METHOD OF SYNTHESIS OF CARBON-SUPPORTED PLATINUM GROUP METAL OR METAL ALLOY NANOPARTICLES

Abstract

The presented invention relates to a method of synthesis of carbon-supported platinum group metal or metal alloy nanoparticles, which comprises the following steps: adsorbing on carbon support complexes of a platinum group metal with a urea complexing agent selected from a group comprising urea, urea derivative, a mixture of urea with at least one urea derivative, and a mixture of at least two urea derivatives; and reducing the complexes adsorbed on the carbon support to metal nanoparticles, forming a product of carbon-supported metal nanoparticles.

The invention also provides the use of the carbon-supported platinum group metal or metal alloy nanoparticles obtained by the method of the invention as catalyst.

The present invention further relates to a method of adsorption of precursors of platinum group metals on the surface of a carbon support and use of complexes of platinum group metals with urea complexing agent for adsorption of platinum group metal precursors on carbon support.

Claims

1.-35. (canceled)

36. A method of synthesis of carbon-supported platinum group metal or platinum group metal alloy nanoparticles, which comprises the following steps: (b) adsorption of complexes of platinum group metals with a urea complexing agent on carbon support, wherein the urea complexing agent is selected from a group comprising urea, urea derivative, a mixture of urea with at least one urea derivative, and a mixture of at least two urea derivatives; and (c) reduction of the complexes of a platinum group metal with a urea complexing agent adsorbed in step (b) on the carbon support to metal nanoparticles with the formation of a product of carbon-supported metal nanoparticles.

37. The method of claim 36, wherein in step (b) adsorption of complexes of a platinum group metal with a urea complexing agent on the carbon support is accompanied by adsorption of other precursors of platinum group metals.

38. The method of claim 36 or 37, wherein in step (b) adsorption of complexes of a platinum group metal with a urea complexing agent on the carbon support is accompanied by adsorption of precursors of metals other than platinum group metals.

39. The method of any of claims 36-38, wherein complexes of a platinum group metal with a urea complexing agent include mixed complexes, in which other ligands are present in addition to urea or urea derivatives.

40. The method of claim 36, wherein step (b), adsorption of metal-urea complexing agent complexes onto carbon support, is carried out in an aqueous solution.

41. The method of claim 36, wherein steps (b) and (c) are preceded by step (a) of complex formation by reacting in a solution a platinum group metal precursor with a urea complexing agent selected from a group comprising urea, urea derivative, a mixture of urea with at least one urea derivative, and a mixture of at least two urea derivatives.

42. The method of claim 41, wherein steps (a) and (b) are carried out concurrently by mixing platinum group metal precursor and urea complexing agent with carbon support to form a suspension, which is subsequently heated, so that the complexes of a platinum group metal with a urea complexing agent are formed and adsorbed on the carbon-support, wherein the adsorbed complexes of a platinum group metal with a urea complexing agent undergo the reduction step (c) resulting in formation of metal nanoparticles.

43. The method of claim 41, wherein step (a) and (b) are carried out separately, and the complexes of a platinum group metal with a urea complexing agent obtained in step (a) are subsequently mixed with the carbon support to enable adsorption of complexes of a platinum group metal with a urea complexing agent onto the carbon support, which undergoes reduction in step (c) resulting in formation of metal nanoparticles.

44. The method of any of claims 41-43, wherein step (a) of the metal-urea complexing agent complex formation is carried out in an aqueous solution.

45. The method of claim 36, wherein reduction in step (c) is carried out by using gaseous hydrogen.

46. The method of claim 45, wherein reduction in step (c) is carried out in temperature of 50-200 C. by placing the carbon support with adsorbed complexes of a platinum group metal with a urea complexing agent in a stream of a gas mixture of hydrogen with an inert gas.

47. The method of claim 46, wherein the gas mixture contains 1-10% of hydrogen.

48. The method of claim 46, wherein the reduction is carried out for 1 to 6 hours.

49. The method of claim 46, wherein the inert gas is argon or nitrogen.

50. The method of any of claims 36-39, wherein reduction in step (c) is carried out by thermal decomposition of adsorbed metal-urea complexing agent in inert atmosphere.

51. The method of claim 50, wherein reduction in step (c) is carried out in temperature of 190-600 C. by placing the carbon support with adsorbed complexes of a platinum group metal with a urea complexing agent in a stream of an inert gas.

52. The method of claim 51, wherein the inert gas is argon or nitrogen.

53. The method of any of claims 36-39, wherein reduction in step (c) is carried out in a solution by using a reducing agent.

54. The method of claim 53, wherein the reducing agent is L-ascorbic acid or citric acid.

55. The method of claim 41, wherein a molar ratio of urea complexing agent to metal used in step (a) is in the range 1-20:1.

56. The method of any of claims 36-39, wherein the amounts of complexes of a platinum group metal with a urea complexing agent and carbon support in step (b) are adjusted to obtain the product comprising 0.001 to 60% of metal by weight calculated based on the total weight of the product.

57. The method of claim 41, wherein the concentrations of the metal precursors and urea complexing agents in the solution used in step (a) are in a range from 1 mM to 5 M.

58. The method of claim 41, wherein in step (a) the solution comprising a platinum group metal precursor and urea or urea derivative is heated at 40 to 100 C. under reflux.

59. The method of claim 58, wherein in step (a) the solution comprising a platinum group metal precursor and urea complexing agents is heated for 10 minutes-10 hours.

60. The method of claim 41, wherein in step (a) the solution comprising a platinum group metal precursor and urea complexing agent is heated at 40 to 100 C. until all the liquid evaporates.

61. The method of claim 41, wherein in step (a) an organic solvent is added to the solution in a volumetric ratio of 0.05-30:1 calculated based on water volume in the solution.

62. The method of claim 41, wherein the metal precursor is selected from a group comprising K.sub.2PtCl.sub.4, K.sub.2PdCl.sub.4 and IrCl.sub.4.

63. The method of any of claims 36-39, wherein the urea derivative is a compound containing a HNCO or HNCONH functional group.

64. The method of claim 63, wherein the urea derivative is selected from a group consisting of methylurea, N,N-dimethylurea, N,N-dimethylurea, ethylurea, trimethylurea, N,N-diethylurea, N,N-diethylurea, N,N-bis(hydroxymethyl)urea, bis(hydroxymethyl)urea.

65. Use of carbon-supported platinum group metal or metal alloy nanoparticles obtained by the method of claims 36-39 as catalysts.

66. Catalysts comprising carbon-supported platinum group metal or metal alloy nanoparticles obtained by the method of claims 36-39.

67. A method of adsorption of precursors of platinum group metals on the surface of a carbon support, wherein the carbon support is immersed in a solution of complexes of platinum group metals with urea complexing agent, the urea complexing agent being selected from a group comprising urea, urea derivative, a mixture of urea with at least one urea derivative, and a mixture of at least two urea derivatives.

68. The method of claim 67, wherein the complex of platinum group metals with urea complexing agent is formed by reacting in a solution a platinum group metal precursor with a urea complexing agent selected from a group comprising urea, urea derivative, a mixture of urea with at least one urea derivative, and a mixture of at least two urea derivatives.

69. The method of claim 68, wherein formation of the complex of platinum group metals with urea complexing agent is carried in the presence of the carbon support and the complexes of a platinum group metal with a urea complexing agent are adsorbed on the carbon-support directly after formation.

70. Use of complexes of platinum group metals with urea complexing agent for adsorption of platinum group metal precursors on carbon support.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0051] The subject of the invention is illustrated in a drawing, in which:

[0052] FIG. 1 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples with different nominal Pt mass content. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0053] FIG. 2 presents TEM images and EDX maps for samples with different nominal Pd mass content (a) 1% Pd and 99% C and (b) 5% Pd and 95% C.

[0054] FIG. 3 presents a cyclic voltammogram recorded in 0.5M H.sub.2SO.sub.4 for a sample containing nominally 5% Rh and 95% C. Cyclic voltammogram of a sample containing pure carbon was added on the graph for comparison. Voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0055] FIG. 4 presents TEM images and EDX maps for a sample containing nominally 5% Rh and 95% C.

[0056] FIG. 5 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 5% Pt and 95% C obtained on different carbon black supports and using different reduction temperature: (a) Ketjenblack EC300J as carbon support, and (b) Vulcan XC-72 as carbon support. Cyclic voltammograms of samples containing 100% carbon (Ketjenblack EC300J or Vulcan XC-72) were added on the graphs for comparison. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0057] FIG. 6 presents TEM images and EDX maps for samples containing nominally 5% Pt and 95% C on different C supports obtained by reduction at 100 C.: (a) Ketjenblack EC300J, and (b) Vulcan XC-72.

[0058] FIG. 7 presents a histogram of Pt nanoparticles calculated based on an image presented on FIG. 6(b) in the 5 nm scale.

[0059] FIG. 8 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 5% Pd and 95% C obtained using different amounts of carbon. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0060] FIG. 9 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 5% Pd and 95% C obtained using urea and urea derivatives: Pd1-Pd complex with urea; Pd2-Pd complex with N,N-dimethylurea; Pd3-Pd complex with N,N-dimethylurea; Pd4-Pd complex with methylurea; Pd5-Pd complex with trimethylurea; Pd6-Pd complex with N,N-diethylurea. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0061] FIG. 10 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 20% Ir and 80% C obtained using urea, N,N-dimethylurea and N,N-dimethylurea. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0062] FIG. 11 presents TEM images and EDX maps for a sample containing nominally 5% Ir and 95% C. Sample obtained using (a) IrCl.sub.4 or (b) IrCl.sub.3 as precursor salt.

[0063] FIG. 12 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 20% Ir and 80% C obtained from fresh solution (48 h) or aged solution (6 months) of IrCl.sub.4. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0064] FIG. 13 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 5% Ir and 95% C obtained using urea complexes synthesized in different temperatures: a) narrow potential window, and b) wide potential window. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0065] FIG. 14 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 45% Pt and 55% C obtained in one-step synthesis using different temperatures. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0066] FIG. 15 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 45% Pt and 55% C obtained in one-step synthesis using different synthesis times. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0067] FIGS. 16 and 17 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 45% Pt and 55% C obtained using different Pt:urea ratios. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0068] FIG. 18 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 20% Pt and 80% C obtained using different initial concentration of Pt and urea. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0069] FIG. 19 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 45% Pt and 55% C obtained with or without heating during complex adsorption step, with urea:Pt ratio equal to (a) 20:1, and (b) 30:1. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0070] FIG. 20 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 40% Pt and 60% C obtained using one-step and two-step synthesis routes. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0071] FIG. 21 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 5% Pd and 95% C obtained using different reducing agents. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0072] FIG. 22 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 5% Pd and 95% C obtained using different reduction temperatures during reduction with H.sub.2/Ar. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0073] FIG. 23 presents TEM images for samples containing nominally 5% Pd and 95% C obtained using different reduction temperatures during reduction with H.sub.2/Ar.

[0074] FIG. 24 presents histograms of diameters of Pd nanoparticles obtained using different reduction temperatures during reduction with H.sub.2/Ar: (a) 50 C., (b) 100 C., and (c) 150 C. The histograms were calculated based on images presented in FIG. 23.

[0075] FIG. 25 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 5% Ir and 95% C obtained using different reduction temperatures during reduction with H.sub.2/Ar: a) narrow potential window, and b) wide potential window. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0076] FIG. 26 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 45% Pt and 55% C obtained in synthesis using urea:Pt ratio equal to 2:1, which underwent or didn't undergo post-synthesis heat-treatment at 350 C. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0077] FIG. 27 presents TEM images and EDX maps for sample containing nominally 45% Pt and 55% C (a) without post-synthesis heat-treatment and (b) with post-synthesis heat-treatment.

[0078] FIG. 28 presents histograms of Pt nanoparticle diameters in samples containing nominally 45% Pt and 55% C (a) without and (b) with the post-synthesis heat-treatment at 350 C. The histograms were calculated based on images presented in FIG. 27.

[0079] FIG. 29 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 45% Pt and 55% C), obtained in synthesis using urea:Pt ratio equal to (a) 2:1 or (b) 4:1, which underwent or didn't undergo post-synthesis heat-treatment at 300 C. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0080] FIG. 30 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 5% Rh and 95% C obtained using metal precursor salt or metal-urea complex in the adsorption step. Cyclic voltammogram of a sample containing 100% carbon was added on the graph for comparison. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0081] FIG. 31 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 20% metal and 80% C with different Pt:Ir nanoalloys: 100% Ir; 75% Ir, 25% Pt; 50% Ir, 50% Pt; 25% Ir, 75% Pt; 100% Pt. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0082] FIG. 32 presents TEM images of (a) 20% Pt 80% C (Vulcan) catalyst from BASF and (b) 20% Pt 80% C (Vulcan) sample obtained by method of the invention.

[0083] FIG. 33 presents histograms of Pt nanoparticle diameters in samples of (a) 20% Pt 80% C (Vulcan) catalyst from BASF and (b) 20% Pt 80% C (Vulcan) sample obtained by method of the invention. The histograms were calculated based on TEM images presented in the 10 nm scale in FIG. 32.

[0084] FIG. 34 presents TEM images of (a) 40% Pt 60% C (Vulcan) catalyst from E-TEK and (b) 40% Pt 60% C (Vulcan) sample obtained by method of the invention.

[0085] FIG. 35 presents histograms of Pt nanoparticle diameters in samples of (a) 40% Pt 60% C (Vulcan) catalyst from E-TEK and (b) 40% Pt 60% C (Vulcan) sample obtained by method of the invention. The histograms were calculated based on TEM images presented in the 10 nm scale in FIG. 34.

[0086] FIG. 36 presents: (a) mass-normalized cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for a sample containing nominally 40% Pt and 60% C (Ketjenblack) obtained by the method of the invention and a commercial catalyst40% Pt 60% C (Vulcan) catalyst from E-TEK and (b) TEM images corresponding to the samples presented in the cyclic voltammograms. The voltammograms were recorded at the scan rate of 5 mV s.sup.1. The charge values written in the voltammogram plots are the total charge values corresponding to the process of desorption of a hydrogen monolayer from the platinum catalyst surface.

[0087] FIG. 37 presents cyclic voltammograms recorded in 0.5M H.sub.2SO.sub.4 for samples containing nominally 20% Pt and 80% C obtained using different reducing agents. The voltammograms were recorded at the scan rate of 5 mV s.sup.1.

[0088] FIG. 38 presents ionic currents determined by mass spectrometry recorded during thermal decomposition of urea complexes of iridium (III) deposited on carbon black (20% Ir and 80% C) at a heating rate of 0.6 C./min. Ionic current of m/z=17 can be attributed to ammonia, m/z=18 can be attributed to water and m/z=44 to carbon dioxide.

[0089] FIG. 39 presents the TEM images and EDX maps for samples containing 20% Ir and 80% C after Ir-urea complex adsorption, a-c) before and d) after thermal Ir-urea complex decomposition in an inert atmosphere.

EXAMPLES

Example 1. Synthesis of Carbon-Supported Pt NanoparticlesDifferent Metal-Carbon Mass Ratio

[0090] 10 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and 0.125 ml 2 mol l.sup.1 urea (urea:Ptratio equal to 2.5:1) were mixed and heated in a Petri dish at 90 C. until all the liquid evaporated. The precipitate was left for 5 minutes under fume hood without heating and, then, it was dissolved in 10 ml of water, so that a 0.01 mol l.sup.1 solution of a platinum-urea complex was obtained. The synthesis was repeated two times so that a total of 30 ml 0.01 mol l.sup.1 solution was obtained. The solution was left for 5 hours and, next, calculated amounts of the solution were added to ca. 50 mg samples of carbon black in order to attain the desired metal:carbon ratio in the dry-mass of the sample (1.28, 6.09 and 16.23 ml for 5, 20 and 40% nominal content of Pt, respectively). The obtained suspensions of carbon in the solution of platinum-urea complex were then heated for two hours at 90 C. under reflux. Afterwards, the suspension was filtered and washed thoroughly with water. The sample was then placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm. Presence of nitrogen after precursor adsorption and before reduction was confirmed using X-ray Photoelectron Spectroscopy. Additionally after the reduction step nitrogen was present, as determined using the same method. Nitrogen can be removed to a large excess from the final sample by washing in water ethanol solution.

[0091] The obtained materials: carbon-Pt nanoparticles, were examined by cyclic voltammetry. Several milligrams of a synthesized material were mixed with 5% Nafion solution (from DuPont) added in such an amount, that Nafion constitutes ca. 32% of the dry mass of the mixture. Next, equal volume of isopropanol is added. For example, for 6.8 mg of material 80 ul of 5% Nafion (density=0.8 g cm-3) and 80 ul isopropanol were used. Next, 1 ul of the obtained suspension is dropped on a gold-disc electrode and left to dry under argon atmosphere. The obtained electrode containing the synthesized material (mixed with Nafion) deposited on a gold-disc electrode is then used as the working electrode in a three-electrode set-up for cyclic voltammetry measurements. A gold-disc electrode is also used as the counter electrode and a sulfur mercury electrode is used as the reference electrode. In all measurements 0.5 M H.sub.2SO.sub.4 is used as the supporting electrolyte. Before measurements the supporting solution is deaerated using argon bubbling through the solution. The examples of the recorded cyclic voltammograms are presented in FIG. 1. All potentials are given with respect to reversible hydrogen electrode.

[0092] A wide range of Pt:carbon mass-ratios can be obtained with the described method, which allows for the preparation of catalysts potentially applicable in different fields.

Example 2. Synthesis of Carbon-Supported Pd NanoparticlesDifferent Metal-Carbon Mass Ratio

[0093] 10 ml of 0.01 mol l.sup.1 K.sub.2PdCl.sub.4 and 0.25 ml of 1 mol l.sup.1 solution of urea (urea:Pd ratio equal to 2.5:1) were mixed and heated in a Petri dish at 80 C. until all the liquid evaporated. The precipitate was dissolved in 10 ml of water and the evaporation/dissolution procedure was repeated two times. Calculated amounts of the obtained 0.01 mol l.sup.1 Pd-urea complex solution were added to ca. 50 mg samples of carbon black in order to attain the desired metal:carbon ratio in the dry mass of the sample (2.26 ml and 0.43 ml for 5% Pd 95% C and 1% Pd 99% C, respectively). The obtained suspensions of carbon in the solution of palladium-urea complex were left for 30 minutes and, afterwards, filtered and washed thoroughly with water. The sample was then placed in a tube furnace, dried under argon atmosphere at 100 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 100 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0094] FIG. 2 (a) and (b) present TEM images and EDX maps of the obtained materials-carbon supported Pd catalysts.

Example 3. Synthesis of Carbon-Supported Rh Nanoparticles

[0095] 10 ml of 0.01 mol l.sup.1 RhCl.sub.3 and 0.25 ml of 1 mol l.sup.1 urea (urea:Rh ratio equal to 2.5:1) were mixed and heated at 90 C. in a Petri dish until all the liquid was evaporated. The obtained precipitate was dissolved in 10 ml of water and the evaporation-dissolution procedure was repeated two times. Ca. 2.43 ml of the resulting 0.01 mol l.sup.1 solution of rhodium urea complex were added to ca. 50 mg of carbon black, in order to obtain the desired rhodium:carbon mass ratio (5% Rh, 95% C). The obtained suspension was left for ca. 5 hours and, then, filtered and washed thoroughly with water. The sample was next placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0096] In order to assess the activity in the hydrogen adsorption-desorption process, the obtained sample was analyzed by means of cyclic voltammetry. Cyclic voltammograms of a sample containing 100% carbon were measured for comparison. The samples were prepared and measurements were recorded in the same way as described in Example 1. The examples of the recorded cyclic voltammograms are presented in FIG. 3. The obtained Rh/C catalyst shows clear activity in the hydrogen adsorption-desorption process (current peaks observed between ca. 0.3 and 0.65 V).

[0097] FIG. 4 presents TEM images and EDX maps of the obtained material-carbon supported Rh catalyst.

Example 4. Synthesis of Carbon-Supported Pt Nanoparticles on Different Types of Carbon Supports

[0098] 10 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and 0.125 ml of 2 mol l.sup.1 urea (urea:Pt ratio equal to 2.5:1) were mixed and heated in a Petri dish at 90 C. until all the liquid evaporated. The precipitate was left for 5 minutes under fume hood without heating and, then, it was dissolved in 10 ml of water, so that a 0.01 mol l.sup.1 solution of a platinum-urea complex was obtained. The solution was left for 5 hours and, next, calculated amounts of the solution were 1 added to ca. 50 mg pre-weighted carbon samples (1.26 and 1.28 ml for Ketjenblack EC300J and Vulcan XC-72, respectively) in order to attain the desired metal:carbon ratio in the dry-mass of the samples (5% metal, 95% carbon). The obtained suspensions were left for 1 hour, filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 100 or 150 C. for 4 hours and, subsequently, reduced in hydrogen argon mixture (10% H.sub.2, 90% Ar) at 100 or 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0099] The materials obtained using different C supports and reduced at different temperatures were examined by cyclic voltammetry as described in Example 1. Examples of the recorded cyclic voltammograms are presented in FIG. 5. It can be observed that independent of the carbon-support type, a higher applied reduction temperature results in lower activity in the hydrogen adsorption-desorption region, as compared to lower reduction temperature. This can be caused by a higher probability of nanoparticle sintering at a higher reduction temperature, which should result in lower surface area and, in turn, lower activity.

[0100] On FIG. 6 selected TEM images and EDX maps of the obtained samples are presented. Also for a sample containing nominally 5% Pt and 95% of Vulcan XC 72 as carbon support, a histogram of nanoparticle diameter is presented in FIG. 7. This histogram was obtained based on a 5 nm scale image presented on FIG. 6(c), i.e. an image of a sample containing nominally 5% Pt and 95% CVulcan XC 72 obtained with a reduction temperature of 100 C. Based on this histogram it can be clearly seen that in case of 5% Pt/Vulcan catalyst a narrow distribution of nanoparticles of very small size (most of the nanoparticles are in the 0.8-1.6 nm diameter range) can be obtained.

Example 5. Synthesis of Carbon-Supported Pd Nanoparticles Using Different Amounts of Carbon Support

[0101] 15 ml of 0.05 mol l.sup.1 K.sub.2PdCl.sub.4 and 1.88 ml of 1 mol l.sup.1 solution of urea were mixed and heated in a Petri dish at 80 C. until all the liquid evaporated. The precipitate was dissolved in 10 ml of water and the evaporation was repeated. Then the precipitate was dissolved in 15 ml of water. Calculated amounts of the obtained 0.05 mol l.sup.1 Pd-urea complex solution were added to pre-weighted amounts of carbon (0.45, 2.7 and 9 ml for ca. 50, 300 and 1000 mg of carbon black, respectively; the carbon samples were first dispersed in water using ultrasound bath for 5 minutes-10 mg of carbon per 1 ml of water) in order to attain the desired metal:carbon ratio in the dry mass of the sample (5% Pd, 95% C). The obtained suspensions of carbon in the solution of palladium-urea complex were left for 30 minutes and, afterwards, filtered and washed thoroughly with water. The sample was then placed in a tube furnace, dried under argon atmosphere at 100 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 100 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0102] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 8. Only small differences in the cyclic voltammograms can be observed between the samples prepared using different amounts of carbon-support. This shows that the method of synthesis according to the invention can be easily used for different amounts of regents, resulting in scalability of this synthesis method.

Example 6. Synthesis of Carbon-Supported Pd Nanoparticles Using Different Urea Derivatives

[0103] 10 ml of 0.01 mol l.sup.1 K.sub.2PdCl.sub.4 and 0.25 ml of 1 mol l.sup.1 solution of urea or urea derivative (methylurea, N,N-dimethylurea, N,N-dimethylurea, trimethylurea, N,N-diethylurea) were mixed and heated in a Petri dish at 80 C. until all the liquid evaporated. The precipitate was dissolved in 10 ml of water and the evaporation/dissolution procedure was repeated. 2.26 ml of each of the obtained 0.01 mol l.sup.1 Pd-complex solutions were added to pre-weighted ca. 50 mg samples of carbon black in order to attain the desired metal:carbon ratio in the dry-mass of the sample (5% Pd, 95% C). The obtained suspensions were left for 30 minutes and, afterwards, filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 100 C. for 4 hours and, subsequently, reduced in hydrogen argon mixture (10% H.sub.2, 90% Ar) at 100 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0104] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 9. The observed activity of the materials in the hydrogen absorption-desorption process (current peaks between ca. 0.6 and 0.7V) was of a similar order of magnitude for all the prepared samples, however samples prepared using urea, methylurea and trimethylurea showed the best performance (i.e. the highest charge associated with the absorption-desorption processes).

Example 7. Synthesis of Carbon-Supported Ir Nanoparticles Using Different Urea Derivatives

[0105] The following solutions were prepared: [0106] a) 10 ml of 0.01 mol l.sup.1 IrCl.sub.4 was added to 0.25 ml of 1 mol l.sup.1 urea (urea:Ir ratio equal to 2.5:1), [0107] b) 10 ml of 0.01 mol l.sup.1 IrCl.sub.4 was added to 0.25 ml of 1 mol l.sup.1 N,N-dimethylurea (N,N dimethylurea:Ir ratio equal to 2.5:1), and [0108] c) 10 ml of 0.01 mol l.sup.1 IrCl.sub.4 was added to 0.25 ml of 1 mol l.sup.1 N,N-dimethylurea (N,Ndimethylurea:Ir ratio equal to 2.5:1).

[0109] The solutions were heated at 80 C. under reflux for 1.5 hours. Next, 3.17 ml of each of the solutions were added to pre-weighted ca. 25 mg samples of carbon black in order to attain the desired iridium:carbon ratio in the dry-mass of the sample (20% Ir, 80% C). The obtained suspensions were left for ca. 15 hours and, then, filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0110] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 10. In case of carbon-supported Ir nanoparticles, a significantly higher activity in the hydrogen adsorption-desorption process (ca. between 0.3 and 0.65 V) was observed for the samples for which urea derivatives (N,N-dimethylurea and N,N-dimethylurea) were used in the synthesis instead of urea.

Example 8. Synthesis of Carbon-Supported Ir Nanoparticles Using Different Precursor Salts

[0111] Carbon supported Ir nanoparticles were obtained as described above using IrCl.sub.3 and IrCl.sub.4 as precursor salts for urea complex synthesis. On FIG. 11 selected TEM images and EDX maps of the obtained samples are presented. No difference was observed in the obtained materials even though different salts were used as starting reagents in the synthesis.

Example 9. Synthesis of Carbon-Supported Ir NanoparticlesInfluence of Hydrolysis of Precursor Salt

[0112] 10 ml of 0.01 mol l.sup.1 IrCl.sub.4 (a solution 48 hours or 6 months after preparation) and 0.25 ml of 1 mol l.sup.1 N,N-dimethylurea (N,N-dimethylurea:Ir ratio equal to 2.5:1) were mixed and heated at 80 C. under reflux for 5 hours. Next, 3.17 ml of each of the obtained Ir complex solutions were added to pre-weighted ca. 25 mg samples of carbon black in order to attain the desired metal:carbon ratio in the dry-mass of the sample (20% Ir, 80% C). The obtained suspensions were left for ca. 15 hours and, then, filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0113] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 12. In the described example a beneficial role of IrCl.sub.4 hydrolysis can be seen. Most probably the hydrolysis process results in creation of mixed chloride- and hydroxy-complexes of iridium, which influences the type of Ir-complexes formed with urea derivatives and in turn the activity of the obtained final samples.

Example 10. Synthesis of Carbon-Supported Ir NanoparticlesInfluence of Complex Synthesis Temperature

[0114] Three solutions consisting of 10 ml of 0.01 mol l.sup.1 IrCl.sub.4 and 0.25 ml of 1 mol l.sup.1 N,N-dimethylurea (N,N-dimethylurea:Ir ratio equal to 2.5:1) were prepared. The solutions were heated under reflux at 35, 55 or 80 C. for 5, 3 and 1.5 hours, respectively. Next, 1.28 ml of each of the solutions were added to pre-weighted ca. 50 mg samples of carbon black in order to attain the desired iridium:carbon ratio in the dry-mass of the sample (5% Ir, 95% C). The obtained suspensions were left for ca. 15 hours and, then, filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 100 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 100 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0115] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 13. Due to no clear distinction between hydrogen adsorption and hydrogen evolution regions expected on cyclic volammograms of Ir in H.sub.2SO.sub.4, it is hard to assess the influence of synthesis temperature and time on catalyst activity. The presence of the current peaks is indicative of presence of Ir nanoparticles. Therefore it can be concluded that Ir nanoparticles on carbon support can be obtained in a wide range of temperatures in Ir-complex synthesis.

Example 11. One-Step Synthesis of Carbon-Supported Pt NanoparticlesInfluence of Complex Synthesis Temperature

[0116] Two samples were prepared where 15.1 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and 0.302 ml of 2 mol l.sup.1 urea (urea:Pt ratio equal to 4:1) were added to ca. 40 mg of carbon black, giving nominal content of 45% Pt and 55% C in the dry mass, and heated at 90 or 100 C. under reflux for 220 minutes. Next, the obtained suspensions were filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0117] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 14. It can be observed that a significantly higher activity of hydrogen adsorption-desorption process (between ca. 0.3 and 0.65 V) is observed for the sample obtained using a higher temperature during adsorption process.

Example 12. One-Step Synthesis of Carbon-Supported Pt NanoparticlesInfluence of Synthesis Time

[0118] Two samples were prepared where 18.9 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and 0.199 ml of 2 mol l.sup.1 urea (urea:Pt ratio equal to 2.1:1) were added to ca. 50 mg of carbon black, giving nominal content of 45% Pt and 55% C in the dry mass, and heated at 100 C. under reflux for 120 or 220 minutes. Next, the obtained suspensions were filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0119] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 15. No difference in activity is observed between the samples prepared in a synthesis with shorter (120 min) and longer (220 minutes) heating time during adsorption.

Example 13. One-Step Synthesis of Carbon-Supported Pt NanoparticlesInfluence of Pt:Urea Ratio

[0120] Two samples were prepared, where 18.9 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and 0.199 ml of 2 mol l.sup.1 urea (urea:Pt ratio equal to 2.1:1) or 0.378 ml of 2 mol l.sup.1 urea (Pt:urea ratio equal to 4:1) were added to ca. 50 mg of carbon black, giving nominal content of 45% Pt and 55% C in the dry mass, and heated at 100 C. under reflux for 220 minutes. Next, the obtained suspensions were filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0121] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 16. Differences between the samples obtained using both ratios of urea:Pt are negligible. It shows that even a very small ratio, such as 2:1, can be used to obtain catalysts with high activity.

Example 14. Synthesis of Carbon-Supported Pt NanoparticlesInfluence of Pt:Urea Ratio

[0122] Several solutions were prepared: [0123] a) 0.6 ml of 2 mol l.sup.1 urea was added to 20 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and (urea:Pt ratio equal to 6:1) [0124] b) 1 ml of 2 mol l.sup.1 urea was added to 20 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and (urea:Pt ratio equal to 10:1) [0125] c) 2 ml of 2 mol l.sup.1 urea was added to 20 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and (urea:Pt ratio equal to 20:1) [0126] d) 3 ml of 2 mol l.sup.1 urea was added to 20 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and (urea:Pt ratio equal to 30:1)

[0127] Each of the solutions was heated at 80 C. under reflux for one hour. Next, calculated amounts of the solutions (10.05, 10.26 and 10.71 ml of the solutions prepared in steps a), b) and c), respectively) were added to ca. 25 mg pre-weighted samples of carbon black in order to attain the desired metal:carbon ratio in the dry-mass of the samples (45% Pt, 55% C). The obtained suspensions of carbon in the solution of platinum-urea complex were then heated for two hours at 100 C. under reflux. Afterwards, the suspensions were filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 100 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 100 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0128] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 17. Performance of all the samples was similar, however it was the best at the smallest and the highest stoichiometric ratio of urea:Pt (6:1 and 30:1). This most probably indicates that more than one effect is influenced by urea:Pt stoichiometric ratio, for example: 1) the influence of the urea:Pt ratio on the type of complex formed, 2) urea adsorption on carbon which may occupy free sites, making them inaccessible for the metal.

Example 15. Synthesis of Carbon-Supported Pt NanoparticlesDifferent Initial Concentrations of Metal Precursor and Urea at a Constant Pt:Urea Ratio

[0129] Solutions of 0.1 mol l.sup.1 K.sub.2PtCl.sub.4, 2 mol l.sup.1 urea and water were mixed in different amounts: [0130] a) 5 ml of 0.1 mol l.sup.1 K.sub.2PtCl.sub.4, 0.625 ml of 2 mol l.sup.1 urea and 4.375 ml of water [0131] b) 2 ml of 0.1 mol l.sup.1 K.sub.2PtCl.sub.4, 0.25 ml of 2 mol l.sup.1 urea and 7.75 ml of water [0132] c) 0.5 ml of 0.1 mol l.sup.1 K.sub.2PtCl.sub.4, 0.063 ml of 2 mol l.sup.1 urea and 9.437 ml of water

[0133] Each of the mixtures was heated in a Petri dish at 90 C. until all the liquid evaporated. The precipitates were left for 5 minutes under fume hood without heating and, then, they were dissolved in such amount of waters, that a 0.025 mol l.sup.1 solution of a platinum-urea complex were obtained (20, 8 and 2 ml of H.sub.2O for a), b) and c), respectively). The solutions were left for 4 hours and, next, 1.95 ml of each of the obtained Pt-urea complex solutions were added to ca. 40 mg samples of carbon black in order to attain the desired metal:carbon ratio (20% Pt, 80% C) in the dry-mass of the sample. The obtained suspensions of carbon in the solution of platinum-urea complex were then heated for two hours at 90 C. under reflux. Afterwards, the suspensions were filtered and washed thoroughly with water. The samples (containing platinum-urea complex adsorbed on carbon) were then placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0134] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 18.

[0135] Similar activity is observed for the carbon supported Pt nanoparticles obtained from the precursor solutions of different concentration (with the highest concentration used close to the maximum concentration possible to obtain for K.sub.2PtCl.sub.4 precursor salt).

Example 16. Synthesis of Carbon-Supported Pt NanoparticlesInfluence of Temperature on Urea Pt Complex Adsorption on the Carbon Support

[0136] Two solutions were prepared: [0137] a) 2 ml of 2 mol l.sup.1 urea was added to 20 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and (urea:Pt ratio equal to 20:1) [0138] b) 3 ml of 2 mol l.sup.1 urea was added to 20 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and (urea:Pt ratio equal to 30:1)

[0139] The solutions were then heated at 80 C. under reflux for one hour. Next, calculated amounts (10.71 ml and 11.21 ml of solutions obtained in steps a) and b), respectively) were added to two pre-weighted carbon black samples (ca. 25 mg) in order to attain the desired metal:carbon ratio in the dry-mass of the samples (45% Pt, 55% C). One of the obtained suspensions of carbon was then heated for two hours at 100 C. under reflux. Two other samples were prepared in the same way using the solution prepared in step b) and ca. 25 mg of carbon black.

[0140] Afterwards, the suspensions were filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 100 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 100 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0141] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 19. A beneficial effect of heating the sample during adsorption on catalytic activity of the final samples can be observed.

Example 17. Synthesis of Carbon-Supported Pt NanoparticlesComparison of One-Step and Multi-Step Synthesis Route

One-Step Synthesis of Platinum-Urea Complex Adsorbed on Carbon

[0142] 18.9 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and 0.236 ml of 2 mol l.sup.1 urea (urea:Pt ratio equal to 2.5:1) were added to 50 mg of carbon black, giving a sample with nominal content of 40% Pt and 60% C in the dry mass, and heated at 100 C. under reflux for 3 hours.

Multistep Synthesis of Platinum-Urea Complex Adsorbed on Carbon

[0143] 10 ml of 0.02 mol l.sup.1 K.sub.2PtCl.sub.4 and 0.25 ml of 2 mol l.sup.1 urea (urea:Pt ratio equal to 2.5:1) were mixed and then heated at 90 C. until all the liquid evaporated. The obtained precipitate was left for five minutes and then dissolved in 20 ml of water. The obtained solution was left for 4 hours and then 15.89 ml of it was added to ca. 50 mg of carbon black, giving a sample with nominal content of 40% Pt and 60% C in the dry mass.

[0144] The suspensions obtained in both routes were filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0145] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 20. Carbon-supported Pt nanoparticles obtained with different routes show similar activity. A more convenient method can be used for synthesis.

Example 18. Synthesis of Carbon-Supported Pd Nanoparticles Using Different Reducing Agents

[0146] 10 ml of 0.01 mol l.sup.1 K.sub.2PdCl.sub.4 and 0.25 ml of 1 mol l.sup.1 solution of urea were mixed and heated in a Petri dish at 80 C. until all the liquid evaporated. The precipitate was dissolved in 10 ml of water and the evaporation/dissolution procedure was repeated two times. 1.35 ml of the obtained solution were added to three ca. 30 mg samples of carbon black in order to attain the desired metal:carbon ratio in the dry-mass of the sample (5% Pd, 95% C). The obtained suspensions of carbon in the solution of palladium-urea complex were left for 30 minutes and, afterwards, filtered and washed thoroughly with water. Next the samples were reduced in one of the following ways: [0147] The sample was dried under argon atmosphere at 100 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 100 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm. [0148] 1.3 ml of 0.4% NaBH4 solution in 0.02M NaOH were added and the sample was left at ambient temperature for one hour (NaBH.sub.4:Pd ratio equal to ca. 10:1). [0149] 1.35 ml of 0.1 M citric acid was added and the sample was heated at 60 C. under reflux for one hour (citric acid:Pd ratio equal to ca. 10:1). [0150] 1.35 ml of 0.1 M L-ascorbic acid was added and the sample was heated at 60 C. under reflux for one hour (L-ascorbic acid:Pd ratio equal to ca. 10:1).

[0151] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 21. Reduction process carried out using L-ascorbic acid results in a material with the best catalytic properties. Reduction with H.sub.2 or citric acid is less beneficial than with L-ascorbic acid, whereas reduction with NaBH.sub.4 results in the worst catalyst performance.

Example 19. Synthesis of Carbon-Supported Pd Nanoparticles Using Hydrogen as a Reducing Agent and Different Reduction Temperatures

[0152] 10 ml of 0.01 mol l.sup.1 K.sub.2PdCl.sub.4 and 0.25 ml of 1 mol l.sup.1 solution of urea were mixed and heated in a Petri dish at 80 C. until all the liquid evaporated. The precipitate was dissolved in 10 ml of water and the evaporation/dissolution procedure was repeated two times. 2.26 ml of the obtained solution were added to pre-weighted amounts of carbon (ca. 50 mg of carbon black) in order to attain the desired metal:carbon ratio in the dry-mass of the sample (5% Pd, 95% C). The obtained suspensions of carbon in the solution of palladium-urea complex were left for 30 minutes and, afterwards, filtered and washed thoroughly with water. The sample was then placed in a tube furnace, dried under argon atmosphere at 100 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 50, 100 or 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0153] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 22. Selected TEM images of the obtained samples and corresponding histograms of nanoparticle diameters are presented on FIGS. 23 and 24, respectively.

[0154] It can be observed that when reduction temperature is increased the distribution of nanoparticle diameters shifts towards higher values. This is most probably indicative of intensified nanoparticle sintering at higher temperatures. This is, however, not reflected in the obtained CVs, where the most active sample was the ones reduced at 100 C. This shows that sintering is not the only process possibly influenced by reduction temperature.

Example 20. Synthesis of Carbon-Supported Ir Nanoparticles Using Hydrogen as a Reducing Agent and Different Reduction Temperatures

[0155] 10 ml of 0.01 mol l.sup.1 IrCl.sub.4 and 0.25 ml of 1 mol l.sup.1 N,N-dimethylurea (N,N-dimethylurea:Ir ratio equal to 2.5:1) were mixed. The solutions was heated under reflux for 1.5 hour at 80 C. Next, 1.28 ml of the solution were added to ca. 50 mg samples of carbon black in order to attain the desired iridium:carbon ratio in the dry-mass of the sample (5% Ir, 95% C). The obtained suspensions were left for ca. 15 hours and, then, filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 100 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 100 or 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0156] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 25. In case of carbon-supported Ir nanoparticles a higher reduction temperature results in higher activity of the materials (higher current associated with hydrogen evolution process between ca. 0.6 and 0.7 V).

Example 21. Influence of Temperature Post-Treatment on Carbon-Supported Pt Nanoparticles Obtained in One-Step Synthesis

[0157] Several samples were prepared: [0158] a) 15.1 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and 0.159 ml of 2 mol l.sup.1 urea (urea:Pt ratio equal to 2.1:1) were added to 40 mg of carbon black. [0159] b) 15.1 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and 0.159 ml of 2 mol l.sup.1 urea (urea:Pt ratio equal to 2.1:1) were added to 40 mg of carbon black. [0160] c) 15.1 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and 0.302 ml of 2 mol l.sup.1 urea (urea:Pt ratio equal to 4:1) were added to 40 mg of carbon black.

[0161] In each sample the nominal mass content of Pt was 45% in the dry mass. Each of the samples was heated at 100 C. under reflux for 220 minutes. Next, the obtained suspensions were filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm. Afterwards, each of the obtained samples was divided into two parts, where one part was subjected to heating at 300 or 350 C. for 4 hours under argon atmosphere.

[0162] The samples both before and after the temperature treatment were investigated using cyclic voltammetry as described in Example 1. The examples of voltammograms recorded for samples containing nominally 45% Pt and 55% C (Ketjenblack), obtained in synthesis using urea:Ptratio equal to 2.1:1, are presented in FIG. 26 (heat treatment at 350 C.). Selected TEM images for these samples before and after temperature treatment and corresponding histograms of nanoparticle diameters are presented on FIGS. 27 and 28, respectively. The examples of voltammograms recorded for samples containing nominally 45% Pt and 55% C, obtained in synthesis using urea:Pt ratio equal to 2.1:1 or 4:1, are presented in FIG. 29 (heat treatment at 300 C.).

[0163] The 45% Pt 55% C samples obtained in this example show excellent temperature stability, which is confirmed by unchanged activity (indicated by similar values of peak currents in the hydrogen adsorption-desorption region of CV) and also no significant changes in distribution of nanoparticle size, i.e. no significant sintering.

Example 22. Comparison of Metal Precursor Adsorption with Adsorption of Metal-Urea Complex

[0164] 10 ml of 0.01 mol l.sup.1 RhCl.sub.3 and 0.25 ml of 1 mol l.sup.1 urea (urea:Rh ratio equal to 2.5:1) were mixed and heated at 90 C. in a Petri dish until all the liquid was evaporated. The obtained precipitate was dissolved in 10 ml of water and the evaporation-dissolution procedure was repeated two times. Next, 2.33 ml of the resulting rhodium-urea complex solution was added to 50 mg of carbon black, in order to obtain the desired rhodium:carbon mass ratio (5% Rh, 95% C). The obtained suspension was left for ca. 5 hours and, then, filtered and washed thoroughly with water. The sample was next placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm. The same procedure was applied for a second sample, where 0.01 mol l.sup.1 RhCl.sub.3 solution was used instead of Rh-urea complex.

[0165] The obtained samples were investigated using cyclic voltammetry as described in Example 1. Cyclic voltammograms of a sample containing 100% carbon were measured for comparison. The examples of recorded voltammograms are presented in FIG. 30. The sample obtained using Rh-urea complex shows significantly higher activity (higher current in the hydrogen adsorption-desorption region between ca. 0.3 and 0.65 V) than the sample obtained using RhCl.sub.3 as the adsorbed compound. The cyclic voltammogram of the sample obtained using RhCl.sub.3 as the adsorbed compound does not significantly differ from the sample containing 100% carbon, which is most probably due to low amount of RhCl.sub.3 adsorbed on the carbon in the adsorption step. Based on the comparison of the presented cyclic voltammograms it can be concluded that the obtained Rh-urea complex adsorbs on carbon surface more easily than the precursor salt, RhCl.sub.3.

Example 23. Synthesis of Carbon-Supported Pt/Ir Alloy Nanoparticles

[0166] Two solutions were prepared: [0167] a) 10 ml of 0.01 mol l.sup.1 IrCl.sub.4 was added to 0.21 ml of 1 mol l.sup.1 urea (urea:Ir ratio equal to 2.1:1) [0168] b) 10 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 was added to 0.21 ml of 1 mol l.sup.1 urea (urea:Pt ratio equal to 2.1:1)

[0169] The solution a) was heated at 80 C. until all the liquid was evaporated. Next 10 ml of water were added and the obtained solution was heated at 80 C. under reflux for 5 hours. The solution b) was heated at 80 C. until all the liquid was evaporated. Next 10 ml of water were added and the evaporation-dissolution procedure was repeated two times. The obtained solutions of Pt-urea and Ir-urea complex were left for ca. 5 hours and then added in calculated amounts to pre-weighted amounts of carbon (ca. 25 mg) in order to attain the desired platinum:iridium and metal:carbon ratio in the dry-mass of the sample. The obtained suspensions were left for ca. 15 hours and, then, filtered and washed thoroughly with water. The samples were then placed in a tube furnace, dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.

[0170] The obtained samples were investigated using cyclic voltammetry as described in Example 1. FIG. 31 presents voltammograms recorded for samples containing nominally 20% metal and 80% C and the following Pt:Ir ratios: 100% Ir; 75% Ir, 25% Pt; 50% Ir, 50% Pt; 25% Ir, 75% Pt; 100% Pt.

[0171] All the obtained samples show good activity in the hydrogen adsorption-desorption process. Based on the charge associated with hydrogen adsorption and desorption (between ca. 0.3 and 0.65 V) it can be concluded that the activity does not change linearly with Pt (or Ir) mass-content, therefore an effect of alloying on catalyst properties is observed.

Example 24. Comparison of the Carbon-Supported Metal Nanoparticles of the Invention with Commercially Available CatalystsNanoparticle Size and Distribution

[0172] The carbon-supported metal nanoparticle of the invention were compared with commercially available catalysts. FIG. 32 presents TEM micrographs of 20% Pt 80% C (Vulcan) catalyst from BASF and 20% Pt 80% C (Vulcan) sample obtained using the method of the invention. The corresponding Pt nanoparticle diameter histograms for both samples, which are calculated based on a 10 nm scale TEM images, are presented in FIG. 33. FIG. 34 presents TEM micrographs of 40% Pt 60% C (Vulcan) catalyst from E-TEK and 40% Pt 60% C (Vulcan) sample obtained using the method of the invention. The corresponding Pt nanoparticle diameter histograms for both samples, which are calculated based on a 10 nm scale TEM images, are presented in FIG. 35.

[0173] It can be seen from the comparison of the samples with the same Pt:C ratio, that the samples prepared by the method of the invention have a more uniform distribution of nanoparticles and a smaller average size of nanoparticles, as compared to the examined commercial catalysts, which translates into a higher active surface area.

Example 25. Comparison of the Carbon-Supported Metal Nanoparticles of the Invention with Commercially Available CatalystsActive Surface Area

[0174] The carbon-supported metal nanoparticles of the invention were compared with a commercially available catalyst with the same Pt:C ratio (40% Pt, 60% C) using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 36. The charge values written in the Figure are the total charge values corresponding to the process of desorption of a hydrogen monolayer from the platinum catalyst surface. Based on the values of the charge, the specific active surface area of the catalysts was calculated to be 54 m.sup.2 g.sup.1.sub.Pt and 86 m.sup.2 g.sup.1.sub.Pt for the commercially available catalyst (E-TEK) and the catalyst obtained by the method of invention, respectively. The method used for the calculations was the method described by Coutanceau et al. (C. Coutanceau, S. Baranton and T. W. Napporn (2012). Platinum Fuel Cell Nanoparticle Syntheses: Effect on Morphology, Structure and Electrocatalytic Behavior, The Delivery of Nanoparticles, Dr. Abbass A. Hashim (Ed.), ISBN: 978-953-51-0615-9, InTech). In short, the current associated with hydrogen desorption (in the potential region between ca. 0.05 and 0.4 V vs RHE in the anodic scan), corrected for the current associated with double-layer charging, is integrated and divided by the scan rate used in the experiment, according to the equation:

[00001]$Q_{H_{\mathrm{des}}}=i\left(t\right)\mathrm{dt}=\frac{1}{v}i\left(E\right)\mathrm{dE}$

where Q.sub.Hdes is the charge corresponding to the integrated current i, E is the electrode potential, t is time and v is the potential scan rate. Next, the active surface area of the catalyst is calculated, assuming that the charge corresponding to desorption of a hydrogen monolayer from the unit area of polycrystalline platinum is 210 C cm.sup.2. Lastly, the obtained active surface area is divided by platinum mass in the sample, in order to obtain the specific active surface area.

[0175] It can be seen from the comparison of the calculated values that the sample prepared by the method of the invention has a significantly higher specific active surface area than the commercially available sample, which most probably results from a more uniform distribution of nanoparticles and a smaller average size of nanoparticles, as compared to the examined commercial catalysts. The highly developed active surface area of the catalysts obtained by the method of invention is a very important feature in terms of cost of catalyst synthesis, due to the fact that a lower mass of noble metal precursors can be used in order to obtain catalysts with desired activity.

Example 26. Synthesis of Carbon-Supported Pt Nanoparticles Using Different Reducing Agents

[0176] 10 ml of 0.01 mol l.sup.1 K.sub.2PtCl.sub.4 and 0.125 ml 2 mol l.sup.1 urea (urea:Ptratio equal to 2.5:1) were mixed and heated in a Petri dish at 90 C. until all the liquid evaporated. The precipitate was left for 5 minutes under fume hood without heating and, then, it was dissolved in 10 ml of water, so that a 0.01 mol l.sup.1 solution of a platinum-urea complex was obtained. The synthesis was repeated so that a total of 20 ml 0.01 mol l.sup.1 solution was obtained. The solution was left for 5 hours and, next, 6.09 ml of the obtained solution were added to three ca. 50 mg samples of carbon black in order to attain the desired metal:carbon ratio in the dry-mass of the sample (20% nominal content of Pt). The obtained suspensions of carbon in the solution of platinum-urea complex were then heated for two hours at 90 C. under reflux. Afterwards, the suspension was filtered and washed thoroughly with water. Next the samples were reduced in one of the following ways: [0177] The sample was dried under argon atmosphere at 150 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm. [0178] 6.09 ml of 0.1 M citric acid was added and the sample was heated at 60 C. under reflux for one hour (citric acid:Pt ratio equal to ca. 10:1). [0179] 6.09 ml of 0.1 M L-ascorbic acid was added and the sample was heated at 60 C. under reflux for one hour (L-ascorbic acid:Pt ratio equal to ca. 10:1).

[0180] The obtained samples were investigated using cyclic voltammetry as described in Example 1. The examples of recorded voltammograms are presented in FIG. 37. Reduction with H.sub.2 is more beneficial than with citric acid or L-ascorbic acid.

Example 27. Synthesis of Carbon-Supported Ir Nanoparticles Using Thermal Decomposition of Adsorbed Ir-Urea Complex

[0181] 10 ml of 0.01 mol l.sup.1 fresh IrCl.sub.4 solution and 0.25 ml of 1 mol l.sup.1 urea (urea:Ir ratio equal to 2.5:1) were mixed and heated at 90 C. in a Petri dish until all the liquid was evaporated. The obtained precipitate was dissolved in 10 ml of water. Next, 4.28 ml of the resulting iridium-urea complex solution was added to 32.6 mg of carbon black, in order to obtain the desired iridium:carbon mass ratio (21% Ir, 79% C).

[0182] The obtained suspensions were left for ca. 15 hours and, then, filtered and washed thoroughly with deionized water. The sample was then placed in a tube furnace, dried under vacuum at 70 C. for 4 hours and, subsequently, heated under argon at temperature 350 C. for 2 h and temperature rise rate of 0.6 C./min. The flow rate of argon was 30 sccm. During the decomposition phase the decomposition products were monitored using mass spectrometry. As can be seen on FIG. 38 adsorbed Ir-urea complex decomposes to ammonia and carbon dioxide above 270 C. The same procedure was utilized to remove the excess of urea from carbon substrate.

Example 28. Synthesis of Carbon-Supported Cu/Pd Alloy Nanoparticles on Carbon Support

[0183] Pre-weighted amount (ca. 100 mg) of carbon black was transferred to a small beaker containing 20 ml of 2 mM water solution of Cu(NO.sub.3).sub.2 and left for 30 minutes and, afterwards, filtered and washed thoroughly with water. 10 ml of 0.01 mol l.sup.1 K.sub.2PdCl.sub.4 and 0.25 ml of 1 mol l.sup.1 solution of urea were mixed and heated in a Petri dish at 80 C. until all the liquid evaporated. The precipitate was dissolved in 10 ml of water and the evaporation/dissolution procedure was repeated two times. 2.26 ml of the obtained solution was added to the beaker containing copper precursor deposited on carbon in order to attain the desired metal:carbon ratio in the dry-mass of the sample (2.5% of Cu, 2.5% Pd, 90% C). The obtained suspensions of Cu/carbon in the solution of palladium-urea complex were left for 30 minutes and, afterwards, filtered and washed thoroughly with water. The sample was then placed in a tube furnace, dried under argon atmosphere at 100 C. for 4 hours and, subsequently, reduced in hydrogen-argon mixture (10% H.sub.2, 90% Ar) at 50, 100 or 150 C. for 4 hours and left to cool down to ambient temperature under argon atmosphere. The flow rate of the gaseous stream (argon or hydrogen-argon mixture) was 15 sccm.