A decoupled water electrolysis hydrogen production system and method

Abstract

The application relates to a decoupled water electrolysis hydrogen production system and method, and belongs to the technical field of hydrogen energy. The system comprises an electrolysis module and an electrolyte separation and circulation module, a transition metal series compound loaded on nickel foam is used as a redox medium, and an oxidation reaction of an organic small molecule is used instead of an oxygen evolution reaction. The system and the method realize the space-time separation of water electrolysis by decoupling an electrolysis tank, hydrogen is obtained at the same time, and a value-added product is obtained by oxidizing an organic small molecule. The traditional water electrolysis hydrogen production step and the oxygen production step are completely decoupled, and a value-added product is obtained, so that the hydrogen production efficiency can be obviously improved, the energy consumption can be reduced, and the economic benefit can be improved.

Description

Technical Field

[0001] This invention relates to the field of hydrogen energy technology, specifically to a decoupled water electrolysis hydrogen production system and method. Background Technology

[0002] Hydrogen energy, as a clean and carbon-free secondary energy source and a high-quality energy carrier, boasts advantages such as being green, environmentally friendly, and abundant in reserves, and is considered the most competitive alternative to fossil fuels. Currently, most hydrogen comes from the reforming process of fossil fuels, inevitably producing large amounts of carbon dioxide. Therefore, it is necessary to find an efficient and environmentally friendly method for hydrogen production. Electrolyzing water using renewable energy sources such as solar and wind power can convert unusable electrical energy into hydrogen, which is an essential path to achieving a green hydrogen economy and an important direction for the future development of the hydrogen economy.

[0003] In traditional water electrolysis systems, the hydrogen evolution reaction (HER) is tightly coupled with the oxygen evolution reaction (OER) in both time and space. Due to thermodynamic limitations, this process requires high instantaneous energy, making it difficult to match with the volatility and intermittency of renewable energy sources. The slow four-electron transfer kinetics of OER also affect the hydrogen production efficiency of HER. Simultaneously, the cross-mixing of hydrogen and oxygen gases is unavoidable, potentially leading to the formation of reactive oxygen species and explosive H2 / O2 mixtures, posing safety hazards and reducing the lifespan of the electrolyzer. Furthermore, traditional water electrolysis requires expensive ion exchange membranes, which have limited lifespans and are prone to degradation in practical use, further increasing the cost of water electrolysis. To overcome these problems, researchers have proposed a decoupled water electrolysis strategy by introducing redox media to pair with either the HER or OER reaction, thereby achieving the separate production of hydrogen and oxygen at different times or locations, avoiding cross-mixing of hydrogen and oxygen gases.

[0004] Currently, most decoupled water electrolysis strategies employ a two-step electrochemical reaction method. The first step pairs the HER (hydrogen ion exchanger) reaction with the oxidation reaction of the medium, and the second step pairs the OER (oxygen ion exchanger reaction) reaction as the anode with the reduction reaction of the medium. The O2 obtained in this process can be readily obtained from the surrounding air, has low added value, and is often discarded during hydrogen production, resulting in energy waste and economic losses in long-term operation and large-scale applications. Therefore, to improve the energy utilization efficiency and economic benefits of decoupled water electrolysis for hydrogen production, there is an urgent need in this field to develop a novel decoupled water electrolysis system and method to overcome the current technical shortcomings. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a decoupled water electrolysis hydrogen production system and method. By replacing the OER reaction in the second step of decoupled water electrolysis with a thermodynamically more favorable organic small molecule oxidation reaction, a more economically advantageous decoupled system is constructed.

[0006] The technical solution of the present invention is as follows: This invention provides a decoupled water electrolysis hydrogen production system, including an electrolysis module and an electrolyte separation and circulation module; The electrolysis module includes an electrolytic cell, a cathode electrode, a redox medium auxiliary electrode, and a power supply. An electrolyte inlet and an electrolyte outlet are respectively provided on both sides below the electrolytic cell. The cathode electrode and the redox medium auxiliary electrode are disposed inside the electrolytic cell and are respectively connected to the power supply through wires. A cathode electrode gas outlet is provided on the side of the electrolytic cell near the cathode electrode. The electrolyte separation and circulation module includes a peristaltic pump I, a peristaltic pump II, a primary electrolyte separation mechanism, a secondary electrolyte separation mechanism, an electrolyte storage tank I, an electrolyte storage tank II, an electrolyte storage tank III, and a product storage tank. The electrolyte storage tanks I, II, and III, and the product storage tank, respectively store alkaline solution, washing solution, aqueous solution of small organic molecules, and oxidation products of small organic molecules. The electrolyte outlet of each electrolytic cell is connected to peristaltic pump II via a pipe. Peristaltic pump II is connected to the primary electrolyte separation tank via a pipe. The primary electrolyte separation mechanism is connected to electrolyte storage tank one and electrolyte storage tank two. The primary electrolyte separation mechanism has two outlets, which are respectively connected to the inlet of electrolyte storage tank three and the inlet of the secondary electrolyte separation mechanism through pipes. The secondary electrolyte separation mechanism has two outlets, which are respectively connected to the inlet of electrolyte storage tank three and the inlet of the product storage tank through pipes. Electrolyte storage tank one, electrolyte storage tank two, and electrolyte storage tank three are respectively connected to peristaltic pump one through pipes. Peristaltic pump one is connected to the electrolyte inlet of the electrolytic cell through a pipe.

[0007] According to a preferred embodiment of the present invention, the redox medium auxiliary electrode is nickel foam loaded with transition metal series compounds, with the transition metal series compounds loaded on the nickel foam serving as the redox medium; the transition metal series compounds are transition metals, transition metal oxides, transition metal hydroxides, transition metal / carbon complexes, or transition metal oxide / nitrogen / carbon complexes; the transition metal is one or two of nickel (Ni), cobalt (Co), iron (Fe), copper (Cu), or manganese (Mn); Preferably, the transition metal series compound is a bimetallic layered double hydroxide; More preferably, the transition metal compound is Ni. x M 1-x (OH)2, where 0 < x < 1, and M is Co, Fe, Cu or Mn; Most preferably, the transition metal series compound is Ni. 0.9 Co 0.1 (OH)2.

[0008] In this invention, the redox potential of the bimetallic layered double hydroxide in alkaline solution lies between the initiation potentials of the hydrogen evolution reaction and the conventional oxygen evolution reaction.

[0009] According to a preferred embodiment of the present invention, the cathode electrode is a Pt-Ti electrode; in the present invention, the Pt-Ti electrode serves as an effective catalyst for the hydrogen evolution reaction at the cathode electrode.

[0010] In this invention, small organic molecules act as reducing agents to reduce redox media and simultaneously generate small organic molecule oxidation products.

[0011] According to a preferred embodiment of the present invention, a fine-pore electrolyte separation membrane is provided in the primary electrolyte separation mechanism; Preferably, the fine-pore electrolyte separation membrane is a molecular sieve membrane; the pore size of the molecular sieve membrane is 0.5 nm.

[0012] In this invention, the function of the fine-pore electrolyte separation membrane is to separate water from the electrolyte. The water flows into the electrolyte storage tank three, while the remaining mixed solution of small organic molecules and their oxidation products flows into the secondary electrolyte separation mechanism.

[0013] According to a preferred embodiment of the present invention, a separation membrane is provided within the secondary electrolyte separation mechanism; Preferably, the separation membrane is a polybenzimidazole membrane (PBI membrane), and the pore size of the PBI membrane is less than 1 nm.

[0014] In this invention, the separation membrane separates the small organic molecules and their oxidation products in the electrolyte. The small organic molecules flow into the electrolyte storage tank, while the oxidation products flow into the product storage tank as byproducts.

[0015] The present invention also provides a decoupled water electrolysis method for producing hydrogen using the above-described system.

[0016] A decoupled water electrolysis method for hydrogen production includes the following steps: (1) The first step reaction in the electrolysis module generates hydrogen gas, and the second step reaction generates small organic molecule oxidation products: In the first step of the reaction, the alkaline solution is pumped from the electrolyte storage tank into the electrolytic cell. Under constant current conditions, the cathode electrode undergoes a hydrogen evolution reaction to generate hydrogen gas. The hydrogen gas is discharged from the cathode electrode gas outlet of the electrolytic cell and collected. At the same time, the redox medium auxiliary electrode undergoes a medium oxidation reaction. After the first step of the reaction, the solution in the electrolytic cell is discharged through the electrolyte outlet into the electrolyte storage tank of the electrolyte separation and circulation module for recycling. In the second step of the reaction, an aqueous solution of small organic molecules is pumped into the electrolytic cell from the electrolyte storage tank. Under conditions where no current is applied, the small organic molecules undergo an oxidation reaction to generate small organic molecule oxidation products. At the same time, the redox medium auxiliary electrode undergoes a reduction reaction, completing the recycling and regeneration of the medium. After the second step of the reaction, the solution in the electrolytic cell is discharged into the electrolyte separation and circulation module through the electrolyte outlet for separation. The first step reaction and the second step reaction are carried out in sequence. After the reaction is completed, the washing liquid is pumped from the electrolyte storage tank 2 into the electrolyte inlet to rinse the electrolytic cell and the electrodes. After that, the washing liquid is discharged through the electrolyte outlet into the electrolyte storage tank 2 of the electrolyte separation and circulation module for recycling. (2) Separation of the solution after the second step reaction in the electrolyte separation circulation module: First, after the second reaction, the solution is pumped into the primary electrolyte separation mechanism to separate the water, which then enters the third electrolyte storage tank for recycling. The remaining mixed solution of small organic molecules and their oxidation products flows into the secondary electrolyte separation mechanism to separate the small organic molecules from their oxidation products. The small organic molecules flow into the third electrolyte storage tank for recycling, while the oxidation products flow into the product storage tank.

[0017] According to a preferred embodiment of the present invention, in step (1), the constant current is 10 ~ 50 mA·cm. -2 .

[0018] According to a preferred embodiment of the present invention, in step (1), the temperature of the first reaction step is room temperature to 80°C.

[0019] According to a preferred embodiment of the present invention, in step (1), after the active components on the redox medium auxiliary electrode have reacted completely in the first step reaction, the total voltage of the system suddenly rises, and the reaction ends at this time.

[0020] According to a preferred embodiment of the present invention, in step (1), the temperature of the second reaction step is room temperature to 80°C.

[0021] According to a preferred embodiment of the present invention, in step (1), the alkaline solution is an aqueous solution of potassium hydroxide with a concentration of 0.1 M to 5 M.

[0022] According to a preferred embodiment of the present invention, in step (1), the concentration of the aqueous solution of the small organic molecule is 0.01 M to 1 M, and the small organic molecule in the aqueous solution of the small organic molecule is a reducing small organic molecule; preferably, the reducing small organic molecule is glycerol, methanol, ethanol or 5-hydroxymethylfurfural.

[0023] According to a preferred embodiment of the present invention, in step (1), the washing liquid is water.

[0024] According to a preferred embodiment of the present invention, in step (1), when the concentration of the alkaline solution in the electrolyte storage tank is lower than 0.1 M, the alkaline solution in the electrolyte storage tank is replaced.

[0025] According to a preferred embodiment of the present invention, in step (1), when the concentration of the organic small molecule aqueous solution in the electrolyte storage tank is lower than 0.01 M, the organic small molecule aqueous solution in the electrolyte storage tank is replaced.

[0026] According to a preferred embodiment of the present invention, in step (1), after the washing solution in the second electrolyte storage tank rinses the electrolytic cell and the electrode 10 to 20 times, the washing solution in the second electrolyte storage tank is replaced.

[0027] The technical features and beneficial effects of this invention are as follows: 1. The method of the present invention decouples the reaction time and space of traditional water electrolysis, reduces the voltage of water electrolysis for hydrogen production, avoids the generation of explosive gases, and significantly reduces the energy consumption and safety risks of water electrolysis for hydrogen production.

[0028] 2. The method of the present invention replaces the oxygen evolution reaction with an organic small molecule oxidation reaction, and obtains a high-value-added product in the second step, thereby improving the economic benefits of decoupled water electrolysis for hydrogen production.

[0029] 3. In the method of the present invention, the oxidation of small organic molecules and the reduction and regeneration of the redox medium are spontaneous steps driven by chemical reactions, which do not require additional voltage input. This makes the system better compatible with fluctuating and intermittent renewable energy sources and achieve rational energy allocation.

[0030] 4. The method of the present invention uses transition metal series compounds as solid redox media, avoiding the use of precious metal catalysts and reducing costs.

[0031] 5. The system of the present invention achieves the separation of by-products and reactants through the primary electrolyte separation mechanism and the secondary electrolyte separation mechanism of the electrolyte separation circulation module. The electrolysis module and the electrolyte separation circulation module are connected by pipelines, realizing the continuous steady-state operation of decoupled hydrogen production by water electrolysis and the oxidation reaction of small organic molecules.

[0032] 6. In the system of this invention, a transition metal series compound loaded on nickel foam is used as the redox medium. The transition metal series compound selected is a cobalt-doped bimetallic layered double hydroxide Ni. 0.9 Co 0.1 Compared with undoped Ni(OH)2, (OH)2 exhibits enhanced electrochemical activity, improved charge storage capacity, significantly improved stability, and accelerated reaction kinetics. Attached Figure Description

[0033] Figure 1This is a schematic diagram of the process flow of the decoupled water electrolysis hydrogen production system according to Embodiment 1 of the present invention; wherein, 1, electrolyte inlet; 2, cathode electrode gas outlet; 3, power supply; 4, cathode electrode; 5, redox medium auxiliary electrode; 6, electrolyte outlet; 7, peristaltic pump one; 8, throttle valve one; 9, electrolyte storage tank one; 10, throttle valve two; 11, three-way valve one; 12, electrolyte storage tank two; 13, throttle valve three; 14, electrolyte storage tank three; 15, throttle valve four; 16, three-way valve two; 17, peristaltic pump two; 18, primary electrolyte separation mechanism; 19, secondary electrolyte separation mechanism; 20, product storage tank; 21, electrolytic cell.

[0034] Figure 2 Ni is the experimental example of this invention. x Co 1-x Cyclic voltammetry curves of (OH)2 / NF as a redox medium-assisted electrode, and linear voltammetry curves of Pt-Ti electrode and RuO2 / IrO2-Ti electrode; where the black curve represents Ni x Co 1-x (OH)2 / NF, the blue curve represents the Pt-Ti electrode (HER), and the red curve represents the RuO2 / IrO2-Ti electrode (OER). Detailed Implementation

[0035] The present invention will be further described below with reference to embodiments and accompanying drawings, but is not limited thereto. The described embodiments are some embodiments of the present invention. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description, and should not be construed as limiting this invention.

[0037] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] Example 1 like Figure 1 As shown, a decoupled water electrolysis hydrogen production system includes an electrolysis module and an electrolyte separation and circulation module; The electrolysis module includes an electrolytic cell 21, a cathode electrode 4, a redox medium auxiliary electrode 5, and a power supply 3. An electrolyte inlet 1 and an electrolyte outlet 6 are respectively provided on both sides below the electrolytic cell 21. The cathode electrode 4 and the redox medium auxiliary electrode 5 are disposed inside the electrolytic cell 21 and are respectively connected to the power supply 3 through wires. A cathode electrode gas outlet 2 is provided on the side of the electrolytic cell 21 near the cathode electrode 4. The electrolyte separation and circulation module includes a peristaltic pump 17, a peristaltic pump 27, a primary electrolyte separation mechanism 18, a secondary electrolyte separation mechanism 19, an electrolyte storage tank 19, an electrolyte storage tank 22, an electrolyte storage tank 34, and a product storage tank 20. The electrolyte storage tanks 19, 22, 34, and 20 respectively store alkaline solution, washing solution, glycerol aqueous solution, and formic acid. The electrolyte outlet 6 of the electrolyte tank 21 is connected to the peristaltic pump 27 via a pipe. The peristaltic pump 27 is connected to the primary electrolyte separation mechanism 18 via pipes. The primary electrolyte separation mechanism 18 has two outlets, which are connected to the inlet of the electrolyte storage tank 34 and the secondary electrolyte separation mechanism 19 via pipes. The outlet of the secondary electrolyte separation mechanism 19 is connected to the inlet of the product storage tank 20 via a pipe. Three... Three-way valve 16 is configured such that its inlet is connected to peristaltic pump 17 via a pipe, one outlet is connected to primary electrolyte separation mechanism 18 via a pipe, and the other outlet is connected to three-way valve 11 via a pipe. The two outlets of three-way valve 11 are respectively connected to electrolyte storage tank 9 and electrolyte storage tank 12 via pipes. A three-way valve is installed on the pipe between three-way valve 11 and electrolyte storage tank 9. Throttling valve 20; the electrolyte storage tank 19, electrolyte storage tank 22, and electrolyte storage tank 314 are respectively connected to peristaltic pump 7 through pipes; throttling valve 18, throttling valve 313, and throttling valve 415 are respectively installed on the pipes between electrolyte storage tank 19 and peristaltic pump 7, between electrolyte storage tank 22 and peristaltic pump 7, and between electrolyte storage tank 314 and peristaltic pump 7; the peristaltic pump 7 is connected to the electrolyte inlet 1 of the electrolytic cell 21 through a pipe.

[0039] In this embodiment, the redox medium auxiliary electrode 5 is a nickel foam loaded with a bimetallic layered double hydroxide, and the bimetallic layered double hydroxide is Ni. 0.9 Co 0.1 (OH)2.

[0040] The method for preparing the redox dielectric auxiliary electrode in this embodiment includes: (1) Pretreatment of nickel foam: After cutting the nickel foam (NF) substrate to a size of 2 cm × 2.5 cm, the following pretreatments were performed sequentially: First, the substrate was ultrasonically treated in 3 M hydrochloric acid aqueous solution for 15 minutes to remove the surface oxide layer; then, it was ultrasonically cleaned in acetone and anhydrous ethanol for 15 minutes each to remove organic impurities; after each cleaning step, the substrate was thoroughly rinsed with plenty of deionized water to remove residual solvent and acid. Finally, the sample was transferred to a 70°C vacuum drying oven and dried for 12 hours to obtain a clean NF substrate.

[0041] (2) Preparation of redox dielectric auxiliary electrode Ni by one-step electrodeposition method 0.9 Co 0.1 (OH)2 / NF: Add 1.45 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), 0.16 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), and 0.03 g of sodium nitrite (NaNO2) to 50 mL of a 40% (v / v) ethanol aqueous solution, stir until completely dissolved, and adjust the pH of the solution to 4 with dilute nitric acid. Immerse the pretreated NF in the above deposition solution and soak under vacuum for 30 min to ensure that the solution fully wets the porous structure of the NF. Electrodeposition is performed in a three-electrode system, using one NF as the working electrode and the other two NFs as counter electrodes, at 80 °C, with an application of 40 mA·cm⁻¹. -2 The cathode current was set at 1800 s, and deposition was carried out. After deposition, the electrode was thoroughly rinsed with deionized water, and then aged in a 1 M KOH aqueous solution at 90 °C for 30 min to obtain the redox-assisted electrode Ni. 0.9 Co 0.1 (OH)2 / NF.

[0042] The cathode electrode 4 is a Pt-Ti electrode; the alkaline solution is a 1M KOH aqueous solution; the organic small molecule aqueous solution is a glycerol aqueous solution with a concentration of 0.5 M; the primary electrolyte separation mechanism 18 is equipped with a fine-pore electrolyte separation membrane, which is a molecular sieve membrane with a pore size of 0.5 nm. The function of the fine-pore electrolyte separation membrane is to separate the water in the electrolyte. The water flows into the electrolyte storage tank three, and the remaining formic acid and glycerol mixed solution flows into the secondary electrolyte separation mechanism. The secondary electrolyte separation mechanism 19 is equipped with a separation membrane, which is a PBI membrane with a pore size of 0.8 nm. The function of the separation membrane is to separate the glycerol and formic acid in the electrolyte. The glycerol flows into the electrolyte storage tank three, and the formic acid flows into the product storage tank 20 as a by-product.

[0043] A decoupled water electrolysis method for hydrogen production includes the following steps: (1) The first step reaction to produce hydrogen gas and the second step reaction to produce formic acid are carried out in the electrolysis module: In the first step of the reaction, the alkaline solution is pumped from the electrolyte storage tank 9 into the electrolytic cell 21 via the peristaltic pump 7, at a pressure of 30 mA·cm⁻¹. -2 Under constant current and room temperature conditions, hydrogen evolution reaction occurs at cathode electrode 4 to produce hydrogen gas, i.e., H2O + e-. - → 1 / 2 H2 + OH - Hydrogen gas is discharged and collected from the cathode electrode gas outlet 2 of the electrolytic cell 21. Simultaneously, the oxidation reaction of the medium occurs at the redox medium auxiliary electrode 5, i.e., Ni... 0.9 Co 0.1 (OH)2+ OH - → Ni 0.9 Co 0.1 OOH + H2O + e - The reaction ends when the total voltage suddenly rises; after the first step reaction, the solution in the electrolytic cell 21 is pumped from the electrolyte outlet 6 through the peristaltic pump 17 into the electrolyte storage tank 9 of the electrolyte separation and circulation module for recycling. In the second step of the reaction, an aqueous glycerol solution is pumped from electrolyte storage tank 14 into electrolytic cell 21. Under conditions of no applied current and room temperature, glycerol undergoes an oxidation reaction to produce formic acid, i.e., C3H8O3 + 11OH-. - → 3HCOO - + 8H2O + 8e - Simultaneously, the redox medium auxiliary electrode 5 undergoes a reduction reaction of the medium, i.e., Ni 0.9 Co 0.1 OOH + H2O + e - →Ni 0.9 Co 0.1 (OH)2+ OH - The medium is regenerated and the reaction time is 15 minutes. After the second reaction, the solution in the electrolytic cell 21 is discharged into the electrolyte separation and circulation module through the electrolyte outlet 6 for separation. The first step reaction and the second step reaction are carried out in a cycle. After the first step reaction and the second step reaction are completed, the washing liquid in the electrolyte storage tank 22 is pumped into the electrolyte inlet 1. The washing liquid used is water. After rinsing the electrolytic cell 21 and the electrodes, the washing liquid is discharged through the electrolyte outlet 6 into the electrolyte storage tank 22 of the electrolyte separation and circulation module for recycling.

[0044] (2) Separation of the solution after the second step reaction in the electrolyte separation circulation module: First, after the second reaction, the solution is pumped into the primary electrolyte separation unit 18 to separate the water, which then enters the electrolyte storage tank 14 for recycling. The remaining formic acid and glycerol mixture flows into the secondary electrolyte separation unit 19 to separate the glycerol from the formic acid. The glycerol flows into the electrolyte storage tank 14 for recycling, while the formic acid flows into the product storage tank 20.

[0045] In this example, when the concentration of the alkaline solution in electrolyte storage tank 1 is lower than 0.1 M, the alkaline solution in electrolyte storage tank 1 is replaced; when the concentration of the organic small molecule aqueous solution in electrolyte storage tank 3 is lower than 0.01 M, the organic small molecule aqueous solution in electrolyte storage tank 3 is replaced; after rinsing the electrolytic cell and electrodes 15 times with the washing solution in electrolyte storage tank 2, the washing solution in electrolyte storage tank 2 is replaced.

[0046] Comparative Example 1 As described in Example 1, the difference is: The redox medium auxiliary electrode is nickel foam loaded with metal hydroxide, and the metal hydroxide is undoped Ni(OH)2.

[0047] In the preparation method of the redox medium-assisted electrode, step (2) of synthesizing the redox medium-assisted electrode is as follows: Ni(OH)₂ / NF was prepared using a one-step electrodeposition method. 1.45 g of nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) and 0.03 g of sodium nitrite (NaNO₂) were added to 50 mL of a 40% (v / v) aqueous ethanol solution and stirred until completely dissolved. The pH of the solution was adjusted to 4 with dilute nitric acid. The pretreated NF was immersed in the above deposition solution and soaked under vacuum for 30 min to ensure that the solution fully wetted the porous structure of the NF. Electrodeposition was performed in a three-electrode system, using one NF electrode as the working electrode and the other two NF electrodes as counter electrodes, at 80 °C with an application rate of 40 mA·cm⁻¹. -2 The cathode current was set, and deposition was carried out for 1800 s. After deposition, the electrode was thoroughly cleaned with deionized water, and then aged in 1 M KOH aqueous solution at 90 °C for 30 min to obtain the redox-assisted electrode Ni(OH)2 / NF.

[0048] Other conditions and steps are the same as in Example 1.

[0049] Test case (1) Using a three-electrode system in 1M KOH aqueous solution, Pt-Ti electrode, RuO2 / IrO2-Ti electrode and Ni 0.9 Co 0.1 Electrochemical tests were performed on the (OH)₂ / NF redox medium-assisted electrode, with the electrode under test as the working electrode, a platinum sheet electrode as the counter electrode, and Hg / HgO as the reference electrode. Ni was measured. 0.9 Co0.1 Cyclic voltammetry curves of the (OH)₂ / NF redox medium-assisted electrode, and linear voltammetry curves of the Pt-Ti electrode and the RuO₂ / IrO₂-Ti electrode, as shown below. Figure 2 As shown.

[0050] Depend on Figure 2 It can be seen that Ni 0.9 Co 0.1 The redox peak of (OH)2 / NF lies between the onset potentials of the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In this invention, the oxidation reaction of small organic molecules replaces the oxygen evolution reaction in the second step of decoupling water electrolysis, thereby enabling Ni... 0.9 Co 0.1 The redox peak of (OH)2 / NF lies between the initiation potentials of the hydrogen evolution reaction and the oxidation reaction of small organic molecules, proving that Ni 0.9 Co 0.1 (OH)2 / NF can act as a redox medium to decouple the water electrolysis reaction.

[0051] (2) Under the same test conditions (1 M KOH aqueous solution, three-electrode system, with the electrode under test as the working electrode, the platinum sheet electrode as the counter electrode, and Hg / HgO as the reference electrode), the Ni from Example 1 was subjected to testing. 0.9 Co 0.1 The electrochemical performance of the (OH)2 / NF electrode and the Ni(OH)2 / NF electrode of Comparative Example 1 was tested, and the electrolysis voltage of water was compared with that of traditional noble metal catalysts. The results are shown in Table 1.

[0052] Table 1 Electrochemical performance test results

[0053] From Table 1, we can conclude that: Ni in Example 1 0.9 Co 0.1 The redox peak potential difference of the (OH)2 / NF electrode (0.12 V) is much smaller than that of the Ni(OH)2 / NF electrode in Comparative Example 1 (0.25 V), indicating that Co 2+ The doping alters the electronic structure of Ni(OH)2, improving the material's conductivity and reversibility, making its redox reactions easier to carry out.

[0054] Redox capacity of Example 1 (98.5 mAh·g) -1 Comparison Example 1 (72.3 mAh·g) -1 The efficiency was increased by approximately 36%, which means that, with the same electrode area, Example 1 can oxidize more media, thereby generating more hydrogen in the first step reaction or oxidizing more glycerol to formic acid in the second step reaction.

[0055] After 500 cycles, the capacity retention rate of Example 1 was as high as 94.2%, while that of Comparative Example 1 was only 81.5%. This proves that the incorporation of cobalt effectively inhibits the structural degradation of the electrode material under alkaline conditions, which is crucial for the long-term stable operation of the system.

[0056] In the second step of the glycerol oxidation reaction, the electrode of Example 1 could be reduced (i.e., the active material was regenerated) within 15 minutes, while Comparative Example 1 required 28 minutes. This indicates that the bimetallic hydroxide also has better catalytic activity or faster electron transfer capability for the glycerol oxidation reaction.

[0057] In summary, this invention selects cobalt-doped bimetallic layered double hydroxide Ni 0.9 Co 0.1 As a redox medium auxiliary electrode, (OH)2 / NF significantly improves the kinetics of redox reactions, charge storage capacity, and long-term operational stability compared to undoped Ni(OH)2 / NF, thereby optimizing the hydrogen production efficiency and operational reliability of the entire decoupled water electrolysis system.

[0058] The above content is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A decoupled water electrolysis hydrogen production system, characterized in that, Includes an electrolysis module and an electrolyte separation and circulation module; The electrolysis module includes an electrolytic cell, a cathode electrode, a redox medium auxiliary electrode, and a power supply. An electrolyte inlet and an electrolyte outlet are respectively provided on both sides below the electrolytic cell. The cathode electrode and the redox medium auxiliary electrode are disposed inside the electrolytic cell and are respectively connected to the power supply through wires. A cathode electrode gas outlet is provided on the side of the electrolytic cell near the cathode electrode. The electrolyte separation and circulation module includes a peristaltic pump I, a peristaltic pump II, a primary electrolyte separation mechanism, a secondary electrolyte separation mechanism, an electrolyte storage tank I, an electrolyte storage tank II, an electrolyte storage tank III, and a product storage tank. The electrolyte storage tanks I, II, and III, and the product storage tank, respectively store alkaline solution, washing solution, aqueous solution of small organic molecules, and oxidation products of small organic molecules. The electrolyte outlet of each electrolytic cell is connected to peristaltic pump II via a pipe. Peristaltic pump II is connected to the primary electrolyte separation tank via a pipe. The primary electrolyte separation mechanism is connected to electrolyte storage tank one and electrolyte storage tank two. The primary electrolyte separation mechanism has two outlets, which are respectively connected to the inlet of electrolyte storage tank three and the inlet of the secondary electrolyte separation mechanism through pipes. The secondary electrolyte separation mechanism has two outlets, which are respectively connected to the inlet of electrolyte storage tank three and the inlet of the product storage tank through pipes. Electrolyte storage tank one, electrolyte storage tank two, and electrolyte storage tank three are respectively connected to peristaltic pump one through pipes. Peristaltic pump one is connected to the electrolyte inlet of the electrolytic cell through a pipe.

2. The decoupled water electrolysis hydrogen production system according to claim 1, characterized in that, The redox medium auxiliary electrode is nickel foam loaded with transition metal series compounds, using the transition metal series compounds loaded on the nickel foam as the redox medium; the transition metal series compounds are transition metals, transition metal oxides, transition metal hydroxides, transition metal / carbon complexes, or transition metal oxide / nitrogen / carbon complexes; the transition metal is one or two of nickel (Ni), cobalt (Co), iron (Fe), copper (Cu), or manganese (Mn); preferably, the transition metal series compound is a bimetallic layered double hydroxide; more preferably, the transition metal series compound is Ni. x M 1-x (OH)₂, wherein 0 < x < 1, and M is Co, Fe, Cu, or Mn; most preferably, the transition metal series compound is Ni. 0.9 Co 0.1 (OH)2.

3. The decoupled water electrolysis hydrogen production system according to claim 1, characterized in that, The cathode electrode is a Pt-Ti electrode.

4. The decoupled water electrolysis hydrogen production system according to claim 1, characterized in that, The primary electrolyte separation mechanism is equipped with a fine-pore electrolyte separation membrane; the fine-pore electrolyte separation membrane is a molecular sieve membrane; the pore size of the molecular sieve membrane is 0.5 nm.

5. The decoupled water electrolysis hydrogen production system according to claim 1, characterized in that, The secondary electrolyte separation mechanism is equipped with a separation membrane; the separation membrane is a polybenzimidazole membrane with a pore size of less than 1 nm.

6. A decoupled water electrolysis hydrogen production method, employing the decoupled water electrolysis hydrogen production system as described in claim 1, characterized in that, Including the following steps: (1) The first step reaction in the electrolysis module generates hydrogen gas, and the second step reaction generates small organic molecule oxidation products: In the first step of the reaction, the alkaline solution is pumped from the electrolyte storage tank into the electrolytic cell. Under constant current conditions, the cathode electrode undergoes a hydrogen evolution reaction to generate hydrogen gas. The hydrogen gas is discharged from the cathode electrode gas outlet of the electrolytic cell and collected. At the same time, the redox medium auxiliary electrode undergoes a medium oxidation reaction. After the first step of the reaction, the solution in the electrolytic cell is discharged through the electrolyte outlet into the electrolyte storage tank of the electrolyte separation and circulation module for recycling. In the second step of the reaction, an aqueous solution of small organic molecules is pumped into the electrolytic cell from the electrolyte storage tank. Under conditions where no current is applied, the small organic molecules undergo an oxidation reaction to generate small organic molecule oxidation products. At the same time, the redox medium auxiliary electrode undergoes a reduction reaction, completing the recycling and regeneration of the medium. After the second step of the reaction, the solution in the electrolytic cell is discharged into the electrolyte separation and circulation module through the electrolyte outlet for separation. The first step reaction and the second step reaction are carried out in sequence. After the reaction is completed, the washing liquid is pumped from the electrolyte storage tank 2 into the electrolyte inlet to rinse the electrolytic cell and the electrodes. After that, the washing liquid is discharged through the electrolyte outlet into the electrolyte storage tank 2 of the electrolyte separation and circulation module for recycling. (2) Separation of the solution after the second step of the reaction in the electrolyte separation circulation module: First, after the second reaction, the solution is pumped into the primary electrolyte separation mechanism to separate the water, which then enters the third electrolyte storage tank for recycling. The remaining mixed solution of small organic molecules and their oxidation products flows into the secondary electrolyte separation mechanism to separate the small organic molecules from their oxidation products. The small organic molecules flow into the third electrolyte storage tank for recycling, while the oxidation products flow into the product storage tank.

7. The decoupled water electrolysis hydrogen production method according to claim 6, characterized in that, Step (1) includes one or more of the following conditions: a. The constant current is 10 ~ 50 mA·cm -2 ; b. The temperature of the first step reaction is room temperature ~ 80℃; c. In the first step of the reaction, after the active components on the redox medium-assisted electrode have reacted completely, the total voltage of the system suddenly rises, at which point the reaction ends; d. The temperature for the second step reaction is room temperature to 80℃.

8. The decoupled water electrolysis hydrogen production method according to claim 6, characterized in that, Step (1) includes one or more of the following conditions: a. The alkaline solution is an aqueous solution of potassium hydroxide with a concentration of 0.1 M to 5 M; b. The concentration of the aqueous solution of the organic small molecule is 0.01 M to 1 M, and the organic small molecule in the aqueous solution is a reducing organic small molecule; the reducing organic small molecule is glycerol, methanol, ethanol or 5-hydroxymethylfurfural; c. The washing solution is water.

9. The decoupled water electrolysis hydrogen production method according to claim 6, characterized in that, Step (1) includes one or more of the following conditions: i. When the concentration of alkaline solution in the electrolyte storage tank is lower than 0.1 M, the alkaline solution in the electrolyte storage tank should be replaced; ii. When the concentration of the organic small molecule aqueous solution in the electrolyte storage tank three is lower than 0.01 M, the organic small molecule aqueous solution in the electrolyte storage tank three shall be replaced.

10. The decoupled water electrolysis method for hydrogen production according to claim 6, characterized in that, In step (1), the washing solution in the second electrolyte storage tank is used to rinse the electrolytic cell and electrodes 10 to 20 times before the washing solution in the second electrolyte storage tank is replaced.

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