cells, for example
for evolution of chlorine in alkaline brine electrolysis cells,
comprising a valve metal substrate and a coating comprising a first
catalytic layer formed on said substrate containing a mixture of
iridium, ruthenium, tin and platinum or their oxides or
combinations thereof and a second catalytic layer formed on said
first catalytic layer containing platinum and tin or their oxides
or combinations thereof, wherein said first layer is obtained from
a platinum-free first precursor solution comprising a mixture of
iridium, ruthenium and tin, applied said substrate and subjected to
a heat treatment, and wherein said second catalytic layer is
obtained from a tin-free second catalytic solution containing
platinum, applied to said first catalytic layer and subjected to a
heat treatment. The terms "platinum-free" and "tin-free" in the
sense of the present invention mean that the platinum concentration
in the first solution is at least an order of magnitude lower that
the average platinum concentration in the first layer obtained from
said first solution and that the tin concentration in the second
solution is at least an order of magnitude lower that the average
tin concentration in second layer obtained from the second
solution. Preferably, a platinum-free solution contains platinum at
most as an impurity and a tin-free solution contains tin at most as
an impurity.
[0016] This double-layer structure, applied to a metal substrate,
typically titanium, titanium alloy or another valve metal, allows a
saving in the energy consumption to be combined with an excellent
purity of chlorine gas produced while maintaining optimal
performance characteristics in terms of catalytic activity and of
selectivity for a long period of time.
[0017] The first catalytic layer, formed on the substrate,
preferably comprises ruthenium oxide, iridium oxide, tin oxide and
metallic platinum or its oxides. RuO2 is widely known for its
excellent catalytic activity and its stability in an alkaline
medium which is improved by the presence of IrO2; the presence of
SnO2 guarantees a slower consumption of the noble metals
present.
[0018] The second catalytic layer, formed on the first layer,
comprises tin or its oxides and one or more metals chosen from
amongst the elements of the platinum group, especially platinum
itself, which are known for increasing the selectivity and for
reducing the energy consumption.
[0019] The inventors have observed that an electrode with a similar
catalytic coating, where said second catalytic layer comprises
platinum in a molar percentage referred to the metal element in the
range between 48 and 96% (or, when taking the tin component not
into account, from 50 and 99.999%) in the form of the metal or its
oxide, can offer the advantage of subsequently reducing the
over-voltage of the reaction for evolution of chlorine.
[0020] In the context of the present invention, ranges denoted by
either "from" or "between" include the specified upper and lower
limits, respectively.
[0021] In another embodiment, aside from platinum and tin, said
second catalytic layer comprises palladium or rhodium in the form
of metals or their oxides, or combinations thereof, in molar
percentage referred to the metal elements in the range between 0
and 24% (or, when taking the tin component not into account,
between 0 and 25%), where the elements are in the form of metals or
oxides thereof. This can guarantee a high catalytic activity by
virtue of the combined presence of two or more noble metals.
[0022] The second catalytic layer preferably comprises tin or its
oxide in an average molar percentage referred to the metal element
in a range from 4 to 12%. As the concentration of the tin component
varies in a direction perpendicular to the interface between the
first and second layers, the tin concentration is an average of the
concentration profile through the second catalytic layer.
[0023] Therefore, in a preferred embodiment, besides unavoidable
impurities, the second catalytic layer consists of platinum and
tin, and optionally palladium and/or rhodium, in molar percentage
referred to the metal elements in the ranges from 48 to 96%
platinum, from 4 to 12% tin, from 0 to 24% palladium and from 0 to
24% rhodium.
[0024] According to a preferred embodiment of the aforementioned
electrode, the first catalytic layer comprises metals or metal
oxides of iridium, ruthenium, tin in molar percentages Ru=24-34%,
Ir=3-13%, Sn=30-70% referred to the metal elements.
[0025] The first catalytic layer preferably comprises platinum or
its oxide in an average molar percentage referred to the metal
element in a range from 3 to 10%. As the concentration of the
platinum component varies in a direction perpendicular to the
interface between the first and second layers, the platinum
concentration is an average of the concentration profile through
the first catalytic layer.
[0026] It goes without saying that those skilled in the art will
select the molar percentages of the individual elements in such a
manner that the total sum of the molar percentages of the
components is 100. Especially, if no other metals are present in
the first catalytic layer, Sn or Sn oxides are preferably present
in concentration of 55-70% referred to the metal element.
[0027] In another embodiment, said first catalytic layer comprises
another valve metal chosen from amongst titanium, tantalum and
niobium, in a quantity, expressed in molar percentage, in the range
between 30 and 40% referred to the metal element; it has in fact
been observed how the presence of another valve metal such as
titanium allows a good catalytic activity to be combined with a
substantial increase in the resistance of the electrode in
processes that require current inversion.
[0028] In a preferred embodiment, besides unavoidable impurities,
the first catalytic layer consists of iridium, ruthenium, tin and
platinum and optionally titanium, in molar percentage referred to
the metal elements in the ranges from 3 to 13% iridium, from 24 to
34% ruthenium, from 30 to 70% tin, from 3 to 10% platinum and from
30 to 40% titanium.
[0029] The inventors have observed that, surprisingly, in the
catalytic coating described above, a phenomenon of diffusion
between layers takes place: the tin of the first catalytic layer
diffuses into the second layer, while the platinum of the second
catalytic layer diffuses into the first layer. The diffusion of tin
into the second catalytic layer takes place across a gradient of
concentration such that the quantity of tin in the second catalytic
layer is maximum at the interface between the two catalytic layers
and decreases towards the external surface of the second catalytic
layer.
[0030] The presence of tin diffused into the second catalytic layer
can advantageously slow the consumption of the noble metals present
in the second catalytic layer, enabling optimum performance
characteristics in terms of catalytic activity and of selectivity
to be maintained for a longer period of time, without compromising
the catalytic performance.
[0031] Likewise, the diffusion of platinum from the second
catalytic layer into the first catalytic layer is such that the
quantity of platinum in the first catalytic layer is maximum at the
interface between the two catalytic layers and decreases gradually
toward the internal surface of the first catalytic layer.
[0032] The diffusion of the platinum into the first catalytic layer
allows the catalytic activity to be enhanced. This furthermore
allows better catalytic performance characteristics to be
maintained throughout the lifetime of the electrode, also where the
prolonged use of the same causes wear of the second layer over
time. The elements present and the particular structure of the
catalytic coating allow better performance characteristics with
respect to the prior art to be guaranteed with the further
advantage of increasing the operating lifetime of the
electrode.
[0033] The electrode according to the invention furthermore
surprisingly allows the better performance characteristics in terms
of activity and of selectivity to be maintained over time.
[0034] The presence of tin has a high impact on the selectivity;
however, if the tin is present in high quantities on the external
surface of the catalytic coating, in combination with the platinum,
it attenuates the increase in catalytic activity of the platinum
itself.
[0035] The diffusion of tin from the first catalytic layer to the
second produces a profile of concentration of the element between
the layers which enables a high catalytic activity together with an
optimum selectivity to be maintained, furthermore allowing the
consumption of the noble metals present in the second catalytic
layer to be slowed. The profile of concentration of tin between the
two catalytic layers is characterized by a monotonic decrease in
concentration of the element within the second layer in the
opposite direction to the first layer.
[0036] In another embodiment, the first catalytic layer has a
specific load of noble metal in the range between 3 and 8 g/m.sup.2
and the second catalytic layer has a specific load of noble metal
in the range between 0.8 and 4 g/m.sup.2. The inventors have found
that loads thus reduced of noble metal are more than sufficient to
impart an optimum catalytic activity.
[0037] According to another aspect, the present invention relates
to a method for obtaining an electrode for evolution of gaseous
products in electrolytic cells, for example for evolution of
chlorine in alkaline brine electrolysis cells, comprising the
following stages:
[0038] application to a valve metal substrate of a platinum-free
first solution comprising a mixture of iridium, ruthenium and tin,
subsequent drying at 50-60.degree. C. and decomposition of said
first solution by heat treatment at 400-650.degree. C. for a period
of 5 to 30 minutes; repetition of the stage a) until said first
catalytic composition is obtained with a desired specific load of
noble metal;
[0039] application of a tin-free second catalytic solution
containing platinum being subsequently dried at 50-60.degree. C.
and decomposition of said first solution by heat treatment at
400-650.degree. C. for a period of 5 to 30 minutes;
[0040] repetition of the stage c) until said first catalytic
composition is obtained with a desired specific load of noble
metal.
[0041] In one embodiment, the temperature of said thermal
decomposition in steps a) and c) is between 480 and 550.degree.
C.
[0042] In one embodiment, said first solution furthermore comprises
titanium.
[0043] In another embodiment, said second solution comprises
palladium and rhodium on their own or in combination with each
other.
[0044] In a preferred embodiment of the present invention, the
two-layers electrode is subjected to a final thermal treatment. In
one embodiment, the final thermal treatment is effected at a
temperature between 400 and 650.degree. C., preferably at a
temperature of around 500.degree. C., for at least 60 minutes,
preferably between 60 and 180 minutes, more preferably between 80
and 120 minutes.
[0045] Preferably, the first solution comprises the iridium,
ruthenium and tin compounds and optionally the titanium compounds
in the form of organometallic complexes. In one embodiment, the
organometallic complexes are aceto-hydroxychloride complexes of
tin, ruthenium, iridium and optionally titanium, respectively.
[0046] Without wishing to be limited to a particular scientific
theory, it is possible for the stages a and c for thermal treatment
or decomposition of the method described above, together with the
elements present and with the concentrations thereof within said
first and said second solution, because their coefficient of
diffusion is also dependent on the temperature, to contribute to
the inter-diffusion of the tin and of the platinum present
respectively from the first catalytic layer to the second catalytic
layer and vice versa.
[0047] According to another aspect, the invention relates to a cell
for the electrolysis of solutions of alkaline chlorides comprising
an anode compartment and a cathode compartment in which the anode
compartment is equipped with the electrode in one of the forms such
as described above, used as an anode for evolution of chlorine.
[0048] According to another aspect, the invention relates to an
industrial electrolyser for the production of chlorine and alkali
from alkali chloride solutions, when also lacking biasing
protection devices and comprising a modular arrangement of
electrolytic cells with the anode and cathode compartments
separated by ion-exchange membranes or by diaphragms, where the
anode compartment comprises an electrode in one of the forms such
as described above used as an anode.
[0049] The following examples are included in order to demonstrate
particular embodiments of the invention, whose practicability has
been amply verified within the range of values claimed. It will be
evident to those skilled in the art that the compositions and the
techniques described in the examples that follow represent
compositions and techniques for which the inventors have
encountered a good operation of the invention in practice; however,
those skilled in the art will furthermore appreciate in the light
of the present description, various modifications could be made to
the various embodiments described still giving rise to identical or
similar results without straying from the scope of the
invention.
EXAMPLE 1
[0050] A mesh of titanium of dimensions 10 cm.times.10 cm was
washed three times in de-ionized water at 60.degree. C., changing
the liquid each time. The washing was followed by a thermal
treatment for 2 hours at 350.degree. C. The mesh was then subjected
to a treatment in a solution of HCl at 20%, boiling for 30
minutes.
[0051] 100 ml of a first acetic solution were then prepared
containing tin complex acetato-hydroxichloride, ruthenium complex
acetato-hydroxichloride and iridium complex acetato-hydroxichloride
and having a molar composition equal to 25% Ru, 11% Ir and 64% Sn
referred to the metals.
[0052] A second solution was also prepared containing a quantity of
Pt diamino dinitrate, Pt(NH3)2(NO3)2 corresponding to 40 g of Pt
dissolved in 160 ml of glacial acetic acid and then made up to a
volume of one litre with acetic acid at 10% by weight.
[0053] The first acetic solution was applied to the mesh of
titanium by painting on in 8 coats. After each coat, a drying step
at 50-60.degree. C. was carried out for around 10 minutes, then a
thermal treatment for 10 minutes at 500.degree. C., the mesh being
each time cooled in air prior to the application of the next
coat.
[0054] The procedure was repeated until a load expressed as the sum
of Ir and Ru referred to the metals equal to 7 g/m.sup.2 was
reached.
[0055] Subsequently, the second solution was applied by painting on
in 4 coats. After each coat, a drying step at 50-60.degree. C. for
around 10 minutes was carried out, then a thermal treatment for 10
minutes at 500.degree. C. Each time, the mesh was cooled in air
before the application of the next coat.
[0056] The procedure was repeated until a total load of Pt equal to
2.5 g/m.sup.2 was reached.
[0057] A final thermal treatment at 500.degree. C. for 100 minutes
was lastly carried out.
[0058] The electrode thus obtained was identified as specimen
#1.
EXAMPLE 2
[0059] A mesh of titanium of dimensions 10 cm.times.10 cm was
washed three times in de-ionized water at 60.degree. C., changing
the liquid each time. The washing was followed by a thermal
treatment for 2 hours at 350.degree. C. The mesh was then subjected
to a treatment in a solution of HCl at 20%, boiling for 30
minutes.
[0060] 100 ml of a first acetic solution were then prepared
containing tin complex acetato-hydroxichloride, ruthenium complex
acetato-hydroxichloride and iridium complex acetato-hydroxichloride
and having a molar composition equal to 26% Ru, 10% Ir and 64% Sn
referred to the metals.
[0061] 100 ml of a second acetic solution were also prepared
containing an organo-metallic complex of platinum and an
organo-metallic complex of palladium and having a molar composition
equal to 87% Pt and 13% Pd referred to the metals.
[0062] The first acetic solution was applied to the mesh of
titanium by painting on in 8 coats. After each coat, a drying step
at 50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0063] The procedure was repeated until a load expressed as the sum
of Ir and Ru referred to the metals equal to 6.7 g/m.sup.2 was
reached.
[0064] Subsequently, the second acetic solution was applied by
painting on in 4 coats. After each coat, a drying step at
50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0065] The procedure was repeated until a total load of noble metal
expressed as the sum of Pt and Pd referred to the metals equal to
2.7 g/m.sup.2 was reached.
[0066] Lastly, a final thermal treatment at 500.degree. C. for 100
minutes was carried out.
[0067] The electrode thus obtained was identified as specimen
#2.
EXAMPLE 3
[0068] A mesh of titanium of dimensions 10 cm.times.10 cm was
washed three times in de-ionized water at 60.degree. C., changing
the liquid each time. The washing was followed by a thermal
treatment for 2 hours at 350.degree. C. The mesh was then subjected
to a treatment in a solution of HCl at 20%, boiling for 30
minutes.
[0069] 100 ml of a first acetic solution were then prepared
containing tin complex acetato-hydroxichloride, ruthenium complex
acetato-hydroxichloride and iridium complex acetato-hydroxichloride
and having a molar composition equal to 26% Ru, 10% Ir and 64% Sn
referred to the metals.
[0070] 100 ml of a second acetic solution were then prepared
containing an organo-metallic complex of platinum, an
organo-metallic complex of palladium and RhCl3 and having a molar
composition equal to 86% Pt, 10% Pd and 4% Rh referred to the
metals.
[0071] The first acetic solution was applied to the mesh of
titanium by painting on in 8 coats. After each coat, a drying step
at 50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0072] The procedure was repeated until a load expressed as the sum
of Ir and Ru referred to the metals equal to 6.7 g/m.sup.2 was
reached.
[0073] Subsequently, the second acetic solution was applied by
painting on in 4 coats. After each coat, a drying step at
50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0074] The procedure was repeated until a total load of noble metal
expressed as the sum of Pt, Pd and Rh referred to the metals equal
to 2.8 g/m.sup.2 was reached.
[0075] Lastly, a final thermal treatment at 500.degree. C. for 100
minutes was carried out.
[0076] The electrode thus obtained was identified as specimen
#3.
EXAMPLE 4
[0077] A mesh of titanium of dimensions 10 cm.times.10 cm was
washed three times in de-ionized water at 60.degree. C., changing
the liquid each time. The washing was followed by a thermal
treatment for 2 hours at 350.degree. C. The mesh was then subjected
to a treatment in a solution of HCl at 20%, boiling for 30
minutes.
[0078] 100 ml of a first acetic solution were then prepared
containing tin complex acetato-hydroxichloride, ruthenium complex
acetato-hydroxichloride, iridium complex acetato-hydroxichloride
and titanium complex acetato-hydroxichloride and having a molar
composition equal to 25% Ru, 10% Ir, 35% Sn and 30% Ti referred to
the metals.
[0079] 100 ml of a second acetic solution were also prepared
containing an organo-metallic complex of platinum and an
organo-metallic complex of palladium and having a molar composition
equal to 87% Pt and 13% Pd referred to the metals.
[0080] The first acetic solution was applied to the mesh of
titanium by painting on in 8 coats. After each coat, a drying step
at 50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0081] The procedure was repeated until a load was reached
expressed as the sum of Ir and Ru referred to the metals equal to
6.7 g/m.sup.2.
[0082] Subsequently, the second acetic solution was applied by
painting on in 4 coats. After each coat, a drying step at
50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0083] The procedure was repeated until a total load of noble metal
expressed as the sum of Pt and Pd referred to the metals equal to
2.7 g/m.sup.2 was reached.
[0084] Lastly, a final thermal treatment at 500.degree. C. for 100
minutes was carried out. The electrode thus obtained was identified
as specimen #4.
EXAMPLE 5
[0085] A mesh of titanium of dimensions 10 cm.times.10 cm was
washed three times in de-ionized water at 60.degree. C., changing
the liquid each time. The washing was followed by a thermal
treatment for 2 hours at 350.degree. C. The mesh was then subjected
to a treatment in a solution of HCl at 20%, boiling for 30
minutes.
[0086] 100 ml of a first acetic solution were then prepared
containing tin complex acetato-hydroxichloride, ruthenium complex
acetato-hydroxichloride, iridium complex acetato-hydroxichloride
and titanium complex acetato-hydroxichloride and having a molar
composition equal to 25% Ru, 10% Ir, 35% Sn and 30% Ti referred to
the metals.
[0087] 100 ml of a second acetic solution were also prepared
containing an organo-metallic complex of platinum, an
organo-metallic complex of palladium and RhCl3 and having a molar
composition equal to 86% Pt, 10% Pd and 4% Rh referred to the
metals.
[0088] The first acetic solution was applied to the mesh of
titanium by painting on in 8 coats. After each coat, a drying step
at 50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0089] The procedure was repeated until a load expressed as the sum
of Ir and Ru referred to the metals equal to 6.7 g/m.sup.2 was
reached.
[0090] Subsequently, the second solution was applied by painting on
in 4 coats. After each coat, a drying step at 50-60.degree. C. for
around 10 minutes was carried out, then a thermal treatment for 10
minutes at 500.degree. C. Each time, the mesh was cooled in air
prior to the application of the next coat.
[0091] The procedure was repeated until a total load of noble metal
expressed as the sum of Pt, Pd and Rh referred to the metals equal
to 2.7 g/m.sup.2 was reached.
[0092] Lastly, a final thermal treatment at 500.degree. C. for 100
minutes was carried out. The electrode thus obtained was identified
as specimen #5.
COUNTER-EXAMPLE 1
[0093] A mesh of titanium of dimensions 10 cm.times.10 cm was
washed three times in de-ionized water at 60.degree. C., changing
the liquid each time. The washing was followed by a thermal
treatment for 2 hours at 350.degree. C. The mesh was then subjected
to a treatment in a solution of HCl at 20%, boiling for 30
minutes.
[0094] 100 ml of a hydro-alcoholic solution were then prepared
containing RuCl3*3H2O, H2IrCl6*6H2O, TiCl3 in a solution of
isopropanol, having a molar composition equal to 23% Ru, 22% Ir,
55% Ti.
[0095] The solution was applied to the mesh of titanium by painting
on in 14 coats. After each coat, a drying step at 50-60.degree. C.
for around 10 minutes was carried out, then a thermal treatment for
10 minutes at 500.degree. C. Each time, the work piece was cooled
in air prior to the application of the next coat.
[0096] The procedure was repeated until a total load of noble metal
expressed as the sum of Ir and Ru referred to the metals equal to
11 g/m.sup.2 was reached. Then, a final thermal treatment at
500.degree. C. for 100 minutes was carried out.
[0097] The electrode thus obtained was identified as specimen
#1C.
COUNTER-EXAMPLE 2
[0098] A mesh of titanium of dimensions 10 cm.times.10 cm was
washed three times in de-ionized water at 60.degree. C., changing
the liquid each time. The washing was followed by a thermal
treatment for 2 hours at 350.degree. C. The mesh was then subjected
to a treatment in a solution at 20% of HCl, boiling for 30
minutes.
[0099] 100 ml of a first acetic solution were then prepared
containing tin complex acetato-hydroxichloride, ruthenium complex
acetato-hydroxichloride and iridium complex acetato-hydroxichloride
and having a molar composition equal to 26% Ru, 10% Ir and 64% Sn
referred to the metals.
[0100] 100 ml of a second acetic solution were also prepared
containing an organo-metallic complex of platinum and a tin complex
acetato-hydroxichloride and having a molar composition equal to 87%
Pt and 13% Sn referred to the metals.
[0101] The first acetic solution was applied to the mesh of
titanium by painting on in 6 coats. After each coat, a drying step
at 50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0102] The procedure was repeated until a total load of noble metal
expressed as the sum of Ir and Ru referred to the metals equal to 6
g/m.sup.2 was reached.
[0103] Subsequently, the second acetic solution was applied by
painting on in 4 coats. After each coat, a drying step at
50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0104] The procedure was repeated until a total load of noble metal
expressed as Pt referred to the metal equal to 2.5 g/m.sup.2 was
reached.
[0105] Lastly, a final thermal treatment at 500.degree. C. for 100
minutes was carried out.
[0106] The electrode thus obtained was identified as specimen
#2C.
COUNTER-EXAMPLE 3
[0107] A mesh of titanium of dimensions 10 cm.times.10 cm was
washed three times in de-ionized water at 60.degree. C., changing
the liquid each time. The washing was followed by a thermal
treatment for 2 hours at 350.degree. C. The mesh was then subjected
to a treatment in a solution of HCl at 20%, boiling for 30
minutes.
[0108] 100 ml of a first acetic solution were then prepared
containing tin complex acetato-hydroxichloride, ruthenium complex
acetato-hydroxichloride, iridium complex acetato-hydroxichloride
and organo-metallic complex of platinum and having a molar
composition equal to 25% Ru, 10% Ir, 35% Sn and 30% Pt referred to
the metals.
[0109] The acetic solution was applied to the mesh of titanium by
painting on in 10 coats. After each coat, a drying step at
50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0110] The procedure was repeated until a total load of noble metal
expressed as the sum of Ir, Ru and Pt referred to the metals equal
to 8 g/m.sup.2 was reached.
[0111] Lastly, a final thermal treatment at 500.degree. C. for 100
minutes was carried out.
[0112] The electrode thus obtained was identified as specimen
#3C.
COUNTER-EXAMPLE 4
[0113] A mesh of titanium of dimensions 10 cm.times.10 cm was
washed three times in de-ionized water at 60.degree. C., changing
the liquid each time. The washing was followed by a thermal
treatment for 2 hours at 350.degree. C. The mesh was then subjected
to a treatment in a solution of HCl at 20%, boiling for 30 minutes.
100 ml of a first hydro-alcoholic solution were then prepared
containing RuCl3*3H2O, H2IrCl6*6H2O, TiOCl2 in a mixture of water
and 1-butanol acidified with HCl, having a molar composition equal
to 26% Ru, 23% Ir, 51% Ti referred to the metals.
[0114] 100 ml of a second hydro-alcoholic solution were also
prepared containing H2PtCl6 and PdCl2.
[0115] The first acetic solution was applied to the mesh of
titanium by painting on in 8 coats. After each coat, a drying step
at 50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0116] The procedure was repeated until a total load of noble metal
expressed as the sum of Ir and Ru referred to the metals equal to 6
g/m.sup.2 was reached.
[0117] Subsequently, the second acetic solution was applied by
painting on in 4 coats. After each coat, a drying step at
50-60.degree. C. for around 10 minutes was carried out, then a
thermal treatment for 10 minutes at 500.degree. C. Each time, the
mesh was cooled in air prior to the application of the next
coat.
[0118] The procedure was repeated until a total load of noble metal
expressed as the sum Pt+Pd referred to the metals equal to 3
g/m.sup.2 was reached.
[0119] Lastly, a final thermal treatment at 500.degree. C. for 100
minutes was carried out.
[0120] The electrode thus obtained was identified as specimen
#4C.
[0121] The specimens of the examples and of the counter-examples
were characterized as anodes for evolution of chlorine in a
laboratory cell filled with a brine solution of sodium chloride at
a concentration of 200 g/l.
[0122] Table 1 reports the over-voltage of chlorine measured at a
current density of 4 kA/m.sup.2 and the percentage by volume of
oxygen in the chlorine produced.
TABLE-US-00001 TABLE 1 Specimens Cell potential (V) O2/Cl2 (Vol %)
1 2.76 0.9 2 2.76 0.7 3 2.76 0.7 4 2.77 0.8 5 2.77 0.7 1C 2.78 1.2
2C 2.76 1.0 3C 2.77 1.5 4C 2.76 0.8
[0123] The specimens of the preceding examples also underwent a
test for operation in beaker. In Table 2, the anode potentials
(CISEP) are reported, measured in a sodium chloride solution at a
concentration of 200 g/I at a temperature of 80.degree. C.,
corrected for the ohmic drop at a current density of 3 kA/m.sup.2.
Furthermore, in order to evaluate the selectivity for the chlorine
reaction, tests were conducted in sulphuric acid at a current
density of 3 kA/m.sup.2; the anode potentials reported (CISEP) have
been corrected for the ohmic drop. The higher the value of the
anode potentials measured in sulphuric acid, the greater the
selectivity for the chlorine reaction.
TABLE-US-00002 TABLE 2 ClSEP in NaCl ClSEP in H2SO4 Specimens vs
NHE vs NHE 1 1.336 1.820 2 1.336 1.872 3 1.336 1.890 4 1.338 1.872
5 1.338 1.890 1C 1.347 1.693 2C 1.336 1.740 3C 1.336 1.647 4C 1.336
1.872
[0124] Some specimens were, in the end, subjected to a longevity
test. The longevity test in question is the simulation, in a cell
divided by the conditions of industrial electrolysis. Table 3
reports the cell voltage for the specimens at the start of the test
and after a simulated period of a year, as an indicator of their
catalytic activity for the evolution of chlorine (Cl O.V.) measured
at a current density of 8 kA/m.sup.2 and the percentage of residual
load of the second catalytic layer after a simulated period of a
year.
TABLE-US-00003 TABLE 3 Cl O.V Cl O.V. after 1 Specimens Start of
test year % residual load 2 0.035 0.035 80% 1C 0.050 0.050 -- 4C
0.037 0.060 50%
[0125] The preceding description is not intended to limit the
invention, which may be used according to various embodiments
without however deviating from the objectives and whose scope is
uniquely defined by the appended claims.
[0126] In the description and in the claims of the present
application, the terms "comprising", "including" and "containing"
are not intended to exclude the presence of other additional
elements, components or process steps.
[0127] The discussion of documents, items, materials, devices,
articles and the like is included in this description solely with
the aim of providing a context for the present invention. It is not
suggested or represented that any or all of these topics formed
part of the prior art or formed a common general knowledge in the
field relevant to the present invention before the priority date
for each claim of this application.
* * * * *