Layered double hydroxide film for alkaline water electrolysis and application thereof

Abstract

The invention belongs to the technical field of new materials, and discloses a layered double hydroxide film for alkaline water electrolysis, and the layered double hydroxide film is obtained by connecting layered double hydroxide particles into a continuous film by using polytetrafluoroethylene as an adhesive. According to the invention, polytetrafluoroethylene (PTFE) is used as an adhesive, and layered double hydroxide (LDH) particles are connected into a continuous compact film by a calendering method. The preparation method does not need or rarely needs to use an organic solvent, and is easy for continuous industrial production. When the prepared layered double hydroxide film is used for alkaline water electrolysis, the sheet resistance and hydrogen permeability which are obviously lower than those of a commodity Zirfon film are shown, and the layered double hydroxide film can be widely applied to industrial production and has relatively high ionic conductivity.

Description

Technical Field

[0001] The invention belongs to the technical field of new materials and relates to an alkaline water electrolysis membrane, in particular to a layered double hydroxide membrane for alkaline water electrolysis and application thereof. Background Art

[0002] Currently, commercial membranes used for AWE include polyphenylene sulfide (PPS) and Zirfon membranes. They show high stability under practical conditions. However, these membranes are usually several hundred microns thick and show high overpotential for water electrolysis. The thick membrane structure makes the transport resistance too large, resulting in low electrolysis efficiency. Therefore, the development of new membranes is particularly important.

[0003] In addition, the production of Zirfon membranes requires the use of an organic solvent for phase conversion, and the organic solvent needs to be post-processed and recovered during the production process, which is a long and complicated process.

[0004] LDHs is a two-dimensional layered anionic clay material that can transport hydroxide ions internally. In addition, LDHs also have good thermal alkaline stability. Therefore, many researchers use LDHs as raw materials to prepare membrane materials for water electrolysis and hydrogen production, including LDH-polymer membranes. ZENG·L et al. used a solution casting method to synthesize a cross-linked polyvinyl alcohol / layered double hydroxide (PVA / LDH) mixed membrane. However, the LDH content in the membrane is low, resulting in very low ionic conductivity. SAILAJA·G·S et al. added hexagonal plate-shaped magnesium aluminum double hydroxide (LDH) to the electrospun polyvinylidene fluoride (PVDF) substrate to obtain a PVDF-LDH membrane, but PVDF has poor alkali resistance. DI·VONA·M·L uses polysulfone grafted with quaternary ammonium groups and dispersed LDH nanoparticles (component is 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 composite anion exchange membrane with gas barrier and OH by assembling LDH nanosheets and quaternary ammonium grafted polysulfone (QAPSF) layer by layer. - Conductive bifunctional organic-inorganic thin films, but the quaternary ammonium groups on polysulfone polymers have poor alkali resistance. Lei Wan et al. prepared PTFE-LDH membranes by growing LDH in porous polytetrafluoroethylene (PTFE), but the in situ growth of LDH takes a long time and is not conducive to the large-scale preparation of membranes. Therefore, it is necessary to develop LDH membrane technology with higher ionic conductivity, more chemical stability and more conducive to large-scale preparation. Summary of the invention

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

[0006] The technical solution adopted by the present invention to solve the technical problem is:

[0007] The invention 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 film by using polytetrafluoroethylene as an adhesive.

[0008] Furthermore, the layered double hydroxide is composed of divalent and trivalent metal hydroxides to form a positively charged main layer, and the main layers contain intercalated negative ions to maintain 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 membrane is obtained by mixing polytetrafluoroethylene and layered double hydroxide particles and then calendering them.

[0011] Furthermore, the mass ratio of the polytetrafluoroethylene in the mixture of polytetrafluoroethylene and layered double hydroxide particles is 30%-1%, and the more preferred mass ratio is 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 carried out by applying force to the mixture at 20-220°C using a calender.

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

[0015] The layered double hydroxide membrane described above is used in alkaline water electrolysis.

[0016] The advantages and positive effects achieved by the present invention are:

[0017] 1 The present invention uses polytetrafluoroethylene (PTFE) as an adhesive and adopts a calendering method to connect layered double hydroxide (LDH) particles into a continuous dense film. The preparation method does not require the use of organic solvents, and the materials and equipment used in the process are easy to obtain, the production cost is low, and it is conducive to mass production and continuous industrial production. Traditional alkaline water electrolysis membranes, such as the commercial Zirfon membrane, are produced by a phase conversion method using organic solvents. The organic solvents need to be post-treated and recycled during the production process, and the process is long and complicated. The present invention does not use organic solvents as solvents, and adopts a dry or near-dry calendering method to produce alkaline water electrolysis membranes, which is of great significance to promoting the industry renewal of alkaline water electrolysis membranes.

[0018] 2 During the calendering preparation process of the layered double hydroxide membrane material for alkaline water electrolysis of the present invention, PTFE undergoes a fiberization process under the action of mechanical shearing. The PTFE filamentous fibers are intertwined to form a three-dimensional network structure, which binds the LDH together and provides a network to support the LDH. In addition, the dispersed LDH needles are also firmly bonded to the PTFE fibers, which can enable the membrane to maintain high mechanical stability and long service life. Figure 1 , Figure 2 shown.

[0019] 3. When the layered double hydroxide membrane prepared by the present invention is used for alkaline water electrolysis, it exhibits significantly lower surface resistance and hydrogen permeability than the commercial Zirfon membrane. Figure 3 It can be seen that the surface resistance of PTFE / LDH membrane is low. At 80℃, the area resistance of 5% PTFE / LDH membrane is 27.53mΩcm 2 , which is only one-fourth of the Zirfon membrane. The PTFE / LDH membrane has better electrolytic performance. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0021] Figure 2 The cross-sectional SEM image of the 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 the present invention;

[0022] Figure 3 The commercial membranes of the present invention, 5% PTFE / LDH membrane, 15% PTFE / LDH membrane, 20% PTFE / LDH membrane and FAA-3-50 membrane, were prepared at 1 mol·L -1 A surface resistance variation curve in KOH solution at 30°C-80°C, wherein the abscissa represents temperature and the ordinate represents surface resistance;

[0023] Figure 4 It is a surface resistance variation curve of the 5% PTFE / LDH membrane, the 15% PTFE / LDH membrane and the Zirfon commercial membrane in the present invention in a 30wt% KOH solution at 30°C-80°C; wherein the abscissa represents temperature and the ordinate represents surface resistance;

[0024] Figure 5 The polarization curves of the 5% PTFE / LDH membrane, the 15% PTFE / LDH membrane and the Zirfon membrane in the present invention are shown in FIG. 1 , wherein the abscissa is the current density and the ordinate is the voltage;

[0025] Figure 6 This is a verification picture showing that the PTFE / LDH membrane cannot be effectively prepared when the comparative example 1 of the present invention is prepared. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the embodiments. The following embodiments are descriptive rather than restrictive, and the protection scope of the present invention cannot be limited by the following embodiments.

[0027] The various experimental operations involved in the specific embodiments are all routine techniques in the art. For parts not specially annotated in this document, ordinary technicians in the art can implement them by referring to various commonly used reference books, scientific and technological literature or related instructions, manuals, etc. before the filing date of this invention.

[0028] The invention 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 film by using polytetrafluoroethylene as an adhesive.

[0029] Preferably, the layered double hydroxide is composed of divalent and trivalent metal hydroxides as its positively charged main layers, and the main layers contain intercalated negative ions to maintain 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 membrane is obtained by mixing polytetrafluoroethylene and layered double hydroxide particles and then calendering them.

[0032] Preferably, the mass ratio of the polytetrafluoroethylene in the mixture of polytetrafluoroethylene and layered double hydroxide particles is 30%-1%, and more preferably, the mass ratio 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 carried out by applying force to the mixture at 20-220°C using a calender.

[0035] Preferably, the calender is used to apply force to form the product at 60-190°C.

[0036] The layered double hydroxide membrane described above is used in alkaline water electrolysis.

[0037] Specifically:

[0038] Embodiment 1:

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

[0040] NiCo-LDH (in the layered double hydroxide, the divalent metal ions are nickel ions and the trivalent metal ions are cobalt ions) was used, NiCo-LDH powder and a 60% mass concentration of PTFE aqueous dispersion were added to a mortar, and then NiCo-LDH and PTFE dispersion were fully mixed by an open mill at 80°C, wherein the mass content of PTFE in the mixture was 5%. Finally, the PTFE / LDH mixture was pressed into a film on a heating plate at 80°C with a rod to obtain a layered double hydroxide film 5% PTFE / LDH.

[0041] Embodiment 2:

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

[0043] NiCo-LDH was used, NiCo-LDH powder and 60% aqueous PTFE dispersion were added to a mortar, and then NiCo-LDH and PTFE dispersion were fully mixed by an open mill at 80°C, wherein the mass content of PTFE in the mixture was 15%. Finally, the PTFE / LDH mixture was pressed into a film on a hot plate at 80°C with a rod to obtain a layered double hydroxide membrane of 15% PTFE / LDH.

[0044] Embodiment 3:

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

[0046] Using NiCo-LDH, NiCo-LDH powder and 60% aqueous PTFE dispersion were added to a mortar, and then NiCo-LDH and PTFE dispersion were fully mixed at 80°C through an open mill, wherein the mass content of PTFE in the mixture was 20%. Finally, the PTFE / LDH mixture was pressed into a film on a hot plate at 80°C with a rod to obtain a layered double hydroxide membrane 20% PTFE / LDH.

[0047] Figure 1 The surface SEM image of the PTFE / LDH membrane with a PTFE content of 5%. Figure 2 The cross-sectional SEM image of the PTFE / LDH membrane with a PTFE content of 5%. Figure 1 , Figure 2 It can be seen that during the calendering process, PTFE undergoes fibrillation under mechanical shearing. PTFE filaments entangle with each other to form a three-dimensional network structure, which binds LDH together and provides a network to support LDH, ensuring the strength of the membrane.

[0048] Figure 3 The results of 5% PTFE / LDH membrane, 15% PTFE / LDH membrane, 20% PTFE / LDH membrane and FAA-3-50 commercial membrane were analyzed at 1 mol·L -1 Surface resistance curves of PTFE / LDH membrane and FAA-3-50 commercial membrane in KOH solution at 30℃-80℃. -1 The comparison in KOH solution showed that the 5% PTFE / LDH membrane had the lowest sheet resistance, outperforming the FAA-3-50 commercial membrane.

[0049] Figure 4 The surface resistance curves of 5% PTFE / LDH membrane, 15% PTFE / LDH membrane and Zirfon membrane in 30wt% KOH solution at 30℃-80℃ are shown. The comparison between PTFE / LDH membrane and commercial Zirfon membrane in 30wt% KOH solution shows that PTFE / LDH membrane has lower surface resistance. At 80℃, the area resistance of 5% PTFE / LDH membrane is 27.53mΩcm 2 , which is only one-fourth of Zirfon's commercial membrane.

[0050] Figure 5 The polarization curves of 5% PTFE / LDH membrane, 15% PTFE / LDH membrane and Zirfon membrane are shown in the figure. It can be seen that the Zirfon membrane has a high polarization current at 1000mAcm -2The voltage at the current density of 15% PTFE / LDH membrane and 5% PTFE / LDH membrane was 1.87V. At the same current density, the voltages of 15% PTFE / LDH membrane and 5% PTFE / LDH membrane were 1.83V and 1.74V, respectively. This result shows that the PTFE / LDH membrane has higher electrolytic performance than the Zirfon membrane. This advantage can be attributed to two main factors. One is that the LDH surface in the membrane has superior OH - Another reason is that LDH has a strong liquid absorption capacity in 30wt.% KOH solution. Therefore, LDH / PTFE membrane can store a large amount of OH - , which is beneficial to the transmission of ions, thereby obtaining better electrolytic performance.

[0051] The relevant detection methods are as follows:

[0052] Figure 1-2 :The surface and cross-sectional morphology of the PTFE / LDH membrane were observed using a scanning electron microscope. When analyzing the surface of the PTFE / LDH membrane, the sample was first completely dried in an oven (60°C, 6 hours). When examining the cross-section of the PTFE / LDH membrane, the sample was first frozen in liquid nitrogen and then a slight force was applied to make it brittle, thereby obtaining the cross-section of the PTFE / LDH membrane.

[0053] Figure 3-4 :H-shaped electrolytic cell was used to test the surface resistance. Electrochemical impedance spectroscopy was performed using an electrochemical workstation.

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

[0055] Table 1 Hydrogen permeability: Before testing, the membrane samples were thoroughly wetted in a 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 the NiCo-LDH used is replaced by NiFe-LDH, the mass percentage of PTFE is replaced by 30wt%, and the molding temperature is changed to 220°C. The surface resistance of the obtained membrane is 115.22mΩcm under the conditions of 30wt% KOH and 80°C. 2 The hydrogen permeability is 47.1×10 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 by CoAl-LDH, the mass percentage of PTFE is replaced by 25wt%, and the molding temperature is changed to 180°C. The surface resistance of the obtained membrane is 105.64mΩcm under the conditions of 30wt% KOH and 80°C. 2 The hydrogen permeability is 30.5×10 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 the NiCo-LDH used is replaced by NiFeCr-LDH, and the mass percentage of PTFE is replaced by 10wt%, and the molding temperature is 120°C. The surface resistance of the obtained membrane is 77.34mΩcm under the conditions of 30wt% KOH and 80°C. 2 The hydrogen permeability is 48.2×10 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 the NiCo-LDH used is replaced by NiCoAl-LDH, and the mass percentage of PTFE is replaced by 1wt%, and the molding temperature is changed to 60°C. The surface resistance of the obtained membrane is 32.36mΩcm under the conditions of 30wt% KOH and 80°C. 2 The hydrogen permeability is 57.7×10 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 by MgAl-LDH, and the molding temperature is changed to 20°C. The surface resistance of the obtained membrane is 56.51 mΩcm under the conditions of 30wt% KOH and 80°C. 2The hydrogen permeability is 27.4×10 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 by ZnAl-LDH. The surface resistance of the obtained membrane is 49.22 mΩcm under the conditions of 30wt% KOH and 80°C. 2 The hydrogen permeability is 19.7×10 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 of Example 1, except that the PTFE used is replaced by polysulfone. Figure 6 As shown, the film cannot be prepared effectively.

[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 by nickel oxide (NiO). The surface resistance of the obtained membrane is 133.47 mΩcm under the conditions of 30wt% KOH and 80°C. 2 The hydrogen permeability is 101.6×10 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 the Zirfon commercial membrane, it can be seen that the PTFE / LDH membrane has better hydrogen permeability, surface resistance and voltage performance.

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

[0066] Table 1

[0067]

[0068] In addition, it can be seen from Table 1 that the surface resistance 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 resistance: 27.53mΩcm 2 . Zirfon commercial film surface resistance: 123.45mΩcm 2 .

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

[0071] The voltage of Zirfon membrane at 1000 mA cm-2 is 1.87 V. At the same current density, the voltages of 15% PTFE / LDH membrane and 5% PTFE / LDH membrane are 1.83 V and 1.74 V, respectively. This result shows that PTFE / LDH membrane has better electrolytic performance than Zirfon membrane.

[0072] In summary, the present invention uses LDH and PTFE as efficient ion conductors and adhesives, respectively, and prepares LDH / PTFE membranes by mixed calendering to form water electrolysis hydrogen production materials that can be widely used in production.

[0073] The advantages of the present invention are that the preparation of the membrane does not involve a phase inversion process, does not require the addition of an organic solvent, avoids the phase inversion 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] In addition, the membrane can change its microstructure to maintain sufficient ion access, and the hydrophilic LDH can adsorb KOH solution and quickly transport OH on its surface and between layers. - PTFE can firmly bind LDHs to form a membrane. The LDH content can be adjusted, and the membrane has a lower surface resistance (27.53 mΩcm at 80°C in a 30wt.% KOH solution) at a high LDH content. 2 ). At the same time, after being treated in 30wt% KOH solution for 1000h, the surface resistance of 5% PTFE / LDH membrane remained unchanged at 1000mA cm-2 The voltage under the film is 1.74 V, which is significantly better than the commercial Zirfon film.

[0075] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present 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 an adhesive.

2. The layered double hydroxide membrane according to claim 1, characterized in that: The layered double hydroxide is composed of divalent and trivalent metal hydroxides to form a positively charged main layer, and intercalated negative ions are contained between the main layers to keep the main layers electrically neutral.

3. The layered double hydroxide membrane according to claim 2, characterized in that: 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.

4. The layered double hydroxide membrane according to claim 1, characterized in that: The layered double hydroxide membrane is obtained by mixing polytetrafluoroethylene and layered double hydroxide particles and then calendering them.

5. The layered double hydroxide membrane according to claim 4, characterized in that: The mass ratio of the polytetrafluoroethylene in the mixture of polytetrafluoroethylene and layered double hydroxide particles is 30%-1%, and the optimal mass ratio is 15%-5%.

6. The layered double hydroxide membrane according to claim 5, characterized in that: The mass ratio of the polytetrafluoroethylene in the mixture of polytetrafluoroethylene and layered double hydroxide particles is 15%-5%.

7. The layered double hydroxide membrane according to any one of claims 4 to 6, characterized in that: The calendering of the mixture of polytetrafluoroethylene and layered double hydroxide particles is carried out by applying force at 20-220° C. using a calender.

8. The layered double hydroxide membrane according to claim 7, characterized in that: The calender is used to apply force to form at 60-190°C.

9. Use of the layered double hydroxide membrane according to any one of claims 1 to 8 in alkaline water electrolysis.

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