A seawater electrochemical carbon capture system and method based on hydrogen cycling

Abstract

This invention relates to the fields of electrochemical engineering and carbon capture technology, and discloses a seawater electrochemical carbon capture system and method based on hydrogen cycle. The system includes an electrolyte circulation unit, a hydrogen circulation unit, a four-chamber electrolytic cell, and an anion exchange membrane and gas diffusion electrode disposed therein. This invention utilizes the anodic hydrogen oxidation reaction and the cathode hydrogen evolution reaction to construct a low-voltage hydrogen cycle for efficient separation of acidic and alkaline components in seawater for carbon capture. By employing a hydrophobic gas diffusion electrode with high bubble point pressure, a large-diameter obliquely cut exhaust pipe at the cathode to achieve zero back pressure exhaust, and a fault diagnosis and recovery method based on voltage monitoring, the invention systematically solves engineering problems such as HOR reaction failure and voltage spikes caused by gas-liquid mass transfer conflict and pressure sensitivity. This invention features low energy consumption, stable operation, and a compact structure, making it particularly suitable for mobile island platforms such as wind and solar power plants, and can utilize surplus electrical energy for efficient carbon capture.

Description

Technical Field

[0001] This invention relates to the fields of electrochemical engineering and carbon capture technology, specifically a technical solution for low-voltage seawater electrochemical carbon capture using hydrogen circulation and pressure management, and particularly a seawater electrochemical carbon capture system and method based on hydrogen circulation. Background Technology

[0002] With the acceleration of global industrialization, the concentration of carbon dioxide (CO2) in the atmosphere continues to rise, and the resulting climate change problems such as the greenhouse effect and ocean acidification have become serious challenges facing all mankind. To achieve the temperature control targets set by the Paris Agreement, countries are vigorously developing carbon capture, utilization, and storage (CCUS) technologies. Against this backdrop, directly capturing CO2 from the ocean, which covers 71% of the Earth's surface, is considered a highly promising negative carbon technology pathway because it does not consume land resources and can alleviate ocean acidification. Seawater, as a vast carbonate buffer system, dissolves a large amount of inorganic carbon (in the form of HCO3-). - and CO3 2- It exists in various forms, and its total carbon content is about 50 times that of the atmosphere. By adjusting the local pH value of seawater through electrochemical methods, this chemical equilibrium can be disrupted, converting dissolved inorganic carbon into CO2 gas for release and collection, or alkaline seawater can be prepared to absorb CO2 from the atmosphere.

[0003] Although the principle of carbon capture based on electrochemical pH swing has been validated, existing technologies have encountered a series of insurmountable technical bottlenecks when applied to seawater scenarios, preventing the system from operating stably and efficiently for extended periods. One promising approach is to construct a hydrogen cycle system, utilizing the hydrogen oxidation reaction (HOR) at the anode to replace the energy-intensive oxygen evolution reaction (OER) in traditional water electrolysis. Theoretically, this could significantly reduce the electrolyzer voltage from >1.8V to <1.0V. However, this approach faces the following technical challenges when moving towards engineering practice:

[0004] First, existing technologies suffer from gas-liquid mass transfer conflicts and electrode failure. The anodic HOR reaction requires smooth hydrogen diffusion to the catalyst layer surface of the gas diffusion electrode (GDL). However, in a seawater electrolyte environment, the porous GDL is easily flooded. Surfactants, impurities, and pressure pulses generated by peristaltic pumping in seawater continuously impact and breach the hydrophobic barrier of the GDL. Once the electrolyte penetrates the electrode and enters the gas chamber, it forms a liquid film in the electrode pores, completely blocking the hydrogen transport channels to the reaction site, leading to gas resistance. Simultaneously, the overflowing electrolyte dissolves or contaminates the catalyst, causing Pt / C catalyst poisoning or high-potential oxidation deactivation, ultimately preventing the HOR reaction from proceeding.

[0005] Secondly, existing technologies suffer from reaction interruptions and voltage spikes due to pressure sensitivity, as hydrogen cycle systems are extremely sensitive to pressure. The hydrogen evolution reaction (HER) at the cathode continuously produces hydrogen. If the exhaust path for this hydrogen is obstructed (e.g., the exhaust pipe is too narrow, bent, or the outlet is liquid-sealed), a small positive pressure (back pressure) will form in the cathode chamber. Because the internal chambers are coupled through porous electrodes and membrane structures, the cathode back pressure is indirectly transmitted to the anode chamber via the electrolyte. A small increase in back pressure in the anode chamber severely hinders the diffusion of H2 molecules to the anode catalyst surface, causing a sharp deterioration in HOR reaction kinetics. At this point, in order to maintain the set current, the system will spontaneously seek other reaction pathways, forced to switch from the low-potential HOR (approximately 0.0 V vs. HER) to the high-potential OER (>1.23 V vs. HER) or the chlorine evolution reaction (CER). This will cause the tank voltage to spike instantly from the expected <1.0V to 1.8V or even higher, resulting in a surge in energy consumption, which contradicts the original intention of low-energy design and accelerates the corrosion failure of electrodes and films.

[0006] Secondly, the system is subject to dynamic fluctuations. In practical engineering, peristaltic pumps or diaphragm pumps used to transport seawater generate periodic pressure pulses. Even if the pressure fluctuation amplitude is small (e.g., ±0.5 kPa), once it exceeds the "bubble point pressure" of the hydrophobic GDL (i.e., the minimum pressure difference required for the liquid to overcome surface tension and penetrate the electrode), it will cause intermittent electrolyte leakage. This "breathing" microleakage not only contaminates the gas chamber but also leads to unstable local dry and wet states on the electrode surface, causing uneven current distribution and local overheating, further damaging the electrode life.

[0007] Finally, existing technologies lack engineered fault diagnosis and recovery methods, and current research largely remains at the level of small-scale, steady-state, and ideal laboratory testing. When faults such as voltage spikes occur, researchers typically intervene only through inefficient means such as cutting off the power supply and rewetting the electrodes, lacking the ability to diagnose the root cause of the fault in real time and a systematic, automatically executable engineered stress management and recovery strategy. This prevents the system from operating autonomously and stably for extended periods under dynamic and non-ideal real-world seawater conditions.

[0008] Therefore, those skilled in the art urgently need a seawater electrochemical carbon capture system and method based on hydrogen cycling. Summary of the Invention

[0009] The core technical problem addressed by this invention is how to stably and continuously maintain a low-voltage, high-efficiency hydrogen cycle under dynamic and complex operating conditions of seawater electrolyte, in order to solve the reaction failure problem caused by gas-liquid mass transfer conflict and pressure sensitivity.

[0010] For those skilled in the art, solving the aforementioned core technical problems is of paramount necessity and importance within the industry.

[0011] First, solving the aforementioned core technical problems is key to overcoming the energy consumption bottleneck. The primary determining factor for the large-scale application of electrochemical carbon capture technology is energy consumption. The HOR / HER cycle is theoretically the optimal path to significantly reduce energy consumption, but without solving its engineering stability issues, low energy consumption will remain only a theoretical concept. Overcoming this core problem means achieving stable operation with a cell voltage of <1.0V, thereby reducing the capture power consumption per ton of CO2 from 3-5 MWh using current mainstream technologies (such as membrane separation and temperature-switching adsorption) or conventional electrolysis schemes to below 1 MWh, making electrochemical carbon capture economically feasible.

[0012] Secondly, solving the aforementioned core technical problems is the bridge from "laboratory principles" to "engineering applications": most current research stops at solving chemical problems (such as catalyst selection and membrane material modification), while this invention directly addresses physical and engineering problems (mass transfer, fluid dynamics, and pressure management). Only by solving these "last mile" engineering challenges can this technology move beyond beakers and constant current power supplies and be deployed in real-world scenarios such as ships and islands. Those skilled in the art urgently need a comprehensive engineering solution integrating structural design, operating processes, and fault diagnosis.

[0013] Finally, solving the aforementioned core technical problems is a prerequisite for achieving autonomous and stable system operation. Offshore wind power and photovoltaic power supply scenarios are characterized by fluctuations, and ship operations are also dynamic. A system that cannot adapt to pressure fluctuations or automatically eliminate backpressure interference will frequently shut down and restart in such an environment, rendering it useless. Solving this core problem enables the system to possess anti-interference and self-recovery capabilities, which are prerequisites for achieving unattended, long-term stable operation.

[0014] The technical solution disclosed in this invention should be applied to island mobile platforms or coastal industrial scenarios where space is limited, power sources fluctuate, and operating conditions are complex. Specific scenarios are as follows:

[0015] Island and Offshore Mobile Platforms: This invention is specifically applicable to islands or mobile marine platforms (such as ships and semi-submersible platforms) equipped with renewable energy sources such as wind and solar power. These scenarios typically face challenges such as limited space, highly fluctuating power sources, and high requirements for equipment compactness and reliability. The hydrogen cycle system and integrated four-chamber electrolyzer design of this invention are compact in structure and low in energy consumption. They can effectively utilize the surplus but intermittent green electricity (such as wind and solar power) on islands, converting distributed power resources into high-purity CO2 products, achieving on-site energy consumption and negative carbon emissions.

[0016] Ship Carbon Emission Reduction: The International Maritime Organization (IMO) has established increasingly stringent standards for greenhouse gas emissions from ships. This invention can serve as an onboard carbon capture system for ships. During navigation, the engine cooling system of a ship continuously draws seawater. Utilizing this seawater and surplus electricity or electricity from an installed fuel cell, carbon can be captured through this system. The captured liquid CO2 can be directly stored on board or indirectly achieved through the discharge of alkaline seawater into the ocean, thus helping the shipping industry meet emission reduction regulations.

[0017] Coastal Industrial Carbon Emission Reduction: Coastal thermal power plants, chemical plants, and steel mills are significant sources of CO2 emissions. These enterprises typically have convenient access to seawater resources. This invention can serve as a downstream carbon capture unit, utilizing surplus electricity from the factory or distributed renewable energy to treat incoming seawater and capture CO2, thereby realizing the development of "blue carbon" resources and the circular transformation of industrial parks.

[0018] To address the aforementioned core technical problems, this invention designs a seawater electrochemical carbon capture system and method based on hydrogen cycling. The aim is to construct an electrode and electrolytic cell structure capable of completely separating the gas and liquid phases and resisting electrolyte penetration; a hardware design capable of precisely managing gas path pressure, particularly ensuring smooth discharge of cathode byproduct hydrogen to prevent back pressure accumulation; and a systematic operation and maintenance method capable of monitoring system status, diagnosing "voltage spike" faults, and quickly restoring to a low-voltage HOR-dominated mode.

[0019] To achieve the above objectives, the specific technical solution of the present invention is a seawater electrochemical carbon capture system based on a hydrogen cycle, comprising:

[0020] An electrolyte circulation unit is configured to store and transport seawater electrolyte containing bicarbonate ions; A hydrogen recycling unit, configured to supply and recycle hydrogen;

[0021] A four-chamber electrolytic cell, comprising an anolyte chamber, an anolyte gas chamber, a catholyte chamber, and a catholyte gas chamber;

[0022] An anion exchange membrane is disposed between the anolyte chamber and the catholyte chamber, and is configured to allow chloride ions in the electrolyte to be transported from the catholyte chamber to the anolyte chamber;

[0023] A first gas diffusion electrode is disposed between the anolyte chamber and the anode gas chamber;

[0024] The second gas diffusion electrode is disposed between the cathode liquid chamber and the cathode gas chamber;

[0025] The anode gas chamber is connected to the hydrogen circulation unit, and the anode gas chamber and the cathode gas chamber are respectively connected to the corresponding liquid chambers through the first gas diffusion electrode and the second gas diffusion electrode for gas-liquid separation.

[0026] Preferably, both the first gas diffusion electrode and the second gas diffusion electrode are carbon paper electrodes loaded with Pt / C catalyst that have undergone hydrophobic treatment; the hydrophobic treatment includes impregnation with polytetrafluoroethylene emulsion and high-temperature sintering, so that its bubble point pressure is greater than the maximum gas-liquid chamber pressure difference during system operation.

[0027] Preferably, the electrolyte circulation unit further includes:

[0028] Electrolyte storage tank;

[0029] A peristaltic pump is connected between the electrolyte storage tank and the four-chamber electrolytic cell;

[0030] A pulsation damper is installed on the pipeline between the peristaltic pump and the four-chamber electrolytic cell, and is configured to absorb the pressure pulses generated by the peristaltic pump.

[0031] Preferably, the exhaust pipe of the cathode chamber adopts a large-diameter, short-distance design, with an inner diameter ≥3mm and a length ≤5cm; the outlet end of the exhaust pipe is cut at 45° and fully open to the atmosphere to minimize exhaust resistance and prevent back pressure accumulation.

[0032] Preferably, the system further includes a pressure management module, the pressure management module comprising:

[0033] A large-diameter obliquely cut exhaust pipe is installed at the outlet of the cathode gas chamber;

[0034] A mass flow controller is disposed between the hydrogen circulation unit and the anode chamber and is configured to regulate the flow rate of hydrogen supplied to the anode chamber;

[0035] An optional pressure gauge is available for monitoring the pressure in the gas chamber.

[0036] Preferably, the anion exchange membrane is configured to selectively transport chloride ions to balance the charges of the anode and cathode under dynamic operating conditions where the pH value changes, rather than transporting hydroxide or bicarbonate ions.

[0037] Preferably, the four-chamber electrolytic cell is formed into an integrated module by the main shell, the anion exchange membrane, the first gas diffusion electrode and the second gas diffusion electrode, wherein the anode gas chamber and the cathode gas chamber are completely sealed to the outside, with only hydrogen inlet and outlet remaining.

[0038] Preferably, the system further includes a collection device and a cryogenic storage system; the collection device is connected to the CO2 outlet of the anolyte chamber and is used to strip the released CO2 and collect it through a hollow fiber membrane contactor; the cryogenic storage system is connected to the collection device and is used to perform multi-stage compression and cooling on the collected CO2 for storage in liquid form.

[0039] Preferably, the flow channels of the anolyte chamber and the catholyte chamber are designed as serpentine or parallel flow fields to optimize the contact between the electrolyte and the electrodes and membranes and reduce concentration polarization.

[0040] Preferably, the geometric dimensions of the first gas diffusion electrode and the second gas diffusion electrode are larger than the inner diameter of the sealing gasket to ensure complete coverage of the sealing area and prevent gas-liquid leakage.

[0041] Preferably, the present invention also discloses an electrochemical carbon capture method, which is implemented using the aforementioned system and includes the following steps:

[0042] a. Start the electrolyte circulation unit to allow seawater electrolyte to flow through the anolyte chamber and the cathode chamber, wetting the anion exchange membrane;

[0043] b. Start the hydrogen circulation unit, introduce excess hydrogen into the anode chamber, and ensure system pressure balance through the pressure management module;

[0044] c. When the power is turned on, a hydroxide reaction occurs at the anode to produce H₂. + This lowers the pH of the anolyte chamber, thus removing HCO3- from the seawater. - and CO3 2- It is converted into CO2; at the cathode, a hydrogen evolution reaction occurs to produce OH. - This causes the pH of the cathode liquid chamber to rise, forming alkaline seawater;

[0045] d. Collect CO2 released from the anolyte chamber or use the alkaline seawater in the catholyte chamber for subsequent carbon capture.

[0046] Preferably, the method further includes fault diagnosis and recovery steps:

[0047] When the system voltage rises above the set threshold, the pressure management module prioritizes checking and ensuring unobstructed venting of the cathode chamber to restore the dominant position of the hydroxide reaction at the anode.

[0048] Preferably, the fault diagnosis and recovery steps further include:

[0049] If the voltage does not recover after checking that the cathode chamber is venting smoothly, increase the anode hydrogen flow rate using the mass flow controller to counteract back pressure interference and force the system back to the state dominated by the hydrogen oxidation reaction.

[0050] Preferably, the method further includes system shutdown and electrode protection steps:

[0051] e. First, disconnect the DC power supply to stop the electrolysis reaction;

[0052] f. Maintain continuous hydrogen flow at the anode for a predetermined time to purge and dry the electrolyte remaining on the surfaces of the first gas diffusion electrode and the second gas diffusion electrode;

[0053] g. Finally, stop the electrolyte circulation pump and shut off the hydrogen source.

[0054] Preferably, in the method, the flow rate of hydrogen gas introduced into the anode chamber is more than 5 times the theoretical requirement, forming a positive purging airflow to remove any trace amounts of water vapor that may have seeped in.

[0055] Preferably, the hydrogen required for the hydroxide reaction occurring at the anode in step c is supplied by the hydrogen circulation unit from an external hydrogen source or recovered from the cathode.

[0056] Preferably, the set threshold is 1.3V. When the tank voltage gradually increases from the normal operating voltage of 0.6-0.9V to more than 1.3V, the fault diagnosis and recovery steps are triggered.

[0057] Preferably, the predetermined time is 3-10 minutes, and the hydrogen flow rate is 5-10 sccm to ensure that the electrode surface is fully dry.

[0058] Preferably, the present invention also discloses a method for preparing a gas diffusion electrode, the method being used in the system described above, comprising the following steps:

[0059] The carbon paper substrate is impregnated in a polytetrafluoroethylene emulsion with a concentration of 10%-30%;

[0060] The impregnated carbon paper is sintered at a high temperature of 300°C-400°C to form a hydrophobic layer;

[0061] A Pt / C catalyst was sprayed onto one side of the sintered carbon paper, with a platinum loading of 0.3-1 mg / cm³. 2 ;

[0062] By controlling the impregnation and sintering processes, the bubble point pressure of the final gas diffusion electrode is made greater than 5 kPa. Compared with existing technologies (such as conventional water electrolysis carbon capture or simple HOR / HER two-chamber systems), the technical solution described in this invention has the following non-obvious technical features:

[0063] First, this invention employs a four-chamber electrolytic cell with pressure isolation design, while existing technologies mostly use two- or three-chamber structures, resulting in severe interference between gas and liquid mass transfer. This invention creatively adopts a four-chamber structure of "anolyte chamber / anolyte gas chamber / cathode liquid chamber / cathode gas chamber," utilizing two gas diffusion electrodes (GDLs) and one anion exchange membrane (AEM) to completely physically isolate the gas and liquid paths. This design is not a simple stacking of components; its non-obviousness lies in: by placing the gas and liquid chambers on opposite sides of the GDL and defining a single ion transport path (Cl... - Through AEM, gas reaction (HOR / HER) and ion balance (Cl) were achieved. - The decoupling of migration creates the possibility of independently optimizing the gas path pressure and the liquid path flow field;

[0064] Second, this invention achieves targeted engineering treatment of GDL with "high bubble point pressure," whereas existing technologies only focus on the catalytic activity or basic hydrophobicity of GDL. This invention specifically proposes to impregnate GDL with PTFE emulsion and then sinter it at high temperature, making its bubble point pressure greater than the maximum gas-liquid chamber pressure difference during system operation. The "non-obvious" aspect of this feature is that it clarifies that the selection criterion for GDL is not merely "hydrophobicity," but rather defines a quantitative engineering indicator (bubble point pressure) related to the system operating pressure. This directly links electrode fabrication with system pressure management, providing a reliable threshold for resisting dynamic interference such as peristaltic pump pulses.

[0065] Third, this invention employs a "zero back pressure" engineering design for cathode exhaust, a feature often overlooked in existing technologies. This invention astutely identifies cathode back pressure as the primary cause of anode HOR failure and proposes a low-resistance, open exhaust scheme. Specifically, this includes: using a large-diameter (≥3mm), short-distance exhaust pipe; a 45° bevel at the outlet end; and complete openness to the atmosphere, avoiding insertion below any liquid surface. The underlying technological insight behind this seemingly simple mechanical design lies in recognizing that even minute pressure changes (on the order of cm water columns) can disrupt the balance of the entire electrochemical system; therefore, the core objective of exhaust is to achieve "zero back pressure," rather than simply "gas removal."

[0066] Fourth, this invention constructs a fault diagnosis and self-recovery method based on the "pressure-voltage" correlation. Existing technologies lack diagnostic and recovery methods for HOR failure mechanisms. This invention proposes an innovative operating logic: when a voltage rise exceeding a set threshold is detected, priority is given to checking and ensuring unobstructed venting of the cathode chamber, or increasing the anode hydrogen flow rate to counteract back pressure interference. This differs from the conventional approach of increasing voltage or stopping operation. Its non-obviousness lies in establishing a clear causal chain (impaired cathode venting → back pressure → obstructed anode HOR → voltage surge → switching to OER / CER), and based on this, a rapid and low-cost physical intervention method is proposed (increasing the anode hydrogen purge flow rate to "push open" the back pressure), achieving proactive recovery of the system state.

[0067] Fifth, this invention establishes a "dry purging" process for shutdown protection. To extend the lifespan of critical components such as the GDL and catalyst, this invention designs a specific shutdown procedure: first, power is cut off, then hydrogen gas is continuously supplied to the anode for several minutes to purge and dry the electrolyte remaining on the electrode surface. This is not a simple shutdown procedure; its innovation lies in recognizing that even after electrolysis stops, residual corrosive seawater remaining on the electrode surface for a long time can still cause catalyst contamination or hydrophobic layer degradation due to capillary action and other factors. Using an inert reaction gas (hydrogen) for purging and drying after shutdown is an effective and economical means of protecting the delicate electrochemical interface.

[0068] Compared with existing technologies, the present invention has the following beneficial effects: 1. The present invention can significantly reduce energy consumption and improve economic efficiency. By constructing a stable hydrogen cycle (HOR / HER), it successfully avoids the oxygen evolution reaction (OER) with high overpotential. Under stable operating conditions, the system cell voltage can be maintained below 1.0V (such as 0.8V in the example), which is far lower than the above 1.8V of traditional water electrolysis schemes. Combined with the pressure management module and optimized electrode design, this low voltage state can be maintained for a long time, thereby significantly reducing the power consumption per ton of carbon dioxide captured, making the electrochemical seawater carbon capture technology more commercially competitive;

[0069] 2. This invention exhibits extremely high operational stability and reliability. Through its four-chamber structural design, the application of high bubble point pressure (GDL), and a "zero back pressure" exhaust system, it fundamentally solves the problems of gas-liquid mass transfer conflict and pressure sensitivity. The system can effectively resist peristaltic pump pressure pulses and operating condition fluctuations, avoiding common engineering failures such as electrolyte penetration of electrodes and accumulation of back pressure in the gas chambers, ensuring the continuous and stable conduct of the HOR reaction, and greatly extending the system's continuous operating time and maintenance-free cycle.

[0070] 3. This invention possesses excellent self-diagnosis and rapid recovery capabilities. Based on the fault diagnosis logic of "voltage-pressure" correlation, the system can quickly identify HOR failure caused by back pressure. By prioritizing the unblocking of cathode exhaust or temporarily increasing the anode hydrogen flow rate, a non-destructive, low-cost rapid recovery method is provided, preventing the system from operating in high-potential, high-energy-consumption modes such as OER / CER for extended periods, thus avoiding irreversible damage to the catalyst and membrane.

[0071] 4. The system structure adopted in this invention is compact and highly adaptable to engineering applications. The integrated four-chamber electrolytic cell design integrates multiple functional units into a single unit, resulting in a compact structure, small size, and easy modular expansion. Furthermore, the supporting engineering solutions (such as pulsation dampers and oblique exhaust pipes) utilize mature, low-cost components, facilitating deployment and maintenance in space- and resource-constrained environments such as ships and island platforms.

[0072] 5. This invention can extend the lifespan of key components and reduce maintenance costs. By performing quantitative hydrophobic treatment (high bubble point pressure) on the GDL and designing a scientifically sound shutdown "dry purging" process, it effectively protects the expensive Pt / C catalyst and gas diffusion electrode. This slows down the rate at which the electrode fails due to liquid flooding, contamination, or catalyst oxidation, significantly extending the service life of core components and thus reducing the total cost of ownership (TCO) of the system. Attached Figure Description

[0073] Figure 1 This is a schematic diagram of the system described in this invention;

[0074] Figure 2 This is a schematic diagram of the structure of the four-chamber electrolytic cell described in this invention;

[0075] Figure 3 This is a schematic diagram of the four-chamber electrolytic cell described in this invention;

[0076] Figure 4 This is a flowchart of the electrochemical carbon capture method described in this invention;

[0077] Figure 5 This is a flowchart of the gas diffusion electrode preparation method described in this invention. Detailed Implementation

[0078] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings;

[0079] refer to Figures 1 to 3 ,in Figure 1 A structural block diagram of a hydrogen cycle-based electrochemical carbon capture system for seawater according to one or more embodiments of this application is shown. Figure 2 A detailed structural diagram of the four-chamber electrolytic cell in this system is shown. Figure 3The electrochemical schematic diagram of a four-chamber electrolyzer is shown. This system is mainly applied in space-constrained, power-fluid, and complex operating conditions on island mobile platforms, ships, or coastal industrial settings for the efficient capture of carbon dioxide from seawater. The system includes the following core modules: an electrolyte circulation unit, a hydrogen circulation unit, a four-chamber electrolyzer, an anion exchange membrane (AEM), and a first gas diffusion electrode and a second gas diffusion electrode.

[0080] In one or more embodiments, the electrolyte circulation unit is configured to store and transport a seawater electrolyte containing bicarbonate ions. The unit includes an electrolyte storage tank, a peristaltic pump, and a pulsation damper disposed between the peristaltic pump and a four-chamber electrolytic cell. The pulsation damper absorbs periodic pressure pulses generated by the peristaltic pump, preventing pressure peaks from exceeding the bubble point pressure of the gas diffusion electrode.

[0081] In one or more embodiments, the hydrogen circulation unit is configured to supply and recover hydrogen. It is connected via piping to the anode chamber of a four-chamber electrolyzer and includes a mass flow controller for precisely regulating the flow rate of hydrogen supplied to the anode chamber.

[0082] In one or more embodiments, the four-chamber electrolytic cell is an integrated module comprising a main shell, an anion exchange membrane, a first gas diffusion electrode, and a second gas diffusion electrode. Specifically, the four-chamber electrolytic cell includes: an anolyte chamber, an anolyte chamber, a catholyte chamber, and a catholyte chamber. Wherein:

[0083] The anion exchange membrane is disposed between the anolyte chamber and the catholyte chamber, and is configured to selectively allow chloride ions (Cl-) in the electrolyte to pass through under dynamic operating conditions where the pH value changes. - The charge is transferred from the cathode chamber to the anolyte chamber to balance the charges at the cathode and anode, rather than to transfer hydroxide or bicarbonate ions.

[0084] The first gas diffusion electrode is disposed between the anolyte chamber and the anolyte gas chamber, and the second gas diffusion electrode is disposed between the catholyte chamber and the catholyte gas chamber. The anolyte gas chamber is connected to the hydrogen circulation unit, and the anolyte gas chamber and the catholyte gas chamber are physically isolated from their respective liquid chambers by the first gas diffusion electrode and the second gas diffusion electrode, respectively.

[0085] In one or more embodiments, both the first gas diffusion electrode and the second gas diffusion electrode are carbon paper electrodes supported on a Pt / C catalyst that have undergone hydrophobic treatment. The hydrophobic treatment includes: impregnating the carbon paper substrate in a 10%-30% polytetrafluoroethylene (PTFE) emulsion, followed by high-temperature sintering at 300°C-400°C, so that its bubble point pressure is greater than the maximum gas-liquid chamber pressure difference during system operation. By controlling the impregnation and sintering processes, the final bubble point pressure of the gas diffusion electrode is made greater than 5 kPa, thereby effectively resisting peristaltic pump pulses and liquid chamber pressure fluctuations, and preventing electrolyte penetration.

[0086] In one or more embodiments, the exhaust pipe of the cathode chamber is designed with a large diameter and short distance, with an inner diameter ≥3 mm and a length ≤5 cm; the outlet end of the exhaust pipe is cut at a 45° angle and is completely open to the atmosphere to minimize exhaust resistance and prevent back pressure accumulation. This "zero back pressure" design avoids the accumulation of hydrogen gas generated at the cathode in the chamber, thereby blocking the path of back pressure transmission to the anode chamber that would cause the hydroxide reaction to fail.

[0087] In one or more embodiments, the system further includes a pressure management module. This module includes: a large-diameter oblique exhaust pipe disposed at the outlet of the cathode chamber; a mass flow controller disposed between the hydrogen circulation unit and the anode chamber; and an optional pressure monitoring instrument (such as a U-tube manometer). The mass flow controller is used to temporarily increase the anode hydrogen flow rate (e.g., from the normal 10 sccm to 15-20 sccm) during fault recovery to counteract back pressure disturbances.

[0088] In one or more embodiments, the system may further include a capture device and a cryogenic storage system. The capture device is connected to the CO2 outlet of the anolyte chamber and is used to strip the released CO2 and capture it through a hollow fiber membrane contactor. The cryogenic storage system is connected to the capture device and is used to perform multi-stage compression and cooling on the captured CO2 for storage in liquid form. The conventional design temperature range of the cryogenic storage system is -20℃ to -50℃. This temperature range is primarily used to meet the needs of space-constrained and complex maritime scenarios such as islands, ships, and coastal industries, and also to meet the general technical specifications for cryogenic storage of liquid CO2. The cryogenic storage system is the core terminal unit of the hydrogen cycle-based seawater electrochemical carbon capture system of this invention. It is directly linked to the front-end capture device and is a key closed-loop link in realizing carbon capture from "gas capture" to "stable storage / productization," undertaking the final product processing function of the entire electrochemical carbon capture process.

[0089] It should be noted that the core process of this invention is as follows: the seawater electrolyte undergoes pH adjustment in a four-chamber electrolysis cell, converting bicarbonate / carbonate ions in the seawater into CO2 gas → the capture device performs stripping and membrane capture of CO2 → the cryogenic storage system performs multi-stage compression and cooling on the captured CO2, ultimately storing it in liquid form. Clearly, the cryogenic storage system is the final unit of the entire carbon capture process, realizing the core transformation from "capturing CO2" to "solidifying and storing CO2," thus forming a complete technological closed loop for carbon capture. The target application scenarios for this invention are islands, offshore mobile platforms (ships), and coastal industries—scenarios with limited space and complex operating conditions. The cryogenic storage system can convert gaseous CO2 into liquid, significantly reducing the storage volume of CO2, adapting to the core requirements of compact equipment and space utilization in scenarios such as ships and island platforms, and solving the pain points of large space occupation and difficulty in deployment of gaseous CO2 in confined environments. More importantly, liquid CO2 is a standardized, transportable, usable (chemical raw materials, oil recovery, food processing, etc.), and sealable form in the industrial field. The cryogenic storage system provides a standardized product form for captured CO2, laying the foundation for subsequent carbon utilization, geological storage, or cross-scenario transfer. This allows the technical solution to not only achieve carbon capture but also meet the full-chain requirements of CCUS (carbon capture, utilization, and storage), truly achieving the technical goal of negative carbon emissions.

[0090] Furthermore, the cryogenic storage system solves the problem of CO2 capture, processing, and storage, upgrading the entire technical solution of this invention from a laboratory principle of "capturing CO2" to a complete engineering system that is "capturing, storing, and deployable." This system has the capability to be implemented in real-world scenarios such as ships, islands, and coastal industries, aligning with the practical needs of the International Maritime Organization (IMO) for ship emission reduction, coastal industrial carbon emission reduction, and negative carbon construction on islands. Simultaneously, by using multi-stage compression and cooling to convert CO2 into a liquid state, the density of liquid CO2 is significantly increased compared to gaseous CO2. The storage volume of the same mass of CO2 can be reduced by several times, significantly reducing the space occupied by storage equipment and perfectly adapting to space-constrained deployment scenarios. At the same time, the standardized form of liquid CO2 also significantly reduces the transportation and operational costs of subsequent transfer and utilization. Furthermore, the cryogenic storage system stably seals the captured CO2 in liquid form, preventing the captured CO2 from escaping back into the atmosphere. This fundamentally ensures the effectiveness of carbon capture, allowing the low-energy consumption and stable carbon capture capabilities of the entire technical solution to ultimately translate into tangible negative carbon emission results, truly achieving the core objectives of mitigating ocean acidification and reducing atmospheric carbon concentration.

[0091] In one or more embodiments, the bubble point pressure index of the gas diffusion electrode is correlated with the system operating pressure in the following manner:

[0092] First, measure or estimate the maximum gas-liquid chamber pressure difference during system operation, which is derived from the peak pulse pressure of the peristaltic pump (e.g., ±0.5 kPa) plus the static pressure difference of the liquid column;

[0093] Then, by controlling the PTFE impregnation concentration (e.g., 20%) and sintering temperature (350°C), the bubble point pressure of the electrode (tested using the bubble method) is stabilized to be greater than 5 kPa. This quantitative relationship ensures that under any operating condition, the gas-liquid two-phase interface is firmly locked within the hydrophobic pores of the electrode, achieving a stable three-phase interface that is "permeable only to gas and impermeable to liquid".

[0094] In one or more embodiments, to ensure the sealing integrity of the four-chamber electrolytic cell under dynamic pressure fluctuations, the geometry of the first and second gas diffusion electrodes is designed to be larger than the inner diameter of the sealing gasket (e.g., exceeding it by 2 mm on each side) to ensure that the electrodes completely cover the sealing area. During assembly, the electrodes and gasket form a mechanical seal through the tightening force of the main housing, preventing gas-liquid leakage. This process does not involve software locking but is a physical-level "atomic" sealing operation.

[0095] In one or more embodiments, when the system detects an abnormal voltage increase (e.g., exceeding 1.3V) and determines that the cathode venting is obstructed, the following error handling procedure is executed: First, check whether the cathode venting pipeline is bent or liquid-sealed; if ineffective, temporarily increase the anode hydrogen flow rate to 15-20 sccm through the mass flow controller to use the airflow to resist the back pressure; if still ineffective, trigger the system alarm and perform a safety shutdown (first disconnect the power, then continuously purge with hydrogen for 5 minutes).

[0096] Through the coordinated operation of the above modules, complete separation of the gas and liquid phases and pressure decoupling are achieved, significantly improving the system's operational stability. Actual measurements show that the system can operate stably for extended periods at a tank voltage of approximately 0.8V, avoiding the high-energy-consumption failure mode where the voltage spikes above 1.8V.

[0097] refer to Figure 4 This paper illustrates a schematic flowchart of an electrochemical carbon capture method according to one or more embodiments of this application. The method is applied to the aforementioned hydrogen cycle-based seawater electrochemical carbon capture system, and is particularly suitable for dynamic operating conditions such as mobile platforms on islands or ships. The method includes the following main steps: system startup and wetting, hydrogen introduction and pressure equilibration, electrolysis reaction and pH control, product collection and fault recovery.

[0098] In step a (system startup and wetting), the control unit (such as a PLC or microcontroller) starts the electrolyte circulation unit, allowing simulated seawater (e.g., 0.5 M NaCl + 2.5 mM NaHCO3, pH 8.0) to flow through the anolyte and catholyte chambers at a flow rate of 3 mL / min, wetting the liquid chamber side of the anion exchange membrane (AEM) and the gas diffusion electrode. This step continues for at least 1 minute to ensure sufficient ion conduction of the membrane and electrodes without the formation of trapped air bubbles.

[0099] In step b (hydrogen introduction and pressure balance), the hydrogen circulation unit is started, and excess hydrogen (e.g., 10 sccm, 5 times the theoretical requirement of 2 sccm) is introduced into the anode chamber through the mass flow controller to form a forward purge airflow. At the same time, ensure that the exhaust pipe of the cathode chamber (4 mm inner diameter, 5 cm length, 45° oblique cut) is completely open to the atmosphere so that the hydrogen generated at the cathode can be discharged without back pressure.

[0100] In step c (electrolysis reaction and pH control), the DC power supply is turned on and the current density is set to 6 mA / cm². 2 .at this time:

[0101] At the anode, the hydrogen oxidation reaction (HOR) occurs: H₂ → 2H₂ + + 2e - The generated H + The solution enters the anolyte chamber, lowering its pH from 8.0 to approximately 6.54, thus removing HCO3- from the seawater. - and CO3 2- It is converted into CO2 gas;

[0102] At the cathode, the hydrogen evolution reaction (HER) occurs: 2H₂O + 2e⁻ - → H2 + 2OH - The generated OH - It enters the catholyte chamber, causing the pH of the catholyte chamber to rise to approximately 9.52, forming alkaline seawater.

[0103] In step d (product collection and utilization), CO2 gas released from the anolyte chamber is collected (e.g., via a stripping tower or hollow fiber membrane contactor), or atmospheric CO2 is absorbed using alkaline seawater from the catholyte chamber.

[0104] In one or more embodiments, the electrochemical carbon capture method further includes a fault diagnosis and recovery step. When the system detects that the cell voltage gradually increases from the normal operating value (0.6-0.9V) to exceed a set threshold of 1.3V, the control unit determines that the HOR (Hot Oxide Resonance) has failed (possibly due to cathode back pressure). At this time, the following process is executed:

[0105] First, check if the exhaust pipe of the cathode chamber is unobstructed (e.g., observe if liquid is flowing out or if the pressure gauge reading exceeds 2 cm of water column). If exhaust is found to be obstructed, immediately clear or adjust the exhaust pipe to ensure it is fully open to the atmosphere;

[0106] If the venting is smooth but the voltage has not recovered, the anode hydrogen flow rate is temporarily increased to 15-20 sccm (lasting 30 seconds to 2 minutes) using the mass flow controller. The high-speed airflow is used to counteract any possible slight back pressure, forcing the anode reaction to switch back to HOR dominance.

[0107] After the voltage is restored to around 0.8V, the anode hydrogen flow rate is adjusted back to the normal value of 10 sccm.

[0108] In one or more embodiments, the electrochemical carbon capture method further includes a system shutdown and electrode protection process:

[0109] First, disconnect the DC power supply to stop the electrolysis reaction;

[0110] Secondly, keep the anode hydrogen gas (5-10 sccm) continuously flowing in for 3-10 minutes to purge and dry the electrolyte remaining on the surface of the first gas diffusion electrode and the second gas diffusion electrode, and prevent corrosion or degradation of the hydrophobic layer.

[0111] Finally, stop the electrolyte circulation pump and shut off the hydrogen source.

[0112] In one or more embodiments, the quantitative relationship between pH change and CO2 conversion efficiency in step c is as follows: According to the seawater carbonate equilibrium system, when the pH of the anolyte chamber decreases from 8.0 to 6.54, the HCO3- in dissolved inorganic carbon (DIC) increases. - and CO3 2- The conversion rate to CO2 can reach approximately 90%. By monitoring the pH value at the anolyte outlet in real time (e.g., using an online pH meter), the current density can be dynamically adjusted to maintain optimal acidification. Similarly, when the pH of the catholyte chamber rises above 9.52, its ability to absorb CO2 from the air is significantly enhanced.

[0113] In one or more embodiments, increasing the anode hydrogen flow rate during fault recovery is a "soft" intervention that does not involve hardware reset. To ensure operational safety, the control unit records the current voltage, current, and pressure values ​​before increasing the flow rate and sets a maximum allowable flow rate limit (e.g., 30 sccm) to prevent excessive gas flow from causing a sudden increase in anode chamber pressure and damaging the membrane electrode assembly.

[0114] In one or more embodiments, if the voltage still cannot be restored after the above fault diagnosis and recovery steps are performed (e.g., it remains above 1.3V for more than 2 minutes), the control unit executes the error handling process: terminates the electrolysis operation, records the fault log (including time, voltage curve, hydrogen flow rate, etc.), and issues an audible and visual alarm through the user interface to prompt the operator to perform a manual check.

[0115] Through the coordinated operation of the above steps, stable carbon capture at low voltage (0.8V) under dynamic seawater conditions was achieved, and the system has rapid self-recovery capability in the event of back pressure disturbance, which significantly improves the engineering practicality and long-term operational reliability of the system.

[0116] refer to Figure 5 This paper illustrates a schematic flowchart of a gas diffusion electrode fabrication method according to one or more embodiments of this application. This gas diffusion electrode fabrication method is used to prepare a first gas diffusion electrode and a second gas diffusion electrode in the aforementioned system, and is particularly suitable for seawater electrochemical carbon capture scenarios requiring high bubble point pressure and a stable three-phase interface. The method includes the following main steps: hydrophobic impregnation, high-temperature sintering, catalyst spraying, and bubble point pressure testing.

[0117] In step e (hydrophobic impregnation), a carbon paper substrate is selected (e.g., Toray 060 carbon paper, approximately 190 μm thick, with a porosity of approximately 78%). The carbon paper is completely impregnated in a 20% (mass fraction) polytetrafluoroethylene (PTFE) emulsion for 5-10 minutes to allow the PTFE particles to fully penetrate the microporous structure of the carbon paper. Afterward, the carbon paper is removed and hung to air dry at room temperature for 30 minutes to remove excess emulsion.

[0118] In step f (high-temperature sintering), the dried carbon paper is placed in a muffle furnace and sintered at 350°C for 30 minutes. During sintering, PTFE particles melt and adhere to the carbon fiber surface, forming a uniform hydrophobic coating. By controlling the number of impregnations (e.g., one impregnation yields a bubble point pressure of approximately 3-4 kPa, and two impregnations yield >5 kPa), the final bubble point pressure of the gas diffusion electrode is made greater than 5 kPa.

[0119] In step g (catalyst spraying), a Pt / C catalyst (40% platinum by mass) is sprayed onto the side of the sintered carbon paper (i.e., the side facing the gas chamber). Ultrasonic spraying equipment is used, and the catalyst loading is controlled at 0.3-1 mg / cm³. 2 (Preferred 2 mg / cm) 2 After spraying, dry in an 80°C vacuum drying oven for 2 hours to remove the solvent.

[0120] In one or more embodiments, to improve hydrophobicity and mechanical strength, steps e and f can be repeated 2-3 times (i.e., multiple impregnation-sintering cycles) to achieve a PTFE loading of 20%-30%. At this point, the bubble point pressure can be increased to 8-10 kPa, making it suitable for high pressure differential scenarios.

[0121] In one or more embodiments, the spraying parameters in step g are further optimized: the distance between the nozzle and the carbon paper is maintained at 15 cm, the spray gun moving speed is 5 cm / s, and the nitrogen carrier gas pressure is 0.2 MPa. During the spraying process, the carbon paper is maintained at 80°C by the heating stage to promote rapid drying of the catalyst layer and prevent the PTFE hydrophobic layer from being damaged by the solvent.

[0122] In one or more embodiments, the bubble point pressure is measured as follows: the prepared gas diffusion electrode is fixed in a specially designed fixture, one side is filled with deionized water, and nitrogen gas is introduced into the other side while the pressure is slowly increased. The pressure value at which the first continuous bubble appears on the back of the electrode is recorded as the bubble point pressure. This application requires the bubble point pressure to be greater than the maximum gas-liquid chamber pressure difference during system operation (typically ≤5 kPa), therefore the preparation target is set as a bubble point pressure ≥6 kPa (considering a safety margin).

[0123] In one or more embodiments, to ensure precise matching of electrode dimensions, a die-cutting process is used when cutting the gas diffusion electrode, making the electrode's outer dimensions 2 mm larger on each side than the inner diameter of the sealing gasket. This "over-size" design ensures that the electrode edges are completely pressed against the gasket after assembly, forming a physical seal and preventing gas and liquid leakage from the edges. This step is an atomic operation at the physical level and requires no software lock.

[0124] In one or more embodiments, if the measured bubble point pressure is below 5 kPa during the bubble point pressure test, the electrode is deemed unqualified. In this case, a second impregnation and sintering process can be performed on the electrode to improve its hydrophobicity; if it still fails to meet the requirements, it is scrapped. Electrodes with detached or cracked catalyst layers are also scrapped.

[0125] The above preparation method yielded a gas diffusion electrode with high bubble point pressure (>5 kPa), good hydrophobicity, and high catalytic activity. In practical systems, this electrode effectively resists peristaltic pump pressure pulses and liquid chamber pressure fluctuations, avoiding "liquid flooding" and HOR failure caused by electrolyte penetration, thus providing a key component guarantee for the long-term stable operation of the system at low voltage.

[0126] The above technical solutions only embody the preferred technical solutions of the present invention. Any modifications that may be made by those skilled in the art to certain parts thereof embody the principles of the present invention and fall within the protection scope of the present invention.

Claims

1. A seawater electrochemical carbon capture system based on hydrogen cycle, characterized in that, include: An electrolyte circulation unit is configured to store and transport seawater electrolyte containing bicarbonate ions; a hydrogen circulation unit is configured to supply and recover hydrogen. A four-chamber electrolytic cell, comprising an anolyte chamber, an anolyte gas chamber, a catholyte chamber, and a catholyte gas chamber; An anion exchange membrane is disposed between the anolyte chamber and the catholyte chamber, and is configured to allow chloride ions in the electrolyte to be transported from the catholyte chamber to the anolyte chamber; A first gas diffusion electrode is disposed between the anolyte chamber and the anode gas chamber; The second gas diffusion electrode is disposed between the cathode liquid chamber and the cathode gas chamber; The anode gas chamber is connected to the hydrogen circulation unit, and the anode gas chamber and the cathode gas chamber are respectively connected to the corresponding liquid chambers through the first gas diffusion electrode and the second gas diffusion electrode for gas-liquid separation.

2. The system according to claim 1, characterized in that, Both the first gas diffusion electrode and the second gas diffusion electrode are carbon paper electrodes supported on Pt / C catalysts that have undergone hydrophobic treatment. The hydrophobic treatment includes impregnating the polytetrafluoroethylene emulsion and sintering it at high temperature, so that its bubble point pressure is greater than the maximum gas-liquid chamber pressure difference during system operation.

3. The system according to claim 1, characterized in that, The electrolyte circulation unit further includes: Electrolyte storage tank; A peristaltic pump is connected between the electrolyte storage tank and the four-chamber electrolytic cell; A pulsation damper is installed on the pipeline between the peristaltic pump and the four-chamber electrolytic cell, and is configured to absorb the pressure pulses generated by the peristaltic pump.

4. The system according to claim 1, characterized in that, The exhaust pipe of the cathode chamber adopts a large-diameter, short-distance design, with an inner diameter ≥3mm and a length ≤5cm; the outlet end of the exhaust pipe is cut at 45° and fully open to the atmosphere to minimize exhaust resistance and prevent back pressure accumulation.

5. The system according to claim 1, characterized in that, It also includes a stress management module, which includes: A large-diameter obliquely cut exhaust pipe is installed at the outlet of the cathode gas chamber; A mass flow controller is disposed between the hydrogen circulation unit and the anode chamber and is configured to regulate the flow rate of hydrogen supplied to the anode chamber; An optional pressure gauge is available for monitoring the pressure in the gas chamber.

6. The system according to claim 1, characterized in that, The anion exchange membrane is configured to selectively transport chloride ions to balance the charges at the anode and cathode under dynamic operating conditions where the pH value changes, rather than transporting hydroxide or bicarbonate ions.

7. The system according to claim 1, characterized in that, The four-chamber electrolytic cell is an integrated module consisting of the main shell, the anion exchange membrane, the first gas diffusion electrode, and the second gas diffusion electrode. The anode and cathode gas chambers are completely sealed to the outside, with only hydrogen inlet and outlet open.

8. The system according to claim 1, characterized in that, It also includes collection devices and cryogenic storage systems; The collection device is connected to the CO2 outlet of the anolyte chamber and is used to strip the released CO2 and collect it through a hollow fiber membrane contactor. The cryogenic storage system is connected to the capture device and is used to perform multi-stage compression and cooling on the captured CO2 to store it in liquid form.

9. An electrochemical carbon capture method, wherein the electrochemical carbon capture method is implemented using the system according to any one of claims 1 to 8, characterized in that, Includes the following steps: a. Start the electrolyte circulation unit to allow seawater electrolyte to flow through the anolyte chamber and the cathode chamber, wetting the anion exchange membrane; b. Start the hydrogen circulation unit, introduce excess hydrogen into the anode chamber, and ensure system pressure balance through the pressure management module; c. When the power is turned on, a hydroxide reaction occurs at the anode to produce H₂. + This lowers the pH of the anolyte chamber, thus removing HCO3- from the seawater. - and CO3 2- It is converted into CO2; at the cathode, a hydrogen evolution reaction occurs to produce OH. - This causes the pH of the cathode liquid chamber to rise, forming alkaline seawater; d. Collect CO2 released from the anolyte chamber or use the alkaline seawater in the catholyte chamber for subsequent carbon capture.

10. A method for preparing a gas diffusion electrode, wherein the method is used in the system according to any one of claims 1 to 8, characterized in that, Includes the following steps: The carbon paper substrate is impregnated in a polytetrafluoroethylene emulsion with a concentration of 10%-30%; The impregnated carbon paper is sintered at a high temperature of 300°C-400°C to form a hydrophobic layer; A Pt / C catalyst was sprayed onto one side of the sintered carbon paper, with a platinum loading of 0.3-1 mg / cm³. 2 ; By controlling the impregnation and sintering processes, the bubble point pressure of the final gas diffusion electrode is made to be greater than 5 kPa.

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