Preparation method of nickel-based composite electrocatalyst doped with different Mn

Abstract

The invention discloses a preparation method of a nickel-based composite electrocatalyst doped with different Mn, and belongs to the field of electrochemistry. The preparation method comprises preparation of a Mn-doped nickel hydroxide precursor and preparation of the Mn-doped nickel-based composite electrocatalyst. The method comprises the following steps: (1) preparing Mn-doped Ni (OH) 2 precursors with different contents by a hydrothermal method; (2) synthesizing a Mn-doped nickel-based composite electrocatalyst by using triethanolamine as a carbon source and utilizing a vapor deposition method, so as to increase the conductivity; (3) nitric oxide, carbon dioxide and other gases volatilized from triethanolamine on the surface of the catalyst form holes to increase active sites; and (4) testing the electrochemical hydrogen evolution performance of the electrocatalyst under an alkaline condition by using an electrochemical workstation. The prepared Mn0.2-NiC / NiO catalyst only needs the overpotential of 56 mV under the current density of 10 mA / cm < 2 >, and the stability exceeds 20 h. The prepared hydrogen evolution heterostructure electrocatalyst is efficient, and the method is simple and convenient.

Description

Technical Field

[0001] The invention relates to a Mn-doped nickel-based composite electrocatalyst and a preparation method thereof, belonging to the technical field of electrochemistry. Background Art

[0002] With the development of society, traditional energy can no longer meet the society's demand for energy development, and excessive use of these energy sources will also bring about a series of environmental problems. Therefore, the clean and efficient use of coal resources, increasing the organic combination of fossil energy and new energy, and increasing the production capacity of new energy are important goals of energy structure transformation. In order to overcome the limitations of commercial Pt and Pt-based precious metals, researchers have focused their attention on transition metal-based compounds with abundant reserves and simple structures. At present, commonly used transition metal compounds mainly include Fe, Co, Ni, Cu, Mo, etc. In the field of catalysis, Ni has certain advantages in reserves, price and toxicity, and is used more frequently than other metals. Among them, NiO has an octahedral salt mine structure and is very sensitive to phase changes. However, due to its low intrinsic activity and poor conductivity, its catalytic performance is not satisfactory. Introducing other small atoms into NiO to make composite materials can significantly improve its catalytic performance. Nadeem et al. ( ACSApplied EnergyMaterials Volume: 2 Issue: 5 Page: 3587–3594) prepared NiO / NiS heterostructure nanoparticles with significantly improved performance; Muhammad et al. (Journal of Alloys and Compounds Volume: 976 Page: 172931-172938) prepared NiO / NiS / NiP heterostructure nanoparticles with good catalytic performance; Xiao et al. (ACS Appl. Mater. Interfaces Volume: 10 Page: 4689-4696) prepared NiS / Ni2P heterostructure with minimum transfer resistance. However, nickel-based compounds are prone to agglomeration during high-temperature doping, resulting in poor HER catalytic activity. NiC has good catalytic activity. By doping with transition metals, the stability of the heterostructure can be significantly improved, and more active sites can be exposed. The above methods do not dope transition metals, and the agglomeration phenomenon seriously limits the exposure of active sites in the heterostructure. Summary of the invention

[0003] Provided is a method for preparing a nickel-based composite electrocatalyst doped with different Mn. The nickel-based composite electrocatalyst doped with different Mn prepared by the method exhibits high catalytic activity and stability in electrochemical hydrogen evolution applications.

[0004] The present invention provides a method for preparing a nickel-based composite electrocatalyst doped with different Mn. In step (1), a trace amount of Mn ion doped Ni(OH)2 precursor is prepared in a weak alkaline environment by a mild hydrothermal method. As the Mn content increases, the layer is embedded with Mn and the precursor is heated to 1 000 ℃ and then heated to 1 000 ℃. 2+ Ions, parallel and equally spaced NiO layers present a vortex structure of disordered layers, the interlayer spacing expands, and the nanosheets become smaller, thereby performing structural regulation. In step (2), a part of C atoms are introduced by high-temperature heat treatment to replace the position of O ions in NiO to form NiC to form a nickel-based composite structure to enhance the overall ion transport properties, stability and electrochemical activity of the composite material, and form a heterogeneous structure with NiO-NiC coexistence. The loaded carbide can not only optimize the electronic structure of the composite surface, but also promote the generation of a large number of vacancies, defects and other highly active sites, providing good catalytic activity. In this process, Mn ions not only regulate the structure of the precursor, but also significantly improve the stability of the heterogeneous structure.

[0005] The first object of the present invention is to provide a method for preparing a nickel-based composite electrocatalyst doped with different Mn.

[0006] In order to achieve the purpose of the present invention, the technical scheme adopted is as follows:

[0007] A method for preparing a nickel-based composite electrocatalyst doped with different Mn, characterized in that it comprises the following preparation steps:

[0008] (1) Synthesis of a nano-microsphere Mn-doped nickel hydroxide precursor composed of nanosheets: dissolving a metal ion source and urea in deionized water to prepare a solution for hydrothermal reaction to obtain a foam nickel-loaded nano-microsphere Mn-doped nickel hydroxide precursor composed of nanosheets, which is placed in a blast drying oven for drying to obtain a nano-microsphere Mn-doped nickel hydroxide precursor composed of nanosheets; the metal ion source comprises a nickel source and a manganese source, the nickel source is nickel nitrate hexahydrate, and the manganese source is manganese sulfate monohydrate.

[0009] (2) Synthesis of Mn-doped nickel-based composite electrocatalyst: The nano-microsphere Mn-doped nickel hydroxide precursor composed of nanosheets prepared in step (1) and the carbon source are placed on a small porcelain boat, the air is evacuated and annealed in an argon atmosphere, and the mixture is kept warm for a period of time and then cooled to room temperature to obtain a Mn-doped nickel-based composite electrocatalyst; the carbon source is triethanolamine, and the phosphorus source is sodium hypophosphite.

[0010] Furthermore, in step (1), the molar ratio of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), manganese sulfate monohydrate (MnSO4·H2O) and urea (CH4N2O) is (2.6-2.9):(0.1-0.4):1.

[0011] Furthermore, in step (1), the hydrothermal reaction parameters are: temperature is 180-200° C., and reaction time is 10-16 h.

[0012] Furthermore, in step (1), the Mn-doped nickel hydroxide nanospheres composed of nanosheets supported by the nickel foam are dried at 60-70° C. for 2-6 hours.

[0013] Furthermore, in step (2), the carbon source is triethanolamine, and the volume percentage concentration of the triethanolamine solution is 20-25%.

[0014] Furthermore, in step (2), annealing is performed at 450-550° C. in an argon atmosphere with a gas flow rate of 100-150 sccm and a holding time of 2-4 hours. After cooling to room temperature, a Mn-doped nickel-based composite electrocatalyst is obtained.

[0015] Furthermore, a Mn-doped nickel-based composite electrocatalyst prepared by the above preparation method is provided.

[0016] Furthermore, a method for using a Mn-doped nickel-based composite electrocatalyst in alkaline electrochemical hydrogen evolution is provided.

[0017] The second object of the present invention is to provide a flower-shaped microsphere Mn-NiC / NiO catalyst composed of nanosheets obtained by the above preparation method.

[0018] The third object of the present invention is to provide an application of the flower-shaped microsphere Mn-NiC / NiO catalyst material composed of the above-mentioned nanosheets in electrochemical hydrogen evolution in an alkaline environment.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The present invention adopts a simple hydrothermal method and a high temperature annealing method, the experimental method is simple to operate, and the reaction environment is mild and controllable. The structure of the catalyst is well stabilized by manganese atom doping, the agglomeration of nickel-based compounds is prevented, and more active sites are provided.

[0021] (2) The Mn-NiC / NiO nanocatalytic material prepared by the present invention uses triethanolamine as a carbon source, which volatilizes gases such as nitric oxide and carbon dioxide at high temperatures, and the remaining carbon atoms replace oxygen atoms to form carbides to form a heterogeneous structure, thereby increasing the electron transfer ability of the catalyst.

[0022] The method of the present invention is simple to prepare and has low cost. The flower-shaped microspheres composed of the prepared nanosheets are Mn 0.2 -NiC / NiO has good electrocatalytic hydrogen evolution performance, showing that only 56 mA overpotential is required to reach 10 mA cm in KOH solution. -2The current density is stable for more than 20 h. This study provides a facile method for the design and preparation of efficient heterostructure electrocatalysts for hydrogen evolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a SEM image of the Mn-doped nickel-based composite electrocatalyst prepared in Examples 1-4 of the present invention;

[0024] Figure 2 This is a SEM image of the Mn-doped nickel-based composite electrocatalyst prepared in Comparative Example 1 of the present invention;

[0025] Figure 3 This is the XRD pattern of the Mn-doped nickel-based composite electrocatalyst prepared in Example 2 after carbonization.

[0026] Figure 4 The linear voltammetry (LSV) polarization curve test graphs of hydrogen evolution of Mn-doped nickel-based composite electrocatalysts prepared for Examples 1-4 and Comparative Example 1.

[0027] Figure 5 The stability test curves of the Mn-doped nickel-based composite electrocatalysts for hydrogen evolution prepared in Examples 1-4 and Comparative Example 1 were measured by chronopotentiometry at 20 h.

[0028] Figure 6 This is a SEM image of the Mn-doped nickel-based composite electrocatalyst of Example 2 of the present invention after stability testing. DETAILED DESCRIPTION

[0029] The following further examples are given to illustrate the present invention in detail. The following examples are only used to further illustrate the present invention, but not to limit the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples in a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description of this article, but are not limited to the specific values ​​​​exemplified below.

[0030] Embodiment 1:

[0031] (1) Synthesis of Mn-doped nickel hydroxide precursor composed of nanosheets: Soak the nickel foam in 3 mol / L hydrochloric acid for 20 minutes to remove the surface oxide layer, and then alternately ultrasonically clean it in deionized water and anhydrous ethanol solution for a total of 5 times, 5 minutes each time. Put it in a blast drying oven and dry it at 75°C for 40 minutes, then take it out for use. Weigh 0.8435g of nickel nitrate hexahydrate, 0.0169g of manganese sulfate monohydrate and 0.06g of urea and put them in a beaker, add 30ml of deionized water to the beaker, and stir it magnetically at room temperature for 10 minutes to obtain a light green transparent solution. Transfer the solution and nickel foam into a 50ml stainless steel reactor with polytetrafluoroethylene lining, put the reactor into an electric blast drying oven, react at 180°C for 12 hours, and then cool it naturally to room temperature. The sample was taken out, rinsed with deionized water, placed in a forced air drying oven, and dried at 60° C. for 2 h to obtain a nano-microsphere Mn-doped nickel hydroxide precursor composed of nanosheets.

[0032] (2) Synthesis of Mn-doped nickel-based composite electrocatalyst: Prepare a triethanolamine solution with a volume percentage concentration of 23%, and stir magnetically for 20 minutes to obtain a clear and transparent solution. Soak the treated nickel foam in the triethanolamine solution for 10 minutes, and then put it into a forced air drying oven to dry at 60°C for 2 hours. Repeat the whole process 5 times to obtain triethanolamine-loaded nickel foam. Place the triethanolamine-loaded nickel foam on the back of the groove of the small porcelain boat, and place the precursor on the groove of the small porcelain boat. The two small porcelain boats are located upstream and downstream of the tubular furnace respectively. Vacuum and introduce argon gas at a gas flow rate of 100sccm. Heat the tubular furnace to 500°C for annealing. After keeping warm for 2 hours, cool it to room temperature with the furnace to obtain flaky Mn. 0.1 -NiC / NiO electrode materials.

[0033] Embodiment 2:

[0034] A method for preparing a Mn-doped nickel-based composite electrocatalyst, referring to Example 1, except that the content ratio of Mn ions is changed by weighing 0.8143 g of nickel nitrate hexahydrate and 0.0338 g of manganese sulfate monohydrate, and other conditions including the mass of each raw material, reaction steps, and reaction time remain unchanged, to prepare a Mn-doped nickel-based composite electrocatalyst, recorded as Mn 0.2 -NiC / NiO.

[0035] Embodiment 3:

[0036] A method for preparing a Mn-doped nickel-based composite electrocatalyst, referring to Example 1, except that the content ratio of nickel and Mn ions is changed, 0.7852 g of nickel nitrate hexahydrate and 0.0507 g of manganese sulfate monohydrate are weighed, and other conditions including the mass of each raw material, reaction steps, and reaction time remain unchanged, and a Mn-doped nickel-based composite electrocatalyst can be prepared, which is recorded as Mn 0.3 -NiC / NiO.

[0037] Embodiment 4:

[0038] A method for preparing a Mn-doped nickel-based composite electrocatalyst, referring to Example 1, except that the content ratio of nickel and Mn ions is changed, 0.7561 g of nickel nitrate hexahydrate and 0.0676 g of manganese sulfate monohydrate are weighed, and other conditions including the mass of each raw material, reaction steps, and reaction time remain unchanged, and a Mn-doped nickel-based composite electrocatalyst can be prepared, which is recorded as Mn 0.4 -NiC / NiO.

[0039] Comparative Example 1:

[0040] A method for preparing a Mn-doped nickel-based composite electrocatalyst is disclosed, with reference to Example 1, except that 0.8143 g of nickel nitrate hexahydrate and 0.0338 g of manganese sulfate monohydrate are weighed, the nickel foam loaded with triethanolamine in step (2) of Example 1 is replaced with 0.3 g of sodium hypophosphite, and other conditions including the mass of each raw material, reaction steps, and reaction time remain unchanged, thereby preparing a Mn-doped nickel-based composite electrocatalyst, recorded as Mn-NiP / NiO.

[0041] The catalysts prepared in Examples 1-4 and Comparative Example 1 were tested in an electrolytic cell using a three-electrode system, including a working electrode, an Ag / AgCl reference electrode, and a carbon rod counter electrode. In the electrochemical test, a 1M KOH solution saturated with H2 was used as the electrolyte, and the electrochemical test was performed using an electrochemical workstation.

[0042] Figure 1 The SEM images of the Mn-doped nickel-based composite electrocatalysts loaded on the nickel foam prepared in Examples 1-4 of the present invention are shown. It can be seen from the figure that the morphology of the catalyst can be changed by regulating the Mn ion content. Example 1 is a semicircular sheet. As the Mn content increases, the nanosheets are reduced and form a vortex to form a nanoflower-like structure. As shown in Example 2, the active sites of the catalyst are greatly increased, and as the Mn content further increases, the crystallinity of the nanosheets decreases to form a sea urchin-like structure.

[0043] Figure 2 This is a SEM image of the Mn-doped nickel-based composite electrocatalyst prepared in Comparative Example 1 of the present invention. Comparative Example 1 presents a spherical nanoflower structure composed of nanosheets, and in addition, the surface of the nanoflower is covered with a few nanofibers.

[0044] Figure 3 This is the XRD diagram of Example 2 of the present invention. No Mn oxide or manganese hydroxide structure is seen in the diagram, proving that it is a NiC / NiO heterojunction doped with trace amounts of manganese ions.

[0045] Figure 4 The LSV test curves of Examples 1-4 and Comparative Example 1 of the present invention are shown in the test potential range of -1.5 to -0.8 V. The prepared Mn-doped nickel-based composite electrocatalyst is used as the working electrode. The obtained curves are IR compensated, and the compensation level is 90%. At 10 mA / cm 2 The overpotentials of hydrogen evolution at current densities of 10 mA / cm2 are 78 mV, 56 mV, 79 mV, 98 mV and 112 mV respectively. It can be seen that the heterojunction formed by doping C atoms greatly improves the catalytic activity of the electrode. 2 The hydrogen evolution overpotential at the current density of is the lowest, indicating that it has the best catalytic activity.

[0046] Figure 5 The stability test of Examples 1-4 and Comparative Example 1 of the present invention was performed using the chronopotentiometry method.

[0047] Figure 6 This is the SEM image of the Mn-doped nickel-based composite electrocatalyst of Example 2 of the present invention after the stability test. The structure of the flower-shaped microspheres Mn-NiC / NiO composed of nanosheets has no obvious change and the structure is well maintained, indicating that this catalyst is relatively stable for the electrocatalytic hydrogen evolution process.

[0048] In summary, the process of the present invention is simple and the cost of raw materials is low. The prepared Mn-doped nickel-based composite electrocatalyst plays a significant role in improving the hydrogen evolution kinetics and exhibits excellent catalytic activity and stability. It provides a simple preparation method for the field of hydrogen evolution electrocatalysis and has broad application prospects.

Claims

1. A method for preparing flower-shaped microsphere Mn-NiC / NiO catalyst composed of nanosheets, characterized in that: The following steps are involved: (1) Synthesis of a nano-microsphere Mn-doped nickel hydroxide precursor composed of nanosheets: dissolving a metal ion source and urea in deionized water to prepare a solution for hydrothermal reaction to obtain a foam nickel-loaded nano-microsphere Mn-doped nickel hydroxide composed of nanosheets, which is placed in a blast drying oven for drying to obtain a nano-microsphere Mn-doped nickel hydroxide precursor composed of nanosheets; the metal ion source comprises a nickel source and a manganese source, the nickel source is nickel nitrate hexahydrate, and the manganese source is manganese sulfate monohydrate; the molar ratio of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), manganese sulfate monohydrate (MnSO4·H2O) and urea (CH4N2O) is (2.6-2.9):(0.1-0.4):1; hydrothermal reaction parameters: temperature is 180-200°C, and reaction time is 10-16h; (2) Synthesis of Mn-doped nickel-based composite electrocatalyst: The nano-microsphere Mn-doped nickel hydroxide precursor composed of nanosheets prepared in step (1) and the carbon source are placed on a small porcelain boat, the air is evacuated and annealed at 450-550° C. in an argon atmosphere, and then cooled to room temperature after keeping the temperature for 2-4 hours to obtain a Mn-doped nickel-based composite electrocatalyst; the carbon source is triethanolamine.

2. The preparation method according to claim 1, characterized in that: In step (1), the Mn-doped nickel hydroxide nanospheres composed of nanosheets supported by nickel foam are dried at 60-70° C. for 2-6 hours.

3. The preparation method according to claim 1, characterized in that: The triethanolamine is added in the form of a triethanolamine solution, and the volume percentage concentration of the triethanolamine solution is 20-25%.

4. The preparation method according to claim 1, characterized in that: The gas flow rate is 100-150 sccm.

5. A Mn-doped nickel-based composite electrocatalyst prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the Mn-doped nickel-based composite electrocatalyst according to claim 5 in alkaline electrochemical hydrogen evolution.

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