Preparation method of cobalt phosphide nanorod material, electrode prepared from cobalt phosphide nanorod material and application of electrode

Abstract

The invention discloses a preparation method of a cobalt phosphide nanorod material, an electrode prepared from the cobalt phosphide nanorod material and application of the cobalt phosphide nanorod material, and belongs to the technical field of electrochemical energy storage. According to the specific scheme, cobalt nitrate hexahydrate, sodium hypophosphite and urea are dissolved in deionized water, and a homogeneous solution is formed through magnetic stirring; transferring the homogeneous solution into a reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction, cooling after the reaction is completed, taking out a product, and centrifugally washing to obtain the cobalt phosphide nanorod material. The cobalt phosphide nanorod material is mixed with conductive carbon black and polyvinylidene fluoride, N-methyl pyrrolidone is added to prepare slurry, foamed nickel is coated with the slurry, vacuum drying is performed, and the cobalt phosphide nanorod electrode is obtained. And assembling by taking the cobalt phosphide nanorod electrode as a positive electrode, the rGO as a negative electrode, KOH as an electrolyte and a cellulose membrane as a diaphragm to obtain the CoP / rGO asymmetric supercapacitor. According to the invention, through collaborative optimization of the nanorod structure design and the charge balance strategy, the comprehensive performance of the supercapacitor is significantly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and more particularly to a method for preparing a cobalt phosphide nanorod material and an electrode prepared therefrom and applications thereof. Background Art

[0002] As a highly efficient energy storage device, supercapacitors have attracted much attention in the field of new energy due to their high power density, fast charge and discharge capabilities, and long cycle life. Transition metal phosphides, such as cobalt phosphide, have high theoretical specific capacity (3458 F·g -1 ) and excellent conductivity are considered to be ideal electrode materials.

[0003] However, the preparation methods of existing CoP materials and their application in supercapacitors still face significant challenges. The traditional high-temperature phosphating method requires multiple steps, involving high temperatures (>500°C) and toxic phosphorus sources (such as PH 3 ), the process is highly dangerous and energy-intensive, and it is easy to cause particle agglomeration, reducing the utilization rate of active sites. Although the existing hydrothermal method simplifies the preparation process, the synthesized CoP is mostly irregular particles or flaky structures with limited specific surface area and long ion diffusion paths, which make it difficult to fully expose active sites, limiting the improvement of electrochemical performance. In addition, the volume expansion of CoP materials is significant during the charge and discharge process, resulting in structural collapse and active material shedding, and rapid capacity decay. At the device level, existing asymmetric supercapacitors have poor matching of positive and negative electrode materials, narrow voltage window (usually <1.5V), and low energy density (<25Wh·kg -1 ).

[0004] The above problems seriously restrict the practical application of CoP materials in supercapacitors. Therefore, it is an urgent problem for technicians in this field to develop a CoP electrode material with simple process, controllable structure and stable performance, and design asymmetric supercapacitor devices with high energy density. Summary of the invention

[0005] In view of this, the present invention provides a method for preparing a cobalt phosphide nanorod material, an electrode prepared therefrom, and an application thereof, aiming to solve the problems of complex preparation process, uncontrollable structure, poor cycle stability, and low energy density of asymmetric supercapacitors of the prior art cobalt phosphide (CoP) materials, and to provide a CoP nanorod electrode material with simple process, low cost and excellent performance, and a supercapacitor application solution thereof.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] First, the present invention provides a method for preparing a cobalt phosphide nanorod material, which specifically comprises the following steps:

[0008] S1, prepare precursor solution

[0009] Dissolve cobalt nitrate hexahydrate, sodium hypophosphite and urea in deionized water and stir magnetically to form a homogeneous solution.

[0010] S2, hydrothermal reaction

[0011] The homogeneous solution was transferred to a polytetrafluoroethylene-lined reactor for hydrothermal reaction. After the reaction was completed, the solution was cooled, the product was taken out, centrifuged, washed, and vacuum dried to obtain cobalt phosphide nanorod material.

[0012] Its beneficial effects are as follows: the technical solution for preparing cobalt phosphide nanorods by hydrothermal phosphating method based on precursor concentration regulation provided by the present invention has the following significant advantages compared with the traditional cobalt phosphide preparation process: by innovatively regulating the molar ratio of cobalt source, phosphorus source and pH regulator, the morphology of nanorods is controlled, and a nanostructure with uniform morphology can be obtained without introducing an exogenous template, which greatly simplifies the process flow and improves the preparation efficiency. At the same time, the nucleation-growth-phosphating process is completed simultaneously through a one-step hydrothermal reaction, which effectively avoids the common phase separation and impurity residue problems in the traditional step-by-step synthesis method, and the obtained CoP nanorods have excellent phase purity and structural stability. This nanorod structure can effectively increase the specific surface area of ​​the electrode material, improve the utilization rate and cycle stability of the material. The results of electrochemical studies show that as an electrode material in supercapacitors, CoP electrode has a high performance at 1A g -1 The current density provided 1826.7Fg -1 The high specific capacitance value of CoP electrode is 86.8% and 88.1% after 10,000 cycles, indicating good cycle stability. Therefore, the preparation process is environmentally friendly, cost-controlled and scalable, providing an innovative solution for the development of high-performance supercapacitor electrode materials.

[0013] Preferably, the molar ratio of cobalt nitrate hexahydrate, sodium hypophosphite and urea in step S1 is 1:1:0.67.

[0014] The concentration of cobalt nitrate hexahydrate in the homogeneous solution is 5-50 mmol / L.

[0015] Preferably, the temperature of the hydrothermal reaction in step S2 is 160-200° C. and the time is 4-8 hours.

[0016] The centrifugal washing is performed with deionized water and ethanol in sequence.

[0017] Secondly, the present invention also provides a cobalt phosphide nanorod electrode, which is specifically prepared by the following steps:

[0018] The nickel foam is cut and cleaned, and then the cobalt phosphide nanorod material prepared by the method described above is mixed with conductive carbon black and polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) is added to make a slurry, which is coated on the nickel foam and vacuum dried to obtain the cobalt phosphide nanorod electrode.

[0019] Its beneficial effects are:

[0020] CoP nanorod structure (1826.7F·g -1 @1A·g -1 ) provides abundant electrochemically active sites, and its one-dimensional directional channels accelerate the ion diffusion kinetics, while the cross-linked rigid skeleton structure effectively suppresses the volume expansion of the electrode, enabling the device to maintain a capacity retention rate of 86.8% and a coulombic efficiency of 88.1% after 10,000 cycles.

[0021] Preferably, the mass ratio of the cobalt phosphide nanorod electrode material, conductive carbon black and polyvinylidene fluoride is 8:1-2:1-2.

[0022] Preferably, the mass of the N-methylpyrrolidone is 12 to 52 times that of the cobalt phosphide nanorod material.

[0023] Preferably, the specific steps of cutting and cleaning the nickel foam are:

[0024] The nickel foam was cut into pieces of 2×2 cm and ultrasonically cleaned with 1 mol / L dilute hydrochloric acid, anhydrous ethanol, and deionized water for 5 to 10 min each to remove surface oxides and impurities, and then vacuum dried at 60°C for 12 h.

[0025] Preferably, the vacuum drying temperature is 60° C. and the time is 24 hours.

[0026] Again, the present invention also provides an application of a cobalt phosphide nanorod electrode in a capacitor, wherein the capacitor is a CoP / / rGO asymmetric supercapacitor, which is assembled with a cobalt phosphide nanorod electrode as a positive electrode, rGO as a negative electrode, 2 mol / L KOH as an electrolyte, and a cellulose membrane as a diaphragm.

[0027] The mass ratio of the positive and negative active materials of the CoP / / rGO asymmetric supercapacitor is determined by a charge balance formula.

[0028]

[0029] in,

[0030] m + is the mass of the positive electrode CoP material;

[0031] m - is the mass of negative electrode rGO material;

[0032] C + is the specific capacitance of the positive electrode CoP material;

[0033] C - is the specific capacitance of the negative electrode rGO material;

[0034] △V + is the discharge voltage window of the positive electrode CoP material;

[0035] △V - is the discharge voltage window of negative electrode rGO material.

[0036] The voltage window of the CoP / / rGO asymmetric supercapacitor is 0-1.6V; the CoP / / rGO asymmetric supercapacitor has a power density of 500W·kg -1 When the energy density is ≥35Wh·kg -1 , the capacity retention rate is ≥90% after 5000 cycles.

[0037] It can be seen from the above technical solutions that, compared with the prior art, the present invention provides a method for preparing a cobalt phosphide nanorod material and an electrode prepared therefrom and its application.

[0038] The beneficial effect of adopting the above technical solution is that the comprehensive performance of supercapacitors is significantly improved through the coordinated optimization of nanorod structure design and charge balance strategy. -1 @1A·g -1 ) provides abundant electrochemical active sites, and its one-dimensional directional channels accelerate the ion diffusion kinetics, while the cross-linked rigid skeleton structure effectively inhibits the volume expansion of the electrode, so that the device still maintains 86.8% capacity retention and 88.1% coulombic efficiency after 10,000 cycles. On the other hand, due to the high specific surface area and structural stability of the CoP nanorod structure, the CoP positive electrode has a wide potential response window dominated by pseudocapacitance in the potential range of 0-0.6V vs.Ag / AgCl in 2M KOH electrolyte (corresponding to the metal Co2+ / Co3+ redox couple), while the rGO negative electrode has a three-dimensional conductive network structure and exhibits double-layer energy storage behavior in the range of -1.0 to 0V vs.Ag / AgCl. By rationally designing the electrode mass ratio (m+ / m-=C- / C+), the positive and negative electrode charge capacities (Q=C×ΔV) are balanced (Q+=Q-). Therefore, based on the charge matching design of CoP positive electrode and rGO negative electrode, the operating voltage of the asymmetric supercapacitor (CoP / / rGO ASC) was extended to 1.6 V, and the working voltage of the supercapacitor was 2.3 V at 500 W kg -1A high energy density of 37.0Wh kg-1 was achieved at a power density of 1.5 W·kg-1, and the cycle stability was significantly improved by suppressing the polarization effect, with a capacity retention rate of 92.3% after 5000 cycles. This dual optimization strategy provides a new idea for the development of high-energy and long-life energy storage devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0040] Figure 1 Electron microscopy image of the surface morphology of CoP-2 nanorods.

[0041] Figure 2 CV curves of CoP-2 under different scanning conditions (a) and GCD curves of CoP-2 at different current densities (b).

[0042] Figure 3 The scan rate was 60 mV s in different voltage windows. -1 CV curves of CoP-2 / / rGO asymmetric supercapacitor (a) and GCD curves of CoP-2 / / rGO ASC (b).

[0043] Figure 4 Cycling performance diagram of CoP-2 / / rGO ASC (a) and relationship diagram between power density and energy density of CoP-2 / / rGO ASC (b). DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Example 1

[0046] 0.1mmol of cobalt nitrate hexahydrate, 0.1mmol of sodium hypophosphite and 0.0667mmol of urea were dissolved in 20mL of deionized water and stirred magnetically for 30min to form a light pink transparent solution. The mixed solution was transferred to a 50mL polytetrafluoroethylene-lined reactor and subjected to hydrothermal reaction at 180℃ for 6h. After cooling, the cobalt phosphide sample was obtained by centrifugation and washing, which was recorded as CoP-1.

[0047] 40 mg of CoP-1 active material was mixed with 5 mg of acetylene black, 5 mg of PVDF binder and 2 mL of NMP were added to prepare the slurry, coated on a 2×2 cm nickel foam current collector, and dried at 60°C in vacuum for 24 h. The three-electrode system test showed that in 2M KOH electrolyte, 1 A·g -1 The specific capacitance at the current density is 1105.2F·g -1 .

[0048] Example 2

[0049] 0.2mmol of cobalt nitrate hexahydrate, 0.2mmol of sodium hypophosphite and 0.1334mmol of urea were dissolved in 20mL of deionized water and stirred magnetically for 30min to form a light pink transparent solution. The mixed solution was transferred to a 50mL polytetrafluoroethylene-lined reactor and subjected to hydrothermal reaction at 180℃ for 6h. After cooling, the cobalt phosphide sample was obtained by centrifugation and washing, which was recorded as CoP-2.

[0050] 40 mg of CoP-2 active material and 5 mg of acetylene black were ground and mixed, 5 mg of PVDF binder and 2 mL of NMP were added to prepare the slurry, coated on a 2×2 cm nickel foam current collector, and dried in vacuum at 60°C for 24 h.

[0051] The CoP-2 cathode and rGO anode were matched according to the following charge balance formula, where the voltage window was 0-1.6 V;

[0052]

[0053] The calculated mass of the CoP-2 positive electrode is 2 mg, and the mass of the rGO negative electrode is 8.4 mg.

[0054] The CoP-2 / / rGO ASC device was assembled using a cellulose separator and 2M KOH as the electrolyte.

[0055] Example 3

[0056] 0.5mmol of cobalt nitrate hexahydrate, 0.5mmol of sodium hypophosphite and 0.3335mmol of urea were dissolved in 20mL of deionized water and stirred magnetically for 30min to form a light pink transparent solution. The mixed solution was transferred to a 50mL polytetrafluoroethylene-lined reactor and subjected to hydrothermal reaction at 180℃ for 6h. After cooling, the cobalt phosphide sample was obtained by centrifugation and washing, which was recorded as CoP-3.

[0057] 40 mg of CoP-3 active material was mixed with 5 mg of acetylene black, 5 mg of PVDF binder and 2 mL of NMP were added to prepare the slurry, coated on a 2×2 cm nickel foam current collector, and dried at 60°C in vacuum for 24 h. The three-electrode system test showed that in 2M KOH electrolyte, 1 A·g -1The specific capacitance at the current density is 764.3F·g -1 .

[0058] Example 4

[0059] 1mmol of cobalt nitrate hexahydrate, 1mmol of sodium hypophosphite and 0.667mmol of urea were dissolved in 20mL of deionized water and stirred magnetically for 30min to form a light pink transparent solution. The mixed solution was transferred to a 50mL polytetrafluoroethylene-lined reactor and subjected to hydrothermal reaction at 180℃ for 6h. After cooling, the cobalt phosphide sample was centrifuged and washed to obtain the sample, which was recorded as CoP-4.

[0060] 40 mg of CoP-4 active material was mixed with 5 mg of acetylene black, 5 mg of PVDF binder and 2 mL of NMP were added to prepare the slurry, coated on a 2×2 cm nickel foam current collector, and dried at 60°C in vacuum for 24 h. The three-electrode system test showed that in 2M KOH electrolyte, 1 A·g -1 The specific capacitance is only 174.75F·g at the current density -1 , proving that excessive precursor concentration will destroy the nanorod morphology and reduce the electrochemical activity.

[0061] Microstructural characterization of CoP nanorods

[0062] The surface morphology of the CoP-2 nanorods prepared in Example 2 was observed using a scanning electron microscope. Figure 1 As can be seen from the figure, the morphology of CoP presents a rod-like structure with a diameter of about 100nm and a relatively uniform length distribution. This nanorod structure has significant benefits for ion transfer in electrochemical reactions and sufficient contact with the electrolyte, which is conducive to improving electrochemical performance. CoP nanorods show clear contours in SEM images, are relatively evenly distributed, and show good crystallinity and dispersibility. CoP nanorods show nanoscale roughness, and the surface is covered with fine particles or protrusions. These structures increase the specific surface area of ​​the material and provide more active sites for chemical reactions.

[0063] Electrochemical performance test of CoP electrode

[0064] Figure 2 (a) is the CV curve of the CoP-2 electrode prepared in Example 2 under different scanning speed conditions. It can be seen that the CV curve in the figure has a pair of redox reaction peaks and forms a closed curve shape, which indicates that the electrode undergoes a typical pseudocapacitive redox reaction. Figure 2 (b) is the GCD curve of CoP-2 prepared in Example 2 under different current density conditions. The GCD of CoP-2 at 0.5, 1, 2, 5 and 10 A g is calculated according to formula (1). -1 The specific capacitances are 2235.8 F g-1 、1826.7Fg -1 ,1673.3F g -1 , 1305.0F g -1 and 1102.7F g -1 In addition, it can be clearly observed from the figure that the charge and discharge curves of the electrode at different current densities are almost symmetrical, and the electrode has a very obvious charge and discharge platform, indicating that the electrode material has good electrochemical reversibility.

[0065] Electrochemical performance test of CoP-2 / / rGO asymmetric supercapacitor

[0066] Figure 3 (a) Scan rate of 60 mV s at different voltage windows -1 CV curve of the CoP-2 / / rGO asymmetric supercapacitor prepared in Example 2. When the voltage window continues to increase, since the oxygen evolution reaction is accompanied by obvious polarization phenomenon, the optimal operating voltage of CoP-2 / / rGO ASC should be controlled at 1.6 V. This shows that CoP-2 / / rGO ASC has a larger voltage window and better reversibility. Figure 3 (b) shows the GCD curve of CoP-2 / / rGO ASC prepared in Example 2. -1 At a current density of 1.54 V, as the potential window increases from 0.8 V to 1.6 V, the GCD curves are all symmetrical, indicating that CoP-2 / / rGO ASC has ideal capacitive performance and high reversibility. The adjustable potential window also shows that CoP-2 / / rGO ASC has certain practical value. Figure 4 (a) is the cycling performance diagram of the CoP-2 / / rGO ASC prepared in Example 2. It can be seen from the figure that after 5000 cycles, the capacitance retention rate of the device is 92.3% and the coulombic efficiency is 94.2%. This shows that the CoP-2 / / rGO ASC can still maintain reversible and efficient charge and discharge characteristics after multiple charge and discharge. Figure 4 (b) is the relationship between the power density and energy density of the CoP-2 / / rGO ASC prepared in Example 2. At different current densities, the maximum energy and power density of the CoP-2 / / rGO ASC asymmetric supercapacitor reached 37.0 W h kg -1 and 500W kg -1 These values ​​are superior to previous supercapacitor data reported in the literature, such as the energy and power densities of CoP electrode materials of 19.0 W h kg -1 and 350.8Wkg -1 ; The energy and power density of CoP hollow microsphere materials are 22.2W hkg-1 and 374.9Wkg -1 , the energy and power density of CoP nanoprism materials are 24.0W h kg -1 and 325.0W kg -1 The energy and power densities of the Ni-CoP@C composite are 17.4 W hkg -1 and 699.1W kg -1 The energy and power densities of the CoP / C composite are 16.14 W h kg -1 and 700.0W kg -1 These results indicate that CoP-2 / / rGO ASC has excellent capacitor charge and discharge performance in different potential windows. Its high energy and power density also indicate that CoP-2 has certain application potential in electrochemical energy storage devices.

[0067] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a cobalt phosphide nanorod material, characterized in that: The specific steps include: S1, prepare precursor solution Dissolve cobalt nitrate hexahydrate, sodium hypophosphite and urea in deionized water and stir magnetically to form a homogeneous solution; S2, hydrothermal reaction The homogeneous solution was transferred to a polytetrafluoroethylene-lined reactor for hydrothermal reaction. After the reaction was completed, the solution was cooled, the product was taken out, centrifuged, washed, and vacuum dried to obtain cobalt phosphide nanorod material.

2. The method for preparing a cobalt phosphide nanorod material according to claim 1, characterized in that: The molar ratio of cobalt nitrate hexahydrate, sodium hypophosphite and urea in step S1 is 1:1:0.67; The concentration of cobalt nitrate hexahydrate in the homogeneous solution is 5-50 mmol / L.

3. The method for preparing a cobalt phosphide nanorod material according to claim 1, characterized in that: The temperature of the hydrothermal reaction in step S2 is 160-200° C. and the time is 4-8 hours; The centrifugal washing is performed with deionized water and ethanol in sequence; The vacuum drying temperature is 60° C. and the time is 12 h.

4. A cobalt phosphide nanorod electrode, characterized in that: Specifically prepared by the following steps: The nickel foam is cut and cleaned, and then the cobalt phosphide nanorod material prepared by any method described in claims 1 to 3 is mixed with conductive carbon black and polyvinylidene fluoride, and N-methylpyrrolidone is added to make a slurry, which is coated on the nickel foam and vacuum dried to obtain the cobalt phosphide nanorod electrode.

5. A cobalt phosphide nanorod electrode according to claim 4, characterized in that: The mass ratio of the cobalt phosphide nanorod material, conductive carbon black and polyvinylidene fluoride is 8:1-2:1-2; The mass of the N-methylpyrrolidone is 12 to 52 times that of the cobalt phosphide nanorod material.

6. The cobalt phosphide nanorod electrode according to claim 4, characterized in that: The specific steps of cutting and cleaning the nickel foam are as follows: The nickel foam was cut into pieces of 2×2 cm and ultrasonically cleaned with 1 mol / L dilute hydrochloric acid, anhydrous ethanol, and deionized water for 5 to 10 min each to remove surface oxides and impurities, and then vacuum dried at 60°C for 12 hours.

7. The cobalt phosphide nanorod electrode according to claim 4, characterized in that: The vacuum drying temperature is 60° C. and the time is 24 h.

8. Use of the cobalt phosphide nanorod electrode as claimed in claim 4 in a capacitor, characterized in that: The capacitor is a CoP / / rGO asymmetric supercapacitor, which is assembled using a cobalt phosphide nanorod electrode as a positive electrode, rGO as a negative electrode, 2 mol / L KOH as an electrolyte, and a cellulose membrane as a diaphragm.

9. The use of the cobalt phosphide nanorod electrode in a supercapacitor according to claim 8, characterized in that: The mass ratio of the positive and negative active materials of the CoP / / rGO asymmetric supercapacitor is determined by a charge balance formula; in, m + is the mass of the positive electrode CoP material; m - is the mass of negative electrode rGO material; C + is the specific capacitance of the positive electrode CoP material; C - is the specific capacitance of the negative electrode rGO material; △V + is the discharge voltage window of the positive electrode CoP material; △V- is the discharge voltage window of the negative electrode rGO material.

10. The use of the cobalt phosphide nanorod electrode in a supercapacitor according to claim 8, characterized in that: The voltage window of the CoP / / rGO asymmetric supercapacitor is 0-1.6V; The CoP / / rGO asymmetric supercapacitor has a power density of 500 W kg -1 When the energy density is ≥35Wh·kg -1 , the capacity retention rate is ≥90% after 5000 cycles.

Images