A hydrogel electrolyte membrane and alkaline water electrolysis device

Abstract

The present invention discloses a hydrogel electrolyte membrane and an alkaline water electrolysis device. The hydrogel electrolyte membrane comprises a membrane prepared by the following method: (1) mixing transition metal hydroxide powder and a highly water-absorbent high molecular polymer, adding water and heating to form a sol; (2) cooling the sol and coating it to form a film; (3) subjecting the sol to a freeze-thaw cycle until a porous structure is formed, and then immersing the film in an alkaline solution and removing it to obtain the hydrogel electrolyte membrane. The alkaline water electrolysis device has a plate-and-frame filter press structure, and its membrane is the hydrogel electrolyte membrane. The present invention has the significant advantages of high ion conduction rate, which can improve the time and space production capacity of the electrolytic cell; and the significant advantages of using non-precious metal electrode catalysts, which prolongs the life of the electrolytic cell and reduces the manufacturing cost of the electrolytic cell.

Description

Technical Field

[0001] The present invention relates to a water electrolysis membrane and an alkaline water electrolysis device, and in particular to a hydrogel electrolyte membrane and an alkaline water electrolysis device. Background Art

[0002] Existing industrialized water electrolysis hydrogen production technologies primarily include alkaline water hydrogen production and proton exchange membrane (PEM) hydrogen production. PEM hydrogen production technology utilizes a gas diffusion electrode on the cathode side, while pure water or steam is introduced as a reactant on the anode side. This structure reduces the problem of insufficient raw material supply due to bubbles. The advantage of PEM water electrolysis hydrogen production is its high time and space production capacity. However, its disadvantage is the use of precious metal catalysts, which precludes the use of cheaper transition metal catalysts. The perfluorosulfonic acid proton exchange membrane (PEM) membrane is also extremely expensive, resulting in current equipment costs nearly ten times that of alkaline water hydrogen production technology. Even if the use of precious metal catalysts is reduced in the future, or if acid-insoluble non-precious metal catalysts are discovered, the high cost of PEM will still make PEM hydrogen production technology more expensive.

[0003] Existing alkaline water hydrogen production technology uses potassium hydroxide (KOH) aqueous solution as the electrolyte and asbestos membrane or polymer fabric as the separator, with both electrodes immersed in the KOH solution. While alkaline water electrolysis allows the use of inexpensive transition metals and their compounds as catalysts, it is a mature technology with low investment and operating costs. However, it suffers from low time and space production capacity and bulky equipment. Therefore, there is a need to improve the time and space production capacity of alkaline water hydrogen production technology. Summary of the Invention

[0004] Purpose of the invention: The present invention provides a hydrogel electrolyte membrane and an alkaline water electrolysis device with simple preparation process, low cost and high time and space production capacity.

[0005] Technical solution: The hydrogel electrolyte membrane of the present invention is prepared by the following method:

[0006] (1) Mix transition metal hydroxide powder and highly absorbent polymer in a mass ratio of (0.5-4):1, then add distilled water to form a sol at 80-90 °C;

[0007] (2) cooling the sol and coating it on a substrate to form a film;

[0008] (3) The membrane is subjected to freeze-thaw cycles until a porous structure is formed, and then the membrane is immersed in an alkaline solution, and the hydrogel electrolyte membrane is obtained after being taken out.

[0009] Furthermore, the highly water-absorbent high molecular polymer described in step (1) contains hydrophilic groups, such as hydroxyl, carboxyl, amino and other groups, which can specifically be one or more of carboxymethyl cellulose, polyvinyl alcohol, polyacrylic acid and polystyrene sulfonic acid. The resulting hydrogel electrolyte membrane has a simple preparation process, low cost and is airtight, preventing hydrogen and oxygen in the electrolytic cell from penetrating and mixing with each other.

[0010] Furthermore, the transition metal hydroxide described in step (1) is a hydroxide powder or several layered hydroxide powders of transition metals Ti, V, Cr, Mo, Mn, Fe, Co, Ni, Cu, Zn, and Sn; the hydroxide powder serves as a diaphragm filler to facilitate the passage of hydroxide ions, and can also serve as an electrode catalyst or replenish the catalyst that has fallen off the electrode to prevent the performance of the electrolytic cell from being degraded due to the falling off of the catalyst, thereby increasing the service life of the electrolytic cell.

[0011] Furthermore, the number of freeze-thaw cycles in step (3) is at least 3 times. The lowest temperature during freezing is -30°C, and the temperature during melting is room temperature. The freeze-thaw cycle can form a stable porous structure inside the diaphragm, thereby increasing the porosity. The higher porosity can increase the ion conduction speed, and the pore size distribution is uniform to avoid local overheating caused by uneven current density, thereby increasing the hydroxide ion conduction rate.

[0012] The alkaline water electrolysis device described in the present invention has a plate-and-frame filter press structure, with a negative terminal plate and a positive terminal plate at the left and right ends respectively. A negative electrode, a hydrogel electrolyte membrane, a positive electrode and a waterproof breathable membrane are sequentially arranged between the positive and negative terminal plates. A cathode chamber is formed between the negative electrode and the negative terminal plates, a hydrogen / electrolyte output port is provided above the cathode chamber and an electrolyte input port is provided below the cathode chamber; an anode chamber is formed between the waterproof breathable membrane and the positive terminal plate, and an oxygen output port is provided above the anode chamber.

[0013] Furthermore, a plurality of electrolysis units consisting of a negative electrode, a hydrogel electrolyte membrane, a positive electrode and a waterproof breathable membrane are provided between the negative terminal plate and the positive terminal plate; a bipolar plate is provided between adjacent electrolysis units; a cathode chamber is formed between the negative electrode and the bipolar plate; an anode chamber is formed between the waterproof breathable membrane and the bipolar plate; the hydrogen / electrolyte output port is connected to a hydrogen / electrolyte separator and a hydrogen purifier; and the oxygen output port is connected to an oxygen demister and a purifier.

[0014] Furthermore, the positive electrode is an electrode coated with a transition metal hydroxide catalyst on the current collector, and the cathode is an electrode coated with a transition metal alloy; a transition metal hydroxide catalyst having a layered structure is grown on the current collector by a hydrothermal method or electrodeposition, and the transition metal hydroxide catalyst can reduce the overpotential, accelerate the oxygen evolution reaction, and improve efficiency; a transition metal alloy catalyst is grown on the current collector by electrodeposition or electroplating; the transition metal alloy catalyst can reduce the overpotential of the water electrolysis reaction and increase the rate of the hydrogen evolution reaction; the current collectors all use nickel mesh electrodes or nickel foam electrodes.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The membrane has low air permeability and good ion conductivity, which reduces the cost of the water electrolysis device and improves the time and space production capacity; (2) The anode of the water electrolysis device uses a gas diffusion electrode, which reduces the bubble barrier effect; (3) The life of the electrolysis device is extended, and the membrane contains layered hydroxides that can serve as or supplement the shedding catalyst on the current collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a physical picture of the hydrogel electrolyte membrane of the present invention;

[0017] Figure 2 This is a scanning electron microscope image of the hydrogel electrolyte membrane of the present invention;

[0018] Figure 3 Graph showing the electrochemical performance of the hydrogel electrolyte membrane prepared at different PVA / LDH mass ratios according to the present invention;

[0019] Figure 4 is the ionic conductivity of the hydrogel electrolyte membrane of the present invention at different temperatures;

[0020] Figure 5 The tensile strength test of the hydrogel electrolyte membrane of the present invention;

[0021] Figure 6 Schematic diagram of the electrolytic cell structure of the present invention;

[0022] Figure 7 The figure is a voltage-current density conversion curve diagram of the electrolytic cell of the present invention at different temperatures. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0024] The raw materials for preparing the hydrogel electrolyte membrane of the present invention are a composite of hydroxide powders of transition metals Ti, V, Cr, Mo, Mn, Fe, Co, Ni, Cu, Zn and Sn and a highly water-absorbing high molecular polymer.

[0025] In terms of the selection of raw material transition metal hydroxide powder, transition metal hydroxide powder has two functions: (1) as a filler to improve the ionic conductivity of the diaphragm; and (2) to replenish the loss of electrode catalyst. In principle, its metal element composition is consistent with that of the electrode catalyst. Limited to the main purpose of this invention, this application only needs to use transition metal hydroxide prepared by conventional methods. Here, we only use a common electrode catalyst, with nickel or nickel-iron alloy as the cathode and nickel-iron-cobalt hydroxide as the anode as an example.

[0026] Similarly, the highly absorbent polymer can be one or more polymers containing hydrophilic groups such as hydroxyl, carboxyl, and amino groups, such as polyvinyl alcohol, sodium polyacrylate, CMC, and sodium polystyrene sulfonate. It is mainly used to absorb water and isolate gas. Here, the common substance polyvinyl alcohol is selected as the raw material.

[0027] Example 1

[0028] (1) The nickel iron cobalt hydroxide powder (LDH) prepared above was mixed with polyvinyl alcohol (PVA) in a mass ratio of 4:1, 40 ml of deionized water was added, and the mixture was stirred at 80-90 °C to obtain a uniform gel;

[0029] (2) Cool to room temperature and evenly coat a thin film on the surface of the substrate;

[0030] (3) Place in a refrigerator for freezing polymerization and cross-linking, and then melt the ice particles at room temperature. In each freeze-thaw cycle, the freezing temperature is -30 ° C, the freezing time is 12 h, and then it is taken out and placed at room temperature for 1 h, and then frozen again. This is repeated three times, and then immersed in potassium hydroxide solution for a period of time. The film is peeled off to obtain the hydrogel electrolyte membrane. The actual photo is shown in the figure. Figure 1 As shown, electron microscope pictures are as follows Figure 2 The electrochemical performance is shown in 3.

[0031] Example 2

[0032] Iron cobalt nickel hydroxide powder (LDH) and polyvinyl alcohol (PVA) were mixed in a mass ratio of 1:1, and then the hydrogel electrolyte membrane was prepared according to the steps of Example 1. The electrochemical performance of the hydrogel electrolyte membrane was as follows: Figure 3 As shown in .

[0033] Example 3

[0034] Iron cobalt nickel hydroxide powder (LDH) and polyvinyl alcohol (PVA) were mixed in a mass ratio of 2:1, and then the hydrogel electrolyte membrane was prepared according to the steps of Example 1. The electrochemical performance of the hydrogel electrolyte membrane was as follows: Figure 3 shown.

[0035] Example 4

[0036] Iron cobalt nickel hydroxide powder (LDH) and polyvinyl alcohol (PVA) were mixed in a mass ratio of 0.5:1, and then the hydrogel electrolyte membrane was prepared according to the steps of Example 1. The electrochemical performance of the hydrogel electrolyte membrane was as follows: Figure 3 shown.

[0037] Example 5

[0038] When the mass ratio of LDH to PVA exceeds 4:1, a flexible gel film material cannot be formed.

[0039] Example 6

[0040] like Figure 3 As shown in the figure, when tested in a 6.0 M KOH solution, as the LDH powder content in the hydrogel electrolyte membrane increases, the electrolysis performance of the membrane becomes better. Among them, at a cell voltage of 2.0 V, the gel membrane prepared with a PVA / LDH mass ratio of 1:4 exhibits the best performance in electrolysis of water, with a current density of 326 mA / cm 2 .like Figure 4 As shown in FIG. 1 , the ionic conductivity of the hydrogel electrolyte membrane obtained in Example 1 at different temperatures increases with increasing temperature. At 70°C, the conductivity σ is around 300 mS / cm. When the temperature is increased to 90°C, the conductivity σ significantly increases to 400 mS / cm, and the electronic conductivity is significantly improved. Figure 5 As shown, the tensile stress of the hydrogel electrolyte membrane obtained in Example 1 is about 0.45 MPa and its tensile elongation at break is about 800%.

[0041] It can be seen that the hydrogel electrolyte membrane prepared according to the method of Example 1 has good flexibility, electrical conductivity and mechanical strength.

[0042] Example 7

[0043] like Figure 6As shown, an alkaline water electrolysis device using the hydrogel electrolyte membrane of Example 3 has a negative terminal plate 1 at the left end and a positive terminal plate 7 at the right end. Between the left and right positive and negative terminal plates are multiple electrolysis units composed of a negative electrode 2, a hydrogel electrolyte membrane 3, a positive electrode 4, and a waterproof breathable membrane 5 in sequence, wherein a bipolar plate 6 is located between the waterproof breathable membrane 5 and the negative electrode 2 of the two electrolysis units; multiple repeated electrolysis units between the left and right positive and negative terminal plates and the end plates are assembled into a filter press structure, between the negative electrode 2 and the negative terminal plate 1, and between the negative electrode 2 and An electrolyte input port 8 is provided between the bipolar plates 6, and a hydrogen output port 9 is provided above the bipolar plates 6, which is connected to a hydrogen / electrolyte separator; an oxygen output port 10 is provided above the waterproof breathable membrane 5 and the positive end plate 7, and between the waterproof breathable membrane 5 and the bipolar plate 6, which is connected to an oxygen demister; a sealing ring is used to seal the positive and negative electrodes, the hydrogel electrolyte membrane 3, and the waterproof breathable membrane 5, and the sealed electrolytic cell is formed by fastening with bolts, and an electrode connection terminal is provided on the end plate of the electrolytic cell.

[0044] When the positive electrode uses a nickel mesh loaded with nickel-iron-cobalt layered hydroxide and the negative electrode uses a nickel mesh loaded with nickel-iron alloy catalyst, and the electrolyte inlet 8 is fed with an alkaline solution of potassium hydroxide, the power supply is connected according to the polarity and the voltage is turned on until it exceeds 1.5 nV (n = the number of bipolar plates used + 1), hydrogen and oxygen can be generated. Figure 7 As shown in Figure 2, when the single cell voltage is 2.0 V, the current density of the electrode is 4000 A / m at 30°C. 2 , close to 10000 A / m at 90°C 2 Compared with the current density of ordinary alkaline water electrolysis cells, which is less than 4000 A / m 2 In comparison, the performance is extremely superior.

Claims

1. A hydrogel electrolyte membrane, characterized in that Including the preparation obtained by the following method: (1) Mix transition metal hydroxide powder and highly absorbent polymer in a mass ratio of (0.5-4):1, then add water to form a sol at 80-90 °C; (2) cooling the sol and coating it on a substrate to form a film; (3) subjecting the membrane to a freeze-thaw cycle until a porous structure is formed, then immersing the membrane in an alkaline solution, and taking it out to obtain the hydrogel electrolyte membrane; The highly water-absorbing polymer described in step (1) contains a hydrophilic group; the highly water-absorbing polymer is one or more of carboxymethyl cellulose, polyvinyl alcohol, polyacrylic acid and polystyrene sulfonic acid; The transition metal hydroxide described in step (1) is one or more hydroxide powders of transition metals Ti, V, Cr, Mo, Mn, Fe, Co, Ni, Cu, Zn, and Sn.

2. The hydrogel electrolyte membrane according to claim 1, wherein The number of freeze-thaw cycles described in step (3) is at least 3 times.

3. The hydrogel electrolyte membrane according to claim 1, wherein The freezing temperature of the freeze-thaw cycle described in step (3) is as low as -30°C.

4. An alkaline water electrolysis device having a plate-and-frame filter press structure, wherein the left and right ends are respectively a negative terminal plate (1) and a positive terminal plate (7), characterized in that: A negative electrode (2), the hydrogel electrolyte membrane (3) according to claim 1, a positive electrode (4) and a waterproof breathable membrane (5) are sequentially arranged between the positive and negative terminal plates; a cathode chamber is formed between the negative electrode (2) and the negative terminal plate (1); a hydrogen / electrolyte output port (9) is provided above the cathode chamber and an electrolyte input port (8) is provided below the cathode chamber; an anode chamber is formed between the waterproof breathable membrane (5) and the positive terminal plate (7); an oxygen output port (10) is provided above the anode chamber.

5. The alkaline water electrolysis device according to claim 4, characterized in that A plurality of electrolytic units consisting of a negative electrode (2), a hydrogel electrolyte membrane (3), a positive electrode (4) and a waterproof breathable membrane (5) are provided between the negative terminal plate (1) and the positive terminal plate (7); a bipolar plate (6) is provided between adjacent electrolytic units; a cathode chamber is formed between the negative electrode (2) and the bipolar plate (6); and an anode chamber is formed between the waterproof breathable membrane (5) and the bipolar plate (6).

6. The alkaline water electrolysis device according to claim 4, characterized in that The hydrogen / electrolyte output port (9) is connected to a hydrogen / electrolyte separator and a hydrogen purifier; the oxygen output port (10) is connected to an oxygen demister and a purifier.

7. The alkaline water electrolysis device according to claim 4, characterized in that The positive electrode is an electrode covered with a transition metal hydroxide catalyst, and the negative electrode is an electrode covered with a transition metal alloy.

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