Iron-doped cobalt phosphide hollow nanocage hydrogen evolution catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of nano material synthesis, and relates to an iron-doped cobalt phosphide hollow nanocage hydrogen evolution catalyst and a preparation method thereof. The catalyst is a composite porous material of Fe-doped CoP nano-particles and nitrogen-doped carbon, and the Fe-doped CoP nano-particles coated with the nitrogen-doped carbon are uniformly loaded on dodecahedral porous nitrogen-doped carbon with the size of 200nm microcosmically. The preparation method comprises the following three steps: (1) reacting cobalt nitrate hexahydrate with 2-methylimidazole in methanol at room temperature, and centrifuging to obtain a ZIF-67 precursor; (2) performing oil bath reflux on ZIF-67 and potassium ferricyanide in ethanol-deionized water, and performing centrifugal drying to obtain a CoFe-PBAs precursor; and (3) annealing CoFe-PBAs for 2 hours at 400 DEG C under the protection of argon, thereby obtaining the target catalyst. The catalyst is excellent in hydrogen evolution activity in a whole pH range, 0.01 Acm <-2 > overpotentials in an acidic system, an alkaline system and a neutral system are 61mV, 133mV and 188mV respectively, only 1.91 V is needed for realizing 1.0 Acm <-2 > current density in a proton exchange membrane electrolytic cell, and the 200-hour operation voltage attenuation rate is as low as 0.1 mVh <-1 >. The method is simple in preparation process, low in cost, outstanding in catalyst activity and stability and suitable for industrial green hydrogen preparation scenes.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial synthesis technology, and relates to an iron-doped cobalt phosphide hollow nanocage hydrogen evolution catalyst and its preparation method. Background Technology

[0002] The production of renewable green hydrogen using water electrolysis is a key measure to promote the transformation of the global energy system. Pt-based materials, due to their fast reaction kinetics and low onset potential, have become the most widely used electrocatalysts in water electrolysis. However, the high price of Pt metal and its limited crustal reserves restrict its large-scale application in practice. Furthermore, the hydrogen evolution reaction (HEP) is highly dependent on the supply of protons in the electrolyte, making it sensitive to solution pH. For electrocatalysts, MH is easily formed in acidic media. ad The formation of this bond is difficult in alkaline and neutral electrolytes. Therefore, developing low-cost, high-efficiency non-precious metal electrocatalysts that can exhibit hydrogen evolution reaction activity over a wide pH range is of great significance, but also faces considerable challenges.

[0003] Transition metal phosphides are considered one of the most promising candidates to replace Pt-based catalysts in industrial applications due to their impressive electrochemical activity. Studies have shown that the excellent hydrogen evolution reaction activity of transition metal phosphides stems from their high electrical conductivity and near-optimal hydrogen intermediate adsorption energy. In particular, Co-based TMPs (e.g., CoP, Co2P, CoP...) x It exhibits strong binding with O and H species, acting as H2O and H during hydrolysis. + Co is an effective acceptor for hydrogen evolution reactions (HEP). The redox properties and corrosion resistance of Co further contribute to its favorable HEP kinetics and stability. Disappointingly, single-metal CoPs still suffer from limited accessible active sites and slow HEP kinetics. Some recent studies have shown that electronic modulation of active sites can promote reaction dissociation and desorption of adsorption intermediates. Furthermore, by optimizing the geometry to accelerate reaction kinetics, suitable reaction mechanisms, such as dual-active-site configurations, can be obtained. Therefore, optimizing electronic structure and geometry can be considered an ideal method to improve the HEP performance of Co-based transition metal phosphide materials.

[0004] Heterogeneous element doping (such as V, Fe, Ni, Cu, Mo, W) and defect engineering have been the focus of optimizing the electronic structure of CoP surfaces. On the one hand, recent studies have shown that iron doping modulates the electronic structure of CoP because Fe has a similar atomic radius and 3d electronic configuration to Co, enabling easy doping and charge redistribution while being cost-effective and environmentally friendly. In recent years, Fe-doped hollow CoP nanoneedles have been prepared, revealing that Fe modulates the electronic defects of CoP and increases the number of active sites, enabling both acidic and basic hydrogen evolution reactions. Xu et al. synthesized Fe-doped porous CoP nanosheets, demonstrating that Fe reduces the electron density of Co, and the specific structure shortens the ion transport path, endowing the electrocatalyst with dual functional properties for both hydrogen evolution and oxygen evolution reactions.

[0005] Furthermore, phosphorus (P) vacancies are an important and effective means of regulating the electronic structure of catalysts. Since P vacancies induce an increase in the electron density of neighboring metal atoms, they can optimize the adsorption strength of reaction intermediates on the catalyst surface, thereby accelerating the hydrogen evolution reaction. The introduction of P vacancies can also generate defect energy levels in the band gap, effectively narrowing the band gap of the material. This can significantly improve the intrinsic conductivity of the catalyst and promote rapid electron transfer during the reaction. On the other hand, selecting metal-organic frameworks (MOFs) with large specific surface area and high porosity as templates for preparing transition metal phosphides is also a wise method to increase the number of electrocatalytic active sites. However, how to achieve uniform Fe doping in CoP to induce P vacancy generation to enhance the synergistic effect of bimetallic active sites remains a challenge. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a Fe-CoP / NC hollow nanocage catalyst derived from a Prussian blue analogue. The Fe-CoP / NC hollow nanocage catalyst is a composite porous material consisting of Fe-doped CoP nanoparticles and nitrogen-doped carbon. The microstructure of the composite material is as follows: Fe-doped CoP nanoparticles coated with nitrogen-doped carbon are uniformly loaded onto a dodecahedral porous nitrogen-doped carbon substrate.

[0007] According to a preferred embodiment of the present invention, the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue has a dodecahedral porous nitrogen-doped carbon with a size of 200 nm.

[0008] The above-mentioned method for preparing Fe-CoP / NC hollow nanocage catalysts derived from Prussian blue analogues includes the following steps: (1) The inorganic cobalt source and the organic ligand were fully dispersed in an organic solvent, reacted at room temperature, and centrifuged to obtain the metal-organic framework ZIF-67 precursor; (2) The metal-organic framework ZIF-67 precursor and iron source were fully dispersed in the solvent, and the reaction was carried out under oil bath reflux, centrifuged and dried to obtain the CoFe-PBAs precursor; (3) The CoFe-PBAs precursor was annealed to obtain a Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst.

[0009] Preferably, in step (1), the inorganic cobalt source is cobalt nitrate hexahydrate and the organic ligand is 2-methylimidazole.

[0010] Preferably, in step (1), the molar ratio of the inorganic cobalt source to the organic ligand is 1:(6-10), and more preferably 1:8.

[0011] According to a preferred embodiment of the present invention, in step (1), the room temperature reaction time is 22-26 hours, preferably 24 hours.

[0012] Preferably, in step (2), the solvent is a mixture of ethanol and deionized water, and the iron source is potassium ferricyanide.

[0013] Preferably, in step (2), the mass ratio of the metal-organic framework ZIF-67 precursor to the iron source is 5-50:1, preferably 17:1.

[0014] Preferably, in step (2), the oil bath reaction temperature is 40-90℃, and more preferably 60℃; the oil bath reaction time is 0.5-2h, and more preferably 1h.

[0015] Preferably, in step (3), the annealing temperature is 300-500℃, the annealing time is 1-3h, and the annealing is carried out under inert gas protection; preferably, the annealing temperature is 400℃ and the annealing time is 2h.

[0016] A preferred technical solution, the Fe-CoP / NC hollow nanocage catalyst derived from Prussian blue analogue and its preparation method, includes the following specific steps: (1) Disperse 5 mmol Co(NO3)2·6H2O and 40 mmol 2-methylimidazole into 100 mL of methanol respectively, and sonicate to form uniform solution A and solution B. Quickly pour solution A into solution B and stir for 10 min. Then let it stand at room temperature for 24 h. Centrifuge the obtained purple sample with methanol to remove unreacted impurities to obtain the metal-organic framework ZIF-67 precursor, and redisperse it into 200 mL of methanol for subsequent use.

[0017] (2) Take 20 mL of methanol solution containing ZIF-67 precursor of metal-organic framework, centrifuge with ethanol and redisperse in 40 mL of ethanol, sonicate to form solution C, disperse 0.03 mmol K3[Fe(CN)6] in 10 mL of deionized water to form solution D, add solution C dropwise to solution D, and add 0.3 mL of 0.2 mol / L CH3COOH solution at the same time. Stir for 10 min, then pour the mixed solution into a three-necked flask and reflux at 60 °C for 1 h. After the reaction is completed and naturally cooled to room temperature, centrifuge the obtained product with deionized water and ethanol, and vacuum dry at 60 °C overnight to obtain CoFe-PBAs precursor.

[0018] (3) Place 20 mg of CoFe-PBAs precursor and 600 mg of NaH2PO2 into two ceramic boats and place them in a tube furnace (NaH2PO2 is upstream and CoFe-PBAs is downstream), and then heat at 5 °C for 5 min. -1 The heating rate was increased to 400℃ in a continuous Ar atmosphere and held for 2 hours. After the reaction was completed, the mixture was naturally cooled to room temperature in an Ar atmosphere and collected to obtain an iron-doped cobalt phosphide hollow nanocage electrocatalyst (Fe-CoP / NC) derived from a Prussian blue analogue.

[0019] The Fe-CoP / NC hollow nanocage catalyst derived from the above-mentioned Prussian blue analogue can electrocatalyze hydrogen evolution across the entire pH range.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention firstly utilizes Co 2+ It coordinates with 2-MIM to form a solid Co-based MOF (ZIF-67) metal-organic framework template. Then, the CH3COOH solvent dissociates to release H. + And the ZIF-67 surface was etched, resulting in some Co 2+ Mismatch. Next, [Fe(CN)6] 3- Competitive replacement for 2-MIM, through Co 2+ Strong ionic bonds are formed, resulting in a CoFe-based MOF (CoFe-PBAs) shell on the ZIF-67 surface. The Co atoms between the core and shell form a strong ionic bond. 2+ The concentration gradient drives the continuous dynamic migration of the precursor to the surface, ultimately forming a hollow CoFe-PBAs precursor. The precursor is pyrolyzed under an inert atmosphere to obtain a nitrogen-doped carbon-supported Fe-doped CoP (Fe-CoP / NC) electrocatalyst. The preparation method of this invention is simple and rapid, and the product is environmentally friendly.

[0021] 2. This invention introduces an iron source to prepare CoFe-PBAs precursors without damaging the physical structure of the metal-organic framework ZIF-67 precursor template; and [Fe(CN)6]3- The introduction of competitively coordinating substituted 2-methylimidazole promotes the recombination of ZIF-67 into hollow CoFe-PBAs, resulting in increased specific surface area and improved utilization of active sites, thereby enhancing electrocatalytic activity. The amount of iron source used in this invention needs to be appropriate; a small amount of iron source causes the dodecahedral structure of Fe-CoP / NC to collapse, while an excessive amount of iron source causes the Fe-CoP / NC nanoparticles to aggregate.

[0022] 3. The powdered electrocatalyst prepared by this invention is more suitable for large-scale preparation of slurry and spraying / coating / transferring onto proton exchange membranes for use in actual PEM electrolysis hydrogen production devices. Furthermore, by introducing nitrogen and carbon sources from the organic ligands during MOF preparation, it is not necessary to introduce an additional carbon source, which reduces raw material loss and lowers costs from an industrial production perspective.

[0023] 4. The Fe-CoP / NC nanomaterial prepared in this invention is a composite material of Fe-doped CoP nanoparticles and nitrogen-doped carbon. Its microstructure consists of Fe-doped CoP nanoparticles coated with nitrogen-doped carbon uniformly loaded onto a porous nitrogen-doped carbon substrate with a dodecahedral structure. Uniform Fe doping promotes the exposure of the active crystal faces of CoP and creates abundant lattice defect sites, increasing the electrochemical active area and achieving synergistic electrocatalysis of bimetallic active sites, thus optimizing the kinetics of the acidic hydrogen evolution reaction.

[0024] 5. The nanomaterials prepared in this invention achieve highly efficient electrocatalytic hydrogen evolution reaction across the entire pH range; and possess excellent hydrogen evolution reaction and PEM water electrolysis activity and stability, showing promising industrial development prospects. Linear polarization curve performance testing revealed that this Fe-CoP / NC hollow nanocage catalyst, derived from a Prussian blue analogue, exhibits excellent intrinsic activity for hydrogen evolution reaction across the entire pH range (0.5 mol / L H₂SO₄: 61 mV @ 0.01 Acm). -2 1.0 mol / L KOH: 133 mV @ 0.01 Acm -2 With 1.0 mol / L PBS: 188 mV @ 0.01 Acm -2 The two-electrode PEM electrolytic cell, composed of these electrodes, requires only 1.91V to achieve 1.0A / cm. -2 The current density shows excellent application prospects for hydrogen production through water electrolysis. Attached Figure Description

[0025] Figure 1 Transmission electron microscope image of the ZIF-67 precursor prepared for Example 1; Figure 2 Transmission electron microscope image of the CoFe-PBAs precursor prepared in Example 1; Figure 3(a) Transmission electron microscope image of the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue prepared in Example 1; (b) High-resolution transmission electron microscope image. Figure 4 (a) Transmission electron microscope image of the CoP / NC nanomaterials prepared for Comparative Example 1; (b) High-resolution transmission electron microscope image. Figure 5 Selected area electron diffraction image of the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue prepared in Example 1; Figure 6 (a) Elemental distribution diagram; (b) EDS spectrum of the Fe-CoP / NC hollow nanocage catalyst derived from Prussian blue analogue prepared in Example 1; Figure 7 Transmission electron microscope image of the Fe-CoP / NC-0.01mmol hollow nanocage catalyst derived from the Prussian blue analog prepared in Example 2; Figure 8 Transmission electron microscopy image of the Fe-CoP / NC-0.09mmol hollow nanocage catalyst derived from the Prussian blue analog prepared in Example 3; Figure 9 (a) ZIF-67 precursor prepared in Example 1; (b) X-ray diffraction pattern of CoFe-PBAs precursor; where the horizontal axis represents degree and the vertical axis represents intensity; Figure 10 X-ray diffraction patterns of the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue prepared in Example 1 and the CoP / NC nanomaterial prepared in Comparative Example 1; where the horizontal axis represents angle and the vertical axis represents intensity. Figure 11 Raman spectra of the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue prepared in Example 1 and the CoP / NC nanomaterial prepared in Comparative Example 1; where the horizontal axis represents the Raman shift and the vertical axis represents the intensity. Figure 12 Electron paramagnetic resonance spectra of the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue prepared in Example 1 and the CoP / NC nanomaterial prepared in Comparative Example 1; where the horizontal axis represents the g value and the vertical axis represents the intensity. Figure 13 BET test images of the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue prepared in Example 1: (a) N2 isothermal adsorption / desorption curve at 77K, where the horizontal axis is relative pressure / P / P0 and the vertical axis is adsorption amount; (b) pore size distribution diagram, where the horizontal axis is pore size and the vertical axis is pore volume. Figure 14 The X-ray photoelectron spectra of the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue prepared in Example 1 are shown in (a) full spectrum, (b) high-resolution spectra of Co2p, (c) Fe2p and (d) P2p; where the horizontal axis represents binding energy and the vertical axis represents intensity. Figure 15 The Fe-CoP / NC hollow nanocage catalyst derived from a Prussian blue analog prepared in Example 1, the CoP / NC nanomaterial prepared in Comparative Example 1, and a commercially available Pt content of 20 wt The acidic hydrogen evolution performance of % Pt / C was tested as follows: (a) linear voltammetry curves, where the x-axis represents the standard hydrogen electrode potential for the Ag / AgCl reference electrode; (b) Tafel curves, where the y-axis represents the potential; (c) double-layer fitting curves, where the x-axis represents the scan rate; (d) AC impedance plots, with the inset plot representing the equivalent circuit diagram; (e) at 0.1 Acm -2 Fe-CoP / NC electrolysis for 200 hours V -t curve, where the horizontal axis is time and the vertical axis is electric potential; Figure 16 The Fe-CoP / NC hollow nanocage catalyst derived from a Prussian blue analog prepared in Example 1, the CoP / NC nanomaterial prepared in Comparative Example 1, and a commercially available Pt content of 20 wt Alkaline hydrogen evolution performance test of % Pt / C; Figure 17 The Fe-CoP / NC hollow nanocage catalyst derived from a Prussian blue analog prepared in Example 1, the CoP / NC nanomaterial prepared in Comparative Example 1, and a commercially available Pt content of 20 wt Neutral hydrogen evolution performance test of % Pt / C; Figure 18 (a) LSV curves of Fe-CoP / NC‖RuO2, CoP / NC‖RuO2, and RuO2‖Pt / C, where the horizontal axis represents potential and the vertical axis represents current; (b) Performance comparison of PEM electrolyzers; (c) Performance of each membrane electrode at 0.1 A / cm². -2 Below V -t curve. Detailed Implementation

[0026] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0027] Example 1: A method for preparing a Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst, comprising the following steps: 5 mmol Co(NO3)2·6H2O and 40 mmol 2-methylimidazole were dispersed in 100 mL of methanol, respectively, and sonicated to form homogeneous solutions A and B. Solution A was quickly poured into solution B and stirred for 10 min. Then, the mixture was allowed to stand at room temperature for 24 h. The resulting purple sample was centrifuged with methanol to remove unreacted impurities, yielding the metal-organic framework ZIF-67 precursor, which was then redispersed in 200 mL of methanol for subsequent use.

[0028] Take 20 mL of methanol solution containing the metal-organic framework ZIF-67 precursor, centrifuge with ethanol, redisperse in 40 mL of ethanol, and sonicate to form solution C. Disperse 0.03 mmol K3[Fe(CN)6] in 10 mL of deionized water to form solution D. Add solution C dropwise to solution D, and simultaneously add 0.3 mL of 0.2 mol / L CH3COOH solution and stir for 10 min. Then pour the mixed solution into a three-necked flask and reflux at 60 °C for 1 h. After the reaction is complete and the mixture is naturally cooled to room temperature, centrifuge the obtained product with deionized water and ethanol, and vacuum dry at 60 °C overnight to obtain the CoFe-PBAs precursor.

[0029] 20 mg of CoFe-PBAs precursor and 600 mg of NaH2PO2 were placed in two separate ceramic boats and placed in a tube furnace (NaH2PO2 upstream and CoFe-PBAs downstream), and then incubated at 5 °C for 1 minute. -1 The heating rate was increased to 400℃ in a continuous Ar atmosphere and held for 2 hours. After the reaction was completed, the mixture was naturally cooled to room temperature in an Ar atmosphere and collected to obtain an iron-doped cobalt phosphide hollow nanocage electrocatalyst (Fe-CoP / NC) derived from a Prussian blue analogue.

[0030] Example 2: A method for preparing a Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst, comprising the following steps: The preparation of ZIF-67 is the same as in Example 1.

[0031] Take 20 mL of methanol solution containing the metal-organic framework ZIF-67 precursor, centrifuge with ethanol, redisperse in 40 mL of ethanol, and sonicate to form solution C. Disperse 0.01 mmol K3[Fe(CN)6] in 10 mL of deionized water to form solution D. Add solution C dropwise to solution D, and simultaneously add 0.3 mL of 0.2 mol / L CH3COOH solution and stir for 10 min. Then pour the mixed solution into a three-necked flask and reflux at 60 °C for 1 h. After the reaction is complete and the mixture is naturally cooled to room temperature, centrifuge the product with deionized water and ethanol, and vacuum dry at 60 °C overnight to obtain the CoFe-PBAs precursor, denoted as CoFe-PBAs-0.01 mmol.

[0032] The preparation of the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue was the same as in Example 1, with the sample labeled Fe-CoP / NC-0.01 mmol.

[0033] Example 3: A method for preparing a Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst, comprising the following steps: The preparation of ZIF-67 is the same as in Example 1; Take 20 mL of methanol solution containing the ZIF-67 metal-organic framework precursor, centrifuge with ethanol, and redisperse in 40 mL of ethanol. Sonicate to form solution C. Disperse 0.01 mmol K3[Fe(CN)6] in 10 mL of deionized water to form solution D. Add solution C dropwise to solution D, and simultaneously add 0.3 mL of 0.2 M CH3COOH solution. Stir for 10 min, then pour the mixture into a three-necked flask and reflux at 60 °C for 1 h. After the reaction is complete and the mixture is naturally cooled to room temperature, centrifuge the product with deionized water and ethanol, and vacuum dry at 60 °C overnight to obtain the CoFe-PBAs precursor, denoted as CoFe-PBAs-0.09 mmol.

[0034] The preparation of the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue was the same as in Example 1, with the sample labeled Fe-CoP / NC-0.09 mmol.

[0035] Comparative Example 1: A method for preparing CoP / NC nanomaterials, comprising the following steps: The preparation of ZIF-67 is the same as in Example 1; Take 20 mL of methanol solution containing the metal-organic framework ZIF-67 precursor, centrifuge with ethanol, redisperse in 40 mL of ethanol, sonicate to form a homogeneous solution, add 0.3 mL of 0.2 M CH3COOH solution and stir for 10 min. Then pour the mixture into a three-necked flask and reflux at 60 °C for 1 h. After the reaction is complete and the mixture is naturally cooled to room temperature, centrifuge the obtained product with deionized water and ethanol, and vacuum dry at 60 °C overnight to obtain the ZIF-67-H precursor.

[0036] 20 mg of ZIF-67-H precursor and 600 mg of NaH2PO2 were placed in two separate ceramic boats and placed in a tube furnace (NaH2PO2 upstream and CoFe-PBAs downstream), and then incubated at 5 °C for 1 minute. -1 The heating rate was increased to 400℃ in a continuous Ar atmosphere and held for 2 hours. After the reaction was completed, the sample was naturally cooled to room temperature in an Ar atmosphere and collected. The resulting sample was denoted as CoP / NC.

[0037] Experimental Example 1: The ZIF-67 precursor, CoFe-PBAs precursor, and Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst prepared in Example 1, the Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalysts prepared in Examples 2 and 3, and the CoP / NC electrocatalyst prepared in Comparative Example 1 were characterized and tested as follows: Transmission electron microscopy and high-resolution transmission electron microscopy: First, transmission electron microscopy images of the ZIF-67 precursor prepared in Example 1 are shown below. Figure 1 As shown, ZIF-67 is a solid dodecahedron with a regular morphology and smooth surface, and its size is approximately 200 nm. Transmission electron microscopy images of the CoFe-PBAs precursor prepared in Example 1 are shown below. Figure 2 As shown, CoFe-PBAs transforms into a hollow dodecahedral structure, indicating that [Fe(CN)6] 3- Competitive coordination substitution of 2-methylimidazole promotes the recombination of ZIF-67 into CoFe-PBAs, and only a sufficient Fe source can support the topological transformation of ZIF-67 to CoFe-PBAs. Transmission electron microscopy (TEM) images and high-resolution transmission electron microscopy (HRTEM) images of the Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst prepared in Example 1 are shown below. Figure 3 As shown, despite the increased surface roughness, the hollow dodecahedral structure is preserved. HRTEM image ( Figure 3 b) shows that Fe-CoP / NC only exposes the characteristic crystal planes of CoP, confirming the formation of Fe-doped CoP rather than a CoP / FeP heterostructure. Fe (117 Å) and Co (116 Å) have similar atomic radii; Fe doping of Co did not cause significant expansion or contraction of the CoP lattice, but it created abundant lattice defect sites, which is beneficial for the adsorption and transformation of H-containing species. Transmission electron microscopy images of the CoP / NC nanomaterials prepared in Comparative Example 1 are shown below. Figure 4 As shown in figure a, the collapse and aggregation of the dodecahedral structure indicate its poor thermal stability. Figure 4 b is the HRTEM image of CoP / NC. The lattice fringes with spacings of 0.231 nm, 0.253 nm, and 0.247 nm correspond to the (201), (200), and (111) crystal planes of CoP, respectively, while a small number of lattice defects are observed. The transmission electron microscope images of the Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalysts prepared in Examples 2 and 3 are shown below. Figure 7 and Figure 8 As shown, the apparent morphology of Fe-CoP / NC-0.01mmol and Fe-CoP / NC-0.09mmol is similar to that of the precursor, confirming that the introduction of Fe improves thermal stability by forming bimetallic MOFs.

[0038] Selected area electron diffraction (SED) images: The SED images of the Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst prepared in Example 1 are shown below. Figure 5 As shown, only the (200) and (220) characteristic crystal planes of CoP were exposed, confirming the formation of an Fe-doped CoP structure.

[0039] Elemental distribution map and EDS spectrum: TEM-Mapping image of Fe-CoP / NC hollow nanocage catalyst derived from Prussian blue analogue ( Figure 6 a) and EDS map ( Figure 6 b) shows that the elements are uniformly distributed in Fe-CoP / NC.

[0040] X-ray diffraction pattern: Figure 9 The X-ray diffraction patterns of the ZIF-67 precursor and the CoFe-PBAs precursor prepared in Example 1 are shown. Figure 9 The results show that the diffraction peaks of the Co-based MOFs are consistent with those of ZIF-67 in the literature, indicating that ZIF-67 was successfully synthesized. [Fe(CN)6] 3- After introduction, characteristic peaks of CoFe(CN)6 (JCPDS no. 75-0039) gradually appeared, indicating that ZIF-67 was successfully transformed into CoFe-PBAs ( Figure 9 b). Figure 10 The X-ray diffraction patterns of the Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst prepared in Example 1 and the CoP / NC nanomaterials prepared in Comparative Example 1 are shown. As can be seen from the figures, the phosphating product of ZIF-67-H exposes the characteristic peaks of the (011), (111), (112), (211), and (301) crystal planes of the orthorhombic CoP (JCPDS no. 89-2747), indicating that CoP nanoparticles were successfully obtained. With [Fe(CN)6]... 3- With the increase in the amount introduced, the intensity of the (211) crystal plane diffraction peak of Fe-CoP / NC is significantly enhanced, which is speculated to be transformed into Fe-doped CoP structure.

[0041] Raman spectrum: Figure 11 Raman spectra of the Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst prepared in Example 1 and the CoP / NC nanomaterial prepared in Comparative Example 1. Located at 1339 cm⁻¹. -1 With 1581cm -1 Defect carbon (D) peaks and graphitic carbon (G) peaks appear at the location, and the intensity ratio of the D peak to the G peak increases with the increase of Fe doping concentration. I D / I GThe volcanic trend indicates that Fe-CoP / NC with appropriate Fe doping has the highest defect carbon content, which is conducive to the capture of intermediate species and thus improves the reactivity.

[0042] Electron paramagnetic resonance spectrum: Figure 12 The electron paramagnetic resonance (EPR) spectra of the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue prepared in Example 1 and the CoP / NC nanomaterial prepared in Comparative Example 1 are shown. The intensity of Fe-CoP / NC at g=2.003 is stronger than that of CoP / NC, indicating that Fe doping increases the defect concentration, which is consistent with the HRTEM image results.

[0043] N2 isothermal adsorption / desorption measurement curves and pore size distribution: The N2 isothermal adsorption / desorption measurement curves and pore size distribution of the Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst prepared in Example 1 are shown in the figure below. Figure 13 As shown, Fe-CoP / NC has a larger specific surface area, which is attributed to the formation of its hollow structure, which is beneficial to the full exposure of active sites. Fe-CoP / NC has a smaller pore size because Fe-doped CoP is loaded in the form of nanoparticles within the surface channels of N-doped carbon. The smaller mesoporous pore size is beneficial to the full contact between the electrocatalyst and the electrolyte, thereby optimizing the reaction kinetics of the electrocatalytic hydrogen evolution reaction.

[0044] X-ray photoelectron spectroscopy: XPS total spectrum as shown Figure 14 As shown in figure a, except for CoP / NC, all other samples exhibited a characteristic peak of the Fe 2p orbital at 714.71 eV, confirming successful Fe doping. From Figure 14 In the high-resolution XPS spectrum of the Co2p orbital of b, fitting peaks at 778.15 eV and 781.06 eV within CoP / NC can be observed, corresponding to Co2p. 3 / 2 Co within the orbit 3+ and Co 2+ The fitting peaks at 793.06 eV and 797.21 eV correspond to Co2p. 1 / 2 Co within the orbit 3+ and Co 2+ The fitted peaks at 784.39 eV and 801.33 eV are satellite peaks. With increasing Fe content, the Co2p values ​​of Fe-CoP / NC-0.01 mmol, Fe-CoP / NC, and Fe-CoP / NC-0.09 mmol increased. 3 / 2 Co within the orbit 3+ and Co 2+ The fitted peak did not shift significantly.

[0045] Similarly, in Fe-CoP / NC-0.01mmol, Fe2p3 / 2 Fe in the orbit 2+ and Fe 3+ The fitting peaks are located at 710.65 eV and 713.58 eV, Fe2p 1 / 2 Fe in the orbit 2+ and Fe 3+ The fitted peaks are located at 723.75 eV and 726.84 eV, while the satellite peaks are located at 716.73 eV and 732.87 eV. In comparison, Fe-CoP / NC and Fe-CoP / NC-0.09 mmol Fe... 3+ The peak did not shift significantly. Figure 14 c). The above indicates that Fe doping did not significantly tune the electronic structure of Co. Figure 14 d is the high-resolution XPS spectrum of the P2p orbitals; all samples contain PO4. 2- P2p 1 / 2 P2p 3 / 2 Orbital characteristic peaks, within CoP / NC, P2p 3 / 2 With P2p 1 / 2 The orbital peaks are located at 129.20 eV and 130.38 eV, PO4. 3- The fitted peak is located at 134.31 eV. With increasing Fe doping concentration, P2p... 1 / 2 and P2p 3 / 2 The peak intensity gradually decreases, which is due to the increase in lattice defect concentration caused by Fe doping.

[0046] Example 2: The hydrogen evolution performance was tested as follows: In a typical three-electrode system, Pt sheet and Ag / AgCl (containing saturated KCl aqueous solution) were used as the counter electrode and reference electrode, respectively. The working electrode was prepared as follows: 5 mg of catalyst sample was dispersed in 500 μL C2H5OH (containing 15 μL Nafion), and sonicated for 0.5 h to obtain a mixed slurry. 100 μL of the slurry was then dropped onto a 1×1 cm plate. 2 On the pretreated CP (ensuring the catalyst sample loading is 1 mg / cm³) -2 ).

[0047] The catalyst samples were: Prussian blue analogue-derived Fe-CoP / NC electrocatalysts prepared in Examples 1-3, CoP / NC nanomaterials prepared in Comparative Example 1, and commercially available Pt content of 20%. wt % of Pt / C.

[0048] All electrochemical tests in this invention were performed on a CHI660 electrochemical workstation. The 1.0 mol / L KOH, 0.5 mol / L H₂SO₄, and 1.0 mol / L PBS electrolytes used in the electrochemical tests required pre-purging with nitrogen for 30 minutes to remove oxygen. The carbon paper used required surface pretreatment with a mixture of concentrated sulfuric acid and concentrated nitric acid to remove oxides and impurities, and the actual surface area immersed in the electrolyte was 1 cm². 2 The sweep rate of the linear polarization curve was set to 5 mV·s. -1 .

[0049] Electrochemical impedance spectroscopy (EIS): at a DC potential (1.0 mol / L KOH: -0.202 V) vs .RHE, 0.5mol / LH2SO4: -0.096V vs. RHE with 1.0 mol / L PBS: -0.297V vs. The current density in the LSV curve corresponding to the hydrogen evolution reaction, obtained by testing under RHE, is 10 mA / cm². -2 The potential was measured at a frequency of 0.01~10. 5 Hz, and the amplitude is 0.005V.

[0050] Tafel Curve: Through iR The compensated linear polarization curve was obtained, and the selected range was the Faraday interval where hydrogen evolution occurs.

[0051] Double-layer capacitor ( C dl ): By using the non-Radaic region of the hydrogen evolution reaction (1.0 mol / L KOH: 0.524-0.624 V) vs. RHE, 0.5mol / LH2SO4: 0.098-0.198V vs. RHE with 1.0 mol / L PBS: 0.111–0.211 V vs. RHE) with different scan rates (5-40mVs) -1 The interval is 5mVs -1 ) Perform CV testing and calculate the results.

[0052] The Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst prepared in Example 1, the CoP / NC nanomaterial prepared in Comparative Example 1, and a commercially available Pt content of 20 wt The electrochemical hydrogen production performance test results of % Pt / C are as follows: The acidic hydrogen evolution performance of the Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst obtained in Example 1 is as follows: Figure 15 As shown. Figure 15Figure a represents the linear polarization curve (LSV). As shown in the figure, the Fe-CoP / NC series electrocatalysts exhibit significantly improved activity compared to CoP / NC, and different samples demonstrate competitive performance in the hydrogen evolution reaction. Specifically, Fe-CoP / NC exhibits relatively superior catalytic activity for the hydrogen evolution reaction, requiring only a 61 mV overpotential to drive 0.01 Acm. -2 The current density was significantly lower than that of Fe-CoP / NC-0.01mmol (155mV), Fe-CoP / NC-0.09mmol (126mV), and CoP / NC (412mV), indicating that appropriate Fe doping and lattice defects significantly improved the hydrogen evolution reaction performance of CoP. In alkaline and neutral media, electrocatalysts typically need to overcome higher hydrogen evolution reaction energy barriers. To expand the application range of electrocatalysts, the hydrogen evolution reaction activity and stability of various samples were tested in alkaline and neutral media. Figure 16 and Figure 17 As shown in the LSV curves, Fe-CoP / NC reached an overpotential of 0.01 Acm in 1.0 mol / L KOH and 1.0 mol / L PBS solutions with overpotentials of 133 mV and 188 mV, respectively. -2 The current density is lower than that of CoP / NC.

[0053] The Tafel curve passes through iR The compensated linear polarization curve is obtained, and the selected range is the Faraday interval where hydrogen evolution occurs. For example... Figure 15 b shows that the Tafel slopes of the Fe-CoP / NC series electrocatalysts and CoP / NC are between 40-120 mVdec. -1 The relationship is consistent with the Volmer-Heyrovsky mechanism. Specifically, the Tafel slope of Fe-CoP / NC (68.24 mVdec) is... -1 Only CoP / NC (108.47mVdec) -1 The 0.63 times higher value indicates that Fe doping also optimizes the reaction kinetics.

[0054] Double-layer capacitor ( C dl By using the non-Radical interval of the hydrogen evolution reaction (1.0 mol / L KOH: 0.524-0.624 V) vs .RHE, 0.5mol / LH2SO4: 0.098-0.198V vs RHE with 1.0 mol / L PBS: 0.111–0.211 V vs .RHE) at different scan rates (5-40mVs) -1 The interval is 5mVs -1The double-layer capacitance of the Fe-CoP / NC hollow nanocage catalyst derived from the Prussian blue analogue obtained in Example 1 was obtained by performing CV tests and calculations. (Image of double-layer capacitance is shown below.) Figure 15 As shown in c, Fe-CoP / NC-0.01mmol, Fe-CoP / NC, Fe-CoP / NC-0.09mmol and CoP / NC... C dl The values ​​were 13.21, 107.11, 101.51, and 13.09 mFcm, respectively. -2 This indicates that Fe-CoP / NC has a larger ECSA and higher surface roughness, suggesting that Fe doping-induced lattice defects increase the active site density and promote the hydrogen evolution reaction process.

[0055] Electrochemical impedance spectroscopy (EIS) at a DC potential (1.0 mol / L KOH: -0.202 V) vs. RHE, 0.5 mol / L H₂SO₄: -0.096 V vs. RHE with 1.0 mol / L PBS: -0.297V vs. The current density in the LSV curve corresponding to the hydrogen evolution reaction, obtained by testing under RHE, is 0.01 Acm. -2 The potential was measured at a frequency of 0.01~10. 5 The Hz values ​​and amplitudes are all 0.005V. The AC impedance images of the Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst obtained in Example 1 are shown below. Figure 15 As shown in d, the charge transfer resistance of Fe-CoP / NC can be seen from the figure. R ct The value is much smaller than CoP / NC, indicating that Fe doping will reduce the charge transfer resistance of the electrocatalyst. R ct This reduces electron exchange between the electrode surface and the reactants, thereby accelerating the reaction kinetics and optimizing the reaction dynamics, consistent with Tafel's findings.

[0056] In long-term stability tests, the Prussian blue analogue-derived Fe-CoP / NC hollow nanocage catalyst obtained in Example 1 showed good stability at 0.1 A cm⁻¹. -2 The following constant current stability test is performed as follows: Figure 15 As shown in figure f. As shown in the figure, Fe-CoP / NC at 0.1 A cm -2 After operating at current density for 200 hours, the voltage decay rate is only 0.1 mVh. -1 This indicates that Fe doping effectively suppresses the dissolution and segregation of Co and P ions, giving it excellent stability in the acidic hydrogen evolution reaction.

[0057] Experimental Example 3: To systematically evaluate the actual industrial water electrolysis performance of the Fe-CoP / NC electrocatalyst, a PEM electrolyzer performance test was conducted. The polarization curves of Fe-CoP / NC‖RuO2, CoP / NC‖RuO2, and Pt / C‖RuO2 in deionized water at 80℃ are shown below. Figure 18 As shown in figure a, with CoP / NC‖RuO2 (2.61V@0.5Acm) -2 Compared to other methods, Fe-CoP / NC‖RuO2 exhibits superior activity, requiring only 1.91V to achieve 1.0Acm. -2 Current density. It is at an advanced level compared to the performance of state-of-the-art PEM electrolyzers reported to date, demonstrating excellent potential and indicating that Fe-CoP / NC is suitable for industrial PEM water electrolysis. Figure 18 b). To verify stability, the electrolytic cell was operated at 0.1 Acm. -2 After 100 hours of continuous operation at current density, the stability was found to be far superior to that of CoP / NC‖RuO2 and Pt / C‖RuO2, confirming that Fe-CoP / NC‖RuO2 also possesses excellent stability. Figure 18 c). As a highly efficient and stable non-precious metal-based hydrogen evolution reaction catalyst, Fe-CoP / NC shows promising practical application prospects in the field of green hydrogen production.

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An iron-doped cobalt phosphide hollow nanocage hydrogen evolution catalyst, characterized in that, The catalyst is a composite porous material of Fe-doped CoP nanoparticles and nitrogen-doped carbon, with the following microstructure: Fe-doped CoP nanoparticles coated with nitrogen-doped carbon are uniformly loaded onto porous nitrogen-doped carbon with a dodecahedral structure.

2. The iron-doped cobalt phosphide hollow nanocage hydrogen evolution catalyst according to claim 1, characterized in that, The porous nitrogen-doped carbon in the dodecahedral structure has a size of 200 nm.

3. A method for preparing the iron-doped cobalt phosphide hollow nanocage hydrogen evolution catalyst as described in claim 1 or 2, characterized in that, Includes the following steps: (1) The inorganic cobalt source and the organic ligand were fully dispersed in an organic solvent, reacted at room temperature and then centrifuged to obtain the metal-organic framework ZIF-67 precursor; (2) The ZIF-67 precursor and the iron source were fully dispersed in the solvent, and after the reaction was carried out by oil bath reflux, the CoFe-PBAs precursor was obtained by centrifugation and drying. (3) The CoFe-PBAs precursor was annealed to obtain an iron-doped cobalt phosphide hollow nanocage hydrogen evolution catalyst.

4. The preparation method according to claim 3, characterized in that, In step (1), the inorganic cobalt source is cobalt nitrate hexahydrate and the organic ligand is 2-methylimidazole.

5. The preparation method according to claim 3, characterized in that, In step (1), the molar ratio of the inorganic cobalt source to the organic ligand is 1:(6-10).

6. The preparation method according to claim 3, characterized in that, In step (1), the room temperature reaction time is 22-26 h; in step (2), the iron source is potassium ferricyanide and the solvent is a mixture of ethanol and deionized water.

7. The preparation method according to claim 3, characterized in that, In step (2), the mass ratio of the ZIF-67 precursor to the iron source is 5-50:1, the oil bath reaction temperature is 40-90℃, and the reaction time is 0.5-2h.

8. The preparation method according to claim 3, characterized in that, In step (3), the annealing process is carried out under inert gas protection, the annealing temperature is 300-500℃, and the holding time is 1-3h.

9. The preparation method according to claim 5, characterized in that, The molar ratio of the inorganic cobalt source to the organic ligand is 1:

8.

10. The preparation method according to claim 7, characterized in that, The mass ratio of the ZIF-67 precursor to the iron source is 17:1, the oil bath reaction temperature is 60℃, and the reaction time is 1h.

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