Iron-based liquid flow decoupling water electrolysis hydrogen production system and method capable of reducing starting voltage

Abstract

The invention discloses an iron-based liquid flow decoupling water electrolysis hydrogen production system and method capable of reducing starting voltage, the system mainly comprises a liquid storage tank, a circulating pump, a proton exchange membrane electrolysis hydrogen production system and other components, and aims to realize hydrogen production under low voltage and separation of hydrogen production and oxygen production in time and space. The working process mainly comprises the steps that ferrous ions are oxidized into ferric ions, and hydrogen ions are reduced into air; ferric ions are reduced into ferrous ions, and water is oxidized into oxygen and hydrogen ions. In the whole process, ferrous ions and ferric ions are introduced as decoupling substances, so that the hydrogen production step and the oxygen production step can be independently carried out, the hydrogen production voltage and the oxygen production voltage are lower than those of a common PEM electrolytic bath, the method is particularly suitable for a photovoltaic system with voltage fluctuation, and the energy efficiency of photovoltaic electrolytic hydrogen production is improved. The device has the advantages of low cost, simple structure, easiness in maintenance and the like.

Description

Technical Field

[0001] The invention belongs to the field of electrochemistry, and in particular relates to an iron-based liquid flow decoupled water electrolysis hydrogen production system and method capable of reducing the starting voltage. Background Art

[0002] Although the production of renewable energy such as wind power and photovoltaic power has increased significantly, the volatility of the energy produced makes it difficult to directly connect to the grid for use. Combining renewable energy with hydrogen production systems to obtain fixed energy storage systems is an important research direction. Water electrolysis combined with renewable energy power generation systems is also considered the "ultimate solution" for green hydrogen production. However, ordinary electrolyzers usually require stable voltage and current, and can only continuously produce hydrogen when the photovoltaic power is stable, which makes it difficult to directly adapt to the volatility of photovoltaic power generation. Summary of the invention

[0003] The purpose of the present invention is to provide an iron-based liquid flow decoupled water electrolysis hydrogen production system and method that can reduce the starting voltage. The present invention can achieve decoupling of hydrogen and oxygen in time and space, and has a starting voltage lower than that of a PEM electrolyzer with the same structure. It has significant advantages over ordinary PEM electrolyzers in terms of efficiency, stability, safety and adaptability.

[0004] In order to achieve the above object, the present invention adopts the following technical solution:

[0005] An iron-based liquid flow decoupling water electrolysis hydrogen production system capable of reducing the starting voltage, comprising a proton exchange membrane water electrolysis hydrogen production site and a redox liquid flow decoupling site;

[0006] The proton exchange membrane water electrolysis hydrogen production site includes an oxygen production solution storage tank, a deaerator and a peristaltic pump arranged at the downstream end of the oxygen production solution storage tank, a hydrogen production solution storage tank arranged at the downstream end of the deaerator, a peristaltic pump arranged at the downstream end of the hydrogen production solution storage tank, and a hydrogen production chamber and an oxygen production chamber arranged at the downstream end of the peristaltic pump; the redox liquid flow decoupling site includes an iron ion storage tank, a peristaltic pump arranged at the downstream end of the iron ion storage tank, and a redox chamber arranged at the downstream end of the peristaltic pump. Two redox chambers are provided, which are respectively connected to the hydrogen production chamber and the oxygen production chamber through proton exchange membranes;

[0007] The iron ion storage tank is connected to the redox chamber through the redox electrolyte inlet, the redox chamber is connected to the iron ion storage tank through the redox electrolyte outlet to form a solution circulation, a redox electrode is arranged in the redox chamber, a hydrogen producing chamber is arranged with a hydrogen producing electrode, an oxygen producing chamber is arranged with an oxygen producing electrode, one redox electrode is connected with the hydrogen producing electrode and the two poles of a direct current power supply, the other redox electrode is connected with the oxygen producing electrode and the two poles of another direct current power supply, and the two redox chambers are respectively connected with the hydrogen producing chamber and the oxygen producing chamber through a proton exchange membrane; the oxygen producing chamber is connected to the oxygen producing solution storage tank through the oxygen producing solution and the oxygen outlet, the oxygen producing solution storage tank is connected to the oxygen producing chamber through the oxygen producing solution inlet via a peristaltic pump to form a circulation, the hydrogen producing chamber is connected to the hydrogen producing solution storage tank through the hydrogen producing solution and the hydrogen outlet, the hydrogen producing solution storage tank is connected to the hydrogen producing chamber through the hydrogen producing solution inlet via a peristaltic pump to form a circulation, and the deaerator is connected between the oxygen producing solution storage tank and the hydrogen producing solution storage tank.

[0008] A further improvement of the present invention is that the redox chamber is connected to the iron ion storage tank, and the iron ion solution is used as a liquid decoupling agent, so that the production of hydrogen and oxygen in the hydrogen production chamber and the oxygen production chamber can be carried out independently, separating hydrogen and oxygen in time and space, and at the same time, the voltage is lower than the electrolytic hydrogen production system that generates hydrogen and oxygen at the same time, and the solution content in the iron ion storage tank is adjusted according to the actual dosage.

[0009] A further improvement of the present invention is that peristaltic pumps are respectively arranged between the two redox chambers and the iron ion storage tank, between the hydrogen production chamber and the hydrogen production solution storage tank, and between the oxygen production chamber and the oxygen production solution storage tank to form solution circulation. After operation, the operating speed of the peristaltic pump is dynamically regulated according to the power of the power supply, and the flow rate thereof ensures that the ions in the solution are reacted to the maximum extent possible.

[0010] A further improvement of the present invention is that a deaerator is provided between the oxygen production solution storage tank and the hydrogen production solution storage tank, and the oxygen production solution storage tank and the hydrogen production solution storage tank are connected as a whole through the deaerator, and the hydrogen ions generated in the oxygen production chamber are used in the hydrogen production chamber, forming a material circulation.

[0011] A further improvement of the present invention is that the proton exchange membrane is a DuPont N117 proton exchange membrane.

[0012] A further improvement of the present invention is that the hydrogen-producing electrode is a platinum sheet electrode, and the oxygen-producing electrode is a ruthenium-iridium electrode.

[0013] A further improvement of the present invention is that the redox electrode is a heat-treated carbon felt electrode.

[0014] A further improvement of the present invention is that the iron ion storage tank contains 1M FeSO4 and 0.5M H2SO4, and the oxygen production solution storage tank contains 0.5M H2SO4 and 0.5M Na2SO4.

[0015] A method for producing hydrogen by decoupling water electrolysis through an iron-based liquid flow capable of reducing a starting voltage, the method being based on the iron-based liquid flow decoupling water electrolysis system capable of reducing a starting voltage, comprising:

[0016] The ferrous iron and ferric iron solution in the iron ion storage tank enter the redox chamber through the redox electrolyte inlet, the ferrous iron is oxidized to ferric iron in the redox chamber connected to the hydrogen production chamber, and the hydrogen ions are reduced to hydrogen in the hydrogen production chamber; the ferric iron is reduced to ferrous iron in the redox chamber connected to the oxygen production chamber, and water is oxidized to oxygen in the oxygen production chamber. The ferrous iron and ferric iron solution after the reaction in the redox chamber return to the iron ion storage tank through the redox electrolyte outlet; The solution in the oxygen solution storage tank enters the oxygen producing chamber through the oxygen producing solution inlet via a peristaltic pump, a reaction of water generating hydrogen ions and oxygen occurs in the oxygen producing chamber, the generated hydrogen ions and oxygen enter the oxygen producing solution storage tank through the oxygen producing solution and the oxygen outlet, the solution in the oxygen producing solution storage tank is removed of dissolved oxygen by a deaerator and enters the hydrogen producing solution storage tank, the solution in the hydrogen producing solution storage tank enters the hydrogen producing chamber through the hydrogen producing solution inlet via a peristaltic pump, a reaction of hydrogen ions being reduced to hydrogen occurs in the hydrogen producing chamber, and the generated hydrogen enters the hydrogen producing solution storage tank through the hydrogen producing solution and the hydrogen outlet.

[0017] A further improvement of the present invention is that a reaction of oxidizing divalent iron ions to trivalent iron ions occurs in the redox chamber connected to the hydrogen production chamber: Fe 2+ =e - +Fe 3+ , the hydrogen ion is reduced to hydrogen gas in the hydrogen production chamber: 2H + +2e - =H2, the overall reaction of the hydrogen production step is: 2H + +2Fe 2+ =2Fe 3+ +H2; the redox chamber connected to the oxygen-producing chamber undergoes a reaction in which trivalent iron ions are reduced to divalent iron ions: Fe 3+ +e - =Fe 2+ , water is oxidized to oxygen in the production of hydrogen and oxygen: 2H2O=O2+4H + +4e - , the overall reaction of the oxygen-generating step is: 4Fe 3+ +2H2O=2Fe 2+ +O2+4H +; The overall reaction is: 2H2O=O2+2H2.

[0018] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0019] Decoupled water electrolysis hydrogen production technology shows significant potential in the field of photovoltaic hydrogen production. By dividing the water electrolysis process into two steps, it can effectively alleviate the intermittent and volatility problems of photovoltaic power generation, improve hydrogen production efficiency, and significantly improve safety. Compared with the combination of traditional photovoltaic power generation and ordinary electrolyzers, the photovoltaic combined with decoupled water electrolysis hydrogen production system has significant advantages in efficiency, stability, safety and adaptability. Especially in terms of economy, decoupled water electrolysis hydrogen production reduces operation and maintenance costs by improving system energy efficiency and extending the life of the electrolyzer. Its flexible operation mode can also use the low-peak electricity price at night to produce hydrogen, and use photovoltaic power to produce oxygen during the day to improve economic benefits.

[0020] The present invention is different from the general electrolyzer coupled with photovoltaics, and has a higher starting voltage, so that shutdown will occur when the voltage fluctuates, and frequent start and stop will also reduce the stability of the system. The present invention combines the advantages of proton exchange membrane electrode tank and liquid flow battery. First, the electrolysis of water is decoupled into separate hydrogen production and oxygen production steps using iron ion solution, so that the hydrogen production process undergoes oxidation of divalent iron to trivalent iron and reduction of hydrogen ions to hydrogen; the oxygen production process undergoes reduction of trivalent iron to divalent iron and oxidation of water to oxygen, separating hydrogen and oxygen in time and space, avoiding the explosion risk of hydrogen and oxygen mixing and the timing of hydrogen and oxygen production that can be regulated on demand. In addition, since the iron ion redox electromotive force is between the HER and OER voltages, the hydrogen production and oxygen production voltages composed thereof are significantly lower than the undecoupled PEM tank starting voltage, having a wider operating voltage, and having higher efficiency when coupled with a photovoltaic system.

[0021] Furthermore, in the present invention, the solutions of the hydrogen production chamber and the oxygen production chamber are connected, and only pure water needs to be added when replenishing the solution, so that the system has a lower maintenance cost.

[0022] Furthermore, the liquid storage tank can freely adjust the amount of redox ions to match the most suitable hydrogen production, thereby improving the overall efficiency of the system.

[0023] Furthermore, the energy required by the present invention can be outdoor photovoltaic or other forms of energy. The whole process is clean, low-cost, efficient, low-carbon and safe. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 Schematic diagram of iron-based liquid flow decoupled water electrolysis for hydrogen production;

[0026] Figure 2 :(a) Fe in iron-based liquid flow battery 2+ / Fe 3+ (a) Cyclic voltammetry (CV) curve, (b) linear sweep voltammetry (LSV) curve of the Pt electrode in the gas production cell and the linear sweep voltammetry (LSV) curve of Fe 2+ / Fe 3+ Cyclic voltammetry (CV) curves on carbon felt electrode; (c) decoupled water electrolysis in an iron-based flow battery at 50 mA / cm 2 Chronopotentiometry curve under current; (d) Iron-based flow battery decoupled water electrolysis at 50 mA / cm 2 Chronopotentiometry at 10 current densities.

[0027] Description of reference numerals:

[0028] 1. Proton exchange membrane, 2. Hydrogen production electrode, 3. Hydrogen production chamber, 4. Oxygen production electrode, 5. Oxygen production chamber, 6. Redox electrode, 7. Redox chamber, 8. Iron electrolyte inlet, 9. Iron electrolyte outlet, 10. Hydrogen chamber solution inlet, 11. Hydrogen production solution and hydrogen outlet, 12. Oxygen chamber solution inlet, 13. Oxygen production solution and oxygen outlet, 14. Iron ion storage tank, 15. Peristaltic pump, 16. Oxygen production solution storage tank, 17. Hydrogen production solution storage tank, 18. Deaerator. DETAILED DESCRIPTION

[0029] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0030] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0031] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0032] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0034] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0035] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0036] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0037] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0038] Example 1

[0039] like Figure 1As shown, the present invention provides an iron-based liquid flow decoupled water electrolysis hydrogen production system capable of reducing the starting voltage, comprising a proton exchange membrane water electrolysis hydrogen production site and a redox liquid flow decoupling site; the proton exchange membrane water electrolysis hydrogen production site comprises an oxygen production solution storage tank 16, a deaerator 18 and a peristaltic pump 15 arranged at the downstream end of the oxygen production solution storage tank 16, a hydrogen production solution storage tank 17 arranged at the downstream end of the deaerator 18, and a peristaltic pump 15 arranged at the downstream end of the hydrogen production solution storage tank 17. A hydrogen production chamber 3 and an oxygen production chamber 5 are arranged at the downstream end of a peristaltic pump 15; the redox liquid flow decoupling site part includes an iron ion storage tank 14, a peristaltic pump 15 arranged at the downstream end of the iron ion storage tank 14, and a redox chamber 7 arranged at the downstream end of the peristaltic pump 15. Two redox chambers 7 are provided, which are respectively connected to the hydrogen production chamber 3 and the oxygen production chamber 5 through a proton exchange membrane 1; the iron ion storage tank 14 is connected to the redox chamber 7 through a redox electrolyte inlet 8, and the redox chamber 7 is connected to the iron ion storage tank 14 through a redox electrolyte outlet 9 to form a solution circulation, a redox electrode 6 is arranged in the redox chamber 7, a hydrogen production electrode 2 is arranged in the hydrogen production chamber 3, and an oxygen production electrode 4 is arranged in the oxygen production chamber 5. One redox electrode 6 is connected to the hydrogen production electrode 2 and the two poles of a DC power supply, and the other redox electrode 6 is connected to the oxygen production electrode 4 and the two poles of another DC power supply. The two redox chambers 7 are respectively connected to the hydrogen production chamber 3 and the oxygen production chamber 5 through the proton exchange membrane 1; oxygen production The chamber 5 is connected to the oxygen producing solution storage tank 16 through the oxygen producing solution and the oxygen outlet 13, and the oxygen producing solution storage tank 16 is connected to the oxygen producing chamber 5 through the oxygen producing solution inlet 12 via the peristaltic pump 15 to form a circulation, the hydrogen producing chamber 3 is connected to the hydrogen producing solution storage tank 17 through the hydrogen producing solution and the hydrogen outlet 11, and the hydrogen producing solution storage tank 17 is connected to the hydrogen producing chamber 3 through the hydrogen producing solution inlet 10 via the peristaltic pump 15 to form a circulation, and the deaerator 18 is connected between the oxygen producing solution storage tank 16 and the hydrogen producing solution storage tank 17.

[0040] In this embodiment, the present invention includes an electrode for an iron-based liquid flow battery to undergo a redox reaction, a gassing electrode for producing hydrogen and oxygen, an electrolyte, and an external power source. The proton exchange membrane 1 is a DuPont N117 proton exchange membrane, the hydrogen-producing electrode 2 is a platinum sheet electrode, the oxygen-producing electrode 4 is a ruthenium-iridium electrode, and the redox electrode 6 is a heat-treated carbon felt electrode. The redox liquid flow electrolyte is partially modified from a liquid flow battery, and the iron ion storage tank 14 contains FeSO4 with a concentration of 1M and H2SO4 with a concentration of 0.5M, and the oxygen-producing solution storage tank 16 contains H2SO4 with a concentration of 0.5M and Na2SO4 with a concentration of 0.5M. The addition of Na2SO4 achieves ion concentration balance on both sides of the proton exchange membrane 1.

[0041] The present invention has found that Fe 2+ / Fe 3+The redox potential of the redox couple is between the onset potentials of the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Figure 2 (b)), therefore using Fe 2+ / Fe 3+ The redox pair can decouple the traditional water electrolysis process into two independent half reactions. The solution enters the redox chamber 7 through the iron electrolyte inlet 8 from the peristaltic pump 15, and oxidation and reduction reactions occur respectively; the corresponding hydrogen production chamber 3 and oxygen production chamber 5 undergo hydrogen production and oxygen production reactions. Since iron ions are added as decoupling substances, the hydrogen production and oxygen production steps can be carried out independently, and the hydrogen production voltage and oxygen production voltage are both lower than the general PEM electrolyzer starting voltage (3.6V).

[0042] The proton exchange membrane water electrolysis hydrogen production system is partially modified from the proton exchange membrane electrolyzer, and the redox liquid flow electrolyte is partially modified from the liquid flow battery, so that it has the advantages of the proton exchange membrane electrolyzer and the advantages of the liquid flow battery. The addition of Na2SO4 achieves the ion concentration balance on both sides of the proton exchange membrane 1, and reduces the iron ions entering the gas production chamber due to osmotic pressure. The hydrogen production solution storage tank 17 is the oxygen production solution after the oxygen production solution storage tank 16 is removed by the deaerator 18. The hydrogen ions generated in the oxygen production chamber 5 can be used in the hydrogen production chamber 3 to form a material cycle. In the subsequent maintenance, it is only necessary to add water to the oxygen production solution storage tank 16 so that the solution in the gas production chamber can be connected for use.

[0043] Decoupled electrolysis technology divides the water electrolysis process into independent steps, which can complete high-voltage oxygen-producing electrolysis when photovoltaic power is sufficient, and complete lower-voltage hydrogen-producing electrolysis when power is low. This flexible step-by-step electrolysis mode smoothes the fluctuations in photovoltaic power output, avoids the frequent startup and shutdown of traditional electrolyzers, and contributes to the durability of the equipment. By dividing the water electrolysis process into multiple steps, it can effectively alleviate the intermittent and volatile problems of photovoltaic power generation, improve hydrogen production efficiency, and significantly improve safety.

[0044] Example 2

[0045] like Figure 1As shown, the present invention provides an iron-based liquid flow decoupled water electrolysis hydrogen production method that can reduce the starting voltage, comprising: the divalent iron ions and the trivalent iron ion solution in the iron ion storage tank 14 enter the redox chamber 7 through the redox electrolyte inlet 8, the divalent iron ions are oxidized to trivalent iron ions in the redox chamber 7 connected to the hydrogen production chamber 3, and the hydrogen ions are reduced to hydrogen in the hydrogen production chamber 3; the trivalent iron ions are reduced to divalent iron ions in the redox chamber 7 connected to the oxygen production chamber 5, and the water is oxidized to oxygen in the oxygen production chamber 5. The divalent iron ions and the trivalent iron ion solution after the reaction in the redox chamber 7 are returned to the redox chamber 7 through the redox electrolyte outlet 9. The iron ion storage tank 14; the solution in the oxygen-producing solution storage tank 16 enters the oxygen-producing chamber 5 through the oxygen-producing solution inlet 12 via the peristaltic pump 15, and a reaction of water generating hydrogen ions and oxygen occurs in the oxygen-producing chamber 5. The generated hydrogen ions and oxygen enter the oxygen-producing solution storage tank 16 through the oxygen-producing solution and the oxygen outlet 13. The solution in the oxygen-producing solution storage tank 16 removes dissolved oxygen through the deaerator 18 and enters the hydrogen-producing solution storage tank 17. The solution in the hydrogen-producing solution storage tank 17 enters the hydrogen-producing chamber 3 through the hydrogen-producing solution inlet 10 via the peristaltic pump 15. A reaction of hydrogen ions being reduced to hydrogen occurs in the hydrogen-producing chamber 3, and the generated hydrogen enters the hydrogen-producing solution storage tank 17 through the hydrogen-producing solution and the hydrogen outlet 11.

[0046] In this embodiment, the oxidation-reduction chamber 7 connected to the hydrogen production chamber 3 undergoes a reaction in which the divalent iron ions are oxidized to the trivalent iron ions: Fe 2+ =e - +Fe 3+ , the hydrogen ion is reduced to hydrogen gas in the hydrogen production chamber 3: 2H + +2e - =H2, the overall reaction of the hydrogen production step is: 2H + +2Fe 2+ =2Fe 3+ + H2; the redox chamber 7 connected to the oxygen producing chamber 5 undergoes a reaction in which trivalent iron ions are reduced to divalent iron ions: Fe 3+ +e - =Fe 2+ , the water is oxidized to oxygen in the hydrogen-oxygen production 5: 2H2O=O2+4H + +4e - , the overall reaction of the oxygen-generating step is: 4Fe 3+ +2H2O=2Fe 2+ +O2+4H + ; The overall reaction is: 2H2O=O2+2H2.

[0047] Compared with the combination of traditional photovoltaic power generation and ordinary electrolyzers, the photovoltaic combined with liquid flow decoupled water electrolysis hydrogen production system has significant advantages in efficiency, stability, safety and adaptability. Especially in terms of economy, decoupled water electrolysis hydrogen production reduces operation and maintenance costs by improving system energy efficiency and extending the life of the electrolyzer. Its flexible operation mode can also use the low-peak electricity price at night to produce hydrogen, and use photovoltaic power to produce oxygen during the day to improve economic benefits.

[0048] The work of the present invention combines liquid flow batteries with decoupled water electrolysis hydrogen production and proton exchange membrane electrolyzers to develop a decoupled water electrolysis hydrogen production system for photovoltaics. The decoupled water electrolysis technology achieves higher power utilization by dividing the hydrogen production process into multiple steps, which can better match the fluctuations of photovoltaic power generation and reduce energy waste. In addition, by optimizing the production conditions of hydrogen and oxygen through step-by-step operation, the system can operate efficiently in the strong and weak changes of photovoltaic power generation, effectively alleviate power fluctuations, and improve the continuity of the system.

[0049] The safety of the decoupled system is also significantly enhanced. Since the production process of hydrogen and oxygen is separated, the risk of mixed gas that is easily produced in traditional electrolyzers is reduced, and the potential explosion hazard is avoided. At the same time, the intelligent control system can adjust the amount of hydrogen and oxygen produced to ensure the safety and stability of the system when the power fluctuation is large.

[0050] The system also extends the life of the equipment. Decoupling technology continues part of the electrolysis process when power fluctuates, avoiding the loss caused by frequent start-up and stop of the electrolyzer, making the equipment operating conditions more stable, and reducing the loss and maintenance costs of the electrolyzer and key components. In addition, decoupled water electrolysis hydrogen production is flexible and scalable, can easily integrate energy storage systems, and flexibly use wind energy or thermal energy to complete different steps, increasing adaptability to combinations with a variety of renewable energy sources.

[0051] Based on this, this embodiment uses an iron-based liquid flow battery as a redox medium, and the decoupled water electrolysis device includes the following components: an electrolyte, a carbon felt electrode for the redox medium to react, a hydrogen evolution cathode platinum electrode, and an oxygen evolution anode ruthenium iridium electrode. The volume of the electrolyte of the iron-based liquid flow battery is 60ml, the concentration of FeSO4 is 1M, the concentration of H2SO4 is 0.5M, the volume of the electrolyte in the gas production pool is 60ml, and the concentration of H2SO4 is 0.5M.

[0052] In order to verify the Fe 2+ / Fe 3+ The redox potential of the redox couple on the carbon felt electrode was tested by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) using a three-electrode system. Figure 2 As shown in (b), Fe 2+ / Fe 3+The redox potential of the redox couple is between the onset potentials of HER and OER, which verifies the feasibility of the redox couple in decoupled water electrolysis. At the same time, according to the LSV test, the onset potential of OER on the carbon felt electrode is 1.39 V vs. SCE, which is higher than that of Fe 2+ / Fe 3+ The oxidation potential of the redox couple was 0.48 V vs. SEC, which effectively suppressed the oxygen evolution side reaction.

[0053] The iron-based liquid flow battery of this embodiment is used to perform decoupled water electrolysis hydrogen production operation. The specific process is as follows: During the hydrogen production process, the working electrode carbon felt in the iron-based liquid flow battery is connected to the hydrogen evolution cathode platinum sheet electrode. At this time, Fe 2+ Oxidation reaction occurs to form oxidized Fe 3+ At the same time, the platinum electrode undergoes a reduction reaction to produce hydrogen; during the oxygen production process, the current direction is reversed, and Fe 3+ The reduction reaction becomes reduced Fe 2+ At the same time, an oxidation reaction occurs at the platinum electrode to produce oxygen. Through this process, hydrogen and oxygen can be decoupled for production.

[0054] The performance of decoupled water electrolysis was further studied by chronopotentiometry. 2 The chronopotentiometry curves ( Figure 2 (c)). At 50 mA / cm 2 At the current density, the input voltage required in the hydrogen and oxygen production processes is low, among which the hydrogen production voltage is lower than the input voltage of the non-decoupled electrolyzer, which can effectively alleviate the intermittent and volatility problems of photovoltaic power generation and improve the hydrogen production efficiency.

[0055] Detection of Fe 2+ / Fe 3+ The redox stability was tested 10 times at a current density of 50 mA / cm 2 The chronoamperometry detection was used to test the cyclic performance of the decoupled water electrolysis. The decoupled water electrolysis using the iron-based liquid flow battery as the redox medium ran stably for 10,000 s. After 10 cycle tests, it was found that the step voltage of the decoupled water electrolysis using the iron-based liquid flow battery as the redox medium did not change basically, which indicates that the decoupled water electrolysis to produce hydrogen and oxygen has good stability.

[0056] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

[0057] In addition, it should be understood that although this specification is described in accordance with the implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. An iron-based liquid flow decoupled water electrolysis hydrogen production system capable of reducing the starting voltage, characterized in that: It includes two parts: a proton exchange membrane water electrolysis hydrogen production site and a redox flow decoupling site; The proton exchange membrane water electrolysis hydrogen production site comprises an oxygen production solution storage tank (16), a deaerator (18) and a peristaltic pump (15) arranged at the downstream end of the oxygen production solution storage tank (16), a hydrogen production solution storage tank (17) arranged at the downstream end of the deaerator (18), a peristaltic pump (15) arranged at the downstream end of the hydrogen production solution storage tank (17), and a hydrogen production chamber (3) and an oxygen production chamber (5) arranged at the downstream end of the peristaltic pump (15); the redox liquid flow decoupling site comprises an iron ion storage tank (14), a peristaltic pump (15) arranged at the downstream end of the iron ion storage tank (14), and a redox chamber (7) arranged at the downstream end of the peristaltic pump (15), wherein two redox chambers (7) are provided, and are respectively connected to the hydrogen production chamber (3) and the oxygen production chamber (5) through the proton exchange membrane (1); The iron ion storage tank (14) is connected to the redox chamber (7) via the redox electrolyte inlet (8); the redox chamber (7) is connected to the iron ion storage tank (14) via the redox electrolyte outlet (9) to form a solution circulation; a redox electrode (6) is arranged in the redox chamber (7); a hydrogen producing electrode (2) is arranged in the hydrogen producing chamber (3); an oxygen producing electrode (4) is arranged in the oxygen producing chamber (5); one redox electrode (6) is connected to the hydrogen producing electrode (2) and to two poles of a direct current power supply; another redox electrode (6) is connected to the oxygen producing electrode (4) and to two poles of another direct current power supply; and the two redox chambers (7) are respectively connected to the hydrogen producing chamber (3) and the oxygen producing chamber (5) via a proton exchange membrane (1); The oxygen production chamber (5) is connected to the oxygen production solution storage tank (16) through the oxygen production solution and the oxygen outlet (13), and the oxygen production solution storage tank (16) is connected to the oxygen production chamber (5) through the oxygen production solution inlet (12) via the peristaltic pump (15) to form a circulation. The hydrogen production chamber (3) is connected to the hydrogen production solution storage tank (17) through the hydrogen production solution and the hydrogen outlet (11), and the hydrogen production solution storage tank (17) is connected to the hydrogen production chamber (3) through the hydrogen production solution inlet (10) via the peristaltic pump (15) to form a circulation. The deaerator (18) is connected between the oxygen production solution storage tank (16) and the hydrogen production solution storage tank (17).

2. The iron-based liquid flow decoupled water electrolysis hydrogen production system capable of reducing the starting voltage according to claim 1, characterized in that: The redox chamber (7) is connected to the iron ion storage tank (14), and the iron ion solution is used as a liquid decoupling agent, so that the generation of hydrogen and oxygen in the hydrogen production chamber (3) and the oxygen production chamber (5) can be carried out independently, and the hydrogen and oxygen are separated in time and space. At the same time, the voltage is lower than that of the electrolytic hydrogen production system that generates hydrogen and oxygen at the same time, and the solution content in the iron ion storage tank (14) is adjusted according to the actual amount used.

3. The iron-based liquid flow decoupled water electrolysis hydrogen production system capable of reducing the starting voltage according to claim 1, characterized in that: Peristaltic pumps (15) are respectively arranged between the two redox chambers (7) and the iron ion storage tank (14), between the hydrogen production chamber (3) and the hydrogen production solution storage tank (17), and between the oxygen production chamber (5) and the oxygen production solution storage tank (16) to form solution circulation. After operation, the operation speed of the peristaltic pump (15) is dynamically regulated according to the power of the power supply, and the flow rate thereof ensures that the ions in the solution are reacted in an economically maximized manner.

4. The iron-based liquid flow decoupled water electrolysis hydrogen production system capable of reducing the starting voltage according to claim 1, characterized in that: A deaerator (18) is provided between the oxygen-producing solution storage tank (16) and the hydrogen-producing solution storage tank (17). The deaerator (18) connects the oxygen-producing solution storage tank (16) and the hydrogen-producing solution storage tank (17) into a whole. The hydrogen ions generated in the oxygen-producing chamber (5) are used in the hydrogen-producing chamber (3), thereby forming a material cycle.

5. The iron-based liquid flow decoupled water electrolysis hydrogen production system capable of reducing the starting voltage according to claim 1, characterized in that: The proton exchange membrane (1) is DuPont N117 proton exchange membrane.

6. The iron-based liquid flow decoupled water electrolysis hydrogen production system capable of reducing the starting voltage according to claim 1, characterized in that: The hydrogen-producing electrode (2) is a platinum sheet electrode, and the oxygen-producing electrode (4) is a ruthenium-iridium electrode.

7. The iron-based liquid flow decoupled water electrolysis hydrogen production system capable of reducing the starting voltage according to claim 1, characterized in that: The redox electrode (6) is a heat-treated carbon felt electrode.

8. The iron-based liquid flow decoupled water electrolysis hydrogen production system capable of reducing the starting voltage according to claim 1, characterized in that: The iron ion storage tank (14) contains FeSO4 with a concentration of 1M and H2SO4 with a concentration of 0.5M, and the oxygen production solution storage tank (16) contains H2SO4 with a concentration of 0.5M and Na2SO4 with a concentration of 0.5M.

9. An iron-based liquid flow decoupled water electrolysis method for producing hydrogen with reduced starting voltage, characterized in that: The method is based on an iron-based liquid flow decoupled water electrolysis hydrogen production system capable of reducing the starting voltage according to any one of claims 1 to 8, comprising: The divalent iron ions and the ferric iron solution in the iron ion storage tank (14) enter the redox chamber (7) through the redox electrolyte inlet (8); the divalent iron ions are oxidized to ferric ions in the redox chamber (7) connected to the hydrogen production chamber (3); the hydrogen ions are reduced to hydrogen in the hydrogen production chamber (3); the ferric iron ions are reduced to divalent iron ions in the redox chamber (7) connected to the oxygen production chamber (5); the water is oxidized to oxygen in the oxygen production chamber (5); the divalent iron ions and the ferric iron solution after the reaction in the redox chamber (7) are returned to the iron ion storage tank (14) through the redox electrolyte outlet (9); the solution in the oxygen production solution storage tank (16) The oxygen-producing solution enters the oxygen-producing chamber (5) through the oxygen-producing solution inlet (12) via the peristaltic pump (15), and a reaction of water generating hydrogen ions and oxygen occurs in the oxygen-producing chamber (5). The generated hydrogen ions and oxygen enter the oxygen-producing solution storage tank (16) through the oxygen-producing solution and the oxygen outlet (13). The solution in the oxygen-producing solution storage tank (16) is deoxygenated by the deaerator (18) and enters the hydrogen-producing solution storage tank (17). The solution in the hydrogen-producing solution storage tank (17) enters the hydrogen-producing chamber (3) through the hydrogen-producing solution inlet (10) via the peristaltic pump (15). A reaction of hydrogen ions being reduced to hydrogen occurs in the hydrogen-producing chamber (3), and the generated hydrogen enters the hydrogen-producing solution storage tank (17) through the hydrogen-producing solution and the hydrogen outlet (11).

10. The method for producing hydrogen by iron-based liquid flow decoupled water electrolysis with reduced starting voltage according to claim 9, characterized in that: In the redox chamber (7) connected to the hydrogen production chamber (3), a reaction occurs in which divalent iron ions are oxidized to trivalent iron ions: Fe 2+ =e - +Fe 3+ , the hydrogen ion is reduced to hydrogen gas in the hydrogen production chamber (3): 2H + +2e - =H2, the overall reaction of the hydrogen production step is: 2H + +2Fe 2+ =2Fe 3+ +H2; the redox chamber (7) connected to the oxygen producing chamber (5) undergoes a reaction in which trivalent iron ions are reduced to divalent iron ions: Fe 3+ +e - =Fe 2+ , water is oxidized to oxygen in the process of hydrogen and oxygen production (5): 2H2O=O2+4H + +4e - , the overall reaction of the oxygen-generating step is: 4Fe 3+ +2H2O=2Fe 2+ +O2+4H + ; The overall reaction is: 2H2O=O2+2H2.

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