Method for coating components of electrolytic cells - Patent Application 20070122997

Abstract

A method for coating an electrolytic cell component is provided. The method includes applying an acidic solution of platinum cations to at least a portion of the component and reducing the applied platinum cations with a reducing agent to form a layer of platinum metal on the component. In contrast to existing coating methods, the method of the present invention is low cost and suitable for use in high-volume manufacturing processes. The method can be performed at low temperatures (e.g., below 350°C) and does not result in oxidation of the metal of the component.

Description

[Technical Field]

[0001] The present invention relates to polymer electrolyte membrane water electrolyzers (also called electrochemical hydrogen generators), and more particularly to a method for coating components of such electrolyzers with platinum. [Background technology]

[0002] Polymer electrolyte membrane (PEM) water electrolysis cells are electrochemical devices that dissociate water to produce hydrogen and oxygen gas. The hydrogen produced by these devices provides a clean energy fuel source for hydrogen fuel cells. PEM water electrolysis cells contain a cathode, an anode, and a polymer electrolyte. Additional components include bipolar plates, porous transport layers, and flow disruptors, which are typically constructed from titanium. Titanium is a preferred metal over iron- and nickel-based materials, which are prone to degradation.

[0003] PEM electrolysis is beneficial because it is more efficient than other types of electrolysis, produces hydrogen with high purity, and can be produced under pressure. However, its efficiency is limited by resistance within the cell. At the start of operation, this efficiency is dominated by the membrane. However, over time, the cell voltage begins to decrease. This is primarily due to an increase in contact resistance within the cell, which is ultimately due to the buildup (thickening) of the titanium dioxide layer on the titanium components. When the titanium dioxide layer reaches a thickness greater than the electron tunneling distance (1.23 nm), an exponential increase in operating voltage occurs, which leads to catastrophic failure of the cell. This typically requires approximately 5,000 to 10,000 hours of operation, but can occur sooner or later depending on other factors, such as operating conditions and balance-of-plant construction materials.

[0004] To solve this problem, components are typically coated with a precious metal, such as gold or a platinum group metal (e.g., platinum, iridium, palladium, rhodium, or ruthenium). The primary use of this coating is for metal-to-metal and metal-to-catalyst contact resistance, so it does not need to be continuous.

[0005] Two common methods for coating titanium components are plating and physical (or chemical) vapor deposition.

[0006] Plating encompasses electroplating and electroless plating, both of which involve immersing a component in a solution of metal ions and reducing the metal ions on the component's surface to produce a metallic coating. Electroplating uses an electric current to reduce the metal ions. A drawback of this process is that to plate large component parts in a production environment, the plating vessel (containing the plating bath) must be large enough to accommodate the entire component and therefore must contain a significant amount of precious metal. The plating bath therefore becomes an expensive asset for a company to maintain, resulting in high production costs.

[0007] Electroless plating creates metal coatings by the autocatalytic chemical reduction of metal cations, with the metal itself acting as the catalytic reducing agent. However, the period required for autocatalysis to complete is too long, making electroless plating unsuitable for coating electrolytic cell components in production processes.

[0008] Other electroless coating methods include pyrolysis and powder sintering, both of which require high temperatures (e.g., above about 300°C). A metal salt solution containing the electrode active coating material is applied, dried, and heat-treated in air at temperatures such as 350°C to 550°C. Examples of platinum metal salts used in these processes include chloroplatinic acid and dinitrodiamine platinum. A disadvantage of using these methods is the high operating costs associated with using such high temperatures, which limits their use in high-volume production processes.

[0009] Similarly, evaporation has the drawback of requiring expensive equipment and high vacuum techniques that are difficult to use in large scale production.

[0010] Therefore, there is a need for a method of coating electrolytic cell components that addresses, at least to some extent, the above problems. Summary of the Invention [Means for solving the problem]

[0011] According to the present invention there is provided a method of coating an electrolytic cell component, the component comprising titanium, the method comprising: applying an acidic solution of platinum cations to at least a portion of the component; reducing the applied platinum cations with a reducing agent to form a layer of platinum metal on the component; Includes.

[0012] In contrast to existing coating methods, the method of the present invention is low cost and suitable for use in high volume manufacturing processes, it can be performed at low temperatures (e.g., below 350°C) and does not result in oxidation of the component metals.

[0013] The method may further include at least partially drying the applied acidic solution of platinum cations, which may be carried out at a temperature between about 0°C and 200°C, between about 25°C and 175°C, between about 50°C and 150°C, between about 75°C and 125°C, between about 80°C and 100°C, between about 90°C and 95°C, or at a temperature less than about 350°C.

[0014] The temperature of this drying step is significantly lower than that used in prior art pyrolysis and powder sintering methods, providing a process that is easier and less costly to operate.

[0015] An acidic solution of platinum cations is applied to the component at a concentration of approximately 0.01 mg / cm 2 ~2.5mg / cm 2 The catalyst may be applied to the component in an amount sufficient to provide a platinum loading of 0.01g, which is comparable to the catalyst loading of conventional commercial components.

[0016] The component may be selected from the group consisting of one or more of a cathode compartment or chamber, an anode compartment or chamber, a bipolar plate, a flow disruptor, and a porous transport layer.

[0017] The acidic solution of platinum cations may be applied to the component by one or more methods selected from the group consisting of brushing, dip coating, spraying, and combinations thereof, which application methods ensure a uniform coating of platinum cations on the component or target portion thereof as desired.

[0018] The applied platinum cations may be reduced by contacting them with a reducing agent. The contacting may include brushing the applied platinum cations with a solution containing the reducing agent, immersing the component in a solution containing the reducing agent, spraying the component with a solution containing the reducing agent, or a combination thereof. The contacting may preferably include immersing the component in a solution containing the reducing agent. These contacting methods allow for maximum reduction of the platinum cations to result in a uniform coating of platinum metal on the component.

[0019] The method may further include at least partially drying the component after reduction of the platinum cations. For example, the drying step may be performed after immersing the component in a solution of the reducing agent. The drying step may be performed at a temperature between about 0°C and 200°C, between about 25°C and 175°C, between about 50°C and 150°C, between about 75°C and 125°C, between about 80°C and 100°C, between about 90°C and 95°C, or at a temperature less than about 350°C.

[0020] The drying step may serve to remove the solvent in which the reducing agent may be present and to accelerate the reduction reaction by concentrating the reducing agent in contact with the platinum cations.

[0021] The acidic solution of platinum cations may contain about 1 wt% to 20 wt%, about 5 wt% to 15 wt%, or about 10 wt% HCl, which maintains the platinum cations in a charged state and limits side reactions.

[0022] The acidic solution of platinum cations may comprise a platinum halide, preferably selected from one or more of platinum chloride, platinum bromide, and / or platinum fluoride. The platinum halide may comprise platinum chloride, which may be selected from platinum(IV) chloride, chloroplatinic acid (HPtCl), and platinum(II) chloride.

[0023] The reducing agent may include a hydride, a phosphine, and / or a borane reducing agent. The hydride reducing agent may be selected from sodium borohydride and / or sodium cyanoborohydride. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a graph showing the difference in interfacial contact resistance between a titanium component coated according to the method of the present invention and subjected to an accelerated corrosion test and an uncoated titanium component. DETAILED DESCRIPTION OF THE INVENTION

[0025] Unless the context requires otherwise, as used in this specification and the appended claims, "comprise" or variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0026] "Consisting essentially of," in reference to the constituents of a component, will be understood to mean that the component contains the indicated component, but may also contain insignificant, trace amounts (i.e., less than 5 wt %, preferably less than 1 wt %) of other components or additives without substantially altering the chemical or physical properties of the component.

[0027] The term "about" as used herein in reference to an expressed amount means that the stated amount may vary by ±5% of the stated amount. For example, about 90 wt% means 90±5 wt%, about 0.1 wt% means 0.1±0.005 wt%, and about 80°C means 80±4°C. When used in reference to a range, the term "about" applies to all values ​​within that range.

[0028] As used herein, the term "reducing agent" (also called a reductant or reducer) refers to a chemical species that participates in an oxidation-reduction reaction by reducing another chemical species. A reducing agent donates at least one electron and, in doing so, becomes oxidized. Examples of reducing agents include hydrides such as metal hydrides (e.g., NaH, LiH, CaH, LiAlH, and Red-Al) and borohydrides (e.g., NaBH, NaBHCN, and LiBH), boranes, and phosphines (e.g., triphenylphosphine). The reducing agents referred to in this disclosure may include one or more chemical species selected from these groups.

[0029] The present disclosure provides a method for coating an electrolytic cell component. The coating minimizes interfacial contact resistance by preventing the formation of titanium dioxide during operation of the electrolytic cell, which maintains the efficiency and extends the life of the electrolytic cell. The method includes applying an acidic solution of platinum cations to at least a portion of the component and reducing the applied platinum cations with a reducing agent to form a layer of platinum metal on the component. The resulting coating may be continuous, discontinuous, or a combination thereof. The degree of continuity of the coating may be determined by electron microscopy, such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), or scanning transmission electron microscopy (STEM), although any suitable method may be used.

[0030] The acidic solution of platinum cations may be applied to the component by one or more application methods selected from the group consisting of brushing, dip-coating, spraying, and combinations thereof. When the method of the present invention is performed in multiple cycles, two or more application methods may be used. For example, a first cycle may include dip-coating, and a second cycle may include spraying. Because different methods typically apply different volumes of solution to the surface of the component, using a combination of different methods may enable a desired platinum loading to be achieved.

[0031] The acidic solution of platinum cations may contain 0.1M to 5M, 0.5M to 2M, 0.5 to 1.5M, or about 1M acid, or about 1 wt% to 20 wt%, about 5 wt% to 15 wt%, or about 10 wt% acid. The acid may be selected from HCl, H2SO4, HNO3, and CH3COOH, preferably HCl.

[0032] The platinum cation may comprise a platinum halide or dinitrodiamine platinum. The platinum halide may preferably be selected from one or more of platinum chloride, platinum bromide, and / or platinum fluoride. Platinum chloride is particularly preferred because the preferred acid, HCl, also has a chloride anion. The platinum chloride may be selected from platinum(IV) chloride, chloroplatinic acid (HPtCl), and platinum(II) chloride. In a preferred embodiment, the platinum cation comprises chloroplatinic acid.

[0033] An acidic solution of platinum cations is applied to the component at a concentration of approximately 0.01 mg / cm 2 ~2.5mg / cm 2 , about 0.01mg / cm 2 ~2.0mg / cm 2 , about 1.0mg / cm 2 ~2.0mg / cm 2 , about 1.25mg / cm 2 ~1.5mg / cm 2 , about 0.1mg / cm 2 ~2.0mg / cm 2 , about 0.01mg / cm 2 ~1.5mg / cm2 , or about 0.01 mg / cm 2 ~1mg / cm 2 The platinum loading may be applied to the component in an amount sufficient to provide a platinum loading of 0.015 to 0.015 .mu.m. The method may be performed repeatedly, or more than once (i.e., over multiple cycles), to achieve the desired platinum loading. For example, the method may be performed 2 to 50 times, 2 to 20 times, 2 to 15 times, 2 to 10 times, or 2 to 5 times.

[0034] The method may further include at least partially drying the component after application of the solution. The acid solution is typically an aqueous solution, and the drying step removes substantially all of the water, leaving a residue of platinum cations on the surface of the component. The drying step may be carried out at a temperature of about 0°C to 200°C, about 25°C to 175°C, about 50°C to 150°C, about 75°C to 125°C, about 80°C to 100°C, about 90°C to 95°C, or at a temperature less than about 350°C, 300°C, 250°C, 200°C, 150°C, 100°C, or 95°C. To accelerate the drying step, a gas, such as air, may be passed over the surface of the component. The gas may optionally be heated.

[0035] The component may be selected from the group consisting of one or more of a cathode compartment or chamber, an anode compartment or chamber, a bipolar plate, a flow disruptor, and a porous transport layer. For example, the component may be a bipolar plate or a porous transport layer. The component may be constructed of a material including titanium. The component may consist essentially of titanium prior to coating. For example, the component may be a titanium component. The component may comprise at least 80 wt%, at least 85 wt%, at least 90 wt%, at least 95 wt%, at least 96 wt%, at least 97 wt%, at least 98 wt%, at least 99 wt%, 100 wt% titanium, or a range between any two of these values.

[0036] The reducing agent is a chemical reducing agent, which may include a hydride, a borane, and / or a phosphine reducing agent. Preferably, the reducing agent includes a hydride, more preferably a borohydride, and even more preferably NaBH4 and / or NaBH3CN. The reducing agent may be present as a solution, such as an aqueous solution.

[0037] The reducing step includes contacting the applied platinum cations with a reducing agent. The contacting may include brushing the applied platinum cations with a solution containing the reducing agent, immersing the component in a solution containing the reducing agent, spraying the component with a solution containing the reducing agent, or a combination thereof. The contacting may preferably include immersing the component in a solution containing the reducing agent. The component may be washed to remove any salts or impurities remaining after reduction.

[0038] The method may further include at least partially drying the component. When the reducing agent is present as a solution, it is typically present as an aqueous solution, and the drying step removes any water that may be present on the surface of the component. The drying step may be carried out at a temperature of about 0°C to 200°C, about 25°C to 175°C, about 50°C to 150°C, about 75°C to 125°C, about 80°C to 100°C, about 90°C to 95°C, or at a temperature less than about 350°C, 300°C, 250°C, 200°C, 150°C, 100°C, or 95°C. To accelerate the drying step, a gas, such as air, may be passed over the surface of the component. The gas may optionally be heated. [Example]

[0039] Titanium sheet metal sections cut to a size of (20 cm x 20 cm) and machined were first washed with water and then degreased in a batch of acetone in an ultrasonic bath for approximately 10 minutes. After drying, the sections were rinsed three times with deionized water. A coating solution was prepared by dissolving 10 g of chloroplatinic acid (HPtCl) in a 1 M hydrochloric acid solution. This solution was applied to the previously prepared titanium sections by brushing, with a coating density of 12.5-15.0 g / m. 2 The coated parts were dried at 90°C and reweighed to reach a chloroplatinate solution loading of 1.25-1.5 g / m 2 The dried part was then quickly immersed in a 1 M NaBH solution for 2 seconds. The platinum salt on the surface of the titanium was reduced to platinum, as evidenced by the appearance of hydrogen bubbles on the surface of the part.

[0040] To simulate the effects of accelerated corrosion in the electrolytic cell, 1 mg / L NaF (2.4 × 10 -5 Titanium parts were placed in an aqueous solution containing HCl (M) for 1 hour. An uncoated (degreased) titanium part was placed in the same solution for the same amount of time. After 1 hour, both parts were rinsed with deionized water and dried at 90°C.

[0041] 1.96N / cm 2 1cm above the surface with a pressure of 2 The contact resistance of these parts was measured by placing a gold-coated copper disk of 1000 kJ / cm2 on the titanium part. A current of 1 A was passed between the copper disk and the titanium part, and the voltage between the copper disk and the titanium part was measured using a calibrated digital voltmeter. Ohm's law was used to calculate the voltage in Ω·cm2. 2 The contact resistance of the coated part was 1 to 6 mΩ cm. 2 The uncoated area had a contact resistance of 100 mΩ cm 2 The results are provided in Table 1 below and shown in Figure 1.

[0042] [Table 1]

Claims

1. 1. A method of coating a component of an electrolytic cell, the component comprising titanium, the method comprising: applying an acidic solution of platinum cations to at least a portion of the component; reducing the applied platinum cations with a reducing agent to form a layer of platinum metal on the component; A method comprising:

2. The method of claim 1 further comprising at least partially drying the applied acidic solution of platinum cations.

3. 3. The method of claim 2, wherein the drying step is carried out at a temperature of 0°C to 200°C, about 25°C to 175°C, about 50°C to 150°C, about 75°C to 125°C, about 80°C to 100°C, about 90°C to 95°C, or a temperature less than about 350°C.

4. The acidic solution of platinum cations is applied to the component at a concentration of 0.01 to 2.5 mg / cm ２ The method of any one of claims 1 to 3, wherein the platinum is applied to the component in an amount sufficient to provide a platinum loading of 0.1 wt.

5. The method of any one of claims 1 to 4, wherein the component is selected from one or more of a cathode compartment or chamber, an anode compartment or chamber, a flow disruptor, and a bipolar plate.

6. The method of any one of claims 1 to 5, wherein the component is a titanium component.

7. The method of any one of claims 1 to 6, wherein the acidic solution of platinum cations is applied to the component by a method selected from the group consisting of brushing, dip coating, spraying, or a combination thereof.

8. 8. The method of claim 1, wherein the reducing step comprises brushing the applied platinum cations with a solution containing the reducing agent, immersing the component in a solution containing the reducing agent, spraying the component with a solution containing the reducing agent, or a combination thereof.

9. The method of any one of claims 1 to 8, wherein the reducing step comprises immersing the component in a solution containing the reducing agent.

10. The method of any one of claims 1 to 9, further comprising the step of drying said components after the contacting step.

11. 11. The method of any one of claims 1 to 10, wherein the acidic solution of platinum cations comprises 1 wt% to 20 wt%, 5 wt% to 15 wt%, or 10 wt% HCl.

12. 12. The method of any one of claims 1 to 11, wherein the acidic solution of platinum cations comprises a platinum halide, preferably selected from one or more of platinum chloride, platinum bromide, and / or platinum fluoride.

13. The platinum halide includes platinum chloride, and the platinum chloride is platinum chloride (IV), chloroplatinic acid (H ２ PtCl ６ 13. The method of claim 12, wherein the platinum group metal is selected from platinum(II) chloride and platinum(II) chloride.

14. The method of any one of claims 1 to 13, wherein the reducing agent comprises a hydride, a phosphine, and / or a borane reducing agent.

15. 15. The method of claim 14, wherein the hydride reducing agent is selected from sodium borohydride and / or sodium cyanoborohydride.

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