A graphene electrode material, its preparation method and application

Abstract

The present invention provides a graphene electrode material, the structure of which includes a graphene sponge; heteroatoms are doped in the graphene sponge; the preparation method of the graphene electrode material comprises the following steps: 1) using graphene oxide and an alkali metal assistant as raw materials, and obtaining a graphene sponge precursor through freeze-drying; 2) subjecting the graphene sponge precursor to pyrolysis treatment to obtain a three-dimensional porous graphene sponge; the graphene electrode material is used as an electrode material in a capacitive mixing salt gradient energy generation device; the graphene electrode material prepared by the present invention has a multi-aperture structure, high conductivity and a stable structure, which helps to improve the ion transport selectivity, and achieves a high desalination capacity, specific capacitance, output power density and excellent cycle stability.

Description

Technical Field

[0001] The present invention relates to a graphene electrode material and a preparation method and application thereof, belonging to the technical field of new energy materials. Background Art

[0002] Graphene is a two-dimensional sheet composed of a single layer of carbon atoms. It has a high specific surface area, a suitable pore size distribution, good chemical stability and double-layer capacitance properties, and is widely used in energy storage and power generation. However, to date, the desalination capacity and output power density of graphene prepared by existing technologies are relatively low, resulting in an inability to meet the requirements for use as electrode materials. For example, existing graphene materials cannot meet the requirements of capacitive mixed salt difference energy power generation technology for electrode materials.

[0003] Energy and water resource issues are the two most important factors plaguing human sustainable development. The vast ocean provides abundant water resources, and obtaining water and energy from the ocean is urgent. As one of the important branches of ocean energy, salinity energy is a new type of clean, "zero-carbon" renewable energy with extensive reserves and strong environmental stability. Capacitor hybrid salinity energy power generation is a technology based on double-layer capacitors. While desalinating seawater, it utilizes the salinity energy in the ocean to convert chemical energy into electrical energy. It has the advantages of low energy consumption, no pollutants, zero carbon dioxide emissions, and high desalination efficiency, and has broad application prospects.

[0004] The performance of high-performance capacitive hybrid salt-difference energy generation devices depends largely on the large ion adsorption capacity, high conductivity, specific surface area and other properties of the electrode material; the design and synthesis of high-efficiency capacitive hybrid salt-difference energy generation electrodes is a key research issue at present; how to both utilize the advantages of graphene materials themselves and overcome the problems of low graphene desalination capacity and output power density, so that graphene materials can be widely used in electrode materials, has become the key to the application of graphene in the field of electrode materials. Summary of the Invention

[0005] The present invention proposes a graphene electrode material and a preparation method and application thereof, and aims to provide an electrode material that can be applied to capacitor mixed salt difference energy generation.

[0006] The technical solution of the present invention is as follows: A graphene electrode material, the structure of which includes a graphene sponge; the graphene sponge is doped with heteroatoms.

[0007] Furthermore, the graphene sponge is a three-dimensional porous graphene sponge formed by graphene nanosheets; the three-dimensional porous graphene sponge has a porous structure.

[0008] Further, the porous structure is distributed between graphene nanosheets, and pores with a diameter less than 1 nm are distributed on a single graphene nanosheet; the porous structure is a microporous-mesoporous-macroporous structure.

[0009] Further, the heteroatom is doped with a non-metal or a metal oxide or a combination of a non-metal and a metal oxide; the non-metal doped in the graphene sponge is one or several of boron, nitrogen, fluorine, phosphorus, and sulfur; the metal oxide doped in the graphene sponge is one or several of iron oxide, cobalt oxide, nickel oxide, and copper oxide; the mass ratio of the heteroatom in the graphene electrode material is 3 wt% to 8 wt%.

[0010] A preparation method of a graphene electrode material, the method comprising the following steps:

[0011] 1) Using graphene oxide and an alkali metal promoter as raw materials, a graphene sponge precursor is prepared by freeze-drying.

[0012] 2) The graphene sponge precursor is pyrolyzed to obtain a three-dimensional porous graphene sponge.

[0013] Further, the preparation of the graphene sponge precursor using graphene oxide and an alkali metal promoter as raw materials by freeze-drying specifically includes the following steps:

[0014] 1-1) Disperse graphene oxide and an alkali metal promoter in absolute ethanol and deionized water, ultrasonicate and stir to obtain a homogeneous mixed solution.

[0015] 1-2) Freeze-dry the mixed solution at a temperature of -30°C to -60°C for 30 hours to 60 hours to obtain a graphene sponge precursor.

[0016] Further, the pyrolysis treatment of the graphene sponge precursor to obtain a three-dimensional porous graphene sponge specifically includes the following steps:

[0017] 2-1) Heat the graphene sponge precursor to a first annealing temperature in an argon atmosphere, anneal at the first annealing temperature for 1 hour to 2 hours, and then cool to room temperature to form a graphene sponge precursor after the first annealing; the first annealing temperature is 300°C to 500°C, and the heating rate when heating to the first annealing temperature is 2°C / min to 5°C / min.

[0018] 2-2) Heat the graphene sponge precursor after the first annealing to the second annealing temperature under an argon atmosphere, anneal at the second annealing temperature for 1 to 2 hours, and then cool it to room temperature again. After the second annealing, a three-dimensional porous graphene sponge is obtained; the second annealing temperature is 500°C to 800°C, and the heating rate when heating to the second annealing temperature is 2°C / min to 5°C / min.

[0019] Furthermore, the alkali metal promoter is one or several of MOH, MCl, M2SO4, M2CO3, MHCO3, CH3COOM, where M is Na or K; the mass ratio of the alkali metal promoter to graphene oxide is 1:1 to 5:1; the volume ratio of absolute ethanol to deionized water is 2:1 to 6:1.

[0020] A preparation method of a graphene electrode material, which further includes non-metal doping, metal oxide doping, or co-doping of non-metal and metal oxide;

[0021] ]>The specific method of non-metal doping includes: before pyrolyzing the graphene sponge precursor, first mix the graphene sponge precursor with a non-metal compound, the non-metal compound is one or several of sodium borohydride, urea, ammonium fluoride, sodium hypophosphite, sulfur, and the mass ratio of the non-metal compound to the graphene sponge precursor is 4:1 to 20:1; after mixing the graphene sponge precursor with the non-metal compound, heat it to the first annealing temperature under an argon atmosphere, anneal at the first annealing temperature for 1 to 2 hours, and then cool it to room temperature to form a graphene sponge precursor with non-metal doping after the first annealing; heat the graphene sponge precursor with non-metal doping after the first annealing to the second annealing temperature under an argon atmosphere, anneal at the second annealing temperature for 1 to 2 hours, and then cool it to room temperature again. After the second annealing, the final non-metal doped three-dimensional porous graphene sponge, that is, the graphene electrode material, is obtained;

[0022] The specific method of metal oxide doping includes: adding a metal precursor to the mixed solution obtained in step 1-1), freeze-drying the mixed solution after adding the metal precursor at a temperature of -30°C to -60°C for 30 to 60 hours to obtain a graphene sponge precursor doped with metal oxide, and then pyrolyzing the graphene sponge precursor doped with metal oxide to obtain a three-dimensional porous graphene sponge doped with metal oxide, that is, the graphene electrode material; the metal precursor is any one or several of ferric chloride, cobalt chloride, nickel chloride, copper chloride, and the mass ratio of the metal precursor to graphene oxide is 4:1 to 20:1.

[0023] Application of a graphene electrode material, which is used as an electrode material in a capacitive hybrid salinity gradient energy generation device. The specific usage method includes: grinding and uniformly mixing graphene electrode material, polyvinylidene fluoride, and hard carbon in a mass ratio of (6-9):(0.5-2):(0.5-2) to obtain a mixed slurry, dropping the mixed slurry onto graphite paper, and drying it at a constant temperature of 70 °C - 90 °C for 4 h - 8 h to obtain a graphene electrode applied in the capacitive hybrid salinity gradient energy generation device.

[0024] Advantages of the present invention:

[0025] 1) By adjusting the microstructure of graphene and through heteroatom doping, the present invention realizes different structures and multiple synergistic effects of graphene, obtaining a three-dimensional porous graphene sponge electrode material with excellent performance, which can meet the requirements of efficient capacitive hybrid salinity gradient energy conversion.

[0026] 2) The preparation method of the graphene electrode material of the present invention is simple, with mild conditions, convenient operation, and low cost. The prepared electrode material has excellent desalination and capacitive hybrid salinity gradient energy conversion performance, which is beneficial to industrial production and promotion.

[0027] 3) The graphene electrode material prepared by the present invention has a multi-aperture structure, high conductivity, and stable structure, which helps to improve the ion transport selectivity, achieving a high desalination capacity, specific capacitance, output power density, and excellent cycle stability. Description of the drawings

[0028] Attached Figure 1 Scanning electron microscope image of the nitrogen-doped three-dimensional porous graphene sponge material (KOH alkali metal promoter; urea: graphene sponge precursor = 16:1) prepared according to Example 2 of the method of the present invention.

[0029] Attached Figure 2 Transmission electron microscope image of the nitrogen-doped three-dimensional porous graphene sponge (KOH alkali metal promoter; urea: graphene sponge precursor = 16:1) prepared in Example 2 of the present invention.

[0030] Attached Figure 3 Element distribution map of the nitrogen-doped three-dimensional porous graphene sponge (KOH alkali metal promoter; urea: graphene sponge precursor = 16:1) prepared in Example 2 of the present invention.

[0031] Attached Figure 4 X-ray diffraction pattern of the nitrogen-doped porous graphene sponge material (KOH alkali metal promoter; urea: graphene sponge precursor = 16:1) prepared in Example 2 of the present invention.

[0032] Attached Figure 5Nitrogen adsorption - desorption isotherm diagram of the nitrogen - doped three - dimensional porous graphene sponge material prepared in Example 2 of the present invention (KOH alkali metal promoter; urea: graphene sponge precursor = 16:1).

[0033] Attachment Figure 6 Pore size distribution diagram of the nitrogen - doped three - dimensional porous graphene sponge material prepared in Example 2 of the present invention (KOH alkali metal promoter; urea: graphene sponge precursor = 16:1).

[0034] Attachment Figure 7 Desalination capacity result diagram of the nitrogen - doped porous graphene sponge electrode prepared in Example 1 of the present invention under different voltage conditions.

[0035] Attachment Figure 8 Desalination capacity result diagram of the nitrogen - doped three - dimensional porous graphene sponge materials with different doping ratios prepared in Example 2 of the present invention (KOH alkali metal promoter; urea: graphene sponge precursor = 4:1; 8:1; 16:1; 20:1) under the condition of an applied voltage of 1.4 V.

[0036] Attachment Figure 9 Desalination capacity cycle stability result diagram of the nitrogen - doped three - dimensional porous graphene sponge material prepared under the condition of a mass ratio of urea to graphene sponge precursor of 16:1 in Example 2 of the present invention under the condition of an applied voltage of 1.4 V.

[0037] Attachment Figure 10 Maximum discharge voltage and maximum power density result diagram of the capacitive hybrid salt - gradient energy generation device based on the nitrogen - doped porous graphene sponge electrode under the conditions of 2 V constant - voltage charging, different constant - current discharges, and high - low salt water switching for the nitrogen - doped three - dimensional porous graphene sponge material prepared under the condition of a mass ratio of urea to graphene sponge precursor of 16:1 in Example 2 of the present invention. Detailed implementation manners

[0038] A graphene electrode material, whose structure includes a graphene sponge, and heteroatoms are doped in the graphene sponge.

[0039] The graphene sponge is a three - dimensional porous graphene sponge formed by graphene nanosheets; the three - dimensional porous graphene sponge has a porous structure, the porous structure is distributed between graphene nanosheets, and pores with a diameter less than 1 nm are distributed on a single graphene nano; the porous structure is a micropore - mesopore - macropore structure, the macropores can provide a large number of channels for ion migration, and the mesopores are beneficial to the diffusion and storage of ions; the diameter of the pores in the porous structure is preferably not greater than 120 nm; the specific surface area of the three - dimensional porous graphene sponge is 500 m²g -1 ~800 m²g -1 .

[0040] The heteroatom is doped with a non-metal or a metal oxide or a combination of a non-metal and a metal oxide; the non-metal doped in the graphene sponge is one or several of boron (B), nitrogen (N), fluorine (F), phosphorus (P), and sulfur (S); the metal oxide doped in the graphene sponge is MO x (M = Fe, Co, Ni or Cu), that is, any one or several of iron oxide, cobalt oxide, nickel oxide, and copper oxide.

[0041] The mass ratio of the heteroatom in the graphene electrode material is 3 wt% to 8 wt%; specifically: when the heteroatom is a non-metal, the mass ratio of the non-metal in the graphene electrode material is 3 wt% to 8 wt%; when the heteroatom is a metal oxide, the mass ratio of the metal oxide in the graphene electrode material is 3 wt% to 8 wt%; when the heteroatom is doped with a combination of a non-metal and a metal oxide, the total mass ratio of the non-metal and the metal oxide in the graphene electrode material is 3 wt% to 8 wt%.

[0042] A method for preparing a graphene electrode material, the method comprising the following steps:

[0043] 1) Using graphene oxide and an alkali metal auxiliary as raw materials, a graphene sponge precursor is prepared by freeze-drying;

[0044] 2) The graphene sponge precursor is pyrolyzed to obtain a three-dimensional porous graphene sponge.

[0045] The preparation of the graphene sponge precursor using graphene oxide and an alkali metal auxiliary as raw materials by freeze-drying specifically includes the following steps:

[0046] 1-1) Disperse graphene oxide and an alkali metal auxiliary in absolute ethanol and deionized water, ultrasonicate and stir magnetically at room temperature to obtain a uniform mixed solution;

[0047] 1-2) Freeze-dry the mixed solution at a temperature of -30°C to -60°C for 30 h to 60 h to obtain a graphene sponge precursor; preferably, transfer the mixed solution to a reaction flask and freeze-dry it at a temperature of -30°C to -60°C for 60 h to obtain a graphene sponge precursor; the reaction flask is further preferably a polytetrafluoroethylene reaction flask.

[0048] The pyrolysis of the graphene sponge precursor to obtain a three-dimensional porous graphene sponge specifically includes the following steps:

[0049] 2-1) Heat the graphene sponge precursor to the first annealing temperature in an argon atmosphere, anneal at the first annealing temperature for 1 h to 2 h, and then cool to room temperature to form the graphene sponge precursor after the first annealing; the first annealing temperature is preferably 300 °C to 500 °C, and the heating rate when heating to the first annealing temperature is preferably 2 °C / min to 5 °C / min;

[0050] 2-2) Heat the graphene sponge precursor after the first annealing to the second annealing temperature in an argon atmosphere, anneal at the second annealing temperature for 1 h to 2 h, and cool to room temperature again to obtain a three-dimensional porous graphene sponge after the second annealing; the second annealing temperature is preferably 500 °C to 800 °C, and the heating rate when heating to the second annealing temperature is preferably 2 °C / min to 5 °C / min.

[0051] The process of pyrolyzing the graphene sponge precursor is preferably to place the graphene sponge precursor in a tube furnace to complete the first annealing and the second annealing.

[0052] In step 1-1), the alkali metal promoter is any one or several of MOH, MCl, M2SO4, M2CO3, MHCO3, and CH3COOM, where M is Na or K;

[0053] The mass ratio of the alkali metal promoter to graphene oxide is preferably 1:1 to 5:1, and the further preferred ratio is 3:1; the volume ratio of absolute ethanol to deionized water is preferably 2:1 to 6:1, and the further preferred ratio is 4:1.

[0054] In the preparation process of the present invention, graphene oxide is reduced to graphene; the use of the alkali metal promoter is beneficial to form tiny pores on individual graphene nanosheets in the graphene sponge. In the graphene sponge prepared by the present invention, individual graphene nanosheets are distributed with pores having a diameter less than 1 nm, which has a high specific surface area and abundant pores, can further provide a large number of active adsorption sites, and promotes the diffusion adsorption and storage of salt ions.

[0055] The three-dimensional porous graphene sponge prepared by the present invention has a porous structure; the porous structure belongs to a microporous-mesoporous-macroporous structure, and the diameter of the pores in the porous structure is distributed below 120 nm. The specific surface area of the prepared three-dimensional porous graphene sponge can reach 500 m² / g -1 ~800 m² / g -1 .

[0056] The preparation method of the graphene electrode material further includes non-metal doping, metal oxide doping, or co-doping of non-metal and metal oxide.

[0057] The specific method of the non-metal doping is as follows: before the graphene sponge precursor is pyrolyzed, the graphene sponge precursor is first mixed with a non-metal compound, and then steps 2-1) and 2-2) are carried out. The non-metal compound is one or a mixture of several of sodium borohydride, urea, ammonium fluoride, sodium hypophosphite, and sulfur. The mass ratio of the non-metal compound to the graphene sponge precursor is 4:1 to 20:1. After the graphene sponge precursor and the non-metal compound are mixed, they are heated to the first annealing temperature in an argon atmosphere, annealed at the first annealing temperature for 1 h to 2 h, and then cooled to room temperature to form a graphene sponge precursor with non-metal doping after the first annealing. The graphene sponge precursor with non-metal doping after the first annealing is heated to the second annealing temperature in an argon atmosphere, annealed at the second annealing temperature for 1 h to 2 h, and cooled to room temperature again. After the second annealing, the final non-metal-doped three-dimensional porous graphene sponge, that is, the graphene electrode material, is obtained. The first annealing temperature, the second annealing temperature, and the heating rate during the first and second annealings in this process are the same as the corresponding ones in steps 2-1) and 2-2).

[0058] The non-metal in the non-metal-doped three-dimensional porous graphene sponge is one or several of boron (B), nitrogen (N), fluorine (F), phosphorus (P), and sulfur (S). The mass percentage of the non-metal in the finally prepared non-metal-doped three-dimensional porous graphene sponge of the present invention is 3 wt % - 8 wt %.

[0059] The non-metal compound is one or a mixture of several of sodium borohydride, urea, ammonium fluoride, sodium hypophosphite, and sulfur. After annealing the mixture of the graphene sponge precursor and sodium borohydride, a boron-doped three-dimensional porous graphene sponge is finally formed. After annealing the mixture of the graphene sponge precursor and urea, a nitrogen-doped three-dimensional porous graphene sponge is finally formed. After annealing the mixture of the graphene sponge precursor and ammonium fluoride, a fluorine-doped three-dimensional porous graphene sponge is finally formed. After annealing the mixture of the graphene sponge precursor and sodium hypophosphite, a phosphorus-doped three-dimensional porous graphene sponge is finally formed. After annealing the mixture of the graphene sponge precursor and sulfur, a sulfur-doped three-dimensional porous graphene sponge is finally formed.

[0060] The specific method for doping with metal oxides is as follows: adding a metal precursor to the mixed solution obtained in step 1-1), freeze-drying the mixed solution after adding the metal precursor at a temperature of -30 °C to -60 °C for 30 h to 60 h to obtain a graphene sponge precursor doped with metal oxides, and then pyrolyzing the graphene sponge precursor doped with metal oxides to obtain a three-dimensional porous graphene sponge doped with metal oxides, i.e., the graphene electrode material; the process of pyrolyzing the graphene sponge precursor doped with metal oxides to obtain a three-dimensional porous graphene sponge doped with metal oxides is the same as the process of pyrolyzing the graphene sponge precursor to obtain the graphene electrode material; the metal precursor is any one or several of ferric chloride, cobalt chloride, nickel chloride, and copper chloride, and the mass ratio of the metal precursor to graphene oxide is 4:1 to 20:1.

[0061] An application of the graphene electrode material, which is used as an electrode material in a capacitive hybrid salt-gradient energy generation device. The specific usage method includes: grinding and mixing the prepared graphene electrode material, polyvinylidene fluoride, and hard carbon in a mass ratio of (6-9):(0.5-2):(0.5-2) to obtain a mixed slurry. Preferably, the graphene electrode material, polyvinylidene fluoride, and hard carbon are ground and mixed evenly in a mass ratio of 8:1:1 to obtain a mixed slurry; dropping the mixed slurry onto graphite paper and drying it at a constant temperature of 70 °C to 90 °C for 4 h to 8 h. Preferably, it is dried at a constant temperature of 80 °C for 6 h to obtain a graphene electrode applied in the capacitive hybrid salt-gradient energy generation device.

[0062] The graphene electrode material prepared by the present invention can be used as an electrode material for a capacitive hybrid salt-gradient energy generation device. It has a multi-aperture structure, high electrical conductivity, and a stable structure, which helps to improve the ion transport selectivity, achieve a high desalination capacity, a large output power density, a high power generation voltage, and excellent desalination cycle stability; the non-metal-doped three-dimensional porous graphene sponge prepared by the present invention, as the graphene electrode material, has a desalination capacity of 45.04 mg g under the condition that the applied voltage is 1.4 V. -1 The above; the present invention provides a new idea for preparing the electrode of a capacitive hybrid salt-gradient energy generation device, and at the same time promotes the application of graphene-based materials in the fields of seawater desalination and capacitive hybrid salt-gradient energy conversion.

[0063] The technical solution of the present invention will be specifically described below in conjunction with embodiments. Example 1

[0064] A preparation method of a graphene electrode material, which includes the following steps:

[0065] Disperse 200 mg of graphene oxide and 300 mg of NaOH in a mixed solution of 400 ml of absolute ethanol and deionized water. The total volume of absolute ethanol and deionized water is 400 ml, and the volume ratio of absolute ethanol to deionized water is 4:1. Ultrasonic disperse and stir magnetically at room temperature to obtain a homogeneous mixed solution; transfer the mixed solution to a polytetrafluoroethylene reaction flask, freeze-dry at -60 °C for 48 h to obtain a graphene sponge precursor; subsequently, mix the graphene sponge precursor with urea, and the mass ratio of urea to the graphene sponge precursor is 20:1. Place it in a tube furnace, anneal at 500 °C for 1 h under an argon atmosphere with a heating rate of 5 °C / min. After cooling to room temperature, anneal again at 700 °C for 2 h under an argon atmosphere with a heating rate of 5 °C / min to obtain a nitrogen-doped three-dimensional porous graphene sponge, that is, the graphene electrode material.

[0066] A preparation method of a graphene electrode includes: grinding and mixing the prepared nitrogen-doped three-dimensional porous graphene sponge, polyvinylidene fluoride, and hard carbon evenly according to a mass ratio of 8:1:1 to obtain a mixed slurry, drop-coating it on graphite paper, and drying it at 80 °C for 6 h to obtain a nitrogen-doped porous graphene sponge electrode.

[0067] Apply the nitrogen-doped porous graphene sponge electrode to a capacitive hybrid salt-gradient energy generation device for desalination capacity and power density experimental tests. The experimental test methods for the desalination capacity and power density of the capacitive hybrid salt-gradient energy generation device are as follows:

[0068] The desalination and power generation performance tests of the electrode are carried out in a cyclic capacitive hybrid salt-gradient energy generation device. The cyclic capacitive hybrid salt-gradient energy generation device includes symmetric positive and negative electrodes and anion and cation exchange membranes. Both the positive and negative electrodes use nitrogen-doped porous graphene sponge electrodes, and the size of the nitrogen-doped porous graphene sponge electrode is 6 cm × 6 cm; the volume of the feed NaCl solution is 80 ml, and the feed NaCl solution is continuously circulated in and out of the capacitive hybrid salt-gradient energy generation device through a peristaltic pump; use a Neware battery test system to test the capacitive hybrid salt-gradient energy generation device.

[0069] The desalination capacity of the electrode is tested under a constant voltage condition, the applied voltage is 1.2 V to 1.6 V, and the initial concentration of NaCl in the feed solution is 500 mg l -1 , and measure the concentration of the solution flowing out of the cyclic capacitive hybrid salt-gradient energy generation device through a conductivity meter.

[0070] The capacitive hybrid salt-gradient energy generation performance of the electrode is tested by charging at a constant voltage of 2 V and discharging at a constant current with different current densities. The concentration of NaCl in the feed solution is 35000 mg l -1 and 500 mg l-1 , switch the concentration of high and low salt water.

[0071] The desalination capacity of the nitrogen-doped three-dimensional porous graphene sponge material prepared in this embodiment under different voltage conditions is shown in the appendix Figure 7 ; appendix Figure 7 is the desalination capacity result diagram of the nitrogen-doped porous graphene sponge electrode prepared in this embodiment under different voltage conditions; according to the data in appendix Figure 7 , it can be seen that the nitrogen-doped three-dimensional porous graphene sponge material exhibits excellent desalination capacity, and with the increase of the applied voltage, the desalination capacity of the nitrogen-doped three-dimensional porous graphene sponge gradually increases. When the voltage exceeds 1.4 V, the desalination capacity will remain unchanged, and the maximum desalination capacity can reach 23 mgg -1 . Example 2

[0072] Disperse 200 mg of graphene oxide and 300 mg of KOH in a mixed solution of 400 ml of absolute ethanol and deionized water. The total volume of absolute ethanol and deionized water is 400 ml, and the volume ratio of absolute ethanol to deionized water is 4:1. Ultrasonic disperse and stir magnetically at room temperature to obtain a uniform mixed solution; transfer the mixed solution to a polytetrafluoroethylene reaction flask, freeze-dry at -60 °C for 48 h to obtain a graphene sponge precursor; then, mix urea and the graphene sponge precursor at a mass ratio of 4:1, 8:1, 16:1, and 20:1 respectively, place them in a tubular furnace, anneal at 500 °C for 1 h under an argon atmosphere, with a heating rate of 5 °C / min. After cooling to room temperature, anneal at 700 °C for 2 h under an argon atmosphere, with a heating rate of 5 °C / min, to obtain nitrogen-doped three-dimensional porous graphene sponges with different doping ratios, that is, graphene electrode materials with different doping ratios.

[0073] Use the preparation method of the graphene electrode in Example 1 to prepare nitrogen-doped porous graphene sponge electrodes with different doping ratios by using the nitrogen-doped three-dimensional porous graphene sponge materials with different doping ratios obtained in this embodiment respectively.

[0074] It can be seen from appendix Figure 1 that the three-dimensional porous graphene sponge in the prepared nitrogen-doped three-dimensional porous graphene sponge is formed by porous graphene nanosheets. The graphene nanosheets are wrinkled and curled, and a porous structure is formed between the graphene nanosheets.

[0075] It can be seen from appendix Figure 2 that the graphene in the prepared nitrogen-doped three-dimensional porous graphene sponge is an ultrathin two-dimensional nanosheet structure. From appendix Figure 2As can be seen from the right figure, dense pores are distributed on the graphene nanosheets. The diameters of the pores on the graphene nanosheets are basically all less than 1 nm. With a high specific surface area and abundant pores, it can provide a large number of active adsorption sites, promoting the diffusion adsorption and storage of salt ions.

[0076] From the attached Figure 3 it can be seen that nitrogen elements (the bright spots in the attached Figure 3 ) are evenly distributed on the graphene nanosheets.

[0077] From the attached Figure 4 it can be seen that in the X-ray diffraction spectrum of the nitrogen-doped three-dimensional porous graphene sponge, the diffraction peaks at 26° and 44.5° correspond to the (002) and (100) crystal planes of graphene respectively, indicating that graphene oxide is reduced to graphene.

[0078] From the attached Figure 5 it can be seen that the nitrogen-doped three-dimensional porous graphene sponge material shows a type-IV adsorption isotherm, indicating that this material is a mesoporous material; based on the nitrogen adsorption-desorption isotherm diagram, the specific surface area of the nitrogen-doped porous graphene sponge material is 507.81 m² g[[ID=I8]] -1 , the pore volume is 0.77 cm 3 )]]g -1 , and the mesoporous ratio is 67.3%, which can provide more adsorption sites.

[0079] From the attached Figure 6 it can be seen that for the nitrogen-doped three-dimensional porous graphene sponge material prepared in Example 2 of the present invention (KOH alkali metal promoter; urea: graphene sponge precursor = 16:1), most of the pore diameters are distributed below 120 nm, showing a microporous-mesoporous-macroporous porous structure, mainly dominated by macropores, which will be beneficial for macropores to provide a large number of channels for ion migration.

[0080] Using the test method described in Example 1, the desalination capacity, desalination cycle stability and capacitive mixed salt-difference energy generation performance of the nitrogen-doped three-dimensional porous graphene sponge materials with different doping ratios were tested respectively, as shown in the attached Figure 8 -attached Figure 10 .

[0081] The attached Figure 8 is the desalination capacity result diagram of the nitrogen-doped three-dimensional porous graphene sponge materials with different doping ratios (KOH alkali metal promoter; urea: graphene sponge precursor = 4:1; 8:1; 16:1; 20:1) prepared according to this embodiment under the condition of an applied voltage of 1.4 V; from the attached Figure 8It can be seen that as the nitrogen doping ratio in the material increases, its desalination capacity first increases and then decreases; however, when the mass ratio of urea to the graphene sponge precursor is 16:1, the desalination capacity reaches the maximum, and the maximum desalination capacity is 45.04 mg g -1 .

[0082] Attached Figure 9 is the graph of the desalination capacity cycle stability of the nitrogen-doped three-dimensional porous graphene sponge material prepared under the condition of the mass ratio of urea to the graphene sponge precursor of 16:1 in this example under the applied voltage of 1.4 V; from the attached Figure 9 it can be seen that after 500 cycles of regeneration of the nitrogen-doped porous graphene sponge electrode, the desalination capacity of the nitrogen-doped three-dimensional porous graphene sponge material does not decay, indicating that this electrode has excellent desalination cycle stability.

[0083] Attached Figure 10 is the graph of the maximum discharge voltage and maximum power density of the capacitive hybrid salt-difference energy generation device based on the nitrogen-doped porous graphene sponge electrode under the conditions of 2 V constant voltage charging, different constant current discharges, and high and low salt water switching for the nitrogen-doped three-dimensional porous graphene sponge material prepared under the condition of the mass ratio of urea to the graphene sponge precursor of 16:1 in this example; from the attached Figure 10 it can be seen that when using three pairs of nitrogen-doped three-dimensional porous graphene sponge material electrodes as both the anode and the cathode simultaneously (three pairs of electrodes were used when testing the performance), at 35000 mg l -1 and 500 mg l -1 when the high and low salt water concentrations are switched, the maximum discharge voltage and maximum power density of the capacitive hybrid salt-difference energy generation device are 1.62 V and 463.7 W cm -2 . Example 3

[0084] Disperse 200 mg of graphene oxide and 300 mg of KOH in a mixed solution of 400 ml of absolute ethanol and deionized water. The total volume of absolute ethanol and deionized water is 400 ml, and the volume ratio of absolute ethanol to deionized water is 4:1. Ultrasonic dispersion and magnetic stirring at room temperature are carried out to obtain a uniform mixed solution; transfer the mixed solution to a polytetrafluoroethylene reaction bottle, freeze-dry at -60 °C for 48 h to obtain a graphene sponge precursor; subsequently, mix the graphene sponge precursor with sodium borohydride, ammonium fluoride, sodium hypophosphite, and sulfur in a mass ratio of 1:16, place it in a tube furnace, anneal at 500 °C for 1 h in an argon atmosphere with a heating rate of 5 °C / min, cool to room temperature, and then anneal at 700 °C for 2 h in an argon atmosphere with a heating rate of 5 °C / min to obtain three-dimensional porous graphene sponges doped with different non-metals (B / F / P / S).

[0085] The desalination capacity of various non-metal (B / F / P / S) doped three-dimensional porous graphene sponge materials prepared in this example was tested using the test method described in Example 1 under the condition that the applied voltage was 1.4 V. The specific data are shown in Table 1. Example 4

[0086] Disperse 200 mg of graphene oxide, 1 g of copper chloride, and 300 mg of KOH in 400 ml of anhydrous ethanol and deionized water. The total volume of anhydrous ethanol and deionized water is 400 ml, and the volume ratio of anhydrous ethanol to deionized water is 4:1. Ultrasonic dispersion and magnetic stirring at room temperature are carried out to obtain a uniform mixed solution; transfer the mixed solution to a polytetrafluoroethylene reaction bottle, freeze-dry at -60 °C for 48 h to obtain a graphene sponge precursor; subsequently, mix the graphene sponge precursor with urea (the mass ratio of urea to the graphene sponge precursor is 16:1), place it in a tubular furnace, anneal at 400 °C for 2 h under an argon atmosphere with a heating rate of 5 °C / min, cool to room temperature, and then anneal at 700 °C for 1 h under an argon atmosphere with a heating rate of 5 °C / min to obtain an N / CuO co-doped three-dimensional porous graphene sponge.

[0087] The desalination capacity of the N / CuO co-doped porous graphene sponge material prepared in Example 4 was tested using the test method described in Example 1 under the condition that the applied voltage was 1.4 V. The specific data are shown in Table 1.

[0088] Table 1 shows the desalination capacity data of some non-metal or metal oxide doped three-dimensional porous graphene sponges prepared by the method of the present invention.

[0089] .

Claims

1. A graphene electrode material, characterized in that The invention relates to a graphene sponge; the graphene sponge is doped with heteroatoms; the graphene sponge is a three-dimensional porous graphene sponge formed by graphene nanosheets; the three-dimensional porous graphene sponge has a porous structure; the porous structure is distributed between the graphene nanosheets, and a single graphene nanosheet has pores with a diameter of less than 1 nm; the porous structure is a microporous-mesoporous-macroporous structure; The method for preparing the graphene electrode material comprises the following steps: 1) Using graphene oxide and alkali metal additives as raw materials, a graphene sponge precursor was prepared by freeze drying; 2) The graphene sponge precursor is pyrolyzed to obtain a three-dimensional porous graphene sponge.

2. A graphene electrode material according to claim 1, characterized in that The heteroatom is a non-metal or a metal oxide or a non-metal and a metal oxide are doped together; the non-metal doped in the graphene sponge is one or more of boron, nitrogen, fluorine, phosphorus and sulfur; the metal oxide doped in the graphene sponge is one or more of iron oxide, cobalt oxide, nickel oxide and copper oxide; the mass proportion of the heteroatom in the graphene electrode material is 3 wt% to 8 wt%.

3. A graphene electrode material according to claim 1, characterized in that The graphene sponge precursor is prepared by freeze-drying using graphene oxide and an alkali metal additive as raw materials, and specifically comprises the following steps: 1-1), dispersing graphene oxide and alkali metal additive in anhydrous ethanol and deionized water, ultrasonically stirring and obtaining a uniform mixed solution; 1-2) Freeze-drying the mixed solution at -30°C to -60°C for 30 to 60 hours to obtain a graphene sponge precursor.

4. A graphene electrode material according to claim 1, characterized in that The method of subjecting the graphene sponge precursor to pyrolysis treatment to obtain a three-dimensional porous graphene sponge specifically comprises the following steps: 2-1) heating the graphene sponge precursor to a first annealing temperature under an argon atmosphere, annealing at the first annealing temperature for 1 to 2 hours, and then cooling to room temperature to form a first annealed graphene sponge precursor; the first annealing temperature is 300° C. to 500° C., and the heating rate when heating to the first annealing temperature is 2° C. / min to 5° C. / min; 2-2) heating the graphene sponge precursor after the first annealing to a second annealing temperature under an argon atmosphere, annealing at the second annealing temperature for 1 to 2 hours, cooling again to room temperature, and obtaining a three-dimensional porous graphene sponge after the second annealing; the second annealing temperature is 500° C. to 800° C., and the heating rate when heating to the second annealing temperature is 2° C. / min to 5° C. / min.

5. A graphene electrode material according to claim 3, characterized in that The alkali metal additive is one or more of MOH, MCl, M2SO4, M2CO3, MHCO3, and CH3COOM, where M is Na or K; the mass ratio of the alkali metal additive to graphene oxide is 1:1 to 5:1; and the volume ratio of anhydrous ethanol to deionized water is 2:1 to 6:

1.

6. A graphene electrode material according to claim 3, characterized in that It also includes non-metal doping or metal oxide doping or co-doping of non-metal and metal oxide; The specific method of non-metal doping includes: before subjecting the graphene sponge precursor to pyrolysis treatment, first mixing the graphene sponge precursor with a non-metal compound, wherein the non-metal compound is one or more of sodium borohydride, urea, ammonium fluoride, sodium hypophosphite, and sulfur, and the mass ratio of the non-metal compound to the graphene sponge precursor is 4:1 to 20:1; after the graphene sponge precursor and the non-metal compound are mixed, heating the graphene sponge precursor to a first annealing temperature under an argon atmosphere, annealing at the first annealing temperature for 1 to 2 hours, and then cooling to room temperature to form a graphene sponge precursor with non-metal doping after the first annealing; heating the graphene sponge precursor with non-metal doping after the first annealing to a second annealing temperature under an argon atmosphere, annealing at the second annealing temperature for 1 to 2 hours, cooling again to room temperature, and obtaining a final non-metal doped three-dimensional porous graphene sponge after the second annealing; The specific method of metal oxide doping includes: adding a metal precursor to the mixed solution obtained in step 1-1), freeze-drying the mixed solution after adding the metal precursor at a temperature of -30°C to -60°C for 30 hours to 60 hours to obtain a metal oxide-doped graphene sponge precursor, and then pyrolyzing the metal oxide-doped graphene sponge precursor to obtain a metal oxide-doped three-dimensional porous graphene sponge; the metal precursor is any one or more of ferric chloride, cobalt chloride, nickel chloride, and copper chloride, and the mass ratio of the metal precursor to graphene oxide is 4:1 to 20:

1.

7. A use of the graphene electrode material according to any one of claims 1 to 6, characterized in that The graphene electrode material is used as an electrode material in a capacitor hybrid salt difference energy power generation device. The specific method of use includes: grinding and mixing the graphene electrode material, polyvinylidene fluoride, and hard carbon in a mass ratio of (6-9): (0.5-2): (0.5-2) to obtain a mixed slurry, drop-coating the mixed slurry on graphite paper, and drying it at a constant temperature of 70°C to 90°C for 4 hours to 8 hours to obtain a graphene electrode used in the capacitor hybrid salt difference energy power generation device.

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