CN113174599B

CN113174599B - Nickel-based hierarchical structure integrated electrode for water electrolysis and preparation method thereof

Info

Publication number: CN113174599B
Application number: CN202110409831.4A
Authority: CN
Inventors: 王荣方; 高登何; 王辉; 王许云
Original assignee: Qingdao University of Science and Technology
Current assignee: Qingdao University of Science and Technology
Priority date: 2021-04-16
Filing date: 2021-04-16
Publication date: 2022-03-11
Anticipated expiration: 2041-04-16
Also published as: CN113174599A

Abstract

The invention discloses a nickel-based hierarchical structure integrated electrode for water electrolysis and a preparation method thereof, wherein a commercial nickel screen is placed in HCl solution for electrochemical etching to obtain an E-NM electrode with an uneven surface; then placing the obtained electrode material E-NM in a water tank, placing an electromagnet at the bottom of the water tank, applying an electromagnetic field perpendicular to the E-NM, mixing a nickel-based metal inorganic salt solution with a certain concentration and a hydrazine hydrate solution in the water tank, reacting at a certain temperature, and washing and drying to obtain a Ni NWs/E-NM electrode; and finally, placing the obtained electrode NiNWs/E-NM in a nickel-based metal inorganic salt electrolyte solution with a certain concentration, carrying out electrochemical deposition on metal simple substance nickel nano particles on the surface of the Ni NWs/E-NM electrode, washing and drying to obtain the Ni/Ni NWs/E-NM electrode with a high active area. Ni nano-particles are deposited on the ultra-long nano-wire array to form a definite hierarchical structure of 'long nano-particles on nano-wires', so that the electrode has higher electro-catalytic performance.

Description

Nickel-based hierarchical structure integrated electrode for water electrolysis and preparation method thereof

Technical Field

The invention belongs to the technical field of hydrogen production and energy storage by water electrolysis, and particularly relates to a nickel-based hierarchical structure integrated electrode for water electrolysis and a preparation method thereof.

Background

The increasing demand for energy and the inevitable depletion of fossil fuels has prompted the search for environmentally friendly, renewable and clean alternative energy sources and for new ways of extracting energy efficiently. The hydrogen has higher energy density (143 MJ.k)g^-1) And only combustion product H₂O is a fuel with great prospect for realizing the sustainable development of energy. Electrolyzed water is a mature commercial technology used to produce clean energy with zero carbon emissions. Although its coupling to photovoltaic modules for direct solar hydrogen production would be an excellent energy conversion system, the large-scale production of high-purity hydrogen is still difficult due to the strong uphill reaction requiring an overpotential significantly greater than the theoretical electrolytic potential. The overpotential is related to the catalytic activity of the electrocatalyst in the water electrolysis process, so that the most active electrocatalyst is required to be used to reduce the overpotential of the electrode in practical application so as to ensure that the hydrogen production process is more energy-saving and efficient. Currently, noble metal catalysts remain the most advanced catalysts, which can achieve lower overpotentials for HER and OER, respectively. However, the expensive cost and scarce content of noble metals limit their large-scale exploitation. Moreover, these noble metal catalysts show the disadvantage of poor stability at high sustained current densities, making them far from meeting the demand for large-scale hydrogen production. Therefore, there is an urgent need to develop a method for preparing a low-cost electrocatalytic material having high activity and stability. There are many methods for improving the catalytic performance of the material, such as improving the conductivity of the material itself, such as metal simple substance and alloy, to further enhance the electron transport, thereby improving the catalytic activity. Metallic nickel has a higher conductivity and is 10 orders of magnitude greater than hydroxides and oxides. Besides improving the intrinsic activity of the catalyst, the hierarchical nano material with an open structure is reasonably designed and constructed to further improve the electro-catalytic activity, and due to the unique structural advantage of high surface area, an effective ion diffusion path is provided for mass and charge transmission in the electrochemical process, thereby attracting wide attention of people. Research in recent years has shown that there is much research on the combination of hierarchical structures with multi-component compounds, but research on the combination of hierarchical nanomaterials with open structures with elemental metals has received little attention. The combination not only has high metal conductivity and homogeneity stability, but also improves the catalytic activity by utilizing a hierarchical structure, thereby researching the catalytic performance of the electrochemical water decompositionWould be a significant problem. Nickel, a typical transition metal element, is an excellent commercial electrocatalytic material and shows excellent performance in electrochemical catalysis due to its many advantages of abundance in the earth, high stability and corrosion resistance. The method is characterized in that a Ni nanowire array grows on the surface of an electrochemically etched nickel net by utilizing the action of an electromagnetic field, and the catalytic performance of electrolyzed water is further enhanced through electrodeposition.

Disclosure of Invention

The invention aims to improve the performance of an electrode material of an electrolytic cell applied to water electrolysis, and the electrode material of a nickel screen is modified by an electrochemical means to form a multidimensional hierarchical structure, and is applied to the water electrolysis hydrogen production industry. Solves the problems of high consumption, low output, low activity and the like of the traditional support body electrode material (nickel screen) for electrolyzing water.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of a nickel-based hierarchical structure integrated electrode for water electrolysis comprises a nickel net subjected to electrochemical etching, an elemental nickel nanowire array structure formed on the nickel net by utilizing the action of an electromagnetic field, and nickel nanoparticles formed by electrodeposition on the surface of a nickel nanowire.

The invention relates to a preparation method of a nickel-based hierarchical structure integrated electrode for water electrolysis, which specifically comprises the following steps:

(1) electrochemical etching to form a primary structure, namely a rough nickel screen substrate: placing a commercial nickel screen (marked as E-NM) in HCl solution, and carrying out electrochemical etching to obtain an E-NM electrode with an uneven surface;

(2) the electromagnetic field acts on a loaded secondary structure, namely a metal simple substance nickel nanowire array Ni NWs: placing the electrode material E-NM obtained in the step (1) in a water tank, placing an electromagnet at the bottom of the water tank, applying an electromagnetic field perpendicular to the E-NM, mixing a nickel-based metal inorganic salt solution with a certain concentration and a hydrazine hydrate solution in the water tank, reacting at a certain temperature, and washing and drying to obtain a Ni NWs/E-NM electrode;

(3) electrochemical oxidation forms a three-level structure, namely a nano-particle nickel-based metal simple substance: and (3) placing the electrode NiNWs/E-NM obtained in the step (2) in a nickel-based metal inorganic salt electrolyte solution with a certain concentration, carrying out electrochemical deposition on metal simple substance nickel nano particles on the surface of the Ni NWs/E-NM electrode, washing and drying to obtain the Ni/Ni NWs/E-NM electrode with a high active area.

Specifically, the concentration of the HCl solution in the step (1) is 3M, and electrochemical etching is carried out by adopting a chronoamperometry for 30-600 s; in the reaction process in the step (2), a continuous magnetic field is adopted to generate directionally-grown nanowires, and the reaction temperature is 50-90 ℃, preferably 80 ℃; in the step (3), electrochemical deposition is performed by a chronoamperometry for 100-1800 seconds.

Preferably, the etching time in the step (1) is 100s, the reaction time in the step (2) is 1h, and the electrodeposition time in the step (3) is 20 min.

Further, the molar ratio of the nickel metal ions to the hydrazine hydrate in the step (2) is 2:1, so that the complete reaction of the nickel-based metal inorganic salt solution is ensured. The electromagnetic field is continuously introduced in the reaction process to ensure the formation of the nanowire structure, the reaction mechanism is that nickel ions form nanoparticles under the reduction of hydrazine hydrate, the nickel nanoparticles have magnetism, the particles are sequentially arranged and stacked into a linear structure under the action of the magnetic field lines, the contact area with electrolyte in the water electrolysis process is increased, and more attachment sites are provided for the growth of electrodeposited nickel nanoparticles. The nickel-based metal inorganic salt solution in the step (2) contains sodium citrate with a certain concentration as a complexing agent, the reaction rate of the reduction reaction is controlled, and the stability of the nanowire structure is ensured; and the catalyst also contains a trace amount of chloroplatinic acid solution as a nucleating agent, so that the nucleation of the nickel nano particles is accelerated, the nucleation time is greatly shortened, the amount of the chloroplatinic acid solution is small, and the water electrolysis process is not influenced in the nickel nano particles.

Specifically, the nickel-based metal inorganic salt solution in the step (2) contains 0.1mol/LNiCl₂·6H₂O、37.5mmol/L Na₃C₆H₅O₇(sodium citrate), and 0.153mmol/L H₂PtCl₆The concentration of the hydrazine hydrate solution is 0.38mol/L, andbefore the reaction, the pH values of the nickel-based metal inorganic salt solution and the hydrazine hydrate solution concentrated solution are adjusted to 12.5 by 6M KOH aqueous solution.

Furthermore, the nickel-based metal inorganic salt solution also contains other metal ions such as cobalt ions, manganese ions and the like, so that a bimetallic alloy such as NiCo, NiMo, NiMn and the like can be conveniently formed in the reaction process, and the addition of the alloy is favorable for forming the heterostructure of the electrode material, so that the catalytic process of the material is further enhanced.

Further, the nickel-based metal inorganic salt electrolyte solution in the step (3) according to the present invention further includes boric acid and sodium sulfate. Boric acid as an acid-base pH buffer and sodium sulfate as an electrolyte increase the conductivity of the solution.

The invention takes the nickel screen as the current collector, utilizes the electrochemical means to modify the electrode material to form a hierarchical structure to improve the performance of the electrode material in the electrolytic tank for electrolyzing water, and the electrode material has good corrosion resistance, high activity and stability, and is suitable for the electrolysis industry under high current density.

Compared with the prior art, the invention has the following beneficial effects: (1) by taking a commercial nickel net as a current collector and utilizing an electrochemical etching method, the roughness of the surface of the current collector is increased, anchoring sites are increased, and the load stability of a load is improved; 2) the ultra-long nanowire array structure is used as a current collector, provides a continuous electron ion transmission path, and effectively shortens the transmission length of ions and free electrons in the electrochemical process; has very large specific surface area and open space-allowing rapid diffusion of electrolyte solution at the electrode surface, making the electrolyte easy to diffuse to the internal region of the electrode, which is an effective way to optimize and improve the utilization rate of metal catalyst; the larger specific surface area provides more nucleation sites for loading of Ni nanoparticles, and the array structure can withstand further loading of active species. 3) The conductive area of electron transport is further increased by the electrodeposited Ni nano particles, and the conductive performance of the Ni nano wire array is improved; the formation of a definite hierarchical structure of 'long nano-particles on nanowires', the hierarchical structure not only provides larger specific surface area and more active sites for oxidation-reduction reaction, but also formsThe staggered open structure (namely, the nano particles are dispersed among the nano wire arrays) is beneficial to the rapid mass transfer and the penetration of electrolyte, thereby endowing the electrode with higher electrocatalytic performance. Experiments prove that the Ni nanoparticles which are granular in the electrodeposition process have continuous electron transmission channels on conductive Ni nanowires and can be used as a promising HER decomposition water catalyst. (3) The preparation method has simple process, short time, low cost, uniform load of prepared product, regular structure, stable performance, and suitability for large-scale industrial application, and the size of the electrolytic cell can be adjusted according to the size of required material, such as nickel mesh size of 1 × 1cm²、5×5cm²、10×10cm²。

Drawings

FIG. 1 is a flow chart of a preparation method of a nickel-based hierarchical structure integrated electrode for water electrolysis according to the present invention.

FIG. 2 is SEM pictures of different hierarchical structures involved in example 1, wherein a and b are E-NM electrode materials after 100s of electrochemical etching; c is Ni NWs/E-NM electrode after growing the nickel nano wire; d is the Ni/Ni NWs/E-NM electrode after electrodeposition.

FIG. 3 is a graph of the linear voltammetry (LSV) test of the Ni/Ni NWs/E-NM electrode material applied to the hydrogen evolution process for different deposition durations in example 1.

FIG. 4 is a LSV test graph of hydrogen evolution process obtained under the optimum experimental conditions for different hierarchical electrode materials E-NM, Ni NWs/E-NM and Ni/Ni NWs/E-NM in example 1 and Ni/E-NM in comparative example 2.

FIG. 5 is a histogram of overpotential obtained under the optimum experimental conditions for different current densities for different graded electrode materials E-NM, Ni NWs/E-NM and Ni NWs/E-NM in example 1 and Ni/E-NM in comparative example 2.

FIG. 6 is a graph showing the impedance of hydrogen evolution process obtained under the optimum experimental conditions in example 1 involving different hierarchical electrode materials E-NM, Ni NWs/E-NM and comparative example 2 Ni/E-NM.

Detailed Description

The synthesis and catalytic activity of the nickel-based hierarchical structure formed by modifying an electrode material represented by a commercial nickel mesh will be further described below by way of specific examples.

Example 1:

1. preparation of Nickel Net (E-NM) having roughened surface

The size of the sample is 1.5X 1cm²The commercial nickel screen (NM) is put into 3M HCl electrolyte solution, a two-electrode system is adopted, NM is used as a positive electrode, a graphite rod is used as a negative electrode, electrochemical etching is carried out by a chronoamperometry it, the set voltage is 1V, and the performance of the obtained E-NM electrode under certain etching time is measured. Specifically, the electrochemical etching time is 30-600s, and the performance is optimal when the electrochemical etching time is 100 s.

FIGS. 2a and 2b are SEM images of NM before and after electrochemical etching, and it can be seen that the surface of the nickel mesh fiber is changed from smooth to rough after electrochemical etching, which is easy to nucleate during subsequent growth of nickel nanowires.

2. Preparation of Nickel nanowire arrays (Ni NWs/E-NM)

(1) Preparing a solution A and a solution B, wherein the solution A is 0.1mol/LNiCl₂·6H₂O，37.5mmol/L Na₃C₆H₅O₇(sodium citrate) and 0.153mmol/L H₂PtCl₆An aqueous solution of (a); the solution B is 0.38mol/L N₂H₄·H₂An aqueous solution of O (hydrazine hydrate solution);

(2) respectively adding KOH solution into the solution A and the solution B to adjust the pH value to 12.5, heating to 80 ℃, and mixing the two solutions;

(3) and (3) putting the E-NM electrode prepared in the step (1) into a mixed solution of the solution A and the solution B, applying an electromagnetic field perpendicular to the E-NM electrode, reacting for 1h at 50-90 ℃ under the action of the electromagnetic field, washing and drying to obtain the Ni NWs/E-NM. In the process, the concentration of the reaction liquid is kept unchanged in the reaction process by controlling the inlet and outlet speed of the reaction liquid, so that dynamic balance is achieved. As shown in fig. 2c, nickel nanowires with uniform thickness are grown perpendicular to the surface of the E-NM along the electromagnetic field direction, and in addition, the surface of the electrode material after reaction has obvious nickel nanowire growth (black material), and the black material is not easy to wash away, which indicates that the bonding force between the nickel nanowires and the E-NM is strong.

3. Preparation of electrode Material (Ni/Ni NWs/E-NM)

The prepared Ni NWs/E-NM is taken as a precursor, a three-electrode electrochemical cell is adopted, Ni NWs/E-NM is taken as a working electrode, a platinum sheet is taken as a counter electrode, Ag/AgCl is taken as a reference electrode, and the Ni NWs/E-NM contains 0.5M NiSO₄·6H₂O、0.2M Na₂SO₄And 0.5M H₃BO₃The solution is electrolyte, and is subjected to electrodeposition for 10min, 20min and 30min under the condition of constant voltage of-1V, and Ni/Ni NWs/E-NM-10, Ni/Ni NWs/E-NM-20 and Ni/Ni NWs/E-NM-30 are respectively obtained after washing and drying. As shown in fig. 2d, nanoparticles are grown on the surface of the nanowires.

FIG. 3 is a linear voltammetry (LSV) test curve of electrode material Ni/Ni NWs/E-NM prepared by different electrodeposition time applied to hydrogen evolution process, and it can be seen from the graph that the electrochemical performance of Ni/Ni NWs/E-NM-20 is the best, because the initial deposition amount is less, less Ni nano-particles are generated on the foamed nickel, the deposition amount is increased along with the increase of the deposition time, the Ni nano-particles are generated on the nano-wires and completely and uniformly cover the foamed nickel, but at 30min, the Ni nano-particles are agglomerated on the surface of the foamed nickel and near the nano-wires, and the catalytic performance is reduced. Therefore, other comparative examples were investigated using Ni/Ni NWs/E-NM-20 as the target electrode.

Example 2

1. Preparation of Nickel Net (E-NM) having roughened surface

The specific steps are the same as those of the example 1

2. Preparation of Nickel nanowire arrays (Ni NWs/E-NM)

The specific steps are the same as those of the example 1

3. Preparation of electrode Material (NiCo/Ni NWs/E-NM)

The prepared Ni NWs/E-NM is taken as a precursor, a three-electrode electrochemical cell is adopted, Ni NWs/E-NM is taken as a working electrode, a platinum sheet is taken as a counter electrode, Ag/AgCl is taken as a reference electrode, and the Ni NWs/E-NM contains 0.25M NiSO₄·6H₂O、0.25M CoSO₄·6H₂O、0.2M Na₂SO₄And 0.5M H₃BO₃The solution is an electrolyte, and the electrodeposition time is adjusted under the condition of constant voltage of-1V to prepare the optimal sample NiCo/Ni NWs/E-NM.

Comparative example 1:

(1) preparing a solution A and a solution B, wherein the solution A is 0.1mol/LNiCl₂·6H₂O，37.5mmol/L Na₃C₆H₅O₇(sodium citrate) and 0.153mmol/L H₂PtCl₆An aqueous solution of (a); the solution B is 0.38mol/L N₂H₄·H₂An aqueous solution of O;

(3) putting a commercial nickel screen (NM) with the size of 1.5 multiplied by 1cm into the mixed solution of the solution A and the solution B, applying an electromagnetic field perpendicular to an E-NM electrode, reacting for 1h under the action of the electromagnetic field, washing and drying to obtain Ni NWs/NM. In the process, the concentration of the reaction solution is kept unchanged in the reaction process by controlling the inlet and outlet rates of the reaction solution, so that dynamic balance is achieved, and the synthesis of the electrode material tends to continuous production.

Obvious nickel nanowires grow on the surface of the electrode material after reaction (black substances), but after washing, the black substances are washed away to expose the color of the nickel net, which indicates that the bonding force between the nickel nanowires and the nickel net is weak, and the stability is poor. The experimental results show that: the nickel nanowire array synthesized by taking the nickel net subjected to electrochemical etching as the current collector is superior to a material directly synthesized by using a commercial nickel net, and the shedding phenomenon does not occur, which indicates that the nickel nanowire array is more tightly combined with the nickel nanowire.

Comparative example 2:

1. preparation of Nickel Net (E-NM) having roughened surface

The specific steps are the same as those of the example 1

2. Depositing nickel nanoparticles on the surface of a rough-surfaced nickel screen

Taking an E-NM electrode material as a precursor, adopting a three-electrode electrochemical cell, taking E-NM as a working electrode, a platinum sheet as a counter electrode, Ag/AgCl as a reference electrode, and electrolyte as follows: 0.5M NiSO₄·6H₂O、0.2M Na₂SO₄And 0.5M H₃BO₃And (4) forming. The electrodeposition time is optimized in the above example at a constant voltage of-1VAnd performing line electrodeposition. And washing and drying to obtain the electrode material Ni/E-NM.

The LSV test graphs of the hydrogen evolution process of E-NM, Ni NWs/E-NM, Ni/Ni NWs/E-NM prepared in example 1 and Ni/E-NM prepared in comparative example 2 were respectively tested, and the results are shown in FIG. 4.

The Ni/Ni NWs/E-NM has excellent electrochemical performance and higher hydrogen production efficiency, and mainly because the nickel nanowire array has very large specific surface area and open space due to the structural advantage, the rapid diffusion of electrolyte solution on the surface of an electrode is allowed, so that the electrolyte is easy to diffuse to the internal area of the electrode, and the method is an effective way for optimizing and improving the utilization rate of a metal catalyst; easy release of gaseous products; the larger specific surface area of the nanowire array surface provides more nucleation sites for loading of nickel nanoparticles, and the array structure can bear further loading of active substances. Furthermore, a definite hierarchical structure of 'long nanoparticles on nanowires' is formed, the hierarchical structure not only provides a larger specific surface area and more active sites for redox reaction, but also forms an interlaced open structure (i.e. nanoparticles are dispersed among nanowire arrays), which is beneficial to rapid mass transfer and electrolyte penetration, thereby endowing the electrode with higher electrocatalytic performance.

FIG. 5 is a histogram of the overpotentials of E-NM, Ni NWs/E-NM, Ni/Ni NWs/E-NM prepared in example 1 and Ni/E-NM prepared in comparative example 2 at different current densities, and it can be seen that Ni/Ni NWs/E-NM has a lower overpotential, facilitating the reaction. When the current density is 10mA cm^-2The HER overpotential on Ni/Ni NWs/E-NM was 70 mV. And the overpotentials of Ni/E-NM lacking the nanowires or Ni NWs/E-NM lacking the nanoparticles are higher, which shows that the Ni nanowires and the nanoparticles play a certain role in improving HER catalytic performance, and the Ni nanowires and deposited Ni have a synergistic effect to jointly promote the improvement of the catalytic performance.

FIG. 6 is a graph showing the impedance of the hydrogen evolution process of the E-NM, Ni NWs/E-NM, Ni/Ni NWs/E-NM prepared in example 1 and the Ni/E-NM prepared in comparative example 2, and it can be seen that the Ni/Ni NWs/E-NM electrode material has a small charge transfer resistance, corresponding to the growth mechanism and structural characteristics of the material.

Claims

1. A preparation method of a nickel-based hierarchical structure integrated electrode for water electrolysis is characterized by comprising the following steps:

(1) electrochemical etching to form a primary structure, namely a rough nickel screen substrate: placing a commercial nickel screen in HCl solution, and carrying out electrochemical etching to obtain an E-NM electrode with an uneven surface;

2. The method for preparing the nickel-based hierarchical structure integrated electrode for electrolyzing water as claimed in claim 1, wherein the concentration of the HCl solution in the step (1) is 3M, and the electrochemical etching is performed by a chronoamperometry for 30-600 s; in the step (2), the molar ratio of nickel metal ions to hydrazine hydrate is 2:1, a continuous magnetic field is adopted to generate directionally-grown nanowires in the reaction process, and the reaction temperature is 50-90 ℃; in the step (3), electrochemical deposition is performed by a chronoamperometry for 100-1800 seconds.

3. The method for preparing a nickel-based hierarchical structure integrated electrode for electrolyzing water as claimed in claim 1, wherein the etching time in step (1) is 100s, the reaction time in step (2) is 1h, and the electrodeposition time in step (3) is 20 min.

4. The method of claim 1, wherein the nickel-based hierarchical structure integrated electrode for electrolyzing water in the step (2) comprises sodium citrate and chloroplatinic acid in the nickel-based metal inorganic salt solution.

5. The method of claim 1, wherein the nickel-based hierarchical structure integrated electrode for electrolyzing water in the step (2) contains 0.1mol/L NiCl in the nickel-based metal inorganic salt solution₂·6H₂O、37.5mmol/L Na₃C₆H₅O₇And 0.153mmol/L of H₂PtCl₆The concentration of the hydrazine hydrate solution is 0.38mol/L, and before reaction, the pH values of the nickel-based metal inorganic salt solution and the hydrazine hydrate solution concentrated solution are adjusted to 12.5 by using 6M KOH aqueous solution.

6. The method of claim 1, wherein the nickel-based metal inorganic salt solution further contains other metal ions.

7. The method of claim 1, wherein the electrolyte solution of the nickel-based metal inorganic salt in the step (3) further comprises boric acid and sodium sulfate.

8. The nickel-based hierarchical structure integrated electrode for electrolyzing water, prepared by the preparation method of any one of claims 1 to 7, comprises a nickel net which is electrochemically etched, an elemental nickel nanowire array structure which is formed on the nickel net by using the action of an electromagnetic field, and nickel nanoparticles which are formed by electrodeposition on the surface of the nickel nanowires.