EP4437166A1

EP4437166A1 - Electrode, and use and preparation method thereof

Info

Publication number: EP4437166A1
Application number: EP23701290.1A
Authority: EP
Inventors: Adriaan JEREMIASSE; Matija LOVRAK; Qite ZHAO
Original assignee: Magneto Special Anodes BV
Current assignee: Magneto Special Anodes BV
Priority date: 2022-01-27
Filing date: 2023-01-17
Publication date: 2024-10-02
Also published as: CA3240739A1; CN116555845A; WO2023143968A1; JP2025501883A; KR20240137603A; IL313659A; AU2023210992A1; TW202340538A

Abstract

An electrode, and use and a preparation method thereof. The electrode includes a metal substrate and a catalytic layer. The electrode includes at least one of the following features: i) the substrate is a corrosion inhibitor-containing titanium alloy, the corrosion inhibitor being selected from at least one metal of platinum, palladium, osmium, iridium, ruthenium, rhodium, tantalum, zirconium and niobium, and the content of the corrosion inhibitor being 0.05 wt%-0.5 wt% of the total mass of the alloy; ii) the catalytic layer is an iridium oxide layer or an iridium-tantalum mixed oxide layer, with a mass ratio of iridium element to tantalum element being 1:4 to 1:0; and iii) an interlayer is disposed between the substrate and the catalytic layer, the interlayer being a titanium-tantalum alloy layer. For the electrode, its corrosion resistance is greatly improved, its lifetime is extended, and its production cost is reduced.

Description

ELECTRODE, AND USE AND PREPARATION METHOD THEREOF

Technical Field

The present application relates to, but is not limited to, the field of electrochemistry, and specifically relates to, but is not limited to, an electrode, and use and a preparation method thereof.

Background of the Related Art

Electrowinning is an important part of electrochemical industry, which is mainly used for electrolytic extraction and purification of metals from their solutions. In the process of electrolytic extraction of metals such as electrolyzing metal nickel, electrolyzing metal zinc and electrolyzing metal manganese, an aqueous solution containing a certain concentration of chloride ions is usually used as the electrolyte. This electrowinning process needs an insoluble anode to form a stable circuit and a continuous electrolytic current.

As an environmentally friendly insoluble anode, a titanium electrode has been widely used in the electrochemical industry, mainly in electrochemical water treatment, extraction of metal elements, electroplating and other finishing processes. A titanium electrode is mainly composed of a titanium metal or titanium alloy substrate and a precious metal oxide catalyst layer on its surface. The substrate provides electrical and mechanical support, while the catalyst layer can greatly reduce oxygen evolution potential through its own redox process to save energy, and also enables, due to its extremely low electrochemical consumption rate, the anode to have a relatively long lifetime.

There is a high concentration of chloride ions in a conventional electrolyte, and the chloride ions increase the corrosion rate of the substrate. Once the corrosion damages the substrate severely, the catalytic layer will detach from the substrate (as shown in FIG. 1), and the anode will stop functioning, making the lifetime of the anode shorter than the expected lifetime. FIG. 1 shows corrosion of a titanium substrate observed from a cross section of an existing anode, wherein the anode was removed from operation after 3 and 6 months, respectively, and its section was observed, wherein the arrow indicates the titanium substrate/catalytic layer interface. Content of the Invention

The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the protection scope of the claims.

In order to overcome the shortcomings in the prior art, the inventors of the present application has improved the corrosion resistance of electrodes through years of careful research.

The present application provides an electrode, comprising a metal substrate and a catalytic layer; wherein the electrode includes at least one of the following features: i) the substrate is a corrosion inhibitor-containing titanium alloy, the corrosion inhibitor being selected from at least one metal of platinum, palladium, osmium, iridium, ruthenium, rhodium, tantalum, zirconium and niobium, and the content of the corrosion inhibitor being 0.05 wt%-0.5 wt% of the total mass of the alloy; ii) the catalytic layer is an iridium oxide layer or an iridium-tantalum mixed oxide layer, with a mass ratio of iridium element to tantalum element being 1:4 to 1:0; and iii) an interlayer is disposed between the substrate and the catalytic layer, the interlayer being a titanium-tantalum alloy layer.

In some embodiments, the corrosion inhibitor may be selected from ruthenium and/or palladium, and may also be selected from palladium.

In some embodiments, the content of the corrosion inhibitor may be 0.12 wt%-0.25 wt% of the total mass of the alloy.

In some embodiments, the corrosion inhibitor-containing titanium alloy may further comprise one or more of the following elements: H, N, C, O and Fe.

In some embodiments, the corrosion inhibitor-containing titanium alloy may further comprise 0.015 wt% of H, 0.03 wt% of N, 0.08 wt% of C, 0.18 wt% of O, 0.020 wt% of Fe, 0.05 wt%-0.5 wt% of corrosion inhibitor, and the balance of Ti, based on the total mass of the alloy. In some embodiments, the electrode may further comprise a catalytic base layer, the catalytic base layer being located between the substrate and the catalytic layer or between the interlayer and the catalytic layer.

In some embodiments, the catalytic base layer may comprise a tantalum oxide layer. In some embodiments, a loading amount of tantalum in the tantalum oxide layer may be 1 g/m2-3 g/m2.

In some embodiments, the loading amount of tantalum in the tantalum oxide layer may be 3 g/m2.

In some embodiments, based on the total mass of the interlayer, the interlayer may comprise 40 wt%-60 wt% of titanium and 40 wt%-60 wt% of tantalum.

In some embodiments, based on the total mass of the interlayer, the interlayer may comprise 60 wt% of titanium and 40 wt% of tantalum.

In some embodiments, a loading amount of iridium in the catalytic layer may be 2 g/m2-20 g/m2, may also be 2 g/m2-10 g/m2, and may also be 5 g/m2.

The present application further provides use of the electrode, the electrode being used for electrowinning, electrolytic synthesis, metal plating, metal foil manufacturing or printed circuit board manufacturing.

In some embodiments, the electrowinning, electrolytic synthesis, metal plating, metal foil manufacturing or printed circuit board manufacturing may comprise electrowinning, electrolytic synthesis, metal plating, metal foil manufacturing or printed circuit board manufacturing for metal nickel, copper, cobalt, zinc, silver, gold or manganese.

In some embodiments, the electrode may be used as an insoluble anode for electrowinning.

The present application further provides a method for preparing the electrode, comprising: providing an electrode substrate; and forming a catalytic layer; optionally, further comprising forming an interlayer on the substrate prior to the forming a catalytic layer.

In some embodiments, the catalytic layer may be formed by a paint-thermal decomposition method or a plasma spraying method.

In some embodiments, the catalytic layer may be formed by providing an iridium- containing, or an iridium and tantalum-containing coating solution to coat a surface of the substrate or a surface of the interlayer, drying and sintering.

In some embodiments, the interlayer may be formed on the substrate by a chemical vapor deposition method or a physical vapor deposition method.

In some embodiments, the interlayer may be formed by a magnetron sputtering method.

In some embodiments, the method may further comprise forming a catalytic base layer on the substrate or on the interlayer, prior to the forming the catalytic layer.

In some embodiments, the catalytic base layer may be formed by a paint-thermal decomposition method or a plasma spraying method.

Compared with the prior art, the present application has the following beneficial effects:

For the electrode of the present application, its corrosion resistance is greatly improved, its lifetime is extended, and its production cost is reduced.

Other features and advantages of the present application will be set forth in the following description, and in part will become apparent from the description, or may be learned by practice of the present application. Other advantages of the present application may be realized and obtained by the solutions described in the description and the drawings. Description of the Drawings

The accompanying drawings are used to provide an understanding of the technical solutions of the present application, and constitute a part of the specification. They are used to explain the technical solutions of the present application together with the examples of the present application, and do not constitute a limitation to the technical solutions of the present application.

FIG. 1 is a diagram showing corrosion of a titanium substrate of an electrode in the prior art.

FIG. 2 is a schematic diagram of a structure of an electrode according to an example of the present application.

FIG. 3 is a diagram of results of accelerated lifetime test of electrodes in Example 1 and Example 2 of the present application.

In the drawings: 1. substrate; 21. catalytic layer; 22. catalytic base layer; and 3. interlayer.

Detailed Description

To further clarify the purpose, technical solutions and advantages of the present application, examples of the present application will be described in detail below in conjunction with the drawings. It should be noted that the examples in the present application and the features in the examples may be arbitrarily combined with each other provided that there is no conflict.

An example of the present application provides an electrode, for example, as shown in FIG. 2, including a substrate 1, an optional interlayer 3, an optional catalytic base layer 22 and a catalytic layer 21 stacked in this order from bottom to top.

The substrate 1 may be provided with the interlayer 3 and the catalytic layer 21 symmetrically on two sides; alternatively, the substrate 1 may be provided with the interlayer 3 and the catalytic layer 21 on one side, and only the catalytic layer 21 on the other side; alternatively, the substrate 1 may be provided with no interlayer 3 on both sides.

The catalytic layer 21 may include multi-layered catalytic layer units, for example, in two, three, four or more layers. The number of units of the catalytic layers 21 on both sides of the substrate may be the same or different.

A conventional electrode substrate is metallic titanium, for example, GR1 grade industrial pure titanium and GR2 grade industrial pure titanium.

The electrode substrate of the present application adopts a corrosion inhibitorcontaining titanium alloy. The corrosion inhibitor may be selected from metals such as platinum group metals, tantalum, zirconium and niobium, for example, may be selected from at least one metal of platinum, palladium, osmium, iridium, ruthenium, rhodium, tantalum, zirconium and niobium. The content of the corrosion inhibitor is 0.05 wt%-0.5 wt%, e.g., 0.08 wt%, 0.10 wt%, 0.12 wt%, 0.13 wt%, 0.15 wt%, 0.18 wt%, 0.20 wt%, 0.23 wt%, 0.25 wt%, 0.30 wt%, 0.35 wt%, 0.40 wt%, 0.45 wt%, etc., based on the total mass of the alloy. Adding the particular corrosion inhibitor to metallic titanium may greatly improve the corrosion resistance of the substrate.

The corrosion inhibitor-containing titanium alloy may further comprise one or more elements of H, N, C, O and Fe; for example, may comprise 0.015 wt% of H, 0.03 wt% of N, 0.08 wt% of C, 0.18 wt% of O, 0.020 wt% of Fe, 0.05 wt%-0.5 wt% of corrosion inhibitor, and the balance of Ti.

In another aspect, the catalytic layer used in the present application is an iridium oxide layer or an iridium-tantalum mixed oxide layer. In the electrolytic nickel environment, in order to improve the chloride ion corrosion resistance of the catalytic layer, the content of iridium element in the catalytic layer is increased in the present application, so that the mass ratio of iridium element to tantalum element is 1 :4 to 1 :0, e.g., 1 :3, 1:2, 1:1 , 2:1 , 3:1, 4:1 , 5:1 , 6:1, 7:1, 8:1 , 9:1 , 10:1 , etc. By optimizing the content ratio of iridium to tantalum, the penetration of chloride ions to the electrode substrate is reduced, the corrosion rate of the substrate is reduced, the corrosion resistance of the catalytic layer is also improved, and therefore the lifetime of the electrode is increased. The loading amount of iridium in the catalytic layer may be 2 g/m2-20 g/m2, for example, 5 g/m2, 8 g/m2, 10 g/m2, 13 g/m2, 15 g/m2, 17 g/m2, 20 g/m2, etc.

In another aspect, an interlayer may be arranged between the substrate and the catalytic layer to protect the interface between the catalytic layer and the substrate, and inhibit corrosion of the interface. The interlayer may be a titanium-tantalum alloy layer, which may include, based on the total mass of the interlayer, 40 wt%-60 wt% of titanium and 40 wt%-60 wt% of tantalum, for example, 45 wt% of titanium and 55 wt% of tantalum, 50 wt% of titanium and 50 wt% of tantalum, 55 wt% of titanium and 45 wt% of tantalum, etc. In the process of electrolytic extraction of metals, the chloride ions contained are very corrosive to the interface, and the titanium-tantalum alloy interlayer provides better corrosion resistance, leading to a very low corrosion rate.

The electrode of the present application may further include a catalytic base layer located between the substrate and the catalytic layer or between the interlayer and the catalytic layer. The catalytic base layer may include a tantalum oxide layer in which the loading amount of tantalum may be 1 g/m2-3 g/m2, e.g., 1.5 g/m2, 2 g/m2, 2.5 g/m2, etc.

The electrode of the present application may use the above-mentioned corrosion inhibitor-containing titanium alloy as the electrode substrate, and also include the above-mentioned interlayer; may also use the above-mentioned corrosion inhibitorcontaining titanium alloy as the electrode substrate, and also use the above- mentioned iridium oxide layer or iridium-tantalum mixed oxide layer as the catalytic layer; may also include the above-mentioned interlayer, and also use the above- mentioned iridium oxide layer or iridium-tantalum mixed oxide layer as the catalytic layer; and may use the above-mentioned corrosion inhibitor-containing titanium alloy as the electrode substrate, also include the above-mentioned interlayer, and use the above-mentioned iridium oxide layer or iridium-tantalum mixed oxide layer as the catalytic layer. All of these solutions may include or not include the catalytic base layer.

For the preparation of the electrode of the present application, the catalytic layer may be formed by the methods such as a paint-thermal decomposition method or a plasma spraying method; the interlayer may be formed by the methods such as a chemical vapor deposition method or a physical vapor deposition method, e.g., by a magnetron sputtering method; and the catalytic base layer may be formed by the methods such as a paint-thermal decomposition method or a plasma spraying method.

First, an electrode substrate is provided. The electrode substrate may use the above-mentioned corrosion inhibitor-containing titanium alloy. Optionally, an interlayer is formed on the substrate. The interlayer may use the above-mentioned titanium-tantalum alloy layer, and the interlayer may be formed on the substrate by a magnetron sputtering method. Optionally, a catalytic base layer is formed on the substrate or on the interlayer. The catalytic base layer may use the above-mentioned tantalum oxide layer, and the catalytic base layer may be formed by providing a tantalum-containing coating solution to coat a surface of the substrate or a surface of the interlayer, drying and sintering. A catalytic layer is formed on the substrate, on the interlayer or on the catalytic base layer. Optionally, the catalytic layer may use the above-mentioned iridium oxide layer or an iridium-tantalum mixed oxide layer, and the catalytic layer may be formed by providing an iridium-containing or an iridium and tantalum-containing coating solution to coat the surface of the substrate, the surface of the interlayer or the surface of the catalytic base layer, drying and sintering.

The electrode of the present application may be used in the fields such as electrowinning, electrolytic synthesis, metal plating, metal foil manufacturing or printed circuit board manufacturing, wherein electrowinning, electrolytic synthesis, metal plating, metal foil manufacturing or printed circuit board manufacturing comprises electrowinning, electrolytic synthesis, metal plating, metal foil manufacturing or printed circuit board manufacturing for metals such as nickel, copper, cobalt, zinc, silver, gold or manganese, etc., and the electrode may be used as an insoluble anode for electrowinning.

Example 1

GR1 grade titanium was used as an electrode substrate, and the specific components are shown in Table 1. An iridium tantalum oxide was used as a catalytic layer, in which the mass ratio of iridium to tantalum was 4:1. The steps were as follows:

First, the electrode substrate was subjected to a degreasing heat treatment at 500°C for 25 minutes in the air, and then acid-pickled in a 90°C 6.5 mol/L hydrochloric acid aqueous solution containing up to 40 g/L of dissolved titanium for 1.5 hours to obtain an active surface. The resultant product was used as an electrode substrate to be coated.

An n-butyl alcohol solution of tantalum ethoxide with the mass concentration of tantalum element being 6% was coated on the surface of the acid-pickled electrode substrate by a brush, followed by drying at room temperature for 15 minutes, and then sintering in the air for 25 minutes in an electric furnace at 500°C. After the completion of sintering, the resultant product was taken out and cooled. The above tantalum loading process was repeated, with a tantalum element loading amount of 1 g/m2 each time to obtain a tantalum element loading amount of a total of 3 g/m2 to obtain a catalytic base layer.

The coating solution used for the catalytic layer was an n-butyl alcohol solution (containing 37% concentrated hydrochloric acid accounting for 6 wt% of the total mass of the coating solution) of chloroiridic acid and tantalum ethoxide, in which the mass concentration of iridium element was 6.5% and the mass concentration of tantalum element was 1.63%. The coating solution was coated on the surface of the catalytic base layer, followed by drying at room temperature for 15 minutes, and then sintering in the air for 25 minutes in an electric furnace at 450°C. After the completion of sintering, the resultant product was taken out and cooled. The above iridium-tantalum loading process was repeated, with an iridium element loading amount of 1 g/m2 each time and a tantalum element loading amount of 0.25 g/m2 each time to obtain an iridium element loading amount of a total of 5 g/m2 and a tantalum element loading amount of a total of 1.25 g/m2 to obtain a catalytic layer of the electrode.

An electrode was prepared. Example 2

A palladium-containing titanium alloy with higher corrosion resistance was used as an electrode substrate, and the specific components are shown in Table 1.

A catalytic base layer and a catalytic layer were prepared using the same preparation process and coating amount as those in Example 1.

Table 1 : Components of electrode substrates in Example 1 and Example 2

Performance test

1. Corrosion rate of electrode substrate

The corrosion rates of the electrode substrates in Example 1 and Example 2 were measured in 8.0 mol/L hydrochloric acid containing 8.5 g/L dissolved titanium at 90°C.

The corrosion rate of the titanium alloy substrate used in Example 1 was 1.9 g/m2min, and the corrosion rate of the palladium-containing titanium substrate used in Example 2 was 1.1 g/m2min. As can be seen, the corrosion rate of the substrate material in Example 2 of the present application was greatly reduced due to the further addition of palladium.

2. Accelerated lifetime test

FIG. 3 shows variations of cell voltage of the electrodes prepared in Example 1 and Example 2 of the present application during accelerated lifetime test.

The conditions of the accelerated lifetime test were as follows: the electrolyte was 25% H2SO4 with added NaCI (16.7 g/L initially; 8.3 g/L added twice a week), the current was 20000 A/m2, and the temperature was 50°C. As can be seen from FIG. 3 and Table 2, the lifetime of the electrodes in both Example 1 and Example 2 of the present application was extended; and due to the further addition of palladium to the substrate material in Example 2 of the present application, the lifetime of the prepared electrode was longer than the lifetime of the electrode in Example 1 , and was extended by 85%. As can be seen, in Example 2, the corrosion resistance of the titanium substrate was improved by adding palladium element, improving the lifetime of the electrode more effectively.

Example 3

A catalytic base layer and a catalytic layer were prepared on the substrate by using the substrate material in Example 1 and the same preparation process as that in Example 1, wherein in the coating solution of the catalytic layer, the mass concentration of iridium element was constant at 6.5 wt%, the mass concentration of tantalum element was adjusted to 0.72 wt%, and the iridium-tantalum loading process was repeated, with an iridium element loading amount of 1 g/m2 each time, and the final catalytic layer had an iridium element loading amount of 5 g/m2 and a tantalum element loading amount of 0.56 g/m2.

Performance test

The above accelerated lifetime test was employed, and as can be seen from Table 2, the lifetime of the electrode in Example 3 of the present application was also extended, which was longer than the lifetime of the electrode in Example 1 , and was extended by 29%. In Example 3, the proportion of iridium in the catalytic layer was increased, which reduces the penetration of chloride ions to the electrode substrate, reduces the corrosion rate of the substrate, and improves the lifetime of the electrode more effectively.

Example 4

Magnetron sputtering was performed by using the substrate material in Example 1 and an alloy target with the weight ratio of titanium to tantalum being 1 :1 to sputter an interlayer of titanium/tantalum (60/40wt%) alloy on the substrate. The total weight of the resultant titanium-tantalum alloy layer was 10g/m2. A catalytic layer was prepared on the interlayer by using the same preparation process and coating amount as those in Example 3.

Performance test

The above accelerated lifetime test was employed, and as can be seen from Table 2, the lifetime of the electrode in Example 4 of the present application was also extended, which was longer than the lifetime of the electrode in Example 1 , and was extended by 44%. In Example 4, a titanium-tantalum alloy was used as the interlayer, improving the lifetime of the electrode more effectively.

Table 2: Different electrodes and performance thereof

Although the embodiments disclosed in the present application are as above, the contents described are only the embodiments adopted for the convenience of understanding the present application, and are not used to limit the present application. Any person skilled in the field to which the present application belongs can make any modifications and changes in the implementation form and details without departing from the spirit and scope disclosed by the present application, but the scope of patent protection of the present application shall still be subject to the scope defined by the appended claims.

Claims

1. An electrode, comprising a metal substrate and a catalytic layer; wherein the electrode includes at least one of the following features: i) the substrate is a corrosion inhibitor-containing titanium alloy, the corrosion inhibitor being selected from at least one metal of platinum, palladium, osmium, iridium, ruthenium, rhodium, tantalum, zirconium and niobium, and the content of the corrosion inhibitor being 0.05 wt% - 0.5 wt% of the total mass of the alloy; ii) the catalytic layer is an iridium oxide layer or an iridium-tantalum mixed oxide layer, with a mass ratio of iridium element to tantalum element being 1 :4 to 1:0; and iii) an interlayer is disposed between the substrate and the catalytic layer, the interlayer being a titanium-tantalum alloy layer.

2. An electrode as claimed in claim 1 , wherein the corrosion inhibitor is selected from ruthenium and/or palladium.

3. An electrode as claimed in claim 2, wherein the corrosion inhibitor is palladium.

4. An electrode as claimed in any preceding claim, wherein the content of the corrosion inhibitor is 0.12 wt% - 0.25 wt% of the total mass of the alloy.

5. An electrode as claimed in any one of claims 2 to 4, wherein the corrosion inhibitor-containing titanium alloy further comprises one or more of the following elements: H, N, C, O and Fe.

6. An electrode as claimed in claim 5, wherein the corrosion inhibitor-containing titanium alloy comprises 0.015 wt% of H, 0.03 wt% of N, 0.08 wt% of C, 0.18 wt% of O, 0.020 wt% of Fe, 0.05 wt%-0.5 wt% of corrosion inhibitor, and the balance of Ti, based on the total mass of the alloy.

7. An electrode as claimed in any preceding claim, wherein the electrode further comprises a catalytic base layer, the catalytic base layer being located between the substrate and the catalytic layer or between the interlayer and the catalytic layer, and comprising a tantalum oxide layer.

8. An electrode as claimed in claim 7, wherein a loading amount of tantalum in the tantalum oxide layer is 1 g/m² - 3 g/m².

9. An electrode as claimed in claim 7, wherein the loading amount of tantalum in the tantalum oxide layer is 3 g/m².

10. An electrode as claimed in any preceding claim, wherein the interlayer comprises, based on the total mass of the interlayer, 40 wt% - 60 wt% of titanium and 40 wt% - 60 wt% of tantalum.

11. An electrode as claimed in claim 10, wherein the interlayer comprises 60 wt% of titanium and 40 wt% of tantalum.

12. An electrode as claimed in any preceding claim, wherein a loading amount of iridium in the catalytic layer is 2 g/m²- 20 g/m²

13. An electrode as claimed in any one of claims 1 to 11, wherein the loading amount of iridium in the catalytic layer is 2 g/m² - 10 g/m².

14. An electrode as claimed in any one of claims 1 to 11, wherein the loading amount of iridium in the catalytic layer is 5 g/m².

15. Use of an electrode according to any one of claims 1 to 14, the electrode being used for electrowinning, electrolytic synthesis, metal plating, metal foil manufacturing or printed circuit board manufacturing.

16. The use of an electrode according to claim 15, comprising electrowinning, electrolytic synthesis, metal plating, metal foil manufacturing or printed circuit board manufacturing for metal nickel, copper, cobalt, zinc, silver, gold or manganese.

17. Use of an electrode according to any one of claims 1 to 14, the electrode being used as an insoluble anode for electrowinning.

18. A method for preparing an electrode according to any one of claims 1 to 14, comprising: providing an electrode substrate; and forming a catalytic layer, preferably by a paint-thermal decomposition method or a plasma spraying method.

19. The method for preparing an electrode according to claim 18, further comprising forming an interlayer on the substrate prior to the forming a catalytic layer.

20. The method for preparing an electrode according to claim 19, wherein the interlayer on the substrate is formed by a chemical vapor deposition method or a physical vapor deposition method.

21. The method according to any one of claims 18 to 20, wherein the catalytic layer is formed by providing an iridium-containing, or an iridium and tantalum- containing coating solution, to coat a surface of the substrate or a surface of the interlayer, drying and sintering.

22. The method according to any one of claims 19 to 21, wherein the interlayer is formed by a magnetron sputtering method.

23. The method according to any one of claims 19 to 22, further comprising forming a catalytic base layer on the substrate or on the interlayer, prior to the forming the catalytic layer.

24. The method according to claim 23, wherein forming the catalytic base layer is by a paint-thermal decomposition method or a plasma spraying method.