Preparation method and electrode system of hydrogel electrode for freeze-induced ion directional diffusion

Abstract

This invention discloses a method for preparing a hydrogel electrode and electrode system for freeze-induced directional ion diffusion, belonging to the field of electrochemistry. The method comprises: constructing a hydrogel layer on the surface of the electrode catalyst layer to form a water blocking zone, which prevents the flow and leakage of free water while ensuring the transport of ions required for the electrochemical reaction. This method solves the problem of liquid leakage that can occur after long-term use of gas diffusion electrodes for gas-liquid-solid three-phase reactions, achieves directional ion transport, and improves the efficiency of electrode gas transport. The method is particularly suitable for various electrochemical systems involving gas-liquid-solid three-phase reactions.

Description

Technical Field

[0001] The present invention relates to the field of electrochemistry, and more specifically to a method for preparing a hydrogel electrode for freeze-induced ion directional diffusion and an electrode system. Background Art

[0002] In the field of electrochemistry, we have found the following technical problems:

[0003] A gas diffusion electrode, typically composed of a gas diffusion layer and a catalyst layer, is an electrode system characterized by porosity, a certain degree of water resistance, good electrical conductivity, a high active surface area, and high catalytic activity. Under operating conditions, the gas and electrolyte are in equilibrium within the micropores of the gas diffusion electrode, forming a stable gas-liquid-solid three-phase interface, where electrochemical reactions occur under certain potential conditions. However, in CO2 mineralization battery systems, two-phase flow occurs on both sides of the electrode (the gas diffusion layer side is in direct contact with the reactant gas, and the catalyst layer side is in direct contact with the electrode liquid). The flow of the electrode liquid across the electrode surface generates a pressure drop, which is related to factors such as the fluid flow pattern, flow rate, and fluid properties. Capillary action in the electrode microporous layer increases the liquid phase volume fraction within the microporous layer, causing the gas channels within the original microporous layer to be occupied by the liquid phase, making it difficult for the reactant gas to reach the catalyst surface, resulting in a decrease in electrolytic performance.

[0004] When a through-type water channel network is formed inside the electrode, the electrolyte will leak to the gas side. From a macroscopic perspective, it manifests as water leakage in the gas diffusion electrode system, resulting in a "water surge" phenomenon. The "water surge" of the electrode will not only reduce the electrochemical performance of the entire battery system, but will also bring various salt ions in the electrolyte into the electrode microporous layer, causing damage to the channels within the electrode microporous layer. In addition, the "inter-flow" of fluids in the gas-liquid two-phase flow zone greatly increases the design difficulty of the device and greatly reduces the stability of the battery system during long-term operation.

[0005] The "water surge" phenomenon is primarily due to the presence of interwoven, interwoven hydrophilic and hydrophobic channels within the microporous layer and catalytic layer of the gas diffusion layer. Water seeps through the hydrophilic channels, while in the hydrophobic channels, under applied pressure, water preferentially enters the larger hydrophobic pores, forming a water network. In the battery, the flow of the electrode liquid phase causes a pressure drop on the electrode surface, and the resistance generated by the local space within the device creates horizontal pressure in the electrode liquid. This accelerates the water surge process in the electrode system.

[0006] To improve the drainage performance of gas diffusion, the gas diffusion layer is generally treated with hydrophobic PTFE to improve the water resistance of the electrode gas diffusion layer, so that the surface and pores of the gas diffusion layer will not be blocked by liquid water. However, due to the poor conductivity of PTFE, and the addition of excessive PTFE will reduce the porosity of the gas diffusion layer, resulting in a decrease in mass transfer performance and reduced electrode electrochemical performance. Moreover, the water resistance of the gas diffusion electrode continues to decline with the use of the electrode system. Taking the fuel cell electrode system with three-phase reaction as an example, with long-term use, the hydrophilicity of the gas diffusion layer surface becomes increasingly stronger, and the concentration polarization during fuel cell operation increases significantly. This is due to the detachment of the PTFE coating, the accumulation of hydrophilic impurities, and the change in the porosity distribution of the gas diffusion layer as the electrode ages. In fact, people have conducted many improvement studies around the problem of water management in gas diffusion electrodes. For example, adding a microporous hydrophobic layer to the single gas diffusion layer and constructing a double-layer gas diffusion layer. However, the double-layer structure still has the problem of water flooding in the base layer, and the electrode life and performance are also limited. In addition, there will be a pore boundary at the junction of multiple layers. When running at high current, the mass transfer driving force is large, and water vapor is easily accumulated at the junction, affecting the mass transfer of the gas diffusion electrode. Summary of the Invention

[0007] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for preparing a hydrogel electrode for freeze-induced ion directional diffusion and an electrode system, which can solve the liquid leakage phenomenon that occurs after long-term use of the gas-liquid-solid three-phase reaction gas diffusion electrode, realize directional ion transport, and improve the efficiency of electrode gas transport, and is particularly suitable for various electrochemical systems with gas-liquid-solid three-phase reactions. In addition, the hydrogel electrode of the present invention can also achieve multi-directional regulation of the performance of the gel layer by matching different directions of freezing gradient induction and selecting different salting-out liquid systems, avoiding the problem of electrode "flooding" caused by long-term contact between the electrode liquid and the gas diffusion electrode catalyst layer, resulting in a decrease in system efficiency, and improving the service life of the electrode. In addition, the presence of the hydrogel layer between the electrolyte and the solid catalyst layer can realize the conversion of interfacial free water to bound water, avoid "water surge", and rely on the directional ion channels constructed inside the hydrogel layer to enhance the transport efficiency of ions and improve the performance of the electrode system.

[0008] The object of the present invention is achieved through the following solutions:

[0009] A method for preparing a hydrogel electrode for freeze-induced ion directional diffusion comprises the following steps:

[0010] Step 1: Pre-coat a layer of polymer precursor solution evenly on the catalyst layer, set a freezing temperature gradient to induce controlled solidification of the polymer solution. During the solidification process, the polymer chains are squeezed by the growth of ice crystals, forming an oriented micron-scale pore structure;

[0011] Step 2: Immerse the electrode after solidification of the hydrogel layer in a salt solution to assist in thawing. Under the influence of the hydrophilic group, the surface tension between the polymer chain and the water molecules changes. At this time, there are multiple interactions between the lyophilic ions, polymer chains and water in the system. These interactions are used to fix and enhance the polymer chain structure in the hydrogel. The polymer solution undergoes a three-phase change of liquid-solid-gel, free water is converted into bound water, and the directional freezing induction and salting-out effect construct ion transport channels inside the gel.

[0012] Furthermore, the freezing temperature gradient is set to induce controlled solidification of the polymer solution. During the solidification process, the polymer chains are squeezed by ice crystal growth to form an oriented micron-scale pore structure, which specifically includes the following sub-steps:

[0013] Construct an oriented structure parallel to the diffusion direction in the gel layer: The direction perpendicular to the plane of the square gel layer is selected as the direction of the freezing temperature gradient. Under the action of this temperature gradient, the water inside the precursor solution grows into ice crystals along this direction. Taking the ion diffusion direction as a reference, the structure finally formed in the gel layer is an oriented porous structure parallel to the diffusion direction.

[0014] Furthermore, the freezing temperature gradient is set to induce controlled solidification of the polymer solution. During the solidification process, the polymer chains are squeezed by ice crystal growth to form an oriented micron-scale pore structure, which specifically includes the following sub-steps:

[0015] Construct an oriented structure perpendicular to the diffusion direction in the gel layer: The direction parallel to the plane of the square gel layer is selected as the direction of the freezing temperature gradient. Under the action of this temperature gradient, the water inside the precursor solution grows into ice crystals along this direction. Taking the ion diffusion direction as a reference, the structure finally formed in the gel layer is an oriented fibrous structure perpendicular to the diffusion direction.

[0016] Furthermore, the precursor solution includes any one of polyvinyl alcohol (PVA) solution, chitosan, sodium alginate, and gelatin.

[0017] Furthermore, the setting of freezing temperature gradient induction includes any one of uniform random freezing, parallel orientation freezing, and vertical orientation freezing.

[0018] Furthermore, the cations in the salt solution include Na + , K + NH4 + , Ca 2+ Any one of; the anion in the salt solution includes citrate, SCN - 、ClO4 - , I - 、NO3 - Br- Any of the ions.

[0019] A hydrogel electrode system for cryo-induced ion directional diffusion, comprising:

[0020] Gas diffusion layer, catalyst layer and hydrogel layer;

[0021] The gas diffusion layer is in direct contact with the reaction gas, and the gas diffuses into the interior of the electrode system through the macroporous base layer and the microporous layer under the action of the concentration gradient; the hydrogel layer is a semi-solid gel and is in direct contact with the electrode liquid. The free water in the electrolyte cannot freely pass through the hydrogel layer to diffuse out of the electrode system under pressure and concentration gradients. There are ion channels inside the hydrogel layer, and the ion channels are used to transport the ions in the electrode liquid to the catalytic layer for reaction, thereby using the hydrogel layer to realize the conversion of free water into bound water; the catalytic layer adsorbs the reaction gas diffused from the gas diffusion layer and the ions transported by the hydrogel layer, and is in direct contact with the electrode liquid; the catalytic layer is attached with a catalyst, which provides reaction sites for the gas adsorbed by the gas diffusion layer and the ions transferred by the hydrogel layer and catalyzes the reaction, and the products after the reaction undergo further diffusion under the concentration gradient.

[0022] Furthermore, the gas diffusion layer is a type of hydrophobic porous medium material, including a macroporous base layer and a microporous layer.

[0023] Furthermore, the catalytic layer is arranged in the anode electrode system of the CO2 mineralization battery system.

[0024] Furthermore, the hydrogel layer is used to establish a "water blocking zone" between the electrode liquid and the catalytic layer, which can effectively avoid the problem of electrode flooding caused by the pressure difference of the two-phase flow on both sides of the electrode and the capillary phenomenon; and the properties of the hydrogel layer can be controlled by changing the process parameters of directional freezing and salting-out treatment, thereby broadening the scope of application of the electrode system.

[0025] The beneficial effects of the present invention include:

[0026] (1) The present invention uses temperature gradient as the driving force and prepares a hydrogel gas diffusion electrode through the synergistic effect of directional freezing and salting-out effect. Microscopic ordered channels are constructed in the hydrogel layer through directional freezing, and the structural stability of the gel layer is further enhanced by salting-out treatment, and the transport rate of ions is increased. The prepared hydrogel layer is flexible and has a certain mechanical strength, and can exist stably in a three-phase environment. In addition, the structure and properties of the hydrogel layer of the electrode system can be regulated by changing the process parameters. The present invention verifies the mass transfer effect of hydrogel layers with different structures on ions and free water, realizes the preparation and regulation of high-performance hydrogel composite electrodes, and can solve the risk of electrode flooding.

[0027] (2) The present invention prepares a directional freezing and salting-out hydrogel gas diffusion electrode. The core innovative idea is to create a hydrogel layer on the electrode surface to achieve ion transport across the gel layer and form a water block to achieve "water surge prevention". The electrode preparation method of the present invention utilizes the synergistic effect of directional freezing and salting-out effect to in situ self-grow a conductive hydrogel electrode layer with certain mechanical strength and microscopic order on the surface of the gas diffusion electrode catalyst layer, thereby constructing a three-layer electrode system with gas diffusion layer-catalytic layer-hydrogel layer. The free water at the contact interface between the hydrogel layer and the solution is induced to transform into bound water, thereby solving the risk of water flooding in the gas diffusion layer, and relying on the microscopic ordered channels of the gel layer to achieve efficient directional diffusion of ions and enhance ion transport.

[0028] (3) The concept of the hydrogel electrode proposed in the present invention is based on the existence of a CO2 mineralization battery system in which the electrode is "flooded", resulting in a loss of electrode life and electrode failure. However, the entire electrode of the present invention is an innovative improvement based on the traditional gas diffusion electrode, which is universal and can be used in a variety of electrochemical systems with gas-liquid-solid three-phase reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1a Schematic diagram of the hydrogel electrode system prepared for targeted cryo-salting out;

[0031] Figure 1b Diagram of the hydrogel electrode system structure prepared for directional freeze-salting;

[0032] Figure 2 This is a flow chart of the preparation method of Example 1 of the present invention;

[0033] Figure 3 Schematic diagram of the structure formed in the gel layer being an oriented porous structure parallel to the diffusion direction;

[0034] Figure 4 Schematic diagram of the structure formed in the gel layer being an oriented fibrous structure perpendicular to the diffusion direction;

[0035] Figure 5 It is the ion chromatography test and calculation results;

[0036] Figure 6 To verify the waterproof effect of the prepared hydrogel layer;

[0037] Figure 7 To verify the electrochemical performance of the hydrogel gas diffusion electrode;

[0038] Figure 8 is the water content data at different swelling times;

[0039] Figure 9 Characterization of the mechanical properties of the hydrogel layer;

[0040] In the figure, 1-gas diffusion layer; 2-catalytic layer; 3-hydrogel layer; 4-reaction gas; 5-electrode liquid. DETAILED DESCRIPTION

[0041] All features disclosed in all embodiments in this specification, or steps in all methods or processes implicitly disclosed, except for mutually exclusive features and / or steps, can be combined and / or expanded or replaced in any manner.

[0042] This invention proposes an effective strategy for addressing the aforementioned technical issues: constructing a hydrogel layer on the surface of the electrode catalyst layer to form a water-blocking zone. This prevents the flow and leakage of free water while ensuring the transport of ions required for the electrochemical reaction. Hydrogels are a class of highly hydrophilic polymers with a three-dimensional network structure, formed by physical or chemical crosslinking of gel monomers. They exhibit high water absorption and retention, as well as excellent structural designability and functional adjustability.

[0043] The high-performance power generation hydrogel electrode with freeze-induced directional ion diffusion proposed in the present invention essentially utilizes the synergistic effect brought about by directional freezing technology and the salting-out effect of polymer solutions. Under the induction of the directional freezing temperature gradient, the liquid water in the polymer solution is controlled to solidify, and the polymer chains are squeezed out by the ice crystals, forming enrichment areas with the ice crystals. During the salting-out process, the ice crystals inside the solid melt, and the solid ice crystals formed by the polymer solution become a flexible and elastic hydrogel. Under the action of directional freezing, a directional pore structure is formed inside the gel. Salting-out further enhances the stability of the internal structure of the electrode hydrogel layer and the ion transport performance. The hydrogel electrode and preparation method solve the risk of electrode flooding and realize directional ion transport by self-growing a high-performance hydrogel layer on the surface of the electrode catalyst layer.

[0044] Specifically, first, a layer of polymer precursor solution (such as polyvinyl alcohol) is uniformly coated on the original gas diffusion electrode catalyst layer. Under the induction of freezing temperature gradient, the polymer solution is controlled to solidify, and the polymer chain is squeezed by ice crystal growth, forming an oriented micron-scale pore structure. Secondly, the electrode with the gel layer solidified is immersed in a salt solution (such as NaOH) to assist in thawing and is exposed to hydrophilic OH. -The surface tension between the polymer chains and water molecules changes due to the influence of the liquid phase. Multiple interactions between lyophilic ions, polymer chains, and water coexist in the system. These interactions stabilize and strengthen the polymer chain structure within the hydrogel. The polymer solution undergoes a three-phase transition from liquid to solid to gel, with free water converted to bound water. Directed freezing induction and salting-out effects construct high-performance ion transport channels within the gel. Compared to traditional gas diffusion electrode systems, this electrode system can simultaneously achieve free water barrier and efficient ion transport.

[0045] The present invention proposes a high-performance hydrogel gas diffusion electrode capable of achieving directional ion diffusion based on directional freezing temperature gradient induction and a preparation method thereof. The structure of the entire electrode mainly includes: ① gas diffusion layer; ② catalyst layer; ③ hydrogel layer. The overall structure is similar to the electrode composition in a hydrogen-oxygen fuel cell system. The gas diffusion layer is in direct contact with the reaction gas, and the catalyst layer is in direct contact with the electrode liquid; the catalyst is attached to the catalyst layer, providing reaction sites for the gas adsorbed by the gas diffusion layer and the ions transferred by the hydrogel layer, and catalyzing the reaction. The three-layer electrode system of gas diffusion layer-catalytic layer-hydrogel layer realizes the transformation of free water into bound water with the help of the hydrogel layer, and at the same time has efficient ion transport performance, which can effectively solve the problem that traditional gas diffusion electrodes are easily flooded with water and thus fail during gas-liquid-solid three-phase reactions.

[0046] Furthermore, the gas diffusion layer (GDL) is a hydrophobic porous dielectric material composed of a macroporous base layer (GDB) and a microporous layer (MPL). It lies between the gas flow field and the catalyst layer, acting as a carrier for water vapor transport, heat transfer, and electron conduction, and providing structural support during assembly and operation. The GDL has a thickness ranging from 100 to 400 μm. The base layer is composed of an anisotropic stack of carbon fibers and is in direct contact with the gas. The microporous layer is a mixture of carbon-based powder and a hydrophobic agent and is in direct contact with the catalyst layer. The performance of the GDL material directly affects the electrochemical reaction and battery efficiency, and it also serves as a critical bridge within the entire electrode structure.

[0047] Furthermore, the catalyst layer is a crucial component of the electrode system. For CO2 mineralization battery systems, the catalyst layer in the anode electrode system promotes the hydrogen oxidation reaction, which involves multiple processes such as oxidation reaction, gas diffusion, electron movement, proton movement, and water migration. A good catalyst layer should have good catalytic activity, high proton conductivity, high electron conductivity, and good water management and gas diffusion capabilities.

[0048] Furthermore, the hydrogel layer is the novelty of this electrode system and the difference between this gas diffusion electrode system and other similar electrode systems in terms of water management. By self-growing the hydrogel layer, a "water blocking zone" is established between the electrode liquid and the catalyst layer, which can effectively avoid the problem of electrode flooding caused by the pressure difference of the two-phase flow on both sides of the electrode and the capillary phenomenon. At the same time, the in-situ hydrogel layer prepared by directional freezing-salting out can ensure the directional diffusion of the reaction ions due to its internal microscopically ordered orientation structure and the inherent characteristics of the high water content of the hydrogel, and is in close contact with the catalyst layer, providing rich reaction sites for the gas-liquid-solid three-phase reaction. In this electrode system, the properties of the hydrogel layer can also be controlled by changing the process parameters of the directional freezing and salting out treatment, further broadening the scope of application of the electrode system; in addition, the hydrogel layer also has excellent softness and elasticity, can adapt to different shapes of surfaces, and maintain the stability and reliability of the electrode. These advantages make this electrode system widely applicable to systems with gas-liquid-solid three-phase reactions, such as CO2 mineralization batteries, CO2 electrochemical capture systems, and electrochemical-related sensors with gas-liquid-solid three-phase states.

[0049] like Figure 1a and Figure 1b As shown in the figure, the principle diagram of the hydrogel electrode system prepared by directional freezing salting out proposed by the present invention is as follows: Figure 1b As shown in Figure 1 , the gas diffusion layer 1 is in direct contact with the reactant gas 4. The gas diffuses into the electrode system through the macroporous base layer and microporous layer under the influence of the concentration gradient. The hydrogel layer 3 is in direct contact with the electrode liquid 5. The hydrogel layer 3 is a semisolid gel, preventing free water in the electrolyte from freely diffusing through the hydrogel layer under pressure and concentration gradients. However, ion channels within the hydrogel layer 3 transport ions from the electrode liquid to the catalytic layer for reaction. The catalytic layer 2 is where the electrochemical reaction occurs in the gas diffusion electrode. It adsorbs the reactant gas diffused from the gas diffusion layer and ions transported by the hydrogel layer. Under the action of the catalyst attached to the catalytic layer, the gas and ions react. The reaction products then further diffuse under the concentration gradient. This electrode system, through the blocking effect of the hydrogel layer, induces the conversion of free water into bound water, solving the problem of "flooding" in traditional gas diffusion electrodes while simultaneously achieving directional ion transport and efficient solid-liquid-gas three-phase reactions.

[0050] The solution of the present invention has the following advantages:

[0051] (1) The electrode system of the present invention is different from the traditional gas diffusion electrode water management concept. It forms a free water blocking zone by in-situ self-growing hydrogel layer and solves the problem of easy flooding of traditional gas diffusion electrode system by inducing the conversion of free water on the interface into bound water.

[0052] (2) The ordered internal microstructure of the hydrogel layer of the electrode system of the present invention can regulate ion transport performance. By controlling the directional freezing temperature gradient, the direction of ice crystal growth within the polymer solution during solidification can be changed, thereby changing the microscopic pore structure within the hydrogel layer. In other words, the gel layers prepared under different freezing directions have different microstructures. When ions in the electrode solution diffuse in hydrogel layers with different structures, the mass transfer paths are different and the diffusion flux is different.

[0053] (3) The present invention can change the salting-out environment during the preparation of the hydrogel layer of the system, and can regulate the mechanical strength and ion transport properties of the hydrogel layer. The electrode system after the gel layer is frozen and solidified is immersed in a salt solution for salting-out assisted thawing. Under the influence of different hydrated ions and polymer system environments, there are differences in the interactions between the lyophilic ions, polymer chains and water in the system, and there are also differences in the internal structure and strength of the hydrogel layer. These differences lead to different diffusion fluxes of the hydrogel layer for the same ion.

[0054] (4) The hydrogel layer of the electrode system of the present invention is flexible and elastic, and can also be applied to flexible electrode systems that require gas-liquid-solid three-phase reactions.

[0055] (5) The electrode of the present invention can be adapted to various application environments by improving the gas diffusion layer, catalytic layer and hydrogel layer; the entire electrode system can be designed as a simple small gas diffusion electrode according to needs, or it can be designed into a large-scale integrated system through system design and series and parallel connection.

[0056] (6) The hydrogel layer in the electrode system of the present invention has high water content and hydrophilic properties. Due to the action of the polymer network inside the hydrogel, the flow of free water in the hydrogel is hindered, which can effectively isolate the passage of free water. However, the ion channels inside the hydrogel can induce ion diffusion.

[0057] (7) The polymer solution system used to construct the hydrogel layer in the electrode system of the present invention is interchangeable, and the solutes in the polymer precursor solution include but are not limited to various hydrophilic polymers such as PVA, sodium alginate, and chitosan.

[0058] (8) The solutes of the salting-out solution for salting-out assisted thawing in the electrode system of the present invention are replaceable, and the cations include but are not limited to Na + , K + NH4 + , Ca 2+ Cations such as citrate, anions include but are not limited to citrate, SCN - 、ClO4 - , I - 、NO3 - Br - Anions.

[0059] It should be noted that within the scope of protection defined in the claims of the present invention, the following embodiments can be combined and / or expanded or replaced in any logical way from the above specific implementation methods, such as disclosed technical principles, disclosed technical features or implicitly disclosed technical features.

[0060] In other embodiments, such as the following embodiments, the raw materials and their sources are as follows: analytically pure PVA2099, trisodium citrate, and sodium hydroxide are directly used as experimental raw materials.

[0061] Example 1

[0062] The process of this embodiment is shown in the attached Figure 2 As shown, the system structure is as Figure 1b As shown, this embodiment provides a hydrogel electrode system for cryo-induced ion directional diffusion. The system includes a reactant gas 4 and an electrode liquid 5, which are in direct contact with a gas diffusion layer 1 and a hydrogel layer 3, respectively. Under the influence of a concentration gradient, the gas diffuses into the interior of the electrode system through the gas diffusion layer composed of a macroporous substrate and a microporous layer. Under the influence of the concentration gradient, the reactant ions in the electrode liquid diffuse through the ion channels in the hydrogel layer, transporting the reactant ions to the catalyst layer 2, where they react with the reactant gas at reaction sites on the catalyst layer 2.

[0063] The catalytic layer 2 in this system absorbs the reactant gas 4 diffused from the gas diffusion layer 1 and the ions transported by the hydrogel layer. Under the action of the catalyst attached to the catalytic layer 2, the gas and ions undergo an electrochemical reaction. The reaction products further diffuse under the influence of the concentration gradient and are transported through the gel layer to the electrode solution.

[0064] In this system, the hydrogel layer 3 is a semisolid gel. Free water in the electrode solution cannot diffuse freely through the hydrogel layer 3 toward the catalyst layer under pressure and concentration gradients. Due to directional freezing, a microscopic pore structure forms within the hydrogel layer 3. The subsequent salting-out process further stabilizes the internal structure and stability of the hydrogel layer under the action of ions. Simultaneously, the hydrogel layer reaches swelling equilibrium, remaining in an ion-rich state. In summary, the hydrogel layer 3 acts as both an ion transporter and a water blocker, resolving the issue of "water surge" in gas diffusion electrodes causing electrode system failure and significantly increasing the lifespan and stability of the electrode system.

[0065] In this embodiment, the effective area of ​​the electrode system can be 4cm 2 , the catalyst is a platinum-carbon catalyst.

[0066] In the corresponding preparation method, the specific preparation process is as follows: cut a 2 cm square gas diffusion layer as the electrode system substrate, spray the catalyst on the contact surface with the catalytic layer, and construct the catalytic layer 2. A layer of PVA solution with a mass fraction of 10% is evenly applied on the surface of the catalytic layer 2 to construct the precursor of the hydrogel layer 3. At this time, the entire electrode system is in contact with a copper plate partially immersed in -80°C ethanol. Under the action of the temperature gradient on the surface of the supercooled copper plate, the hydrogel layer 3 quickly solidifies from liquid to solid. Next, the solidified electrode system is immersed in a sodium hydroxide solution with a mass fraction of 50%. In the sodium hydroxide solution, the hydrogel layer 3 thaws and changes from a solid state to a gel state. At the same time, a salting-out effect occurs in the ionic environment. The polymer chains in the hydrogel layer 3 undergo a certain degree of crystallization behavior, and the structure is stabilized and strengthened to a certain extent. As the thawing and salting-out proceed, the gel layer reaches swelling equilibrium in the sodium hydroxide solution.

[0067] Example 2

[0068] This embodiment is a refinement of embodiment 1, and further introduces how to construct an oriented structure parallel to the diffusion direction in the gel layer 3 and a test method for characterizing the ion mass transfer performance of the prepared hydrogel layer. According to the preparation process of embodiment 1, when the electrode system precursor with the attached gel solution is in contact with the surface of the supercooled copper plate, the direction perpendicular to the plane of the square gel layer is selected as the direction of the freezing temperature gradient. Under the action of this temperature gradient, the water inside the PVA solution grows into ice crystals along this direction. Taking the ion diffusion direction as a reference, the structure finally formed in the gel layer is an oriented porous structure parallel to the diffusion direction, such as Figure 3 When ions in the electrode solution diffuse through the oriented porous structure, the mass transfer path is short, the mass transfer resistance is small, and the ion diffusion rate is high, making it suitable for gas-liquid-solid electrochemical three-phase reaction systems with high reaction rate requirements.

[0069] The corresponding preparation method includes the following specific test process: the prepared hydrogel layer is fixed between two liquid phase chambers, the left chamber is deionized water at a certain height, and the right chamber is 0.5 mol / L NaCl solution at the same height. At room temperature and pressure, the Cl in the right chamber is - Under the action of concentration gradient, it diffuses to the left. After a certain period of diffusion, the solution in the left chamber is taken and its Cl is measured using ion chromatography. - According to the thickness and mass transfer area of ​​the hydrogel layer, the Cl content per unit of the hydrogel layer can be calculated. - Transmittance.

[0070] Example 3

[0071] This example is a refinement of Example 1, which further introduces how to construct an oriented structure perpendicular to the diffusion direction in the gel layer and analyzes the ion mass transfer performance of the hydrogel layer prepared in parallel and perpendicular directions (relative to the ion diffusion direction). According to the preparation process of Example 1, when the electrode system precursor is in contact with the surface of the supercooled copper plate, the direction parallel to the plane of the square gel layer is selected as the direction of the freezing temperature gradient. Under the action of this temperature gradient, the water inside the PVA solution grows into ice crystals along this direction. Taking the ion diffusion direction as a reference, the structure finally formed in the gel layer is an oriented fibrous structure perpendicular to the diffusion direction, such as Figure 4 When ions in the electrode solution diffuse through the oriented porous structure, the mass transfer path is long, subject to large mass transfer resistance, and the ion diffusion rate is low, making it suitable for gas-liquid-solid electrochemical three-phase reaction systems with low reaction rate requirements.

[0072] The corresponding preparation method includes the following hydrogel layer ion mass transfer performance analysis process: Figure 5 As shown in the figure, the ion chromatography test and calculation results show that the hydrogel layer prepared under the temperature gradient parallel to the diffusion direction in Example 2 has a higher unit transmittance of 76.48 mg mm cm -2 d -1 The hydrogel layer prepared under the temperature gradient perpendicular to the diffusion direction in Example 3 has a lower unit transmittance of 43.76 mg mm cm -2 d -1 , which is 57.2% of the parallel direction test results. Figure 3 Figure 4 SEM images show that the ion mass transfer performance of the hydrogel layer is related to its internal microstructure, and there is a certain structure-activity relationship.

[0073] Example 4

[0074] This example is to verify the anti-surge effect of the hydrogel layer prepared in Example 1. Figure 6 As shown in the figure, the corresponding preparation method also includes the following specific operation process: the catalyst carbon paper and the hydrogel-catalyst carbon paper are cut to appropriate sizes and clamped in the middle of an H-shaped electrolytic cell. 20mL of clean water is added to one side of the electrolytic cell, and a rubber stopper is installed. The cell is left to stand for 12 hours under hydrostatic pressure, and the carbon paper is observed for water leakage on the other side of the cell. The experimental results show that the catalyst carbon paper clamping device exhibits significant water leakage after 12 hours of standing, while the hydrogel-catalyst carbon paper device does not show any significant water leakage after 12 hours of standing, demonstrating that the prepared hydrogel gas diffusion electrode has excellent water surge resistance.

[0075] Example 5

[0076] This example is to verify the electrochemical performance of the hydrogel gas diffusion electrode in Example 1. Figure 7As shown, the corresponding preparation method also includes the following operational process: using an electrochemical workstation, single-pole hydrogen evolution tests were performed on carbon paper, catalyst carbon paper, and hydrogel-catalyst carbon paper. LSV test results showed that the uncoated catalyst carbon paper had a higher overpotential, and the current was much lower than that of the catalyst carbon paper and hydrogel-catalyst carbon paper at the same voltage. Compared with the best-performing catalyst carbon paper, the performance of the hydrogel-catalyst carbon paper declined slightly, still maintaining a lower overpotential and a higher hydrogen evolution current.

[0077] Comparative Example 6

[0078] The preparation process of this comparative example is basically the same as that of Example 1, except that the salting-out liquid is replaced with trisodium citrate solution of different concentrations, and the swelling behavior of the prepared different hydrogel layers in clean water is compared and studied. The specific operation process is: the electrode system precursor prepared by freezing under a vertical temperature gradient is immersed in clean water, and thawed and salted out in 0.5M, 1.0M, 1.5M, and 2.0M trisodium citrate solutions for 1 day to prepare different hydrogel layers. These different hydrogel layers are immersed in clean water respectively, and the change of their mass with the soaking time is tested using a balance. Combined with the dry weight of the gel layer after air drying, the water content data at different swelling times are calculated. The results are as follows. Figure 8 As shown, in general, the water content of the hydrogel layer prepared by the method of the present invention shows a swelling process in which the water content first increases and then stabilizes during the swelling process, which is limited swelling and shows stability in an aqueous environment. The hydrogel layer prepared using different trisodium citrate solutions has different swelling characteristics in deionized water: as the concentration of the trisodium citrate solution increases, the time for the hydrogel layer to reach swelling equilibrium gradually shortens, and the water content gradually decreases at the same swelling time. This shows that different concentrations of salting-out liquid treatment will also have different effects on the structure of the hydrogel layer. Therefore, the present invention can achieve a certain degree of regulation on the structure and properties of the hydrogel layer by changing the concentration of the salting-out liquid.

[0079] Example 7

[0080] This example characterizes the mechanical properties of the hydrogel layer prepared in Example 3. The corresponding preparation method also includes the following specific operation process: the prepared hydrogel layer is cut into 5 dog bone-shaped splines of similar size, and a universal material testing machine is used to perform a tensile test to obtain the stress-strain data of the hydrogel layer splines, such as Figure 9 The results show that the stress-strain curve data of the hydrogel layer are relatively concentrated, indicating good uniformity of the hydrogel layer. Furthermore, the stress of the five splines ranged from 5.44 to 7.46 MPa, and the elongation at break ranged from 534 to 684%, indicating that the prepared hydrogel layer has good mechanical properties.

[0081] In summary, the high-performance hydrogel electrode system with freeze-induced directional ion diffusion disclosed in the present invention utilizes the synergistic effect of directional freezing and salting-out effect to self-grow a hydrogel layer in situ on the surface of the catalyst layer of the traditional gas diffusion electrode, thereby converting the catalyst layer-electrode liquid contact surface of the traditional gas diffusion electrode system into a catalyst layer-gel layer-electrode liquid, inducing the catalyst layer contact surface to be converted from free water to bound water, and realizing water blocking and ion transport through the hydrogel layer, thereby realizing the "water surge" prevention function of the gas diffusion electrode.

[0082] Secondly, the hydrogel layer produced by the electrode system of the present invention exhibits good swelling stability in clear water and possesses high mechanical properties. The properties of the gel layer can be further manipulated by adjusting parameters such as the direction of the freezing temperature gradient and the salting-out environment. By adjusting the ion transport properties of the gel layer while maintaining water isolation, the gel layer can be adapted to different application environments.

[0083] The above examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. It should be noted that, without departing from the principles of this patent, those skilled in the art may make several improvements and modifications based on the technical solution and patent concept of the present invention, and such improvements and modifications shall also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a hydrogel electrode with freeze-induced ion directional diffusion, characterized in that: The following steps are involved: Step 1: Pre-coat the catalyst layer with a polymer precursor solution, set a freezing temperature gradient to induce controlled solidification of the polymer solution. During the solidification process, the polymer chains are squeezed by ice crystal growth, forming an oriented micron-scale pore structure. Step 2: The electrode after solidification of the hydrogel layer is immersed in a salt solution to assist thawing. The surface tension between the polymer chain and the water molecules changes due to the influence of the hydrophilic group. At this time, multiple interactions between the lyophilic ions, polymer chains and water exist in the system. These interactions fix and strengthen the polymer chain structure in the hydrogel. The polymer solution undergoes a liquid-solid-gel three-phase change. Free water is converted into bound water. The directional freezing induction and salting-out effect construct ion transport channels inside the gel. The freezing temperature gradient is set to induce controlled solidification of the polymer solution. During the solidification process, the polymer chains are squeezed by the growth of ice crystals to form an oriented micron-scale pore structure. The method specifically includes the following sub-steps: Constructing an oriented structure parallel to the diffusion direction in the gel layer: The direction perpendicular to the plane of the square gel layer is selected as the direction of the freezing temperature gradient. Under the action of this temperature gradient, the water inside the precursor solution grows into ice crystals along this direction. Using the ion diffusion direction as a reference, the structure finally formed in the gel layer is an oriented porous structure parallel to the diffusion direction. or, Construct an oriented structure perpendicular to the diffusion direction in the gel layer: The direction parallel to the plane of the square gel layer is selected as the direction of the freezing temperature gradient. Under the action of this temperature gradient, the water inside the precursor solution grows into ice crystals along this direction. Taking the ion diffusion direction as a reference, the structure finally formed in the gel layer is an oriented fibrous structure perpendicular to the diffusion direction.

2. The method for preparing a hydrogel electrode with freeze-induced ion directional diffusion according to claim 1, characterized in that: The precursor solution includes any one of polyvinyl alcohol (PVA) solution, chitosan, sodium alginate, and gelatin.

3. The method for preparing a hydrogel electrode with freeze-induced ion directional diffusion according to claim 1, characterized in that: The freezing temperature gradient induction setting includes any one of uniform random freezing, parallel orientation freezing, and vertical orientation freezing.

4. The method for preparing a hydrogel electrode with freeze-induced ion directional diffusion according to claim 1, characterized in that: The cations in the salt solution include Na + , K + NH4 + , Ca 2+ Any one of; the anion in the salt solution includes citrate, SCN - 、ClO4 - , I - 、NO3 - Br - Any of the ions.

5. A hydrogel electrode system for cryo-induced ion directional diffusion, characterized in that: The method for preparing a hydrogel electrode for performing freeze-induced ion directional diffusion according to claim 1 further comprises: Gas diffusion layer, catalyst layer and hydrogel layer; The gas diffusion layer is in direct contact with the reaction gas, and the gas diffuses into the interior of the electrode system through the macroporous base layer and the microporous layer under the action of the concentration gradient; the hydrogel layer is a semi-solid gel and is in direct contact with the electrode liquid. The free water in the electrolyte cannot freely pass through the hydrogel layer to diffuse out of the electrode system under pressure and concentration gradients. There are ion channels inside the hydrogel layer, and the ion channels are used to transport the ions in the electrode liquid to the catalytic layer for reaction, thereby using the hydrogel layer to realize the conversion of free water into bound water; the catalytic layer adsorbs the reaction gas diffused from the gas diffusion layer and the ions transported by the hydrogel layer, and is in direct contact with the electrode liquid; the catalytic layer is attached with a catalyst, which provides reaction sites for the gas adsorbed by the gas diffusion layer and the ions transferred by the hydrogel layer and catalyzes the reaction, and the products after the reaction undergo further diffusion under the concentration gradient.

6. The hydrogel electrode system for cryo-induced ion directional diffusion according to claim 5, characterized in that: The gas diffusion layer is a type of hydrophobic porous medium material, comprising a macroporous base layer and a microporous layer.

7. The hydrogel electrode system for cryo-induced ion directional diffusion according to claim 5, characterized in that: The catalytic layer is arranged in the anode electrode system of the CO2 mineralization battery system.

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