BIPOLAR PLATE FOR FUEL CELL AND FUEL CELL

Abstract

A bipolar plate for a fuel cell is provided. The bipolar plate for the fuel cell has a plurality of flow channels, and a rib is defined between neighboring two flow channels. A side surface of the rib is non-porous. A top surface of the rib may be a roughened surface in order to improve performance of the fuel cell.

Claims

1. A bipolar plate for a fuel cell, the bipolar plate comprising a plurality of flow channels, wherein a rib is defined between neighboring two of the flow channels, and the bipolar plate is characterized in that: a top surface of the rib is a roughened surface and a side surface of the rib is non-porous.

2. The bipolar plate for the fuel cell according to claim 1, wherein the roughened surface of the rib has a pore diameter of approximately 20 m to 200 m.

3. The bipolar plate for the fuel cell according to claim 1, wherein the roughened surface of the rib has a pore area fraction of approximately 50% to 90%.

4. The bipolar plate for the fuel cell according to claim 1, wherein the roughened surface of the rib has a roughness of approximately 0.1 m to 10 m.

5. The bipolar plate for the fuel cell according to claim 1, wherein a material of the bipolar plate comprises metal, graphite, or a composite material.

6. A bipolar plate for a fuel cell, the bipolar plate comprising a plurality of flow channels, wherein a rib is defined between neighboring two of the flow channels, and the bipolar plate is characterized in that: a top surface of the rib is a roughened surface, wherein the roughened surface of the rib is made through surface polishing and ultrasonic cavitation techniques or an electrical discharge processing technique.

7. The bipolar plate for the fuel cell according to claim 6, wherein the roughened surface of the rib has a pore diameter of approximately 20 m to 200 m.

8. The bipolar plate for the fuel cell according to claim 6, wherein the roughened surface of the rib has a pore area fraction of approximately 50% to 90%.

9. The bipolar plate for the fuel cell according to claim 6, wherein the roughened surface of the rib has a roughness of approximately 0.1 m to 10 m.

10. The bipolar plate for the fuel cell according to claim 6, wherein a material of the bipolar plate comprises metal, graphite, or a composite material.

11. A fuel cell, comprising: a plurality of bipolar plates, wherein each of the bipolar plates has a plurality of flow channels, and a rib is defined between neighboring two of the flow channels; and at least one membrane electrode assembly (MEA), disposed among the bipolar plates, wherein a top surface of the rib is a roughened surface and a side surface of the rib is non-porous.

12. The fuel cell according to claim 11, wherein the roughened surface of the rib has a pore diameter of approximately 20 m to 200 m.

13. The fuel cell according to claim 11, wherein the roughened surface of the rib has a pore area fraction of approximately 50% to 90%.

14. The fuel cell according to claim 11, wherein the roughened surface of the rib has a roughness of approximately 0.1 m to 10 m.

15. The fuel cell according to claim 11, wherein a material of the bipolar plate comprises metal, graphite, or a composite material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the disclosure.

[0010] FIG. 1A is a cross-sectional view of a conventional fuel cell.

[0011] FIG. 1B is an enlarged partial view of FIG. 1A.

[0012] FIG. 2 is a schematic cross-sectional view of a bipolar plate for a fuel cell according to a first exemplary embodiment.

[0013] FIG. 3 is a schematic cross-sectional view of a bipolar plate for a fuel cell according to a second exemplary embodiment.

[0014] FIG. 4 is a schematic cross-sectional view of a fuel cell according to a third exemplary embodiment.

[0015] FIG. 5A is a SEM picture of a bipolar plate in Reference Experiment.

[0016] FIG. 5B is a SEM picture of a bipolar plate in Experiment 1.

[0017] FIG. 5C is a SEM picture of a bipolar plate in Experiment 2.

[0018] FIG. 5D is a SEM picture of a bipolar plate in Experiment 3.

[0019] FIG. 6 is a polarization curve diagram of the fuel cells respectively using each of the bipolar plates provided in Reference Experiment and the Experiments on conditions of cell temperature at 66 C., the temperature of humidification being 60 C. at anode, and the temperature of humidification being 55 C. at cathode.

[0020] FIG. 7 is a polarization curve diagram of the fuel cells respectively using each of the bipolar plates provided in Reference Experiment and the Experiments on conditions of fuels with 65% RH and cell temperature at 70 C.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

[0021] FIG. 2 is a schematic cross-sectional view of a bipolar plate for a fuel cell according to a first exemplary embodiment.

[0022] With reference to FIG. 2, a bipolar plate 200 of the first exemplary embodiment has a plurality of flow channels 200a, wherein a rib 202 is defined between neighboring two of the flow channels 200a, and a top surface of the rib 202 is a roughened surface 202a. Further, if a pore diameter of the roughened surface 202a of the rib 202 is approximately between 20 m and 200 m, the fuel supply (lateral diffusion) capacity may be increased to improve overall performance of the fuel cell.

[0023] In the first exemplary embodiment, if a pore area fraction of the roughened surface 202a of the rib 202 is approximately between 50% and 90%, the fuel supply capacity may also be increased. The so-called pore area fraction is the result of the following formula:

A.sub.P/(A.sub.R+A.sub.P)100%

wherein A.sub.R denotes the area of the top surface of the rib 202; A.sub.P denotes the pore area of the roughened surface 202a of the rib 202.

[0024] In addition, in the first exemplary embodiment, if roughness of the roughened surface 202a of the rib 202 is approximately between 0.1 m and 10 m, the fuel supply capacity may also be increased to improve the overall performance of the fuel cell.

[0025] A side surface 202b of the rib 202 may be a flat surface but is not limited thereto. The flow channels 200a are generally formed through mechanical processing, so that the bipolar plate 200 is an integral structure.

[0026] In the first exemplary embodiment, a material of the bipolar plate 200 may be metal, graphite, or a composite material. For example, the material of the bipolar plate 200 may be metal, such as aluminum, titanium, stainless steel, and so on. A protection film may be formed on all surfaces of the bipolar plate 200 in order to prevent the metal from oxidation. For example, when the bipolar plate 200 is made of titanium, a titanium nitride thin film may be deposited on the surface of the bipolar plate 200 to prevent titanium from oxidation and to maintain the conductivity of titanium.

[0027] FIG. 3 is a schematic cross-sectional view of a bipolar plate for a fuel cell according to a second exemplary embodiment.

[0028] With reference to FIG. 3, a bipolar plate 300 of the second exemplary embodiment has a plurality of flow channels 300a, wherein a rib 302 is defined between neighboring two of the flow channels 300a. A top portion of the rib 302 has a porous structure 304 with hydrophobicity and a porosity range of, for example, 30%-80%. The thickness T.sub.0 of the porous structure 304 is approximately 1/10 to 3/10 of the thickness T.sub.r of the rib 302.

[0029] In the second exemplary embodiment, the porous structure 304 is composed of a conductive material and a hydrophobic material but is not limited thereto. The conductive material may be, for example, carbon black, graphite, carbon fiber, or metal; the hydrophobic material includes any proper material, such as tetrafluoroethylene and the likes. The addition amount of the hydrophobic material, for example, is less than 60 wt %. The material of the bipolar plate 300 may be referred to as those described in the first exemplary embodiment.

[0030] FIG. 4 is a schematic cross-sectional view of a fuel cell according to a third exemplary embodiment, wherein the reference numbers of the second exemplary embodiment are used to denote like or similar elements.

[0031] With reference to FIG. 4, the fuel cell of the third exemplary embodiment includes two bipolar plates 300 and a membrane electrode assembly (MEA) 400. The MEA 400 at least includes a membrane 402, a catalyst 404, and a gas diffusion layer (GDL) 406. The MEA 400 between the bipolar plates 300 is in contact with the bipolar plates 300 through the GDL 406. More particularly, a porous structure 304 on a top surface of a rib 302 is compressed in contact with the MEA 400. As such, not only the fuel supply (lateral diffusion) capacity may be increased, but also the conductivity between the rib 302 and the GDL 406 may be ensured. For example, the porosity of the porous structure 304 is in inverse proportion to the compression degree of the porous structure 304. The less the porosity, the greater the compression degree, and vice versa.

[0032] The so-called compression degree refers to the ratio of (T.sub.0T.sub.x)/T.sub.0, which is the original thickness T.sub.0 of the porous structure 304 minus the thickness T.sub.x after forming the fuel cell, and divided by the original thickness T.sub.0; for example, the compression degree of the porous structure 304 of the third exemplary embodiment is approximately between 40% and 80%.

[0033] Several experiments are described below to prove the efficacy of the above exemplary embodiments.

Reference Experiment

[0034] A graphite carbon plate is applied as a bipolar plate, and flow channels are formed on the bipolar plate through mechanical processing. The result is as shown in the SEM picture of FIG. 5A.

Experiment 1

[0035] Experiment 1 is similar to Reference Experiment. Namely, a graphite carbon plate is applied as a bipolar plate, except that after the flow channels are formed, the top surface of the rib is roughened through applying surface polishing and ultrasonic cavitation techniques. The result is as shown in the SEM picture of FIG. 5B. Upon comparison of FIG. 5A and FIG. 5B, it is known that the surface of the rib in contact with the MEA may be roughened through applying the surface treatment technique, and the pore diameter thereof is approximately 20 m.

Experiment 2

[0036] Experiment 2 is similar to Reference Experiment. Namely, a graphite carbon plate is applied as a bipolar plate except that after the flow channels are formed, the top surface of the rib is roughened through applying an electrical discharge processing technique. The result is as shown in the SEM picture of FIG. 5C. Upon comparison of FIG. 5A and FIG. 5C, it is known that the surface of the rib in contact with the MEA is roughened through applying the surface treatment technique, and the pore diameter thereof is greater than 50 m.

Experiment 3

[0037] Experiment 3 is similar to Reference Experiment. Namely, a graphite carbon plate is applied as a bipolar plate, except that after the flow channels are formed, the structure of the top portion of the rib is changed to a porous structure through applying a porous material lamination technique. The result of changing the surface portion of the rib is as shown in the SEM picture of FIG. 5D. In view of FIG. 5D, it is known that the porous material structure is composed of conductive carbon powder, carbon fiber, and hydrophobic material. The original porosity of the porous material is approximately 80%, while the hydrophobicity of the porous material is approximately 23%. After forming the fuel cell, the compression degree of the porous material is approximately 50%, while the porosity thereof is approximately 60%.

Measurement 1

[0038] Each pore area fraction of the bipolar plates is calculated from the SEM pictures of Reference Experiment and Experiments 1 and 2, and the roughness of the roughened surface of the rib of each of the bipolar plates is measured. The result is shown in TABLE 1 below.

TABLE-US-00001 TABLE 1 Reference Experiment Experiment 1 Experiment 2 Pore area fraction of the 5 63 77 rib surface (%) Average roughness Ra of 0.1~0.2 0.4~0.9 3.5~4.2 the rib surface (m)

Measurement 2

[0039] Each of the bipolar plates provided in Reference Experiment and Experiments 1-3 is composed together with a MEA to form single cells, and a performance test is carried out on each of the single cells.

[0040] FIG. 6 is a polarization curve diagram of the fuel cells respectively using each of the bipolar plates provided in Reference Experiment and the Experiments under a humidified environment, in which the temperature of cell is 66 C., the temperature of anodic humidification is 60 C. and the temperature of cathodic humidification is 55 C. In view of FIG. 6, it is apparent that the performance of the fuel cells in Experiments 1-3 is better than that in Reference Experiment.

[0041] FIG. 7 is a polarization curve diagram of the fuel cells respectively using each of the bipolar plates provided in Reference Experiment and the Experiments on conditions of fuels with 65% RH and cell temperature at 70 C. It is also apparent that the performance of the fuel cells in Experiments 1-3 is better than that in Reference Experiment.

[0042] In view of the above, the disclosure utilizes surface structure processing technique to roughen the surface of the rib and to form the porous structure thereof, so as to respectively improve transmission of electrons (by reducing contact resistance) and enhance the fuel supply (lateral diffusion) capacity. As such, the overall performance of the fuel cell may be improved.

[0043] It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.