WO2018224987A1 - A method of electroless deposition of platinum group metals and their alloys and a plating bath used therein - Google Patents

Abstract

The invention relates to a method of electroless deposition of platinum group metals and their alloys from a plating bath onto a substrate, comprising a reduction step of one or more platinum group metal precursors with a reducing agent, wherein the reducing agent is a primary or secondary monohydroxyalcohol or a mixture of primary or secondary monohydroxyalcohols. The invention also provides a plating bath suitable for use in said method.

Description

A METHOD OF ELECTROLESS DEPOSITION OF PLATINUM GROUP METALS AND THEIR ALLOYS AND A PLATING BATH USED THEREIN

TECHNICAL FIELD

The invention provides a method of electroless deposition of platinum group metals and their alloys and a plating bath used therein.

BACKGROUND ART

Platinum group metals (PGMs) consist of six elements - platinum, palladium, rhodium, iridium, ruthenium and osmium. Interest in plating of platinum group metals and PGM alloys results from a very broad range of their applications. PGM layers can provide corrosion resistance, and can be also used as decorative or tarnishing layers. Rhodium is typically plated as wear-resistant, decorative finishing layers. PGMs are also known for their catalytic activity for many chemical reactions. PGMs are used for manufacturing of electronic devices and components, as well as layers providing protection against corrosion of non-precious metals. For example, galvanized palladium, ruthenium and their alloys are used as gold substitute contacts on connectors and printed circuit boards.

Platinum layer can also replace gold-on-copper plating. In such material, the copper atoms tend to diffuse through the gold layer, causing tarnishing of its surface and formation of an oxide and/or sulphide layer. For gold-on-copper layers typically the layer of nickel has to be used to provide mechanical backing for the gold layer. However, at higher frequencies, in so modified gold-on-copper layers the skin effect is observed due to higher electrical resistance of nickel. Also soldering gold-plated parts can be problematic as gold dissolves in solder. A 2-3 μιη layer of gold dissolves completely within one second during typical wave soldering conditions. Palladium and ruthenium are used as metal contacts on semiconductors, for example GaAs and InP.

Plating of PGMs is particularly suitable method for cost-effective use of PGMs since by using this approach PGMs (and their alloys) can be plated on different low cost substrates. Electroless PGMs plating is particularly suitable because in this method the layer can be plated on non-conductive supports. PGM plating on plastics can be applied in production of flexible electronics and flexible dye-sensitized solar cells [Dao V-D, et al.: Dry plasma reduction to synthesize supported platinum nanoparticles for flexible dye- sensitized solar cells. J. Mater. Chem. A 2013, 1:4436-4443].

To date, a few processes of PGM electroless deposition was described in the literature [Electroless Plating: Fundamentals and Applications; Glenn O. Mallory and Juan B. Hajdu, Ed., William Andrew, 1990]. Moreover, most of them lead to the formation of fragile and not uniform deposits with high tendency to peel. Literature survey suggests that most studies on PGM plating are focused on the development of plating bath additives with much less emphasis placed on the reducing agents. In virtually all methods of electroless deposition of PGMs one of the following reducing agents is used: hydrazine and its derivatives, borohydride or hydrogen hypophosphite. Redox potentials of these reducing agents are very low and therefore PGM plating is accompanied by hydrogen evolution, which results in unfavourable conditions for PGM deposition, such as hydrogen embrittlement, peeling, rough deposits, etc.

It is commonly know that platinum plating is a complicated and difficult process. Electrochemical methods of Pt deposition lead to formation of poorly adhesive platinum black deposits. In the classical method introduced by Keitel and Zschiegner the Pt deposition is performed form "Pt"-salts precursors. This is one of the few methods leading to relatively smooth Pt coatings [Keitel W and Zschiegner H: Electrodeposition of Platinum, Palladium and Rhodium. Trans. Electrochem. Soc. 1931, 59:273-275]. However, the plating requires high temperature operation and very low cathodic current efficiency of platinum deposition - typically lower than 10%. A solution containing sulphato- dinitritoplatinum (II) has been prepared for commercial use under the name DNS Platinum Plating Solution and patent applications covering baths of this type have been filed in a number of countries [Hopkin N and Wilson L: Bright platinum plating. Platinum Metals Review 1960, 4:56-58]. Currently used platinum plating solutions contain many additives in order to improve the quality of the deposits. However, this approach may be expensive and has its own limitations and potential problems. Platinum metals are chemically inert, however their surfaces are extremely reactive and therefore these metals are widely used in the heterogeneous catalysis. Platinum alloyed with palladium, rhodium and other PGMs are used in various chemical industrial scale processes. Production of nitric acid and agricultural fertilizers, wherein ammonia oxidation is required, creates the highest demand for PGMs catalysts. However, important applications for platinum catalysts can also be found in manufacturing of polymer materials, for example in the process of production of silicones and vinyl acetate monomers. The PGMs are used as catalysts in reforming and isomerization reactions in the petroleum industry. Rhodium catalysts are used in the manufacturing of oxo-alcohols and acetic acid, the latter is also produced with ruthenium and iridium as catalysts. Dimensionally stable anodes, which consist of titanium coated with either ruthenium or ruthenium-iridium alloy, are used in chlorine evolution on an industrial scale. Rough PGM deposits can be applied in fuel cells, etc. For all these applications rough PGM deposits are beneficial since higher specific area results in higher catalytic activity of the layer.

However, platinum coatings obtained in brightener-free baths are usually fragile and poorly adhesive [Feltham A and Spiro M: Platinized platinum electrodes. Chem. Reviews 1971, 71: 177-193]. Often the process is accompanied by hydrogen evolution and platinum is reduced in the solution. For over half a century Pt black deposition has been performed from solutions containing small amounts of lead acetate, which inhibits hydrogen evolution and improves Pt adhesion. However, in this procedure lead is incorporated into the layer and the resulting Pt deposits are contaminated with Pb, which is particularly unfavourable for catalytic applications.

Currently there is no technology for producing platinum layers on a very large specific surface area and strongly adherent to the substrates. Ultrathin layer or metal clusters can be obtained on oxides or silicon [M.B. Vukmirovic et al., ChemElectroChem 2016, 3: 1-7; A. Mufioz-Noval, Electrochemistry Communications, 2016, 71: 9-12]. A few electroplating and electroless plating technology is available for platinum. Comparison of catalytic layers comprising platinum-ruthenium bimetallic clusters on graphite obtained by vapor deposition and electroless deposition methods were recently described in R. P. Galhenage, Phys. Chem. Chem. Phys., 2015, 17, 28354. In the most of the other known plating methods, only platinum layers are obtained (i.e. no means for plating platinum in combination with other PGMs have been disclosed). In all known methods, plating can be carried out on a specific solid support, such as copper or titanium. It is also necessary to control plating conditions, especially temperature and pH. Also, such typically used plating baths are very difficult to obtain, as they contain many additives and reducing agents, such hydrazine and its derivatives or hypophosphite. Finally, any smooth layers can be obtained only via electroplating, however with very low current efficiency.

Chemical reduction of platinum precursors is, on the other hand, widely used for production of platinum nanoparticles. Very popular reducing agents for platinum nanoparticles preparation are aliphatic alcohols and aldehydes. One of the necessary conditions for nanoparticles preparation is fast reduction step, usually performed in relatively high temperatures (typically the temperature of the reduction step is higher than 70°C). At lower temperatures stronger reducing agents have to be used, such as hydrazine [WO2013186740].

Owing to their possible use in fuel cells, oxidation of alcohols has been extensively studied. Most extensive studies have been carried out for methanol and to the lesser extent for ethanol. Oxidation of other alcohols is occasionally reported. Polihydroxy compounds, namely sugars and sugars derivatives, have been previously used as reducing agents for plating silver and gold, e.g. glucose, ascorbic acid [Kato M et al.: Electroless Gold Plating Bath Using Ascorbic Acid as Reducing Agent-Recent Improvements. In Proceedings of AESF Technical Conf SUR/FIN'95: 1995:805-813]. Aliphatic and aromatic mono-alcohols have never been previously used as reducing agents in electroless plating.

Due to a large demand for platinum and other PGM covered articles, there exists a great need for development of a method for electroless deposition of platinum and other PGMs, which would result in formation of well- adhering metal layers. Moreover, there exists a need for a PGM electroless plating method wherein the properties of the formed metal layer can be easily controlled simply by changing the process conditions. It would also be advantageous if a plating bath used in such a method of PGM electroless plating would be free of brighteners (e.g. saccharin and polyethylene glycol) and other additives and reducing agents (e.g. hydrazine, lead or hypophosphite).

DISCLOSURE OF INVENTION

The inventors of the present invention have developed a method for electroless deposition of platinum and other PGMs, as well as their alloys, in which aromatic and aliphatic alcohols are used as reducing agents. A PGM layer as used herein refers to both layers of a single metal (e.g. platinum, palladium, rhodium, iridium, ruthenium and osmium) and metal alloy layers comprising platinum group metals (e.g. platinum - rhodium, platinum - iridium, platinum - ruthenium, etc.), as well as metal alloy layers comprising platinum group metals with other metals, such as gold, nickel and copper (e.g. platinum - gold, platinum - copper, platinum - nickel, platinum - rhodium - gold, rhodium - nickel, etc.). In the most preferred aspect of the invention, an alloy layer is deposited on a substrate, wherein said alloy comprises one or more metals from a group comprising: platinum, palladium, rhodium, iridium, ruthenium, osmium, gold, nickel and copper.

In the method of the invention both primary and secondary alcohols are used and the deposition is carried out on a wide variety of substrates, including metals and alloys, polymeric materials, graphite and silicon. The process of PGM plating of the invention is carried out in the temperature range from the freezing point to the boiling point of the plating bath. Both layer thickness and surface morphology of the deposited layer can be controlled in a simple manner by adjusting the experimental conditions, in particular the reducing agent, temperature, pH and concentration of both the reducing agent and the platinum group metal precursor.

In particular, according to the invention, the method of electroless deposition of platinum group metals and their alloys, from a plating bath onto a substrate, comprises a reduction step of one or more platinum group metal precursors with a reducing agent, wherein the reducing agent is a primary or secondary monohydroxyalcohol or a mixture of primary or secondary monohydroxyalcohols. The term "monohydroxyalcohol" as used herein refers to aliphatic and aromatic alcohols comprising a single hydroxyl group. The term "primary alcohol" should be understood as an alcohol, in which the hydroxyl group is connected to a primary carbon atom - a carbon atom having only one carbon atom neighbor (i.e. an alcohol having the following group "-CH2OH"). The term "secondary alcohol" should be understood as an alcohol, in which the hydroxyl group is connected to a secondary carbon atom - a carbon atom having two carbon atom neighbors (i.e. an alcohol having the following group "-CHROH", where "R" is a carbon-containing group (aliphatic or aromatic)). The term "a mixture of primary or secondary monohydroxyalcohols" as used herein refers to a mixture of different primary monohydroxyalcohols, a mixture of different secondary monohydroxyalcohols, as well as a mixture comprising both primary and secondary monohydroxyalcohols. The term "electroless deposition" is well-known to a person skilled in the art and refers to a process of metal deposition on a substrate by reduction of metal ions from solution without using an external source of electrons.

Preferably the monohydroxyalcohol has a general formula

wherein Ri and R₂ are the same or different and each of them independently is selected from a group comprising hydrogen atom, a straight or branched Ci-7-alkyl group, C₃-s-aryl group, C₄-8-aralkyl group and C₄-8-alkaryl group. "Alkyl" means an acyclic, branched or unbranched, saturated monovalent hydrocarbyl group. Alkyl is exemplified by, but not limited to, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl, as well as branched saturated monovalent hydrocarbyl groups. "Aryl" means a cyclic, fully unsaturated, hydrocarbyl group. Aryl is exemplified by, but not limited to, cyclopentadienyl and phenyl. "Aralkyl" means an aryl group having a pendant alkyl group. "Alkaryl" means an alkyl group having a pendant and/or terminal aryl group.

Preferably, Ri and R₂ in the above formula are independently selected from a group comprising -H, -CH₃, -C2H5, -C₃H₇, -CH(CH₃)₂, -C₄H₉, -CH₂CH(CH₃)₂, -CH(CH₃)C₂H₅, -C(CH₃)₃, -C5H11, -CH(CH₃)C H₇, -CH₂CH(CH₃)C₂H₅, -C₂H₄CH(CH₃)₂, -C(CH₃)₂C₂H₅, -CH(CH₃)CH(CH₃)₂, -CH₂C(CH₃)₃, -CH(C₂H₅)₂, -C₆Hi₃, -C7H15, and -CH(C₂H₅)(C₄H₉). More preferably, monohydroxyalcohol is selected from the group comprising methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methylpropan-l-ol, 1-pentanol, 3- methylbutan-l-ol, 2-methylbutan-l-ol, 2,2-dimethylpropan-l-ol, 3-pentanol, 2-pentanol, 3- methyl-2-butanol, 1-hexanol, 2-hexanol, 2-methyl- 1-pentanol, 3 -methyl- 1-pentanol, 4- methyl- 1-pentanol, 3-methyl-2-pentanol, 4-methyl-2-pentanol, 2-methyl-3-pentanol, 2,2- dimethylbutan-l-ol, 2,3-dimethylbutan-l-ol, 3,3-dimethylbutan-l-ol, 3,3-dimethylbutan-2- ol, 2-ethylbutan-l-ol, 1-heptanol, 2-heptanol, 3-heptanol, 4-heptanol, 1-octanol, 2-octanol and 2-ethylhexan-l-ol. Most preferably, monohydroxyalcohol is selected from the group comprising methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2- methylpropan-l-ol, 1-pentanol, 3-methylbutan-l-ol, 2-methylbutan-l-ol, 2,2- dimethylpropan-l-ol, 3-pentanol, 2-pentanol, 3-methyl-2-butanol, 1-hexanol, 1-heptanol and 1-octanol.

Certain of the above mentioned monohydroxyalcohols, exist in particular stereoisomeric forms. For example 2-butanol can be obtained as either of two stereoisomers - (R)-(-)-2-butanol and (S)-(+)-2-butanol. The present invention contemplates use of such stereoisomers as separate isomers, as well as racemic and other mixtures thereof.

The concentration of the monohydroxyalcohol in the plating bath used in the method of the invention is in the range from 0.02 to 12 M, more preferably in the range from 0.1 to 5 M. The solubility of monohydroxyalcohols poorly soluble in water can be increased by addition of 2-methylpropan-2-ol. Therefore, in one aspect of the invention the plating bath used in the method of the invention further comprises 2-methylpropan-2-ol.

According to the invention the platinum group metal precursor used in the method of the invention is preferably selected from a group comprising H₂PtCl6, H6Cl₂N₂Pt, PtCl₂, PtBr₂, K₂[PtCl₄], Na₂[PtCl₄], Li₂[PtCl₄], H₂Pt(OH)₆, Pt(N0 )₂, [Pt(NH₃)₄]Cl₂, [Pt(NH₃)₄](HC0 )₂, [Pt(NH₃)₄](OAc)₂, (NH₃)₄Pt(N0 )₂, (NH₄)₂PtBr₆, K₂PtCl₆, PtS0₄, Pt(HS0₄)₂, Pt(C10₄)₂, K₂PtI₆, K₂[Pt(CN)₄], cis-[Pt(NH₃)₂Cl₂], H₂PdCl₆, H₆Cl₂N₂Pd, PdCl₂, PdBr₂, K₂[PdCl₄], Na₂[PdCl₄], Li₂[PdCl₄], H₂Pd(OH)₆, Pd(N0 )₂, [Pd(NH₃)₄]Cl₂, [Pd(NH₃)₄](HC0₃)₂, [Pd(NH₃)₄](OAc)₂, (NH₄)₂PdBr₆, (NH₃)₂PdCl₆, PdS0₄, Pd(HS0₄)₂, Pd(C10₄)₂, Pd(OAc)₂, RuCl₂ ((CH3)₂SO)₄, RuCl , [Ru(NH₃)₅(N₂)]Cl2, Ru(N0 ) , RuBr₃, RuF₃, Ru(C10₄) , K₂RuCl₆, Osl, OsI₂, OsBr₃, OsCl₄, OsF₅, OsF₆, OsOF₅, OsF₇, IrF₆, IrCl , IrF₄, IrFs, Ir(C10₄) , Κ₃[Κ1₆], Κ₂[Κ1₆], Na₃[IrCl₆], Ν ₂[Κ1₆], Li₃[IrCl₆], Π₂[Κ1₆], [Ir(NH₃)₄Cl2]Cl, RhF₃, RhF₄, RhCl , [Rh(NH₃)₅Cl]Cl₂, RhCl[P(C₆H₅)₃]₃, K[Rh(CO)₂Cl₂], Na[Rh(CO)₂Cl₂] Li[Rh(CO)₂Cl₂], Rh₂(S0₄) , Rh(HS0₄) and Rh(C10₄) , their hydrates and mixtures of these salts and/or hydrates. The term "the platinum group metal precursor" should be understood as any platinum group metal salt or complex soluble in the plating bath, which can be reduced to a metallic form, which is deposited on a substrate.

In the preferred embodiment the platinum group metal precursor concentration in the plating bath used in the method of the invention is in the range from 1 mM to 1 M, more preferably in the range from 5 mM to 100 mM, and most preferably in the range from 10 mM to 50 mM.

In the preferred embodiment, the reduction step in the method of the invention is carried out in the temperature between the freezing point to the boiling point of the plating bath. Preferably, the temperature of the reduction step in the method of the invention is between -10 to 80°C, more preferably between 0 to 40°C, and most preferably between 10 to 25°C.

In the preferred embodiment the pH of the plating bath used in the method of the invention is below 7, more preferably between 3 and 5, and most preferably about 4. The best deposits are obtained when the pH of the plating bath is about 4.

A substrate or support as used herein refers to any material onto which PGMs and their alloys are deposited. The examples of suitable substrates/supports comprise metals, such as platinum, palladium, nickel and gold, metal alloys, such as steel, iron-chromium- aluminum alloys (Kanthal®), polymer materials, such as Nafion®, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), carbon (e.g. graphite) and silicon. Preferably, the substrate used in the method of the invention is selected from a group comprising metals, metal alloys, polymeric materials, carbon and silicon. More preferably the substrate is selected from the group comprising platinum, palladium, nickel, gold, steel, iron-chromium-aluminum alloys, Nafion®, polyethylene, polypropylene, polyethylene terephthalate, carbon, graphite and silicon.

In the preferred embodiment of the invention the surface of the substrate onto which PGM is deposited is seeded prior to the reduction step. Any standard process of surface seeding can be used according to the invention. One suitable seeding method is a zincation method, wherein zinc is deposited on the substrate surface from a solution containing zincate ions in the presence of metallic zinc. Alternatively, seeding can be performed using tin (II) ions.

After PGM is deposited on the surface it can undergo a high temperature treatment. This thermal treatment is used to convert a rough surface deposits into deposits having smooth surface. This step can be performed only for PGM layers deposited on substrates, which can withstand high temperatures (such as metals, alloys and silicon). Therefore, in the preferred embodiment the method of the invention further comprises a step of a high temperature treatment after the plating process is completed. The high temperature treatment is preferably carried out in temperature between 700 - 1000 °C. More preferably, the substrate with the PGM deposit is flame annealed. Most preferably, the high temperature treatment is carried out in a hydrogen flame.

In order to avoid pH changes during the PGM deposition process, in the preferred embodiment the plating bath further comprises pH buffer. Preferably, the Britton-Robins buffer is used in the plating bath. Other buffers can also be used. The examples of such buffers include phosphate, acetate, citrate, and borate buffers.

Even though addition of brighteners is not required in the method of the invention, their addition is also contemplated herein. Therefore, in the preferred embodiment the plating bath used in the method of the invention further comprises brighteners, such as saccharin polyethylene glycol, paratoluene sulfonamide, benzene sulphonic acid sodium allyl sulfonate, pyridinum propyl sulfonate. Moreover, in the method of the invention further reducing agents can be used in addition to the primary or secondary monohydroxyalcohol or a mixture of primary or secondary monohydroxyalcohols. Therefore, in another aspect of the invention the plating bath used in the method of the invention further comprises hydrazine and its derivatives, borohydride or hydrogen hypophosphite as additional reducing agents.

In another aspect, the invention provides a plating bath for electroless deposition of platinum group metals and their alloys, wherein said bath is an aqueous solution comprising a primary or secondary monohydroxyalcohol or a mixture of primary or secondary monohydroxyalcohols as the reducing agent and one or more platinum group precursors. The plating bath of the invention, as well as its components are described above in reference to the method of the invention.

Finally, the invention provides a use of the plating bath as defined above in electroless deposition of platinum group metals.

Based on numerous experiments carried out by the inventors, no simple tendency in the kinetics of deposition of platinum and other PGMs, as well as in molecular weight of alcohol in the homologous series could be observed. At ambient temperature, in the series of low chain water miscible alcohols, the electroless deposition kinetics decreased in the following series of reducing agents: ethanol, methanol, 2-propanol, 1-propanol, 2-butanol. The higher PGM deposition rate (in the presence of ethanol or at higher temperatures), the higher specific surface of the deposit, which is characteristic for rough deposits. For catalytic applications, where a high specific area is beneficial, ethanol should be used as the reducing agent. Alcohols poorly soluble in water such as 1-butanol and 1-pentanol used as reducing agents also lead to the formation of very rough deposits. The most lustrous deposits were obtained for 1-propanol and 2-propanol at ambient temperature.

The observed trends for different monohydroxyalcohols used in the method of the invention can be summarized as follows:

• methanol - results in formation of rough layers;

· ethanol - results in formation of rough grey-black deposits; however when the deposition is carried out in a lower temperature (about 4°C) results in formation of smoother deposits;

• 2-propanol - results in formation of smooth deposits (smooth and bright). In general, when the method of the invention is carried out in lower temperature, the smoother deposits are obtained. Moreover, when the method of the invention is carried out in the presence of a secondary alcohol as the reducing agent, the deposit is more likely to form on a metal substrate. In case of primary alcohols, the deposit is more likely to form on a polymeric materials. This way depending on properties of the substrate, a selective deposition can be carried out by choosing an appropriate monohydroxyalcohol as the reducing agent.

The inventors have also observed the following mechanisms for the method of the invention:

• the temperature can be used to control the process;

• the kinetics of the process is crucial for the characteristics of the deposit (the slower the kinetics, the smoother deposit layer is obtained)

• in the method of the invention carbon monoxide is formed as one of the intermediates in alcohol oxidation reaction and it may act as a brightener;

• the good adherence of the deposits can be related to the seeding process, rather than to the kinetics of the reaction.

The method of the invention has numerous advantages. First of all, well-adhering layers of PGMs and their alloys are obtained. The PGM layers deposited by the method of the invention are very stable and durable (e.g. they have remained unchanged for over twelve months after deposition; they have remained stable in the electrochemical experiments; they remain stable under mechanical stress). These layers can be compact and uniform or alternatively can have a very rough surface, depending on deposition conditions. The PGM layers are obtained on different substrates including metals (e.g. platinum, palladium, nickel and gold), metal alloys (steel, Kanthal®), polymer materials (e.g. Nafion®, PE, PP, PET), carbon (e.g. graphite) and silicon. The process can be carried out in a wide range of temperatures (from -10 to 80°C) and, depending on reducing agent used, the temperature control is not crucial. It is, therefore, possible to carry out the plating process in room temperature. Moreover, the plating bath of the invention has a very simple composition, can be easily prepared and is very stable. Thanks to its universal character, especially due to the fact that it can be used for plating PGMs on different supports, the method of the invention is very useful in different fields of technology, for example:

• PGM-plated Nafion® and graphite can be used as electrodes and in fuel cells;

• PGM-plated plastic (polymer materials) can be used in flexible electronics (flex circuits);

• PGM-plated common metals (steel, Kanthal®) can be used as catalysts;

• PGM-plated silicon can be used as electrical contact;

• PGM-plating can also be used for production of non-corroding electrical contacts and in jewelry manufacturing.

BRIEF DESCRIPTION OF DRAWINGS

The subject of the invention is illustrated in a drawing, in which:

Figure 1 presents a photograph of Pt-plated platinum foil, obtained as described in Example 1.

Figure 2 presents a photograph of Pt plated Kanthal® (a), Nafion® (b), PP (c) and PET (d), obtained as described in Example 2.

Figure 3 presents (a) a photograph of platinum-coated gold plate obtained as described in Example 3 and (b) a SEM micrograph of platinum layer thus obtained.

Figure 4 presents (a) a photograph of a platinum coated graphite disc and (b) a photograph of a platinum coated steel plate obtained as described in Example 4.

Figure 5 presents a photograph of platinum deposited on palladium-coated copper rod obtained as described in Example 5.

Figure 6 presents XP spectrum in Pt 4 /Ir 4f region for alloy deposit prepared as described in Example 7.

Figure 7 presents SEM micrographs of alloy layers obtained on gold substrate as described in Example 8: (a) alloy Rh-Pt (MeOH); (b) Ru (MeOH) (magnification 2,50K x); (c) Ru (MeOH) (magnification ΙΟΟ,ΟΟΚ x); (d) alloy Pt-Ir (MeOH) (magnification 50.00 K x) (e) alloy Pt-Ir (MeOH) (magnification 1.00 K x); (f) alloy Rh-Pt (EtOH); (g) alloy Ru-Pt (EtOH); (h) alloy Ir-Pt (EtOH); (i) alloy Rh-Pt (isopropanol) (magnification IK x); (j) alloy Ir-Pt (isopropanol) (magnification 1.00 K x); (k) Ru (isopropanol) (magnification 5.00 K x); (1) Ru (isopropanol) (magnification 50.00 K x); (m) alloy Pd-Pt (isopropanol); (n) alloy Ir-Pt (isopropanol) (magnification 1.00 K x); (o) Ir-Pt (isopropanol) (magnification 50.00 K x).

Figure 8 presents micrographs of alloy layers obtained on gold substrate in Example 9: (a) alloy Ru-Pt 1:2 (EtOH) (magnification 2.50 K x); (b) alloy Ru-Pt 1:6 (EtOH) (magnification 25.00 K x); (c) alloy Pt-Ir (BuOH) (magnification 1.00 K x); (d) alloy Pt-Ir (BuOH) (magnification 50.00 K x).

Figure 9 presents a photograph of platinum deposits on PET and PP substrates obtained as described in Example 10.

Figure 10 presents data for platinum deposits obtained using different reducing agents, as described in Example 11 : (a) Cyclic voltammogram recorded for platinum layers plated on Pt by electroless deposition according to the invention using different reducing agents. Cyclic voltammograms were recorded in 0.5 M sulfuric acid at scan rate v = 1 mVs^"1; (b) Scanning electron micrograph of a platinum layer deposited on platinum from a methanol containing bath; (c) Scanning electron micrograph of a platinum layer deposited on platinum from a 2-propoanol containing bath; (d) Scanning electron micrograph of a platinum layer deposited on platinum from a 2-butanol containing bath.

Figure 11 presents voltammograms recorded in 0.5 mol dm^-3 H₂S0₄ and 0.5 mol dm^-3 ethanol at Pt-Ir alloy deposits obtained using different reducing agents as described in Example 13.

EXAMPLES

Example 1. Platinum deposition on platinum foil

Platinum foil 0.7 x 0.7 x 0.01 cm in diameter was hydrogen flame annealed and quenched in deionized water. The substrate was subsequently immersed in a solution containing 2.2 M 2-propanol; 0.01 M [PtCl₄]^2~ + Britton-Robins buffer prepared from aqueous solution containing 0.04 M H3BO3, 0.04 M H₃P0₄ and 0.04 M CH₃COOH adjusted to pH=4.06 with sodium hydroxide. The plating bath was kept at room temperature for 10 hours. Metallic silver shine coating of 2 μιη in thickness was thus obtained with the 98% yield. The thickness of the deposited layer and deposition yield was determined based on a weight change of the substrate. Fig. 1 presents a photograph of the Pt-plated platinum foil.

Example 2. Platinum deposition on Kanthal®, PET, PP, Nafion® and silicon substrates

A Kanthal® plate was immersed in a solution containing 2.2 M 2-propanol, 0.01 M

[PtCl₄]^2~ + Britton-Robins buffer prepared from aqueous solution containing 0.04 M

H3BO3, 0.04 M H₃P0₄ and 0.04 M CH₃COOH adjusted to pH=4.06 with sodium hydroxide. The plating bath was kept at room temperature for 12 hours. Metallic silver shine coating was obtained on Kanthal® surface. Fig. 2(a) presents a photograph of a platinum plated Kanthal® plate.

The above method was also used for platinum deposition on polypropylene (PP), polyethylene terephthalate (PET), Nafion® and silicon. Metallic silver shine coating was obtained on silicon, PP i PET substrate, whereas grey-black coating on Nafion®.

Photographs of platinum coated Nafion®, PP and PET are presented on Fig. 2 b - d, respectively.

In a corresponding manner platinum a metallic silver shine layer was obtained on PP substrate using 2.5 M 1-propanol from the solution having pH 4 and containing 7.5 mM of [PtCl₄]^2".

Example 3. Platinum deposition on a gold substrate

A gold plate 0.7 x 0.7 x 0.05 cm in diameter was seeded using a zincating method (in an aqueous solution containing 1 M of Na₂[Zn(OH)₄] in the presence of metallic zinc, the mass of deposited Zn was equal to 50 μg). The substrate was subsequently immersed in a solution containing 2.2 M 2-propanol; 0.01 M [PtCl₄]^2~ + Britton-Robins buffer prepared from aqueous solution containing 0.04 M H B0₃, 0.04 M H P0₄ and 0.04 M CH COOH adjusted to pH=4.06 with sodium hydroxide. The plating bath was kept at room temperature for 12 hours. Metallic silver shine coating of 2.4 μιη in thickness was thus obtained with the 95% yield. Fig. 3a presents a photograph of platinum-coated gold plate.

A SEM micrograph of the deposit is shown in Fig 3b.

Example 4. Platinum deposition on nickel, steel and graphite substrates

Platinum deposits on nickel, steel and graphite substrates were obtained as described in Example 3. Metallic silver shine platinum coating was obtained on all substrates. Fig. 4 presents a photograph of a platinum-coated graphite disc (a) and a photograph of a platinum-coated steel plate (b).

Example 5. Platinum deposition on silver, palladium, PET, PP and Nafion® substrates

Platinum deposits on silver, palladium, PET, PP and Nafion® substrates were obtained as described in Example 3, with that difference that instead of Na₂[Zn(OH)₄], tin (II) chloride (SnCl₂) was used for seeding of the substrate surface. Metallic silver shine platinum coating was obtained on all substrates. Fig. 5 presents a photograph of a platinum deposit on a palladium-coated copper rod with 200 nm of palladium.

Example 6. Preparation of rough platinum layers for catalytic applications

Platinum foil 0.7 x 0.7 x 0.01 cm in diameter was hydrogen flame annealed and quenched in deionized water. The substrate was subsequently immersed in a solution containing 2.85 M of ethanol; 0.01 M [PtCl₄]^2~ + Britton-Robins buffer prepared from aqueous solution containing 0.04 M H3BO3, 0.04 M H₃P0₄ and 0.04 M CH₃COOH adjusted to pH=4.06 with sodium hydroxide. The plating bath was kept at room temperature for 1 hour. An adherent grey-black coating of 0.4 μιη in thickness was thus obtained with the specific roughness factor, Rf = A_specific / Ageometric = 130, where A_specific and Ageometric is the specific and geometric surface area of the deposit, respectively. Taking into account the mass of the deposit m=1.63 mg, this correspond to 16.3 m²/g of mass specific surface area.

This type of platinum deposit is particularly suitable for use in catalytic applications. Example 7. Preparation of platinum-iridium alloy on a gold substrate

Gold disc 0.2 x 0.05 cm in diameter was seeded using a zincating method (in an aqueous solution containing 1 M of Na₂[Zn(OH)₄] in the presence of metallic zinc, the mass of deposited Zn was equal to 20 μg). The substrate was subsequently immersed in a solution containing 4 M methanol; 0.01 M [PtCl₄]^2" + 0.01 M [IrCl₄]^2" + Britton-Robins buffer prepared from aqueous solution containing 0.04 M H3BO3, 0.04 M H₃P0₄ and 0.04 M CH₃COOH adjusted to pH=4.06 with sodium hydroxide. The plating bath was kept at room temperature for 24 hours. Metallic silver shine coating of 1 μιη in thickness was obtained with the 95% yield.

The chemical composition and chemical characteristics of the deposit was investigated by X-ray photoelectron spectroscopy. This method was used to confirm the metallic characteristics of the iridium. XP spectrum in Pt 4//Ir 4f region reveals two doublets. The doublet with components at 60.71 eV and 63.69 eV can be attributed to metallic Ir (Ir 4/7/2 and Ir 4/5/2 signals, respectively), whereas signals at 71.34 eV and 74.67 eV can be attributed to metallic Pt (Pt 4/7/2 and Pt 4/5/2 signals, respectively). Literature positions for metallic Ir and Pt: 60.81 eV and 63.76 eV for Ir 4/7/2 and Ir 4/5/2 signals, respectively and 71.09 eV and 74.42 eV for Pt 4/7/2 and Pt 4/5/2 signals, respectively (NIST X-ray Photoelectron Spectroscopy Database, Version 4.1 [National Institute of Standards and Technology, Gaithersburg, 2012); http://srdata.nist.gov/xps/.]) were marked with vertical lines. Small difference between the measured and literature peak positions are most probably caused by alloy formation [Adam Lewera et al.: Core-level Binding Energy Shifts in Pt-Ru nanoparticles: A puzzle resolved. Chem. Phys. Lett. 2007, 44: 39-43). Small doublet at ca. 76.69 eV and 80.02 eV is probably associated with presence of small amount of unreduced Pt, most probably in the form of Pt(IV) compounds. Pt to Ir ratio, determined from XPS data, is equal to 75:25 atomic percent (Pt:Ir). Fig. 6 presents XP spectrum in Pt 4//Ir 4/ region. Two signal doublets, one for Pt and second for Ir can be clearly seen. Reference position of Pt and Ir signals for completely reduced metals are marked with vertical lines. Example 8. Preparation of platinum-rhodium, -ruthenium, -palladium and -iridium alloys on a gold substrate

A possibility of alloy formation was investigated further for different alcohols used as reducing agents and for that purpose the following alloy layers on gold substrate were 5 prepared: platinum-rhodium, platinum-ruthenium, platinum-palladium and platinum- iridium. The process of plating was carried out in a corresponding manner as described in Example 7, however 3 mM K₂PtCl6 was used as platinum precursor, in consecutive examples 5 M MeOH, 3,5 M EtOH and 2,6 M isopropanol were used as reducing agents, and 6 mM Rh²⁺, 6 mM Ru²⁺, 7 mM Pd²⁺, and 6 mM Ir(IV) were used as precursors of the l o second PGM in an alloy. The table below summarizes the conditions used for alloy plating of the substrate, as well as the properties of the obtained layer. The alloy formation and composition thereof was determined by EDS (data included in the table).

Table 1

15 Example 9. Preparation of platinum-rhodium, -ruthenium, -palladium and -iridium alloys on a Kanthal® substrate

Alloy platinum-ruthenium and platinum-iridium layers were formed using procedure described in Examples 8 and 9, with a difference that a Kanthal® substrate was used as a solid support for the formed layer and different alcohols - ethanol and sec- 20 butanol - were used as reducing agents. The table below summarizes the conditions used for alloy plating of the substrate, as well as the properties of the obtained layer. The alloy formation and composition thereof was determined by EDS (data presented in the table).

Table 2

Example 10. Platinum layers on PET and PP substrates obtained using ethanol

Platinum layers were obtained on PET and PP substrates, as described in Example 2. However, ethanol was used as a reducing agent instead of 2-propanol. Metallic silver shine coating of was obtained. Fig. 9 presents a photograph of platinum deposits on PET and PP substrates.

Example 11. Deposition of platinum layers on platinum substrates using different reducing agents

The influence of different reducing agent on the deposit properties was investigated. Therefore platinum layers on platinum substrates using different reducing agents were obtained. Prior to deposition, platinum electrodes were flame annealed and quenched in deionized water. Platinum was deposited from plating bath as in Example 1 but different reducing agents were used in concentration 2 M. After 12 hours of deposition cyclic voltammograms have been recorded in 0.5 H₂S0₄.

The roughest deposit was obtained in methanol containing bath, which corresponds to the highest current densities at cyclic voltammograms (Fig. 10a).

Scanning electron micrographs of the surface of selected deposits are shown in Fig. 10b, c and d. The material has typical 'cauliflower-like' surface composed of spherical structures of micrometers size. High magnifications recorded for obtained layers show nanocrystalline/amorphous like structuration of the material. On the lower magnification a tendency to stress fractures of the material can be seen (not shown here). Also some tendency to dendrite-like growth of the coating can be observed. The cross-fracture exhibit some internal fibrous structuration of the coating (Fig. 10b) in the growth direction.

The sample obtained from a 2-propanol containing bath is much smoother in comparison to other samples. High magnification micrographs exhibit structuration material on the nanometer scale. Some tendency to fracture can be seen, however their number is much smaller. Also, their shape suggest higher plasticity of this coating. Most likely, some of fractures that can be seen are related to the stresses in the base (substrate) material. Cross -fracture of the sample exhibits no tendency to internal structuration of the coating.

Morphology of the sample obtained from 2-buthanol is shown in Fig. 10c. The surface of the deposit is rather smooth. Alike the sample obtained with methanol, some nodular structures of micrometer scale can be seen, but with much lower number. The cross -fracture exhibit no internal structuration of the material. All three samples highly mimic the morphology of the base support. Moreover, even when fractured, the deposits remain adhesive to the substrate material (Fig. 10b). The defects of the coatings can be eliminated by use of additives in the process of metallization or slight changes of physical parameters of the process (i.e. temperature).

Example 12. Mechanical properties of platinum layers on PET, PP and Nafion® substrates

Platinum coated substrates of PET, PP and Nafion® obtained in Examples 2 and 5 have undergone a mechanical stress test. All the platinum coated substrates were bent, stretched and twisted manually. After the test all substrates were examined with respect to platinum coating integrity. No changes, such as cracks or peeling, of the deposited layers were observed. The fact that the platinum layers remained intact during the mechanical stress test shows a significant integrity and a very good adherence of the deposited platinum layer to the polymer material substrate. Example 13. Electrochemical properties of PGM deposit layers on gold, Kanthal®, and platinum substrates

Electrochemical properties of PGM deposit layers on gold, Kanthal® and platinum substrates were investigated. In one of the experiments oxidation of ethanol was carried out using the deposit-substrate assemblies obtained in Examples 1 - 11.

Exemplary results are shown in Fig. 11, which presents voltammograms recorded in 0.5 mol dm^-3 H₂S0₄ and 0.5 mol dm^-3 ethanol at Pt-Ir alloy deposits obtained using different reducing agents: grey - ethanol; black - butanol. The voltammograms were recorded at the scan rate of 5 mV s-1 and the currents were normalized to geometric area. As shown in Fig. 11, the electroless deposited layers have been found to be very active towards ethanol oxidation in terms of both the onset potential of ethanol oxidation and the overall voltamperometric current. The most active layers were deposited by using ethanol and butanol as reducing agents. These reducing agents, as described above, enhance significantly surface roughness, which in turn increases the oxidation currents.

Claims

Patent claims

1. A method of electroless deposition of platinum group metals and their alloys from a plating bath onto a substrate, comprising a reduction step of one or more platinum group metal precursors with a reducing agent, wherein the reducing agent is a primary or secondary monohydroxyalcohol or a mixture of primary or secondary monohydroxyalcohols.

2. The method of claim 1 , wherein the monohydroxyalcohol has a general formula

R₂

I

Ri— C— OH

I

H , wherein Ri and R2 are the same or different and each of them is independently selected from a group comprising hydrogen atom, a straight or branched Ci-7-alkyl group, C3-8- aryl group, C4-8-aralkyl group and C₄-8-alkaryl group.

3. The method of claim 1 or 2, wherein Ri and R2 are independently selected from a group comprising -H, -CH₃, -C2H5, -C₃H₇, -CH(CH₃)₂, -C4H9, -CH₂CH(CH₃)₂, -CH(CH₃)C₂H₅, -C(CH₃)₃, -C5H11, -CH(CH₃)C₃H₇, -CH₂CH(CH₃)C₂H₅, -C₂H4CH(CH₃)₂, -C(CH₃)₂C₂H₅, -CH(CH₃)CH(CH₃)₂, -CH₂C(CH₃)₃, -CH(C₂H₅)₂, -C₆Hi₃, -C₇Hi₅, and -CH(C₂H₅)(C₄H₉).

4. The method of anyone of claims 1-3, wherein the monohydroxyalcohol is selected from a group comprising methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2- methylpropan-l-ol, 1-pentanol, 3-methylbutan-l-ol, 2-methylbutan-l-ol, 2,2-dimethylpropan- l-ol, 3-pentanol, 2-pentanol, 3-methyl-2-butanol, 1-hexanol, 2-hexanol, 2-methyl- 1-pentanol, 3-methyl- 1-pentanol, 4-methyl- 1-pentanol, 3-methyl-2-pentanol, 4-methyl-2-pentanol, 2- methyl-3-pentanol, 2,2-dimethylbutan-l-ol, 2,3-dimethylbutan-l-ol, 3,3-dimethylbutan-l-ol, 3,3-dimethylbutan-2-ol, 2-ethylbutan-l-ol, 1-heptanol, 2-heptanol, 3-heptanol, 4-heptanol, 1- octanol, 2-octanol and 2-ethylhexan-l-ol.

5. The method of anyone of claims 1-4, wherein the monohydroxyalcohol is selected from the group comprising methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2- methylpropan-l-ol, 1-pentanol, 3-methylbutan-l-ol, 2-methylbutan-l-ol, 2,2-dimethylpropan- l-ol, 3-pentanol, 2-pentanol, 3-methyl-2-butanol, 1-hexanol, 1-heptanol and 1-octanol.

6. The method of anyone of claims 1-5, wherein the concentration of the monohydroxyalcohol in the plating bath is in the range from 0.02 to 12 M.

7. The method of claim 6, wherein concentration of the monohydroxyalcohol in the plating bath is in the range from 0.1 to 5 M.

5 8. The method of anyone of claims 1-7, wherein the platinum group metal precursor is selected from a group comprising H₂PtCl₆, H₆Cl₂N₂Pt, PtCl₂, PtBr₂, K₂[PtCl₄], Na₂[PtCl₄], Li₂[PtCl₄], H₂Pt(OH)₆, Pt(N0₃)₂, [Pt(NH₃)₄]Cl₂, [Pt(NH₃)₄](HC0₃)₂, [Pt(NH₃)₄](OAc)₂, (NH₃)₄Pt(N0₃)₂, (NH₄)₂PtBr₆, K₂PtCl₆, PtS0₄, Pt(HS0₄)₂, Pt(C10₄)₂, K₂PtI₆, K₂[Pt(CN)₄], cis-[Pt(NH₃)₂Cl₂], H₂PdCl₆, H₆Cl₂N₂Pd, PdCl₂, PdBr₂, K₂[PdCl₄], Na₂[PdCl₄], Li₂[PdCl₄], H₂Pd(OH)₆, Pd(N0₃)₂, o [Pd(NH₃)₄]Cl₂, [Pd(NH₃)₄](HC0₃)₂, [Pd(NH₃)₄](OAc)₂, (NH₄)₂PdBr₆, (NH₃)₂PdCl₆, PdS0₄,

Pd(HS0₄)₂, Pd(C10₄)₂, Pd(OAc)₂, RuCl₂ ((CH3)₂SO)₄, RuCl₃, [Ru(NH₃)₅(N₂)]Cl₂, Ru(N0₃)₃, RuBr₃, RuF₃, Ru(C10₄)₃, K₂RuCl₆, Osl, OsI₂, OsBr₃, OsCl₄, OsF₅, OsF₆, OsOF₅, OsF₇, IrF₆, IrCl₃, IrF₄, IrF₅, Ir(C10₄)₃, K₃[IrCl₆], K₂[IrCl₆], Na₃[IrCl₆], Na₂[IrCl₆], Li₃[IrCl₆], Li₂[IrCl₆], [Ir(NH₃)₄Cl₂]Cl, RhF₃, RhF₄, RhCl₃, [Rh(NH₃)₅Cl]Cl₂, RhCl[P(C₆H₅)₃]₃, K[Rh(CO)₂Cl₂], 5 Na[Rh(CO)₂Cl₂] Li[Rh(CO)₂Cl₂], Rh₂(S0₄)₃, Rh(HS0₄)₃, Rh(C10₄)₃, their hydrates and

mixtures of these salts and/or hydrates.

9. The method of anyone of claims 1-8, wherein the reduction step of one or more platinum group metal precursors is carried out in the presence of a precursor or precursors of different metals, thus forming of alloy comprising one or more platinum group metal and a different 0 metal.

10. The method of claim 9, wherein the formed alloy comprises two or more metals selected from a group comprising: platinum, palladium, rhodium, iridium, ruthenium, osmium, gold, nickel and copper

11. The method of anyone of claims 1-10, wherein the precursor concentration in the plating 5 bath is in the range from 1 mM to 1 M, preferably 5 mM to 100 mM, and more preferably from 10 mM to 50 mM.

12. The method of anyone of claims 1-11, wherein the reduction step is carried out in the temperature between the freezing point and the boiling point of the plating bath.

13. The method of claim 12, wherein the reduction step is carried out in the temperature from - 10 to 80°C, preferably from 0 to 40°C, and more preferably from 10 to 25°C.

14. The method of anyone of claims 1-13, wherein the plating bath further comprises pH buffer.

15. The method of anyone of claims 1-14, wherein the pH of the plating bath is below 7.

16. The method of claim 15, wherein the pH of the plating bath is between 3 and 5.

17. The method of claim 16, wherein the pH of the plating bath is about 4.

18. The method of anyone of claims 1-17, wherein the substrate is selected from a group comprising metals, metal alloys, polymeric materials, carbon and silicon.

19. The method of claim 18, wherein the substrate is selected from the group comprising platinum, palladium, nickel, gold, steel, iron-chromium-aluminum alloys, Nafion®, polyethylene, polypropylene, polyethylene terephthalate, graphite and silicon.

20. The method of anyone of claims 1-19, wherein prior to the reduction step of platinum group metal precursors the surface of the substrate is seeded.

21. The method of anyone of claims 1-20, wherein after the plating process is completed, the plated substrate undergoes a high temperature treatment.

22. The method of anyone of claims 1-21, wherein the plating bath further comprises brighteners.

23. The method of anyone of claims 1-22, wherein the plating bath further comprises an additional reducing agent, preferably a reducing agent selected from a group comprising hydrazine and its derivatives, borohydride or hydrogen hypophosphite

24. The method of anyone of claims 1-23, wherein the plating bath further comprises 2- methylpropan-2-ol.

25. A plating bath for electroless deposition of platinum group metals and their alloys, wherein said bath is an aqueous solution comprising a primary or secondary monohydroxyalcohol, or a mixture of primary or secondary monohydroxyalcohols, as the reducing agent and one or more platinum group precursors.

26. The bath of claim 25, wherein the monohydroxyalcohol has a general formula

, wherein Ri and R2 are the same or different and each of them independently is selected from a group comprising hydrogen atom, a straight or branched Ci-7-alkyl group, C3-8- aryl group, C₄-8-aralkyl group and C₄-8-alkaryl group.

27. The bath of claim 26, wherein Ri and R2 are independently selected from a group comprising -H, -CH₃, -C2H5, -C₃H₇, -CH(CH₃)₂, -C4H9, -CH₂CH(CH₃)₂, -CH(CH₃)C₂H₅, -C(CH₃)₃, -C5H11, -CH(CH₃)C₃H₇, -CH₂CH(CH₃)C₂H₅, -C₂H4CH(CH₃)₂, -C(CH₃)₂C₂H₅, -CH(CH₃)CH(CH₃)₂, -CH₂C(CH₃)₃, -CH(C₂H₅)₂, -C₆Hi₃, -C₇Hi₅, and -CH(C₂H₅)(C₄H₉).

28. The bath of claim 27, wherein the monohydroxyalcohol is selected from the group comprising methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methylpropan- l-ol, 1-pentanol, 3-methylbutan-l-ol, 2-methylbutan-l-ol, 2,2-dimethylpropan-l-ol, 3- pentanol, 2-pentanol, 3-methyl-2-butanol, 1-hexanol, 2-hexanol, 2-methyl- 1-pentanol, 3- methyl- 1-pentanol, 4-methyl- 1-pentanol, 3-methyl-2-pentanol, 4-methyl-2-pentanol, 2-methyl- 3-pentanol, 2,2-dimethylbutan-l-ol, 2,3-dimethylbutan-l-ol, 3,3-dimethylbutan-l-ol, 3,3- dimethylbutan-2-ol, 2-ethylbutan-l-ol, 1-heptanol, 2-heptanol, 3-heptanol, 4-heptanol, 1- octanol, 2-octanol and 2-ethylhexan-l-ol.

29. The bath of claim 28, wherein the monohydroxyalcohol is selected from the group comprising methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methylpropan- l-ol, 1-pentanol, 3-methylbutan-l-ol, 2-methylbutan-l-ol, 2,2-dimethylpropan-l-ol, 3- pentanol, 2-pentanol, 3-methyl-2-butanol, 1-hexanol, 1-heptanol and 1 -octanol.

30. The bath of anyone of claims 25-29, wherein the concentration of the monohydroxyalcohol is in the range from 0.02 to 12 M, preferably in the range from 0.1 to 5 M.

31. The bath of anyone of claims 25-30, wherein it further comprises an additional reducing agent, preferably a reducing agent selected from a group comprising hydrazine and its derivatives, borohydride or hydrogen hypophosphite

32. The bath of anyone of claims 25-31, wherein the platinum group metal precursor is selected from a group comprising H₂PtCl₆, H₆Cl₂N₂Pt, PtCl₂, PtBr₂, K₂[PtCl₄], Na₂[PtCl₄], Li₂[PtCl₄], H₂Pt(OH)₆, Pt(N0₃)₂, [Pt(NH₃)₄]Cl₂, [Pt(NH₃)₄](HC0 )₂, [Pt(NH₃)₄](OAc)₂, (NH₃)₄Pt(N0 )₂, (NH₄)₂PtBr₆, K₂PtCl₆, PtS0₄, Pt(HS0₄)₂, Pt(C10₄)₂, K₂PtI₆, K₂[Pt(CN)₄], cis-[Pt(NH₃)₂Cl2], H₂PdCl₆, H₆Cl₂N₂Pd, PdCl₂, PdBr₂, K₂[PdCl₄], Na₂[PdCl₄], Li₂[PdCl₄], H₂Pd(OH)₆, Pd(N0₃)₂, [Pd(NH₃)₄]Cl₂, [Pd(NH₃)₄](HC0 )₂, [Pd(NH₃)₄](OAc)₂,

(NH₄)₂PdBr₆, (NH₃)₂PdCl₆, PdS0₄, Pd(HS0₄)₂, Pd(C10₄)₂, Pd(OAc)₂, RuCl₂ ((CH3)₂SO)₄, RuCl , [Ru(NH₃)₅(N₂)]Cl2, Ru(N0 ) , RuBr₃, RuF₃, Ru(C10₄) , K₂RuCl₆, Osl, OsI₂, OsBr₃, 5 OsCl₄, OsFs, OsF₆, OsOFs, OsF₇, IrF₆, IrCl , IrF₄, IrF₅, Ir(C10₄) , K₃[IrCl₆], Κ₂[Κ1₆], Na₃[IrCl6], Na₂[IrCl₆], Π₃[Κ1₆], Li₂[IrCl₆], [Ir(NH₃)₄Cl₂]Cl, RhF₃, RhF₄, RhCl ,

[Rh(NH₃)₅Cl]Cl₂, RhCl[P(C₆H₅)₃]₃, K[Rh(CO)₂Cl₂], Na[Rh(CO)₂Cl₂] Li[Rh(CO)₂Cl₂], Rh₂(S0₄)₃, Rh(HS0₄)₃ and Rh(C10₄)₃, their hydrates or mixtures of these salts and/or hydrates.

0 33. The bath of anyone of claims 25-32 wherein the precursor concentration is in the range from 1 mM to 1 M.

34. The bath of claim 33, wherein the precursor concentration is in the range from 5 mM to 100 mM.

35. The bath of claim 34, wherein the precursor concentration is in the range from 10 mM5 to 50 mM.

36. The bath of anyone of claims 25-36, wherein the pH of the plating bath is below 7.

37. The bath of claim 36, wherein the pH is between 3 and 5.

38. The bath of claim 37, wherein the pH of the plating bath is about 4.

39. The bath of anyone of claims 25-21, wherein it further comprises pH buffer.

o 40.The bath of anyone of claims 25-39, wherein it further comprises brighteners.

41. The bath of anyone of claims 25-40, wherein it further comprises 2-methylpropan-2-ol.

42. Use of a plating bath as defined in anyone of claims 25-41 in electroless deposition of platinum group metals.