A method for removing fuel cell contaminants to enhance cell performance

Abstract

This invention discloses a method for removing contaminants from fuel cells and improving battery performance, belonging to the field of fuel cell technology. Addressing the problem of metal cations in platinum-based transition metal alloy catalysts leaching and poisoning the proton exchange membrane, leading to decreased battery performance, this method constructs a purification fixture comprising a cation trapping layer and a driving electrode on at least the outer side of the catalyst coating membrane to be treated. Under conditions of hydrogen gas flowing through the anode and oxygen-containing gas flowing through the cathode, the fuel cell is connected to a fuel cell testing system and controlled to discharge at a constant operating voltage. Utilizing the spontaneously generated electrolyte potential gradient and proton flow during discharge, free transition metal cations are directionally driven away and enriched in the cation trapping layer. The fixture is then disassembled and the trapping layer is discarded. This invention utilizes the power generated by the battery itself to achieve in-situ, non-destructive decontamination, significantly improving the battery's peak power density. It is primarily used for the fabrication and maintenance of high-performance proton exchange membrane fuel cells.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and to a method for removing contaminants from fuel cells and improving battery performance, specifically a method for removing metal cation contaminants from the membrane electrode assembly (MEA) of a fuel cell and improving battery performance. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are clean energy devices that directly convert chemical energy into electrical energy. To reduce the amount of precious metal platinum used and improve the activity of the cathode oxygen reduction reaction (ORR), the use of platinum-based transition metal alloy catalysts (such as PtCo and PtNi) has become the mainstream technological direction. However, base metal elements (such as Co and Ni) in these alloy catalysts slowly dissolve during the membrane electrode preparation process (such as ultrasonic dispersion of the slurry) and during long-term operation of the fuel cell stack, forming free transition metal cations. These cations readily migrate from the catalyst layer into the proton exchange membrane, undergoing ion exchange with the sulfonic acid groups of the Nafion resin within the membrane and binding firmly. This leads to a significant decrease in the membrane's ion conductivity, ultimately causing irreversible degradation of the fuel cell's performance.

[0003] To address this issue, one approach proposes in-situ cleaning of the membrane electrode assembly (MEA) by introducing an acidic solution into the MEA and applying an electric current, without disassembling the MEA stack, to remove contaminants. Another method involves introducing more stable elements such as iridium and gold during the catalyst synthesis stage to inhibit base metal leaching at the material source.

[0004] Therefore, there is an urgent need for a method to remove metal cation contaminants from the membrane electrode assembly of fuel cells and improve battery performance in order to solve the problems existing in the prior art. Summary of the Invention

[0005] The purpose of this application is to address the aforementioned problems in the prior art by providing a method for removing contaminants from fuel cells and improving battery performance. This method involves adding a proton exchange membrane as a cation trapping layer to at least the outer side of the catalyst coating membrane to be treated. By connecting the fuel cell to a fuel cell testing system under the conditions of hydrogen gas flowing through the anode and oxygen-containing gas flowing through the cathode, the fuel cell is controlled to discharge at a constant operating voltage. Utilizing the electrolyte potential gradient and proton flow spontaneously generated during the discharge process, free transition metal cations are directionally driven away and enriched in the cation trapping layer, and ultimately discarded.

[0006] To achieve the aforementioned objectives, this application employs the following technical solution: a method for removing contaminants from a fuel cell and improving battery performance, comprising the following steps:

[0007] A catalyst coating membrane to be treated is provided, the catalyst coating membrane comprising a proton exchange membrane and a catalyst layer supported thereon, and at least the catalyst layer on the cathode side comprises a platinum-based transition metal alloy catalyst. Construct a purification fixture, including setting an ion-conducting polymer film, which is separate from the catalyst coating film and serves as a cation capture layer, on the outer side of the catalyst coating film at least on the cathode side, and setting a driving electrode on the outer side of the cation capture layer. With hydrogen gas introduced into the anode and oxygen-containing gas introduced into the cathode, the fuel cell test system is connected and the purification equipment is controlled to perform actual discharge operation under a constant working voltage. The electrolyte potential gradient and proton flow generated inside during the discharge process are used to drive the free transition metal cations in the catalyst layer in a directional manner, causing them to migrate to the cathode side and finally deposit and accumulate in the cation capture layer and the adjacent driving electrode. Disassemble the purification equipment, remove the treated catalyst coating membrane, and discard the cation capture layer.

[0008] Furthermore, in the step of constructing the purification tooling, a cation capture layer is provided on the outer side of both the anode and cathode sides of the catalyst coating film.

[0009] Furthermore, the cation trapping layer is a proton exchange membrane.

[0010] Furthermore, the proton exchange membrane is a perfluorosulfonic acid resin film.

[0011] Furthermore, in the step of performing actual discharge operation under a constant operating voltage, the constant operating voltage ranges from 0.4V to 0.6V, and the discharge operation time is from 6 hours to 12 hours.

[0012] Furthermore, in the step of providing a catalyst coating film to be treated, the anodic side catalyst layer of the catalyst coating film is a platinum-carbon catalyst layer, and the cathode side catalyst layer is a platinum-based transition metal alloy catalyst layer.

[0013] Furthermore, the driving electrode is a gas diffusion electrode, and its catalyst side is assembled facing the cation capture layer.

[0014] Furthermore, transition metal cations include Co. 2+ Ni 2+ At least one of them.

[0015] Furthermore, the method also includes assembling the treated catalyst coating membrane with a clean gas diffusion layer into a fuel cell; wherein the peak power density of the fuel cell is increased by more than 20% compared to a fuel cell assembled for the first time from untreated catalyst coating membranes prepared in the same batch.

[0016] Furthermore, after disassembling the purification tooling, the driving electrode adjacent to the cation capture layer is discarded, and a new gas diffusion layer is used in subsequent reassembly.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Significantly and permanently improves battery performance: This invention implements electric field-driven deep purification after the process, which can completely migrate and lock the dissolved toxic cations inside to the independent sacrificial membrane on the outside. This allows the fuel cell assembled from the purified membrane electrode to have a peak power density that exceeds its initial state after contamination, achieving a performance improvement of more than 20%, overcoming the limitation of traditional methods that can only recover to a limited extent.

[0018] 2. Avoids secondary damage to core components of fuel cells: The entire process of this invention does not require the introduction of any liquid acid or chemical cleaning agent. It relies entirely on electric field force to achieve the physical dispersal and transfer of ions. Therefore, it eliminates the risk of corrosion that acid may cause to the catalyst carbon support and gas diffusion layer, and also avoids the residue of harmful anions inside the membrane electrode, ensuring the integrity and long-term stability of the material structure.

[0019] 3. Simple and efficient process with wide applicability: This invention is based on the hydrogen and oxygen-containing gases required for fuel cell operation and can be implemented using existing fuel cell testing systems. The processing steps are clear and easy to operate. Its principle is applicable to Co... 2+ Ni 2 + Various transition metal cations are generally effective and widely applicable to fuel cell systems using various platinum-based alloy catalysts. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the battery configuration and principle of the PEMFC potential gradient driven clamped PtCo / C CCM for Co²⁺ removal according to the present invention, wherein (a) is a schematic diagram of the battery configuration; (b) is a schematic diagram of Co²⁺ removal. 2+ Remove the schematic diagram; Figure 2 For the removal of Co by the self-made PtCo ordered alloy catalyst in Example 1 2+ Performance graphs of PEMFC before and after; Figure 3 For the removal of Co by the commercial Pt3Co catalyst in Example 2 2+ Performance graphs of PEMFC before and after; Figure 4 The graph shows the performance of PEMFC before and after electrodialysis treatment of the commercial PtC catalyst in Comparative Example 1. Figure 5 The diagram shows the performance of PEMFC before and after perchloric acid was introduced through the cathode in Comparative Example 2.

[0021] In the figure, 10 is the driving electrode; 20 is the cation capture layer; and 30 is the catalyst coating film. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0023] This invention provides a method for removing contaminants from fuel cells and improving their performance. The core idea is to construct a temporary purification fixture, placing a physically separated cation capture layer as a sacrificial layer on the outside of the catalyst coating membrane to be treated. Utilizing the potential gradient and high-flux protons established by the fuel cell itself under high-current discharge conditions, free transition metal cations inside the membrane electrode assembly are directionally driven away and enriched in this sacrificial layer. Finally, by disassembling the fixture and discarding the sacrificial layer, deep purification of the membrane electrode assembly is achieved. This method not only eliminates the need for any liquid acid or chemical cleaning agents, fundamentally avoiding secondary damage to the membrane electrode assembly from chemical reagents, but also enables the treated fuel cell to significantly outperform its initial contaminated state.

[0024] like Figure 1 As shown in part (a) of the diagram, the core components and assembly relationships of the purification fixture used to implement the method of the present invention are as follows: The tooling includes a catalyst coating membrane 30 to be processed, a cation capture layer 20 disposed on the outer side of the catalyst coating membrane 30 at least on the cathode side, and a drive electrode 10 disposed on the outer side of the cation capture layer 20. In actual operation, the above components are stacked, fastened, and pressed together using conventional fuel cell components (not shown separately in the figure) such as gaskets, flow field plates, and end plates to ensure close physical contact between the layers.

[0025] The catalyst coating membrane 30 comprises a central proton exchange membrane and catalyst layers coated on its cathode and anode sides, respectively, wherein at least the cathode-side catalyst layer comprises a platinum-based transition metal alloy catalyst. Preferably, this embodiment employs an asymmetric structure, i.e., the anode-side catalyst layer is a platinum-carbon (PtC) catalyst layer, and the cathode-side catalyst layer is a platinum-based transition metal alloy catalyst layer. This structure ensures that the pollutant source (transition metal cations) is concentrated on the cathode side, facilitating efficient and interference-free targeted removal.

[0026] The cation trapping layer 20 is a separate component physically isolated from the catalyst coating membrane 30. It is composed of a polymer film with ionic conductivity, preferably a proton exchange membrane, and more preferably a Nafion series perfluorosulfonic acid resin film. The function of this cation trapping layer 20 is to act as a "sacrificial layer," receiving and firmly trapping transition metal cations migrating from the catalyst coating membrane 30 under the action of an electric field, and then discarding them in subsequent steps.

[0027] The driving electrode 10 is preferably a gas diffusion electrode (such as a PtC gas diffusion electrode), consisting of a gas diffusion layer and a platinum-carbon (PtC) catalyst layer coated thereon. During assembly, the catalyst surface of the driving electrode 10 must be tightly fitted to the inner cation capture layer 20. The driving electrode 10 not only serves as a conductive current collector, but more importantly, it provides a stable electrochemical reaction interface. On the anode side, hydrogen is catalyzed to generate a proton flow, thereby establishing a directional migration power source within the tooling.

[0028] Figure 1 Part (b) schematically illustrates the decontamination principle of the present invention. The topmost element in the figure shows a conventional fuel cell testing system (such as a test bench with an electronic load, model 850G, rather than an externally powered potentiostat). Under actual H2 / Air discharge conditions, a hydroxide reaction (HOR) occurs at the anode. The oxygen reduction reaction (ORR) occurs at the cathode. During continuous discharge, an electrolyte potential gradient will be generated inside the stack along its thickness. This potential difference is not only due to protons (H) + The migration provides a powerful driving force, enabling high-speed transport of these protons from the anodic HOR reaction interface to the cathode ORR reaction interface; more importantly, this internally generated strong potential gradient and high-flux protons synergistically induce transition metal cations (with Co) within the composite membrane electrode (CCM). 2+ (For example) it dissociates from its initial poisoning site and undergoes directional migration, gradually moving towards the cathode ORR side, eventually crossing the interface and depositing and remaining in the reaction region of the cation trapping layer 20 and the cathode driving electrode 10 on the cathode side. Simultaneously, the liquid water generated at the cathode can fully wet the cation trapping layer 20, improving its ionic conductivity and accelerating the reaction of Co. 2+ The influx and consolidation of [the land].

[0029] Example 1 This embodiment uses a self-made PtCo ordered alloy catalyst as the research object to explain in detail the specific processing steps of the present invention.

[0030] Step 1: Provide a catalyst coating film 30 to be treated.

[0031] First, a catalyst coating film 30 is prepared. A cathode catalyst slurry is prepared by dispersing a PtCo ordered alloy catalyst in a mixed solvent of water and isopropanol; an anode catalyst slurry is prepared by dispersing a PtC catalyst in a mixed solvent of water and isopropanol. Using an ultrasonic spraying process, the cathode catalyst slurry is coated onto one side of the proton exchange membrane to form a cathode catalyst layer, and the anode catalyst slurry is coated onto the other side to form an anode catalyst layer, ultimately obtaining an asymmetric double-sided catalyst coating film 30 with PtC on the anode side and PtCo on the cathode side. In this step, due to the physical effects of the slurry preparation process (such as ultrasonic dispersion), some cobalt is released as free Co. 2+ The morphology dissolves and poisons the Nafion resin inside the membrane electrode, resulting in impaired initial performance.

[0032] Step 2: Construct cleanroom fixtures.

[0033] Preparation of driving electrode 10: PtC catalyst slurry is sprayed onto the gas diffusion layer to form PtC gas diffusion electrode, i.e. driving electrode 10.

[0034] Subsequently, referring to Figure 1 The sequence shown in part (a) is as follows, stacked sequentially from anode to cathode: anode-side driving electrode 10, proton exchange membrane serving as cation trapping layer 20, catalyst coating membrane 30, another proton exchange membrane serving as cation trapping layer 20, and cathode-side driving electrode 10. During assembly, it must be ensured that the catalyst surfaces of both driving electrodes 10 face inwards and are tightly fitted with the adjacent cation trapping layer 20. Finally, the entire fixture is tightened using end plates and fasteners. In this embodiment, the cation trapping layer 20 is disposed on both sides of the catalyst coating membrane 30, forming a symmetrical sandwich structure; however, in an optional simplified embodiment, only one cation trapping layer 20 may be disposed in the main migration direction, i.e., on the cathode side.

[0035] Step 3: Perform electrodialysis treatment.

[0036] Hydrogen gas was introduced into the anode-side flow channel of the assembled purification fixture, while air was introduced into the cathode-side flow channel. It was then connected to a standard fuel cell testing system, and an electronic load was used to control its actual discharge operation at a constant operating voltage of 0.5V for 10 hours. During this process, no external power source was required; the operation relied entirely on the fuel cell's own power generation reaction. 0.5V represents a typical high-current, heavy-load discharge region, resulting in a significant electrolyte potential gradient distributed along the thickness direction within the stack. Under the combined effect of this strong internal electric field and proton drag, free Co within the catalyst layer... 2+ Directed away, it gradually moves toward the cathode side, eventually penetrating the boundary of the catalyst coating film 30, depositing and accumulating in the outer cation capture layer 20 and the adjacent driving electrode 10.

[0037] Step 4: Disassemble and discard the sacrificial parts.

[0038] After the constant voltage discharge treatment is completed, disconnect the electronic load and gas supply, and disassemble the purification fixture. Remove the catalyst coating film 30 located in the center; at this point, the free Co inside it... 2+ It has been largely removed. Co was adsorbed on both sides. 2+ The cation capture layer 20 was identified as a pollutant-rich aggregate and disposed of as waste. Simultaneously, to avoid back pollution, the driving electrode 10, which was in contact with the cation capture layer 20, was also discarded.

[0039] Step 5: Standard assembly and performance testing.

[0040] The removed and purified catalyst coating membrane 30 is assembled with two brand-new, clean gas diffusion layers to form a standard "gas diffusion layer-CCM-gas diffusion layer" three-in-one fuel cell structure, and then performance testing is carried out.

[0041] The performance of a fuel cell directly assembled for the first time using a standard structure, based on catalyst coating membranes 30 prepared in the same batch without the treatment in steps 2 to 4 of this invention, was used as a comparison benchmark. The test results are as follows: Figure 2 As shown: After treatment by the method of this invention, the peak power density of the battery (located in the high current region) is increased by approximately 280 mW / cm². -2 At a current density of 1.5 A cm⁻¹ -2 At that time, the battery voltage increased by about 90 mV, and the overall power density increased by more than 20%.

[0042] Example 2 The only difference between this embodiment and Example 1 is that the cathode catalyst layer of the catalyst coating membrane 30 uses a commercial Pt3Co catalyst instead of the self-made PtCo ordered alloy catalyst. All other steps and parameters are the same as in Example 1. The constant operating voltage controlled by the fuel cell testing system can be adjusted within the range of 0.4 V to 0.6 V, and the discharge operation time can be selected within the range of 6 hours to 12 hours; for example, it can be operated at 0.6 V for 6 hours.

[0043] Test results are as follows Figure 3 As shown: After treatment with the method of this invention, the peak power density of the battery using the commercial Pt3Co catalyst was increased by approximately 140 mW / cm². -2 , at 1.5 A cm -2 The battery voltage increased by approximately 66 mV. This strongly demonstrates that the method of the present invention has significant and universal decontamination and performance improvement effects on different types of platinum-based transition metal alloy catalysts (such as PtNi).

[0044] Comparative Example 1 To demonstrate that the performance improvement of this method specifically stems from the removal of transition metal cations rather than physical or chemical activation, the cathode catalyst of CCM 30 in Example 1 was replaced with a commercial PtC catalyst, and parallel treatment was carried out under the exact same purification setup and electrodialysis conditions (0.5 V constant potential, hydrogen / air atmosphere, 10 hours of operation).

[0045] Test results are as follows Figure 4 As shown, the performance of the PtC catalyst cell remained almost unchanged before and after treatment. This indicates that the proposed method is specifically effective against metal cation contamination present in the membrane electrode of platinum-based transition metal alloy catalysts.

[0046] Comparative Example 2 To demonstrate that the method of the present invention is superior to the traditional acid washing method, a PtCo ordered alloy CCM prepared in the same batch as in Example 1 was washed for about 30 minutes by passing a 0.1M perchloric acid (HClO4) solution through the cathode, followed by rinsing with deionized water.

[0047] Test results are as follows Figure 5 As shown, the battery performance was not improved after acid washing. This indicates that simple acid rinsing cannot effectively remove cobalt ions that are tightly bonded to the ionomer, and may even lead to performance degradation due to anion residue or material corrosion. In contrast, the electric field-driven physical purification fixture of this invention exhibits significant advantages.

[0048] In summary, the method of this invention, by introducing a separated "sacrificial" cation capture layer into the purification apparatus and performing discharge treatment under a suitable potential range and atmosphere, can remove transition metal cations (including but not limited to Co) inside the membrane electrode. 2+ Ni 2+ This method efficiently and non-destructively removes and seals away pollutants, ultimately eradicating them through physical disposal. It is simple to operate, highly versatile, and can not only restore battery performance but also elevate it to a level far exceeding its initial state, demonstrating significant application value in the field of fuel cells.

[0049] The parts not described in detail in this application are prior art, and therefore are not described in detail in this application.

[0050] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0051] Although this document uses a significant amount of technical terminology, the possibility of using other terms is not excluded. These terms are used merely to facilitate the description and explanation of the nature of this application; interpreting them as any additional limitation would be contrary to the spirit of this application.

[0052] This application is not limited to the above-described preferred embodiments. Anyone can derive other products in various forms under the guidance of this application. However, regardless of any changes made to their shape or structure, any technical solution that is the same as or similar to that of this application falls within the protection scope of this application.

Claims

1. A method for removing contaminants from fuel cells to improve performance, characterized in that, Includes the following steps: A catalyst coating membrane to be treated is provided, the catalyst coating membrane comprising a proton exchange membrane and a catalyst layer supported thereon, and the catalyst layer on at least the cathode side comprises a platinum-based transition metal alloy catalyst; A purification fixture is constructed, comprising: a ion-conducting polymer film, which is separated from the catalyst coating film and serves as a cation capture layer, is disposed on the outer side of the catalyst coating film at least on the cathode side; and a driving electrode is disposed on the outer side of the cation capture layer. With hydrogen gas introduced into the anode and oxygen-containing gas introduced into the cathode, the fuel cell test system is connected and the purification equipment is controlled to perform actual discharge operation under a constant working voltage. The electrolyte potential gradient and proton flow generated inside during the discharge process are used to drive the free transition metal cations in the catalyst layer in a directional manner, causing them to migrate to the cathode side and finally deposit and accumulate in the cation capture layer and the adjacent driving electrode. Disassemble the purification apparatus, remove the treated catalyst coating film, and discard the cation capture layer.

2. The method according to claim 1, characterized in that, In the step of constructing the purification apparatus, the cation capture layer is provided on the outer side of both the anode and cathode sides of the catalyst coating film.

3. The method according to claim 1 or 2, characterized in that, The cation capture layer is a proton exchange membrane.

4. The method according to claim 3, characterized in that, The proton exchange membrane is a perfluorosulfonic acid resin film.

5. The method according to claim 1, characterized in that, In the step of performing actual discharge operation under constant operating voltage, the constant operating voltage ranges from 0.4V to 0.6V, and the discharge operation time is from 6 hours to 12 hours.

6. The method according to claim 1, characterized in that, In the step of providing a catalyst coating film to be treated, the anodic side catalyst layer of the catalyst coating film is a platinum-carbon catalyst layer, and the cathode side catalyst layer is a platinum-based transition metal alloy catalyst layer.

7. The method according to claim 1, characterized in that, The driving electrode is a gas diffusion electrode, and its catalyst side is assembled facing the cation capture layer.

8. The method according to claim 1, characterized in that, The transition metal cations include Co. 2+ Ni 2+ At least one of them.

9. The method according to claim 1, characterized in that, The method further includes assembling the treated catalyst coating membrane with a clean gas diffusion layer to form a fuel cell; wherein the peak power density of the fuel cell is increased by more than 20% compared to a fuel cell assembled for the first time from untreated catalyst coating membranes prepared in the same batch.

10. The method according to claim 1, characterized in that, After disassembling the purification fixture, the driving electrode adjacent to the cation capture layer is discarded, and a new gas diffusion layer is used in subsequent reassembly.

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