Composite electrocatalyst, preparation method and application thereof, electrode and application thereof

Abstract

The present application relates to the technical field of hydrogen production by water electrolysis, and particularly relates to a composite electrocatalyst, a preparation method and application thereof, an electrode and application thereof, the catalyst comprising: a conductive substrate, a first metal phosphide on the surface of the conductive substrate, and a second metal sulfide on the surface of the first metal phosphide; the first metal is selected from at least two of iron-based metals and metals in group VIB; the second metal is selected from one or more of iron-based metals, and the composite electrocatalyst is used for water electrolysis, especially alkaline water electrolysis, and has high HER electrocatalytic activity.

Description

Technical Field

[0001] This invention relates to the field of water electrolysis for hydrogen production, specifically to a composite electrocatalyst, its preparation method and application, and an electrode and its application. Background Technology

[0002] The hydrogen evolution reaction (HER) is a two-electron transfer process involving the adsorption of hydrogen (H+) by an intermediate. ads The adsorption and desorption of H. Noble metal Pt has a theoretically optimal H. ads Binding energy is generally considered the benchmark catalyst for hydrogen evolution reaction (HER); however, the scarcity and high price of Pt limit its application in industrial hydrogen evolution catalysts. In contrast, non-precious metal materials, especially transition metal materials, are abundant and inexpensive. Designing transition metal HER catalysts with catalytic performance comparable to or exceeding that of precious metal materials is of great significance.

[0003] HER typically follows the Volmer-Heyrovsky or Volmer-Tafel reaction mechanism, where the Volmer step is an essential pathway. It reacts with abundant H3O in acidic media. + Depending on the environment, under alkaline conditions, the catalyst needs to provide H2O through the cracking of H2O adsorbed at the interface. ads This process requires not only additional energy to break the strong H-OH bonds in water molecules, but also involves H2O and the H+ produced by dissociation. ads and hydroxide species (OH) ads The adsorption and dissociation of hydrogen on the electrode surface. Based on this, the Volmer step, with its slow water dissociation and limited proton supply rate, will directly or indirectly affect the reaction rate of basic HER. Therefore, constructing transition metal catalysts that integrate the dual functions of water dissociation and hydrogen adsorption into the same material is a key task in hydrogen production by water electrolysis.

[0004] Furthermore, during electrode service, catalyst stability degradation is caused by structural stress changes in electrode materials, leaching of active sites, and mechanical damage resulting from the desorption of large amounts of bubbles. This makes it difficult for most non-precious metal catalysts to operate continuously at industrial-grade high current densities, and their service life cannot meet the requirements of industrial applications. Therefore, constructing transition metal catalysts that balance alkaline HER catalytic activity with long-term high current density service life is a critical scientific problem that urgently needs to be solved. Summary of the Invention

[0005] To overcome the problems of low catalytic activity and low catalytic stability leading to short service life in existing HER electrocatalysts, a composite electrocatalyst, its preparation method and application, and its electrode and application are provided. This composite electrocatalyst is used for water electrolysis, especially alkaline water electrolysis, and has high catalytic activity and high catalytic stability, exhibiting excellent service performance.

[0006] To achieve the above objectives, a first aspect of the present invention provides a composite electrocatalyst comprising: a conductive substrate and a first metal phosphide on the surface of the conductive substrate, and a second metal sulfide on the surface of the first metal phosphide; the first metal is selected from at least two of iron-based metals and group VIB metals; and the second metal is selected from one or more of iron-based metals.

[0007] A second aspect of the present invention provides a method for preparing a composite electrocatalyst, the method comprising:

[0008] (1) An electrodeposition system is formed by the conductive substrate, the counter electrode and the first electrolyte, and a first electrodeposition is performed;

[0009] (2) The conductive substrate, the counter electrode and the second electrolyte after the first electrodeposition are formed into an electrodeposition system, and the second electrodeposition is performed;

[0010] The first electrolyte contains a first metal salt, a phosphorus source, and a complexing agent;

[0011] The second electrolyte contains a second metal salt and a sulfur source.

[0012] A third aspect of the present invention provides an electrode comprising the composite electrocatalyst described in the present invention.

[0013] A fourth aspect of the present invention provides the application of the composite electrocatalyst or the electrode described herein in the electrolysis of water to produce hydrogen.

[0014] Through the above technical solution, the composite electrocatalyst of the present invention exhibits highly efficient HER electrocatalytic activity in water electrolysis, especially alkaline water electrolysis. It is speculated that the synergistic effect between different metal sites of the first metal phosphorus and the second metal sulfide in the composite catalyst imparts abundant and closely adjacent H₂ sites. ads and OH ads The adsorption sites enable it to have dual functions of water dissociation and hydrogen adsorption, thereby accelerating the Volmer step of the reaction and exhibiting excellent catalytic activity for alkaline HER. On the other hand, the surface of the composite electrocatalyst is hydrophilic and gas-repellent, which is beneficial to the mass transfer of bubbles and electrolyte during high current density operation, ensuring the catalytic activity of the electrode under industrial-grade high current density.

[0015] The composite electrocatalyst described in this invention exhibits excellent electrocatalytic stability and service performance in water electrolysis, particularly alkaline water electrolysis, for HER (hydrochemical reaction). This is presumably because the composite electrocatalyst consists of an easily leached inner first metal phosphide layer and an outer second metal sulfide layer. The easily leached inner first metal phosphide layer ensures the accessibility of the catalyst's active sites to the electrolyte during alkaline HER, while the outer second metal sulfide layer stabilizes the catalyst by preventing excessive loss of the inner active sites. Therefore, the composite electrocatalyst described in this invention can balance catalytic activity and stability in alkaline HER, thus demonstrating excellent service performance.

[0016] Furthermore, the composite electrocatalyst described in this invention is constructed by in-situ electrochemical reduction of metal ions in an electrolyte on a conductive substrate. The catalyst layer and the substrate are tightly bonded at the atomic level, resulting in a stable electrode material structure with low interfacial impedance between the substrate and the catalyst layer. It also maintains good mechanical stability during continuous gas production at high current density.

[0017] This invention prepares the electrocatalyst by depositing a first metal phosphide on the surface of a conductive substrate and then depositing a second metal sulfide on the surface of the first metal phosphide. The preparation method described in this invention is mild, simple, and convenient, and can complete the preparation of the electrode material in a short time with low energy consumption, offering advantages in terms of time and energy costs. Furthermore, unlike traditional powdered catalysts, the electrochemical deposition method of this invention eliminates the step of drop-coating the catalyst powder onto the conductive substrate surface, simplifying experimental operations and avoiding the use of binders with poor conductivity, thus improving the conductivity of the catalyst.

[0018] Furthermore, the composite electrocatalyst described in this invention, by regulating the deposition time and current density of the underlying phosphide and the surface sulfide, ensures catalytic activity while avoiding cracking, and exhibits good mechanical stability.

[0019] Furthermore, the two-step continuous layer-by-layer electrochemical deposition method described in this invention is easy to scale up. By replacing the conductive substrate with a larger size, a larger area of ​​catalytic electrode can be obtained, which is convenient for industrial application. Attached Figure Description

[0020] Figure 1 SEM images of the nickel foam electrodes with deposited first metal phosphide layers prepared in Examples 1 and 7;

[0021] Figure 2 SEM images of the composite electrocatalysts prepared in Examples 1-4;

[0022] Figure 3 Linear sweep voltammetry (LSV) curves of the composite electrocatalysts prepared in Examples 1-4 are shown.

[0023] Figure 4 The cross-sectional SEM image of the composite electrocatalyst prepared in Example 1 is shown below.

[0024] Figure 5 Linear sweep voltammetry (LSV) curves of the electrocatalysts prepared in Example 1 and Comparative Examples 1-3 are shown.

[0025] Figure 6 The electrocatalysts prepared in Example 1 and Comparative Example 3 were used in 1.0 mol L... -1 LSV curves before and after multiple cyclic voltammetry (CV) scans in KOH solution;

[0026] Figure 7 The chronopotential (CP) test curves of the electrocatalysts prepared in Example 1 and Comparative Example 3 are shown below.

[0027] Figure 8 The image shows the composite electrocatalyst prepared in Example 1 after CP testing (SEM image).

[0028] Figure 9 The images show the physical images of the composite electrocatalysts prepared in Examples 11 and 12. Detailed Implementation

[0029] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0030] The first aspect of this invention provides a composite electrocatalyst, comprising: a conductive substrate and a first metal phosphide on the surface of the conductive substrate, and a second metal sulfide on the surface of the first metal phosphide; the first metal is selected from at least two of iron-based metals and group VIB metals; the second metal is selected from one or more of iron-based metals. The composite electrocatalyst of this invention exhibits high catalytic activity and high catalytic stability in water electrolysis, particularly alkaline water electrolysis, demonstrating excellent performance.

[0031] According to one embodiment of the present invention, the first metal phosphide is attached to the surface of the conductive substrate by electrodeposition.

[0032] According to one embodiment of the present invention, the second metal sulfide is attached to the surface of the first metal phosphide.

[0033] According to one embodiment of the present invention, the second metal sulfide is attached to the surface of the first metal phosphide by electrodeposition.

[0034] According to one embodiment of the present invention, the composite electrocatalyst includes a conductive substrate and a first metal phosphide layer on the surface of the conductive substrate, and a second metal sulfide layer on the surface of the first metal phosphide layer.

[0035] According to one embodiment of the present invention, the first metal phosphide is attached to the surface of the conductive substrate by electrodeposition.

[0036] According to one embodiment of the present invention, the second metal sulfide is attached to the surface of the first metal phosphide.

[0037] According to one embodiment of the present invention, the second metal sulfide is attached to the surface of the first metal phosphide by electrodeposition.

[0038] According to one embodiment of the present invention, the composite electrocatalyst includes a conductive substrate and a first metal phosphide layer on the surface of the conductive substrate, and a second metal sulfide layer on the surface of the first metal phosphide layer.

[0039] In this invention, the range of materials that can be selected for the conductive substrate is relatively wide. This is an illustrative example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conductive substrate is selected from one or more of metal foam materials, metal sheets, and metal felts; the metal is selected from nickel and / or stainless steel.

[0040] In this invention, any first metal that meets the aforementioned range can achieve the purpose of this invention. According to a preferred embodiment of this invention, the first metal is selected from at least two of Fe, Co, Ni and Mo. Preferably, the content of any one first metal is not less than 10 mol% of the total first metal, which is beneficial to improving catalytic activity and stability.

[0041] According to one embodiment of the present invention, the first metal may be selected from Co and Fe, Co and Ni, or Co and Mo.

[0042] According to one embodiment of the present invention, the first metal phosphide contains at least Co, and Co accounts for 80 mol%-90 mol% of the total first metal, preferably 83 mol%-87 mol%, more preferably 84 mol%-86 mol%, which is beneficial to improving catalytic activity and stability. According to a preferred embodiment of the present invention, the other metal in the first metal phosphide is Mo.

[0043] According to a preferred embodiment of the present invention, the second metal is selected from one or more of Fe, Co and Ni, preferably the second metal sulfide contains only one metal, preferably selected from Fe, Co or Ni, and most preferably Co.

[0044] In this invention, when the second metal in the second metal sulfide is the same as one of the two first metals in the first metal phosphide layer, the electrocatalyst has better catalytic activity.

[0045] According to a preferred embodiment of the present invention, the molar ratio of the first metal to phosphorus in the first metal phosphide is 1:0.1-0.5, preferably 1:0.15-0.2, for example, it can be 1:0.15, 1:0.16, 1:0.17, 1:0.18, 1:0.19, 1:0.2, or any value between these values, more preferably 1:0.17-0.19.

[0046] According to a preferred embodiment of the present invention, the molar ratio of the second metal to sulfur in the second metal sulfide is 1:0.5-1, preferably 1:0.5-0.6, for example, it can be 1:0.5, 1:0.52, 1:0.54, 1:0.55, 1:0.56, 1:0.58, 1:0.6, or any value between these values, more preferably 1:0.54-0.56.

[0047] According to a preferred embodiment of the present invention, in the composite electrocatalyst, the molar ratio of phosphorus to sulfur is 1:0.1-1, preferably 1:0.6-0.91.

[0048] A second aspect of the present invention provides a method for preparing a composite electrocatalyst, the method comprising:

[0049] (1) An electrodeposition system is formed by the conductive substrate, the counter electrode and the first electrolyte, and a first electrodeposition is performed;

[0050] (2) The conductive substrate, the counter electrode and the second electrolyte after the first electrodeposition are formed into an electrodeposition system, and the second electrodeposition is performed;

[0051] The first electrolyte contains a first metal salt, a phosphorus source, and a complexing agent;

[0052] The second electrolyte contains a second metal salt and a sulfur source.

[0053] This invention prepares the electrocatalyst by depositing a first metal phosphide on the surface of a conductive substrate and then depositing a second metal sulfide on the surface of the first metal phosphide. The preparation method described in this invention is mild, simple, and convenient, enabling the preparation of electrode materials in a short time with low energy consumption, offering advantages in terms of time and energy costs. Furthermore, unlike traditional powdered catalysts, the electrochemical deposition method of this invention eliminates the step of drop-coating catalyst powder onto the conductive substrate surface, simplifying experimental operations and avoiding the use of binders with poor conductivity, thus improving the conductivity of the catalyst. The prepared composite electrocatalyst exhibits high catalytic activity and high catalytic stability in water electrolysis, especially alkaline water electrolysis, demonstrating excellent performance.

[0054] In this invention, the first electrodeposition conditions can be selected from a wide range, and conventional electrodeposition conditions in the art are sufficient. According to a preferred embodiment of this invention, the first electrodeposition conditions include: a current density of -0.05 to -0.2 A cm⁻¹. -2 The deposition time is 5–20 min; preferably, the first electrodeposition conditions include a current density of -0.08 to -0.12 A cm⁻¹. -2 Preferably, the value is -0.09 to -0.11 Å cm. -2 The deposition time is 8 to 17 minutes, preferably 14 to 16 minutes.

[0055] According to a preferred embodiment of the present invention, the first metal salt, calculated as a first metal, has a concentration of 0.02–0.08 mol / L. -1 .

[0056] According to a preferred embodiment of the present invention, the concentration of the first metal salt in the first electrolyte is 0.05-0.07 mol / L. -1 Specifically, it can be 0.05 mol L. -1 0.052 mol L -1 0.055 mol L -1 0.057 mol L -1 0.06 mol / L -1 0.062 mol L -1 0.065 mol L -1 0.067 mol L -1 0.07 mol L -1 Or any value between these values, more preferably 0.055-0.065 mol L. -1 This is beneficial for improving catalytic activity and stability.

[0057] In this invention, the phosphorus source in the first electrolyte can be selected from a wide range, as long as it is a phosphorus-containing soluble salt. This is an illustrative example, but does not limit the scope of the invention. According to a preferred embodiment of the invention, the phosphorus source is selected from one or more of phosphate, monohydrogen phosphate, dihydrogen phosphate, hypophosphite, and dihydrogen hypophosphite; preferably one or more of NaH2PO2, NH4H2PO4, and (NH4)2HPO4.

[0058] In this invention, the concentration of the phosphorus source in the first electrolyte can be selected within a wide range, which is illustrative but does not limit the scope of the invention. According to a preferred embodiment of the invention, the concentration of the phosphorus source, calculated as phosphorus, is 0.2–0.8 mol / L. -1 Preferably, it is 0.4-0.6 mol L. -1 More preferably, it is 0.45-0.55 mol L. -1 .

[0059] In this invention, the sources of the complexing agent in the first electrolyte can be selected from a wide range. This is an illustrative example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the complexing agent is selected from one or more of citrate, malate and tartrate, preferably sodium citrate.

[0060] In this invention, the concentration of the complexing agent in the first electrolyte can be selected within a wide range, which is illustrative but does not limit the scope of the invention. According to a preferred embodiment of the invention, the concentration of the complexing agent is 0.1–0.2 mol / L. -1 Preferably, it is 0.13-0.17 mol L. -1 More preferably, it is 0.14-0.16 mol L. -1 .

[0061] In this invention, the first metal salt is a soluble salt of the first metal, such as a nitrate, sulfate, or chloride of the first metal. According to a preferred embodiment of the invention, the first metal salt is selected from at least two of Fe salts, Co salts, Ni salts, and Mo salts. Preferably, the content of any one of the first metal salts is not less than 10 mol% of the total mass of the first metal salt, which is beneficial to improving catalytic activity and stability.

[0062] According to one embodiment of the present invention, the first metal salt contains a Co salt, and the Co salt accounts for 70 mol%-80 mol% of the total amount of the first metal salt, preferably 72 mol%-78 mol%, more preferably 74 mol%-76 mol%, which is beneficial to improving catalytic activity and stability.

[0063] In this invention, the range of selectable second electrodeposition conditions is relatively wide; conventional electrodeposition conditions in the art are sufficient. According to a preferred embodiment of this invention, the second electrodeposition conditions include a current density of -0.005 to -0.02 A / cm². -2 The deposition time is 1–4 min; preferably, the second electrodeposition conditions include a current density of -0.008 to -0.012 A / cm³. -2 More preferably, it is -0.009 to -0.011 Å cm. -2 The preferred deposition time is 2.5 to 3.5 min, more preferably 2.8 to 3.2 min.

[0064] In this invention, the second metal salt in the second electrolyte is a soluble salt of the second metal, such as a nitrate, sulfate, or chloride of the second metal. According to a preferred embodiment of this invention, the second metal salt is selected from one or more of Fe salts, Co salts, and Ni salts, and more preferably, the second metal salt is selected from Fe salts, Co salts, or Ni salts.

[0065] According to a preferred embodiment of the present invention, in the second electrolyte, the concentration of the second metal salt, calculated as a second metal, is 0.04-0.06 mol / L. -1 Specifically, it can be 0.04 mol L. -1 0.042 mol L -1 0.046 mol L -1 0.048 mol L -1 0.05 mol L -1 0.052 mol L -1 0.054 mol L -1 0.056 mol L -1 0.058 mol L -1 0.06 mol L -1 Or any value between these values, more preferably 0.045-0.055 mol.

[0066] In this invention, the source of sulfur in the second electrolyte can be selected from a wide range, as long as it is a soluble salt containing sulfur. This is an illustrative example, but does not limit the scope of the invention. According to a preferred embodiment of the invention, the sulfur source is selected from one or more of thiosulfates, thiourea and sulfides, preferably one or more of Na2S2O3, thiourea and sodium sulfide.

[0067] In this invention, the concentration of the sulfur source in the second electrolyte can be selected within a wide range, which is illustrative but does not limit the scope of the invention. According to a preferred embodiment of the invention, the concentration of the sulfur source, expressed as sulfur, is 0.05–0.3 mol / L. -1Preferably, the concentration is 0.08-0.24 mol / L. -1 More preferably, it is 0.09-0.22 mol L. -1 .

[0068] According to a preferred embodiment of the present invention, the concentration of the second metal salt in the second electrolyte is 0.04-0.06 mol / L. -1 Preferably, the concentration is 0.045-0.055 mol / L. -1 .

[0069] In this invention, in step (1), a conductive substrate is used as the working electrode, a graphite electrode or a platinum electrode is used as the counter electrode, and a dual-electrode system is constructed with the first electrolyte. Preferably, a graphite electrode is used as the counter electrode. By using this preferred counter electrode to construct the dual-electrode system, no counter electrode deposition will occur at the cathode, thus avoiding the impact of counter electrode deposition on the true evaluation of catalyst activity.

[0070] In this invention, in step (2), a conductive substrate after the first electrodeposition is used as the working electrode, a graphite electrode or a platinum electrode is used as the counter electrode, and a second electrolyte is used to construct a dual-electrode system. Preferably, a graphite electrode is used as the counter electrode. By using this preferred counter electrode to construct the dual-electrode system, no counter electrode deposition will occur at the cathode, thus avoiding the impact of counter electrode deposition on the true evaluation of catalyst activity.

[0071] According to a preferred embodiment of the present invention, the preparation method further includes: before performing step (1), pretreating the conductive substrate to remove oil stains, impurities and metal oxide layers from the surface of the conductive substrate, for example by immersing the conductive substrate in ethanol and dilute hydrochloric acid solutions in sequence, ultrasonically cleaning them respectively, and then ultrasonically cleaning the conductive substrate with deionized water until the pH of the cleaning solution is neutral and then vacuum drying.

[0072] A third aspect of the present invention provides an electrode comprising the composite electrocatalyst described herein. The electrocatalyst described herein can be used to prepare the electrode or directly as an electrode for alkaline water electrolysis to produce hydrogen (e.g., alkaline water electrolysis to produce hydrogen).

[0073] A fourth aspect of this invention provides the application of the composite electrocatalyst described herein in hydrogen production through water electrolysis. The composite electrocatalyst of this invention exhibits high catalytic activity and high catalytic stability in water electrolysis, particularly alkaline water electrolysis, demonstrating excellent performance.

[0074] According to a preferred embodiment of the present invention, the composite electrocatalyst is used for alkaline water electrolysis to produce hydrogen.

[0075] In the context of this specification, including the following embodiments, the content of each element was measured by inductively coupled plasma emission spectroscopy (ICP).

[0076] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0077] In the following embodiments, nickel foam was used as the conductive substrate material. The cut nickel foam was sequentially immersed in ethanol and dilute hydrochloric acid solutions, and ultrasonically cleaned for 10 minutes each to remove oil, impurities, and the metal oxide layer from the metal substrate surface. Subsequently, the substrate was ultrasonically cleaned with deionized water, replacing the deionized water during this process until the pH of the cleaning solution was neutral. The pretreated nickel foam was then dried in a vacuum drying oven at 60°C for later use. Before use, the nickel foam was cut to a predetermined size; unless otherwise specified, the size of the nickel foam was 1cm × 1cm.

[0078] Example 1

[0079] (1) Weigh out cobalt sulfate, sodium molybdate, NaH2PO2, and Na3C6H5O7 and dissolve them in deionized water to prepare a cobalt sulfate concentration of 0.045 mol / L. -1 The concentration of sodium molybdate is 0.015 mol / L. -1 The concentration of NaH2PO2 is 0.5 mol / L. -1 The concentration of Na3C6H5O7 is 0.15 mol / L. -1 The solution is used as the first electrolyte, with nickel foam as the working electrode and a carbon rod as the counter electrode, forming a two-electrode system.

[0080] The working electrode and the counter electrode were immersed in the first electrolyte at a current of -0.1 A cm⁻¹. -2 The electrode was deposited under constant current for 15 minutes. After being cleaned and dried with deionized water, a foam nickel electrode with the first metal phosphide layer was obtained.

[0081] (2) Weigh out cobalt sulfate and Na2S2O3 and dissolve them in deionized water to prepare a cobalt sulfate concentration of 0.05 mol / L. -1 The concentration of Na2S2O3 is 0.1 mol / L. -1 The solution is used as the second electrolyte;

[0082] A nickel foam electrode with a first metal phosphide layer deposited on it was used as the working electrode, and a carbon rod was used as the counter electrode. Both were immersed in the second electrolyte at -0.01 A cm⁻¹. -2 A composite electrocatalyst, denoted as N1, was obtained by constant current deposition for 3 min and then drying in a vacuum oven. The first metal phosphide layer was deposited on the surface of the nickel foam, and the second metal sulfide layer was deposited on the surface of the first metal phosphide layer.

[0083] In Example 1, the SEM image of the nickel foam electrode with the first metal phosphide layer deposited is shown below. Figure 1 As shown, the first metal phosphide at the bottom layer has a nanoparticle morphology.

[0084] ICP testing revealed that in the first metal phosphide layer, the molar ratio of Co to Mo was 1:0.17, and the molar ratio of the first metal to phosphorus was 1:0.18. In the second metal sulfide layer, the molar ratio of the second metal to sulfur was 1:0.55. In the composite electrocatalyst, the molar ratio of phosphorus to sulfur was 1:0.87.

[0085] Example 2

[0086] The method of Example 1 is different in that the constant current deposition time in step (2) is 1 min, and the other conditions are the same as in Example 1. The resulting composite electrocatalyst is denoted as N2.

[0087] ICP testing revealed that in the first metal phosphide layer, the molar ratio of Co to Mo was 1:0.17, and the molar ratio of the first metal to phosphorus was 1:0.18. In the second metal sulfide layer, the molar ratio of the second metal to sulfur was 1:0.52. In the composite electrocatalyst, the molar ratio of phosphorus to sulfur was 1:0.42.

[0088] Example 3

[0089] The method of Example 1 is different in that the constant current deposition time in step (2) is 2 min, and the other conditions are the same as in Example 1. The resulting composite electrocatalyst is denoted as N3.

[0090] ICP testing revealed that in the first metal phosphide layer, the molar ratio of Co to Mo was 1:0.17, and the molar ratio of the first metal to phosphorus was 1:0.18. In the second metal sulfide layer, the molar ratio of the transition metal to sulfur was 1:0.53. In the composite electrocatalyst, the molar ratio of phosphorus to sulfur was 1:0.58.

[0091] Example 4

[0092] The method of Example 1 is different in that the constant current deposition time in step (2) is 4 min, and the other conditions are the same as in Example 1. The resulting composite electrocatalyst is denoted as N4.

[0093] ICP testing revealed that in the first metal phosphide layer, the molar ratio of Co to Mo was 1:0.17, and the molar ratio of the first metal to phosphorus was 1:0.18. In the second metal sulfide layer, the molar ratio of the transition metal to sulfur was 1:0.56. In the composite electrocatalyst, the molar ratio of phosphorus to sulfur was 1:0.91.

[0094] The composite electrocatalysts prepared in Examples 1-4 were subjected to SEM testing, and the test results are as follows: Figure 2As shown. From Figure 2 It is evident that the second metal sulfide on the surface exhibits a nanosheet cluster morphology. As the deposition time increases from 1 min to 2 min, the surface sulfide completely covers the underlying phosphide. Further extending the secondary deposition time to 3 min significantly increases the electrode surface roughness. When the sulfide deposition time is further increased to 4 min, significant cracking occurs on the surface of the bilayer composite electrocatalyst, posing a risk of the catalyst layer detaching from the nickel foam substrate. At a deposition time of 3 min, the surface sulfide completely covers the underlying phosphide, and the electrode surface roughness significantly increases.

[0095] The cross-sectional area SEM test was performed on the composite electrocatalyst prepared in Example 1, and the results are as follows: Figure 4 As shown, it has a distinct double-layer composite structure, with a bottom layer of first metal phosphide and a top layer of second metal sulfide tightly bonded together, exhibiting robust mechanical stability. The thicknesses of the bottom layer phosphide and the top layer sulfide are 0.6 μm and 0.65 μm, respectively.

[0096] Example 5

[0097] (1) Weigh out cobalt sulfate, sodium molybdate, NaH2PO2, and Na3C6H5O7, dissolve them in deionized water, and prepare a cobalt sulfate concentration of 0.015 mol / L. -1 The concentration of sodium molybdate is 0.005 mol / L. -1 The concentration of NaH2PO2 is 0.2 mol / L. -1 The concentration of Na3C6H5O7 is 0.1 mol / L. -1 The solution is used as the first electrolyte, with nickel foam as the working electrode and a carbon rod as the counter electrode, forming a two-electrode system.

[0098] The working electrode and the counter electrode are immersed in the first electrolyte at a current of -0.2 A cm. -2 The electrode was deposited under constant current for 15 minutes. After being cleaned and dried with deionized water, a foam nickel electrode with the first metal phosphide layer was obtained.

[0099] (2) Weigh out cobalt sulfate and Na2S2O3 and dissolve them in deionized water to prepare a cobalt sulfate concentration of 0.02 mol / L. -1 The concentration of Na2S2O3 is 0.05 mol / L. -1 The solution is used as the second electrolyte;

[0100] A nickel foam electrode with a first metal phosphide layer deposited on it was used as the working electrode, and a carbon rod was used as the counter electrode. Both were immersed in the second electrolyte at -0.02 A cm⁻¹. -2 The composite electrocatalyst, denoted as N5, was obtained by constant current deposition for 3 min and then vacuum drying in a vacuum oven.

[0101] ICP testing revealed that in the first metal phosphide layer, the molar ratio of Co to Mo was 1:0.2, and the molar ratio of the first metal to phosphorus was 1:0.16. In the second metal sulfide layer, the molar ratio of the transition metal to sulfur was 1:0.55. In the composite electrocatalyst, the molar ratio of phosphorus to sulfur was 1:0.78.

[0102] Example 6

[0103] (1) Weigh out cobalt sulfate, sodium molybdate, NaH2PO2, and Na3C6H5O7, dissolve them in deionized water, and prepare a cobalt sulfate solution with a concentration of 0.06 mol / L. -1 The concentration of sodium molybdate is 0.02 mol / L. -1 The concentration of NaH2PO2 is 0.8 mol / L. -1 The concentration of Na3C6H5O7 is 0.2 mol / L. -1 The solution is used as the first electrolyte, with nickel foam as the working electrode and a carbon rod as the counter electrode, forming a two-electrode system.

[0104] The working electrode and the counter electrode are immersed in the first electrolyte at a current of -0.05 A cm⁻¹. -2 The electrode was deposited under constant current for 15 minutes. After being cleaned and dried with deionized water, a foam nickel electrode with the first metal phosphide layer was obtained.

[0105] (2) Weigh out cobalt sulfate and Na2S2O3 and dissolve them in deionized water to prepare a cobalt sulfate concentration of 0.08 mol / L. -1 The concentration of Na2S2O3 is 0.15 mol / L. -1 The solution is used as the second electrolyte;

[0106] A nickel foam electrode with a first metal phosphide layer deposited on it was used as the working electrode, and a carbon rod was used as the counter electrode. Both were immersed in the second electrolyte at -0.005 A cm⁻¹. -2 The composite electrocatalyst, denoted as N6, was obtained by constant current deposition for 3 min and then vacuum drying in a vacuum oven.

[0107] ICP testing revealed that in the first metal phosphide layer, the molar ratio of Co to Mo was 1:0.15, and the molar ratio of the first metal to phosphorus was 1:0.2. In the second metal sulfide layer, the molar ratio of the second metal to sulfur was 1:0.58. In the composite electrocatalyst, the molar ratio of phosphorus to sulfur was 1:0.71.

[0108] Example 7

[0109] The method of Example 1 is different in that the constant current deposition time in step (1) is 20 min, and the other conditions are the same as in Example 1. The first deposition yields a foam nickel electrode with a first metal phosphide layer.

[0110] The second deposition yielded a composite electrocatalyst, denoted as N7.

[0111] ICP testing revealed that in the first metal phosphide layer, the molar ratio of Co to Mo was 1:0.18, and the molar ratio of the first metal to phosphorus was 1:0.22. In the second metal sulfide layer, the molar ratio of the second metal to sulfur was 1:0.56. In the composite electrocatalyst, the molar ratio of phosphorus to sulfur was 1:0.84.

[0112] SEM image of the nickel foam electrode with the first metal phosphide layer deposited as shown below Figure 7 As shown, when the deposition time of the foam nickel electrode with the first metal phosphide layer was further extended to 20 min compared with Example 1, cracking occurred on the surface of the electrode in Example 7, especially at the edge of the catalyst framework. When the deposition time of the first metal phosphide layer was 15 min, the surface roughness of the catalyst was optimal, and it had the best apparent activity.

[0113] Example 8

[0114] The method of Example 1 is different in that, in step (1), nickel sulfate of equal concentration is used instead of cobalt sulfate, and the other conditions are the same as in Example 1, to obtain a composite electrocatalyst, denoted as N8.

[0115] Example 9

[0116] The method of Example 1 is different in that, in step (2), nickel sulfate of equal concentration is used instead of cobalt sulfate, and the other conditions are the same as in Example 1, to obtain a composite electrocatalyst, denoted as N9.

[0117] Example 10

[0118] Following the method of Example 1, except that the size of the nickel foam is 2cm × 2cm, and the other conditions are the same as in Example 1, a composite electrocatalyst, denoted as N10, was prepared.

[0119] Example 11

[0120] The method of Example 1 was followed, except that the size of the nickel foam was 10cm × 10cm, and the other conditions were the same as those in Example 1 to prepare the composite electrocatalyst, which was denoted as N11.

[0121] Comparative Example 1

[0122] The difference between Comparative Example 1 and Example 1 is that the first deposition step is omitted, and the second deposition step is performed directly; specifically:

[0123] Weigh out cobalt sulfate and Na₂S₂O₃ and dissolve them in deionized water to prepare a cobalt sulfate concentration of 0.05 mol / L. -1 The concentration of Na2S2O3 is 0.1 mol / L.-1 The solution is used as the electrolyte;

[0124] Nickel foam was used as the working electrode, and a carbon rod as the counter electrode; both were immersed in the electrolyte at -0.01 A cm⁻¹. -2 The electrocatalyst obtained by constant current deposition for 3 min and then vacuum drying in a vacuum oven is denoted as D1.

[0125] Comparative Example 2

[0126] Compared to Example 1, the second deposition step is omitted, and the first electrolyte contains only one metal salt, cobalt sulfate. That is, the cobalt sulfate and sodium molybdate in Example 1 are replaced with cobalt sulfate at a concentration of 0.06 mol / L. -1 Everything else is the same as in Example 1. The electrocatalyst obtained in Comparative Example 2 is denoted as D2.

[0127] Comparative Example 3

[0128] Weigh out cobalt sulfate, sodium molybdate, NaH₂PO₂, and Na₃C₆H₅O₇, dissolve them in deionized water, and prepare a cobalt sulfate solution with a concentration of 0.045 mol / L. -1 The concentration of sodium molybdate is 0.015 mol / L. -1 The concentration of NaH2PO2 is 0.5 mol / L. -1 The concentration of Na3C6H5O7 is 0.15 mol / L. -1 The solution is used as the electrolyte, with nickel foam as the working electrode and a carbon rod as the counter electrode, forming a two-electrode system.

[0129] Immerse the working electrode and counter electrode in the electrolyte at -0.1 A cm⁻¹ -2 The electrode was deposited under constant current for 15 minutes. After being cleaned and dried with deionized water, a foam nickel electrode with the first metal phosphide layer was obtained, denoted as D3.

[0130] Test Example 1

[0131] The alkaline HER performance of the composite HER electrocatalysts prepared in Examples 1-12 and the electrocatalysts prepared in Comparative Examples 1-3 was evaluated by LSV curve testing. Specifically:

[0132] In the three-electrode system, the electrocatalysts prepared in Examples 1-12 and Comparative Examples 1-3 were used as working electrodes, with the Hg / HgO electrode as the reference electrode and the carbon rod as the counter electrode. The electrolyte was 1.0 mol L⁻¹. -1 KOH solution, scan rate 10 mVs -1 LSV curve testing was performed at -500mA cm. 2 The test results of the potential (or overpotential) values ​​at that time are shown in Table 1. The LSV test curves of the composite electrocatalysts in Examples 1-4 are shown in Table 1. Figure 3 As shown, from Figure 3 It can be seen that when the deposition time of surface sulfides is extended, the catalytic activity of the composite electrocatalyst will decrease slightly. When the deposition time reaches 4 min, the catalytic activity decays significantly. In Example 1, the deposition time is 3 min, and its catalytic activity is better.

[0133] Figure 5 The LSV test curves for the composite electrocatalyst prepared in Example 1 and the electrocatalyst prepared in the comparative example are shown. The composite electrocatalyst of Example 1 is measured at -500 mA cm⁻¹. 2 The overpotential at that time was 226mV; the foam nickel electrode of Comparative Example 3 with the first metal phosphide layer deposited was -500mA cm 2 The overpotential at that time was 212mV.

[0134] Table 1

[0135] serial number Overpotential / mV Example 1 226 Example 2 220 Example 3 223 Example 4 243 Example 5 247 Example 6 239 Example 7 271 Example 8 276 Example 9 288 Example 10 233 Example 11 238 Comparative Example 1 445 Comparative Example 2 374 Comparative Example 3 212

[0136] Test Example 2: Electrocatalyst Stability Test

[0137] Cyclic CV and CP tests were performed on the composite electrocatalysts prepared in Examples 1-12 and the electrocatalysts prepared in Comparative Examples 1-3, respectively.

[0138] Cyclic CV test: at 1.0 mol L -1 In KOH solution, at 50 mV s -1 The scanning rate was cycled 5000 times, and the test results are shown in Table 2.

[0139] Table 2

[0140] serial number The decaying potential value mv after 5000 cycles Example 1 6 Example 2 8 Example 3 7 Example 4 8 Example 5 9 Example 6 9 Example 7 10 Example 8 10 Example 9 9 Example 10 11 Example 11 13 Comparative Example 1 21 Comparative Example 2 22 Comparative Example 3 17

[0141] Figure 6 The figures show the LSV curves of electrocatalyst N1 in Example 1 and electrocatalyst D1 in Comparative Example 3 before and after CV testing. Figure 6 (a) shows the LSV plots before and after the CV test of D3, after 5000 cycles, -10mA cm -2 The potential decay at that point is 17mV. Figure 6 (b) shows the LSV plots of N1 before and after the CV test. After 5000 cycles, its polarization curve basically coincides with the initial LSV curve. -10mA cm -2 The potential decay at that point is only 6mV. Figure 6 The test results demonstrate that the composite electrocatalyst described in this invention can improve the stability of the electrocatalyst under rapid start-stop conditions.

[0142] CP test: at 1.0 mol L -1 KOH solution at -500mA cm-2 The metering performance retention rate after 1000 hours of continuous operation at current density is shown in Table 3.

[0143] Table 3

[0144] serial number Metering performance retention rate (%) after 1000 hours of continuous operation Example 1 94.8 Example 2 92.3 Example 3 93.5 Example 4 92.2 Example 5 90.1 Example 6 90.7 Example 7 88.9 Example 8 89.2 Example 9 86.8 Example 10 94.3 Example 11 93.1 Comparative Example 1 62.1 Comparative Example 2 58.8 Comparative Example 3 57.3

[0145] Figure 7 The graphs show the performance retention rates of the electrocatalysts in Example 1 and Comparative Example 3 after 1000 hours of continuous operation. The electrocatalyst in Example 1 retained 94.8% of its performance after 1000 hours of continuous operation, while the electrocatalyst in Comparative Example 3 retained 57.3% of its performance after 1000 hours of continuous operation. Figure 7 The test results show that the composite electrocatalyst of the present invention, by depositing a second metal sulfide on the surface of the first metal phosphide, can improve the overall stability of the catalyst without obscuring the active sites of the first metal phosphide inside, demonstrating the key role of the construction of the bilayer composite structure in balancing the catalytic activity and stability of alkaline HER.

[0146] The electrode morphology after stability testing in Example 1 was characterized by SEM. Figure 8 The image shows the SEM spectrum of N1 after stability testing. Figure 8 It can be seen that N1 remains firmly loaded on the metal substrate surface after alkaline HER test, maintaining the morphology of the nanosheet clusters and without structural cracking or collapse, thus exhibiting structural mechanical stability.

[0147] Examples 1, 10, and 11 demonstrate how composite electrocatalysts of different sizes can be prepared using nickel foam substrates of different sizes. Figure 9 As shown, the two-step layer-by-layer assembly electrochemical reduction method for preparing composite electrocatalysts in this application is convenient, time-saving, and scalable. It is easy to scale up, and by replacing the conductive substrate with a larger one, a larger catalytic electrode can be obtained, which is convenient for industrial application.

[0148] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite electrocatalyst, characterized in that, The catalyst comprises: a conductive substrate and a first metal phosphide on the surface of the conductive substrate, and a second metal sulfide on the surface of the first metal phosphide; the first metal is selected from at least two of iron-based metals and group VIB metals; the second metal is selected from one or more of iron-based metals.

2. The composite electrocatalyst according to claim 1, wherein, The conductive substrate is selected from one or more of metallic foam materials, metal sheets, and metal felts; the metal is selected from nickel and / or stainless steel; and / or The first metal is selected from at least two of Fe, Co, Ni and Mo. Preferably, the content of any one first metal is not less than 10 mol% of the total amount of the first metal. Preferably, the first metal contains at least Co, and Co accounts for 80 mol%-90 mol% of the total first metal, preferably 83 mol%-87 mol%, more preferably 84 mol%-86 mol%; and / or The second metal is selected from one or more of Fe, Co, and Ni.

3. The composite electrocatalyst according to claim 1 or 2, wherein, The composite electrocatalyst comprises a conductive substrate and a first metal phosphide layer on the surface of the conductive substrate, and a second metal sulfide layer on the surface of the first metal phosphide layer; and / or The molar ratio of the first metal to phosphorus in the first metal phosphide is 1:0.1-0.5, preferably 1:0.15-0.2; and / or The molar ratio of the second metal to sulfur in the second metal sulfide is 1:0.5-1, preferably 1:0.5-0.6; and / or In the composite electrocatalyst, the molar ratio of phosphorus to sulfur is 1:0.1-1.

4. The method for preparing the composite electrocatalyst according to any one of claims 1-3, characterized in that, The method includes: (1) An electrodeposition system is formed by the conductive substrate, the counter electrode and the first electrolyte, and a first electrodeposition is performed; (2) The conductive substrate, the counter electrode and the second electrolyte after the first electrodeposition are formed into an electrodeposition system, and the second electrodeposition is performed; The first electrolyte contains a first metal salt, a phosphorus source, and a complexing agent. The second electrolyte contains a second metal salt and a sulfur source.

5. The preparation method according to claim 4, wherein, In the first electrolyte, the first metal salt, calculated as the first metal, has a concentration of 0.02–0.08 mol / L. -1 Preferably, the concentration is 0.05-0.07 mol / L. -1 ; The phosphorus source is expressed as phosphorus, and its concentration is 0.2–0.8 mol / L. -1 ; and / or The concentration of the complexing agent is 0.1–0.2 mol / L. -1 ; and / or The phosphorus source is selected from one or more of phosphates, monohydrogen phosphates, dihydrogen phosphates, hypophosphites, and dihydrogen hypophosphite; preferably one or more of NaH₂PO₂, NH₄H₂PO₄, and (NH₄)₂HPO₄; and / or The complexing agent is selected from one or more of citrate, malate, and tartrate, preferably sodium citrate; and / or Preferably, the first metal salt is selected from at least two of Fe salt, Co salt, Ni salt and Mo salt, and more preferably, the content of any one of the first metal salts is not less than 10 mol% of the total mass of the first metal salt; Preferably, the first metal salt contains at least a Co salt, and the Co salt accounts for 70 mol%-80 mol% of the total amount of the first metal salt, more preferably 72 mol%-78 mol%, and even more preferably 74 mol%-76 mol%.

6. The preparation method according to claim 4, wherein, In the second electrolyte, the second metal salt, calculated as a second metal, has a concentration of 0.02–0.08 mol / L. -1 Preferably, it is 0.04-0.06 mol / L. -1 ; The sulfur source is expressed as sulfur, with a concentration of 0.05–0.3 mol / L. -1 ; and / or The sulfur source is selected from one or more of thiosulfates, thioureas, and sulfides, preferably one or more of Na₂S₂O₃, thioureas, and sodium sulfide; and / or The second metal salt is selected from one or more of Fe salts, Co salts, and Ni salts.

7. The preparation method according to any one of claims 4-6, wherein, The first electrodeposition conditions include a current density of -0.05 to -0.2 A / cm³. -2 Preferably, the Å value is -0.08 to -0.12 Å cm. -2 The deposition time is 5–20 min, preferably 8–17 min; and / or The second electrodeposition conditions include a current density of -0.005 to -0.02 A / cm³. -2 Preferably, the value is -0.008 to -0.012 Å cm. -2 The deposition time is 1 to 4 minutes, preferably 2.5 to 3.5 minutes.

8. The preparation method according to any one of claims 4-6, wherein, In step (1), a conductive substrate is used as the working electrode, a graphite electrode or a platinum electrode is used as the counter electrode, and a dual-electrode system is constructed with the first electrolyte. and / or In step (2), a dual-electrode system is constructed using the conductive substrate after the first electrodeposition as the working electrode, the graphite electrode or the platinum electrode as the counter electrode, and the second electrolyte. Preferably, the graphite electrode is the counter electrode.

9. An electrode, characterized in that, The composite electrocatalyst includes any one of claims 1-3.

10. The application of the composite electrocatalyst according to any one of claims 1-3 or the electrode according to claim 9 in hydrogen production by water electrolysis, preferably in hydrogen production by alkaline water electrolysis.

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