Preparation method of polyacid-hydrogel derived atomic-scale Pt modified Mo2C electrocatalyst

Abstract

The invention discloses a polyacid-hydrogel derived atomic-scale Pt modified Mo2C electrocatalyst for electrocatalytic hydrogen evolution and a preparation method of the polyacid-hydrogel derived atomic-scale Pt modified Mo2C electrocatalyst, and belongs to the technical field of new energy materials. Polyoxometallate is used as a precursor, the polyoxometallate is loaded on the surface of cationic polyvinyl alcohol-chitosan hydrogel modified carbon cloth by using the anion characteristic of the polyoxometallate, and the monodisperse Pt atom-doped Mo2C composite material loaded on the nitrogen-doped carbon surface is obtained through high-temperature heat treatment. The material prepared by the invention has excellent electro-catalytic hydrogen evolution performance, even the activity exceeds that of commercial platinum carbon, and the material has important guiding significance on preparation of an electro-catalytic hydrogen evolution catalyst.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new materials, and particularly relates to a preparation method of a polyacid-hydrogel derived atomic Pt modified Mo2C electrocatalyst. BACKGROUND

[0002] Hydrogen energy is considered as the most promising future energy to replace fossil fuels due to its environmental friendliness and high energy density. Electrochemical water splitting driven by wind or solar energy technology is considered as a sustainable development strategy. Proton exchange membrane water electrolysis (PEMWE) can be compatible with dynamic current load and can be better coupled with renewable energy (i.e. wind energy, solar energy) in application to produce high-purity hydrogen using green electricity. Platinum (Pt) is a standard catalyst for cathodes in proton exchange membrane water electrolysis (PEMWEs) due to its excellent activity and stability in acidic conditions. However, the high cost and scarcity of Pt hinder its large-scale application. In order to overcome this challenge and reduce the cost of hydrogen production by electrolytic water, it is necessary to reduce the amount of Pt used in proton exchange membrane water electrolysis and improve the utilization, and to develop a high-efficiency and stable low-platinum-loading catalyst.

[0003] Mo is relatively abundant in the earth's crust, and using Mo-based materials as a carrier to disperse and stabilize Pt can reduce the amount of noble metal Pt used, thereby reducing the overall cost of the catalyst. Molybdenum carbide (Mo2C) has an electronic structure similar to Pt and has good bonding ability with Pt, making it an ideal Pt catalyst carrier. Anchoring atomic-level dispersed Pt catalytic sites on the surface of Mo2C is expected to improve the utilization of Pt catalysts.

[0004] However, the Pt-Mo2C materials reported in the literature are generally obtained by high-temperature calcination. In the high-temperature calcination process, it is difficult to achieve uniform carbonization, and it is also difficult to avoid particle agglomeration. The existing material synthesis method is difficult to form Pt atomic-level doped Mo2C materials, and the sintering and agglomeration of Pt in the high-temperature heat treatment process hinder the exposure of the catalytic active sites of the material. Therefore, loading atomic-level dispersed Pt on the Mo2C carrier is of great significance for electrocatalytic hydrogen evolution. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of a polyacid-hydrogel derived atomic Pt modified Mo2C electrocatalyst. The method utilizes the advantages of polyoxometalates (referred to as polyacids) as precursors, such as clear structure, flexible heteroatoms, and small size (about 1-2 nm). A layer of cationic polyvinyl alcohol (PVA)-chitosan (CS) hydrogel is modified on the surface of commercial carbon cloth (CC), thereby uniformly dispersing and adsorbing anionic polyacids on the surface. Through heat treatment, a monodisperse Pt atom doped Mo2C material loaded on the surface of nitrogen-doped carbon is formed.

[0006] The present invention discloses a method for preparing a polyacid-hydrogel-derived atomic-level Pt-modified Mo2C electrocatalyst. First, a polyacid precursor is synthesized. Then, carbon cloth loaded with polyvinyl alcohol-chitosan composite hydrogel is uniformly impregnated into a polyacid solution, so that the negatively charged polyacid is uniformly adsorbed onto the positively charged hydrogel surface. Subsequently, monodisperse Pt atom-doped Mo2C material is obtained by high-temperature heat treatment.

[0007] Furthermore, the preparation method includes the following steps:

[0008] Step 1: Pt-Anderson type polyacid Na4[H4PtMo6O] 24 Synthesis of ·2H₂O (abbreviated as PtMo₆): 2.4 mmol of anhydrous sodium molybdate (Na₂MoO₄) was dissolved in 30 mL of deionized water, heated to boiling, and 20 mL of 0.4 mmol of sodium hexahydroxyplatinate (Na₂Pt(OH)₆) solution was slowly added. The reaction was repeated by adding 3 mol L⁻¹ of solution dropwise. -1 HNO3 was used to maintain the pH value at around 5.4. The solution was continuously heated and stirred until it evaporated to 4 mL. After cooling to room temperature, pale yellow crystals were separated.

[0009] Step 2: Preparation of carbon cloth loaded with polyvinyl alcohol-chitosan composite hydrogel (CC-PVA-CS): Weigh 0.5g of chitosan (CS) and dissolve it in 20mL of 1% glacial acetic acid solution, denoted as 2.5% CS solution. Weigh 2g of polyvinyl alcohol (PVA) and add it to 18g of deionized water, stirring continuously at 55℃ for 1h until dissolved, denoted as 10% PVA solution. Mix 4mL of 10% PVA solution with 4mL of 2.5% CS solution evenly, denoted as PVA-CS solution. Immerse the hydrophilic carbon cloth (CC) in the above solution and sonicate for 20min. After removal, rapidly freeze in liquid nitrogen, then place in a freeze dryer and freeze-dry for 24h to obtain CC-PVA-CS.

[0010] Step 3: Preparation of atomically modified Pt-Mo2C material (Pt-Mo2C@NC) loaded on a nitrogen-doped carbon substrate: CC-PVA-CS was pre-oxidized in a muffle furnace at 180℃ for 3 hours, followed by further oxidation at a concentration of 1 mol L⁻¹. -1 The CC-PVA-CS was acidified in HNO3 solution for 1 hour. The treated CC-PVA-CS was then impregnated in 10 mL of PtMo6 (1.6 mg / mL). -1 In the solution, the PtMo6 solution was pre-treated with 3 mol L... -1HNO3 was adjusted to pH 3, and after 10 min, CC-PVA-CS-PtMo6 was taken out and dried at 80 DEG C under vacuum. Then, CC-PVA-CS-PtMo6 was heated to 800 DEG C in a high-temperature tube furnace under Ar atmosphere to obtain Pt-Mo2C@NC composite materials.

[0011] Further, the carbon cloth in step 2 is pre-treated with hydrophilicity, i.e., ultrasonic treatment in anhydrous ethanol solution for 20 min, ultrasonic treatment in 1 mol / L hydrochloric acid for 20 min, and heating in 30% hydrogen peroxide solution at 80 DEG C for 30 min. -1 Further, the carbon cloth in step 2 is pre-treated with hydrophilicity, i.e., ultrasonic treatment in anhydrous ethanol solution for 20 min, ultrasonic treatment in 1 mol / L hydrochloric acid for 20 min, and heating in 30% hydrogen peroxide solution at 80 DEG C for 30 min.

[0012] Further, the drying process in step 2 utilizes freeze-drying technology to ensure that the precursor of the polyvinyl alcohol-chitosan composite hydrogel has a porous structure, thereby achieving a high specific surface area.

[0013] Further, the atomic-level Pt-modified Mo2C material loaded on the nitrogen-doped carbon substrate obtained by the preparation method is used for electrocatalytic hydrogen evolution.

[0014] The present application provides a new strategy for synthesizing high-performance electrocatalytic hydrogen evolution catalyst materials, which has the following outstanding advantages: ① the Pt-Mo2C@NC composite material formed by using a polyacid as a precursor can form atomic-level Pt-modified Mo2C, which has a small size; ② the polyacid-hydrogel composite system under electrostatic interaction enables Pt to be uniformly dispersed, and Mo2C and the conductive substrate are firmly combined, thereby avoiding the agglomeration and sintering of Mo2C and enabling it to have excellent stability; ③ the synthesized composite material has a three-dimensional conductive network structure, which increases the specific surface area and the conductivity of the material; ④ the preparation method is simple and efficient, which provides a possibility for actual production. In summary, the present application provides a new idea for synthesizing monodisperse atomic-level Pt-modified Mo2C catalysts, and has guiding significance for the preparation and industrialization of high-performance electrocatalytic hydrogen evolution materials. BRIEF DESCRIPTION OF DRAWINGS

[0015] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the following drawings, in which:

[0016] Figure 1 is an infrared spectrum obtained by using a polyacid to load on a polyvinyl alcohol-chitosan hydrogel precursor (PVA-CS-PtMo6) according to an embodiment of the present application;

[0017] Figure 2 is an XRD spectrum obtained by using Pt-Mo2C@NC according to an embodiment of the present application;

[0018] Figure 3 These are scanning electron microscope (SEM) images obtained using Pt-Mo2C@NC according to embodiments of the present invention;

[0019] Figure 4 These are aberration-corrected scanning transmission electron microscope (AC-STEM) images obtained using Pt-Mo2C@NC according to an embodiment of the present invention.

[0020] Figure 5 These are comparative performance and stability graphs of hydrogen evolution through water electrolysis obtained using Pt-Mo2C@NC according to embodiments of the present invention. Detailed Implementation

[0021] The embodiments of the present invention are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary. The embodiments of the present invention are described in detail below.

[0022] (1) Pt-Anderson type polyacid Na4[H4PtMo6O 24 Synthesis of ·2H₂O (abbreviated as PtMo₆): 2.4 mmol of anhydrous sodium molybdate (Na₂MoO₄) was dissolved in 30 mL of deionized water, heated to boiling, and 20 mL of 0.4 mmol of sodium hexahydroxyplatinate (Na₂Pt(OH)₆) solution was slowly added. The reaction was repeated by adding 3 mol L⁻¹ of solution dropwise. -1 HNO3 was used to maintain the pH value at around 5.4. The solution was continuously heated and stirred until it evaporated to 4 mL. After cooling to room temperature, pale yellow crystals were separated.

[0023] (2) Preparation of carbon cloth loaded with polyvinyl alcohol-chitosan composite hydrogel (CC-PVA-CS): 0.5 g of chitosan (CS) was dissolved in 20 mL of 1% glacial acetic acid solution, denoted as 2.5% CS solution. 2 g of polyvinyl alcohol (PVA) was added to 18 g of deionized water and stirred continuously at 55℃ for 1 h until dissolved, denoted as 10% PVA solution. 4 mL of 10% PVA solution and 4 mL of 2.5% CS solution were mixed evenly, denoted as PVA-CS solution. The carbon cloth was then subjected to ultrasonic treatment in anhydrous ethanol solution for 20 min and in a 1 mol / L solution. -1 The PVA-CS was subjected to hydrophilic treatment by sonicating in hydrochloric acid for 20 min and heating in 30% hydrogen peroxide solution at 80°C for 30 min. A 1*2cm hydrophilic carbon cloth (CC) was cut, immersed in the above PVA-CS solution, sonicated for 20 min, removed and rapidly frozen in liquid nitrogen, and then placed in a freeze dryer for 24 h to obtain CC-PVA-CS.

[0024] (3) Preparation of Pt-Mo2C@NC: CC-PVA-CS was pre-oxidized in a muffle furnace at 180℃ for 3 hours, and then subjected to oxidation at a concentration of 1 mol L. -1 The mixture was acidified in HNO3 solution for 1 hour. The treated CC-PVA-CS (0.18 g) was then impregnated in 10 mL of PtMo6 (1.6 mg / mL). -1 In the solution, the PtMo6 solution was pre-treated with 3 mol L... -1 The pH was adjusted to 3 with HNO3, and after 10 minutes, it was removed and dried under vacuum at 80℃ to obtain CC-PVA-CS-PtMo6. Subsequently, CC-PVA-CS-PtMo6 was placed in a high-temperature tube furnace and heated to 800℃ under Ar atmosphere, and held for 3 hours to obtain Pt-Mo2C@NC composite material.

[0025] (4) Preparation of the hydrogen evolution anode for water electrolysis: The self-supported Pt-Mo2C@NC material prepared at 1 cm 2 For electrode plates.

[0026] (5) To test the electrocatalytic hydrogen evolution performance of the prepared electrode material, a Shanghai Chenhua electrochemical workstation (CHI770E) was used. Electrochemical tests were conducted using a reversible hydrogen electrode as the reference electrode, a carbon rod as the counter electrode, and the electrode prepared in step (4) as the working electrode. 0.5 mol L -1 The test was conducted using a three-electrode system with H2SO4 solution as the electrolyte solution.

[0027] in, Figure 1 The infrared spectrum obtained in the examples using polyacid-loaded polyvinyl alcohol-chitosan hydrogel precursor (PVA-CS-PtMo6) was characterized at 527 cm⁻¹. -1 There is a clear presence of Mo-O-Pt bonds at 436 cm⁻¹. -1 The presence of obvious Pt-O bonds indicates that the polyacid PtMo6 was successfully adsorbed on the surface of the polyvinyl alcohol-chitosan (PVA-CS) hydrogel.

[0028] in, Figure 2 The XRD pattern obtained using Pt-Mo2C@NC in the examples demonstrates the successful synthesis of Mo2C material.

[0029] in, Figure 3 The scanning electron microscope (SEM) images obtained using Pt-Mo2C@NC in the examples show that the prepared material has a three-dimensional porous cross-linked network structure.

[0030] in, Figure 4The aberration-corrected scanning transmission electron microscope (AC-STEM) images obtained using Pt-Mo2C@NC in the examples show that the synthesized Mo2C has a small size and is modified with atomically dispersed Pt on its surface.

[0031] in, Figure 5 The examples show a comparison of the hydrogen evolution performance and stability of water electrolysis using Pt-Mo2C@NC. Figure a shows the linear sweep voltammetry (LSV) curves of commercial 20% Pt / C material and Pt-Mo2C@NC, indicating that at 100 mA cm⁻¹... -2 At a current density of [value missing], Pt-Mo2C@NC exhibits the smallest overpotential, superior to commercial hydrogen evolution catalysts, indicating its excellent hydrogen evolution activity. b corresponds to the voltage-time (vt) curve of Pt-Mo2C@NC at 10 mA cm⁻¹. -2 At the specified current density, the catalyst can operate for over 200 hours without significant degradation, demonstrating excellent electrochemical hydrogen evolution stability.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, alterations, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a polyacid-hydrogel-derived atomic-level Pt-modified Mo2C electrocatalyst, characterized in that: PtMo6 polyacid nanoclusters were designed and synthesized, and then composited with a carbon cloth substrate modified with polyvinyl alcohol-chitosan hydrogel. Monodisperse atomically doped Mo2C electrocatalysts were obtained after high-temperature heat treatment, and their electrocatalytic hydrogen evolution performance was then studied. The polyacid anionic nanoclusters (1-2 nm in diameter) serve as precursors for platinum and molybdenum sources, enabling uniform dispersion of platinum and molybdenum. By modifying the surface of commercial carbon cloth with a layer of polyvinyl alcohol-chitosan (PVA-CS) hydrogel, electrostatic interactions are formed between the cationic chitosan hydrogel and the anionic polyacid, uniformly adsorbing the polyacid onto the hydrogel surface. During high-temperature pyrolysis, monodisperse atomic-level Pt-doped Mo2C electrocatalysts are formed in situ. The synthesis of atomically Pt-modified Mo2C electrocatalysts includes the following steps: Step 1: Polyacid (Anderson type Na4[H4PtMo6O) 24 Synthesis of ·2H₂O (abbreviated as PtMo₆): 2.4 mmol of anhydrous sodium molybdate (Na₂MoO₄) was dissolved in 30 mL of deionized water, heated to boiling, and 20 mL of 0.4 mmol of sodium hexahydroxyplatinate (Na₂Pt(OH)₆) solution was slowly added. The reaction was carried out by adding 3 mol L⁻¹ of solution dropwise. -1 HNO3 was used to maintain the pH value at around 5.

4. The solution was continuously heated and stirred until it evaporated to 4 mL. After cooling to room temperature, pale yellow crystals were separated. Step 2: Synthesis of carbon cloth loaded with polyvinyl alcohol-chitosan composite hydrogel (CC-PVA-CS): 0.5 g of chitosan (CS) was dissolved in 20 mL of 1% glacial acetic acid solution, denoted as 2.5% CS solution. 2 g of polyvinyl alcohol (PVA) was added to 18 g of deionized water and stirred continuously at 55℃ for 1 h until dissolved, denoted as 10% PVA solution. 4 mL of 10% PVA solution was mixed thoroughly with 4 mL of 2.5% CS solution, denoted as PVA-CS solution. Hydrophilic carbon cloth (CC) was immersed in the above solution and sonicated for 20 min. After removal, it was rapidly frozen in liquid nitrogen, and then placed in a freeze dryer for 24 h to obtain CC-PVA-CS. Step 3: Synthesis of atomically modified Mo2C material (Pt-Mo2C@NC) supported on a nitrogen-doped carbon substrate: CC-PVA-CS was pre-oxidized in a muffle furnace at 180℃ for 3 hours, followed by further oxidation at a concentration of 1 mol L⁻¹. -1 The CC-PVA-CS was acidified in HNO3 solution for 1 hour. The treated CC-PVA-CS was then impregnated in 10 mL of PtMo6 (1.6 mg / mL). -1 In the solution, the PtMo6 solution was pre-treated with 3 mol L... -1 The pH was adjusted to 3 with HNO3, and after 10 minutes, it was removed and dried under vacuum at 80°C to obtain CC-PVA-CS-PtMo6. Subsequently, CC-PVA-CS-PtMo6 was placed in a high-temperature tube furnace and heated to 800°C under an Ar atmosphere to obtain Pt-Mo2C@NC composite material.

2. The preparation method of the polyacid-hydrogel-derived atomic-level Pt-modified Mo2C electrocatalyst as described in claim 1, characterized in that: Polyacid precursors are one or more of Anderson-type, Keggin-type, Dawson-type, and Weakly-type polyacids.

3. The preparation method of the polyacid-hydrogel-derived atomic-level Pt-modified Mo2C electrocatalyst as described in claim 1, characterized in that: Hydrogels modified with carbon cloth substrates are one or more types of cationic hydrogels such as chitosan and polyacrylamide.

4. The preparation method of the polyacid-hydrogel-derived atomic-level Pt-modified Mo2C electrocatalyst as described in claim 1, characterized in that: The hydrogel-modified self-supporting substrate is one or more conductive substrates such as carbon cloth, carbon paper, nickel foam, and titanium.

5. The preparation method of the polyacid-hydrogel-derived atomic-level Pt-modified Mo2C electrocatalyst as described in claim 1, characterized in that: Using the polyacid and hydrogel precursor, atomic-level Pt-modified Mo2C electrocatalytic nanomaterials are obtained through step 3.

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