Ni-NiO / CeO2 heterojunction nano-catalyst as well as preparation method and application thereof

Abstract

The invention discloses a Ni-NiO / CeO2 heterojunction nano-catalyst as well as a preparation method and an application of the Ni-NiO / CeO2 heterojunction nano-catalyst. The catalyst is prepared by taking nickel and cerium ions as precursors through a one-step controllable incomplete reduction method, the process is simple, the yield is close to 100%, and the catalyst is suitable for mass production. In the catalyst, CeO2 effectively promotes water molecule dissociation, NiO species finely regulates and controls a hydrogen intermediate (H *) adjacent to a nickel active site to adsorb free energy, the bottleneck problems that a traditional nickel-based material is too high in H * adsorption and slow in water dissociation kinetics are synergistically solved, the catalyst shows excellent hydrogen evolution reaction activity in a 1M KOH electrolyte, and the catalyst can be applied to the field of hydrogen production. The overpotential is only 62 mV (relative to a reversible hydrogen electrode) under the current density of 10 mA cm <-2 >, and the performance is equivalent to that of a commercial 60% Pt / C catalyst; after the electrode is pressed into an integral electrode, the electrode can stably run for 300 hours under the ultrahigh current density of 1A cm <-2 > without activity attenuation. The catalyst disclosed by the invention is suitable for cathode hydrogen evolution reaction of alkaline electrolyzed water and anion exchange membrane electrolyzed water systems, and has an important industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation and water electrolysis for hydrogen production technology, specifically relating to a Ni-NiO / CeO2 heterojunction nanocatalyst and its preparation method. This catalyst is suitable for the cathode catalytic reaction of alkaline water electrolysis for hydrogen production and anion exchange membrane water electrolysis for hydrogen production systems. Background Technology

[0002] In anion exchange membrane electrolysis (AEMWE) technology, developing efficient, stable, and low-cost non-precious metal hydrogen evolution reaction (HER) catalysts is crucial for promoting the large-scale production of green hydrogen. Nickel-based catalysts are considered ideal alternatives to platinum-based catalysts due to their abundant reserves and low cost; however, their intrinsic activity is limited, particularly the slow kinetics of the Volmer step (water molecule dissociation) in alkaline environments and the insufficient adsorption / desorption energy barriers of hydrogen intermediates (H*), which restricts their widespread application.

[0003] To overcome these challenges, researchers have focused on modulating the electronic structure of nickel by constructing heterojunctions. Introducing cerium oxide (CeO2) to form a Ni-CeO2 heterojunction is considered an effective strategy. Research by Associate Professor Hao Xiaodong's team at Shaanxi University of Science and Technology shows that at the NiO / CeO2 heterojunction interface, electron transfer occurs from Ni to Ce, leading to a decrease in the Ce valence state and the generation of more oxygen vacancies. These oxygen vacancies not only optimize the hydrogen adsorption free energy (ΔG) H *), and can also significantly promote the dissociation process of water molecules, thereby enabling the catalyst to operate at 10 mA cm⁻¹ -2 It exhibits a low overpotential of 99 mV and a decant of 78.4 mV at current density. -1The Tafel slope was obtained (Hao, X., et al., Atomic-scale insights into the interfacial charge transfer in a NiO / CeO2 heterostructure for electrocatalytic hydrogenevolution. Journal of Colloid and Interface Science, 2023. 643: p. 282-291.). Research from China University of Petroleum (East China) also confirms the importance of interface engineering. Significant electronic state changes and optimized oxygen vacancy concentrations at the NiO-CeO2 interface can effectively improve the performance of the CO2 reduction reaction, providing a reference for understanding the role of similar interfaces in HER (Wang, X., et al., Tailoring CeO2 catalysts via oxygen vacancies and Ni loading: Boosting RWGS reaction performance and uncovering underlying mechanisms. Molecular Catalysis, 2026. 589.). Research from Tianjin University reveals from a theoretical perspective that using CeO2(110) as a support can enhance metal-support interaction (MSI), thereby promoting the methane steam reforming reaction, illustrating the importance of support crystal plane regulation (Wu Chan, Design and reaction mechanism of nickel-based catalysts for alkane steam reforming. 2021, Tianjin University.).

[0004] Despite the progress made in improving the intrinsic activity of catalysts, existing preparation methods still have significant limitations, hindering their industrial application. Currently widely used hydrothermal or co-precipitation methods typically require high-temperature and high-pressure reaction conditions, resulting in complex processes, demanding equipment, and difficulties in precisely controlling the uniformity and consistency of products during large-scale production. For example, in the synthesis of NiO / CeO2 heterostructures, the amount of nickel precursor added needs to be precisely controlled (e.g., 20%) to form the ideal heterojunction, rather than simple doping, which increases the complexity of process control. Furthermore, how to achieve nickel species (especially metallic nickel Ni) remains a challenge. 0 Achieving high dispersion and stable anchoring of nickel oxide (NiO) on the CeO2 surface, and precisely controlling their ratio to synergistically optimize water molecule dissociation and H* adsorption / desorption processes, remains a major challenge for current preparation techniques. Some studies have attempted multi-step impregnation-calcination or the use of complex templates, but these methods are often cumbersome or may introduce impurities, which are detrimental to the large-scale preparation and long-term stability of the catalyst.

[0005] In summary, while existing technologies have demonstrated the potential of Ni-CeO2 interfacial interactions to enhance HER performance, they have not recognized the regulatory role of insufficiently reduced nickel oxide on nickel metal sites. Furthermore, the preparation methods still require breakthroughs in terms of large-scale production, cost control, process simplification, and precise control of active sites. Therefore, developing a simple, easily mass-producible, and precisely controllable Ni-based catalyst synthesis method is of great significance for promoting the industrialization of AEMWE technology. Summary of the Invention

[0006] The purpose of this invention is to provide a Ni-NiO / CeO2 heterojunction nanocatalyst, which promotes the dissociation of water molecules by introducing CeO2 heterojunction into nickel-based materials; at the same time, it controls the degree of nickel reduction so that the insufficiently reduced nickel oxide modulates the hydrogen adsorption barrier of the metallic nickel sites, thereby synergistically optimizing the hydrogen evolution activity of water electrolysis.

[0007] The Ni-NiO / CeO2 heterojunction nanocatalyst provided by this invention is composed of three phases: metallic Ni, NiO, and CeO2. The catalyst has a coral-like microscopic heterostructure formed by cross-linking of nanoparticles. The metallic Ni forms a porous framework, the surface of which is coated with NiO and loaded with CeO2 nanoparticles rich in oxygen vacancy defects. With the total molar number of metallic Ni, NiO, and CeO2 in the catalyst being 100%, the molar percentages of each phase are 30%–80%, 10%–50%, and 10%–20%, respectively.

[0008] Furthermore, in the above-mentioned Ni-NiO / CeO2 heterojunction nanocatalyst, with the total molar number of the three phases of metallic Ni, NiO and CeO2 in the catalyst being 100%, the preferred molar percentages of each phase are 40% to 60%, 30% to 50%, and 10% to 20%, respectively.

[0009] Furthermore, in the above-mentioned Ni-NiO / CeO2 heterojunction nanocatalyst, the CeO2 rich in oxygen vacancy defects contains Ce... 3 + The relative content of it accounts for 20% to 30% of the total Ce element.

[0010] The preparation method of Ni-NiO / CeO2 heterojunction nanocatalyst provided by the present invention includes the following steps:

[0011] Step 1: Ni 2+ Soluble salts with Ce 4+ The soluble salt is dissolved in deionized water to obtain a precursor solution; the total metal ion concentration in the precursor solution is 0.3–0.5 mol / L, Ni 2+ With Ce4+ The molar ratio is 1:8 to 16:1.

[0012] Step 2: Remove the solvent from the precursor solution from Step 1 to obtain a solid precursor.

[0013] Step 3: The solid precursor from Step 2 is annealed in air atmosphere and then in reducing atmosphere to obtain Ni-NiO / CeO2 heterojunction nanocatalyst.

[0014] Furthermore, in step 1 above, the Ni 2+ The soluble salt is selected from any one or more of nickel nitrate, nickel acetate, and nickel chloride; the Ce 4+ The soluble salt is selected from any one or more of cerium nitrate, cerium ammonium nitrate, cerium chloride, and cerium sulfate.

[0015] Furthermore, in step 2 above, the solvent removal method is vacuum distillation, rotary evaporation, or natural evaporation, with a solvent removal temperature of 50–100 °C and a time of 0.5–12 hours. This process does not require gelation treatment; the enrichment and uniform mixing of metal ions are achieved directly through solvent removal.

[0016] Furthermore, in step 3 above, the preferred air annealing temperature is 300–600 °C, and the annealing time is 5–10 hours. This process allows the metal salt to completely decompose and crystallize, forming a composite powder containing Ni and Ce oxides.

[0017] Furthermore, in step 3 above, the reducing atmosphere is a mixture of H2 and Ar or N2 with a volume concentration of 5% to 50%.

[0018] Furthermore, in step 3 above, the preferred annealing temperature in the reducing atmosphere is 300–600 °C, and the annealing time is 1–6 hours. This process achieves Ni reduction by precisely controlling the reduction temperature and time. 2+ Incomplete reduction, retaining an appropriate amount of NiO.

[0019] The present invention also provides the use of the above-mentioned Ni-NiO / CeO2 heterojunction nanocatalyst in the cathodic hydrogen evolution reaction of alkaline water electrolysis or anion exchange membrane water electrolysis.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. This invention successfully constructs a three-phase heterojunction composed of metallic nickel (Ni), nickel oxide (NiO), and oxygen-vacancy-rich cerium dioxide (CeO2) through a controllable incomplete reduction process. Its unique coral-like (i.e., three-dimensional interconnected porous network) microstructure is characterized by a porous metallic Ni framework uniformly distributed with appropriate amounts of NiO, and loaded with Ce-rich... 3+ / Ce4+ This study describes defective CeO2 nanoparticles. In this structure, the oxygen-loving CeO2 efficiently promotes the dissociation of water molecules (H2O), while the tightly coupled NiO phase precisely modulates the adsorption free energy of H* at the adjacent active sites of metallic Ni. The synergistic effect of these two components fundamentally optimizes the bottleneck problems commonly found in traditional nickel-based materials, such as excessively strong H* adsorption and slow water dissociation kinetics.

[0022] 2. The catalyst of this invention exhibits excellent hydrogen evolution reaction (HER) performance, combining high activity with ultra-high stability. In 1 M KOH electrolyte, it demonstrates HER activity close to that of commercial noble metal benchmark catalysts: at 10 mA cm⁻¹ -2 The overpotential at current density is as low as 62 mV (relative to the reversible hydrogen electrode, vs. RHE). More notably, it exhibits significant advantages in long-term operational stability at high currents: at 1 A cm⁻¹... -2 At ultra-high current densities, the potential can remain stable at 230–260 mV (vs. RHE) for over 300 hours with an activity decay rate of less than 3%; at 200 mA cm⁻¹ -2 At higher current densities, the stability can be extended to over 700 hours. This indicates that the catalyst not only exhibits excellent activity but also has the potential to meet the demanding operating conditions required for industrial applications.

[0023] 3. The catalyst of this invention has a simple and efficient preparation process, which is easy to scale up for production. The preparation method does not require complex high-temperature and high-pressure equipment, the process route is simple, the operating conditions are mild, the reaction yield is close to 100%, and the reproducibility is good. This simple and efficient synthesis strategy greatly reduces production costs, laying a solid foundation for the commercial-scale preparation and application of the catalyst. Furthermore, while achieving high activity comparable to noble metal platinum-based catalysts, the catalyst of this invention exhibits excellent stability and significant cost advantages, making it of significant industrial application value in alkaline water electrolysis and anion exchange membrane water electrolysis for hydrogen production. Attached Figure Description

[0024] Figure 1 The images shown are scanning electron microscope (SEM) images (a), energy scattering spectroscopy (EDS) elemental mapping (b to d: Ni, Ce, O elemental distribution), and X-ray diffraction (XRD) patterns (f) of the catalyst prepared in Example 1.

[0025] Figure 2 This is the energy scattering (EDS) spectrum of the catalyst prepared in Example 1.

[0026] Figure 3This is a comparison of the LSV polarization curves of the catalyst prepared in Example 1 and the comparative catalyst (1 M KOH, no iR compensation, rotating disk electrode diameter 5 mm); Curve 1 is the catalyst of Example 1, Curve 2 is the nickel-based catalyst (Ni-NiO) without CeO2 in Comparative Example 1, Curve 4 is the catalyst with complete nickel reduction (Ni / CeO2) in Comparative Example 3, Curve 5 is the catalyst with unreduced nickel (NiO / CeO2), and Curve 6 is the commercial precious metal platinum-carbon (60% Pt / C) catalyst in Comparative Example 5.

[0027] Figure 4 The catalyst prepared in Example 1 was tested at 1 A cm⁻¹. –2 Stability curves at current density (1 M KOH).

[0028] Figure 5 Example 1 is at 200 A cm –2 Stability curves at current density (1 M KOH).

[0029] Figure 6 The images show scanning electron microscope (SEM) images and X-ray diffraction (XRD) patterns of a heterojunction catalyst with a high degree of reduction (Example 2).

[0030] Figure 7 This is the energy scattering (EDS) spectrum of the catalyst prepared in Example 2.

[0031] Figure 8 These are LSV polarization curves of Examples 2 and 3 (1 M KOH, no iR compensation, glassy carbon electrode diameter 3 mm); Curve 1 is the heterojunction catalyst with a higher degree of reduction, and Curve 2 is the heterojunction catalyst with a lower degree of reduction.

[0032] Figure 9 The images show scanning electron microscope (SEM) images and X-ray diffraction (XRD) patterns of a heterojunction catalyst with a low degree of reduction (Example 3).

[0033] Figure 10 This is the energy scattering (EDS) spectrum of the catalyst prepared in Example 3.

[0034] Figure 11 The images show scanning electron microscope (SEM) images and X-ray diffraction (XRD) patterns of the nickel-based catalyst (Ni-NiO) without CeO2 in Comparative Example 1.

[0035] Figure 12 This is the energy scattering (EDS) spectrum of the catalyst prepared in Comparative Example 1.

[0036] Figure 13The images show scanning electron microscope (SEM) images and X-ray diffraction (XRD) patterns of a cerium-based catalyst (CeO2) without Ni (Comparative Example 2).

[0037] Figure 14 This is the energy scattering (EDS) spectrum of the catalyst prepared in Comparative Example 2.

[0038] Figure 15 The images show scanning electron microscope (SEM) images and X-ray diffraction (XRD) patterns of the catalyst for complete reduction of nickel (Ni / CeO2) (Comparative Example 3).

[0039] Figure 16 This is the energy scattering (EDS) spectrum of the catalyst prepared in Comparative Example 3.

[0040] Figure 17 The images show scanning electron microscope (SEM) images and X-ray diffraction (XRD) patterns of the nickel-unreduced catalyst (NiO / CeO2) (Comparative Example 4).

[0041] Figure 18 This is the energy scattering (EDS) spectrum of the catalyst prepared in Comparative Example 4. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0043] Example 1

[0044] 1. Catalyst Preparation

[0045] Step 1: Weigh 29.1 g of nickel nitrate hexahydrate and 13.7 g of anhydrous cerium ammonium nitrate, add them to 250 mL of deionized water, and stir magnetically for 40 min to completely dissolve the solids, obtaining a precursor solution. The total metal ion concentration in the precursor solution is 0.5 mol / L, Ni 2+ With Ce 4+ The molar ratio is 4:1.

[0046] Step 2: The precursor solution from Step 1 was subjected to rotary evaporation to remove the solvent. The rotary evaporation temperature was 65 °C, the rotation speed was 200 rpm, and the evaporation time was 1 h, resulting in a yellow-green dry solid precursor.

[0047] Step 3: The solid precursor from Step 2 was placed in a muffle furnace and annealed at 550 °C for 10 h in air atmosphere to obtain composite oxide powder. The composite oxide powder was placed in a tube furnace, and an Ar / H2 mixed gas (H2 volume fraction of 5%) was introduced. It was reduced at 500 °C for 2 h, and after natural cooling, Ni-NiO / CeO2 heterojunction nanocatalyst was obtained.

[0048] Scanning electron microscopy (SEM) characterization results showed that the catalyst is a coral-like microscopic heterostructure formed by cross-linking of nanoparticles. Figure 1 a) Energy scattering spectroscopy (EDS) confirmed that the peaks for Ce, O, and Ni were inconsistent. Figure 1 b to d); X-ray diffraction (XRD) patterns show characteristic diffraction peaks for metallic Ni (PDF#01-070-0989), NiO (PDF#01-075-0197), and CeO2 (PDF#01-073-6318). Figure 1 f), confirming the coexistence of the three phases; energy dispersive spectroscopy (EDS) measured the atomic percentages of Ni, Ce, and O elements (f). Figure 2 According to Table 1, the molar percentages of metallic Ni, NiO, and CeO2, after conversion, are 43.28%, 45.65%, and 11.07%, respectively; X-ray photoelectron spectroscopy (XPS) measured Ce... 4+ Ce 3+ The proportions are 71.27% and 28.73%.

[0049] 2. Catalytic hydrogen evolution reaction

[0050] 0.01 g of Ni-NiO / CeO2 heterojunction nanocatalyst was dispersed in a mixture of 480 μL water, 480 μL ethanol, and 40 μL 5% Nafion D-520, and sonicated for 30 min to prepare a homogeneous slurry, which was then loaded onto a glassy carbon electrode. Testing was performed in 1 M KOH solution using a three-electrode system: a saturated calomel electrode (Hg|Hg2Cl2) as the reference, a graphite rod as the counter electrode, and a rotating disk electrode (5 mm in diameter, with a loading of approximately 0.65 mg / cm³). –2 ( ) is the working electrode, and the polarization curve (LSV) scan rate is 2 mV s. –1 Without iR compensation; measured at 10 A cm –2 Overpotential 62 mV vs. RHE (reversible hydrogen electrode) Figure 3 Curve 1).

[0051] 0.5 g of Ni-NiO / CeO2 heterojunction nanocatalyst was compressed and loaded onto a 0.5 × 0.5 cm⁻¹ substrate. -2 An integral electrode is formed on nickel foam, at 1 A cm –2Stable operation for 300 hours ( Figure 4 The potential remained at 230–260 mV vs. RHE (reversible hydrogen electrode), with no significant potential decay at 200 mA cm⁻¹. –2 After 700 hours of stable operation, the potential remained at 60–90 mV vs. RHE (reversible hydrogen electrode), with no significant potential decay. Figure 5 ).

[0052] Example 2

[0053] In step 3 of the catalyst preparation in Example 1, the solid precursor from step 2 was placed in a muffle furnace and annealed at 600 °C for 10 h in air atmosphere to obtain composite oxide powder. The composite oxide powder was placed in a tube furnace, and an Ar / H2 mixed gas (H2 volume fraction of 5%) was introduced. It was reduced at 600 °C for 2 h, and after natural cooling, Ni-NiO / CeO2 heterojunction nanocatalyst was obtained.

[0054] SEM characterization results showed that the catalyst was a coral-like heterostructure formed by cross-linking of nanoparticles. Figure 6 a) The X-ray diffraction (XRD) pattern shows characteristic diffraction peaks of metallic Ni, NiO, and CeO2. Figure 6 (b) This confirms the coexistence of the three phases of metallic Ni, NiO, and CeO2; the atomic percentages of Ni, Ce, and O were determined by energy dispersive spectroscopy (EDS). Figure 7 According to Table 1, the molar percentages of metallic Ni, NiO, and CeO2, after conversion, are 70.36%, 14.75%, and 14.89%, respectively; X-ray photoelectron spectroscopy (XPS) measured Ce... 4+ Ce 3+ The atomic percentages are 76.47% and 23.53%.

[0055] The catalytic hydrogen evolution reaction was carried out using the method of Example 1. The catalyst was supported on a glassy carbon electrode (3 mm in diameter, with a loading of approximately 0.65 mg cm⁻¹) in 1 M KOH solution. –2 ), 10 A cm –2 Overpotential 215 mV vs. RHE (reversible hydrogen electrode) Figure 8 Curve 1).

[0056] Example 3

[0057] In step 3 of the catalyst preparation in Example 1, the solid precursor from step 2 was placed in a muffle furnace and annealed at 500 °C for 10 h in an air atmosphere to obtain composite oxide powder. The composite oxide powder was placed in a tube furnace, and an Ar / H2 mixed gas (H2 volume fraction of 5%) was introduced. It was reduced at 300 °C for 2 h, and after natural cooling, Ni-NiO / CeO2 heterojunction nanocatalyst was obtained.

[0058] SEM characterization results showed that the catalyst was a coral-like heterostructure formed by cross-linking of nanoparticles. Figure 9 a) The X-ray diffraction (XRD) pattern shows characteristic diffraction peaks of metallic Ni, NiO, and CeO2. Figure 9 (b) This confirms the coexistence of the three phases of metallic Ni, NiO, and CeO2; the atomic percentages of Ni, Ce, and O were determined by energy dispersive spectroscopy (EDS). Figure 10 According to Table 1, the molar percentages of metallic Ni, NiO, and CeO2, after conversion, are 30.50%, 50%, and 19.50%, respectively; X-ray photoelectron spectroscopy (XPS) measured Ce... 4+ Ce 3+ The atomic percentages are 70.84% ​​and 29.16%.

[0059] The catalytic hydrogen evolution reaction was carried out using the method of Example 1. The catalyst was supported on a glassy carbon electrode (3 mm in diameter, loading ~0.65 mg cm⁻¹) in 1 M KOH solution. –2 ), 10 A cm –2 Overpotential 142 mV vs. RHE (reversible hydrogen electrode) Figure 8 Curve 2).

[0060] Comparative Example 1

[0061] Weigh 30 g of nickel acetate and add it to 250 mL of deionized water. Stir magnetically for 40 min until completely dissolved to obtain a precursor solution. Remove the solvent from the precursor solution according to step 2 of Example 1, and then anneal it in air and reducing atmosphere according to step 3 of Example 1 to obtain the Ni-NiO catalyst.

[0062] SEM characterization results showed that the catalyst had a coral-like structure. Figure 11 a) The X-ray diffraction (XRD) pattern shows characteristic diffraction peaks of metallic Ni and NiO. Figure 11 b), confirming the coexistence of metallic Ni and NiO phases; energy dispersive spectroscopy (EDS) determined the atomic percentages of Ni and O elements ( Figure 12(As shown in Table 1), the molar percentages of elemental Ni and NiO, after conversion, are 80.93% and 19.07%, respectively. The catalyst prepared by this method is a heterostructure of metallic Ni and NiO.

[0063] The catalytic hydrogen evolution reaction was carried out using the method of Example 1. The catalyst was supported on a rotating disk electrode (5 mm in diameter, with a loading of approximately 0.65 mg cm⁻¹) in 1 M KOH solution. –2 ), 10 A cm –2 Overpotential 345 mV vs. RHE (reversible hydrogen electrode) Figure 3 Curve 2).

[0064] Comparative Example 2

[0065] Weigh 30 g of cerium nitrate and add it to 250 mL of deionized water. Stir magnetically for 40 min until completely dissolved to obtain a precursor solution. Remove the solvent from the precursor solution according to step 2 of Example 1, and then anneal it in air and reducing atmosphere according to step 3 of Example 1 to obtain the CeO2 catalyst.

[0066] SEM characterization results showed that the catalyst had a particulate aggregate morphology. Figure 13 a) The X-ray diffraction (XRD) pattern shows characteristic diffraction peaks of CeO2 (a). Figure 13 b), confirming the presence of CeO2; energy dispersive spectroscopy (EDS) determined the atomic percentages of Ce and O elements ( Figure 14 (and Table 1), which conforms to the atomic ratio of CeO2.

[0067] The catalytic hydrogen evolution reaction was carried out using the method of Example 1. The catalyst was supported on a rotating disk electrode (5 mm in diameter, with a loading of approximately 0.65 mg cm⁻¹) in 1 M KOH solution. –2 ), with no obvious electrochemical hydrogen evolution activity ( Figure 3 Curve 3).

[0068] Comparative Example 3

[0069] In step 3 of the catalyst preparation in Example 1, the solid precursor from step 2 was placed in a muffle furnace and annealed at 550 °C for 10 h in an air atmosphere to obtain composite oxide powder. The composite oxide powder was placed in a tube furnace, and an Ar / H2 mixed gas (H2 volume fraction of 5%) was introduced. It was reduced at 800 °C for 2 h, and after natural cooling, a Ni / CeO2 catalyst was obtained.

[0070] SEM characterization results showed that the catalyst was a coral-like heterostructure formed by particle aggregation. Figure 15 a) The X-ray diffraction (XRD) pattern shows characteristic diffraction peaks of metallic Ni and CeO2. Figure 15 b), confirming the coexistence of metallic Ni and CeO2 in two phases; energy dispersive spectroscopy (EDS) measured the atomic percentages of Ni, Ce, and O elements ( Figure 16 According to Table 1, the molar percentages of Ni and CeO2 after conversion are 80.93% and 19.07%, respectively.

[0071] The catalytic hydrogen evolution reaction was carried out using the method of Example 1. The catalyst was supported on a rotating disk electrode (5 mm in diameter, with a loading of approximately 0.65 mg cm⁻¹) in 1 M KOH solution. –2 ), 10 A cm –2 Overpotential 299 mV vs. RHE (reversible hydrogen electrode) Figure 3 Curve 4).

[0072] Comparative Example 4

[0073] In step 3 of the catalyst preparation in Example 1, the solid precursor from step 2 was placed in a muffle furnace and annealed at 550 °C in air for 10 h. After natural cooling, the NiO / CeO2 catalyst was obtained.

[0074] SEM characterization results showed that the catalyst was a coral-like heterostructure formed by particle aggregation. Figure 17 a) The X-ray diffraction (XRD) pattern shows characteristic diffraction peaks for NiO and CeO2. Figure 17 b), confirming the coexistence of NiO and CeO2 phases; energy dispersive spectroscopy (EDS) measured the atomic percentages of Ni, Ce, and O elements ( Figure 18 According to Table 1, the molar percentages of NiO and CeO2 after conversion are 79.95% and 20.05%, respectively.

[0075] The catalytic hydrogen evolution reaction was carried out using the method of Example 1. The catalyst was supported on a rotating disk electrode (5 mm in diameter, with a loading of approximately 0.65 mg cm⁻¹) in 1 M KOH solution. –2 ), 10 A cm –2 Overpotential 620 mV vs. RHE (reversible hydrogen electrode) Figure 3 Curve 5).

[0076] Comparative Example 5

[0077] Commercially available precious metal platinum-carbon (60% Pt / C) was used to carry out a catalytic hydrogen evolution reaction using the method described in Example 1. Figure 3 Curve 6 shows that the catalyst in Example 1 performs close to the overpotential of commercial precious metal platinum-carbon (60% Pt / C) at low current density, which is 17 mV vs. RHE (reversible hydrogen electrode).

[0078] Table 1

[0079]

[0080] Table 2

[0081]

[0082] The experimental results above demonstrate that incomplete reduction of NiO during catalyst preparation is crucial for forming a high-performance three-phase heterojunction. Comparative analysis revealed that if higher temperatures or longer reduction times are used during preparation, the resulting product contains almost no NiO, becoming a Ni / CeO2 binary composite material, and its hydrogen evolution catalytic activity significantly decreases. This comparison strongly confirms the necessity of the Ni-NiO-CeO2 three-phase heterojunction in this invention, whose performance is significantly superior to most reported non-noble metal-based hydrogen evolution catalysts. The Ni-NiO / CeO2 heterojunction nanocatalyst provided by this invention successfully constructs a coral-like heterostructure of metallic Ni, NiO, and oxygen-vacancy-rich CeO2 three-phase composite via a "one-step controllable incomplete reduction method," exhibiting significant comprehensive advantages in catalytic performance, structural design, and preparation process. This catalyst not only demonstrates excellent activity, but also exhibits high performance at 10 mA cm⁻¹. -2 With an overpotential as low as 62 mV at current density, comparable to commercial Pt / C catalysts, it also exhibits superior industrial stability, with its monolithic electrode capable of operating at 1 A cm⁻¹. -2 It can operate stably for over 300 hours at ultra-high current densities with a decay rate of less than 3%. Its performance advantage stems from its unique structural design: the oxygen-loving CeO2 effectively promotes water molecule dissociation, while the NiO phase precisely controls the hydrogen adsorption energy at adjacent Ni sites. Together, they overcome the bottlenecks of traditional nickel-based materials. Meanwhile, its preparation process is simple, efficient, and easy for mass production, requiring no complex equipment or templates, with a yield of nearly 100%. This lays a solid foundation for low-cost, large-scale applications and shows broad industrial prospects in alkaline and anion exchange membrane water electrolysis for hydrogen production.

Claims

1. A Ni-NiO / CeO2 heterojunction nanocatalyst, characterized in that, The catalyst is composed of a three-phase composite of metallic Ni, NiO, and CeO2. The catalyst has a coral-like microscopic heterostructure formed by cross-linking of nanoparticles; In this structure, metallic Ni forms a porous framework, the surface of which is coated with NiO and loaded with CeO2 nanoparticles rich in oxygen vacancy defects. With the total molar number of the three phases of metal Ni, NiO and CeO2 in the catalyst being 100%, the molar percentages of each phase are 30%–80%, 10%–50% and 10%–20%, respectively.

2. The Ni-NiO / CeO2 heterojunction nanocatalyst according to claim 1, characterized in that, With the total molar number of the three phases of metal Ni, NiO and CeO2 in the catalyst being 100%, the molar percentages of each phase are 40%–60%, 30%–50%, and 10%–20%, respectively.

3. The Ni-NiO / CeO2 heterojunction nanocatalyst according to claim 1, characterized in that, CeO2 rich in oxygen vacancy defects 3+ The relative content of it accounts for 20% to 30% of the total Ce element.

4. A method for preparing the Ni-NiO / CeO2 heterojunction nanocatalyst according to claim 1, characterized in that, The method includes the following steps: Step 1: Ni 2+ Soluble salts with Ce 4+ The soluble salt is dissolved in deionized water to obtain a precursor solution; the total metal ion concentration in the precursor solution is 0.3–0.5 mol / L, Ni 2+ With Ce 4+ The molar ratio is 1:8 to 16:1; Step 2: Remove the solvent from the precursor solution from Step 1 to obtain a solid precursor; Step 3: The solid precursor from Step 2 is annealed in air atmosphere and then in reducing atmosphere to obtain Ni-NiO / CeO2 heterojunction nanocatalyst.

5. The method for preparing the Ni-NiO / CeO2 heterojunction nanocatalyst according to claim 4, characterized in that, In step 1, the Ni 2+ The soluble salt is selected from any one or more of nickel nitrate, nickel acetate, and nickel chloride; the Ce 4+ The soluble salt is selected from any one or more of cerium nitrate, cerium ammonium nitrate, cerium chloride, and cerium sulfate.

6. The method for preparing the Ni-NiO / CeO2 heterojunction nanocatalyst according to claim 4, characterized in that, In step 2, the solvent removal method is vacuum distillation, rotary evaporation, or natural evaporation, with a solvent removal temperature of 50–100 °C and a time of 0.5–12 hours.

7. The method for preparing the Ni-NiO / CeO2 heterojunction nanocatalyst according to claim 4, characterized in that, In step 3, the air annealing temperature is 300–600 °C, and the annealing time is 5–10 hours.

8. The method for preparing the Ni-NiO / CeO2 heterojunction nanocatalyst according to claim 4, characterized in that, In step 3, the reducing atmosphere is a mixture of H2 with Ar or N2 at a volume concentration of 5% to 50%.

9. The method for preparing the Ni-NiO / CeO2 heterojunction nanocatalyst according to claim 4 or 8, characterized in that, In step 3, the reducing atmosphere annealing temperature is 300–600 °C, and the annealing time is 1–6 hours.

10. The use of the Ni-NiO / CeO2 heterojunction nanocatalyst according to claim 1 in the cathodic hydrogen evolution reaction of alkaline water electrolysis or anion exchange membrane water electrolysis.

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