Preparation method and application of Pd-Cu2O / TF composite electrode

Abstract

The invention belongs to the technical field of preparation of environmental functional materials, and provides a preparation method and application of a Pd-Cu2O / TF composite electrode, and a catalyst is prepared through a one-pot method. The preparation method comprises the following steps: (1) taking copper sulfate pentahydrate (CuSO4. 5H2O), potassium sodium tartrate (C4H4O6KNa), potassium hydroxide (KOH) and palladium chloride (PdCl2) as raw materials to obtain a Pd-Cu2O composite solution; and (2) preparing the Pd-Cu2O catalyst through centrifugal drying in a continuous heating and stirring manner, and changing the heating temperature of the catalyst to obtain the Pd-Cu2O catalyst at different temperatures. The catalyst prepared by the method has the capability of reducing nitrate radicals and bicarbonate radicals so as to generate urea, and has a good application prospect in the field of environmental protection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental functional material preparation, and relates to a preparation method of a Pd-Cu2O / TF composite electrode and application of the Pd-Cu2O / TF composite electrode in electrocatalytic reduction of nitrate and bicarbonate to generate urea, and belongs to the field of environmental protection. BACKGROUND

[0002] Urea, as an organic material with high nitrogen content, is widely used in the field of agriculture. At the same time, urea can also be converted into ammonium carbonate, ammonium bicarbonate and other ammonium nitrogen for crops to absorb, and the urea production of China accounts for more than half of the total global fertilizer market. In addition, urea is also an indispensable key raw material in industrial production, which can be used to produce urea formaldehyde, barbiturate and other fine chemicals. The good moisturizing property of urea is also applied in the cosmetic industry. With the rapid growth of population and the rapid development of industry, urea will face greater demand in the country and even the world. Among them, the Haber-Bosch method still dominates the industrial production of urea, of which the synthesis of urea accounts for 80%. Using ammonia and carbon dioxide as raw materials, urea synthesis is carried out at high temperature (150-200℃) and high pressure (150-250bar). The energy consumption of the Haber-Bosch process accounts for 1%-2% of the global energy consumption, and such excessive consumption has intensified greenhouse gas emissions. Using renewable electric energy technology to carry out urea electro-synthesis is expected to overcome these shortages. So far, many metal-based materials (Bi, Au, etc.) or non-metallic materials (B, P, etc.) represent the most advanced electrocatalysts for high-efficiency synthesis of ammonia. However, the further synthesis of industrial urea through the reaction of ammonia and carbon dioxide also depends on extreme conditions, which leads to complexity and impracticality. In recent years, nitrogen and carbon dioxide are used as nitrogen source and carbon source respectively to synthesize urea by electrochemical method. Although the use of electrocatalysts has achieved high-efficiency C-N coupling, there are still difficulties in breaking the nitrogen-nitrogen bond of N2. However, the high dissociation energy of N≡N (941kJ mol -1 ) and the limited solubility of N2 in water (0.02v / v, 298K, 1atm) inevitably lead to low yield and efficiency of urea, in this regard, nitrate (NO3 - ) is a very ideal solid nitrogen-containing reactant. Given the advantage of lower dissociation energy of N=O (204kJ mol -1 ) compared with N≡N (941kJ mol-1). And CO2 into water to form HCO3 - can provide the carbon source required for reduction, although the solubility of CO2 is higher than that of N2, but it is still in the gas dissolved in water, and the solubility at room temperature (25℃) is 0.144g / 100g water, which is much smaller than that of HCO3 - .

[0003] Then the current stage of the research of electrocatalytic reduction of nitrate and carbon dioxide to generate urea is mostly with low urea yield and low faradic efficiency, which cannot be applied to the actual.

[0004] Therefore, it is urgent to seek a preparation method of Pd-Cu2O / TF composite electrode to improve the urea yield and faradic efficiency. SUMMARY

[0005] In view of the existing problems, a preparation scheme of Pd-Cu2O / TF composite electrode is provided, and the preparation scheme has low implementation cost and simple raw materials.

[0006] In order to achieve the above purpose, one embodiment of the present application provides a preparation method of Pd-Cu2O / TF composite electrode, which comprises the following steps:

[0007] (1) Preparation of Pd-Cu2O electrocatalyst

[0008] CuSO4·5H2O (0.7g), C4H4O6KNa (2.51g) and KOH (0.448g) were dissolved in 250mL deionized water to obtain an alkaline complex solution. After stirring for 30 minutes, ultrasonic was performed for 5 minutes, then 5mg PdCl2 and 10mL of 0.25mol / L glucose solution were added to the above complex solution in turn, ultrasonic was performed for 5min to obtain a light brown solution. Constant temperature heating was performed in a water bath at 65, 75, 85℃ for 2.5h, the final product was collected by centrifugation, washed with water and ethanol for several times, and then dried in a vacuum oven at 50℃ for 10h to obtain Pd-Cu2O-X℃ powder.

[0009] (2) Preparation of Pd-Cu2O composite electrode

[0010] 8mg of powdered Pd-Cu2O catalyst, 2mg of conductive material and 40μL of adhesive were dispersed in 760μL of anhydrous ethanol, and ultrasonic was performed for 1h to form a uniform ink. 10μL of the homogeneous ink was drop-casted on a titanium foam electrode with an area of 1×1cm2.

[0011] In the step (1), the Pd-Cu2O-X℃ powder was prepared at a temperature of 65, 75, 85℃ respectively;

[0012] In the step (1), the ultrasonic power was 500W, the ultrasonic time was 5min; the water bath pot rotation speed was 1000rpm, and the stirring time was 2.5h;

[0013] In the step (2), the conductive material was graphite, and the adhesive was Nafion solution (5wt.%);

[0014] In the step (2), the foam titanium electrode needs to be pretreated.

[0015] According to one embodiment of the present application, the Pd-Cu2O-X℃ / TF composite electrode prepared by the above preparation method is provided, and the prepared Pd-Cu2O-X℃ / TF composite electrocatalyst is applied to the co-reduction of nitrate and bicarbonate to generate urea.

[0016] Material source

[0017] Copper sulfate pentahydrate, anhydrous glucose, potassium sodium tartrate, palladium chloride, thiosemicarbazide, ethanedioyl monooxime, and anhydrous ferric chloride are all analytically pure and are provided by Aladdin. Potassium hydroxide is analytically pure and is provided by Macklin.

[0018] Beneficial effects

[0019] In summary, the present application has the following beneficial effects:

[0020] As can be seen from the technical scheme provided by the above preparation method and application of the Pd-Cu2O-X℃ / TF composite electrode, the Pd-Cu2O-X℃ electrocatalyst is loaded on the foam titanium. The Pd-Cu2O prepared at 75℃ has the highest electrocatalytic activity, and the urea yield of the reduction of 100ml of a mixed solution of nitrate and bicarbonate with a concentration of 0.1mol / L and 0.15mol / L can reach 1173μgh -1 mg cat -1 within 2 hours, and the Faraday efficiency can reach 52%. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a preparation diagram of Pd-Cu2O-75℃ catalyst.

[0022] Figure 2 It is an SEM diagram of Pd-Cu2O-75℃.

[0023] Figure 3 It is an x-ray diffraction spectrum diagram of Pd-Cu2O-75℃ electrocatalyst.

[0024] Figure 4 It is an x-ray photoelectron spectroscopy diagram of Pd-Cu2O-75℃ electrocatalyst.

[0025] Figure 5 It is a urea yield diagram of Pd-Cu2O-75℃ / TF composite electrode

[0026] Figure 6 It is an electrode stability diagram of Pd-Cu2O-75℃ / TF composite electrode

[0027] Figure 7Pd-Cu2O-75 °C catalyst reduction mechanism diagram DETAILED DESCRIPTION

[0028] In order for those skilled in the art to more clearly understand the present application, the following further describes the present application in conjunction with the examples, but it should be understood that the following examples are merely preferred embodiments of the present application, and the scope of the present application claimed is not limited only to this.

[0029] Example 1:

[0030] The following method is used to prepare the Pd-Cu2O-75 °C / TF composite electrode according to the present application:

[0031] (1) 0.7 g of CuSO4·5H2O, 2.51 g of C4H4O6KNa and 0.448 g of KOH were weighed separately and dissolved in 250 mL of deionized water to obtain an alkaline composite solution. After stirring for 30 minutes, ultrasonic treatment was performed for 5 minutes, and then 5 mg of PdCl2 and 10 mL of a glucose solution with a concentration of 0.25 mol / L were added to the above composite solution in sequence, ultrasonic treatment was performed for 5 min, and a light brown solution was obtained. Constant temperature heating was performed in a water bath at 65, 75 and 85 °C for 2.5 h, respectively, the final product was collected by centrifugation, washed with water and ethanol several times, and then dried in a vacuum oven at 50 °C for 10 h to obtain Pd-Cu2O-X °C powder.

[0032] (2) 8 mg of powdered Pd-Cu2O-X °C catalyst, 2 mg of conductive material and 40 μL of adhesive were dispersed in 760 μL of anhydrous ethanol, and ultrasonic treatment was performed for 1 h to form a uniform ink. 10 μL of the homogeneous ink was drop-casted on a titanium foam electrode with an area of 1 × 1 cm 2 .

[0033] Example 2:

[0034] The same steps as in Example 1 were followed, except that the performance of the sample was evaluated by the yield of urea generated by the co-reduction of nitrate and bicarbonate. The Pd-Cu2O-X °C catalyst prepared at the above three different preparation temperatures was loaded on a titanium foam to form a composite electrode, which was placed in an H-type electrolytic cell, and a three-electrode system was used to apply a potential of -1.4 V vs Ag / AgCl to perform the reduction reaction. Under magnetic stirring, the reduction was performed for 2 h, and after the reaction was completed, 2 mL of the solution was removed and its concentration was determined by oxaldehyde spectrophotometry at λ = 525 nm. The urea yield and Faraday efficiency were calculated according to the loading amount. Each group of experiments was repeated three times to ensure the accuracy of the experiments.

[0035] Example 3:

[0036] The preparation process of Example 1 is carried out by the same steps, except that the prepared Pd-Cu2O-75℃ / TF composite electrode is taken out every 30 minutes in 0.15 mol / L KHCO3 and 0.1 mol / L KNO3 solution in an H-type electrolytic cell, 4 mL of the solution is filtered and then analyzed for catalytic ability. After the completion of the catalytic experiment, the composite electrode is taken out, the surface of the electrode is cleaned, and then used. The above reduction experiment is repeated to test the stability of the Pd-Cu2O-75℃ / TF composite electrode. Referring to Figure 5 It can be seen that the urea yield of the Pd-Cu2O-75℃ / TF composite electrode of the present application is still up to 1165 μg / h -1 mg cat -1 and the faradic efficiency is up to 50%, so the electrode has good stability.

[0037] Example 4:

[0038] The preparation process of Example 1 is carried out by the same steps, except that the (111) crystal surface of Pd-Cu2O-75℃ is taken as the calculation model, and four N-containing intermediates *NO, *N, *NH and *NH2 that may occur C-N coupling are considered. Since the protonation process of the intermediate competes with the C-N coupling process, the energy barriers of the protonation and C-N coupling of the N-containing intermediate on the (111) crystal surface of Pd-Cu2O-75℃ are analyzed and compared respectively. Referring to Figure 6 It can be seen that the Pd-Cu2O-75℃ / TF composite electrode of the present application can reduce the energy barrier of carbon-nitrogen coupling after breaking the energy barrier twice, so that the energy required for the generation of adsorbed urea is reduced, and the generation process is relatively mild, without a large amplitude of energy transition, so the electrode can reduce the energy barrier of carbon-nitrogen coupling

[0039] The above is only a preferred embodiment of the present application, and is not a limitation on the form and substance of the present application. It should be noted that for ordinary skilled persons in the art, some improvements and supplements can be made without departing from the method of the present application, and these improvements and supplements should also be considered as the protection scope of the present application. For those skilled in the art, some minor changes, modifications and equivalent changes made by utilizing the disclosed technical content without departing from the spirit and scope of the present application are equivalent embodiments of the present application; at the same time, any equivalent changes, modifications and evolution of the above-mentioned embodiments made according to the essential technology of the present application are still within the scope of the technical solutions of the present application.

Claims

1. A method for preparing a Pd-Cu2O / TF composite electrode, the preparation method steps are as follows: Powdered Pd-Cu₂O catalyst was prepared using a one-pot method. 0.7 g of CuSO₄·5H₂O and 2.51 g of C₄H₂O were weighed out. -4 O6KNa and 0.448g KOH were added to 250mL of deionized water, stirred for 30 minutes, and then sonicated for 5 minutes. 5mg PdCl2 and 10mL of 0.25mol / L glucose solution were then added sequentially. (2) The solution after adding PdCl2 was heated in a water bath at 1000 rpm for 2.5 hours. After the reaction was complete and allowed to cool naturally, the sample was removed, centrifuged, and the solid product was collected. The product was thoroughly washed with anhydrous ethanol and deionized water, and then dried in a forced-air drying oven for several hours to obtain powdered Pd-Cu2O catalyst. 8 mg of powdered Pd-Cu₂O catalyst, 2 mg of conductive material, and 40 μL of binder were dispersed in 760 μL of anhydrous ethanol and sonicated for 1 h to form a uniform ink. 10 μL of the homogeneous ink was then drop-coated in batches onto a surface with an area of ​​1 × 1 cm². 2 Each time the foam titanium electrode is coated, it is dried.

2. The preparation method according to claim 1, characterized in that, In step (2), The Pd-Cu₂O is octahedral cuprous oxide, and the average mass loading of the Pd-Cu₂O catalyst is approximately 0.1 mg·cm⁻¹. -2 . The conductive material is carbon black, and the binder is Nafion solution (5 wt%).

3. The preparation method according to claim 1, characterized in that, In step (2), The preparation temperatures of Pd-Cu2O were 65, 75, and 85 °C, respectively. The conductive material is carbon black, and the binder is Nafion solution (5 wt%).

4. The preparation method according to claim 1, characterized in that, In step (1): the ultrasonic power is 500W and the ultrasonic time is 5min; the water bath stirring speed is 1000rpm and the stirring time is 30min.

5. The preparation method according to claim 1, characterized in that, In step (1): the ultrasonic power is 500W and the ultrasonic time is 5min; the water bath stirring speed is 1000rpm and the stirring time is 30min.

6. The preparation method according to claim 1, characterized in that, In step (1): the centrifuge speed is 5000 rpm, the centrifugation time is 10 min; the drying temperature is 60℃, and the drying time is 10-12 h.

7. The Pd-Cu2O / TF composite electrode prepared by the synthesis method according to claim 1 is applied to the co-reduction of nitrate and bicarbonate to generate urea.

Images