Note: Descriptions are shown in the official language in which they were submitted.
WO 2023/037010
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AN ELECTROLYZER ELECTROCATALYST COMPRISING COBALT (CO) OXIDE,
ZIRCONIUM (ZR) AND A NOBLE METAL, AN ELECTRODE COMPRISING THE
ELECTROCATALYST AND THE USE OF THE ELECTROCATALYST IN AN
ELECTROLYSIS PROCESS
Description
Electrolysis is a promising option for carbon-free hydrogen production from
renewable and nuclear resources. Electrolysis is the process of using
electricity to
split water into hydrogen and oxygen. The process of electrolysis is performed
in a
unit called an electrolyzer. Electrolyzers can range in size from small,
appliance-size
equipment that is well-suited for small-scale distributed hydrogen production,
to
large-scale, central production facilities that, for instance, could be
directly connected
to renewable or other non-greenhouse-gas-emitting forms of electricity
production.
Background of the technology
In 2021, the U.S. Department of Energy's (DOE's) has formulated an objective
to
reduce the costs of clean hydrogen by 80% to $1 per 1 kilogram in 1 decade.
The
objective of reducing the production of hydrogen to $1 per 1 kilogram in 1
decade is
referred to as the hydrogen "1 1 1" initiative. Electrolysis is a leading
hydrogen
production pathway to achieve this goal.
Hydrogen produced via electrolysis can result in zero greenhouse gas
emissions,
depending on the source of the electricity used. The source of the required
electricity, including its cost and efficiency, as well as emissions resulting
from
electricity generation, must be considered when evaluating the benefits and
economic viability of hydrogen production via electrolysis. In many regions in
the
world, today's power grid is not ideal for providing the electricity required
for
electrolysis. The reason for this is the greenhouse gases released during the
actual
production of the electricity and the amount of fuel required to produce
electricity due
to the low efficiency of the electricity generation process.
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Hydrogen production via electrolysis is being pursued for renewable and
nuclear
energy options, including wind, solar, hydro and geothermal energy production.
These pathways result in virtually zero greenhouse gas and criteria pollutant
emissions, provided the electricity that is used for electrolysis is obtained
by means
of renewable energy sources. Moreover, it is important that the overall
production
cost for the energy decrease significantly to be competitive with more mature
carbon-based pathways such as natural gas reforming.
In view of the above, there is a growing need for improved electrolyzers which
show
improved energy efficiency and lifetime. In particular, there appears to be a
need for
providing improved coatings for electrodes used in electrolyzers, such as
improved
coatings directed to oxygen evolution as target reaction.
Summary of the invention
According to a first aspect, the disclosure relates to an electrolyzer
electrocatalyst,
comprising Cobalt (Co) oxide, Zirconium (Zr) and a noble metal.
According to a second aspect, the disclosure relates to an electrode for use
in an
electrolyzer, the electrode comprising a support and a coating, wherein the
coating
comprises Cobalt (Co) oxide, Zirconium (Zr) and a noble metal.
According to a third aspect, the disclosure relates to an electrochemical
system
comprising an electrolyser, the electrolyser having a cathode, an anode, and
an
electrolyte or electrolytes, wherein the cathode, the anode or both the
cathode and
the anode comprise an electrocatalyst, the electrocatalyst comprising Cobalt
(Co)
oxide, Zirconium (Zr) and a noble metal.
According to a fourth aspect, the disclosure relates to the use of an
electrocatalyst
for catalysing an electrolysis process, wherein the electrocatalyst comprises
Cobalt
(Co) oxide, Zirconium (Zr) and a noble metal.
According to a fifth aspect, the disclosure relates to a method for
electrolysing water
comprising the steps of:
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(i) providing a water electrolyser comprising an anode, a cathode, and an
electrolyte
or electrolytes, wherein at least one of the anode and the cathode comprises
an
electrocatalyst comprising Cobalt (Co) oxide, Zirconium (Zr) and a noble
metal;
(ii) contacting the water electrolyser with water;
(iii) creating an electrical bias between the cathode and the anode; and
(iv) generating hydrogen and/or oxygen.
According to a sixth aspect, the invention relates to the use of a cathode
electrocatalyst comprising Cobalt (Co) oxide, Zirconium (Zr) and a noble metal
for
producing hydrogen via an electrolysis process.
According to a seventh aspect, the disclosure relates to a method for
producing an
electrode for use in an electrolyzer, the electrode comprising a support and a
coating, the method comprising the steps of:
- preparing a metal support comprising Nickel (Ni) or Titanium (Ti),
- applying on the support a coating comprising Cobalt (Co), Zirconium (Zr) and
a
noble metal, and
- heating the support comprising the coating in air.
Brief description of the drawings
Figure 1 shows an exemplary embodiment of an electrolyzer 10 according to the
prior art;
Figure 2 illustrates the effect of adding Zirconium and Ruthenium to a Cobalt-
oxide
coating on the initial potential (Ei) of a coated electrode;
Figure 3 provides a comparison between the lifetime of a Cobalt oxide coating,
shown in units of total electrical charge passed per surface area (kAh/m2)
before
coating deactivation, and the Cobalt loading in the coating;
Figures 4a and 4b illustrate respectively the lifetime and the initial
potentials of
Cobalt oxide coatings with a fixed Cobalt / Ruthenium mass ratio and varying
Zirconium mass fractions;
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Figures 5a and 5b illustrate the relationship between the lifetime and initial
potential
of Cobalt oxide coatings with a fixed Cobalt / Zirconium ratio and an
increasing
Ruthenium loading;
Figure 6a shows the results of short-term electrolysis experiments run at 10
kA/m2
for a Nickel plate and respectively a Titanium support and a Nickel support
comprising a Cobalt/Zirconium/Ruthenium coating;
Figure 6b show the relative wear rates of Cobalt and Zirconium measured on a
Co/Zr/Ru coating on a Titanium support;
Figure 7 shows the result of measurements in KOH 30% at a temperature of 20 0C
with a Nickel plate and a Nickel support electrode and a Titanium support
electrode
both provided with a Co-Zr/Ru coating 100-9/1;
Figure 8 represent the results of tests that were run to assess the effect of
using a
Cobalt oxide coating comprising Zirconium as dispersing agent and Gold (Au) to
promote electrical conductivity throughout the bulk coating; and
Figure 9 represent the results of tests that were run to assess the effect of
using a
Cobalt oxide coating comprising Au in terms of activity.
Detailed description of the invention
The phraseology and terminology used in this disclosure is for the purpose of
description and should not be regarded as limiting. As used herein, the term
"plurality" refers to two or more items or components. The terms "comprising,"
"including," "carrying," "having," "containing," and "involving," whether in
the written
description or the claims and the like, are open-ended terms, i.e., to mean
"including
but not limited to." Thus, the use of such terms is meant to encompass the
items
listed thereafter, and equivalents thereof, as well as additional items. Only
the
transitional phrases "consisting of" and "consisting essentially of," are
closed or
semi-closed transitional phrases, respectively, with respect to the claims.
The use of
ordinal terms such as "first," "second," "third," and the like in the claims
to modify a
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claim element does not by itself connote any priority, precedence, or order of
one
claim element over another or the temporal order in which acts of a method are
performed, but are used merely as labels to distinguish one claim element
having a
certain name from another element having a same name (but for use of the
ordinal
term) to distinguish the claim elements.
Hydrogen (H2) is an important feedstock for various branches of the chemical
industry, such as petrochemicals and semiconductor manufacturing. Moreover, it
holds high potential as an agent to make the global energy infrastructure more
environmentally sustainable. Hydrogen can serve as energy carrier to replace
fossil
fuels in a hydrogen economy, and it is also able to reduce CO2 emissions in
energy-
intensive applications such as steel and aluminium refining.
The most prominent way of producing hydrogen that is truly 'green' is through
water
electrolysis powered by renewable energy sources. However, water electrolysis
suffers from energy inefficiencies due to the difficulty of catalyzing the
reaction.
Better electrocatalysts are needed to make the process more economically
competitive.
The overall reaction in water electrolysis is given by
21120 ¨> E2 +0.2
The process is carried out in either acid or alkaline electrolyzers, where
acid
electrolyzers use a wet acidic ion exchange membrane as electrolyte, and
alkaline
electrolyzers use concentrated aqueous base, typically KOH in range of 15-30%
mass, as electrolyte with a Zirfon separator.
Acidic systems benefit from compactness, low electrolyte resistance and good
gas
separation capabilities, which allows them to run at higher current densities
of
typically 10-30 kA/m2, and makes them more flexible in terms of ramping
activity up
and down. One of the main disadvantages is the reliance of this type of
electrolyzer
on iridium as electrocatalyst on the anode, which is an exceedingly rare and
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therefore expensive element. Alkaline systems rely much less on critical
materials,
but are bulkier, have higher internal resistances and lower power flexibility.
The overall reaction consists of two electrochemical half reactions, the
hydrogen
evolution reaction (HER) and oxygen evolution reaction (OER), which are
described
respectively in acidic and alkaline electrolytes by
4 II+ + 4 e- ¨ 2 Hz
4 Hz 0 4 e- 2 H2 + 4 0H-
2 H20 ¨> 0 2 4 H.+ + 4 e-
4 0HT ¨,' 0 + H2 + 4 e-
The largest energy loss originates from the oxygen-evolving anodic half-
reaction. A
better electrocatalyst for this reaction would have a smaller overpotential
and higher
energy efficiency. In this disclosure an electrode comprising an improved
electrocatalyst is presented.
Fig. 1 shows an exemplary embodiment of an electrolyzer 10 to explain the
basic
principle of electrolysis. The electrolyzer 10 comprises a container 11 with a
liquid
alkaline solution of sodium or potassium hydroxide as the electrolyte 12.
The electrolyzer 10 further comprises an anode 21 and a cathode 22 which are
placed in the electrolyte 12. The anode 21 and the cathode 22 are connected to
a
source of electrical energy 30. In the electrolyzer 10, a diaphragm 13 is
positioned in
between the anode 21 and the cathode 22.
As indicated in Fig. 1, in general, alkaline electrolyzers operate via
transport of
hydroxide ions (OH-) through the electrolyte from the cathode 22 to the anode
21.
The evolution of oxygen at the anode 21 side is indicated with reference
number 41.
The generation of hydrogen on the cathode 22 side is indicated with reference
number 42.
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Electrolyzers using a liquid alkaline solution of sodium or potassium
hydroxide as the
electrolyte have been commercially available for many years. One important
parameter of alkaline hydrolysis is the type of electrodes and coatings that
are used.
Evolution of oxygen in alkaline water electrolyzers is usually catalyzed on
anodes
made with massive nickel, massive steel, or nickel coated steel. While these
materials offer long lifetimes, the overpotential for oxygen evolution is
relatively high.
One of the effects thereof is a relatively high level of corrosion, for
instance for steel-
based anodes. The specific circumstances of this corrosion are not well-
understood
at the moment. In view of corrosion prevention, the anodes 21 and cathodes 22
used in electrolyzers 10, normally comprise an adapted coating to improve the
lifetime of the electrodes.
In the prior art alternative solutions for producing electrolyzers are known,
which use
solid alkaline exchange membranes (AEM) as the electrolyte. This anion
exchange
membrane can be used with pure water or a KOH solution as additional
electrolyte.
These alternative solutions using an anion exchange membrane to separate anode
and cathode compartments are showing promise on laboratory scale.
The present disclosure relates to an electrocatalyst which is used in the form
of a
coating for an electrode, in particular an anode 21, which can improve the
properties
of the electrode and in particular the lifetime of the electrode. The coating
according
to the disclosure is directed to oxygen evolution as target reaction. The
coating is a
Cobalt (Co) oxide based coating comprising Zirconium (Zr) as dispersing agent
and
a noble metal to promote electrical conductivity throughout the bulk coating.
According to the disclosure, the noble metal is preferably selected from
Ruthenium
(Ru), Gold (Au), Iridium (Ir), Platinum (Pt) and Palladium (Pd). It has been
established, as described in more detail below, that the lifetime of the
coating
comprising Cobalt oxygen, Zirkonium and in particular Ruthenium and/or Gold is
much higher than known coatings. The coating described in the disclosure
provides
longer lifetimes than other well-known Ni substitutes, such as Ni-Fe
oxyhydroxides,
due to the much higher robustness of cobalt oxide.
In one embodiment, an anode comprising a Cobalt oxide coating comprising Zr
and
Ru and/or Au allows for catalyzing oxygen evolution at a lower overpotential
due to
the relatively high electrochemical activity of Cobalt, and benefits from the
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incorporation of Zr as a dispersing agent and Ru and/or Au to promote
electrical
conductivity throughout the bulk coating.
According to the disclosure, the mentioned coating comprising the Cobalt
oxygen,
Zirconium and a noble metal such as Ruthenium or Gold is deposited on an
adapted
metal support. Preferably, the coating is deposited on a Titanium (Ti) or
Nickel (Ni)
support. Alternatively, the support comprises a Titanium alloy, a Nickel
alloy, steel or
stainless steel.
Titanium is an especially attractive substrate, due to its dimensional
stability and high
availability. A known drawback of using Titanium as a support material for
obtaining
an electrode, is the possibility of forming an electrically insulating oxide
interlayer
during the coating preparation or actual electrolysis. However, according to
present
disclosure, the risk of forming such an electrically insulating oxide
interlayer is
negated by the presence of Ru in the coating, which has the ability to form a
passivation-resistant interlayer at the interface Titanium - coating.
Nickel is particularly suitable for the preparation of electrodes since it is
dimensionally stable and is capable of strongly interacting with Co by forming
NiCo204. spinels.
Cobalt oxide (Co304) is a well-known oxygen evolution electrocatalyst and,
along
with mixtures of nickel iron oxides and cobalt iron oxides, one of the
materials with
the highest power efficiency. This means that the material allows in use for a
low
overpotential. The material has a lower overpotential than nickel oxide grown
on
massive Ni, which is the standard material in alkaline electrolyzers today,
and which
tends to deactivate over time.
To utilize Co304 layers in alkaline electrolyzers, significant layer
thicknesses need to
be deposited; although it was found that the cobalt wear rate during operation
is on
the same scale as iridium oxide, a state-of-the-art electrocatalyst with very
high rarity
and price, the extremely high lifetime requirements of alkaline electrolyzers
necessitate significant loadings. Co304 however suffers from poor bulk
electrical
conductivity, which makes thick layers of the pre-formed oxides unfeasible.
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In one embodiment, attempts to circumvent this issue are achieved by adding to
the
Co304 layer both a) Zr and b) Ru or Au, which serve as a) a dispersing agent
to
increase the volume and active surface area of the electrocatalyst, and b) a
conductivity agent, to improve the electrical conductivity in the bulk coating
and
prevent the formation of a passivating layer at the interface of the coating
and the
massive metal support during repeated calcination in air and electrolytic
operation of
the coating.
According to the disclosure it has been established that, surprisingly, very
small
amounts of Zirconium in combination with a very small amount of a noble metal,
such as Ruthenium or Gold importantly alters and improves the properties of a
coating comprising Cobalt oxide comprising coating, in particular when
considering
oxygen evolution.
It is noted that the coatings according to the disclosure allow electrolyzers
using
electrodes and in particular anodes provided with the coating to operate at a
higher
power efficiency. The power efficiency is the key factor in determining the
OPEX,
which term refers to the operating expenses. If the gain in efficiency at high
currents
densities is sufficient, it may also reduce the needed stack size, which
decreases the
CAPEX, which term refers to the capital expenses.
Figures 2 and 3 illustrate the beneficial effects of the inclusion of
Zirconium and
Ruthenium in Cobalt oxide on oxygen evolution electrocatalysis.
Figure 2 illustrates the effect of adding Zirconium and Ruthenium to Cobalt-
oxide
coatings on the initial potential (E,), which is shown on the Y-axis. On the X-
axis the
Cobalt loading of the coating is indicated. Figure 2 relates to the
application of an
Cobalt oxide coating on a Titanium support.
Figure 2 firstly shows the relationship between Cobalt loading of pure Co304
deposited on a Titanium support and the initial potential (E). As shown in
Figure 2,
pure Co304 deposited on Titanium sees a gradual rise of the electrode
potential as a
function of Cobalt loading.
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As further shown in Figure 2, the addition of only Zirconium lowers the
electrode
potential at low Cobalt loadings but leads to a sharp rise in potential with
increasing
Cobalt loading. Figure 2 clearly shows that the addition of a small amount of
Ruthenium in addition to Zirconium significantly lowers the electrode
potential over
the full range of low Cobalt loadings to higher Cobalt loadings.
In the example of Figure 2, the presence Ruthenium is in the order of 5% mass
relative to Cobalt. This means that for each gram of Cobalt in the coating
0.05 gram
Ruthenium is present. In view of the price of Ruthenium, it is important to
note that
very small quantities already show a beneficial effect on the properties of
the
coating.
Figure 3 provides a comparison between on the Y-axis the lifetime of a Cobalt
oxide
coating, shown in units of total electrical charge passed per surface area
(IcAh/m2)
before coating deactivation, and on the X-axis the Cobalt loading in the
coating.
Figure 3 shows the effect of adding Zirconium to the coating and the effect of
adding
both Zirconium and Ruthenium to the coating. Figure 3 refers to the
application of a
Cobalt oxide coating applied on a Titanium support.
According to Figure 3, a coating of pure Co3O4 deposited on Titanium shows a
linear
increase of the lifetime of the coating as a function of Cobalt loading.
Figure 3
further shows that the addition of Zirconium has a beneficial effect on the
lifetime of
the coating and at low Cobalt loadings the addition of Zirconium clearly
increases the
lifetime. The Zirconium containing coating shows a linear trend in the
increase of the
lifetime related to the increasing Cobalt loading, but the beneficial effect
wears off at
higher Cobalt loadings.
Figure 3 finally shows that the further addition of Ruthenium leads to an
increase of
the lifetime of the coating at lower Cobalt leadings comparable to the coating
only
comprising Zirconium. However, the coating comprising both Zirconium and
Ruthenium shows a continuing and linear increase of the lifetime with an
increasing
Cobalt loading. In the example of Figure 3, a small amount of Ruthenium, in
the
order of 5% mass relative to Cobalt, is used to obtain the shown beneficial
effect. As
shown, the Ruthenium containing coating has similar effect at lower Cobalt
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as the coating only comprising Zirconium, but the effect is no longer limited
to lower
Cobalt loadings.
It is noted that the results shown in Figures 2 and 3 were obtained using
electrodes
with Cobalt oxide coatings that were formed by spin-coating water-based
solutions of
the metal salt precursors onto Titanium supports. These Titanium supports were
in
advance etched in hydrochloric (HCI) acid.
In general, the coating can be painted on the support. According to an
ambodiment,
prior to the step of applying the coating, a viscosity modifier is added. An
adapted
viscosity modifier for use in the production of electrodes according to the
disclosure
is polyethylene glycol.
After the application of the coating on the support, the production process
was
followed by thermal decomposition at 400 C for 15 minutes in air. That means
that
the Titanium supports were heated in an oven. The mentioned step of heating
could
be done be a temperature between about 300 C and 600 C, preferably by a
temperature between about 350 C and 450 C
The metal salt referred above could, for instance, comprise CoC12, RuC13, and
ZrCl2.
Alternatively, the salts could comprise Co(NO3)2, Zr(NO3)2 and Ru(No)(NO3).
The so obtained electrodes were then electrolyzed at 600 A/m2 in strong acid
(H2SO4, 25%). Although the coatings are intended to be used under strongly
alkaline
conditions, electrolysis in strong acid serves as an accelerated lifetime
test, since
one of the primary degradation mechanisms is local acidification at the
catalyst
surface due to the nature of oxygen evolution reaction.
The dispersing effect of Zirconium and the conductivity-promoting effect of
Ruthenium were further analyzed varying their fractions and noting the effect
on the
initial potential and the lifetime of the coating.
Figure 4a and 4b illustrate respectively the lifetime and the initial
potentials of Cobalt
oxide coatings with a fixed Cobalt / Ruthenium mass ratio and varying
Zirconium
mass fractions. In the examples of Figures 4a and 4b, the Cobalt / Ruthenium
mass
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ratio equals 20. That means that the coating comprises for every gram of
Cobalt
0.05 gram of Ruthenium. For the examples of Figures 4a and 4b, the Cobalt
loading
of the coating is approximately 2.1 g/m2 for each sample. It is further noted
that in
the examples of Figure 4a and 4b, the coating is applied on a Titanium
support.
Figure 4a shows that the addition of Zirconium increases the lifetime, up
until a
Zirconium / Cobalt mass fraction of approximately 25%. A further increase of
the
Zirconium up to Zirconium / Cobalt mass fractions of 50%, show a decrease of
the
coating lifetime.
Figure 4b shows that an increase of Zirconium above a mass fraction of
approximately 5 %, has no obvious positive effect on the initial potential,
provided
that in addition to the Zirconium, Ruthenium is present in the coating, as is
the case
in the example of Figure 4b.
Figures 5a and 5b illustrate the relationship between the lifetime and initial
potential
of Cobalt oxide coatings with a fixed Cobalt / Zirconium ratio and an
increasing
Ruthenium loading. In the examples of Figures 5a and 5b, the Cobalt /
Zirconium
mass ratio equals 10, which means that there is 0.1 gram of Zirconium for each
gram
of Cobalt. It is further noted that for the examples of Figures 5a and 5b, the
Cobalt
loading is approximately 2.3 g/m2. For the examples of Figure 4a and 4b, the
coating is applied on a Titanium support.
Figure 5a shows that the addition of Ruthenium above a minimum amount of 2.5 %
of the mass of Cobalt, does not importantly affect the lifetime of the
coating. The
reason for this is presumably the small amount of Ruthenium present in the
coating
compared to the amount of Cobalt.
Figure 5b shows that an increasing Ruthenium / Cobalt fraction leads to lower
potentials. The reason for this phenomenon is presumably because RuO2 (itself
an
efficient oxygen evolving catalyst) itself starts participating in the
reaction. The
beneficial effect in potential is already apparent at very small Ruthenium
concentrations. A pure RuO2 sample of comparable loading is shown as
reference.
Figure 6a shows the results of short-term electrolysis experiments run at 10
kA/m2
for a Nickel plate and respectively a Titanium support and a Nickel support
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comprising a Cobalt/Zirconium/Ruthenium coating with a mass ratio
Cobalt/Zirconium that equals 10 and a Cobalt/Ruthenium mass ratio that equals
80.
The Cobalt loading for the coating in Figure 6a is approximately 3.5 gram/m2.
Figure
6a shows that the supports with the Co/Zr/Ru coating have a lower (over)
potential
than pure Ni.
Figure 6b show the relative wear rates of Cobalt and Zirconium measured on a
Co/Zr/Ru coating on a Titanium support. The relevant Cobalt loading for Figure
6b is
approximately 10 gram/m2.
The experiments shown in Figure 6b were run in KOH 30% at a temperature of 50
0C.
Figure 7 shows the result of measurements in KOH 30% at a temperature of 20 0C
with a Nickel plate and a Nickel support electrode and a Titanium support
electrode
both provided with a Co-Zr/Ru coating 100-9/1. These tests were limited to KOH
30% electrolyte due to the vulnerability of Nickel to acid. The Y-axis of
Figure 7
shows the electric current density.
The Co-Zr/Ru 100-9/1 coating show a clear activity enhancement for the Nickel
support electrode when compared to pure Nickel, the benefit however is not as
high
as on the Titanium support electrode.
The difference in effectivity between the coating present on the Nickel
support and
on the Titanium support is presumably the fact that the Ruthenium component is
less
efficient at promoting the conductivity when the substrate is Nickel instead
of
Titanium. The short-term stability is sufficient for both substrates.
It is further noted that the data shown in Figure 7 were recorded using cyclic
voltammetry at a scan rate of 10mVs-1.
Figure 8 represent the results of tests that were run to assess the effect of
using a
Cobalt oxide coating comprising Zirconium as dispersing agent and Gold (Au) to
promote electrical conductivity throughout the bulk coating. On a Titanium
support
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electrode, respectively, the efficiency of the lifetime enhancing effect of
four different
coatings was tested:
1) pure Cobalt oxide (C0304);
2) a Cobalt oxide coating comprising Gold (Co304-AU);
3) a Cobalt oxide coating comprising Zirconium and Gold (Co304-Zr02/Au); and
4) a Cobalt oxide coating comprising Zirconium and Ruthenium (Co304-Zr02/Ru02)
According to the tests presented in Figure 8, instead of using Ruthenium as a
promoting agent, Gold was incorporated into the coating.
As shown in Figure 8, it was found that the presence of Gold in the Cobalt
oxide
coating can have a beneficial effect on the lifetime of the coating, provided
that the
coating also comprises Zirconium as dispersing agent.
The coatings shown in Figure 8 have a Cobalt/Gold mass ratio of 200.
The data provided for the Cobalt oxide coating comprising Zirconium and
Ruthenium
in Figure 8 relate to a Co-ZR/RU 1100-9/1 electrode and these data are shown
in
Figure 8 as a reference. The lifetime in the accelerated lifetime test in
H2SO4 25%
was also improved relative to pure cobalt oxide, but only when ZrO2 was also
included. From characterization cyclic voltammograms, it appears that the
inclusion
of Gold promotes the electrical conductivity in the coating, similar to
Ruthenium.
Figure 9 represent the results of tests that were run to assess the effect of
using a
Cobalt oxide coating comprising Au in terms of activity. The effect of Au on
the
activity was also tested in KOH 30% electrolyte using cyclic voltammetry at 20
0C.
While Co-Au coatings offer higher activity than pure Nickel, the enhancement
is not
as large as for Co/Zr/Ru coatings.
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