Preparation method of composite electrode of cellulose carbon aerogel loaded nickel-cobalt phosphide and electrode

Abstract

The invention discloses a cellulose carbon aerogel loaded nickel cobalt phosphide composite electrode preparation method and an electrode, and the method comprises the steps: taking bacterial cellulose as a raw material, and constructing a nitrogen-doped conductive carbon aerogel skeleton through supercritical drying and one-step catalytic carbonization-nitrogen doping treatment in sequence; then, nickel-cobalt phosphide nano-particles grow on the substrate in situ by adopting an ultrasonic-assisted pulse electrochemical deposition technology; according to the method, the uniform and firm loading of the active substance in the three-dimensional porous skeleton is realized; the prepared composite electrode has high specific capacitance and excellent cycling stability, the comprehensive electrochemical performance of the supercapacitor is effectively improved, the process is green, and the cost is relatively low.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage materials technology, specifically to a method for preparing a composite electrode of nickel cobalt phosphide supported on cellulose carbon aerogel and the electrode itself. Background Technology

[0002] With the continuous growth of global energy demand and the increasing awareness of environmental protection, the development of efficient and sustainable electrochemical energy storage devices has become a key direction for scientific research and industrial development. Supercapacitors, as an energy storage device between traditional capacitors and batteries, have attracted widespread attention due to their advantages such as high power density, fast charging and discharging capabilities, and long cycle life. However, compared with lithium-ion batteries, the energy density of supercapacitors is still relatively low, which limits their widespread application in more fields.

[0003] Electrode materials are the core components that determine the performance of supercapacitors. Currently, the mainstream electrode materials mainly include carbon-based materials, which provide double-layer capacitance, and transition metal compounds, which provide pseudocapacitance. However, both of these types of materials face severe challenges in practical applications.

[0004] Cellulose carbon aerogels are considered ideal electrode matrix materials due to their three-dimensional porous network structure, high specific surface area, and renewable raw materials. However, pure cellulose carbon aerogels mainly rely on the double-layer energy storage mechanism, and their specific capacitance is usually low, generally below 300 F / g, which is difficult to meet the requirements of high energy density. Although their specific surface area can be increased through activation, conventional activation and doping processes, such as KOH activation, are often cumbersome, time-consuming, and highly corrosive to equipment. In addition, carbon materials such as electrospun carbon nanofibers often face the problem of insufficient conductivity and difficulty in balancing mechanical strength and high specific surface area.

[0005] To improve energy density, researchers often introduce transition metal compounds with Faraday pseudocapacitive properties. Among them, nickel-cobalt bimetallic phosphides (NiCoP) have become a research hotspot due to their high theoretical specific capacitance and superior metal-like conductivity compared to their oxides / hydroxides. However, these materials exhibit significant volume expansion and contraction during charge and discharge, which can easily lead to the active material being pulverized and detached from the current collector, resulting in a sharp decline in cycle stability. For example, pure nickel-cobalt hydroxide electrode materials have poor conductivity and stability, and are prone to structural collapse and material agglomeration during high-current charge and discharge and cycling, leading to a rapid decay in electrochemical performance.

[0006] Combining high-capacity nickel-cobalt phosphides with highly conductive carbon materials is a feasible approach to solving the above problems. However, simple physical mixing or conventional composite methods have significant drawbacks:

[0007] The uneven distribution of active materials makes it difficult to achieve uniform and firm loading of nickel cobalt phosphide nanoparticles on the carbon skeleton at the microscale using traditional mechanical mixing or hydrothermal growth methods. Active materials are prone to agglomeration and detachment.

[0008] Poor structural adaptability: The volume changes of large-sized active material structures such as nanoneedles and nanosheets during charging and discharging can easily block the pores of carbon aerogel, hinder electrolyte ion transport, and may damage the integrity of the carbon network structure.

[0009] The weak interfacial bonding and the weak physical adsorption between the active material and the carbon matrix are insufficient to buffer the stress during the cycling process, resulting in poor interfacial stability and serious loss of active material.

[0010] In the existing technology, although some studies have attempted to combine metal compounds with porous carbon materials, there are often problems such as complex preparation processes, such as the need for multiple hydrothermal and phosphating steps, failure to synergistically leverage the advantages of each component in the composite material, and unsatisfactory overall electrode structural stability. For example, some composite materials based on metal-organic framework (MOF) precursors have fine structures, but their preparation processes are complex and costly, making it difficult to achieve large-scale production.

[0011] Therefore, there is an urgent need in this field for a new technical solution that can design and fabricate a composite electrode that combines high specific capacitance, excellent rate performance and ultra-long cycle stability. This solution should effectively solve the problems of uniform loading and strong interfacial bonding of active materials on carbon matrix, while optimizing the microstructure of the electrode to promote rapid ion / electron transport and simplifying the process to facilitate practical applications. Summary of the Invention

[0012] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0013] A method for preparing a composite electrode of cellulose carbon aerogel supported on nickel cobalt phosphide includes the following steps:

[0014] A nanofiber network hydrogel formed from purified and dispersed bacterial cellulose is provided;

[0015] Supercritical carbon dioxide drying of the hydrogel yielded bacterial cellulose aerogel;

[0016] In a nitrogen-containing inert atmosphere, bacterial cellulose aerogel was subjected to a one-step catalytic carbonization-nitrogen doping treatment to obtain nitrogen-doped bacterial cellulose carbon aerogel.

[0017] The catalyst used for catalytic carbonization is a mixture of zinc chloride and urea, and the carbonization temperature is 650-850℃.

[0018] Nickel-cobalt phosphide nanoparticles were simultaneously deposited on the three-dimensional framework of nitrogen-doped bacterial cellulose carbon aerogel using an ultrasound-assisted electrochemical deposition method.

[0019] The electrolyte is an aqueous solution containing nickel salt, cobalt salt and sodium hypophosphite, and the duty cycle and frequency of the pulse current are controlled during the deposition process.

[0020] Preferably, the nitrogen-doped bacterial cellulose carbon aerogel has a solid content of 0.5% to 1.5%, and the nanofibers have a diameter of 20-100 nm, forming a three-dimensional interconnected porous structure with a pore size of 100 nm to 2 μm.

[0021] Preferably, in the one-step catalytic carbonization-nitrogen doping treatment, the mass ratio of zinc chloride to urea is 1:1 to 1:3, and the mass ratio of the mixture of zinc chloride and urea to bacterial cellulose aerogel is 1:1 to 3:1; the heating rate of the carbonization process is 2-5℃ / min, and the temperature is maintained at the target temperature for 1-2 hours.

[0022] Preferably, in ultrasonic-assisted electrochemical deposition, the ultrasonic power is 100-500W and the frequency is 20-40kHz; the pulse current density is 10-50mA / cm², the duty cycle is 10%-50%, and the frequency is 100-1000Hz.

[0023] Preferably, in the electrolyte, the molar ratio of nickel ions to cobalt ions is 1:2 to 2:1, the concentration of sodium hypophosphite is 0.1-0.5 mol / L, and the pH of the electrolyte is adjusted to 8-10 by adding ammonia.

[0024] Preferably, after the ultrasound-assisted electrochemical deposition method, an in-situ transient laser annealing step is also included:

[0025] The deposited composite material was scanned using a pulsed laser with a laser energy density of 50-300 mJ / cm² and a pulse width of 10-100 ns.

[0026] Preferably, the nitrogen-doped bacterial cellulose carbon aerogel is subjected to oxygen plasma surface activation treatment before deposition, with a treatment power of 50-200W and a treatment time of 6-10 minutes, to increase the oxygen-containing functional groups on the surface.

[0027] Preferably, the preparation method of the composite electrode of cellulose carbon aerogel supported on nickel cobalt phosphide involves supercritical carbon dioxide drying under the following conditions: temperature 35-45℃, pressure 8-15MPa, and drying time 4-8 hours.

[0028] Preferably, the composite electrode prepared by the method of preparing a composite electrode of cellulose carbon aerogel loaded with nickel cobalt phosphide has a self-supporting three-dimensional network structure. The nickel cobalt phosphide is uniformly anchored on the fiber surface of nitrogen-doped bacterial cellulose carbon aerogel in the form of 5-50 nm nanoparticles with a spacing of 10-100 nm. The nitrogen content of the composite electrode is 2-8 at.

[0029] The beneficial effects of this invention are as follows:

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] To achieve a balance between high specific capacitance and high cycle stability, this invention constructs a robust and highly conductive carbon framework through one-step catalytic carbonization-nitrogen doping, and combines this with ultrasonic-assisted electrochemical deposition to achieve uniform confined loading of nickel-cobalt phosphide nanoparticles. The synergistic effect of these two methods provides high pseudocapacitance while effectively buffering volume strain during charge and discharge, preventing active material shedding and aggregation. This allows the composite electrode to maintain a high specific capacitance of no less than 800 F / g while possessing an ultra-long cycle life.

[0032] The process is simplified and green and economical. The bacterial cellulose raw material used in this invention is widely available and renewable. The one-step catalytic carbonization-nitrogen doping process integrates pore formation, carbonization and doping into one step. Compared with the traditional multi-step process of carbonization followed by activation, the process is shortened, energy consumption and cost are reduced. The entire preparation process does not require expensive template agents or complex equipment, which is conducive to industrialization and promotion.

[0033] The electrode has a unique structure and excellent performance. The resulting composite electrode has a self-supporting three-dimensional porous structure, which avoids the use of inactive binders and current collectors, reduces internal resistance, and achieves lightweight electrode design. Nitrogen doping not only improves the conductivity of the carbon skeleton, but its strong electronic interaction with the active material further enhances the rate performance and structural stability of the electrode. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of a method for preparing a composite electrode of cellulose carbon aerogel supported on nickel cobalt phosphide, as disclosed in Example 1 of the present invention.

[0035] Figure 2 The image shows the cyclic voltammetry curves of the composite electrode prepared in Example 1 of this invention at different scan rates.

[0036] Figure 3 The graph shows the constant current charge-discharge curves of the composite electrode prepared in Example 1 at different current densities.

[0037] Figure 4This is a comparison graph showing the cycling stability of the electrodes prepared in Example 1 and Comparative Example 1 at a current density of 10 A / g. Detailed Implementation

[0038] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, exemplary embodiments will be described in detail below, examples of which are illustrated in the accompanying drawings. In the following description relating to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of methods and systems consistent with some aspects of this application as detailed in the appended claims.

[0039] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0040] To better illustrate the purpose, technical solutions, and advantages of this application, the following description, in conjunction with specific embodiments and comparative examples, aims to provide a detailed understanding of the content of this application, rather than limiting it. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this application. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this application are commonly used reagents and instruments. In this application, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0041] The following detailed description of the specific implementation methods, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided in detail.

[0042] Example 1

[0043] Please see Figure 1-4 This invention provides a method for preparing a composite electrode of cellulose carbon aerogel supported on nickel cobalt phosphide;

[0044] A bacterial cellulose wet film, approximately 5 mm thick and with a solid content of approximately 0.8%, was obtained from static fermentation of Acetobacter xylinum for 7 days.

[0045] The bacterial cellulose was treated with 1 mol / L sodium hydroxide solution at 80℃ for 2 hours to remove bacteria and impurities. Then it was repeatedly washed with deionized water until neutral. The purified bacterial cellulose wet film was mixed with deionized water at a mass ratio of 1:99 and treated with a high-speed dispersion homogenizer at 10000 rpm for 30 minutes to obtain a bacterial cellulose nanofiber suspension with a solid content of 1.0%. The diameter of the nanofibers in the suspension ranged from 20 to 100 nm and formed a three-dimensional interconnected porous structure with a pore size of 100 nm to 2 μm.

[0046] The above hydrogel was placed in a supercritical CO2 drying vessel, and the drying temperature was set to 40℃ and the pressure to 10MPa. Under these conditions, it was dried for 6 hours to obtain bacterial cellulose aerogel, denoted as BC-A.

[0047] Weigh zinc chloride (ZnCl2) and urea (CO(NH2)2), mix and grind them at a mass ratio of 1:2 to obtain a catalyst mixture;

[0048] Take the above BC-A aerogel and mix it thoroughly with the catalyst mixture at a mass ratio of 2:1.

[0049] The mixture was placed in a tube furnace and heated to 800°C at a rate of 3°C / min under a nitrogen atmosphere and a flow rate of 200 sccm, and held at that temperature for 2 hours.

[0050] After the procedure was completed, the product was allowed to cool naturally to room temperature. It was then thoroughly washed with 0.1M dilute hydrochloric acid and deionized water until the filtrate was neutral to remove residual zinc species. Finally, it was dried in a vacuum drying oven at 80℃ for 12 hours to obtain nitrogen-doped bacterial cellulose carbon aerogel, denoted as N-BC-CA.

[0051] The above-mentioned N-BC-CA is placed in the reaction chamber of the oxygen plasma processor;

[0052] Set the processing power to 100W and the processing time to 5 minutes;

[0053] Weigh out nickel nitrate hexahydrate Ni(NO3)2·6H2O and cobalt chloride hexahydrate CoCl2·6H2O and dissolve them in deionized water;

[0054] The nickel ion concentration was controlled at 0.1 mol / L and the cobalt ion concentration was controlled at 0.1 mol / L, that is, the Ni:Co molar ratio was 1:1;

[0055] Add sodium hypophosphite (NaH2PO2·H2O) and control its concentration to 0.3 mol / L;

[0056] Adjust the pH of the electrolyte to 9.0 using concentrated ammonia.

[0057] A three-electrode system was constructed using N-BC-CA (1cm×2cm) activated in step 4 as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode.

[0058] Place the electrolytic cell in the ultrasonic cleaner and set the ultrasonic power to 200W and the frequency to 28kHz.

[0059] The pulsed electrodeposition method was used, with the pulse current density controlled at 20 mA / cm², the duty cycle at 30%, the frequency at 500 Hz, and the deposition time at 30 minutes.

[0060] After gently rinsing the deposited composite electrode with deionized water, it was placed on the sample stage of the pulsed laser deposition system.

[0061] An Nd:YAG laser with a wavelength of 1064 nm was used, with a laser energy density of 150 mJ / cm² and a pulse width of 20 ns. The entire area of ​​the electrode surface was scanned under a nitrogen atmosphere.

[0062] The final composite material was thoroughly washed with deionized water and then dried in a vacuum drying oven at 80°C for 12 hours to obtain the target product: a composite electrode of cellulose carbon aerogel supported on nickel cobalt phosphide, denoted as NiCoP / N-BC-CA.

[0063] Example 2

[0064] The steps are exactly the same as in Example 1, resulting in a bacterial cellulose nanofiber suspension with a solid content of 1.0%.

[0065] The drying temperature is set at 40℃, the pressure at 10MPa, and the drying time at 6 hours.

[0066] Catalyst mixing: Weigh zinc chloride and urea, mix and grind them in a mass ratio of 1:1;

[0067] Mix with aerogel to achieve a mass ratio of 1:1 between the catalyst mixture and the bacterial cellulose aerogel;

[0068] The carbonization process was carried out in a nitrogen atmosphere, with the temperature increased to 650°C at a rate of 2°C / min, and then held at that temperature for 1 hour.

[0069] The subsequent cooling, washing, and drying steps are the same as in Example 1, to obtain nitrogen-doped bacterial cellulose carbon aerogel;

[0070] Set the processing power to 50W and the processing time to 1 minute;

[0071] The electrolyte was prepared with the nickel ion concentration controlled at 0.067 mol / L and the cobalt ion concentration at 0.133 mol / L, i.e., the Ni:Co molar ratio was 1:2.

[0072] The sodium hypophosphite concentration is 0.1 mol / L;

[0073] Adjust the pH of the electrolyte to 8.0 using ammonia.

[0074] Set the ultrasonic power to 100W and the frequency to 20kHz;

[0075] The pulsed electrodeposition method was used, with the pulse current density controlled at 10 mA / cm², the duty cycle at 10%, the frequency at 100 Hz, and the deposition time at 30 minutes.

[0076] The laser energy density is set to 50 mJ / cm², and the pulse width is 10 ns.

[0077] The resulting composite material was thoroughly washed with deionized water and then dried in a vacuum drying oven at 80°C for 12 hours to obtain the composite electrode.

[0078] Example 3

[0079] The steps are exactly the same as in Example 1, resulting in a bacterial cellulose nanofiber suspension with a solid content of 1.0%.

[0080] The drying temperature is set at 40℃, the pressure at 10MPa, and the drying time at 6 hours.

[0081] Catalyst mixing: Weigh zinc chloride and urea, mix and grind them in a mass ratio of 1:3;

[0082] Mix with aerogel to achieve a mass ratio of catalyst mixture to bacterial cellulose aerogel of 3:1;

[0083] The carbonization process was carried out in a nitrogen atmosphere, with the temperature increased to 850°C at a rate of 5°C / min, and then held at that temperature for 2 hours.

[0084] The subsequent cooling, washing, and drying steps are the same as in Example 1, to obtain nitrogen-doped bacterial cellulose carbon aerogel;

[0085] Set the processing power to 200W and the processing time to 10 minutes;

[0086] The electrolyte was prepared with the nickel ion concentration controlled at 0.133 mol / L and the cobalt ion concentration at 0.067 mol / L, i.e., the Ni:Co molar ratio was 2:1.

[0087] The sodium hypophosphite concentration is 0.5 mol / L;

[0088] Adjust the pH of the electrolyte to 10.0 using ammonia.

[0089] Set the ultrasonic power to 500W and the frequency to 40kHz;

[0090] The pulsed electrodeposition method was used, with the pulse current density controlled at 50 mA / cm², the duty cycle at 50%, the frequency at 1000 Hz, and the deposition time at 30 minutes.

[0091] The laser energy density is set to 300 mJ / cm², and the pulse width is 100 ns.

[0092] The resulting composite material was thoroughly washed with deionized water and then dried in a vacuum drying oven at 80°C for 12 hours to obtain the composite electrode.

[0093] Comparative Example 1

[0094] This step is exactly the same as in Example 1. The bacterial cellulose wet film obtained by static fermentation of Acetobacter xylinum is purified and dispersed to obtain a bacterial cellulose nanofiber suspension with a solid content of 1.0%.

[0095] This step is exactly the same as in Example 1. The above hydrogel is dried by supercritical CO2 under the following conditions: temperature 40°C, pressure 10MPa, time 6 hours, to obtain bacterial cellulose aerogel.

[0096] The bacterial cellulose aerogel was placed directly in a tube furnace without adding a catalyst mixture of zinc chloride and urea.

[0097] Under a nitrogen atmosphere, the temperature was increased to 800°C at a heating rate of 3°C / min and held at this temperature for 2 hours. This carbonization temperature and time were consistent with those in Example 1 to ensure a single variable.

[0098] After the procedure is completed, the product is allowed to cool naturally to room temperature. The product is then washed with deionized water and dried in a vacuum drying oven at 80°C for 12 hours to obtain undoped bacterial cellulose carbon aerogel, denoted as BC-CA.

[0099] To maintain consistency with Example 1, BC-CA was subjected to oxygen plasma treatment with the same parameters as in Example 1: treatment power 100W, treatment time 5 minutes;

[0100] Electrolyte preparation: exactly the same as in Example 1, with nickel ion concentration of 0.1 mol / L, cobalt ion concentration of 0.1 mol / L, Ni:Co molar ratio of 1:1, sodium hypophosphite concentration of 0.3 mol / L, and pH adjusted to 9.0 with ammonia.

[0101] The parameters were exactly the same as in Example 1: ultrasonic power 200W, frequency 28kHz; pulse current density 20mA / cm², duty cycle 30%, frequency 500Hz, and deposition time 30 minutes.

[0102] In-situ transient laser annealing is performed, and this step is exactly the same as in Example 1, with a laser energy density of 150 mJ / cm² and a pulse width of 20 ns.

[0103] The final composite material was thoroughly washed with deionized water and then dried in a vacuum drying oven at 80°C for 12 hours to obtain a control electrode, denoted as NiCoP / BC-CA.

[0104] The NiCoP / BC-CA control electrode obtained above was subjected to the same structural and electrochemical performance tests as in Example 1.

[0105] Performance indicators Example 1 (NiCoP / N-BC-CA) Comparative Example 1 (NiCoP / BC-CA) Effect Analysis microstructure Nickel-cobalt phosphide is uniformly anchored on the fiber surface as 20-50 nm nanoparticles. Nickel-cobalt phosphide particles exhibit significant agglomeration, uneven size, with some exceeding 100 nm, and poor density. Nitrogen doping effectively improves the conductivity and surface defects of the carbon framework, providing more and more stable nucleation sites for active materials and preventing aggregation. Area specific capacitance (1A / g) 2250mF / cm² 980mF / cm² The capacitance performance was improved by about 130%, which proves that stronger electronic interactions were generated between the nitrogen-doped carbon framework and the active material, thus increasing the contribution of pseudocapacitance. Cyclic stability (10 A / g, after 10,000 cycles) Capacity retention rate: 92% Capacity retention rate 65% Significantly enhanced stability. This demonstrates that nitrogen doping creates a robust conductive network and strong interfacial bonding, effectively buffering volumetric strain during charge and discharge processes and preventing the shedding of active materials.

[0106] This comparative example clearly shows that if the core step of catalytic carbonization-nitrogen doping is omitted, even if all subsequent fine processes are exactly the same, the overall performance of the final electrode will drop precipitously. This is not only reflected in the lower specific capacitance, but more importantly, the severely deteriorated cycle stability.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A method for preparing a composite electrode of cellulose carbon aerogel supported on nickel cobalt phosphide, characterized in that, Includes the following steps: A nanofiber network hydrogel formed from purified and dispersed bacterial cellulose is provided; The hydrogel was dried with supercritical carbon dioxide to obtain bacterial cellulose aerogel; In a nitrogen-containing inert atmosphere, the bacterial cellulose aerogel is subjected to a one-step catalytic carbonization-nitrogen doping treatment to obtain nitrogen-doped bacterial cellulose carbon aerogel. The catalyst used in the catalytic carbonization is a mixture of zinc chloride and urea, and the carbonization temperature is 650-850℃. Nickel-cobalt phosphide nanoparticles were simultaneously deposited on the three-dimensional framework of the nitrogen-doped bacterial cellulose carbon aerogel using an ultrasound-assisted electrochemical deposition method. The electrolyte is an aqueous solution containing nickel salt, cobalt salt and sodium hypophosphite, and the duty cycle and frequency of the pulse current are controlled during the deposition process.

2. The method for preparing the composite electrode according to claim 1, characterized in that, The nitrogen-doped bacterial cellulose carbon aerogel has a solid content of 0.5% to 1.5%, and the nanofibers have a diameter of 20-100 nm, forming a three-dimensional interconnected porous structure with a pore size of 100 nm to 2 μm.

3. The method for preparing the composite electrode according to claim 1, characterized in that, In the one-step catalytic carbonization-nitrogen doping treatment, the mass ratio of zinc chloride to urea is 1:1 to 1:3, and the mass ratio of the mixture of zinc chloride and urea to bacterial cellulose aerogel is 1:1 to 3:1; the heating rate of the carbonization process is 2-5℃ / min, and it is kept at the target temperature for 1-2 hours.

4. The method for preparing the composite electrode according to claim 1, characterized in that, In the ultrasound-assisted electrochemical deposition, the ultrasound power used is 100-500W, the frequency is 20-40kHz, the pulse current density is 10-50mA / cm², the duty cycle is 10%-50%, and the frequency is 100-1000Hz.

5. The method for preparing the composite electrode according to claim 1, characterized in that, In the electrolyte, the molar ratio of nickel ions to cobalt ions is 1:2 to 2:1, the concentration of sodium hypophosphite is 0.1-0.5 mol / L, and the pH value of the electrolyte is adjusted to 8-10 by adding ammonia.

6. The method for preparing the composite electrode according to claim 1, characterized in that, Following the ultrasound-assisted electrochemical deposition method, an in-situ transient laser annealing step is also included: The deposited composite material was scanned using a pulsed laser with a laser energy density of 50-300 mJ / cm² and a pulse width of 10-100 ns.

7. The method for preparing the composite electrode according to claim 1, characterized in that, Before deposition, the nitrogen-doped bacterial cellulose carbon aerogel undergoes oxygen plasma surface activation treatment with a power of 50-200W and a treatment time of 6-10 minutes to increase the oxygen-containing functional groups on the surface.

8. The method for preparing a composite electrode according to any one of claims 1-7, characterized in that, The conditions for supercritical carbon dioxide drying are: temperature 35-45℃, pressure 8-15MPa, and drying time 4-8 hours.

9. A composite electrode of cellulose carbon aerogel supported on nickel cobalt phosphide, prepared by the composite electrode preparation method according to any one of claims 1-7, characterized in that, The composite electrode is a self-supporting three-dimensional network structure. Nickel-cobalt phosphide is uniformly anchored on the fiber surface of nitrogen-doped bacterial cellulose carbon aerogel in the form of 5-50 nm nanoparticles with a spacing of 10-100 nm. The nitrogen content of the composite electrode is 2-8 at.

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