Laser-induced multi-stage patterning method for proton exchange membrane

Abstract

The invention discloses a laser-induced multi-stage patterning method for a proton exchange membrane, and belongs to the field of laser and substance interaction and proton exchange membrane processing. Under the conditions of no template, no additional material and no chemical modification, the membrane material is guided to be physically rearranged and solidified in the cooling process by utilizing local transient heating and melting effects generated when pulse laser acts on the surface of the proton exchange membrane, and a patterned structure with multi-scale and multi-level characteristics is directly formed on the surface of the membrane. A micron-scale primary structure is constructed on the surface of the proton exchange membrane by regulating and controlling parameters such as laser wavelength, pulse width, scanning speed, point engraving time, repetition frequency and scanning path, and a nanometer or submicron-scale secondary structure is formed in a local area of the proton exchange membrane, so that controllable construction of a multistage pattern is realized. The method is suitable for various proton exchange membrane materials, has the advantages of simple process, high structural designability, high digitalization degree in the processing process and the like, effectively improves the membrane surface appearance and the membrane-electrode interface state, and has a good engineering application prospect.

Description

Technical Field

[0001] This invention belongs to the field of laser-matter interaction and proton exchange membrane processing, and relates to a laser-induced multi-level patterning method for proton exchange membranes. Specifically, it relates to a method for constructing multi-level patterned structures on the surface of a proton exchange membrane under template-free conditions by using laser-induced material physical rearrangement. Background Technology

[0002] Electrochemical devices such as fuel cells and water electrolysis for hydrogen production provide key technological pathways for the efficient utilization and conversion of hydrogen energy. Proton exchange membranes, as crucial functional components in these devices, play vital roles in proton conduction, reactant isolation, and reaction initiation; their performance directly impacts the overall efficiency and stability of the electrochemical device.

[0003] During electrochemical operation, the performance losses associated with proton exchange membranes typically manifest as increased activation polarization, ohmic polarization, and mass transfer polarization, corresponding to the reaction kinetic resistance at the reaction interface, the membrane's intrinsic resistance, and the resistance to reactant transport to the reaction interface, respectively. With long-term operation, the membrane material may undergo structural and morphological changes, leading to intensified polarization behaviors and thus limiting performance improvements in the electrochemical device.

[0004] Patterning the surface of proton exchange membranes to introduce micron- or nanoscale structures is an effective way to improve the membrane-electrode interface and increase the effective area of ​​the electrochemical reaction interface. Related studies have shown that, compared to single-scale structures, constructing multi-level patterns on the membrane surface, formed by the superposition of structures of different scales, helps to improve the mass transfer conditions of reactants while increasing the interfacial reaction area. This, in turn, synergistically alleviates the performance limitations imposed by activation polarization and mass transfer polarization across different operating current density ranges. Therefore, constructing multi-level, multi-scale patterned structures on the surface of proton exchange membranes has significant application value.

[0005] However, existing technologies for constructing multi-level structures mostly rely on template imprinting, multiple transfers, or multi-layer stacking, which involve complex processes, limited processing flexibility, and the potential introduction of foreign matter or defects into the membrane surface during template processing and use, affecting the intrinsic properties of the membrane material. These template-dependent methods also have limitations in terms of process scale-up and continuous production. Therefore, there is an urgent need for a multi-level patterning method for proton exchange membrane surfaces that simplifies the processing flow, offers flexible structural control, and does not introduce exogenous substances. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies, this invention proposes a laser-induced multi-level patterning method for proton exchange membranes. This method utilizes the instantaneous heating, melting, and subsequent physical rearrangement processes that occur in a localized region of the proton exchange membrane material under laser irradiation to directly form multi-scale, multi-level patterned structures on the membrane surface without a template, without introducing any external materials or chemical modification steps.

[0007] To achieve the above objectives, the following technical solution is adopted:

[0008] A laser-induced multi-level patterning method for proton exchange membranes (PEMs) involves controlling the laser energy in time and / or space, applying the laser to the PEM surface in one or more applications. Without the need for a physical template, this causes a transient temperature rise in a localized area of ​​the PEM material. During vaporization and recrystallization, thermally induced surface softening, melting, and physical rearrangement occur sequentially or cumulatively, resulting in a multi-level patterned morphology on the membrane surface composed of superimposed structures of different scales. The chemical composition of the PEM remains unchanged before and after patterning. The method specifically includes the following steps:

[0009] Step 1: Select the proton exchange membrane to be processed;

[0010] Step 2: Based on the material properties and expected pattern structure of the proton exchange membrane, determine the laser processing parameters, including but not limited to laser wavelength, laser pulse width, laser scanning speed, dot engraving time and laser repetition frequency. The above laser processing parameters are matched with each other to make the proton exchange membrane transiently heated in the laser action area, inducing the membrane material to undergo restricted softening, melting and physical rearrangement, so as to form a controllable multi-level patterned structure.

[0011] Step 3: Adjust the laser focus to the surface of the proton exchange membrane and perform laser scanning on the surface of the proton exchange membrane according to the predetermined scanning path;

[0012] Step 4: After laser processing, the film is cooled at room temperature for 5-10 seconds, eventually forming a multi-level patterned morphology on the film surface composed of superimposed structures of different scales. The formation of the patterned structure originates from the thermal softening, melting, flow and / or recrystallization process of the film material under the thermally controlled conditions of laser processing.

[0013] Furthermore, the proton exchange membrane mentioned in step 1 is selected from perfluorosulfonic acid proton exchange membranes, aromatic heterocyclic proton exchange membranes, or aromatic heterocyclic proton exchange membranes after acid doping.

[0014] Furthermore, the selection principles for laser processing parameters in step 2 include:

[0015] The laser wavelength is in the range of 200 nm to 2000 nm, preferably a wavelength in which the proton exchange membrane has low transmittance.

[0016] The laser pulse width is selected according to the expected structural scale, ranging from 1 ns to 10 ms, preferably from 200 ns to 3000 ns.

[0017] The laser scanning speed is adjusted according to the pattern period and structural scale, ranging from 10 mm / s to 3000 mm / s, preferably from 200 mm / s to 2000 mm / s.

[0018] The dot engraving time is 1 ns - 10 ms, preferably 0.01ms - 0.1ms;

[0019] The laser repetition frequency is selected according to the required structural level, ranging from 1 kHz to 500 kHz, preferably from 100 kHz to 300 kHz.

[0020] Furthermore, the laser processing parameters also include the laser spot diameter, which ranges from 0.1 μm to 500 μm.

[0021] Furthermore, the laser processing parameters are not independent of each other; their combination and adjustment can affect the temporal and spatial scales of the melting and rearrangement behavior on the film surface, thereby determining the hierarchical characteristics of the resulting pattern structure. It should be understood that any adjustment or combination of the above parameters without departing from the technical principles of this invention falls within the scope of protection of this invention.

[0022] Furthermore, in step 3, laser energy is applied to the surface of the proton exchange membrane by scanning, point-by-point application, or a combination thereof.

[0023] Furthermore, in step 3, the scanning path is used to determine the primary structure morphology of the pattern, while the remaining laser processing parameters are used to control the secondary structure features formed on the surface of the primary structure.

[0024] Furthermore, in step 4, the patterned structure has at least one micrometer-scale and / or nanometer-scale morphological feature, wherein the structural feature size is 100 nm - 1 mm.

[0025] Furthermore, by adjusting the time interval, spatial spacing, scanning path, or repetition frequency of laser action, a multi-level patterned structure with superimposed different scales can be formed on the surface of the proton exchange membrane.

[0026] A patterned proton exchange membrane, prepared by the above method, is used in electrochemical energy conversion or energy storage devices. Through the synergistic improvement of the membrane-electrode interface state and reactant transport conditions by a multi-level patterned structure, it reduces activation polarization and / or mass transfer polarization.

[0027] The method of this invention is based on the following principle: When a pulsed laser acts on the surface of a proton exchange membrane, rapid energy deposition can be achieved in a localized area, causing the membrane material to vaporize, soften, or melt for a short period. During the subsequent cooling process, under the combined influence of surface tension, temperature gradient, and cooling rate, the membrane material in the molten area undergoes spontaneous rearrangement and eventually solidifies to form a surface morphology structure with certain periodicity and hierarchical characteristics. By controlling the laser parameters and scanning method, the above physical rearrangement process can be guided to occur at different spatial scales, thereby forming a multi-level pattern composed of superimposed primary and secondary structures on the same membrane surface. By rationally selecting laser parameters and setting the laser scanning path, a micrometer-scale primary structure can be constructed on the surface of the proton exchange membrane, and nanometer-scale or submicrometer-scale secondary structures can be further formed in localized areas of the primary structure, thereby obtaining a multi-level patterned morphology.

[0028] The beneficial effects of this invention are as follows:

[0029] 1) This invention achieves the construction of a multi-level structure on the surface of a proton exchange membrane without introducing exogenous substances, thus maintaining the purity and compatibility of the membrane material system;

[0030] 2) This invention improves the membrane-electrode interface state and reactant transport conditions through the synergistic effect of multi-scale structures, which is beneficial to reducing the overall resistance in the electrochemical process;

[0031] 3) The laser processing parameters of the present invention are continuously adjustable, the pattern design is flexible, and multiple structural morphologies can be achieved under the same process platform;

[0032] 4) The processing of this invention is highly digitalized, suitable for rapid parameter iteration and integration with existing membrane processing technologies, and has good potential for engineering applications. Attached Figure Description

[0033] Figure 1 A represents the transmission spectrum of the commercial proton exchange membrane in the embodiment; Figure 1 B is Figure 1 A magnified view of the area selected by the rectangle in section A;

[0034] Figure 2 The patterned structure formed by laser induction in Example 1;

[0035] Figure 3 The height distribution of the primary and secondary structures formed by laser induction of the commercial film in Example 1;

[0036] Figure 4 The X-ray diffraction patterns are those of the commercial film and the laser-induced patterned commercial film in Example 1.

[0037] Figure 5 The images show the Raman spectra of the commercial film and the laser-induced patterned commercial film in Example 1.

[0038] Figure 6 The patterned structure formed by laser induction in Example 2;

[0039] Figure 7 The height distribution of the primary and secondary structures formed by laser induction of the commercial film in Example 2;

[0040] Figure 8 The X-ray diffraction patterns are those of the commercial film and the laser-induced patterned commercial film in Example 2.

[0041] Figure 9 The images show the Raman spectra of the commercial film and the laser-induced patterned commercial film in Example 2.

[0042] Figure 10 A represents the polarization curve and power density curve of the battery assembled from the commercial film and the laser-induced patterned commercial film in Example 3. Figure 10 B is Figure 10 A magnified view of the area selected by the rectangle in section A;

[0043] Figure 11 The impedance curve of the battery assembled from the commercial film and the laser-induced patterned commercial film in Example 3;

[0044] Figure 12 The polarization curve of the battery assembled from a commercial film and a laser-induced patterned commercial film with oxygen-nitrogen mixed gas passing through the cathode in Example 3 is shown.

[0045] Figure 13 The polarization curve is shown for the battery assembled from a commercial film and a laser-induced patterned commercial film with oxygen-helium mixed gas passing through the cathode in Example 3. Detailed Implementation

[0046] The technical solutions in the embodiments of the present invention are described in detail and completely below; the described embodiments are only a part of the numerous embodiments of the present invention. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative effort are all within the scope of protection of the present invention.

[0047] Embodiments 1 and 2 of this invention constitute a set of progressive embodiments to illustrate how, under the same scanning path conditions, a stable single-level master structure can gradually evolve into a multi-level patterned structure with clear hierarchical characteristics by adjusting key parameters such as the laser repetition frequency. Embodiment 1 establishes the baseline processing conditions for the formation of the master structure, while Embodiment 2 further induces the generation of secondary structures based on these conditions. Embodiment 3 aims to illustrate the gain effect of this technical solution on the proton exchange membrane used in the embodiments of this invention in a high-temperature fuel cell. Specifically, as follows:

[0048] Example 1:

[0049] Using the technical solution of this invention The surface of the commercial proton exchange membrane (manufacturer: Fumatech GmbH, Germany) is processed with a periodic stripe array. The specific steps are as follows:

[0050] Step 1: Measure the transmission spectrum of the proton exchange membrane to be processed, such as... Figure 1 As shown, the proton exchange membrane has low transmittance in the 355-425 nm range, meaning that the applicable laser wavelength range is 355 nm - 425 nm.

[0051] Step 2, from Figure 1 The selected laser operating wavelength is 355 nm;

[0052] Step 3: Determine that the pattern to be processed is a 3 cm × 3 cm groove array with a groove spacing of 100 μm and a groove width of 50 μm;

[0053] Step 4: Set the laser repetition frequency to 200 kHz, the laser scanning speed to 1200 mm / s, the dot engraving time to 0.01 ms, the laser pulse width to 3 μs, and the laser spot size to 10 μm.

[0054] Step 5: Set the laser scanning path to the pattern to be processed, where the line width is set to the stripe width and the spacing of the line array is set to the stripe spacing.

[0055] Step 6: Focus the laser on the surface of the commercial proton exchange membrane and perform a laser scan;

[0056] Step 7: The surface morphology of the film in Example 1, measured using a white light interferometer, is as follows. Figure 2 The height distribution of the primary and secondary structures is as follows: Figure 3It can be observed that, under a repetition frequency of 200 kHz, the laser-induced rearrangement of the film material mainly manifests as the formation of stable and continuous micron-scale primary trench structures along the scanning path. The secondary structures within the trenches have not yet significantly differentiated, indicating that this parameter combination corresponds to the primary structure construction stage in the multi-level structure formation process. There are upward protrusions at the bottom of the trenches, which are caused by the molten film material at the bottom of the trenches being sputtered to both sides during laser induction, followed by cooling and recrystallization.

[0057] Step 8: To ensure that laser induction does not introduce new substances onto the film surface, the unprocessed commercial film and the patterned commercial film from Example 1 were characterized using X-ray diffraction spectroscopy and Raman spectroscopy, respectively. The resulting small-angle X-ray diffraction spectra and Raman spectra are shown below. Figure 4 and Figure 5 It can be observed that the peak shape of the X-ray spectrum is significantly enhanced after laser induction, indicating that laser induction improves the crystallinity of the film surface. Figure 4 and Figure 5 No new peaks were found, indicating that laser induction did not introduce any other impurities.

[0058] Example 2:

[0059] Based on the primary structure formation conditions established in Example 1, by reducing the laser repetition frequency, the film material can be further induced to undergo periodic rearrangement in the longitudinal and transverse directions within the primary trenches, forming a defined secondary structure. The principle of processing a multi-level periodic stripe array is as follows: the pulsed laser sweeps the film surface point-by-point, and the size of the point is determined by the size of the laser spot after focusing. In this example, the laser spot size used is approximately 10 μm. Reducing the laser repetition frequency increases the distance between points during laser sweeping, thereby obtaining a multi-level structure in the longitudinal and transverse directions within a single stripe of the periodic stripe array. The specific steps and effects are as follows:

[0060] Step 1: Set the laser repetition frequency to 100 kHz, and keep the other parameters the same as in Example 1;

[0061] Step 2: Set the laser scanning path as in Example 1;

[0062] Step 3: Focus the laser onto the film surface, and cool to room temperature after laser scanning;

[0063] Step 4: The surface morphology of the film in Example 2, measured using a white light interferometer, is as follows. Figure 6 The height distribution of the primary and secondary structures is as follows: Figure 7It can be observed that at a repetition frequency of 100 kHz, there are obvious periodic peak secondary structures inside the trench structure. The formation principle of the peaks is the same as described in step 8 of Example 1. The lateral dimensions of these peaks are 9 μm-10 μm, and the depth is 100 nm-200 nm. The period of the longitudinal peaks is determined by the repetition frequency, scanning speed, and dot-etching time. A smaller repetition frequency, a larger scanning speed, and a shorter dot-etching time will result in a larger period. The number of lateral peaks is determined by the laser spot size.

[0064] Step 5: Characterize the unprocessed commercial film and the patterned commercial film from Example 2 using X-ray diffraction spectroscopy and Raman spectroscopy, respectively. The obtained small-angle X-ray diffraction spectra and Raman spectra are shown below. Figure 8 and Figure 9 It can be seen that the results obtained are the same as those in step 8 of Example 1, that is, the laser induces the generation of a film material with higher crystallinity on the film surface without introducing other impurities.

[0065] Example 3:

[0066] This technical solution provides a laser-induced multi-level patterning method for proton exchange membranes, the ultimate goal of which is to provide a flexible and low-cost patterning method that can improve the performance of commercial proton exchange membranes. This embodiment inspects the quality of the patterned membrane obtained by this technical solution.

[0067] In this embodiment, the patterned AP40 membrane with a multi-level trench structure prepared in Example 2 and the untreated commercial AP40 membrane (hereinafter referred to as the patterned membrane and the commercial membrane) were loaded into a high-temperature fuel cell system. Their performance in the fuel cell was characterized by electrochemical testing methods. The specific steps are as follows:

[0068] Step 1: Immerse the patterned film of Example 2 and the commercial film in an 80% (w / w) phosphoric acid solution at 80°C for 400 minutes;

[0069] Step 2, Assemble the battery: Use Pt with a loading of 0.7 mg / cm³. 2 Carbon paper is used as the cathode and anode, respectively, and is bonded to both sides of the patterned film and the commercial film. The patterned side of the patterned film faces the cathode. After bonding, it is hot-pressed at 130°C for 5 minutes. Finally, the membrane electrodes are installed into bipolar plates.

[0070] Step 3, using 0.2 A / cm 2 The patterned film battery and the commercial film battery were activated for 7 days using a constant current method with different current densities.

[0071] Step 4: Under the conditions of air flowing through the cathode, hydrogen flowing through the anode, an air-to-hydrogen stoichiometric ratio of 2 / 1, no back pressure, and an operating temperature of 160℃, the polarization curves of the patterned film battery and the commercial film battery at different current densities were measured as follows: Figure 10 Compared to commercial films, patterned films differ mainly in the following three aspects:

[0072] (1) The voltage of the patterned film battery under low current density is always higher than that of the commercial film battery, which indicates that the patterned film obtained by this technical solution improves the electrochemical reaction interface and reduces the original activation polarization.

[0073] (2) The patterned film battery has a higher open-circuit voltage (0.908 V for patterned film and 0.871 V for commercial film), which indicates that the patterned film obtained by this technical solution improves at least one of the ohmic polarization and mass transfer polarization;

[0074] (3) The patterned film has higher voltage and power density at high current density, indicating that the patterned film obtained by this technical solution optimizes mass transfer polarization;

[0075] Step 5: Further, air is passed through the cathode and hydrogen is passed through the anode. The operating temperature is 160℃ and the current density is 0.8A / cm². 2 Under the conditions, the impedance curves of patterned film batteries and commercial film batteries were tested, such as... Figure 11 The left end of the impedance curve and the X-intercept represent the ohmic resistance of the battery. The area enclosed by the impedance curve and the X-axis is inversely proportional to the electrochemical reaction resistance. Compared with commercial membranes, the patterned membrane battery obtained using this technology has a slightly increased ohmic resistance but a smaller electrochemical reaction resistance.

[0076] Step 6: Further, the polarization curve was measured under the conditions of a mixture of 1% oxygen and 99% nitrogen passing through the cathode, hydrogen passing through the anode, and an operating temperature of 160℃, as shown in the figure. Figure 12 With other conditions remaining unchanged, the gas flowing through the cathode was changed to a mixture of 1% oxygen and 99% helium. The measured polarization curve is as follows: Figure 13 The difference in maximum current density between batteries with the same membrane composition in an oxygen-nitrogen mixture and an oxygen-helium mixture reflects the battery's gas-phase transport resistance; under an oxygen-helium mixture, the maximum current density of different batteries is inversely proportional to their liquid-phase transport resistance. (Combined) Figure 12 and Figure 13 It can be observed that the difference in maximum current density between patterned film batteries and commercial film batteries under different gas mixtures is similar, but the patterned film battery has a larger maximum current under an oxygen-helium mixture, indicating that the patterned film obtained by this technical solution can improve the liquid phase transport resistance of the battery.

[0077] The system electrochemical characterization in Example 3 revealed that the patterned film treated with this technical solution reduced activation polarization and mass transfer polarization compared to the commercial film, resulting in improved overall battery performance.

[0078] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A laser-induced multi-level patterning method for proton exchange membranes, characterized in that, The aforementioned multi-level patterning method for proton exchange membranes modulates laser energy in time and / or space, applying the laser to the surface of the proton exchange membrane in one or more applications. Without the need for a physical template, this causes transient heating of the proton exchange membrane material in a localized area. During vaporization and recrystallization, thermally induced surface softening, melting, and physical rearrangement occur sequentially or cumulatively, resulting in a multi-level patterned morphology on the membrane surface composed of superimposed structures of different scales. The chemical composition of the proton exchange membrane remains unchanged before and after patterning. Specifically, the method includes the following steps: Step 1: Select the proton exchange membrane to be processed; Step 2: Determine the laser processing parameters based on the material properties and expected pattern structure of the proton exchange membrane; Step 3: Adjust the laser focus to the surface of the proton exchange membrane and perform laser scanning on the surface of the proton exchange membrane according to the predetermined scanning path; Step 4: After laser processing is completed, the film is cooled at room temperature for 5-10 seconds, and finally a multi-level patterned morphology composed of superimposed structures of different scales is formed on the film surface.

2. The laser-induced multi-level patterning method for proton exchange membranes according to claim 1, characterized in that, In step 2, the proton exchange membrane is selected from perfluorosulfonic acid proton exchange membranes, aromatic heterocyclic proton exchange membranes, or aromatic heterocyclic proton exchange membranes after acid doping.

3. The laser-induced multi-level patterning method for proton exchange membranes according to claim 1, characterized in that, The laser processing parameters in step 2 include laser wavelength, laser pulse width, laser scanning speed, spot engraving time, and laser repetition frequency. These laser processing parameters are matched with each other, and the specific selection principle for these laser processing parameters is as follows: The laser wavelength is in the range of 200 nm - 2000 nm. The laser pulse width is selected according to the expected structural scale, ranging from 1 ns to 10 ms. The laser scanning speed is adjusted according to the pattern period and structural scale, ranging from 10 mm / s to 3000 mm / s. The point engraving time is 1 ns - 10 ms; The laser repetition frequency is selected according to the required structural level, ranging from 1 kHz to 500 kHz.

4. The laser-induced multi-level patterning method for proton exchange membranes according to claim 3, characterized in that, The specific principles for selecting the laser processing parameters are as follows: The laser wavelength is preferably a wavelength in which the proton exchange membrane has low transmittance. The laser pulse width is preferably 200 ns - 3000 ns; The laser scanning speed is preferably 200 mm / s - 2000 mm / s; The preferred dot engraving time is 0.01 ms - 0.1 ms. The laser repetition frequency is preferably 100 kHz - 300 kHz.

5. The laser-induced multi-level patterning method for proton exchange membranes according to claim 3, characterized in that, The laser processing parameters also include the laser spot diameter, which is 0.1 μm - 500 μm.

6. The laser-induced multi-level patterning method for proton exchange membranes according to claim 5, characterized in that, In step 3, laser energy is applied to the surface of the proton exchange membrane by scanning, projection, point-by-point application, or a combination thereof.

7. The laser-induced multi-level patterning method for proton exchange membranes according to claim 6, characterized in that, In step 3, the scanning path is used to determine the morphology of the primary structure of the pattern, while the remaining laser processing parameters are used to control the secondary structure features formed on the surface of the primary structure.

8. The laser-induced multi-level patterning method for proton exchange membranes according to claim 1, characterized in that, In step 4, the patterned structure has at least one micrometer-scale and / or nanometer-scale morphological feature, wherein the structural feature size is 100 nm - 1 mm.

9. The laser-induced multi-level patterning method for proton exchange membranes according to claim 1, characterized in that, By controlling the time interval, spatial spacing, scanning path, or repetition frequency of laser action, a multi-level patterned structure with superimposed different scales can be formed on the surface of the proton exchange membrane.

10. A patterned proton exchange membrane, characterized in that, The preparation method described in any one of claims 1-9 is used in electrochemical energy conversion or energy storage devices. Through the synergistic improvement of the membrane-electrode interface state and reactant transport conditions by the multi-level patterned structure, it can reduce activation polarization and / or mass transfer polarization.

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