Polymer electrolyte membrane fuel cell including tungsten oxide coated components and method of manufacturing same

Abstract

The present invention relates to a polymer electrolyte membrane fuel cell including a tungsten oxide-coated part, which is characterized in that the surface of at least one of the membrane electrode assembly, gas diffusion layer, and separator constituting the unit cell is coated with tungsten oxide, and a method for manufacturing the same. The present invention has the advantages of being able to prevent the generation of high voltage that occurs under start-up / shutdown conditions of the fuel cell while still using a platinum (Pt / C) catalyst that has been conventionally used in polymer electrolyte membrane fuel cells, thereby reducing carbon oxidation and ensuring the durability of the catalyst and cell, and being able to maintain performance without a decrease in current density even under start-up / shutdown conditions.

Description

[Technical Field]

[0001] The present invention relates to a polymer electrolyte membrane fuel cell including a tungsten oxide-coated component and a manufacturing method thereof. Specifically, the present invention relates to a polymer electrolyte membrane fuel cell including a unit cell composed of a membrane electrode assembly (MEA) in which an electrolyte membrane and a catalyst layer are integrally bonded, a gas diffusion layer, and a separator, wherein the surface of at least one of the membrane electrode assembly, gas diffusion layer, and separator constituting the unit cell is coated with tungsten oxide, and a manufacturing method thereof. [Background technology]

[0002] During start-up and shutdown of a polymer electrolyte membrane fuel cell (PEMFC), residual oxygen at the anode causes an abnormal oxygen reduction reaction at the anode. This reaction causes a high voltage outside the normal voltage range across the cell, which corrodes the carbon support of the platinum (Pt / C) catalyst that makes up the cathode, resulting in durability issues. Various solutions have been proposed to resolve this issue, and Patent Document 1 provides a fuel cell separator that is not only thin and lightweight but also has excellent conductivity and corrosion resistance, as well as a manufacturing method thereof.

[0003] Meanwhile, the development of a selective catalyst that prevents the oxygen reduction reaction at the anode, which is the ultimate cause of problems that occur under start-up / shutdown conditions, and only promotes the hydrogen oxidation reaction, which should be promoted, has been attracting the most attention in recent years. Among such selective catalysts, Pt / H, which is platinum supported on tungsten oxide, is one of the most popular. x The WO3 catalyst has attracted attention in academic circles after being introduced in recent academic journals, and it has the advantages of being excellent in both performance and durability. xWhen WO3 catalyst is actually commercialized, it must be chemically synthesized, which involves more randomness than mechanical processes, and therefore the quality stability, i.e., the quality of the catalyst with respect to its selectivity function, is not stable. Furthermore, the use of tungsten oxide, a non-conductive material, as a support leads to instability in quality, which causes problems such as a decrease in the performance and durability of fuel cells.

[0004] Currently, platinum (Pt / C) catalysts are being commercialized for both the anode and cathode. x The use of WO3 catalyst requires significant changes compared to the existing manufacturing process that uses platinum (Pt / C) catalyst, and therefore the existing manufacturing process cannot be utilized, so limitations remain in commercialization and application.

[0005] Therefore, there is a need to develop a highly efficient and durable polymer electrolyte membrane fuel cell and a manufacturing process thereof that utilizes a tungsten oxide material that has stable quality, can increase catalyst selectivity, and can improve fuel cell efficiency and durability, and can be easily applied to existing manufacturing processes rather than requiring a separate process. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been devised to solve the problems and limitations of the prior art as described above, and the object of the present invention is to provide a polymer electrolyte membrane fuel cell and a manufacturing method thereof that prevent the oxygen reduction reaction at the anode, which is the ultimate cause of problems that occur under start-up / shutdown conditions in polymer electrolyte membrane fuel cells, and cause only the hydrogen oxidation reaction to occur, thereby maintaining the efficiency of the fuel cell and preventing corrosion of the platinum catalyst (Pt / C), thereby improving durability. [Means for solving the problem]

[0007] The polymer electrolyte membrane fuel cell including a tungsten oxide-coated part according to the present invention is a polymer electrolyte membrane fuel cell including a unit cell composed of a membrane electrode assembly (MEA) in which an electrolyte membrane and a catalyst layer are integrally bonded, a gas diffusion layer, and a separator, and is characterized in that the surface of at least one of the membrane electrode assembly, gas diffusion layer, or separator constituting the unit cell is coated with tungsten oxide.

[0008] At this time, the tungsten oxide is preferably deposited and coated to a thickness of 450 to 500 nm, because if the thickness of the coated tungsten oxide is less than 450 nm, the amount of intercalation is insufficient, limiting the improvement of fuel cell performance, and if the thickness exceeds 500 nm, the non-conductive characteristics of tungsten oxide become dominant, resulting in poor conductivity.

[0009] Meanwhile, the deposition is performed by physical vapor deposition (PVD), but can also be performed by sputtering or electron beam evaporation.

[0010] Furthermore, in the present invention, it is more preferable that the surface of the membrane electrode assembly (MEA) among the components constituting the polymer electrolyte membrane fuel cell is coated with tungsten oxide.

[0011] According to another aspect of the present invention, a method for manufacturing a polymer electrolyte membrane fuel cell including a tungsten oxide-coated component includes: a membrane electrode assembly forming step of forming a membrane electrode assembly by forming catalyst layers on both sides of a polymer electrolyte membrane; a membrane electrode assembly coating step of depositing and coating tungsten oxide by physical vapor deposition on the surface of the membrane electrode assembly formed through the membrane electrode assembly forming step; a gas diffusion layer coating step, which is performed simultaneously with or before or after the membrane electrode assembly coating step, of depositing and coating tungsten oxide on the surface of a gas diffusion layer by physical vapor deposition; a separator coating step, which is performed simultaneously with or before or after the membrane electrode assembly coating step, of depositing and coating tungsten oxide on the surface of a separator by physical vapor deposition; and a fuel cell assembling step of assembling unit cells including at least one of the membrane electrode assemblies, gas diffusion layers, and separators coated with tungsten oxide to form a polymer electrolyte membrane fuel cell including the unit cells.

[0012] Specifically, the membrane electrode assembly forming step includes a catalyst coating step of coating a catalyst slurry on the surface of an imide film and drying the coating; and a catalyst layer forming step of attaching the catalyst-coated imide films to the front and back of a polymer electrolyte membrane, laminating them, and then applying external pressure and heat to transfer the catalyst to the front and back of the polymer electrolyte membrane to form catalyst layers, and then removing the imide films.

[0013] Preferably, the physical vapor deposition performed in the membrane electrode assembly coating step, the gas diffusion layer coating step, and the separator coating step is either sputtering or electron beam deposition. [Effects of the Invention]

[0014] The present invention uses the platinum (Pt / C) catalyst that has traditionally been used in polymer electrolyte membrane fuel cells, but prevents the generation of high voltage that occurs under start-up / shutdown conditions of the fuel cell, reduces carbon oxidation reactions, and ensures the durability of the catalyst and cell. It also has the advantage of maintaining performance without a decrease in current density under start-up / shutdown conditions.

[0015] Furthermore, the present invention has another advantage in that it is economically advantageous because it can improve performance retention and durability under start-up / shutdown conditions by simply adding a step of vapor-depositing tungsten oxide onto the surface of one of the fuel cell components while still using the platinum (Pt / C) catalyst that has been commercially available. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing all the steps of a method for producing a polymer electrolyte membrane fuel cell including a tungsten oxide coated part according to the present invention. [Figure 2] Figure 2 shows a comparison of the surface conditions before and after tungsten oxide was vapor-deposited onto the surface of each part using sputtering. [Figure 3] FIG. 3 shows the structure of a polymer electrolyte membrane fuel cell and the deposition position of tungsten oxide. [Figure 4] Figure 4 shows the results of an experiment comparing the performance of a fuel cell constructed by coating tungsten oxide on the separator (BP), gas diffusion layer (GDL), and membrane electrode assembly (MEA) that make up a polymer electrolyte membrane fuel cell under start-up / shutdown conditions with that constructed by using a conventional platinum (Pt / C) catalyst without coating the components with tungsten oxide. [Figure 5]FIG. 5 shows the results of a Dynamic Hydrogen Electrode (DHE) experiment conducted on the fuel cells fabricated according to the comparative example and the example to determine whether a high voltage of 1.5 V, which causes a carbon oxidation reaction in a cell, is instantaneously applied under start / stop conditions. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0018] FIG. 1 shows all the steps of the method for producing a polymer electrolyte membrane fuel cell including a tungsten oxide coated component according to the present invention.

[0019] The membrane electrode assembly forming step S100 is a step of forming a membrane electrode assembly by forming catalyst layers on the front and back surfaces of a polymer electrolyte membrane. Specifically, the process includes a catalyst application step S110 of applying a catalyst slurry to the surface of an imide film and drying it, and a catalyst layer forming step S120 of attaching the catalyst-coated imide films to the front and back surfaces of the polymer electrolyte membrane, laminating them, and then applying external pressure and heat to transfer the catalyst to the front and back surfaces of the polymer electrolyte membrane to form catalyst layers, followed by removing the imide films.

[0020] In this embodiment, platinum (Pt / C) was used as the catalyst material for constructing the membrane electrode assembly (MEA), and 40 wt% of commercial platinum (Pt / C) catalyst was applied to the oxidation electrode (anode) at a concentration of 0.1 mg / cm. 2 The cathode is supported at 0.4 mg / cm 2 The polymer electrolyte membrane in the membrane electrode assembly (MEA) was made of Nafion 211.

[0021] In the step of coating the membrane electrode assembly (S200), tungsten oxide is deposited and coated on the surface of the membrane electrode assembly (MEA) formed through the step of forming the membrane electrode assembly (S200) by physical vapor deposition. Physical vapor deposition (PVD) can be performed by sputtering or electron beam deposition, and in this embodiment, tungsten oxide is deposited on the surface of the membrane electrode assembly to a thickness of about 500 nm by sputtering.

[0022] Meanwhile, the gas diffusion layer coating step S300 and the separator coating step S400 can be performed simultaneously with the membrane electrode assembly coating step S200, or separately before or after the step S200. In this embodiment, the membrane electrode assembly, gas diffusion layer, and separator were placed together in a sputtering chamber, and tungsten oxide was deposited and coated to a thickness of about 500 nm on each surface by sputtering. The separator (Bipolar Plate, BP) used was a serpentine type with channels 1 mm deep and wide and made of graphite material with no coating on the surface.

[0023] The gas diffusion layer (GDL) was made of porous carbon with a waterproof surface treatment of 20% PTFE.

[0024] Thereafter, in the fuel cell assembling step S500, a unit cell is assembled including at least one of the tungsten oxide coated membrane electrode assembly, the gas diffusion layer, and the separator, and then a polymer electrolyte membrane fuel cell including the unit cell is constructed.

[0025] Figure 2 compares the surface conditions of each component before and after tungsten oxide deposition coating using sputtering, and Figure 3 shows the structure of a polymer electrolyte membrane fuel cell and the location of tungsten oxide deposition.

[0026] Figure 2 compares the conditions before and after tungsten oxide is deposited on the surface of each component, shown at the top and bottom: a and d show a comparison of the conditions before and after tungsten oxide is deposited on the surface of the separator to form a coating layer, b and e show a comparison of the conditions before and after tungsten oxide is deposited on the surface of the gas diffusion layer to form a coating layer, and c and f show a comparison of the conditions before and after tungsten oxide is deposited on the surface of the membrane electrode assembly (MEA) to form a coating.

[0027] More specifically, Fig. 2(a), (b), and (c) show the surfaces of the separator (BP), gas diffusion layer (GDL), and membrane electrode assembly (MEA), respectively, before tungsten oxide was deposited thereon, and Fig. 2(d), (e), and (f) show the surfaces of the separator (BP), gas diffusion layer (GDL), and membrane electrode assembly (MEA), respectively, after tungsten oxide was deposited thereon.

[0028] 3 shows the structure of a polymer electrolyte membrane fuel cell and the deposition position of tungsten oxide. Referring to FIG. 3, the polymer electrolyte membrane fuel cell includes a first current collector 310, a first separator (BP) 320 including an anode flow path, a first gas diffusion layer (GDL) 330, a first gasket 340, a membrane electrode assembly (MEA) 350, a second gas diffusion layer 360, a second gasket 370, a second separator 380 including a cathode flow path, and a second current collector. In this case, the first separator (BP) 320 including an anode flow path, the first gas diffusion layer (GDL) 330, the membrane electrode assembly (MEA) 350, the second gas diffusion layer 360, and the second separator 380 including a cathode flow path are stacked in order.

[0029] In this case, tungsten oxide may be deposited in the oxidation electrode flow path of the first separator 320 as shown in Fig. 3a. Alternatively, tungsten oxide may be deposited between the first gas diffusion layer 330 and the membrane electrode assembly 350 on the first gas diffusion layer 330 side or the membrane electrode assembly 350 side as shown in Fig. 3b. In this case, Fig. 3a corresponds to Fig. 2d, Fig. 3b corresponds to Fig. 2e, and Fig. 3c corresponds to Fig. 2f.

[0030] By comparing images before and after tungsten oxide is vapor-deposited onto the surface of each part to form a coating layer, it is easy to visually confirm that the tungsten oxide layer has formed and the color has changed.

[0031] Figure 4 shows the results of an experiment comparing the performance of a fuel cell constructed by coating tungsten oxide on the separator (BP), gas diffusion layer (GDL), and membrane electrode assembly (MEA) that make up a polymer electrolyte membrane fuel cell under start-up / shutdown conditions with that constructed by using a conventional platinum (Pt / C) catalyst without coating the components with tungsten oxide.

[0032] In the case of a polymer electrolyte membrane fuel cell, which is composed only of parts that have no coating but have tungsten oxide deposited on their surfaces, it is composed of an anode, a separator made of uncoated graphite material, a gas diffusion layer made of porous carbon with a PTFE (Poly Tetra Fluoro Ethylene) coating on its surface, and a membrane electrode assembly (MEA) and a cathode with platinum (Pt / C) catalyst bonded to the front and back of the polymer electrolyte membrane, respectively.

[0033] In contrast to this conventional polymer electrolyte membrane fuel cell (Comparative Example, a), the performance of a fuel cell employing a separator surface coated with tungsten oxide to a thickness of 500 nm (Example 1, b), a fuel cell employing a gas diffusion layer surface coated with tungsten oxide to a thickness of 500 nm (Example 2, c), and a fuel cell employing a membrane electrode assembly (MEA) surface coated with tungsten oxide to a thickness of 500 nm (Example 3, d) was compared at a current density of approximately 0.6 V.

[0034] In this experiment, basic performance was measured under conditions of a cell temperature of 70°C and 100% relative humidity. The start-up / shutdown protocol test was conducted by flowing hydrogen to the oxidation electrode and oxygen to the reduction electrode under normal operating conditions, and flowing oxygen to the oxidation electrode until the open circuit voltage (OCV) dropped to 0.2V under start-up / shutdown conditions, with one cycle being considered, and the fuel cell performance was evaluated after 100 cycles.

[0035] As shown in FIG. 4a, in the start / stop protocol test, the current density was measured under the condition of maintaining 0.6 V for a conventional fuel cell using only a platinum catalyst according to the comparative example. At the beginning of the test, the current density was 0.95 A / cm 2 However, after 100 cycles of start / stop protocol, it was 0.25A / cm 2 On the other hand, as shown in Figure 4b, the results of an experiment on the fuel cell according to Example 1 under the same operating conditions showed that the decrease in current density after 100 cycles of the start-up / shutdown protocol was small, confirming that the performance of the cell itself did not deteriorate, but that the electrical resistance was large and the initial performance itself was not high. Furthermore, as shown in Figure 4c, the results of an experiment on the fuel cell according to Example 2 showed that the decrease in current density after 100 cycles of the start-up / shutdown protocol was also small, and the performance decrease was less than that of the fuel cell of the comparative example, but not at a level that was significantly different.

[0036] Meanwhile, referring to FIG. 4d, the decrease in current density before and after the experiment was measured for the fuel cell according to Example 3 under the same conditions and by the same method as those used for the Comparative Example and the Example. As a result, it was confirmed that the fuel cell manufactured according to Example 3, i.e., the fuel cell having a tungsten oxide vapor-deposited coating on the surface of the membrane electrode assembly (MEA), showed almost no decrease in current density even after 100 cycles of the start / stop protocol, and no degradation in performance occurred.

[0037] FIG. 5 shows the results of a Dynamic Hydrogen Electrode (DHE) experiment conducted on the fuel cells prepared according to the comparative example and the example to determine whether a high voltage of 1.5 V, which causes a carbon oxidation reaction in a cell, is instantaneously applied under start / stop conditions.

[0038] This experiment involved observing the potential profile for 100 seconds. The experiment was started under normal operating conditions, and after 30 seconds, the conditions were switched to start / stop conditions to check whether a high voltage of 1.5V was generated in the cell, which could cause a carbon oxidation reaction in the fuel cell and reduce the durability of the platinum (Pt / C) catalyst.

[0039] FIG. 5a shows the results of an experiment on a conventional fuel cell using the platinum catalyst manufactured according to the comparative example, and FIGS. 5b to 5d show the results of experiments on fuel cells manufactured according to Examples 1 to 3, respectively, under similar conditions and methods.

[0040] According to the results of this experiment, it was confirmed that in the case of a normal fuel cell according to the comparative example, the voltage within the cell rose sharply to 1.5 V, whereas in the case of the fuel cells manufactured according to Examples 1 to 3, even when the same experiment was performed, it was confirmed that the voltage of the cell itself did not rise sharply to 1.5 V.

[0041] Therefore, in the case of the polymer membrane fuel cell according to the present invention, even if the normal operating state is suddenly changed to a start-up / shutdown condition, the voltage inside the cell does not rise suddenly, and the occurrence of a carbon oxidation reaction that reduces the durability of the catalyst can be prevented, thereby maintaining the durability of the fuel cell.

Claims

1. A polymer electrolyte membrane fuel cell including a unit cell composed of a membrane electrode assembly (MEA) in which an electrolyte membrane and a catalyst layer are integrally bonded, a gas diffusion layer, and a separator, a surface of at least one of a membrane electrode assembly, a gas diffusion layer, and a separator constituting the unit battery is coated with tungsten oxide; A polymer electrolyte membrane fuel cell including a tungsten oxide coated component, wherein the tungsten oxide is a vapor-deposited layer having a thickness of 450 to 500 nm.

2. 2. The polymer electrolyte membrane fuel cell comprising the tungsten oxide coated part according to claim 1, wherein the surface of the membrane electrode assembly is coated with tungsten oxide.

3. forming a membrane electrode assembly by forming catalyst layers on the front and back surfaces of the polymer electrolyte membrane; a coating step of depositing and coating tungsten oxide on the surface of the membrane electrode assembly formed by the forming step of the membrane electrode assembly by physical vapor deposition; a gas diffusion layer coating step, which is performed simultaneously with or before or after the membrane electrode assembly coating step, and deposits and coats tungsten oxide on the surface of the gas diffusion layer by physical vapor deposition; a separator coating step, which is performed simultaneously with or before or after the membrane electrode assembly coating step, of depositing and coating tungsten oxide on the surface of the separator by physical vapor deposition; a fuel cell assembly step of assembling a unit cell including at least one of a membrane electrode assembly, a gas diffusion layer, and a separator coated with tungsten oxide, and then constructing a polymer electrolyte membrane fuel cell including the unit cell; Including, The tungsten oxide is deposited and coated to a thickness of 450 to 500 nm.

4. The step of forming a membrane electrode assembly includes: a catalyst coating step of coating a catalyst slurry on the surface of the imide film and drying the same; a catalyst layer forming step of attaching and laminating catalyst-coated imide films to the front and back of a polymer electrolyte membrane, and then transferring the catalyst to the front and back of the polymer electrolyte membrane by applying external pressure and heat to form catalyst layers, and then removing the imide films; 4. A method for manufacturing a polymer electrolyte membrane fuel cell including the tungsten oxide coated part according to claim 3, comprising:

5. 5. The method for manufacturing a polymer electrolyte membrane fuel cell including a tungsten oxide coated part according to claim 3 or 4, wherein the physical vapor deposition performed in the steps of coating the membrane electrode assembly, coating the gas diffusion layer, and coating the separator is either sputtering or electron beam evaporation.

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