Hydroxide-phosphide heterojunction, preparation method thereof and application of hydroxide-phosphide heterojunction in electrolysis of high-chlorine-content oilfield fracturing wastewater

Abstract

The invention provides a hydroxide-phosphide heterojunction, a preparation method thereof and application of the hydroxide-phosphide heterojunction in electrolysis of high-chlorine-content oilfield fracturing wastewater, and belongs to the field of electrolysis of oilfield wastewater. The problems that existing oilfield wastewater treatment is difficult, treatment equipment is prone to corrosion due to high-concentration chloride ions, energy consumption is high, and economic cost is high are solved. The method comprises the following steps: cleaning and drying a conductive carrier; performing metal phosphide deposition on the conductive carrier by using an electrochemical deposition method; and carrying out layered metal hydroxide deposition on the conductive carrier coated with the metal phosphide by using an electrochemical deposition method to obtain the conductive carrier coated with the hydroxide-phosphide heterojunction. The method is simple, efficient and low in cost, the oxygen evolution reaction catalyst which is more efficient than a single phosphide and a layered metal hydroxide can be prepared, and the oxygen evolution reaction catalyst has a good inhibition effect on the chlorine evolution reaction, so that generation of high-corrosivity chlorine-containing byproducts is slowed down.

Description

Technical Field

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

[0002] With the continuous growth of global energy demand, the problem of wastewater generated during oil extraction has attracted wide attention. Especially the wastewater generated during oilfield fracturing, which usually contains a large amount of suspended solids, organic matter, heavy metal ions, and high concentrations of 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 also hydrogen can 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: To solve the problem that the existing oilfield wastewater treatment is difficult, and the high concentration of chloride ions will cause the treatment equipment to be prone to corrosion, high energy consumption, and high economic cost.

[0006] The technical solution adopted by the present invention to solve the above technical problem: The present invention provides a preparation method of a hydroxide-phosphide heterojunction, comprising the following steps: S100. Place the conductive carrier in acetone, aqueous HCl solution, ethanol, and deionized water in sequence for ultrasonic cleaning. After cleaning, put it into a vacuum drying oven for overnight drying; S200. Deposit metal phosphide on the conductive carrier obtained in step S100 by electrochemical deposition method 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; S300. Deposit layered metal hydroxide on the conductive carrier coated with metal phosphide obtained in step S200 by electrochemical deposition method 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.

[0007] The metal source for preparing phosphide and the metal source for preparing hydroxide are each one or more combinations of metal element chlorides, nitrates, sulfates, or acetates; further define that the metal source for preparing phosphide is 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, where the metal source for preparing hydroxide is mainly nitrate, and further define its types as Ni(NO 3 ) 2 ·6H 2 O, Fe(NO 3 ) 3 ·9H 2 O, Ce(NO 3 ) 3 ·6H 2 O, La(NO 3 ) 3 ·6H 2 O, Al(NO 3 ) 3 ·9H 2 O, KNO 3 。

[0008] 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.

[0009] Further, in step S100, the conductive carrier is ultrasonically cleaned in acetone for 10 min - 20 min, then ultrasonically cleaned in 1 mol / L HCl aqueous solution for 10 min - 20 min, and finally ultrasonically cleaned in ethanol and deionized water for 5 min - 15 min each, and then placed in a vacuum drying oven at 70 °C for drying overnight.

[0010] Further, 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.

[0011] Further, the ratio of the ammonium salt, the phosphorus source, and the metal source for preparing the phosphide is 1:1 - 60:1.

[0012] Further, the ammonium salt is a 0.3 mol / L NH 4 Cl solution, the phosphorus source is a 1.0 mol / L NaPO 2 H 2 solution, and the metal source for preparing the phosphide is a 50 mmol / L CoCl 2 solution, a 50 mmol / L CuCl 2 solution, and a 10 mmol / L C 2 H 3 NaO 2 aqueous electrolyte solution.

[0013] Further, in steps S200 and S300, the electrochemical deposition method is 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 in both cases.

[0014] Further, in step S200, the electrochemical deposition method is constant current deposition, which is carried out in a two - electrode system. A Ti sheet is used as the counter electrode, and a clean blank NF is used as the working electrode. Deposition is carried out under a constant current, and 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 drying overnight, and thus a conductive carrier coated with metal phosphide can be obtained.

[0015] Further, 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.

[0016] 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.

[0017] Further, the present invention protects a hydroxide-phosphide heterojunction prepared by the above-mentioned preparation method.

[0018] Further, the present invention protects an application of the hydroxide-phosphide heterojunction in electrolyzing high-chlorine oilfield fracturing wastewater.

[0019] (1) The material synthesis technology only needs a simple two-step electrodeposition method to synthesize the layered metal hydroxide / phosphide heterojunction catalyst, 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.

[0020] (2) During the synthesis process, the layered metal hydroxide grows on the surface of the transition metal phosphide and forms an M 1 -O-M 2 atomic interface (M 1 and M 2 are the metal elements in the layered metal hydroxide and the transition metal phosphide respectively), enhancing the stability of the heterojunction catalyst.

[0021] (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.

[0022] (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.

[0023] (5) In the heterojunction catalyst, the phosphide acts as an electron buffer layer, which can optimize the electronic structure of the active species layered metal hydroxide, which is the fundamental reason for achieving the improvement of the oxygen evolution reaction activity and effectively inhibiting the chlorine evolution reaction.

[0024] (6) The heterojunction catalyst has good structural tunability, and different types of heterojunction catalysts can be synthesized by changing the types of metal elements.

[0025] (7) According to experiments, a heterojunction catalyst Ce@NiFeLDH / CoCuP(98.5%) was prepared by a two-step electrodeposition method. Compared with the individual phosphide (85.7%) or metal hydroxide (92.4%), its oxygen evolution chlorine resistance performance was significantly improved, providing an efficient and robust anode catalyst for electrolyzing oilfield fracturing wastewater. Description of the Drawings

[0026] Figure 1 It is a 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; Figure 2 It is an energy dispersive spectroscopy (EDS) analysis image of each element in the Ce@NiFeLDH / CoCuP heterojunction catalyst prepared in Example 1 of the present invention. Among them, Energy is used to qualitatively identify the element types, and cps is used to semi-quantitatively reflect the relative content of the elements; Figure 3 It is the X-ray diffraction (XRD) spectra of the Ce@NiFeLDH / CoCuP, Ce@NiFeLDH, and CoCuP catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2. Among them, 2Theta is the diffraction angle, and Intensity is the photoelectron signal intensity; Figure 4 It is the X-ray photoelectron spectroscopy (XPS) analysis result images 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 image of the Ni active site, (b) is the X-ray photoelectron spectroscopy image of the Co active site, Binding energy is the binding energy, and Intensity is the photoelectron signal intensity; Figure 5 It is a schematic diagram of the electrolysis device used in the present invention to fully decompose oilfield fracturing wastewater; Figure 6 It is the polarization curve graph of the overall water splitting experiment using the membrane electrode assembly in Examples 1-3 and Comparative Examples 1-3 of the present invention; Figure 7 It is the chromatogram of the cathode product H 2 after the overall water splitting experiment of Ce@NiFeLDH / CoCuP prepared in Example 1 of the present invention in the membrane electrode assembly; Figure 8This is the stability test result diagram of Ce@NiFeLDH / CoCuP in the MEA component in Example 1 of the present invention. Detailed implementation mode

[0027] 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 in conjunction with the accompanying drawings.

[0028] Example 1: A preparation method of a hydroxide-phosphide heterojunction, specifically including: S100. Place commercial nickel foam (size 1 cm * 2 cm * 1 mm) in acetone and ultrasonically clean for 15 min, then place it in 1 mol / L HCl aqueous solution and ultrasonically clean for 15 min. Finally, ultrasonically clean with ethanol and deionized water for 10 min each, and then put it into a vacuum drying oven at 70 °C to dry overnight to obtain the treated nickel foam. 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 CoCl 2 , 50 mmol / L CuCl 2 , 0.3 mol / L NH 4 Cl, 1.0 mol / L NaPO 2 H 2 and 10 mmol / L C 2 H 3 NaO 2 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 for 2 min; continuously stir during the deposition process. After the deposition is completed, repeatedly rinse the working electrode with ethanol and deionized water 3 times, and then place it in a vacuum drying oven at 70 °C to dry overnight to obtain the CoCuP electrode. 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 Ni(NO) 3 , 10 mmol / L Fe(NO) 3 and 4 mmol / L Ce(NO) 3 as the precursor solution, use a Pt sheet as the counter electrode, CoCuP / NF as the working electrode, 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 with ethanol and deionized water 3 times, and then place it in a vacuum drying oven at 70 °C to dry overnight to obtain the Ce@NiFe LDH / CoCuP heterojunction catalyst.

[0029] Example 2: A method for preparing a hydroxide-phosphide heterojunction, specifically including: S100. Place commercial nickel foam (with dimensions of 1 cm * 2 cm * 1 mm) in acetone and ultrasonically clean it for 15 min, then 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 and dry it overnight at 70 °C to obtain the treated nickel foam. S200. The phosphide is deposited by constant current deposition in a two-electrode system. Prepare an electrolyte aqueous solution containing 50 mmol / L CoCl 2 , 50 mmol / L NH 4 VO 3 , 0.3 mol / L NH 4 Cl, 1.0 mol / L NaPO 2 H 2 and 10 mmol / L C 2 H 3 NaO 2 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 for 2 min. Continuously stir during the deposition process. After the deposition is completed, repeatedly rinse the working electrode with ethanol and deionized water 3 times, and then place it in a vacuum drying oven at 70 °C and dry it overnight to obtain the CoVP electrode. S300. The layered metal hydroxide is deposited by constant voltage deposition in a three-electrode system. Prepare an electrolyte aqueous solution containing 30 mmol / L Ni(NO) 3 , 10 mmol / L Fe(NO) 3 and 4 mmol / L 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 min. Continuously stir during the deposition process. After the deposition is completed, repeatedly rinse the working electrode with ethanol and deionized water 3 times, and then place it in a vacuum drying oven at 70 °C and dry it overnight to obtain the Ce@NiFe LDH / CoVP heterojunction catalyst.

[0030] Example 3: A method for preparing a hydroxide-phosphide heterojunction, specifically including: S100. Place commercial nickel foam (sized 1 cm * 2 cm * 1 mm) in acetone and ultrasonically clean it for 15 min. Subsequently, place it in 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; S200. The way to deposit phosphide is by constant current deposition, carried out in a two - electrode system; Prepare an electrolyte aqueous solution containing 50 mmol / L of CoCl 2 , 50 mmol / L of Na 2 MoO 4 , 0.3 mol / L of NH 4 Cl, 1.0 mol / L of NaPO 2 H 2 and 10 mmol / L of C 2 H 3 NaO 2 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 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 CoMoP electrode; S300. The way to deposit layered metal hydroxide is by constant voltage deposition, 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, 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 / CoMoP heterojunction catalyst.

[0031] Comparative Example 1: A preparation method of a Ce@NiFe LDH oxygen evolution electrocatalyst, including the following steps: The way to deposit the Ce@NiFe LDH electrode is by constant voltage deposition, 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) 3An aqueous electrolyte solution was used as the precursor solution. A Pt sheet was used as the counter electrode, a clean NF was used as the working electrode, and Ag / AgCl was used as the reference electrode. Deposition was carried out at a constant voltage of -1 V for 10 min. Stirring was continued during the deposition process. After deposition, the working electrode was repeatedly rinsed 3 times with ethanol and deionized water, and then placed in a vacuum drying oven at 70 °C and dried overnight to obtain the Ce@NiFe LDH electrode.

[0032] Comparative Example 2: A method for preparing a CoCuP oxygen evolution electrocatalyst, comprising the following steps: The CoCuP electrode was deposited by constant current deposition in a two-electrode system. An aqueous electrolyte solution containing 50 mmol / L CoCl 2 , 50 mmol / L Na 2 MoO 4 , 0.3 mol / L NH 4 Cl, 1.0 mol / L NaPO 2 H 2 and 10 mmol / L C 2 H 3 NaO 2 was used as the precursor solution; a Ti sheet was used as the counter electrode, a clean blank NF was used as the working electrode, and deposition was carried out at a constant current of -25 mA cm -2 for 2 min. Stirring was continued during the deposition process. After deposition, the working electrode was repeatedly rinsed 3 times with ethanol and deionized water, and then placed in a vacuum drying oven at 70 °C and dried overnight to obtain the CoCuP electrode.

[0033] Comparative Example 3: A method for preparing a RuO 2 oxygen evolution electrocatalyst, comprising the following steps: 10 mg of RuO 2 powder and 30 μL of 5 wt.% Nafion solution were dispersed in 970 μL of absolute ethanol and sonicated for at least 30 min to obtain a uniform mixture. Subsequently, 50 μL of the mixture was dropped onto a 1 cm * 2 cm nickel foam and the operation was repeated twice, and then placed in a vacuum drying oven at 70 °C for drying and waiting for measurement.

[0034] Comparative experiments The catalysts prepared in Examples 1-3 and Comparative Examples 1-3 were used for electrocatalytic oxygen evolution reaction in oilfield fracturing wastewater containing 1 mol / L KOH. The specific test conditions were as follows: electrocatalytic oxygen evolution and chlorine resistance performance tests were carried out in a standard three-electrode system; the oilfield fracturing wastewater was taken from the fracturing flowback fluid of Daqing Gulong shale oil; the carbon rod was used as the counter electrode, Hg / HgO was used as the reference electrode, and the catalyst supported on nickel foam was used as the working electrode; the polarization curve scanning range was 1-2 V (relative to the reversible hydrogen electrode), and the scanning rate was 5 mV / s; the oxygen evolution chlorine resistance performance was evaluated by testing the Faraday efficiency of oxygen after constant current electrolysis, and the results are shown in Table 1.

[0035] The catalysts prepared in Examples 1-3 and Comparative Examples 1-3 were used as the anode, and the carbon felt was used as the cathode to carry out the overall water splitting reaction in a membrane electrode assembly. The diaphragm material was Nafion 117 proton exchange membrane. The specific test conditions were as follows: the effective areas of the anode and cathode were 2 cm 2 , and the oilfield fracturing wastewater electrolyte containing 1 mol / L KOH was pumped into the serpentine flow channels of the anode and cathode plates at a flow rate of 50 mL / min by a dual-channel peristaltic pump; the polarization curve test condition was 20 mV / s; after electrolysis at 2.0 V for 10 min, the cathode gas product was collected, and the purity of the hydrogen product was tested by gas chromatography, and the results are shown in Table 2.

[0036] Table 1 Summary of electrocatalytic oxygen evolution chlorine resistance performance results

[0037] 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 after the electrolysis is completed, the Faraday efficiency of O 2 is calculated.

[0038] Table 2 Summary of overall water splitting of oilfield fracturing wastewater test results in the membrane electrode assembly

[0039] 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 after the electrolysis is completed, the Faraday efficiency of O 2 is calculated.

[0040] Combined with Figure 1 As shown, the surface of the catalyst synthesized by the method of Example 1 has a relatively high roughness. This surface morphological feature has dual 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 reactant molecules on the catalyst surface, thereby increasing the overall reaction rate. This unique surface structure feature provides favorable conditions for optimizing the performance of the catalyst.

[0041] Combined with Figure 2 As 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.

[0042] Combined with Figure 3 As shown, the XRD pattern of Ce@NiFeLDH / CoCuP contains the characteristic peaks at 23.2°, 34.1°, 59.9° (corresponding to the LDH phase), 23.4°, 43.7°, and 27.6° (corresponding to the phosphide phase) simultaneously, further confirming the successful synthesis of the heterojunction catalyst.

[0043] Combined with Figure 4 As shown, through comparison, it can be found that the binding energy of the Ni active sites in C@NFL / CCP is more moderate compared to 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 M 1 -O-M 2 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.

[0044] Combined with Figure 5 and Figure 6 As shown, in Figure 5 , the structure of the membrane electrode assembly is: C@NFL / CCP prepared in Examples 1-3 is used as the anode, carbon felt is used as the cathode, the separator material in the center of the anode and cathode is Nafion 117 proton exchange membrane, and the outer parts of the anode and cathode are Gasket (sealing gasket) and Plate (bipolar plate) respectively. As can be seen from the figure, the electrochemical 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 (RuO 2). 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 enhancing the catalytic activity of oilfield fracturing wastewater.

[0045] Combined with Figure 7 as shown, this result indicates that the catalyst has a high purity for electrocatalytic hydrogen production from oilfield fracturing wastewater and good oxygen evolution selectivity.

[0046] 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 degradation. This result fully demonstrates the excellent electrochemical stability of the catalyst and shows its great potential in practical applications such as industrial oilfield fracturing wastewater.

[0047] 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. A method for preparing a hydroxide-phosphide heterojunction, characterized in that: The following steps are involved: S100, placing the conductive carrier in acetone, HCl aqueous solution, ethanol and deionized water in turn for ultrasonic cleaning, and after cleaning, placing it in a vacuum drying oven for overnight drying; S200, depositing metal phosphide on the conductive carrier obtained in step S100 by an electrochemical deposition method to obtain a conductive carrier coated with metal phosphide; Using a first precursor solution in the electrochemical deposition process, the first precursor solution is an ammonium salt, a phosphorus source, and a metal source for preparing a phosphide dissolved in deionized water; S300, using an electrochemical deposition method to deposit a layered metal hydroxide on the conductive carrier coated with the metal phosphide obtained in step S200 to obtain a conductive carrier coated with a hydroxide-phosphide heterojunction; A second precursor solution is used during the electrochemical deposition process, which is a metal source for preparing the hydroxide dissolved in deionized water.

2. The method for preparing a hydroxide-phosphide heterojunction according to claim 1, characterized in that: 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. The conductive carrier is ultrasonically cleaned in acetone for 10 min to 20 min, then ultrasonically cleaned in a 1 mol / L HCl aqueous solution for 10 min to 20 min, and finally ultrasonically cleaned in ethanol and deionized water for 5 min to 15 min respectively, and then placed in a vacuum drying oven at 70° C. for drying overnight.

3. The method for preparing a hydroxide-phosphide heterojunction according to claim 2, characterized in that: 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 sodium monohydrogen phosphate, sodium dihydrogen phosphate, sodium hexametaphosphate, calcium hydrogen phosphate or sodium hypophosphite; the metal source used to prepare the phosphide and the metal source used to prepare the hydroxide are both one or more combinations of chlorides, nitrates, sulfates, nitrites, carbonates or acetates of metal elements, the metal element in the metal source used to prepare the phosphide is Co, Cu, Mo, V, Cr or Mn, and the metal element in the metal source used to prepare the hydroxide is Ni, Fe, Ce, La, Al or K.

4. The method for preparing a hydroxide-phosphide heterojunction according to claim 3, characterized in that: The ratio of the ammonium salt, the phosphorus source and the metal source for preparing the phosphide is 1:1-60:

1.

5. The method for preparing a hydroxide-phosphide heterojunction according to claim 4, characterized in that: 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 sources used to prepare the phosphide are a 50 mmol / L CoCl2 solution, a 50 mmol / L CuCl2 solution and a 10 mmol / L C2H3NaO2 electrolyte aqueous solution.

6. The method for preparing a hydroxide-phosphide heterojunction according to claim 5, characterized in that: In step S200 and step S300, the electrochemical deposition method is constant current deposition or constant voltage deposition.

7. The method for preparing a hydroxide-phosphide heterojunction according to claim 6, characterized in that: In step S200, the electrochemical deposition method is constant current deposition, which is carried out in a two-electrode system, with a Ti sheet as a counter electrode and a clean blank NF as a working electrode. Deposition is carried out under constant current, and stirring is continued 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 70°C vacuum drying oven to dry overnight to obtain a conductive carrier coated with a metal phosphide.

8. The method for preparing a hydroxide-phosphide heterojunction according to claim 7, characterized in that: In step S300, the electrochemical deposition method is constant voltage deposition, which is carried out in a three-electrode system, with a Pt sheet as a counter electrode, a conductive carrier wrapped with a metal phosphide as a working electrode, and Ag / AgCl as a reference electrode, and deposition is performed under constant voltage; stirring is continued during the deposition process, and after the deposition is completed, the working electrode is repeatedly rinsed 3 times with ethanol and deionized water, and then placed in a 70°C vacuum drying oven for overnight drying to obtain a hydroxide-phosphide heterojunction.

9. A hydroxide-phosphide heterojunction, wherein the hydroxide-phosphide heterojunction is prepared by the method according to any one of claims 1 to 8.

10. Use of the hydroxide-phosphide heterojunction as claimed in claim 9 in electrolysis of high-chlorine oilfield fracturing wastewater.

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