Surface modification method of spent nickel-based electrode, catalytic electrode and electrochemical cell

Abstract

The embodiments of the present disclosure disclose a surface modification method of a waste nickel-based electrode, a catalytic electrode and an electrochemical cell. The surface modification method comprises: taking the waste nickel-based electrode as a target substrate; immersing the target substrate into an acid solution for etching treatment, to form a nickel hydroxide nanosheet array on the surface of the target substrate; immersing the target substrate after the etching treatment into a metal salt solution, to perform electrochemical conversion treatment on the nickel hydroxide nanosheet array, to obtain a nickel-based composite nanosheet array containing metal cations in the metal salt solution; immersing the target substrate after the electrochemical conversion treatment into an alkaline solution, to perform electrochemical activation treatment on the nickel-based composite nanosheet array, to obtain a modified nickel-based electrode with a nickel-based active nanosheet array formed on the surface. The embodiments of the present disclosure can form a nickel-based active nanosheet array on the surface of the waste nickel-based electrode, to realize recycling and reuse of the waste nickel-based electrode.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of electrochemical cells, and particularly relates to a surface modification method of a waste nickel-based electrode, a catalytic electrode and an electrochemical cell. BACKGROUND

[0002] Water electrolysis hydrogen production is considered as a clean energy technology. Nickel-based catalytic electrodes are widely used as catalysts for commercial alkaline electrolytic cells due to their good hydrogenation activity and impurity resistance. In practical application, complex working conditions such as high temperature, high humidity, high pressure, high current and wide power fluctuation can cause the activity of nickel-based catalysts to gradually decrease and the function to decline after a certain service period, and even inactivation.

[0003] The existing waste nickel recovery path mainly includes atmospheric acid leaching methods, such as adding sulfuric acid, hydrochloric acid or nitric acid and oxidizing agents under high temperature and high acid conditions to leach metal elements in the waste nickel-based catalyst into the solution, and then recovering through extraction purification, evaporation crystallization and other processes.

[0004] However, the above method has problems such as long recovery process, complex operation and high cost, and cannot meet the green, economic and efficient waste-to-resource demand. SUMMARY

[0005] Therefore, the embodiments of the present disclosure provide a surface modification method of a waste nickel-based electrode, a catalytic electrode and an electrochemical cell, which can form a nickel-based active nanosheet array on the surface of the waste nickel-based electrode on the basis of retaining the original skeleton structure of the waste nickel-based electrode, realize the recycling of the waste nickel-based electrode, have advantages such as simple method, less pollution emission, low cost and improved catalytic performance, and can meet the green, economic and efficient waste-to-resource demand.

[0006] In a first aspect, the embodiments of the present disclosure provide a surface modification method of a waste nickel-based electrode, which comprises:

[0007] The waste nickel-based electrode is used as a target substrate;

[0008] The target substrate is immersed in an acid solution for etching treatment to form a nickel hydroxide nanosheet array on the surface of the target substrate;

[0009] The target substrate after the etching treatment is immersed in a metal salt solution to perform electrochemical conversion treatment on the nickel hydroxide nanosheet array, so as to obtain a nickel-based composite nanosheet array containing metal cations in the metal salt solution;

[0010] The target substrate after the electrochemical conversion treatment is immersed in an alkaline solution to perform electrochemical activation treatment on the nickel-based composite nanosheet array, so as to obtain a modified nickel-based electrode with a nickel-based active nanosheet array formed on the surface.

[0011] Optionally, the target substrate after etching treatment is immersed in a metal salt solution, comprising: washing the target substrate after etching treatment; soaking the washed target substrate in deionized water for a period of time; naturally drying the soaked target substrate in air; and immersing the dried target substrate in a metal salt solution.

[0012] Optionally, the metal cations in the metal salt solution include one or more of the following metal cations: cobalt ions, cadmium ions, manganese ions and iron ions.

[0013] Optionally, the concentration of the metal cations in the metal salt solution is 0.05 mol / L to 0.2 mol / L.

[0014] Optionally, the nickel hydroxide nanosheet array is subjected to electrochemical conversion treatment, comprising: taking the target substrate after etching treatment as a working electrode, placing the working electrode, a counter electrode and a reference electrode together in a metal salt solution, and continuously applying a predetermined direct current voltage to the target substrate for a period of time.

[0015] Optionally, the predetermined direct current voltage is -0.5 V to -1.5 V compared with the voltage of the reference electrode.

[0016] Optionally, the nickel-based composite nanosheet array is subjected to electrochemical activation treatment, comprising: taking the target substrate after electrochemical conversion treatment as a working electrode, placing the working electrode, a counter electrode and a reference electrode together in an alkaline solution, and performing electrochemical activation treatment on the target substrate by cyclic voltammetry.

[0017] Optionally, the cyclic voltammetry adopts a scanning voltage range of 0 V to 1.6 V compared with the voltage of the reference electrode.

[0018] In a second aspect, the embodiments of the present disclosure provide a catalytic electrode, which comprises a nickel-based electrode and a nickel-based active nanosheet array modified on the surface of the nickel-based electrode, and the catalytic electrode is prepared by the surface modification method of the waste nickel-based electrode as described above.

[0019] In a third aspect, the embodiments of the present disclosure provide an electrochemical cell, which comprises a working electrode, a counter electrode and a reference electrode, wherein the working electrode is the catalytic electrode as described above.

[0020] As above, the embodiments of the present disclosure take the waste nickel-based electrode as the target substrate, immerse the target substrate in an acid solution for etching treatment to form a nickel hydroxide nanosheet array on the surface of the target substrate, immerse the target substrate after the etching treatment in a metal salt solution to perform electrochemical conversion treatment on the nickel hydroxide nanosheet array to obtain a nickel-based composite nanosheet array containing other metal ions, and immerse the target substrate after the electrochemical conversion treatment in an alkaline solution to perform electrochemical activation treatment on the nickel-based composite nanosheet array to obtain a modified nickel-based electrode with a nickel-based active nanosheet array formed on the surface. That is, the embodiments of the present disclosure obtain an oxygen evolution catalyst with fast kinetics and long-term stability that can be directly used for alkaline electrolytic water reaction through simple acid solution etching, salt solution electrochemical conversion and subsequent electrochemical activation method.

[0021] Compared with the existing technology of recycling waste electrodes, on the one hand, the high-temperature treatment process is omitted, and the method has the advantages of simplicity, low energy consumption, less pollution emission and low cost; on the other hand, the recovered nickel-based electrode does not exist in the form of powder / crystal, but still retains the original skeleton structure, can be directly used as an electrolytic water oxygen evolution reaction electrode material, and because the surface of the modified nickel-based electrode is decorated with a nickel-based active nanosheet array, the specific surface area is increased, the exposure degree of the surface active sites is enhanced, which is helpful for the full contact of the electrolyte and the rapid migration of the electric charge in the electrolytic water heterogeneous catalysis process, has more excellent oxygen evolution reaction activity and catalytic performance, and can fully meet the demand of turning waste into treasure in a green, economic and efficient manner.

[0022] The above description is only a summary of the technical solutions of the present disclosure, in order to more clearly understand the technical means of the present disclosure, the content of the specification can be implemented, and in order for the above and other purposes, features and advantages of the present disclosure to be more obvious and easy to understand, the following preferred embodiments are described in detail below, and the accompanying drawings are described as follows. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and those skilled in the art can also obtain other drawings according to these drawings without creating any creative labor.

[0024] Figure 1 The flowchart of the surface modification method of the waste nickel-based electrode provided by the embodiments of the present disclosure;

[0025] Figure 2 The scanning electron microscope image 1 provided by the embodiments of the present disclosure;

[0026] Figure 3A scanning electron microscope image provided by an embodiment of the present disclosure;

[0027] Figure 4 An X-ray photoelectron spectrum provided by an embodiment of the present disclosure Figure 1 ;

[0028] Figure 5 An X-ray photoelectron spectrum provided by an embodiment of the present disclosure Figure 2 ;

[0029] Figure 6 An X-ray photoelectron spectrum provided by an embodiment of the present disclosure Figure 3 ;

[0030] Figure 7 A linear sweep voltammogram of the waste nickel foam and the nickel foam after surface modification provided by an embodiment of the present disclosure;

[0031] Figure 8 A constant current stability test diagram of the nickel foam after surface modification provided by an embodiment of the present disclosure;

[0032] Figure 9 A working process schematic diagram of an electrochemical cell provided by an embodiment of the present disclosure. DETAILED DESCRIPTION

[0033] The present disclosure will be described in further detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related content, and not to limit the present disclosure. In addition, it should be noted that, for the sake of description, only parts related to the present disclosure are shown in the drawings.

[0034] It should be noted that the embodiments in the present disclosure and the features in the embodiments can be combined with each other without conflict. The technical solutions of the present disclosure will be described in detail below with reference to the drawings and in combination with the embodiments.

[0035] Unless otherwise specified, the exemplary embodiments / instances shown will be understood as providing exemplary features of various details that can implement the technical concepts of the present disclosure in practice. Therefore, unless otherwise specified, the features of various embodiments / instances can be additionally combined, separated, interchanged and / or rearranged without departing from the technical concepts of the present disclosure.

[0036] The use of cross-hatching and / or shading in the drawings is generally for clarity and is not intended to limit the scope of the disclosure to a specific material, material property, dimension, ratio, etc. Unless otherwise specified, the presence of cross-hatching and / or shading in any figure means that the cross-hatching and / or shading is not a requirement for the embodiment being described. Furthermore, the dimensions and the relative dimensions of the portions of the figures can be exaggerated or rendered larger in the drawings for clarity. The exemplary embodiments can be carried out in various ways, and the specific arrangements illustrated and described are simply exemplary embodiments. For example, the order in which steps are carried out can differ from what is described. Furthermore, non-dependent claims can describe alternate implementations of the same embodiment or alternate embodiments.

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, to the extent that the terms "including," "includes," "having," "has," "a" or "an," or any variation thereof, are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprising" as an assisting grammatical predicate, but are not intended to be limiting.

[0038] At present, the reserves of nickel in China are limited, while the demand in fields such as cemented carbide, aerospace, chemical industry, and battery energy storage is growing. Recycling the valuable nickel resources from waste nickel catalyst electrodes can not only alleviate the consumption of natural resources and produce objective economic benefits, but also has important significance for reducing environmental pollution. Therefore, from the perspective of resource efficient utilization and environmental protection, it is necessary to recycle and utilize the nickel-based catalyst electrodes that have reached the end of their service life. Recycling and utilizing catalyst electrode materials through simple, efficient and green methods can reduce environmental pollution and obtain well-performing catalyst electrodes, providing a reference for the value-added application of waste metals.

[0039] The common waste nickel recycling route is mainly the method of atmospheric acid leaching. Specifically, sulfuric acid, hydrochloric acid or nitric acid and oxidizing agents are added, and the metal elements in the waste catalyst electrode are leached into the solution under high temperature and high acid conditions, and then recovered through extraction purification, evaporation crystallization and other processes. However, the above method has problems such as long recycling process, complex operation and high cost, so in order to realize the green, economic and efficient "waste to treasure", a near-zero pollution, low-cost and simple method strategy needs to be developed.

[0040] Based on this, the surface modification method of the waste nickel-based electrode provided by the embodiments of the present disclosure aims to solve the problems of complex process, high energy consumption and high cost in the field of waste nickel-based catalytic electrode recycling technology. It provides a simple process, less pollution emission and cost advantage for recycling nickel-based electrode for oxygen evolution reaction in water electrolysis, and further application in electrochemical cells.

[0041] Referring to Figure 1 The surface modification method of the waste nickel-based electrode provided by the embodiments of the present disclosure includes the following steps S1 to S4.

[0042] S1, taking the waste nickel-based electrode as the target substrate.

[0043] Exemplarily, the waste nickel-based electrode includes nickel plate, nickel mesh and nickel foam. Among them, the nickel foam is a commercialized functional metal material with three-dimensional open pores and interconnected metal skeleton, which is mainly used in nickel-hydrogen battery electrode materials, fuel cells and other fields.

[0044] Exemplarily, the waste nickel-based electrode material can be pretreated by cleaning and drying before use, so as to remove dust, organic matter and inorganic matter and other impurities on the surface.

[0045] Specifically, the pretreatment operation can include the following steps:

[0046] (1) Put the target substrate into the hydrochloric acid solution for ultrasonic cleaning;

[0047] (2) Rinse the target substrate after the first ultrasonic cleaning with deionized water;

[0048] (3) Put the rinsed target substrate into acetone, ethanol and deionized water in sequence for continuous ultrasonic cleaning;

[0049] (4) Put the target substrate after continuous ultrasonic cleaning in a drying oven for heat preservation and drying.

[0050] Exemplarily, taking the waste nickel foam as an example, it can be ultrasonically treated in the hydrochloric acid solution for 5min~15min, rinsed with deionized water, and then placed in acetone and anhydrous ethanol in sequence for ultrasonic cleaning for 5min~15min, and then ultrasonically washed in deionized water for 5min~15min. Finally, it is placed in a vacuum drying oven with a constant temperature of 40℃~70℃ for constant temperature drying and reserved for use.

[0051] S2, immerse the target substrate in an acid solution for etching treatment to form a nickel hydroxide nanosheet array on the surface of the target substrate.

[0052] Among them, the acid solution can be hydrochloric acid, nitric acid or sulfuric acid, which is not limited here.

[0053] The etching process can be represented by the following reaction equations:

[0054] Ni + 2H + → Ni 2+ + H2 (1)

[0055] Ni 2+ + 2H2O → Ni(OH)2+ 2H + (2)

[0056] Wherein, under the action of H + in the acidic solution, the Ni on the surface of the nickel-based electrode is deposited into the solution to form Ni 2+ , and the Ni 2+ reacts with water to form a Ni(OH)2nanosheet array through a hydrolysis reaction.

[0057] Exemplarily, the concentration of the acidic solution can be 0.001 mol / L to 0.1 mol / L. Within this concentration range, the H + concentration is moderate, which can form a relatively ideal etching morphology on the surface of the nickel-based electrode, thereby providing a good active substrate for the growth of the nanosheet array structure. Conversely, a H + concentration that is too high or too low will inhibit the etching reaction

[0058] Exemplarily, the etching processing time can be 0.5 h to 1.5 h. After the etching processing is completed, the target substrate after etching processing usually needs to be washed first; then the washed target substrate is soaked in deionized water for a period of time; and then the soaked target substrate is naturally dried in the air for the next step processing. For example, the nickel-based electrode after pretreatment can be etched on the surface with an acidic solution of a certain molar fraction for 0.5 h to 1.5 h, and then placed in deionized water for 5 h to 40 h after washing, and then naturally dried in the air to obtain a nickel-based electrode with a clean and dry surface to form a nickel hydroxide nanosheet array.

[0059] S3, immersing the target substrate after etching processing in a metal salt solution to perform electrochemical conversion processing on the nickel hydroxide nanosheet array to obtain a nickel-based composite nanosheet array containing metal cations in the metal salt solution.

[0060] Wherein, the metal cations in the metal salt solution include one or more of the following metal cations: cobalt ions, cadmium ions, manganese ions, and iron ions. Through the electrochemical conversion processing, other metal cations except nickel ions can be introduced into the nickel hydroxide nanosheet array from the metal salt solution containing different metal cations.

[0061] Specifically, the electrochemical conversion processing step includes:

[0062] The etched target substrate is used as the working electrode. After the counter electrode and the reference electrode are placed together in the metal salt solution, a predetermined DC voltage is continuously applied to the target substrate for a certain period of time.

[0063] With Fe 2+ For example, the electrochemical conversion process based on DC voltage can be represented by the following reaction equation:

[0064] Ni(OH)2+ xFe 2+ → Ni 1-x Fe x (OH)2+ xNi 2+ (3)

[0065] Among them, Ni(OH)2 is a nickel hydroxide nanosheet array, which, after electrochemical conversion treatment, Fe 2+ Introduced into a nickel hydroxide nanosheet array structure, forming Ni 1-x Fe x (OH)2, i.e., nickel-iron hydroxide nanosheet array.

[0066] For example, the concentration of metal cations in the metal salt solution can be 0.05 mol / L to 0.2 mol / L. This concentration range provides a suitable level of metal cation concentration, which is beneficial for introducing a large amount of metal cations into the nickel hydroxide nanosheet array structure, forming a stable nickel-based composite nanosheet array. Compared to the reference electrode voltage, the predetermined DC voltage can be -0.5V to -1.5V. This range provides a suitable voltage applied to the nickel-based electrode, which is beneficial for promoting the formation of the nickel-based composite nanosheet array.

[0067] For example, in implementation, the etched nickel-based electrode can be used as the working electrode, the graphite rod as the counter electrode, and Ag / AgCl as the reference electrode. In a solution with a metal cation concentration of 0.05 mol / L to 0.2 mol / L, a DC voltage of -0.5 V to -1.5 V (vs. Ag / AgCl) is applied to the working electrode for 0.1 h to 2 h to convert Ni(OH)2 on the surface of the nickel-based electrode into Ni. 1-x Fe x (OH)2.

[0068] S4. The target substrate after electrochemical conversion treatment is immersed in an alkaline solution to perform electrochemical activation treatment on the nickel-based composite nanosheet array, thereby obtaining a modified nickel-based electrode with a nickel-based active nanosheet array formed on its surface.

[0069] The alkaline solution can be a potassium hydroxide solution. Through electrochemical activation treatment, the main components on the surface of the nickel-based electrode (such as nickel-based composite nanosheet arrays) can be transformed into the main active substances for the oxygen evolution reaction.

[0070] Specifically, the step of electrochemical activation treatment comprises:

[0071] The target substrate after the electrochemical conversion treatment is taken as a working electrode, and after the counter electrode and the reference electrode are put into an alkaline solution, the electrochemical activation treatment is performed on the target substrate by cyclic voltammetry.

[0072] The operation method of cyclic voltammetry is that a linear scanning voltage is applied to the working electrode, and the scanning is performed from a starting potential to a vertex potential at a certain rate, and then from the vertex potential to another vertex potential in two stages, and the scanning can be repeated between the two vertex potentials. This method can control the electrode potential to be scanned at different rates in a triangular waveform once or multiple times with time, and the potential range is to enable different reduction reactions and oxidation reactions to occur alternately on the electrode.

[0073] Taking the generation of Ni(Fe)OOH as an example, the process of electrochemical activation treatment based on cyclic voltammetry can be represented by the following reaction equation:

[0074] Ni 1-x Fe x (OH)2+ OH - → Ni 1-x Fe x OOH + H2O + e - (4)

[0075] Wherein, Ni 1-x Fe x (OH)2 is a nickel-iron hydroxide nanosheet array, and after the electrochemical activation treatment, an active substance Ni 1-x Fe x OOH is formed, which can be denoted as Ni(Fe)OOH, and Ni(Fe)OOH is considered to be one of the most effective catalysts for oxygen evolution reaction.

[0076] Exemplarily, the scanning voltage range used by cyclic voltammetry is 0V~1.6V compared with the reference electrode voltage. The voltage applied to the nickel-based electrode in this range is moderate, which is conducive to promoting the formation of nickel-based activated nanosheet array.

[0077] Exemplarily, when implemented, the nickel-based electrode after the electrochemical conversion treatment can be cleaned several times with deionized water, and then taken as a working electrode to be subjected to electrochemical activation treatment by cyclic voltammetry in a 0.5mol / L~2mol / L potassium hydroxide solution, the scanning voltage range is 0V~1.6V (vs. RHE), and the scanning number is 30~60, so that the Ni 1-x Fe x (OH)2 on the surface of the nickel-based electrode is converted into Ni(Fe)OOH, wherein RHE represents that the reference electrode is a reversible hydrogen electrode.

[0078] As above, the surface modification method of the waste nickel-based electrode in the embodiments of the present disclosure and its performance advantages are described in specific embodiments as follows.

[0079] Compared with the existing technology for recycling waste nickel-based electrodes, on the one hand, the high-temperature treatment process is omitted, and the method has the advantages of simplicity, low energy consumption, less pollution emission, and low cost; on the other hand, the recovered nickel-based electrode does not exist in the form of powder / crystal, but still retains the original skeleton structure, can be directly used as an electrolytic water oxygen evolution reaction electrode material, and due to the modification of the nickel-based electrode surface decorated with nickel-based active nanosheet array, the specific surface area is increased, the exposure degree of the surface active site is enhanced, which is helpful for the full contact of the electrolyte and the rapid migration of the electric charge in the electrolytic water heterogeneous catalysis process, has more excellent oxygen evolution reaction activity and catalytic performance, and can fully meet the demand of turning waste into treasure in a green, economic and efficient way.

[0080] In addition, the embodiments of the present disclosure also provide a catalytic electrode, which comprises a nickel-based electrode and a nickel-based active nanosheet array decorated on the surface of the nickel-based electrode, and the catalytic electrode is prepared by the surface modification method of the waste nickel-based electrode described above.

[0081] In order to make the person skilled in the art more clearly understand the surface modification method of the waste nickel-based electrode and its performance advantages in the embodiments of the present disclosure, the embodiments of the present disclosure are described in specific embodiments as follows.

[0082] The waste nickel-based electrode in the present embodiment uses pure nickel foam (Nickle Foam, NF), and the surface modification method of the waste pure nickel foam includes the following steps:

[0083] (1) A piece of waste nickel foam is treated with ultrasonic in a hydrochloric acid solution for 10 min, washed with deionized water, and then sequentially placed in acetone and anhydrous ethanol for ultrasonic cleaning for 10 min, and finally ultrasonic washed in deionized water for 10 min, and then placed in a 60°C vacuum drying box for constant temperature drying, and stored for standby use;

[0084] (2) the nickel foam after cleaning and drying is subjected to surface etching treatment with an acidic solution with a concentration of 0.001 mol / L to 0.1 mol / L for 0.5 h to 1.5 h, is washed and then soaked in deionized water for 5 h to 40 h and is naturally dried in air;

[0085] (3) the nickel foam subjected to etching treatment is subjected to electrochemical conversion treatment in a salt solution containing different metal cations, and the specific operation is that the nickel foam to be treated is used as a working electrode, a graphite rod is used as a counter electrode, an Ag / AgCl electrode is used as a reference electrode, a direct current voltage of -1.1 V (vs. Ag / AgCl) is applied to the working electrode in a salt solution with a metal cation concentration of 0.05 mol / L to 0.2 mol / L for 0.1 h to 2 h;

[0086] (4) the nickel foam subjected to electrochemical conversion treatment is washed several times with deionized water and used as a working electrode, a graphite rod is used as a counter electrode, an RHE electrode is used as a reference electrode, and the nickel foam is subjected to electrochemical activation treatment by cyclic voltammetry in a 1 mol / L potassium hydroxide solution, a scanning voltage range is 0 V to 1.6 V (vs. RHE), and the number of scanning cycles is 50, to obtain modified nickel foam, denoted as Ni(Fe)OOH@NF.

[0087] Figure 2 The surface morphology of the nickel foam subjected to etching treatment is shown in FIG. 2. As can be seen, the nickel foam surface forms a regular nanosheet array structure, and the etching component is mainly Ni(OH)2. Compared with a smooth plane, the structure is more conducive to introducing more other metal cations.

[0088] Figure 3 The surface morphology of the nickel foam subjected to electrochemical activation treatment is shown in FIG. 3. As can be seen, the nickel foam surface forms a uniform nanosheet array structure, and the main component is nickel-iron oxyhydroxide Ni(Fe)OOH. Ni(Fe)OOH is a main active substance for oxygen evolution reaction and can be directly used as an electrode material for electrolytic water oxygen evolution reaction.

[0089] Figures 4-6 FIG. 4 shows the X-ray photoelectron spectrogram of the nickel foam Ni(Fe)OOH@NF after surface modification. As can be directly seen from the figure, the existence of divalent iron indicates that the iron element is successfully introduced into the structure to regulate the electronic structure of the nickel foam.

[0090] Figure 7 FIG. 5 shows the linear sweep voltammetry curves of the waste nickel foam and the nickel foam after surface modification. As can be seen from FIG. 5, Figure 7 Compared with the waste nickel foam, the nickel foam Ni(Fe)OOH@NF after surface modification has higher electrocatalytic oxygen evolution activity, and the overpotential reaches 260 mV at a current density of 10 mA / cm 2 Figure 8 ​The constant current stability test curve of the surface modified nickel foam is shown. From Figure 8 It can be seen that the constant current stability curve of the surface modified nickel foam Ni(Fe)OOH@NF is very smooth and no obvious potential rising trend appears after 45h long service, which shows that the performance of the surface modified nickel foam has no obvious decline and has good stability.

[0091] As above, the surface modification of the waste nickel-based electrode disclosed in the embodiments of the present disclosure takes the waste nickel-based electrode after long-term service as the treatment target, and through the simple acid solution etching, salt solution electrochemical conversion and subsequent electrochemical activation method, the waste nickel-based electrode with low activity or activity decline after use in the electrolytic cell is prepared through recycling, to obtain a nanosheet array electrode material with regular surface arrangement and good bonding effect between the substrate, which exhibits good reaction activity and service stability. At the same time, the potential application prospect of the controllable recovery of nickel-based electrolytic water catalytic material through simple immersion and electrochemical conversion is revealed, which provides a research idea for the green and economic recovery of failed catalytic electrodes.

[0092] In addition, the method for recycling waste nickel-based materials designed in the embodiments of the present disclosure has the technical advantages of simple process, environmental protection and energy saving, and low cost; and when applied to the electrolytic water oxygen evolution reaction again, the oxygen evolution performance is higher than that of the original nickel-based electrode, which has great application potential.

[0093] In addition, the embodiments of the present disclosure provide an electrochemical cell, which comprises a working electrode, a counter electrode and a reference electrode, wherein the above-mentioned catalytic electrode is used as the working electrode.

[0094] In the electrochemical cell, platinum sheet or stone mill rod / graphite sheet is used as the counter electrode, Ag / AgCl or Hg / HgO or saturated calomel electrode is used as the reference electrode, and the reference electrode is mainly used as the reference of the potential of the working electrode, which is convenient for the conversion of the potential of the electrode in the subsequent process. Generally, an electrode system with stable potential is selected. The electrochemical workstation studies the working performance of the electrochemical cell by controlling and monitoring the voltage and current. When an anode potential is applied to the working electrode, the working electrode undergoes an oxidation reaction to produce oxygen (OH - oxidized to O2), and the counter electrode undergoes a reduction reaction to produce hydrogen (H + reduced to H2), and the measured voltage and current curve reflects the oxygen evolution performance of the working electrode.

[0095] In combination with Figure 9The working principle of the electrochemical cell is explained. Specifically, when using the catalytic electrode described above as the working electrode, a positive potential is applied to it, while a graphite rod is used as the electrode with a negative potential, and the Hg / HgO electrode is used as the reference electrode. The voltage-current curve obtained with Hg / HgO as the reference electrode can be converted using the following formula to obtain the reversible hydrogen electrode potential.

[0096] E(RHE)=E(Hg / HgO)+0.098+0.059*pH

[0097] The oxygen evolution reaction of water electrolysis was tested in a 1 mol / L alkaline KOH electrolyte at 25°C. O2 was introduced for a period of time before the test to ensure stability. The reaction mechanism of the catalytic electrode in an alkaline environment is as follows (where M represents the active site; in this embodiment, M is a Ni or Fe site):

[0098] After electrochemical conversion treatment, Ni(Fe)OOH@NF is formed through surface reconstruction, with Ni and Fe acting as OH groups. - The active site for adsorption is associated with an OH group. - After bonding, M*OH is formed. M*OH is then deprotonated to form M*O. M*O then combines with another OH group. - Combine losing one e - Following bonding, M*OOH is formed. Finally, M*OOH undergoes deprotonation and further releases adsorbed oxygen*O2 to yield product O2. The chemical reactions occurring throughout the process are as follows:

[0099] M*+OH - →M*OH+e -

[0100] M*OH+OH - →M*O+H2O+ e -

[0101] M*O+ OH - →M*OOH+ e -

[0102] M*OOH+ OH - →M*O2+ H2O+ e -

[0103] M*O2→M*+O2

[0104] The overall reaction is: 4OH - →2H₂O + O₂ + 4e -

[0105] Here, * refers to the adsorption site on the surface of the catalytic electrode.

[0106] In the description of the specification, the description of the terms "one embodiment / way", "some embodiments / ways", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment / way or example are included in at least one embodiment / way or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment / way or example. Also, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments / ways or examples. In addition, the person skilled in the art can combine and combine the different embodiments / ways or examples described in the specification and the features of the different embodiments / ways or examples, without contradiction.

[0107] In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0108] The person skilled in the art should understand that the above-mentioned embodiments are only for clearly illustrating the present disclosure, and are not intended to limit the scope of the present disclosure. Based on the above disclosure, other changes or modifications can also be made by those skilled in the art, and these changes or modifications are still within the scope of the present disclosure.

Claims

1. A method for surface modification of waste nickel-based electrodes, characterized in that, include: Used scrap nickel-based electrodes as the target substrate; The target substrate is immersed in an acidic solution for etching to form an array of nickel hydroxide nanosheets on the surface of the target substrate. The etched target substrate is immersed in a metal salt solution to perform an electrochemical conversion treatment on the nickel hydroxide nanosheet array, transforming it into a nickel-based composite nanosheet array containing metal cations from the metal salt solution, wherein the metal cations in the metal salt solution are Fe. 2+ The nickel-based composite nanosheet array containing the metal cations in the metal salt solution is nickel-iron hydroxide (Ni). 1-x Fe x (OH)₂ nanosheet array; The target substrate after electrochemical conversion treatment is immersed in an alkaline solution to electrochemically activate the nickel-based composite nanosheet array, thereby converting the nickel-based composite nanosheet array into a Ni(Fe)OOH nickel-based active nanosheet array, resulting in a modified nickel-based electrode with a Ni(Fe)OOH nickel-based active nanosheet array formed on its surface.

2. The surface modification method according to claim 1, characterized in that, The step of immersing the etched target substrate in a metal salt solution includes: The target substrate after washing and etching; The washed target substrate was soaked in deionized water for a period of time. The soaked target substrate is then allowed to air dry naturally. The dried target substrate is then immersed in a metal salt solution.

3. The surface modification method according to claim 1, characterized in that, The concentration of metal cations in the metal salt solution is 0.05 mol / L to 0.2 mol / L.

4. The surface modification method according to claim 1, characterized in that, The electrochemical conversion treatment of the nickel hydroxide nanosheet array includes: The etched target substrate is used as the working electrode. After the counter electrode and the reference electrode are placed together in the metal salt solution, a predetermined DC voltage is continuously applied to the target substrate for a certain period of time.

5. The surface modification method according to claim 4, characterized in that, Compared to the reference electrode voltage, the predetermined DC voltage is -0.5V to -1.5V.

6. The surface modification method according to claim 1, characterized in that, The electrochemical activation treatment of the nickel-based composite nanosheet array includes: The target substrate after electrochemical conversion treatment is used as the working electrode. After the counter electrode and reference electrode are placed together in the alkaline solution, the target substrate is electrochemically activated by cyclic voltammetry.

7. The surface modification method according to claim 6, characterized in that, Compared to the reference electrode voltage, the scanning voltage range used in the cyclic voltammetry method is 0V~1.6V.

8. A catalytic electrode, characterized in that, The invention includes a nickel-based electrode and a nickel-based active nanosheet array modified on the surface of the nickel-based electrode, wherein the catalytic electrode is prepared by a surface modification method for a waste nickel-based electrode as described in any one of claims 1 to 7.

9. An electrochemical battery, characterized in that, include: The electrode comprises a working electrode, a counter electrode, and a reference electrode, wherein the working electrode is the catalytic electrode as described in claim 8.

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