Cobalt phosphide self-supporting material and preparation method and application thereof
By preparing cobalt phosphide self-supporting materials on conductive substrates, the problems of high preparation cost and small active site coverage of precious metal catalytic materials during electrolytic hydrogen production process are solved, and efficient hydrogen production performance and low overpotential are achieved in electrolytic hydrogen production.
Patent Information
- Application Number
- CN202311813118.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-26
- Publication Date
- 2025-06-27
AI Technical Summary
In the process of electrolyzing hydrogen production, existing precious metal catalytic materials have problems such as high preparation cost, small coverage area of active sites, poor conductivity and adhesive performance impacts, which are difficult to apply on a large scale.
The Co precursor micelle solution was prepared by surfactant sodium oleate and cobalt salt solution. The cobalt phosphide self-supporting material was formed on the conductive substrate by phosphating treatment, forming a multi-grain boundary three-dimensional structure, improving conductivity and active site exposure.
It realizes efficient hydrogen production performance of electrolytic water, and the overpotential is lower than that of commercial Pt/C electrodes, and has excellent charge transfer capability and catalytic activity, which simplifies the preparation process and reduces production costs.
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Figure CN120210855A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the fields of new energy and hydrogen production by electrolyzing water, and relates to a method for preparing an electrode of a cobalt phosphide self-supporting material and its application. Background Art
[0002] The global population is growing rapidly, and fossil energy is being consumed at an accelerating rate. Mankind is facing an unprecedented energy crisis. To resolve this unprecedented crisis and meet the needs of future social development, mankind has begun to explore reusable and environmentally friendly energy sources. Hydrogen (H2), due to its high energy density (120 - 140 MJ / kg), no carbon emissions, water as the combustion product, and being clean and pollution-free, is the most suitable energy carrier at present. In addition, hydrogen energy can also be used in the refining of petroleum and the production of ammonia, and is one of the indispensable raw materials in key areas of the chemical industry. However, commercial hydrogen production on the market mainly uses coal-based hydrogen production and methane cracking to produce hydrogen, that is, using fossil energy to produce hydrogen, which greatly consumes limited fossil energy and runs counter to the green environmental protection concept of reducing greenhouse gas emissions and environmental pollution. Different from fossil fuel-based hydrogen production, hydrogen production by electrolyzing water, which uses renewable electric energy as the power source and abundant water resources as the raw material, has the advantages of simple operation, no carbon emissions, and green recycling, and is considered an ideal hydrogen production method. However, the overpotential of the hydrogen evolution reaction (HER) in hydrogen production by electrolyzing water cannot be ignored.
[0003] The HER reaction needs to overcome the slow reaction kinetics and carrier migration kinetics on the electrode surface. Pt, Pd, Ru and their compounds, as catalytic materials, are located at the tip of the hydrogen evolution reaction volcano plot and have good advantages in HER catalytic reactions. However, this type of catalytic material has two major problems. First, most of these materials are in powder form and inevitably need to be adhered to a conductive substrate through adhesives (such as common polytetrafluoroethylene (PTEE) and 5% Nafion membrane solution). However, the presence of adhesives will cause many problems: First, it reduces the contact area between the active sites and the electrolyte and covers the active sites of the catalytic material; Second, it may reduce the conductivity of the material due to poor contact; Third, the large generation of bubbles leads to a decrease in the adhesion ability between the catalytic material and the substrate, and even peeling from the substrate, thereby reducing the catalytic performance. Second, noble metals such as Pt, Pd, and Ru have low natural abundances and high preparation costs, and it is not very realistic to popularize their use on a large scale.
[0004] Self-supporting electrodes are a type of electrode where the catalytic material is directly and firmly connected to the conductive substrate without the need for adhesives. The direct connection between the catalytic material and the conductive substrate has the following advantages: First, through the intimate interfacial interaction, it is beneficial to improve the conductivity of the electrocatalytic material and promote charge transfer; Second, the three-dimensional structure and high specific surface area enable the catalytic material to be evenly distributed on its surface, with the possibility of high loading, and at the same time, it can form a unique morphology, providing more abundant active sites and increasing the contact area between the catalytic material and the electrolyte solution; Third, the binder-free working electrode avoids the coating operation of the catalytic material, simplifies the electrode preparation process, ensures the structural integrity and stability of the working electrode, and reduces production costs. These advantages have attracted high attention to self-supporting materials. According to recent literature reports, conductive substrates can be divided into carbon fiber paper (CFP), carbon cloth (CC), metal foils (Ti / Cu foils), metal foams (Ni / Cu foams), etc., which have advantages such as 3D microstructures, large specific surface areas, good electrical conductivity, and charge transfer rates.
[0005] To solve the problems of high preparation cost and difficulty in large-scale production of noble metals, it is necessary to find materials with low prices, abundant raw material reserves, and excellent catalytic performance as HER catalytic materials. In recent years' research, great efforts have been made in seeking HER catalytic materials that can replace noble metals. In the research, a large number of studies have been carried out based on transition metal phosphides, sulfides, carbides, nitrides, selenides, and alloys such as iron, cobalt, nickel, copper, molybdenum, and tungsten. In order to pursue high catalytic activity, researchers have tried to design self-supporting electrodes for catalytic materials from the perspective of improving the intrinsic conductivity of the materials. For example, growing the materials on carbon cloth or metal foils. However, the preparation process of this strategy is relatively cumbersome and has great limitations in application.
[0006] Therefore, it is of great significance to explore a simple method for preparing self-supporting electrodes to increase conductivity and expose more CoP active sites. Summary of the Invention
[0007] In view of this, the present invention provides a cobalt phosphide self-supporting material, its preparation method and application. Through a simple preparation method, a cobalt phosphide self-supporting material with excellent conductivity and capable of exposing multiple active sites is obtained, making it a catalyst for the HER reaction and reducing the overpotential of the HER reaction.
[0008] To achieve the above object, the present invention adopts the following technical solutions.
[0009] According to the first aspect of the present invention, a preparation method of a cobalt phosphide self-supporting material is provided, including the following steps:
[0010] 1) Mix water, organic alcohol, and surfactant to form solution A; mix water, organic alcohol, and cobalt salt to form solution B; then mix solution A, solution B, and organic solvent, and let the mixture stand. After the mixture is layered, take the upper clear liquid to obtain the Co precursor micelle solution.
[0011] 2) Drop the Co precursor micelle solution obtained in step 1) onto a conductive substrate. After the organic solvent evaporates, a Co precursor micelle-conductive substrate is formed. Subject the Co precursor micelle-conductive substrate and a phosphorus source to a phosphating reaction at a high temperature under a protective atmosphere to obtain a CoP-conductive substrate catalyst, i.e., the cobalt phosphide self-supporting material.
[0012] In the preparation method of the above cobalt phosphide self-supporting material, in step 1), the molar ratio of the surfactant to the cobalt salt is 4 - 4.5:1.
[0013] In the preparation method of the above cobalt phosphide self-supporting material, in step 1), when forming solution A, the volume ratio of water to organic alcohol is 3.8 - 4.2:2.8 - 3.2.
[0014] In the preparation method of the above cobalt phosphide self-supporting material, in step 1), when forming solution B, the volume ratio of water to organic alcohol is 1.8 - 2.2:0.8 - 1.2.
[0015] In the preparation method of the above cobalt phosphide self-supporting material,
[0016] In the preparation method of the above cobalt phosphide self-supporting material, in step 1), the organic alcohol includes at least one of methanol, ethanol, propanol, isopropanol, butanol, and isobutanol.
[0017] In the preparation method of the above cobalt phosphide self-supporting material, in step 1), the surfactant has a long-chain alkyl structure, that is, the surfactant is selected from fatty acid salt surfactants. For example, the surfactant includes sodium oleate.
[0018] In the preparation method of the above cobalt phosphide self-supporting material, in step 1), the cobalt salt includes at least one of cobalt nitrate and cobalt chloride.
[0019] In the preparation method of the above cobalt phosphide self-supporting material, in step 1), the organic solvent includes at least one of n-hexane, cyclohexane, n-pentane, and n-heptane.
[0020] In the preparation method of the above cobalt phosphide self-supporting material, in step 1), when forming solution A or forming solution B or mixing solution A, solution B, and the organic solvent, the mixing is carried out under stirring.
[0021] In the preparation method of the cobalt phosphide self-supporting material described above, in step 2), the molar ratio of the Co precursor micelles to the phosphorus source is 1:100 - 500.
[0022] In the preparation method of the cobalt phosphide self-supporting material described above, in step 2), the Co content in the Co precursor micelle - conductive substrate is 0.5 - 20 mg / cm 2 .
[0023] In the preparation method of the cobalt phosphide self-supporting material described above, in step 2), the Co - precursor micelle - conductive substrate and the phosphorus source are kept at a first temperature under a protective atmosphere, then cooled to a second temperature, and finally naturally cooled under the protective atmosphere to obtain a CoP - conductive substrate catalyst.
[0024] In the preparation method of the cobalt phosphide self-supporting material described above, in step 2), the first temperature is 420 - 480 °C.
[0025] In the preparation method of the cobalt phosphide self-supporting material described above, in step 2), the holding time at the first temperature is 1.5 - 2.5 h.
[0026] In the preparation method of the cobalt phosphide self-supporting material described above, in step 2), the second temperature is 110 - 90 °C.
[0027] In the preparation method of the cobalt phosphide self-supporting material described above, in step 2), during the process of cooling to the second temperature, the cooling rate is 4.5 - 5.5 °C / min.
[0028] In the preparation method of the cobalt phosphide self-supporting material described above, in step 2), the protective atmosphere includes any one of nitrogen (N2) and argon.
[0029] In the preparation method of the cobalt phosphide self-supporting material described above, in step 2), the phosphidation reaction is carried out in a glass tube of a high-temperature tube furnace.
[0030] In the preparation method of the cobalt phosphide self-supporting material described above, in step 2), when carrying out the phosphidation reaction, the formed Co precursor micelle - conductive substrate is placed in container C1; the phosphorus source is placed in container C2; container C2 is placed on the upper side of the gas flow in the glass tube of the high-temperature tube furnace, and container C1 is placed on the lower side of the gas flow.
[0031] In the present invention, the distance between container C1 and container C2 is not particularly limited as long as the phosphidation treatment effect of the Co precursor micelle - conductive substrate can be achieved. Preferably, the horizontal distance between container C1 and container C2 is 4 - 6 cm.
[0032] In the above method for preparing the cobalt phosphide self-supporting material, in step 2), the conductive substrate includes any one of carbon fiber paper (CFP), carbon cloth (CC), carbon felt, graphene foam, graphene aerogel, metal foil (e.g., Ti foil or Cu foil), and metal foam (e.g., Ni foam or Cu foam).
[0033] In the above method for preparing the cobalt phosphide self-supporting material, the method for preparing the cobalt phosphide self-supporting material includes the following steps:
[0034] 1) Mix water, ethanol, and sodium oleate to form solution A; mix water, ethanol, and cobalt nitrate hexahydrate to form solution B; then mix solution A, solution B, and hexane, and let the mixture stand. After the mixture is layered, take the upper clear liquid to obtain a cobalt precursor micelle solution;
[0035] 2) Drop the cobalt precursor micelle solution obtained in step 1) onto carbon fiber paper (abbreviation: carbon paper). After the hexane volatilizes, a cobalt precursor micelle-conductive substrate is formed. Subject the cobalt precursor micelle-carbon fiber paper and sodium hypophosphite to a phosphidation reaction at a high temperature under a protective atmosphere to obtain a cobalt phosphide (CoP)-carbon fiber paper (CFP) catalyst, that is, the cobalt phosphide self-supporting material.
[0036] According to the second aspect of the present invention, a cobalt phosphide self-supporting material is provided. The cobalt phosphide self-supporting material includes a conductive substrate, a carbon coating film, and cobalt phosphide (CoP); wherein, the mass ratio of the conductive substrate, the carbon coating film, and cobalt phosphide is 20-40%:5-20%:30%-70%.
[0037] For the above cobalt phosphide self-supporting material, the cobalt phosphide self-supporting material has a three-dimensional structure with multiple grain boundaries; the carbon coating film adheres to the surface of the conductive substrate; the cobalt phosphide is dispersed in the carbon coating film in the form of nanoparticles.
[0038] For the above cobalt phosphide self-supporting material, the cobalt phosphide self-supporting material is prepared by the above preparation method.
[0039] According to the third aspect of the present invention, an application of the above cobalt phosphide self-supporting material as a HER reaction electrode in the field of water electrolysis for hydrogen production is provided.
[0040] In the above application, when the cobalt phosphide self-supporting material is in a 1 mol / L KOH alkaline solution and the current density is 10 mA cm -2 the hydrogen evolution overpotential is 78 mV.
[0041] In the present invention, without conflict, the above technical features can be freely combined to form new technical solutions.
[0042] The above technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art:
[0043] (1) In the present invention, sodium oleate, a surfactant, is used to prepare a micellar solution of Co through simple operations such as stirring, standing, and separation, and it is dropped onto the surface of clean carbon paper. Through further phosphating treatment, a cobalt phosphide self-supporting material (CoP-CFP) is formed, which can be used as an electrode in the HER reaction;
[0044] (2) The cobalt phosphide self-supporting material according to the present invention (i.e., CoP-CFP catalytic material) has a rich three-dimensional structure, a large specific surface area, and excellent charge transport ability, enabling it to have good HER performance. The overpotential at 10 mA cm -2 is 78 mV, and the overpotentials at 50 mA cm -2 and 100 mA cm -2 are 125 mV and 148 mV respectively; in addition, the current density can exceed that of the commercial Pt / C electrode only at an overpotential of 121 mV; the Tafel slope of the CoP-CFP catalytic material is 57.8 mV dec -1 , which is close to 51.7 mV dec -1 of the Pt / C electrode, ( Figure 4 ) indicating its good charge transport ability;
[0045] (3) For the cobalt phosphide self-supporting material according to the present invention, compared with the cobalt self-supporting material, the phosphated Co has a higher binding energy, which is beneficial to the adsorption and desorption of hydrogen, and improves its HER catalytic performance;
[0046] (4) The preparation method of the cobalt phosphide self-supporting material according to the present invention is simple and highly efficient, providing a feasible idea for the development of self-supporting catalytic materials. BRIEF DESCRIPTION OF THE DRAWINGS
[0047] The drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present invention, and are used together with the specification to explain the principles of the present invention.
[0048] Figure 1 is the SEM image of the CoP-CFP catalytic material prepared in Example 1 of the present invention.
[0049] Figure 2 is Figure 1 the partially enlarged SEM image.
[0050] Figure 3TEM image (a), HRTEM image (b), partial enlarged view of image (b) (c), dark field electron microscopy image (d), Co element Mapping image (e), and P element Mapping image (f) of the CoP-CFP catalytic material prepared in Example 1 of the present invention.
[0051] Figure 4 is the LSV diagram of the electrodes prepared in Example 1 and Comparative Examples 1-2 and the electrode prepared in Example 1 at different current densities when the current density is 10 mA cm -2 at that time.
[0052] Figure 5 Is the overpotential diagram of the CoP-CFP catalytic materials prepared in Examples 1-5 of the present invention.
[0053] Figure 6 Is the LSV diagram of the CoP-CFP catalytic materials with different sodium hypophosphite contents in Examples 1-5 of the present application. Detailed implementation manners
[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
[0055] According to some specific embodiments of the first aspect of the present invention, a preparation method of a cobalt phosphide self-supporting material is provided, including the following steps:
[0056] 1) Mix water, organic alcohol, and surfactant to form solution A; mix water, organic alcohol, and cobalt salt to form solution B; then mix solution A, solution B, and organic solvent, and let the mixture stand. After the mixture is layered, take the upper clear liquid to obtain a Co precursor micelle solution;
[0057] 2) Drop the Co precursor micelle solution in step 1) on a conductive substrate. After the organic solvent evaporates, a Co precursor micelle-conductive substrate is formed. Subject the Co-precursor micelle-conductive substrate and a phosphorus source to a phosphating reaction at a high temperature under a protective atmosphere to obtain a CoP-conductive substrate catalyst.
[0058] According to some embodiments of the first aspect of the present invention, the molar ratio of the surfactant to the cobalt salt is 4 to 4.5:1 (for example, 4.1:1, 4.2:1, 4.3:1, or 4.4:1).
[0059] According to some embodiments of the first aspect of the present invention, when forming solution A, the volume ratio of water to organic alcohol is 3.8 - 4.2:2.8 - 3.2 (for example, 3.8:3, 4:3 or 4.2:3).
[0060] According to some embodiments of the first aspect of the present invention, when forming solution B, the volume ratio of water to organic alcohol is 1.8 - 2.2:0.8 - 1.2, preferably 1.8 - 2.2:1 (for example, 1.9:1, 2:1 or 2.1:1).
[0061] According to some embodiments of the first aspect of the present invention, the organic alcohol includes at least one of methanol, ethanol, propanol, isopropanol, butanol and isobutanol.
[0062] According to some embodiments of the first aspect of the present invention, the surfactant has a long-chain alkyl structure and includes sodium oleate.
[0063] In the present invention, the surfactant contains an alkyl long-chain structure. In the high-temperature phosphating reaction, it can form a carbon film (i.e., a carbon coating layer) on the surface of the conductive substrate and the surface of CoP particles, thereby facilitating the improvement of the conductivity of the cobalt phosphide self-supporting material.
[0064] According to some embodiments of the first aspect of the present invention, the cobalt salt includes at least one of cobalt nitrate and cobalt chloride.
[0065] According to some embodiments of the first aspect of the present invention, the organic solvent includes at least one of n-hexane, cyclohexane, n-pentane and n-heptane.
[0066] According to some embodiments of the first aspect of the present invention, in step 1), when forming solution A or forming solution B or mixing solution A, solution B with the organic solvent, the mixing is carried out under stirring.
[0067] According to some embodiments of the first aspect of the present invention, in step 2), the Co-precursor micelle-conductive substrate and the phosphorus source are kept at a first temperature in a protective atmosphere, then cooled to a second temperature, and finally naturally cooled in a protective atmosphere to obtain a CoP-conductive substrate catalyst.
[0068] According to some embodiments of the first aspect of the present invention, in step 2), the molar ratio of the Co precursor micelle to the phosphorus source is 1:100 - 500 (for example, 1:150, 1:200, 1:250, 1:300, 1:350, 1:400 or 1:450).
[0069] According to some embodiments of the first aspect of the present invention, in step 2), the Co content in the Co-precursor micelle-conductive substrate is 0.5 - 20 mg / cm 2 (for example, 1 mg / cm2 , 5 mg / cm 2 , 8 mg / cm 2 , 10 mg / cm 2 , 12 mg / cm 2 , 15 mg / cm 2 or 18 mg / cm 2 ).
[0070] According to some embodiments of the first aspect of the present invention, in step 2), the first temperature is 420 - 480 °C (for example, 430 °C, 440 °C, 450 °C, 460 °C or 470 °C).
[0071] According to some embodiments of the first aspect of the present invention, in step 2), the holding time at the first temperature is 1.5 - 2.5 h (for example, 1.6 h, 1.8 h, 2.0 h, 2.2 h, 2.4 h).
[0072] According to some embodiments of the first aspect of the present invention, in step 2), the second temperature is 90 - 110 °C (for example, 92 °C, 95 °C, 98 °C, 100 °C, 102 °C, 105 °C or 108 °C).
[0073] According to some embodiments of the first aspect of the present invention, in step 2), during the process of cooling down to the second temperature, the cooling rate is 4.5 - 5.5 °C / min (for example, 4.7 °C / min, 4.8 °C / min, 5.0 °C / min, 5.2 °C / min or 5.4 °C / min).
[0074] According to some embodiments of the first aspect of the present invention, in step 2), the protective atmosphere includes any one of nitrogen (N2) and argon.
[0075] According to some embodiments of the first aspect of the present invention, in step 2), the phosphating reaction is carried out in the glass tube of a high-temperature tube furnace.
[0076] According to some embodiments of the first aspect of the present invention, in step 2), when carrying out the phosphating reaction, the formed Co precursor micelle - conductive substrate is placed in container C1; the phosphorus source is placed in container C2; container C2 is placed on the upper side of the gas flow in the glass tube of the high-temperature tube furnace, and container C1 is placed on the lower side of the gas flow.
[0077] According to some embodiments of the first aspect of the present invention, in step 2), the distance between container C1 and container C2 is 4 - 6 cm (for example, 4.2 cm, 4.5 cm, 4.7 cm, 5.0 cm, 5.2 cm, 5.5 cm, 5.7 cm or 5.9 cm).
[0078] According to some embodiments of the first aspect of the present invention, in step 2), the container comprises a porcelain boat.
[0079] According to some embodiments of the first aspect of the present invention, in step 2), the conductive substrate includes any one of carbon fiber paper (CFP), carbon cloth (CC), carbon felt, graphene foam, graphene aerogel, metal foil (Ti / Cu foil), and metal foam (Ni / Cu foam).
[0080] According to some embodiments of the second aspect of the present invention, a cobalt phosphide self-supporting material is provided, which comprises a conductive substrate, a carbon coating film and cobalt phosphide (CoP); wherein the mass ratio of the conductive substrate, the carbon coating film and the cobalt phosphide is 20-40%: 5-20%: 30%-70%.
[0081] According to some embodiments of the second aspect of the present invention, the cobalt phosphide self-supporting material has a three-dimensional structure with multiple crystal boundaries; the carbon coating film is attached to the surface of the conductive substrate; and the cobalt phosphide is dispersed in the carbon coating film in the form of nanoparticles.
[0082] According to some embodiments of the second aspect of the present invention, the cobalt phosphide self-supporting material is prepared by the above-mentioned preparation method.
[0083] According to some embodiments of the third aspect of the present invention, there is provided an application of the above-mentioned cobalt phosphide self-supporting material as a HER reaction electrode in the field of hydrogen production by electrolysis of water.
[0084] According to some embodiments of the third aspect of the present invention, the cobalt phosphide self-supporting material is in a 1 mol / L KOH alkaline solution at a current density of 10 mA cm -2 When , the hydrogen evolution overpotential is 78mV.
[0085] Example 1
[0086] A method for preparing an electrode of a cobalt phosphide self-supporting material (CoP-CFP), comprising the following steps:
[0087] (1) Preparation of Co-CFP precursor micelle solution; specifically,
[0088] S1: 4 ml of deionized water and 3 ml of anhydrous ethanol were fully mixed, 4 g of sodium oleate was added thereto, and the mixture was stirred and dissolved with a magnetic stirrer to form a solution A;
[0089] S2: 2 ml of deionized water and 1 ml of anhydrous ethanol were fully mixed, 3.0 mmol (0.8731 g) of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) solid was added thereto, and the mixture was stirred and dissolved with a magnetic stirrer, and the mixture was mixed evenly to form a solution B;
[0090] S3: Add 14 ml of n-hexane to Solution B, and at the same time, slowly inject Solution A while stirring.
[0091] S4: After the above operations are completed, in order to allow the mixed solution to fully contact, further stirring is required. Set the rotation speed of the mixed solution to 400 rpm and stir for 1 h. After the stirring ends, let the mixed solution stand and separate into layers. Take the upper layer (n-hexane layer) solution to obtain the Co-CFP precursor micelle solution.
[0092] (2) Preparation of CoP-CFP catalytic material; specifically,
[0093] S5: Pipette 154 μl of the Co-CFP precursor micelle solution and evenly drop it on a clean carbon paper of 1 cm 2 (1 cm × 1 cm).
[0094] S6: After the n-hexane has evaporated, place the formed Co-CFP precursor micelle carbon paper into a clean porcelain boat C1; weigh 0.7 g of sodium hypophosphite solid and put it into another clean porcelain boat C2.
[0095] S7: Place porcelain boat C2 on the upper side of the gas flow in the high-temperature tubular furnace glass tube, and place porcelain boat C1 on the lower side of the gas flow. The distance between the two porcelain boats is 5 cm. Then, under a N2 atmosphere, heat at a heating rate of 5 °C / min to 450 °C; after holding for 2 h, cool down to 100 °C at a rate of -5 °C / min; then let the sample cool naturally in the N2 atmosphere to obtain the CoP-CFP self-supporting material, where the mass ratio of the conductive substrate (CFP), the carbon coating film, and cobalt phosphide (CoP) is 1:40:400.
[0096] Example 2
[0097] This example provides a method for preparing an electrode of a cobalt phosphide self-supporting material (CoP-CFP), which is different from Example 1 in that the mass of the sodium hypophosphite solid weighed in step S6 is 0.1 g.
[0098] In the CoP-CFP self-supporting material prepared in this example, the mass ratio of the conductive substrate (CFP), the carbon coating film, and cobalt phosphide (CoP) is 1:40:200.
[0099] Example 3
[0100] This example provides a method for preparing an electrode of a cobalt phosphide self-supporting material (CoP-CFP), which is different from Example 1 in that the mass of the sodium hypophosphite solid weighed in step S6 is 0.3 g.
[0101] In the CoP-CFP self-supporting material prepared in this example, the mass ratio of the conductive substrate (CFP), the carbon-coated film, and cobalt phosphide (CoP) is 1:40:300.
[0102] Example 4
[0103] This example provides a method for preparing an electrode of a cobalt phosphide self-supporting material (CoP-CFP), which is different from Example 1 in that the mass of the sodium hypophosphite solid weighed in step S6 is 0.5 g.
[0104] In the CoP-CFP self-supporting material prepared in this example, the mass ratio of the conductive substrate (CFP), the carbon-coated film, and cobalt phosphide (CoP) is 1:40:350.
[0105] Example 5
[0106] This example provides a method for preparing an electrode of a cobalt phosphide self-supporting material (CoP-CFP), which is different from Example 1 in that the mass of the sodium hypophosphite solid weighed in step S6 is 1.0 g.
[0107] In the CoP-CFP self-supporting material prepared in this example, the mass ratio of the conductive substrate (CFP), the carbon-coated film, and cobalt phosphide (CoP) is 1:40:400.
[0108] Comparative Example 1
[0109] A method for preparing a cobalt self-supporting material (Co-CFP) includes the following steps:
[0110] (1) Preparation of the Co-CFP precursor micelle solution, and the preparation method is the same as that in step (1) of Example 1;
[0111] (2) Preparation of the Co-CFP catalytic material, which specifically includes the following steps;
[0112] S1: Transfer an appropriate amount of the prepared Co-CFP precursor micelle solution to a clean and smooth porcelain boat, and wait for the n-hexane to volatilize to form a viscous substance of the Co-CFP precursor micelle, showing a brown color;
[0113] S2: Place the porcelain boat containing the viscous substance of the Co-CFP precursor micelle on the upper side of the gas flow in the high-temperature tube furnace glass tube; weigh 0.7 g of sodium hypophosphite solid, put it into another clean porcelain boat, and place it on the lower side of the gas flow in the tube furnace glass tube;
[0114] S3: Subsequently, under an N₂ atmosphere, the temperature is raised to 450 °C at a heating rate of 5 °C / min and held for 2 h, and then cooled to 100 °C at -5 °C / min over 70 min. Then, the sample is naturally cooled in an N₂ atmosphere to obtain Co / CFP solid powder;
[0115] S4: Weigh a certain amount of Co / CFP solid powder and disperse it in a mixed solution of absolute ethanol and Nafion (mass ratio 920:80), and ultrasonically homogenize to obtain a mixed solution. Then, evenly drip the mixed solution onto a clean carbon paper of 1 cm 2 (1 cm × 1 cm) so that the loading amount is 1.5 mg·cm -2 ⁻²; After the ethanol in the catalytic material mixed solution has fully evaporated, Co / CFP catalytic material is obtained.
[0116] Comparative Example 2
[0117] A preparation method of a Pt / electrode includes the following steps:
[0118] S1: Take a certain amount of Pt / C and dissolve it in a mixed solution of absolute ethanol and Nafion (mass ratio 920:80), and ultrasonically homogenize;
[0119] S2: Evenly drip the mixed solution onto a clean carbon paper of 1 cm 2 (1 cm × 1 cm) so that the loading amount is 1.5 mg·cm -2 ⁻². After the ethanol in the mixed solution has fully evaporated, a Pt / C electrode can be obtained.
[0120] Structure Test
[0121] Use scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to observe the overall morphology of the CoP-CFP catalytic material in Example 1, the Co-CFP catalytic material in Comparative Example 1, and the Pt / C electrode in Comparative Example 2. Figure 1 The SEM image of the CoP-CFP catalytic material prepared in Example 1 of the present invention is shown. Figure 2 Shown is Figure 1 the partially enlarged SEM image. Figure 3 The TEM image (a), HRTEM image (b), partially enlarged image of (b) (c), dark field electron microscopy image (d), Co element Mapping image (e), and P element Mapping image (f) of the CoP-CFP catalytic material prepared in Example 1 of the present invention are shown.
[0122] From Figure 1It can be seen that this figure is the SEM image of a single carbon fiber on the CFP. It can be observed that the surface of the CoP-CFP carbon fiber does not have a smooth surface like the clean CFP, but instead has a layer of densely packed "sesame seed" - shaped substances "grown" on the CFP surface. Figure 2 is Figure 1 a partial enlarged view. Under low - magnification SEM, the densely packed "sesame seed" - shaped substances are individual approximately spherical nanoparticles. The nanoparticles are closely distributed, and the spaces between the particles are wrapped and connected by a film - like substance. This substance is the "carbon film" formed after the high - temperature carbonization of sodium oleate. The existence of this "carbon film" can promote the charge conduction between the nanoparticles and at the same time fix the nanoparticles so that they firmly adhere to the CFP surface, providing strong guarantees for the current stability and material stability of CoP - CFP.
[0123] From Figure 3 (a), it can be seen that the morphology of CoP - CFP under TEM is basically the same as that of CoP - CFP under high - magnification SEM( Figure 1 ). Among them, CoP - CFP is closely connected, and the gaps are wrapped by carbonized sodium oleate, which is beneficial to charge conduction.
[0124] Figure 3 (b) is the HRTEM image of a single CoP - CFP nanoparticle. Since the CoP lattice fringes are very fine, it is not conducive to resolution. For further analysis, we further magnify a part of a single CoP - CFP( Figure 3 (the part within the dotted white box in (b)) and obtain Figure 3 (c). From Figure 3 (c), it can be seen that the CoP - CFP nanoparticle has a polycrystalline boundary structure. The yellow represents the (201) crystal plane, the green is the (112) crystal plane, the blue is the (111) crystal plane, the pink is the (211) crystal plane, and the blue - purple is the (020) crystal plane. According to the literature reports, mutual - crossing grain boundaries can be formed between different crystal planes. The existence of grain boundaries is conducive to the formation of defects, which can expose abundant active sites, improve the reaction activity and efficiency, and thus improve the HER catalytic performance.
[0125] In addition, in order to verify the existence of phosphorus (P) element, the prepared CoP - CFP was also characterized by Mapping. Figure 3 (d) is the electron microscope photograph of a single CoP - CFP particle under dark field, Figure 3 (e) and Figure 3 (f) show the distribution of Co and P elements at the corresponding positions.
[0126] From Figure Figure 3 (e) and Figure 3(f) It can be seen that Co element exists throughout the CoP-CFP nanoparticles and is uniformly distributed. The signal response of P element is lower than that of Co element, indicating that sodium hypophosphite pyrolyzes into the form of PH3 during the preparation process and reacts with the Co micelle solution.
[0127] Electrochemical performance test
[0128] Using the self-supporting CoP-CFP material prepared in Example 1, the Co / CFP catalytic material prepared in Comparative Example 1, and the Pt / C electrode prepared in Comparative Example 2 as electrodes, in a 1 mol / L KOH alkaline solution at room temperature, when the current density is 10 mA cm -2 the hydrogen evolution reaction of the electrodes was tested, where the counter electrode was a carbon rod and the reference electrode was a saturated calomel electrode. And the hydrogen evolution reaction of the electrodes of the self-supporting CoP-CFP material prepared in Example 1 was tested at different current densities. Figure 4 Shows the LSV diagrams of the electrodes prepared in Example 1 and Comparative Examples 1-2 when the current density is 10 mA cm -2 and the electrodes prepared in Example 1 at different current densities.
[0129] From Figure 4 it can be known that for the self-supporting CoP-CFP material prepared in Example 1 in a 1 mol / L KOH alkaline solution, when the current density is 10 mA cm -2 , 50 mA cm -2 and 100 mA cm -2 the hydrogen evolution overpotentials are 78 mV, 125 mV, and 148 mV respectively.
[0130] For the Co / CFP catalytic material prepared in Comparative Example 1 as an electrode, in a 1 mol / L KOH alkaline solution, when the current density is 10 mA cm -2 the hydrogen evolution overpotential is 172 mV (as Figure 4 shown).
[0131] For the Pt / C electrode prepared in Comparative Example 2 in a 1 mol / L KOH alkaline solution, when the current density is 10 mA cm -2 the hydrogen evolution overpotential is 38 mV.
[0132] From Figure 4 it can be seen that when the self-supporting CoP-CFP material prepared in Example 1 of the present invention is used as an electrode, in a 1 mol / L KOH alkaline solution, the current density can exceed that of the commercial Pt / C electrode only at an overpotential of 121 mV.
[0133] Figure 5 Shows the overpotential diagrams of the self-supporting CoP-CFP materials prepared in Examples 1-5 of the present invention. From Figure 5It can be seen that the Tafel slope of the CoP-CFP catalytic material prepared in Example 1 of the present invention is 57.8 mV dec -1 , which is close to the Tafel slope (51.7 mV dec -1 ) of the Pt / C electrode, indicating that it has good charge transfer ability.
[0134] Figure 6 This is the LSV diagram at different sodium hypophosphite contents in each embodiment of the present application. It can be seen that the overpotential is optimal when the sodium hypophosphite content is 0.7 g. Specifically, as Figure 6 shown, it can be seen from the LSV diagram that at a current density of 10 mA cm -2 , the overpotentials of the samples from large to small are: CoP-CFP-0.1 (108 mV) > CoP-CFP-0.3 (101 mV) > CoP-CFP-0.5 (95 mV) > CoP-CFP-1.0 (82 mV) > CoP-CFP-0.7 (78 mV). Obviously, when the sodium hypophosphite content is 0.7 g, the minimum overpotential can be achieved after the PH3 generated reacts with the Co micelle CFP.
[0135] In summary, according to the CoP-CFP catalytic material of the present invention, compared with the Co-CFP catalytic material, since the CoP-CFP catalytic material has more grain boundary structures, it thus has more active sites. Therefore, the phosphated Co has a higher binding energy, which is beneficial to the adsorption and desorption of hydrogen and improves its HER catalytic performance. The non-precious metal electrode (CoP-CFP catalytic material electrode) prepared by the present invention can be comparable to or exceed the Pt / C electrode under certain conditions.
[0136] In addition, the preparation method of the cobalt phosphide self-supporting material (CoP-CFP) according to the present invention is simple and highly efficient, providing a feasible idea for the development of self-supporting catalytic materials.
Claims
1. A preparation method of a cobalt phosphide self-supporting material, characterized in that, The preparation method includes the following steps: 1) Mix water, organic alcohol, and surfactant to form solution A; mix water, organic alcohol, and cobalt salt to form solution B; then mix solution A, solution B, and organic solvent, and let the mixture stand. After the mixture is stratified, take the upper clear liquid to obtain a Co precursor micelle solution; 2) Drop the Co precursor micelle solution obtained in step 1) onto a conductive substrate. After the organic solvent volatilizes, a Co precursor micelle-conductive substrate is formed. Subject the Co precursor micelle-conductive substrate and a phosphorus source to a phosphorization reaction at a high temperature under a protective atmosphere to obtain a CoP-conductive substrate catalyst, that is, the cobalt phosphide self-supporting material.
2. The preparation method of the cobalt phosphide self-supporting material according to claim 1, wherein, In step 1), the molar ratio of the surfactant to the cobalt salt is 4 - 4.5:1; When forming solution A, the volume ratio of water to organic alcohol is 4:3; When forming solution B, the volume ratio of water to organic alcohol is 2:
1.
3. The preparation method of the cobalt phosphide self-supporting material according to claim 1, characterized in that, In step 1), the organic alcohol includes at least one of methanol, ethanol, propanol, isopropanol, butanol, and isobutanol; The surfactant has a long-chain alkyl structure; The cobalt salt includes at least one of cobalt nitrate and cobalt chloride; The organic solvent includes at least one of n-hexane, cyclohexane, n-pentane, and n-heptane.
4. The preparation method of the cobalt phosphide self-supporting material according to claim 1, wherein In step 1), when forming solution A or forming solution B or mixing solution A, solution B, and organic solvent, the mixing is carried out under stirring.
5. The preparation method of the cobalt phosphide self-supporting material according to claim 2, wherein, In step 2), the molar ratio of Co in the Co precursor micelle to P in the phosphorus source is 1:100 - 500.
6. The preparation method of the cobalt phosphide self-supporting material according to claim 2, characterized in that, In the step 2), the Co content in the Co precursor micelle-conductive substrate is 0.5 to 20 mg / cm 2 .
7. The preparation method of the cobalt phosphide self-supporting material according to claim 1, characterized in that, In step 2), keep the Co-precursor micelle-conductive substrate and the phosphorus source at a first temperature under a protective atmosphere, then cool down to a second temperature, and finally naturally cool under a protective atmosphere to obtain a CoP-conductive substrate catalyst.
8. The preparation method of the cobalt phosphide self-supporting material according to claim 7, wherein, In step 2), the first temperature is 420 - 480 °C; the holding time at the first temperature is 1.5 - 2.5 h.
9. The preparation method of the cobalt phosphide self-supporting material according to claim 7, characterized in that, In step 2), the second temperature is 110 - 90 °C.
10. The preparation method of the cobalt phosphide self-supporting material according to claim 7, characterized in that, In step 2), during the process of cooling down to the second temperature, the cooling rate is 4.5 - 5.5 °C / min.
11. The preparation method of the cobalt phosphide self-supporting material according to claim 1, characterized in that, In step 2), the protective atmosphere includes any one of nitrogen and argon.
12. The preparation method of the cobalt phosphide self-supporting material according to claim 1, wherein, In step 2), the phosphorization reaction is carried out in the glass tube of a high-temperature tube furnace.
13. The preparation method of the cobalt phosphide self-supporting material according to claim 1, characterized in that, In step 2), when carrying out the phosphorization reaction, put the formed Co precursor micelle-conductive substrate into container C1; put the phosphorus source into container C2; place container C2 on the upper side of the gas flow in the glass tube of the high-temperature tube furnace, and place container C1 on the lower side of the gas flow.
14. The preparation method of the cobalt phosphide self-supporting material according to claim 1, wherein In step 2), the conductive substrate includes any one of carbon fiber paper, carbon cloth, carbon felt, graphene foam, graphene aerogel, metal foil, and metal foam.
15. The preparation method of the cobalt phosphide self-supporting material according to claim 1, characterized in that, In step 2), the phosphorization temperature is 420 - 500 °C, and the holding time is 1 - 5 hours.
16. A cobalt phosphide self-supporting material, characterized in that, The cobalt phosphide self-supporting material includes a conductive substrate, a carbon coating film, and cobalt phosphide; wherein, the mass ratio of the conductive substrate, the carbon coating film, and cobalt phosphide is 20 - 40%:5 - 20%:30% - 70%.
17. The cobalt phosphide self-supporting material according to claim 16, characterized in that, The cobalt phosphide self-supporting material has a three-dimensional structure with multiple grain boundaries; the carbon-coated film is attached to the surface of the conductive substrate; the cobalt phosphide is dispersed in the carbon-coated film in the form of nanoparticles.
18. The cobalt phosphide self-supporting material according to claim 16 or 17, characterized in that, The cobalt phosphide self-supporting material is prepared by using the preparation method of the cobalt phosphide self-supporting material according to any one of claims 1-15.
19. An application of the cobalt phosphide self-supporting material according to any one of claims 16-18 as a HER reaction electrode in the field of hydrogen production by electrolysis of water.
20. Use of the cobalt phosphide self-supporting material according to claim 19 as an HER reaction electrode in the field of electrolytic water hydrogen production, characterized in that, The cobalt phosphide self-supporting material has a hydrogen evolution overpotential of 78 mV at a current density of 10 mA cm -2 in 1 mol / L KOH alkaline solution.