Nickel-copper-based heterojunction catalyst, preparation method and application thereof

Abstract

The invention discloses a copper-nickel-based heterojunction catalyst and a preparation method and application thereof, foamy copper (CF) is used as a substrate, and a NiCuO / Cu2O catalyst layer is synthesized on the surface of the foamy copper substrate through solution etching, oxidation-reduction reaction and annealing treatment. The NiCuO / Cu2O / CF catalyst prepared by the invention has the following advantages: the NiCuO / Cu2O / CF catalyst can show relatively good catalytic activity under relatively low potential, and the electric energy input required by reaction is reduced, so that the NiCuO / Cu2O / CF catalyst can be applied to the aspect of industrial-grade current. Ni and Cu are relatively abundant metal elements in the earth crust, the preparation cost of oxides of Ni and Cu is relatively low, and compared with some catalysts using noble metals or rare metals as active components, the NiCuO / Cu2O / CF catalyst has a greater cost advantage in large-scale industrial application, and the production cost can be reduced. Electrocatalytic oxidation of HMF is a reaction process driven by renewable electric power, and a NiCuO / Cu2O / CF catalyst can effectively convert HMF derived from biomass into FDCA with a high added value in the process, so that effective utilization of renewable energy sources and high-value conversion of biomass are realized; the method has positive significance in reducing dependence on traditional fossil energy and reducing carbon emission.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and relates to a NiCuO / Cu 2 O / CF heterojunction catalyst, a preparation method thereof, and an application in electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to prepare 2,5-furandicarboxylic acid (FDCA). Background Art

[0002] With the continuous development of the economic society, due to the continuous consumption of fossil fuels by humans, there is an urgent need to research and develop various renewable energy sources to replace traditional fossil fuels. Biomass is a renewable organic carbon source in nature, with a huge storage capacity and low price. Therefore, it can be a favorable alternative to traditional fossil energy. According to the list of the most valuable biomass-derived platform chemicals currently, 5-hydroxymethylfurfural (HMF) is considered a compound with wide applications. HMF can be obtained from renewable biomass resources and has great potential in industry. Many high-value-added chemicals can be prepared through HMF. 2,5-Furandicarboxaldehyde (DFF), 2,5-furandicarboxylic acid (FDCA), 5-hydroxymethyl-2-furoic acid (HMFCA), and maleic acid (MA) can be prepared by oxidizing HMF. Among them, FDCA is the product with the most extensive application prospects. The application of this green chemical method in the field of biomass conversion has received increasing attention.

[0003] FDCA can be synthesized by oxidizing HMF through conventional thermal catalysis. However, thermal catalysis is usually carried out under harsh reaction conditions (i.e., high temperature or high oxygen pressure). Therefore, an electrocatalytic oxidation method for HMF (HMFOR) to produce FDCA has been developed. However, the copper-based catalysts developed for HMFOR will undergo severe and uncontrollable surface reconstruction under alkaline conditions, resulting in the inevitable formation of oxides or hydroxides. Therefore, it is inevitable to further study the catalytic activity of oxides or hydroxides. In the prior art, among most of the reported synthesis methods of 2,5-furandicarboxylic acid (FDCA), only a few catalytic systems can conduct HMFOR with HMF at an industrial-scale current density (>500 mA cm -2 ), and even fewer systems can reach an ampere-level current density. Therefore, it is very important to construct a robust and stable oxide electrocatalyst to achieve high-current-density HMFOR.

[0004] Therefore, there is an urgent need to develop a method that can improve the stability of HMF electrocatalytic process at an industrial-level current density, and realize low-cost, stable, and long-term operation during the electrocatalytic oxidation process of HMF. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a NiCuO / Cu 2 O / CF heterojunction catalyst, a preparation method thereof and an application thereof. By means of solution etching, redox reaction and annealing treatment, a NiCuO / Cu 2 O catalytic layer is synthesized on the surface of a copper foam substrate (CF), so as to form a self-supporting OER NiCuO / Cu 2 O / CF electrode with high stability under industrial-grade current density conditions. This heterojunction catalyst can withstand a higher current density in a strong alkaline environment to catalyze the conversion of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA).

[0006] In order to achieve the above purpose, the technical scheme adopted by the present invention is as follows:

[0007] The present invention provides a NiCuO / Cu 2 O / CF heterojunction catalyst, with a copper foam (CF) as the substrate. Through solution etching, redox reaction and annealing treatment, a NiCuO / Cu 2 O catalytic layer is loaded on the surface of the copper foam substrate (CF).

[0008] The present invention also provides a preparation method of the NiCuO / Cu 2 O / CF heterojunction catalyst, including the following steps:

[0009] (1) Cut the copper foam carrier and set it aside for use;

[0010] (2) Prepare a NaOH and (NH4) 2 S 2 O 8 mixed solution to provide the alkaline environment and oxidant required for etching, and set it aside for use;

[0011] (3) Immerse the copper foam carrier obtained in step (1) into the NaOH and (NH4) 2 S 2 O 8 mixed solution to obtain a Cu(OH) 2 / CF foam carrier;

[0012] (4) Prepare a NiCl 2 solution and set it aside for use;

[0013] (5) Immerse the Cu(OH) 2 / CF foam carrier prepared in step (3) into the NiCl 2 solution obtained in step (4), add H 2 O 2 for reaction to obtain a composite carrier;

[0014] (6) Anneal the composite support prepared in step (5) in an air atmosphere, and obtain the NiCuO / Cu 2 O / CF heterojunction catalyst after cooling.

[0015] In the present invention, the copper foam is cut into a shape of a certain size, and at the same time, a mixed solution of NaOH and (NH 4 ) 2 S 2 O 8 is prepared for etching the copper foam. By immersing the copper foam in the mixed solution, a redox reaction occurs to obtain the Cu(OH) 2 / CF foam support. At this time, an NiCl 2 solution is prepared, and then the Cu(OH) 2 / CF foam support is immersed in the NiCl 2 solution to obtain a composite support, and finally an annealing treatment is carried out to form the NiCuO / Cu 2 O / CF heterojunction catalyst.

[0016] In some possible implementation manners, in step (2), the preparation process of the mixed solution is as follows:

[0017] 2-1) Weigh flaky NaOH and place it in a beaker;

[0018] 2-2) Weigh (NH 4 ) 2 S 2 O 8 powder and place it in a beaker;

[0019] 2-3) Mix the drugs weighed in steps 2-1) and 2-2), add ultrapure water, and place it in an ultrasonic dissolution tank for ultrasonic dissolution to obtain an (NH 4 ) 2 S 2 O 8 and NaOH mixed solution.

[0020] In some specific implementation manners, in step 2-3), the prepared (NH 4 ) 2 S 2 O 8 has a molar concentration of 0.1 to 0.3 M, and the NaOH molar concentration is 1 to 5 M.

[0021] In some possible implementation manners, in step (3), the preparation process of the Cu(OH) 2 / CF foam support is as follows:

[0022] The foam copper carrier cut in step (1) is completely immersed in the mixed solution prepared in step (2) for etching for 10 to 90 minutes to obtain Cu(OH) 2 / CF foam carrier.

[0023] In some possible embodiments, in step (3), after etching is completed, the Cu(OH) 2 / CF foam carrier needs to be rinsed with methanol and deionized water respectively.

[0024] In some possible embodiments, in step (4), the molar concentration of the NiCl 2 solution is 5 to 30 mM.

[0025] In some possible embodiments, in step (5), the reaction time between the Cu(OH) 2 / CF foam carrier and the NiCl 2 solution is 20 to 120 minutes.

[0026] In some possible embodiments, in step (6), the annealing temperature is 100 to 300 °C and the annealing time is 20 to 120 minutes.

[0027] The present invention also provides the application of the NiCuO / Cu 2 O / CF heterojunction catalyst in the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to prepare 2,5-furandicarboxylic acid (FDCA) under industrial-grade current.

[0028] A preparation method of a NiCuO / Cu 2 O / CF heterojunction catalyst of the present invention uses foam copper that collects and transports electrons as a substrate and NiCuO / Cu 2 O oxide as an electrocatalyst layer. The catalyst structure of NiCuO / Cu 2 O / CF can support the passage of a stable large current, thereby enhancing the electrode stability, enabling the self-supporting electrode of NiCuO / Cu 2 O / CF to be applied to the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), especially for the electrocatalytic oxidation of HMF under industrial-grade current density, and having good application prospects.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The NiCuO / Cu 2 O / CF catalyst prepared by the present invention has the following advantages. Different from many traditional non-precious metal catalysts that require a higher potential to drive the HMF oxidation reaction, NiCuO / Cu 2The O / CF catalyst can exhibit good catalytic activity at relatively low potentials, reducing the electrical energy input required for the reaction. It can be used for the electrocatalytic oxidation of HMF at industrial current densities. Moreover, Ni and Cu are relatively abundant metal elements in the earth's crust, and the preparation cost of their oxides is relatively low. Compared with some catalysts using precious metals or rare metals as active components, NiCuO / Cu 2 The O / CF catalyst has a greater cost advantage in large-scale industrial applications, which can reduce production costs. The electrocatalytic oxidation of HMF is a reaction process driven by renewable electricity. NiCuO / Cu 2 The O / CF catalyst can effectively convert biomass-derived HMF into high-value FDCA in this process, realizing the effective utilization of renewable energy and the high-value conversion of biomass, which is of positive significance for reducing dependence on traditional fossil energy and reducing carbon emissions. In summary, NiCuO / Cu 2 The O / CF catalyst shows great potential in the electrocatalytic oxidation of HMF and its application at industrial currents.

[0031] In the present invention, through etching, redox reaction and annealing treatment on the copper foam substrate, a NiCuO / Cu 2 O / CF heterojunction catalyst with a compact structure, high electrocatalytic activity and stability is prepared on the copper foam substrate. Description of the Drawings

[0032] Figure 1 XRD pattern of the NiCuO / Cu 2 O / CF prepared in Example 1.

[0033] Figure 2 Infrared spectrum of the NiCuO / Cu 2 O / CF prepared in Example 1.

[0034] Figure 3 SEM images of CF (3a), CuO / CF (3b), NiO / CF (3c) and NiCuO / Cu 2 O / CF (3d).

[0035] Figure 4 Tafel slopes calculated for the catalysts obtained in Comparative Examples 1-2, Example 1 and CF.

[0036] Figure 5 ECSA values of the catalysts obtained in Comparative Examples 1-2, Example 1 and CF.

[0037] Figure 6 For CF, CuO / CF, NiO / CF and NiCuO / Cu 2LSV curves of O / CF.

[0038] Figure 7 For NiCuO / Cu 2 obtained at different NiCl 2 concentrations in Example 2, the LSV curves of O / CF.

[0039] Figure 8 For NiCuO / Cu 2 obtained at different reaction times of the Cu(OH) 2 support in the NiCl 2 aqueous solution in Example 3, the LSV curves of O / CF.

[0040] Figure 9 The LSV curves obtained in Application Example 4. Detailed implementation manners

[0041] The present invention will be further described in detail below with reference to the accompanying drawings in combination with embodiments. These embodiments are only used to illustrate the present invention and do not limit the protection scope of the present invention.

[0042] Example 1

[0043] Take copper foam with a size of 1 cm × 2 cm and immerse it completely in a mixed solution containing 2.5 M NaOH and 0.125 M (NH 4 ) 2 S 2 O 8 for 30 minutes. After the immersion is completed, take out the etched Cu(OH) 2 support, carefully wash it with an ultrasonic cleaning device, and then place it in an aqueous solution containing 10 mM NiCl 2 , and add 1 ml of hydrogen peroxide with a concentration of 30%, and continuously react for 1 hour under a specific reaction environment. After the reaction is completed, rinse it repeatedly with ultrapure water to ensure no impurity residue, and then put it into a muffle furnace at 200 °C for 60 min of annealing treatment. After natural cooling, a NiCuO / Cu 2 O / CF heterojunction catalyst is successfully obtained.

[0044] In this example, the electrocatalytic oxidation effect of this catalyst on 5-hydroxymethylfurfural (HMF) at an industrial current density is experimentally studied. In the three-electrode system test simulating the industrial environment, the prepared NiCuO / Cu 2 O / CF heterojunction catalyst is used as the working electrode, a platinum sheet is used as the counter electrode, and a mercury oxide electrode is used as the reference electrode. The electrolyte uses a mixed solution of 5-hydroxymethylfurfural and KOH. Set the electrochemical workstation to make the working electrode carry out a constant current electrolysis reaction at an industrial current density (greater than 500 mA / cm 2 ).

[0045] Figure 1 shows the XRD pattern of the NiCuO / Cu 2 O / CF heterojunction catalyst prepared in Example 1. It can be clearly seen from the figure that the nanomaterial is mainly composed of CuO and NiO, and the interaction between the two constructs a unique heterojunction catalyst structure. At the same time, a small amount of Cu 2 O is also contained in the material.

[0046] Figure 2 is the infrared spectrum of the catalyst. Through infrared scanning, it is found that there is a Ni-O bond at 540 cm -1 and a Cu-O bond at 673 cm -1 . The existence of these chemical bonds provides the basis for the electrocatalytic performance of the catalyst.

[0047] Figure 3 gives the scanning electron micrographs of CF (3a), CuO / CF (3b), NiO / CF (3c) and NiCuO / Cu 2 O / CF (3d). It can be seen from the figure that the morphologies of CuO / CF, NiO / CF and NiCuO / Cu 2 O / CF are all composed of nanoparticles, and this microstructure is beneficial to increasing the active sites of the catalyst.

[0048] Figure 4 presents the Tafel slopes calculated for Comparative Examples 1-2, the catalysts obtained in Example 1, and CF. In the electrochemical experiment, first set appropriate scanning rates and potential ranges for linear sweep voltammetry (LSV) tests. During the test, the system records the current response of the electrode at different potentials in real time. Subsequently, plot the LSV curve, focusing on the linear region at lower overpotentials. This region usually represents the initial stage of the change in current with potential, where the current density increases rapidly. Take the logarithm of the current density, select the linear region of the LSV curve, and convert the current density values in this region to logarithmic form to linearize the exponential relationship for subsequent slope calculation. Finally, determine the slope of the linear region of the graph of logarithmic current density versus potential. The absolute value of this slope is the Tafel slope, with the unit of mv / dec. It can be clearly seen from Figure 4 that the slope of the NiCuO / Cu 2 O / CF catalyst is the smallest, indicating that the electrochemistry reaction kinetics of this electrode is the fastest, the energy loss during the reaction at industrial current density is the smallest, and it can exhibit a high current density at a relatively small overpotential, fully demonstrating that this electrode has extremely high catalytic activity, especially suitable for the electrocatalytic oxidation of HMF at industrial current density.

[0049] Figure 5Shows the electrochemically active surface area (ECSA) values of Comparative Examples 1-2, the catalysts obtained in Example 1, and CF. Different nanosheets were used as the anode electrode and tested by cyclic voltammetry (CV) in a three-electrode system. Scanning rates of 20, 40, 60, 80, 100, and 120 mV / s were selected for testing and data collection. The data were plotted into images, and the central potential position corresponding to each scan rate was found in the images, and the central current value at this position was calculated. As Figure 5 shown, comparing different nanosheets, the ECSA values of NiCuO / Cu 2 O / CF are greater than those of other catalysts, which fully indicates that the charge transfer rate of this catalyst electrode is faster than that of other catalysts, and it can perform the electrocatalytic oxidation of HMF more efficiently at industrial current densities. After testing at industrial current densities for a long time (such as continuous reaction for 100 hours), the conversion rate of HMF is stably maintained above 90%, and the selectivity of the target product 2,5-furandicarboxylic acid (FDCA) reaches above 85%, demonstrating the excellent performance and stability of this catalyst for the electrocatalytic oxidation of HMF at industrial current densities.

[0050] Comparative Example 1

[0051] The copper foam (CF) with a size of 1 cm × 2 cm was immersed in a mixed solution of 2.5 M NaOH and 0.125 M (NH 4 ) 2 S 2 O 8 for 30 minutes, and then the etched Cu(OH) 2 support was taken out. After being washed clean with an ultrasonic cleaning device, it was annealed in a muffle furnace at 200 °C for 60 min. After cooling, a CuO catalytic layer (CuO / CF) was loaded on the surface of the copper foam substrate.

[0052] Example 2

[0053] The copper foam with a size of 1 cm × 2 cm was immersed in a mixed solution of 2.5 M NaOH and 0.125 M (NH 4 ) 2 S 2 O 8 for 30 minutes. Using the stability and strong corrosiveness of this solution in the industrial environment, a Cu(OH) 2 support with a specific microstructure was precisely etched, and this structure is beneficial to charge transfer at high current densities.

[0054] The etched Cu(OH) 2The carrier was washed with an ultrasonic cleaning device to ensure no impurity residue, avoiding affecting the reaction efficiency during the industrial electrocatalysis process. Subsequently, it was placed in aqueous solutions containing 5 mM, 10 mM, 20 mM, 25 mM, and 30 mM NiCl 2 respectively, and 1 ml of 30% hydrogen peroxide was added, followed by reacting for 60 min. By controlling different concentrations of NiCl 2 , the influence on the catalyst performance under industrial current density was explored. The results showed that the catalyst prepared under the condition of 10 mM NiCl 2 exhibited the optimal electrocatalytic activity.

[0055] After the reaction, it was rinsed thoroughly with ultrapure water, and the sample was annealed in a muffle furnace at 200 °C for 60 min to further optimize the crystal structure of the catalyst and improve its stability under industrial current shock. After cooling, the NiCuO / Cu 2 O / CF heterojunction catalyst was obtained.

[0056] After testing, under the industrial current density of 1000 mA / cm 2 , the electrocatalytic oxidation reaction of HMF was carried out. The conversion rate of HMF was as high as 95%, the selectivity of the target product 2,5-furandicarboxylic acid (FDCA) reached 90%, and after continuous operation for 100 hours, the activity decay of the catalyst was less than 5%, showing good industrial application prospects.

[0057] Comparative Example 2

[0058] The copper foam with a size of 1 cm × 2 cm was immersed in an aqueous solution of 10 mM NiCl 2 and 1 ml of 30% hydrogen peroxide was added. After reacting for 1 hour, it was rinsed thoroughly with ultrapure water and placed in a muffle furnace at 200 °C for 60 min. After cooling, a NiO catalytic layer (NiO / CF) was loaded on the surface of the copper foam substrate.

[0059] Example 3

[0060] The copper foam with a size of 1 cm × 2 cm was immersed in a mixed solution of 2.5 M NaOH and 0.125 M (NH 4 ) 2 S 2 O 8 for 30 minutes. Utilizing the strong oxidizing property of this mixed solution, the surface of the copper foam was etched to form a rough and high specific surface area microstructure for better loading of active substances in the subsequent process. After the etching was completed, the etched Cu(OH) 2 carrier was taken out and washed with an ultrasonic cleaning device to ensure no impurity residue on the surface, avoiding affecting the subsequent catalytic performance.

[0061] Subsequently, the washed carriers were respectively placed in 10 mM NiCl 2 aqueous solution, and 1 ml of 30% hydrogen peroxide was added. By controlling the reaction time, the reactions were carried out for 30 min, 60 min, and 90 min respectively. Using redox reactions, nickel-based active substances were loaded on the surface of the carriers to construct catalytic active sites with different microstructures and compositions. After the reaction, it was rinsed thoroughly with ultrapure water to remove the unreacted substances, and then annealed in a muffle furnace at 200 °C for 60 min. Through the annealing treatment, the crystal structure and electronic structure of the catalyst were optimized, and its conductivity and catalytic activity were enhanced. After cooling, the NiCuO / Cu 2 O / CF heterojunction catalyst was obtained.

[0062] After testing and verification, at an industrial current density of 1000 mA / cm 2 ², using this catalyst for the electrocatalytic oxidation of HMF, the HMF conversion rate was high, and the selectivity of the main product 2,5-furandicarboxylic acid (FDCA) was high. Moreover, after continuous electrolysis for 100 hours, the catalytic performance remained stable, showing good industrial application potential.

[0063] Application Example 1

[0064] Taking the catalysts obtained in Comparative Examples 1-2 and Example 1 and 1 cm × 2 cm copper foam as the anode for electrocatalysis, 30 mL of a mixed solution of 20 mM 5-hydroxymethylfurfural and 1 M KOH was taken, the counter electrode was a platinum sheet, and the mercury / mercuric oxide electrode was used as the reference electrode. The electrocatalytic activity was tested by linear sweep voltammetry (LSV) in a three-electrode system. First, the anode material was activated by cyclic voltammetry (CV), and then LSV was used for testing after activation to obtain the LSV curve. The results are as Figure 6 shown. It can be seen that the composite catalyst (NiCuO / Cu₂O / CF) significantly improved the catalytic performance through the component synergy effect. Especially in the high-voltage region, it could still maintain a high current density and was suitable for high-energy-consuming electrochemical reactions (which can be used in industrial production). In contrast, the performance of single metal oxides (CuO, NiO) and CF was poor.

[0065] Application Example 2

[0066] Taking the NiCuO / Cu 2 O / CF heterojunction catalyst obtained in Example 2 as the anode for electrocatalysis, 30 mL of a mixed solution of 20 mM 5-hydroxymethylfurfural and 1 M KOH was taken, the counter electrode was a platinum sheet, and the mercury / mercuric oxide electrode was used as the reference electrode. The electrocatalytic activity was tested by linear sweep voltammetry (LSV) in a three-electrode system. The anode material was activated by cyclic voltammetry (CV), and then LSV was used for testing after activation to obtain the LSV curve. The results are as Figure 7 shown. It can be seen that NiCl 2When the concentration is 0.01M, at the same voltage, the current density is significantly higher than other curves in the higher voltage range (after about 1.3V), indicating that the catalytic performance of the heterojunction catalyst is optimal at this concentration. In the lower voltage range (about 1.0-1.3V), the current density of each curve is not much different, but as the voltage increases, the current density of the curve corresponding to the 0.01M concentration rises rapidly. After 1.4V, its current density value far exceeds the curves corresponding to other concentrations, indicating that at this concentration, the catalyst can more effectively catalyze the decomposition of HMF at a higher voltage, promote the electrochemical reaction, generate a larger current density, and reflect better catalytic activity and reaction efficiency.

[0067] Application Example 3

[0068] The heterojunction catalyst obtained in Example 3 was used as an electrocatalytic anode. 30 mL of a 20 mM 5-hydroxymethylfurfural and 1 M KOH mixed solution was taken. The counter electrode was a platinum sheet and a mercury / mercuric oxide electrode was used as a reference electrode. The electrocatalytic activity was tested using linear sweep voltammetry (LSV) in a three-electrode system. The anode material was activated using cyclic voltammetry (CV). After activation, an LSV test was performed to obtain an LSV curve. The results are shown in FIG. Figure 8 As shown, it can be seen that the current density of the curve with a reaction time of 60 minutes is significantly higher than that of the other two curves at the same voltage, indicating that 60 minutes is the optimal reaction time. In the lower voltage range (about 1.0-1.3V), the current densities of the three curves are relatively close, but when the voltage rises to about 1.3V, the current density of the curve corresponding to 60 minutes rises rapidly, and the gap with the other two curves is widened. After 1.4V, its current density value is much higher than the curves corresponding to 30 minutes and 90 minutes. This shows that the heterojunction catalyst produced at a reaction time of 60 minutes can more effectively catalyze the decomposition of HMF at a higher voltage, has better catalytic activity and reaction efficiency, and can promote the electrochemical reaction to produce a larger current density.

[0069] Application Example 4

[0070] The nanosheet obtained in Example 1 was used as an electrocatalytic anode. 30 mL of a 20 mM 5-hydroxymethylfurfural and 1 M KOH mixed solution and 30 mL of a solution containing only 1 M KOH were taken. The counter electrode was a platinum sheet and a mercury / mercuric oxide electrode was used as a reference electrode. The electrocatalytic activity was tested using linear sweep voltammetry (LSV) in a three-electrode system. The anode material was activated using cyclic voltammetry (CV). After activation, an LSV test was performed to obtain an LSV curve. The results are shown in FIG. Figure 9As shown, it can be seen that the selectivity for the HMF oxidation reaction is relatively high. In the curve of HMF, in the lower voltage range (about 1.0 - 1.25 V), the current density increases relatively slowly; when the voltage exceeds about 1.25 V, the current density begins to rise rapidly. At about 1.4 V, the current density reaches a relatively high value, and then continues to rise rapidly until it exceeds 1100 mA cm-2 near about 1.6 V. This indicates that when the heterojunction catalyst catalyzes the decomposition of HMF, it has a relatively high catalytic activity after the voltage reaches a certain level, can effectively promote the decomposition reaction of HMF, and generate a relatively large current density. Compared with the curve (OER) in KOH, the curve in HMF begins to rise significantly at a lower voltage, and at the same voltage, the current density of the curve in the HMF solution is higher than that of the curve in KOH in most ranges, indicating that the catalytic performance of this catalyst in the HMF solution is superior to that in the KOH solution in some aspects.

[0071] The above description of the embodiments is to enable those of ordinary skill in the art to understand and apply the present invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the embodiments herein, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A NiCuO / Cu2O / CF heterojunction catalyst, characterized in that: With copper foam (CF) as substrate, a NiCuO / Cu2O catalytic layer is loaded on the surface of the copper foam substrate (CF) through solution etching, redox reaction and annealing treatment.

2. The method for preparing the NiCuO / Cu2O / CF heterojunction catalyst according to claim 1, characterized in that: The following steps are involved: (1) Cutting the foam copper carrier for standby use; (2) preparing a mixed solution of NaOH and (NH4)2S2O8 to provide an alkaline environment and an oxidant required for etching, and setting aside for use; (3) immersing the copper foam carrier obtained in step (1) into a mixed solution of NaOH and (NH4)2S2O8 prepared in step (2) to obtain a Cu(OH)2 / CF foam carrier; (4) Prepare NiCl2 solution, stand-by; (5) immersing the Cu(OH)2 / CF foam carrier prepared in step (3) into the NiCl2 solution obtained in step (4), adding H2O2 to react, and obtaining a composite carrier; (6) Annealing the composite carrier prepared in step (5) in an air atmosphere, and obtaining a NiCuO / Cu2O / CF heterojunction catalyst after cooling.

3. The method for preparing the NiCuO / Cu2O / CF heterojunction catalyst according to claim 2, characterized in that: In step (2), the preparation process of the mixed solution is: 2-1) Weigh the NaOH flakes and place them in a beaker; 2-2) Weigh (NH4)2S2O8 powder and place it in a beaker; 2-3) Mix the drugs weighed in step 2-1) and step 2-2), add ultrapure water, and place in an ultrasonic dissolution tank for ultrasonic dissolution to obtain a mixed solution of (NH4)2S2O8 and NaOH.

4. The method for preparing the NiCuO / Cu2O / CF heterojunction catalyst according to claim 3, characterized in that: In step 2-3), the molar concentration of the prepared (NH4)2S2O8 is 0.1-0.3M, and the molar concentration of NaOH is 1-5M.

5. The method for preparing the NiCuO / Cu2O / CF heterojunction catalyst according to claim 2, characterized in that: In step (3), the preparation process of Cu(OH)2 / CF foam carrier is as follows: The foam copper carrier cut in step (1) is completely immersed in the mixed solution prepared in step (2) for etching. The etching time is 10 to 90 minutes to obtain a Cu(OH)2 / CF foam carrier.

6. The method for preparing the NiCuO / Cu2O / CF heterojunction catalyst according to claim 2, characterized in that: In step (3), after etching is completed, the Cu(OH)2 / CF foam carrier needs to be rinsed with methanol and deionized water respectively.

7. The method for preparing the NiCuO / Cu2O / CF heterojunction catalyst according to claim 2, characterized in that: In step (4), the molar concentration of the NiCl2 solution is 5 to 30 mM.

8. The method for preparing the NiCuO / Cu2O / CF heterojunction catalyst according to claim 2, characterized in that: In step (5), the reaction time of the Cu(OH)2 / CF foam carrier and the NiCl2 solution is 20 to 120 minutes.

9. The method for preparing the NiCuO / Cu2O / CF heterojunction catalyst according to claim 2, characterized in that: In step (6), the annealing temperature is 100 to 300° C., and the annealing time is 20 to 120 min.

10. Use of the NiCuO / Cu2O / CF heterojunction catalyst according to any one of claims 1 to 9 in the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) under industrial-grade current to prepare 2,5-furandicarboxylic acid (FDCA).

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