A gradient pore foam catalytic electrode and its preparation method

Abstract

The present invention belongs to the technical field of electrochemical catalytic electrodes, and specifically discloses a gradient pore foam catalytic electrode and a preparation method thereof. The preparation method is as follows: First, micro-dispersoids are gradient-dispersed in a three-dimensional network foam, and through stabilization treatment, a substrate with a gradient pore structure is formed; then, a catalyst is plated on the surface of the substrate by electroless plating to form a porous catalytic electrode with a gradient pore structure. The overall catalytic electrode is a three-dimensional network structure, having gradient pores in at least one dimension; this structural electrode can greatly improve the interfacial reaction rate between the membrane layer and the catalyst layer, and is beneficial to gas-liquid mass transfer. The preparation method is simple to operate, can continuously prepare large-area electrodes, and has industrial application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemically catalytic electrodes, and particularly relates to a gradient pore foam catalytic electrode and a preparation method thereof. Background Art

[0002] The catalytic electrode is the core component of the electrocatalytic reaction, and the rational design of the catalytic electrode structure is closely related to its performance. For different application scenarios, various forms of electrodes have been developed currently, such as flat electrodes, membrane electrodes, mesh electrodes, and foam structure catalytic electrodes. Among them, the foam structure electrode can effectively promote the occurrence of electrochemical reactions due to its high porosity, high specific surface area, and high active site density. Currently, catalytic electrodes have been widely used in the fields of chemical engineering, energy, biomedicine, environmental protection, etc.

[0003] Electrolytic water hydrogen production is a typical electrochemical reaction. With the continuous deepening of the concepts of energy conservation, emission reduction, and development of renewable energy, hydrogen energy, as a clean and efficient energy source, has received increasing attention. Electrolytic water hydrogen production is a clean hydrogen production method and has received key attention. In this technical method, a highly efficient catalytic electrode is a major key. Industrial electrolytic water has strict requirements for the electrode, such as high electrochemical activity, large current density tolerance, strong chemical corrosion resistance, low gas-liquid mass transfer resistance, high mechanical stability, long service life, etc. Among them, fast reaction kinetics at high current density and low bubble mass transfer resistance are an important bottleneck in the development of electrocatalytic electrodes for practical electrolytic water hydrogen production.

[0004] The structure of the electrode is a major key factor affecting the performance of industrial practical electrodes. Common electrodes involved in gas-liquid mass transfer such as electrolytic water hydrogen production are metal mesh structures with ordered pores. However, the metal mesh structure with limited vertical depth is difficult to provide sufficient space for bubble growth separation and ion exchange. The three-dimensional porous structure can provide a larger contact area between the catalyst and the electrolyte than the planar porous structure, and can reduce the diffusion path of ions, promoting the migration of ions inside the substrate. However, at high current densities in industrial water electrolysis, the rate of the electrochemical reaction is faster, and reactants will be consumed at a higher rate and hydrogen / oxygen products will be generated. When the gas products cannot quickly escape from the inside of the electrode, it will cause a serious bubble blocking effect, affecting the charge transfer at the electrode-electrolyte interface, resulting in a decrease in activity; severe bubble scouring and gradually increasing internal pressure are likely to cause catalyst peeling, reducing stability; in addition, the adhesion of bubbles causes a decrease in the number of electrochemically active sites and an increase in impedance, resulting in an increase in ohmic loss and mass transfer obstruction, thereby affecting the catalytic performance of the catalytic electrode. Therefore, a reasonable design of the three-dimensional porous structure substrate, which can not only meet sufficient active sites but also timely remove the formed bubbles from the catalytic electrode, has important practical value for the development of the electrolytic water technology field. Summary of the Invention

[0005] In view of the problem that in the prior art, three-dimensional porous electrodes cannot timely detach the formed bubbles from the inside of the electrodes during electrolysis of water, resulting in increased resistance, blocked mass transfer, and reduced active sites, the present invention proposes a gradient pore foam catalytic electrode and a preparation method thereof. The provided gradient pore catalytic electrode has a high specific surface area and is conducive to bubble discharge, and the preparation method is simple and easy to operate, being suitable for mass production in industrial preparation.

[0006] To achieve the above object, the specific technical solutions adopted by the present invention are as follows:

[0007] In the first aspect, the present invention provides a preparation method of a gradient pore foam catalytic electrode, and the specific steps are as follows:

[0008] S1. Gradiently disperse minute dispersoids in a three-dimensional network foam, and through stabilization treatment, form a substrate with a gradient pore structure having a pore size distribution from large to small.

[0009] S2. For the substrate with the gradient pore structure obtained after the above stabilization treatment, deposit a catalyst on its surface by electroless plating to obtain a porous catalytic electrode with a gradient pore structure.

[0010] Preferably, in step S1, the minute dispersoids are polymer materials (such as polymethyl methacrylate) or inorganic non-metallic materials (such as silicon dioxide), with morphologies being spherical, linear, flaky, porous structures or a mixed system of multiple morphological structures, and the size is between 0.01 - 100 microns; the three-dimensional network foam is a polymer sponge, foam metal or foam ceramic, and the pore size of the network is between 0.01 - 150 microns.

[0011] Preferably, in step S1, the method for gradient dispersion of the minute dispersoids is to flow them through the three-dimensional network foam by gas-phase suspension or liquid-phase suspension methods. The formed network structure is an open-cell network structure, having gradient pores in at least one dimension, and the pore size distribution is between 0.01 - 150 microns.

[0012] Further, the liquid-phase suspension method is to mix minute dispersoids, a binder and a solvent, and ultrasonically disperse them into a liquid suspension, and pour it on the three-dimensional network foam; the concentrations of the minute dispersoids and the binder in the liquid suspension are both 5 - 100 g•L -1 .

[0013] Further, the gas-phase suspension method is to mix minute dispersoids, a binder and a solvent, and ultrasonically disperse them into a gas suspension, and spray the suspension onto the three-dimensional network foam through an atomizing spray gun; the flow rate range of the atomizing spray gun is 0.5 - 4 mL•s -1 .

[0014] Preferably, in step S1, the stabilization treatment method is heat curing and / or adhesive curing and shaping.

[0015] Preferably, in step S2, the catalyst is one or more of metals, alloys, metal borides, metal phosphides, etc., and the coating thickness is 5-50 microns.

[0016] In a second aspect, the present invention provides a gradient pore foam catalytic electrode prepared by the above preparation method.

[0017] The present invention has the following beneficial effects:

[0018] By adjusting the size and proportion content of the fine dispersoids and integrating the gas-phase suspension or liquid-phase suspension method, the present invention constructs a three-dimensional electrode structure with a gradient pore structure in which the catalyst loading on one side is high and the structure is dense, and the catalyst loading on the other side is low and the structure is loose. This gradient pore catalytic electrode has a high specific surface area and is conducive to the discharge of bubbles, and can combine high activity and high gas-liquid mass transfer characteristics, effectively improving the efficiency of the electrocatalytic reaction. Description of the Drawings

[0019] Figure 1 : Flow chart of the preparation method of the gradient pore catalytic electrode of the present invention.

[0020] Figure 2 : Schematic diagram of the stabilization treatment process in the preparation method of the foam substrate with a gradient pore structure of the present invention.

[0021] Figure 3 : Schematic diagram and stereomicroscope photograph of the foam substrate with a gradient pore structure in Example 1.

[0022] Figure 4 : SEM image and pore size distribution diagram of the porous catalytic electrode with a gradient pore structure in Example 1.

[0023] Figure 5 : Hydrogen evolution performance of the gradient pore catalytic electrode with different amounts of fine dispersoids in Example 1 during water electrolysis.

[0024] Figure 6 : Oxygen evolution performance of the gradient pore catalytic electrode with different amounts of fine dispersoids in Example 1 during water electrolysis. Detailed Embodiments

[0025] The present invention provides a gradient pore foam catalytic electrode and its preparation method to solve the problems of bubble blockage and the resulting mass transfer hindrance and reduction of active sites in existing catalytic electrodes. The process of this preparation method is as Figure 1As shown, the method innovatively uses the gas-phase suspension / liquid-phase suspension method to compound micro-dispersoids with foam materials to construct a gradient-porous foam substrate, and then uses electroless plating to coat the catalyst to obtain a gradient-porous foam catalytic electrode; among them, the preparation quality of the gradient-porous foam substrate is crucial, directly affecting the pore distribution, specific surface area, ease and quality of electroless plating of the electrode. Through the optimization of raw material parameters, gas-phase suspension / liquid-phase suspension process parameters, etc., the substrate obtains a high-quality gradient pore structure, overcomes bubble blockage and a series of problems caused by it, and effectively improves the electrochemical performance of the catalytic electrode. The specific steps of this preparation method are as follows:

[0026] S1. Use the gas-phase suspension or liquid-phase suspension method to make the micro-dispersoids flow through the three-dimensional network foam, and gradiently disperse the micro-dispersoids in the three-dimensional network foam; and carry out stabilization treatment by heating and curing and / or adhesive curing and shaping methods to form a substrate with a gradient pore structure with pore sizes distributed from large to small. Among them:

[0027] The micro-dispersoids are polymer materials such as polymethyl methacrylate or inorganic non-metallic materials such as silica, with morphologies of spherical, linear, flaky, porous structures or a mixed system of various morphological structures, and the size is between 0.01-100 microns (referring to that the sizes in all directions of the material with any morphology are within this range); the three-dimensional network foam is a polymer sponge, foam metal or foam ceramic, and the pore size is between 0.01-150 microns; the network structure formed by the gradient dispersion of the micro-dispersoids in the foam substrate is an open-cell network structure, with gradient pores in at least one dimension, and the pore size distribution is between 0.01-150 microns.

[0028] The liquid-phase suspension method is to mix the micro-dispersoids, binder and solvent, and ultrasonically disperse them into a liquid-phase suspension, and pour it on the three-dimensional network foam; the liquid pouring flow rate range is 0.5-4 mL•s -1 , and the concentrations of the micro-dispersoids and the binder in the liquid-phase suspension are both 5-100 g•L -1 . In the liquid-phase suspension method, the concentrations of the micro-dispersoids and the binder have obvious effects on the quality of the gradient pore structure and the electrochemical performance of the catalytic electrode.

[0029] The gas-phase suspension method is to mix the micro-dispersoids, binder and solvent, and ultrasonically disperse them into a gas-phase suspension, and spray the suspension onto the three-dimensional network foam through an atomizing spray gun; the flow rate range of the atomizing spray gun is 0.5-4mL•s -1 , and the concentrations of the micro-dispersoids and the binder in the gas-phase suspension are both 5-100 g•L -1 . In the gas-phase suspension method, the flow rate of the suspension controlled by the atomizing spray gun has obvious effects on the quality of the gradient pore structure and the electrochemical performance of the catalytic electrode.

[0030] S2. The substrate with the gradient pore structure after the above stabilization treatment is loaded with active sites through conventional electrode activation methods (such as physical vapor deposition, solution impregnation reaction, etc.); after activation, the catalyst is plated on its surface through a conventional electroless plating process to obtain a porous catalytic electrode with a gradient pore structure. Among them: the catalyst is one or more of metals, alloys, metal borides, metal phosphides, etc., and the coating thickness is 5-50 microns.

[0031] The following are specific examples of the preparation of the gradient pore foam catalytic electrode using the above method, which are used to further illustrate the present invention.

[0032] Example 1: Preparation of NiMoB gradient pore catalytic electrode

[0033] (1) Tiny dispersions of polymethyl methacrylate (PMMA) microspheres and toner C (binder) are poured into ethanol in a certain proportion and ultrasonicated to disperse them into a liquid suspension; among them, the concentration of PMMA microspheres in the suspension is 5-20 g•L -1 , and the concentration of toner C is 5-20 g•L -1 . Specifically, five groups of concentrations were tested in this example, including: 0 g•L -1 PMMA-0 g•L -1 toner C, 5 g•L -1 PMMA-5 g•L -1 toner C, 10•g L -1 PMMA-10 g•L -1 toner C, 15 g•L -1 PMMA-15 g•L -1 toner C, 20 g•L -1 PMMA-20 g•L -1 toner C, briefly recorded as Without PMMA / C, 5 PMMA / 5 C, 10 PMMA / 10 C, 15 PMMA / 15C, 20 PMMA / 20C.

[0034] (2) The above different concentration liquid suspensions flow uniformly through the melamine foam substrate with an open pore network structure in a liquid suspension manner, and the liquid pouring flow rate is 4 mL•s -1 , and due to gravity, the PMMA microspheres and toner C are gradiently distributed on the foam. Among them, the PMMA / C load content on the foam skeleton of the pouring surface is large, reducing the porosity, which is recorded as the dense surface; the PMMA / C content on the foam skeleton of the bottom surface is less, which is the high porosity layer, recorded as the loose surface (such as Figure 3 ).

[0035] (3) Place the foam substrate with the micro-dispersions gradient-dispersed in step (2) in an oven. Through the method of heating and adhesive curing, heat it at 120 °C for 10 min to melt toner C, and toner C acts as a binder to adhere to PMMA microspheres, fixing them to the foam substrate. As Figure 2 shown, a foam substrate with a gradient pore structure is obtained.

[0036] (4) Activate the foam substrate with a gradient pore structure prepared in step (3), and carry out palladium deposition through physical vapor deposition process to load the gradient pore foam substrate with active sites. The physical vapor deposition process in this embodiment is as follows: First, clean the workpiece to be plated; then use a diffusion pump to pump the vacuum chamber to a background vacuum of 6×10 -3 Pa; then carry out ion bombardment on the foam substrate, control the vacuum degree at 10 Pa - 10 -1 Pa, the ion bombardment voltage at 200 V - 1 kV negative high voltage, and the ion bombardment time at 5 min - 30 min; finally, adjust the evaporation current to melt palladium and evaporate and deposit it onto the foam substrate.

[0037] (5) Immerse the activated foam substrate with a gradient pore structure obtained in step (4) into the NiMoB electroless plating solution, and obtain a NiMoB catalytic electrode with a gradient pore structure after electroless plating. By optimizing the suspension concentration in step (2), the pore distribution of the gradient pore foam substrate is optimized, and then the gradient pore structure of the NiMoB catalytic electrode is optimized. Gradient pore structures are successfully formed in all four concentration groups except for the WithoutPMMA / C control group. When the suspension concentration is 15PMMA / 15C, the best pore structure is obtained. The average pore diameter of the dense surface is about 66 µm, and the pore diameter of the loose surface is about 108 µm. The morphology and pore size distribution are as Figure 4 shown, that is, the pore gradient range in the optimized gradient pore structure catalytic electrode is 66 microns - 108 microns.

[0038] The NiMoB catalytic electrodes with several different gradient pore structures prepared by optimizing the above step (2) are used for water electrolysis to test their catalytic hydrogen evolution and oxygen evolution performances. The performance of the series of gradient pore porous electrodes is tested using a three-electrode system. Using KOH (1 mol•L -1 ) as the electrolyte solution, a graphite carbon rod as the counter electrode, and a mercury / mercuric oxide as the reference electrode, the prepared gradient pore catalytic electrode is used as the working electrode. The test results are as Figure 5 、 6 shown. The catalytic performances of the NiMoB catalytic electrodes with several different gradient pore structures prepared by optimization for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are improved to varying degrees. The reaction overpotential is reduced, and the reaction energy consumption decreases. Among them, the current density of the non-gradient pore (Without PMMA / C) catalytic electrode is 100 mA•cm-2 The hydrogen evolution overpotential at this point is 136 mV. After optimizing the best pore structure catalytic electrode (15PMMA / 15C), the hydrogen evolution overpotential at this current density is only 68 mV, showing a significant decrease. At the same time, the oxygen evolution catalytic activity of this electrode also shows the same trend. The oxygen evolution overpotential of the non-gradient pore catalytic electrode at a current density of 100 mA•cm -2 is 370 mV. After treatment, the oxygen evolution overpotential at a current density of 100 mA•cm -2 is only 270 mV.

[0039] Example 2: Preparation of NiP gradient pore catalytic electrode

[0040] Basically the same as Example 1, the difference is that paper fiber (PVA) and toner C (binder) are mixed with ethanol in a certain proportion and ultrasonicated to disperse them into a liquid suspension. Among them, the concentration of paper fiber in the suspension is 5 - 20 g•L -1 , and the concentration of toner C is 5 - 20 g•L -1 , that is, corresponding to: 5 g•L -1 PVA - 5 g•L -1 C, 10 g•L -1 PVA - 10 g•L -1 C, 15 g•L -1 PVA - 15 g•L -1 C, 20 g•L -1 PVA - 20 g•L -1 C; several groups of concentrations finally prepared NiP catalytic electrodes with different gradient pore structures. Compared with the non-gradient pore catalytic electrode, the HER and OER overpotentials are both reduced, the reaction energy consumption decreases, and the electrochemical performance is significantly improved. Among them, the non-gradient pore NiP catalytic electrode (that is, the electrode prepared under 0 g•L-1 PVA - 0 g•L-1 C) has a hydrogen evolution overpotential of 187 mV and an oxygen evolution overpotential of 411 mV at 100 mA•cm-2. The NiP catalytic electrode prepared at a concentration of 10 g•L-1 PVA - 10 g•L-1 C has the lowest overpotential. The hydrogen evolution overpotential at 100 mA•cm-2 is 105 mV, and the oxygen evolution overpotential is 310 mV, which is nearly 80 mV lower than that of the non-gradient pore catalytic electrode for hydrogen evolution overpotential and nearly 100 mV lower for oxygen evolution overpotential.

[0041] Example 3: Preparation of NiFeP gradient pore catalytic electrode

[0042] (1) Disperse zeolite powder and copolyester (PA) hot melt powder binder into water to form a suspension. The concentrations of zeolite powder and copolyester in the suspension are both 10 g•L -1; Spray the suspension onto the nickel foam through an atomizing spray gun; the flow rate range of the atomizing spray gun is 0.5 mL•s -1 to 4 mL•s -1 and optimize within this range. Further dry the obtained substrate in an oven, and after the binder is cured, a nickel foam substrate with a gradient pore structure is obtained.

[0043] (2) Activate the prepared nickel foam substrate with a gradient pore structure, and through a solution impregnation reaction, load the gradient pore foam substrate with active sites; the process of the solution impregnation reaction in this embodiment is as follows: Dissolve NiSO4·6H2O (0.2 mol•L -1 ) and Me4NB3H8 (0.2 g) in 10 mL of deionized water to obtain an activation solution; soak the foam substrate with a gradient pore structure in the activation solution at room temperature for 10 minutes, and wash it with deionized water to obtain the activated substrate.

[0044] (3) Immerse the activated foam substrate with a gradient pore structure into the electroless plating solution of NiFeP, and after electroless plating, a NiFeP catalytic electrode with a gradient pore structure is obtained.

[0045] The results of this embodiment show that when the flow rate is 2 mL•s -1 a substrate with the best gradient structure is obtained, and the OER overpotential of the prepared catalytic electrode is lower (NiFeP is an oxygen evolution catalyst). The oxygen evolution overpotential of the non-gradient pore NiFeP catalytic electrode (the catalytic electrode prepared by plating NiFeP on pure nickel foam without adding zeolite powder and PA) at 100 mA•cm-2 is 380 mV in the specification. The oxygen evolution overpotential of the NiFeP gradient pore catalytic electrode prepared at a flow rate of 2 mL•s-1 at 100 mA•cm-2 is 285 mV, which is nearly 100 mV lower than that of the non-gradient pore electrode.

[0046] Example 4: Preparation of Cu gradient pore catalytic electrode

[0047] (1) Disperse silica microspheres and polyurethane (TPU) hot melt powder binder into water, and the formed mixed solution forms a gas-phase suspension through an atomizing spray gun and blows through a through-hole honeycomb ceramic plate at a flow rate of 4 mL•s -1 ; Heat-treat the obtained substrate in a muffle furnace and then cool it to obtain a foam ceramic substrate with a gradient pore structure.

[0048] (2) Activate the prepared ceramic substrate with a gradient pore structure, and use the same method as in Example 3 to load the gradient pore foam substrate with active sites.

[0049] (3) Immerse the activated foam substrate with a gradient pore structure into a Cu electroless plating solution, and a Cu catalytic electrode with a gradient pore structure is obtained after electroless plating.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a gradient pore foam catalytic electrode, characterized in that: The specific steps are as follows: S1. Gradient dispersion of microdispersants in a three-dimensional network foam by gas phase suspension or liquid phase suspension, and stabilization treatment to form a substrate with a gradient pore structure with pore sizes distributed from large to small; wherein: The micro-dispersed matter is a polymer material or an inorganic non-metallic material, and the size of each direction is between 0.01-100 microns; the three-dimensional network foam is a polymer sponge, foam metal or foam ceramic, and the mesh size is between 0.01-150 microns; The liquid suspension method is to mix the micro-dispersed matter, binder and solvent, ultrasonically disperse them into a liquid suspension, and pour them on the three-dimensional network foam. The concentration of the micro-dispersed matter and binder in the liquid suspension is 5-100 g•L -1 ; The gas phase suspension method is to mix the micro-dispersed material, binder and solvent, ultrasonically disperse them into a gas phase suspension, and spray the suspension onto the three-dimensional network foam through an atomizing spray gun. The flow rate of the atomizing spray gun ranges from 0.5 to 4 mL•s -1 ; The stabilization treatment method is heat curing or adhesive curing; S2. The substrate with gradient pore structure after the stabilization treatment is first loaded with active sites by an electrode activation method, and then the catalyst is plated on its surface by a chemical plating method to obtain a porous catalytic electrode with a gradient pore structure.

2. The method for preparing a gradient pore foam catalytic electrode according to claim 1, characterized in that: In step S1, the micro-dispersed matter has a morphology of one or more of spherical, linear, lamellar, and porous structures.

3. The method for preparing a gradient pore foam catalytic electrode according to claim 1, characterized in that: In step S2, the catalyst is one or more of metals, alloys, metal borides, and metal phosphides, and the coating thickness is 5-50 microns.

4. A gradient pore foam catalytic electrode prepared by the preparation method according to any one of claims 1 to 3.

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