NiCoS / NiCoB nanocube electrocatalyst derived from Prussian blue analogue as well as preparation method and application of NiCoS / NiCoB nanocube electrocatalyst

Abstract

The invention relates to a Prussian blue analogue derived NiCoS / NiCoB nanocube electrocatalyst and a preparation method and application thereof.NiCo PBA serves as a template, PVP K30 is coated to serve as a structural stabilizer, completeness of morphology is ensured, and the NiCoS / NiCoB nanocube electrocatalyst is successfully prepared through sulfuration calcination and NaBH4 chemical anion etching. According to the method, the complete morphology of the nanocube is kept, the overpotential in the OER process is effectively reduced through the synergistic effect of sulfide and boride of the obtained material, and ultrahigh stability is shown in a 1M KOH solution. The preparation method is simple, high in efficiency and safety performance and low in price, and opens up a new way for basic research and implementation of non-noble metal nanostructures.

Description

Technical Field

[0001] The present invention relates to a Prussian blue analogue-derived NiCoS / NiCoB nanocube electrocatalyst, a preparation method thereof, and an application thereof, belonging to the technical field of electrocatalysis. Background Art

[0002] Hydrogen is a clean and high energy density future fuel, which is crucial for achieving the transformation of sustainable energy and low-carbon economy. Hydrogen production by electrolysis of water is the most promising green hydrogen production technology, which can achieve zero carbon emissions. Hydrogen production by electrolysis of water includes two simultaneous half-reactions, namely the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Compared with HER with only 2 electron transfers, OER is accompanied by 4 electron transfers and is kinetically slower. An efficient oxygen evolution electrocatalyst is required to lower the reaction energy barrier to accelerate the progress of OER. Ir-based and Ru-based noble metal materials are benchmark catalysts for OER, with good activity and stability, but their high cost and scarcity severely limit their large-scale applications. Therefore, it is of great significance to develop non-noble metal catalysts with high activity and long-term stability.

[0003] Prussian blue analogues (PBAs) have an open three-dimensional (3D) stereoscopic framework and have been widely used in energy development and synthesis preparation due to their uniform size, adjustable composition, controllable structure, excellent OER performance, and high stability (Reference: DOI: 10.1016 / j.ccr.2021.214260). Nickel-cobalt Prussian blue analogue (NiCo PBA) is formed by the reaction of potassium cobalt cyanide and nickel salt, and the reaction equation is: 2K3Co(CN)6 + 3Ni(NO)3·6H2O → Ni3[Co(CN)6]2·12H2O + 6H2O + 6KNO3 (Reference: DOI: 10.1002 / smll.202311452), and it can be used as a sacrificial template to prepare non-noble metal compounds through sulfidation / phosphidation / oxidation, etc. Compared with the low electrical conductivity of transition metal oxides, transition metal sulfides have a relatively narrow band gap, superior electrical conductivity, and more efficient and rapid electron transfer; moreover, transition metal sulfides also have the advantages of adjustable microstructure and chemical composition. Combining with the open 3D stereoscopic framework structure of PBAs, they have a large surface area, which is conducive to the exposure of more active sites and maintaining good structural stability, and is conducive to the improvement and stability of OER performance.

[0004] So far, a variety of preparation methods for improving catalytic performance by sulfiding through the PBAs system have been successively developed and applied to electrocatalytic water splitting. Patent document CN 113388847 A prepared a cubic cage-like nano-catalytic material for HER and OER by sulfiding and ammonia etching using cobalt-iron PBA as a template. However, the etching at high temperature and with ammonia will damage the edges and the framework structure of the cube. Therefore, there is an urgent need to explore a mild chemical etching method that can not only maintain a good framework structure but also enhance the intrinsic activity. Research shows that etching the framework structure of PBAs with NaBH4 not only eliminates the need to introduce additional metal sources but also fully activates the utilization of metal sites inside the PBAs body, while accelerating gas diffusion, electrolyte penetration, and the transport of reactive substances during the electrocatalytic reaction process. Patent document CN 117721494 A obtained an iron-doped hollow nanoarray (V0-Fe-Co3O4) rich in oxygen vacancies with nickel foam as the substrate using NaBH4. However, its preparation process involves synthesizing a Co-ZIF-L nanoarray precursor using 2-methylimidazole, then forming Fe-Co PBA using potassium ferricyanide, and finally calcining the Fe-CoPBA and soaking it with NaBH4 to obtain the final product V0-Fe-Co3O4. This method lacks the concept of environmental friendliness and the preparation process is relatively complex. Currently, there are few reports on the research work regarding the preparation process that synergistically combines calcination sulfiding and anion chemical etching using NiCo PBA as a template. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the present invention provides a Prussian blue analogue-derived NiCoS / NiCoB nano-cubic electrocatalyst, its preparation method and application. Overview of the Invention:

[0007] The present invention uses NiCo PBA as a template and coats PVP K30 as a structure stabilizer to ensure the integrity of the morphology. Through sulfiding calcination and NaBH4 chemical anion etching, a NiCoS / NiCoB nano-electrocatalytic material is successfully prepared. This method not only maintains the complete morphology of the nano-cubes but also obtains the synergistic effect of the sulfide and boride of the material, effectively reducing the overpotential during the OER process and showing ultra-high stability in 1M KOH solution. The preparation method is simple, with high efficiency and safety performance, and low cost, opening up a new way for the basic research and realization of the development of non-precious metal nanostructures.

[0008] Term Explanation:

[0009] Room temperature: Generally refers to 20 - 25 °C. Detailed Description of the Invention

[0011] The technical solution of the present invention is as follows:

[0012] A Prussian blue analogue-derived NiCoS / NiCoB nanocube electrocatalyst, the microscopic morphology of the NiCoS / NiCoB nanocube electrocatalyst is three-dimensional nanocubes with uniform size and smooth surface, and the side length of the cube is 280 - 310 nm.

[0013] The preparation method of the above-mentioned Prussian blue analogue-derived NiCoS / NiCoB nanocube electrocatalyst includes the following steps:

[0014] (1) Dissolve nickel nitrate hexahydrate, sodium citrate and PVP K30 in ultrapure water, stir until completely dissolved to form a clear solution a, slowly pour the potassium hexacyanoferrate aqueous solution into solution a, stir well, let stand at room temperature, wash, centrifuge and dry with ultrapure water and absolute ethanol respectively to obtain a light blue NiCo PBA precursor powder;

[0015] (2) Place the NiCo PBA precursor powder and sublimed sulfur powder in the same porcelain boat and calcine under a protective gas atmosphere to obtain NiCoS nanocube powder;

[0016] (3) Immerse the NiCoS nanocube powder in the NaBH4 solution for a period of time, wash, centrifuge and dry with ultrapure water and absolute ethanol respectively to obtain the Prussian blue analogue-derived NiCoS / NiCoB nanocube electrocatalyst.

[0017] Preferably according to the present invention, in step (1), the molar ratio of nickel nitrate hexahydrate to sodium citrate is (1 - 4):(4 - 8).

[0018] Preferably according to the present invention, in step (1), the mass ratio of PVP K30 to the molar amount of sodium citrate is (0.5 - 3):(4 - 8), unit: g / mmol.

[0019] More preferably, in step (1), the mass ratio of PVP K30 to the molar amount of sodium citrate is 1:(4 - 8), unit: g / mmol.

[0020] Preferably according to the present invention, in step (1), the molar volume ratio of nickel nitrate hexahydrate to ultrapure water is (1 - 4):100, unit: mmol / mL.

[0021] Preferably according to the present invention, in step (1), the stirring time is 20 - 60 min.

[0022] Preferably according to the present invention, in step (1), the concentration of the potassium hexacyanoferrate aqueous solution is 0.01 - 0.05 mmol / mL.

[0023] Preferably according to the present invention, in step (1), the volume ratio of solution a to the aqueous potassium hexacyanoferrate solution is 1:1.

[0024] Preferably according to the present invention, in step (1), the standing time is 20 - 30 h.

[0025] Preferably according to the present invention, in step (1), the drying is carried out in a vacuum drying oven at 60 °C.

[0026] Preferably according to the present invention, in step (2), after the NiCo PBA precursor powder and the sublimed sulfur powder are respectively placed in the tubular furnace, the tubular furnace is evacuated 2 - 4 times, and then a protective gas is introduced at one end of the tubular furnace, and the gas is nitrogen / argon.

[0027] Preferably according to the present invention, in step (2), when placing, the sublimed sulfur powder is close to the gas inlet end of the tubular furnace protective gas, and the NiCo PBA precursor powder is close to the gas outlet end of the protective gas.

[0028] Preferably according to the present invention, in step (2), the mass ratio of the NiCo PBA precursor to the sublimed sulfur powder is 1:10 - 20.

[0029] Preferably according to the present invention, in step (2), during the calcination process, the protective gas is continuously introduced into the tubular furnace, and the gas outlet end of the tubular furnace is connected to the tail gas absorption liquid through a pipeline, and the bubble rate of the gas discharged from the pipeline in the tail gas absorption liquid is 1 bubble / (1 - 3) s.

[0030] Preferably according to the present invention, in step (2), the calcination conditions are: the calcination temperature is 300 - 600 °C, more preferably 400 - 500 °C, and the calcination time is 2 h.

[0031] Preferably according to the present invention, in step (3), the concentration of the NaBH4 solution is 0.4 - 0.6 M.

[0032] Preferably according to the present invention, in step (3), the soaking time of the NiCoS nanocube powder is 0 h - 2 h, more preferably 1 h.

[0033] The present invention also provides the application of the above NiCoS / NiCoB three-dimensional nanocubes as an electrocatalyst for alkaline OER.

[0034] The present invention adopts a one-step liquid co-precipitation method. During the preparation process, polyvinylpyrrolidone (PVP K30) is added as a structure stabilizer to ensure the integrity of the morphology, and the NiCo PBA precursor is prepared. Using NiCo PBA as the precursor, a transition metal sulfide / transition metal boride heterostructure is synthesized through calcination sulfidation and NaBH4 chemical anion etching. Significant progress has been made in the 3D framework structure by etching with NaBH4, not only with mild conditions but also without damaging the morphology.

[0035] Technical features and beneficial effects of the present invention:

[0036] 1. All raw materials of the present invention are inexpensive non-precious metals with rich energy storage. The preparation process is simple, easy to operate, and has a high repetition rate. Only water is used as the solvent throughout the process without the participation of organic solvents, which conforms to the concept of green environmental protection.

[0037] 2. The present invention prepares excellent NiCoS / NiCoB electrode materials. The synergistic effect of transition metal sulfides and borides reduces the overpotential of the OER reaction, promotes reaction kinetics, and improves electrocatalytic activity.

[0038] 3. The material of the present invention is used as an electrocatalyst for OER: in 1M KOH, when the current density reaches 10 mA cm -2 , the overpotential of OER is only 253 mV. When the current density is 20 mA cm -2 , oxygen can be continuously produced for 24 h, and the catalytic performance only decreases by 1.3%, showing good catalytic stability and activity. The catalyst material of the present invention is of great significance for reducing the overpotential of the electrolytic water reaction, improving the natural environment and water resource utilization.

[0039] 4. The present invention cleverly combines the means of sulfidation calcination and NaBH4 etching to successfully prepare a heterostructure of transition metal sulfide / boride and apply it to OER electrocatalysis. It has excellent performance. When the current density is 10 mA cm -2 , the overpotential is only 253 mV; it has high stability, and the performance hardly decays when continuously producing oxygen for 24 h at a current density of 20 mA cm -2 ; moreover, the etching method is mild and the morphology remains intact. Brief Description of the Drawings

[0040] Figure 1 It is the scanning electron microscope (SEM) image of the NiCo PBA precursor prepared in Example 1 of the present invention.

[0041] Figure 2 It is the transmission electron microscope (TEM) image of the NiCo PBA precursor prepared in Example 1 of the present invention.

[0042] Figure 3 XRD pattern of the NiCo PBA precursor prepared in Example 1 of the present invention.

[0043] Figure 4 XRD pattern of the NiCoS prepared in Example 1 of the present invention.

[0044] Figure 5 SEM image of the NiCoS prepared in Example 1 of the present invention.

[0045] Figure 6 Corresponding elemental mapping images of the NiCoS prepared in Example 1 of the present invention.

[0046] Figure 7 XRD pattern of the NiCoS / NiCoB prepared in Example 1 of the present invention.

[0047] Figure 8 SEM and TEM images of the NiCoS / NiCoB prepared in Example 1 of the present invention.

[0048] Figure 9 Corresponding elemental mapping images of the NiCoS / NiCoB prepared in Example 1 of the present invention.

[0049] Figure 10 Linear sweep voltammetry (LSV) polarization curves of the catalyst materials prepared in Examples 1-2 and Comparative Examples 1-8 of the present invention for alkaline OER.

[0050] Figure 11 Stability diagram of the catalyst material prepared in Example 1 of the present invention for alkaline OER. Detailed Description of the Invention

[0051] The present invention will be further described below in conjunction with specific embodiments, but is not limited thereto.

[0052] Meanwhile, the experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents, materials and devices are all commercially available unless otherwise specified.

[0053] Example 1

[0054] A preparation method of a Prussian blue analogue-derived NiCoS / NiCoB nanocube electrocatalyst is as follows:

[0055] (1) Take 3 mmol of nickel nitrate hexahydrate, 5 mmol of sodium citrate and 1 g of PVP K30 and add them to 100 mL of ultrapure water, stir for 30 min, and obtain a clear solution a after complete dissolution.

[0056] (2) Add 2 mmol of potassium hexacyanoferrate to 100 mL of ultrapure water, stir for 30 min, and a transparent and clear solution b is obtained after complete dissolution.

[0057] (3) Slowly pour solution b into solution a, and stir well to obtain solution c.

[0058] (4) After standing solution c at room temperature (25 °C) for 24 h, the obtained product is washed with ultrapure water and absolute ethanol respectively, centrifuged, and then dried in a vacuum drying oven at 60 °C to obtain a light blue NiCo PBA precursor powder, denoted as NiCo PBA;

[0059] The scanning electron microscope (SEM) and transmission electron microscope (TEM) of the prepared light blue NiCo PBA precursor powder are as Figure 1 and Figure 2 shown. It can be seen from the figure that the precursor is a three-dimensional nanocube with a side length of about 300 nm, uniform in size and smooth on the surface, and the TEM image clearly shows a thin layer at the edge of the cube, indicating the successful coating of PVP K30. Figure 3 is the XRD pattern of the NiCo PBA precursor powder. The diffraction peaks match those of Ni3[Co(CN)6]2·12H2O (JCPDS: 89-3738), and no other impurity peaks appear, indicating the successful preparation of the NiCo PBA precursor.

[0060] (5) Place 50 mg of the NiCo PBA precursor obtained in step (4) and 500 mg of sublimed sulfur powder at both ends of an independent porcelain boat and cover it. When placing, the sublimed sulfur powder is close to the inlet of the tube furnace, and the NiCo PBA precursor is close to the outlet. Evacuate the tube furnace continuously three times to remove the air in the tube furnace; then introduce nitrogen, and nitrogen is continuously introduced into the tube furnace; the outlet end of the tube furnace is connected to the tail gas absorption liquid, and the bubble rate generated in the tail gas absorption liquid is 1 per (1-3) s. Set the heating program of the tube furnace, and increase the temperature to 450 °C at a heating rate of 2 °C min -1 , keep it warm for 2 h, and after cooling to room temperature, take out the porcelain boat to obtain a black powder.

[0061] The XRD of the black powder is as Figure 4As shown, the diffraction peaks at 27.47°, 31.82°, 35.70°, 39.24°, 45.62°, 54.08°, 61.71° and 66.50° are respectively attributed to the (111), (200), (210), (211), (220), (311), (321) and (400) crystal planes of NiS2 (JCPDS: 80 - 0375). They exist and there are no impurity peaks, indicating the successful preparation of the material. The absence of Co - S peaks in the XRD diffraction peaks may be because part of Co is inserted into NiS2 (Reference: DOI: 10.1016 / j.cej.2022.138515), denoted as NiCoS.

[0062] The SEM and corresponding elemental mapping of NiCoS are shown in Figure 5 , Figure 6. It can be seen from Figure 5 that the overall morphology of NiCoS obtained after sulfidation calcination is consistent with that of the NiCo PBA precursor, and there is no sign of structural collapse. The overall size is uniform, with a side length of about 300 nm, and the surface changes from a smooth surface to a rough granular surface. Figure 6 The corresponding elemental mapping shows the uniform distribution of Ni, Co and S elements in the sample, proving the success of sulfidation.

[0063] (6) Take 40 mg of the NiCoS obtained in step (5) and soak it in 40 mL of 0.5 M NaBH4 solution for 1 h, then wash it successively with ultrapure water and absolute ethanol, centrifuge it, and finally dry it in a 60 °C vacuum drying oven to obtain the final black product, which is the NiCoS / NiCoB nanocube electrocatalyst.

[0064] The XRD, SEM and TEM of the NiCoS / NiCoB nanocube electrocatalyst are shown in Figure 7 , Figure 8, and the corresponding elemental mapping is shown in Figure 9 . The XRD pattern shows that after soaking in NaBH4, the crystallinity becomes weaker, but the main characteristic peaks of NiS2 are still maintained, and there are no obvious NiCoB characteristic peaks because the crystallinity of boride is relatively low. It can be seen from the SEM image that the structure of the nanocube does not change significantly after soaking in NaBH4, and the TEM shows an evolution from a nanocube to a hollow nanocube structure. The elemental mapping verifies the presence of Ni, Co, S, B elements in NiCoS / NiCoB, confirming the formation of NiCoB and the partial reservation of NiCoS.

[0065] Example 2

[0066] A preparation method of a Prussian blue analogue - derived NiCoS / NiCoB nanocube electrocatalyst is as follows:

[0067] (1) Take 3 mmol of nickel nitrate hexahydrate, 5 mmol of sodium citrate, and 1 g of PVP K30 and add them to 100 mL of ultrapure water. Stir for 30 min. After complete dissolution, a clear solution a is obtained.

[0068] (2) Take 2 mmol of potassium hexacyanoferrate(II) and add it to 100 mL of ultrapure water. Stir for 30 min. After complete dissolution, a transparent and clear solution b is obtained.

[0069] (3) Slowly pour solution b into solution a and stir well to mix, obtaining solution c.

[0070] (4) After allowing solution c to stand at room temperature (25 °C) for 24 h, the obtained product is washed with ultrapure water and absolute ethanol respectively, centrifuged, and then placed in a vacuum drying oven at 60 °C for drying. Finally, a light blue precursor powder is obtained.

[0071] (5) The same as step (5) of Example 1.

[0072] (6) Take 40 mg of the NiCoS obtained in step (5) and soak it in 40 mL of 0.5 M NaBH4 solution for 0.5 h. Then wash it with ultrapure water and absolute ethanol in turn, centrifuge it, and finally place it in a vacuum drying oven at 60 °C for drying to obtain the final black product.

[0073] Comparative Example 1

[0074] (1) Take 3 mmol of nickel nitrate hexahydrate, 5 mmol of sodium citrate, and 0.1 g of PVP K30 and add them to 100 mL of ultrapure water. Stir for 30 min. After complete dissolution, a clear solution a is obtained.

[0075] (2) Take 2 mmol of potassium hexacyanoferrate(II) and add it to 100 mL of ultrapure water. Stir for 30 min. After complete dissolution, a transparent and clear solution b is obtained.

[0076] (3) Slowly pour solution b into solution a and stir well to mix, obtaining solution c.

[0077] (4) After allowing solution c to stand at room temperature (25 °C) for 24 h, the obtained product is washed with ultrapure water and absolute ethanol respectively, centrifuged, and then placed in a vacuum drying oven at 60 °C for drying. Finally, a light blue precursor powder is obtained.

[0078] (5)(5) The same as step (5) of Example 1.

[0079] (6) Take 40 mg of the (NiCo)S2 obtained in step (5) and soak it in 40 mL of 0.5 M NaBH4 solution for 1.5 h. Then wash it with ultrapure water and absolute ethanol in turn, centrifuge it, and finally place it in a vacuum drying oven at 60 °C for drying to obtain the final black product.

[0080] Comparative Example 2

[0081] (1) Take 3 mmol of nickel nitrate hexahydrate, 5 mmol of sodium citrate, and 5 g of PVP K30 and add them to 100 mL of ultrapure water. Stir for 30 min. After complete dissolution, a clear solution a is obtained.

[0082] (2) Take 2 mmol of potassium hexacyanoferrate and add it to 100 mL of ultrapure water. Stir for 30 min. After complete dissolution, a transparent and clear solution b is obtained.

[0083] (3) Slowly pour solution b into solution a and stir well to obtain solution c.

[0084] (4) After leaving solution c to stand at room temperature (25 °C) for 24 h, the obtained product is washed with ultrapure water and absolute ethanol respectively, centrifuged, and then placed in a vacuum drying oven at 60 °C for drying to finally obtain a light blue precursor powder.

[0085] (5) (5) The same as step (5) of Example 1.

[0086] (6) Take 40 mg of (NiCo)S2 obtained in step (5) and soak it in 40 mL of 0.5 M NaBH4 solution for 1 h, then wash it with ultrapure water and absolute ethanol in turn, centrifuge it, and finally place it in a vacuum drying oven at 60 °C for drying to obtain the final black product.

[0087] Comparative Example 3

[0088] (1) Take 3 mmol of nickel nitrate hexahydrate, 5 mmol of sodium citrate and add them to 100 mL of ultrapure water. Stir for 30 min. After complete dissolution, a clear solution a is obtained.

[0089] (2) Take 2 mmol of potassium hexacyanoferrate and add it to 100 mL of ultrapure water. Stir for 30 min. After complete dissolution, a transparent and clear solution b is obtained.

[0090] (3) Slowly pour solution b into solution a and stir well to obtain solution c.

[0091] (4) After leaving solution c to stand at room temperature (25 °C) for 24 h, the obtained product is washed with ultrapure water and absolute ethanol respectively, centrifuged, and then placed in a vacuum drying oven at 60 °C for drying to finally obtain a light blue powder.

[0092] Comparative Example 4

[0093] (1) Take 3 mmol of nickel nitrate hexahydrate, 5 mmol of sodium citrate and add them to 100 mL of ultrapure water. Stir for 30 min. After complete dissolution, a clear solution a is obtained.

[0094] (2) Add 2 mmol of potassium hexacyanoferrate to 100 mL of ultrapure water, stir for 30 min, and obtain a transparent and clear solution b after complete dissolution.

[0095] (3) Slowly pour solution b into solution a, and stir well to obtain solution c.

[0096] (4) After leaving solution c to stand at room temperature (25 °C) for 24 h, wash the obtained catalyst with ultrapure water and absolute ethanol respectively, centrifuge it, and then place it in a vacuum drying oven at 60 °C for drying to finally obtain a light blue precursor powder.

[0097] (5) Place 50 mg of the precursor obtained in step (4) and 500 mg of sublimed sulfur powder at both ends of an independent porcelain boat and cover them. Place the porcelain boat in the tube furnace in the order that the end with sublimed sulfur powder is placed at the inlet of the tube furnace and the end with the precursor is placed at the outlet of the tube furnace, and evacuate the tube furnace continuously three times to remove the air in the tube furnace; then introduce nitrogen. Keep nitrogen flowing into the tube furnace; connect the outlet end of the tube furnace to the tail gas absorption liquid, and the bubble rate generated in the tail gas absorption liquid is 1 bubble per (1 - 3) s. Set the heating program of the tube furnace, and raise the temperature to 450 °C at a heating rate of 2 °C / min -1 and keep it at this temperature for 2 h. After cooling to room temperature, take out the porcelain boat to obtain a black powder.

[0098] Comparative Example 5

[0099] (1) Take 3 mmol of nickel nitrate hexahydrate, 5 mmol of sodium citrate, and 1 g of PVP K30 and add them to 100 mL of ultrapure water, stir for 30 min, and obtain a clear solution a after complete dissolution.

[0100] (2) Add 2 mmol of potassium hexacyanoferrate to 100 mL of ultrapure water, stir for 30 min, and obtain a transparent and clear solution b after complete dissolution.

[0101] (3) Slowly pour solution b into solution a, and stir well to obtain solution c.

[0102] (4) After leaving solution c to stand at room temperature (25 °C) for 24 h, wash the obtained product with ultrapure water and absolute ethanol respectively, centrifuge it, and then place it in a vacuum drying oven at 60 °C for drying to finally obtain a light blue powder, denoted as NiCo PBA.

[0103] Comparative Example 6

[0104] (1) Take 3 mmol of nickel nitrate hexahydrate, 5 mmol of sodium citrate, and 1 g of PVP K30 and add them to 100 mL of ultrapure water, stir for 30 min, and obtain a clear solution a after complete dissolution.

[0105] (2) Add 2 mmol of potassium hexacyanoferrate to 100 mL of ultrapure water, stir for 30 min, and obtain a transparent and clear solution b after complete dissolution.

[0106] (3) Slowly pour solution b into solution a, and stir well to obtain solution c.

[0107] (4) After leaving solution c to stand at room temperature (25 °C) for 24 h, wash the obtained product with ultrapure water and absolute ethanol respectively, centrifuge it, and then place it in a vacuum drying oven at 60 °C for drying to finally obtain a light blue precursor powder.

[0108] (5) Place 50 mg of the precursor obtained in step (4) and 500 mg of sublimed sulfur powder at both ends of an independent porcelain boat and cover it. Place the porcelain boat in the tube furnace in the order that the sublimed sulfur powder end is placed at the inlet of the tube furnace and the precursor end is placed at the outlet. Then evacuate the tube furnace three times continuously to remove the air in the tube furnace; then introduce nitrogen. Keep nitrogen flowing into the tube furnace continuously; connect the outlet end of the tube furnace to the tail gas absorption liquid, and the bubble rate generated in the tail gas absorption liquid is 1 bubble per (1 - 3) s. Set the heating program of the tube furnace, and raise the temperature to 450 °C at a heating rate of 2 °C / min, and keep the temperature for 2 h. After cooling to room temperature, take out the porcelain boat to obtain a black powder. -1 After cooling to room temperature, take out the porcelain boat to obtain a black powder.

[0109] Comparative Example 7

[0110] (1) Take 3 mmol of nickel nitrate hexahydrate, 5 mmol of sodium citrate, and 1 g of PVP K30 and add them to 100 mL of ultrapure water, stir for 30 min, and obtain a clear solution a after complete dissolution.

[0111] (2) Add 2 mmol of potassium hexacyanoferrate to 100 mL of ultrapure water, stir for 30 min, and obtain a transparent and clear solution b after complete dissolution.

[0112] (3) Slowly pour solution b into solution a, and stir well to obtain solution c.

[0113] (4) After leaving solution c to stand at room temperature (25 °C) for 24 h, wash the obtained catalyst with ultrapure water and absolute ethanol respectively, centrifuge it, and then place it in a vacuum drying oven at 60 °C for drying to finally obtain a light blue precursor powder.

[0114] (5) Place 50 mg of the precursor obtained in step (4) and 500 mg of sublimed sulfur powder at both ends in an independent porcelain boat and cover them. Place the porcelain boat in the tube furnace in the order that the sublimed sulfur powder end is placed at the inlet of the tube furnace and the NiCo PBA precursor end is placed at the outlet, and evacuate the tube furnace three times continuously to remove the air in the tube furnace; then introduce nitrogen. Nitrogen is continuously introduced into the tube furnace; the outlet end of the tube furnace is connected to the tail gas absorption liquid, and the bubble rate generated in the tail gas absorption liquid is 1 per (1 - 3) s. Set the heating program of the tube furnace and raise the temperature to 290 °C at a heating rate of 2 °C min -1 and keep it at this temperature for 2 h. After cooling to room temperature, take out the porcelain boat to obtain a black powder.

[0115] Comparative Example 8

[0116] (1) Take 3 mmol of nickel nitrate hexahydrate, 5 mmol of sodium citrate and 1 g of PVP K30 and add them to 100 mL of ultrapure water, stir for 30 min, and obtain a clear solution a after complete dissolution.

[0117] (2) Take 2 mmol of potassium hexacyanoferrate and add it to 100 mL of ultrapure water, stir for 30 min, and obtain a transparent and clear solution b after complete dissolution.

[0118] (3) Slowly pour solution b into solution a and stir well to mix them to obtain solution c.

[0119] (4) Let solution c stand at room temperature (25 °C) for 24 h, then wash the obtained catalyst with ultrapure water and absolute ethanol respectively, centrifuge it and then put it into a vacuum drying oven at 60 °C to dry, and finally obtain a light blue precursor powder.

[0120] (5) Place 50 mg of the precursor obtained in step (4) and 500 mg of sublimed sulfur powder at both ends in an independent porcelain boat and cover them. Place the porcelain boat in the tube furnace in the order that the sublimed sulfur powder end is placed at the inlet of the tube furnace and the precursor end is placed at the outlet, and evacuate the tube furnace three times continuously to remove the air in the tube furnace; then introduce nitrogen. Nitrogen is continuously introduced into the tube furnace; the outlet end of the tube furnace is connected to the tail gas absorption liquid, and the bubble rate generated in the tail gas absorption liquid is 1 per (1 - 3) s. Set the heating program of the tube furnace and raise the temperature to 650 °C at a heating rate of 2 °C min -1 and keep it at this temperature for 2 h. After cooling to room temperature, take out the porcelain boat to obtain a black powder.

[0121] Experimental Example 1

[0122] Perform electrochemical alkaline oxygen evolution (OER) performance tests on the samples prepared in Examples 1 - 2 and Comparative Examples 1 - 8. The specific test method is as follows.

[0123] (1) Catalyst ink preparation: 7 mg of the prepared sample and 2 mg of XC-72 carbon black were dispersed in a mixed solution of 0.75 mL of isopropanol and 0.25 mL of Nafion. The resulting mixture was ultrasonically treated for 40 min to obtain a uniform ink. Then, 10 μL of the ink was evenly dropped onto the glassy carbon electrode in two portions and dried under vacuum for 10 h.

[0124] (2) LSV test method for catalyst OER: A standard three-electrode system was used, with the glassy carbon electrode with the dropped ink as the working electrode, a graphite rod as the counter electrode, and a Hg / HgO electrode as the reference electrode. The electrolyte was 1 M KOH. Before the test, oxygen was introduced to saturate the oxygen in the electrolyte. The scan rate was set at 5 mV s -1 for the OER LSV polarization curve.

[0125] Figure 10 are the LSV curves of the OER of the electrocatalysts prepared in Examples 1-2 and Comparative Examples 1-8. As can be seen from the figure, when the current density of the prepared electrocatalyst was 10 mA cm -2 , the overpotentials reached 253 mV, 280 mV, 331 mV, 333 mV, 389 mV, 331 mV, 381 mV, 309 mV, 385 mV, and 336 mV, respectively. From this experimental data, it can be concluded that the NiCoS / NiCoB electrocatalyst prepared in Example 1 has the lowest overpotential and thus has more excellent OER activity. Figure 11 shows the stability of Example 1 at a current density of 20 mA cm -2 . After continuous oxygen production for 24 h, the performance only decreased by 1.3%, indicating that the electrocatalyst of the present invention has good oxygen production stability.

[0126] The present invention successfully prepared a hollow nanocube NiCoS / NiCoB electrocatalyst by combining the methods of liquid co-precipitation, sulfidation calcination, and NaBH4 chemical anion etching processes. The catalyst exhibits excellent OER activity and long-term durability in a 1 M KOH medium. Through the combination of sulfidation calcination and NaBH4 chemical anion etching, the catalyst gradually transforms from NiCo PBA cubes to NiCoS / NiCoB hollow nanocubes. This method combines the advantages of transition metal sulfides and borides, and the two cooperate with each other to form a strongly coupled heterojunction interface, which can provide more active sites and thus exhibit more excellent electrocatalytic activity. The sulfidation calcination temperature, NaBH4 soaking time, and PVP K30 addition amount in the present invention are all key factors affecting the electrocatalytic performance. Each link is closely linked and indispensable.

Claims

1. A Prussian blue analogue-derived NiCoS / NiCoB nanocube electrocatalyst, wherein the microscopic morphology of the NiCoS / NiCoB nanocube electrocatalyst is three-dimensional nanocubes with uniform size and smooth surface, and the side length of the cube is 280 - 310 nm.

2. The preparation method of the Prussian blue analogue-derived NiCoS / NiCoB nanocube electrocatalyst according to claim 1, comprising the following steps: (1) Dissolve nickel nitrate hexahydrate, sodium citrate and PVP K30 in ultrapure water, stir until completely dissolved to form a clear solution a, slowly pour the aqueous potassium hexacyanoferrate solution into solution a, stir well, let stand at room temperature, wash, centrifuge and dry with ultrapure water and absolute ethanol respectively to obtain a light blue NiCo PBA precursor powder; (2) Place the NiCo PBA precursor powder and sublimed sulfur powder in the same porcelain boat, calcine under a protective gas atmosphere to obtain NiCoS nanocube powder; (3) Immerse the NiCoS nanocube powder in the NaBH4 solution for a period of time, wash, centrifuge and dry with ultrapure water and absolute ethanol respectively to obtain the Prussian blue analogue-derived NiCoS / NiCoB nanocube electrocatalyst.

3. The preparation method according to claim 2, characterized in that, In step (1), the molar ratio of nickel nitrate hexahydrate to sodium citrate is (1 - 4):(4 - 8).

4. The preparation method according to claim 2, wherein, In step (1), the mass ratio of PVP K30 to the molar amount of sodium citrate is (0.5 - 3):(4 - 8), unit: g / mmol, and the molar volume ratio of nickel nitrate hexahydrate to ultrapure water is (1 - 4):100, unit: mmol / mL.

5. The preparation method according to claim 2, characterized in that, In step (1), the stirring time is 20 - 60 min, the concentration of the aqueous potassium hexacyanoferrate solution is 0.01 - 0.05 mmol / mL, the volume ratio of solution a to the aqueous potassium hexacyanoferrate solution is 1:1, the standing time is 20 - 30 h, and the drying is carried out in a vacuum drying oven at 60 °C.

6. The preparation method according to claim 2, characterized in that In step (2), after placing the NiCo PBA precursor powder and sublimed sulfur powder in the tube furnace, evacuate the tube furnace 2 - 4 times, then introduce a protective gas at one end of the tube furnace, the gas is nitrogen / argon, when placing, the sublimed sulfur powder is close to the inlet end of the protective gas of the tube furnace, and the NiCoPBA precursor powder is close to the outlet end of the protective gas.

7. The preparation method according to claim 2, wherein, In step (2), the mass ratio of the NiCo PBA precursor to the sublimed sulfur powder is 1:10 - 20. During the calcination process, keep the protective gas continuously introduced into the tube furnace, the outlet end of the tube furnace is connected to the tail gas absorption liquid through a pipeline, and the bubble rate of the gas discharged from the pipeline in the tail gas absorption liquid is 1 bubble / (1 - 3) s.

8. The preparation method according to claim 2, wherein In step (2), the calcination conditions are: the calcination temperature is 300 - 600 °C, further preferably 400 - 500 °C, and the calcination time is 2 h.

9. The preparation method according to claim 2, characterized in that, In step (3), the concentration of the NaBH4 solution is 0.4 - 0.6 M, and the soaking time of the NiCoS nanocube powder is 0 h - 2 h.

10. Use of the NiCoS / NiCoB three-dimensional nanocubes according to claim 1 as an electrocatalyst for alkaline OER.

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