Patent Application
20100210454
1. Field of the Invention
The present invention relates generally to catalysts and, more specifically, to nanocomposite catalyst materials for electrochemical devices.
2. Description of the Prior Art
A fuel cell produces electrons via the electrocatalytic oxidation of a fuel (e.g., H2, methanol, etc.) and reduction of an oxidizer (e.g., O2) as written in Equations 1 and 2, respectively. The H2 (fuel) is oxidized at the anode to protons that flow through an electrolyte and recombine at the cathode via the reduction of oxygen to water. The electrons flow through an external circuit and bear the potential of the voltage difference between the electrocatalytic reactions at the cathode and anode, minus ohmic losses. The ohmic losses are decreased by using platinum electrocatalysts that lower the polarization losses of the fuel-oxidation and oxygen-reduction reactions, resulting in an increase in efficiency.
H2→2H++2e− [1]
O2+4H++4e−→2H2O [2]
The best catalysts for hydrogen oxidation and oxygen reduction are presently nanoscale platinum and platinum based alloys supported on carbon. Significant effort is taking place worldwide to increase the activity of the catalysts so that less catalyst can be used, and the cost of the fuel cell can be lowered.
Another challenge in the development of new fuel cell catalysts is their long-term operation in an acidic, electrochemical environment. At fuel cell cathodes, the catalyst faces highly oxidizing conditions that corrode most materials. During operation of fuel cells, the Pt dissolves resulting in particle migration and growth over time and therefore loses surface area and activity. Pt in contact with carbon also catalyzes the breakdown of the carbon support via oxidation to CO2.
Other researchers have noted that the oxygen reduction reaction (ORR) on Pt is promoted in the presence of phosphotungstic acid, but, in that experiment, the Pt and phosphates were not prepared together as a single catalyst and the phosphotungstic acid was dispersed in solution (Giordana et al. Electrochim. Acta, 38, 1733 (1993), the entire contents are incorporated herein by reference). Phosphate-based catalysts can be used for direct conversion of methane into oxygenates and oxidative dehydrogenation. Typically, anhydrous materials are used for these applications. (Otsuka et al., “Direct conversion of methane into oxygenates,” Applied Catal. A: General, 222, 145-161 (2001); Ohdan et al., “Oxidation by iron phosphate catalyst,” J. Molec. Catal. A: Chemical, 159, 19-24 (2000), the entire contents of each are incorporated herein by reference). Hydrous iron phosphates have been investigated as corrosion barriers, paint additives and friction coatings. A polymorph of a hydrous FePO4 has been tested as a positive electrode in Li-ion batteries (Padhi et al., “Phospho-olivines as positive-electrode materials for rechargeable lithium batteries,” J. Electrochem. Soc., 144 (4): 1, the entire contents of which is incorporated herein by reference).
The aforementioned problems are overcome in the present invention which provides a nanocomposite catalyst material for electrochemical devices such as fuel cells, comprising metal nanoparticles impregnated on a conductive support that is coated with a transition metal compound. The metal nanoparticles may comprise platinum; the transition metal compound may comprise tantalum oxyphosphate, niobium oxyphosphate, tantalum oxide, niobium oxide, or any combination thereof; and the conductive support may comprise carbon. In addition, the present invention provides for a method of making the catalyst material.
The purpose of the present invention is to make a more active catalyst. One potential use for this invention is for the oxygen reduction reaction in electrochemical devices such as proton exchange membrane (PEM) fuel cells. New compositions are developed for catalysts comprised of metal (e.g., Pt) nanoparticles dispersed on a transition metal compound such as a metal phosphate (e.g., tantalum and niobium oxyphosphates) and a conductive high-surface-area support (Vulcan carbon). The new compositions of the present invention include nanoscale Pt impregnated on a nanoscale layer of metal oxy-phosphate, all deposited on high surface area carbon to make a nanocomposite. These new nanocomposite compositions are enabled by new synthetic approaches of the present invention.
One advantage of the Pt-phosphate catalysts of the present invention is that they have higher electrocatalytic behavior for the oxygen reduction reaction as compared to standard carbon-supported Pt catalysts under conditions of a proton exchange membrane fuel cell. This will enable a fuel cell with lower Pt loadings or a more powerful fuel cell with the same Pt loading, which would make fuel cells less costly/more effective and therefore more viable for commercialization.
The improved behavior of these Pt-phosphate-carbon catalysts is attributed to a catalyst-support interaction which improves how oxygen is catalyzed on the Pt. Phosphates are known for their oxygen affinity, so the phosphate structure may increase the amount of oxygen “dragged” to the electrode for the ORR. Another advantage is that the Pt is fully distributed throughout the material, which should prevent migration and ripening of the Pt nanoparticles. The phosphate also stands between the Pt and the carbon, and may help mitigate carbon corrosion. The support might also mitigate migration of the Pt nanoparticles.
The catalysts of the present invention may also be used for oxygen evolution (the conversion of water to oxygen), hydrogen oxidation and hydrogen evolution. They might be used for oxygen reduction in other electrochemical devices, such as metal-air batteries. These catalysts might also be useful in heterogeneous catalysis reactions that normally utilize platinum, such as dehydrogenation reactions.
These and other features and advantages of the invention, as well as the invention itself, will become better understood by reference to the following detailed description, appended claims, and accompanying drawings.
a) shows ORR polarization curves recorded for Pt/VC (NRL standard), Pt/[TaOPO4/VC]_SD-1 HT, and Pt/[TaOPO4/VC]_SD-1 HT2 in 0.1 M HClO4 solution saturated with O2; 1600 rpm, 20 mV s−1. Anodic scans shown.
One embodiment of the present invention provides a method to increase the contact between Pt nanoparticles catalysts with an insulating oxy-phosphate phases and the carbon support through the use of high surface area nanoparticles. Earlier catalysts were made by a physical mixture of Pt-impregnated metal oxy-phosphate with Vulcan carbon (VC), as shown in
Embodiments of the present invention include new compositions and methods derived from synthesizing the catalysts by directly impregnating the platinum nanoparticles onto nanoscale metal oxy-phosphate that is supported on the Vulcan carbon support. While earlier work demonstrated compositions in the range of 10% Pt with 40% metal phosphate and 50% carbon, with no more than 30% Pt by weight; the present invention discloses nanocomposites with a broader range of compositions of trace to 70% Pt, trace to >99% metal oxy-phosphate, with the remainder (0 to 70%) being a conductive support (e.g., carbon). A schematic is shown in
With the new nanocomposite formulations, the Pt is separated from the carbon support by the transition metal compound. Future testing may show that the Pt-activated corrosion of carbon may be mitigated. The new synthetic methods of preparing the materials include reverse micelle synthesis and solution deposition methodologies. All the new composites were tested for catalytic activity via testing in small membrane electrode assemblies. Platinum supported simply on the oxides of tantalum (Ta2O5) and niobium (Nb2O5) were also investigated.
Another embodiment of the present invention is a synthetic approach to making the Pt/[TaOPO4/VC] composite materials via a “one-pot procedure” which will be simple to scale up, and to use only small amounts of the expensive components (such as tantalum). A solution deposition method is used to make materials this way.
The new synthetic approaches of the present invention significantly improve the architecture and physical characteristics of the catalyst, making it more robust and having much greater activity. The mass activity of the new platinum on tantalum oxy-phosphates and Vulcan carbon [Pt/[TaOPO4/VC] is four times higher than our standard Pt/VC, with still a 1.6 times increase in SA as measured in MEAs.
In addition to the Pt—FePOx and Pt—NbPOx compounds described in this application, other viable catalysts compositions include phosphates of the following: Ti, Y, Sb, W, Mo and Ta, and mixed-metal phosphates including Fe and Nb and doped with other transition-metal elements. Moreover, the catalyst may be further improved and optimized for activity and durability by using various variables including, but not limited to, any one or combination of the following:
To increase the surface area of a transition metal compound in contact with both the Pt and Vulcan carbon, a reverse micelle method was adapted from the literature synthesis of zirconium phosphate (ZrPO4) nanoparticles to make TaOPO4 nanoparticles (Bellezza et al., Colloid. Polym. Sci., 285, 19 (2006), the entire contents of which are incorporated herein by reference). This synthesis used Igepal surfactant with a water/cyclohexane solvent system. The main difficulty with the adaptation of this synthesis was the instability of the Ta alkoxide precursors (Ta(OEt)5) in water. The Ta alkoxides spontaneously reacted and precipitated from solution, presumably due to the formation of insoluble oxo-Ta polymeric/oligomeric species, making this traditional reverse micelle approach not possible. A new synthesis was developed where only the H3PO4 was dissolved in the aqueous reverse micelle phase, while the Ta(OEt)5 was introduced directly into the organic (cyclohexane) phase.
The Pt/[TaOPO4/VC] catalyst was prepared in two steps. The first step, which involved the synthesis of tantalum oxy-phosphate (TaOPO4) nanoparticles directly on Vulcan carbon (VC) by reverse micelle method, was adapted from the literature synthesis of zirconium phosphate (ZrPO4) nanoparticles, but was modified to compensate for the extreme reactivity of Ta(EtO)5 with water by introducing the Ta(EtO)5 drop-wise.
A stock solution of 0.15 M Igepal 520 in cyclohexane was prepared. 30 mL of this surfactant solution was mixed with the appropriate amount of 1.2 M H3PO4 to obtain a target water-to-surfactant molar ratio RW and oil-to-water ratio Ro. The resulting microemulsion was sonicated for 40 min to 2 h. Then, in a N2 glove box, a stock solution of Ta(OEt)5 was diluted to 0.246 M with 10 mL of cyclohexane. Using an addition funnel, 3 mL of 0.246 M Ta(OEt)5/cyclohexane solution was added to the sonicated microemulsion under constant stirring. After addition of the Ta(OEt)5/cyclohexane aliquot, the solution was kept under constant stiffing for 1 h at room temperature. Meanwhile, 150 mg of VC was dispersed into 30 mL of cyclohexane, and sonicated for 60 min.
Then the 30 mL VC/cyclohexane mixture was added to the microemulsion to form hydrated tantalum oxyphosphate particles in micelles. This suspension was kept under constant stirring overnight. The resulting TaOPO4/VC sample was recovered by centrifugation and a black powder obtained. This black powder was washed with cyclohexane (3×25 mL), then with EtOH (3×25 mL) with centrifugation done between each washing step, and finally dried at 80° C. under vacuum for 2 h. A fraction of the resulting black powder was heat treated at 150° C. for 12 h in air in a furnace oven.
The following procedures were used in all of the synthesis methods to make Pt nanoparticles from Pt colloids. Pt colloids were prepared according to Wang et al., Chem. Mater., 12, 1622 (2000), the entire contents of which are incorporated herein by reference. Under an inert (N2) atmosphere, an ethylene glycol solution of NaOH (50 mL, 0.5 M) was added to an ethylene glycol solution of H2PtCl6.6H2O (50 mL, 1.93 mmol). The resulting orange-yellow solution was heated to 160° C. for 3 h under nitrogen flow. A transparent brown Pt colloidal solution was obtained and stored under N2. Upon cooling to room temperature, the solution was filtered to remove small amounts of macroscopic Pt residues and the concentration of the colloid was determined by subtracting the residue mass from the theoretical Pt content.
The platinum nanoparticles were precipitated from the platinum colloid by acidification via the addition of an aqueous solution of 0.1 M HClO4. (e.g., ˜7.70 mL of Pt solution was added to ˜12 mL 0.1 M HClO4 while stiffing.) Deposition occurred at pH<4, in agreement with prior observations. The resulting nanoparticles were separated by centrifugation and dispersed in absolute EtOH by sonication in an ultrasonic bath for 5 min immediately before addition to the metal oxy-phosphate supports.
Deposition of Pt Nanoparticles onto the TaOPO4/VC:
100 mg of heat-treated TaOPO4/VC powder was dispersed in 15 mL absolute ethanol using a high shear mixer for 2 min. After sonication, the TaOPO4/VC solution was transferred to a 100 mL round bottom flask, and an additional 25 mL of absolute ethanol was added to this solution under stirring. A dispersion of Pt nanoparticles in ethanol was added to the 40 mL TaOPO4/VC solution and kept under constant and vigorous stiffing for a minimum of 45 h. The resulting Pt/[TaOPO4/VC] deposit was isolated by centrifugation and washed by repeated (6 times) redespersion-centrifugation procedure with absolute ethanol. The Pt/TaOPO4 was dried in a vacuum oven at room temperature for 12 h and heated in air at 200° C. for 4 h in a furnace oven before use in inks formulation.
The development of a stable water-soluble tantalum species was complicated by the instability of Ta(OEt)5 in water. The approach of stabilizing the tantalum in the form of a tantalate anion equivalent was chosen as one having the most probability for success. This approach for stabilization of Ta(EtO)5 in water was published, although the stabilized complex was not isolated, characterized, or used synthetically in the same manner (Shenghai et al., Rare Metals Materials and Engineering, 36, 282 (2007), the entire contents of which are incorporated herein by reference.).
Tetramethylammonium was chosen as the counter-ion for the preparation of a tantalum-salt due to its high solubility in aqueous media. Tetramethylammonium hydroxide was dissolved in EtOH, and Ta(OEt)5 was added to it slowly drop-wise under inert atmosphere while stirring vigorously. The preparation was optimized to where it produced no precipitate. Since the product was to be used in aqueous reactions in the reverse micelle preparations, the EtOH had to be removed (in vacuo), or else it would interfere with the polarity of the microemulsion solvent system and possibly disrupt the micelles (EtOH is used to break up microemulsions/reverse micelles). (Prep: Ta(OEt)5 (1.0 mL, 3.8 mmol) was dissolved in a flask with 15 mL EtOH. While stirring vigorously under a N2(g) atmosphere, 1.58 g (4.3 mmol) of a ˜25% Me4NOH solution in water was added. All solvents were removed under vacuum leaving a white solid.)
After the dry material was prepared, it was highly water soluble and indefinitely stable in aqueous solution; however, in dry form the material was not stable, and over time ceased to fully dissolve in water. It was presumed that this instability in dry form was due to the decomposition of ammonium hydroxides leading to elimination of water and polymerization of the tantalate ions producing insoluble tantalum-oxide/hydroxides. As already mentioned, this problem was easily corrected by keeping the species dissolved in water and used as a stock solution.
Synthesis of Pt/[TaOPO1/VC] by Reverse Micelle with Water Stable Ta-Salt:
A microemulsion designated μA was obtained by adding an aliquot of aqueous solution of 0.16 M H3PO4 (325 μL) to 20 mL of 0.15 M cyclohexane/Igepal solution, to obtain a surfactant/water molar ratio (RW) equal to 6.
A microemulsion designated μB was obtained by adding an aliquot of aqueous solution of 0.15 M Me4NTaO4 (325 μL) to 20 mL of 0.15 M cyclohexane/Igepal solution, to obtain a surfactant/water molar ratio (RW) equal to 6.
μA & μB were sonicated for 55 min. Meanwhile, 150 mg of VC was dispersed into 10 mL of cyclohexane, and sonicated for 60 min. Then, μA & μB were added simultaneously to 150 mL cyclohexane solution and stirred for 2 h at room temperature. The μA & μB+cyclohexane mixture was then added to VC/cyclohexane mixture to form the tantalum oxy-phosphate nanoparticles in micelles. This suspension was kept under constant stirring overnight. The resulting TaOPO4/VC sample was recovered by centrifugation. This black powder was washed with cyclohexane (3×25 mL), then with EtOH (3×25 mL) with centrifugation done between each washing step, and finally dried at 80° C. under vacuum for 2 h. A fraction of the resulting black powder was heat treated at 150° C. for 12 h in air in a furnace oven.
111 mg of the heat treated TaOPO4/VC catalyst was dispersed in 17 mL EtOH using a high-shear mixer for 1 min. Then the TaOPO4/VC solution was sonicated for 155 min. After sonication, the TaOPO4/VC solution was transferred to a 100 mL round bottom flask, and an additional 50 mL of EtOH was added to this solution under stirring. Then, a dispersion of Pt nanoparticles in EtOH (as described above under Method 1) was added to 65 mL TaOPO4/VC solution and kept under constant and vigorous stiffing for a minimum of 45 h. The resulting Pt/[TaOPO4/VC] deposit was isolated by centrifugation and cleaned by repeated (6 times) redespersion-centrifugation procedure with EtOH. The Pt/[TaOPO4/VC] was dried in vacuum at room temperature for 12 h and heated in air at 200° C. for 4 h in a furnace oven before using the ink formulation.
A procedure was developed to deposit predetermined amounts of metal salts onto the VC substrate by a one-pot method using solution deposition methods. Ultrasound was used to disperse the constituents within the substrate, for which a simple bench-top ultrasonic cleaning bath was used. Aqueous H3PO4 was dried to make polyphosphoric acid which was subsequently dissolved into EtOH along with VC, and these components were sonicated before the addition of Ta(OEt)5. Pt nanoparticles were crashed out, washed, and subsequently re-suspended in EtOH, and then added to the reaction (as described above in Method 1). All the components were sonicated together over several days. The same procedure was used for the preparation of the NbOPO4 treated material, and a similar procedure was used to make the Ta2O5 and Nb2O5 treated materials, but instead of polyphosphoric acid, water was added to the reactions following the dispersion of the metal alkoxide on the VC substrate to lead to the oxides.
80% H3PO4 was dried at 150° C. in a vacuum oven overnight (producing polyphosphoric acid), and then dissolved in EtOH. The VC was suspended in EtOH and mixed with the polyphosphoric acid EtOH solution and left sonicating for 2 h. Ta(EtO)5 in EtOH was then added to the reaction, and it was sonicated overnight. The appropriate amount of Pt colloid was precipitated, re-suspended in EtOH and injected into the same flask. The reaction was sonicated for 2 days and then the material was spun at 9300 g in the centrifuge, dried under vacuum and then heat treated in inert atmosphere (N2) to various temperatures (100 to 800° C.) that depend on Pt loading of the material for a variable period, depending on the final particle morphology that we wanted to achieve, in a furnace oven before using in the ink formulation for rotating disc electrode (RDE) or membrane electrode assembly (MEA) testing.
Using the RDE methodology, the performance of the catalysts was compared to a standard Pt/VC catalyst prepared with the same Pt deposited on the TaOPO4/VC in the composite materials made by both reverse micelle (RM) and solution deposition (SD) methods. Detailed experimental procedures are in Garsany et al., J. Electrochem. Soc., February 2010, the entire contents of which are incorporated herein by reference.
The results of the elemental analysis on the Pt/[TaOPO4/VC] catalysts are presented in Table I. Elemental analysis performed by Columbia Analytical Services, Inc. Particle sizes are determined via X-ray diffraction (XRD).
Cyclic voltammograms (CVs) are presented in
The RDEs Pt loading and electrochemical surface area (ECSA), APt,cat(m2Pt gPt−1) of the tested catalysts are summarized in Table II. The ECSA of the Pt in each sample was calculated by integrating the columbic charge Q in (C) under both the hydrogen adsorption and desorption region from ca. 0.10 V-0.40 V (using cyclic voltammograms recorded at 30° C., and at a ν=200 mV s−1), and then corrected for H2 crossover and double layer capacitance of the carbon support and Pt/TaOPO4 using Equation 3.
A
Pt,cat
={Q/(210 μC cm−2Pt(LcaAg)}×105 (3)
where Lca is the cathode loading (mgPt cm−2) and Ag is the geometric surface area of the MEA (i.e. 0.196 cm2).
Table II shows that the platinum ECSA is ˜5 to 7.5 times higher for Pt/TaOPO4 catalysts synthesized by directly impregnated the Pt/TaOPO4 composite on the VC support by reverse micelle synthesis vs. the ECSA of the Pt/TaOPO4 composite mixed mechanically with the VC support (i.e. ˜75 m2gPt−1 compared to only 12 m2 gPt−1). The ECSA of RM-1 and RM-2 catalysts are 63 and 56 m2 gPt−1, or statistically equivalent to the 61 m2 gPt−1 of the Pt/VC (NRL standard). The Pt/[TaOPO4/VC]_SD-1 HT2 catalyst has the highest ECSA of all the catalysts of 89 m2PtgPt−1. The lower ECSA of the Pt on the TaOPO4 mixed mechanically with VC support vs. the nanoscale tantalum oxy-phosphate on the VC support is probably due to poor electronic contact between the Pt and the carbon, resulting in much of its Pt being electrochemically inactive. By directly impregnating the platinum nanoparticles on nanoscale tantalum oxy-phosphate on the VC support, the Pt particles only have a thin layer of tantalum oxy-phosphate separating them from the carbon, and thus they are not longer electrochemically isolated. Although tantalum oxyphosphate is highly insulating, it is well known that electrons tunnel through thin oxide films such as Al2O3.
A single, steep reduction wave with a well developed limiting current density plateau, Jlim, is observed in the potential region 0.20 V<E<0.70 V, followed by a mixed kinetic-diffusion control region between 0.75 V<E<1.00 V for all of the catalysts. The ORR polarization curves for the Pt/VC, SD-1 HT, and SD-1 HT2 Pt/[TaOPO4/VC] catalysts measured at 1600 rpm, have their Jlim value of ˜−6 mA cm−2 (geometric) in good agreement with the Jlim value observed for the Pt/TaOPO4+VC catalyst and also well within the 10% margin of the theoretical diffusion limiting current (i.e. −5.7 mA cm−2) calculated using the Levich's equation, clearly indicating a negligible contribution from O2 diffusion through the Nafion film and tantalum oxy-phosphate. All the catalysts supported on tantalum oxy-phosphate have nearly the same Pt loading (15-20 μgPt cm−2, see Table II) as the Pt/C catalysts (˜24 μgPt cm−2); therefore their catalytic activity for the ORR can be compared visually by their arrangement on
The E vs. log |jk| curves or Tafel plots for the ORR are shown in
The actual electrocatalytic activity of catalysts is best compared by their mass- and area-specific activities using the mass transport-correction for thin-film RDEs. For this relative comparison, J is taken from the value of the curve at 0.90 V and the Jlim at 0.35 V. The mass-specific activities (A mgPt−1) are estimated via calculation of Jk and normalization to the Pt-loading of the disk electrode. The area-specific activities (μA cm2Pt) are estimated via the calculation of Jk and normalization to the platinum surface area, APt,cat. Mass-specific and area-specific activities are listed in Table III and also compared to literature values.
Our Pt/VC standard has lower mass- and area-specific activities than 46% Pt/C (TKK) (0.21 A mgPt−1 and 265 μA cm−2Pt) (1), possibly due to the 1.2 nm size of our Pt clusters. The mass-specific activity at 0.90 V of the Pt/TaOPO4+VC is ˜2.5 times lower than of the Pt/VC (0.06±0.02 A mgPt−1 vs. 0.15±0.02 A mgPt−1), and its area-specific activity is ˜2 times higher (495 μA cm−2Pt vs. 244 μA cm−2Pt). Low mass-specific activity is the result of poor electrochemical utilization of the Pt on the support, as discussed above. The SD-1 Pt/[TaOPO4/VC] catalyst has ˜1.3 times higher mass activity than the Pt/VC (i.e. 0.26 A mgPt−1 vs. 0.15 A mgPt−1), and its area-specific activity is ˜1.3 times higher than that of the standard Pt/VC (324 μA cm−2Pt vs. 244 μA cm−2Pt). Further, the mass specific-activity of the SD-1 catalyst is 2.2 times higher than that of the commercial Pt/C catalyst (i.e. 0.26 A mgPt−1 vs. 0.12 A mgPt−1) and their area specific activities are very comparable. The RM-1 and RM-2 Pt/[TaOPO4/VC] catalysts have ˜1.3 times higher mass activity than our Pt/VC standard (i.e. 0.19 A mgPt−1 vs. 0.15 A mgPt−1), but their area-specific activities are very comparable to that of the Pt/VC. The mass-specific activities of the tantalum oxy-phosphate catalysts synthesized directly on the VC (i.e. RM-1, RM-2 and SD-1) are ˜3.5 times higher than that Pt/TaOPO4+VC (mechanical mixture), but their specific-area activities are ˜1.6 times lower.
Both heat treated Pt/[TaOPO4/VC] (i.e. SD-1 HT and SD-1 HT2) catalysts have higher mass and area-specific activities than the commercial 46% Pt/C (TKK) and our standard Pt/VC. The mass and area-specific activities of the SD-1 HT2 catalyst is ˜4 times and ˜2 times higher than that of the commercial TKK catalyst respectively. The most active catalysts are based on Pt/TaOPO4, which show the highest mass and specific activities. The NbOPO4 based catalyst is almost as active.
Some of the catalysts were also tested at the cathode catalysts in 10 cm2 membrane electrode assemblies (MEAs).
The above descriptions are those of the preferred embodiments of the invention. Various modifications and variations are possible in light of the above teachings without departing from the spirit and broader aspects of the invention. It is therefore to be understood that the claimed invention may be practiced otherwise than as specifically described. Any references to claim elements in the singular, for example, using the articles “a,” “an,” “the,” or “said,” is not to be construed as limiting the element to the singular.
The present application claims priority from U.S. Provisional Application No. 61/151,576 filed on Feb. 11, 2009 by Albert Epshteyn et al., entitled “METHOD OF SYNTHESIS OF NANOCOMPOSITE MATERIALS COMPRISED OF CARBON, METAL PHOSPHATE, AND METAL NANOPARTICLES,” the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61151576 | Feb 2009 | US |
