Patent Application
20230335767
The present disclosure relates to a polymer electrolyte membrane fuel cell including a tungsten oxide-coated part and a method for manufacturing the same. Specifically, the disclosure pertains to a polymer electrolyte membrane fuel cell comprising a unit cell with an integrated membrane-electrode assembly (MEA) that combines an electrolyte membrane and a catalyst layer, a gas diffusion layer, and a separator plate. Notably, the tungsten oxide is coated on the surface of at least one component among the membrane-electrode assembly, gas diffusion layer, or separator plate. The disclosure also covers a method for manufacturing such a fuel cell.
During start-up and shut-down situations of a Polymer Electrolyte Membrane Fuel Cell (PEMFC), an abnormal oxygen reduction reaction occurs at an oxidation electrode (anode) due to the presence of residual oxygen. This reaction causes an unusually high voltage, beyond the normal voltage range, to be applied to the cell, which in turn leads to corrosion of the carbon support of the platinum (Pt/C) catalyst in the cathode and creates durability issues. Various solutions have been proposed to address these problems. Prior Patent Document 1 provides a fuel cell bipolar plate that is not only thin and lightweight, but also exhibits excellent conductivity and corrosion resistance, as well as a method for manufacturing the same.
Meanwhile, recently, the development of a selective catalyst that prevents oxygen reduction reactions at the oxidation electrode (anode), which can be considered the ultimate cause of problems during start-up/shut-down (SU/SD) conditions, and only promotes the intended hydrogen oxidation reaction, has been attracting significant attention. Among these selective catalysts, a Pt/HxWO3-x, catalyst carrying platinum on tungsten oxide has been introduced in an academic journal, garnering interest from the academic community and boasting excellent performance and durability. However, during the commercialization stage of the Pt/HxWO3-x, catalyst, the chemical synthesis process that the catalyst must undergo results in relatively random outcomes compared to mechanical processes, leading to unstable quality, specifically in terms of the catalyst's selectivity function. Moreover, using tungsten oxide, a non-conductive material, as a support contributes to the instability in quality and consequently causes issues such as decreased performance and durability of the fuel cells.
Currently, platinum (Pt/C) catalysts are being used for both the anode and cathode in commercial applications. As a result, adopting the new concept of Pt/HxWO3-x catalysts would inevitably lead to significant changes compared to the existing manufacturing processes using platinum (Pt/C) catalysts, and thus the existing processes cannot be utilized, leaving limitations in commercialization and application.
Therefore, there is a need to develop a polymer electrolyte membrane fuel cell that not only increases the selectivity of the catalyst but also has a stable quality capable of enhancing the efficiency and durability of the fuel cell. Furthermore, it is necessary to utilize tungsten oxide materials that can be easily applied to existing manufacturing processes instead of separate processes, resulting in a highly efficient and durable fuel cell, as well as its manufacturing process.
The present disclosure aims to solve the problems and limitations of the conventional technology as described above. The objective is to provide a polymer electrolyte membrane fuel cell that prevents oxygen reduction reactions at the oxidation electrode (anode), which can be considered the ultimate cause of issues during start-up and/or shut-down (SU/SD) conditions, allows only hydrogen oxidation reactions to occur, maintains fuel cell efficiency, and increases durability by preventing corrosion of the platinum (Pt/C) catalyst, as well as a method for manufacturing the same.
A polymer electrolyte membrane fuel cell according to the present disclosure may include a unit cell composed of a membrane-electrode assembly (MEA), where an electrolyte membrane and catalyst layer are integrally combined, a gas diffusion layer, and a bipolar plate. Tungsten oxide is coated on the surface of at least one of the membrane-electrode assembly, the gas diffusion layer, or the bipolar plate constituting the unit cell.
In this case, it is preferable for the tungsten oxide to be deposited and coated at a thickness of 450 to 550 nm. This is because if the coated tungsten oxide thickness is less than 450 nm, the amount available for intercalation is insufficient, limiting fuel cell performance improvement, and if the thickness exceeds 550 nm, the non-conductive characteristics of tungsten oxide become dominant, causing a decrease in conductivity. The deposition may be performed through physical vapor deposition (PVD) and may also be carried out by sputtering or electron beam vapor deposition.
Furthermore, in the present disclosure, it is more preferable for the tungsten oxide to be coated on the surface of the MEA among the components constituting the polymer electrolyte membrane fuel cell.
Another aspect of the present disclosure is a method for manufacturing a polymer electrolyte membrane fuel cell containing a tungsten oxide-coated component. This method may include forming a catalyst layer on both the front and back surfaces of a polymer electrolyte membrane to create a membrane-electrode assembly and assembling a unit cell by sequentially stacking the membrane-electrode assembly, the gas diffusion layer, and the bipolar plate, with tungsten oxide coated on the surface of at least one of the membrane-electrode assembly, the gas diffusion layer, or the bipolar plate constituting the unit cell.
The forming of the membrane-electrode assembly may involve applying a catalyst by coating a catalyst slurry onto an imide film surface and drying it and forming a catalyst layer by attaching and stacking the catalyst-coated imide film to the front and back surfaces of the polymer electrolyte membrane, applying external pressure and heat to transfer the catalyst to the front and back surfaces of the polymer electrolyte membrane, forming a catalyst layer, and then removing the imide film.
In addition, the physical vapor deposition performed in the coating of the membrane-electrode assembly, the gas diffusion layer, and the bipolar plate is preferably either sputtering or electron beam vapor deposition.
Furthermore, the forming of the membrane-electrode assembly may comprise: forming a tungsten oxide layer on a first imide film; forming a catalyst layer on the tungsten oxide layer; stacking the first imide film on which the catalyst layer and the tungsten oxide layer are formed on the surface of the polymer electrolyte membrane; and compressing the first imide film with a heating press and then removing the first imide film.
In this case, the forming of the tungsten oxide layer may comprise dropping a tungsten slurry on the first imide film, uniformly applying the tungsten slurry with a blade and drying the tungsten slurry, and the forming of the catalyst layer may comprise dropping a catalyst slurry on the tungsten oxide layer, uniformly applying the catalyst slurry with a blade, and drying the catalyst slurry.
The stacking may further comprise forming a catalyst layer on a second imide film and then stacking the second imide film on which the catalyst layer is formed on the back surface of the polymer electrolyte membrane.
The removing of the imide film may comprise removing the first imide film and the second imide film with a heating press after sequentially stacking the second imide film, the catalyst layer, the polymer electrolyte membrane catalyst layer, the tungsten oxide layer, and the first imide film.
The present invention has advantages in that although a platinum (Pt/C) catalyst, which has been conventionally used, is employed as is in the polymer electrolyte membrane fuel cell, catalyst and cell durability can be ensured by reducing carbon oxidation reactions through the prevention of high voltage occurrence under SU/SD (start-up/shut-down) conditions of the fuel cell. Additionally, performance can be maintained due to the absence of current density reduction even under SU/SD conditions.
Furthermore, the present invention has an additional advantage of being economically simple, in that although the platinum (Pt/C) catalyst, which has been conventionally commercialized and used, is employed as is, performance can be maintained under SU/SD conditions and durability can be improved simply by adding a process of depositing and coating tungsten oxide on the surface of any one of the constituent parts of the fuel cell.
Hereinafter, an exemplary embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.
The membrane-electrode assembly forming step (S100) is a process of forming a membrane-electrode assembly by forming a catalyst layer on both the front and back surfaces of a polymer electrolyte membrane. Specifically, the membrane-electrode assembly forming step includes a catalyst applying step (S110), where a catalyst slurry is applied to the surface of an imide film and dried, and a catalyst layer forming step (S120), where the catalyst-applied imide film is attached to both the front and back surfaces of the polymer electrolyte membrane, stacked, and then subjected to external pressure and heat to transfer the catalyst to the front and back surfaces of the polymer electrolyte membrane, forming a catalyst layer on each surface, followed by the removal of the imide film.
In this embodiment, platinum (Pt/C) was chosen as the catalyst to form the membrane-electrode assembly (MEA). A 40 wt. % commercial platinum (Pt/C) catalyst was loaded onto the anode at 0.1 mg/cm2 and onto the cathode at 0.4 mg/cm2 using a decal method. Nafion 211 was used as the material for the polymer electrolyte membrane in the MEA.
The membrane-electrode assembly coating step (S200) involves depositing and coating tungsten oxide onto the surface of the formed MEA using physical vapor deposition (PVD). PVD includes sputtering and electron beam vacuum deposition methods. In this embodiment, tungsten oxide is deposited onto the surface of the MEA to a thickness of, for example, about 500 nm using the sputtering method with a sputter.
The gas diffusion layer coating step (S300) and the bipolar plate coating step (S400) can be performed simultaneously with the MEA coating step (S200) or separately before or after it. In this embodiment, the gas diffusion layer and bipolar plate were placed in the sputter chamber together with the MEA, and tungsten oxide was deposited and coated onto each surface to a thickness of about 500 nm using the sputtering method. The bipolar plate (BP) used in this case was made of graphite material with no surface coating and featured a serpentine-type flow path with a depth and width of 1 mm.
The gas diffusion layer (GDL) was made of a carbon material with a porous structure, and its surface was waterproofed using 20% PTFE.
However, the MEA coating step (S200), gas diffusion layer coating step (S300), and bipolar plate coating step (S400) are optional. Only one of the three steps can be performed to coat tungsten oxide onto a surface of either the MEA, gas diffusion layer, or bipolar plate, and a tungsten oxide layer can also be coated by applying, for example, a decal method in the MEA forming step (S100).
Then, in the fuel cell assembly step (S500), a polymer electrolyte membrane fuel cell including a unit cell is assembled, where the unicell includes at least one of the MEA, gas diffusion layer, or bipolar plate, each coated with tungsten oxide.
In
More specifically, a, b, and c in
In this case, tungsten oxide can be deposited on the oxidation electrode flow path of the first bipolar plate (320), as shown in
When comparing images before and after depositing tungsten oxide on the surface of each component to form a coating layer, it is easy to visually confirm that the color has changed due to the formation of the tungsten oxide layer.
A polymer electrolyte membrane fuel cell includes parts without tungsten oxide deposition and coating was constructed with an oxidation electrode (anode), an uncoated graphite bipolar plate, a gas diffusion layer with a PTFE (Poly Tetra Fluoro Ethylene) treated porous carbon surface, a membrane-electrode assembly (MEA) with a platinum (Pt/C) catalyst attached to both the front and back surfaces of the polymer electrolyte membrane, and a reduction electrode (cathode).
Compared to the conventional polymer electrolyte membrane fuel cell (Comparative Example, a), the performances of fuel cells with tungsten oxide deposited and coated to a thickness of 500 nm on the surface of the bipolar plate (Example 1, b), the gas diffusion layer (Example 2, c), and the membrane-electrode assembly (MEA) (Example 3, d) were mutually compared by the current density at about 0.6 V.
In this experiment, the basic performance was measured under conditions of a cell temperature of 70° C. and a relative humidity of 100%. The SU/SD protocol test involved evaluating the fuel cell's performance after 100 cycles, where one cycle includes allowing hydrogen to flow through the oxidation electrode and oxygen through the reduction electrode under normal operating conditions, and under SU/SD conditions allowing oxygen to flow through the oxidation electrode until the open circuit voltage (OCV) dropped to 0.2 V.
Referring to
On the other hand, as shown in
This experiment involves observing the potential profile for 100 seconds. The objective is to determine whether a high voltage of 1.5 V, which triggers a carbon oxidation reaction in the fuel cell when the experiment starts under normal operating conditions and switches to SU/SD conditions after 30 seconds, subsequently degrading the durability of the platinum (Pt/C) catalyst, is generated in the cell.
Based on the experimental results, it was confirmed that the voltage in the cell rapidly increased up to 1.5 V in the case of the conventional fuel cell according to the Comparative Example, whereas in the case of the fuel cells manufactured according to Examples 1 to 3, the voltage did not rise rapidly up to 1.5 V in the cell itself even when the same experiment was performed.
Therefore, it can be confirmed that in the case of the polymer electrolyte membrane fuel cell according to the present disclosure, even when the condition is suddenly switched from normal operating conditions to SU/SD conditions, the voltage inside the cell does not rapidly increase, preventing the occurrence of carbon oxidation reactions that reduce the durability of the catalyst and maintaining the durability of the fuel cell.
Furthermore,
In this case, it can be inferred that the greater the reduction in thickness in the SEM image is, the more severe the carbon corrosion is. Referring to
According to another embodiment of the present disclosure, WO3 can be coated using the decal technique in addition to the PVD method. In this case, the WO3 layer is preferably coated on the anode side of the MEA, and the WO3 layer is stacked on the polymer electrolyte membrane (e.g., Nafion membrane) together with a catalyst layer to prepare an MEA. That is, when using the decal technique, the catalyst layer and the WO3 layer are formed on the polymer electrolyte membrane in the step of combining the MEA.
More specifically, referring to
Next, after dropping a catalyst slurry on the WO3-coated imide film, i.e., on the tungsten oxide layer, the catalyst slurry is coated to a uniform thickness using the doctor blade and is then sufficiently dried (S220).
Following this, the imide film with the catalyst layer and WO3 layer formed on it is cut to an appropriate size and laminated onto a Nafion membrane for forming an MEA. At this stage, the catalyst layer is stacked in such a way that it comes into contact with the Nafion membrane and is stacked on the anode-side surface of the Nafion membrane. At this point, an imide film with only a uniformly formed catalyst layer may be laminated onto the cathode side (back surface) of the Nafion membrane.
Finally, a laminate in which the imide film, catalyst layer, Nafion membrane, catalyst layer, WO3 layer, and imide film are sequentially stacked (in the cathode→anode direction) is compressed using a heating press while adjusting pressure and temperature(S230). Then, the imide films on both sides are peeled off, leaving the catalyst layer (cathode side) and the catalyst layer+WO3 layer (anode side) on both surfaces of the membrane (S240).
Referring to
Although the preferred embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, changes, and substitutions are possible without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Therefore, the embodiments and accompanying drawings of the present disclosure are presented only for illustrative purposes, not for limiting the technical concept of the present disclosure, and the scope of the technical concept of the present disclosure is not limited by the embodiments and accompanying drawings. The scope of the present disclosure should be construed according to the following claims, and all technical ideas within the equivalent range should be interpreted as being included in the scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2021-0075212 | Jun 2021 | KR | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/KR2022/006868 | May 2022 | US |
| Child | 18140734 | US |
