Corn straw biochar composite electrode material and preparation method and application thereof

Abstract

The invention discloses a corn straw biochar composite electrode material and a preparation method and application thereof.The composite electrode material is formed by compounding corn straw biochar and graphene, the corn straw biochar is of a three-dimensional pore channel structure, the cross section of the corn straw biochar is in a honeycomb shape, and the corn straw biochar is of a hollow tubular array structure in the longitudinal direction; the graphene nanosheets are attached to the surface of the pore structure of the corn straw biochar. Through combination of the corn straw biochar and the graphene, the material has a rich porous honeycomb structure, a large specific surface area and a large pore volume, and has excellent electrochemical performance, and the electro-adsorption desalination performance of the electrode material is improved.

Description

Technical Field

[0001] The present invention relates to an electrode and a preparation method and application thereof, and in particular to a biochar composite electrode material and a preparation method and application thereof. Background Art

[0002] Despite approximately 70% of Earth's surface being covered by water, holding a total of 326 trillion gallons of water, the water crisis continues to plague humanity. Seawater, which accounts for 97% of the total, is too saline to be used directly. Of the remaining 3% of freshwater resources, over two-thirds is trapped in the polar regions and high altitudes as ice sheets, glaciers, and permanent snow, making it difficult to develop in the near future. Furthermore, recoverable liquid freshwater accounts for only 1% of global water reserves, primarily reliant on rainfall and surface runoff. Traditional water sources, including groundwater aquifers, are facing rapid depletion due to overexploitation. This imbalance in distribution and utilization poses a major challenge to global water security.

[0003] Traditional methods for converting seawater into freshwater, including multi-effect distillation, multi-stage flash evaporation, and reverse osmosis, all have drawbacks such as high cost, high energy consumption, high investment costs, frequent maintenance, and potential environmental pollution. Capacitive deionization, an emerging desalination technology primarily used for brackish water desalination and wastewater purification, is a promising alternative based on electrosorption technology and is gaining attention for its renewable nature, ease of operation, low cost, and low energy consumption.

[0004] In recent years, biomass-derived carbon materials have attracted widespread attention in the field of CDI due to their renewable properties, structural controllability, and environmental friendliness. Porous carbon materials prepared from agricultural waste (rice husks, corn stalks, corn straw, etc.) are naturally rich in cellulose, hemicellulose, and lignin composite structures, and have multi-level pore characteristics, making them ideal precursors for constructing high-performance carbon-based electrodes. Among them, corn straw, as a typical agricultural waste with an annual global production of over 1 billion tons, has three unique advantages:

[0005] (1) Its fiber skeleton presents a honeycomb cross-section and longitudinal tubular arrangement in an orderly manner. After carbonization, it can retain the through-pore structure, thereby significantly promoting ion diffusion efficiency;

[0006] (2) The cellulose content is as high as 35%-45%, which can form abundant defect sites through pyrolysis reaction during the pre-carbonization stage, thus improving the surface activity of the material;

[0007] (3) The raw materials are widely available and low-cost, which meets the needs of green chemistry and circular economy.

[0008] However, single biochar materials still have problems. Although corn straw biochar has a multi-level pore structure, its low degree of graphitization limits its charge transfer efficiency. In high salt concentrations or complex water conditions, ion migration resistance increases, making it difficult to further increase the desalination rate. Summary of the Invention

[0009] Purpose of the invention: The first purpose of the present invention is to provide a corn straw biochar composite electrode material that improves the desalination rate; the second purpose of the present invention is to provide a method for preparing the corn straw biochar composite electrode material; the third purpose of the present invention is to provide an application of the corn straw biochar composite electrode material.

[0010] Technical solution: The corn straw biochar composite electrode material described in the present invention is composed of corn straw biochar and graphene. The corn straw biochar has a three-dimensional pore structure, a honeycomb shape in cross section, and a hollow tubular array structure in the longitudinal direction. Graphene nanosheets are attached to the surface of the corn straw biochar pore structure.

[0011] Preferably, the mass ratio of the corn straw biochar to graphene is (19:1) to (10:1). The desalination capacity of the material is further improved after the introduction of graphene into the corn straw biochar. As the graphene content increases, the desalination capacity of the material first increases and then decreases.

[0012] Further preferably, the mass ratio of the corn straw biochar to graphene is (15:1) to (12:1).

[0013] The method for preparing the corn straw biochar composite electrode material of the present invention comprises the following steps:

[0014] (1) Corn straw biochar powder (CS-4) and graphene powder (GNPs) were added to a solvent to form a uniform mixture;

[0015] (2) The mixed liquid is ultrasonically dispersed to form a stable composite precursor, which is then washed and dried to obtain a graphene / corn straw biochar composite electrode material.

[0016] Preferably, in step (1), the solvent is water.

[0017] Preferably, in step (2), the ultrasonic power is 50-100 Hz and the time is 30-60 min. This process promotes the dispersion of GNPs in the CS-4 three-dimensional pore structure through the cavitation effect to form a stable composite precursor.

[0018] Preferably, in step (1), the method for preparing corn straw biochar powder comprises the following steps:

[0019] (1) Crush the corn stalks, wash them, and dry them;

[0020] (2) carbonizing the corn stalks treated in step (1) at a temperature of 300 to 500° C. for 40 to 80 minutes;

[0021] (3) mixing the carbonized product with an activator, sodium hydroxide, and then performing high-temperature activation at a temperature of 700 to 900° C. for 40 to 80 minutes;

[0022] (4) washing and drying the product after high-temperature activation to obtain corn straw biochar;

[0023] Preferably, in step (3), the mass ratio of the carbonized product to the activator is (1:5) to (1:2).

[0024] The electrode of the present invention contains the biochar composite electrode material.

[0025] Preferably, the preparation method of the electrode is: uniformly mixing the biochar composite electrode material with the adhesive and the solvent, and then coating it on the substrate to obtain the bioelectrode, wherein the mass ratio of the biochar composite electrode material to the adhesive is (1:1) to (1:2).

[0026] Application of the electrode of the present invention in electric adsorption desalination.

[0027] The salt includes anions and cations, the anions are inorganic anions and organic anions, the inorganic anions are F - 、Cl - Br - , I - 、NO3 - etc., the organic anion is acetate etc., the cation is a metal cation, and the metal cation is Li + 、Na + , Ca 2+ Mg 2+ wait.

[0028] Preferably, during desalination, the voltage applied across the electrode sheet is 0.8 to 1.6 V, and the flow rate of the solution is 5.7 to 17.0 mL / min.

[0029] Invention Mechanism: Corn straw, a common agricultural waste, can be converted into a carbon material with a well-defined pore structure through appropriate carbonization and activation treatments, showing promising application in desalination technologies such as ion adsorption and electrosorption. However, simple corn straw biochar still suffers from insufficient conductivity and limited surface area during desalination, limiting its adsorption capacity and cyclic stability. To enhance the overall performance of corn straw biochar, a composite material was prepared by incorporating graphene, a two-dimensional carbon material with high conductivity and large surface area, into the composite material. Graphene, due to its high surface area and excellent conductivity, can be incorporated into the composite material to effectively construct a three-dimensional conductive network, enhancing the electrode's charge transfer capacity. Its layered structure also inhibits pore clogging in the biochar, improving its anti-pollution properties. The three-dimensional framework of corn straw biochar and graphene nanosheets inhibits the stacking of graphene sheets, exposing more active sites. The high conductivity of graphene improves the material's charge transfer efficiency. Through the synergistic effect of these two elements, the electrosorption desalination performance is enhanced.

[0030] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The combination of corn straw biochar and graphene improves the electrical adsorption and desalination performance of the electrode material; (2) The preparation method is simple and easy to industrialize; (3) The biochar composite electrode material of the present invention is used for the electrical adsorption and desalination electrode, and has a high desalination rate, which increases with the increase of salt concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 SEM images of the transverse cross section (left) and longitudinal cross section (right) of corn straw biochar;

[0032] Figure 2 SEM image of corn straw biochar composite electrode material;

[0033] Figure 3 XRD patterns of GNPs, CS-4 prepared in Comparative Example 1, and G / CS-7.5 prepared in Example 1;

[0034] Figure 4 (a) is a graph showing the N2 adsorption and desorption curves of the materials of Examples 1 to 3 and Comparative Examples 1 to 2; Figure 4 (b) is a pore size distribution curve of the materials of Examples 1 to 3 and Comparative Examples 1 to 2; Figure 4 (c) is a partial enlarged view of the pore size distribution curve;

[0035] Figure 5 Raman spectra of GNPs, CS-4 prepared in Comparative Example 1, and G / CS-7.5 prepared in Example 1;

[0036] Figure 6The desalination conductivity diagrams of the materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2;

[0037] Figure 7 The desalination capacity bar graph of the materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2;

[0038] Figure 8 The bar graph of the desalination capacity of G / CS-7.5 prepared in Example 1 at different concentrations;

[0039] Figure 9 The bar graph of the desalination capacity of G / CS-7.5 prepared in Example 1 at different pump speeds;

[0040] Figure 10 The bar graph of the desalination capacity of G / CS-7.5 prepared in Example 1 at different voltages;

[0041] Figure 11 This is the adsorption and desorption cycle curve of G / CS-7.5 prepared in Example 1. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be further described below in conjunction with embodiments.

[0043] Example 1

[0044] The rice straw biochar composite electrode material of the present invention comprises the following steps:

[0045] (1) Preparation of corn straw carbon materials:

[0046] ① Pre-cleaning: Wash the corn stalks repeatedly with deionized water 3 to 5 times.

[0047] ② Low-temperature carbonization: Place the dried and cleaned corn stalks into a porcelain boat, then place the porcelain boat into a tubular furnace and gradually heat it to 450°C at a heating rate of 5°C / min, and keep it at this temperature for 1 hour, then take out the carbonized product.

[0048] ③ High-temperature activation: 3 g of carbonized corn straw product and 12 g of activator NaOH were placed in a mortar and ground thoroughly, then activated in a nitrogen atmosphere at 800 °C for 1 hour with a heating rate of 5 °C / min.

[0049] ④ Cleaning of materials after activation: Wash the product with 1M hydrochloric acid to remove impurities, then wash with deionized water until electrically neutral, and finally place in an oven to dry at 80°C for 8 hours.

[0050] (2) Composite of graphene and corn straw derivative carbon

[0051] ① Pretreatment: First, 46.25 mg of the prepared activated corn straw biochar powder (CS-4) and 3.75 mg of graphene powder (GNPs) were weighed in a mass ratio of 92.5:7.5 and placed in a beaker. After adding 30 mL of deionized water, the mixture was magnetically stirred for 10 minutes to form a uniform mixture.

[0052] ② Ultrasonic treatment: Place the mixed solution in an ultrasonic instrument and continue ultrasonic treatment at a frequency of 100 kHz for 1 hour.

[0053] ③ After the mixed solution was vacuum filtered, it was washed with deionized water for multiple cycles to remove impurities. The filtered material was then placed in a vacuum drying oven at 60°C for 12 hours to finally obtain the G / CS-7.5 composite material (7.5 represents the mass percentage of GNPs).

[0054] Example 2

[0055] On the basis of Example 1, in step (2), the mass ratio of activated corn straw biochar powder and graphene powder was changed to 95:5, and the other conditions remained unchanged to obtain a G / CS-5 composite material.

[0056] Example 3

[0057] On the basis of Example 1, in step (2), the mass ratio of the activated corn straw biochar powder and the graphene powder was changed to 90:10, and the other conditions remained unchanged to obtain a G / CS-10 composite material.

[0058] Comparative Example 1

[0059] On the basis of Example 1, only step (1) was performed to obtain corn straw carbonaceous material.

[0060] Comparative Example 2

[0061] On the basis of Example 1, in step (2), the mass ratio of activated corn straw biochar powder and graphene powder was changed to 97.5:2.5, and the other conditions remained unchanged to obtain a G / CS-2.5 composite material.

[0062] Structural characterization

[0063] The morphology and structure of the rice straw biochar composite electrode materials prepared in Examples 1 to 3 and Comparative Example 1 were characterized.

[0064] (1) The morphology of the corn straw biochar composite electrode material prepared in Example 1 was analyzed using a scanning electron microscope. Figure 1 and Figure 2 shown.

[0065] Depend on Figure 1It can be seen that the addition of NaOH did not significantly destroy the structure of the corn straw carbon material, but retained the natural cross-sectional honeycomb shape of the corn straw ( Figure 1 Left) and longitudinal hollow tubular array structure ( Figure 1 Right), providing abundant macropores and micropores, which are beneficial to the transport of sodium ions and the diffusion of electrolytes.

[0066] Depend on Figure 2 It can be seen that graphene nanosheets are evenly distributed in the fiber structure of corn straw, and the surface roughness of the composite material is significantly increased.

[0067] (2) XRD was used to characterize the rice straw biochar composite electrode material, corn straw biochar (CS-4), and graphene (GNPs) prepared in Example 1. The results are as follows: Figure 3 shown.

[0068] from Figure 3 As can be seen in the figure, the graphene nanosheets have a sharp diffraction peak at 2θ = 26.50°, which is the characteristic diffraction peak of graphene, indicating its highly ordered crystal structure. From the XRD patterns of CS-4 and G / CS-7.5, broad peaks corresponding to the (002) and (100) crystal planes of graphite can be observed, indicating that graphite has an amorphous structure. When GNPs are composited with CS-4, the XRD characteristic peaks of the composite appear at around 2θ = 26.50° and 44.20°. Compared with the CS-4 material, the (002) and (100) crystal planes of the composite material shift to the right, and the interlayer spacing d002 value decreases from 0.35nm to 0.33nm, indicating that the composite material has a stronger degree of graphitization. In addition, two characteristic peaks appear in the XRD pattern of the composite material, indicating that the graphene nanosheets are successfully combined with CS-4. Moreover, the addition of graphene does not change the basic structure of corn straw fiber, but forms a composite structure.

[0069] (2) The nitrogen adsorption and desorption tests were performed on Examples 1 to 3 and Comparative Examples 1 to 2, and the specific surface area and pore structure were analyzed. The results are as follows: Figure 4 shown.

[0070] Depend on Figure 4 It can be seen that the specific surface area of ​​the corn straw biochar composite electrode material of Example 1 is 1550.80 m 2 / g, corresponding to a total pore volume of 1.13 cm 3 / g, with an average pore size of 2.92nm; the specific surface area of ​​the corn straw biochar composite electrode material of Example 2 is 1703.47m 2 / gm 2 / g, corresponding to a total pore volume of 1.27 cm 3 / g cm 3 / g, and an average pore size of 2.98nm; the specific surface area of ​​the corn straw biochar composite electrode material of Example 3 is 1500.28m 2 / g, and the corresponding total pore volume is 1.10 cm 3 / g, with an average pore size of 2.94nm; the specific surface area of ​​the corn straw biochar composite electrode material of Comparative Example 2 is 1766.41m 2 / g, corresponding to a total pore volume of 1.27 cm 3 / g, the average pore size is 2.87nm; the specific surface area of ​​graphene is 402.89m 2 / g, and the corresponding total pore volume is 0.86 cm 3 / g, with an average pore size of 8.52nm; the specific surface area of ​​the corn straw biochar in Comparative Example 1 is 2875.38m 2 / g, corresponding to a total pore volume of 1.70 cm 3 / g, with an average pore size of 2.53nm. It can be seen that as the graphene ratio increases, the specific surface area gradually decreases, but it is still much larger than the specific surface area of ​​graphene itself. This may be because the introduction of graphene increases the mesopore content and reduces the pore volume, resulting in a higher efficiency of the composite material in adsorbing small molecules and ions.

[0071] (3) The corn straw biochar composite electrode material, corn straw biochar (CS-4) and graphene (GNPs) prepared in Example 1 were analyzed by Raman spectrometer. The results were as follows: Figure 5 shown.

[0072] Depend on Figure 5 Can obtain, Example 1 material I D / I G =1.19, CS-4's I D / I G The value is 5.77, and the I D / I G The value is 0.91. D / I G The value is higher than that of GNPs, I D / I G The higher the value, the higher the degree of disorder of the carbon material and the more defects it has. The disordered carbon structure can increase the number of active sites, thereby improving the electrochemical performance, while the graphitized structure can improve the conductivity of the carbon material.

[0073] Desalination performance test

[0074] Preparation of desalination unit:

[0075] (1) Electrode preparation:

[0076] First, the graphite paper was cut into a size of 6×6 cm and washed alternately with deionized water and anhydrous ethanol to ensure that there was no impurity on its surface. Finally, it was placed in an oven and dried at 60°C for 6 hours. After taking it out, it was cooled to room temperature.

[0077] 0.05g of electrode material and 0.0833g of polytetrafluoroethylene dispersion were weighed and placed in a beaker. Similarly, a small amount of ethanol was added to form a slurry. Then, it was thoroughly stirred to achieve uniform mixing. The beaker was then placed in an ultrasonic device for 30 minutes. After the material was formed, it was evenly coated on a graphite sheet measuring 6×6cm (the effective coating area was 3×3cm). Two electrodes were prepared using the same operation. The coated electrode sheets were then placed in an oven and dried at a constant temperature of 80°C for 12 hours, thus preparing a pair of electrode sheets suitable for a device.

[0078] (2) The capacitive deionization and desalination device consists of a CDI unit, a DC power supply, a peristaltic pump, a liquid storage tank, a magnetic stirrer, and a conductivity meter. First, a sodium chloride salt solution of a certain concentration is prepared as the original solution and pumped into the CDI module through a peristaltic pump. Subsequently, the power supply is turned on and a certain voltage is set. At the same time, the conductivity of the NaCl solution is read and recorded. The conductivity change of the solution is monitored in real time by the conductivity meter, and the concentration of the solution is calculated based on the conductivity.

[0079] 1. Desalination performance of materials with different proportions of graphene

[0080] The desalination amount and desalination rate of the materials of Test Examples 1 to 3 and Comparative Examples 1 to 2 were tested in a 100 mg / L NaCl solution with a directional voltage of 1.6 V and a flow rate of 11.3 mL / min and a volume of 100 mL. The results are as follows: Figure 6 and 7 shown.

[0081] Figure 6 The desalination conductivity diagram is shown in Figure 2. The desalination amount calculated based on the conductivity is as follows: Figure 7 As shown. Figure 6 It can be seen that G / CS-7.5 exhibits the fastest conductivity decrease rate, indicating that it has the best ion adsorption kinetics performance.

[0082] Depend on Figure 7The results show that the desalination capacity of the corn straw biochar alone in Comparative Example 1 was 15.78 mg / g; the desalination capacity of Comparative Example 2, with a ratio of 97.2:2.5, reached 14.5 mg / g; the desalination capacity of Example 1, with a ratio of 92.5:7.5, reached 19.57 mg / g; the desalination capacity of Example 2, with a ratio of 95:5, reached 16.26 mg / g; and the desalination capacity of Example 3, with a ratio of 90:10, reached 17.64 mg / g. The desalination capacity of the materials composited with corn straw biochar and graphene in Examples 1-3 was further improved. With the increase in the amount of graphene in the materials, the desalination capacity of the materials first increased and then decreased. The material in Example 1 had the best desalination performance. The performance of Comparative Example 2, with too little graphene added, actually declined compared to the corn straw biochar. This may be due to insufficient graphene doping, which failed to form an effective conductive network, and localized aggregation, which blocked adsorption sites and interfered with the adsorption system, resulting in a slight decline in performance.

[0083] 2. Desalination performance under different salt concentration conditions

[0084] Test method: The electrode prepared by the corn straw biochar composite electrode material prepared in Example 1 was tested for desalination performance in NaCl solutions with concentrations of 50 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L, at a voltage of 1.6 V and a flow rate of 11.3 mL / min. The results are as follows: Figure 8 shown.

[0085] Depend on Figure 8 The results show that the desalination capacity of the electrode prepared from the rice straw biochar composite electrode material increased from 12.48 mg / g to 19.57 mg / g with increasing concentrations of the desalting solution at 50 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L, respectively. The higher the initial salt concentration, the stronger the material's desalination capacity and the higher its desalination efficiency. This is mainly because high electrolyte concentrations reduce the diffusion barrier of solutes in the solution, thereby reducing mass transfer resistance and accelerating ion transfer and adsorption.

[0086] 3. Desalination performance at different flow rates

[0087] Test method: The electrode prepared by the corn straw biochar composite electrode material prepared in Example 1 was subjected to a constant voltage of 1.6 V in a 100 mg / L NaCl solution and tested for desalination performance at flow rates of 5.7 mL / min, 11.3 mL / min, and 17.0 mL / min, respectively. The results are as follows: Figure 9 shown.

[0088] Depend on Figure 9 It can be found that when the flow rate is 5.7mL / min, 11.3mL / min, and 17.0mL / min, the desalination capacity is 15.77mg / g, 19.57mg / g, and 23.8mg / g, respectively. When the solution flow rate is gradually increased from 5.7mL / min to 17.0mL / min, the final adsorption capacity of the electrode shows a clear upward trend. As the flow rate increases, the number of ions passing through the CDI electrode per unit time increases, resulting in more ions adsorbed on the electrode, increasing the desalination capacity. The increase in flow rate also leads to an increase in the amount of water treated per unit time, thereby reducing energy consumption.

[0089] 4. Desalination performance test under different voltages

[0090] Test method: The electrode prepared by the corn straw biochar composite electrode material prepared in Example 1 was tested for desalination performance at different voltages (0.8V, 1.2V, 1.6V) in 100mg / L NaCl solution at a flow rate of 11.3mL / min. The results are as follows: Figure 10 shown.

[0091] Depend on Figure 10 It can be seen that under the conditions of voltages of 0.8V, 1.2V, and 1.6V, the desalination amounts were 11.67mg / g, 14.43mg / g, and 19.57mg / g, respectively. As the voltage increases, the change in conductivity gradually increases. Under the condition of 0.8V, the desalination amount in 14 minutes is only 11.67mg / g; when the voltage is increased to 1.2V, the desalination amount increases to 14.43mg / g. When the voltage is further increased to 1.6V, the desalination amount increases to 19.57mg / g. This is because the higher the voltage, the stronger the electric field, which promotes the Coulomb interaction between ions and electrodes, enhances the transport and penetration of ions, and is conducive to the formation of a stronger double layer behavior.

[0092] 5. Desalination stability

[0093] Test method: The electrode prepared by the corn straw biochar composite electrode material prepared in Example 1 was subjected to a constant voltage of 1.6V in a 100mg / L NaCl solution to perform a cyclic stability test to further evaluate the desalination performance of the G / CS-7.5 electrode. Five desalination experiments were conducted, and the results were as follows: Figure 11 shown.

[0094] like Figure 11 As shown in the figure, the electrode underwent five desalination experiments, and the initial salt adsorption capacity decreased from 19.57 to 18.64 mg / g. After five cycles, the salt adsorption capacity retention rate was 95.24%. The salt adsorption capacity did not decrease significantly, demonstrating that the homemade electrode material in this study has good cycling stability.

Claims

1. A corn straw biochar composite electrode material, characterized in that: It is composed of corn straw biochar and graphene. The corn straw biochar has a three-dimensional pore structure, a honeycomb shape in the cross section, and a hollow tubular array structure in the longitudinal direction. Graphene nanosheets are attached to the surface of the corn straw biochar pore structure.

2. The corn straw biochar composite electrode material according to claim 1, characterized in that: The mass ratio of the corn straw biochar to the graphene is (19:1) to (10:1).

3. The corn straw biochar composite electrode material according to claim 1, characterized in that: The mass ratio of the corn straw biochar to the graphene is (14:1) to (12:1).

4. A method for preparing a corn straw biochar composite electrode material according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) adding corn straw biochar powder and graphene powder to a solvent to form a uniform mixed solution; (2) The mixed liquid is ultrasonically dispersed to form a stable composite precursor, which is then washed and dried to obtain a graphene / corn straw biochar composite electrode material.

5. The method for preparing the corn straw biochar composite electrode material according to claim 4, characterized in that: In the step (2), the ultrasonic power is 50 to 100 Hz, and the time is 30 to 60 minutes.

6. The method for preparing the corn straw biochar composite electrode material according to claim 4, characterized in that: In step (1), the method for preparing corn straw biochar powder comprises the following steps: (1) Crush the corn stalks, wash them, and dry them; (2) carbonizing the corn stalks treated in step (1) at a temperature of 300 to 500° C. for 40 to 80 minutes; (3) mixing the carbonized product with an activator, sodium hydroxide, and then performing high-temperature activation at a temperature of 700 to 900° C. for 40 to 80 minutes; (4) The product after high-temperature activation is washed and dried to obtain corn straw biochar.

7. The method for preparing the corn straw biochar composite electrode material according to claim 6, characterized in that: In the step (3), the mass ratio of the carbonized product to the activator is (1:5) to (1:2).

8. An electrode comprising the corn straw biochar composite electrode material according to any one of claims 1 to 3.

9. The electrode according to claim 8, characterized in that The electrode is prepared by uniformly mixing a biochar composite electrode material with an adhesive and a solvent, and then coating the mixture on a substrate to obtain a bioelectrode, wherein the mass ratio of the biochar composite electrode material to the adhesive is 1:1 to 1:

2.

10. Use of the electrode according to claim 8 or 9 in electrosorption desalination.

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