Ni / NiO composite material and preparation method and application thereof

Abstract

The invention provides a Ni / NiO composite material and a preparation method and application thereof, and belongs to the technical field of hydrogen production through water electrolysis. According to the invention, the three-dimensional foamed nickel with good conductivity and large specific surface area is used as a substrate material of the MOF for hydrothermal reaction, so that the MOF material grows in the foamed nickel in situ, the conductivity of the material can be improved, the catalytic activity of the material is improved, the pore structure of the material is further enriched, and a channel is established for transmission of water molecules and hydrogen; the obtained foamed nickel loaded Ni-MOF is used as a composite material precursor, the porosity and abundant metal nodes enable the material structure to be uniform, the specific surface area is large, and agglomeration of a nickel-based catalyst is avoided; the precursor is calcined in air to remove the MOF material to form NiO with a MOF material and foamed nickel double skeleton structure, part of NiO is reduced into Ni through two-stage reduction, the structure is optimized, and the stability and catalytic activity of the material are improved.

Description

TECHNICAL FIELD

[0002] The application belongs to the technical field of hydrogen production by water electrolysis, and particularly relates to a Ni / NiO composite material and a preparation method and application thereof. BACKGROUND

[0003] With the exhaustion of traditional energy and the increasing demand for environmental protection, the development of clean energy has become a research hotspot. Hydrogen energy, as a high-calorific value, carbon-free and pollution-free clean energy, has attracted widespread attention in its development and utilization.

[0004] Water electrolysis is considered to be the most economical and environmentally friendly hydrogen production scheme. The electrolytic decomposition of water involves two half-reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which undergo multi-electron transfer processes, so the kinetics is relatively slow. So far, platinum, ruthenium and iridium are considered to be the materials with the highest activity in electrocatalytic water splitting. Although noble metal catalysts have excellent performance, they are high in cost and low in reserves, and are difficult to be applied on a large scale. In contrast, transition metal-based catalysts have the advantages of low cost, superior electronic structure and good electrical conductivity, and become ideal alternative materials. However, the Ni / NiO catalyst prepared by the prior art has poor electrical conductivity and is easy to aggregate, so that its electrochemical activity is difficult to achieve the expected effect.

[0005] Compared with water electrolysis, the anode of electrolysis of urea water undergoes urea oxidation reaction (UOR), which has a lower potential requirement, can effectively reduce energy consumption, and can also treat urea-rich wastewater, which has both environmental and economic benefits. It is a more sustainable and efficient hydrogen production path. Seawater accounts for more than 96% of global water resources. The use of seawater for hydrogen production not only can alleviate the problem of water shortage, but also can help promote the development of marine hydrogen economy. However, seawater is highly corrosive and can easily poison the catalyst. Moreover, the anode oxygen evolution reaction (OER) has a high overpotential during the electrolysis of water, and chlorine and other by-products are easily produced in seawater and can cause anode corrosion. Therefore, it is of great significance to develop a catalyst that can catalyze the electrolysis of urea water and has resistance to seawater corrosion for the development of hydrogen production by water electrolysis. SUMMARY

[0006] The purpose of the present application is to provide a Ni / NiO composite material and a preparation method and application thereof. The material prepared by the preparation method provided by the present application has high electrochemical activity in water, seawater and urea water, and good stability.

[0007] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions: The present application provides a preparation method of a Ni / NiO composite material, comprising the following steps: mixing a nickel source, an organic ligand, a solvent and a foamed nickel to perform a hydrothermal reaction, to obtain a foamed nickel loaded Ni-MOF; The nickel-supported Ni-MOF foam was subjected to three-stage calcination to obtain a Ni / NiO composite material; The three-stage calcination includes: a first stage of calcination in an air atmosphere, followed by a second and third stage of calcination in a reducing atmosphere; the first stage of calcination is performed at a temperature of 250~350℃ for 2~4 hours; the second stage of calcination is performed at a temperature of 330~380℃ for 0.5~1.5 hours; and the third stage of calcination is performed at a temperature of 400~500℃ for 1~3 hours.

[0008] Preferably, the nickel source includes an organic nickel salt or an inorganic nickel salt; the organic ligand is an aromatic polycarboxylic acid ligand.

[0009] Preferably, the mass ratio of the nickel source, organic ligand, and nickel foam is (1~3):(1~2):(1~3).

[0010] Preferably, the solvent is a mixture of water, ethanol and DMF.

[0011] Preferably, the hydrothermal reaction is carried out at a temperature of 140-160°C for 10-20 hours.

[0012] Preferably, the reducing atmosphere is a mixture of hydrogen and an inert gas, wherein the volume fraction of hydrogen in the mixture is 5-10%.

[0013] The present invention also provides a Ni / NiO composite material prepared by the preparation method described in the above technical solution.

[0014] The present invention also provides a Ni / NiO / Ni(OH)2 composite material, wherein the Ni / NiO / Ni(OH)2 composite material is obtained by activating the Ni / NiO composite material described in the above technical solution; the activation is carried out by electrochemical activation in an alkaline electrolyte.

[0015] The present invention also provides a method for producing hydrogen by electrolysis of water, using the Ni / NiO composite material or the Ni / NiO / Ni(OH)2 composite material described in the above technical solution as a catalyst.

[0016] Preferably, the water includes water, seawater, urea-containing water, and / or human urine.

[0017] This invention provides a method for preparing Ni / NiO composite materials, comprising the following steps: mixing a nickel source, an organic ligand, a solvent, and nickel foam, followed by a hydrothermal reaction to obtain nickel foam-supported Ni-MOF; subjecting the nickel foam-supported Ni-MOF to a three-stage calcination to obtain the Ni / NiO composite material; the three-stage calcination includes: a first stage calcination in an air atmosphere, followed by a second stage calcination and a third stage calcination sequentially in a reducing atmosphere; the first stage calcination temperature is 250~350℃, and the time is 2~4h; the second stage calcination temperature is 330~380℃, and the time is 0.5~1.5h; the third stage calcination temperature is 400~500℃, and the time is 1~3h. This invention uses three-dimensional nickel foam, which has good conductivity and a large specific surface area, as the substrate material for a metallurgical fungicide (MOF) via a hydrothermal reaction. This allows the MOF material to grow in situ within the nickel foam, enriching the material's porous structure and establishing channels for the transport of water molecules and hydrogen. The resulting nickel foam-supported Ni-MOF serves as a precursor for the composite material. Its porosity and abundant metal nodes ensure a uniform material structure and a large specific surface area, preventing the aggregation of nickel-based catalysts. The precursor is calcined in air to remove the MOF material, forming NiO with a dual framework structure of MOF material and nickel foam. A two-stage reduction process further reduces some of the NiO to Ni, optimizing the structure of the Ni / NiO composite material and improving its stability and catalytic activity. The results of the embodiments show that the composite material prepared by the method provided in this invention exhibits a conductivity of 100 mA / cm² in seawater. 2 The overpotential of the current density is 186mV, 10mA / cm. 2 The overpotential at current density is 6 mV, and the Tafel slope is 63 mV / dec; it also exhibits good stability within 100 h; in 1 M KOH + 0.33 mol / L urea solution, the Tafel slope is 28 mV / dec. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the preparation of the Ni / NiO / Ni(OH)2 composite material of the present invention; Figure 2 The XRD patterns are of the materials obtained in Examples 1-3 and Comparative Examples 1-3 of this invention, as well as the nickel foam raw material. Figure 3 XPS images of the materials obtained in Example 1 and Comparative Example 2 of this invention; Figure 4 These are SEM images of the materials obtained in Embodiment 1 and Comparative Examples 1-3 of the present invention; Figure 5 These are SEM images of the materials obtained in Examples 2-3 of this invention; Figure 6 The TEM image and analysis diagram of the material obtained in Example 1 of this invention are shown. Figure 7 The image shown is the EDX image of the material obtained in Example 1 of this invention. Figure 8 These are electrochemical analysis diagrams of the materials obtained in Example 1 and Comparative Examples 1-3 of the present invention, as well as the nickel foam raw material, in a neutral electrolyte. Figure 9 These are electrochemical analysis diagrams of the materials obtained in Examples 1-3 of this invention in neutral electrolytes; Figure 10 The CV diagrams are shown for the materials obtained in Examples 1-3 and Comparative Examples 1-3 of this invention, as well as the nickel foam raw material, in a neutral electrolyte. Figure 11 This is a graph showing the test results of the material obtained in Example 1 of this invention in a neutral electrolyte for 100 hours. Figure 12 The electrochemical analysis diagrams of the materials obtained in Example 1 and Comparative Examples 1-3 of this invention and the nickel foam raw material in acidic electrolyte are shown. Figure 13 These are electrochemical analysis diagrams of the materials obtained in Examples 1-3 of this invention in acidic electrolytes; Figure 14 This is a graph showing the test results of the material obtained in Example 1 of this invention in an acidic electrolyte for 100 hours. Figure 15 This is a CP test diagram of the material obtained in Example 1 of the present invention in an alkaline electrolyte; Figure 16 The electrochemical analysis diagrams of the materials obtained in Examples 1 and 4, and Comparative Examples 1 to 3 of this invention, as well as the nickel foam raw material, in alkaline electrolyte are shown. Figure 17 These are electrochemical analysis diagrams of the materials obtained in Examples 1-3 of this invention in alkaline electrolytes; Figure 18 These are electrochemical analysis diagrams of the materials obtained in Examples 1 and 4 of this invention in alkaline electrolytes; Figure 19 The CV diagrams are shown for the materials obtained in Examples 1-4 and Comparative Examples 1-3 of this invention, as well as the nickel foam raw material, in alkaline electrolyte. Figure 20 The diagram shows the contact angle changes of the materials obtained in Examples 1 and 4 of this invention and the nickel foam raw material in alkaline electrolyte. Figure 21 The XRD pattern of the material obtained in Example 4 of this invention; Figure 22 The Raman spectrum, infrared spectrum, and EPR spectrum of the material obtained in Example 4 of this invention are shown below. Figure 23 These are the XPS spectra of the materials obtained in Examples 1 and 4 of this invention; Figure 24 This is a SEM image of the material obtained in Example 4 of the present invention; Figure 25 The TEM image and analysis diagram of the material obtained in Example 4 of this invention are shown below. Figure 26 The image shown is the EDX diagram of the material obtained in Example 4 of this invention. Figure 27 The molecular structure model diagram constructed for Test Example 15 of this invention; Figure 28 This is a calculated analysis graph of the water molecule adsorption energy, activation energy, and reaction energy in Test Example 15 of the present invention; Figure 29 The graph shows the calculated adsorption energy of the hydroxyl group and the Gibbs free energy of hydrogen in Test Example 15 of this invention. Figure 30 These are electrochemical analysis diagrams of the materials obtained in Example 1 and Comparative Examples 1-3 of the present invention, as well as the nickel foam raw material, in alkaline seawater. Figure 31 These are electrochemical analysis diagrams of the materials obtained in Examples 1-3 of this invention in alkaline seawater; Figure 32 The CV diagrams are shown for the materials obtained in Examples 1-3 and Comparative Examples 1-3 of this invention, as well as the nickel foam raw material, in alkaline seawater. Figure 33 The electrochemical analysis diagrams of the materials obtained in Example 1 and Comparative Examples 1-3 of this invention and the nickel foam raw material in urea electrolyte are shown. Figure 34 The CV diagrams of the materials obtained in Examples 1-3 of this invention in urea electrolyte are shown. Figure 35 These are test images of materials under different oxidation conditions obtained in Example 1 of this invention; Figure 36 The images show the electrolysis test results of the material obtained in Example 1 of this invention in different electrolytes. Detailed Implementation

[0019] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0020] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses raw materials of analytical grade or conventional purity used in the field of hydrogen production by water electrolysis.

[0021] This invention provides a method for preparing Ni / NiO composite materials, comprising the following steps: Nickel source, organic ligand, solvent and nickel foam were mixed and subjected to hydrothermal reaction to obtain nickel foam-supported Ni-MOF; The nickel-supported Ni-MOF foam was subjected to three-stage calcination to obtain a Ni / NiO composite material; The three-stage calcination includes: a first stage of calcination in an air atmosphere, followed by a second and third stage of calcination in a reducing atmosphere; the first stage of calcination is performed at a temperature of 250~350℃ for 2~4 hours; the second stage of calcination is performed at a temperature of 330~380℃ for 0.5~1.5 hours; and the third stage of calcination is performed at a temperature of 400~500℃ for 1~3 hours.

[0022] This invention involves mixing a nickel source, an organic ligand, a solvent, and nickel foam, followed by a hydrothermal reaction to obtain nickel foam-supported Ni-MOF.

[0023] In this invention, the nickel source preferably comprises an organic nickel salt or an inorganic nickel salt, more preferably an inorganic nickel salt; the inorganic nickel salt preferably comprises nickel nitrate hexahydrate, nickel chloride hexahydrate, or nickel sulfate hexahydrate, more preferably nickel nitrate hexahydrate. The above-mentioned nickel sources have good solubility and reactivity, which is beneficial for improving the structural stability of MOF materials.

[0024] In this invention, the organic ligand is preferably an aromatic polycarboxylic acid ligand; the aromatic polycarboxylic acid ligand preferably includes 2,5-dihydroxyterephthalic acid, terephthalic acid, or trimesolic acid, more preferably 2,5-dihydroxyterephthalic acid. The above-mentioned organic ligands have good coordination ability with nickel ions, which is beneficial to improving the structural stability of MOF materials.

[0025] As one embodiment of the present invention, the foamed nickel can be pretreated before use. The pretreatment includes: cutting the foamed nickel and then cleaning it; the cleaning includes sequentially performing acetone cleaning, acid washing, anhydrous ethanol cleaning and deionized water cleaning; the acid used for acid washing can be 3 mol / L hydrochloric acid.

[0026] In this invention, the preferred mass ratio of the nickel source, organic ligand, and nickel foam is (1~3):(1~2):(1~3), more preferably 3:1:(1~3); as one embodiment of this invention, the mass ratio of the nickel source, organic ligand, and nickel foam can be 3:1:1, 3:1:2, or 3:1:3. A mass ratio of nickel source, organic ligand, and nickel foam within the above ranges is beneficial for the bonding of MOF materials with nickel foam, further improving the structural stability of the composite material.

[0027] In this invention, the solvent is preferably a mixture of water, ethanol, and DMF. This invention does not impose any particular limitation on the ratio of water, ethanol, and DMF in the mixed solvent; any ratio well-known to those skilled in the art can be used. In an embodiment of this invention, the volume ratio of water, ethanol, and DMF is 2.5:2.5:35.

[0028] The present invention does not have any particular limitation on the mixing method, as long as the raw materials can be mixed evenly.

[0029] In this invention, the hydrothermal reaction temperature is preferably 140~160℃, more preferably 145~155℃; as one embodiment of this invention, the hydrothermal reaction temperature can be 140℃, 143℃, 147℃, 150℃, 153℃, or 157℃. A hydrothermal reaction temperature within the above range is beneficial for further improving the structural stability of MOF materials.

[0030] In this invention, the hydrothermal reaction time is preferably 10-20 hours, more preferably 13-18 hours; as one embodiment of this invention, the hydrothermal reaction time can be 11 hours, 13 hours, 15 hours, 16 hours, 17 hours, or 19 hours. A hydrothermal reaction time within the above range is beneficial for further improving the structural stability of MOF materials.

[0031] In one embodiment of the present invention, the hydrothermal reaction can be carried out in a Teflon autoclave.

[0032] In one embodiment of the present invention, after the hydrothermal reaction is completed, the obtained product can be washed and dried; the washing can be done by washing with water and anhydrous ethanol in sequence; the drying can be done by drying at 60°C for 12 hours.

[0033] After obtaining the nickel-supported Ni-MOF foam, the present invention performs three-stage calcination on the nickel-supported Ni-MOF foam to obtain a Ni / NiO composite material.

[0034] In this invention, the three-stage calcination includes: a first stage of calcination in an air atmosphere, followed by a second stage of calcination and a third stage of calcination in a reducing atmosphere.

[0035] In this invention, the temperature of the first stage of calcination is 250~350℃, preferably 270~320℃; as one embodiment of this invention, the temperature of the first stage of calcination can be 260℃, 280℃, 300℃, or 330℃. In this invention, the calcination time of the first stage is 2~4 hours, preferably 3 hours. This invention forms NiO with a dual framework of MOF material and nickel foam by calcining and ablating MOF material in the first stage; the parameters of the first stage of calcination are within the above range, which can control the ablation rate of MOF material and improve the structural stability of NiO.

[0036] In this invention, the temperature of the second stage calcination is 330~380℃, preferably 350℃; the calcination time of the second stage is 0.5~1.5h, preferably 1h. This invention reduces part of the NiO generated in the first stage calcination to Ni through the second stage calcination; with the parameters of the second stage calcination within the above range, nano-sized Ni particles can be obtained, improving the catalytic performance of the composite material.

[0037] In this invention, the temperature of the third-stage calcination is 400~500℃, preferably 450℃; the calcination time is 1~3h, preferably 2h. This invention further reduces NiO to Ni through the third-stage calcination, optimizing the structure of the composite material. When the parameters of the third-stage calcination are within the above range, the Ni-NiO structure can be optimized, improving the catalytic performance of the composite material.

[0038] In one embodiment of the present invention, the heating rate of the three-stage calcination can be 5°C / min.

[0039] In this invention, the reducing atmosphere is preferably a mixture of hydrogen and an inert gas, and the volume fraction of hydrogen in the mixture is preferably 5-10%, more preferably 6-8%. As one embodiment of this invention, the volume fraction of hydrogen in the mixture can be 5%, 6%, 7%, 8%, 9%, or 10%. Using a mixture of hydrogen and an inert gas is beneficial for the stable conduct of the reduction reaction and further improves the catalytic performance of the composite material.

[0040] In one embodiment of the present invention, the inert gas in the reducing atmosphere can be nitrogen or argon.

[0041] This invention uses three-dimensional nickel foam with good conductivity and large specific surface area as the substrate material of MOF (Metal-O-Factory) in a hydrothermal reaction, allowing the MOF material to grow in situ within the nickel foam. This improves the conductivity and catalytic activity of the material, and further enriches its porous structure, establishing channels for the transport of water molecules and hydrogen. The resulting nickel foam-supported Ni-MOF serves as a precursor for the composite material. Its porosity and abundant metal nodes result in a uniform material structure and a large specific surface area, preventing the agglomeration of nickel-based catalysts. The precursor is calcined in air to remove the MOF material, forming NiO with a dual framework structure of MOF material and nickel foam. Through two-stage reduction, some NiO is reduced to Ni, and the structure of the Ni / NiO composite material is optimized to improve its stability and catalytic activity.

[0042] The present invention also provides a Ni / NiO composite material prepared by the preparation method described in the above technical solution.

[0043] The present invention also provides a Ni / NiO / Ni(OH)2 composite material, wherein the Ni / NiO / Ni(OH)2 composite material is obtained by activating the Ni / NiO composite material described in the above technical solution.

[0044] In this invention, the activation is performed electrochemically in an alkaline electrolyte; as one embodiment of the invention, the alkaline electrolyte can be a 1 mol / L KOH aqueous solution; the current density of the electrochemical activation can be 100 mA / cm². 2 The activation time can be 3 hours.

[0045] A schematic diagram of the preparation of the Ni / NiO / Ni(OH)2 composite material according to the present invention is shown below. Figure 1 As shown: After pretreatment, nickel foam is placed in the MOF material preparation system and subjected to hydrothermal reaction to obtain nickel foam-supported Ni-MOF composite material (Ni-MOF). Ni / NiO composite material (Ni / NiO) is obtained by calcination, and then Ni / NiO / Ni(OH)2 composite material (Ni / NiO / Ni(OH)2) is obtained by reconstruction.

[0046] The present invention also provides a method for producing hydrogen by electrolysis of water, using the Ni / NiO composite material or the Ni / NiO / Ni(OH)2 composite material described in the above technical solution as a catalyst.

[0047] In this invention, the water preferably includes water, seawater, urea-containing water, and / or human urine.

[0048] The present invention does not impose any particular limitation on the specific parameters for the electrolysis of water to produce hydrogen; parameters well known to those skilled in the art can be used.

[0049] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0050] Example 1 A method for preparing a Ni / NiO composite material, comprising the following steps: 0.6980 g Ni(NO3)2·6H2O, 0.2378 g 2,5-dihydroxyterephthalic acid, 35 mL DMF, 2.5 mL deionized water and 2.5 mL anhydrous ethanol were added to a beaker and stirred evenly. Then, the mixture was added to a 100 mL Teflon autoclave along with the pretreated nickel foam sheet (2 cm × 4 cm, 0.2543 g). The reaction was carried out at 150 °C for 15 h. After the reaction was completed, the product was washed with deionized water and anhydrous ethanol in sequence and then dried at 60 °C for 12 h to obtain nickel foam-supported Ni-MOF. The nickel-supported Ni-MOF foam was subjected to a three-stage calcination process: the heating rate was 5℃ / min, and the first calcination was carried out at 300℃ for 3h in an air atmosphere; the second calcination was carried out at 350℃ for 1h in an H2 / Ar (H25%) atmosphere, and the third calcination was carried out at 450℃ for 2h to obtain the Ni / NiO composite material, denoted as Ni / NiO.

[0051] Example 2 A method for preparing a Ni / NiO composite material is the same as in Example 1, except that the third calcination time is 1 hour, and the product is denoted as Ni / NiO-1h.

[0052] Example 3 A method for preparing a Ni / NiO composite material is the same as in Example 1, except that the third calcination time is 3 hours, and the product is denoted as Ni / NiO-3h.

[0053] Example 4 A Ni / NiO / Ni(OH)2 composite material, denoted as r-Ni / NiO; The preparation method is as follows: The Ni / NiO composite material obtained in Example 1 is electrochemically activated using a 1 mol / L KOH aqueous solution as the electrolyte and a current density of 100 mA / cm². 2 The activation time is 3 hours.

[0054] Comparative Example 1 A nickel foam-supported Ni-MOF composite material, denoted as Ni-MOF, is prepared using the same method as the nickel foam-supported Ni-MOF in Example 1.

[0055] Comparative Example 2 A NiO material, denoted as NiO. The preparation method is the same as in Example 1, except that the second and third stages of calcination are omitted.

[0056] Comparative Example 3 A Ni@C composite material, denoted as Ni@C, is prepared using the same method as in Example 1, except that the first and second calcinations are omitted.

[0057] Test Example 1 The materials obtained in Examples 1-3 and Comparative Examples 1-3, as well as the nickel foam raw material (denoted as NF), were analyzed using an X-ray diffractometer, and the XRD patterns are shown below. Figure 2 As shown in the figure, Ni / NiO is mainly composed of four distinct peaks. The peaks at 44.5°, 51.8°, and 76.3° correspond to the (111), (200), and (220) crystal planes of Ni (PDF#04-0850), respectively, while the peak at 37.2° corresponds to the 200 crystal plane of NiO (PDF#47-1049). Other synthesized samples, Ni@C and NiO, contain characteristic peaks of Ni and NiO, respectively. Even samples Ni / NiO-1h and Ni / NiO-3h synthesized at different calcination times have similar crystal forms to Ni / NiO. These results preliminarily prove that the samples were successfully synthesized.

[0058] Test Example 2 The materials obtained in Example 1 and Comparative Example 2 were analyzed using X-ray photoelectron spectroscopy, and the XPS patterns are shown below. Figure 3 As shown, (a) and (b) are the XPS spectra of O 1s and Ni 2p in Ni / NiO and NiO, respectively.

[0059] from Figure 3 (a) It can be seen that the peak at around 529.7 eV in the O 1s spectrum of Ni / NiO is the lattice oxygen of MO. The MO bond peak intensity of NiO is significantly stronger than that of Ni / NiO, which should be due to the reduction of metal-oxygen bonds caused by partial reduction. The peak at around 531.9 eV is related to oxygen vacancies, and the peak at around 533.2 eV is surface oxygen. From Figure 3 (b) It can be seen that, for the XPS spectrum of Ni 2p of the catalyst, the peaks at 852.7 eV and 871.6 eV represent Ni. 0 Compared to NiO, Ni / NiO has a higher Ni content. 0 The binding energy of the spectrum underwent a negative shift, indicating that in Ni... 0 The surrounding electron density increases. Since the sample was ultrasonically treated on NF, NiO inevitably contains some elemental Ni. The peaks at 855.3 eV and 873.2 eV represent Ni-O, while the other two peaks are satellite peaks. The changes in the binding energy of the above peaks indicate that the composite material Ni / NiO has strong electronic interactions and chemical coupling.

[0060] Test Example 3 The materials obtained in Examples 1-3 and Comparative Examples 1-3 were observed using a scanning electron microscope, and the SEM images are shown below. Figure 4 , Figure 5 As shown; Figure 4In the image, (a) and (a1) are SEM images of Ni-MOF, (b) and (b1) are SEM images of NiO, (c) and (c1) are SEM images of Ni@C, and (d) and (d1) are SEM images of Ni / NiO. Figure 5 In the image, (a) and (a1) are SEM images of Ni / NiO-1h, and (b) and (b1) are SEM images of Ni / NiO-3h.

[0061] from Figure 4 It can be seen that NiO consists of many tiny nanorods bonded together to form a spherical shape; while Ni@C exhibits many microporous structures similar to those found in Ni-MOF; and Ni / NiO is a needle-like sphere formed on the porous basis of Ni@C. From Figure 5 It can be seen that the morphologies of Ni / NiO-1h and Ni / NiO-3h obtained by different reduction times are different. The surface of Ni / NiO-1h is relatively smooth and still maintains the spherical shape of the precursor Ni-MOF, while the morphology of Ni / NiO-3h is also spherical, but the particle diameter is smaller and the calcination is more thorough.

[0062] Test Example 4 The material obtained in Example 1 was observed using transmission electron microscopy and high-resolution transmission electron microscopy, and analyzed using ImageJ software to obtain images as shown below. Figure 6 , Figure 7 As shown; Figure 6 In the image, (a) is a TEM image, (b) is an HRTEM image, (c) is a Fourier transform image, (d) is a HAADT-STEM image, and (e) is an element mapping image. Figure 7 This is an EDX graph.

[0063] from Figure 6 (a) It can be seen that Ni / NiO has a spherical structure and exhibits obvious light and dark phases; this contrast difference indicates that the material has porous properties, and these pores provide channels for the diffusion of gas molecules; the corresponding HRTEM image shows the lattice stripes of the catalyst, where the lattice spacing of 0.209 nm is the (200) crystal plane of NiO, and 0.203 nm and 0.176 nm correspond to the (111) and (200) crystal planes of Ni, respectively; Figure 6 (c) The corresponding Fast Fourier Transform (FFT) plots of the (200) crystal plane of Ni are given; in addition, SAED also confirmed the existence of three crystal phases, consistent with the previous XRD results; at the same time, O, Ni and C can be seen to be uniformly distributed on the spheres from HAADF-STEM and elemental diffraction; in addition, the relative contents of O, Ni and C on the spheres can be seen by EDX, with the C content being relatively high, due to the C framework obtained after calcination of organic ligands.

[0064] Test Example 5 Electrochemical tests were performed on the materials obtained in Examples 1-3 and Comparative Examples 1-3, as well as the nickel foam raw material, using an electrochemical workstation. A saturated calomel electrode was used as the reference electrode, a platinum rod as the counter electrode, and the materials provided in the examples and comparative examples as the working electrodes. The potential relative to the reversible hydrogen electrode (RHE) was: E vs. RHE (V) = E vs. Hg / HgO (V) + 0.059pH + 0.098V. The electrolyte solution used for linear sweep voltammetry (LSV) was a 1 mol / L PBS standard solution. The potential scan range was -0.8 to 0V, and the scan rate was 5 mV / s. The test results are as follows: Figure 8 , Figure 9 , Figure 10 As shown; Figure 8 (a) shows the LSV curves for NF, Ni-MOF, Ni@C, NiO, and Ni / NiO; (b) shows the corresponding Tafel slopes; (c) shows the Nyquist plot; and (d) shows the double-layer capacitance (C). dl Figure (e) shows the multi-step chronoamperometry curves, and (f) shows the radar plots of the electrochemical properties of different materials. Figure 9 In the figure, (a) shows the LSV curves of Ni / NiO, Ni / NiO-1h, and Ni / NiO-3h, (b) shows the corresponding Tafel slope, and (c) shows the Nyquist plot. Figure 10 In the middle, (a)~(g) are the CV plots of NF, Ni-MOF, NiO, Ni@C, Ni / NiO, Ni / NiO-1h and Ni / NiO-3h, respectively, and (h) is the C plot of Ni / NiO, Ni / NiO-1h and Ni / NiO-3h. dl value.

[0065] from Figure 8 (a) and Figure 9 (a) It can be seen that Ni / NiO at η 100 The overpotential at this point was 281 mV, significantly lower than that of Ni-MOF (715 mV), Ni@C (523 mV), NiO (594 mV), Ni / NiO-1h (358 mV), and Ni / NiO-3h (411 mV); Figure 8 (b) and Figure 9 (b) It can be seen that Ni / NiO has a low Tafel slope, indicating that the catalyst has fast catalytic kinetics, which is consistent with the LSV polarization curve; from Figure 8 (c) and Figure 9 (c) It can be seen that the Rct of Ni / NiO is 38Ω, exhibiting the smallest resistance; the double-layer capacitance was measured by CV. Figure 10 (a)~(g)) indicates that Ni / NiO has a large catalytic active area;Figure 8 (f) represents Ni / NiO at 100 mA / cm 2 and 10mA / cm 2 The pie charts of overpotential, Tafel, and Rct at current density indicate that Ni / NiO exhibits excellent catalytic performance, demonstrating its good reaction kinetics and electron transport capabilities. Multi-step chronopotential testing (…) Figure 8 In (e), the catalyst exhibits better stability and faster reaction capability at lower current densities, but its response capability is slightly worse at higher current densities.

[0066] The Ni / NiO electrode was subjected to a 100-hour continuous operation test. After 50 hours, the electrolyte was re-added, and the current density-time curve was obtained as shown in the figure. Figure 11 As shown. From Figure 11 It can be seen that the current density decreases after 50 hours, but after adding electrolyte again after 50 hours, it can maintain stability in a short time; the above results indicate that Ni / NiO has good stability.

[0067] Test Example 6 Electrochemical tests were performed on the materials obtained in Examples 1-3 and Comparative Examples 1-3, as well as the nickel foam raw material, using an electrochemical workstation. The test method was the same as in Test Example 5, except that the electrolyte solution was a 0.5 mol / L H₂SO₄ solution. The test results are as follows: Figure 12 , Figure 13 As shown; Figure 12 (a) shows the LSV curves for NF, Ni-MOF, Ni@C, NiO, and Ni / NiO; (b) shows the corresponding Tafel slopes; (c) shows the Nyquist plot; and (d) shows the double-layer capacitance (C). dl Figure (e) shows the multi-step chronoamperometry curves, and (f) shows the radar plots of the electrochemical properties of different materials. Figure 13 In the figure, (a) shows the LSV curves for Ni / NiO, Ni / NiO-1h, and Ni / NiO-3h, (b) shows the corresponding Tafel slope, and (c) shows the Nyquist plot.

[0068] from Figure 12 (a) and Figure 13 (a) It can be seen that Ni / NiO at η 100 The overpotential at this point is 302mV, significantly lower than that of other materials; from Figure 12 (b) and Figure 13 (b) It can be seen that Ni / NiO has a low Tafel slope (41 mV / dec), indicating that the catalyst has fast catalytic kinetics; from Figure 12 (c) and Figure 13 (c) It can be seen that the Rct of Ni / NiO is 19Ω, exhibiting the lowest resistance; fromFigure 12 (d) It can be seen that the C of Ni / NiO dl The value is 10.2 mF / cm 2 This indicates that the catalyst has a large active surface area in a 0.5 mol / L H2SO4 solution; Figure 12 (e) shows the multi-step chronoampere curve of the material, which shows that the material has a good current response. Figure 12 (f) represents Ni / NiO at 100 mA / cm 2 and 10mA / cm 2 The pie charts of overpotential, Tafel, and Rct at current density show that Ni / NiO exhibits excellent catalytic performance, demonstrating its good reaction kinetics and electron transport capabilities.

[0069] The Ni / NiO electrode was subjected to a 100-hour continuous operation test. After 50 hours, the electrolyte was re-added, and the current density-time curve was obtained as shown in the figure. Figure 14 As shown. From Figure 14 It can be seen that the current density decreases slightly with the extension of the running time, indicating that its stability under acidic conditions is poor, which may be related to the presence of Ni in the material.

[0070] Test Example 7 The material obtained in Example 1 was subjected to electrochemical activity treatment using an electrochemical workstation (CP test, electrolyte was 1 mol / L KOH aqueous solution, current density 100 mA / cm²). 2 ), the result is as follows Figure 15 As shown. From Figure 15 It can be seen that the potential increases steadily with the increase of operation time, and gradually rises to the highest peak within 0-3 hours. It is worth noting that the potential decreases after 3 hours, but the potential is still about 34.43mV higher than the original value, and then gradually stabilizes after a period of time.

[0071] Test Example 8 Electrochemical tests were performed on the materials obtained in Examples 1-4 and Comparative Examples 1-3, as well as the nickel foam raw material, using an electrochemical workstation. The test conditions were the same as in Test Example 5, except that the electrolyte solution was a 1 mol / L KOH aqueous solution. The test results are as follows: Figure 16 , Figure 17 , Figure 18 , Figure 19 As shown; Figure 16 (a) shows the LSV curves for NF, Ni-MOF, Ni@C, NiO, Ni / NiO, and r-Ni / NiO; (b) shows the corresponding Tafel slopes; (c) shows the Nyquist plot; and (d) shows the double-layer capacitance (C). dlFigure 1 shows the normalized curve of ECSA, and Figure 2 shows the radar plot of the electrochemical properties of NF, Ni-MOF, Ni@C, NiO, Ni / NiO and r-Ni / NiO. Figure 17 In the figure, (a) shows the LSV curves of Ni / NiO, Ni / NiO-1h, and Ni / NiO-3h, (b) shows the corresponding Tafel slope, and (c) shows the Nyquist plot. Figure 18 (a) shows the multi-step chronoamperometric curves of Ni / NiO and r-Ni / NiO, and (b) shows the stability test results of Ni / NiO and r-Ni / NiO. Figure 19 In the middle, (a)~(h) are the CV diagrams of NF, Ni-MOF, NiO, Ni@C, Ni / NiO, r-Ni / NiO, Ni / NiO-1h and Ni / NiO-3h, respectively, and (i) is the C of Ni / NiO, Ni / NiO-1h and Ni / NiO-3h. dl value.

[0072] Figure 16 As can be seen from (a) and 17(a), r-Ni / NiO exhibits superior catalytic activity compared to Ni / NiO. r-Ni / NiO only requires 126mV to reach 100mA / cm 2 The values ​​were significantly lower than those for Ni / NiO (157 mV), Ni@C (282 mV), NiO (364 mV), Ni-MOF (365 mV), NF (415 mV), Ni / NiO-1h (227 mV), and Ni / NiO-3h (263 mV); the results indicate that the material after CP testing can further improve the catalytic activity of HER.

[0073] from Figure 16 (b) Figure 17 (b) It can be seen that r-Ni / NiO exhibits the lowest Tafel slope, with a value of 27 mV / dec; Figure 16 (c) and Figure 17 (c) It can be seen that r-Ni / NiO exhibits the smallest charge transfer resistance (34Ω); from Figure 16 (d) and Figure 19 As can be seen from (i), r-Ni / NiO has the largest C. dl Value (53.7 mF / cm) 2 The electrochemically active area of ​​these materials is much larger than that of other comparative samples; in order to elucidate the inherent activity of these materials, the ECSA of the corresponding materials was normalized (j ECSA ), and the corresponding curves are as follows Figure 16 As shown in (e), the results indicate that r-Ni / NiO exhibits higher intrinsic catalytic activity in the HER reaction; Figure 16(f) indicates that the catalyst has significant electrocatalytic activity.

[0074] like Figure 18 As shown in (a), multi-step chronoamperometry (ChOC) curves were performed on the catalysts r-Ni / NiO and Ni / NiO. r-Ni / NiO exhibited a faster current response and the lowest current density at the same voltage. I-t tests were also performed on the catalysts. Figure 18 (b) shows that r-Ni / NiO has long-term stability within 100h.

[0075] Test Example 9 The contact angles between the materials prepared in Examples 1 and 4 and the raw material nickel foam in a 1 mol / L KOH aqueous solution were tested, and the results are as follows: Figure 20 As shown. Rapid mass transfer of the catalyst is crucial for the stability of the electrolysis process and the rapid replenishment of the solute; from Figure 20 It can be seen that r-Ni / NiO can reach 6° in only about 2.3 seconds, which is more hydrophilic than Ni / NiO. It can quickly replenish electrolytes and ensure stable electrolysis in the water decomposition process.

[0076] Test Case 10 The material prepared in Example 4 was tested using an X-ray diffractometer, and the XRD pattern is shown below. Figure 21 As shown. From Figure 21 It can be seen that three new diffraction peaks appeared at around 33°, 38.5° and 70° in r-Ni / NiO. These peaks correspond to the characteristic peaks of Ni(OH)2 (JCPDS.14-0117), which preliminarily proves that a new phase Ni(OH)2 is generated on the tested r-Ni / NiO.

[0077] Test Example 11 The materials prepared in Examples 1 and 4 were tested using Raman spectroscopy, infrared spectroscopy, and electron paramagnetic resonance spectroscopy, respectively, and the images obtained are shown below. Figure 22 As shown; Figure 22 In the image, (a) is the Raman spectrum, (b) is the infrared spectrum, and (c) is the EPR spectrum.

[0078] from Figure 22 (a) It can be seen that the two materials at 260cm -1 and 490cm -1 The Raman peak vibrations in the vicinity are basically consistent, indicating that Ni-O is present in both the catalyst before and after the test; in the 1000~1200cm range... -1 The peak appearing in the image is related to the Ni-O bond vibration of Ni(OH)2, indicating that the material after CP contains Ni(OH)2, and the peak at 1630 cm⁻¹ is related to the Ni-O bond vibration of Ni(OH)2. -1 And 3200cm -1The peaks appearing on the left and right can be attributed to the bending vibration of HOH and the adsorption of H2O, respectively. The appearance of this peak with the occurrence of the CP process indicates that the catalyst promotes the adsorption of H2O during the HER process; while the 1330 cm⁻¹ peak... -1 1581cm -1 And 2655cm -1 The peaks at 2655 cm⁻¹ correspond to the D, G, and 2D bands of the carbon substrate, respectively. -1 The relatively large peak at this point may be due to the exposure of the carbon skeleton during the reconstruction process.

[0079] from Figure 22 (b) It can be seen that the infrared spectra of Ni / NiO and r-Ni / NiO are at 1630 cm⁻¹. -1 A large peak appeared at the location, which is due to the adsorption of H2O, corresponding to the Raman results.

[0080] from Figure 22 (c) It can be seen that NiO does not show a characteristic peak at g=2.003, indicating that it does not contain oxygen vacancies (as recorded in the prior art), while Ni / NiO and r-Ni / NiO both show obvious signal peaks at g=2.003, indicating the presence of oxygen vacancies. This result further demonstrates the successful introduction of oxygen vacancies into Ni / NiO and r-Ni / NiO catalysts, which can enhance catalytic activity by regulating the electronic structure during catalysis. However, compared to Ni / NiO, the concentration of oxygen vacancies in r-Ni / NiO is lower. This change may originate from OH - The continuous filling and consumption of oxygen vacancies reduces oxygen vacancies, thereby forming Ni(OH)2 and further promoting the formation of new phases.

[0081] Test Example 12 The materials prepared in Example 1 and Example 4 were tested using X-ray photoelectron spectroscopy, and the XPS images are shown below. Figure 23 As shown; Figure 23 (a) is the XPS total spectrum, (b) is the Ni 2p spectrum, and (c) is the O 1s spectrum.

[0082] from Figure 23 (b) It can be seen that the number of Ni-O bonds increased after CP, Ni 0 The peak area is relatively decreasing, which is related to the Ni(OH)2 generated during reconstruction; more importantly, Figure 23 (c) The change in the peak intensity of O 1s during the reconstruction process shows that oxygen vacancies are gradually decreasing while lattice oxygen is gradually increasing, which is consistent with the above characterization results.

[0083] Test Example 13 The material prepared in Example 4 was observed using a scanning electron microscope, and the SEM image is shown below.Figure 24 As shown. With Figure 4 Comparing (d) and (d1), it can be seen that the morphology of r-Ni / NiO and Ni / NiO remains basically unchanged, but the surface of the material has a wrinkle-like morphology. Based on the above characterization results, the wrinkle should be Ni(OH)2.

[0084] Test Example 14 The material obtained in Example 4 was observed using transmission electron microscopy and high-resolution transmission electron microscopy, and analyzed using ImageJ software to obtain images as shown below. Figure 25 , Figure 26 As shown; Figure 25 (a) is the TEM image, (b) is the HRTEM image, (c) is the Fourier transform image, and (d) is the HAADT-STEM image. Figure 26 In the diagram, (a) is the EDX graph and (b) is the element mapping graph.

[0085] from Figure 25 (a) It can be seen that r-Ni / NiO exhibits an interlaced lamellar morphology in TEM; the 0.184 nm lattice stripe in the HRTEM image is the middle (102) crystal plane of Ni(OH)2; the middle (102) lattice diffraction ring of Ni(OH)2 is present in the HAADF-STEM image; in addition, the proportion of O in the EDX image is also increased compared to Ni / NiO; all results indicate that the material after CP testing underwent reconstruction and Ni(OH)2 was generated.

[0086] Test Example 15 To elucidate the mechanism of enhanced catalytic activity, a Ni / NiO model and a reconstructed Ni / NiO / Ni(OH)2 model were constructed, as follows: Figure 27 As shown. Using density functional theory, the adsorption energy, activation energy, and reaction energy of water molecules on the material's surface were calculated, as follows: Figure 28 As shown; the adsorption energy of the hydroxyl group and the Gibbs free energy of hydrogen were also calculated, such as Figure 29 As shown.

[0087] Water molecule adsorption energy (ΔG) H2O ΔG is typically used to assess the initial rate in alkaline solutions. H2O The more negative the value, the stronger the bond between the material and the adsorbed water under alkaline conditions; Figure 28 In (a), the ΔG of Ni / NiO was observed. H2O The value is -0.30 eV, while that of Ni / NiO / Ni(OH)2 is -0.60 eV; obviously, water molecules are more strongly adsorbed on Ni / NiO / Ni(OH)2, which is beneficial to the subsequent water dissociation reaction. Figure 28(b) is the Gibbs free energy (ΔG) of hydrogen adsorption in the Ni / NiO and Ni / NiO / Ni(OH)2 models. H* The value of ΔG can be seen from the figure; as can be seen from the figure, the ΔG values ​​for the Ni / NiO and Ni / NiO / Ni(OH)2 catalyst models are... H* The values ​​are -0.60 eV and -0.72 eV, respectively. This result indicates that Ni / NiO / Ni(OH)2 has significant catalytic activity for hydrogen evolution under alkaline conditions, and also shows that there is potential for catalyst structure optimization.

[0088] like Figure 29 As shown, the blue curve corresponds to Ni / NiO, and the orange curve corresponds to Ni / NiO / Ni(OH)2. This is based on the adsorption of water molecules (H2O→H2O). * ); water dissociation (H) * +OH * ); OH * Desorption (H) * +OH); formation of H2. The free energy of the Ni / NiO / Ni(OH)2 system decreases more significantly, indicating that it is more favorable for water molecule activation and hydrogen adsorption processes; especially in the water dissociation stage (H2O→H2O). * ) and proton-electron transfer (H2O) * →OH * +H * In the reaction, the introduction of Ni(OH)₂ significantly lowered the reaction energy barrier and promoted the reaction. This may be attributed to the fact that Ni(OH)₂ provides additional active sites, enhances electron transfer capabilities, and optimizes adsorption energy, thereby accelerating hydrogen generation and improving HER catalytic efficiency. Overall, the reconstructed Ni(OH)₂ not only alters the surface electronic structure of the Ni / NiO system but also effectively modulates the reaction free energy, resulting in superior catalytic performance in the alkaline hydrogen evolution reaction.

[0089] Test Example 16 Electrochemical tests were performed on the materials obtained in Examples 1-3 and Comparative Examples 1-3, as well as the nickel foam raw material, using an electrochemical workstation. The test conditions were the same as in Test Example 5, except that the electrolyte solution was alkaline seawater (1 mol / L KOH + seawater solution). The test results are as follows: Figure 30 , Figure 31 , Figure 32 As shown; Figure 30 (a) shows the LSV curves for NF, Ni-MOF, Ni@C, NiO, and Ni / NiO; (b) shows the corresponding Tafel slopes; (c) shows the Nyquist plot; and (d) shows the double-layer capacitance (C). dl(e) is a multi-step chronoamperometry curve, (f) is a radar chart of the electrochemical properties of different materials, and (g) is a stability test of Ni / NiO. Figure 31 In the figure, (a) shows the LSV curves of Ni / NiO, Ni / NiO-1h, and Ni / NiO-3h, (b) shows the corresponding Tafel slope, and (c) shows the Nyquist plot. Figure 32 In the middle, (a)~(g) are the CV plots of NF, Ni-MOF, NiO, Ni@C, Ni / NiO, r-Ni / NiO, Ni / NiO-1h and Ni / NiO-3h, respectively, and (h) is the C of Ni / NiO, Ni / NiO-1h and Ni / NiO-3h. dl value.

[0090] from Figure 30 (a) and Figure 31 (a) It can be seen that Ni / NiO only requires an overpotential of 186 mV to reach 100 mA / cm in alkaline seawater. 2 It has the lowest overpotential; such as Figure 30 As shown in (b) and 31(b), Ni / NiO has the lowest Tafel slope in alkaline seawater, with a value of 63 mV / dec; Figure 30 (c) and Figure 31 (c) This indicates that Ni / NiO has low charge transfer resistance and fast electron transport capability. Figure 30 (d) and Figure 32 (h) indicates that Ni / NiO also has a large reactive surface area in alkaline seawater, approximately 29.9 mF / cm². 2 It is far superior to other materials; Figure 30 (f) is the material at 100 mA / cm 2 10mA / cm 2 The pie charts of overpotential, Tafel, and Rct at current density were presented. Furthermore, the durability and stability of Ni / NiO in seawater electrolytes were investigated using the same testing methods as for alkaline water. Figure 30 As shown in (e), a multi-step chronopotential method was used at 10 different potentials. The instability of the curves caused by slow stirring during the test indicates that its long-term stability in alkaline seawater environments still has certain limitations. For Ni / NiO at 100 mA / cm²... 2 An it test was conducted for 100 hours at a constant current density. Figure 30 (g)), the results show that the catalyst has good stability and corrosion resistance.

[0091] Test Example 17 Electrolysis tests were conducted using the materials obtained in Examples 1-3 and Comparative Examples 1-3, as well as the nickel foam raw material, as electrodes with different electrolytes. The electrolyte solutions were alkaline electrolyte (1 mol / L KOH aqueous solution), urea electrolyte (1 mol / L KOH + 0.33 mol / L urea), and human urine (1 mol / L KOH + human urine), respectively. The test results are as follows: Figure 33 , Figure 34 , Figure 35 As shown; Figure 33 (a) shows the LSV curves of UOR for NF, Ni-MOF, Ni@C, NiO, and Ni / NiO in urea electrolyte; (b) shows the LSV curves of Ni / NiO in different electrolytes; (c) shows the corresponding Tafel slope; (d) shows the Nyquist plot; and (e) shows the double-layer capacitance (C0). dl Figure (f) shows the normalized curve of ECSA; Figure 34 In the middle, (a), (b), and (c) are the CV diagrams for Ni / NiO, Ni / NiO-1h, and Ni / NiO-3h, respectively.

[0092] from Figure 33 It can be seen that Ni / NiO exhibits good electrocatalytic activity at 100 mA / cm². 2 The voltage was 1.40V. Next, the OER of the catalyst and the corresponding anodic tests were performed in actual human urine. Figure 33 (b) The voltage difference between UOR and OER is 290mV, indicating that Ni / NiO has excellent UOR selectivity. However, the catalyst showed reduced catalytic activity in human urine oxidation compared to UOR. The performance reduction may be due to the presence of uric acid and a large number of inorganic ions in human urine, indicating that pollutants may hinder the catalytic efficiency of UOR, but it is still better than the oxidation of pure water.

[0093] Figure 33 (c) represents the Tafel slope of the catalyst. The Tafel value of UOR is 28 mV / dec, which has the lowest Tafel slope, indicating that the reaction kinetics of UOR are relatively fast. Figure 33 (d) shows that Ni / NiO exhibits the smallest charge transfer resistance in 0.33 mol / L urea water; Figure 33 (e) and Figure 33 (f) indicates that the catalyst has a large active surface area and good intrinsic activity, as shown in the corresponding CV plot. Figure 34 As shown.

[0094] To better reflect the efficiency of Ni / NiO, other small molecules (methanol oxidation reaction (MOR) and ammonia oxidation reaction (AOR)) were added for oxidation testing, and the results are as follows. Figure 35 As shown. Figure 35(a) shows the oxidation of Ni / NiO in methanol and ammonia compared with UOR and OER, and (b) shows the stability test of Ni / NiO.

[0095] from Figure 35 (a) It can be seen that adding small molecules to water can reduce the anodic oxidation potential, among which UOR has the lowest potential; Figure 35 (b) describes the long-term electrolysis of the Ni / NiO catalyst in urea electrolyte (1 mol / L KOH + 0.33 mol / L urea). The electrolysis curve did not decrease significantly, indicating that the catalyst has good stability.

[0096] Test Example 18 The Ni / NiO composite material prepared in Example 1 was used as the electrode, serving as the anode and cathode of the membrane-free electrolyzer. Electrolysis tests were conducted using different electrolytes: alkaline electrolyte (1 mol / L KOH aqueous solution), urea electrolyte (1 mol / L KOH + 0.33 mol / L urea), and human urine electrolyte (1 mol / L KOH + human urine). The test results are as follows: Figure 36 As shown; Figure 36 (a) is a schematic diagram of the water decomposition process in an alkaline environment, (b) is the polarization curve of Ni / NiO in different electrolytes, (c) is the LSV curve of Ni / NiO in different electrolytes, (d) is the step of Ni / NiO in human urine electrolytes, and (e) is the stability test of Ni / NiO.

[0097] like Figure 36 As shown in (b), in order to achieve 100 mA / cm 2 The current density required for urea electrolysis is 1.62V, for human urine it is 1.70V, and for alkaline water it is 1.90V. Urea / human urine electrolysis requires 280 / 200mV less current than alkaline water electrolysis, indicating that urea / human urine electrolysis can more effectively and easily replace OER performance. Figure 36 (d) To evaluate the stability of the dual-electrode electrolyzer, a step test was conducted on the Ni / NiO‖Ni / NiO electrode in human urine for 10 hours at different current densities. The results showed that the material possesses certain stability and rapid response capability. Figure 36 (e) Ni / NiO in human urine electrolytes 100 mA / cm 2 Electrolysis was carried out for 50 hours. As can be seen from the figure, there is a very small potential deviation, which may be due to the influence of inorganic small molecules in urine. The results show that the catalyst can also be used in practical applications, which can improve the efficiency of hydrogen production and solve the problem of urine pollution to a certain extent.

[0098] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a Ni / NiO composite material, comprising the following steps: Nickel source, organic ligand, solvent and nickel foam were mixed and subjected to hydrothermal reaction to obtain nickel foam-supported Ni-MOF; The nickel-supported Ni-MOF foam was subjected to three-stage calcination to obtain a Ni / NiO composite material; The three-stage calcination includes: the first stage of calcination in an air atmosphere, followed by the second and third stages of calcination in a reducing atmosphere. The first stage of calcination is carried out at a temperature of 250~350℃ for 2~4 hours; the second stage of calcination is carried out at a temperature of 330~380℃ for 0.5~1.5 hours; and the third stage of calcination is carried out at a temperature of 400~500℃ for 1~3 hours.

2. The preparation method according to claim 1, characterized in that, The nickel source includes organic nickel salts or inorganic nickel salts; the organic ligand is an aromatic polycarboxylic acid ligand.

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the nickel source, organic ligand, and nickel foam is (1~3):(1~2):(1~3).

4. The preparation method according to claim 1, characterized in that, The solvent is a mixture of water, ethanol and DMF.

5. The preparation method according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 140~160℃ for a time of 10~20h.

6. The preparation method according to claim 1, characterized in that, The reducing atmosphere is a mixture of hydrogen and an inert gas, wherein the volume fraction of hydrogen in the mixture is 5-10%.

7. The Ni / NiO composite material prepared by the preparation method according to any one of claims 1 to 6.

8. A Ni / NiO / Ni(OH)2 composite material, characterized in that, The Ni / NiO / Ni(OH)2 composite material is obtained by activating the Ni / NiO composite material of claim 7; the activation is carried out by electrochemical activation in an alkaline electrolyte.

9. A method for producing hydrogen by electrolysis of water, characterized in that, The Ni / NiO composite material of claim 7 or the Ni / NiO / Ni(OH)2 composite material of claim 8 is used as a catalyst.

10. The method according to claim 9, characterized in that, The water includes water, seawater, urea-containing water, and / or human urine.

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