A METHOD FOR COATING A COMPONENT OF AN ELECTROLYSER

Abstract

A method of coating a component of an electrolyser is provided. The method comprises 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.

Claims

1. A method of coating a component of an electrolyser, wherein the component comprises titanium, the method comprising: 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.

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

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

4. The method of claim 1, wherein the acidic solution of platinum cations is applied to the component in an amount sufficient to provide a platinum loading of from 0.01 to 2.5 mg/cm.sup.2 on the component.

5. The method of claim 1, 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 claim 1, wherein the component is a titanium component.

7. The method of claim 1, 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. The method of claim 1, wherein the reducing includes brushing the applied platinum cations with a solution comprising the reducing agent, immersing the component in a solution comprising the reducing agent, spraying the component with a solution comprising the reducing agent, or a combination thereof.

9. The method of claim 1, wherein the reducing comprises immersing the component in a solution comprising the reducing agent.

10. (canceled)

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

12. The method of claim 1, 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 method of claim 12, wherein the platinum halide comprises platinum chloride and the platinum chloride is selected from platinum(IV) chloride, chloroplatinic acid (H.sub.2PtCl.sub.6), and platinum(II) chloride.

14. The method of claim 1, wherein the reducing agent comprises a hydride, phosphine and/or borane reducing agent.

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

Description

BRIEF DESCRIPTION OF THE FIGURE

[0026] In the accompanying FIGURE:

[0027] FIG. 1 is a graph illustrating differences in interfacial contact resistance between titanium components which have been coated and undergone an accelerated corrosion test according to the method of the present invention and uncoated titanium components.

DETAILED DESCRIPTION

[0028] As used herein and in the accompanying claims, unless the context requires otherwise, 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.

[0029] Consisting essentially of with respect to the constituents of a component will be understood to mean that the component contains the indicated constituents but may also contain minor trace quantities (i.e. less than 5 wt %, preferably less than 1 wt %) of other constituents or additives without substantially altering the chemical or physical properties of the component.

[0030] As used herein, the term about in relation to the amounts expressed means that the stated amount can vary by 5% of the stated amount. For example, about 90 wt % means 905 wt %, about 0.1 wt % means 0.10.005 wt %, about 80 C. means 804 C. When used with reference to a range, the term about applies to all values in the range.

[0031] As used herein, the term reducing agent (also called a reductant or a reducer) refers to a chemical species which participates in a redox reaction by reducing another chemical species. It donates at least one electron and in doing so becomes oxidised. Examples of reducing agents include hydrides, such as metal hydrides (e.g. NaH, LiH, CaH.sub.2, LiAlH.sub.4 and Red-Al) and borohydrides (e.g. NaBH.sub.4, NaBH.sub.3CN and LiBH.sub.4), boranes, and phosphines (e.g. triphenylphosphine). The reducing agent referred to in the present disclosure may comprise one or more chemical species selected from these groups.

[0032] The present disclosure provides a method of coating a component of an electrolyser. The coating minimise interfacial contact resistance by preventing titanium dioxide from forming during operation of the electrolyser, which maintains the efficiency of the electrolyser cell and prolongs its lifetime. The method comprises 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 coating produced may be continuous or discontinuous, or a combination thereof. The degree of continuity of the coating may be determined by electron microscopy, for example, transmission electron microscopy (TEM), scanning electron microscopy (SEM), or scanning transmission electron microscopy (STEM), although any suitable method may be used.

[0033] 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. More than one application method may be used where the method of the invention is performed in multiple cycles. For example, a first cycle may comprise dip coating and a second cycle may comprise spraying. The use of combinations of different methods may permit a desired platinum loading to be achieved, since different methods typically apply different volumes of solution to the component surface.

[0034] The acidic solution of platinum cations may comprise from 0.1 M to 5 M, from 0.5 M to 2 M, from 0.5 to 1.5 M, or about 1M of an acid, or from about 1 wt % to 20 wt %, from about 5 wt % to 15 wt %, or about 10 wt % of an acid. The acid may be selected from HCl, H.sub.2SO.sub.4, HNO.sub.3, and CH.sub.3COOH, and is preferably HCl.

[0035] The platinum cations may comprise a platinum halide or dinitrodiamineplatinum. The platinum halide may preferably be selected from one or more of platinum chloride, platinum bromide and/or platinum fluoride. Platinum chlorides are particularly preferred since the chloride anion is also present in the preferred acid, HCl. The platinum chloride may be selected from platinum(IV) chloride, chloroplatinic acid (H.sub.2PtCl.sub.6), and platinum(II) chloride. In a preferred embodiment, the platinum cations comprise chloroplatinic acid.

[0036] The acidic solution of platinum cations may be applied to the component in an amount sufficient to provide a platinum loading of from about 0.01 mg/cm.sup.2 to 2.5 mg/cm.sup.2, from about 0.01 mg/cm.sup.2 to 2.0 mg/cm.sup.2, from about 1.0 mg/cm.sup.2 to 2.0 mg/cm.sup.2, from about 1.25 mg/cm.sup.2 to 1.5 mg/cm.sup.2, from about 0.1 mg/cm.sup.2 to 2.0 mg/cm.sup.2, from about 0.01 mg/cm.sup.2 to 1.5 mg/cm.sup.2, or from about 0.01 mg/cm.sup.2 to 1 mg/cm.sup.2 on the component. The method may be performed iteratively or more than once (i.e. over multiple cycles) to achieve a desired platinum loading. For example, the method may be performed from 2 to 50 times, from 2 to 20 times, from 2 to 15 times, from 2 to 10 times or from 2 to 5 times.

[0037] The method may further comprise 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 to leave a residue of the platinum cations on the surface of the component. The drying step may be carried out at a temperature of from about 0 C. to 200 C., from about 25 C. to 175 C., from about 50 C. to 150 C., from about 75 C. to 125 C., from about 80 C. to 100 C., from about 90 C. to 95 C., or at a temperature below about 350 C., 300 C., 250 C., 200 C., 150 C., 100 C. or 95 C. A gas, such as air, may be passed over the surface of the component to accelerate drying. The gas may optionally be heated.

[0038] 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 from a material comprising 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.

[0039] The reducing agent is a chemical reductant which may comprise a hydride, a borane and/or a phosphine reducing agent. Preferably, the reducing agent comprises a hydride, more preferably a borohydride, or even more preferably NaBH.sub.4 and/or NaBH.sub.3CN. The reducing agent may be present as a solution, for example, an aqueous solution.

[0040] The reducing step includes contacting the applied platinum cations with the reducing agent. The contact may include brushing the applied platinum cations with a solution comprising the reducing agent, immersing the component in a solution comprising the reducing agent, spraying the component with a solution comprising the reducing agent, or a combination thereof. The contacting may preferably include immersing the component in a solution comprising the reducing agent. The component may be washed to remove any salts or impurities remaining after the reduction.

[0041] The method may further comprise 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 which may be present on the surface of the component. The drying step may be carried out at a temperature of from about 0 C. to 200 C., from about 25 C. to 175 C., from about 50 C. to 150 C., from about 75 C. to 125 C., from about 80 C. to 100 C., from about 90 C. to 95 C., or at a temperature below about 350 C., 300 C., 250 C., 200 C., 150 C., 100 C. or 95 C. A gas, such as air, may be passed over the surface of the component to accelerate drying. The gas may optionally be heated.

Example

[0042] A piece of titanium sheet metal cut and machined to size (20 cm20 cm) was first cleaned in water then degreased in a batch of acetone in an ultrasonic bath for about 10 minutes. After drying the piece was rinsed three times with deionised water. A coating solution was made by dissolving 10 g of chloroplatinic acid (H.sub.2PtCl.sub.6) in a 1M hydrochloric acid solution. The solution was applied to the previously prepared titanium piece by brushing, reaching a chloroplatinic acid salt solution loading of 12.5-15.0 g/m.sup.2. The coated part was dried at 90 C. and reweighed to ensure a loading of 1.25-1.5 g/m.sup.2 of H.sub.2PtCl.sub.6. The dried part was instantaneously then dipped into a 1M Na.sub.2BH.sub.4 solution for 2 seconds. The platinum salt was reduced to platinum on the surface of the titanium, as evidenced by the appearance of bubbles of hydrogen on the surface of the part.

[0043] To simulate the effects of accelerated corrosion in an electrolyser cell the titanium part was placed in an aqueous solution containing 1 mg/l NaF (2.410.sup.5 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 in deionised water and dried at 90 C.

[0044] The contact resistance of the parts was measured by placing 1 cm.sup.2 gold coated copper disc on the surface with a pressure of 1.96 N/cm.sup.2. A current of 1 A was passed between the copper disc and the titanium part and the voltage between the copper disc and the titanium was measured using a calibrated digital voltmeter. Using Ohms law the voltage was converted directly into a contact resistance in .Math.cm.sup.2. The coated part had a contact resistance of between 1 and 6 m.Math.cm.sup.2, whereas the uncoated part had a contact resistance above 100 m.Math.cm.sup.2. The results are provided in Table 1 below and illustrated in FIG. 1.

TABLE-US-00001 TABLE 1 Interfacial Contact Resistance Start of Test End of Test Uncoated 1 8.4 176 Uncoated 2 7.2 189 Coated 1 3.6 5.8 Coated 2 2.8 4.5