Water electrolysis hydrogen production system and development and application of cathode assembly of water electrolysis hydrogen production system

Abstract

The invention relates to the field of green energy equipment development, and discloses a water electrolysis hydrogen production system and development and application of a cathode assembly of the water electrolysis hydrogen production system, the cathode assembly comprises a nitrogen-doped carbon catalyst jointly loaded by ruthenium single atoms and ruthenium atom clusters, and the ruthenium single atoms and the ruthenium atom clusters are jointly anchored on a nitrogen-doped carbon carrier. The invention further discloses application of the cathode assembly in a water electrolysis hydrogen production system. The cathode assembly comprising the nitrogen-doped carbon catalyst jointly loaded by the ruthenium single atoms and the ruthenium atom clusters, provided by the invention, shows high catalytic activity, excellent structural stability and long cycle life when being applied to an alkaline electrolysis water HER process.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of green energy equipment development, in particular to the development and application of a water electrolysis hydrogen production system and a cathode assembly thereof. BACKGROUND

[0002] With the increasing demand for clean energy worldwide, the technology of using renewable energy such as solar and wind power to drive water decomposition to produce hydrogen has become one of the most sustainable ways to produce "green hydrogen". Among the many water electrolysis hydrogen production technologies, anion exchange membrane water electrolysis (AEM) technology has developed rapidly. In an alkaline electrolyte (such as potassium hydroxide or sodium hydroxide solution), water is decomposed into hydrogen and oxygen through an electrocatalytic reaction. Compared with proton exchange membrane water electrolysis or solid oxide water electrolysis technology, AEM water electrolysis hydrogen production technology has the significant advantages of relatively simple equipment structure and lower cost. However, in the process of alkaline water electrolysis, the efficiency of the hydrogen evolution reaction (HER) on the cathode is the key to determining the overall energy efficiency. The HER reaction kinetics in an alkaline environment is much slower than in an acidic environment: the reaction mechanism is not directly from protons (H + ) to electrons to generate hydrogen, but first undergoes a water molecule dissociation step (H2O→H + +OH - ) to generate hydrogen ions / protons, and then the generated protons participate in the reduction reaction. This additional step increases the HER reaction energy barrier, resulting in a higher overpotential. The increase in overpotential not only increases the energy consumption of the water electrolysis hydrogen production process, but also reduces the overall hydrogen production efficiency. Therefore, high-performance noble metal catalysts are needed to reduce the reaction overpotential and improve the HER electrolysis efficiency.

[0003] In the field of alkaline water electrolysis HER reaction, an ideal catalyst needs to have high catalytic activity, excellent stability, and low cost. Although platinum-based catalysts are considered to be highly efficient HER catalysts, their resource scarcity and high cost have severely limited their large-scale application, thus promoting the research progress of non-platinum efficient catalysts. Among them, ruthenium (Ru) is considered a potential platinum alternative catalyst because its cost is significantly lower than platinum, it has similar hydrogen adsorption free energy, lower water dissociation energy barrier, and good durability. In recent years, alkaline HER catalysts with Ru as the active center have been widely studied, but the low utilization rate of noble metals is still the key to the high cost. Therefore, the synergistic catalyst system composed of isolated single atoms and a few to dozens of atomic clusters has attracted widespread attention in recent years. This structure has a high proportion of surface active sites, unique electronic structure, and synergistic effect of atomic dispersion and aggregation state, which is of great significance to promote the electrocatalytic HER reaction.

[0004] As disclosed in CN116219485A, a Fe single-atom ring Ru nanocluster electrolytic water hydrogen production catalyst is disclosed, in which amorphous FeN rings the crystalline Ru nanocluster structure is uniformly dispersed on the carbon material, and through the structural coordination optimization of Ru atoms, high efficient HER and oxygen evolution (OER) performance in electrolytic water is realized, and the atomically dispersed noble metal Ru realizes efficient utilization of metal atoms, which has economic value and market application prospect.

[0005] As disclosed in CN116288475A, a preparation method of a Ru-based single-atom catalyst is disclosed, in which the carrier WO2 can spontaneously adsorb dissociated water molecules and produce a large number of hydrogen protons, ensuring high concentration of proton coverage on the catalyst interface; the metal Ru single-atom site drives proton transfer to couple hydrogen gas to escape, realizing efficient electrolytic water hydrogen production system.

[0006] Currently, the atomically dispersed Ru catalysts reported in the research still have problems such as limited atom utilization and easy agglomeration of metal Ru single atoms in the electrolytic water HER reaction. Therefore, developing a scalable and low-cost atomically dispersed Ru-based electrolytic water HER catalyst preparation strategy has become a key research direction to promote the practical application in this field. SUMMARY

[0007] The purpose of the present application is to disclose a development and application of an electrolytic water hydrogen production system and a cathode assembly thereof, and the present application proposes a cathode assembly including a nitrogen-doped carbon-based catalyst loaded with Ru single atoms and Ru atomic clusters as a synergistic catalytic center. The cathode assembly exhibits high catalytic activity, excellent structural stability and long cycle life in the alkaline electrolytic water HER process.

[0008] The first invention purpose of the present application is realized by the following technical scheme: A cathode assembly of an electrolytic water hydrogen production system, the cathode assembly comprising a nitrogen-doped carbon catalyst loaded with ruthenium single atoms and ruthenium atomic clusters, the ruthenium single atoms and ruthenium atomic clusters being jointly anchored on the nitrogen-doped carbon carrier.

[0009] Further, the preparation method of the catalyst comprises the following steps: (1) dispersing and dissolving carbon black, nitrogen-containing organic precursor and ruthenium salt together to obtain a suspension; (2) heating the suspension until the solvent is completely volatilized to obtain a precursor powder; (3) under the protection of inert atmosphere, the precursor powder is heat treated to obtain a nitrogen-doped carbon catalyst loaded with ruthenium single atoms and ruthenium atomic clusters.

[0010] The present application adopts the strategy of in-situ adsorption combined with high-temperature pyrolysis, and successfully constructs a nitrogen-doped carbon composite catalyst containing Ru single atoms and Ru atomic clusters on a nitrogen-doped carbon carrier.

[0011] In step (1), the mass ratio of the carbon black and the nitrogen-containing organic precursor is 1-8:1. The mass ratio of the nitrogen-containing organic precursor and the ruthenium salt is 100 mg:31-41.4 mg. The nitrogen-containing organic precursor is urea, and the ruthenium salt is ruthenium chloride.

[0012] In step (3), the temperature of the heat treatment is 450-600 DEG C.

[0013] In the preparation method provided by the present application, sufficient anchoring sites are provided by the appropriate amount of nitrogen source in step (1), and part of the Ru atoms are stably limited to the metal single atom state; at the same time, through the synergistic effect of the limited amount of Ru salt in step (1) and the optimized pyrolysis temperature in step (3), part of the Ru atoms are promoted to undergo controllable migration and nucleation under the premise of avoiding the formation of large-size nanoparticles, thereby forming well-dispersed sub-nano-sized Ru atomic clusters. Therefore, by accurately adjusting the amount of introduced metal Ru salt and the calcination temperature, a nitrogen-doped carbon composite catalyst containing Ru single atoms and Ru atomic clusters and having a suitable ratio of the two is successfully constructed on a nitrogen-doped carbon carrier.

[0014] In step (1), the carbon black, the nitrogen-containing organic precursor and the ruthenium salt are dispersed in anhydrous ethanol, and they are fully mixed by alternately performing mechanical stirring and ultrasonic treatment; wherein: the stirring and ultrasonic treatment are alternately performed, and the total time is 24 h.

[0015] In step (2), the suspension is transferred to an oil bath environment at a set temperature, and continuously heated at a certain stirring speed until the solvent is completely volatilized, to obtain a dry precursor powder; the oil bath temperature is 60 DEG C, and the stirring speed is 250 rpm.

[0016] In step (3), the protective gas is argon, and the flow rate of the protective gas is 20 mL / min; the heat treatment includes: increasing the temperature to 450-600 DEG C at a rate of 4 DEG C / min and maintaining for 2 h.

[0017] The second application purpose of the present application is realized by the following technical scheme: The application of a cathode assembly including a nitrogen-doped carbon catalyst co-loading ruthenium single atoms and ruthenium atomic clusters in the water electrolysis HER reaction, especially in the alkaline water electrolysis for hydrogen production.

[0018] The cathode assembly is used as a working electrode in a three-electrode system, or as a cathode in an anion exchange membrane electrolytic cell.

[0019] In the ruthenium monatomic and ruthenium atomic cluster co-loaded nitrogen-doped carbon catalyst, the Ru monatomic site can provide high intrinsic catalytic activity and maximum atomic utilization rate, and the Ru atomic cluster can help to promote water molecule dissociation and optimize hydrogen adsorption free energy, and both of them can improve the alkaline HER reaction performance through electronic coupling and structural synergistic effect. For example, at 10 mA cm -2 The current density is 32 mV, which is lower than that of the commercial 20 wt.% Pt / C catalyst (42 mV); in addition, when it is applied as a cathode in an anion exchange membrane electrolysis cell, a high current density of 1.9 A cm -2 at 2.0 V cell voltage can be realized, which shows good application potential.

[0020] Compared with the prior art, the present application has the following beneficial effects: 1. The ruthenium monatomic and ruthenium atomic cluster co-loaded nitrogen-doped carbon catalyst provided or prepared by the present application is anchored on the nitrogen-doped carbon carrier in the form of ruthenium monatomic and ruthenium atomic cluster, which fully utilizes the synergistic advantages of high intrinsic activity of Ru monatomic and high water dissociation capacity of Ru atomic cluster, and significantly improves the alkaline water electrolysis HER performance.

[0021] 2. The catalyst provided by the present application shows high catalytic activity, excellent structural stability and long cycle life in the alkaline water electrolysis HER process; and due to the low metal loading and high stability, the catalyst shows better water electrolysis HER performance (electrochemical activity and long-term stability) than the commercial 20 wt.% Pt / C in alkaline medium, which is a new type of high-efficiency alkaline HER electrocatalyst with wide application prospect; thereby solving the problems of low metal atom utilization rate, insufficient catalytic activity and poor stability of the existing supported Ru-based catalyst in the alkaline water electrolysis HER reaction. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The X-ray absorption near-edge structure (XANES) spectrum of the ruthenium monatomic and ruthenium atomic cluster co-loaded nitrogen-doped carbon catalyst prepared in Example 1 of the present application is shown in the figure; Figure 2 The extended X-ray absorption fine structure (EXAFS) spectrum of the ruthenium monatomic and ruthenium atomic cluster co-loaded nitrogen-doped carbon catalyst prepared in Example 1 of the present application is shown in the figure; Figure 3 The in-situ X-ray absorption near-edge structure (XANES) spectrum of the ruthenium monatomic and ruthenium atomic cluster co-loaded nitrogen-doped carbon catalyst prepared in Example 1 of the present application is shown in the figure; Figure 4The image shows the in-situ extended X-ray absorption fine structure (EXAFS) spectrum of the nitrogen-doped carbon catalyst co-supported by ruthenium single atoms and ruthenium atom clusters prepared in Example 1 of this invention. Figure 5 The HER linear sweep voltammetry of the catalysts prepared in Examples 1-3 and Comparative Examples 1-3 of this invention in 1.0 M KOH electrolyte is shown. Figure 6 This is a linear voltammetry diagram of an anion exchange membrane electrolyzer for a nitrogen-doped carbon catalyst co-supported by ruthenium single atoms and ruthenium atom clusters prepared in Example 1 of this invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0024] All raw materials used in the following specific implementation methods were purchased from the market.

[0025] Example 1 This embodiment describes a nitrogen-doped carbon catalyst co-supported by ruthenium single atoms and ruthenium atom clusters. The preparation method includes the following steps: (a) First, 400 mg carbon black, 100 mg urea and 31 mg ruthenium trichloride were dispersed in 200 mL anhydrous ethanol. The mixture was then subjected to alternating stirring and ultrasonic treatment for 24 h to form a uniformly dispersed mixture. The mixture was then placed in an oil bath at 60 °C and stirred until dry. After drying and grinding, fine granular precursor powder was obtained. (b) The obtained precursor powder was subjected to high-temperature pyrolysis in an argon atmosphere (flow rate controlled at 20 mL / min), and the temperature was programmed to rise to 600 °C at a rate of 4 °C / min and held at a constant temperature for 2 h to finally obtain a nitrogen-doped carbon catalyst supported by ruthenium single atoms and ruthenium atom clusters.

[0026] like Figure 1 and Figure 2As shown, X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra were performed on the nitrogen-doped carbon catalyst supported by ruthenium single atoms and ruthenium atom clusters. The XANES spectrum shows that the absorption edge of Ru lies between the Ru metal foil and RuO2, indicating that the average oxidation state of Ru in this catalyst is between 0 and +4, exhibiting a mixed valence state. In the extended edge region analysis, significant Ru-N coordination peaks and Ru-Ru metal coordination peaks were observed. The Ru-N coordination corresponds to the Ru single-atom sites anchored on the nitrogen-doped carbon support, while the Ru-Ru coordination confirms the existence of sub-nanometer-scale Ru atom clusters. This result demonstrates that the catalyst simultaneously contains atomically dispersed Ru single atoms and Ru atom clusters with metallic characteristics, which together constitute a synergistic catalytic active center, providing the structural basis for its excellent electrocatalytic performance.

[0027] Table 1 shows the extended X-ray absorption fine structure (EXAFS) fitting results of the nitrogen-doped carbon catalyst co-supported with ruthenium single atoms and ruthenium atom clusters prepared in this embodiment. The fitting data show that the coordination number of Ru-N in this composite catalyst is approximately 4.2, indicating a stable coordination environment between the Ru single atom and the nitrogen-doped carbon support; while the coordination number of Ru-Ru is approximately 1.9, confirming the presence of small-sized Ru atom clusters.

[0028] Table 1. EXAFS curve fitting analysis results of nitrogen-doped carbon co-loaded by ruthenium single atoms and ruthenium atom clusters. In Table 1, Path: coordinating element, representing the types of coordinating atoms in the sample that bond with the central element; N: coordination number, representing the types of coordinating atoms in the sample that bond with the central element; R: bond length, representing the average distance between coordinating atoms; σ 2 : Debyeval factor, representing the degree of disorder in the atomic arrangement of the sample; ∆E: internal potential correction value, representing the magnitude of energy change during the fitting process; R-factor: goodness of fit, used to evaluate the accuracy of the fitting results.

[0029] Figure 3 The X-ray absorption near-edge structure (XANES) spectrum of Example 1, measured at the Ru K absorption edge under in-situ testing conditions, is shown. It can be seen that the absorption edge position of Example 1 did not shift significantly with increasing applied potential, indicating that its electronic state remained stable during the reaction. Figure 4The Fourier transform results of the extended X-ray absorption fine structure (EXAFS) spectrum of Example 1 are shown. The intensities of both the Ru-N coordination peak and the Ru-Ru coordination peak did not change significantly with increasing applied potential, indicating that the Ru single-atom and Ru atom cluster structures remained stable during the reaction.

[0030] Inductively coupled plasma atomic emission spectrometry (ICP-AES / MS) analysis showed that the mass fraction of Ru in the nitrogen-doped carbon catalyst supported by ruthenium single atoms and ruthenium atom clusters was approximately 3 wt.%.

[0031] Example 2 The mass of RuCl3 in step (a) was adjusted to 41.4 mg according to the process of Example 1 to obtain the catalyst.

[0032] Example 3 Following the process of Example 1, the calcination temperature in step (c) was changed to 450 °C to obtain the catalyst.

[0033] Comparative Example 1 The other conditions and operations are the same as in Example 1, except that the calcination holding time in step (c) is changed from 2 h to 1 h to obtain the catalyst.

[0034] Comparative Example 2 The mass of RuCl3 in step (a) was adjusted to 20.7 mg according to the process of Example 1 to obtain the catalyst.

[0035] Comparative Example 3 A commercial Pt / C with a mass fraction of 20 wt.% was used as a comparative catalyst for this catalyst.

[0036] Application Example 1 The catalysts prepared in Examples 1-3 and Comparative Examples 1-3 were applied to the alkaline water electrolysis HER reaction. The nitrogen-doped carbon catalyst supported by ruthenium single atoms and ruthenium atom clusters was used as the working electrode, Ag / AgCl was used as the reference electrode, and a graphite electrode was used as the counter electrode. 1.0 mol / L KOH was used as the electrolyte solution to form a three-electrode system. Cyclic voltammetry (CV) activation was performed using a Shanghai Chenhua CHI 660E electrochemical workstation: a CV program was used, with the test range being 0 to -0.4 V vs. RHE, a scan rate of 50 mV / s, and 20 cycles to bring the electrode to a stable state.

[0037] Linear sweep voltammetry (LSV) was used for testing. After electrode activation, the process was switched to the LSV program. The LSV curves for the HER reaction of water electrolysis using the catalysts prepared in Examples 1-3 and Comparative Examples 1-3 are shown below.Figure 5 As shown, it can be seen that, compared to Examples 2-3 and Comparative Examples 1-3, Example 1 at 100 mA cm⁻¹ -2 The overpotential at the point is 34 mV, which is superior to the catalysts prepared in Examples 2-3 and Comparative Examples 1-3.

[0038] Application Example 2 The catalyst prepared in Example 1 was used in an anion exchange membrane electrolyzer for a complete water splitting reaction. The cathode was the catalyst prepared in Example 1, the anode was a commercial RuO2 catalyst, and the anion exchange membrane was a Sustainion® X37-50 Grade 60 membrane. MGL-280 carbon paper was added between the cathode catalyst and the electrode as a gas diffusion layer. 1.0M KOH was used as the electrolyte, heated to 80 °C, and introduced into the electrolyzer via a peristaltic pump. The polarization curve of the catalyst prepared in Example 1 in the anion exchange membrane electrolyzer is shown below. Figure 6 As shown, the catalyst prepared in Example 1 can achieve 1.9 A cm⁻¹ at 2.0 V. -2 The current density exhibits excellent hydrogen evolution performance in water electrolysis.

Claims

1. A cathode assembly of a hydrogen production system by electrolysis of water, characterized in that, The cathode assembly comprises a nitrogen-doped carbon catalyst co-loaded with ruthenium monomers and ruthenium atomic clusters, and the ruthenium monomers and ruthenium atomic clusters are co-anchored on a nitrogen-doped carbon carrier.

2. The cathode assembly of the water electrolysis hydrogen production system according to claim 1, characterized in that, The preparation method of the catalyst comprises the following steps: (1) dispersing and dissolving carbon black, a nitrogen-containing organic precursor and a ruthenium salt together to obtain a suspension; (2) heating the suspension until the solvent is completely volatilized to obtain a precursor powder; (3) performing heat treatment on the precursor powder under the protection of an inert atmosphere to obtain a nitrogen-doped carbon catalyst co-loaded with ruthenium monomers and ruthenium atomic clusters.

3. The cathode assembly of the water electrolysis hydrogen production system according to claim 2, characterized in that, In step (1), the mass ratio of the carbon black to the nitrogen-containing organic precursor is 1-8:

1.

4. The cathode assembly of the water electrolysis hydrogen production system according to claim 3, wherein, The mass ratio of the nitrogen-containing organic precursor to the ruthenium salt is 100 mg:31-41.4 mg.

5. The cathode assembly of the water electrolysis hydrogen production system according to claim 4, wherein, The nitrogen-containing organic precursor is urea, and the ruthenium salt is ruthenium chloride.

6. The cathode assembly of the water electrolysis hydrogen production system according to claim 2, wherein, In step (3), the temperature of the heat treatment is 450-600 ℃.

7. The cathode assembly according to any one of claims 1-6 is applied in a water electrolysis hydrogen production system.

8. Use according to claim 7, characterized in that, The application in water electrolysis hydrogen production under alkaline conditions.

9. Use according to claim 8, characterized in that, The cathode catalyst serves as a working electrode.

10. Use according to claim 8, characterized in that, The cathode catalyst serves as a cathode in an anion exchange membrane electrolyzer.

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