Electrode coating containing nanomaterials or microfibers

Abstract

An electrode for use in an electrochemical process includes a coating having nanomaterials or microfibers.

Description

Cross-references to related applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 597,659, filed November 9, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0002] This disclosure generally relates to electrode coatings on substrates intended for use as electrodes in electrochemical processes, such as gas-generating electrodes, and is referred to herein as electrode coatings. Background Technology

[0003] Many commercial manufacturing processes utilize electrochemistry. For example, the chlor-alkali process electrolyzes aqueous solutions of sodium chloride or potassium chloride to form valuable commercial materials such as chlorine, caustic sodium hydroxide or potassium hydroxide, and hydrogen. Water is electrolyzed to produce hydrogen and oxygen. Other electrochemical processes are used to prepare a variety of commercial chemicals and intermediates for the chemical and pharmaceutical industries. Current efforts in commercial electrochemical processes involve reducing energy consumption, lowering manufacturing costs, and improving electrode efficiency and durability.

[0004] The specific electrochemical processes intended for use in the technical field described herein are those in which chloride salts are present in solution and where chlorine or hypochlorite is the main product. These processes include chlor-alkali membrane electrolyzer processes and diaphragm electrolyzer processes, chlorate production, and the generation of hypochlorite in dilute to concentrated brine for disinfection purposes. The use and composition of the gas evolution electrode will be understood to present different problems and results than those of other electrode applications.

[0005] Most conductive materials can be used as electrodes. Preferably, the material used to fabricate the electrode is resistant to corrosion by the electrolyte and / or the resulting products. Many other suitable electrode materials lack the ability to efficiently catalyze electron transfer to the electrolyte, which requires additional power. And the greater the amount of additional power used, the greater the cost of performing the electrochemical process. Coatings can be applied to the electrodes to promote electron transfer and reduce the overpotential required in the electrolytic process. Thus, coatings help reduce the total operating voltage and power consumption of the electrolytic process. Further details regarding electrode coatings are described in International Application No. PCT / US2020 / 037426, filed June 12, 2020, which is incorporated herein by reference in its entirety. In addition, the published article Kariman, A. & Marshall, A. (2019), Improving the Stability of DSAElectrodes by the Addition of TiO2 Nanoparticles, Journal of The Electrochemical Society, 166 (8) E248-E251 is incorporated herein by reference in its entirety. Summary of the Invention

[0006] Embodiments of the present invention relate to coatings on electrodes used in electrochemical applications, such as electrosynthesis. In electrochemical processes, oxidation occurs at the anode, or reduction occurs at the cathode. The substrate is a conductive material, and in this invention, the substrate used for the electrode is not oxidized or reduced during operation, while the electroactive coating acts as an electrocatalyst, reducing or oxidizing substances contained in the electrolyte.

[0007] An example of such a coating on a titanium substrate is a coating containing a chloride oxidation anode electrocatalyst, which is made of noble metal oxides or mixtures thereof, such as ruthenium, iridium, osmium, rhodium, platinum, or palladium. These noble metals are optionally mixed with oxides or mixtures thereof of elements such as titanium, tantalum, zirconium, niobium, hafnium, lanthanides, actinides, or tin. Typically, these coatings are applied by forming an aqueous or alcoholic solution of a soluble salt using any suitable uniform application method, followed by drying and baking at a temperature sufficient to substantially decompose the salt into oxides.

[0008] In embodiments of the invention, insoluble nanomaterials are added to the coating solution in an amount less than about 50% by volume, and preferably less than about 10%, of the dry solids content of the coating solution. Electrode coatings wear down over time due to mechanical or chemical means, typically at a rate proportional to the square of the current passing through the electrode. As the coating wears down, the voltage required to drive the process increases, and in some cases, the Faraday efficiency of the electrochemical process decreases.

[0009] One problem addressed by embodiments of the present invention is the preparation of electrode coatings that have an increased lifespan relative to the amount of precious metal used.

[0010] Another problem addressed by the implementation plan is reducing the power required for electrolysis.

[0011] Another problem addressed by embodiments of the present invention is that mud cracks form in the coating as it dries and bakes when an electrocatalyst is coated onto a substrate. Mud cracks slightly increase the surface area of ​​the coating but also significantly reduce its mechanical integrity and durability. In one practice of the invention, the loading of electrocatalyst provided on each coating can be increased independently of the application method, while avoiding mud crack formation during coating drying and baking.

[0012] Another advantage of embodiments of the present invention is that coatings containing nanomaterials can be better used for dip coating of expanded mesh or woven wire cloth substrates. When using prior art coatings in this application, particularly when the coating solution contains water and surfactants, the openings of the substrate can be covered by a membrane that dries and seals the mesh openings. The unwanted coating on the mesh openings must then be brushed off. However, when the coatings of the present invention are prepared, even when the volume percentage of the coating is less than 3%, the presence of fibers makes these membranes unstable during drying, causing them to no longer cover the mesh openings after drying and baking.

[0013] Other features and iterations of the invention are described in more detail below. Attached Figure Description

[0014] Figure 1 The image shown is a scanning electron microscope (SEM) image of the additive-free electrode coating sample labeled ID 32 in Table 2.

[0015] Figure 2 The image shown is a scanning electron microscope (SEM) image of the electrode coating sample with Magneli nanopowder labeled ID 44 in Table 2.

[0016] Figure 3 The image shows a scanning electron microscope / energy dispersive X-ray spectroscopy (SEM-EDS) image of the electrode coating sample (including Maneli nanopowder) labeled ID 44, revealing no phase separation in the noble metal oxide. Detailed Implementation

[0017] When describing the elements of the embodiments described herein, the articles “a,” “an,” “the,” and “said” are intended to indicate the presence of one or more elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and indicate the possibility of the presence of additional elements besides those listed.

[0018] This invention relates to electrode coatings containing non-catalytic micromaterials or nanomaterials or combinations thereof, wherein the non-catalytic micromaterials or nanomaterials or combinations thereof are combined with an active electrocatalyst to form a reinforcing network, the active electrocatalyst being composed of a mixed oxide, which is optionally mixed with other oxides such as titanium, tantalum, etc. In one aspect, nanomaterials are defined as inorganic materials having at least one external dimension of less than about 1000 nm, preferably between about 1 nm and 100 nm. The term nanomaterial is broad and includes inorganic nanofibers (with a diameter from about 10 nm to 1000 nm and a length at least ten times the diameter) and nanoparticles (nanomaterials with an average particle size of less than about 100 nm). Furthermore, microfibers with a diameter of less than about 10 micrometers, more preferably less than about 5 micrometers, and even more preferably less than 1 micrometer can also be used in the coatings of this invention to achieve similar advantages. In some embodiments, nanoparticles and glass microfibers having at least one submicron external dimension can be particularly advantageous, said nanoparticles ideally having a low packing density of less than about 700 g / L, and preferably less than about 200 g / L, or preferably less than about 100 g / L, characterized by a filamentous structure acting similarly to fibrous nanomaterials used to inhibit and stabilize mud cracking. The coating is formed by the following steps: suspending the nanomaterial in a solution containing an electrocatalyst; then applying the solution to a substrate and drying it into a film; followed by a final baking step to form an electrocatalyst oxide. An optional step may be required to disperse the nanomaterial in a first solution containing a dispersant, which may or may not be acidified, before mixing the nanomaterial with a second solution containing only the electrocatalyst component.

[0019] The nanomaterials to be used are formed from materials compatible with the electrolyte of the electrode application and must remain insoluble in the electrocatalyst solution used for coating, typically forming colloidal dispersions that may require stirring to maintain dispersion. The nanofiber materials must maintain their fibrous form at the baking temperature of the coating process. These fibers are preferably fibers or filaments with a thickness of less than about 1 micrometer and a length at least 1 to 10 times their thickness. The filaments can be conductive or non-conductive and are typically selected from metals, ceramics, glass, or carbon. The term nanomaterials is intended to be very broad and includes nanofibers and nanoparticles assembled in aggregates having a high surface area and a packing density of about 20% less than the intrinsic density of the solid material. For example, fumed silica, with a typical packing density of about 5% of the density of silica and a specific surface area of ​​50 m² / g to 500 m² / g, has been found to be an effective additive in the coatings of this invention.

[0020] The unique additive of nanofibers used in the coatings of this invention is preferably used in an amount defined by the volume ratio of solid fibers to the dry volume of the coating. Using volume ratios from 0.3:100 to 15:100 achieves the benefits of increased lifetime, reduced mud cracking, and lower overvoltage. At the lower limit of this range, fibers with high aspect ratios (e.g., 100:1) effectively reduce mud cracking in the coating or, despite mud cracking, still enhance the coating while providing increased surface area. In the middle of the range, in one example at 5% and with nanofibers having a 10:1 L / D ratio, the coating exhibits the greatest voltage reduction.

[0021] At the upper limit of the range, as the coating dries and bakes, pores are created in the coating, which increases the surface area of ​​the coating without compromising its structural stability. The nanofibers used in the coatings of this invention are wetted by the coating solution, such that as the solution containing the dispersed fibers dries, surface tension compresses the fibers and orients them in a random direction parallel to the substrate. This self-orientation behavior allows the fibers to reinforce the coating as it dries, preventing mud cracking and stabilizing any mud cracks that do form. As the coating bakes, the fibers maintain their shape and reinforce the final coating, preventing it from cracking under the mechanical stresses of operation. By using up to 50% of the dried volume of the coating as fibers, the coating maintains conductivity even though the fibers themselves are not conductive. In coatings applied to valve metals (such as titanium, niobium, or tantalum) used as anodes, the coating must protect the metal from oxidation. In this case, it has been shown that coatings containing too many microfibers can become too porous and have a reduced lifespan. Examples of electrode coatings of the present invention Example 1 (Comparative Example)

[0022] Titanium mesh samples were prepared by sandblasting and washing. A coating solution was prepared using 0.967% titanium and 0.88% ruthenium in isopropanol containing 5.6% hydrochloric acid. The materials used to prepare this solution were: tetrapropyl titanate (brand name Tyzor TPT), an alcoholic solution containing 16.8% titanium; ruthenium(III) chloride hydrate crystals containing 59.7% ruthenium; and a stock solution of anhydrous HCl in isopropanol containing 27.8% HCl. The solution was diluted to the desired final concentration using anhydrous isopropanol. The coating was applied as follows:

[0023] 1. Immerse the mesh in the paint solution and then hang it vertically to allow excess paint to flow over the surface.

[0024] 2. Allow the paint to dry in an environment with airflow for approximately 10 minutes.

[0025] 3. Then transfer the coated mesh to a drying oven at 100ºC for 20 minutes to remove all solvent.

[0026] 4. Then bake the coated and dried mesh in an oven at 490ºC for 20 minutes.

[0027] Repeat steps 1 through 4 seven times, flipping the mesh vertically after each cycle and then baking it at 490ºC for 40 minutes. Prepare multiple coated mesh samples using this procedure; label the samples with ID 26 and ID 27. Example 2:

[0028] Following the steps of Comparative Example 1, except that a certain amount of glass microfibers was added to achieve 2% of the dry weight of the coating in oxide form. The weights of titanium and ruthenium in the solution were converted to equivalent weights of RuO2 (MW 133.07) and TiO2 (MW 79.87). The calculated total dry weight of the coating (RuO2, TiO2) in Example 1 was calculated to be 2.766% of the total weight of the coating solution. A suspension of glass microfibers B-X9-F, purchased from Unifrax (Tonawada, NY) and with an average diameter of approximately 0.2 to 0.3 micrometers, was prepared by adding 5.2 g of dry microfibers to 194.8 g of DI water, and acetic acid was added to adjust the pH to 2.8. The mixture was suspended using an 800-watt kitchen blender for approximately 5 minutes, after which the fibers were observed to remain suspended without settling and to form a thick slurry. This slurry (3.24 g) was added to 147.6 g of the coating solution from Example 1. The titanium mesh samples were dip-coated using a coating containing glass microfibers. These samples were prepared and coated in exactly the same manner as the samples from Example 1, except that only five dip-and-bake cycles were performed. Four coated mesh samples, labeled ID 41 to ID 44, were prepared using this procedure.

[0029] Accelerated lifetime testing was performed on the coated anodes of Examples 1 and 2, with XRF measurements to determine the ruthenium loading. One sample from each type was operated in a diaphragm test cell, where voltage was measured over a 60-day period. The comparison of these test results is summarized in Table 1 below: Table 1 Example 3 (Comparative Example)

[0030] Titanium mesh samples were prepared using methods known in the art to ensure good adhesion. A coating solution was prepared using 0.55% titanium, 0.18% ruthenium, 0.21% iridium, and 0.07% palladium in isopropanol containing 5.6% hydrochloric acid and 0.3% hydrogen peroxide. The materials used to prepare this solution were: tetrapropyl titanate (brand name Tyzor TPT), an alcoholic solution containing 16.8% titanium; ruthenium(III) chloride hydrate crystals containing 40.9% ruthenium; hexachloroiridium hydrogen(IV) hydride crystals containing 39.2% iridium; palladium(II) chloride crystals containing 59.9% palladium; anhydrous HCl in isopropanol containing at least 22% HCl; and anhydrous isopropanol for diluting the solution to the desired final concentration. The coating was applied using the following steps:

[0031] The mesh is immersed in the paint solution and then hung vertically to allow excess paint to flow over the surface.

[0032] Allow the paint to dry completely, then bake at 490ºC for 20 minutes.

[0033] Steps 1 and 2 were repeated 7 times, with the mesh periodically flipped back and forth in the same vertical orientation. A final baking was performed for 2 hours after the 7th impregnation at 490ºC. As detailed in Table 2, the samples were labeled ID 32 and ID 34. Example 4:

[0034] The steps of Example 3 (Comparative Example) were followed, except as follows. N82 titanium dioxide nanopowder obtained from MagneliMaterials, LLC was also added to the coating solution in an amount equal to 4% by weight of the total coating solids. Note that the nanopowder was pre-dispersed in isopropanol by shearing before being added to the coating solution. The coating was applied in the same manner as previously described, with a total of 9 dip-and-bake cycles, followed by a final 2-hour bake. Before each dip, the coating solution was recirculated / stirred by stirring to suspend the nanopowder additive. As detailed in Table 2 below, samples are labeled ID 41 and ID 44.

[0035] Voltage evaluations were performed on Examples 3 (Comparative Examples) and 4. The results from these evaluations are summarized in Table 2 below. Notably, ID 41 and ID 44 showed greater coating solution absorption compared to the control sample without additives, as demonstrated by the increased iridium loading per impregnation.

[0036] Voltage assessments were performed in a laboratory cells electrolyzer operating at a current density of approximately 7 kA / m². Cell temperature was maintained at 85ºC; saline strength and anolyte strength were maintained at approximately 18% to 23%. Anode voltage was monitored using a Luggin probe connected to a reservoir backfilled with anolyte, with an Ag|AgCl reference electrode. Voltages were collected over approximately four weeks of operation, with ID 44 showing a 30 mV advantage over the control ID 32. Table 2

[0037] Imaging was performed on both the control sample without additives and the sample containing Magneli nanopowder. Note that even with a thicker coating and a higher iridium loading, mud cracking was visually reduced in ID 44, providing a coated surface with increased resistance to mechanical abrasion and improved durability.

[0038] refer to Figures 1 to 3 ID 32 (additive-free) is shown. Figure 1 ) and ID 44 (Magneli nanopowder) Figure 2 SEM imaging of TiO2 nanopowder. The addition of TiO2 nanopowder significantly reduced the presence of mud cracks while increasing the durable surface area. Figure 3 This shows that there was no obvious phase separation of noble metal oxides (IrO2, etc.) in the SEM-EDS analysis at ID 44. Example 5 (Comparative Example)

[0039] The steps of Example 3 (Comparative Example) were followed, except as follows. A diluted coating solution was prepared using 0.40% titanium, 0.13% ruthenium, 0.15% iridium, and 0.05% palladium in isopropanol containing 5.6% hydrochloric acid and 0.3% hydrogen peroxide. The coating was applied in the same manner as previously described, with a total of 9 dips, followed by a final bake at 490ºC for 2 hours. Sample groups (number 9) were coated on a production scale; the results reported in Table 3 are averages. Examples 6 to 8

[0040] The procedure was similar to that of Example 4, with key exceptions. Titanium dioxide (IV) and Aeroxide® P25, with a specific surface area of ​​35 m² / g to 65 m² / g and a particle size < 100 nm, were added to the coating solution in amounts equal to 3%, 5%, and 7% by volume of the dry solids content of the coating solution, respectively. Note that the titanium dioxide nanopowder was pre-dispersed in isopropanol by shearing before being added to the coating solution. The coating was applied via nine dip-and-bake cycles, with a final bake following the last dip. Samples are labeled ID 16, ID 17, and ID 18 in Table 3. Example 9

[0041] Recognizing the advantages of thicker coatings while avoiding undesirable mud cracking, the coating solution was prepared starting with 0.65% titanium and maintaining the same metal molar ratio. The materials used to prepare this solution were: titanium oxychloride, an acidic aqueous solution containing 12.1% titanium; ruthenium(III) chloride hydrate crystals containing 40.9% ruthenium; iridium(IV) chloride crystals containing 52.0% iridium; palladium(II) chloride crystals containing 59.9% palladium; anhydrous HCl in isopropanol containing at least 22% HCl; and anhydrous isopropanol and water for diluting the solution to maintain a total concentration of 50% isopropanol by weight. CAB-O-SIL®EH-5, a high-surface-area fumed silica, was added to the coating solution in an amount equal to 4% by volume of the dry solids content of the coating solution. The fumed silica was pre-dispersed in water by shearing before being added to the coating solution. The coating was applied via eight dip-and-bake cycles, with a final bake following the last dip. The sample is labeled ID 19 in Table 3.

[0042] Accelerated corrosion tests and voltage assessments were performed on Examples 5 (Comparative Examples) and Examples 6 through 9. The results from these assessments are summarized in Table 3 below. Accelerated lifetime tests were conducted at 60ºC in 1.5 M sodium sulfate (pH adjusted to 2 with sulfuric acid). The addition of nanomaterials significantly extended the anolyte lifetime relative to the amount of iridium. Table 3

[0043] Given the improvements provided by this invention, global applications are anticipated, including uses in fuel cells, water electrolysis, battery packs, and the electrosynthesis of chlorine and caustic soda, hypochlorite, and chlorate.

[0044] The invention has been described in detail, and it will be apparent that modifications and variations are possible without departing from the scope of the invention as described herein.

Claims

1. An apparatus comprising: An electrode having a core substrate, wherein the electrode is in an aqueous solution and the product is generated via an electrochemical process; as well as The coating on the substrate, wherein the coating comprises nanomaterials.

2. The device of claim 1, wherein the core substrate comprises titanium.

3. The device according to claim 2, wherein the electrode is a gas evolution electrode.

4. The device according to claim 1, wherein the electrode is a gas evolution electrode.

5. The device according to claim 4, wherein the nanomaterial comprises glass microfibers.

6. The device of claim 1, wherein the nanomaterial comprises glass microfibers.

7. The device according to claim 2, wherein the nanomaterial comprises glass microfibers.

8. The apparatus of claim 1, wherein the aqueous solution comprises sodium chloride or potassium chloride.

9. The device of claim 8, wherein the nanomaterial comprises glass microfibers.

10. The device of claim 1, wherein the coating comprises an oxide of one or more noble metals selected from ruthenium, iridium, osmium, rhodium, platinum and palladium.

11. The device of claim 10, wherein the coating further comprises one or more oxides of titanium, tantalum, zirconium, niobium, hafnium, lanthanides, actinides and tin.

12. The device of claim 2, wherein the coating comprises an oxide of one or more noble metals selected from ruthenium, iridium, osmium, rhodium, platinum and palladium.

13. The device of claim 12, wherein the coating further comprises one or more oxides of titanium, tantalum, zirconium, niobium, hafnium, lanthanides, actinides and tin.

14. The device of claim 1, wherein the microfiber has a thickness or diameter of less than about 1 micrometer and a length of at least 10 times the thickness or diameter.

15. The device of claim 2, wherein the microfiber has a thickness or diameter of less than about 1 micrometer and a length of at least 10 times the thickness or diameter.

16. The device of claim 1, wherein the coating comprises nanomaterials in an amount between about 2% and about 20% of the dry weight of the coating.

17. The device of claim 1, wherein the coating comprises glass microfibers in an amount between about 2% and about 20% of the dry weight of the coating.

18. The device of claim 1, wherein the nanomaterial comprises nanoparticles.

19. The device of claim 2, wherein the nanomaterial comprises nanoparticles.

20. The equipment according to claim 1, wherein the electrochemical process is a chlor-alkali membrane electrolyzer process or a diaphragm electrolyzer process.

21. The device according to claim 2, wherein the electrochemical process is a chlor-alkali membrane electrolyzer process or a diaphragm electrolyzer process.

22. The apparatus of claim 1, wherein the electrode and the aqueous solution produce salt.

23. The apparatus of claim 2, wherein the electrode and the aqueous solution produce a salt.

24. The apparatus of claim 1, wherein the electrode and the aqueous solution produce sodium hypochlorite.

25. The apparatus of claim 2, wherein the electrode and the aqueous solution produce sodium hypochlorite.

26. An apparatus comprising: An electrode having a core substrate, wherein the electrode is in an aqueous solution and the product is generated via an electrochemical process; as well as The coating on the substrate, wherein the coating comprises microfibers.

27. The device of claim 26, wherein the microfiber comprises glass microfiber.

28. The device of claim 27, wherein the glass microfibers have a diameter of less than 5 micrometers.

29. The device of claim 26, wherein the microfiber has a diameter of less than 10 micrometers.

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