Preparation method of high-stability electrode material for all-vanadium redox flow battery

Abstract

The invention discloses a preparation method of a high-stability electrode material for an all-vanadium redox flow battery, which is characterized in that a metal-doped ZrB2 film is deposited on the surface of a graphite felt with low cost, chemical stability and high conductivity by adopting a magnetron sputtering coating technology, so that the hydrophilicity is remarkably improved, and the active site density is increased; the electrochemical activity on a vanadium ion solution is obviously improved, and meanwhile, the original graphite felt resistance is reduced. The preparation method of the electrode material is simple and easy to operate, the preparation period is extremely short, large-area preparation can be achieved, the hydrophilic performance and the electrochemical performance of the electrode material before and after modification are remarkably improved, and the electrode material shows higher efficiency retention rate and cycling stability in a vanadium electrolyte.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-vanadium redox flow battery electrode materials, and particularly relates to a preparation method of a high-stability electrode material for an all-vanadium redox flow battery. Background Art

[0002] Currently, due to the long-term unregulated utilization of fossil energy, the world is facing the dual challenges of energy crisis and environmental problems. Renewable energy represented by wind energy, solar energy, and tidal energy is regarded as an ideal alternative to fossil energy due to its cleanliness and renewability. However, its intermittent and fluctuating characteristics result in poor compatibility with the power grid. To overcome this bottleneck, energy storage systems achieve energy regulation through the mutual conversion of chemical energy and electrical energy. Among them, redox flow batteries have become a research hotspot due to their long cycle life, flexible design, and energy decoupling characteristics. Vanadium redox flow batteries use vanadium ions in different valence states as the negative and positive active materials respectively, successfully avoiding the problem of metal ion transmembrane pollution and showing significant commercial potential.

[0003] In an all-vanadium redox flow battery (VRFB) system, the electrode, as a core component, directly affects the cost and performance of the battery. Its function is to provide active sites for the oxidation-reduction reaction of vanadium ions in the positive and negative electrolyte solutions (sulfuric acid medium). Current research focuses on developing low-cost and high-performance electrode materials. Among them, graphite felt has become the mainstream choice due to its excellent chemical stability, high conductivity, and economy. However, its inherent hydrophobicity and insufficient surface active sites limit its catalytic activity for the oxidation-reduction reaction of vanadium ions. To address this problem, existing modification strategies can be divided into two categories: one is to introduce oxygen-containing functional groups (-COOH, -OH, etc.) or heteroatoms (N, B, P, etc.) through surface modification techniques such as heat treatment and plasma treatment to enhance hydrophilicity and active site density; the other is to load catalysts to improve electrocatalytic performance.

[0004] The catalyst system mainly includes carbon-based materials (such as carbon nanotubes, graphene, etc.) and metal-based materials (metals / metal oxides / nitrides). Although noble metals (such as Pt, Ir, etc.) have high catalytic activity, their high cost and tendency to trigger side hydrogen evolution reactions limit their practical applications. In contrast, metal oxides (such as PbO2, WO3, TiO2, etc.) have attracted attention due to their low cost and adjustable catalytic properties. However, problems such as their low conductivity, weak interfacial binding force, and difficulty in nanosizing still need to be overcome. Recent studies have shown that by heteroatom doping or compounding with conductive carbon materials such as graphene, the electron conductivity and dispersion of metal oxides can be effectively improved. It has been found that ZrO2 has excellent catalytic stability for the redox reaction of vanadium ions, and its mechanism may be related to Zr promoting hydroxyl adsorption and improving the hydrophilicity of the electrode. Oxygen-containing groups such as hydroxyl groups can serve as active sites in the all-vanadium redox flow battery. Zr promoting hydroxyl adsorption can enhance the density of active sites of the electrode material and significantly enhance the electrocatalytic activity. The significant increase in oxygen-containing groups such as hydroxyl groups is externally manifested as a significant improvement in hydrophilicity. Another study has found that TiB2 has excellent catalytic activity for the redox reaction of vanadium ions, which is related to the excellent physical and chemical stability, conductivity, and large specific surface area of transition metal borides. Summary of the Invention

[0005] Aiming at the defects such as hydrophobicity and insufficient active sites existing in the commonly used electrode material graphite felt in large all-vanadium redox flow batteries, the present invention provides a preparation method for an electrode material for all-vanadium redox flow batteries, which has low cost, can be prepared on a large scale, and has both high electrochemical activity and high cycle stability.

[0006] For the above purpose, the preparation method for the electrode material for all-vanadium redox flow batteries provided by the present invention is as follows: Place the graphite felt on the substrate in the chamber of a magnetron sputtering coating machine, place the ZrB2 target on the DC sputtering target position in the magnetron sputtering coating machine, and place the metal target on the RF sputtering target position in the magnetron sputtering coating machine. Co-sputter deposit a ZrB2 thin film doped with metal on the graphite felt under a vacuum environment and inert gas to obtain an electrode material modified with in-situ heterodoped ZrB2.

[0007] Further, the above metal is any one of Ag, W, Bi, and Cr.

[0008] Further, in the above preparation method, it is preferably carried out under a vacuum degree of 5×10 -4 ~5×10 -5 Pa, an inert gas flow rate of 10 - 50 sccm, a chamber pressure of 0.8 - 2.0 Pa, a DC sputtering power of 25 - 150 W, and an RF sputtering power of 25 - 100 W to co-sputter deposit a ZrB2 thin film doped with metal on the graphite felt, and the sputtering time is 10 - 20 min.

[0009] Further, in the above preparation method, it is more preferably carried out under a vacuum degree of 1×10-4 ~5×10 -5 Pa, the flow rate of the inert gas is 30 - 50 sccm, the pressure inside the chamber is 1.3 - 2.0 Pa, the DC sputtering power is 25 - 50 W, and the RF sputtering power is 50 - 100 W. A ZrB2 thin film doped with metal is co-sputter deposited on the graphite felt, and the sputtering time is 10 - 20 min.

[0010] Furthermore, the above-mentioned inert gas is argon or nitrogen.

[0011] Furthermore, the thickness of the above-mentioned ZrB2 thin film doped with metal is 600 - 1000 nm.

[0012] The beneficial effects of the present invention are as follows:

[0013] 1. The present invention introduces ZrB2 doped with metal to modify the graphite felt, promotes the adsorption of oxygen-containing groups such as hydroxyl groups, significantly improves the hydrophilicity of the graphite felt, and effectively inhibits the hydrogen evolution side reaction. Moreover, the introduction of C - B and C - X bonds (X is the doped metal) by doping metal into ZrB2 in the present invention significantly increases the density of active sites and enhances the electrochemical activity.

[0014] 2. The present invention uses multi-target co-sputtering technology to in-situ hetero-dope ZrB2 to modify the graphite felt, without changing the loose and porous structure of the original graphite felt, ensuring the flow channel of the vanadium ion electrolyte. The ZrB2 thin film doped with metal introduced by the magnetron sputtering technology shows a unique nanocrystalline / amorphous mixed state on the graphite felt, with uniform distribution and stable properties. Moreover, the introduction of metal doping by multi-target co-sputtering improves the utilization rate of the target material and reduces the raw material consumption of ZrB2.

[0015] 3. The electrode modification method of the present invention is simple and easy to operate, has an extremely short preparation period, and can be prepared on a large scale. Description of the Drawings

[0016] Figure 1 are the scanning electron microscope images and energy dispersive spectrometer element analysis diagrams of the graphite felt (left) and the ZrB2 modified graphite felt in Comparative Example 1 (right).

[0017] Figure 2 are the scanning electron microscope images and energy dispersive spectrometer element analysis diagrams of the graphite felt (left) and the Ag-doped ZrB2 modified graphite felt in Example 1 (right).

[0018] Figure 3 is the XRD test of the graphite felt, the ZrB2 modified graphite felt in Comparative Example 1, and the Ag-doped ZrB2 modified graphite felt in Example 1.

[0019] Figure 4 is the water droplet contact angle test diagram of the graphite felt (left), the ZrB2 modified graphite felt in Comparative Example 1 (middle), and the Ag-doped ZrB2 modified graphite felt in Example 1 (right).

[0020] Figure 5 These are the cyclic voltammetry test diagrams of graphite felt, ZrB2-modified graphite felt in Comparative Example 1, and Ag-doped ZrB2-modified graphite felt in Example 1.

[0021] Figure 6 These are the electrochemical impedance spectroscopy diagrams of graphite felt, ZrB2-modified graphite felt in Comparative Example 1, and Ag-doped ZrB2-modified graphite felt in Example 1. Detailed implementation manners

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments only.

[0023] Comparative Example 1

[0024] Put the ZrB2 target on the DC sputtering target position in the magnetron sputtering coating machine, and the purity of the target is 99.99%; then put the graphite felt into the magnetron sputtering coating machine and fix it, evacuate to 5×10 -4 Pa, set the substrate rotation speed to 10 rpm, the argon flow rate to 30 sccm, the chamber pressure to 1.5 Pa, the DC sputtering power to 50 W, and the sputtering time to 20 min, and magnetron sputter deposit a ZrB2 thin film on the graphite felt to obtain a ZrB2-modified electrode material.

[0025] Example 1

[0026] Put the ZrB2 target on the DC sputtering target position in the magnetron sputtering coating machine, and the Ag target on the RF sputtering target position in the magnetron sputtering coating machine, and the purity of both targets is 99.99%; then put the graphite felt into the magnetron sputtering coating machine and fix it, evacuate to 5×10 -4 Pa, set the substrate rotation speed to 10 rpm, the argon flow rate to 30 sccm, the chamber pressure to 1.5 Pa, the DC sputtering power to 50 W, the RF sputtering power to 100 W, and the sputtering time to 20 min, and magnetron sputter deposit an in-situ Ag-doped ZrB2 thin film (i.e., magnetron sputter deposit a ZrB2@Ag thin film) on the graphite felt to obtain an in-situ hetero-doped ZrB2-modified electrode material.

[0027] Example 2

[0028] Put the ZrB2 target on the DC sputtering target position in the magnetron sputtering coating machine, and the Ag target on the RF sputtering target position in the magnetron sputtering coating machine, and the purity of both targets is 99.99%; then put the graphite felt into the magnetron sputtering coating machine and fix it, evacuate to 5×10 -4Set the rotation speed of the substrate to 10 rpm, the argon flow rate to 20 sccm, the chamber pressure to 1.0 Pa, the DC sputtering power to 100 W, the RF sputtering power to 100 W, and the sputtering time to 20 min. Magnetron sputter deposit an in-situ Ag-doped ZrB2 film on the graphite felt to obtain an electrode material modified with in-situ heterogeneously doped ZrB2.

[0029] Example 3

[0030] Place the ZrB2 target on the DC sputtering target position in the magnetron sputtering coating machine, and place the Ag target on the RF sputtering target position in the magnetron sputtering coating machine. The purity of both targets is 99.99%; then place the graphite felt in the magnetron sputtering coating machine and fix it, and evacuate to 5×10 -4 Pa, set the rotation speed of the substrate to 10 rpm, the argon flow rate to 15 sccm, the chamber pressure to 0.8 Pa, the DC sputtering power to 50 W, the RF sputtering power to 100 W, and the sputtering time to 20 min. Magnetron sputter deposit an in-situ Ag-doped ZrB2 film on the graphite felt to obtain an electrode material modified with in-situ heterogeneously doped ZrB2.

[0031] Example 4

[0032] In this example, replace the Ag target with a W target, and magnetron sputter deposit an in-situ W-doped ZrB2 film on the graphite felt. Other steps and conditions are the same as those in Example 1.

[0033] Example 5

[0034] In this example, replace the Ag target with a Bi target, and magnetron sputter deposit an in-situ Bi-doped ZrB2 film on the graphite felt. Other steps and conditions are the same as those in Example 1.

[0035] Example 6

[0036] In this example, replace the Ag target with a Cr target, and magnetron sputter deposit an in-situ Cr-doped ZrB2 film on the graphite felt. Other steps and conditions are the same as those in Example 1.

[0037] Perform structural characterization and performance testing on the electrode materials prepared in the above Example 1 and Comparative Example 1. The results are shown in Figures 1 to 6 .

[0038] From Figure 1 and Figure 2 it can be seen that in Comparative Example 1, a ZrB2 film was deposited on the graphite felt, and in Example 1, an in-situ Ag-doped ZrB2 film was deposited on the graphite felt, both of which can well retain the porous and multi-channel structure of the graphite felt.

[0039] From Figure 3XRD analysis shows that no new diffraction peaks appeared in the electrode materials of Comparative Example 1 and Example 1, indicating that no new crystal phases were generated. Combining Figure 1 and Figure 2 elemental analysis, it can be obtained that the deposits in Comparative Example 1 and Example 1 are both amorphous / nanocrystalline particles, indicating that the films deposited in Comparative Example 1 and Example 1 are both amorphous / nanocrystalline films.

[0040] From Figure 4 the water droplet contact angle test, it can be seen that the water droplet contact angle of the original graphite felt is greater than 90°, showing hydrophobicity; the water droplets in Comparative Example 1 and Example 1 directly infiltrate, showing hydrophilicity, indicating that the hydrophilicity of the graphite felt modified by the methods in Comparative Example 1 and Example 1 has been significantly improved.

[0041] From Figure 5 the cyclic voltammetry test results, it can be seen that the modification of the graphite felt with ZrB2 film in Comparative Example 1 shows a significant improvement in electrochemical activity compared with the original graphite felt (oxidation peak 206→363 mA cm -2 / reduction peak -138→-195 mA cm -2 ), and the modification of the graphite felt with ZrB2@Ag film in Example 11 further improves the electrochemical activity compared with Comparative Example 1 (oxidation peak 363→467 mA cm -2 / reduction peak -195→-201 mA cm -2 ), indicating that the in-situ heterogeneous doping of metal in ZrB2 shows enhanced electrochemical activity. Figure 6 The electrochemical impedance diagram shows that the modification of the graphite felt with ZrB2 film in Comparative Example 1 shows slightly enhanced electrode reaction kinetics compared with the original graphite felt, and the resistance is slightly reduced. The modification of the graphite felt with ZrB2@Ag film in Example 1 further shows significantly enhanced electrode reaction kinetics and greatly reduces the impedance.

[0042] In the full cell test, the power efficiency of the electrode material in Comparative Example 1 reached 82.6% at a current density of 100 mA cm -2 , and it could not work stably at a current density of 200 mA cm -2 ; the power efficiency of the electrode material in Example 1 reached 86.6% at a current density of 100 mA cm -2 , and the power efficiency reached 81.7% at a current density of 200 mA cm -2 , higher than that reported in the literature for TiB2 modified graphite felt (power efficiency of 70% at a current density of 200 mA cm -2 ) and ZrO2 (power efficiency of 75.2% at a current density of 200 mA cm -2 ).

[0043] From the above results, it can be seen that in the present invention, a metal-doped amorphous / nanocrystalline ZrB2 film is modified on the surface of the graphite felt, significantly improving the hydrophilicity of the electrode and showing enhanced electrochemical activity and stability in the vanadium electrolyte.

Claims

1. A preparation method of a high-stability electrode material for a vanadium redox flow battery, characterized in that: Place the graphite felt on the substrate in the chamber of the magnetron sputtering coating machine, place the ZrB2 target on the DC sputtering target position in the magnetron sputtering coating machine, and place the metal target on the RF sputtering target position in the magnetron sputtering coating machine. Under a vacuum environment and inert gas, co-sputter and deposit a ZrB2 film doped with metal on the graphite felt to obtain an electrode material modified with in-situ hetero-doped ZrB2; the metal is any one of Ag, W, Bi, and Cr.

2. The preparation method of the high-stability electrode material for all-vanadium redox flow batteries according to claim 1, wherein: At a vacuum degree of 5×10- 4 ~5×10- 5 Pa, an inert gas flow rate of 10 - 50 sccm, a chamber pressure of 0.8 - 2.0 Pa, a DC sputtering power of 25 - 150 W, and an RF sputtering power of 25 - 100 W, a ZrB2 thin film doped with metal is co-sputter deposited on a graphite felt, and the sputtering time is 10 - 20 min.

3. The preparation method of the high-stability electrode material for all-vanadium redox flow batteries according to claim 1, wherein: At a vacuum degree of 1×10- 4 ~5×10- 5 Pa, an inert gas flow rate of 30 - 50 sccm, a chamber pressure of 1.3 - 2.0 Pa, a DC sputtering power of 25 - 50 W, and an RF sputtering power of 50 - 100 W, a ZrB2 thin film doped with metal is co-sputter deposited on a graphite felt, and the sputtering time is 10 - 20 min.

4. The preparation method of the high-stability electrode material for all-vanadium redox flow batteries according to any one of claims 1 to 3, characterized in that: The inert gas is argon or nitrogen.

5. The preparation method of the high-stability electrode material for an all-vanadium redox flow battery according to any one of claims 1 to 3, characterized in that: The thickness of the ZrB2 film doped with metal is 600 - 1000 nm.

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