A phosphide composite electrode material and a preparation method thereof

Abstract

The application discloses a phosphide composite electrode material and a preparation method thereof. A precursor is prepared by using M source, N source and a complexing agent as raw materials through a solid phase grinding method at room temperature. Then, the precursor powder is placed in a crucible, and a phosphate is used as a phosphating agent to in-situ phosphorize in a tube furnace, so that the phosphide composite material with a coral structure is prepared. The prepared material has a low internal resistance, a fast ion diffusion rate and an ultra-low charge transfer resistance in an electrochemical process. The specific capacitance of the prepared phosphide composite electrode material can reach 804.3 F g ‑1 under preferred conditions when the current density is 1 A g ‑1 After 5000 charge-discharge cycles, the sample can still maintain 90.5% of the initial capacitance. The application has the advantages of simple operation process, low material cost, good super capacitor performance and good application prospect when used as an electrode material of a super capacitor.

Description

Technical Field

[0001] This invention relates to a method for preparing a metal phosphide composite material and its application field. Specifically, it involves the rapid preparation of a coral-like composite phosphide electrode material by solid-state grinding and one-step phosphating, which can be applied to energy storage devices—supercapacitors. Background Technology

[0002] With the development of next-generation wearable devices, health monitors, smart sensors, and electric vehicles, the global demand for efficient, economical, and environmentally friendly energy storage technologies is increasing. Among various electrochemical energy storage systems, supercapacitors, with their high power density, long cycle life, and fast charge / discharge processes, have become a hot topic in current research and development. In recent years, transition metal phosphides have attracted much attention in the fields of energy storage and electrocatalysis, mainly because they have better conductivity, higher theoretical capacity, and outstanding thermal stability compared to oxides and hydroxides. Furthermore, phosphorus has a lower electronegativity than oxygen, thus transition metal phosphides possess metal-like high conductivity and a small band gap, which improves electron transfer and enhances the kinetics of redox reactions. Patent CN114804045A reports "A method for preparing and applying iron-nickel phosphide nanosheets constituting capacitor materials," using nickel foam as a current collector and support, growing an iron-nickel bimetallic hydroxide precursor on its surface using a solvothermal method, and then forming a honeycomb-shaped iron-nickel phosphide nanosheet array structure supercapacitor click material through heat treatment and phosphating, exhibiting high specific capacity and excellent long-term cycling capability. Patent CN111192762 A reports "A Cu-Co-P composite material and its preparation method and application," which involves dissolving soluble copper salt and soluble cobalt salt in water and carrying out a hydrothermal reaction to obtain a Cu-Co precursor. The Cu-Co precursor is then mixed with sodium hypophosphite and calcined under a protective atmosphere to obtain the Cu-Co-P composite material. This composite material is applied to supercapacitor electrode materials, exhibiting abundant mesopores and micropores to achieve excellent electrochemical performance. Patent CN113299492B reports "A MOF-derived porous metal phosphide nanosheet array and its application," which utilizes nickel chloride hexahydrate, terephthalic acid, and copper foam under relatively mild conditions to prepare an electrode material with excellent supercapacitor performance after reduction phosphating, and exhibits good redox reversibility. Patent CN110157006A reported "Preparation of bimetallic phosphide materials and preparation and application of electrode materials containing bimetallic phosphide materials". This invention uses 2,3-pyrazine dianhydride and Mn sulfate to prepare a manganese metal-organic framework precursor by hydrothermal synthesis. The precursor is then immersed in Ni(NO3)2 solution to obtain a nickel-modified metal-organic framework. Finally, a low-temperature solid-phase phosphating reaction is carried out with NaH2PO2·H2O to obtain Mn-Ni bimetallic phosphide. The total reaction time is as long as 5 to 6 days, which is very time-consuming and complex, making it unsuitable for practical production applications.

[0003] As can be seen from the examples above, although there are many methods for preparing transition metal phosphide composite materials, most of them use liquid-phase / solvothermal methods to synthesize precursors, and there are few reports on preparing phosphide precursor materials through solid-phase grinding. This invention, however, uses a simple solid-phase grinding method with soluble M-source, N-source, and a ligand as raw materials and a suitable solvent. After grinding to obtain the precursor, a coral-like composite phosphide electrode material is prepared by low-temperature solid-phase phosphating in a tube furnace under a nitrogen atmosphere, using a suitable phosphorus source. Summary of the Invention

[0004] This invention proposes a method to obtain transition metal phosphide precursors through solid-state grinding, and then prepare a coral-like composite phosphide electrode material assembled from nanoparticles by in-situ phosphating in a tube furnace. Due to its high specific surface area and numerous active sites, the prepared coral-like composite phosphide exhibits good specific capacitance and cycle stability as an electrode material for supercapacitors.

[0005] The preparation method of the composite phosphide in this invention includes the following steps:

[0006] Place 1-2 mmol of M source, 1-2 mmol of N source and 2-3 mmol of complexing agent in a mortar, add 1-2 mL of anhydrous ethanol, grind at room temperature, add anhydrous ethanol in small amounts several times during the grinding process until the reaction is complete, and continue grinding for 5-15 min.

[0007] The above sample was transferred to an oven at 50-70 °C and dried for 20-40 min to obtain a milky white powder;

[0008] Weigh out 0.04–0.06 g of the above white powder and place it in a quartz boat, positioning it downstream of the tube furnace. Weigh out 0.4–0.6 g of phosphorus source and place it in the quartz boat, positioning it upstream of the tube furnace. Under a nitrogen atmosphere, incubate at 1–3 °C for 1 min. -1 The heating rate was adjusted to 300~400 ℃ and held for 1~3 h. The final MP / NP composite phosphide was a black powder.

[0009] Steps for testing electrochemical properties:

[0010] The prepared MP / NP composite phosphide was used as the electrode material for a supercapacitor, and its capacitance performance was tested using 6 M KOH as the electrolyte solution. Cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) were obtained. The electrochemical performance of the electrode material was tested on an electrochemical workstation using a Hg / HgO electrode as the reference electrode, nickel foam coated with the prepared material as the working electrode, and a platinum wire electrode as the counter electrode.

[0011] The reactant M source is one of cobalt acetate tetrahydrate, nickel acetate tetrahydrate, and ferrous acetate tetrahydrate;

[0012] The reactant N source is one of copper acetate monohydrate and silver acetate;

[0013] The ligand is oxalic acid;

[0014] The phosphorus source is sodium hypophosphite;

[0015] The tubular furnace mentioned is model Hefei Kejing OTF-1200X;

[0016] The electrochemical workstation mentioned is the Shanghai Chenhua workstation (CHI600E). Attached Figure Description

[0017] Figure 1 and Figure 2 The image shown is a scanning electron microscope (SEM) image of the Cu3P / CoP composite phosphide prepared in Example 1.

[0018] Figure 3 The image shows the X-ray powder diffraction (XRD) pattern of the Cu3P / CoP composite phosphide prepared in Example 1.

[0019] Figure 4 The X-ray photoelectron spectroscopy (XPS) spectrum of the Cu3P / CoP composite phosphide prepared in Example 1 is shown in the full scan.

[0020] Figure 5 The nitrogen adsorption-desorption curve (BET) of the Cu3P / CoP composite phosphide prepared in Example 2 is shown.

[0021] Figure 6 The cyclic voltammetry (CV) curves were obtained from tests conducted at different scan rates in Example 2.

[0022] Figure 7 The image shows the galvanostatic charge-discharge (GCD) curves tested at different current densities in Example 2.

[0023] Figure 8 The electrochemical impedance spectroscopy (EIS) spectrum of the sample obtained in Example 1 is shown below.

[0024] Figure 9 The graph shows the cycling performance of the sample obtained in Example 1. Detailed Implementation

[0025] The present invention will be specifically described below with reference to the embodiments, which are preferred preparation methods of the present invention, including reagent amounts and reaction conditions. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0026] Example 1: Preparation method of Cu3P / CoP composite phosphide:

[0027] Accurately weigh 1 mmol cobalt acetate tetrahydrate, 1 mmol copper acetate monohydrate, and 2 mmol oxalic acid into a mortar, then add 2 mL of anhydrous ethanol. Grind at room temperature, adding small amounts of anhydrous ethanol repeatedly until the reaction is complete, and continue grinding for 10 min. Transfer the sample to a 60 ℃ oven and dry for 30 min to obtain a milky white powder. Weigh 0.05 g of the white powder and place it in a quartz boat downstream of a tube furnace. Weigh 0.5 g of NaH2PO2·H2O and place it in the quartz boat upstream of the tube furnace. Under a nitrogen atmosphere, heat at 2 ℃ for 1 min. -1 The heating rate was adjusted to 350 °C and held for 2 h. The resulting Cu3P / CoP composite phosphide was a black powder.

[0028] The morphology of the final product obtained in Example 1 was characterized using a Japanese S-4800 field emission scanning electron microscope (SEM), the phase of the final product in Example 1 was characterized using a Japanese SmartLab 9 KW X-ray diffractometer (XRD), the elemental composition of the final product in Example 1 was characterized using a British VG ESCA X-ray photoelectron spectroscopy (XPS), and the specific surface area of ​​the final product in Example 1 was characterized using an American ASAP2460 specific surface area and porosity analyzer (BET).

[0029] from Figure 1 and Figure 2 As can be seen from the scanning electron microscope image of Cu3P / CoP composite phosphide, the sample has a coral-like structure formed by the self-assembly of nanoparticles, which effectively increases the specific surface area of ​​the electrode material. Figure 3 The XRD pattern of the final product in Example 1 shows that the Cu3P / CoP composite phosphide with a seabed coral structure is composed of Cu3P (PDF#74-1067), CoP (PDF#29-0497) A complex composed of two substances. Figure 4 The XPS full scan spectrum of the final product in Example 1 shows that the sample mainly contains Co, Cu, P, O and C elements. The oxygen and carbon elements are derived from oxygen adsorbed from the air on the sample surface and the results of carbon as a standard reference in the test, respectively. Figure 5 The N2 adsorption-desorption curve of the final product in Example 1 shows a distinct hysteresis loop within the relative pressure range of 0.6-1.0, with the slope gradually decreasing at lower relative pressures. The calculated BET specific surface area is 107.2 m². 2 g −1 .

[0030] Example 2: Testing of the electrochemical properties of Cu3P / CoP composite phosphide:

[0031] The Cu3P / CoP composite phosphide prepared in Example 1 was coated onto prepared nickel foam, dried, and the electrolyte was 6 M potassium hydroxide. The coated nickel foam was clamped with electrode clips and connected to an electrochemical workstation to test its electrochemical properties.

[0032] The specific steps are as follows:

[0033] (I) Washing the foamed nickel: Cut the foamed nickel into pieces with an actual size of 1 cm × 1 cm for testing and place them in a beaker. Add acetone and deionized water to just cover the foamed nickel. Place the beaker in an ultrasonic cleaner and ultrasonically clean for 15 min. Then add 8% dilute hydrochloric acid and ultrasonically clean for 25 min. Then rinse with deionized water several times until the pH of the cleaning solution is neutral. Finally, add anhydrous ethanol and ultrasonically clean for 30 min. Place the beaker containing the cleaned foamed nickel in a vacuum drying oven at 65 ℃ and remove it after 24 hours for use.

[0034] (II) Sample coating: Weigh 8 mg of the final product obtained in Example 1, 1 mg of acetylene black and 1 mg of polyvinylidene fluoride into a mortar, add 2-3 drops of N-methylpyrrolidone as a solvent, grind until a uniform paste is formed, and coat it onto a previously cleaned nickel foam with a size of 1 cm × 1 cm; place the coated nickel foam in a vacuum drying oven at 65°C and dry for 24 h, take out the dried nickel foam and press it into a tablet under a tablet press to ensure that the sample is tightly adhered to the nickel foam; subtract the uncoated nickel foam from the nickel foam tableted with the coated sample to further calculate the mass of the Cu3P / CoP phosphide composite material actually used for testing.

[0035] (III) Electrochemical Properties Testing: Nickel foam coated with electrode material was used as the working electrode, platinum wire as the counter electrode, and an Hg / HgO electrode as the reference electrode. These electrodes were placed in a 6 M potassium hydroxide solution using a three-hole electrode holder. The tests were conducted using a Shanghai Chenhua electrochemical workstation (CHI600E) in Cyclic Voltammetry mode within a voltage range of 0–0.6 V. The voltage scan rates were measured to be 10, 20, 30, 50, 80, and 100 mV s. -1 The cyclic voltammetry curve (CV) at time is Figure 6 The CV curve maintained a good shape as the scan speed increased, indicating that the sample has good capacitance performance. In Chronopotentionmetry mode, the test current densities were 1, 2, 3, 5, 8, and 10 A g. -1 The constant current charge-discharge diagram (GCD) at that time is as follows: Figure 7 Calculations show that at a current density of 1 A g -1 At that time, the specific capacitance can reach 804.3 F g -1 In ACImpedance mode, the electrochemical impedance spectroscopy (EIS) was measured as follows: Figure 8 The impedance diagram shows that the prepared product has a large slope and an internal resistance of 0.48 Ω. It exhibits a fast ion diffusion rate and ultra-low charge transfer resistance during electrochemical processes, indicating high capacitive behavior. Figure 9 The graph shows the cycling performance of the Cu3P / CoP phosphide composite electrode material. As can be seen from the graph, after 5000 charge-discharge cycles, the sample still retains 90.5% of its initial capacitance, demonstrating good cycling stability. Due to the good synergistic effect in the heterostructure, the Cu3P / CoP phosphide composite electrode material possesses good electrochemical performance and cycling stability.

Claims

1. A method for preparing a phosphide composite electrode material, characterized in that: Place 1–2 mmol of M source, 1–2 mmol of N source, and 2–3 mmol of ligand in a mortar, then add 1–2 mL of anhydrous ethanol. Grind at room temperature, adding small amounts of anhydrous ethanol repeatedly until the reaction is complete, and continue grinding for 5–15 min. Transfer the sample to an oven at 50–70 °C and dry for 20–40 min to obtain a milky white powder. Weigh 0.04–0.06 g of the milky white powder and place it in a quartz boat downstream of a tube furnace. Weigh 0.4–0.6 g of phosphorus source and place it in the same quartz boat upstream of the tube furnace. In a nitrogen atmosphere, heat at 1–3 °C for 1 min. -1 The heating rate was adjusted to 300-400℃ and held for 1-3 hours. The final MP / NP composite phosphide was a black powder. The M source is cobalt acetate tetrahydrate; The N source is copper acetate monohydrate; The ligand is oxalic acid; The phosphorus source is sodium hypophosphite.

2. The method for preparing a phosphide composite electrode material as described in claim 1, characterized in that: accurate... Weigh 1 mmol of cobalt acetate tetrahydrate, 1 mmol of copper acetate monohydrate, and 2 mmol of oxalic acid into a mortar, add 2 mL of anhydrous ethanol, and grind at room temperature. During grinding, add small amounts of anhydrous ethanol repeatedly until the reaction is complete, then continue grinding for 10 min. Transfer the sample to an oven at 50–70 °C and dry for 20–40 min to obtain a milky white powder. Weigh 0.05 g of the milky white powder and place it in a quartz boat downstream of a tube furnace. Weigh 0.5 g of NaH₂PO₂·H₂O and place it in the same quartz boat upstream of the tube furnace. In a nitrogen atmosphere, heat at 2 °C for 1 min. -1 The heating rate was adjusted to 350℃ and held for 2 hours to obtain a black powder, which is the phosphide composite electrode material. At a current density of 1Ag -1 At that time, the specific capacitance of the prepared phosphide composite electrode material reached 804.3 F g. -1 ; The prepared phosphide composite electrode material has an internal resistance of 0.48Ω, and after 5000 charge-discharge cycles, the sample still retains 90.5% of its initial capacitance.

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