Nickel foam loaded with nickel sulfide as urea oxidation catalyst electrode and preparation method thereof

Abstract

The present invention relates to a nickel foam-supported nickel sulfide as a urea oxidation catalyst electrode and a preparation method thereof. The preparation method is as follows: S1: Synthesize a precursor with a multi-level dendritic nanostructure: Mix an aqueous deionized solution of nickel chloride and sodium citrate dihydrate and an aqueous deionized solution of potassium hexacyanocobaltate, obtain a precipitate through centrifugation and washing, and dry to obtain the precursor; S2: Remove the oxide layer of the nickel foam, rinse with deionized water and ethanol, and dry for standby; S3: Prepare a urea oxidation catalyst electrode by a hydrothermal method. Prepare the precursor obtained in S1 into a suspension, mix the Na2S solution with the suspension, then put the nickel foam pretreated in S2, and finally obtain a nickel sulfide composite material with a multi-level dendritic structure on the surface of the nickel foam through the hydrothermal method of the mixed liquid, and use the obtained composite material to prepare a urea oxidation catalyst electrode. The preparation method of the present invention can achieve excellent electrocatalytic activity and reaction stability for urea oxidation.

Description

Technical Field

[0001] The invention relates to the technical field of electrocatalytic nanomaterial preparation, and in particular to a nickel foam loaded nickel sulfide as a urea oxidation catalyst electrode and a preparation method thereof. Background Art

[0002] In recent years, the problems of energy shortage and environmental pollution have become issues that humans have to consider, forcing people to seek greener and more environmentally friendly energy. As a sustainable clean energy, hydrogen is considered to be an ideal energy source that can replace fossil energy. The environmental friendliness of water electrolysis to produce hydrogen makes it a promising and practical technology among many hydrogen production methods, and it is also a method of hydrogen production that is currently being studied more. However, the reaction kinetics of the oxygen evolution reaction, a core reaction in water electrolysis, is slow, which seriously limits the electrolysis efficiency and causes energy loss. Ruthenium-based and other precious metal materials are commercial catalysts for the oxygen evolution reaction, but their reserves are scarce and expensive, which further limits the widespread application of this method. Therefore, it is of great significance for the production of hydrogen to select the urea oxidation reaction with a lower theoretical potential at the anode end instead of the oxygen evolution reaction.

[0003] At the same time, urea electrolysis can not only produce hydrogen efficiently, but also treat urea, a pollutant in domestic and industrial wastewater. The urea electrolysis reaction that replaces the oxygen evolution reaction with urea oxidation reaction can not only achieve efficient hydrogen production, but also treat urea, a pollutant. However, the urea oxidation reaction is limited by its slow electron transfer process, and it also requires the use of electrocatalysts to accelerate the reaction process. Nickel-based catalysts are the most commonly used type of transition metal catalysts in catalyzing urea oxidation reactions in alkaline environments. This is because the nickel species in the catalyst will spontaneously form Ni(OH) in alkaline solutions. 2 , during the electrolysis process Ni(OH) 2 It will be oxidized to NiOOH, which has a high catalytic activity for the oxidation reaction of urea. In the prior art, a porous flower-shaped molybdenum-doped NiS was synthesized on a titanium mesh, achieving a 50 mA / cm 2 current density; Chinese patent application CN 114388830 A discloses a method for improving the catalytic activity of NiO by introducing rhodium nanoparticles. The above-mentioned known methods all use precious metals to improve the catalytic activity, which will limit large-scale industrial production.

[0004] In summary, the catalytic performance of the electrode is not only related to the activity of the surface material itself, but also to the electronic conductivity of the material itself. In order to obtain excellent electrocatalytic performance and reduce production costs, it is necessary to rationally plan the activity of the catalyst electrode and the conductivity of the prepared material in order to give full play to the catalytic ability of the active substance. Summary of the invention

[0005] Technical issues to be solved:

[0006] The purpose of the present invention is to provide a nickel sulfide composite material having a multi-level dendritic structure on the surface of nickel foam as a urea oxidation catalyst electrode Ni x S y / NF preparation method to achieve excellent electrocatalytic urea oxidation activity and reaction stability, only 1.343 ~ 1.352V vs. RHE potential is required to obtain 10mA / cm 2 of current density.

[0007] The technical solutions adopted are as follows:

[0008] The invention relates to a method for preparing a urea oxidation catalyst electrode using nickel foam loaded with nickel sulfide. The method comprises the following steps: firstly synthesizing a precursor containing nickel and sulfur and having a multi-level tree-like nanostructure; then combining the precursor on a conductive substrate through a one-step hydrothermal method to obtain a nickel sulfide composite material; and finally applying the nickel sulfide composite material as the catalyst electrode.

[0009] It is further defined that the conductive substrate is nickel foam.

[0010] It is further defined that the specific steps of the method for preparing the urea oxidation catalyst electrode also include:

[0011] S1: Synthesis of a precursor having a multi-level tree-like nanostructure: a deionized water solution of nickel chloride and sodium citrate dihydrate and a deionized water solution of potassium hexacyanocobaltate are fully mixed, and then a precipitate is obtained by centrifugation washing and drying to obtain the precursor;

[0012] S2: Pretreatment of nickel foam: removing the oxide layer of nickel foam, rinsing with deionized water and ethanol, and drying for later use;

[0013] S3: Prepare the urea oxidation catalyst electrode by a hydrothermal method: prepare the precursor obtained in step S1 into a suspension, 2 The S solution is mixed with the suspension, and then the nickel foam pretreated in step S2 is added. Finally, the mixed liquid is subjected to a hydrothermal method to obtain a nickel sulfide composite material with a multi-level tree-like structure on the surface of the nickel foam. The obtained composite material is used to prepare the urea oxidation catalyst electrode.

[0014] It is further defined that the specific synthesis steps of the precursor described in S1 are:

[0015] S11: dissolving nickel chloride and sodium citrate dihydrate in deionized water;

[0016] S12: Dissolve potassium hexacyanocobaltate in an equal amount of deionized water as in S11;

[0017] S13: mixing the two solutions obtained in steps S11 and S12, stirring them thoroughly and then standing them at room temperature for 24 hours;

[0018] S14: washing the mixed solution in S13 by centrifugation for multiple times to obtain a precipitate, and drying the precipitate in an oven to obtain the precursor.

[0019] It is further defined that in S11, the molar ratio of nickel chloride to sodium citrate dihydrate is 2:3.

[0020] It is further defined that in S11 and S12, specifically: 6 mmol nickel chloride and 9 mmol sodium citrate dihydrate are dissolved in 200 mL deionized water; and 4 mmol potassium hexacyanocobaltate is also dissolved in 200 mL deionized water.

[0021] It is further defined that the specific steps of pre-treating the nickel foam in S2 include:

[0022] S21: Cut the nickel foam into 2×3cm 2 size, and remove the oxide layer of nickel foam by ultrasound;

[0023] S22: Rinse with deionized water and ethanol until neutral, and dry at room temperature for later use.

[0024] It is further defined that the step of preparing the catalyst electrode by a hydrothermal method in S3 further includes the following steps:

[0025] S31: dispersing a certain amount of the precursor in ethanol, and obtaining a uniform suspension after ultrasonic treatment;

[0026] S32: Dissolve a certain amount of sodium sulfide nonahydrate in deionized water to obtain Na 2 S solution;

[0027] S33: The Na obtained in step S32 2 After the S solution is mixed with the suspension obtained in step S31, the nickel foam pretreated in step S2 is added;

[0028] S34: Finally, the mixture is placed in a hydrothermal kettle and maintained at 100° C. for 6 hours. The obtained product is repeatedly rinsed with deionized water and ethanol, and dried at 40° C. to obtain the catalyst electrode.

[0029] Further defined, in S31 and S32, specifically, 100 mg of the precursor can be dispersed in 20 mL of ethanol and subjected to ultrasonic treatment for 40 min to form a uniform suspension; at the same time, 2.5 mmol of sodium sulfide nonahydrate is dissolved in 10 mL of deionized water to prepare Na 2S solution.

[0030] A urea oxidation catalyst electrode obtained by the above preparation method is used for decomposing urea and releasing hydrogen.

[0031] The beneficial effects of the present invention are:

[0032] 1. The preparation method of the present invention can be prepared by only one step of hydrothermal method at a relatively low temperature, has low energy consumption, is easy to control, has low raw material cost, and has a simple preparation method.

[0033] 2. The present invention obtains a multi-level tree-like nanostructure on the surface of the nickel foam after the reaction, wherein the hollow NiS nanoframe structure has a good morphology and is conducive to exposing active sites. 3 S 2 Microrods help disperse the NiS nanoframe structure to avoid accumulation of active ingredients, Ni 3 S 2 The Ni-Ni bonds in the crystal structure are conducive to the rapid transfer of electrons, thus having good electronic conductivity.

[0034] 3. Based on the unique structure of nickel foam surface, the present invention obtains excellent electrocatalytic urea oxidation activity. Only 1.343V vs. RHE (reversible hydrogen electrode) is required to achieve 10mA / cm 2 The performance of the electrolyzer was only 3.0% lower after 25 h of continuous electrolysis at this current density. It was also able to electrolyze an aqueous solution containing 1M KOH and 0.33M urea at a current density of 1.352V vs. RHE at 10mA / cm 2 Real urine containing 1 M KOH was electrolyzed at a current density of 2.3 Å, showing the potential for treating urine as well as urea-rich wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 Ni is the catalyst electrode x S y / NF SEM image;

[0037] Figure 2 a. Figure 2 b are catalyst electrode Ni x S y Fractured Ni / NF prepared by ultrasonication3 S 2 TEM images and HRTEM lattice images of microrods and NiS nanoframes;

[0038] Figure 3 a. Figure 3 b are the precursors PBA and Ni x S y XRD patterns of / NF and nickel foam;

[0039] Figure 4 Ni is the catalyst electrode x S y LSV curves of / NF in 1M KOH+0.33M urea aqueous solution and real urine containing 1M KOH;

[0040] Figure 5 Ni is the catalyst electrode x S y / Tafel curve of NF;

[0041] Figure 6 Ni is the catalyst electrode x S y / NF at 10mA / cm 2 The chronopotentiometry curve below. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0043] The materials required for the preparation method of the nickel foam loaded with nickel sulfide as a urea oxidation catalyst electrode include nickel chloride (NiCl 2 ), sodium citrate dihydrate (C 6 H 5 Na 3 O 7 ·2H 2 O), potassium hexacyanocobaltate (K 3 Co(CN) 6 ), sodium sulfide nonahydrate (Na 2 S·9H 2 O), nickel foam, potassium hydroxide (KOH), urea.

[0044] The present invention discloses a method for preparing a urea oxidation catalyst electrode using nickel foam loaded with nickel sulfide, wherein a nickel sulfide composite material having a multi-level dendritic structure is obtained on the surface of nickel foam (NF) and the catalyst electrode Ni is prepared by using the composite material. x S y / NF, x and y are natural numbers, wherein the specific method for obtaining a nickel sulfide composite material with a multi-level tree-like structure on the surface of nickel foam is as follows:

[0045] (1) Synthesis of a precursor PBA (Prussian Blue analogue) with a multi-level tree-like nanostructure: First, 6 mmol nickel chloride and 9 mmol sodium citrate dihydrate were dissolved in 200 mL of deionized water; 4 mmol potassium hexacyanocobaltate was also dissolved in 200 mL of deionized water. The two solutions were then mixed, stirred for 3 min, left to stand at room temperature for 24 h, and repeatedly centrifuged and washed with deionized water to obtain a precipitate, which was then dried in an oven at 60°C overnight to obtain the precursor PBA.

[0046] (2) Pretreatment of nickel foam: First, cut the nickel foam with a thickness of about 1 mm into 2×3 cm 2 The sample was placed in a 3M HCl ultrasonic device for about 15 min to remove the oxide layer, and then rinsed repeatedly with deionized water and ethanol and dried at room temperature.

[0047] (3) Preparation of catalyst electrode Ni by one-step hydrothermal method x S y / NF: First, 100 mg of the precursor PBA prepared above was dispersed in 20 mL of ethanol and ultrasonicated for 40 min to form a uniform suspension. At the same time, 2.5 mmol of sodium sulfide nonahydrate was dissolved in 10 mL of deionized water, and then Na 2 The S solution was poured into the above suspension, stirred for 3 minutes, and the treated nickel foam was added. Finally, the mixture was transferred to a 50 mL hydrothermal autoclave and kept at 100 ° C for 6 hours. The final product was repeatedly rinsed with deionized water and ethanol, and then dried at 40 ° C.

[0048] The composite material obtained by the method is used to prepare the catalyst electrode and applied to the electrolysis of urea and the evolution of hydrogen.

[0049] Through experiments, it is verified that the urea oxidation catalyst electrode obtained by the preparation method of the present invention has excellent electrocatalytic urea oxidation activity and reaction stability, as follows:

[0050] Experimental Example 1 - Catalyst Electrode Ni x S y / NF for phase analysis

[0051] The Ni in Example 1 was observed using a scanning electron microscope (SEM, JSM 6010, JEOL, Japan). x S y / NF, by Figure 1 It can be observed that dense multi-level tree-like nanostructured microrods are formed on the surface of the substrate nickel foam.

[0052] The Ni x S y / NF samples obtained after ultrasonic pretreatment, Figure 2 a is Ni x S y TEM image of a broken microrod after ultrasonic pretreatment of NF, and its corresponding HRTEM image shows a lattice spacing of 0.286nm, corresponding to Figure 2 a shows Ni 3 S 2 (110). Figure 2 As shown in b, we found a hollow nanoframe structure of about 100 nm in size in the prepared TEM sample, and its corresponding HRTEM image showed a lattice spacing of 0.273 nm, corresponding to Figure 2 b shows NiS(300).

[0053] The X-ray diffraction (XRD, D / MAX-2500, Rigaku, Japan) was carried out using CuKα radiation. Obtain diffraction patterns of the precursor PBA and the catalyst electrode, Figure 3 The XRD pattern in a shows that Ni 3 [Co(CN) 6 ] 2 The obvious characteristic peaks of (JCPDS:89-3738) indicated that the precursor PBA was successfully synthesized. Figure 3 The XRD pattern of b shows that Ni x S y There are three strong diffraction peaks (44.5°, 51.8° and 76.4°) and five weak diffraction peaks (21.8°, 31.1°, 37.8°, 49.7° and 54.6°) in NF-3, which correspond to nickel foam (JCPDS: 04-0850) and Ni in situ grown on nickel foam. 3 S 2(JCPDS:44-1418).

[0054] Experimental Example 2 - Catalyst Electrode Ni x S y / NF conducts electrolysis hydrogen test analysis

[0055] The performance of the electrode material in catalyzing the urea oxidation reaction was tested using an electrochemical workstation CHI 760e (CH instrument, Shanghai, China) and a three-electrode system. Considering the application of treating urea in urine, an aqueous solution with a suitable urea concentration needs to be selected as the electrolyte. Human urine contains about 2-2.5% urea by mass, which is converted to about 0.33M (M is mol / L). Therefore, the performance test of the electrode will be carried out in an aqueous solution containing 1M potassium hydroxide + 0.33M urea. In addition, in order to further limit the practical application of the research electrode, it was tested in fresh urine (containing 1M KOH).

[0056] The three-electrode system is composed of a working electrode, a reference electrode and a counter electrode, and is used to test the electrolytic performance of a single electrode. x S y The electrolysis performance of a single electrode was tested as follows using a three-electrode system consisting of MgSO4 / NF as the working electrode, mercury / mercury oxide electrode as the reference electrode and a carbon rod as the counter electrode.

[0057] To you x S y / NF electrode for linear sweep voltammetry (LSV), Figure 4 The LSV curves in 1M KOH + 0.33M urea aqueous solution and real urine containing 1M KOH are shown. In the 1M KOH + 0.33M urea aqueous solution, only low potentials of 1.343V vs.RHE and 1.391V vs.RHE are needed to reach 10mA / cm 2 and 100mA / cm 2 It is worth noting that compared with the test of 1M KOH and 0.33M urea, at 50mA / cm 2 The potential of the real urine electrolyzed at a current density of only 15 mV increased slightly, indicating that the catalyst electrode has the potential to be used in actual urine electrolysis. Figure 5 The Tafel curve of Ni x S y / NF has a smaller Tafel slope (34.8mVdec-1), which means it has faster reaction kinetics. x S y The long-term working stability of the / NF electrode was evaluated. Figure 6 When the current density is 10 mA / cm 2 When x S y / NF-3 only showed a 3.0% drop in performance after 25 hours, demonstrating excellent working stability.

[0058] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing a urea oxidation catalyst electrode using nickel foam loaded with nickel sulfide. It is characterized in that The method comprises: S1: synthesizing a precursor: fully mixing a deionized aqueous solution of nickel chloride and sodium citrate dihydrate and a deionized aqueous solution of potassium hexacyanocobaltate, then centrifugally washing to obtain a precipitate and drying to obtain the precursor; S2: Pretreatment of nickel foam: removing the oxide layer of nickel foam, rinsing with deionized water and ethanol, and drying for later use; S3: Prepare the urea oxidation catalyst electrode by a hydrothermal method: prepare the precursor obtained in step S1 into a suspension, 2 The S solution is mixed with the suspension, and then the nickel foam pretreated in step S2 is added. Finally, the mixed liquid is subjected to a hydrothermal method to obtain a nickel sulfide composite material with a multi-level tree-like structure on the surface of the nickel foam. The obtained composite material is used to prepare the urea oxidation catalyst electrode.

2. A method for preparing a urea oxidation catalyst electrode using nickel foam loaded with nickel sulfide according to claim 1, It is characterized in that The specific synthesis steps of the precursor in S1 are: S11: dissolving nickel chloride and sodium citrate dihydrate in deionized water; S12: Dissolve potassium hexacyanocobaltate in an equal amount of deionized water as in S11; S13: mixing the two solutions obtained in steps S11 and S12, stirring them thoroughly and then standing them at room temperature for 24 hours; S14: washing the mixed solution in S13 by centrifugation for multiple times to obtain a precipitate, and drying the precipitate in an oven to obtain the precursor.

3. A method for preparing a urea oxidation catalyst electrode using nickel foam loaded with nickel sulfide as claimed in claim 2, It is characterized in that In S11, the molar ratio of nickel chloride to sodium citrate dihydrate is 2:

3.

4. The method for preparing a urea oxidation catalyst electrode using nickel foam loaded with nickel sulfide as claimed in claim 2, It is characterized in that Specifically in S11 and S12: 6 mmol nickel chloride and 9 mmol sodium citrate dihydrate are dissolved in 200 mL deionized water; 4 mmol potassium hexacyanocobaltate is also dissolved in 200 mL deionized water.

5. The method for preparing a nickel foam loaded with nickel sulfide as a urea oxidation catalyst electrode according to claim 1, It is characterized in that The specific steps of nickel foam pretreatment in S2 include: S21: Cut the nickel foam into 2×3cm 2 size, and remove the oxide layer of nickel foam by ultrasound; S22: Rinse with deionized water and ethanol until neutral, and dry at room temperature for later use.

6. The method for preparing a nickel foam loaded with nickel sulfide as a urea oxidation catalyst electrode according to claim 1, It is characterized in that In S3, the catalyst electrode is prepared by a hydrothermal method, which specifically includes the following steps: S31: dispersing a certain amount of the precursor in ethanol, and obtaining a uniform suspension after ultrasonic treatment; S32: Dissolve a certain amount of sodium sulfide nonahydrate in deionized water to obtain Na 2 S solution; S33: The Na obtained in step S32 2 After the S solution is mixed with the suspension obtained in step S31, the nickel foam pretreated in step S2 is added; S34: finally, the mixture is placed in a hydrothermal kettle and maintained at 100° C. for 6 hours, and then the obtained product is repeatedly rinsed with deionized water and ethanol, and dried at 40° C. to obtain the composite material.

7. A method for preparing a urea oxidation catalyst electrode using nickel foam loaded with nickel sulfide according to claim 6, It is characterized in that In S31 and S32, the steps specifically include: dispersing 100 mg of the precursor in 20 mL of ethanol, and subjecting the mixture to ultrasonic treatment for 40 min to form a uniform suspension; at the same time, dissolving 2.5 mmol of sodium sulfide nonahydrate in 10 mL of deionized water to prepare Na 2 S solution.

8. A urea oxidation catalyst electrode obtained according to the method for preparing a urea oxidation catalyst electrode using nickel foam loaded with nickel sulfide as a catalyst according to any one of claims 1 to 7, It is characterized in that The urea oxidation catalyst electrode is used to decompose urea and release hydrogen.

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