CoFe double-metal phosphide high-current alkaline full-electrolysis water electrode and preparation method thereof

Abstract

The preparation method comprises the following steps: taking foamed nickel as a working electrode, a platinum sheet as a counter electrode and a saturated calomel electrode as a reference electrode, and growing a Co (OH) 2 nanosheet in situ by adopting a constant potential deposition method to obtain a Co (OH) 2 / NF composite material; the preparation method comprises the following steps: dissolving Co (NO3) 2.6 H2O, FeCl3. 6H2O and an organic ligand in DMF (Dimethyl Formamide), stirring to form a homogeneous solution, immersing the Co (OH) 2 / NF composite material into the homogeneous solution, carrying out solvothermal reaction, natural cooling and vacuum drying under the conditions of heating and heat preservation, and carrying out gas-phase phosphating treatment on the obtained CoFe-MOF / NF precursor to obtain the CoFe bimetallic phosphide which has hydrogen evolution and oxygen evolution properties as a large-current alkaline full-electrolysis water electrode. The symmetrical electrolytic cell assembled as a cathode and an anode can realize high stability of large-current alkaline complete water splitting.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and in particular relates to a CoFe bimetallic phosphide high-current alkaline complete water splitting electrode and a preparation method thereof. Background Art

[0002] Transition metal-based catalysts are considered ideal candidates to replace precious metal catalysts due to their abundant reserves, significant cost advantages, and tunable electronic structures. Among the numerous transition metal compounds, transition metal phosphides (TMPs) show broad prospects for electrocatalytic research due to their unique d-orbital electron configuration at the metal center, diverse chemical valence state distribution, and excellent charge transport capabilities. However, the stability of existing phosphides needs to be improved, and the development of highly active and stable multifunctional electrode materials is crucial for the industrialization of hydrogen production by water electrolysis.

[0003] At present, the reported stability of phosphide complete water splitting is about <36h @ low current (such as 10mA cm -2 ), only a few reports exceed 1000h. In order to improve the catalytic performance of TMPs under actual working conditions, heteroatom doping strategies are widely adopted. For example, by introducing appropriate amounts of heterogeneous metal elements, the coordination microenvironment of the active site is effectively regulated, the adsorption / desorption balance of reaction intermediates (such as H*, OOH*, etc.) is optimized, and the intrinsic activity and reaction rate of the catalyst are significantly improved. In the prior art, a high-entropy phosphosulfide MnFeCoNiVPS3 (1200h@100mA cm) with excellent seawater electrolysis durability has been reported. -2 ), which is due to the oxidation of P and S in the material and the formation of anionic protective layer to repel chloride ions and prevent further corrosion of the material. At the same time, the V2O x Species can effectively prevent further oxidation of the material. V-doped CoFeP nanoparticles have also been reported. The introduction of V restructures the surface electron cloud distribution of bimetallic phosphides, promotes directional charge migration, and induces a negative shift in the d-band center of the metal sites, thereby optimizing the binding strength between the catalyst and the intermediate during the HER process. This suggests that compared to single-metal phosphides, polymetallic materials can enhance the catalytic activity and stability of the material due to their rich active site composition.

[0004] Appropriate metal doping can also induce catalyst reconstruction. For example, cation-induced Zn-FeNiP@Zn-Fe2P spontaneously transforms into a Zn-Ni2P / FeOOH heterointerface during electrochemical cycling, where the dynamic dissolution of Fe2P and the directional deposition of FeOOH synergistically enhance the bifunctional catalytic activity of the material. Electrode surfaces are prone to reconstruction with increasing oxidation potential. For example, studies have reported that NF@CoFeP catalysts undergo a phase transition from Co2P / Fe2P to CoOOH / FeOOH at high OER potentials. Other studies have reported that the surface of F-FeCoPv@IF materials reconstructs to generate highly active FeCoOOH species during OER polarization, both of which reveal the important influence of dynamic reconstruction on catalytic performance. Furthermore, introducing a carbon layer to protect the active species is another strategy for improving stability. For example, calcining metal-organic frameworks can simultaneously introduce carbon layers and active metal centers. Furthermore, using nickel foam (NF) as a conductive substrate to construct binder-free, self-supporting materials can create hierarchical heterostructures, which enhance overall performance by strengthening the conductive network, accelerating charge transport, and exposing abundant active sites. Summary of the Invention

[0005] Based on this, the main purpose of the present invention is to provide a method for preparing a CoFe bimetallic phosphide high-current alkaline water splitting electrode, which is self-supported by nickel foam, has morphology control, is electrochemically pre-activated in situ, and is combined with the introduction of a carbon layer to solve the problem in the prior art that there are few stability tests in high-current water electrolysis and the stability time does not exceed 1000 hours.

[0006] Another object of the present invention is to provide a CoFe bimetallic phosphide high current alkaline complete water splitting electrode, which is prepared by the preparation method of the CoFe bimetallic phosphide high current alkaline complete water splitting electrode and has the hydrogen evolution and oxygen evolution performance of the enhanced material.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] The first aspect of the present invention provides a method for preparing a CoFe bimetallic phosphide high current alkaline water splitting electrode, characterized in that it comprises the following steps:

[0009] (1) First, a standard three-electrode electrochemical system was constructed using nickel foam (NF) as a conductive substrate, with nickel foam as the working electrode, platinum as the counter electrode, and a saturated calomel electrode as the reference electrode. Then, Co(OH)2 nanosheets were in situ grown by constant potential deposition to obtain Co(OH)2 / NF composite materials.

[0010] (2) Co(NO3)2·6H2O, FeCl3·6H2O and an organic ligand were dissolved in DMF and magnetically stirred to form a homogeneous solution. The Co(OH)2 / NF composite material was then immersed in the homogeneous solution and transferred as a whole to a hydrothermal reactor containing a polytetrafluoroethylene liner. A solvothermal reaction was carried out under heating and heat preservation conditions. After completion, the mixture was naturally cooled to room temperature, repeatedly rinsed with DMF solution to remove unreacted products, and vacuum dried to obtain a CoFe-MOF / NF precursor.

[0011] (3) The CoFe-MOF / NF precursor is subjected to a gas phase phosphating treatment to obtain a CoFe bimetallic phosphide, which is used as a high current alkaline water splitting electrode.

[0012] Preferably, in step (2), the organic ligand is prepared by compounding terephthalic acid and trimesic acid in a molar ratio of 1-10:10-1.

[0013] Preferably, in step (2), the mass volume ratio of Co(NO3)2·6H2O, FeCl3·6H2O, organic ligand and DMF is 0.25mmol:0.25mmol:0.33mmol:20mL.

[0014] Preferably, in step (2), the heating temperature is 120°C, the solvent thermal reaction time is 6 hours, and the vacuum drying temperature is 60°C.

[0015] Preferably, in step (3), the process of gas-phase phosphating the CoFe-MOF / NF precursor comprises: weighing NaH2PO2·H2O and uniformly loading it into a porcelain boat, placing the porcelain boat carrying the CoFe-MOF / NF precursor in the downstream area of ​​a tube furnace, and continuously introducing a protective atmosphere of high-purity nitrogen gas, using a programmed temperature control mode to linearly increase the temperature to 350°C at 3°C / min, and maintaining the constant temperature for 2h to complete the phosphorus doping process, and naturally cooling to room temperature with the furnace to obtain the product.

[0016] In a second aspect of the present invention, a CoFe bimetallic phosphide high-current alkaline complete water splitting electrode is provided, which is obtained by the preparation method of the CoFe bimetallic phosphide high-current alkaline complete water splitting electrode.

[0017] The third aspect of the present invention provides a high-current alkaline complete water splitting symmetrical electrolytic cell, which is assembled using the CoFe bimetallic phosphide high-current alkaline complete water splitting electrode as the cathode and / or anode.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Using NF as a conductive substrate, uniformly distributed Co(OH)2 nanosheets were grown in situ by electrodeposition as a template. A bimetallic MOF was obtained by dual tuning of the metal center and organic ligands. Subsequently, NF-supported CoFe bimetallic phosphide was prepared by vapor phase phosphating. The CoFe bimetallic phosphide was prepared by self-supporting nickel foam, regulating the morphology, electrochemical in situ pre-activation, and introducing a carbon layer. It can be used as a high-current alkaline water splitting electrode to enhance the hydrogen and oxygen evolution performance of the electrode.

[0020] Second, the CoFe bimetallic phosphide of the present invention can well preserve the integrity of the sheet structure and obtain a carbon layer, exposing a large surface area while having good conductivity. Thanks to the advantages of precisely controlled hierarchical nanostructure and the electronic synergistic effect between the bimetallic atoms, a symmetrical electrolytic cell assembled with CoFeP / NF as the anode and cathode can drive 10 mA cm under alkaline conditions with only 1.56 V voltage. -2 The total hydrolysis current density was 200 mA cm -2 It can run stably for 1100 hours at a high current density, achieving high stability of large current alkaline water splitting. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 : This is an SEM image of flake Co(OH)2 deposited on nickel foam using electrodeposition in the examples.

[0022] Figure 2 These are SEM images of flaky Co(OH)2 deposited on nickel foam using electrodeposition in the examples; a: preparation flow chart of CoFeP / NF, b: SEM characterization diagram; c: SEM characterization diagram of the fluffy porous structure; d: high-resolution TEM image.

[0023] Figure 3 : is the XRD spectrum of CoFeP / NF in the embodiment.

[0024] Figure 4 This is the XPS spectrum of CoFeP / NF in the example.

[0025] Figure 5 LSV curves of (a) CoFeP / NF||CoFeP / NF in 1.0 M KOH solution in the embodiment; (b) other complete water splitting catalysts at 200 mA cm -2 The symbols "+" and "-" represent the anode and cathode materials of the electrolytic cell respectively; (c) at 200 mA cm -2 (d) CoFeP / NF full water stability and the comparison of the full water stability of the control sample, the symbols "+" and "-" represent the anode and cathode materials of the electrolytic cell, respectively.

[0026] Figure 6 This is the SEM image of the anode of CoFeP / NF in the embodiment after 1100h full water splitting stability test. DETAILED DESCRIPTION

[0027] In order to more fully understand and demonstrate the technical solutions, objectives, and advantages of the present invention, the following is a further detailed and complete description of the technical effects produced by the present invention in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some of the embodiments of the present invention, and not all of them. It should be pointed out that for those skilled in the art, other embodiments obtained without departing from the concept of the present invention are all within the scope of protection of the present invention.

[0028] Example 1

[0029] This embodiment prepares a CoFe bimetallic phosphide, and the steps are as follows:

[0030] (1) Weigh 0.25 mmol Co(NO3)2·6H2O, 0.25 mmol FeCl3·6H2O, and 0.33 mmol organic ligand (PTA:BTC molar ratio gradient set to 0:10, 2:8, 5:5, 8:2, 10:0), dissolve them together in 20 mL DMF, and stir magnetically to form a homogeneous solution.

[0031] (2) The homogeneous solutions of each ratio were dispensed into a 50 mL polytetrafluoroethylene-lined hydrothermal reactor. The electrodeposited nickel foam substrate (Co(OH)2 / NF) was then cut into 1 cm × 1 cm specimens and immersed in the homogeneous solution reaction system. The solvent thermal reaction was carried out at a constant temperature of 120°C for 6 h. After the reaction was completed, the mixture was naturally cooled to room temperature, repeatedly rinsed with DMF solution to remove unreacted products, and finally dried in a vacuum oven at 60°C to obtain a series of CoFe-MOF / NF precursors.

[0032] (3) The obtained CoFe-MOF / NF precursor was subjected to vapor phase phosphating treatment. The process was as follows: 0.6g of sodium hypophosphite monohydrate (NaH2PO2·H2O) was weighed and evenly loaded into a porcelain boat. The porcelain boat containing the CoFe-MOF / NF precursor (CoFe-MOF / NF) was placed in the downstream area of ​​a tube furnace. Under the continuous flow of high-purity nitrogen protective atmosphere, the temperature was linearly increased at 3°C / min to the target temperature of 350°C using a programmed temperature control mode. The temperature was then maintained at a constant temperature for 2 hours to complete the phosphorus doping process. Finally, the furnace was naturally cooled to room temperature to obtain CoFe bimetallic phosphide.

[0033] At the same time, the CoFe bimetallic phosphide prepared in Example 1 was used as the anode and cathode to assemble a high-current alkaline full water splitting symmetrical electrolyzer for performance testing.

[0034] like Figure 1 As shown in the figure, Co(OH)2 nanosheets were successfully prepared on a nickel foam substrate by electrodeposition. By optimizing the electrodeposition conditions, the Co(OH)2 nanosheets exhibited good regularity and consistency, and the sample morphology showed a uniformly distributed nanosheet structure, providing an ideal substrate for the subsequent uniform growth of bimetallic MOFs.

[0035] like Figure 2 As shown in the figure, the surface morphology and microstructure of the CoFeP / NF material were systematically characterized by SEM and TEM. The results show that the surface of the material presents a highly ordered nanosheet structure with uniform geometric distribution and significant two-dimensional features. These nanosheets contact and cross each other to form a grid structure, providing a fast channel for electron transmission ( Figure 2 b). Figure 2 The fluffy porous structure shown in c can be attributed to the large amount of amorphous carbon species generated in the phosphide matrix during the high-temperature annealing process. High-resolution TEM images further reveal regular lattice fringes of 0.207 nm and 0.221 nm, which match the theoretical spacing values ​​of Co2P (201) and (111) planes, respectively ( Figure 2 d).

[0036] like Figure 3 As shown in Figure 2, the phase composition and chemical state characteristics of the CoFeP / NF composite material were analyzed by XRD characterization. The characteristic diffraction peaks at 16.4°, 26.1°, 31.8°, 36.7°, 41.1°, 48.5°, and 56.5° in the XRD spectrum match the (100), (001), (101), (200), (111), (210), and (211) crystal planes of hexagonal Co2P (JCPDS 01-072-9563), respectively. Referring to the standard card of Co2P, the positions of all peaks are shifted, which may be caused by the partial substitution of Fe for Co.

[0037] Since there is an isomorphous system, namely hexagonal Fe2P (JCPDS No.01-074-2533), and Fe and Co have similar radius and chemical properties, a small amount of Fe may replace Co, resulting in the shift of the peak in XRD. That is, in the bimetallic phosphide, iron replaces part of the cobalt atoms in the form of doping and the two metals coexist in the lattice and combine with phosphorus to form Co 2-x Fe x In addition, the high-intensity diffraction signals at 44.5°, 51.8°, and 76.2° originate from the characteristic crystal planes of the nickel foam substrate. No peaks of Co(OH)2 and CoFe-MOF were detected in the XRD spectrum, indicating that the MOF precursor was successfully phosphated.

[0038] like Figure 4As shown in Figure 2, XPS analysis shows that the C 1s spectrum can be deconvoluted into 284.5 eV (CC), 285 eV (CO) and 288.7 eV (CC=O), and the O 1s spectrum presents four groups of characteristic peaks in the range of 530.9-533.7 eV ( Figure 4 c), corresponding to the C=O (530.9eV), CO (531.6eV), OP (532.7eV), and C=CO (533.7eV) bonding modes. In the P 2p spectrum, the two peaks at about 130eV are caused by the P 2p of M(Co,Fe)-P. 3 / 2 and P2p 1 / 2 The peak at 133.9 eV is caused by the partial oxidation of surface metal phosphide in air to form PO species ( Figure 4 d). Fe 2p spectrum ( Figure 4 e) can be deconvoluted into six peaks, the two peaks at 708eV and 720.7eV (the corresponding spin-orbit splitting energy level difference is 12.7eV) can be attributed to Fe 2+ 2p 3 / 2 and Fe 2+ 2p 1 / 2 The two peaks at 713.1eV and 724.3eV (the spin-orbit splitting energy level difference is 11.2eV) can be attributed to Fe 3+ 2p 3 / 2 and Fe 3+ 2p 1 / 2 The two peaks at 717.2eV and 728.2eV are Fe 3+ 2p 3 / 2 and 2p 1 / 2 Satellite peaks of Co 2p spectrum ( Figure 4 f) The peaks at 782.1eV and 798.2eV can be attributed to Co 3+ 2p 3 / 2 and Co 3+ 2p 1 / 2 The spin-orbit difference of the corresponding spin-orbit splitting energy level is 16.1eV.

[0039] like Figure 5 As shown in Figure 2, water electrolysis experiments were performed in alkaline (1.0 M KOH) solution using CoFeP / NF as cathode and anode. Figure 5 As shown in a, the assembled CoFeP / NF||CoFeP / NF electrolyzer only requires a voltage of 1.57 V to achieve 10 mA cm -2 The current density is 1.86 V and the voltage reaches 200 mA cm -2 The current density of the bifunctional catalyst is compared with that of the Figure 5b), such as: Zn-Ni2P / Ni 12 P5 / NF||Zn-Ni2P / Ni 12 P5 / NF(1.88V at 200mA cm -2 ), FeS2 / Fe-Ni3S2 / NF||FeS2 / Fe-Ni3S2 / NF(1.73V at 200mA cm -2 )、Ni-P / NiSex / NF||Ni-P / NiSex / NF(1.92V at 200mA cm -2 ),NiCoP / NF||NiCoP / NF(1.73V at 200mA cm -2 ), Ce1-CoP / CP||Ce1-CoP / CP(1.84V at200mA cm -2 ),NiFeP / NM||NiFeP / NM(1.71V at 200mA cm -2 ), Fe-Ni2P@C / NF||Fe-Ni2P@C / N(1.70V at 200mA cm -2 ), Co6Ni4P / NF||Co6Ni4P / NF(1.69V at 200mA cm -2 ). In order to further verify the application prospects of the synthesized electrocatalyst in the production of H2 using green energy, such as Figure 5 As shown in c, the assembled electrolytic cell can be operated at 200 mA cm -2 The stability of other related high current water splitting catalysts is as follows: Figure 5 As shown in d.

[0040] After the stability test, it can be seen from the anode SEM image that CoFeP / NF still has a good sheet structure ( Figure 6 ), the mesoporous nanosheet structure is conducive to exposing more active sites to improve catalytic activity, and is also conducive to gas-liquid transport, making it easier for the electrolyte to reach the surface of the active material, thereby improving the activity and stability of the catalyst at high current density.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a CoFe bimetallic phosphide high current alkaline water splitting electrode, characterized in that: The following steps are involved: (1) Using nickel foam as the working electrode, platinum sheet as the counter electrode, and saturated calomel electrode as the reference electrode, Co(OH)2 nanosheets were in situ grown by constant potential deposition to obtain Co(OH)2 / NF composite materials; (2) Co(NO3)2·6H2O, FeCl3·6H2O and an organic ligand were dissolved in DMF and magnetically stirred to form a homogeneous solution. The Co(OH)2 / NF composite material was then immersed in the homogeneous solution and transferred as a whole to a hydrothermal reactor containing a polytetrafluoroethylene liner. A solvothermal reaction was carried out under heating and heat preservation conditions. After completion, the mixture was naturally cooled to room temperature, repeatedly rinsed with DMF solution to remove unreacted products, and vacuum dried to obtain a CoFe-MOF / NF precursor. (3) The CoFe-MOF / NF precursor is subjected to a gas phase phosphating treatment to obtain a CoFe bimetallic phosphide, which is used as a high current alkaline water splitting electrode.

2. The method for preparing the CoFe bimetallic phosphide high current alkaline water splitting electrode according to claim 1, characterized in that: In step (2), the organic ligand is prepared by compounding terephthalic acid and trimesic acid in a molar ratio of 1-10:10-1.

3. The method for preparing the CoFe bimetallic phosphide high current alkaline water splitting electrode according to claim 1, characterized in that: In step (2), the mass volume ratio of Co(NO3)2·6H2O, FeCl3·6H2O, organic ligand and DMF is 0.25mmol:0.25mmol:0.33mmol:20mL.

4. The method for preparing the CoFe bimetallic phosphide high current alkaline water splitting electrode according to claim 1, characterized in that: In step (2), the heating temperature is 120°C, the solvent thermal reaction time is 6 hours, and the vacuum drying temperature is 60°C.

5. The method for preparing the CoFe bimetallic phosphide high current alkaline complete water splitting electrode according to claim 1, characterized in that: In step (3), the process of gas-phase phosphating treatment of the CoFe-MOF / NF precursor includes: weighing NaH2PO2·H2O and evenly loading it into a porcelain boat, placing the porcelain boat containing the CoFe-MOF / NF precursor in the downstream area of ​​a tube furnace, and continuously introducing a protective atmosphere of high-purity nitrogen. The temperature is linearly increased to 350°C at 3°C / min using a programmed temperature control mode, and the temperature is maintained at a constant temperature for 2h to complete the phosphorus doping process, and the product is naturally cooled to room temperature with the furnace.

6. A CoFe bimetallic phosphide high current alkaline water splitting electrode, characterized in that: The electrode is obtained by using the method for preparing the CoFe bimetallic phosphide high-current alkaline complete water splitting electrode.

7. A high current alkaline complete water splitting symmetrical electrolyzer, characterized in that: The method is assembled using the CoFe bimetallic phosphide high-current alkaline water splitting electrode as claimed in claim 6 as a cathode and / or anode.

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