Durable nickel-based coatings

Abstract

A feedstock that provides enhanced durability to coatings, such as, for example, catalytic coatings used in electrolyzer technologies. The feedstock including an active feedstock material and an inactive feedstock material.

Description

DURABLE NICKEL-BASED COATINGSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This International application claims the benefi ( / priority of U.S. Provisional Application No. 63 / 646,244 filed May 13, 2024, the disclosure of which is expressly incorporated by reference herein in its entirety.BACKGROUND OF THE INVENTION1. Field of the Disclosure

[0002] The present disclosure relates to preparation and modification of nickel-based materials. Some embodiments of present disclosure relate to nickel-based coatings containing aluminum which are intended to react with an alkaline solution to form a high surface area coating. In some embodiments, the nickel-based materials may comprise nickel and one or more of aluminum and zinc, such as a material of the class of materials known as Raney Nickels (e.g., those that are typically used to form surfaces of high catalytic activity). In some embodiments, the nickel-based materials may be prepared in a manner such that one or more components thereof is capable of reacting with alkaline solutions.2. Background Information

[0003] The electrodes of alkaline electrolyzers are typically coated with nickel to enhance the catalytic activity of the hydrogen evolution reaction (HER), which is the splitting of water into hydrogen and oxygen on the cathode side of the electrolyzer. Nickel coatings offer a good balance between price and performance and thus are the most widely used coatings even though precious metals offer improved performance. A typical method of providing a nickel coating is to electroplate nickel onto a stainless steel cathode plate. In order to increase the catalyzing behavior of the nickel layer porosity can be introduced into the coating providing a higher surface area which is known to increase catalytic activity. One method of creating a porous Nickel metal surface is to deposit nickel oxide in some fashion onto the electrode. Thenickel oxide is then reduced when exposed to hydrogen at elevated temperatures either in-situ during the operation of the electrolyzer or via other processing techniques such as a hydrogen atmosphere heat treatment.

[0004] The reduction of NiO to nickel involves changes in the size of the crystal leaving behind a pore structure in the coating. Thermal spray is one of the conventional techniques which can be used to deposit the initial NiO coating. Such conventional techniques are known to those skilled in the art, and are described, for example, in International Publication Nos. WO 2013 / 191140 Al and WO 2013 / 141211 Al. Raney Nickel is another known material which can be used to create a porous Nickel surface. Raney Nickel refers to a class of alloys comprising Ni and one or more of Al and Zn. Typically, the Al and / or Zn content is in the range of 40-60 wt.% and the alloy comprises nickel intermetallic phases.

[0005] In the case of the more commonly used Ni-Al type Raney Nickel, the intermetallic phases are nickel aluminides of the AhNi, AI3N12, AlNi, or A 1 N i ? stoichiometry. The nickel, aluminum alloy base composition can be alloyed with additional elements such as molybdenum to enhance catalytic performance. A nickel aluminum molybdenum alloy (in which the Al: 37-55, Mo: 13-20 and the balance is Ni (also referred to as Ni-Al-Mo (BAL / 37- 55 / 13-20 in wt.%)) is an example of a Ni-Al-Mo variety of Raney Nickel that is known to deliver good performance and used commonly in the industry. Ni-Al-Mo is further advantageous as it can be manufactured using the gas atomization process and deposited onto a surface using the thermal spray process. Razmjooei et al., demonstrated the effectiveness of this Ni-Al-Mo Raney Nickel alloy using the thermal spray process. See Razmjooei et al., “Improving plasma sprayed Raney-type nickel-molybdenum electrodes towards high-performance hydrogen evolution in alkaline medium’", Scientific Reports, 2020, 10: 10948.

[0006] Raney Nickel produces a porous nickel coating by way of a leaching process. When exposed to an alkaline environment, the Al in the Raney Nickel alloy is leached out leaving behind a highly porous Nickel coating of high surface area. This porous nickel is known to be a more effective catalyst than an electroplated nickel coating due to the enhanced surface area.

[0007] However, the increased surface area and porosity has a detrimental effect on the structural integrity of the coating. And, even in view of the academic development that hasoccurred to date, there is still a need to develop Raney Nickel type catalytic coatings for enhanced stability.

[0008] While the current technology of Raney Nickel coatings yields a porous nickel coating, which has good catalytic behavior, such coatings will spall off or break away from the substrate causing downstream problems in the operation of the electrolyzer. Furthermore, a nickel-based coating that is leached in advance of being inserted into the electrolyzer (a common industrial practice) must be handled very delicately. Some conventional Raney Nickel coatings will spontaneously combust and spall off from the electrode substrate if exposed to an open-air environment post leaching. Whether leached in situ, i.e., during the normal function of the electrolyzer, or in advance of being inserted into the electrolyzer stack, conventional Raney Nickel coatings are known to have low adhesion (e.g., in the range of 10- 40 psi). For reference, such a poorly adhered coating can be pulled off with Scotch tape. Thus, there is a need to develop technologies to make such nickel-based coatings more durable while retaining catalytic performance.SUMMARY

[0009] The aim of the present disclosure is to provide a feedstock including an active feedstock material and an inactive feedstock material that is used to obtain nickel-based coatings (containing aluminum or zinc) that are intended to react with an alkaline solution to form a durable high surface area coating.

[0010] In embodiments, the active feedstock material includes either a Ni-Al alloy and / or an alloy material including Ni, Mo, and 40-60 wt% of one or more of Al and Zn. In some embodiments, the active feedstock material may include the following elements in wt.%: Al: 37-55, Mo: 13-20, and Ni: Balance. In other embodiments, the active feedstock material may include the following elements in wt.%: Al: 40-50, Mo: 1-10, and Ni: Balance.

[0011] In some embodiments, the active feedstock material has a particle size of 10- 200 pm, or a particle size of 10-60 pm. In some embodiments, such particles have a substantially spherical shape.

[0012] In embodiments, the inactive feedstock material includes one or more member selected from the group consisting of a nickel-based alloy, a precious metal, gold, platinum, and iridium. In some embodiments, the inactive feedstock material includes pure nickel, Inconel 625, or a Ni-Al alloy that includes: 2-8 wt.% Al, and Ni as the balance. In otherembodiments, the inactive feedstock material is pure nickel, Inconel 625, or a Ni-Al alloy that has 2-8 wt.% Al, and Ni as the balance.

[0013] In embodiments, 50-95 wt.% of the total weight of the feedstock is the active feedstock material, preferably 60-85 wt.% of the total weight of the feedstock is the active feedstock material, more preferably 65-75 wt.% of the total weight of the feedstock is the active feedstock material.

[0014] Embodiments are also directed to a coating formed from the feedstock according to any of the above-described embodiments. In embodiments, the coating has a thickness in the range of from 1 pm to 200 pm, preferably a thickness in the range of from 1 pm to 50 pm, more preferably a thickness in the range of from 1 pm to 20 pm.

[0015] In some embodiments, a porosity of the coating is 10% or less, or 8% or less.

[0016] In some embodiments, the coating passes the scratch testing without being worn down according to ASTM D6677 standard after leaching in alkaline solution.

[0017] In some embodiments, the coating comprises a dual phase structure of 50-90 vol.% active material and 10-50 vol.% inactive material.

[0018] Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is further described in the detailed description which follows, in reference to the drawing by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawing.

[0021] Figure 1 shows an optical micrograph of coating prepared with an exemplary feedstock of the present disclosure (the active material 102 forms the darker phase (the continuous matrix in the coating) and inactive material 101 forms the lighter phase in the optical micrograph occupying 20-40 volume% of the total coating structure in the form of pancake particles 5-20 pm in thickness and 15-75 pm in length).

[0022] Figure 2A and 2B show plots of cyclic electrochemical testing data acquired for Coating Sample 9.

[0023] Figure 3 A and 3B show plots of cyclic electrochemical testing data acquired for Coating Sample 9.

[0024] Figure 4A-4D each depict illustrations of various coatings before and after being subjected to long term electrochemical testing.DETAILED DESCRIPTION

[0025] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

[0026] As used herein, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. For example, reference to “a powder material” would also mean that mixtures of one or more powder materials can be present unless specifically excluded. As used herein, the indefinite article “a” indicates one as well as more than one and does not necessarily limit its referent noun to the singular.

[0027] Except where otherwise indicated, all numbers expressing quantities used in the specification and claims are to be understood as being modified in all examples by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by embodiments of the present disclosure. At the very least, and not to be considered as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding conventions.

[0028] Additionally, the recitation of numerical ranges within this specification is considered to be a disclosure of all numerical values and ranges within that range (unless otherwise explicitly indicated). For example, if a range is from about 1 to about 40, it is deemed to include, for example, 1, 7, 23.7, 34, 36. 1, 40, or any other value or range within the range.

[0029] As used herein, the terms “about” and “approximately” indicate that the amount or value in question may be the specific value designated or some other value in itsneighborhood. Generally, the terms “about” and “approximately” denoting a certain value is intended to denote a range within ±5% of the value. As one example, the phrase “about 100” denotes a range of 100+5, i.e., the range from 95 to 105. Generally, when the terms “about” and “approximately” are used, it can be expected that similar results or effects according to the disclosure can be obtained within a range of +5% of the indicated value.

[0030] The terms “substantially” and “essentially” are used to denote that the following feature, property or parameter (such as, for example, being substantially spherical) is either completely (entirely) realized or satisfied or to a major degree (such as 90%, 95%, or 99% (e.g., in terms of the degree to which a particle approximates the shape of a sphere)) that does not adversely affect the intended result.

[0031] The term “comprising” as used herein is intended to be non-exclusive and open- ended. Thus, for example a composition comprising alloy A may include other alloys besides A. However, the term “comprising” also covers the more restrictive meanings of “consisting essentially of” and “consisting of, so that for example “a composition comprising alloy A” may also (essentially) consist of the alloy A.

[0032] In the present disclosure, unless otherwise noted, all weight percentages pertaining to an elemenl / component of a composition / material / feedstock are based on the total weight of the composition / material / feedstock including any unavoidable impurities that may be present.

[0033] The present disclosure describes a feedstock which provides enhanced durability to coatings, such as, for example, catalytic coatings used in electrolyzer technologies.

[0034] In some embodiments, the feedstock may be a blend of an active feedstock material and an inactive feedstock material.

[0035] The active feedstock material can comprise a NiAl alloy, preferably an alloy within the Raney Nickel family. In some embodiments, the active feedstock material in the Raney Nickel family can be a material of NiX (BAL / 40-60 in weight percent (wt.%)), where X is one or more of Al and Zn. The active feedstock material can further comprise additional elements, such as, for example, Mo. In a preferred embodiment, the active feedstock material can be a material of NiAlMo (BAL / 37-55 / 13-20 in wt.%), hereinafter referred to as “Raney Nickel #1”. In other embodiments, the active feedstock material can be a material of NiAlMo (BAL / 40-50 / 1-10 in wt.%), hereinafter referred to as “Raney Nickel #2”

[0036] The active feedstock material can be of any suitable shape and / or form depending on the coating fabrication methodology that is selected. In some embodiments, the active feedstock material is in the form of a powder. For example, such a powder may have particles that are spherical or substantially spherical. In some embodiments, spherical particles or substantially spherical particles of the powder may have a particle size distribution (in terms of the diameter of the individual spherical particles) that is in the range of from 10-200 pm, or even more preferably in the range of from 10-60 pm. In some embodiments, the spherical particles or substantially spherical particles of the powder may have and average particle size (in terms of the diameter of the individual spherical particles) that is in the range of from 15 pm to 53 pm.

[0037] In embodiments, the active feedstock material can be blended with an inactive feedstock material, such as an inactive feedstock material in the form of a powder, such as a spherical powder (e.g., a powder of spherical particles that have particle size distribution (in terms of the diameter of the individual spherical particles) of that is in the range of from 10- 200 pm, or even more preferably in the range of from 10-60 pm).

[0038] In embodiments, the active feedstock material can be blended with the inactive feedstock material at any desired predetermined ratio. For example, in some embodiments, the active feed stock material can be blended with an inactive feedstock material such that the active feed stock material represents 50-90 wt.% of the total powder blend {((wt.% active feedstock material) / ((wt.% active feedstock material) + (wt.% inactive feedstock material)))}, more preferably 60-85 wt.% of the total powder blend, and still more preferably 65-75 wt.% of the total powder blend.

[0039] The inactive feedstock material can be any suitable inactive material known to be unreactive in the presence of an alkaline solution. In embodiments, the inactive feedstock material may be an effective catalytic material. For example, in some embodiments, the inactive feedstock material can comprise a precious metal, such as, for example, gold, platinum, or iridium. However, for cost reasons, it is preferable if the inactive feedstock material is Ni-based.

[0040] In some embodiments, the inactive feed stock material can be pure nickel, a known Nickel superalloy, such as Inconel 625, or a single phase Ni-Al alloy (e.g., an NiAl alloy containing 2-8 wt.% Al and Ni as the balance). In a preferred embodiment, the inactive feed stock material comprises NiAl (BAL / 2-8 in wt.%), hereinafter defined as “Ni5Al”. Ni5Alcan provide strong bond strength to a coating when deposited via a thermal spray process. In other embodiments, the inactive material can be NiAl (BAL / 2-30 in wt.%), more preferably NiAl (BAL / 10-30 in wt.%), still more preferably NiAl (BAL / 20-30 in wt.%). In some embodiments, the inactive material is a gamma prime forming Nickel alloy or Nickel superalloy.

[0041] In some embodiments, thermal spray process conditions, the active feedstock material and the inactive feedstock material are selected such that the coating that is deposited via the thermal spray process is a coating that meets a minimum scratch resistance as set via ASTM D6677. In some embodiments, thermal spray process conditions, the active feedstock material and the inactive feedstock material are selected such that the coating that is deposited via the thermal spray process is a coating can survive >10 scratches after exposure to a solution of 100 mL deionized water, 38.89 g of KOH, and 8.00 grams of Potassium Sodium Tartrate at a temperature of 70°C for 24 hours. For example, in some embodiments, the active material may be selected to be NiAlMo (BAL / 37-55 / 13-20 in wt.%) and the inactive material may be selected to be NiAl (BAL / 2-8 in wt.%), where the active feed stock material is blended with an inactive feedstock material such that the active feed stock material represents 10-75 wt.% of the total powder blend (and the inactive material makes up the balance of the total powder blend). For example, in the active material may be selected to be NiAlMo (BAL / 37-55 / 13-20 in wt.%) and the inactive material may be selected to be NiAl (BAL / 2-8 in wt.%), where the active feed stock material is blended with an inactive feedstock material such that the active feed stock material represents 10-25 wt.% of the total powder blend, or represents 25-45 wt.% of the total powder blend, or represents 45-65 wt.% of the total powder blend, or preferably represents 65-75 wt.% of the total powder blend (and the inactive material makes up the balance of the total powder blend).

[0042] In some embodiments, the active feedstock material and inactive feedstock material are selected such that the coating exhibits less than 0.05 (<0.05) grams mass loss as measured via the ISO 8502-3 dust tape test after exposure to a solution of 100 milliliters (mL) deionized water, 38.89 grams of KOH, and 8.00 grams of potassium sodium tartrate at a temperature of 70°C for 24 hours. In preferred embodiments, the coating exhibits <0.04 grams mass loss after described exposure. In preferred embodiments, the coating exhibits <0.03 grams mass loss after described exposure.

[0043] Thermal spray processes (such as Atmospheric Plasma Spray (APS)) are known in the art, as disclosed in International Publication Nos. WO 2013 / 191140 Al and WO2013 / 141211 Al and the article by Razmjooei et al., “Improving plasma sprayed Raney-type nickel-molybdenum electrodes towards high-performance hydrogen evolution in alkaline medium”, Scientific Reports, 2020, 10:10948, the disclosures of which are expressly incorporated by reference herein in their entireties. Thermal spray processing parameters, the active feedstock material and the inactive feedstock material may be selected depending on the desired microstructure, morphology and elemental composition of the coating.

[0044] In some embodiments, thermal spray process conditions, the active feedstock material and the inactive feedstock material are selected such that the coating comprises a dual phase structure of 50-90 vol.% active material and 10-50% inactive material. In preferred embodiments, the active material is NiAlMo (BAL / 37-55 / 13-20 in wt.%) and the inactive material is NiAl (BAL / 2-8 in wt.%). In some embodiments, the coating is prepared (such as by APS) to be 1 pm to 200 pm in thickness, in preferred embodiments, the coating is prepared (such as by APS) to be 1 pm to 50 pm thick. In still further preferred embodiments, the coating is prepared such that the thickness of the coating is 1 pm to 20pm. In some embodiments, the coating is prepared (such as by APS) such that the porosity of the coating is 10% or less, or 8% or less.

[0045] In some embodiments, the inactive material, such as NiAl (BAL / 2-8 in wt.%), may be selected such that it forms a pancake like morphology in the coating (e.g., structures that are 5-20 pm in thickness and 15-75 pm in length). In some embodiments, the inactive material phases in the coating are isolated or not interconnected. Figure 1 shows an exemplary coating example where the processing conditions were selected such that the inactive material NiAl (BAL / 2-8 in wt.%)

[0101] forms a lighter phase in the optical micrograph occupying 20- 40 volume% of the total coating structure in the form of pancake particles 5-20 pm in thickness and 15-75 pm in length. The active material (NiAlMo (BAL / 37-55 / 13-20 in wt.%) (

[0102] in Figure 1) is the darker phase of the optical micrograph, and forms a continuous matrix in the coating.

[0046] The present invention is further illustrated by the following non-limiting examples where all parts, percentages, proportions, and ratios are by weight, all temperatures are in ° C., and all pressures are atmospheric unless otherwise indicated.EXAMPLES

[0047] Example 1 : Three coating samples (i.e., Coating Sample 1, Coating Sample 2, and Coating Sample 3) were sprayed with pure Raney Nickel #1 (Coating Sample 1) and avariety of blends (Coating Samples 2 and 3) to understand coating durability after leaching. It was determined that a 70% Raney Nickel #1 blend with 30% Ni5Al was useful for providing enhanced coating durability.

[0048] Coating Sample 1 : A 50- 100 pm coating of 100% Raney Nickel #1 was formed on pure a nickel substrate via a plasma spray apparatus in which an atmospheric plasma spray process was employed (Current: 350A; Voltage: 80-95V; Ar at 60 Normal Liters Per Minute (NLPM); H2at 2 NLPM).

[0049] Coating Sample 2: A 50-100 pm coating of 85 / 15 wt.% blend of Raney Nickel #1 and N15A1 was formed on a pure nickel substrate via a plasma spray apparatus in which an atmospheric plasma spray process was employed (Current: 350A; Voltage: 80-95V; Ar at 60 NLPM; H2at 2 NLPM).

[0050] Coating Sample 3: A 50-100 pm coating of 70 / 30 wt.% blend of Raney Nickel #1 and Ni5Al was formed on a pure nickel substrate via a plasma spray apparatus in which an atmospheric plasma spray process was employed (Current: 350A; Voltage: 80-95V; Ar at 60 NLPM; H2at 2 NLPM).

[0051] The following tests were conducted in order to characterize and compare the durability of the above-mentioned Coating Samples: Each of the Coating Samples were first leached in a solution of 100 mL deionized water, 38.89 g of KOH, and 8.00 grams of potassium sodium tartrate at a temperature of 70°C for 24 hours. This leaching solution is comparable to how Raney Nickel coatings are leached both ex situ and in situ of the electrolyzer. Because leached coatings are very delicate to handle, in order to evaluate the Coating Samples prior to potential damage by exposure to air, the coating was scratched while still in solution after the 24 leaching period was completed. ASTM D6677 “Standard Test Method for Evaluating Adhesion by Knife” was used to evaluate coating durability. Briefly, the ASTM D6677 test requires a qualitative assessment of the coating after a predetermined amount of scratching. For the purposes of this application, a Coating Sample that could be completely scratched away during the test (i.e., such that the substrate was revealed) was deemed a non-durable coating, whereas a Coating Sample which survived the scratch testing without being worn down to the substrate during the test was deemed a durable coating.

[0052] Coating Sample 1 (100% Raney Nickel #1) completely scratched away during the test to reveal the substrate and thus was determined to be non-durable (i.e., ASTM D6677 Scratch Test Result = Fail).

[0053] Coating Sample 2 (85 / 15 wt.% blend of Raney Nickel #1 and Ni5Al) completely scratched away during the test to reveal the substrate and thus was determined to be nondurable (i.e., ASTM D6677 Scratch Test Result = Fail).

[0054] Coating Sample 3 (70 / 30 wt.% blend of Raney Nickel #1 and Ni5Al) was not completely scratched away during the test and thus was determined to be durable (i.e., ASTM D6677 Scratch Test Result = Pass). Inspection of Coating Sample 3 appeared to reveal that the Ni5Al particles (being unreactive to the alkaline solution) provide sufficient structure to the overall coating after the Raney Nickel #1 has leached.

[0055] Example 2: Three coating samples (i.e., Coating Sample 4, Coating Sample 5, and Coating Sample 6) were applied to again test durability. In the Example 2 set of experiments, in addition to the scratch test (performed as discussed above), a dust tape test per ISO 8502-3 was used to quantify coating durability. The dust tape test measures the amount of dust, or in this case degraded coating, which can be pulled from the surface and sticks to the tape. It is quantified in terms of mass gain of the tape before and after.

[0056] Coating Sample 4: 100% Raney Nickel #1 was sprayed via similar parameters / conditions to those employed to generate Coating Sample 1 (i.e., an atmospheric spray process using the following parameters / conditions: Current: 350A; Voltage: 80-95V; Ar at 60 NLPM; H2 at 2 NLPM) such that Coating Sample 4 can serve as an effective control or repeat of experimentation performed in Example 1.

[0057] Coating Sample 5: 70 / 30 wt.% blend of Raney Nickel #1 and Ni5Al was sprayed via similar parameters / conditions to those employed to generate Coating Sample 3 (i.e., an atmospheric spray process using the following parameters / conditions: Current: 350A; Voltage: 80-95V; Ar at 60 NLPM; H2 at 2 NLPM) such that Coating Sample 5 a repeat of Coating Sample 3, which was deemed the ideal material in the Example 1 experimentation.

[0058] Coating Sample 6: 100 wt.% of Raney Nickel #1 was formed on pure a nickel substrate via a plasma spray apparatus in which an atmospheric plasma spray process aw follows was employed: Current: 500A; Ar at 50 NLPM; H2 at 0 NLPM.

[0059] All of the samples were leached under similar conditions as described in Example 1: leached in a solution of 100 mL deionized water, 38.89 g of KOH, and 8.00 grams of potassium sodium tartrate at a temperature of 70°C for 24 hours. The results of the testing are shown below in Table 1.Table 1: Summarized results of Example 2

[0060] As reflected by the results set forth in Table 1, the 100% Raney Nickel Sample Coatings could be made to be a durable coating with suitable condition / parameter control. However, further testing with slightly modified conditions / parameters for generating the coating revealed that the durability of the 100% Ranel Nickel #1 coatings could become undesirable (i.e., a failed scratch testing result) with only slight changes in the conditions / parameters for generating the coating (e.g. , the undesirable durability / unsatisfactory structural integrity could be brought about by the following changes to the conditions / parameters: Current: 400A; Ar at 60 NLPM; H2 at 0 NLPM, to the methodology that was used to prepare Coating Samples 1 and 4).

[0061] Example 3: Three different coatings were sprayed to evaluate the electrochemical behavior of the coatings.

[0062] A key measure of the catalytic behavior of such coatings is the overpotential. The overpotential is a measure of the efficiency of the electrochemical cell with the applied coating and it is desirable to have a low as possible overpotential. It is not sufficient for such coatings to simply have good durability in the alkaline environment, they must also perform well electrochemically to have industrial value.

[0063] In the experiments set forth below, a comparison was made between: (i) 100% Raney Nickel #1, and (ii) the blend of 70 / 30 wt.% blend of Raney Nickel #1 and Ni5Al. In addition to testing the material chemistry, different particle sizes were also evaluated. The typical particle size distribution for a thermal spray process is 11-45 micrometers (pm). In this regard, Coating Samples 1-6 (discussed in Examples 1 and 2 above) were sprayed with 11-45 pm powder. For cost improvement, a particle size distribution of 11-75 micrometers (pm) was evaluated in this Example (Example 3).

[0064] To obtain the overvoltage towards hydrogen evolution reaction (HER), as sprayed and / or activated specimens were used as a cathode in a three-electrode electrochemical cell. Platinum mesh and reversible hydrogen electrodes were used as counter and reference electrodes, respectively. All voltages reported should be read as IR corrected by high frequency resistance from impedance signal.

[0065] In the following experiments: 500 mL of 30% KOH in DI water, thermostated at 70°C, was used as the electrolyte. The electrochemical cell was sealed with a condenser to avoid any electrolyte evaporation. A geometrical area of 1 cm2was defined as the working electrode. Before measuring the overvoltages, all samples underwent a pretreatment step (-0.2 A / cm2) to stabilize the surface chemistry and removal of oxides on the electrode. Electrochemical techniques (like voltammetry chronopotentiometry) were used to obtain the I- V curves. Each sample underwent the following sequence (for about 24 hours) and the sequence was looped three times (for at total period of about 72h) and an average of overvoltages was presented:Pre-electrolysis treatment (-0.2 A / cm2for 30 min);I-V curves up to 1 A / cm2(minimum 5 per sample); andChrono potentiometric polarization at -0.25, -0.5, -0.75, -1 A / cm2(for 5h each)

[0066] Coating Samples 7-9 were sprayed with similar conditions / parameters — i.e., an atmospheric spray process using the following conditions / parameters: Current: 500A; Ar at 50 NLPM; H2 at 0 NLPM with powder having a particle size distribution of 11-75 pm being obtained. As seen above, such methodology provided good durability to the 100% Ranel Nickel #1 coating. In particular, Coating Sample 7 is a powder having a particle size distribution of 11-75 pm obtained from 100% Raney Nickel #1; Coating Sample 8 is a powder having a particle size distribution of 11-75 pm obtained from the 70 / 30 wt.% blend of Raney Nickel #1 and Ni5Al; and Coating Sample 9 is a powder having a particle size distribution of 11-45 pm obtained from the 70 / 30 wt.% blend of Raney Nickel #1 and Ni5Al.

[0067] The results of the above electrochemical tests (relating to overpotentials) are shown below in Table 2.Table 2: Electrochemical Properties of Coating Samples 7-9

[0068] The results set forth in Table 2 show that the overpotential of the 70 / 30 wt.% blend of Raney Nickel #1 and Ni5Al is actually equivalent to or lower than that of the 100% Raney Nickel #1 coating.

[0069] Furthermore, the lack of electrochemical degradation and even slight improvement in electrochemical behavior is an unexpected result when blending a significant portion of inactive material into the coating.

[0070] Additional tests using a 50 / 50 wt.% blend of Raney Nickel #1 and Ni5Al were conducted to explore this boundary further. The results of these additional tests are set forth in Table 3 (below). All coating presented in Table 3 were sprayed with similar (i.e., to that of Coating Samples 7-9) conditions / parameters — i.e., an atmospheric spray process using the following conditions / parameters: Current: 500A; Ar at 50 NLPM; H2 at 0 NLPM (such methodology being used to afford the good durability of the tested 100% Ranel Nickel #1 coatings).

[0071] In this regard, overpotential values at 60 mA / cm2showed that electrochemical behavior was not substantially degraded with further increases in inactive material content. While the results are varied, the results to reflect that a blended material, particularly 70 / 30 wt.% blend Raney Nickel #l / Ni5Al sprayed as a powder having a particle size distribution of 10-90 pm can be made to exceed the performance of Raney Nickel #1.Table 3: Electrochemical Properties of Various Coatings

[0072] Example 4: Coating Sample 9, as described above, was subjected to longer term cyclic electrochemical testing whereby the applied current was varied under otherwise similar testing conditions to that as described above (in Example 3). The data acquired from such electrochemical testing is plotted in Figures 2 and 4.

[0073] Such cyclic / long term testing is the most critical to understanding the behavior of the coating in application. It is generally desirable for the coating to survive and furthermore retain desirable catalytic behavior over the lifetime of the electrolyzer, which is typically on the order of 10 years.

[0074] Figures 2A-3B show the electrochemical output and recorded voltage, as a function of applied current for such testing. As illustrated in Figures 2A-3B, over the course of several days the current was switched on and off and the voltage recorded.

[0075] As shown in Figure 2A, the beginning of life (BOL) voltage

[0201] (of Figure 2 A) and

[0401] (of Figure 3 A) evolves over time which can result in both an increase in overpotential as occurs in Day 4

[0202] (of Figure 2A) or a decrease in overpotential

[0203] (of Figure 2A) and

[0402] (of Figure 3A). Such shifts in overpotential are a result in the system reaching equilibrium as the coating porosity evolves over the course of the testing. It is desirable for the coating to have a low overpotential over the duration of its life. As shown in results and data depicted in Figures 2A-3B, the overpotential of the coating formed from the feedstock of the present disclosure does not increase substantially over the term of the testing.

[0076] In such testing, while it may be difficult to quantify the improved performance of the 70 / 30 wt.% blend Raney Nickel #l / Ni5Al against the 100% Raney Nickel #1, it is clear(qualitatively) that the blended feedstock of the present disclosure exhibited improved electrochemical performance as a function of enhanced durability.

[0077] In addition, as can be seen in Figures 4 A and 4B, the deposited Ranel Nickel # 1 sample

[0301] (of Figure 4A) resulted in extreme coating spallation early in the intended long term testing

[0302] (of Figure 4B). The area of exposure is clearly seen

[0303] (of Figure 4B) as the entire coating has spalled off. Thus, while it was possible to measure beginning of life electrochemical performance, the coating was not durable enough to make any cyclic measurements (especially at elevated currents). In contrast, and as can be seen in Figures 4C and 4D, the 70 / 30 wt.% blend Raney Nickel #l / Ni5Al blend, as sprayed coating

[0304] (of Figure 4C) does not show any significant degradation (aside from some slight discoloration

[0305] (of Figure 4D) after completion of the entire duration of the cyclic testing).

[0078] It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.

Claims

What is claimed:

1. A feedstock comprising an active feedstock material and an inactive feedstock material.

2. The feedstock according to claim 1, wherein the active feedstock material is a Ni-Al alloy.

3. The feedstock according to claim 1, wherein the active feedstock material comprises Ni, Mo, and 40-60 wt% of one or more of Al and Zn.

4. The feedstock according to claim 1, wherein the active feedstock material comprises the following elements in wt.%:Al: 37-55,Mo: 13-20, andNi: Balance.

5. The feedstock according to any of claim 1 , claim 2 orclaim 3, wherein the active feedstock material comprises the following elements in wt.%:Al: 40-50,Mo: 1-10, andNi: Balance.

6. The feedstock according to any of the preceding claims, wherein the active feedstock material has a particle size of 10-200 pm, or the active feedstock material has a particle size of 10-60 pm.

7. The feedstock according to any of the preceding claims, wherein the active feedstock material is in the form of particles that have a substantially spherical shape.

8. The feedstock according to any of the preceding claims, wherein the inactive feedstock material comprises one or more member selected from the group consisting of a nickel-based alloy, a precious metal, gold, platinum, and iridium.

9. The feedstock according to any of claims 1-7, wherein the inactive feedstock material comprises: pure nickel,Inconel 625, or a Ni-Al alloy that comprises:2-8 wt.% Al, andNi as the balance.

10. The feedstock according to any of claims 1-7, wherein the inactive feedstock material is pure nickel,Inconel 625, or a Ni-Al alloy that comprises:2-8 wt.% Al, andNi as the balance.

11. The feedstock according to any of the preceding claims, wherein 50-95 wt.% of the total weight of the feedstock is the active feedstock material; or 60-85 wt.% of the total weight of the feedstock is the active feedstock material; or 65-75 wt.% of the total weight of the feedstock is the active feedstock material.

12. A coating formed from the feedstock according to any of the preceding claims, the coating being formed on a substrate.

13. The coating according to claim 12, wherein the coating, after leaching in alkaline solution, passes a scratch test according to ASTM D6677 standard without being worn down to reveal the substrate.

14. The coating according to claim 12, wherein the coating comprises a dual phase structure of 50-90 vol.% active material and 10-50 vol.% inactive material.

15. The coating according to claim 12, wherein the coating has a thickness in the range of from 1 pm to 200 pm, or the coating has a thickness in the range of from 1 pm to 50 pm, or the coating has a thickness in the range of from 1 pm to 20 pm; and a porosity of the coating is 10% or less, or a porosity of the coating is 8% or less.

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