Oxygen / sulfur heterostructure oxygen evolution electrocatalyst, and preparation method and application thereof

Abstract

The application relates to the technical field of electrocatalysis, in particular to an oxygen / sulfur heterostructure oxygen evolution electrocatalyst as well as a preparation method and application thereof. Based on an in-situ oxidation strategy, a CuFeO layer is generated on the surface of CuFeS to obtain a CuFeS@CuFeO high-performance oxygen evolution electrocatalyst with a heterostructure. By constructing a sulfide-oxide heterojunction, a built-in electric field can be formed at the interface to promote charge separation and transfer, thereby significantly improving the electrocatalytic activity. On the other hand, the CuFeO layer in the outer layer acts as a "cuirass" to solve the oxidation problem of the CuFeS surface. The electrocatalytic performance and long-term stability are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, specifically to an oxygen / sulfur heterostructure oxygen evolution electrocatalyst, its preparation method, and its application. Background Technology

[0002] The increasing global energy crisis and environmental problems make the development of green and sustainable energy sources to replace non-renewable energy sources such as fossil fuels crucial. Renewable energy sources, represented by photovoltaic and wind power, are characterized by intermittency and uneven geographical distribution, necessitating efficient and clean energy carriers for large-scale, long-term energy storage and inter-regional transportation. Hydrogen, with its high energy density (142 MJ / kg), combustion product consisting only of water, and its potential as an industrial feedstock (e.g., for ammonia synthesis, oil refining, and chemical processing), is considered an ideal secondary energy carrier. Utilizing unstable photovoltaic and wind power to convert water into stable, environmentally friendly, and storable "green hydrogen" through water electrolysis is the most promising technological approach. The water splitting reaction includes the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode, which is thermodynamically an energy-absorbing process (ΔG). 0 =+237.2kJ / mol), exhibiting a high activation energy barrier kinetically, particularly in the oxygen evolution reaction (OER) involving four-electron transfer. This complex multi-step proton-electron coupling transfer process leads to low efficiency and high energy consumption, making it the rate-determining step for overall energy conversion efficiency. Currently, noble metal-based electrocatalysts exhibit the most efficient activity for water splitting, especially Pt-based hydrogen evolution reaction (HER) catalysts and Ir / Ru-based oxygen evolution reaction (OER) catalysts. However, the best-performing electrocatalysts (such as Pt-based materials for HER and IrO2 and RuO2 for OER) heavily rely on scarce and expensive noble metal resources. Their limited global reserves, uneven distribution, and high prices pose a key bottleneck to the large-scale application of a "green hydrogen" economy. Therefore, developing efficient and stable catalysts based on abundant and inexpensive transition metals (Fe, Co, Ni, Mn, Mo, W, etc.) or non-metallic elements is an urgent need to reduce system costs and ensure the sustainability of the technological approach. Transition metal sulfides (TMSs) are considered to be more promising electrocatalysts that can replace precious metals due to their low cost, abundance on Earth, unique two-dimensional layered structure, and suitable electronic band structure.

[0003] Currently, research on TMSs electrocatalysts mainly focuses on metal sulfides composed of first-group transition metals (such as Fe, Co, Ni, Cu, Mn, and Zn), fifth-group transition metals (V, Nb, and Ta), and sixth-group transition metals (Mo and W). TMSs exhibit excellent intrinsic activity due to the interaction between the vacant or unpaired p orbitals of the non-metallic element S and the orbitals of the metal element, which stabilizes intermediates in the water splitting reaction. These materials demonstrate catalytic performance comparable to noble metals such as Pt, and transition metal sulfides offer advantages such as low cost and ease of synthesis. Further construction of bimetallic sulfides allows for the adjustment of the d-band center position through the synergistic effect of the bimetals, optimizing the adsorption energy for oxygen intermediates. Multiple valence states participate in redox reactions, forming abundant electron transfer pathways and charge compensation mechanisms, significantly improving electrocatalytic performance and long-term stability.

[0004] However, under the high anodic potential and strong oxidizing environment of alkaline OER, transition metal sulfides are prone to surface oxidation, in which the sulfur element is oxidized to sulfoxide anions (such as SO42-). 2- This leads to material structural collapse, loss of active sites, and progressive performance degradation, limiting its long-term application at industrial-grade current densities. Therefore, seeking solutions is imperative. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide an oxygen / sulfur heterostructure oxygen evolution electrocatalyst, its preparation method, and its application. Based on an in-situ oxidation strategy, a CuFeO layer is generated on the surface of CuFeS, resulting in a high-performance CuFeS@CuFeO oxygen evolution electrocatalyst with a heterostructure. By constructing a sulfide-oxide heterojunction, a built-in electric field can be formed at the interface, promoting charge separation and transfer, thereby significantly improving electrocatalytic activity. Furthermore, the outer CuFeO layer acts as an "armor," solving the oxidation problem on the CuFeS surface.

[0006] The present invention provides a method for preparing an oxygen / sulfur heterostructure oxygen evolution electrocatalyst, which specifically includes the following steps: (1) Take a certain amount of iron salt, copper salt and sulfur source and add them to deionized water in sequence. Stir evenly to form a homogeneous solution. Then carry out hydrothermal reaction. After the reaction is completed, cool naturally to room temperature. Centrifuge the solution obtained from the reaction, discard the supernatant, wash the precipitate with deionized water and anhydrous ethanol respectively by centrifugation, dry and collect the obtained product. (2) The product obtained in step (1) is placed in a tube furnace and calcined under an atmosphere containing oxygen to obtain an oxygen / sulfur heterostructure oxygen evolution electrocatalyst.

[0007] Furthermore, in step (1), a certain amount of iron salt, copper salt and sulfur source are added to deionized water in sequence, stirred evenly to dissolve them fully and form a homogeneous solution, and then transferred to a sealed hydrothermal reactor. The hydrothermal reactor is then placed in a constant temperature drying oven for hydrothermal reaction.

[0008] Furthermore, in step (1), the iron salt is one of ferrous chloride, ferric chloride, ferric nitrate, and ferrous sulfate; the copper salt is one of copper sulfate, copper nitrate, copper chloride, and copper acetate; and the sulfur source is one of thiourea, thioacetamide, sodium sulfide, and L-cysteine.

[0009] Furthermore, in step (1), the ratio of iron salt: copper salt: sulfur source = 0.6-1.2 mmol: 0.5-1.4 mmol: 2-8 mmol; the volume of deionized water is 15-80 mL.

[0010] Furthermore, in step (1), the volume of the hydrothermal reactor is 20-100 mL.

[0011] Furthermore, in step (1), the temperature of the hydrothermal reaction is 90-220℃, and the reaction time is 5-15h.

[0012] Furthermore, in step (1), the precipitate is washed at least three times by centrifugation with deionized water and anhydrous ethanol.

[0013] Furthermore, in step (1), the drying process specifically involves placing the product in a vacuum drying oven at 60°C for 6 hours.

[0014] Furthermore, in step (2), calcination under an oxygen-containing atmosphere means calcination in an air-filled environment with both ends of the tubular furnace open, or calcination in an air atmosphere (commercially available air cylinders, with a N2:O2 volume ratio of approximately 78:21) or an oxygen atmosphere.

[0015] Furthermore, in step (2), the calcination temperature is 120-300℃ and the calcination time is 1-8h.

[0016] The present invention also provides an oxygen / sulfur heterostructure oxygen evolution electrocatalyst obtained according to the above preparation method and its application as an oxygen evolution electrocatalyst.

[0017] Furthermore, the oxygen / sulfur heterostructure oxygen evolution electrocatalyst is a nanosphere assembled from nanosheets, with CuFeO particles generated on the surface of the nanosheet layer, and the nanosphere diameter is approximately 3 μm.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The interaction between the vacant or unpaired p orbitals of the nonmetal element S and the orbitals of the metal element in the structure of transition metal sulfides can stabilize the intermediates in the water splitting reaction process, showing catalytic performance comparable to noble metals such as Pt. Moreover, transition metal sulfides have the advantages of low cost and easy synthesis.

[0019] (2) The inner CuFeS bimetallic sulfide core constructed in this invention can adjust the d-band center position through the synergistic effect of the bimetals, optimize the adsorption energy of oxygen intermediates, participate in redox reactions in multiple valence states, form rich electron transfer pathways and charge compensation mechanisms, and significantly improve electrocatalytic performance and long-term stability.

[0020] (3) Based on the in-situ oxidation strategy, the present invention generates a CuFeO layer on the surface of CuFeS core. By constructing a sulfide-oxide heterojunction, a built-in electric field can be formed at the interface to promote charge separation and transfer, thereby significantly improving electrocatalytic activity.

[0021] (4) The present invention constructs a CuFeO “armor” outside the CuFeS core to solve the oxidation problem on the CuFeS surface, avoid the collapse of the material structure and loss of active sites, and promote its long-term application at industrial-grade current density.

[0022] (5) The CuFeS@CuFeO catalyst prepared in this invention has significantly improved performance compared to the CuFeS catalyst. Attached Figure Description

[0023] Figure 1 These are the XRD patterns of CuFeS-2 obtained in step (1) and CuFeS@CuFeO-2 obtained in step (2) of Example 2; Figure 2 These are FESEM images of CuFeS-2 obtained in step (1) and CuFeS@CuFeO-2 obtained in step (2) of Example 2, where images a and b correspond to CuFeS-2, and images c and d correspond to CuFeS@CuFeO-2; Figure 3 These are the linear voltammetric scan curves of CuFeS-2 obtained in step (1) and CuFeS@CuFeO-2 obtained in step (2) of Example 2; Figure 4 These are the Tafel slope curves of CuFeS-2 obtained in step (1) and CuFeS@CuFeO-2 obtained in step (2) of Example 2. Detailed Implementation

[0024] To better understand the content of this invention, it will be further described below with reference to specific embodiments and accompanying drawings. The following embodiments are based on the technology of this invention and provide detailed implementation methods and operating steps, but the scope of protection of this invention is not limited to the following embodiments.

[0025] Example 1: (1) 0.6 mmol ferrous chloride, 0.6 mmol copper nitrate and 2 mmol sodium sulfide were added to 15 mL of deionized water and stirred until fully dissolved to form a homogeneous solution. The solution was then transferred to a 20 mL closed hydrothermal reactor and placed in a constant temperature drying oven at 90 °C for 12 h. After the reaction was completed, the hydrothermal reactor was allowed to cool naturally to room temperature. The solution obtained from the reaction was centrifuged and the supernatant was discarded. The precipitate was washed at least 3 times with deionized water and anhydrous ethanol. Then it was placed in a vacuum drying oven at 60 °C for 6 h and the product was collected. The obtained sample was named CuFeS-1. (2) The above sample was placed in a tube furnace and calcined at 120°C for 8 hours in an oxygen atmosphere to obtain an oxygen / sulfur heterostructure oxygen evolution electrocatalyst, denoted as CuFeS@CuFeO-1.

[0026] Example 2: (1) Add 1 mmol ferric chloride, 1.4 mmol copper chloride and 8 mmol thiourea to 80 mL of deionized water in sequence, stir until fully dissolved to form a homogeneous solution, then transfer to 100 mL of closed hydrothermal reactor, place the hydrothermal reactor in a constant temperature drying oven and react at 180 °C for 5 h. After the reaction is completed, the hydrothermal reactor is naturally cooled to room temperature. Centrifuge the solution obtained from the reaction, discard the supernatant, and wash the precipitate at least 3 times with deionized water and anhydrous ethanol, respectively. Then place it in a vacuum drying oven at 60 °C for 6 h and collect the product. The obtained sample is named CuFeS-2. (2) The above sample was placed in a tube furnace and calcined at 250°C for 2 hours in an oxygen atmosphere to obtain an oxygen / sulfur heterostructure oxygen evolution electrocatalyst, denoted as CuFeS@CuFeO-2.

[0027] The material obtained in Example 2 was analyzed by XRD (X-ray diffraction, D8 Advance), and the results are shown in the figure. Figure 1 .like Figure 1The figures show the XRD patterns of CuFeS-2 obtained in step (1) and CuFeS@CuFeO-2 obtained in step (2) of Example 2, respectively. In the XRD pattern of CuFeS-2, the characteristic diffraction peaks at approximately 29.8°, 32°, 33°, and 49° are consistent with the characteristic peaks of JCPDS#42-0586, proving the successful synthesis of Cu5FeS4. After calcination, the XRD pattern of CuFeS@CuFeO-2 showed the characteristic peak of CuFeO2 (36.5°, JCPDS#21-029), indicating the formation of CuFeO2 in the Cu5FeS4 material. These results prove the successful synthesis of CuFeS@CuFeO-2.

[0028] The material obtained in Example 2 was analyzed by FESEM (Field Emission Scanning Electron Microscopy, JSM-7600F), and the results are as follows. Figure 2 As shown, the obtained CuFeS-2 ( Figure 2 Figures a and b show nanospheres assembled from nanosheets, with a diameter of approximately 3 μm. After calcination, the material retains its initial nanoflower structure, but CuFeO particles are generated on the surface of its sheets, resulting in CuFeS@CuFeO-2 ( Figure 2 (Figures c and d in the middle)

[0029] All prepared electrodes were electrochemically tested using a CHI 660e electrochemical workstation. A solution was prepared by mixing 980 μL of deionized water and 20 μL of Nafion, then adding 10 mg of the prepared catalyst and ultrasonically dispersing to obtain a homogeneous catalyst slurry. 10 μL of the prepared catalyst slurry was dropped onto the surface of a glassy carbon electrode and allowed to dry. The glassy carbon electrode, reference graphite electrode, and Ag / AgCl reference electrode (filled with saturated KCl) were then inserted into a 1 mol L… -1 In a NaOH electrolyte, a glassy carbon electrode (4 mm in diameter) is used as the working electrode, a graphite electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode, forming a three-electrode system. All potentials are converted according to the reversible hydrogen potential formula. The reversible hydrogen potential formula is as follows: E RHE =E Ag / AgCl +0.0592×pH+0.098V Among them, E RHE E is the reversible hydrogen electrode potential. Ag / AgCl The potential is the reading under the condition of Ag / AgCl as the reference electrode, and pH is the acidity or alkalinity of the electrolyte.

[0030] When testing OER performance using the linear voltammetric scan (LSV) method, the voltage range was 1.2–1.8 V, the scan rate was 5 mV / s, and the ohmic compensation was 90%. The results are as follows: Figure 3As shown, during the oxygen evolution process, the overpotential of the CuFeS@CuFeO-2 electrode is 392.8 mV, which is lower than that of CuFeS-2 (421.8 mV).

[0031] By fitting the polarization curve, the Tafel slope of the material can be obtained, such as... Figure 4 As shown, the Tafel slope of CuFeS@CuFeO-2 is 97mV dec. -1 The Tafel slope is lower than that of CuFeS-2 (154 mV dec). -1 Compared with CuFeS-2, CuFeS@CuFeO-2 showed improvements in both OER performance and Tafel slope performance parameters, indicating that the composite material CuFeS@CuFeO-2 prepared in this invention has enhanced catalytic activity as an oxygen evolution catalyst.

[0032] Example 3: (1) 0.6 mmol ferrous sulfate, 1.2 mmol copper acetate and 3 mmol L-cysteine ​​were added to 40 mL of deionized water and stirred until fully dissolved to form a homogeneous solution. The solution was then transferred to a 50 mL closed hydrothermal reactor and placed in a constant temperature drying oven at 160 °C for 8 h. After the reaction was completed, the hydrothermal reactor was allowed to cool naturally to room temperature. The solution obtained from the reaction was centrifuged and the supernatant was discarded. The precipitate was washed at least 3 times with deionized water and anhydrous ethanol by centrifugation. The precipitate was then placed in a vacuum drying oven at 60 °C for 6 h and the product was collected. The obtained sample was named CuFeS-3. (2) The above sample was placed in a tube furnace and calcined at 300°C for 1 hour in an oxygen atmosphere to obtain an oxygen / sulfur heterostructure oxygen evolution electrocatalyst, denoted as CuFeS@CuFeO-3.

[0033] Example 4: (1) 0.8 mmol ferrous chloride, 0.8 mmol copper chloride and 4 mmol thiourea were added to 40 mL of deionized water and stirred until fully dissolved to form a homogeneous solution. The solution was then transferred to a 50 mL closed hydrothermal reactor and placed in a constant temperature drying oven at 200 °C for 6 h. After the reaction was completed, the hydrothermal reactor was allowed to cool naturally to room temperature. The solution obtained from the reaction was centrifuged and the supernatant was discarded. The precipitate was washed at least 3 times with deionized water and anhydrous ethanol by centrifugation. The precipitate was then placed in a vacuum drying oven at 60 °C for 6 h and the product was collected. The obtained sample was named CuFeS-4. (2) The above sample was placed in a tube furnace and calcined at 280°C for 1.5 h in an oxygen atmosphere to obtain an oxygen / sulfur heterostructure oxygen evolution electrocatalyst, denoted as CuFeS@CuFeO-4.

[0034] Example 5: (1) 0.6 mmol ferrous chloride, 1 mmol copper sulfate and 4 mmol thioacetamide were added to 40 mL of deionized water and stirred until fully dissolved to form a homogeneous solution. The solution was then transferred to a 50 mL closed hydrothermal reactor and placed in a constant temperature drying oven at 100 °C for 10 h. After the reaction was completed, the hydrothermal reactor was allowed to cool naturally to room temperature. The solution obtained from the reaction was centrifuged and the supernatant was discarded. The precipitate was washed at least 3 times with deionized water and anhydrous ethanol by centrifugation. The precipitate was then placed in a vacuum drying oven at 60 °C for 6 h and the product was collected. The obtained sample was named CuFeS-5. (2) The above sample was placed in a tube furnace and calcined at 200°C for 2 hours in an oxygen atmosphere to obtain a heterostructure oxygen evolution electrocatalyst, denoted as CuFeS@CuFeO-5.

[0035] Example 6: (1) 1.2 mmol ferrous sulfate, 1 mmol copper chloride and 8 mmol sodium sulfide were added to 80 mL of deionized water and stirred until fully dissolved to form a homogeneous solution. The solution was then transferred to a 100 mL closed hydrothermal reactor and placed in a constant temperature drying oven and reacted at 180 °C for 8 h. After the reaction was completed, the hydrothermal reactor was allowed to cool naturally to room temperature. The solution obtained from the reaction was centrifuged and the supernatant was discarded. The precipitate was washed at least 3 times with deionized water and anhydrous ethanol by centrifugation. The precipitate was then placed in a vacuum drying oven and dried at 60 °C for 6 h. The product was collected and the sample was named CuFeS-6. (2) The above sample was placed in a tube furnace and calcined at 300°C for 2 hours in an oxygen atmosphere to obtain a heterostructure oxygen evolution electrocatalyst, denoted as CuFeS@CuFeO-6.

[0036] The above description is merely an embodiment of the present invention and is not intended to limit the present invention in any way. The present invention can also have other embodiments based on the above structure and function, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing an oxygen / sulfur heterostructure oxygen evolution electrocatalyst, characterized in that, Specifically, the following steps are included: (1) Take iron salt, copper salt and sulfur source and add them to deionized water in sequence. The ratio of iron salt: copper salt: sulfur source = 0.6-1.2 mmol: 0.5-1.4 mmol: 2-8 mmol. Stir well to form a homogeneous solution, and then carry out hydrothermal reaction. After the reaction is completed, cool naturally to room temperature. Centrifuge the solution obtained from the reaction, discard the supernatant, wash the precipitate with deionized water and anhydrous ethanol by centrifugation, and then dry and collect the product. (2) The product obtained in step (1) is placed in a tube furnace and calcined under an atmosphere containing oxygen to obtain an oxygen / sulfur heterostructure oxygen evolution electrocatalyst. The calcination temperature is 120-300℃ and the calcination time is 1-8h.

2. The preparation method of the oxygen / sulfur heterostructure oxygen evolution electrocatalyst as described in claim 1, characterized in that, In step (1), a certain amount of iron salt, copper salt and sulfur source are added to deionized water in sequence and stirred until fully dissolved to form a homogeneous solution. Then, the solution is transferred to a sealed hydrothermal reactor and placed in a constant temperature drying oven for hydrothermal reaction. The volume of the hydrothermal reactor is 20-100 mL.

3. The preparation method of the oxygen / sulfur heterostructure oxygen evolution electrocatalyst as described in claim 1, characterized in that, In step (1), the iron salt is one of ferrous chloride, ferric chloride, ferric nitrate, and ferrous sulfate; the copper salt is one of copper sulfate, copper nitrate, copper chloride, and copper acetate; and the sulfur source is one of thiourea, thioacetamide, sodium sulfide, and L-cysteine.

4. The preparation method of the oxygen / sulfur heterostructure oxygen evolution electrocatalyst as described in claim 1, characterized in that, In step (1), the volume of deionized water is 15-80 mL.

5. The preparation method of the oxygen / sulfur heterostructure oxygen evolution electrocatalyst as described in claim 1, characterized in that, In step (1), the temperature of the hydrothermal reaction is 90-220℃ and the reaction time is 5-15h.

6. The method for preparing the oxygen / sulfur heterostructure oxygen evolution electrocatalyst as described in claim 1, characterized in that, In step (1), the drying process specifically involves placing the product in a vacuum drying oven at 60°C for 6 hours.

7. The method for preparing the oxygen / sulfur heterostructure oxygen evolution electrocatalyst as described in claim 1, characterized in that, In step (2), calcination in an oxygen-containing atmosphere means calcination in air with both ends of the tubular furnace open, or calcination in an air atmosphere or an oxygen atmosphere.

8. The oxygen / sulfur heterostructure oxygen evolution electrocatalyst prepared by any one of the preparation methods described in claims 1-7.

9. The application of the oxygen / sulfur heterostructure oxygen evolution electrocatalyst as described in claim 8 as an oxygen evolution electrocatalyst.

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