Composite membrane material for alkaline system as well as preparation method and application of composite membrane material

Abstract

The invention discloses a composite membrane material for an alkaline system and a preparation method and application thereof, and belongs to the field of membrane materials. The composite membrane material for the alkaline system comprises a porous diaphragm and a cross-linked chitosan separation layer, the cross-linked chitosan separation layer is attached to the surface of the porous diaphragm in a cross-linked manner. According to the composite membrane material for the alkaline system, due to the compact structure of the cross-linked chitosan separation layer, the composite membrane has excellent selectivity, and meanwhile, cross-linked chitosan has excellent hydroxyl ion conductivity, so that the composite membrane material has excellent ionic conductivity and has excellent device performance on an alkaline flow battery system and an alkaline water electrolysis hydrogen production device.

Description

Technical Field

[0001] The present application relates to a composite membrane material for an alkaline system, its preparation method and application, belonging to the field of membrane materials. Background Art

[0002] With the development of society, the demand for energy by humans has gradually increased. However, non-renewable energy sources such as fossil energy are gradually exhausted, while renewable energy sources such as wind energy, solar energy, and tidal energy have received extensive attention due to their renewable and environmentally friendly characteristics. However, the characteristics of renewable energy power generation such as discontinuity, instability, and unpredictability have seriously hindered its wide application, and energy storage technology is an important support for realizing the safe and stable power supply of renewable energy. Alkaline flow batteries such as alkaline zinc-iron flow batteries and alkaline organic matter / iron flow batteries have received extensive attention in the field of energy storage due to their rich resources, low price, and high kinetics, and have good development prospects. In addition, hydrogen energy is a good bridge, and its main advantages are: the conversion between hydrogen and electricity can be achieved efficiently through fuel cells, hydrogen has a relatively high energy density and is relatively easy to store; the conversion of hydrogen to electricity has the potential for large-scale application. Among many electrolytic water hydrogen production technologies, alkaline electrolytic water hydrogen production technology avoids the use of precious metal catalysts and has advantages such as low cost.

[0003] As a key core material for energy storage and hydrogen energy, the main role of the membrane material is to separate the positive and negative active substances / gas interpenetration and transfer carriers to form an internal circuit of the battery. The membrane material is required to have characteristics such as high selectivity, high ion conductivity, high stability, and low cost. Perfluorosulfonic acid ion membranes (Nafion series membranes) are a widely used type of membrane material in flow batteries. The ion conductivity of this type of membrane material in an alkaline system is low, which is not conducive to improving the battery performance; the stability of anion exchange membranes is poor and the ion conductivity is limited, which restricts the life and electrolysis performance of electrolytic cells.

[0004] Therefore, the design and development of high-performance and low-cost membrane materials are of great significance for improving the performance of energy storage and hydrogen energy devices, reducing material costs, and promoting their large-scale application. Summary of the Invention

[0005] According to one aspect of the present application, a composite membrane material for an alkaline system is provided. The dense structure of the cross-linked chitosan separation layer enables the composite membrane to have excellent selectivity. At the same time, the cross-linked chitosan has excellent hydroxide ion conductivity, making it have excellent ionic conductivity and excellent device performance in an alkaline flow battery system and an alkaline water electrolysis hydrogen production device.

[0006] The composite membrane material for an alkaline system described in the present application includes a porous diaphragm and a cross-linked chitosan separation layer;

[0007] The crosslinked chitosan separation layer is crosslinked and attached to the surface of the porous membrane.

[0008] In this application, the crosslinked chitosan separation layer being crosslinked and attached to the surface of the porous membrane means that the crosslinked chitosan is crosslinked and attached on the surface of the porous membrane.

[0009] Optionally, the material of the crosslinked chitosan separation layer is chitosan crosslinked by metal ions;

[0010] The metal ions are selected from any one or more of copper ions, zinc ions, and lanthanum ions.

[0011] Optionally, the porous membrane is AGFA ZIRFON PERL UTP 500, a polyolefin porous membrane (Daramic);

[0012] or is prepared by phase inversion from a blend of one or more of sulfonated polysulfone, sulfonated polyimide, sulfonated polyether ketone, polyethylene glycol, and polyvinylpyrrolidone with one or more of polysulfone and polyethersulfone.

[0013] Optionally, the chitosan is substituted by amino groups and / or carboxymethyl groups.

[0014] Optionally, the relative molecular weight of the chitosan is 100,000 - 300,000; preferably, the relative molecular weight of the chitosan is 150,000 - 250,000.

[0015] Optionally, the relative molecular weight of the chitosan is independently selected from any one value of 100,000, 150,000, 200,000, 250,000, 300,000 or a range value between any two of the above.

[0016] Optionally, the deacetylation degree of the chitosan is 70% - 95%.

[0017] On the other hand, the present invention provides a method for preparing the composite membrane material for the basic system, including the following steps:

[0018] (1) Dissolve chitosan in an organic acid solution to obtain a chitosan solution, immerse the porous membrane in the chitosan solution or coat the chitosan solution on the surface of the porous membrane to obtain a chitosan / porous membrane composite membrane;

[0019] (2) Place the chitosan / porous membrane composite membrane in an alkali solution and react to obtain the composite membrane material for the basic system.

[0020] Optionally, the alkali solution contains metal cations.

[0021] Optionally, the alkali solution is selected from any one or more of Na2Cu(OH)4 solution, K2Cu(OH)4 solution, Li2Cu(OH)4 solution, La(OH)3 solution, Na2Zn(OH)4 solution, K2Zn(OH)4 solution, NaOH, KOH, and LiOH.

[0022] Optionally, the alkali solution is a saturated alkali solution.

[0023] Optionally, the concentration of NaOH in the Na2Cu(OH)4 solution is 0.1 - 8 mol / L -1 , preferably 1 - 8 mol / L -1 .

[0024] Optionally, the concentration of KOH in the K2Cu(OH)4 solution is 0.1 - 8 mol / L -1 , preferably 1 - 8 mol / L -1 .

[0025] Optionally, the concentration of LiOH in the Li2Cu(OH)4 solution is 0.1 - 8 mol / L -1 , preferably 1 - 8 mol / L -1 .

[0026] Optionally, the concentration of NaOH in the Na2Zn(OH)4 solution is 0.1 - 8 mol / L -1 , preferably 1 - 8 mol / L -1 .

[0027] Optionally, the concentration of KOH in the K2Zn(OH)4 solution is 0.1 - 8 mol / L -1 , preferably 1 - 8 mol / L -1 .

[0028] Optionally, the thickness of the chitosan film is 1 - 50 μm; preferably, the thickness of the chitosan film is 20 - 40 μm.

[0029] Optionally, the thickness of the chitosan film is independently selected from any one of 1 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 50 μm or the range values between any two of the above.

[0030] Optionally, in the step (2), the reaction time is 1 - 50 h; preferably, the reaction time is 20 - 30 h.

[0031] Specifically, in the step (2), the reaction time is 24 h.

[0032] Optionally, the organic acid solution is an acetic acid solution.

[0033] Optionally, the concentration of the organic acid solution is 0.5 - 4 wt%; preferably, the concentration of the organic acid solution is 0.5 - 2 wt%.

[0034] Optionally, the concentration of the chitosan solution is 0.1 - 5 wt%; preferably, the concentration of the chitosan solution is 1 - 5 wt%.

[0035] Optionally, the concentration of the chitosan solution is independently selected from any value of 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt% or the range value between any two of the above.

[0036] On the other hand, the present application provides an application of the composite membrane material for the alkaline system in energy conversion and storage devices of the alkaline system.

[0037] Optionally, the energy conversion and storage devices of the alkaline system include flow batteries and water electrolysis for hydrogen production. In the energy conversion and storage devices of the alkaline system including flow batteries and water electrolysis for hydrogen production, the crosslinked chitosan separation layer is oriented towards the negative electrode of the device to avoid oxidative degradation of the crosslinked chitosan separation layer by positive electrode oxidation species.

[0038] The beneficial effects that the present application can produce include:

[0039] 1. By compositing a chitosan separation layer with a crosslinked structure on a polymer porous matrix, while ensuring a high ionic conductivity of the membrane material, the selectivity (ion selectivity, gas barrier property) of the membrane material is improved, solving the problems of low ionic conductivity, high price of perfluorosulfonic acid ion membranes, and poor stability of traditional anion exchange membranes in alkaline solutions.

[0040] 2. By regulating the degree of deacetylation of chitosan and the reaction time with an alkaline solution containing metal cations to regulate the crosslinked structure in chitosan, controllable transfer of the ionic conductivity of the composite membrane can be achieved.

[0041] 3. Orienting the crosslinked chitosan separation layer towards the negative electrode of the device can effectively avoid oxidative degradation of the crosslinked chitosan by oxidizing substances on the positive electrode side, thereby effectively maintaining the function of the crosslinked chitosan separation layer.

[0042] 4. The composite membrane material proposed in the present application has excellent alkali stability, expanding the selection range of membrane materials for energy conversion and storage devices in the alkaline system. Description of the Drawings

[0043] Figure 1 It is a structural diagram of the crosslinking reaction of chitosan and copper ions;

[0044] Figure 2Physical diagram of Daramic composite membrane with cross-linked chitosan separation layer. Detailed implementation mode

[0045] The present application will be described in detail below in conjunction with embodiments, but the present application is not limited to these embodiments.

[0046] Unless otherwise specified, the raw materials in the embodiments of the present application are all purchased through commercial channels.

[0047] The test instrument for electrical properties is Arbin BT 2000 instrument.

[0048] Comparative example 1

[0049] A Daramic alkaline zinc-iron flow battery with a thickness of 200 μm was assembled. The composition of the positive electrolyte: 0.8 mol L -1 Fe(CN)6 4- + 3 mol L -1 KOH; the composition of the negative electrolyte: 0.4 mol L -1 Zn(OH)4 2- + 3 mol L -1 NaOH; the volume of the positive and negative electrolytes is 80 mL each; the positive and negative electrodes are both porous carbon felt electrodes, and the graphite plate is used as the current collector plate. The effective area of the electrode: 48 cm 2 ; the battery adopts a constant current charge-discharge mode, charges for 18 min under the current density condition of 80 mA cm -2 , and then discharges to 0.1 V under the condition that the voltage is cut off and the current density is 80 mA cm -2 . The Coulomb efficiency of the battery is 92.11%, and the voltage efficiency is 90.12%. The battery runs continuously for about 5 cycles, and the Coulomb efficiency gradually decreases. At this time, the silica in the membrane dissolves, resulting in a change in the membrane structure and serious intermixing of the electrolytes, leading to an increase in battery polarization.

[0050] Example 1

[0051] 2.5 g of chitosan (degree of deacetylation is 90%, relative molecular weight is 200,000) was dissolved in 60 g of acetic acid solution (acetic acid mass fraction is 1 wt%) to obtain a chitosan solution. The above solution was spin-coated on a Daramic membrane with a thickness of 200 μm to obtain a chitosan / Daramic composite membrane, where the thickness of the chitosan thin film is 33 μm.

[0052] The above chitosan / Daramic composite membrane was placed in a saturated Na2Cu(OH)4 solution (NaOH concentration is 4 mol L -1 ), so that chitosan reacts with metal ions in the solution to cross-link ( Figure 1), with a reaction time of 24 h, to obtain a Daramic composite membrane with a crosslinked chitosan separation layer( Figure 2 ).

[0053] Using the above composite membrane to assemble an alkaline zinc-iron flow battery, the composition of the positive electrolyte: 0.8 mol L -1 Fe(CN)6 4- + 3 mol L -1 KOH; the composition of the negative electrolyte: 0.4 mol L -1 Zn(OH)4 2- + 3 mol L -1 NaOH; the volume of the positive and negative electrolytes is 80 mL each; the positive and negative electrodes are both porous carbon felt electrodes, and the graphite plate is used as the current collector plate. The effective area of the electrode: 48 cm 2 ; the battery adopts a constant current charge-discharge mode, charges for 18 min under a current density condition of 80 mA cm -2 , and then discharges to 0.1 V under a current density condition of 80 mA cm -2 as the voltage cut-off condition. The Coulombic efficiency of the battery is 98.57%, the voltage efficiency is 90.33%, and the battery continuously and stably operates for 80 cycles with stable performance.

[0054] Comparative Example 2

[0055] Using a Zirfon membrane with a thickness of 500 μm to assemble an alkaline zinc-iron flow battery, the composition of the positive electrolyte: 0.8 mol L - 1 Fe(CN)6 4- + 3 mol L -1 KOH; the composition of the negative electrolyte: 0.4 mol L -1 Zn(OH)4 2- + 3 mol L -1 NaOH; the volume of the positive and negative electrolytes is 80 mL each; the positive and negative electrodes are both porous carbon felt electrodes, and the graphite plate is used as the current collector plate. The effective area of the electrode: 48 cm 2 ; the battery adopts a constant current charge-discharge mode, charges for 18 min under a current density condition of 80 mA cm -2 , and then discharges to 0.1 V under a current density condition of 80 mA cm -2 as the voltage cut-off condition. The Coulombic efficiency of the battery is 94.31%, the voltage efficiency is 88.35%, and the battery operates for about 3 cycles, and the Coulombic efficiency gradually decreases (serious intermixing of the electrolytes leads to an increase in battery polarization).

[0056] Example 2

[0057] Dissolve 2.5 g of chitosan (degree of deacetylation is 90%, relative molecular weight is 200,000) in 60 g of acetic acid solution (acetic acid mass fraction is 1 wt%) to obtain a chitosan solution. Coat the above solution on a Zirfon membrane with a thickness of 500 μm to obtain a chitosan / Zirfon composite membrane, where the thickness of the chitosan thin film is 33 μm.

[0058] Place the above chitosan / Zirfon composite membrane in a saturated Na2Cu(OH)4 solution (NaOH concentration is 4 mol / L -1 ), and make chitosan react with metal ions in the solution for crosslinking. The reaction time is 24 h to obtain a Zirfon composite membrane with a crosslinked chitosan separation layer.

[0059] Assemble an alkaline zinc-iron flow battery using the above composite membrane. The composition of the positive electrolyte: 0.8 mol / L -1 Fe(CN)6 4- + 3 mol / L -1 KOH; the composition of the negative electrolyte: 0.4 mol / L -1 Zn(OH)4 2- + 3 mol / L -1 NaOH; the volume of the positive and negative electrolytes is 80 mL each; the positive and negative electrodes are both porous carbon felt electrodes, and a graphite plate is used as the current collector. The effective area of the electrode: 48 cm 2 ; the battery adopts a constant current charge-discharge mode. Charge for 18 min under the condition of a current density of 80 mA / cm -2 , and then cut off the voltage as the condition. Discharge to 0.1 V under the condition of a current density of 80 mA / cm -2 . The Coulomb efficiency of the battery is 97.92%, the voltage efficiency is 87.85%, and the battery continuously and stably operates for 105 cycles with stable performance.

[0060] Comparative Example 3

[0061] Blend polyethersulfone (PES) and sulfonated polyether ether ketone (SPEEK) (polymer solid content is 30 wt%, PES:SPEEK (mass ratio) = 5:5, DMAc is the solvent), and prepare a PES / SPEEK porous ion-conducting membrane with a thickness of about 70 μm by the immersion precipitation phase inversion method at room temperature and a humidity not higher than 30%. Use the PES / SPEEK porous ion-conducting membrane as the matrix to assemble an alkaline zinc-iron flow battery. The composition of the positive electrolyte: 0.8 mol / L -1 Fe(CN)6 4- + 3 mol / L -1 KOH; the composition of the negative electrolyte: 0.4 mol / L -1 Zn(OH)4 2- + 3 mol / L-1 NaOH; The volume of the positive and negative electrolytes is 80 mL each; The positive and negative electrodes are both porous carbon felt electrodes, and the graphite plate is used as the current collector plate. The effective area of the electrode: 48 cm 2 ; The battery adopts a constant current charge-discharge mode, and is charged for 18 min under the current density condition of 80 mA cm -2 , and then the voltage is cut off as the condition, and discharged to 0.1 V under the current density condition of 80 mA cm -2 . The Coulomb efficiency of the battery is 86.52%, and the voltage efficiency is 91.03%. The battery operates for about 6 cycles, and the Coulomb efficiency gradually decreases (serious intermixing of the electrolytes leads to an increase in battery polarization).

[0062] Comparative Example 4

[0063] 2.5 g of chitosan (degree of deacetylation is 90%, relative molecular weight is 200,000) is dissolved in 60 g of acetic acid solution (acetic acid mass fraction is 1 wt%) to obtain a chitosan solution. The above solution is scrape-coated on a Zirfon membrane with a thickness of 500 μm to obtain a chitosan / Zirfon composite membrane, wherein the thickness of the chitosan thin film is 33 μm.

[0064] The above chitosan / Zirfon composite membrane is placed in a saturated Na2Cu(OH)4 solution (NaOH concentration is 4 mol L -1 ), so that chitosan reacts with metal ions in the solution for crosslinking. The reaction time is 24 h to obtain a Zirfon composite membrane with a crosslinked chitosan separation layer.

[0065] An alkaline zinc-iron flow battery is assembled using the above composite membrane, with the crosslinked chitosan separation layer facing the positive electrode side of the battery. Composition of the positive electrolyte: 0.8 mol L -1 Fe(CN)6 4- + 3 mol L -1 KOH; Composition of the negative electrolyte: 0.4 mol L -1 Zn(OH)4 2- + 3 mol L -1 NaOH; The volume of the positive and negative electrolytes is 80 mL each; The positive and negative electrodes are both porous carbon felt electrodes, and the graphite plate is used as the current collector plate. The effective area of the electrode: 48 cm 2 ; The battery adopts a constant current charge-discharge mode, and is charged for 18 min under the current density condition of 80 mA cm -2 , and then the voltage is cut off as the condition, and discharged to 0.1 V under the current density condition of 80 mA cm -2 . The Coulomb efficiency of the battery is 95.67%, and the voltage efficiency is 88.13%. The battery operates for about 5 cycles, and the crosslinked chitosan separation layer is gradually oxidized by ferricyanide ions on the positive electrode side, resulting in a gradual decrease in its selectivity and a gradual decrease in the Coulomb efficiency of the battery.

[0066] Example 3

[0067] Dissolve 2.5 g of chitosan (degree of deacetylation is 90%, relative molecular weight is 200,000) in 60 g of acetic acid solution (mass fraction of acetic acid is 1 wt%) to obtain a chitosan solution. Coat the above solution on the PES / SPEEK porous ion-conducting membrane substrate in Comparative Example 3 to obtain a chitosan / PES / SPEEK composite membrane. Among them, the thickness of the chitosan film is 25 μm.

[0068] Place the above chitosan / PES / SPEEK composite membrane in a saturated Na2Cu(OH)4 solution (NaOH concentration is 4 mol / L -1 ), and make chitosan react with metal ions in the solution for crosslinking. The reaction time is 24 h to obtain a PES / SPEEK composite membrane with a crosslinked chitosan separation layer.

[0069] Assemble an alkaline zinc-iron flow battery using the above composite membrane. The composition of the positive electrolyte: 0.8 mol / L -1 Fe(CN)6 4- + 3 mol / L -1 KOH; the composition of the negative electrolyte: 0.4 mol / L -1 Zn(OH)4 2- + 3 mol / L -1 NaOH; the volume of the positive and negative electrolytes is 80 mL each; the positive and negative electrodes are both porous carbon felt electrodes, and a graphite plate is used as the current collector plate. The effective area of the electrode: 48 cm 2 ; The battery adopts a constant current charge-discharge mode, charges for 18 min under the current density condition of 80 mA / cm -2 , and then discharges to 0.1 V under the condition that the voltage is cut off and the current density is 80 mA / cm -2 . The Coulomb efficiency of the battery is 98.62%, the voltage efficiency is 89.99%, and the battery continuously and stably operates for 94 cycles with stable performance.

[0070] Comparative Example 5

[0071] Assemble an alkaline electrolytic cell with a Zirfon membrane with a thickness of 500 μm. Use a nickel mesh with a mesh number of 60 and an integrated electrode loaded with a nickel-iron catalyst layer (the thickness of the nickel-iron catalytic layer is ~140 nm, atomic ratio Fe / Ni ~12:100) as the HER electrode, and a nickel mesh with a mesh number of 60 as the OER-side electrode. The effective area of the electrode is 9 cm 2 , a stainless steel plate as the current collector, and 6 mol / L - 1 KOH solution. Test conditions: 400 mA / cm -2Constant current charging, test temperature 70°C. The structure of the electrolytic cell consists of a current collector, an integrated electrode loaded with a HER catalyst, a membrane, an alkaline solution, and a current collector arranged in sequence. The electrolytic voltage of the electrolytic cell is 1.78 V, and the hydrogen content in oxygen measured by gas chromatography is 200 ppm.

[0072] Example 4

[0073] An alkaline electrolytic cell was assembled with the composite membrane in Example 2. A nickel mesh with a mesh size of 60 meshes and an integrated electrode loaded with a nickel-iron catalyst layer (the thickness of the nickel-iron catalytic layer is ~140 nm, atomic ratio Fe / Ni ~12:100) was used as the HER electrode, and a nickel mesh with a mesh size of 60 meshes was used as the electrode on the OER side. The effective area of the electrode is 9 cm 2 , and a stainless steel plate was used as the current collector, 6 mol L -1 KOH solution. Test conditions: 400 mA cm -2 Constant current charging, test temperature 70°C. The structure of the electrolytic cell consists of a current collector, an integrated electrode loaded with a HER catalyst, a membrane, an alkaline solution, and a current collector arranged in sequence. The electrolytic voltage of the electrolytic cell decreased to 1.79 V, without significantly increasing the electrolytic cell voltage, but the hydrogen content in oxygen decreased to 5 ppm, which plays an important role in improving gas purity and reducing subsequent gas purification.

[0074] Example 5

[0075] 2.5 g of chitosan (deacetylation degree 90%, relative molecular weight 200,000) was dissolved in 60 g of acetic acid solution (acetic acid mass fraction 1 wt%) to obtain a chitosan solution. The above solution was spin-coated on a Zirfon membrane with a thickness of 500 μm to obtain a chitosan / Zirfon composite membrane, where the thickness of the chitosan thin film is 33 μm.

[0076] The above chitosan / Zirfon composite membrane was placed in 4 mol L -1 of NaOH solution to change the hydrogen bonds inside chitosan and increase the compactness of the chitosan separation layer. The reaction time was 24 h to obtain a Zirfon composite membrane with a chitosan separation layer.

[0077] An alkaline electrolytic cell was assembled with the above composite membrane. A nickel mesh with a mesh size of 60 meshes and an integrated electrode loaded with a nickel-iron catalyst layer (the thickness of the nickel-iron catalytic layer is ~140 nm, atomic ratio Fe / Ni ~12:100) was used as the HER electrode, and a nickel mesh with a mesh size of 60 meshes was used as the electrode on the OER side. The effective area of the electrode is 9 cm 2 , and a stainless steel plate was used as the current collector, 6 mol L -1 KOH solution. Test conditions: 400 mA cm -2Constant current charging, test temperature 70°C. The structure of the electrolytic cell consists of a current collector, an integrated electrode loaded with a HER catalyst, a membrane, an alkaline solution, and a current collector arranged in sequence. The electrolytic voltage of the electrolytic cell is reduced to 1.84V, which to a certain extent increases the electrolytic cell voltage (the chitosan separation layer increases the membrane resistance), but the hydrogen content in oxygen is reduced to 4ppm, which plays an important role in improving gas purity and reducing subsequent gas purification.

[0078] As described above, these are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, makes some changes or modifications using the technical content disclosed above, which are all equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A composite membrane material for alkaline systems, characterized in that, It includes a porous diaphragm and a crosslinked chitosan separation layer; The crosslinked chitosan separation layer is crosslinked and attached to the surface of the porous diaphragm.

2. The composite membrane material for alkaline systems according to claim 1, characterized in that, The material of the crosslinked chitosan separation layer is chitosan crosslinked by metal ions; The metal ions are selected from any one or more of copper ions, zinc ions, and lanthanum ions; Preferably, the porous diaphragm is AGFA ZIRFON PERL UTP 500 or a polyolefin porous membrane (Daramic); Or it is prepared by phase inversion from a blend of one or more of sulfonated polysulfone, sulfonated polyimide, sulfonated polyether ketone, polyethylene glycol, and polyvinylpyrrolidone with one or two of polysulfone and polyethersulfone; Preferably, the chitosan is substituted by amino groups and / or carboxymethyl groups.

3. The composite membrane material for alkaline systems according to claim 1, characterized in that, The relative molecular weight of the chitosan is 100,000 - 300,000; Preferably, the relative molecular weight of the chitosan is 150,000 - 250,000; Preferably, the deacetylation degree of the chitosan is 70% - 95%.

4. A preparation method of the composite membrane material for alkaline systems according to any one of claims 1 - 3, characterized in that, It includes the following steps: (1) Dissolve chitosan in an organic acid solution to obtain a chitosan solution, immerse the porous diaphragm in the chitosan solution or coat the chitosan solution on the surface of the porous diaphragm to obtain a composite membrane of chitosan / porous diaphragm; (2) Place the composite membrane of chitosan / porous diaphragm in an alkaline solution and react to obtain the composite membrane material for the alkaline system.

5. The preparation method of the composite membrane material for alkaline systems according to claim 4, characterized in that, The alkaline solution contains metal cations; Preferably, the alkaline solution is selected from any one or more of Na2Cu(OH)4 solution, K2Cu(OH)4 solution, Li2Cu(OH)4 solution, La(OH)3 solution, Na2Zn(OH)4 solution, K2Zn(OH)4 solution, NaOH, KOH, and LiOH; Preferably, the concentration of NaOH in the Na2Cu(OH)4 solution is 0.1 - 8 mol / L -1 ; Preferably, the concentration of KOH in the K2Cu(OH)4 solution is 0.1 - 8 mol / L -1 ; Preferably, the concentration of LiOH in the Li2Cu(OH)4 solution is 0.1 - 8 mol / L -1 ; Preferably, the concentration of NaOH in the Na2Zn(OH)4 solution is 0.1 - 8 mol / L -1 ; Preferably, the concentration of KOH in the K2Zn(OH)4 solution is 0.1 - 8 mol / L -1 .

6. The preparation method of the composite membrane material for alkaline systems according to claim 4, characterized in that, The thickness of the chitosan thin film is 1 - 50 μm; Preferably, the thickness of the chitosan thin film is 20 - 40 μm.

7. The preparation method of the composite membrane material for alkaline systems according to claim 4, characterized in that, In the step (2), the reaction time is 1 - 50 h; Preferably, the reaction time is 20 - 30 h.

8. The preparation method of the composite membrane material for alkaline systems according to claim 4, characterized in that, The organic acid solution is an acetic acid solution; Preferably, the concentration of the organic acid solution is 0.5 - 4 wt%; Preferably, the concentration of the chitosan solution is 0.1 - 5 wt%; Preferably, the concentration of the chitosan solution is 1 - 5 wt%.

9. Use of the composite membrane material for alkaline systems according to any one of claims 1-3 in energy conversion and storage devices in alkaline systems.

10. The use according to claim 9, characterized in that, The energy conversion and storage device of the alkaline system includes a flow battery and hydrogen production by electrolyzing water; Preferably, the crosslinked chitosan separation layer faces the negative electrode of the device.

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