Self-supporting FeCo alloy phosphide electrocatalyst, preparation method and application

Abstract

The invention discloses a self-supporting FeCo alloy phosphide electrocatalyst as well as a preparation method and application thereof. The preparation method of the electrocatalyst comprises the following steps: S1, pretreating a conductive substrate; s2, preparing a FeCo precursor stacked by an iron-cobalt hydroxide from the conductive substrate, an iron source and a cobalt source through a hydrothermal method; and S3, performing chemical vapor deposition on the catalytic base layer by using a phosphorus source to prepare the self-supporting FeCo alloy phosphide electrocatalyst, wherein the self-supporting FeCo alloy phosphide electrocatalyst is in a nano sheet shape or a pine needle shape. The catalyst has the advantages of low overpotential, good stability, low cost, simple preparation method and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and in particular to a self-supporting FeCo alloy phosphide electrocatalyst, a preparation method and an application thereof. Background Art

[0002] Energy is the foundation of modern economic development. The rapid consumption of traditional fossil energy and the increasing environmental problems have led to the urgent need to develop renewable energy and conversion technologies. Among many renewable energy sources (wind energy, biomass energy, solar energy, hydrogen energy, ocean energy, etc.), hydrogen energy has the advantages of high energy density and zero pollution, and is one of the most promising energy sources. Currently, more than 95% of hydrogen energy comes from fossil energy, and the shortage of fossil energy has limited the development of hydrogen energy. Electrocatalytic water splitting is simple to operate and the hydrogen produced is of high purity. It is considered to be one of the most effective strategies for large-scale production of hydrogen.

[0003] In the industrial application of hydrogen evolution by water electrolysis, the high hydrogen evolution overpotential and slow reaction kinetics of the electrode lead to excessively high energy consumption during the hydrogen evolution process, which is difficult to meet the requirements of large-scale production. Therefore, designing efficient, stable and low-cost HER catalysts is of great practical significance for large-scale production of hydrogen.

[0004] Non-precious metals (Fe, Co, Ni, etc.) are abundant and low-cost, and are currently the main research targets for hydrogen evolution reaction catalysts. Reasonable nanostructured electrocatalysts are one of the most powerful strategies to improve catalytic activity and durability. Therefore, selecting appropriate non-precious metals and designing an efficient and stable catalyst are crucial to improving hydrogen evolution performance. Summary of the invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes a self-supporting FeCo alloy phosphide electrocatalyst, a preparation method and an application thereof. The catalyst has the advantages of low overpotential, good stability, low cost and simple preparation method.

[0006] The preparation method of the self-supporting FeCo alloy phosphide electrocatalyst proposed in the present invention comprises the following steps:

[0007] S1: Pretreatment of conductive substrate;

[0008] S2: A FeCo precursor with iron-cobalt hydroxide stacking is prepared by a hydrothermal method using a conductive substrate, an iron source and a cobalt source;

[0009] S3: chemical vapor deposition of a catalytic substrate using a phosphorus source to obtain a self-supporting FeCo alloy phosphide electrocatalyst;

[0010] Wherein, the self-supporting FeCo alloy phosphide electrocatalyst is in the shape of nanosheets or pine needles.

[0011] Preferably, the conductive substrate in S1 is nickel foam; and the pretreatment method is pickling.

[0012] Preferably, the method steps for preparing the FeCo precursor in S2 are as follows: add an iron source and a cobalt source to a reaction kettle, then add ammonium fluoride and urea until the solution becomes a transparent yellow liquid, and then add nickel foam to react. The product after the reaction is washed and vacuum dried to obtain a FeCo precursor.

[0013] Preferably, the iron source in S2 is one or more of ferric nitrate and its hydrate, ferric chloride and its hydrate, ferric sulfate and its hydrate; the cobalt source is one or more of cobalt nitrate and its hydrate, cobalt chloride and its hydrate; the molar ratio of the iron source to the cobalt source is 1:0.5-20; the molar ratio of ammonium fluoride to urea is 1:1-2.

[0014] Preferably, the reaction temperature is 80-100°C and the reaction time is 7-15h.

[0015] Preferably, the vacuum drying temperature is 50-120° C., and the time is 1-12 h.

[0016] Preferably, the method steps of chemical vapor deposition in S3 are as follows: the FeCo precursor and phosphorus source of S2 are heated in a tube furnace to perform chemical vapor deposition to obtain a self-supporting FeCo alloy phosphide electrocatalyst.

[0017] Preferably, the phosphorus source is sodium hypophosphite or sodium dihydrogen phosphate; the mass ratio of the cobalt source to the phosphorus source is 0.1-0.5:1; the tubular furnace is heated to 300-400°C, the heating rate is 3-5°C / min, and the temperature is kept for 2-5h.

[0018] The present invention provides a self-supporting FeCo alloy phosphide electrocatalyst prepared by the above method.

[0019] The present invention proposes the use of the self-supporting FeCo alloy phosphide electrocatalyst in hydrogen evolution by alkaline water electrolysis.

[0020] Beneficial technical effects of the present invention:

[0021] 1. The present invention increases the local concentration of Co at the active site of the catalyst. Due to the strong directional intermolecular interaction, the crystals will grow rapidly in one direction and gradually form a pine needle shape. A local high concentration distribution appears around the tip structure of the catalyst, thereby accelerating the kinetic process of the chemical reaction and ultimately obtaining better catalytic performance. The P-doped FeCo catalyst is converted into a transition metal phosphate. Since the polarity of the generated PO bond is not as good as the MO (M = Fe, Co) bond, the MO bond can be indirectly weakened by reducing the electron density around the O atom. The electronegativity difference between P and O is very small, so it can weaken the interaction between the adsorbed Hads and oxygen in the FeCo precursor, thereby accelerating the release of hydrogen, achieving a faster H2 release process and electron / proton transfer steps, and thus accelerating the entire HER process. In addition, the pine needle shape inhibits the excessive growth of surface bimetallic phosphides, prevents agglomeration, and improves the stability of the structure.

[0022] 2. The catalyst prepared by the present invention has a low hydrogen evolution overpotential, a large catalytic active area, and a high catalytic hydrogen evolution activity. Different from the previous method of controlling the morphology by regulating the content of ammonium fluoride or urea, the present invention controls the sample morphology by the ratio of the cobalt source. The difference in the ratio of the cobalt source and the iron source can change the solution saturation and affect the morphology growth rate. The change in morphology effectively increases the specific surface area of ​​the electrode, contains more hydrogen evolution active sites, and the morphology of the sample does not change much after the present invention is deposited by CVD chemical vapor deposition, but the FeCo metal phosphides are combined by strong chemical bonds to expose more active sites, and the catalytic performance is greatly improved.

[0023] 3. The present invention controls the final sample morphology by adjusting the ratio of cobalt source and iron source, and then obtains better hydrogen evolution activity and stability through phosphating. Finally, two electrocatalysts with nanosheet and pine needle morphologies can be obtained. At the same time, under the test conditions of 1M potassium hydroxide solution, the current density in the linear sweep voltammetry curve is 10mA / cm 2 The required overpotentials are 163mV, 139mV, and 37mV, respectively. This paper provides a research idea for improving the hydrogen evolution performance of FeCo hydroxide and preparing iron-cobalt phosphide electrocatalysts with controllable morphology. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a SEM image of the electrocatalyst prepared in Example 1 of the present invention;

[0025] Figure 2 The SEM images of the dot catalyst prepared in Example 3 of the present invention, (a) and (b) are FeCo precursors; (c) and (d) are self-supporting FeCo alloy phosphide electrocatalysts;

[0026] Figure 3This is the linear sweep voltammogram of the electrocatalyst proposed in the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further explained below in conjunction with specific embodiments.

[0028] Example 1

[0029] The preparation method of the self-supporting FeCo alloy phosphide electrocatalyst proposed in the present invention comprises the following steps:

[0030] S1: Pretreatment of nickel foam

[0031] First, use 3 mol / L hydrochloric acid to ultrasonically remove the surface oxide layer for 15 minutes; take out the treated nickel foam, rinse it with water and ethanol ultrasonically for 10 minutes in turn until the pH value is neutral, store it in anhydrous ethanol to prevent secondary oxidation, and finally put it into a vacuum drying oven for drying.

[0032] S2: Preparation of FeCo precursor with iron-cobalt hydroxide stacking by hydrothermal method using conductive substrate, iron source and cobalt source

[0033] First, weigh 0.404 g Fe(NO3)3·9H2O and dissolve it in water, stir until it is completely dissolved, then add 0.145 g Co(NO3)2·6H2O and continue stirring for 15 min, then add 40 mL deionized water, 0.296 g NH4F and 0.6 g CO(NH2)2 until the solution turns light yellow; the molar ratio of Fe(NO3)3·9H2O to Co(NO3)2·6H2O is 1:0.5.

[0034] Then, the mixed solution was transferred to a 100 mL hydrothermal reactor and reacted at 120 °C. After cooling to room temperature, the obtained sample was taken out, washed repeatedly with anhydrous ethanol and water for 3 times, and dried at 60 °C for 3 h under vacuum to obtain a FeCo precursor.

[0035] S3: Chemical vapor deposition of the catalytic substrate using a phosphorus source to produce a self-supporting FeCo alloy phosphide electrocatalyst

[0036] The FeCo precursor of S2 was placed in the downstream of the tube furnace, and sodium hypophosphite was placed in the upstream. It was heated to 350°C at 4°C / min and maintained for 2h. It was naturally cooled to room temperature under nitrogen to obtain a nanosheet-shaped self-supporting FeCo alloy phosphide electrocatalyst.

[0037] Example 2

[0038] The amount of Co(NO3)2·6H2O in this example is changed to 0.291 g, that is, the molar ratio of Fe(NO3)3·9H2O to Co(NO3)2·6H2O is 1:1, and the other conditions are the same as those in Example 1.

[0039] Example 3

[0040] The amount of Co(NO3)2·6H2O in this example was changed to 0.437 g, that is, the molar ratio of Fe(NO3)3·9H2O to Co(NO3)2·6H2O was 1:1.5, and the other conditions were the same as those in Example 1. The obtained self-supporting FeCo alloy phosphide electrocatalyst was in the shape of pine needles.

[0041] Figure 1 This is a SEM image of the self-supporting FeCo alloy phosphide electrocatalyst prepared in Example 1. The electrocatalyst prepared under this condition is in the form of nanosheets.

[0042] The figure is a SEM image of the FeCo precursor and electrocatalyst prepared in Example 3. The electrocatalyst prepared in this example is in the shape of pine needles, and the phosphating treatment does not change the morphology of the catalyst.

[0043] Figure 3 This is the linear sweep voltammogram of the P-FeCo / NF electrocatalyst. The test method is: using a three-electrode system, the prepared electrode is the working electrode, Hg / HgO is the reference electrode, the graphite rod is the auxiliary electrode, the electrolyte is a KOH solution with a mass concentration of 1 mol / L, the scan rate is 5 mV / s, and the linear sweep voltammogram test is performed on a Chenhua electrochemical workstation (760e). Figure 3 It can be seen that by adjusting the proportion of the Co source, we can obtain that as the molar concentration of the Co source increases, the overpotential of the sample gradually decreases after P-treatment, and the electrocatalytic performance of Example 3 is significantly better than that of Example 1 and Example 2, indicating that Example 3 has a faster H2 release process and electron / proton transfer step, thereby accelerating the entire HER process.

Claims

1. A method for preparing a self-supporting FeCo alloy phosphide electrocatalyst, characterized in that: The steps are as follows: S1: Pretreatment of conductive substrate; S2: FeCo precursor with iron-cobalt hydroxide stacking is prepared by hydrothermal method using conductive substrate, iron source and cobalt source; S3: chemical vapor deposition of a catalytic substrate using a phosphorus source to obtain a self-supporting FeCo alloy phosphide electrocatalyst; Wherein, the self-supporting FeCo alloy phosphide electrocatalyst is in the shape of nanosheets or pine needles.

2. The method for preparing the self-supporting FeCo alloy phosphide electrocatalyst according to claim 1, characterized in that: The conductive substrate in S1 is nickel foam; the pretreatment method is pickling.

3. The method for preparing the self-supporting FeCo alloy phosphide electrocatalyst according to claim 1, characterized in that: The steps of the method for preparing the FeCo precursor in S2 are as follows: add an iron source and a cobalt source to a reaction kettle, then add ammonium fluoride and urea until the solution becomes a transparent yellow liquid, then add nickel foam to react, and the product after the reaction is washed and vacuum dried to obtain a FeCo precursor.

4. The method for preparing the self-supporting FeCo alloy phosphide electrocatalyst according to claim 3, characterized in that: The iron source in S2 is one or more of ferric nitrate and its hydrate, ferric chloride and its hydrate, ferric sulfate and its hydrate; the cobalt source is one or more of cobalt nitrate and its hydrate, cobalt chloride and its hydrate; the molar ratio of the iron source to the cobalt source is 1:0.5-20; the molar ratio of ammonium fluoride to urea is 1:1-2.

5. The method for preparing the self-supporting FeCo alloy phosphide electrocatalyst according to claim 3, characterized in that: The reaction temperature is 80-100°C and the reaction time is 7-15h.

6. The method for preparing the self-supporting FeCo alloy phosphide electrocatalyst according to claim 3, characterized in that: The vacuum drying temperature is 50-120°C and the time is 1-12h.

7. The method for preparing the self-supporting FeCo alloy phosphide electrocatalyst according to claim 1, characterized in that: The steps of the chemical vapor deposition method in S3 are as follows: the FeCo precursor and phosphorus source of S2 are heated in a tubular furnace for chemical vapor deposition to obtain a self-supporting FeCo alloy phosphide electrocatalyst.

8. The method for preparing the self-supporting FeCo alloy phosphide electrocatalyst according to claim 1, characterized in that: The phosphorus source is sodium hypophosphite or sodium dihydrogen phosphate; the mass ratio of the cobalt source to the phosphorus source is 0.1-0.5:1; the tubular furnace is heated to 300-400°C, the heating rate is 3-5°C / min, and the temperature is kept for 2-5h.

9. A self-supporting FeCo alloy phosphide electrocatalyst prepared by the method according to any one of claims 1 to 8.

10. Use of the self-supporting FeCo alloy phosphide electrocatalyst as claimed in claim 9 in hydrogen evolution by alkaline water electrolysis.

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