Electrode coatings, their method of production and use, electrodes and electrolysers employing the same

Abstract

The present invention relates to electrode coatings comprising a bifurcated porous network, the bifurcated porous network comprising bifurcated pores including globular pores and nanopores, wherein the globular pores open up to the surface of the electrode coating, the nanopores are connected within the outer walls of the globular pores and the nanopores have a lower diameter than the globular pores. The invention further relates to the use of the electrode coatings of the invention in the production of electrochemical catalyst systems, electrodes for energy storage or energy conversion applications. Finally, the present invention relates to electrodes comprising a substrate coated with the composite materials according to the invention.

Description

[0001] Adele Hydrogen SAS P043-24PCT

[0002] ELECTRODE COATINGS, THEIR METHOD OF PRODUCTION AND USE, ELECTRODES AND ELECTROLYSERS EMPLOYING THE SAME

[0003] FIELD OF THE INVENTION

[0004]

[0001] The present invention relates to electrode coatings, their methods of production, their structure and their uses. The invention further relates to electrodes and electrochemical energy conversion and storage systems as well as electrocatalyst systems employing the electrodes of the invention.

[0005] BACKGROUND OF THE INVENTION

[0006]

[0002] Electrochemical processes and devices are constantly gaining in popularity and commercial relevance. Electrochemical energy storage systems are in high demand, for example as batteries for cars, bicycles and hand-held devices, and as capacitors or supercapacitors for electronic memories or short-term energy storage applications. Electrochemical energy conversion systems are expected to become a cornerstone of the green economy, for example as fuel cells, electrolysers, pH swings, or for the production of e-fuels.

[0007]

[0003] All these processes have in common the requirement for suitable surfaces on which electrochemical reactions can occur, in particular on electrodes of secondary batteries, electrolysers and fuel cells. These are referred to as electrocatalysts.

[0008]

[0004] It is known that the suitability of electrodes and electrocatalysts is greatly dependent, besides their chemical composition and surface structure, on the electrical impedance and electrical conductivity of the surfaces on which electrochemical reactions occur. There is a constant need for improving the surface properties of functional electrodes and electrocatalysts, contingent on the requirements of specific applications.

[0009]

[0005] The skilled person in the art is aware that catalytic activity on functional electrode surfaces is limited by the accessibility of the electrode surface to the starting materials, which requires (i) good wettability of the surface with respect to the concerned medium and (ii) evacuation of the reaction products from the functional electrode surface during operation.

[0010]

[0006] Alkaline electrolyzers (AELs) have been widely used for water electrolysis due to their robustness, relatively low cost, and long-term stability. The electrodes in conventional AELs typically feature large porous structures to allow for catalyst loading and electrolyte access. However, these designs often faceperformance limitations due to the formation and accumulation of gas bubbles (hydrogen or oxygen) on the catalyst surface, which reduces the effective active surface area for further electrochemical reactions. A reduction of activity may occur when contact of the reactants with the electrode is impeded by low wettability of the functional electrode surface and / or by gas bubble coverage of the catalyst, which blocks access / contact and reaction between the electrolyte and reactant water, thereby impairing the efficiency of the electrolyser. As a result, a significant portion of the catalyst is rendered inactive during operation, reducing the overall performance and increasing reaction overpotential and thereby energy consumption.

[0011]

[0007] It is therefore advantageous for a functional electrode surface to have good wettability with respect to the immersion medium and to support evacuation of gaseous reaction products.

[0012]

[0008] EP 3 159433 B1 discloses a nickel electrode for alkaline water electrolysis, including a coating which is a porous nickel layer and which has a gradually increasing pore size with increasing distance from the electrode body, and wherein the porous nickel layer comprises a dendrite structure. The porous layer may be formed by galvanic deposition of a nickel containing alloy, where the concentration of the alloying component (Al, Zn, or Cr) gradually increases, and is subsequently removed. An improved overvoltage characteristic with regards to gases formed during operation may be obtained.

[0013] SHORT DESCRIPTION OF THE INVENTION

[0014]

[0009] The present invention is defined in the appended claims.

[0015]

[0010] In particular, the present invention is embodied by an electrode coating comprising a bifurcated porous network. According to the invention, the bifurcated porous network comprises bifurcated pores including globular pores and nanopores, wherein the globular pores open up to the surface of the electrode coating, the nanopores are connected within the outer walls of the globular pores and the nanopores have a lower diameter than the globular pores.

[0016]

[0011] According to one embodiment, the globular pores are pores have an average diameter of 0.5 pm to 30 pm, as measured by mercury intrusion porosimetry (MIP). In some embodiments, the globular pores may have an average diameter of 1 pm to 20 pm, such as 2.5 pm to 15 pm or 5 pm to 10 pm.

[0017]

[0012] According to one embodiment, the nanopores have a length of 1 pm to 30 pm and / or a diameter of 300 nm or less. In some embodiments, the nanopores may have an average length of 1.0 pm to 20 pm, such as 2.5 pm to 15 pm or 5 pm to 10 pm.In some embodiments, the nanopores may have an average diameter of 300 nm or less, such as for example 200 nm or less, or 100 nm or less or 50 nm or less. There is no specific lower limit for the diameter of the nanopores, but in practically achievable terms, the nanopores may have an average diameter of 0.5 nm or more, or 1 nm or more, or 5 nm or more.

[0018]

[0013] According to one embodiment, some of the nanopores connect individual globular pores with each other. For example, at least one of the nanopores connect individual globular pores with each other. In some embodiments, at least 1% of nanopores connect individual globular pores with each other, or 5% or more, or 10% or more, or 20% or more of nanopores connect individual globular pores with each other.

[0019]

[0014] According to one embodiment, the electrode coating material may be a composite material comprising 30 wt.-% or more nickel, with respect to the total weight of the composite material. In some embodiments, the electrode coating material may be a composite material comprising up to 70 wt.-% nickel, for example from 35 to 65 wt.-% nickel, or from 40 to 53 wt.-% nickel.

[0020]

[0015] According to one embodiment, the composite material may further comprise one or more elements selected from molybdenum, iron, chromium, zinc, aluminium, copper, oxygen or combinations thereof.

[0021]

[0016] According to one embodiment, the electrode material may have a thickness of 10 to 1000 pm, as measured by micro-gauge. In some embodiments, the electrode material may have a thickness of 70 to 400 pm.

[0022]

[0017] According to one aspect of the present invention, the electrode coating may be formed by a method comprising the steps of (i) providing a feedstock metallic powder having a desired elemental composition, (ii) thermal spraying of the feedstock powder onto a substrate to form a metallic coating, and (iii) activating the formed metallic coating by submerging in an alkaline aqueous solution, thereby creating a bifurcated porous network.

[0023]

[0018] According to one embodiment, the feedstock metallic powder may comprise 30 wt.-% or more nickel, with respect to the total weight of the composite material. In some embodiments, the feedstock metallic powder may comprise up to 70 wt.-% nickel, for example from 35 to 65 wt.-% nickel, or from 40 to 53 wt.-% nickel.

[0024]

[0019] According to one embodiment, the feedstock metallic powder may further comprise one or more elements selected from molybdenum, iron, chromium, zinc, aluminium, copper or combinations thereof.

[0020] According to one embodiment, the metallic coating formed in the thermal spraying step may have a thickness of 10 to 1000 pm, as measured by micro-gauge. In some embodiments, the electrode material may have a thickness of 70 to 400 pm.

[0025]

[0021] According to one embodiment, the alkaline aqueous solution in the activation step may comprise one or more selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, calcium hydroxide, or combinations thereof, optionally in the presence of a secondary reducing agent such as K-Na tartrate hydrate.

[0026]

[0022] According to one embodiment, the activation step may be carried out at elevated temperature. In some embodiments, the activation step may be carried out at 50°C, or at 60°C, or at 70°C or at 80°C or at 90°C.

[0027]

[0023] Also part of the present invention is an electrode comprising an electrode coating according to the present invention, or an electrode coating formed according to a method of the present invention.

[0028]

[0024] Finally, the use of an electrode of the present invention in electrochemical catalyst systems, electrodes for energy storage electrochemical energy conversion systems, such as electrolysers, fuel cells or secondary batteries, or apparatus designed to absorbing CO2 from air or flue gases by the means of a pH swing also forms part of the present invention.

[0029] SHORT DESCRIPTION OF THE FIGURES

[0030]

[0025] The invention will be further illustrated by reference to the following figures:

[0031] Fig. 1 shows a schematic illustration of an electrode including a coating according to the present invention - the blue areas indicate interlinked capillary nanopores;

[0032] Fig. 2 shows a representation of an electrode coating according to the present invention exhibiting globular pores before activation (a), and globular pores along with connecting nano-pores after activation (b);

[0033] Fig. 3 shows a schematic representation of a cell configuration for the measurement of iV curves and impedance spectroscopy data of the Examples of the application;

[0034] Fig. 4 shows current-voltage curves of an electrode not having the porous structure of the present invention (prior to activation) of Example 1 and the inventive electrode prepared in accordance with Example 2;Fig. 5 shows a Nyquist plot from electrochemical impedance spectroscopy (EIS) measurements for cells with an electrode not having the porous structure of the present invention (prior to activation) of Example 1 and the inventive electrode prepared in accordance with Example 2, at 0.05 A / cm2;

[0035] Fig. 6 shows a Nyquist plot from electrochemical impedance spectroscopy (EIS) measurements for cells with an electrode not having the porous structure of the present invention (prior to activation) of Example 1 and the inventive electrode prepared in accordance with Example 2, at 2 A / cm2.

[0036]

[0026] It is understood that the following description and references to the figures concern exemplary embodiments of the present invention and shall not be limiting the scope of the claims.

[0037] DETAILED DESCRIPTION OF THE INVENTION

[0038]

[0027] The present invention according to the appended claims provides electrode coatings for functional electrodes to achieve improved properties during operation. In particular, the electrode coatings according to the present invention have a bifurcated porous network. As used herein, a bifurcated porous network is a set of pores wherein at least a portion of the pores are bifurcated pores, each bifurcated pore including a globular pore section and at least one nanopore section. According to the present invention, the globular pores of the bifurcated porous network open up to the surface of the electrode coating, and the nanopores of the bifurcated porous network are located within the internal or outer walls of the globular pores, and the nanopores have a lower diameter than the globular pores. In other words, the porous network of the coatings according to the present invention comprises primary and secondary pores, wherein the secondary pores are located entirely within the primary pores, and the primary pores form openings on the surface of the coating.

[0039]

[0028] Alkaline electrolyzers (AELs) have been widely used for water electrolysis due to their robustness, relatively low cost, and long-term stability. The electrodes in conventional AELs typically feature large porous structures to allow for catalyst loading and electrolyte access. However, these designs often face performance limitations due to the formation and accumulation of gas bubbles (hydrogen or oxygen) on the catalyst surface, which reduces the effective active surface area for further electrochemical reactions. Gas bubble coverage of the catalyst blocks access / contact and reaction between the electrolyte and reactant water, which impairs the efficiency of the electrolyzer. As a result, a significant portion of the catalystis rendered inactive during operation, reducing the overall performance and increasing reaction overpotential and thereby energy consumption.

[0040]

[0029] According to the present invention, a capillary nanoporous electrode design for use in AELs and AEMs is proposed, which significantly mitigates gas bubble formation by utilizing a capillary-type porous structure. Nanopores, of diameter of less than 300 nm and ranging in length from 1 to 30 micrometers, lead into globular or larger pores that allow the electrolyser to maintain enhanced electrolyte contact with the catalyst while suppressing gas bubble accumulation at critical sites. As a result, the capillary pressure and the bubble point are reduced, which leads to lower transport polarization and enhanced performance.

[0041]

[0030] The presence of capillary-type nanopores allows for improved fluid transport and continuous electrolyte wetting of the catalyst surface, while at the same time suppressing the formation and trapping of gas bubbles within the electrode matrix. The nanopores are generally arranged in a random or arbitrary pattern. They fill with liquid electrolyte during operation, effectively preventing gas bubbles from forming adjacent to the catalyst surface, and only letting dissolved gas and transport of this dissolved gas towards globular pores.

[0042]

[0031] At the opening ends of the nanopores, larger globular pores are present, acting as reservoirs of electrolyte and allowing for bubble formation, while at the same time leading to faster diffusion of gases (hydrogen or oxygen) away from the electrode surface. This ensures that gas bubbles do not block the catalyst's active sites. Without wishing to be bound to theory, it is believed that the continuous wetting of the catalyst by the electrolyte, facilitated by the nanopores (since here gas is mostly in dissolved form and may or may not appear in bubble form only marginally), ensures that more of the catalyst remains exposed to the reactants, increasing the number of available active sites for electrochemical reactions.

[0043]

[0032] Finally, it is believed that the structure of the nanopores helps to suppress gas bubble nucleation by providing a confined space that maintains the electrolyte in close contact with the catalyst, whereas the formed hydrogen and oxygen species remain predominantly as dissolved species in the electrolyte. This capillary action prevents the formed oxygen and hydrogen from adhering to the catalyst surface and promotes transport of dissolved product gasses into the larger globular pores. This is estimated by low capillary pressure for the drainage and imbibition of water / electrolyte in the electrodes for a given test volume. In the connected globular pores, larger bubbles form but these can be transported more effectively away from the surface due to low pore tortuosity.

[0033] According to some embodiments, the nanopores may be oriented and sized such that they connect individual globular pores to each other. Such a structure further increases the active surface area of the electrode and improves evacuation of oxygen and hydrogen formed during operation.

[0044]

[0034] It follows that the design according to the present invention increases the effective active surface area of the catalyst, leading to improved reaction kinetics, lower overpotentials, and overall increased efficiency of the electrolyser. By preventing gas bubbles from covering the catalyst surface, the electrode coating according to the present invention ensures continuous electrochemical reaction, thereby reducing energy consumption and improving overall system efficiency. Improved fluid dynamics and the prevention of gas accumulation around the catalyst further reduce wear and degradation, thereby extending the operational life of the catalyst and the entire electrolyser system.

[0045]

[0035] According to the present invention, the electrode coating comprising a bifurcated porous network may be formed by thermal spraying and subsequent activation. The coating is initially formed by thermal spraying of an alloy powder. At this stage, it is preferable that the oxygen content in the powder is 5 ppm by weight or less. The elemental composition of the alloy powder corresponds to the desired elemental composition of the initial coating prior to activation. The particle size distribution of the feedstock powder obtained after gas atomisation may be such that it is suitable for use in thermal spraying applications. The particle sizes may range from 0.5 pm to 220 pm. In a preferred embodiment, the particle size distribution is such that d10 = 5 pm and d90 = 45 pm, as determined using a laser diffraction particle size distribution analyser. If necessary, the powder obtained after gas atomisation may be classified into a desired particle size range. The powder comprises an imbedded nanometric sacrificial material, such as for example aluminium and / or zinc, in the form of partly percolated particles of a solvable phase. The coating initially formed may comprise closed pores, or voids, which are comprised within the coating and have no opening to the coating surface.

[0046]

[0036] The thermal spray deposition of electrodes may be specifically designed through operating the process in a regime of particle temperature and particle velocity to build a coating by successive impact and controlled rapid solidification of molten droplets on the substrate. By defining the temperature and velocity of impacting particles as well as substrate surface state, the pore structure may be influenced. To achieve a desired structure, a median particle temperature at impact may be in therange of 1890°C to 2470°C, for example 1900°C to 2310°C. A median particle velocity at impact may be in the range of 90 m / s to 720 m / s, such as for example 100 m / s to 690 m / s. A mean plasma gas flow may be in the range of 45 slm to 250 slm, such as for example 55 slm to 220 slm. A plasma current intensity in the range of 220 A to 850 A, such as for example 250 A to 750 A may be applied. Using parameters outside these ranges, the geometry of the obtained porosity may be lamellar or crack-like, which is undesirable.

[0047]

[0037] After application of the coating, the electrode is activated by placing it in an activation bath enabling removal of a portion of the sacrificial material connected to a larger pore. The activation bath may comprise an alkaline aqueous solution, for example an aqueous hydroxide solution such as one or more selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, calcium hydroxide, or combinations thereof, optionally in the presence of a secondary reducing agent such as K-Na tartrate hydrate. In addition to the removal of sacrificial material, activation may lead to opening of closed pores present within the coating, thereby creating an additional pathway for the creation of nanopores, as well as nanopores connecting individual globular pores.

[0048]

[0038] Alternatively, electrochemical etching, 3D-nanoprinting, template-assisted synthesis, or nano-moulding may be employed to achieve precise control over pore size and structure.

[0049]

[0039] It should be noted that the present invention may comprise any combination of the features and / or limitations referred to herein, except for combinations of such features which are mutually exclusive. The foregoing description is directed to particular embodiments of the present invention for the purpose of illustrating it. It will be apparent, however, to one skilled in the art, that many modifications and variations to the embodiments described herein are possible. All such modifications and variations are intended to be within the scope of the present invention, as defined in the appended claims.

[0050] EXAMPLE 1 - PRODUCTION OF AN INITIAL COATING

[0051]

[0040] In the following, an initial coating is formed by conversion of a feedstock powder into a functional electrode on top of a substrate. In order to achieve this, a feedstock powder is provided by vacuum melting and inert gas atomisation. This allows high level of control and the oxygen content may be kept low. The elemental composition of the feedstock powder corresponds to the desired elemental compositionof the initial coating. The particle size distribution of the feedstock powder obtained after gas atomisation may be such that it is suitable for use in thermal spraying applications. The particle size distribution is such that d10 = 5 pm and d90 = 45 pm, as determined using a laser diffraction particle size distribution analyser. To achieve this, the powder obtained after gas atomisation may be classified into a desired particle size range.

[0052]

[0041] The obtained feedstock powder is then converted into a functional electrode on top of a substrate. This is done by using thermal spraying with a build-up customised gun on a multi-mesh structured substrate. Ar may be used as the primary forming gas whereas N2or H2or a mixture thereof may be used as the secondary gas. The feedstock powder is injected through external injection nozzles into a thermal spray flame with an enthalpy in the range of 20 to 40 MJ / kg. The heated and accelerated particles are impacted on the multi-mesh substrate to form an electrode.

[0053]

[0042] The obtained initial coating may have a thickness in the range of 10 to 1000 pm, as measured by micro-gauge. The elemental composition of the initial coating was about 35 to 40 wt.-% Ni, about 13 to 15 wt.-% Mo, about 34 to 38 wt.-% Al, about 4 to 6 wt.-% Cr, about 3 to 5 wt.-% Cu and about 2 to 4 wt.-% O.

[0054] EXAMPLE 2 -ACTIVATION OF THE INITIAL COATING

[0055]

[0043] While the initial coating displays good properties as an electrode in electrochemical applications, it was further activated to create the microstructure described in this invention to improve electrochemical properties. In order to do this, the initial coating was submerged in an activation solution for 24 hours at 70°C. The activation solution was a mixture of water and 30 wt.-% KOH and 1 to 10 wt.-% K-Na-tartrate-tetra hydrate solution.

[0056]

[0044] The activation treatment serves to increase the surface by forming a porous structure as exemplified by Fig. 1 and defined in claim 1.

[0057] EXAMPLE 3 - TWO-STAGE PORE EVOLUTION

[0058]

[0045] Cross-sectional SEM analysis of thermal spray coatings before and after chemical activation was performed using calibrated image analysis. Fig. 2 shows representation of the as-sprayed (a) and activated (b) samples, which most clearly illustrate the structural transformation. The data demonstrate a distinct structural transformation upon activation. Fig. 2(a) shows the as-sprayed electrode, with a globular porosity of 9.8% and a median globular pore size 2.02 pm. Fig. 2(b) shows the activated electrode, with a globular Porosity of 7.2%, a median globular pores sizeof 1.59 m, a fine pore porosity of 33.7%, a median length of connected pores of 0.85 pm, and a median width of connected pores of 0.07 pm. Globular pores were measured using mercury intrusion porosimetry and high resolution SEM. Connected pores were measured using high resolution SEM and conversion to digital images and grey to white shades analysis.

[0059] EXAMPLE 4 - STUDY OF ELECTROCHEMICAL PROPERTIES

[0060]

[0046] In the following, the current-voltage characteristics and electrochemical impedance spectroscopy (EIS) measurements were carried out on a state of the art nickel cathode, and a cathode coated with the composite material obtained in Example 2 above.

[0061] Electrode preparation

[0062]

[0047] A cathode coated with the composite material obtained at the end of Example 1 was compared to a cathode coated with the composite material and treated as in Example 2 above.

[0063] Electrode testing

[0064]

[0048] The electrodes were tested in a zero-gap electrolyzer cell as schematically represented in Fig. 3. The cell consisted of four main parts: nickel bipolar plates, nickel wire mesh as the current collector, test electrodes and Zirfon PERL UTP 500 as a diaphragm.

[0065]

[0049] The tests were carried out under atmospheric pressure in 30 wt.-% KOH at 70°C, by recording polarization curves at a scan rate of 10 mA s’1, after 30 min activation at constant current of 0.2 A, and using a biologic potentiostat.

[0066]

[0050] EIS was performed at low and high current densities and plotted from 50 kHz to 100 MHz to identify the ohmic and activation losses. The operating conditions and cell hardware were kept the same for all the tests. The fitting of Nyquist plots was done by RelaxIS software.

[0067] Results

[0068]

[0051] The current-voltage curves in Fig. 4 show a clear improvement of the intrinsic surface activity of the electrode having an activated surface coating with the composite according to the present invention over the non-activated coating. The activated electrodes, featuring a porous structure, exhibit consistently lower voltagesacross the tested current range. This confirms that the introduced porosity significantly enhances performance by reducing overpotentials.

[0069]

[0052] As can be seen in Fig. 5, at low current density (0.05 A / cm2), both cells exhibit the same ohmic resistance (X-axis intersection at high frequency). With activated electrodes at 0.02998 ohm vs unactivated at 0.03012 ohm. This is expected, as bubble formation is minimal at such low currents. Consequently, transport through the electrode pores is not yet a limiting factor, and porosity plays a negligible role. However, the activated electrodes show a significantly lower total resistance (X-axis intersection at low frequency), indicating faster reaction kinetics attributed to a higher electrochemically active surface area (ECSA). With activated electrodes to be around 0.17 ohm (when extrapolated to X-axis intersection) vs unactivated at approximately 0.23 ohm (when extrapolated to X-axis intersection).

[0070]

[0053] As can be seen in Fig. 6, at high current density (2.0 A / cm2), the impedance response reveals that both ohmic resistance (X-axis intersection at high frequency), with activated electrodes at 0.03089 ohm vs unactivated at 0.0330 ohm and overall resistance (X-axis intersection at low frequency), with activated electrodes to be 0.0473 ohm vs unactivated to be 0.0507 ohm, are significantly lower for the activated electrode.. This indicates that charge transfer and mass transport limitations — such as gas bubble accumulation and electrolyte depletion — become less severe in the presence of the porosity according to the present invention. The activated electrodes, by contrast to the non-activated electrodes, maintain lower resistances, confirming that the porous structure of this innovation facilitates improved electrolyte penetration and gas evacuation, thereby enhancing overall performance at high currents.

Claims

Adele Hydrogen SAS P043-24PCTC LA I M S1. Electrode coating comprising a bifurcated porous network, the bifurcated porous network comprising bifurcated pores including globular pores and nanopores, wherein the globular pores open up to the surface of the electrode coating, the nanopores are connected within the outer walls of the globular pores and the nanopores have a lower diameter than the globular pores.

2. Electrode coating according to claim 1, wherein the said globular pores are pores having an average diameter of 0.5 pm to 30 pm, as measured by mercury intrusion porosimetry (MIP).

3. Electrode coating according to claim 1 or 2, wherein the said nanopores have a length of 1 pm to 30 pm and / or a diameter of 300 nm or less, as measured by mercury intrusion porosimetry.

4. Electrode coating according to any one of the previous claims, wherein at least one of the nanopores connects individual globular pores.

5. Electrode coating according to any one of the previous claims, wherein the electrode coating material is a composite material comprising 30 wt.-% or more nickel, with respect to the total weight of the composite material.

6. Electrode coating according to claim 5, wherein the said composite material further comprises one or more elements selected from molybdenum, iron, chromium, zinc, aluminium, copper, oxygen or combinations thereof.

7. Electrode coating according to any one of the previous claims, wherein the electrode material has a thickness of 10 to 1000 pm, as measured by microgauge.

8. Method of production for an electrode coating of any one of claims 1 to 7, comprising the steps ofproviding a feedstock metallic powder having a desired elemental composition,thermal spraying of the feedstock powder onto a substrate to form a metallic coating,activating the formed metallic coating by submerging in an alkaline aqueous solution, thereby creating a bifurcated porous network.

9. Method of production according to claim 8, wherein the said feedstock metallic powder comprises 30 wt.-% or more nickel, with respect to the total weight of the composite material.

10. Method of production according to claim 9, wherein the said feedstock metallic powder further comprises one or more elements selected from molybdenum, iron, chromium, zinc, aluminium, copper or combinations thereof.

11. Method of production according to any one of claims 8 to 10, wherein the said metallic coating formed in the thermal spraying step has a thickness of 10 to 1000 pm, as measured by micro-gauge.

12. Method of production according to any one of claims 8 to 11, wherein the said alkaline aqueous solution in the activation step comprises one or more selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, calcium hydroxide, or combinations thereof, optionally in the presence of a secondary reducing agent such as K-Na tartrate hydrate.

13. Method of production according to any one of claims 8 to 12, wherein the said activation step is carried out at a temperature of 50°C or more.

14. Electrode comprising an electrode coating as defined in any one of claims 1 to 7 or formed using the method as defined in any one of claims 1 to 13.

15. Use of an electrode as defined in claim 14 in electrochemical catalyst systems, electrodes for energy storage, electrochemical energy conversion systems, such as electrolysers, fuel cells or secondary batteries, or apparatus designed for absorbing CO2 from air or flue gas by the means of a pH swing.

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