A layered double hydroxide membrane for alkaline water electrolysis and its application

Abstract

This invention belongs to the field of new materials technology and discloses a layered double hydroxide membrane for alkaline water electrolysis. The layered double hydroxide membrane is obtained by connecting layered double hydroxide particles into a continuous thin film using polytetrafluoroethylene (PTFE) as a binder. This invention uses PTFE as a binder and employs a calendering method to connect layered double hydroxide (LDH) particles into a continuous, dense film. This preparation method requires little or no organic solvents and is easily scalable for continuous industrial production. When the prepared layered double hydroxide membrane is used for alkaline water electrolysis, it exhibits significantly lower sheet resistivity and hydrogen permeability than commercial Zirfon membranes, making it widely applicable in industrial production while also possessing high ionic conductivity.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology and relates to alkaline water electrolysis membranes, especially a layered double hydroxide membrane for alkaline water electrolysis and its applications. Background Technology

[0002] Currently, commercially available membranes for AWE include polyphenylene sulfide (PPS) and Zirfon membranes. They exhibit high stability under real-world conditions. However, these membranes are typically several hundred micrometers thick, exhibiting high overpotentials for water electrolysis. The thick membrane structure results in excessive transport resistance, leading to low electrolysis efficiency. Therefore, the development of new thin films is particularly important.

[0003] In addition, the production of Zirfon membranes requires the use of organic solvents for phase inversion, and the organic solvents need to be post-treated and recycled during the production process, which is a long and complex process.

[0004] LDHs are two-dimensional layered anionic clay materials capable of transporting hydroxide ions internally. Furthermore, LDHs exhibit good thermal alkalinity stability. Therefore, many researchers have used LDHs as raw materials to prepare membrane materials for water electrolysis hydrogen production, including LDH-polymer membranes. ZENG·L et al. synthesized a cross-linked polyvinyl alcohol / layered double hydroxide (PVA / LDH) hybrid membrane using solution casting. However, the low LDH content in their membrane resulted in very low ionic conductivity. SAILAJA·G·S et al. added hexagonal plate-shaped magnesium aluminum double hydroxide (LDH) to an electrospun polyvinylidene fluoride (PVDF) substrate to obtain a PVDF-LDH membrane, but PVDF exhibited poor alkali resistance. DI·VONA·M·L used polysulfone grafted with quaternary ammonium groups and dispersed LDH nanoparticles (composed of Mg...) 0.62 Al 0.38 (OH)2(Cl) 0.38-0.6 Hydrogen (O) was used as an inorganic filler to prepare a composite anion exchange membrane; XU·X et al. prepared a membrane with gas barrier properties and OH- ion exchange properties by assembling LDH nanosheets and quaternary ammonium-grafted polysulfone (QAPSF) layer by layer. - Bifunctional organic-inorganic thin films exhibit high conductivity, but the quaternary ammonium groups on polysulfone polymers exhibit poor alkali resistance. Lei Wan et al. prepared PTFE-LDH membranes by growing LDH in porous polytetrafluoroethylene (PTFE), but in-situ LDH growth is time-consuming, which is not conducive to large-scale membrane preparation. Therefore, there is a need to develop LDH membrane technology with higher ionic conductivity, greater chemical stability, and better suitability for large-scale preparation. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a layered double hydroxide membrane for alkaline water electrolysis and its application.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A layered double hydroxide membrane for alkaline water electrolysis, wherein the layered double hydroxide membrane is obtained by connecting layered double hydroxide particles into a continuous film using polytetrafluoroethylene as a binder.

[0008] Furthermore, the layered double hydroxide is composed of divalent and trivalent metal hydroxides forming its positively charged main body layer, with intercalated negative ions between the main body layers to maintain its electrical neutrality.

[0009] Furthermore, in the divalent and trivalent metal hydroxides, the divalent metal ions include magnesium, nickel, copper, and zinc ions, and the trivalent metal ions include aluminum, iron, cobalt, chromium, and gallium ions. The divalent metal ions in the hydroxides are single ions or several ions, and the trivalent metal ions are single ions or several ions.

[0010] Furthermore, the layered double hydroxide film is obtained by calendering polytetrafluoroethylene and layered double hydroxide particles after mixing.

[0011] Furthermore, the mass ratio of the polytetrafluoroethylene in the mixture of polytetrafluoroethylene and layered double hydroxide particles is 30%-1%, and more preferably 15%-5%.

[0012] Furthermore, the mass ratio of the polytetrafluoroethylene in the mixture of polytetrafluoroethylene and layered double hydroxide particles is 15%-5%.

[0013] Furthermore, the calendering of the mixture of polytetrafluoroethylene and layered double hydroxide particles is performed by applying force at 20-220°C using a calender.

[0014] Furthermore, a calender is used to apply force and form the product at 60-190℃.

[0015] The application of the layered double hydroxide membrane described above in alkaline water electrolysis.

[0016] The advantages and positive effects of this invention are as follows:

[0017] This invention uses polytetrafluoroethylene (PTFE) as a binder and employs a calendering method to connect layered double hydroxide (LDH) particles into a continuous, dense film. This preparation method does not require organic solvents, the materials and equipment used in the process are readily available, production costs are low, and it is conducive to mass production and continuous industrial production. Traditional alkaline water electrolysis membranes, such as commercial Zirfon membranes, are produced using organic solvents for phase inversion, requiring post-treatment and recovery of the organic solvents during production, resulting in a long and complex process. This invention does not use organic solvents as a solvent and employs a dry or near-dry calendering method to produce alkaline water electrolysis membranes, which is of great significance for promoting the upgrading of the alkaline water electrolysis membrane industry.

[0018] 2. In the alkaline water electrolysis layered double hydroxide membrane material of the present invention, during the calendering process, PTFE undergoes a fibrous process under mechanical shearing. The PTFE filaments intertwine to form a three-dimensional network structure, binding the LDH together and providing a supporting network for the LDH. Furthermore, the dispersed LDH needles are also firmly bonded to the PTFE fibers, enabling the membrane to maintain high mechanical stability and a long service life. Figure 1 , Figure 2 As shown.

[0019] 3. When the layered double hydroxide membrane prepared in this invention is used in alkaline water electrolysis, it exhibits significantly lower sheet resistivity and hydrogen permeability than commercial Zirfon membranes. From... Figure 3 As can be seen, the sheet resistivity of the PTFE / LDH film is relatively low. At 80℃, the sheet resistivity of the 5% PTFE / LDH film is 27.53 mΩcm. 2 It is only one-quarter the size of a Zirfon membrane, and the PTFE / LDH membrane has better electrolysis performance. Attached Figure Description

[0020] Figure 1 This is a surface SEM image of a PTFE / LDH membrane with a PTFE content of 5% in the layered double hydroxide membrane material for alkaline water electrolysis in this invention.

[0021] Figure 2 The image shows a cross-sectional SEM image of a PTFE / LDH membrane with a PTFE content of 5% in the SEM image of the layered double hydroxide membrane material for alkaline water electrolysis in this invention.

[0022] Figure 3 The 5% PTFE / LDH membrane, 15% PTFE / LDH membrane, 20% PTFE / LDH membrane, and FAA-3-50 membrane used in this invention are commercial membranes at 1 mol·L⁻¹. -1 The graph shows the change in surface resistivity of KOH solution between 30℃ and 80℃; where the horizontal axis represents temperature and the vertical axis represents surface resistivity.

[0023] Figure 4 This is a graph showing the change in sheet resistivity of the 5% PTFE / LDH membrane, 15% PTFE / LDH membrane, and Zirfon commercial membrane in 30 wt% KOH solution at 30℃-80℃; where the horizontal axis represents temperature and the vertical axis represents sheet resistivity.

[0024] Figure 5 The graphs show the polarization curves of the 5% PTFE / LDH membrane, 15% PTFE / LDH membrane, and Zirfon membrane in this invention, where the horizontal axis represents current density and the vertical axis represents voltage.

[0025] Figure 6 These are verification images showing the failure to effectively form a PTFE / LDH membrane in Comparative Example 1 of this invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0027] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0028] A layered double hydroxide membrane for alkaline water electrolysis, wherein the layered double hydroxide membrane is obtained by connecting layered double hydroxide particles into a continuous film using polytetrafluoroethylene as a binder.

[0029] Preferably, the layered double hydroxide is composed of divalent and trivalent metal hydroxides forming its positively charged main body layer, and intercalated negative ions are contained between the main body layers to maintain its electrical neutrality.

[0030] Preferably, in the divalent and trivalent metal hydroxides, the divalent metal ions include magnesium, nickel, copper, and zinc ions, and the trivalent metal ions include aluminum, iron, cobalt, chromium, and gallium ions. The divalent metal ions in the hydroxides are single ions or several ions, and the trivalent metal ions are single ions or several ions.

[0031] Preferably, the layered double hydroxide film is obtained by calendering polytetrafluoroethylene and layered double hydroxide particles after mixing.

[0032] Preferably, the mass ratio of the polytetrafluoroethylene in the mixture of polytetrafluoroethylene and layered double hydroxide particles is 30%-1%, and more preferably, it is 15%-5%.

[0033] Preferably, the mass ratio of the polytetrafluoroethylene in the mixture of polytetrafluoroethylene and layered double hydroxide particles is 15%-5%.

[0034] Preferably, the calendering of the mixture of polytetrafluoroethylene and layered double hydroxide particles is performed by applying force at 20-220°C using a calender.

[0035] Preferably, a calender is used to apply force and form the material at 60-190℃.

[0036] The application of the layered double hydroxide membrane described above in alkaline water electrolysis.

[0037] Specifically:

[0038] Example 1:

[0039] A method for preparing a layered double hydroxide membrane for alkaline water electrolysis includes the following steps:

[0040] Using NiCo-LDH (a layered double hydroxide in which nickel ions are divalent and cobalt ions are trivalent), NiCo-LDH powder and an aqueous dispersion of 60% PTFE were added to a mortar. The NiCo-LDH and PTFE dispersions were then thoroughly mixed at 80°C using a two-roll mill, with PTFE comprising 5% of the mixture by mass. Finally, the PTFE / LDH mixture was pressed into a film using a rod on an 80°C hot plate to obtain a 5% PTFE / LDH layered double hydroxide film.

[0041] Example 2:

[0042] A method for preparing a layered double hydroxide membrane for alkaline water electrolysis includes the following steps:

[0043] Using NiCo-LDH, NiCo-LDH powder and a 60% (w / w) aqueous PTFE dispersion were added to a mortar. The NiCo-LDH and PTFE dispersion were then thoroughly mixed at 80°C using a two-roll mill, with PTFE comprising 15% of the mixture by mass. Finally, the PTFE / LDH mixture was pressed into a film using a rod on an 80°C hot plate to obtain a layered double hydroxide film of 15% PTFE / LDH.

[0044] Example 3:

[0045] A method for preparing a layered double hydroxide membrane for alkaline water electrolysis includes the following steps:

[0046] Using NiCo-LDH, NiCo-LDH powder and a 60% (w / w) aqueous PTFE dispersion were added to a mortar. The NiCo-LDH and PTFE dispersion were then thoroughly mixed at 80°C using a two-roll mill, with PTFE comprising 20% ​​of the mixture by mass. Finally, the PTFE / LDH mixture was pressed into a film using a rod on an 80°C hot plate to obtain a layered double hydroxide film of 20% PTFE / LDH.

[0047] Figure 1 The image shows a surface SEM image of a PTFE / LDH membrane with a PTFE content of 5%. Figure 2 This is a cross-sectional SEM image of a PTFE / LDH membrane with a PTFE content of 5%. (Source: [Original Source Name]) Figure 1 , Figure 2 It is known that during the calendering process, PTFE undergoes a fibrillation process under mechanical shearing. The PTFE filaments intertwine to form a three-dimensional network structure, which binds the LDH together and provides a supporting network for the LDH, ensuring the strength of the film.

[0048] Figure 3 For 5% PTFE / LDH membranes, 15% PTFE / LDH membranes, 20% PTFE / LDH membranes, and FAA-3-50 commercial membranes at 1 mol·L⁻¹ -1 Sheet resistivity curves in KOH solution at 30℃-80℃. Comparison of PTFE / LDH membrane and FAA-3-50 commercial membrane at 1 mol·L⁻¹. -1 Comparisons in KOH solution showed that the 5% PTFE / LDH membrane had the lowest sheet resistivity and outperformed the commercial FAA-3-50 membrane.

[0049] Figure 4 The areal resistivity curves of 5% PTFE / LDH membrane, 15% PTFE / LDH membrane, and Zirfon membrane in 30 wt% KOH solution are shown between 30℃ and 80℃. A comparison of the PTFE / LDH membrane with the commercial Zirfon membrane in 30 wt% KOH solution indicates that the PTFE / LDH membrane has a lower areal resistivity. At 80℃, the areal resistivity of the 5% PTFE / LDH membrane is 27.53 mΩcm. 2 It is only a quarter of Zirfon's commercial membranes.

[0050] Figure 5 The graph shows the polarization curves of 5% PTFE / LDH membrane, 15% PTFE / LDH membrane, and Zirfon membrane. As can be seen from the graph, the Zirfon membrane exhibits the highest polarization at 1000 mA / cm². -2The voltage at the specified current density was 1.87 V. At the same current density, the voltages of the 15% PTFE / LDH membrane and the 5% PTFE / LDH membrane were 1.83 V and 1.74 V, respectively. This result indicates that the PTFE / LDH membrane exhibits superior electrolytic performance compared to the Zirfon membrane. This advantage can be attributed to two main factors. One is the superior OH- ion exchange capacity of the LDH surface in the membrane. - Transfer capacity. Another reason is the strong liquid absorption capacity of LDH in 30 wt.% KOH solution. Therefore, LDH / PTFE membranes can store large amounts of OH. - This facilitates ion transport, thereby achieving better electrolysis performance.

[0051] The relevant testing methods are as follows:

[0052] Figures 1-2 The surface and cross-sectional morphology of the PTFE / LDH membrane were observed using scanning electron microscopy. For surface analysis, the sample was first completely dried in an oven (60°C, 6 hours). For cross-section examination, the sample was first frozen in liquid nitrogen, then subjected to a slight force to induce brittle fracture, thus obtaining the cross-section of the PTFE / LDH membrane.

[0053] Figures 3-4 The surface resistivity was measured using an H-shaped electrolytic cell. Electrochemical impedance spectroscopy was performed using an electrochemical workstation.

[0054] Figure 5 The alkaline water electrolysis performance in a 30 wt% KOH solution was measured using a DC power supply at 80 °C and a flow rate of 100 mL·min⁻¹. After stabilization at 80 °C for 2 hours, polarization curves were obtained by recording the voltage within the current range of 0 to 5 A.

[0055] Table 1 Hydrogen permeability: Before testing, the membrane sample was thoroughly wetted in 30 wt% KOH solution for 24 hours. The hydrogen permeability was tested using the limiting current density method.

[0056] Example 4: The preparation method of the PTFE / LDH membrane provided in this example is basically the same as that in Example 1, except that NiCo-LDH is replaced with NiFe-LDH, the mass percentage of PTFE is changed to 30wt%, and the molding temperature is changed to 220℃. The resulting membrane has a sheet resistivity of 115.22 mΩcm under the conditions of 30wt% KOH and 80℃. 2 The hydrogen permeability is 47.1 × 10⁻⁶. 14 mol·s -1 ·cm -1 ·kpa -1The voltage at 1000mAcm⁻² is 1.85V.

[0057] Example 5: The preparation method of the PTFE / LDH membrane provided in this example is basically the same as that in Example 1, except that the NiCo-LDH used is replaced with CoAl-LDH, the mass percentage of PTFE is replaced with 25wt%, and the molding temperature is changed to 180℃. The resulting membrane has a sheet resistivity of 105.64 mΩcm under the conditions of 30wt% KOH and 80℃. 2 The hydrogen permeability is 30.5 × 10⁻⁶. 14 mol·s -1 ·cm -1 ·kpa -1 The voltage at 1000mAcm⁻² is 1.84V.

[0058] Example 6: The preparation method of the PTFE / LDH membrane provided in this example is basically the same as that in Example 1, except that NiCo-LDH is replaced with NiFeCr-LDH, the mass percentage of PTFE is replaced with 10wt%, the molding temperature is 120℃, and the resulting membrane has a sheet resistivity of 77.34mΩcm under the conditions of 30wt% KOH and 80℃. 2 The hydrogen permeability is 48.2 × 10⁻⁶. 14 mol·s -1 ·cm -1 ·kpa -1 The voltage at 1000mAcm⁻² is 1.86V.

[0059] Example 7: The preparation method of the PTFE / LDH membrane provided in this example is basically the same as that in Example 1, except that NiCo-LDH is replaced with NiCoAl-LDH, the mass percentage of PTFE is replaced with 1wt%, and the molding temperature is changed to 60℃. The resulting membrane has a sheet resistivity of 32.36mΩcm under the conditions of 30wt% KOH and 80℃. 2 The hydrogen permeability is 57.7 × 10⁻⁶. 14 mol·s -1 ·cm -1 ·kpa -1 The voltage at 1000mAcm⁻² is 1.75V.

[0060] Example 8: The preparation method of the PTFE / LDH membrane provided in this example is basically the same as that in Example 1, except that the NiCo-LDH used is replaced with MgAl-LDH, and the molding temperature is changed to 20℃. The resulting membrane has a sheet resistivity of 56.51 mΩcm under the conditions of 30wt% KOH and 80℃. 2The hydrogen permeability is 27.4 × 10⁻⁶. 14 mol·s -1 ·cm -1 ·kpa -1 The voltage at 1000mAcm⁻² is 1.81V.

[0061] Example 9: The preparation method of the PTFE / LDH membrane provided in this example is basically the same as that in Example 1, except that the NiCo-LDH used is replaced with ZnAl-LDH. The resulting membrane has a sheet resistivity of 49.22 mΩcm under the conditions of 30wt% KOH and 80℃. 2 The hydrogen permeability is 19.7 × 10⁻⁶. 14 mol·s -1 ·cm -1 ·kpa -1 The voltage at 1000mAcm⁻² is 1.79V.

[0062] Comparative Example 1: The preparation method of the PTFE / LDH membrane provided in this comparative example is basically the same as that in Example 1, except that the PTFE used is replaced with polysulfone, as shown below. Figure 6 As shown, it cannot be effectively used to form a film.

[0063] Comparative Example 2: The preparation method of the PTFE / LDH membrane provided in this comparative example is basically the same as that in Example 1, except that the NiCo-LDH used is replaced with nickel oxide (NiO). The resulting membrane has a sheet resistivity of 133.47 mΩcm under the conditions of 30 wt% KOH and 80°C. 2 The hydrogen permeability is 101.6 × 10⁻⁶. 14 mol·s -1 ·cm -1 ·kpa -1 The voltage at 1000mAcm⁻² is 1.88V.

[0064] As shown in Table 1, by comparing Examples 1-9, Comparative Examples 1-2, and Zirfon commercial membranes, it can be seen that the PTFE / LDH membrane has better hydrogen permeability, sheet resistance, and voltage performance.

[0065] It can also be seen that there is a synergistic effect between polytetrafluoroethylene (PTFE) and layered double hydroxide particles in the method of the present invention, which can synergistically improve the relevant properties of the prepared layered double hydroxide film. In particular, there is a significant synergistic effect between PTFE and NiCo-LDH in the method of the present invention, which can significantly synergistically improve the relevant properties of the prepared layered double hydroxide film.

[0066] Table 1

[0067]

[0068] Furthermore, as can be seen from Table 1, the surface resistivity and hydrogen permeability of the 5% PTFE / LDH membrane prepared in Example 1 are 22.30% and 6.39% of those of the Zirfon commercial membrane, respectively.

[0069] 5% PTFE / LDH surface resistivity: 27.53 mΩcm 2 Zirfon commercial film surface resistivity: 123.45 mΩcm 2 .

[0070] 5% PTFE / LDH hydrogen permeability: 8.9 × 10⁻⁶ 14 mol·s -1 ·cm -1 ·kpa -1 Zirfon commercial membrane hydrogen permeability: 139.2 × 10⁻⁶ 14 mol·s -1 ·cm -1 ·kpa -1 .

[0071] The Zirfon membrane exhibits a voltage of 1.87 V at 1000 mA cm⁻². At the same current density, the voltages of the 15% PTFE / LDH membrane and the 5% PTFE / LDH membrane are 1.83 V and 1.74 V, respectively. This result demonstrates that the PTFE / LDH membrane exhibits superior electrolytic performance compared to the Zirfon membrane.

[0072] In summary, this invention uses LDH and PTFE as highly efficient ion conductors and binders, respectively, to prepare LDH / PTFE membranes through mixed calendering, forming a water electrolysis hydrogen production material that can be widely used in production.

[0073] The advantages of this invention are: the preparation of the membrane does not involve a phase transformation process, does not require the addition of organic solvents, avoids the phase transformation method used in the preparation of traditional Zrfion commercial membranes, opens up a new method for the preparation of alkaline water electrolysis membranes, and provides new manufacturing process guidance for the large-scale production of alkaline water electrolysis membranes.

[0074] Furthermore, the membrane can alter its microstructure to maintain sufficient ion pathways; the hydrophilic LDH can adsorb KOH solution and rapidly transport OH- on its surface and between layers. - PTFE is used to firmly bind LDHs to form a membrane. The LDH content is adjustable; at high LDH contents, the membrane exhibits a lower sheet resistivity (27.53 mΩcm in 30 wt.% KOH solution at 80°C). 2 Meanwhile, the sheet resistivity remained unchanged after treatment in 30wt% KOH solution for 1000 h. The 5% PTFE / LDH membrane at 1000 mA cm⁻¹-2 The voltage is 1.74V, which is significantly better than that of commercial Zirfon membranes.

[0075] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A layered double hydroxide membrane for alkaline water electrolysis, characterized in that: The layered double hydroxide film is obtained by connecting layered double hydroxide particles into a continuous film using polytetrafluoroethylene as a binder. The layered double hydroxide film is obtained by calendering polytetrafluoroethylene and layered double hydroxide particles after mixing. The method for preparing the layered double hydroxide membrane by alkaline water electrolysis includes the following steps: NiCo-LDH was used, in which the divalent metal ion is nickel ion and the trivalent metal ion is cobalt ion. NiCo-LDH powder and an aqueous dispersion of 60% PTFE were added to a mortar. Then, the NiCo-LDH and PTFE dispersion were thoroughly mixed at 80°C using a two-roll mill, wherein the mass content of PTFE in the mixture was 5%. Finally, the PTFE / LDH mixture was pressed into a film on an 80°C heating plate using a rod to obtain a 5% PTFE / LDH layered double hydroxide film.

2. The application of the layered double hydroxide membrane as described in claim 1 in alkaline water electrolysis.

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