Preparation method of gradient porous electrode, gradient porous electrode and electrochemical sewage treatment system

Abstract

The invention relates to the technical field of electrode material preparation and electrochemical water treatment, in particular to a composite electrode with a gradient porous structure and a preparation method of the composite electrode, and provides a preparation method of a gradient porous electrode which is clear in structural gradient, high in interface stability and excellent in conductivity and has self-regeneration capacity. An electrochemical sewage treatment system based on the electrode is further constructed, so that deep purification of heavy metal wastewater and efficient recovery of metal resources are realized, and the overall operation efficiency and engineering suitability of the system are improved; comprising the following steps: 1) mixing and filling: sequentially filling mixed powder comprising diamond powder, copper powder, tin powder, titanium powder and a pore forming agent into a mold with a vertical cavity dividing structure according to a preset porosity to form a surface layer, a middle layer and a bottom layer; 2) pore forming: heating in a vacuum environment to decompose a pore forming agent to obtain a porous structure, and 3) dense sintering: performing hot pressed sintering under a protective atmosphere to sinter and form metal powder, and forming an oxygen-doped non-stoichiometric titanium carbide layer at the interface of diamond and titanium powder.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode material preparation and electrochemical water treatment, and specifically to a composite electrode with a gradient porous structure and a preparation method thereof, in particular to a preparation method of a diamond-copper-tin-titanium gradient porous electrode and its application in electrochemical wastewater deep treatment and metal resource recovery. Background Art

[0002] With the accelerating pace of industrialization, the discharge of large amounts of heavy metals and organic wastewater from industries such as electroplating, electronics, and chemicals has become a significant source of water pollution. To achieve standard wastewater discharge and resource recovery, electrochemical treatment technology has attracted widespread attention due to its high efficiency, environmental friendliness, and strong controllability. Electrode materials, as the core of electrochemical systems, directly determine reaction efficiency, service life, and operating costs.

[0003] Currently, commonly used electrode materials include graphite electrodes, noble metal oxide electrodes (such as IrO2 and RuO2), and boron-doped diamond (BDD) electrodes. While BDD electrodes offer high electrochemical stability and broad-spectrum oxidation capabilities, their preparation relies on chemical vapor deposition (CVD) technology, which is expensive and prohibitive. Furthermore, the inability to mass-produce porous structures has limited their widespread adoption in engineering applications.

[0004] On the other hand, porous structure electrodes have a larger specific surface area, stronger reactivity and better mass transfer performance, and have been widely used in scenarios such as filtration, capacitance, and catalysis. However, most existing porous electrodes have uniform pore structures, which are prone to surface blockage or short circuit problems. At the same time, the coupling degree between the conductive layer and the functional layer structure is low, and the interfacial bonding force is poor, resulting in insufficient cycle stability. In addition, the metal ions deposited on the electrode surface are difficult to remove efficiently, and usually rely on acid washing or replacement of the electrode, which not only increases operation and maintenance costs, but also brings the risk of secondary pollution.

[0005] Therefore, there is an urgent need for an electrode material with reasonable structural classification, controllable preparation process, strong interface stability and self-regeneration ability to improve the comprehensive performance of the electrochemical wastewater treatment system and promote its engineering implementation in the fields of deep treatment of heavy metal wastewater and resource recovery. Summary of the Invention

[0006] The present invention aims to overcome the problems of existing porous electrodes such as single structure, poor interface bonding strength, short service life and difficulty in achieving efficient self-regeneration. It proposes a preparation method for a gradient porous electrode with a clear structural gradient, high interface stability, excellent conductivity and self-regeneration ability, and further constructs an electrochemical sewage treatment system based on the electrode to achieve deep purification of heavy metal wastewater and efficient recovery of metal resources, thereby improving the overall operating efficiency and engineering adaptability of the system.

[0007] The technical solution of the present invention is as follows: A method for preparing a gradient porous electrode comprises the following steps: 1) Mixed filling: A mixed powder including diamond powder, copper powder, tin powder, titanium powder and pore-forming agent is sequentially filled into a mold with a vertical cavity structure according to a preset porosity to form a surface layer, a middle layer and a bottom layer; 2) Pore formation: heating in a vacuum environment to decompose the pore-forming agent to obtain a porous structure; 3) Dense sintering: Hot pressing sintering is carried out under a protective atmosphere to sinter the metal powder into shape and form an oxygen-doped non-stoichiometric titanium carbide layer at the interface between diamond and titanium powder.

[0008] Furthermore: in the mixed powder, diamond powder has a particle size of 5-20 μm and accounts for 30-40 weight percent, copper powder has a particle size of 50-100 μm and accounts for 50-55 weight percent, tin powder accounts for 3-8%, titanium powder accounts for 2-5%, and a pore-forming agent accounts for 5-10%, wherein the pore-forming agent is a complex of ammonium bicarbonate and starch, with a weight ratio of 1:3; The three-layer structure formed in the mold has different porosities, namely: 60-70% for the surface layer, 40-50% for the middle layer, and 20-30% for the bottom layer.

[0009] Furthermore: the pore-forming step is carried out at 500°C-700°C, the hot pressing sintering is carried out at 900°C-1000°C and a pressure of 40MPa-60MPa, and the protective atmosphere is a mixed gas of argon and hydrogen with a volume ratio of 9:1.

[0010] A gradient porous electrode prepared by any of the above methods: the electrode has a three-layer pore structure, the surface pore size is 10-50μm, the middle layer is 1-10μm, the bottom layer is less than 1μm, and the bottom layer diamond particles are coated with Sn-Cu eutectic alloy, and the overall resistivity of the electrode is less than 10⁻ 5 Ω·m.

[0011] An electrochemical sewage treatment system comprises a cathode module and an anode module, wherein the cathode module comprises the gradient porous electrode as claimed in claim 4.

[0012] Furthermore: the cathode module is configured to periodically apply a reverse pulse voltage, switching between +1V for 30 seconds and -2V for 10 seconds, so as to utilize the electroplasticity of tin to achieve electrode self-regeneration.

[0013] Furthermore: the electrode surface of the anode module is provided with a laser-etched micro-groove array with a width of 20 μm and a depth of 50 μm, which is used to guide the directional overflow of hydroxyl radicals and inhibit organic carbonization scaling.

[0014] Technical Effects This invention significantly improves the overall performance of electrodes in electrochemical wastewater treatment through collaborative innovation in material composition, structural construction, and system functionality. The specific technical effects are as follows: Preparation method: The present invention uses a vertical cavity mold to fill mixed powders of different porosities, and constructs an electrode with a three-layer gradient pore structure by combining layered forming and step-by-step sintering. The preparation process does not rely on expensive equipment such as CVD, is compatible with traditional powder metallurgy processes, significantly reduces production costs, and improves process controllability and industrial feasibility.

[0015] Electrode structure: The electrode of the present invention has a three-layer pore structure of surface layer (10-50μm macropores), middle layer (1-10μm micropores) and bottom layer (<1μm dense conductive layer), which respectively undertake the functions of particle interception, electrical adsorption and conductive support, realizing the coordinated division of structure and function; the bottom diamond surface is coated with Sn-Cu eutectic conductive layer, which has excellent conductivity, and oxygen-doped TiC is generated during the hot pressing process. x The Oᵧ non-stoichiometric compound interface layer has an interface bonding strength of 150MPa, significantly higher than the 80MPa level of conventional TiC structures. It has excellent thermal shock resistance and electrochemical stability. This interface bonding effect is unexpected in existing technologies.

[0016] System operation: In a wastewater treatment system constructed using gradient electrodes, periodic electrical pulses at the cathode trigger the electroplastic behavior of tin. Combined with a high-frequency ultrasonic oscillator, this effectively removes deposited metal particles, enabling electrode self-regeneration without the need for chemical cleaning. Field measurements have shown an electrode flux recovery rate of up to 98%, with a continuous operating life exceeding 6,000 hours, significantly exceeding the lifespan of traditional electrodes (<2,000 hours), demonstrating unexpected durability and self-maintenance capabilities. The laser-etched microgroove array on the anode surface guides the targeted release of hydroxyl radicals, effectively inhibiting organic carbonization scaling and improving the overall stability and continuous treatment capacity of the system.

[0017] Comprehensive synergistic effects: The present invention realizes functional nesting and response optimization from the material level, structural level to the system level. The electrode has a high specific surface area, high conductivity, strong interface bonding force and self-regeneration ability. The system has the characteristics of low maintenance, high efficiency, and resource recycling. It is particularly suitable for deep treatment scenarios of heavy metal wastewater and organic wastewater. The synergistic effect produced by similar structural combinations has not been seen in existing porous electrodes and electrochemical treatment systems. It has significant engineering application prospects and promotion value.

[0018] In addition to being used as cathode modules in electrochemical wastewater treatment systems, the gradient porous electrode of the present invention can also be widely used in fields such as electrocatalysis, metal ion enrichment, water electrolysis for hydrogen production, microbial fuel cells, and electrochemical sensors. It is particularly suitable for scenarios with high requirements for electrode structural strength, specific surface area, and interface binding performance. To meet different application requirements, those skilled in the art can adjust the material ratio, pore structure, and surface modification method according to different reaction systems. Such adjustments should be considered as reasonable expansions of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of the preparation method of this technical solution; Figure 2 It is a structural diagram of the porous electrode of the present technical solution; Figure 3 It is a structural diagram of the anode plate of this technical solution; Among them, 1: surface layer; 2: middle layer; 3: bottom layer. DETAILED DESCRIPTION

[0020] To more clearly illustrate the present invention, the present invention will be further described below in conjunction with specific examples. However, it should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various modifications and variations without departing from the spirit and substance of the present invention, and these modifications and variations should still fall within the scope of protection of the present invention.

[0021] Example 1: Preparation of gradient porous electrode Diamond powder (approximately 10 μm in diameter) (33 wt%), copper powder (approximately 80 μm in diameter) (52 wt%), tin powder (5 wt%), titanium powder (4 wt%), and a composite pore-forming agent (1:3 weight ratio) of ammonium bicarbonate and starch were mixed uniformly. The resulting mixed powder was then loaded into a mold with a vertical three-cavity structure in three layers. The preset porosities for the three layers were: 1:65% for the surface layer, 2:45% for the middle layer, and 3:25% for the bottom layer.

[0022] The pore-forming treatment was performed at 600°C in a vacuum environment to decompose the pore-forming agent to form a porous structure. Subsequently, hot pressing sintering was performed in a protective atmosphere of argon and hydrogen (volume ratio 9:1). The sintering temperature was set at 900°C–1000°C, the applied pressure was 40–60 MPa, and the holding time was 30 minutes.

[0023] The obtained electrode structure is dense and clearly layered. Under the electron microscope, the surface of the bottom particles is covered with a Sn-Cu eutectic layer. XPS detection shows that TiC is formed at the diamond-titanium interface. x Oᵧ transition layer, the overall resistivity of the electrode is 8.5×10⁻ 6 Ω·m.

[0024] Example 2: Performance Verification of Gradient Structure Electrode The electrode prepared by the method in Example 1 was observed by scanning electron microscopy (SEM), which showed a clear three-layer pore structure. The surface pore size ranged from 10–50 μm, the middle pore size was 1–10 μm, and the bottom pore size was less than 1 μm. The overall resistivity of the electrode was measured by the four-probe method to be 8.2×10⁻ 6 Ω·m.

[0025] Combined with the shear test to test the interface bonding strength, the shear strength between the bottom particles and the intermediate matrix reached 150MPa, verifying the bonding strength between titanium powder and diamond through TiC x The strengthening effect of the Oᵧ interface bonding layer.

[0026] Example 3: Application in electrochemical sewage treatment system The electrode prepared in Example 1 was assembled into an electrochemical reaction cell and used as the cathode module. The electrolyte consisted of synthetic wastewater containing 50 mg / L of Cu²⁺ and approximately 300 mg / L of COD. After operating at a voltage of +2V for 60 minutes, the Cu²⁺ removal rate reached 98.5%, and the COD degradation rate reached 83%.

[0027] At the same time, by applying periodic reverse pulse voltage (alternating between +1V for 30 seconds and -2V for 10 seconds) and running for 20 hours, no obvious scaling was observed on the electrode surface, and the flux remained above 93% of the initial value, showing good electrode self-regeneration ability.

[0028] Example 4: Preparation-Structure-Application Integrated Performance Test The electrode prepared in Example 2 was applied to a static enrichment experiment in a simulated wastewater containing 20 mg / L of Au³⁺. After 90 minutes of electrolysis at 1.2 V constant potential in a 0.1 mol / L Na2SO4 electrolyte, the residual concentration of Au³⁺ dropped to 0.2 mg / L, and the enrichment efficiency reached 99%.

[0029] The electrode's performance was stable after five enrichment-release cycles, and its structure was not damaged, verifying its suitability for precious metal recovery and resource recycling.

[0030] Example 5: Application in the enrichment of precious metal ions The electrode prepared in Example 2 was applied to a static enrichment experiment in a simulated wastewater containing 20 mg / L of Au³⁺. After 90 minutes of electrolysis at 1.2 V constant potential in a 0.1 mol / L Na2SO4 electrolyte, the residual concentration of Au³⁺ dropped to 0.2 mg / L, and the enrichment efficiency reached 99%.

[0031] The electrode's performance was stable after five enrichment-release cycles, and its structure was not damaged, verifying its suitability for precious metal recovery and resource recycling.

[0032] Example 6: Preparation and comparative testing of low-ratio electrodes The material is composed of 30 wt% diamond powder, 55 wt% copper powder, 8 wt% tin powder, 2 wt% titanium powder, and 10 wt% pore-forming agent. Diamond powder (particle size: 20 μm) and copper powder (particle size: 90 μm) are loaded into a mold to form a three-layer pore structure: 60% surface layer, 40% middle layer, and 20% bottom layer.

[0033] The electrode was prepared under the same pore formation and hot pressing sintering conditions. Its surface specific area increased significantly and its adsorption capacity was enhanced, but the conductive path was slightly shorter and the electrode resistivity was 1.1×10⁻ 5 Ω·m. It still has strong adsorption / mass transfer capabilities and is suitable for high-flow wastewater treatment or heavy metal enrichment scenarios.

Claims

1. A method for preparing a gradient porous electrode, characterized in that: The following steps are involved: 1) Mixed filling: A mixed powder including diamond powder, copper powder, tin powder, titanium powder and pore-forming agent is sequentially filled into a mold with a vertical cavity structure according to a preset porosity to form a surface layer, a middle layer and a bottom layer; 2) Pore formation: heating in a vacuum environment to decompose the pore-forming agent to obtain a porous structure; 3) Dense sintering: Hot pressing sintering is carried out under a protective atmosphere to sinter the metal powder into shape and form an oxygen-doped non-stoichiometric titanium carbide layer at the interface between diamond and titanium powder.

2. The method for preparing a gradient porous electrode according to claim 1, wherein: In the mixed powder, diamond powder has a particle size of 5-20 μm and accounts for 30-40 weight percent, copper powder has a particle size of 50-100 μm and accounts for 50-55 weight percent, tin powder accounts for 3-8%, titanium powder accounts for 2-5%, and a pore-forming agent accounts for 5-10%, wherein the pore-forming agent is a compound of ammonium bicarbonate and starch, with a weight ratio of 1:3; The three-layer structure formed in the mold has different porosities, namely: 60-70% for the surface layer, 40-50% for the middle layer, and 20-30% for the bottom layer.

3. The method according to claim 1 or 2, characterized in that: The pore-forming step is performed at 500° C.-700° C., the hot-pressing sintering is performed at 900° C.-1000° C. and a pressure of 40 MPa-60 MPa. The protective atmosphere is a mixed gas of argon and hydrogen with a volume ratio of 9:

1.

4. A gradient porous electrode prepared by the method according to any one of claims 1 to 3, characterized in that: The electrode has a three-layer pore structure, with a surface pore size of 10-50 μm, a middle pore size of 1-10 μm, and a bottom pore size of less than 1 μm. The surface of the bottom diamond particles is coated with Sn-Cu eutectic alloy, and the overall resistivity of the electrode is less than 10⁻ 5 Ω·m.

5. An electrochemical sewage treatment system, characterized by: It comprises a cathode module and an anode module, wherein the cathode module comprises the gradient porous electrode as claimed in claim 4.

6. The electrochemical wastewater treatment system according to claim 5, characterized in that: The cathode module is configured to periodically apply a reverse pulse voltage, switching between +1 V for 30 seconds and -2 V for 10 seconds, so as to realize electrode self-regeneration by utilizing the electroplasticity of tin.

7. The electrochemical wastewater treatment system according to claim 5 or 6, characterized in that: The electrode surface of the anode module is provided with a laser-etched micro-groove array with a width of 20 μm and a depth of 50 μm, which is used to guide the directional overflow of hydroxyl radicals and inhibit organic carbonization scaling.

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