OER electrocatalyst as well as preparation method and application thereof

Abstract

The invention discloses an OER electrocatalyst as well as a preparation method and application thereof, and belongs to the technical field of electrolyzed water. The OER electrocatalyst is a Ni (OH) 2-CoWO4 / Co3W3C-coated CNF heterojunction composite material with a 3D (three-dimensional) structure. According to the preparation method, a CNF nano array is taken as a substrate, and the Ni (OH) 2-CoWO4 / Co3W3C-coated CNF multilevel heterostructure composite material is prepared through in-situ growth of CoWO4 / Co3W3C and in combination with water bath etching treatment. The in-situ constructed heterostructure catalyst not only improves the stability of the material structure, but also effectively improves the catalytic performance of OER. The preparation technology is simple, large-scale implementation is easy, and the method is suitable for preparing the high-performance OER anode material in batches.

Description

Technical Field

[0001] The present invention belongs to the technical field of water electrolysis, and in particular relates to an OER electrocatalyst and a preparation method and application thereof. Background Art

[0002] With the rapid development of global society and the continued growth of the population, energy demand is steadily increasing. As a green and sustainable energy carrier, hydrogen offers significant advantages over fossil fuels due to its environmentally friendly nature, with its combustion product being solely water. To meet energy demand and unleash the potential of hydrogen energy, electrocatalytic water splitting technology achieves efficient hydrogen production through two coupled half-reactions: the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode.

[0003] However, the slow reaction kinetics of the OER (Oelt-Hydrogen Evolution) process are a key bottleneck limiting overall hydrogen production efficiency. While noble metals and their oxides, such as IrO2 and RuO2, exhibit excellent OER catalytic activity, their high cost and scarcity severely hinder their large-scale application. Therefore, developing non-noble metal catalysts that combine high catalytic performance with cost advantages is of great practical significance for promoting the practical application of hydrogen energy technology. Summary of the Invention

[0004] To address the challenges of the aforementioned background technology, the present invention provides a noble metal-free OER electrocatalyst, its preparation method, and its application. By constructing a Ni(OH)2-CoWO4 / Co3W3C@CNF heterostructure, the present invention achieves the following technological breakthroughs: 1) significantly reducing the OER overpotential; 2) increasing the current density; and 3) enhancing catalyst stability.

[0005] The technical solution of the present invention is achieved through the following technical solutions:

[0006] One of the technical solutions of the present invention is a method for preparing an OER electrocatalyst, comprising the following steps:

[0007] S1, CoW PAN sample, i.e. cobalt-tungsten (Co-W)-doped polyacrylonitrile (PAN)-based material, was prepared by electrospinning technology;

[0008] S2, CoW PAN was placed in a CVD tube furnace and carbonized in a N2 atmosphere to obtain Co3W3C@CNF;

[0009] S3, calcining the Co3W3C@CNF in a muffle furnace to obtain CoWO4 / Co3W3C@CNF;

[0010] S4, immersing the CoWO4 / Co3W3C@CNF in a nickel nitrate solution and performing water bath etching to obtain a Ni(OH)2-CoWO4 / Co3W3C@CNF heterojunction composite material having a 3D structure, namely the OER electrocatalyst.

[0011] The electrospinning solution used in step S1 is prepared by dissolving cobalt acetate tetrahydrate, tungstate, and polyacrylonitrile (Mw = 150,000) in an N,N-dimethylformamide solution, followed by ultrasonic dispersion and magnetic stirring to obtain an electrospinning solution. The mass ratio of cobalt acetate tetrahydrate, tungstate, and polyacrylonitrile is 1:0-2:1, preferably 2:1:1.

[0012] Furthermore, in step S1, the total concentration of cobalt acetate tetrahydrate, tungstate and polyacrylonitrile in the N,N-dimethylformamide solution is 200-400 mg / mL.

[0013] Furthermore, the electrospinning conditions in step S1 are specifically as follows: ultrasonically stirring the electrospinning solution at room temperature for 18-20 hours; controlling the distance between the aluminum foil collector and the electrospinning needle to be 15 cm, and using a No. 17 electrospinning needle; and controlling the feed rate of the electrospinning solution to be 0.1 mm / min.

[0014] Furthermore, the carbonization conditions described in step S2 are as follows: the carbonization reaction conditions in step S2 are specifically as follows: under N2 atmosphere, heating to 900°C at a rate of 5°C / min, and carbonizing at 900°C for 3 hours to obtain a black Co3W3C@CNF nanofiber membrane.

[0015] Furthermore, the calcination conditions described in step S3 are as follows: placing Co3W3C@CNF into a muffle furnace, heating it to 250°C at a heating rate of 2°C / min and calcining it at 250°C for 3 hours to obtain CoWO4 / Co3W3C@CNF.

[0016] Furthermore, in step S4, the molar ratio of nickel nitrate to CoWO4 / Co3W3C@CNF is 0.25-1:1.

[0017] Furthermore, the specific conditions described in step S4 are: a mixed solution of nickel nitrate and CoWO4 / Co3W3C@CNF is placed in a 40-80°C water bath and etched for 1-4 hours to obtain a Ni(OH)2-CoWO4 / Co3W3C@CNF heterojunction composite material, namely the OER electrocatalyst.

[0018] As a preferred embodiment of the present invention, the concentration of the nickel nitrate solution is 0.2-1 mM. The molar ratio of nickel nitrate to CoWO4 / Co3W3C@CNF in step S4 is 0.5:1. The optimal water bath condition is to react in a water bath at 60°C for 2 hours.

[0019] In the preparation method of the present invention, if the reaction temperature in step S4 is too high, the surface Ni(OH)2 nanosheet structure will be destroyed; if the temperature is too low, it will be difficult to etch the Ni(OH)2 nanosheets on the CoWO4 / Co3W3C@CNF substrate. In addition, if the reaction time is too long, the morphological integrity of the Ni(OH)2-CoWO4 / Co3W3C@CNF will be damaged, while if the reaction time is too short, it will be difficult to achieve complete derivatization of the Ni(OH)2. Therefore, the preferred reaction conditions of the present invention are: 60°C for 2 hours.

[0020] The second technical solution of the present invention is an OER electrocatalyst, which is a Ni(OH)2-CoWO4 / Co3W3C@CNF heterojunction composite material with a 3D structure, wherein the interior is a CoWO4 / Co3W3C@CNF nanostructure and the exterior is a Ni(OH)2 nanosheet, so it has a 3D structure.

[0021] The third technical solution of the present invention is the use of the above-mentioned OER catalyst as an anode catalyst in hydrogen production by electrolysis of water.

[0022] The technical concept of the present invention:

[0023] Carbon nanofibers (CNFs), due to their high electrical conductivity and large surface area, offer unique advantages as substrate materials for efficient electrocatalysts: high conductivity accelerates interfacial electron transport and shortens charge migration pathways; their large surface area provides abundant anchoring space for active sites, promoting reactant adsorption and product desorption, thereby enhancing catalytic reaction kinetics. Electrospinning, an effective method for preparing nanofibers, can precisely construct CNFs with self-supporting structures, high porosity, and excellent chemical stability by manipulating spinning parameters such as solution viscosity, electric field strength, and receiving distance.

[0024] This invention is based on an in-situ growth mechanism on a highly conductive CNF substrate, and constructs a Ni(OH)2-CoWO4 / Co3W3C@CNF heterostructure through a series of processes including carbonization, calcination, and water-bath synthesis. This design facilitates spatial charge migration between reaction interfaces, thereby improving the catalyst's OER performance. The porous nanofiber structure after carbonization and calcination provides abundant catalytic active sites and effectively enhances mass transfer. The formation of the heterointerface promotes the adsorption of oxygen intermediates, while the change in the valence state of the reaction phase accelerates electron transport and regulates the electronic structure of the catalyst during the OER process.

[0025] The process of the present invention is simple and easy to implement, and can prepare high-performance electrode materials in batches. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required in the embodiments. Obviously, the drawings described below are only drawings of some embodiments of the present invention. For those skilled in the art, other relevant drawings can be obtained based on these drawings without inventive efforts.

[0027] Figure 1 TEM (transmission electron microscopy) image of 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF of Example 1 of the present invention;

[0028] Figure 2 This is a SEM (scanning electron microscope) image of 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF prepared in Example 1 of the present invention;

[0029] Figure 3 XRD patterns of 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF and CoWO4 / Co3W3C@CNF;

[0030] Figure 4 The voltammetric linear polarization curves of 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF and CoWO4 / Co3W3C@CNF prepared in Example 1 of the present invention in 1 M potassium hydroxide solution;

[0031] Figure 5 The voltammetric linear polarization curves of the catalysts with different Co:W mass ratios prepared in Example 1 of the present invention in 1 M potassium hydroxide solution;

[0032] Figure 6 This is the chronopotentiometry diagram of 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF prepared in Example 1 of the present invention;

[0033] Figure 7 The pore size distribution of different catalysts prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described and illustrated below in conjunction with specific embodiments. The embodiments are merely illustrative of the present disclosure and do not limit its scope. The technical features of the various embodiments of the present invention may be combined accordingly, provided that there is no conflict between them.

[0035] 1. Preparation of Ni(OH)2-CoWO4 / Co3W3C@CNF Heterostructure Catalyst

[0036] The present invention constructs a Ni(OH)2-CoWO4 / Co3W3C@CNF heterostructure through a series of processes such as electrospinning carbonization, calcination, and water bath synthesis.

[0037] Weigh 0.5g(CH3COO)2Co·4H2O, ag(NH4)6W7O 24 6H2O (where a = 0.1, 0.25, 0.5, or 1) and 0.4 g of polyacrylonitrile (Mw = 150,000) were dissolved in 5 mL of N,N-dimethylformamide and ultrasonically stirred for 24 hours to prepare the electrospinning solution. The homogenized, viscous solution was then poured into a 2 mL plastic syringe and connected to a high-voltage power supply (16 kV). High-voltage electrospinning was performed at room temperature using a 17-gauge needle with a distance of 15 cm between the aluminum foil collector and the needle tip. The syringe pump controlled the feed rate at 0.1 mm / min. Four sets of CoW PAN samples with different a values ​​were collected on the aluminum foil on the collector.

[0038] The collected CoW PAN was placed in a CVD tube furnace (chemical vapor deposition tube furnace) and carbonized at 900°C for 3 hours at a rate of 5°C / min in a nitrogen atmosphere to produce black Co3W3C@CNF nanofiber membranes. These membranes were then calcined at 250°C for 3 hours at a rate of 2°C / min in a muffle furnace to produce four groups of CoWO4 / Co3W3C@CNF with different a values. Electrochemical performance testing of the resulting CoWO4 / Co3W3C@CNF revealed that the optimal performance was achieved when a = 0.25. Subsequent experiments were conducted based on an a value of 0.25.

[0039] This example takes the preparation of 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF as an example to introduce the preparation of Ni(OH)2-CoWO4 / Co3W3C@CNF heterostructure catalyst.

[0040] First, 0.5 mmol Ni(NO3)2 was dissolved in 40 mL distilled water as the synthesis liquid, and the prepared CoWO4 / Co3W3C@CNF powder was ground. 0.05 g of the powder was weighed and placed in the synthesis liquid. The powder was then placed in a 60°C water bath for reaction for 2 hours. After the reaction was completed, the powder was washed three times by centrifugation with distilled water and ethanol, and dried in a 60°C oven for 12 hours to obtain 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF.

[0041] The morphology of the samples was analyzed in depth by TEM images. Figure 1As shown. Figure 1 a and Figure 1 As can be seen in b, the oxide layer surface of the nanofibers is evenly covered with hydroxide nanosheets. Figure 1 c analysis, the lattice spacing of 0.174 nm on the nanosheet corresponds to the (102) crystal plane of Ni(OH)2, while the lattice spacings of 0.216 nm and 0.274 nm correspond to the (012) crystal plane of CoWO4 and the (400) crystal plane of Co3W3C, respectively.

[0042] The crystal structure of 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF was determined by XRD test. Figure 3 Other diffraction peaks were observed at 23.8°, 24.5°, 30.6°, 31.5°, 36.3°, 48.8° and 52.1°, which can be attributed to the crystal plane of CoWO4 (JCPDS15-0867). (011), (020), (200), The characteristic diffraction peaks observed at 32.5°, 35.5°, 40.1°, 42.5°, 46.6°, and 72.4° correspond precisely to the crystalline surface of Co3W3C (JCPDS271125), specifically representing the (400), (331), (422), (511), (440), and (822) crystal planes. After water bath etching, characteristic peaks corresponding to the hydroxide Ni(OH)2 (JCPDS14-0117) with the (001), (101), (102), and (200) crystal planes were detected at 19.1°, 38.4°, 52.1°, and 69.2°, respectively.

[0043] from Figure 2 It can be seen that the ultrathin Ni(OH)2 nanosheets on the carbon nanofiber CNF have a large number of pores and show a very high specific surface area. Figure 1 In the high-resolution TEM images presented in

[15] , the lattice spacing of 0.24 nm on the nanosheets is attributed to the (101) plane of Ni(OH)2. In addition, the lattice spacings of 0.21 nm and 0.33 nm are associated with the (511) and (311) planes of Co3W3C, respectively, while the lattice spacing of 0.36 nm is associated with the (011) plane of CoWO4.

[0044] Gas adsorption was performed on different catalyst materials to test their pore structure and size distribution: an appropriate amount of sample (50-200 mg) was ground and placed in a sample tube. The sample was heated and degassed at 77K under vacuum conditions for 8 hours to remove impurities. After degassed, the sample was weighed and installed in the adsorption instrument. The instrument was calibrated with high-purity nitrogen (purity ≥99.99%). Liquid nitrogen was used as the adsorption temperature. Nitrogen adsorption isotherm data was collected in the relative pressure (P / P0) range of 0.05-0.30 to determine the specific surface area of ​​the sample. Figure 7 The analysis in Figure 1 shows that the surface area increases with increasing pressure, which is consistent with the significant rise of the relative high-pressure isotherm. In addition, with the successful synthesis of sodium hydroxide nanosheets, 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF has a larger specific surface area. In addition, according to the pore size distribution diagram ( Figure 7 In (bc), the average pore size of the catalyst gradually increases, indicating a hierarchical pore size distribution. For 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF, the measured average pore size is 6.15 nm. The large specific surface area and gradually increasing porosity provide ample contact between the catalyst and the electrolyte, facilitating the rapid diffusion of reactants to the active sites. Furthermore, the high specific surface area also exposes more active sites, improving the overall reaction efficiency of the OER.

[0045] 2. Electrochemical performance of 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF catalyst

[0046] The experimental process used a standard three-electrode system to test the performance of the catalyst. The prepared catalyst (10 mg) was dispersed in a mixture of ethanol (950 μl) and 5% Nafion (50 μl) and ultrasonicated for 30 minutes to form a uniform suspension. 100 μL of this suspension was drop-coated onto a 1×0.5 cm 2 The working electrode was a graphite rod electrode and a Hg / HgO electrode were selected as the counter electrode and reference electrode, respectively, of the three-electrode system. The potentials of all electrochemical measurements were converted to reversible hydrogen electrode (RHE) potentials using the following equation:

[0047] E RHE =E Hg / Hg +0.059×pH+0.098

[0048] 1M KOH at room temperature was selected as the electrolyte for the alkaline OER experiment. -1 The linear sweep voltammetry curve was obtained at a scan rate of 10 mA cm. The stability test was performed by chronopotentiometry to evaluate the stability of the 10 mA cm -2 The stability of the catalyst.

[0049] Comprehensive evaluation of the synergistic effect of interface optimization on catalysts Figure 4 shown and extensively compared with commercially available iridium oxide. Figure 4 The polarization curves in Figure 3 clearly demonstrate the remarkable synergistic effect of the multi-level interface of 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF, which significantly enhances the OER catalytic performance with an overpotential as low as 250 mV (10 mA cm -2 ). In contrast, CoWO4 / Co3W3C@CNF exhibits an overpotential of 290 mV, both values ​​significantly lower than the overpotential of commercial IrO2 (320 mV). In addition, Figure 5 It shows that CoWO4 / Co3W3C@CNF-2:1 is the optimal ratio for the synthesis of this catalyst.

[0050] Figure 6 Displayed at 10mAcm -2 The voltage change during the stability test performed under 370 nm was shown, which demonstrated that 0.5-Ni(OH)2-CoWO4 / Co3W3C@CNF can be effectively and stably operated at room temperature for 200 h.

[0051] The above-described embodiments merely illustrate the implementation methods of the present invention. Although the descriptions thereof are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. A person skilled in the art would be able to make various modifications and improvements without departing from the scope of the present invention, and all such modifications and improvements fall within the scope of protection of the present invention.

Claims

1. A method for preparing an OER electrocatalyst, characterized in that: The following steps are involved: S1, CoW PAN sample prepared by electrospinning technology; S2, CoW PAN was placed in a CVD tube furnace and carbonized in a N2 atmosphere to obtain Co3W3C@CNF; S3, calcining the Co3W3C@CNF in a muffle furnace to obtain CoWO4 / Co3W3C@CNF; S4, immersing the CoWO4 / Co3W3C@CNF in a nickel nitrate solution and performing water bath etching to obtain a Ni(OH)2-CoWO4 / Co3W3C@CNF heterojunction composite material having a 3D structure, namely the OER electrocatalyst.

2. The preparation method according to claim 1, characterized in that In step S1, the electrospinning solution used for electrospinning is prepared by dissolving cobalt acetate tetrahydrate, tungstate and polyacrylonitrile in N,N-dimethylformamide solution, performing ultrasonic dispersion and magnetic stirring to obtain the electrospinning solution.

3. The preparation method according to claim 1, characterized in that In step S1, the mass ratio of the cobalt acetate tetrahydrate, tungstate and polyacrylonitrile is 1:0 to 2:1; and the total concentration of the cobalt acetate tetrahydrate, tungstate and polyacrylonitrile in the N,N-dimethylformamide solution is 200-400 mg / mL.

4. The preparation method according to claim 1, characterized in that The electrospinning conditions in step S1 are as follows: the electrospinning solution is ultrasonically stirred at room temperature for 18-20 hours; the distance between the aluminum foil collector and the electrospinning needle is controlled to be 15 cm, and a No. 17 electrospinning needle is used; and the feeding speed of the electrospinning solution is controlled to be 0.1 mm / min.

5. The preparation method according to claim 1, characterized in that The carbonization reaction conditions in step S2 are specifically as follows: heating to 900°C at a rate of 5°C / min and carbonizing at 900°C for 3 hours; the calcination conditions in the muffle furnace in step S3 are specifically as follows: heating to 250°C at a heating rate of 2°C / min and calcining at 250°C for 3 hours.

6. The preparation method according to claim 1, characterized in that In step S4, the molar ratio of nickel nitrate to CoWO4 / Co3W3C@CNF is 0.25-1:1; the mixed solution of nickel nitrate and CoWO4 / Co3W3C@CNF is placed in a 40-80°C water bath and etched for 1-4 hours to obtain the OER electrocatalyst.

7. The preparation method according to claim 1, characterized in that The concentration of the nickel nitrate solution is 0.2-1 mM, and the water bath etching is carried out at 60° C. for 2 hours.

8. An OER electrocatalyst prepared by the method according to any one of claims 1 to 7.

9. The OER electrocatalyst according to claim 8, characterized in that The OER electrocatalyst is a Ni(OH)2-CoWO4 / Co3W3C@CNF heterojunction composite material with a 3D structure, in which the interior is a CoWO4 / Co3W3C@CNF nanostructure and the exterior is a Ni(OH)2 nanosheet.

10. Use of the OER electrocatalyst according to claim 8 as an anode catalyst in hydrogen production by water electrolysis.

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