KR101813405B1 - Bipolar plate based on iridium oxide coated titanium for vanadium redox flow battery and preparing method thereof - Google Patents

Abstract

The present invention relates to a titanium-based bipolar plate coated with iridium oxide for vanadium redox flow battery and a manufacturing method thereof and, more specifically, to a titanium-based bipolar plate coated with iridium oxide for vanadium redox flow battery, which includes a titanium substrate and a porous titanium dioxide (TiO_2) nanotube layer formed in a nanotube shape on the titanium substrate, wherein the porous TiO_2 nanotube layer is coated with iridium oxide on the outside and the inside. The titanium-based bipolar plate coated with iridium oxide for vanadium redox flow battery can: improve electrical resistance and electron transfer capability more than a carbon material which is a material used as an existing bipolar plate; and improve charging-discharging efficiency of the vanadium redox flow battery and secure spatial advantages by manufacturing the vanadium redox flow battery of a multi-stack through a titanium material having a thin thickness.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium-based bipolar plate coated with iridium oxide for a vanadium redox flow battery, and a method for manufacturing the same,

The present invention relates to a titanium-based bipolar plate coated with iridium oxide for a vanadium redox flow battery and a method of manufacturing the same, and more particularly to a bipolar plate coated with iridium oxide for a vanadium redox flow battery by replacing a conventional graphite bipolar plate, Redox flow can improve battery performance.

An all-vanadium redox battery (hereinafter referred to as 'VRB') oxidizes V ₅ ⁺ of vanadium ions in both electrolytic tanks to V ₄ ⁺ by reducing V ₃ ⁺ , a vanadium ion in a negative electrolyte tank, to V ₂ ⁺ Rechargeable flow battery.

An all-vanadium redox flow battery (hereinafter referred to as 'VRFB') is described by the following formula.

[Chemical Formula 1]

VO ₂ ⁺ + 2H ⁺ + e ^- VO ₂ ⁺ + H ₂ O (E = 0.991 V)

(2)

V ₂ ⁺ ↔ V ₃ ⁺ + e ^- (E = -0.255 V): cathode

(3)

VO ₂ ⁺ + V ₂ ⁺ + 2H ^{+ +} VO ₂ ⁺ + V ₃ ⁺ + H ₂ O (E ₀ = 1.2 V)

Most vanadium batteries are being considered for grid energy capacity in power plants or electric grids because the energy storage capacity of VRFB can be increased by increasing tank storage capacity.

In general, the VRFB is composed of six cells: a cell frame, a current collector, a bipolar plate, a carbon felt electrode, a flow frame, and a membrane. And a constituent part.

In particular, the bipolar plate is made of graphite, carbon, or carbon plastic having high electrical conductivity and low density, and the bipolar plate is made of a corrosion inhibitor and a cell stack And thus plays an important role as an electron path for reducing the internal resistance of the transistor.

Especially since strong corrosive electrolytes are mainly used, the bipolar plate has an internal characteristic. For this reason, carbon materials are mainly used for bipolar plates rather than copper materials. However, when forming the thin film, the carbon-based material has a relatively poor electrochemical characteristic and a weak mechanical strength. As a result, the processing cost is increased and a thick bipolar plate can not be used.

However, the design of dense multi-stack VRFB is possible by reducing the bipolar plate volume. In this regard, there has been a recent report on the application of bipolar plates based on metal oxide / metal substrates to VRFB.

In particular, a Ti / IrO _x : Ta ₂ O ₅ substrate was used on both sides of the bipolar plate and this material exhibited increased voltage efficiency due to hydrogen evolution at the electrode rather than V ₂ ⁺ formation, but Coulomb and energy efficiency A problem has been reported.

Recently, a carbon composite bipolar plate has been proposed, which exhibits electrical stability and strong chemical stability to strong acids.

Dimensionally stable anodes (DSA) were developed in the mid-1960s for use in the chlor-alkali industry and have since been extensively used in electrochemical processes.

Generally, DSA is composed of a noble metal electrode catalyst deposited on a TiO ₂ / Ti substrate. Specifically, the TiO ₂ / Ti substrate provides reliable corrosion resistance in a chlorine generating environment and makes it possible to maintain dimensional tolerance.

Therefore, it is urgent to research and develop new materials for a bipolar plate which can obtain long-term stability by using an inner Ti metal substrate and an electrochemically active catalyst and can reduce an overvoltage in an electrochemical reaction.

Korean Patent Publication No. 2016-0043830

An object of the present invention is to provide a method for forming a porous titanium dioxide nanotube structure by forming a porous titanium dioxide nanotube structure on a surface of a titanium substrate and then coating the iridium oxide to improve the adhesion between the iridium oxide coating layer and the porous titanium dioxide nanotube structure, The iridium oxide coating layer is maintained without being separated, thereby improving the electrochemical performance of the vanadium redox flow battery.

According to an aspect of the present invention, there is provided a semiconductor device comprising: a titanium substrate; (TiO ₂ ) nanotube layer having a nanotube shape on the titanium substrate, and the porous TiO ₂ nanotube layer is coated on the outer and inner surfaces with iridium oxide. Provides a titanium-based bipolar plate coated with iridium oxide for a toxic flow battery.

The present invention also provides a method of manufacturing a semiconductor device, comprising: washing a titanium substrate; Anodizing the washed titanium substrate with an electrolyte solution containing sodium hydroxide, phosphoric acid, and hydrofluoric acid to form a porous TiO ₂ nanotube structure on the surface of the titanium substrate; Heat treating the titanium substrate on which the porous TiO ₂ nanotube structure is formed; Adding an iridium precursor to an organic solvent and stirring the mixed solution to prepare a mixed solution; And a step of injecting a mixed solution onto the surface of the titanium substrate on which the heat-treated porous TiO ₂ nanotube structure is formed, and then injecting the mixed solution into an electric furnace and performing heat treatment. The barium oxide- And a manufacturing method thereof.

The titanium-based bipolar plate coated with iridium oxide for the vanadium redox flow battery according to the present invention can improve the electric resistance and electron transfer ability as compared with the carbon material used as the conventional bipolar plate, It is possible to manufacture a multi-stack vanadium redox flow battery, thereby improving the charging-discharging efficiency of the vanadium redox flow battery and also securing a spatial advantage.

1 is an exploded view of an all-vanadium redox flow battery (hereinafter referred to as 'VRFBs'),
2 is as shown the surface shape of the bipolar plate coated with the IrO _X, specifically, of the TiO ₂ nanotubes bipolar plate for (a), the barrier-type TiO _2, the bipolar plate (b) coated with an IrO _X coated with IrO _X SEM (scanning electron microscope; hereinafter 'SEM') images a top view (Top view), and nano the TiO ₂ coated with IrO _X tube bipolar plate (c), of a barrier-type coatings as IrO _X TiO ₂ bipolar plate ( d) is a SEM image cross-sectional view,
FIG. 3 is a top view of a TiO ₂ nanotube structure prepared by anodizing for 3 hours by applying a voltage of 20 V to an electrolyte solution containing 1 M NaOH, 1 MH ₃ PO ₄ , and 0.5 wt% HF. And a cross-sectional SEM image (b), wherein
Figure 4 is a focused ion beam scanning electron microscopy of the TiO ₂ nanotubes bipolar plate for (a), the barrier-type TiO ₂ the bipolar plate (b) coated with an IrO _X coated with IrO _X (Focussed Ion Beam Scanning Electron Microscope; hereinafter 'FIB -SEM '), and blue, yellow, and green of the EDX analysis are Ti, Ir, and O elements, respectively, in the EDX analysis. ,
5 shows a high-resolution transmission electron microscope (HR-TEM) image of titanium (Ti), iridium (Ir) and oxygen (O) TEM image (b) of the individual porous TiO ₂ nanotube layer inner pores corresponding to a)
6 is a cross-sectional digital photograph of a graphite bipolar plate (left) and a TiO ₂ nanotube bipolar plate coated with IrO _x (right) for comparison of thickness,
7 is a TiO ₂ nanotubes bipolar plate, IrO the barrier-type TiO ₂ the bipolar plate coated with _X, and X-ray diffraction analysis of the TiO ₂ nanotubes bipolar plate coated with the IrO _X (X-ray diffractiometry; "XRD Analysis) shown as a pattern, a diagram confirming the JCPDS # 15-0870, JCPDS # 21-1272, and the JCPDS # 44-1294, based on IrO _X, anatase TiO ₂ and Ti,
FIG. 8 shows Tafel plots of various bipolar plates, where the Tappel line in the voltage range of -0.3 V to 0 V is a plot of Tappel's line in an aqueous solution of 0.3 M VOSO ₄ /0.6 MH ₂ SO ₄ ,
Figure 9 shows the electrochemical properties for various types of bipolar plates with a polarization curve (a) measured at a scan rate of 1 mA / cm ² ,, 10 ^-3 Hz to 10 < RTI ID = 0.0 > Electrochemical impedance spectroscopy analysis (EIS analysis) (b) at ⁵ Hz, and FIG.
10 shows a digital photograph of a TiO ₂ bipolar plate coated with IrO _x reflected on a Ti substrate after a potentiodynamic polarization test, wherein the TiO ₂ nanotube bipolar plate (a) coated with IrO _x , and (B) a barrier type TiO ₂ bipolar plate coated with IrO _x ,
Figure 11 shows a full-charge test of a charged-discharge (VRB) test for a TiO ₂ nanotube bipolar plate coated with graphite or IrO _x , comparing a first charge-discharge curve and a 100 charge- , Coulomb efficiency (b), voltage efficiency (c), and energy efficiency (d)
Figure 12 shows the circulation characteristics for a VRFB single cell based on a graphite bipolar plate (a) and a TiO ₂ nanotube bipolar plate (b) coated with IrO _x ,
13 shows the TiO ₂ nanotube bipolar plate capacity (a) coated with IrO _x measured as a function of charge-discharge current density (right Y axis) and coulomb efficiency (left Y axis), and after 100 charge- (HR, SEM) images (b, c) of TiO ₂ nanotubes coated with IrO _x on a high-resolution scanning electron microscope.

Hereinafter, a titanium-based bipolar plate coated with iridium oxide for a vanadium redox flow battery of the present invention and a method of manufacturing the same will be described in detail.

The inventors of the present invention have been studying an all-vanadium redox flow battery (hereinafter, referred to as 'VRFB'), while the conventional bipolar plate, which is a component in the battery of VRFB, is mainly made of carbon, In order to increase the cell volume and improve the efficiency and the spatial efficiency, the bipolar plate material is replaced with the metal material, thereby improving the electric resistance and electron transferring ability compared to the carbon material. It is possible to increase the efficiency of the VRFB and to obtain the spatial advantage of the thin metal material as a matter of course, thereby completing the present invention.

The present invention relates to a titanium substrate; (TiO ₂ ) nanotube layer having a nanotube shape on the titanium substrate, and the porous TiO ₂ nanotube layer is coated on the outer and inner surfaces with iridium oxide. Provides a titanium-based bipolar plate coated with iridium oxide for a toxic flow battery.

The porous TiO ₂ nanotube layer may include pores having an average diameter of 50 nm to 100 nm, but is not limited thereto.

The porous TiO ₂ nanotube layer may include an iridium oxide coating layer having an average thickness of 100 nm to 500 nm on the outer surface and an iridium oxide coating layer having an average thickness of 700 nm to 1.5 μm on the inner surface.

The iridium oxide may be represented by IrO _x , x is an integer of 1 to 2, and iridium oxide may be represented by IrO ₂ .

The present invention also provides a method of manufacturing a semiconductor device, comprising: washing a titanium substrate; Anodizing the washed titanium substrate with an electrolyte solution containing sodium hydroxide, phosphoric acid, and hydrofluoric acid to form a porous TiO ₂ nanotube structure on the surface of the titanium substrate; Heat treating the titanium substrate on which the porous TiO ₂ nanotube structure is formed; Adding an iridium precursor to an organic solvent and stirring the mixed solution to prepare a mixed solution; And a step of injecting a mixed solution onto the surface of the titanium substrate on which the heat-treated porous TiO ₂ nanotube structure is formed, and then injecting the mixed solution into an electric furnace and performing heat treatment. The barium oxide- And a manufacturing method thereof.

The cleaning of the titanium substrate may be performed by immersing the titanium substrate in acetone, ethanol, and distilled water for 15 minutes, 10 minutes, and 5 minutes, respectively, but is not limited thereto.

The electrolyte solution may include, but is not limited to, 1.0 to 1.5 M sodium hydroxide, 1.0 to 1.5 M phosphoric acid, and 0.5 wt% hydrofluoric acid.

Particularly, when anodic oxidation of a titanium substrate is carried out using an electrolyte solution containing 1.0 M sodium hydroxide, 1.0 M phosphoric acid, and 0.5 weight% hydrofluoric acid, nanotubes having relatively uniform pores and lengths are obtained at a low voltage There is an advantage.

The step of forming the porous TiO ₂ nanotube structure may be performed by anodizing the washed titanium substrate at an electrolyte solution containing sodium hydroxide, phosphoric acid, and hydrofluoric acid at 10 to 20 V for 3 to 6 hours, But is not limited to.

Particularly, in the step of forming the porous TiO ₂ nanotube structure, when the washed titanium substrate is anodized at 20 V for 3 hours with an electrolyte solution containing sodium hydroxide, phosphoric acid, and hydrofluoric acid, It is advantageous to obtain nanotubes having pores having an average diameter of 50 to 100 nm.

The porous TiO ₂ nanotube structure formed on the surface of the titanium substrate serves as an anchor for improving adhesion between the coating layer and the porous TiO ₂ nanotubes before coating the iridium oxide.

The porous TiO ₂ nanotube structure may include pores having an average diameter of 50 nm to 100 nm, but the present invention is not limited thereto.

In the step of heat-treating the titanium substrate, the titanium substrate on which the porous TiO ₂ nanotube structure is formed may be heat-treated at a temperature of 100 to 120 ° C, but is not limited thereto.

Specifically, when the titanium substrate on which the porous TiO ₂ nanotube structure is formed is heat-treated, there is an advantage that Cl is vaporized and Ir, Ti, and O are uniformly diffused in the coating layer.

The iridium precursor may be any one selected from the group consisting of IrCl ₂ , IrCl ₃ , IrCl _4, and H ₂ IrCl ₆ , but is not limited thereto.

The preparation of the mixed solution may be performed by adding 0.01 to 0.05 M of an iridium precursor to the organic solvent, followed by stirring for 6 to 12 hours, but the present invention is not limited thereto.

Particularly, when an 0.05 M iridium precursor is added to the organic solvent, the organic solvent is volatilized during the heat treatment and the iridium can be coated on the porous TiO 2 nanotube structure.

The heat treatment may be performed by injecting a mixed solution onto the surface of the titanium substrate on which the heat-treated porous TiO ₂ nanotube structure is formed, charging the mixture into an electric furnace maintained at 300 to 350 ° C, and performing heat treatment for 5 to 10 minutes. But is not limited to.

If the temperature is outside the range of 300 to 350 ° C, the Cl may not vaporize properly at a temperature lower than 300 ° C. When the temperature exceeds 350 ° C, the Ti substrate is oxidized to thicken the barrier type TiO ₂ structure And there is a problem that crystallinity is changed.

The heat treatment may be repeated 5 to 8 times, but is not limited thereto.

Particularly, considering that less heat treatment is performed, the generation of the barrier type TiO ₂ structure becomes less, and it is more preferable to perform the heat treatment step six times.

The method may further include repeating the heat treatment for 5 to 8 times to inject the heat-treated titanium substrate into an electric furnace maintained at 300 to 350 ° C., spraying the mixed solution, and heat-treating the mixed solution for 1 to 2 hours. But is not limited to.

If the additional heat treatment step is further included after the heat treatment step, there is an advantage that Cl is fully vaporized and Ti, Ir, and O of the coating layer are uniformly diffused and mixed.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by these examples.

≪ Example 1 > IrO _X Coated TiO ₂ Nanotubes Bipolar plate Produce

To remove foreign substances from the surface, Ti foil (purity 99.7%, thickness 0.127 mm, Sigma-Aldrich) was dipped in 4 x 4 cm ² and immersed in acetone, ethanol and distilled water (DI water) Min, and 5 minutes, respectively.

The washed Ti foil was immersed in 500 ml of a solution containing 1 M NaOH and 1 M H ₃ PO ₄ in a beaker and anodic oxidation at 20 V for 3 hours in an electrolyte solution containing 0.5 wt% A porous TiO ₂ nanotube structure having an average diameter of 100 nm was formed on the surface of the foil.

An IrCl ₃ / EtOH solution was prepared by adding 0.05 M of IrCl ₃ (Sigma-aldrich) to 20 ml of ethanol (EtOH) and stirring for 6 hours.

The Ti foil containing the porous TiO ₂ nanotube structure was raised obliquely on a hot plate heated at 100 ° C to 120 ° C, and the IrCl ₃ / EtOH solution was sprayed uniformly in 2-ml dry spray, Lt; RTI ID = 0.0 > 300 C < / RTI > to < RTI ID = 0.0 > 350 C. < / RTI >

The injection of IrCl ₃ / EtOH solution and the heat treatment in the electric furnace of Ti foil were repeated six times, and the weight immediately after the heat treatment was measured. Finally, IrCl ₃ / EtOH solution was sprayed in an electric furnace maintained at 300 ° C. to 350 ° C. Thereafter, the TiO ₂ nanotubes were heat-treated for 1 hour to form IrO _x coated TiO ₂ nanotubes Bipolar plates were prepared.

≪ Comparative Example 1 > IrO _X Coated type TiO ₂ Bipolar plate Produce

To remove foreign substances from the surface, Ti foil (purity 99.7%, thickness 0.127 mm, Sigma-Aldrich) was dipped in 4 x 4 cm ² and immersed in acetone, ethanol and distilled water (DI water) Min, and 5 minutes, respectively.

The washed Ti foil was placed at an angle on a hot plate heated to 100 ° C to 120 ° C, and the IrCl ₃ / EtOH solution was uniformly sprayed in a 2-ml dry spray, and then the Ti foil was heated at 300 ° C to 350 ° C Lt; / RTI > for 5 minutes.

The injection of IrCl ₃ / EtOH solution and the heat treatment in the electric furnace of Ti foil were repeated six times, and the weight immediately after the heat treatment was measured. Finally, IrCl ₃ / EtOH solution was sprayed in an electric furnace maintained at 300 ° C. to 350 ° C. And then heat-treated for 1 hour to prepare a barrier type TiO ₂ bipolar plate coated with IrO _x .

≪ Comparative Example 2 > ₂  Nanotube bipolar plate manufacturing

To remove foreign substances from the surface, Ti foil (purity 99.7%, thickness 0.127 mm, Sigma-Aldrich) was dipped in 4 x 4 cm ² and immersed in acetone, ethanol and distilled water (DI water) Min, and 5 minutes, respectively.

The washed Ti foil was immersed in 500 ml of a solution containing 1 M NaOH and 1 M H ₃ PO ₄ in a beaker and anodic oxidation at 20 V for 3 hours in an electrolyte solution containing 0.5 wt% Porous TiO ₂ nanotube bipolar plates with a porosity of 100 nm were prepared on the surface of the foil.

<Experimental Example 1> SEM image analysis

Figure 2 shows a TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1 using a scanning electron microscope (Hitachi HR-SEM SU8010) and a barrier type coated with IrO _x prepared according to Comparative Example 1 The shape of the TiO ₂ bipolar plate is shown by SEM image.

2 (a) and 2 (b), a TiO ₂ nanotube bipolar plate and a barrier type TiO ₂ bipolar plate All _X IrO coating layer formed on the exhibited the tortoise-shell (turtle-shell) form.

On the other hand, the cross-sectional views of all the IrO _x coating layers formed on the TiO ₂ nanotube structure and the barrier type TiO ₂ structure showed different shapes.

2 (c), an IrO _x coating layer formed by repetitively spraying an IrCl ₃ / EtOH solution due to anchoring between IrO _x and a TiO ₂ nanotube structure is formed on the surface of the TiO ₂ nanotube structure It penetrated deeply into the inside. That is, it was confirmed that IrO _x was uniformly distributed in the porous TiO ₂ nanotube structure.

On the other hand, referring to FIG. 2D, the barrier type TiO ₂ bipolar plate coated with IrO _x prepared according to Comparative Example 1 exhibited a dense oxide layer having an interface separating between the IrO _x coating layer and the Ti substrate. This resulted in the formation of a separate interface between the IrO _x coating layer and Ti due to the formation of a TiO ₂ barrier layer having a thickness of several nanometers.

FIG. 3 is a graph showing the results of a comparison between a porous TiO ₂ film prepared by anodizing a Ti foil for 3 hours by applying a voltage of 20 V to an electrolyte solution prepared by mixing 1 M NaOH, 1 MH ₃ PO ₄ , and 0.5 wt% (A), and a cross-sectional SEM image (b) of a nanotube structure.

3 (a), which is an image of a top view, it was confirmed that a TiO ₂ nanotube structure having an average diameter of 100 nm was obtained at a voltage of 20 V, and with reference to FIG. 3 (b) It was confirmed that the porous TiO ₂ nanotube structure had an average thickness of 1.5 μm.

&Lt; Experimental Example 2 > SEM & EDX analysis

In order to observe the shape of the TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1, a focused ion beam scanning including energy-dispersive X-ray spectroscopy (EDS) mapping (FIB-SEM, XVISON 200DB, Hitachi). The distribution of the elements was observed with an electron microscope (Focussed Ion Beam Scanning Electron Microscope;

Referring to FIG. 4 (a), a cross-sectional HR-SEM image showing the mapping of the TiO ₂ nanotube bipolar plate to the Ti, Ir, and O elements of IrO _x coated according to Example 1 is shown.

Specifically, it has been clearly shown that the element mapping of the TiO ₂ nanotube bipolar plate coated with IrO _x is uniformly composed of titanium, iridium, and oxide on the Ti substrate.

On the other hand, referring to FIG. 4 (b), the elemental mapping of the barrier type TiO ₂ bipolar plate coated with IrO _x prepared according to Comparative Example 1 clearly shows that the thick IrO _x coating layer and the TiO ₂ / Ti substrate are clearly divided Respectively.

That is, Example 1 TiO ₂ nano-tubes coated with the prepared IrO _X according to the bipolar plate is IrO _X is that evenly penetrates into the porosity of the TiO ₂ nanotube structure in combination with the IrO _X coating with TiO ₂ nanotube structure and I could confirm. On the other hand, Comparative Example 1 in accordance with the coating in the manufactured IrO _X barrier type TiO ₂ the bipolar plate is the _X IrO barrier type TiO ₂ structure It was confirmed that it was coated only on the surface and did not penetrate into the inside.

5, in order to observe the detailed geometrical characteristics of the TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1, a high-resolution transmission electron microscope electron microscope (HR-TEM, JEM-2100F, JEOL).

Specifically, the titanium, iridium, and oxide configurations were uniformly observed in a TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1.

Thus, IrO _x was coated on both the outer and inner surfaces of the TiO ₂ nanotube structure with an average thickness of 200 nm and 1 μm, respectively, which enabled strong anchoring between the iridium oxide layer and the TiO ₂ nanotube structure.

&Lt; Experimental Example 3 > A graphite bipolar plate and IrO2 prepared according to Example 1 _X Coated TiO ₂  Comparison of thickness of nanotube bipolar plate

Figure 6 is a cross-sectional digital photograph of a graphite bipolar plate (left) and a TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1 (right) for comparison of thickness.

Referring to FIG. 6, when the TiO ₂ nanotube bipolar plate coated with IrO _x according to Example 1 was used for VRFB, the difference in thickness was remarkably exhibited, and the total volume reduction effect of the existing VRFB .

Specifically, the TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1 exhibited an average thickness of 0.127 mm, while the graphite bipolar plate exhibited an average thickness of approximately 3 mm, indicating that the bipolar plate volume Of the VRFBs can be designed through the reduction of the VRFBs.

<Experimental Example 4> XRD pattern analysis

Referring to FIG. 7, in order to analyze the structural characteristics of the IrO _x coating layer, a TiO ₂ nanotube coated with IrO _x prepared according to Example 1 using an X-ray diffractometer (Rigaku D / MAX 2500 diffractometer, Rigaku) The X-ray diffractiometry ('XRD analysis') pattern of the bipolar plate was compared to the XRD pattern of the barrier type TiO ₂ bipolar plate coated with IrO _x prepared according to Comparative Example 1.

Specifically, in the TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1, the crystal structure of the iridium oxide (110), (101), and (211), the anatase TiO ₂ 101 (JCPDS No. 21-1272) and a Ti-metal (JCPDS No. 44-1294).

On the other hand, in the barrier type TiO ₂ bipolar plate coated with IrO _x prepared according to Comparative Example 1, no diffraction peak of anatase TiO ₂ was observed. This means that the thick oxide layer on the surface does not contain a TiO ₂ layer, which is consistent with the FIB-SEM observation (see Fig. 4 (b)).

<Experimental Example 5> Electrochemical performance analysis

Figure 8 shows the potentiodynamic polarization curves of the various bipolar plates.

The measurements can be used to evaluate corrosion behavior and indicate the availability of TiO ₂ nanotube structures coated with IrO _x as bipolar plates.

We used a 0.3 M VOSO ₄ with 0.6 MH ₂ SO ₄ aqueous solution at room temperature, a platinum mesh and an Ag / the AgCl each of the counter electrode, and a reference were used as electrodes, the embodiment of TiO ₂ nano-coated with an IrO _X prepared according to the 1 A tube bipolar plate, a barrier type TiO ₂ bipolar plate coated with IrO _x prepared according to Comparative Example 1, a pure TiO ₂ nanotube bipolar plate manufactured according to Comparative Example 2, a copper foil plate (current collector), and a graphite bipolar Galvanic corrosion test was performed using the plate as a working electrode, respectively.

Example coated with the prepared IrO _X TiO according to ₁₂ nanotubes bipolar plate, coated with the IrO _X prepared according to Comparative Example 1, a barrier-type TiO _2, the bipolar plate, Comparative Example 2, a pure TiO ₂ nanotubes prepared according to The individual corrosion potentials (E _corr ) of the bipolar plate, the copper foil plate (current collector), and the graphite bipolar plate are -0.107 V, -0.117 V, -0.216 V, -0.164 V, and -0.123 V, respectively.

Referring to the above results, the pure TiO ₂ nanotube bipolar plate prepared according to Comparative Example 2 exhibited much lower E _corr behavior than the other bipolar plates.

In contrast, in Example 1 was coated with the IrO _X prepared according to the TiO ₂ nanotubes bipolar plates and Comparative Example 1 was coated with the IrO _X prepared according to the barrier-type TiO ₂ the bipolar plate is thermodynamically corrosion properties than graphite bipolar plate , And it was confirmed that it can exhibit the same or better performance in corrosion to strongly acidic electrolyte.

From the above results, it was confirmed that E _corr and electrochemical stability of TiO ₂ nanotube bipolar plate can be improved by performing IrO _x coating.

Therefore, the electrochemical characteristics of TiO ₂ bipolar plates coated with graphite bipolar plates and two types of IrO _x coated according to Example 1 and Comparative Example 1 as bipolar plates for protecting copper (Cu) current collectors from strong acid electrolytes .

Referring to FIG. 9 (a), in order to analyze electrochemical characteristics of TiO ₂ bipolar plates coated with two types of IrO _x prepared according to Example 1 and Comparative Example 1, it was found that -20 to 20 mA / cm ² of The overvoltage of V ₄ ⁺ / V ₅ ⁺ redox reaction was measured through charge / discharge under current density.

The pure TiO ₂ nanotube bipolar plate (blue line) without metal catalyst prepared according to Comparative Example 2 abruptly increased in potential and reached the maximum limit as the applied current density increased.

Conventional graphite bipolar plates (black lines) exhibited the highest overvoltages of 1.90 V and -1.12 V at current densities of ± 20 mA / cm ² .

In contrast, the TiO ₂ nanotube bipolar plate (red line) coated with IrO _x prepared according to Example 1 exhibited the lowest overvoltage of 0.93 V and -0.36 V at a current density of ± 20 mA / cm ² .

In addition, the barrier type TiO ₂ bipolar plate (green line) coated with IrO _x prepared according to Comparative Example 1 exhibited suitably low overvoltage.

Overall, the TiO ₂ bipolar plates coated with two types of IrO _x prepared according to Example 1 and Comparative Example 1 exhibited relatively low cell overcharges compared to graphite bipolar plates, which were coated with two types of IrO _x Suggesting that the TiO ₂ bipolar plate can improve the electrochemical performance of VRFB.

However, it was confirmed that the TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1 through the overvoltage test showing remarkable difference can significantly lower the resistance performance when applied to VRFB.

Referring to FIG. 9 (b), in order to analyze electrochemical characteristics of graphite bipolar plates and TiO ₂ bipolar plates coated with two types of IrO _x prepared according to Example 1 and Comparative Example 1, electrochemical impedance spectroscopy electrochemical impedance spectroscopy analysis (EIS).

Graphite bipolar plates and TiO ₂ bipolar plates coated with two types of IrO _x prepared according to Example 1 and Comparative Example 1 were proved to have similar bulk solution resistance through Nyquist impedance lines Respectively.

However, the TiO ₂ bipolar plates coated with the two types of IrO _x prepared according to Example 1 and Comparative Example 1 exhibited remarkably small semicircles compared to the semicircle of the graphite bipolar plate. In Example 1 and Comparative Example 1 The charge transfer resistance in the high frequency region of the TiO ₂ bipolar plate coated with the two types of IrO _x prepared according to the present invention is considerably smaller than that of the graphite bipolar plate.

This is consistent with the previous results that TiO ₂ coated with two types of IrO _x prepared according to Example 1 and Comparative Example 1 is suitable to apply a bipolar plate to VRFB and VRFB cell performance is significantly improved.

VRFB To evaluate the electrochemical performance after applying a TiO ₂ bipolar plate coated with two types of IrO _x prepared according to Example 1 and Comparative Example 1 in a single cell, a mixture of 0.3 M VOSO ₄ and 0.6 MH ₂ SO ₄ The charge-discharge cycle was performed using Nafion 117 from the solution to the membrane.

Comparative Example 2 A pure TiO ₂ nano-tubes made according to the bipolar plate is VRFB based on pure TiO ₂ nanotubes bipolar plate because it contains a high cell overcurrent above has not been charged at a high current density 5 mA / cm ^2.

10, the case of the TiO ₂ nanotubes bipolar plate coated with the IrO _X prepared according to Example 1 after the electrochemical performance test, also all as shown on the left of the 10 Shone appear as a black bar, IrO _X yet remaining .

On the other hand, in the case of the barrier type TiO ₂ bipolar plate coated with IrO _x prepared according to Comparative Example 1 in which a porous TiO ₂ nanotube structure is not formed as shown in the right side of FIG. 10, The VRFB single cell test with a barrier type TiO ₂ bipolar plate coated with IrO _x could no longer be performed because the IrO _x was easily separated from the test run.

That is, it was confirmed that the TiO ₂ nanotube structure improves the adhesion between the IrO _x coating layer and the Ti substrate to assist the separation of the IrO _x coating layer for a long time even when applied to VRFB.

A VRFB single cell test was performed to compare graphite bipolar plates with TiO ₂ nanotube bipolar plates coated with IrO _x .

Referring to FIG. 11 (a), the charge / discharge voltage of a VRFB cell based on a TiO ₂ nanotube bipolar plate coated with a graphite bipolar plate and an IrO _x at a current density of 40 mA / cm ² during one charge / A comparison of the capacity profiles is shown.

Compared to the graphite bipolar plate, the TiO ₂ nanotube bipolar plate coated with IrO _x exhibited a low charging voltage of 27 mV and a high discharge voltage of 47 mV.

These results suggest that IrO _x coated on a porous TiO ₂ nanotube structure is an active catalyst and can reduce the charge transfer resistance.

Referring to FIG. 12, when the charge / discharge test is performed more than 100 times in a fixed voltage window, the TiO ₂ nanotube bipolar plate coated with IrO _x as compared with the graphite bipolar plate has excellent cycleability and Respectively.

These results demonstrate the low resistivity and corrosion resistance of bipolar plates that affect cell performance. That is, it has been proved that the cell performance can be improved by applying the TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1 to VRFB.

11 (b) to 11 (d), coulomb efficiency, voltage efficiency, and energy efficiency when various bipolar plates were applied to a VRFB cell were shown.

Specifically, when the graphite bipolar plate and the TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1 were applied to VRFB, the coulombic efficiency was similar, but the IrO _x the TiO ₂ nanotubes bipolar voltage efficiency of VRFB due to the low charge transfer charge applied to the TiO ₂ nanotubes bipolar plate coated with the IrO _X of the plate is higher for 3 to 4% compared to VRFB applying graphite bipolar plates coated with.

Overall, the energy efficiency of a VRFB cell employing a TiO ₂ nanotube bipolar plate coated with IrO _x due to the active catalytic effect of the IrO _x coating and the high corrosion resistance of the porous TiO ₂ nanotube structure was found to be between 3 and 4 %, Indicating excellent cyclic stability. It was confirmed that the volume can be reduced by applying the TiO ₂ nanotube bipolar plate coated with IrO _x to the VRFB cell, and excellent electrochemical performance can be provided.

In addition, various current densities were applied to the VRFB cells to verify the current stability.

13 (a), circulation performance and speed characteristics of the TiO ₂ nanotube bipolar plate coated with IrO _x were shown. When the current density was increased up to 60 mA / cm ² , the charge- It was not abruptly decreased.

On the other hand, when the current density was reduced to 20 mA / cm ² , the coulombic efficiency and charge-discharge capacity were restored.

That is, in the TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1, the current restoring force is attributed to significantly reduced over-potential, low charge transport resistance, and anti-corrosion property.

This result agrees with the SEM image showing the surface shape (see Fig. 13 (b)) of the TiO ₂ nanotube bipolar plate coated with IrO _x prepared according to Example 1 after 100 cycles.

Specifically, rotation around the IrO (see Fig. 2 (a)) the TiO ₂ nano-tubes coated with _X as compared to help the upper surface SEM image of a bipolar plate, after rotation of 100 times the TiO ₂ nanotubes bipolar plate coated with the IrO _X is any crack The turtle-shell shape was still maintained.

In addition, FIG. 13 (c) Referring to, it has been a great deal of IrO _X still held on the TiO ₂ nanotube structure, after vigorous VRFB movable TiO ₂ nanotube structure was still connected to the Ti substrate without destruction or damage, It was confirmed that the IrO _x and TiO ₂ nanotube structure composite layers were more dense and became more solid after the circulation test.

The observed result is TiO ₂ nano-tubes, and found to be caused by the shape characteristics of the structure, the TiO ₂ nanotube structure coated with IrO _X is and structurally robust, and can maintain a high electric conductivity and corrosion resistance, Showed high stability under acidic conditions for VRFB operation.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It is to be understood that various modifications and changes may be made without departing from the scope of the appended claims.

Claims (14)

A titanium substrate;
And a porous titanium dioxide (TiO ₂ ) nanotube layer in the form of a nanotube on the titanium substrate,
Wherein the porous TiO ₂ nanotube layer is coated with an iridium oxide on the outer and inner surfaces, the iridium oxide-coated titanium-based bipolar plate for a vanadium redox flow battery. The method according to claim 1,
The porous TiO ₂ nanotube layer may be formed,
A barium titanate-based bipolar plate coated with iridium oxide for a vanadium redox flow battery, characterized in that it comprises pores having an average diameter of 50 nm to 100 nm. The method according to claim 1,
The porous TiO ₂ nanotube layer may be formed,
An iridium oxide coating layer having an average thickness of 100 nm to 500 nm on the outer surface and an iridium oxide coating layer having an average thickness of 700 nm to 1.5 μm on the inner surface. Bipolar plates. Cleaning the titanium substrate;
Anodizing the washed titanium substrate with an electrolyte solution containing sodium hydroxide, phosphoric acid, and hydrofluoric acid to form a porous TiO ₂ nanotube structure on the surface of the titanium substrate;
Heat treating the titanium substrate on which the porous TiO ₂ nanotube structure is formed;
Adding an iridium precursor to an organic solvent and stirring the mixed solution to prepare a mixed solution; And
A titanium-based bipolar plate coated with iridium oxide for a vanadium redox flow battery, comprising the steps of injecting a mixture solution onto the surface of a titanium substrate on which the heat-treated porous TiO ₂ nanotube structure is formed, Way. The method of claim 4,
Wherein the cleaning of the titanium substrate comprises:
Wherein the titanium substrate is immersed in acetone, ethanol, and distilled water, and ultrasonically cleaned for 15 minutes, 10 minutes, and 5 minutes, respectively, for the iridium oxide-coated titanium-based bipolar plate for a vanadium redox flow battery. The method of claim 4,
The electrolyte solution may contain,
Characterized in that it comprises 1.0 to 1.5 M sodium hydroxide, 1.0 to 1.5 M phosphoric acid, and 0.5 weight% hydrofluoric acid. The method of claim 4,
The forming of the porous TiO ₂ nanotube structure may include:
Characterized in that the washed titanium substrate is formed by anodic oxidation at 10 to 20 V for 3 to 6 hours with an electrolytic solution containing sodium hydroxide, phosphoric acid, and hydrofluoric acid. The iridium oxide-coated titanium substrate for a vanadium redox flow battery Based bipolar plate. The method of claim 4,
In the porous TiO ₂ nanotube structure,
Characterized in that it comprises pores having an average diameter of from 50 nm to 100 nm. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The method of claim 4,
Wherein the heat treatment of the titanium substrate comprises:
Wherein the titanium substrate on which the porous TiO ₂ nanotube structure is formed is subjected to a heat treatment at a temperature of 100 to 120 ° C. 11. A method of manufacturing a titanium-based bipolar plate coated with iridium oxide for a vanadium redox flow battery, The method of claim 4,
The iridium precursor,
Wherein the iridium oxide-coated titanium-based bipolar plate is one selected from the group consisting of IrCl ₂ , IrCl ₃ , IrCl _4, and H ₂ IrCl ₆ . The method of claim 4,
The step of preparing the mixed solution includes:
A process for producing a titanium-based bipolar plate coated with iridium oxide for a vanadium redox flow battery, which comprises adding 0.01 to 0.05 M of an iridium precursor to an organic solvent, followed by stirring for 6 to 12 hours. The method of claim 4,
The step of heat-
Wherein the mixed solution is injected onto the surface of the titanium substrate on which the heat-treated porous TiO ₂ nanotube structure is formed, and then the mixture is injected into an electric furnace maintained at 300 to 350 ° C. and heat-treated for 5 to 10 minutes. A method of manufacturing a titanium-based bipolar plate coated with an iridium oxide for a battery. The method of claim 4,
The step of heat-
Wherein the bipolar plate is repeated five to eight times. 6. The method of claim &lt; RTI ID = 0.0 &gt; 1, &lt; / RTI &gt; The method of claim 4,
After the heat treatment step
Further comprising the step of injecting the mixed solution into the electric furnace maintained at a temperature of 300 to 350 DEG C for 1 to 2 hours after the heat treatment of the vanadium redox flow A method of manufacturing a titanium-based bipolar plate coated with an iridium oxide for a battery.

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