A hydroxide-phosphide heterojunction, a preparation method thereof, and an application thereof in electrolyzing high-chloride oilfield fracturing wastewater

Abstract

The present invention provides a hydroxide-phosphide heterojunction, a preparation method thereof, and an application thereof in electrolyzing high-chloride oilfield fracturing wastewater, belonging to the field of electrolyzing oilfield wastewater. In order to solve the problems that the existing oilfield wastewater treatment is difficult, and the high concentration of chloride ions can cause easy corrosion of treatment equipment, high energy consumption and high economic cost. The present invention includes cleaning and drying a conductive carrier; depositing metal phosphide on the conductive carrier by an electrochemical deposition method; depositing layered metal hydroxide on the conductive carrier wrapped with metal phosphide by an electrochemical deposition method to obtain a conductive carrier wrapped with a hydroxide-phosphide heterojunction. The present invention is simple, efficient and low-cost, and can prepare an oxygen evolution reaction catalyst more efficient than single phosphide and layered metal hydroxide, and has a good inhibitory effect on the chlorine evolution reaction, thereby slowing down the generation of highly corrosive chlorine-containing by-products.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolyzing oilfield wastewater, and in particular, to a hydroxide-phosphide heterojunction, a preparation method thereof, and an application thereof in electrolyzing high-chloride oilfield fracturing wastewater. Background Art

[0002] With the continuous growth of global energy demand, the problem of wastewater generated in the process of oil extraction has attracted wide attention. In particular, the wastewater generated during oilfield fracturing usually contains a large amount of suspended solids, organic matter, heavy metal ions, and high-concentration salts, especially chloride ions. High-chloride fracturing wastewater not only causes serious environmental pollution but also poses great challenges to traditional water treatment methods. The high concentration of chloride ions makes conventional water treatment technologies, such as chemical deposition methods and membrane filtration technologies, prone to equipment corrosion, high energy consumption, and increased economic costs while removing harmful substances. Therefore, developing an efficient, corrosion-resistant electrolysis technology suitable for treating high-chloride fracturing wastewater has important practical significance.

[0003] In recent years, electrocatalytic technology has gradually been applied to the fields of water treatment and resource recovery, and the technology based on electrolytic water hydrogen production has developed rapidly. By electrolyzing wastewater, not only can wastewater treatment be achieved, but hydrogen can also be produced simultaneously as a clean energy source. However, during the process of electrolyzing high-chloride wastewater, due to the presence of chloride ions, the electrode material is prone to corrosion, reducing the stability and efficiency of the electrolysis process. To solve this problem, developing electrode materials with high catalytic activity, stability, and chlorine corrosion resistance has become the focus of current research.

[0004] The present invention uses a two-step electrodeposition method to prepare a hydroxide / phosphide heterojunction, aiming to develop an efficient and corrosion-resistant electrode material for electrolyzing high-chloride oilfield fracturing wastewater to achieve the dual goals of wastewater treatment and hydrogen production. Through this technology, not only can the efficiency of electrocatalytic water decomposition be significantly improved, but also the corrosion problem of the electrode material caused by high-concentration chloride ions can be effectively overcome, providing a feasible solution for the resource utilization of high-chloride wastewater. Summary of the Invention

[0005] The technical problem to be solved by the present invention is:

[0006] To solve the problem that it is difficult to treat existing oilfield wastewater, and the high concentration of chloride ions will cause easy corrosion of treatment equipment, high energy consumption, and high economic cost.

[0007] The technical solution adopted by the present invention to solve the above technical problem:

[0008] The present invention provides a preparation method of a hydroxide-phosphide heterojunction, comprising the following steps:

[0009] S100. Place the conductive carrier in acetone, aqueous HCl solution, ethanol, and deionized water in sequence for ultrasonic cleaning. After cleaning, place it in a vacuum drying oven for overnight drying.

[0010] S200. Use the electrochemical deposition method to deposit metal phosphide on the conductive carrier obtained in step S100 to obtain a conductive carrier coated with metal phosphide. In the electrochemical deposition process, use a first precursor solution, and the first precursor solution is an ammonium salt, a phosphorus source, and a metal source for preparing phosphide dissolved in deionized water.

[0011] S300. Use the electrochemical deposition method to deposit layered metal hydroxide on the conductive carrier coated with metal phosphide obtained in step S200 to obtain a conductive carrier coated with a hydroxide-phosphide heterojunction. In the electrochemical deposition process, use a second precursor solution, and the second precursor solution is a metal source for preparing hydroxide dissolved in deionized water.

[0012] The metal source for preparing phosphide and the metal source for preparing hydroxide are both one or more combinations of metal element chlorides, nitrates, sulfates, or acetates; further limit the metal source for preparing phosphide to be one or more combinations of metal element chlorides, nitrates, sulfates, nitrites, carbonates, or acetates; the metal element in the metal source for preparing phosphide is Co, Cu, Mo, V, Cr, or Mn, and the metal element in the metal source for preparing hydroxide is Ni, Fe, Ce, La, Al, or K. Among them, the metal source for preparing hydroxide is mainly nitrate, and its types are further limited to Ni(NO3)2·6H2O, Fe(NO3)3·9H2O, Ce(NO3)3·6H2O, La(NO3)3·6H2O, Al(NO3)3·9H2O, KNO3.

[0013] Furthermore, the conductive carrier is a transition metal, an alloy, or a carbon material. When the conductive carrier is a transition metal, the transition metal is nickel, iron, copper, or titanium.

[0014] Furthermore, in step S100, place the conductive carrier in acetone for ultrasonic cleaning for 10 min - 20 min, then place it in a 1 mol / L aqueous HCl solution for ultrasonic cleaning for 10 min - 20 min, and finally ultrasonically clean it with ethanol and deionized water for 5 min - 15 min each, and then place it in a vacuum drying oven at 70 °C for overnight drying.

[0015] Furthermore, the ammonium salt is one or more combinations of ammonium chloride, ammonium sulfate, ammonium nitrate, or ammonium bicarbonate; the phosphorus source is one or more combinations of monosodium phosphate, disodium phosphate, sodium hexametaphosphate, calcium hydrogen phosphate, or sodium hypophosphite.

[0016] Further, the ratio of the ammonium salt, the phosphorus source, and the metal source for preparing the phosphide is 1:1 - 60:1.

[0017] Further, the ammonium salt is a 0.3 mol / L NH4Cl solution, the phosphorus source is a 1.0 mol / L NaPO2H2 solution, and the metal source for preparing the phosphide is an aqueous solution of 50 mmol / L CoCl2 solution, 50 mmol / L CuCl2 solution, and 10 mmol / L C2H3NaO2 electrolyte.

[0018] Further, in steps S200 and S300, the electrochemical deposition method is either constant current deposition or constant voltage deposition; when the electrochemical deposition method is constant current deposition, the constant current range is 20 mA / cm 2 - 600 mA / cm 2 , and when the electrochemical deposition method is constant voltage deposition, the constant voltage range is 0.2 V - 6 V, and the deposition time is 3 min - 90 min.

[0019] Further, in step S200, the electrochemical deposition method is constant current deposition, which is carried out in a two - electrode system. Using a Ti sheet as the counter electrode and a clean blank NF as the working electrode, deposition is carried out under a constant current. During the deposition process, continuous stirring is maintained. After the deposition is completed, the working electrode is repeatedly rinsed 3 times with ethanol and deionized water, and then placed in a vacuum drying oven at 70 °C for overnight drying to obtain a conductive carrier coated with metal phosphide.

[0020] Further, in step S300, the electrochemical deposition method is constant voltage deposition, which is carried out in a three - electrode system. Using a Pt sheet as the counter electrode, the conductive carrier coated with metal phosphide as the working electrode, and Ag / AgCl as the reference electrode, deposition is carried out under a constant voltage; continuous stirring is maintained during the deposition process. After the deposition is completed, the working electrode is repeatedly rinsed 3 times with ethanol and deionized water, and then placed in a vacuum drying oven at 70 °C for overnight drying to obtain a hydroxide - phosphide heterojunction.

[0021] Further, the cleaning agent used for cleaning in step S300 is one or a combination of deionized water, ethanol, or acetone; the drying temperature range is 25 °C - 100 °C.

[0022] Further, the present invention protects a hydroxide - phosphide heterojunction prepared by the above - mentioned preparation method.

[0023] Further, the present invention protects an application of the hydroxide - phosphide heterojunction in electrolyzing high - chloride oilfield fracturing wastewater.

[0024] (1)The material synthesis technology can synthesize the layered metal hydroxide / phosphide heterojunction catalyst only by a simple two-step electrodeposition method, which greatly shortens the time cost and reduces the difficulty of material synthesis, providing a new idea for the preparation of the layered metal hydroxide / phosphide heterojunction.

[0025] (2)During the synthesis process, the layered metal hydroxide grows on the surface of the transition metal phosphide and forms an M1-O-M2 atomic interface (M1 and M2 are the metal elements in the layered metal hydroxide and the transition metal phosphide respectively), enhancing the stability of the heterojunction catalyst.

[0026] (3)The OER activity and stability of the heterojunction catalyst are significantly improved compared with those of the single phosphide and the single-layered metal hydroxide.

[0027] (4)The oilfield fracturing wastewater contains abundant chloride ions, and the chlorine evolution reaction will lead to the generation of highly corrosive chlorine-containing by-products. The heterojunction catalyst has a good inhibitory effect on the chlorine evolution reaction, thus slowing down the corrosion of the electrode and the electrolysis device.

[0028] (5)In the heterojunction catalyst, the phosphide acts as an electron buffer layer, which can optimize the electronic structure of the active species, the layered metal hydroxide, and is the fundamental reason for achieving the improvement of the oxygen evolution reaction activity while effectively inhibiting the chlorine evolution reaction.

[0029] (6)The heterojunction catalyst has good structural tunability. By changing the types of metal elements, different types of heterojunction catalysts can be synthesized.

[0030] (7)According to the experiment, the heterojunction catalyst Ce@NiFeLDH / CoCuP(98.5%) was prepared by a two-step electrodeposition method. Compared with the single phosphide (85.7%) or the metal hydroxide (92.4%), its oxygen evolution and chlorine resistance performance was significantly improved, providing an efficient and robust anode catalyst for the electrolysis of oilfield fracturing wastewater. Description of the Drawings

[0031] Figure 1 This is the scanning electron microscope (SEM) image of the Ce@NiFeLDH / CoCuP catalyst prepared in Example 1 of the present invention. Among them, (a) is the electron microscope at a resolution of 100 nm Figure 1 , (b) is the electron microscope at a resolution of 500 nm Figure 2 , (c) is the electron microscope image at a resolution of 1 pm;

[0032] Figure 2Energy-dispersive spectroscopy (EDS) mapping of each element in the Ce@NiFeLDH / CoCuP heterojunction catalyst prepared in Example 1 of the present invention. Here, Energy is used to qualitatively identify the element species, and cps is used to semi-quantitatively reflect the relative content of the elements.

[0033] Figure 3 X-ray diffraction (XRD) patterns of the Ce@NiFeLDH / CoCuP, Ce@NiFeLDH, and CoCuP catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2. Here, 2Theta is the diffraction angle, and Intensity is the photoelectron signal intensity.

[0034] Figure 4 X-ray photoelectron spectroscopy (XPS) analysis results of the Ce@NiFeLDH / CoCuP, Ce@NiFe LDH, and CoCuP catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. Among them, (a) is the X-ray photoelectron spectroscopy pattern of the Ni active site, (b) is the X-ray photoelectron spectroscopy pattern of the Co active site, Binding energy is the binding energy, and Intensity is the photoelectron signal intensity.

[0035] Figure 5 Schematic diagram of the electrolysis device used in the full decomposition of oilfield fracturing wastewater in the examples of the present invention.

[0036] Figure 6 Polarization curves of the overall water splitting experiments using membrane electrode assemblies in Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0037] Figure 7 Chromatogram of the cathode product H2 after the overall water splitting experiment of Ce@NiFeLDH / CoCuP prepared in Example 1 of the present invention in the membrane electrode assembly.

[0038] Figure 8 Test result diagram of the stability of Ce@NiFeLDH / CoCuP in the MEA assembly in Example 1 of the present invention. Detailed implementation manners

[0039] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given with reference to the accompanying drawings.

[0040] Example 1: A method for preparing a hydroxide-phosphide heterojunction, specifically including:

[0041] S100. Place commercial nickel foam (with dimensions of 1 cm * 2 cm * 1 mm) in acetone and ultrasonically clean it for 15 min. Subsequently, place it in a 1 mol / L HCl aqueous solution and ultrasonically clean it for 15 min. Finally, ultrasonically clean it with ethanol and deionized water for 10 min each, and then put it into a vacuum drying oven at 70 °C to dry overnight, thus obtaining the treated nickel foam;

[0042] S200. The method of depositing phosphide is constant current deposition, which is carried out in a two-electrode system; prepare an electrolyte aqueous solution containing 50 mmol / L of CoCl2, 50 mmol / L of CuCl2, 0.3 mol / L of NH4Cl, 1.0 mol / L of NaPO2H2 and 10 mmol / L of C2H3NaO2 as the precursor solution; use a Ti sheet as the counter electrode, a clean blank NF as the working electrode, and deposit at a constant current of -25 mA cm -2 Deposit for 2 min; continuously stir during the deposition process. After the deposition is completed, repeatedly rinse the working electrode 3 times with ethanol and deionized water, and then place it in a vacuum drying oven at 70 °C to dry overnight, thus obtaining the CoCuP electrode;

[0043] S300. The method of depositing layered metal hydroxide is constant voltage deposition, which is carried out in a three-electrode system; prepare an electrolyte aqueous solution containing 30 mmol / L of Ni(NO)3, 10 mmol / L of Fe(NO)3 and 4 mmol / L of Ce(NO)3 as the precursor solution, use a Pt sheet as the counter electrode, CoCuP / NF as the working electrode, and Ag / AgCl as the reference electrode, and deposit at a constant voltage of -1 V for 10 min. Continuously stir during the deposition process. After the deposition is completed, repeatedly rinse the working electrode 3 times with ethanol and deionized water, and then place it in a vacuum drying oven at 70 °C to dry overnight, thus obtaining the Ce@NiFe LDH / CoCuP heterojunction catalyst.

[0044] Example 2: A preparation method of a hydroxide-phosphide heterojunction, specifically including:

[0045] S100. Place commercial nickel foam (with dimensions of 1 cm * 2 cm * 1 mm) in acetone and ultrasonically clean it for 15 min. Subsequently, place it in a 1 mol / L HCl aqueous solution and ultrasonically clean it for 15 min. Finally, ultrasonically clean it with ethanol and deionized water for 10 min each, and then put it into a vacuum drying oven at 70 °C to dry overnight, thus obtaining the treated nickel foam;

[0046] S200. The way of depositing phosphide is constant current deposition, which is carried out in a two-electrode system. Prepare an electrolyte aqueous solution containing 50 mmol / L of CoCl2, 50 mmol / L of NH4VO3, 0.3 mol / L of NH4Cl, 1.0 mol / L of NaPO2H2 and 10 mmol / L of C2H3NaO2 as the precursor solution. Use a Ti sheet as the counter electrode and a clean blank NF as the working electrode, with a constant current of -25 mA cm -2 Deposit for 2 minutes. Stir continuously during the deposition process. After the deposition is completed, rinse the working electrode with ethanol and deionized water repeatedly for 3 times, and then place it in a vacuum drying oven at 70 °C to dry overnight to obtain the CoVP electrode.

[0047] S300. The way of depositing layered metal hydroxide is constant voltage deposition, which is carried out in a three-electrode system. Prepare an electrolyte aqueous solution containing 30 mmol / L of Ni(NO)3, 10 mmol / L of Fe(NO)3 and 4 mmol / L of Ce(NO)3 as the precursor solution. Use a Pt sheet as the counter electrode, CoVP / NF as the working electrode, and Ag / AgCl as the reference electrode, and deposit at a constant voltage of -1 V for 10 minutes. Stir continuously during the deposition process. After the deposition is completed, rinse the working electrode with ethanol and deionized water repeatedly for 3 times, and then place it in a vacuum drying oven at 70 °C to dry overnight to obtain the Ce@NiFe LDH / CoVP heterojunction catalyst.

[0048] Example 3: A preparation method of a hydroxide-phosphide heterojunction, specifically including:

[0049] S100. Place commercial foam nickel (size: 1 cm * 2 cm * 1 mm) in acetone and ultrasonically clean it for 15 minutes, then place it in a 1 mol / L HCl aqueous solution and ultrasonically clean it for 15 minutes. Finally, ultrasonically clean it with ethanol and deionized water for 10 minutes each, and then put it into a vacuum drying oven at 70 °C to dry overnight to obtain the treated foam nickel.

[0050] S200. The way of depositing phosphide is constant current deposition, which is carried out in a two-electrode system. Prepare an electrolyte aqueous solution containing 50 mmol / L of CoCl2, 50 mmol / L of Na2MoO4, 0.3 mol / L of NH4Cl, 1.0 mol / L of NaPO2H2 and 10 mmol / L of C2H3NaO2 as the precursor solution. Use a Ti sheet as the counter electrode and a clean blank NF as the working electrode, with a constant current of -25 mA cm -2Deposit for 2 min; continuously stir during the deposition process. After the deposition is completed, repeatedly rinse the working electrode 3 times with ethanol and deionized water, and then place it in a vacuum drying oven at 70 °C to dry overnight to obtain the CoMoP electrode;

[0051] S300. The method for depositing the layered metal hydroxide is constant voltage deposition, which is carried out in a three-electrode system. Prepare an electrolyte aqueous solution containing 30 mmol / L of Ni(NO)3, 10 mmol / L of Fe(NO)3, and 4 mmol / L of Ce(NO)3 as the precursor solution. Use a Pt sheet as the counter electrode, CoMoP / NF as the working electrode, and Ag / AgCl as the reference electrode. Deposit at a constant voltage of -1 V for 10 min. Continuously stir during the deposition process. After the deposition is completed, repeatedly rinse the working electrode 3 times with ethanol and deionized water, and then place it in a vacuum drying oven at 70 °C to dry overnight to obtain the Ce@NiFe LDH / CoMoP heterojunction catalyst.

[0052] Comparative Example 1: A method for preparing a Ce@NiFe LDH oxygen evolution electrocatalyst, comprising the following steps:

[0053] The method for depositing the Ce@NiFe LDH electrode is constant voltage deposition, which is carried out in a three-electrode system. Prepare an electrolyte aqueous solution containing 30 mmol / L of Ni(NO)3, 10 mmol / L of Fe(NO)3, and 4 mmol / L of Ce(NO)3 as the precursor solution. Use a Pt sheet as the counter electrode, a clean NF as the working electrode, and Ag / AgCl as the reference electrode. Deposit at a constant voltage of -1 V for 10 min. Continuously stir during the deposition process. After the deposition is completed, repeatedly rinse the working electrode 3 times with ethanol and deionized water, and then place it in a vacuum drying oven at 70 °C to dry overnight to obtain the Ce@NiFe LDH electrode.

[0054] Comparative Example 2: A method for preparing a CoCuP oxygen evolution electrocatalyst, comprising the following steps:

[0055] The method for depositing the CoCuP electrode is constant current deposition, which is carried out in a two-electrode system. Prepare an electrolyte aqueous solution containing 50 mmol / L of CoCl2, 50 mmol / L of Na2MoO4, 0.3 mol / L of NH4Cl, 1.0 mol / L of NaPO2H2, and 10 mmol / L of C2H3NaO2 as the precursor solution; use a Ti sheet as the counter electrode and a clean blank NF as the working electrode, with a constant current of -25 mA cm -2 Deposit for 2 min. Continuously stir during the deposition process. After the deposition is completed, repeatedly rinse the working electrode 3 times with ethanol and deionized water, and then place it in a vacuum drying oven at 70 °C to dry overnight to obtain the CoCuP electrode.

[0056] Comparative Example 3: A preparation method of a RuO2 oxygen evolution electrocatalyst, comprising the following steps:

[0057] Disperse 10 mg of RuO2 powder and 30 μL of 5 wt.% Nafion solution in 970 μL of absolute ethanol, ultrasonically treat for at least 30 min to obtain a uniform mixture, then take 50 μL of the mixture and drop-coat it on a 1 cm * 2 cm nickel foam, repeat the operation twice, and place it in a vacuum drying oven at 70 °C for drying and testing.

[0058] Comparative experiment

[0059] Perform electrocatalytic oxygen evolution reaction on the catalysts prepared in Examples 1 - 3 and Comparative Examples 1 - 3 in oilfield fracturing wastewater containing 1 mol / L KOH. The specific test conditions are as follows: perform electrocatalytic oxygen evolution and chlorine resistance performance tests in a standard three-electrode system; the oilfield fracturing wastewater is taken from the fracturing flowback fluid of Daqing Gulong shale oil; the carbon rod is the counter electrode, Hg / HgO is the reference electrode, and the nickel foam-supported catalyst is the working electrode; the polarization curve scanning range is 1 - 2 V (relative to the reversible hydrogen electrode), and the scanning rate is 5 mV / s; the oxygen evolution chlorine resistance performance is evaluated by testing the Faraday efficiency of oxygen after constant current electrolysis, and the results are shown in Table 1.

[0060] Use the catalysts prepared in Examples 1 - 3 and Comparative Examples 1 - 3 as the anode, and carbon felt as the cathode to perform overall water splitting reaction in a membrane electrode assembly. The diaphragm material is Nafion 117 proton exchange membrane. The specific test conditions are as follows: the effective areas of the anode and cathode are 2 cm 2 , use a two-channel peristaltic pump to pump the oilfield fracturing wastewater electrolyte containing 1 mol / L KOH into the serpentine flow channels of the anode and cathode plates at a flow rate of 50 mL / min respectively; the polarization curve test condition is 20 mV / s; after electrolyzing for 10 min at a voltage of 2.0 V, collect the cathode gas product, and test the purity of the hydrogen product by gas chromatography, and the results are shown in Table 2.

[0061] Table 1 Summary of electrocatalytic oxygen evolution chlorine resistance performance results

[0062]

[0063] Note: η 10 、η 100 represent the overpotentials required when the polarization currents reach 10 and 100 mA / cm 2 respectively; FE O2(100 mA cm -2 ) represents electrolysis at a constant current of 100 mA / cm 2 , and calculate the Faraday efficiency of O2 after the electrolysis ends.

[0064] Table 2 Summary of the test results of the complete solution of oilfield fracturing wastewater in the membrane electrode assembly

[0065]

[0066] Note: E 100 、E 200 represent the voltages required when the polarization currents reach 100 and 200 mA respectively; FE H2(100 mA cm -2 ) represents electrolysis at a constant current of 100 mA / cm 2 and calculating the Faraday efficiency of O2 after the electrolysis ends.

[0067] Combined with Figure 1 shown, the surface of the catalyst synthesized by the method of Example 1 has a relatively high roughness. This surface morphological feature has double advantages: First, the relatively high roughness can significantly increase the specific surface area of the catalyst, thereby exposing more active sites, which is beneficial to improving the efficiency of the catalytic reaction; Second, the rough surface structure can effectively shorten the diffusion distance of the reactant molecules on the catalyst surface, thereby increasing the overall reaction rate. This unique surface structure feature provides favorable conditions for optimizing the catalyst performance.

[0068] Combined with Figure 2 shown, the characteristic peaks of Ce, Ni, Fe, O, Co, Cu and P elements can be clearly observed from the figure, and this result confirms the successful synthesis of the heterojunction catalyst.

[0069] Combined with Figure 3 shown, the XRD pattern of Ce@NiFeLDH / CoCuP contains the characteristic peaks at 23.2°, 34.1°, 59.9° (corresponding to the LDH phase) and 23.4°, 43.7°, and 27.6° (corresponding to the phosphide phase) simultaneously, further confirming the successful synthesis of the heterojunction catalyst.

[0070] Combined with Figure 4 shown, it can be found by comparison that the binding energy of the Ni active sites in C@NFL / CCP is more moderate compared with that of Ce@NiFeLDH obtained in Comparative Example 1. This is because the introduction of the phosphide layer absorbs the excessive electron donation effect caused by the Ce dopant through the M1-O-M2 atomic interface, so that the electronic structure of the Ni active sites in the heterojunction catalyst is in the optimal state. This optimized electronic structure is beneficial to improving the charge transfer efficiency in the catalytic reaction, thereby endowing C@NFL / CCP with more excellent electrocatalytic activity.

[0071] Combined with Figure 5 and Figure 6 shown, at Figure 5Among them, the structure of the membrane electrode assembly is as follows: C@NFL / CCP prepared in Examples 1-3 is used as the anode, carbon felt is used as the cathode, the separator material at the center of the anode and the cathode is Nafion 117 proton exchange membrane, and the outer parts of the anode and the cathode are Gasket (sealing gasket) and Plate (bipolar plate) respectively. It can be seen from the figure that the electrocatalytic activity of the Ce@NiFeLDH / CoCuP heterojunction catalyst prepared in Example 1 is significantly better than that of Comparative Example 1 (Ce@NiFe LDH), Comparative Example 2 (CoCuP) and Comparative Example 3 (RuO2). In addition, the activities of Example 1 (Ce@NiFeLDH / CoCuP) and Example 3 (Ce@NiFeLDH / CoMoP) are similar, while the activity of Example 2 (Ce@NiFeLDH / CoVP) is slightly lower. These results indicate that the heterojunction strategy has a significant promoting effect on improving the catalytic activity of oilfield fracturing wastewater.

[0072] Combined with Figure 7 As shown, this result indicates that the catalyst has high purity in electrocatalytic hydrogen production from oilfield fracturing wastewater and good oxygen evolution selectivity.

[0073] Combined with Figure 8 As shown, during the continuous operation of the electrolysis system for 50 hours at a cell voltage of 1.5 V, the system can continuously output a stable current density without obvious performance decay. This result fully demonstrates that the catalyst has excellent electrochemical stability and shows its great potential in practical applications such as industrial oilfield fracturing wastewater.

[0074] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will all fall within the protection scope of the present invention.

Claims

1. Application of a hydroxide-phosphide heterojunction in electrolyzing high-chlorine oilfield fracturing wastewater, characterized in that, The preparation method of the hydroxide-phosphide heterojunction comprises the following steps: S100: Sequentially place the conductive carrier in acetone, HCl aqueous solution, ethanol and deionized water for ultrasonic cleaning, and after cleaning, put it into a vacuum drying oven for overnight drying; the conductive carrier is nickel foam; S200: Use the electrochemical deposition method to deposit metal phosphide on the conductive carrier obtained in step S100 to obtain a conductive carrier wrapped with metal phosphide; in the electrochemical deposition process, use a first precursor solution, and the first precursor solution is an ammonium salt, a phosphorus source and a metal source for preparing phosphide dissolved in deionized water; the metal phosphide is CoCuP, CoVP or CoMoP; S300: Use the electrochemical deposition method to deposit layered metal hydroxide on the conductive carrier wrapped with metal phosphide obtained in step S200 to obtain a conductive carrier wrapped with hydroxide-phosphide heterojunction; in the electrochemical deposition process, use a second precursor solution, and the second precursor solution is a metal source for preparing hydroxide dissolved in deionized water, and the hydroxide-phosphide heterojunction is Ce@NiFe LDH / CoCuP heterojunction, Ce@NiFe LDH / CoVP heterojunction or Ce@NiFe LDH / CoMoP heterojunction.

2. Application of a hydroxide-phosphide heterojunction in electrolyzing high-chlorine oilfield fracturing wastewater according to claim 1, characterized in that: Place the conductive carrier in acetone for ultrasonic cleaning for 10 min - 20 min, then place it in 1 mol / L HCl aqueous solution for ultrasonic cleaning for 10 min - 20 min, and finally ultrasonically clean it with ethanol and deionized water for 5 min - 15 min each, and then put it into a vacuum drying oven at 70 °C for overnight drying.

3. The application of a hydroxide-phosphide heterojunction according to claim 2 in electrolyzing high-chlorine oilfield fracturing wastewater, characterized in that: The ammonium salt is one or a combination of more than one of ammonium chloride, ammonium sulfate, ammonium nitrate or ammonium bicarbonate; the phosphorus source is one or a combination of more than one of sodium hydrogen phosphate, sodium dihydrogen phosphate, sodium hexametaphosphate, calcium hydrogen phosphate or sodium hypophosphite.

4. Use of a hydroxide-phosphide heterojunction according to claim 3 in electrolyzing high-chlorine oilfield fracturing wastewater, characterized in that: The ratio of the ammonium salt, the phosphorus source and the metal source for preparing phosphide is 1:1 - 60:

1.

5. Use of a hydroxide-phosphide heterojunction according to claim 4 in electrolyzing high-chlorine oilfield fracturing wastewater, characterized in that: The ammonium salt is 0.3 mol / L NH4Cl solution, the phosphorus source is 1.0 mol / L NaPO2H2 solution, and the metal source for preparing phosphide is 50 mmol / L CoCl2 solution, 50 mmol / L CuCl2 solution and 10 mmol / L C2H3NaO2 electrolyte aqueous solution.

6. Use of a hydroxide-phosphide heterojunction according to claim 5 in electrolyzing highly chlorinated oilfield fracturing wastewater, characterized in that: In step S200 and step S300, the electrochemical deposition method is constant current deposition or constant voltage deposition.

7. Use of a hydroxide-phosphide heterojunction according to claim 6 in electrolyzing high-chlorine oilfield fracturing wastewater, characterized in that: In step S200, the electrochemical deposition method is constant current deposition, which is carried out in a two-electrode system. Using a Ti sheet as the counter electrode and a clean blank NF as the working electrode, deposit at a constant current. During the deposition process, continuously stir. After the deposition is completed, repeatedly rinse the working electrode 3 times with ethanol and deionized water, and then place it in a vacuum drying oven at 70 °C for overnight drying to obtain a conductive carrier wrapped with metal phosphide.

8. Use of a hydroxide-phosphide heterojunction according to claim 7 in electrolyzing high-chlorine oilfield fracturing wastewater, characterized in that: In step S300, the electrochemical deposition method is constant voltage deposition, which is carried out in a three-electrode system. A Pt sheet is used as the counter electrode, a conductive carrier wrapped with metal phosphide is used as the working electrode, and Ag / AgCl is used as the reference electrode for deposition under constant voltage. During the deposition process, continuous stirring is carried out. After the deposition is completed, the working electrode is repeatedly rinsed 3 times with ethanol and deionized water, and then placed in a vacuum drying oven at 70 °C for overnight drying to obtain the hydroxide-phosphide heterojunction.

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