Oxygen-vacancy-enriched chromium ion doped nickel phosphate nanoflower and preparation method and application thereof

Abstract

The invention relates to the field of electrocatalyst catalytic energy conversion, and particularly discloses an oxygen-vacancy-enriched chromium ion doped nickel phosphate nanoflower as well as a preparation method and application thereof. The preparation method comprises the following steps: S1, dissolving nickel nitrate hexahydrate, chromic nitrate nonahydrate, urea, sodium tartrate and polyethylene glycol into water, and then carrying out heating reaction; s2, mixing the chromium ion doped nickel hydroxide nanoflowers prepared in the step S1 with sodium hypophosphite, uniformly dispersing the mixture in water, and then performing freeze drying and sealed calcination; and S3, carrying out plasma reaction on the chromium ion doped nickel phosphate nanoflower prepared in the step S2 under the condition of introducing inert discharge gas to obtain the oxygen vacancy-enriched chromium ion doped nickel phosphate nanoflower. The oxygen-vacancy-rich chromium ion doped nickel phosphate nanoflower has relatively high conductivity and surface activity, and can reduce overpotential, promote the kinetic process of water decomposition reaction, reduce energy loss and improve the efficiency of hydrogen production by electrolysis of water.

Description

Technical Field

[0001] The present application relates to the field of electrocatalyst-catalyzed energy conversion, and more specifically, to an oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflower, a preparation method thereof, and an application thereof. Background Art

[0002] Electrolyzing water to produce hydrogen is one of the main ways to obtain hydrogen energy at present. In this process, a two-electron reduction reaction occurs at the cathode to produce hydrogen, while a four-electron oxidation reaction occurs at the anode to produce oxygen. The theoretical decomposition voltage of this process is 1.23 V. However, in actual operation, due to the existence of various energy barriers, the actual applied voltage often far exceeds this value. The use of electrocatalysts can significantly reduce the reaction energy barrier, thereby significantly reducing the overpotential and energy loss. Therefore, designing and developing economical and efficient electrocatalysts is the key to realizing biomass oxidation conversion and energy-saving hydrogen production.

[0003] At present, noble metal catalysts are recognized as the catalytic materials with the best performance, but their low global reserves seriously hinder their further commercial applications. Transition metal materials, due to their high reserves and excellent catalytic activity, are considered the most promising materials to replace noble metal catalysts. However, the low electronic conductivity, limited number of active sites, and weak electrocatalytic activity of transition metal materials make it impossible to reduce the overpotential to an ideal state when used alone. Therefore, appropriate modification and modification are required to meet the needs of the future industrial electrolytic water hydrogen production industry.

[0004] Existing heteroatom doping strategies, including cation doping and anion doping, can improve the intrinsic electronic structure of materials, increase the conductivity of materials, improve the adsorption and desorption energy of the material surface and reaction intermediates, and also construct certain defects on the material surface. These defect sites will also maximize the intrinsic activity of the material. However, with continuous research by technicians, it has been found that there is still room for further improvement in the electrocatalytic activity of heteroatom-doped transition metal material catalysts and low-potential hydrogen production. Summary of the Invention

[0005] In order to solve the above technical problems, the present application provides an oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflower, a preparation method thereof, and an application thereof.

[0006] In the first aspect, a preparation method of an oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflower provided by the present application adopts the following technical scheme: A preparation method of an oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflower includes the following steps: S1. Dissolving nickel nitrate hexahydrate, chromium nitrate nonahydrate, urea, sodium tartrate and polyethylene glycol in water, and then heating for reaction, cooling, washing and drying to obtain chromium ion-doped nickel hydroxide nanoflowers; S2, mixing the chromium ion-doped nickel hydroxide nanoflowers prepared in step S1 with sodium hypophosphite and uniformly dispersing them in water, and then freeze-drying, sealing and calcining, and then cooling, washing, and drying to obtain chromium ion-doped nickel phosphate nanoflowers; S3. The chromium ion-doped nickel phosphate nanoflowers prepared in step S2 are subjected to a plasma reaction under the condition of passing an inert discharge gas to obtain oxygen-vacancies-rich chromium ion-doped nickel phosphate nanoflowers.

[0007] Through the above technical scheme, the present application combines the hydrothermal method, the frozen mixed phosphating method and the plasma treatment method to prepare the oxygen-rich vacancy chromium ion doped nickel phosphate nanoflower. Among them, the frozen mixed phosphating method used in step S2 can ensure that the phosphorus source is fully in contact with the nickel hydroxide precursor. At the same time, the two ends of the tube mouth of the tube furnace are sealed during the sealed calcination, but the inert gas is not introduced to ensure that it is not directly phosphated to form nickel phosphide or oxidized to form nickel oxide, thereby obtaining chromium ion doped nickel phosphate nanoflowers with good dual-functional properties; the plasma treatment method used in step S3 can utilize the inert gas molecules in the plasma under the action of strong voltage to decompose and release inert atoms, attack the oxygen atoms in the original lattice, and make it detach, and finally successfully prepare the oxygen-rich vacancy chromium ion doped nickel phosphate nanoflower. The preparation method of the present application has the advantages of simple equipment, short reaction time, easy control, good process repeatability, and stable product quality.

[0008] Moreover, the preparation method of the present application combines cation engineering with oxygen vacancy engineering, which not only utilizes the doping of chromium ions to partially replace the position of nickel atoms in the nickel phosphate lattice, thereby adjusting the electronic structure of active nickel atoms, and further optimizing the adsorption energy of reaction intermediates; it also utilizes the introduction of oxygen vacancies to reduce the band gap, thereby improving the conductivity of the material, and can optimize the electronic structure of the active site, and enhance the adsorption energy of oxygen-containing intermediates with higher free energy levels. Compared with nickel phosphate nanoflowers with a single component, or nickel phosphate nanoflowers doped with only heteroatoms, or nickel phosphate nanoflowers rich in oxygen vacancies, the oxygen-vacancy chromium ion-doped nickel phosphate nanoflowers of the present application have significantly improved electronic conductivity and intrinsic electrocatalytic activity. It is used as a bifunctional electrocatalyst to construct a dual-electrode system for full water splitting and hydrogen production, and can show significantly enhanced electrocatalytic hydrogen evolution / oxygen evolution / full water splitting performance, which has broad application prospects for promoting efficient and energy-saving hydrogen production.

[0009] Preferably, in the step S1, the weight ratio of nickel nitrate hexahydrate, chromium nitrate nonahydrate, urea, sodium tartrate and polyethylene glycol is (0.5-1.0):(0.02-0.04):(0.7-1.2):(0.8-1.2):(0.5-1.5).

[0010] Through the above technical solution, the application optimizes the ratio range of nickel nitrate hexahydrate, chromium nitrate nonahydrate, urea, sodium tartrate and polyethylene glycol, so that the prepared chromium ion-doped nickel hydroxide nanoflowers have a more uniform composition distribution and higher crystallinity. This helps to improve the electrocatalytic activity of the oxygen vacancy-rich chromium ion-doped nickel phosphate nanoflowers formed in the subsequent steps, thereby reducing the overpotential in the process of electrolytic water hydrogen production, reducing energy loss and improving the hydrogen production efficiency.

[0011] Preferably, in the step S1, the temperature of the heating reaction is 170-190 °C and the time is 15-20 h.

[0012] Through the above technical solution, the application optimizes the reaction temperature and reaction time in the hydrothermal method, which can ensure the sufficient reaction of nickel nitrate hexahydrate, chromium nitrate nonahydrate, urea, sodium tartrate and polyethylene glycol in the aqueous solution to form uniform and stable chromium ion-doped nickel hydroxide nanoflowers. The reaction under this condition can effectively promote the uniform dispersion and crystal growth of the precursor, thereby obtaining a nanoflower structure with regular morphology and uniform size, improving the specific surface area of the material and the number of exposed active sites, and further enhancing its electrocatalytic activity and stability.

[0013] Preferably, in the step S2, the weight ratio of the chromium ion-doped nickel hydroxide nanoflowers to sodium hypophosphite is (0.03-0.05):(0.5-1.0).

[0014] Through the above technical solution, the application optimizes the ratio range of the chromium ion-doped nickel hydroxide nanoflowers to sodium hypophosphite, which can ensure that chromium ions fully participate in the reaction in the subsequent phosphidation reaction to form a stable chromium ion-doped nickel phosphate nanoflower structure. The chromium ion-doped nickel phosphate nanoflower structure has higher crystallinity and more uniform morphology distribution, thereby improving the electrochemical stability and catalytic activity of the material. Among them, the effective doping of chromium ions not only enhances the electron conductivity of the material, but also increases the number of active sites on the surface of the material, thereby significantly reducing the overpotential and improving the hydrogen evolution efficiency of electrolytic water.

[0015] Preferably, in the step S2, the temperature of the sealed calcination is 400-500 °C and the time is 1-2 h.

[0016] Through the above technical solution, the present application optimizes the reaction temperature and reaction time during sealed calcination, which can effectively promote the chemical reaction between chromium ion-doped nickel hydroxide nanoflowers and sodium hypophosphite, enabling the product to more uniformly form chromium ion-doped nickel phosphate nanoflowers. The heat treatment under such conditions not only helps improve the crystallinity and stability of the material but also ensures the effective doping of chromium ions, thereby enhancing the electrocatalytic activity and conductivity of the material, further reducing the overpotential during the electrolytic hydrogen production process, and improving the energy utilization efficiency.

[0017] Preferably, in the step S3, the inert discharge gas is nitrogen or argon, and the gas flow rate is 100 - 2000 sccm.

[0018] Through the above technical solution, the present application optimizes the type of inert discharge gas and the range of gas flow rate, which can effectively control the plasma reaction environment, ensuring that the oxygen vacancy-rich chromium ion-doped nickel phosphate nanoflowers generated have a more uniform oxygen vacancy distribution. This not only improves the electronic conductivity of the material and the number of surface active sites but also optimizes the material's adsorption and dissociation ability for hydrogen molecules, thereby significantly reducing the overpotential during the electrolytic hydrogen production process and enhancing the catalytic efficiency. Specifically, nitrogen or argon as an inert gas can maintain stable chemical properties at low temperatures, avoiding unnecessary side reactions. At the same time, the gas flow rate range of 100 - 2000 sccm ensures the stability and controllability of the plasma reaction, contributing to the formation of a high-quality oxygen vacancy-rich structure.

[0019] Preferably, in the step S3, the pressure of the plasma reaction is 15 - 20 mTorr, the power is 50 - 60 W, and the time is 3 - 5 min.

[0020] Through the above technical solution, the present application optimizes the pressure of the plasma reaction, which can effectively promote the formation of oxygen vacancies and increase the number of active sites on the material surface. At the same time, the optimization of the plasma reaction power ensures sufficient energy input, making the plasma reaction more uniform and stable, and further improving the electrocatalytic activity of the material. Moreover, the optimization of the plasma reaction time not only ensures sufficient reaction time but also avoids the destruction of the material structure caused by long-term reaction, thereby achieving the high-efficiency catalytic performance of oxygen vacancy-rich chromium ion-doped nickel phosphate nanoflowers in the electrolytic hydrogen evolution.

[0021] In a second aspect, the present application provides an oxygen vacancy-rich chromium ion-doped nickel phosphate nanoflower prepared by the above method for preparing an oxygen vacancy-rich chromium ion-doped nickel phosphate nanoflower.

[0022] Through the above technical solution, the oxygen vacancy-rich chromium ion-doped nickel phosphate nanoflower prepared by the present application not only has excellent electrocatalytic activity but also exhibits remarkable stability and a long service life.

[0023] Thirdly, the present application provides an application of the above-mentioned oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers in electrolytic water hydrogen evolution.

[0024] By adopting the above technical solutions, the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers prepared in the present application can exhibit significant advantages in the application of electrolytic water hydrogen evolution. First of all, the doping of chromium ions optimizes the electronic structure of the material, improves the electrical conductivity, and promotes the electron transfer efficiency. Secondly, the abundant oxygen vacancies not only increase the number of surface active sites of the material, but also reduce the adsorption energy barrier of reaction intermediates, effectively enhancing the catalytic activity. Finally, this catalyst can significantly reduce the overpotential, reduce energy consumption, realize efficient and stable electrolytic water hydrogen production, and show good industrial application potential.

[0025] To sum up, the present application has the following beneficial technical effects: 1. The preparation method of the present application significantly improves the electrical conductivity and surface activity of the transition metal electrocatalyst, reduces the overpotential, promotes the kinetic process of water decomposition reaction, reduces energy loss, and improves the efficiency of electrolytic water hydrogen production; 2. The preparation method of the present application is simple and easy to operate, with low cost, suitable for large-scale industrial production, and is conducive to promoting the development of low-cost and high-efficiency electrolytic water hydrogen production technology. Description of the Drawings

[0026] Figure 1 is the process flow chart of the preparation method of the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers of the present application; Figure 2 is the scanning electron microscope image of the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers prepared in Example 1 of the present application; Figure 3 is the X-ray diffraction pattern of the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers prepared in Example 2 of the present application; Figure 4 is the X-ray photoelectron spectroscopy pattern of the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers prepared in Example 3 of the present application; Figure 5 is the electron paramagnetic resonance image of the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers prepared in Example 1 of the present application; Figure 6 is the electrocatalytic hydrogen evolution polarization curve of the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers prepared in Example 1 of the present application; Figure 7 is the electrocatalytic oxygen evolution polarization curve of the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers prepared in Example 2 of the present application; Figure 8 is the overall water splitting performance polarization curve of the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers prepared in Example 3 of the present application as a bifunctional electrocatalyst. Detailed Embodiments

[0027] The present application will be further described in detail below with reference to the accompanying drawings.

[0028] As Figure 1 shown, the preparation method of oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers of the present application includes the following steps: S1. Dissolve nickel nitrate hexahydrate, chromium nitrate nonahydrate, urea, sodium tartrate and polyethylene glycol in water, then carry out a heating reaction, and then cool down, wash and dry to obtain chromium-ion-doped nickel hydroxide nanoflowers; S2. Mix the chromium-ion-doped nickel hydroxide nanoflowers prepared in step S1 with sodium hypophosphite and disperse them evenly in water, then freeze-dry, seal and calcine, and then cool down, wash and dry to obtain chromium-ion-doped nickel phosphate nanoflowers; S3. Carry out a plasma reaction on the chromium-ion-doped nickel phosphate nanoflowers prepared in step S2 under the condition of introducing an inert discharge gas to obtain oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers.

[0029] In some preferred specific embodiments, in S1, the weight ratio of nickel nitrate hexahydrate, chromium nitrate nonahydrate, urea, sodium tartrate and polyethylene glycol is (0.5 - 1.0):(0.02 - 0.04):(0.7 - 1.2):(0.8 - 1.2):(0.5 - 1.5).

[0030] In some preferred specific embodiments, in S1, the temperature of the heating reaction is 170 - 190 °C and the time is 15 - 20 h.

[0031] In some preferred specific embodiments, in S2, the weight ratio of the chromium-ion-doped nickel hydroxide nanoflowers to sodium hypophosphite is (0.03 - 0.05):(0.5 - 1.0).

[0032] In some preferred specific embodiments, in S2, the temperature of the sealed calcination is 400 - 500 °C and the time is 1 - 2 h.

[0033] In some preferred specific embodiments, in S3, the inert discharge gas is nitrogen or argon, and the gas flow rate is 100 - 2000 sccm.

[0034] In some preferred specific embodiments, in S3, the pressure of the plasma reaction is 15 - 20 mTorr, the power is 50 - 60 W, and the time is 3 - 5 min.

[0035] Based on the above content, the applicant further uses the following 3 examples and 2 comparative examples to verify and illustrate the structure and performance of the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared by the present application.

[0036] Except as otherwise specified, the raw materials used in this application are all commercially available products.

[0037] Example 1 A preparation method of oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers, comprising the following steps: S1. Dissolve 0.5 g of nickel nitrate hexahydrate, 0.02 g of chromium nitrate nonahydrate, 0.7 g of urea, 0.8 g of sodium tartrate, and 0.5 g of polyethylene glycol completely in 30 mL of ultrapure water, then transfer it to a 50 mL polytetrafluoroethylene reaction kettle, and then keep it at a constant temperature of 170 °C for 15 h, then naturally cool down, and wash it by centrifugation with ethanol and ultrapure water at least 3 times, and then dry it at a temperature of 75 °C for 12 h to obtain chromium ion-doped nickel hydroxide nanoflowers; S2. Mix 0.03 g of the chromium ion-doped nickel hydroxide nanoflowers prepared in step S1 with 0.5 g of sodium hypophosphite and disperse them evenly in 20 mL of ultrapure water, then freeze-dry for 12 h to obtain a powder, and then place the obtained powder in a tube furnace, seal both ends of the tube mouth, and calcine it at a temperature of 400 °C for 1 h, then naturally cool down, and wash it by centrifugation with ethanol and ultrapure water at least 3 times, and then dry it at a temperature of 75 °C for 12 h to obtain chromium ion-doped nickel phosphate nanoflowers; S3. Place the chromium ion-doped nickel phosphate nanoflowers prepared in step S2 in a plasma reactor, and at a pressure of 15 mTorr and a power of 50 W, introduce nitrogen discharge gas into the reactor at a flow rate of 100 sccm for 3 min, then the reaction ends, and oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers are obtained.

[0038] Example 2 A preparation method of oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers, comprising the following steps: S1. Dissolve 0.8 g of nickel nitrate hexahydrate, 0.03 g of chromium nitrate nonahydrate, 1.0 g of urea, 1.0 g of sodium tartrate, and 1.0 g of polyethylene glycol completely in 40 mL of ultrapure water, then transfer it to a 50 mL polytetrafluoroethylene reaction kettle, and then keep it at a constant temperature of 180 °C for 18 h, then naturally cool down, and wash it by centrifugation with ethanol and ultrapure water at least 3 times, and then dry it at a temperature of 75 °C for 12 h to obtain chromium ion-doped nickel hydroxide nanoflowers; S2. Mix 0.04 g of the chromium ion-doped nickel hydroxide nanoflowers prepared in step S1 with 0.8 g of sodium hypophosphite and disperse them evenly in 30 mL of ultrapure water, then freeze-dry for 12 h to obtain a powder, and then place the obtained powder in a tube furnace, seal both ends of the tube mouth, and calcine it at a temperature of 450 °C for 1.5 h, then naturally cool down, and wash it by centrifugation with ethanol and ultrapure water at least 3 times, and then dry it at a temperature of 75 °C for 12 h to obtain chromium ion-doped nickel phosphate nanoflowers; S3. Place the nickel phosphate nanoflowers doped with chromium ions prepared in step S2 into a plasma reactor. At a pressure of 18 mTorr and a power of 55 W, introduce nitrogen discharge gas into the reactor at a flow rate of 1000 sccm for 4 min, and then end the reaction to obtain nickel phosphate nanoflowers doped with chromium ions rich in oxygen vacancies.

[0039] Example 3 A preparation method of nickel phosphate nanoflowers doped with chromium ions rich in oxygen vacancies, comprising the following steps: S1. Completely dissolve 1.0 g of nickel nitrate hexahydrate, 0.04 g of chromium nitrate nonahydrate, 1.2 g of urea, 1.2 g of sodium tartrate, and 1.5 g of polyethylene glycol in 50 mL of ultrapure water, then transfer it to a 100 mL polytetrafluoroethylene reaction kettle, and then keep it at a constant temperature of 190 °C for 20 h. After that, let it cool naturally, and centrifuge and wash it with ethanol and ultrapure water at least 3 times, and then dry it at a temperature of 75 °C for 12 h to obtain nickel hydroxide nanoflowers doped with chromium ions; S2. Mix 0.05 g of the nickel hydroxide nanoflowers doped with chromium ions prepared in step S1 with 1.0 g of sodium hypophosphite and disperse them evenly in 40 mL of ultrapure water. Then, freeze-dry them for 12 h to obtain a powder. Then, place the obtained powder in a tubular furnace, seal both ends of the tube mouth, and calcine it at a temperature of 500 °C for 2 h. After that, let it cool naturally, and centrifuge and wash it with ethanol and ultrapure water at least 3 times, and then dry it at a temperature of 75 °C for 12 h to obtain nickel phosphate nanoflowers doped with chromium ions; S3. Place the nickel phosphate nanoflowers doped with chromium ions prepared in step S2 into a plasma reactor. At a pressure of 20 mTorr and a power of 60 W, introduce nitrogen discharge gas into the reactor at a flow rate of 2000 sccm for 5 min, and then end the reaction to obtain nickel phosphate nanoflowers doped with chromium ions rich in oxygen vacancies.

[0040] Comparative Example 1 The difference from Example 2 is that step S3 is removed, that is, no oxygen vacancies are created, and the rest is the same as Example 2.

[0041] Comparative Example 2 The difference from Example 2 is that chromium nitrate nonahydrate is not added in step S1, that is, no chromium doping is carried out, and the rest is the same as Example 2.

[0042] Performance detection 1. Conduct electron microscopy scanning on the nickel phosphate nanoflowers doped with chromium ions rich in oxygen vacancies prepared in the above examples, and the results are as Figure 2 shown.

[0043] From Figure 2It can be seen that the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared in Example 1 of this application have a hollow nanoflower structure assembled by ultrathin nanosheets. This structure helps to fully expose the surface active sites and make full contact with the electrolyte, improving the utilization rate of the active sites and thus enhancing the catalytic performance of the transition metal electrocatalyst. Since the SEM images of Examples 2-3 are similar to those of Example 1, the SEM image of Example 1 is used as an example for illustration, and the SEM images of Examples 2 and 3 are not listed repeatedly in this application.

[0044] 2. Using monoclinic cyclic tetraphosphate nickel Ni 2 P 4 O 12 as the composition counterpart, an X-ray diffraction experiment was carried out on the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared in the above examples, and the results are as Figure 3 shown. Since there are no significant differences among the X-ray diffraction patterns of the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared in Examples 1-3, the X-ray diffraction pattern of the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared in Example 2 is used as an example in this application.

[0045] 3. An X-ray photoelectron experiment was carried out on the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared in the above examples, and the results are as Figure 4 shown. Since there are no significant differences among the X-ray photoelectron spectra of the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared in Examples 1-3, the X-ray photoelectron spectrum of the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared in Example 3 is used as an example in this application.

[0046] It can be seen from Figure 4 that nickel element, chromium element, oxygen element and phosphorus element coexist, and the atomic ratio of nickel element, phosphorus element, chromium element and oxygen element is 12.5:24.7:3.2:59.6.

[0047] 4. An electron paramagnetic resonance experiment was carried out on the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared in the above examples, and the results are as Figure 5 shown. Since there are no significant differences among the electron paramagnetic resonance spectra of the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared in Examples 1-3, the electron paramagnetic resonance spectrum of the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared in Example 1 is used as an example in this application.

[0048] It can be seen from Figure 5 that the oxygen-vacancy-rich chromium-ion-doped nickel phosphate nanoflowers prepared in Example 1 have a relatively high resonance intensity at g = 2.01, indicating that the surface of this material has abundant oxygen vacancies.

[0049] 5. The linear sweep voltammetry (LSV) curves of the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers prepared in the above embodiments were respectively detected for electrocatalytic hydrogen evolution performance, electrocatalytic oxygen evolution performance, and overall water splitting performance. Using the initial nickel phosphate, chromium ion-doped nickel phosphate prepared in Comparative Example 1, and oxygen-rich vacancy nickel phosphate prepared in Comparative Example 2 as comparisons, the results are as Figures 6 - 8 shown.

[0050] It can be seen from Figures 6 - 8 that the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers prepared in Examples 1-3 of this application have more excellent electrocatalytic hydrogen evolution activity, electrocatalytic oxygen evolution activity, and electrocatalytic overall water splitting activity compared with the initial nickel phosphate, chromium ion-doped nickel phosphate prepared in Comparative Example 1, and oxygen-rich vacancy nickel phosphate prepared in Comparative Example 2.

[0051] Specifically, in an alkaline medium, the overpotential of the hydrogen evolution reaction of the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers prepared in this application is η 10 = 46 ± 2 mV, the overpotential of the oxygen evolution reaction is η 50 = 227 ± 2 mV, and the overall water splitting voltage is E 50 = 1.47 ± 0.003 V; The overpotential of the hydrogen evolution reaction of the chromium ion-doped nickel phosphate nanoflowers prepared in Comparative Example 1 is η 10 = 57 ± 3 mV, the overpotential of the oxygen evolution reaction is η 50 = 236 ± 2 mV, and the overall water splitting voltage is E 50 = 1.50 ± 0.004 V; The overpotential of the hydrogen evolution reaction of the oxygen-rich vacancy nickel phosphate nanoflowers prepared in Comparative Example 2 is η 10 = 63 ± 3 mV, the overpotential of the oxygen evolution reaction is η 50 = 245 ± 2 mV, and the overall water splitting voltage is E 50 = 1.53 ± 0.004 V; The overpotential of the hydrogen evolution reaction of the initial nickel phosphate nanoflowers is η 10 = 78 ± 2 mV, the overpotential of the oxygen evolution reaction is η 50 = 256 ± 2 mV, and the overall water splitting voltage is E 50 = 1.55 ± 0.003 V.

[0052] In summary, the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers exhibit the lowest electrocatalytic hydrogen evolution, oxygen evolution, and overall water splitting potentials.

[0053] The embodiments of this specific implementation manner are all preferred embodiments of this application. Without limiting the protection scope of this application accordingly, therefore: Any equivalent changes made according to the structure, shape, and principle of this application shall be covered within the protection scope of this application.

Claims

1. A method for preparing oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers, characterized in that: The following steps are involved: S1. Dissolving nickel nitrate hexahydrate, chromium nitrate nonahydrate, urea, sodium tartrate and polyethylene glycol in water, and then heating for reaction, cooling, washing and drying to obtain chromium ion-doped nickel hydroxide nanoflowers; S2, mixing the chromium ion-doped nickel hydroxide nanoflowers prepared in step S1 with sodium hypophosphite and uniformly dispersing them in water, and then freeze-drying, sealing and calcining, and then cooling, washing, and drying to obtain chromium ion-doped nickel phosphate nanoflowers; S3. The chromium ion-doped nickel phosphate nanoflowers prepared in step S2 are subjected to a plasma reaction under the condition of passing an inert discharge gas to obtain oxygen-vacancies-rich chromium ion-doped nickel phosphate nanoflowers.

2. The method for preparing the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers according to claim 1, characterized in that: In the S1, the weight ratio of nickel nitrate hexahydrate, chromium nitrate nonahydrate, urea, sodium tartrate and polyethylene glycol is (0.5-1.0):(0.02-0.04):(0.7-1.2):(0.8-1.2):(0.5-1.5).

3. The method for preparing the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers according to claim 1, characterized in that: In S1, the heating reaction temperature is 170-190° C. and the time is 15-20 hours.

4. The method for preparing the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers according to claim 1, characterized in that: In S2, the weight ratio of chromium ion-doped nickel hydroxide nanoflowers to sodium hypophosphite is (0.03-0.05): (0.5-1.0).

5. The method for preparing the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers according to claim 1, characterized in that: In S2, the temperature of the sealed calcination is 400-500°C and the time is 1-2h.

6. The method for preparing the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers according to claim 1, characterized in that: In the step S3, the inert discharge gas is nitrogen or argon, and the gas flow rate is 100-2000 sccm.

7. The method for preparing the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers according to claim 1, characterized in that: In S3, the pressure of the plasma reaction is 15-20 mTorr, the power is 50-60 W, and the time is 3-5 min.

8. An oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflower prepared by the preparation method of oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers according to any one of claims 1 to 7.

9. Use of the oxygen-rich vacancy chromium ion-doped nickel phosphate nanoflowers according to claim 8 in hydrogen evolution by electrolysis of water.

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