A nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst and its preparation method

Abstract

The present invention belongs to the technical field of electrocatalytic oxygen evolution coatings, and in particular to a nickel-coated graphite-doped FeCoNi oxygen evolution electrocatalyst and a preparation method thereof, comprising ball milling powder mixing, surface degreasing, sandblasting roughening and plasma spraying to obtain a FeCoNi‑Ni3C oxygen evolution coating catalyst. The coating prepared by the present invention has good bonding with the metal substrate, and the atmospheric plasma spraying technology can make the coating well bonded to the substrate. The structure of the coating does not change before and after the stability test. In addition, due to the characteristics of the APS technology itself, the coating prepared therefrom contains a certain amount of unmelted or semi-melted Fe, Co and Ni metal elements. This characteristic can make the metal elements in the coating have a tendency to move towards higher binding energy during electrochemical testing.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic oxygen evolution coatings, in particular to a nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst and a preparation method thereof. Background Art

[0002] Hydrogen production by water electrolysis has the advantages of wide sources and no pollution, making it an ideal hydrogen production process. However, the slow kinetics of the anodic oxygen evolution reaction (OER) has greatly restricted the current development of water electrolysis technology. Catalysts based on precious metals such as Pt, Ru, and Ir have been shown to have excellent HER performance, but are limited by the low reserves and high application costs of precious metals, making it difficult for them to become ideal electrocatalysts for the popularization of electrocatalytic hydrogen production processes. It is known that increasing the surface area of ​​the catalyst can promote its reaction rate. Therefore, preparing catalysts with different porosities by adjusting the surface morphology of the catalyst is considered to be a feasible method.

[0003] Coated catalysts have high economic efficiency. The use of atmospheric plasma spraying (APS) technology to prepare the coating can produce certain pores on the surface of the coating, increase active sites, and promote the process of electrocatalytic reaction. In addition, among various three-dimensional metal catalysts, Fe, Co, and Ni oxides or hydroxides show excellent OER potential and activity, which is mainly due to the high reserve content and theoretical high catalytic properties of these three metals. This patent uses APS technology to prepare coated catalysts, and controls the number of pores on the surface of the coating by controlling the atomic ratio of Ni3C in FeCoNi powder. C can play a supporting role in the coating and stabilize the coating structure. It can also interact with the metal in the coating to inhibit the oxidation of the metal elements in the coating. At the same time, the synergistic effect between Fe, Co, and Ni can improve the OER performance of the coating.

[0004] Invention patent CN117604554A discloses a method for preparing an electrocatalytic water splitting catalyst based on FeCo-P. The preparation method uses FeCoMOF-74 as a precursor and then obtains FeCo-P through high-temperature phosphating. The FeCo-P prepared by the present invention can efficiently achieve electrocatalytic complete water splitting; however, its preparation process is cumbersome, has high temperature requirements, and a long preparation cycle.

[0005] Invention patent CN118390096A The present invention provides a high-performance Co-NC oxygen evolution catalyst and a preparation method thereof, which belongs to the field of oxygen evolution electrocatalysis technology. The catalyst is composed of a CoNx active center part and nitrogen-doped carbon jointly supported on a carbon material. The method is: γ-cyclodextrin (a family of cyclic oligosaccharides) and a cobalt salt are mixed in a liquid phase, and Co@MOF is obtained using a solution method. Subsequently, Co@MOF is mixed with a nitrogen source (dicyandiamide), placed in a protective atmosphere, and heated at high temperature to obtain a Co-NC catalyst. The oxygen evolution catalyst prepared by this process has an oxygen evolution overpotential higher than commercial IrO2, and the overpotential is higher than many current catalysts, but there is still a lot of room for improvement compared to precious metal-based catalysts.

[0006] From the above prior art, it can be seen that great efforts have been made in various fields to improve the HER or OER performance of transition metal-based (TM) catalysts. TM-based compound catalysts in the past decade include oxides, carbides, (oxy)hydroxides, etc. Among them, TM-based (oxy)hydroxides have attracted great attention in OER due to their easily adjustable three-dimensional electronic structure and satisfactory electrocatalytic performance. However, at higher current densities, the activity and durability of this catalyst are poor. It is known that exposing more active sites by adjusting the morphology of the catalyst is considered to be an extremely effective and highly economical method. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention provides a nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst and a preparation method thereof.

[0008] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0009] One of the objects of the present invention is to provide a method for preparing a nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst, comprising the following steps:

[0010] S1. Mixing FeCoNi powder and nickel-coated graphite Ni3C powder and then ball-milling to obtain FeCoNi-Ni3C powder, wherein the atomic ratio of Ni3C in the FeCoNi-Ni3C powder is 25% to 75%;

[0011] S2. Degreasing the surface of the metal substrate with a sodium hydroxide alkaline cleaning solution, followed by ultrasonic cleaning;

[0012] S3. Sandblasting the surface of the metal substrate until the surface roughness of the metal substrate is Ra5.5μm to Ra6.5μm;

[0013] S4. Plasma spraying is performed on the surface of the metal substrate after sandblasting using FeCoNi-Ni3C powder to obtain a FeCoNi-Ni3C oxygen evolution coating catalyst with a thickness of 400 to 500 μm.

[0014] The principle of the present invention is that iron, cobalt and nickel are three metals with wide sources, low prices, and similar performance to the precious metals Pt and Ir in the free energy volcano diagram, and are considered to be ideal substitutes for precious metal catalysts. Under a light microscope, the FeCoNi coating prepared by atmospheric plasma spraying technology was found to have a certain number of pores distributed on its surface. These pores can increase the specific surface area of ​​the catalyst to a certain extent, thereby providing more active sites to promote electrocatalytic reactions. At the same time, the synergistic effect between the three metal elements FeCoNi will also promote the OER reaction. From the perspective of electronegativity, the electronegativity of Ni is about 1.91, which is between Fe (about 1.83) and Co (about 1.88). The higher electronegativity of Ni means that it can play a role in adjusting the overall electronic environment, promoting the redistribution of electrons in the Fe-Co-Ni alloy, and thus affecting the electron density on the catalyst surface. Appropriate electronic structure adjustment helps to optimize the adsorption capacity of the catalyst, thereby improving the catalytic activity. On the one hand, the doping of Ni3C can adjust the surface morphology of the coating and increase the porosity of the coating, thereby exposing more active sites. The Ni-rich coating will also have a certain promoting effect on the oxygen evolution process; on the other hand, the C element can promote electron transfer and stabilize the coating structure.

[0015] Furthermore, in step S1, glass balls are used for ball milling, the diameter of the glass balls is 4 mm to 10 mm, the ball-to-powder ratio is 4:1, the ball mill speed is 1200 rad / min to 1600 rad / min, and the ball milling time is 18 h to 22 h.

[0016] Furthermore, in step S1, the particle size of the FeCoNi powder is 300-400 mesh, and the powder is spherical powder; the particle size of the nickel-coated graphite Ni3C powder is 300-400 mesh, and the powder is flake powder.

[0017] Furthermore, the metal substrate is one of copper, copper alloy, aluminum, aluminum alloy, and stainless steel.

[0018] Furthermore, in step S2, the mass percentage of the sodium hydroxide alkaline cleaning solution is 4.0% to 5.0%, and the metal substrate is immersed for 3.0 minutes to 5.0 minutes at a temperature of 60° C. to 70° C. to remove oil stains on the surface of the metal substrate.

[0019] Furthermore, in step S3, the surface of the metal substrate is sandblasted using white corundum abrasive particles of 180-200 mesh, the sandblasting angle is 75°-85°, the pressure of the compressed air is 0.56 MPa-0.60 MPa, and the sandblasting distance is 80 mm-110 mm.

[0020] Furthermore, in step S4, the plasma spraying process parameters are: welding current 650A~700A, voltage 42V~45V; spraying speed is 1800mm / min~2000mm / min, spraying distance is 150mm~180mm, powder output of powder feeding pipe is 10mg / s-15mg / s, powder feeder speed is 0.55rad / min~0.7rad / min, powder feeding gas is argon, powder feeding gas flow rate is 38psi~42psi, shielding gas is argon, shielding gas flow rate is 42psi~46psi, combustion-supporting gas is hydrogen, and gas flow rate is 8psi~12psi.

[0021] The second object of the present invention is to provide a nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst prepared by the above method.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The coating produced by this invention bonds well with the metal substrate. Atmospheric plasma spraying technology ensures excellent bonding between the coating and the substrate, and the coating's structure remains unchanged before and after stability testing. Furthermore, due to the inherent characteristics of APS technology, the coating produced contains a certain amount of unmelted or semi-melted Fe, Co, and Ni metal elements. This characteristic causes the metal elements in the coating to tend to move toward higher binding energies during electrochemical testing.

[0024] When the atomic ratio of Ni3C in FeCoNi-Ni3C is 50%, the overall porosity of the coating can reach 22%. This property ensures that the coating can provide a larger surface area and more active sites to promote OER performance during electrochemical measurements. The carbon element not only stabilizes the overall structure of the coating with a larger porosity, but also promotes electron transfer during the electrochemical process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The microscopic morphology of the FeCoNi-Ni3C oxygen evolution coating catalyst before the oxygen evolution reaction under an electron microscope in Example 1 of the present invention and the porosity of the coating calculated based on the microscopic morphology;

[0026] Figure 21 is the linear sweep voltammetry (LSV) curve of the FeCoNi-Ni3C oxygen evolution coating catalyst before and after the stability test in Example 1 of the present invention;

[0027] Figure 3 is the double layer capacitance (Cdl) of the FeCoNi-Ni3C oxygen evolution coating catalyst in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] Example 1

[0030] 1) Ball milling powder mixing: In a stainless steel crucible, FeCoNi powder is mixed with nickel-coated graphite (Ni3C) powder in an equal molar ratio, wherein FeCoNi is a spherical powder and nickel-coated graphite (Ni3C) is a flake powder. The particle size of both powders is between 400 and 500 mesh. The ball mill uses glass balls with a diameter of 4mm-10mm, the ball mill speed is 1200rad / min, and the ball milling time is 20h to obtain FeCoNi-Ni3C powder. The atomic ratio of Ni3C in the FeCoNi-Ni3C powder is 50%.

[0031] 2) Surface degreasing: Remove oil stains from the metal substrate surface using a sodium hydroxide alkaline solution at a mass percentage of 5.0% at 60°C for 5.0 minutes. The metal substrate was a 100 mm x 100 mm copper plate (grade T2) with a thickness of 2 mm.

[0032] 3) Sandblasting: Use 180-200 mesh white corundum abrasive to sandblast the surface of the copper plate. The sandblasting angle is 75°-85°, the compressed air pressure is 0.56 MPa, and the sandblasting distance is 100 mm, until the surface appears a silver-gray rough luster. The surface roughness of the copper plate after sandblasting is Ra6.0 μm. After sandblasting, use compressed air to blow away the sticky sand on the surface.

[0033] 4) Plasma spraying: The ball-milled FeCoNi-Ni3C powder was sprayed on the surface of the copper plate after sandblasting roughening. The plasma spraying process parameters were: welding current 700A, voltage 43V, and FeCoNi-Ni3C oxygen evolution coating catalyst thickness of 420μm; the spraying speed of the FeCoNi-Ni3C oxygen evolution coating catalyst was 1800mm / min, the spraying distance was 160mm, the powder output of the powder feeder was 12mg / s, the powder feeder speed was 0.65rad / min, the powder feeding gas was argon, the powder feeding gas flow rate was 40psi, the shielding gas was argon, the shielding gas flow rate was 46psi, the combustion-supporting gas was hydrogen, and the gas flow rate was 10psi; before plasma spraying, the metal powder for plasma spraying was preheated and dried in a drying oven at 70°C and for 1h.

[0034] Example 2

[0035] The atomic ratio of Ni3C in the FeCoNi-Ni3C powder is 25%, and the rest is the same as in Example 1.

[0036] Example 3

[0037] The atomic ratio of Ni3C in the FeCoNi-Ni3C powder is 75%, and the rest is the same as in Example 1.

[0038] Comparative Example 1

[0039] The atomic ratio of Ni3C in the FeCoNi-Ni3C mixed powder is 0%, and the prepared coating is an original coating with an equal molar ratio of FeCoNi.

[0040] The specific operating steps of the prepared oxygen evolution catalyst coating are as follows:

[0041] 1) Surface degreasing: Use sodium hydroxide alkaline cleaning solution to remove oil stains on the surface of the copper plate; the mass percentage of the sodium hydroxide alkaline cleaning solution is 4.0%, and the temperature is 60° C. and the immersion time is 5.0 min.

[0042] 2) Sandblasting: Use 180-200 mesh white corundum abrasive to sandblast the surface of the copper plate. The sandblasting angle is 75°-85°, the compressed air pressure is 0.56 MPa, and the sandblasting distance is 80 mm, until the surface appears a silver-gray rough luster. The surface roughness of the copper plate after sandblasting is Ra5.5 μm. After sandblasting, use compressed air to blow away the sticky sand on the surface.

[0043] 3) Plasma spraying: FeCoNi spherical alloy powders of equal molar ratio were sprayed on the surface of the sandblasted copper plate. The plasma spraying process parameters were as follows: welding current 650A, voltage 42V, and FeCoNi alloy coating thickness 450μm; the spraying speed of the FeCoNi alloy coating was 2000mm / min, the spraying distance was 150mm, the powder output of the powder feeder was 12mg / s, the powder feeder speed was 0.6rad / min, the powder feeding gas was argon, the powder feeding gas flow rate was 40psi, the shielding gas was argon, the shielding gas flow rate was 44psi, and the combustion-supporting gas was hydrogen, with a gas flow rate of 8psi. Before plasma spraying, the metal powder for plasma spraying was preheated and dried in a drying oven at 70°C for 2h.

[0044] In order to test the performance of the catalyst, the copper plates after plasma spraying of Examples 1 to 3 and Comparative Example 1 were cut into standard test blocks of 10 mm × 5 mm × 2 mm in size using a wire cutting device (DK7720). The coating surface of the cut sample was polished using 800-2000 mesh sandpaper. The purpose of this step is to remove the oxide scale produced on the coating surface during the APS coating preparation and wire cutting process. In addition, polishing with 800-2000 mesh sandpaper can make the coating surface flat and smooth, which is convenient for subsequent electrochemical characterization. Since the porosity of the coating needs to be calculated, a polishing machine is used to polish the coating after sandpaper polishing. The surface morphology of the polished coating is analyzed by SEM, and the porosity of the coating is calculated accordingly.

[0045] Electrochemical Characterization: The treated coating was used as the working electrode, Hg / HgO as the reference electrode, and a carbon rod electrode as the counter electrode. The working, reference, and counter electrodes were placed in a standard three-electrode electrolytic cell containing 1 M KOH, with the coated surface of the working electrode facing the counter electrode. The oxygen evolution performance of the coating was tested using an electrochemical workstation (CHI640E).

[0046] See Figure 1 The following figure shows the micromorphology of the FeCoNi-Ni3C oxygen evolution coating catalyst before the oxygen evolution reaction, as observed by scanning electron microscopy, along with a calculated porosity plot. The structure exhibits a typical thermal spray coating. The coating porosity, measured using Image software, is approximately 22.1%. Oxygen evolution stability testing reveals the formation of oxidation products around the pores on the coating surface.

[0047] See Figure 2 , Linear sweep voltammetry (LSV) curves of oxygen evolution of FeCoNi-Ni3C oxygen evolution coating catalyst before and after stability test. LSV overpotential of FeCoNi-Ni3C oxygen evolution coating catalyst after doping with 50% Ni3C at 10mA cm-2 At a current density of 1.5 GHz, the oxygen evolution overpotential is only 212 mV. The overpotential performance corresponding to the LSV curve shows that the prepared coating has excellent oxygen evolution performance.

[0048] See Figure 3 , is the double-layer capacitance (Cdl) of the 50% Ni3C-doped FeCoNi-Ni3C oxygen evolution coating catalyst, which reflects the activity of the catalyst. The double-layer capacitance of the prepared coating is 162.68 mF cm -2 The higher double-point capacitance indicates that the prepared coating can provide more active sites to promote the OER reaction. The specific test results are shown in Table 1.

[0049] Table 1

[0050]

[0051] As shown in Table 1, when the atomic ratio of Ni3C in FeCoNi-Ni3C is 50%, the overall porosity of the coating can reach 22%. This feature ensures that the coating can provide a larger surface area and more active sites to promote OER performance during electrochemical measurements.

[0052] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. Any technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst, characterized in that: The following steps are involved: S1. Mixing FeCoNi powder and nickel-coated graphite Ni3C powder and then ball-milling to obtain FeCoNi-Ni3C powder, wherein the atomic ratio of Ni3C in the FeCoNi-Ni3C powder is 50% to 75%; S2. Degreasing the surface of the metal substrate with a sodium hydroxide alkaline cleaning solution, followed by ultrasonic cleaning; S3. Sandblast the surface of the metal substrate until the surface roughness of the metal substrate is Ra5.5μm~Ra6.5μm; S4. Plasma spraying of FeCoNi-Ni3C powder is performed on the surface of the metal substrate after sandblasting to obtain a FeCoNi-Ni3C oxygen evolution coating catalyst with a thickness of 400-500 μm.

2. The method for preparing the nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst according to claim 1, wherein In step S1, glass balls are used for ball milling, the diameter of the glass balls is 4 mm to 10 mm, the ball-to-powder ratio is 4:1, the ball mill speed is 1200 rad / min to 1600 rad / min, and the ball milling time is 18 h to 22 h.

3. The method for preparing the nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst according to claim 1, wherein: In the step S1, the particle size of the FeCoNi powder is 300-400 mesh, and the powder is spherical powder; the particle size of the nickel-coated graphite Ni3C powder is 300-400 mesh, and the powder is flake powder.

4. The method for preparing the nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst according to claim 1, wherein The metal substrate is one of copper, copper alloy, aluminum, aluminum alloy and stainless steel.

5. The method for preparing the nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst according to claim 1, wherein: In the step S2, the mass percentage of the sodium hydroxide alkaline cleaning solution is 4.0% to 5.0%, and the metal substrate is immersed for 3.0 minutes to 5.0 minutes at a temperature of 60° C. to 70° C. to remove oil stains on the surface of the metal substrate.

6. The method for preparing the nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst according to claim 1, wherein: In step S3, the surface of the metal substrate is sandblasted using white corundum abrasive particles of 180-200 mesh, the sandblasting angle is 75°-85°, the pressure of the compressed air is 0.56 MPa-0.60 MPa, and the sandblasting distance is 80 mm-110 mm.

7. The method for preparing the nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst according to claim 1, wherein: In step S4, the plasma spraying process parameters are: welding current 650A~700A, voltage 42V~45V; spraying speed is 1800mm / min~2000mm / min, spraying distance is 150mm~180mm, powder output of powder feeding pipe is 10mg / s-15mg / s, powder feeder speed is 0.55rad / min~0.7rad / min, powder feeding gas is argon, powder feeding gas flow rate is 38psi~42psi, shielding gas is argon, shielding gas flow rate is 42psi~46psi, combustion-supporting gas is hydrogen, and gas flow rate is 8psi~12psi.

8. A nickel-coated graphite-doped FeCoNi oxygen evolution coating catalyst prepared by the method according to any one of claims 1 to 7.

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