A dual positive iron air battery coupled with a fuel cell hydrogen recovery power generation system, comprehensive energy efficiency evaluation method and application

Abstract

The application discloses a kind of dual positive pole iron air cell and fuel cell coupling's by-product hydrogen recovery power generation system and comprehensive energy efficiency evaluation method and application, belong to new energy storage technology field.The system includes dual positive pole iron air cell, hydrogen evolution gas collection unit, gas-liquid separation and drying purification unit, buffer hydrogen storage unit, flow control unit, fuel cell power generation unit, load unit and data acquisition and control unit.Dual positive pole iron air cell uses the structure that discharge air positive pole and charging oxygen evolution positive pole are independent of each other, and by-product hydrogen generated in charging process is sent into fuel cell anode to generate electricity after being collected, separated, dried and stabilized.Data acquisition and control unit calculates system comprehensive energy efficiency according to iron air cell charging energy, discharging energy, by-product hydrogen volume or flow, fuel cell output voltage and output current.The application converts by-product hydrogen evolution side reaction generated in iron air cell charging process from energy loss into available electric energy.

Description

Technical Field

[0001] This invention relates to the fields of metal-air batteries, fuel cells, hydrogen energy recovery and utilization, and new energy storage technologies. In particular, it relates to a by-product hydrogen recovery and power generation system coupled with a dual-positive-electrode iron-air battery and a fuel cell, a comprehensive energy efficiency evaluation method, and its application. Background Technology

[0002] Iron-air batteries possess advantages such as abundant iron resources, low cost, high safety, high theoretical energy density, and environmental friendliness, making them promising for applications in long-term energy storage, backup power, and low-cost electrochemical energy storage. Iron-air batteries typically use iron or iron oxides as the negative electrode active material and an air electrode as the positive electrode. During discharge, iron oxidation and oxygen reduction reactions occur on the air electrode, while the corresponding reverse reactions occur during charging.

[0003] In traditional iron-air batteries, the air electrode must undertake both the oxygen reduction reaction during discharge and the oxygen evolution reaction during charging. Because the oxygen reduction and oxygen evolution reactions have different requirements for catalysts, pore structures, wettability, and the gas-liquid-solid three-phase interface, a single air electrode is prone to increased polarization, catalyst layer degradation, and decreased mass transfer performance during repeated charge-discharge cycles. Existing technologies have proposed solutions that functionally separate the discharge air cathode and the charging oxygen evolution cathode. Adopting a dual-cathode structure helps reduce charging polarization, improve air electrode stability, and increase battery energy efficiency.

[0004] However, hydrogen evolution is an unavoidable side reaction in iron-air batteries during charging and resting. This side reaction consumes some of the charging capacity, reducing the effective charging ratio and battery energy efficiency. Furthermore, if the byproduct hydrogen accumulates disorderly inside or outside the battery, it can pose safety hazards. Current research and applications typically consider hydrogen evolution as a side reaction that needs to be suppressed, but there is a lack of systematic plans for collecting, metering, and reusing the unavoidably generated byproduct hydrogen.

[0005] Fuel cells can directly convert the chemical energy of hydrogen into electrical energy, featuring high energy conversion efficiency and clean operation. Therefore, if the byproduct hydrogen generated during the charging process of iron-air batteries can be safely collected, purified, and fed into fuel cells for power generation, the energy that would otherwise be lost in side reactions can be reused, thereby improving the overall energy efficiency of the iron-air battery system.

[0006] Existing patent CN101728598A discloses an integrated power supply combining a metal-oxygen battery and a hydrogen-oxygen fuel cell. Although it mentions the utilization of by-product hydrogen, it adopts a traditional single-air electrode structure. During charging, oxygen evolution and oxygen reduction occur on the same electrode, leading to increased electrode polarization and accelerated catalyst layer decay. Furthermore, the hydrogen evolution by-reaction products contain a large amount of oxygen and electrolyte mist, resulting in low hydrogen purity, which directly affects the power generation efficiency and lifespan of the fuel cell. Simultaneously, this prior art does not perform gas-liquid separation and drying purification of the by-product hydrogen, nor does it establish a comprehensive energy efficiency evaluation method for the coupled system, making it difficult to fully assess the actual contribution of by-product hydrogen recovery to the overall system energy efficiency.

[0007] Currently, there is a lack of a comprehensive energy efficiency evaluation method for a byproduct hydrogen recovery and power generation system based on dual-cathode iron-air batteries, capable of simultaneously realizing iron-air battery charging and discharging, quantitative analysis of battery hydrogen evolution side reactions, byproduct hydrogen collection and purification, fuel cell power generation, and system energy efficiency calculation. Therefore, it is necessary to propose a dual-cathode iron-air battery coupled with a fuel cell system and its comprehensive energy efficiency evaluation method. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a byproduct hydrogen recovery and power generation system coupled with a dual-positive-electrode iron-air battery and a fuel cell, a comprehensive energy efficiency evaluation method, and its application. This invention collects, separates, purifies, buffers, stabilizes, and controls the flow of byproduct hydrogen generated during the charging process of the dual-positive-electrode iron-air battery, and then inputs it into the fuel cell power generation unit, thereby realizing the electrical utilization of the byproduct hydrogen. Simultaneously, a comprehensive energy efficiency evaluation method is established. This invention transforms the unavoidable hydrogen evolution side reaction during the charging process of the iron-air battery from energy loss into usable electrical energy, and achieves the safe collection, quantitative utilization, and system energy efficiency evaluation of byproduct hydrogen.

[0009] The technical means employed in this invention are as follows: A byproduct hydrogen recovery and power generation system coupled with a dual-positive-electrode iron-air battery and a fuel cell includes a dual-positive-electrode iron-air battery, a hydrogen evolution gas collection unit, a gas-liquid separation unit, a drying and purification unit, a buffer hydrogen storage unit, a flow control unit, a fuel cell power generation unit, a load unit, and a data acquisition and control unit.

[0010] The dual-positive-electrode iron-air battery includes a battery casing, an iron negative electrode, a discharge air positive electrode, a charging oxygen evolution positive electrode, an electrolyte, and a circuit switching unit. The discharge air positive electrode and the charging oxygen evolution positive electrode are functionally separate. The discharge air positive electrode is used for the oxygen reduction reaction during the discharge process of the iron-air battery, and the charging oxygen evolution positive electrode is used for the oxygen evolution reaction during the charging process of the iron-air battery. The circuit switching unit is used to connect the charging oxygen evolution positive electrode and the iron negative electrode to form a charging circuit in the charging state, and to connect the discharge air positive electrode and the iron negative electrode to form a discharge circuit in the discharging state. A hydrogen-oxygen isolation partition is provided inside the battery casing. The hydrogen-oxygen isolation partition divides the gas phase space in the upper part of the battery casing into a hydrogen evolution zone above the corresponding iron negative electrode and an oxygen evolution zone above the corresponding charging oxygen evolution positive electrode, realizing the separate export of hydrogen and oxygen. The hydrogen evolution gas collection unit is connected to the gas evolution region of the dual-positive-electrode iron-air battery and is used to collect by-product hydrogen generated during charging or resting of the iron-air battery. The oxygen evolution region is provided with an independent exhaust channel. Specifically, the hydrogen evolution region refers to the top gas phase space near the iron negative electrode surface and above the electrolyte surface inside the battery casing. The collection port of the hydrogen evolution gas collection unit is located on the top cover plate of the battery casing and faces the area above the iron negative electrode to ensure that the hydrogen generated on the iron negative electrode side during charging or resting rises naturally due to the density difference and enters the collection port. The gas-liquid separation unit is used to remove electrolyte droplets entrained in the by-product hydrogen, the drying and purification unit is used to remove water vapor and alkaline droplets, the buffer hydrogen storage unit is used for temporary storage and voltage stabilization, and the flow control unit is used to regulate the flow rate of hydrogen entering the fuel cell anode.

[0011] The fuel cell power generation unit consumes byproduct hydrogen and generates electricity, with its output connected to a load unit or an energy testing unit. The data acquisition and control unit collects parameters such as the iron-air battery charging voltage, charging current, discharging voltage, discharging current, fuel cell output voltage, fuel cell output current, byproduct hydrogen volume, gas flow rate, temperature, and pressure. The hydrogen evolution gas collection unit, gas-liquid separation unit, drying and purification unit, buffer hydrogen storage unit, and flow control unit are sequentially connected to the anode inlet of the fuel cell power generation unit via pipelines. The data acquisition and control unit collects operating parameters of the iron-air battery and fuel cell and calculates the overall system energy efficiency.

[0012] Furthermore, the charging oxygen evolution positive electrode is one or more of the following: nickel mesh electrode, nickel foam electrode, stainless steel mesh electrode, nickel-based catalytic electrode, or conductive porous electrode with oxygen evolution catalytic function. The discharge air positive electrode and the charging oxygen evolution positive electrode are arranged parallel to each other on the same side of the iron negative electrode, and an insulating structure is provided between the two positive electrodes.

[0013] The hydrogen evolution gas collection unit includes one or more of the following: a sealed gas collection hood, a gas guide pipeline, a water seal structure, a one-way valve, a flame arrester, and a pressure relief structure. The hydrogen evolution gas collection unit is fastened to the top of the hydrogen evolution zone and is used to collect and safely export by-product hydrogen generated on the iron negative electrode side or in the upper space of the battery.

[0014] Furthermore, the gas-liquid separation unit is used to remove electrolyte droplets entrained in the by-product hydrogen, the drying and purification unit is used to remove water vapor and alkaline mist droplets from the by-product hydrogen, and the buffer hydrogen storage unit is used to stabilize the pressure, temporarily store, and buffer the flow of the by-product hydrogen.

[0015] Furthermore, the fuel cell power generation unit is a proton exchange membrane fuel cell, an alkaline fuel cell, a solid oxide fuel cell, or other fuel cells that use hydrogen as fuel; the output terminal of the fuel cell power generation unit is connected to a load unit or an energy testing unit.

[0016] Furthermore, the data acquisition and control unit includes one or more of the following: voltage sensor, current sensor, gas flow meter, pressure sensor, temperature sensor, hydrogen concentration sensor, and controller, for recording charging energy, discharging energy, by-product hydrogen volume, fuel cell output power, and safety status.

[0017] On the other hand, the present invention also discloses a method for evaluating the comprehensive energy efficiency of the dual-positive-electrode iron-air battery and fuel cell coupling system of the aforementioned system, including the following steps: S1, connecting the charging circuit through the circuit switching unit to perform constant current charging on the dual-positive-electrode iron-air battery, recording the charging voltage and charging current throughout the process, and calculating the charging input energy E. ch ; S2. During the charging process, the by-product hydrogen generated in the hydrogen evolution zone is exported through the hydrogen evolution gas collection unit, and then undergoes gas-liquid separation, drying and purification treatment in sequence. It is then stored in the buffer hydrogen storage unit for temporary storage, and the total volume of by-product hydrogen under standard conditions is recorded at the same time. S3. Based on the by-product hydrogen production rate and the IV characteristic curve of the fuel cell, determine the operating current of the fuel cell, ensuring that the operating current does not exceed the theoretical limit current corresponding to the by-product hydrogen supply rate; use a flow control unit to supply the by-product hydrogen to the anode of the fuel cell power generation unit at a set flow rate, and introduce air or oxygen into the cathode; record the fuel cell's output voltage, output current, and operating time, and calculate the fuel cell's output electrical energy E. FC ; S4. After charging is complete, the discharge circuit is switched on via the circuit switching unit to perform constant current discharge of the iron-air battery until the set cutoff voltage. The discharge voltage and discharge current are recorded, and the discharge output energy E is calculated. dis ; S5, based on the charging input energy E ch Discharge output energy Edis With the output power E of the fuel cell FC Calculate the overall energy efficiency η of the system sys .

[0018] Furthermore, the overall energy efficiency η sys Calculate η using the following formula: sys =(E dis +E FC ) / E ch ×100%, where E ch E provides energy input for charging a dual-positive-electrode iron-air battery. dis For the discharge output energy of a dual-positive-electrode iron-air battery, E FC E is the electricity generated after the byproduct hydrogen enters the fuel cell. FC =∫U FC I FC dt, U FC I is the output voltage of the fuel cell. FC t represents the fuel cell output current, and t represents the fuel cell operating time. The theoretically convertible electricity from by-product hydrogen is expressed as Q. H2 =2Fn H2 Calculate, where F is the Faraday constant, n H2 The amount of by-product hydrogen is calculated from the gas volume, temperature, and pressure, or obtained by integrating the gas flow rate.

[0019] Furthermore, the operating current of the fuel cell is determined based on the IV curve of the fuel cell and the by-product hydrogen supply rate, so that the operating current of the fuel cell is not greater than the theoretical limit current corresponding to the by-product hydrogen supply rate. The method also includes calculating the by-product hydrogen recovery efficiency η. rec η rec =E FC / E H2 ×100%, where E H2 The low calorific value of by-product hydrogen, the theoretical electrochemical energy of fuel cells, or the chemical energy of hydrogen selected according to preset standards.

[0020] The comprehensive energy efficiency evaluation method includes: recording the charging input energy E of the dual positive electrode iron-air battery. ch Record the discharge output energy E of the dual-positive-electrode iron-air battery. dis Byproduct hydrogen is fed into the fuel cell and the fuel cell output electrical energy E is recorded. FC According to η sys =(E dis +E FC ) / E ch Calculate the overall energy efficiency of the system by multiplying by 100%.

[0021] On the other hand, the system and method of the present invention can be applied in long-term energy storage, backup power, low-carbon energy systems, laboratory battery performance evaluation, quantitative analysis of side reactions in iron-air batteries, and fuel cell coupled power generation.

[0022] Compared with the prior art, the present invention has the following advantages: 1. This invention transforms the byproduct hydrogen generated during the charging process of an iron-air battery from a traditional energy loss into usable fuel for the fuel cell. In existing iron-air battery technology, hydrogen evolution byproducts are considered a negative factor reducing charging efficiency and are typically suppressed by adding hydrogen evolution inhibitors. This invention changes this technical approach, converting the unavoidable byproducts of hydrogen evolution into usable energy, thereby improving the overall energy utilization rate of the system.

[0023] 2. This invention adopts a dual-positive-electrode iron-air battery structure, which separates the functions of the discharge oxygen reduction electrode and the charging oxygen evolution electrode. The discharge air positive electrode mainly undertakes the oxygen reduction reaction, while the charging oxygen evolution positive electrode mainly undertakes the oxygen evolution reaction. This avoids the problems of increased polarization, catalyst layer decay and decreased mass transfer performance of a single air electrode during repeated charging and discharging, and helps to reduce charging polarization and improve the stability of the air electrode.

[0024] 3. This invention incorporates units for gas-liquid separation, drying and purification, buffer hydrogen storage, flow control, one-way valves, flame arresters, and hydrogen monitoring to ensure the safe removal of by-product hydrogen. The gas-liquid separation and drying and purification units remove electrolyte droplets, water vapor, and alkaline mist, improving hydrogen purity and meeting the fuel gas requirements of fuel cells. The buffer hydrogen storage unit achieves pressure stabilization and flow buffering, improving system operational stability. This contributes to enhancing the safety and stability of the by-product hydrogen utilization process.

[0025] 4. This invention proposes a comprehensive energy efficiency evaluation method based on the charging energy, discharging energy, and output power of the iron-air battery and fuel cell, which can be used for quantitative analysis of side reactions in iron-air batteries and performance evaluation of battery-fuel cell coupling systems. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This diagram shows the structure of a dual-positive-electrode iron-air battery coupled with a fuel cell.

[0028] Figure 2This diagram illustrates the reaction zone and byproduct hydrogen collection in a dual-positive-electrode iron-air battery. Detailed Implementation

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0032] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0033] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0034] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0035] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0036] like Figure 1 As shown, this embodiment discloses a by-product hydrogen recovery and power generation system coupled with a dual-positive-electrode iron-air battery and a fuel cell, including a dual-positive-electrode iron-air battery, a hydrogen evolution gas collection unit, a gas-liquid separation unit, a drying and purification unit, a buffer hydrogen storage unit, a flow control unit, a fuel cell power generation unit, a load unit, and a data acquisition and control unit.

[0037] The internal structure of the dual-positive-electrode iron-air battery mainly consists of an iron negative electrode, an alkaline separator, a nickel oxygen evolution electrode, a KOH electrolyte chamber, and an air electrode. Externally, it is pressed and sealed by an acrylic plate and a silicone gasket. The iron negative electrode, located on one side of the battery, is the main active electrode for storing and releasing electrical energy. The pouch-type iron negative electrode contains iron-based oxides, graphite conductive agents, functional additives, and binders. The separator, an alkaline separator with interconnected micropores, is positioned between the iron negative electrode and the nickel electrode. Its main functions include: preventing direct contact between the iron negative electrode and the nickel positive electrode to avoid internal short circuits; and allowing OH- ions from the KOH electrolyte to pass through. - Migration occurs through micropores; diffusion of reaction products from the iron anode to the positive electrode is reduced; self-discharge and chemical corrosion caused by oxygen permeation to the iron anode are decreased. The membrane itself does not participate in the main electrochemical reactions, but it has a significant impact on ion transport, internal impedance, and operational safety. An independent nickel electrode is arranged on the other side of the membrane as the charging positive electrode. During charging, the nickel electrode undertakes the oxygen evolution reaction, producing oxygen. This separates the oxygen evolution function, originally performed by the air electrode, thus avoiding the air electrode being exposed to a high potential and oxygen bubble erosion environment for extended periods.

[0038] The discharge air electrode is located on the other side of the casing, with one side in contact with the KOH electrolyte and the other side in contact with the outside air. The discharge air positive electrode can be an air electrode with oxygen reduction catalysis, and the charging oxygen evolution positive electrode can be a nickel mesh electrode, a foamed nickel electrode, or other oxygen evolution catalytic electrodes. The iron negative electrode can be an iron powder electrode, an iron sheet electrode, an iron oxide composite electrode, or a porous iron-based electrode.

[0039] During discharge, the positive air electrode and the negative iron electrode form a working circuit. Oxygen undergoes an oxygen reduction reaction at the positive air electrode, while oxidation occurs at the negative iron electrode, generating electrical energy. During charging, the positive oxygen electrode and the negative iron electrode form a charging circuit. The negative iron electrode undergoes a reduction reaction, while oxygen evolution occurs at the positive charging electrode. Simultaneously, hydrogen evolution occurs as a side reaction at the negative iron electrode, producing hydrogen as a byproduct.

[0040] In this embodiment, a gas collection space is provided on the upper part of the battery casing, and the gas collection space is connected to the gas-liquid separation unit through a gas guide pipe. The gas-liquid separation unit can adopt a condensation type, gravity sedimentation type, cyclone type, or packing type structure to remove electrolyte droplets entrained in hydrogen gas. The drying and purification unit can adopt a desiccant, alkaline mist absorption material, microporous filter, or a combination of these structures to reduce the content of water vapor and alkaline mist droplets in hydrogen gas.

[0041] The dried and purified byproduct hydrogen enters the buffer hydrogen storage unit. The buffer hydrogen storage unit can be a water-sealed gas collection bottle, a flexible gas bag, a low-pressure hydrogen storage tank, or other low-pressure buffer container. A flow control unit is installed after the buffer hydrogen storage unit. The flow control unit can include one or more of the following: needle valve, mass flow controller, rotor flow meter, electronic valve, or micro gas pump, to control the flow rate of hydrogen input to the fuel cell anode.

[0042] The fuel cell power generation unit can be selected from proton exchange membrane fuel cells, alkaline fuel cells, or solid oxide fuel cells depending on the actual application. Air or oxygen is introduced into the fuel cell cathode, and hydrogen produced as a byproduct from a dual-cathode iron-air battery is introduced into the anode. The fuel cell output is connected to a load unit or an energy testing unit, and a data acquisition and control unit records the fuel cell output voltage and current.

[0043] like Figure 2 As shown, the dual-cathode iron-air battery structurally separates the discharge air positive electrode and the charging oxygen evolution positive electrode. This structure allows the discharge air positive electrode to primarily handle the oxygen reduction reaction, while the charging oxygen evolution positive electrode primarily handles the oxygen evolution reaction, thereby reducing the multi-functional burden on a single air electrode during repeated charge-discharge processes. A hydrogen byproduct extraction channel is provided at the top of the battery or on the iron negative electrode side to extract the hydrogen gas produced by the hydrogen evolution side reaction.

[0044] The workflow of this system is as follows: (1) Start the charging circuit of the dual positive electrode iron-air battery and open the gas outlet pipeline valve of the hydrogen evolution gas collection unit at the same time. (2) The by-product hydrogen generated during the charging process is successively removed by the gas-liquid separation unit to remove electrolyte droplets, and by the drying and purification unit to remove water vapor and alkaline droplets, and then enters the buffer hydrogen storage unit for temporary storage; (3) When the hydrogen pressure in the buffer hydrogen storage unit reaches the preset start-up pressure threshold, the flow control unit automatically turns on and sends hydrogen into the fuel cell anode at a set flow rate; air or oxygen pressurized by an air pump is simultaneously introduced into the fuel cell cathode. (4) After the fuel cell output voltage stabilizes, connect the load unit to realize continuous power generation of by-product hydrogen; (5) After the iron-air battery is fully charged, continue to send all the remaining hydrogen in the buffer hydrogen storage unit into the fuel cell until the pressure drops to the preset termination pressure threshold and then shut down the system.

[0045] Example 1 This embodiment discloses a comprehensive energy efficiency evaluation process based on a dual-positive-electrode iron-air battery coupled with a fuel cell. The dual-positive-electrode iron-air battery was continuously charged for 100 h under a constant current charging condition of 50 mA, with a charging input of 5 Ah; during this charging process, 840 mL of by-product hydrogen was collected, and the average hydrogen evolution rate was 8.4 mL / h.

[0046] Byproduct hydrogen is fed into the fuel cell anode after gas-liquid separation, drying, purification, and buffering / voltage stabilization. The effective area is 0.785 cm². 2Taking a fuel cell as an example, with a hydrogen flow rate of 8.4 mL / h, based on the estimation of complete electrochemical utilization of hydrogen, it can support a fuel cell output current of approximately 18.4 mA, corresponding to a current density of approximately 0.023 A / cm². 2 The operating point voltage can be estimated to be approximately 1.07 V based on the fuel cell IV curve, therefore the fuel cell output power is approximately 0.020 W.

[0047] If byproduct hydrogen is continuously supplied for 100 hours, the theoretical output energy of the fuel cell is approximately 1.97 Wh. If the discharge output energy of this dual-positive-electrode iron-air battery is 3.80 Wh and the charging input energy is 7.31 Wh, then the overall energy efficiency of the system can be calculated according to η. sys The calculation is (3.80+1.97) / 7.31×100%, yielding approximately 78.9%. If the chemical energy of by-product hydrogen is used for ideal recovery evaluation, the ideal comprehensive energy efficiency can be calculated separately according to the preset hydrogen energy calculation standard.

[0048] Example 2 This embodiment discloses another comprehensive energy efficiency evaluation process based on a dual-positive-electrode iron-air battery coupled with a fuel cell. The dual-positive-electrode iron-air battery was continuously charged for 25 hours under a constant current of 200 mA, with a charging input of 5 Ah; during this charging process, 590 mL of by-product hydrogen was collected, and the average hydrogen evolution rate was 23.6 mL / h.

[0049] The byproduct hydrogen is collected, separated, dried, and buffered before being fed into the same fuel cell power generation unit. At a hydrogen flow rate of 23.6 mL / h, based on the assumption of complete electrochemical utilization of hydrogen, it can support a fuel cell output current of approximately 51.7 mA, corresponding to a current density of approximately 0.066 A / cm³. 2 The operating point voltage can be estimated to be approximately 1.05 V based on the fuel cell IV curve, therefore the fuel cell output power is approximately 0.054 W.

[0050] If byproduct hydrogen is continuously supplied for 25 hours, the theoretical output energy of the fuel cell is approximately 1.36 Wh. If the discharge output energy of this dual-positive-electrode iron-air battery is 3.64 Wh and the charging input energy is 8.95 Wh, then the overall energy efficiency of the system can be calculated according to η. sysCalculated as (3.64+1.34) / 8.95×100%, approximately 55.6% is obtained. This result indicates that while the hydrogen evolution rate per unit time is higher under higher charging current conditions, the total charging time is shorter. The total amount of by-product hydrogen and recoverable electrical energy still need to be comprehensively evaluated considering charging current, charging time, and the rate of hydrogen evolution side reactions. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A byproduct hydrogen recovery and power generation system coupled with a dual-positive-electrode iron-air battery and a fuel cell, characterized in that, It includes a dual-positive-electrode iron-air battery, a hydrogen evolution gas collection unit, a gas-liquid separation unit, a drying and purification unit, a buffer hydrogen storage unit, a flow control unit, a fuel cell power generation unit, a load unit, and a data acquisition and control unit; The dual-positive-electrode iron-air battery includes a battery casing, an iron negative electrode, a discharge air positive electrode, a charging oxygen evolution positive electrode, an electrolyte, and a circuit switching unit. The discharge air positive electrode and the charging oxygen evolution positive electrode are functionally separate. The discharge air positive electrode is used for the oxygen reduction reaction during the discharge process of the iron-air battery, and the charging oxygen evolution positive electrode is used for the oxygen evolution reaction during the charging process of the iron-air battery. The circuit switching unit is used to connect the charging oxygen evolution positive electrode and the iron negative electrode to form a charging circuit in the charging state, and to connect the discharge air positive electrode and the iron negative electrode to form a discharge circuit in the discharging state. A hydrogen-oxygen isolation partition is provided inside the battery casing. The hydrogen-oxygen isolation partition divides the gas phase space in the upper part of the battery casing into a hydrogen evolution zone above the corresponding iron negative electrode and an oxygen evolution zone above the corresponding charging oxygen evolution positive electrode, realizing the separate export of hydrogen and oxygen. The hydrogen evolution gas collection unit is connected to the hydrogen evolution region of the dual positive electrode iron-air battery and is used to collect the by-product hydrogen generated during the charging or resting process of the iron-air battery; the oxygen evolution region is provided with an independent exhaust channel. The hydrogen evolution gas collection unit, gas-liquid separation unit, drying and purification unit, buffer hydrogen storage unit, flow control unit, and anode inlet of fuel cell power generation unit are connected in sequence via pipelines; the data acquisition and control unit is used to collect the operating parameters of the iron-air battery and fuel cell and calculate the overall energy efficiency of the system.

2. The system according to claim 1, characterized in that, The charging oxygen evolution positive electrode is one or more of the following: nickel mesh electrode, nickel foam electrode, stainless steel mesh electrode, nickel-based catalytic electrode, or conductive porous electrode with oxygen evolution catalytic function. The discharge air positive electrode and the charging oxygen evolution positive electrode are arranged parallel to each other on the same side of the iron negative electrode, and an insulating structure is provided between the two positive electrodes.

3. The system according to claim 1, characterized in that, The hydrogen evolution gas collection unit includes one or more of the following: a sealed gas collection hood, a gas guide pipeline, a water seal structure, a one-way valve, a flame arrester, and a pressure relief structure. The hydrogen evolution gas collection unit is fastened to the top of the hydrogen evolution zone and is used to collect and safely export by-product hydrogen generated on the iron negative electrode side or in the upper space of the battery.

4. The system according to claim 1, characterized in that, The gas-liquid separation unit is used to remove electrolyte droplets entrained in the by-product hydrogen, the drying and purification unit is used to remove water vapor and alkaline mist droplets from the by-product hydrogen, and the buffer hydrogen storage unit is used to stabilize the pressure, temporarily store, and buffer the flow of the by-product hydrogen.

5. The system according to claim 1, characterized in that, The fuel cell power generation unit is a proton exchange membrane fuel cell, an alkaline fuel cell, a solid oxide fuel cell, or other fuel cells that use hydrogen as fuel; the output terminal of the fuel cell power generation unit is connected to a load unit or an energy testing unit.

6. The system according to claim 1, characterized in that, The data acquisition and control unit includes one or more of the following: voltage sensor, current sensor, gas flow meter, pressure sensor, temperature sensor, hydrogen concentration sensor, and controller, used to record charging energy, discharging energy, by-product hydrogen volume, and fuel cell output power.

7. A method for evaluating the comprehensive energy efficiency of a dual-positive-electrode iron-air battery and fuel cell coupling system based on the system described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. The charging circuit is connected through the circuit switching unit to perform constant current charging on the dual positive electrode iron-air battery. The charging voltage and charging current are recorded throughout the process, and the charging input energy E is calculated. ch ; S2. During the charging process, the by-product hydrogen generated in the hydrogen evolution zone is exported through the hydrogen evolution gas collection unit, and then undergoes gas-liquid separation, drying and purification treatment in sequence. It is then stored in the buffer hydrogen storage unit for temporary storage, and the total volume of by-product hydrogen under standard conditions is recorded at the same time. S3. Based on the by-product hydrogen production rate and the IV characteristic curve of the fuel cell, determine the operating current of the fuel cell, ensuring that the operating current does not exceed the theoretical limit current corresponding to the by-product hydrogen supply rate; use a flow control unit to supply the by-product hydrogen to the anode of the fuel cell power generation unit at a set flow rate, and introduce air or oxygen into the cathode; record the fuel cell's output voltage, output current, and operating time, and calculate the fuel cell's output electrical energy E. FC ; S4. After charging is complete, the discharge circuit is switched on via the circuit switching unit to perform constant current discharge of the iron-air battery until the set cutoff voltage. The discharge voltage and discharge current are recorded, and the discharge output energy E is calculated. dis ; S5, based on the charging input energy E ch Discharge output energy E dis With the output power E of the fuel cell FC Calculate the overall energy efficiency η of the system sys .

8. The method according to claim 7, characterized in that, Overall energy efficiency η sys Calculate η using the following formula: sys =(E dis +E FC ) / E ch ×100%, where E ch E provides energy input for charging a dual-positive-electrode iron-air battery. dis For the discharge output energy of a dual-positive-electrode iron-air battery, E FC E is the electricity generated after the byproduct hydrogen enters the fuel cell. FC =∫U FC I FC dt, U FC I is the output voltage of the fuel cell. FC t represents the fuel cell output current, and t represents the fuel cell operating time. The theoretically convertible electricity from by-product hydrogen is expressed as Q. H2 =2Fn H2 Calculate, where F is the Faraday constant, n H2 The amount of by-product hydrogen is calculated from the gas volume, temperature, and pressure, or obtained by integrating the gas flow rate.

9. The method according to claim 8, characterized in that, The operating current of the fuel cell is determined based on the IV curve of the fuel cell and the by-product hydrogen supply rate, so that the operating current of the fuel cell is not greater than the theoretical limit current corresponding to the by-product hydrogen supply rate. The method also includes calculating the by-product hydrogen recovery efficiency η. rec η rec =E FC / E H2 ×100%, where E H2 The low calorific value of by-product hydrogen, the theoretical electrochemical energy of fuel cells, or the chemical energy of hydrogen selected according to preset standards.

10. The application of the system according to any one of claims 1 to 6 or the method according to any one of claims 7 to 9 in long-term energy storage, backup power supply, low-carbon energy system, laboratory battery performance evaluation, quantitative analysis of side reactions in iron-air batteries, and fuel cell coupled power generation.

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