WO2013191674A1

WO2013191674A1 - Method and apparatus for analyzing a material

Info

Publication number: WO2013191674A1
Application number: PCT/US2012/042884
Authority: WO
Inventors: Minhua Shao
Original assignee: United Technologies Corporation
Priority date: 2012-06-18
Filing date: 2012-06-18
Publication date: 2013-12-27

Abstract

An exemplary method of analyzing a material including platinum and palladium includes exposing the material to hydrogen. The hydrogen-exposed material is irradiated. A determination is made regarding a characteristic of the material based on a result of the irradiation.

Description

METHOD AND APPARATUS FOR ANALYZING A MATERIAL

BACKGROUND

[0001 ] Fuel cells are useful for generating electricity. Fuel cells operate based upon an electrochemical reaction. One of the challenges associated with fuel cells is that the materials required for facilitating the electrochemical reaction tend to be expensive. For example, catalyst layers within a fuel cell typically comprise platinum. When a catalyst layer is made entirely of platinum, the relatively expensive platinum material increases the cost of the fuel cell.

[0002] Other catalyst materials have been proposed. For example, it has been proposed to utilize a catalyst comprising a monolayer of platinum deposited onto a layer of palladium. Including the palladium as part of the catalyst reduces the amount of platinum that is required and, therefore, reduces the cost. While this technique appears promising, there are challenges associated with realizing economic benefits from using such a catalyst layer.

[0003] For example, it has proven difficult to control the process of achieving a consistent monolayer of platinum over the palladium. This is especially true when attempting to make relatively large batches of material for forming such catalysts. Large batch processes tend to have associated drawbacks including the formation of platinum clusters or an undesired thickness of the platinum layer. The presence of either of those characteristics reduces the effectiveness of the oxygen reduction activity of the catalyst material.

SUMMARY

[0004] An exemplary method of analyzing a material including platinum and palladium includes exposing the material to hydrogen. The hydrogen-exposed material is irradiated. A determination is made regarding a characteristic of the material based on a result of the irradiation.

[0005] An exemplary apparatus for analyzing a material including platinum and palladium includes a chamber, a source of radiation and an output device. The chamber is configured to contain a sample of the material. An inlet to the chamber is configured for introducing hydrogen into the chamber for exposing the material in the chamber to hydrogen. The output device is configured to provide a representation of a result of irradiating the material. The representation indicates a characteristic of the material.

[0006] The various features and advantages of a disclosed example embodiment will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 schematically illustrates an example apparatus designed according to an embodiment of this invention.

[0008] Figure 2 schematically illustrates a representation of a result of irradiating a palladium material before and after exposing that material to hydrogen.

[0009] Figure 3 schematically illustrates a representation of a result of irradiating a hydrogen-exposed material that has at least one undesired platinum characteristic.

[00010] Figure 4 schematically illustrates a representation of another result of irradiating a hydrogen-exposed material that has at least one undesired platinum characteristic.

[00011] Figure 5 schematically illustrates a representation of another result of irradiating a hydrogen-exposed material that has at least one undesired platinum characteristic.

[00012] Figure 6 schematically illustrates a representation of a result of irradiating a hydrogen-exposed material that has a desired platinum characteristic. DETAILED DESCRIPTION

[00013] Figure 1 schematically illustrates an example apparatus 20 for analyzing a material that includes platinum and palladium. In one example, the material comprises a fuel cell catalyst material that is useful for forming a catalyst layer to be used in a fuel cell for facilitating an electrochemical reaction for generating electricity. In one example, the material comprises a platinum layer over a palladium core layer. In one example, a desired characteristic of the material is that the platinum establishes a monolayer of platinum having a consistent thickness.

[00014] Figure 1 schematically illustrates a sample 22 of the material within a chamber 24. The chamber 24 is configured to contain the sample 22 and to allow the sample to be exposed to a desired environment. A radiation source 26 irradiates the sample 22 within the chamber 24. In one example, the radiation comprises x-ray radiation. The chamber 24 is configured to allow the sample of material 22 to be exposed to the radiation from the source 26.

[00015] An output device 28 provides an output that is a representation of a result of irradiating the sample of material 22 within the chamber 24. The representation indicates a characteristic of the material based on a result of the radiation exposure.

[00016] In one example, the output device 28 provides a graphical representation of a result of the radiation. In one example, the representation corresponds to an x-ray diffraction pattern from the sample of material 22.

[00017] The chamber 24 is configured to facilitate exposing the material 22 to a gas such as helium, coming from a source schematically shown at 30. The chamber 24 also facilitates exposing the material 22 to hydrogen from a source schematically shown at 32. Exposing the sample of material 22 to hydrogen causes a change in the x-ray diffraction pattern of palladium within the material. Exposing the palladium to hydrogen of a sufficient concentration for a sufficient amount of time allows for the palladium to form a hydride. This phenomenon effectively expands the lattice constant of the palladium resulting in a different x-ray diffraction pattern compared to one prior to hydrogen exposure.

[00018] As schematically shown in Figure 2, the output device 28 provides an example output 40 that includes representations of an x-ray diffraction pattern resulting from irradiating palladium. The example of Figure 2 includes two x-ray diffraction patterns shown in the curves 42 and 44. In this example, the curve 42 corresponds to an x-ray diffraction pattern of irradiated palladium material schematically represented at 46. The x-ray diffraction pattern corresponding to the curve 44 results from irradiating the palladium material after it has been exposed to hydrogen. As schematically shown at 48, hydrogen molecules react with the palladium molecules 46 resulting in a hydride and a lattice constant expansion of approximately 4%. This occurs because palladium is capable of absorbing hydrogen at a rate of up to 900 times its own volume.

[00019] As can be appreciated from Figure 2, a peak in the intensity of the curve 42 is in a different angular position compared to a peak of the curve 44 (i.e., the peak shifts to the left in the drawing). This shift in the peak of the x-ray diffraction pattern represented by the curve 44 compared to the curve 42 is a result of the lattice constant expansion resulting from the exposure of the palladium to hydrogen.

[00020] In the case of a sample material 22 including platinum deposited onto palladium, if the platinum has a desired characteristic such as comprising a monolayer of platinum of a consistent thickness, the x-ray diffraction pattern of the material will demonstrate that the lattice constant of the platinum monolayer will follow that of the palladium core after the material has been exposed to hydrogen. On the other hand, if the material includes platinum clusters or an undesirable thickness of the platinum shell, the peaks of the x-ray diffraction patterns of the platinum and palladium will be angularly separated from each other or shifted relative to each other.

[00021] One example implementation includes exposing the sample of material 22 to helium from the source 30, irradiating the material and obtaining a result of the radiation. A graphical representation of the intensity of the x-ray diffraction pattern including helium exposure should include a single peak because of the similarities in the lattice constants of platinum and palladium. The irradiation may be performed during or after helium exposure.

[00022] The material 22 will then be exposed to hydrogen from the source 32 sufficiently to allow for the palladium and hydrogen to form a hydride, which expands the lattice constant of the palladium.

[00023] The hydrogen-exposed material is irradiated. The irradiation may be performed while the material is exposed to hydrogen in the chamber 24. Other approaches may be used provided that the palladium will have had sufficient exposure to the hydrogen to achieve a desired expansion of the lattice constant to provide a recognizable shift in the peak of the intensity of the x-ray diffraction pattern of the palladium.

[00024] Figure 3 schematically shows a representation 40 from the output device 28 that includes a curve 50 corresponding to an x-ray diffraction pattern of a sample of hydrogen-exposed material 22. In this example, the curve 50 includes a peak 52. As can be appreciated by considering the line 54, the curve 50 is not symmetric about the peak 52. In other words, the shape of the curve 50 on the right side of the line 54 (according to the drawing) is not the same as the shape of the curve 50 on the left side of the line 54.

[00025] In particular, the curve 50 includes a second peak at 56. This corresponds to a shift between the peak of the x-ray diffraction pattern of the platinum of the material (represented at the peak 52) and a peak in the x-ray diffraction pattern of the hydrogen charged palladium of the material (represented by the peak or shoulder at 56). It follows that the representation 40 in Figure 3 provides an indication that the sample of material 22 has an undesired characteristic. The platinum layer may include platinum clusters, for example. The platinum layer may have an undesired thickness.

[00026] Figure 4 schematically shows another representation 40 from the output device 28 that includes a curve 60 corresponding to an x-ray diffraction pattern of a sample of hydrogen-exposed material 22. In this example, the curve 60 includes a peak 62 and a small shoulder 64. This corresponds to a shift between the peak of the x-ray diffraction pattern of the platinum of the material (represented at the peak 62) and a peak in the x-ray diffraction pattern of the hydrogen charged palladium of the material (represented by the peak or shoulder at 64). It follows that the representation 40 in Figure 4 provides an indication that the sample of material 22 has an undesired characteristic. The platinum layer may include platinum clusters, for example.

[00027] Figure 5 schematically shows another representation 40 from the output device 28 that includes a curve 70 corresponding to an x-ray diffraction pattern of a sample of hydrogen-exposed material 22. This sample is an alloy of platinum and palladium. In this example, the curve 70 includes a single peak 72. The position of peak 72, however, is only shifted a relatively small amount compared to a peak of the same material before hydrogen exposure. For example, the peak 72 shifted a much less degree to the left (according to the drawings) compared to the shift of the peak of the curve 44 compared to that of curve 42 (Figure 2). The relatively minor or low amount of shift in the example of Figure 5 indicates that the material is not fully charged with hydrogen. In other words, only a limited amount of hydrogen is able to penetrate into the alloy due to the blocking effect from the platinum atoms in the alloy. A monolayer of platinum of a desired thickness does not have such a blocking effect. Figure 5 provides an indication that the sample of material 22 has an undesired characteristic.

[00028] When the material includes platinum having desired characteristics, such as a monolayer of uniform thickness, the peak of the intensity of the x-ray diffraction pattern of the platinum will track that of the palladium. Figure 6 schematically shows an output representation 40 that includes a curve 80 of a resulting overall x-ray diffraction pattern of a sample of material 22 after it has been exposed to hydrogen. In this example, the curve 80 includes a single peak 82 at a position that indicates that the palladium is fully charged with hydrogen. As can be appreciated from the illustration, the curve 80 is generally symmetric about the line 84, which indicates that the curve is generally symmetric about the peak 82 without noticeable shoulders. This symmetry and the peak position indicate that the resulting x-ray diffraction pattern of the platinum tracked that of the palladium. This indicates that the platinum has a desired characteristic, such as being a monolayer of platinum of a consistent, desired thickness.

[00029] One example includes setting a minimum threshold or tolerance level within which a shift between the peaks resulting from irradiating the platinum and the palladium are considered acceptable. An exact match between the peaks is not always required for making a determination that the material has a desired platinum characteristic. Given this description, those skilled in the art will be able to set an acceptable tolerance for determining when the platinum of the material has desired characteristics.

[00030] The disclosed example apparatus and technique allow for analyzing a material that includes platinum and palladium. The disclosed example makes it possible to determine whether a platinum coating on a palladium core has desired characteristics. The disclosed example is useful, for example, for determining whether a material made from a batch process is of an acceptable quality for using that material to make catalysts for use in fuel cells. It follows that the disclosed example facilitates realizing improved economies for making catalysts that are useful for facilitating electrochemical reactions within fuel cells.

[00031] The disclosed example apparatus and method are not limited to characterize palladium-platinum materials. They can also be used to characterize materials consisting of other materials exhibiting x-ray diffraction patterns.

[00032] The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.

Claims

CLAIMS I claim:

1. A method of analyzing a material, comprising the steps of:

exposing the material to hydrogen;

irradiating the hydrogen-exposed material;

determining a characteristic of the material based on a result of the irradiation.

2. The method of claim 1, wherein the material includes platinum and palladium and determining the characteristic comprises

determining a characteristic of the platinum of the material based on the result of the irradiation.

3. The method of claim 2, comprising

determining whether a platinum layer over the palladium has a desired consistency based on the result of the irradiation.

4. The method of claim 3, comprising

determining whether the platinum layer is a consistent monolayer.

5. The method of claim 3, comprising

determining whether the result of the irradiation indicates that the platinum layer includes at least one of platinum clusters or an undesired thickness.

6. The method of claim 1 , wherein exposing the material to hydrogen comprises placing the material in a chamber;

introducing hydrogen of a selected concentration into the chamber; and allowing the material to be exposed to the hydrogen in the chamber for a time sufficient to form a hydride prior to performing the irradiating.

7. The method of claim 1, comprising

irradiating the material prior to exposing the material to the hydrogen;

obtaining a first irradiation result pattern from irradiating the material prior to exposing the material to the hydrogen;

obtaining a second irradiation result pattern from irradiating the hydrogen- exposed material; and

determining the characteristic based on difference between the first and second irradiation result patterns.

8. The method of claim 1, wherein

the irradiating comprises using x-ray radiation; and

the result of the irradiation comprises an x-ray diffraction pattern.

9. The method of claim 8, wherein the material includes platinum and palladium and the method comprises

determining whether an intensity of the x-ray diffraction pattern indicates a difference between a first peak intensity corresponding to palladium x-ray diffraction and a second peak intensity corresponding to platinum x-ray diffraction.

10. The method of claim 9, comprising

determining a shift between the first and second peak intensities; and determining that the platinum of the material has a desired characteristic when the shift is below an acceptable shift tolerance; or

determining that the platinum of the material has an undesirable characteristic when the shift exceeds the acceptable shift tolerance.

11. The method of claim 9, comprising

determining whether a curve representing an overall x-ray diffraction pattern of the material includes a single peak; and

determining that the platinum of the material has a desired characteristic when the curve is generally symmetric about a single peak of the curve; or

determining that the platinum of the material has an undesirable characteristic when the curve is not symmetric about a peak in the curve or there is more than one peak.

12. The method of claim 1, comprising

performing the irradiating while the material is exposed to the hydrogen.

13. An apparatus for analyzing a material, comprising:

a chamber configured to contain a sample of the material;

an inlet to the chamber configured for introducing hydrogen into the chamber for exposing the material in the chamber to hydrogen;

a source of radiation; and

an output device configured to provide a representation of a result of irradiating the material, the representation indicating a characteristic of the material.

14. The apparatus of claim 13, wherein

the material includes platinum and palladium; and

the representation from the output device provides an indication whether a platinum layer over the palladium has a desired consistency.

15. The apparatus of claim 14, wherein the representation provides an indication whether the platinum layer is a consistent monolayer.

16. The apparatus of claim 14, wherein the representation provides an indication whether the platinum layer includes at least one of platinum clusters or an undesired thickness.

17. The apparatus of claim 13, wherein the representation corresponds to an x-ray diffraction pattern.

18. The apparatus of claim 17, wherein

the material includes platinum and palladium; and

the representation indicates a difference between a first peak intensity corresponding to palladium x-ray diffraction and a second peak intensity corresponding to platinum x-ray diffraction.

19. The apparatus of claim 18, wherein

the representation indicates a shift between the first and second peak intensities;

the platinum of the material has a desired characteristic when the shift is below an acceptable shift tolerance; and

the platinum of the material has an undesirable characteristic when the shift exceeds the acceptable shift tolerance.

20. The apparatus of claim 18, wherein

the representation comprises a curve representing an overall x-ray diffraction pattern of the material;

the platinum of the material has a desired characteristic when the curve is generally symmetrical about a single peak in the curve; and

the platinum of the material has an undesirable characteristic when the curve is not symmetric about a peak in the curve or there is more than one peak in the curve.