A BIMETALLIC CATALYST AND FUEL FOR USE IN A DIRECT DIMETHYL ETHER FUEL CELL

Abstract

A bimetallic catalyst alloy is provided for use in fuel cells, particularly in the oxidation of dimethyl ether in a direct dimethyl ether fuel cell.

Claims

1.-41. (canceled)

42. A bimetallic catalyst alloy of the structure PtM, wherein Pt is platinum and M is a transition metal selected from copper, nickel, cobalt, manganese, chromium and titanium; the molar ratio of the platinum to the transition metal (Pt:M) is between about 1:4 to 2:1, the catalyst having an L1.sub.0 structure; for use in oxidation of dimethyl ether in a direct dimethyl ether fuel cell.

43. The catalyst according to claim 42, wherein the molar ratio is between about 1:1 to 2:1, or the molar ratio is between 4:3 to 6:3, or the molar ratio is 3:2 or 3:3 or 4:3 or 6:3.

44. A bimetallic catalyst comprising: (a) platinum; and (b) a transition metal selected from copper, nickel, cobalt, manganese, chromium and titanium; wherein the platinum is at a concentration of less than about 70 atomic percent, the catalyst having an L1.sub.0 structure; for use in a direct dimethyl ether fuel cell.

45. The catalyst according to claim 42, having a structure different from L1.sub.2.

46. The catalyst according to claim 42, having an XRD spectrum lacking a peak at a 2θ in the range of 31-34°, or having an XRD spectrum lacking a peak at a 2θ below 40°.

47. The catalyst according to claim 42, having an XRD pattern comprising one of the following patterns 2θ: a. 43° (111), 50° (200), 74° (220) and 90° (311); or b. 43° (111), 47° (200), 70° (220) and 84° (311); or c. 41° (111), 45° (200), 69° (220) and 87° (311); or d. a peak between 40 and 42° (111), a peak between 46 and 48° (200), a peak between 67 and 70° (220) and a peak between 83 and 85° (311); or e. an X-ray diffraction (XRD) pattern of any one FIGS. 1A-1D.

48. The catalyst according to claim 42, supported on a solid support material, being optionally elected from the group consisting of a carbonaceous material, a conductive material and a metal oxide.

49. The catalyst according to claim 42, wherein M is copper such the catalyst alloy has the structure being PtCu.

50. A process for the preparation of a bimetallic catalyst alloy according to claim 42, the process comprising: a. contacting a precursor of a transition metal M with a platinum precursor in a liquid medium to obtain a mixture, b. heating said mixture at a temperature above room temperature and below 300° C., to afford the catalyst alloy; c. optionally isolating said alloy; and d. optionally contacting said isolated alloy or in solution with at least one solid carrier to afford a solid supported catalyst.

51. The process according to claim 50, wherein the temperature is selected not to cause transformation of the catalyst into the L1.sub.2 structure.

52. A direct dimethyl ether fuel cell, DDMEFC, comprising at least one anode having a catalytic layer of a bimetallic catalyst according to claim 42.

53. A direct dimethyl ether fuel cell, DDMEFC, comprising at least one anode, at least one cathode and a membrane disposed therebetween, the membrane having a catalytic layer of a bimetallic catalyst according to claim 42.

54. An anode of a DDMEFC having a catalytic layer of a bimetallic catalyst according to claim 42.

55. An electrode for use in a fuel cell, the electrode comprising a catalyst layer comprising at least one bimetallic catalyst according to claim 42.

56. A membrane electrode assembly (MEA) for use in a direct dimethyl ether fuel cell, the MEA comprising an anode, a cathode and a membrane disposed therebetween; said anode comprising a bimetallic catalyst according to claim 42.

57. A fuel cell comprising an anode associated with a bimetallic catalyst according to claim 42.

58. A direct dimethyl ether fuel cell, comprising: an anode comprising a conductive support and a catalyst layer dispersed thereon, a cathode comprising a conductive support and optionally a catalyst layer dispersed thereon, and a proton conducting membrane disposed between said anode and said cathode; wherein said anode catalyst layer comprising a bimetallic catalyst alloy of the structure PtM, consisting: (i) platinum (Pt); and (ii) a transition metal M selected from copper, nickel, cobalt, manganese, chromium and titanium; said bimetallic catalyst having a Pt:M molar ratio of 1:4 to 2:1, the alloy having L1.sub.0 structure; and wherein said anode is configured to directly oxidize fuel comprising a mixture of dimethyl ether and water.

59. The DDMEFC according to claim 58, for use in an electronic device, selected from a portable electronic device and a stationary electronic device.

60. The DDMEFC according to claim 59, wherein the electronic device is selected from a drone, a personal computer, a portable phone, a digital camera, a household device, an electric bicycles, a toy, a portable game machine, a video camcorder and a backup power device.

61. The DDMEFC according to claim 60, wherein the electronic device is a drone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0115] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0116] FIGS. 1A-1D provide XRD patterns of Pt:Cu (1:1 molar ratio) metallic catalyst having Pt-to-Cu molar ratio of: (FIG. 1A) 1:1 in accordance with Example 1 of the invention, (FIG. 1B) 4:3 in accordance with Example 2 of the invention, (FIG. 1C) 2:1 in accordance with Example 3 of the invention and (FIG. 1D) 3:2 in accordance with Example 4 of the invention.

[0117] FIGS. 2A-2C provide SEM images of (FIG. 2A) particles of the Pt:Cu (1:1 molar ratio) bimetallic catalyst alloy, (FIG. 2B) mapping of copper particles, and (FIG. 2C) mapping of platinum particles; according to Example 1 of the present invention.

[0118] FIGS. 3A-3E provide HR-TEM images of (FIG. 3A) particles of the Pt:Cu (1:1 molar ratio) bimetallic catalyst alloy, (FIG. 3B) mapping of platinum particles, and (FIG. 3C) mapping of copper particles, (FIG. 3D) magnification of (FIG. 3A), and (FIG. 3E) EDX graph confirming that the alloy is platinum:copper 1:1; according to Example 1 of the present invention.

[0119] FIG. 4 provide different HR-TEM images of particles of the Pt:Cu (2:1 molar ratio) bimetallic catalyst alloy according to Example 3 of the present invention at different regions of the sample and magnifications.

[0120] FIGS. 5A-5B provide electrochemical activity tests (FIG. 5A) of Pt:Cu (1:1) bimetallic catalyst according to Example 1 of the invention and comparison with the Reference Samples Pt and Pt:Ru (1:1), and (FIG. 5B) different ratios of Pt-to-Cu in accordance with FIGS. 1A-1D.

[0121] FIGS. 6A-6B provide fuel cell test station (Scribner associates inc.), in which the catalyst was loaded onto the anode of a Nafion™ membrane (N-117). The cathode was loaded with carbon black supported platinum 20% (E-TEK), and reported as whole cell voltage.

DETAILED DESCRIPTION OF EMBODIMENTS

[0122] The inventors of the technology disclosed herein have found that in a bimetallic catalyst comprising platinum and a transition metal of the kind described herein, platinum is oxidized to produce carbon dioxide, while carbon monoxide is removed from the active site of the platinum, resulting in a bimetallic catalyst that is tolerant of carbon monoxide poisoning, thereby maintaining a high activity for dimethyl ether oxidation. When the two elements in the bimetallic catalyst (i.e., platinum and a transition metal as described herein) having a defined structure, a defined molar ratio, a specific surface area, and/or a specific particle size are mixed at atomic level, an unexpectedly higher activity for DOR is exhibited. For example, when the atomic components of a bimetallic catalyst of the present invention comprising platinum and a transition metal are mixed to provide an alloy, the catalyst exhibits high activity for DOR. Thus, in some embodiments, the bimetallic catalyst disclosed herein, is an alloy.

Experimental Techniques

[0123] Structure and morphology were acquired using scanning electron microscopy (SEM, FEI Quanta FEG 250, operating at 30 kV, secondary electrons operating mode, working distance 10 mm).

[0124] The atomic structure and morphology of a catalyst particle were acquired using high-resolution transmission electron microscopy (HR-TEM, JEOL-JEM-2100, (operating at 200 kV, LaB.sub.6 filament, bright field).

[0125] XRD measurements were recorded with D8 Advance diffractometer using Cu Kα1 radiation. Full profile fitting of the collected data was performed using Diffrac. EVA software (Bruker AXS, Karlsruhe, Germany).

[0126] For compositional analysis, energy dispersive X-ray spectroscopy (EDX) measurements were performed, using Thermo-Fischer Ultra-dry silicon detector (TEM).

Materials and Methods of Preparation

Bimetallic Catalysts Synthesis

Example 1—Obtaining Platinum-Copper (1:1) Alloy Catalyst

[0127] Platinum-Copper alloy was synthesized in the following method: 0.15 mmol of H.sub.2PtCl.sub.6.6H.sub.2O and 0.15 mmol of CuCl.sub.2.2H.sub.2O were dissolved in a mixture solvent containing 20 ml of water and 40 ml of ethylene glycol. Subsequently, 0.001 mmol of Pluronic F127 was added to the solution, which was stirred for 60 min to obtain a clear solution. The solution was then transferred to a 100 ml Teflon-lined stainless autoclave. The autoclave was heated to 180° C. and kept at this temperature for 12 hours before it was cooled to room temperature. The products were Buchner vacuumed and washed with ethanol-water mixture for several times. The products were collected for characterization and catalyst tests.

Characterization of the Bimetallic Catalyst of Example 1

Structure and Morphology

[0128] The XRD data displayed in FIG. 1A indicates that the bimetallic catalyst of Example 1 is a Pt—Cu alloy with a ratio of 1:1 and that the particle size is about 7 nm (nanocrystallite size calculated by applying “Scherrer Equation” on a XRD pattern).

[0129] SEM imaging (FIG. 2A) and mapping (FIGS. 2B-2C) reveal that the product is an alloy rather than separated particles of platinum and copper. The mapping images in FIGS. 2B-2C show that the morphology in both copper (FIG. 2B) and platinum (FIG. 2C) has no significant areas which contain only one of these elements.

[0130] HR-TEM was used to image substantially smaller particles than the SEM and provides information down to nanometric resolution. In the HR-TEM images (FIGS. 3A-3C), a single particle of the bimetallic catalyst of Example 1 contains both elements, platinum (FIG. 3B) and copper (FIG. 3C). In addition, the EDX mapping image (FIG. 3D) and result table (FIG. 3E) confirms that the alloy has platinum:copper atomic ratio of 1:1. The gold presented in the EDX result originates from the HR-TEM grid.

TABLE-US-00001 TABLE 1 EDX results for the bimetallic catalyst of Example 1 Element Line Weight % Weight % Error Atom % Cu K 25.82 +/−0.30 51.66 Cu L — — — Pt L 74.18 +/−0.94 48.34 Pt M — — — Au L — — — Au M — — — Total 100.00 100.00

[0131] All the above structure and morphology techniques performed on the bimetallic catalyst of Example 1 confirm that the platinum:copper alloy has an atomic ratio of 1:1. There is about 10% w/w of carbon in the product, which remains from the ethylene glycol used to reduce the precursors.

Example 2—Obtaining Platinum-Copper (4:3) Alloy Catalyst

[0132] Platinum-Copper alloy was synthesized in the following method: 155 mg of 6H.sub.2O.H.sub.2PtCl.sub.6, which are 0.3 mmol, were added to a 51 mg of 2H.sub.2O.CuCl.sub.2, which are also 0.3 mmol, in a biker. 25 mg of Pluronic F127 (0.002 mmol) were added to the mixture in a 20 ml H.sub.2O: 40 ml Ethylene glycol solution and was stirred for 1 h. Then the solution was poured to an autoclave, which was heated for 14 h at 180° C. It was cooled down to room temp and filtered using a Buchner. Ethanol: H.sub.2O mixture was added to the Buchner. The product was scraped with a spatula from the filtration paper.

Characterization of the Bimetallic Catalyst of Example 2

Structure and Morphology

[0133] The XRD data displayed in FIG. 1B indicates that the bimetallic catalyst of Example 2 is a Pt—Cu alloy with a ratio of 4:3 and that the particle size is 6.5 nm as calculated by “Scherrer Equation” (not shown here).

Example 3—Obtaining Platinum-Copper (2:1) Alloy Catalyst

[0134] Platinum-Copper alloy was synthesized in the following method: Platinum-Copper alloy was synthesized in the following method: 0.3 mmol of H.sub.2PtCl.sub.6.6H.sub.2O and 0.3 mmol of CuCl.sub.2.2H.sub.2O were dissolved in a mixture solvent containing 20 ml of water and 40 ml of ethylene glycol. Subsequently, 0.002 mmol of Pluronic F127 was added to the solution, which was stirred for 60 min to obtain a clear solution. The solution was then transferred to a 100 ml Teflon-lined stainless autoclave. The autoclave was heated to 180° C. and kept at this temperature for 12 hours before it was cooled to room temperature. The products were Buchner vacuumed and washed with ethanol-water mixture for several times. The products were collected for characterization and catalyst tests.

Characterization of the Bimetallic Catalyst of Example 3

Structure and Morphology

[0135] The XRD data displayed in FIG. 1C indicates that the bimetallic catalyst of Example 3 is a Pt—Cu alloy with a ratio of 2:1 and that the particle size is 7.3 nm as calculated by “Scherrer Equation” (not shown here).

[0136] HR-TEM images displayed in FIGS. 4A-4D show that the bimetallic catalyst of Example 3 has Pt—Cu nanoparticles size of 3.2-3.9 nm.

Example 4—Obtaining Platinum-Copper (3:2) Alloy Catalyst

[0137] Platinum-Copper alloy was synthesized in the following method:

[0138] 77 mg of 6H.sub.2O.H.sub.2PtCl.sub.6, which are 0.15 mmol, were added to a 25 mg of 2H.sub.2O.CuCl.sub.2, which are also 0.15 mmol, in a biker. 12.5 mg of Pluronic F127 (0.001 mmol) were added to the mixture in a 20 ml H.sub.2O: 40 ml Ethylene glycol solution and was stirred for 1 h. Then the solution was poured to an autoclave, which was heated for 14 h at 180° C. It was cooled down to room temp and filtered using a Buchner. Ethanol: H.sub.2O mixture was added to the Buchner. The product was scraped with a spatula from the filtration paper.

Characterization of the Bimetallic Catalyst of Example 4

Structure and Morphology

[0139] The XRD data displayed in FIG. 1D indicates that the bimetallic catalyst of Example 4 is a Pt—Cu alloy with a ratio of 3:2 and that the particle size is 6.7 nm as calculated by “Scherrer Equation” (not shown here).

Electrochemical Characterization

[0140] a) Cyclic Voltammetry Measurements

[0141] Electrochemical activity measurements were conducted in order to test the catalysis of DME electro-oxidation with the Pt—Cu alloy catalyst according to Example 1 of the present invention. Carbon black (Vulkan XC-72, E-TEK) supported Pt catalyst and Pt—Ru, catalyst (Aldrich, 20 w/w % and 10 w/w % respectively) were also tested as Reference Samples. The measurements were conducted in a half cell designed for gas diffusion electrode (Sigracet 25 BC GDL), allowing DME to flow and diffuse within the electrode surface, in 0.5M H.sub.2SO.sub.4. These results are reported in reference to a Real Hydrogen Electrode (RHE) and are displayed in FIG. 5A.

[0142] Further, electrochemical activity measurements were conducted in a half cell designed for gas diffusion electrode (Sigracet 25 BC GDL), allowing DME to flow and diffuse within the electrode surface in 0.5M H.sub.2SO.sub.4, for the Pt—Cu alloy catalyst according to Examples 1-4 of the present invention. These results are reported in reference to a Real Hydrogen Electrode (RHE) and are displayed in FIG. 5B. The results show that the DME oxidation with the Pt—Cu alloy catalyst of 4:3 and 2:1 ratios have the highest peak currents.

Fuel Cell Tests

[0143] Fuel cell test station (Scribner associates inc. 850e), in which 10 mg/cm.sup.2 catalyst according to Example 1 of the present invention was loaded onto the anode of a Nafion™ membrane (N-117). The cathode was loaded with carbon black supported platinum 20% (E-TEK). For comparison, a similar fuel cell using an anode loaded with a Pt—Ru catalyst (1:1) was also tested as a Reference Sample. Humidified DME was supplied to the anode at a flow rate of 20 and 40 sccm (standard cubic cm per minute, i.e., ml/min) and temperature of 80° C. and 90° C., then the current density was scanned and cell voltage and the power density of the fuel cells were measured. The results are reported as whole cell voltage and displayed in FIG. 6A. As displayed in FIG. 6A, the cell performance of the Pt—Cu catalyst of the present invention is noticeably improved in comparison to the Pt—Ru Reference catalyst.

[0144] Further, the effect of DME mass transfer on a direct DME fuel cell (“DDMEFC”) performance was tested as a function of flow rates of 20 and 40 sccm (standard cubic centimeters per minute) of humidified DME gas at 80° C. 90° C. using the catalyst (10 mg/cm.sup.2 loading) according to Example 1 of the present invention loaded onto the anode of a Nafion™ membrane (N-117). The cathode was loaded with carbon black supported platinum 20% (E-TEK) and the results are displayed as whole cell voltage in FIG. 6B. A peak power of 0.44 Watt (namely, 0.088 W/cm.sup.2 for a 5 cm.sup.2 cell) was measured at a current density of 105 mA/cm.sup.2. This indicates that the Pt—Cu alloy of the present invention has remarkable DME oxidation activity. In addition, the difference in performance at 20 and 40 sccm DME flow rates has small effect on the DDMEFC performance.