Formation of catalytic Pt nanodots by pulsed / sequential CVD or molecular layer deposition

Abstract

The present disclosure describes a method for depositing a plurality of Pt metal-containing nanodots onto a catalytic carbon support structure by generating Pt(PF3)4 vapor, exposing a surface of a catalyst support to the Pt(PF3)4 vapor, purging the surface of the catalyst support with a purge gas to remove the Pt(PF3)4 vapor, exposing the surface of the catalyst support to a second reactant in gaseous form, purging the surface of the catalyst support with a purge gas to remove the second reactant, and repeating these steps to form a plurality of Pt metal-containing nanodots.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 072,562, filed August 31, 2020, the entire contents of which are incorporated herein by reference.

[0002] Formation of catalytic Pt nanodots by pulsed / sequential CVD or atomic layer deposition. [Background technology]

[0003] The state of the art is summarized in Van Bui, H., F. Grillo, and J.R. Van Ommen. “Atomic and molecular layer deposition: off the beaten track.” Chemical Communications 53.1(2017):45-71 (reference numbers omitted):

[0004] ALD of Pt. The development of ALD of Pt began in 2003 with the seminal work of Aaltonen et al., who demonstrated thermal ALD of Pt thin films using methylcyclopentadienyl-(trimethyl)platinum (MeCpPtMe3) as the Pt precursor and O2 as the co-reactant. This remains the most commonly used ALD process to date for growing both thin films and Pt NPs on a variety of substrates, including planar surfaces, nanowires, nanoparticles, and carbon nanomaterials. With the potential applications of ALD of Pt in mind, several research groups have conducted fundamental studies aimed at elucidating the interfacial chemistry behind the formation of metallic Pt. These studies suggest that the interfacial chemistry depends on oxidation reactions upon exposure of both MeCpPtMe3 and O2. The chemisorption of MeCpPtMe3 is thought to occur through partial oxidation of organic ligands by active oxygen adsorbed on the substrate surface. Such reactions then reach saturation when the available active surface oxygen is consumed. Thus, the O2 oxidation step serves a dual purpose: it oxidizes the remaining ligands and replaces the adsorbed oxygen layer, which is necessary for the subsequent chemisorption of MeCpPtMe3. This work shows that oxygen dissociates on the platinum surface, forming a residual monoatomic oxygen layer, which is particularly active as the organic ligands of MeCpPtMe3 are burned out. The ALD window typically reported for such interface chemistry is 200–350 °C. In particular, 200 °C is widely accepted as the lower temperature limit, although more recently, growth at slightly lower temperatures (i.e., 175 °C) has been achieved. This lower limit has been attributed to the low reactivity of oxygen toward ligand combustion at temperatures below 200 °C. Such high deposition temperatures make this thermal process unsuitable for heat-sensitive substrates. Furthermore, when used for NP deposition, high temperatures are undesirable because they can promote sintering, thereby limiting the ability to control NP dimensions. To circumvent this limitation, the use of plasma and ozone has been explored.However, plasma processes are mainly suitable for depositing Pt thin films and NPs on flat substrates, and their application to substrates with complex shapes, such as powders, is still limited.

[0005] As discussed in the review above, state-of-the-art approaches to plasma-enhanced deposition have not previously been successfully extended to low deposition temperatures on cathode carbon supports for use in catalytic Pt nanodots. To date, the art lacks a Pt deposition solution for cathode carbon supports that allows for the formation of sufficient nanodots without excess Pt oxide formation to meet the practical requirements of vehicular fuel cells, particularly those using polymer electrolyte membrane designs. Summary of the Invention [Means for solving the problem]

[0006] The present invention can be understood in connection with the following non-limiting exemplary embodiments, which are described as enumerated sentences. 1. A method for depositing Pt metal-containing nanodots onto a catalytic support structure, preferably a catalytic carbon support structure, comprising: a. Producing Pt(PF3)4 vapor; b. exposing the surface of the catalyst support structure to Pt(PF3)4 vapor; c. purging the surface of the catalyst support structure with a purge gas to remove Pt(PF3)4 vapor; d. exposing a second reactant in gaseous form to the surface of the catalytic structure; e. purging the surface of the catalyst support structure with a purge gas to remove the second reactant; f. repeating steps a.-e. to form a plurality of Pt metal-inclusive nanodots on the catalyst support structure; A process wherein the temperature of the catalyst support structure during step a. and / or step b. is between 50°C and 300°C, preferably between 100°C and less than 200°C, more preferably between 100°C and 175°C or less than 175°C, for example 100°C or 150°C. 2. The method of sentence 1, wherein the second reactant comprises an oxidizing agent selected from the group consisting of H2O, O2, O3, oxygen radicals, and mixtures thereof; preferably O2. 3. The method of sentence 1, wherein the second reactant is selected from the group consisting of H2, NH3, SiH4, Si2H6, Si3H8, SiH2Me2, SiH2Et2, N(SiH3)3, hydrogen radical, hydrazine, methylhydrazine, amines, and mixtures thereof; and includes a reducing agent which is preferably H2. 4. The method of sentence 1, wherein the second reactant is selected from the group consisting of H2, O2, and combinations thereof. 5. Any of the methods of sentences 1 to 4, in which steps a. to e. are repeated 5 to 20 times. 6. The method of any of sentences 1-5, wherein the plurality of Pt metal-containing nanodots are formed by an atomic layer deposition reaction. 7. The method of any of sentences 1-6, wherein the nanodots have a maximum linear dimension in the range of 0.25 nm to 15 nm and / or an average of 2 nm to 7 nm. 8. The catalyst support structure comprises a plurality of discrete particles having an outer surface, and the discrete particles are, after step f., 2 8. The method of any of sentences 1-7, having a coverage of Pt metal-containing nanodots that averages at least one nanodot per nanodot. 9. The method of any of sentences 1-8, wherein each nanodot comprises sufficient Pt such that a) the atomic percentage of Pt in the catalytic support structure comprising the plurality of Pt-containing nanodots is between 0.5% and 3%, preferably between 1% and 2%, and / or b) the weight percentage of Pt is between 5% and 50%, preferably between 10% and 30%. 10. The method of any of sentences 1-9, wherein the catalytic support structure is a catalytic carbon support structure. 11. The method of sentence 10, wherein a plurality of Pt nanodots are formed directly on the carbon component of the catalytic carbon support. 12. The catalytic carbon support structure is C 60 and C 7212. The method of sentence 10 or 11, wherein the fullerene is a single-walled fullerene, a multi-walled fullerene, a single-walled or multi-walled nanotube, a nanohorn, and / or a specialty carbon such as VULCAN or Imerys' SUPER C65, having a density of about 0.2 g / cm to about 1.9 g / cm. 13. The method of any of sentences 1-12, further comprising exposing the surface of the catalytic structure to a third reactant in gaseous form, wherein if the second reactant is an oxidizing agent, the third reactant is a reducing agent, and vice versa. 14. The method of sentence 13, wherein the step of exposing the surface of the catalytic structure to a third reactant is separated from step d. by step e. 15. The method of sentence 14, wherein the second reactant is oxygen and the third reactant is hydrogen. 16. A method for depositing Pt metal-containing nanodots onto a catalytic support structure, preferably a catalytic carbon support structure, comprising: a. Producing Pt(PF3)4 vapor; b. exposing the surface of the catalyst support structure to Pt(PF3)4 vapor; Step b. is performed for a time sufficient to form a plurality of Pt metal-containing nanodots on the catalytic support structure; the catalytic support structure is not exposed to any additional reactants to form a plurality of Pt metal-containing nanodots on the catalytic support structure; A method wherein the temperature of the surface of the catalyst support structure during step a. and / or step b. is between 50°C and 300°C, preferably between 100°C and less than 200°C, more preferably between 100°C and 175°C or less than 175°C, for example 100°C or 150°C. 17. The method of sentence 16, wherein the nanodots have a maximum length dimension in the range of 0.25 nm to 15 nm and / or an average of 2 nm to 7 nm. 18. The catalyst support structure comprises a plurality of discrete particles having an outer surface, and the discrete particles are, after step b., 2 18. The method of sentence 16 or 17, having a coverage of Pt metal-containing nanodots that averages at least one nanodot per nanodot. 19. The method of any of sentences 16-18, wherein each nanodot comprises sufficient Pt such that a) the atomic percentage of Pt in the catalytic support structure comprising the plurality of Pt-containing nanodots is between 0.5% and 3%, preferably between 1% and 2%, and / or b) the weight percentage of Pt is between 5% and 40%, preferably between 10% and 30%. 20. The method of any of sentences 16-19, wherein the catalytic support structure is a catalytic carbon support structure. 21. The method of sentence 20, wherein a plurality of Pt nanodots are formed directly on the carbon component of the catalytic carbon support. 22. The catalytic carbon support structure is C 60 and C 72 22. The method of sentence 20 or 21, wherein the fullerene is a single-walled fullerene, a multi-walled fullerene, a single-walled or multi-walled nanotube, a nanohorn, and / or a specialty carbon such as VULCAN or Imerys' SUPER C65, having a density of about 0.2 g / cm to about 1.9 g / cm. 23. A method for depositing Pt metal-containing nanodots onto a catalytic support structure, preferably a catalytic carbon support structure, comprising: a. Producing Pt(PF3)4 vapor; b. simultaneously exposing the surface of the catalyst support structure to Pt(PF3)4 vapor and an oxidant; Step b. is performed for a time sufficient to form a plurality of Pt metal-containing nanodots on the catalytic support structure; the catalytic support structure is not exposed to any additional reactants to form a plurality of Pt metal-containing nanodots on the catalytic support structure; A method wherein the temperature of the surface of the catalyst support structure during step a. and / or step b. is between 50°C and 300°C, preferably between 100°C and less than 200°C, more preferably between 100°C and 175°C or less than 175°C, for example 100°C or 150°C. 24. The method of sentence 23, wherein the oxidizing agent is selected from the group consisting of H2O, O2, O3, oxygen radicals, and mixtures thereof; preferably O2. 25. The method of sentence 23 or 24, wherein the nanodots have a maximum length dimension in the range of 0.25 nm to 15 nm and / or an average of 2 nm to 7 nm. 26. A catalyst support structure comprising a plurality of discrete particles having an outer surface, the discrete particles having a surface area of ​​1 nm or less of the particle surface after step b. 2 26. The method of any of sentences 23-25, having a coverage of Pt metal-containing nanodots that averages at least one nanodot per nanodot. 27. The method of any of sentences 23-26, wherein each nanodot comprises sufficient Pt such that a) the atomic percentage of Pt in the catalytic support structure comprising the plurality of Pt-containing nanodots is between 0.5% and 3%, preferably between 1% and 2%, and / or b) the weight percentage of Pt is between 5% and 40%, preferably between 10% and 30%. 28. The method of any of sentences 23-27, wherein the catalytic support structure is a catalytic carbon support structure. 29. The method of sentence 28, wherein a plurality of Pt nanodots are formed directly on the carbon component of the catalytic carbon support. 30. The catalytic carbon support structure is C 60 and C 72 29. The method of claim 28, wherein the fullerene is a single-walled fullerene, a multi-walled fullerene, a single-walled or multi-walled nanotube, a nanohorn, and / or a specialty carbon such as VULCAN or Imerys' SUPER C65, having a density of about 0.2 g / cm to about 1.9 g / cm. 31. The method of any of sentences 1-30, wherein the plurality of Pt nanodots are composed of face-centered cubic Pt crystals. 32. The method of any of sentences 1-31, wherein the utilization efficiency is between 30 weight percent and 99 weight percent, preferably at least 50 weight percent, more preferably at least 75 weight percent, for example, between 50 weight percent and 90 weight percent or between 75 weight percent and 80 weight percent. [Brief explanation of the drawings]

[0007] [Figure 1] Vapor pressure versus temperature for MeCpPtMe3 (lower line) and Pt(PF3)4 (upper line). [Figure 2]1 shows the powder deposition apparatus used to expose C65 powder to Pt(PF3)4 in the experiments described herein. [Figure 3] Figure 1 shows Pt nanodot deposition on C65 by CVD using hydrogen as a co-reactant (reproduction of prior art). XPS data are presented as X-axis = normalized intensity (arbitrary units) and Y-axis = eV. [Figure 4] Figure 1 shows the deposition of Pt nanodots on C65 by ALD using hydrogen as a co-reactant. XPS data is presented as X-axis = normalized intensity (arbitrary units) and Y-axis = eV. The vertical line defines the eV of Pt0. Most of the Pt was deposited at 100°C, and most of the Pt0 was deposited at 150°C. [Figure 5] A scanning electron microscope (SEM) image of C65 from the experiment in Figure 4 deposited at 100°C is shown. [Figure 6] Representative results from pyrolytic deposition without hydrogen are shown. XPS data are presented as X-axis = normalized intensity (arbitrary units) and Y-axis = eV. The vertical line defines the eV of Pt. The amount of Pt nanodots increased with each increase in temperature. However, most of the Pt was completely oxidized at all temperatures. [Figure 7] Representative results of oxygen CVD are shown. XPS data are presented as X-axis = normalized intensity (arbitrary units) and Y-axis = eV. The vertical line defines the eV of PtO. Pt nanodot deposition increased with increasing temperature up to 150°C, then decreased to approximately the level of reaction at 100°C at 200°C. All conditions had significant amounts of oxidized Pt, but deposition at 150°C produced the most PtO. [Figure 8] Using oxygen as a co-reactant in sequential exposures (e.g., ALD) shows that more Pt nanodots were produced on C65. XPS data are presented as X-axis = normalized intensity (arbitrary units) and Y-axis = eV. The vertical line defines the eV of PtO. The amount of both Pt and some of these in the form of PtO increased with temperature from 50°C to 150°C, with results at 200°C being comparable to those at 150°C. [Figure 9]A scanning electron microscope (SEM) image of C65 from the experiment in FIG. 8 deposited at 100° C. is shown. DETAILED DESCRIPTION OF THE INVENTION

[0008] "Nanodot" refers to, for example, individual deposits of Pt having a maximum cross-sectional dimension of 1 nanometer to 100 nanometers. Nanodots are often roughly hemispherical or roughly circular, but can be any shape, including irregularly shaped structures.

[0009] "Catalyst support structure" refers to a material used to support a catalytic material, such as Pt nanodots, in the cathode of a lithium-ion battery. See, e.g., Ye, Siyu, Miho Hall, and Ping He. "PEM fuel cell catalysts: the importance of catalyst support." ECS Transactions 16.2 (2008): 2101; Shao, Yuyan, et al. "Novel catalyst support materials for PEM fuel cells: current status and future prospects." Journal of Materials Chemistry 19.1 (2009): 46-59.

[0010] "Catalytic carbon support structure" means a catalytic support structure having carbon as a constituent component. Examples include carbon black, graphite, graphene, C 60 ("Buckyball", "Fullerene"), C 72 (Ma, Jian-Li, et al. “C 72 :A novel low energy and direct band gap carbon phase.” Physics Letters A(2020):126325), carbon layered nanotubes (including multi-walled nanotubes), carbon nanofibers, and silicon mesoporous carbon composites such as C65.

[0011] "C65" refers to a catalytic carbon support structure with silicon mesoporous carbon composite as described in Spahr, Michael E., et al. "Development of carbon conductive additives for advanced lithium ion batteries." Journal of Power Sources 196.7 (2011):3404-3413.

[0012] Tetrakis(trifluorophosphine)platinum (Pt(PF3)4) is a known chemical (CAS number 19529-53-4). As shown in Figure 1, Pt(PF3)4 has a much higher vapor pressure than the current platinum deposition precursor, Pt(MeCp)Me3.

[0013] Previous work with Pt(PF3)4 described its use as a CVD precursor for thin film deposition. Rand, Myron J. "Chemical Vapor Deposition of Thin-Film Platinum." Journal of the Electrochemical Society 120.5 (1973):686-693. Previous work focused on thermal CVD for the deposition of Pt thin films. A feasible temperature range was determined to be above 175°C, specifically 200°C to 300°C, to form metallic Pt as the predominant Pt component of the film. Lower temperatures resulted in incomplete thermal decomposition, resulting in inferior films. An oxidizing environment was avoided, even in nitrogen, which had a negative impact on film quality.

[0014] The inventors have repeatedly verified the above. CVD of H2 at 50°C, 100°C, 150°C, and even 200°C resulted in the formation of very few Pt nanodots on a C65 substrate (as described in the Experimental Section below). The small amount of Pt deposited was mostly oxidized. Therefore, prior art and our own results indicated that Pt(PF3)4 was not a good candidate for Pt nanodot deposition at low temperatures. Therefore, our subsequent work to establish successful deposition conditions was highly unexpected and surprising.

[0015] General conditions for depositing Pt nanodots with Pt(PF3)4 The substrate of interest for depositing Pt nanodots was C-NERGY™ Super C65, a conductive carbon black. Spahr, Michael E., et al. “Development of carbon conductive additives for advanced lithium ion batteries.” Journal of Power Sources 196.7 (2011): 3404-3413.

[0016] Depositions were carried out in a laboratory-scale powder deposition system as shown in Figure 2. Unless otherwise noted, all Pt nanodot depositions were carried out under the following conditions: Pt precursor (supplied by MFC) Pt(PF3)4 flow rate: Approximately 0.56 sccm (measured value) (2 sccm for N2MFC) Canister T: 30℃ Canister P: PPF VP Flow rate of co-reactant O2 or H2: 10 sccm Push N235sccm Reactor pressure: 10 Torr Support substrate (carbon support): C-NERGY super C65: 1 gram (carbon powder supported on an 8 mm stainless steel ball to prevent clumping).

[0017] Reference XRD and XPS data were collected from new C65, Pt metal foil, and C65 and Pt metal mesh. XRD patterns corresponding to the Pt and C patterns were observed at 100°C, 150°C, 175°C, and 200°C, indicating that metallic platinum can be formed under these conditions. From the reference materials, the XPS Pt4f 7 / 2 The peak position is 71.2 eV (Pt 0 The peak position of C1 was 284.6 eV. XPS data are presented as X-axis = normalized intensity (arbitrary units) and Y-axis = eV. [Example]

[0018] Comparative Example: CVD of Pt(PF3)4 using hydrogen CVD was performed for 2400 seconds using the above conditions at 50°C, 100°C, 150°C, and 200°C. Representative XPS data are shown in Figure 3. As expected based on prior art, even at 200°C (the highest amount in this series of experiments), very little Pt was deposited under these conditions, and most of the resulting Pt was oxidized. The prior art deposition process was therefore confirmed to be unsuitable for thin film deposition as well as Pt nanodot deposition below 200°C.

[0019] Sequential evaporation or atomic layer deposition of Pt(PF3)4 using hydrogen In direct contrast to the CVD results, alternating delivery of Pt(PF3)4 and hydrogen to individual substrate exposure steps (such as atomic layer deposition processes) produced dramatically different and surprising results. Representative results from ALD deposition using hydrogen are shown in Figure 4. (Number of ALD cycles: 12; ALD sequence: PPF 200 s; purge 600 s; H2 500 s; purge 600 s; 100 °C, 150 °C, and 200 °C). Compared to Figure 3, there is a clear and dramatic improvement in Pt deposition, which is fully viable for Pt nanodot deposition. Most of the Pt was metallic (denoted by vertical - - - - lines) rather than oxidized (denoted by ----- lines), which is also favorable for catalytic materials. Figure 5 shows a scanning electron microscope (SEM) image of C65 from Figure 4 deposited at 150 °C. Notably, the amount of Pt deposited actually drops off at 200°C, indicating that the optimum temperature for Pt nanodot deposition is >100°C to <200°C, contrary to prior art conclusions regarding Pt thin film deposition. This result, along with the oxygen deposition results, indicates that, contrary to expectations, there is no meaningful correlation between prior art Pt thin film deposition and Pt nanodot deposition on catalytic support structures or materials.

[0020] The inventors performed further analyses of the deposited Pt nanodots described above, specifically powder X-ray diffraction, differential thermal analysis, and thermogravimetric analysis in air. The XRD results indicate that the metallic Pt deposited at 150°C is crystalline with a face-centered cubic (FCC) structure. FCC-crystallized Pt (rather than amorphous Pt) is the preferred form of metallic Pt for catalytic activity.

[0021] For industrial applications, the amount of metallic Pt deposited on the catalyst support and its stability are important considerations. TGA and DTA analyses showed that Pt nanodots formed at 150 °C were thermally stable up to approximately 575 °C. The final residual mass at 1000 °C in the TGA indicated that approximately 9 weight percent of the material was deposited Pt. By varying the number of cycles, pulse width, and temperature, 30 weight percent Pt (or more) was achieved, with the best results obtained at 150 °C among the temperatures tested.

[0022] The utilization efficiency is the amount of Pt deposited on the catalyst support divided by the amount of Pt introduced as Pt(PF3)4 and can be expressed as a fraction or a percentage. By varying the number of cycles, pulse width, and temperature, Pt utilization efficiencies of 75% (or higher) were achieved, with the best results obtained at 150 °C among the temperatures tested.

[0023] Deposition (thermal decomposition) of Pt(PF3)4 without co-reactants Given the unexpected and counterintuitive results produced by alternating delivery of Pt(PF3)4 and hydrogen, we investigated a pure pyrolytic CVD process without any co-reactant (2400 s reaction time; 50 °C, 100 °C, 150 °C, and 200 °C). Representative results of pyrolytic deposition without hydrogen are shown in Figure 6. SEM of the C65 sample showed Pt nanodots similar to those seen in Figure 5.

[0024] Pt(PF3)4: CVD deposition with oxygen; sequential evaporation or atomic layer deposition with oxygen In light of the unexpected and unanticipated Pt nanodot deposition observed without a co-reactant and with alternating hydrogen co-reactants, the inventors investigated the use of oxygen as a representative oxidizing co-reactant. Based on the prior art, oxygen is not compatible with Pt film deposition using Pt(PF3)4. By replacing hydrogen with oxygen (but maintaining otherwise identical conditions), the inventors determined that oxygen is not only compatible with Pt nanodot deposition, but is in some respects superior to hydrogen.

[0025] Figure 7 shows representative results for oxygen CVD. In contrast to the results using hydrogen shown in Figure 3, CVD with oxygen as a co-reactant resulted in the formation of substantially more Pt nanodots on C65 (SEM not shown). Similarly, using oxygen as a co-reactant for sequential exposures (e.g., ALD) produced more Pt nanodots on C65 (Figure 8). A representative SEM of Pt nanodots formed at 100°C is shown in Figure 9.

[0026] Preferred Pt nanodot deposition In contrast to prior art Pt film deposition, Pt nanodot deposition occurs at temperatures below 200°C, preferably below 175°C, e.g., 150°C, 100°C, or even 50°C. The industry specifically requires deposition at temperatures below 175°C, based on the thermal resistance of current catalyst substrate materials such as C65. While the inventors have demonstrated robust Pt nanodot deposition at low temperatures, the preferred Pt state is metallic Pt rather than oxidized Pt. Therefore, favorable conditions for containing metallic Pt in Pt nanodots are preferred. Further optimization of parameters is anticipated to further improve these results. One exemplary optimization is to deposit using oxygen and then hydrogen as co-reactants sequentially, resulting in a blend of their relative benefits while mitigating their relatively undesirable characteristics. For example, oxygen (or any oxidizing agent) could be used for the majority of the ALD cycle, followed by the use of hydrogen (or any other reducing agent) in the ALD cycle.

Claims

1. 1. A method for depositing Pt-containing nanodots onto a catalytic carbon support structure, comprising: a. Pt(PF ３ ) ４ generating a vapor of b. The catalytic carbon support structure is coated with the Pt(PF ３ ) ４ and exposing the resulting mixture to steam of c. Purging the exterior surface of the catalytic carbon support structure with a purge gas to remove the Pt(PF ３ ) ４ removing the vapor of d. exposing a second reactant in gaseous form to the exterior surface of the catalytic carbon support structure; e. purging the exterior surface of the catalytic carbon support structure with a purge gas to remove the second reactant; and f. repeating steps a. through e. to form a plurality of the Pt-containing nanodots on the exterior surface of the catalytic carbon support structure; The method of claim 1, wherein the temperature of the catalytic carbon support structure during step a. and / or step b. is greater than or equal to 100°C and less than 200°C.

2. The second reactant is H ２ O, O ２ , O ３ , NO ２ 10. The method of claim 1, comprising an oxidizing agent selected from the group consisting of oxygen radicals and mixtures thereof.

3. The second reactant is H ２ , N.H. ３ , SiH ４ , Si ２ H ６ , Si ３ H ８ , SiH ２ Me ２ , SiH ２ Et ２ , N(SiH ３ ) ３ , hydrogen radical, hydrazine, methylhydrazine, amine, NO, N ２ 2. The method of claim 1 , comprising a reducing agent selected from the group consisting of O, and mixtures thereof.

4. 3. The method of claim 2, wherein the catalytic carbon support structure is not exposed to any additional reactants to form the plurality of Pt-containing nanodots on the catalytic carbon support structure.

5. The method of claim 1 or 2, wherein the Pt-containing nanodots have a maximum linear dimension in the range of 0.25 nm to 15 nm and / or an average of 2 nm to 7 nm.

6. 3. The method of claim 1 or 2, wherein each Pt-containing nanodot comprises sufficient Pt such that a) the atomic percentage of Pt in the catalytic carbon support structure comprising a plurality of said Pt-containing nanodots is between 1% and 2%, and / or b) the weight percentage of Pt is between 10% and 30%.

7. 3. The method of claim 1 or 2, wherein the catalytic carbon support structure contains at least 30% by weight carbon.

8. The method of claim 7, wherein a plurality of the Pt-containing nanodots are formed directly on the carbon component of the catalytic carbon support structure.

9. The method of any one of claims 1 to 8, wherein the utilization efficiency is between 50 weight percent and 90 weight percent.

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