A hydrophobicity-tunable nanotube array electrode for fuel cells and preparation and application thereof
By fabricating hydrophobic alloy nanotube array electrodes in fuel cells, the flooding problem was solved, the utilization rate and stability of the catalyst were improved, and rapid transport of protons, electrons, gases and water was achieved, thereby enhancing the overall performance of the fuel cell.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DALIAN UNIV OF TECH
- Filing Date
- 2023-01-06
- Publication Date
- 2026-07-14
AI Technical Summary
The existing fuel cells suffer from water flooding, which causes the active sites of the catalyst to fail, resulting in slow mass transfer, unsatisfactory cell performance, low catalyst utilization and mass transfer efficiency, and difficulty in achieving efficient transport of protons, electrons, gases and water.
Alloy nanotube arrays were grown on a substrate using a hydrothermal method, then converted into metal nanotube arrays using a self-sacrificing template method. The arrays were then heat-treated at different temperatures to enhance the bonding force and uniform distribution of the hydrophobic agent with the nanotube arrays. Finally, the arrays were transferred onto a proton exchange membrane to form a nanotube array electrode with tunable hydrophobicity.
It achieves low catalyst loading, high catalyst utilization, good durability and good water management, improves the single-cell performance of fuel cells, adapts to water management under high current, and enhances catalyst stability and catalytic activity.
Smart Images
Figure CN116314882B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polymer membrane fuel cell technology, and relates to a hydrophobic alloy nanotube array electrode for fuel cells, its preparation and application. Background Technology
[0002] Proton exchange membrane fuel cells (PEMFCs) have attracted widespread attention due to their high energy conversion efficiency, low operating temperature, and environmental friendliness, showing great promise in fields such as automotive, aerospace, and stationary power plants. However, the high cost and insufficient durability of membrane electrode assemblies (MEAs) hinder their large-scale commercialization. In MEAs, the cathode requires more expensive platinum to catalyze the sluggish kinetics of the oxygen reduction reaction (ORR). To address these issues, significant efforts have been made, primarily in developing low-platinum or non-platinum catalysts with high activity and durability, including platinum-based alloys, core-shell structures, and transition metal (Fe, Co, Mn, etc.) and nitrogen-co-doped carbon-based catalysts. While some catalysts exhibit excellent catalytic activity and stability in half-cells, they perform poorly in full-cells. The actual operating environment in PEMFCs is completely different from the testing environment of half-cells. In half-cell testing, researchers use rotating (ring) disk electrodes (RDEs) to enhance mass transfer and eliminate concentration polarization to maximize the inherent catalytic activity. In practice, the continuous flow of gas, accompanied by the evolution of liquid water, can cause severe flooding within the catalyst layer, leading to the failure of some active sites, slow mass transfer, and unsatisfactory battery performance. Therefore, we need to design a reasonable electrode structure to ensure the rapid transport of gas, water, protons, and electrons, in order to achieve an effective conversion of catalyst activity into single-cell performance.
[0003] Currently, the mainstream preparation process uses a direct coating method to directly coat or spray the catalyst onto both sides of the proton exchange membrane, and finally hot-presses the anode and cathode gas diffusion layers onto the catalyst layers on both sides to obtain the MEA. The catalyst layer of the MEA is made of a mixture of Pt / C catalyst and resin. The water, gas, electron, and proton transport channels are in a disordered state, making it difficult to construct a rich three-phase reaction interface. This results in low catalyst utilization and mass transfer efficiency, which seriously restricts the high-current discharge performance of the membrane electrode. Ordering the MEA structure can achieve efficient transport of protons, electrons, gases, and water, improve the overall performance of PEMFC, increase Pt utilization, and effectively reduce the cost of MEA.
[0004] Patents CN104900893.A and CN 109509888.A utilize light-driven or ligand-mediated synthesis to synthesize catalyst layers composed of nano-crown or branched metal catalysts on one or both sides of the membrane; however, the catalysts have low crystallinity and poor durability.
[0005] Patent CN 107623131.A describes the preparation and application of a membrane electrode based on platinum or platinum alloy nanotubes. First, a regularly oriented Co-OHCO3 nanorod array is grown on a substrate. Then, platinum is supported on the array using magnetron sputtering, followed by annealing to obtain a highly crystalline or alloyed catalyst material. However, due to the high hydrophilicity of metals such as platinum, the platinum catalyst on the cathode side is coated with water, causing flooding. This drastically reduces the effective three-phase interface for the ORR reaction, leading to a sharp decrease in the power density of the battery at high current densities.
[0006] To address the flooding problem, patent CN 112993349 A provides a method for fabricating a hollow nanogroove membrane electrode that can be used in fuel cells or PEM water electrolysis. The hollow nanogrooves are interconnected in three dimensions to form a layered structure. This structure has a drainage mechanism similar to that of grasses, giving the integrated membrane electrode excellent water management capabilities. However, this method requires sophisticated equipment and the construction process is relatively complex. Summary of the Invention
[0007] The purpose of this invention is to provide a hydrophobically tunable nanotube array electrode for fuel cells, its preparation, and its application. This electrode has advantages such as low catalyst loading, high catalyst utilization, good durability, and good water management.
[0008] The following technical solution is adopted:
[0009] A hydrophobicity-tunable alloy nanotube array electrode for fuel cells, the electrode comprising a highly stable and highly catalytically active alloy nanotube array, wherein the alloy nanotube array is modified with hydrophobic agents of varying degrees and subjected to heat treatment at different temperatures to enhance the bonding force and uniform distribution of the hydrophobic agents with the nanotube array.
[0010] The alloy is a Pt-Zn alloy, or an alloy composed of Pt-Zn and one or more of Au, Ir, Pd, Rh, Ag, Fe, Ru, Cu and Ni.
[0011] Based on the above technical solutions, preferably, the diameter of the nanotube is 20-50 nm and the length is 0.2-2.0 μm.
[0012] Based on the above technical solutions, preferably, the hydrophobic agent is PVDF, PTFE, or Nafion resin. One or more of the amorphous perfluoropolymers.
[0013] Based on the above technical solutions, preferably, the heat treatment temperature is 100-500℃, more preferably 100-400℃, and the heat treatment time is 10-200min.
[0014] The method for fabricating the hydrophobically tunable nanotube array electrode for fuel cells includes the following steps:
[0015] 1) ZnO nanowire arrays were grown on a substrate using a hydrothermal method. The specific synthesis steps are as follows:
[0016] A. Drop-coat or spin-coat the substrate with a 10-100mM zinc acetate solution. The volume of zinc acetate solution used is 0.1-1 mL / cm². -2 The substrate is then annealed at 200-500℃ for 10-60 minutes.
[0017] B. Prepare the reaction solution with a concentration of 10-100 mM zinc nitrate, 10-100 mM hexamethylenetetramium and 2-20 mM polyethyleneimine;
[0018] C. Immerse the substrate from A into the reaction solution, then seal it in a polytetrafluoroethylene reactor and react at 60-110℃ for 3-10 hours to obtain a ZnO nanowire array.
[0019] Based on the above technical solutions, preferably, the substrate can be one of stainless steel sheet, copper sheet, PTFE film, plastic sheet, nickel sheet, aluminum foil or titanium sheet.
[0020] 2) The ZnO nanowire array was converted into a metal nanotube array using the self-sacrificing template method. The specific preparation process is as follows:
[0021] A. Prepare a mixed solution of metal precursor and reducing agent as the reaction solution, wherein the reaction solution consists of 0.1-10 mM metal precursor and 1-100 mM reducing agent;
[0022] B. Place the substrate with the ZnO nanowire array into the reaction solution and react at 30-100℃ for 30-100 min;
[0023] C. Remove the substrate containing the metal nanotube array, rinse it with deionized water, and then dry it at 50-100℃.
[0024] Based on the above technical solutions, preferably, the metal precursor is a noble metal precursor, or a mixture of noble metal precursor and non-noble metal precursor. The noble metal precursor is one or more of the metal salts of Pt, Ru, Ir, Au, Rh, Pd and Ag, such as H2PtCl6, PtCl2, PtCl4, K2PtCl4, RuCl2, HAuCl4, RhCl3, IrCl3 and K2PdCl4, etc. The non-noble metal precursor is one or more of the metal salts of Ni, Co, Cu, Fe and Mn, such as Ni(NO3)2, Cu(NO3)2, Fe(NO3)2, NiCl2, Co(NO3)2 and CoCl2, etc.
[0025] Based on the above technical solutions, preferably, the reducing agent is one or more of ascorbic acid, sodium citrate, citric acid, sodium borohydride, formic acid and hydroxylamine hydrochloride, and the concentration of the reducing agent is preferably 0.1-20 mM.
[0026] Based on the above technical solutions, preferably, the number of times the deionized water is rinsed is 3-5 times.
[0027] 3) The alloying and hydrophobication engineering of metal nanotube arrays, the specific process is as follows:
[0028] A. Prepare solutions of hydrophobic agents with different mass fractions, the mass fraction of the hydrophobic agent in the solution being 0.1-10 wt%, and the solvent being one or more of deionized water, ethanol, toluene, diethyl ether, methanol, and chloroform. The hydrophobic agent is PVDF, PTFE, Nafion resin, etc. One or more of the amorphous perfluoropolymers.
[0029] B. Immerse the substrate carrying the metal nanotube array in the solution of the hydrophobic agent for 0-100 min, or disperse the solution of the hydrophobic agent on the metal nanotube array using ultrasonic spraying, with a spraying amount of 1-100 μL / cm³. -2 A nanotube array loaded with a hydrophobic agent was obtained;
[0030] C. Nanotube arrays loaded with hydrophobic agents are alloyed and hydrophobically engineered through heat treatment under a protective atmosphere.
[0031] Based on the above technical solutions, preferably, the heat treatment atmosphere is H2 or a mixture of H2-Ar, H2-N2 and H2-He, and the mass fraction of H2 in the mixture is 3-99%; the preferred heat treatment temperature is 100-500℃, the more preferred heat treatment temperature is 100-400℃, and the heat treatment time is 10-200min.
[0032] 4) The transfer and cleaning of the membrane electrode are carried out as follows:
[0033] A. A nanotube array is transferred onto a proton exchange membrane using a hot-pressing method. The hot-pressing temperature is 125-140℃, the pressure is 0.3-5MPa, and the hot-pressing time is 1-10min, to obtain a membrane electrode based on an alloy nanotube array.
[0034] B. Immerse the membrane electrode in a 1-10 wt% H₂SO₄ solution for 30-60 min, then rinse with deionized water at 50-100°C as one step. Repeat this step 1-3 times to achieve cleaning of the membrane electrode based on the alloy nanotube array.
[0035] Based on the above technical solutions, preferably, the number of times the deionized water is rinsed is 3-5 times.
[0036] The present invention also relates to protecting the above-mentioned hydrophobic tunable alloy nanotube array electrode or the hydrophobic tunable alloy nanotube array electrode prepared by the above method for application in fuel cells, especially proton exchange membrane fuel cells.
[0037] This invention provides a hydrophobically tunable alloy nanotube array electrode for fuel cells and its preparation method, including the preparation of a metal nanotube array, alloying and hydrophobication engineering of the metal nanotube array, and assembly of the membrane electrode assembly. First, a metal nanotube array is constructed on a substrate surface using a two-step hydrothermal method; then, a hydrophobic material is introduced onto the metal nanotube array using impregnation or ultrasonic spraying; next, pyrolysis is performed to achieve alloying and hydrophobication engineering of the nanotube array; finally, the nanotube array is transferred onto a proton exchange membrane, and the membrane electrode assembly is cleaned. The hydrophobically tunable nanotube array electrode prepared by this invention exhibits high catalyst activity and stability, and low platinum loading (<100 μg / cm³). -2 Advantages include good water management and ease of scale-up. The quasi-ordered ultrathin nanotube array electrode facilitates the rapid transport of protons, electrons, gas, and water, improving catalyst utilization. Appropriate hydrophilicity / hydrophobicity helps maintain water balance on the membrane electrode, ensuring that electrochemical reactions occur at a sufficient number of catalytic active sites at the three-phase interface, thereby improving membrane electrode performance. The highly stable platinum alloy catalyst can meet the durability requirements of automotive proton exchange membrane fuel cells under actual operating conditions.
[0038] Compared with the prior art, the present invention has the following advantages:
[0039] (1) The method is simple and easy to operate, the process equipment cost is low, and it is easy to scale up;
[0040] (2) Alloy nanotube arrays can effectively reduce mass transfer resistance and catalyst dosage, and significantly improve catalyst durability and catalytic activity;
[0041] (3) Reasonable hydrophobic engineering can alleviate the flooding phenomenon of the catalyst layer under high current and improve the single-cell performance of membrane electrode. Attached Figure Description
[0042] Figure 1 This is a scanning electron microscope image of the ZnO nanowire array in this invention.
[0043] Figure 2 This is a scanning electron microscope image of the Pt@ZnO nanotube array in this invention.
[0044] Figure 3 This is a transmission electron microscope (TEM) image of the Pt-Zn alloy nanotubes used in this invention.
[0045] Figure 4 The images show the XRD patterns of the ZnO nanowire array before and after hydrothermal treatment in this invention.
[0046] Figure 5 The images show the X-ray diffraction patterns of different hydrophobic array electrodes in this invention.
[0047] Figure 6 These are scanning electron microscope images of different hydrophobic alloy nanotube arrays in this invention.
[0048] Figure 7 These are the contact angle test results for different hydrophobic alloy nanotube arrays in this invention.
[0049] Figure 8 This is an optical photograph of the Pt-Zn alloy nanotube array in this invention.
[0050] Figure 9 This is an optical photograph of the alloy nanotube array film electrode used in this invention.
[0051] Figure 10 The images show cross-sectional scanning electron microscope (SEM) images and elemental scans of the hydrophobic alloy nanotube array membrane electrode used in this invention.
[0052] Figure 11 The graph shows the fuel cell performance of the traditional membrane electrode (Pt / C) and the array electrodes of different hydrophobic alloy nanotubes in H2 / O2.
[0053] Figure 12 The graph shows the fuel cell performance of the conventional membrane electrode (Pt / C), the unhydrophobicated and the 10-min hydrophobic alloy nanotube array electrode in H2 / Air.
[0054] Figure 13 Impedance spectra of the conventional membrane electrode (Pt / C), the non-hydrophobic, and the 10-min hydrophobic alloy nanotube array electrode in this invention under H2 / Air.
[0055] Figure 14 Accelerated durability testing was conducted on (a) a conventional membrane electrode (Pt / C), (b) an unhydrophobicated electrode, and (c) a 10-minute hydrophobic alloy nanotube array electrode in this invention.
[0056] Figure 15 This is a scanning electron microscope image of the platinum-palladium nanotube array in this invention. Detailed Implementation
[0057] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the invention.
[0058] Example 1
[0059] 1) ZnO nanowire arrays were grown on a substrate using a hydrothermal method. The synthesis steps are as follows:
[0060] A. Drop 0.3 mL of 50 mM zinc acetate solution onto a stainless steel sheet (3*8 cm). 2 , denoted as SS), and then annealed at 350℃ for 15 min;
[0061] B. Prepare 50 mL of reaction solution with the following concentrations: 25 mM zinc nitrate, 25 mM hexamethylenetetramium, and 10 mM polyethyleneimine.
[0062] C. Immerse the stainless steel sheet from A into the above reaction solution, then seal it in a polytetrafluoroethylene reactor and react at 100°C for 6 hours to obtain a ZnO nanowire array, denoted as ZnO / SS. Figure 1 Here is a scanning electron microscope image of the ZnO nanowire array, as shown below. Figure 1 As shown, many needle-like nanowires are uniformly arranged in an array on stainless steel. The nanowires have smooth surfaces and are independent of each other, with diameters mostly between 20-30 nm.
[0063] 2) The ZnO nanowire array was converted into a metal nanotube array using the self-sacrificing template method. The preparation process is as follows:
[0064] A. Prepare 5 mL of reaction solution, which is a solution of 3 mM K2PtCl4 and 0.1 mM citric acid;
[0065] B. Place the substrate with the ZnO nanowire array into the above reaction solution and perform a hydrothermal reaction at 80°C for 60 min;
[0066] C. Remove the substrate containing the platinum nanotube array, rinse it three times with deionized water, and then dry it overnight at 70°C to obtain the platinum nanotube array sample, denoted as Pt@ZnO / SS.
[0067] Figure 2 This is a scanning electron microscope (SEM) image of a platinum nanotube array. We can see that the array structure remains intact; however, as the nanowire array transforms into a nanotube array, its surface becomes rougher. Its transmission electron microscope (TEM) image is shown below. Figure 3 As shown, the nanotubes have a size of 25-35 nm and a wall thickness of 5-8 nm. Figure 4 X-ray diffraction patterns of the ZnO nanowire array before and after the B-step hydrothermal reaction. Figure 4 As shown, compared to stainless steel sheets (ZnO / SS) containing ZnO nanowire arrays, the characteristic peak intensity of ZnO in the post-reaction sample remains, albeit at a lower intensity. No characteristic peak of platinum is observed, possibly due to the low crystallinity of platinum synthesized via hydrothermal synthesis. This indicates that some ZnO was sacrificed as a template, and the nanotubes are Pt@ZnO.
[0068] 3) The alloying and hydrophobication engineering of metal nanotube arrays is as follows:
[0069] A. Prepare 15 mL of 0.5 wt% PVDF ethanol solution.
[0070] B. Immerse the substrate carrying the metal nanotube array in 5 mL of the above solution for 0, 5, 10 and 20 min respectively.
[0071] C. The nanotube array loaded with hydrophobic agent was heat-treated at 500℃ for 30 min in a 5% H2 / Ar atmosphere to achieve alloying and hydrophobic engineering, and different hydrophobic nanotube array electrode samples were obtained (the hydrophobic nanotube array electrode samples obtained by hydrophobic treatment for 0, 5, 10 and 20 min were denoted as 0-PFNT / SS, 5-PFNT / SS, 10-PFNT / SS and 20-PFNT / SS, respectively).
[0072] Figure 5 X-ray diffraction patterns of different hydrophobic nanotube array electrodes, such as Figure 5 As shown, compared to Pt@ZnO / SS, all pyrolyzed samples exhibited a characteristic peak located between the {111} characteristic peak of Pt and the {101} characteristic peak of Zn. This indicates that during the heat treatment process, Pt alloys with Zn in ZnO, and the crystallinity of the metal also increases, which is beneficial to the durability of the catalyst.
[0073] 4) Transfer and cleaning of membrane electrodes
[0074] A. Nanotube arrays were transferred onto a proton exchange membrane (Nafion212) using a hot-pressing method. The hot-pressing temperature was 125℃, the pressure was 0.3MPa, and the hot-pressing time was 5min.
[0075] B. The membrane electrode was immersed in 3 wt% H2SO4 solution for 30 min, and then rinsed three times with deionized water at 80 °C. This step was repeated twice to clean the nanotube array-based membrane electrode, resulting in alloy nanotube array-based membrane electrode samples (the alloy nanotube array-based membrane electrodes obtained after hydrophobic treatment for 0, 5, 10, and 20 min were denoted as 0-PFNT, 5-PFNT, 10-PFNT, and 20-PFNT, respectively).
[0076] Example 2
[0077] 1) ZnO nanowire arrays were grown on a substrate using a hydrothermal method. The synthesis steps are as follows:
[0078] A. Apply 0.3 mL of 50 mM zinc acetate solution to a stainless steel (3*8 cm) surface. 2 , denoted as SS), and then annealed at 350℃ for 15 min;
[0079] B. Prepare 50 mL of reaction solution with the following concentrations: 25 mM zinc nitrate, 25 mM hexamethylenetetramium, and 10 mM polyethyleneimine.
[0080] C. Immerse the stainless steel sheet from A into the above reaction solution, then seal it in a polytetrafluoroethylene reactor and react at 100°C for 6 hours to obtain a ZnO nanowire array, denoted as ZnO / SS.
[0081] 2) The ZnO nanowire array was converted into a metal nanotube array using the self-sacrificing template method. The preparation process is as follows:
[0082] A. Prepare 5 mL of reaction solution, which is a solution of 3 mM K2PtCl4 and 0.1 mM citric acid;
[0083] B. Place the substrate with the ZnO nanowire array into the reaction solution and react at 80°C for 60 min;
[0084] C. Remove the substrate containing the platinum nanotube array, rinse it three times with deionized water, and then dry it overnight at 70°C to obtain the platinum nanotube array sample, denoted as Pt@ZnO / SS.
[0085] 3) The alloying and hydrophobication engineering of metal nanotube arrays is as follows:
[0086] A. Prepare 5 mL of 1 wt% PTFE aqueous solution.
[0087] B. Immerse the substrate carrying the metal nanotube array in the above solution for 0, 5, 10 and 20 min respectively.
[0088] C. The nanotube array loaded with hydrophobic agent was heat-treated at 500℃ for 30 min in a 5% H2 / Ar atmosphere to achieve alloying and hydrophobic engineering, and different hydrophobic nanotube array electrode samples were obtained (the hydrophobic nanotube array electrode samples obtained by hydrophobic treatment for 0, 5, 10 and 20 min were denoted as 0-PFNT / SS, 5-PFNT / SS, 10-PFNT / SS and 20-PFNT / SS, respectively).
[0089] Figure 6 These are scanning electron microscope (SEM) images of different hydrophobic alloy nanotube arrays. The array structure of the nanotubes remains intact after alloying and hydrophobication processes. With prolonged immersion time, PTFE aggregates appear on the alloy nanotube arrays. Figure 7 The results show the contact angle measurements of different hydrophobic alloy nanotube arrays. Figure 7As shown, the contact angle of the electrode without hydrophobic treatment was 56.2°, indicating that the electrode is hydrophilic and prone to flooding under high current conditions. With increasing hydrophobicity, the electrode's hydrophobicity gradually increased. The contact angles of the electrode after treatment for 5, 10, and 20 minutes were 104.7°, 126.9°, and 131.6°, respectively.
[0090] Figure 8 This is an optical image of a Pt-Zn alloy nanotube array, with a membrane electrode size of 5.2 x 5.2 cm. 2 The catalyst layer is uniformly distributed and appears black. We can prepare membrane electrodes of different sizes by changing the substrate size according to requirements. This process is convenient to operate and easy to scale up.
[0091] 4) Transfer and cleaning of membrane electrodes
[0092] A. Nanotube arrays were transferred onto a proton exchange membrane (Nafion212) using a hot-pressing method. The hot-pressing temperature was 125℃, the pressure was 0.3MPa, and the hot-pressing time was 5min.
[0093] B. The membrane electrode was immersed in 3 wt% H2SO4 solution for 30 min, and then rinsed three times with deionized water at 80 °C. This step was repeated twice to clean the nanotube array-based membrane electrode, resulting in an alloy nanotube array-based membrane electrode sample. (The alloy nanotube array-based membrane electrodes obtained after hydrophobication treatment for 0, 5, 10, and 20 min were denoted as 0-PFNT, 5-PFNT, 10-PFNT, and 20-PFNT, respectively).
[0094] Figure 9 This is an optical photograph of an alloy nanotube array film electrode. Figure 9 As shown, the catalyst layer was successfully transferred onto the proton exchange membrane, and the catalyst layer was uniformly distributed. ICP testing showed a platinum loading of 62 μg / cm³. -2 . Figure 10 These are cross-sectional scanning electron microscope (SEM) images and elemental scans of a hydrophobic alloy nanotube array film electrode. (Example:) Figure 10 As shown, the catalyst layer thickness is 500 nm, which is less than the 2 μm thickness of traditional membrane electrodes. The elemental distribution diagram shows that F is uniformly distributed in the catalyst layer, indicating that PTFE is uniformly modified on the nanotube array.
[0095] The above-mentioned membrane electrode was used to test fuel cell performance using either the alloy nanotube array electrode or the Pt / C electrode (with a platinum loading of 0.1 mg / cm³). -2 The cathode is a 60% Pt / C electrode (platinum loading of 0.2 mg / cm²). -2 The anode was used, and the test conditions were: H2 / O2 flow rate of 0.1 / 0.2 L / min. -1The battery temperature is 80℃, the added humidity of H2 / O2 is 100%RH, and the battery back pressure is 0.2MPa. Figure 11 For traditional membrane electrodes (Pt / C, platinum loading 0.1 mg cm⁻¹) -2 The graphs show the performance of fuel cells with different hydrophobic alloy nanotube array electrodes. When the hydrophobication time is 0, 5, 10, and 20 min, the peak power of the fuel cell corresponding to the hydrophobicated membrane electrode is 0.887, 0.945, 0.992, and 0.924 W / cm², respectively. -2 Among them, the alloy nanotube array electrode after 10 minutes of hydrophobication exhibited the best performance. Appropriate hydrophobication enhances the membrane electrode's water management capabilities, thus preventing flooding under high current and ultimately achieving higher fuel cell performance. The fuel cell performance of a conventional membrane electrode is 0.894 W / cm². -2 The cathode platinum loading is 0.1 mg / cm³. -2 Its specific energy density is 8.95 kWg. -1 Lower than alloy nanotube array electrodes (14.3 kWg) -1 ).
[0096] For traditional membrane electrodes (Pt / C, platinum loading 0.1 mg cm⁻¹), -2 Fuel cell tests were conducted under H2 / Air conditions using both unhydrophobicated alloy nanotube array electrodes and alloy nanotube array electrodes that had been hydrophobized for 10 min. The test conditions were: H2 / O2 flow rate of 0.1 / 0.2 L / min. -1 The battery temperature is 80℃, the added humidity (H2 / O2) is 100% RH, and the battery back pressure is 0.2 MPa. Figure 12 As shown, the unhydrophobic alloy nanotube array electrode (0.519 W cm⁻¹) -2 The superior performance compared to traditional membrane electrode assemblies indicates that the ultrathin, ordered nanotube array structure facilitates the rapid transport of protons, electrons, gas, and water, thereby improving catalyst utilization. After appropriate hydrophobication, the fuel cell performance was further enhanced, reaching 0.619 W / cm². -2 This is mainly due to the electrode's excellent water management capabilities. However, excessive hydrophobication treatment can cover a large number of catalytically active sites, which is detrimental to the overall performance of the MEA. Electrochemical impedance spectroscopy is used, such as... Figure 13 As shown, the appropriately hydrophobicated electrode exhibits lower charge transfer resistance and oxygen diffusion resistance, further demonstrating the advantages of ultrathin nanotube arrays and hydrophobication engineering.
[0097] For traditional membrane electrodes (Pt / C, platinum loading 0.1 mg cm⁻¹), -2Accelerated durability tests (ADTs) were conducted on both the unhydrophobicated alloy nanotube array electrode and the alloy nanotube array electrode after hydrophobization for 10 min. The test conditions were: H2 / N2 (anodine / cathode) flow rate of 0.1 / 0.2 L / min. -1 The battery temperature was 80℃, the added humidity (H2 / N2) was 100% RH, the scan voltage was 1.0-1.5V, and the scan rate was 500mV s. -1 .like Figure 14 The fuel cell performance before and after 3000 ADTs cycles is as follows: Figure 14 As shown, the power density of the conventional membrane electrode decreased from 894.8 mW / cm² to 444.1 mW / cm². -2 The retention rate was 49.6%; the power density of the alloy nanotube array electrode decreased from 886.8 mW / cm² to 746.3 mW / cm². -2 The retention rate was 84.2%; the power density of the hydrophobic alloy nanotube array electrode decreased from 992.7 mW / cm² to 858.1 mW / cm². -2 The retention rate was 86.4%. Compared with the JM 60% Pt / C electrode, the alloy nanotube array electrode synthesized in this invention exhibits better cycling stability. Furthermore, appropriate hydrophobic engineering optimizes the water management of the electrode, further promoting the cycling stability of the catalyst layer.
[0098] Example 3
[0099] 1) ZnO nanowire arrays were grown on a substrate using a hydrothermal method. The synthesis steps are as follows:
[0100] A. Disperse a 50mM zinc acetate solution onto a 3*8cm stainless steel sheet using ultrasonic spraying. 2 (referred to as SS), spraying amount is 0.1 mL / cm -2 Then anneal at 350℃ for 15 minutes;
[0101] B. Prepare 50 mL of reaction solution with the following concentrations: 25 mM zinc nitrate, 25 mM hexamethylenetetramium, and 10 mM polyethyleneimine.
[0102] C. Immerse the stainless steel sheet from A into the reaction solution, then seal it in a polytetrafluoroethylene reactor and react at 100°C for 6 hours to obtain a ZnO nanowire array.
[0103] 2) The ZnO nanowire array was converted into a metal nanotube array using the self-sacrificing template method. The preparation process is as follows:
[0104] A. Prepare 5 mL of reaction solution, which is a solution of 1.5 mM K2PtCl4, 1.5 mM K2PdCl4 and 0.1 mM citric acid;
[0105] B. Place the substrate with the ZnO nanowire array into the reaction solution and react at 80°C for 60 min;
[0106] C. Remove the substrate containing the platinum nanotube array, rinse it three times with deionized water, and then dry it overnight at 70°C to obtain the platinum-palladium nanotube array.
[0107] Figure 15 This is a scanning electron microscope image of a platinum-palladium nanotube array. We can see that the array structure remains intact, and the nanowire array has been transformed into a nanotube array.
[0108] 3) The alloying and hydrophobication engineering of metal nanotube arrays is as follows:
[0109] A. Prepare 5 mL of 0.5 wt% PVDF ethanol solution.
[0110] B. Immerse the substrate carrying the metal nanotube array in the above solution for 0, 5, 10, and 20 minutes, respectively.
[0111] C. Nanotube arrays loaded with hydrophobic agents were heat-treated at 200℃ for 30 min in a 5% H2 / Ar atmosphere to achieve alloying and hydrophobicization, resulting in electrode samples of different hydrophobic nanotube arrays.
[0112] 4) Transfer and cleaning of membrane electrodes
[0113] A. Nanotube arrays were transferred onto a proton exchange membrane (Nafion212) using a hot-pressing method. The hot-pressing temperature was 125℃, the pressure was 0.3MPa, and the hot-pressing time was 5min.
[0114] B. The membrane electrode was immersed in 3 wt% H2SO4 solution for 30 min, and then rinsed three times with deionized water at 80 °C. This step was repeated twice to clean the nanotube array-based membrane electrode, resulting in an alloy nanotube array-based membrane electrode sample. (The alloy nanotube array-based membrane electrodes obtained after hydrophobication treatment for 0, 5, 10, and 20 min were denoted as 0-PFNT, 5-PFNT, 10-PFNT, and 20-PFNT, respectively).
[0115] Example 4
[0116] 1) ZnO nanowire arrays were grown on a substrate using a hydrothermal method. The synthesis steps are as follows:
[0117] A. Apply 0.3 mL of 50 mM zinc acetate solution to a 5*8 cm area. -2 On stainless steel, then anneal at 350℃ for 15 minutes;
[0118] B. Prepare 50 mL of reaction solution with the following concentrations: 25 mM zinc nitrate, 25 mM hexamethylenetetramium, and 10 mM polyethyleneimine.
[0119] C. Immerse the stainless steel sheet from A into the reaction solution, then seal it in a polytetrafluoroethylene reactor and react at 100°C for 6 hours to obtain a ZnO nanowire array.
[0120] 2) The ZnO nanowire array was converted into a metal nanotube array using the self-sacrificing template method. The preparation process is as follows:
[0121] A. Prepare 5 mL of reaction solution, which consists of 1.5 mM K2PtCl4, 1.5 mM K2PdCl4 and 0.1 mM citric acid;
[0122] B. Place the substrate with the ZnO nanowire array into the reaction solution and react at 80°C for 60 min;
[0123] C. Remove the substrate containing the platinum nanotube array, rinse it three times with deionized water, and then dry it overnight at 70°C to obtain the platinum-palladium nanotube array sample.
[0124] 3) The alloying and hydrophobication engineering of metal nanotube arrays is as follows:
[0125] A. Prepare 5 mL of 0.5 wt% PVDF ethanol solution.
[0126] B. The above solution was dispersed onto the metal nanotube array using ultrasonic spraying, with a spraying amount of 100 μL / cm². -2 .
[0127] C. The nanotube array loaded with hydrophobic agent was heat-treated at 200℃ for 30 min in a 5% H2 / Ar atmosphere to achieve alloying and hydrophobicity engineering.
[0128] 4) Transfer and cleaning of membrane electrodes
[0129] A. Nanotube arrays were transferred onto a proton exchange membrane (Nafion212) using a hot-pressing method. The hot-pressing temperature was 125℃, the pressure was 0.3MPa, and the hot-pressing time was 5min.
[0130] B. The membrane electrode was immersed in 3 wt% H2SO4 solution for 30 min, and then rinsed with deionized water at 80 °C. This step was repeated twice to clean the nanotube array-based membrane electrode, resulting in a sample of an alloy nanotube array-based membrane electrode.
[0131] Example 5
[0132] 1) ZnO nanowire arrays were grown on a substrate using a hydrothermal method. The synthesis steps are as follows:
[0133] A. Apply 0.3 mL of 50 mM zinc acetate solution to a 5*8 cm area. -2 On stainless steel, then anneal at 350℃ for 15 minutes;
[0134] B. Prepare 50 mL of reaction solution with the following concentrations: 25 mM zinc nitrate, 25 mM hexamethylenetetramium, and 10 mM polyethyleneimine.
[0135] C. Immerse the polytetrafluoroethylene membrane from A into the reaction solution, then seal it in a polytetrafluoroethylene reactor and react at 100°C for 6 hours to obtain a ZnO nanowire array.
[0136] 2) The ZnO nanowire array was converted into a metal nanotube array using the self-sacrificing template method. The preparation process is as follows:
[0137] A. Prepare 5 mL of reaction solution, which consists of 1 mM K2PtCl4, 1 mM K2PdCl4, 5 mM K2IrCl4 and 0.1 mM citric acid;
[0138] B. Place the substrate with the ZnO nanowire array into the reaction solution and react at 80°C for 60 min;
[0139] C. The substrate containing the platinum-palladium-iridium ternary metal nanotube array was removed, rinsed three times with deionized water, and then dried overnight at 70°C to obtain the platinum-palladium-iridium nanotube array sample.
[0140] 3) The alloying and hydrophobication engineering of metal nanotube arrays is as follows:
[0141] A. Prepare 5 mL of 0.1 wt% Nafion ethanol solution.
[0142] B. Immerse the substrate carrying the metal nanotube array in the above solution for 0, 5, 10 and 20 min respectively;
[0143] C. The nanotube array loaded with hydrophobic agent was heat-treated at 150℃ for 30 min in a 5% H2 / Ar atmosphere to achieve alloying and hydrophobic engineering, and different hydrophobic nanotube array electrode samples were obtained (the hydrophobic nanotube array electrode samples obtained by hydrophobic treatment for 0, 5, 10 and 20 min were denoted as 0-PFNT / SS, 5-PFNT / SS, 10-PFNT / SS and 20-PFNT / SS, respectively).
[0144] 4) Transfer and cleaning of membrane electrodes
[0145] A. Nanotube arrays were transferred onto a proton exchange membrane (Nafion212) using a hot-pressing method. The hot-pressing temperature was 125℃, the pressure was 0.3MPa, and the hot-pressing time was 5min.
[0146] B. The membrane electrode was immersed in 3 wt% H2SO4 solution for 30 min, and then rinsed three times with deionized water at 80 °C. This step was repeated twice to clean the nanotube array-based membrane electrode, resulting in alloy nanotube array-based membrane electrode samples (the alloy nanotube array-based membrane electrodes obtained after hydrophobic treatment for 0, 5, 10, and 20 min were denoted as 0-PFNT, 5-PFNT, 10-PFNT, and 20-PFNT, respectively).
[0147] Example 6
[0148] 1) ZnO nanowire arrays were grown on a substrate using a hydrothermal method. The synthesis steps are as follows:
[0149] A. Apply 0.3 mL of 50 mM zinc acetate solution to a 5*8 cm area. -2 On stainless steel, then anneal at 350℃ for 15 minutes;
[0150] B. Prepare 50 mL of reaction solution with the following concentrations: 25 mM zinc nitrate, 25 mM hexamethylenetetramium, and 10 mM polyethyleneimine.
[0151] C. Immerse the stainless steel sheet from A into the reaction solution, then seal it in a polytetrafluoroethylene reactor and react at 100°C for 6 hours to obtain a ZnO nanowire array.
[0152] 2) The ZnO nanowire array was converted into a metal nanotube array using the self-sacrificing template method. The preparation process is as follows:
[0153] A. Prepare 5 mL of reaction solution, which consists of 1.5 mM K2PtCl4, 1.5 mM K2PdCl4 and 0.1 mM citric acid;
[0154] B. Place the substrate with the ZnO nanowire array into the reaction solution and react at 80°C for 60 min;
[0155] C. Remove the substrate containing the platinum nanotube array, rinse it three times with deionized water, and then dry it overnight at 70°C to obtain the platinum-palladium nanotube array sample.
[0156] 3) The alloying and hydrophobication engineering of metal nanotube arrays is as follows:
[0157] A. Prepare 5 mL of 0.5 wt% An aqueous solution.
[0158] B. Immerse the substrate carrying the metal nanotube array in the above solution for 30 minutes.
[0159] C. The nanotube array loaded with hydrophobic agent was heat-treated at 100℃ for 30 min in a 5% H2 / Ar atmosphere to achieve hydrophobicity engineering, and the hydrophobic nanotube array electrode sample was obtained.
[0160] 4) Transfer and cleaning of membrane electrodes
[0161] A. Nanotube arrays were transferred onto a proton exchange membrane (Nafion212) using a hot-pressing method. The hot-pressing temperature was 125℃, the pressure was 0.3MPa, and the hot-pressing time was 5min.
[0162] B. The membrane electrode was immersed in 3 wt% H2SO4 solution for 30 min, and then rinsed three times with deionized water at 80 °C. This step was repeated twice to clean the nanotube array-based membrane electrode, resulting in a sample of an alloy nanotube array-based membrane electrode.
[0163] Example 7
[0164] 1) ZnO nanowire arrays were grown on a substrate using a hydrothermal method. The synthesis steps are as follows:
[0165] A. Apply 0.3 mL of 50 mM zinc acetate solution to a 5*8 cm area. -2 On stainless steel, then anneal at 350℃ for 15 minutes;
[0166] B. Prepare 50 mL of reaction solution with the following concentrations: 25 mM zinc nitrate, 25 mM hexamethylenetetramium, and 10 mM polyethyleneimine.
[0167] C. Immerse the stainless steel sheet from A into the reaction solution, then seal it in a polytetrafluoroethylene reactor and react at 100°C for 6 hours to obtain a ZnO nanowire array.
[0168] 2) The ZnO nanowire array was converted into a metal nanotube array using the self-sacrificing template method. The preparation process is as follows:
[0169] A. Prepare 50 mL of reaction solution, which consists of 1.5 mM K2PtCl4, 3 mM CuCl2, and 3 mM formic acid;
[0170] B. Place the substrate with the ZnO nanowire array into the reaction solution and react at 80°C for 300 min;
[0171] C. Remove the substrate containing the platinum-copper nanotube array, rinse it three times with deionized water, and then dry it overnight at 70°C to obtain the platinum-palladium nanotube array sample.
[0172] 3) The alloying and hydrophobication engineering of metal nanotube arrays is as follows:
[0173] A. Prepare 5 mL of 0.5 wt% solution. Aqueous solution.
[0174] B. Immerse the substrate carrying the metal nanotube array in the above solution for 30 minutes.
[0175] C. The nanotube array loaded with hydrophobic agent was heat-treated at 100℃ for 30 min in a 5% H2 / Ar atmosphere to achieve hydrophobicity engineering, and the hydrophobic nanotube array electrode sample was obtained.
[0176] 4) Transfer and cleaning of membrane electrodes
[0177] A. Nanotube arrays were transferred onto a proton exchange membrane (Nafion212) using a hot-pressing method. The hot-pressing temperature was 125℃, the pressure was 0.3MPa, and the hot-pressing time was 5min.
[0178] B. The membrane electrode was immersed in 3 wt% H2SO4 solution for 30 min, and then rinsed three times with deionized water at 80 °C. This step was repeated twice to clean the nanotube array-based membrane electrode, resulting in a sample of an alloy nanotube array-based membrane electrode.
Claims
1. A hydrophobically tunable alloy nanotube array electrode for fuel cells, characterized in that: The electrode comprises an alloy nanotube array, which is modified with a hydrophobic agent and then subjected to heat treatment. The alloy is a Pt-Zn alloy, or an alloy composed of Pt-Zn and one or more of Au, Ir, Pd, Rh, Ag, Fe, Ru, Cu, Ni, Co or M; the nanotubes have a diameter of 20-50 nm and a length of 0.2-2.0 μm. The method for fabricating the hydrophobically tunable nanotube array electrode for fuel cells includes the following steps: (1) A ZnO nanowire array is grown on a substrate by a hydrothermal method, wherein the substrate is one of stainless steel sheet, stainless steel mesh, copper sheet, PTFE film, plastic sheet, nickel sheet, aluminum foil or titanium sheet; (2) Using the self-sacrificing template method to convert ZnO nanowire arrays into metal nanotube arrays; (3) Alloying and hydrophobicization engineering of metal nanotube arrays; (4) The nanotube array was transferred onto the proton exchange membrane by hot pressing, and then the membrane electrode was obtained after cleaning. Step (3) The metal nanotube array undergoes alloying and hydrophobication treatment, the specific process of which is as follows: A. Prepare a solution of the hydrophobic agent, wherein the mass fraction of the hydrophobic agent solution is 0.1-10 wt%, and the solvent is one or more of deionized water, ethanol, toluene, diethyl ether, methanol and chloroform; the hydrophobic agent is one or more of PVDF, PTFE, Nafion resin and Hyflon® amorphous perfluoropolymer. B. Immerse the substrate carrying the metal nanotube array in a solution of hydrophobic agent for 0-100 min, and the concentration is not zero, or disperse the hydrophobic agent solution on the metal nanotube array using ultrasonic spraying, with a spraying amount of 0-100 μL / cm³. -2 A nanotube array loaded with a hydrophobic agent was obtained; C. Nanotube arrays loaded with hydrophobic agents are alloyed and hydrophobized through heat treatment under a protective gas atmosphere.
2. The method for fabricating a hydrophobically tunable nanotube array electrode for fuel cells according to claim 1, characterized in that, Includes the following steps: (1) A ZnO nanowire array is grown on a substrate by a hydrothermal method, wherein the substrate is one of stainless steel sheet, stainless steel mesh, copper sheet, PTFE film, plastic sheet, nickel sheet, aluminum foil or titanium sheet; (2) Using the self-sacrificing template method to convert ZnO nanowire arrays into metal nanotube arrays; (3) Alloying and hydrophobicization engineering of metal nanotube arrays; (4) The nanotube array is transferred onto the proton exchange membrane by hot pressing, and then the membrane electrode is obtained after cleaning.
3. The preparation method according to claim 2, characterized in that, Step (2) uses the self-sacrificing template method to convert the ZnO nanowire array into a metal nanotube array. The specific preparation process is as follows: A. Prepare a mixed solution of the metal precursor and the reducing agent; B. Place the substrate with the ZnO nanowire array into the reaction solution and heat at 30-100°C. ο React at C for 30-200 min; C. Remove the substrate containing the metal nanotube array, rinse with deionized water, and then place it at 50-100°C. ο Drying at C.
4. The preparation method according to claim 3, characterized in that, The metal precursor is a noble metal precursor, or a mixture of a noble metal precursor and a non-noble metal precursor, wherein the concentration of the metal precursor in the mixed solution is 0-10 mM and not 0; the noble metal precursor is one or more of the metal salts of Pt, Ru, Ir, Au, Rh, Pd and Ag, and the non-noble metal precursor is one or more of the metal salts of Ni, Co, Cu, Fe and Mn. The reducing agent is one or more of ascorbic acid, sodium citrate, citric acid, sodium borohydride, formic acid, and hydroxylamine hydrochloride, and the concentration of the reducing agent in the mixed solution is 0.1-100 mM.
5. The preparation method according to claim 4, characterized in that, The noble metal precursors are one or more of H2PtCl6, PtCl2, PtCl4, K2PtCl4, RuCl2, HAuCl4, RhCl3, IrCl3 and K2PdCl4, and the non-noble metal precursors are one or more of Ni(NO3)2, Cu(NO3)2, Fe(NO3)2, NiCl2, Co(NO3)2 and CoCl2.
6. The preparation method according to claim 2, characterized in that, Step (3) The metal nanotube array undergoes alloying and hydrophobication treatment, the specific process of which is as follows: A. Prepare a solution of the hydrophobic agent, wherein the mass fraction of the hydrophobic agent solution is 0.1-10 wt%, and the solvent is one or more of deionized water, ethanol, toluene, diethyl ether, methanol and chloroform; the hydrophobic agent is one or more of PVDF, PTFE, Nafion resin and Hyflon® amorphous perfluoropolymer. B. Immerse the substrate carrying the metal nanotube array in a solution of hydrophobic agent for 0-100 min, and the concentration is not zero, or disperse the hydrophobic agent solution on the metal nanotube array using ultrasonic spraying, with a spraying amount of 0-100 μL / cm³. -2 A nanotube array loaded with a hydrophobic agent was obtained; C. Nanotube arrays loaded with hydrophobic agents are alloyed and hydrophobized through heat treatment under a protective gas atmosphere.
7. The preparation method according to claim 6, characterized in that, The heat treatment atmosphere is H2 or a mixture of H2-Ar, H2-N2 and H2-He, with the mass fraction of H2 in the mixture being 3-99%; the heat treatment temperature is 100-500°C. ο C, heat treatment time is 10-200 min.
8. The preparation method according to claim 2, characterized in that, Step (4) The nanotube array is transferred onto the proton exchange membrane using a hot-pressing method, and then cleaned to obtain the membrane electrode. The specific process is as follows: A. Nanotube arrays were transferred onto a proton exchange membrane using a hot-pressing method, with the hot-pressing temperature between 125-142°C. ο C, pressure is 0.3-5MPa, hot pressing time is 1-10min; B. Immerse the transferred proton exchange membrane in 1-10wt% H2SO4 solution for 30-60 min, then rinse with deionized water as one operation. Repeat this operation 1-3 times.
9. The hydrophobic tunable alloy nanotube array electrode of claim 1 or the hydrophobic tunable alloy nanotube array electrode prepared by any one of claims 2-7 is used in a fuel cell.