阅读说明：本技术 一种镍纳米线阵列电极的制备方法及其作为电化学析氧活性材料的应用 (Preparation method of nickel nanowire array electrode and application of nickel nanowire array electrode as electrochemical oxygen evolution active material ) 是由 严勇 刘春越 刘浩岑 于 2020-12-18 设计创作，主要内容包括：一种镍纳米线阵列电极的制备方法及其作为电化学析氧活性材料的应用涉及电化学析氧领域。首先结合深反应离子刻蚀技术和电镀法制备高比表面积的镍纳米线阵列电极；其次在镍纳米线阵列电极基底上修饰能够强化或激发其催化活性的掺杂金属原子(Fe、Co、Mo),制备得到各类复合材料电催化剂,进而强化镍纳米线阵列电极的催化活性；最后深入表征所得材料的晶体微结构并测试其电催化析氧性能,探究镍纳米线阵列电极作为高效电化学析氧活性材料的应用。通过该方法制备的镍纳米线阵列电极具有高比表面积及优良的响应信号,表现出较好的电催化析氧活性和稳定性,此项发明将为设计构筑稳定高效的电催化析氧活性材料提供直接的科学依据和技术手段。(A preparation method of a nickel nanowire array electrode and application of the nickel nanowire array electrode as an electrochemical oxygen evolution active material relate to the field of electrochemical oxygen evolution. Firstly, preparing a nickel nanowire array electrode with a high specific surface area by combining a deep reactive ion etching technology and an electroplating method; secondly, modifying doped metal atoms (Fe, Co and Mo) capable of strengthening or exciting the catalytic activity on the nickel nanowire array electrode substrate to prepare various composite material electrocatalysts so as to strengthen the catalytic activity of the nickel nanowire array electrode; finally, the crystal microstructure of the obtained material is deeply characterized, the electrocatalytic oxygen evolution performance of the material is tested, and the application of the nickel nanowire array electrode as a high-efficiency electrochemical oxygen evolution active material is explored. The nickel nanowire array electrode prepared by the method has high specific surface area and excellent response signals, shows better electrocatalytic oxygen evolution activity and stability, and provides direct scientific basis and technical means for designing and constructing a stable and efficient electrocatalytic oxygen evolution active material.)

1. A method for preparing a nickel nanowire array electrode is characterized by comprising the following steps:

s1, preparing a silicon template; preparing a silicon nanowire array electrode structure as a template by utilizing a deep reactive ion etching technology, wherein the etching technology is based on continuous passivation and etching circulation, the pressure of a reactor is 90-95mTorr, the power of radio frequency plasma is set to be 400-ion 500W, and 70-80 continuous etching circulation is adopted;

s2, preparing a nickel nanowire array electrode; depositing nickel on the silicon template obtained in step S1 by electroplating at a pH of 3.0-3.5 and a temperature of 55 deg.C under an average current density of 1-3 A.dm^-2Depositing is realized under the condition, the whole process lasts for 4-6 hours, and finally the nickel nanowire array electrode material with the nanowire array structure is obtained;

s3, modifying the nickel nanowire array electrode; preparing FeCl with the concentration of 0.5g/100mL by using ultrapure water₃、0.5g/100mL CoCl₂0.5g/100mL molybdic acid solution; respectively putting the nickel nanowire array electrodes obtained in the step S2 into the prepared solution, soaking for 20-40min, taking out, washing with deionized water, and drying; and (3) calcining the dried material in a tubular furnace at the temperature rising rate of 5 ℃/min from room temperature to 200-300 ℃ in an argon atmosphere, and maintaining for 2h to finally obtain the Fe, Co or Mo metal atom doped modified nickel nanowire array electrode material.

2. The method of claim 1, wherein the pressure of the whole etching process reactor is 94mTorr, the power of the rf plasma is set to 450W, and the silicon nanowire array structure is obtained by using 75 consecutive etching cycles in step S1.

3. The method of claim 1, wherein the electroplating process of step S2 has a pH of 3.2 and is carried out at a constant current of 1.31A and 10V, corresponding to 2A dm^-2To achieve deposition, the entire process lasts for 5 hours.

4. The method of claim 1, wherein the nickel nanowire array electrode is immersed in the solution for 30min at the calcining temperature of 250 ℃ in step S3.

Technical Field

The invention relates to a method for preparing and modifying a nickel nanowire array (hereinafter referred to as Ni-NG) electrode, and the obtained Ni-NG electrode material is applied to the field of electrocatalysis, in particular to the field of electrochemical oxygen evolution.

Background

With the gradual exhaustion of the traditional fossil fuel and the increasingly serious problem of environmental pollution, the development of cheap and efficient electrocatalytic Oxygen Evolution (OER) active material for the development of electrochemical hydrogen and CO production₂Reduction and other clean energy technologies are of great importance. Typically, the noble metal-based material, IrO/ruthenium oxide (IrO)₂/RuO₂) Is the most active OER catalyst. But large-scale deployment using these materials is difficult to achieve due to high price and scarce resources. Accordingly, much research has been devoted to the development of relatively inexpensive, readily available non-noble metal electrocatalysts. Transition metal (cobalt (Co), nickel (Ni), iron (Fe), manganese (Mn)) based perovskite structure, spinel structure oxides, layered structure hydroxides (or oxyhydroxides) are also considered to be more potential OER catalysts, of which most materials have better catalytic performance under alkaline reaction conditions.

Ni is used as an ideal non-noble metal electrocatalyst for many energy-related key applications due to low price, high element abundance, strong corrosion resistance, and high electrical conductivity; because Ni and high-activity electrocatalyst platinum (Pt) are positioned in the same period in a periodic table, the structure and electronic parameters of the Ni-based material are similar to those of Pt, and the Ni-based material has obvious electrocatalytic activity and stability on OER; in addition, there is a high synergistic effect between Ni and the adjacent heteroatoms, which may lead to better surface adsorption, contributing to improved electrocatalytic activity. However, the activity and durability of most Ni-based electrocatalytic materials are still far from satisfactory. Researchers believe that the electrocatalytic performance depends largely on the chemical structure and surface morphology of the outer layer or sublayer atoms surrounding the Ni particles that directly interact with the reactants, which can provide a large number of active sites. In order to obtain better electrocatalytic performance, the Ni-NG electrode has high specific surface area and excellent response signal, and can remarkably improve electrocatalytic efficiency, so that the Ni-NG electrode is widely concerned in electrocatalytic research.

In the electrocatalytic OER process, the electrocatalytic OER activity of the Ni-NG electrode is not high enough, and the introduction of transition metal atoms can enable the Ni-NG electrode interface to have good OER catalytic activity. Some research works indicate that the Ni-NG electrode interface can have good OER electrocatalytic activity by modifying the Ni-NG electrode structure through doping of specific transition metal elements to change the surface electronic structure characteristics of the Ni-NG electrode structure. Pettersson et al conducted systematic and thorough theoretical exploration of such studies and revealed a series of important information. Firstly, the type, valence state and concentration of the introduced transition metal atom play an important role in the OER catalytic performance of the Ni-NG electrode interface; secondly, some of the confinement metal atoms (such as Fe and Co) are not only direct reaction active sites, but also can play a role in regulating the electronic structure of the interface of the peripheral Ni-NG electrode, so as to activate the catalytic activity of the peripheral Ni atoms, and are indirect active centers.

In combination with the current situation, the invention aims to solve the problems of low catalytic activity, insufficient durability and the like of the Ni-based catalyst in the process of electrocatalysis OER, and aims to improve the electrocatalysis OER performance by optimizing the composition and the structure of the Ni-based catalyst.

Disclosure of Invention

The invention firstly adopts an electroplating method to prepare the Ni-NG electrode with high specific surface area, secondly introduces doped metal atoms (Fe, Co and Mo) capable of strengthening or exciting the catalytic activity on the Ni-NG electrode substrate to prepare various composite electrocatalysts of Ni-NG-Fe, Ni-NG-Co and Ni-NG-Mo to strengthen the catalytic activity of the Ni-NG electrode, and finally researches the application of the Ni-NG electrode as a high-efficiency electrochemical oxygen evolution active material through various structural representations and catalytic performance tests. The specific technical scheme of the invention is as follows:

(1) preparing a silicon template: preparing a silicon nanowire array electrode structure as a template by utilizing a deep reactive ion etching technology, wherein the etching technology (hereinafter referred to as a Bosch technology) is based on continuous passivation and etching circulation, the pressure of a reactor is 90-95mTorr, the power of radio frequency plasma is set to be 400-500W, and 70-80 continuous etching circulation is adopted;

(2) and preparing a Ni-NG electrode. Depositing nickel on the silicon template obtained in the step (1) by an electroplating method, and electroplatingThe pH value is 3.0-3.5, the temperature is 55 deg.C, and the average current density value is 1-3 A.dm^-2Depositing is realized under the condition, the whole process lasts for 4-6 hours, and finally the nickel nanowire array electrode material with the nanowire array structure is obtained;

(3) and (4) modification of a Ni-NG electrode. Preparing FeCl with the concentration of 0.5g/100mL by using ultrapure water₃、0.5g/100mL CoCl₂0.5g/100mL molybdic acid solution; respectively putting the nickel nanowire array electrodes obtained in the step S2 into the prepared solution, soaking for 20-40min, taking out, washing with deionized water, and drying; and (3) calcining the dried material in a tubular furnace at the temperature rising rate of 5 ℃/min from room temperature to 200-300 ℃ in the argon (Ar) atmosphere for 2 hours, and finally obtaining the Fe, Co and Mo metal atom doped modified nickel nanowire array electrode material.

In the preparation process of the silicon template in the step (1), the reactor pressure is 94mTorr, the radio frequency plasma power is set to be 450W, and a silicon nanowire array structure with the depth of 20 micrometers is obtained by adopting continuous 75 etching cycles.

The electroplating process described in step (2) was carried out at a pH of 3.2 and a constant current of 1.31A and 10V, corresponding to 2A dm^-2To achieve deposition, the entire process lasts for 5 hours.

And (3) soaking the Ni-NG electrode in the solution for 30min, wherein the calcining temperature is 250 ℃.

Due to the adoption of the technical scheme, the invention has the following advantages:

(1) the preparation and modification method of the Ni-NG electrode is simple, mild in condition and easy to operate.

(2) The prepared Ni-NG electrode material has high specific surface area and excellent response signal, and shows better electrocatalytic OER activity.

(3) The transition metal atoms (Fe, Co and Mo) doped on the Ni-NG substrate can strengthen or excite more active sites, remarkably optimize the catalytic activity and durability of the Ni-NG electrode material and provide a new direction for the development and modification of the OER electrocatalyst.

Drawings

FIG. 1 is a flow chart of the production of a Ni-NG electrode in the present invention.

FIG. 2 is a schematic diagram of the front and back sides of the Ni-NG electrode prepared in the present invention.

FIG. 3 is a graph of (A) LSV versus OER for Ni reference (virgin), Ni-NG-Fe, Ni-NG-Co, Ni-NG-Mo samples in 1mol/L KOH electrolyte in accordance with the present invention; (B) tafel plot and related data; (C) a Nyquist plot at a 270mV overpotential; (D) CP graph of long-term durability test.

FIG. 4 is an XRD pattern of Ni-NG, Ni-O (Ni-NG calcined in oxygen), Ni-NG-Fe, Ni-NG-Co, Ni-NG-Mo samples according to the present invention.

FIG. 5 is a (A) SEM (front view) and (C) SEM (side view) of the Ni-NG electrode according to the present invention; SEM (front view) and SEM (side view) of Ni-NG-Fe electrode.

FIG. 6 is a high resolution STEM-HADDF graph of a Ni-NG-Fe electrode according to the present invention;

FIG. 7 is an EDS mapping spectrum of a Ni-NG-Fe electrode according to the present invention.

Detailed Description

In order to make the technical solutions of the present invention better understood and enable those skilled in the art to practice the present invention, the following embodiments are further described, but the present invention is not limited to the following embodiments.

Example 1: preparation of silicon template

The silicon nanowire array structure prepared by utilizing the Deep Reactive Ion Etching (DRIE) technology is used as a template. In this work, silicon wafers were used as starting materials, the detailed parameters of which are shown in table 1:

TABLE 1 detailed parameters of silicon wafers

Experiments were conducted using a high density plasma etcher (IPC-multiplex) manufactured by Surface Technology Systems (STS) of the united kingdom, where wafers were transferred to a chamber that maintained a highly anisotropic etch, based on successive passivation and etch cycles. The true bookThe experiment adopts 75 continuous etching cycles to obtain a silicon nanowire array structure with the depth of 20 mu m, and octafluorocyclobutane (C) is firstly introduced in each cycle₄F₈) Passivating the gas for 11s at a flow rate of 85 sccm; then, in sulfur hexafluoride (SF)₆) And O₂The etching time of the first two cycles is slightly longer, 11s and 10s respectively, in order to ensure the quality of the subsequent etching process, the etching time of the first two cycles is 9s and 13sccm respectively. Throughout the Bosch process, the reactor pressure was typically 94mTorr and the rf plasma power was set at 450W. In addition, in order to avoid excessive temperature during etching, the back surface of the substrate is cooled by helium (He) gas with a flow rate of 10-40 sccm.

Example 2: preparation of Ni-NG electrode

In order to obtain the nickel nanowire array structure with high surface area, nickel is deposited on the silicon template by adopting an electroplating method. Firstly, putting a prepared silicon template into a platform groove made of polymethyl methacrylate (PMMA), and then fixing the silicon template by using an adhesive tape and connecting the silicon template by using a copper wire to serve as a cathode material; a high-purity (99.99%) electrolytic nickel sheet coated by a polypropylene (pp) mesh sheet is taken as an anode material; preparing electrolyte from analytically pure chemical reagent and deionized water, wherein the electrolyte contains nickel sulfamate (Ni (NH)₂SO₃)₂·4H₂O), boric acid (H)₃BO₃) And sodium dodecyl sulfate (NaC)₁₂H₂₅SO₄) In which Ni (NH)₂SO₃)₂·4H₂O provides nickel ions and H with the concentration of 120g/L₃BO₃30g/L of NaC in powder form, 0.5g per litre of electrolyte₁₂H₂₅SO₄Stirring until the solution is completely dissolved, and then beginning electroplating; before the solution is put into the plating solution, the solution is filtered to remove impurities. Electroplating at pH 3.2 with sulfanilic acid (H)₃NSO₃) An initial pH adjustment and a discontinuous pH correction were carried out, another important parameter being that the whole process was carried out at a temperature of 55 ℃. The deposition is carried out at a constant current of 1.31A and 10V, corresponding to 2A dm^-2To achieve deposition, at mostAll components are then connected to an external power source by wires.

The greatest challenge in the electroplating process is the connection between the silicon template and the copper wires and the electrical conductivity of the silicon template, which will have a significant impact on the electrical conductivity of the overall circuit and further impact the nickel plating process. To solve these problems, three different approaches have been tried:

the method comprises the following steps: firstly, a copper wire is directly immersed in the solution for about 10 minutes. A certain amount of nickel is deposited on the copper wire, so that the contact area with the silicon template is increased, and the conductivity of the whole circuit is improved;

the second method comprises the following steps: depositing Au with the thickness of 20nm on the silicon template through Physical Vapor Deposition (PVD) to improve the conductivity of the silicon template, and directly connecting a copper wire with the Au area to improve the conductivity of the whole circuit;

the third method comprises the following steps: a small copper foil is pasted on the silicon template by conductive silver adhesive, and a copper wire is directly connected with the copper foil, so that the connection area can be greatly enlarged. Therefore, the conductivity of the entire circuit will be improved.

After several attempts, the copper foil adhered by the third method is found to achieve the best effect. After plating, the covered silicon template was removed and etched with 40% potassium hydroxide (KOH) solution at 90 ℃ for about 7 hours to obtain a Ni-NG electrode material (FIG. 2).

Example 3: modification of Ni-NG electrodes

In the electrocatalytic oxidation process, the electrocatalytic OER activity of the Ni-NG is not high enough, and the OER catalytic activity and durability of the Ni-NG can be obviously optimized by introducing a transition metal atom to modify the Ni-NG interface. First, FeCl was prepared with ultrapure water at a concentration of 0.5g/100mL, respectively₃、0.5g/100mL CoCl₂0.5g/100mL molybdic acid solution, and soaking three Ni-NG electrodes with the area of 1cm multiplied by 1cm in prepared FeCl respectively₃、CoCl₂Soaking in molybdic acid solution for 30min, slightly washing with deionized water for 2-3min after soaking, then placing the sample in a drying oven for drying, finally heating the dried material in a tubular furnace at the heating rate of 5 ℃/min to 250 ℃ under the Ar atmosphere, calcining and maintaining for 2h to obtain the final productNi-NG-Fe, Ni-NG-Co, Ni-NG-Mo electrode material.

Example 4: application of Ni-NG electrode as electrochemical oxygen evolution active material

The Ni-NG electrode provided by the invention is used for carrying out electrochemical test on the electro-catalytic performance of OER in 1mol/L KOH, and the application of the Ni-NG electrode as an electrochemical oxygen evolution active material is explored. As can be seen from a Linear Sweep Voltammetry (LSV) curve, the Ni-NG electrode doped with transition atoms of Fe, Co and Mo has a lower Tafel slope, which shows that the surface of the Ni-NG electrode has faster reaction kinetics (shown in figures 3A and 3B); under the condition of 270mV overpotential, the Nyquist graphs of the Ni-NG-Fe, Ni-NG-Co and Ni-NG-Mo electrode materials show smaller charge transfer resistance, which indicates that the electronic and ionic conductivity in the electrolyte solution is improved (figure 3C); CP testing indicated that overpotentials of Ni-NG-Fe, Ni-NG-Co, and Ni-NG-Mo electrodes were substantially stable over 10000s, indicating that the materials had good durability to OER (FIG. 3D).

The electrode material is detected by a polycrystalline X-ray diffractometer (XRD), and the result shows that Ni-NG-Fe, Ni-NG-Co and Ni-NG-Mo samples have the same phase as Ni-NG and belong to a cubic system, which is probably caused by that the doping amount of Fe, Co and Mo is too small to be measured by XRD (figure 4); the morphology of the product was characterized by Scanning Electron Microscopy (SEM), which indicated that there was an attachment formation at the tip of the Ni nanowires, probably due to Fe atom doping (fig. 5); the morphology of the Ni-NG-Fe material is characterized by a high-angle annular dark field image-scanning transmission electron microscope (STEM-HADDF), and the result shows that NiFeO is possible_xCluster presence (fig. 6); the appearance of the product is characterized by a Transmission Electron Microscope (TEM) and EDS analysis shows that Ni, Fe and O elements exist on the Ni-NG-Fe material, and the ratio of Ni to Fe in a high/low concentration staggered area is 13: 1.

The results show that the Ni-NG electrode has high specific surface area and excellent response signals, shows better electrocatalytic OER activity and stability, and can be used as a high-efficiency electrocatalyst material to be applied to an electrochemical Oxygen Evolution (OER) process.