An iron-cobalt-nickel nanomaterial, an electrolytic water hydrogen production device, and a preparation method and application thereof

Abstract

The present invention relates to an iron-cobalt-nickel nanomaterial, an electrolytic water hydrogen production device, and a preparation method and application thereof. The preparation method of the iron-cobalt-nickel nanomaterial comprises the following steps: S1. Dissolving an iron source, a cobalt source, and a nickel source in a solvent to obtain a precursor solution; S2. Immersing nickel foam in the precursor solution and performing electrochemical deposition on the nickel foam to obtain the iron-cobalt-nickel nanomaterial. The iron-cobalt-nickel nanomaterial can be used as an electrode material to carry out hydrogen evolution, oxygen evolution, and overall water splitting reactions in an alkaline environment. At the same time, it also has good hydrogen evolution performance in a neutral solution. The iron-cobalt-nickel nanomaterial can be applied to a bipolar membrane-based electrolytic water device with large changes in the pH value and conductivity of the electrolyte, which is beneficial to long-term stable operation. In addition, since this method does not use precious metals such as platinum and ruthenium, and does not require long-term hydrothermal treatment or high-temperature calcination, the preparation process is simple and rapid, and the cost is low.

Description

Technical Field

[0001] The present invention relates to the field of new energy, and more specifically, to an iron-cobalt-nickel nanomaterial, an electrolytic water hydrogen production device, a preparation method thereof, and an application thereof. Background Art

[0002] Hydrogen is an economical, non-toxic, and easily available carbon-neutral energy carrier, with a calorific value of 122 MJ·kg -1 , which is nearly 2.75 times that of hydrocarbon fuels and more than twice that of typical solid fuels (50 MJ·kg -1 ). At the same time, due to the multiple production routes of hydrogen and relatively easy storage and transportation, using hydrogen instead of carbon as an energy carrier is an inevitable trend to achieve the country's "dual carbon" goal and an inevitable choice for social sustainable development. Currently, common hydrogen production methods include chemical methods, water electrolysis methods, biological methods, etc. Most commercial hydrogen is mainly extracted from fossil fuels through steam reforming, which basically does not reduce the consumption of fossil energy. At the same time, this process emits carbon dioxide, has relatively low efficiency, high energy consumption, and low hydrogen production purity. Currently, the most ideal way to produce pure hydrogen is electrolytic water. Electrolytic water hydrogen production uses water resources to produce hydrogen, mainly including alkaline water electrolysis (alkaline electrolytic cell), proton exchange membrane water electrolysis (proton exchange membrane electrolyzer), anion exchange membrane water electrolysis (anion exchange membrane electrolytic cell), solid oxide water electrolysis (solid oxide electrolytic cell), and bipolar membrane water electrolysis (bipolar membrane electrolytic cell) and other technologies.

[0003] The bipolar membrane consists of an interfacial layer, a cation exchange layer, and an anion exchange layer, and can separately optimize the catalysts or electrolytes for the two water decomposition half-reactions, thus opening a new door for the design of electrolytic water devices. Research shows that the use of bipolar membranes may change the properties of electrolytes, that is, due to the imbalance in the rates of water dissociation and water electrolysis and the possible ion crossover, it is difficult to maintain the pH value on both sides of the membrane stable for a long time, thereby affecting the reactions occurring on the electrodes. In addition, different configuration directions of the bipolar membrane in the electrolytic water device have different effects on the electrolytic water performance of the device. In short, many electrolytic water devices based on bipolar membranes can only maintain a short operation time or continuously update the electrolyte during long-term operation. For example, in a Chinese patent named Application of a Powdered Photocatalyst on the Surface of a Bipolar Membrane in Water Decomposition, the powdered catalyst is attached to both sides of the bipolar membrane for photocatalytic water decomposition to produce hydrogen, and the reaction device operated continuously for 10 to 48 hours.

[0004] In addition, the catalysts used in many electrolyzed water devices are noble metal-based catalysts. Noble metal-based catalysts have problems such as high cost, low natural abundance, and poor stability. On the other hand, in electrolyzed water devices based on bipolar membranes, the pH values in the anode and cathode chambers fluctuate as the reaction progresses. Therefore, it is particularly important to develop bifunctional electrolyzed water catalysts that are cheaper, more stable, and can be applied to a wider pH range.

[0005] Therefore, it is necessary to solve the problems of the current expensive catalysts for electrolyzed water, narrow pH application range, and poor operation effect based on bipolar membrane technology. Summary of the Invention

[0006] The primary object of the present invention is to overcome the above problems of the current expensive catalysts for electrolyzed water, narrow pH application range, and poor operation effect based on bipolar membrane technology, and to provide a preparation method of iron-cobalt-nickel nanomaterials. The iron-cobalt-nickel nanomaterials obtained by this preparation method can be used as electrode materials for hydrogen evolution, oxygen evolution, and overall water splitting reactions in an alkaline environment. At the same time, they also have good hydrogen evolution performance in neutral solutions. Therefore, the iron-cobalt-nickel layered hydroxide nanomaterials can be applied to electrolyzed water devices based on bipolar membranes with large changes in electrolyte pH value and conductivity, which is conducive to long-term stable operation. In addition, since this method does not use noble metals such as platinum and ruthenium, and does not require long-term hydrothermal treatment or high-temperature calcination, the preparation process is simple, fast, and has low cost.

[0007] A further object of the present invention is to provide an iron-cobalt-nickel nanomaterial.

[0008] A further object of the present invention is to provide the application of the above iron-cobalt-nickel nanomaterial as a cathode and / or anode in the preparation of an electrolyzed water hydrogen production device.

[0009] A further object of the present invention is to provide an electrolyzed water hydrogen production device.

[0010] A further object of the present invention is to provide a method for producing hydrogen by electrolyzing water.

[0011] The above objects of the present invention are achieved by the following technical solutions:

[0012] A preparation method of iron-cobalt-nickel nanomaterials includes the following steps:

[0013] S1. Dissolve an iron source, a cobalt source, and a nickel source in a solvent to obtain a precursor solution;

[0014] S2. Immerse nickel foam in the precursor solution and perform electrochemical deposition on the nickel foam to obtain the iron-cobalt-nickel nanomaterials;

[0015] In the precursor solution described in step S1, the mass ratio of the sum of the iron source, cobalt source, and nickel source to the volume of the solvent is (4 - 5) g / 50 mL; in step S2, the voltage of the electrochemical deposition is -1.0 to -5.0 V, and the deposition time is 10 to 30 min.

[0016] In the present invention, nickel foam is placed in a precursor solution containing an iron source, a cobalt source, and a nickel source and subjected to electrochemical deposition. By controlling the mass ratio of the sum of the iron source, cobalt source, and nickel source to the volume of the solvent in the precursor solution, as well as controlling the voltage and deposition time of the electrochemical deposition, an iron-cobalt-nickel nanomaterial is prepared. In the iron-cobalt-nickel nanomaterial prepared by this preparation method, iron, cobalt, and nickel are loaded on the nickel foam in the form of hydroxides, and these hydroxides have a nanosheet structure. This enables the iron-cobalt-nickel nanomaterial to have excellent hydrogen evolution, oxygen evolution, and overall water splitting performance as an electrode material. Specifically, the iron-cobalt-nickel nanomaterial can perform hydrogen evolution, oxygen evolution, and overall water splitting reactions in an alkaline environment as an electrode material. At the same time, it also has good hydrogen evolution performance in a neutral solution. Therefore, the iron-cobalt-nickel nanomaterial can be applied to an electrolytic water device based on a bipolar membrane with a large change in the pH value and conductivity of the electrolyte solution, which is beneficial for long-term stable operation. In addition, since this method does not use precious metals such as platinum and ruthenium, and does not require long-term hydrothermal or high-temperature calcination, the preparation process is simple and fast, and the cost is low.

[0017] If the mass ratio of the sum of the iron source, cobalt source, and nickel source to the volume of the solvent is too large, or the voltage of the electrochemical deposition is too large, or the electrodeposition time is too long, the iron-cobalt-nickel layered hydroxide will grow excessively on the surface of the nickel foam, which is not conducive to the transfer of electrons between the iron-cobalt-nickel layered hydroxide and the nickel foam, thereby limiting the hydrogen evolution and oxygen evolution rates; if the mass ratio of the sum of the iron source, cobalt source, and nickel source to the volume of the solvent is too small, or the voltage of the electrochemical deposition is too small, or the electrodeposition time is too short, the amount of iron-cobalt-nickel layered hydroxide loaded on the surface of the nickel foam by the catalyst will decrease, and the number of reaction active sites will decrease, thereby reducing the efficiency of catalyzing hydrogen evolution and oxygen evolution.

[0018] Preferably, the solvent in step S1 is water.

[0019] Preferably, in the precursor solution described in step S1, the molar ratio of iron, cobalt, and nickel elements is 1:(1 - 5):(1 - 10).

[0020] Controlling the molar ratio of the three elements of iron, cobalt, and nickel within this range results in better catalytic performance of the obtained iron-cobalt-nickel nanomaterial.

[0021] Preferably, the iron source in step S1 is ferrous sulfate, the cobalt source is cobalt nitrate, and the nickel source is nickel nitrate.

[0022] Preferably, before immersing the nickel foam in the precursor solution in step S2, it further includes a step of cleaning the nickel foam.

[0023] More preferably, the specific process of the cleaning is as follows: first, ultrasonically clean the nickel foam with hydrochloric acid for 10 - 25 min, then ultrasonically clean the nickel foam with an organic solvent for 10 - 25 min, then ultrasonically clean the nickel foam with deionized water for 10 - 25 min, and finally dry it.

[0024] Further preferably, the concentration of the hydrochloric acid is 1 - 3 mol / L.

[0025] Further preferably, the inorganic solvent is acetone or ethanol.

[0026] Further preferably, the drying temperature is 60 - 80 °C.

[0027] Preferably, the size of the nickel foam in step S2 is 2 × 2 cm.

[0028] Preferably, the average pore diameter of the nickel foam in step S2 is 0.1 - 0.15 mm, and the porosity is 96% - 97%.

[0029] Preferably, the electrochemical deposition in step S2 is carried out in a three - electrode system. In the three - electrode system, the nickel foam is the working electrode, the platinum wire electrode is the counter electrode, and the saturated calomel electrode is the reference electrode.

[0030] Preferably, after the electrochemical deposition in step S2, there are also steps of cleaning and drying.

[0031] More preferably, the drying temperature is 60 - 80 °C.

[0032] A kind of iron - cobalt - nickel nanomaterial is prepared by the above - mentioned preparation method.

[0033] The application of the above - mentioned iron - cobalt - nickel nanomaterial as a cathode and / or an anode in the preparation of an electrolytic water hydrogen - production device is also within the protection scope of the present invention.

[0034] An electrolytic water hydrogen - production device includes an anode chamber, a cathode chamber, an anode, a cathode, anolyte, catholyte and a bipolar membrane; the bipolar membrane separates the anode chamber and the cathode chamber; the materials of the anode and the cathode are both the above - mentioned iron - cobalt - nickel nanomaterial; the anolyte is a potassium hydroxide solution, and the catholyte is a phosphate buffer solution.

[0035] The present invention constructs an electrolytic water hydrogen - production device based on a bipolar membrane with the iron - cobalt - nickel nanomaterial as the anode and the cathode and the bipolar membrane as the diaphragm. The Faraday efficiency of hydrogen evolution and oxygen evolution of this electrolytic water device can be close to 100%. In addition, this electrolytic water device can operate stably for 192 h without replacing the electrolyte.

[0036] Preferably, the concentration of the potassium hydroxide solution is 0.5 - 2 mol / L.

[0037] More preferably, the concentration of the potassium hydroxide solution is 0.5 to 1 mol / L.

[0038] Preferably, the concentrations of the solutes in the phosphate buffer solution are as follows: potassium chloride 0.26 to 0.78 g / L; ammonium chloride 0.62 to 1.86 g / L; sodium dihydrogen phosphate dihydrate 6.7 to 20.1 g / L; disodium hydrogen phosphate dodecahydrate 20.7 to 62.1 g / L.

[0039] More preferably, the concentrations of the solutes in the phosphate buffer solution are: potassium chloride 0.26 g / L, ammonium chloride 0.62 g / L, sodium dihydrogen phosphate dihydrate 3.7 g / L, and disodium hydrogen phosphate dodecahydrate 20.7 g / L.

[0040] Preferably, the anion exchange layer of the bipolar membrane faces the cathode, and the cation exchange layer faces the anode.

[0041] The anion exchange layer of the bipolar membrane facing the cathode and the cation exchange layer facing the anode belong to the forward configuration, while the cation exchange layer of the bipolar membrane facing the cathode and the anion exchange layer facing the anode belong to the reverse configuration. Compared with the reverse configuration, the electrolytic water hydrogen production device of the present invention requires a lower applied voltage under the forward configuration, thereby reducing energy consumption.

[0042] Preferably, the distance between the anode and the cathode is 0.5 to 1.0 cm.

[0043] Preferably, the cathode liquid and the anode liquid are circulated under the action of a peristaltic pump.

[0044] More preferably, the flow rate of the peristaltic pump is 20 to 60 mL / min.

[0045] Preferably, the applied voltage of the electrolytic water hydrogen production device is provided by a DC power supply.

[0046] More preferably, the current density provided by the DC power supply is 10 to 100 mA / cm 2 .

[0047] A method for producing hydrogen by electrolyzing water is carried out based on the above electrolytic water hydrogen production device, and when the electrolytic water hydrogen production device operates for 12 to 36 hours, the anode liquid and the cathode liquid are alternately exchanged 1 to 3 times.

[0048] It should be understood that the alternation of the anode liquid and the cathode liquid of the present invention means that: the initial anode liquid of the electrolytic water hydrogen production device is a potassium hydroxide solution, and the initial cathode liquid is a phosphate buffer solution. After operating for 12 to 36 hours, the potassium hydroxide solution is used as the cathode liquid and the phosphate buffer solution is used as the anode liquid, and then continue to operate.

[0049] The anolyte and catholyte can be alternated in the following manner: The catholyte in the cathode chamber is transferred to a reaction flask for storing the catholyte through a peristaltic pump, the anolyte in the anode chamber is transferred to a reaction flask for storing the anolyte, and then the reaction flasks connected to the cathode chamber and the anode chamber are exchanged.

[0050] This operation mode solves the problem that the electrolyte changes with the increase of reaction time, thereby corroding the electrode material and affecting the hydrogen evolution and oxygen evolution efficiency. Moreover, during long-term operation, there is no need to frequently replace the new electrolyte, which simplifies the operation process and reduces the cost.

[0051] Preferably, for every 24 hours of operation of the water electrolysis hydrogen production device, the anolyte and catholyte are exchanged once.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] (1) The iron-cobalt-nickel nanomaterial obtained by the preparation method of the present invention can be used as an electrode material for hydrogen evolution, oxygen evolution and overall water splitting reactions in an alkaline environment. At the same time, it also has good hydrogen evolution performance in a neutral solution. Therefore, the iron-cobalt-nickel layered hydroxide nanomaterial can be applied to a bipolar membrane-based water electrolysis device with large changes in the pH value and conductivity of the electrolyte, which is beneficial to long-term stable operation. In addition, since this method does not use precious metals such as platinum and ruthenium, and does not require long-term hydrothermal or high-temperature calcination, the preparation process is simple and rapid, and the cost is low.

[0054] (2) The present invention constructs a bipolar membrane-based water electrolysis hydrogen production device with the iron-cobalt-nickel nanomaterial as the anode and cathode and the bipolar membrane as the diaphragm. The Faraday efficiency of hydrogen evolution and oxygen evolution of this water electrolysis device can be close to 100%. In addition, this water electrolysis device can operate stably for 192 h without updating the electrolyte. Description of the Drawings

[0055] Figure 1 It is a schematic structural diagram of the water electrolysis hydrogen production device for Example 4. Among them, 1 is the anode chamber, 2 is the cathode chamber, 3 is the anode, 4 is the cathode, and 5 is the bipolar membrane.

[0056] Figure 2 It is a scanning electron microscope image of the iron-cobalt-nickel nanomaterial at different magnification for Example 1.

[0057] Figure 3 It is an XRD pattern of the iron-cobalt-nickel nanomaterial for Example 1.

[0058] Figure 4 It is an XPS pattern of the iron-cobalt-nickel nanomaterial for Example 1.

[0059] Figure 5 It is a transmission electron microscope image and a selected area electron diffraction pattern of the iron-cobalt-nickel nanomaterial for Example 1.

[0060] Figure 6 The test result diagrams of the iron-cobalt-nickel nanomaterial in Example 1 for hydrogen evolution in neutral electrolyte, hydrogen evolution and oxygen evolution in alkaline electrolyte, and overall water splitting performance.

[0061] Figure 7 The voltage-current density curve diagrams of the electrolytic water hydrogen production devices in Examples 4 to 8.

[0062] Figure 8 The hydrogen evolution rate result diagrams of the electrolytic water hydrogen production devices in Examples 4 to 8.

[0063] Figure 9 The oxygen evolution rate result diagrams of the electrolytic water hydrogen production devices in Examples 4 to 8.

[0064] Figure 10 The stability result diagrams of the electrolytic water hydrogen production devices in Examples 9 to 11 operating for 192 h in the operating mode of reversing the electrolyte.

[0065] Figure 11 The hydrogen evolution rate diagrams of the electrolytic water hydrogen production devices in Examples 9 to 11 operating for 192 h in the operating mode of reversing the electrolyte.

[0066] Figure 12 The oxygen evolution rate diagrams of the electrolytic water hydrogen production devices in Examples 9 to 11 operating for 192 h in the operating mode of reversing the electrolyte. Detailed implementation manners

[0067] In order to more clearly and completely describe the technical solutions of the present invention, the present invention will be further described in detail below through specific examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention, and various changes can be made within the scope defined by the rights of the present invention.

[0068] Example 1

[0069] This example provides a preparation method of an iron-cobalt-nickel nanomaterial, including the following steps:

[0070] 1. First, pretreat a 2×2 cm nickel foam to remove the grease and oxides on its surface: ultrasonically clean the nickel foam with an organic solvent, then ultrasonically clean it with hydrochloric acid, and finally ultrasonically clean it with deionized water and set it aside;

[0071] Among them, the organic solvent is ethanol, and the concentration of hydrochloric acid is 1 mol / L; the ultrasonic cleaning time is 20 min for all.

[0072] 2. Preparation of iron-cobalt-nickel nanomaterials by electrochemical deposition method: Dissolve ferrous sulfate, nickel nitrate hexahydrate, and cobalt nitrate hexahydrate in 50 mL of deionized water. After stirring for 10 min, an electrochemical deposition precursor solution is obtained. Place the pretreated nickel foam into the precursor solution. Using the pretreated nickel foam as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode as the reference electrode to construct a three-electrode system, and perform electrochemical deposition at a voltage of -1.0 V for 20 min. After the reaction is completed, rinse repeatedly with deionized water and dry to obtain iron-cobalt-nickel nanomaterials;

[0073] Among them, in the precursor solution, the molar concentration ratio of iron element, cobalt element, and nickel element is 1:1:2; the mass ratio of the sum of ferrous sulfate, cobalt nitrate hexahydrate, and nickel nitrate hexahydrate to the volume of deionized water is 4.74 g:50 mL; the drying temperature is 60 °C, and the drying time is 12 h.

[0074] Example 2

[0075] This example provides a preparation method of iron-cobalt-nickel nanomaterials, which is different from Example 1 in that:

[0076] 1) Perform electrochemical deposition at a voltage of -1.0 V for 30 min; 2) The mass ratio of the sum of ferrous sulfate, cobalt nitrate hexahydrate, and nickel nitrate hexahydrate to the volume of deionized water is 4 g:50 mL.

[0077] Example 3

[0078] This example provides a preparation method of iron-cobalt-nickel nanomaterials, which is different from Example 1 in that:

[0079] 1) Perform electrochemical deposition at a voltage of -5.0 V for 10 min; 2) The mass ratio of the sum of ferrous sulfate, cobalt nitrate hexahydrate, and nickel nitrate hexahydrate to the volume of deionized water is 5 g:50 mL.

[0080] Example 4

[0081] This example provides an electrolytic water hydrogen production device, which includes an anode chamber, a cathode chamber, an anode arranged in the anode chamber, a cathode arranged in the cathode chamber, anolyte contained in the anode chamber, catholyte contained in the cathode chamber, and a bipolar membrane separating the anode chamber and the cathode chamber; among them, the materials forming the main bodies of the anode chamber and the cathode chamber are silica gel gaskets and plexiglass, and the materials of the anode and the cathode are both iron-cobalt-nickel nanomaterials prepared in Example 1; the anolyte is 1 M potassium hydroxide solution, the catholyte is 0.1 M phosphate buffer solution, and the composition of the phosphate buffer solution is: potassium chloride 0.26 g / L, ammonium chloride 0.62 g / L, sodium dihydrogen phosphate dihydrate 3.7 g / L, disodium hydrogen phosphate dodecahydrate 20.7 g / L.

[0082] The structure of the electrolytic water hydrogen production device is as follows Figure 1 shown. The anode 3 is in direct contact with the anolyte, and the cathode 4 is in direct contact with the catholyte. The anode chamber 1 and the cathode chamber 2 are separated by a bipolar membrane 5. The anion exchange layer of the bipolar membrane 5 faces the anode 3, and the cation exchange layer faces the cathode 4. The anode 3 and the cathode 4 are connected to a DC power supply through titanium wires. The anode chamber 1 and the cathode chamber 2 are both cylinders with a diameter of 3 cm, and the volume is about 9.8 mL. The effective areas of the anode 3 and the cathode 4 are both 4 cm 2 , and the distance between them is 1 cm. The volumes of the catholyte and the anolyte are 100 mL respectively, and the circulation of the electrolyte is realized by a peristaltic pump during the whole operation process. The current of the DC power supply is set to 0.08 A, and the current density on the electrodes is 20 mA / cm 2 . The flow rate of the peristaltic pump is set to 40 mL / min.

[0083] Hydrogen is produced by electrolyzing water based on the electrolytic water hydrogen production device of this embodiment.

[0084] Example 5

[0085] This embodiment provides an electrolytic water hydrogen production device. This electrolytic water device is basically the same as the device in Example 4, except that the anion exchange layer of the bipolar membrane faces the cathode, and the cation exchange layer faces the anode.

[0086] Example 6

[0087] This embodiment provides an electrolytic water hydrogen production device. This device is basically the same as the electrolytic water device in Example 5, except that the current of the DC power supply is set to 40 mA / cm 2 .

[0088] Example 7

[0089] This embodiment provides an electrolytic water hydrogen production device. This device is basically the same as the electrolytic water device in Example 5, except that the current of the DC power supply is set to 60 mA / cm 2 .

[0090] Example 8

[0091] This embodiment provides an electrolytic water hydrogen production device. This device is basically the same as the electrolytic water device in Example 5, except that the current of the DC power supply is set to 80 mA / cm 2 .

[0092] Example 9

[0093] This embodiment provides a method for hydrogen production by electrolyzing water, specifically: based on the electrolytic water device of Embodiment 5, first operate for 24 hours, then alternate the anolyte and catholyte, operate for 24 hours, and then alternate the anolyte and catholyte again, that is, alternate the anolyte and catholyte every 24 hours, and operate like this for 192 hours. The alternation of the anolyte and catholyte is carried out as follows: transfer the catholyte in the cathode chamber to the reaction flask storing the catholyte through a peristaltic pump, transfer the anolyte in the anode chamber to the reaction flask storing the anolyte, and then exchange the reaction flasks connected to the cathode chamber and the anode chamber.

[0094] Embodiment 10

[0095] This embodiment provides an electrolytic water hydrogen production device. This device has basically the same configuration as the electrolytic water hydrogen production device of Embodiment 9, except that the anolyte is 1M potassium hydroxide and the catholyte is 1M potassium hydroxide.

[0096] Embodiment 11

[0097] This embodiment provides an electrolytic water hydrogen production device. This device has basically the same configuration as the electrolytic water hydrogen production device of Embodiment 9, except that the anolyte is 0.5M potassium hydroxide and the catholyte is 0.5M potassium hydroxide.

[0098] Performance Test

[0099] 1. Morphology and Substance Composition Characterization

[0100] Take the iron-cobalt-nickel nanomaterial obtained in Embodiment 1 for scanning electron microscopy. The results are as Figure 2 shown, Figure 2 (a), (b), and (c) are scanning electron microscope images of the iron-cobalt-nickel nanomaterial at different magnifications. From Figure 2 (a) and (b), it can be seen that the iron-cobalt-nickel layered hydroxide nanosheets are evenly distributed on the nickel foam substrate, forming a uniform nanoflower-like structure; from Figure 2 (c), it can be seen that the iron-cobalt-nickel nanomaterial presents a nanosheet structure. Take the iron-cobalt-nickel nanomaterial of Embodiment 1 for X-ray diffraction (XRD) analysis. The results are as Figure 3 shown. From Figure 3It can be seen that in the XRD pattern of the electrode, there are almost only the diffraction peaks of nickel foam (JCPDS No. 04-0850). This may be because the diffraction peaks of the hydroxides of iron, cobalt, and nickel in the iron-cobalt-nickel nanomaterial are too weak compared to those of nickel foam and thus not visible. Therefore, the catalyst powder attached to the nickel foam substrate was scraped off and collected for testing. The results show that the diffraction peaks at 10.6°, 22.4°, 34.1°, and 60.5° of the iron-cobalt-nickel nanomaterial correspond to its (003), (006), (012), and (0015) crystal planes (JCPDS No. 51-0463), indicating that the iron-cobalt-nickel nanomaterial is a nanoflower-like structure composed of layered nanosheets.

[0101] The iron-cobalt-nickel nanomaterial obtained in Example 1 was subjected to X-ray photoelectron spectroscopy (XPS, Figure 4 ), to characterize the elemental composition and chemical state of the material. The two fitting peaks at 710.06 eV and 725.07 eV in the XPS spectrum of Fe 2p ( Figure 4 (a)) correspond to Fe 2+ 2p 3 / 2 and Fe 2+ 2p 1 / 2 , and the other two fitting peaks at 713.4 eV and 721.52 eV correspond to Fe 3+ 2p 3 / 2 and Fe 3+ 2p 1 / 2 , respectively. In addition, 718.45 eV and 733.35 eV are satellite peaks. The above results show that there are two valence states of Fe element, Fe 2+ and Fe 3+ , in the material. From the XPS spectrum of Co 2p ( Figure 4 (b)), the fitting peaks at 781.13 eV and 796.83 eV correspond to Co 3+ 2p 3 / 2 and Co 3+ 2p 1 / 2 , respectively, while the fitting peaks at 783.83 eV and 799.33 eV correspond to Co 2+ 2p 3 / 2 and Co 2+ 2p 1 / 2 , respectively. The fitting peaks at 788.13 eV and 803.08 eV are satellite peaks. The above results show that there are two valence states of Co element, Co 3+ and Co 2+ , in the material. The Ni 2p spectrum ( Figure 4 (c)) has two peaks at 855.56 eV and 873.21 eV, corresponding to Ni 2+ 2p 3 / 2 and Ni 2+ 2p1 / 2 , 861.24 eV and 879.37 eV are satellite peaks, and the Ni 2p spectrum indicates that the Ni element in the material is Ni 2+ . The XPS spectrum of O 1s ( Figure 4 (d)) shows that the peak at 530.32 eV is related to lattice oxygen, the peak at 531.1 eV indicates the presence of typical M-OH (M = Fe, Co, Ni), and the fitting peak at 532.2 eV is adsorbed water. The above results prove that iron-cobalt-nickel hydroxide is formed on the surface of the iron-cobalt-nickel nanomaterial.

[0102] The iron-cobalt-nickel nanomaterial obtained in Example 1 was characterized by transmission electron microscopy, and the results are as Figure 5 shown. Figure 5 (a) is the transmission electron microscopy image of the iron-cobalt-nickel nanomaterial; consistent with the scanning electron microscopy image, the transmission electron microscopy image also shows the two-dimensional nanostructure of the iron-cobalt-nickel nanomaterial. The high-resolution transmission electron microscopy image ( Figure 5 (b)) shows that the lattice fringe with a spacing of 0.244 nm corresponds to the (112) crystal plane of the material. The selected area electron diffraction pattern ( Figure 5 (c)) shows the diffraction rings of the (012) and (0015) crystal planes of the iron-cobalt-nickel nanomaterial, which is consistent with the XRD results, indicating the successful synthesis of the material. The two-dimensional nanosheet structure of the iron-cobalt-nickel nanomaterial has a large specific surface area, which can increase the contact area between the catalyst and the electrolyte, thereby accelerating the interfacial reaction.

[0103] 2. Electrochemical performance test

[0104] The iron-cobalt-nickel nanomaterial obtained in Example 1 was placed in a three-electrode system to test its hydrogen evolution, oxygen evolution, and overall water splitting performance, and the results are as Figure 6 shown. Figure 6 is the linear voltammetry scan analysis result graph. It can be seen from Figure 6 that in a neutral electrolyte (0.1 M phosphate buffer solution), the iron-cobalt-nickel nanomaterial (labeled as iron-cobalt-nickel layered hydroxide / nickel foam in the figure) can obtain a current density of about 100 mA·cm at a voltage of -0.7 V (vs. RHE), while nickel foam can only obtain 20 mA·cm -2 around, and -2 ( Figure 6 (a)). When 1 M potassium hydroxide is used as the electrolyte, the hydrogen evolution overpotentials of the iron-cobalt-nickel nanomaterial at 10 and 20 mA·cm -2 are 68 and 207 mV respectively ( Figure 6 (b)); the oxygen evolution overpotentials at 10 mA·cm -2 and 50 mA·cm -2 are 117 and 197 mV respectively ( Figure 6(c)). When using the iron-cobalt-nickel nanomaterial as a bifunctional catalyst for overall water splitting, the voltages required to reach 10 and 20 mA·cm -2 are only 1.52 and 1.62 V ( Figure 6 (d)). Therefore, the iron-cobalt-nickel nanomaterial has good hydrogen evolution, oxygen evolution, and overall water splitting performance, and can carry out hydrogen evolution reaction in electrolytes with a wide pH value range, showing the potential for application in bipolar membrane-based water electrolysis devices.

[0105] The voltage-current density curves of the bipolar membrane-based water electrolysis hydrogen production devices using the iron-cobalt-nickel nanomaterial obtained in Example 1 as the cathode and anode in Examples 4 to 8 are as Figure 7 shown, the hydrogen evolution rate is as Figure 8 shown, and the oxygen evolution rate is as Figure 9 shown. From Figure 7 it can be seen that the water electrolysis hydrogen production device in Example 4 requires 2.95 V to obtain a current density of 20 mA·cm -2 , while the water electrolysis hydrogen production device in Example 5 only requires 2.06 V, indicating that in the forward configuration (i.e., the anion exchange layer of the bipolar membrane faces the cathode and the cation exchange layer faces the anode), the voltage required for the water electrolysis hydrogen production device is lower; from Figure 8 and Figure 9 it can be seen that the hydrogen evolution rates obtained under the two configurations (Example 4 and Example 5) are 1.59 and 1.55 mmol·h -1 , and the oxygen evolution rates are 0.81 and 0.74 mmol·h -1 . This shows that for both the forward configuration (i.e., the anion exchange layer of the bipolar membrane faces the cathode and the cation exchange layer faces the anode) and the reverse configuration (i.e., the anion exchange layer of the bipolar membrane faces the anode and the cation exchange layer faces the cathode) of the two bipolar membranes, the water electrolysis reaction can be carried out. The forward configuration of the bipolar membrane can reduce the applied voltage and save energy. In addition, when the current is set to 40, 60, and 80 mA·cm -2 (Examples 6 to 8), the applied voltages required for the water electrolysis hydrogen production device are 2.40, 2.85, and 3.30 V, the hydrogen evolution rates are 3.03, 4.79, and 6.73 mmol·h -1 , and the oxygen evolution rates are 1.50, 2.39, and 3.74 mmol·h -1 . This shows that the iron-cobalt-nickel nanomaterial can be applied to bipolar membrane-based water electrolysis devices with large changes in electrolyte conductivity, which is beneficial for long-term stable operation.

[0106] Examples 9 to 11 were based on Example 5 to investigate whether a water electrolysis hydrogen production device with a bipolar membrane in a forward configuration using iron-cobalt-nickel nanomaterials as the cathode and anode could achieve long-term operation without frequent electrolyte replacement and its applicability in different electrolytes under an operating mode of inverted electrolyte (alternating cathode liquid and anode liquid). The voltage-time curves are as Figure 10 shown, the hydrogen evolution rate is as Figure 11 shown, and the oxygen evolution rate is as Figure 12 shown. It can be seen from Figure 10 that the devices with three different electrolytes can all achieve an operation of 192 h without replacing the electrolyte. When the initial electrolyte is 1 M KOH (anode liquid) || 1 M KOH (cathode liquid), the applied voltage required by the water electrolysis device at 20 mA·cm -2 is basically stable. When the initial electrolyte is 0.5 M KOH (anode liquid) || 0.5 M KOH (cathode liquid), the voltage continuously rises within every 24 h. After exchanging the cathode liquid and the anode liquid, the voltage returns to near the initial value, and the device can achieve long-term operation without replacing the electrolyte. When the initial electrolyte is 1 M KOH (anode liquid) || 0.1 M PBS (cathode liquid) (Example 9), it is similar to Example 11 and can achieve long-term operation without replacing the electrolyte. This indicates that iron-cobalt-nickel nanomaterials are applicable to bipolar membrane-based water electrolysis devices with a large change in the pH value of the electrolyte, which is beneficial to long-term stable operation.

[0107] In addition, it can be seen from Figure 11 and Figure 12 that within 192 h, the hydrogen evolution rate per 24 h of the water electrolysis hydrogen production devices in Examples 9 to 11 is basically maintained stable, and the oxygen evolution rate decreases slightly. Specifically, for the water electrolysis device with an initial electrolyte of 1 M KOH (anode liquid) || 0.1 M PBS (cathode liquid), the hydrogen evolution rate within the 0 - 12 h is 1.23 mmol·h -1 , the oxygen evolution rate is 0.72 mmol·h -1 , the hydrogen evolution rate within the 180 - 192 h is 1.39 mmol·h -1 , the oxygen evolution rate is 0.71 mmol·h -1 , the average hydrogen evolution rate within 0 - 192 h is 1.45 mmol·h -1 , and the average oxygen evolution rate is 0.75 mmol·h -1 ; for the water electrolysis device with an initial electrolyte of 1 M KOH (anode liquid) || 1 M KOH (cathode liquid), the hydrogen evolution rate within the 0 - 12 h is 1.68 mmol·h -1 , the oxygen evolution rate is 0.8 mmol·h -1 , the hydrogen evolution rate within the 180 - 192 h is 1.35 mmol·h -1, the oxygen evolution rate is 0.48 mmol·h -1 , the average hydrogen evolution rate within 0 - 192 h is 1.44 mmol·h -1 , the average oxygen evolution rate is 0.66 mmol·h -1 ; for the water electrolysis device with the initial electrolyte of 0.5 M KOH (catholyte) || 0.5 M KOH (anolyte), the hydrogen evolution rate within the 0 - 12 h is 1.53 mmol·h -1 , the oxygen evolution rate is 0.71 mmol·h -1 , the hydrogen evolution rate at 180 - 192 h is 1.27 mmol·h -1 , the oxygen evolution rate is 0.69 mmol·h -1 , the average hydrogen evolution rate within 0 - 192 h is 1.44 mmol·h -1 , the average oxygen evolution rate is 0.69 mmol·h -1 . This indicates that the operation mode of inverting the electrolyte of the water electrolysis hydrogen production device based on bipolar membranes can stably produce hydrogen for a long time without the need to update the electrolyte, and this operation mode can also be applicable to lower electrolyte concentrations.

[0108] The electrochemical properties of the iron-cobalt-nickel nanomaterials prepared in Example 2 and Example 3 are similar to those of Example 1. In summary, the iron-cobalt-nickel nanomaterials of the present invention can carry out hydrogen evolution, oxygen evolution and overall water splitting reactions in an alkaline environment. At the same time, they also have good hydrogen evolution performance in a neutral solution. When applied to the water electrolysis hydrogen production device based on bipolar membranes, they can maintain good stability and do not require replacement of the new electrolyte when the device operates in the operation mode of inverting the electrolyte.

[0109] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation modes of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation modes here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A method for preparing an iron-cobalt-nickel nanomaterial, characterized in that, It includes the following steps: S1. Dissolve an iron source, a cobalt source, and a nickel source in a solvent to obtain a precursor solution; S2. Immerse nickel foam in the precursor solution and perform electrochemical deposition on the nickel foam to obtain the iron-cobalt-nickel nanomaterial; In the precursor solution in step S1, the mass ratio of the sum of the iron source, cobalt source, and nickel source to the volume of the solvent is (4-5) g / 50 mL; in the precursor solution in step S1, the molar ratio of iron, cobalt, and nickel elements is 1:1:2; in step S2, the voltage of the electrochemical deposition is -1.0 to -5.0 V, and the deposition time is 10 to 30 min; the electrochemical deposition in step S2 is carried out in a three-electrode system.

2. The preparation method according to claim 1, characterized in that, The iron source in step S1 is ferrous sulfate, the cobalt source is cobalt nitrate, and the nickel source is nickel nitrate.

3. An iron-cobalt-nickel nanomaterial, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 2.

4. The application of the iron-cobalt-nickel nanomaterial according to claim 3 as a cathode and / or anode in the preparation of an electrolytic water hydrogen production device.

5. An electrolytic water hydrogen production device, characterized in that, It includes an anodic chamber (1), a cathodic chamber (2), an anode (3), a cathode (4), anolyte, catholyte, and a bipolar membrane (5); the bipolar membrane (5) separates the anodic chamber (1) and the cathodic chamber (2); the materials of the anode (3) and the cathode (4) are both the iron-cobalt-nickel nanomaterial according to claim 3; the anolyte is a potassium hydroxide solution, and the catholyte is a phosphate buffer solution.

6. The electrolytic water hydrogen production device according to claim 5, characterized in that, The concentration of the potassium hydroxide solution is 0.5 to 2 mol / L.

7. The electrolytic water hydrogen production device according to claim 5, characterized in that, The concentrations of the solutes in the phosphate buffer solution are: potassium chloride 0.26 to 0.78 g / L; ammonium chloride 0.62 to 1.86 g / L; sodium dihydrogen phosphate dihydrate 6.7 to 20.1 g / L; disodium hydrogen phosphate dodecahydrate 20.7 to 62.1 g / L.

8. The electrolytic water hydrogen production device according to claim 5, characterized in that, The distance between the anode and the cathode is 0.5 to 1.0 cm.

9. A method for producing hydrogen by electrolyzing water, characterized in that, It is carried out based on the electrolytic water hydrogen production device according to any one of claims 5 to 8, and the anolyte and the catholyte of the electrolytic water hydrogen production device are alternated 1 to 3 times every 12 to 36 hours of operation.

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