NiFe bimetallic MOF self-supported bifunctional electrode for electrolysis of water and method for electrolysis of water

Abstract

The application belongs to the technical field of electrolysis of water, and particularly relates to a NiFe bimetallic MOF self-supporting bifunctional electrode for electrolysis of water and a method for electrolysis of water. The electrode takes foamed nickel as a substrate, and the surface of the substrate is uniformly coated with NiFe bimetallic MOF. The coating method comprises the following steps: two pieces of foamed nickel after cleaning and pretreatment are taken as anodes, one piece of foamed nickel after cleaning and pretreatment is taken as a cathode, and the anodes and the cathode are immersed in an electrolyte; under the condition of a constant current of 14-16 mA of a direct current power supply, electrodeposition is performed for 15-55 min; the area of the anode foamed nickel is larger than that of the cathode; in the electrolyte, N,N-dimethylformamide is taken as a solvent, and nickel salt, iron salt, 1,3,5-benzene tricarboxylic acid and triethylamine hydrochloride are uniformly dissolved in the solvent; the molar ratio of Ni to Fe is 40-75:1; and the concentration of triethylamine hydrochloride is 0.01-0.1 mol L⁻¹. The application adopts a double-anode electrodeposition process to improve deposition uniformity, fully expose active sites and reduce electrodeposition energy consumption; and the synergistic effect of the Ni-Fe bimetallic MOF optimizes the HER and OER catalytic performance of the electrode.

Description

Technical Field

[0001] This invention belongs to the field of water electrolysis technology, specifically relating to a NiFe bimetallic MOF self-supporting bifunctional electrode for water electrolysis and a water electrolysis method. Background Technology

[0002] Currently, commercially available high-efficiency electrocatalytic materials for water splitting are still mainly based on noble metals such as platinum, ruthenium, and iridium. Although these materials can achieve high current density catalysis at low overpotentials, they suffer from problems such as resource scarcity, high preparation costs, and poor long-term stability, which severely limit the large-scale promotion of water electrolysis technology. To address the aforementioned shortcomings of noble metal-based materials, researchers have shifted their focus to non-noble metal-based electrocatalytic materials. Among them, nickel-based metal-organic frameworks (MOFs) have become the preferred direction for non-noble metal electrodes in water electrolysis due to their advantages such as porous structure, high specific surface area, and strong designability of active sites, as well as the abundance and low cost of nickel resources. At the same time, self-supporting electrode design is widely used in the preparation of nickel-based MOF electrodes because it does not require additional binders, can reduce the electronic impedance between the electrode and the substrate, and improve the bonding force between the catalytic material and the substrate, becoming an important technical solution to replace traditional coated electrodes. In the existing technology, there have been many studies and technological improvements on nickel-based self-supporting electrodes. For example, MOF self-supporting hydrogen evolution or oxygen evolution electrodes have been prepared on nickel foam substrates through processes such as three-electrode electrodeposition, hydrothermal synthesis, and solvothermal methods. However, a nickel-based self-supporting bifunctional electrode preparation technology that can simultaneously solve problems such as the imbalance of bifunctional catalytic performance, uneven deposition in traditional deposition processes, and insufficient exposure of active sites has not yet been developed. Therefore, it is particularly urgent to develop a self-supporting bifunctional electrode that is simple to process, low in cost, scalable, and capable of achieving synergistic and efficient catalysis of HER and OER, which is also the research motivation of this invention. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a NiFe bimetallic MOF self-supporting bifunctional electrode for water electrolysis and a water electrolysis method. This invention solves the problems of insufficient activity of existing water electrolysis electrodes under high current density and poor OER catalytic performance of single Ni metal MOF electrodes. It also solves the technical defects of uneven deposition and insufficient exposure of active sites in traditional preparation processes.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A self-supporting bifunctional NiFe bimetallic MOF electrode for water electrolysis is disclosed. The electrode uses nickel foam as a substrate, and its surface is uniformly coated with NiFe bimetallic MOF. The coating method includes the following steps:

[0006] Two pieces of pre-cleaned nickel foam were used as anodes and one piece of pre-cleaned nickel foam was used as cathode. They were both immersed in the electrolyte and electrodeposited for 15-55 minutes under a constant current of 14-16mA DC power supply.

[0007] The electrolyte uses N,N-dimethylformamide as a solvent, in which nickel salt, iron salt, 1,3,5-benzenetricarboxylic acid and triethylamine hydrochloride are uniformly dissolved. The molar ratio of Ni to Fe is 40~75:1, and the concentration of triethylamine hydrochloride is 0.01-0.1 mol L⁻¹.

[0008] The electrode provided by this invention uses nickel foam as a substrate and coats nickel-iron bimetallic MOF with a dual-anodine electrodeposition process. On the one hand, the electrode has both good OER and HER activity, and on the other hand, it has good stability in use. In particular, the nickel-iron bimetallic MOF has good adhesion to nickel foam.

[0009] Furthermore, the pretreatment method for cleaning nickel foam includes: cutting nickel foam into 1.0×2.0 cm² and 2.0×2.0 cm² sizes, immersing them sequentially in hydrochloric acid, ultrapure water and ethanol solutions for ultrasonic treatment, and obtaining pretreated nickel foam.

[0010] Furthermore, to obtain better OER activity, the concentration of nickel salt in the electrolyte was 0.15 mol L⁻¹, and the concentration of 1,3,5-benzenetricarboxylic acid was 0.041 mol L⁻¹.

[0011] And / or, the iron salt is ferric nitrate nonahydrate, and the nickel salt is nickel nitrate hexahydrate;

[0012] And / or, the molar ratio of Ni to Fe is 40~50:1;

[0013] And / or, the triethylamine hydrochloride concentration is 0.01 mol L⁻¹ or 0.08~0.1 mol L⁻¹;

[0014] And / or, electrodeposit for 40~55 minutes under a constant current of 15mA DC power supply.

[0015] Furthermore, to obtain better HER activity, the electrolyte concentration of nickel salt was 0.15 mol L⁻¹ and the concentration of 1,3,5-benzenetricarboxylic acid was 0.041 mol L⁻¹.

[0016] And / or, the iron salt is ferric nitrate nonahydrate, and the nickel salt is nickel nitrate hexahydrate;

[0017] And / or, the molar ratio of Ni to Fe is 50~75:1;

[0018] And / or, triethylamine hydrochloride concentration 0.01~0.08 mol L⁻¹;

[0019] And / or, electrodeposit for 25-40 minutes under a constant DC current of 15mA.

[0020] Furthermore, the process includes a post-electrode treatment step: the coated loaded nickel foam is repeatedly washed with N,N-dimethylformamide, ultrapure water and ethanol, and then dried under vacuum.

[0021] Furthermore, the preparation of the electrolyte includes the following steps: dissolving nickel salt, 1,3,5-benzenetricarboxylic acid and triethylamine hydrochloride in N,N-dimethylformamide, placing it in an ultrasonic bath and sonicating for 20-30 min until completely dissolved, with an ultrasonic power of 20-25 W / L; then adding iron salt and continuing to sonicate to fully dissolve the iron salt and mix it evenly with the original components.

[0022] Alternatively, nickel salt, iron salt, 1,3,5-benzenetricarboxylic acid and triethylamine hydrochloride are dissolved in N,N-dimethylformamide and placed in an ultrasonic bath for 20-30 minutes until completely dissolved, with an ultrasonic power of 20-25 W / L.

[0023] The present invention also provides a method for electrolyzing water, comprising the following steps: using a three-electrode electrolyzer reactor, wherein the NiFe bimetallic MOF self-supporting bifunctional electrode for water electrolysis as described in any one of claims 1 to 6 is used as the working electrode.

[0024] Furthermore, this includes controlling the current density to be 500~1000 mA cm⁻¹ under alkaline conditions. -2

[0025] Furthermore, the aforementioned cathode nickel foam was cut into two specifications: 1.0 × 2.0 cm² and 2.0 × 2.0 cm². The NiFe-MOF / NF electrode exhibited optimal overall performance in terms of HER and OER when the electrolyte system was controlled with a nickel nitrate hexahydrate concentration of 0.15 mol L⁻¹, a 1,3,5-benzenetricarboxylic acid concentration of 0.041 mol L⁻¹, a triethylamine hydrochloride concentration of 0.01 mol L⁻¹, a nickel-iron molar ratio of 50:1, and a constant current of 15 mA and an electrodeposition time of 40 min.

[0026] The bimetallic MOF self-supporting bifunctional electrode prepared by the above-mentioned preparation method of the present invention uses nickel foam as a self-supporting substrate. The raw material system is simple and low in cost, and the synthesis steps are simple. The surface of the NiFe bimetallic MOF is uniformly grown with abundant porous structure and sufficient exposure of active sites. The prepared bifunctional electrode can replace noble metal electrodes and has a low overpotential at high current density, which can meet the needs of industrial applications.

[0027] In a preferred embodiment of the preparation method described in this invention, the size of the nickel foam is 1.0 × 2.0 cm. 2 ~2.0×2.0cm 2 .

[0028] In a preferred embodiment of the preparation method described in this invention, the concentration of triethylamine hydrochloride in the electrolyte is 0.01~0.1 mol L⁻¹, and the concentration of ferric nitrate nonahydrate is 0.0015~0.006 mol L⁻¹; more preferably, the concentration of triethylamine hydrochloride in the electrolyte is 0.01 mol L⁻¹, and the concentration of ferric nitrate nonahydrate is 0.003 mol L⁻¹.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The present invention adopts a DC power supply dual anode electrodeposition process, which effectively improves the deposition uniformity of NiFe bimetallic MOF on nickel foam substrate compared with traditional single anode electrodeposition, avoids the problem of active sites being wrapped, and fully exposes the active sites on the electrode surface, significantly improving the catalytic activity and stability of the electrode under high current density, while also reducing electrodeposition energy consumption.

[0031] (2) This invention introduces Fe metal and Ni to construct a bimetallic MOF, and utilizes the synergistic catalytic effect of NiFe to fundamentally solve the problem of insufficient OER catalytic performance of a single Ni metal electrode, and realizes the simultaneous optimization of the dual-function catalytic performance of the electrode HER and OER.

[0032] (3) The NiFe bimetallic MOF self-supporting electrode prepared by the present invention has excellent physicochemical properties and is an ideal candidate to replace noble metal electrodes, with good prospects for industrial application. Attached Figure Description

[0033] Figure 1 The LSV diagrams of the HER reaction of electrodes in Examples 1-4 of this invention are shown.

[0034] Figure 2 The LSV diagrams of the OER reaction of electrodes in Examples 1-4 of this invention are shown.

[0035] Figure 3 For the reason Figure 1 The Tafel curve derived from the LSV plot.

[0036] Figure 4 For the reason Figure 2 The Tafel curve derived from the LSV plot.

[0037] Figure 5 The LSV diagrams show the HER reaction of electrodes in Examples 5-8 and Example 3.

[0038] Figure 6 The LSV diagrams show the OER reaction of electrodes in Examples 5-8 and Example 3.

[0039] Figure 7 The LSV diagrams show the HER reaction of electrodes in Examples 9 and 3.

[0040] Figure 8 The LSV diagrams show the OER reaction of electrodes in Examples 9 and 3.

[0041] Figure 9 The LSV diagrams for the HER reaction of electrodes in Examples 10-13 are shown.

[0042] Figure 10 The LSV diagrams for the electrode OER reaction in Examples 10-13 are shown.

[0043] Figure 11 For the reason Figure 9 The Tafel curve derived from the LSV plot.

[0044] Figure 12 For the reason Figure 10 The Tafel curve derived from the LSV plot.

[0045] Figure 13 These are electrodeposition photographs of the electrodes in Examples 3 and 9.

[0046] Figure 14 These are photographs of the electrodes from Examples 3 and 9 after activity testing.

[0047] Figure 15 This is a schematic diagram of the electrodeposition apparatus in an embodiment of the present invention.

[0048] Figure 16 This is a schematic diagram of the electrochemical testing device in an embodiment of the present invention. Detailed Implementation

[0049] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0050] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0051] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0052] The proposed strategy of NiFe bimetallic MOF self-supported electrocatalysts successfully solved the above problems. This is because the catalyst has the following advantages: (1) The self-supported system has better conductivity. The electrocatalyst synthesized with nickel foam as the growth substrate has high conductivity due to the high conductivity of the 3D integrated framework of nickel foam itself, which can provide a large number of efficient electron transfer channels, greatly accelerate the electron transfer rate of the electrocatalytic reaction, and facilitate the rapid progress of hydrogen evolution and oxygen evolution reactions; (2) Compared with traditional powder catalysts, the self-supported structure of the catalytic material grown directly on the nickel foam substrate is less prone to agglomeration. The specific surface area of ​​the material is greatly increased, which can fully expose more catalytic active sites. The abundant active sites are the key to improving H The key to HER and OER catalytic performance; (3) In the MOF multi-metal catalytic system constructed by NiFe bimetal, significant synergistic catalytic effects can be generated between different phases of Ni and Fe, which can not only optimize HER catalytic activity, but also greatly improve OER catalytic performance, and achieve simultaneous improvement of bifunctional catalytic efficiency; (4) The self-supporting NiFe bimetal MOF nanostructure electrocatalyst can be directly used as a conductive electrode for HER and OER testing without the need to add additional binder to coat the current collector surface, effectively avoiding problems such as increased electronic impedance and coverage of active sites caused by binder, and ensuring the high efficiency of electrocatalytic reaction.

[0053] In some embodiments of the present invention, a NiFe bimetallic MOF self-supporting bifunctional electrode for water electrolysis is provided. The electrode uses nickel foam as a substrate, and its surface is uniformly coated with NiFe bimetallic MOF. The coating method includes the following steps:

[0054] Two pieces of pre-cleaned nickel foam were used as anodes and one piece of pre-cleaned nickel foam was used as cathode. They were both immersed in the electrolyte and electrodeposited for 15-55 minutes under a constant current of 14-16mA DC power supply. The area of ​​the nickel foam on the anode was larger than that on the cathode (multiple experiments have verified that a more uniform coating can be obtained when the anode area is larger than that on the cathode).

[0055] The electrolyte uses N,N-dimethylformamide as a solvent, in which nickel salt, iron salt, 1,3,5-benzenetricarboxylic acid and triethylamine hydrochloride are uniformly dissolved. The molar ratio of Ni to Fe is 40~75:1, and the concentration of triethylamine hydrochloride is 0.01-0.1 mol∙L⁻¹.

[0056] The adoption of a dual-anod electrodeposition process improves deposition uniformity, increases the exposure of active sites, and reduces electrodeposition energy consumption. The synergistic effect of Ni and Fe bimetallic MOFs optimizes the HER and OER catalytic performance of the electrode, effectively overcoming the problems of insufficient activity of existing electrodes under high current density and poor OER performance of single Ni metal MOF electrodes. It has good application prospects in the field of electrode material technology and is expected to improve energy and environmental issues.

[0057] To balance performance and cost, in some preferred embodiments, the Ni:Fe molar ratio is 40~50:1, more preferably 50~75:1; and / or, the triethylamine hydrochloride concentration is 0.01 mol∙L⁻¹ or 0.08~0.1 mol∙L⁻¹, more preferably 0.01~0.08 mol∙L⁻¹.

[0058] In some specific embodiments, the electrode is prepared using the following methods:

[0059] 1. Pretreatment of nickel foam: Commercial nickel foam is cut into two specifications: 1.0×2.0 cm² and 2.0×2.0 cm². It is then immersed in 1 mol L⁻¹ hydrochloric acid, ultrapure water and ethanol solution and sonicated for 15-20 minutes to remove the surface oxide layer, oil and impurities. After removal, it is rinsed with ultrapure water until neutral and placed in a ventilated place to air dry naturally to obtain pretreated nickel foam for later use.

[0060] 2. Preparation and Optimal Formulation of Single Nickel-Based Electrolyte: Nickel nitrate hexahydrate, 1,3,5-benzenetricarboxylic acid, and triethylamine hydrochloride were dissolved in N,N-dimethylformamide and sonicated in an ultrasonic bath for 20-30 min until completely dissolved to obtain a single nickel-based electrolyte. The optimal formulation was determined by HER / OER activity testing to be: nickel nitrate hexahydrate concentration 0.15 mol L⁻¹, 1,3,5-benzenetricarboxylic acid concentration 0.041 mol L⁻¹, and triethylamine hydrochloride concentration 0.01 mol L⁻¹. Furthermore, the Ni-MOF / NF electrode prepared from a single Ni metal exhibited the best performance under a constant current of 15 mA and a deposition time of 40 min.

[0061] 3. Preparation of NiFe bimetallic electrolyte: Add ferric nitrate nonahydrate to the above-mentioned single nickel-based optimal electrolyte, control its concentration in the range of 0.0015~0.006 mol L⁻¹, and sonicate again for 20~30 min to fully dissolve the ferric nitrate nonahydrate and mix it evenly with the original components to obtain a stable NiFe bimetallic electrolyte, and let it stand for later use;

[0062] 4. Dual-anode electrodeposition: A customized dual-anode electrodeposition apparatus was used, with two 2.0×2.0 cm² pretreated nickel foam pieces as dual anodes and one 1.0×2.0 cm² pretreated nickel foam piece as cathode, both immersed in NiFe bimetallic electrolyte, ensuring complete immersion and no contact between the electrodes; the dual anodes were connected to the positive terminal of a DC regulated power supply, and the cathode was connected to the negative terminal, with a constant DC current of 15 mA applied, and the deposition time controlled at 25~55 min to complete the electrodeposition reaction;

[0063] 5. Post-treatment: After electrodeposition, the nickel foam loaded with NiFe bimetallic MOF is immediately removed and washed repeatedly with DMF, ultrapure water and ethanol 3 to 5 times to remove unreacted raw materials and electrolyte residues adsorbed on the surface; the washed electrode is placed in a vacuum drying oven and vacuum dried at 60-80℃ for 2 to 3 hours to obtain the NiFe bimetallic MOF self-supporting bifunctional electrode of the present invention.

[0064] Finally, the prepared electrode was subjected to electrochemical testing using a three-electrode electrolyzer to test its water desorption hydrogen performance.

[0065] Electrochemical water splitting performance evaluation:

[0066] Tests were conducted using the Donghua Electrochemical Workstation;

[0067] In the three-electrode system, the working electrode is a loaded nickel foam, the reference electrode is an Hg / HgO electrode, and the counter electrode is a platinum mesh.

[0068] The three-electrode system is used to study two half-reactions in water electrolysis, including a reduction reaction at the cathode to produce hydrogen and an oxidation reaction at the anode to produce oxygen.

[0069] The device was tested at room temperature and pressure using 1 M KOH as the electrolyte. The HER performance was tested within a suitable potential range (-1 to -3 V) using the linear sweep method (LSV).

[0070] Subsequently, CV curves were continuously tested at different scan rates (-2 to -3 V);

[0071] Finally, the impedance of the electrodes was tested.

[0072] Current density based on the macroscopic area of ​​the electrode: 500 / 1000 mA cm⁻¹ -2 This serves as an indicator for evaluating the catalytic activity of the electrode.

[0073] Example 1

[0074] Preparation and testing of electrode S1:

[0075] Nickel nitrate hexahydrate and 1,3,5-benzenetricarboxylic acid were fully dissolved in N,N-dimethylformamide to form the electrolyte (the concentration of nickel nitrate hexahydrate in the electrolyte system was calculated to be 0.15 mol / L). -1 The concentration of 1,3,5-benzenetricarboxylic acid was 0.041 mol / L. -1 The concentration of triethylamine hydrochloride is 0.01 mol / L. -1 Two 2.0×2.0 cm² pretreated nickel foam pieces were used as anodes and one 1.0×2.0 cm² pretreated nickel foam piece was used as cathode. The electrodes were immersed in electrolyte and deposited for 10 min using a constant current method (CC) with a current of 15 mA (corresponding deposition voltage of 3.5V~3.63V). After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol, and then vacuum dried (time 2-3 h, temperature 60-80℃) to obtain electrode S1, abbreviated as Ni-MOF / NF-10.

[0076] Electrochemical water desorption hydrogen test was performed on the above-mentioned Ni-MOF / NF-10, which showed that Ni-MOF / NF-10 has certain catalytic performance.

[0077] For HER, this Ni-MOF / NF-10 drives 500 / 1000 mA cm⁻¹ in 1 M KOH electrolyte. -2 The overpotentials at current densities were 366 / 498 mV; the OER was driven at 500 mA cm⁻¹ in 1 M KOH electrolyte. -2 The overpotential at the current density is 465 mV;

[0078] Example 2

[0079] Preparation and testing of electrode S2:

[0080] Using the same electrolyte formulation as in Example 1, two 2.0 × 2.0 cm² pretreated nickel foam pieces were used as anodes and one 1.0 × 2.0 cm² pretreated nickel foam piece was used as cathode. The electrodes were immersed in the electrolyte and deposited for 25 min using a constant current method (CC) with a current of 15 mA (corresponding to a deposition voltage of 3.3 V to 3.4 V). After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol, and then vacuum dried (time 2-3 h, temperature 60-80 ℃) to obtain electrode S2, abbreviated as Ni-MOF / NF-25.

[0081] Electrochemical water desorption hydrogen removal (HER) tests on the above-mentioned Ni-MOF / NF-25 showed that it possesses certain catalytic performance. For HER, this Ni-MOF / NF-25 achieved a driving force of 500 / 1000 mA cm⁻¹ in a 1 M KOH electrolyte. -2The overpotentials at the current densities were 139 / 146 mV, respectively. The OER was driven at 500 mA cm⁻¹ in a 1 M KOH electrolyte. -2 The overpotential at the current density is 437 mV;

[0082] Example 3

[0083] Preparation and testing of S3 electrode

[0084] Using the same formulation as in Example 1, two 2.0×2.0 cm² pretreated nickel foam sheets were used as anodes and one 1.0×2.0 cm² pretreated nickel foam sheet was used as cathode. The electrodes were immersed in the electrolyte and deposited for 40 min using a constant current method (CC) with a current of 15 mA (corresponding to a deposition voltage of 3.4V~3.5V). After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol. After vacuum drying (time 2-3 h, temperature 60-80℃), electrode S3, abbreviated as Ni-MOF / NF-40, was obtained.

[0085] Electrochemical water desorption hydrogen removal (HER) tests were performed on the above electrodes, revealing that Ni-MOF / NF-40 exhibits certain catalytic performance. For HER, Ni-MOF / NF-40 drives a catalytic flow rate of 500 / 1000 mA cm⁻¹ in 1 M KOH electrolyte. -2 The overpotentials at the current densities were 113 / 126 mV, respectively. For OER, Ni-MOF / NF-40 drove 500 mA cm⁻¹ in 1 M KOH electrolyte. -2 The overpotential of the current density is 419mV.

[0086] Example 4

[0087] Preparation and testing of S4 electrode

[0088] Using the same formulation as in Example 1, two 2.0 × 2.0 cm² pretreated nickel foam pieces were used as anodes and one 1.0 × 2.0 cm² pretreated nickel foam piece was used as cathode. The electrodes were immersed in electrolyte and deposited for 55 min using a constant current method (CC) with a current of 15 mA (corresponding to a deposition voltage of 3.2 V to 3.7 V). After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol. After vacuum drying (time 2-3 h, temperature 60-80 °C), electrode S4, abbreviated as Ni-MOF / NF-55, was obtained.

[0089] Electrochemical water desorption hydrogen removal tests were performed on the above electrodes, indicating that Ni-MOF / NF-55 exhibits certain catalytic performance. For HER, Ni-MOF / NF-55 achieved a driving force of 500 / 1000 mA cm⁻¹ in 1 M KOH electrolyte. -2The overpotentials at the current densities were 203 / 289 mV, respectively. For the OER (Ni-MOF / NF-55), a 500 mA cm⁻¹ current density was achieved in 1 M KOH electrolyte. -2 The overpotential at the current density is 407 mV.

[0090] Examples 1-4 show the HER and OER activities of the electrodes. Figure 1-2 It can be seen that, according to η 500 -HER and η 1000 -HER, the catalytic performance of these electrodes is ordered as follows: Ni-MOF / NF-40 > Ni-MOF / NF-25 > Ni-MOF / NF-55 > Ni-MOF / NF-10; according to η 500 The catalytic performance of -OER is in the following order: Ni-MOF / NF-55 > Ni-MOF / NF-40 > Ni-MOF / NF-25 > Ni-MOF / NF-10.

[0091] The Tafel curve (the Tafel slope value is obtained by linearly fitting the Tafel equation using overpotential and corresponding current density data obtained from the LSV curve: η = a + b × log j, where η is the overpotential, a is a constant, b is the Tafel slope, and j is the current density.) See Figure 3-4 As can be seen from the figure, the Tafel slopes for hydrogen evolution at these electrodes are as follows: Ni-MOF-10 is 127.28 mV dec. -1 Ni-MOF-25 has a dec V of 84.58 mV. -1 Ni-MOF-40 has a dec V of 49.84 mV. -1 Ni-MOF-55 has a dec V of 114.96 mV. -1 Among them, Ni-MOF-40 has the smallest Tafel slope, indicating its highest activity. The Tafel slopes for oxygen evolution at the electrodes are as follows: Ni-MOF-10 is 66.05 mV dec. -1 The Ni-MOF-25 value is 54.75 mVdec. -1 Ni-MOF-40 has a dec V of 35.73 mV. -1 The Ni-MOF-55 has a dec V of 43.59 mV. -1 Among them, Ni-MOF-40 has the smallest Tafel slope, indicating that it has the best activity.

[0092] Example 5

[0093] Nickel nitrate hexahydrate and 1,3,5-benzenetricarboxylic acid were fully dissolved in N,N-dimethylformamide to form the electrolyte (the concentration of nickel nitrate hexahydrate in the electrolyte system was calculated to be 0.15 mol / L).-1 The concentration of 1,3,5-benzenetricarboxylic acid was 0.041 mol / L. -1 (Without triethylamine hydrochloride), two 2.0×2.0 cm² pretreated nickel foam pieces were used as anodes and one 1.0×2.0 cm² pretreated nickel foam piece was used as cathode. The electrodes were immersed in the electrolyte and deposited using a constant current method (CC) with a current of 15 mA for 40 min. After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol and vacuum dried (time 2-3 h, temperature 60-80 ℃). The results were not satisfactory after testing (see Table 1).

[0094] Example 6

[0095] Nickel nitrate hexahydrate, 1,3,5-benzenetricarboxylic acid, and triethylamine hydrochloride were fully dissolved in N,N-dimethylformamide to form the electrolyte (the concentration of nickel nitrate hexahydrate in the electrolyte system was calculated to be 0.15 mol / L). -1 The concentration of 1,3,5-benzenetricarboxylic acid was 0.041 mol / L. -1 Triethylamine hydrochloride concentration 0.05 mol / L -1 Two 2.0×2.0 cm² pretreated nickel foam pieces were used as anodes and one 1.0×2.0 cm² pretreated nickel foam piece was used as cathode. The electrodes were immersed in electrolyte and a 15 mA current was applied using the constant current method (CC) for 40 min for electrodeposition. After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol and vacuum dried (time 2-3 h, temperature 60-80 ℃). The results were not satisfactory after testing (see Table 1).

[0096] Example 7

[0097] Nickel nitrate hexahydrate, 1,3,5-benzenetricarboxylic acid, and triethylamine hydrochloride were fully dissolved in N,N-dimethylformamide (DMF) to form the electrolyte (the concentration of nickel nitrate hexahydrate in the electrolyte system was calculated to be 0.15 mol / L). -1 The concentration of 1,3,5-benzenetricarboxylic acid was 0.041 mol / L. -1 Triethylamine hydrochloride concentration 0.08 mol L -1 Two 2.0×2.0 cm² pretreated nickel foam pieces were used as anodes and one 1.0×2.0 cm² pretreated nickel foam piece was used as cathode. The electrodes were immersed in electrolyte and a 15 mA current was applied using the constant current method (CC) for 40 min for electrodeposition. After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol and vacuum dried (time 2-3 h, temperature 60-80 ℃). The results were not satisfactory after testing (see Table 1).

[0098] Example 8

[0099] Nickel nitrate hexahydrate, 1,3,5-benzenetricarboxylic acid, and triethylamine hydrochloride were fully dissolved in N,N-dimethylformamide (DMF) to form the electrolyte (the concentration of nickel nitrate hexahydrate in the electrolyte system was calculated to be 0.15 mol / L). -1 The concentration of 1,3,5-benzenetricarboxylic acid was 0.041 mol / L. -1 Triethylamine hydrochloride concentration 0.1 mol L -1 Two 2.0×2.0 cm² pretreated nickel foam pieces were used as anodes and one 1.0×2.0 cm² pretreated nickel foam piece was used as cathode. The electrodes were immersed in electrolyte and a 15 mA current was applied using the constant current method (CC) for 40 min for electrodeposition. After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol and vacuum dried (time 2-3 h, temperature 60-80 ℃). The results were not satisfactory after testing (see Table 1).

[0100] The activity of Examples 5-8 is shown in the figure. Figure 5-6 It can be seen that according to η 500 -HER and η 1000 -HER, the catalytic performance of these electrodes is in the following order: Example 3 > Example 7 > Example 6 > Example 8 > Example 5. According to η 500 -OER, the catalytic performance order is: Example 3 > Example 7 > Example 8 > Example 5 > Example 6.

[0101] Table 1

[0102]

[0103] Example 9

[0104] Single-anode electrodeposition: Nickel nitrate hexahydrate and 1,3,5-benzenetricarboxylic acid were fully dissolved in N,N-dimethylformamide as the electrolyte (the concentration of nickel nitrate hexahydrate in the electrolyte system was calculated to be 0.15 mol / L). -1 The concentration of 1,3,5-benzenetricarboxylic acid was 0.041 mol / L. -1 Triethylamine hydrochloride concentration 0.01 mol L -1 A 2.0×2.0 cm² pretreated nickel foam sheet was used as the anode, and a 1.0×2.0 cm² pretreated nickel foam sheet was used as the cathode. The electrodes were immersed in the electrolyte and a 15 mA current was applied using the constant current method (CC) for 40 min for electrodeposition. After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol, and then vacuum dried (time 2-3 h, temperature 60-80 ℃). However, the results were not satisfactory after testing.

[0105] refer to Figure 13 and Figure 14It can be seen that the stability of single-anode deposited Ni-MOF / NF is not as good as that of dual-anode deposited Ni-MOF / NF. The former showed obvious detachment after activity testing, and the NF substrate was clearly exposed. For HER, this electrode was driven at 500 / 1000 mA cm⁻¹ in 1 M KOH electrolyte. -2 The overpotentials at the current densities were 257 / 403 mV, significantly worse than the activity of the electrode in Example 3. For OER, this electrode was driven at 500 mA cm⁻¹ in 1 M KOH electrolyte. -2 The overpotential of the current density was 572mV, which was also far worse than the activity effect of the electrode in Example 3.

[0106] Example 10

[0107] In Example 3, ferric nitrate nonahydrate was added to the optimal electrolyte formulation (0.15 mol L⁻¹ nickel nitrate hexahydrate, 0.041 mol L⁻¹ 1,3,5-benzenetricarboxylic acid, and 0.01 mol L⁻¹ triethylamine hydrochloride). The Fe:Ni molar ratio was controlled at 1:100 (ferric nitrate nonahydrate concentration 0.0015 mol L⁻¹). The electrolyte was sonicated for 20-30 min to ensure complete dissolution of all components, thus obtaining a NiFe bimetallic electrolyte. Two 2.0 × 2.0 cm² pretreated nickel foam sheets were used as anodes, and one 1.0 × 2.0 cm² pretreated nickel foam sheet was used as cathode. The electrodes were immersed in the electrolyte, and a constant current (CC) of 15 mA (corresponding to a deposition voltage of 3.6 V-3.8 V) was applied for deposition for 40 minutes. After electrodeposition, the loaded nickel foam is repeatedly washed with DMF, ultrapure water and ethanol, and then vacuum dried (time 2-3h, temperature 60-80℃) to obtain electrode S10, abbreviated as NiFe-MOF / NF-100:1.

[0108] Electrochemical water evolution and hydrogen evolution tests were performed on the NiFe-MOF / NF-100:1, revealing its excellent bifunctional catalytic performance. For HER, the overpotentials of NiFe-MOF / NF-100:1 driven by a current density of 500 / 1000 mA cm⁻² in 1 M KOH electrolyte were 395 / 487 mV, respectively; for OER, the overpotentials driven by a current density of 500 mA cm⁻² in 1 M KOH electrolyte were 418.6 mV.

[0109] Example 11

[0110] Ferric nitrate nonahydrate was added to the optimal electrolyte formulation in Example 3, and the Fe:Ni molar ratio was controlled at 1:75 (ferric nitrate nonahydrate concentration 0.00375 mol L⁻¹). The electrolyte was sonicated for 20-30 min to fully dissolve the components, thus obtaining a NiFe bimetallic electrolyte. Two 2.0×2.0 cm² pretreated nickel foam pieces were used as anodes and one 1.0×2.0 cm² pretreated nickel foam piece was used as cathode. The electrodes were immersed in the electrolyte and deposited using a constant current method (CC) with a current of 15 mA (corresponding deposition voltage of 3.2V~3.5V) for 40 min. After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol, and then vacuum dried (time 2-3 h, temperature 60-80℃) to obtain electrode S11, abbreviated as NiFe-MOF / NF-75:1.

[0111] Electrochemical water evolution and hydrogen evolution tests were performed on the NiFe-MOF / NF-75:1, revealing its excellent bifunctional catalytic performance. For HER, the overpotentials of NiFe-MOF / NF-75:1 driven by a current density of 500 / 1000 mA cm⁻² in 1 M KOH electrolyte were 155 / 181 mV, respectively; for OER, the overpotentials driven by a current density of 500 mA cm⁻² in 1 M KOH electrolyte were 343 mV.

[0112] Example 12

[0113] Ferric nitrate nonahydrate was added to the optimal electrolyte formulation in Example 3, and the Fe:Ni molar ratio was controlled at 1:50 (ferric nitrate nonahydrate concentration 0.003 mol L⁻¹). The electrolyte was sonicated for 20-30 min to fully dissolve the components, thus obtaining a NiFe bimetallic electrolyte. Two 2.0×2.0 cm² pretreated nickel foam pieces were used as anodes and one 1.0×2.0 cm² pretreated nickel foam piece was used as cathode. The electrodes were immersed in the electrolyte and deposited for 40 min using a constant current method (CC) with a current of 15 mA (corresponding deposition voltage of 3.4 V~3.5 V). After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol, and then vacuum dried (time 2-3 h, temperature 60-80 °C) to obtain electrode S12, abbreviated as NiFe-MOF / NF-50:1.

[0114] Electrochemical water evolution and hydrogen evolution tests were performed on the NiFe-MOF / NF-50:1, revealing its optimal bifunctional catalytic performance. For HER, the overpotentials of NiFe-MOF / NF-50:1 driven by a current density of 500 / 1000 mA cm⁻² in 1 M KOH electrolyte were 145 / 155 mV, respectively; for OER, the overpotentials driven by a current density of 500 mA cm⁻² in 1 M KOH electrolyte were 294 mV.

[0115] Example 13

[0116] Ferric nitrate nonahydrate was added to the optimal electrolyte formulation in Example 3, and the Fe:Ni molar ratio was controlled at 1:40 (ferric nitrate nonahydrate concentration 0.00375 mol L⁻¹). The electrolyte was sonicated for 20-30 min to fully dissolve the components, thus obtaining a NiFe bimetallic electrolyte. Two 2.0×2.0 cm² pretreated nickel foam pieces were used as anodes and one 1.0×2.0 cm² pretreated nickel foam piece was used as cathode. The electrodes were immersed in the electrolyte and deposited for 40 min using a constant current method (CC) with a current of 15 mA (corresponding deposition voltage of 3.4V~3.5V). After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol, and then vacuum dried (time 2-3 h, temperature 60-80℃) to obtain electrode S13, abbreviated as NiFe-MOF / NF-40:1.

[0117] Electrochemical water evolution and hydrogen evolution tests were performed on the NiFe-MOF / NF-40:1, revealing its excellent bifunctional catalytic performance. For HER, the overpotentials of NiFe-MOF / NF-40:1 driven by a current density of 500 / 1000 mA cm⁻² in 1 M KOH electrolyte were 165 / 207 mV, respectively; for OER, the overpotentials driven by a current density of 500 mA cm⁻² in 1 M KOH electrolyte were 302 mV, respectively.

[0118] Example 14

[0119] Ferric nitrate nonahydrate was added to the optimal electrolyte formulation in Example 3, and the Fe:Ni molar ratio was controlled at 1:25 (ferric nitrate nonahydrate concentration 0.006 mol L⁻¹). The electrolyte was sonicated for 20-30 min to fully dissolve the components, thus obtaining a NiFe bimetallic electrolyte. Two 2.0×2.0 cm² pretreated nickel foam pieces were used as anodes and one 1.0×2.0 cm² pretreated nickel foam piece was used as cathode. The electrodes were immersed in the electrolyte and deposited for 40 min using a constant current method (CC) with a current of 15 mA (corresponding deposition voltage of 3.4V~3.5V). After electrodeposition, the loaded nickel foam was repeatedly washed with DMF, ultrapure water and ethanol, and then vacuum dried (time 2-3 h, temperature 60-80℃) to obtain electrode S14, abbreviated as NiFe-MOF / NF-25:1.

[0120] Electrochemical water evolution and hydrogen evolution tests were performed on the NiFe-MOF / NF-25:1, revealing its excellent bifunctional catalytic performance. For HER, the overpotentials of NiFe-MOF / NF-25:1 driven by a current density of 500 / 1000 mA cm⁻² in 1 M KOH electrolyte were 231 / 338 mV, respectively; for OER, the overpotentials driven by a current density of 500 mA cm⁻² in 1 M KOH electrolyte were 449 mV.

[0121] Examples 10-14 show the HER and OER activities of the electrodes. Figure 9-10 It can be seen that, according to η 500 -HER and η 1000 -HER, the catalytic performance of these electrodes is ordered as follows: NiFe-MOF / NF-50:1 > NiFe-MOF / NF-75:1 > NiFe-MOF / NF-40:1 > NiFe-MOF / NF-25:1 > NiFe-MOF / NF-100:1; according to η 500 The catalytic performance of -OER is in the following order: NiFe-MOF / NF-50:1>NiFe-MOF / NF-40:1>NiFe-MOF / NF-75:1>NiFe-MOF / NF-100:1>NiFe-MOF / NF-25:1.

[0122] See Figure 11-12 In Examples 10-14, the Tafel slope of the hydrogen evolution reaction at the electrode is as follows: for NiFe-MOF / NF-100:1, it is 190.51 mV dec. -1 The NiFe-MOF / NF-75:1 value is 82.38 mV dec. -1 The NiFe-MOF / NF-50:1 ratio is 61.49 mVdec. -1The NiFe-MOF / NF-40:1 ratio is 131.04 mV dec. -1 The NiFe-MOF / NF-25:1 ratio is 158.49 mV dec. -1 Among them, the Tafel slope of NiFe-MOF / NF-50:1 is the smallest, indicating that it has the highest activity. The Tafel slopes of oxygen evolution at the electrodes are as follows: NiFe-MOF / NF-100:1 is 161.91 mV dec. -1 The NiFe-MOF / NF-75:1 value is 68.75 mV dec. -1 The NiFe-MOF / NF-50:1 ratio is 45.71 mV dec. -1 The NiFe-MOF / NF-40:1 value is 48.57 mV dec. -1 The NiFe-MOF / NF-25:1 value is 225.37 mV dec. -1 Among them, NiFe-MOF / NF-50:1 has the smallest Tafel slope, indicating that it has the best activity.

[0123] In some embodiments, the following experiments were also conducted:

[0124] 1. Based on Example 3, electrodeposition at 10mA, 15mA, and 20mA was tested. The sample deposited at 10mA showed lower uniformity and was more prone to detachment (poor stability) compared to that deposited at 15mA, and the activity test results were not as good as those at 15mA. During deposition at 20mA, the voltage was very high and unstable (>5V and continuously increasing). Due to the excessive voltage, a white-green substance adhered to the Ni-BTC surface of the wafer, which detached during testing and yielded poor results. It was verified that electrodeposition at a constant DC current of 14~16mA for 15~55min yielded a coating with better uniformity and stability (adhesion), and the activity test results were good, with 15mA being the optimal value.

[0125] 2. Based on Example 3, replacing 1,3,5-triphenylcarboxylic acid with terephthalic acid resulted in inferior HER and OER performance compared to trimesolic acid. Replacing it with 2-methylimidazolium resulted in a high deposition voltage (>10V), poor test stability, and poor performance.

[0126] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

Claims

1. A NiFe bimetallic MOF self-supporting bifunctional electrode for water electrolysis, characterized in that, The electrode uses nickel foam as a substrate, and its surface is uniformly coated with NiFe bimetallic MOF. The coating method includes the following steps: Two pieces of pre-cleaned and pre-treated nickel foam were used as anodes and one piece of pre-cleaned and pre-treated nickel foam was used as cathode. They were immersed in the electrolyte and electrodeposited for 15 to 55 minutes under a constant current of 14 to 16 mA DC power supply. The area of ​​the nickel foam anode was larger than that of the cathode. The electrolyte uses N,N-dimethylformamide as a solvent, in which nickel salt, iron salt, 1,3,5-benzenetricarboxylic acid and triethylamine hydrochloride are uniformly dissolved. The molar ratio of Ni to Fe is 40~75:1, and the concentration of triethylamine hydrochloride is 0.01-0.1 mol L⁻¹.

2. The NiFe bimetallic MOF self-supporting bifunctional electrode for water electrolysis according to claim 1, characterized in that, The pretreatment method for cleaning nickel foam includes: cutting nickel foam into 1.0×2.0 cm² and 2.0×2.0 cm² sizes, immersing them sequentially in hydrochloric acid, ultrapure water and ethanol solutions for ultrasonic treatment, and obtaining pretreated nickel foam.

3. The NiFe bimetallic MOF self-supporting bifunctional electrode for water electrolysis according to claim 1, characterized in that, The electrolyte contains a nickel salt concentration of 0.15 mol L⁻¹ and a 1,3,5-benzenetricarboxylic acid concentration of 0.041 mol L⁻¹. And / or, the iron salt is ferric nitrate nonahydrate, and the nickel salt is nickel nitrate hexahydrate; And / or, the molar ratio of Ni to Fe is 40~50:1; And / or, the triethylamine hydrochloride concentration is 0.01 mol L⁻¹ or 0.08~0.1 mol L⁻¹; And / or, electrodeposit for 40~55 minutes under a constant current of 15mA DC power supply.

4. The NiFe bimetallic MOF self-supporting bifunctional electrode for water electrolysis according to claim 1, characterized in that, The electrolyte contains a nickel salt concentration of 0.15 mol L⁻¹ and a 1,3,5-benzenetricarboxylic acid concentration of 0.041 mol L⁻¹. And / or, the molar ratio of Ni to Fe is 50~75:1; And / or, triethylamine hydrochloride concentration 0.01~0.08 mol L⁻¹; And / or, electrodeposit for 25~40 min under a constant current of 15mA DC power supply.

5. The NiFe bimetallic MOF self-supporting bifunctional electrode for water electrolysis according to claim 1, characterized in that, It also includes an electrode post-treatment step: the coated loaded nickel foam is washed repeatedly with N,N-dimethylformamide, ultrapure water and ethanol in sequence, and then dried under vacuum.

6. The NiFe bimetallic MOF self-supporting bifunctional electrode for water electrolysis according to claim 1, characterized in that, The preparation of the electrolyte includes the following steps: dissolving nickel salt, 1,3,5-benzenetricarboxylic acid and triethylamine hydrochloride in N,N-dimethylformamide, placing it in an ultrasonic bath and sonicating for 20-30 min until completely dissolved, with an ultrasonic power of 20-25 W / L; then adding iron salt and continuing to sonicate to fully dissolve the iron salt and mix it evenly with the original components. Alternatively, nickel salt, iron salt, 1,3,5-benzenetricarboxylic acid and triethylamine hydrochloride are dissolved in N,N-dimethylformamide and placed in an ultrasonic bath for 20-30 minutes until completely dissolved, with an ultrasonic power of 20-25 W / L.

7. A method for electrolyzing water, characterized in that, The process includes the following steps: using a three-electrode electrolysis cell reactor, wherein the NiFe bimetallic MOF self-supporting bifunctional electrode for water electrolysis as described in any one of claims 1 to 6 is used as the working electrode.

8. The water electrolysis method according to claim 7, characterized in that: This includes controlling the current density to 500~1000 mA cm⁻¹ under alkaline conditions. -2 .

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