Efficient platinum electroplating solution

Abstract

The description describes a method of preparing an electroplating solution comprising the steps of: (i) providing a solution comprising tetraammineplatinum dihydroxide (II) or tetraammineplatinum bicarbonate (II); and (ii) reducing the pH of the solution obtained from step (i) by adding one or more acids selected from the group consisting of sulfuric acid, precursors forming sulfuric acid in situ, or methanesulfonic acid. Also described are an electroplating solution or an electroplating method which can be prepared by the method, comprising a step of electroplating on a substrate using the electroplating solution prepared by the method. Also described is an electroplating method comprising the step of electroplating on a substrate using an electroplating solution wherein the electroplating solution comprises tetraammineplatinum (II) sulfate or tetraammineplatinum (II) methanesulfonate.

Description

Technical Field

[0001] The present invention relates to platinum electroplating solutions and their use in the coating of substrates. Background Art

[0002] Dinitrosulfatoplatinic acid (hereinafter referred to as "H.DNS") and related complexes such as potassium dinitrosulfatoplatinate (hereinafter referred to as "K.DNS") and potassium tetranitroplatinate K2[Pt(NO2)4] are used to produce thin platinum films on various substrates. For example, the article "The Electrodeposition of Platinum and Platinum Alloys" (Platinum Metals Rev., 1988, 32, (4), 188-197) describes that these electrolytes can be used to coat platinum on a wide range of materials including copper, brass, silver, nickel, lead and titanium. CN105132964A describes a platinum plating solution comprising K2[Pt(NO2)4], a water-soluble phosphate, alkyltrimethylammonium bromide and sulfuric acid. The article "Hot corrosion behaviour of single-phase platinum-modified aluminide coatings: Effect of Pt content and pre-oxidation" (Corrosion Science 2017, 127, 82-90) describes the use of K.DNS (K2[Pt(NO2)2(SO4)] for electroplating Ni-based superalloys.

[0003] References herein to "DNS" should be understood to mean dinitrothioplatinate or dinitrothioplatinic acid, unless the context requires a specific alternative.

[0004] One use of platinum electroplating baths (including DNS) is to coat components of fuel cells and electrolyzers. It is expected that the world's demand for hydrogen will increase significantly in the coming decades, so there is a need to reduce the cost of components of fuel cells and electrolyzers and allow these components to be coated quickly and efficiently. Despite their use in industry, DNS baths do have some disadvantages.

[0005] First, their cathode current efficiency (CCE) is low, ranging from about 10% to 25% at 40°C to 90°C.

[0006] Second, they are industrially prepared in a multi-step process with low yields. In addition, their production usually requires the use of platinum chloride salts as sensitizing compounds. The preparation of DNS is described in GB897690A and Platinum Metals Rev., 1988, 32, (4), 188-197.

[0007] There is a need for platinum electroplating solutions that have a higher CCE than DNS and a higher plating rate than DNS while still producing deposits with favorable properties. Ideally, they should be easy to manufacture. The present invention meets this need. Summary of the invention

[0008] Surprisingly, the inventors have found that electroplating solutions that solve the above problems can be prepared starting from commercially available salts or solutions containing tetraamine platinum (II) ions. Salts containing tetraamine platinum (II) ions are generally non-sensitized, which is different from the platinum halide salts conventionally used in DNS solution manufacturing. The inventors have found that efficient electroplating solutions can be prepared by treating solutions containing tetraamine platinum (II) dihydroxide or tetraamine platinum (II) bicarbonate with specific acids.

[0009] Therefore, in a first aspect, the present invention relates to a method for preparing an electroplating solution, the method comprising the following steps:

[0010] (i) providing a solution comprising tetraammineplatinum(II) dihydroxide or tetraammineplatinum(II) bicarbonate; and

[0011] (ii) reducing the pH of the solution obtained from step (i) by adding one or more acids selected from the group consisting of sulphuric acid, a precursor forming sulphuric acid in situ or methanesulphonic acid.

[0012] The plating solution prepared by this method offers several advantages over DNS.

[0013] First, these baths typically have a CCE of 60% to 95% at a plating temperature of 90°C, compared to 10% to 25% for DNS at a plating temperature of 60°C to 90°C. This is a particularly high CCE, and therefore these baths are more efficient and more suitable for high throughput processes. It is expected that in the coming decades it will be necessary to coat a large number of titanium electrolyser components in order to support the hydrogen economy, so it is important to have baths with high efficiency and high plating rates to achieve this.

[0014] Second, these baths are capable of producing thin, adherent, uniform coatings with good covering power on properly pretreated substrates.

[0015] Third, DNS as supplied is typically dark brown and, in early use, difficult to see through unless diluted. In contrast, the electroplating solution prepared according to the method of the present invention is not strongly colored, is typically colorless when plating titanium, and produces a light lime color when continuously plating stainless steel. The substrate to be coated can be observed in the bath, which allows the anode to cathode distance to be easily set and the plating process to be observed.

[0016] Fourth, unlike multi-step, low-yield routes to produce DNS that often involve sensitizing platinum chloride species, these baths can be prepared in high yield and in a single step from commercially available tetraammineplatinum(II) salts.

[0017] Fifth, the bath according to the invention is able to operate over a wider pH range than DNS which operates only under highly acidic conditions. This means that the bath has greater substrate compatibility than DNS.

[0018] It is known to produce an electroplating bath by acidifying a solution containing a source of tetraamine platinum (II) ions. WO 2012 / 095667 A2 describes an electroplating bath comprising a source of platinum ions and a source of polyphosphate anions, wherein the bath has a pH in the range of 2 to 9 when in use or ready for use. In most examples, the bath is prepared by adding an oxo-salt or oxo-acid containing phosphorus to a solution of tetraamine platinum (II) hydrogen phosphate, tetraamine platinum (II) hydrogen pyrophosphate or tetraamine platinum (II) dihydrogen pyrophosphate. A disadvantage of baths containing polyphosphate anions is that these anions dissociate from the phosphate under acidic conditions, resulting in a deterioration of the coating quality and a decrease in CCE under acidic conditions.

[0019] CN114752975A and JP2022107487A describe a platinum electrolytic plating bath comprising a platinum (II) complex and free sulfuric acid or aminosulfonic acid in addition to anionic surfactants. The presence of anionic surfactants is interpreted as inhibiting the interaction between platinum (II) and (O) complexes in solution, and thus helping platinum particles to deposit in the form of a dense coating. Although it is suggested that tetraammine platinum hydrogen phosphate is used as a possible platinum (II) complex for the present invention, in the examples, DNS or P salts are used as platinum sources to which acid and anionic surfactants are added.

[0020] It is believed that the electroplating solution prepared by the method according to the first aspect is chemically different from the electroplating solutions that have been previously described. Evidence for this comes from the fact that the solution prepared according to the present method is initially clear and colorless, whereas a comparative solution prepared by dissolving a P salt slurry (diamminedinitroplatinum (II), also known as diammineplatinum (II) dinitrite) in a simple sulfur-based acid is colored acid orange or yellow and remains colored for a period of time when used.

[0021] Thus, in a second aspect, the invention relates to an electroplating solution prepared according to the method of the first aspect.

[0022] The corresponding palladium bath tetraamminepalladium(II) sulfate has been described previously.

[0023] EP0107308 A2 (Engelhard Corporation) describes an electroplating bath comprising a substantially halogen-free solution of: (a) a tetraammine compound obtained by reacting Pd(R)2(NO2)2 with ammonium hydroxide; (b) anions selected from a mixture of sulfate and sulfamate anions; (c) ammonium cations; and (d) optionally alkali metal cations. At least 25% of the cations are ammonium and the bath has a pH of about 5 to 7.

[0024] EP0280510 A1 (Engelhard Corporation) describes an aqueous palladium electroplating bath containing a tetraaminepalladium salt. Specific salts include tetraaminepalladium sulfate, nitrate, phosphate, citrate and sulfamate.

[0025] While tetraamminepalladium(II) sulfate is a known and common palladium electroplating salt, its counterpart tetraammineplatinum(II) sulfate is less widely known and utilized.

[0026] The electroplating solution may be used for electroplating a substrate. Thus, in a third aspect, the invention relates to a method comprising (i) preparing an electroplating solution according to the first aspect; and (ii) electroplating a substrate using the electroplating solution.

[0027] The process of the first aspect is believed to produce a solution which at least initially comprises complex tetraamineplatinum(II) sulfate (where sulfuric acid or a precursor is used) or tetraamineplatinum(II) methanesulfonate (where methanesulfonic acid is used).

[0028] Therefore, in a fourth aspect, the present invention relates to an electroplating method, which comprises the step of electroplating on a substrate using an electroplating solution, wherein the electroplating solution comprises tetraamineplatinum(II) sulfate or tetraamineplatinum(II) methanesulfonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The CCE performance over time of the electroplating solution of Comparative Example 1 prepared from P salt and methanesulfonic acid is shown.

[0030] Figure 2 The CCE performance over time of the electroplating solution of Example 2 prepared from tetraammineplatinum(II) dihydroxide and methanesulfonic acid is shown.

[0031] Figure 3 The CCE performance over time of the electroplating solution of Example 4 prepared from tetraammineplatinum(II) dihydroxide and sulfuric acid is shown. DETAILED DESCRIPTION

[0032] Any sub-headings are for convenience only and are not intended to limit the invention.

[0033] Preparation of electroplating solution

[0034] Step (i)

[0035] Step (i) involves preparing an aqueous solution containing tetraamine platinum (II) ions. This can be conveniently prepared by dissolving tetraamine platinum (II) dihydroxide [Pt (NH3) 4] (OH) 2 or tetraamine platinum (II) bicarbonate [Pt (NH3) 4] (HCO3) 2 in deionized water.

[0036] In a preferred embodiment, the solution in step (i) is an aqueous solution consisting of tetraamine platinum (II) dihydroxide or tetraamine platinum (II) bicarbonate. Because the hydroxide ions or bicarbonate ions are removed during step (ii) as described below, a high-purity tetraamine platinum (II) acid salt solution can be produced. For this reason, it is preferred that in step (i), the solution consists of tetraamine platinum (II) dihydroxide or tetraamine platinum (II) bicarbonate so that there are no other components that may interfere with plating during subsequent steps.

[0037] Preferably, the solution does not contain polyphosphate anions. In this specification, "polyphosphate" refers to a group comprising two or more phosphoric acid groups linked together via a shared oxygen atom. Polyphosphates are used in the production of the electroplating baths described in WO2012 / 095667A2, but the disadvantage is that polyphosphates and / or phosphates can accumulate in the bath over time, resulting in a degradation of the bath efficiency and the plating quality. Baths that do not contain polyphosphate anions do not have this disadvantage.

[0038] The advantage of using tetraammineplatinum(II) dihydroxide as the source of platinum(II) ions is that no gas is evolved during the pH reduction in step (ii), unlike tetraammineplatinum(II) bicarbonate which evolves carbon dioxide. This can allow the use of simpler equipment and a safer process when using tetraammineplatinum(II) dihydroxide.

[0039] In an alternative embodiment, tetraamine platinum (II) hydrogen phosphate [Pt (NH3) 4] (HPO4), commercially available from Johnson Matthey as the platinum Q salt, can be used as the source of tetraamine platinum (II) ions in step (i). The inventors have found that baths with high CCE can be prepared from [Pt (NH3) 4] (HPO4), particularly when acidified using sulfuric acid. However, hydrogen phosphate ions in acidic solutions (e.g., from dihydrogen phosphate or phosphoric acid) accumulate during use of the bath, and this affects plating performance and efficiency. Baths according to this embodiment initially have good bright plates, but often darken and become inferior with continued use or replenishment, unlike baths prepared from tetraamine platinum (II) dihydroxide or tetraamine platinum (II) hydrogen carbonate.

[0040] Step (ii)

[0041] In step (ii), the pH of the solution obtained from step (i) is reduced by adding one or more acids selected from the group consisting of sulfuric acid (H2SO4), precursors forming sulfuric acid in situ, or methanesulfonic acid (CH3SO3H).

[0042] The pH is reduced to ensure that the hydroxide anion or bicarbonate anion in the starting solution is removed and the required tetraamine platinum (II) sulfate or tetraamine platinum (II) methanesulfonate is formed. Hydroxide is converted into water under this condition. Bicarbonate is converted into water and carbonic acid gas under this condition. Usually, the pH is reduced to the end value between pH 0 to 7 to ensure complete conversion, usually lower than pH 4, such as between pH 0 to 4 or between pH 0.5 to 2.5.

[0043] In some embodiments, a mixture of two or more (preferably two) of the above acids is used to adjust the pH. In some embodiments, a single acid selected from the above acids is used to adjust the pH. Preferably, a single acid is used to adjust the pH.

[0044] The number of equivalents of acid added when adjusting the pH is generally selected to be sufficient to ensure that at least an equimolar amount of acid is present relative to the amount of tetraamine platinum (II) ions, and in many cases an excess of acid relative to Pt (II). Briefly, the reaction can be described as:

[0045] [Pt(NH3)4] 2+ +H2SO4→[Pt(NH3)4](SO4)+2H +

[0046] [Pt(NH3)4] 2+ +2CH3SO3H→[Pt(NH3)4](CH3SO3)2+2H +

[0047] It should be understood that the actual substances in the solution may be more complex than described above.

[0048] In some embodiments, the precursor for in situ formation of sulfuric acid is an acid salt. Preferred acid salts include: - An ionic hydrogen sulfate salt, preferably a Group I hydrogen sulfate salt, particularly sodium hydrogen sulfate (NaHSO4) or potassium hydrogen sulfate.

[0049] Alternatively, in some embodiments, the precursor for the in situ formation of sulfuric acid is aminosulfonic acid (HSO3NH2).

[0050] In step (ii), sulfuric acid is most preferred for lowering the pH as it produces a bath with a high CCE and consistently produces bright boards.

[0051] Acid salts are less preferred than sulfuric acid for pH reduction because they typically include metal cations which can accumulate over time during use of the bath and can adversely affect coating properties.

[0052] Methanesulfonic acid is less preferred than sulfuric acid for pH reduction because baths prepared using methanesulfonic acid tend to produce darker boards over time.

[0053] Optional step (iii) - pH adjustment

[0054] In some cases, the pH of the solution formed during step (ii) may be incompatible with the substrate to be coated. For example, nickel substrates are unstable at highly acidic pH. Therefore, in some cases, a further pH adjustment step (iii) may be performed. The pH is preferably adjusted downward using the same acid used in step (ii) to avoid further complicating the species formation in the solution. The pH is preferably adjusted upward using an ammonia solution to avoid further complicating the species formation in the solution. Typically, the pH of the solution after pH adjustment is in the range of 0 to 9.

[0055] Electroplating method

[0056] The present invention also relates to a method of electroplating on a substrate using the electroplating solution produced by step (i) and step (ii), and optionally step (iii).

[0057] The electroplating solution can be used to electroplate a wide variety of substrates. In a preferred embodiment, the substrate is a metal or alloy substrate, preferably a titanium or titanium alloy substrate. Titanium alloys are often used in medical applications, such as the nickel-titanium alloy "Nitinol".

[0058] It is particularly preferred to carry out the electroplating process with an electroplating solution having a pH of 1 to 9, since the resulting panels at this pH are bright, which indicates a good coating. The process is preferably carried out with an electroplating solution having a pH of 1 to 8, preferably 1 to 7.

[0059] It is particularly preferred that the electroplating process is carried out at a temperature above 80°C (i.e. the temperature of the electroplating solution in the bath is above 80°C). At 80°C or below, CCE is significantly reduced and plating is slow. Plating is preferably carried out at a temperature of 80°C to 95°C, preferably 85°C to 95°C.

[0060] In a preferred embodiment, the substrate is a component of a fuel cell or an electrolyzer (e.g., a water electrolyzer). Many components in a fuel cell or an electrolyzer are required to be conductive. For example, a bipolar plate is a component of a PEM fuel cell and an electrolyzer, which has various functions, including uniformly distributing fuel gas and air, conducting current from cell to cell, removing heat from the effective area, and preventing gas and coolant leakage; for further details, see International Journal of Hydrogen Energy 30 (2005) 1297–1302. Another example is a porous transport layer (PTL). One of the functions of the PTL is to transport water and oxygen to the anode side and hydrogen to the cathode side (in the case of a fuel cell), and to act as a current collector; for further details, see Adv. Energy Mater. 2021, 11, 2002926. Therefore, in a preferred embodiment, the substrate is a bipolar plate or a porous transport layer; the article produced after the coating method is a bipolar plate or a porous transport layer with a coating. The bipolar plates are often made of stainless steel, and in preferred embodiments, the substrate is a bipolar plate made of stainless steel.The porous transport layer is often made of titanium, and in preferred embodiments, the substrate is a porous transport layer made of titanium.

[0061] The preferred aspects described above in conjunction with the method are applicable to the methods of the third and fourth aspects of the present invention.

[0062] Example

[0063] General process of electroplating

[0064] The cathode test piece was placed between two flat platinum-coated titanium anodes in a sample holder supported in a 250 mL or 400 mL tall glass beaker. 2 Up to 14cm 2The cathode test piece is threaded onto the threaded steel rod support, and the cathode test piece is fully immersed in the bath solution. The bath volume is in the range of 250mL to 300mL. A 30 volt 2 ampere capacity laboratory power source (Aim TTi, model EL302R) is used to provide constant ampere. Current density is recorded in amperes per square foot (ASF). The bath solution is heated by a laboratory heater unit (Stuart heatstir model US152), and the magnetic stirring bar coated with PTFE is stirred.

[0065] Calculation of CCE

[0066] The theoretical maximum value of the plated platinum in grams (100% CCE) is calculated by the following formula:

[0067] Applied current (A) × plating time (s) × 0.001010457 (g·A -1 ·s -1 )

[0068] CCE is calculated by dividing the actual amount of plated Pt by the ratio of the theoretical value of the above equation. The amount of plated Pt is measured by removing the coated test piece from the steel rod, drying the coated test piece, and subtracting the mass of the uncoated test piece. The amount of platinum plated on the steel rod can be ignored and is not considered for CCE calculations.

[0069] Bath Color

[0070] Comparative Example P salts with methanesulfonic acid (Comparative Example 1) or sulfuric acid (Comparative Example 3) prepared at room temperature were yellow (tartrate yellow if more diluted), but these solutions turned to lime yellow when plated at 90° C. In contrast, the baths in Examples 2, 4, and 5 were colorless when prepared and when plated at 90° C.

[0071] Example 1 (Comparative) (Pt salt = P salt, acid = methanesulfonic acid)

[0072] A P salt slurry (Johnson Matthey UK product 155061, 27.21 g, 3.93 g Pt, 0.0201 mol) was added to a rapidly stirred solution of 2.5 mL methanesulfonic acid (3.70 g, 0.0385 mol) in 250 mL water. The plating conditions were as follows:

[0073] Initial [Pt] = 15.7 g / L

[0074] Plating temperature = 90°C

[0075] Bath pH = 1-2

[0076]

[0077] The CCE values ​​for each run are shown in Figure 2 Medium. CCE is consistently 15% to 30%.

[0078] Example 2 (Pt salt = [Pt(NH3)4](OH)2, acid = methanesulfonic acid)

[0079] Methanesulfonic acid (22.5 mL, 33.3 g, 0.347 mol in total) was added dropwise by pipette to a solution of tetraammine platinum dihydroxide solution (300 mL, about 20 g / L Pt, 6 g Pt) at 40°C, during which white crystals precipitated. The mixture was heated; the crystals dissolved above 55°C. The plating conditions were as follows:

[0080] [Pt] = 20 g / L-25 g / L

[0081] Plating temperature = 90°C

[0082] Bath pH = 1-2

[0083]

[0084] *The bath was diluted to approximately 300 mL before the start of Run 4 and the pH was restored to pH 2 by adding 0.5 mL of methanesulfonic acid.

[0086] After the gas started, the bath settled down quickly. The initial panels were bright matte, but as the bath usage increased, they became gray matte for thick coatings (several microns), while thin coatings (less than 1 micron) remained bright.

[0087] The CCE values ​​for each run are shown in Figure 3 The CCE was consistently 70% to 80%. The CCE dropped in Runs 5 and 6 due to plating out.

[0088] Example 3 (Comparative) (Pt salt = P salt, acid = sulfuric acid)

[0089] The P salt slurry (14.46 g Pt as metal, 10.05 g per 100 g, 1.453 g total Pt, 0.00745 mol Pt) was added dropwise at 90°C to a stirred solution containing 2 mL of concentrated sulfuric acid in 170 mL to produce a light acid orange solution. After cooling, another 2 mL of concentrated sulfuric acid was added. The volume was made up to 250 mL and used for plating under the following conditions. The plating conditions were as follows:

[0090] Initial [Pt] = 5.8 g / L

[0091] Plating temperature = 90°C

[0092] Current density = 7ASF

[0093] The board was bright, silvery, and shiny, but the CCE was as low as 18.72%.

[0094] Example 4 (Pt salt = [Pt(NH3)4](OH)2, acid = sulfuric acid)

[0095] Concentrated sulfuric acid (3.6 mL in total) was added dropwise to a solution of tetraammine platinum dihydroxide solution (about 20 g / L platinum) (200 mL, 4 g Pt, 0.205 mol Pt) at room temperature by a pipette. During the addition, the solution evolved gas at about pH 6, and the pH of the final solution was about 1-2. The solution was used to plate using the following conditions in a 250 mL glass beaker. The plate was bright silver and matte. The plating conditions were as follows:

[0096] [Pt]=20g / L

[0097] Plating temperature = 90°C

[0098] Bath pH = 1-2

[0099]

[0100] *Additional sulfuric acid (5 drops, approximately 0.25 mL) was added before Run 2 began.

[0101] Run 1 has a high cathode current efficiency of 79.07% at 6 ASF, 90°C despite gas onset. The CCE values ​​for each run are shown in Figure 4. The CCE is consistently 70% to 80%. The CCE drops in Runs 5 and 6 due to plating out of platinum.

[0102] Examples 2 and 4, both prepared starting from tetraammineplatinum(II) dihydroxide, have much higher CCEs than comparable processes starting from P salts (Examples 1 and 3).

[0103] Example 5 (Pt salt = [Pt(NH3)4](HCO3)2, acid = sulfuric acid)

[0104] Example 5 follows a variation of the general procedure. The effects of pH, current density and plating temperature were studied. The bath was used in the unbuffered state to show plating performance over the entire acidic pH range.

[0105] Sulfuric acid was added to 200 mL of tetraammine platinum (II) bicarbonate solution ([Pt] = 14.4 g / L) in a glass beaker while stirring with a magnetic stirrer. A polished and cleaned titanium strip with a plating area of ​​7.5 cm × 2.5 cm was used as the cathode. The cathode was placed between two parallel flat Pt / Ti fine grid plates measuring 8 cm × 4 cm with a distance of 2 cm from the anode to the cathode. The solution was heated to 90°C before starting electroplating. The pH between sequential platings was adjusted by adding concentrated sulfuric acid under stirring.

[0106]

[0107] These results indicate that the bath operates with high efficiency over a wide pH range and at various current densities. Plating temperatures above 80°C are required for high efficiency. The higher CCE compared to Examples 2 and 4 is believed to be due, at least in part, to the use of optimized anode to cathode size and optimized anode to cathode distance.

Claims

1. A method for preparing an electroplating solution, the method comprising the following steps: (i) providing a solution comprising tetraammineplatinum(II) dihydroxide or tetraammineplatinum(II) bicarbonate; and (ii) reducing the pH of the solution obtained from step (i) by adding one or more acids selected from the group consisting of sulfuric acid, a precursor forming sulfuric acid in situ or methanesulfonic acid.

2. The method according to claim 1, wherein the solution in step (i) is a solution consisting of tetraammineplatinum(II) dihydroxide or tetraammineplatinum(II) bicarbonate.

3. A method according to claim 1 or claim 2, wherein in step (ii), the pH is lowered to a value in the range between pH 0 and 7.

4. The process according to any one of claims 1 to 3, wherein in step (ii), the pH is lowered to a value in the range between pH 0 and 4.

5. The process according to any one of claims 1 to 4, wherein sulfuric acid is used to adjust the pH.

6. The process according to any one of claims 1 to 4, wherein methanesulfonic acid is used to adjust the pH.

7. The process according to any one of claims 1 to 4, wherein the pH is adjusted using a precursor which forms sulfuric acid in situ.

8. The method of claim 7, wherein the precursor is an acid salt.

9. The method of claim 7, wherein the precursor is aminosulfonic acid.

10. The method according to any one of claims 1 to 9, comprising the additional step (iii) of adjusting the pH of the solution obtained from step (ii) to a pH in the range of 0 to 9.

11. An electroplating solution prepared or producible by the method according to any one of claims 1 to 10.

12. An electroplating method, comprising: (i) preparing an electroplating solution according to the method of any one of claims 1 to 10; as well as (ii) performing electroplating on a substrate using the electroplating solution.

13. The method of claim 12, wherein within the substrate are components of a fuel cell or an electrolyser.

14. The method of claim 13, wherein among the substrates is a bipolar plate or a porous transport layer.

15. The method according to any one of claims 12 to 14, wherein step (ii) is carried out at a temperature above 80°C.

16. An electroplating method, comprising the step of electroplating on a substrate using an electroplating solution, wherein the electroplating solution contains tetraamine platinum (II) sulfate or tetraamine platinum (II) methanesulfonate.

17. The electroplating method of claim 16, wherein the solution is free of polyphosphate anions.

18. A method of electroplating according to claim 16 or claim 17, wherein the solution consists essentially of tetraamine platinum (II) sulphate or tetraamine platinum (II) methane sulphonate.

19. A method according to any one of claims 16 to 18, wherein within the substrate is a component of a fuel cell or an electrolyser.

20. The method of any one of claims 16 to 19, wherein among the substrates is a bipolar plate or a porous transport layer.

21. The method according to any one of claims 16 to 20, wherein step (ii) is carried out at a temperature above 80°C.

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