A MOOH-MOF / BNF electrode, a preparation method and application thereof in electrocatalytic water decomposition oxygen evolution reaction

Abstract

The application belongs to the technical field of electrocatalytic water decomposition, and particularly relates to a MOOH-MOF / BNF electrode and a preparation method and application thereof. The application aims to solve the problems of insufficient activity and poor stability of an oxygen evolution reaction (OER) catalyst in the prior art. The MOOH-MOF / BNF electrode is prepared by a synthesis strategy of "room-temperature deposition-solvothermal-electrochemical activation". The electrode has a three-dimensional network structure with nanosheets as a skeleton and nanoneedles as branches, and the surface is uniformly composed of Ni, Co, Fe, C, N, O and B elements. Ni3(BO3)2 is introduced as an "interface bonding enhancer" in the application, a "chemical rivet" is formed through strong Ni-O-B bonding, and the catalytic layer is firmly anchored. The overpotential of the electrode is only 207 mV at a current density of 10 mA·cm-2, the Tafel slope is 66.4 mV dec-1, and the potential remains stable after continuous operation for 500 hours at a large current of 100 mA·cm-2, which shows excellent catalytic activity and long-term durability, and is suitable for electrocatalytic water decomposition for the oxygen evolution reaction under alkaline conditions.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic water splitting technology, specifically relating to a method for preparing a MOOH-MOF / BNF electrode and its application in the electrocatalytic water desorption oxygen reaction under alkaline conditions. Background Technology

[0002] With the continued growth of global energy demand and the increasing environmental challenges posed by fossil fuel consumption, developing clean and renewable energy alternatives has become a key research focus. Hydrogen energy, with its high energy density and zero carbon emissions, is considered an ideal future energy source. Among these technologies, water electrolysis utilizes electricity generated from intermittent renewable energy sources such as solar and wind power to decompose water into high-purity hydrogen and oxygen, achieving efficient conversion from renewable energy to green fuels—a promising green hydrogen production route. However, the large-scale application of water electrolysis is limited by the oxygen evolution reaction (OER) at the anolyte—a complex process involving four electron transfers. Its slow kinetics and high theoretical overpotential form the main energy barrier for water decomposition. Currently, the best-performing OER electrocatalysts still rely on precious metal materials (such as IrO2 and RuO2), but their high cost and limited reserves restrict widespread application. Therefore, developing highly active, stable, and low-cost non-precious metal OER electrocatalysts is crucial for advancing water electrolysis technology.

[0003] Metal-organic frameworks (MOFs) exhibit significant advantages in constructing self-supporting electrodes due to their high specific surface area, tunable pore structure, and well-defined active sites. However, in catalytic processes such as the oxygen evolution reaction (OER), the MOF surface often undergoes electrochemical self-reconstruction, transforming in situ into highly active amorphous hydroxyl oxides (such as M-OOH). While this reconstruction optimizes intrinsic activity, it can also lead to the exfoliation of the active layer, severely limiting the long-term operational stability of the electrode.

[0004] Therefore, how to enhance the interfacial bonding strength and charge transport capability by reasonably modifying the substrate interface or active layer is a key challenge in constructing MOF-based self-supporting electrodes that combine high activity and high durability. Summary of the Invention

[0005] In view of the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide a high-performance, high-stability electrocatalytic electrode, the electrode material of which exhibits excellent catalytic activity and outstanding long-range durability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A MOOH-MOF / BNF electrode material is disclosed, which is synthesized using a "room temperature deposition-solvothermal-electrochemical activation" strategy. The MOOH-MOF in the electrode possesses a three-dimensional network structure with nanosheets of 5-7 μm diameter as the framework and nanoneedles of 3-5 μm length as branches. The nanosheets are vertically grown in an array on a boron-modified nickel foam substrate, interwoven to form an open porous network. The MOOH-MOF on the electrode surface is composed of Ni, Co, Fe, C, N, O, and B elements, which are uniformly distributed and without phase separation. This electrode structure exhibits a large electrochemical active area and excellent electrolyte permeation and ion diffusion capabilities.

[0008] This invention also provides a method for preparing a MOOH-MOF / BNF electrode. The method for preparing the electrode material includes the following steps:

[0009] Step 1. Preparation of BNF:

[0010] The purchased raw nickel foam (NF) was cut to suitable dimensions and ultrasonically treated with 2.0 M hydrochloric acid solution, deionized water, and anhydrous ethanol for 10 min each. Finally, it was washed with deionized water and dried in a forced-air drying oven for later use. The pretreated NF was then completely immersed in 0.4 M NaBH4 solution and allowed to react for 1 h. After the reaction was complete, the sample was removed and dried in an 80°C forced-air drying oven for 12 h. The final sample obtained was BNF.

[0011] Step 2. Preparation of MOF / BNF:

[0012] 1 mmol of 2-aminoterephthalic acid was dissolved together with a mixed metal salt in a mixed solvent consisting of 5 mL of deionized water and 5 mL of anhydrous ethanol, and the solution was ultrasonically dispersed to form a homogeneous precursor solution. The solution and the BNF substrate were then transferred together into a 25 mL high-pressure reactor, ensuring complete immersion of the BNF. After solvothermal reaction, the sample was removed, repeatedly washed with anhydrous ethanol, and dried at 80 °C for 12 hours to obtain MOF / BNF.

[0013] Step 3. Preparation of MOOH-MOF / BNF:

[0014] MOOH-MOF / BNF (M = Ni, Fe, Co) was prepared by electrochemical activation of MOF / BNF precursors. The activation process was carried out in a standard three-electrode system using a nitrogen-saturated 0.1 M KOH solution as the electrolyte. The target product, MOOH-MOF / BNF, was finally obtained by performing 20 linear sweep voltammetric cycles within a potential range of 0.306 to 0.806 V (vs. RHE).

[0015] As a preferred embodiment of the present invention, the blocky nickel foam described in step 1 is cut into a rectangular size of 3×0.3×0.15 cm, and the cleaned NF is placed in a vacuum drying oven at 60 ℃ and dried for 12 h.

[0016] As a preferred embodiment of the present invention, in step 1, 0.154 g of sodium borohydride is dissolved in 10 mL of deionized water.

[0017] As a preferred embodiment of the present invention, the mixed metal salts in step 2 are: nickel nitrate hexahydrate, 1 mmol; ferric chloride hexahydrate, 0.1 mmol; and cobalt chloride hexahydrate, 0.1 mmol.

[0018] As a preferred embodiment of the present invention, the solvothermal reaction conditions in step 2 are 150 °C and the reaction time is 3 h.

[0019] As a further preferred embodiment of the present invention, the standard three-electrode system in step 3 is as follows: the working electrode is MOF / BNF, the reference electrode is Hg / HgO, and the counter electrode is a carbon rod.

[0020] The MOOH-MOF / BNF electrode material described in this invention can be used as an anode in the electrocatalytic desorption of oxygen from water under alkaline conditions.

[0021] Advantages and positive effects of the present invention:

[0022] (1) The MOOH-MOF / BNF electrode prepared in this invention exhibits excellent OER performance. Its overpotentials at current densities of 10 mA·cm⁻² and 100 mA·cm⁻² are only 213 mV and 274 mV, respectively, which are significantly better than those of the comparative electrode. At the same time, the Tafel slope of this electrode is as low as 24.6 mV dec⁻¹, which is much lower than the 85.6 mV dec⁻¹ of the unactivated sample, indicating that it effectively accelerates the reaction kinetics.

[0023] (2) The electrode described in this invention has superior charge transport capability and structural characteristics. EIS testing confirms that it has the lowest charge transfer resistance and the highest conductivity. At the same time, its electrochemical double-layer capacitance is as high as 21.4 mF cm⁻², thanks to the unique three-dimensional network structure of "nanosheets as the framework and nanoneedles as branches". This structure provides a huge electrochemical active area, which is conducive to electrolyte penetration and ion diffusion.

[0024] (3) The electrode described in this invention exhibits excellent long-term stability. At 10 mA·cm⁻², the MOOH-MOF / BNF can operate stably for 150 hours, far exceeding the 17 hours of the comparative electrode. At a high current of 100 mA·cm⁻², its potential remains essentially unchanged after 500 hours of continuous operation. Furthermore, under frequent current switching of 10-200 mA·cm⁻², the electrode responds rapidly and exhibits excellent dynamic adaptability.

[0025] (4) After long-term stability testing, the electrode of the present invention still maintains a stable chemical structure. SEM shows that its nanosheet morphology is intact; FT-IR confirms that the organic framework structure is completely preserved; XPS shows that the core energy levels of Ni, Co, and Fe have not changed significantly; EDS confirms that the elements are still uniformly distributed.

[0026] (5) This invention achieves synergistic effect through innovative material design. The catalytic activity of the Ni, Fe, Co ternary metal system is significantly better than that of single metal or binary metal systems. At the same time, Ni3(BO3)2 is introduced as an interface bonding enhancer, forming "chemical rivets" through strong Ni-OB bonding, firmly anchoring the catalyst layer and optimizing charge transport, thereby achieving a leapfrog improvement in stability.

[0027] (6) The electrode described in this invention has outstanding potential in practical applications. An electrolyzer using MOOH-MOF / BNF as the anode can achieve 10 mA·cm⁻² with only 1.486 V, outperforming similar MOF-based catalysts recently reported. This invention provides a new approach for the rational design of highly active and stable self-supporting electrodes through interface engineering, possessing significant scientific research value and industrialization prospects.

[0028] (7) The process used to prepare the electrode material in this invention is simple and has a low cost. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating the synthesis of the MOOH-MOF / BNF material in this invention;

[0030] Figure 2 This is a morphological characterization diagram of the present invention; wherein, (a1-a2) are SEM images of BNF; (b1-b2) are SEM images of MOF / BNF; (c1-c2) are SEM images of MOOH-MOF / BNF; and (d) is an EDS mapping image of MOOH-MOF / BNF.

[0031] Figure 3 XRD patterns of MOF / BNF and MOOH-MOF / BNF in this invention;

[0032] Figure 4The FT-IR spectra of MOF / BNF and MOOH-MOF / BNF in this invention;

[0033] Figure 5 XPS values ​​for NF, BNF, MOF / BNF, and MOOH-MOF / BNF in this invention are shown below. Specifically, (a) is the overall XPS spectrum of BNF, MOF / BNF, and MOOH-MOF / BNF; (b) is the Ni element XPS spectrum of NF, BNF, MOF / BNF, and MOOH-MOF / BNF; (c) is the B element XPS spectrum of BNF, MOF / BNF, and MOOH-MOF / BNF; (d) is the Fe element XPS spectrum of MOF / BNF and MOOH-MOF / BNF; (e) is the Co element XPS spectrum of MOF / BNF and MOOH-MOF / BNF; and (f) is the M element XPS spectrum of MOF / BNF and MOOH-MOF / BNF. 3+ / M 2+ Proportional comparison;

[0034] Figure 6 The following are performance comparison charts of NF, BNF, MOF / BNF, and MOOH-MOF / BNF in this invention; (a) and (b) are LSV curves of MOOH-MOF / BNF and other related electrodes for oxygen evolution reaction (OER); (c) is a Tafel slope diagram; (d) is an electrochemical impedance spectroscopy (EIS) diagram; (d) is a double layer capacitance (Cdl) diagram; (e) is the LSV curve of MOOH-MOF / BNF for complete water splitting in 1 M KOH; (f) is a comparison of the overpotential of MOOH-MOF / BNF with other reported catalysts at a current density of 10 mA cm⁻².

[0035] Figure 7 This is a comparison of the overpotentials of MOOH-MOF / NF and MOOH-MOF / BNF in this invention;

[0036] Figure 8 The figures show the OER stability test results and the comparison of morphology and chemical structure after the test in this invention; (a) is a comparison of chronopotential testing of MOOH-MOF / NF and MOOH-MOF / BNF; (b) is the multi-step chronopotential curve of MOOH-MOF / BNF; (c) is the chronopotential test of MOOH-MOF / BNF at high current density; (d) is the FT-IR spectrum of MOOH-MOF / BNF after OER stability testing; (eg) XPS of Ni 2p, Fe 2p and Co 2p of MOOH-MOF / BNF after OER stability testing. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the technical solutions described herein, but this does not limit the present invention.

[0038] In this invention, all chemicals and reagents used were of analytical grade and were used directly without further purification. Specifically, nickel nitrate hexahydrate (Ni(NO3)2·6H2O) was purchased from Sinopharm Chemical Reagent Co., Ltd.; cobalt chloride hexahydrate (CoCl2·6H2O) was purchased from Sinopharm Chemical Reagent Co., Ltd.; ferric chloride hexahydrate (FeCl3·6H2O) was purchased from Sinopharm Chemical Reagent Co., Ltd.; sodium borohydride (NaBH4, analytical grade) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; 2-aminoterephthalic acid (C8H7NO4, analytical grade) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; and potassium hydroxide (KOH) was purchased from Sinopharm Chemical Reagent Co., Ltd. Commercially available nickel foam (NF, thickness: 1.5 mm) was purchased from Longshengbao Technology Co., Ltd.

[0039] X-ray diffraction (XRD) patterns of the samples were recorded using a PC2500 X-ray diffractometer; scanning electron microscopy (SEM) images were acquired using a HITACHI-Regulus 8100 scanning electron microscope; transmission electron microscopy (TEM) characterization was performed using a JEM-2100F transmission electron microscope; the functional groups of the catalyst were characterized using Fourier transform infrared spectroscopy (FT-IR, Thermoscientific Nicolet 4700); and X-ray photoelectron spectroscopy (XPS) analysis was performed using an ESCALAB250X X-ray photoelectron spectrometer. All electrochemical tests for the oxygen evolution reaction (OER) were performed at room temperature using a CHI760E electrochemical workstation.

[0040] Example 1: Synthesis of BNF

[0041] The block-shaped nickel foam was cut into rectangles of 3 × 0.3 × 0.15 cm. It was then ultrasonically cleaned sequentially in 2 M hydrochloric acid, deionized water, and anhydrous ethanol for 10 min each. The cleaned NF was then dried in a vacuum oven at 60 °C for 12 h. A 0.4 M NaBH4 solution was prepared by dissolving 0.154 g of sodium borohydride in 10 mL of deionized water. The pretreated NF was completely immersed in this solution and allowed to react for 1 h. After the reaction, the sample was removed and dried in a forced-air drying oven at 80 °C for 12 h. The final sample obtained was BNF (boron-modified nickel foam).

[0042] Example 2 Synthesis of MOF / BNF

[0043] 2-Aminoterephthalic acid (1 mmol) and a mixture of metal salts (nickel nitrate hexahydrate, 1 mmol; ferric chloride hexahydrate, 0.1 mmol; cobalt chloride hexahydrate, 0.1 mmol) were dissolved in a mixed solvent of 5 mL deionized water and 5 mL anhydrous ethanol, and the solution was sonicated to form a homogeneous precursor solution. The solution and a BNF substrate (3 × 0.3 × 0.15 cm) were then transferred to a 25 mL high-pressure reactor, ensuring complete immersion of the BNF. After reacting at 150 °C for 3 h, the sample was removed, repeatedly washed with anhydrous ethanol, and dried at 80 °C for 12 h to obtain MOF / BNF (metal-based boron-modified nickel foam).

[0044] Example 3 Synthesis of MOOH-MOF / BNF

[0045] MOOH-MOF / BNF (M = Ni, Fe, Co) was prepared by electrochemical activation of the MOF / BNF precursor synthesized in Example 2. The activation process was carried out in a standard three-electrode system: the working electrode was MOF / BNF (3 × 0.3 × 0.15 cm), the reference electrode was Hg / HgO, and the counter electrode was a carbon rod. The electrolyte was a 0.1 M KOH solution saturated with nitrogen. Twenty linear scan voltammetric cycles were performed within the potential range of 0.306 to 0.806 V (vs. RHE) at a scan rate of 1 mV·s. -1 And 80% iR compensation was performed. The final product MOOH-MOF / BNF was obtained. Figure 1 This is a schematic diagram of the synthesis pathway of MOOH-MOF / BNF.

[0046] Effect verification:

[0047] (1) Morphological characteristics

[0048] Its morphology and elemental distribution were revealed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Figure 1 Image a shows a SEM image of BNF, revealing fine nanoparticles formed on the BNF surface. Figure 1 In figure b, the MOF / BNF surface exhibits a dense and uniform nanosheet array structure. In figure 1c, the MOOH-MOF / BNF surface forms a complex three-dimensional network with "nanosheets as the framework and nanoneedles as branches". These nanosheets grow vertically on the surface of the nickel foam framework, interlacing and connecting to form an open porous network, which can expose more active edge sites, further increasing the electrochemical active surface area and facilitating electrolyte penetration and rapid ion diffusion. Figure 1The image shows a uniform distribution of Ni, Co, Fe, C, N, O, and B on the MOOH-MOF / BNF surface, indicating that B has been successfully loaded and the active components have been uniformly loaded on the NF substrate without significant phase separation.

[0049] (2) Structural characterization

[0050] To further determine the material structure, X-ray diffraction (XRD) was used to analyze the crystal structures of MOF / BNF and MOOH-MOF / BNF. To eliminate interference from substrate diffraction peaks, the catalyst was scraped off the substrate before testing. Figure 3 As shown, the results indicate that the structure of MOF / BNF is similar to that of NH2-MIL-88B(Fe); and in the XRD pattern of MOOH-MOF / BNF, the characteristic diffraction peaks corresponding to NiOOH, FeOOH, CoOOH and Ni can be clearly identified.

[0051] It was discovered through Fourier transform infrared spectroscopy (FT-IR) that... Figure 4 The MOF / BNF and MOOH-MOF / BNF exhibit similar characteristic bands. This indicates that although the MOF structure collapses after electroactivation, the ligands still exist on the electrode surface. The absorption peaks at 1546 cm⁻¹ and 1402 cm⁻¹ are attributed to the characteristic vibrations of the -COO⁻ group, while the vibrational band at 1234 cm⁻¹ originates from the stretching vibration of the C-N bond in the benzene ring. The metallic Ni-O vibrational peak appears near 448 cm⁻¹. Furthermore, the organic ligands exhibit C-H bending vibrations at 2924 cm⁻¹ and 764 cm⁻¹, the absorption peak at 3308 cm⁻¹ corresponds to the asymmetric vibration of the -NH₂ group, and the broad peak near 3400 cm⁻¹ can be attributed to the stretching vibration of OH. It is noteworthy that the OH vibration band near 3400 cm⁻¹ in MOOH-MOF / BNF is significantly enhanced and broadened, indicating that after the self-reconstruction process, a rich metal hydroxide (M-OOH) structure is formed on the material surface, and the stretching vibration of its OH bonds leads to a significant enhancement of the absorption signal in this region.

[0052] X-ray photoelectron spectroscopy (XPS) was used for further analysis of the surface chemical state. The total spectrum showed the presence of C, N, O, B, Ni, Fe, and Co elements in MOF / BNF and MOOH-MOF / BNF. Figure 5 a). For example Figure 5As shown in b, high-resolution Ni 2p XPS spectra reveal the evolution of the chemical state of nickel in different samples. The pristine NF exhibits characteristic peaks of Ni²⁺ at binding energies of 873.6 eV and 855.9 eV. After growing a Ni³(BO³)² layer, the corresponding Ni²⁺ peaks in the resulting BNF shift to 873.4 eV and 855.5 eV. This shift in binding energy towards lower binding energies indicates electron transfer from B to empty d orbitals in Ni, increasing the electron density of Ni²⁺. In the MOF / BNF, the Ni²⁺ peaks further shift to 873.6 eV and 856.1 eV, showing a shift towards higher binding energies compared to BNF, indicating that Ni²⁺ loses electrons and partially transforms into Ni³⁺. In contrast, the characteristic peaks of both Ni²⁺ and Ni³⁺ were present in the MOOH-MOF / BNF material obtained through the self-reconstruction process, and the Ni³⁺ / Ni²⁺ ratio increased from 0.83 to 0.98, indicating that self-reconstruction promoted the generation of Ni³⁺ species and increased the number of active sites on the material surface. Figure 5 As shown in Figure c, the high-resolution B 1s XPS spectrum reveals a distinct characteristic peak at 192.1 eV in BNF, which can be attributed to BO in nickel borate. x The characteristic signal was observed. This result further confirms that nickel borate has been formed on the surface of the nickel foam, achieving modification of its surface properties. However, with the in-situ growth of MOF and the formation of active MOOH, the intensity of the B 1s type is significantly weakened. In particular, B is almost undetectable in MOOH-MOF / BNF, because Ni3(BO3)2 is located between the substrate and the catalytically active layer (MOOH-MOF). Figure 5 In Figure d, the high-resolution XPS spectrum of Fe 2p in MOOH-MOF / BNF exhibits characteristic peaks corresponding to Fe²⁺ and Fe³⁺. Specifically, the peaks at 707.1 eV and 723.1 eV belong to Fe²⁺, while the peaks at 726.3 eV and 712.4 eV belong to Fe³⁺, and the remaining two peaks can be classified as satellite peaks. Compared to MOOH-MOF / BNF, the characteristic peaks of Fe²⁺ and Fe³⁺ are also present in the Fe 2p spectrum of the MOF / BNF sample. Figure 5 As shown in Figure e, characteristic peaks of Co²⁺ and Co³⁺ can be observed in the Co 2p high-resolution XPS spectrum of the MOOH-MOF / BNF sample. The peaks at 782.6 eV and 803 eV are attributed to Co²⁺, while the peaks at 777.6 eV and 797.2 eV are attributed to Co³⁺. The remaining accompanying peaks can be identified as satellite peaks. Further comparison with MOF / BNF reveals that its Co 2p spectrum also exhibits characteristic peaks corresponding to Co²⁺ and Co³⁺. It is worth noting that, similar to Ni, the M₂⁺ peaks in Fe and Co on the reconstructed electrode surface... 3+ / M2+ The proportion has increased, further indicating MOOH speciation ( Figure 5 f).

[0053] (3) Stable and efficient OER performance

[0054] The OER performance of the prepared electrode was evaluated using a typical three-electrode system in a 1 M KOH alkaline electrolyte. First, to demonstrate the activity-enhancing behavior of MOF alkaline electrochemical reconstruction, the overpotential of 20 consecutive LSVs at 10 mA cm⁻² was analyzed. Figure 6 As shown in figure a, as the MOF gradually reconstructs into MOOH-MOF, the overpotential gradually decreases and stabilizes. Compared with the precursor, MOOH-MOF / BNF exhibits the best OER activity. Figure 6 As shown in b, the overpotential of MOOH-MOF / BNF at 10 mA cm⁻² is only 207 mV, and only 268 mV is required to reach 100 mA cm⁻². In contrast, the overpotentials of NF, BNF, and MOF / BNF at 10 mA cm⁻² are 347 mV, 358 mV, and 237 mV, respectively. Furthermore, the Tafel slope calculated based on the steady-state polarization curve is as follows... Figure 5 As shown in Figure c, the Tafel slope of the activated MOOH-MOF / BNF is 66.4 mV dec⁻¹, significantly lower than that of the unactivated MOF / BNF (101.6 mV dec⁻¹). This result indicates that the formation of MOOH-MOF / BNF effectively promotes the rate-determining step (Volmer step), thereby significantly enhancing OER kinetics. Figure 5 As shown in d, the MOOH-MOF / BNF electrode has the smallest Tafel slope and the lowest overpotential, and the error bars represent three independent measurement results.

[0055] Electrochemical impedance spectroscopy (EIS) was performed on different electrodes. For example... Figure 6 As shown in Figure e, the MOOH-MOF / BNF electrode has the smallest Nyquist curve diameter, indicating that it has high conductivity and excellent charge transfer capability. Figure 5 f shows the electrochemical double-layer capacitance (C) of MOOH-MOF / BNF. dl The specific surface area (SSA) is 19.15 mF cm⁻², which is larger than that of other electrodes, demonstrating its larger electrochemical active surface area (ECSA). This result indicates that the MOOH-MOF / BNF catalyst generated through the LSV activation process has a larger specific surface area, which can effectively support the MOOH active phase, thereby exposing more active sites that can contact the electrolyte.

[0056] In the full hydrolysis performance test, an electrolytic cell was constructed using MOOH-MOF / BNF as the anode and Pt / C as the cathode. A current density of 10 mA cm⁻² was achieved in 1 MKOH with only a working voltage of 1.49 V. Figure 6 g), under the same conditions, it outperforms the RuO2 reference material (1.64 V). Furthermore, compared with recently reported MOF-based electrocatalysts, MOOH-MOF / BNF exhibits superior activity in both oxygen evolution reaction and total water splitting performance (Figure 6h). The elemental composition of MOOH-MOF / BNF was determined by inductively coupled plasma mass spectrometry (ICP-MS). As shown in Figure 6i, Ni is the main element (96.11 wt%), with trace amounts of Fe (0.23 wt%), Co (0.33 wt%), and B (0.08 wt%). The detection of B, together with XPS analysis results, confirms the successful formation of the Ni3(BO3)2 interface layer. In addition, the advantages of Ni3(BO3)2 modification and the trimetallic mixing strategy were further investigated. First, regardless of whether Ni3(BO3)2 modification was performed, the ternary metal MOOH system composed of Ni, Fe, and Co (i.e., MOOH-MOF / BNF (M=Ni, Fe, Co)) exhibited the lowest overpotential, and its performance was significantly better than the comparative systems containing only Ni or binary metals (Ni / Fe, Ni / Co), indicating that this ternary combination has the best catalytic activity. Figure 7 ).

[0057] Figure 8 OER stability tests were conducted on MOOH-MOF / BNF, and the morphological and chemical structural evolution after the tests were analyzed. Although the overpotential values ​​of MOOH-MOF / NF and MOOH-MOF / BNF (M=Ni, Fe, Co) are similar, the long-term operational stability of the latter was significantly enhanced after modification with Ni3(BO3)2, showing a significant difference between the two. Figure 8 As shown in figure a, under long-term stability testing at a current density of 10 mA·cm⁻², MOOH-MOF / BNF exhibited superior stability compared to MOOH-MOF / NF, with a stable operating time of up to 150 h, while the latter only lasted 17 h. Furthermore, during chronopotential testing under frequent current switching conditions ranging from 10 to 200 mA·cm⁻², MOOH-MOF / BNF showed a rapid potential response (…). Figure 8 (b) This demonstrates excellent dynamic response capability. Under a high current density of 100 mA cm⁻², the potential of MOOH-MOF / BNF remains essentially unchanged after 500 hours of continuous operation, indicating its superior structural stability and durability. Figure 8c). A two-electrode system was used, with MOOH-MOF / BNF as the anode and Pt / C as the cathode, to evaluate the stability of the total water splitting process. As shown in Figure 4e, the electrolyzer operated stably for 200 hours at a constant current density of 10 mA cm⁻² with negligible voltage increase, confirming the excellent stability of the MOOH-MOF / BNF anode under actual operating conditions.

[0058] The FT-IR spectra were highly consistent with the initial sample, indicating that the organic framework structure was preserved after electrochemical testing. Figure 8 d). The changes in Ni, Fe, Co, and B contents in the electrode after the OER stability test were evaluated by ICP-MS analysis. Compared with the initial MOOH-MOF / BNF, Fe and Co showed significant dissolution after the test, indicating partial dissolution in the catalyst layer. In contrast, the dissolution rates of Ni and B were only 0.2% and 5.9%, respectively, further confirming the good structural stability of the Ni3(BO3)2 interface layer (Figure 4f). Figure 8 As shown in g-8i, XPS analysis further revealed the chemical stability of the material surface: the core energy level spectra of Ni 2p, Co 2p, and Fe 2p showed a slight increase in the M³⁺ / M²⁺ ratio compared to the initial state, indicating a slight (structural) reconstruction during the test, but no other significant changes were observed. These multi-dimensional characterization results consistently demonstrate that MOOH-MOF / BNF exhibits excellent long-term structural stability during the OER process.

[0059] This invention innovatively introduces Ni3(BO3)2 as an "interfacial bonding enhancer" to construct a three-tiered stable structure of "substrate-Ni3(BO3)2 interface-self-reconstructed MOF catalyst layer," synergistically enhancing the activity and stability of the electrocatalytic oxygen evolution reaction (OER). Results show that the prepared MOOH-MOF / BNF catalyst exhibits excellent OER performance, with overpotentials of only 207 mV and 268 mV at current densities of 10 and 100 mA cm⁻², respectively. Further experimental analysis reveals that boron atoms can form strong interactions with Ni and O atoms, which not only firmly anchors the catalyst layer and optimizes charge transport but also ensures the structural integrity of the electrode. This allows the electrode to maintain potential stability even after 500 hours of continuous operation at a high current of 100 mA cm⁻², demonstrating excellent long-range durability. This research provides a new approach for designing efficient and stable self-supporting electrodes through interface engineering.

[0060] The above-described specific examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various simple deductions, modifications, or substitutions based on the principles of this invention. Therefore, the scope of protection of this invention should be determined by the scope of the claims.

Claims

1. A method for preparing a MOOH-MOF / BNF electrode, characterized in that, Includes the following steps: Step 1. Preparation of BNF: After cutting, cleaning and drying the nickel foam, it was immersed in a 0.3~0.5 M NaBH4 solution, allowed to stand for 1 hour, and then dried to obtain BNF. Step 2. Preparation of MOF / BNF: 2-Aminoterephthalic acid and a mixed metal salt were dissolved in a mixed solvent of water and ethanol to form a precursor solution. The BNF obtained in step 1 was immersed in the solution and subjected to a solvothermal reaction at 140-160°C for 2-5 h. After washing and drying, MOF / BNF was obtained. The mixed metal salt in the precursor solution was a mixture of soluble salts of iron, cobalt and nickel, and the molar ratio of 2-aminoterephthalic acid to the mixed metal salt was 1:(1-1.2). Step 3. Preparation of MOOH-MOF / BNF: Using the MOF / BNF obtained in step 2 as the working electrode, a linear sweep voltammetric cycle was performed in a nitrogen-saturated 0.1 M KOH solution within a potential range of 0.306 to 0.806 V (vs. RHE) to complete electrochemical activation, thus obtaining the MOOH-MOF / BNF electrode.

2. The method for preparing the MOOH-MOF / BNF electrode according to claim 1, characterized in that, In step 1, the nickel foam cleaning process involves ultrasonic cleaning for 10 min each with 2.0 M hydrochloric acid solution, deionized water, and anhydrous ethanol, and finally rinsing with deionized water.

3. The method for preparing the MOOH-MOF / BNF electrode according to claim 1, characterized in that, In step 2, the mixed metal salt is a mixture of nickel nitrate hexahydrate, ferric chloride hexahydrate, and cobalt chloride hexahydrate.

4. The method for preparing the MOOH-MOF / BNF electrode according to claim 3, characterized in that, The preparation method for the precursor solution is as follows: 1 mmol of 2-aminoterephthalic acid was dissolved together with a mixed metal salt consisting of 1 mmol of nickel nitrate hexahydrate, 0.1 mmol of ferric chloride hexahydrate and 0.1 mmol of cobalt chloride hexahydrate in a mixed solvent consisting of 5 mL of deionized water and 5 mL of anhydrous ethanol, and the solution was sonicated to form a homogeneous precursor solution.

5. The method for preparing the MOOH-MOF / BNF electrode according to claim 3, characterized in that, In step 2, the solvothermal reaction is carried out in a high-pressure reactor with a volume of 25 mL.

6. The method for preparing the MOOH-MOF / BNF electrode according to claim 1, characterized in that, In step 3, the linear scan voltammetric cycle is performed 20 times at a scan rate of 1 mV·s. -1 And 80% iR compensation will be provided.

7. The method for preparing the MOOH-MOF / BNF electrode according to claim 1, characterized in that, In step 3, the linear scanning voltammetric cycle uses a standard three-electrode system, with the reference electrode being Hg / HgO and the counter electrode being a carbon rod.

8. A MOOH-MOF / BNF electrode prepared by the method according to any one of claims 1 to 7, characterized in that, The electrode contains a three-dimensional network structure of MOOH-MOF with nanosheets of 5-7 μm in diameter as the framework and nanoneedles of 3-5 μm in length as branches. The nanosheets are vertically grown in an array on the surface of boron-modified nickel foam substrate and interweave to form an open porous network. The MOOH-MOF on the electrode surface is composed of Ni, Co, Fe, C, N, O and B elements, which are uniformly distributed and without phase separation.

9. The application of the MOOH-MOF / BNF electrode as described in claim 8 in the electrocatalytic water desorption oxygen reaction.

10. The application of the MOOH-MOF / BNF electrode according to claim 9 in the electrocatalytic water desorption oxygen reaction, characterized in that, Using the MOOH-MOF / BNF electrode as the anode, an electrocatalytic water desorption and oxygen removal reaction was carried out under alkaline conditions.

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