A method for evaluating fuel cell ionomer based on thin liquid film electrode and application thereof

Abstract

The application discloses a kind of fuel cell ionomer evaluation method and application based on thin liquid film electrode, belong to automobile fuel cell technical field.The method in the application first disperses catalyst and ionomer to be measured in solvent to form electrode slurry, is coated to the surface of gas diffusion layer and forms gas diffusion electrode;Gas diffusion electrode is assembled into working electrode with sealing gasket and graphite flow field plate again and is fixed in electrolytic cell;Add electrolyte to electrolytic cell, adopt lifting method or steam wetting method to construct continuous uniform thin liquid film on the surface of catalytic layer of working electrode, form gas-liquid-solid three-phase interface;Reaction gas is introduced to carry out electrochemical test, and the performance of ionomer is evaluated according to test result.The application simulates the three-phase interface environment in real fuel cell catalytic layer by constructing thin liquid film electrode, realizes the decoupling evaluation of ionomer intrinsic performance and three-phase interface construction effect, and can be applied to fuel cell ionomer screening.

Description

Technical Field

[0001] This invention belongs to the field of automotive fuel cell technology, specifically relating to a method and application for evaluating fuel cell ionomers based on a thin liquid membrane electrode. Background Technology

[0002] With the arrival of the energy crisis and the demand for sustainable development, fuel cell vehicles, with their advantages of high energy density and zero emissions, are gradually becoming the development direction of the automotive industry. In fuel cells, ionomers are one of the key components in the fuel cell catalyst layer, typically playing multiple roles including catalyst layer bonding, ion conduction, and interface regulation. The distribution state of ionomers in the catalyst layer, their ion conduction capacity, water absorption and retention characteristics, and their interaction with the catalyst surface directly affect reactant transport, active site utilization, and the overall electrochemical performance of the membrane electrode assembly (MEA). Especially in the fuel cell catalyst layer, ionomers not only construct ion transport channels but also participate in the formation of the catalyst / ionomer / gas three-phase interface. Their interface construction ability has a significant impact on the local microenvironment of the catalyst layer and the electrode reaction efficiency. Therefore, establishing a technical method that can effectively evaluate the performance of ionomers and their three-phase interface construction effect is of great significance for the screening of fuel cell ionomer materials, optimization of catalyst layer structure, and improvement of device performance.

[0003] In existing technologies, the evaluation of ionomer performance typically relies on rotating disk electrode (RDE) testing, full-cell testing, and some physicochemical characterization methods. While RDE systems can evaluate catalyst activity in a relatively ideal liquid environment, the reaction primarily occurs at the solid-liquid interface because the test electrode is usually fully submerged. This makes it difficult to reflect the ability of ionomers to construct gas-liquid-solid three-phase interfaces in actual membrane electrode catalytic layers, and also hinders the effective evaluation of the true impact of ionomers on local hydration states, gas mass transfer, and interfacial reactions. Although full-cell testing more closely approximates actual operating conditions, the results are simultaneously influenced by multiple factors such as membrane conduction, gas diffusion, catalyst layer structure, water management, interfacial contact, and assembly conditions, making it difficult to independently, quantitatively, and controllably evaluate the intrinsic properties of ionomers and their interfacial effects. Furthermore, existing ionomer evaluation methods focus more on single physicochemical properties such as water absorption rate, contact angle, and spectroscopic characterization. While these methods can reflect some characteristics of ionomers, they still cannot directly explain their film-forming ability, interfacial construction ability, and electrochemical effects under near-real-world conditions. In summary, most existing ionomer characterization methods are conducted under ideal conditions. The fine structure and behavior of ionomers on the catalyst surface and at the gas-liquid-solid three-phase interface are the most difficult to characterize, making it difficult to isolate the individual contribution of ionomers, which is the key to performance.

[0004] Based on this, developing a characterization technique that can simulate the working conditions of a real fuel cell catalyst layer and achieve decoupled evaluation of the intrinsic properties of ionomers and the three-phase interface construction effect has become a core requirement for breaking through the current technical bottleneck. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention discloses a method and application for evaluating ionomers in fuel cells based on thin liquid membrane electrodes, so as to solve the technical problem that the existing ionomer evaluation methods are difficult to truly reflect the three-phase interface construction ability, local hydration state regulation effect and intrinsic ion conduction characteristics of ionomers in the actual membrane electrode catalyst layer.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a method for evaluating fuel cell ionomers based on a thin liquid film electrode, which includes the following steps: S1: The catalyst and the ionomer to be tested are dispersed in a solvent to form a uniform and stable electrode slurry. The electrode slurry is then uniformly coated onto the surface of the gas diffusion layer to form a gas diffusion electrode. S2: Assemble the gas diffusion electrode, sealing gasket and graphite flow field plate with inlet and outlet gas pipes into a working electrode, and fix the working electrode in the predetermined position of the electrolytic cell to form a test system. S3: Add electrolyte to the electrolytic cell and construct a continuous and uniform thin liquid film on the surface of the catalyst layer of the working electrode by means of the pulling method or the steam wetting method to form a gas-liquid-solid three-phase interface. S4: Introduce the reaction gas into the electrolytic cell, perform electrochemical tests, and evaluate the performance of the ionomer to be tested based on the test results.

[0007] Based on the above solution, the present invention can also be improved in the following ways.

[0008] Furthermore, the catalyst is a platinum-based alloy catalyst or a non-precious metal catalyst, and the non-precious metal catalyst includes at least one of Ni-based catalyst and Fe-NC catalyst; the amount of the ionomer to be tested added is 10 to 100% of the catalyst mass.

[0009] Furthermore, the platinum-based alloy catalyst is Pt / C, PtRu / C, PtCo / C, or PtNi / C; the Ni-based catalyst is Ni-Cu, Ni-Pt, Ni-Pd, or Ni-Fe.

[0010] Furthermore, the solvent mentioned in step S1 is water, an alcohol solvent, or a mixture of water and an alcohol solvent.

[0011] Furthermore, in step S2, the electrolytic cell is a two-electrode system or a three-electrode system.

[0012] Furthermore, the lifting method in step S3 is as follows: the working electrode is completely immersed in the electrolyte, and then the working electrode is lifted upward at a uniform speed of 0.1~1mm / s, so that the bottom of the working electrode is still immersed in the electrolyte at a height of 0.1~0.12cm. A thin liquid film is formed on the surface of the catalyst layer of the working electrode by means of capillary action and surface tension.

[0013] Furthermore, the operation of the steam wetting method in step S3 is as follows: when fixing the working electrode, the bottom of the working electrode does not contact the surface of the electrolyte. The electrolyte is heated to 25~100℃ to generate steam. The relative humidity in the electrolytic cell is controlled to be 50~100%RH. The steam condenses on the surface of the catalyst layer of the working electrode to form a thin liquid film.

[0014] Furthermore, after constructing the thin liquid film in step S3, the method also includes monitoring the stability of the thin liquid film through cyclic voltammetry testing until three consecutive cyclic voltammetry curves coincide, indicating that the thin liquid film has reached a stable state.

[0015] Furthermore, the reaction gas in step S4 is oxygen or hydrogen; the electrochemical test includes linear voltammetry, chronoamperometry, or AC impedance spectroscopy.

[0016] The present invention also discloses the application of the above evaluation method in the screening of fuel cell ionomers.

[0017] The beneficial effects of this invention are: 1. This invention constructs a thin liquid film in situ on the surface of the working electrode, thereby expanding the interface from the traditional solid-liquid two-phase interface to a gas-liquid-solid three-phase coupling interface that is closer to the actual working state of the membrane electrode. This allows for a more effective evaluation of the three-phase interface construction capability, hydration regulation capability, and ion conduction performance of the ionomer in the actual working environment.

[0018] 2. The invention takes into account both the controllability of the model system and the representativeness of the test environment. Compared with the rotating disk electrode test method, it can more effectively reflect the film-forming behavior, wetting regulation and interfacial electrochemical performance of ionomers under near-real-world conditions. Compared with the full-cell test method, it can achieve independent evaluation of the intrinsic properties and interfacial effects of ionomers with fewer coupling factors.

[0019] 3. This invention can construct and evaluate different ionomers and different interface states by adjusting parameters such as the type of ionomer, electrode composition, electrolyte properties, temperature conditions, lifting height, humidification conditions and test mode, and has good applicability and scalability.

[0020] 4. This invention is not only applicable to the screening of ionomer materials for fuel cells and the optimization of membrane electrodes, but can also be extended to the testing and evaluation of other electrochemical systems involving the construction of gas-liquid-solid three-phase interfaces and the regulation of ion conduction, and has a wide range of application prospects. Attached Figure Description

[0021] Figure 1 Linear sweep voltammetry (LSV) curves of ionomer-based electrodes under three testing methods: rotating disk electrode (RDE), gas diffusion electrode (GDE), and thin liquid film electrode (LFE). Figure 2 The graphs show the chronoamperometry curves of the thin liquid film electrodes constructed with different ionomers in Examples 2-4 at a constant potential of 0.3V. Figure 3 Linear sweep voltammetry curves of thin liquid film electrodes constructed with different ionomers in Examples 2-4 under oxygen saturation conditions; Figure 4 Electrochemical impedance spectroscopy (EIC) spectra of thin liquid film electrodes constructed with different ionomers in Examples 2-4 at 0.3 V; Figure 5 This is a statistical comparison of the ohmic impedance of different ionomer-based electrodes obtained based on AC impedance spectroscopy fitting. Figure 6 The graphs show the polarization curves and power density curves of hydrogen-oxygen fuel cells assembled based on different ionomers in Examples 2-4. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0023] Preparation method of diphenyl ionomer A polyarylpiperidine polymer precursor was synthesized in one step using a superacid-catalyzed polymerization reaction. Quaternary ammonium salt groups were then introduced via quaternization, followed by film formation, ion exchange, and redissolution steps to obtain the target ionomer solution. The specific synthesis process is as follows: 1. Synthesis of biphenyl polyarylpiperidine precursor In a 100 mL round-bottom flask, 4.4 g of N-methyl-4-piperidinone, 5 g of biphenyl, and 12 mL of dichloromethane were added sequentially. At 0 °C, 2 mL of trifluoroacetic acid and 30 mL of trifluoromethanesulfonic acid were slowly added dropwise, and the reaction was continued at this temperature until a blue viscous slurry was formed. The resulting viscous, dark blue slurry was slowly poured into an aqueous ethanol solution, filtered, and a white fibrous solid was obtained. After washing with water, the solid was soaked in a 1 M KOH solution at 60 °C for 12 h. The final product was filtered, washed with water, and thoroughly dried at 80 °C to obtain a white fibrous polyarylpiperidine precursor.

[0024] 2. Quaternization reaction The biphenyl precursor was suspended in 100 mL of dimethyl sulfoxide, and 1 g of anhydrous potassium carbonate was added, followed by the rapid addition of iodomethane. The reaction mixture was stirred at room temperature in the dark for 48 h to obtain a viscous yellow solution. This solution was added dropwise to ethyl acetate, precipitating a pale yellow solid. After filtration, the solid was washed three times with deionized water and dried completely at 60 °C to obtain quaternized polyarylpiperidine in the iodide ion form.

[0025] 3. Preparation of ion exchange membranes The quaternized biphenyl was dissolved in DMSO to prepare a 10 mg / mL film-forming solution. A clean glass plate was placed in a dust-free environment, and the film-forming solution was filtered through an 800-mesh filter cloth to remove impurities and defects. The solution was then cast onto the glass plate at 80°C and completely dried to obtain an iodide ion-type biphenyl anion exchange membrane.

[0026] 4. Preparation of ion exchange and ionomer solutions The obtained membrane was immersed in 1M KOH solution for ion exchange for 48 hours, during which the alkali solution was replaced three times. After the exchange was completed, the membrane was washed with deionized water until neutral and dried in an oven at 80°C. The dried hydroxide-type membrane was redissolved in DMSO to prepare a 5 wt% diphenyl ionomer solution.

[0027] The preparation method of PFBP-14 is as follows: A polyarylpiperidine polymer precursor was synthesized in one step using a superacid-catalyzed polymerization reaction. Quaternary ammonium salt groups were then introduced via quaternization, followed by film formation, ion exchange, and redissolution steps to obtain the target ionomer solution. The specific synthesis process is as follows.

[0028] 1. Synthesis of polyarylpiperidine precursor (PFBP) In a 250 mL round-bottom flask, 6.2237 g of N-methyl-4-piperidinone, 1.3599 g of 9,9-dimethylfluorene, 6.6310 g of biphenyl, and 37.5 mL of dichloromethane were added sequentially. At 0 °C, 2.5 mL of trifluoroacetic acid and 37.5 mL of trifluoromethanesulfonic acid were slowly added dropwise, and the reaction was continued at this temperature until a blue viscous slurry was formed. The resulting viscous, dark blue slurry was slowly poured into an aqueous ethanol solution, filtered, and a white fibrous solid was obtained. After washing with water, the solid was soaked in a 1 M KOH solution at 60 °C for 12 h. The final product was filtered, washed with water, and thoroughly dried at 80 °C to obtain a white fibrous polyarylpiperidine precursor.

[0029] 2. Quaternization reaction 5 g of PFBP was suspended in 100 mL of dimethyl sulfoxide, and 1 g of anhydrous potassium carbonate was added, followed by the rapid addition of iodomethane. The reaction mixture was stirred at room temperature in the dark for 48 h to obtain a viscous yellow solution. This solution was added dropwise to ethyl acetate, and a pale yellow solid precipitated. After filtration, the solid was washed three times with deionized water and dried completely at 60 °C to obtain quaternized polyarylpiperidine in the iodide form (denoted as PFBP-14-I).

[0030] 3. Preparation of ion exchange membranes The above-mentioned PFBP-14-I was dissolved in DMSO to prepare a film-forming solution of 10 mg / mL. A clean glass plate was placed in a dust-free environment. The film-forming solution was filtered through an 800-mesh filter cloth to remove impurities and defects. The solution was then cast onto the glass plate at 80°C and completely dried to obtain an iodide ion-type polyarylpiperidine anion exchange membrane.

[0031] 4. Preparation of ion exchange and ionomer solutions The obtained membrane was immersed in 1M KOH solution for ion exchange for 48 hours, during which the alkali solution was replaced three times. After the exchange was completed, the membrane was washed with deionized water until neutral and dried in an oven at 80°C. The dried hydroxide-type membrane was redissolved in DMSO to prepare a 5 wt% PFBP-14 ionomer solution.

[0032] TP-100 was purchased from Versogen in the United States, 5 wt%.

[0033] Pention D35 was purchased from Xergy, USA, 5wt%.

[0034] Example 1 (Construction of a thin liquid film model electrode LFE based on the dip-coating method) A method for evaluating ionomers in fuel cells based on thin-film liquid electrodes, comprising the following steps: S1: 0.5 mg of 60% Pt / C catalyst (60% refers to the mass fraction of Pt) and biphenyl ionomer solution (the amount added is based on the mass of the pure ionomer, and is 30% of the catalyst mass) are uniformly dispersed in 0.5 mL of mixed solvent (water and isopropanol volume ratio of 4:1) to form a non-agglomerated and homogeneous stable electrode slurry; the electrode slurry is then uniformly coated onto a 5 cm² area using a spray gun. 2 On the surface of the gas diffusion layer, the coating speed is controlled at 10 mm / s during the coating process, and the nozzle scans and sprays along a serpentine path. The spacing between adjacent spraying trajectories (i.e., the flow channel spacing) is 3 mm to form a gas diffusion electrode. S2: Assemble the prepared gas diffusion electrode with a graphite flow field plate connected to inlet and outlet gas pipes and a PTFE sealing gasket to form the working electrode. The counter electrode is a graphite rod; the reference electrode is Hg / HgO. Fix the working electrode at the predetermined position in the electrolytic cell to form the test system. The inlet and outlet gas pipes of the graphite flow field plate are used for subsequent N2 introduction to ensure the gas phase environment on the electrode surface; the PTFE sealing gasket is used for sealing to prevent electrolyte leakage and also serves as insulation to prevent short circuits between the working electrode and other components, ensuring the stability of the test system; during assembly, the assembly pressure must be controlled to be uniform to ensure tight contact between all components and avoid affecting the test results due to poor contact. S3: Add the prepared 0.1M KOH electrolyte to the readable electrolytic cell, and saturate the electrolyte with N2 to remove oxygen from the electrolyte, preventing oxygen from participating in the electrode reaction and interfering with the test results, and ensuring that the test system is in an inert environment; then completely immerse the working electrode in the N2-saturated 0.1M KOH electrolyte. In the KOH electrolyte, the working electrode surface is completely covered by the electrolyte, forming a solid-liquid two-phase interface between the electrode and the electrolyte. The working electrode is then slowly and uniformly pulled upwards until only 0.1 cm of its bottom is immersed in the electrolyte. The electrode is then fixed in place. At this point, due to capillary action and surface tension, the 0.1 cm portion of the working electrode immersed in the electrolyte will adsorb the electrolyte onto the entire surface of the working electrode, forming a continuous and uniform thin liquid film on the catalytic layer surface (at this point, a clear gas-liquid-solid three-phase interface is formed on the electrode surface: solid phase: catalyst + ionomer; liquid phase: thin liquid film; gas phase: N2 atmosphere above the electrolytic cell). N2 is then continuously introduced into the electrolytic cell chamber. After 10 minutes, the gas flow is stopped, and the electrochemical workstation is started to perform CV testing. The CV curves are repeated until the previous three cycles coincide, indicating that the thin liquid film has reached a stable state and subsequent electrochemical tests can be performed.

[0035] S4: Quickly replace the N2-saturated 0.1M KOH electrolyte in the electrolytic cell with an O2-saturated 0.1M KOH electrolyte. Avoid touching the working electrode during the replacement process to prevent the thin liquid film from breaking. After replacement, introduce high-purity O2 into the electrolyte and ventilate for 30 minutes to ensure the electrolyte is completely saturated with O2. Then start the electrochemical workstation and scan according to the preset parameters (scanning potential window 0~1.2V, scan speed 10mV·s). - ¹) Perform LSV testing, keep O2 ventilation stable during the test, and record the test curve; repeat the test 3 times, and take the average curve of the 3 tests as the final LSV curve of the LFE method.

[0036] Comparative Example 1 To explore the testing differences between the RDE method, GDE method, and LFE method in Example 1, the same electrolyte, counter electrode, reference electrode, and test parameters were used to perform LSV tests on RDE and GDE respectively. The specific operations are as follows: 1. RDE test: A glassy carbon electrode with a diameter of 5 mm was selected as the working electrode. 60% Pt / C catalyst was uniformly modified on the surface of the glassy carbon electrode, and the modification amount was the same as that of the LFE working electrode (0.1 mg / cm²). The modified RDE working electrode, graphite rod counter electrode, and Hg / HgO reference electrode were placed in O2-saturated 0.1 M KOH electrolyte and tested according to the same LSV test parameters. The LSV curve of RDE was recorded.

[0037] 2. GDE test: The gas diffusion electrode (assembly without graphite flow field plate and PTFE sealing gasket) was prepared using the same method as the LFE working electrode. It was used as the GDE working electrode and placed in O2-saturated 0.1M KOH electrolyte. After complete immersion, the test was carried out according to the same LSV test parameters, and the LSV curve of GDE was recorded.

[0038] The LSV curves for the three testing methods, RDE, GDE, and LFE, are as follows: Figure 1 As shown.

[0039] The RDE curves show that when the potential drops to the range of 0.9 to 1.1 V, the ORR enters the kinetic control region; in the intermediate potential range of 0.7 to 0.9 V, the reaction enters the mixed control region, where the current is simultaneously affected by oxygen mass transfer and electrochemical kinetics; when the potential continues to drop below 0.6 V, the reaction completely enters the diffusion control region.

[0040] The GDE curve shows that the anode current is higher than that of RDE in the high potential region of 1.0~1.2V. When the potential drops below 1.0V, the current response exhibits a sloping characteristic.

[0041] The LFE curve shows that it exhibits a larger anodic current in the high potential region, while when the potential continues to drop below 0.9V, the thin liquid film electrode exhibits a steeper current slope. This is because the reaction in the solution test system occurs at the electrode-solution two-phase interface, while the reaction in the thin liquid film system is located at the solid-liquid-gas three-phase interface, which significantly improves the reaction efficiency.

[0042] Example 2 (Construction of Thin Liquid Film Electrode (LFE) based on vapor wetting method) A method for evaluating ionomers in fuel cells based on thin-film liquid electrodes, comprising the following steps: S1: Disperse 0.5 mg of 60% Pt / C catalyst (60% refers to the mass fraction of Pt) and PFBP-14 ionomer solution (the amount added is based on the mass of the pure ionomer, and the amount added is 30% of the mass of the catalyst) uniformly in 0.5 mL of mixed solvent (water and isopropanol volume ratio of 4:1) to form a non-agglomerated and homogeneous stable electrode slurry; use a spray gun to uniformly coat the electrode slurry onto an area of ​​5 cm². 2 On the surface of the gas diffusion layer, the coating speed is controlled at 10 mm / s during the coating process, and the nozzle scans and sprays along a serpentine path. The spacing between adjacent spraying trajectories (i.e., the flow channel spacing) is 3 mm to form a gas diffusion electrode. S2: Assemble the prepared gas diffusion electrode with the graphite flow field plate connected to the inlet and outlet gas pipes and the PTFE sealing gasket to form the working electrode; fix the assembled working electrode in the electrode installation position of the electrolytic cell, adjust the electrode height to ensure that the bottom of the electrode does not contact the electrolyte surface in the electrolytic cell, ensure that all parts are aligned during assembly, the PTFE sealing gasket is tightly fitted to prevent vapor leakage and electrode short circuit, and the assembly pressure is uniform to ensure tight contact; S3: Pour the prepared 0.1M KOH electrolyte into the electrolytic cell, adjust the electrode height to ensure that the bottom of the electrode does not touch the electrolyte surface in the electrolytic cell, but is only in the steam environment of the electrolytic cell; start the constant temperature water bath, set the temperature to 25℃, and start heating the KOH electrolyte in the electrolytic cell, so that the electrolyte slowly evaporates to produce water vapor; ensure that the humidity (100%RH) in the electrolytic cell is uniform and stable. At this time, the water vapor will form a uniform and continuous thin liquid film on the surface of the catalyst layer of the working electrode (at this time, a clear gas-liquid-solid three-phase interface is formed on the electrode surface, solid phase: catalyst + ionomer / no ionomer; liquid phase: thin liquid film formed by steam condensation; gas phase: O2 steam atmosphere in the electrolytic cell); after the thin liquid film is constructed, keep the water bath temperature constant and maintain 100%RH humidity, and prepare for electrochemical testing. S4: Introduce high-purity O2 into the electrolytic cell for 30 minutes to ensure that the air in the cell is completely purged and that the thin liquid film is in full contact with the O2, providing sufficient oxygen for the ORR reaction; start the electrochemical workstation and scan according to the preset parameters (scan potential window 0~1.2V, scan rate 10mV·s). - ¹), LSV testing was performed, maintaining stable O2 ventilation and humidity throughout the test, and the test curves were recorded. Additionally, AC impedance testing was conducted at a 0.3V overpotential (vs RHE) and a test frequency range of 10 Hz. - ²~10 5 Hz, AC signal amplitude 5mV, record AC impedance curve.

[0043] The difference between Example 3 and Example 2 is that the ionomer is TP-100.

[0044] The difference between Example 4 and Example 2 is that the ionomer is Pention D35.

[0045] The thin-film electrodes constructed with different ionomers in Examples 2-4 above were electrochemically tested in oxygen to explore the performance of different ionomers in constructing the three-phase interface. The results are as Figures 2-6 shown, where Figure 2 is the chronoamperometry test at 0.3 V; Figure 3 is the linear voltammetry scan curve; Figure 4 is the electrochemical impedance spectroscopy test at 0.3 V; Figure 5 is the statistical result of the Ohmic impedance obtained by fitting. The influence of the ionomer on the performance of the Pt / C cathode was studied at an overpotential of 0.3 V. The TP-100 system showed the smallest current gain (4.35 mA cm -2 ), because it forms a limited hydration layer only relying on the water molecules physically adsorbed on the surface, resulting in insufficient water molecules required for ORR. Pention D35 is the second, and the PFBP-14 system shows a larger current gain, because PFBP-14 is more hydrophilic than Pention D35, introducing more hydrated interfaces, and at the same time the conductive quaternary ammonium groups promote the discharge of the product OH - . Therefore, the order of the ORR output performance of the three is PFBP14 > Pention D35 > TP-100.

[0046] The results of the electrochemical impedance spectroscopy test show that the order of the Ohmic impedance is: PFBP14 < Pention D35 < TP-100. It is negatively correlated with the cathode output performance. The TP-100 system shows the highest Ohmic impedance (1.23 Ω), because it is difficult to maintain a stable hydrated interface, which limits the ion transport and cannot provide sufficient OH - for the reaction. The Ohmic impedance of the Pention D35 system is the second, and the PFBP-14 system shows the lowest Ohmic impedance (1.01 Ω). This phenomenon demonstrates the importance of the ionomer in constructing an efficient thin-film mass transfer network.

[0047] To verify the above conclusions, the aforementioned ionomers were combined with catalysts to prepare membrane electrodes. The membrane electrode preparation methods are as follows: In the anode catalyst ink preparation, a commercially available 75% PtRu / C catalyst was selected as the anode catalyst, and the anode ionomer was fixed as TP-100, controlling the ionomer content in the anode catalyst slurry to be 25% of the catalyst mass. In the cathode catalyst ink preparation, a commercially available 60% Pt / C catalyst was selected as the cathode catalyst, and cathode catalyst inks were prepared with ionomers PFBP-14, Pention D35, and TP-100, respectively, controlling the ionomer content in the cathode catalyst slurry to be 30% of the catalyst mass. Both anode and cathode inks used a solution of water and isopropanol in a 4:1 ratio, with a solid content (i.e., catalyst concentration) of 20 mg / mL. After ultrasonic treatment in a water bath for 15 minutes, a non-agglomerated and homogeneous stable electrode slurry was formed. The anode and cathode catalyst inks were uniformly coated onto the gas diffusion layer surface using a spray gun. The coating speed was controlled at 10 mm / s, and a serpentine flow pattern was employed to ensure uniform thickness. The flow channels were spaced 3 mm apart until coating was complete, forming the gas diffusion electrode. This was then combined with the commercial membrane PiperION-A20-HCO3 (Versogen, USA) to form a membrane electrode assembly. Testing was conducted in an AEMFC at 80°C, with a symmetrical pressure of 200 kPa applied to both electrodes, and H2 / O2 gas flow rates of 0.3 / 0.5 L / min. -1 The result is as follows Figure 6 As shown.

[0048] from Figure 6 As can be seen, the membrane electrode fabricated using PFBP-14 has the highest power output, with a peak power density as high as 2.24 W / cm². 2 The Pention D35 has a peak power density of 1.07 W / cm³. 2 The TP-100 exhibits the lowest peak power density, at only 0.48 W / cm². 2 This is consistent with the results of the thin-film test. Although the actual operating conditions of a fuel cell are complex, this thin-film evaluation system has successfully decoupled the microscopic behavior of ionomers, providing a key basis for predicting their performance in a full cell.

[0049] I. Correlation between test results and the three-phase interface building ability of ionomers The ability of ionomers to construct three-phase interfaces refers to their ability to guide the formation of a continuous and stable gas-liquid-solid three-phase interface on the surface of the catalyst layer. This directly determines the electrode reaction efficiency (reactant transport and active site utilization) and is one of the core performance characteristics of fuel cell ionomers.

[0050] The LSV curves obtained from the RDE, GDE, and LFE testing methods show that the LFE system exhibits significantly better LSV curve performance than RDE and GDE, demonstrating that the thin liquid film system of this invention can simulate the three-phase interface environment of a real fuel cell catalyst layer. Ionicomers, as key building blocks of the three-phase interface, directly influence the quality of interface formation through their film-forming properties and surface wettability. High-quality ionomers can form a continuous and uniform thin liquid film on the catalyst layer surface, achieving effective coupling of the solid-liquid-gas three phases and reducing mass transfer resistance.

[0051] The test results of Examples 2-4 further verify that the thin liquid film electrode constructed with PFBP-14 exhibits the best LSV curve and chronocurrent test performance, with a current gain greater than 4.35 mA·cm. - ² indicates that it has the strongest three-phase interface construction capability; the TP-100 system has the smallest current gain, indicating that it is difficult to construct a stable three-phase interface, resulting in insufficient oxygen mass transfer and reaction site utilization.

[0052] II. Correlation between test results and the hydration regulation ability of ionomers The hydration regulation capability of ionomers refers to their ability to adsorb and retain water molecules and form a stable hydration layer, which directly affects ion transport efficiency and electrode reaction continuity. The core influencing factor is the hydrophilic properties of the ionomers. A stable hydration layer can provide channels for ion conduction and ensure the supply of water molecules required for the reaction.

[0053] Tests in Examples 2-4 showed that the hydration regulation capabilities of different ionomers varied significantly: PFBP-14 was more hydrophilic than Pention D35, allowing for the introduction of more hydration interfaces, providing sufficient water molecules for the oxygen reduction reaction (ORR), and promoting OH-. - The discharge results in a more stable and higher chronocurrent curve output; TP-100 can only form a limited hydration layer through physical adsorption, which cannot meet the ORR reaction requirements, resulting in the smallest current gain and poor stability.

[0054] III. Correlation between test results and ion conductivity of ionomers The ion conduction performance of ionomers is characterized by ohmic impedance. The smaller the ohmic impedance, the higher the ion conduction efficiency. It is the core indicator that determines the energy conversion efficiency of fuel cells. Its performance depends on the characteristics of ion exchange groups and stable hydration channels.

[0055] The AC impedance test results of Examples 2-4 show that the ohmic impedance of different ionomers is in the order of PFBP-14 < Pention D35 < TP-100. This difference stems from the hydration regulation ability and the characteristics of the ionic groups: PFBP-14 has strong hydrophilicity, sufficient quaternary ammonium salt groups, and a complete hydration channel, resulting in high OH content. - It has low transport resistance; TP-100 has an unstable hydration interface, which hinders ion transport; Pention D35's performance is between the two.

[0056] The above results show that the thin liquid film electrode evaluation method of the present invention can effectively decouple the three-phase interface construction ability, hydration control ability and ion conduction performance of ionomers, and realize independent quantitative evaluation of the intrinsic properties of ionomers.

[0057] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A method for evaluating fuel cell ionomers based on thin liquid film electrodes, characterized in that, Includes the following steps: S1: The catalyst and the ionomer to be tested are dispersed in a solvent to form a uniform and stable electrode slurry, and then the electrode slurry is uniformly coated onto the surface of the gas diffusion layer to form a gas diffusion electrode. S2: Assemble the gas diffusion electrode, sealing gasket, and graphite flow field plate with inlet and outlet gas pipes into a working electrode, and fix the working electrode in a predetermined position in the electrolytic cell to form a test system; S3: Add electrolyte to the electrolytic cell and construct a continuous and uniform thin liquid film on the surface of the catalyst layer of the working electrode by means of the pulling method or the steam wetting method to form a gas-liquid-solid three-phase interface. S4: Introduce the reaction gas into the electrolytic cell, perform electrochemical tests, and evaluate the performance of the ionomer to be tested based on the test results.

2. The method for evaluating fuel cell ionomers based on thin liquid film electrodes according to claim 1, characterized in that, The catalyst mentioned in step S1 is a platinum-based alloy catalyst or a non-precious metal catalyst, wherein the non-precious metal catalyst includes at least one of Ni-based catalyst and Fe-NC catalyst; the amount of ionomer to be tested added is 10 to 100% of the catalyst mass.

3. The method for evaluating fuel cell ionomers based on thin liquid film electrodes according to claim 2, characterized in that, The platinum-based alloy catalyst is Pt / C, PtRu / C, PtCo / C, or PtNi / C; the Ni-based catalyst is Ni-Cu, Ni-Pt, Ni-Pd, or Ni-Fe.

4. The method for evaluating fuel cell ionomers based on thin liquid film electrodes according to claim 1, characterized in that, The solvent mentioned in step S1 is water, an alcohol solvent, or a mixture of water and an alcohol solvent.

5. The method for evaluating fuel cell ionomers based on thin liquid film electrodes according to claim 1, characterized in that, In step S2, the electrolytic cell is either a two-electrode system or a three-electrode system.

6. The method for evaluating fuel cell ionomers based on thin liquid film electrodes according to claim 1, characterized in that, The lifting method in step S3 is as follows: the working electrode is completely immersed in the electrolyte, and then the working electrode is lifted upward at a uniform speed of 0.1~1mm / s, so that the bottom of the working electrode is still immersed in the electrolyte at a height of 0.1~0.12cm. A thin liquid film is formed on the surface of the catalyst layer of the working electrode by means of capillary action and surface tension.

7. The method for evaluating fuel cell ionomers based on thin liquid film electrodes according to claim 1, characterized in that, The operation of the steam wetting method in step S3 is as follows: when fixing the working electrode, the bottom of the working electrode does not contact the surface of the electrolyte. The electrolyte is heated to 25~100℃ to generate steam. The relative humidity in the electrolytic cell is controlled to be 50~100%RH. The steam condenses on the surface of the catalyst layer of the working electrode to form a thin liquid film.

8. The method for evaluating fuel cell ionomers based on thin liquid film electrodes according to claim 1, characterized in that, After constructing the thin liquid film in step S3, the stability of the thin liquid film is monitored by cyclic voltammetry until three consecutive cyclic voltammetry curves coincide, indicating that the thin liquid film has reached a stable state.

9. The method for evaluating fuel cell ionomers based on thin liquid film electrodes according to claim 1, characterized in that, The reaction gas in step S4 is oxygen or hydrogen; the electrochemical test includes linear voltammetry, chronoamperometry, or AC impedance spectroscopy.

10. The application of the fuel cell ionomer evaluation method based on thin liquid film electrode according to any one of claims 1 to 9 in the screening of fuel cell ionomers.

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