Porous nanometer nickel, and preparation method and application thereof

Abstract

The application discloses a preparation method of porous nanometer nickel, which comprises the following steps: taking a first hydrogen bond donor, a second hydrogen bond donor and choline chloride according to a molar ratio of 0.3-4:0.001-0.005:1, wherein the first hydrogen bond donor is a polyhydric alcohol, and the second hydrogen bond donor is an amide; uniformly mixing the three by constant temperature and ultrasonic oscillation to obtain a multi-component eutectic solvent; adding a soluble nickel source into the eutectic solvent, and continuing constant temperature and ultrasonic oscillation until no crystallization is precipitated at room temperature; inserting a cathode electrode and an anode electrode into the solution obtained in the last step, wherein the anode electrode is made of nickel, and performing constant current electrodeposition; taking out the cathode electrode, and washing and drying the cathode electrode to obtain porous nanometer nickel on the surface of the cathode electrode. The application further discloses the porous nanometer nickel obtained by the method and application of the porous nanometer nickel as a catalyst in electrocatalytic water decomposition for hydrogen production. The nanometer nickel obtained by the method has a porous structure, good electrocatalytic activity, and is easy to obtain, low in cost, mild in action condition, non-toxic and environment-friendly.

Description

TECHNICAL FIELD

[0001] The application belongs to porous catalytic materials and its preparation and application, and particularly to a porous nanometer nickel and its preparation method and application. BACKGROUND

[0002] Due to the advantages of high energy capacity and environmental emission, hydrogen is widely considered as the most promising and preferred alternative of modern energy. Electrocatalytic water splitting is a clean and efficient hydrogen production technology. Water electrolysis includes anode oxygen evolution reaction (OER) and cathode hydrogen evolution reaction (HER). However, the two-electron transfer cathode HER and four-proton electron coupling anode OER have a slow kinetic barrier, so a higher cell voltage than the theoretical potential (1.23 V) is required to split water. The efficiency of water splitting is limited by the electrode catalyst. Currently, platinum-based and ruthenium / iridium-based catalysts have been recognized as commercial catalysts for efficient HER and OER. Although the noble metal catalyst has high activity, it is expensive and scarce in resources. Therefore, developing low-cost, high-efficiency, and stable non-noble metal catalysts is an important research direction in the field of water splitting. Nickel (Ni) and nickel-based alloy electrodes are the research focus of non-noble metal catalysts for hydrogen production by water electrolysis today due to their relatively low cost, availability, and relatively high catalytic activity.

[0003] Among these materials, nickel has a good application prospect in HER due to its low cost, high corrosion resistance, and relatively high catalytic activity compared to other non-noble metal electrode materials, although the catalytic performance of nickel is still far from satisfactory. One of the most effective ways to improve the electrocatalytic activity of Ni is to design electrodes with porous structures, considering that the surface morphology at the macro-pore level has a significant impact on the electrocatalytic activity. The commonly used methods for synthesizing nickel-based catalysts with porous structures include hydrothermal method, solvothermal method, chemical deposition method, and electrodeposition. The electrodeposition synthesis method is favored by people in the field of catalytic synthesis because of its simplicity, economy, and efficiency. However, the electrodeposition of nickel is mostly based on aqueous solution, which has limitations such as toxic plating solution, the need for complexing agents and grain refinement additives, and difficulty in handling the hydrogen evolution process leading to hydrogen embrittlement. SUMMARY

[0004] The purpose of the application is to overcome the deficiencies in the prior art, and the purpose of the application is to provide a preparation method of porous nanometer nickel with low cost, mild conditions, and non-toxic environmental protection. Another purpose of the application is to provide a porous nanometer nickel with good electrocatalytic activity. Another purpose of the application is to provide an application of porous nanometer nickel as a catalyst in electrocatalytic water splitting for hydrogen production.

[0005] Technical solution: The preparation method of the porous nanometer nickel comprises the following steps:

[0006] S1, the first hydrogen bond donor, the second hydrogen bond donor, choline chloride are taken in a molar ratio of 0.3-4:0.001-0.005:1, the first hydrogen bond donor is a polyol, the second hydrogen bond donor is an amide, constant temperature, ultrasonic oscillation and mixing, a multi-component deep eutectic solvent is obtained, a soluble nickel source is added to the deep eutectic solvent, and constant temperature, ultrasonic wave is continued to room temperature without crystallization;

[0007] S2, the cathode electrode and the anode electrode are inserted into the solution obtained in step S1, the anode electrode is nickel, and constant current electrodeposition is carried out;

[0008] S3, the cathode electrode is taken out, washed and dried, and a porous nano-nickel is obtained on the surface of the cathode electrode.

[0009] Further, in step S1, the first hydrogen bond donor is ethylene glycol, and the second hydrogen bond donor is nicotinamide. The temperature of constant temperature is 30-100 DEG C, and the ultrasonic oscillation power is 50-100 W. The soluble nickel source is one or more of nickel chloride, nickel oxide, nickel sulfate, nickel nitrate, nickel sulfamate and hydrates thereof. The molar volume ratio of nickel salt to deep eutectic solvent is 0.001-1 mol:1-1000 mL.

[0010] Further, in step S2, the distance between the cathode electrode and the anode electrode is 0.5-3 cm, the cathode is any one of stainless steel, graphite, red copper and brass. The temperature of constant current electrodeposition is 50-75 DEG C, the current density of the cathode is 0.05-0.15 A / dm 2 , and the electrodeposition time is 0.5-10 h.

[0011] Further, in step S3, the drying is vacuum drying at 25-80 DEG C.

[0012] The porous nano-nickel obtained by the preparation method of the porous nano-nickel has a grain size of 5-100 nm.

[0013] The porous nano-nickel can be used as a catalyst in the application of electrocatalytic water decomposition to produce hydrogen.

[0014] Preparation principle: the nucleation mode of nickel in the multi-component deep eutectic solvent undergoes a transition from three-dimensional instantaneous nucleation to three-dimensional continuous nucleation, a large number of nucleation sites are generated in the initial stage, a small amount of free nicotinamide in the solution is adsorbed to the electrode surface, hindering the growth of nickel atomic nucleus, resulting in that the nickel fails to completely cover the electrode surface in the process of layer-by-layer growth to form staggered and overlapped holes, and the specific surface area is further improved.

[0015] At a certain current density, a small amount of nicotinamide is ionized to generate nicotinic acid and generate gas, and the product nicotinic acid also hinders the nucleation and growth of nickel, refines the grain size of nickel, and makes the grown nickel nanoparticles insufficient to fill the pores caused by the gas, thereby causing the generation of a porous structure.

[0016] The electrodeposition adopts a double electrode and a constant current method, and when the deposition is carried out, the contact interface between the working electrode and the solution changes with the continuous deposition of nickel, and the original brass becomes the nanometer nickel continuously deposited on the surface of the brass, and the potential of the nickel on the surface of the electrode also dynamically changes, thereby affecting the deposition behavior of the nickel and causing the porous nanostructure.

[0017] Beneficial effects: Compared with the prior art, the present application has the following remarkable features:

[0018] 1. The obtained nanometer nickel has a porous structure and good electrocatalytic activity.

[0019] 2. The raw material of the eutectic solvent is easy to obtain, the cost is low, the action condition is mild, and it is non-toxic and environmentally friendly.

[0020] 3. The method for preparing porous nickel by electrodeposition is simple and efficient, soluble nickel is used as the anode to provide metal ions and maintain the stability of the electrolyte, and the recycling rate of the electrodeposition solution is enhanced. BRIEF DESCRIPTION OF DRAWINGS

[0021] Fig. 1 The SEM graph of the product obtained in Example 1 of the present application;

[0022] Fig. 2 The EDS graph of the product obtained in Example 1 of the present application;

[0023] Fig. 3 The XRD graph of the products obtained in Example 1 and Example 2 of the present application and the product obtained in Comparative Example 1;

[0024] Fig. 4 The SEM graph of the product obtained in Comparative Example 1;

[0025] Fig. 5 The HER polarization curve of the water electrolysis of the products obtained in Example 1 and Example 2 of the present application and the product obtained in Comparative Example 1;

[0026] Fig. 6 The Tafel slope graph of the water electrolysis of the products obtained in Example 1 and Example 2 of the present application and the product obtained in Comparative Example 1;

[0027] Fig. 7 The SEM graph of the product obtained in Comparative Example 2. DETAILED DESCRIPTION

[0028] In the following examples, XRD was characterized by Ulitima IV X (Rigaku, Japan) device. SEM was characterized by JSM-6510LA (JEOL, Japan) device. The grain size of the porous nanometer nickel is 5-100 nm.

[0029] Example 1

[0030] A method for preparing porous nanometer nickel, comprising the following steps:

[0031] S1, liquid preparation: add ethylene glycol, nicotinamide and choline chloride in a container in sequence, the total volume is 1L, the molar ratio is 2:0.0025:1, ultrasonic oscillation mixing under constant temperature 65℃ and power 80W, to obtain a multi-component deep eutectic solvent; add 0.2mol of nickel chloride hexahydrate into the above deep eutectic solvent, continue ultrasonic oscillation under constant temperature 65℃ and power 80W until no crystallization is precipitated at room temperature, and the liquid preparation is completed.

[0032] S2, electrodeposition: use a nickel plate as a soluble anode and a brass as a cathode, insert them into the solution prepared in step S1, the direct distance between the anode and the cathode is 2cm, and the direct current density is 0.15A / dm 2 direct current electrodeposition under constant current density, the electrodeposition temperature is kept at 65℃ throughout the process, and the deposition is performed for 1h;

[0033] S3, washing and drying: after the electrodeposition is completed, take out the brass electrode, rinse it with anhydrous ethanol, and vacuum dry it at 70℃ to obtain porous nanometer nickel on the surface of the electrode.

[0034] The morphology and structure of the porous nanometer nickel obtained in this example are characterized, as shown in Figs. 1-2 the SEM results. The nickel nanoparticles are granular, distributed randomly in space, and present a porous structure. The EDS results only show the peak of nickel, indicating that the electrodeposition product is pure nickel without other impurities.

[0035] Example 2

[0036] A method for preparing porous nanometer nickel, comprising the following steps:

[0037] S1, liquid preparation: add ethylene glycol, nicotinamide and choline chloride in a container in sequence, the total volume is 1L, the molar ratio is 2:0.005:1, ultrasonic oscillation mixing under constant temperature 65℃ and power 80W, to obtain a multi-component deep eutectic solvent; add 0.2mol of nickel sulfate into the above deep eutectic solvent, continue ultrasonic oscillation under constant temperature 65℃ and power 80W until no crystallization is precipitated at room temperature, and the liquid preparation is completed.

[0038] S2, electrodeposition: use a nickel plate as a soluble anode and a brass as a cathode, insert them into the solution prepared in step S1, the direct distance between the anode and the cathode is 2cm, and the direct current density is 0.11A / dm 2Direct current deposition at constant current density, the deposition temperature is kept at 65℃ all the time, and the deposition time is 1h;

[0039] S3. Washing and drying: after the electrodeposition, the brass electrode is taken out, washed with anhydrous ethanol, and dried at 70℃ in vacuum, and then porous nanometer nickel is obtained on the surface of the electrode.

[0040] Comparative Example 1

[0041] A method for preparing nanometer nickel, comprising the following steps:

[0042] S1. Liquid preparation: in a container, add ethylene glycol and choline chloride in sequence, the total volume is 1L, and the molar ratio is 2:1. Ultrasonic oscillation is carried out at a constant temperature of 65℃ and a power of 80W until the liquid is uniformly mixed. Then, 0.2mol of nickel chloride is added to the above low-eutectic solvent, and ultrasonic oscillation is continued at a constant temperature of 65℃ and a power of 80W until no crystal is precipitated at room temperature. The liquid preparation is completed.

[0043] S2. Electrodeposition: a nickel plate is used as a soluble anode, and a brass electrode is used as a cathode. The anode and the cathode are inserted into the solution prepared in step S1, and the distance between the anode and the cathode is 2cm. Direct current is applied at a constant current density of 0.15A / dm 2 Direct current deposition at constant current density, the deposition temperature is kept at 65℃ all the time, and the deposition time is 1h;

[0044] S3. Washing and drying: after the electrodeposition, the brass electrode is taken out, washed with anhydrous ethanol, and dried at 70℃ in vacuum, and then non-porous nanometer nickel is obtained on the surface of the electrode. Nicotinamide is used as a comparative example.

[0045] The X-ray diffraction results of the electrodeposition products of Comparative Example 1, Example 2, and Comparative Example 1 are shown in Table 1. Fig. 3 The results show that nickel is electrodeposited on the brass electrode under the three experimental conditions. Compared with the diffraction peak at the 111 crystal plane of Comparative Example 1, which shows high and narrow, the diffraction peak at the 111 crystal plane of Example 1 and Example 2 shows low and wide. In order to further compare the results, Scherrer calculation is performed on the diffraction peak results under the three conditions, and finally, the grain sizes at the 111 crystal plane of Comparative Example 1, Example 1, and Example 2 are 31.9nm, 10.8nm, and 12.4nm respectively. This shows that the porous structure is beneficial to the formation of nanometer nickel with smaller grain size. Fig. 4 The surface of the nanometer nickel film obtained in Comparative Example 1 is in a spherical particle shape as a whole, and the particles are obviously uneven, and some needle-shaped objects also exist.

[0046] Structure determines performance, in order to understand the performance changes brought by the porous structure, the HER performance of the electrodeposited nano-nickel is studied. The HER hydrogen evolution curve is obtained by linear sweep voltammetry (LSV), and the Tafel slope is obtained by chronoamperometry (CA). For specific test content, please refer to the application example. The HER hydrogen evolution curve and the Tafel slope of the electrodeposited products of Comparative Example 1, Example 2, and Comparative Example 1 are compared, as shown in Figs. 5-6 , Example 1 and Example 2 have smaller overpotential and Tafel slope, which indicates that the electrodeposited porous nano-nickel exhibits better HER catalytic activity than the non-porous nano-nickel, because the existence of the pores increases the specific surface area of the nickel, which can provide more catalytically active sites, and at the same time, the pores are beneficial to the diffusion and mass transfer in the solution. The porous nano-nickel exhibits good potential as an electrolytic water catalyst.

[0047] Comparative Example 2

[0048] This comparative example is the same as Example 1 in steps, and the only difference is that the constant current density in S2 is replaced by 0.2 A / dm 2 .

[0049] The obtained nano-nickel is characterized for morphology, as shown in Fig. 7 It can be seen that the electrode surface is distributed in blocks, and a large number of cracks are generated, in addition, the deposited layer surface is black, and the deposited layer quality is poor, which is more difficult to play a catalytic role compared with the dense porous nano-nickel.

[0050] Comparative Example 3

[0051] This comparative example is the same as Example 1 in steps, and the only difference is that the constant current density in S2 is replaced by 0.02 A / dm 2 . It is found that the nucleation potential of nickel on the electrode surface cannot be met, and nickel cannot be deposited on the electrode surface. Therefore, it is difficult to be used as an electrolytic water catalyst.

[0052] Comparative Example 4

[0053] This comparative example is the same as Example 1 in steps, and the only difference is that the molar ratio of ethylene glycol, nicotinamide, and choline chloride in S1 is replaced by 2:0.01:1. It is found that as the electrodeposition proceeds, the solution begins to become turbid, and the electrode surface is attached with light blue flocculent substances, and the nickel content of the deposited layer is extremely low. Therefore, it is difficult to be used as an electrolytic water catalyst.

[0054] Comparative Example 5

[0055] The comparative example is the same as the steps and example 1, the only difference is that the electrodeposition temperature in S2 is kept at 25℃ throughout. It is found that under this deposition condition, due to the low temperature, the viscosity of the electrodeposition solution is large, the conductivity is low, and the electrodeposition is not conducive to occur, the deposition rate is quite slow, and the deposited layer has large grain size, poor adhesion, and is easy to fall off, and is difficult to be used as an electrolytic water catalyst.

[0056] Comparative example 6

[0057] The comparative example is the same as the steps and example 1, the only difference is that the electrodeposition temperature in S2 is kept at 100℃ throughout. It is found that the electrodeposited nickel surface is uniform, dense and has no pores, but shows strong hydrophobic properties, and water molecules cannot be attached to the surface, so it is difficult to be used as an electrolytic water catalyst.

[0058] Table 1 shows the differences in electrodeposition parameters and deposition results of example 1 and comparative examples 2-6.

[0059]

[0060] The differences in electrodeposition parameters and deposition results of example 1 and comparative examples 2-6 are shown in Table 1, (the default is the same as the parameters of example 1 without giving numerical values, the specific content can be referred to Table 2. From Table 1, it can be seen that only under the molar ratio of ethylene glycol: nicotinamide: choline chloride, electrodeposition temperature, and current density of example 1 of the present application, can the product with uniform nickel surface size and small size be obtained, which has a porous nanostructure and can be used as a catalyst for electrocatalytic water splitting to produce hydrogen.

[0061] Example 3

[0062] A method for preparing a porous nano-nickel, comprising the following steps:

[0063] S1, liquid preparation: add ethylene glycol, nicotinamide, and choline chloride into a container in sequence, the total volume is 1 mL, the molar ratio is 0.3:0.001:1, ultrasonic oscillation is carried out under constant temperature of 30℃ and power of 50W to mix uniformly, and a multi-component eutectic solvent is obtained; 0.001 mol of nickel oxide is added to the above eutectic solvent, and ultrasonic oscillation is continued under constant temperature of 30℃ and power of 50W until no crystal is precipitated at room temperature, and the liquid preparation is completed;

[0064] S2, electrodeposition: a nickel plate is used as a soluble anode, and a stainless steel is used as a cathode, which is inserted into the solution prepared in step S1, the direct distance between the cathode electrode and the anode electrode is 0.5 cm, and direct current electrodeposition is carried out under constant current density of 0.05 A / dm 2 The electrodeposition temperature is kept at 50℃ throughout, and the deposition is carried out for 0.5h;

[0065] S3, washing and drying: after the electrodeposition is completed, the cathode electrode is taken out, washed, and vacuum dried at 25°C, and then porous nanometer nickel is obtained on the surface of the cathode electrode.

[0066] Example 4

[0067] A method for preparing porous nanometer nickel comprises the following steps:

[0068] S1, liquid preparation: ethylene glycol, nicotinamide and choline chloride are sequentially added in a container, the total volume is 0.5L, the molar ratio is 4:0.005:1, and ultrasonic oscillation is performed under constant temperature of 100°C and power of 100W to uniformly mix, thereby obtaining a multi-component deep eutectic solvent; 1 mol of nickel nitrate hexahydrate is added to the deep eutectic solvent, and ultrasonic oscillation is continued under constant temperature of 100°C and power of 100W until no crystals are precipitated at room temperature, and the liquid preparation is completed;

[0069] S2, electrodeposition: a nickel plate is used as a soluble anode, and graphite is used as a cathode, which is inserted into the solution prepared in step S1, the direct distance between the cathode electrode and the anode electrode is 1 cm, and direct current electrodeposition is performed under constant current density of 0.07 A / dm 2 The direct current electrodeposition is performed under constant current density, the electrodeposition temperature is kept at 75°C throughout the process, and the deposition is performed for 10 h;

[0070] S3, washing and drying: after the electrodeposition is completed, the cathode electrode is taken out, washed, and vacuum dried at 80°C, and then porous nanometer nickel is obtained on the surface of the cathode electrode.

[0071] Example 5

[0072] A method for preparing porous nanometer nickel comprises the following steps:

[0073] S1, liquid preparation: ethylene glycol, nicotinamide and choline chloride are sequentially added in a container, the total volume is 0.3L, the molar ratio is 1:0.005:1, and ultrasonic oscillation is performed under constant temperature of 80°C and power of 70W to uniformly mix, thereby obtaining a multi-component deep eutectic solvent; 0.5 mol of nickel sulfamate tetrahydrate is added to the deep eutectic solvent, and ultrasonic oscillation is continued under constant temperature of 80°C and power of 70W until no crystals are precipitated at room temperature, and the liquid preparation is completed;

[0074] S2, electrodeposition: a nickel plate is used as a soluble anode, and graphite is used as a cathode, which is inserted into the solution prepared in step S1, the direct distance between the cathode electrode and the anode electrode is 1 cm, and direct current electrodeposition is performed under constant current density of 0.07 A / dm 2 The direct current electrodeposition is performed under constant current density, the electrodeposition temperature is kept at 55°C throughout the process, and the deposition is performed for 8 h;

[0075] S3, washing and drying: after the electrodeposition is completed, the cathode electrode is taken out, washed, and vacuum dried at 40°C, and then porous nanometer nickel is obtained on the surface of the cathode electrode.

[0076] Table 2: specific parameters and Tafel slope of examples 1-5

[0077]

[0078] The specific parameters of all the above examples are shown in Table 2. As can be seen from Table 2, in all the examples, the porous nanometer nickel prepared in Example 1 has the smallest Tafel slope, i.e., the optimal example, and has the best effect as a water electrolysis hydrogen production catalyst.

[0079] Application Example

[0080] The alkaline water electrolysis HER simulation application of the catalyst is completed by using a standard three-electrode system through a Zennium-E4 electrochemical workstation (Germany Zahn Electrochemistry Company). The porous nanometer nickel of Example 1, the non-porous nanometer nickel of Comparative Example 1, a graphite electrode, and mercury / mercury oxide are used as the working electrode, the counter electrode, and the reference electrode, respectively. High-purity argon is introduced into the test solution (1M KOH) to remove oxygen before the HER test. The LSV test is used to test the HER performance curve, and the test interval is 0.1V to -0.6V (vs. RHE). A CA test is performed every 50mV, and the current density value at the 100th second of each test is recorded, which is considered to be the steady state of the catalyst. A plurality of such steady-state current density values are plotted, and the Tafel slope is calculated by substituting the Tafel formula. The exchange current density is calculated from the Tafel slope. The greater the exchange current density, the more significant the HER performance. As shown in Table 3 below, compared with the existing nickel-based catalyst, the porous nanometer nickel prepared in Example 1 has a larger exchange current density, and exhibits excellent HER catalytic performance.

[0081] Table 3 Comparison of HER performance of different nickel-based materials

[0082]

Claims

1. A method for preparing porous nanometer nickel, characterized in that, The method comprises the following steps: S1, taking first hydrogen bond donor, second hydrogen bond donor and choline chloride according to a molar ratio of 0.3-4:0.001-0.005:1, the first hydrogen bond donor is ethylene glycol, the second hydrogen bond donor is nicotinamide, constant temperature, ultrasonic oscillation mixing, a multi-component deep eutectic solvent is obtained, a soluble nickel source is added into the deep eutectic solvent, and constant temperature, ultrasonic wave is continued until no crystallization is precipitated at room temperature; S2, inserting a cathode electrode and an anode electrode into the solution obtained in step S1, the anode electrode is nickel, and constant current electrodeposition is carried out; S3, taking out the cathode electrode, washing and drying, and obtaining a porous nano nickel on the surface of the cathode electrode; The temperature of the constant current electrodeposition in the step S2 is 50-75℃, the current density of the cathode is 0.05-0.15 A / dm 2 , and the electrodeposition time is 0.5-10 h.

2. The method of claim 1, wherein: In the step S1, the constant temperature is 30-100 DEG C, and the ultrasonic oscillation power is 50-100 W. 3.The method of claim 1, wherein: In the step S1, the soluble nickel source is one or more of nickel chloride, nickel sulfate, nickel nitrate, nickel sulfamate and hydrates thereof.

4. The method for preparing porous nickel nanoparticles according to claim 1, characterized in that: In the step S1, the molar volume ratio of the nickel salt to the deep eutectic solvent is 0.001-1 mol:1-1000 mL.

5. The method of claim 1, wherein: In the step S2, the distance between the cathode electrode and the anode electrode is 0.5-3 cm, and the cathode is any one of stainless steel, graphite, red copper and brass.

6. The method of claim 1, wherein: In the step S3, the drying is vacuum drying at 25-80 DEG C.

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