Method for producing hydrogen by decoupling electrolyzed water

Abstract

The invention belongs to the technical field of new energy hydrogen production and biomass resource utilization, and particularly relates to a method for decoupling water electrolysis hydrogen production. According to the method, on the basis of a transition metal complex with reversible oxidation-reduction characteristics, electrolysis water is decoupled by constructing a closed-loop path of an electrochemical-chemical reaction on the anode side, the high-energy-consumption oxygen evolution process in traditional electrolysis water is effectively avoided, and the system operation voltage and the safety risk are reduced. In the system of the method, a transition metal complex is used as a redox medium and continuously participates in an electron transfer process of cathode water reduction hydrogen evolution and anode oxidation, and generated high-valence species are then reduced by biomass in electrolyte, so that valence cycle and continuous electron transfer are realized; and the biomass synchronously realizes high-value conversion. The method has the advantages of low energy consumption, high safety and high added value of products, and is suitable for distributed green hydrogen preparation and gradient utilization of biomass resources.

Description

Technical Field

[0002] This invention belongs to the technical field of new energy hydrogen production and biomass resource utilization, specifically relating to a method for decoupled water electrolysis to produce hydrogen. Background Technology

[0003] Currently, mainstream water electrolysis for hydrogen production generally adopts a coupled mode of "cathode hydrogen evolution – anode oxygen evolution." However, the kinetics of the anode oxygen evolution reaction are slow and the potential is too high, which not only leads to high overall system energy consumption but also poses safety hazards due to low oxygen production value and the risk of mixed gas. Especially under the drive of intermittent renewable energy sources such as wind and solar power, the water electrolysis system has a lag in response and insufficient operational stability and safety, which seriously restricts its promotion in distributed energy scenarios.

[0004] To address the aforementioned issues, researchers have proposed a "decoupled" water electrolysis system that incorporates a redox mediator to separate hydrogen and oxygen production in time or space, thereby reducing operating voltage and explosion risks. This type of system typically replaces the oxygen evolution reaction by driving a cyclic charge-discharge process of the redox pair with an applied voltage, thus improving operational safety and some energy efficiency. However, most existing "electrochemical-electrochemical" decoupling strategies still suffer from high energy consumption, complex equipment, and poor energy utilization efficiency, limiting their large-scale promotion and application. Summary of the Invention

[0005] The purpose of this invention is to provide a decoupled method for hydrogen production via water electrolysis, addressing the aforementioned shortcomings. This method is based on transition metal complexes with reversible redox properties. By constructing a closed-loop pathway for the "electrochemical-chemical" reaction on the anode side, it decouples water electrolysis, effectively avoiding the energy-intensive oxygen evolution process of traditional water electrolysis and reducing system operating voltage and safety risks. In this system, the transition metal complexes act as redox mediators, continuously participating in the electron transfer processes of cathode water reduction and hydrogen evolution, and anodic oxidation. The generated high-valence species are subsequently reduced by biomass in the electrolyte, thus achieving valence state cycling and continuous electron transfer; meanwhile, biomass simultaneously achieves high-value conversion. This method has the advantages of low energy consumption, high safety, and high product added value, and is suitable for distributed green hydrogen production and the cascade utilization of biomass resources.

[0006] The technical solution of this invention is as follows: A method for decoupled water electrolysis to produce hydrogen includes the following steps: (1) Preparation of redox medium solution: Weigh the transition metal complex, dissolve it in deionized water, add electrolyte, and stir until homogeneous to obtain a redox medium solution; the concentration of the transition metal complex in the prepared redox medium solution is 0.001-6M; the concentration of the electrolyte is 0.001-10M.

[0007] The transition metal complex is one or more of iron-based complexes, cobalt-based complexes, or nickel-based complexes.

[0008] Preferably, the iron-based complex is potassium ferricyanide (K3[Fe(CN)6]) or sodium iron ethylenediaminetetraacetate (C 10 H 12 FeN2NaO8) or iron phthalocyanine (C 32 H 16 At least one of FeN8).

[0009] The cobalt-based complex is potassium cobalt cyanide (K3[Co(CN)6]) or dicobalt ethylenediaminetetraacetic acid (C2000). 10 H 12 Co2N2NaO8) or cobalt phthalocyanine (C 32 H 16 At least one of CoN8).

[0010] The nickel-based complex is potassium nickel cyanide (K2Ni(CN)4) or disodium nickel ethylenediaminetetraacetate (C2Ni(CN)4). 10 H 12 (N2Na2NiO8·xH2O) or nickel phthalocyanine (C 32 H 16 At least one of NiN8).

[0011] The electrolyte is at least one of KOH, NaOH, H2SO4, HNO3, HCl, or H3PO4.

[0012] (2) Constructing an electrochemical-chemical decoupled water electrolysis system: First, the system consists of an electrolytic cell, a chemical reaction tank, and a circulation transport system. The circulation transport system includes a circulation pump and circulation pipelines. The electrolytic cell and the chemical reaction tank are connected via the circulation pump to achieve efficient transfer and recycling of the redox medium. The circulation transport system, including the circulation pump and circulation pipelines, forms a closed loop, ensuring continuous reaction and recycling of the electrolyte in the reaction tank.

[0013] Applying voltage or current in an electrolytic cell allows the transition metal complex at the anode to act as a reversible redox medium (such as Fe). 2+ / Fe 3+ Ni 2+ / Ni 3+Oxidation occurs at the anode, while the reduction of water and hydrogen evolution reaction continuously occur at the cathode. Secondly, the high-valence medium generated at the anode is introduced into an independent chemical reaction tank via a circulation system, where it undergoes redox reactions with biomass at different heating temperatures. Simultaneously, the reduced low-valence species are transported to the electrolyzer via the circulation system for recycling. The redox medium dissolves in the electrolyte and is transported along with the electrolyte, undergoing different reactions in different reaction tanks.

[0014] The anode and cathode are placed in an electrolytic cell. The electrode that can undergo the hydrogen evolution reaction is used as the cathode, and the electrode that undergoes the oxidation reaction is used as the anode.

[0015] The redox medium solution prepared in step (1) is then injected into the electrolyzer, and the circulation pipeline is connected to connect the electrolyzer with the chemical reaction tank (reactor) containing biomass or its derivatives, forming an "electrochemical-chemical" decoupled water electrolysis hydrogen production system.

[0016] The cathode is any one of Pt mesh, Pt sheet, Ni electrode, NiMo, carbon cloth, graphite felt, or a cathode catalyst supported on a support, wherein the cathode catalyst is a catalyst with hydrogen evolution function. The support is a Pt mesh, Pt sheet, Ni electrode, carbon cloth, or graphite felt.

[0017] The electrolytic cell can be an H-type electrolytic cell, an alkaline water electrolytic cell, a proton exchange membrane electrolytic cell, or an anion exchange membrane electrolytic cell.

[0018] The anode is a Ni electrode, carbon cloth, graphite felt, or other electrode that can undergo electron transfer and has a current collector function.

[0019] (3) Decoupled water electrolysis for hydrogen production: Turn on the power and set it to constant current, pulse, or step power input mode.

[0020] Under conditions of 25-90℃, in an electrolytic cell, the transition metal complex at the anode is electrochemically oxidized to a higher valence state species, while water reduction to produce hydrogen occurs at the cathode.

[0021] The chemical reaction tank is heated to a temperature of 25-90℃. Subsequently, high-valence species in the electrolytic cell flow into the chemical reaction tank through a circulation system, where they undergo a chemical oxidation-reduction reaction with the biomass or its derivatives in the chemical reaction tank. In this process, the biomass or its derivatives generate high-value-added organic products, and the high-valence species flowing into the electrolytic cell are reduced back to a low-valence state.

[0022] Low-valence species are then returned to the electrolyzer to continue the cycle, achieving continuous hydrogen production and biomass conversion.

[0023] The biomass mentioned is methanol, ethanol, glycerol, glucose, 5-hydroxymethylfurfural, cellulose or lignin, or their derivatives.

[0024] The concentration of biomass in the chemical reaction tank is 0.001-10M.

[0025] Cellulose or lignin is a solid powder that exists in suspension after being added to the electrolyte. The solvent is water, and it coexists with the electrolyte and redox medium in the electrolyte.

[0026] The power supply applies a constant current ranging from 1mA to 3000mA; the power supply applies a constant voltage ranging from 0.1V to 30V.

[0027] The beneficial effects of the present invention are as follows: The decoupled electrolysis water production method of the present invention uses transition metal complexes as reversible redox media. The process of reducing water at the cathode to produce hydrogen and oxidizing the transition metal complex at the anode is completed in the electrolyzer. The high-valence metal complexes are then reacted with biomass or its derivatives in the electrolyte to undergo chemical redox reactions, selectively converting them into high-value-added products such as aldehydes and acids. At the same time, the metal complexes are restored to a low-valence state and recycled.

[0028] By utilizing transition metal complexes in an electrolytic cell to achieve hydrogen evolution at the cathode and electron transfer at the anode, and then selectively oxidizing biomass and completing the reduction reaction in the electrolyte by the generated high-valence species, a closed-loop cycle can be formed.

[0029] The specific principle is as follows: This invention is based on the principle of electrochemical-chemical decoupling. By introducing a transition metal complex with reversible redox properties as a medium for electron / proton transfer, it achieves synergistic coupling between hydrogen production from water electrolysis and biomass oxidation reaction.

[0030] During the electrochemical phase, water reduction occurs at the cathode to generate hydrogen gas, while the anode drives the metal complex to be electrochemically oxidized from a low valence state to a high valence state species. In the chemical stage, high-valence metal complexes undergo chemical redox reactions with biomass or its derivatives in the electrolyte, selectively generating high-value-added organic products, and reducing the metal complexes back to low-valence states, which are then recycled back to the electrolytic cell to continue participating in electron transfer.

[0031] This closed-loop mechanism of "electrochemical oxidation-chemical reduction" breaks the rigid coupling of "cathode hydrogen evolution-anode oxygen evolution" in traditional water electrolysis, thereby avoiding the high energy consumption and safety risks of anode oxygen evolution in traditional water electrolysis, significantly reducing the electrolysis voltage and improving intrinsic safety.

[0032] This strategy not only achieves the synergistic conversion of electrical energy into hydrogen energy and high-value-added biomass derivatives, but also, through the reversible valence state transition of transition metal complexes, possesses charge storage and release characteristics, endowing the system with excellent dynamic buffering capabilities. By introducing a molecular-level charge buffering and energy storage mechanism, it reduces the energy consumption and safety risks of water electrolysis, while improving the electrolysis system's adaptability to instantaneous wide-range power disturbances. It enhances its adaptability to dynamic power fluctuations from wind and solar power, enabling it to accommodate power fluctuations from renewable energy sources such as wind and solar power, ensuring long-term stable operation.

[0033] Meanwhile, this system can achieve selective oxidation of biomass during hydrogen production, obtaining high-value-added products such as aldehydes and acids, improving energy and quality utilization efficiency and economic viability, and has broad application prospects in distributed green hydrogen production and cascade utilization of biomass resources. It realizes the synergistic conversion and enhancement of electrical energy into hydrogen energy and high-value chemical energy from biomass utilization.

[0034] In summary, this method not only avoids the energy-intensive oxygen evolution reaction, but also achieves the synergistic conversion of electrical energy into hydrogen energy and high-value-added biomass derivatives.

[0035] More importantly, the charge buffering properties at the molecular level of transition metal complexes can significantly improve the system's dynamic adaptability to wind and solar power fluctuations, ensuring operational stability and safety, and making it suitable for decoupled water electrolysis hydrogen production under wide-range dynamic power input conditions.

[0036] Therefore, research on the electronic structure regulation of transition metal complexes, the energy-mass coupling law under dynamic power perturbation, and their selective regulation mechanism on biomass oxidation reaction has important theoretical significance and engineering application value. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the "electrochemical-chemical" decoupled water electrolysis hydrogen production system described in this invention.

[0038] Among them, 1 is a chemical reaction tank, 2 is an electrolytic cell, 3 is a circulating pump, and 4 is a circulating pipeline.

[0039] Figure 2 The polarization curves are for the decoupled water electrolysis hydrogen production system in Example 1.

[0040] Figure 3 The polarization curve of the graphite felt electrode in Example 1 is shown in a three-electrode system.

[0041] Figure 4 The image shows the Tafel plot after fitting the polarization curve of the graphite felt electrode in the three-electrode system in Example 1.

[0042] Figure 5 This is a stability test diagram of the graphite felt electrode in the three-electrode system of Example 2.

[0043] Figure 6 The polarization curves of the graphite felt electrode in Example 3 are shown in a three-electrode system and an acidic electrolyte.

[0044] Figure 7 The polarization curves of the graphite felt electrode in Examples 4-8 are shown in the three-electrode system. Detailed Implementation

[0045] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0046] Example 1 The specific steps of the decoupled water electrolysis hydrogen production method are as follows: (1) Preparation of redox medium solution: Metal complex K3[Fe(CN)6] was added to a 1 M electrolyte KOH solution and stirred until homogeneous to obtain a redox medium solution with a K3[Fe(CN)6] concentration of 0.1 M.

[0047] (2) Constructing an electrochemical-chemical decoupled water electrolysis hydrogen production system: The system consists of an electrolytic cell 1, a chemical reaction cell 2, and a circulation transport system, wherein the circulation transport system includes a circulation pump 3 and a circulation pipeline 4; the electrolytic cell 1 and the chemical reaction cell 2 are connected by the circulation pump 3.

[0048] The anode and cathode are placed in electrolytic cell 1. The cathode of electrolytic cell 1 is a Pt / C electrode, and the anode is a graphite felt electrode.

[0049] The redox medium solution prepared in step (1) is then injected into the electrolyzer 1, and the circulation pipeline 4 is connected to connect the electrolyzer 1 with the chemical reaction tank 2 containing biomass ethanol, forming an "electrochemical-chemical" decoupled water electrolysis hydrogen production system.

[0050] (3) Decoupled water electrolysis for hydrogen production: First, a voltage of 1.4V is applied to the electrochemical cell to reversibly redox the anode medium Fe. 2+ / Fe 3+ An oxidation reaction occurs at the cathode, while the reduction of water and hydrogen evolution reaction continue at the cathode.

[0051] Then, the generated high-valence medium is introduced into a separate chemical reaction tank and undergoes a redox reaction with 0.5 M biomass ethanol at 60°C, which promotes the further conversion of carbonaceous components.

[0052] Simultaneously, regenerated low-valence species are returned to the electrolyzer, achieving recycling.

[0053] Figure 2Using the redox medium solution prepared in Example 1, with ethanol as biomass, nickel foam loaded with Pt / C catalyst as cathode, and graphite felt as anode, the polarization curves of the electrodes at an operating temperature of 60°C were recorded using a BioLogic-VMP3 electrochemical workstation in a two-electrode system.

[0054] from Figure 2 It can be seen that the decoupled water electrolysis system can achieve 0.2 A·cm⁻¹ at a voltage of 1.43V. –2 The hydrogen production current density.

[0055] Figure 3 Using the redox medium solution prepared in Example 1, ethanol as biomass, Pt sheet as counter electrode, mercury / mercury oxide electrode as reference electrode, and graphite felt as working electrode, the polarization curve of the working electrode at an operating temperature of 60°C was recorded using a BioLogic-VMP3 electrochemical workstation in a three-electrode system.

[0056] from Figure 3 It can be seen that, with the assistance of ethanol and redox mediators, the anode is at 1.34 V. vs. RHE can drive 400 mA / cm 2 It has a high current density and excellent oxidation activity.

[0057] Figure 4 for Figure 3 The Tafel slope of the oxidation reaction of the metal complex in Example 1 was measured under the following conditions: Figure 3 As stated above.

[0058] from Figure 4 It can be seen that: [Fe(CN)6] 4– The Tafel slope of the oxidation reaction is only 25.1 mV / dec, indicating that the activation energy of the oxidation reaction of the metal complex is low and the dependence of the reaction rate on overpotential is weakened.

[0059] Example 2 The difference between this embodiment and embodiment 1 is that the applied current in step (3) is 0.1 A·cm. –2 The other steps and parameters are the same as in Example 1.

[0060] Figure 5 To achieve the desired effect in a three-electrode system, with the anode applied as in Example 2 at a pressure of 0.1 A·cm –2 The current was continuously used for electrolysis, and the other steps and test parameters were the same as in Example 1.

[0061] from Figure 5 It can be seen that the reaction system can continue at 0.1 A·cm –2 It can operate stably for more than 2.5 hours under the specified current density.

[0062] Example 3 The difference between this embodiment and embodiment 1 is that the electrolyte in step (1) is 0.5 M H2SO4.

[0063] The other steps and parameters are the same as in Example 1.

[0064] Figure 6 In the three-electrode system, the redox medium solution prepared in Example 3 was used, and the other steps and test parameters were the same as in Example 1.

[0065] from Figure 6 It can be seen that in acidic electrolytes, metal complexes can still be reduced by ethanol, and the resulting low-valence metal complexes undergo further electrochemical oxidation at the anode.

[0066] Example 4: The difference between this embodiment and embodiment 1 is that the biomass in steps (2) and (3) is 0.5M methanol, and the operating temperature of the electrolytic cell and the chemical reaction cell in step (3) is 25℃.

[0067] The other steps and parameters are the same as in Example 1.

[0068] Example 5: The difference between this embodiment and embodiment 1 is that the biomass in steps (2) and (3) is 0.5M methanol, and the operating temperature of the electrolytic cell and the chemical reaction cell in step (3) is 40℃.

[0069] The other steps and parameters are the same as in Example 1.

[0070] Example 6: The difference between this embodiment and embodiment 1 is that the biomass in steps (2) and (3) is 0.5M methanol, and the operating temperature of the electrolytic cell and the chemical reaction cell in step (3) is 60℃.

[0071] The other steps and parameters are the same as in Example 1.

[0072] Example 7: The difference between this embodiment and embodiment 1 is that the biomass in steps (2) and (3) is 0.5M methanol, and the operating temperature of the electrolytic cell and the chemical reaction cell in step (3) is 70℃.

[0073] The other steps and parameters are the same as in Example 1.

[0074] Example 8: The difference between this embodiment and embodiment 1 is that the biomass in steps (2) and (3) is 0.5M methanol, and the operating temperature of the electrolytic cell and the chemical reaction cell in step (3) is 80℃.

[0075] The other steps and parameters are the same as in Example 1.

[0076] Figure 7 In a three-electrode system, using the redox medium solution prepared in Example 1, methanol as biomass in Examples 4-8, a Pt sheet as the counter electrode, and a mercury / mercury oxide electrode as the reference electrode, the polarization curves of the working electrode at operating temperatures of 25℃ (Example 4), 40℃ (Example 5), 60℃ (Example 6), 70℃ (Example 7), and 80℃ (Example 8) were recorded using a BioLogic-VMP3 electrochemical workstation.

[0077] from Figure 7 It can be seen that as the operating temperature increases, the metal complex is more easily reduced by methanol, thereby giving the anode higher oxidation activity.

Claims

1. A method for decoupled water electrolysis to produce hydrogen, characterized in that, Includes the following steps: (1) Preparation of redox medium solution: Weigh the transition metal complex, dissolve it in deionized water, add electrolyte, stir well, and obtain a redox medium solution; In the prepared redox medium solution, the concentration of the transition metal complex was 0.001-6 M, and the concentration of the electrolyte was 0.001-10 M. The transition metal complex is one or more of iron-based complexes, cobalt-based complexes, or nickel-based complexes; (2) Constructing an electrochemical-chemical decoupled water electrolysis hydrogen production system: First, the system consists of an electrolytic cell, a chemical reaction cell, and a circulation transport system, wherein the circulation transport system includes a circulation pump and circulation pipelines; the electrolytic cell and the chemical reaction cell are connected by the circulation pump. Place the anode and cathode into the electrolytic cell; The redox medium solution prepared in step (1) is then injected into the electrolyzer, and the circulation pipeline is connected to connect the electrolyzer with the chemical reaction tank containing biomass or its derivatives, forming an electrochemical-chemical decoupled water electrolysis hydrogen production system. (3) Decoupled water electrolysis for hydrogen production: When the power is turned on, under conditions of 25-90℃, in the electrolytic cell, the transition metal complex at the anode is electrochemically oxidized to a higher valence state species, and water reduction to produce hydrogen occurs at the cathode. The chemical reaction tank is heated to a temperature of 25-90℃; then, the high-valence species in the electrolytic cell flow into the chemical reaction tank through a circulation system, and undergo a chemical oxidation-reduction reaction with the biomass or its derivatives in the chemical reaction tank. In this process, the biomass or its derivatives generate organic products, and the high-valence species flowing into the electrolytic cell are reduced back to a low-valence state. Low-valence species are then returned to the electrolyzer to continue the cycle.

2. The method for decoupled water electrolysis to produce hydrogen according to claim 1, characterized in that, The iron-based complex is at least one of potassium ferricyanide, sodium iron ethylenediaminetetraacetate, or iron phthalocyanine.

3. The method for decoupled water electrolysis to produce hydrogen according to claim 1, characterized in that, The cobalt-based complex is at least one of potassium cobalt cyanide, dicobalt ethylenediaminetetraacetic acid, or cobalt phthalocyanine.

4. The method for decoupled water electrolysis to produce hydrogen according to claim 1, characterized in that, The nickel-based complex is at least one of potassium nickel cyanide, disodium nickel ethylenediaminetetraacetate, or nickel phthalocyanine.

5. The method for decoupled water electrolysis to produce hydrogen according to claim 1, characterized in that, The electrolyte is at least one of KOH, NaOH, H2SO4, HNO3, HCl, or H3PO4.

6. The method for decoupled water electrolysis to produce hydrogen according to claim 1, characterized in that, The cathode is any one of Pt mesh, Pt sheet, Ni electrode, NiMo, carbon cloth, graphite felt, or a cathode hydrogen evolution catalyst supported on a support; wherein the support for the cathode hydrogen evolution catalyst is a Pt mesh, Pt sheet, Ni electrode, carbon cloth, or graphite felt. The anode is any one of a Ni electrode, carbon cloth, or graphite felt.

7. The method for decoupled water electrolysis to produce hydrogen according to claim 1, characterized in that, The electrolytic cell may be any one of the following: an H-type electrolytic cell, an alkaline water electrolytic cell, a proton exchange membrane electrolytic cell, or an anion exchange membrane electrolytic cell.

8. The method for decoupled water electrolysis to produce hydrogen according to claim 1, characterized in that, The biomass is at least one of methanol, ethanol, glycerol, glucose, 5-hydroxymethylfurfural, cellulose, or lignin.

9. The method for decoupled water electrolysis to produce hydrogen according to claim 1, characterized in that, The concentration of biomass in the chemical reaction tank is 0.001-10M.

10. The method for decoupled water electrolysis to produce hydrogen according to claim 1, characterized in that, The power supply applies a constant current ranging from 1mA to 3000mA; the power supply applies a constant voltage ranging from 0.1V to 30V.

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