Preparation method of nickel metal organic framework for electrocatalysis SOR-assisted water electrolysis hydrogen production

Abstract

The invention discloses a preparation method of a nickel metal organic framework for electro-catalysis SOR assisted water electrolysis hydrogen production, and belongs to the field of electro-catalysis hydrogen evolution, the method comprises the following steps: S1, dissolving Ni (NO) 2.6 H2O and terephthalic acid in N, N-dimethylformamide, ethanol and deionized water, and carrying out ultrasonic treatment on the mixture to obtain a uniform solution; s2, foamed nickel is put into the uniform solution and subjected to ultrasonic treatment to ensure that the foamed nickel is completely immersed; s3, transferring the mixture into a teflon-lined stainless steel high-pressure kettle for heating reaction; and cooling, taking out a sample, washing with deionized water, and drying to obtain the foamed nickel supported thin vertically-oriented nanosheet array-shaped nickel metal organic framework, thereby solving the problems of low conductivity and low activity and stability of the catalyst in the prior art.

Description

Technical Field

[0001] The present invention relates to the field of electrocatalytic hydrogen evolution, and specifically to a preparation method of nickel metal-organic framework for electrocatalytic SOR-assisted electrolytic water hydrogen production. Background Art

[0002] With the increasing global emphasis on environmental protection and sustainable development, new energy is playing an increasingly important role in the transformation of the global energy structure towards a cleaner, renewable, and low-carbon emission one. Hydrogen energy has become a key area of research due to its wide availability, high energy density, zero emissions, and strong sustainability. However, a significant drawback of contemporary hydrogen production technologies (especially grey hydrogen and blue hydrogen) is the large amount of greenhouse gas emissions, which has led to an exacerbation of environmental pollution problems. Therefore, finding a low-cost and pollution-free hydrogen production method is crucial for the industrialization of hydrogen energy. Electrolytic water hydrogen production is a clean and sustainable method that can produce high-purity hydrogen. This method can decompose water into hydrogen and oxygen by using electricity. In addition, it can also utilize intermittent energy sources such as wind energy, tidal energy, and solar energy to provide the required electrical energy to achieve zero-carbon emission hydrogen production. However, electrolytic water hydrogen production involves two half-reactions: the oxidation reaction at the anode and the reduction reaction at the cathode. These two half-reactions work together to decompose water into hydrogen and oxygen. Among them, the anodic oxygen evolution reaction (OER) is a four-electron transfer process that requires water molecules to overcome a considerable thermodynamic potential to be oxidized. This limitation significantly hinders the large-scale application of electrolytic water hydrogen production.

[0003] The sulfur ion oxidation reaction (SOR) is thermodynamically more favorable than the oxygen evolution reaction (OER) of water. Specifically, the theoretical total potential of sulfur ion oxidation (-0.48 V vs. SHE, pH = 14) is significantly lower than the total potential of water electrolysis (1.23 V vs. SHE, pH = 14), which means that under the same conditions, SOR is easier to proceed than OER. Therefore, replacing the anodic OER with SOR is an effective way to reduce the energy consumption of water electrolysis hydrogen production. In addition, coupling SOR with the hydrogen evolution reaction (HER) at the cathode to form a two-electrode system (HER-SOR) is not only beneficial for low-energy-consumption hydrogen production but also enables the recovery of sulfur sources without additional catalysts, thus enhancing environmental remediation efforts.

[0004] However, sulfur species have a strong poisoning effect on metal electrocatalysts, which will significantly reduce the activity and stability of the catalysts, thus posing a major challenge to industrial applications. Therefore, designing high-performance SOR electrocatalysts that can effectively degrade pollutants while achieving low-energy-consumption hydrogen production remains a major challenge.

[0005] Metal-Organic Frameworks (MOFs) are a class of porous materials formed by the self-assembly of metal ions and organic ligands. MOFs have the characteristics of adjustable structure, large specific surface area, and high porosity, and can provide a large number of active sites. However, since most coordination polymers are non-conductive, the MOF structure lacks effective electron transport ability. Summary of the Invention

[0006] The present invention provides a preparation method of nickel metal-organic framework for electrocatalytic SOR-assisted electrolytic water hydrogen production, which solves the problems of low conductivity, low activity and stability of the catalyst existing in the prior art.

[0007] To solve this technical problem, the present invention provides the following technical solutions:

[0008] A preparation method of nickel metal-organic framework for electrocatalytic SOR-assisted electrolytic water hydrogen production, comprising the following steps:

[0009] S1. Dissolve Ni(NO)2·6H2O and terephthalic acid in N,N-dimethylformamide, ethanol and deionized water, and ultrasonically treat the mixture to obtain a homogeneous solution;

[0010] S2. Put nickel foam into the homogeneous solution and ultrasonically treat it to ensure complete immersion;

[0011] S3. Transfer the mixture to a Teflon-lined stainless steel autoclave for heating reaction; after cooling, take out the sample, wash it with deionized water, and dry it to obtain a nickel metal-organic framework in the form of a foam nickel-supported thin vertical-oriented nanosheet array.

[0012] Preferably, the concentration of Ni(NO)3·6H2O in the solution of step S1 is 0.033 mol / L; the concentration of terephthalic acid is 0.046 mol / L.

[0013] Preferably, the volume ratio of N,N-dimethylformamide, ethanol and deionized water in step S1 is 4:1:1.

[0014] Preferably, the ultrasonic treatment time in steps S1 and S2 is 30 minutes.

[0015] Preferably, the heating temperature in step S3 is 120 °C and the heating time is 4 hours.

[0016] Preferably, the drying temperature in step S3 is 80 °C and the drying time is 12 hours.

[0017] The nanosheet array-shaped nickel metal-organic framework prepared by the above preparation method of the nanosheet array-shaped nickel metal-organic framework.

[0018] The nickel-based metal-organic framework (Ni-MOF) nanosheets were successfully and uniformly deposited onto the nickel foam (NF) substrate using a one-step hydrothermal method. The ultrathin MOF nanosheets exhibit uniformly high-density Ni centers in their framework structure, which can serve as active catalytic sites and enhance electrical conductivity. This increases the number of surface-bound catalytic sites for SOR. More importantly, by successfully forming a three-dimensional electrode (Ni-PTA / NF) on the nickel foam substrate, the contact area between the catalyst and the reactants is increased, thus effectively enhancing the electrochemistry activity.

[0019] This solution also provides a system for electrocatalytic SOR-assisted electrolytic water hydrogen production, including a cathode electrolyte, an anode electrolyte, and a cation exchange membrane. The cation exchange membrane separates the anode mass and the cathode mass. An anode catalytic electrode and a cathode catalytic electrode are respectively provided in the anode electrolyte and the cathode electrolyte. The anode catalytic electrode is the nanosheet array-like nickel metal-organic framework prepared by the above method or the above-mentioned nanosheet array-like nickel metal-organic framework.

[0020] Preferably, the cathode electrolyte is a 0.5M H2SO4 solution, and the anode electrolyte is a 1M NaOH solution containing 1M Na2S.

[0021] Preferably, the cathode catalytic electrode is Pt-C / CP.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] Through a one-step hydrothermal synthesis method, a thin vertically oriented nanosheet array-like nickel metal-organic framework (Ni-PTA / NF) supported by nickel foam was successfully prepared and used as a pre-catalyst for the anodic alternative reaction of electrolytic water - the sulfur ion oxidation reaction (SOR). The unique vertical nanosheet structure endows the catalyst with excellent electrochemistry activity. In addition, introducing S element during the SOR process significantly accelerates the reaction kinetics of SOR, thus achieving high catalytic activity. The Ni-PTA / NF catalyst only requires an extremely low potential of 0.344V vs. RHE at a current density of 50mA cm -2 and has strong catalytic stability within 48 hours.

[0024] The main reason for the excellent electrocatalytic activity of Ni-PTA / NF is its characteristics of adjustable structure, large specific surface area, and high porosity, which can expose a large number of active sites. And during the sulfur ion oxidation reaction (SOR), the MOF structure makes it easier for Ni-PTA / NF to transform into a Ni-PTA-S / NF catalyst with a porous structure, further increasing the electrochemistry active area, active sites, and intrinsic activity. Description of the Drawings

[0025] The accompanying drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0026] Figure 1 are the SEM image and TEM image of the sample;

[0027] Figure 2 is the XRD pattern of the sample;

[0028] Figure 3 is the XPS spectrum of Ni-PTA / NF;

[0029] Figure 4 is the XPS spectrum of Ni-O / NF;

[0030] Figure 5 is the XPS spectrum of NF;

[0031] Figure 6 are the polarization curves of different catalysts and the corresponding Tafel slopes, potential comparisons, and electrochemical impedance spectra;

[0032] Figure 7 are the CV curves of different catalysts and the linear fitting graph for evaluating C dl versus the scan rate;

[0033] Figure 8 are the CV curves of the catalysts after the sulfur oxidation reaction and the linear fitting graph for evaluating C dl versus the scan rate;

[0034] Figure 9 are the polarization current density and stability test graphs normalized to the electrochemically active area and loading;

[0035] Figure 10 are the polarization curves, potential, ultraviolet-visible spectrum of the electrolyte sample, and XRD pattern of the product;

[0036] Figure 11 are the XRD patterns of Ni-PTA / NF, Ni-O / NF, and NF after SOR;

[0037] Figure 12 are the SEM image and TEM image of the sample after the SOR process;

[0038] Figure 13 is the XPS spectrum of Ni-PTA / NF after the SOR process;

[0039] Figure 14 is the XPS spectrum of Ni-O / NF after the sulfidation process;

[0040] Figure 15XPS spectrum of NF after the vulcanization process;

[0041] Figure 16 Polarization curves for two - electrode tests of different electrolyte combinations and the energy consumption required to produce 1 kg of hydrogen. Detailed implementation manners

[0042] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. The illustrative implementation manners of the present invention and their descriptions are only used to explain the present invention and do not serve as a limitation to the present invention.

[0043] Example 1

[0044] Immerse 0.5 cm × 3 cm nickel foam (NF) in 1 M HCl and ultrasonically treat it for 15 minutes while continuously stirring with a glass rod. Subsequently, wash the nickel foam several times with deionized water and ethanol and dry it for subsequent use. Dissolve Ni(NO)2·6H2O (0.29 g) and terephthalic acid (0.23 g) in 20 mL of N,N - dimethylformamide, 5 mL of ethanol and 5 mL of deionized water, and ultrasonically treat the mixture for 30 minutes to obtain a homogeneous solution. Place the pickled nickel foam into the homogeneous solution and perform ultrasonic treatment to ensure its complete immersion. Subsequently, transfer the mixture to a 50 ml Teflon - lined stainless - steel autoclave and heat it at 120 °C for 4 hours. After cooling, take out the sample, wash it several times with deionized water, and dry it at 80 °C for 12 hours to obtain a nickel metal - organic framework Ni - PTA / NF in the form of a thin vertically - oriented nanosheet array supported by nickel foam. The mass loading of Ni - PTA / NF is 8.8 mg cm -2 。

[0045] Comparative Example 1

[0046] The difference between this comparative example and Example 1 is that the synthesis of Ni - O / NF follows the same procedure, except that terephthalic acid is replaced by urea (0.30 g) and ammonium fluoride (0.09 g), and dissolved in 30 ml of deionized water; the mass loading of Ni - O / NF is 2.8 mg cm -2 。

[0047] Example 2

[0048] Electrochemical tests were carried out on an Autolab 128N (Switzerland) workstation using a three-electrode system: nickel foam, the catalysts prepared in Example 1 and Comparative Example 1 were used as the working electrode, a graphite rod was used as the counter electrode, and the reference electrode was selected as Hg / HgO (in alkaline electrolyte) or Ag / AgCl (in acidic electrolyte) according to the different electrolytes. All the potential values of the tests were converted to relative to the reversible hydrogen electrode (RHE). Linear sweep voltammetry (LSV) was carried out in an electrolyte containing (SOR reaction) and without (OER reaction) 1 mol L -1 Na2S in 1 mol L -1 NaOH at a scan rate of 0.01 V s -1 .

[0049] Cyclic voltammetry (CV) was carried out in an acetonitrile solution containing 0.15 mol L -1 potassium hexafluorophosphate at scan rates of 10, 20, 50, 100, and 150 mV s -1 respectively. Chronopotentiometry was used to evaluate the stability of the catalyst in a 1 M KOH electrolyte solution containing 1 mol L -1 Na2S.

[0050] In a mixed electrolyte of 1 mol L -1 Na2S and 1 mol L -1 NaOH, the electrochemical impedance spectroscopy (EIS) was tested at a potential of 0.27 V vs. RHE in the frequency range of 0.01 Hz - 100000 Hz.

[0051] Example 3

[0052] A two-electrode system was constructed using Ni-PTA / NF as the anode and Pt-C / CP as the cathode, and polarization curves were measured under four different electrolytes. Among them, Electrolyte 1: Anode electrolyte: 1 M NaOH solution containing 1 M Na2S; Cathode electrolyte: 0.5 M H2SO4 solution, HER (pH = 0) + SOR (pH = 14); Electrolyte 2: 1 M NaOH (anode) || 1 M NaOH (cathode), HER (pH = 14) + OER (pH = 14);

[0053] Electrolyte 3: 1 M NaOH + 1 M NaOH containing 1 M Na2S (anode) || 1 M NaOH (cathode), HER (pH = 14) + SOR (pH = 14);

[0054] Electrolyte 4 for the asymmetric acid-base coupled electrolytic cell: 0.5 M H2SO4 (cathode) || 1 M NaOH (anode), HER (pH = 0) + OER (pH = 14);

[0055] The preparation method of Pt-C / CP is as follows: 4 mg Pt / C (20%) was weighed into a centrifuge tube, and then 375 μL deionized water, 125 μL isopropanol and 20 μL Nafion were added. Then, the mixture was ultrasonicated for 30 minutes to obtain an ink-like solution. Next, 100 μL of the ink-like solution was carefully dropped onto carbon paper, and the sample was allowed to dry naturally at room temperature. The resulting electrode is called Pt-C / CP. The electrolyte is a 1M NaOH solution containing 1M Na2S.

[0056] Example 4

[0057] A three-electrode system was established using nickel foam, the catalysts prepared in Example 1 and Comparative Example 1 as working electrodes, a graphite rod as a counter electrode, and Hg / HgO as a reference electrode. All potential values ​​tested were converted to relative to a reversible hydrogen electrode (RHE). Linear sweep voltammetry was performed under the three-electrode system in a solution containing 1 mol L -1 1 mol L of Na2S -1 In NaOH, 10 mV s -1 The SOR was performed at a rate of 4 times from -1 V to 0 V vs. Hg / HgO. The Ni-PTA / NF, Ni-O / NF and nickel foam after SOR were recorded as Ni-PTA-S / NF, Ni-OS / NF and S / NF electrodes, respectively.

[0058] The composition and crystal structure of the catalytic material were characterized using an X-ray diffractometer. The microstructure was characterized using scanning electron microscopy and transmission electron microscopy. The elemental valence and composition of the catalyst were analyzed using an X-ray photoelectron spectrometer.

[0059] Example 1 A thin vertically oriented nanosheet array nickel metal organic framework (Ni-PTA / NF) supported by nickel foam was successfully prepared by a simple one-step hydrothermal synthesis method, and the surface morphology of the Ni-PTA / NF catalyst was studied in detail by scanning electron microscopy (SEM). Figure 1 The SEM image of Ni-PTA / NF shows that vertically aligned nanosheet arrays (Ni-MOF) are successfully grown on a nickel foam substrate (NF). This unique three-dimensional structure not only provides a large surface area, but also ensures excellent conductivity and efficient material transport, which is crucial to improving the electrochemical performance of the catalyst. Figure 1 b is the SEM image of Ni-O / NF, from which it can be seen that many nanosheets are loaded on NF in a crisscross manner. Figure 1 Figure c is the SEM image of NF. It can be seen that there are not too many impurities on the NF and the surface is smooth and flat. Figure 1Figure d is the TEM image of Ni-PTA / NF. As can be seen from the scales of 100 nm and 20 nm, thin nanosheets are attached to nickel foam, corresponding to the SEM image of Ni-PTA / NF.

[0060] It can be seen from Figure 2 that Ni-PTA / NF and Ni-O / NF show characteristic peaks at 44.508°, 51.847° and 76.372°, corresponding to the (111), (200) and (220) crystal planes of NF (PDF#00-004-0850). In addition, other weak diffraction peaks observed in Ni-PTA / NF can be attributed to the simulated spectrum (CCDC No. 638866), and its structural formula is Ni3(OH)2(C8H4O4)2(H2O)4·2H2O. This indicates that the Ni-PTA / NF sample contains a nickel-based metal-organic framework (MOF) phase, endowing it with a unique crystal structure. At the same time, the diffraction peaks appearing at 19.217°, 33.571° and 38.969° in Ni-O / NF correspond to Ni(OH)2 (PDF#01-073-6992).

[0061] As Figure 3 shown in a of 3 / 2 , the full-scan XPS spectrum of Ni-PTA / NF shows obvious peaks attributed to C, O and Ni, indicating that these elements are indeed present on the surface of the catalyst. The high-resolution Ni 2p 3 / 2 XPS spectrum of Ni-PTA / NF ( Figure 3 b) shows two prominent peaks with binding energies of 856.11 eV and 861.75 eV respectively. The peak at 856.11 eV corresponds to the Ni 2+ species, while the peak at 861.75 eV is attributed to the satellite peak. At the same time, for Ni-PTA / NF ( Figure 3 c), the O 1s XPS spectrum shows multiple peaks. Specifically, the peaks at 531.27 eV and 532.0 eV are attributed to the oxygen species in the -O-H and C-O groups respectively. In addition, the peaks at 530.58 eV and 533.15 eV correspond to the metal-oxygen bond and the oxygen species in adsorbed water respectively. Similarly, the full-scan XPS spectra of Ni-O / NF ( Figure 4 a) and NF ( Figure 5 a) also show the elements C, O and Ni. In addition, the Ni 2p Figure 4 XPS spectra of Ni-O / NF ( Figure 5 b) and NF ( Figure 5 b) also show the characteristics of Ni 3 / 2 and the satellite peak at approximately 856.11 eV and 861.75 eV. It should be noted that in addition to Ni 2+ 2+In addition, NF also shows a peak at 852.54 eV, attributed to the presence of Ni 0 . Finally, the O1s XPS spectra of Ni-O / NF ( Figure 4 c) and NF ( Figure 5 c) show the same peaks as those of Ni-PTA / NF.

[0062] The electrocatalytic performance of the SOR was evaluated by a three-electrode system in a 1.0 M NaOH solution containing 1.0 M Na2S. As Figure 6 a shows, the polarization curves clearly show that Ni-PTA / NF is significantly superior to Ni-O / NF and NF, showing excellent SOR catalytic activity. In addition, the Tafel slope values of Ni-PTA / NF, Ni-O / NF, and NF are 117 mV dec -1 , 192 mV dec -1 , and 201 mV dec -1 ( Figure 6 b). The smaller Tafel slope indicates that Ni-PTA / NF can increase the current density faster with a smaller potential change. In other words, for the same voltage increment, Ni-PTA / NF can achieve a greater increase in current density, highlighting its efficient catalytic performance. As Figure 6 c shows, Ni-PTA / NF only requires a low potential of 0.344 V vs. RHE to reach a current density of 50 mA cm -2 , which is much lower than the potentials required for Ni-O / NF (0.591 V vs. RHE) and NF (0.666 V vs. RHE). In addition, Figure 6 d shows the electrochemical impedance spectroscopy (EIS) data. The Nyquist plot shows that Ni-PTA / NF has the smallest semicircle, indicating that its interfacial charge transfer resistance is significantly lower than that of Ni-O / NF and NF. This property promotes the transport and separation of carriers, thus enhancing the overall electrochemical performance and stability of the catalyst.

[0063] There is a linear relationship between the electrochemically active surface area (ECSA) and the double-layer capacitance (C dl ). Figure 7 And Figure 8 show the results of determining the double-layer capacitance (C dl ) by cyclic voltammetry (CV) measurements outside the Faraday region. Table 1 shows that the double-layer capacitances (C dl ) of Ni-PTA / NF, Ni-O / NF, and NF are 1.97 mF cm -2 , 0.58 mF cm -2 , and 0.39 mF cm -2, these values are significantly lower than those of Ni-PTA-S / NF (13.46 mF cm -2 ), Ni-O-S / NF (0.92 mF cm -2 ), and NF-S (0.58 mF cm -2 ). This finding indicates that during the sulfur ion oxidation reaction (SOR), the introduction of sulfur increases C dl , thus increasing the ECSA. In addition, the electrochemically active specific surface area of Ni-PTA / NF is always superior to that of Ni-O / NF and NF. This result shows that Ni-PTA / NF has more available active sites, which is beneficial to the improvement of electrochemistry activity.

[0064] Table 1

[0065] Catalyst <![CDATA[Double-layer capacitance (mFcm -2 )]]> <![CDATA[Electrochemically active surface area (cm -2 )]]> Ni-PTA / NF 1.97 49.25 Ni-O / NF 0.58 14.5 NF 0.39 9.75 Ni-PTA-S / NF 13.46 336.5 Ni-O-S / NF 0.92 23 S / NF 0.57 14.25

[0066] ECSA can reflect the actual exposed area of the catalytic electrode in the electrolyte. Therefore, compared with the current density normalized to the geometric area (GA), normalizing the current density to the ECSA can more accurately express the intrinsic activity of the catalytic electrode. In addition, the normalization analysis based on the mass loading is also an effective means to measure the intrinsic activity and utilization rate of the active substance. To gain a deeper understanding of the influence of the MOF structure in Ni-PTA / NF on the intrinsic catalytic performance of SOR, the current density is further normalized to the ECSA and the mass loading respectively. As shown in Figure 9 a and Figure 9 b, the current density of Ni-PTA / NF based on different normalization requirements (including ECSA and mass loading) is higher than that of other catalytic electrodes at the same potential, indicating that Ni-PTA / NF has the highest intrinsic catalytic performance. Stability is one of the key parameters for evaluating the performance of SOR catalysts and directly affects its feasibility and competitiveness in practical applications. Under the conditions of 1 M KOH and 1 M Na2S as the electrolyte, the stability test of the Ni-PTA / NF catalyst was carried out at a constant current density of 100 mA cm -2 , and the test results are shown in Figure 9 c. During the 48-hour stability test, the potential of Ni-PTA / NF increased by only 0.018 V. This extremely small potential change demonstrates the excellent stability of Ni-PTA / NF.

[0067] To evaluate the electrocatalytic performance of sulfur oxidation reduction (SOR) and oxygen evolution reaction (OER), we conducted polarization curve tests in 1 M NaOH solution with or without 1 M Na2S ( Figure 10 a). Ni-PTA / NF reached 200 mA cm during the SOR process -2It only requires a low potential of 0.366 V vs. RHE for the current density of, while a potential of 1.325 V vs. RHE is needed during the OER process to reach the same current density. Figure 10 Figure b is intended to visually show the potential difference between OER and SOR at the same current density. Whether it is 200 mA cm -2 or 400 mA cm -2 of current density, the potential corresponding to OER is always higher than that of SOR. These results indicate that replacing OER with SOR can reduce energy consumption. To clarify the reaction process of SOR, we conducted a constant current test at a current density of 100 mA cm -2 and identified the products generated during the reaction in the electrolyte by ultraviolet-visible spectroscopy. After the reaction proceeded for 36 hours, the electrolyte showed a dark yellow color ( Figure 10 the inset in Figure c), which indicates that the concentration of polysulfides gradually increased with the prolongation of the reaction time. As shown in Figure 10 Figure c, the peak observed at 297 nm corresponds to the presence of chain-like polysulfides (S2 2- -S n 2- ) in the electrolyte. After the reaction for 36 hours, the signal intensity of polysulfides increased significantly, indicating that soluble polysulfides transformed from shorter chains to longer chains. After the reaction was completed, the pH of the electrolyte was adjusted by adding sulfuric acid to form a yellow powder. Subsequently, X-ray diffraction (XRD) analysis confirmed that this powder was composed of elemental sulfur ( Figure 10 Figure d). These results show that the Ni-PTA / NF catalytic electrode can not only efficiently oxidize sulfide ions but also extract sulfur from the electrolyte after the reaction, thus contributing to environmental protection.

[0068] To comprehensively understand the reason for the improvement of catalytic performance, we conducted a detailed analysis of the morphology and composition of the Ni-PTA / NF, Ni-O / NF, and NF samples after sulfidation treatment (SOR). As Figure 11 shown, the XRD pattern shows that only Ni-PTA-S / NF shows peaks corresponding to Ni X S6 (PDF#00-051-0718). The peaks in the Ni-O-S / NF sample can be attributed to Ni(OH)2 (PDF#01-073-6992). In addition, the S / NF material only shows peaks related to nickel foam.

[0069] From Figure 12The SEM image of a in [reference] shows that after the sulfidation process, the surface of Ni-PTA / NF exhibits a porous structure, which is conducive to the exposure of active sites in the electrolyte, thus improving the electrochemical performance. Through the above analysis, it can be seen that the sulfidation treatment has a significant impact on the structure and composition of the Ni-PTA / NF sample, thereby enhancing its catalytic performance. After the sulfidation process, the SEM images of Ni-O / NF( Figure 12 in b) and NF( Figure 12 in c) show no obvious changes compared with the SEM image of the non-sulfidated sample( Figure 1 ), indicating that the MOF structure helps in the generation of active sites and the increase of the electrochemically active specific surface area during the sulfidation process, thereby enhancing the catalytic performance. From the TEM image of Ni-PTA / NF after sulfidation in Figure 12 d), it can be seen that part of the MOF structure is in-situ transformed into amorphous materials during the sulfidation process, further increasing the exposure of active sites and being beneficial to the improvement of electrochemical performance.

[0070] From the full X-ray photoelectron spectroscopy (XPS) spectrum, it can be known that after SOR, S is successfully introduced into Ni-PTA / NF, Ni-O / NF and NF( Figure 13 in a, Figure 14 in a and Figure 15 in a). The Ni 2p 3 / 2 XPS spectrum shows( Figure 13 in b, Figure 14 in b and Figure 15 in b) that for Ni-PTA / NF after SOR treatment, the two chemical states correspond to Ni at 855.59 eV 2+ and Ni at 856.84 eV 3+ , and the satellite peak is at 861.42 eV. The valence state of nickel changes from divalent to trivalent, indicating that nickel undergoes electron transfer during the SOR process. As is well known, Ni 3+ acts as an effective active center for enhancing electrochemical performance. In addition, the increase in the Ni 3+ / Ni 2+ ratio in Ni-PTA / NF can lead to enhanced electron-electron interactions, thereby promoting electron transfer and improving electrochemical performance. As shown in Table 2, the content of trivalent nickel atoms in Ni-PTA / NF after SOR treatment is 54%, higher than that of Ni-O / NF (48.81%) and NF (37.33%). These findings indicate that there are more effective active centers in Ni-PTA / NF than in Ni-O / NF and NF, resulting in better electrochemical performance of Ni-PTA / NF than Ni-O / NF and NF. The S2p XPS spectrum of Ni-PTA / NF after SOR treatment( Figure 13d) reveals a peak at 168.5 eV corresponding to sulfur oxides, while the peaks at 163.3 eV and 162.2 eV are attributed to sulfide species. Meanwhile, the S2p XPS spectra of Ni-O / NF and NF after SOR treatment show similar peaks at 168.5 eV, 163.3 eV, and 162.2 eV( Figure 14 d, Figure 15 d). In addition, the peak positions in the O1s XPS spectra of Ni-PTA / NF, Ni-O / NF, and NF after SOR treatment remain unchanged( Figure 13 c, Figure 14 c and Figure 15 c).

[0071] Table 2

[0072]

[0073] To study the actual energy consumption in hydrogen production, we assembled an asymmetric acid-base coupled electrolyzer with a cation exchange membrane. The anode was made of Ni-PTA / NF, and the electrolyte was 1 M NaOH solution containing 1 M Na2S. The cathode was composed of Pt-C / CP, and the electrolyte was 0.5 M H2SO4 catalyst solution. As Figure 16 a shows, the actual energy consumption of hydrogen production under different electrolyte systems was compared. The traditional alkaline overall water splitting electrolyzer (1 M NaOH||1 M NaOH) needed to apply a voltage as high as 1.662 V to achieve a current density of 100 mA cm -2 . When the anode solution (1 M NaOH) in the electrolyzer was replaced with 1 M NaOH electrolyte containing 1 M Na2S, a current density of 100 mA cm -2 could be achieved at a voltage of only 0.479 V, which was 1.183 V lower than the traditional overall hydrolysis voltage. It is worth noting that the asymmetric acid-base coupled electrolyzer composed of 0.5 M H2SO4 cathode solution and 1 M NaOH anode solution containing 1 M Na2S could also reach a current density of 100 mA cm -2 at a voltage of only -0.064 V. This voltage was significantly lower than the 0.874 V of the traditional asymmetric acid-base coupled electrolyzer (0.5 M H2SO4||1 M NaOH). In addition, at 100 mA cm -2At a current density of, the voltage of this asymmetric acid-base coupled electrolyzer is generally lower than that of the corresponding alkaline electrolyzer, indicating that the pH gradient between the cathode and the anode provides additional electrochemical neutralization energy for the electrolyzer, thus promoting water decomposition. Notably, the voltage of -0.064 V is lower than 0 V, indicating that hydrogen can be produced through the asymmetric acid-base coupled electrolyzer without additional electrical energy. In addition, the energy consumption required to produce 1 kg of hydrogen in different coupling systems was further analyzed ( Figure 16 b) of. At a current density of 100 mA cm -2 the electrical energy required to produce 1 kg of hydrogen by the SOR-based asymmetric acid-base electrolyzer is -1.701 kW·h. In contrast, 23.235 kW·h, 12.734 kW·h, and 44.184 kW·h of electrical energy are required by the acid-base electrolyzer, the SOR-based alkaline electrolyzer, and the traditional alkaline electrolyzer, respectively, to produce 1 kg of hydrogen. This indicates that the SOR-based asymmetric acid-base electrolyzer requires the lowest electrical energy to produce 1 kg of hydrogen.

[0074] In summary, through a one-step hydrothermal synthesis method, a thin vertical-oriented nanosheet array-like nickel metal-organic framework (Ni-PTA / NF) supported by nickel foam was successfully prepared and used as a pre-catalyst for the alternative reaction of water electrolysis anode - sulfur ion oxidation reaction (SOR). The Ni-PTA / NF catalyst requires only an extremely low potential of 0.344 V vs. RHE at a current density of 50 mA cm -2 and has strong catalytic stability within 48 hours. According to the analysis results of the physical and electrochemical properties of the catalyst, the main reason for the excellent electrocatalytic activity of Ni-PTA / NF is its characteristics of adjustable structure, large specific surface area, and high porosity, which can expose a large number of active sites. During the sulfur ion oxidation reaction (SOR), the MOF structure makes it easier for Ni-PTA / NF to transform into a Ni-PTA-S / NF catalyst with a porous structure, further increasing the electrochemically active area, active sites, and intrinsic activity. By designing the MOF structure and exploring the mechanism of in-situ surface transformation during the SOR process, this solution provides new insights into the preparation of highly efficient SOR catalysts and constructs an advanced hydrogen production coupling system, providing certain reference significance for the rapid development of hydrogen energy.

[0075] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. Preparation method of nickel metal-organic framework for electrocatalytic SOR-assisted electrolytic water hydrogen production, characterized in that, It includes the following steps: S1. Dissolve Ni(NO)2·6H2O and terephthalic acid in N,N-dimethylformamide, ethanol and deionized water, and ultrasonically treat the mixture to obtain a homogeneous solution; S2. Put nickel foam into the homogeneous solution and ultrasonically treat it to ensure complete immersion; S3. Transfer the mixture to a Teflon-lined stainless steel autoclave for heating reaction; After cooling, take out the sample, wash it with deionized water, and dry it to obtain a nickel metal-organic framework for electrocatalytic SOR-assisted electrolytic water hydrogen production.

2. The preparation method of the nickel metal-organic framework for electrocatalytic SOR-assisted electrolytic water hydrogen production according to claim 1, characterized in that, In the solution of step S1, the concentration of Ni(NO)3·6H2O is 0.033 mol / L; the concentration of terephthalic acid is 0.046 mol / L.

3. The preparation method of the nickel metal-organic framework for electrocatalytic SOR-assisted electrolytic water hydrogen production according to claim 1, wherein, In step S1, the volume ratio of N,N-dimethylformamide, ethanol and deionized water is 4:1:

1.

4. The preparation method of the nickel metal-organic framework for electrocatalytic SOR-assisted electrolytic water hydrogen production according to claim 1, characterized in that, The ultrasonic treatment time in steps S1 and S2 is 30 minutes.

5. The preparation method of the nickel metal-organic framework for electrocatalytic SOR-assisted electrolytic water hydrogen production according to claim 1, characterized in that, In step S3, the heating temperature is 120 °C and the heating time is 4 hours.

6. The preparation method of the nickel metal-organic framework for electrocatalytic SOR-assisted electrolytic water hydrogen production according to claim 1, characterized in that, In step S3, the drying temperature is 80 °C and the drying time is 12 hours.

7. The nickel metal-organic framework prepared by the preparation method of the nickel metal-organic framework for electrocatalytic SOR-assisted electrolytic water hydrogen production according to any one of claims 1-6.

8. A system for electrocatalytic SOR-assisted electrolytic water hydrogen production, characterized in that, It includes a cathode electrolyte, an anode electrolyte and a cation exchange membrane. The cation exchange membrane separates the anode mass and the cathode mass. An anode catalytic electrode and a cathode catalytic electrode are respectively provided in the anode electrolyte and the cathode electrolyte. The anode catalytic electrode uses the nickel metal-organic framework prepared by the method according to any one of claims 1-6 or the nickel metal-organic framework according to claim 7.

9. The system for electrocatalytic SOR-assisted electrolytic water hydrogen production according to claim 8, wherein The cathode electrolyte is a 0.5 M H2SO4 solution, and the anode electrolyte is a 1 M NaOH solution containing 1 M Na2S.

10. The system for electrocatalytic SOR-assisted electrolytic hydrogen production according to claim 8, wherein The cathode catalytic electrode is Pt-C / CP.

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