A method for preparing and applying a copper-titanium oxide composite electrode for the electrocatalytic reduction of nitrate to ammonia.

Abstract

This invention provides a method for preparing a copper-titanium oxide composite electrode for the electrocatalytic reduction of nitrate to ammonia and its application, relating to the fields of electrocatalytic materials and water pollution resource treatment technology. The method includes: preparing a titanium oxide support using a titanium source as raw material; constructing oxygen vacancies on the surface of the titanium oxide through reduction treatment; subsequently reducing the copper source to generate copper oxide in situ on the surface of the oxygen-vacancy-containing titanium oxide, forming a copper-titanium oxide composite catalyst with an interfacial coupling structure; and finally loading it onto a conductive substrate surface using a binder to obtain the composite electrode. This invention improves the adsorption and activation capacity of nitrate and the charge transport efficiency through the synergistic effect of the copper oxide active sites, the oxygen-vacancy-containing titanium oxide support, and the interfacial coupling structure, thereby enhancing the Cu... + The stability of the active center improves ammonia yield, nitrate removal efficiency, and cycle stability. The process of this invention is simple, the conditions are mild, and the repeatability is good, enabling the removal of nitrate pollutants and the resource recovery of ammonia.

Description

Technical Field

[0001] This invention relates to the fields of electrocatalytic materials and water pollution resource utilization technology, and in particular to a method for preparing and applying a copper-titanium oxide composite electrode for electrocatalytic reduction of nitrate to ammonia. Background Technology

[0002] With the continuous growth of energy demand and the increasing prominence of environmental pollution, the development of green and efficient energy conversion and pollution control technologies has become an important research direction. Ammonia (NH3), as an important basic chemical raw material and a potential clean energy carrier, has wide applications in agriculture, chemical industry, and energy. The traditional Haber-Bosch ammonia synthesis process requires high temperature and high pressure conditions, resulting in high energy consumption, large carbon emissions, and demanding equipment requirements, making it difficult to meet the requirements of green and low-carbon development. In contrast, electrocatalytic reduction of nitrates to ammonia can be carried out under ambient temperature and pressure conditions, achieving not only the green synthesis of ammonia but also the simultaneous resource-based conversion of nitrate pollutants, demonstrating significant application prospects.

[0003] In the electrocatalytic reduction of nitrate, the structure and electronic properties of the catalytic material have a decisive influence on the reaction performance. Copper-based materials, due to the energy matching between their d orbitals and the LUMO π* orbitals of the nitrate molecule, exhibit better intrinsic nitrate reduction activity, especially Cu. + Species play a crucial role in the initial reduction step of nitrate. However, single copper-based materials are prone to dissolution, aggregation, and valence state changes during electrochemical reactions, leading to instability of active sites and thus affecting catalytic performance and lifespan. Summary of the Invention

[0004] This invention proposes a method for preparing a copper-titanium oxide composite electrode for electrocatalytic reduction of nitrate to ammonia and its application, aiming to solve the problems of dissolution and aggregation, and instability of active sites caused by valence state changes in existing copper-based catalysts during the electrocatalytic reduction of nitrate to ammonia.

[0005] In a first aspect, the present invention provides a method for preparing a copper-titanium oxide composite electrode for the electrocatalytic reduction of nitrate to ammonia, comprising the following steps: Step S1: Add the titanium source to anhydrous ethanol and mix. After adding hydrofluoric acid aqueous solution dropwise, carry out a hydrothermal reaction to obtain titanium dioxide support. Step S2: The TiO2 support is mixed with sodium borohydride and then calcined under an inert atmosphere to obtain an oxygen-rich vacancy TiO2-x support; Step S3: Add the oxygen-rich vacancy TiO2-x support to the reaction solution containing the copper source precursor, and add polyvinylpyrrolidone, sodium hydroxide and ascorbic acid to react, so that the copper source precursor is transformed in situ on the surface of the oxygen-rich vacancy titanium dioxide support to obtain Cu2O / TiO2-x composite catalyst. Step S4: The Cu2O / TiO2-x composite catalyst is mixed with a binder and a solvent to form a catalyst dispersion, and the catalyst dispersion is loaded onto the surface of a conductive substrate. After drying, the oxygen-rich TiO2-supported Cu2O composite electrode is obtained.

[0006] Specifically, this invention prepares a TiO2 support using a titanium source as raw material. Oxygen vacancies are constructed on the surface of the TiO2 support through sodium borohydride reduction treatment. Subsequently, polyvinylpyrrolidone, sodium hydroxide, and ascorbic acid are introduced into a reaction system containing a copper source precursor, causing Cu2O to be generated and loaded in situ on the surface of the oxygen-vacancy-rich TiO2-x support, forming a Cu2O / TiO2-x composite catalyst with a tightly coupled interfacial structure. Finally, it is loaded onto a conductive substrate surface using a binder to obtain an oxygen-vacancy-rich TiO2-supported Cu2O composite electrode. This invention improves the nitrate adsorption activation capacity and charge transport efficiency through the synergistic effect of copper oxide active sites, oxygen-vacancy-rich titanium oxide support, and interfacial coupling structure, thereby enhancing Cu… + The stability of the active site is improved, thereby enhancing the ammonia yield, nitrate removal efficiency, and cycle stability in the electrocatalytic reduction of nitrate to ammonia.

[0007] Further, the titanium source in step S1 is selected from one or more of titanate titanium sources, inorganic titanium salt titanium sources, titanium oxy salt titanium sources, titanate titanium sources, and titanium sol; wherein the titanate titanium source includes one or more of tetrabutyl titanate, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, and tetraisobutyl titanate.

[0008] Further, in step S1, based on the Ti element in the titanium source, every 0.005~0.05 mol Ti corresponds to 15~50 mL of anhydrous ethanol and 0.5~3.0 mL of hydrofluoric acid aqueous solution; the hydrothermal reaction temperature is 160~200℃, and the reaction time is 8~16h.

[0009] Further, in step S2, the mass ratio of TiO2 support to sodium borohydride is 1:0.5~1.0; the calcination temperature is 250~350 ℃, and the holding time is 30~90 min; the inert atmosphere is argon or nitrogen.

[0010] Furthermore, the copper source precursor mentioned in step S3 is selected from one or more of copper chloride, copper nitrate, copper sulfate, copper acetate, cuprous chloride, or their hydrates.

[0011] Further, in step S3, the components are as follows by mass: 1 part by mass of oxygen-rich vacancy titanium dioxide carrier, 0.15-2.0 parts by mass of copper source precursor (based on the mass of copper element), 50-150 parts by mass of polyvinylpyrrolidone, 4-12 parts by mass of sodium hydroxide (based on the solute), and 5-15 parts by mass of ascorbic acid (based on the solute); the reaction temperature is 45-65 ℃, and the reaction time is 2-5 h.

[0012] Further, the conductive substrate in step S4 is one of carbon cloth, carbon paper, nickel foam, or conductive titanium mesh, and the adhesive is one of Nafion, polyvinylidene fluoride, or polytetrafluoroethylene.

[0013] Further, in step S4, the dispersion is composed of ethanol, water, Cu2O / TiO2-x composite catalyst and binder, wherein the volume ratio of ethanol to water is 1:0.5 to 1:2, the concentration of Cu2O / TiO2-x composite catalyst in the dispersion is 2 to 20 mg / mL, and the concentration of the effective component of the binder in the dispersion is 2 to 10 mg / mL.

[0014] Secondly, the present invention provides an oxygen-vacancy titanium dioxide-supported cuprous oxide composite electrode prepared by the above preparation method, comprising a conductive substrate and a composite catalytic active layer supported on the surface of the conductive substrate, wherein the composite catalytic active layer is composed of a Cu2O / TiO2-x composite catalyst and a binder.

[0015] Thirdly, the present invention provides an application of the above-mentioned oxygen-enriched vacancy titanium dioxide supported cuprous oxide composite electrode in the electrocatalytic reduction of nitrate to ammonia. The oxygen-enriched vacancy titanium dioxide supported cuprous oxide composite electrode is used as the working electrode for the electrocatalytic reduction treatment of nitrate-containing water bodies, so as to convert nitrate into ammonia or ammonium salt; the nitrate-containing water body is one or more of nitrate-containing wastewater, groundwater, surface water or experimental simulated water bodies.

[0016] Compared with the prior art, the present invention has the following advantages: This invention prepares a TiO2 support using titanium as a raw material and constructs an oxygen-rich vacancy TiO2-x support through sodium borohydride reduction treatment. This modulates the surface electronic structure of TiO2, enhancing its adsorption and activation capacity for nitrate molecules and its charge transport ability. The invention utilizes an in-situ generation method to load Cu2O onto the oxygen-rich vacancy TiO2-x surface, which improves the dispersibility and loading stability of the Cu2O active component and reduces the possibility of agglomeration and detachment. The Cu2O / TiO2-x heterointerface constructed in this invention enhances the interfacial coupling between Cu2O and TiO2-x, promotes interfacial charge transfer, reduces charge transport resistance, and improves the kinetics of nitrate reduction. In the composite electrode obtained by this invention, Cu2O provides nitrate reduction active sites, while the oxygen-rich vacancy TiO2-x provides a stable support and adsorption activation sites; their synergistic effect enhances the Cu2O / TiO2-x adsorption and activation capacity. + The active center is stable, improving ammonia yield, nitrate removal efficiency, and cycle stability. Furthermore, the preparation process of this invention is simple, the reaction conditions are mild, and the resulting composite electrode can be used in the electrocatalytic reduction of nitrate-containing water to produce ammonia, achieving nitrate pollutant removal and nitrogen resource recovery, demonstrating promising application prospects.

[0017] Based on the implementation methods provided in the above aspects, this application can be further combined to provide more implementation methods. Attached Figure Description

[0018] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, with the same or corresponding reference numerals denoteing the same or corresponding parts, wherein: Figure 1 High-resolution transmission electron microscopy (HRTEM) image of the Cu2O / TiO2-x composite catalyst provided by this invention; Figure 2 The XRD pattern of the Cu2O / TiO2-x composite catalyst provided by this invention; Figure 3 NO3 obtained by constant potential electrolysis for 2 h using the Cu2O / TiO2-x composite electrode provided by this invention - Graph showing the relationship between -N concentration and ammonia selectivity; Figure 4 A comparison chart of ammonia yields after constant potential electrolysis for 2 h using different Cu2O / TiO2-x composite electrodes and single-component electrodes provided by the present invention; Figure 5 Cyclic stability test results for the Cu2O / TiO2-x composite electrode provided by this invention. Detailed Implementation

[0019] The exemplary embodiments disclosed in this application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of this application and to fully convey the scope of this application to those skilled in the art. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0020] TiO2 materials possess good chemical stability and certain carrier transport capabilities, making them suitable for use as catalyst supports. Among them, oxygen-vacancy-rich TiO2-x not only modulates the electronic structure of the material but also enhances its adsorption capacity for nitrate molecules and, to some extent, suppresses the hydrogen evolution side reaction, thus improving the selectivity for ammonia formation. Therefore, combining copper-based active components with TiO2 supports is considered an effective strategy for improving electrocatalytic performance.

[0021] Composites of Cu₂O and oxygen-vacancy-rich TiO₂-x can form a Cu₂O / TiO₂-x heterostructure. This heterostructure facilitates interfacial charge transfer, enhances the interaction between the active component and the support, and improves the efficiency of Cu₂O. + The stability of the active center during the electrocatalytic reaction process. Meanwhile, Cu₂O provides active sites for nitrate reduction, and oxygen-rich vacancies in TiO₂-x enhance nitrate adsorption and activation capacity and support stability. The synergistic effect between the two contributes to improving the efficiency of nitrate reduction for ammonia production.

[0022] This invention provides a method for preparing a copper-titanium oxide composite electrode for the electrocatalytic reduction of nitrate to ammonia, comprising the following steps: Step S1: Add the titanium source to anhydrous ethanol and mix. After adding hydrofluoric acid aqueous solution dropwise, carry out a hydrothermal reaction to obtain TiO2 support. Step S2: The TiO2 support is mixed with sodium borohydride and then calcined under an inert atmosphere to obtain an oxygen-rich vacancy TiO2-x support; Specifically, by mixing sodium borohydride with a TiO2 support and calcining it under an inert atmosphere, the reducing effect of sodium borohydride during heat treatment can be used to regulate defects on the TiO2 support surface, thereby constructing an oxygen vacancy structure on the TiO2 support surface to obtain an oxygen-vacancy-rich TiO2-x support. The introduction of oxygen vacancies can regulate the surface electronic structure of TiO2, improve the electron transport capacity of the support, and enhance its adsorption and activation of nitrate molecules. At the same time, the defect sites on the surface of the oxygen-vacancy-rich TiO2-x support are conducive to the adsorption, nucleation, and in-situ transformation of subsequent copper source precursors on its surface, improving the dispersibility and loading stability of the Cu2O active component, reducing Cu2O agglomeration and shedding, thus contributing to improving the nitrate reduction activity and cycle stability of the composite electrode.

[0023] Step S3: Add the oxygen-rich vacancy titanium dioxide support to the reaction solution containing the copper source precursor, and add polyvinylpyrrolidone, sodium hydroxide and ascorbic acid to react, so that the copper source precursor is transformed in situ on the surface of the oxygen-rich vacancy titanium dioxide support to obtain Cu2O / TiO2-x composite catalyst. Step S4: The Cu2O / TiO2-x composite catalyst is mixed with a binder and a solvent to form a catalyst dispersion, and the catalyst dispersion is loaded onto the surface of a conductive substrate. After drying, the oxygen-rich TiO2-supported Cu2O composite electrode is obtained.

[0024] Optionally, the titanium source in step S1 is selected from one or more of titanate titanium sources, inorganic titanium salt titanium sources, titanium oxy salt titanium sources, titanate titanium sources, and titanium sol; wherein the titanate titanium source includes one or more of tetrabutyl titanate, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, and tetraisobutyl titanate.

[0025] Specifically, the titanium source is a titanium-containing precursor that can form a TiO2 support through hydrolysis or hydrothermal conversion in an alcohol system or an alcohol-water system, and is not limited to titanate titanium sources; the titanium source is selected from one or more of titanate titanium sources, inorganic titanium salt titanium sources, titanium oxy salt titanium sources, titanate titanium sources, and titanium sol. The titanium ester source includes one or more of tetrabutyl titanate, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, and tetraisobutyl titanate; the inorganic titanium salt source includes one or more of titanium tetrachloride, titanium trichloride, and titanium sulfate; the titanium oxychloride source includes one or more of titanium oxysulfate and titanium oxychloride; and the titanium acid source includes one or more of metatitanic acid and titanic acid. The titanium sol comprises a sol system containing titanium dioxide colloidal particles, hydrated titanium dioxide colloidal particles, metatitanic acid colloidal particles, or peroxytitanic acid colloidal particles. The titanium sol can be one or more of aqueous titanium sol, alcoholic titanium sol, acidic titanium sol, neutral titanium sol, or alkaline titanium sol. For different types of titanium sources, the amount of anhydrous ethanol and hydrofluoric acid aqueous solution added can be adjusted according to the molar amount of Ti element to obtain a TiO2 support.

[0026] Optionally, in step S1, based on the Ti element in the titanium source, every 0.005~0.05 mol Ti corresponds to 15~50 mL of anhydrous ethanol and 0.5~3.0 mL of hydrofluoric acid aqueous solution; the hydrothermal reaction temperature is 160~200℃, and the reaction time is 8~16 h.

[0027] Specifically, the titanium source and hydrofluoric acid aqueous solution undergo a hydrothermal reaction. On the one hand, this promotes the hydrolysis, condensation, and crystallization of the titanium source, leading to the formation of a structurally stable TiO2 support. On the other hand, the fluoride ions in the hydrofluoric acid aqueous solution can play a role in complexation, etching, and crystal facet regulation during the hydrothermal process, which is beneficial for adjusting the morphology, crystal facet exposure, and number of surface active sites of the TiO2 support. By controlling the dosage range of the titanium source, anhydrous ethanol, and hydrofluoric acid aqueous solution, the TiO2 support can possess good crystallinity, surface reactivity, and adaptability to subsequent reduction modification, thus providing a stable foundation for the subsequent construction of oxygen-rich vacancy TiO2-x supports and the loading of Cu2O active components.

[0028] Preferably, when the titanium source is tetrabutyl titanate, the volume ratio of tetrabutyl titanate, anhydrous ethanol, and hydrofluoric acid aqueous solution is 5:(15~25):(1.0~1.5).

[0029] Optionally, in step S2, the mass ratio of TiO2 support to sodium borohydride is 1:0.5~1.0; the calcination temperature is 250~350 ℃, and the holding time is 30~90 min; the inert atmosphere is argon or nitrogen.

[0030] Optionally, the copper source precursor in step S3 is selected from one or more of copper chloride, copper nitrate, copper sulfate, copper acetate, cuprous chloride, or their hydrates.

[0031] Optionally, in step S3, the components are as follows by mass: 1 part by mass of oxygen-rich vacancy titanium dioxide carrier, 0.15-2.0 parts by mass of copper source precursor (based on the mass of copper element), 50-150 parts by mass of polyvinylpyrrolidone, 4-12 parts by mass of sodium hydroxide (based on the solute), and 5-15 parts by mass of ascorbic acid (based on the solute); the reaction temperature is 45-65 ℃, and the reaction time is 2-5 h.

[0032] Specifically, using the aforementioned mass fraction range for each component balances the generation amount, dispersibility, crystal growth degree, and loading stability of the Cu2O active component. The amount of copper source precursor, controlled between 0.15 and 2.0 parts by mass, is beneficial for forming an appropriate amount of Cu2O active component on the surface of the oxygen-vacancy-rich TiO2-x support. If the amount of copper source precursor is too low, there will be insufficient Cu2O active sites, resulting in limited improvement in nitrate reduction activity; if the amount of copper source precursor is too high, it can easily cause Cu2O particle agglomeration or excessive coverage of the TiO2-x surface, affecting interfacial charge transport and active site exposure. The addition of polyvinylpyrrolidone helps improve the dispersion stability of the oxygen-vacancy-rich TiO2-x support and the copper source precursor in the reaction system and plays a certain regulatory role in Cu2O crystal nucleation and growth. Sodium hydroxide provides an alkaline reaction environment, promoting the formation of copper hydroxyl intermediates from the copper precursor, which can be further reduced and transformed. Ascorbic acid, as a mild reducing agent, reduces the copper precursor and promotes the in-situ generation of Cu2O on the oxygen-vacancy-rich TiO2-x support surface. By combining these proportions, the uniformity of Cu2O loading on the TiO2-x surface and the stability of interfacial bonding can be improved, thereby enhancing the charge transport efficiency, nitrate adsorption activation capacity, and cycle stability of the composite catalyst.

[0033] In a preferred embodiment, the oxygen-rich vacancy TiO2-x support is first dispersed in a reaction solution containing a copper-based precursor. Then, polyvinylpyrrolidone (PVP) is added, allowing PPVP to fully adsorb or coat the support and the copper-based precursor, which improves the dispersion stability of the reaction system and inhibits excessive aggregation of Cu2O particles. Subsequently, sodium hydroxide is added to create a suitable alkaline environment, promoting the conversion of the copper-based precursor into a copper hydroxyl intermediate. Finally, ascorbic acid is added, allowing the copper hydroxyl intermediate to gradually convert to Cu2O under mild reducing conditions, preferentially nucleating and growing in situ on the surface of the oxygen-rich vacancy TiO2-x support. This feeding sequence facilitates a reaction process of "first dispersion and stabilization, then alkalinization and conversion, followed by mild reduction," thereby improving the uniformity of Cu2O loading and the degree of interfacial coupling. It should be noted that, without affecting the dispersion of the oxygen-rich TiO2-x support, the in-situ generation of Cu2O, and the loading effect, the addition method of sodium hydroxide and ascorbic acid can be appropriately adjusted according to the reaction system; however, the above-mentioned order of addition is the preferred method of the present invention, which is more conducive to obtaining a uniformly dispersed Cu2O / TiO2-x composite catalyst with stable interfacial bonding.

[0034] Preferably, the concentration of copper source in the reaction solution is 0.05~0.2 mol / L, the concentration of sodium hydroxide is 1~3 mol / L, the concentration of ascorbic acid is 0.3~0.8 mol / L, the volume of the basic reaction solution is 80~115 mL, and the total volume of the reaction system is 90~150 mL.

[0035] Optionally, the conductive substrate in step S4 is one of carbon cloth, carbon paper, nickel foam, or conductive titanium mesh, and the adhesive is one of Nafion, polyvinylidene fluoride, or polytetrafluoroethylene.

[0036] Optionally, in step S4, the dispersion is composed of ethanol, water, Cu2O / TiO2-x composite catalyst and binder, wherein the volume ratio of ethanol to water is 1:0.5 to 1:2, the concentration of Cu2O / TiO2-x composite catalyst in the dispersion is 2 to 20 mg / mL, and the concentration of the effective component of the binder in the dispersion is 2 to 10 mg / mL.

[0037] This invention provides an oxygen-vacancy-rich titanium dioxide-supported cuprous oxide composite electrode prepared by the above-described method, comprising a conductive substrate and a composite catalytic active layer supported on the surface of the conductive substrate. The composite catalytic active layer is composed of a Cu₂O / TiO₂-x composite catalyst and a binder. In the Cu₂O / TiO₂-x composite catalyst, Cu₂O is supported on the surface of TiO₂-x, and an interfacial coupling structure is formed between Cu₂O and TiO₂-x. Furthermore, the Cu₂O / TiO₂-x composite catalyst contains Cu. + Species and oxygen vacancy structure.

[0038] This invention provides an application of the above-mentioned oxygen-vacancy titanium dioxide-supported cuprous oxide composite electrode in the electrocatalytic reduction of nitrate to ammonia. The oxygen-vacancy titanium dioxide-supported cuprous oxide composite electrode is used as the working electrode for the electrocatalytic reduction treatment of nitrate-containing water, so as to convert nitrate into ammonia or ammonium salt. The nitrate-containing water is one or more of nitrate-containing wastewater, groundwater, surface water, or experimental simulated water. The supporting electrolyte is one or more of sulfate, carbonate, or bicarbonate. The working potential is -2.3 to -1.8 V relative to the saturated calomel electrode.

[0039] Example 1 This embodiment provides a method for preparing an oxygen-rich vacancy TiO2-supported Cu2O composite electrode for electrocatalytic reduction of nitrate to ammonia, and describes the structure and electrocatalytic performance of the obtained composite electrode.

[0040] 5 mL of tetrabutyl titanate was added to 20 mL of anhydrous ethanol and stirred at room temperature for 30 min to ensure thorough mixing. Then, 1.2 mL of hydrofluoric acid aqueous solution was added dropwise to the solution, and stirring continued for another 30 min to obtain a mixed precursor solution. The mixed precursor solution was transferred to a 50 mL polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180 °C for 12 h. After the reaction, the solution was allowed to cool naturally to room temperature, washed sequentially with deionized water and anhydrous ethanol until neutral, and dried at 60 °C to obtain the TiO2 support.

[0041] 2.0 g of the above TiO2 support was mixed with 1.5 g of sodium borohydride and ground for 30 min to ensure full contact between the two. The mixture was then heat-treated at 300 °C for 60 min under an argon atmosphere. After calcination, the mixture was allowed to cool naturally to room temperature. The resulting product was washed sequentially with deionized water and anhydrous ethanol, and dried at 60 °C to obtain the oxygen-rich vacancy TiO2-x support.

[0042] 90 mL of deionized water and 10 mL of 0.1 mol / L copper chloride solution were added to a beaker and stirred until homogeneous. Then, 0.10 g of oxygen-rich vacancy TiO2-x support was added and uniformly dispersed. Subsequently, 11 g of polyvinylpyrrolidone was added to the reaction solution and stirred at 55 °C until completely dissolved. 10 mL of 2 mol / L sodium hydroxide solution was added to the system, and after stirring for 30 min, 10 mL of 0.6 mol / L ascorbic acid solution was added. The reaction was continued at 55 °C for 3 h, allowing Cu2O to be generated and loaded in situ on the surface of the oxygen-rich vacancy TiO2-x support. After the reaction was completed, the mixture was centrifuged, washed three times with deionized water and anhydrous ethanol, and dried at 60 °C to obtain the Cu2O / TiO2-x composite catalyst.

[0043] The carbon cloth was cut into 1 cm × 1.5 cm pieces, ultrasonically cleaned in acetone and anhydrous ethanol for 30 min, rinsed with deionized water, and dried at 60 ℃. 10 mg of the above Cu₂O / TiO₂-x composite catalyst was added to a mixed solvent of 1 mL ethanol and 1 mL deionized water, ultrasonically dispersed for 2 min, and then 100 μL of 5% Nafion solution was added. Ultrasonication continued for 1 h to obtain a uniform catalyst dispersion. 80 μL of the dispersion was drop-coated onto the surface of the pretreated carbon cloth and allowed to dry naturally at room temperature to obtain an oxygen-vacancy TiO₂-supported Cu₂O composite electrode.

[0044] The Cu2O / TiO2-x composite catalyst obtained in this embodiment was characterized by high-resolution transmission electron microscopy, and the results are as follows: Figure 1 As shown. By Figure 1 As can be seen, clear lattice fringes can be observed in the composite catalyst. Among them, the lattice fringes with a spacing of about 0.239 nm correspond to the (111) crystal plane of Cu2O, and the lattice fringes with a spacing of about 0.187 nm correspond to the (001) crystal plane of TiO2. A relatively tight contact interface is formed between Cu2O and oxygen-rich vacancy TiO2-x, indicating that Cu2O can be generated and stably loaded in situ on the surface of oxygen-rich vacancy TiO2-x support, thereby forming a copper-titanium oxide composite catalytic system with an interfacial coupling structure.

[0045] X-ray diffraction tests were performed on the Cu2O / TiO2-x composite catalyst obtained in this embodiment, and the results are as follows: Figure 2 As shown. By Figure 2 As can be seen, characteristic diffraction peaks of TiO2 and Cu2O can be observed in different composite catalysts, and they match those of the Cu2O standard card PDF#05-0667 and the TiO2 standard card PDF#21-1272, indicating that Cu2O was successfully loaded onto the TiO2-x support surface and formed a copper-titanium oxide composite structure. The differences in diffraction peak intensities among different samples suggest that the crystal plane combination and crystal orientation between Cu2O and TiO2-x have a certain influence on the structural characteristics of the composite catalyst.

[0046] The oxygen-vacancy-rich TiO2-supported Cu2O composite electrode prepared in this embodiment was used as the working electrode, a platinum electrode as the counter electrode, and a saturated calomel electrode as the reference electrode to construct a three-electrode electrochemical reaction system. The initial nitrate concentration was set as NO3. - -N concentration was 100 mg / L, and the supporting electrolyte was a sulfate electrolyte. The three electrodes were placed in the electrolyte, and the electrocatalytic reduction reaction was carried out under constant potential conditions. The working potential was -2.3 to -1.8 V relative to the saturated calomel electrode, and the reaction time was 2 h.

[0047] Figure 3NO3 after 2 h of constant potential electrolysis using different Cu2O / TiO2-x composite electrodes - -N concentration and ammonia selectivity results. Figure 3 It is evident that the composite electrode obtained in this embodiment can effectively promote the nitrate reduction reaction and convert nitrate into ammonia or ammonium salt, indicating that the composite electrode has good electrocatalytic reduction activity for ammonia production from nitrate.

[0048] Figure 4 This section presents a comparison of ammonia yields using different composite electrodes and single-component electrodes. Figure 4 As can be seen, the ammonia yield of the composite electrode obtained in this embodiment is higher than that of the Cu2O electrode alone and the TiO2-based electrode alone. This result indicates that the Cu2O / TiO2-x composite structure is not a simple physical mixture, but rather improves the efficiency of ammonia production from nitrate electrocatalytic reduction through the synergistic effect between the Cu2O active sites, the oxygen-rich vacancy TiO2-x support, and the interfacial coupling structure.

[0049] Cyclic stability test results are as follows Figure 5 As shown. By Figure 5 As can be seen, after multiple cycles, the oxygen-rich vacancy TiO2-supported Cu2O composite electrode obtained in this embodiment can still maintain good performance of nitrate electrocatalytic reduction to ammonia, indicating that the composite electrode has good structural stability and recyclability.

[0050] Depend on Figures 1 to 5 It can be seen that this embodiment can successfully prepare an oxygen-vacancy TiO2-supported Cu2O composite electrode. The resulting composite electrode has a tight Cu2O / TiO2-x interface coupling structure and exhibits good nitrate conversion ability, ammonia generation ability and cycle stability in the electrocatalytic reduction of nitrate to ammonia.

[0051] Example 2 This embodiment provides another method for preparing an oxygen-rich TiO2-supported Cu2O composite electrode, the specific steps of which are as follows.

[0052] 5 mL of tetraisopropyl titanate was added to 18 mL of anhydrous ethanol, and stirred at room temperature for 30 min. Then, 1.0 mL of hydrofluoric acid aqueous solution was added dropwise, and stirring was continued for another 30 min to obtain a mixed precursor solution. The mixed precursor solution was transferred to a 50 mL polytetrafluoroethylene-lined reactor and hydrothermally reacted at 160 °C for 16 h. After the reaction was completed, the mixture was naturally cooled to room temperature, washed successively with deionized water and anhydrous ethanol, and dried at 50 °C to obtain the TiO2 support.

[0053] Take 1.0 g of the above TiO2 support and mix it with 0.5 g of sodium borohydride, and grind it for 30 min. Place the mixture in a tube furnace and calcine it at 250 ℃ for 90 min under a nitrogen atmosphere. After naturally cooling to room temperature, wash it with deionized water and anhydrous ethanol in sequence, and dry it at 50 ℃ to obtain the oxygen-rich vacancy TiO2-x support.

[0054] 80 mL of deionized water and 5 mL of 0.05 mol / L copper chloride solution were added to a beaker and stirred until homogeneous. Then, 0.05 g of oxygen-rich vacancy TiO2-x support was added and uniformly dispersed in the reaction solution. Subsequently, 3.0 g of polyvinylpyrrolidone was added and stirred at 45 °C until completely dissolved. Next, 5 mL of 1 mol / L sodium hydroxide solution was added to the system, and after stirring for 30 min, 5 mL of 0.3 mol / L ascorbic acid solution was added, and the reaction was carried out at 45 °C for 5 h. After the reaction was completed, the mixture was centrifuged, washed successively with deionized water and anhydrous ethanol, and dried at 50 °C to obtain the Cu2O / TiO2-x composite catalyst.

[0055] Five mg of the above Cu₂O / TiO₂-x composite catalyst was added to a mixed solvent of ethanol and water in a volume ratio of 1:0.5, and Nafion solution was added, wherein the effective component of Nafion was 2 mg by mass. After ultrasonic dispersion, a catalyst dispersion was formed. The catalyst dispersion was coated on the surface of carbon paper and dried to obtain an oxygen-vacancy TiO₂-supported Cu₂O composite electrode.

[0056] Example 3 This embodiment provides another method for preparing an oxygen-rich TiO2-supported Cu2O composite electrode, the specific steps of which are as follows.

[0057] 5 mL of tetraethyl titanate was added to 25 mL of anhydrous ethanol, and stirred at room temperature for 30 min. Then, 1.5 mL of hydrofluoric acid aqueous solution was added dropwise, and stirring was continued for another 30 min to obtain a mixed precursor solution. The mixed precursor solution was transferred to a 50 mL polytetrafluoroethylene-lined reactor and hydrothermally reacted at 200 °C for 8 h. After the reaction was completed, the mixture was naturally cooled to room temperature, washed successively with deionized water and anhydrous ethanol, and dried at 80 °C to obtain the TiO2 support.

[0058] The above-mentioned TiO2 support and sodium borohydride were mixed at a mass ratio of 1:1 and ground for 30 min. The mixture was placed in a tube furnace and calcined at 350 °C for 30 min under an argon atmosphere. After naturally cooling to room temperature, it was washed successively with deionized water and anhydrous ethanol, and dried at 80 °C to obtain the oxygen-rich vacancy TiO2-x support.

[0059] 100 mL of deionized water and 15 mL of 0.2 mol / L copper chloride solution were added to a beaker and stirred until homogeneous. Then, 0.20 g of oxygen-rich vacancy TiO2-x support was added and uniformly dispersed in the reaction solution. Subsequently, 20 g of polyvinylpyrrolidone was added and stirred at 65 °C until completely dissolved. Next, 15 mL of 3 mol / L sodium hydroxide solution was added to the system, and after stirring for 30 min, 15 mL of 0.8 mol / L ascorbic acid solution was added, and the reaction was carried out at 65 °C for 2 h. After the reaction was completed, the mixture was centrifuged, washed successively with deionized water and anhydrous ethanol, and dried at 80 °C to obtain the Cu2O / TiO2-x composite catalyst.

[0060] 20 mg of the above Cu2O / TiO2-x composite catalyst was added to a mixed solvent of ethanol and water in a volume ratio of 1:2, and Nafion solution was added, wherein the effective component of Nafion was 10 mg by mass. After ultrasonic dispersion, a catalyst dispersion was formed. The catalyst dispersion was loaded onto the surface of nickel foam and dried to obtain an oxygen-vacancy TiO2-supported Cu2O composite electrode.

[0061] Comparative Example 1 This comparative example provides a Cu2O / TiO2 composite electrode without oxygen vacancies, and the specific steps are as follows.

[0062] TiO2 support was prepared according to the method in Example 1, but without the sodium borohydride thermal reduction treatment. The obtained TiO2 support was directly added to the reaction solution containing the copper source precursor, and polyvinylpyrrolidone, sodium hydroxide and ascorbic acid were added to generate and load Cu2O on the TiO2 surface, thus obtaining the Cu2O / TiO2 composite catalyst.

[0063] Subsequently, following the electrode forming method of Example 1, 10 mg of Cu2O / TiO2 composite catalyst was added to a mixed solvent consisting of 1 mL ethanol and 1 mL deionized water, and 100 μL of 5% Nafion solution was added. After ultrasonic dispersion, a catalyst dispersion was formed. The catalyst dispersion was then dropped onto the surface of carbon cloth and dried to obtain the Cu2O / TiO2 composite electrode.

[0064] Compared with Example 1, the TiO2 support in this comparative example was not subjected to sodium borohydride reduction treatment, and its oxygen vacancy structure was relatively small, resulting in insufficient adsorption and activation capacity for nitrates and relatively weak interfacial charge transport capacity.

[0065] Comparative Example 2 This comparative example provides a single Cu2O electrode, and the specific steps are as follows.

[0066] 90 mL of deionized water and 10 mL of 0.1 mol / L copper chloride hydrate solution were added to a beaker and stirred until homogeneous. Then, 11 g of polyvinylpyrrolidone was added and stirred at 55 °C until completely dissolved. Subsequently, 10 mL of 2 mol / L sodium hydroxide solution was added, and the mixture was stirred for 30 min. Then, 10 mL of 0.6 mol / L ascorbic acid solution was added, and the reaction was carried out at 55 °C for 3 h. After the reaction was complete, the Cu₂O material was obtained by centrifugation, washing, and drying.

[0067] Take 10 mg of the above Cu2O material and add it to a mixed solvent consisting of 1 mL of ethanol and 1 mL of deionized water. Add 100 μL of 5% Nafion solution and ultrasonically disperse to form a dispersion. Drop the dispersion onto the surface of carbon cloth and dry to obtain a Cu2O electrode.

[0068] Compared with Example 1, this comparative example lacks the oxygen-rich vacancy TiO2-x support and the Cu2O / TiO2-x interface coupling structure. The Cu2O active component is more prone to agglomeration and valence state changes on the electrode surface, so its charge transport efficiency, ammonia generation capacity and cycle stability are relatively insufficient.

[0069] Comparative Example 3 This comparative example provides a single oxygen-rich vacancy TiO2-x electrode, and the specific steps are as follows.

[0070] TiO2 support was prepared according to the method in Example 1, and oxygen-rich vacancy TiO2-x support was obtained by thermal reduction treatment with sodium borohydride, but without in-situ Cu2O loading. 10 mg of the obtained oxygen-rich vacancy TiO2-x support was added to a mixed solvent of 1 mL ethanol and 1 mL deionized water, and 100 μL of 5% Nafion solution was added. After ultrasonic dispersion, a dispersion was formed. The dispersion was dropped onto the surface of carbon cloth, and after drying, an oxygen-rich vacancy TiO2-x electrode was obtained.

[0071] Compared with Example 1, this comparative example lacks Cu2O active component and has insufficient nitrate reduction active sites. Therefore, its electrocatalytic reduction of nitrate to ammonia is lower than that of Cu2O / TiO2-x composite electrode.

[0072] It should be noted that the oxygen-rich vacancy TiO2-x support mentioned in this invention refers to a TiO2 support with oxygen vacancy structures on its surface after reduction treatment; for ease of annotation in the figures, oxygen-rich vacancy TiO2-x is abbreviated as TiO2 in some figures, but this does not affect the limitation of this invention on the oxygen-rich vacancy TiO2-x support and its composite electrode structure.

[0073] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a copper-titanium oxide composite electrode for the electrocatalytic reduction of nitrate to ammonia, characterized in that, Includes the following steps: Step S1: Add the titanium source to anhydrous ethanol and mix. After adding hydrofluoric acid aqueous solution dropwise, carry out a hydrothermal reaction to obtain TiO2 support. Step S2: The TiO2 support is mixed with sodium borohydride and then calcined under an inert atmosphere to obtain an oxygen-rich vacancy TiO2-x support; Step S3: Add the oxygen-rich vacancy titanium dioxide support to the reaction solution containing the copper source precursor, and add polyvinylpyrrolidone, sodium hydroxide and ascorbic acid to react, so that the copper source precursor is transformed in situ on the surface of the oxygen-rich vacancy titanium dioxide support to obtain Cu2O / TiO2-x composite catalyst. Step S4: The Cu2O / TiO2-x composite catalyst is mixed with a binder and a solvent to form a catalyst dispersion, and the catalyst dispersion is loaded onto the surface of a conductive substrate. After drying, the oxygen-rich TiO2-supported Cu2O composite electrode is obtained.

2. The method for preparing a copper-titanium oxide composite electrode for electrocatalytic reduction of nitrate to ammonia according to claim 1, characterized in that, The titanium source mentioned in step S1 is selected from one or more of the following: titanate titanium source, inorganic titanium salt titanium source, titanium oxy salt titanium source, titanate titanium source, and titanium sol.

3. The method for preparing a copper-titanium oxide composite electrode for electrocatalytic reduction of nitrate to ammonia according to claim 1, characterized in that, In step S1, based on the Ti element in the titanium source, every 0.005~0.05 mol of Ti corresponds to 15~50 mL of anhydrous ethanol and 0.5~3.0 mL of hydrofluoric acid aqueous solution; the hydrothermal reaction temperature is 160~200 ℃, and the reaction time is 8~16 h.

4. The method for preparing a copper-titanium oxide composite electrode for electrocatalytic reduction of nitrate to ammonia according to claim 1, characterized in that, In step S2, the mass ratio of TiO2 support to sodium borohydride is 1:0.5~1.0; The calcination temperature is 250~350 ℃, and the holding time is 30~90 min; The inert atmosphere is argon or nitrogen.

5. The method for preparing a copper-titanium oxide composite electrode for electrocatalytic reduction of nitrate to ammonia according to claim 1, characterized in that, The copper source precursor mentioned in step S3 is selected from one or more of copper chloride, copper nitrate, copper sulfate, copper acetate, cuprous chloride, or their hydrates.

6. The method for preparing a copper-titanium oxide composite electrode for electrocatalytic reduction of nitrate to ammonia according to claim 1, characterized in that, In step S3, the components are as follows by mass: 1 part by mass of oxygen-rich vacancy titanium dioxide carrier, 0.15 to 2.0 parts by mass of copper source precursor, 50 to 150 parts by mass of polyvinylpyrrolidone, 4 to 12 parts by mass of sodium hydroxide, and 5 to 15 parts by mass of ascorbic acid. The reaction temperature is 45~65 ℃, and the reaction time is 2~5 h.

7. The method for preparing a copper-titanium oxide composite electrode for electrocatalytic reduction of nitrate to ammonia according to claim 1, characterized in that, The conductive substrate mentioned in step S4 is one of carbon cloth, carbon paper, nickel foam, or conductive titanium mesh; The adhesive is one of Nafion, polyvinylidene fluoride, or polytetrafluoroethylene.

8. The method for preparing a copper-titanium oxide composite electrode for electrocatalytic reduction of nitrate to ammonia according to claim 1, characterized in that, The catalyst dispersion in step S4 is composed of ethanol, deionized water, Cu2O / TiO2-x composite catalyst and binder, wherein the volume ratio of ethanol to water is 1:0.5~1:2; The concentration of the Cu2O / TiO2-x composite catalyst in the dispersion is 2~20 mg / mL; The amount of adhesive added is 2~10 mg / mL, based on the effective component of the adhesive.

9. A titanium dioxide-supported cuprous oxide composite electrode with oxygen-vacancy sites prepared by the method described in claim 1, characterized in that, It includes a conductive substrate and a composite catalytic active layer supported on the surface of the conductive substrate, wherein the composite catalytic active layer is composed of a Cu2O / TiO2-x composite catalyst and a binder.

10. The application of the oxygen-vacancy-enriched titanium dioxide-supported cuprous oxide composite electrode as described in claim 9 in the electrocatalytic reduction of nitrate to ammonia.

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