Preparation method of copper-doped nickel hydroxide self-supporting electroreduction nitrate catalyst

Abstract

The invention provides a preparation method of a copper-doped nickel hydroxide self-supporting electroreduction nitrate catalyst. The preparation method comprises the following steps: ultrasonically washing foamed nickel with ethanol, diluted hydrochloric acid and ultrapure water respectively; and then transferring the treated foamed nickel to a polytetrafluoroethylene lining containing a hydrogen peroxide aqueous solution and copper salt, assembling a reaction kettle, finally putting the reaction kettle into a drying oven for reaction, cooling to room temperature, taking out the self-supporting catalyst, cleaning with water, and drying to obtain the copper-doped nickel hydroxide material. The preparation method of the catalyst is an innovative construction method of an electro-catalysis nitrate reduction catalyst, a brand-new catalysis strategy is provided for normal-temperature and normal-pressure electro-catalysis water body nitrate reduction synthesis of ammonia, meanwhile, the preparation process route of the catalyst is simple and easy to implement, high electro-catalysis performance is achieved, and the method is suitable for industrial production. Certain potential application prospects are realized.

Description

Technical Field

[0001] The invention belongs to the field of nano material design and synthetic ammonia technology research, and relates to a method for preparing a copper-doped nickel hydroxide self-supporting electrocatalyst, which is applied to the electrocatalytic nitrate reduction synthetic ammonia reaction. Background Art

[0002] Ammonia (NH3) is a basic chemical raw material with a hydrogen content of up to 17.6wt.%. It is very easy to liquefy at room temperature and is a clean energy carrier. However, the current industrial NH3 production relies on the fossil fuel-driven Haber-Bosch process, which consumes about 1% to 2% of global energy and accounts for about 1.5% of global carbon dioxide emissions. Using nitrogen as a nitrogen source, synthesizing ammonia through electrochemical reduction reaction is expected to replace the Haber-Bosch process, but the N≡N triple bond energy is high (945kJ·mol -1 ), and the solubility of N2 in water is low. In addition, the quantification of ammonia in the electrochemical nitrogen reduction reaction remains challenging due to low yields and potential contamination from different sources. 3- ) has a lower N=O bond energy (204 kJ·mol -1 ), and NO 3- Due to its higher solubility in aqueous solution, the electrochemical reduction of nitrate is thermodynamically more favorable, making it a suitable nitrogen source for electrically driven NH3 synthesis under ambient conditions. However, the electrocatalytic reduction of nitrate to synthesize ammonia is a complex 8-electron process, which requires high-performance electrocatalysts to improve the activity and selectivity of the target product NH3.

[0003] At present, most of the reported electrocatalytic nitrate reduction to ammonia catalysts are coated on glassy carbon electrodes or carbon paper electrodes, and catalyst peeling is prone to occur during testing, causing performance degradation. Self-supporting electrocatalysts grow or anchor catalytically active substances directly on a conductive substrate without the need for adhesives, and their own three-dimensional porous network structure can not only ensure sufficient electrolyte infiltration, but also expose the electrochemically active sites on its surface as much as possible, which is beneficial to increase the effective contact area of ​​the catalyst. During the catalytic reaction, it can also quickly contact the reactants to form effective reaction intermediates, thereby increasing the reaction rate and product selectivity. In the field of electrocatalytic nitrate reduction to ammonia, there are still few research reports on self-supporting electrodes. Summary of the invention

[0004] Based on the above, the present invention discloses a method for preparing a copper-doped nickel hydroxide self-supporting nitrate reduction electrocatalyst.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] Add nickel foam to a polytetrafluoroethylene lining containing hydrogen peroxide and copper salt, assemble a reactor, put it into an oven and react at a certain temperature for a period of time. After cooling to room temperature, take out the self-supporting catalyst, wash it with water and then dry it to obtain a copper-doped nickel hydroxide self-supporting electrode material.

[0007] In the above technical solution, the area of ​​the nickel foam is 1 x 1 cm 2 ~1x 6cm 2 , the preferred range is 1x 2cm 2 ~1x4cm 2 .

[0008] In the above technical solution, the copper salt is any one of copper nitrate, copper chloride, copper acetate and copper sulfate.

[0009] In the above technical solution, the volume of the hydrogen peroxide is 20ml to 100ml, preferably in the range of 40ml to 70ml.

[0010] In the above technical solution, the mass fraction of hydrogen peroxide in water is 1wt.% to 10wt.%, preferably in the range of 3wt.% to 5wt.%.

[0011] In the above technical solution, the molar concentration of copper in water is 0.1 mmol L -1 ~2mmol L -1 , the preferred range is 0.2 mmol L -1 ~1mmol L -1 .

[0012] In the above technical solution, the reaction time is 2h to 12h, preferably in the range of 4h to 10h.

[0013] In the above technical solution, the oven temperature is 100-220°C, preferably in the range of 120-180°C.

[0014] In the above technical solution, the catalyst exhibits good electrocatalytic nitrate synthesis of ammonia activity in an alkaline electrolyte, the nitrate is potassium nitrate or sodium nitrate, the alkali is potassium hydroxide or sodium hydroxide, and the molar concentration ratio of the nitrate to the alkali is 0.1:1 to 2:1.

[0015] Compared with the prior art, the present invention has the following advantages and effects:

[0016] (1) The self-supporting electrocatalyst does not require a binder and effectively inhibits the shedding of active substances during the electrocatalytic nitrate reduction process.

[0017] (2) The nickel hydroxide formed in situ can effectively anchor copper and achieve high dispersion of copper.

[0018] (3) Copper promotes NO 3- The adsorption and conversion on the catalyst surface reduces the probability of hydrogen intermediates (*H) combining to form hydrogen and inhibits the competitive reaction of hydrogen evolution.

[0019] (4) Nickel hydroxide accelerates water dissociation, realizes precious metal-like *H supply and adsorption capacity at low potential, and promotes highly selective synthesis of ammonia.

[0020] (5) The catalyst preparation process is simple, highly reproducible, and easy to scale up.

[0021] In summary, the catalyst preparation method provided in this scheme is an innovative method for constructing electrocatalytic nitrate reduction catalysts, which provides a new catalytic strategy for synthesizing ammonia by electrocatalytic nitrate reduction in water at room temperature and pressure.

[0022] The catalyst preparation process proposed in the present invention is simple and feasible, achieves high electrocatalytic performance, and has certain potential application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 X-ray diffraction pattern of the catalyst of Example 1.

[0024] Figure 2 Scanning electron microscope image of the catalyst of Example 1. DETAILED DESCRIPTION

[0025] The present invention is further explained below in conjunction with the accompanying drawings and specific implementation methods.

[0026] Example 1

[0027] Take 1x3 cm 2 The nickel foam of the same area was ultrasonically washed with ethanol, dilute hydrochloric acid and ultrapure water for 10 minutes respectively; the treated nickel foam was transferred to a polytetrafluoroethylene liner containing 60 ml of a 4.5 wt.% hydrogen peroxide aqueous solution and 8 mg of cupric chloride, a reactor was assembled, and the reactor was put into an oven and reacted at 160°C for 6 hours. After the reaction was completed, it was cooled to room temperature, the foam electrode was taken out, washed with water and then dried to obtain a copper-doped nickel hydroxide self-supporting catalyst.

[0028] Example 2

[0029] Take 1x 2cm 2 The treated nickel foam was ultrasonically washed with ethanol, dilute hydrochloric acid and ultrapure water for 10 minutes respectively; the treated nickel foam was transferred to a polytetrafluoroethylene liner containing 60 ml of a 5 wt.% hydrogen peroxide aqueous solution and 6 mg of copper acetate, a reactor was assembled, and the reaction was carried out in an oven at 160°C for 8 hours. After the reaction was completed, the foam electrode was cooled to room temperature, taken out, washed with water and then dried to obtain a copper-doped nickel hydroxide self-supporting catalyst.

[0030] Example 3

[0031] Take area 1x 3cm 2 The nickel foam was ultrasonically washed with ethanol, dilute hydrochloric acid and ultrapure water for 10 minutes respectively; the treated nickel foam was transferred to a polytetrafluoroethylene liner containing 70 ml of a 4.5 wt.% hydrogen peroxide aqueous solution and 8 mg of copper sulfate, a reaction kettle was assembled, and the reaction was placed in an oven at 180°C for 6 hours. After the reaction was completed, it was cooled to room temperature, the foam electrode was taken out, washed with water and then dried to obtain a copper-doped nickel hydroxide self-supporting catalyst.

[0032] Example 4

[0033] Take area 1x 2cm 2 The nickel foam was ultrasonically washed with ethanol, dilute hydrochloric acid and ultrapure water for 10 minutes respectively; the treated nickel foam was transferred to a polytetrafluoroethylene liner containing 80 ml of a 3 wt.% hydrogen peroxide aqueous solution and 8 mg of copper nitrate, a reaction kettle was assembled, and the reaction was placed in an oven at 170°C for 10 hours. After the reaction was completed, the reaction was cooled to room temperature, the foam electrode was taken out, washed with water and then dried to obtain a copper-doped nickel hydroxide self-supporting catalyst.

[0034] Comparative Example 1

[0035] Take area 1x 3cm 2 The nickel foam was ultrasonically washed with ethanol, dilute hydrochloric acid and ultrapure water for 10 minutes respectively; the treated nickel foam was transferred to a polytetrafluoroethylene liner containing 60 ml of a 4.5 wt.% hydrogen peroxide aqueous solution, a reaction kettle was assembled, and the reaction was carried out in an oven at 160° C. for 6 hours. After the reaction was completed, the nickel foam loaded with copper was taken out, washed with water and then dried to obtain copper-doped nickel hydroxide.

[0036] Electrochemical test: The electrochemical test was carried out using an H-type electrolytic cell, where the working electrode was the self-supporting electrode prepared above (area 0.5 x 1 cm 2 ), fixed with a glassy carbon electrode clip, the reference electrode is an Ag / AgCl electrode, both are located in the cathode chamber, the counter electrode is a Pt sheet, located in the anode chamber, separated by an ion exchange membrane. 80 ml of electrolyte is added to the cathode chamber and the anode chamber respectively, and the time-current curve at the specified potential is tested under an inert atmosphere. The voltage test range is -1V to -0.1V (compared to the reversible hydrogen electrode), and the test time is 0.5h. The electrolyte after the reaction is taken out from the cathode cell, and the ammonia in the reaction solution is quantified by the indophenol blue colorimetric method.

[0037] 1) Ammonia yield calculation formula:

[0038]

[0039] n is the NH3 concentration measured by UV spectrophotometer (μg mL -1 ), V is the volume of electrolyte in the electrolytic cell (80 mL), t is the reaction time (0.5 h), and A is the area of ​​the self-supporting electrode (0.5 cm 2 ).

[0040] 2) Calculation formula of Faraday efficiency (FE):

[0041]

[0042] F is the Faraday constant (96485C mol -1 ); n is the number of electrons gained or lost (8); c is the NH3 concentration (g mL -1 ); V is the volume of the electrolyte (80 mL); M is the relative molecular mass of ammonia (17 g mol -1 ); Q is the total charge Q(C).

[0043] 3) X-ray diffractometer was used to characterize the phase composition of Example 1 and Comparative Example 1, as shown in FIG. Figure 1 As shown, the horizontal axis is the diffraction angle and the vertical axis is the diffraction peak intensity. The results show that there is no obvious characteristic peak of copper metal. Figure 1 same.

[0044] 4) Figure 2 The scanning electron microscope image and element distribution diagram of Example 1 show that when nickel hydroxide is used as a carrier to load copper, there are no obvious agglomerated nanoparticles on the carrier surface, and the Ni and Cu elements are evenly distributed, reflecting the important role of nickel hydroxide in dispersing metals. Figure 1 same.

[0045] The electrocatalytic test results are shown in Table 1. The results show that the ammonia yield of Examples 1-4 at -0.9 V vs. RHE is as high as 5 mg h - 1 cm -2 , which is much higher than that of pure nickel hydroxide electrode, indicating the important role of copper metal doping in improving electrochemical performance.

[0046] Table 1 Performance results of electrochemical ammonia synthesis

[0047]

[0048] It can be seen from the above examples that by using nickel hydroxide as a carrier, a highly dispersed copper-based electrocatalyst can be prepared, and the design and construction of a self-supporting catalyst for electrochemical nitrate reduction to synthesize ammonia under mild conditions is realized, showing excellent performance and potential application value.

[0049] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above-mentioned implementation mode, but also include technical schemes composed of any combination of the above technical features.

Claims

1. A method for preparing a copper-doped nickel hydroxide self-supporting electrochemical nitrate reduction catalyst, characterized in that: The following steps are involved: In the first step, the nickel foam is ultrasonically washed with ethanol, dilute hydrochloric acid and ultrapure water respectively; In the second step, the treated nickel foam is transferred to a polytetrafluoroethylene liner containing an aqueous hydrogen peroxide solution and a copper salt, and a reactor is assembled; The third step is to place the reactor in an oven for reaction, cool to room temperature, wash with water and then dry to obtain a copper-doped nickel hydroxide material.

2. The method for preparing the copper-doped nickel hydroxide self-supporting electrocatalyst according to claim 1, characterized in that: In the first step, the nickel foam has an area of ​​1 x 1 cm 2 ~ 1 x 6 cm 2 .

3. The method for preparing the copper-doped nickel hydroxide self-supporting electrocatalyst according to claim 1, characterized in that: In the second step, the copper salt is any one or two of copper nitrate, copper chloride, copper acetate and copper sulfate.

4. The method for preparing the copper-doped nickel hydroxide self-supporting electrocatalyst according to claim 1, characterized in that: In the second step, the volume of the hydrogen peroxide aqueous solution is 20 ml to 100 ml, the mass fraction of hydrogen peroxide in water is 1 wt.% to 10 wt.%, and the molar concentration of copper is 0.1 mmol L -1 ~ 2 mmol L -1 .

5. The method for preparing the copper-doped nickel hydroxide electrocatalyst according to claim 1, characterized in that: In the third step, the reaction time of the reactor is 2 to 12 hours, and the oven temperature is 100 to 220°C.

6. An application of the catalyst as a catalyst for electrochemical nitrate reduction to synthesize ammonia, characterized in that: The catalyst prepared by the preparation method according to any one of claims 1 to 5 exhibits good electrocatalytic nitrate synthesis of ammonia performance in an alkaline electrolyte, the nitrate used in the electrolyte ratio is potassium nitrate or sodium nitrate, the alkali is potassium hydroxide or sodium hydroxide, and the molar concentration ratio of nitrate to alkali is 0.1:1 to 2:1.

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