Preparation method and application of nano-copper-based integrated electrode material

Abstract

The invention discloses a preparation method of a nano-copper-based integrated electrode material and application of the nano-copper-based integrated electrode material in an electrocatalytic hydrogenation reaction of a biomass derived platform compound 5-hydroxymethylfurfural (HMF). According to the electrode system, a pure copper material is used as a substrate, an in-situ growth self-supporting nano-copper-based integrated electrode can be obtained through a simple chemical oxidation method, and then more excellent and stable hydrogenation performance is obtained through electrochemical reduction activation treatment. The preparation method of the catalytic electrode has the advantages of wide raw material source, low price, simplicity in operation, cleanness, environment friendliness and easiness in scale amplification, the preparation cost can be effectively reduced, and environmental pollution and consumption of rare metals are avoided. Meanwhile, the prepared nano-copper-based integrated electrode can efficiently catalyze HMF hydrogenation in a wide pH range to obtain a high value-added product 2, 5-bis (hydroxymethyl) furan (BHMF), shows excellent stability, and has a good industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of materials science, and particularly to a preparation method and application of a nano copper-based integrated electrode material. Background Art

[0002] Biomass resources have attracted much attention as the only renewable and sustainable non-fossil carbon source. Among them, lignocellulose is the most abundant biomass resource on the earth, and the total amount generated by photosynthesis every year reaches 100-200 billion tons. Therefore, governments of various countries are strongly supporting and encouraging scientific and technological innovation in the fields of producing fuels, bulk chemicals, high-value-added fine chemicals, etc. from lignocellulose. The traditional method of thermocatalytic biomass conversion has harsh reaction conditions, requires high temperature, high-pressure gas and the introduction of additional oxidizing / reducing agents, and has certain limitations. The electrocatalytic conversion method is only driven by the electrochemical potential, can occur in an aqueous medium without adding additional oxidizing and reducing agents and under normal temperature and pressure conditions, and has the advantages of controllability, cleanliness and economy. In addition, electricity can be provided by renewable energy sources such as solar energy and wind energy, which has important practical significance for alleviating the dual pressures of energy and environment, and shows broad application prospects.

[0003] At present, the research on the electrocatalytic hydrogenation process of lignocellulose-based platform compounds has received extensive attention. For example, Chinese Patent CN113373464B discloses a method for electrocatalytic conversion of lignin derivatives to prepare cycloalkanes. This method uses a carbon-based material loaded with noble metals such as ruthenium, platinum, palladium, and rhodium as the cathode catalyst, and at the same time adds a sodium borohydride reducing agent to the cathode electrolyte. The conversion rate of lignin-derived phenols reaches more than 90%, and the Faraday efficiency exceeds 90%. Although noble metal materials show high activity, their high price severely restricts the wide application of such catalysts. Therefore, there is an urgent need to design efficient non-noble metals to replace noble metals.

[0004] Research shows that copper-based compounds exhibit high charge efficiency and stability in electrocatalytic hydrogenation reactions. For example, Chinese Patent CN117721487A discloses a copper-based catalyst supported on rod-shaped zinc oxide, which can electrocatalytically semi-hydrogenate alkynes with an olefin selectivity of up to 93.4% and a Faraday efficiency of 30%. This method first obtains a zinc oxide support by heating and reacting a zinc source with ammonia water and reducing it with sodium borohydride, then loads a copper source by the impregnation method, and further calcines it in a muffle furnace to obtain catalyst powder. Finally, the catalyst powder is dispersed and bonded to a conductive substrate to obtain a catalytic electrode. However, limited by the poor intrinsic activity of transition metal-based materials, the electrochemistry activity involved in the above technology still needs to be improved; by bonding a heterogeneous catalytic material on the electrode substrate, its bonding strength with the substrate is weak, often resulting in poor electrode stability. More importantly, high-temperature calcination is commonly used in the existing preparation methods to prepare electrode catalysts. This method has high energy consumption and great danger, and is also affected by the magnification effect, making it difficult to achieve large-scale batch production. Summary of the Invention

[0005] To overcome the above problems, the purpose of the present invention is to provide a method for in-situ preparing an efficient copper-based electrocatalytic hydrogenation electrode. The preparation method involves a simple two-step chemical oxidation-electrochemical reduction method to prepare a nano-copper-based integrated electrode with a high electrochemically active surface area and a specific crystal plane composition. The obtained electrode exhibits high electrocatalytic hydrogenation activity and long-term chemical and performance stability for biomass-based platform compound HMF in a wide pH range of media from strong acid to strong base, and the method is simple to operate and applicable to large-scale production.

[0006] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0007] The present invention provides a preparation method of a nano-copper-based integrated electrode material, including the following steps:

[0008] (1) Dissolve an alkali source in pure water, stir and add a persulfate to prepare a mixed solution. Then, place the pure copper conductive substrate obliquely in the mixed solution, let it stand for reaction, and after the reaction is completed, wash and dry it to obtain an electrode material;

[0009] (2) Use the electrode material prepared above as a working electrode and perform electroreduction activation treatment in an alkaline electrolyte. After the reaction is completed, wash and dry it.

[0010] As a possible implementation manner, further, in step (1), the pure copper conductive substrate is selected from any one of copper plates, copper foams, copper felts, and copper meshes; before use, it is pretreated for deoxidation, deoiling, and impurity removal by a conventional acidification treatment method; specifically, the pure copper conductive substrate is ultrasonically washed successively with absolute ethanol, deionized water, dilute hydrochloric acid, and deionized water.

[0011] As a possible implementation, further, the base source in step (1) is selected from any one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium bicarbonate, potassium bicarbonate, sodium carbonate, and potassium carbonate; the concentration of the base source in the mixed solution is 0.1 - 5 mol / L;

[0012] The sulfate is selected from any one or more of ammonium persulfate, sodium persulfate, and potassium persulfate; the concentration of the sulfate in the mixed solution is 0.05 - 2 mol / L.

[0013] As a possible implementation, further, the static reaction time in step (1) is 5 - 100 min.

[0014] As a possible implementation, further, the pH of the electrolyte in step (2) is 11 - 15, and the concentration of the electrolyte in the electrolyte is 0.1 - 5 mol / L.

[0015] As a possible implementation, further, the electroreduction activation treatment is selected from one of chronoamperometry, chronopotentiometry, linear sweep voltammetry, and cyclic voltammetry;

[0016] The constant potential of the chronoamperometry is in the range of 0 - -1.5 V (versus reversible hydrogen electrode, the same below), and the reaction time is 1 - 120 min;

[0017] The constant current density of the chronopotentiometry is in the range of -5 - -100 mA / cm 2 range, and the reaction time is 1 - 120 min;

[0018] The scanning potential range of the linear sweep voltammetry is 0 - -1.5 V, the scanning rate is 1 - 200 mV / s, and the number of scanning cycles is 5 - 200 cycles;

[0019] The scanning potential range of the cyclic voltammetry is 0 - -1.5 V, the scanning rate is 1 - 200 mV / s, and the number of cyclic scanning cycles is 5 - 200 cycles.

[0020] The present invention also provides a nano - copper - based integrated electrode material, which has a high proportion of Cu(110) crystal planes and is prepared by the above - mentioned preparation method. The prepared nano - copper - based integrated electrode material can be applied to the electrocatalytic hydrogenation reaction of 5 - hydroxymethylfurfural in a medium with a wide pH range; where the pH range is 1 - 15.

[0021] As a possible implementation, further, a two - electrode / three - electrode system is composed of a nano - copper - based integrated electrode, and a biomass - based platform compound 5 - hydroxymethylfurfural is added to the electrolyte;

[0022] The concentration of the electrolyte is 0.1 to 5 mol / L; the concentration of 5-hydroxymethylfurfural (HMF) is 1 to 500 mmol / L.

[0023] During the performance test, linear sweep voltammetry test and cyclic stability test are carried out respectively. During the cyclic stability test, a certain voltage is applied to the electrode, the reaction is carried out cyclically for many times, the current-time curve is recorded, and the products in the reaction process are analyzed by high performance liquid chromatography.

[0024] In the present invention, a nano-copper-based integrated electrode is prepared by a simple two-step method of chemical immersion oxidation-electrochemical reduction and applied to the electrocatalytic hydrogenation reaction of HMF. In the electro-hydrogenation reaction, the reduced zero-valent metallic copper is the main active site for electrocatalytic hydrogenation. The increase in the electrochemical specific surface area of metallic copper helps to improve the conversion rate of substrate HMF hydrogenation. More importantly, the crystal planes exposed by the metallic copper sites have an important influence on the selectivity of HMF hydrogenation products and the charge efficiency. Among them, the Cu(110) crystal plane has a more moderate adsorption capacity for HMF, which can effectively promote the hydrogenation of substrate HMF and avoid the formation and polymerization of free radical molecules, inhibit the formation of by-products dimers 5,5-bis(hydroxymethyl)dihydrofuran (BHH) and hydrogen, and thus highly selectively generate 2,5-bis(hydroxymethyl)furan (BHMF).

[0025] In the present invention, a chemical oxidation reaction occurs between an alkali source and persulfate and a copper substrate to in-situ grow a copper hydroxide precursor on the substrate, showing a smooth nano-linear structure on the surface, increasing the electrochemical active specific surface area of the electrode substrate. In the subsequent electrochemical reduction activation process, the copper hydroxide precursor is in-situ reduced to metallic copper. During the reduction process, with the breaking of the Cu-O bond and the release of OH, the surface atoms of copper are reconstructed, and the smooth surface on the original nano-wire structure is further broken to form irregular nano-copper grains, increasing the surface roughness and obtaining a higher electrochemical active specific surface area. Moreover, there are greater advantages in carrying out electro-reduction activation in an alkaline medium compared with acidic and neutral media. This is because in an alkaline medium, the presence of OH - ions will make the reduction and reconstruction speed of the copper surface slower than that in acidic and neutral media, which is beneficial to the growth of the non-dominant crystal plane Cu(110) crystal plane, thus exposing more Cu(110) crystal planes with better adsorption effect on the substrate HMF.

[0026] In addition, in the technical solution of the present invention, the electrode with a copper hydroxide precursor is not calcined under different atmospheres, but directly electrochemically reduced and activated. During the calcination process, copper precursors with different oxidation states are obtained. Due to different bond-breaking speeds during the reduction process of copper precursors with different oxidation states, different crystal plane compositions and boundary sites will be exposed, thereby affecting the adsorption capacity for the substrate HMF and reaction intermediates, and further affecting the selectivity and charge efficiency of the HMF hydrogenation product. For example, the copper hydroxide precursor without calcination can form a higher proportion of Cu(110) crystal planes during the reduction process, while the cuprous oxide precursor is generated after calcination in an inert atmosphere, and a higher proportion of Cu(100) crystal planes are formed after reduction, with an increase in hydrogen generation selectivity and a decrease in the production efficiency of BHMF.

[0027] Finally, since no additional copper source and other heterogeneous raw materials are added during the preparation process, copper hydroxide is in-situ grown with the copper substrate as the copper source to form an integrated electrode. Therefore, it has an extremely high bonding strength with the substrate and can have good cyclic stability during the long-term reaction process.

[0028] The present invention has the following beneficial effects compared with the prior art:

[0029] 1) The present invention uses a simple two-step method of chemical oxidation - electrochemical reduction to prepare a nano copper-based integrated electrode. This method has a simple and easy operation process, wide raw material sources, and low prices. During the subsequent reduction process, a copper-based electrode with a high electrochemically specific surface area and a high (110) crystal plane composition can be obtained, which can optimize the selectivity and charge efficiency of the hydrogenation product of 5-hydroxymethylfurfural (HMF), enabling it to obtain more excellent and stable hydrogenation performance.

[0030] 2) The nano copper-based integrated electrode prepared by the present invention can realize the electrocatalytic hydrogenation of HMF in a medium with a wide pH (pH range from 1 to 15), with high product selectivity and charge efficiency, good stability, and the reaction conditions are at room temperature, normal pressure, green and pollution-free, having good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is a schematic flow chart of the preparation method for Example 1 and the corresponding scanning electron microscope (SEM) images of the electrode material surface in the corresponding process; among them, Fig. (a) is for the preparation of Cu(OH) by the chemical oxidation - electrochemical reduction method2 -Schematic diagram of the ER / CF process; Figure (b) is the SEM image of CF after pretreatment; Figure (c) is the SEM image of Cu(OH) 2 / CF after chemical oxidation; Figure (d) is the SEM image of Cu(OH) 2 -SEM image of ER / CF.

[0033] Figure 2 For the nano copper-based integrated electrode (Cu(OH) 2 -ER / CF) after chemical oxidation-electrochemical reduction and the foam copper substrate (CF-ER) electrode that has not undergone chemical oxidation and has only been electrochemically reduced, the activity comparison of 5-hydroxymethylfurfural (HMF) hydrogenation in different pH media; among them, Figures (a-d) are linear sweep voltammetry (LSV) curves in strong base (1M KOH, pH = 14), weak base (0.5M KHCO 3 , pH = 10.3), neutral (0.1M PBS, pH = 7.4), and strong acid (0.5M H 2 SO 4 , pH = 1) electrolytes.

[0034] Figure 3 Structural characterization of the electrode precursors obtained under different oxidation treatment conditions and the corresponding electrodes after electrochemical reduction: (a) X-ray diffraction spectrum (XRD) of the precursor; (b) X-ray photoelectron spectroscopy (XPS) of the precursor; (c) Raman spectrum of the precursor; (d) XRD after reduction; (e) XPS after reduction; (f) In-situ Raman spectrum of the Cu(OH) 2 / CF electrode during the reduction process. Among them, the electrode without any oxidation treatment is CF, and after reduction it is CF-ER; the electrode after chemical oxidation is Cu(OH) 2 / CF, and after reduction it is Cu(OH) 2 -ER / CF; the electrode further calcined in air after chemical oxidation is CuO / CF, and after reduction it is CuO-ER / CF. The electrode further calcined in argon after chemical oxidation is Cu 2 O / CF, and after reduction it is Cu 2 O-ER / CF.

[0035] Figure 4 For Cu(OH) 2 / CF (a, b), CuO / CF (c, d) before and after reduction, and Cu 2O / CF(e,f) Electrode Performance Comparison: Among them, Figures (a), (c), and (e) show the comparison of the conversion (Conv.) of HMF, the selectivity of BHMF, and the Faraday efficiency (FE) results of HMF at a potential of -0.15 V vs RHE in 0.1 M KOH containing 5 mM HMF; Figures (b), (d), and (f) show the linear sweep voltammetry (LSV) curve comparison in 0.1 M KOH containing 50 mM HMF.

[0036] Figure 5 The comparison of the conversion rate (Conv.) of HMF, the product 2,5-bis(hydroxymethyl)furan (BHMF), hydrogen (H 2 ), dimer 5,5-bis(hydroxymethyl)hydrofuran (BHH), and the Faraday efficiency (FE) of other by-products (other) as well as the productivity of BHMF for the electrodes after electrochemical reduction of four different oxidation state precursors in 0.1 M KOH electrolyte containing 5 mM HMF at a potential of -0.15 V.

[0037] Figure 6 Characterization of the surface crystal plane composition of the electrodes after electrochemical reduction of different oxidation state precursors: (a) Grazing incidence XRD (GIXRD) spectra; (b) In-situ OH - electrochemical adsorption (OH - EA) and (c) cyclic voltammetry (CV) curves of in-situ lead underpotential deposition (Pb UPD) and (d) Pb UPD fitting results; (e) Surface crystal plane composition of the four electrodes after electroreduction.

[0038] Figure 7 For the cyclic stability results of the HMF electroreduction reaction of the Cu(OH) 2 -ER / CF electrode; among them, Figure (a) shows the 5-cycle results of HMF Conv., BHMF selectivity (Sel), and FE; Figure (b) shows the 5-cycle results of the current density changing with time. Detailed Implementation Manner

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0040] Example 1

[0041] 1) Pretreatment of copper foam (CF): Ultrasonic treatment is carried out twice in acetone or ethanol to degrease and remove oil, ultrasonic cleaning is carried out in ultrapure water for 10 min and repeated twice, then ultrasonic acidification activation is carried out in 1-2 mol / L dilute hydrochloric acid solution for 20 min to remove surface oxides, and finally ultrasonic cleaning is carried out in ultrapure water for 10 min and repeated twice. The pretreated CF is soaked in ultrapure water for standby to relieve its surface oxidation.

[0042] 2) Weigh 4 g of sodium hydroxide and dissolve it in 40 mL of deionized water. While stirring, add 0.1920 g of ammonium persulfate to prepare a mixed solution. The pretreated substrate material is placed obliquely in the solution, and the static reaction time is 20 min. After the reaction is completed, it is rinsed with deionized water and dried at 60 °C to obtain Cu(OH) 2 / CF.

[0043] 3) Using a three-electrode system, the electrode obtained in step 2) is used as the working electrode, and in 0.1 M KOH electrolyte, electroreduction treatment is carried out by linear sweep voltammetry. The scanning range is 0.2~-0.4 V, and the number of scanning cycles is 20 cycles to obtain Cu(OH) 2 -ER / CF electrode.

[0044] SEM characterization was carried out on CF, Cu(OH) 2 / CF, and Cu(OH) 2 -ER / CF electrodes at each stage in Example 1. Figure 1 The preparation flow chart of Example 1 and the SEM photos of the above three electrodes are shown. From Figure 1 (b), it can be seen that the surface of CF is relatively smooth, and at the same time, it can be observed that there are some cubic particles on the surface, which may be formed due to the oxidation of the material exposed to the air; Figure 1 (c) corresponds to Cu(OH) 2 / CF. It can be seen that after chemical oxidation in an alkaline solution, a nanowire structure grows on the surface of CF. Further, after the electroreduction treatment of Cu(OH) 2 / CF, broken irregular nano-Cu grains are formed on the electrode surface, with significantly increased grain boundaries and boundary positions, as shown in Figure 1 (d).

[0045] Example 2

[0046] 1) Pretreatment of CF: Ultrasonic treatment is carried out twice in acetone or ethanol to degrease and remove oil, ultrasonic cleaning is carried out in ultrapure water for 10 min and repeated twice, then ultrasonic acidification activation is carried out in 1-2 mol / L dilute hydrochloric acid solution for 20 min to remove surface oxides, and finally ultrasonic cleaning is carried out in ultrapure water for 10 min and repeated twice. The pretreated CF is soaked in ultrapure water for standby to relieve its surface oxidation.

[0047] 2) Weigh 4 g of sodium hydroxide, dissolve it in 40 mL of deionized water, and add 0.1920 g of ammonium persulfate while stirring to prepare a mixed solution. Place the pretreated substrate material obliquely in the solution, let it stand for 20 min for the reaction, after the reaction is completed, rinse it with deionized water, and dry it at 60 °C to obtain Cu(OH) 2 / CF.

[0048] 3) Use the electrode obtained in step 2) to calcine the prepared Cu(OH) 2 / CF in air at 200 °C with a heating rate of 1 °C / min and a calcination time of 2 h to obtain CuO / CF.

[0049] 4) Adopt a three-electrode system, use the electrode obtained in step 3) as the working electrode, in 0.1 M KOH electrolyte solution, perform electroreduction treatment by linear sweep voltammetry, with the scanning range of 0.2 - 0.4 V, to obtain the CuO-ER / CF-ER electrode.

[0050] Example 3

[0051] 1) Pretreatment of CF: Ultrasonic it twice in acetone or ethanol to degrease and remove oil, ultrasonic clean it in ultrapure water for 10 min and repeat twice, then ultrasonic acidify and activate it in 1 - 2 mol / L dilute hydrochloric acid solution for 20 min to remove surface oxides, and finally ultrasonic clean it in ultrapure water for 10 min and repeat twice. Immerse the pretreated CF in ultrapure water for standby to relieve its surface oxidation.

[0052] 2) Weigh 4 g of sodium hydroxide, dissolve it in 40 mL of deionized water, and add 0.1920 g of ammonium persulfate while stirring to prepare a mixed solution. Place the pretreated substrate material obliquely in the solution, let it stand for 20 min for the reaction, after the reaction is completed, rinse it with deionized water, and dry it at 60 °C to obtain Cu(OH) 2 / CF.

[0053] 3) Use the electrode obtained in step 2) to calcine the prepared Cu(OH) 2 / CF in argon at 550 °C with a heating rate of 1 °C / min and a calcination time of 3 h.

[0054] 4) Adopt a three-electrode system, use the electrode obtained in step 3) as the working electrode, in 0.1 M KOH electrolyte solution, perform electroreduction treatment by linear sweep voltammetry, with the scanning range of 0.2 - 0.4 V, to obtain Cu 2 O-ER / CF electrode.

[0055] Example 4

[0056] 1) Pretreatment of CF: Ultrasonic twice in acetone or ethanol to degrease and remove oil, ultrasonic clean in ultrapure water for 10 min and repeat twice, then ultrasonic acidify and activate in 1 - 2 mol / L dilute hydrochloric acid solution for 20 min to remove surface oxides, and finally ultrasonic clean in ultrapure water for 10 min and repeat twice. Immerse the pretreated CF in ultrapure water for standby to relieve its surface oxidation.

[0057] 2) Adopt a three - electrode system, use the electrode obtained in step 1) as the working electrode, and perform electro - reduction treatment by linear sweep voltammetry in 0.1 M KOH electrolyte with a scanning range of 0.2 - 0.4 V to obtain the CF - ER electrode.

[0058] The electrocatalytic hydrogenation performance test of the electrodes prepared in Examples 1 - 4 is carried out according to the following method:

[0059] Adopt a three - electrode system, the working electrode is the prepared copper - based electrode, the counter electrode is a platinum sheet electrode, and the reference electrode is a saturated calomel electrode. The electrochemical test is carried out on an admiral electrochemical workstation, and the electrolyte is different medium electrolytes with or without a certain concentration of HMF. When testing the linear sweep voltammetry curve, the scanning rate is 5 mV / s, the electrode potential is corrected for iR and converted to the electrode potential relative to the reversible hydrogen electrode (RHE). The electrolysis test and the cyclic performance test adopt chronoamperometry (it), and a constant - potential test is carried out at - 0.15 V in 30 mL of 0.1 M KOH containing 5 mM HMF for 60 min.

[0060] For the analysis of electro - hydrogenation products, after the reaction is completed, collect 20 μL of the electrolyte sample and dilute it to 1 mL with ultrapure water, and then perform high - performance liquid chromatography (HPLC) analysis on Thermo Fisher Scientific UltiMate 3000. The HPLC is equipped with an ultraviolet - visible (UV) detector and a C18 column (4.6 mm×250 mm, 5 μm). Set the ultraviolet detection wavelength to 240 nm, the column temperature and the detector temperature to 45 °C. Adopt a binary gradient method, use water and acetonitrile as the eluent, and the flow rate is 0.6 mL / min. The specific steps of the binary gradient method: from 0 - 5 min, the acetonitrile / water (v / v) is 15%, from 5 - 8.33 min, it increases from 15% to 30%, then from 8.33 - 10 min, it increases from 30% to 50%, and finally from 10 - 13 min, it decreases to 15% and maintains this ratio until 20 min ends. In addition, H 2 The product is N 2As the carrier gas, it is discharged from the airtight cell through a gas flowmeter and subjected to gas chromatography (GC) analysis on a Shimadzu GC-2014ATFSPL-230C. The GC is equipped with a MolSieve column and a thermal conductivity detector (TCD).

[0061] The test results are compared with the standard calibration curve to determine the concentrations of all components except BHH. The calibration of BHH is estimated to be twice that of the BHMF standard curve. According to the HPLC test results, the corresponding HMF conversion rate, product selectivity, FE, and average productivity can be calculated by the following formulas:

[0062] Conv.(HMF) (%) = n(HMF) consumed / n(HMF) initial ×100% (1)

[0063] Sel. (%) = n(BHMF) formed / n(HMF) consumed ×100% (2)

[0064] FE (%) = n(certain product) formed × N e × F / Q passed ×100% (3)

[0065] Productivity (mmol·h -1 ·cm -2 ) = n(BHMF) formed / (A× T) ×100% (4)

[0066] where n is the molar amount of a certain component, N e is the molar ratio of electrons transferred in a specific product, F is the Faraday constant (96485 C·mol -1 ), Q is the amount of charge recorded by the electrochemical workstation, A is the geometric area of the electrode, and T is the reaction time.

[0067] Figure 2 (a-d) shows Cu(OH) in four media: strong base (1 M KOH, pH = 14), weak base (0.5 M KHCO 3 , pH = 10.3), neutral (0.1 M PBS, pH = 7.4), and strong acid (0.5 M H 2 SO 4 , pH = 1). 2-LSV curves of ER / CF and CF. As can be seen from the figure, in a wide pH range, the activity of electro-hydrogenation of HMF (containing HMF) is superior to that of hydrogen evolution (HER, without HMF). At the same time, after oxidation-reduction, Cu(OH) 2 - The electro-hydrogenation performance of HMF on the ER / CF electrode is much better than that of the CF-ER electrode without chemical oxidation treatment.

[0068] Figure 3 Structural characterizations of the four different oxidation state electrode precursors before and after reduction. As can be seen from Figure (a), strong metal Cu diffraction peaks are shown in the XRD patterns of the four electrodes, and the strong diffraction peaks are located at 43.3, 50.5 and 74.1° corresponding to the (111), (100) and (110) crystal planes. At the same time, the corresponding Cu 2 O, CuO and Cu(OH) 2 diffraction peaks exist for the electrodes with different oxidation treatments. The XPS spectra (Figure (b)) prove that the electrodes with different oxidation treatments have different Cu oxidation states on the surface. The Raman spectra further prove the formation of Cu 2 O, CuO and Cu(OH) 2 structures. The structures of the above four different oxidation state electrode precursors after electrochemical reduction are further characterized. As can be seen from the XRD (Figure (d)), only the diffraction peaks of metallic Cu are shown after reduction of different electrodes. The XPS (Figure (e)) results also show that the oxidized Cu is reduced to zero valence. Further in-situ Raman results show that during the reduction process, the Cu-O bond gradually disappears with the increase of the reduction potential. The above results indicate that after electrochemical reduction, the four different oxidation state electrode precursors are completely reduced to zero-valent metallic Cu.

[0069] Figure 4 Shows the effect of electrochemical reduction treatment on the electro-hydrogenation performance of the pre-oxidized electrodes. As can be seen from the figure, compared with the catalytic performance of the electrodes before electrochemical reduction (i.e., Cu(OH) 2 / CF, CuO / CF and Cu 2 O / CF), the HMF conversion rate, BHMF selectivity and FE of the electrodes after reduction (i.e., Cu(OH) 2 -ER / CF, CuO-ER / CF and Cu 2 O-ER / CF) are significantly improved, and the current density shown in their LSV is also significantly enhanced.

[0070] Figure 5Product analysis results of electrocatalytic hydrogenation of HMF on electrodes reduced from four different oxidation state precursors. As can be seen from the figure, on the electrodes modified by pre-oxidation, the conversion rate of HMF, the Faraday efficiency and the production efficiency of the reduction product BHMF are all better than those of the electrodes with other oxidation state precursors and the unoxidized CF-ER electrode. Among them, the Cu(OH) 2 -ER / CF electrode has the best performance, while on CF-ER, the FE of the by-product BHH reaches more than 30%.

[0071] Figure 6 Characterization results of the crystal plane composition on the surfaces of four electrodes after electrochemical reduction are shown. After fitting and quantification, the results are shown in Figure (e). The crystal plane composition on CF is changed after redox treatment. Among them, Cu(110) is most exposed on Cu(OH) 2 -ER / CF and least exposed on CF-ER. Taking GIXRD characterization as an example, the exposure trend of its Cu(110) crystal plane is: Cu(OH) 2 -ER / CF(0.28) > CuO-ER / CF(0.24) > Cu 2 O-ER / CF(0.22) > CF-ER(0.17). The exposure trend of Cu(100) is opposite. Since the surfaces of the four comparison electrodes are all zero-valent metal Cu, it can be considered that the exposure trend of the Cu(110) crystal plane is positively correlated with the reaction performance. Among them, Cu(OH) 2 -ER / CF with the highest proportion of the Cu(110) crystal plane has the best performance.

[0072] Figure 7 Cyclic stability test of the Cu(OH) 2 -ER / CF electrode. As shown in the figure, after 5 consecutive cycles, the conversion rate of HMF, the selectivity of BHMF and the FE all remain above 90%, and the change in the it curve can be ignored.

[0073] In summary, the present invention can prepare a nano copper-based integrated electrode through a simple two-step method of chemical oxidation-electrochemical reduction. The design idea of this preparation method is clear and novel, and the operation is simple. When this electrode is applied to the electrocatalytic hydrogenation reaction of 5-hydroxymethylfurfural (HMF), the reduced metallic copper is the main active site, and the chemical oxidation treatment can change the morphology of the copper substrate to form a nanowire structure, greatly increasing the electrochemically active surface area. At the same time, electroreduction activation in an alkaline medium is beneficial to the growth of the non-preferred crystal plane Cu(110) crystal plane, making the reduced metallic copper expose more (110) crystal planes, which can more effectively adsorb and activate the substrate HMF and intermediates, thus accelerating the hydrogenation reaction of the reaction substrate (HMF) to the specific product (BHMF). This catalyst exhibits excellent catalytic performance, achieving a HMF conversion rate of over 90% within 60 min of the reaction, and the production efficiency of BHMF reaches 0.12 mmol·h -1 ·cm -1 , and the BHMF yield and Faraday efficiency of over 90% can be achieved in five consecutive cycle reactions. This method has mild reaction conditions, a high BHMF yield, and is characterized by being clean, environmentally friendly, and economical.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a nano copper-based integrated electrode material, characterized in that: The steps include: (1) dissolving an alkali source in pure water, stirring and adding persulfate to prepare a mixed solution, placing a pure copper conductive substrate obliquely in the mixed solution, allowing it to react, and washing and drying after the reaction is completed to obtain an electrode material; (2) The electrode material prepared as above is used as a working electrode and subjected to an electro-reduction activation treatment in an alkaline electrolyte. After the reaction is completed, the electrode material is cleaned and dried.

2. The method for preparing the nano copper-based integrated electrode material according to claim 1, characterized in that: The pure copper conductive substrate in step (1) is selected from any one of copper plate, copper foam, copper felt and copper mesh; before use, it is pretreated by conventional acidification to remove oxygen, oil and impurities.

3. The method for preparing the nano copper-based integrated electrode material according to claim 1, characterized in that: The alkali source in step (1) is selected from any one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium bicarbonate, potassium bicarbonate, sodium carbonate, and potassium carbonate; the concentration of the alkali source in the mixed solution is 0.1 to 5 mol / L; The sulfate is selected from any one or more of ammonium persulfate, sodium persulfate, and potassium persulfate; the concentration of the sulfate in the mixed solution is 0.05-2 mol / L.

4. The method for preparing the nano copper-based integrated electrode material according to claim 1, characterized in that: The standing reaction time in step (1) is 5 to 100 minutes.

5. The method for preparing the nano copper-based integrated electrode material according to claim 1, characterized in that: The pH of the electrolyte in step (2) is 11 to 15, and the concentration of the electrolyte in the electrolyte is 0.1 to 5 mol / L.

6. The method for preparing the nano copper-based integrated electrode material according to claim 1, characterized in that: The electroreduction activation treatment in step (2) is performed by using one of chronoamperometry, chronopotentiometry, linear sweep voltammetry, and cyclic voltammetry; The constant potential of the chronoamperometry is in the range of 0 to -1.5 V, and the reaction time is 1 to 120 min; The constant current density of the chronopotentiometry is between -5 and -100 mA / cm 2 Within the range, the reaction time is 1 to 120 min; The linear scanning voltammetry method has a scanning potential range of 0 to -1.5 V, a scanning rate of 1 to 200 mV / s, and a scanning number of 5 to 200 circles; The scanning potential range of the cyclic voltammetry is 0 to -1.5 V, the scanning rate is 1 to 200 mV / s, and the number of cyclic scanning circles is 5 to 200 circles.

7. A nano copper-based integrated electrode material, characterized in that: The nano copper-based integrated electrode material has a high proportion of Cu (110) crystal planes and is prepared by the preparation method according to any one of claims 1 to 6.

8. An application of the nano copper-based integrated electrode material as claimed in claim 7, characterized in that: The nano copper-based integrated electrode material is applied to the electrocatalytic hydrogenation reaction of 5-hydroxymethylfurfural in a medium within a wide pH range; the pH range is 1-15.

9. The use according to claim 8, characterized in that: A two-electrode / three-electrode system is formed using nano-copper-based integrated electrodes, and the biomass-based platform compound 5-hydroxymethylfurfural is added to the electrolyte; The electrolyte concentration is 0.1-5 mol / L; the 5-hydroxymethylfurfural concentration is 1-500 mmol / L.

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