阅读说明：本技术 一种四氧化三钴-多孔镍复合电极及其制备方法和在硒离子检测中的应用 (Cobaltosic oxide-porous nickel composite electrode, preparation method thereof and application thereof in selenium ion detection ) 是由 奚亚男 胡保帅 崔皓博 于 2021-08-05 设计创作，主要内容包括：本发明提供了一种四氧化三钴-多孔镍复合电极及其制备方法和在硒离子检测中的应用。本发明采用电沉积-去合金的方法制备多孔镍基底,并在镍层表面修饰四氧化三钴,获得四氧化三钴-多孔镍复合电极。三维有序的多孔结构和催化活性粒子的相互结合,增大了材料的比表面积,保证了电极在氧化还原反应过程中能进行快速的离子传输和电子转移,提高了四氧化三钴-多孔镍复合电极对硒离子响应的灵敏性。本发明制备的四氧化三钴-多孔镍复合电极可应用于环境污染物微量硒离子的快速检测。(The invention provides a cobaltosic oxide-porous nickel composite electrode, a preparation method thereof and application thereof in selenium ion detection. The invention adopts an electrodeposition-dealloying method to prepare the porous nickel substrate, and modifies cobaltosic oxide on the surface of the nickel layer to obtain the cobaltosic oxide-porous nickel composite electrode. The three-dimensional ordered porous structure and the catalytic active particles are combined with each other, so that the specific surface area of the material is increased, the rapid ion transmission and electron transfer of the electrode in the oxidation-reduction reaction process are ensured, and the sensitivity of the cobaltosic oxide-porous nickel composite electrode on the response of selenium ions is improved. The cobaltosic oxide-porous nickel composite electrode prepared by the invention can be applied to the rapid detection of trace selenium ions in environmental pollutants.)

1. The cobaltosic oxide-porous nickel composite electrode takes a metal electrode as a substrate and comprises an electrode modification layer positioned above the substrate, and is characterized in that the electrode modification layer comprises a cobaltosic oxide-porous nickel modification layer.

2. The cobaltosic oxide-porous nickel composite electrode according to claim 1, wherein the cobaltosic oxide-porous nickel modification layer has a uniformly distributed micro-pore structure, the substrate is a porous nickel film layer, the pore diameter is 10-50 nm, and the surface of the cobaltosic oxide-porous nickel modification layer is modified with feather-like cobaltosic oxide.

3. A method of preparing a cobaltosic oxide-porous nickel composite electrode according to claim 1, comprising the steps of:

s1, preparation of porous nickel: preparing a copper-nickel alloy by adopting an electrodeposition method, and then obtaining a porous nickel layer by an alloy removal method;

S2、Co₃O₄preparation of @ Ni electrode: preparing Co by using porous nickel as a substrate and modifying a cobaltosic oxide layer on the surface of the porous nickel by an electrochemical method₃O₄@ Ni electrode.

4. The method according to claim 3, wherein in step S1, the electrodeposition method is specifically: preparing a copper-nickel alloy solution, and placing a platinum mesh anode and a polished copper sheet or iron sheet cathode into the electrodeposition solution, wherein the stirring speed is 450-600 rmp; the electro-deposition temperature is 45-55 ℃, the pH value of the solution is 9.0-9.5, and the current density is 3.0-6.0 ASD.

5. The method for preparing the cobaltosic oxide-porous nickel composite electrode according to claim 4, wherein the copper-nickel alloy solution comprises the following components: 0.5-1.5 mol/L of nickel nitrate, 0.05-0.10 mol/L of copper nitrate, 1.0-5.0 mol/L of triethanolamine, 0.005-0.010 g/L of sodium hydroxymethyl sulfonate and 0.1-0.3 g/L of 1- (2-hydroxy-3-sulfopropyl) pyridine betaine.

6. The method for preparing a cobaltosic oxide-porous nickel composite electrode according to claim 3, wherein in the step S1, the dealloying method specifically comprises: and (3) placing the copper-nickel alloy in a 10% nitric acid solution, wherein the alloy removing temperature is 50-60 ℃, and the alloy removing time is 500-600 min.

7. The method for preparing a cobaltosic oxide-porous nickel composite electrode according to claim 3, wherein in the step S2, the electrochemical method specifically comprises: preparing a cobalt deposition solution, performing electrodeposition by using a porous nickel layer as a cathode and titanium as an anode, setting the pH value to be 9.0-10.0 and the current density to be 5.0-10.0A/dm²The temperature is 40-50 ℃, and the deposition time is 10-15 min; after the reaction is finished, the mixture is heated for 30-40 min at 400-500 ℃.

8. The method of claim 7, wherein the cobalt deposition solution comprises: 0.1-0.5 mol/L of cobalt nitrate, 80-110 g/L of KOH, 60-80 g/L of triethanolamine and 50-70 g/L of sodium citrate.

9. Use of the cobaltosic oxide-porous nickel composite electrode of any one of claims 1 to 8 in selenium ion detection.

10. The use of the cobaltosic oxide-porous nickel composite electrode in selenium ion detection according to claim 9, wherein the cobaltosic oxide-porous nickel composite electrode can be used for detecting trace selenium ions in complex environments, including liquids, soils and foods.

Technical Field

The invention belongs to the field of electrochemical sensors, and relates to a cobaltosic oxide-porous nickel composite electrode, a preparation method thereof and application thereof in selenium ion detection.

Background

Selenium pollution refers to the pollution of selenium and its compounds to the environment. The coal burning industry, the copper, zinc and lead ore roasting industry, the semiconductor and electronics industry, and the pigment, dye, rubber, metallurgy industries all produce or use selenium and selenium compounds. In the industrial production and application processes, metal dust containing selenium is discharged or enters the atmosphere, water bodies and soil in the form of selenium compounds to cause environmental pollution. In industry, it appears as a residue or waste. When the selenium-containing material is melted, the selenium content in the discharged smoke dust can reach 90 percent. Selenate and selenite are readily soluble in water and are often present in contaminated water in this form. Selenium can be enriched in the soil and absorbed by the crops. Selenium is a necessary trace element for human, animals and partial plants, the detection of the selenium content in soil is an important subject for the planting research of selenium-rich crops, white muscle diseases of cattle, sheep, horses and chickens can be caused in selenium-deficient areas, small-dose sodium selenite can be taken by people in mountaineering epidemic areas to prevent the white muscle diseases, but excessive selenium intake, such as selenium-containing dust, smoke and steam in workshops, can stimulate human eyes and respiratory systems, and seriously cause gastrointestinal dysfunction and the like.

At present, the detection method of selenium content comprises the following steps: atomic absorption spectrometry, inductively coupled plasma mass spectrometry, and neutron activation analysis. However, the existing method has the disadvantages of multiple testing steps, complex operation, long detection period, large deviation of detection results and low detection limit. The electrochemical detection method has the advantages of quick response, high sensitivity, simple preparation, convenience in carrying and the like, and is the best method for quickly and accurately detecting molecules at present. An active catalytic material is loaded onto the electrode, reacts with the target analyte, and generates an electrical signal proportional to the concentration of the target analyte. The content of the measured object can be estimated by measuring the response parameters such as the current or the impedance of the electrode.

The active material of the electrode surface can significantly enhance the sensing response capability. This enhancement is mainly due to material geometry characteristics such as irregularities, large specific surface area and high porosity, which makes more active sites on the electrode surface and increases the probability of charge transfer between the molecules and the electrode surface. Meanwhile, the metal material with high specific surface area is compounded with the oxide with high catalytic activity by adopting an in-situ modification technology, and the speed of ion transmission and electron transfer is greatly improved under the synergistic action of the structure and the performance of the composite material, so that the sensitivity and the stability of the sensing electrode are improved.

In summary, there is a need in the art for a sensing electrode with a simple preparation process and capable of rapidly detecting selenium ions to promote the industrialization process of the rapid environmental pollution detection device, in response to the increasing requirements for environmental protection and life health.

Disclosure of Invention

The invention aims to provide a cobaltosic oxide-porous nickel composite electrode, a preparation method thereof and application thereof in selenium ion detection.

The invention provides a cobaltosic oxide-porous nickel composite electrode, which takes a metal electrode as a substrate and comprises an electrode modification layer positioned above the substrate, wherein the electrode modification layer comprises a cobaltosic oxide-porous nickel modification layer.

The cobaltosic oxide-porous nickel modification layer has a micro-pore structure which is uniformly distributed, the substrate is a porous nickel film layer, the pore diameter is 10-50 nm, and the surface of the substrate is modified with a feather-shaped cobaltosic oxide modification layer.

The cobaltosic oxide-porous nickel composite electrode provided by the invention solves the problem that selenium ions in soil or in tea cannot be rapidly detected. Specifically, the cobaltosic oxide is modified on the surface of the porous nickel in situ, the structure has a large electrochemical surface area, and the high sensitivity and the high stability of the electrode are ensured based on a structural framework compounded by high catalytic activity substances.

The invention also aims to provide a preparation method of the cobaltosic oxide-porous nickel composite electrode.

The method specifically comprises the following steps:

s1, preparation of porous nickel: preparing copper-nickel alloy by adopting an electrodeposition method, and then obtaining the porous nickel layer by an alloy removing method.

S2、Co₃O₄Preparation of @ Ni electrode: using porous nickel as substrate and adopting electricityModifying cobaltosic oxide layer on the surface by a chemical method to prepare Co₃O₄@ Ni electrode.

The specific continuous framework and porous structure of the porous nickel have larger electrochemical active area, and can obviously improve the reaction efficiency. But the stability of the porous structure material is poor, so that the cobaltosic oxide is modified on the surface in situ, and the stability of the composite electrode test is further improved.

When Ni is in the plating solution²⁺/Cu²⁺When the concentration ratio is increased, the nickel content in the plating layer is increased when the temperature is increased and the current density is increased, and the nickel content in the plating layer is decreased when the stirring speed and the pH of the plating solution are increased.

Further, in step S1, the electrodeposition method specifically includes: preparing a copper-nickel alloy solution, and placing a platinum mesh anode and a polished copper sheet or iron sheet cathode into the electrodeposition solution, wherein the stirring speed is 450-600 rmp; the electro-deposition temperature is 45-55 ℃, the pH value of the solution is 9.0-9.5, and the current density is 3.0-6.0 ASD.

The composition of the copper-nickel alloy solution is as follows: 0.5-1.5 mol/L of nickel nitrate, 0.05-0.10 mol/L of copper nitrate, 1.0-5.0 mol/L of triethanolamine, 0.005-0.010 g/L of sodium hydroxymethyl sulfonate and 0.1-0.3 g/L of 1- (2-hydroxy-3-sulfopropyl) pyridine betaine.

After the copper-nickel alloy is subjected to electrochemical dealloying, a mesoporous porous nickel material with the aperture of 10-50 nm can be obtained. This pore size range is suitable for the transport exchange of ions between the electrolyte and the electrodes.

Further, in step S1, the dealloying method specifically includes: and (3) placing the copper-nickel alloy in a 10% nitric acid solution, wherein the alloy removing temperature is 50-60 ℃, and the alloy removing time is 500-600 min.

The cobaltosic oxide particles are modified in situ on the porous nickel by adopting an electrodeposition method, and if the electrodeposition time is too long, the obtained cobalt oxide coating is thick, the structure of the porous nickel is covered, so that the detection performance of the electrode is reduced.

Further, in step S2, the electrochemical method specifically includes: preparing a cobalt deposition solution, performing electrodeposition by using a porous nickel layer as a cathode and titanium as an anode, and setting the pH value to be 9.0-10.0, current density of 5.0 to 10.0A/dm²The temperature is 40-50 ℃, and the deposition time is 10-15 min; after the reaction is finished, the mixture is heated for 30-40 min at 400-500 ℃.

When the cobaltosic oxide particles are electrodeposited, cobalt nitrate and cobalt sulfate can be selected as main salts of cobalt ions, and the cobalt nitrate with the concentration of 0.1-0.5 mol/L is selected. 60-80 g/L of triethanolamine and 50-70 g/L of sodium citrate are selected as the cobalt ion complexing agent. The cobaltosic oxide needs to be electrodeposited in an alkaline solution to form cobalt hydroxide, and then the cobaltosic oxide is obtained through high-temperature calcination. Therefore, the electrochemical reaction is carried out in 80-110 g/L KOH solution.

The cobalt deposition solution consists of: 0.1-0.5 mol/L of cobalt nitrate, 80-110 g/L of KOH, 60-80 g/L of triethanolamine and 50-70 g/L of sodium citrate.

Scanning and observing the surface appearance of the cobaltosic oxide-porous nickel composite electrode prepared by the invention by adopting an SEM electron microscope.

As shown in the attached figure 1, is an SEM topography of the cobaltosic oxide-porous nickel composite electrode prepared by the present invention. As can be seen from the figure, the composite electrode substrate is a uniform porous structure, and the pore diameter is about 50-100 nm. The surface of the porous structure is modified with feather-shaped cobaltosic oxide. The structure has larger specific surface area, can provide more reactive sites and greatly improves the sensitivity of the electrode. Meanwhile, the cobaltosic oxide is loaded on the surface of the porous structure, so that the stability of the electrode structure is improved.

The invention also aims to provide an application of the cobaltosic oxide-porous nickel composite electrode in selenium ion detection.

The cobaltosic oxide-porous nickel composite electrode can be used for detecting trace selenium ions in complex environments, including liquid, soil and food.

The cobaltosic oxide-porous nickel composite electrode prepared by the method is subjected to response performance and stability tests by adopting methods such as cyclic voltammetry, differential pulse voltammetry and the like.

As shown in fig. 2, a differential pulse voltammetry curve diagram for detecting selenium ions by using the cobaltosic oxide-porous nickel composite electrode prepared by the invention is specifically to add selenium ions with different concentrations into acetic acid-sodium acetate solution with ph of 4.5 and perform differential pulse voltammetry detection. It can be seen from the figure that the current peak at 0.95V, which is marked by the dashed line frame, is the oxidation peak of the selenium ion, and meanwhile, the intensity of the characteristic current peak gradually increases as the addition amount of the selenium ion increases from 0.1mg to 0.8mg, which indicates that the cobaltosic oxide-porous nickel composite electrode prepared by the invention has good response performance to the selenium ion.

FIG. 3 is a fitting graph of the concentration and current density of selenium ions detected by the cobaltosic oxide-porous nickel composite electrode prepared by the invention. It can be seen from the figure that there is a good linear relationship between the response current density and the concentration of the detected object, and the fitting value is 0.9709, which indicates that the cobaltosic oxide-porous nickel composite electrode prepared by the invention can realize accurate electrochemical detection of selenium ions within a certain concentration range.

Stability is a determining factor in determining whether or not the composite electrode can be continuously operated for a long time.

As shown in fig. 4, it is a stability test chart of the cobaltosic oxide-porous nickel composite electrode prepared by the present invention, specifically a current density average decreasing amplitude curve chart of continuous test 2000 s. It can be seen from the figure that the current density gradually decreases with the extension of the test time, and after the continuous operation for 2000s, the current signal respectively decreases to about 94%, and the variation value is within 15%, which indicates that the cobaltosic oxide-porous nickel composite electrode prepared by the invention can ensure the catalytic activity to be at a higher level under the state of long-time continuous operation, so that the electrode has better long-term test stability.

The repeatability is an important index for judging the long-term continuous service performance condition of the composite electrode.

As shown in fig. 5, a repeatability test chart of the cobaltosic oxide-porous nickel composite electrode prepared by the invention is shown, and specifically, a current density reduction degree curve chart of the same cobaltosic oxide-porous nickel composite electrode after 5 days of testing. It can be seen from the figure that after 5 days of continuous test, the peak current intensity is only reduced by 8.6% compared with that of the current intensity on the 1 st day, which shows that the cobaltosic oxide-porous nickel composite electrode prepared by the invention has better repeatability.

The inventionPreparing a porous nickel substrate by adopting an electrodeposition-dealloying method, and modifying cobaltosic oxide on the surface of a nickel layer to obtain a cobaltosic oxide-porous nickel composite electrode (Co)₃O₄@ Ni electrode). By combining the three-dimensional ordered porous structure and the catalytic active particles with each other, the specific surface area of the material is increased, the rapid ion transmission and electron transfer of the electrode in the oxidation-reduction reaction process are ensured, and the sensitivity of the cobaltosic oxide-porous nickel composite electrode on the response of selenium ions is improved. The cobaltosic oxide-porous nickel composite electrode prepared by the invention can be applied to the rapid detection of trace selenium ions in environmental pollutants.

The invention has the beneficial effects that:

(1) high responsiveness of the electrode: the invention combines the porous nickel with high active area and the cobaltosic oxide with high catalytic performance, thereby realizing the accurate detection of trace selenium ions.

(2) High stability of the electrode: the cobaltosic oxide is modified on the surface of the porous nickel in situ, so that a stable skeleton structure is formed, and the stability of the electrode is greatly improved.

(3) Popularization and application: the method adopts simple in-situ electrochemical preparation process, can be directly connected with electrochemical detection equipment, realizes the purpose of immediately detecting the selenium ions, and is favorable for pushing the rapid detection application of the selenium ions into the industrialization process.

Drawings

The invention is further illustrated by means of the attached drawings, but the embodiments in the drawings do not constitute any limitation to the invention, and for a person skilled in the art, other drawings can be obtained on the basis of the following drawings without inventive effort.

FIG. 1 is an SEM topography of a cobaltosic oxide-porous nickel composite electrode prepared by the invention;

FIG. 2 is a differential pulse voltammetry curve diagram for detecting selenium ions by using a cobaltosic oxide-porous nickel composite electrode prepared by the invention;

FIG. 3 is a fitting graph of the concentration of selenium ions detected by the cobaltosic oxide-porous nickel composite electrode prepared by the invention and the current density;

FIG. 4 is a stability test chart of the cobaltosic oxide-porous nickel composite electrode prepared by the invention;

FIG. 5 is a repeatability test chart of the cobaltosic oxide-porous nickel composite electrode prepared by the invention.

Detailed Description

In order that the objects, aspects and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the following detailed description and the accompanying drawings.

Example 1

Preparing a cobaltosic oxide-porous nickel composite electrode:

s1, preparation of porous nickel: preparing a copper-nickel alloy solution for electrodeposition, which specifically comprises the following steps: 0.5mol/L of nickel nitrate, 0.05mol/L of copper nitrate, 1.0mol/L of triethanolamine, 0.005g/L of sodium hydroxymethyl sulfonate and 0.1g/L of 1- (2-hydroxy-3-sulfopropyl) pyridine betaine. Then placing the platinum mesh anode and the polished copper sheet or iron sheet cathode into the electrodeposition solution, and stirring at the speed of 450 rmp; the temperature is set to be 45 ℃, the pH value of the solution plating solution is 9.0, and the current density is 3.0ASD, so that the copper-nickel alloy is obtained. Then, an alloy removing method is adopted, the copper-nickel alloy is placed in 10% nitric acid solution, the alloy removing temperature is 50 ℃, the alloy removing time is 500min, and the porous nickel layer is obtained.

S2、Co₃O₄Preparation of @ Ni electrode: preparing an electrodeposition cobalt solution, specifically: 0.1mol/L of cobalt nitrate, 80g/L of KOH, 60g/L of triethanolamine and 50g/L of sodium citrate. The porous nickel layer is used as a cathode, the titanium is used as an anode, the pH is 9.0, and the current density is 5.0A/dm²Setting the temperature at 40 ℃, depositing for 10min, and then heating the composite electrode at 400 ℃ for 30min to obtain the cobaltosic oxide-porous nickel composite electrode.

Example 2

Preparing a cobaltosic oxide-porous nickel composite electrode:

s1, preparation of porous nickel: the preparation of the copper-nickel alloy solution for electrodeposition specifically comprises the following steps: 1.5mol/L of nickel nitrate, 0.1mol/L of copper nitrate, 5.0mol/L of triethanolamine, 0.010g/L of sodium hydroxymethyl sulfonate and 0.3g/L of 1- (2-hydroxy-3-sulfopropyl) pyridine betaine. Then placing the platinum mesh anode and the polished copper sheet or iron sheet cathode into the electrodeposition solution, and stirring at the speed of 600 rmp; setting the temperature to 55 ℃, the pH value of the solution plating solution to 9.5 and the current density to 6.0ASD, and obtaining the copper-nickel alloy. Then, an alloy removing method is adopted, the copper-nickel alloy is placed in 10% nitric acid solution, the alloy removing temperature is 60 ℃, the alloy removing time is 600min, and the porous nickel layer is obtained.

S2、Co₃O₄Preparation of @ Ni electrode: preparing an electrodeposition cobalt solution, specifically: 0.5mol/L of cobalt nitrate, 110g/L of KOH, 80g/L of triethanolamine and 70g/L of sodium citrate. Taking a porous nickel layer as a cathode peptide as an anode, the pH value is 10.0, and the current density is 10.0A/dm²Setting the temperature at 50 ℃, depositing for 15min, and then heating the composite electrode at 500 ℃ for 40min to obtain the cobaltosic oxide-porous nickel composite electrode.

Example 3

Preparing a cobaltosic oxide-porous nickel composite electrode:

s1, preparation of porous nickel: preparing a copper-nickel alloy solution for electrodeposition, which specifically comprises the following steps: 1.0mol/L of nickel nitrate, 0.08mol/L of copper nitrate, 3.0mol/L of triethanolamine, 0.007g/L of sodium hydroxymethyl sulfonate and 0.2g/L of 1- (2-hydroxy-3-sulfopropyl) pyridine betaine. Then placing the platinum mesh anode and the polished copper sheet or iron sheet cathode into the electrodeposition solution, and stirring at the speed of 500 rmp; setting the temperature at 50 ℃, the pH value of the solution plating solution at 9.2 and the current density at 5.0ASD to obtain the copper-nickel alloy. Then, an alloy removing method is adopted, the copper-nickel alloy is placed in a 10% nitric acid solution, the alloy removing temperature is 55 ℃, the alloy removing time is 550min, and the porous nickel layer is obtained.

S2、Co₃O₄Preparation of @ Ni electrode: preparing an electrodeposition cobalt solution, specifically: 0.3mol/L of cobalt nitrate, 90g/L of KOH, 70g/L of triethanolamine and 60g/L of sodium citrate. The porous nickel layer is used as a cathode, the titanium is used as an anode, the pH is 9.5, and the current density is 8.0A/dm²Setting the temperature at 44 ℃ and depositing for 15min, and then heating the composite electrode at 450 ℃ for 30min to obtain the cobaltosic oxide-porous nickel composite electrode.

Example 4

The cobaltosic oxide-porous nickel composite electrode prepared in example 1 was used as a working electrode, platinum was used as a counter electrode, and silver-silver chloride was used as a reference electrode, and the working electrode was placed in an acetic acid-sodium acetate buffer solution (pH 4.5), and 0.1mg, 0.2mg, 0.3mg, 0.4mg, 0.5mg, 0.6mg, 0.7mg, and 0.8mg of selenium ion solutions were gradually added thereto, and differential pulse voltammetry was measured, whereby fig. 2 was obtained.

Fig. 2 illustrates that when the selenium ion concentration ranges from 0.1 to 0.8mg, the peak current density increases with the increase of the concentration of the detection substance, and thus the cobaltosic oxide-porous nickel composite electrode prepared in example 1 has excellent response characteristics to the trace element selenium ion.

The fitted curve was calculated from figure 2, resulting in figure 3. It is illustrated that the cobaltosic oxide-porous nickel composite electrode prepared in example 1 can be used for electrochemical detection of selenium ions.

Example 5

The cobaltosic oxide-porous nickel composite electrode prepared in example 1 was placed in an acetic acid-sodium acetate buffer solution with a pH of 4.5, 0.5mg of a selenium ion solution was added, differential pulse tests were performed at different time intervals, with the time selection being 200s, 400s, 600s, 800s, 1000s, 1200s, 1400s, 1600s, 1800s, 2000s, respectively, and the test applied potential being 0.95V. The decrease of the test current density was examined to obtain FIG. 4.

After the continuous reaction of 2000s, the response current is only slightly changed, and the current is attenuated by 6% compared with the initial current, which indicates that the catalytic activity of the cobaltosic oxide-porous nickel composite electrode prepared in example 1 is not obviously attenuated under the condition of continuous operation, and the cobaltosic oxide-porous nickel composite electrode can be used for long-time measurement and has better test stability.

Example 6

The cobaltosic oxide-porous nickel composite electrode prepared in example 2 was selected, placed in an acetic acid-sodium acetate buffer solution with a pH of 4.5, 0.7mg of selenium ion solution was added, and subjected to differential pulse voltammetry for 5 consecutive days. The test is only carried out once every day, the electrodes are washed by deionized water and placed in an oven for constant-temperature drying after each independent test, so as to ensure that no solution is left on the surfaces of the electrodes, and the change of the peak current intensity is recorded, so that the attached figure 5 is obtained.

The peak current intensity of the selenium ions after 5 days is reduced by 8.6% only compared with that of the selenium ions after 1 day, which shows that the cobaltosic oxide-porous nickel composite electrode prepared in example 2 has better repeatability.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single technical solution, and such description is for clarity only, and those skilled in the art should take the description as a whole, and the technical solutions in the embodiments may be combined appropriately to form other embodiments that those skilled in the art can understand. The technical details not described in detail in the present invention can be implemented by any of the prior arts in the field. In particular, all technical features of the invention which are not described in detail can be achieved by any prior art.