A hydroxide electrode and a preparation method thereof
By soaking K2S2O8 and NaOH solutions in nickel oxalate electrodes and performing hydrothermal treatment, Ni(OH)2 nanosheets are generated, which solves the problem of insufficient electrochemical performance of nickel hydroxide electrodes and realizes the preparation of high-performance electrodes with excellent electrochemical performance and environmental protection characteristics.
Patent Information
- Application Number
- CN202210997208.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-08-19
- Publication Date
- 2025-09-19
- Estimated Expiration
- 2042-08-19
AI Technical Summary
The electrical properties of existing nickel hydroxide electrodes have not yet met the growing energy demand, and their electrochemical performance needs to be improved.
A nickel oxalate electrode was immersed in K2S2O8 and NaOH solution, and a columnar structure was grown in situ by a hydrothermal method. Subsequently, an alkaline conversion was performed to generate Ni(OH)2 nanosheets, thereby increasing the specific surface area and active sites to prepare a high-performance hydroxide electrode.
The prepared hydroxide electrode has a specific capacitance of 4878mF/cm2 at a current density of 2mA/cm2, showing excellent electrochemical performance. It is also easy to operate, environmentally friendly, and low-cost, without the need for additional binders or conductive agents.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the field of electrode materials, and in particular relates to a hydroxide electrode and a preparation method thereof. Background Art
[0002] Modern society has entered a period of rapid development, with a booming global economy and a continuously improving quality of life. However, this has also brought with it the challenge of energy consumption. Fossil fuels have been overconsumed, and carbon emissions have seriously exceeded standards in recent years. Consequently, multifunctional portable electronic devices, household appliances, and renewable energy generation facilities (such as solar and wind power generation) have become widely used, with batteries and electrochemical capacitors becoming popular energy storage devices.
[0003] Electrochemical capacitors, also known as supercapacitors, are a new type of energy storage device that has emerged in recent years, combining the technical advantages of conventional batteries and capacitors. Supercapacitors are a new type of energy storage device that boasts greater power density and longer cycle life than traditional rechargeable batteries. The high performance of supercapacitors has attracted numerous scientists to join their research, representing a new trend in addressing humanity's growing demand for new energy sources.
[0004] Nickel hydroxide is considered a very promising pseudocapacitive electrode material due to its high power density, high energy density, environmental friendliness, and wide availability. However, its electrical properties need to be further improved to meet the growing demand. Summary of the Invention
[0005] The purpose of the present invention is to solve the deficiencies of the prior art and provide a hydroxide electrode and a preparation method thereof, specifically adopting the following technical solutions:
[0006] A method for preparing a hydroxide electrode comprises the following steps: placing a nickel oxalate electrode in a soaking solution for 4-10 hours, taking it out and washing it until the washing solution is neutral, and drying it to obtain the hydroxide electrode; the soaking solution is obtained by dissolving K2S2O8 and NaOH in water.
[0007] The present invention grows nickel oxalate columnar structures in situ on the surface of the nickel mesh by a hydrothermal method, and then obtains nickel hydroxide by alkali conversion. The electrochemical test results show that the obtained electrode has better electrochemical performance. The preparation method of the electrode adopted in this article has the advantages of simple operation, environmental friendliness, and lower cost. In addition, it does not require the addition of any additional nickel source, template, binder or surfactant, thereby increasing the utilization rate of the active material on the electrode; the specific surface area of the Ni(OH)2 nanosheets generated after the alkali conversion is increased, the number of reactive sites is increased, and the supercapacitor performance of the electrode is improved.
[0008] Preferably, in the soaking solution, the ratio of K2S2O8, NaOH and water is 0.5g:2.51g:30mL.
[0009] Preferably, the nickel oxalate electrode is prepared by a hydrothermal method using a nickel foam mesh, specifically, placing the nickel foam mesh in an oxalic acid solution, reacting at 120° C. for 2-8 hours, removing the mesh from the solution, washing it until the washing solution is neutral, and drying it to obtain the nickel oxalate electrode.
[0010] Preferably, the concentration of the oxalic acid solution is 4.5×10 -3 mol / L.
[0011] Preferably, before preparing the nickel oxalate electrode, the nickel foam mesh is pretreated, specifically: the nickel foam mesh is immersed in a 1M hydrochloric acid solution and ultrasonicated for 15 minutes, the hydrochloric acid solution is replaced every 5 minutes, and then the nickel foam mesh is immersed in water and anhydrous ethanol in turn and ultrasonicated for 15 minutes respectively, and finally taken out and dried.
[0012] Preferably, the nickel oxalate electrode is placed in the soaking solution at 30°C.
[0013] The beneficial effects of the present invention are: the method of the present invention is simple to operate, economical, environmentally friendly, and does not require a binder or a conductive agent. The prepared Ni(OH)2 nanosheet electrode material exhibits excellent performance at a current density of 2 mA / cm 2 The specific capacitance was measured to be 4878mF / cm 2 The method of the present invention is also applicable to other electrode materials based on nickel foam, providing reference value for the preparation of related electrode materials and offering great potential for them to be used as active electrodes of electrochemical capacitors. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 Shown are SEM images of the electrode surface before and after immersion: (a) before immersion; (b) and (c) after immersion;
[0015] Figure 2 Shown are the XRD pattern of the nickel hydroxide electrode and the element distribution diagram of the nickel hydroxide electrode;
[0016] Figure 3 The following is a comparison of the electrochemical performance of electrodes obtained by immersing in a NaOH+K2S2O8 mixed solution for different times: (a) CV curve at a scan rate of 10 mV / s; (b) current density of 2 mA / cm 2 (c) Capacitance comparison at different current densities; (d) Nyquist plot of the electrode. Electrochemical performance comparison diagram under optimal performance conditions: (e) CV curves at different scan rates; (f) Charge and discharge curves at different current densities;
[0017] Figure 4 (a) Comparison of CV curves of electrodes obtained after immersion in NaOH+K2S2O8 solution, NaOH solution, and K2S2O8 solution for 6 h, respectively; Figure 4 (b) The current density is 2 mA / cm 2 Comparison of electrode charge and discharge curves when ; Figure 4 (c) is a comparison of the capacitance of each immersion solution at different current densities; Figure 4 (d) is the Nyquist plot of the electrode obtained in NaOH solution, K2S2O8 solution, and NaOH+K2S2O8 solution. DETAILED DESCRIPTION
[0018] The following will provide a clear and complete description of the concept and technical effects of the present invention in conjunction with the embodiments and drawings to fully understand the purpose, scheme and effects of the present invention.
[0019] Example 1:
[0020] (1) Pretreatment of nickel foam: Cut a 1cm×1cm×0.5mm porous nickel foam and ultrasonicate it with 1M dilute hydrochloric acid for 15 minutes, changing the solution every 5 minutes to remove the oxide layer on the surface of the nickel mesh. Repeat the above operation with deionized water and anhydrous ethanol. Finally, place the treated nickel foam mesh in a 60℃ oven for 2 hours to dry it for later use.
[0021] (2) Preparation of nickel oxalate electrode by hydrothermal method: Weigh 0.1418 g of H2C2O4˙2H2O solid and prepare 250 mL of 4.5×10 -3 mol / L oxalic acid solution. The treated nickel foam mesh was placed in a polytetrafluoroethylene bracket and fixed to the bottom of the reactor. 35 mL of oxalic acid solution was added to the reactor. The reactor was sealed and the hydrothermal reaction was carried out in a 120°C oven for 2-8 hours. After the reaction, the oven was closed and the nickel mesh was removed after cooling to room temperature. It was rinsed with deionized water until the eluate was neutral. The nickel mesh was then dried in a 60°C oven to prepare the nickel oxalate electrode.
[0022] (3) Preparation of nickel hydroxide electrode by in-situ alkaline conversion: Add 0.5 g of K2S2O8 solid and 2.51 g of NaOH solid to 30 mL of deionized water. Stir to mix the solution evenly. Then, place the nickel oxalate electrode in the mixed solution and soak it at 30°C for 4, 6, 8, and 10 hours. The surface of the nickel mesh can be observed to change from light green to black. After soaking, rinse with deionized water until the washing solution is neutral. Dry in an oven at 60°C for 2 hours to obtain the nickel hydroxide electrode.
[0023] Example 2:
[0024] The products prepared in the process of Example 1 and finally obtained were tested, and the results were as follows: Figure 1-4 shown.
[0025] like Figure 1 As shown in the figure, in order to analyze the effect of immersion on the morphology of electrode materials, this experiment carried out scanning electron microscopy (SEM) testing on the electrodes before and after immersion. Figure 1 (a) is the SEM image of the electrode surface before immersion. It can be seen from the figure that the grown nickel oxalate precursor crystals have a columnar structure, a relatively smooth surface, and the particles are generally large with uneven size distribution. Figure 1 (b) is the SEM image of the electrode material after immersion at the same magnification. It can be seen that the particles still maintain a columnar structure, but the particle size is significantly reduced, the distribution uniformity is improved, and the crystal surface becomes rough. This may be due to the corrosion and partial dissolution of the crystal surface during the immersion process. In order to observe the surface characteristics of the particles more clearly, the red box area is further enlarged [ Figure 1 (c)], nanosheet structures can be seen on the particle surface. This is likely due to the dissolution and recrystallization of the crystals during immersion, which may have formed a core-shell structure of NiC2O4@nickel hydroxide. The newly formed lamellar structure increases the specific surface area of the active material and the number of active sites, which is beneficial to the electrochemical performance of the electrode.
[0026] like Figure 2 As shown in the figure, the diffraction peaks at 2θ=44.8°, 52.1° and 76.6° belong to the peaks of the foam nickel base material, corresponding to the (111), (200) and (220) crystal planes of Ni (PDF#04-0850), respectively. In addition, no other obvious peaks were observed. It is possible that the generated nickel hydroxide has a low crystallinity and is in an amorphous state. The element distribution of the electrode surface area after immersion was analyzed by EDS. Figure 2 It can be seen that the electrode material mainly contains O and Ni elements, and is evenly distributed, indicating that nickel hydroxide or oxide is the main component. The presence of a small amount of C element indicates that the nickel oxalate precursor may not have been completely converted. In addition, very small amounts of Na and K elements were also detected, which may be due to the embedding of a small amount of Na in the lamellar structure generated after immersion. + and K + Whether the presence of these two ions has a certain impact on the structure of electrode materials and the improvement of electrochemical properties needs further study.
[0027] like Figure 3 As shown, Figure 3(a) is a comparison of the CV curves of the electrodes obtained when immersed in a mixed solution of NaOH + K2S2O8 for 4h, 6h, 8h, and 10h, respectively, at a scan rate of 10mV / s. A clear oxidation peak can be seen from the CV graph, while the reduction peak is almost invisible. This may be because the nickel hydroxide electrode has a strong oxidizing property and low reversibility. The software origin can be used to fit the integral areas of the CV curves when the immersion time is 4h, 6h, 8h, and 10h, respectively. It can be seen that the electrode shows the largest curve area when immersed for 6h, and the specific capacitance of the electrode is the highest when immersed for 6h.
[0028] Figure 3 (b) The current density is 2 mA / cm 2 The comparison of the electrode charge-discharge curves at 200 nm and 250 nm shows that the GCD curves maintain a certain degree of symmetry and have a plateau, indicating that the capacitance is primarily derived from the Faradaic redox reaction, which is consistent with the CV curves. This is because the active material particles generated on the electrode surface are small and evenly distributed, increasing the specific surface area of the crystals, thereby enhancing the ion transport capacity of the electrode surface and achieving better electrochemical performance. Figure 3 (c) is a capacitance comparison chart under different current densities. It can be seen intuitively from the figure that the area specific capacitance decreases with the increase of current density, and the rate performance is best at 6h.
[0029] Figure 3 (d) is the Nyquist curve of the electrode obtained by immersion for 4h, 6h, 8h, and 10h. It can be seen from the figure that the AC impedance curves of the four immersion times in the low-frequency region are approximately straight lines. The slope of the straight line of the electrode when immersed for 6h is the largest, indicating that the diffusion impedance of the electrode immersed for 6h is the smallest, which is more conducive to the diffusion of electrolyte ions and helps to improve the capacitance performance. Figure 3 (e) is a CV comparison diagram at scan rates of 10, 20, 50, and 100 mV / s. It can be seen from the figure that the CV curves have similar shapes, all of which belong to Faraday pseudocapacitance. Figure 3 (f) is at 3, 5, 7, 10, 20, 30 mA / cm 2 The charge and discharge diagrams under current density are 4878, 4010, 3563, 3154, 2396, and 1938 mF / cm 2 .
[0030] like Figure 4 As shown, Figure 4(a) Comparison of CV curves obtained after immersion for 6 hours in a NaOH+K2S2O8 solution, a NaOH solution, and a K2S2O8 solution. According to Origin software, the integrated areas of the CV curves measured in these three solutions are 0.01027, 0.005419, and 0.005047, respectively. It can be seen that the integrated areas measured for the electrodes immersed in NaOH and K2S2O8 solutions are similar, while the integrated area of the electrode immersed in the mixed solution is significantly larger, indicating that the electrode has a larger specific capacitance, indicating that both NaOH and K2S2O8 are essential components of the immersion solution. Figure 4 (b) The current density is 2 mA / cm 2 From the comparison of the electrode charge and discharge curves, it can be calculated that the area specific capacitance in NaOH solution, K2S2O8 solution, and NaOH+K2S2O8 solution is 3042, 3120, and 4878 mF / cm2, respectively. 2 The area specific capacitance of the electrode obtained by immersing in NaOH+K2S2O8 solution is the largest, which is consistent with the CV curve. During the immersion process, the color of the electrode surface changes from light green to black, indicating that the electrode composition has changed. It may be that nickel oxalate undergoes a redox reaction [Ni(OH)2+OH - =NiOOH+H2O+e - ], generating a mixture of nickel hydroxide and nickel oxyhydroxide, Ni 2+ with Ni 3+ The presence of is beneficial to the improvement of the electrochemical performance of the material. Figure 4 (c) is a capacitance comparison chart of each immersion solution at different current densities. It can be seen intuitively from the figure that when the immersion solution is NaOH+K2S2O8, the electrode has a higher capacitance and better rate performance.
[0031] In order to further explore the effect of the solution on the electrode, an electrochemical impedance spectroscopy (EIS) test was performed in this experiment. Figure 4 (d) Nyquist plots for the electrodes obtained in NaOH solution, K2S2O8 solution, and NaOH + K2S2O8 solution. As can be seen from the figure, the three curves have similar intercepts on the x-axis in the high-frequency region, indicating that the impedance of the electrolyte system is essentially the same for the three electrodes. The electrode obtained in the NaOH + K2S2O8 solution exhibits almost no semicircle in the high-frequency region. This means that its semicircle diameter in the high-frequency region is the smallest compared to the other two electrodes, indicating that this electrode generates the smallest impedance during charge transfer.
[0032] The above description is merely a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. As long as the technical effects of the present invention are achieved by the same means, they shall fall within the scope of protection of the present invention. Within the scope of protection of the present invention, various modifications and variations of the technical solutions and / or implementation methods may be made.
Claims
1. A method for preparing a hydroxide electrode, characterized in that: The method comprises the following steps: placing a nickel oxalate electrode in a soaking solution at 30° C. for 6 hours, taking it out and washing it until the washing solution is neutral, and drying it to obtain the hydroxide electrode; the soaking solution is obtained by dissolving K2S2O8 and NaOH in water; the ratio of K2S2O8, NaOH and water in the soaking solution is 0.5 g:2.51 g:30 mL; The particles of the hydroxide electrode are columnar in structure, and nanosheet structures are deposited on the surface of the particles; The preparation process of the nickel oxalate electrode is as follows: placing the nickel foam mesh in an oxalic acid solution, reacting at 120° C. for 2-8 hours, taking it out and washing it until the washing solution is neutral, and drying it to obtain the nickel oxalate electrode.
2. The preparation method according to claim 1, characterized in that The concentration of oxalic acid solution is 4.5×10 -3 mol / L.
3. The preparation method according to claim 1, characterized in that Before preparing the nickel oxalate electrode, the nickel foam mesh was pretreated by immersing the nickel foam mesh in a 1M hydrochloric acid solution and ultrasonicating it for 15 minutes, replacing the hydrochloric acid solution every 5 minutes, and then immersing the nickel foam mesh in water and anhydrous ethanol in turn and ultrasonicating it for 15 minutes respectively, and finally taking it out and drying it.
4. A hydroxide electrode, characterized in that Prepared by the preparation method according to any one of claims 1 to 3.