Preparation method of high-activity transition metal phosphide catalyst

Abstract

The invention relates to a preparation method of a high-activity transition metal phosphide catalyst, which comprises the following steps: taking basic nickel cobalt carbonate (NiCo-OH / NF) grown on foamed nickel in situ as a precursor, placing the precursor at the downstream of a tubular furnace, placing NaH2PO2 at the upstream of the tubular furnace, annealing in a nitrogen atmosphere at 350 DEG C for 2 hours, and naturally cooling to obtain NiCoP / NF; the preparation method comprises the following steps: soaking NiCoP / NF in a potassium salt solution of a boride, washing, and carrying out vacuum drying to obtain a boron-potassium modified catalyst precursor NiCoP-BK / NF; in a three-electrode system, electrodeposition is carried out in an electrolyte containing a Ni source, a Fe source and deionized water, and the high-activity transition metal phosphide-nickel iron hydroxide NiCoP-BK-coated NiFe-LDH / NF heterojunction composite catalyst is obtained. The activity and stability of the transition metal phosphide catalyst can be remarkably improved, and the preparation method is simple and low in cost.

Description

Technical field:

[0001] The invention relates to the field of electrocatalysis and energy materials, and in particular to a method for preparing a high-activity transition metal phosphide catalyst. Background technology:

[0002] Electrochemical water splitting is a simple and rapid method for producing H 2 and O 2 The method involves two processes, oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, the kinetics of these processes are slow, which seriously restricts production efficiency. Due to the low Gibbs free energy, precious metals (such as Pt and Ir) have been used to solve this problem, but their high price and scarcity limit their large-scale application. Transition metal phosphide (TMP)-based catalysts have shown great potential in overall water splitting. However, their activity has not yet reached the ideal value. In addition, non-precious metal catalysts have problems such as catalyst shedding from the electrode sheet and adverse changes in the microstructure of the active component during long-term reaction, which limits further large-scale application. Therefore, it is particularly important to study and develop highly active transition metal phosphide catalysts.

[0003] In recent years, a lot of research has been done at home and abroad on improving the activity of water electrolysis catalysts. Chinese patent document CN114990608A provides "a sub-nanometer thick NiCoP two-dimensional ultra-thin film and its preparation method", which is a sub-nanometer thick NiCo(OH) 2 The two-dimensional film is converted into a NiCoP phase by low-temperature phosphating to obtain a NiCoP two-dimensional film with a sub-nanometer thickness. Chinese patent document CN116695165A discloses "a transition metal Mn-Ni, P / NiFe-LDH catalyst and its preparation method and application", which obtains the Mn-Ni, P / NiFe-LDH catalyst by hydrothermal synthesis, low-temperature phosphating and secondary hydrothermal method. Chinese patent document CN118127530A discloses "the preparation and electrolysis application of NiCoP@NiCo LDH@C three-dimensional electrode", and prepares a three-dimensional self-supporting NiCoP@NiCo LDH@C electrode by hydrothermal method, modified phosphating method and electrodeposition method, which effectively improves the activity of the electrode in the catalytic process. However, the preparation process of these materials is relatively complicated, costly, energy-intensive, and the degree of stability improvement is also limited.

[0004] Since the electrocatalytic activity of a single transition metal is limited, its electrocatalytic performance is often further improved by constructing a heterojunction composite catalyst. In a heterojunction composite catalyst, there is electron transfer or sharing between different components at the heterojunction interface, which changes the electronic structure of each component, thereby affecting its adsorption and activation ability for reactants. This electronic interaction can enhance the adsorption strength of the catalyst on the reactants, reduce the activation energy of the reaction, and increase the catalytic reaction rate. Therefore, in recent years, the construction of transition metal heterojunction catalysts has become a hot topic in the preparation of high-performance HER catalysts.

[0005] From the principle of heterojunction catalysts to improve HER activity, it can be seen that regulating the atomic arrangement, chemical bonding mode and electronic structure between different components at the interface of heterojunction composite catalysts can optimize the adsorption performance and reaction mode of reactants at the interface, promote HER catalytic reaction, and is the key to improving catalyst activity. NiCoP nanosheet HER catalyst is considered to be a very promising electrocatalyst, but it has problems such as limited number of HER active sites, low intrinsic activity, and poor stability. Therefore, developing a new structure NiCoP-based heterojunction catalyst to regulate and optimize the atomic arrangement, chemical bonding mode and electronic structure at the heterojunction interface through a simple and low-cost method is the key to solving its limited number of HER active sites, low intrinsic activity, and poor stability. Summary of the invention:

[0006] The purpose of the present invention is to provide a method for preparing a high-activity transition metal phosphide catalyst, which is used to solve the problems of limited number of HER active sites, low intrinsic activity and poor stability of NiCoP nanosheet catalysts in the prior art.

[0007] The technical solution adopted by the present invention to solve the technical problem is: the preparation method of the high-activity transition metal phosphide catalyst comprises the following steps:

[0008] Step 1: NiCo-OH / NF, a basic nickel cobalt carbonate in situ grown on nickel foam, is used as a precursor and placed downstream of a tube furnace. 2 PO 2 Placed upstream, the molar ratio of P to Ni is 3 to 6:1; in a nitrogen atmosphere at 2 °C·min -1 The NiCoP / NF was obtained by annealing at 350 °C for 2 h and cooling naturally.

[0009] Step 2: Soak the obtained NiCoP / NF in a 0.05-3M potassium salt solution of a boride for 5-60 minutes, remove the surface residue, wash, and vacuum dry to obtain a boron-potassium modified catalyst precursor NiCoP-BK / NF;

[0010] Step 3: In a three-electrode system, electrodeposition is carried out in an electrolyte containing a Ni source, an Fe source and deionized water, the molar ratio of the Ni source, the Fe source and the deionized water is 1:1 to 4:80, the deposition voltage is -1.5 to 0.5 V, and the deposition time is 400 s to 1200 s, thereby obtaining a highly active transition metal phosphide-nickel iron hydroxide NiCoP-BK@NiFe-LDH / NF heterojunction composite catalyst with optimized interface properties and atomic arrangement.

[0011] Preparation method of NiCo-OH / NF in step 1 of the above scheme: Ni source and Co source, NH 4 F. Preparation by in-situ growth on nickel foam in urea aqueous solution, wherein the initial molar ratio of Ni to Co is 1-2:1, the molar ratio of Ni to deionized water is 1:500-1000, and the molar ratio of Ni to NH 4 The molar ratio of F to urea is 1:5:20.

[0012] In step 2 of the above scheme, washing is performed by alternating ethanol and water for 3 times; vacuum drying is performed at 60° C. for 12 hours.

[0013] The potassium salt solution of the boride in the above scheme refers to a mixture of potassium borate and potassium borohydride, wherein the molar ratio of potassium borate to potassium borohydride is 0.5:1-10.

[0014] In the above scheme, the three-electrode system is composed of NiCoP-BK / NF as the working electrode, saturated calomel electrode SCE as the reference electrode, and Pt sheet as the counter electrode.

[0015] In step 3 of the above scheme, the Ni source is any one of nickel chloride, nickel nitrate, and nickel acetate.

[0016] In step 3 of the above scheme, the Fe source is any one of ferrous chloride, ferrous nitrate, and ferrous acetate.

[0017] Beneficial effects:

[0018] 1. Simplified preparation process: It provides a simple and efficient preparation method for the NiCoP-BK@NiFe-LDH heterojunction electrocatalyst with high activity, high stability, optimized interface properties and atomic arrangement. This method can not only significantly improve the activity and stability of transition metal phosphide catalysts, but also has a simple preparation method and low cost.

[0019] 2. Excellent HER catalytic activity: (a) In the catalyst preparation route, a NiFe hydroxide heterojunction composite catalyst fixed on NiCoP nanosheets was constructed, and the electron transfer or sharing between NiCoP and NiFe hydroxide was used to optimize the electronic structure, reduce the activation energy of the reaction, and improve the catalytic activity; (b) Boron-potassium modification regulated the interface properties of the heterostructure of NiCoP and NiFe hydroxide and the atomic arrangement at the interface, enhanced and regulated the built-in electric field, and thus improved the catalytic activity; Boron-potassium modification increased the specific surface area of ​​the catalyst and the high dispersion of active sites, and increased the number of exposed active sites. (c) Potassium interacted with the active components of the NiCoP-BK@NiFe-LDH / NF catalyst, causing electrons to transfer between the catalyst and potassium, further regulating the electronic structure of the NiCoP-BK@NiFe-LDH / NF catalyst; Potassium formed new active sites with atoms or groups on the catalyst surface, and these active sites further improved the catalytic activity. Therefore, the coupling method of constructing NiCoP@NiFe-LDH / NF heterojunction and boron-potassium modification treatment proposed in the present invention effectively solves the bottleneck problem of limited number of NiCoP / NF active sites and low catalytic activity.

[0020] 3. Improved stability: (a) The built-in electric field formed between different components of the heterojunction reduces the damage to the catalyst structure caused by improper adsorption of intermediates, which helps to improve the stability of the catalyst; (b) Potassium ions can interact with impurities or poisoning substances on the catalyst surface, slowing down their impact on the active components of the catalyst, thereby extending the life of the catalyst.

[0021] 4. Broad application prospects: Under alkaline conditions, when the NiCoP-BK@NiFe-LDH / NF catalyst prepared by the method provided by the present invention is used as a hydrogen evolution catalyst, its HER catalytic activity is better than that of the precious metal Pt-C / NF catalyst; and under constant current, the current is almost not attenuated for 100 hours, and it has good stability, which fully demonstrates that the NiCoP-BK@NiFe-LDH / NF catalyst has good industrial application prospects. The preparation method proposed by the present invention can be widely used in a variety of important electrochemical reactions such as water / seawater decomposition, carbon dioxide reduction, and microbial fuel cells, and has important industrial application value. Description of the drawings:

[0022] Figure 1 The preparation process of NiCo-OH / NF precursor;

[0023] Figure 2 The present invention is a process for preparing the catalyst;

[0024] Figure 3XRD pattern of NiCoP-BK@NiFe-LDH / NF catalyst;

[0025] Figure 4 SEM (a) and TEM (b) images of NiCoP-BK@NiFe-LDH / NF catalyst;

[0026] Figure 5 LSV curve of hydrogen evolution of NiCoP-BK@NiFe-LDH / NF catalyst;

[0027] Figure 6 The effect of boron-potassium modification on the NiCoP-BK@NiFe-LDH / NF heterojunction interface;

[0028] Figure 7 is the Tafel slope curve of NiCoP-BK@NiFe-LDH / NF catalyst;

[0029] Figure 8 is the stability curve of NiCoP-BK@NiFe-LDH / NF catalyst under alkaline conditions;

[0030] Fig. 9 This is the theoretical calculation result. Specific implementation method:

[0031] The present invention will be further described below in conjunction with the accompanying drawings:

[0032] The preparation method of this high-activity transition metal phosphide-nickel iron heterojunction catalyst is to firstly obtain NiCoP / NF catalyst precursor by hydrothermal method-assisted low-temperature nitrogen atmosphere phosphating on nickel foam, and then obtain NiCoP-BK / NF by boron-potassium modification, and then deposit it in a three-electrode system containing Ni and Fe ions to prepare NiCoP-BK@NiFe-LDH heterostructure composite catalyst. This high-activity transition metal phosphide-nickel iron hydroxide heterojunction catalyst is composed of NiFe hydroxide fixed on NiCoP nanosheets with optimized heterojunction interface properties and atomic arrangement. The present invention provides a simple and low-cost preparation method for regulating the atomic arrangement, chemical bonding mode and electronic structure at the heterojunction interface of the transition metal phosphide composite catalyst, thereby solving the problems of limited number of HER active sites, low intrinsic activity and poor stability of NiCoP nanosheet catalysts, thereby opening up a new way to improve the HER performance of transition metal phosphides by regulating the interface properties and atomic arrangement of heterojunction catalysts.

[0033] Embodiment 1:

[0034] This example illustrates the preparation and XRD and TEM characterization of NiCoP-BK@NiFe-LDH / NF catalyst. Figure 2. The preparation method of this highly active transition metal phosphide-nickel iron heterojunction catalyst:

[0035] 1) Preparation of nickel cobalt carbonate (NiCo-OH / NF) precursor grown in situ on nickel foam:

[0036] The preparation process of NiCo-OH / NF precursor is shown in Figure 1 The nickel foam was treated with acetone, 1 mol·L -1 The mixture was washed with hydrochloric acid solution and deionized water, and dried for later use. 4 F, urea, deionized water (Ni, Co, NH 4 F, urea, and deionized water (molar ratio of 1:1:5:20:1000) were mixed to form a uniform solution, which was transferred to a reactor containing a vertically placed nickel foam, and hydrothermally reacted at 120° C. for 12 hours. After cooling to room temperature, the mixture was washed alternately with ethanol and deionized water for 3 times, and vacuum dried at 60° C. for 12 hours to obtain a basic nickel cobalt carbonate (NiCo-OH / NF) precursor.

[0037] 2) Preparation of NiCoP-BK / NF catalyst precursor and boron-potassium modification:

[0038] The obtained NiCo-OH / NF precursor and sodium hypophosphite were placed in two quartz boats respectively, with a molar ratio of sodium hypophosphite to nickel nitrate of 3:1. After being placed in a tube furnace, the temperature was raised to 350 °C in a nitrogen atmosphere at a heating rate of 2 °C·min -1 , phosphating for 2 hours to obtain transition metal phosphide NiCoP / NF catalyst precursor. After soaking it in 25mL 0.5M potassium borate and potassium borohydride solution (molar ratio of 0.5:1) for 30 minutes, remove the surface residue, wash it with ethanol and water alternately for 3 times, and vacuum dry it at 60°C for 12 hours to obtain boron-potassium modified catalyst precursor NiCoP-BK / NF.

[0039] 3) Preparation of NiCoP-BK@NiFe-LDH / NF catalyst:

[0040] The obtained NiCoP-BK / NF catalyst was used as the working electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the Pt thin sheet was used as the counter electrode. Electrodeposition was performed in an electrolyte consisting of nickel nitrate and ferrous nitrate (the molar ratio of Ni source, Fe source and deionized water was 1:2:80) in deionized water. The NiCoP-BK@NiFe-LDH / NF catalyst was obtained by electroplating at a voltage of -0.5V relative to the saturated calomel electrode for 400s. The preparation process is simple, and no expensive reagents are used, and no complicated process or expensive equipment is required, which greatly reduces the cost of the catalyst.

[0041] XRD, SEM and TEM characterization of the NiCoP-BK@NiFe-LDH / NF catalyst obtained in this example:

[0042] The obtained NiCoP-BK@NiFe-LDH / NF catalyst was characterized by XRD and the active phase in the catalyst was analyzed. Figure 3 . The characteristic peaks of NiCoP-BK@NiFe-LDH / NF catalyst at 2θ=44.50, 51.85, and 76.38° correspond to the (111), (200), and (220) crystal planes of nickel foam, respectively. The characteristic peaks at 2θ=40.99, 44.90, and 54.44° are attributed to the (111), (201), and (300) crystal planes of NiCoP phase, respectively (PDF#71-2336). The characteristic peaks at 2θ=11.53, 23.28, and 34.56° are attributed to the (003), (006), and (012) crystal planes of NiFe phase, respectively (PDF#51-0463). No diffraction peaks of other phases are observed in the spectrum, indicating that the main phases of the catalyst are NiCoP and NiFe phases, without other impurity phases. The NiCoP-BK@NiFe-LDH / NF catalyst was characterized by SEM and TEM. Figure 4 .Depend on Figure 4 It can be seen that the catalyst has a certain number of mesh structures formed by interweaving nanowires and a sparse nanoflower morphology with a diameter of about 8 to 10 μm distributed on the surface. The stripe spacing exposed by the TEM image is about 0.226 and 0.248 nm, which belongs to the (111) and (201) lattice planes of NiCoP, and 0.102 and 0.260 nm, which belongs to the (003) and (012) lattice planes of NiFe. There is a clear interface between NiCoP and NiFe hydroxide, indicating the formation of a heterogeneous structure.

[0043] Embodiment 2:

[0044] This example illustrates the HER activity of NiCoP-BK@NiFe-LDH / NF catalyst under alkaline conditions.

[0045] Preparation method of this highly active transition metal phosphide-nickel iron heterojunction catalyst:

[0046] 1) Preparation of nickel cobalt carbonate (NiCo-OH / NF) precursor grown in situ on nickel foam:

[0047] The nickel foam was treated with acetone, 1 mol·L -1 The mixture was washed with hydrochloric acid solution and deionized water, and dried for later use. 4 F, urea, deionized water (Ni, Co, NH4 F, urea, and deionized water (molar ratio of 1:2:5:20:500) were mixed to form a uniform solution, which was transferred to a reactor containing a vertically placed nickel foam, and hydrothermally reacted at 120° C. for 12 hours. After cooling to room temperature, the mixture was washed alternately with ethanol and deionized water for 3 times, and vacuum dried at 60° C. for 12 hours to obtain a basic nickel cobalt carbonate (NiCo-OH / NF) precursor.

[0048] 2) Preparation of NiCoP-BK / NF catalyst precursor and boron-potassium modification:

[0049] The obtained nickel cobalt carbonate (NiCo-OH / NF) precursor and sodium hypophosphite were placed in two quartz boats, respectively, with a molar ratio of sodium hypophosphite to nickel nitrate of 6:1. After being placed in a tube furnace, the temperature was raised to 350°C in a nitrogen atmosphere at a heating rate of 2°C·min -1 The catalyst precursor NiCoP / NF was obtained by phosphating it for 2 hours. After soaking it in 25 mL of a 1.5 M solution of potassium borate and potassium borohydride with a molar ratio of 0.5:5 for 20 minutes, the surface residue was removed, and it was washed alternately with ethanol and water for 3 times and vacuum dried at 60°C for 12 hours to obtain a boron-potassium modified catalyst precursor NiCoP-BK / NF.

[0050] 3) Preparation of NiCoP-BK@NiFe-LDH / NF catalyst:

[0051] The obtained NiCoP-BK / NF catalyst was used as the working electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the Pt thin sheet was used as the counter electrode. Electrodeposition was performed in an electrolyte consisting of nickel nitrate and ferrous nitrate (the molar ratio of Ni source, Fe source and deionized water was 1:1:80) in deionized water. The NiCoP-BK@NiFe-LDH / NF catalyst was obtained by electroplating at a voltage of -1.2 V relative to the saturated calomel electrode for 600 s.

[0052] For comparison, NiCoP / NF (modified with potassium borohydride only), NiCoP@NiFe-LDH / NF (not modified with boron or potassium), NiCoP / NF and NiFe-LDH / NF catalysts were prepared by the same method with other conditions unchanged.

[0053] Under alkaline conditions, the HER performance test was carried out using the sample obtained in this example. The results are shown in Figure 5 And Table 1. Figure 5 As shown in Table 1, the NiCoP-BK@NiFe-LDH / NF catalyst prepared by the present invention has a -2 The HER overpotential at 10=32mV, significantly better than the precious metal Pt-C / NF (η 10 =44mV) catalyst; compared with NiCoP / NF (η 10 =106mV), the overpotential decreased by 70%, indicating that the NiCoP-BK@NiFe-LDH / NF catalyst prepared by the present invention can significantly improve the HER activity of NiCoP / NF. 1 @NiFe-LDH / NF compared with (η 10 =36mV), the overpotential of NiCoP-BK@NiFe-LDH / NF decreased by 12.5%, indicating that the synergistic effect of potassium borate and potassium borohydride can achieve excellent results. Compared with NiCoP / NiFe-LDH / NF without boron-potassium modification (η 10 =45mV), the overpotential of NiCoP-BK@NiFe-LDH / NF was reduced by 29%, indicating that the boron-potassium modification method of the present invention is an effective way to further improve the activity of NiCoP / NiFe-LDH / NF heterojunction catalyst.

[0054] In order to illustrate the effect of boron-potassium modification on NiCoP / NiFe-LDH / NF heterojunction catalyst, the influence of boron-potassium modification on the NiCoP-BK@NiFe-LDH / NF heterojunction interface was analyzed. Figure 6. During the preparation process, first, the NiCo-OH precursor is phosphated to obtain the NiCoP / NF precursor, which is then modified with boron and potassium to embed B and K on the surface and form P vacancies, thereby obtaining NiCoP-BK / NF; secondly, NiFe is electrodeposited on its surface to fix it on NiCoP. In this process, new voids (see the dotted circle in the figure) and defects are formed at the heterojunction interface, which optimizes the interface properties and atomic arrangement of the heterostructure, and forms a specific pore structure, reaction channel or interface through the mutual matching and mutual influence of the geometric structures of the different active components NiCoP and NiFe-LDH. In addition, the built-in electric field generated by the combined action of the heterojunction and P vacancies optimizes the charge distribution on the catalyst surface and improves the conductivity of the electrocatalyst; at the same time, the built-in electric field optimizes the hydrogen adsorption energy of the catalyst and enhances the water adsorption energy by adjusting the adsorption energy, thereby improving the catalytic activity. Therefore, (a) boron-potassium modification optimizes the electron redistribution and atomic rearrangement at the heterogeneous interface of NiCoP-BK@NiFe-LDH / NF catalyst through B and K embedding and P vacancies, enhances and regulates the built-in electric field, further regulates the electronic structure, optimizes the hydrogen adsorption energy of the catalyst, enhances the water adsorption energy, and thus improves the catalytic activity. (b) Boron-potassium modification and NiFe deposition work synergistically to form many new voids and defects at the heterogeneous structure interface, forming a specific pore structure, reaction channel or interface, increasing the specific surface area of ​​the catalyst and the high dispersion of active sites, thereby promoting the catalytic process. (c) Potassium interacts with the active components of NiCoP-BK@NiFe-LDH / NF catalyst, causing electrons to transfer between the catalyst and potassium, regulating the electronic structure of NiCoP-BK@NiFe-LDH / NF catalyst; potassium forms new active sites with atoms or groups on the catalyst surface, and these active sites further improve the catalytic activity.

[0055] With NiCoP-B 1 @NiFe / NF (modified with potassium borohydride only) compared with (η 10 =36mV), NiCoP-BK@NiFe-LDH / NF prepared with mixed potassium salt containing boron (η 10 =32 mV) was reduced by 12.5%, indicating that the synergistic effect of potassium borohydride and sodium borate is the key to obtaining the highly active NiCoP-BK@NiFe-LDH / NF catalyst by boron-potassium modification.

[0056] Table 1 Comparison of HER activity of different catalysts

[0057]

[0058] Example 3

[0059] This example illustrates the electrocatalytic activity area (ECSA) of the NiCoP-BK@NiFe-LDH / NF catalyst.

[0060] Preparation method of this highly active transition metal phosphide-nickel iron heterojunction catalyst:

[0061] 1) Preparation of nickel cobalt carbonate (NiCo-OH / NF) precursor grown in situ on nickel foam:

[0062] The nickel foam was treated with acetone, 1 mol·L -1 The mixture was washed with hydrochloric acid solution and deionized water, and dried for later use. 4 F, urea, deionized water (Ni, Co, NH 4 F, urea, and deionized water (molar ratio of 1:2:5:20:500) were mixed to form a uniform solution, which was transferred to a reactor containing a vertically placed nickel foam, and hydrothermally reacted at 120° C. for 12 hours. After cooling to room temperature, the mixture was washed alternately with ethanol and deionized water for 3 times, and vacuum dried at 60° C. for 12 hours to obtain a basic nickel cobalt carbonate (NiCo-OH / NF) precursor.

[0063] 2) Preparation of NiCoP-BK / NF catalyst precursor and boron-potassium modification:

[0064] The obtained nickel cobalt carbonate (NiCo-OH / NF) precursor and sodium hypophosphite were placed in two quartz boats, respectively, with a molar ratio of sodium hypophosphite to nickel nitrate of 4:1. After being placed in a tube furnace, the temperature was raised to 350°C in a nitrogen atmosphere at a heating rate of 2°C·min -1 , phosphating for 2 hours to obtain transition metal phosphide NiCoP / NF catalyst precursor. After soaking it in 25mL 1.5M potassium borate and potassium borohydride solution with a molar ratio of 0.5:8 for 20 minutes, the surface residue was removed, and it was washed alternately with ethanol and water for 3 times, and vacuum dried at 60°C for 12 hours to obtain boron-potassium modified catalyst precursor NiCoP-BK / NF.

[0065] 3) Preparation of NiCoP-BK@NiFe-LDH / NF catalyst:

[0066] The obtained NiCoP-BK / NF catalyst was used as the working electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the Pt thin sheet was used as the counter electrode. Electrodeposition was performed in an electrolyte consisting of nickel nitrate and ferrous nitrate (the molar ratio of Ni source, Fe source and deionized water was 1:1:80) in deionized water. The NiCoP-BK@NiFe-LDH / NF catalyst was obtained by electroplating at a voltage of -1.2V relative to the saturated calomel electrode for 600s. For comparison, the NiCoP@NiFe-LDH / NF catalyst without boron-potassium modification and the NiCoP / NF catalyst were prepared by the same method under the premise that other conditions remained unchanged.

[0067] The electrochemical double layer capacitance (Cdl) of the catalytic material was obtained by cyclic voltammetry (CV) at different scan rates and the catalyst activity area (ECSA) was calculated (Table 2). The results show that the ECSA values ​​of NiCoP@NiFe-LDH / NF are 1062 cm 2 / mg -1 , significantly higher than NiCoP / NF (502cm 2 / mg -1 )、NiFe-LDH / NF(60cm 2 / mg -1 ), indicating that the construction of heterogeneous structure is beneficial to increase the number of active sites of NiCoP / NF catalyst. More importantly, the ECSA of NiCoP-BK@NiFe / NF prepared by the present invention is 1732cm 2 / mg -1 Compared with NiCoP@NiFe-LDH / NF without boron-potassium modification, the ECSA increased by 63%; compared with NiCoP / NF, the ECSA increased by 111%. This further proves that boron-potassium modification and NiFe deposition work synergistically to form many new vacancies and defects at the interface of the heterostructure, increasing the number of exposed active sites and effectively solving the bottleneck problem of limited number of active sites and low catalytic activity of NiCoP / NF.

[0068] Table 2 Comparison of electrochemical active areas of different catalysts

[0069]

[0070] Example 4

[0071] This example illustrates the Tafel slope test of NiCoP-BK@NiFe-LDH / NF catalyst under alkaline conditions.

[0072] Preparation method of this highly active transition metal phosphide-nickel iron heterojunction catalyst:

[0073] 1) Preparation of nickel cobalt carbonate (NiCo-OH / NF) precursor grown in situ on nickel foam:

[0074] The nickel foam was treated with acetone, 1 mol·L -1 The mixture was washed with hydrochloric acid solution and deionized water, and dried for later use. 4 F, urea, deionized water (Ni, Co, NH 4 F, urea, and deionized water (molar ratio of 1:1.5:5:20:800) were mixed to form a uniform solution, which was transferred to a reactor containing a vertically placed nickel foam, and hydrothermally reacted at 120° C. for 12 hours. After cooling to room temperature, the mixture was washed alternately with ethanol and deionized water for 3 times, and vacuum dried at 60° C. for 12 hours to obtain a basic nickel cobalt carbonate (NiCo-OH / NF) precursor.

[0075] 2) Preparation of NiCoP-BK / NF catalyst precursor and boron-potassium modification:

[0076] The obtained nickel cobalt carbonate (NiCo-OH / NF) precursor and sodium hypophosphite were placed in two quartz boats, respectively, with a molar ratio of sodium hypophosphite to nickel nitrate of 3:1. After being placed in a tube furnace, the temperature was raised to 350°C in a nitrogen atmosphere at a heating rate of 2°C·min -1 The catalyst precursor NiCoP / NF was obtained by phosphating for 2 hours. After soaking it in 25 mL of a 2.0 M solution of potassium borate and potassium borohydride with a molar ratio of 0.5:10 for 40 minutes, the surface residue was removed, and the catalyst precursor NiCoP-BK / NF was obtained by vacuum drying at 60°C for 12 hours.

[0077] 3) Preparation of NiCoP-BK@NiFe-LDH / NF catalyst:

[0078] The obtained NiCoP-BK / NF catalyst was used as the working electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the Pt thin sheet was used as the counter electrode. Electrodeposition was performed in an electrolyte consisting of nickel nitrate and ferrous nitrate (the molar ratio of Ni source, Fe source and deionized water was 1:2:80) in deionized water. The NiCoP-BK@NiFe-LDH / NF catalyst was obtained by electroplating at a voltage of -1.3V relative to the saturated calomel electrode for 800s. For comparison, the NiCoP@NiFe-LDH / NF catalyst without boron-potassium modification was prepared by the same method under the premise that other conditions remained unchanged.

[0079] The NiCoP-BK@NiFe-LDH / NF catalyst obtained in this example was subjected to Tafel slope test under alkaline conditions. The results are shown in Figure 7 .Depend on Figure 7 It can be seen that the Tafel slope of the HER of NiCoP-BK@NiFe-LDH / NF catalyst is 36.3 mV·dec -1 , compared with 35.5 mV·dec of Pt-C / NF catalyst -1 The Tafel slope is comparable to and much lower than that of the NiCoP@NiFe-LDH / NF (not modified with boron-potassium) catalyst, indicating that boron-potassium modification promotes fast electron transfer and excellent HER kinetics. The main reasons are: (1) Boron-potassium modification can manipulate the electron redistribution at the interface of the NiCoP-BK@NiFe-LDH / NF catalyst and the rearrangement of atoms on the interface, thereby further enhancing and regulating the built-in electric field and promoting fast electron transfer and HER kinetics; (2) Potassium ions interact with the active components of the NiCoP-BK@NiFe-LDH / NF catalyst, allowing electrons to transfer between the catalyst and potassium, promoting charge transfer, making electron transfer in the electrocatalytic reaction smoother, and improving reaction kinetics. (3) Boron-potassium modification and the construction of the NiCoP-BK@NiFe-LDH / NF heterojunction form many vacancies and defects at the interface, thereby promoting fast electron transfer and HER kinetics.

[0080] Example 5

[0081] This example illustrates the HER stability of NiCoP-BK@NiFe-LDH / NF catalyst under alkaline conditions.

[0082] Preparation method of this highly active transition metal phosphide-nickel iron heterojunction catalyst:

[0083] 1) Preparation of nickel cobalt carbonate (NiCo-OH / NF) precursor grown in situ on nickel foam:

[0084] The nickel foam was treated with acetone, 1 mol·L -1 The mixture was washed with hydrochloric acid solution and deionized water, and dried for later use. 4 F, urea, deionized water (Ni, Co, NH 4 F, urea, and deionized water (molar ratio of 1:1:5:20:1000) were mixed to form a uniform solution, which was transferred to a reactor containing a vertically placed nickel foam, and hydrothermally reacted at 120° C. for 12 hours. After cooling to room temperature, the mixture was washed alternately with ethanol and deionized water for 3 times, and vacuum dried at 60° C. for 12 hours to obtain a basic nickel cobalt carbonate (NiCo-OH / NF) precursor.

[0085] 2) Preparation of NiCoP-BK / NF catalyst precursor and boron-potassium modification:

[0086] The obtained nickel cobalt carbonate (NiCo-OH / NF) precursor and sodium hypophosphite were placed in two quartz boats, respectively, with a molar ratio of sodium hypophosphite to nickel nitrate of 6:1. After being placed in a tube furnace, the temperature was raised to 350°C in a nitrogen atmosphere at a heating rate of 2°C·min -1 The catalyst precursor NiCoP / NF was obtained by phosphating for 2 hours. After soaking it in 25 mL of a 3.0 M solution of potassium borate and potassium borohydride with a molar ratio of 0.5:8 for 60 minutes, the surface residue was removed, and the catalyst precursor NiCoP-BK / NF was obtained by vacuum drying at 60°C for 12 hours.

[0087] 3) Preparation of NiCoP-BK@NiFe-LDH / NF catalyst:

[0088] The obtained NiCoP-BK / NF catalyst was used as the working electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the Pt thin sheet was used as the counter electrode. Electrodeposition was performed in an electrolyte consisting of nickel nitrate and ferrous nitrate (the molar ratio of Ni source, Fe source and deionized water was 1:4:80) in deionized water. The NiCoP-BK@NiFe-LDH / NF catalyst was obtained by electroplating at a voltage of -1.5V relative to the saturated calomel electrode for 1200s.

[0089] Under alkaline conditions, the HER stability of the NiCoP-BK@NiFe-LDH / NF catalyst obtained in this example is shown in Figure 8 .Depend on Figure 8 (a) It can be seen that after 3000 cycles of testing, the LSV curve of hydrogen evolution of NiCoP-BK@NiFe-LDH / NF catalyst is very different from that in the initial state. -2 The catalyst was tested at a constant current density for 100 hours. Figure 8 (b) By Figure 8 (b) It can be seen that the performance of NiCoP-BK@NiFe-LDH / NF catalyst is almost unchanged after 100 hours of constant current test, indicating that NiCoP-BK@NiFe-LDH / NF catalyst has good stability under alkaline conditions.

[0090] The main reasons are: (a) Theoretical calculations show (see Fig. 9), the formation of a built-in electric field can adjust the charge distribution on the surface of the catalyst heterojunction, thereby affecting the adsorption behavior of the reaction intermediates on the catalyst surface, allowing the reaction intermediates to be adsorbed on the catalyst surface with appropriate strength, promoting the reaction, and also reducing the damage to the catalyst structure caused by improper adsorption of the intermediates, which helps to improve the stability of the catalyst. (b) The built-in electric field can enhance the interaction between the active components and the carrier or other components through chemical bonding, inhibit the agglomeration and loss of the active components, and make the metal active components more firmly adsorbed on the semiconductor carrier, maintaining the structural integrity and activity stability of the catalyst. (c) Potassium ions can interact with impurities or poisoning substances on the catalyst surface, reducing their impact on the catalyst, thereby extending the service life of the catalyst.

[0091] The preparation process of the present invention is simple and low in cost, and can greatly improve the stability and catalytic activity of the catalyst. The method can be widely used in various important electrochemical reactions such as water / seawater decomposition, carbon dioxide reduction, and microbial fuel cells, and has important industrial application value.

Claims

1. A method for preparing a highly active transition metal phosphide catalyst, characterized in that: The preparation method of the high-activity transition metal phosphide catalyst comprises the following steps: Step 1: NiCo-OH / NF, a basic nickel cobalt carbonate in situ grown on nickel foam, is used as a precursor and placed downstream of a tube furnace. NaH2PO2 is placed upstream. The molar ratio of P to Ni is 3 to 6:

1. The precursor is heated at 2°C∙min in a nitrogen atmosphere. -1 The NiCoP / NF was obtained by annealing at 350 °C for 2 h and cooling naturally. Step 2: Soak the obtained NiCoP / NF in a 0.05-3M potassium salt solution of a boride for 5-60 minutes, remove the surface residue, wash, and vacuum dry to obtain a boron-potassium modified catalyst precursor NiCoP-BK / NF; Step 3. In a three-electrode system, electrodeposition is carried out in an electrolyte containing a Ni source, an Fe source and deionized water. The molar ratio of the Ni source, the Fe source and the deionized water is 1:1 to 4:80, the deposition voltage is -1.5 to 0.5 V, and the deposition time is 400 s to 1200 s to obtain a highly active transition metal phosphide-nickel iron hydroxide NiCoP-BK@NiFe-LDH / NF heterojunction composite catalyst with optimized interface properties and atomic arrangement.

2. The method for preparing a highly active transition metal phosphide catalyst according to claim 1, characterized in that: The preparation method of NiCo-OH / NF in step 1 is as follows: in-situ growth preparation on nickel foam in Ni source and Co source, NH4F, and urea aqueous solution, wherein the initial molar ratio of Ni to Co is 1-2:1, the molar ratio of Ni to deionized water is 1:500-1000, and the molar ratio of Ni to NH4F and urea is 1:5:

20.

3. The method for preparing a highly active transition metal phosphide catalyst according to claim 2, characterized in that: In the step 2, washing is performed by alternating ethanol and water for 3 times; vacuum drying is performed at 60° C. for 12 hours.

4. The method for preparing a highly active transition metal phosphide catalyst according to claim 3, characterized in that: The boride potassium salt solution refers to a mixture of potassium borate and potassium borohydride, wherein the molar ratio of potassium borate to potassium borohydride is 0.5:1-10.

5. The method for preparing a highly active transition metal phosphide catalyst according to claim 4, characterized in that: The three-electrode system is composed of NiCoP-BK / NF as a working electrode, a saturated calomel electrode SCE as a reference electrode, and a Pt sheet as a counter electrode.

6. The method for preparing a highly active transition metal phosphide catalyst according to claim 5, characterized in that: In the step 3, the Ni source is any one of nickel chloride, nickel nitrate and nickel acetate.

7. The method for preparing a highly active transition metal phosphide catalyst according to claim 6, characterized in that: In the step 3, the Fe source is any one of ferrous chloride, ferrous nitrate and ferrous acetate.

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