Liquid metal three-dimensional porous electrode based on fluidity regulation and preparation method thereof

Abstract

The invention relates to a liquid metal three-dimensional porous electrode based on fluidity regulation and control. The liquid metal three-dimensional porous electrode comprises a three-dimensional porous substrate, the liquid metal layer is arranged on the three-dimensional porous substrate, and the liquid metal layer and the three-dimensional porous substrate form a conductive network; wherein the fluidity of the liquid metal layer can be regulated and controlled through the temperature, and the liquid metal layer can be uniformly coated on the three-dimensional porous matrix in different flowing states, so that based on the setting, the regulation and control effect of the temperature on the fluidity of the liquid metal can be utilized to realize accurate control on an electro-catalysis reaction path; particularly, hydroxylamine is prepared in a high-selectivity manner in a nitrate reduction reaction.

Description

Technical Field

[0001] This invention relates to the fields of functional materials and electrochemical technology, and in particular to a liquid metal three-dimensional porous electrode based on flowability control and its preparation method. Background Technology

[0002] Gallium-based liquid metals (such as gallium, gallium-indium alloys, and gallium-indium-tin alloys) are liquid at near room temperature. They combine the high electrical and thermal conductivity of metallic materials with the excellent deformability of fluid materials, showing great application potential in flexible electronic devices, advanced thermal management systems, and energy and catalysis fields. Especially in the field of electrocatalysis, the atoms on the surface of liquid metals exhibit a disordered liquid arrangement, without the grain boundaries and lattice defects found in traditional solid metals, theoretically possessing unique interfacial electron transport characteristics and catalytic activity.

[0003] However, liquid metals have extremely high surface tension (for example, the surface tension of gallium-based alloys is approximately...). With a surface tension of 700 millinewtons per meter (far higher than water), liquid metals tend to contract into spherical shapes to reduce their surface energy, making them extremely difficult to coat onto conventional substrates. Existing techniques typically employ mechanical coating, ultrasonic dispersion, or oxidation-assisted coating onto two-dimensional planar substrates. However, when constructing three-dimensional porous substrates with high specific surface areas (such as copper foam and nickel foam), the high surface tension of the liquid metal makes it difficult to penetrate deep into the porous framework, easily leading to pore blockage or surface agglomeration, hindering the formation of a uniform, continuous, and thin three-dimensional coating structure. This non-uniform loading not only limits the effective and uniform exposure of electrode active sites but also impedes its practical applications in efficient heat dissipation and mass transport.

[0004] Furthermore, in the field of energy and environmental catalysis, electrocatalytic nitrates (such as nitrate (NO3)) are used. - ), nitrite (NO2) - Reduction is an important pathway for the resource utilization of nitrogen-containing nutrient wastewater. This reaction involves a complex proton-electron transfer process (PCET), producing a wide variety of products, including ammonia, nitrogen, nitrite, and hydroxylamine. Among these, hydroxylamine (NH2OH), as a high-value-added fine chemical raw material (widely used in nylon production and pharmaceutical synthesis), has extremely high economic value in its targeted preparation.

[0005] However, nitrate reduction is a kinetically highly competitive process. On traditional solid metal electrodes or liquid metal electrodes under normal conditions, the reaction pathway is often thermodynamically driven, primarily favoring excessive electrohydrogenation to generate thermodynamically more stable ammonia (NH3), resulting in extremely low selectivity for the high-value intermediate product hydroxylamine. How to effectively truncate the excessive reduction pathway through electrode microstructure design or external physical field modulation, and precisely stop the reaction at the specific intermediate hydroxylamine to achieve its high selectivity and high Faradaic efficiency, is a pressing technical bottleneck in this field.

[0006] Existing applications of liquid metal electrodes primarily utilize their flexibility, ductility, or self-healing capabilities due to their room-temperature fluidity, or their rigid support after complete solidification. However, current technologies generally overlook the structure-activity relationship between the unique rheological properties and interfacial catalytic characteristics of liquid metals in the temperature-sensitive region or the critical region of liquid-solid phase transition. Typically, the high fluidity of liquid metals at room temperature means that their surface atoms are in a state of intense thermal motion, resulting in extremely rapid adsorption, activation, and transformation of reactants at the interface, making it difficult to control the reaction to remain in the intermediate stage using kinetic barriers. Currently, there is a lack of a technical solution that can utilize a three-dimensional porous framework to provide high specific surface area and excellent conductivity, while simultaneously controlling the fluidity and phase state of liquid metals in situ through temperature and other means, thereby precisely controlling the electrocatalytic reaction pathway (e.g., inhibiting excessive electrohydrogenation of nitrate to improve hydroxylamine yield).

[0007] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0008] This invention aims to solve at least one technical problem existing in the prior art, particularly how to provide an electrode with in-situ controllable interfacial properties to achieve precise control of complex electrocatalytic reaction pathways. Specifically, it addresses how to provide an electrode structure whose liquid metal layer's fluidity can be controlled by temperature, maintaining uniform coating on a three-dimensional framework without agglomeration or detachment under different flow states. This fluidity control allows for precise control of electrocatalytic reaction pathways, such as significantly improving the selectivity of nitrate reduction to hydroxylamine. To this end, this application provides a fluidity-controlled liquid metal three-dimensional porous electrode and its preparation method.

[0009] The technical solution adopted in this application to solve the above-mentioned technical problems is as follows.

[0010] This application provides a liquid metal three-dimensional porous electrode based on fluidity control, comprising: a three-dimensional porous substrate; and a liquid metal layer disposed on the three-dimensional porous substrate, wherein the liquid metal layer and the three-dimensional porous substrate form a conductive network; wherein the fluidity of the liquid metal layer can be controlled by temperature.

[0011] In some embodiments, the three-dimensional porous matrix is ​​selected from one of foam metal, conductive polymer porous scaffold, three-dimensional printed metal mesh structure or conductive composite material mesh structure; wherein, the foam metal is made of at least one of copper (Cu), nickel (Ni), cobalt (Co), iron (Fe), titanium (Ti), silver (Ag) and stainless steel.

[0012] In some embodiments, the liquid metal includes at least one of gallium (Ga) and gallium alloys; wherein the gallium alloy is composed of gallium (Ga) and at least one element selected from indium (In), tin (Sn), zinc (Zn), and bismuth (Bi).

[0013] This application also provides an electrochemical device, including: a reactor; and a three-dimensional porous liquid metal electrode based on flow control, which is disposed in the reactor as a working electrode.

[0014] This application also provides a thermal management device, including: a device to be cooled; and a liquid metal three-dimensional porous electrode based on flow control, which is in thermal contact with the device to be cooled.

[0015] This application also provides a method for preparing a three-dimensional porous electrode of liquid metal based on flowability control, comprising the following steps: pretreating a three-dimensional porous substrate to remove its surface oxide layer to improve its hydrophilicity; providing a liquid metal raw material; treating the liquid metal raw material with an acid solution or an alkaline solution at a temperature higher than the melting point of the liquid metal raw material to remove its surface oxide film; coating the treated liquid metal raw material onto the surface of the pretreated three-dimensional porous substrate to form a liquid metal layer; and removing excess liquid metal raw material to obtain a three-dimensional porous electrode of liquid metal based on flowability control.

[0016] In some embodiments, the pretreatment includes ultrasonic cleaning of the three-dimensional porous matrix in sequence using an organic solvent and an acid solution.

[0017] In some embodiments, the coating method includes mechanical application, ultrasonic-assisted impregnation, or vacuum infusion.

[0018] In some embodiments, a liquid metal is also provided, which is an alloy composed of the following components in weight percentage: indium (In): 3 wt.%~29 wt.%; tin (Sn): 3 wt.%~13.5 wt.%; zinc (Zn): 0.5 wt.%~4 wt.%; bismuth (Bi): 1 wt.%~8.5 wt.%; the remainder being gallium (Ga); wherein the indium (In), tin (Sn), zinc (Zn), and bismuth (Bi) are not simultaneously zero.

[0019] This application also provides a method for electrocatalytic reduction of reactants, using the fluidity-controlled liquid metal three-dimensional porous electrode of this application as the working electrode. By controlling the working environment temperature during the electrolysis process, the fluidity properties of the liquid metal layer are regulated to control the selectivity of the reaction products.

[0020] In some embodiments, the reactants include nitrate (NO3) - ) or nitrite (NO2) - The reaction product includes hydroxylamine (NH2OH).

[0021] This application also provides a method for preparing hydroxylamine, comprising the following steps: providing an electrolytic cell containing an electrolyte containing nitrate or nitrite; placing the liquid metal three-dimensional porous electrode based on flowability control of this application in the electrolyte as a working electrode; controlling the working temperature of the electrolytic cell to reduce the flowability of the liquid metal layer, so that the liquid metal layer is in a liquid-solid critical state; and applying a negative potential to the working electrode to electroreduce nitrate or nitrite to generate hydroxylamine (NH2OH).

[0022] This application also provides an electrocatalytic system, including: the electrochemical device of this application; and a temperature control unit coupled to the electrochemical device for controlling the temperature of the environment of the liquid metal three-dimensional porous electrode based on flow regulation.

[0023] The present invention has the following beneficial effects: This application provides a three-dimensional porous electrode of liquid metal based on fluidity control, in which the fluidity of the liquid metal layer can be precisely controlled in situ and reversibly by ambient temperature. When high interfacial atomic activity is required, the temperature can be increased to achieve a high fluidity state; when it is necessary to suppress certain side reaction pathways requiring high activation energies, the temperature can be decreased to achieve a low fluidity state or a liquid-solid critical state. This physical field (temperature)-based control method is simple, efficient, and requires no additional chemical substances, providing a novel technical means to achieve multiple functions or control reaction pathways on a single electrode platform.

[0024] Another aspect of this application provides a method for preparing a three-dimensional porous electrode of liquid metal based on flowability control. Through specific pretreatment (such as acid washing) and oxide film removal treatment (such as treating the liquid metal with acid / alkali solutions), the surface tension of the liquid metal and the surface energy of the three-dimensional porous framework are significantly reduced, enhancing the wettability of the liquid metal on the framework. This overcomes the technical obstacle of the difficulty in uniformly spreading liquid metal on a high specific surface area three-dimensional structure. As a result, the liquid metal layer forms a uniform, continuous, and stable coating on the surface and internal pores of the framework, constituting a highly efficient conductive and thermally conductive network. This structure ensures that the active layer remains intact and uniform even when the electrode experiences temperature changes that alter the flowability of the liquid metal, avoiding problems such as agglomeration, detachment, or pore blockage caused by flowability changes, significantly improving the structural stability and service life of the electrode.

[0025] The method for preparing hydroxylamine provided in this application utilizes the characteristics of the aforementioned electrode. By precisely controlling the operating temperature to a low-fluidity state or a liquid-solid critical state near the melting point of the liquid metal, the intense thermal motion of atoms at the liquid metal interface is effectively suppressed. This increases the residence time of reactant molecules at the active sites or alters their adsorption configuration, thereby significantly raising the energy barrier for the formation of the semi-hydrogenation product (hydroxylamine) in the nitrate reduction reaction, while simultaneously suppressing the side reaction pathway of excessive hydrogenation to ammonia. This method achieves precise control over complex electrocatalytic reaction pathways, enabling the highly selective and high Faradaic efficiency synthesis of hydroxylamine, and providing an innovative solution for the resource utilization of nitrogen-containing wastewater and the green synthesis of high-value-added chemicals.

[0026] The thermal management device provided in another aspect of this application utilizes the high thermal conductivity of the liquid metal continuous network in the aforementioned electrode and its heat storage / release characteristics during the phase change process (solid-liquid transition). When used for heat dissipation of electronic devices, this electrode can not only quickly remove heat from the heat source through the high thermal conductivity network, but also absorb a large amount of heat through the phase change of the liquid metal, thereby efficiently controlling the device temperature and improving heat dissipation efficiency and system reliability.

[0027] Other beneficial effects of the present invention will be further described below. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a schematic diagram of a three-dimensional porous electrode of liquid metal based on fluidity control; Figure 2This is a schematic diagram of the preparation of a liquid metal three-dimensional porous electrode in an embodiment of the present invention, where a is a preparation flowchart, b1 and b2 are optical microscope images of the three-dimensional porous skeleton of copper foam and nickel foam after pretreatment, and c1 and c2 are optical microscope images of the electrode surface after loading liquid metal, showing that the liquid metal is uniformly coated on the skeleton surface. Figure 3 This is a graph showing the change in fluidity (viscosity) of the liquid metal prepared in Example 1 of this invention as a function of temperature; Figure 4 This is a comparison chart of the Faraday efficiency of the liquid metal three-dimensional porous electrode in the embodiments of the present invention for the electroreduction of nitrate to ammonia and hydroxylamine under different temperature conditions; Figure 5 This is a schematic diagram of the mechanism proposed in this invention for achieving highly selective electrocatalytic reduction of nitrates based on temperature-controlled liquid metal fluidity; the diagram shows the process of electro-hydrogenation of liquid metal to produce ammonia or highly selective generation of hydroxylamine at room temperature (high fluidity) and preset temperature (low fluidity / phase transition critical region); Figure 6 The figures shown are linear sweep voltammetry (LSV) curves and faradaic efficiency comparisons of the electroreduction of hydroxylamine to nitrate in electrolytes with different concentration gradients at a reaction temperature of 15°C using a liquid metal three-dimensional porous electrode in this invention. Figure a is the linear sweep voltammetry (LSV) curve of hydroxylamine electroreduction, and figure b is the faradaic efficiency comparison. Detailed Implementation

[0029] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0030] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0031] This invention aims to provide a liquid metal three-dimensional porous electrode based on fluidity regulation. Its core lies in solving the problem of uniform loading of liquid metal on a three-dimensional porous substrate, and utilizing the effect of temperature on the fluidity of liquid metal to achieve precise control of electrocatalytic reaction pathways, especially for the highly selective preparation of hydroxylamine in nitrate reduction reaction.

[0032] In some embodiments, a three-dimensional porous liquid metal electrode based on flowability control includes a three-dimensional porous substrate (such as copper foam) and a liquid metal layer disposed on the three-dimensional porous substrate; the liquid metal layer forms a continuous conductive network with the three-dimensional porous substrate through wetting, and maintains the uniformity of the macroscopic structure at low temperatures; the electrode is characterized in that the flowability and phase state of the liquid metal layer can be controlled in situ by temperature, and under different flow states, the liquid metal layer can maintain uniform coating on the three-dimensional porous substrate without agglomeration or detachment.

[0033] It should be noted that other specific methods covered by "setting" include, but are not limited to: injecting liquid metal into the pores of a three-dimensional porous matrix; embedding and fixing liquid metal in the form of microspheres into the framework of a three-dimensional porous matrix; the three-dimensional porous matrix itself is formed into a porous structure by dehumidification treatment of liquid metal; covering the surface of a three-dimensional porous matrix with liquid metal, etc.

[0034] Alternatively, the three-dimensional porous matrix may also be selected from foamed nickel, foamed cobalt, foamed iron, foamed titanium, foamed stainless steel, foamed silver, or alloy foam matrices including the above-mentioned metal elements (such as foamed nickel iron, foamed nickel molybdenum, foamed nickel cobalt and foamed copper zinc), conductive polymer porous scaffolds, three-dimensional printed metals, conductive composite material mesh structures, etc.

[0035] In some embodiments, the liquid metal is selected from gallium (Ga) and its alloys, wherein the alloy is an alloy of gallium (Ga) and at least one element selected from indium (In), tin (Sn), zinc (Zn), and bismuth (Bi). Examples include GaIn, GaSn, GaBi, GaZn, GaInSn, GaInZn, GaSnZn, and GaInSnBi. When the liquid metal is heated and liquefied, the heating temperature of gallium (Ga) does not exceed 35°C, and the heating temperature of the other alloys is 25°C. The liquid metal forms a continuous conductive network with the framework through wetting.

[0036] In some embodiments, a method for preparing a three-dimensional porous electrode of liquid metal based on flowability regulation is also provided, comprising the following steps: pretreating a three-dimensional porous substrate to remove its surface oxide layer to improve its hydrophilicity; providing a liquid metal raw material; treating the liquid metal raw material with an acid solution or an alkaline solution at a temperature higher than the melting point of the liquid metal raw material to remove its surface oxide film; coating the treated liquid metal raw material onto the surface of the pretreated three-dimensional porous substrate to form a liquid metal layer; and removing excess liquid metal raw material to obtain a three-dimensional porous electrode of liquid metal based on flowability regulation.

[0037] In some embodiments, liquid metal can be prepared by referring to the following steps: Weigh each metal raw material according to the predetermined ratio, place them in a muffle furnace, and melt them under an inert atmosphere (N2). The melting temperature should be 50-100℃ higher than the melting point of the component with the highest melting point in the alloy to ensure thorough melting and mixing. Hold the mixture at this temperature for 2-5 hours, and allow it to cool naturally to room temperature after melting. To ensure the uniformity of the alloy composition, the melted alloy needs to be repeatedly melted 2-3 times, resulting in a liquid metal. Furthermore, the composition ratio of the obtained liquid metal alloy is as follows: For binary gallium alloys: indium (In) is 5wt.%~25wt.%, tin (Sn) is 5wt.%~13.5wt.%, and the remainder is gallium; for ternary or higher gallium alloys: indium (In) is 3wt.%~29wt.%, tin (Sn) is 3wt.%~13.5wt.%, bismuth (Bi) is 1wt.%~8.5wt.%, zinc (Zn) is 0.5wt.%~4wt.%, and the remainder is gallium.

[0038] In some embodiments, surface pretreatment of a three-dimensional porous substrate to remove the surface oxide layer to improve hydrophilicity includes the following steps: Pretreatment process: Degrease with anhydrous ethanol by ultrasonication, remove surface oxides with hydrochloric acid by ultrasonication, and rinse thoroughly with pure water after each process; the purity of anhydrous ethanol is 95%, the ultrasonication time is 3-6 min, the concentration of hydrochloric acid is 2-3 mol / L, and the ultrasonication time is 5-10 min.

[0039] In some embodiments, the liquid metal raw material is treated with an acid solution or an alkaline solution at a temperature higher than the melting point of the liquid metal raw material to remove its surface oxide film and remove excess liquid metal raw material, thereby obtaining a three-dimensional porous electrode of liquid metal based on flowability control, comprising the following steps: Hydrochloric acid or potassium hydroxide solution is added dropwise to liquid metal at a certain volume ratio. The oxide film formed on its surface can be quickly removed by gentle shaking. Then, the high fluidity of the liquid metal is utilized to uniformly coat the surface of the three-dimensional porous substrate by manual shaking-assisted impregnation, ultrasonic-assisted impregnation, or vacuum infusion. Specific implementation methods include: If ultrasonic-assisted impregnation is used: the treated three-dimensional porous substrate is completely immersed in the liquid metal after removing the oxide film, and ultrasonic treatment is performed for 3 min to 10 min under ultrasonic power of 100 W-500 W. The cavitation effect of ultrasound forces the liquid metal to overcome capillary resistance and penetrate deep into the porous skeleton.

[0040] If a manual shaking-assisted impregnation method is used: Completely immerse the three-dimensional porous substrate in a container filled with deoxidized liquid metal and an acid / alkali solution. After sealing the container, manually shake it back and forth. The shaking frequency should be controlled at 10-30 times / minute, and the shaking time should be 1-3 minutes. During this process, the inertial force generated by shaking and the wettability of the deoxidized liquid metal on the porous substrate allow the liquid metal to overcome pore resistance and rapidly fill the internal pores of the three-dimensional porous substrate.

[0041] If vacuum infusion is used: place the three-dimensional porous matrix and liquid metal in a vacuum container, adjust the vacuum to -0.08 MPa to -0.1 MPa, and maintain the pressure for 5 min to 10 min. The liquid metal is then forced into the pores of the matrix by the pressure difference.

[0042] After impregnation, the sample is removed, and excess liquid metal is removed by centrifugation to obtain a liquid metal three-dimensional porous electrode. The concentration of hydrochloric acid is 0.02-2 mol / L, the concentration of potassium hydroxide is 0.5-3 mol / L, and the volume ratio of liquid metal to hydrochloric acid or potassium hydroxide is 3:1 to 10:1; the centrifugation parameters are 800-3000 rpm for 1-5 minutes.

[0043] In some embodiments, a liquid metal is also provided, which is an alloy composed of the following components in weight percentage: indium (In): 3 wt.%~29 wt.%; tin (Sn): 3 wt.%~13.5 wt.%; zinc (Zn): 0.5 wt.%~4 wt.%; bismuth (Bi): 1 wt.%~8.5 wt.%; the remainder being gallium (Ga); wherein indium (In), tin (Sn), zinc (Zn), and bismuth (Bi) are not simultaneously zero.

[0044] In some embodiments, a method for electrocatalytic reduction of reactants is also provided, using the fluidity-controlled liquid metal three-dimensional porous electrode of this application as the working electrode. By controlling the working environment temperature during the electrolysis process, the fluidity properties of the liquid metal layer are adjusted to regulate the selectivity of the reaction products. The reactants include nitrate (NO3). - ) or nitrite (NO2) - The reaction product includes hydroxylamine (NH2OH).

[0045] In some embodiments, a method for preparing hydroxylamine is also provided, comprising the following steps: Provide an electrolytic cell containing an electrolyte containing nitrates or nitrites; The liquid metal three-dimensional porous electrode based on fluidity regulation of this application is placed in the electrolyte as the working electrode; The working temperature of the electrolytic cell is adjusted to a preset temperature, and the conditions of the preset temperature are met to make the liquid metal layer in a low fluidity state or a liquid-solid critical state; and a negative potential is applied to the working electrode to electroreduce nitrate or nitrite to generate hydroxylamine (NH2OH).

[0046] It should be noted that the liquid-solid critical state can be understood as "the liquid metal layer in the supercooled liquid range above its melting point" or "the state corresponding to a narrow temperature window near the melting point of the liquid metal layer (e.g., 0.1°C to 5°C above the melting point)".

[0047] In some embodiments, the electrolytic cell is an H-type electrolytic cell, using a three-dimensional porous liquid metal electrode as the working electrode, a platinum mesh as the counter electrode, and Ag / AgCl as the reference electrode. The electrolyte is 0.1 mol / L KHCO3 + 0.04 mol / L KNO3, with a nitrate concentration ranging from 0.01 to 0.5 mol / L. High-purity argon gas is purged into the electrolyte for 30 minutes before use to remove dissolved oxygen. The preset temperature is adjusted to ensure the fluidity of the liquid metal layer is close to its minimum, approximately 1 degree Celsius above the melting point (the melting point of the liquid metal is determined by differential scanning calorimetry (DSC)). Simultaneously, the liquid metal is uniformly distributed on the porous substrate, with reaction parameters used for comparison between the liquid metal in a highly fluid state and in a solid state. Electrolysis is then performed by applying voltage, utilizing the interfacial characteristics of the liquid metal in a low-fluidity state to electroreduce nitrate to hydroxylamine. The reaction input potential range is -0.18 to -1.08 V vs. RHE, and the electrolysis time is 30 to 120 minutes. It should be noted that the preset temperature is a low-temperature region close to the melting point of liquid metal. By lowering the temperature, the thermal motion and surface fluidity of liquid metal atoms are suppressed, thereby inhibiting the excessive hydrogenation pathway of liquid metal and promoting the formation of the semi-hydrogenation product hydroxylamine.

[0048] In some embodiments, an electrochemical device is also provided, comprising: a reactor; and a three-dimensional porous liquid metal electrode based on flowability control of this application, which is disposed within the reactor as a working electrode.

[0049] In some embodiments, a thermal management device is also provided, including: a device to be cooled; and a three-dimensional porous liquid metal electrode based on flowability control of this application, which is in thermal contact with the device to be cooled.

[0050] In some embodiments, an electrocatalytic system is also provided, including: the electrochemical device of this application; and a temperature control unit coupled to the electrochemical device for controlling the temperature of the environment in which the liquid metal three-dimensional porous electrode based on flow regulation is located.

[0051] The following will further describe specific embodiments of the present invention. These embodiments are merely illustrative and do not mean that the present invention is limited to the following examples.

[0052] Example 1: Step 1, preparation of liquid metal by melting: Mix Ga, Sn and Zn metals in a weight ratio of 86:11:3, melt at 400°C for 3 hours under N2 protection, and cool to obtain GaSnZn liquid metal (alloy).

[0053] Step 2, Pretreatment of copper foam (CF) and coating with liquid metal layer: CF was sequentially degreased by sonication with anhydrous ethanol for 4 min, and then by sonication with 2 mol / L hydrochloric acid for 5 min to remove surface oxides. The CF was rinsed with pure water between each step. At room temperature, GaSnZn liquid metal (alloy) was mixed with 2 mol / L hydrochloric acid at a volume ratio of 5:1 to remove the oxide film on the liquid metal surface. Then, the liquid metal was uniformly coated onto the CF using an immersion method and centrifuged at 800 r / min for 3 min to remove excess liquid. This process was repeated twice to obtain a CF-loaded GaSnZn three-dimensional porous electrode. Figure 2 (As shown in Figures a, b1, and c1).

[0054] Step 3, Application Testing and Results: In an H-type electrolytic cell, CF-loaded GaSnZn was used as the working electrode, a platinum mesh as the counter electrode, and Ag / AgCl as the reference electrode. The electrolyte was 0.1 M KHCO3 + 0.04 M KNO3. At a potential of -1.5 V vs. Ag / AgCl, the fluidity (viscosity) decreased with decreasing temperature at reaction temperatures of 25 / 15 (close to the melting point of 14.7°C) / 5°C. Figure 3 Electrolysis for 30 min at 15°C showed that the Faradaic efficiency of nitrate to hydroxylamine was as high as 99.9±0.05%, while the Faradaic efficiency of ammonia was 0%. When the temperature was raised to 25°C (high-fluidity state) or lowered to 5°C (solid state), the Faradaic efficiencies of hydroxylamine were 88.53±1.3% and 90.37±1.6%, respectively, while the corresponding Faradaic efficiencies of ammonia were 6.14±0.15% and 5.35±0.2%, respectively. Figure 4 The LSV diagrams a and b are shown.

[0055] Experiments have confirmed that when the liquid metal layer is in the minimum fluidity / semi-solid critical region, i.e., by controlling the fluidity of the liquid metal through temperature regulation according to the present invention, the excessive hydrogenation behavior that occurs during the electroreduction of nitrates can be effectively suppressed, thereby significantly improving the selectivity of the intermediate product hydroxylamine (e.g., Figure 5 ).

[0056] Example 2: The only difference from Example 1 is that the matrix in step 2 is replaced with nickel foam (NF), resulting in an NF-loaded GaSnZn three-dimensional porous electrode. Figure 2As shown in Figures b2 and c2), under the same test conditions, the Faradaic efficiencies for the electroreduction of nitrate to hydroxylamine were 83.06±1.3%, 92.1±0.83%, and 78.95±1.6%, respectively, while the corresponding Faradaic efficiencies for ammonia were 13.5±0.83%, 4.14±0.47%, and 9.66±0.88%, respectively. Figure 4 Figure c.

[0057] Example 3: The only difference from Example 1 is that the liquid metal in step 1 is replaced with GaInZn, with the same weight ratio as in Example 1. The reaction temperature in step 3 is adjusted to 25 / 13 (melting point 13°C, semi-solid critical region) / 5°C. Under the same test conditions, the Faradaic efficiencies of nitrate electroreduction to hydroxylamine are 46.13±1.14%, 64.93±1.37%, and 17.18±1.27%, respectively, while the Faradaic efficiencies for ammonia are 43.87±2.03%, 15.07±0.96%, and 8.22±0.98%, respectively.

[0058] Example 4: The only difference from Example 1 is that the liquid metal in step 1 is replaced with GaInSn in a weight ratio of 67:20.5:12.5, the melting temperature is adjusted to 250°C, and the reaction temperature in step 3 is adjusted to 25 / 11 (close to the melting point of 10.5°C) / 5°C. Under the same test conditions, the Faradaic efficiencies of nitrate electroreduction to hydroxylamine are 17.98±0.83%, 51.13±2.46%, and 20.45±1.08%, respectively, while the corresponding Faradaic efficiencies of ammonia are 52.02±3.21%, 28.87±1.34%, and 29.55±1.29%, respectively.

[0059] Example 5: The only difference from Example 1 is that the liquid metal in step 1 is replaced with GaInSnBi in a weight ratio of 50.25:28.2:13.27:8.28, the melting temperature is adjusted to 280°C, and the reaction temperature in step 3 is adjusted to 25 / 22 (melting point 21.7°C) / 15°C. Under the same test conditions, the Faradaic efficiencies of nitrate electroreduction to hydroxylamine are 59.87±1.35%, 73.05±2.21%, and 38.96±1.11%, respectively, while the corresponding Faradaic efficiencies of ammonia are 30.13±1.26%, 11.95±0.76%, and 11.04±0.65%, respectively.

[0060] Example 6: The only difference from Example 1 is that the liquid metal in step 1 is replaced with GaZn at a weight ratio of 97:3, and the reaction temperature in step 3 is adjusted to 30 / 25 (close to the melting point of 24.7°C) / 15°C. Under the same test conditions, the Faradaic efficiencies of the electroreduction of nitrate to hydroxylamine are 14.88±1.16%, 24.53±1.8%, and 19.52±2.54%, respectively, while the corresponding Faradaic efficiencies for ammonia are 31.57±1.52%, 19.94±1.06%, and 22.94±1.29%, respectively. Figure 4 As shown in Figure d.

[0061] Example 7: The only difference from Example 1 is that the liquid metal in step 1 is replaced with GaIn, with a weight ratio of 91.7:8.3, the melting temperature is adjusted to 180°C, and the reaction temperature is 25 / 16 (melting point 15.5°C) / 5°C. The Faradaic efficiencies for the electroreduction of nitrate to hydroxylamine are 33.53±2.04%, 48.44±1.3%, and 18.39±0.83%, respectively, while the corresponding Faradaic efficiencies for ammonia are 56.47±1.93%, 31.56±0.89%, and 31.61±1.05%. Figure 4 As shown in Figure e.

[0062] Example 8: The only difference from Example 1 is that the liquid metal in step 1 is replaced with GaSn at a weight ratio of 91.7:8.3, the melting temperature is adjusted to 250°C, and the reaction temperature in step 3 is adjusted to 25 / 20 (melting point 20.5°C, semi-solid critical region) / 15°C. Under the same test conditions, the Faradaic efficiencies of nitrate electroreduction to hydroxylamine are 7.29±1.07%, 11.34±1.72%, and 1.57±0.63%, respectively, while the corresponding Faradaic efficiencies for ammonia are 55.01±3.32%, 39.29±1.91%, and 66.25±2.75%, respectively. Figure 4 As shown in Figure f.

[0063] Example 9: The only difference from Example 1 is that the liquid metal in step 1 is replaced with Ga, and the reaction temperature in step 3 is adjusted to 35 / 30 (melting point 29.8°C) / 25°C. Under the same test conditions, the Faradaic efficiencies of the electroreduction of nitrate to hydroxylamine are 10.78±1.57%, 17.25±2.01%, and 9.27±1.09%, respectively, while the corresponding Faradaic efficiencies for ammonia are 15.54±2.76%, 22.97±1.79%, and 8.87±3.05%, respectively. Figure 4 As shown in the g-graph.

[0064] Example 10: Electrocatalytic performance and universality verification of GaSnZn / CF electrode at different nitrate concentrations.

[0065] The only difference from Example 1 is that in step 3, the reaction temperature was controlled at 15°C, and the electrocatalytic reduction performance of the electrode was investigated under nitrate concentration gradients of 0.01, 0.04, 0.07, and 0.1 mol / L. Keeping other electrochemical parameters constant, the linear sweep voltammetry (LSV) curves were recorded and the product Faradaic efficiency was calculated. The test results are as follows: Figure 6 As shown, the system consistently maintained excellent electrosynthetic activity for hydroxylamine with varying nitrate concentrations. Specifically, the Faradaic efficiencies for hydroxylamine were 99.77±0.21%, 99.9±0.05%, 89.59±1.71%, and 71.45±3.87% for nitrate concentrations of 0.01, 0.04, 0.07, and 0.1 mol / L, respectively. These results confirm that the liquid metal catalyst can achieve effective nitrate reduction under different substrate concentrations, validating its versatility and process flexibility in the electrosynthetic application of hydroxylamine.

[0066] Example 11: Application of GaIn / CF electrodes in thermal management systems for flexible electronic devices.

[0067] The only difference from Example 1 is that the liquid metal in step 1 was replaced with GaIn at a weight ratio of 77:23, and the melting temperature was adjusted to 180°C, resulting in a three-dimensional porous GaIn composite material supported on copper foam. Thanks to the good fluidity of the GaIn alloy at room temperature, this material constructs a seamless, continuous metal thermally conductive network within the micropores, effectively eliminating the thermal resistance at the solid-solid interface. Testing showed that the thermal conductivity of this material reached 45.5 W / m·K, exceeding that of conventional commercial thermal pads (~3.0 W / m·K). In a 5W constant power simulated chip heat dissipation test, the equilibrium temperature of the heat source surface was controlled at approximately 48.5°C, a reduction of about 30°C compared to the control group.

[0068] The beneficial effects of this invention are as follows: (1) The liquid metal three-dimensional porous electrode provided by this invention overcomes the problems of high surface tension and difficulty in wetting of liquid metal through specific pretreatment and acid / alkali-assisted film removal processes, and achieves uniform and continuous coating on a complex three-dimensional framework. This structure retains the high specific surface area of ​​the porous framework and leverages the unique interfacial catalytic properties of liquid metal. It also maintains the integrity and uniformity of the structure in both low-temperature curing and flow states, avoiding the problems of pore blockage or active layer detachment that are prone to occur in traditional coating methods, and significantly improving the conductivity and mechanical stability of the electrode.

[0069] (2) The nitrate electroreduction method provided by this invention utilizes the in-situ control mechanism of temperature on the fluidity and phase state of liquid metal, solving the problem of poor selectivity of intermediate products in the prior art. By controlling the reaction temperature near the melting point or in the supercooled range, the violent thermal motion of atoms on the surface of liquid metal is effectively suppressed, thereby increasing the kinetic barrier of the excessive hydrogenation reaction, successfully blocking the excessive reduction path of nitrate ions to ammonia, and realizing the preparation of high-value-added product hydroxylamine with high selectivity and high Faradaic efficiency.

[0070] (3) The electrode material provided by this invention has the engineering value of "one material for multiple uses". In addition to its excellent performance in the field of electrocatalysis, the electrode can also be used as a high-efficiency heat dissipation component in the thermal management system of flexible electronic devices due to the high thermal conductivity of the liquid metal continuous network and the heat storage capacity of solid-liquid phase change, thus meeting the cross-domain application needs.

[0071] The background section of this invention may include background information about the problems or environment in which the invention is being developed, and is not necessarily a description of prior art. Therefore, the content included in the background section does not constitute an admission of prior art by the applicant.

[0072] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A three-dimensional porous electrode of liquid metal based on flowability control, characterized in that, include: Three-dimensional porous matrix; And a liquid metal layer disposed on the three-dimensional porous substrate, wherein the liquid metal layer and the three-dimensional porous substrate form a conductive network; wherein the fluidity of the liquid metal layer can be controlled by temperature.

2. The three-dimensional porous electrode of liquid metal based on flowability control according to claim 1, characterized in that, The three-dimensional porous matrix is ​​selected from one of foam metal, conductive polymer porous scaffold, three-dimensional printed metal mesh structure or conductive composite material mesh structure; wherein, the foam metal is selected from at least one of copper (Cu), nickel (Ni), cobalt (Co), iron (Fe), titanium (Ti), silver (Ag) and stainless steel.

3. The three-dimensional porous electrode of liquid metal based on flowability control according to claim 1, characterized in that, The liquid metal includes at least one of gallium (Ga) and gallium alloys; wherein the gallium alloy is composed of gallium (Ga) and at least one element selected from indium (In), tin (Sn), zinc (Zn), and bismuth (Bi).

4. An electrochemical device, characterized in that, include: Reactor; And a liquid metal three-dimensional porous electrode based on flowability control as described in any one of claims 1 to 3, which is disposed in the reactor as a working electrode.

5. A thermal management device, characterized in that, include: Devices to be cooled; And a liquid metal three-dimensional porous electrode based on fluidity control as described in any one of claims 1 to 3, which is in thermal contact with the device to be cooled.

6. A method for preparing a three-dimensional porous liquid metal electrode based on flowability control as described in any one of claims 1 to 3, characterized in that, Includes the following steps: The three-dimensional porous matrix is ​​pretreated to remove its surface oxide layer in order to improve its hydrophilicity; Provide liquid metal raw materials; At a temperature higher than the melting point of the liquid metal raw material, the liquid metal raw material is treated with an acid solution or an alkaline solution to remove its surface oxide film; The processed liquid metal raw material is coated onto the surface of the pretreated three-dimensional porous substrate to form a liquid metal layer; And by removing excess liquid metal raw materials, the liquid metal three-dimensional porous electrode based on flowability control is obtained.

7. The method according to claim 6, characterized in that, The pretreatment includes ultrasonic cleaning of the three-dimensional porous matrix using an organic solvent and an acid solution in sequence.

8. The method according to claim 6, characterized in that, The coating methods include mechanical application, ultrasonic-assisted impregnation, or vacuum infusion.

9. A liquid metal, characterized in that, The liquid metal is an alloy composed of the following components in weight percentage: indium (In): 3wt.%~29wt.%; tin (Sn): 3wt.%~13.5wt.%; zinc (Zn): 0.5wt.%~4wt.%; bismuth (Bi): 1wt.%~8.5wt.%; the remainder being gallium (Ga); wherein the indium (In), tin (Sn), zinc (Zn), and bismuth (Bi) are not all zero at the same time.

10. A method for electrocatalytic reduction of reactants, characterized in that, Using the liquid metal three-dimensional porous electrode based on fluidity regulation as described in any one of claims 1 to 3 as the working electrode, the fluidity properties of the liquid metal layer are regulated by controlling the working environment temperature during the electrolysis process, thereby regulating the selectivity of the reaction products.

11. The method for electrocatalytic reduction of reactants according to claim 9, characterized in that, The reactants include nitrate (NO3) - ) or nitrite (NO2) - The reaction products include hydroxylamine (NH2OH).

12. A method for preparing hydroxylamine, characterized in that, Includes the following steps: Provide an electrolytic cell containing an electrolyte containing nitrates or nitrites; The liquid metal three-dimensional porous electrode based on flow regulation as described in any one of claims 1 to 3 is placed in the electrolyte as a working electrode; The operating temperature of the electrolytic cell is controlled to reduce the fluidity of the liquid metal layer, so that the liquid metal layer is in a liquid-solid critical state. And apply a negative potential to the working electrode to electroreduc the nitrate or nitrite to generate hydroxylamine (NH2OH).

13. An electrocatalytic system, characterized in that, include: The electrochemical device as described in claim 4; And a temperature control unit, which is coupled to the electrochemical device, for controlling the temperature of the environment in which the fluidity-controlled liquid metal three-dimensional porous electrode is located.

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