Fuel cell stack

Abstract

The present disclosure relates to a fuel cell stack having a cathode-side separator and an anode-side separator which are made of different materials to prevent performance degradation of stacks and corrosion and damage of components. A fuel cell stack according to exemplary embodiments of the present disclosure may have multiple unit cells stacked therein, in which each unit cell of the multiple unit cells may include: a membrane electrode assembly (MEA); a pair of gas diffusion layers (GDLs) disposed on opposite surfaces of the MEA; and an anode-side separator and a cathode-side separator disposed to face each other, the MEA and the pair of GDLs being disposed therebetween, in which the cathode-side separator has a corrosion resistance higher than a corrosion resistance of the anode-side separator.

Claims

1. A fuel cell stack having multiple unit cells stacked therein, wherein each unit cell of the multiple unit cells includes: a membrane electrode assembly (MEA); a pair of gas diffusion layers (GDLs) disposed on opposite surfaces of the MEA; and an anode-side separator and a cathode-side separator disposed to face each other, the MEA and the pair of GDLs being disposed therebetween, wherein each unit cell of the multiple unit cells includes the anode-side separator and the cathode-side separator having different corrosion resistances from each other, a metal constituting the cathode-side separator has a corrosion resistance higher than a metal constituting the anode-side separator, and the number of unit cells that include the anode-side separator and the cathode-side separator having different corrosion resistances from each other is more than or equal to one unit cell and less than or equal to 10% of an entire number of the multiple unit cells.

2. The fuel cell stack of claim 1, wherein each unit cell of the multiple unit cells includes the anode-side separator and the cathode-side separator having different corrosion resistances from each other, and the anode-side separator has a thermal expansion coefficient greater than a thermal expansion coefficient of the cathode-side separator.

3. The fuel cell stack of claim 1, wherein each unit cell of the multiple unit cells includes the anode-side separator and the cathode-side separator having different corrosion resistances from each other, and the anode-side separator includes austenitic stainless steel and the cathode-side separator includes ferritic stainless steel.

4. The fuel cell stack of claim 1, wherein each unit cell of the multiple unit cells includes the anode-side separator and the cathode-side separator having different corrosion resistances from each other, and the anode-side separator includes aluminum or aluminum alloy and the cathode-side separator includes titanium or titanium alloy.

5. The fuel cell stack of claim 1, wherein the anode-side separator is configured with multiple channels guiding flows of fuel gas and coolant, and the cathode-side separator is configured with multiple channels guiding flows of air and the coolant.

6. The fuel cell stack of claim 1, wherein the anode-side separator is configured with multiple channels guiding flows of fuel gas and coolant, and the cathode-side separator is configured with porous bodies disposed toward the GDLs and a flat plate supporting the porous bodies, wherein the porous bodies and the flat plate of the cathode-side separator are configured to have multiple channels through which air flows, and wherein the porous bodies and the flat plate include a same material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The fuel cell stack of the present disclosure have other features and other advantages of the present disclosure which will be apparent from or set forth in more detail in the following detailed description and the accompanying drawings, which together serve to explain certain principles of the present disclosure. The accompanying drawings are as follows:

(2) FIGS. 1 and 2 are views each illustrating a configuration of a fuel cell stack having unit cells stacked therein according to the related art;

(3) FIGS. 3 and 4 are views each illustrating a configuration of a fuel cell stack having unit cells stacked therein according to exemplary embodiments of the present disclosure;

(4) FIG. 5A is a graph illustrating a result of measuring stack performance five times for a fuel cell according to Example;

(5) FIG. 5B is a graph illustrating a result of measuring stack performance five times for a fuel cell stack according to Comparative Example;

(6) FIG. 6 is a graph illustrating a result of measuring performance of a stack in which unit cells including separators prepared according to Example and Comparative Example are stacked in one single stack; and

(7) FIG. 7 is a graph illustrating a result of measuring voltage values of a stack including unit cells stacked therein and having the separators prepared according to the Example and voltage values of a stack including unit cells stacked therein and having the separators prepared according to the Comparative Example, with respect to current density.

(8) It may be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the disclosure. The specific design features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particularly intended application and use environment.

(9) In the figures, reference numbers refer to the same or equivalent parts of the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

(10) Hereinbelow, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. While the present disclosure will be described in conjunction with exemplary embodiments thereof, it is to be understood that the present description is not intended to limit the present disclosure to those exemplary embodiments. On the contrary, the present disclosure is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents, and other embodiments that may be included within the spirit and scope of the present disclosure as defined by the appended claims. Throughout the drawings, the same reference numerals will refer to the same or like parts.

(11) FIGS. 3 and 4 are views each illustrating a configuration of a fuel cell stack in which unit cells are stacked according to exemplary embodiments of the present disclosure.

(12) As illustrated in FIG. 3, a fuel cell stack according to an exemplary embodiment of the present disclosure is configured such that multiple unit cells are stacked.

(13) Each unit cell includes: a membrane electrode assembly (MEA) 10; a pair of gas diffusion layers (GDLs) 20 disposed on opposite surfaces of the MEA 10; an anode-side separator 100 and a cathode-side separator 200 that are disposed to face each other between the MEA 10 and the pair of GDLs 20.

(14) The MEA 10 is implemented as a general MEA which is configured with a proton-exchange membrane (PEM) allowing protons to pass therethrough, and catalyst layers, i.e., a cathode and an anode, provided on opposite surfaces of the PEM.

(15) The pair of GDLs 20 serves to diffuse fuel gas and air flowing through the anode-side separator 100 and the cathode-side separator 200 to the MEA 10 and facilitate flow of product water.

(16) The anode-side separator 100 is disposed to come into contact with a GDL 20 of a region where the anode is disposed (hereinafter, referred to as ‘anode side’) to guide the flow of the fuel gas. As illustrated in FIG. 3, the anode-side separator 100 is configured with multiple channels 105 guiding the flow of the fuel gas. Here, a flow of coolant is guided to flow to the opposite side of the flow of the fuel gas.

(17) The cathode-side separator 200 is disposed to come into contact with a GDL 20 of a region where the cathode is disposed (hereinafter, referred to as ‘cathode region’) to guide the flow of air reacting with the fuel gas. Like the anode-side separator 100, the cathode-side separator 200 is configured with multiple channels 205 guiding flow of air and providing a path for discharging the product water. Here, the flow of the coolant is guided to flow to the opposite side of the flow of air.

(18) Meanwhile, since multiple unit cells are stacked to configured one fuel cell stack, the anode-side separator 100 of any one unit cell is arranged and stacked to face the cathode-side separator 200 of an adjacent unit cell, as illustrated in FIG. 3.

(19) This exemplary embodiment has been proposed to improve corrosion resistance and minimize performance degradation of the fuel cell stack. Accordingly, in consideration of characteristics of the fuel cell stack having different operating environments for the anode side and the cathode side with respect to the MEA 10, the anode-side separator 100 and the cathode-side separator 200 are made of different materials. In addition, at least the cathode-side separators 200 constituting unit cells disposed in opposite end portions of stacked unit cells, i.e., unit cells disposed adjacent to end plates (not illustrated) disposed at opposite ends of the fuel cell stack, are required to have excellent corrosion resistance compared with anode-side separators 100 constituting the same. Accordingly, in this exemplary embodiment, a metal constituting the cathode-side separator 200 has excellent corrosion resistance compared with a metal constituting the anode-side separator 100.

(20) In addition, in this exemplary embodiment, at least the anode-side separators 100 constituting unit cells disposed in the opposite end portions of the stacked unit cells are required to have a thermal expansion coefficient greater than the cathode-side separator 200 constituting the same. Accordingly, in this exemplary embodiment, the metal constituting the anode-side separator 100 has a thermal expansion coefficient greater than the metal constituting the cathode-side separator 200.

(21) For example, a unit cell in which the separators of different materials are used is configured such that the anode-side separator 100 is formed of austenitic stainless steel (300 series stainless steel) having a relatively great thermal expansion coefficient and the cathode-side separator 200 is formed of ferritic stainless steel (400 series stainless steel) having relatively excellent corrosion resistance. In addition, the unit cell in which the separators of different materials are used is configured such that the anode-side separator 100 is formed of aluminum or aluminum alloy and the cathode-side separator 200 is formed of titanium or titanium alloy.

(22) Here, surfaces of the anode-side separator 100 and the cathode-side separator 200 may be coated with an element having excellent conductivity to obtain conductivity of the anode-side separator 100 and the cathode-side separator 200. For example, the surfaces of the anode-side separator 100 and the cathode-side separator 200 are coated with an element such as gold (Au) and carbon.

(23) Meanwhile, the separators of different materials may be applied to all unit cells stacked for the implementation of a fuel cell stack, but it is preferable that the separators of different materials are applied to only unit cells disposed adjacent to the end plates in which corrosion occurs and excessive pressure is applied on the contact face. Here, it is preferable that the separators of different materials are applied to 10% or less of the total unit cells. This is because, in a region, which accounts for about 10% of the stack and is adjacent to the end plates, mainly product water is accumulated and a side reaction in which H.sub.2O.sub.2 is produced rather than H2O occurs such that the region is more exposed to the corrosion-inducing environment.

(24) Meanwhile, a fuel cell stack of the present disclosure may be configured such that a shape of the separator is different from that of the fuel cell stack described above.

(25) As illustrated in FIG. 4, a fuel cell stack according to another exemplary embodiment of the present disclosure is configured such that multiple unit cells are stacked as is the fuel cell stack described above. Each unit cell includes: a MEA 10; a pair of GDLs 20 disposed on opposite surfaces of the MEA 10; an anode-side separator 100 and a cathode-side separator 300 that are disposed to face each other between the MEA 10 and the pair of GDLs 20.

(26) Here, as in the above-described exemplary embodiment, the anode-side separator 100 is disposed to come into contact with a GDL 20 of an anode side to guide the flow of the fuel gas. As illustrated in FIG. 4, the anode-side separator 100 is configured with multiple channels 105 guiding the flow of the fuel gas. Here, a flow of coolant is guided to flow to the opposite side of the flow of the fuel gas.

(27) The cathode-side separator 300 is disposed to come into contact with a GDL 20 of a cathode side to guide the flow of air reacting with the fuel gas. The cathode-side separator 300 may be configured with porous bodies 320 disposed toward the GDLs 20 and a flat plate 310 supporting the porous bodies 320. The porous bodies 320 and the flat plate 310 of the cathode-side separator 300 are configured to have multiple channels 305 through which air flows. Here, it is preferable that the porous bodies 320 and the flat plate 310 are formed of the same material.

(28) As in the above-described exemplary embodiment, the porous bodies 320 and the flat plate 310 constituting the cathode-side separator 300 is required to have excellent corrosion resistance compared with the anode-side separator 100. Accordingly, in this exemplary embodiment, a metal constituting the porous bodies 320 and the porous bodies 320 has excellent corrosion resistance compared with a metal constituting the anode-side separator 100.

(29) In addition, the anode-side separator 100 is required to have a thermal expansion coefficient greater than that of the porous bodies 320 and the porous bodies 320. Accordingly, in this exemplary embodiment, the metal constituting the anode-side separator 100 has a thermal expansion coefficient greater than the metal constituting the porous bodies 320 and the porous bodies 320.

(30) For example, the anode-side separator 100 is formed of austenitic stainless steel (300 series stainless steel) having a relatively great thermal expansion coefficient and the porous bodies 320 and the flat plate 310 are formed of ferritic stainless steel (400 series stainless steel) having relatively excellent corrosion resistance.

(31) The fuel cell stack according to the exemplary embodiments of the present disclosure configured as described above will be described in comparison with Comparative Example.

(32) According to the Example, a fuel cell stack was manufactured such that an anode-side separator was made of SUS 304, which is a 300 series stainless steel having a relatively high thermal expansion coefficient, and a cathode-side separator was made of SUS 410, which is a 400 series stainless steel having a relatively low thermal expansion coefficient. On the other hand, according to the Comparative Example, a fuel cell stack was configured such that an anode-side separator and a cathode-side separator were made of SUS 410, which has a relatively low thermal expansion coefficient.

(33) Stack performance was measured five times for each of the prepared fuel cell stacks of the Example and the Comparative Example, and the results are illustrated in FIGS. 5A and 5B. FIG. 5A is the result of the fuel cell stack of the Example and FIG. 5B is the result of the fuel cell stack of the Comparative Example. Cell numbers were sequentially numbered from a unit cell adjacent to an end plate.

(34) FIG. 5A, shows a result of the test performed five times on the fuel cell stack of the Example, wherein the performance of all the unit cells tended to decrease slightly with each subsequent test. However, it was confirmed that the stack performance was mostly uniform in all the unit cells. FIG. 5B shows a result of the test performed five times on the fuel cell stack of the Comparative Example, wherein the performance of all the unit cells tended to decrease with each subsequent test. In particular, it was confirmed that the stack performance was degraded remarkably with each subsequent test for a unit cell disposed in a region close to the end plate.

(35) Next, unit cells having the separators prepared according to the Example and the Comparative Example were stacked together to configure one single stack, and performance of the stack was measured. The results are illustrated in FIG. 6. Here, unit cells numbered 1 to 10 were stacked whereby cell numbers 1 to 5 were unit cells having the separators prepared according to the Example, and cell numbers 6 to 10 were unit cells having the separators prepared according to the Comparative Example.

(36) As illustrated in FIG. 6, it was confirmed that the stack performance of the unit cells having the separators prepared according to the Example was excellent compared with the unit cells having the separators prepared according to the Comparative Example, even in the one single stack.

(37) Next, voltage values of a stack in which unit cells having the separators prepared according to the Example were stacked and of a stack in which unit cells having the separators prepared according to the Comparative Example were stacked were measured with respect to current density. The results are illustrated in FIG. 7.

(38) As illustrated in FIG. 7, it was confirmed that the voltage values of the Example were higher than those of the Comparative Example in almost all current density ranges.

(39) Accordingly, it was confirmed that when the anode-side separator and the cathode-side separator were made of materials having different thermal expansion coefficients as in the exemplary embodiments, the pressure applied to the contact face in the stack was prevented from being lowered such that the durability of the stack is maintained and the stack performance was excellent.

(40) The foregoing descriptions of specific exemplary embodiments of the present disclosure have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the inventive concept(s) to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described to explain certain principles of the present disclosure and their practical application, to enable others skilled in the art to make and utilize various exemplary embodiments of the present disclosure, as well as various alternatives and modifications thereof. It is intended that the scope of the inventive concept(s) be defined by the Claims appended hereto and their equivalents.