Preparation method and application of Co-CoC2O4-Co electrode supported by nickel foam

Abstract

The invention discloses a method for preparing a Co‑CoC2O4‑Co electrode supported by nickel foam and its application in catalyzing sodium borohydride electro-oxidation. The invention adopts an electrodeposition method to load cobalt on nickel foam, then etches with oxalic acid, and finally uses sodium borohydride to reduce elemental cobalt on its surface, thereby obtaining a Co‑CoC2O4‑Co / Ni Foam electrode and assembling it to a cylindrical rotating bed for improving the performance of sodium borohydride electro-oxidation. The electrode material of the invention is not doped with precious metals, is inexpensive, and is suitable for industrial applications; the synergistic effect between elemental cobalt, cobalt oxalate, and cobalt oxide is utilized to improve the electro-oxidation performance of NaBH4, making it a very potential electrode; the electrode is assembled to a cylindrical rotating bed, and the working electrode is rotated by a rotating shaft or the reaction solution is circulated using a circulating pump, so as to achieve the effect of weakening the bubble effect and strengthening the mass transfer, thereby greatly improving the performance of sodium borohydride electro-oxidation.

Description

Technical Field

[0001] The invention relates to a preparation method of a Co-CoC2O4-Co electrode supported by nickel foam and application of the electrode in catalyzing electro-oxidation of sodium borohydride, belonging to the field of electro-catalytic oxidation. Background Art

[0002] Energy conservation and emission reduction are important measures for countries around the world to protect the environment. To achieve this goal, it is important to find a clean and renewable energy source. Direct borohydride fuel cell (DBFC) has great development potential. NaBH4 is a common fuel for DBFC. It has a high hydrogen content (10.6 wt.%), is solid at room temperature, and is easy to transport. In alkaline solution, the theoretical electrooxidation rate of NaBH4 is 8e - Reaction (see the formula below). No sulfide or carbide is produced during the operation of the battery, and the reaction products are non-flammable and low in toxicity.

[0003]

[0004] The oxidizability of NaBH4 is one of the important factors affecting the performance of DBFC, and the key to catalyzing the electrooxidation of NaBH4 lies in the anode catalyst. According to literature research, cobalt-based materials can make BH4 - The BH bond in NaBH4 is broken, and it is widely available and inexpensive, so it has attracted widespread attention as a catalyst for the electro-oxidation of NaBH4.

[0005] Ye K et al. (Ye K, Ma X, Huang X, et al. The optimal design of Cocatalyst morphology on a three-dimensional carbon sponge with low cost, inducing better sodium borohydride electrooxidation activity [J]. RSCAdvances, 2016, 6(47): 41608-41617.) used the special three-dimensional porous structure of sponge to load Co to prepare CoNF@carbon sponge electrode, which was used to improve the catalytic NaBH4 electrooxidation performance. However, due to the relatively simple composition of the prepared electrode, its catalytic performance needs to be further improved. Song C et al. (Song C, Zhang D, Wang B, et al. Uniformly grown PtCo-modified Co3O4 nanosheets as a highly efficient catalyst for sodium borohydride electrooxidation [J]. Nano Research, 2016, 9(11):3322-3333) prepared a PtCo-modified Co3O4 nanosheets (PtCo / Co3O4 NSs) electrode, which was doped with precious metal Pt during preparation. This not only improved the electro-oxidation performance, but also increased the production cost. Therefore, the present invention improves the catalytic performance of the electrode by improving the electrode structure and composition and improving its testing device. Summary of the invention

[0006] The present invention aims to provide a method for preparing a Co-CoC2O4-Co electrode supported by nickel foam and its application in catalyzing the electro-oxidation of sodium borohydride, and improves the electro-oxidation performance of NaBH4 by preparing a high-efficiency electrode and applying it to a special cylindrical rotating bed device.

[0007] The present invention improves the electro-oxidation performance of NaBH4 by designing electrode materials with special structures and multiple components and applying them to new reaction equipment. The present invention designs a special three-dimensional flower-like structure to enrich the active sites of the catalyst, and utilizes the synergistic effect between different substances (Co, CoC2O4, Co oxide) to improve the catalytic performance; at the same time, the prepared electrode is placed in a cylindrical rotating bed to weaken the bubble effect brought about by the reaction and strengthen mass transfer, promote the contact between the active sites on the electrode surface and NaBH4, so as to improve the electro-oxidation performance of NaBH4.

[0008] The present invention provides a method for preparing a Co-CoC2O4-Co electrode supported by nickel foam, wherein cobalt is loaded on the nickel foam by an electrodeposition method, then etched with oxalic acid, and finally sodium borohydride is used to reduce the elemental cobalt on the surface to obtain a Co-CoC2O4-Co / Ni Foam electrode. In the present invention, the performance of sodium borohydride electro-oxidation is improved by assembling the electrode to a cylindrical rotating bed.

[0009] The above-mentioned preparation method specifically comprises the following steps:

[0010] (1) Use nickel foam (10 mm × 10 mm, 10 mm × 180 mm) as the electrode support;

[0011] The two sizes of nickel foam mentioned above are designed based on two reaction devices. The small electrode of 10 mm×10 mm is used in an electrolytic cell filled with 50 mL of reaction solution, while the large electrode of 10 mm×180 mm needs to be made into a cylindrical shape and used in a cylindrical rotating bed filled with 3 L of reaction solution.

[0012] (2) The nickel foam prepared in step (1) was used as the working electrode, the platinum sheet was used as the counter electrode, and the Ag / AgCl (saturated KCl) electrode was used as the reference electrode. -3 The Co / NF electrode was prepared by deposition in an aqueous solution of CoCl2·6H2O at a potential of -1.0 V to -3.0 V for 400 s to 1200 s using chronoamperometry;

[0013] (3) The Co / NF electrode prepared in (2) was placed in a solution containing 0.2 mol·dm -3 ~1.0 mol·dm -3 The Co / NF-CoC2O4 electrode was prepared by placing the H2C2O4 solution at 298.15 K~338.15 K for 1.0 h~3.0 h.

[0014] (4) The Co / NF-CoC2O4 electrode obtained in step (3) was placed in a solution containing 1 mol·dm -3 NaOH+0.1 mol·dm -3 The nickel foam supported Co-CoC2O4-Co electrode (referred to as Co / NF-CoC2O4-Co electrode) was prepared by reducing the oxygen-containing compounds on its surface to elemental Co in a mixed solution of NaBH4 for 1.0 h~3.0 h using the reducing property of NaBH4, and the electrode was used to catalyze the electro-oxidation of NaBH4.

[0015] The present invention also provides a Co-CoC2O4-Co electrode supported by nickel foam obtained by the above preparation method.

[0016] The present invention also provides the use of the Co-CoC2O4-Co electrode supported by the nickel foam in the electrocatalytic oxidation of NaBH4.

[0017] The above application process is as follows: a conventional three-electrode system is used, with Co-CoC2O4-Co supported by nickel foam as the working electrode, platinum as the counter electrode, and Ag / AgCl (saturated KCl) electrode as the reference electrode. Cyclic voltammetry is used to catalyze the electro-oxidation of NaBH4. The scanning range of the cyclic voltammetry is -1.2 V to -0.2 V, and the scanning rate is 10 mV·s -1 , the test solution is 1.0 mol·dm -3 ~3.0 mol·dm -3 NaOH and 0.01 mol·dm -3 ~0.5 mol·dm -3 NaBH4.

[0018] In order to improve the performance of sodium borohydride electro-oxidation, the present invention assembles the above-mentioned electrode to a cylindrical rotating bed. The structure of the cylindrical rotating bed is as follows: the working electrode is fixed on the bottom disc, the reference electrode and the counter electrode are vertically inserted into the working electrode (cylindrical electrode), the disc is connected to the rotating shaft, and can drive the working electrode to rotate. The reaction liquid can flow in from the upper end of the cylindrical rotating bed and flow out from the bottom, and then the reaction liquid flowing out from the bottom is brought to the upper end of the cylindrical rotating bed by a circulation pump and flows in again, forming a cycle.

[0019] Beneficial effects of the present invention:

[0020] (1) The electrode material provided by the present invention is not doped with any precious metal, is low in price, and is suitable for industrial application;

[0021] (2) The present invention uses electrodeposition to deposit cobalt without using any organic binder, and a large amount of elemental cobalt can provide a fast transfer channel for electrons, thereby ensuring good conductivity of the electrode;

[0022] (3) The cobalt surface is modified by etching and reduction, so that the electrode surface has a three-dimensional porous nanoflower structure, providing abundant active sites;

[0023] (4) The synergistic effect between elemental cobalt, cobalt oxalate and cobalt oxide is used to improve the electro-oxidation performance of NaBH4, making it a very promising electrode;

[0024] (5) The electrode is assembled onto a cylindrical rotating bed, and the working electrode is rotated by a rotating shaft or the reaction solution is circulated using a circulating pump, so as to achieve the effect of weakening the bubble effect and enhancing mass transfer, thereby greatly improving the performance of sodium borohydride electro-oxidation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are the cyclic voltammetry curves of the NF (curve a), Co / NF (curve b), Co / NF-CoC2O4 (curve c), and Co / NF-CoC2O4-Co (curve d) electrodes in Example 1.

[0026] Figure 2 Schematic diagram of a cylindrical rotating bed equipped with Co-CoC2O4-Co electrodes supported by nickel foam.

[0027] Figure 3 Cyclic voltammograms of the Co-CoC2O4-Co electrodes supported by nickel foam prepared in Example 2 (curve a) and Example 3 (curve b).

[0028] Figure 4 The Co-CoC2O4-Co electrode (10 mm×180 mm) supported by nickel foam in Example 4 was assembled on a cylindrical rotating bed at a stationary state (curve a) and a rotation speed of 112 r·min -1 (curve b) and a circulation flow rate of 400 mL min -1 (Curve c) is the cyclic voltammetry curve.

[0029] Figure 5 This is a scanning electron microscope image of the product obtained in Example 1.

[0030] In the figure: 1 is a reference electrode, 2 is a counter electrode, 3 is a working electrode, 4 is a disk, 5 is a rotating shaft, and 6 is a circulation pump. DETAILED DESCRIPTION

[0031] The present invention is further illustrated by the following examples, but is not limited to the following examples.

[0032] Figure 2 The structure of the cylindrical rotating bed is shown. The cylindrical rotating bed includes a cylinder, and a cylindrical electrode, namely the working electrode 3, is arranged at the bottom of the cylinder. The working electrode 3 is fixed on the bottom disk 4. The reference electrode 1 and the counter electrode 2 are vertically inserted into the working electrode 3 (cylindrical electrode). The disk 4 is connected to the rotating shaft 5. The rotating shaft 5 rotates under the action of the motor, which can drive the working electrode 3 to rotate. The reaction liquid can flow into the upper mouth of the cylindrical rotating bed and flow out from the bottom. Then, the reaction liquid flowing out from the bottom is brought to the upper mouth of the cylindrical rotating bed by the circulation pump 6 and flows in again to form a cycle.

[0033] Example 1

[0034] Method for preparing nickel foam supported Co-CoC2O4-Co electrode:

[0035] (1) Use nickel foam (10 mm × 10 mm) as the electrode support;

[0036] (2) The nickel foam prepared in step (1) was used as the working electrode, the platinum sheet was used as the counter electrode, and the Ag / AgCl (saturated KCl) electrode was used as the reference electrode. -3 The Co / NF electrode was prepared by deposition in an aqueous solution of CoCl2·6H2O at a potential of −2.5 V for 800 s using chronoamperometry;

[0037] (3) The Co / NF electrode prepared in (2) was placed in a solution containing 0.6 mol·dm -3 The Co / NF-CoC2O4 electrode was prepared by placing the H2C2O4 solution at 318.15K for 2.0 h.

[0038] (4) The Co / NF-CoC2O4 electrode obtained in step (3) was placed in a solution containing 1 mol·dm -3 NaOH+0.1 mol·dm -3 The NF-CoC2O4-Co electrode was prepared by immersing the NF-CoC2O4-Co electrode in a mixed solution of NaBH4 for 2.0 h and reducing the oxygen-containing compounds on its surface to elemental Co using the reducing property of NaBH4.

[0039] An electrolytic cell containing 50 mL of reaction solution was used, with NF electrode, Co / NF electrode, Co / NF-CoC2O4 electrode and Co / NF-CoC2O4-Co electrode as working electrodes, platinum electrode as counter electrode, Ag / AgCl (saturated KCl) electrode as reference electrode, and 1 mol·dm -3 NaOH and 0.1 mol·dm -3 Cyclic voltammetry was performed in NaBH4 solution with a scan range of -1.2 V to -0.2 V and a scan rate of 10 mV·s -1 When the potential is -0.58 V, the oxidation current density reaches 315.52 mA·cm -2 , which is much higher than that of NF electrode (0.17 mA·cm -2 )、Co / NF electrode(15.39 mA·cm -2 )Co / NF-CoC2O4 electrode(232.33mA·cm -2 ).

[0040] Figure 1The cyclic voltammograms of NF electrode, Co / NF electrode, Co / NF-CoC2O4 electrode and Co / NF-CoC2O4-Co electrode show that the oxidation current density of the Co-CoC2O4-Co electrode supported by nickel foam is much higher than that of other electrodes, indicating that the electrode has greater catalytic activity after etching and reduction.

[0041] The morphology of the product was observed using a scanning electron microscope (SEM). Figure 5 As shown. Figure 5 It can be seen that the microstructure of the Co-CoC2O4-Co electrode supported by nickel foam is a three-dimensional flower-like structure.

[0042] Example 2

[0043] Method for preparing nickel foam supported Co-CoC2O4-Co electrode:

[0044] (1) Use nickel foam (10 mm × 10 mm) as the electrode support;

[0045] (2) The nickel foam prepared in step (1) was used as the working electrode, the platinum sheet was used as the counter electrode, and the Ag / AgCl (saturated KCl) electrode was used as the reference electrode. -3 The Co / NF electrode was prepared by deposition in an aqueous solution of CoCl2·6H2O at a potential of −2.5 V for 800 s using chronoamperometry;

[0046] (3) The Co / NF electrode prepared in (2) was placed in a solution containing 0.6 mol·dm -3 The Co / NF-CoC2O4 electrode was prepared by placing the H2C2O4 solution at 318.15K for 2.0 h.

[0047] (4) The Co / NF-CoC2O4 electrode obtained in step (3) was placed in a solution containing 1 mol·dm -3 NaOH+0.1 mol·dm -3 The NF-CoC2O4-Co electrode was prepared by immersing the NF-CoC2O4-Co electrode in a mixed solution of NaBH4 for 2.0 h and reducing the oxygen-containing compounds on its surface to elemental Co using the reducing property of NaBH4.

[0048] The Co / NF-CoC2O4-Co electrode was used as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl (saturated KCl) electrode as the reference electrode. -3 NaOH and 0.3 mol·dm -3Cyclic voltammetry was performed in NaBH4 solution with a scan range of -1.2 V to -0.2 V and a scan rate of 10 mV·s -1 At a temperature of 296.15 K and a potential of -0.2 V, the oxidation current density is 773.62 mA·cm -2 .

[0049] Example 3

[0050] Method for preparing nickel foam supported Co-CoC2O4-Co electrode:

[0051] (1) Use nickel foam (10 mm × 10 mm) as the electrode support;

[0052] (2) The nickel foam prepared in step (1) was used as the working electrode, the platinum sheet was used as the counter electrode, and the Ag / AgCl (saturated KCl) electrode was used as the reference electrode. -3 The Co / NF electrode was prepared by deposition in an aqueous solution of CoCl2·6H2O at a potential of −2.5 V for 800 s using chronoamperometry;

[0053] (3) The Co / NF electrode prepared in (2) was placed in a solution containing 0.6 mol·dm -3 The Co / NF-CoC2O4 electrode was prepared by placing the H2C2O4 solution at 318.15K for 2.0 h.

[0054] (4) The Co / NF-CoC2O4 electrode obtained in step (3) was placed in a solution containing 1 mol·dm -3 NaOH+0.1 mol·dm -3 The NF-CoC2O4-Co electrode was prepared by immersing the NF-CoC2O4-Co electrode in a mixed solution of NaBH4 for 2.0 h and reducing the oxygen-containing compounds on its surface to elemental Co using the reducing property of NaBH4.

[0055] The Co / NF-CoC2O4-Co electrode was used as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl (saturated KCl) electrode as the reference electrode. -3 NaOH and 0.3 mol·dm -3 Cyclic voltammetry was performed in NaBH4 solution with a scan range of -1.2 V to -0.2 V and a scan rate of 10 mV·s -1 At a temperature of 326.15 K and a potential of -0.2 V, the oxidation current density is 1101.38 mA·cm -2 .

[0056] Figure 3The cyclic voltammetry curves of the Co-CoC2O4-Co electrode supported by nickel foam at test temperatures of 296.15 K (curve a) and 326.15 K (curve b) corresponding to Example 2 and Example 3. When the test temperature is 326.15 K, the oxidation current density is much higher than that at 296.15 K, indicating that the increase of the test temperature is conducive to the electro-oxidation of NaBH4.

[0057] Example 4

[0058] Method for preparing nickel foam supported Co-CoC2O4-Co electrode:

[0059] (1) Use nickel foam (10 mm × 180 mm) as the electrode support;

[0060] (2) The nickel foam prepared in step (1) was used as the working electrode, the platinum sheet was used as the counter electrode, and the Ag / AgCl (saturated KCl) electrode was used as the reference electrode. -3 The Co / NF electrode was prepared by deposition in an aqueous solution of CoCl2·6H2O at a potential of −2.5 V for 800 s using chronoamperometry;

[0061] (3) The Co / NF electrode prepared in (2) was placed in a solution containing 0.6 mol·dm -3 The Co / NF-CoC2O4 electrode was prepared by placing the H2C2O4 solution at 318.15K for 2.0 h.

[0062] (4) The Co / NF-CoC2O4 electrode obtained in step (3) was placed in a solution containing 1 mol·dm -3 NaOH+0.1 mol·dm -3 The NF-CoC2O4-Co electrode was prepared by immersing the NF-CoC2O4-Co electrode in a mixed solution of NaBH4 for 2.0 h and reducing the oxygen-containing compounds on its surface to elemental Co using the reducing property of NaBH4.

[0063] use Figure 2 The cylindrical rotating bed shown in the figure was equipped with a Co / NF-CoC2O4-Co electrode as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl (saturated KCl) electrode as the reference electrode. -3 NaOH and 0.01 mol·dm -3 Cyclic voltammetry was performed in NaBH4 solution with a scan range of -1.2 V to -0.2 V and a scan rate of 10 mV·s -1 , in the static state, the oxidation current is 237.64 mA (-2 V); when the speed is 112 r·min -1When the circulation flow rate is 400 mL·min -1 When , the oxidation current is 931.39 mA.

[0064] Figure 4 The Co-CoC2O4-Co electrode supported by nickel foam was assembled on a cylindrical rotating bed at different states (curve a is static state, curve b is rotating at a speed of 112 r·min -1 Curve c is the circulation flow rate of 400 mL min -1 As can be seen from the figure, the oxidation current of curve b and curve c is much higher than that of curve a, indicating that the rotation of the working electrode and the circulation of the reaction solution both play a certain role in strengthening the electro-oxidation of NaBH4.

Claims

1. A method for preparing a Co-CoC2O4-Co electrode supported by nickel foam, characterized in that: Cobalt was loaded on nickel foam by electrodeposition to obtain a Co / NF electrode, which was then etched with oxalic acid to obtain a Co / NF-CoC2O4 electrode. Finally, sodium borohydride was used to reduce elemental cobalt on its surface to obtain a Co-CoC2O4-Co electrode supported by nickel foam.

2. The method for preparing the nickel foam supported Co-CoC2O4-Co electrode according to claim 1, characterized in that The specific steps include: (1) Using nickel foam as an electrode support; (2) The nickel foam prepared in step (1) was used as the working electrode, the platinum sheet was used as the counter electrode, and the Ag / AgCl / saturated KCl electrode was used as the reference electrode. -3 The Co / NF electrode was prepared by deposition in an aqueous solution of CoCl2·6H2O at a potential of -1.0 V to -3.0 V for 400 s to 1200 s using chronoamperometry; (3) The Co / NF electrode prepared in (2) was placed in a solution containing 0.2 mol·dm -3 ~1.0 mol·dm -3 The Co / NF-CoC2O4 electrode was prepared by placing the H2C2O4 solution at 298.15 K~338.15 K for 1.0 h~3.0 h. (4) The Co / NF-CoC2O4 electrode obtained in step (3) was placed in a solution containing 1 mol·dm -3 NaOH+0.1 mol·dm -3 The nickel foam supported Co-CoC2O4-Co electrode was prepared by reducing the oxygen-containing compounds on its surface to elemental Co using the reducing property of NaBH4 in a mixed solution of NaBH4 for 1.0 h~3.0 h.

3. The method for preparing the Co-CoC2O4-Co electrode supported by nickel foam according to claim 2, characterized in that: The size of the nickel foam is 10 mm×10 mm or 10 mm×180 mm; the small electrode of 10 mm×10 mm is used in an electrolytic cell filled with 50 mL of reaction solution, while the large electrode of 10 mm×180 mm needs to be made into a cylindrical shape and used in a cylindrical rotating bed filled with 3 L of reaction solution.

4. A Co-CoC2O4-Co electrode supported by nickel foam obtained by the preparation method according to any one of claims 1 to 3.

5. Use of the nickel foam supported Co-CoC2O4-Co electrode according to claim 4 in NaBH4 electro-oxidation.

6. The use according to claim 5, characterized in that The application process is as follows: a conventional three-electrode system is used, with Co-CoC2O4-Co supported by nickel foam as the working electrode, platinum as the counter electrode, and Ag / AgCl / saturated KCl electrode as the reference electrode. Cyclic voltammetry is used to catalyze the electrooxidation of NaBH4. The scanning range of the cyclic voltammetry is -1.2 V to -0.2 V, and the scanning rate is 10 mV·s -1 , the test solution is 1.0 mol·dm -3 ~3.0 mol·dm -3 NaOH and 0.01 mol·dm -3 ~0.5mol·dm -3 NaBH4.

7. The use according to claim 6, characterized in that: The Co-CoC2O4-Co electrode supported by nickel foam was assembled into a cylindrical rotating bed to improve the performance of sodium borohydride electrooxidation; The structure of the cylindrical rotating bed is as follows: the working electrode is fixed on the bottom disc, the reference electrode and the counter electrode are vertically inserted into the working electrode, the working electrode is the cylindrical electrode, the disc is connected to the rotating shaft, and the rotating shaft drives the working electrode to rotate when it rotates. The reaction liquid flows in from the upper surface of the cylindrical rotating bed and flows out from the bottom, and then the reaction liquid flowing out from the bottom is brought to the upper surface of the cylindrical rotating bed by a circulation pump and flows in again, forming a cycle.

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